Carica papaya seed− derived functionalized biochar: an environmentally friendly and efficient alternative for dye adsorption

Abstract Biochar is emerging as a sustainable material for addressing critical environmental challenges, including water pollution and carbon sequestration. In this study, biochar derived from papaya seed biomass via slow pyrolysis was investigated for its efficacy in removing organic dyes from aqueous solutions. Both biochar and chemically functionalized biochar were comprehensively characterized using XRD, FTIR, XPS, BET surface area analysis, and SEM/EDS to elucidate their structural, morphological, and surface properties. The adsorption performance was assessed using methylene blue (MB), rhodamine B (RhB), malachite green (MG), and methyl orange (MO) as model contaminants, with particular attention to adsorption kinetics and equilibrium behavior. The unmodified biochar exhibited moderate adsorption capacities, primarily driven by π − π interactions and a limited number of functional groups, achieving removal efficiencies of 55.5, 97.8, and 12.9% for MB, MG, and RhB, respectively, while MO showed negligible adsorption. Remarkably, chemical functionalization with KMnO₄ significantly enhanced biochar performance, increasing surface area and functional group diversity. This modification enabled the complete removal (100%) of MB and MG within six minutes, alongside substantial improvements for RhB and MO, achieving 100 and 88% removal, respectively. Adsorption kinetics followed a pseudo‒second‒order model ( R 2 > 0.99), indicating chemisorption as the dominant mechanism, while Langmuir isotherms ( R 2 = 0.993 − 0.999) suggested monolayer adsorption. Additionally, the intraparticle diffusion model highlighted the synergistic contributions of surface interactions and pore diffusion to overall adsorption efficiency. These findings establish chemically functionalized papaya seed biochar as a highly efficient, low‒cost adsorbent for dye removal, underscoring its potential for environmental remediation. The innovative utilization of papaya seed biomass not only adds value to agricultural waste but also advances sustainable water treatment strategies, reinforcing its significance in environmental science and engineering.