Nanocomposite Catalyst Research Articles

Synthesis, characterization, catalytic reduction of Eosin B dye and C, N cross coupling reactions of sodiumalginate/V2O5 nanocomposite

BackgroundA low cost with high efficiency sodiumalginate (SA)/V2O5 nanocomposite catalyst was synthesized by complexation followed by reduction method. The V2O5 catalyst and SA was chemically linked with each other and hence restriction in diffusion of the catalyst into the reaction medium during the course of the reaction. The catalytic activity of SA/V2O5 bio-nano catalyst system was tested towards the C, N cross coupling reaction and reduction of EB dye. MethodsThe bio-polymer nanocomposite formation was confirmed by FT-IR spectroscopy, 1H-NMR spectroscopy, DSC (Tg) and TGA (Td) and HR-TEM (size) like analytical tools. The cross coupling reaction between rosebengal (RB) and nitrogen containing heterocyclic compounds like indole, benzimidazole, 2-methylimidazole were carried out. Same type of reaction was carried out with congored (CR), acidfuchsin (AF) and safranine O (SO) dyes. Further, the catalytic activity of SA/V2O5 nanocomposite catalyst was tested towards the reduction of Eosin blue (EB) dye. Significant findingsThe FTIR spectrum showed a peak at 615 cm−1 due to the V-O stretching. The 1H-NMR spectrum confirmed that the OH group of SA involved in the complex formation with V atom of V2O5. The Tg and Td of the SA/V2O5 bio-polymer nanocomposite system was higher than that of the neat polymer. The apparent rate constant (kapp) value was found to be higher in the presence of SA/V2O5 catalyst system. The C,N cross coupling reaction was successfully carried out with significant % yield in the presence of low cost and eco-friendly SA/V2O5 nano catalyst. The catalyst was stable up to several cycles of operations.

Grape-like CNTs/BaTiO3 nanocatalyst boosted hydraulic-driven piezo-activation of peroxymonosulfate for carbamazepine removal

• Grape-like CNTs/BT nanocomposite catalyst with Ti − C bond was synthesized. • CNTs/BT boosted hydraulic-driven piezo-activation of PMS for CBZ removal. • CNTs/BT-PMS system generated much more ROS than BT-PMS and CNTs-PMS systems with less energy. • CNTs acted as fast electron lanes for accelerating separation of piezoelectric carriers. • Piezoelectric field effectively suppressed destruction of CNTs in PMS system. Both carbon nanotubes (CNTs) and piezoelectric materials can activate peroxymonosulfate (PMS). However, the activation of PMS by CNTs suffers from poor reusability while hydraulic-driven piezo-activation of PMS faces the problem of limited charge separation. To solve the above problems, grape-like CNTs/BaTiO 3 (CNTs/BT) nanocatalyst with a Ti − C bond was prepared. Results indicated that hydraulic-driven CNTs/BT-PMS system offered remarkable carbamazepine removal efficiency (91.93%, 120 min) with satisfactory reusability. The energy consumption of PMS activation by CNTs/BT was only 39.33% and 26.59% of those by CNTs and BT, respectively. Piezoresponse force microscopy and finite element simulation further suggested that these superior performances were mainly responsible for the synergistic effects of CNTs and BT, leading to stronger piezoelectric response with efficient piezo-generated charge separation, which in turn improved the efficiency for producing reactive species. Notably, the built-in piezoelectric field of BT constantly replenished electrons to CNTs and effectively suppressed the destruction of CNTs caused by chemical oxidation. This durable composite might be a promising catalyst for PMS activation with potential utilization of residual hydraulic power during water treatment.

Ultrafast Preparation of Metal/Carbon Nanocomposite Electrocatalysts by Magnetic Induction Heating toward Efficient Hydrogen Evolution Reaction

Hydrogen, which can be readily produced by electrochemical water splitting, has been hailed as one of the most promising green energy sources. In a water electrolyzer, catalysts are needed for the hydrogen evolution reaction (HER) at the cathode, which are traditionally based on platinum-based materials. Recently, carbon-based nanocomposites have emerged as viable alternatives, which are mostly prepared by pyrolysis or wet chemistry methods, which are time- and energy-consuming. We have exploited magnetic induction heating (MIH) for ultrafast and green preparation of high-performance HER electrocatalysts. A novel MIH method was developed for the ultrafast and green preparation of carbon-supported Ru NPs toward HER in alkaline media, where the size and morphology of the Ru NPs can be readily manipulated by the heating current and duration. It is expected that MIH can be exploited for the design and engineering of high-performance nanocomposite catalysts for important electrochemical energy technologies.

