Photocatalytic Oxidation Activity Research Articles

Pyrene-Alkyne-Based Conjugated Porous Polymers with Skeleton Distortion-Mediated •O2- and 1O2 Generation for High-Selectivity Organic Photosynthesis.

Reactive oxygen species (ROS) play a crucial role in determining photocatalytic reaction pathways, intermediate species, and product selectivity. However, research on ROS regulation in polymer photocatalysts is still in its early stages. Herein, we successfully achieved series of modulations to the skeleton of Pyrene-alkyne-based (Tetraethynylpyrene (TEPY)) conjugated porous polymers (CPPs) by altering the linkers (1,4-dibromobenzene (BE), 4,4'-dibromobiphenyl (IP), and 3,3'-dibromobiphenyl (BP)). Experiments combined with theoretical calculations indicate that BE-TEPY exhibits a planar structure with minimal exciton binding energy, which favors exciton dissociation followed by charge transfer with adsorbed O2 to produce •O2-. Thus BE-TEPY shows optimal photocatalytic activity for phenylboronic acid oxidation and [3+2] cycloaddition. Conversely, the skeleton of BP-TEPY is significantly distorted. Its planar conjugation decreases, intersystem crossing (ISC) efficiency increases, which makes it more prone for resonance energy transfer to generate 1O2. Therefore, BP-TEPY displays best photocatalytic activity in [4+2] cycloaddition and thioanisole oxidation. Both above reactant conversion and its product selectivity exceed 99%. This work systematically reveals the intrinsic structure-activity relationship among the skeleton structure of CPPs, excitonic behavior, and selective generation of ROS, providing new insights for the rational design of highly efficient and selective CPPs photocatalysts.

A novel recyclable photocatalytic composite TiO2NTs@Bi25FeO40 for tetracycline mineralization

Titanium dioxide nanotubes (TiO2NTs) are prepared by anodizing Ti substrates, which is a good solution to the problem that powdered materials are more difficult to recycle. Hence, a novel recyclable TiO2NTs@Bi25FeO40 (TiO2/BFO) photocatalyst was prepared by anodic oxidation combined with hydrothermal deposition. The photocatalytic ability of TiO2NTs prepared at different factors and Bi25FeO40 compound was evaluated. The TiO2/BFO showed the optimal photocatalytic efficiency, which the removal ratio of tetracycline hydrochloride (TC-HCl) higher than that of TiO2NTs under visible-light irradiation. UV–vis diffuse reflectance spectra (DRS) analysis proved that the band gap of TiO2/BFO was narrower than that of TiO2NTs. The narrow band gap of TiO2/BFO results in a broadening of its light absorption region. Meanwhile, the combination of free radical quenching experiments and EPR measurement showed that ·O2− was the main active radical in the photocatalytic process, and the presence of Bi25FeO40 effectively promoted the generation and transfer of electrons. Mechanistic analysis showed that a unique II-type heterojunction electron transfer structure was formed between TiO2NTs and Bi25FeO40, which promoted the photogenerated electron-hole separation and improved the photocatalytic oxidation activity. The preparation of TiO2/BFO provided a new strategy for synthesizing more efficient and environmentally friendly photocatalyst.

Rational Conversion of Imine Linkages to Amide Linkages in Covalent Organic Frameworks for Photocatalytic Oxidation with Enhanced Photostability.

Covalent organic frameworks (COFs) and their applications in photocatalysis have been extensively studied, but the instability of imine-linked COFs is an important factor limiting their performance. In this work, two imine-linked COFs were successfully converted to amide-linked COFs through post synthetic modification (PSM). The oxidized COFs presented lower binding energy to O2, exhibited higher photocatalytic activity for oxidation of thioethers and coupling of benzylamines with excellent stability. The present work can serve as a reliable reference for the development of novel highly active and stable COF-based photocatalysts.

Recent progress in defect-engineered metal oxides for photocatalytic environmental remediation.

