Functionalised Seed Pods for the Sorption of Crystal Violet from Aqueous Solution: Kinetics and Equilibrium Studies

Abstract

The release of dye-containing effluents from several industries into natural water bodies continues to pose a serious threat to the  ecosystem. Even though several conventional wastewater treatment technologies abound, their usage in developing nations has been  limited due to their high cost. This has prompted research into the use of low-cost materials, such as agricultural waste biomass for  sequestering such dyes from wastewater. The ability of CH₃COOH-functionalised Millettia thonningii seed pods (FMTP), an agricultural  waste, as an adsorbent for the sequestration of Crystal Violet (CV) dye from aqueous solutions is investigated in this study. Fourier  Transform Infrared (FTIR) spectroscopy was used to characterize the functionalized adsorbent and its precursor. The pseudo-first-order, pseudo-second-order, and Elovich's kinetic models were used to analyze the kinetic data, while Langmuir and Freundlich isotherm  models were used to analyze the equilibrium data using the non-linear regression method. To evaluate the adsorption data and identify  the best-fitting kinetic and isotherm models, four error functions were used: Coefficient of Determination (R² ), Chi-Square (χ² ), Sum of  Error Squares (SSE), and Percent Deviation (% D). The adsorption kinetics was best described by Elovich's kinetic model, while the  adsorption equilibrium was better described by the Freundlich model, indicating that the mechanism of adsorption is predominantly  chemisorption onto a heterogeneous adsorbent surface. The maximum adsorption capacity of the functionalized adsorbent was 34.8270  mg/g as given by the Langmuir Qmax. Experimental results revealed that acetic acid functionalized biomass is a suitable adsorbent for  removing CV from aqueous solutions. Its application in the treatment of industrial wastewater should be investigated further.