Photoelectrocatalytic Process Research Articles

Photoelectrocatalytic degradation of sulphonamide antibiotics in aquatic media using a novel Co-doped ZnO nanocomposite: evaluation of performance, kinetic studies

ABSTRACT It is well known that antibiotics’ residues in aquatic environments are a great threat to human health and ecology. Thus, it is vital to develop efficient strategies to overcome the mentioned threat and degrade the pointed out residues as much as possible. Herein, a novel Co-doped ZnO nanocomposite was fabricated and deposited on fluorine-doped tin oxide glass sheets (FTO) and eventually applied for the photoelectrocatalytic degradation of four sulphonamides (SAs), namely sulphacetamide (SCT), sulphathiazole (STZ), sulfamethoxazole (SMX) and sulphadiazine (SDZ) under visible light irradiation. In this regard, the effect of initial pH (3–11), applied current (0.5–1.5 mA/cm2), initial concentration of SAs (5–20 mg/L) were thoroughly investigated. The results indicated that under the optimal conditions (pH = 9, [SAs] = 5 mg/L and applied current = 1.5 mA/cm2), the degradation efficiencies obtained under a 90-min of reaction time were as follows: SCT (97.1%), SMX (95.8%), SDZ (93.2%) and STZ (91.8%). In addition, the degradation of the SAs by the applied photoelectrocatalytic process (PECP) followed the first-order kinetic model. Meanwhile, the applied PECP exhibited an excellent performance with regard to real samples. Finally, PECP is reckoned to be associated with ‘green’ technologies as electricity is involved and the used catalyst will not end up in the environment as secondary toxic materials.

Progress in Development of Photocatalytic Processes for Synthesis of Fuels and Organic Compounds under Outdoor Solar Light.

With photovoltaics becoming a mature, commercially feasible technology, society is willing to allocate resources for developing and deploying new technologies based on using solar light. Analysis of projects supported by the European Commission in the past decade indicates exponential growth of funding to photocatalytic (PC) and photoelectrocatalytic (PEC) technologies that aim either at technology readiness levels (TRLs) TRL 1–3 or TRL > 3, with more than 75 Mio€ allocated from the year 2019 onward. This review provides a summary of PC and PEC processes for the synthesis of bulk commodities such as solvents and fuels, as well as chemicals for niche applications. An overview of photoreactors for photocatalysis on a larger scale is provided. The review rounds off with the summary of reactions performed at lab scale under natural outdoor solar light to illustrate conceptual opportunities offered by solar-driven chemistry beyond the reduction of CO2 and water splitting. The authors offer their vision of the impact of this area of research on society and the economy.

Incorporating Oxygen Atoms in a SnS2 Atomic Layer to Simultaneously Stabilize Atomic Hydrogen and Accelerate the Generation of Hydroxyl Radicals for Water Decontamination.

Photoelectrocatalysis (PEC) is an efficient way to address various pollutants. Surface-adsorbed atomic hydrogen (H*) and hydroxyl radicals (•OH) play a key role in the PEC process. However, the instability of H* and low production of •OH considerably limit the PEC efficiency. In this study, we noted that incorporating oxygen atoms could regulate the behavior of H* by creating a locally favorable electron-rich state of S atoms in the SnS2 catalyst. The finely modulated H* led to a 12-fold decrease in the overpotential of H2O2 generation (H*-OOH*-H2O2-•OH) by decreasing the activation energy barrier of OOH* (rate-determining step). Considering density functional theory calculations, an H*-•OH redox pair suitable for a wide pH range (3-11) was successfully constructed based on the photocathode. The optimal SnS1.85O0.15 AL@TNA photocathode exhibited a ∼90% reduction in Cr(VI) in 10 min and ∼70% TOC removal of 4-nitrophenol, nearly 2- and 3-fold higher than that without oxygen incorporation. Electron spin resonance spectrometry and radical quenching experiments verified that H* and the derived •OH via 1-electron and 3-electron reduction were the main active species. Operando Raman spectroscopy confirmed that the stable SnO2 phase helped constantly activate the production of H* and •OH.

