Carbon quantum dots (CQDs) generally refer to zero-dimensional carbon materials with a particle size of less than 10 nm. Due to their excellent optical properties, they have been used extensively in the fields of bioimaging, optical devices, biocomposite materials, biosensing, etc., and can be expected to become one of the most widely used carbon material in the future. The optical properties of CQDs are affected by particle size, surface functional groups, synthesis temperature, type of solvent, and pH. In order to precisely control their optical properties and further expand their scope of application, their photoluminescence (PL) mechanisms need to be elucidated in details, however, the PL mechanism of CQDs is currently not complete clear. At present, the proposed PL mechanism includes quantum confinement effect, surface states emission, molecular fluorophores and carbogenic core, polycyclic aromatic hydrocarbon molecular emission, self-trapped exciton emission, surface dipole emission center, aggregate emission center, multiple emission center, slowed solvent relaxation and solvatochromic shift etc. But each mechanism can only explain part of the PL phenomenon of CQDs to a certain extent. No mechanism can explain all the PL phenomena of CQDs, which seriously restricts the regulation of the optical properties of CQDs. This review classifies and summarizes the different PL mechanisms of CQDs, its purpose is to provide a reference for further elucidating its PL mechanism and achieving controllable adjustment of the optical characteristics of CQDs.

Ammonia (NH₃) is one of the most important nitrogen-based fertilizers and chemicals, and is also a novel hydrogen storage material. It is made on an industrial scale via the Haber-Bosch process, which requires high temperature and high pressure to consume a large amount of energy. It is very urgent to find an environmentally benign alternative process to alleviate the crises for energy and environment. Electrocatalytic nitrogen reduction reaction (NRR) has attracted worldwide research interest. However, such process is actually hard to perform due to the inherent inertness of N₂ molecules together with the low solubility in aqueous solutions. Although great research efforts have been made to explore and design suitable electrocatalysts for ammonia synthesis, the yield of ammonia is still very low. In addition, the ambiguous mechanism still remains as a major barrier for the development of NRR systems. In this review, we firstly introduced the catalytic reaction mechanisms towards NRR. Then we overviewed of the latest progress of the state-of-art catalysts in the electrocatalytic NRR. Moreover, we put more emphasis on the various rational strategies for electrocatalyst design to enhance the NRR performance, such as size effects, facets regulation, defects engineering, amorphization, which are aiming to increasing the exposed active sites or altering the electronic structure to further improve the apparent or intrinsic activity. Finally, we briefly discussed the main challenges in this field. We hope this review will offer a helpful guidance for the reasonable design of electrocatalysts towards NRR, arouse more interests in the new research field of NRR, and promote the green ammonia synthesis industrialization as soon as possible.

Graphene aerogel is a three-dimensional macroscopic material assembled from two-dimensional graphene sheets. Due to its high porosity, large specific surface area and low density, it has a broad application prospect in the adsorption and removal of water pollutants and has become a research hotspot. However, most of the related researches focused on bulk graphene aerogels, and few researches on graphene-based aerogel beads. This review summarizes the preparation methods of graphene-based aerogel beads, including electrostatic spray, electrostatic spinning, microfluidic technology and wet spinning. Taking the wet spinning method as the representative, the influencing factors for aerogel beads formation are analyzed, such as the concentration and viscosity of GO dispersion, extrusion parameters, the type and concentration of coagulation bath, etc. Furthermore, the factors of adjusting the pore size of the material are further analyzed. For example, the pore size of the material can be adjusted within a certain range by controlling the GO concentration, the GO layer sizes, and the temperature of freezing treatment. In view of the different treatment objects in the wastewater, the design of graphene-based aerogel beads with excellent adsorption performance, recycling performance and controllable micromorphology and the optimization and innovation of preparation methods are still the key points of exploration in future.

Nowadays, development of a sustainable, green, new and efficient energy system has drawn much attention with the increasingly prominent energy and environmental problems. Photocatalytic production of H₂ utilizing solar energy appears to be a promising strategy to solve the energy issues since it is clean, low-cost, and environmentally friendly. It is difficult for single semiconductor photocatalyst to meet all the requirements of photocatalysis because of its low utilization efficiency of light, fast recombination rate of electron-hole pairs, and insufficient active sites. Cocatalysts are often used to improve the photocatalytic activity. The loading of cocatalyst could facilitate charge separation and enhance the photocatalytic efficiency. In this review, we mainly outline the roles of cocatalysts in photocatalytic hydrogen production, such as enhancing light absorption, promoting charge separation, increasing active sites, and improving the ability of H adsorption, and introduce the loading method of cocatalysts. Moreover, the influencing factors of cocatalysts on activity, including size effect, position effect, configuration effect and quantity quantal effect are summarized, which sheds light on designing efficient and stable cocatalysts, and the concluding perspectives on future development of cocatalysts for photocatalytic hydrogen production are also presented.

