Synergistic Catalytic Effect Research Articles

Nickel substituted polyoxometalates in layered double hydroxides as metal-based nanomaterial of POM–LDH for green catalysis effects

Three nickel substituted Keggin-type polyoxometalates, α-[SiW9O37{Ni(H2O)}3]−10 (denoted as SiW9Ni3), was intercalated into Zn3Al based Layered Double Hydroxide (Zn3Al-LDH) by the selective ion-exchange technique. The as-synthesized nanocomposite, SiW9Ni3@Zn3Al, was used as heterogeneous nanoreactor to promote the synthesis of drug-like aminoimidazopyridine small molecule skeletons via the well-known Ugi-type Groebke–Blackburn–Bienaymé reaction (GBB 3-CRs) in the absence of any acid/additive and under mild and solvent-free conditions. A synergistic catalytic effect between SiW9Ni3 polyoxometalate and Zn3Al-LDH precursors is evidenced by a higher catalytic property of the SiW9Ni3@Zn3Al composite compared to the individual constituents separately. Lewis/Bronsted acidity of the SiW9Ni3 polyoxometalate and Zn3Al-LDH precursors appear to be essential for the catalytic performance of the composite. Furthermore, the catalytic performance of SiW9Ni3@Zn3Al was also tested in GBB 3-CRs synthesis of amino imidazothiazole under mild and solvent-free conditions.

Double enzyme mimetic activities of multifunctional Ag nanoparticle-decorated Co3V2O8 hollow hexagonal prismatic pencils for application in colorimetric sensors and disinfection

Since the catalytic activity of most nanozymes is still far lower than the corresponding natural enzymes, there is urgent need to discover novel highly efficient enzyme-like materials. In this work, Co3V2O8 with hollow hexagonal prismatic pencil structures were prepared as novel artificial enzyme mimics. They were then decorated by photo-depositing Ag nanoparticles (Ag NPs) on the surface to further improve its catalytic activities. The Ag NPs decorated Co3V2O8 (ACVPs) showed both excellent oxidase- and peroxidase-like catalytic activities. They can oxidize the colorless 3,3’,5,5’-tetramethylbenzidine rapidly to induce a blue change. The enhanced enzyme mimetic activities can be attributed to the surface plasma resonance (SPR) effect of Ag NPs as well as the synergistic catalytic effect between Ag NPs and Co3V2O8, accelerating electron transfer and promoting the catalytic process. ACVPs were applied in constructing a colorimetric sensor, validating the occurrence of the Fenton reaction, and disinfection, presenting favorable catalytic performance. The enzyme-like catalytic mechanism was studied, indicating the chief role of ⋅O2- radicals in the catalytic process. This work not only discovers a novel functional material with double enzyme mimetic activity but also provides a new insight into exploiting artificial enzyme mimics with highly efficient catalytic ability.

Biomass derived bifunctional catalyst for the conversion of cassava dreg into sorbitol

A biomass derived bifunctional catalyst (Ru/CCD-SO3H) was used for one-pot conversion of cassava dreg and cassava starch into sorbitol. The cassava dreg is mainly composed of residual cassava starch and holocellulose. The highest sorbitol yield of 11.43 % was achieved using cassava dreg as reactant. A synergistic catalytic effect of acid and metal sites of Ru/CCD-SO3H on cassava starch conversion to sorbitol was observed. The maximum sorbitol yield reached 82.51 % using cassava starch as reactant. A kinetic model of cassava starch degradation was performed. The reaction rate constants of cassava starch degradation, glucose conversion and sorbitol generation improved with enhancing temperature. The activation energy of cassava starch hydrolysis is larger than that of glucose hydrogenation, indicating the cassava starch hydrolysis is rate-determining step of cassava starch conversion into sorbitol. This work not only realizes the comprehensive utilization of cassava dreg, but also provides useful guidance for developing kinetic model of polysaccharide conversion.

