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In this review, various graphene-based/TiO2 and graphene-based magnetic nanocomposites which were developed as highly efficient photocatalysts for degrading organic dyes, pharmaceuticals and efficient adsorbent materials for the adsorption of heavy metal ions were reviewed. The nanocomposites revealed the effective adsorptive potential of graphene-based magnetic materials and the efficient photocatalytic ability of graphene-based/TiO2 nanocomposites in decontaminating industrial wastewater containing toxic heavy metals and organic pollutants. The magnetic properties of graphene-based magnetic materials facilitate easy magnetic separation after adsorption of pollutants. The efficient photocatalytic ability of TiO2 semiconductor helps in rapid degradation of organic pollutants while graphene-based materials increase the surface area for adsorption of pollutants. Literature studies show that combinations of synthetic methods have been employed for the generation of various nanocomposite materials such as GO/TiO2, rGO/TiO2, and Fe3O4/GO, that possess photocatalytic activity and magnetic properties for the commercial removal of organic and inorganic pollutants found in water/wastewaters. The photocatalytic performance is connected to the large surface area of graphene derivatives (e.g. GO) that limit electron–hole recombination for TiO2, while the presence of magnetic nanoparticles (e.g. Fe3O4) in heavy metal adsorbent materials facilitates magnetic separation when an external magnetic field is applied.

Soil is a vital media in transmitting contaminants in the environment. Contamination of soils by trace metals has received much attention due to their associated toxicity, persistence, bioaccumulation and non-biodegradability that is harmful to the ecology. This study assayed the concentrations of trace metals in topsoils of the vicinity of Roundhill landfill using inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray fluorescence (XRF), compared the detection capabilities of the two techniques and determined ecological risks of the contaminants using geographical information system. Soils were collected from nine sampling sites around Roundhill landfill in the Eastern Cape and analysed for five trace metals using the two techniques. Mean concentrations of Cr, Cu, Ni and Zn determined by ICP-MS and XRF were normally distributed (p

Polymers derived from plant and animal sources are of great interest in wastewater remediation due to their cost-effectiveness and renewable adsorption capabilities, one such polymer is nanocellulose (NC). NC has gained a lot of attention in various research fields due to its abundance in nature, nano-dimension, high surface area, stability and bio-compatibility. As a result, NC has emerged as a great potential adsorbent for the removal of contaminants such as heavy metals, organic dyes, oils, pharmaceutical and etc. in the environmental remediation. This review focuses on the description of the building blocks, structure, properties, isolation and also discusses the potential of nanocellulose based composites materials with reinforcements such as activated carbon, carbon nanotube, graphene oxides, metals, non-metals and ceramics that were effectively used as an adsorbents for diverse organic and inorganic contaminants in water.

The deterioration of water quality by pollutants is a major health issue. Actual remediation methods are limited, and, as a consequence, there is a need for new remediation technologies. In particular, nanomaterials of unique properties have been recently developed for remediation. Here, we review mechanisms and applications of carbon-based nanomaterials for the adsorption and photocatalytic removal of organic and inorganic pollutants in wastewaters. Nanomaterials allow enhanced adsorption due to strong interactions between pollutants and adsorption sites. In photocatalysis, enhanced efficiency is attributed to the improved light harvesting and reduced recombination of photo-induced electrons and holes.

In the current study, a direct S-scheme titanium dioxide/graphitic carbon nitride (TiO

(3-aminopropyl) triethoxysilane (APTES) modified magnetic graphene oxide was synthesized and applied in the adsorption of three heavy metals, Pb(II), Cd(II) and Ni(II) from aqueous solution. An approach to prepare magnetic GO was adopted by using (3-aminopropyl) triethoxysilane (APTES) as a functionalizing agent on magnetic nanosilica coupled with GO to form the Fe3O4@SiO2-NH2/GO nanocomposite. FT-IR, XRD, BET, UV, VSM, SAXS, SEM and TEM were used to characterize the synthesized nanoadsorbents. Batch adsorption studies were conducted to investigate the effect of solution pH, initial metal ion concentration, adsorbent dosage and contact time. The maximum equilibrium time was found to be 30 min for Pb(II), Cd(II) and 60 min for Ni(II). The kinetics studies showed that the adsorption of Pb(II), Cd(II) and Ni(II) onto Fe3O4@SiO2-NH2/GO followed the pseudo-second-order kinetics. All the adsorption equilibrium data were well fitted to Langmuir isotherm model and maximum monolayer adsorption capacity for Pb(II), Cd(II) and Ni(II) were 13.46, 18.58 and 13.52 mgg-1, respectively. The Fe3O4@SiO2-NH2/GO adsorbents were reused for at least 7 cycles without the leaching of mineral core, showing the enhanced stability and potential application of Fe3O4@SiO2-NH2/GO adsorbents in water/wastewater treatment.

