Visible Light-induced Photocatalysis Research Articles

Visible Light-Induced Photocatalysis: Self-Fenton Degradation of p-ClPhOH Over Graphitic Carbon Nitride by a Polyethylenimine Bifunctional Catalyst

Visible Light-Induced Photocatalysis: Self-Fenton Degradation of p-ClPhOH Over Graphitic Carbon Nitride by a Polyethylenimine Bifunctional Catalyst

Cobalt-doped iron-based metal–organic gels as efficient visible-light-driven peroxymonosulfate activators for the efficient degradation of norfloxacin with simultaneous antibacterial activity

A strategically fabricated cobalt-doped iron-based metal–organic gel (CFM) synergistically promotes peroxymonosulfate (PMS) activation and visible light-induced photocatalysis to remove norfloxacin (NOR). Cobalt incorporation into the metal–organic gel significantly optimizes its electronic structure, leading to the exceptional performance of CFM in synergistically activating PMS, amplifying visible light absorption, and enhancing photoinduced charge separation efficiency. The Vis/50 %-CFM/PMS system enables a NOR removal rate of up to 96.8 % within 60 min and a total organic carbon (TOC) removal rate of 78.3 %, signifying excellent decontamination performance. Exhibiting robust mineralization potential, the Vis/CFM/PMS system has undergone comprehensive analysis of the intermediary degradation process using Density Functional Theory (DFT) calculations. The toxicity of degradation intermediates was assessed employing the quantitative structure–activity relationship (QSAR) model. In addition, the Vis/CFM/PMS system showed antibacterial effects against E. coli and S. aureus. This investigation furnishes a novel perspective toward developing innovative PMS activation photocatalyst coupling systems for environmental remediation.

Decarboxylative Oxidation of Carboxylic Acids Using Photocatalysis and Copper Catalysis

AbstractA decarboxylative oxidation of carboxylic acids was developed through visible-light-induced photocatalysis with molecular oxygen as a green oxidant and copper as a co-catalyst. This reaction worked smoothly on various type of acids, and could potentially be used in modifications of natural products. The high efficiency of this transformation was demonstrated on over 40 substrates.

Bicarbonate-enhanced generation of hydroxyl radical by visible light-induced photocatalysis of H2O2 over WO3: Alteration of electron transfer mechanism

The generation of hydroxyl radical (•OH) by visible light-illuminated tungsten oxide (WO3) was found to be significantly improved in the presence of hydrogen peroxide (H2O2) and bicarbonate ion (HCO3−). A ternary system of hν/WO3/H2O2/HCO3− showed synergistic enhancement in oxidation of benzoic acid (BA, a •OH probe compound) into hydroxybenzoic acids (HBAs), exhibiting even less consumption of H2O2 than hν/WO3/H2O2. Analyses of HBAs from BA oxidation (three HBA isomers and 18O-labelled HBA from H218O2) suggested that hν/WO3/H2O2/HCO3−, contrary to hν/WO3/H2O2, generated •OH mainly via one-electron transfer from the conduction band of WO3 to H2O2. The dominant one-electron reduction of H2O2 over HCO3−-treated WO3 was further evidenced by Koutecký–Levich plots obtained with a rotating disk electrode setup. Based on different experiments using electron paramagnetic resonance spectroscopy, radical scavengers and probes, (photo-)electrochemical measurements, and density functional theory calculations, the mechanisms underlying the enhanced generation of •OH by hν/WO3/H2O2/HCO3− were discussed.

Photoredox-Catalyzed Oxidative Radical–Polar Crossover Enables the Alkylfluorination of Olefins

The three-component alkylfluorination of olefins via an oxidative radical-polar crossover under visible light-induced photocatalysis is disclosed. A key feature of this reaction is the incorporation of two synthetically meaningful components involving a three-dimensional alkyl group and a fluorine atom using easily preparable N-hydroxyphthalimide esters as the alkyl donors and a low-cost hydrogen fluoride as the fluorine source. Furthermore, a one-step procedure using commercially available carboxylic acids demonstrated the versatility of this new method.

