Mg-modified graphitic carbon nitride/converter slag composites as an efficient photocatalyst for sugar conversion

Abstract

The development of a strategy for the resource utilisation of converter slag (CS) in the photocatalysis of biomass for high-value chemical production is essential for application in advanced purposes and for establishing a sustainable and economic solar-driven photoreforming process. This work reports a viable approach to using CS for the synthesis of Mg-modified graphitic carbon nitride/CS (Mg–CN/CS) composites with Mg doping contents ranging from 2 to 7 wt%. Then, the Mg–CN/CS composites served as efficient photocatalysts for the conversion of biomass-derived sugars to lactic acid under visible-light irradiation. The experimental findings indicated that CS served as a supporting material to facilitate the dispersion of CN particles on the CS surface. In addition, CS played a role in the formation of a Mg–CN/Ca₂Fe₂O₅-bearing CS heterojunction, which was enabled by the presence of the photoactive semiconductor Ca₂Fe₂O₅ in CS. Interestingly, the surface area and porosity of Mg–CN/CS samples slightly improved after Mg doping possibly due to the formation of structural defects. Contrary to pristine CN and Mg–CN, the Mg–CN/CS composites exhibited superior photocatalytic performance for lactic acid production, which could be attributed to the efficient separation of photogenerated charge carriers and improved light absorption capability facilitated by the synergetic impact of Mg doping and the Mg–CN/CS heterostructure. Under visible-light irradiation, 4.7Mg–CN/CS, at its optimal Mg content, achieved 97% glucose conversion and 71% lactic acid production within 2 h at 50 °C. This work provides an efficient approach to promoting the resource utilisation of CS, industrial solid waste, in the field of biomass photorefinery for the production of valuable chemicals and other photocatalytic applications.