Rapid industrial advancement over the last few decades has led to an alarming increase in pollution levels in the ecosystem. Among the primary pollutants, harmful organic dyes and pharmaceutical drugs are directly released by industries into the water bodies which serves as a major cause of environmental deterioration. This warns of a severe need to find some sustainable strategies to overcome these increasing levels of water pollution and eliminate the pollutants before being exposed to the environment. Photocatalysis is a well-established strategy in the field of pollutant degradation and various metal oxides have been proven to exhibit excellent physicochemical properties which makes them a potential candidate for environmental remediation. Further, with the aim of rapid industrialization of photocatalytic pollutant degradation technology, constant efforts have been made to increase the photocatalytic activity of various metal oxides. One such strategy is the introduction of defects into the lattice of the parent catalyst through doping or vacancy which plays a major role in enhancing the catalytic activity and achieving excellent degradation rates. This review provides a comprehensive analysis of defects and their role in altering the photocatalytic activity of the material. Various defect-rich metal oxides like binary oxides, perovskite oxides, and spinel oxides have been summarized for their application in pollutant degradation. Finally, a summary of existing research, followed by the existing challenges along with the potential countermeasures has been provided to pave a path for the future studies and industrialization of this promising field.

Photocatalytic Activity and Antibacterial Properties of Mixed-Phase Oxides on Titanium Implant Alloy Substrates

Titanium alloys are commonly used for implants, but the naturally forming oxides are bioinert and not ideal for bacterial resistance or osseointegration. Anodization processes are a modification technique that can crystallize the oxides, alter oxide surface topography, and introduce beneficial chemistries. Crystalline titanium oxides are known to exhibit photocatalytic activity (PCA) under UVA light. Anodization was used to create mixed-phase oxides on six titanium alloys including commercially pure titanium (CPTi), Ti-6Al-4V (TAV), Ti-6Al-7Nb (TAN), two forms of Ti-15Mo (TiMo-β and TiMo-αβ), and Ti-35Nb-7Zr-5Ta (TNZT). Combined EDS and XPS analyses showed uptake of the electrolyte and substrate alloying elements into the oxides. The relative oxide PCA was measured using methylene blue degradation assays. CPTi and TAN oxides exhibited increased PCA compared to other alloys. Combined XRD and EBSD oxide phase analyses revealed an unfavorable arrangement of anatase and rutile phases near the outermost surfaces, which may have reduced PCA for other oxides. The relative Staphylococcus aureus attachment to each oxide was also assessed. The CPTi and TiMo-αβ oxides showed significantly reduced S. aureus attachment after 1 h of UVA compared to un-anodized CPTi. Cell culture results verified that the UVA irradiation did not negatively influence the MC3T3-E1 attachment or proliferation on the mixed-phase oxides.

Self‐Adaptive Aromatic Cation‐π Driven Dimensional Polymorphism in Supramolecular Polymers for the Photocatalytic Oxidation and Separation of Aromatic/Cyclic Aliphatic Compounds

AbstractThe phenomenon of polymorphism is ubiquitous in nature, the controlled manipulation of which not only increases our ontological understanding of nature but also facilitates the conceptualization and realization of novel functional materials. However, achieving targeted polymorphism in supramolecular assemblies (SAs) remains a formidable challenge, largely because of the constraints inherent in controlling the specific binding motifs of noncovalent interactions. Herein, we propose self‐adaptive aromatic cation‐π binding motifs to construct polymorphic SAs in both the solid and solution states. Using distinct discrete cation‐π‐cation and long‐range cation‐π binding motifs enables control of the self‐assembly directionality of a C2h‐symmetric bifunctional monomer, resulting in the successful formation of both two‐dimensional and three‐dimensional crystalline SAs (2D‐CSA and 3D‐CSA). The differences in the molecular packing of 3D‐CSA compared with that of 2D‐CSA significantly improve the charge separation and carrier mobility, leading to enhanced photocatalytic activity for the aerobic oxidation of thioanisole to methyl phenyl sulfoxide (yield of 99 % vs 57 %). 2D‐CSA, which has a vertical extended structure with favorable stronger interaction with toluene though face‐to‐face cation‐π interactions than methylcyclohexane, shows higher toluene/methylcyclohexane separation efficiency than 3D‐CSA (96.9 % for 2D‐CSA vs 56.3 % for 3D‐CSA).