This work presents smart pathways to enhance the photocatalytic activity of TiO2 via co-doping with fluorine (F) and platinum (Pt) to form F–Pt co-doped TiO2 photocatalysts and investigates the unique and unusual fluorination of the floated products. Our investigations indicate that the crystalline structure of the photocatalysts was a mixture of anatase and brookite phases and that the nanoparticles of the synthesized nanocomposites had nanometric sizes (4–25 nm). The F–Pt co-doped TiO2 nano-photocatalysts demonstrated degradation of sulfamethoxazole (SMX) drug of >93% within 90 min under direct solar light and 58% degradation within 360 min under a solar simulator. Thus, co-doping TiO2 with F and Pt atoms to form F–Pt co-doped TiO2 nanocomposite is an efficient pathway to achieve high photocatalytic performance escorted with the formation of floating metal-fluoropolymer, unlike pristine TiO2 which has less photocatalytic degradation and no generation of a floating polymer. Our photocatalytic protocol demonstrates that the degradation of SMX started with redox reactions of oxygen and water absorbed on the surface of the prepared nanocomposites to form superoxide anions (O2˙−) and hydroxy radicals (˙OH) which have oxidation superpower. The resultant products were subsequently fluorinated by fluoride radical ions and floated as metal-fluoropolymer.

Heavy metals such as lead ions Pb (II) are a primary concern in the aquatic environment. These is because Pb (II) is poisonous at a threshold limit above 0.01 mg/L, when consumed over a long period of time. Pb (II) poisoning is very harmful to various organs viz. heart, intestine and kidneys. Besides, it affects bones, tissues, nervous and reproductive systems. Hence, it is important to remove Pb (II) from aquatic environment. Polypropylene (PP) and polypropylene grafted-maleic-anhydride (PP-g-MA) based nanocomposites reinforced with Chitosan (CS) and modified montmorillonite clay nanofiller (CL120DT) were successfully fabricated using twin screw melt extrusion for adsorption of Pb (II). The resulting nanocomposites were characterized by XRD to analyze the dispersion properties of the material, TEM and SEM for surface morphology, FTIR analysis for the functional groups and TGA for thermal stability. Pure PP showed two sharp peaks, but there was decreased in the intensity upon adding of CS and CL120DT. Among series of nanocomposites 2.0 phr and 4.0 phr loaded samples shows better storage module than that of pure PP. The uptake of Pb (II) from lead nitrate aqueous solution by PP + PP-g-MA/CL120DT-CS 2.0 phr nanocomposites followed the Langmuir isotherm model, with a remediation of 90.9% at pH 8 and was verified by pseudo-second order kinetic model. These results indicate that PP + PP-g-MA//CL120DT-CS 2.0 phr nanocomposites performed as a superabsorbent for the Pb (II) ion removal from aqueous solution.

Photoactive erbium-modified titanium dioxide grafted onto multiwalled carbon nanotubes (Er:TiO2/MWCNT) nanopowders were synthesized via a facile sol–gel route. Studies showed that the photocatalyst...

A thin disc-shaped Fenton-like catalyst sized 28.59*1.39 mm in diameter and thickness was produced by ball milling a hemi-dried silica xerogel with iron (III) acetylacetonate, followed by mold pressing and calcination. The developed compact catalyst facilitated its application and recovery. The whole fabrication process was free of wastewater emission. Plasticizers or binders indispensable for shaping commercial powders into compact green bodies were not necessary in the present method. The bulky catalyst was mesoporous and had a large surface area of 580 m2/g, providing access to the activation of H2O2 by the active iron sites inside the sample. It removed 100% of methylene blue (MB) in solution with a total TOC reduction by 92.13% mainly via the Fenton degradation. No washing, chemical elution of the adsorbed dye before the next application was applied. After five cycles, ca.93% of the removal efficiency was maintained. The TOC reduction increased from the 1st to 3rd cycle and ca.88% of the initial capacity was kept after the 5th cycle, while the iron leaching was only 0.021% of the applied catalyst. The excellent performance of the bulky catalyst was due to its large surface area, uniformly distributed and chemically bonded iron species. The present work provides a scalable and green way to produce Fenton-like catalysts for environmental application.

