Inexpensive Co-catalyst Research Articles

Robust photocatalytic hydrogen evolution performance of 0D/1D NiO/CdS S-scheme heterojunction

Constructing heterojunction, especially S-scheme heterojunction, is an effective strategy for achieving effective separation of photogenerated electron-hole pairs and obtaining high electrode potential. In this study, a unique 0D/1D NiO/CdS S-scheme heterojunction was constructed by solvent evaporation induced self-assembly method. The loading of NiO was found to greatly enhance the photogenerated carrier separation efficiency of CdS by photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), Kelvin probe force microscopy (KPFM) and transient photocurrent tests. The best photogenerated carrier separation effect was observed at a NiO loading ratio of 15 wt% and the largest photocatalytic hydrogen evolution rate reached 7.89 mmol h-1g−1 under visible light, which was 24.66 times that of pristine CdS. In addition, the cycling experiments showed that the loading of NiO led to the alleviation of the photocorrosion phenomenon of CdS, and the performance remained at 94.2 % after five cycles. This is due to the fact that the formation of S-type heterojunction combines the photogenerated holes of CdS with the photogenerated electrons of NiO, which hinders the oxidation of S2- on the surface of CdS, thus alleviating the photocorrosion phenomenon of CdS and improving the stability of CdS. This work furnishes a new strategy for the development of stable and high-performance photocatalysts with inexpensive co-catalysts.

Enhanced hydrogen production performance via noble-metal-free amorphous NiZnSx-CS co-catalyst with novel gradient coating structure

In photocatalytic water splitting for hydrogen production, co-catalyst is a key factor in enhancing the efficiency of photocatalyst. Various inexpensive co-catalysts besides noble metal co-catalysts have been developed; however, the illumination of the relationship between the structure and performance remains a challenge. Here, we present a bimetallic sulfide co-catalyst denoted as NiZnSx-CS with amorphous and gradient coating structures to achieve highly efficient hydrogen production activity. Upon coupling the co-catalyst with CdS, the hydrogen production rate of CdS loaded with NiZnSx-CS reaches 38.0 mmol/g/h, 11.0, 40.0 and 161.0 times higher than that loaded with bulk NiZnSx, 1.0 %Pt and naked CdS, respectively. The co-catalyst with an amorphous and gradient coating structure shows large capacitance and thus facilitates efficient storage, transfer, and separation of photo-excited electrons of semiconductors, effectively reducing the over-potential of hydrogen production. The co-catalyst also has a large specific surface area and excellent hydrophilicity attributed to the abundant active sites and intimate contact with the reactant. Additionally, the coordination structure and chemical environment of NiZnSx-CS elucidated using X-ray absorption spectroscopy (XAS). The intermediates and the role of lactic acid and water on the surface of NiZnSx-CS after irradiation are determined by in situ Fourier transform infrared spectroscopy (in situ FT-IR). This work proposes a strategy to develop a highly efficient special structure co-catalyst with suitable capacitance, specific surface area and hydrophilicity.

Photocatalytic CO2 reduction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx MXene heterojunctions with enhanced interfacial charge transfer

Photocatalytic CO2 reduction reaction (CO2RR) synthesis of recycled fuel is a promising pathway to assist the mitigating fossil fuel depletion. Finding efficient and inexpensive high performance CO2RR semiconductor photocatalysts is a giant challenge in the field of photocatalytic reduction. This work constructs the novel-designed interfacial Schottky junction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx via electrostatic spinning and electrostatic self-assembly techniques. The catalysts exhibit tight contact heterogeneous interface companies with enhanced CO2 chemisorption capability and proved by various characterizations for efficient carrier separation and migration capacity. The optimized ZCO/Ti3C2Tx nanosheet composites significantly improved their photocatalytic performance. The best samples yielded 5.855 and 2.518 μmol g−1 h−1 of CO and CH4, which are 6 and 1.73 times higher than the conversion of ZCO, respectively, and maintain stability after four cycles without the use of sacrificial agents. In addition, the mechanism and reaction pathways of the photocatalytic process are proposed through In-situ diffuse reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTS) and X-ray absorption near edge structure (XANES) analysis. This work provides a new semiconductor/co-catalyst system for the photocatalytic reduction of CO2 and demonstrates that Ti3C2Tx MXene is a hopeful and inexpensive co-catalyst.

