Photoelectrocatalytic Research Articles

MoS2 grown on hollow carbon nanospheres as photoanode for improved photoelectrocatalytic degradation of Bisphenol A

Photoelectrocatalytic (PEC) technology capable of fully mineralizing hazardous substances is a promising strategy to address growing environmental problems. Herein, MoS2 nanosheets grown on nitrogen doped hollow carbon spheres (MoS2–NHCS) composites was prepared, and then bonded on a foamed nickel matrix by electrodeposition as photoanode for PEC degradation of Bisphenol A (BPA). Due to the integrated synergistic effect of unique composites structure and photocatalysis/electrocatalysis, the separation efficiency and survival life of photogenerated carriers were improved, and then accelerated the degradation of pollutants. The maximum reaction rate constant was 7.30 × 10−3 min−1. Photoelectrochemical characterization and key influencing parameters were discussed to clarify the relations between structure and function. The activity loss of MoS2–NHCS photoanode after four cycles was less than 10%, showing the long-term stability of BPA removal. The radicals quenching results revealed that this composite system was dominated by •OH together with moiety contributed by h+ and O2•-. Based on the detection results of intermediates, a possible decomposition pathway of BPA was proposed. The mixed pollution experiments suggested that the synergistic effect between organic matter and heavy metal greatly increased the treatment load of this composite electrode, providing a new idea for the study of practical wastewater treatment by the PEC system.

Novel dual-photoelectrode photoelectrocatalytic system based on TiO2 nanoneedle arrays photoanode and nitrogen-doped carbon dots/Co3O4 photocathode for efficient water purification at low/no applied voltage

A novel tandem photoelectrocatalysis (PEC) cell consisting of TiO2 nanoneedle arrays (TiO2 NNs/Ti mesh) photoanode and nitrogen-doped carbon dots (NCDs) modified Co3O4 photocathode (NCDs/Co3O4/Ti mesh) is designed to work at low/no applied voltage. Electrochemical impedance spectroscopy, incident photo-to-current conversion efficiency, and open-circuit voltage confirmed enhancement in the photogenerated charge transfer efficiency and internal photovoltage, which is due to synergistic effect in combination of two photoelectrodes. Under light-emitting diode (LED) light irradiation and cell voltage of 0.4 V, the system represented high activity and stability (0.0527 min−1 after 20 cycles) and energy efficiency (2.09 kWh m−3 order−1) for sulfadiazine removal. Based on the main •OH-induced reaction, the cooperative operation mechanism of TiO2 NNs/Ti mesh and NCDs/Co3O4/Ti mesh for sulfadiazine degradation was elaborated. Finally, the high performance under real water matrices or real sunlight irradiation without external voltage confirmed the feasibility of this PEC system in practical application for efficient water purification.

Selective Control and Characteristics of Water Oxidation and Dioxygen Reduction in Environmental Photo(electro)catalytic Systems.

ConspectusEmploying semiconductor materials is a popular engineering method to harvest solar energy, which is widely investigated for photocatalysis (PC) and photoelectrocatalysis (PEC) that convert solar light to chemical energy. In particular, environmental photo(electro)catalysis has been extensively studied as a sustainable method for water treatment, air purification, and resource recovery. Environmental PC/PEC processes working in ambient conditions are initiated mainly through hole transfer to water (water oxidation) and electron transfer to dioxygen (O2 reduction) and the subsequent photoredox transformation of water and dioxygen serves as a base of various PC/PEC systems. Through the redox transformations, different products can be generated depending on the number of transferred electrons and holes. The single electron/hole transfer generates radical species and reactive oxygen species (ROS) which initiate the degradation/transformation of various pollutants in water and air, while the multicharge transfer can generate energy-rich chemicals (e.g., H2, H2O2). Therefore, understanding the characteristics of the photoredox reactions of water and dioxygen on the semiconductor surface is critically important in controlling the selectivity and efficiency of photoconversion processes.In this Account, we describe various environmental PC/PEC conversions with a particular focus on how the phototransformation of dioxygen and water is related to the overall processes occurring on diverse semiconductor materials. The activation of water or dioxygen can be controlled by modifying the properties of semiconductors, changing the kind of counterpart half-reaction and the experimental conditions. If water can be used as a ubiquitous reductant under solar irradiation, many kinds of reductive transformations can be carried out under ambient environmental conditions. For example, various toxic oxyanions (or metal ions) can be reductively transformed to harmless or less harmful species or useful chemicals/fuels can be synthesized under ambient conditions if water can provide electrons and protons via solar water oxidation. On the other hand, dioxygen can turn into reactive oxygen species (ROS) as a versatile oxidant or to a chemical like H2O2. There should be many more possibilities of utilizing the photoconversion of water and dioxygen for environmentally significant purposes, which are yet to be further developed and demonstrated. In this Account, we highlight the recent strategies and the novel functional materials for effective activation of water and dioxygen in environmental PC/PEC systems. Design of environmentally functional PC/PEC systems should be based on better understanding of water and dioxygen activation.

