Abstract
Nano titanium dioxide (TiO2) with photocatalytic activity was firstly modified by diethanolamine, and it was then doped with broad spectrum antibacterial silver (Ag) by in situ method. Further, both Ag doped TiO2-chitosan (STC) and TiO2-chitosan (TC) composites were prepared by the inverse emulsion cross-linking reaction. The antibacterial activities of STC composites were studied and their antibacterial mechanisms under visible light were investigated. The results show that in situ doping and inverse emulsion method led to good dispersion of Ag and TiO2 nanoparticles on the cross-linked chitosan microsphere. The STC with regular particle size of 1–10 μm exhibited excellent antibacterial activity against E. coli, P. aeruginosa and S. aureus under visible light. It is believed that STC with particle size of 1–10 μm has large specific surface area to contact with bacterial cell wall. The increased antibacterial activity was attributed to the enhancement of both electron-hole separations at the surface of nano-TiO2 by the silver ions under the visible light, and the synergetic and sustained release of strong oxidizing hydroxyl radicals of nano-TiO2, together with silver ions against bacteria. Thus, STC composites have great potential applications as antibacterial agents in the water treatment field.
Highlights
Antibacterial compounds, including inorganic compounds and organic polymers, have been applied as the new functional material in the field of water purification
Whereas TC and silver doped titania-chitosan (STC) composites were yellow, which might result from the cross-linking reaction between glutaraldehyde and chitosan in the context of the Schiff mechanism (The –NH2 of chitosan reacted with –CHO of glutaraldehyde to form C=N) due to the photochromic properties of Schiff base that led to the yellowing of TC and STC under illumination [30,31]
The intensity of the superimposed peaks of hydroxyl and amino groups was significantly reduced in TC and STC, which could be attributed to the reduction of the primary amine groups by the reaction of the amino groups on the chitosan molecular chains with glutaraldehyde [33]
Summary
Antibacterial compounds, including inorganic compounds and organic polymers, have been applied as the new functional material in the field of water purification. The composites of chitosan with inorganic materials (such as titanium dioxide) [9,10] or metallic materials (such as gold and silver nanoparticles) [11,12] can offer specific properties, such as broad. Transition metals, such as silver (Ag) nanoparticles (NPs) doped titanium dioxide nanomaterials can offer enhanced visible light photocatalysis [23,24,25]. It is expected that silver doped titanium dioxide-chitosan composites would obtain enhanced antibacterial activity. The preparation of silver doped titanium dioxide-chitosan composites by the inverse emulsion cross-linking reaction is crucial for optimizing the antibacterial activities. Antibacterial properties of chitosan, titania-chitosan (TC), and Ag doped TiO2 -chitosan (STC) composites were compared under both visible light and dark conditions. When compared to TC, enhanced antibacterial activity of STC makes it possible to be used as an antibacterial agent in the field of water treatment
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