Functionalized biochars with highly-efficient malachite green adsorption property produced from banana peels via microwave-assisted pyrolysis

In this study, functionalized banana peel biochar (BPB) was prepared by microwave-assisted pyrolysis for the first time to investigate its adsorption to malachite green (MG) dye. Adsorption experiments showed that the maximum adsorption capacity of BPB500 and BPB900 to malachite green reached 1790.30 and 2297.83 mg·g-1 within 120 min. The adsorption behaviour was well-fitted by the pseudo-second-order kinetic model and Langmuir isotherm model, and ΔG0 < 0, ΔH0 > 0, indicated that the adsorption process was endothermic and spontaneous, dominated by chemisorption. The adsorption mechanism of MG dye on BPB included hydrophobic interaction, hydrogen bonding, π-π interaction, n-π interaction, and ion exchange. Meanwhile, through regeneration tests, simulated wastewater treatment experiments, and cost calculations, it was found that BPB has great potential for practical applications. This work demonstrated that microwave-assisted pyrolysis is a viable low-cost approach for producing excellent sorbents from biomass, and banana peel is a promising feedstock to prepare biochar for dye removal.