Transient Photocurrent Response Research Articles

In situ construction of Flowerlike bismuth oxide (BiO2-x)/N-rich carbon nitride (C3N5) S-scheme heterojunctions with enhanced structural defects for the efficient photocatalytic removal of tetracycline antibiotic and RhB

Efficient photocatalysts for the simultaneous removal of organic dyes and antibiotics are crucial for sustainable environmental management. In this study, we designed and synthesized a C3N5/BiO2-x S-type heterojunction photocatalyst with structural defects using a hydrothermal method, aimed at degrading both Rhodamine B (RhB) and tetracycline (TC). The degradation kinetic constants for RhB and TC were 0.0809 min−1 and 0.0535 min−1, respectively, showing improvements of 9.52 and 25.48 times over pure C3N5, and 2.90 and 1.49 times over BiO2-x. This enhanced performance is attributed to the unique electron transfer mechanism of the S-scheme heterojunction and the structural defects that facilitate efficient separation of electron-hole (e−-h+) pairs. Free radical trapping experiments indicated that the main reactive oxygen species (ROS) involved are ·O2− and h+. Additionally, electrochemical impedance spectroscopy (EIS) and transient photocurrent response (TPR) measurements confirmed improved separation and transfer of photogenerated e−-h+ pairs in the C3N5/BiO2-x heterojunction. The higher density of structural defects in C3N5/BiO2-x compared to individual BiO2-x counterparts enhances its ability to activate and photo-oxidize TC and degrade RhB. Consequently, C3N5/BiO2-x demonstrates significant potential as a photocatalyst for improving water quality.

Modulation of the Microstructure and Enhancement of the Photocatalytic Performance of g-C3N4 by Thermal Exfoliation

This work explores the impact of reaction temperature during thermal exfoliation treatment of bulk-g-C3N4 in the air atmosphere on the structure and performance of the resulting CN photocatalyst. The analysis conducted using XRD, FT-IR, XPS, SEM, and elements mapping tests, illustrated an increase in nitrogen-vacancy and oxygen content on the surface of the CN photocatalyst, resulting in a porous and sparse structure, changes in crystal size, and improved visible light absorption performance. The photocatalytic reduction experiments of hexavalent chromium (Cr(VI)) showed that the CN-540 showed the highest reduction rate of 96.9%, with a reaction rate constant 6.21 times that of bulk-g-C3N4. After 100 min of illumination, the photocatalytic degradation rates of CN-540 for TC-HCl and RhB were 66.7% and 60.6%, respectively. The TOC test results indicated mineralization rates of 51.5% for TC-HCl and 46.6% for RhB. Room temperature fluorescence spectroscopy (PL), transient photocurrent response (TPC), and electrochemical impedance spectroscopy (EIS) measurements confirmed the excellent photogenerated charge carrier separation and transport efficiency of CN-540. The photocatalytic mechanism for reducing Cr(VI) by CN-540 was elucidated based on the active species •OH and •O2– and Mott-Schottky (M-S) tests. This study provides experimental data for optimizing the photocatalytic performance of g-C3N4 and paves a new way for developing efficient photocatalysts. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Near-Infrared Light-Driven CO2 Reduction on Cup-Stacked Carbon Nanotubes.

Carbon nanotubes feature one-dimensional nature of collective excitations, wherein strong confinement of surface plasmons severely hinders the liberation of hot electrons (HEs), posing grand challenges for their utilization in photochemistry. In this study, we prototypically achieved directed HEs flow and extraction in hybrid plasmonic CNN based on cup-stacked carbon nanotubes (CSCNTs), taking advantage of their privileged edge-plane sites. The localized pz electronic states and accessible intersubband plasmon excitations in the near-infrared (NIR) regime stands in striking contrast to the conventional concentric carbon nanotubes, as evidenced by combined photo-induced force microscopy (PiFM) and transient photocurrent response. The hybrid comprising intimately integrated CSCNTs-C3N4 effectively sustains interfacial electronic states and underlies the energy extraction out of plasmonic components. The CNN demonstrates almost near-unity NIR light-driven CO2 reduction to CO with a rate of 1.35 µmol g-1 h-1. This work sheds light on the exploitation of metal-free carbon-based plasmonic nanostructures for photocatalytic applications.