Enhanced Visible Light Photocatalytic Degradation of Methylene Blue by CdS-ZnS-BiPO4 Nanocomposites Prepared by a Solvent-Assisted Heating Method

In this study, a ternary CdS-ZnS-BiPO4 nanocomposite, synthesized by a solvent-assisted heating method, demonstrated the highest visible light-induced photocatalysis towards the degradation of methylene blue (MB) when comparing with BiPO4, CdS-BiPO4, and ZnS-BiPO4. Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) were used to characterize the prepared nanocomposites. From UV-DRS results, the energy band gap of the prepared BiPO4 structures was 4.51 eV. When CdS nanoparticles were deposited on BiPO4 surface by a solvent-assisted heating method, the prepared nanocomposites exhibited visible light-responsive photocatalytic degradation toward MB (20 ppm). At a molar ratio of Cd to Zn as 1:7, the prepared CdS-ZnS-BiPO4 nanocomposites exhibited the best photocatalytic activity in degrading 95% of MB dyes, out-performing pure BiPO4, CdS-BiPO4, and ZnS-BiPO4 due to its enhanced charge separation efficiency and the lowered carrier recombination from the efficient p-n junction of unprecedented ternary composites. The investigations on mechanism conclude that the major reactive species responsible for MB degradation are holes and oxygen radicals. For practicality, the degradation efficiency for different dyestuff (Fast Green FCF, Rhodamine 6G, Acid Blue 1, methyl orange, and methyl red) degradation in the different water matrix samples (pond water, seawater, and lake water) by the prepared CdS-ZnS-BiPO4 nanocomposites was evaluated.

Novel Pt-Ag3PO4/CdS/Chitosan Nanocomposite with Enhanced Photocatalytic and Biological Activities.

Decorating photocatalysts with noble metal nanoparticles (e.g., Pt) often increases the catalysts’ photocatalytic activity and biomedical properties. Here, a simple and inexpensive method has been developed to prepare a Pt-Ag3PO4/CdS/chitosan composite, which was characterized and used for the visible light-induced photocatalytic and antibacterial studies. This synthesized composite showed superior photocatalytic activity for methylene blue degradation as a hazardous pollutant (the maximum dye degradation was observed in 90 min of treatment) and killing of Gram positive bacterial (Staphylococcus aureus and Bacillus cereus) as well as Gram negative bacteria (Klebsiella pneumoniae, Salmonella typhimurium, Escherichia coli, and Pseudomonas aeruginosa) under visible light irradiation. The antibacterial activity of CdS, CdS/Ag3PO4, and Pt-Ag3PO4/CdS/chitosan against E. coli, Pseudomonas aeruginosa, Salmonella typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, and Bacillus cereus showed the zone of inhibition (mm) under visible light and under dark conditions at a concentration of 20 µg mL−1. Furthermore, the cell viability of the CdS/chitosan, Ag3PO4, Ag3PO4/CdS/chitosan, and Pt-Ag3PO4/CdS/chitosan were investigated on the human embryonic kidney 293 cells (HEK-293), Henrietta Lacks (HeLa), human liver cancer cell line (HepG2), and pheochromocytoma (PC12) cell lines. In addition, the results indicated that the photodegradation rate for Pt-Ag3PO4/CdS/chitosan is 3.53 times higher than that of CdS and 1.73 times higher than that of the CdS/Ag3PO4 composite. Moreover, Pt-Ag3PO4/CdS/chitosan with an optimal amount of CdS killed large areas of different bacteria and different cells separately in a shorter time period under visible-light irradiation, which shows significantly higher efficiency than pure CdS and other CdS/Ag3PO4 composites. The superb performances of this composite are attributed to its privileged properties, such as retarded recombination of photoinduced electron/hole pairs and a large specific surface area, making Pt-Ag3PO4/CdS/chitosan a valuable composite that can be deployed for a range of important applications, such as visible light-induced photocatalysis and antibacterial activity.

