Synthesis strategies of covalent organic frameworks: An overview from nonconventional heating methods and reaction media

Covalent organic frameworks(COFs), as an emerging class of porous crystalline materials constructed by covalent links between the building monomers, have gained tremendous attention. Over the past 15 years, COFs have made rapid progress and substantial development in the chemistry and materials fields. However, the synthesis of COFs has been dominated by solvothermal methods for a long time and it usually involves high temperature, high pressure and toxic organic solvents, which created many challenges for environmental considerations. Recently,the exploration of new approaches for facile fabrication of COFs has aroused extensive interest. Hence, in this review, we comprehensively describe the synthetic strategies of COFs from the aspects of nonconventional heating methods and reaction media. In addition, the advantages,limitations and properties of the preparation methods are compared. Finally, we outline the main challenges and development prospects of the synthesis of COFs in the future and propose some possible solutions.

Atomic Level Dispersed Metal–Nitrogen–Carbon Catalyst toward Oxygen Reduction Reaction: Synthesis Strategies and Chemical Environmental Regulation

For development and application of proton exchange membrane fuel cell(PEMFC) energy transformation technology, the cost performance must be elevated for the catalyst. At present, compared with noble metal-based catalysts, such as Pt-based catalysts, atomically dispersed metal–nitrogen–carbon(M–N–C) catalysts are popularity and show great potential in maximizing active site density, high atom utilization and high activity,making them the first choice to replace Pt-based catalysts. In the preparation of atomically dispersed metal–nitrogen–carbon catalyst, it is difficult to ensure that all active sites are uniformly dispersed, and the structure system of the active sites is not optimal. Based on this, we focus on various approaches for preparing M–N–C catalysts that are conducive to atomic dispersion, and the influence of the chemical environmental regulation of atoms on the catalytic sites in different catalysts. Therefore, we discuss the chemical environmental regulation of the catalytic sites by bimetals, atom clusters, and heteroatoms(B, S, and P). The active sites of M–N–C catalysts are explored in depth from the synthesis and characterization, reaction mechanisms, and density functional theory(DFT)calculations. Finally, the existing problems and development prospects of the current atomic dispersion M–N–C catalyst are proposed in detail.

High entropy materials based electrocatalysts for water splitting:Synthesis strategies,catalytic mechanisms,and prospects

Among various electrocatalysts,high entropy materials(HEMs)have attracted great attention due to the distinctive designing concept and unique properties with captivating electrocatalytic activity and stability.To date,HEMs have been a new family of advanced electrocatalysts in the research field of water electrolysis.In this work,the structural features and synthesis strategies of high entropy catalysts are reviewed,especially,their performances for catalyzing hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in water electrolysis are presented,in which the crucial roles of structure,composition,multisites synergy,and“four core effects”for enhancing catalytic activity,stability,and resistance of electrochemical corrosion are introduced.Besides,the design tactics,main challenges,and future prospects of HEM-based electrocatalysts for HER and OER are discussed.It is expected to provide valuable information for the development of low-cost efficient HEM-based electrocatalysts in the field of water electrolysis.

Recent advances in synthesis strategies and solar-to-hydrogen evolution of 1T phase MS_(2)(M=W,Mo)co-catalysts

Photocatalytic water splitting is a promising strategy to produce hydrogen as a sustainable and clean energy carrier,based on abundant solar energy and semiconductor photocatalysts,and it has received extensive research and discussion over the past several decades.It is challenging,however,to achieve an efficient solar-to-hydrogen evolution process with a single particulate photocatalyst due to the weak solar spectrum harvest and the rapid recombination of photogenerated electron-hole pairs during the photocatalysis reaction.Combining semiconductors to create different co-catalysts presents a viable solution to the above issues.Recently,semiconductor photocatalysts modified by different transition metal sulfidebased co-catalysts with designed functions,especially in light absorption enhancement and chargecarrier-separation efficiency promotion,have attracted much attention.As continued breakthroughs have been made in the preparation,modification,and solar-to-hydrogen evolution application of the 1T phase MS_(2)(M=W,Mo)co-catalyst-based photocatalysis system in recent years,we believe that a comprehensive review of this kind of co-catalyst would further promote its research and development to address the energy and environmental challenges that we are currently facing.Herein,recent studies and progress are summarized on the fabrication of 1T phase MS_(2)(M=W,Mo)-based co-catalyst materials,as well as their roles and functional mechanisms for photocatalytic H;evolution.Finally,concluding perspectives on the opportunities in and challenges for the further exploration of the 1T-MS_(2)(M=W,Mo)-based solar-tohydrogen evolution system are presented.

