Photoelectrocatalytic Process Research Articles

3D-TNAs/N-TiO2 photoanode assisted heterogeneous electro-Fenton with a novel Fe-MOFs@CF cathode for efficient synergetic oxidation of organic contaminants

Photoelectro-catalysis (PEC) and heterogeneous electro-Fenton (HEF) reactions are two frontier research fields for real effluent treatments. In the present work, a synergetic system with integration of both PEC and HEF has been developed for pollutant removal. PEC process with lower external bias results in the efficient separation of photogenerated hole and electrons, which can also modulate the HEF catalytic performance at the counter electrode, and in other cases the active HEF reaction can in turn affect the intrinsic activity of PEC. In this system, three dimensional TiO2 nanotube arrays coupled with nitrogen doped TiO2 nanoparticles (3D-TNAs/N-TiO2) was prepared as photoanode for solar light-driven PEC process while NH2-MIL-101 loaded on carbon felt (Fe-MOFs@CF) have been used as the cathode for HEF reaction. The performances of the synergetic system showed much higher degradation efficiency, which were evaluated by degrading typical organic containments in water (with the best of∼95 % in 5 min with 2*3 cm2 electrode area). The reaction rate in the coupling system were ∼7.25 and 1.18 times higher than single PEC or HEF with a wide pH applied range, well recycled and good stability for further application in water purification.

Two-Dimensional Layered Heterojunctions for Photoelectrocatalysis.

Two-dimensional (2D) layered nanomaterial heterostructures, arising from the combination of 2D materials with other low-dimensional species, feature a large surface area to volume ratio, which provides a high density of active sites for catalytic applications and for (photo)electrocatalysis (PEC). Meanwhile, their electronic band structure and high electrical conductivity enable efficient charge transfer (CT) between the active material and the substrate, which is essential for catalytic activity. In recent years, researchers have demonstrated the potential of a range of 2D material interfaces, such as graphene, graphitic carbon nitride (g-C3N4), metal chalcogenides (MCs), and MXenes, for (photo)electrocatalytic applications. For instance, MCs such as MoS2 and WS2 have shown excellent catalytic activity for hydrogen evolution, while graphene and MXenes have been used for the reduction of carbon dioxide to higher value chemicals. However, despite their great potential, there are still major challenges that need to be addressed to fully realize the potential of 2D materials for PEC. For example, their stability under harsh reaction conditions, as well as their scalability for large-scale production are important factors to be considered. Generating heterojunctions (HJs) by combining 2D layered structures with other nanomaterials is a promising method to improve the photoelectrocatalytic properties of the former. In this review, we inspect thoroughly the recent literature, to demonstrate the significant potential that arises from utilizing 2D layered heterostructures in PEC processes across a broad spectrum of applications, from energy conversion and storage to environmental remediation. With the ongoing research and development, it is likely that the potential of these materials will be fully expressed in the near future.

Ag-TiO2 Photovoltaic Synergistic Field-catalyzed Degradation Performance of Tetracycline

