Preparation And Properties Of Nano-silver/hydroxyapatite/diatomite Composite Ceramics

Nowdays water pollution has become increasingly prominent with the rapid development of global industry.In recent years,kinds of water pollution incidents continue to occur and conventional water treatment materials are difficult to solve the problem,which posing a threat to drinking water safety.Therefore,searching safe,effective and cheap point-of-use water treatment materials is of great significance.Ag doped hydroxyapatites(Ag-HA)were synthesized by precipitation and hydrothermal method in this paper.Then they were mixed with diatomite to prepare Ag doped hydroxyapatite/diatomite composite ceramics by sintering process at 1050 ?.Crystal structure and microstructure of Ag-HA,and pore structure and antibacterial properties of the composite ceramics were investigated.Nanosilver/hydroxyapatite/diatomite composite ceramics with different silver content(0.16wt%,0.21wt%,0.24wt% and 0.64wt%)were prepared by in-situ method.And their microstructure,antimicrobial properties,filtering bacteria effect and silver release behavior under different water quality were studied.The main results of the experiment are as follows:Ag doped hydroxyapatite synthesized by precipitation method is short rods or granules,while the hydrothermal method synthesis of Ag doped hydroxyapatite is long rod shape with a higher crystallinity and aspect ratio.The higher synthesis temperature favors the growth of Ag doped hydroxyapatite crystals,resulting in a larger particle size of products.As Ag+ replaced Ca2+ into the hydroxyapatite lattice,the Ag doped hydroxyapatite grain size and unit cell parameters are increased.All Ag doped hydroxyapatite with different silver content synthesized by hydrothermal method have good bactericidal effect and antibacterial durability against E.coli and S.aureus,and their bactericidal rate are all 100% in 1h,3h,6h,12 h or 24 h.In Ag doped hydroxyapatite/diatomite composite ceramics,diatomite particles still retain the original pore structure.The abundant pore structure of composite ceramics are mainly made up of the pores in diatomite particles and those between particles.Composite ceramics can effectively kill the bacteria in contact with water and keep the material itself aseptic.As silver content increase,the sample antibacterial activity increase.When silver content is 0.098%,the minimum inhibitory concentration of E.coli and S.aureus are 100?g/mL and 50?g/mL,respectively,and the bactericidal rate of block and powdery composite ceramics reache 100% after 3h.In nanosilver/hydroxyapatite/diatomite composite ceramics,the surface and pores of diatomite particles are uniformly dispersed with 10~20nm spherical or short rod-like Ag-HA and spherical nanosilver particles.The pore size distribution of the composite ceramics is narrow,the average pore size,median diameter and porosity are 510.20 nm,1521.90 nm and 52.23%.The pore structure of composite ceramics are mainly made up of the pores in diatomite particles and those between particles.The amount of released silver from composite ceramics in ultrapure water is slowly increasing over time.The maximum release in the short term is 0.43?g/L,those is 0.88?g/L in the long term,and 1.8?g/L under filtration,which are much lower than the drinking water standard.In the medium with chlorine,the amount of released silver increases with increasing NaClO concentration.In the 4mg/L NaClO solution,the amount of released silver increased over time in the early period,but changed little after 6h,which remained at about 10?g/L.Acid or alkaline environment can also increase the amount of released silver from composite ceramics,and the higher acidity the larger released amount.But the maximum release is only 34.5?g/L which is lower than the drinking water standard.Microbiological test results show that the sustaining and stable released silver from composite ceramics can not only inhibit the growth of bacteria,and have good bactericidal properties for high concentration(105cfu/mL)and super high concentration(10~9cfu/mL)of E.coli or S.aureus,but also have excellent effect of filtering bacteria.When silver content is 0.64wt%,the LRV values against super high concentration E.coli and S.aureus(10~9cfu/mL)are 5.89 and 5.22,respectively,and 106cfu/mL of bacteria could be completely filtered when silver content reach 0.24wt%.The nanosilver/hydroxyapatite/diatomite composite ceramics with abundant pore structure,silver sustained-release performance and high safety have good bactericidal activity and strong effect of filtering bacteria under the premise of silver released amount far below drinking water standard,which is expected to be applied in the field of point-of-use water treatment.