Strategies on improving the electrocatalytic hydrogen evolution performances of metal phosphides

Among the sustainable energy sources,hydrogen is the one most promising for alleviating the pollution issues related to the usage of conventional fuels,as it can be produced in an efficient and eco-friendly way via electrocatalytic water splitting.The hydrogen evolution reaction(HER,a half-reaction of water splitting)plays a pivotal role in decreasing the price and increasing the catalytic efficiency of hydrogen production and is efficiently promoted by metal phosphides in different electrolytes.Herein,we summarize the recent advances in the development of metal phosphides as HER electrocatalysts,focus on their synthesis(post-treatment,in situ generation,and electrodeposition methods)and the enhancement of their electrocatalytic activity(via elemental doping,interface and vacancy engineering,construction of specific supports and nanostructures,and the design of bior polymetallic phosphides),and highlight the crucial issues and challenges of future development.

Recent advances in the synthesis of nanoscale hierarchically porous metal–organic frameworks

Nanoscale hierarchically porous metal–organic frameworks(NHP-MOFs)have received unprecedented attention in many fields owing to their integration of the strengths of nanoscale size(<1μm)and hierarchical porous structure(micro-,meso-and/or macro-pores)of MOFs.This review focuses on recent advances in the main synthetic strategies for NHP-MOFs based on different metal ions(e.g.,Cu,Fe,Co,Zn,Al,Zr,and Cr),including the template method,composite technology,post-synthetic modification,in situ growth and the grind method.In addition,the mechanisms of synthesis,regulation techniques and the advantages and disadvantages of various methods are discussed.Finally,the challenges and prospects of the commercialisation of promising NHP-MOFs are also presented.The purpose of this review is to provide a road map for future design and development of NHP-MOFs for practical application.

Synthesis and modification strategies of g-C_(3)N_(4) nanosheets for photocatalytic applications

Graphitic carbon nitride nanosheets(CNNs)become the most promising member in the carbon nitride family benefitted from their two-dimensional structural features.Recently,great endeavors have been made in the synthesis and modification of CNNs to improve their photocatalytic properties,and many exciting progresses have been gained.In order to elucidate the fundamentals of CNNs based catalysts and provide the insights into rational design of photocatalysis system,we describe recent progress made in CNNs preparation strategies and their applications in this review.Firstly,the physicochemical properties of CNNs are briefly introduced.Secondly,the synthesis approaches of CNNs are reviewed,including top-down stripping strategies(thermal,gas,liquid,and composite stripping)and bottom-up precursor molecules design strategies(solvothermal,template,and supramolecular self-assembly method).Subsequently,the modification strategies based on CNNs in recent years are discussed,including crystal structure design,doping,surface functionalization,constructing 2D heterojunction,and anchoring single-atom.Then the multifunctional applications of g-C_(3)N_(4) nanosheet based materials in photocatalysis including H_(2) evolution,O_(2) evolution,overall water splitting,H_(2)O_(2) production,CO_(2) reduction,N_(2) fixation,pollutant removal,organic synthesis,and sensing are highlighted.Finally,the opportunities and challenges for the development of high-performance CNNs photocatalytic systems are also prospected.

Synthesis of TP3 FragmentviaOne Pot Strategy and Its Immune Regulatory Activity

We have modified the previously described one-pot peptide synthesis method. The modified method has been successfully applied to the synthesis of TP3. Furthermore, the immune regulatory activity of TP3 has been characterized. The results show that the modified one-pot method can be used to synthesize the biological active peptide with the advantages of low cost and high productivity. Moreover, TP3 has a higher immune regulatory activity than TP5.

