As a typical kind of soft materials, molecular gels have attracted increasing attention during the last few decades owing to their great potential in the applications including biomedicals, soft electronics, controlled growth of organic crystals, water purification, and preparation of 3D printing materials, micro-/nano-materials, high-density energetic materials, etc. It is believed that the main focuses of molecular gel research include: 1) increasing the efficiency of structural modification, 2) extending the functionality of molecular gels, and 3) promoting the real-life applications of molecular gels. In this feature review, we introduce the progress of molecular gel research with dynamic covalent bonds-based molecular gels, controlled growth of organic crystals in molecular gels and soft template-based preparation of high-performance porous polymeric materials as the main contents. In addition, a brief prospect for the future development of molecular gel research is provided.

Due to the wide applications of zeolites in various fields, efficient and reliable synthesis of zeolite has become an important research issue. Compared with traditional high-pressure hydrothermal batch synthesis, continuous flow synthesis is one of the new methods for fast preparation of zeolite owing to its short crystallization time and high space-time yield. The high crystalline zeolites can be harvested in minute- and even second-level thanks to the specific characteristics of continuous flow reactors(CFR), such as low thermal lag, controllable mass transfer and good expansibility, which significantly enhance the synthesis efficiency and controllability. In this paper, based on the recent progress, the component of CFR equipment, the advantages and limitations of CFR for zeolite synthesis, and the future applications are introduced and prospected.

Polymer microspheres are considered to be the typical soft materials which are widely used in catalysis, drug delivery, biosensing, microreactors, chemical separation and coating fields because of their unique properties, such as the micro-scale, diffusion, penetration and ease of modification. In order to meet the requirement for use in hostile environments, stimuli-responsive microspheres whose properties significantly change in response to the minor variation of environmental conditions have been developed. This paper reviews the diverse fabrication strategies and morphologies of the responsive polymer microspheres which are sensitive to temperature, pH, magnetic field, ionic strength, light and CO₂ stimulus, respectively. The relevant stimuli-response mechanisms, applications and the demerits of the responsive microspheres are summarized and discussed, then the potential applications and future prospects of the sensitive microspheres are also analyzed.

Covalent organic frameworks(COFs) are a class of crystalline porous organic material, constructed with light elements by reversible covalent bonds. Due to their high surface area, low density, regular channel structure and facile functionalization, COFs have attracted much attention and shown high perspectives in gas adsorption, chemical sensing, heterogeneous catalysis, etc. Recently, COFs have shown potential applications in enzyme immobilization and mimic enzymes. COFs present an attractive category of enzyme immobilization matrix, because the functional groups on COFs can be readily tailored to hold specific interactions between COFs and enzymes. Moreover, the continuous and confined open channels of COFs provide a favorable micro-environment for infiltrating enzymes. Meanwhile, the mimic enzyme features of COFs are explored, COF mimic enzymes are designed either by “from bottom to top” method or post modification strategy. As a result, not only the carrier materials for enzyme immobilization are expanded, but also it provides new ideas for biomimetic catalysis of mimic enzymes. This review focuses on recent advances of COFs immobilized enzyme and COFs mimic enzymes(nanozyme) applied in biocatalysis. Special emphasis is placed on the deliberation of synthetic and functional strategies, immobilization methods of COFs carrier, as well as the design concept, catalytic activity and selectivity of COFs mimic enzymes. Finally, the remaining challenges of COFs in enzyme catalysis and prospects in this field are summarized.

The wood-based carbon skeleton is derived from natural wood after pyrolysis. The wood-derived carbon inherits the hierarchical structural of the pore morphology and connectivity formed by the long-term evolution of wood. Due to its special structure, the carbon skeleton has huge application potential in the aspects of biological templates, sensors, oil absorbent, nanomaterial preparation, etc. The hierarchical wood-derived carbon skeleton could be further treated as a new type of scaffold, after the micro-/nano- scale modification and secondary regulation of the pores, it has extremely broad application in many innovative fields such as seawater desalination, environmental remediation, energy storage materials and electrochemical catalysis. This article first introduces the hierarchical structure of wood, describes several important stages of structural changes in the process of the wood pyrolysis, and then summarizes the application of wood-derived carbon skeleton as advanced materials in recent years. We also discuss the pros and cons of the functional carbon in the application, and prospect the future research works of wood-based carbon materials. The purposes of this review are to re-examine and functionally develop the wood hierarchical structure and to promote the development of wood as advanced materials.

