Development of hybrid gel beads of lignocellulosic compounds derived from agricultural waste: Efficient lead adsorbents for a comparative biosorption

Novel alginate/lignocellulosic compounds hybrid gel beads for enhanced removing Pb (II) ions from aqueous solution is successfully fabricated via a facile glutaraldehyde and calcium chloride cross-linking reactions. In this work, an extensive and comparative biosorption study between prepared biocomposites consisting of lignocellulosic compounds including cellulose, hemicellulose, and lignin extracted from barley straw incorporated in calcium alginate beads was carried out. The prepared biocomposites characterized by field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and nitrogen adsorption-desorption analysis. Biocomposite beads were used as an efficient adsorbent in the lead removal from aqueous solutions in different conditions. Also, swelling tests and models, point of zero charge studies, and the effective parameters on adsorption such as contact time, pH, temperature and initial concentration, kinetics, isotherms, and thermodynamics of the adsorption, and adsorbent regeneration and reuse were investigated. The maximum experimental adsorption capacity of 206.75, 24450, and 365.43 mg/g has resulted in cellulose, hemicellulose, and lignin-based biocomposites, respectively. The experimental kinetic and equilibrium data were well adjusted with the pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The thermodynamics results showed an endothermic and spontaneous adsorption process. It was concluded that with increasing the pH, the adsorption capacity of lead was increased. As the pH increased (pH > 35), the distribution coefficient increased (K-d > 10 L/g) indicating that the biocomposites had a high affinity for Pb2+. The points of zero charge for cellulose, hemicellulose, and lignin based biocomposite were obtained 9.15, 8.30, and 8.95, respectively. With increasing the solution pH. the swelling was increased. Regeneration and reuse results represented highly adsorption efficiency after five adsorption cycle stages. These biocomposites with high adsorption efficiency and low-cost material can be a promising adsorbent for practical wastewater treatment and purification processes. (C) 2020 Elsevier B.V. All rights reserved.