Nanocomposite Catalyst for High-Performance and Durable Intermediate-Temperature Methane-Fueled Metal-Supported Solid Oxide Fuel Cells.

CH4-fueled metal-supported solid oxide fuel cells (CH4-MS-SOFCs) are propitious as CH4 is low-priced and readily available, and its renewable production is possible, such as biomethane. However, the current CH4-MS-SOFCs suffer from either poor power density or short durable operation, which is ascribed to the low catalytic activity and poor coking tolerance of the metallic anode support. Herein, we have deliberately designed and synthesized a highly active nanocomposite catalyst, Sm-doped CeO2-supported Ni, as the internal steam methane reforming catalyst, to optimize CH4-MS-SOFCs. Both power densities and durability of optimized CH4-MS-SOFCs have been dramatically enhanced compared to the pristine CH4-MS-SOFCs. The optimized CH4-MS-SOFCs deliver the highest performances among all zirconia-based CH4-MS-SOFCs. Furthermore, the operating temperature has been reduced to 600 °C. At 600 °C, a viable peak power density of >350 mW/cm2 is achieved, which is more than three times as high as the pristine CH4-MS-SOFCs. Furthermore, the optimized CH4-MS-SOFC achieves >1000 h of stable operation.

Metal-oxide nanocomposite catalyst simultaneously boosts the oxygen reduction reactivity and chemical stability of solid oxide fuel cell cathode

Conductive perovskite oxides have received much attention as promising candidates for solid oxide fuel cell (SOFC) cathodes. However, they show chemical instability due to the segregation of A-site cations on the surface at high temperatures, which causes their performance to degrade. Moreover, the high activation barrier to oxygen reduction reactions makes these materials more difficult to use as electrodes at lower temperatures (less than 700 °C). Herein, by combining two general techniques: nanoparticle infiltration and atomic layer deposition (ALD), we significantly improve both the durability and reactivity of a state-of-the-art perovskite oxide, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). Ag nanocatalysts are dispersed onto an LSCF cathode via wet infiltration, after which they are covered with a thin ZrO2 layer via ALD to prevent the agglomeration of nanocatalysts and the segregation of Sr ions. Accordingly, the Ag/ZrO2 nanocomposite-deposited LSCF cathode shows the electrode resistance of 0.085 Ωcm2 at 650 °C over 200 h, which is, to the best of our knowledge, the near-record level among all nanocatalyst-infiltrated LSCF cathode to date. Our result suggests a new research direction to fully utilize nanocatalysts and perovskite oxides in SOFCs, which can be a shortcut to their commercialization.

Construction of heterostructure interface with FeNi2S4 and CoFe nanowires as an efficient bifunctional electrocatalyst for overall water splitting and urea electrolysis

The design of high-performance non-noble-metal-based electrocatalysts for electrooxidation reactions involving splitting of water molecule for energy and environmental applications is the need of the hour. In this study, we report the electrocatalytic performance of a nanocomposite catalyst of FeNi2S4 nanoparticles/CoFe nanowires supported on nickel foam that was prepared by a simple hydrothermal method. The electrocatalyst has several advantages, such as the nanocomposite structure, relatively high electrical conductivity, and synergistic effect between FeNi2S4 and CoFe. These characteristics enhanced the catalytic efficiency of FeNi2S4/CoFe electrode, gaining small overpotentials of 380 and 207 mV for oxygen and hydrogen evolution reactions, respectively, at a current density of 100 mA cm−2. The charge transfer processes are significantly improved by the electron pairs from FeNi2S4 and CoFe, as well as by the enhanced active sites at the electrode-electrolyte interface and their bonding interactions. The electrooxidation of urea was also explored, which showed a lower overpotential of 230 mV to reach 100 mA cm−2 current density. Interestingly, FeNi2S4/CoFe was successfully employed as cathode and anode for urea-assisted water electrolysis, utilizing 1.56 V to produce 10 mA cm−2 current density, which is approximately 160 mV below that for water electrolysis, thus verifying the lower energy consumption during electrolysis. These results indicate that nanoparticle and nanowire composite catalysts can be used for wastewater treatment and green energy production applications.

