ZnO/TiO2 composites for photocatalytic inactivation of Escherichia coli.

ZnO/TiO2 composite was synthesized from zinc nitrate and anatase TiO2 by using the incipient wet impregnation method followed by calcination at 350°C for 3h. These samples were characterized through several characterization techniques. XRD peaks confirms the presence of single anatase phase of titania in the 3 and 6wt% ZnO/TiO2 composite, whereas in all other composites both anatase titania and zinc oxide phases were found. UV-visible (diffuse) reflectance spectra show titania and ZnO absorbs in the ultraviolet (UV) region whereas ZnO/TiO2 absorbs both UV and visible light. The shift in absorbance facilitates ZnO/TiO2 composites to exhibit photocatalytic activity under UV-visible light irradiation. FE-SEM and TEM analysis reveals that the particle size of ZnO is around 0.2µm and its size significantly reduced to 25nm when it is deposited on TiO2 support. The E. coli inactivation study shows that ZnO/TiO2 composites exhibit high inactivation compared to ZnO and titania under UV alone and the combination of both UV-visible. With the increasing loading concentration of ZnO, the photocatalytic inactivation potential of ZnO/TiO2 composites also increases. The E. coli inactivation of ZnO/TiO2 is explained based on the photocatalytically generated ROS, ZnO dissolution and charge carrier separation due to hybrid structures.

Photocatalytic destruction of Escherichia coli in water by V2O5 /TiO2.

Vanadia modified titania (V2O5/TiO2) photo-catalysts are prepared by incipient wet impregnation method using aqueous ammonium metavanadate and anatase (Aldrich) titania. Titania with various loading concentrations of vanadia from 0 to 10 wt.% have been prepared and characterized by X-ray diffraction (XRD), Thermogravimetry (TGA), Laser Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), UV-Visible Spectrophotometry and Transmission Electron Microscopy (TEM). XRD study reveals that vanadia loading on titania does not bring any phase change of titania, however, diffuse (UV-Vis) reflectance spectra show that absorption edge of titania shifted from UV to visible region. TEM confirms that titania and vanadia modified titania have the particle size below 50 nm. XPS shows alteration of 2p3/2 peak of V(V) in the V2O5/TiO2 samples whereas no such change is noticed in pure V2O5 indicating the interaction between vanadia and titania support. Antibacterial activity of each sample has been investigated against Escherichia coli present in the water under both UV-Visible irradiation and UV alone. V2O5/TiO2 catalysts exhibit better photocatalytic effect than the unmodified titania and pure V2O5. It is observed that with increasing loading concentrations of V2O5 from 0 to 10 wt.% on titania support, the photocatalytic annihilation of E.coli is also increased and found to be little higher under UV alone than the UV-Visible irradiation.

Synthesis and characterization of titania nanorods from ilmenite for photocatalytic annihilation of E. coli.

Titania nanorod structures have been obtained by thermal plasma reduction of ilmenite (FeTiO3) followed by chemical treatments. Inherently present iron in the titania nanorods acts as a dopant which results in shifting the absorption edge of titania from ultraviolet to visible region. X-ray diffraction (XRD) study confirms the existence of rutile phase of titania. X-ray Photoelectron Spectroscopy (XPS) reveals the presence of Ti(4+), O(2-), Fe(3+) and surface hydroxyl group. Transmission Electron Microscopy (TEM) confirms the formation of nanorod structure having width of 6 nm and length of 32 nm. Photocatalytic annihilation property of titania nanorods derived from ilmenite (titania-I), rutile titania obtained from titanium(IV) butoxide (titania-A) and Degussa P25 titania was studied under UV and UV-Visible irradiation conditions separately and compared. The time required for complete photocatalytic annihilation of Escherichiacoli cells are 10, 15 and 45 min under UV irradiation whereas it has taken 15, 10-15, 30 min under UV-Visible irradiation for titania-A, Degussa P25 titania and titania-I respectively. It is observed that titania-I shows significantly stronger antibacterial property under UV-Visible irradiation compared to UV alone.

Water disinfection through photoactive modified titania.

TiO(2), N-TiO(2) and S-TiO(2) samples have been prepared by various chemical methods. These samples were characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Laser Raman spectrometer, UV-Visible spectrophotometer, field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). X-ray powder diffraction study reveals that all three samples are single anatase phase of titania and the crystallinity of titania decreases with sulphur doping whereas nitrogen doping does not affect it. UV-Visible (diffuse) reflectance spectra shows that doping of titania with nitrogen and sulphur shift the absorption edge of titania from ultraviolet to visible region. XPS study confirms that both nitrogen and sulphur are well doped in the titania lattice. It is observed that nitrogen occupies at both substitutional and interstitial position in the lattice of titania. FE-SEM and TEM studies demonstrate that the particles are below 50nm range. It is found that S and N doping of titania increased its water disinfection property in the order TiO(2)