Adsorptive-removal of bromothymol blue & keto-bromothymol blue from wastewater using antioxidant curcumin: thermodynamic assessment, kinetic and isotherm modeling

Our research objective is using a spectrophotometer method at a wavelength of 430 nm to explore the removal of bromthymol blue (BTB) & keto-bromothymol blue (KBTB) dyes utilizing curcumin (CUR) as an adsorbent. The impacts of several factors such as initial dye concentration, adsorbent dose, contact time, and temperature, were examined. The adsorption equilibrium data were assessed utilizing Langmuir and Freundlich, as well as an appropriate reaction mechanism, were put forth and discussed. CUR, (CUR -BTB) and (CUR -KBTB) dye were confirmed using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) techniques. The highest percentages of curcumin elimination of BTB, KBTB were 43 & 90%, respectively, at 430 nm and 25 °C, and dye adsorption by the adsorbent increased with increasing initial dye concentration but decreased with increasing adsorbent dose. First-order kinetic models in elimination of BTB and KBTB with correlation 0.97 & 0.98, respectively, were fitted using the experimental data for removal of BTB & KBTB by CUR. This demonstrated that chemisorption, which involves valence forces through the sharing or exchange of electrons, is the rate-limiting phase. Hence, the exothermic nature of BTB adsorption onto CUR is indicated by the negative value of ΔH°(-54.216 kJmol^{- 1}). Once more, the non-spontaneous nature of the adsorption process is indicated by the positive ΔG° value (+ 49.65 kJmol^{- 1}). Furthermore, the non-affinity of CUR for BTB dye is illustrated by the -ve of change of entropy, ΔS° (-166.78 J/mol K).