Preparation Of Ag-Bi₂WO₆-TiO₂/Starch Antibacterial Nanocomposites Films And And Its Photocatalytic Performance On Ethylene Degradation

In this paper,Ag nanoparticles(Ag NPs)was reduced by gamma-ray irradiation.Bi₂WO₆-TiO₂(BT)heterojunction was synthesized via solvent thermal method,and Ag-TiO₂-Bi₂WO₆(ABT)was prepared by deposition.ABT/starch nanocomposite films which have photocatalytic and antibacterial properties,were prepared by loading the prepared ABT photocatalyst onto the starch matrix.The effects of preparation conditions,loading modes and the loading amount of ABT photocatalyst on the visible light catalytic activity of ethylene and the antibacterial performance of ABT/starch films was studied.The microstructure and physicochemical properties of ABT and ABT/starch films were characterized.The mechanism of improving visible-light photocatalytic degradation performance on ethylene of ABT and ABT/starch films were discussed.The main research contents and conclusions are as follows:(1)⁶⁰Co-?ray irradiation was used to prepare Ag NPs,and silver nanoparticles with small size and good dispersion were prepared by the controlling the addition amount of silver nitrate,PVP-K30 and irradiation dose.TEM results show that when the dosage of silver nitrate is 0.5wt%,the dosage of PVP-K30 is 0.6wt%,and the irradiation dosage is20KGy,the size distribution of silver nanoparticles is narrow,and the size of Ag NPs is between 2 and 15 nm.The dispersion of silver nanoparticles is relatively good.ABT photocatalyst was prepared by mixing ABT and BT dispersion solution under these conditions.The photocatalytic activity of ABT was evaluated by loading it on starch film.The results showed that the photocatalytic degradation rate constant K?value of ABT was the highest and the photocatalytic activity was the best.(2)The effects of doping amount of Ag NPs on the physical and chemical properties and the photocatalytic degradation performance on ethylene of ABT were studied.The doping of silver nanoparticles did not change the crystallinity.The photocatalytic activity showed:With the increase of Ag NPs,the photocatalytic degradation rate constant K?of ABT showed a trend of decrease after the first increases,When the doping amount of Ag NPs was 3%,the K?value reached the maximum.(3)The ABT prepared under the above optimum conditions.The microstructures and physicochemical properties of TiO₂,Bi₂WO₆,BT and ABT were characterized,and their photocatalytic properties for ethylene degradation under visible light were compared.The characterization results showed that the TiO₂ nano particle diameter is about20?40 nm,and the particle diameter of Bi₂WO₆ is between 40 and 60 nm;TiO₂ contacts Bi₂WO₆ interface to form nanocomposite BT.Ag NPs mainly exist in ABT in the form of zero valence.There are five elements(Bi,Ti,Ag,W and O)in ABT,and a small amount of Ag nanoparticles dotted on the surface of BT,which indicating that Ag and BT have formed composite.The doping of Ag NPs can effectively broaden its visible light response range and the absorption range of BT was broadened to infrared light.Meanwhile,the doping of Ag NPs results in obvious surface plasmon resonance(LSPR)effect and Schottky barrier,which greatly reduces the recombination rate of ABT compared with pure TiO₂,pure Bi₂WO₆ and BT,and the doping of Ag NPs significantly increases the electron transport capacity,which is of great significance to the improvement of the photocatalytic activity of ABT.This is very important to improve the photocatalytic activity of ABT.Under visible light and simulated sunlight,ABT exhibited better photocatalytic performance than TiO₂,Bi₂WO₆,BT,Ag-Bi₂WO₆ and Ag-TiO₂.Under simulated sunlight,the rate constant K?of ABT increased by 188.13%,150.51%,64.62%,29.95%and 33.12%compared with sole TiO₂,Bi₂WO₆,BT,Ag-Bi₂WO₆ and Ag-TiO₂ respectively.Under visible light,the rate constant K?of ABT increased by232.47%,143.82%and 74.67%compared with sole TiO₂,Bi₂WO₆ and BT respectively.