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A new high-flow, compact aerosol concentrator, using rapid, turbulent mixing to grow aerosol particles into droplets for dry spot sample collection, has been designed and tested. The "TCAC (Turbulent-mixing, Condensation Aerosol Concentrator)" is composed of a saturator for generating hot vapor, a mixing section where the hot vapor mixes with the cold aerosol flow, a growth tube where condensational droplet growth primarily occurs, and a converging nozzle that focuses the droplets into a beam. The prototype concentrator utilizes an aerosol sample flow rate of 4 L min−1. The TCAC was optimized by varying the operating conditions, such as relative humidity of the aerosol flow, mixing flow ratio, vapor temperature, and impaction characteristics. The results showed that particles with a diameter ≥ 25 nm can be grown to a droplet diameter > 1400 nm with near 100% efficiency. Complete activation and growth were observed at relative humidity ≥ 25% of the aerosol sample flow. A consistent spot sample with a diameter of D90 = 1.4 mm (the diameter of a circle containing 90% of the deposited particles) was obtained regardless of the aerosol particle diameter (dp = 20–1900 nm). For fiber counting applications using phase contrast microscopy, the TCAC can reduce the sampling time, or counting uncertainty, by two to three orders of magnitude, compared to the 25-mm-filter collection. The study shows that the proposed mixing-flow scheme enables a compact spot sample collector suitable for handheld or portable applications, while still allowing for high flow rates. [ABSTRACT FROM AUTHOR]

Due to exponential industrialization and rapid population growth, the global energy crisis and environmental pollution have become two of the greatest humanitarian challenges of the 21st century [[1]]. Interestingly, the modification of photocatalysts' surface with metals has been shown in all these studies, confirming their crucial functions for various reactions, being co-catalysts, dopants, and sensitizers. The first-generation Z-scheme photocatalysts need a redox mediator dissolved in a liquid phase (traditional Z-scheme), then a solid mediator has been used (all-solid-state/second generation Z-scheme), and, finally, the direct Z-scheme photocatalysts without redox mediator have been developed [[10]]. The ternary photocatalyst, composed of titania, copper, and graphene (TiO SB 2 sb /Cu/G), was obtained by Lewandowski et al. in a fluidized bed reactor [[16]]. [Extracted from the article]

Concentrated collection of aerosol particles on a substrate is essential for their chemical analysis using various microscopy and laser spectroscopic techniques. An impaction-based aerosol concentration system was developed for focused collection of particles using a multi-stage nozzle that consists of a succession of multiple smooth converging stages. Converging sections of the nozzle were designed to focus and concentrate a particle diameter range of 900–2500 nm into a relatively narrower particle beam to obtain particulate deposits with spot diameters of 0.5–1.56 mm. A slightly diverging section before the last contractions was included to allow for better focusing of particles at the lower end of the collectable diameter range. The characterization of this multi-stage nozzle and the impaction-based aerosol concentration system was accomplished both numerically and experimentally. The numerical and experimental trends in collection efficiency and spot diameters agreed well qualitatively; however, the quantitative agreement between numerical and experimental results for wall losses was poor, particularly for larger particle diameters. The resulting concentrated particulate deposit, a spot sample, was analysed using Raman spectroscopy to probe the effect of spot size on analytical sensitivity of measurement. The method's sensitivity was compared against other conventional techniques, such as filtration and aerosol focused impaction, implementing condensational growth. Impaction encompassing the multi-stage focusing nozzle is the only method that can ensure high sensitivity at Reynolds numbers greater than 2000, that can be supported by small pumps which renders such method suitable for portable instrumentation. • Aerosol collection through a multi-stage focusing nozzle (MSN) is suitable for microscopy and laser spectroscopy analysis. • The MSN concentrates a particle diameter range of 900–2500 nm into a narrow particle beam. • The spectroscopic sensitivity achieved with the MSN is four times higher compared to the one-stage conventional nozzle. • The MSN probes better analytical spectroscopic sensitivity compared to the filter-based collection method. • Aerosol impaction through the MSN is ideal for portable instrumentation. [ABSTRACT FROM AUTHOR]

The 'water reuse' option is increasingly becoming crucial in the context of global warming and water scarcity. Water reuse consists in the recycling of water toward sectors requiring different water qualities, such as industry, agriculture and human consumption. Water treatment by biological methods is cheap, yet they do not to remove completely recalcitrant pollutants. Alternatively, advanced oxidation processes (AOP) for wastewater treatment are more efficient because a strong oxidizing agent such as the hydroxyl radical (•OH) is generated under mild conditions. In particular, processes of electrochemical advanced oxidation have recently attracted attention because they allow continuous and in situ electrocatalytic generation of strong oxidizing species under mild conditions, with the advantage of avoiding external addition of chemicals. In addition, energy can be provided by solar light in photochemical electrolysis systems. Here we review photoelectrochemical reactors. We present reactions and synergetic mechanisms. Under optimal conditions, eight •OH production sites are identified in photoelectro-Fenton combined with photoanodic oxidation and photocatalysis or photoelectrocatalysis. Reactions are controlled by pH, applied wavelength, and competition between reactions requiring the same reagent. Then we discuss reactor design and catalysis. Various reactor configurations are presented: sequential and hybrid reactors, divided and undivided cells, flow cell and stirred tank reactor; and light source positioning can be external, immersed, vertical, horizontal, at the top, at the bottom, or on the side of the reactor. The distance between the light source and the electrode should be minimized to obtain maximal synergy and maximum quantum yields. Hybrid reactors in undivided flow cells are best for the lower footprint, the possibility to regenerate iron catalysts, and the enhancement of mass transfer, compared with stirred tank reactors. Moreover, the interelectrode gap can be easily controlled in flow cell, which allows the optimization of the penetration depth when the light is applied through the reactor. [ABSTRACT FROM AUTHOR]

• Sr/Ce/AC BNC was synthesized via microwave reduction method. • Photocatalytic degradation ability for Rhodamine B was evaluated. • High charge separation and low electron-hole recombination was achieved. • Hydroxyl radicals were the active degrading species in photo-degradation. • Degradation intermediates were identified by LC–MS. In the present paper, we report the synthesis of activated carbon supported strontium/cerium bimetallic nanocomposite (Sr/Ce/AC BNC) that has been prepared by simple microwave reduction method. X- Ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Transmission electron microscopy (TEM) analyses were performed to characterize the fabricated Sr/Ce/AC BNC. Sr/Ce/AC BNC has been found to be efficient photocatalyst and has been explored for the degradation of rhodamine B under natural sunlight irradiation. The photocatalytic activity of Sr/Ce/AC was evaluated based on reaction kinetics to remove rhodamine B, chemical oxygen demand (COD), and total organic content (TOC). Hydroxyl radicals have been found to be the active participating species which was confirmed by using appropriate radical scavengers. Degradation intermediate products of rhodamine B has been identified using LC–MS and the reaction pathways were proposed and discussed in the manuscript. In short, this work provides a deep insight into the utilization of Sr/Ce/AC BNC as effective photocatalyst. [ABSTRACT FROM AUTHOR]

Zinc oxide-coated zeolite (ZOCZ) and zinc oxide (ZnO) were compared in terms of their effectiveness in removing Staphylococcus aureus (S. aureus) from nutrient broth and phosphate-buffered saline (PBS) solution. ZOCZ was found to be extremely efficient in removing S. aureus. ZnO initially was much less effective. Photographs of removal S. aureus from PBS solution with ZOCZ confirmed that a multilayer of S. aureus cells forms on the surface of ZOCZ particles. The comparison of the images of confocal laser scanning microscope and inverted contrast fluorescence microscope further proved that a multilayer of S. aureus cells formed on the surface of ZnO-30N-zeolite. The FESEM images showed that the cell membranes of S. aureus attached to the surface of ZnO-30N-zeolite collapsed. Energy Dispersive X-Ray Spectrum and the atomic absorption spectroscopic analysis confirmed that zinc ions penetrate into S. aureus cells, causing their death. The dead cells were easily removed, allowing ZOCZ to be reused. Image 105 • A multi-layer of S. aureus apparently formed on the surface of ZOCZ. • Effective removal of S. aureus is attributed to electrostatic interaction. • S. aureus cells in the outer layer are the result of settling. • Zinc ions accumulate in the S. aureus cells resulting in the death of cells. • Dead S. aureus cells close to the surface of ZOCZ allow easy reuse of ZOCZ. [ABSTRACT FROM AUTHOR]