Development of Cobalt Oxide Nanocomposite Catalyst from Cobalt Aluminum Layered Double Hydroxide Precursor Towards Aerobic Alcohol Oxidation

Development of Cobalt Oxide Nanocomposite Catalyst from Cobalt Aluminum Layered Double Hydroxide Precursor Towards Aerobic Alcohol Oxidation

Efficient activation of peroxydisulfate by FeNC for chloramphenicol degradation: Performance and mechanisms

In this study, a green Fe and FeN co-doped carbon nanocomposite catalyst (FeNC) was synthesized by a simple and economical method and applied to activate peroxodisulfate (PDS) for the efficient oxidation of chloramphenicol (CAP). Characterization analysis found that the surface of Fe and FeN nanoparticles supported on nitrogen-doped carbon was wrapped by nitrogen-doped carbon nanosheets, forming a "core-shell" structure. The FeNC@PDS system has good catalytic activity, and the CAP degradation efficiency reaches 91.2% within 60 min. FeNC@PDS system exhibits excellent catalytic degradation performance under a wide pH range (2.4–8.3) and shows good reusability. The calculated % reaction stoichiometric efficiency (RSE) reached values up to 18.86%, which exceeds than those of various reported heterogeneous Fenton-like systems. Quenching experiments and electron paramagnetic resonance characterization confirmed that both free-radicals and non-radicals were involved in the activation of PDS by FeNC. In addition, the possible mechanism of the PDS activation by FeNC was proposed. Finally, the degradation pathway of CAP was determined based on the intermediates. This work provided a novel reference for the design of efficient heterogeneous catalysts to remove organic pollutants efficiently.

One-Pot Synthesis of 1,8-Dioxodecahydroacridines using Ag-TiO2 Nanocomposite as a Mild and Heterogeneous Catalytic System

Abstract:Ag-TiO2 nanocomposite is reported to be an efficient, active, and benign recyclable catalyst for highly efficient synthesis of 1,8-dioxodecahydroacridine derivatives from dimedone, aromatic aldehydes, and several anilines or ammonium acetate in ethanol as a solvent at room temperature in a short reaction time and suitable yield. This catalyst is effortlessly recycled by simple filtration and can be reused up to five times with only a negligible loss in its catalytic effectiveness. Low catalyst loading, cost-effectively mild conditions, non-chromatographic purification of target compounds, excellent atom economy, informal procedure, use of a cheaply accessible nanocomposite catalyst, and recyclability of the catalyst are all significant benefits of this method. AFM analysis is performed to confirm the structure, topography, and morphology of Ag-TiO2 nanocomposite. 1,8-dioxodecahydroacridine derivatives having natural significance possess a wide range of pharmacological activities; for instance, antibacterial, antimalarial, anticancer, and mutagenic properties. In terms of the distinctions between aldehydes and anilines, this approach offers a wide range of applications.

Covalent organic frameworks@ZIF-67 derived novel nanocomposite catalyst effectively activated peroxymonosulfate to degrade organic pollutants

