Optimization of Microwave-Assisted Carbonization for the Fabrication of Waste Banknotes-Derived Biochar with Enhanced Adsorption Performance

This study aimed to develop an efficient carbonization process to convert cellulose-based waste banknotes, produced in large quantities annually, into biochar, a high-value carbon material.Microwave-assisted carbonization, recognized for its energy efficiency, was applied and optimized.To overcome the low dielectric loss of waste banknotes, bio-activated carbon was introduced as an initiator.Using a central composite design, 17 experimental conditions were generated with moisture content, carbonization time, and microwave power as independent variables, while carbon content was the dependent variable.Elemental analysis and response surface methodology identified the optimal conditions as 800 W microwave power, 47 min reaction time, and 55% moisture content.Biochar obtained under these conditions (MW-WBNC) contained 64.16% carbon, confirming successful carbonization.Compared to furnace-carbonized char (F-WBNC), MW-WBNC exhibited a 2.7-fold increase in surface area (290.83m 2 /g) and more uniform micropore formation.Adsorption evaluation showed that the water-holding capacity of MW-WBNC (2.5 g/g) was 4.4 times higher than that of F-WBNC.These findings demonstrate that optimized microwave-assisted carbonization yields biochar with superior pore structure and moisture retention, suitable for agricultural applications.Overall, the study high-