Self-Adaptive Aromatic Cation-π Driven Dimensional Polymorphism in Supramolecular Polymers for the Photocatalytic Oxidation and Separation of Aromatic/Cyclic Aliphatic Compounds.

The phenomenon of polymorphism is ubiquitous in nature, the controlled manipulation of which not only increases our ontological understanding of nature but also facilitates the conceptualization and realization of novel functional materials. However, achieving targeted polymorphism in supramolecular assemblies (SAs) remains a formidable challenge, largely because of the constraints inherent in controlling the specific binding motifs of noncovalent interactions. Herein, we propose self-adaptive aromatic cation-π binding motifs to construct polymorphic SAs in both the solid and solution states. Using distinct discrete cation-π-cation and long-range cation-π binding motifs enables control of the self-assembly directionality of a C2h-symmetric bifunctional monomer, resulting in the successful formation of both two-dimensional and three-dimensional crystalline SAs (2D-CSA and 3D-CSA). The differences in the molecular packing of 3D-CSA compared with that of 2D-CSA significantly improve the charge separation and carrier mobility, leading to enhanced photocatalytic activity for the aerobic oxidation of thioanisole to methyl phenyl sulfoxide (yield of 99 % vs 57 %). 2D-CSA, which has a vertical extended structure with favorable stronger interaction with toluene though face-to-face cation-π interactions than methylcyclohexane, shows higher toluene/methylcyclohexane separation efficiency than 3D-CSA (96.9 % for 2D-CSA vs 56.3 % for 3D-CSA).

Antibacterial and sunlight-driven photocatalytic activity of graphene oxide conjugated CeO2 nanoparticles

This work focuses on the structural, morphological, optical, photocatalytic, antibacterial properties of pure CeO2 nanoparticles (NPs) and graphene oxide (GO) based CeO2 nanocomposites (GO-1/CeO2, GO-5/CeO2, GO-10/CeO2, GO-15/CeO2), synthesized using the sol–gel auto-combustion and subsequent sonication method, respectively. The single-phase cubic structure of CeO2 NPs was confirmed by Rietveld refined XRD, HRTEM, FTIR and Raman spectroscopy. The average crystallite size was calculated using Debye Scherrer formula and found to increase from 20 to 25 nm for CeO2 to GO-15/CeO2 samples, respectively. The related functional groups were observed from Fourier transform infrared (FTIR) spectroscopy, consistent with the outcomes of Raman spectroscopy. The optical band gap of each sample was calculated by using a Tauc plot, which was observed to decrease from 2.8 to 1.68 eV. The valence state of Ce (Ce3+ and Ce4+) was verified using X-ray photoelectron spectroscopy (XPS) for CeO2 and GO-10/CeO2. The poisonous methylene blue (MB) dye was used to evaluate the photocatalytic activity of each sample in direct sunlight. The GO-15/CeO2 nanocomposite showed the highest photocatalytic activity with rate constant (0.01633 min–1), and it degraded the MB dye molecules by 100% within 120 min. The high photocatalytic activity of this material for degrading MB dye establishes it as an outstanding candidate for wastewater treatment. Further, these nanocomposites also demonstrated excellent antimicrobial activity against Pseudomonas aeruginosa PAO1.

Solar-powered commercial diesel fuel desulfurization: Exploring the factors affecting and recyclability of mesoporous Tl-doped TiO2 nanofiber photocatalysts

The study aims to fabricate mesoporous TiO2 nanofibers (NFs) with different thallium (Tl) doping ratios (1–2 wt%) using the solution electrospinning method and examine their photocatalytic oxidation activity in the desulfurization of commercial diesel fuel. The results show that the Tl doping restricted the transition of the anatase to rutile fraction, shifting it from an initial composition of 58.3% rutile and 41.7% anatase to a significantly altered state with only 2.4% rutile and 97.6% anatase. Additionally, Tl-doping resulted in a decrease in crystalline size (from 55.4 to 9.5 nm), a reduction in the band gap from 3.2 to 2.93 eV, and a decrease in the diameter of the nanofibers from 200 nm to 100 nm, compared to pristine TiO2 NFs. The most efficient photocatalyst, 1 wt% Tl-doped TiO2 NFs, demonstrated remarkable performance with 98.74% sulphur removal under Xenon lamp irradiation (450 nm, 500 Watts) for 90 min. Under sunlight, the photocatalytic oxidation activity in the desulfurization process resulted in a remarkable reduction of 99.2% in sulphur content, decreasing from 11500 ppm to 98 ppm. Notably, this photocatalyst demonstrated efficient oxidative photocatalytic desulfurization and maintained the recyclability of the solvent over eight cycles without any loss.