Near‐Infrared Light‐Driven CO2 Reduction on Cup‐Stacked Carbon Nanotubes

Carbon nanotubes feature one‐dimensional nature of collective excitations, wherein strong confinement of surface plasmons severely hinders the liberation of hot electrons (HEs), posing grand challenges for their utilization in photochemistry. In this study, we prototypically achieved directed HEs flow and extraction in hybrid plasmonic CNN based on cup‐stacked carbon nanotubes (CSCNTs), taking advantage of their privileged edge‐plane sites. The localized pz electronic states and accessible intersubband plasmon excitations in the near‐infrared (NIR) regime stands in striking contrast to the conventional concentric carbon nanotubes, as evidenced by combined photo‐induced force microscopy (PiFM) and transient photocurrent response. The hybrid comprising intimately integrated CSCNTs‐C3N4 effectively sustains interfacial electronic states and underlies the energy extraction out of plasmonic components. The CNN demonstrates almost near‐unity NIR light‐driven CO2 reduction to CO with a rate of 1.35 µmol g–1 h–1. This work sheds light on the exploitation of metal‐free carbon‐based plasmonic nanostructures for photocatalytic applications.

Seed‐Mediated Growth of a High‐Nuclearity Titanium‐Oxide Cluster with Enhanced Photocatalytic Activities in CO2/Epoxide Cycloaddition

AbstractA high‐nuclearity titanium‐oxide cluster (TOC), Ti31O52(OiPr)4Bz24 (denoted as Ti31; Bz=PhCO2), was synthesized via a seed‐mediated synthesis method during the solvothermal reaction of the super‐Keggin cluster Ti17O24(OiPr)20 (denoted as Ti17) and Ti(OiPr)4. Single‐crystal X‐ray diffraction analyses indicate that Ti17 acts as a template for the addition of two Ti7O6 rings to form Ti31. The optical absorption edge of Ti31 slightly shifts to 446 nm, relative to the 419 nm absorption edge of Ti17. Ti31 has much better visible‐light response and charge‐separation properties than Ti17, as confirmed by electrochemical impedance, photoluminescence spectroscopy, and transient photocurrent response. Ti31 also shows much better activity and stability than Ti17 in the solar synthesis of cyclocarbonate through CO2/epoxide cycloaddition. This study not only provides a high‐nuclearity member of the TOC family, but also suggests a potential method to enhance the photocatalytic activity of the known TOCs for more efficient solar energy harvesting.

Modulating stacking mode and molecular polarization in CTF/molecule heterojunction for meliorating photocatalytic CO2 conversion with nearly 100% CO selectivity

Herein, two conjugated molecules, i.e., D-π-A TAPT and non-D-A TAPB, are finely designed to incorporate with covalent triazine framework (CTF) in A-A and A-B stacking mode via π-π interaction, respectively. The transient photocurrent response of the generated AA-CTF/TAPT Z-Scheme heterostructure is 1.14 × 10-7 A, significantly higher than that of the other two metal-free heterostructures (AA-CTF/TAPB and AB-CTF/TAPT). The promoted photocarrier transportation is attributed to strong polarization (dipole moment = 2.634 D) imposed by the D-π-A effect in TAPT that motivates the interfacial charge separation, and the coexisting charge transfer channel built by the ordered A-A stacking mode in AA-CTF that expedites the charge delivery. The photocatalytic CO2 conversion conducted by AA-CTF/TAPT gives the optimal CO conversion rate as 7.47 μmol·g−1·h−1, and with nearly 100 % product selectivity obtained, which is attributable to the lower energy barrier of CO desorption barrier (−1.07 eV) rather than that of CHO* formation (1.52 eV) for generating CH4.

