Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 μM and 0.49 μM, respectively, which has potential application value in biological sciences and biotechnology.

Carbazolic Conjugated Organic Polymers for Visible-Light-Driven CO2 Photoreduction with H2 O to CO with High Efficiency and Selectivity

Visible-light-driven CO₂ photoreduction with H₂ O to value-added chemicals in high efficiency and selectivity is significant but challenging. Herein, a series of carbazolic conjugated organic polymers (CB-COPs) with electron donor-acceptor (D-A) structures were prepared, which showed high efficiency for visible-light-driven photocatalytic reduction of CO₂ with H₂ O in a solid-gas mode, affording CO as the exclusive carbonaceous product. Especially, CB-COP-mpd derived from 3,5-di(9H-carbazol-9-yl)pyridine exhibited the highest CO evolution rate up to 191.46 μmol g^-1  h^-1 with a selectivity of 100 %. Mechanism studies showed that carbazolyl is a promising electron donor candidate for constructing CB-COPs with D-A structures, capable of improving the catalytic efficiency and suppressing H₂ generation. The acceptor building block with excessive electron withdrawing capability was favorable to H₂ O adsorption, thus resulting in the generation of H₂ . This work provides new insights for designing COPs photocatalysts for CO₂ photocatalytic reduction.

Selective Aerobic Oxidation of Csp3-H Bonds Catalyzed by Yeast-Derived Nitrogen, Phosphorus, and Oxygen Codoped Carbon Materials

Nitrogen, phosphorus, and oxygen codoped carbon catalysts were successfully synthesized using dried yeast powder as a pyrolysis precursor. The yeast-derived heteroatom-doped carbon (yeast@C) catalysts exhibited outstanding performance in the oxidation of C_sp³-H bonds to ketones and esters, giving excellent product yields (of up to 98% yield) without organic solvents at low O₂ pressure (0.1 MPa). The catalytic oxidation protocol exhibited a broad range of substrates (38 examples) with good functional group tolerance, excellent regioselectivity, and synthetic utility. The yeast-derived heteroatom-doped carbon catalysts showed good reusability and stability after recycling six times without any significant loss of activity. Experimental results and DFT calculations proved the important role of N-oxide (N⁺-O^-) on the surface of yeast@C and a reasonable carbon radical mechanism.

Construction of a transition-metal-free mesoporous organic phenanthroline-based polymeric catalyst for boosting direct activation of aromatic C–H bonds

A novel transition-metal-free mesoporous organic phenanthroline-based polymer for boosting direct activation of aromatic C–H bonds.

Recent advances in metal-free heteroatom-doped carbon heterogonous catalysts

The development of cost-effective, efficient, and novel catalytic systems is always an important topic for heterogeneous catalysis from academia and industrial points of view. Heteroatom-doped carbon materials have gained more and more attention as effective heterogeneous catalysts to replace metal-based catalysts, because of their excellent physicochemical properties, outstanding structure characteristics, environmental compatibility, low cost, inexhaustible resources, and low energy consumption. Doping of heteroatoms can tailor the properties of carbons for different utilizations of interest. In comparison to pure carbon catalysts, these catalysts demonstrate superior catalytic activity in many organic reactions. This review highlights the most recent progress in synthetic strategies to fabricate metal-free heteroatom-doped carbon catalysts including single and multiple heteroatom-doped carbons and the catalytic applications of these fascinating materials in various organic transformations such as oxidation, hydrogenation, hydrochlorination, dehydrogenation, etc.

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.

Nucleobase derived boron and nitrogen co-doped carbon nanosheets as efficient catalysts for selective oxidation and reduction reactions

The search for active, stable and cost-efficient carbocatalysts for selective oxidation and reduction reactions could make a substantial impact on the catalytic technologies that do not rely on conventional metal based catalysts. Here we report a facile strategy for the synthesis of boron (B) and nitrogen (N) co-doped carbon nanosheets (BNC) by using biomolecule guanine as a carbon (C) and N source and boric acid as the B precursor. The whole synthesis process which leads to the formation of a two dimensional (2D) structure and mesoporosity with high surface areas is simple, metal-free and template-free. The as-synthesized carbon nanosheets possess a series of merits, such as relatively high specific surface area, satisfactory pore structure, enough structural defects, abundant B and N dopants as well as oxygen functional groups. The catalytic assessments demonstrate that the presented carbon catalyst is highly active and selective for the liquid phase oxidation of ethyl lactate to ethyl pyruvate and the reduction of nitrobenzene to aniline and outperforms other equivalent benchmarks. Control experiments confirm the importance of the B and N co-doping as well as the carbon matrix which benefit the electron transfer. The carbonyl group masking test indicates that carbonyl groups play an important role in both the selective oxidation and reductions. Given the diversity in the structure of the nucleobase moiety, they represent ideal building blocks for the catalyst-free and metal-free formation of 2D carbon architectures, only induced by hydrogen bonds. This B and N co-doped synthesis strategy provides guidance for the design of carbon-based catalysts for selective oxidation and reductions.