Photoelectrocatalytic sterilization on thorn-like ZIF-67/ZnO hybrid photoanodes

A new type of ZIF-67/ZnO hybrid coated on Co foil was prepared via an electrochemical etching and hydrothermal processes for photoelectrocatalytic sterilization. The thorn-like ZnO nanorods in the photoanode films play an important role of capturing bacteria from solution. The porous ZIF-67 with high specific surface area efficiently adsorbed the leaked K+ ions assisted by the hERG release, and realizes the visible-light photocatalytic activity with the generation of charge carriers. The visible-light photoelectrocatalytic antibacterial effect on ZIF-67/ZnO hybrid is further promoted by applying a potential to the photoelectrode to promote the separation and transfer of charge carriers. As a result, the visible-light photoelectrocatalytic antibacterial effect was powerful for rapid destroy of cell integrity. At the same time, the decomposition of bacteria cell was also facilitated to further accelerate the K+ leakage. Thus, the simultaneous process of destroying cell membrane integrity and leaking K+ ions is achieved during the photoelectrocatalytic process, leading to the complete destruction of bacteria. This photoelectrocatalytic antibacterial system based on ZIF-67/ZnO@Co foil offers a potential way for sterilization application in the future.

Photoelectrocatalytic degradation of refractory pollutants over WO3/W network photoelectrode with heterophase junction for enhancing mass transportation and charge separation

The most crucial factors limiting the degradation performance of photoelectrocatalytic (PEC) process are the low charge separation efficiency and slow mass transportation. Herein, we report a WO3 network photoelectrode by constructing heterophase junction of WO3 on tungsten mesh (hm-m-WO3/W mesh), which exhibits superior PEC performance, as high as 5.6 mA cm−2 of photocurrent density at 1.2 VRHE, achieving a complete degradation (99.9%) and nearly total mineralization (84.5%) of bisphenol A, reaching an apparent reaction rate constant of 5.7 × 10−2 min−1, 1.5 times of WO3 based photoelectrode ever reported. A Schottky junction is formed at m-WO3/W interface which greatly promotes the charge transfer between catalysts and support. The catalysts show appropriate phase alignment, where the parallel directions between built-in electric field of heterophase junction and external potential benefit charge separation. Computational fluid dynamics simulations indicate the network structure favors the diffusion of the fluid containing pollutants. This work demonstrates a viable strategy for designing the photoelectrode with high charge separation efficiency and fast mass transportation in PEC wastewater treatment.

A Convenient Procedure for Preparing BiOX-TiO2 Photoelectrocatalytic Electrodes from a Titanium-Oxo Compound-Modified Carbon Fiber Cloth.

Photoelectrocatalysis (PEC) has shown great advantages in sustainable organic synthesis and wastewater treatment because the PEC process can minimize electron-hole recombination, thereby improving the photocatalytic performance. Here, we report a convenient procedure for preparing immobilized BiOX-TiO2 photoelectrocatalytic electrodes from a titanium-oxo compound (TOC)-modified carbon fiber cloth (CFC). Crystalline TOCs composed of Ti12 cations and bismuth halide anions, [Ti12O14(OiPr)18][Bi3Br11(THF)2] (1) and [Ti12O14(OiPr)18][Bi4I14(THF)2] (2), were grown on CFC. Taking advantage of the easy hydrolysis of the titanium-oxo cation and bismuth halide anion, we could easily transform these CFC-immobilized crystals into BiOX-TiO2/CFC (X = Br or I) photocatalysts, which facilitates recycling of the catalysts. The photocatalytic dye degradation test showed that the efficiency did not decrease obviously after 10 photocatalytic cycles. Using BiOX-TiO2-modified CFC as electrodes, electrocatalysis (EC), photocatalysis (PC), and PEC were examined. PEC showed an attractive synergistic effect of EC and PC. These TOC-modified CFCs would be potential candidates for catalytic electrodes for sustainable wastewater purification.

