Co-catalytic Properties Research Articles

EGCG mildly reduced single atom Co-MXene catalytic membrane: Catalytic and antioxidant properties

As a 2D nanomaterial with high hydrophilic and co-catalytic properties, MXene has been widely studied in the field of membrane separation and advanced oxidation. However, its susceptibility to oxidation in catalytic environments poses a significant challenge to its long-term stability and performance. Therefore, constructing an oxidation-resistant MXene catalytic membrane technology and ensuring its excellent flux and catalytic performance are important for the practical application of MXene membranes. Herein, we prepared a cobalt monoatomic intercalated M/E0.1-Co catalytic separation membrane by mild reduction of epigallocatechin-3-gallate (EGCG). EGCG not only connects the MXene lamellae during filtration through strong hydrogen bonding, but also protects the chemical stability of the MXene substrate through its antioxidant ability. Furthermore, the trace amount of EGCG in the confined domain space also promotes the rate-limiting step of the transition from the high-valent state to the low-valent state in Co single-atom catalysis. The stability of the catalytic separation layer was ensured along with a 100% degradation performance of sulfamethoxazole. This study establishes a bridge between the catalytic oxidation and chemical stability of a wide range of MXene-based materials nowadays and provides a viable proposal for the practical application of long-term utilized MXene materials in catalysis.

BiVO4 Film Coupling with CoAl2O4 Nanoparticles for Photoelectrochemical Water Splitting Utilizing Broad Solar Spectrum through p-n Heterojunction, Photothermal, and Cocatalytic Synergism.

Water oxidation is an endothermic and kinetics-sluggish reaction; the research of photoanodes with photothermal and cocatalytic properties is of great significance. Herein, BiVO4/CoAl2O4 film photoanodes were studied for solar water splitting through coupling spinel p-type CoAl2O4 nanoparticles on n-type BiVO4 films. Compared to the BiVO4 photoanode, better performance was observed on the BiVO4/CoAl2O4 photoanode during water oxidation. A photocurrent of 3.47 mA/cm2 was produced on the BiVO4/CoAl2O4 photoanode at 1.23 V vs RHE, which is two-fold to the BiVO4 photoanode (1.70 mA/cm2). Additionally, the BiVO4/CoAl2O4 photoanodes showed an acceptable stability for water oxidation. The BiVO4/CoAl2O4 photoanode being of higher water oxidation performance could be attributed to the presence of p-n heterojunction, cocatalytic, and photothermal effects. In specific, under the excitation of λ < 520 nm light, the holes produced in/on BiVO4 can be transferred to CoAl2O4 owing to the p-n heterojunctions of BiVO4/CoAl2O4. Meanwhile, the temperature on the BiVO4/CoAl2O4 photoanode rises quickly up to ∼53 °C under AM 1.5 G irradiation due to the photothermal property of CoAl2O4 through capturing the 520 < λ < 720 nm light. The temperature rising on the BiVO4/CoAl2O4 photoanode improves the cocatalytic activity of CoAl2O4 and modifies the wettability of BiVO4/CoAl2O4 for effective water oxidation.

Carboxymethyl chitosan modification of cobalt-zinc bimetallic MOF for tetracycline hydrochloride removal: Exploration of the enhancement mechanism of the process

This study synthesized a carboxymethyl chitosan-modified bimetallic Co/Zn-ZIF (CZ@CMC) with strong hydrophilicity and adsorption performance via the one-pot method. Tetracycline hydrochloride (TCH) was used as the model contaminant to evaluate the adsorption and peroxymonosulfate (PMS) activation properties of CZ@CMC. Mechanism showed that the adsorption behavior occurred through pore filling, electrostatic attraction, surface complexation, hydrogen bonding, and π-π stacking. In addition, a CZ@CMC/PMS system was constructed, which had excellent catalytic performance. The hydrophilicity and selective adsorption properties of CMC conferred a greatly accelerated CZ@CMC in catalyzing the PMS process with kobs of 0.095 min−1, in which OH, 1O2, SO4–, O2–, and Co(III) were the main ROS which quenching tests, EPR, and chemical probe experiments verified. In addition, the degradation pathways of TCH were obtained utilizing DFT and HPLC-MS and analyzed to show that the system possessed a good detoxification capacity. This work is expected to provide a green, efficient, and stable strategy to enhance the adsorption properties of catalytic materials and subsequently their co-catalytic properties.