Heavy metal contamination in soils results from anthropogenic and lithologic factors and is a potential hazard to land and water resources. Sources of such pollution include landfills, domestic sewage, agricultural fertilisers and industries. In this work, soils from Roundhill landfill vicinity in South Africa were sampled and analyzed to determine the concentrations of particular heavy metals, namely As, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn. The main objectives of this work were to: quantify the concentration levels of heavy metals in the soil; determine the mobility of the heavy metals in the soil; and establish their origins and interrelationships. The soils were collected at various distances and depths from the landfill facility. The concentrations of heavy metals in the soil samples were analysed by ICP-MS and statistical analysis was carried out to establish their relationships and sources. From the analysis, some elements including Cr, Mn, Cu and Ni had measured concentrations beyond the threshold limits in most sampling sites irrespective of their distance and depth from the landfill vicinity. Conversely, some elements were observed to be immobile and had higher concentrations on the top soils closer to the landfill, such as As, Pb, Zn, Co and V. Iron (Fe) had high concentrations in all the sampling sites due to its natural occurrence in the parent rocks. In conclusion, the potential of soil quality deterioration due to heavy metal pollution in a landfill vicinity was observed. Furthermore, all heavy metals observed showed positive correlation to each other except for As and Co, indicating same origin.

An FeOx included SiO2 thin slice was prepared by ball milling the mixture of silica xerogel and iron (III) acetylacetonate, followed by uniaxial pressing and calcination. The slice is highly mesoporous. The incorporated iron is not crystalline but exists as isolated Fe3+ ions (30%), Fex3+Oy clusters (9%) and bulky form of FeOx (61%). The relative contents of Fe2+ and Fe3+ are 39.1 and 60.9%. The sample removed lowly concentered (20 mg/L) methylene blue (MB) from water via adsorption. It showed a very efficient removal (99.94%) of MB with a concentration of 1000 mg/L via Fenton-like catalytic degradation, contrast to a removal of 38.34% by the iron-free slice. It is evidenced that 83.09% of the dye molecules was degraded into CO2 and H2O and 6.40% into small molecules by the active iron species in the slice. Compared with traditional adsorbents and catalysts, the thin slice is easy to prepare, use and collect.

The particle size distribution (PSD) of soil influences its micro- and macro-structure although individual particle roles in relation to the elemental and mineralogical composition is rarely unders...

Nylon 6 (PA6) reinforced Flax Linum composites were synthesized by melt mix extrusion and molded through Mucell\ ® injection technique for adsorption application for removal of Cd(II) and Pb(II) metal ions. The structural morphologies of all samples were evaluated using X-ray diffraction (XRD), Transmittance emission microscopy (TEM) and Scanning emission microscopy (SEM), indicating crystallized materials with pore-like cells and Thermographic analysis (TGA) illustrated the thermally stable., Microscopic PA6 revealed the effects of Flax content on both cell density and cell size of the foamed samples. The cell size of neat PA6 (48 μm) changed to 36, 17, and 15 μm after incorporation of Flax compositions for 1.0, 3.0 and 5.0 wt%. The removal of Cd(II)and Pb(II) with PA6/Flax 1.0 wt% composite was found to follow the Langmuir isotherm model. The results indicated that PA6 1.0 wt% composite can be efficiently used as a superabsorbent for the removal of Cd(II) and Pb(II) from aqueous solution.