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are a new class of functional lipids. It has been reported that they play important roles in mammals, such as improving glucose tolerance, enhancing insulin sensitivity, maintaining blood glucose homeostasis, and anti-inflammatory. Since its discovery in 2014, FAHFA has been attracting more and more attention of scientists, and has become a new branch of lipid research. This review summarizes the research advances of FAHFA since its discovery, covering the physiological function, metabolism, storage in organism, analysis and chemical synthesis of FAHFA.

Photonic crystal biochemical sensing is a promising analytical method which amplifies or converts biochemical signals into photoelectrically readable signals and performs quantitative or semi-quantitative analysis by instruments or naked eyes, based on the structural characteristics of photonic crystals. This review mainly focuses on the three aspects of the photonic crystal biochemical sensor: material selection and fabrication, sensing mechanism, design and application. Firstly, in terms of material selection and fabrication, this article reviews the monodisperse colloidal nanoparticles, electromagnetic composite colloidal nanoparticles, nanowires, metal organic frameworks and so on. Secondly, the sensing mechanism is briefly introduced from three aspects: structure color, slow light effect and photoelectric conversion mechanism. Further, the design and application of visible photonic crystal biochemical sensor, fluorescence enhanced photonic crystal biochemical sensor, Raman enhanced photonic crystal biochemical sensor, evanescent wave enhanced photonic crystal biochemical sensor, surface infrared absorption enhanced photonic crystal biochemical sensor and photoelectric signal enhanced photonic crystal biochemical sensor are reviewed, based on the perspective of interaction effect of photonic crystal and light. Finally, the future of photonic crystal biochemical sensor is prospected.

Microfluidic chip is one of the most representative technologies of micro-analysis platform in this century. It has many advantages such as low reagent consumption, analytical miniaturization, easy control and integration, high automation and good biological compatibility. It has outstanding performances in many fields such as biology, medicine, food and environment, especially in the field of drug screening which has achieved a series of achievements with its own advantages. This article summarizes the research progress of concentration gradient microfluidic chips for drug screening in recent years, including paper chip, hydrogel chip, droplet chip and polydimethylsiloxane (PDMS) chip. Furthermore, the advantages and disadvantages of concentration gradient microfluidic chip in single cell analysis, combination drug screening, three-dimensional (3D) cell culture, cell microenvironment simulation are described. Finally, we provide a perspective for its application prospects.

The polymeric microneedles, which has excellent mechanical property and biocompatibility, can pierce the stratum corneum in a minimally-invasive manner and result in efficient transdermal delivery of drugs. Thereby the polymeric microneedles can effectively treat various diseases, such as diabetes, cancer, obesity, eye diseases and so on. How to control the release behavior of the loaded drug is the key point in the polymeric microneedles. Stimuli-responsive polymeric microneedles, as an emerging technology for on-demand drug delivery, can achieve topical accurate release of drugs according to the change of the external environment or the physiological signal in cutaneous environment, making it the current research hotspot in transdermal drug delivery. At present, stimuli-responsive polymeric microneedles are always designed based on light response, pH response, enzyme response and glucose response. This paper reviews the recent researches of the stimuli-responsive polymeric microneedles in detail. Challenges and prospects of stimuli-responsive polymeric microneedles are also discussed.

The increasing demand for high-performance supercapacitor has promoted the rapid development of separators and electrode materials. Recently, electrospun nanofibers have been widely used as separators and electrode materials of supercapacitor, which is due to the high porosity, high electrochemical activity, large specific surface area and good structural stability. In this survey, the recent research progress in separator membranes and electrode materials of supercapacitor is reviewed. The discussion focuses on obtaining electrode materials for supercapacitor by electrospinning and other post-processing methods, including carbon nanofibers, carbon-based composite nanofibers, conductive polymer-based composite and metal oxide nanofibers. These investigation demonstrate that pore structure construction, activation treatment, and heteroatom doping can improve the specific surface area, electrochemical activity, wettability, and graphitization degree of carbon nanofibers, furthermore the electrochemical properties of electrode materials are enhanced. Moreover, combining carbon nanofibers with metal oxides, conductive polymers via blending, chemical deposition, electrochemical deposition, etc., can also improve capacitance, rate performance, and cycling stabilities of electrode materials. In addition, the existing problems of the regarding studies are pointed out. Finally, the future developments of electrospun nanofiber materials in supercapacitor is prospected.