Background: Tetracycline (TC), a commonly used antibiotic, is extensively utilized in the medical sector, leading to a significant annual discharge of tetracycline effluent into the water system, which harms both human health and the environment. background: Tetracycline (TC), a commonly used antibiotic, is extensively utilized in the medical sector, leading to a significant annual discharge of tetracycline effluent into the water system. This harms both human health and the environment. Objective: A novel technique was developed to address the issues of photogenerated carrier complexation and photocatalyst immobilization. Compared to traditional photocatalytic photoelectrodes, the suspended catalyst used in the photovoltaic synergy field is more stable and increases the solidliquid contact area between the catalyst and the pollutant. objective: This paper uses sol-gel-prepared Ag-doped-TiO2 materials for the photoelectrocatalytic degradation of TC. Methods: This paper uses sol-gel-prepared Ag-doped-TiO2 materials for the photoelectric synergistic field-catalyzed degradation of TC. The study examined how the Ag doping ratio, calcination conditions, catalyst injection, pH, electrolytes, and electrolyte injection affected photoelectric synergistic field-catalyzed degradation. The experiments were performed in a photocomposite field with a constant 50 mA current and a 357 nm UV lamp for 60 minutes. The composites underwent characterization using XRD, TEM, and XPS techniques. method: The study examined how the Ag doping ratio, calcination conditions, catalyst injection, pH, electrolytes, and electrolyte injection affected photoelectrocatalytic activity. The experiments were done in a photocomposite field with a constant 50 mA current and a 357 nm UV lamp for 60 minutes. The composites underwent characterization using XRD, TEM, and XPS techniques. Results: Ag-TiO2 photoelectric synergistic field-catalyzed reaction with 357 nm ultraviolet lamp irradiation for 60 min and a constant current of 50 mA degraded 5 mg/LTC under preparation conditions of molar doping ratio of Ti: Ag=100:0.5, roasting temperature of 500 °C, and roasting time of 2 h. The photoelectric synergistic field-catalyzed degradation process achieved a degradation rate of 90.49% for 5 mg/L TC, surpassing the combined degradation rates of electrocatalysis and photocatalysis. The quenching experiments demonstrated that the degradation rate of TC decreased from 90.49% in the absence of a quencher to 53.23%, 42.58%, and 74.52%. The presence of •OH had a more significant impact than h+ and •O2-. Conclusion: The findings suggest that Ag-TiO2 significantly enhanced the efficacy of photoelectric synergistic field-catalyzed degradation and can be employed to treat high-saline and lowconcentration TC. This establishes a benchmark for using photoelectrocatalytic materials based on titanium in treating organic wastewater. result: Ag-TiO2 photoelectrocatalytic reaction with 357 nm ultraviolet lamp irradiation for 60 min and constant current (50 mA) degraded 5 mg/LTC under preparation conditions of molar doping ratio of Ti: Ag=100:0.5, roasting temperature of 500 °C, and roasting time of 2 h. The photoelectrocatalytic process achieved a degradation rate of 90.49 % for 5 mg/L TC, surpassing the combined degradation rates of electrocatalysis and photocatalysis. The quenching experiments demonstrated that the degradation rate of TC decreased from 90.49 % in the absence of a quencher to 53.23 %, 42.58 %, and 74.52 %. The presence of •OH had a more significant impact than h+ and •O2-.

Novel Fenton-like system based on bifunctional MgO/g-C3N4 S-scheme heterojunction photoanode for efficient tetracycline degradation

A novel photoelectrocatalytic (PEC) system consisting of S-scheme MgO/g-C3N4 photoanode and modified carbon felt (MCF) cathode was designed for efficient degradation of tetracycline, in which photoanode had both efficient photocatalytic performance and activation of H2O2 produced by the MCF cathode. After 30 min of LED irradiation, the PEC system could completely remove tetracycline at cathodic bias of −0.5 V (vs. Ag/AgCl), and the degradation rate constants were 5.3 and 1.5 times that of electrocatalysis and photocatalysis. The charge transfer mechanism of S-scheme MgO/g-C3N4 was verified by experimental studies and DFT calculations. Mg-N coordination was the key to activate H2O2 to produce singlet oxygen (1O2) and hydroxyl radicals (•OH). The PEC system had excellent degradation performance at pH ranges 4–10, which solved the bottleneck that Fenton system is effective at narrow pH range. This study provides new ideas for preparation of bifunctional photoanodes and new insights into the PEC process.

Evaluation of sol-gel and solvothermal method on titanium dioxide and reduced graphene oxide nanocomposite

The present study compares two synthesis routes to obtain titanium dioxide and reduced graphene oxide nanocomposites that could be used as photoelectrodes in a water-splitting photoelectrocatalytic system. The nanocomposites were obtained using in-situ sol-gel and solvothermal methods as fabrication routes. Subsequently, the materials obtained were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy techniques. The results indicated a strong interaction between reduced graphene oxide and titanium dioxide nanomaterials using both synthesis processes; however, the in-situ sol-gel method exhibited more significant conservation of the aromatic rings of the graphene structure and a lower bandgap (2.45 eV), which are suitable characteristics for its potential use in photoelectrocatalytic processes.

