New applications of advanced functional materials based on calcium carbonate

As an important non-metallic mineral basic raw material in daily industrial production, calcium carbonate is known as "industrial food" and is closely related to the national economy and life. Calcium carbonate is widely used in plastics, architectural coatings, paints, paper, rubber, inks, pigments, adhesives, sealants, daily chemicals, toothpaste, food, medicine and other fields. Due to its wide source, low cost, wide application, simple process and flexible technology, calcium carbonate is valued by the industry and is an important supporting material for the development of emerging industries and high-tech.

Application of calcium carbonate in polymer matrix composites: The preparation and application of traditional calcium carbonate have been widely reported, and calcium carbonate whiskers have attracted the attention of researchers because of the columnar fiber structure, which can improve the tensile strength, bending strength, impact toughness and other mechanical properties of polymer materials. The results show that the mass fraction of 0.1% calcium carbonate can increase the dynamic elastic modulus of PHBV by 76% and the loss modulus by 175. Due to the increase of the crystallinity of the composite material and the increase of the tortuosity of the gas transmission path, the oxygen transmission rate and water vapor transmission rate are obviously decreased.

Application in flame retardant materials: In terms of flame retardant, calcium carbonate is mainly used in polymer matrix composites, wood modification, etc., especially polymer/natural fiber composites. Calcium carbonate, especially crystalline calcium carbonate, can be used both as a reinforcing agent for polymers and as a flame retardant for polymers. Calcium carbonate is heated to decompose carbon dioxide gas, which can reduce the surface temperature of the combustion material, dilute the concentration of combustible gas, and at the same time isolate the internal diffusion of oxygen to the combustion material, so as to achieve the purpose of flame retardant.

Application in hydrogel: under acidic conditions, calcium carbonate can promote the regeneration of biological tissues, and calcium carbonate can be degraded in vivo, weak acid environment can regulate the release of calcium ions of calcium carbonate; calcium ions can form ionic bonds in the hydrogel to improve the mechanical strength of the hydrogel. Moreover, in order to obtain the excellent biological properties of hydrogels, researchers often use calcium carbonate in combination with other inorganic materials.

The application research in photocatalytic materials shows that the elimination rate of nitrogen oxides by carbon nitride after the synergistic effect of cyano defects and calcium carbonate reaches 51.18%, which is significantly higher than that of nitrogen oxides by 34.05%. The principle is that calcium carbonate is used as an alkaline compound to compound calcium carbonate with graphite phase carbon nitride, which can not only exert the acid-base neutralization effect of calcium carbonate and nitrogen oxide to adsorb nitrogen oxide, assist carbon nitride to eliminate nitrogen oxide through photocatalysis, but also calcium carbonate can be used as the transfer center of photogenerated carriers, so that carriers and nitrogen oxide can contact each other, effectively exerting the photocatalytic effect of carbon nitride.

Application in new energy materials: Zinc-air battery is the 1 water-based rechargeable battery. It has the advantages of safety, low cost, and environmental friendliness. It is a green energy storage device with development prospects. However, the capacity decay of zinc-air battery is fast and the cycle stability is poor. Some scholars have coated nano calcium carbonate on the surface of the zinc negative electrode, because nano calcium carbonate induces zinc ions to be evenly and orderly embedded and released on the surface of the zinc negative electrode, thereby improving the durability of the battery.

Application in radiation refrigeration materials: the infrared emission groups of inorganic materials are mainly anionic groups, calcium carbonate has good infrared emission properties in the atmospheric window (8~13 μm), and the source of raw materials is wide, shells, eggshells and other wastes are calcium carbonate raw materials, can recycle biomass resources to prepare calcium carbonate radiation refrigeration materials, not only has cost advantages, but also is conducive to the sustainable development of the technology. At present, more methods are used to prepare calcium carbonate and other polymer materials and additives into composite coatings, and often combine radiation refrigeration technology with other functions to strengthen other effects through radiation refrigeration technology.

Application in thermal energy storage: calcium carbonate has good thermal conductivity, mechanical properties, sealing performance and chemical stability, can be used for microcapsule coating phase change materials, the preparation of microcapsule skin has a good protective effect, and has a longer service life. Moreover, calcium carbonate is green and environmentally friendly, and the prepared microcapsule-coated phase change material is environmentally friendly and is a sustainable development material. The coated phase change materials are mainly octadecane or compounded paraffin system.

Application in tumor treatment: calcium carbonate can be used as a drug release system for tumor treatment due to its low cost, easy bioabsorption and good biocompatibility. However, due to the high crystallinity of typical micron-sized calcium carbonate, the degradation rate of calcium carbonate in biological systems is reduced, and the drug release efficiency is seriously damaged. The scientists used amorphous calcium carbonate nanoparticles as a drug delivery system. Compared with crystalline calcium carbonate, amorphous calcium carbonate is more likely to be hydrolyzed in the intracellular environment, which is more conducive to drug release.

Application in the field of new papermaking: Some scholars use nanocellulose as a template to prepare flexible deformable calcium carbonate with high aspect ratio. First, the nanocellulose is dispersed in water, and carbon dioxide is introduced after stirring evenly, so that calcium oxide surrounds the nanocellulose to generate calcium carbonate in situ. The generated calcium carbonate was 10-30 μm wide and 30-200 μm long, adsorbed on the surface of nano-cellulose, and was not easy to collapse. The flexible deformable calcium carbonate is added to the wood pulp, and the paper is made by wet pressing method. The cellulose of the high calcium paper has strong bonding force and excellent tensile strength. The variability of calcium carbonate gives the paper a smoother surface. This method can change the paper from wood to calcium carbonate, reduce the use of wood, and contribute to the sustainable development of the paper industry.

Application in building materials: calcium carbonate whiskers and cement compatibility agent is better, commonly used in cement reinforcement. The general concrete is easy to crack by impact, and calcium carbonate whiskers can control the development of cracks. Moreover, in recent years, the use of calcium carbonate whiskers, stainless steel fibers, basalt fibers and other multi-scale hybrid fiber reinforced concrete has become a 1 trend of development.

Application in water treatment: Calcium carbonate has good buffering effect, neutralization ability and adsorption performance, and can be used in water treatment and wastewater treatment. In terms of water treatment, calcium carbonate can adjust pH, remove polluting ions and adjust water hardness, and play an important role in alleviating scale formation, preventing water pipe blockage, and improving water resource utilization efficiency. In terms of wastewater treatment, calcium carbonate can absorb organic pollutants and heavy metal ions in wastewater, reduce the content of harmful substances in wastewater, so as to achieve the purpose of purifying water resources.

application in soil treatment: in the treatment of contaminated soil, calcium carbonate can precipitate a variety of heavy metal ions, but also can adjust the pH of the soil, is an important repair agent for contaminated soil. In practical applications, calcium carbonate is often used in conjunction with other clays to obtain better treatment effects. Because the production of calcium carbonate requires high energy consumption and large carbon emissions, in recent years, the use of microbial induced calcium carbonate precipitation technology (MICP) has low energy consumption and low carbon emissions, which is one of the most promising technologies for contaminated soil treatment. MICP has excellent performance in sewage treatment and contaminated soil treatment.