N Simultaneously Doped TiO2@Carbon Hollow Spheres with Enhanced Photocatalytic CO2 Reduction Activity

Converting carbon dioxide (CO2) into solar fuels through photocatalysis represents an appealing approach to tackling the escalating energy crisis and mitigating the greenhouse effect. In this study, using melamine-formaldehyde (MF) nanospheres as a nitrogen source, a N element was simultaneously doped into the TiO2 nanoparticle structure supported by carbon hollow spheres using a one-step carbonization method to form a heterojunction N-CHS@N-TiO2 (marked as (N-(CHS@TiO2)). The composite showed superior photocatalytic activity in reducingCO(2) compared with TiO2 and N-CHS: after 6 h of visible light irradiation, the CO yield was 4.3 times that of N-CHS and TiO2; 6 h of UV irradiation later, the CO yield reached 2.6 times that of TiO2 and 7 times that of N-CHS. The substantial enhancement in photocatalytic activity was attributed to the nitrogen simultaneously doped carbon hollow spheres and TiO2, mesoporous structure, small average TiO2 crystal size, large surface areas, and the heterostructure formed by N-CHS and N-TiO2. The UV-vis diffuse reflectance spectra (DRS) exhibit a significant improvement in light absorption, attributed to the visible-light-active carbon hollow sphere and the N element doping, thereby enhancing solar energy utilization.