Metal organic frameworks-Covalent organic frameworks (MOFs-COFs) nanocomposites could improve the catalytic performance. Herein, a novel nanocomposite catalyst (CC@Co3O4) derived from MOFs-COFs (COF@ZIF-67) was prepared on peroxymonosulfate (PMS) activation for bisphenol A (BPA) and rhodamine B (RhB) degradation. Owing to the Co species, oxygen vacancy (OV), surface hydroxyl (-OH), graphite N and ketone groups (C=O), the CC@Co3O4 exhibited higher catalytic degradation performance and total organic carbon (TOC) for BPA (93.8% and 22.3%) and RhB (98.2% and 82.5%) with a small quantity of catalyst (0.10 g/L) and low concentration of PMS (0.20 g/L) even without pH adjustment. Sulfate radicals (•SO4−), hydroxyl radicals (•OH), single oxygen (1O2), superoxide radicals (•O2−) and electron transfer process were all involved in the degradation of BPA and RhB. Among them, the degradation of BPA and RhB mainly depended on •O2− and 1O2, respectively. Meanwhile, the degradation pathways of BPA and RhB were proposed, and the biotoxicity of the degradation products was evaluated by freshwater chlorella. The results illustrated that the degradation products were environmentally friendly to organisms. In addition, the role of COF in the nanocomposites was also studied. The addition of COF remarkably improved the catalytic performance of CC@Co3O4 due to the faster electron transfer, more graphite N and C=O. Overall, this work may open the door to the development of COF-based catalysts in the field of water pollutant remediation.

Mg-O-F Nanocomposite Catalysts Defend against Global Warming via the Efficient, Dynamic, and Rapid Capture of CO2 at Different Temperatures under Ambient Pressure.

The utilization of Mg-O-F prepared from Mg(OH)2 mixed with different wt % of F in the form of (NH4F·HF), calcined at 400 and 500 °C, for efficient capture of CO2 is studied herein in a dynamic mode. Two different temperatures were applied using a slow rate of 20 mL·min-1 (100%) of CO2 passing through each sample for only 1 h. Using the thermogravimetry (TG)-temperature-programed desorption (TPD) technique, the captured amounts of CO2 at 5 °C were determined to be in the range of (39.6-103.9) and (28.9-82.1) mgCO2 ·g-1 for samples of Mg(OH)2 mixed with 20-50% F and calcined at 400 and 500 °C, respectively, whereas, at 30 °C, the capacity of CO2 captured is slightly decreased to be in the range of (32.2-89.4) and (20.9-55.5) mgCO2 ·g-1, respectively. The thermal decomposition of all prepared mixtures herein was examined by TG analysis. The obtained samples calcined at 400 and 500 °C were characterized by X-ray diffraction and surface area and porosity measurements. The total number of surface basic sites and their distribution over all samples was demonstrated using TG- and differential scanning calorimetry-TPD techniques using pyrrole as a probe molecule. Values of (ΔH) enthalpy changes corresponding to the desorption steps of CO2 were calculated for the most active adsorbent in this study, that is, Mg(OH)2 + 20% F, at 400 and 500 °C. This study's findings will inspire the simple preparation and economical design of nanocomposite CO2 sorbents for climate change mitigation under ambient conditions.

Electrostatic Spinning Strategy to Prepare Cage-like PAN-Fiber Network-Wrapped Co–N–C Structures for the Oxygen Reduction Reaction

Zeolitic imidazolate framework (ZIF)-derived carbon materials are highly desirable cathode catalysts for the oxygen reduction reaction (ORR). Unfortunately, ZIF-derived materials undergo microscale migration, structural collapse, and aggregation of Co atoms during high-temperature pyrolysis. Here, we used an electrospinning technique to combine polyacrylonitrile (PAN) with carbonized ZIF-67 that can obtain cage-like nanocomposite catalysts (Co–N–C@PAN) by repyrolysis. It is found that the obtained composite Co–N–C@PAN has a hierarchical structure, and a high surface area and pore space with a volume is favorable for the adequate disclosure of ORR active sites. More importantly, this cage-like structure forms a stable Co–N–C structure and allows Co nanoparticles to be uniformly found in the Co–N–C substrate, which improves the active site of Co–NX. The as-prepared samples exhibit superior performance for the ORR with an onset potential (Eonset) of 1.05 V versus the reversible hydrogen electrode (RHE) and a half-wave potential (E1/2) of 0.93 V versus the RHE, both of which are higher than commercial Pt/C. In addition, Co–N–C@PAN was applied as a cathode for zinc–air batteries and display a superior power density (132 mW cm–2) at a discharge current density of 219 mA cm–2. Furthermore, at a constant discharge current density of 10 mA cm–2, a specific capacity of 761 mA h gZn–1 was obtained. This study may provide an idea for the design and synthesis of nanostructures prepared by electrostatic spinning/ZIF composites.

