Photoelectrocatalytic Research Articles

Unveiling an S-scheme F–Co3O4@Bi2WO6 heterojunction for robust water purification

Devising a desirable nano-heterostructured photoelectrode based on the charge transfer kinetics mechanism is a pivotal strategy for implementing efficient photoelectrocatalytic (PEC) technology, since the charge separation and utilization efficiency of a photoelectrode is critical to its PEC performance. Herein, we fabricate a F–Co3O4@Bi2WO6 core–shell hetero-array photoanode by coupling Bi2WO6 nanosheets with F–Co3O4 nanowires using a simple solvothermal solution method. The three-dimensional hierarchical heterostructure has a homogeneous chemical interface, helping it to promote an S-scheme-based carrier transport kinetics and maintain excellent cycling stability. Charge density difference calculations verify the electron migration trend from F–Co3O4 to Bi2WO6 upon hybridization and the formation of an internal electric field in the heterojunction, consistent with the S-scheme mechanism, which is identified by in situ irradiation X-ray photoelectron spectroscopy and by ultraviolet photoelectron spectroscopy. The optimized F–Co3O4@Bi2WO6-2 photoelectrode achieves high carrier utilization efficiency and exhibits superior PEC degradation performance for various organic pollutants, including reactive brilliant blue KN-R, rhodamine B, sulfamethoxazole, and bisphenol A. This work not only reveals that F–Co3O4@Bi2WO6-2 is effective for PEC water remediation but also provides a strategy to enhance carrier transport kinetics by designing binary oxides.

Boosted photoelectrocatalytic removal of bisphenol A in a wide spectral range on 3D BiVO4/TiO2 nanoforest

Nanostructure construction and heterojunction engineering are effective strategies for designing highly efficient photoelectrodes. Herein, we report a BiVO4 quantum dots (BQDs)/TiO2 nanoforest photoanode with 3D configuration that exhibited improved light harvesting and charge transfer efficiency. Enhanced and directional charge separation were attributed to the synergetic effect of TiO2 facet heterojunction and BiVO4/TiO2 type-II heterojunction, which were confirmed by in-situ XPS and KPFM technology. Finally, a boosted photoelectrocatalytic (PEC) bisphenol A (BPA) removal for 97.28 % in 30 min under a wide spectral range was achieved. This work offers insight into the rational design of nanostructure and heterojunction of photoelectrode.

WO3‐based Materials for Photocatalytic and Photoelectrocatalytic Selective Oxidation Reactions

AbstractSelective oxidation reactions are crucial in producing various chemicals in the industry. However, most catalytic processes for these reactions use harsh reaction conditions. Recently, heterogeneous photo(electro)catalysis has been considered promising for selective oxidation reactions under mild conditions. Semiconductor materials are frequently used as heterogeneous photocatalysts because they can produce active species that contribute to the oxidation of organic compounds under light irradiation. Among various semiconductor photocatalysts, tungsten oxide (WO3) is one of the most promising candidates due to its advantages, including high stability, wide light adsorption range, proper band structures, and unique catalytic mechanism. This paper reviews the WO3‐based materials for photocatalytic (PC) and photoelectrocatalytic (PEC) selective oxidations. We summarize the strategies for designing WO3 structures, which include morphology control, crystal facet optimization, and defect engineering. Then, the finely designed WO3 structures for PC and PEC oxidation of several typical organic compounds have been discussed based on catalytic mechanism and performance. Finally, we propose the prospects and challenges of WO3 photocatalysts and photoanodes in selective oxidation reactions.

