Hydrothermal Synthesis Of Small Particle Size Of A Zeolite And Its Application For Antibacterial Materials

A zeolite is applied widely in membrane separation, host-guest materials self-assembly and carriers of antibacterial materials as well as adsorption, ion-exchange and catalysis, because of its abundant pores, high specific surface area and excellent ion-exchange capacity. Small particle size of A zeolite has smaller grain, shorter channel comparing with conventional molecular sieve, thus it have more active sites, bigger volume and porosity, excellent adsorption properties, small intracrystalline diffusion resistance, higher reaction activity owing to reactant and product entering and exiting the channel easily. Antibacterial materials supporting silver ions into the pores of molecular sieve carrier has better safety and antibacterial durability than traditional antibacterial materials. Antibacterial zeolite materials prepared using small particle size of A zeolite as carrier can increase the amount of silver and reduce the value of MIC, then enhance antibacterial ability. So antibacterial zeolite materials have bright application prospect. Small particle size of A zeolite was synthesized using different silicon sources by hydrothermal method and Ag-loaded zeolite materials were prepared using small particle size of A zeolite as carriers and its antibacterial properties were estimated basing on the comprehensive analysis the research progress of preparation of small particle size of A zeolite and its application using as the carrier of antibacterial materials supported Ag+. It has important significance to study the application of small particle size of A zeolite for preparing efficient antibacterial materials. The main study results are as follows:1. The small particle size of A zeolite was prepared by hydrothermal method with sodium silicate, colloidal silica and solid silicone as silicon sources and sodium metaaluminate as aluminum source. The zeolite type, crystallinity, morphology, particle size and distribution of crystalline products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and Fourier Transform Infrared Spectroscopy(FT-IR). The influences of alkalinity, aging conditions, crystallization conditions on product were investigated. Further, the growth mechanism of zeolite was discussed.(1)When sodium silicate was used as the silicon source, A zeolite had well-defined crystal and uniform particle about 500 nm. The optimal parameters were determined as follows: n(H2O)/n(Na2O)=30, aging temperature was 30°C, aging time was 24 h, crystallization temperature was 100°C and crystallization time was 1h.(2)When colloidal silica was used as the silicon source, A zeolite had small particle size of 300-500 nm. The optimal parameters were that n(H2O)/n(Na2O)=30, aging temperature was 30°C, aging time was 24 h, crystallization temperature was 100°C and crystallization time was 1h.(3)When solid silicone was used as the silicon source, A zeolite with well-defined crystal and uniform particle size of 600 nm were obtained with relatively low alkalinity and sodalite(SOD) were obtained with relatively high alkalinity. The optimal parameters were determined as follows: n(H2O)/n(Na2O)=30, aging temperature was 20°C, aging time was 20 h, crystallization temperature was 100°C, crystallization time was 4h.(4)The final products had high crystallinity and uniform cystal morphology, when sodium silicate was used as the silicon source. While, using colloidal silica as the silicon source, the final products had defective surface and wide distribution of particle size. When solid silicone was used as the silicon source, the particle was relatively big, about 600 nm. It was proposed that sodium silicate provides not only silicon source, but also Na+ and OH- and Na+ has the role of structure guiding in the synthesis of zeolite. The growth process of A zeolite in three systems belongs to liquid transformation mechanism.2. NH4 A zeolite was prepared by ion exchange in solution with the carrier of A zeolite of 500 nm prepared using sodium silicate as the silicon source. Ag-loaded zeolite was prepared by solid phase ionic exchange method. The content of silver of Ag-loaded zeolite was determined by AAS and antibacterial properties were studied by spectroturbidity method. The influence of the amont of Ag NO3, reaction temperature and time on the content of silver and antibacterial properties were investigated.(1)The amount of silver supported in zeolite increased with the increasing of the amont of Ag NO3. When the ratio of n(NH4A) and n(Ag NO3) was less than 1/2, the amount of sliver improved linearly; When it was more than 1/2, the amount of sliver increased slowly. When reaction temperature was 350°C, the amount of silver reached a maximum value. When reaction time was 4h, the content of silver reached saturation. The amount of silver was 3.8% under the optimal conditions, which exceeded the theoretical calculating value. When silver was loaded completely, the content of silver was 3.4%.(2)The optimal conditions of preparation of zeolite supported Ag were that the ratio of n(NH4A) and n(Ag NO3) was 1/2, reaction temperature was 350°C, reaction time was 4h. The MIC for Escherichia coli was 21 ppm, and antibacterial properties was superior to the results that reported in literature(31.3~500ppm).