Harvesting solar light on a tandem of Pt or Pt-Ag nanoparticles on layered double hydroxides photocatalysts for p-nitrophenol degradation in water

Abstract

The quest to provide clean water has led to a tremendous boost in the synthesis of advanced photocatalysts that are able to decontaminate water by harvesting the solar energy. Herein, a tandem of Pt or both Pt-Ag nanoparticles on layered double hydroxides (LDH) photocatalysts were obtained via a green chemical procedure in which LDH serve a dual function of both facilitating the synthesis of nanoparticles of Pt and Ag and acting as a support. Detailed characterization showed that the LDH structure is well-retained, while small nanoparticles of Pt or Pt-Ag are formed and dispersed on the larger nanoparticles of the LDH. The effects of the heterometallic composition of the 2-D LDH layers (e.g. Zn2Al; Zn2FeAl) and the mono/bi-metal (Pt/Pt-Ag) identity on the solar-light-induced catalytic performances were investigated using p-nitrophenol (p-NPh) as a targeted pollutant. Pt-Ag synergistic activity was superior to Pt alone to promote p-NPh degradation and Pt-Ag/Zn2Al exhibited the best photocatalytic activity approaching 77% degradation and 71% mineralization of p-NPh, after 6 h under solar light, at room temperature. The introduction of Fe in the LDH layers caused a significant change in the degradation pathway of p-NPh and drastically decreased the catalytic response such that p-NPh mineralization was only 10% for Pt-Ag/Zn2FeAl. Even though UV–vis analysis showed that Pt-Ag/Zn2FeAl had a stronger absorption of the visible light than Pt-Ag/Zn2Al, the PL data indicated a significant increase in the photoluminescence signal for Pt-Ag/Zn2FeAl as compared to Pt-Ag/Zn2Al. This suggested a retard recombination of electrons-holes in Pt-Ag/Zn2Al and revealed the active role of the LDH multimetallic composition to establish an effective electronic coupling between the constituent nanounits. These findings may aid in the rational design of multimetallic heterostructures that can effectively harvest sunlight for environmental cleanup.