Horseradish Peroxidase-Coupled Ag3 PO4 /BiVO4 Photoanode for Biophotoelectrocatalytic Degradation of Organic Contaminants.

Photoelectrocatalysis (PEC) is regarded as a promising and sustainable process for removal of organic contaminants from wastewater. Meanwhile, enzymatic catalysis also provides an effective way to carry out polluted environment remediation under mild conditions. In this study, a biophotoelectrocatalytic (BPEC) system is designed to remove 4-nitrophenol (4-NP) based on a combination of PEC and enzymatic catalysis. The developed BPEC system is constructed with a Ag3 PO4 /BiVO4 photoanode and a horseradish peroxidase (HRP)-loaded carbon cloth (CC) cathode. On the photoanode, the construction of a direct Z-scheme Ag3 PO4 /BiVO4 heterojunction enhanced the separation efficiency of photogenerated carriers, which promoted the PEC degradation of 4-NP under visible light irradiation. After HRP was immobilized on the cathode, the degradation efficiency of 4-NP reached 97.1 % after 60 min PEC treatment. The result could be ascribed to the HRP-catalyzed oxidation reaction via in situ-generated H2 O2 from the CC cathode during the PEC process. Moreover, the possible degradation pathways of 4-NP in such a BPEC system are also discussed.

Ti3+ self-doped and nitrogen-annealed TiO2 nanocone arrays photoanode for efficient visible-LED-light-driven photoelectrocatalytic degradation of sulfamethazine

Developing efficient, durable and visible-light-driven photoanode with excellent environmental adaptability is of great significance for photoelectrocatalytic (PEC) degradation of organic pollutants. In this work, a novel Ti3+ self-doped and nitrogen-annealed TiO2 nanocone arrays (Ti3+-TiO2NCs(N2)) photoanode was prepared for efficiently photoelectrocatalytic degradation of sulfamethazine (SMT) under visible light emitting diode (LED) irradiation, which obtained 98.68% removal for initial SMT concentration of 10 mg/L within 60 min. The visible light harvesting and charge transfer of TiO2NCs were significantly improved after nitrogen annealing treatment. Additionally, the introduction of moderate Ti3+ sites further lowered charge transport resistance and introduced a new impurity energy level, which efficiently accelerated the transmission of photogenerated carriers and then generated more h+ and active species to degrade pollutants. After 15 recycling degradation experiments, Ti3+-TiO2NCs(N2) still obtained more than 97% SMT removal, demonstrating highly durable. Also, it exhibited promising application prospect for treatment of real wastewaters (secondary effluent, pharmaceutical wastewater and mariculture wastewater).

