Photocatalytic Oxidation Of Benzyl Alcohol Research Articles

TiO2 supported-reduced graphene oxide co-doped with gallium and sulfur as an efficient heterogeneous catalyst for the selective photochemical oxidation of alcohols; DFT and mechanism insights

Achieving organic transformation reactions using green synthesis methods under mild conditions is always an aspiration of scientists. In this study, Ga, S co-doped TiO2/reduced graphene oxide (GaxSy@TRG) nanocomposite was synthesized by an innovative surfactant-free ultrasonic-assisted solvothermal method and used to catalyze the selective photocatalytic oxidation of benzyl alcohol under visible light irradiation. The prepared photocatalyst was analyzed via XRD, FT-IR, Raman, N2 adsorption–desorption, SEM, TEM, EDX, ICP-MS, UV–Vis absorption, and electrochemical impedance spectroscopy (EIS) measurement. The characterization outcomes indicated the prepared co-doped TiO2 nanoparticles with anatase crystal structure possessed a mesoporous texture and were uniformly distributed on the RGO surface. The conversion of GO to RGO was confirmed through FT-IR and Raman spectra. The prepared nanocomposites were examined for their ability in artificial photocatalysis and displayed remarkable catalytic activity for the selective oxidation of alcohols into benzaldehyde. The co-doped catalysts showed significantly enhanced photocatalytic ability, due to improved photogenerated electrons transfer, enhanced charge carriers separation and extended optical absorption to the visible light range. Moreover, the synergistic effect of dopants that could act as electron trapping centers and RGO as a powerful acceptor material efficiently reduced photogenerated electron-hole recombination and promoted charge migration. A high conversion rate of 85% was obtained over the Ga5.0S10.0@TRG photocatalyst after 110 min under visible light irradiation. The results from density functional theory (DFT) calculations revealed that the hybridization of Ga 4s and S 3p orbitals with valance band can remarkably affect the decreasing of band gap energy. The mechanism of photocatalytic oxidation of benzyl alcohol under visible light irradiation was proposed using the combination of experimental and computational methods.

High-loading single-atom Pt/TiO2 mesoporous catalysts for superior photocatalytic oxidation of benzyl alcohol

Photocatalysis utilized solar energy with metal oxide semiconductors has been considered as one of the attractive green routes for organics’ conversion. The construction of high-density co-catalytic sites is essential for the surface reaction kinetics. In this work, a high-efficiency mesoporous TiO2 decorated with single atomic Pt loading of 1 at% (2.1 wt%) had been successfully achieved. The high specific surface area of mesoporous TiO2 affords adequate physical surface for the resident of atomic Pt, thus stabilizing a high areal density of single-atom reaction sites. The optimized single-atom Pt/TiO2 revealed a performance of 4.1 mmol/h/gcat for photocatalytic oxidation of benzyl alcohol under visible light irradiation that is 3.8 folds than that of Pt-modified commercial TiO2 photocatalysts. The reactivity will further enhance after the introduction of plasmonic Au nanoparticles and the finally sample (1 at% Pt-0.075 at% Au)/TiO2-MP exhibited salient activity (4.5 mmol/h/gcat) and stability. This work paves a potential way to boost the performance of metal oxide semiconductors for green photocatalytic conversion of organics.

Highly crystalline lead-free Cs3Sb2Br9 perovskite microcrystals enable efficient and selective photocatalytic oxidation of benzyl alcohol

Selective oxidation of alcohols to the corresponding aldehydes constitutes a great challenge in organic and green chemistry, which typically requires environmentally unfriendly oxidants/catalysts or relatively harsh conditions (high temperature & pressure). Herein, we report an eco-friendly perovskite-based photocatalyst, in which all-inorganic perovskite Cs3Sb2Br9 microcrystals with high crystallinity were prepared using a facile antisolvent method at various temperatures. For the photocatalytic oxidation of benzyl alcohol, the Cs3Sb2Br9 microcrystal photocatalysts exhibited up to 77% conversion and 88% selectivity toward benzaldehyde under oxygen atmosphere and visible-light illumination. More significantly, the comparative experimental results in air were close to those in oxygen, with the observation of 96% conversion and 94% selectivity for the optimized conditions under air atmosphere. Notably, the conversion of our best-performing photocatalyst was 32 and 6.4 times higher than that of the lead-based CsPbBr3 and FAPbBr3 (FA: formamidinium) perovskites, respectively. Furthermore, the underlying photocatalytic oxidation mechanism was proposed by the electron spin resonance (ESR) and the controlled experiments using specific scavengers. This study sheds light on promising new photocatalytic applications of the lead-free metal halide perovskites.

