Photocatalytic Oxidation of Alcohols over TiO2 Covered with Nb2O5

Efficient Photocatalytic Partial Oxidation of Aromatic Alcohols by Using ZnIn2S4 under Green Conditions

The ternary chalcogenide ZnIn2S4 (ZIS) has been synthesized by a simple hydrothermal method in which the carcinogen thiacetamide, universally used as a precursor, has been, for the first time, replaced successfully with the harmless thiourea. ZIS has been used as photocatalyst for the partial oxidation of different aromatic alcohols to their corresponding aldehyde in water solution, under ambient conditions and simulated solar light irradiation. The photocatalytic performance of ZnIn2S4 was better than TiO2 P25. In the presence of ZIS for 4-methoxybenzyl alcohol, piperonyl alcohol, and benzyl alcohol, a selectivity towards the corresponding aldehyde of 99 % for a conversion of 46 %, 75 % for a conversion of 81 %, and 87 % for a conversion of 25 %, respectively, was obtained. For the same alcohols a selectivity of 19 % for a conversion of 41 %, 19 % for a conversion of 13 %, and 16 % for a conversion of 26 %, was observed in the presence of TiO2 P25.

Visible Light-Mediated Selective Aerobic Oxidation of Alcohols Catalyzed by Disulfide in Batch and Flow

Selective aerobic oxidation of alcohols in batch and flow can be realized under light irradiation, utilizing disulfide as the photocatalyst, and a variety of primary and secondary alcohols were converted to the corresponding aldehydes or ketones in up to 99% yield and high selectivity. The reaction efficiency could be increased even further by combining a continuous-flow strategy. Detailed mechanistic studies have also been achieved to determine the role of oxygen and disulfides in this oxidation.

Tailored Cl- Ligation on Supported Pt Catalysts for Selective Primary C-H Bond Oxidation

It is challenging to achieve high selectivity over Pt-metal-oxide catalysts widely used in many selective oxidation reactions because Pt is prone to over-oxidize substrates. Herein, our sound strategy for enhancing the selectivity is to saturate the under-coordinated single Pt atoms with Cl^- ligands. In this system, the weak electronic metal-support interactions between Pt atoms and reduced TiO₂ cause electron extraction from Pt to Cl^- ligands, resulting in strong Pt-Cl bonds. Therefore, the two-coordinate single Pt atoms adopt a four-coordinate configuration and thus inactivated, thereby inhibiting the over-oxidation of toluene over Pt sites. The selectivity for the primary C-H bond oxidation products of toluene was increased from 50.1 to 100%. Meanwhile, the abundant active Ti³⁺ sites were stabilized in reduced TiO₂ by Pt atoms, leading to a rising yield of the primary C-H oxidation products of 249.8 mmol g_cat^-1. The reported strategy holds great promise for selective oxidation with enhanced selectivity.

Applications of Vanadium, Niobium, and Tantalum Complexes in Organic and Inorganic Synthesis

Organometallic catalysis is a powerful strategy in chemical synthesis, especially with the cheap and low toxic metals based on green chemistry principle. Thus, the selection of the metal is particularly important to plan relevant and applicable processes. The group VB metals have been the subject of exciting and significant advances in both organic and inorganic synthesis. In this Review, we have summarized some reports from recent decades, which are about the development of group VB metals utilized in various types of reactions, such as oxidation, reduction, alkylation, dealkylation, polymerization, aromatization, protein synthesis, and practical water splitting.

Metal nanoparticle-decorated germanane for selective photocatalytic aerobic oxidation of benzyl alcohol

Two dimensional materials such as germanane have attracted substantial research interest due to their unique chemical, optical, and electronic properties. A variety of methods for introducing diverse functionalities to their surfaces have been reported and these materials have been exploited as photocatalysts. Herein, we report the preparation of metal nanoparticle (Au, Ag, Cu, Pd, Pt) decorated germanane (M@GeNSs) via facile surface-mediated reduction and investigate their structure, composition, as well morphology using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These functional materials were subsequently explored as photocatalysts for selective visible light-induced oxidation of benzyl alcohol to benzaldehyde as freestanding nanosystems and thin films and a reaction mechanism of the photocatalytic oxidation of benzyl alcohol is proposed.