Bifunctional Catalytic Activity of γ-NiOOH toward Oxygen Reduction and Oxygen Evolution Reactions in Alkaline Solutions

Nickel oxyhydroxides (NiOOHs) are well-known for their superior activity toward oxygen evolution reaction (OER) in alkaline solutions. However, their activity toward oxygen reduction reaction (ORR) has been largely unexplored. There exist three NiOOH polymorphs: α-, β-, and γ-NiOOH, characterized by different interlayer spacing. Although still debated, γ-NiOOH with a large layer spacing has been indicated as the active phase for OER. Here, a highly crystalline γ-NiOOH was prepared in a carbon matrix by the in situ electrochemical transformation of nickel dithiooxamide Ni(dto) in 1 M KOH solution. The catalyst prepared in this way showed low overpotential not only for OER, but also for ORR in alkaline solutions. The onset potential for ORR is ~0.81 V vs. RHE, and the reaction proceeds via the 2e− transfer pathway. The high OER catalytic activity and relatively low ORR overpotential make this nanocomposite catalyst a good candidate for bifunctional OER/ORR catalyst, stable in alkaline solutions.

(PEFC&E 2022 Student Poster Award Winner - 3rd Place) PEFC Electrocatalysts Using Sn-Based Materials Dispersed on Mesoporous Carbon

Introduction Cathode catalysts of polymer electrolyte fuel cells (PEFCs) are subjected to a severe environment of strong acidity and high potential, leading to catalyst degradation[1]. In particular, catalyst degradation in fuel cell vehicles is often caused by oxidative corrosion of their carbon support during start-stop cycles, and by dissolution and re-deposition of platinum particles during load cycles[2]. Our research group has been studying nanocomposite catalysts (Pt-oxide) combining Pt with metal oxides (TiO2, SnO2) of a few nm in size, suppressing the aggregation and degradation of Pt catalysts during load cycles and also during start-stop cycles[3]. Here in this study, we prepare nanocomposite catalysts using SnO2 as a metal oxide, evaluate their electrochemical performance, and control support framework and heat treatment conditions to consider design guidelines for higher performance and durability of PEFC electrocatalysts. Experimental Pt-SnO2 nanocomposite electrocatalysts were prepared by the acetylacetonate (acac) method[4], in which Pt and Sn are loaded simultaneously to form nanocomposite of Pt and SnO2. This study used mesoporous carbon (MC) with 10 nm diameter mesopores as a support framework to impregnate the nanocomposite within the mesopores. The loading of Pt-SnO2 was 42 wt.%, and the volume ratio of Pt:SnO2 was 1:2. Loadings of Pt and SnO2 in the prepared Pt-SnO2/MC were confirmed by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and TG analysis. Microstructure was observed by STEM. The initial activity and durability of the electrocatalysts were evaluated by half-cell measurements. Results and discussion ICP-AES and TG analysis of the prepared Pt-SnO2/MC confirmed that Pt-SnO2 nanocomposite was loaded at a volume ratio of Pt:SnO2=1:2, which was close to the designated ratio. EDS elemental analysis confirmed the presence of Sn between the Pt particles, suggesting the formation of a nanocomposite structure. STEM microstructural observation confirmed that catalyst particles were loaded inside the mesopores besides on MC (agglomerate) surfaces. The ratio of internal particles was 55 %. The obtained catalyst was subjected to load cycle tests (100,000 cycles), and was found to be more durable in catalytic activity. In this presentation, electrochemical properties using related materials will be presented. Acknowledgment This research was partly supported by the New Energy and Industrial Technology Development Organization (NEDO).

