Synthesis of tannic acid based composite for efficient Congo red removal: Isotherm, kinetics, and thermodynamic studies

To remediate the toxic organic dyes in sewage is a challenge task nowadays, because they will pose significant health risks to the ecological system. This work ingeniously developed a pristine composite alpha-FeOOH@poly (tannic acid-1,6-hexanediamine) (FeOOH@PTHA) with respect to effectively remove the hazardous Congo red (CR) from simulated solution. Many physicochemical methods were employed to characterize the structure and properties of the resultant adsorbent, such as SEM, EDS, BET, FT-IR, TGA and so on. An elaborate explanation for the influence factors on CR uptake was carried out with batch mode experiments, including initial pH, CR concentration, adsorbent dosage, contact time and temperature. Results revealed that the repulsive forces per unit area (RF-PUA) retarded the adsorption progress until it reaching equilibrium state. A favorable monolayer adsorption with the maximum amount (303.03 mg g-1 at 40 degrees C) occurred on the homogeneous surface of FeOOH@PTHA, which was ascertained by the Langmuir isotherm model. The well-fitting of pseudo-second-order (P2O) kinetic model and intra-particle diffusion verified the CR chemisorption with a rate-limiting step over FeOOH@PTHA. The thermodynamic analysis demonstrated that the removal of CR presented an inherently spontaneous and endothermic character. The hydrogen bonding, it-it stacking and electrostatic attracting between FeOOH@PTHA and CR were responsible for the adsorption motivation. Accordingly, the creditable adsorbent FeOOH@PTHA has potential as a green and efficient option for the remediation of CR-wastewater effluents and solving environmental issues.