Preparation of ZnWO4 (Sanmartinite) Powder Through Mechanochemical Method for Visible Light-Induced Photocatalysis

ZnWO4 (sanmartinite) powders were produced by mechanochemical synthesis using ZnO and WO3 at 700 rpm for 25, 50 and 100 min, respectively. SEM indicated the ratio of sub-micron-sized ZnWO4 particles was raised, and particle size distribution was homogenized by increasing process time. XRD results revealed the formation of sanmartinite after 100 min milling with 700 rpm. Raman Spectroscopy confirmed the XRD results except detection of WO3 and ZnO traces. The surface area of the samples was ranged between 3.65 and 4.05 m2/g. Optical band-gap energies of the samples increased from 2.68 to 2.86 eV with further process time. Under the visible light, the highest photocatalytic efficiency for degradation of malachite green dyes was observed in sample ball milled at 700 rpm for 25 min. Samples ball milled at 700 rpm for 100 min have lower photocatalytic activity compared to samples ball milled at 700 rpm 25 and 50 min. The efficiency of photocatalytic activities changed from 45 to 83% after 120-min photocatalysis process. It is possible to claim that ZnWO4 powders are promising photocatalyst.

Polymeric Carbon Nitride Armored Centimeter-Wide Organic Droplets in Water for All-Liquid Heterophase Emission Technology.

High potential of emission chemistry has been visualized in many fields, from sensors and imaging to displays. In general, conjugated polymers are the top rankers for such chemistry, despite the fact that they bring solubility problems, high expenses, toxicity and demanding synthesis. Metal-free polymeric semiconductor graphitic carbon nitride (g-CN) has been an attractive candidate for visible light-induced photocatalysis, and its emission properties have been optimized and explored recently. Herein, we present modified g-CN nanoparticles as organodispersible conjugated polymer materials to be utilized in a heterophase emission systems. The injection of a g-CN organic dispersion in aqueous polymer solution not only provides retention of the shape by Pickering stabilization of g-CN, but high intensity emission is also obtained. The heterophase all-liquid emission display can be further modified by the addition of simple conjugated organic molecules to the initial g-CN dispersion, which provides a platform for multicolor emission. We believe that such shape-tailored and stabilized liquid–liquid multicolor emission systems are intriguing for sensing, displays and photonics.

New insight into reactive oxidation species (ROS) for bismuth-based photocatalysis in phenol removal

Bismuth-based semiconductors (BBS) are a group of promising candidates applied to visible light-induced photocatalysis. With deep positions of valence bands (2.34–4.04 eV), BBS exhibited excellent activity in oxidation processes. Fundamental studies on the reactive oxidation species primarily focused on TiO2 under ultraviolet, and it was recognized that OH radicals were effective reactive oxidative species in photocatalytic oxidation processes. This verdict may not be applicable for all other photocatalytic systems. In this study, the reactive oxidation species for BBS in the photocatalytic decomposition of phenol were explored. BBS were prepared with Hierarchical structures and high crystallinity. It was found that OH radicals and superoxide radicals were negligibly produced in most BBS photocatalytic systems. Instead, separated holes on the valence band may directly react with adsorbed species including organics, and acted as the primary ROS. One of the possible explanations of this phenomenon may be due to the shorter lifetime of photogenerated charge carriers on most BBS (212.3–415.7 ms) compared to that of TiO2 (1193.8 ms). Photocatalytic reaction pathways of degradation of phenol were also different between BBS and TiO2, which were proposed. This work shed light on the significance of addressing and clarifying the reactive oxidation species in BBS photocatalysis.

A General Method for Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids.

A general and practical method for decarboxylative hydroxylation of carboxylic acids was developed through visible light-induced photocatalysis using molecular oxygen as the green oxidant. The addition of NaBH4 to in situ reduce the unstable peroxyl radical intermediate much broadened the substrate scope. Different sp3 carbon-bearing carboxylic acids were successfully employed as substrates, including phenylacetic acid-type substrates, as well as aliphatic carboxylic acids. This transformation worked smoothly on primary, secondary, and tertiary carboxylic acids.