Achieving High-Efficient Photoelectrocatalytic Degradation of 4-Chlorophenol via Functional Reformation of Titanium-Oxo Clusters

Rational design of crystalline catalysts with superior light absorption and charge transfer for efficient photoelectrocatalytic (PEC) reaction coupled with energy recovery remains a great challenge. In this work, we elaborately construct three stable titanium-oxo clusters (TOCs, Ti10Ac6, Ti10Fc8, and Ti12Fc2Ac4) modified with a monofunctionalized ligand (9-anthracenecarboxylic acid (Ac) or ferrocenecarboxylic acid (Fc)) and bifunctionalized ligands (Ac and Fc). They have tunable light-harvesting and charge transfer capacities and thus can serve as outstanding crystalline catalysts to achieve efficient PEC overall reaction, that is, the integration of anodic organic pollutant 4-chlorophenol (4-CP) degradation and cathodic wastewater-to-H2 conversion. These TOCs can all exhibit very high PEC activity and degradation efficiency of 4-CP. Especially, Ti12Fc2Ac4 decorated with bifunctionalized ligands exhibits better PEC degradation efficiency (over 99%) and H2 generation than Ti10Ac6 and Ti10Fc8 modified with a monofunctionalized ligand. The study of the 4-CP degradation pathway and mechanism revealed that such better PEC performance of Ti12Fc2Ac4 is probably due to its stronger interactions with the 4-CP molecule and better •OH radical production. This work not only presents the effective combination of organic pollutant degradation and simultaneously H2 evolution reaction using crystalline coordination clusters as both anodic and cathodic catalyst but also develops a new PEC application for crystalline coordination compounds.

Recent progress of applied TiO2 photoelectrocatalysis for the degradation of organic pollutants in wastewaters

Photoelectrocatalysis (PEC) is a promising powerful electrochemical advanced oxidation process (EAOP) that combines photocatalysis and electrolysis. Upon light irradiation over a semiconductor photocatalyst, electrons of its valence band are promoted to its conduction band giving rise to positively charged holes. The external bias potential applied to the photoanode extracts the photoexcited electrons toward the cathode of the electrolytic cell. Organics can then be oxidized directly by the holes or with hydroxyl radical formed by their reaction with H2O/OH−, and at lesser extent with other reactive oxygen species formed. The extensive study of TiO2 photoanodic nanomaterials and their applicability in environmental remediation makes necessary a further analysis of the state of the art and the actual understanding of potentials and shortcomings. This paper presents a comprehensive and critical review on the application of PEC with TiO2 photoanodes to remove organic pollutants from wastewaters from 2017 to May 2022. Fundamentals of this technique with pristine TiO2 photoanodes are explained, with special emphasis on the understanding of ROS origination mechanisms and the analytical techniques used for their characterization. Typical PEC systems and key operating variables related to the effectiveness of the process are examined. Recent advances obtained by TiO2 and TiO2-based photoanodes treatment of chemicals, dyes, pharmaceuticals, and pesticides are described and discussed. The preparation of TiO2 nanocomposites and their heterojunction mechanism, as well as the application of hybrid processes are detailed. Finally, prospects are proposed for the future research of PEC with perspectives to industrial application at higher technology readiness level.

Unconventional Substitution for BiVO4 to Enhance Photoelectrocatalytic Performance by Accelerating Polaron Hopping.

Bismuth vanadate (BiVO4) as a fascinating semiconductor for photoelectrocatalytic (PEC) water oxidation with suitable band gap (Eg) has been limited by the issue of poor separation and transportation of charge carriers. Herein, we propose an unconventional substitution of V5+ sites by Ti4+ in BiVO4 (Ti:BiVO4) for the similar ionic radii and accelerated polaron hopping. Ti:BiVO4 increased the photocurrent density 1.90 times up to 2.51 mA cm-2 at 1.23 V vs RHE and increased the charge carrier density 1.81 times to 5.86 × 1018 cm-3. Compared with bare BiVO4, Ti:BiVO4 improves the bulk separation efficiency to 88.3% at 1.23 V vs RHE. The DFT calculations have illustrated that Ti-doping modification could decrease the polaron hopping energy barrier, narrow the Eg, and decrease the overpotential of the oxygen evolution reaction (OER) concurrently. With further spin-coated FeOOH cocatalyst, the photoanode has a photocurrent density of 3.99 mA cm-2 at 1.23 V vs RHE. The excellent PEC performance of FeOOH/Ti:BiVO4 is attributed to the synergistic effect of the FeOOH layer and Ti doping, which could promote charge carrier separation and transfer by expediting polaron migration.