Facile one-step preparation of Co2CrO4 spinel from heterometallic compounds – Structural, magnetic, electrical and photocatalytic studies

Two isostructural heterometallic complex salts with mononuclear units, [NH(CH3)2(C2H5)][Cr(terpy)2][CoCl4]2 (1) and [NH(CH3)(C2H5)2][Cr(terpy)2][CoCl4]2 (2), were synthesized using a building block approach and characterized by single-crystal and powder X-ray diffraction (XRD), impedance spectroscopy and magnetization measurements. They exhibit particular humidity-sensing properties and very high proton conductivity at room temperature. The magnetization of complexes shows the high spin state of 3/2 for tetrahedrally coordinated CoII ions, which on cooling remain in the paramagnetic state within the CrIII network, which is antiferromagnetically correlated. The prepared compounds were thoroughly explored as single-source precursors for the formation of the spinel oxide Co2CrO4 by their thermal decomposition. By optimizing the annealing temperature, heating/cooling rates and holding times, the phase composition of thermal processing of 1 or 2 was evaluated: phase pure spinel Co2CrO4 was obtained by thermal treatment already at 450 °C. The structure, morphology, and optical properties of spinel oxides prepared at different temperatures were characterized using powder XRD, field emission scanning electron microscopy (SEM) and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), while electrical and magnetic by impedance spectroscopy and magnetization measurements. The determined band gap energy and nanosized crystallites prompted us to investigate the photocatalytic activity of spinel oxide produced at 450 °C in the degradation of dyes Rhodamine B (RhB) and Methylene blue (MB) under Vis irradiation without and with assistance of hydrogen peroxide (H2O2). The results show that the Co2CrO4/H2O2 system exhibits a significantly higher photoactivity response; the degradation efficiency of MB and RhB was found to be 86.1% and 80.3%, respectively. The electrical conductivity spectra and the activation energy for the DC conductivity demonstrate the electronically semiconducting behaviour of the Co2CrO4 oxide. The Co2CrO4 spinel has a ferrimagnetic ground state, with mixed CoII and CoIII ions on the tetrahedral and octahedral sites: CoII having a high spin state on both sites and CoIII having a high spin state on the tetrahedral site and a low spin state on the octahedral site. Different thermal treatments affect the magnetization according to the different sizes of the obtained crystallites.

LDH/MXene Synergistic Carrier Separation Effects to Improve the Photoelectric Catalytic Activities of Bi2WO6 Nanosheet Arrays.

Photoelectric catalysis is a green and efficient way to degrade pollutants, which has been paid more and more attention by researchers. Among them, Bi2WO3 has been proved to have excellent photocatalytic oxidation activity on its {001} facets. In this study, {001}-oriented facets with high exposure were successfully integrated into Bi2WO6 nanoplate arrays (Bi2WO6 NAs) to create a photoelectrode. This structure was grown in situ on an indium tin oxide (ITO) substrate. To promote photogenerated carrier separation efficiency and reduce agglomeration of Bi2WO6 photocatalysts, the electrochemical deposition of NiFe-layered double hydroxide (NiFe-LDH) and Ti3C2 (MXene) were introduced in this research to synergistically catalyze pollutant degradation. Morphology, spectral characterization, and electrochemical analysis jointly confirmed that the outstanding performance of hole capture behavior with LDH and electron conduction properties with MXene were the main reasons for the improvement in catalytic activity of the photoelectrode. Taking bisphenol A (BPA) as the model pollutant, the rate constant k of the NiFe-LDH/Ti3C2/Bi2WO6 NAs photoelectrode reaches 0.00196 min-1 under photoelectrocatalytic (PEC) conditions, which is 4.5 times that of the pure Bi2WO6 NAs photoelectrode. This work provides a new way to improve the reaction kinetics of the PEC degradation of pollutants.