Fabrication of SrTiO3/g-C3N4 heterostructures for visible light-induced photocatalysis

We investigated a new method for the preparation of visible light-activated heterostructured photocatalysts made up of SrTiO3 (STO) and g-C3N4 (CN). The photocatalysts were synthesized by the polymeric precursor method to obtain STO, which was further thermally treated at 550 °C for 2 h in presence of melamine at different proportions for CN formation. The SrTiO3/g-C3N4 heterostructures were termed as STOCN-Mel88%, STOCN-Mel92%, STOCN-Mel95%, STOCN-Mel97% and STOCN-Mel99% indicating the use of melamine at 88%, 92%, 95%, 97% or 99%. The SrTiO3/g-C3N4 heterostructures were characterized for their crystalline structure, optical properties, thermal stability, morphology and surface composition, and photocatalytic potential, which was evaluated by photodegradation of methylene blue dye and amiloride under visible light. The melamine content exhibited a strong influence on the formation of CN, as well as on the bulk structure, surface and photocatalytic properties of the SrTiO3/g-C3N4 heterostructures. The heterostructures were catalytically active under visible light due to their reduced band gap energy. The presence of oxygen vacancies in the STO phase associated with the CN phase improved the photogenerated electron-hole charge separation in the SrTiO3/g-C3N4 catalysts. The synthesis described here is efficient in obtaining visible light-activated photocatalysts that are applicable to photocatalytic processes under solar light.

Assessment of tailor-made mesoporous metal doped TiO2 monolithic framework as fast responsive visible light photocatalysts for environmental remediation applications

The article reports on the facile one-pot synthesis of a structurally organized mesoporous crack-free monolithic network of Bi3+ doped TiO2, as a visible light workable photocatalyst materials for environmental remediation. The monolithic photocatalyst efficacy has been investigated using Acid Blue 113, an organic textile dye as the model organic pollutant, thereby rooting its decontamination potential towards dye effluents from textile and dye industries. The controlled stoichiometric surface doping of Bi3+ with the continuous framework of the TiO2 monolithic material not only ensures visible light-induced photocatalysis but also high quantum yield upon light impingement thereby leading a rapid generation of reactive radical species. The monolith structural properties and its morphology are characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDAX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PLS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm analysis. The anatase phase TiO2 monolith offers a high surface area that promotes the voluminous generation of photo-induced e−/h+ pairs that proceed towards the formation of reactive radical intermediates for the fast dissipation of pollutants. To valid the efficiency and effectiveness of the Bi3+ doped TiO2 monolith photocatalyst, a comprehensive study on the physicochemical parameters such as solution pH, dopant stoichiometry, photocatalyst quantity, light intensity, photosensitizers, and reusability, proves crucial. The results reveal that under optimized conditions, the photocatalyst has an ultra-fast response time of ≤0.2 h for complete mineralization, with 0.06 g of monolithic photocatalysts that are recoverable and reusable.

Photocatalytic degradation of a model textile dye using Carbon-doped titanium dioxide and visible light

Rhodamine B (RhB), a dye widely used in the textile manufacturing, contributes with other dyes to harm the environment. Here, with the final goal to provide new tools for the removal of dyes from water, visible light activated carbon-doped titanium dioxide was used to investigate on the decolourization and the photocatalytic degradation of RhB dye from water solutions. The photodegradation activity was tested varying the initial concentration of RhB and the amount of carbon-doped titanium dioxide, taking into account the ratio between the amount of catalyst and the amount of RhB (TiO2/RhB), thus obtaining a parameter that allows the method to be scaled up without losing its effectiveness. Values of k2 and t0.5 were obtained by fitting kinetics data to a second-order kinetic adsorption model. The important role played by doped TiO2 particles is demonstrated by the highly efficient color removal obtained during the visible light-induced photocatalysis. The presence of different degradation intermediates was demonstrated by means of UV–vis Absorption and Fluorescence spectroscopy. Such results underline that the whole photodegradation process does not end with the decolourization occurrence.

