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The global increase in energy demand requires a continuous search for renewable and clean alternative resources to fossil fuels. Hydrogen is emerging as a promising energy carrier for the future; its production via photocatalysis, driven by sunlight, can directly convert solar energy into a usable or storable energy resource. However, water splitting requires sacrificial agents or electron donors/hole scavengers, such as short-chain organic acids. This research explores the use of lactic acid as a source for photocatalytic hydrogen production, offering valuable alternatives for wastewater management and renewable energy production. This study employed the innovative supercritical antisolvent (SAS) technique to micronize the precursors of both the active phase (CeO 2) and co-catalyst (CuO), ensuring rapid and complete solvent removal and size reduction of photocatalyst precursors. The prepared samples were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS) analysis, Brunauer-Emmett-Teller (BET) analysis and thermogravimetric analysis (TGA). This study has shown that the micronization process resulted in a notable improvement in CeO 2 photocatalytic activity, attributed to the reduction of the dimensions of the powders. Hydrogen production was equal to 3989 μmol L−1 for the SAS-produced photocatalyst while using a commercial CeO 2 sample resulted in H 2 production of 2519 μmol L−1. The enhanced photoactivity of CeO 2 -CuO composites was found to be related to the presence of CuO. The optimal CuO amount was equal to 0.5 wt%, determining a hydrogen production of 9313 μmol L−1 after 4 h of UV irradiation time. A photocatalytic test carried out with deuterated water (D 2 O) instead of distilled H 2 O demonstrated that hydrogen was preferentially produced from water splitting reaction, whereas lactic acid acted as a sacrificial agent being oxidized from positive holes photogenerated in the valence band of CuO. [Display omitted] • ScCO 2 was used for the micronization of ceria and copper oxide precursors. • The scCO 2 -assisted process ensured the formation of nanometric particles. • Obtained photocatalysts were tested for H 2 production using lactic acid. • Micronization of the precursors ensured an improvement in hydrogen productivity. [ABSTRACT FROM AUTHOR]

Azo dyes, the most common synthetic dyes used in the textile industry, are known xenobiotic compounds and recalcitrant to conventional degradation treatments. As consequence, such contaminants are often discharged into the effluents, treating aquatic ecosystems. Among several processes, the use of zero valent iron (ZVI) represents a suitable alternative to degrade organic molecules containing azo bonds. However, its applications are limited by corrosion and loss of reactivity over the time. To overcome these constraints, ZVI has been coupled to a suitable semiconductor (ZnS) to get a catalytic composite (ZVI-ZnS) active under UV light. The present work deals with the degradation of acid orange (AO7), used as model azo dye, by UV/ZVI-ZnS, as one step treatment and in combination with an adsorption process by biochar. The influence of ZVI-ZnS concentration (0.25, 0.5, 1 and 2 g/L) and reaction time (0–160 min) on degradation of AO7 were investigated. Intermediates formation was monitored by ESI-FT-ICR-MS analysis and the effluent toxicity was assessed by using Artemia franciscana. The experimental results showed that the UV/ZVI-ZnS process at 1 g/L of catalyst allowed to achieve a removal of AO7 up to 97% after 10 min. An increase of the dye relative concentrations as well as the toxicity related to intermediates formations has been observed for treatment time higher than 10 min. The total removal of AO7 together with effluent toxicity reduction was obtained only after the combined treatment (UV/ZVI-ZnS + biochar). [Display omitted] • A removal of AO7 up to 97% after 10 min was achieved by UV/ZVI-ZnS process. • Reaction intermediates were identified. • Dye relative concentrations increased for treatment time higher than 10 min. • Total removal of AO7 and toxicity was obtained after a combined treatment. [ABSTRACT FROM AUTHOR]