Tailoring of efficient electron-extracting system: S-scheme g-C3N4/CoTiO3 heterojunction modified with Co3O4 quantum dots for photocatalytic hydrogen evolution

• g-C 3 N 4 /CoTiO 3 S-scheme heterojunction was successfully designed and prepared. • Co 3 O 4 quantum dots were uniformly and tightly attached to the surface of the heterojunction. • The integration of S-scheme/promoter realized an efficient electronic-extracting system. • The hydrogen evolution performance of the ternary nanoreactor exceeds the binary system. Enhancing the utilization rate of photogenerated electrons has been considered as one of the bottlenecks in obtaining efficient photocatalytic hydrogen production system. This work deals with Co 3 O 4 quantum dots (CDs) modified S-scheme g-C 3 N 4 /CoTiO 3 (CN/CTO) heterojunction as a photocatalyst for water splitting. The S-scheme heterojunction retains a good carrier separation, and the built-in electric field also endows vigorous driving force for charge transport. CDs can be used as the electron acceptor, providing more active sites and achieving rapid capture of photogenerated electrons. The synergistic utilization of S-scheme structure and promoter considerably optimizes the electron transfer path, with enhanced spatial charge separation leading to more useful electrons with higher reducing capacity to participate in hydrogen evolution reaction. Using triethanolamine solution as sacrificial agent and eosin-Y as photosensitizer, the average H 2 evolution rate of optimized CN/CTO/CDs within 5 h of visible light irradiation was 1971.7 μmol g -1 h −1 , which was 102.7, 2.5 and 2.3 times higher than that of pure CN, CN/CTO and CN/CDs, respectively, with a corresponding apparent quantum efficiency was 3.39 %. Additionally, the charge transfer mechanism of S-scheme and the co-catalytic properties of CDs were further verified by the results of photoluminescence and photoelectrochemistry. This research contributes a valuable opinion for the integration of multicomponent photocatalytic systems.

Mo-activated VC as effective cocatalyst for an enhanced photocatalytic hydrogen evolution activity of CdS

Seeking an efficient and stable cocatalyst is of importance for semiconductor-based photocatalytic water splitting to produce hydrogen. In this sense, Mo-activation of VC for better cocatalytic properties was proposed for the first time, aiming to attain improved hydrogen generation of CdS. Our novel, yet facile physical preparation method permits intimate coupling of Mo-activated VC cocatalyst to CdS (through electrostatic attraction force), thereby promises drastic activity enhancement for hydrogen generation. Results indicate the best VC-activating competency of Mo against other transition metals (Co, Fe, Ni, Zn and Cu), which induces highest H2 productivity of CdS after modifying with Mo-activated VC. Under optimum setting, CdS/Mo(0.38)-VC(5 wt%) manifested highest photocatalytic hydrogen production rate of 2267 μmol h−1 g−1, associated to 300 % and 440 % improvement as compared to that of CdS/VC(5 wt%) and pure CdS, respectively. Such activity also outperformed those that yielded by MoSx- or noble metals(Pt, Au or Ag)-co-catalyzed CdS, attributed to the promoted interfacial charges transfer and lowered overpotential of CdS/Mo(0.38)-VC(5 wt%) in hydrogen generation. Correspondingly, high apparent hydrogen production quantum efficiency of 4.3 % was also recorded by the same photocatalyst at 420 nm. In term of stability test, CdS/Mo(0.38)-VC(5 wt%) manifested excellent longevity in 24 h continuous photoreaction and fair recyclability over five consecutive photoreaction cycles. This work provides a new insight to cocatalysts design and synthesis, thereby realizing economic alternatives to precious metal (Pt, Au, Ag) in solar-derived H2 production.

