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

• BPM-COFs are constructed using benzene 1,3,5-tricarbohydrazide (BTCH) and pyromellitic dianhydride (PMDA) in one step. • The BPM-COF enables highly efficient Rhodamine B (RhB) adsorption. • BPM-COF shows a 78.63% removal rate after three cyclic desorption-adsorption cycles. • The adsorption isotherm (Langmuir) and kinetics (pseudo-second-order) were studied. 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 m 2 .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 (R 2 = 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.