Topology engineering of UiO-66@TiO2-based photoelectrocatalyst for highly efficient degradation of binary pollutants

Photoelectrocatalysis (PEC) is an efficient strategy for addressing organic pollutants in the environmental water system. Titanium dioxide (TiO2) based composite photoelectrodes have been widely researched due to excellent photocatalytic performance and chemical durability. However, light transmission and mass transport at the active sites inside photoelectrode are substantially limited because of topological irrationality. Herein, topology engineering of UiO-66@TiO2-based photoelectrocatalyst is presented to overcome this disadvantage. Compared to the edge-structure of cubic UiO-66 wrapped TNFs (CU@T/T), center-structure of octahedral UiO-66 embedded TNFs (OU@T/T) can enhance the light capture capability and mass transport, and then improve the PEC activity. Simultaneously photoelectrocatalytic degradation of RhB and MO also shows that topologically optimized OU@T/T exhibits excellent catalytic activity and durability. At 2.0 V of bias potential, RhB and MO (both 5 mg/L) can be almost completely removed at 200 min (99.06 % and 98.81 %) in the solution with 7.0 of pH under the action of active species (⋅O2– and ⋅OH), and no attenuation after five cycles. This work highlights that topology engineering of UiO-66@TiO2-based photoelectrocatalyst not only facilitates charge transfer but also promotes mass transport, which greatly improves the PEC degradation performance of binary pollutants.

Photoelectrocatalytic degradation of pharmaceuticals promoted by a metal-free g‑C3N4 catalyst

Graphitic carbon nitride (g-C3N4) recently emerged as a remarkable photoelectrocatalyst for water treatment. Advanced oxidation processes (AOPs) consisting of photoelectrocatalytic (PEC) systems are being researched towards the development of sustainable strategies for the complete removal of refractory contaminants from effluents of urban wastewater treatment plants (WWTPs). This work consists of the optimisation of a PEC system, composed of a boron-doped diamond (BDD) anode, titanium cathode, and a suspended g-C3N4 photoelectrocatalyst, for the treatment of both synthetic and real urban waste waters spiked with pharmaceutical active compounds (PhACs). Different working parameters were considered and optimised to improve degradation and mineralisation rates, such as the cathode material, anode-to-cathode distance, electrolyte resistivity, and matrix composition. The optimal conditions allowed removals of 100 % diclofenac, 88 % fluoxetine and 77 % ibuprofen in the complex wastewater matrix. Moreover, it was observed that the presence of other refractory organic molecules offered a greater impediment to PEC treatment than residual co-existing substances. The main oxidative agents were investigated by scavenging experiments, showing that generated holes and reactive oxy-species, i.e. hydroxyl and superoxide radicals, take a major role in the degradation of PhACs. The recyclability of the g-C3N4 suspension as photoelectrocatalyst in the PEC process provides a promising perspective for the development of wastewater treatment units.

Unleashing the power of solar light: WO3 nanorods decorated onto BiVO4 dendrites for tetracycline detoxification and water splitting.

The coupling of different oxide materials in a nanohybrid enables the customization of their optical and charge transport properties, leading to improved interfacial charge segregation and migration. In this study, BiVO4/WO3 (BVW), a sunlight-driven photocatalyst with distinct mole ratios was synthesized via a facile hydrothermal approach. The resultant catalyst exhibits a nanorods shape morphology decorated onto dendrite-like matrix and is studied for photocatalytic elimination of tetracycline (TC) and photoelectrocatalytic (PEC) H2 production. The effect of illumination time, solution pH, photocatalyst concentration, and mole ratios of BiVO4 to WO3 on the photocatalytic abatement of TC were tested sequentially as effective operating factors. Under optimal condition, 3:1 BiVO4:WO3 (31BVW) nanohybrid demonstrated a maximum degradation efficacy of 96.2% (rate constant ~0.0241 min-1), which is much better than its individual components and commercial TiO2-P25 (50.9%). The resultant by-products of TC decomposition were analyzed using GC-MS to explain the degradation mechanism. Moreover, as a photoanode, 31BVW showed a high photocurrent density of 0.64 mA/cm2 at 1.23 V vs RHE and a steady photocurrent for ~6 h under chronoamperometry study at1.23 V vs RHE. However, bare BiVO4 and WO3 exhibited the photocurrent density of 0.001 mA/cm2, and 0.015 mA/cm2, respectively at 1.23 V vs RHE. The Mott-Schottky analysis of 31BVW confirms their n-type behavior, with a calculated flat band potential of -0.067 V. The hydrogen production rate was theoretically calculated as 4.56 mmolcm-2 s-1 from chronoamperometric measurements. The photocatalyst's efficacy in TC degradation was further established via its reusability upto 7 cycles. Post degradation characterization of catalyst confirms its stability in lieu of practical usage. Comparative studies with existing literature revealed the superiority of reported photocatalysts in both applications. Overall, the binary BVW photocatalyst shows great potential for removing detrimental contaminants as well as H2 production via PEC water splitting due to efficient charge separation, reduced recombination, high surface area, and widen absorption window of the nanohybrid.