This work presents smart pathways to enhance the photocatalytic activity of TiO

In this review, the state-of-the-art of screen, inkjet, and three-dimensional (3D) printing electrode technologies of diverse types, manufacturing processes, and applications are critically reviewed for the first time. Emerging printing electrode-based technologies for advanced fabrication of printed electrode materials have given rise to the development of printed electrode devices and systems, thereby opening new avenues for several electrochemical applications. Additionally, their properties can be fine-tuned for specific electrochemical applications by embedding and/or immobilizing nano-structured materials. Nano-based printed or modified electrodes exhibit attractive features such as enhanced performance, cost-effectiveness, scalability, and high selectivity towards various targeted electroactive analytes. Furthermore, these nano-sized printed electrodes are flexible and portable, and thus are applicable for on-site measurements. However, their performance is affected by the type of printed electrode materials and fabrication methods employed. Hence, this review delves on the various electrode materials, printing methods and their applications for biosensors as well as for the detection of organic and inorganic compounds. The printed electrode materials that focus on properties such as selectivity, sensitivity and limit of detection available in the literature are highlighted in this review. Finally, future prospects, possibilities, and challenges of these advanced printing electrode technologies are deliberated.

The focus of the this work is to develop mesoporous silica and amine modified sand loaded with iron (Fe) and copper (Cu) species from electroplating wastewater for a further removal of phosphorus (P) from wastewater. First, it is shown that Fe or Cu supported sand adsorbent can effectively remove phosphorus (P) from aqueous solutions. The influence of pH, initial ion concentration (C0), contact time (t) on the adsorption of P by both sand adsorbents was studied. The maximum adsorption efficiency at room temperature reached 98% for the Fe-supported adsorbent under conditions of pH = 4, C0 = 25 mg/L, t = 180min and 96.3% for the Cu-supported sand under conditions of pH = 2, C0 = 5 mg/L, t = 120min respectively. The kinetics of P adsorption by the Fe or Cu supported sands followed the pseudo second-order kinetic model, while the adsorption isotherms fitted the Langmuir model. Based on the above results, an iron and copper co-supported sand adsorbent was prepared successfully by encapsulating Fe and Cu from a copper electroplating wastewater. In the meantime, Cu in the electroplating wastewater was reduced from 222 to 0.12 mg/L. This wastewater derived sand-based adsorbent had the same efficiency as the Fe-supported sand adsorbent. It was used to remove P from aqueous solution until the residual P in solution met China National Standard of WastewaterEmission. By this way, a dual approach to synergistically purify both anions and cations polluted wastewaters is developed.

Polypropylene (PP) reinforced montmorillonite (MMT) clay nanocomposites were synthesized with and without the polypropylene-grafted-maleic anhydride (PP-g-MA) as compatibiliser, by melt mix extrusion and molded through Mucell® injection technique. The PP and PP-g-MA based nanocomposites were fabricated for adsorption application for removal of Pb(II) metal ion. The structural morphologies of all samples evaluated on XRD, TEM, SEM, and TGA illustrated the thermally stable, and crystallined materials with pore-like cells. Microscopic MMT revealed the effects of maleic acid (MA) and MMT content on both cell density and cell size of the foamed samples. The cell size of neat PP (200 µm) changed to 100, 105, and 75 µm for MMT compositions of 0.5, 1.0, and 3.0 wt%, respectively while 96, 78, and 85 µm for 0.5, 1.0, and 3.0 wt% for MMT composition of PP-g-MA (60 µm) were obtained. The existence of platelet morphologies of well dispersed MMT within the polymer matrix were shown by TEM analysis. The removal of Pb(II) with neat PP and The PP-g-MA/MMT 0.5 wt% nanocomposite was found to follow the Langmuir isotherm model. The results indicated that PP-g-MA/MMT 0.5 wt% nanocomposite can be efficiently used as a superabsorbent for the removal of Pb(II) from aqueous solution.

The polymer polypyrrole (PPy)/polyvinyl alcohol (PVA) polymer blend incorporated with Fe3O4 nanoparticle is synthesized successfully using solution blending technique. The study is focused on developing core shell nanocomposite using magnetite nanoparticles as core layered with the shell of a blend of conducting PPy and PVA prepared via in-situ polymerization in the presence of magnetite precursor. The surface area, pore size and pore volume for the blend improved upon reinforcement of magnetite nano filler. The surface morphology show the single phase for the blend indicating the uniform dispersion the two polymers with the smooth surface. The internal structure shows the magnetite nanoparticles were uniformly reinforced into the bulk of the blend and were of formed in the size range of 50 nm and above. The structural morphologies was evaluated using scanning electrode microscope. Thermogravimetric analysis show that thermal stability of polymer blend has improved with the addition of iron oxide improved almost by 200 °C. X-ray diffraction analysis for the crystallinity. The nanocomposite was applied to remove As(III) trivalent arsenide from aqueous solution using adsorption technology and kinetics models and isotherms model were applied to study the course of adsorption. The bionanocomposite show adsorbent efficiency of 1.21 mg/g.