• Photocatalytic oxidation of As(III) to As(V) was studied. • Visible LEDs photocatalytic floating-bed reactor was used. • Cu-doped ZnO was supported on polystyrene pellets (PS). • The optimal Cu-doped ZnO loading on PS was 5 wt%. • The formulated visible light active structured photocatalyst was highly stable. The performances of a visible light active structured photocatalyst in the oxidation of arsenite to arsenate in aqueous solution were investigated. In particular, the photocatalytic active phase was Cu-doped ZnO, while polystyrene (PS) pellets were used as support. The Cu-doped ZnO photocatalyst was immobilized on polystyrene pellets surface by "solvent casting method" and characterized by different techniques. The photocatalytic tests were performed in a floating bed reactor using a visible LEDs strip as light source. The complete As(III) oxidation was achieved after 120 min of visible irradiation at a Cu-doped ZnO loading on polystyrene pellets equal to 5 wt%. Furthermore, the optimized photocatalyst was reused for several cycles without any substantial decrease of photocatalytic performances. In order to determine which reactive species plays a more significant role in the oxidation of As(III), the effects of different radical scavengers were tested. The results evidenced that OH and O 2 − seem not to be the main oxidant for the direct As(III) oxidation, whereas the oxidation mechanism of As(III) using Cu-doped ZnO structure photocatalyst seems to be related to the h+ holes generated under visible light irradiation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • ZnO photocatalyst was modified with different noble metals (Pt, Ag and Au). • Photocatalytic treatment of caffeine aqueous solutions under UV and visible light. • The optimal photocatalyst was ZnO modified with Ag. • Complete caffeine degradation also under visible light. Abstract In this work, ZnO photocatalyst was modified with different noble metals (Pt, Ag and Au) through photodeposition method and then characterized by different techniques (XRD, XRF, BET, UV–vis DRS, FESEM, and XPS). The addition of noble metals produces important changes in the light absorption properties with a significant absorbance in the visible region due to the existence of surface plasmon resonance (SPR) observed at about 450 nm and 550 nm for ZnO modified with Ag and Au, respectively. The morphology of the samples was studied by TEM and the size ranges of the different metals were estimated. Noble metal nanoparticles were in every case heterogeneously deposited on the larger ZnO particles. All the prepared photocatalysts were tested in the photocatalytic removal of caffeine (toxic and persistent emerging compound) under UV and visible light irradiation. It was observed an enhancement of photocatalytic caffeine removal from aqueous solutions under UV light irradiation with the increase of metal content (from 0.5 to 1 wt %) for ZnO modified with Ag and Au (Ag/ZnO and Au/ZnO). In particular, Ag/ZnO and Au/ZnO with higher Ag and Au content (1 wt %) allowed to achieve the almost complete caffeine degradation after only 30 min and a TOC removal higher than 90% after 4 h of UV light irradiation. These two photocatalysts were investigated also under visible light irradiation and it was found that their photocatalytic performances were strongly enhanced in presence of visible light compared to unmodified ZnO. In particular, Ag/ZnO photocatalyst was able to reach the complete caffeine degradation and a TOC removal of about 70% after 4 h of visible light irradiation. [ABSTRACT FROM AUTHOR]

Abstract The aim of this work is to minimize the consumption of electricity associated with the light source in a photocatalytic process for the removal of pollutants from wastewater. For this purpose, an optimized visible light active nitrogen-doped TiO 2 was used. To reduce electric energy consumption, nitrogen-doped TiO 2 was coupled with long-afterglow blue phosphors (chemical formula: Sr 2.90 Eu 0.03 Dy 0.07 Al 4 SiO 11) able to emit visible light when excited with UV light. Specifically, the experimental tests were performed using crystal violet dye as a model pollutant at 10 mg L−1 initial concentration. The experimental campaign has been carried out with the aim of assessing whether the photocatalytic activity of the nitrogen-doped TiO 2 catalyst is still present in dark conditions, thanks to the light emitted by phosphors and consequently to determine the energy saving in terms of electrical consumption and related costs. After having established the optimal content of nitrogen-doped TiO 2 in the physical mixture with phosphors, tests were carried out by alternating lighting periods with dark periods in order to identify the optimal irradiation time to obtain not only the total crystal violet degradation, but also the highest energy savings. In particular, the simultaneous presence of long-afterglow photoluminescent materials, nitrogen-doped TiO 2 photocatalyst and UV light emitting diodes resulted in an economic and energy saving of about 40% thanks to the possibility of alternating "light" and "dark" periods. Graphical abstract Image 1 Highlights • Crystal violet dye was photocatalytically removed from water with light modulation. • Nitrogen-doped TiO 2 was mixed with persistent luminescence material (SrSiP). • SrSiP excites Nitrogen-doped TiO 2 (N-TiO 2) after turning off the UV light. • The use of N-TiO 2 and SrSiP determines an economic and energy saving of about 42%. [ABSTRACT FROM AUTHOR]