Copper Sulfide Nanosheets for Photocatalytic Oxidation of Benzyl Alcohols and Hydroxylation of Arylboronic Acids

Copper Sulfide Nanosheets for Photocatalytic Oxidation of Benzyl Alcohols and Hydroxylation of Arylboronic Acids

Improved efficiency of photo-induced synthetic reactions enabled by advanced photo flow technologies.

In this article, we discuss how effective photo-induced organic reactions became when applied evolving photo flow technologies through our experiences over these two last decades. We started with the flow update of traditional [2 + 2] cycloaddition using Mikroglas Dwell device as a flow reactor and a compact light source, such as blacklight, instead of a high-pressure mercury lamp. Then we examined Barton nitrite reaction using a photo flow reactor consisting of stainless-steel channels and a quartz glass top provided by DNS. Again the use of blacklight was successful. However, the energy profile of these reactions was improved further by the use of LED lights. We used a photo-flow set-up, consisting of stainless steel engraved microchannels covered by a quartz top (MiChS L-1) and a sodium lamp, for the isomerization of a fulleroid to PCBM. Photo-redox-catalyzed alkene alkylation proceeded within a shortened reaction time when the same photo flow reactor and white LED were used instead of a batch reactor. Photo-induced reductive 5-exo-dig radical cyclization and reduction of alkenyl halides proceeded smoothly, thanks to the combination of a photo flow reactor and low-pressure Hg lamp. We also applied flow technologies for photo-bromination and chlorination of C-H bonds. Photocatalytic oxidation of benzyl alcohol by molecular oxygen became quick when high-power LED irradiation was employed.

Steric effects of a homogeneous CuCl2/solvent system for photocatalytic selective oxidation of benzyl alcohol

Sterically hindered solvents change the production and selectivity of benzaldehyde in photocatalytic oxidation of benzyl alcohol by homogeneous CuCl2/solvent.

Visible-Light Responsive Cu–MOF–NH2 for Highly Efficient Aerobic Photocatalytic Oxidation of Benzyl Alcohol

Visible-Light Responsive Cu–MOF–NH2 for Highly Efficient Aerobic Photocatalytic Oxidation of Benzyl Alcohol

Highly metallic Co-doped MoS2 nanosheets as an efficient cocatalyst to boost photoredox dual reaction for H2 production and benzyl alcohol oxidation

Developing appropriate cocatalyst to couple with photocatalyst is a promising strategy to simultaneously realize efficient benzyl alcohol oxidation to aldehydes and water reduction to H2. Herein, two-dimensional (2D) Co-doped MoS2 nanosheets with an edge-enriched 1T phase were uniformly embedded onto 2D g-C3N4 (CN) nanosheets to fabricate a 2D/2D Co-doped MoS2/CN nano-junction, wherein the Co-doped MoS2, acting as a cocatalyst, can induce fast charge transfer and realize synchronously utilization of photo-electrons and photo-holes. The optimal Co-doped MoS2/CN nano-junction presented a high photocatalytic oxidation of benzyl alcohol with benzaldehyde generation rate of 0.48 mmol g−1 h−1 and photocatalytic reduction of water with H2 generation of 0.31 mmol g−1 h−1. This greatly enhanced photocatalytic performance is attributed to the fact that the Co-doped MoS2, with an edge-enriched 1T phase as the cocatalyst, presented higher metallic characteristics, lower H∗ adsorption, and more active sites than the pure MoS2 cocatalyst. Additionally, the Co-doped MoS2 cocatalyst and CN nanosheets formed a 2D/2D ohmic-junction with a chemical linkage (N–Mo–S–Co), providing a rapid charge transfer channel to accelerate charge transfer. This work replenishes a train of thought for the design of novel cocatalysts as a bridge for enhancing the H2 production and value chemical production.

