Z-scheme Bi2O2CO3-shell-Bi2O3-core/Ag modified g-C3N4 heterostructured photocatalysts were synthesized via an ultrasonic-assisted wet impregnation technique at room temperature. A comprehensive physicochemical characterization was performed to elucidate the composition, chemical states, morphology, and optical properties using XRD, XPS, TEM, PL, and UV-Vis spectroscopy. Results revealed a significantly suppressed charge-carrier recombination rate in the synthesized quaternary photocatalyst, core-shell heterostructure formation, and electron sink effect induced by silver nanoparticles within the heterojunction. Electrochemical characterization provided insights into charge-carrier transport dynamics, redox behavior, and the alignment of the valence and conduction band edges. The superior photoresponse of the heterojunction was demonstrated using photocurrent transients under chopped visible-light illumination. The as-synthesized heterojunction photo-catalysts exhibited improved photocatalytic activity for the degradation of cationic and anionic model pollutant dyes and the photoreduction of hexavalent chromium under visible-light illumination. The reusability of catalyst was ensured through successive photodecomposition cycles. The reactive oxygen species involved were identified using radical-scavenging assays. As demonstrated by its superior photocurrent response and lowest charge transfer resistance, BAG 1 performs better than other photocatalysts due to an ideal balance between Ag nanoparticle loading, core-shell heterostructure formation, and preserved surface area. These factors together improve charge separation, extend carrier lifetime, and reduce recombination.

The present study reports the versatile synthesis of photocatalysts composed of nitrogen-doped reduced graphene oxide (NrGO) flakes coated with TiO2-FeOx nanostructures using ultraviolet (UV) pulsed laser irradiation in a liquid environment. Different commercial graphene oxide (GO) sources were used, revealing a significant influence on the structural, compositional, and functional properties of the final photocatalysts. The H2 production via water-splitting reaction using glycerol as sacrificial agent (photoreforming), ranged from 0.06 to 2.1 mu mol H2/g in 3.5 h depending on the GO precursor used. The best photocatalysts were those that showed a reduction in the TiO2 material with a Ti(IV)/Ti(III) atomic ratio about 2.0-2.4, as well as a reduction and N-doping of GO, with 20-23 at % of C, and 4-6 at % of N. The light-scattering nature of the photocatalysts also had a significant effect on the H2 production yield.

Bismuth vanadate nanopowders were obtained by co-precipitation at room temperature using Bi(NO3)3 and NH4VO3, as precursor salts. The effect of pH was comprehensively evaluated on the crystallization of the monoclinic scheelite-type (ms), and tetragonal zircon-type (tz) phases of BiVO4. Preferential crystallizations of the tz-phase and ms-phase were observed at acid and basic pH-values, respectively. The mixture of two poly-morphs influenced the morphological and optical properties of the materials compared with those of pristine powders. The photoactivity of the as-synthesized powders was evaluated during the photoreduction of Cr(VI) to Cr(III) under visible-light irradiation using formic acid (65 mM) as a hole scavenger in synthetically contaminated water (30 mg L-1). The samples obtained at pH values between 4 and 8 succeeded in achieving complete reduction of Cr (VI) in less than an hour. Thus, the BiVO4 phase-type in a monoclinic scheelite predominating mixture (pH 4 and 6) seems to be the most important structural factor accounting for the photoactivity towards Cr(VI) reduction, rather than the oxygen vacancy content or crystallite size.

Accidents in chemical laboratories are usually less significant than in the chemical industry but, sometime, they have serious consequences. As mandated by legislation, risk assessment is also needed at laboratory. In the present work, risk analysis is applied to laboratory dedicated to wastewater treatment by Advanced Oxidation Processes (AOPs). The analysis was carried out according to widely accepted methodologies, although innovative aspects, such as a new occupational risk index or the specific application to AOP laboratories, are introduced. Based on the hazards detected, a risk level with a normalized score between 0 and 10 is established. Based on the suggested prevention measures, their cost and their execution time, an annual cost and its relation to the previously assigned score are calculated. This gives a new index (another novelty) for the prioritization of preventive measures. To be able to identify the accident causes, Root Cause Analysis techniques were also included in the risk assessment. AcciMap, Why technique as well as the Ishikawa diagram, that shows the relationship between risk factors and accidents or occupational diseases have been used. This innovative risk assessment has been also framed in the implementation of management system for occupational health and safety, according to ISO45001:2018. The here proposed improvements in safety are also a way of achieving the UN Sustainable Development Goals.

