Preparation, Characterization And Photocatalytic Activities Of Supported And Doped Nano-TiO₂

Titanium dioxide (TiO₂) has been regarded as an excellent semiconductorphotocatalyst due to its nontoxicity, stability and low cost, high photocatalytic activity tooxidize pollutants. However, separation of the fine TiO₂ powder from the solution afterdegradation is difficult and costly thereby hinders the practical utilization. TiO₂ can only beactivated under UV light of wavelengths＜387nm irradiation because of its large band gapof 3.2eV, thereby the effective utilization of solar energy is limited. Therefore, variousTiO₂-loaded exfoliated graphite photocatalysts was prepared with exfoliated graphite (EG)as carrier via sol-gel method as well as (N, S) doped nano-TiO₂ were also prepared.The obtained samples were characterized by means of XRD, SEM, BET, UV-Vis,TEM, IR, PL, XPS and EDS. The influence of preparation parameters on the structure andproperties of photocatalysts were studied. The performance of photodegradation of thesamples was examined using methyl orange (MO) as a contaminant. The activities ofphotocatalysis of the samples were investigated with different light sources. The resultsshowed:TiO₂ was loaded on the flakes of exfoliated graphite firmly in the forms ofnano-particles. The worm-like exfoliated graphite provided a three dimensionalenvironment for photocatalytic reaction. The photocatalyst exhibited excellent adsorptionand degradation capability to MO. The photocatalyst loaded two times and calcinated at500℃for 3h showed high photocatalytic reactivity under UV light irradiation inphotodegradation of highly concentrated MO solutions with a removal rate of up to 96.9%.Addition of P25 powder into the pure TiO₂ sol during the preparation enhanced theperformance of the photocatalysts and the removal rate was up to 92.5% after 30min UVlight irradiation.N-doped nano-TiO₂ photocatalyst (N/TiO₂) was prepared by hydrolysis-depositionmethod with tetra-butyl titanate and ammonia as the precursors and the N/TiO₂ powdershad absorption in the visible light region under the wavelength of 550nm. Thephotodegradation on methylene orange showed that the N/TiO₂ powders calcined at 700℃exhibited the best photocatalytic activity and the removal rate was up to 69.7% under120min light irradiation.Thiourea suppressed the crystalline transformation and enhanced the thermal stabilityof TiO₂. N,S-codoped TiO₂ exhibited highly visible-light photocatalytic activities due to itsstrong adsorption in UV-Vis region with an obvious red shift of its adsorption edge. The XPS anslysis showed that N atoms were incorporated into the lattice of TiO₂ in the form ofN-O-Ti and the concentration of N was up to 2.68%. S^2- was oxided to S⁶⁺ during the heattreatment. Sulfur ions(S⁶⁺) substituted partially for the lattice titanium ions(Ti⁴⁺), whichresulted in the localized crystal deformation of TiO₂. The bandgap between valence bandand conduction band was narrowed, and the absoption was shifted to visible light region.The photodegradation of methylene orange showed that the N,S-codoped TiO₂ powderscalcined at 500℃exhibited the best photocatalytic activity and the removal rate was up to76.7% under 180min visible light irradiation.