Construction of the novel PMA@Bi-MOF catalyst for effective fatty acid esterification

A novel Bi-based metal-organic framework impregnated phosphomolybdic acid (PMA@Bi-MOF) catalyst has been fabricated via a simple hydrothermal procedure, and successfully applied in the preparation of biodiesel using oleic acid (OA) as the raw material. The PMA@Bi-MOF composites were exhaustively characterized with the help of FTIR, XRD, TPD-NH3, SEM-EDX, N2-physisorption, TGA, and XPS analyses. Experimental findings showed that the PMA@Bi-BTC exhibited a higher activity than that of PMA@Bi-BDC and Bi-BTC, attributed to its textural property, the presence of more acid sites with higher strength, and synergistic catalytic effects between PMA and Bi-BTC. The optimum conditions for esterification of OA, with a conversion of up to 92.5%, were found to be a molar ratio of methanol to OA of 20:1 and 0.15g PMA@Bi-BTC catalyst at 160 °C in 3 h. Meanwhile, reused studies indicated that the OA conversion reached more than 80% after seven reaction cycles. Furthermore, the activation energy of esterification catalyzed by PMA@Bi-BTC was also calculated as 54.8 kJ/mol. It is expected that our study provides an efficient route to biofuel production involving polyoxometalates/MOF synergistic catalysts.

Peroxymonosulfate activation by graphene oxide-supported 3D-MoS2/FeCo2O4 sponge for highly efficient organic pollutants degradation

To address conventional powder catalysts' recovery and aggregation issues that greatly restrain their practical application, a recoverable graphene oxide (GO)-supported 3D-MoS2/FeCo2O4 sponge (SFCMG) was developed through a simple impregnation pyrolysis method. SFCMG can efficiently activate peroxymonosulfate (PMS) to produce reactive species for rapid degradation of rhodamine B (RhB), with 95.0% and 100% of RhB being removed within 2 min and 10 min, respectively. The presence of GO enhances the electron transfer performance of the sponge, and the three-dimensional melamine sponge serves as a substrate to provide a highly dispersed carrier for FeCo2O4 and MoS2/GO hybrid sheets. SFCMG exhibits a synergistic catalytic effect of Fe and Co, and facilitates the redox cycles of Fe(III)/Fe(II) and Co(III)/Co(II) by MoS2 co-catalysis, which enhances its catalytic activity. Electron paramagnetic resonance results demonstrate that SO4•−, ·O2− and 1O2 are all involved in SFCMG/PMS system, and 1O2 played a prominent role in RhB degradation. The system has good resistance to anions (Cl−, SO42−, and H2PO4−) and humic acid and excellent performance for many typical contaminants degradation. Additionally, it works efficiently over a wide pH range (3–9) and possesses high stability and reusability with the metal leaching far below the safety standards. The present study extends the practical application of metal co-catalysis and offers a promising Fenton-like catalyst for the treatment of organic wastewater.

An efficient approach for the treatment of radioactive waste perfluoropolyether lubricants via a synergistic effect of thermal catalysis and immobilization

Perfluoropolyether (PFPE) lubricants are a kind of high-molecular polymer with many excellent properties. However, the use of PFPEs in the nuclear industry can lead to partial decomposition and carrying radionuclides, resulting in a large amount of radioactive waste PFPE lubricants annually. Moreover, radioactive waste PFPE lubricants are difficult to be effectively treated due to their high stability, the risk of possible leakage of radionuclides, and hypertoxic fluorine-containing by-products. In this study, without any precedent, a strategy of MnO2-catalyzed decomposition and Na2CO3-immobilized conversion was proposed for PFPE lubricant decomposition and fluorine immobilization simultaneously based on the Lewis acid-base and oxygen vacancies concept. A high fluorine conversion efficiency of 95.4% was achieved. Meanwhile, the mechanism of decomposition suggested that MnO2 mainly provided Lewis acid sites and attacked the (basic) fluorine or oxygen atoms in PFPE molecules. The decomposition of PFPE chains was proceed down and volatile fluorine-containing gas was released by partial electron transfer, intramolecular disproportionation reaction, and unzipping fashion. Subsequently, gas by-products could be further oxidized and then immobilized into fluoride salts by carbonate solid absorbents. Overall, this study provides a simple, safe, and potentially practical strategy for the harmless conversion of refractory fluorinated organic wastes, especially perfluoropolymers.