The main goal of the present study was to explore photocatalytic performance of the TiO2 -CuO mixture, for solar to hydrogen conversion at pilot plant scale under two different irradiation conditions (sunny and partly cloudy), focusing on high-temperature pretreat-ment of the catalyst mixture to try to improve TiO2 doping with copper. P25-TiO2 and commercial CuO were used with different amounts of Cu (2 wt% or 7 wt% Cu) calcined at 200-400 degrees C during several hours. Catalysts were tested at pilot plant scale using solar compound parabolic collectors, with glycerol as the sacrificial agent. The photocatalyst prepared after heating at 200 degrees C for 3 h and with 7 wt% Cu, resulted in higher hydrogen production than under the other heating conditions, and results were slightly better (5 -10%) than the reference values with the untreated catalysts. Photocatalytic efficiency was slightly lower at the higher calcination temperature (400 degrees C). CO2 production and formation of formate and glycolate clearly demonstrated glycerol photoreforming. The Cu from the calcined catalyst remaining on the solid was significantly less (2.5%) than on the non -calcined catalyst (4.2%), with an important fraction of lixiviated copper and copper deposition on the reactor walls. This is a critical drawback that must be considered for large-scale applications.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Cu2O/Pt-BiVO4 and Cu2O/Au-BiVO4 photocatalysts are synthesized using a mild reducing agent (ascorbic acid) by an in -situ chemical reduction method at 25 degrees C. Pt and Au nanoparticles with an approximate size from 15 to 25 nm were incorporated onto BiVO4 powders. Crystalline phases are refined with the Rietveld method to evidence whether structural parameters contribute to enhance the photoactivity of the composites. The influences of structural defects and deposited metal are investigated to establish a relationship with their photoactivities. The as-synthesized BiVO4-based ternary photocatalysts displayed a strong optical absorption from UV to visible light shorter than 514 nm, with a blue-shift compared to that of pure BiVO4, resulting from the addition of the Au and Pt nanoparticles. The photocatalytic activities of the as-synthesized materials are evaluated under visiblelight irradiation using the mineralization of 4-chlorophenol (4-CP) and dicloxacillin (DCX). The mineralization percentages achieved with Cu2O/Pt-BVO4 and Cu2O/Au-BiVO4 after 240 min of irradiation were 85% for 4-CP and 33% for DCX. It is assumed that those levels of TOC removal are due to the lowest content of oxygen vacancies in the photocatalysts, decreasing hole trapping, and subsequently hindering their recombination with the photoexcited electrons. Under this premise, structural defects (i.e. oxygen deficiency) present a more important effect on the photoactivity of the BiVO4-based materials than crystallite size, or other structural parameters. Moreover, the activity can also be ascribed to the Z-scheme Cu2O/BiVO4 heterojunction enhancing redox potentials of charge carriers, the incorporation of Pt and Au nanoparticles, enhancing charge separation either by trapping photo-generated electrons, generating the electron sink effect.

Glycerol is a by-product in biodiesel production (in the range of g·L−1), so its photoreforming by photocatalysis is a way of valorising it. TiO2 in photocatalysis has been widely studied, although its efficiency is limited by the high energy band gap, and the electron-hole recombination. Its combination with different semiconductors should improve charge separation, extending also the absorption from UV to visible light. Cu and Ni oxides are two of the most efficient low-cost transition metal oxide catalysts. Experiments were carried out in a 25 L pilot plant connected to a compound parabolic solar collector. Different combinations of the three semiconductors, based on the concentration of each metal on TiO2 (Me, 5%, 7.2% and 10%) were evaluated. Evonik P25-TiO2, CuO and NiO were combined by mechanical mixing. Hydrogen was quantified by a micro gas chromatograph, and copper and nickel leaching by ICP-MS. The best hydrogen production (0.060 mMol kJ−1) was attained with a proportion of 10:1 of TiO2:MeO, that corresponds to a total metal concentration of 7.2 wt%, being Cu and Ni in the same proportion. Metal content in solution increased as the reaction progressed, but Ni lixiviation of <0.012 mg L−1 was not significant. Significant Cu leaching (>1 mg L−1) was observed. This article presents novel results, in a solar pilot plant, for determining which ternary mixture can give better results, as well as metal leaching into water. Handling relevant volume of water in anoxic conditions can help to understand the application of this technology for the production of hydrogen.