Metal Sulfide S-Scheme Homojunction for Photocatalytic Selective Phenylcarbinol Oxidation.

Metal sulfide-based homojunction photocatalysts are extensively explored with improved photocatalytic performance. However, the construction of metal sulfide-based S-scheme homojunction remains a challenge. Herein, the fabrication of 2D CdIn2S4 nanosheetscoated 3D CdIn2S4 octahedra (referred to as 2D/3D n-CIS/o-CIS) S-scheme homojunction photocatalyst is reported by simply adjustment of polyvinyl pyrrolidone amount during the solvothermal synthesis. The formation of S-scheme homojunction within n-CIS/o-CIS is systematically investigated via a series of characterizations, which can generate an internal electric field to facilitate the separation and migration of photogenerated electron-hole pairs. The 2D/3D n-CIS/o-CIS composite exhibits significantly improved photocatalytic activity and stability in the selective oxidation of phenylcarbinol (PhCH2OH) to benzaldehyde (PhCHO) when compared to pure n-CIS and o-CIS samples under visible light irradiation. It is hoped that this work can contribute novel insights into the development of metal sulfides S-scheme homojunction photocatalysts for solar energy conversion.

Magnetically separable and visible light-driven photocatalytic activity of graphene oxide based α-Fe2O3 nanocomposite

This work investigates the impact of graphene oxide (GO) on the structural, morphological, optical, and photocatalytic investigations of Fe2O3, an excellent photocatalyst for industrial wastewater treatment. Using the straightforward and inexpensive sol-gel auto-combustion, hummer's method and sonication method, Fe2O3 nanoparticle (NPs), GO nanosheet, and GO-based Fe2O3 (GO/Fe2O3) nanocomposite have been synthesized, respectively. The XRD patterns, Raman spectra, and FTIR spectroscopy were used for the structural analysis, which verifies the single phase hexagonal geometry of Fe2O3 NPs. The average size of the crystallites is seen to have reduced from 50 nm to 44 nm for Fe2O3 and GO/Fe2O3. The SEM along with EDS were applied to investigate the surface morphology and confirm the existence of the elements Fe and O in pure Fe2O3, and C, Fe and O in GO/Fe2O3. From UV–vis absorbance spectra, the decrease in optical band gap (2.5 eV–1.9 eV) caused by GO incorporation has been inferred, as clearly displayed in the Tauc plots. X-ray photoelectron spectroscopy (XPS) confirms the presence of Fe2+/Fe+3 ionic states and large oxygen vacancies in the GO/Fe2O3 nanocomposite. The photocatalytic properties of both materials for the toxic MB (methylene blue) dye photodegradation in an aqueous solution was evaluated while being exposed to sunlight. It makes an excellent choice for wastewater treatment due to the high photocatalytic activity of magnetically separable GO/Fe2O3 nanocomposite for decomposing the MB dye.

Ca-doped birnessite for enhanced photocatalysis of water oxidation

Birnessite is an affordable and high-efficiency catalyst for water oxidation. In this study, we attempted to doping Ca into birnessite to investigate the influence on its photocatalytic oxidation activity. The study was carried out through a combination of experimental investigations and DFT calculations of the relevant crystal and electronic structures. The analysis of Raman spectra using 2T2D correlation and DFT indicates that Ca contributes more to the high frequency regions (400–600 cm−1) than K. DFT further reveals that the introduction of Ca leads to an increase in the number of localized electrons at the Fermi energy level and in the conduction band. Photo-electrochemical experiments demonstrate a significant reduction of 100 mV/dec in the Tafel slope, along with a 1.48-fold increase in photo-current density for Ca-birnessite when compared to K-birnessite. In general, the results demonstrate that Ca-birnessite can effectively heighten visible light absorption, reduce the band gap, and enhance water oxidation activity.