Construction of a BaTiO3/tubular g-C3N4 dual piezoelectric photocatalyst with enhanced carrier separation for efficient degradation of tetracycline

One-dimensional tubular g-C3N4 (TCN) with piezoelectric properties was prepared by self-assembly and hydrothermal method, and BaTiO3/TCN composite with excellent dual piezoelectric properties was constructed by further hydrothermal reaction. The piezoelectric degradation rate of tetracycline hydrochloride (TCH) by TCN (18.2 %) within 60 min under ultrasonic vibration was about 2.8 times higher than that by bulk g-C3N4 (CN) (6.6 %). Furthermore, the BaTiO3/TCN composite, a dual piezoelectric photocatalyst, exhibited excellent piezoelectric photocatalytic activity with TCH degradation rate of 91.0 % within 60 min under visible light (VSL) illumination and ultrasonic vibration, which was higher than that of ultrasonic vibration (27.8 %) and VSL illumination (81.8 %). The polarization electric fields were formed in both TCN and BaTiO3 under ultrasonic vibration, which could maintain the built-in electric field strength between the heterojunction interfaces, accelerate the photogenerated carrier migration, and thus improve the separation efficiency to achieve the synergic catalytic effect of dual piezoelectric under VSL irradiation. This work demonstrated that TCN had better piezoelectric photocatalytic properties than CN, and the efficient pollutant removal performance of dual piezoelectric photocatalysis, which provided new ideas for the development of piezoelectric photocatalysts.

Insight into n-CaO2/SBC/Fe(II) Fenton-like system for glyphosate degradation: pH change, iron conversion, and mechanism

Glyphosate has significant adverse effects on creature and ecological balance. Therefore, the efficient treatment of glyphosate wastewater is of great significance. In this study, nano calcium peroxide (n-CaO2) was loaded onto activated sludge biochar (SBC), and then Fe(II) was added to construct a Fenton-like system (n-CaO2/SBC/Fe(II)). SBC played the role of both a dispersant and catalyst, which greatly improved the removal capability of glyphosate. The removal efficiency of glyphosate in the n-CaO2/SBC/Fe(II) system was as high as 99.6%. The persistent free radicals (PFRs) on SBC can promote the conversion of Fe(III) to Fe(II) in the reaction system, and Fe(II) can be maintained at about 15 mg L−1 until the reaction reached equilibrium. Due to the synergistic effect of Fe(II) hydrolysis and SBC catalysis, n-CaO2/SBC/Fe(II) system can effectively remove glyphosate in a wide initial pH range (4.0–10.0), and the pH of the reaction system can be remained in a suitable environment (4.0–6.0) for Fenton-like reaction. Advanced oxidation and chemical precipitation were the main mechanisms for the removal of glyphosate. Most of glyphosate could be oxidized into H2PO-4 anions by breaking the bonds of C–P and C–N, and the H2PO-4 can be further adsorbed and bounded on the surface of the composites. This system overcomes the shortcomings of pH rising and Fe(III) precipitation in the CaO2-based oxidation systems, and realizes the efficient and complete degradation for glyphosate.

Al and Zr addition to improve the hydrogen storage kinetics of Mg-based nanocomposites: Synergistic effects of multiphase nanocatalysts

Solid-state hydrogen storage is regarded as the key technology to develop commercial application of hydrogen energy, and Mg added with high efficiency catalysts is a promising candidate to break through the barrier of hydrogen storage materials. Herein, Mg−Al and Mg−Al−Zr nanocomposites have been prepared by adding the single-metal (Al) and bimetal (Al, Zr) into Mg nanoparticles by the hydrogen plasma-metal reaction (HPMR) method. The two kinds of nanocomposites have an approximate size of 100 nm. With the expansion of the plasma current, the content of Al and Zr in Mg−Al−Zr nanocomposites increases gradually, and the addition of Al and Zr conspicuously accelerates the kinetics of hydrogen absorption and desorption of Mg. Compared with the nanocomposites with the single-metal (Al), the addition of bimetal (Al, Zr) can further enhance the hydrogen absorption kinetics of Mg, and the content of Zr has a positive effect on the reduction of activation energy (Ea). The Ea of Mg88.3Al7.6Zr4.1 for hydrogen absorption is 68.6 kJ/mol, which is significantly lower than that of Mg92.6Al7.4 (80.6 kJ/mol) and other two Mg−Al−Zr nanocomposites with low Al and Zr (70.7 and 69.8 kJ/mol, respectively). Both the nanostructure of Mg and the synergistic catalytic effects of active “catalytic sites” and H “diffusion channels” provided by the multiphase nanocatalysts of MgAl and AlZr3 contribute to the reduction of Ea. This work provides guidance for the development of Mg-based hydrogen storage materials with high catalytic efficiency.