Selective and efficient aerobic oxidation of benzyl alcohols using plasmonic Au-TiO2: Influence of phase transformation on photocatalytic activity

Chemical processes using heterogeneous photocatalytic systems are widely used for the synthesis of valuable fine chemicals. To improve these chemical processes both environmental and energy aspects must be kept in mind for favorable reaction conditions, such as optimum temperature and atmospheric pressure. In this study, plasmonic Au nanoparticles (Au NP) dispersed over TiO2 photocatalyst with different phases of TiO2 (amorphous, anatase and rutile) have been synthesized by using a facile sol–gel method followed by calcination for the photocatalytic oxidation of benzyl alcohol (BnOH) to benzaldehyde (BzH) under visible light irradiation at ambient conditions. The best photocatalyst exhibits high surface area and excellent catalytic conversion efficiency (96%) for the oxidation of BnOH to BzH in less reaction time using a green solvent, acetonitrile at room temperature. The detailed optimization of reaction parameters was performed for alcohol conversion. In addition the corresponding green metrics parameters were also calculated. The photocatalyst also shows excellent stability and reusability for multiple cycles. This work suggests that the Au-TiO2 catalyst provides a novel green and sustainable approach for the selective and efficient aerobic oxidation of BnOH to BzH under visible light irradiation. Furthermore, the impact of different phases of TiO2 on the photocatalytic activity has also been discussed.

Selective Production of Secondary Amine by the Photocatalytic Cascade Reaction Between Nitrobenzene and Benzyl Alcohol over Nanostructured Bi2 MoO6 and Pd Nanoparticles Decorated with Bi2 MoO6.

The synthesis of secondary amine by the photoalkylation of nitrobenzene with benzyl alcohol using a simple light source and sunlight is a challenging task. Herein, a one-pot cascade protocol is employed to synthesize secondary amine by the reaction between nitrobenzene and benzyl alcohol. The one-pot cascade protocol involves four reactions: (a) photocatalytic reduction of nitrobenzene to aniline, (b) photocatalytic oxidation of benzyl alcohol to benzaldehyde, (c) reaction between aniline and benzaldehyde to form imine, and (d) photocatalytic reduction of imine to a secondary amine. The cascade protocol to synthesize secondary amine is accomplished using Bi2 MoO6 and Pd nanoparticles decorated Bi2 MoO6 catalysts. The surface characteristics, oxidation states, and elemental compositions of the materials are characterized by several physicochemical characterization techniques. Optoelectronic and photoelectrochemical measurements are carried out to determine the bandgap, band edge potentials, photocurrents, charge carrier's separation, etc. An excellent yield of secondary amine is achieved with simple household white LED bulbs. The catalyst also exhibits similar or even better activity in sunlight. The structure-activity relationship is established using catalytic activity data, control reactions, physicochemical, optoelectronic characteristics, and scavenging studies. Bi2 MoO6 and Pd nanoparticles decorated Bi2 MoO6 exhibit excellent photostability and recyclability. The simple catalyst design with a sustainable and economical light source for the synthesis of useful secondary amine from the nitrobenzene and benzyl alcohol would attract the researchers to develop similar catalytic protocols for other industrially important chemicals.

Planar heterojunction boosts solar-driven photocatalytic performance and stability of halide perovskite solar photocatalyst cell

The excellent optoelectronic properties of metal halide perovskites (MHPs) have been employed in various photocatalytic applications, but their poor water stability is considered as the main bottleneck for further development. Herein, we protect the light-absorbing CsPbBr3 MHP with a NiOx and TiO2 hole and electron extracting layer. This planar NiOx/CsPbBr3/TiO2 architecture can easily be fabricated through solution-processing. When applied to selective photocatalytic oxidation of benzyl alcohol, this system presents a 7-fold enhancement of photoactivity and an improved stability for over 90 h compared to CsPbBr3 counterpart. Interestingly, we find that trace amounts of water improve photoactivity. Through experimental and theoretical analyses, this improvement could be attributed to water-induced structural reorganization of MHP, leading to improved crystal quality and decreased effective masses of charge carriers. This work indicates planar heterojunction helps improve the photoactivity and stability of MHP photocatalyst, and our findings provide insights into the effect of water on MHPs.

