Photocatalytic NO removal over calcium-bridged siloxenes under ultraviolet and visible light irradiation

Abstract

Ca-Bridged siloxenes (Ca-siloxenes) composed of two-dimensional siloxene planes with Ca bridging were prepared and their photocatalytic properties for nitrogen oxide (NO) removal were investigated. Ca-Siloxenes were synthesized via a solid-state metathesis reaction using TaCl₅ to extract Ca from CaSi₂ with different Cl₂/Ca molar ratios of 0.25, 1.25 and 2.5 (CS0.25, CS1.25 and CS2.5, respectively) in an attempt to control the extent of Ca extraction. Ca-Siloxenes have a wide optical absorption band from the visible to ultraviolet region with absorption edges of 1.5, 2.9, and 3.1 eV for CS0.25, CS1.25, and CS2.5, respectively. Ca-Siloxenes exhibited photocatalytic activity for NO removal under irradiation with visible (λ > 400 nm (<3.10 eV)) and ultraviolet light (λ > 290 nm (<4.28 eV)). The photocatalytic activity was particularly improved by mixing the Ca-siloxene with acetylene black as a conductive material, which might have inhibited the recombination of photogenerated electrons and holes. The mixture of Ca-siloxene and acetylene black exhibited improved photocatalytic activity in the presence of ¹O₂ as one of the active oxygen species formed under ultraviolet light irradiation.