Activated carbon coated silica sand (AC@sand) was successfully synthesized by hydrothermal carbonization of glucose with the addition of ethylenediamine (EDA), followed by the activation with KOH. The sample was characterized by XRD, SEM, N2-sorption, FTIR, XPS measurements. It is shown that EDA not only influenced the carbon coating on the silica sand but also introduced amino groups to the AC@sand. The microporous carbon coating and the introduced amino groups improved the adsorption performance of the composite toward Cr(VI) in water. The adsorbed Cr(VI) retained in the spent adsorbent was used as a colorant in glass preparation.

Activated carbon coated glass fiber fabric (AC@GFF) was successfully synthesized by the carbonization of polyvinylpyrrolidone with the assistance of KOH onto waste glass fiber fabric (GFF). The samples were characterized by XRD, SEM, N2-sorption, FTIR, XPS, TG, and DSC measurements. It is shown that KOH not only acted as an activator during the carbonization process but also facilitated the adherence of PVP onto the surface of the glass fibers by increasing the viscosity of the PVP precursor solutions. The prepared AC@GFF was applied to uptake Cr(VI) from synthetic wastewater, and the factors such as the pH, initial concentration of adsorbate, contact time, and adsorption temperature influencing the adsorption of the Cr(VI) were investigated. The adsorption data were fitted with the isotherm and kinetic models. The adsorption of metal ions by the AC@GFF from a real metal passivation wastewater proved that the synthesized adsorbent was highly selective to Cr(VI) against its inferring Zn(II). The spent adso...

Using post-consumer waste polystyrene (WPS), a conjugated microporous polymer (CMP) was synthesised and activated into a sulphonic-group carrying resin (SCMP). The surface chemistry of the materials showed a decline in both the aromatic CH and aliphatic CH2 stretching vibrations confirming successful crosslinking. The synthesised polymers were thermally stable with decomposition temperatures above 300 °C, had surface heterogeneity, and BET surface areas of 752 and 510 m2/g, respectively. A distribution of pores ranging from meso- to micro-pores was comparable to other CMPs. The materials had maximum adsorption capacities of 500 and 357 mg/g for Congo Red (CR) on CMP and SCMP, respectively. Converting waste polystyrene to an adsorbent is a cost effective way of handling waste and simultaneously providing material for wastewater remediation.

Emerging organic pollutants (EOPs) pose a challenge to water treatment facilities and are a potential hazard to the environment and human health. Potential ways of removing these pollutants in tertiary wastewater treatment processes to make it potable include the use of porous materials like biochar, zeolites, metal organic frameworks (MOFs), covalent organic frameworks (COFs), polymers of intrinsic microporosity (PIMs), zirconium based porous materials and, more recently, conjugated microporous polymers (CMPs). CMPs have attracted research attention owing to their porosity and π-conjugation which can easily be engineered for a wide range of applications. The synthesis of CMPs is relatively easily done through established pathways that include the Suzuki coupling, Sonogashira-Hagihara cross-coupling, Friedel-Crafts reactions, oxidative coupling, Ullmann reaction and the Yamamoto coupling. Post-synthetic functionalisation approaches have been used to obtain CMPs which have specific motifs suited for particular applications. Despite their potential, use of CMPs in removing EOPs from water has not received adequate research attention, and is therefore an area that needs research. This short communication highlights the challenges posed by EOPs, presents some of the possible porous materials that can be used for their removal, and proposes CMPs as suitable potential adsorbents. Basing on recent literature covering the period 2003–2016, the synthetic methods, properties and applications of these materials have been presented.

Solid waste management (SWM) is a challenge in developing countries such as the Republic of South Africa (RSA). This book chapter highlights the drivers and state of SWM in RSA and suggests alternatives to make solid waste a resource. The SWM strategy of the country has a role in pushing waste up its hierarchy towards minimal generation, reuse, and recycling through extended producer responsibility and economic instruments. However, the lack of an all-inclusive planning and management has challenged the success of these initiatives. In recognition of these flaws, the private sector is teaming up with the government and individuals to bridge service and value chains in sustainable SWM by formalising waste pickers, initiating waste-to-energy initiatives, promoting recycling at all stages of the waste cycle, and adopting practices that divert wastes from landfills. These initiatives if taken up will promote better economic turnover through the production of alternative energy, environmental conservation, and creation of employment opportunities in RSA.