CO Oxidation Catalytic Effects of Intrinsic Surface Defects in Rhombohedral LaMnO3.

There is an ongoing effort to replace rare and expensive noble-element catalysts with more abundant and less expensive transition metal oxides. With this goal in mind, the intrinsic defects of a rhombohedral perovskite-like structure of LaMnO3 and their implications on CO catalytic properties were studied. Surface thermodynamic stability as a function of pressure (P) and temperature (T) were calculated to find the most stable surface under reaction conditions (P=0.2 atm, T=323 K to 673 K). Crystallographic planes (100), (111), (110), and (211) were evaluated and it was found that (110) with MnO2 termination was the most stable under reaction conditions. Adsorption energies of O2 and CO on (110) as well as the effect of intrinsic defects such as Mn and O vacancies were also calculated. It was found that O vacancies favor the interaction of CO on the surface, whereas Mn vacancies can favor the formation of carbonate species.

Gas-sensing performance of In2O3@MoO3 hollow core-shell nanospheres prepared by a two-step hydrothermal method

Core-shell semiconductor nanostructures can be suitable for high-performance gas sensors due to their unique structural features. In this study, In2O3@MoO3 core-shell hollow spheres were synthesized by a facile two-step solvo-thermal method, followed by post-heat treatment. The synthesis results in 20-nm thick MoO3 shells coated on In2O3 hollow spheres (200-nm diameter). The effects of the morphology and composition on gas sensing performance were systematically investigated by adjusting the molar ratio of In to Mo. The sensing tests suggest that the core-shell structure with the In to Mo molar ratio of 1:1 exhibits the highest sensing response (28.1) towards 100-ppm n-butylamine at the optimized working temperature of 300 °C. This response is two times higher than that of the In2O3 & MoO3 binary mixture (11.1) and five times than that of the pristine In2O3 hollow spheres (4.8). The sensing performance is a result of the unique core-shell structures including both the catalytic reaction mechanism of MoO3 and the co-catalytic properties of the In2O3 hollow spheres. This study may shed light on the design of practical, high-performance amine gas sensors in the future.

Enhancing co-catalysis of MoS2 for persulfate activation in Fe3+-based advanced oxidation processes via defect engineering

• Defective MoS 2 enhanced PCA removal of Fe 3+ /PS system compared with pristine MoS 2 . • S defects in MoS 2 facilitated the cycle of Fe 3+ /Fe 2+ to enhance PCA degradation. • S defects in MoS 2 increased the electron density around Mo. • S defects in MoS 2 enhanced the adsorption of Fe 3+ . Advanced oxidation processes (AOPs) based on persulfate (PS) has attracted great attention because of its outstanding performance for decomposing chlorinated aromatic hydrocarbons in wastewater. While Fe-based materials can effectively activate PS and are environment-friendly, the low stability of Fe 2+ and little activation capability of Fe 3+ limit the broad applications of Fe 2+ (or Fe 3+ ) activated PS system in practical applications. In this work, taking molybdenum disulfide (MoS 2 ) as the co-catalyst in Fe 3+ /PS system, we report a strongly enhanced persulfate activation efficiency of Fe 3+ /PS system by engineering S defects in MoS 2 . The combination of experiments and density functional theory (DFT) calculation demonstrate that S defects in MoS 2 modify the surface charge distribution, leading to the formation of an electron deficient center near S defect and increasing the electron density near Mo site. As a result, more Fe 3+ in Fe 3+ /PS system is reduced into Fe 2+ by MoS 2 with S defects, resulting in more reactive oxygen species generated. Furthermore, S defects promote the adsorption of Fe 3+ on the MoS 2 surface, which further enhance the activating performance for PS through promoting to form cycle of Fe 3+ /Fe 2+ . This work provides a new strategy for improving co-catalytic properties of MoS 2 and expands the application of Fe 3+ /PS system for contaminants remediation.

