Functionalization of walnut shell by grafting amine groups to enhance the adsorption of Congo red from water in batch and fixed-bed column modes

Abstract

Several pollutants found in industrial wastewater, such as Congo red dyes (CR), have been shown to be toxic to organisms. To protect human health and the environment, industrial effluents must be purified before being released into bodies of water. In order to effectively remove CR from the solution, amino functionalized walnut shells (WNS) were synthesized. Batch and fixed-bed column systems were used in this research. The Langmuir isotherm model fits the experimental findings well in these two systems, whereas the pseudo-second-order and Thomas kinetic models characterize batch and column CR adsorption, respectively. The adsorption capacity of ACWNS toward CR was to 224.4 mg g−1 at 303 K from Langmuir model. Electrostatic interactions and hydrogen bonding may be the mechanisms. The column research showed that adsorption was more favorable at low inlet solution concentration, low flow rate, or high column depth. The column mass transfer capacity parameter (B) increased with increasing concentration (0.461, 1.59, and 2.47 for 50, 100, and 150 mg L−1, respectively) owing to a greater driving force for CR adsorption onto ACWNS, while adsorbate–adsorbent affinity (β) exhibited a reverse trend. The regeneration property of CR-loaded ACWNS was excellent using NaOH solution. The thermodynamic study revealed that CR removal was both spontaneous and endothermic. ACWNS is promising to remove CR from the solution.