Hydrogen sulfide(H₂S), owing to the extremely toxic, malodorous and corrosive nature, is a detrimental and undesirable environmental pollutant widely generated in the petrochemical industry. How to handle H₂S effectively and convert it into highly-valued products is vital. Photocatalysis is one of the most ideal routes to realize the resource utilization of H₂S. Recently, metal sulphides are widely used as desirable photocatalysts for H₂ production from waste H₂S due to their remarkable visible-light response, proper band structure and strong resistance against H₂S poisoning. Here, we summarize the current status, and challenges of this field. The photocatalytic H₂S splitting mechanism are overviewed in different reaction medium. Particularly, promising strategies for highly efficient photocatalytic conversion of H₂S are systematically discussed, which is aimed to inspire researchers interested in this field. Finally, some challenges in the H₂S splitting process and their future research directions are outlined.

DNA molecules have shown unique advantages and high potential in enhancing drug targeting and reducing drug toxicity because of their unique biocompatibility and programmability. And spurred by the development of tumor microenvironment research and the development of environmentally responsive DNA triggers, many DNA nanostructure delivery systems based on tumor microenvironment have been reported in recent years. These DNA nanostructures combine the favorable biodistribution and pharmacokinetic properties of nanodelivery vehicles and the rapid diffusion and penetration properties of smaller drug cargos. By targeting a wide range of tumor habitats rather than tumor specific receptors, the strategy is likely to overcome the problem of tumor heterogeneity and can be used to design nanoparticles for diagnosis and treatment of multiple solid tumors. They can be transported steadily in the blood circulation, releasing drugs under the unique microenvironmental stimulation of tumor tissue, effectively controlling the drug release site and release speed, and greatly reducing the toxic and side effects of tumor treatment. In this article, the latest research progress of tumor microenvironment responsive DNA nanostructure drug delivery systems is reviewed from five aspects of pH responsive systems, GSH responsive systems, ATP responsive systems, enzyme responsive systems, and antigen responsive systems. The design strategy and responsive release mechanism of corresponding DNA nanocarriers are discussed in great detail. In addition, the prospects and main challenges in this area are also discussed.

Cyclodextrin has gained great attention since its discovery, due to its special cavity structure. Combining the cavity with multi-hydroxyl groups of cyclodextrin and the multi-arms of star-like polymer, a star-like polymer based on cyclodextrin has three-dimensional structure, special functional groups and features of cyclodextrin. These make star-like cyclodextrin polymers possess wide application and great development potential. Herein, this review summarizes the preparation methods of star-like polymer using cyclodextrin as reaction center, and the corresponding applications in biomedical, electrochemistry, wastewater treatment and other aspects. Furthermore, the new research trends and development direction of star-like polymer based on cyclodextrin are presented.

Proton exchange membrane fuel cell(PEMFC) is being paid to special attention around the world duo to their zero pollution, low noise, high energy density, high efficiency and fast response, thus it is developing rapidly in recent years. However, the lifespan of PEMFC vehicle is an important issue that restricts its commercialization. Local current density is an important parameter during the operation of PEMFC, which can be used as the fault diagnosis and positioning tool, improving the operation durability and stability of PEMFC. Moreover, the internal information of an operating PEMFC can be also revealed by the local current density, providing comprehensive understanding of the reaction mechanism and guidance for the optimization design of PEMFC. In consequence, it is of great importance for the thorough and comprehensive research of the local current density. In this paper, the methods for the in-situ and real-time measurement of the local current density are introduced and analyzed, and the results obtained by previous experiments and numerical simulation are compared. The effect of operation parameters on local current density have been summarized in detail and the applications of local current density in fuel cell analysis are reviewed. Finally, the development tendency is proposed based on the research progress of this topic.