Bifunctional Ru-Cluster-Decorated Co3 B-Co(OH)2 Hybrid Catalyst Synergistically Promotes NaBH4 Hydrolysis and Water Splitting.

Developing a highly efficient bifunctional catalyst for hydrolysis of metal hydrides and spontaneous hydrogen evolution reaction (HER) is essential for substituting conventional fuels for H2 production. Herein, Ru-cluster-modified Co3 B-Co(OH)2 supported on nickel foam (Ru/Co3 B-Co(OH)2 @NF) is constructed by electroless deposition, calcination and chemical reduction. The catalyst exhibits an excellent hydrogen generation rate (HGR) of 4989 mL min-1 and good reusability, superior to most previously reported catalysts. Besides, Ru/Co3 B-Co(OH)2 @NF displays a prominent hydrogen evolution reaction catalytic capability with a low overpotential of 153.0 mV at 100 mA cm-2 (50.5 mV at 10 mA cm-2 ), a small Tafel slope of 40.0 mV dec-1 and long-term stability (100 h@10 mA cm-2 ) in 1.0 M KOH. The excellent catalytic H2 generation capacity benefits from the rapid charge transfer promoted by metallic Co3 B, the synergistic catalytic effect of Co3 B-Co(OH)2 and Ru clusters, and the unique composite structure favorable for solute transport and gas emission.

Co-CoO-Co3O4 Realizes ultra highly sensitive detection of 4-nitrochlorobenzene based on synergistic effect of adsorption and catalysis

Accurate determination of 4-nitrochlorobenzene (4-NCB) concentrations in water environment always keeps its challenge due to the high toxicity and redox inertness of organic pollutants. Herein, cobalt-based oxide nanomaterials with different oxidation states were prepared by annealing ZIF-67 under N2 protection and subsequent oxidation in air. The products obtained from non-oxidation, oxidation for 4 and 8 h were named Co, Co-CoO-Co3O4 and Co3O4, respectively. Compared with Co and Co3O4, incompletely oxidized Co-CoO-Co3O4 exhibited the best detection performance for the electroanalytical behavior of 4-NCB, with a high sensitivity of 2.29 μA μM−1 in the concentration range of 0.5–4 μM. The results show that the Co-CoO-Co3O4 composite obtained by Co oxidation for 4 h has a slight decrease in the adsorption capacity of 4-NCB, but its catalytic reduction performance is improved by about 4 times, and the improvement of catalytic ability makes it have more excellent electrochemical detection performance. It is confirmed that the synergistic effect of adsorption and catalysis affects the electrochemical detection performance of organic pollutants, and the catalytic behavior of the material is a more critical factor affecting electrochemical detection.

Synthesis of the Ni2P–Co Mott–Schottky Junction as an Electrocatalyst to Boost Sulfur Conversion Kinetics and Application in Separator Modification in Li-S Batteries

To overcome the shuttling effect and sluggish conversion kinetics of polysulfides, a large number of catalysts have been designed for lithium-sulfur (Li-S) batteries. Herein, a Mott-Schottky junction catalyst composed of Co nanoparticles and Ni2P was designed to improve polysulfide kinetics. Our investigations reveal the rearrangement of charges at the Schottky junction interface and the construction of the built-in electric field are crucial for lowering the activation energy of the dissolved Li2Sn reduction and Li2S nucleation reaction. Furthermore, a series of experimental and electrochemical tests were performed to demonstrate that the Schottky catalytic effect enhanced the synergistic catalytic effect. With a Ni2P-Co@CNT catalyst, the battery exhibits an initial specific capacity of 874 mAh g-1 at a rate of 4.0 C, and the decay rate per cycle is 0.049% in 700 cycles. Meanwhile, the battery shows 0.118% decay rate per cycle at 0.5 C in 100 cycles at a high sulfur loading of 10 mg cm-2. The Schottky heterojunction structure proposed here has been shown to have a good catalytic effect on the reduction of Li2Sn and nucleation of Li2S, which provides a profound guidance for efficient and rational catalyst design.

