Unifying CO2-to-fuel and biomass valorization over a metal-free 2D carbon nitride-fullerene heterostructure: a solar-driven chemical circular economy

Abstract

Photocatalytic CO₂ photoreduction integrated with biomass oxidation is highly attractive to produce fuels and fine chemicals. Herein, for the first time, we manifested CO₂ photoreduction to CO (>95% sel.) in synergy with biomass-based alcohol oxidation via a metal-free fullerene/2D carbon-nitride (C60/TUCN) semiconductor under solar simulated light. We observed that the composite, 5-C₆₀/TUCN showed the highest CO₂ to CO (selectivity >95%) conversion efficiency along with lignin biomass model substrate p-methoxybenzyl alcohol (p-MBA) oxidation to p-methoxybenzyaldehyde (p-MBAL) under solar simulated light with an excellent CO production rate of 8.92 mmol h⁻¹ g⁻¹ and p-MBAL production rate of 0.65 mmol h⁻¹ g⁻¹. The apparent quantum yield (AQY) of CO evolution was determined to be 3.38% at λ = 450 nm. DFT calculations confirmed that the C₆₀ loading improved the activation and reduction of CO₂ to CO while considerably lowering the formation barrier of COOH* intermediates. Besides, the accelerated separation and charge transfer kinetics of TUCN after C₆₀ modification was confirmed from EPR, PL, and photocurrent studies. ¹³CO₂ labeling experiments and EPR studies established the mechanistic pathway of the CO₂ reduction reaction. Thus, the current study showed an excellent proof-of-concept for upscaling CO₂ and biomass synergistically into solar fuels and fine chemicals, featuring a sustainable approach to boost the overall (bio)-chemical economy.