Microporous Nanotubes and Nanospheres with Iron-Catechol Sites: Efficient Lewis Acid Catalyst and Support for Ag Nanoparticles in CO2 Fixation Reaction

Removal of Pb(II) ions by cellulose modified-LaFeO3 sorbents from different biomasses

LaFeO3 perovskite is prepared by the cellulose-modified microwave-assisted citrate method using two different biomasses as a cellulose source; rice straw (RS) and banana peel (BP). The prepared samples are assigned as LaFeO3/cellulose-RS and as LaFeO3/cellulose-BP, respectively. Raman Spectra prove the presence of perovskite and cellulose phases, as well as biochar resulted from the thermal treatment of the cellulose. LaFeO3/cellulose-RS has a cauliflower morphology while, two phases are observed for LaFeO3/cellulose-BP, mesoporous cellulose phase and octahedral LaFeO3 nanoparticles as shown by scanning electron microscope (SEM) images. LaFeO3/cellulose-BP has higher porosity and larger BET surface area than LaFeO3/cellulose-RS. Both samples are applied for the removal of Pb(II) ions from aqueous solution by adsorption. The adsorption follows Langmuir isotherm, with maximum adsorption capacities of 524 and 730 mg/g for LaFeO3/cellulose-RS and LaFeO3/cellulose-BP, respectively. Cellulose precursors from different biomasses affect structural and morphological properties of LaFeO3/cellulose samples as well as the sorption performance for Pb(II) ions. BP is more recommended than RS, as a biomass, in the present study.

Regio- and Stereoselective Hydrochlorination/Cyclization of 1,n-Enynes by FeCl3 Catalysis

A highly regio- and stereoselective hydrochlorination/cyclization of enynes has been reported by FeCl₃ catalysis. A variety of enynes undergo this cyclization transformation with acetic chloride as the chlorine source and H₂O providing protons via a cationic pathway. This protocol provides a cheap, simple, stereospecific, and effective cyclization to afford heterocyclic alkenyl chloride compounds as Z isomers with high yields (≤98%) and regioselectivity.

Catechol-Based Porous Organic Polymers for Effective Removal of Phenolic Pollutants from Water

Phenolic pollutants released from industrial activities seriously damage natural freshwater resources, and their elimination or reduction to safe levels is an urgent challenge. In this study, three catechol-based porous organic polymers, CCPOP, NTPOP, and MCPOP, were prepared using sustainable lignin biomass-derived monomers for the adsorption of phenolic contaminants in water. CCPOP, NTPOP, and MCPOP showed good adsorption performance for 2,4,6-trichlorophenol (TCP) with theoretical maximum adsorption capacities of 808.06 mg/g, 1195.30 mg/g, and 1076.85 mg/g, respectively. In addition, MCPOP maintained a stable adsorption performance after eight consecutive cycles. These results indicate that MCPOP is a potential material for the effective treatment of phenol pollutants in wastewater.

Novel and sustainable carboxylation of terminal alkynes and CO2 to alkynyl carboxylic acids using triazolium ionic liquid-modified PMO-supported transition metal acetylacetonate as effective cooperative catalysts

Efficient and sustainable chemical fixation of CO₂ into value-added chemicals is one of the most promising objectives in environmental chemistry. In this work, transition metal acetylacetonate immobilized onto triazolium ionic liquid-modified periodic mesoporous organosilica PMO-IL-M(x) was successfully prepared and investigated as an effective and heterogeneous catalyst in the direct carboxylation of terminal alkynes and CO₂ to the desired alkynyl carboxylic acids. It was found that the catalyst PMO-IL-Sn(0.3) exhibited extraordinary catalytic performance in terms of excellent activity, stability, productivity, and excellent yields under mild reaction conditions. Moreover, the catalyst PMO-IL-Sn(0.3) could be easily recovered and reused at least six times without considerable loss in catalytic activity. This work provides a sustainable and efficient synergistic strategy for the chemical fixation of carbon dioxide into valuable alkynyl carboxylic acids.