Dye-sensitized TiO2-catalyzed photodegradation of sulfamethoxazole under blue or yellow light.

Visible light-induced photocatalysis is potentially advantageous and could be an efficient approach to degrade contaminants because it can be used to selectively target specific wavelength for decomposition of organic contaminants in water and wastewater. This study demonstrates the photodegradation of sulfamethoxazole (SMX) using [Pt(3,3'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 1)-sensitized and [Pt(4,4'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 2)-sensitized titanium dioxide (TiO2) under blue or yellow light (420 or 580nm, respectively) irradiation in water. The Complex 1-sensitized TiO2 photocatalytic oxidation of SMX reached almost 100% removal under 420nm irradiation for 3h in water. In addition, the formation of hydroxyl radicals can be facilitated by bubbling O2 during the photodegradation in which an effective decomposition of SMX was observed. Based on HPLC and UV-Vis studies of the decomposed products, it was found that SMX underwent cleavage of aromatic rings during the photodegradation process.

Efficient α/β-Bi2O3 composite for the sequential photodegradation of two-dyes mixture

A mixture of α/β-Bi2O3 and α-Bi2O3 powders were obtained by a simple solid state reaction–annealing route at 550°C. The structure, optical properties and surface area of the commercial α and β-Bi2O3 and the synthesized α-phase and α/β-composite were well characterized by X-ray diffraction, diffuse reflectance spectra and N2 physisorption. The annealed sample at 550°C showed 20% of β-phase, forming a heterojunction of α/β-Bi2O3 whereas annealing at elevated temperature (650°C) lead to the α-phase. Optical properties showed that the presence of the β-phase is mainly responsible for narrowing the energy band gap. The photocatalytic activity of the commercial α and β-Bi2O3 and the synthesized α-phase and α/β-composite were investigated in degradation of single dyes, Indigo Carmine (IC) and Rhodamine-B (RhB) under both UV and visible light-induced photocatalysis. For the best photocatalyst, the photodegradation in a two-dye mixture solution was systematically studied considering the type of dye, the adsorption capacity of the samples and the behavior of dye photodegradation. The photocatalytic performance of α/β-Bi2O3 was comparatively much higher than the commercial α and β-Bi2O3, indicating that better performance of efficient charge separation and transfer across α/β-Bi2O3 composite was obtained. Possible mechanism of the single dye and two-dye mixture degradation was given by using α/β-Bi2O3 composite.

Electronic and optical properties of N-doped Bi2O3 polymorphs for visible light-induced photocatalysis.

The effect of N doping on the crystal structure, electronic, and optical properties of α-Bi2O3 and β-Bi2O3 has been studied in detail based with first principle calculations. The crystallographic features of Bi2O3 polymorphs are not substantially changed through N doping, whereas charge transfer from Bi to N results in large variations of charge density distribution. N-doped β-Bi2O3 exhibits improved thermal stability due to stronger Bi-N covalent bonds and lower defect formation energy, and the convenient preparative access agrees well with experimental observations. Calculated band structures and optical properties indicate that N doping does not induce major band gap narrowing, but leads to the presence of isolated bands above the VBM induced by N 2p for both α-Bi2O3 and β-Bi2O3 which induce large red-shifts of their visible light absoprtion properties. These isolated bands act as acceptor levels and facilitate electron transition under visible light illumination through introduction of steps between VB and CB, thereby rendering the materials quite promising for photocatalytic applications.

