Highly Dispersed Nickel Oxide Nanoparticles Anchored on a Tubular Biochar Framework for Selective Photocatalytic CO₂ Reduction to CH₄

Photocatalytic reduction of CO2 is considered as a promising approach to achieving carbon neutrality and producing value-added chemicals in a sustainable way, utilizing CO2 as a feedstock and solar energy as the driving force. Constructing novel photocatalysts with sufficient active sites and efficient charge separation efficiency is crucial for optimizing CO2 conversion. Herein, the activated pinecone-derived biochar (APC) possesses a porous tubular carbon framework, a high degree of graphitization, and abundant oxygen-containing functional groups. NiO nanoparticles were successfully embedded in the APC supporter to manufacture NiO/APC composites. The obtained NiO/APC sample demonstrates remarkably enhanced photocatalytic properties and high selectivity (95.6%) for CH4 production with respect to pure NiO. The coupling of APC and NiO can fully expose NiO nanoparticles, regulate the band structure of NiO, and establish a close interfacial interaction, which can significantly increase CO2 adsorption, improve light absorption, prohibit charge recombination, and accelerate separation and migration of photoexcited charge carriers. Especially, the tubular APC framework not only serves as a supporter to inhibit the aggregation of NiO nanoparticles and as electron shuttles to accelerate the charge separation but also as a reactive site to realize the efficient conversion of CO2 to CH4. This work affords a paragon for the construction of highly efficient photocatalysts, which pave the way for practical applications in photocatalysis.