Yuan Yu

Food safety is connected to public health, making it crucial to protecting people’s health. Food analysis and detection can assure food quality and effectively reduce the entry of harmful foods into the market. Carbon dots (CDs) are an excellent choice for food analysis and detection attributable to their advantages of good optical properties, water solubility, high chemical stability, easy functionalization, excellent bleaching resistance, low toxicity, and good biocompatibility. This paper focuses on the optical properties, synthesis methods, and applications of CDs in food analysis and detection, including the recent advances in food nutritional composition analysis and food quality detection, such as food additives, heavy metal ions, foodborne pathogens, harmful organic pollutants, and pH value. Moreover, this review also discusses the potentially toxic effects, current challenges, and prospects of CDs in basic research and applications. We hope that this review can provide valuable information to lay a foundation for subsequent research on CDs and promote the exploration of CDs-based sensing for future food detection.

As an important chemical raw material and potential energy, the preparation method of NH₃ has gradually attracted the attention of scholars. Due to the increasing pressure on environmental protection and the growing reduction of energy resources, researchers have been committed to do the research on the reduction of N₂ to NH₃ by electric energy, instead of the traditional preparation method. The electric energy is a kind of environmental-protection material compared with traditional materials. However, there are still many defects of these methods, such as slow reaction kinetics and competitive hydrogen evolution reaction (HER). Therefore, how to improve the reaction rate and Faraday efficiency have become an urgent problem to be solved in the study of electrocatalytic nitrogen reduction. In this paper, Au³⁺ ions were electrostatically adsorbed on the surface of Ti₃C₂ nanosheets, which was a new ultra-thin two-dimensional conductive material, and Au@Ti₃C₂ samples with different contents were prepared by self-reduction of Au³⁺ ions to Au. The structure and performance tests showed that the Au nanoparticles on the surface of two-dimensional Ti₃C₂ nanosheets were nano sized. The nano scaled Au could promote the reduction of nitrogen and when the addition ratio of Au was 1%, Au@Ti₃C₂ showed the best performance and good stability.

Copper sulfide was prepared successfully by reflux method in the research. To improve the dispersion and conductivity of copper sulfide, CuS/NCNTs composites were prepared by one-step hydrothermal method using nitrogen doped carbon nanotubes (NCNTs) and copper sulfide. The conductivity and dispersion of the composites were improved, and the catalytic effect of oxygen reduction was significantly increased. The precursor of CuS/NCNTs oxygen reduction catalyst was calcined to obtain CuS/NCNTs oxygen reduction catalyst with good stability and methanol resistance. The onset potential, current density and half-wave potential were significantly improved. In the process of composite materials calcination, the oxygen reduction catalyst with high catalytic rate was obtained by adjusting the proportion of CuS, CNTs and nitrogen sources, which provided a practical experimental method for sulfide oxidant catalysis. This cheap catalytic material was expected to replace noble metal catalyst like Pt/C, and be widely used in the field of oxygen reduction catalyst.

In recent years, fluorescent carbon dots have attracted great attention due to their good luminescence and low toxicity. Here, blue fluorescent core–shell structured carbon polymer dots (CPDs) with high stability under a wide range of pH values, long storage time, and excellent fluorescence in various solvents and even in the solid state were prepared by hydrothermal synthesis of dendritic tris(2-aminoethyl)amine (TAEA) and citric acid. The CPD core structure provides strong fluorescent luminescence; a shell structure of the core possesses a high amount of dendritic primary amino groups connected by ethylene groups to the core. This unique structure prevents aggregation of the cores and the self-quenching effect of CPDs. As a result, the CPDs have high fluorescence in both aqueous and hydrophobic solutions and even as pure solid-state powder. In addition, the CPDs are also insensitive to pH of solutions, and the fluorescence intensity of the solution was stable in the pH range of 4–14. The CPD embedded polymer films and fibers revealed excellent fluorescent properties.