WO3@MOF heterostructure in-situ transformed and deposited on La-Bi2WO6-BiFeWOx composite with enhanced photocatalytic performance for degradation of harmful and toxic substances produced by tobacco

Nowadays, tobacco is widely cultivated, and there are millions of people who smoke around the world. The cultivation of tobacco, along with the handling of cigarettes and the consumption of tobacco products, can produce numerous harmful and toxic substances. Many researchers are working diligently to eliminate these harmful and toxic substances. However, the results have been minimal. In this paper, we successfully prepared a novel La-Bi2WO6-BiFeWOx-WO3@MOF using hydrothermal and in-situ transformation methods. All samples were thoroughly investigated using various characterization techniques, including XRD, SEM, TEM, XPS, UV–Vis absorption spectra, transient photocurrent responses, and electron spin resonance. Furthermore, La-Bi2WO6-BiFeWOx-WO3@MOF was utilized as a catalyst for the degradation of harmful and toxic substances produced by tobacco, including phenol, nicotine, benzopyrene, and nitrosamines. The results indicate that La-Bi2WO6-BiFeWOx-WO3@MOF exhibits efficient separation and transfer of photo-generated electron-hole pairs under visible light irradiation. La-Bi2WO6-BiFeWOx-WO3@MOF also exhibits excellent photocatalytic activity, efficiently degrading phenol (98.62%), nicotine (92.41%), benzopyrene (81.74%), and nitrosamine (98.23%). Furthermore, the effects of varying catalyst dosage, phenol concentration, and pH values, as well as the degradation of nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF, were also investigated. The main active radicals are ·OH and ·O2– during the degradation process. Finally, a potential degradation mechanism for phenol, nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF is proposed.

Synergistic photocatalytic activity of Bi2O3/g-C3N4/ZnO ternary heterojunction with dual Z-scheme charge transfer towards textile dye degradation

It is clear that a wide range of organic substances, including synthetic textile dyes, have the potential to negatively impact the environment. It is crucial to rationally develop highly effective photocatalysts for the degradation of such type of pollutants. In this regard, a heterostructured photocatalyst comes with enhanced charge separation and extended light absorption ability that improves photocatalytic performance. Therefore, In this study, a Bi2O3/g-C3N4/ZnO (BCNZ) ternary heterojunction photocatalyst was synthesized for the degradation of methylene blue (MB) textile dye.. Thermal polycondensation method was opted to synthesize g-C3N4, while ZnO and Bi2O3 photocatalysts were fabricated using co-precipitation method. Similarly, ternary heterojunction of BCNZ was constructed through co-precipitation method. The ternary heterojunction photocatalyst demonstrated better photodegradation ability due to dual Z-scheme charge transfer route. The dual Z-scheme heterojunction enabled the ternary heterojunction to exhibit enhanced light absorption capabilities with reduced recombination rates as well as enhanced charge separation and migration efficiency (confirmed via transient photocurrent response) that resulted in improved photocatalytic performance. The BCNZ dual Z-scheme photocatalyst displayed 92 % of degradation efficiency which was much higher than that of other (binary and pristine) photocatalysts. Scavenging tests and electron spin resonance spectroscopy revealed the significant role of the •O2−, and •OH radicals in the photodegradation of MB. Furthermore, the reusability test presented good stability and recyclability of the ternary photocatalyst with 80 % degradation efficiency after five catalytic cycles.