Scalable and efficient extraction of two-dimensional MoS2 nanosheets from dispersions as a co-catalyst for enhancing Fenton reactions

Here, two-dimensional molybdenum disulfide (2D-MoS2) nanosheets were efficiently extracted from dispersions by precipitation method and then directly applied as co-catalyst for enhancing Fenton reactions. The 2D-MoS2 nanosheets were completely extracted in a short time, while surfactant was left in dispersion. The average length and layer number of extracted 2D-MoS2 nanosheets are 110.41 nm and 2.6, respectively. Due to the loose structure and a small amount of adsorbed surfactant, the extracted 2D-MoS2 nanosheets exhibited excellent dispersibility in various solvents. The 2D-MoS2 nanosheets as co-catalyst promoted greatly the production rate of reactive hydroxyl radicals (·OH) and thus decreased remarkably the dosage of ferrous salts and H2O2. The co-catalytic property of 2D-MoS2 nanosheets is much better than that of commercial bulk MoS2 because 2D-MoS2 provides abundant active edge sites. This work not only demonstrated a scalable and efficient method for extracting 2D-MoS2 nanosheets from dispersions, but also widened the applications areas of 2D-MoS2 and provided an excellent co-catalyst for Fenton reactions.

Principal Descriptors of Ionic Liquid Co-catalysts for the Electrochemical Reduction of CO2

Electrochemical reduction of carbon dioxide (CO2RR) is promoted by ionic liquid (IL) co-catalysts, and several mechanisms have been proposed to explain their role. Due to the complexity of the CO2RR and the limited number of active IL co-catalysts, a consensus on the precise role of ILs has not been reached, and it is not possible to improve their activity in a rational way. Herein, we describe guanidinium (Gua) ILs that act as co-catalysts for the CO2RR when employed in non-aqueous electrolytes. The peripheral substituents of the Gua cation were systematically modified allowing the IL co-catalytic properties to be fine-tuned, and on the basis of the observed substitution effects, charge delocalization and availability were shown to be the critical descriptors determining co-catalytic activity. These descriptors can be used to rationalize activity trends for other classes of IL co-catalysts.

Platinum like cocatalysts tungsten carbide loaded hollow tubular g-C3N4 achieving effective space separation of carriers to degrade antibiotics

A novel P-doped hollow tubular g-C3N4/tungsten carbide (P-TCN/WC) photocatalyst was newly synthesized by a simple one-pot calcination process and used to degrade two typical antibiotics, tetracycline (TC) and ciprofloxacin (CIP) under visible light irradiation. The P-TCN/WC showed excellent photocatalytic activities toward degradation of antibiotics. The 8% P-TCN/WC showed the best photocatalytic activity, which could degrade 93.76% TC and 76.21% CIP within 120 min. The enhanced photocatalytic activity of P-TCN/WC was due to the expansion of light absorption and the reduction of carrier recombination. P doping and WC loading expanded light absorption of P-TCN/WC over the whole visible light spectrum. Meanwhile, the hollow tubular morphology boosted the utilization of light. Furthermore, the platinum like noble metal cocatalytic properties of WC loading and P doping made the recombination of carriers of P-TCN/WC decreased significantly no matter bulk or space. The intermediates of CIP were measured and the possible degradation pathway was tentatively proposed. The photocatalysts have high stability, superb light absorption, and prominent photocatalytic activity, which could be used as an effective method for antibiotics degradation.

Ni-Mo ternary nitrides based one-dimensional hierarchical structures for efficient hydrogen evolution