In this work, composite monolithic aerogels based on syndiotactic polystyrene (s-PS) and N-doped TiO 2 (NdT) photocatalyst characterized by high surface areas (up to 280 m 2 /g) and low density (0.1 g cm −3 ) are presented. These aerogels are obtained by supercritical carbon dioxide extraction of NdT/s-PS gels prepared by s-PS dissolution with NdT in suitable organic solvent. X-ray diffraction measurements and SEM analysis showed that a highly efficient dispersion of NdT nanoparticles can be achieved in the composite aerogels avoiding thus the aggregation phenomena that typically occur when the photocatalyst is used in slurry reactors. The optimization of NdT amount dispersed in s-PS was evaluated using phenol as model pollutant both under UV and visible light irradiation. The photoactivity of NdT/s-PS samples increased with increase of the amount of NdT dispersed in aerogel matrix up to NdT/s-PS weight ratio equal to 10/90 (10NdT/s-PS), for which the highest phenol degradation and TOC removal were achieved both under UV and visible light irradiation. Moreover, the photocatalytic activity of the optimized photocatalyst 10NdT/s-PS did not change significantly after several reuses underlining that any NdT particles are removed from the polymeric matrix. [ABSTRACT FROM AUTHOR]

A visible light active structured photocatalyst consisting of Nitrogen-doped TiO 2 particles immobilized on polystyrene spheres by solvent cast method was developed for possible application as tertiary treatment in small municipal wastewater treatment plants. The structured catalyst was characterized by spectroscopic and morphological techniques evidencing that the preparation method was able to disperse evenly anatase Nitrogen-doped TiO 2 particles on polystyrene spheres and that the structured catalyst can be activated by visible light. The photocatalytic tests were driven first in a laboratory scale reactor configuration irradiated through visible light emitted by light emitting diodes and then using a solar compound triangular collector based reactor for outdoor experiments. The results from laboratory scale experiments did not show any photocatalyst deactivation after several treatment cycles; the photocatalytic process was effective in methylene blue degradation experiments and real wastewater disinfection (92.6% indigenous Escherichia coli inactivation after 120 min of irradiation time). In outdoor experiments under direct solar light, the structured photocatalyst confirmed its efficiency in the inactivation of indigenous Escherichia coli present in a municipal wastewater (87% inactivation after 120 min treatment and 2 kJ/L of cumulative energy per unit of volume) because the residual bacterial count met the limit (50 CFU/mL) established by Italian law for wastewater disposal in surface water. [ABSTRACT FROM AUTHOR]

A novel visible light-active photocatalyst formulation (NdT/OP) was obtained by supporting N-doped TiO 2 (NdT) particles on up-conversion luminescent organic phosphors (OP). The photocatalytic activity of such catalysts was evaluated for the mineralization process of spiramycin in aqueous solution. The effect of NdT loading in the range 15–60 wt.% on bulk and surface characteristics of NdT/OP catalysts was investigated by several chemico-physical characterization techniques. The photocatalytic performance of NdT/OP catalysts in the removal of spyramicin from aqueous solution was assessed through photocatalytic tests under visible light irradiation. Total organic carbon (TOC) of aqueous solution, and CO and CO 2 gas concentrations evolved during the photodegradation were analyzed. A dramatic enhancement of photocatalytic activity of the photostructured visible active NdT/OP catalysts, compared to NdT catalyst, was observed. Only CO 2 was detected in gas-phase during visible light irradiation, proving that the photocatalytic process is effective in the mineralization of spiramycin, reaching very high values of TOC removal. The photocatalyst NdT/OP at 30 wt.% of NdT loading showed the highest photocatalytic activity (58% of TOC removed after 180 min irradiation against only 31% removal after 300 min of irradiation of NdT). We attribute this enhanced activity to the high effectiveness in the utilization of visible light through improved light harvesting and exploiting. OP particles act as “photoactive support”, able to be excited by the external visible light irradiation, and reissue luminescence of wavelength suitable to promote NdT photomineralization activity. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation of terephthalic acid (TPA) has been studied on commercial ZnO immobilized on polystyrene (PS) beads (mean size: 1.5 × 1.5 × 0.1 cm) and located in a stainless steel flat plate reactor with an irradiation window realized in a UV transparent polymethylmethacrylate (PMMA UVT) in order to make the system able to work also at high pressure. In this way, it is possible to overcome, both the problems related to the photocatalysts separation after the wastewater treatment and those ones caused by the inlet pressure (which may be higher than atmospheric one) of incoming wastewater. The solvent casting-method used for photocatalyst preparation is able to induce the formation of ZnO particles in form of isles dispersed on PS macro surface. Moreover XRD analysis evidenced that the PS support didn’t influence the crystalline arrangement of ZnO in wurtzite phase. The structured composite photocatalyst ZnO-PS showed high ability in the degradation of TPA giving its total mineralization under UV irradiation at atmospheric pressure. Increasing the pressure, similar levels of TPA removal were observed. This finding demonstrated the possibility, for the developed photocatalytic system, to operate under moderate pressure without worsening the photocatalytic performances. [ABSTRACT FROM AUTHOR]