The heterogeneous uptake reactions of hydroperoxyl radicals(HO₂) on ambient atmospheric aerosols have been proposed to be a significant sink of HO₂ radicals, thus could influence the atmospheric oxidation capacity and properties of atmospheric particles. The quantitative description of the heterogeneous reaction process of HO₂ is of great significance to the exploration of atmospheric oxidation and ozone generation capacity in different regions. The HO₂ uptake coefficients measured by different research groups can differ by 3 to 5 orders of magnitude. Exploration of the heterogeneous uptake mechanism of HO₂ radical on different types of aerosols under different conditions, accurately parameterized expression of the uptake coefficient is the key to quantifying its environmental impacts. This article introduces the mechanism and parameterized expressions of HO₂ heterogeneous uptake, reviews the existing research results and progress, summarizes and analyzes the different influencing factors, and makes suggestions and prospects for the future development.

Ozone pollution is a serious problem now prevailing in China. Ozone and its secondary pollutants generated indoor severely threaten human health. The catalytic decomposition of ozone at room temperature is an effective way to prevent the pollution. This review firstly summarizes the catalytic activity of carbon, zeolite, noble metal, transitional metal oxides and other materials; then focuses on manganese oxides, compares the activity of manganese oxides with different crystal structures and elaborates the research progress in mechanisms of ozone decomposition on manganese oxides. Currently, the major challenge in this field is the catalyst deactivation caused by water vapor. The comprehensive understanding in mechanisms of ozone decomposition and catalyst deactivation is the essential key to synthesize efficient catalysts.

Emerging organic contaminants are widely present in the waters and have potential threat to the ecosystem and human health. How to remove the emerging organic contaminants has become a growing concern for researchers. High valent manganese and iron, i.e. potassium permanganate (Mn(Ⅶ), KMnO₄) and potassium ferrate (Fe(Ⅵ), K₂FeO₄), are two effective inorganic chemicals for decomposing emerging organic contaminants in water treatment. Permanganate and ferrate are environmentally friendly, and have been drawing more and more attention due to their high efficiency. Permanganate and ferrate have similar chemical properties and close behavior in the removal of emerging organic contaminants. Recent studies on the oxidative degradation of emerging organic contaminants by permanganate and ferrate mainly focus on the kinetic models, the role of manganese- and iron-intermediates, the role of free radicals generated when permanganate and ferrate are combined with other chemicals or processes, and their application in real waters. Therefore, this paper summarizes the reaction kinetics of permanganate and ferrate, and compares the roles of permanganate- and ferrate-intermediates and free radicals, and their performance in real waters.

Lithium-sulfur batteries have a theoretical discharge specific capacity (1675 mAh /g) and energy density (2600 Wh /kg) that are much higher than those of lithium-ion batteries. Lithium-sulfur batteries are considered as very promising battery systems, thus they have been widely concerned and researched. However, the poor conductivity of sulfur, low utilization, and the shuttle effect of polysulfides make the cycling performance of lithium-sulfur batteries unstable. In order to overcome the impact of the shuttle effect, a variety of new separator designs and preparation methods have been developed in recent years to improve the cycle stability of the battery. This article reviews the latest research progress from the perspective of 2D material modification of the separator, and uses high-quality separators to suppress the shuttle effect, which will better achieve high stability of Li-S batteries. Besides, future developments are prospected.

Compared with the traditional luminescent materials such as organic dyes and quantum dots, rare-earth upconversion nanophosphors (UCNPs) have the unique advantages of large anti-Stokes shift, shaper and multicolor emission bands, long fluorescence life, high photostability and chemical stability, no photoblinking and photobleaching. The combination of UCNPs, graphical coding and anticounterfeiting printing technologies enables the formulation of invisible fluorescent patterns that are difficult to counterfeit. This has become a research hotspot in the field of anticounterfeiting and security. In this paper, the upconversion mechanism and synthetic methods of UCNPs are first introduced. Afterwards, the research status of UCNPs in the field of anticounterfeiting and security is elaborated, and four forms of upconversion anticounterfeiting and security patterns are summarized (i.e. NIR single-wavelength excitation, NIR dual-wavelength excitation, NIR/UV dual-wavelength excitation and three-wavelength excitation). Finally, the problems and challenges that UCNPs are facing in the field of anticounterfeiting and security, and future development directions are also proposed.

Fuel cell technology and its industrialization have been developed rapidly in China in recent years. However, the high cost of the fuel cell caused mainly by the using of precious Pt catalysts is still one of the most important factors restricting the development of fuel cell commercialization. It is of great significance to develop low Pt catalysts with much higher catalytic efficiency and lower Pt loadings. In recent years, Pt-based catalysts with three-dimensional morphology or/nanostructures have been emerged as a type of ultra-important low Pt catalysts, due to their special morphology/structures, their catalytic activity are usually much higher than that of the widely used Pt/C catalysts. In this paper, the research progress of Pt-based catalysts with special three-dimensional morphology(such as nanoframe structure, flower-like structure, nanocage structure, sea urchin structure, etc.) and their applications in fuel cells are reviewed. Meanwhile, some weaknesses and challenges of these catalysts are concluded. Furthermore, the future development and application of these catalysts are prospected.