Peroxymonosulfate enhanced photoelectrocatalytic oxidation of organic contaminants and simultaneously cathodic recycling of silver

Degradation of organic contaminants with simultaneous recycling of Ag+ from silver-containing organic wastewater such as photographic effluents is desired. Although photoelectrocatalysis (PEC) technology is a good candidate for this type of wastewater, its reaction kinetics still needs to be improved. Herein, peroxymonosulfate (PMS) was employed to enhance the PEC kinetics for oxidation of phenol (PhOH) at the anode and reduction of Ag+ at the cathode. The degradation efficiency of phenol (PhOH, 0.1 mmol/L) was increased from 42.8% to 96.9% by adding 5 mmol/L PMS at a potential of 0.25 V. Meanwhile, the Ag (by wt%) deposited on the cathode was 28.1% (Ag2O) in PEC process, while that of Ag (by wt%) was 69.7% (Ag0) by adding PMS. According to the electrochemistry analysis, PMS, as photoelectrons acceptor, enhances the separation efficiency of charges and the direct h+ oxidation of PhOH at the photoanode. Meantime, the increasing cathode potential avoided H2 evolution and strongly alkaline at the surface of cathode, thus enabling the deposition of Ag+ in the form of metallic silver with the help of PMS. In addition, PMS combined with PEC process was effective in treating photographic effluents.

NIR Photothermal-Enhanced Electrocatalytic and Photoelectrocatalytic Hydrogen Evolution by Polyaniline/SnS2 Nanocomposites

A series of polyaniline (PANI)-decorated SnS2 nanoplates (PANI/SnS2) were produced via a hydrothermal method followed by a liquid–solid mixing. The PANI/SnS2 nanocomposites were composed of amorphous PANI and hexagonal-phase SnS2 nanoplates. Infrared thermal images revealed that PANI had an excellent near-infrared (NIR)-induced photothermal effect. Overall, the PANI/SnS2 nanocomposites showed better NIR-enhanced electrocatalytic and photoelectrocatalytic hydrogen evolution activity than bare SnS2 nanoplates. The optimized 4% PANI/SnS2 (which contained 4 wt % PANI) displayed the largest electrochemical double-layer capacitance (Cdl) value (0.85 mF cm–2) and the lowest Tafel slope of 66 mV dec–1 in 0.5 M H2SO4 under NIR irradiation. It was investigated and confirmed that the photothermal effect and the synergistic effects between SnS2 and PANI heterostructure played important roles in promoting electrocatalytic and photoelectrocatalytic hydrogen evolution processes.

Controlling electrocatalytic, photoelectrocatalytic, and load release processes using soft material-modified electrodes

• Hemin/G-quadruplex hydrogel-modified electrode reveals triggered stiffness and switchable electrocatalysis. • Enzyme-loaded pH-responsive hydrogel-modified electrode show electroswitchable stiffness and load release functions. • An integrated photosystem I/glucose oxidase-modified electrode act as photoelectrochemical cell. Soft materials, such as hydrogels, polymers or biomaterials associated with electrodes provide interfaces revealing electrocatalytic, photoelectrocatalytic and controlled release of loads functions. These will be addressed by three examples demonstrated by our laboratory, including: (i) The assembly of a stimuli-responsive nucleic acid-based hydrogel on an electrode support, consisting of a hydrogel matrix crosslinked by duplex nucleic acid bridges and K + -ion-stabilized G-quadruplex bridges. By cyclic and reversible formation and dissociation of the G-quadruplexes by K + -ions and crown ether (CE), the switchable stiffness properties of the hydrogel are demonstrated. The integration of hemin into the G-quadruplex bridging units on electrocatalytic interface for the electrocatalyzed reduction of H 2 O 2 is introduced. In the presence of K + -ions/crown ether the switchable electrocatalytic functions of the electrode are demonstrated. (ii) A pH-responsive nucleic acid-based hydrogel matrix is immobilized on an electrode surface. The hydrogel interface is crosslinked by permanent nucleic acid bridges and pH-responsive crosslinking units. At acidic pH values, the pH responsive bridges are unlocked via generating i-motif structures, leading to an hydrogel interface of lower stiffness. Immobilization of ferrocene-modified glucose oxidase (GOx) in the hydrogel yields an electrically contacted enzyme electrode that stimulates the bioelectrocatalyzed oxidation of glucose and the acidification of the hydrogel. By incorporating a load into the hydrogel, the electrocatalyzed oxidation of glucose and the accompanying acidification of the hydrogel lead to a hydrogel of lower stiffness, allowing the controlled release of the load. (iii) A supramolecular, electrochemically contacted, photoresponsive matrix consisting of native photosystem I (PS I) interlinked to glucose oxidase (GOx) by an electrically contacting redox polymer consisting of polyvinyl imidazole Os 2+/3+ (bipyridine) 2 Cl complex is introduced. The organized assembly acts as a photobioelectrochemical fuel cell where photoinduced electron transfer from PS I to the electrode stimulates the bioelectrocatalyzed oxidation of glucose. The system demonstrates the light-induced oxidation of the glucose-fuel and the concomitant generation of electrical power.