ReS2 with unique trion behavior as a co-catalyst for enhanced sunlight hydrogen production

The interfacial catalytic reaction plays a crucial role in determining hydrogen production efficiency of a photocatalyst. In this work, hollow spherical nano-shell composite (g-C3N4/CdS/ReS2) formed by graphitic carbon nitride (g-C3N4), cadmium sulfide (CdS), and rhenium disulfide (ReS2) was prepared for photocatalytic hydrogen production, with ReS2 introduced as a relatively inexpensive co-catalyst with excellent performance. It was found that two-electron catalytic reaction took place in this photocatalytic system due to the unique trion behavior of ReS2 co-catalyst, which greatly enhances the rate of photocatalytic hydrogen production. The tightly bound excitons in the ReS2 co-catalyst could easily capture the photogenerated electrons in the photocatalytic system to form trions, while g-C3N4 in the inner shell and CdS in the middle shell provided sufficient electrons for the formation of trions. The active edge sites of ReS2 also facilitated the generation and desorption of hydrogen, which creates conditions favoring two-electron catalytic reaction. In addition, oxidation and reduction reactions occurred inside and outside of the hollow spherical nano-shell, respectively, which effectively inhibits the recombination of photogenerated carriers. The unique trion behavior of ReS2 alters the interfacial catalytic reaction compared to the widely used platinum (Pt) co-catalyst in photocatalytic hydrogen production, which provides a new approach for enhancing the activity of photocatalytic systems.

Metal-free boron-assisted Fe(III)/peracetic acid system for ultrafast removal of organic contaminants: Role of crystalline nature and interfacial suboxide boron intermediates

Peracetic Acid (PAA) has emerged as an alternative candidate oxidant for H2O2 and persulfate-mediated catalytic oxidation. However, the sluggish kinetics of Fe3+/Fe2+ recycling still severely causes its limited applications. In this work, boron, for the first time, a metal-free and inexpensive co-catalyst, was introduced into the Fe3+/PAA Fenton-like system to remarkably accelerate the Fe2+ regeneration, further facilitating organic wastewater decontamination (an almost 145.0-fold kinetic increase on BPA removal). More excitingly, the crystalline nature of boron significantly modulated the activation system, and the crystalline boron and amorphous boron exhibited contrasting Fe3+ reduction characteristics. The amorphous boron-contained system enabled ultra-fast deterioration of various micro-pollutants. Validation experiments and theoretical calculations demonstrate that the surface B-B bonds with the formed interfacial suboxide boron continuously donated electrons to boost the rapid reduction of Fe3+. This work opens a new research avenue to promote the application of Fe3+-activated PAA systems with high activity in continuity and also guides the development of a new series of co-catalysts in wastewater treatment.

Bismuth vanadate/MXene (BiVO4/Ti3C2) heterojunction composite: enhanced interfacial control charge transfer for highly efficient visible light photocatalytic activity.

We have synthesized BiVO4/Ti3C2 nanocomposite via a low-cost hydrothermal method and investigate its photocatalytic degradation activity against monoazo (methyl orange) and diazo dye (Congo red) in an aqueous solution under visible light. The physiochemical characterization exhibited that the addition of MXene in pristine BiVO4 nanocomposite led to an increase in specific surface area and reduction in optical band gap energy. MXene also helps in enhancing visible light response via a higher electron-hole pair generation rate and long lifetime. The synthesized BiVO4/Ti3C2 heterojunction composite exhibited 99.5 % degradation efficiency within 60 min for Congo red and 99.1 % for methyl orange solution in 130 min owed to a large specific surface area (1.79 m2/g), reduced band gap (1.99 eV), and low recombination rate of charge carriers. The chemical mechanism for BiVO4/Ti3C2 nanocomposite proposes that Ti3C2 role-plays as electron capture because of the higher potential of MXenes, tuning band gap energy which paves the way to excellent photocatalytic action. This work opens a new basis for developing Ti3C2 based promising and inexpensive co-catalyst for efficient solar utilization in photocatalytic-related applications in the future.

