Efficient Photocatalytic Oxidation Research Articles

Direct recycle waste silicon wafer as the charge transfer bridge to assemble a Z-scheme heterojunction for enhanced photocatalytic performance

The retirement wave of photovoltaic (PV) panels is expected to result in a significant number of discarded panels in the near future. Recycling PV silicon in a rational manner will not only help reduce the environmental impact but also lead to substantial economic gains. In this study, aaste solar silicon wafers were ball-milled to obtain recycled silicon (r-Si) powder. The TiO2/r-Si carrier was prepared through a simple hydrothermal process, followed by the creation of a novel Ag3PO4/TiO2/r-Si (APO/TIO/r-Si) ternary heterojunction composite using a co-precipitation method. The photocatalytic properties of the materials doped with different concentrations of Ag3PO4 were examined using Rhodamine B (RhB) degradation rate as a performance metric. Among them, 40 %APO/TIO/r-Si heterojunction exhibits excellent photodegradation activity under visible light irradiation. The photocatalytic degradation efficiency reached 93.0 % in 30 min, with a removal rate of 82.8 % after 5 cycles. It was found that superoxide radicals and hydroxyl radicals are the main drivers of RhB photodecomposition. The decomposition pathways of RhB dye were identified using high performance liquid chromatography mass spectroscopy (HPLC-MS), revealing N-de-ethylated intermediates as the main intermediate. The photoreaction mechanism and RhB degradation pathway over APO/TIO/r-Si were elucidated, showing a direct Z-Scheme heterojunction electron transfer pathway with r-Si acting as charge transfer center. The formation of the heterojunction not only minimizes interfacial resistance effectively but also enhances disintegration and preservation of photo-carriers, leading to improved photo-redox ability and increased photoactivity. This study presents a win–win approach for recycling waste silicon wafers from retired PV panels as potential heterojunction photocatalysts for efficient photocatalytic oxidation of dye contamination.

Boosting photocatalytic NO oxidation mediated by high redox charge carriers from visible light-driven C3N4/UiO-67 S-scheme heterojunction photocatalyst

The construction of CN/UiO-67 (CNU) S-scheme heterojunction composites through in situ formation of UiO-67 on carbon nitride (C3N4) helps to address the limitations of carbon nitride (CN) in photocatalytic NO elimination. The optimized CNU3 demonstrates superior photocatalytic efficiency, which is attributed to electronic channels constructed by Zr-N bonds and S-scheme electron transport mechanism, effectively promoting the efficient separation of photogenerated charge carriers with high redox potentials. Density Functional Theory (DFT) calculations reveal redistributed electronic orbitals in CNU3, with progressive and continuous energy levels near the Fermi level, which bolsters electronic conduction. Comprehensive quenching experiments, Electron Paramagnetic Resonance (EPR), and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analyses highlight a synergistic interplay of electrons, holes, and superoxide radicals in CNU3, inhibiting the generation of toxic nitrogen oxide intermediates and culminating in highly efficient photocatalytic NO oxidation. This study not only elucidates the mechanisms underpinning the enhanced performance of CNU3 heterojunctions but also offers new perspectives on the preparation and interfacial charge separation of heterojunction photocatalysts.

2D N-doped graphene/CoFe MOFs heterostructure functionalized CNF aerogels impart highly efficient photocatalytic oxidation of gaseous VOCs

Developing efficient photocatalysts for degrading volatile organic compounds (VOCs) has aroused great interest. Herein, the 3D composite aerogel catalysts (CLGM-A) with cellulose nanofibers (CNF) skeleton-supported 2D CoFe bimetallic metal-organic frameworks (2D CoFe MOFs) and 2D N-doped graphene (2D N-GE) heterostructures were prepared by freeze-drying and were successfully applied to the photocatalytic degradation of toluene. With 2D–2D (face-contact) heterojunction, the separation efficiency of photo-generated electron-hole pairs was significantly improved by the rapid transfer of electrons and inhibition of electron backflow on the N-GE/2D CoFe MOFs (GM) during the photocatalytic process. As a result, the CLGM-A achieved 95.4% toluene removal in 120 minutes, 83.6% mineralization efficiency, and demonstrated good stability and reusability in continuous cycle tests. Radical analysis suggested that •O2- was the main active species produced in the CLGM-A system, which could realize the efficient degradation of volatile organic pollutants at room temperature.

