Study of Porous Carbon Derived from Municipal Sludge Hydrothermal Carbonization and Its Potential in CO₂-to-Urea Reduction

Rational and efficient treatment of municipal sludge holds broad prospects for sustainable economic and environmental development. In this study, hydrothermal carbon derived from municipal sludge was used as the precursor to prepare a series of chemically activated modified porous carbon materials. The sample with the highest specific surface area was selected as the support and, combined with a hydrothermal loading strategy, was successfully used to fabricate a high-surface-area CuS-modified porous carbon material (CuS-ZnCl₂-ss). When applied for CO₂ reduction to urea, CuS-ZnCl₂-ss exhibited excellent CO₂ capture and conversion performance, benefiting from the synergistic effect between the high surface area of the porous carbon and the basic adsorption sites of CuS. Under a voltage of −1.1 V (vs RHE), CuS-ZnCl₂-ss achieved a CO₂ conversion rate of 8.32 mmol g^–1 h^–1 with high conversion efficiency, significantly surpassing that of conventional CuS-loaded activated carbon. This work provides an innovative route for the high-value utilization of municipal sludge and highlights the potential of biomass-derived carbon materials in CO₂ conversion and functional applications.