This work is focused on the study of the correlation between the photocatalytic activity of N-doped TiO 2 particles, achieved by a designed synthesis, and their degree of aggregation in aqueous suspension. N-doped TiO 2 photocatalyst particles, suspended in bidistilled water, presented a trimodal (in the nano-micro metric range) aggregate size distribution. This distribution resulted monomodal, in the nanometric range, when in the aqueous solution was added an organic dispersing agent (azulene). This behavior was associated to the presence, on the N-doped TiO 2 particle surfaces, of an organic phase which was detected by thermal and infrared analysis. This organic phase was assumed to have a stabilizing function for nanoparticles. The influence of aggregate size of N-doped TiO 2 photocatalyst on the photocatalytic degradation of methylene blue has been studied. The aggregate size distribution of photocatalyst influenced the amount of methylene blue adsorbed on catalyst surface and increased the photocatalytic activity. The influence of operating parameters such as the amount of dispersing agent and the amount of photocatalyst in aqueous suspensions has also been examined. [ABSTRACT FROM AUTHOR]

Monolithic composite aerogel based on N-doped TiO 2 (NdT) photocatalyst dispersed into syndiotactic polystyrene (sPS) matrix was used for atrazine (ATZ) degradation under ultra-violet (UV) and visible light (Vis) irradiation. sPS/NdT composite aerogel, with a polymer/photocatalyst 90/10 wt ratio, was achieved by super critical CO 2 extraction of chloroform from the relative sPS/NdT gel. Testing of the sPS/NdT photocatalytic activity was performed by using initial ATZ concentration of 0.1 mg/L and a sPS/NdT composite in monolithic aerogel form. ATZ removal was equal to 47% and 25% under UV or Vis light, respectively, after 180 min of irradiation. The efficiency of the photocatalytic process was also investigated by monitoring the ecotoxicity of the treated water to Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna. The results indicated that, for both UV and Vis irradiation, even for high ATZ removal efficiency (i.e., UV treatment), the toxicity of process effluent is greater than the initial one, most likely because of the generation of toxic by-products. The UV treatment was effective only after 72 h when the solution appeared not toxic to D. magna and presented a very low effect to R. subcapitata. On the other hand, under Vis light irradiation, a very high level of toxicity was still detected after 72 h of treatment time. Toxicity tests are confirmed as an indispensable tool for a correct assessment of the environmental impact of water treatment processes. [Display omitted] • Effective synergy between NdT and sPS aerogel was observed. • sPS/NdT was always more active in the atrazine degradation than NdT powder. • Degradation kinetic of atrazine was independent from its initial concentration. • Photocatalytic activity of sPS/NdT not decreased after five reusability tests. • After 72 h no or low toxicity was observed under investigated treatments. [ABSTRACT FROM AUTHOR]

The aim of this preliminary investigation was to verify the possibility of increasing the photoactivity of semiconductors, such as TiO 2 and ZnO, with the goal to minimize the volume of slurry-photoreactors to be used in wastewater treatment. The enhancement of photocatalytic activity has been reached through the doping of ZnO and TiO 2 nanoparticles with nitrogen and supporting them on ZnS-based luminescent microparticles (phosphors). The coupling of ZnS-based phosphors with N-TiO 2 and N-ZnO leads to an increase of the photocatalytic reaction rate in removal of organic dyes from wastewater allowing to reach the process intensification for the large scale design of a photocatalytic system. [ABSTRACT FROM AUTHOR]

