Preparation Of Silver-doped Titania Antibacterial Material

Inorganic antibacterial agents have been widely applied in many products for their advantages in safety,stability and broad antibacterial activity,especially photocatalytic titanium dioxide and silver-doped antibacterial materials.But the photocatalysis of titanium dioxide is activated only when it is exposed in the light; moreover,only 5%of solar spectrum is used.For practical application,the photocatalytic activity of titanium dioxide needs further improvement.Silver has a broad spectrum of antibacterial activity and exhibited low toxicity towards human cells,but silver ion is unstable and easily transformed to black metallic silver or brown silver oxide during illumination or thermal treatment and results in influencing its application.In order to avoid their defects,silver-doped titanium dioxide antibacterial powder with good stability and long-lasting antibacterial activity were prepared in this work.Preparation and characterization of precursor of titania and silver-doped titanium dioxide powder were investigated systematically.The main results of this paper are following:The precursor of titanium dioxide was synthetized by hydrolysis from titanium sulfate solution prepared from industrial H₂TiO₃.In the thermohydrolysis system, effects of the technical parameters of hydrolysis including acidity,TiOSO₄ concentration,temperature,time of hydrolysis,species and contents of the surfactants on the particle size and yield of precusor were investigated.The results show that the optimal process parameters to obtain homogeneous dispersion of precursor(D[4,3]=4.7?m,SD=0.88)are:the titanic solution concentration range from 25 to 35g/L(TiO₂),H⁺ concentration range from 2.6 to 3.0mol·L^-1,hydrolysis temperature 125?,hydrolysis time 50min and solution heated by steam.Based on above condition,the hydrolysis rate of solution is over 94%.In addition,effects of species and contents of the surfactants on the hydrolysis rate and dispersion of precursor were investigated.The results indicate that the hydrolysis rates and the mean size of precursor decrease with increasing of the surfactants contents of DBS, TEA and glycerol.It is should be noted that when the content of TEA is 50ml/L,the mean size of precursor decreases significantly from 4.7 to 0.28?m and the SD of precursor decreases from 0.88 to 0.49.The silver-doped titania powders prepared by adsorption method and mixing method were investigated,the results show that the stability and antibacterial activity of powder prepared by adsorption method is better than that prepared by mixing method.Adsorption of silver ions from aqueous solution onto the precursor (H₂TiO₃)was investigated.The results show that silver ions adsorbed on the surface of the precursor connect with the atomic oxygen with chemical bond and the adsorption is strongly dependent on pH value.The equilibrium absorption capacity of H₂TiO₃ increased with the increase of pH value and the decrease of the mean size of particle.The maximum adsorption capacities of H₂TiO₃(D[4,3]=2.55?m)is 23.64,29.76 and 40.82mg/g at the pH 5,6 and 7,respectively,the maximum adsorption capacities of H₂TiO₃(D[4,3]=8.89?m)is 12.75,16.83 and 25.54mg/g at the pH 5,6 and 7,respectively.The adsorption of silver ion obeys the Langmuir isothermal equation well in the concentration range studied.The precursor contains a great deal of hydroxyl group and SO₄^2-group.The smaller the precursor is,more water the precursor contain;moreover,for the precursor with small size,the precursor need to be calcined at higher temperatures to lost the adsorbed water,the structural hydroxyl group,and SO₄^2-group and transform into rutile phase.As the silver-doped titanium dioxide powders were synthesized by adsorption of silver ions onto the surface of precursor with the small mean size(D[4,3]=0.26?m), silver ion was dispersed in the powder uniformly and silver cluster was not observed in the powder even the silver content is increased to 5wt%.However,Silver ion was dispersed in the precursor with the mean size of 8.89?m(D[4,3]=8.89?m),silver cluster was found in the powder when the silver content is increased to 3wt%.It is found that the powder prepared by the high dispersion of precursor have white color and show good stability and long-lasting antibacterial activity.Silver can promote the transformation of the structure of titania and retard the growth of particle,but PO₄^3-group doped in titania can improve the stability and durability of composite and retard the transformation of the structure of titania.As titania is doped by 1wt% silver,the red-shift of the adsorbed edge of the composite powders was observed and the photocatalytic activity of titania was enhanced greatly.The preparation process of silver-doped tiania coated with alumina or silicon dioxide film was described as follow:the solution of NaOH was dropped gradually into the solution of 0.20mol/LAl(NO₃)₃ containing silver-doped titania powder at 70-80?with pH=5.0 to coat the alumina film.The dilute sulfate acid and the solution of 0.1mol/LNa₂SiO₃ were added into solution containing silver-doped titania powder at 80?with pH=9-9.5 to coat the silicon dioxide film.The results show that the thickness of coating film presented at the surface of silver-doped titania particle is about 30-40nm.The release rate of silver ion of the composite powder is affected by the coating film and the release rate of silver ion of the composite powder coated alumina or silicon dioxide decrease and its stability was improved.Comparing to silver-doped titania,the powder coated alumina or silicon dioxide have three times of long-lasting antibacterial period.Coating improves the stability of composite and prolongs the lifetime of silver-doped titania powder.Base on above study,the technical route to produce new kind of silver-doped titanic coated film antibacterial material has been set up and the workshop manufactured 30t/a silver-doped titania antibacterial powder for industrial-scale production has been designed.The process factors in industrialization have been discussion in detail and industrialization of silver-doped titania antibacterial material has been completed satisfactorily and the product manufactured has many advantages such as safety,stability,effective and long-lasting antibacterial activity. The antibacterial activity of product was measured by Guangdong detection center of microbiology,the result show that 99.99%of E.coli and S.aureus was killed,and the MICs of product against E.coli and S.aureus are 100mg/L,which is smaller than Japanese standard of the antibacterial material(800mg/L).