Selective oxidation of benzyl alcohol using a Ni(OH)2-modified CdS-MoS2 composite photocatalyst under ambient conditions

The selective photocatalytic oxidation of alcohols to aldehydes is difficult to accomplish in pure water, which is a substantial obstacle for the practical application of the photocatalytic synthesis of aldehydes. In this work, a composite photocatalyst was constructed by assembling Ni(OH)2 on a CdS-MoS2 heterostructure, which allowed for the effective photocatalytic oxidation of benzyl alcohol to benzaldehyde by photogenerated holes in anaerobic pure water. The conversion of benzyl alcohol was increased from 18.9% to 94.2%. Ni(OH)2 loaded on CdS-MoS2 could serve as a hole-transport layer, enhancing the transport of holes to the catalytic surface to achieve more efficient benzyl alcohol oxidation. A part of Ni2+ was reduced to Ni0 by a small amount of photoinduced electrons. Both Ni2+ and Ni0 adsorbed the α-H of benzyl alcohol, which was the dehydrogenation unit, thus providing more active sites for the conversion of benzyl alcohol to benzaldehyde. The self-reduction of Ni2+ on the surface may be reduced to Ni0 and it may protect the inner Ni2+ from self-reduction due to the fast electron transfer and electron active site, which benefited the photocatalytic stability of the Ni(OH)2-modified CdS-MoS2 heterostructures. The synergistic effect of Ni(OH)2 and metallic Ni significantly improved the photocatalytic oxidation properties.

Nanostructure Shape-Effects in ZnO heterogeneous photocatalysis

Selective oxidation of alcohols is an essential reaction for fine chemical production. Here, the photocatalytic oxidation of benzyl alcohol by zinc oxide (ZnO) nanocrystals was investigated to clarify the mechanism of selective oxidation with this process. Reactivity when in contact with three distinct ZnO nanocrystal shapes: nanocones, nanorods and nanoplates, was studied in order to compare crystal facet-specific effects in the reaction system. The same non-hydrothermal and non-hydrolytic aminolysis method was used to synthesise all three nanocrystal shapes. The ZnO catalysts were characterized using by a range of techniques to establish the key properties of the prominent ZnO crystal facets exposed to the reaction medium. The ZnO nanocrystals photocatalysed the benzyl alcohol oxidation reaction when irradiated by a 370 – 375 nm LED output and each ZnO crystal morphology exhibited different reaction kinetics for the oxidation reaction. ZnO nanocones displayed the highest benzyl alcohol conversion rate while nanorods gave the lowest. This established a facet-dependent kinetic activity for the benzyl alcohol reaction of (101¯1) > (0001) > (101¯0). Experimental and density functional theory computation results confirm that the {101¯1} facet is a surface that exposes undercoordinated O atoms to the reaction medium, which explains why the reactant benzyl alcohol adsorption on this facet is the highest. Light irradiation can excite valence band electrons to the conduction band, which are then captured by O2 molecules to yield superoxide (O2•–). In a non-aqueous solvent, the photogenerated holes oxidise benzyl alcohol to form a radical species, which reacts with O2•– to yield benzaldehyde. This results in 100% product selectivity for benzaldehyde, rather than the carboxylic acid derivative.

Enhancement of photocatalytic oxidation of benzyl alcohol by edge-functionalized modified carbon nitride: A DFT evaluation

New dye functionalized polymeric carbon nitrides with increased visible light response were designed and fabricated. In this research, Rose Bengal (RB) was immobilized on g-C3N4 (CN) and carboxylated g-C3N4 (CCN) through the formation of a covalent bond. The covalent bonding of Rose Bengal to the CN or CCN resulted in the transfer of electrons from the dye to the semiconductor and the enhancement of the light harvesting performance, which promoted the photocatalytic efficiency. The photocatalytic activity of CN, CCN, and their hybrids with RB toward selective oxidation of benzyl alcohol was investigated under the visible light irradiation. The results obtained from the GC–MS analyses related to the oxidation reaction displayed the highest percentage of benzyl alcohol conversion and benzaldehyde selectivity for the hybrid structures compared to the bare RB, CN, CCN, or a mixture of RB and CN (or CCN). The effect of several parameters, including the amount of photocatalyst and promoter, irradiation time, and photocatalyst type, was studied and optimized. The recovery of RB-CCN (the most active catalyst) was surveyed in five runs, and the results verify that the activity is mostly maintained. Finally, the optimized structure, energy gap, and frontier orbitals of Rose Bengal/graphitic carbon nitride were investigated by DFT methods.