Boosting formaldehyde catalytic oxidation of novel Au/mPVB fiber membrane with microreactor-like structure

In this study, a novel and well-constructed composite fiber membrane (Au/mPVB) is provided for removing the low-concentration formaldehyde gas continuously released in indoor environments at room temperature. The Au/mPVB provides a microreactor-like structure for catalytic reaction, in which the fiber has a homogeneous macroporous structure, and Au NPs are uniformly loaded onto the inner wall of the macropores in the amino-modified fiber (mPVB) by template sacrifice. Formaldehyde can be enriched in the mPVB fiber under the adsorption to the amino groups, and the catalytic performance can be improved effectively under the synergistic effect of adsorption and catalysis. In the experimental results of performance tests, 1 wt% Au/mPVB exhibited a high removal efficiency of 97.5% for 0.8 ppm formaldehyde in the indoor environment, which improved the performance by 25% compared to mPVB, and no obvious decrease of catalytic activation occurred after the continuous formaldehyde-releasing experiment without catalyst regeneration.

Synergistic Catalytic Effect of Ag and MgO Nanoparticles Supported on Defective BN Surface in CO Oxidation Reaction.

Micron-sized supports of catalytically active nanoparticles (NPs) can become a good alternative to nanocarriers if their structure is properly tuned. Here, we show that a combination of simple and easily scalable methods, such as defect engineering and polyol synthesis, makes it possible to obtain Ag and MgO nanoparticles supported on defective hexagonal BN (h-BN) support with high catalytic activity in the CO oxidation reaction. High-temperature annealing in air of Mg-containing (<0.2 at.%) h-BN micropellets led to surface oxidation, the formation of hexagonal-shaped surface defects, and defect-related MgO NPs. The enhanced catalytic activity of Ag/MgO/h-BN materials is attributed to the synergistic effect of h-BN surface defects, ultrafine Ag and MgO NPs anchored at the defect edges, and MgO/Ag heterostructures. In addition, theoretical simulations show a shift in the electron density from metallic Ag towards MgO and the associated decrease in the negative charge of oxygen adsorbed on the Ag surface, which positively affects the catalytic activity of the Ag/MgO/h-BN material.

Phase transition of individual anatase TiO2 microcrystals with large percentage of (001) facets: a Raman mapping and SEM study.

TiO2 has been extensively studied in many fields including photocatalysis, electrochemistry, optics, etc. Understanding the mechanism of the anatase-rutile phase transition (ART) process is critical for the design of TiO2-based high-activity photocatalysts and tuning its properties for other applications. In this work, the ART process using individual anatase micro-particles with a large percentage of (001) facets was monitored and studied. Phase concentration evolution obtained via Raman microscopy was correlated with the morphological evolution observed in scanning electron microscope (SEM) images. The ART of anatase microcrystals is dominated by surface nucleation and growth, but the ART processes of individual anatase particles are distinctive and depend on the various rutile nucleation sites. Two types of transformation pathways are observed. In one type of ART pathway, the rutile phase nucleated at a corner of an anatase microcrystal and grew in one direction along the edge of the crystal firstly followed by propagation over the rest of the microcrystal in the orthogonal direction on the surface and to the bulk of the crystal. The kinetics of the ART follows the first-order model with two distinct rate constants. The fast reaction rate is from the surface nucleation and growth, and the slow rate is from the bulk nucleation and growth. In the other type of ART pathway, multiple rutile nucleation sites formed simultaneously on different edges and corners of the microcrystal. The rutile phase spread over the whole crystal from these nucleation sites with a small contribution of bulk nucleation. Our study on the ART of individual micro-sized crystals bridges the material gap between bulk crystals and nano-sized TiO2 particles. The anatase/rutile co-existing particle will provide a perfect platform to study the synergistic effect between the anatase phase and the rutile phase in their catalytic performances.

Dinuclear metal synergistic catalysis for energy conversion.