Ni(II)-doped CuWO4 photoanodes with enhanced photoelectrocatalytic activity

CuWO4 has emerged in the last years as a ternary metal oxide material for photoanodes application in photoelectrochemical cells, thanks to its relatively narrow band gap, high stability and selectivity toward the oxygen evolution reaction, though largely limited by its poor charge separation efficiency. Aiming at overcoming this limitation, we investigate here the effects that Cu(II) ion substitution has on the photoelectrocatalytic (PEC) performance of copper tungstate. Optically transparent CuWO4 thin-film photoanodes, prepared via spin coating and containing different amounts of Ni(II) ions, were fully characterized via UV–Vis spectroscopy, XRD and SEM analyses, and their PEC performance was tested via linear sweep voltammetry, incident photon to current efficiency and internal quantum efficiency analyses. From tests performed in the presence of a hole scavenger-containing electrolyte, the charge injection and separation efficiencies of the electrodes were also calculated. Pure-phase crystalline and/or heterojunction materials were obtained with higher PEC performance compared to pure CuWO4, mainly due to a significantly enhanced charge separation efficiency in the bulk of the material.Graphic abstract

Synergistic Mechanism of 0D Internal and Surface Defects Regulation Coupled with Pyroelectric Effects for Optimizing the Photoelectrocatalytic Properties of CdS

AbstractRational defect regulation is an effective way to enhance the performance of photoelectrocatalytic (PEC) water splitting. In this paper, we firstly constructed internal and surface defects to modulate the crystal structure of CdS, and investigated the synergistic impact of 0D (0‐dimensional) internal and surface defects regulation coupled with pyroelectric effects for optimizing the photoelectrocatalytic properties of CdS. It was found that the synergistic impact had a significant enhancement effect on the carrier separation and transfer, and the current density reached 3.93 mA/cm2 at 1.23 V vs. RHE increased by 16.38 times, meanwhile, the stability of the photoelectrodes was greatly promoted. The advantages and intrinsic relationships are also described: the formation of 0D dual‐type of defects alters the atomic arrangement in the crystal, optimizes the energy band structure, reduces carrier recombination, and increases carrier density. What's more, the introduction of defects induces electron redistribution and changes the state of dipoles inside the crystal, thus increasing built‐in electric field and generating more thermally generated carriers to optimize the pyroelectric effect. This work demonstrates the feasibility of defect modulation for optimizing pyroelectric performance and photocatalytic performance and bringing new light to PEC water splitting.

Exploring enhanced interfacial charge separation in ZnO/reduced graphene oxide hybrids on alkaline photoelectrochemical water splitting and photocatalytic pollutant degradation

Visible light-driven photocatalysis and photoelectrocatalysis have been intensively investigated for environmental remediation and green fuel generation. A highly efficient dual functional catalyst based on rGO decorated ZnO was synthesized by a hydrothermal method. The rGO incorporation facilitates the effective utilization of solar energy and improves the charge carrier separation and transportation efficiency. 0.5 wt% GO incorporated ZnO/rGO hybrid shows the highest photocatalytic activity towards pollutant degradation. Pure ZnO shows photocatalytic efficiency of 85 %, while ZnO/rGO shows 95 % degradation efficiency. The apparent rate constant of ZnO/rGO (67 × 10−3 min−1) showed 2.7 fold enhancement in comparison to bare ZnO (24 × 10−3 min−1). Consequently, ZnO/rGO shows highest hydrogen evolution activity by photoelectrocatalytic (PEC) water splitting in alkaline medium with a significantly lower overpotential of only 755 mV at 10 mA/cm2. The Tafel slope 101 mV/dec obtained for the ZnO/rGO hybrid is much lower than that of ZnO (149 mV/dec). This significant enhancement in photoelectrocatalytic activity of the hybrid can be attributed to the enhanced visible light absorption and reduced charge carrier recombination upon rGO incorporation. PL, TCSPC, and photocurrent response measurements deepens the investigation of the separation efficiency of photogenerated electron-hole pairs. The observations provide novel insights into the development of photocatalysts that possess dual functions for the water-solar energy nexus.