Abstract Pharmaceuticals and many other chemicals are an important basis for nearly all sectors including for example, food and agriculture, medicine, plastics, electronics, transport, communication, and many other products used nowadays. This comes along with a tremendous chemicalization of the globe, including ubiquitous presence of products of chemical and pharmaceutical industries in the aquatic environment. Use of these products will increase with population growth and living standard as will the need for clean water. In addition, climate change will exacerbate availability of water in sufficient quantity and quality. Since its implementation, conventional wastewater treatment has increasingly contributed to environmental protection and health of humans. However, with the increasing pollution of water by chemicals, conventional treatment turned out to be insufficient. It was also found that advanced effluent treatment methods such as extended filtration, the sorption to activated charcoal or advanced oxidation methods have their own limitations. These are, for example, increased demand for energy and hazardous chemicals, incomplete or even no removal of pollutants, the generation of unwanted products from parent compounds (transformation products, TPs) of often-unknown chemical structure, fate and toxicity. In many countries, effluent treatment is available only rarely if at all let alone advanced treatment. The past should teach us, that focusing only on technological approaches is not constructive for a sustainable water quality control. Therefore, in addition to conventional and advanced treatment optimization more emphasis on input prevention is urgently needed, including more and better control of what is present in the source water. Measures for input prevention are known for long. The main focus though has always been on the treatment, and measures taken at the source have gained only little attention so far. A more effective and efficient approach, however, would be to avoid pollution at the source, which would in turn allow more targeted treatment to meet treated water quality objectives globally. New developments within green and sustainable chemistry are offering new approaches that allow for input prevention and a more targeted treatment to succeed in pollution elimination in and at the source. To put this into practice, engineers, water scientists and chemists as well as microbiologists and scientists of other related disciplines need to cooperate more extensively than in the past. Applying principles such as the precautionary principle, or keeping water flows separate where possible will add to this. This implies not minimizing the efforts to improve wastewater treatment but to design effluents and chemicals in such a way that treatment systems and water environments can cope successfully with the challenge of micropollutants globally (Kümmerer et al., 2018). This paper therefore presents in its first part some of the limitations of effluent treatment in order to demonstrate the urgent need for minimizing water pollution at the source and, information on why source management is urgently needed to improve water quality and stimulate discussions how to protect water resources on a global level. Some principles of green and sustainable chemistry as well as other approaches, which are part of source management, are presented in the second part in order to stimulate discussion. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The treatment of healthcare acquired infections (HAIs) is extremely costly. • This review addresses innovative composite antibacterial coated 2D and 3D-surfaces. • Cu, Ag and Cu-Ag presenting uniformity and adhesion catalytic coatings are reviewed. • The multidisciplinary aspect making the proposed review useful for large audience. Abstract The design, synthesis, fundamentals and evaluation of 2D/3D antimicrobial surfaces are addressed in detail in the current review. Recent advances in the antimicrobial mechanism, kinetics and properties of Ag, Cu and Ag-Cu surfaces in the dark and under light irradiation are described and discussed. The structure-reactivity relations in the catalyst/photocatalyst layers were described by way of the surface characterization and the observed antibacterial kinetics. Escherichia coli (E. coli) and Methicillin resistant Staphylococcus aureus MRS A bacteria are selected as model pathogens to evaluate the antimicrobial inactivation kinetics. The separate antimicrobial properties of ions and the antimicrobial surface-contact effects are presented in a detailed way. The interfacial charge transfer (IFCT) mechanism and the identification of the most relevant reactive oxygen species (ROS) leading to bacterial disinfection are considered. The recently developed monitoring of the changes of the film surface potential (Eigenvalues) during bacterial inactivation and the redox reactions associated with catalyst/photocatalyst surfaces are also presented. The potential for practical applications of these innovative 2D films and 3D sputtered medical devices in health-care facilities are accounted for in the present review. [ABSTRACT FROM AUTHOR]

To improve the peroxymonosulfate (PMS) utilization and the catalyst stability, a dual-reaction center catalyst, Cu-Mg 0.388 Al 2.408 O 4 -BN, was fabricated free of expensive rare metals. The presence of Mg leads to a positive-charged surface that was highly favorable for adsorbing bisphenol A (BPA) and PMS anions under neutral pH conditions. The relatively low electronegativity of Mg, together with the electronic compensation of cation-π between Cu and boron nitride (BN), resulted in the formation of the electron-rich Cu center. The combination of the electrostatic attraction and dual-reaction center led to the rapid degradation of BPA via a fast electron transfer step from BPA to the electron-rich Cu center, and then to PMS for effective activation. This unique design renders excellent reusability and stability of the catalyst by avoiding the redox cycle of Cu(I)/Cu(II). This research work opens new horizons to use common metals for efficient activation of PMS as economical alternatives over expensive rare metal catalysts in Fenton-like processes. [Display omitted] • Common metals (Cu, Ma, Al)-based catalyst was designed for efficient PMS activation. • Dual-reaction center avoids the redox cycle of Cu to keep catalytic stability. • Strong positive-charged catalyst surface promotes the adsorption of PMS and BPA. • Dual-reaction center and PMS adsorption enhanced e − transfer and PMS utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Humic acid coated magnetic nanoparticles effectively remove glyphosate. • Adsorption fits with the pseudo second-order kinetic and Langmuir isotherm models. • Nitrate and phosphate highly compete with GLY adsorption to HA-MNP. • The initial concentration/sorbent dose ratio is proposed as a controlling variable. Glyphosate, the most used herbicide in the world, poses a serious threat to terrestrial and aquatic ecosystems. Magnetic nanosorbents composed of magnetite (Fe 3 O 4) cores coated with humic acid were synthesized, characterized, and used to investigate the removal of glyphosate (GLY) through adsorption. The spherical-type particles (average particle size = 9 nm), highly crystalline spinel structure of the iron core and surface morphology were unchanged before and after GLY adsorption. Adsorption fits with the pseudo second-order kinetic and Langmuir isotherm models. The humic acid coated magnetic nanomaterials (HA-MNP) exhibit a high maximum adsorption capacity for GLY in pH 4.2, 30.4 mg g−1. The result of thermodynamics study indicated the adsorption is endothermic and spontaneous. Removal efficiency increased with decreasing solution pH. Chloride ions exhibit no inhibition, while nitrate and phosphate compete with GLY adsorption to HA-MNP. Although multi-parameter models have been successfully applied to model adsorption processes, such studies often require large sets of experiments and complex mathematical representations to capture the interactive play of different variables. We observed excellent agreement between predicted and experimental results using a new approach employing dimensional analyses with the application of Buckingham's π theorem for the combined concentration and dosing effects in the removal of GLY. In addition, error functions (r2 = 0.88) confirm the applicability of this model in the batch scale design independently of the sorbent dose and initial concentration. The accurate demonstration of this modeling approach for the adsorption of GLY on HA-MNP illustrates promise for predicting and optimizing adsorption treatment processes for different sorbents and target pollutants. The humic acid magnetic nanoparticles could be reused after regeneration and the removal efficiency of HA-MNPs decreased less than 35% after four adsorption-desorption cycles. [ABSTRACT FROM AUTHOR]

Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO 2 -derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification. Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed including doping with metals and non-metals, formation of hetero-junctions between TiO 2 and other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites. Different mechanisms such as band-gap narrowing, formation of localized energy levels within the bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account for the improved activity of doped TiO 2 photocatalysts . Various preparation routes for developing efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photo-controlled surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications in solar cells and flat panel displays have also been provided. Discussion is provided on TiO 2 based self-cleaning materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities in water management, antifouling applications and separation of oil in water emulsions are discussed. In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66 (BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials developed based on the principle of photo-induced hydrophilic conversion of TiO 2 surfaces have also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials suggest further development to improve their efficiency and utilities. It was concluded that a rational fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with tunable wettability would be favorable to address a number of existing environmental concerns. [ABSTRACT FROM AUTHOR]

The article discusses wastewater treatment methods that rely less on chemicals, so as to reduce water pollution. An overview of the use of organic compounds to treat wastewater, including lack of degradation of organic silicon compounds, is provided.