The aim of the present work was to optimize the performance of the Non-Thermal Plasma (NTP) technology coupled with a structured catalyst for the degradation of organic and recalcitrant pollutants in aqueous solution. Specifically, the catalyst consists of CeO 2 supported onto ɣ-Al 2 O 3 spheres, synthesized by the wet-impregnation method, and characterized through Raman spectroscopy, specific surface area (BET) by N 2 adsorption at − 196 °C and Scanning Electron Microscopy (SEM). All experiments were carried out in a Dielectric Barrier Discharge (DBD) reactor. The first sets of tests were accomplished to optimize the degradation of Acid Orange 7 (AO7) azo dye in aqueous solution. The effect of catalyst formulation and oxygen flow rate in the reactor, as well as the reusability of the catalyst, were studied in detail. Moreover, the effect of radical scavengers was examined to suggest a plausible degradation mechanism, and an HPLC analysis was performed to understand to which extent degradation proceeds with the formation of intermediates. The best performance of the system in terms of total degradation and mineralization efficiencies is found for 15 min run time using 2.9 wt% CeO 2 /ɣ-Al 2 O 3 , with a voltage equal to 12 kV and 0.045 NL/min oxygen flow rate. The catalyst showed reusability properties after 5 runs and no intermediates were found by HPLC analysis, suggesting that AO7 degradation takes place with complete mineralization. Scavenger analysis showed that ozone is the most important reactive species responsible for degradation since its decomposition leads to the generation of effective secondary oxygen reactive species. Furthermore, given the semiconductor features of CeO 2 , it may also be excited by the plasma-generated UV radiation, suggesting that electron-hole pairs were also involved in the degradation mechanism. The remarkable efficiency of the proposed catalytic NTP treatment shows the potential of the system for the decontamination of aqueous solutions containing organic and recalcitrant pollutants. To confirm the potentiality of the system, the degradation of glyphosate (GLY) was also assessed under the optimal conditions set up for AO7 degradation, obtaining 84% degradation efficiency after 30 min run time. [Display omitted] • AO7 dye and glyphosate degradation was obtained with catalytic DBD reactor. • The presence of catalyst showed excellent improvements for NTP performance. • Ceria based catalyst promoted the mineralization of the target pollutants. • Ozone was the main oxidizing species responsible for AO7 degradation. [ABSTRACT FROM AUTHOR]

• Textile dyes (EBT and MeO) can represent a serious environmental threat. • EBT and MeO were treated by a continuous flow UV-LEDs TiO 2 packed-bed reactor. • A single photocatalytic step achieved the total decolourization and toxicity removal of EBT. • Only combining photocatalysis and activated carbon treatments MeO and its toxictywere removed. A continuous flow photocatalytic packed-bed reactor irradiated by UV-LEDs was employed for the degradation of two toxic anionic azo dyes: Eriochrome Black-T (EBT) and Methyl Orange (MeO). Commercial anatase TiO 2 in pellets form was used as packing material for the photoreactor. The experimental tests were carried out using both distilled and tap water as aqueous matrix for the two selected dyes. The influence of the liquid flow rate on the performances of the photocatalytic packed-bed reactor was investigated in the range 0.5–2.1 mL/min. Photocatalytic results showed that, under UV light, the system allows to achieve steady-state dyes concentration values without deactivation phenomena in 510 min irradiation time. Using distilled water, the highest efficiency of the process (EBT and MeO decolorization of about 100 % and 90 %, respectively) was observed with a liquid flow rate of 0.5 mL/min (contact time =6.6 min). In the presence of tap water and using the same contact time, the EBT decolourization was still total whereas MeO degradation was lower and equal to 70 %. For this reason, the photocatalytic reactor was followed by an adsorption unit based on the use of activated carbon. With such configuration, the complete MeO decolourization was achieved. The total removal of toxicity for EBT was achieved with just one packed-bed reactor being the toxicity of potential by-products not relevant. In the case of MeO, the full toxicity removal was obtained only after powdered activated carbon filtration. [ABSTRACT FROM AUTHOR]