Peroxydisulphate activated FTO-WO3 nanorods based photoelectrocatalytic degradation of tetracycline: Intermediate products, degradation pathway and ecotoxicity studies.

This work reports sulphate radical assisted photoelectrocatalytic (SR-PEC) degradation of tetracycline using a visible light active fluorine-doped tin oxide - tungsten trioxide nanorods (FTO-WO3 NRs) photoanode. The WO3 NRs were synthesised via the hydrothermal method and then conducted on the FTO glass to form a photoanode. When the photoanode was applied without sulphate radicals for PEC degradation, 10 % of the tetracycline was degraded. Conversely, when 3 mM persulphate was added, the extent of tetracycline degraded was 88 % using the UV-vis spectrophotometer and 99 % using the ultra-performance liquid chromatography mass spectrometer (UPLC-MS) within 90 min at 1.5 V. The mechanism of tetracycline degradation was proposed based on the intermediate products identified using UPLC-MS and the extent of toxicity was evaluated using quantitative structure activity relationship (QSAR) analysis. Trapping experiment revealed that the photogenerated holes, sulphate radicals, and hydroxyl radicals were the oxidants that significantly took part in the degradation of tetracycline. Overall, the electrode was stable and reusable, therefore suggesting the suitability of FTO-WO3 NRs photoanode in the presence of sulphate radicals towards the decontamination of water laden with pharmaceutical pollutants.

S-Scheme 2D/2D Heterojunction of ZnTiO3 Nanosheets/Bi2WO6 Nanosheets with Enhanced Photoelectrocatalytic Activity for Phenol Wastewater under Visible Light.

The pollution of phenol wastewater is becoming worse. In this paper, a 2D/2D nanosheet-like ZnTiO3/Bi2WO6 S-Scheme heterojunction was synthesized for the first time through a two-step calcination method and a hydrothermal method. In order to improve the separation efficiency of photogenerated carriers, the S-Scheme heterojunction charge-transfer path was designed and constructed, the photoelectrocatalytic effect of the applied electric field was utilized, and the photoelectric coupling catalytic degradation performance was greatly enhanced. When the applied voltage was +0.5 V, the ZnTiO3/Bi2WO6 molar ratio of 1.5:1 had highest degradation rate under visible light: the degradation rate was 93%, and the kinetic rate was 3.6 times higher than that of pure Bi2WO6. Moreover, the stability of the composite photoelectrocatalyst was excellent: the photoelectrocatalytic degradation rate of the photoelectrocatalyst remained above 90% after five cycles. In addition, through electrochemical analysis, XRD, XPS, TEM, radical trapping experiments, and valence band spectroscopy, we found that the S-scheme heterojunction was constructed between the two semiconductors, which effectively retained the redox ability of the two semiconductors. This provides new insights for the construction of a two-component direct S-scheme heterojunction as well as a feasible new solution for the treatment of phenol wastewater pollution.

Photoelectrocatalytic Degradation of Methylene Blue on Electrodeposited Bismuth Ferrite Perovskite Films.

Electrodeposited bismuth ferrite (BiFeO3) thin films on fluorine-doped tin oxide (FTO) substrate were employed as photoanodes in the photoelectrocatalytic degradation of methylene blue. The BiFeO3 thin films electrodeposited for 300 s, 600 s, 1200 s, 1800 s and 3600 s were characterised with XRD, field emission scanning electron microscopy (FESEM) and UV-vis diffuse reflectance spectroscopy. SEM images displayed different morphology at different electrodeposition times which affects the photoelectrocatalytic (PEC) performances. The FESEM cross-sectional area was used to measure the thickness of the film. The optical properties showed that the band gaps of the photoanodes were increasing as the electrodeposition time increased. The photocurrent response obtained showed that all thin film photoanodes responded to visible light and lower charge transfer resistance (from electrochemical impedance spectroscopy studies) was observed with photoanodes electrodeposited at a shorter time compared to those at a longer time. The PEC application of the photoanode for the removal of methylene blue (MB) dye in water showed that the percentage degradation decreased with an increase in electrodeposition time with removal rates of 97.6% and 70% observed in 300 s and 3600 s electrodeposition time, respectively. The extent of mineralisation was measured by total organic carbon and reusability studies were carried out. Control experiments such as adsorption, photolysis, photocatalysis and electrocatalysis processes were also investigated in comparison with PEC. The electrodeposition approach with citric acid exhibited improved electrode stability while mitigating the problem of catalyst leaching or peeling off during the PEC process.