Investigation of Photocatalyst Composites for Pollutant Degradation in a Microslit Reactor Utilizing High Throughput Screening Techniques

The high-throughput screening investigations on TiO₂ based photocatalyst composites presented here have been carried out in a 60-fold parallel photoreactor. Additional catalyst testing was performed in a microslit reactor system with immobilized catalysts. For further enhancing the photocatalytic activity of TiO₂ (P25), composites of P25 and, for example, Bi₂ O₃ , CeO₂ , g-C₃ N₄ , WO₃ or ZnO were formulated in different nominal molar ratios. The catalysts' performances were assessed by their conversion of 17α-ethinyl estradiol (EE2) in aqueous solutions, determined by LC-MS. Findings show rapid EE2 conversions in short residence times. The extensive testing of catalysts led to the conclusion that the photocatalytic conversion is rather a function of residence time than a function of the materials utilized. This makes adequate process development seem more important than material development. The novelty of this contribution lies in the unique combination of testing a wide range of composite catalysts in a unique microreactor geometry.

Toward the Photocatalytic Valorization of Lignin: Conversion of a Model Lignin Hexamer with Multiple Functionalities

The valorization of biomass via photocatalysis is an area of expanding research with advances in new technologies and materials with a view toward enhanced sustainability being reported. A significant challenge within this field, however, is understanding the impact photocatalysis has on more recalcitrant compounds present in biomass, such as lignin. Moreover, the current state of lignin model compound research is still largely focused on the breakdown of small models containing typically only one linkage. Described herein is the use of TiO₂-mediated photocatalysis for the degradation of a representative hexameric lignin model compound which contains multiple linkages (e.g., 5-5', β-5, and β-O-4). The results revealed that while cleavage of the β-5 and β-O-4 occurred, the 5-5' appeared to remain intact within the identified reaction intermediates. To understand some of the more fundamental questions, a dimeric compound with a biphenyl linkage was synthesized and studied under photocatalytic conditions. The proposal of intermediates and pathways of degradation based on the studies conducted is presented and discussed herein.

Acetal photocatalytic formation from ethanol in the presence of TiO2 rutile and anatase

The decomposition of ethanol, one of the most important biomass platform molecules, was investigated under green conditions, ambient temperature, atmospheric pressure and air for the synthesis of acetal in the presence of TiO₂ activated under UV-A radiation. The impact of ethanol concentration, of the nature of TiO₂ (rutile, anatase or mixture), of the photo-deposition of Pt under air or argon were all factors under investigation. Whatever the conditions and the nature of catalyst used, acetaldehyde was initially formed before reacting with ethanol to form acetal, a promising fuel additive. However, the subsequent generation of acetal differs depending on the conditions and the nature of catalyst. In the absence of a noble metal, rutile TiO₂ leads to an increase in acetal formation at equivalent acetaldehyde formation. This behavior is discussed considering the acidic and basic properties of rutile and anatase phases together with H⁺ generated under UV. In the presence of Pt, under air or Ar, the acetal formation begins at a lower concentration of acetaldehyde due to the in-situ photo-deposition of Pt. However, whereas acetal formation is similar for Pt/anatase and Pt/rutile phase under air, under Ar, less acetal is generated on Pt/rutile in agreement with the production of more H₂.

