Methylene blue coupled with Ti₃C₂ MXene for boosting photocatalytic CO₂ reduction to CH₄ over TiO₂

Photocatalytic CO₂ reduction to CH₄ over titanium dioxide (TiO₂) is thermodynamically feasible, but it is restricted by core shortcomings such as low light utilization, rapid recombination of photo-generated charge carriers, and poor product selectivity. Therefore, developing high-performance TiO₂-based photocatalysis remains a critical challenge. In this work, using Ti₃C₂ MXene as raw materials and template, the in situ growth of TiO₂ nanoparticles on Ti₃C₂ MXene was synchronously coupled with methylene blue (MB) to successfully fabricate the TiO₂/Ti₃C₂/MB (TTM) composites via one-step ultrasonic method for photocatalytic CH₄ generation. The resulting TTM composites display the accordion-like layered structure, and the introduction of MB narrows band gap, boosts CO₂ adsorption capacity, and induces the formation of small-sized TiO₂ nanoparticles. The optimized TTM sample (TTM-0.20) displays the CH₄ yield rate of 54.34 μmol·g⁻¹·h⁻¹, surpassing accordion-like TiO₂ and TiO₂/Ti₃C₂ composite by 12.9 and 3.1 folds, and achieves a 96.1% CH₄ selectivity. The enhanced photocatalytic performance may be attributed to the improved visible light utilization by the MB photosensitizer, the accelerated separation and transfer of photo-generated charge carriers through the tight Schottky junction and multiple tight interfaces, and effective capture of CO₂ molecules along with the stabilization of reaction intermediates at Ti₃C₂ MXene reactive sites. By employing dye-sensitization and heterojunction strategies, the TiO₂/Ti₃C₂/MB ternary composite was successfully constructed. The synergistic effect of multiple components achieves highly selective photoconversion of CO₂ to CH₄, providing a new approach for CO₂ resource utilization.