Small organic molecules with tailored structures: initiators in the transition-metal-free C–H arylation of unactivated arenes

A small organic molecule was tailored for the efficient synthesis of biphenyl and its derivatives from aryl iodides.

Recent Advances in Homogeneous Metal-Catalyzed Aerobic C–H Oxidation of Benzylic Compounds

Csp3–H oxidation of benzylic methylene compounds is an established strategy for the synthesis of aromatic ketones, esters, and amides. The need for more sustainable oxidizers has encouraged researchers to explore the use of molecular oxygen. In particular, homogeneous metal-catalyzed aerobic oxidation of benzylic methylenes has attracted much attention. This account summarizes the development of this oxidative strategy in the last two decades, examining key factors such as reaction yields, substrate:catalyst ratio, substrate scope, selectivity over other oxidation byproducts, and reaction conditions including solvents and temperature. Finally, several mechanistic proposals to explain the observed results will be discussed.

Strategies toward High-Performance Cathode Materials for Lithium-Oxygen Batteries

Rechargeable aprotic lithium (Li)-O₂ batteries with high theoretical energy densities are regarded as promising next-generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round-trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li-O₂ batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high-performance cathode catalysts for stable Li-O₂ batteries. Perspectives on enhancing the overall electrochemical performance of Li-O₂ batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high-performance lithium-O₂ batteries.

Synthesis of a molecularly defined single-active site heterogeneous catalyst for selective oxidation of N-heterocycles

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

Solid-State Synthesis of Conjugated Nanoporous Polycarbazoles

A novel solid-state synthetic approach has been developed for the generation of conjugated nanoporous polymer networks. Using mechanochemical-assisted oxidative coupling polymerization, we demonstrated a rapid and solvent-free synthesis of conjugated polycarbazoles with high porosities and promising CO₂ storage abilities. This innovative approach constitutes a new direction for the development of novel nanoporous polymer frameworks through sustainable solid-state assembly pathways, and may open up new possibilities for the rational design and synthesis of nanoporous materials for carbon capture.

Control Synthesis of Tubular Hyper-Cross-Linked Polymers for Highly Porous Carbon Nanotubes

Porous carbon nanotubes (PCNTs) have attracted considerable attention due to their large specific surface areas and unique one-dimensional (1D) structures. However, most of the reported synthetic strategies for PCNTs are complex and expensive. Herein, we present a self-templated, surfactant-free strategy for the synthesis of high-quality PCNTs with high surface area by direct carbonization of 1D hyper-cross-linked polymer nanotubes. The precursors of the 1D hyper-cross-linked polymer nanotubes were synthesized by FeCl₃ catalyzed Friedel-Crafts alkylation of aromatic hydrocarbons with formaldehyde dimethyl acetal. It was found that the monomer concentration and mechanical agitation play crucial roles in the formation of the 1D tubular hyper-cross-linked polymer precursor. The tube size of the resulting PCNTs could be finely controlled by the aromatic monomers with different molecular sizes. The excellent electrochemical performances of the supercapacitors fabricated from the PCNTs demonstrate that these PCNTs are promising for the electrode materials of high-performance supercapacitors. This work highlights that the facile synthetic strategy for PCNTs would open up new avenues of porous carbon nanotube materials with promising applications.

Cobalt nanoparticles supported on N-doped mesoporous carbon as a highly efficient catalyst for the synthesis of aromatic amines

Inexpensive and reusable transition metal heterogeneous catalysts exhibiting excellent catalytic performance represent an attractive alternative to noble metal and homogeneous catalysts. In this work, we fabricated a novel nanocatalyst comprised of Co nanoparticles (NPs) supported on a N-doped mesoporous carbon (Co/mCN-900) by simple one-pot pyrolysis of a homogeneous mixture of melamine, polyacrylonitrile, and Co(NO₃)₂·6H₂O under a N₂ atmosphere at 900°C. The as-obtained Co/mCN-900 catalyst displayed a fluffy mesoporous structure with highly dispersed and accessible Co NPs acting as catalytic active sites. The Co/mCN-900 catalyst was effective in hydrogenating nitroarenes at milder conditions (i.e., 1MPa H₂ and 120°C) as compared to previously reported Co- and Ni-based catalysts. The Co/mCN-900 catalyst also catalyzed the reductive N-alkylation of nitroarenes with carbonyl compounds to form the corresponding aromatic secondary amines under very mild reaction conditions. In addition, the Co/mCN-900 catalyst showed good reusability since its morphology and activity were maintained after several reaction cycles. Therefore, this work provides a facile and promising method for fabricating non-precious transition metal-based catalysts with excellent performance and great potential for sustainable chemistry applications.

Pyridine-functionalized organic porous polymers: applications in efficient CO2 adsorption and conversion

Pyridine-functionalized porous organic polymers showed excellent CO₂ uptake capacity and served as efficient catalysts for the formylation of amines with CO₂/H₂ after metallization with Ru(0) nanoparticles.