• NEO inventory in Lingdingyang Estuary was estimated with a mean of 76.8 tons/yr. • Net deposition fluxes of 5 NEOs experienced an exponential increase over time. • Western waters accumulated more NEO contamination than eastern waters. • Imidacloprid was the NEO with highest mean concentration of 7.66 ± 8.76 ng/g dw. • 65.1% of sediment samples exceeded the chronic threshold for aqueous organisms. Neonicotinoids (NEOs), as the most-consumed pesticides on a global scale, have posed a serious threat to human health and ecological environment. Information regarding the emission history of NEOs is of great importance to improve the prediction of their environmental loading and biological risk potential. In the present study, contamination levels and compositions of 12 NEOs were identified in 8 sediment cores from the Lingdingyang Estuary, which was impacted by agricultural emissions in riverine runoff of the Pearl River Basin for centuries. The total concentration of 12 target NEOs (∑ 12 NEOs) ranged from 0.02 to 69.5 ng/g dw along the sediment core profile, with a mean of 12.9 ± 15.9 ng/g dw. Net deposition fluxes and concentrations of 5 parent NEOs experienced a remarkable exponential increase in the vertical profile of sediment cores, except for imidacloprid (IMI). Despite the similar exponential growth before 2012, subsequent decreased levels of IMI in historical sediment indicated its gradual replacement by other NEOs. IMI was the NEO with the highest frequency of 80.3% and the highest mean concentration of 7.66 ± 8.76 ng/g dw. The ecological risk assessment of NEOs suggests that 65.1% of sediment samples exceeded the chronic threshold for aqueous organisms using equilibrium partitioning approach. Since downward diffusion of NEOs in the Lingdingyang Estuary was rectified by their rapid desorption, the sedimentary record probably provided an accurate illustration of agricultural NEO emissions in the Pearl River Basin, China. The recent NEO inventory in the adjacent waters of core sites was estimated with a mean of 76.8 tons/yr. This study provides insights into the role of agricultural emission in riverine runoff in the environmental loads of NEOs in the historical sediment. [Display omitted]. [ABSTRACT FROM AUTHOR]

Hydrophilic organic pollutants (HLOPs) in effluents of wastewater treatment plants are more prevalent than hydrophobic counterparts, therefore development of upstream processes that can effectively enhance the removal of HLOPs can substantially enhance overall treatment performance. To bridge this gap, 3D electrodes made of biochar-supported Al-ZnO nanoparticles (NAZO@BC) applied in heterogeneous electro-Fenton (EF) system, abbreviated as NBE−EF system, is rationally designed for enhanced elimination of HLOPs in wastewater. Our analysis indicates the NBE−EF system results in an efficient THM elimination, 42.4 times greater than that of conventional EF system. MoS 2 as an efficient cocatalyst plays an important role in the conversion from Fe(III) to Fe(II). Singlet oxygen (1O 2) and hydroxyl radical (•OH) are identified as the primary reactive oxygen species (ROS) in the NBE−EF system. NAZO@BC electrodes could concentrate HLOPs on their surface and degrade it effectively, achieving also a self-cleaning effect. Effective elimination of four HLOPs, i.e., thiamethoxam (THM), dinotefuran (DIN), nitenpyram (NIT), and acetamiprid (ACE), demonstrated the high degradation performance of the NBE−EF system, even at neutral and alkaline conditions. This study provides a new approach for enhanced elimination of HLOPs in wastewater treatment and mechanical insights into degradation pathways and toxicity attenuation. [Display omitted] • THM removal in the EF system is 42.4 times enhanced by NAZO@BC electrodes. • NEB-EF plays an important role in HLOP removal at neutral and alkaline conditions. • NAZO@BC electrodes concentrate HLOPs on the surface and achieve self-cleaning effect. • 1O 2 and •OH play important roles in the degradation and detoxification of HLOPs. • Eight mechanisms possibly account for THM degradation in the NBE−EF system. [ABSTRACT FROM AUTHOR]

One of the main goals of organic chemists is to find easy, environmentally friendly, and cost effective methods for the synthesis of industrially important compounds. Photocatalysts have brought revolution in this regard as they make use of unlimited source of energy (the solar light) to carry out the synthesis of organic compounds having otherwise complex synthetic procedures. However, selectivity of the products has been a major issue since the beginning of photocatalysis. The present article encompasses state of the art accomplishments in harvesting light energy for selective organic transformations using photocatalysts. Several approaches for the development of photocatalysts for selective organic conversions have been critically discussed with the objective of developing efficient, selective, environmental friendly and high yield photocatalytic methodologies. [ABSTRACT FROM AUTHOR]

Highlights: [•] The recent advances in ZVI are reviewed. [•] A review of contaminants removed by ZVI from groundwater and wastewater is made. [•] Excellent removal efficiencies of contaminants by ZVI are reported. [•] Reaction mechanisms of ZVI with contaminants are discussed. [•] The review suggests research needs for future work. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of an oxalic acid-modified swede rape straw (SRSOA). [•] SRSOA is a competitive and promising substitute for activated carbons. [•] SRSOA was systematically characterized and applied to dye adsorption study. [•] The disposal methodology of the depleted bioadsorbents was investigated. [•] Production of a biochar based on the dye-loaded bioadsorbents for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Increasing attention has been paid to persulfate due to its high efficiency in degrading organic pollutants. This paper investigated the transformation of a selected polychlorinated biphenyl (PCB) by sodium persulfate without activators at near ambient temperature (10–40°C). The results showed that 2,4,4′-CB was completely decomposed by persulfate at 30°C in 8h. The products were identified by gas chromatography–mass spectrometry (GC–MS), and transformation pathways could be divided into two steps as dechlorination and hydroxylation. Electron paramagnetic resonance (EPR) technique was used to identify the generated radical species at different pH values at ambient temperature. The results showed that sulfate radicals () were predominant under acidic condition and hydroxyl radicals (•OH) were predominant under basic condition. This behavior was also confirmed by the quenching studies and kinetic model. Decreasing the solution pH resulted in increasing the degradation efficiency of 2,4,4′-CB. Moreover, the degradation of other PCBs such as 2-CB, 4-CB, 2,4-CB, 2,4′-CB, and 2,4,6-CB with persulfate was examined. The findings of this study can provide guidance in the remediation of PCBs contaminated soil and water with persulfate. [Copyright &y& Elsevier]

Abstract: Magnetite nanoparticles (MNPs) are ubiquitous components of the subsurface environment, and increasing attention has been paid to MNPs due to their highly reductive and heterogeneous catalysis reactivity for the degradation of organic contaminants. However, most previous research studies neglected the generation of reactive oxygen species (ROS) by MNPs, which plays an important role in the transformation of contaminants. In this paper, we investigated the activation of persulfate (PS) by MNPs for the degradation of 2,4,4′-CB (PCB28), a selected model compound, and the underlying mechanism was elucidated. The results indicated that the PS can be activated by MNPs efficiently for the degradation of PCB28 at neutral pH. Electron paramagnetic resonance (EPR) technique was used to detect and identify the radical species in these processes. The mechanism of the activation of PS by MNPs was that superoxide radical anion (O2 −) generated by MNPs could activate the PS to produce more sulfate radicals (SO4 −), which favored the degradation of PCB28. The conclusion was further confirmed by quenching studies with the addition of superoxide dismutase (SOD). The effects of Fe(II) and pH on the degradation of PCB28 by PS/MNPs as well as the generation of ROS by MNPs were also studied. Both sorbed Fe(II) on MNPs surface and increased pH led to production of more O2 −, which activated the PS to give more SO4 − to degrade PCB28. In addition, increasing the oxygen concentration in the reaction solution favored the generation of O2 − as well as the degradation of PCB28. The findings of this study provide new insights into the mechanism of heterogeneous catalysis based on MNPs and the reactivity of MNPs toward environmental contaminants. [Copyright &y& Elsevier]

Abstract: Advanced oxidation processes (AOPs) based on sulfate radical (SO4 −) have been recently used for soil and groundwater remediation. The presence of chloride ion in natural or wastewater decreases the reactivity of sulfate radical system, but explanations for this behavior were inconsistent, and the mechanisms are poorly understood. Therefore, in this paper we investigated the effect of chloride ion on the degradation of 2,4,4′-CB (PCB28) and biphenyl (BP) by persulfate, based on the produced SO4 −. The results showed that the presence of chloride ion greatly inhibited the transformation of PCB28 and BP. Transformation intermediates of BP were monitored, suggesting that the chloride ion can react with SO4 − to produce chlorine radical, which reacts with BP to generate chlorinated compounds. To better understand the underlying mechanisms of these processes, a kinetic model was developed for predicting the effect of chloride ion on the types of radical species and their distributions. The results showed that chloride ion could influence the selectivity of radical species and their distribution, and increase the concentration of the sum of radical species. In addition, the second-order rate constants of sulfate radical with PCBs were determined, and quantum-chemical descriptors were introduced to predict the rate constants of other PCBs based on our experimental data. [Copyright &y& Elsevier]

