Self-heating photothermal synergistic catalytic decomposition of carcinogenic formaldehyde by α-MnO2 at ambient temperature: Functional roles of surface acidic-basic sites

Abstract

Formaldehyde is a major pollutant in indoor atmosphere, and the realization of complete mineralization of formaldehyde at room temperature is of great significance and practical demand for improving indoor air quality. Surface acidic-basic sites, as one of the important surface properties that have significant influence on catalytic oxidation of formaldehyde, revealing their functions is beneficial for the development of efficient formaldehyde decomposition materials. Herein, the α-MnO2 acidic-basic sites were regulated and its effects on self-heating photothermal catalytic oxidation of formaldehyde were further contrastive investigated. The acidic-basic sites showed distinct functions: the basic sites exhibited a significant promotion on formaldehyde oxidation; While the acidic sites greatly inhibited the reactivity. Particularly, the basicity enhanced α-MnO2 could reach the 100% conversion of formaldehyde at ambient temperature. Furthermore, the self-heating photothermal mechanism was consonant with the thermal-assisted photocatalysis mechanism, rather than traditional photo-drive thermal catalysis mechanism. The strength of basic sites significantly increased the content of surface hydroxyl groups, and the electron-rich basic sites were favorable for the activation of oxygen, thereby generating more reactive oxygen species for the decomposition of formaldehyde. Moreover, in-situ DRIFTS reveals that the enhancement of basic sites can accelerate the rate oxidation of HCHO to generate formates and carbonates. This work clarified the influence of surface acid-base properties on formaldehyde photothermal decomposition.