Facile synthesis of NiCo2O4 nanostructures with abundant surface oxygen vacancies, and reduced content of Co and Ni valence states for the efficient and bifunctional electrochemical and photocatalytic oxidation of methylene blue

An abundant, low cost, scale up and ecofriendly method has been designed about the preparation of NiCo2O4 nanostructures and the electrode material was employed for the electrochemical oxidation and photocatalytic degradation of methylene blue (MB) under the irradiation of natural sunlight. The NiCo2O4 nanostructures prepared with and without spoiled bitter gourd juice were characterized with respect to morphology, crystalline quality, and surface chemical composition. The morphology of NiCo2O4 nanostructures was transformed from nanorod to low dimension nanoparticles using bitter gourd juice. The surface of NiCo2O4 nanostructures was enriched with the abundant surface oxygen vacancies and low content of different Co and Ni valence states using 10 mL of bitter gourd juice. The NiCo2O4 nanostructures obtained with the 10 mL of bitter gourd were observed highly electroactive towards the oxidation of MB in the phosphate buffer solution of pH 7.4. The linear working range of electrode material for the electrochemical oxidation of MB was estimated from 0.1 mM to 7 mM and a low limit of detection of 0.002 mM was found. A10 mL of bitter gourd juice assisted NiCo2O4 nanostructures were characterized by excellent selectivity, stability and reproducibility. Moreover, the NiCo2O4 nanostructures synthesized with the use of 10 mL of bitter gourd extract were also found active to degrade the MB in aqueous solution under the illumination of natural sunlight. The percent removal of MB was found almost 100 % for the time period of 210 min using NiCo2O4 nanostructures. The phytochemicals from spoiled bitter gourd juice has shown high potential to enhance the electrochemical and photocatalytic properties of NiCo2O4 nanostructures, thus it could be used for the preparation of new generation of electrode materials for the diverse applications.

Efficient photocatalytic selective oxidation of benzyl alcohol by nano-Pd/TiO2−x with synergistic effect of oxygen vacancy and shell structure

TiO2 hollow spheres, TiO2−x hollow spheres, and a series of Pd/TiO2 and Pd/TiO2−x hollow spheres with different Pd mass fractions were successfully synthesized by a template-based and NaBH4 reduction method. The as-synthesized catalysts are hollow sphere structures that provide a large number of active sites for photocatalytic reactions. The synergistic effect of Pd nanoparticles (NPs) and oxygen vacancy facilitated photogenerated charge transportation and separation. In particular, the optimized 4 wt% Pd/TiO2−x shows an excellent conversion (88.3%) for the photocatalytic selective oxidation of benzyl alcohol (BA) under visible light. In addition, it was observed that the catalyst had high stability and recyclability under the study conditions. The band structure, density of states and the charge difference distribution were calculated with density functional theory (DFT) methods to deeply reveal that the synergistic effect of oxygen vacancies and Pd NPs to enhance the photocatalytic performance. Consequently, a possible photocatalytic reaction mechanism has also been put forward based on the DFT and experimental results.

Defective ZnO Nanoplates Supported AuPd Nanoparticles for Efficient Photocatalytic Methane Oxidation to Oxygenates

AbstractDirect photocatalytic methane oxidation into value‐added oxygenates under mild conditions enables the sustainable chemical production but suffers from the lack of active photocatalysts and the overoxidation issue. Herein, defective ZnO nanoplates supported AuPd nanoparticles for efficient methane oxidation with O2 as the oxidant at room temperature are reported. A maximum liquid oxygenates productivity of 152.2 mm g−1 h−1 and a selectivity of 86.7%, more than half of which is CH3OH, are achieved over the optimized AuPd/ZnO photocatalyst, resulting in a 16.5% apparent quantum efficiency at 380 nm. The superior photocatalytic performance is benefited from the synergistic effect between defective ZnO substrate and AuPd cocatalyst, wherein the former facilitates CH4 adsorption, and the latter promotes light absorption, charge separation, as well as O2 activation into the reactive oxygen species. This work provides new guidance for regulating the activity and selectivity of the photocatalyst toward methane oxidation.

