Synergy-driven catalysis in biochar-calcite-Ag nanocomposites for rapid 4-nitrophenol reduction

Rising concern about environmental contamination from untreated industrial effluents, particularly organic pollutants such as 4-nitrophenol (4-NP), has necessitated the development of efficient remediation strategies. In this study, silver nanoparticle-supported biochar (Ag@EB) and biochar-calcite (Ag@EB cal) composites were prepared via co-pyrolysis using Eucalyptus globulus as a carbon source and waste leghorn eggshell as a natural calcite source and a chemical reduction method. Various characterization techniques, including UV-Vis DRS, XRD, FTIR, XPS, SEM, TEM and BET were employed to analyze the prepared composites. Morphological analysis confirmed the successful deposition of silver nanoparticles (Ag 0 ) onto biochar surface, along with the coexistence of amorphous carbon and a crystalline calcite phase. Furthermore, composites were employed as heterogeneous catalysts for the hydrogenation of 4-NP in the presence of NaBH 4 . Ag@EB 450 1:1 composite efficiently reduced 4-NP to 4-aminophenol (4-AP) within 12 s (100%). The reaction followed pseudo-first-order kinetics and the apparent rate constant increased with the NaBH 4 concentration and composites. This rapid reduction was attributed to the synergetic interaction between the biochar structure, calcite adsorption ability, and AgNP electron transfer efficiency. Notably, the composites showed high stability and were retained for up to ten consecutive cycles without structural degradation. This study suggests an efficient method to convert low-cost biowaste into efficient composites for sustainable water purification. Additionally, to forecast the reduction time of the chosen alternatives, a gradient boosting model was used. Following validation procedure, optimal variables were readily determined using this model. The entire work also supports Sustainable Development Goals (SDG) 6, SDG 9 and SDG 12 through efficient pollutant removal and waste to resource utilization.