A novel SO3•- mediated photoelectrocatalytic system based on MoS2/Fe2O3 and CuNW@CF for the efficient treatment of sulfurous and nitrogenous oxides

Sulfurous and nitrogenous oxides, including NOx and SO2, and the generated substances NOx- and SO32- widely exist in air and water as pollutants and thus are difficult to control in the environment. In this study, we designed a novel photoelectrocatalytic (PEC) system for the efficient conversion of SO2 and NOx in mixed gases and NOx- and SO32- in wastewater to N2 and SO42-, respectively, by activating SO32- to form SO3•-. The key ideas include the conversion of SO32- from SO2 and efficient activation of SO32- into SO3•- and further conversion into SO4•- by the MoS2/Fe2O3 photoanode. Simultaneously, NO3-/NO2- originating from NOx was rapidly reduced to NH4+ on the CuNW@CF cathode. Ultimately, the generated NH4+ was selectively oxidized to N2 by SO4•- and SO4•- was reduced to SO42-. The results indicated that 99.9 % of TN was removed and 100 % of SO32- was converted to harmless SO42-. This study provides new insights into the treatment of sulfurous and nitrogenous oxides in air and water.

Peroxymonosulfate activation for preferential generation of hydroxyl radical with atomic Mn anchored TiO2 in photoelectrochemical process

The threaten of ubiquitous antibiotics to human and ecosystem makes it urgent to seek efficient treatment technologies. Peroxymonosulfate (PMS)-based advanced oxidation processes have revealed wide prospects for wastewater treatment via controllable PMS activation for desired ROS generation. Herein, a novel TiO2 photoelectrode decorated with atomically distributed Mn (SA-MnTiO2) was designed via a modified molten salt method (MSM) for photo-electro-catalytic (PEC) activation of PMS. The electron transfer in reduction-/oxidation-state Mn(II)/Mn(III)/Mn(IV) cycles facilitated the cleavage of intramolecular O–O bonds in PMS to preferentially generate hydroxyl radical (HO•). Almost complete degradation of norfloxacin (NOR) was occurred with optimal SA-Mn0.6TiO2 within 15 ​min, exhibiting high turnover frequency (0.066 min−1). Around 74.8% of total organic carbon was eliminated with a low specific energy consumption of 0.94 ​kW ​h/g. The key operational parameters during actual wastewater treatment were inspected for SA-Mn0.6TiO2/PMS system, suggesting the satisfactory stability for practical applications.

Construction of Z-scheme MnCo2O4/Sn3O4 heterostructured photoanodes with enhanced photoelectrocatalytic degradation of reactive brilliant blue KN-R

Rapid and efficient handling of the printing and dyeing wastewater benefits environmental conservation. Photoelectrocatalysis (PEC) technology is a novel method used to mineralize large molecules of non-degradable organic dye molecules in water completely into small molecules in recent years. By generating intermediate reactive species (e.g., superoxide radicals and hydroxyl radicals) during the processing, the products of PEC technology are cleaner and pollution-free, making it a desirable environment-friendly approach. In this work, a composite semiconductor material with Z-Scheme heterostructure was constructed as a photoanode to promote the generation of intermediate reactive radicals for the efficient degradation of organic dyestuff wastewater. A series of composite materials with Sn3O4 nanosheets decorated spinel-type MnCo2O4 nanorods were synthesized through a simple two-step hydrothermal process on the titanium metal substrate. The degradation reaction cell was assembled with these Ti/MnCo2O4-Sn3O4 photoanodes, and the PEC approach was used to decolorize the reactive brilliant blue KN-R. The synthesized photoelectrode exhibited a large electroactive region, low charge transfer resistance, high hydroxyl radical generation efficiency, and excellent PEC activity. The optimal composite photoanode presented 86.4 % reactive brilliant blue KN-R removal in 2 h and practical stability in 5 circulation tests. The mechanism during the PEC process was also analyzed and discussed on the basis of radical trapping experiments. In this work, MnCo2O4-Sn3O4 materials possessing Z-scheme heterojunction were constructed, providing insight into the techniques for catalytic purification of organic wastewater.

