Copper-decorated Biochar derived from sludge as eco-friendly nano-catalyst for efficient p-nitrophenol reduction

Abstract

In the present study, Biochar produced from municipal sludge was used as support for copper nanoparticles (Cu NPs) to develop an efficient catalyst for environmental remediation and resource recovery. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH₄ was chosen as a benchmark reaction to evaluate the performance of the catalyst. This reaction is significant as it converts a toxic pollutant into a valuable intermediate with applications in pharmaceuticals and fine chemicals. Biochar-supported copper catalysts (Cu/Biochar) were synthesized with different Cu loadings (1, 2.5, 5, 7 and 10 wt%). Among these, 5.5 %Cu/Biochar showed good catalytic activity, achieving a 97 % reduction of 4-NP to 4-AP in eight minutes, with an apparent rate constant (K_app) of 0.0045 s⁻¹, using only 4 mg of catalyst. The catalyst demonstrated excellent stability and reusability for five consecutive cycles. Comprehensive characterization of the 5.5 %Cu/Biochar catalyst was performed using XRD, SEM-EDX, TEM, FTIR, TGA, and pH at the point of zero charge (pHₚzc). The results confirm that Biochar serves as an effective, low-cost, and sustainable support, enhancing the catalytic performance and stability of Cu NPs.