Coercivity Ageing Effect on FePt Nanoparticles in Mesoporous Silica via Stepwise Synthesis Strategy

FePt nanoparticles in mesoporous silica are fabricated by a simple stepwise synthesis strategy.A pre-annealing temperature-dependent coercivity-ageing effect in FePt nanoparticles is observed at room temperature.For facecentered cubic（fcc）structured FePt nanoparticles,the ageing effect is sensitive to the pre-annealing temperature,especially when the temperature is close to the phase-transition.The special magnetic behavior of FePt nanoparticles reveals that the physical properties gradually change between fee and face-centered tetragonal structures,and will deepen our understanding of the mechanism of such magnetism in FePt nanoparticles.

Superior oxygen electrocatalyst derived from metal organic coordination polymers by instantaneous nucleation and epitaxial growth for rechargeable Li-O_(2) battery

Rechargeable aprotic Li-O_(2)batteries have attractea increasing attention due to their extremely high capacity,and it is very important to design appropriate strategies to synthesize efficient catalysts used as oxygen cathode.In present work,we present an expedient "instantaneous nucleation and epitaxial growth"(INEG) synthesis strategy for convenient and large-scale synthesis of ultrafine MOCPs nanoparticles(size 50-100 nm) with obvious advantages such as fast synthesis,high yields,low costs and reduced synthetic steps.The bimetallic Ru/Co-MOCPs are further pyrolyzed to obtain bimetallic Coand low content of Ru-based nanoparticles embedded within nitrogen-doped carbon(Ru/Co@N-C) as an efficient catalyst used in Li-O_(2)battery.The Ru/Co@N-C provides porous carbon framework for the ion transportation and O_(2)diffusion,and has large amounts of metal/nonmetal sites as active site to promote the oxygen reduction reaction(ORR)/oxygen evolution reaction(OER) in Li-O_(2)batteries.As a consequence,a high discharge specific capacity of 15246 mA h g^(-1)at 250 mA g^(-1), excellent rate capability at different current densities,and stable overpotential during cycling,are achieved.This work opened up a new understanding for the industrialized synthesis of ultrafine catalysts for Li-O_(2)batteries with excellent structural characteristics and electrochemical performance.

Controlled Synthesis of Polymers

Controlled synthesis is central to obtaining polymers with accurate structures and excellent performances.Recent research in the controlled synthesis of polymers has focused on optimizing monomers,initiation systems,and reaction conditions.The satisfactory sequence,topological structure,and dispersity have been achieved to satisfy the growing demand for functional polymers.This re-view summarizes the selection of monomers of various types and structures,the innovation of initiation systems,and the optimiza-tion of reaction conditions in the controlled synthesis of polymers and discusses their challenges and opportunities.

Recent advances in memristors based on two-dimensional ferroelectric materials

In this big data era, the explosive growth of information puts ultra-high demands on the data storage/computing, such as high computing power, low energy consumption, and excellent stability. However, facing this challenge, the traditional von Neumann architecture-based computing system is out of its depth owing to the separated memory and data processing unit architecture. One of the most effective ways to solve this challenge is building brain inspired computing system with in-memory computing and parallel processing ability based on neuromorphic devices. Therefore, there is a research trend toward the memristors, that can be applied to build neuromorphic computing systems due to their large switching ratio, high storage density, low power consumption, and high stability. Two-dimensional (2D) ferroelectric materials, as novel types of functional materials, show great potential in the preparations of memristors because of the atomic scale thickness, high carrier mobility, mechanical flexibility, and thermal stability. 2D ferroelectric materials can realize resistive switching (RS) because of the presence of natural dipoles whose direction can be flipped with the change of the applied electric field thus producing different polarizations, therefore, making them powerful candidates for future data storage and computing. In this review article, we introduce the physical mechanisms, characterizations, and synthetic methods of 2D ferroelectric materials, and then summarize the applications of 2D ferroelectric materials in memristors for memory and synaptic devices. At last, we deliberate the advantages and future challenges of 2D ferroelectric materials in the application of memristors devices.