One-pot synthesis of SnO2 nanoparticles decorated multi-walled carbon nanotubes using pulsed laser ablation for photocatalytic applications

This work reports the synthesis and characterization of SnO2/CNT nanocomposites and their photocatalytic performance. The nanocomposite catalysts were assembled via a pulsed laser ablation technique. Characterization was then undertaken by employing transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and ultraviolet–visible spectroscopy. The photocatalytic activities of the SnO2/CNT nanocomposite variants were studied based on the photodegradation of the methylene blue dye (MB). In this, the kinetics and mechanisms of the photocatalytic reactions were evaluated. The results from the various analyses were all correlated in confirming the composition, the incorporation of the dopant species and the structure of the nanocomposite catalysts. In particular, the crystallite sizes in the SnO2 and the fabricated SnO2-CNT 5 % and SnO2-CNT 10 % materials were confirmed as 26.40 nm, 30.90 nm, and 28.69 nm, respectively. The UV light-induced photocatalytic reactions were rapid, leading to 94 % removal of the MB dye in 60 min and 120 min of UV irradiation, in the presence of the SnO2-CNT 10 % and the SnO2-CNT 5 %, respectively. The overall reactions follow pseudo-first order kinetics, yielding rate constants of 2.82 × 10−2 min−1 and 4.24 × 10−2 min−1, for the SnO2-CNT 5 % and the SnO2-CNT 10 % photocatalyzed reactions, respectively. The overall findings of this work demonstrate the effectiveness of laser-based synthesized SnO2-CNT nanocomposites in the UV light-induced degradation of the MB dye pollutant and show a potential application for the removal of a wide range of other dyes from wastewater.

Nanocomposite Co-catalysts, based on smectite and biowaste-derived carbon, as peroxymonosulfate activators in degradation of tartrazine

Chitosan (Ch)-derived from biowaste along with smectite, an abundant clay mineral, were used in a low-cost and eco-friendly synthesis of a new type of catalyst. Nanocomposite catalysts constituted of Co supported on smectite with chitosan-derived carbon loading were obtained using an impregnation‑carbonization procedure and denoted as Co/cCh-S-T (T stands for applied carbonization temperature). The carbonization was performed in the temperature range from 400 °C to 700 °C in the flow of N2 providing inert atmosphere. The temperature of 500 °C was found to be the most suitable for catalyst synthesis regarding catalytic performance in a peroxymonosulfate activated degradation of tartrazine. The incorporation of carbonized chitosan structure within the interlamellar space of the smectite was confirmed using X-ray powder diffraction. The high-resolution transmission electron microscopy confirmed a layered structure of nanocomposites characteristic for smectite, as well as the presence of small spherical cobalt containing nanoformations (confirmed by energy dispersive X-ray spectroscopy) well dispersed within structure. The existance of cobalt in the CoII and CoIII oxidation state was proven by X-ray photoelectron spectroscopy. The Co/cCh-S-500 catalyst was proven to be stable and efficient after 5 consecutive cycles. This work showed that nanocomposite Co-catalysts, based on smectite and biowaste-derived carbon, as peroxymonosulfate activators exhibited a very promising performance in the degradation of water pollutants.

Nanocomposite catalysts of non-purified MoVNbTeOx with CeO2 or TiO2 for oxidative dehydrogenation of ethane

The phase-pure M1 of MoVNbTeOx has been demonstrated as a highly active catalyst for oxidative dehydrogenation of ethane (ODHE) reaction. However, the MoVNbTeOx without further purification shows poor catalytic performance so that the M2 phase has to be removed from the bulk material to approach the high purity of M1 phase. This work presents new discovery that the nanocomposite catalyst by adding CeO2 to the MoVNbTeOx using sol–gel method can effectively promote its catalytic performance. As a comparison, the sample combining TiO2 and MoVNbTeOx is also prepared which presents limited influence. The characterization results show that the enhanced catalyst performance can be attributed to the increased active species at the catalyst surface due to the addition of CeO2. This work would provide a new solution to greatly simplify the preparation procedure of MoVNbTeOx catalysts for the ODHE process and avoid the mass loss during the purification procedure.