Porous TiWO3/SrWO4 with high titanium molar ratio for efficient photoelectrocatalytic nitrogen reduction under mild conditions

Ammonia synthesized by nitrogen reduction is the most promising new energy material. Photoelectrocatalytic (PEC) nitrogen reduction reaction (NRR) occurs under ambient conditions and is the optimal alternative to the energy-intensive Haber-Bosch method. Here, we report the one-step reaction synthesis of Ti–WO3/SrWO4 as a photocathode for ammonia synthesis. First-principles calculations demonstrate that Ti doping can afford nitrogen-adsorption sites, and Ti3+ undergoes chemical adsorption and becomes a nitrogen-activation site by providing electrons to nitrogen. Under light irradiation, the photogenerated electrons are captured by Ti4+; this is conducive to the activation and regeneration of Ti3+, thus forming a nitrogen fixation cycle and improving the nitrogen fixation yield. At − 0.5 V vs. RHE, the ammonia synthesis efficiency reaches 11.17 μg h-1 cm-2, which is four times that of SrWO4. Furthermore, the high stability and N-gas sensitivity of Ti–WO3/SrWO4 in the NRR indicate that it can be used as an efficient and stable photoelectrocatalyst for ammonia synthesis.

Photoelectrocatalytic modification of nanofiltration membranes with SrF2/Ti3C2Tx to simultaneously enhance heavy metal ions rejection and permeability

Heavy metal pollution can significantly harm water systems and human health. Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membrane separation technologies can effectively remove heavy metal ions from wastewater. In this study, a water bath method was used to form SrF2/Ti3C2Tx (ST) nanoparticles on the surface of polyvinylidene fluoride (PVDF) membranes and an additional polyamide (PA) functional layer was formed at the interface by crosslinking. ST@PA composite NF membranes (STPP) with good photocatalytic performance were obtained. The separation and catalytic properties of the STPP membranes were controlled by the ST content, which modifies the surface structure and properties of the membranes. The membrane with optimal ST crosslinking exhibited a water contact angle of 50.8°, pure water flux of 24.6 L·m−2·h−1·bar−1, and rejection rates of Mn2+, Ni2+, Cu2+, and Zn2+ of 98.8%, 95.3%, 95.7%, and 97.3%, respectively, under PEC-assisted separation with visible light illumination from a Xe lamp (300 W) and an applied voltage (2 V). The STPP membranes showed improved rejection rates of heavy metal ions under PEC-assisted operation. The mechanism for the improved membrane performance under PEC conditions was preliminarily clarified considering the relationship between the photocatalytic and filtration properties of STPP membranes along with the influence of light irradiation and an external voltage on the heavy metal ions. The generation of electrons, holes, superoxide radicals, and hydroxyl radicals during membrane operation enhances the rejection rates of heavy metal ions. Based on these results, STPP membranes are considered a promising technology for industrial applications in heavy metal removal.

Photoelectrocatalytic degradation of wastewater and simultaneous synthesis of NH3 on Fe-CNTs-supported octahedral Cu2O composite nanocatalysts

Fe-core carbon nanotubes (Fe-CNTs) were produced by vapor deposition using coal as a carbon source. Then, octahedral copper oxide nanoparticles (Cu2ONO) (prepared by solvent reduction method) were loaded on Fe-CNTs by hydrothermal method to prepare the composite catalyst Cu2ONO/Fe-CNTs. While characterizing (TEM, XRD, FTIR, XPS, N2-TPD, BET, etc.) the material structure, the performance of Cu2ONO/Fe-CNTs in photoelectrocatalytic (PEC) degradation of cotton pulp black liquor (CPBL an organic wastewater with high CODCr) and simultaneous synthesis of NH3 was studied. The PEC reaction was carried out in an H-type reactor. CPBL was oxidized at the anode to produce H+, CO2, H2O and other small molecules, where H+ passes through a proton exchange membrane and is reduced with N2 to produce NH3 at the cathode. After 4 h of reaction, the CODCr removal rate of CPBL in the anode chamber reached 95.42%, and the yield of NH3 in the cathode chamber reached 9.06 mmol L−1 cm−2. The dual purpose of synthesizing NH3 while degrading wastewater was achieved.