Synthetic strategies for piperazine derivatives

As important constitutes in many drugs, piperazine comprised compounds are of great interest for drug design. In this paper, two piperazine-based compounds were synthesized for the first time, with different strategies exploited. For one compound, a highly reactive intermediate of isothiocyanate was constructed to get the desired piperazinecarbothioamide. The synthesis of the other compound was completed sequentially through Friedel-Crafts acylation, coupling reaction and Michael addition. Both synthetic routes have short steps and acceptable yields, and such strategies can be applied to the synthesis of similar oioerazine-containin~ comoounds.

A general bottom-up synthesis of CuO-based trimetallic oxide mesocrystal superstructures for efficient catalytic production of trichlorosilane

Mesocrystals, the non-classical crystals with highly ordered nanoparticle superstructures, have shown great potential in many applications because of their newly collective properties. However, there is still a lack of a facile and general synthesis strategy to organize and integrate distinct components into complex mesocrystals, and of reported application for them in industrial catalytic reactions. Herein we report a general bottom-up synthesis of CuO-based trimetallic oxide mesocrystals (denoted as CuO-M1Ox-M2Oy, where M1 and M2 = Zn, In, Fe, Ni, Mn, and Co) using a simple precipitation method followed by a hydrothermal treatment and a topotactic transformation via calcination. When these mesocrystals were used as the catalyst to produce trichlorosilane (TCS) via Si hydrochlorination reaction, they exhibited excellent catalytic performance with much increased Si conversion and TCS selectivity. In particular, the TCS yield was increased 19-fold than that of the catalyst-free process. The latter is the current industrial process. The efficiently catalytic property of these mesocrystals is attributed to the formation of well-defined nanoscale heterointerfaces that can effectively facilitate the charge transfer, and the generation of the compressive and tensile strain on CuO near the interfaces among different metal oxides. The synthetic approach developed here could be applicable to fabricate versatile complicated metal oxide mesocrystals as novel catalysts for various industrial chemical reactions.

A review on the rational design and fabrication of nanosized highentropy materials

High-entropy materials are mainly composed of high-entropy alloys(HEAs)and their derivates.Among them,HEAs account for a big part.As a new kind of alloy,they are now arousing great interests because of their high mechanical strength,extraordinary fracture toughness,corrosion resistance compared with traditional alloys.These characteristics allow the use of HEAs in various fields,including mechanical manufacturing,heat-resistant,radiation-resistant,corrosion-resistant,wear-resistant coatings,energy storage,heterocatalysis,etc.In order to promote the extensive application of HEAs,it is of significance to realize their rational design and preparation.In this paper,a systematic review focusing on the rational design and fabrication of nanosized HEAs is given.The design principles of how to match different elements in HEAs and the premise for the formation of single-phase solid solution HEAs are first illustrated.Computation methods for the prediction of formation conditions and properties of HEAs are also in discussion.Then,a detailed description and comparison of the synthesis methods of HEAs and their derivate,as well as their growing mechanism under various synthetic environments is provided.The commonly used characterization methods for the detection of HEAs,along with the typical cases of the application of HEAs in industrial materials,energy storage materials and catalytic materials are also included.Finally,the challenges and perspectives in the design and synthesis of HEAs would be proposed.We hope this review will give guidance for the future development of HEAs materials.

Recent Advances in Covalent Organic Framework Electrode Materials for Alkali Metal-Ion Batteries

Owing to the shortcomings of traditional electrode materials in alkalimetal-ion batteries(AIBs),such as limited reversible specific capacity,low power density,and poor cycling performance,it is particularly important to develop new electrode materials.Covalent organic frameworks(COFs)are crystalline porous polymers that incorporate organic building blocks into their periodic structures through dynamic covalent bonds.COFs are superior to organic materials because of their high designability,regular channels,and stable topology.Since the first report of D_(TP)-A_(NDI)-COF as a cathode material for lithium-ion batteries in 2015,research on COF electrode materials has made continuous progress and breakthroughs.This review briefly introduces the characteristics and current challenges associated with COF electrode materials.Furthermore,we summarize the basic reaction types and active sites according to the categories of covalent bonds,including B–O,C=N,C–N,and C=C.Finally,we emphasize the perspectives on basic structure and morphology design,dimension and size design,and conductivity improvement of COFs based on the latest progress in AIBs.We believe that this review provides important guidelines for the development of high-efficiency COF electrode materials and devices for AIBs.

