Enhanced Photoactivity of V-N Codoped TiO2 Derived from a Two-Step Hydrothermal Procedure for the Degradation of PCP-Na under Visible Light Irradiation

A new route to synthesize V-doped and V-N codoped titania nanocatalysts using a novel two-phase hydrothermal method applied in hazardous PCP-Na decomposition was reported. The physicochemical properties were characterized, indicating that the crystallite surface area increased after both first hydrothermal (FH) V impregnation and second hydrothermal (SH) N implantation, whereas mesoporous framework shrinkage and enlargement resulted from FH and SH, respectively. ICP and EPR demonstrated that SH did not alter V content, but rather it induced paramagnetic V4+ increase. The V species was enhanced from the inner to the catalyst surface with V5+ as the dominant mode and the N dopant existed with substitutional nitrogen as the main structure. The optical red shift by low vanadium implantation was ascribed to the V2p state, mainly from V4+ species in the matrix. After SH incorporation, the substitutional N1s state, interstitial N-O state, and concomitant NOx were responsible for the strong visible absorption of V-N-TiO2. The photodegradation rates of PCP-Na by the remodified catalysts after SH were much larger than that of the mono-V-TiO2 precursors fabricated in FH. SHNV02, SHNV05, and SHNV10 exhibited 2.4, 1.6, and 3.1 times promotion toward PCP-Na decomposition, respectively. Moreover, other variations and the synergetic effects after two-phase treatments were adequately discussed and proven to be useful in facilitating photocatalytic promotion. This work provided a strategy for obtaining further enhancement of the synthesized catalyst by second-step modification to achieve the deep removal effect of contaminants.