Effect of Cu/Bi ratio on the photoelectrochemical performance of CuBi2O4/CuO nanocomposite films for CO2 reduction

Abstract Solar energy is free, clean, and virtually limitless; however, its conversion into a storable form presents technological challenges. One avenue towards solar energy utilization is the photoelectrochemical (PEC) reduction of CO2 to one- or two-carbon fuels, employing a semiconductor configured as an electrode. A potential material for this application is the p-type copper bismuth oxide (CuBi2O4) with a band gap capable of visible light absorption and a conduction band edge position suitable for CO2 reduction. In this study, CuBi2O4 nanocomposite films of varying Cu/Bi ratios (0.25, 0.51, 0.68, 0.94, 2.04) were prepared via an electrodeposition-spray deposition-annealing route. Where the Cu/Bi ratio exceeded the stoichiometric value of 0.5, a bilayered film composed of a copper (II) oxide (CuO) phase on top of CuBi2O4 was formed, creating a planar heterojunction between the two oxide layers. With increasing Cu/Bi ratio, the light absorption range of the films broadened due to the CuO phase. Analysis of the photocurrent-potential behavior of the films under visible-light illumination showed a 4–7-fold increase in the photocurrent from an inert electrolyte to a CO2-saturated electrolyte, confirming potential activity for CO2 reduction of the CuBi2O4/CuO films. A higher Cu/Bi ratio resulted to an improved charge separation efficiency, enhancing the photocurrent generation. However, the transient photocurrent response of the films showed a 70-80% decrease in the photocurrent after only 15 mins of testing. When tested in an electrolyte with an electron scavenger, the percent decrease was lowered to <10%, indicating that the instability of the films resulted from poor interfacial kinetics. While the CuBi2O4/CuO nanocomposite films can accomplish CO2 reduction, further strategies to improve their efficiency and stability are needed to realize practical application.

Preparation of C@CuNi/TiO2 with a local surface plasmon resonance for photocatalytic degradation of organic dyes and antibiotics under visible light irradiation

A composite photocatalyst with carbon-coated CuNi nanoparticles-loaded TiO2 nanotubes (C@CuNi/TiO2) was synthesized via a microwave hydrothermal alkali stripping method combined with subsequent in-situ carbothermal reduction. The structure, morphology, and surface chemical composition were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The findings demonstrate that the microwave hydrothermal alkali peeling enables the formation of a three-dimensional C@CuNi/TiO2 composite structure. The results of transient photocurrent response (i-t) and electrochemical impedance spectroscopy under visible light demonstrate that C@CuNi/TiO2 exhibits a reduced rate of electron-hole recombination and lower surface resistance compared to C@TiO2, C@Cu/TiO2, and C@Ni/TiO2. After a two-hour exposure to visible light, the composite photocatalyst C@CuNi/TiO2, featuring a molar ratio of 2 % CuNi nanoparticles to TiO2 nanotubes, exhibited remarkable degradation activity towards organic dyes (Rhodamine B (RhB), Methylene Blue (MB), Methyl Orange (MO)), as well as antibiotics (tetracycline (TC) and levofloxacin (LVFX)). After 5 cycles of photocatalytic reaction, the photodegradation activity of RhB remained above 79 %. It is indicated that CuNi nanoparticles effectively trap and enrich photoelectrons through the photoexcitation of TiO2 nanotubes. Additionally, the local surface plasmonic resonance (LSPR) effect of CuNi nanoparticles reduces the recombination rate of photogenerated electron/hole and the electron transport resistance in the composite photocatalyst, thereby enhancing its overall photocatalytic activity.

Fabrication and Self-Assembly Behavior of BPEF and BBPEF Composite Langmuir-Blodgett Films with Photovoltaic Conversion Properties.