Cyanotoxins are potent toxic compounds produced by cyanobacteria during algal blooms, which threaten drinking water supplies. These compounds can poison and kill animals and humans. The host-guest interactions of α, β, and γ-cyclodextrins (CD) with problematic cyanotoxins, including microcystins (MCs) and nodularin (NOD), were investigated to demonstrate the potential application of CDs for the removal of these toxins from drinking water or applications related to their separation or purification. MCs and NOD have a hydrophobic Adda chain, which contains diene and benzene functional groups. The complexation of these cyanotoxins with CDs was monitored by nuclear magnetic resonance (NMR). The ¹H NMR spectra for MCs are unchanged upon addition of α-CD (smallest host). However, addition of larger hosts, β-CD and γ-CD, leads to significant changes in chemical shifts of the benzene and diene resonances on the 3-amino-9-methoxy-2,6,8-trimethal-10-phenyldeca-4,6-dienoic acid (Adda) chain of MCs and NOD. Solution pH, natural organic matter, and salinity do not appreciably influence the host-guest complexation under our experimental conditions. The experimental binding constants for MCs and NOD with γ-CD are relatively strong, ranging from 1155 to 507 M-1. The observed changes in chemical shifts for specific protons and competitive binding experiments demonstrate a 1:1 inclusion complex between γ-CD and MCs or NOD, with the Adda chains threading through the CD ring, resulting in an inclusion complex. Our results suggest that CD-type substrates are useful hosts for the complexation of MCs and NOD. CDs can be readily attached to a number of polymeric or solid supports and their functionality tailored to strengthen specific host—guest interactions. With further development of such materials, CD host—guest chemistry may find direct application in the removal and/or separation science of these compounds. [ABSTRACT FROM AUTHOR]

The mutual influence of humic acid and Cr(Ⅵ) on water purification using ZnO–30N-zeolite was investigated in the laboratory. The removal of humic acid by ZnO–30N-zeolite with both pollutants present reached 90% in 5 min. With humic acid alone, more than one day was required to reach the same level of removal. Synergy between humic acid and chromium was thus demonstrated in their removal process by ZnO–30N-zeolite. However, the presence of humic acid showed no obvious effect on the removal capacity of Cr(Ⅵ) by ZnO–30N-zeolite. X-ray photoelectron spectra showed that Cr(VI) was reduced to Cr(Ⅲ) in the process by both humic acid and ZnO–30N-zeolite. The kinetic mechanism of synergistic removal of humic acid and Cr(Ⅵ) by ZnO–30N-zeolite in binary pollutant system was also proposed. [Display omitted] • The competitive adsorption of Cr(VI) and HA on ZnO–30N-zeolite was investigated. • The formation of complexes between Cr and HA accelerated the removal of HA by ZnO–30N-zeolite. • Part of Cr(VI) was reduced to Cr(III) by both humic acid and ZnO–30N-zeolite. • Electrostatic interaction is the main driving force for the removal of Cr(VI) by ZnO–30N-zeolite. [ABSTRACT FROM AUTHOR]

Abstract: Prior studies have shown the effectiveness of Fenton reagent (FR) for degrading low concentrations (1.0–2.0mg/L) of methyl tert-butyl ether (MTBE), similar to those found in contaminated groundwater. The present study investigates the effect of increasing FR doses on the extent of degradation and mineralization of a given initial MTBE concentration. The FR to MTBE molar ratio (FMMR) was the operating variable, and was investigated at values between 0.5:1 and 200:1. This approach provided sequential snapshots of the MTBE degradation process, which may help to improve the understanding of MTBE degradation with FR. The initial MTBE concentration (MTBE0) was approximately 22.7μM (∼2.0mg/L), and FR was used in a 1:1 molar ratio of ferrous iron (Fe2+) and hydrogen peroxide (H2O2). The concentrations of MTBE and the following main reaction byproducts: tert-butyl formate (TBF), tert-butyl alcohol (TBA), acetone and methyl acetate were determined from samples collected at specific intervals over a total reaction time of 1h. Total organic carbon (TOC) was monitored to determine MTBE mineralization, and the total concentration of tert-butyl compounds (tBC) was monitored due to the suspected toxicity associated with this functional group. The results showed that the minimum FMMR necessary for achieving complete MTBE degradation was 20:1, but at that FMMR, TOC and tBC reduction were only 45.6% and 24.9%, respectively. Complete MTBE mineralization was not achieved in any case, even at FMMRs as high as 200:1, where only 63.3% of mineralization was observed (although tBC reduction reached 99.6%, since traces of TBA were still detected). These results confirm the relative inability of FR to achieve complete mineralization of a target substrate, even those that are highly reactive with the hydroxyl radical. [Copyright &y& Elsevier]

Abstract: Bimodal mesoporous TiO2–P25 composite thick films with improved structural integrity (less crack formation) were successfully synthesized by employing an environmental friendly and highly viscous nonionic surfactant Tween 20 as a tri-functional template, which can simultaneously improve film texture, bimodal mesopore structure and structural integrity in the films. It was found that increasing Tween 20 loading from 10% to 50% (v/v) could simultaneously increase both volumes of small mesopore and secondary large mesopore. Degussa P25 nanoparticle can function as a kind of pore wall contributing to the formation of secondary large mesopore. Optimizing the loading of Tween 20 could result in optimum film thickness, even with only one dip-coating cycle. The final film at optimum Tween 20 loading (50%, v/v) exhibited large porosity (50.6%) and bimodal mesoporous size distribution with small mesopore size of ∼5nm and large mesopore size of ∼34nm. Compared with mono-modal mesoporous TiO2 film (no Degussa P25) at optimum preparation conditions (Tween 20, 50% (v/v), six dip-coating layers), the TiO2–P25 composite films prepared with the same Tween 20 loading (one dip-coating layer) or with 25% (v/v) Tween 20 loading (two dip-coating layers) demonstrated higher photocatalytic activities in the degradation of creatinine, an important human metabolite present in human urine. These results prove that bimodal mesoporous TiO2–P25 composite films have promising properties for photocatalytic water treatment. [Copyright &y& Elsevier]

Abstract: In this project, immobilized titanium dioxide photocatalysis was utilized as a post-treatment technology for the destruction of model organic contaminants found in wastewater streams produced on-board during space exploration. Phenol, a known human carcinogen, and creatinine, a human metabolite found in urine, were the compounds tested in this study. Phenol and creatinine have cyclic structures consisting of six and five member rings, respectively. In addition, creatinine is a methyl guanidine derivative, with almost 40% (w/w) nitrogen. The degradation and carbon mineralization efficiencies of the target contaminants were investigated at different initial concentrations. Their photocatalytic degradation appears to follow pseudo-first-order reaction with phenol giving higher organic carbon reduction rates than creatinine. The presence and position of the functional groups of creatinine (amine, imine and peptide bond) are primarily responsible for the significantly slower mineralization. The degradation of creatinine was also tested at different pHo values. Statistical analysis showed that there is an effect of pH on the treatment of creatinine. Besides the carbon mineralization, the extent of nitrogen mineralization and the mass balance of nitrogen were conducted for three pH values (pHo 3.0, 6.2 and 11.0). Overall, the transformation of nitrogen was low, and the total maximum conversion (<20%) occurred at basic conditions. [Copyright &y& Elsevier]

Abstract: Two types of photocatalytic films, macroporous TiO2-P25 (Degussa) composite films (PPMSGF-PEG) and macroporous TiO2 films (TiO2-PEG), have been synthesized by a P25-PEG modified sol–gel method and a PEG modified sol–gel method, respectively. The physicochemical properties, including thermal behavior, surface morphology, crystallinity, crystal size, specific surface area (BET), pore volume and adhesion on the stainless steel substrate, of the two types of films were investigated by TGA, SEM, XRD, Raman spectroscopy, HRTEM, N2 adsorption and the tape test. The photocatalytic activities of the films were compared using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant in water. It was found that adding 10g/L P25 in the sol can improve not only the amount of crystalline material immobilized on the support, but also the BET surface area and pore volume of the films calcined at temperatures between 500 and 600°C. N2 adsorption results suggested that the enhanced BET surface area and pore volume were due to the formation of large pores induced by the presence of P25 powders, which could help retain a relatively high pore volume during calcination at higher temperatures. The results on photocatalytic degradation of 4-CBA showed that the increase in photocatalytic activity caused by P25 powders reached maximum for PPMSGF-PEG calcined at 500°C, compared with that of TiO2-PEG film. The tape test showed that adding 10g/L P25 in the sol did not affect the critical calcination temperature (i.e., 500°C) at or above which excellent adhesion between the films and the stainless steel substrate can be maintained. This study proves that optimizing calcination temperature is still an important strategy for the preparation of macroporous TiO2-P25 composite films with enhanced photocatalytic activity and excellent adhesion on the stainless steel substrate. [Copyright &y& Elsevier]