Catalysts featuring dinuclear metal sites are regarded as superior systems compared with their counterparts with mononuclear metal sites. The dinuclear metal sites in catalysts with appropriate spatial separations and geometric configurations can confer the dinuclear metal synergistic catalysis (DMSC) effect, and thus boost the catalytic performance, in particular for reactions involving multiple reactants, intermediates and products. In this review, we summarize the related reports on the design and synthesis of both homogeneous and heterogeneous dinuclear metal catalysts, and their applications in energy conversion reactions, including photo-/electro-catalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), CO2 reduction reaction (CO2RR), and N2 reduction reaction (N2RR). Particularly, we focus on the analysis of the relationship between the catalyst structure and catalytic performances, where the design principles are presented. Finally, we discuss the challenges in the design and preparation of dinuclear metal catalysts with the DMSC effect and present a perspective on the future development of dinuclear metal catalysts in energy conversion. This review aims to comprehensively summarize the up-to-date research progress on the synthesis and energy-related application of dinuclear metal catalysts and provide guidance for designing energy-conversion catalysts with superior performances.

Synergistic catalytic effect of triple dynamic bonds for fast-reprocessing and high-performance cross-linked polymers

This work demonstrated high-performance and fast-reprocessing dynamic cross-linked polymers (DCPs) based on a synergistic catalytic system of triple dynamic bonds.

Enhancing catalytic efficiency of carbon dots by modulating their Mn doping and chemical structure with metal salts.

Nanozymes are emerging materials in various fields owing to their advantages over natural enzymes, such as controllable and facile synthesis, tunability in catalytic activities, cost-effectiveness, and high stability under stringent conditions. In this study, the effect of metal salts on the formation and catalytic activity of carbon dots (CDs), a promising nanozyme, is demonstrated. By introducing Mn sources that possess different counter anions, the chemical structure and composition of the CDs produced are affected, thereby influencing their enzymatic activities. The synergistic catalytic effect of the Mn and N-doped CDs (Mn&N-CDs) is induced by effective metal doping in the carbogenic domain and a high proportion of graphitic and pyridinic N. This highly enhanced catalytic effect of Mn&N-CDs allows them to respond sensitively to the interference factors of enzymatic reactions. Consequently, ascorbic acid, which is an essential nutrient for maintaining our health and is a reactive oxygen scavenger, can be successfully monitored using color change by forming oxidized 3,3',5,5'-tetramethylbenzidine with H2O2 and Mn&N-CDs. This study provides a basic understanding of the formation of CDs and how their catalytic properties can be controlled by the addition of different metal sources, thereby providing guidelines for the development of CDs for industrial applications.

Insights into alloy/oxide or hydroxide interfaces in Ni-Mo-based electrocatalysts for hydrogen evolution under alkaline conditions.

Nickel-molybdenum (Ni-Mo) alloys are promising non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water; however, the kinetic origins of their catalytic activities still remain under debate. In this perspective, we systematically summarize the structural characteristics of Ni-Mo-based electrocatalysts recently reported and find that highly active catalysts generally have alloy-oxide or alloy-hydroxide interface structures. Based on the two-step reaction mechanism under alkaline conditions, water dissociation to form adsorbed hydrogen and combination of adsorbed hydrogen into molecular hydrogen, we discuss in detail the relationship between the two types of interface structures obtained by different synthesis methods and their HER performance in Ni-Mo based catalysts. For the alloy-oxide interfaces, the Ni4Mo/MoO x composites produced by electrodeposition or hydrothermal combined with thermal reduction exhibit activities close to that of platinum. For only the alloy or oxide, their activities are significantly lower than that of composite structures, indicating the synergistic catalytic effect of binary components. For the alloy-hydroxide interfaces, the activity of the Ni x Mo y alloy with different Ni/Mo ratios is greatly improved by constructing heterostructures with hydroxides such as Ni(OH)2 or Co(OH)2. In particular, pure alloys obtained by metallurgy must be activated to produce a layer of mixed Ni(OH)2 and MoO x on the surface to achieve high activity. Therefore, the activity of Ni-Mo catalysts probably originates from the interfaces of alloy-oxide or alloy-hydroxide, in which the oxide or hydroxide promotes water dissociation and the alloy accelerates hydrogen combination. These new understandings will provide valuable guidance for the further exploration of advanced HER electrocatalysts.

Kinetic effects of cationic surfactants on the photocatalytic degradation of anionic dyes in aqueous TiO2 dispersions

The synergistic catalytic effect of surfactants is highlighted in the photodegradation of Orange G and Eosin Y by TiO2 at alkaline pH.