Catalytic Activity Of Composite Research Articles

Encapsulating Halide Perovskite Quantum Dots in Metal–Organic Frameworks for Efficient Photocatalytic CO2 Reduction

Halide perovskite has shown great potential in photocatalysis owing to its diversity, suitable energy band alignment, rapid charge transfer, and excellent optical properties. However, poor stability, especially under humid conditions, hinders their practical application in photocatalysis. In this work, we report the encapsulation of inorganic–organic hybrid perovskite QDs into MIL-101(Cr) through an in situ growth strategy to prepare a series of MAPbBr3@MIL-101(Cr) (MA = CH3NH3+) composites. The perovskite precursors, i.e., MABr and PbBr2, were successively introduced into the pores of MOF, where the perovskite quantum dots were self-assembled in the confined environment. In photocatalytic CO2 reduction, 11%MAPbBr3@MIL-101(Cr) composite displayed the best performance among the composites with a total CO and CH4 yield of 875 μmol g−1 in 9 h, which was 8 times higher than that of the pure MAPbBr3. Such high gas production efficiency could be maintained for 78 h at least without structural and morphologic decomposition. The remarkable stability and catalytic activity of composites are mainly due to the synergistic effect and improved electron transfer between MAPbBr3 and MIL-101(Cr). Moreover, these composites revealed a novel mechanism, showing switched CH4 selectivity with the controlling of the perovskite location and contents. Those with perovskites encapsulated in the mesopores of MIL-101(Cr) were more preferential for CO production, while those with perovskites encapsulated in both meso- and micropores could produce CH4 dominantly.

New bidental sulfur-doped graphene quantum dots modified with gold as a catalyst for hydrogen generation

Disadvantages of fossil fuels encourage researchers to develop clean combustion sources, in particular, H2 due to the high potential energy and safe by-products. Herein, Au was deposited on S-doped graphene quantum dots to obtain a heterogeneous photocatalyst for the degradation of formic acid toward H2 generation. Insertion of thiol groups on graphene quantum dots was carried out by self-condensation reaction of citric acid in the presence of Dimaval, as the thiol groups carrier. After the complexation of Au with the prepared S-doped graphene quantum dots, the catalytic activity of composite was evaluated in formic acid degradation to generate H2 under visible light. Au@S-doped graphene quantum dots demonstrated superior catalytic activity with the turnover frequency up to 112 h−1. The reaction enjoys significant benefits such as stability and recyclability of the catalyst, excellent reaction rate, and mild reaction conditions.

Microcrystalline cellulose modified with Fe(II)– and Ni(II)–phthalocyanines: Syntheses, characterizations, and catalytic applications

Phthalocyanines of Fe(II) and Ni(II) were immobilized on microcrystalline cellulose (MCC) via chemical binding. MCC was obtained from cotton as a cheap and abundant source of cellulose. The new composites were characterized by FT-IR, Flame Absorption Atomic Spectroscopy, Brunauer–Emmett–Teller analysis, Energy Dispersive X-ray Spectroscopy, Scanning Electron Microscope, and Transmission Electron Microscope. The nanocomposites showed high surface areas due to use of MCC as the support in the syntheses procedures. The catalytic activities of composites were examined in the oxidations of alcohols, and ethylbenzene. The oxidation of alcohols to the corresponding aldehydes or ketones and ethylbenzene to acetophenone were carried out with high yields and excellent selectivities. The catalysts are recyclable for 6 times without any decrease in the oxidation reaction yield.

One-step synthesis of N-doped metal/biochar composite using NH3-ambiance pyrolysis for efficient degradation and mineralization of Methylene Blue

A series of new biochar-supported composite based on the combination of biochar and metallic nanoparticles (NPs) were produced through single-step pyrolysis of FeCl3–Ti(OBu)4 laden agar biomass under NH3 environment. The physiochemical properties of composites were characterized thoroughly. It has found that heating temperature and N-doping through NH3-ambiance pyrolysis significantly influence the visible-light sensitivity and bandgap energy of composites. The catalytic activities of composites were measured by degradation of Methylene Blue (MB) in the presence or absence of H2O2 and visible-light irradiation. Our best catalyst (N–TiO2–Fe3O4-biochar) exhibits rapid and high MB removal competency (99.99%) via synergism of adsorption, photodegradation, and Fenton-like reaction. Continuous production of O2− and OH radicles performs MB degradation and mineralization, confirmed by scavenging experiments and degradation product analysis. The local trap state Ti3+, Fe3O4, and N-carbon of the catalyst acted as active sites. It has suggested that the Ti3+ and N-doped dense carbon layer improve charge separation and shuttle that prolonged photo-Fenton like reaction. Moreover, the catalyst is highly stable, collectible, and recyclable up to 5 cycles with high MB degradation efficiency. This work provides a new insight into the synthesis of highly visible-light sensitized biochar-supported photocatalyst through NH3-ambiance pyrolysis of NPs-laden biomass.