Photocatalytic oxidation of benzyl alcohol and the photoelectrochemical water splitting of visible light-activated TiO2 nanostructures prepared by one-step titanium anodization

Doped TiO2 nanostructures have been prepared by one-step anodization of titanium in an ethylene glycol-based electrolyte with different concentrations of potassium hexacyanocobaltate and their catalytic activity in photocatalytic oxidation of benzyl alcohol to benzaldehyde, and photoelectrochemical water splitting under visible light has been investigated in this work. Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and UV–visible techniques have been used to determine the effect of the concentration of the doping agent on the morphology, structure and optical properties of doped TiO2 thin films. Doped TiO2 nanostructures show significant morphological differences in comparison with commercial bare TiO2 nanotube samples, based on SEM analysis. Different electrochemical methods have been used to study the effect of the concentration of the doping agents on the photoelectrocatalytic activity of the samples. The as-anodized doped TiO2 electrodes were observed to show higher photocatalytic activity compared with the bare TiO2 due to the high absorption of visible light and reduction in the recombination of photogenerated charges. Very high surface area, good photocatalytic performance, moderate conversion (about 42%) and high selectivity ( > 99%) for oxidation of benzyl alcohol to benzaldehyde at ambient temperature under visible light illumination in acetonitrile solvent were shown by the doped TiO2 nanoporous sample anodized in electrolyte containing 0.015 M potassium hexacyanocobaltate (sample CT15). Finally, the photoelectrochemical water splitting efficiency of the samples prepared has also been investigated.

TiO2/Ti3C2 as an efficient photocatalyst for selective oxidation of benzyl alcohol to benzaldehyde

Photocatalytic selective oxidation of alcohols into corresponding aldehydes has received enormous attention. However, it remains a great challenge to explore photocatalysts with high conversion efficiency and selectivity. Herein, we developed a composite consisted of TiO2 and Ti3C2 through a simple calcination of Ti3C2 nanosheets. It was found that Ti3C2 could stabilize the oxygen vacancies and Ti3+ species in the TiO2/Ti3C2 composite, which could subsequent promote the production of active intermediates during the photocatalytic oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Additionally, the valence band of TiO2 in the composites was found to be up-shifted, which would avoid the further oxidation of BAD and enhance selectivity. As a result, the optimal composite exhibits the BA conversion efficiency of 97 % and BAD selectivity of 98 %, which is 2.8 and 1.2 folds higher than that of pristine TiO2. Our work may provide insights for designing efficient photocatalysts for selective oxidation of alcohols.

Phosphorization-derived MoP@MoO3-x nanowires for selective photocatalytic oxidation of benzyl alcohol to benzaldehyde

The selective oxidation of small molecules to high-value-added products is regarded as a promising approach to alleviating the worldwide energy crisis. In this work, heterogenous non-noble-metal molybdenum(III) phosphide (MoP) catalysts were anchored onto MoO3−x nanowires (MoP@MoO3−x) via a facile phosphorization method using various amounts of phosphorus precursor. Because of the combined attributes of the MoP and the MoO3−x nanowires, the novel MoP@MoO3−x nanowire catalysts not only provide more active sites but also enhance electron–hole separation efficiency. The results show that the selective transformation of benzyl alcohol to benzaldehyde was achieved with 67% selectivity. A comprehensive study including field-emission transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller analysis, X-ray diffraction analysis, UV–vis diffuse reflectance spectrum, electron-spin resonance, photocurrent measurements, electrochemical impedance spectroscopy, and density functional theory (DFT) computations was conducted. The selective photocatalytic oxidation results and the DFT calculations indicate that the MoP particles anchored onto the MoO3−x substrate display an important role in enhancing the selective photocatalytic oxidation of benzyl alcohol.