Zirconium-based Metal-Organic Frameworks for highly efficient solar light-driven photoelectrocatalytic disinfection

Two synthesized zirconium-based Metal-Organic Frameworks (Zr-MOFs), using 2,6-naphthalenedicarboxylic acid (NDC) and amino-functionalized NDC (4,8-diaminonaphthalene-2,6-dicarboxylic acid, NDC-2NH2) as linkers, have been studied in photoelectrocatalytic disinfection processes. The Zr-based MOFs were deposited onto graphite paper and were deeply analysed to unravel their behaviour in electrocatalytic (EC), photocatalytic (PC) and photoelectrocatalytic (PEC) configurations under solar (Xe-arc lamp), visible (Xe-arc lamp + 400 nm cut-off filter) and 365 nm UV-LED irradiation. TPC results showed reproducible photocurrent response upon repeated on–off cycles and bandgaps were calculated to be 3.13 and 2.11 eV for Zr-NDC and Zr-NDC-2NH2, respectively. The highest photocurrent was obtained for 365 nm UVA in Zr-NDC and was similar for both UVA and solar irradiation in the case of Zr-NDC-2NH2. The Zr-MOFs catalytic electrodes were evaluated for their disinfection activity using a strain of Staphylococcus aureus and performance tracked by measuring colony forming units (CFU). The disinfection efficiency was higher in PEC than PC studies (>2-log reduction or 99 % CFU inhibition) under 365 nm UVA irradiation, suggesting that the anodic bias potential effectively minimized the recombination of the photogenerated electron-hole pairs. A complete disinfection was reached after 60 and 20 min under irradiation of full Xe-arc (solar) spectrum in PC and PEC runs, respectively, for both Zr-MOFs. The high disinfection capacity under solar irradiation was attributed to the transfer of photoexcited electrons from ligand to cluster by high energy photons.

Electropolymerization process dependent poly(1,4-di(2-thienyl)benzene) based full spectrum activated photocathodes for efficient photoelectrochemical hydrogen evolution

In this work, with the help of different electrochemical polymerization methods, the surface morphology of poly-1,4-bis(2-thienyl)benzene (PDTB) photocathode and S oxidation state were modulated. Thus, PDTB photocathodes with strong light absorption (310–2500 nm) and strong charge separation ability were successfully prepared. • Controllable composition, morphology and performance of PDTB photocathodes. • A novel strategy for design photocathodes with low band gap. • The enhanced photoelectrochemical performance was confirmed by detailed experiments. Electrochemical surfaces are essential for photoelectrocatalytic processes occuring on semiconductor electrodes, which influence light harvesting capability and charge separation of photoelectrochemical (PEC) hydrogen evolution process. In this work, electrochemical processes through cyclic voltammetry (CV), chronoamperometry (CA) and amperometry ( i-t ) show different abilities to electropolymerization. It results in poly-1,4-bis(2-thienyl)benzene (PDTB) photoelectordes with various microporous structures and regulated S oxidation states. Benifiting from these effect factors, the light absorption ability and charge separation of PDTB photoelectordes are expanded and promoted. In particular, PDTB photoelectrodes prepared by CA with 1.23 eV band gap and strong light absorption (310–2500 nm) show the best photoelectrochemical activity with a charge transfer resistance of 7 Ω, a photocurrent of 0.9 mA cm −2 and increases the onset hydrogen production potential to 0.92 V. The incident photon to current efficiency (IPCE) can reach 14.16 % at 850 nm. It suggests that photoelectrodes from electropolymerization may offer a simple and efficient strategy by adjusting the degree of polymerization to get a promising low band gap semiconductor for efficient PEC water reduction.