A review of the main ideas related to the capture and valorization of CO2 by using electrochemical processes is presented. The advantages of using an electrode-controlled potential that provides the possibility of reducing CO2 to non-fossil carbon-based fuels, or of using this atmospheric pollutant in organic synthesis processes that rely on electrocarboxylation steps are outlined. The implications of a reduction in atmospheric CO2 emissions in the global climate change emergency, while at the same time finding alternative and clean ways of producing valuable fuels and chemicals, are emphasized. Particular attention is paid to the powerful role that ionic liquids can play as ideal solvents and electrolytes in such electrochemical reactions. A general description of the advantages that these liquids have for the solubilization and the support of the electrochemical reduction of CO2 is presented.

To improve TiO2 for H2 generation, one strategy for the separation of photogenerated charges is the formation of heterostructures with other materials. In particular, NiO is a photocatalyst known for its good stability and low cost. However, no studies at pilot scale using solar energy have been described. Consequently, an evaluation of a physical NiO:TiO2 mixture at pilot scale (25 L) with natural irradiation (2.10 m2 of sun-exposed surface) and with simultaneous glycerol photoreforming was explored. NiO:TiO2 50 mg & sdot;L- 1 resulted in the highest hydrogen production, showing an STH = 1.44%, considering only the UV fraction of the solar irradiation. H2 and CO2 production were analysed by on-line GC; Glycerol, dissolved organic carbon, carboxylic acids and nickel leaching were also evaluated. The NiO:TiO2 mixtures rendered a systematically lower H2 production in natural water than in high-purity water. The increase of ionic strength increased the mean size of particle clusters, promoting rapid sedimentation. All this indicates the importance of testing under real field conditions for attaining reliable solar to hydrogen (STH) efficiency.

The main goal of the present study was to explore pilot-scale combination of H-2 generation with simultaneous water disinfection or decontamination. Performance of a TiO2-CuO mixture for solar-to-hydrogen (STH) con-version was studied, focusing on treatment optimization (catalyst dose, proportion of semiconductors in the mixture and concentration of the sacrificial agent). Experiments were performed in a 25-L compound parabolic collector (2 m(2)) solar pilot plant specifically designed for photocatalytic hydrogen generation. The best operating conditions were 100 mg L-1 TiO2-CuO (10:1) with 0.075 M glycerol as the sacrificial agent. The best STH conversion attained was 0.9%. 25 mg L-1 imidacloprid was completely degraded (over 99%). The synergetic effect of anoxic conditions, TiO2:CuO and solar radiation caused a significant reduction (> 5 Log) in concen-tration of E. coli, used as a model waterborne pathogen, in less than 10 min.

Brain-like nanostructures of BiVO4 were synthesized by ultrasonic spray pyrolysis (USP) using citric acid as chelating agent at 350 degrees degrees C. Synthesis variables such as carrier gas flow, structural agent concentration and temperature were herein studied. The samples were characterized by XRD, SEM, TEM, UV-Vis DRS and N-2 physisorption. Particularly, HRTEM was used to calculate the crystallite size, d-spacing and assigned plane of all BiVO4 samples. The photoactivity of the as-synthesized BiVO4 was measured during the degradation of methyl orange under visible-light irradiation, while the hydroxyl radical production was rated in terms of its reactivity against terephthalic acid. The morphology of the samples revealed that the use of small flow of N-2 allows the formation of spherical hollow porous particles with brain-like structure with slightly smaller crystallite size. The photocatalytic activity of the BiVO4 photocatalysts prepared by USP displayed a performance three times greater compared to the powders produced by co-precipitation. The PL spectra measured revealed that the charge separation process of the BiVO4 powders synthesized by the USP technique was better compared to those obtained by co-precipitation. The energy diagram of the photocatalyst reveals that the usage of the USP technique does not require the formation of a heterojunction to efficiently promote the separation of photogenerated carriers, since it removes defects in the gap which generating states which that induce the recombination; and shorten down the transferring distance from the excitation zone to the active site on the surface of the BiVO4 due to the production of nanostructures.