Cucurbit[6]uril-Supported Fe3O4 Magnetic Nanoparticles Catalyzed Green and Sustainable Synthesis of 2-Substituted Benzimidazoles via Acceptorless Dehydrogenative Coupling

A new composite, cucurbit[6]uril (CB[6])-supported magnetic nanoparticles, Fe3O4-CB[6], was synthesized via a co-precipitation method in air and fully characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, inductively coupled plasma-mass spectrometry, and vibrating sample magnetometry techniques. It has been found to be a highly efficient, economic, and sustainable heterogeneous catalyst and has been employed for the first time for the synthesis of a series of biologically important 2-substituted benzimidazoles from various benzyl alcohols and 1,2-diaminobenzenes under solvent-free conditions via acceptorless dehydrogenative coupling to afford the corresponding products in good to excellent yields (68-94%). The magnetic nature of the nanocomposite facilitates the facile recovery of the catalyst from the reaction mixture by an external magnet. The catalyst can be reused up to five times with negligible loss in its catalytic activity. All the isolated products were characterized by 1H and 13C{1H} NMR spectroscopy.

Metal-Organic Polymer-Derived Interconnected Fe-Ni Alloy by Carbon Nanotubes as an Advanced Design of Urea Oxidation Catalysts

The electrochemical urea oxidation reaction (UOR) is considered as a promising renewable source for harvesting energy from waste. We report a new synthetic design approach to produce an iron-nickel alloy nanocatalyst from a metal-organic polymer (MOP) by a single-step carbonization process at 500 °C, thus forming a core-shell of iron-nickel-coated carbon (C@FeNi) nanostructures wired by embedded carbon nanotubes (CNTs) (CNT/C@FeNi). Powder X-ray diffraction confirmed the formation of metallic FeNi₃ alloy nanoparticles (∼20 to 28 nm). Our experimental results showed that MOP containing CNTs acquired an interconnected hierarchical topology, which prevented the collapse of its microstructure during pyrolysis. Hence, CNT/C@FeNi shows higher porosity (10 times) than C@FeNi. The electrochemical UOR in alkaline electrolytes on these catalysts was studied using cyclic voltammetry (CV). The result showed a higher anodic current (3.5 mA cm^-2) for CNT/C@FeNi than for C@FeNi (1.1 mA cm^-2) at 1.5 V/RHE. CNT/C@FeNi displayed good stability in chronoamperometry experiments and a lower Tafel slope (33 mV dec^-1) than C@FeNi (41.1 mV dec^-1). In this study, CNT/C@FeNi exhibits higher exchange current density (3.2 μA cm^-2) than does C@FeNi (2 μA cm^-2). The reaction rate orders of CNT/C@FeNi and C@FeNi at a kinetically controlled potential of 1.4 V/RHE were 0.5 and 0.9, respectively, higher than the 0.26 of β-Ni(OH)₂, Ni/Ni(OH)₂ electrodes. The electrochemical impedance result showed a lower charge-transfer resistance for CNT/C@FeNi (61 Ω·cm^-2) than for C@FeNi (162 Ω·cm^-2), due to faster oxidation kinetics associated with the CNT linkage. Moreover, CNT/C@FeNi exhibited a lower Tafel slope and resistance and higher heterogeneity (25.2 × 10^-5 cm s^-1), as well as relatively high faradic efficiency (68.4%) compared to C@FeNi (56%). Thus, the carbon-coated FeNi₃ core connected by CNT facilitates lower charge-transfer resistance and reduces the UOR overpotential.

Morphologically controlled cobalt oxide nanoparticles for efficient oxygen evolution reaction

Electrochemical water oxidation is one of the thrust areas of research today in solving energy and environmental issues. The morphological control in the synthesis of nanomaterials plays a crucial role in designing efficient electrocatalyst. In general, various synthetic parameters can direct the morphology of nanomaterials and often this is the main driving force for the electrocatalyst in tuning the rate of the oxygen evolution reaction (OER) for the electrochemical water-splitting. Here, a facile and cost-effective synthesis of spinel cobalt oxides (Co₃O₄) via a one-pot hydrothermal pathway with tunable morphology has been demonstrated. Different kinds of morphologies have been obtained by systematically varying the reaction time i.e. nanospheres, hexagon and nanocubes. Their catalytic activity has been explored towards OER in 1.0 M alkaline KOH solution. The catalyst Co₃O₄-24 h nanoparticles synthesized in 24 h reaction time shows the lowest overpotential (η) value of 296 mV at 10 mA cm^-2 current density, in comparison to that of other as-prepared catalysts i.e. Co₃O₄-pH9 (311 mV), Co₃O₄-12 h (337 mV), and Co₃O₄-6 h (342 mV) with reference to commercially available IrO₂ (415 mV). Moreover, Co₃O₄-24 h sample shows the outstanding electrochemical stability up to 25 h time.