Sustainable Highly Selective Toluene Oxidation to Benzaldehyde

Thanks to the well-recognized role of benzaldehyde in industry, nowadays the research of new and sustainable approaches to selectively synthesize such an interesting product is receiving great attention from the chemists’ community. In this paper, a V-based catalytic biphasic system is adopted to perform toluene oxidation to benzaldehyde. Importantly, to pursue sustainability, organic solvents have been avoided, so toluene is used as substrate and co-solvent, together with water. Also, the use of hydrophobic ionic liquids has been explored. To perform oxidation, NH4VO3 catalyst, H2O2, and a safe and inexpensive co-catalyst are used. Among the tested co-catalysts, KF and O2 were found to be the best choice, to guarantee good yields, in mild reaction conditions. In fact, with such a sustainable method, up to 30% of benzaldehyde can be obtained at 60 °C and, more interestingly, the oxidative system can be recharged, raising-up the yield. The entire process results highly selective, since no traces of benzyl alcohol or benzoic acid are detected. Hence, it constitutes a very appealing synthetic route, even suitable to be easily scaled-up at an industrial level.

CoSe as non-noble-metal cocatalyst integrated with heterojunction photosensitizer for inexpensive H2 production under visible light

The development of inexpensive cocatalysts based on earth-abundant-elements, is highly demanding strategy to produce large-scale photocatalytic H2 for real-life applications. Herein, we report the utilization of CoSe as a highly efficient cocatalyst to significantly improve the photocatalytic H2 production on ZnSe/CdS under visible irradiation. The maximum H2 production rate of 785 μmol h−1 was attained under optimized conditions. Furthermore, the current system showed robust stability up to 30 h of irradiation and more than 23 mmol of H2 was produced. The highest apparent quantum yield of the system was 55.3% at monochromatic 420 nm light. Photocurrent responses, UV–vis diffuse reflectance absorption spectroscopy, electrochemical impedance spectroscopy and photoluminescence (PL) spectroscopy were used to explain the mechanistic roles of CoSe and ZnSe in current photocatalytic system. This work showcased the successful usage of CoSe as cocatalyst and ZnSe as visible light active semiconductor for inexpensive conversion of solar energy to H2.

High-efficiency carrier separation heterostructure improve the photocatalytic hydrogen production of sulfide

Loading co-catalyst is one of the essential ways to strengthen the performance of photocatalyst. Here, a novel non-precious metal co-catalyst Ti2C/TiO2 was successfully synthesized and Zn0.5Cd0.5S nanoparticle grown on the surface of Ti2C/TiO2 equably. In our work, 0.01 g photocatalysts were used in photocatalytic activity measurement. Zn0.5Cd0.5S/Ti2C/TiO2 composite (2 wt% Ti2C/TiO2) exhibited the highest photocatalytic activity and the H2 yield is 32.57 mmol/g−1/h−1 under visible light irradiation. The photoelectrochemical results reveal that Ti2C/TiO2 could improve the separation of the photo-induced carriers in Zn0.5Cd0.5S/Ti2C/TiO2 heterojunction. And DFT calculations demonstrate that the Gibbs free energy of oxygen-terminated Ti2C and TiO2 are much lower than that of Zn0.5Cd0.5S. Therefore, the Ti2C/TiO2 has an active impact on improving the H2 production of Zn0.5Cd0.5S. This study provides a new way to explore the application of inexpensive co-catalysts on a large scale.

CdS nanorods anchored with CoS2 nanoparticles for enhanced photocatalytic hydrogen production

Herein, we report the use of cobalt sulfide (CoS2) as efficient and inexpensive co-catalyst of CdS nanorods for photocatalytic water splitting. The aim is to explore the use of earth-abundant cobalt species to replace precious metals for the photocatalytic reactions. The results of first-principles DFT simulation and planar-averaged differential charge density calculation reveal that at the CoS2/CdS interface, CoS2 has zero band gap which is a class nature of precious metals, and functions as electron trap to enhance the transfer of hot electrons from CdS to CoS2. Owing to the merits of efficient charge separation, high exposure of active sites as well as large surface area, the CoS2/CdS composites exhibit outstanding photocatalytic activity in H2 production under visible light (˜58 mmol·g−1 h−1), which is about 19 times that of CdS nanorods alone and 3 times that of 1 wt%Pt/CdS under the same conditions.