Construction of S-scheme heterojunctions of a Ti-doped Ce-MOF and BiOCl for efficient photocatalytic selective oxidation of amines

Regulating the microenvironment of the S-scheme heterojunction interface to promote efficient photocatalytic aerobic organic reactions under mild conditions.

Copper-containing POM-based hybrid P2Mo22V4Cu4 nanocluster as heterogeneous catalyst for the light-driven hydroxylation of benzene to phenol.

The current traditional phenol production process has many shortcomings, and the efficient and clean photocatalytic one-step oxidation to phenol is gradually attracting attention. Heteropolyacids (PMo10V2) with high-density Lewis acid active sites and excellent photoelectron transfer ability are ideal choices for catalytic reactions. In this study, a copper-modified isolated dimeric hybrid nanocluster, [Cu(pyim)2]2[Cu(pyim)2(P2MoVI20MoV2VIV4O82)]2·(H2O) (pyim = [2-(pyridin-2-yl)imidazole]), was synthesized by a convenient hydrothermal method. The structural analysis demonstrated that the compound was composed of metal-organic complexes containing pyim ligands, Keggin-type heteropolyacids, and transition metal copper ions. Remarkably, this not only solves the difficulty that the heteropolymeric acid cannot be recovered by dissolving in the solvent but also introduces the copper atom as a second active center. The catalyst exhibited a benzene conversion of 15.6% and a selectivity of 85.2% in a mixed solution of acetonitrile and acetic acid under optimal reaction conditions. After four catalytic cycles, the PXRD pattern proved that the catalyst was still stable. This study provides a good idea for photocatalytic reactions and other environmental applications.

Investigation of α-Fe2O3 catalyst structure for efficient photocatalytic fenton oxidation removal of antibiotics: preparation, performance, and mechanism.

Currently, the surface structure modification of photocatalysts is one of the effective means of enhancing their photocatalytic efficiency. Therefore, it is critically important to gain a deeper understanding of how the surface of α-Fe2O3 photocatalysts influences catalytic activity at the nanoscale. In this work, α-Fe2O3 catalysts were prepared using the solvothermal method, and four distinct morphologies were investigated: hexagonal bipyramid (THB), cube (CB), hexagonal plate (HS), and spherical (RC). The results indicate that the hexagonal bipyramid (THB) exhibits the highest degradation activity towards tetracycline (TC), with a reaction rate constant of k = 0.0969 min-1. The apparent reaction rate constants for the cube (CB), hexagonal plate (HS), and spherical (RC) morphologies are 0.0824, 0.0726, and 0.0585 min-1, respectively. In addition, it has been observed that the enhancement of photocatalytic activity is closely related to the increase in surface area, which provides more opportunities for interactions between Fe2+ and holes. The quenching experiments and electron paramagnetic resonance (EPR) results indicate that the ˙O2, ˙OH and h+ contribute mainly to the degradation of TC in the system. This research contributes to a more comprehensive understanding of catalyst surface alterations and their impact on catalytic performance.

Selective photocatalytic oxidation of methane to methanol by enhancing H2O2 utilization over Au-Pd/In2O3

Hydrogen peroxide (H2O2) is widely used as an oxidant for photocatalytic oxidation of methane to value-added chemicals under mild conditions, but suffers from low utilization efficiency. Herein, we propose a comprehensive strategy for the proper amount of hydroxyl radicals (•OH) generation from H2O2 by regulating the Pd/Au molar ratios and the total Au-Pd contents loaded on In2O3. For the photocatalytic oxidation of methane at ambient temperature, the yield and selectivity of CH3OH over the optimized 1.0% AuPd0.5/In2O3 catalyst were as high as 2187.0 μmol g−1 h−1 and 94.0% respectively, exceeding most reported literatures. Mechanism investigations revealed that the formation of Au-Pd alloys may contribute to the homolytic cleavage of H2O2 into •OH radicals and improve the selectivity of •OH generation. This work provides some guidance for the delicate design of photocatalysts to manipulate selective H2O2 activation and efficient photocatalytic methane oxidation.