(4)Starch film was prepared by casting method,and nanocomposite starch film was prepared by loading photocatalyst with internal doping method.The effects of ABT doping on the microstructure,physicochemical properties and photocatalytic degradation of ethylene were characterized.The thickness of ABT/starch composite films and control starch film ranged from 150to 200 microns.With the increase of ABT loading,the thickness,opacity and tensile strength of the nanocomposite films increased,but the elongation at break decreased.The ABT nanoparticles distributed in starch network structure,the nanoparticles in the starch film were distributed inhomogeneously and only locally,and some nanoparticles were aggregated to form small aggregates,but there were still obvious gaps between the particles.The surface of the ABT/starch film is smooth and compact,without cracks and stomata.A small amount of exposed nanoparticle aggregates can be observed on the surface of the film.When the loading of nanocomposite increases,the exposure probability of nanoparticles on the surface of the starch nanocomposite films increases.The dispersion of ABT in starch film increased the roughness of the film surface.There were some star-dotted nanoparticles dispersed and some aggregates of nanoparticles on the surface of the cross section,and the excessive addition of ABT aggravates the agglomeration phenomenon,the diameter of the aggregates increased.The doping of ABT did not cause the chemical change of starch film,and the starch film did not change the crystal structure of nanomaterials,but there was interaction between the interface of ABT and starch.The addition of ABT could improve the decomposition temperature and thermal stability of the films to a certain extent.With the increase content of ABT,the degradation rate constant K?of nanocomposite starch films first increased and then decreased.When the loading was 3%and 5%,the difference in K'value between them was extremely insignificant.When the loading was 5%,the K'value of ABT/starch composite film was the highest,which is 3.0127×10^-4 min^-1.(5)Starch film was prepared by casting method.ABT/starch composite film was prepared by composite method.The result showed that ABT was successfully loaded on the surface of the starch film,and the original morphology of the nanoparticles was retained after loading.In addition,the loading of ABT greatly increased the roughness of the film surface.When the loading amount was 2.0%,the best effect of ethylene degradation achieved,and the synergy of the two methods of loading was strongest.However,when the load exceeded 2.0%,the synergistic effect decreased and the photocatalytic degradation effect of ethylene decreased.(6)ABT/starch film prepared by composite method was used as the research object to evaluate the effect of catalytic conditions(light intensity and initial ethylene concentration)on photocatalytic performance for ethylene degradation of ABT/starch film.With the increase of light intensity,the rate constant K?of ABT/starch film increased first and then decreased.When the light intensity was 60.5 mw/cm²,the K?value of ABT/starch film reached the maximum value.The initial concentration of ethylene also has some influence on the photocatalytic performance of ABT/starch film.With the increase of initial concentration of ethylene,the rate constant K?value of the ABT/starch film increases first and then decreases.When the initial concentration of ethylene increases to 0.15 mg/L,the K?value of composite photocatalyst reaches the maximum.(7)The bacteriostatic effect of nanocomposite starch film on typical Gram-negative bacteria(Escherichia coli)and Gram-positive bacteria(Staphylococcus aureus)was investigated by the halo method.The results confirmed that the doping of Ag NPs had obvious inhibitory effects on the growth of Staphylococcus aureus and Escherichia coli.The control starch film and the starch nanocomposite film loaded with TiO₂,Bi₂WO₆ and BT did not form the bacteriostatic ring on Staphylococcus aureus and Escherichia coli,while the ABT/starch composite film formed obvious bacteriostatic ring on Staphylococcus aureus and Escherichia coli.Under the internal doping loading method and the composite method,the antimicrobial effect of ABT/starch film on Escherichia coli and Staphylococcus aureus increased with the increase of ABT content.The bacteriostatic effect of ABT/starch films on Escherichia coli was slightly better than that of Staphylococcus aureus.