Photoreforming of lignocellulose into CO and lactic acid over a single-atom Fe-dispersed order/disorder polymeric carbon nitride homojunction

Abstract

Photoreforming lignocellulose into valuable fuels and chemicals represents an environmentally friendly and energy-saving technology. Herein, a single-atom Fe-dispersed order/disorder polymeric carbon nitride homojunction (Fe-SA/PCN-HJ) is constructed for highly efficient photocatalytic reforming of lignocellulose into CO and lactic acid, wherein Fe single atoms are confined to the surface of the PCN-HJ. Experimental investigations and density functional theory (DFT) calculations reveal that the homojunctions and dispersed Fe atoms on the surface greatly improve the separation efficiency and transport of photogenerated charge carriers. As such, driven by the internal electric field across the entire junction, the photoinduced electrons can rapidly migrate from the bulk to the surface, leading to the enrichment of surface electrons at the dispersed Fe-N4 sites. In addition, the Fe-N4 sites optimize the adsorption and activation of molecular oxygen and facilitate electron transfer to the adsorbed molecular oxygen, thereby promoting the formation of reactive oxygen species for lignocellulose photoreforming. Under full spectrum irradiation for 2 h, the Fe-SA/PCN-HJ exhibits an ultrahigh CO generation rate of 92.33 mmol g-1 and yields 136.21 mg of lactic acid by using 900 mg of fructose as the model substrate. Moreover, we have further demonstrated that the Fe-SA/PCN-HJ photocatalyst presents universally applicable capabilities for the photoreforming of various types of lignocellulosic biomass. This work provides an approach for the production of CO and lactic acid through the photoreforming of lignocellulose, which is promising for the production of fuels and valuable chemicals.