Cocatalyst Modified Polymeric Carbon Nitride Photoanode for Enhanced Photoelectrochemical Properties.

As a new organic photocatalyst, polymeric carbon nitride (CN) has shown good application potential in the field of photoelectrochemistry due to its unique physical and chemical properties, but its application has been seriously hindered due to its inherent characteristics such as the difficulty in charge separation. In this study, FeOOH modified CN photoanode (CN-Fe) was constructed to investigate the effect of the cocatalyst on the charge injection capacity of organic semiconductor photoelectrodes. The experimental results demonstrate significant improvement in the charge injection efficiency of the photoanode due to the introduction of FeOOH cocatalyst, leading to enhanced photoelectrochemical performance with approximately 2.4 times increase in photocurrent density. By thoroughly investigating the mechanism behind the loading of FeOOH on the polymeric carbon nitride photoanode, we gained profound insights into the behavior of charge carriers and reaction kinetics during the photoelectrocatalytic process.

Robust photoelectrocatalytic degradation of antibiotics by organic-inorganic PDISA/Bi2WO6 S-scheme heterojunction membrane

Ensuring the stability of the photoelectrode is paramount for optimal photoelectrocatalysis performance. In this investigation, a hybrid nanofiber film, incorporating the π-π conjugated self-assembly of perylene diimide monomers (PDISA) with Bi2WO6 (PDISA/Bi2WO6), was fabricated through the electrospinning process. Subsequently, this flexible electrospun film was pressed onto a Ni mesh to create a robust PDISA/Bi2WO6 electrode membrane. Results from photoelectrocatalytic studies reveal that the devised PDISA/Bi2WO6 photoanode significantly enhances the photoelectrocatalytic degradation efficiency of tetracycline (TC) and ciprofloxacin (CIP). Specifically, the apparent rate constants for the photoelectrocatalytic degradation of TC by 30%PDISA/Bi2WO6, compared to pristine PDISA and Bi2WO6, are elevated by 1.9 and 2.0 times, respectively. Moreover, the reaction rates of the photoelectrocatalytic (PEC) process surpass those of photocatalysis (PC) and electrocatalysis (EC) by 1.9 times and 8.0 times, respectively. Impressively, even after five cycles of PEC degradation of TC, the photoelectrode maintains 98.4% of its initial degradation rate, indicating its exceptional stability. These improvements in degradation efficiency and stability are attributed to the creation of the PDISA/Bi2WO6 S-scheme heterojunction membrane photoanode and the synergistic effects of photoelectrocatalysis.

Interface-engineered dual Z-scheme of BiVO4/NH2-MIL-125(Ti)/POF photoanode with enhanced photoelectrochemical performance

The key factors that restrain the decomposition activity of photoelectrocatalysis (PEC) are poor redox ability and low charge separation rate. In this work, the dual Z-scheme BiVO4/NH2-MIL-125(Ti)/POF (BiVO4/NM125(Ti)/POF) heterojunctions were successfully established for visible-light driven PEC degradation of phenol. As expected, the optimum BiVO4/NM125(Ti)/POF photoanode exhibited outstanding PEC performance with near-total degradation of phenol within 2 h of illumination. The evaluated activity was assigned to high charge transfer rate and dual Z-scheme heterostructures with double electron transport channels. The fabrication of dual Z-scheme heterojunctions improved a more efficient separation of photo-induced charge carriers while holding a higher redox ability to generate more reactive oxygen species (ROS) such as O2•− and •OH to decompose organic pollutants. In addition, excellent chemical stability and recyclability were also achieved after five times cycles, and the degradation pathway of phenol was also put forward. Finally, the quantitative structure-activity relationship (QSAR) was applied to forecast phenol and its degradation products toxicity. This research gives novel insights into establishing highly effective photoanode with promising applications for organic contaminants degradation, and offers in-depth understanding of charge separation and migration in PEC process.

