Anti-Bacteria Coating based on Photo-synthesized Silver Nanoparticle by UV irradiation of Phosphotungstate Ormosils doped with Core@Shell SiO2@TiO2

LIDIANE P. GONCALVES; ALEJANDRO MIÑAN; MÓNICA A. FERNANDEZ LORENZO DE MELE; MARÍA ELENA VELA; P. L. SCHILARDI; WAGNER RAFAEL CORRER; ORLANDO ELGUERA YSNAGA; ELIAS PAIVA FERREIRA NETO; UBIRAJARA PEREIRA RODRIGUES FILHO

Encuentro; XIV Encontro da SBPMat; 2015

Coatings with anti-bacterial activity are highly relevant due to growing concernon antibiotics resistant bacteria infections [1] as well as on improvement ofpersonal face mask in Hospitals and clinics [2]. Sol-gel processing is a versatilemethodology for coatings with multifunctional purpose. Despite, the sol-gelprocess viability to produce versatile coating for interaction with biomaterialsand living cells, very few has been done to exploit the use of this procedure toobtain anti-bacteria coatings]. Silver nanoparticle loaded materials display veryinteresting anti-bacteria properties, The phosphotungstic acid act as an efficientcatalysis of the hydrolysis co-condensation reactions to obtain the sol used forcoating preparation. Moreover, phosphotungstate Keggin clusters are excellentphotocatalysts, especially after adsorption on wide band semiconductors suchas TiO 2 . This photocatalytical enhancement is based on photoelectron transferfrom the semiconductor to the LUMO of the phosphotungstate yieldingheteropolyblues formation [3]. Although the use of titania nanoparticles isattractive they tend to agglomerate inside the films forming agglomerates, thusresulting on lower surface area and lower activity. It turns out theseagglomeration can be overwhelmed by using titania nanoparticles dispersed onsilica sub-micron particles [4]. Chemical tempering is a glass hardeningtechnique based on ion-exchange in molten salts, such approach for cationmetal doping induces a cation gradient in the films due to diffusion and resultingon enrichment of the surface with cations. Phosphotungstate in ormosil coatingcan act as a cation exchange site, exchanging protons by Ag + and forming H 3-x Ag x [PW 12 O 40 ] species, [5]. Photoreduction of silver cations by polyoxometalatewas demonstrated by Mandal et al [6 and later on the polyoxometalate/TiO2heterojunction was first used by Pearson et al [7] to produce Au decoratedphosphotungstate@TiO2 particles. As an alternative, reproducible and easilyprepared coating with anti-bacteria activity we report a hybrid PhosphotungstateOrmosil loaded with Silver Nanoparticles photosynthesized by UV irradiation ofthe phosphotungstate/SiO 2 @TiO 2 heterojunction entrapped in the ormosilcoating. It is important to remark the low content of the SiO 2 @TiO 2 necessary toachieve the effects. Silver nanoparticle with 20-30nm diameter were obtainedbased on UV-vis plasmonic absorption band at 420nm inside the ormosil.Microprobe analysis by EDX coupled to Field Emission Scanning ElectronMicroscopy with selected primary electron beam energy (8keV) showSiO 2 @TiO 2 @PW@Ag agglomerates of 5 to 7 submicron particles up to 150nmlarge underneath its surface..Anatase phase on SiO 2 particles was confirmed by399, 513 and 637 cm -1 Raman shifts as well as by the diffraction peaks at 25.7,38.4 and 48.5 o (2). Maximum silver loading into the ormosils was achievedafter 10min of ion exchange (chemical tempering) at 2% (Ag/ total film mass) byX-ray Fluorescence. X-ray photoelectron spectroscopy confirms silver on theormosil surfaces. Anti-bacteria essays against Pseudomonas aeruginosa andStaphylococcus aureus showed low bacteriostatic effect for the unloadedormosil while silver loaded ormosil showed bactericide effect toward bothbacteria.