Impact of Polarization Reversal during Photoelectrocatalytic Treatment of WWTP Effluents

Photoelectrocatalysis (PEC) has been already proposed as a polishing treatment for wastewater treatment plants (WWTPs) effluents. In this work, the impact of polarization reversal during PEC process has been studied and evaluated on the basis of the removal of organic substance and color, biodegradability of the matrix, and inactivation of the catalyst. Effluents were sampled from a full-scale WWTP and alternatively treated by electrochemical oxidation (EC), photolysis (PL), photocatalysis (PC), photoelectrocatalysis, and photoelectrocatalysis with reverse polarization (PECr). The efficiency and the kinetics of the process, in terms of removal of organic substance and color, were not affected by reverse polarization and very similar results were obtained by PEC and PECr. The biodegradability of the effluents strongly increased both by PECr (RSBR: 0.84 ± 0.07), and by PEC and PL (0.89 ± 0.11, and 0.78 ± 0.02, respectively). In the selected polarization reversal mode (100 s at −0.1 V every 500 s at 4 V, cell voltage), a similar photocurrent loss after PEC and PECr was observed, suggesting no effect on the activity of the TiO2 mesh. This study can serve as a base for future research on polarization reversal to optimize operation parameters and exploit the procedure to preventing fouling and inactivation of the catalyst.

First PEM photoelectrolyser for the simultaneous selective glycerol valorization into value-added chemicals and hydrogen generation

The photoelectrocatalytic (PEC) valorization of glycerol is emerging for the co-generation of hydrogen and value-added organics like glyceraldehyde (GAD) or dihydroxyacetone (DHA). In this work, we have designed, tested and optimized a pioneering photoelectrolyser with a non-noble metal-based photoanode (WO3), operating in near-neutral conditions and using a proton-exchange membrane (PEM) which ensures the elution of a purified hydrogen stream from the cathode side while selectively oxidizing glycerol on the anode. The influence of light irradiation, external bias and cell temperature has been investigated, leading to GAD and DHA production rates of 11.1 and 5.2 mmol m−2 h−1 at 60 ºC and 1.2 V, along with 44.0 mmol H2 m−2 h−1. The long-term stability of the photoelectrolyser has also been validated and the particularities of this system with respect to other conventional devices have been discussed. PEC stands as a promising sustainable technology for the simultaneous H2 generation and biomass valorization.

Self-Interspersed mesoporous nanoplates assembled WO3 boosts photoelectrocatalytic pollutants degradation: Enhancing separation and transfer of hole/electron pairs

Photoelectrocatalysis (PEC) technology requires catalysts with narrow bandgap for high visible-light activity and efficient charge separation. In this study, self-interspersed porous nanoplates assembled WO3 (s-i-WO3) are synthesized via a dissolution-calcination method in the absence of templates. The results show that the s-i-WO3 catalyst exhibits excellent PEC activity and high stability. The bisphenol A (BPA) degradation efficiency of PEC system (93.7%) is significantly higher than those of photocatalysis (22.0%) and electrocatalysis (43.8%) systems. The two-dimensional porous structure and small-size mesopores of s-i-WO3 improve PEC reactions by enlarging specific surface area and providing more catalytic sites. Furthermore, the self-interspersed structure promotes the separation and transfer of photogenerated electron/hole pairs under light irradiation. Moreover, hydroxyl radicals are demonstrated to be the most prevalent reactive oxygen species in the developed PEC system. Our work sheds light on designing photoelectrocatalysts with high visible-light activity, abundant catalytic sites, and efficient charge separation.