Magnetically Recyclable Fe3O4@TMU-32 Metal-Organic Framework Photocatalyst for Tetracycline Degradation Under Visible Light

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials being used as photocatalysts for efficient pollutant removal and environmental remediation. In this study, the TMU-32 MOF was synthesized as an effective photocatalyst for the photodegradation of tetracycline (TC) with 96% efficiency in 60 min under visible light. The high photocatalytic activity of the TMU-32 MOF is mainly due to its large specific surface area, which is beneficial for promoting both the adsorption of TC and the separation of the photoinduced charges. Moreover, its desired crystallinity makes it a semiconductor with an appropriate band gap energy. Next, a composite of the TMU-32 MOF with Fe₃O₄ nanoparticles (as Fe₃O₄@TMU-32) was prepared as a magnetically recyclable photocatalyst. The results showed that the photocatalytic activity of the Fe₃O₄@TMU-32 nanocomposite is slightly lower (68% degradation of TC within 60 min) than that of TMU-32 toward TC degradation since Fe₃O₄ nanoparticles are not acting as a photocatalyst and are used only to make the host photocatalyst (here, TMU-32) magnetically separable. The effects of the photocatalyst concentration and recyclability on the photodegradation of TC were studied under similar conditions. We found that the Fe₃O₄@TMU-32 composite is easily recycled without a significant loss of photocatalytic activity after being used several times, indicating the stability of the photocatalyst. Finally, a density functional theory study was also conducted to investigate the structural and electronic properties such as the band gap energy and density of states of the TMU-32 MOF and the Fe₃O₄@TMU-32 composite. Our computational results are in good agreement with the experimental ones. A photocatalytic degradation mechanism was finally proposed under visible-light photoirradiation.

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

We have developed a cerium-photocatalyzed aerobic oxidation of primary and secondary benzylic alcohols to aldehydes and ketones using inexpensive CeCl₃·7H₂O as photocatalyst and air oxygen as the terminal oxidant.

Light-driven transformation of biomass into chemicals using photocatalysts - Vistas and challenges

Lignocellulosic biomass has become an important sustainable resource for fuels, chemicals and energy. It is an attractive source for alternative fuels and green chemicals because it is non-edible and widely available in the planet in huge volumes. The use of biomass as starting material to produce fuels and chemicals leads to closed carbon cycle and promotes circular economy. Although there are many thermo-chemical methods such as pyrolysis, liquefaction and gasification close at hand for processing lignocellulosic biomass and transforming the derived compounds into valuable chemicals and fuels, the photocatalytic method is more advantageous as it utilizes light and ambient conditions for reforming the said compounds. Appraisal of recent literature indicates a variety of photocatalytic systems involving different catalysts, reactors and conditions studied for this purpose. This article reviews the recent developments on the photocatalytic oxidation of biomass and its derivatives into value-added chemicals. The nature of the biomass and derived molecules, nature of the photocatalysts, efficiency of the photocatalysts in terms of conversion and selectivity, influence of reaction conditions and light sources, effect of additives and mechanistic pathways are discussed. Importance has been given also to discuss the complementary technologies that could be coupled with photocatalysis for better conversion of biomass and biomass-derived molecules to value-added chemicals. A summary of these aspects, conclusions and future prospects are given in the end.

Nb2O5-Based Photocatalysts

Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is eco-friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Brønsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5-based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5-based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.

Multiple Roles of Unconventional Heteroatom Dopants in Chalcogenide Thermoelectrics: The Influence of Nb on Transport and Defects in Bi2Te3