Density‐Functional Theory Studies on Photocatalysis and Photoelectrocatalysis: Challenges and Opportunities

Density‐functional theory (DFT) is pivotal in the advancement of photocatalysis and photoelectrocatalysis. Its capability to explore electronic structures of materials contributes significantly to clarifying the mechanisms of photocatalytic (PC) and photoelectrocatalytic (PEC) processes. DFT calculations enable a deeper understanding of how these processes work at a molecular level, which is essential for designing versatile photocatalysts and photoelectrodes and optimizing reaction pathways. In this perspective, key PC and PEC applications, such as H2 production, CO2 reduction, dye degradation, and N2 reduction, where DFT is instrumental in optimizing materials designs and reaction pathways, are highlighted. Exploration on the synergy between experimental research and DFT calculations is highlighted, which is crucial for the development of efficient and environmentally friendly energy solutions. The discussion further extends to challenges and future directions, emphasizing the need for incorporating factors, including discrepancy in scale, light illumination, electrolyte presence, and applied bias, into DFT calculations, to achieve a more comprehensive understanding of PC and PEC systems. In this perspective, it is aimed to provide a holistic view of the current state and potential advancements in photocatalyst and photoelectrode modeling, thereby guiding future research toward more effective and sustainable energy and chemical production processes in PC and PEC systems.

Progress in Promising Semiconductor Materials for Efficient Photoelectrocatalytic Hydrogen Production.

Photoelectrocatalytic (PEC) water decomposition provides a promising method for converting solar energy into green hydrogen energy. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. However, the fairly low PEC efficiency of water decomposition by a semiconductor photoelectrode and photocorrosion seriously restrict the practical application of photoelectrochemistry. In this review, the mechanisms of PEC water decomposition are first introduced to provide a solid understanding of the PEC process and ensure that this review is accessible to a wide range of readers. Afterwards, notable achievements to date are outlined, and unique approaches involving promising semiconductor materials for efficient PEC hydrogen production, including metal oxide, sulfide, and graphite-phase carbon nitride, are described. Finally, four strategies which can effectively improve the hydrogen production rate-morphological control, doping, heterojunction, and surface modification-are discussed.

Utilization of glycerol solution for hydrogen production by a combination of photocatalysis and electrolysis processes with Fe-TiO2 nanotubes

A combination of photocatalysis and electrolysis (photoelectrocatalysis) for the simultaneous degradation of glycerol and hydrogen production using Fe-TiO2 nanotubes has been studied. This photocatalyst was synthesized through Ti anodization followed by Fe deposition with Fe(NO3)3 as precursor using the SILAR (successive ionic layer adsorption and reaction) method. The effects of Fe loading (based on the number of SILAR cycles) on TiO2 nanotubes and glycerol concentration were examined. The generated TiO2 nanotubes were 100% anatase phase with crystallite size between 25 and 29 nm. The results of UV-Vis DRS showed that the number of SILAR cycles of Fe dopant determined the magnitude of the decrease in the band gap of photocatalysts up to 2.74 eV, notably lower than a typical value of 3.15 eV associated with TiO2 anatase. FESEM/EDX, TEM, and HRTEM characterizations indicated the formation of neatly arranged TiO2 nanotubes with Fe deposited on the surface. The photoelectrocatalytic process increased the hydrogen produced by up to 5 times compared to a single photocatalytic or electrolysis process. The photocatalyst sample with Fe deposited on TiO2 nanotubes via a SILAR method with 15 cycles outperformed its bare TiO2 nanotube counterpart by producing hydrogen by 2.5 times (405.8 mmol/m2). Glycerol photo-reforming at 10% concentration produced hydrogen 6 times greater than water splitting (0% glycerol).

