Preparation Of Gelatin-Silica/Ag Hybrid Materials For Wastewater Treatment

Environmental pollution is one of the major problems that seriously affect human health.Phenols and microbial contaminants are the two main pollutants in wastewater.Removal of those two substances can significantly improve water quality and achieve the purpose of purifying wastewater.Ag nanoparticles(NPs)are one typical inorganic nanomaterials,have received considerable attention because of the easy synthesis route and low cost.Ag NPs not only show strong catalytic activity,especially for degradation of phenols,but also show strong anti-bacterial property to inhibit the growth of microbial contaminants.Therefore,Ag NPs have been widely used as multifunctional materials in the wastewater treatment.However,their ultrafine size not only easily causes the serious agglomeration,but also reduces their catalytic and anti-bacterial properties.Gelatin is one type of natural protein that is cheap and readily available, and can reduce Ag ions to Ag NPs in situ.Silica is a typical inorganic nanomaterial,and shows excellent biocompatibility,aqueous solution stability and low-cost.Gelatin-silica hybrid materials have the advantages of both gelatin and silica.Therefore,in this study,gelatin-silica hybrid materials were used as matrix materials for the immobilization of Ag NPs.Two types of gelatin-silica/Ag nanoparticle hybrid materials were developed:hybrid microspheres and hybrid nanofiber membranes.Their catalytic activity and anti-bacterial property were both evaluated,to explore their potential application in removal of phenols and microbial contaminants in wastewater.The content of the present work was constructed by following two parts:(1)Synthesis and characterization of gelatin-silica/Ag NPs hybrid microspheres Firstly,GSi Ms were synthesized through emulsification of gelatin,TEOS and GPTMS solution in the paraffin oil.SEM observation showed that the GSi Ms were spherical in shape with the diameter of 5-15?m.They were then soaked in the solution of Ag NO₃ and subject to a hydrothermal treatment at 80 ? to produce gelatin-silica/Ag NPs hybrid microspheres.SEM spectra indicated that the Ag@GSi Ms had the similar diameter with GSi Ms.An EDS specturm showed that Ag@GSi Ms were rich in C,O,Si and Ag elements.After incubation in the solution of 4-nitrophenol and Na BH₄,Ag@GSi Ms showed good catalytic activity for reduction of 4-NP,the catalytic reaction was basically completed within 10minutes.Ag@GSi Ms were then exposed to Escherichia coli(E.coli)for 24 hours,they showed strong anti-bacterial activity and highly inhibited the growth of E.coli.(2)Synthesis and characterization of Ag@gelatin-silica hybrid nanofiber membranes The Ag@gelatin NPs were synthesized through in situ reduction of Ag NO₃ by gelatin at low concentration after stirred under 60 ?.Gelatin served as reducing and stabilizing agent in the reaction.TEM observation showed that most of the Ag@gelatin NPs had the diameter of 20-40 nm and they were well distributed in the gelatin matrix.The Ag@gelatin-silica hybrid nanofiber membranes were synthesized through addition of Ag@gelatin NPs in the gelatin solution at high concentration followed by cross-linking with GPTMS.TEM and SEM spectra showed that the hybrid nanofiber membranes were constructed by numerous of Ag@gelatin-silica hybrid nanofibers and had the porous structure.Numerous Ag@gelatin NPs were clearly observed on the surface of Ag@gelatin-silica hybrid nanofibers and no significant agglomeration was observed.The catalytic and anti-bacterial activities were both examined.The results indicated that the catalytic activity of Ag@gelatin-silica hybrid nanofibers were controllable through adjustment of the content of Ag in the hybrid nanofibers and had good recyclability.Moreover,they could easily be recycled with a high recovery efficiency.To examine their anti-bacterial property,E.coli was used as model microbial contaminant.Optical density and digital photos indicated that the Ag@gelatin-silica hybrid nanofiber membranes had strong anti-bacterial property and highly inhibited the growth of E.coli.