Controllable spatial distribution of La dopants in perovskite NaTaO3 enhancing its photocatalytic performance of formaldehyde solution degradation and simultaneous hydrogen evolution

Abstract

Photocatalytic degradation of aqueous organic pollutant while hydrogen evolution has become an attractive and potential approach to address environmental pollution and energy shortages. The design of highly efficient photocatalyst and the mechanism study are the keys for this issue. For this purpose, a series of rare earth La doped perovskite NaTaO3 were prepared by an easy solid-phase synthesis method. La doping changed the morphology, structure and physicochemical properties of NaTaO3 crystal. More importantly, it also found that controllable La dopants formed a concentration gradient between the surface and bulk of NaTaO3 crystal, which would cause a gradient of energy band structure. Noteworthy, 0.5La/NaTaO3 was identified as the intermediate state with the La doping from A sites to B sites and from bulk to surface in NaTaO3 crystal. It possessed a large La concentration gradient, leading to the better photoelectrochemical properties and photocatalytic performance than any other xLa/NaTaO3 catalyst. For the photocatalytic reaction over 0.5La/NaTaO3, HCHO was partially mineralized and gradually converted to HCOOH due to the large energy barriers of the intermediate reaction steps, while H2 was produced stably in the five recycle runs. The active species of •O2−, •OH and h+ were detected by the control experiments with trapping agents, and •O2− was confirmed to be the dominant one in the photocatalytic reaction. On this basis, the possible mechanism was proposed to understand the photocatalytic system in depth.