Fabrication of a WO3-Bi2WO6 Composite Electrode by Electrodeposition and its Application for Microbial Degradation

Photoelectrocatalytic (PEC) techniques are an innovative and promising method for eliminating microorganisms. Developing and applying such advanced technologies is essential for protecting public health and the environment. Semiconductor electrode development is a major issue in the advancement of such methods. We have developed a technique for fabricating WO3-Bi2WO6 electrodes using cyclic voltammetry (CV), focusing on the efficiency of the reaction and investigating key aspects for its use in microbial degradation. The optimization of the CV method parameter and calcination temperature was conducted in order to enhance the characteristics of composite WO3-Bi2WO6 electrodes for the aqueous oxidation process. The properties of the fabricated composited WO3-Bi2WO6 electrode were analyzed by several techniques, including UV-visible spectrophotometry, scanning electron microscopy, X-ray diffraction, Energy Dispersive X-ray Spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The PEC water oxidation and total microorganism elimination efficiencies were investigated to validate the application of the developed composite WO3-Bi2WO6 electrode properties. The characteristics of the prepared composite WO3-Bi2WO6 electrodes are significantly influenced by the calcination temperature. We were able to satisfactorily verify the electrodes' properties in a reaction involving different calcining temperatures. At a calcining temperature of 450 °C, WO3-Bi2WO6 electrodes exhibited excellent PEC activity in water oxidation and electron transfer rate at the electrode surface. The composited WO3-Bi2WO6 electrode can effectively remove 96% of total microorganisms under the PEC process within 15 minutes. This study provides important background information for future work on composite semiconductor thin film preparations with potential applications in microbe eradication and environmental protection.

Photo-electrocatalytic degradation of remdesivir from aqueous solutions using Ni-doped ZnO nanocomposite: Kinetic, degradation pathway, toxicity reduction and reusability

Currently, there has been increasing interest in developing active photocatalysts for the treatment of wastewaters. In this study, Nickel (Ni)-doped Zinc oxide on a fluorine tin oxide (ZnO/FTO) was synthesized and utilized as an electrocatalyst for efficient degradation and mineralization of remdesivir (REMD). Ni-ZnO/FTO electrode was characterized using XRD, SEM, EDX, LSV, and DRS analyses. The influence of operational parameters on the degradation efficiency procedure was explored in a batch photo-reactor and their optimum values were selected. At optimized conditions (e.g. initial REMD concentration = 1 mg/L, electrolyte concentration = 0.1 g/L, current intensity = 0.03 A, and pH = 7), within 2 h under UV-A, the removal efficiency of initial REMD concentration was 92 %, whereas TOC and COD removal efficiency were found as 80.1 % and 69.5 %, respectively. The assessment of the degradation rate within 2 h indicates that REMD degradation obeyed first order kinetic model. Additionally, in the comparison of degradation and mineralization efficiency of electrolysis, photolysis and photocatalytic and photoelectrocatalysis (PECP) processes for REMD removal, PECP gave the highest efficiency. The toxicity evaluations showed that the toxicity of solutions treated by the proposed PEC process significantly decreased in comparison with untreated controls. Based on reusability investigations, Ni-ZnO/FTO can be reused for at least five repetitive times with suitable efficiency. Moreover, by taking into account all results, it was concluded that the affordability, high potentiality, and well regenerability of Ni-ZnO/FTO make it an attractive electrocatalyst in terms of drug-containing wastewater treatment.

