Synthesis, performance, and reaction mechanisms of titanium dioxide-silicon carbide as a step-scheme heterojunction photocatalyst against formaldehyde in air

Abstract

In the present research, titanium dioxide (TiO2) is paired with silicon carbide (SiC) as TiO2-SiC-x (x (wt.% of SiC over TiO2) = 1, 5, and 10). The prepared photocatalysts are anchored on the filter unit of a portable air purifier and used for removing formaldehyde (FA) from indoor air under ultraviolet (UV) irradiation (0.98 W). TiO2-SiC-5 is superior to the others when tested against 1 ppm FA (0 % relative humidity at 160 L min−1) with kinetic removal rate of 2.09E + 02 μmol g−1 h−1 (at 100 % removal efficiency (XFA)), space–time yield (STY: 1.91E-05 molecules photon−1 mg−1), and clean air delivery rate (CADR: 18.53 L min−1)). Furthermore, TiO2-SiC-5 maintains stable performance (e.g., XFA = 100 % and CADR = 18.50 L min−1 over five reuse cycles) to reflect the unique properties of n-n type step (S)-scheme photocatalysts in the separation and migration of photogenerated charge carriers, as evidenced through various routes (e.g., electrochemical impedance spectroscopy, UV–visible diffuse reflectance spectroscopy, and transient photocurrent response). The FA molecules are mineralized into carbon dioxide and water through multiple reaction intermediates (e.g., dioxymethylene and formate). Density functional theory simulations indicate that both the silicon and carbon centers are involved in activating molecular oxygen while FA oxidation reaction occurs primarily near the carbon sites on the TiO2-SiC surface. The overall findings provide better insights into the efficacy of TiO2-SiC as S-scheme photocatalysts for practical use in environmental remediation.