Enhanced Visible Light-Driven Photoelectrocatalytic Degradation of Paracetamol at a Ternary z-Scheme Heterojunction of Bi2WO6 with Carbon Nanoparticles and TiO2 Nanotube Arrays Electrode.

In this study, a ternary z-scheme heterojunction of Bi2WO6 with carbon nanoparticles and TiO2 nanotube arrays was used to remove paracetamol from water by photoelectrocatalysis. The materials and z-scheme electrode were characterised using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), EDS mapping, ultraviolet diffuse reflection spectroscopy (UV-DRS), photocurrent measurement, electrochemical impedance spectroscopy (EIS), uv-vis spectroscopy and total organic carbon measurement (TOC). The effect of parameters such as current density and pH were studied. At optimal conditions, the electrode was applied for photoelectrocatalytic degradation of paracetamol, which gave a degradation efficiency of 84% within 180 min. The total organic carbon removal percentage obtained when using this electrode was 72%. Scavenger studies revealed that the holes played a crucial role during the photoelectrocatalytic degradation of paracetamol. The electrode showed high stability and reusability therefore suggesting that the z-scheme Bi2WO6-CNP-TiO2 nanotube arrays electrode is an efficient photoanode for the degradation of pharmaceuticals in wastewater.

Photoelectrocatalytic degradation of p-chloronitrobenzene by g-C3N4/TiO2 nanotube arrays photoelectrodes under visible light irradiation.

As a typical refractory pollutant, p-chloronitrobenzene (p-CNB) from industrial wastewater poses a serious threat to the aquatic environment safety and human health. The photoelectrocatalytic (PEC) technology is regarded as a promising and cleaner approach for p-CNB removal. Therefore, the graphitic carbon nitride (g-C3N4) modified TiO2 nanotube arrays (g-C3N4/TNAs) were prepared as the photoelectrodes for p-CNB degradation. The PEC degradation efficiency for p-CNB by g-C3N4/TNAs (0.00484 min-1) was much higher than that by bare TNAs (0.00135 min-1) under visible light. The g-C3N4/TNAs photoelectrodes exhibited excellent visible-light response, efficient charges separation and high redox potentials of electron/hole, which was favorable for p-CNB degradation. The radical scavenging experiments indicated that both reductive electrons and oxidized species (holes and ·OH) played crucial roles simultaneously during the dechlorination process, whereas the mineralization of p-CNB mainly depended on the photo-generated holes and ·OH. The degradation pathways of p-CNB were proposed through GC/MS spectra. The acute toxicity, bioaccumulation factor and mutagenicity of identified intermediates were reduced after PEC degradation by g-C3N4/TNAs photoelectrodes. The Z-scheme g-C3N4/TNAs provided an efficient approach for simultaneous dechlorination and mineralization of refractory pollutants.

TiO2 Nanotubes/Ag/MoS2 Meshy Photoelectrode with Excellent Photoelectrocatalytic Degradation Activity for Tetracycline Hydrochloride.

A novel type of TiO2 nanotubes (NTs)/Ag/MoS2 meshy photoelectrode was fabricated with highly oriented TiO2 nanotube arrays grown from a Ti mesh supporting Ag nanoparticles and three-dimensional MoS2 nanosheets. In this structure, Ag nanoparticles act as bridges to connect MoS2 and TiO2 and pathways for electron transfer, ensuring the abundant production of active electrons, which are the source of •O2-. The TiO2 NTs/Ag/MoS2 mesh can be used as both photocatalyst and electrode, exhibiting enhanced photoelectrocatalytic efficiency in degrading tetracycline hydrochloride under visible light irradiation (λ ≥ 420 nm). Compared to unmodified TiO2 NTs, the improved photoelectrocatalytic activity of the TiO2 NTs/Ag/MoS2 arise from the formation of Z-scheme heterojunctions, which facilitate the efficient separation of photogenerated electron-hole pairs through the Schottky barriers at the interfaces of TiO2 NTs⁻Ag and Ag⁻MoS2.

A novel visible-light responsive photocatalytic fuel cell with a heterostructured BiVO4/WO3 photoanode and a Pt/C air-breathing cathode.