Various Pt–Cu2O–BiVO4 ternary and binary hybrid composite catalysts were synthesized using in-situ methods. Cuprous oxide and platinum were obtained by chemical reduction of copper sulfate and hexachloroplatinic acid, respectively, while BiVO4 was synthetized by ultrasonic spray pyrolysis. All the synthesis routes allowed the formation of ternary and binary catalysts without the presence of impurities. The materials were structurally characterized using X-ray diffraction, morphologically by scanning electron microscopy and transmission electron microscopy, optically with UV–vis diffuse reflectance spectroscopy, and photocatalytically during the degradation of methyl orange (MO) under visible-light irradiation. TEM images confirmed the formation of heterojunctions and the deposition of metallic particles on the semiconductor surfaces. A similar performance was displayed by Cu2O/Pt–BiVO4, Pt-(Cu2O/BiVO4), Pt–BiVO4 and Cu2O/BiVO4 photocatalysts showing ca. 90% of MO degradation, which could indicate a competitive mechanism between Pt and Cu2O as co-catalysts of ternary composites. A significant content of Cu2O in the photocatalysts generated an important dye absorption, like in Cu2O and Pt–Cu2O catalysts. Cu2O/Pt–BiVO4 exhibited the highest production of hydroxyl radicals, indicating the important role of Pt deposition to increase the photocatalytic performance of the semiconductors via the electron sink effect.

A CuO + TiO2 mixture, based on two commercial and well characterized CuO and TiO2 photocatalyst, has been used to produce hydrogen by solar light irradiation and in presence of different organic compounds (methanol, glycerol, formic acid, and the components of a wastewater coming from the biodiesel industry) acting as sacrificial electron donors. The experiments have been conducted at Plataforma Solar de Almeria (PSA, south of Spain) with a pilot plant scale reactor using a CPC (compound parabolic collector) configuration. The tested system has shown similar hydrogen generation capacity and energy efficiency than more expensive ones based on the use of noble metal/photocatalyst composites. Formic acid has shown to be the most effective electron donor, although very close amounts of hydrogen are also produced with glycerol, and this is found as a waste compound released in large quantities at the biodiesel industry wastewaters. As seen in previous similar studies, the increase of solution conductivity hampers the hydrogen generation, and a slightly basic solution pH (pH approximate to 9) gives the best reaction conditions. Finally, the composite can be recovered and successfully reused giving the ensuing and sustained generation of H-2 while removing more than 50% of TOC.

BiOCl/BiVO4 photocatalysts with different ratios of gold particles were synthesized by a facile method at room temperature. The gold was in situ incorporated on the BiOCl/BiVO4 powders through the chemical reduction of HAuCl4 using ascorbic acid as reducing agent. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance spectroscopy were conducted to perform the textural, structural and composition characterizations of the materials; while their photoactivities were evaluated using the methyl orange degradation under visible-light irradiation. The detailed morphology and microstructure of the 1.50Au-(BiOCl/BiVO4 ) catalyst reveals nanometer and micro-meter sized particles in a range from 20 to 500 nm with sphere and elongated-like shapes. Polycrystalline features are observed with preferred (121) surface orientation and interplanar distance values corresponding to (112), (004) and (022) planes of monoclinic BiVO4, while (011), (110), (102) planes can be related to tetragonal BiOCl with the direction (111). The surface chemical analysis showed that the most active Au-(BiOCl/BiVO4) catalyst presents the highest V4+/V(5+ )ratio (0.85), a 43 at.% BiOCl content and a percentage of Au-decoration of about 1 at.%. A synergic behavior between these chemical compositions enhances the MO photocatalytic degradation. It was found that photodegradation rates strongly relied on the gold content, and the Au-(BiOCl/ BiVO4) photocatalyst was highly stable after six reuses and easy to be recovered by centrifugation. A possible electronic transfer mechanism in the different as-synthesized photocatalysts upon visible illumination is proposed, thus elucidating the roles of Au, BiOCl and BiVO4 components. Presumably, the synergistic interaction arising between semiconducting and metallic nanoparticles induces the charge separation responsible for the enhanced photocatalytic behavior.