Surface Modification of TiO2/g-C3N4 Electrode with N, P Codoped CQDs for Photoelectrocatalytic Degradation of 1,4-Dioxane

The aim of this study was to synthesize N, P codoped CQDs modifying TiO2/g-C3N4 nanorod array (i.e., N, P-CQD/TCN NA) photoanodes for the degradation of 1,4-dioxane (1,4-D) and to explore the possibility of the photoelectrocatalytic (PEC) process in wastewater treatment. With the characterization of N, P-CQD/TCN NA anodes, 1,4-D degradation and pesticide wastewater was tested in the PEC cell, respectively. Under a bias voltage of 1.2 V and visible light, the current density of the N, P-CQD/TCN NAs was much higher than that of the CQD/TCN NAs (0.15 vs. 0.11 mA/cm2). The removal of 1,4-D reached 97% in the PEC cell within 6 h. The high performance of the N, P-CQD/TCN NA anodes could be attributed to the efficient charge separation, narrowed energy gap, and high upconverted PL properties. The C4 and C6 positions of 1,4-D were the preferential sites for the nucleophilic attack to form intermediates. The COD removal in the pesticide wastewater was kept stable at ~80% in a five-cycle operation using the PEC cell with the N, P-CQD/TCN NA photoelectric anodes. The results from this study should provide a promising way to develop novel photoelectric catalysts and to expand PEC application in wastewater treatment.

Self-cleaning photoelectrocatalytic filtration based on Ca(OH)2/Ti3C2Tx composite nanofiltration membranes for synergistically enhanced separation and degradation of phenolic compounds

Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membranes has emerged as an attractive technology for removing organic pollutants in wastewater treatment, however, the separation and degradation performance are still challenging. Herein, novel composite NF membranes were constructed by cross-linking a Ca(OH)2/Ti3C2Tx (CT) catalyst to a polyamide membrane using tannic acid (TA). In these CT@TA (CTTP) membranes, Ti3C2Tx reduces the charge-transfer resistance and recombination rate of CT, leading to enhanced PEC activity. The optimal CTTP membrane had a high water flux (27.9 L·m−2·h−1·bar−1) and excellent rejection rates for phenolic compounds (phenol: 85.1 %, 4-nitrophenol: 91.1 %, and bisphenol A (BPA): 94.6 %). Under visible-light irradiation with electrical assistance (3 V), the BPA degradation rate (92.2 %) was 13.7 % higher than that under light irradiation alone, and a higher flux recovery rate was achieved (94.1 %). Superoxide (O2−) and hydroxyl (OH) radicals were critical active species in catalytic BPA degradation, and the observed intermediates suggested that the degradation pathway involves oxidation, hydroxylation, and aromatic ring cracking. The developed NF membranes, which exhibit synergistic separation and degradation effects and self-cleaning properties, provide an innovative solution for the treatment of organic pollutants in wastewater.