The LB films prepared through the Langmuir-Blodgett (LB) technique are of significant importance for the fabrication of functional films such as optoelectronic materials and sensors. In this study, 9,9-bis (4-(2-hydroxy-ethoxy) phenyl) fluorene (BPEF) and 9,9-bis [3-phenyl-4-(β-hydroxy-ethoxy) phenyl] fluorene (BBPEF) were combined with saffron T (ST), methylene blue (MB) and Rhodamine B (RhB) dyes by LB technique to prepare ordered composite films. The nanostructures and morphologies of the composite films were analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the films exhibited distinct aggregation morphologies. The UV-VIS absorption spectra showed that the concentration of dye molecules had a significant effect on the spectral characteristics. The contact Angle test shows that the prepared composite films are hydrophobic. The photovoltaic conversion performance of LB composite films was studied by transient photocurrent response experiments. It was found that BPEF/dye and BBPEF/dye composite films exhibited significant responses in photocurrent. In particular, BPEF/RhB and BBPEF/RhB composite films demonstrated excellent photoresponsive performance. This study used LB technology in combination with BPEF and BBPEF to demonstrate enhanced photocurrent and stable performance of LB film, which provided ideas for expanding the application range of materials.

Synthesis of leek-based N,S self-doped CQDs/TiO2 and its application in the photocatalytic degradation of organic pollutants

In this work, N,S self-doped CQDs (N,S-CQDs/TiO2) were synthesized from leeks via a microwave method, and a new leek-based N,S-CQDs/TiO2 composite photocatalytic material was prepared by roasting. The structural characteristics, optical properties, and electrical properties of the N,S-CQDs/TiO2 composites were characterized by Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray powder diffraction (XRD), Solid ultraviolet–visible diffuse reflectance (UV–vis-DRS), Fourier transform infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transient photocurrent response, and Electrochemical impedance spectroscopy (EIS). In addition, the catalytic degradation effect of N,S-CQDs/TiO2 was evaluated by the photocatalytic degradation of Rhodamine B (RhB) and ibuprofen (IBU). The experimental results showed that the photocatalytic degradation effect of leek-based N,S-CQDs/TiO2 was significantly better than that of TiO2, and N,S-CQDs/TiO2 with 1.86 wt% N,S-CQDs (1.86-N,S-CQDs/TiO2), which demonstrated optimal photocatalytic degradation. The photocatalytic degradation rate of RhB (20 mg/L) was 94.65 % within 120 min of high-voltage mercury lamp irradiation, which was 41.15 % higher than that of TiO2(53.50 %), and the degradation rate was 80.10 % after four cycles. After 180 min, the photocatalytic degradation rate of IBU (10 mg/L) was 96.92 %, which was 26.39 % higher than that of TiO2 (70.53 %), and the degradation rate could still reach 78.94 % after four cycles. In this work, the photocatalytic degradation mechanisms of RhB and IBU by N,S-CQDs/TiO2 were explored by free radical capture and ESR free radical detection experiments. This study may serve as an important reference for enhancing the photocatalytic degradation effect by using biomass self-doped CQDs/TiO2 composite photocatalytic materials, and as a reference for the photocatalytic treatment of organic pollutants in water.

Facilistic preparation of zinc oxide nanoarrays on nickel foam via a one-step chemical bath method for photocatalysis

One-dimensional ZnO nanoarrays (ZnO NAs) were prepared on nickel foam using a one-step chemical bath deposition method. SEM and XRD confirmed the successful preparation of ZnO nanoarrays. TEM and Raman spectroscopy confirmed the preferential orientation of the ZnO nanorods along the (002) crystal plane. The Ni/ZnO NAs composites exhibited excellent photocatalytic degradation activity for ciprofloxacin (CIP) under UV light. UV–visible diffuse reflectance and transient photocurrent response characterization revealed that compared with ZnO nanorod powder, the Ni/ZnO NA composites increased the light absorption and reduced the complexation rate of photogenerated electron-hole pairs, thus improving the photocatalytic efficiency. In addition, the electron work functions of the two substances were calculated by using the crystal faces of Ni (111) and ZnO (002), and the calculation results confirmed the electron transfer paths. Electron transfer pathways further confirmed the possible reaction mechanism of Ni/ZnO NA degradation of CIP. Finally, Mott–Schottky tests were used to investigate the structure of the energy bands of the material and reveal its photocatalytic mechanism.