Lead-free perovskite Cs3Bi2Br9/TiO2 composites for atmospheric photocatalytic oxidation of sulfides

Herein, a lead-free halide perovskite Cs3Bi2Br9 combined with TiO2 was facilely synthesized and applied for photocatalytic selective oxidation of sulfides to sulfoxides with high yields and good compatibility under mild conditions.

Sunlight induced efficient photocatalytic oxidation of benzylamines and CO2 reduction over a 2D–2D MoS2/FP-BTA heterojunction catalyst

The photocatalytic production of fuels and chemicals utilizing highly effective catalysts has garnered a lot of interest as a sustainable and clean strategy.

A novel Cu(I)-based coordination polymer for efficient photocatalytic oxidation of C(sp3)-H bonds.

A novel coordination polymer CuCl-Pyhc was successfully synthesized, which can catalyze efficient and selective oxidation of C(sp3)-H bonds under mild conditions, exhibiting exceptional stability and remarkable recyclability. Furthermore, CuCl-Pyhc can mimic natural monooxygenases and activate oxygen into singlet oxygen (1O2).

Novel BODIPY-based MOFs toward high-efficiency photocatalytic oxidation of sulfides and arylboronic acids

Novel visible-light-responsive BODIPY-based MOFs exhibited excellent photocatalytic activity toward oxidation of sulfides and arylboronic acids under ambient conditions, which was attributed to the active oxygen species produced in the reaction.

Efficient photocatalytic oxidation of CH4 over Ag-modified ZnO nanorods

ZnO nanorods were used to prepare nAg/r-ZnO photocatalysts with promoted carrier separation, and an excellent oxygenate (CH3OOH, CH3OH, and HCHO) yield of 15 551.60 μmol g−1 h−1 with a high selectivity of 98.46% were thus obtained during photooxidation of CH4.

Aerobic Benzylic C(sp3)-H Bond Oxygenations Catalyzed by NBS under Visible Light Irradiation.

An efficient photocatalytic oxidation of benzylic C(sp3)-H bonds to ketones, esters, and amides has been developed using NBS as a metal-free photocatalyst and O2 as an oxidant. A variety of synthetically and biologically valuable compounds are assembled in moderate to excellent yields. The synthetic utility of this approach has been demonstrated by gram-scale experiments. A possible free radical mechanism was proposed to rationalize the reaction procedure.

Visible-light-driven efficient photocatalytic oxidation of 5-hydroxymethylfurfural over a metal-free recyclable anthraquinone derivative

Visible-light-driven upgrading of biomass and its derivatives into value-added chemicals under mild reaction conditions is an economical and sustainable strategy for biomass valorization. In this contribution, industrially-accessible anthraquinone and its derivatives (AQs) have been developed as efficient metal-free photocatalysts for the photo-oxidation of 5-hydroxymethylfurfural (HMF). Especially, a quantitative furans selectivity containing 86.0 % of 2,5-diformylfuran (DFF) and 13.6 % of 5-formyl-2-furancarboxylic acid (FFCA) was implemented at HMF conversion of 88.8 % over 2,6-dibromoanthraquinone (2,6-DB-AQ) catalyst under visible light illumination. In addition, the homogeneous 2,6-DB-AQ catalyst can be readily separated and recycled from the reaction mixture by a “water-assisted” precipitate method. Photophysical characterizations indicated that the introduction of bromine substituents on AQ enhances its visible light absorption ability, decrease its band gap energy and enables the catalyst with a more stable photoexcitation state. It has also been demonstrated that the lower photoexcitation energy of O2 over 2,6-DB-AQ endowed the catalyst with better capacity for the activation of O2 than that of AQ. These contributions should be in charge of the excellent catalytic activity of 2,6-DB-AQ for the photo-oxidation of HMF. This work demonstrates an efficient and recyclable organo-photocatalyst for the visible-light-mediated valorization of biomass-derived alcohols and aldehydes to value-added chemicals.