Efficient photoelectrocatalytic degradation of amoxicillin using nano-TiO2 photoanode thin films: A comparative study with photocatalytic and electrocatalytic methods

Excessive utilization of antibiotics in human, animal, and aquaculture poses a substantial threat to human health and the environment. Photoelectrochemical processes are increasingly applied for water remediation because they generate oxidizing species and mineralize organic pollutants, making even small water quantities more amenable for utilization. Thus, this study presents the fabrication of an efficient nano-TiO2 photoanode thin film (PATF) specifically designed for the photoelectrocatalytic (PEC) degradation of amoxicillin (AMX). The TiO2 PATFs were deposited on fluorine-doped tin oxide (FTO) substrate using an ultrasonic spray pyrolysis process with various titanium isopropoxide (TTIP) acetylacetone (AcacH) molar ratios (1:1 to 1:10). The PEC oxidation of AMX was investigated using various molar ratios of TTIP:AcacH TiO2 PATF/FTO by linear sweep voltammetry, and a 1:8 M ratio of PATF exhibited superior PEC oxidation activity than other TiO2 PATFs. Subsequently, the PEC degradation efficiency of AMX was compared with that of photocatalytic (PC) and electrocatalytic (EC) methods. The results demonstrated that the PEC process effectively eliminated 76.2% of AMX within 120 min at 0.8 V, outperforming the removal rates attained by the EC (32.3%) and PC (52.6%). Notably, increasing the voltage to 1.0 V accelerated the PEC degradation of AMX, attaining a removal efficiency of 91.2% within 90 min and exceeding 95% within 120 min.

Photoelectrocatalytic treatment of municipal wastewater with emerging concern pollutants using modified multi-layer catalytic anode

Municipal wastewater contains emergent chemical and biological pollutants that are resistant to conventional wastewater treatments. Therefore, the focus of the current study was to address the challenge of removing emergent chemical and biological pollutants present in municipal wastewater. To achieve this, a photo electro-catalytic (PEC) treatment approach was employed, focusing on the removal of both micro and biological pollutants that are of emergent concern, as well as the reduction of Chemical Oxidation Demand (COD) and Total Organic Carbon (TOC). The treatment involved the use of a modified multi-layer catalytic anode photo-electroactive anode as an effective anode for PEC treatment of municipal wastewater. In the continuous mode of operation, %COD removal was optimized for the treatment of municipal wastewater under Ultra-Violet C (UVc), 280 nm, and Visible (Vis) radiation, 400 nm. Therefore, a comparative study was performed to investigate the effect of Vis radiation on %COD removal, micropollutants removal, and disinfection of municipal wastewater. Micropollutants present in municipal wastewater were effectively oxidized/degraded with the highest reduction rate between 100% and 80% under the influence of UVc and Vis radiation respectively by the PEC treatment process. Disinfection of various microorganisms present in the wastewater with the effect of UVc and Vis assisted PEC treatment was also monitored. Overall, 75–80% of the disinfection of municipal wastewater was contributed by the modified multi-layer catalytic anode. The UVc in the PEC system, contributes approximately 20–25% to the overall disinfection of municipal wastewater.

Binary regulation of photoelectron-heterojunction Sg-CN/BMO using sulfur-doping and oxygen vacancy construction for boosting chloroquine degradation

Photoelectrocatalysis (PEC) is a promising method for contaminant treatment, the preparation of photoelectrocatalyst is momentous for realization of superior PEC degradation efficiency. Herein, sulfur-doping g-CN and oxygen vacancy regulated bismuth molybdate heterojunction Sg-CN1/BMO5 was synthesized for chloroquine phosphate (CQ) degradation. Benefiting from band gap re-building and enhanced electronic transmission, the heterojunction displayed outstanding photoelectrocatalytic ability, and 90.2% of CQ can be degraded within 120 min. The degradation activity of Sg-CN1/BMO5 has been testified by pseudo-first-order rate constant, which was 3.03 and 2.66 folds of g-CN and BM. The enhanced photoelectrocatalytic effect was attributed to the boosted visible light adsorption ability, recombination suppression of photogenerated carriers and accelerated charge transfer process of the heterojunction. Radical capture experiments and electron spin-resonance (ESR) results revealed that the hydroxyl radical (OH), superoxide radical (O2–) and hole (h+) dominated the CQ degradation. Furthermore, the CQ degradation pathway and toxicity evaluation of intermediates were proposed based on DFT calculation and LC-MS identification.