Photoactive Donor–Acceptor Covalent Organic Framework Material for Synergistic Cyclization Approach to Imidazole Derivatives

ABSTRACTAs one of the most potential platforms for heterogeneous catalysis, two‐dimensional porphyrin‐based covalent organic frameworks (COFs) have attracted great research interests. In this work, following the correlation of COF structure and their performance, a type of donor–acceptor 2D COF (Por‐COF‐Zn) based on porphyrin and thiophene units was designed and easily constructed by one‐pot method using 5,10,15,20‐tetra‐(4‐aminophenyl)porphyrin (TAPP), thieno[3,2‐b]thiophene‐2,5‐dicarbaldehyde, and zinc acetate. The as‐synthesized COF material is tested to show high crystallinity and good thermal and chemical stability. The Brunauer–Emmett–Teller (BET) measure results show that the specific surface area of Por‐COF‐Zn is 413.6 m2g−1, and the pore volume is 0.279 cm3g−1. Transient photocurrent response and EIS measurement also demonstrate that Por‐COF‐Zn exhibits an efficient separation of photogenerated electron/hole pairs. The photocatalytic performance of the resulted COF was further evaluated by using intramolecular cyclization of N‐phenyl‐o‐phenylenediamine and benzaldehyde to form benzimidazole derivative. The catalyst system exhibited good to high conversion efficiency, moderate substrate applicability, and excellent stability and recyclability for the catalytic cyclization approach of benzimidazoles. The catalytic mechanism should be contributed to the synergistic effect of organic framework and metallic zinc. Our current work also provides valuable information for understanding COF‐based photocatalytic systems and further highlight new insights to meet new challenges of heterogeneous photocatalysis.

Visible Light-Driven Photocatalytic CH4 Production from an Acetic Acid Solution with Cetyltrimethylammonium Bromide-Assisted ZnIn2S4

Photocatalytic methods have been popular in energy production and environmental remediation. Designing high-efficiency photocatalysts is still challenging in converting solar energy into chemical fuels. Herein, a series of surfactant-assisted ZnIn2S4 (ZIS) photocatalysts were synthesized by utilizing the one-pot hydrothermal method. Photocatalytic methane production from an acetic acid solution was carried out under LED light (450 nm) irradiation, and the evolved gas was analyzed by the GC-FID system. Reaction factors (surfactant amount, catalyst dose, reaction temperature, substrate concentration, and reaction pH) were optimized for photocatalytic production. With the increase in cetyltrimethylammonium bromide (CTAB) amount, CH4 production gradually increased. The ZIS-3.75 photocatalyst exhibited the highest photocatalytic CH4 production rate (0.102 µmol g−1·h−1), which was approximately 1.8 times better than that of pure ZIS (0.058 µmol g−1·h−1). The presence of CTAB reduced the charge transfer resistance and improved photocurrent response efficiency. Structure and morphology were characterized by XRD, FTIR, SEM, TEM, and N2 adsorption–desorption isotherm analysis. Optical properties were investigated by UV-DRS and PL spectroscopic techniques. The electrochemical evaluation was measured through EIS, Mott–Schottky, and transient photocurrent response analysis. The CTAB-modified catalyst showed excellent stability and reusability, even after five irradiation cycles. Methane production was enhanced by lowering the photogenerated charge transfer resistance and boosting the dispersion of ZIS-3.75 under visible light (450 nm) irradiation.