Works studying the economic aspects of the advanced oxidation processes (AOPs) are very scarce. This work tries to offer a structured methodology for the evaluation of the costs of AOPs used at laboratory and pilot plant scale. The methodology is applied to photo-Fenton experiments as a case study; however, it can be applied to any AOP, included heterogeneous photocatalysis. The methodology includes cost of devices, analysis instruments, reagents, electricity, maintenance, labor, etc. Results show that costs related to AOP experiments can be high, as analytical equipment and experimental devices have an important weight in the total cost; therefore it is important that facilities allow different types of experiments. A very careful planning of the type, number, and duration of experiments and samples to analyze should reduce time of use of the experimental installations and the corresponding costs. Labor shows the highest percentage of total costs, which also implies a good planning to reduce time. A detailed analysis of costs per published paper is presented.

In this work, beta-Bi2O3 was synthesized by Pechini method and its photocatalytic performance was compared with a commercial oxide. Catalysts were characterized by ultraviolet diffuse reflectance spectroscopy (DRS-UV), X-ray diffraction (XRD), scanning electron microscopy (SEM) and textural analysis by N-2 physisorption. Photocatalytic activity was tested under UV-vis light on the degradation of isoniazid, an antibiotic used in tuberculosis disease. Effects of pH and catalyst loading were evaluated and better results were achieved at pH 7 using 1.0 g L-1 of catalyst. beta-Bi2O3 synthesized (S-Bi2O3) presented a higher mineralization percentage and stability during photocatalytic treatment than the commercial oxide (C-Bi2O3). Photo-holes were identified as the main reactive species responsible for the isoniazid oxidation. By-products were identified by electrospray ionization mass spectrometry (ESI-MS) and the incomplete mineralization (24% mineralization in 2 h) was explained by the presence of those compounds. Toxicity of isoniazid was assessed against Vibrio fischeri and it was reduced after photocatalytic oxidation in both, deionized water and real wastewater as matrix. Antimycobacterial activity against Mycobacterium tuberculosis was inhibited after 150 min when complete isoniazid degradation was achieved. Results indicated that photocatalytic treatment with Bi2O3 is a suitable method to eliminate contaminants such as isoniazid and reduce environmental risk to aquatic life.

A Cu/TiO2 photocatalyst has been synthesised by reducing a Cu precursor with NaBH4 onto the surface of a sulphate pretreated TiO2 obtained by a sol-gel procedure. The catalyst, that shows a clearly defined anatase phase with high crystallinity and relatively high surface area, and contains Cu2O and CuO deposits on its surface, has been used to produce hydrogen in a solar driven pilot plant scale photocatalytic reactor. Different electron donor aqueous solutions (methanol, glycerol, and a real municipal wastewater treatment plant influent) have been tested showing similar or even higher energy efficiency than those obtained using more expensive noble metal based photocatalytic systems. The glycerol solutions have provided the best reactive environments for hydrogen generation.

The synthesis of metal-free graphene-based photocatalysts has received great attention recently due to their expected contributions to the development of solar-based hydrogen generation via water-splitting in a low cost and ecological manner. In this work, a new method for the generation of nitrogen-doped graphene-based powder employing an alternative solution to commonly used toxic and hazardous organic solvents is presented. The procedure involves ultraviolet pulsed laser irradiation of graphene oxide (GO) flakes dispersed in 1-butyl-3-methylimidazolium [bmim]-based ionic liquids using both chloride and acetate anions. The structural and compositional analysis using transmission electron microscopy, X-ray photoelectron and infrared spectroscopy indicate that the irradiated GO becomes partially reduced and doped with graphitic, pyrrolic and pyridinic nitrogen species. Interestingly, the relative content of the nitrogen functionalities is controlled by the anion in the ionic liquid and its concentration, with the obtained graphene-based powders showing higher photocatalytic activity than GO. Furthermore, a remarkable synergistic effect is observed for GO-[bmim]-acetate powder (acting as co-catalyst) in combination with anatase TiO2 nanoparticles. The presented method opens new research avenues for the cost-effective mass production of graphene-based photocatalysts for water splitting applications.

In the present study, a facile synthesis of visible-light-driven Cu2O/BiVO4 composites, with different Cu2O co-catalysts, towards to the mineralization of 4-chlorophenol (4-CP) in aqueous media is reported.

TiO2 surface lattice oxygens are actively involved in the photocatalytic oxidation of water as demonstrated by isotopic tracing experiments with Ti18O2.