Palladium supported on structurally stable phenanthroline-based polymer nanotubes as a high-performance catalyst for the aqueous Suzuki–Miyaura coupling reaction

One-dimensional Pd-supported catalyst exhibits excellent catalytic activity since its TOF value is 3077 h⁻¹ for the Suzuki–Miyaura coupling reaction of bromobenzene and phenylboronic acid under ambient conditions.

Metalation of Catechol-Functionalized Defective Covalent Organic Frameworks for Lewis Acid Catalysis

Covalent organic frameworks (COFs) have emerged as a fascinating crystalline porous material and are widely used in the field of catalysis. However, developing simple approaches to fabricate conjugated COFs with specific functional groups remains a significant challenge. In this study, the construction of defective COF-LZU1 with Lewis acid sites embedded into the frameworks is fulfilled by a facile solvent-assisted ligand exchange method. A monodentate ligand, protocatechualdehyde, is successfully introduced into the skeleton of COF-LZU1, which endows the defects in the structure of COF-LZU1 via replacement of the original coordinated benzene-1,3,5-tricarbaldehyde ligand. As-synthesized defective COF-LZU1 decorated with protocatechualdehyde is rich of free hydroxy groups for chelating with active metal ions. Specifically, after combining with Fe³⁺ , the defective COF-LZU1 shows excellent activity in catalytic alcoholysis of epoxides under mild conditions. The method reported here will open up the opportunity to incorporate different functional groups into COFs and enrich the strategies for creating new types of porous catalysts.

AgNPs encapsulated by an amine-functionalized polymer nanocatalyst for CO2fixation as a carboxylic acid and the oxidation of cyclohexane under ambient conditions

A novel catalyst comprising Ag NPs grafted to a porous polystyrene material was synthesized for the production of valuable propiolic acid derivativesviaCO₂(1 atm) incorporation, and the oxidation of cyclohexane under ambient reaction conditions.

Size-Controlled Growth of Silver Nanoparticles onto Functionalized Ordered Mesoporous Polymers for Efficient CO2 Upgrading

Highly dispersed metallic silver nanoparticles (AgNPs) are promising heterogeneous catalysts for carboxylative coupling of terminal alkynes with CO₂ under mild conditions. Yet, their size-controlled synthesis is very challenging because of the high surface energy. Here, we prepared a series of amino-functionalized ordered mesoporous polymers as hosts for anchoring AgNPs. Control experiments and computations showed that electron-rich amines were confined in mesochannels with varying electron density and steric hindrance, creating "localized active zones (LAZ)" to control the growth of AgNPs. The particle size of AgNPs grows along with the increased volume of LAZ around nitrogen species. We also revealed that the catalytic activity of Ag-based catalysts is size-dependent and increases with decreasing particle size. Building on these findings, we report a facile one-pot synthesis strategy for preparing an amine-incorporated ordered mesoporous polymer (NOMP) with a high specific surface area, small LAZ volume, and uniform amine sites with controllable loading. These features result in the formation of ultrasmall and monodispersed Ag nanoparticles. Remarkably, Ag@NOMP gave a quantitative target yield under the conditions of 1 atm CO₂ pressure and 50 °C, showing superior catalytic activity in CO₂ carboxylation compared to other mesoporous analogues.

Double-Helical Ag-S Rod-Based Porous Coordination Polymers with Double Activation: σ-Active and π-Active Functions

As common coinage metals, silver and silver compounds have very rich application in the organic catalytic reaction. Immobilization of silver compounds on heterogeneous media is the most common way used in industrial catalytic reactions. In this work, we designed and synthesized a new heterogeneous porous silver catalyst, with in situ-formed Ag-S rods as connecting nodes and thiosemicarbazide-functionalized linear ligands, used in both σ- and π-catalytic transformations. Strong Ag-S bonds bypassed the loss of noble silver elements and inhibited the formation of nonporous silver particles which always led to the decrease of yields in homogenous reactions. Furthermore, various derivatives of propargylamines and phenylacetylenes were applied as both σ and π-active substrates with moderate to good yields.