Preparation and performance of g-C3N4/g-C3N5 homojunction photocatalyst activated peroxymonosulfate for ceftriaxone sodium degradation

As the overuse of antibiotics increasingly contaminates the environment, one of modern chemistry's objectives is to identify high-performance photocatalytic materials to degrade antibiotics. This study initially utilized NH4Cl as a gas template to synthesize porous lamellar g-C3N4 (CNS) through a high-temperature calcination process. Building upon this, a homojunction catalyst, CNS/g-C3N5 (S-CN), was developed via a secondary sintering technique using different amount of 3-amino-1,2,4-triazole addition to evaluate its efficacy in activating peroxymonosulfate (PMS) for degrading the antibiotic ceftriaxone sodium. Under neutral conditions, the photocatalytic system composed of S-CN catalysts prepared by 50 mg of 3-amino-1,2,4-triazole addition and PMS (S3-CN/PMS) exhibited degradation rates that were 3.37 and 8.11 times higher than those of the CNS/PMS and g-C3N5/PMS, respectively. At a pH of 8, the S3-CN/PMS system attained a 99.7 % degradation efficiency within 75 min. Based on results from UV–visible diffuse reflectance spectroscopy (DRS), transient photocurrent response, electrochemical impedance spectroscopy (EIS), photoluminescence spectroscopy and radical scavenging experiments, this high efficiency is attributed to a homojunction Z-type charge transfer mechanism that enhances the separation of photogenerated carriers. Furthermore, the study found that the optimal PMS addition was 20 mg and the optimal pH was 8. Chloride ions promoted the reaction, while other ions decreased the reaction rate. In conclusion, this paper provides valuable insights for the morphological modification of carbon nitride homojunction materials and the efficient activation of PMS for pollutant degradation.

In situ loading of Ag2MoO4 nanoparticles onto oxygen-doped porous g-C3N4 for enhanced photocatalytic H2 evolution

Photogenerated carriers transfer and separation from the substance itself to produce spatial isolated electron-hole pairs is crucial for the utilization of composite photocatalysts in the field of photocatalytic hydrogen (H2) evolution. Herein, novel oxygen-doped porous graphitic carbon nitride (g-C3N4) micro-sheets decorated with Ag2MoO4 have been fabricated by a facile calcination method followed by in situ deposition strategy. The physicochemical properties of the obtained Ag2MoO4/OC3N4 composites were characterized via SEM, TEM, EDS, XRD, N2 adsorption-desorption, XPS, UV–vis DRS, PL, transient photocurrent response, and EIS, as well as DFT calculation. In addition, the effects of Ag2MoO4 content, type of scavengers, pH value of reaction solution and dosage of scavenger on photocatalytic H2 production were investigated. The results show that the modification of ammonium acetate thermal polymerization with urea could enhance the porosity of g-C3N4 and its specific surface area. The Ag2MoO4 nanoparticles are highly dispersed on the OC3N4 surface, reducing the charge transfer resistance at their interfaces. The OC3N4 photocatalyst achieves H2 yield of 8629.11 μmol/g over 2 h, which is about 1.46 times higher than that of C3N4. The H2 production amount over the optimal Ag2MoO4/OC3N4 composite photocatalyst (50 mg) is further enhanced to 16619 μmol/g, which is 1.93 and 180 times higher than that of OC3N4 and Ag2MoO4, respectively. The S-scheme charge transfer mechanism of Ag2MoO4/OC3N4 is proposed based on the DFT calculation. This work provides a facile and easy strategy to develop g–C3N4–based photocatalysts through adjusting chemical composition and photocatalytic properties.

Preparation of SnOx/N-GQDs composites with oxygen-rich vacancies for enhanced photoelectric properties

SnOx with oxygen-rich vacancies and SnOx/N-GQDs (Nitrogen-doped graphene quantum dots) composites were prepared by high temperature annealing and hydrothermal method, respectively. The annealing process introduced a large number of oxygen vacancies and produced defect energy levels in the band gap. The existence of the defect level effectively reduced the band gap of SnOx, enlarged the optical absorption range, and improved the light utilization. The introduction of N-GQDs also improved the carrier density and electron transport rate, and extended the carrier lifetime (τ = 7.44 ms). I-T (Transient photocurrent response) analysis results showed that when the mass ratio of Sn/SnO2 was 1:4 and N-GQDs doping content was 1 wt%, the transient photocurrent response of SnOx/N-GQDs could reach 5.51 × 10−4 A/cm2, which was 25 times higher than that of pure SnO2, and the photocurrent response value maintained 80.1 % within 500 s. EIS (Electrochemical impedance) and M-S (Mott-Schottky) analyses indicated that the appropriate amount of oxygen vacancies and N-GQDs were beneficial to reducing the charge transport resistance, inhibiting the electron-hole pair recombination, and increasing the carrier density of SnOx. The results show that SnOx/N-GQDs composites present the improved photoelectric properties with the addition of oxygen vacancies and N-GQDs, which provides a new idea for promoting the properties of semiconductors.