Improvements in the thermoelectric performance of n-type Bi₂Te₃ materials to more closely match their p-type counterparts are critical to promote the continued development of bismuth telluride thermoelectric devices. Here the unconventional heteroatom dopant, niobium, has been employed as a donor in Bi₂Te₃. Nb substitutes for Bi in the rhombohedral Bi₂Te₃ structure and exhibits multiple roles in its modulation of electrical transport and defect-induced phonon scattering. The carrier concentration is significantly increased as electrons are afforded by aliovalent doping and formation of vacancies on the Te sites. In addition, incorporation of Nb in the pseudoternary Bi_2-xNb_xTe_3-δ system increases the effective mass, m*, which is consistent with cases of "conventional" elemental doping in Bi₂Te₃. Lastly, inclusion of Nb induces both point and extended defects (tellurium vacancies and dislocations, respectively), enhancing phonon scattering and reducing the thermal conductivity. As a result, an optimum zT of 0.94 was achieved in n-type Bi_0.92Nb_0.08Te₃ at 505 K, which is dramatically higher than an equivalent undoped Bi₂Te₃ sample. This study suggests not only that is Nb an exciting and novel electron dopant for the Bi₂Te₃ system but also that unconventional dopants might be utilized with similar effects in other chalcogenide thermoelectrics.

Metal–organic framework/carbon nitride nanosheets composites (TMU-49/CNNSs): efficient photocatalyst for aerobic oxidation of alcohols under visible light

The TMU-49/CNNSs composite was used as a photocatalyst for oxidation of alcohols.

An overview on recent development in visible light-mediated organic synthesis over heterogeneous photo-nanocatalysts

The implementation of heterogeneous photo-nanocatalysts in organic syntheses has been investigated greatly in the last decade as a result of the increasing demand to achieve the organic reactions via the use of green approaches and through the availability of visible light source. Herein, the presented results describe the basic concepts and state-of-the-art of fundamental insight into key features that influence the catalytic performance in organic reactions to investigate and optimize a broad range of catalyzed organic transformations, that benefit the researchers in academia and chemical industry fields.

Facile Synthesis of BiVO4 for Visible-Light-Induced C-C Bond Cleavage of Alkenes to Generate Carbonyls

BiVO₄ crystals synthesized by an ultrasonic-assisted method (Sono-BiVO₄ ) showed improved efficiency as a heterogeneous photocatalyst under visible-light irradiation. Sono-BiVO₄ was successfully used for the C-C bond cleavage of alkenes to generate carbonyl compounds. Styrene derivatives were converted into carbonyl compounds in the presence of Sono-BiVO₄ under highly sustainable conditions requiring only natural sources, that is, molecular oxygen, visible light, and water at room temperature. Additionally, Sono-BiVO₄ could be easily separated from the reaction mixture and reused.

A Photo-Enzymatic Cascade to Transform Racemic Alcohols into Enantiomerically Pure Amines

The consecutive photooxidation and reductive amination of various alcohols in a cascade reaction were realized by the combination of a photocatalyst and several enzymes. Whereas the photocatalyst (sodium anthraquinone-2-sulfonate) mediated the light-driven, aerobic oxidation of primary and secondary alcohols, the enzymes (various ω-transaminases) catalyzed the enantio-specific reductive amination of the intermediate aldehydes and ketones. The system worked in a one-pot one-step fashion, whereas the productivity was significantly improved by switching to a one-pot two-step procedure. A wide range of aliphatic and aromatic compounds was transformed into the enantiomerically pure corresponding amines via the photo-enzymatic cascade.

A hierarchical Nb2O5@NiFe-MMO rod array, fabricated and used as a structured photocatalyst

Recently, using sunlight as a driving force with transitional metal oxides as photocatalysts, due to their unique optical and catalytic properties for organic reactions, has been considered to be a promising strategy in synthetic chemistry. Here, a hierarchically structured photocatalyst, a NiFe mixed metal oxide coated Nb2O5 (denoted as Nb2O5@NiFe-MMO) rod array has been successfully fabricated using Nb foil as a substrate. The Nb2O5 rod array was synthesized by the oxidative etching of Nb metal on the surface of the a substrate. The coating NiFe-MMO was obtained by the calcination of a NiFe layered double hydroxide (NiFe-LDH) precursor via the in situ epitaxial growing technique. The Nb2O5@NiFe-MMO rod array extended the photoresponse light region from ultraviolet light around 400 nm to visible light around 600 nm. With the well-designed architecture and highly dispersed NiO and Fe2O3, the as-prepared photocatalyst exhibited excellent activity and recyclability toward the reaction of aerobic coupling under relatively green conditions, with catalytic efficiency of 228 μmol cm-2 (the area is that of the Ni foil substrate) at 30 °C for 5 h. The present work provides a new strategy for the exploration of excellent structured photocatalysts based on transition metal oxide materials for selective aerobic oxidation of benzylamine to imine.