Sulphate radical enhanced photoelectrochemical degradation of sulfamethoxazole on a fluorine doped tin oxide - copper(I) oxide photoanode

• Visible light active FTO-Cu 2 O photoanode was successfully synthesised. • Sulphate radical was produced from persulphate salt at the surface of the Cu 2 O. • Degradation of sulfamethoxazole was markedly enhanced by sulphate radicals. • Mechanism of radicals generation and sulfamethoxazole degradation were proposed. • Application in real wastewater matrix was carried out with TOC removal of 43%. We report a sulphate radical enhanced photoelectrochemical degradation of sulfamethoxazole on a solar light driven fluorine doped tin oxide - copper(I) oxide photoanode. Copper(I) oxide was prepared by a template-free method and dispersed onto the surface of a fluorine doped tin oxide glass to form the photoanode. UV–Vis diffuse reflectance spectroscopy showed that the photoanode absorbed in the visible light region. With sodium persulphate as the source of sulphate radical, photoelectrochemical degradation studies showed that sodium persulphate markedly enhanced the degradation of sulfamethoxazole. Studies on the effects of change in concentration of the persulphate and the absence of the persulphate on the photoelectrocatalytic degradation process were conducted. Overall, the extent of degradation and mineralisation of sulfamethoxazole in water was found to be 86% and 67% respectively with bias potential of 1.5 V for the sulphate radical enhanced process. Scavenger studies showed that the photogenerated holes and sulphate radicals were the primary active species in the abatement of sulfamethoxazole. The effectiveness of sulfamethoxazole removal in real matrices by the use of FTO-Cu 2 O photoanode and sulphate radical was also confirmed.

Synthesis of TiO2 Photoelectrode Nanostructures for Sensing and Removing Textile Compounds Rhodamine B

The study of the sensing and removal of Rhodamine B (RhB) textile compounds is the photoelectrocatalytic system applications development. RhB was used as a model to study the performance of TiO2 (NTiO2) photoelectrode nanostructures as environmentally friendly sensors. The synthesis of NTiO2 was carried out on the surface of the Titanium electrode by applying a potential bias of 25.0 V. The NTiO2 formed on the surface of the Titanium electrode (NTiO2/Ti) was characterized using SEM, XRD, FTIR, and Cyclic Voltammetry (CV). The formation of NTiO2 is characterized by the formation of a honeycomb-like tube on the Ti electrode surface. In addition, it is strengthened by diffractogram peaks at 2ϴ = 25 o and 48 o and IR absorption at wavenumbers of 3441.01 cm-1 (-OH groups) and 1629.85 cm-1 (Ti-O group). As for the results of sensing RhB using CV, it is known that RhB is oxidized on the surface of NTiO2/Ti with a value of Ea = 1.54 V. The oxidation process that occurs is controlled by the diffusion rate. Based on the results of photoelectrocatalytic RhB removal for 60 minutes, it was shown that using 0.10 M NaCl support electrolyte effectively increased the RhB removal rate. The decrease in RhB concentration during the photoelectrocatalytic removal process was 74.21%.

Photoelectrochemistry-driven selective hydroxyl oxidation of polyols: Synergy between Au nanoparticles and C3N4 nanosheets

