Two-dimensional imide-based covalent organic frameworks for cationic dye adsorption: Synthesis, characterization, isotherm, kinetics, and thermodynamic analysis

The present study reports the construction of imide-based covalent organic frameworks (BPM-COFs) from benzene 1,3,5-tricarbohydrazide (BTCH) and pyromellitic dianhydride (PMDA) using one-step approaches, resulting in solvent stability and acidity and alkalinity resistance. Multiple analytical techniques, including FT-IR, XRD, SEM, BET, AFM, and HRTEM, were employed to ascertain the successful synthesis of BPM-COF adsorbent. The BET surface areas of BPM-COF adsorbent measuring were performed at 11 m².g⁻¹. Adsorption capacity at optimal conditions (pH = 8, 0.005 g of adsorbent, 6 min of agitation, 120 mg. l^-1 pollutants concentration) is achieved to 192.54 mg.g^-1 and removal efficiency is 80.22 %. The experimental adsorption data fitted well with Langmuir's nonlinear isotherm model. The adsorption kinetic data were closely related to the Weber-Morris intraparticle diffusion nonlinear model (R² = 1.00). In addition to its excellent recyclability, BPM-COF adsorbent shows a 73.01 % removal rate after three cyclic desorption-adsorption cycles. A decrease in entropy seemed to favour spontaneity and an exothermic adsorption process, which were indicated by Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°). The SEM analysis of BPM-COF after RhB adsorption revealed the presence of spherical particles on the surface of BPM-COF nanorods, indicating that RhB was adsorbed on the surface of BPM-COF adsorbents via hydrogen bonds, electrostatic interactions, and van der Waals interactions. Since BPM-COF exhibits excellent performance, is easy to synthesize, and is reusable, it is an ideal material for future studies in small- and large-scale water treatment projects.