Morphology-maintaining synthesis of NbN and its catalytic performance in epoxidation

A strategy for the synthesis of NbN with different morphologies was provided and the reactivity for epoxidation was investigated.

Application of metal oxide semiconductors in light-driven organic transformations

Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

NaYF4:Yb,Tm@TiO2 core@shell structures for optimal photocatalytic degradation of ciprofloxacin in the aquatic environment

The removal of antibiotic residues in the aquatic environment is still a big challenge in environmental protection. Here, we developed NaYF₄:Yb,Tm@TiO₂ as a highly efficient photocatalyst for photocatalytic degradation of ciprofloxacin (CIP), a representative antibiotic in water under simulated solar irradiation. NaYF₄:Yb,Tm@TiO₂ can efficiently utilize a broad spectrum of solar energy to improve the efficiency of ciprofloxacin removal from an aquatic environment. The optimum operation conditions of photocatalyst dosage, pH value, and initial concentrations of CIP were determined by a series of contrast experiments. The dynamic process of CIP removal was monitored by UV-vis spectrophotometry, and can be well predicted by a pseudo first order model. The optimal conditions of photocatalyst dosage, initial concentration of CIP and pH value for CIP photocatalytic degradation were 1 g L⁻¹, 10⁻⁵ M and 8, respectively. This study provides an efficient method for antibiotic removal and enables a promising strategy for other organic water pollutant treatments.

The study indicated the optimum operation conditions to effectively remove ciprofloxacin from aquatic environment by NaYF₄:Yb,Tm@TiO₂ structures.

WS2 and C-TiO2 Nanorods Acting as Effective Charge Separators on g-C3 N4 to Boost Visible-Light Activated Hydrogen Production from Seawater

Semiconductor photocatalysis is regarded as an ideal method for use in solving the energy shortage and environmental issues by converting solar energy to chemical energy. Herein, we have designed a facile synthetic methodology to obtain a ternary co-modified g-C₃ N₄ composite via WS₂ and carbon-doped TiO₂ (C-TiO₂ ) nanorods with highly efficient photocatalytic activity for hydrogen production from deionized (DI) water and a natural seawater system under visible-light illumination. This composite exhibits enhanced photocatalytic activity compared to the pristine g-C₃ N₄ , WS₂ , C-TiO₂ nanorods, and the reference-modified g-C₃ N₄ composite with individual WS₂ or C-TiO₂ nanorods. Co-modified g-C₃ N₄ composite shows a great photostability in both DI water and seawater. Under λ=420 nm monochromatic light illumination, the apparent quantum efficiency of the co-modified g-C₃ N₄ composite in seawater solution is 13.08 %, which is higher than pure g-C₃ N₄ (5.06 %). WS₂ , TiO₂ , and g-C₃ N₄ constitute a ternary heterojunction boosting the fast separation of photoinduced electron-hole pairs, which plays a crucial role in enhancing photocatalytic activity. Therefore, the WS₂ and C-TiO₂ nanorod co-modified g-C₃ N₄ composite with high photocatalytic performance provides a promising candidate for rationally utilizing the seawater resource to produce clean chemical energy.