(Invited) In Situ Photoelectron Spectroscopy Reveals the Chemical Nature of Semiconductor Surface States

The accessible photovoltage of semiconducting photoabsorbers is typically 0.5-1 V below the theoretically achievable values predicted by the Shockley-Queisser limit [1]. Although the reason for this is still not well understood, surface and interface states within the photoabsorbers energy band gap may play a crucial role as they generally induce Fermi level pinning [2]. Within the PEC community, two key elements have been identified for the maximization of the photovoltage in photoelectrodes for water splitting: (i) the passivation of surface defects which is needed to avoid Fermi level pinning, and (ii) the increase of the minority carrier concentration at the interface to improve contact selectivity and optimize carrier extraction [3,4].To understand the role of surface defects on Fermi level pinning, detailed information on the chemical nature and electronic properties of surface states is needed. Such information is usually obtained with UHV surface science techniques such as XPS, but the photoelectrode surface under UHV conditions has little, if any, relevance to the electrified surface when immersed in the electrolyte. Moreover, recent studies have shown that semiconductor surfaces are not static, but undergo extensive structural and chemical transformations during PEC device operation [5,6]. In this talk, we will show our recent development of state-of-the-art techniques to study the structure and dynamics of semiconductor/water interfaces under practically relevant conditions [7]. The chemical nature of the electronic states for selected semiconductors prepared at the Institute for Solar Fuels has been explored using synchrotron-based resonant, ambient pressure soft and hard X-ray photoelectron spectroscopy (AP-XPS and AP-HAXPES) [6,8-11], and with in situ/operando Raman and photoluminescence spectroscopy. In particular, we will show that it is possible to study photon-induced chemical changes at solid/liquid interfaces using AP-XPS and AP-HAXPES [6,8].We will conclude this contribution by discussing about future perspectives and technical implementations for multimodal in situ/operando investigations of photoelectrocatalytic processes.[1] M.T. Mayer. Curr. Opin. Electrochem. 2017, 2, 104.[2] A. J. Bard et al. J. Am. Chem. Soc. 1980, 102, 3671.[3] A.G. Scheuermann et al., Nat. Mater. 2016, 15, 99.[4] M. Schleuning et al., Sustainable Energy Fuels, 2022, 6, 3701.[5] F.M. Toma et al., Nat. Commun. 2016, 7, 12012.[6] M. Favaro et al., J. Phys. Chem. B 2018, 122, 801.[7] M. Favaro et al., Surf. Sci. 2021, 713, 121903.[8] M. Favaro et al., J. Phys. D: Appl. Phys. 2021, 54, 164001.[9] M. Favaro et al., J. Phys. Chem. C 2019, 123, 8347.[10] W. Wang et al., J. Am. Chem. Soc. 2022, 144, 17173.[11] P. Schnell et al., Sol. RRL 2023, 2201104.

Photoelectrocatalytic Processes of TiO2 Film: The Dominating Factors for the Degradation of Methyl Orange and the Understanding of Mechanism.

Various thicknesses of TiO2 films were prepared by the sol-gel method and spin-coating process. These prepared TiO2 films exhibit thickness-dependent photoelectrochemical performance. The 1.09-μm-thickTiO2 film with 20 spin-coating layers (TiO2-20) exhibits the highest short circuit current of 0.21 mAcm-2 and open circuit voltage of 0.58 V among all samples and exhibits a low PEC reaction energy barrier and fast kinetic process. Photoelectrocatalytic (PEC) degradation of methyl orange (MO) by TiO2 films was carried out under UV light. The roles of bias, film thickness, pH value, and ion properties were systematically studied because they are the four most important factors dominating the PEC performance of TiO2 films. The optimized values of bias, film thickness, and pH are 1.0 V, 1.09 μm, and 12, respectively, which were obtained according to the data of the PEC degradation of MO. The effect of ion properties on the PEC efficiency of TiO2-20 was also analyzed by using halide as targeted ions. The "activated" halide ions significantly promoted the PEC efficiency and the order was determined as Br > Cl > F. The PEC efficiency increased with increasing Cl content, up until the optimized value of 30 × 10-3 M. Finally, a complete degradation of MO by TiO2-20 was achieved in 1.5 h, with total optimization of the four factors: 1.0 V bias, 1.09-μm-thick, pH 12, and 30 × 10-3 M Cl ion content. The roles of reactive oxygen species and electric charge of photoelectrodes were also explored based on photoelectrochemical characterizations and membrane-separated reactors. Hydrogen peroxide, superoxide radical, and hydroxyl radical were found responsible for the decolorization of MO.