Sand used for glass production was first hydrothermally treated in a sodium hydroxide solution followed by silica coating that created nanoporosity in the residual sand particles increasing the surface area by ca. 740 times when compared to parent sand particles. The hydrothermally treated sand was named as reconstructed sand (R-sand) and was further functionalized with 3-aminopropyltriethoxysilane (F-Sand) and both sands were later used as adsorbents to remove toxic chromium from aqueous solutions. The influence of pH, initial ion concentration, contact time, adsorption temperature, and dosage of adsorbent on the adsorption performance of both sands were investigated and compared. The kinetics of Cr6+ adsorption by both sands follows the pseudo-second-order kinetic model, while the adsorption of Cr6+ of R-sand and F-sand fits Langmuir and Freundlich models, respectively. The F-sand has shown improved adsorption performance and was used to adsorb chromium from electroplating wastewater. Since the hydrothe...

Studies on the modification of the hydration products of fly ash (FA), β-cyclodextrin (β-CD) and fly ash-β-cyclodextrin (FA-β-CD) composite cement paste samples as hydration progressed were done using X-ray diffraction analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. This paper investigates the effect of FA, β-CD and FA-β-CD composite on the hydration and pozzolanic reactions. It was evident from all the analyses that β-CD improved the hydration reaction from the 7 day hydration period, while improvement on pozzolanic reaction was revealed from the 28 day hydration period. The study contributed to the knowledge of FA performance as a composite with cyclodextrin and promoted the continued inclusion of FA in concrete.

Silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) could assemble with alkylamines to form silica gel. Herein, it was evidenced that part of the added amines, including butylamine (BA), octylamine (OA) or dodecylamine (DA), was protonated in the mixture of water and ethanol. Therefore, besides the hydrogen bonding between neutral silica species and the micelles composed of the non-protonated amines (Tanev and Pinnavaia, 1995), there existed strong electrostatic attraction between negatively charged silica species and the micelles composed of the protonated amines. This coexisting assembly mechanism could explain why the uncalcined BA- and OA-gels were millimeter-sized small blocks with large porosities and synthesized without waste water emission, while the uncalcined DA-gel was almost non-porous and formed via precipitation from its reaction medium. The uncalcined BA gel was proved to be efficient as a solid basic catalyst, replacing the commonly used ammonia solution which is easily volatilized and has a pungent smell, for the hydrolysis and condensation of TEOS to prepare silica microspheres.

As a result of poor MSW management in South Africa, leachate generation has been reported in lined and unlined landfills, which calls for measures to quantify and safely return it to the environmen...

We report the doping of TiO2 with fluorine (F) and palladium (Pd) to synthesize F-Pd co-doped TiO2 nanocomposites via a microwave-assisted hydrothermal synthesis method as a smart pathway to achieve efficient photocatalytic degradation of sulfamethoxazole (SMX) using both a solar simulator and direct sunlight irradiation. SMX is an emerging persistent drug that might have toxic effects on aquatic organisms because of its antibiotic-resistance. The F-Pd co-doped TiO2 nanocomposites produced in this work have an outstanding extension effect on the photocatalytic activity of TiO2 to the visible and near infrared regions; thus, showing efficient photocatalytic degradation of SMX and floatation of fluorinated products. TEM images shows that the particles of the F-Pd co-doped TiO2 nanocomposites have average particle sizes ranging between 5−25 nm. The band gap of the F-Pd co-doped TiO2 shifted down to 0.54 eV which is a significant shift from the band gap of TiO2 i.e., 3.26 eV. Thus, the photodegradation of 94.4 % of SMX was achieved within 20 min and 98.8 % after 70 min under direct sunlight irradiation. In addition, more than 42.5 % of SMX was degraded by F-Pd co-doped TiO2 nanocomposites with 3 % and above of Pd after just 5 min of adsorption in the dark. By doping TiO2 with F and Pd, three processes were thus achieved: 1) photocatalytic degradation, 2) fluorination of the degraded products and 3) floatation as fluoropolymer. These three processes, therefore, present one of the smart pathways to provide an efficient water treatment system for wastewater.