Abstract: A transparent, relatively dense and thick TiO2 film with good mechanical properties and enhanced photocatalytic activity has been successfully immobilized on 304 stainless steel. The study included optimization of structural properties and film thickness. Experiments on the photocatalytic degradation of 4-chlorobenzoic acid (4-CBA) as a model organic contaminant showed that the photocatalytic activity of this kind of thick film can be significantly improved by decreasing calcination temperature (i.e. from 600 to 500°C), which is due to an increase in BET surface area and porosity, decrease in crystal size, and decrease in foreign metal diffusion from stainless steel support to the surface of the film. The observed apparent rate constant of TiO2-500 (500°C, two dip coating layers) was found to be approximately 5.2 times that of TiO2-600 (600°C, two dip coating layers). The results showed that increasing film thickness within a certain range (up to 10μm) could significantly improve the photocatalytic activity without causing crack formation for the thick TiO2-500 film (500°C). The optimum film thickness is 10μm (four dip coating cycles), under which the observed apparent rate constant of TiO2-500 is approximately 2.3 times higher than that of TiO2-500 with 2.5μm film thickness (one dip coating layer). Based on several advantages of TiO2-500 film (500°C, four dip coating layers), including high photocatalytic activity, absence of foreign metal ions at the film surface, optimum film thickness, good structural integrity, and excellent adhesion on the stainless steel support, this kind of sol–gel-derived thick film immobilized on stainless steel support is a promising potential photocatalyst for water treatment applications. [Copyright &y& Elsevier]

Abstract: The role of Degussa P-25 loading (0–100g/L) in the alkoxide sol was investigated for the synthesis of immobilized TiO2 photocatalytic films on 304 stainless steel using the P-25 powder-modified sol–gel method (PPMSGM). The structural properties of the films (PPMSGFs) obtained after gel drying and calcination at 600°C were examined using different materials characterization techniques including X-day diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of films with good adherence to the stainless steel support were evaluated using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant and UV-A radiation. The P-25 loading did not have a significant effect on the size of the crystallites in the films. However, increasing the P-25 loading in the sol resulted in an increase in (i) the amount of crystalline material retained on the support (i.e., for both anatase (101) and rutile (110) crystal phases); (ii) the number of grains (aggregates of P-25 particles and crystallites formed from the alkoxide sol); (iii) the number of pores in the film (in the range of 0–50g/L); and (iv) the number of microcracks on the surface of PPMSGFs. On the other hand, increasing the P-25 loading in the sol resulted in a decrease in the size of grains on the surface of PPMSGFs. XPS analysis revealed the presence of Cr3+, Mn3+ and Fe3+ on the surface of PPMSGFs as a result of diffusion of these species from the stainless steel support during film calcination at 600°C. The concentration of these foreign species on the film surface decreased with an increase in the P-25 loading in the sol. Increasing P-25 loading in the sol yielded films with higher photocatalytic activity but a concentration of 50g/L P-25 in the sol was found as the maximum for obtaining films with good adherence on the stainless steel support. Increase in the photocatalytic activity of the films with increasing P-25 loading in the sol was mainly attributed to the enhancement of the number of P-25 active sites exposed to the solution due to film morphology and surface characteristics and to the reduction in Cr3+ and Fe3+ concentrations on the surface of the films. [Copyright &y& Elsevier]

The sulfate radical pathway of the room-temperature degradation of two phenolic compounds in water is reported in this study. The sulfate radicals were produced by the cobalt-mediated decomposition of peroxymonosulfate (Oxone) in an aqueous homogeneous system. The major intermediates formed from the transformation of 2,4-dichlorophenol were 2,4,6-trichlorophenol, 2,3,5,6-tetrachloro-1,4-benzenediol, 1,1,3,3-tetrachloroacetone, pentachloroacetone, and carbon tetrachloride. Those resulting from the transformation of phenol in the presence of chloride ion were 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6- dichlorophenol, 1,1,3,3-tetrachloroacetone, and pentachloroacetone. In the absence of chloride ion, phenol transformed into 2,5-cyclohexadiene-1,4-dione (quinone), 1,2-benzenediol (catechol), and 1,4-benzenediol (hydroquinone). Several parameters were varied, and their impact on the transformation of the organic compounds is also discussed. The parameters varied were the initial concentration of the organic substrate, the dose of Oxone used, the cobalt counteranion, and in particular the impact of chloride ions and the quenching agent utilized for terminating the reaction. This is one of the very few studies dealing with intermediates formed via sulfate radical attack on phenolic compounds. It is also the first studythat explores the sulfate radical mechanism of oxidation, when sulfate radicals are generated via the Co/Oxone reagent. Furthermore, it provides strong evidence on the interaction of chloride ions with sulfate radicals leading to halogenation of organics in water. [ABSTRACT FROM AUTHOR]

Abstract: TiO2 films on 304 stainless steel with optimum P-25 loading (PPMSGFs-50) were prepared by the P-25 powder-modified sol–gel method (PPMSGM) at calcination temperatures from 400 to 700°C. The as-prepared PPMSGFs-50 were characterized by differential scanning colorimetry/thermogravimetric analyses (DSC/TGA), scanning electron microscopy (SEM), TEM/high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), N2 adsorption and X-ray photoelectron spectroscopy (XPS). Their adhesion properties were tested by the scratch test and cross-hatch adhesion test and their photocatalytic activities were evaluated using 4-CBA as a model organic contaminant in water. It was found that decreasing calcination temperature leads to a decrease in the critical loading, which has a detrimental effect on the mechanical stability of the films. On the other hand, decreasing calcination temperature leads to an enhancement of photocatalytic activity. The optimum calcination temperature is 500°C under which both enhanced photocatalytic activity and good adherence on the support could be obtained. The 4-CBA removal efficiency for PPMSGF-50 at 500°C was approximately four times that of PPMSGF-50 at 600°C after 10h of photocatalytic oxidation. Increasing calcination temperature in the range between 500 and 700°C caused a significantly increase in the diffusion of foreign metals (i.e. chromium, iron and manganese) from the stainless steel support to the TiO2 film. It is believed that the enhancement of the photocatalytic activity at lower calcination temperatures (400–500°C) is due to an increase in the amount of two type of crystallites exposed to the solid–liquid interface and decrease in foreign metal ion concentrations (i.e. Cr3+) on the surface of the films. [Copyright &y& Elsevier]

Abstract: The fundamentals of the Fenton reagent-based degradation of low concentrations of methyl tert-butyl ether (MTBE) in batch reactors under initially anaerobic conditions are discussed in this work. The objective of the study was to quantitatively verify the feasibility of MTBE degradation with Fenton reagent under such conditions. The conclusions may be potentially helpful to further develop an effective in situ treatment of MTBE-contaminated groundwater. Initial MTBE concentrations ([MTBE]0) of 11.4 and 22.7μM (approximately 1.0 and 2.0mg/L, respectively) were treated with Fenton reagent (FR) using a [FR]0:[MTBE]0 molar ratio of 10:1. FR was used in equimolar mixture of Fe2+and H2O2 (i.e., [Fe2+]0:[H2O2]0=1:1). This analysis considers the hydroxyl radicals (OH ) produced by FR as the main species responsible for the degradation processes. The effects of [MTBE]0 and pH on the oxidation kinetics were investigated. Under these conditions it was observed that: (i) MTBE was degraded at high extent (90–99%) after 1h of reaction time, (ii) MTBE mineralization was low in all cases and reached only 31.7% at the best conditions, and (iii) In all cases, most of MTBE degradation occurred during the initial 3–5min of reaction. During this brief initial phase, MTBE transformation followed pseudo-first order kinetics, while the subsequent phase exhibited a sharp drop in degradation rate and had almost negligible contribution to the overall degradation. Experiments performed at acidic pH exhibited the best degradation results, while at neutral pH the degradation rates dropped significantly. Other parameters included in this analysis were: TOC reduction and total concentration of compounds containing the tert-butyl group in their structure (tBC). These compounds were analyzed because of the concerns related to their potential toxicity. Tert-butyl formate (TBF), Tert-butyl alcohol (TBA), acetone and methyl acetate were identified and quantified as major reaction intermediates. [Copyright &y& Elsevier]

