Experimental Study on Evaluation of Pumpkin Waste in Removal of Textile Dyes: Preparation, Characterization, Adsorption, and Desorption

In this study, the use of natural waste containing the outer shell and seed shells of pumpkin (WSSP) in synthetic Reactive Blue 3R (RB) and Reactive Red P4BN (RR) dye removal processes was investigated. The chemical characterization of WSSP was presented by Fourier transform infrared spectroscopy (FTIR) analysis. Scanning electron microscopy (SEM) images showed the morphologies of the samples. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) curves were obtained to investigate the thermal behavior of the WSSP. Batch adsorption studies were carried out between pH 1-8, and the highest removals were obtained for RB and RR dyes as 66% at pH 3 and 92% at pH 1, respectively. The equilibrium was reached in 180 min for RB and 300 min for RR dye removal processes. The decreased particle size of the WSSP encouraged the adsorption rate. Adsorption kinetics of both processes fit pseudo-second-order kinetics. The equilibrium studies of the dye removal processes were best clarified by the Langmuir isotherm model. Enthalpy (Delta H0) and entropy (Delta S0) values of the RB dye adsorption process were 41.49 kJ mol-1 and 139.65 J mol-1K-1, respectively. For the RR dye removal process, Delta H0 value was obtained as -38.94 kJ mol-1 and Delta S0 value as -118.49 J mol-1K-1. Negative Gibb's free energy (Delta G0) values were determined for both dyes. In desorption studies, the highest desorption percentage was determined for both dyes with pH 12 distilled water. It has been determined that WSSP provides effective dye removal as an alternative and a low-cost adsorbent.