Effects of graphene oxide and sacrificial reagent for highly efficient hydrogen production with the costless Zn(O,S) photocatalyst

Searching for noble metal-free co-catalyst is still a strenuous part in photocatalytic hydrogen evolution reaction (HER), as most of the great catalysts contain noble metals like the expensive platinum. The present work demonstrates a feasible synthesis method of Zn(O,S)/GO nanocomposite with graphene oxide (GO) to serve as an inexpensive co-catalyst. Raman spectra and transmission electron microscopy (TEM) images clearly verified that GO was successfully loaded on the surface of Zn(O,S). This GO layer could effectively decrease the charge transfer resistance and promote the charge carrier separation for enhancing hydrogen production rate. By optimizing the GO content, the best hydrogen production rate of 2840 μg h−1 was achieved with Zn(O,S)/0.5 wt% GO catalyst under 16 W UV lamp with illumination light at a wavelength of 352 nm, which showed about two times higher for GO-free Zn(O,S). The effect of sacrificial reagent on the hydrogen production rate of Zn(O,S)/0.5 wt% GO catalyst was also evaluated. The sacrificial reagent showed the efficiency with the following trend: ethanol > methanol > isopropanol > ethylene glycol. The mechanism for enhancing hydrogen production rate is elucidated in this paper. We consider the simple synthesis method and its low cost to make Zn(O,S)/GO a great potential for practical application.

Nanoconfined Nickel@Carbon Core-Shell Cocatalyst Promoting Highly Efficient Visible-Light Photocatalytic H2 Production.

The realization of large-scale solar hydrogen (H2 ) production relies on the development of high-performance and low-cost photocatalysts driven by sunlight. Recently, cocatalysts have demonstrated immense potential in enhancing the activity and stability of photocatalysts. Hence, the rational design of highly active and inexpensive cocatalysts is of great significance. Here, a facile method is reported to synthesize Ni@C core-shell nanoparticles as a highly active cocatalyst. After merging Ni@C cocatalyst with CdS nanorod (NR), a tremendously enhanced visible-light photocatalytic H2 -production performance of 76.1 mmol g-1 h-1 is achieved, accompanied with an outstanding quantum efficiency of 31.2% at 420 nm. The state-of-art characterizations (e.g., synchrotron-based X-ray absorption near edge structure) and theoretical calculations strongly support the presence of pronounced nanoconfinement effect in Ni@C core-shell nanoparticles, which leads to controlled Ni core size, intimate interfacial contact and rapid charge transfer, optimized electronic structure, and protection against chemical corrosion. Hence, the combination of nanoconfined Ni@C with CdS nanorod leads to significantly improved photocatalytic activity and stability. This work not only for the first time demonstrates the great potential of using highly active and inexpensive Ni@C core-shell structure to replace expensive Pt in photocatalysis but also opens new avenues for synthesizing cocatalyst/photocatalyst hybridized systems with excellent performance by introducing nanoconfinement effect.

Catalytic conversion of glucose to 5-hydroxymethyl furfural using inexpensive co-catalysts and solvents

Efficient conversion of glucose to 5-hydroxymethyl furfural (5-HMF), a platform chemical for fuels and materials, was achieved using CrCl2 or CrCl3 as the catalysts with inexpensive co-catalysts and solvents including halide salts in dimethyl sulfoxide (DMSO) and several ionic liquids. 5-HMF (54.8%) yield was achieved with the CrCl2/tetraethyl ammonium chloride system at mild reaction conditions (120°C and 1h). The 5-HMF formation reaction was found to be faster in ionic liquids than in the DMSO system. Effects of water in the reaction system, chromium valence and reaction temperature on the conversion of glucose into 5-HMF were discussed in this work.

Polymerization of ethylene using a nickel α-diimine complex covalently supported on SiO2–MgCl2 bisupport

Bisupported catalyst for ethylene polymerization was prepared by mixing alcohol solution of MgCl2 with pretreated SiO2 in heptane, and further treating with bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino) acenaphtheneNiBr2 (abbreviated as NiLBr2) solution. The bisupported catalyst could be used to polymerize ethylene with high activity using alkylaluminum halides as inexpensive cocatalysts. According to high-temperature GPC, the weight-average molecular weights of the polymers obtained ranged from 2.15 × 105 to 9.27 × 105, with molecular weight distributions of 3.12–4.23. By adjusting the polymerization temperatures, the products with good morphologies could be obtained. The resultant polyethylenes were confirmed by 13C-NMR to contain significant amounts not only of methyl but also of ethyl, propyl, butyl, amyl, and longer side chains (longer than six carbons).