Single-atom catalyst has the advantages of low coordination number, special coordination environment, high atomic utilization, and high uniformity of catalytic sites. It is the bridge between homogeneous and heterogeneous catalysts, which helps to better understand the nature of catalytic reaction. In this paper, the synthetic methods of graphene-based single-atom catalysts in recent years are reviewed, including atomic layer deposition, impregnation-calcination, defect trapping, coordination anchoring and some other novel methods, with a focus on the preparation process, principle and characterization results of these methods. Based on this, the performance of graphene-based metal single-atom catalysts in catalysis is illustrated and analyzed, and the purpose is to provide guidance and reference for the preparation of single-atom catalysts.

Microfluidics, which can precisely manipulate micron-sized particles, has been widely used in medical, pharmaceutical, biological and chemical fields. The passive manipulation technologies without external field effect have become a research hotspot because of their simplicity and autonomy. Compared with other passive manipulation technologies, viscoelastic focusing technology makes it easier to achieve three-dimensional focusing of particles, and can manipulate particles with a large-scale span and a wide range of fluid flow. Therefore, this paper reviews the latest research on viscoelastic fluids in particle passive manipulation applications. Firstly, the force mechanism of particles in viscoelastic fluid in different microchannel structure is introduced. Then, the research progress of viscoelastic focusing, sorting, mixing and other viscoelastic particle manipulation applications is further elaborated. Finally, the numerical simulation method for studying the flow characteristics of viscoelastic fluids and the movement law of particles in it are introduced, and some prospects for the future development of viscoelastic microfluidics are made based on the analysis of existing problems.

For the demands of sustainable development and green chemistry, the use of heterogeneous catalysts instead of conventional homogeneous ones has received increasing attention. Among various heterogeneous catalysts, mesoporous solid bases are extremely desirable in green catalytic processes, due to their advantages of high specific surface, negligible corrosion, accelerated mass transport and easy separation. Great progress has been made in mesoporous solid bases in the last decade. In addition to their wide applications in the catalytic synthesis of organics and fine chemicals, mesoporous solid bases have also been used in the field of energy and environmental catalysis. In this review, we provide an overview of recent research progress in the preparation and application of metal-based mesoporous solid bases(including MgO,hydrotalcite-like compounds, modified-Al₂O₃,modified-ZrO₂, and modified-CeO₂), which is basically grouped by the metal type and illustrated with typical examples. The advantage, disadvantages and mechanisms for four main synthesis methods, including soft-template method, hard-template method, solvent evaporation-induced self-assembly(EISA) synthesis and solvent-free synthesis are discussed and compared in detail. Moreover, their applications in the fields of catalysis, energy storage and environment are briefly introduced as well. Finally, the existing problems of the preparing metal-based mesoporous oxides are briefly discussed, and the strategies are provided for the construction of novel metal-based mesoporous solid bases.

Fluorescent carbon dots have attracted significant interest for their non-toxicity, low cost and unique photoluminescence properties. Generally, the preparation and usage of carbon dots(CDs) are in solution. With the increase of CDs concentration, their fluorescence intensity may be reduced or even quenched. Following, the solid-state fluorescent CDs powder obtained by simple drying often lack of fluorescence properties. Therefore, there are relatively few researches on the preparation and related applications of solid-state fluorescent CDs. The article describes recent preparation methods of solid-state fluorescent CDs, including post-processing methods(matrix dispersion method, surface engineering) and direct synthesis method. The changes of fluorescence properties of CDs before and after treatment are compared, and the main problems in preparation and application of solid CDs are summarized. Meanwhile, the preparation, performance modulation of solid-state fluorescent CDs are prospected. It is very crucial to exploit the CDs with the enhancement of aggregation induced emission, which provides a new strategy for the development of solid-state fluorescence CDs.

