Lignocellulosic based materials from kapok husk (Ceiba Pentandra L. Gaertn) wastes for indigo carmine dye removal: Isotherms, kinetics, thermodynamics, and reusability studies

The recent study has employed kapok husk for indigo carmine removal from wastewater. The biosorption process was carried out using batch by investigating some parameters. The optimum conditions were achieved at pH 2, a concentration of 1100 mg/L, and a contact time of 60 min with an adsorption capacity of 45.83 mg/g at room temperature. The adsorption process of indigo carmine followed the Freundlich isotherm model (R² = 0.9572), indicating the formation of a multilayer adsorption. The kinetic data were fitted to the pseudo-second-order kinetic model. Thermodynamic adsorption studies indicated that the adsorption process was spontaneous and exothermic. The Fourier Transform Infra-Red (FTIR) spotted that the S=O group wavenumber was shifted from 1094.73 to 1095.57 cm⁻¹ after indigo carmine uptake. The Scanning Electron Microscopy (SEM) and Brunauer-Emmett–Teller (BET) exhibited that the adsorbent surface has become smoother and a reduction of surface area after adsorption occurred. x-ray Fluorescence (XRF) analysis indicated that the percentage of Sulfur (S) increased, confirming indigo carmine existence in the adsorbent. Thermogravimetric Analysis (TGA) denoted greater weight loss at 230°C as the active sites of the biosorbent had been damaged. The percent removal of kapok husk did not significantly change after fourdsorption–desorption cycles using 30% glycerol as the desorbing agent. Kapok husk has successfully removed indigo carmine from batik textile wastewater by as much as 77.04%. These facts have proven that kapok husk is a promising adsorbent for indigo carmine removal.