Titanium dioxide-based nanocomposite materials are the most widely used materials to enhance the photocatalytic activity of titanium dioxide (TiO2) due to their excellent light absorbing properties. However, the wide use of TiO2 is restricted by its large band gap. Doping TiO2 with iron (Fe) is one of the strategies that have been employed in order to narrow the band gap of TiO2, thus promoting its photocatalytic activity to the visible light region. In this work, new energy levels between the valence band and the conduction band were introduced by incorporating Fe in the TiO2 lattice resulting to an effective shift of the light absorption to the visible light region. On the other hand, the incorporation of NaF in the TiO2 lattice led to significant changes on its crystal phases from brookite-anatase to anatase-rutile phases. In this study, the hydrothermal synthesis route was combined with microwave heating as a smart pathway of reducing the synthesis cost by reducing synthesis temperature and time while achieving an efficient photocatalytic activity of the TiO2 nano-photocatalysts. XRD diffraction patterns demonstrated that a mixture of brookite-anatase was obtained, which was transformed to the anatase-rutile phases after doping TiO2 with Fe in the presence of NaF. Microscopic investigations further showed that the doped TiO2 nano-photocatalyts exhibited a spherical shape with an average particle size in the range of 10–20 nm. UV–Vis analysis showed that the indirect and direct band gap of Fe-doped TiO2 in the presence of NaF was significantly narrowed to 1.67–1.83 eV and 2.05–2.17 eV, respectively. The synergistic effect of NaF on the crystallinity of Fe-doped TiO2 calcined at 400 °C in air was demonstrated to form an anatase-rutile phase.

Smart polymeric materials demonstrate high-quality properties when exposed to slight changes from their external environments. The external stimuli that promote phase transitions in smart polymeric materials can either be physical (temperature, light, magnetic, ultrasounds), chemical (pH, solvent, and ionic strength), or biological (enzymes) in nature. Therefore, their ability to respond to very slight changes in stimuli leads to their wide application in water purification processes, energy generation, biomedical engineering, and catalysis. Poly (N-isopropylacrylamide) (PNIPAAm)-encapsulated metal nanoparticle smart polymer catalysts have been confirmed to demonstrate tunable catalytic ability in water. The covalently pairing of an enzyme and a smart polymer material in a hydrogel influences polymer conformation and largely impacts the performance of the enzyme, in addition to causing shifts in substrate-enzyme orientations. Recently, significant exploration of smart polymer catalysts in the areas such as medical and biotechnological fields has gained much momentum. In this chapter, much focus will be given to in-depth discussions on the most common types of smart polymeric materials, their brief synthesis methods and technological applications in various fields such as water purification processes and biological systems.

This chapter mainly outlines the progress made thus far in removing some of the nanotoxicant from aqueous solutions using organic and inorganic polymer-based engineered adsorbents and catalysts. It commences with a summary of the organic and inorganic polymer composites and nanocomposites engineered for wastewater purification. Acknowledging the significance of nanomaterial, the chapter also highlights recent efforts and physicochemical merits of various nanomaterials for wastewater purification. In contrast, the nanotoxicity health concerns of both organic and inorganic nanomaterials found in water are also mentioned; therefore, more emphasis was put onto polymeric adsorbents and catalysts designed for the removal of nanotoxicity in wastewater. The chapter concludes by stating the common methods used for the preparations of polymer-based catalysts and adsorbent material used in wastewater treatment.

Titanium carbide was synthesized from biochar, an agricultural waste material. Sol-gel technology was used to develop organic-inorganic hybrid of titania and biochar. The hybrid was carbothermally reduced at a higher temperature of 1450 °C in an inert atmosphere. Reduction of as-prepared TiC at different concentrations, resulted in production of khamrabaevite TiC polytypes. The lattice constants obtained for TiC phase in different samples were 0.45964 nm and 0.45112 nm respectively, indicating a decreasing order with increasing contents of Ti- contents.