As a new type of energy storage devices with rapid development momentum, lithium ion batteries(LIBs)alleviate the dependence on fossil fuels in energy field and reduce the increasingly severe environmental pressure. A large number of spent lithium ion batteries are not only hazardous wastes, but also resources with high added value from different perspectives. Therefore, it is of great challenge and practical significance to realize high-efficient recycling and reuse of spent lithium ion batteries with progressively diverse components through innovation and combination of different technical means. Starting from the pretreatment process, the technical means and requirements of a series of processes such as deactivation and discharge, dismantling and classification, crushing and sieving, separation process, acid leaching and impurity removal are described in detail. This review discusses the typical strategies of reuse from three aspects and analyzes the advantages and disadvantages of various techniques in the process of material regeneration, structural repair and re-synthesis of cathode materials. In addition, the harmless treatment and recovery of spent electrolyte are discussed, especially the application of supercritical CO₂ extraction process. Finally, the outlook is put forward in view of the existing problems at the present stage to provide references for subsequent research and industrial applications of spent lithium ion battery recycling.

Perovskite solar cells(PSCs) have achieved more than 25% efficiency in just a decade, which are of great commercial value. This is because the three-dimensional(3D) perovskite(PVK) layer has many advantages, such as suitable bandgap, high absorption coefficient and long electron diffusion length. However, unstability is still an urgent problem to be solved in 3D PSCs. Comparing with 3D perovskite materials, 2D perovskite crystals have recently attracted increasing attention due to some unique properties for improving stability. The hydrophobic bulky alkylammonium cations in 2D perovskite lattices can block the accessible pathways of moisture invasion, making them promising candidates for optoelectronic devices. Meanwhile, due to the tolerance of 2D perovskite to organic and inorganic elements, its chemical composition and energy band also change. This review highlights the importance of energy bands in 2D PSCs and summarizes bandgap regulation and energy level alignment(ELA) of 2D perovskite, which plays an important role in guiding the preparation of high-efficiency and stable low-dimensional perovskite solar cells.

Advanced oxidation technology(AOPs) is a hot issue in current water treatment research, such as the representative Heterogeneous Fenton catalytic oxidation. It can generate active oxygen species such as hydroxyl radicals(·OH) during the reaction, which attack organic pollutants unselectively and gradually decompose organic macromolecules into small molecules, achieving the efficient removing of toxic and harmful pollutants. Compared with homogeneous Fenton reactions, heterogeneous Fenton reactions have various advantages, such as wide pH response, recyclability of catalysts, and no generation of iron mud. However, considering their intrinsic characteristics and limits of solid-phase catalysts, there are still some problems inhibiting the large-scale application, such as low activity under neutral conditions, low utilization of hydrogen peroxide(H₂O₂), and low conversion rate of Fe(Ⅲ)/Fe(Ⅱ). This article summarizes the heterogeneous Fenton reaction mechanism involving different active oxygen species as well as various heterogeneous Fenton catalysts and their applications in control of organic pollutants and provides a reference for continuing research on heterogeneous Fenton catalysts.

Imprinted composite membranes(IcMs) not only possess the efficient separation performance of membranes, but also possess the selective separation performance of imprinted polymers, which have attracted extensive attention all over the world for their well and precise separation property for target substances and high membrane flux. However, the research progress on IcMs has not been summarized yet, and problems existed in research process and the future perspective of IcMs are not analyzed and forecast. This paper summarizes the research and development process of IcMs and the research progress in preparation technology of IcMs, then classify IcMs according to their structure to several categories, namely, IcMs of a single-layer structure, IcMs of a dual-layer structure, IcMs of a multi-layer structure, IcMs of 3D macroporous structure and IcMs with smart sensing and separation properties. Finally, the preparation methods, structural characteristics and identification/separation properties of IcMs, and the potential problems coupled with those aspects are summarized and a future developing direction of this field is prospected.

Lithium-sulfur batteries have the advantages of high theoretical energy density, low cost and environmental friendliness, and they are the most promising next-generation high-energy density secondary battery systems. Currently, liquid lithium-sulfur batteries based on organic electrolytes have some problems such as lithium polysulfides(LiPSs) shuttle effect, electrolyte flammability and lithium dendrite, resulting in low coulombic efficiency and poor cycle stability of lithium-sulfur batteries, and there are serious safety hazards. The uses of solid electrolytes(gel polymers, solid polymers, ceramics, composite electrolytes, etc.) in place of organic liquid electrolytes are effective strategies to address the above problems. Herein, we present the research status of solid-state electrolytes of lithium-sulfur batteries, and summarize their advantages/disadvantages and improvement strategies, and focuses on the research progress of ceramic solid electrolytes. Finally, we forecast future development trends of solid lithium-sulfur batteries.