Preparation of N-Doped Bi2WO6 Microspheres for Efficient Visible Light-Induced Photocatalysis

The N-doped bismuth tungstate (Bi2WO6) photocatalysts with high visible light activity were prepared by the hydrothermal method using urea as a nitrogen source. The as-prepared N-doped Bi2WO6 samples were characterized by X-ray diffraction, scanning electron microscopy, specific surface area, photocurrent analysis, and UV–Vis diffuse reflectrance spectroscopy. The photocatalytic activity was evaluated by photocatalytic degradation of rhodamine B (RhB) solution under visible light irradiation. The photocatalytic mechanisms were analyzed by active species trapping experiments which revealed that the holes were the main active species of N-doped Bi2WO6 products in aqueous solution under visible light irradiation, rather than ·OH and O 2 •− . With the assistance of H2O2, the photocatalytic activity for degradation of RhB could be further improved because H2O2 reacted with conduction band electrons to generate more hydroxyl radicals.

Facile large-scale synthesis of β-Bi2O3 nanospheres as a highly efficient photocatalyst for the degradation of acetaminophen under visible light irradiation

A facile solvothermal–calcining route for the large-scale synthesis of uniform β-Bi2O3 nanospheres has been demonstrated. The morphology, structure, and photoabsorption of β-Bi2O3 were characterized, and the effects of the preparation conditions on the structural properties of products were analyzed. The results show that monodisperse bismuth nanospheres are formed through the solvothermal reaction where the d-fructose acting as the dominant reductant, and subsequently converted to β-Bi2O3 nanospheres after the calcination in air. It is shown that the composition and structure of the products are greatly affected by the amount of d-fructose, the solvothermal and calcination temperature. The formation mechanism of β-Bi2O3 nanospheres is assumed to undergo the “in situ reduction” of Bi(III)–ethylene glycol complex spheres which serve as self-sacrificing templates, followed by the “in situ oxidation” of bismuth nanospheres by oxygen during the calcination in air. The visible light-induced photocatalysis of the synthetic photocatalysts applied to the degradation of acetaminophen (APAP, a widely occurring human-derived pharmaceutical found in the environment) has been studied systematically. The photocatalytic reaction of APAP over the β-Bi2O3 nanospheres follows pseudo first-order kinetics according to the Langmuir–Hinshelwood model, and exhibits a higher reaction rate constant, which is 2.5, 7, 8.1, and 79 times higher than that of commercial Bi2O3, synthetic α-Bi2O3, nitrogen doped TiO2 (N-TiO2), and Degussa P25, respectively. The superior photocatalytic activity is attributed to the narrower band gap energy (approximately 2.36eV), nanostructure, good dispersion and high oxidation power of the β-Bi2O3 nanospheres. Only one intermediate at m/z 110 can be detected by liquid chromatography/mass spectrometry (LC/MS) in the photodegradation process, while several low-molecular-weight organic acids were identified by ion chromatography (IC) analysis. By combining with the experimental determination of reactive oxygen species in the photocatalytic process and the theoretical calculation of frontier electron density of APAP, a simple, hole-predominated photodegradation pathway is proposed. In addition, the high mineralization efficiency indicates that the as-synthesized β-Bi2O3 nanospheres photocatalyst can avoid secondary pollution during photocatalysis, which is important in practical applications.

Decorating hierarchical Bi2MoO6 microspheres with uniformly dispersed ultrafine Ag nanoparticles by an in situ reduction process for enhanced visible light-induced photocatalysis

In this work, we have demonstrated an efficient Sn (II) mediated in situ reduction strategy to assemble silver nanoparticles on Bi2MoO6 microspheres. The Ag loading can be readily controlled by varying the volume of Ag (NH3)2OH aqueous solution. Meanwhile, the ultrafine silver spherical nanoparticles with uniform diameters are free of protection ligands and are well dispersed on the surface of Bi2MoO6 nanosheet without aggregation even at high loading. Photocatalytic test demonstrated that as-adopted in situ reduction strategy was an effective means to enhance the photocatalytic activity of Bi2MoO6 nanosheet-based microspheres under visible light irradiation (λ>420nm). The enhancement performance is believed to be induced by the intimate contact interface, where silver nanoparticles serve as good electron acceptor for facilitating quick photoexcited electron transfer and thus decreasing electron–hole recombination.