Selective and efficient oxidation of a certain hydroxyl group in biomass-derived polyols is quite appealing but challenging. We herein propose a new photoelectrochemical strategy for enhancing the selectivity and kinetics of the middle hydroxyl oxidation in glycerol molecules using Au/C 3 N 4 catalyst. The introduction of illumination and usage of C 3 N 4 are first demonstrated to have a direct bearing on enhancing the selectivity of middle hydroxyl oxidation on Au through the electron transfer and accelerating the kinetics by accumulating photogenerated holes with moderate oxidizability. By this strategy, the selectivity of glycerol to dihydroxyacetone and turnover frequency are achieved as high as 53.7% and unprecedented 4,619 h −1 . The synergy of electronic interaction, localized surface plasmon resonance effect, and photogenerated carriers dual injection is revealed to account for such high selectivity and kinetics of the middle hydroxyl oxidation during the photoelectrochemical process. Our results sheds light on the photoelectrocatalysis-driven selective hydroxyl oxidation in polyols. • Photoelectrochemical strategy to tackle challenging selective hydroxyl oxidation • Reasonably designed polymeric C 3 N 4 nanosheets supported Au as catalyst • Unprecedented kinetics and good selectivity are reported • Synergy mechanism for photoelectrocatalytic process is revealed Different from the harsh conditions of thermocatalysis such as high temperatures and pressures, electrochemical synthesis (i.e., electro-valorization or electro-refinery) promises to handle the chemical production under ambient conditions. The widely known electrochemical synthesis includes nitrogen reduction reaction, carbon dioxide reduction reaction (CO 2 RR), and hydrogen evolution reaction. Actually, the electrochemical synthesis promises to handle more reactions; for example, allylic C-H oxidation ( https://doi.org/10.1038/nature17431 ), desaturation of carbonyl compounds ( https://doi.org/10.1038/s41557-021-00640-2 ), and hydroxyl oxidation (the target reaction in this work). We herein propose a photo-assistant electrochemical strategy to drive hydroxyl oxidation of polyols with high selectivity and unprecedented reaction rate. We hope electrochemical synthesis can be complementary to conventional thermocatalysis and help to build a better society. Simultaneous selectivity and kinetics enhancement of hydroxyl oxidation in polyols is demonstrated using glycerol as the model molecule, which benefits from a photo-assistant electrochemical strategy using heterogeneous Au/p-C 3 N 4 as the catalyst.

Photoelectrocatalytic activity of perovskite YFeO3/carbon fiber composite electrode under visible light irradiation for organic wastewater treatment

BackgroundA considerable amount of azo dye wastewater is generated from textile industry every day, which jeopardizes human health and environment. To treat azo dye-containing wastewater in visible-light environment, a perovskite YFeO3/carbon fiber (CF) electrode was developed. MethodsA sol-gel process combined with calcination was adopted to synthesize YFeO3 catalysts, and the composite electrode was fabricated using a facile dip-coating method. Significant findingsThe YFeO3 powder that was calcined at 700 °C consisted of mixed hexagonal and orthorhombic phases with crystallite sizes of 15–30 nm. The particles tended to aggregate, forming a porous structure, and they exhibited a photocatalytic degradation capability for Reactive Black 5 (RB5) dyes. Notably, the YFeO3/CF composite electrode enabled significant photoelectrocatalytic activity over RB5 under visible light irradiation, with a removal efficiency of 99% in a 60 min treatment. In addition, the composite electrode demonstrated its high stability during the repeated treatments. The synergetic effect of photo- and electrocatalysis accounted for breaking the N=N bonds, as well as the benzene and naphthalene structures of RB5, resulting in a favorable pollutant degradation. Moreover, the photoelectrocatalytic treatment system kinetics followed a pseudo-first-order rate equation, corresponding to a single-molecule reaction. The improved photoelectrocatalytic activity of the composite electrode can be attributed to the reduced surface and charge transfer resistances during the photoelectrocatalysis process.

CO2 Utilization Through its Reduction to Methanol: Design of Catalysts Using Quantum Mechanics and Machine Learning.

Reducing levels of CO2, a greenhouse gas, in the earth’s atmosphere is crucial to addressing the problem of climate change. An effective strategy to achieve this without compromising the scale of industrial activity involves use of renewable energy and waste heat in conversion of CO2 to useful products. In this perspective, we present quantum mechanical and machine learning approaches to tackle various aspects of thermocatalytic reduction of CO2 to methanol, using H2 as a reducing agent. Waste heat can be utilized effectively in the thermocatalytic process, and H2 can be generated using solar energy in electrolytic, photocatalytic and photoelectrocatalytic processes. Methanol being a readily usable fuel in automobiles, this technology achieves (a) carbon recycling process, (b) use of renewable energy, and (c) portable storage of H2 for applications in automobiles, alleviating the problem of rising CO2 emissions and levels in atmosphere.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS2 (DMS) of TiO2 nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Using BCN nanostructure as anode electrode for photoelectrocatalytic degradation of organics: a statistical approach