A series of heterostructured BiVO4/WO3 photoanodes were successfully prepared via a two-step method of hydrothermal deposition and impregnation. The optimized BiVO4/WO3 sample showed the highest photocurrent density of ∼880 µA/cm2 at 0.8 V (vs Ag/AgCl) in 0.1 M KH2PO4 aqueous solution (pH 7) under simulated AM1.5 illumination. The optimized BiVO4/WO3 photoanode was coupled with a Pt/C air-breathing cathode to build up a visible-light responsive PFC system. The as-prepared PFC system showed outstanding photoelectrocatalytic performances in converting organics into electricity, and when glucose was used as the 'fuel', the maximum power density (Pmax) and the short-circuit current density (Isc) were 8.58 µW/cm2 and 91.8 µA/cm2, respectively. Degradation experiments showed that the removal rate of tetracycline hydrochloride in PFC with BiVO4/WO3 photoanode and Pt/C air-breathing cathode was ∼87.2% in 8 h, which was much higher than photolysis and photocatalysis process. The mechanism responsible for the enhanced photoelectrocatalytic performance of the as-prepared PFC system was also discussed.

Highly efficient degradation of berberine chloride form wastewater by a novel three-dimensional electrode photoelectrocatalytic system.

Fe2O3/graphite (Fe2O3/C) and nano-TiO2-coated glass bead were prepared by impregnation and sol-gel method respectively and employed as the catalyst of a novel three-dimensional electrode photoelectrocatalytic (3-D PEC) system. The photoexcited electrons can transfer from TiO2, Fe2O3 to counter electrode. It improves the migration of photoexcited charges, retards the fast recombination of electron-hole, and increases the lifetime of photogenerated holes (h+). In addition, the cycle reaction of Fe3+/Fe2+ on Fe2O3/C surface enhanced the Fenton reaction which can produce more hydroxyl radicals (·OH) and promote the capacity of mineralization of the pollutants. This novel 3-D PEC system showed excellent performance for the degradation of berberine chloride form (BCF). At the pH value of 3, 93% BCF was removed within 60 min; besides, 98.64% COD removal rate, 78.96% mineralization, 21.47% mineralization current efficiency, and just 3.16 kW h g-1TOC energy cost were obtained in 120 min. In this study, we proposed the 3-D PEC mechanism. Electron spin resonance (ESR) and scavenging experiments suggest that the major reactive oxygen species (ROS) are superoxide radicals (O2·-), ·OH, and h+, while the role of sulfate radical (SO4·-) is insignificant. This work provides a new dimension for the design of reactors for wastewater treatment and the construction of the 3-D PEC system can potentially be utilized in water purification.

Degradation of refractory organic compounds by photocatalytic fuel cell with solar responsive WO3/FTO photoanode and air-breathing cathode.

A novel solar responsive photocatalytic fuel cell (PFC) consisted of a WO3/FTO photoanode and an air-breathing cathode was successfully prepared for simultaneous pollutant degradation and power production. The as-prepared PFC system exhibited outstanding photocurrent performances, which were attributed to the combined effects of the large specific surface area and the improved oxygen transportation by air-breathing cathode design, as well as the enhanced light absorption by transparent FTO substrate. Oxytetracycline hydrochloride was used as the model compound in this paper, and parametric effects on the PFC performances were deeply investigated. Results showed that increasing electrolyte concentration and light density were effective approaches to enhance power outputs. In terms of oxytetracycline hydrochloride concentration, the maximum power density firstly enhanced when oxytetracycline hydrochloride concentration increased to 0.5mmol/L, then dropped dramatically with further increasing of oxytetracycline hydrochloride concentration to 2.0mmol/L. The highest short-circuit current density of 372.4µA/cm2 and maximum power density of 36.3µW/cm2 were obtained when the PFC operated at the optimum operation condition of 0.1mol/l Na2SO4 electrolyte, 200mW/cm2 light density and 0.5mmol/L oxytetracycline hydrochloride. The PFC-assisted photocatalytic degradation experiments also suggested a promising application of the as-prepared PFC system in refractory wastewater treatment.

Heterostructured ZnFe(2)O(4)/TiO(2) nanotube arrays with remarkable visible-light photoelectrocatalytic performance and stability.