Synthesis of bentonite-supported Fe(II) and heteropolyacid (HPW) composite through a mechanochemical processing

Abstract In this work, a mechanochemical synthesis process was introduced as a facile method for producing bentonite-supported Fe(II) and heteropolyacid (HPW) composite, a catalyst used for photo-Fenton reaction and conventionally produced only by liquid-phase synthesis method. The composite was successfully synthesized under solid-phase condition in a ball mill through three stages of mechanical milling. The optimum synthesis conditions of composite were obtained, and the effects from the synthesis conditions on the catalytic activity of composite were discussed. The composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy disperse spectroscopy (EDS), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The characterization results showed that the composite was a material with smooth surface, loose and clear layered structure, and had crystalline and amorphous phases in the microscopic scale. The characterization demonstrated the functional components of Fe(II) and HPW were successfully immobilized on the composite. Based on the characterization, the formation mechanism of composite in the mechanochemical synthesis was presented. The composite synthesized through the mechanochemical processing showed both high catalytic ability and excellent long-term stability in use. The results indicated that mechanochemical synthesis, as a green, simple and efficient preparation technology, was suitable for the industrial production of bentonite-supported Fe(II) and HPW composite.

Co2SnO4/Carbon Nanotubes Composites: A Novel Approach for Electrochemical Sensing of Hydrogen Peroxide

AbstractFor the first time Co2SnO4 (CTO)/Carbon nanotubes (CNT) composites were prepared and used to modify glassy carbon electrodes for the amperometric determination of hydrogen peroxide. The catalytic activity of composites towards the oxidation of hydrogen peroxide was dependent on the quantity of CNT present in the composite and to the pH of the medium. The pure cobalt stannate phase with a ratio of 3 : 1 (CTO:CNT) exhibited the best catalytic activity towards hydrogen peroxide oxidation at low potentials (0.200 and 0.500 V). A linear relationship between current and hydrogen peroxide concentration was obtained with a sensitivity of 95 and 258 μA mM−1 and a detection limit of 0.130 and 0.08 μM respectively.

Co−doped stannates ⁄reduced graphene composites: Effect of cobalt substitution on the electrochemical sensing of hydrogen peroxide

Co−doped stannates, Zn2-xCoxSnO4 (0.5≤x≤1.5), were produced by ceramic synthesis starting from the ZnSnO4 phase. Morphology, structure, and composition of synthesized compounds were examined using scanning electron microscopy, X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). Using XPS, cobalt ions are shown to have an oxidation state of 2+, and XRD patterns showed the same crystalline structure for all Zn2-xCoxSnO4 (0.5≤x≤1.5) phases, i.e., they are isostructural. The morphology of synthesized compounds shows appreciable differences in particle sizes which range from 80nm to 500nm, depending on how the ceramic was synthesized and the cobalt concentration. Co−doped stannates ⁄reduced graphene (rGO) composites were prepared and used to modify glassy carbon electrodes (GCE). The resulting electrodes were evaluated for the amperometric determination of hydrogen peroxide. The catalytic activity of composites towards the oxidation of hydrogen peroxide was highly dependent on quantity of cobalt in the ceramic compound, and also on the quantity of rGO present in the composite. The pure cobalt stannate phase with a ratio of 8:1 (ceramic:rGO) exhibited the best catalytic activity towards hydrogen peroxide oxidation at low potentials (0.400V). A linear relationship between current and hydrogen peroxide concentration was obtained with a sensitivity of 0.43μAmM−1cm−2 and a detection limit of 0.31μM.

Emerging Parallel Dual 2D Composites: Natural Clay Mineral Hybridizing MoS2 and Interfacial Structure

MoS2/montmorillonite (MoS2/MMT) composite nanosheets have been successfully synthesized by a facile hydrothermal method, and the catalytic activities of composites are evaluated by reduction reaction of methyl orange in aqueous phase. A preparation strategy demonstrates that MoS2 can be in situ formed on the surface of MMT from Na2MoO4· and H2NCSNH2. The microstructures and morphologies characterization indicates that few‐layered MoS2 nanosheets are uniformly grown on the surface of montmorillonite, and the hydrogen bonds are formed at the interfaces. The catalytic activity of MoS2/MMT is enhanced by support of montmorillonite, which can be attribu­ted to the large surface area, more reactive sites, dispersibility of MoS2/MMT, and the synergistic adsorption property of montmorillonite. Based on density functional theory calculations, the preferred adsorption configurations of MoS2 cluster on MMT are studied. The supporting effect of MMT on MoS2 nanoparticles will lead to the anchoring of these reactive MoS2 nanoparticles on clay surface and enhance the absorption ability of MoS2 to the organics and meanwhile improving the catalytic properties of the MoS2/MMT composite. The MoS2/MMT composite nanosheets show prospective application to treat effectively wastewater of dyes.