Gold nanoparticle supported on mesoporous vanadium oxide for photo-oxidation of 2-naphthol with hydrogen peroxide and aerobic oxidation of benzyl alcohols

Vanadium oxide supported gold nanocatalysts designated as AuVOx was found to be highly efficient for photocatalytic oxidation of benzyl alcohol and 2-naphthol. The photocatalytic ability of the AuVOx catalyst towards the selective oxidation of 2-naphthol to BINOL was found to be dependent on the nature of the support. The selectivity of the reaction was found to be significantly altered on hybridization with multi-walled carbon nanotubes (AuVOx-MWCNTs). The well-resolved surface plasmon resonance (SPR) band originated from the gold nanoparticles (Au-NPs) on the vanadium oxides support helped in stimulating the photo-oxidation of benzyl alcohol to benzaldehyde and 2-naphthol to BINOL with almost 100% selectivity. The most notable achievement using the AuVOx and AuVOx-MWCNTs catalyst was in the successful photo-oxidation of 2-naphthol to BINOL in presence of hydrogen peroxide (H2O2). The photo-activity of the material and the creation of oxygen defect sites participated in the photochemical processes were estimated from photoluminescence analysis and ESR study. The photochemical reaction was supposed to proceed via superoxide radical generation favored by the oxygen defect sites.

Boosting multiple photo-assisted and temperature controlled reactions with a single redox-switchable catalyst: Solvents as internal substrates and reducing agent

An alternative and economically viable process for the synthesis of β-aryl enals, enones and the aryl amines has been developed by partial oxidation of ethanol, isopropanol and N, N-dimethyl formamide (DMF). The formation of β-aryl enals, enones and the aryl amines was catalyzed by a mixed metal oxides layer of cobalt and chromium supported on halloysite nanotubes, designated as CoCr2O4-HNT. The CC and CN bond formation reactions were found to be influenced by temperature and the nature of base. The condensation of aldehyde with in situ generated acetaldehyde by ethanol oxidation forming β-aryl enals occurred selectively at 120 °C. The partial oxidation of isopropanol to acetone and its condensation with aldehydes forming β-aryl enones occurred at room temperature. Increase in temperature caused the liberation of hydrogen gas from isopropanol and allowed the reversible reduction of aldehydes to alcohols. Increase in temperature in isopropanol and increase in base concentration in ethanol causes the selective reduction of aldehydes to alcohols. Besides being active for the Claisen-Schmidt type of reactions and the aryl halides amination process, the synthesized catalyst was also found to be highly active for the photocatalytic oxidation of benzyl alcohols in absence of any external oxidizing agent. The positive holes (h+) generated at the Co(II) site as evident from EPR analysis was considered to be responsible for high photocatalytic activity of the material reducing the recombination rate of holes and electrons (e−). Density Functional Theory calculations were performed to understand the mechanism of ethanol oxidation to acetaldehyde.

Selective Photocatalytic Oxidation of Benzyl Alcohol at Ambient Conditions using Spray-Dried g-C3N4/TiO2 Granules

In the 2010-decade, significant progresses have been made in the photocatalytic properties of graphitic-carbon nitride (g-C3N4). In this study, we synthesized and characterized a new photocatalyst, spray-dried g-C3N4/TiO2 granules, through a simple pyrolysis process of urea and TiCl4 as the precursors. The photocatalytic oxidation of benzyl alcohol (BA) to benzaldehyde (BAL) was carried out in a batch reactor in the presence of pure g-C3N4, g-C3N4/TiO2, and spray-dried g-C3N4/TiO2 granules at ambient pressure and under visible light irradiation at different conditions, including reaction time, temperature, and catalyst loading. The results showed that the new photocatalyst, spray-dried g-C3N4/TiO2 granules (TCNg), is much more effective on the photocatalytic oxidation of benzyl alcohol and also possesses high atom efficiency, high yield, and an average turnover frequency (TOF) of over 550 h-1. Finally, the DFTB + method was used to investigate the frontier orbitals and to determine the band gap of TiO2, g-C3N4, and g-C3N4/TiO2.