Optimization of Malachite Green Removal from Water by TiO₂ Nanoparticles under UV Irradiation

TiO₂ nanoparticles with surface porosity were prepared by a simple and efficient method and presented for the removal of malachite green (MG), a representative organic pollutant, from aqueous solution. Photocatalytic degradation experiments were systematically conducted to investigate the influence of TiO₂ dosage, pH value, and initial concentrations of MG. The kinetics of the reaction were monitored via UV spectroscopy and the kinetic process can be well predicted by the pseudo first-order model. The rate constants of the reaction kinetics were found to decrease as the initial MG concentration increased; increased via elevated pH value at a certain amount of TiO₂ dosage. The maximum efficiency of photocatalytic degradation was obtained when the TiO₂ dosage, pH value and initial concentrations of MG were 0.6 g/L, 8 and 10⁻⁵ mol/L (M), respectively. Results from this study provide a novel optimization and an efficient strategy for water pollutant treatment.

Synthesis of novel sonocatalyst Er3+:YAlO3/Nb2O5 and its application for sonocatalytic degradation of methamphetamine hydrochloride

The composited sonocatalyst Er³⁺:YAlO₃/Nb₂O₅ was prepared by ultrasonic dispersion and high temperature calcinations method. The microstructure of Er³⁺:YAlO₃ was prepared via sol-gel method and Nb₂O₅ was prepared by hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), ultraviolet-visible (UV-vis) spectra and photoluminescence (PL) spectra, respectively. The sonocatalytic decomposition activity of composite sonocatalyst Er³⁺:YAlO₃/Nb₂O₅ was investigated by using ultrasound as sound source and methamphetamine hydrochloride as the target degradation product. The influences of composite sonocatalyst Er³⁺:YAlO₃/Nb₂O₅ with different ratios, calcination temperature, ultrasonic power, ultrasonic temperature and recycle times were investigated. The results showed that the sonocatalytic degradation rate was 82.17% after 5 h sonocatalytic decomposition under the condition of ultrasonic power of 700 W, frequency of 45 kHz and surrounding temperature of 30 °C. The sonocatalytic degradation ability of composite sonocatalyst for methamphetamine hydrochloride in aqueous solution was still good after recycled five times. The hydroxyl radicals (OH) and holes (h⁺) are identified and hydroxyl radicals (OH) plays a major role during the oxidation process. The experimental results show that sonocatalytic is a new idea for the harmless treatment of amphetamine-type stimulants.

NGQD active sites as effective collectors of charge carriers for improving the photocatalytic performance of Z-scheme g-C3N4/Bi2WO6 heterojunctions

NGQDs as effective active sites and collectors of charge carriers in Z-scheme g-C₃N₄/Bi₂WO₆ heterojunctions.

In situ formation of NbOx@NbN microcomposites: seeking potential in photocatalytic and Li-ion battery applications

A NbO_x@NbN microcomposite formed by in situ partial thermal oxidation is revealed to be potentially advantageous in photocatalytic hydrogen production and lithium-ion storage.

Visible-light-induced photocatalytic benzene/cyclohexane cross-coupling utilizing a ligand-to-metal charge transfer benzene complex adsorbed on titanium oxides

High selectivity was achieved in the photocatalytic cross-coupling of benzene and cyclohexane by photoexcitation of a surface benzene complex.

Intermediate selectivity in the oxidation of phenols using plasmonic Au/ZnO photocatalysts

Tunable reaction selectivity on a single catalyst is a continual goal in chemical syntheses. Herein, we report an unexpected light-directed intermediate selectivity using well-known plasmonic photocatalysts. We observed distinct intermediate selectivity behaviors between using UV and visible light irradiations. Chemical computations and quenching experiments suggest that the radicals generated by the plasmonic excitation govern the light-directed selectivity. The broader impact of this work ranges from selective yield of desirable intermediates for subsequent syntheses without tedious separation procedures, to arousing interest in examining new opportunities for plasmonic photocatalysts.

A green and efficient photo-driven route for the selective oxidation of aqueous isopropanol solution to pinacol (C6) with hydrogen peroxide

The proposed strategy provides a green solution for the synthesis of aliphatic pinacol and offers a new design for the construction of C–C bonds with alphatic alcohol.