Catalytic activity of polypyrrole nanotubes decorated with noble-metal nanoparticles and their conversion to carbonized analogues

Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the presence of methyl orange. They were subsequently used as a substrate for the reductive deposition of noble metal particles. Polypyrrole nanotubes decorated with palladium, platinum, rhodium, or ruthenium nanoparticles were characterized by electron microscopy, conductivity, energy dispersive X-ray analysis, and FTIR and Raman spectroscopies. A typical metal content varied between 15 and 20wt.%. The catalytic activity of composites was illustrated on the reduction of 4-nitrophenol to 4-aminophenol. The carbonization of composites has been followed by thermogravimetric analysis in nitrogen atmosphere. The nanotubular morphology of polypyrrole was retained after carbonization up to 830°C. The noble-metal nanoparticles, nanometres in size, fused to clusters during this process, except for ruthenium. Polypyrrole nanotubes were converted to a nitrogen-containing carbon and platinum nanoparticles still preserved during carbonization at 400–500°C.

A Facile Synthesis of Cu/Ta@SBA composite for the degradation of Methyl Orange under UV irradiation

The mesoporous silica grafted tantalum and copper(II) composite was synthesised. The composites i.e.,SBA15, CuSBA (CuSi) and Cu/Ta@SBA (TaCuSi) grafting and stability was investigated by several spectroscopic, sorption, thermal analysis and microscopic techniques, i.e, Fourier-Transform Infrared spectroscopy (FTIR), Diffuse Reflections UV-visible spectroscopy (DRS), X-ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA), Electron paramagnetic resonance (EPR), RAMAN spectroscopy and the catalytic activity of composites were studied in photo degradation of the methyl orange (MO) under UV light irradiation. The catalytic activity of TaCuSi was higher when compared to that of CuSi. The photo oxidation ability of photocatalysts was determined by the spectrophotometrically. The percentage of degradation and rate of reaction was more for TaCuSi. The catalytic activity of recovered and purified TaCuSi was checked with the fresh catalyst. The recovered catalyst shows comparable activity with fresh catalyst.

Silicate anodic coatings on aluminum containing oxides of cobalt and/or copper and/or cerium and their activity in CO oxidation

Coatings on aluminum alloy containing one or several crystalline oxides of cobalt, copper, and cerium deposited in different sequences have been obtained by a combination of methods of plasma electrolytic oxidation and impregnation followed by annealing. It has been established that the composition of surface layers and the catalytic activity of composites depend on the sequence of deposition of active components on the substrate. Cu2+, Cu+, Co3+, Ce4+, and Ce3+ are present in the surface and subsurface layers. All the studied composites are characterized by catalytic activity in the reaction of oxidation of CO into CO2. Of the studied composites, the following are most active: CexOy/CuO/SiO2 + Al2O3/Al, CexOy/Co3O4/CuO/SiO2 + Al2O3/Al, and CexOy/CuO/Co3O4/SiO2 + Al2O3/Al.

New type of organic/gold nanohybrid material: Preparation, properties and application in catalysis

Microcrystals of 1,4-bis(terpyridine-4′-yl)benzene (BTB) adsorb gold nanoparticles (AuNPs) with an average size of 15nm or 25nm from the solution forming an organic–gold composite with ∼20wt% of Au. The composite with 15nm nanoparticles was characterized by thermal gravimetric analysis (TGA), transition electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Gold nanoparticles are uniformly distributed on the organic surface and retain the same size and shape distribution even after heating at 600°C which removes the organic matrix of 1,4-bis(terpyridine-4′-yl)benzene and effectively deposits nanoparticles onto solid substrate (mica). The catalytic activity of composites was demonstrated using a model reaction of the reduction of 4-nitrophenol to 4-aminophenol. The values of the apparent rate constants at 295K, ca. 1.9×10−3s−1 for the Au(15nm)–BTB and 7.2×10−4s−1 for the Au(25nm)–BTB, obtained using UV–vis spectroscopy, are comparable to those reported for other catalytic systems based on supported Au nanoparticles. The catalytic activity is found to be size-dependent; the bigger nanoparticles show lower activity and longer reaction induction period. Au–BTB catalyst can be recovered from the reaction mixture and used again.

Catalytic Activity of Complex-Oxide Perovskite-containing Compositions in Reactions of Oxidation of CO and Organic Compounds

The catalytic activity of composites constituted by a porous metallic or ceramic support, intermediate layers of oxide nature, and perovskite coatings, including those doped with silver, was studied in reactions of deep oxidation of CO and organic compounds of various classes. The relationship between the catalytic activity of a composite and its composition and nature of substances being oxidized was analyzed.