This study explores the effect of ultraviolet (UV) light radiation and/or transition metals (M) for the activation of common oxidants (Ox) with the objective of treating recalcitrant organic contaminants in water. Hydrogen peroxide, potassium peroxymonosulfate and potassium persulfate were combined with iron, cobalt and silver, respectively, and/or with UV light (254nm) and were tested for the treatment of 2,4-dichlorophenol (2,4-DCP). Results from our previous studies indicated that these particular transition metals are the best catalysts for the activation of the respective oxidants [G.P. Anipsitakis, D.D. Dionysiou, Environ. Sci. Technol. 37 (2003) 4790; G.P. Anipsitakis, D.D. Dionysiou, Environ. Sci. Technol. 38 (2004) 3705]. From the combined use of UV, the oxidants and the transition metals, four general categories of advanced oxidation technologies were evaluated and compared for the degradation and mineralization of 2,4-DCP. Those were (i) the dark conjunction of each oxidant with its favorable metal activator (M/Ox), (ii) the use of UV alone, (iii) the combination of UV with each oxidant (UV/Ox) and (iv) the use of UV combined with each metal/oxidant systems (UV/M/Ox). In particular, the systems UV/KHSO5, UV/Co(II)/KHSO5 and UV/Ag(I)/K2S2O8 and the sulfate radicals generated thereby have never been tested before for water decontamination, as opposed to the extensively investigated hydroxyl radicals generated by UV/H2O2 and the photo-Fenton. The comparison of the results with respect to the transformation of 2,4-DCP and the extent of organic carbon removal led to the construction of the following order of efficiencies: UV/K2S2O8 > UV/KHSO5 > UV/H2O2 for the UV/Ox processes and UV/Fe(III)/H2O2 > UV/Fe(II)/H2O2 > UV/Co(II)/KHSO5 > UV/Ag(I)/K2S2O8 for the UV/M/Ox processes tested here. All experiments were homogeneous and conducted at ambient room temperature. The relative absorbance of the species participating in the reactions supports the former order of efficiency, since persulfate followed by peroxymonosulfate were proven more photosensitive than hydrogen peroxide. Among the metals tested, only iron species such as Fe(OH)2+ were found to absorb strongly at 254nm and to this is attributed the higher efficiencies obtained with the photo-Fenton reagents. [Copyright &y& Elsevier]

The photolytic degradation of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) and pentachlorophenol (PCP) in 1-butyl-3-methylimidazolium hexafluorophosphate {[bmim+]PF6-} and 1-ethyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide {[emim+]beti} room temperature ionic liquids (RTILs) has been investigated using UV radiation of 253.7 nm. Stability study revealed that these RTILs are relatively resistant to phototransformation when used as pure phases. At low concentrations (less than 1.57 mM), chlorinated phenols could be degraded in these RTILs following pseudo-first-order kinetics. Intermediate product identification using Electrospray TOF MS, GC–MS and HPLC revealed the formation of phenol among the stable phototransformation intermediates of 2-CP. It is proposed here that two possible pathways, via formation of phenoxyl radical or carbene, could lead to phenol generation. In these two mechanisms, {[bmim+]PF6-} may participate in the reaction as H-donor. The increase of the chlorine atoms in the phenolic ring generally resulted in a decrease in the phototransformation rates, with exception of 2,4,6-TCP. UV absorbing impurities present in the ionic liquids as received from the manufacturer had a significant negative effect on the phototransformation rate of chlorophenols. Purification of RTILs using activated carbon enhanced the photodegradation rates. On the other hand, these impurities could, at some extent, protect the ionic liquid from photolysis and enhance the stability of the solvent. Recyclability study indicated that the recycling of the solvents was hindered at some extend by the presence of organic impurities that were resistant to photolysis or by the generation of byproducts that were resistant to photolytic degradation and compete with the chlorophenols for photon absorption. While further research is necessary to examine all aspects of this system, including the use of non-toxic RTILs, it is feasible that this technology can be further developed into a two-step process for extraction of organic pollutants from solid matrices, such as contaminated soils or dredged sediments, using ionic liquid solvents followed by in situ photodegradation of the organic contaminants in the ionic liquid extractant phase while achieving simultaneously regeneration of the solvent. [Copyright &y& Elsevier]

The effect of hydrogen peroxide on the photocatalytic degradation of organic contaminants in water was investigated using a TiO2-rotating disk photocatalytic reactor (RDPR) operated in a continuous-mode and at steady state. The experiments were performed at pH 3.0, in the presence of near-UV radiation, and using 4-chlorobenzoic acid (4-CBA) as a model non-volatile organic contaminant at influent concentration of 300 μmol l-1. Experiments were performed at concentrations of hydrogen peroxide in the range 0–10.74 mmol l-1. Addition of hydrogen peroxide at small concentrations (<2 mmol l-1) had a synergistic effect and increased considerably the rates of photocatalytic reactions. An optimum influent hydrogen peroxide concentration was observed at 1.6 mmol l-1, which caused an increased in the rates of 4-CBA degradation and total organic carbon (TOC) mineralization by 1.72 and 2.13 times, respectively. This corresponded to an optimum oxidant to contaminant molar ratio of 5.33. At higher concentrations, hydrogen peroxide was found to cause an inhibiting effect on the photocatalytic reactions. The synergistic and inhibiting effects of hydrogen peroxide were rationalized based on the reaction rate constants between relevant radical species. [Copyright &y& Elsevier]

Nine transition metals were tested for the activation of three oxidants and the generation of inorganic radical species such as sulfate, peroxymonosulfate, and hydroxyl radicals. From the 27 combinations, 14 M/Ox couples demonstrated significant reactivity toward transforming a model organic substrate such as 2,4-dichlorophenol and are further discussed here. It was found that Co(ll) and Ru(lll) are the best metal catalysts for the activation of peroxymono-sulfate. As expected on the basis of the Fenton reagent, Fe(IlI) and Fe(lI) were the most efficient transition metals for the activation of hydrogen peroxide. Finally, Ag(l) showed the best results toward activating persulfate. Quenching studies with specific alcohols (tert-butyl alcohol and ethanol) were also performed to identify the primary radical species formed from the reactive M/Ox interactions. The determination of these transient species allowed us to postulate the rate-determining step of the redox reactions taking place when a metal is coupled with an oxidant in aqueous solution. It was found that when Co(ll), Ru(III), and Fe(ll) interact with peroxymonosulfate, freely diffusible sulfate radicals are the primary species formed. The same was proven for the interaction of AgO) with persulfate, but in this case caged or bound to the metal sulfate radicals might be formed as well. The conjunction of Ce(lII), Mn(Il), and Ni(Il) with peroxymonosulfate showed also to generate caged or bound to the metal sulfate radicals. [ABSTRACT FROM AUTHOR]

In a previous paper [J. Mater. Sci. 38 (2003) 823] we have described the preparation and characterization of conventional alkoxide sol–gel derived TiO2 films [J. Mater. Sci. 23 (1988) 2259] and of TiO2 powder enriched alkoxide sol–gel derived films. The powder films were prepared on flat stainless steel substrates and on glass beads. These films were characterized for various parameters like particle size, crystal phase, pore size, thickness and mechanical properties. In our current study, the photocatalytic activities of these sol–gel derived TiO2 films were studied utilizing a quartz batch reactor. The quartz batch reactor was characterized for parameters like mixing, recycle, aeration and UV radiation flux, and the TiO2 coated substrates were used as the photocatalyst. The activities of the catalyst films were evaluated by measuring the degradation rate of 4-chlorobenzoic acid used as a model organic pollutant. Immobilized TiO2 powder films on stainless steel containing a mixture of anatase and rutile phases were found to be more effective than films that were substantially composed of anatase phase particles. The activity of glass beads coated with TiO2 powder was compared to the activity of commercially available TiO2 catalyst beads. While the activity of the commercially available TiO2 catalyst beads was higher there was significant attrition of the TiO2 catalyst film. The films on the glass beads possessed better mechanical properties than the commercial catalyst beads and their activity can be significantly improved by optimizing the film synthesis process parameters. [Copyright &y& Elsevier]