Metal-organic frameworks based surface-enhanced Raman spectroscopy technique for ultra-sensitive biomedical trace detection

Metal-organic frameworks(MOFs)have attracted widespread interest due to their unique and unprecedented advantages in microstructures and properties.Besides,surface-enhanced Raman scattering(SERS)technology has also rapidly developed into a powerful fingerprint spectroscopic technique that can provide rapid,non-invasive,non-destructive,and ultra-sensitive detection,even down to single molecular level.Consequently,a considerable amount of researchers combined MOFs with the SERS technique to further improve the sensing performance and broaden the applications of SERS substrates.Herein,representative synthesis strategies of MOFs to fabricate SERS-active substrates are summarized and their applications in ultra-sensitive biomedical trace detection are also reviewed.Besides,relative barriers,advantages,disadvantages,future trends,and prospects are particularly discussed to give guidance to relevant researchers.

Recent progress on FeS_(2) as anodes for metal-ion batteries

The ever-growing demand for advanced battery technologies with high energy and power density,high security,prolonged cycle life,and sustainably low cost requires the development of novel electrode materials for lithium-ion batteries(LIBs),as well as the alternative electrochemical energy storage technologies of sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)for their abundant alkali metal elements resources.Among various anode materials,such as graphite,organic compounds,metal oxides,and chalcogenides,iron sulfides have attracted substantial interests for their high theoretical capacity and low price.Specifically,as a common mineral that has been already applied as electrode for primary battery,ferrous disulfide(FeS_(2))has been regarded as one of the promising candidate anode materials and studied widely.Unfortunately,there are some inherent problems handicapping its practical application for alkali-ion batteries,including limited ionic/electrical conductivity,the formation of soluble polysulfides,and large volume change.In the last decade,massive efforts have been devoted to solving those problems.In this review,the various synthesis strategies,the effect of morphologies and particle sizes,the energy storage mechanisms,and the electrochemical performances of FeS_(2) as anode for alkaliion batteries(LIBs,SIBs,and PIBs)are summarized.Furthermore,the existing challenges and prospects of the development of FeS_(2)-based anode materials for alkali-ion batteries are presented at last.

Two-dimensional noble transition-metal dichalcogenides for nanophotonics and optoelectronics:Status and prospects

An emerging subclass of transition-metal dichalcogenides(TMDs),noble-transition-metal dichalcogenides(NMDs),has led to an increase in nanoscientific research in two-dimensional(2D)materials.NMDs feature a unique structure and several useful properties.2D NMDs are promising candidates for a broad range of applications in areas such as photodetectors,phototransistors,saturable absorbers,and meta optics.In this review,the state of the art of 2D NMDs research,their structures,properties,synthesis,and potential applications are discussed,and a perspective of expected future developments is provided.

Towards single-atom photocatalysts for future carbon-neutral application

The implementation of carbon neutrality to achieve the goal of controlling global warming in the Paris Climate Agreement is currently the most important international climate issue.Efficient utilization of solar energy through photocatalysts is of great significance to the adjustment of energy structure.Single-atom photocatalysts have excellent catalytic activity and selectivity in a variety of applications,including sustainable energy conversion,chemical synthesis,CO_(2)reduction,environmental remediation,and other areas,owing to their unique electronic structure and high atom usage.Here,we elaborated on the content and implementation direction of the carbon neutrality policy and demonstrated the design principles of single-atom photocatalysts.Recent single-atom synthesis strategies are summarized,and representative characterization methods have been shown to further reveal the structure–performance relationship.Then,we focus on the application of single-atom photocatalysts in CO_(2)reduction,sustainable energy conversion,and environmental remediation.Finally,the opportunities and challenges in the application of single-atom photocatalysts were discussed based on its current development.