Design and investigation of photoelectrochemical water treatment using self-standing Fe3O4/NiCo2O4 photoanode: In-situ H2O2 generation and fenton-like activation

Photoelectrocatalytic advanced oxidation processes (PEC AOPs) show great promise for solar-driven water treatment due to their energy efficiency and environmental compatibility. This study focuses on two key aspects: 1) creating an efficient photoanode and 2) utilizing the cathodic process simultaneously to enhance water treatment. Herein, a self-standing photoanode with stemmed nanospikes made from Fe3O4@NiCo2O4 (FNCO) was developed and seamlessly integrated into a PEC system. FNCO photoanode significantly improves PEC cell performance, using half the energy (12 Wh/g-pollutant) and achieving a four-fold higher rate constant (7.9×10−2 s−1) compared to NiCo2O4 (NCO). The in-situ generation of H2O2 and its Fenton-like activation amplifies the generation of reactive oxygen species (ROS), contributing to the PEC degradation activity. Detailed analysis reveals that the presence of surface-Fe3O4 enhances surface hydrophilicity and contributes to the high density of catalytically active sites in FNCO. We conducted a comprehensive investigation into the in-situ formation and activation pathways of H2O2 molecules through a series of experiments. The designed PEC water treatment system achieved almost 60 % total organic carbon (TOC) removal efficiency with consistent performance across a range of real-world water treatment scenarios, underscoring its versatility and robustness.

Sterically attenuated electronic communication in cobalt complexes of meridional isoquinoline-derived ligands for applications in electrocatalysis.

The ability to synthetically tune the ligand frameworks of redox-active molecules is of critical importance to the economy of solar fuels because manipulating their redox properties can afford control over the operating potentials of sustained electrocatalytic or photoelectrocatalytic processes. The electronic and steric properties of 2,2':6',2″-terpyridine (Terpy) ligand frameworks can be tuned by functional group substitution on ligand backbones, and these correlate strongly to their Hammett parameters. The synthesis of a new series of tridentate meridional ligands of 2,4,6-trisubstituted pyridines that engineers the ability to finely tune the redox potentials of cobalt complexes to more positive potentials than that of their Terpy analogs is achieved by aryl-functionalizing at the four-position and by including isoquinoline at the two- and six-positions of pyridine (Aryl-DiQ). Their cobalt complex syntheses, their electronic properties, and their catalytic activity for carbon dioxide (CO2) reduction are reported and compared to their Terpy analogs. The cobalt derivatives generally experience a positive shift in their redox features relative to the Terpy-based analogs, covering a complementary potential range. Although those evaluated fail to produce any quantifiable products for the reduction of CO2 and suffer from long-term instability, these results suggest possible alternate strategies for stabilizing these compounds during catalysis. We speculate that lower equilibrium association constants to the cobalt center are intrinsic to these ligands, which originate from a steric interaction between protons on the pyridine and isoquinoline moieties. Nevertheless, the new Aryl-DiQ ligand framework has been engineered to selectively tune homoleptic cobalt complexes' redox potentials.

Use of nickel-electroplating wastewater to synthesize Ni-doped TiO2 and NiTiO3 coatings by plasma electrolytic oxidation to treat hexavalent chromium in real electroplating wastewater