Phenol degradation by a combined hydrogenation and photocatalytic oxidation over the bifunctional Rh/WO3 catalyst

The combination of hydrogenation and photocatalytic oxidation (PCO) was proposed and successfully applied for phenol degradation. A new bifunctional Rh/WO3 catalyst, with both hydrogenation ability and PCO activity, was developed for the combined hydrogenation-PCO process by depositing Rh on WO3. The synergistic catalytic effect occurs between Rh and WO3, resulting in a high hydrogenation-PCO performance of the Rh/WO3 catalyst. The hydrogenation-PCO over Rh/WO3 catalyst exhibited an excellent phenol removal efficiency (almost 100%) in the first 15 min hydrogenation step, which is much higher than PCO. Furthermore, the TOC removal efficiency of hydrogenation-PCO (27.6%) is more than four times that of PCO (5.7%). This work suggests that the combined hydrogenation-PCO strategy has a promising prospect for the treatment of wastewater containing phenolic compounds.

Photodegradation of methylene blue dye using graphene oxide incorporated, post-transition metal doped zinc oxide thin films by spray pyrolysis

Photocatalytic activity of graphene oxide incorporated pure and metal doped zinc oxide thin films were studied against methylene blue dye under simulated solar irradiation. Thin films were deposited on a glass substrate using an automated spray pyrolysis technique at a temperature of 425 °C. Aluminium, gallium, and indium were the post-transition metals used for doping. Graphene oxide content in the precursor solution was fixed at 0.00375 g/l. The formation of the wurtzite structure of zinc oxide has been confirmed using structural analysis. The average crystallite size of all the thin film samples was found to be in the range of 45–55 nm. The morphology and elemental composition of the films were studied using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The energy band gap of the material was determined from UV–vis-NIR spectroscopic measurements using Tauc’s plot and it is in the range of 3.25–3.28 eV. Photoluminescence spectra of the as-deposited films were recorded. Intensity of the near band emission at 395 nm was found to decrease upon metal doping, indicating a better photocatalytic property. All the films were used for heterogeneous photocatalysis and the indium doped zinc oxide thin film incorporated with graphene oxide was found to be a better catalyst with an efficiency of 94.9% for degrading methylene blue dye in 180 min.

Niobium Oxide Photocatalytically Oxidizes Ammonia in Water at Ambient Conditions

Ammonia contamination in water is a significant environmental issue since it is toxic and leads to eutrophication. Photocatalysis has been investigated as a strategy for ammonia degradation but can potentially form toxic nitrite (NO2 – ) and nitrate (NO3 – ) byproducts. This work reports on the ability of niobium oxide (Nb2O5) to photocatalytically oxidize aqueous-phase ammonia (NH3). Whereas as-synthesized Nb2O5 showed little catalytic activity (< 1% NH3 conversion after 6 h of UV-C irradiation, at room temperature and atmospheric pressure, and under O2 headspace), Nb2O5 treated in basic solution (OH-Nb2O5) was able to photocatalytically degrade NH3 at ca. 9% conversion after six hours, with ca. 70% selectivity to the desired N2, with a first-order rate constant of ca. 12 times higher than the as synthesize catalyst (1.6 × 10–3 min–1 vs. 2.0 × 10–2 min–1). Raman spectroscopic analysis indicated the presence of terminal Nb=O species after base treatment of Nb2O5, implicating them as catalytically active sites. These results underscore how a simple structural modification can significantly affect photocatalytic activity for aqueous ammonia oxidation.

Enhanced photocatalytic performance of ZnO under visible light by co-doping of Ta and C using hydrothermal method.