BiVO4/boron-doped diamond heterojunction photoanode with boron doping engineering and enhanced photoelectrocatalytic activity

Photoelectrocatalysis is one of the most promising strategies to address ever-growing wastewater problems. A novel heterojunction photoanode formed by depositing a photocatalyst on a boron-doped diamond (BDD) layer has been considered an ideal material for the practical application of photoelectrocatalytic (PEC) degradation due to its advantages of light responsiveness, excellent charge transport, and robustness. In this study, various BiVO4/BDD heterojunction photoanodes with different diamond crystalline qualities and electrical conductivities were successfully fabricated by tuning the boron (B) doping concentration of the BDD layer. It was proposed that the charge transport efficiency of the photoanodes is promoted by optimizing the crystalline qualities and electrical conductivities of BDD films, thereby enhancing the PEC activity of the BiVO4/BDD heterojunction photoanode. Our results suggested that the electrical conductivity of BDD increased and the crystalline quality of BDD deteriorated with increasing B doping concentration. As a result, the PEC activity of the BiVO4/BDD heterojunction photoanode first increased and then decreased. The optimal PEC activity of the BiVO4/BDD heterojunction photoanode was achieved corresponding to the [B]/[C] gas ratio at 500 ppm, producing a current density of 3.3 mA/cm2 at 1.6 VRHE (the potential versus a reversible hydrogen electrode) in 0.1 M Na2SO4 under AM 1.5 irradiation, which was 1.7 times (1.9 mA/cm2) that of the photoanode with a [B]/[C] gas ratio of 3000 ppm. Meanwhile, the optimized tetracycline hydrochloride (TCH) degradation efficiency was 63.5 % within 9 min (500 ppm gas phase), which was 2.5 times (25.1 %) that of the highly doped photoanode with a [B]/[C] gas ratio of 3000 ppm. This study revealed that the excellent PEC performance benefited from the high crystalline quality and high electrical conductivity of BDD, which depended on the optimized B doping concentration. The idea of enhancing the PEC activity of the photoanode by optimizing the properties of the conductive electrode material proposed in this study provides a conceptual reference for fabricating potential high-performance photoanodes in the future.

Photoelectrocatalytic degradation of tetracycline through C3N5/TiO2 nanotube arrays photoanode under visible light: Performance, DFT calculation and mechanism

TiO2 nanotube arrays (TNAs) has been widely applied as a photoanode to improve the chemical stability of electrodes in the photoelectrocatalytic (PEC) system, whereas the practical application of TNAs in organic pollutant degradation is restricted due to low visible-light response and high recombination efficiency of photoinduced carriers. In the present work, the nitrogen-rich carbon nitride (C3N5) modified TNAs (C3N5/TNAs) photoanode was constructed for tetracycline (TC) degradation in the PEC system under visible light. The introduction of C3N5 promoted the photoconversion efficiency and improved the photocatalytic performance by reducing the recombination efficiency of photoinduced carriers. The radical capture experiments verified that •OH and holes were the predominant reactive species, while 1O2, •O2- and electron participated in TC degradation in the PEC system. The density functional theory calculations and HPLC-MS spectra revealed the possible degradation pathway of TC. The toxicity estimation indicated that the overall toxicities of TC were diminished after degradation in PEC system.

Energy-oriented utilization from organic wastewater: Directional photoelectrocatalytic conversion of phenol to C1 fuels

To solve the problems of energy consumption, carbon emissions and pollution simultaneously, the directional conversion of phenol to hydrocarbon fuels through a pathway of “phenol → CO2 → HCO3–→HCOOH” was explored, with self-supplied CO2 as both carbon-based transition carrier and electron acceptor. In this economic approach, photoelectrocatalytic (PEC) deep mineralization of phenol was realized on the photoanode to provide CO2, together with the waste electrons from mineralization, was PEC converted into formate as the major liquid product on photocathode under an applied potential of 3 V and simulated sunlight. The total carbon utilization efficiency of phenol to hydrocarbons is 6.76%, and the conversion efficiency of formic acid is as high as 94.8% within 8 h PEC reaction. The integrated cell achieved the recovery of 2.75% waste electrons from phenol oxidation to produce liquid fuel. This work provides a promising “carbon neutral” strategy, which is important for realizing pollutant resource utilization and alleviating energy shortage.