Peroxymonosulfate enhanced photoelectrocatalytic degradation of 17α-ethinyl estradiol

This work aimed at the degradation of the synthetic estrogen 17α-ethinyl estradiol (EE2) via a combined photoelectrocatalysis (PEC) and peroxymonosulfate (PMS) process. Pristine and combined TiO2/WO3 photoanodes were fabricated and used in this work. The removal of 1 mg L−1 of EE2 increased from 47.9 % to 88.8 % in 60 min by adding 10 mg L−1 of PMS and an external bias of 1 V. EE2 was degraded in the presence of 0.05 M sodium sulfate as the electrolyte. The rate constant for the combined PEC-PMS process was 0.044 min−1 which was higher than the rate constant of light-activated PMS process (0.0053 min−1) and PEC process (0.01 min−1). The rate of EE2 degradation was increased with an increase in the voltage and PMS concentration. EE2 removal was decreased and reached 62.5 % and 48.5 % when 0.05 M NaCl or 0.05 M NaClO4 was used respectively as the electrolyte, highlighting the crucial role of electrolytes in process efficiency. Both radical and non-radical mechanisms participated in the destruction of EE2, however the role of the photogenerated carriers was dominant. Ecotoxicity using Vibrio fischeri as an indicator was decreased, although not proportionately to the parent compound EE2 in the combined Solar/TiO2/WO3/PMS system.

Efficient Bias-Free Degradation of Sulfamethazine by TiO2 Nanoneedle Arrays Photoanode and Co3O4 Photocathode System under LED-Light Irradiation

Solving high electrical-energy input for pollutants degradation is one of the core requirements for the practical application of photoelectrocatalytic (PEC) technology. Herein, we developed a self-driven dual-photoelectrode PEC system (TiO2 NNs-Co3O4) composed of a TiO2 nanoneedle arrays (TiO2 NNs) photoanode and Co3O4 photocathode for the first time. Under light-emitting-diode (LED) illumination, the bias-free TiO2 NNs-Co3O4 PEC system exhibited excellent PEC performance, with an internal bias as high as 0.19 V, achieving near complete degradation (99.62%) of sulfamethazine (SMT) with a pseudo-first-order rate constant of 0.042 min−1. The influences of solution pH, typical inorganic anions, natural organic matter, and initial SMT concentration on the PEC performance were investigated. Moreover, the main reactive oxygen species (h+, •OH, •O2−) in the dual-photoelectrode PEC system for SMT decomposition were elaborated. The practical application feasibility for efficient water purification of this unbiased PEC system was evaluated. It was proved that the TiO2 NNs photoanode provided a negative bias while the Co3O4 photocathode provided a positive bias for the photoanode, which made this system operate without external bias. This work elucidated the cooperative mechanism of photoelectrodes, providing guidance to develop a sustainable, efficient, and energy-saving PEC system for wastewater treatment.

CQDs improved the photoelectrocatalytic performance of plasma assembled WO3/TiO2-NRs for bisphenol A degradation.

Carbon quantum dots (CQDs) have been supported on WO3/TiO2-NRs using a hydrothermal method and a novel CQDs/WO3/TiO2-NRs composite formed via dielectric barrier discharge. The composite electrodes were characterized using morphology, structural, optical and electrochemical analysis. The CQDs were successfully prepared on the composite electrode with the highest photocurrent density reaching 2.51mA·cm-2 under UV-visible light irradiation (100mW·cm-2) and an applied voltage of 0.6V vs. Ag/AgCl. The CQDs/WO3/TiO2-NRs electrode exhibited a good degradation effect toward bisphenol A (BPA) (75.66 %) combined with the production of hydrogen (0.89mmol) in Na2SO4 system after 2h of the photoelectrocatalytic (PEC) reaction and the BPA degradation rate reached 100 % after 7min of reaction in both simulated and real seawater. The CQDs/WO3/TiO2-NRs exhibited excellent stability and efficient PEC performance in which the CQDs acted as electron reservoirs to capture and promote charge separation. Our analysis of intermediates of BPA degradation indicated the possible degradation pathways that mainly formed BPA polymers in the Na2SO4 system or chlorinated compounds in the high chloride salt system.