A highly efficient advanced oxidation process for the destruction of organic contaminants in water is reported. The technology is based on the cobalt-mediated decomposition of peroxymonosulfate that leads to the formation of very strong oxidizing species (sulfate radicals) in the aqueous phase the system is a modification of the Fenton Reagent, since an oxidant is coupled with a transition metal in a similar manner. Sulfate radicals were identified with quenching studies using specific alcohols. The study was primarily focused on camparing the cobalt/peroxymonosulfate (Co/PMS) reagent with the traditional Fenton Reagent [Fe(II)/H[sub2]/O[sub2]] in the dark, at the pH range 2.0-9.0 with and without the presence of buffers such as phosphate and carbonate. Three model contaminants that show diversity in structure were tested: 2,4-dichlorophenol, atrazine, and naphthalene. Cobalt/peroxymonosulphate at acidic pH, but, at higher pH (neutral), the latter was proven much more effective. The extent of mineralizatio, as total organic carbon removed, was also monitored, and again the Co/PMS reagent demonstrated higher efficiencies than the Fenton Reagent. Cobalt showed true catalytic activity in the overall process, since extremely low concentrations (in the range of μg/l) were sufficient for the decomposition of the oxidant and thus the radical generation. The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling. [ABSTRACT FROM AUTHOR]

Discusses the effect of oxygen in a thin film rotating disk photocatalytic reactor. Effect on photocatalytic degradation rates; Effect of oxygen uptake on the increase of dissolved oxygen; Limitations of oxygen transport in the thin liquid film.

In a previous study, the chemical oxidation of methyl tert-butyl ether (MTBE) at low concentrations in water using Fenton's reagent (FR) was investigated. At certain reaction conditions the process achieved 99.99% degradation of MTBE but it did not result in complete MTBE mineralization. In the present study, the major intermediate by-products generated during the reaction, such as tert-butyl formate (TBF), tert-butyl alcohol (TBA), methyl acetate, and acetone were separately used as parent contaminants and treated under the same reaction conditions initially used for MTBE (i.e., pH of the water, molar ratio of pollutant to FR) in order to compare their degradability by hydroxyl radicals generated from Fenton's reaction. The results were compatible with the second order reaction rate constants for the reaction of hydroxyl radicals with each contaminant commonly available in the literature. The comparison of the degradation kinetics for each intermediate by-product provided information that aims at unveiling the limiting step(s) of the entire MTBE degradation pathway. In this context, it was found that (1) TBA was generated by reactions subsequent to those that produced TBF, (2) acetone was originated by at least three independent pathways involving direct hydroxyl radical attack on MTBE, TBF, and TBA, and (3) methyl acetate was formed exclusively from MTBE. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of a model non-volatile chlorinated aromatic compound 4-chlorobenzoic acid (4-CBA) was investigated as a function of disk angular velocity, contaminant concentration, and incident light intensity using a rotating disk photocatalytic reactor (RDPR). The study was designed to investigate the effect of all three parameters on the degradation rate as well as their importance on unveiling the existence of mass transfer limitations in the liquid phase under specific conditions. The results showed that the reaction rate increased with disk angular velocity in accordance with a saturation-type dependency. In the range of 2–6 rpm the degradation rate increased almost linearly with disk angular velocity. Above 6 rpm, however, the influence of disk angular velocity was not significant. The initial increase in the reaction rate with disk angular velocity was attributed to the longer time available per rotation resulting in higher down flow of liquid carried by the disk and to the increase in the overall mass transfer coefficient. The rates of 4-CBA acid decomposition and Cl− mineralization at 6 rpm as a function of initial 4-CBA concentration followed Langmuir–Hinshelwood kinetics. At 6 rpm, the rates of 4-CBA degradation followed a linear dependency with incident light intensity. This was attributed to the existence of low local values of incident light intensity on the illuminated disk. With respect to the effect of these three parameters on the degradation rate, the obtained results suggested the absence of significant mass transfer limitations at disk angular velocities higher than 6 rpm. The latter was verified by additional calculations of the Damko¨hler (Da) number based on dimensionless analysis. The Da number was found to decrease significantly with disk angular velocity and at high disk angular velocities (ω>15 rpm), Da was much lower than 0.1, even when the concentration of the contaminant in the bulk was extremely small (i.e. 1 μmol/l). [Copyright &y& Elsevier]

Heterogeneous Fenton catalysts are emerging as excellent materials for applications related to water purification. In this review, recent trends in the synthesis and application of heterogeneous Fenton catalysts for the abatement of organic pollutants and disinfection of microorganisms are discussed. It is noted that as the complexity of cell wall increases, the resistance level towards various disinfectants increases and it requires either harsh conditions or longer exposure time for the complete disinfection. In case of viruses, enveloped viruses (e.g. SARS-CoV-2) are found to be more susceptible to disinfectants than the non-enveloped viruses. The introduction of plasmonic materials with the Fenton catalysts broadens the visible light absorption efficiency of the hybrid material, and incorporation of semiconductor material improves the rate of regeneration of Fe(II) from Fe(III). A special emphasis is given to the use of Fenton catalysts for antibacterial applications. Composite materials of magnetite and ferrites remain a champion in this area because of their easy separation and reuse, owing to their magnetic properties. Iron minerals supported on clay materials, perovskites, carbon materials, zeolites and metal-organic frameworks (MOFs) dramatically increase the catalytic degradation rate of contaminants by providing high surface area, good mechanical stability, and improved electron transfer. Moreover, insights to the zero-valent iron and its capacity to remove a wide range of organic pollutants, heavy metals and bacterial contamination are also discussed. Real world applications and the role of natural organic matter are summarised. Parameter optimisation (e.g. light source, dosage of catalyst, concentration of H 2 O 2 etc.), sustainable models for the reusability or recyclability of the catalyst and the theoretical understanding and mechanistic aspects of the photo-Fenton process are also explained. Additionally, this review summarises the opportunities and future directions of research in the heterogeneous Fenton catalysis. ga1 • Generalised mechanisms of electron transfer in Fenton catalysts. • Heterogeneous photo-Fenton for the removal of bacteria and viruses. • Advanced hybrid catalysts of MOFs, perovskites, g-C3N4 etc. • ZVI for removing heavy metal ions and halogenated organic compounds. • Future research directions for improving heterogeneous Fenton catalysis. [ABSTRACT FROM AUTHOR]

• The cross-coupling catalytic reactions of methanol with its by-products were studied. • A fixed-film UV photoreactor consisting of Pt/TiO 2 thin film was developed. • The methyl formate produced from photooxidation reaction of the methoxy and formaldehyde. • The chemisorbed methanol converts firstly to formaldehyde and then to methyl formate. • Yield and selectivity of oxidative by-products were dependent on methanol surface coverage. The photocatalytic assessment of methanol conversion through cross-coupling reaction of methanol with its products was studied in a UV reactor consisting of platinum nanoparticles deposited onto a mesoporous TiO 2 film. The temperature-programmed desorption (TPD) analysis showed excess methanol can affect the selective formation of formaldehyde, formic acid, and methyl formate (MF). The TPD results showed the methanol surface coverage, UV photon energy and irradiation time have mutual effects on the oxidation products. At saturated fraction of methanol coverage, formaldehyde was converted to MF and the desorption temperature of MF shifts to lower value. At 266 nm, the photooxidation reaction was more than two orders of magnitude faster than at 355 nm, suggesting that the selectivity of MF increases by the saturated fraction of methanol and increasing photon energy, while the formation of formaldehyde decreases at the same conditions. The formaldehyde conversion to formic acid gradually increases with increasing irradiation time. [ABSTRACT FROM AUTHOR]