The use of residual water from nickel plating for the synthesis of Ni/TiO2 coatings using the PEO technique was carried out in this work. Evaluation by response surface methodology (RSM) for the studied coatings in the reduction of Cr(VI) present in chrome-plating wastewater is presented. Duty cycle variations between 2 % and 50 % on Ti substrates of 20 × 20 × 1 mm was employed to obtain the studied coatings. The coatings were characterized by XRD, AFM, SEM/EDS, XPS, and DRS, and computational analysis using DFT was performed. A strong dependence of the duty cycle on the anatase/rutile relation, surface roughness, and Ni incorporation in the coatings is showed. The sample obtained at 50 % of the duty cycle, in addition to the anatase and rutile phase, showed the formation of NiTiO3. Additionally, the incorporation of Ni in Ti sites in TiO2 as a consequence of the d orbitals of Ni, which generated a shift of the absorption band towards the visible and a decrease in the bandgap, is observed. The response surfaces obtained for the reduction of Cr(VI) in the samples of 2 % and 50 % of duty cycle, indicating that the voltage and the concentration of Cr(VI) are the variables with the greatest influence in the process, being the 2 % sample the one that presented the best performance in the photoelectrocatalysis process. In this sense, the optimal conditions for the 2 % sample were determined. Furthermore, the kinetic study to a pseudo-first order kinetic model was adjusted, and the efficiency of the material after 16 cycles of reuse is greater than ∼ 99.4 % in 10 min. Taking advantage of industrial wastewater as a resource using the PEO technique has potential applications in contributing to environmental sustainability.

Enhanced tetracycline degradation by a confinement structure rGO/Fe1/C3N4 photocathode during the sequential oxygen reduction process

Photoelectrocatalytic (PEC) process based on hydroxyl radicals (•OH) can effectively remove refractory pollutants, however, reducing molecular oxygen to •OH by a PEC process remains a challenge. In this work, an atomically dispersed Fe catalyst (rGO/Fe1/C3N4) was proposed. The rGO/Fe1/C3N4 photocathode showed high efficiency (88.3%, 60 min) and low energy consumption (0.072 kWh/g) in removing tetracycline (TC), and •OH was the main active species for TC degradation. The results of experimental and theoretical calculations revealed that the efficient TC degradation is due to the coupling effect of rGO and Fe atoms. The rGO enhances light absorption and effective electron transfer, thus facilitating the reduction of O2 to H2O2. Subsequently benefiting from the low H2O2 adsorption energy on Fe single atoms, enhanced electron and mass transfer between Fe single atoms and the coordination environment, H2O2 is further reduced to •OH in the confinement structure. Stability test and toxicity analysis in TC degradation demonstrate that the PEC process is an environmentally friendly technology that is stable in the long term. This work provides a new idea for designing photoelectrocatalysts with excellent •OH generation and TC degradation capacity.

Advancing photo-electrocatalysis: Selective degradation using graphene oxide–cerium oxide functionalized synthetic nanochannels

This study introduces a novel approach using a nanofluidic-based photo-electrocatalytic system to investigate the degradation ability of synthetic nanochannels functionalized with graphene oxide – cerium oxide GO-CeO2 (GCF) for methylene blue (MB) dye. The formation of heterojunctions is achieved through the in-situ growth of CeO2 nanostructures on a GO matrix via the Sono-chemical synthesis route. The crystallographic, surface, optical, and charge transfer dynamics of GO-CeO2 nanocomposites are analyzed using various techniques. The photo-electrocatalysis process is conducted in an electrochemical cell consisting of track-etched GCF-modified nanochannels, MB solution, transmembrane voltage sweep, and irradiation of the visible light spectrum. The current-voltage (I-V) response is recorded to evaluate the selective degradation ability of GCF nanochannels. The photo-electrocatalytic activity of GCF nanochannels is determined by observing the increasing trend of cationic and anionic currents. Higher transmembrane potentials up to ± V led to an exponential increase in anionic current up to −3.69 μA and significantly affect the kinetics of the photo-electrocatalytic process. The electrocatalytic process is supported under neutral and basic pH conditions. The enhanced and selective photo-electrocatalytic activity of GCF nanochannels can be attributed to the adsorption between the nanochannel surface and the MB molecules, visible light photoexcitation resulting from a lower bandgap, effective charge transfer, and separation at heterojunctions of GO-CeO2. Additionally, the suitable alignment of band potentials of functionalized nanocomposites and the molecular orbital position of MB further contribute to the process of selective degradation.