This study attempted to improve the photocatalytic activity of zinc oxide (ZnO) semiconductors in the visible light region by introducing the co-doping of carbon (C) and tantalum (Ta) to ZnO (ZTC) using a simple hydrothermal method with the respective precursors. The obtained uniform ZTC nanoparticles with an average crystal size of 29.30 nm (according to Scherrer's equation) revealed a redshift with a decrease in bandgap (Eg) from 3.04 eV to 2.88 eV, allowing the obtained photocatalyst to absorb the energy of the visible light for photocatalysis. Furthermore, the Zn 2p and Ta 4f core level spectra confirmed the presence of Zn2+ and Ta5+ in the ZTC sample. In addition, the infrared spectra identified hydrogen-related defects (HRDs), while the O 1s spectra indicated the existence of oxygen vacancies (VO). Electrochemical tests revealed improvement in the electron conductivity and charge separation of the obtained materials. To follow, the photocatalytic performance assessment was conducted by varying the C/Zn2+ ratios (5, 10, and 15 mol%) in ZTC samples, the initial RhB concentration (7, 15, and 30 ppm), and the pH of the RhB solution (3.0-10.0). The photodegradation on ZTC samples showed the most effectiveness for a 7 ppm RhB solution with a C/Zn2+ ratio of 10 mol% in the slightly alkaline medium (pH 9.0). Additionally, ZTC also exhibited commendable durability after being reused several times. The nature of RhB photodegradation was proposed and discussed via a mechanism at the end of this work.

Accurate assembly of thiophene-bridged titanium-oxo clusters with photocatalytic amine oxidation activity.

Designing and synthesizing well-defined crystalline catalysts for the photocatalytic oxidative coupling of amines to imines remains a great challenge. In this work, a crystalline dumbbell-shaped titanium oxo cluster, [Ti10O6(Thdc)(Dmg)2(iPrO)22] (Ti10, Thdc = 2,5-thiophenedicarboxylic acid, Dmg = dimethylglyoxime, iPrOH = isopropanol), was constructed through a facile one-pot solvothermal strategy and treated as a catalyst for the photocatalytic oxidative coupling of amines. In this structure, Thdc serves as the horizontal bar, while the {Ti5Dmg} layers on each side act as the weight plates. The molecular structure, light absorption, and photoelectrochemical properties of Ti10 were systematically investigated. Remarkably, the inclusion of the Thdc ligand, with the assistance of the Dmg ligand, broadens the light absorption spectrum of Ti10, extending it into the visible range. Furthermore, the effective enhancement of charge transfer within the Ti10 was achieved with the successful incorporation of the Thdc ligand, as opposed to PTC-211, where terephthalic acid replaces the Thdc ligand, while maintaining consistency in other aspects of Ti10. Building on this foundation, Ti10 was employed as a heterogeneous molecular photocatalyst for the catalytic oxidative coupling reaction of benzylamine (BA), demonstrating very high conversion activity and selectivity. Our study illustrates that the inclusion of ligands derived from Thdc enhances the efficiency of charge transfer in functionalized photocatalysts, significantly influencing the performance of photocatalytic organic conversion.

Oxygen evolution reaction (OER) active sites in BiVO4 studied using density functional theory and XPS experiments.

Bismuth vanadate (BiVO4/BVO) has been widely studied as a photocatalytic water splitting semiconductor material in recent years because of its many advantages, such as its ease of synthesis and suitable band gap (2.4 eV). However, BVO still has some disadvantages, one of which is the low photocatalytic water oxidation activity. It is intriguing and unexpected to note that in the current literature, Bi atoms are taken as the oxygen evolution reaction (OER) active sites, while V metal atoms are not investigated in the OER, and the underlying reason for this remains unknown. In this work, using density functional theory (DFT) calculations and ab initio molecular dynamics simulations, we found that in BVO, the VO4 tetrahedron structure is very stable and there is strong surface reconstruction that leads to the V atoms on the surface having the same coordinates as in the bulk. For some high index surfaces, there are some theoretically predicted unsaturated V sites, but it is very easy to form a VO4 tetrahedron structure again by taking oxygen atoms from water. The other intermediates of OER are difficult to adsorb or desorb on this VO4 structure, which makes the V sites in BVO unsuitable as OER active sites. This VO4 structure remained stable during the molecular dynamics simulation at 300 and 673 K. The XPS characterization of various BVO morphologies validates our primary findings from DFT and molecular dynamics simulations. It reveals the presence of unsaturated Bi sites on the BVO surface, while unsaturated V sites are not observed. This study provides novel insights into the enhancement of OER activity of BVO and offers a fundamental understanding of OER activity in other photocatalysts containing V atoms.