Abstract
To utilize sunlight more efficiently on photocatalysis, in this study, we planed to modify TiO2 by using Pt or carbon species as a visible photo-sensitizer. The modification would expand applications on visible-light photocatalytic degradation of NOx. In addition, various characterizations were employed. Finally, a possible photocatalysis mechanism was proposed. In the aspect of Pt-modified TiO2, Pt(NH3)4(NO3)2 or H2Pt(OH)6 was added in TiO2 matrix or loaded on TiO2 surface by sol-gel process or impregnation method, respectively, followed by calcinations at 200℃. Some modified samples were reduced in H2 flow, and then applied on NOx degradation, for comparison of their reaction behavior related to their Pt oxidation states. In the aspect of carbon-modified TiO2, several different alcoholic precursors were loaded on a commercially available TiO2 (UV100) by impregnation method, followed by calcinations at 200℃, for comparison of the different carbon-numbers and structures of precursors how to influence on visible-light reaction and their bonding forms of carbonic residues. The results of photocatalytic degradation of NOx were connected with the characterizations of FE-SEM, TEM, BET, XRPD, Raman, UV-VIS, XPS, TGA and PL spectra. In terms of Pt-modified TiO2, the activies of PtOx-loaded TiO2 were higher than those of unmodified TiO2. Moreover, the surfacial PtOx existed on TiO2 surface in forms of PtO-PtO2 mixed valence states and was main in PtO state. In addition, the reduced Pt0-loaded TiO2 showed no visible-light activity, while facilitated the NOx reaction completely. In terms of carbon-modified TiO2, the higher carbon-number precursor loaded on TiO2 surface, the better visible-light activity it presented. The carbonic residues existed in a form of C=O bonding structure, which was speculated as the visible-light responsive source. Both of the Pt- and carbon-modified TiO2 substantially improved the visible-light activities, even under red light illumination with the total NOx removal of 33% and 54%, respectively.