• The MoS 2 intercalated CTAB was applied to remove Cr(VI) and Ni(II) simultaneously. • The enlarged interlayer spacing of MoS 2 was confirmed by XRD results. • The q max of Cr(VI) and Ni(II) for MoS 2 /CTAB was 79 and 88 mg g−1, respectively. • Redox reaction between Cr(VI) and Mo(IV) was first verified. • MoS 2 /CTAB possessed outstanding reusability in the removal of Cr(VI) and Ni(II). The treatment of heavy metal pollution in aquatic environment, especially the pollution caused by multiple heavy metal ions, has been a growing global concern for decades. To address this problem, it is urgent to explore effective and low cost adsorbents which can remove multiple heavy metal ions simultaneously. Herein, Cr(VI) and Ni(II) removal from water by MoS 2 with widened interlayer spacing was systematically investigated in comparison with pure MoS 2. A series of techniques, including X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) surface area and porosimetry analysis were applied to characterize the nanocomposites. The XRD results confirmed the enlarged interlayer spacing of MoS 2 by intercalating cetyl trimethyl ammonium bromide (CTAB) into the interlamination. The maximum adsorption capacities of Cr(VI) and Ni(II) for MoS 2 /CTAB were 79.4 mg g−1 and 88.3 mg g−1, respectively. Moreover, a synergistic effect in the simultaneous removal of Cr(VI) and Ni(II) was observed. A new Cr(VI) removal mechanism involving redox reaction between Cr(VI) and Mo(IV) in MoS 2 /CTAB was verified. The removal efficiencies of Cr(VI) and Ni(II) still remained high at the end of fifth cycle, indicating that MoS 2 /CTAB has a great potential to remove heavy metals from wastewater. [ABSTRACT FROM AUTHOR]

• Black phosphorous (BP)-based nanostructures emerge as promising nanomaterials in remediation. • BP with large surface area removes arsenic(III) and chromium(VI) efficiently. • Adsorption capacity, isotherms, and mechanisms of BP are presented. • BP has broadband light absorption that bestows photocatalytic activity under solar light irradiation. • Photocatalytic activity of BP and involved oxidative species are described. In recent years, increased attention has been given to black phosphorous (BP)-based materials (i.e., 2D nanomaterials) due to their applications in electronics, biomedical equipment, energy conversion and storage, and environmental remediation. The uses of BP-based materials in pollution control are emerging. BP possesses puckered honeycomb like structure with high surface area, high charge-carrier mobility, and layer-dependent direct-bandgap (0.3–2.0 eV) for broadband light absorption. These properties make BP a superior material to carry out solar light-based photocatalytic processes. This review presents the current status of these materials in adsorption and photocatalytic processes in removing a wide range of pollutants from water and air. The progress made in elucidating the mechanisms of the processes is discussed. The strong interactions between the active sites of BP and the pollutants (e.g., As(III) and Cr(VI)) result in the excellent efficiency of the materials in pollution remediation of the spiked clean water samples. In the photocatalytic processes, the superior performance for eliminating pollutants (e.g., dyes) is attributed to the improved light harvesting and reduced recombination of the photo-induced electrons and holes. Importantly, BP-based composites possess significantly enhanced stability and excellent reusability in both adsorptive and photocatalytic processes. Future investigations on BP-based materials should include their structural development to enhance their stability and usability in real environmental matrices. [ABSTRACT FROM AUTHOR]

• FA enhanced CT reduction in the oxygenated nZVI/FA suspension. • The enhancement of FA on Fe2+ elution in nZVI suspension was investigated. • Oxidant H 2 O 2 and CP for CT removal in nZVI/FA system was conducted. • The linkage between Fe2+, HO and CO 2 − for CT removal was established. Although the utilization of formic acid (FA) as a target compound for modeling the kinetic and mechanism in several Fenton processes has been previously reported, this study explored the potential of FA as an efficient hydroxyl radical (HO) scavenger to generate reductive carbon dioxide radical (CO 2 −) for carbon tetrachloride (CT) degradation in nanoscale zero valent iron (nZVI) suspension in the presence and absence of oxidant. The results showed that the presence of 3.12 mM FA enhanced CT removal from 11.4% to 85.0% within 60 min in oxygenated 0.5 g/L nZVI suspension. Meanwhile, the presence of 3.12 mM FA improved Fe2+ elution by 5 folds under pH = 3. The generation of H 2 O 2 in oxygenated nZVI suspension was also monitored. Hence, it was hypothesized that the rapid CT degradation in nZVI/FA system was initiated by reductive CO 2 − radical. In anaerobic nZVI/oxidant/FA system, CT degradation of 69.3% and 75.1% was achieved when using H 2 O 2 or calcium peroxide (CP) as the oxidant, respectively. The addition of oxidant at 10 min reaction performed the best for CT removal as enough Fe2+ has been released after the dissolution of nZVI. These results demonstrated that a suitable dose of released Fe2+ was the key factor to enhance HO and CO 2 − radical generation in nZVI/oxidant/FA system. This study provided new information about effective usage of nZVI and FA for enhancing CT degradation in heterogeneous Fenton system. [ABSTRACT FROM AUTHOR]

Thus, emissions from WWTPs are considered as one of the main sources of MPs to the environment because plenty of effluent is directly discharged into surface water every year ([14]; [18]). Microplastics (MPs) (particle size HT ht ) have been found in almost all environments on Earth, including urban centers, terrestrial areas, and freshwater environments as well as in remote uninhabited islands, deep seafloor, and polar regions ([52]; [60]; [93]). Generally, most PCP-derived MPs enter municipal sewage networks, along with runoff and other kinds of wastewater from domestic and industrial activities, all of which contain many kinds of MPs ([6]). Another noteworthy research gap in the study of MPs in the environment is emission source apportionment, particularly for atmospheric MPs. Currently, secondary sources are estimated to emit the majority of MPs to the environment even though breaking large plastic waste into MPs under natural conditions takes years ([2]). [Extracted from the article]

Silver nanoparticles (AgNPs) are the most widely used engineered nanomaterials in consumer products, primarily due to their antimicrobial properties. This widespread usage has resulted in concerns regarding potential adverse environmental impacts and increased probability of human exposure. As the number of AgNP consumer products grows, the likelihood of interactions with other household materials increases. AgNP products have the potential to interact with household cleaning products in laundry, dishwashers, or during general use of all-purpose surface cleaners. This study has investigated the interaction between surfactant-based surface cleaning products and AgNPs of different sizes and with different capping agents. One AgNP consumer product, two laboratory-synthesized AgNPs, and ionic silver were selected for interaction with one cationic, one anionic, and one nonionic surfactant product to simulate AgNP transformations during consumer product usage before disposal and subsequent environmental release. Changes in size, morphology, and chemical composition were detected during a 60 min exposure to surfactant-based surface cleaning products using ultraviolet-visible (UV/Vis) spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and dynamic light scattering (DLS). Generally, once AgNP suspensions were exposed to surfactant-based surface cleaning products, all the particles showed an initial aggregation, likely due to disruption of their capping agents. Over the 60 min exposure, cleaning agent-1 (cationic) showed more significant particle aggregates than cleaning agent-2 (anionic) and cleaning agent-3 (nonionic). In addition, UV/Vis, TEM-EDX, and DLS confirmed formation of incidental AgNPs from interaction of ionic silver with all surfactant types. [ABSTRACT FROM AUTHOR]

[Display omitted] • Imidacloprid (IMD) degradation rate increased by 10.5–15.2 times in paddy water than in ultrapure water. • Reactive intermediates generated from paddy water contributed to IMD degradation. • 3CDOM* accounted for 88–92% of IMD degradation under sunlight. • 3CDOM* regulated the pathways and toxicity of IMD degradation. Imidacloprid (IMD) is a neonicotinoid pesticide used ubiquitously in rice cultivation, but its photo-transformation process in rice fields is largely unknown. This study examined the photo-transformation of IMD during rice growth. The degradation rate of IMD was enhanced by 10.5–15.2 times in the presence of different reactive intermediates (RIs) including triplet chromophoric dissolved organic matter (3CDOM*), hydroxyl radicals (•OH), and singlet oxygen (1O 2) generated from paddy water under sunlight. The 3CDOM* was the dominant RI and contributed to 88–92% of IMD degradation with a second order reaction rate constant of 3.77 × 108 M−1 s−1, while 1O 2 and •OH only contributed 5.7–7.6% and 0.1–0.3% of IMD degradation with second order reaction rate constants of 3.78 × 106 M−1 s−1 and 2.52 × 109 M−1 s−1, respectively. The products of IMD photo-transformation and their potential toxicity were evaluated. We found that the primary denitrified intermediate is highly toxic, and cleavage and ring-opening products are harmful to aquatic animals. In contrast, the hydroxylation and further oxidation pathway associated with 3CDOM* and •OH are detoxification processes for IMD. An APEX model was developed to predict the photodegradation kinetics of IMD in paddy waters at different stages of rice growth. The IMD photodegradation rate is expected to gradually decline with time since rice cultivation, ascribing to the decline of RIs as influenced by the change of DOM characteristics and NO 2 – concentrations. The findings of this study provide valuable information for understanding the transformation and potential risk of neonicotinoid insecticide during rice growth. [ABSTRACT FROM AUTHOR]