Selective breakage of C H bonds in the key oxidation intermediates of gaseous formaldehyde on self-doped CaSn(OH)6 cubes for safe and efficient photocatalysis

Production of toxic intermediates is a vital issue that remains as the major hindrance to the advancement of photocatalysts for air purification applications. It is predicted theoretically that the reaction pathway of photocatalysis can be regulated effectively by the interactions between key intermediate reactant (e.g., HCOOH) and photocatalyst. Inspired by such prediction, a new strategy is proposed and validated to control the reaction pathway and the associated formation of toxic intermediates via selective breakage of chemical bonds of reactants. Herein, we introduce a Sn self-doped CaSn(OH)6 photocatalyst to realize safe and efficient photocatalytic oxidation of formaldehyde through selective breakage of C–H bonds in HCOOH formed as reaction intermediate. This photocatalyst altered the charge transfer direction to promote charge separation and to modify the surface distribution of electrons for the activation of the C–H bond. Through selective attack on the C–H bond by hydroxyl radicals, the reaction pathway was altered to avoid generation of toxic by-products (e.g., CO). The combination of in situ DRIFTS and continuous flow reaction tests indicated that enhanced photochemical destruction of formaldehyde can be achieved by effectively suppressing generation of toxic intermediates. The obtained Sn-CaSn(OH)6 reached a quantum efficiency of 1.43 × 10−8 molecules/photon and a high photocatalytic formaldehyde degradation activity of 79 %, much higher than those of Sn-CaSn(OH)6(m) (30 %) and pristine CaSn(OH)6 (no activity). This is attributed to the advantages of Sn self-doping that optimized the local electron structure. This research could provide new insight for pursuit of safe and efficient photocatalysts for air pollution control.