Nanotechnology and Water Sustain-ability (NanoWS) Research Unit, University of South Africa, NationalResearch Foundation

Textile industries are essential in the global economy. However, their failure to implement environmental regulations and comprehensive wastewater treatment has resulted to situations where unexhausted dye is discharged into natural streams without thorough treatment by some industries. Titanium dioxide has been widely used for photocatalytic decolorization of dyes. Its photoactivity in the UV-region of the electromagnetic spectrum has limited its commercial success in environmental depollution applications. This has necessitated the development of titania-based composites with superior efficiency. The use of carbon as a heterogeneous photocatalyst support is discussed in this chapter. A brief introduction to semiconductor-mediated advanced oxidation processes and the various approaches, both physical and chemical, for enhancing the efficacy of the photocatalyst is presented. The different allotropes of carbon are described in detail, and where appropriate, their application as photocatalyst supports used in the degradation of organic dyes. The techniques that have been employed in the synthesis and coupling of carbon to the photocatalyst are presented, where the physicochemical properties of carbon have been exploited to enhance the photocatalytic properties of titania. The synthesis methods employed highlight the shift by researchers toward facile, scalable and ultimately results that can be replicated at commercial level. The chapter ends with examples of photocatalysts supported on various carbon forms used in the decomposition of organic dyes.

This article reports biosorption properties of Gum ghatti and acrylic acid based graft co-polymers for the adsorption of methylene blue (MB) and rhodamine B (RhB). Gg–cl–PAA removed 99% MB and 98% RhB from the respective dye solutions. Adsorption isotherm followed Langmuir isotherm with maximum adsorption capacity of 909.09 mg/g (MB) and 819.67 mg/g (RhB). Both the dyes followed pseudo second order rate equation. Eco-friendliness of Gg–cl–PAA was studied by assessing its susceptibility to biodegradation by Pseudomonas aeruginosa in phosphate buffered saline (PBS) and mineral salt medium (MSM). Gg–cl–PAA degraded faster in PBS (18%) than MSM (15.1%) using P. aeruginosa National Research Foundation (NRF), South Africa

In view of dwindling fresh water sources, water pollution due to dyes and toxic metals is cause for concern. The increase in industrial activity around the world results in the emission of dyes and toxic metals into the aquatic environment and exerts pressure on water treatment plants. The removal of these contaminants is problematic because they can be available in very low concentrations, and water treatment plants are not designed to remove them effectively. A number of approaches including coagulation, precipitation, membrane filtration, and activated carbon adsorption, have been used for the remediation of contaminated water, but these methods are generally limited by high cost and poor selectivity. Lignin- and chitosan-based nanocomposites are potentially useful for these applications because they have minimal environmental footprints, are cost effective, and are compatible with a wide range of materials in composites. Laboratory scale experiments carried out to evaluate these materials have shown that the composites of these materials have remarkable dye and heavy metal (HM) removal capacities, thus making the technology accessible and potentially manageable at a large scale. Using Web of Science, Scopus, Sciencedirect, Springer, and Google Scholar, we evaluated literature on (1) the prevalence and environmental and health impact of pollution due to dye- and metal-laden effluents, (2) available remediation technologies, (3) the synthetic pathways for different chitosan-based nanocomposites, and (4) the potential of chitosan-based nanocomposites for dye and HM removal. There has been a gradual increase in the research of the use of lignin/chitosan-based adsorbent, showing the rapid interest and potential in the materials.

A polypyrrole-coated halloysite nanotube nanocomposite (PPy-HNTs NC) was prepared via in situ polymerization of pyrrole (Py) in the dispersion of HNTs and assessed for the removal of toxic Cr(VI) from aqueous solutions. ATR-FTIR and XRD results confirmed the formation of the nanocomposite. The FE-SEM and TEM images revealed the coating of PPy in the halloysite matrix and the surface morphology of the PPy-HNTs NC. Batch adsorption study showed that the adsorption process was very fast and kinetic data well fitted with pseudo-second-order kinetic model. Adsorption isotherms followed the Langmuir isotherm model and the maximum adsorption capacity was found to be 149.25 mg/g at pH 2.0 at 25 °C. The adsorption process was spontaneous and endothermic in nature. XPS study confirmed the adsorption of Cr(VI) onto the NC where some part of Cr(VI) reduced to Cr(III) by electron-rich PPy moiety. The desorption study suggested that the nanocomposite (NC) can be reused three times without loss of its original removal efficiency. Tests on contaminated groundwater and chrome mine water indicated the potential applicability of the adsorbents for the removal of Cr(VI) for actual field application.