Nanopore-based single molecular detection technology is a sensing technology that combines the advantages of simple operation, high sensitivity, fast speed, and no labeling. It is widely used in protein detection, gene sequencing, and marker detection. The cost, sensitivity and accuracy are the main challenges in developing such technology, and to develop new nanopore materials is the key to solve them. From the perspective of selecting and designing nanopore materials, the application status of three different nanopores: biological nanopore, solid-state nanopore and novel two-dimensional(2D) material nanopore in biomolecule detection are reviewed. Meanwhile, the differences between biological nanopores and solid-state nanopores are compared in details. The article also emphasizes the experimental and simulation research progress of 2D material nanopores in biomolecule detection. Finally, the future development of nanopore-based detection technology is also discussed.

Digital PCR(dPCR) assay is a highly sensitive absolute quantitative analysis technique for nucleic acids. Digital PCR systems perform amplification by equally dividing the reaction mixtures into a large number of independent reaction units, and calculates the nucleic acid copy number based on the Poisson distribution and the positive ratio. With the advantages of high sensitivity, accuracy and tolerance, digital PCR assay enables absolute quantitative analysis of samples. In recent years, with the maturity of microfluidic technology, digital PCR assay based on microfluidic technology has been rapidly developed, and widely applied in the analysis of gene mutation, copy number variation, viral microbial, genetically modified foods and DNA sequencing. In this article, the principle, development and applications of the digital PCR technique are reviewed.

Biotin is a water-soluble vitamin and serves as a coenzyme for carboxylases in human body. It is widely favored by chemists and biologists in recent years. In addition, it exhibits low toxicity in various physiological and pathological processes, and can be designed as a selectivity targeting drug carriers, which can efficiently deliver therapeutic drugs to cells. Nowadays, small molecules containing biotin have developed into a class of biofunctional molecules of high utility value. These compounds have the advantages of simple synthesis, easy functionalization, and high specificity. In this paper, the progress of biotin and its derivatives in biosensors, drug release and other fields are systematically reviewed, and the prospects for their development are presented.

Liquid chromatography-mass spectrometry(LC-MS) combines the high separation efficiency of chromatography with the powerful structural determination of mass spectrometry, which not only enables more accurate analysis for the compounds, but also simplifies the pre-treatment of samples and makes the analysis more convenient. LC-MS, as an important tool for the qualitative and quantitative analysis of organic compounds, has been widely used in various fields such as pharmaceutical analysis, food and environmental monitoring, biological and medical research etc. As the key component of LC-MS, the role of the interface is to introduce and ionize the fractions from LC, and transfer the generated ions into the MS. Therefore, the improvement of ionization technology for the interface directly affects the advance and application of LC-MS. In order to obtain a higher sensitivity and a wider range of applicability, researchers have focused on the ionization technology to promote the desorption of chemicals, improve their ionization and transport efficiency, and reduce the interference of matrix effect. In this work, the development of traditional ionization technologies and the novel technologies reported for the interface of LC-MS in recent years are reviewed, including the ionization principle, interface construction, influencing factors, and the related applications. Their characteristics, advantages and disadvantages are discussed in details. Finally, the trend of ionization technology in development for the interface of LC-MS is prospected.

Polyurethane(PU), one of the most multifunctional polymers, is produced by polyaddition reaction of polyols and isocyanates. It has found wild applications in coatings, elastomers, adhesives, foams. However, one of the problems related to the production of PU is its dependence on petroleum-based resources. With the consumption of petroleum resources and the destruction of environment, the searching for renewable raw materials has become a research hotspot. At present, most reports are based on biobased polyols replacing petroleum-based polyols to prepare polyurethane, among which vegetable oil and lignin are the most used. Lignin, a natural organic carbon resource with abundant reserves, is low value-added and wasted as fuel at present. Compared with vegetable oil, lignin does not compete with human for food and the performance of related products is superior. However, the utilization of lignin has some problems, such as isolation, heterogeneity, aggregation, steric hindrance and low activity. These disadvantages make the unmodified utilization and modified utilization of lignin become the key problem. This paper introduces the development status and latest research progress of lignin in bio-based polyurethane synthesis. Finally, the development prospects of lignin-based polyurethane materials in different fields are prospected.

