Study on Adsorption Characteristics and Mechanism of Cr(Ⅵ) by Waste Banana Peel Powder

In this study, the adsorption characteristics and mechanism of chromium Cr(Ⅵ) by waste banana peel powder were investigated. The research focused on various influencing factors and quantitatively by analyzing the adsorption process with isotherm, kinetic, and thermodynamic equations. The adsorption mechanism was studied through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It indicate that banana peel powder is an excellent adsorbent, outperforming other biomass in terms of Cr(Ⅵ) adsorption. The optimal pH value of adsorption was found to be 2, with equilibrium achieved in 24 hours. Higher initial Cr(Ⅵ) concentrations and temperatures improved the adsorption performance. The adsorption capacity of Cr(Ⅵ) with banana peel powder remained at 93.7% after three adsorption-desorption cycles. Both Langmuir and Freundlich isotherm equations accurately described the adsorption process which indicates the presence of both monolayer and multilayer adsorption, suggesting favorable adsorption conditions. The maximum adsorption capacities of Cr(Ⅵ) at 298, 308, and 318 K were 149.25, 161.29, and 169.49 mg·g^-1, respectively. The adsorption process was best described by the quasi-second-order kinetic model, implying that chemisorption was predominant and involved electron transfer. Thermodynamic parameters revealed that the adsorption was spontaneous, endothermic, and entropy-increasing. It shows that banana peel powder has a lamellar morphology with diameters ranging from tens to hundreds of microns in SEM, featuring folds and pores on the surface that provides multiple active sites. The combined results from SEM, FTIR, and XPS analyses indicate that the adsorption mechanism of Cr(Ⅵ) by banana peel powder involved electrostatic attraction, oxidation-reduction, surface chelation, and ion exchange.