A series of heterostructured ZnFe2O4/TiO2-nanotube arrays (NTAs) with remarkable visible-light photoelectrocatalytic (PEC) activity were successfully prepared via a two-step process of anodization and impregnation, followed by annealing. The structure and morphology of the as-prepared ZnFe2O4/TiO2-NTAs samples, PEC degradation abilities and photoelectrochemical performances, as well as long-term stabilities toward degradation of methyl orange (MO) solution under visible-light irradiation were deeply investigated. Results showed that forming a heterojunction by combination of TiO2-NTAs with ZnFe2O4 successfully extended the absorption edge of TiO2-NTAs to visible-light region. Among all the ZnFe2O4/TiO2-NTAs samples, the 2-ZnFe2O4/TiO2-NTAs sample, named ZT(2), obtained the best PEC activity and the highest photocurrent density under visible-light irradiation. Moreover, the ZT(2) sample retained a good reproducibility and high stability after 20days of PEC degradation. The outstanding visible-light PEC activity and photocurrent response of the ZT(2) sample were attributed to the proper amount of ZnFe2O4 nanoparticles loaded onto the TiO2-NTAs, which not only dramatically improved the visible-light absorption of TiO2-NTAs, but also assisted the separation of photo-induced electron-hole pairs and reduced their recombination by forming a ZnFe2O4/TiO2-NTAs heterojunction. The reaction mechanism responsible for the enhanced visible-light PEC performance of the ZnFe2O4/TiO2-NTAs heterostructure was also discussed.

The effect of the UV photon flux on the photoelectrocatalytic degradation of endocrine-disrupting alkylphenolic chemicals.

The photoelectrocatalytic (PEC) degradation of 4-nonylphenol ethoxylate (NP4EO) using a low, moderate, or high UV photon flux in different treatment times was investigated. The byproducts were verified using gas chromatography with flame ionization detection (GC-FID) and gas chromatography with quadrupole mass analyzer (GC-qMS). The GC results showed that the use of a low (2.89 µmol m(-2)s(-1)) or a high (36.16 µmol m(-2)s(-1)) UV photon flux reaching the anode surface was associated to the production of alcohols and the toxic byproduct nonylphenol (NP), leading to the same degradation pathway. Meanwhile, the use of a moderate UV photon flux (14.19 µmol m(-2)s(-1)) reaching the anode surface did not produce alcohols or the NP toxic byproduct. This study demonstrates that different UV photon fluxes will have an influence in the degradation of NP4EO with or without generation of toxic byproducts. Furthermore, it is concluded that, after the determination of the UV photon flux able to degrade NP4EO without NP formation, the treatment time is essential in removal of NP4EO, since increasing the treatment time of 4 to 10 h, when using the PEC best conditions (moderate UV photon flux), implies in a higher treatment efficiency.

The Promotion Effect of Low-Molecular Hydroxyl Compounds on the Nano-Photoelectrocatalytic Degradation of Fulvic Acid and Mechanism.

ABSTRACT: A significant promotion effect of low-molecular hydroxyl compounds (LMHCs) was found in the nano-photoelectrocatalytic (NPEC) degradation of fulvic acid (FA), which is a typical kind of humic acid existing widely in natural water bodies, and its influence mechanism was proposed. A TiO2 nanotube arrays (TNAs) material is served as the photoanode. Methanol, ethanediol, and glycerol were chosen as the representative of LMHCs in this study. The adsorption performance of organics on the surface of TNAs was investigated by using the instantaneous photocurrent value. The adsorption constants of FA, methanol, ethanediol, and glycerol were 43.44, 19.32, 7.00, and 1.30, respectively, which indicates that FA has the strongest adsorption property. The degradation performance of these organics and their mixture were observed in a thin-layer reactor. It shows that FA could hardly achieve exhausted mineralization alone, while LMHCs could be easily oxidized completely in the same condition. The degradation degree of FA, which is added LMHCs, improves significantly and the best promotion effect is achieved by glycerol. The promotion effect of LMHCs in the degradation of FA could be contributed to the formation of a tremendous amount of hydroxyl radicals in the NPEC process. The hydroxyl radicals could facilitate the complete degradation of both FA and its intermediate products. Among the chosen LMHCs, glycerol molecule which has three hydroxyls could generate the most hydroxyl radicals and contribute the best effective promotion. This work provides a new way to promote the NPEC degradation of FA and a direction to remove humus from polluted water.