Abstract In this study, boron carbon nitride (BCN) nanostructures were used as a photocatalyst which was synthesized in a chemical vapor deposition reactor. Photoelectrocatalysis was used for degradation organic pollutants from produced water. BCN nanostructures were coated on a coil-type copper wire to act as anode electrode in the photoelectrocatalytic process. The effect of different parameters on chemical oxygen demand (COD) removal efficiency from produced water was investigated by a central composite design (CCD) to maximize photoelectrocatalysis influence as one of the most used methods of wastewater treatment. A 12 run Plackett–Burman design was used for screening of the parameters (initial COD, electrical conductivity, applied cell voltage, UV lamp wavelength, H2O2 concentration, residence time, and initial pH) which led to the selection of residence time and initial pH as effective parameters. Since the core goal of this study was to maximize the COD removal efficiency, the steepest ascent method was used to propel these two parameters to the optimum region. Finally, CCD showed that applying photoelectrocatalysis could lead to 88.79% of the COD removal efficiency which would be an optimum value at a residence time of 15.85 min and a pH value of 3.3. Ultimately, this result was confirmed by experimentation at those conditions.

Fabricating Bi2MoO6@Co3O4 core–shell heterogeneous architectures with Z‑scheme for superior photoelectrocatalytic water purification

The decomposition efficiency of refractory organic contaminants depends strongly on the characteristics of photoanode semiconductors during the photoelectrocatalytic (PEC) process, and selecting an excellent material with superior PEC efficiency is a challenge for the current PEC oxidation technique's practical application. Herein, a novel Bi2MoO6@Co3O4 hierarchical core–shell heterogeneous photoanode is fabricated by the simple hydrothermal process. Moreover, the amount of Bi2MoO6 nanosheets adhered to the surface of the Co3O4 nanowire can be easily tuned by changing the concentration of the Bi2MoO6 precursor solution. The as-prepared Bi2MoO6@Co3O4 photoanode exhibited larger electroactive surface area, lower charge transfer resistance, more negative flat band potential, and high separation efficiency of induced e-/h+ pairs, as compared with that of bare Co3O4 nanowire. It is worth mentioning that the Z-scheme heterojunction structure formed by the combination of Bi2MoO6 and Co3O4 maintained the more vital redox ability of induced e-/h+. Consequently, the as-prepared Bi2MoO6@Co3O4 photoanodes showed better PEC performance than Bi2MoO6 or Co3O4 for the degradation of reactive brilliant blue KN-R. The optimized Bi2MoO6@Co3O4-2.0 exhibited the highest degradation rate of 88.43% and accelerated stability of 110 min at the current density of 500 mA·cm−2 in 1.0 mol·L-1 H2SO4 solution. The strategy of fabricating core–shell heterostructure Bi2MoO6@Co3O4 photoanode with superior PEC efficiency may guide other heterogeneous designs.

Understanding photoelectrocatalytic degradation of tetracycline over three-dimensional coral-like ZnO/BiVO4 nanocomposite

The coral-like BiVO4 was successfully constructed on ZnO nanorods grown on FTO substrates to reveal exceptional photoinduced charge migration kinetics as well as the underlying photoelectrocatalytic degradation process. The orderly ZnO nanorods array accelerated the separation of photogenerated carriers, while the three-dimensional coral structure of ZnO/BiVO4 nanocomposite increased the efficiency of light absorption and mass transfer, thus improving the photoelectrochemical properties. Fine interfacial contact between ZnO and BiVO4 led to the optimized photoelectrochemical performance with a photocurrent density of 0.29 mA/cm2 at 0 V vs. Ag/AgCl under visible light illumination (λ ≧ 420 nm), which was 3.2 times, 1.6 times of that of pristine ZnO and BiVO4. Moreover, the photoelectrocatalytic degradation efficiency of tetracycline from the ZnO/BiVO4 nanocomposite on was c. a. 84.5% and the main degradation paths were analyzed by LC-MS. Radical scavengers were employed to evaluate the capability to produce •O2− and •OH active species upon visible light illumination. This study elucidated the reaction mechanisms of the ZnO/BiVO4 nanocomposite during the photoelectrocatalytic degradation process.