Investigating the effectiveness of bifacial mixed metal MOF electrodes for the photoelectro-catalytic treatment of municipal wastewater

The effectiveness of bifacial mixed metal-metal organic framework (MOF) anodes for municipal wastewater's photoelectro-catalytic (PEC) treatment has been rarely explored. Herein, pollutants removal efficiency from the municipal wastewater and the effect of operational parameters is verified under a visible range of light in a PEC system using TiO2–Bi(mixed metal)-MOF and TiO2–Sb(mixed metal)-MOF anodes, respectively. The comparable efficiency of pollutant removal from municipal wastewater in the PEC system with TiO2–Bi(mixed metal)-MOF anodes is high. At optimum operation parameters, TiO2–Bi(mixed metal)-MOF anodes in the PEC system play a positive role in the removal of micropollutants and the disinfection of municipal wastewater. This study reveals that PEC treatment of municipal wastewater contributes (35% of relative luminescence inhibition) to toxic biproducts.

Bismuth Vanadate-Nanostructured Graphite Electrodes for Rhodamine B Photoelectrochemical Degradation

Electrocatalysis is a promising way to treat water contaminated by harmful organic compounds. The combination of nanoparticles supported on a conductive substrate allows degradation to occur under less energetic conditions. This work evaluated the effect of deposition of bismuth vanadate (BVO) particles on pencil-type graphite electrodes. BVO particles were obtained by ultrasonic irradiation with coprecipitation. Then, they were deposited on the surface of a graphite electrode by the impregnation method. A 23-design was used to optimize electrode fabrication. Matter Dispersion Spectroscopy (SEM/EDS), X-Ray Diffraction (XRD) and Dynamic Light Scattering (DLS) were used for characterization. Electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results confirmed the synthesis of BVO@C (BVO/graphite). Furthermore, BVO@C significantly increased the electroactive surface area of the electrode, decreased the electron transfer resistance, and significantly increased the electron transfer rate to a greater extent than the electrode without any modification. To prove that the performance of BVO@C is better than the pure electrode, photoelectrocatalysis (PEC) and electrocatalysis (EC) were performed in a rhodamine B (RhB) solution. The results showed that in 5 min of treatment with unmodified electrode, BVO@C EC system and BVO@C PEC system, there was degradation of 31.53%, 46.09% and 58.17% respectively, reaching 95%, 98% and 99.64%, respectively, in 30 min. The reaction rate constants were calculated and to be found k = 0.10272 m−1, k = 0.12221 m−1 and k= 0.15022 m−1 for the unmodified graphite, BVO@C EC System and BVO@C PEC system, respectively. These results demonstrate that the BVO@C electrodes are efficient for application in a wide range of treatments, including the treatment of organic pollutants.

Solar-Light-Responsive Nanomaterials for the Photoelectrocatalytic Degradation of Stubborn Pollutants

Due to the ever increasing demand for cleaner water, a remarkable focus has been on the use of nanomaterials in wastewater treatment application. Photoelectrocatalytic (PEC) degradation, an advanced oxidation process which combines light and electrical energy, has been identified as a suitable technique capable of achieving total mineralisation of recalcitrant organic pollutants in wastewater. PEC degradation is non-selective, environmentally friendly and possesses great efficiency. The efficiency of PEC degradation has been enhanced by fabricating the photoanodes on a nanoscale with distinct morphologies. These nanostructured photoanodes have been extensively used for the removal of pharmaceuticals, dyes and phenolic water from wastewater. In many cases, total degradation of the pollutants is achieved within 2 h with significant TOC removal. This review presents an overview of the remarkable success that has been recorded with the use of nanostructured photoanodes in PEC degradation in the presence of visible light. The techniques that are commonly employed to improve the solar light responsiveness of these photoanodes are well discussed. Additionally, the use of nanostructured photoanodes consisting of heterojunction in PEC degradation is also presented. It is our aim that this review will help researchers to make informed decisions regarding the use of nanomaterials in PEC water treatment.