Photocatalytic Performance of Titania Nanosheets Templated by Graphene Oxide

A facile process was developed to fabricate two dimensional titania nanosheets (t-NS) by using graphene oxide (GO) as template. In-situ growth of anatase TiO2 on GO suspended in butanol was achieved by combining sol-gel and solvothermal process without further calcination. Stoichiometric amounts of acetic acid were added to introduce esterification with butanol to release sufficient water for the rate-controlled hydrolysis of titanium butoxide. The two-dimensional GO prevented the agglomeration of TiO2 particles, and simultaneously established the interaction between two phases. For comparison, a following thermal treatment in air was applied to partially remove GO and increase the crystalline size of t-NS. TiO2-decorated samples showed better charge transfer efficiency and thus produced more photoinduced radicals and weaker photoluminescence. Electron paramagnetic resonance (EPR) spectra were utilized to in-situ identify the concentrations and types of photo-induced radicals by mixing various nitroxide spin traps with t-NS suspensions under ambient conditions. In aqueous suspension, hydroxyl radicals produced from illuminated t-NS and trapped by 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) immediately within 30 second. The following decay in the hydroxyl adducts of DMPO suggested the presence of strong reductants in the illuminated sample suspension. A sample with a higher production rate of spin adduct (DMPO-OH) or a higher reduction rate of DMPO-OH demonstrated a more efficient decoloration on methylene blue (MB). Spin trapping results indicated that the hydroxyl radicals were produced from both photoinduced holes and electrons. Hence, an optimum rate of hole titration by ethylenediaminetetraacetic acid was essential to efficiently reduce the recombination of charge carriers and consequently to produce more active radicals to decolor MB. The strong interaction between graphitic and titania structures, rather than the crystallite size of anatase, dominated the photoreduction capability of t-NS.