Synthesis and Optimization of Ti/Li/Al Ternary Layered Double Hydroxides for Efficient Photocatalytic Reduction of CO2 to CH4

Abstract

A series of Ti/Li/Al ternary layered double hydroxides (TiLiAl-LDHs) with different Ti:Li:Al molar ratios were prepared by a coprecipitation method for photocatalytic CO₂ reduction. It was demonstrated that the contents of anions between the layers of Ti/Li/Al-LDHs greatly determined the photocatalytic activity for CO₂ reduction. With Ti:Li:Al molar ratios optimized to be 1:3:2, the largest contents of ${\mathbf{CO}}_{\mathbf{3}}^{\mathbf{2}}$⁻ anion and hydroxyl group were obtained for the Ti₁Li₃Al₂-LDHs sample, which exhibited the highest photocatalytic activity for CO₂ reduction, with CH₄ production rate achieving 1.33 mmol h⁻¹ g⁻¹. Moreover, the theoretical calculations show that Ti₁Li₃Al₂-LDHs is a p-type semiconductor with the narrowest band gap among all the obtained TiLiAl-LDHs. After calcined at high temperatures such as 700 °C, and the obtained TiLiAl-700 sample showed much increased photocatalytic activity for CO₂ reduction, with CH₄ production rate reaching about 1.59 mmol h⁻¹ g⁻¹. This calcination induced photocatalytic enhancement should be related to the cystal structure transformation from hydrotalcite to mixed oxides containing high reactive oxygen species for more efficient CO₂ reduction.