Ca‐Doped PrFeO3 Photocathodes with Enhanced Photoelectrochemical Activity

Perovskite oxides, renowned for their adaptable structure and optoelectronic characteristics, hold significant potential for applications in catalysis and photoelectrochemical (PEC) processes. In this research, the preparation of praseodymium iron oxide (PrFeO3) by spin coating and the impact of incorporating a calcium (Ca) dopant on its PEC efficacy as photocathodes are investigated. Spin coating of a polymer containing sol–gel yields thin films with uniform morphology and porosity, facilitating effective semiconductor/electrolyte interactions, as characterized by scanning electron microscopy analyses. Evaluation of transient photocurrent responses reveals that introducing Ca at a 5 at% doping level significantly enhances the PEC activity of PrFeO3, resulting in an optimal photocurrent of −124 μA cm−2 at +0.43 V vs. a reversible hydrogen electrode (VRHE) under simulated sunlight conditions. This enhancement is accompanied by an incident photon‐to‐current efficiency (IPCE) of 3.8% at +0.43 VRHE and 350 nm, along with an onset potential of +1.1 VRHE. Ultraviolet and visible spectroscopy analyses indicate an increase in light‐absorption capabilities in the Ca‐doped films and a noticeable reduction in bandgap compared to the undoped counterparts, further supported by IPCE measurements. In the findings, the significant role of dopants in augmenting the photocurrent performance of stable perovskite oxides, highlighting their potential in advancing photon conversion technologies, is underscored.

Electrocoagulation-photocatalysis sequential combined method for the removal of anticancer drugs from pharmaceutical wastewater using NH2-MIL-125(Ti)/cobalt ferrite nanorods composite photocatalyst

This research reports that the novel NH2-MIL-125(Ti)/cobalt ferrite nanorods composite photocatalyst based on metal-organic framework (MOF) has been synthesized by the microwave heating method. Herein, the sequential electrocoagulation (EC)-photocatalysis combination method was used to remove the chemical oxygen demand (COD), doxorubicin hydrochloride (DOX), and 5-Fluorouracil (5-FU) antineoplastic drugs from wastewater by the composite photocatalyst under a simulated sunlight irradiation. The synthesized photocatalysts were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Brauner-Emmet-Teller surface area analyzer, vibrating sample magnetometer, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, transient photocurrent response, and electrochemical impedance spectroscopy. In the EC process, three-level, three-factor Box-Behnken design was used to investigate the interaction effects of pH (3−8), time (10–60 min), and current density (100–200 A/m2) on the removal of contaminants. The maximum experimental removal efficiencies of COD, DOX, and 5-FU were 68.2 %, 21.1 %, and 24.5 %, respectively, under EC time of 60 min, pH of 5.98, and current density of 176.77 A/m2. About 99.2 % COD, 93.8 % DOX, and 97.0 % 5-FU were removed from pharmaceutical wastewater using NH2-MIL-125(Ti)/ cobalt ferrite nanorods photocatalyst under cobalt ferrite content of 0.288 g, reaction time of 58.48 min, pH of 7.54, and catalyst dosage of 0.5 g/L. The obtained results demonstrated that the combined process of EC and photocatalysis in the presence of MOFs-based photocatalysts is an effective treat strategy for the pharmaceutical wastewater.