Yan Lin,Shaohua Wu,Xiang Li,Xin Wu,Chunping Yang,Guangming Zeng,Yanrong Peng,Qi Zhou,Li Lu
Visible-light-driven photocatalysis as a promising technology has recently attracted great attention in environmental remediation. In this work, novel Z-scheme heterojunction photocatalysts Ag 3 PO 4 @MWCNTs@Cr:SrTiO 3 with excellent visible-light-driven photocatalytic performance and photostability were successfully synthesized and characterized. The photocatalytic activity for malachite green (MG) degradation was measured, and photodegradation mechanisms were investigated using GC–MS, ESR, and radical trapping experiments. On consideration of the practical applications, the effects of coexisting ions and pH were also evaluated. Results showed that significant changes of crystal size and micro-morphology for Ag 3 PO 4 were observed before and after the addition of MWCNTs, which transformed from a polyhedron with a diameter of about 30 μm into a spherical-like crystal with a diameter of 0.28–0.69 μm. This phenomenon was reported for the first time. The optimal catalyst with a dosage of 100 mg/g (the mass ratio of pollutant to photocatalyst) could reach 100% MG removal in 6 and 10 min under natural solar radiation and visible light irradiation, respectively. Results from the radical trapping experiments and ESR analysis confirmed that there existed the Z-scheme transfer mechanisms, and O 2 − and h + played an important role during the photocatalytic degradation. Several small molecular organic acids such as acetic acid, glyoxylic acid, fumaric acid and benzoic acid were detected by GC–MS in the photodegradation products of MG, which further indicates that photocatalytic degradation pathway involved N -demethylation, benzene removal and open-ring reactions. The performance of the photocatalyst would be inhibited under strong acid condition or at the coexistence of certain concentration of Cr 6+ and Cl − . The novel addition of MWCNTs in the preparation and the changes of crystal structure and properties for the photocatalysts have the potential to promote the application of the photocatalysts for environmental remediation.
Jiangping Jing,Zhuoyuan Chen,Yuyu Bu,Mengmeng Sun,Wenqiang Zheng,Weibing Li
SrTiO 3 is a promising material for the photoelectrochemical (PEC) cathodic protection technology due to its intrinsic band structure . Its disadvantage of light absorption only in the ultraviolet region can be effectively solved by Cr doping. The Cr dopant usually exists as two states of Cr 3+ and Cr 6+ , among which the latter one usually behaves as the trapping center for the photoinduced electrons and leads to the decrease of the PEC performance. In this paper, a hydrogen treatment process is performed on the Cr-doped SrTiO 3 to reduce the Cr 6+ . It is verified that hydrogen treatment reduces Cr 6+ to Cr 3+ , leading to the increase of the concentration of the charge carriers and the decrease of the charge transfer resistance. And also, hydrogen treatment induces the formation of oxygen vacancy , which leads to the negative shift of conduction band potential and the increase of the concentration of the charge carriers. The effect of the hydrogen treatment temperature is further studied in this work. Higher temperature will promote the reduction degree of Cr 6+ and increase the concentration of oxygen vacancy . However, hydrogen treatment with excessively high temperature will induce too high concentration of oxygen vacancy, which would act as the recombination centers of the photogenerated charge carriers, suppress the mobility conduction and thus lead to the decrease of the PEC performance. Therefore, benefiting from the Cr 6+ reduction and modification with appropriate concentration of oxygen vacancy, the Cr-doped SrTiO 3 with hydrogen treatment at 250 °C shows the optimal PEC cathodic protection performance in NaCl solution.
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