Efficient semiconductor-cocatalyst junctions are of direct relevance to solar energy based fuel generation. Here, Ni-Mo ternary nitrides based one-dimensional hierarchical structures (In2S3-Ni0.2Mo0.8N(Ni)) have been successfully prepared and used to achieve visible light driven H2 evolution. Because of the metallic-like properties of the transition metal nitrides, Ni0.2Mo0.8N(Ni) as co-catalysts can promote photo-generated charge-carriers transportation/separation and decrease the overpotential of H2-evolution. Thus, the photocatalytic property of optimal 1 wt% In2S3-Ni0.2Mo0.8N(Ni) exhibits a hydrogen evolution rate of 614.2 μmol g-1 h−1, which is about 10 times as high as that of blank In2S3 (61.4 μmol g−1 h−1). Besides, the pure Ni0.2Mo0.8N shows higher co-catalytic properties than Ni0.2Mo0.8N(Ni). This indicates that the metallic Ni (and related species) lowers the co-catalytic role of ternary nitrides. Another robust indication of this is the fact that In2S3-Ni0.2Mo0.8N nanohybrid displays about 2 times higher H2 evolution rate than In2S3-Ni0.2Mo0.8N(Ni).

Remarkable improvement of cycling Fenton process for catalytic degradation of phenol: Tuning of triggering effect

A kind of effective cyclic Fenton process was investigated, in which Fe species were reused as homogeneous catalysts after the acid dissolution of Fe-containing sludge. It was observed that the degradation of phenol was abruptly accelerated (i.e., triggering effect) after an induction phase of ca. 30min for non-first runs. The abrupt acceleration was attributed to the rapid reduction of Fe(III) by poly-phenol intermediates, such as 1,2-hydroquinone, 1,4-hydroquinone and 1,2,4-trihydroxybenzene. Specially, it was found that sludge carbon (SC) could not only improve the precipitation performance of Fe and Al species, decreasing residual concentration of Fe and Al species to 0.11mgL−1 and 4.6mgL−1, respectively, but also reduce considerably induction phase of the degradation, promoting the advent of the triggering effect in advance. The promotion of SC was stemmed from its unique co-catalytic property, by which Fe(III) was continuously reduced to active Fe(II) and H2O2 was turned to stronger oxidizing OH and 1O2.

Mesoporous-shelled CeO2 hollow nanospheres synthesized by a one-pot hydrothermal route and their catalytic performance

Uniform-sized and monodisperse CeO2 mesoporous hollow nanospheres composed of ceria nanocrystals were synthesized via a template-free and surfactant-assisted benign hydrothermal route. On the basis of a time-dependent experiment, the precipitation–dissolution–renucleation–assembly and Ostwald ripening processes mechanism is proposed for the formation of the CeO2 mesoporous hollow spheres. Poly(vinyl-pyrrolidone) (PVP) was applied as a surfactant to facilitate the reassembly of the CeO2 nanoparticles and the formation of the mesoporous shell of the hollow nanospheres. By increasing the amount of PVP, the mesoporous shell of the hollow spheres could be fabricated and became more apparent. Meanwhile, altering the amounts of H2O2 could control the size of the primary nanocrystals via affecting the nucleation/growth process of them, which is another key factor in the formation of the hollow structure and the uniform, monodispersed nanoparticles. The catalytic test results show that the as-obtained CeO2 mesoporous hollow spheres exhibited desirable CO catalytic properties. The synthesized Au–CeO2 nanospheres demonstrate a higher catalytic activity in CO oxidation than pure ceria nanospheres.

Template synthesis and cocatalytic behavior of phosphorus donor containing trans-Fe(0) metallacrown ethers

Same new phosphorus donors containing trans-Fe(0) metallacrown ethers were obtained by template synthesis. The co-catalytic properties of these complexes and the X-ray diffraction structure of complex 1 were discussed.

Synthesis of poly(1-oxo-2-phenyltrimethylene) catalyzed by palladium-rare earth catalyst

Poly(1-oxo-2-phenyltrimethylene) was successfully synthesized in the presence of palladium acetate and rare earth acetate RE(OAc)3 (RE=Pr, Nd, Eu, Dy, Ho) multiplex catalyst system. The final products were characterized by elemental analysis, nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of various reaction parameters including molar ratio of rare earth/Pd2+, methanol usage, 2,2-bipyridyl,p-toluensulfonic acid, andp-benzoquinone were studied in detail, and the influence of different rare earths on the copolymerization was also discussed. It is found that the rare earths have favorable co-catalytic properties and palladium-rare earth multiplex catalyst showed higher catalytic activity than palladium catalyst in the copolymerization of carbon monoxide (CO) and styrene (ST).

