Surface-Defect-Engineered Agrowaste-Based Biochar-NiAl Layered Double Hydroxide Composite for Congo Red Removal

Abstract

Biochar-based composite materials have recently emerged as efficient and sustainable adsorbents for wastewater treatment, enabling the removal of diverse organic and inorganic pollutants via their hierarchical porosity and surface functionality. Layered Double Hydroxides (LDHs) are also recognized as efficient adsorbents for removing anionic and cationic pollutants. This work explores the [Ni0.752+Al0.253+.(OH)2 ].(CO32−)0.125.H2Oor NiAl LDH and Biochar-based LDH for Congo Red (CR) removal. Comprehensive characterization techniques, including XRD, FTIR, SEM, TEM, BET, zeta potential, XPS, and Raman spectroscopy, were performed to analyze the physical and chemical properties. Variable key operational constraints such as adsorbent dosage, solution pH, temperature, reaction time, and dye concentration were investigated to study the adsorption behavior. The Langmuir isotherm and pseudo-second-order kinetic models are suitably fitted to describe the reaction behavior between the adsorbent and adsorbate. The NiAl LDH revealed a maximum equilibrium removal capacity of CR of 90.10 mg/g, whereas the composite attained 132.71 mg/g. The regeneration study for both materials shows up to the fifth cycle. The negative enthalpy value (−66.57 kJ/mol) and negative entropy value (−193.33 J/mol.K) at high temperatures indicate that the adsorption process is endothermic and predominantly physical in nature. This work presents an efficient synthesis approach for constructing defect-engineered, Biochar-based LDH, highlighting its potential as a highly effective adsorptive material for wastewater treatment.