One-Walled Phthalimide Extended Calix[4]Pyrrole-Based Supramolecular Adsorbent for Alleviating Nitrate From Simulated Water

Abstract

In this investigation, meso-substituted one-walled phthalimide appended calix[4]pyrrole (mPth–C4P) was prepared from pthalimide functionalized dipyrromethane (DPM, 4), acetone, and freshly distilled pyrrole via both conventional as well as green protocols utilizing the deep eutectic solvent (DES) of N,N'-dimethyl urea (DMU) & l-(+)-tartaric acid (TA) in an appropriate ratio of 7:3. In order to lessen the nitrate (NO₃⁻) ion endowed eutrophication peril, the mPth–C4P was effectively employed as a supramolecular adsorbent for the sequestration of NO₃⁻ ion from aquatic phase. The mPth–C4P was extensively characterized by FTIR, ¹H-NMR, SEM–EDX, and elemental mapping to corroborate the synthesis and adsorption of NO₃⁻ ion. The surface area was found to be 11.465 m² g⁻¹ and the pore size of 3.2 nm, pointed out to the mesoporous nature of mPth–C4P. Batch methodology was exploited for detailing the influence of process parameters on %efficiency and adsorption capacity. The mPth–C4P demonstrated excellent adsorption competence (> 91%) within 16 min from a [NO₃⁻] of 20 mg L⁻¹, which translates into a good pseudo-second order rate constant value of 0.026 g mg⁻¹ min⁻¹. Freundlich model was the best-fit model pointing out multilayer adsorption. The maximum saturation capacity was 239.03 mg g^‒1 at 298 K, which is far better than most of the reported adsorbents indicating the potential of mPth–C4P to confiscate NO₃⁻. The dynamics appraisal elucidated pseudo-second order to favor the uptake with both intraparticle and liquid film diffusion models governing the rate of reaction. Thermodynamic parameters suggested that the uptake of NO₃⁻ was spontaneous, favorable, and exothermic which is in harmony with the isotherm studies. The mPth–C4P can be used consecutively up to 4 cycles along with good potential in real water > 80% uptake. All these results established mPth–C4P as an efficacious scavenger for NO₃⁻ from simulated water.