Efficient adsorption and photocatalysis over a photorenewable uranyl-organic framework for removal of diquat herbicide

Adsorption and photocatalysis are generally considered an environmental friendliness and effective methods for eliminating organic pollutants. Developing bifunctional materials that integrate adsorption and photocatalysis can fully leverage the adsorption effect to increase the interaction between herbicides and photocatalysts, thus improving their photocatalytic degradation efficiency. To achieve the absorption and photocatalytic activity on contaminants, a light-sensitive three-dimensional uranyl-organic framework (UOF) named HNU-80 with an anionic skeleton was synthesized in this work. The charge characteristics of its electrostatic attraction with cations and the suitable band structure for producing reactive oxygen endow it with the potential for efficient adsorption and photocatalytic oxidation of the cationic diquat herbicide. The maximum adsorption capacity is up to 97.92 mg·g−1, and the adsorbed diquat could be completely degraded under light irradiation. In addition, the regenerated HNU-80 exhibits high reusability in subsequent adsorption cycle experiments. The adsorption mechanism is attributed to the electrostatic and π…π interaction between HNU-80 and diquat, while the photodegradation mechanism is due to the oxidation and decomposition of diquat by reactive oxygen species generated from the radiation of HNU-80. This work provides a promising candidate for the harmless treatment of organic pollutants, and the combination of photocatalytic property also promotes the regeneration of the UOF adsorbents for continued use.

A construction of core–shell dual zeolite imidazole skeleton derived composite to facilitate photocarrier separation and distribution of active sites for photocatalytic water oxidation

Limited by the severe carrier recombination and insufficient active sites of the catalyst, achieving efficient photocatalytic water oxidation remains a major challenge. Herein, a core–shell zeolite imidazole skeleton (ZIF) based material with rich active sites in its interior is obtained by in-situ growth carbonization two steps method. According to characterization, performance testing and photoelectric experiments, it is confirmed that the ZIF67@ZIF8-2-800 material has good photogenerated carrier separation efficiency and surprising O2 production. The reason for the performance improved is that ZIF8 as a shell prevents the agglomeration of active sites CoO in the carbonization process of ZIF67. Theoretical calculations reveal that the core–shell structure has a favorable influence on the separation of photogenerated carriers. The N atom acts as an electron transport mediator, transferring electrons from the CoO core to the NC shell, while the holes remain in the CoO to participate in the photocatalytic water oxidation reaction.

Bimetallic synergy significantly enhances the photocatalytic performance of lanthanide porphyrin-based MOFs: Efficient photocatalytic oxidation of benzyl alcohol and benzylamine under mild conditions in air

Metal-organic frameworks as photocatalysts for the conversion of light energy into chemical energy applied to organic conversion is an efficient and sustainable strategy. Lanthanide organometallic frameworks perform poorly in photocatalytic organic reactions owing to their high electron and hole complexation rates. Inspired by the synergistic effect of biomacromolecule porphyrin as a photosensitizer with bimetallic pairs that can boost electron transport efficiency. We synthesized a series of lanthanide porphyrin mechanism MOFs (Nd PMOFs, Co–Nd PMOFs, Ni–Nd PMOFs). These PMOFs are endowed with a novel three-dimensional structure. It is noteworthy that Ni in the middle of the porphyrin ring enhances the photocatalytic performance of Ni–Nd PMOFs. The reasons can be attributed to the introduced Ni and the coordinated Nd elements, which interact synergistically with the porphyrin skeleton. This interaction results in a good photoresponse and promotes an efficient separation of photogenerated electrons and holes. The photocatalytic performance of Ni–Nd PMOFs was tested under mild conditions (12 W visible light, air) using the photocatalytic oxidation of benzyl alcohol and the oxidative coupling of benzylamine as model reactions. The conversion rate for benzyl alcohol was 90 % with a selectivity 94 %, and the conversion rate for benzylamine was 85 % with a selectivity 83 %. The photocatalytic oxidation performance of Ni–Nd PMOFs has been found to be excellent for a wide range of reactions and substrates, indicating that it is a promising photocatalyst. To some extent, the presentation of this work expands the possibilities of lanthanide metal frameworks for photocatalytic organic transformations and sheds new light on the multidirectional applications of lanthanide metal–organic frameworks.