Anti‐Bacterial coating based on photo‐synthesized silver nanoparticle by UV irradiation of phosphotunstate ormosils doped with core@shell SiO2@TiO2

L.P.GONCALVES; A.MIÑÁN; M.FERNÁNDEZ LORENZO; M.E.VELA; P. L. SCHILARDI; W.R.CORRER; O.E.YSNAGA; E.P.FERREIRA NETO; U.PEREIRA RODRIGUES FILHO

Congreso; SBPMAT, XIV Brazilian MRS Meeting; 2015

Coatings with anti-bacterial activity are highly relevant due to growing concern on antibiotics resistant bacteria infections [1] as well as on improvement of personal face mask in Hospitals and clinics [2]. Sol-gel processing is a versatile methodology for coatings with multifunctional purpose. Despite, the sol-gel process viability to produce versatile coating for interaction with biomaterials and living cells, very few has been done to exploit the use of this procedure to obtain anti-bacteria coatings]. Silver nanoparticle loaded materials display very interesting anti-bacteria properties, The phosphotungstic acid act as an efficient catalysis of the hydrolysis co-condensation reactions to obtain the sol used for coating preparation. Moreover, phosphotungstate Keggin clusters are excellent photocatalysts, especially after adsorption on wide band semiconductors such as TiO2. This photocatalytical enhancement is based on photoelectron transfer from the semiconductor to the LUMO of the phosphotungstate yielding heteropolyblues formation [3]. Although the use of titania nanoparticles is attractive they tend to agglomerate inside the films forming agglomerates, thus resulting on lower surface area and lower activity. It turns out these agglomeration can be overwhelmed by using titania nanoparticles dispersed on silica sub-micron particles [4]. Chemical tempering is a glass hardening technique based on ion-exchange in molten salts, such approach for cation metal doping induces a cation gradient in the films due to diffusion and resulting on enrichment of the surface with cations. Phosphotungstate in ormosil coating can act as a cation exchange site, exchanging protons by Ag+ and forming H3-xAgx[PW12O40] species, [5]. Photoreduction of silver cations by polyoxometalate was demonstrated by Mandal et al [6 and later on the polyoxometalate/TiO2 heterojunction was first used by Pearson et al [7] to produce Au decorated phosphotungstate@TiO2 particles. As an alternative, reproducible and easily prepared coating with anti-bacteria activity we report a hybrid Phosphotungstate Ormosil loaded with Silver Nanoparticles photosynthesized by UV irradiation of the phosphotungstate/SiO2@TiO2 heterojunction entrapped in the ormosil coating. It is important to remark the low content of the SiO2@TiO2 necessary to achieve the effects. Silver nanoparticle with 20-30nm diameter were obtained based on UV-vis plasmonic absorption band at 420nm inside the ormosil. Microprobe analysis by EDX coupled to Field Emission Scanning Electron Microscopy with selected primary electron beam energy (8keV) show SiO2@TiO2@PW@Ag agglomerates of 5 to 7 submicron particles up to 150nm large underneath its surface..Anatase phase on SiO2 particles was confirmed by 399, 513 and 637 cm-1 Raman shifts as well as by the diffraction peaks at 25.7, 38.4 and 48.5o (2). Maximum silver loading into the ormosils was achieved after 10min of ion exchange (chemical tempering) at 2% (Ag/ total film mass) by X-ray Fluorescence. X-ray photoelectron spectroscopy confirms silver on the ormosil surfaces. Anti-bacteria essays against Pseudomonas aeruginosa and Staphylococcus aureus showed low bacteriostatic effect for the unloaded ormosil while silver loaded ormosil showed bactericide effect toward both bacteria.