Particulate brown carbon(BrC) has strong wavelength dependence with absorption increasing sharply from visible to UV ranges and has attracted much attention due to its significant climate effects. The composition, sources, evolution and optical properties of BrC remain highly uncertain, which contributes significantly to the uncertainty in estimating aerosol radiation forcing by climate models. The chemical compositions, sources and formation pathways of particulate BrC in the atmosphere are summarized in this review, which focuses on the relationship between molecular-level compositions, secondary formation mechanisms and light absorption properties. Particulate BrC are classfied into several major compound categories, including methanol soluble organic carbon(MSOC), water soluble fractions WSOC(Water Soluble Organic Carbon) and HULIS-C(Carbon Component of HUmic-like Substances). Nitroaromatic compounds(NACs) and N-heterocyclic compounds are major BrC chromophores. The sources of BrC include primary emissions from inefficient combustion, especially biomass burning, and secondary formation via the oxidation of volatile organic compounds(VOCs) in gas and particle phases. Secondary formation pathways include oxidation of aromatics and reactions between carbonyls and ammonia/amines. Oxidation of anthropogenic aromatic hydrocarbons in the presence of NO_x produces BrC dominated by nitrogen-containing organic compounds(e.g. NACs). Reactions between carbonyls and ammonia/amines generate BrC dominated by N-heterocyclic compounds and oligomers. Precursors and reaction conditions are important factors influencing the compositions and light absorption of secondary BrC. The chromophores would go through decomposition and BrC light absorption would change rapidly during transport in the atmosphere, which is usually named photobleaching. Molecular-level identification of BrC chromophores and further understanding on the secondary formation mechanisms and atmospheric evolution of BrC are required in future studies.

The rapid development of nanomaterials and nanotechnology provides the water treatment new opportunities. MoS₂, as a graphene-like two dimensional(2D) nanomaterial, has attracted much attention due to its unique 2D sheet structure as well as physical and chemical properties. In this paper, we review the applications of 2D MoS₂ and its composites on adsorption, membrane separation, catalysis, antibacterial, and detection applications in water treatment area, of which adsorption and membrane separation are highlighted and discussed to achieve the goal of high removal efficiency of ions, dyes, antibiotics, bacteria and many other environmental pollutants. In the end, the applications of MoS₂ and its composites in water treatment are evaluated, and their potential development and faced challenges are discussepd, hopefully to be a novel nanomaterial and technical strategy to solve water environmental pollution and water resource shortage problems.

Zeolitic imidazolate framework-8(ZIF-8) is a class of porous crystalline materials formed by the self-assembly of zinc ions and 2-methylimidazole. It shows potential advantages in encapsulation and transportation of functional materials owing to its high porosity, large specific surface,convenient synthesis and controllable size. More importantly, ZIF-8 is an ideal carrier for drug delivery and release due to its excellent biocompatibility, stability under physiological conditions and responsiveness to the weak acidic environment associated with malignant tumors and other diseases. In fact, the small molecular drugs(doxorubicin, 5-fluorouracil) and biological macromolecules(antibody, nuclein) have all been loaded into ZIF-8 for chemotherapy, photothermal therapy, photodynamic therapy and biosensing. The particle size of ZIF-8 is very important for biomedical applications, and accurate functional regulation of ZIF-8 is agreat challenge for its biomedical application. Herein, we review the synthesis methods, size-control and biomedicalapplications of ZIF-8.

Hydrogen storage is the key technological problem for a viable hydrogen economy and so far, finding an efficient and safe method of storing hydrogen remains an indomitable challenge. Chemical sorption via solid-state hydrides, offering reliable, compact and high capacity features, is considered one of the most promising avenues for hydrogen storage. Among the diverse hydrides, metal borohydrides are excellent candidates on account of their high gravimetric and volumetric density. However, these hydrides generally suffer from high temperatures of de/rehydrogenation, slow sorption rate, limited reversiblity and poor cyclability due to the intrinsic thermodynamic stability and/or sluggish kinetics. In this review, we summarize recent researches and applications on the aspect of optimizing performance through substitution, composite, doping, and nanostructure, cognizing the relevant reaction mechanism for the metal borohydride-based system. The challenges and countermeasures are illustrated, and the direction to further enhancing the hydrogen storage properties of the system is also pointed out.