Methanol electrooxidation on smooth platinum modified with Ru: The influence of Ru coverage and potentials on oxidative current and products

AbstractMethanol oxidation on smooth Pt electrode modified with different coverage of Ru was studied using cyclic voltammetry and potential step combined with differential electrochemical mass spectroscopy. The current efficiency of formed CO2 was calculated from faraday current and ion current of m/z = 44. The results show that Ru modified Pt electrode with the coverage of ca. 0.3 has the highest catalytic activity for methanol electrooxidation, i.e. faraday current and the current efficiency of CO2 at the low potentials reach to the maximum. In addition, Ru loses its co‐catalytic properties at the high potentials.

A novel lanthanocene catalyst system for the polymerization of methyl methacrylate Me2Si(CpSiMe3)2NdCl-n-BuMgCl

Me2Si(CpSiMe3)2NdCl activated by n-BuMgCl at low molar ratio (1 : 1.2) was successfully used to polymerize methyl methacrylate (MMA) for the first time. Grignard reagent indicated better co-catalytic properties than alkyl aluminum. Effects of the catalyst concentration, polymerization time, temperature, and solvents were studied in bulk and solution polymerization respectively. The results showed that this catalyst system was very active for MMA polymerization in toluene at 40°C, producing PMMA with high molecular weight (53.5 × 104) and high conversion (100%). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2245–2250, 2001

Influence of Molecular Weight of Ionenes on the Cobalt Phthalocyanine-Catalyzed Oxidation of 1-Dodecanethiol

The cocatalytic properties of monodisperse 2,4-ionene oligomers were tested in the cobalt(II) phthalocyaninetetrakis(sodium sulfonate) (CoPc(NaSO 3 ) 4 )-catalyzed autoxidation of 1-dodecanethiol. A tremendous rate increase in the dodecanethiol oxidation by a factor of 100, as compared with the polymer-free system, was observed for monodisperse ionene oligomers, with four quaternary ammonium groups and with 4-bromobutyl end groups. By contrast, the same oligomers terminated with the more hydrophilic dimethylamino end groups showed no enhancement in the catalytic activity. These differences can be ascribed to very effective interactions between the hydrophobic 4-bromobutyl end groups with the hydrophobic thiol, resulting in an enormous increase of the thiol-water interface, due to a decrease in dodecanethiol droplet size. The effects of the end groups decrease with increasing number of N + . 2,4-Ionenes with at least eight quaternary ammonium groups showed similar cocatalytic properties as the high molecular weight 2,4-ionenes. Moreover, the effect of end-capping of polymeric 2,4- and 3,3-ionenes even with long n-alkyl bromides is limited

Synthesis and Cocatalytic Properties of Polystyrene-Ionene-Stabilized Lattices

Cationic latices with excellent cocatalytic properties were designed by emulsion polymer- ization of styrene using monodisperse amphiphilic polystyrene-ionene diblock copolymers as surfactant. The amphiphilic block copolymers built in during the emulsion polymerization of styrene, with the water- soluble initiator 2,2'-azobis(2-amidinopropane) dihydrochloride, possess electrostatic as well as steric stabilization properties. A major advantage of the preparative procedure used is that no extensive cleaning procedures need to be applied. After immobilization of the tetrasodium cobalt(I1) phthalocyaninetetra- sulfonate (CoPc(NaSO&) catalyst onto the latex, reactive latices were obtained which show very high catalytic oxidation rates toward the mercaptoethanol autoxidation. The highest catalytic activity (500 mol of Odmol of Cess)), 15 times higher as compared with the polymer-free system, was achieved with latices with relatively short ionene blocks with 7 quaternary ammonium groups at their particle surface. Despite relatively low surface charge densities, apparently enough ionene chains of sufficient length are present at the particle surface to stabilize the highly active CoPc(NaSO& dimers and to achieve substrate enrichment.