Directed self-assembled pathways of 3D rose-shaped PtNi@CeO2 electrocatalyst for enhanced hydrogen evolution reaction

The development of high electrocatalytic activity and low-cost Pt-containing catalyst is highly feasible for hydrogen evolution reactions under alkaline conditions. In this study, a series of three-dimensional (3D) rose-shaped cerium (IV) oxide (CeO2)-supported Pt and Ni alloy nanocomposite catalysts were prepared by a direct solvothermal method (PtxNiy @CeO2), and the catalytic activity of the prepared catalysts in hydrogen evolution reactions was studied. The experimental results show that the rose-shaped CeO2 as a carrier can provide abundant oxygen vacancies, and when combined with Pt and Ni, it will trigger the rearrangement of metal electrons. At the same time, this special structure can provide a larger specific surface area and expose more active sites. Bimetallic catalysts have higher hydrogen evolution reaction (HER) activity than monometallic catalysts due to the interaction between metals. In the composite catalyst with a molar ratio of Pt to Ni of 1:1 (Pt1Ni1 @CeO2), electrons are transferred from Ni to Pt. At this time, the catalyst exhibits the most excellent HER catalytic performance. Exhibits low HER overpotential (59 mV) and Tafel slope (56.50 mV dec−1) at a current density of 10 mA cm−2. In addition, the composite catalyst exhibits distinguished long-term electrochemical stability within 15 h. This work provides new possibilities for the effective combination of rare earth oxides and Pt-based materials as high-efficiency HER electrocatalysts under alkaline conditions.

A Novel Recyclable Bi-Mg-O Composite Nano-Catalyst Promoted Rapid and Efficient Synthesis of Spirooxindole and 4H-Pyran Derivatives

A novel Bi-Mg-O composite nano-catalyst was prepared by using Bi(NO3)3 and nano-MgO. Prepared catalyst was characterized using x-ray diffraction (XRD) analysis, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) technique which confirms its nano-crystalline nature and composition. The synthesized novel catalyst Bi-Mg-O was found to be competent catalyst for the synthesis of spirooxindole derivatives by multicomponent reaction of isatin, dimedone, malononitrile and 4H-pyran derivatives by reaction of dimedone, aryl aldehydes and malononitrile using ethanol as solvent at room temperature. The nanocatalyst proved to be recyclable as it is recycled and recovered for three runs without notable loss in catalytic activity. All synthesized derivatives were obtained in exemplary yields. Novel recyclable nanocatalyst, good yields of products, and benign reaction conditions are the noteworthy aspects of the present protocol.

Revealing the fundamental role of MoO2 in promoting efficient and stable activation of persulfate by iron carbon based catalysts: Efficient Fe2+/Fe3+ cycling to generate reactive species

Electron-rich iron sites are the main sites for iron-based catalysts to activate persulfate (PS) to generate reactive species, while blocked Fe2+/Fe3+ cycling usually reduces the catalytic performance of iron-based materials and hinders the generation of reactive species in the reaction. To solve the bottleneck, we synthesized an iron-carbon nanocomposite catalyst loaded with MoO2 (Fe/Mo-CNs). The promotion of MoO2 on the Fe2+/Fe3+ cycle in the system allowed Fe/Mo-CNs to exhibit excellent catalytic performance and environmental adaptability. The degradation rate of bisphenol S (BPS) by the Fe/Mo-CNs/PS system was significantly increased to 0.080 min−1 compared with the iron-carbon based catalyst/persulfate system, and the degradation efficiency of BPS was maintained at around 85% after four cycles. Density functional theory (DFT) calculations showed that the introduction of MoO2 reduced the reaction energy barrier of persulfate activated by catalysts to produce reactive species, especially promoted the production of more high valent iron (Fe(IV)). Fe(IV) and reactive oxygen species (SO4·−, ·OH, ·O2− and 1O2) worked together on the efficient degradation of BPS. In addition, the test of an automatic circulating degradation plant had proved that Fe/Mo-CNs had a good practical application prospect. BPS was mainly degraded by ring cleavage and O=S=O bond cleavage, and the toxicity of BPS and its intermediates were also evaluated. This work clarifies the mechanism of improving the catalytic performance of heterogeneous iron-based catalysts by MoO2 in sulfate radical-based advanced oxidation processes (SR-AOPs), providing a new idea for solving the blockage of Fe2+/Fe3+ cycle in SR-AOPs.