Hydroxylamine-Anchored Covalent Aromatic Polymer for CO₂ Adsorption and Fixation into Cyclic Carbonates

Hydroxylamine-anchored covalent aromatic polymer (CAP-DAP) was synthesized from <i>p</i>-terphenyl and 1,3,5-benzene tricarbonyl chloride, followed by subsequent functionalization with 1,3-diamino-2-propanol for CO₂ capture and metal-free catalysis in CO₂–epoxide cycloaddition reactions. The novel CAP-DAP material was characterized using various analytical techniques. It showed very good CO₂ adsorption capacity of 153 mg/g along with a high (CO₂/N₂) selectivity of 86 at 273 K/1 bar, in contrast to bare CAP, which exhibited moderate CO₂ adsorption of 136 mg/g with a CO₂/N₂ selectivity of 47. CAP-DAP also displayed high catalytic activity for CO₂–epoxide cycloaddition reactions under mild and solvent-free conditions. The synergistic effect between metal-free CAP-DAP and tetrabutylammonium bromide (<i>n</i>-Bu₄NBr) enabled a high epoxide conversion of 98% coupled with an excellent product selectivity of 99% at 60 °C, 1 bar CO₂, and a reaction time of 12 h. Faster reaction kinetics with reaction times <6 h was possible at 80 °C. The catalyst also showed excellent reusability and no leaching of active species was observed from the spent catalyst. Based on experimental results, a plausible reaction mechanism for CO₂–epoxide cycloaddition reaction over CAP-DAP catalyst has been proposed

Selective Adsorption of Rare Earth Elements over Functionalized Cr-MIL-101

Efficient rare earth elements (REEs) separation and recovery are crucial to meet the ever-increasing demand for REEs extensively used in various high technology devices. Herein, we synthesized a highly stable chromium-based metal–organic framework (MOF) structure, Cr-MIL-101, and its derivatives with different organic functional groups (MIL-101-NH₂, MIL-101-ED (ED: ethylenediamine), MIL-101-DETA (DETA: diethylenetriamine), and MIL-101-PMIDA (PMIDA: <i>N</i>-(phosphonomethyl)­iminodiacetic acid)) and explored their effectiveness in the separation and recovery of La³⁺, Ce³⁺, Nd³⁺, Sm³⁺, and Gd³⁺ in aqueous solutions. The prepared materials were characterized using various analytical instrumentation. These MOFs showed increasing REE adsorption capacities in the sequence MIL-101 < MIL-101-NH₂ < MIL-101-ED < MIL-101-DETA < MIL-101-PMIDA. MIL-101-PMIDA showed superior REE adsorption capacities compared to other MOFs, with Gd³⁺ being the element most efficiently adsorbed by the material. The adsorption of Gd³⁺ onto MIL-101-PMIDA was examined in detail as a function of the solution pH, initial REE concentration, and contact time. The obtained adsorption equilibrium data were well represented by the Langmuir model, and the kinetics were treated with a pseudo-second-order model. A plausible mechanism for the adsorption of Gd³⁺ on MIL-101-PMIDA was proposed by considering the surface complexation and electrostatic interaction between the functional groups and Gd³⁺ ions under different pH conditions. Finally, recycling tests were carried out and demonstrated the higher structural stability of MIL-101-PMIDA during the five adsorption–regeneration runs

Aminoethanethiol-Grafted Porous Organic Polymer for Hg²⁺ Removal in Aqueous Solution

A highly porous organic polymer, CBAP-1, was synthesized from terephthaloyl chloride and 1,3,5-triphenylbenzene via the Friedel–Crafts reaction, and functionalized with either ethylenediamine (EDA) or 2-aminoethanethiol (AET) for Hg²⁺ removal from water. Both materials were characterized by X-ray diffraction, N₂ adsorption–desorption isotherms, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis, and the stability of the porous polymers under different pH and temperature conditions was examined. The adsorption experiments were carried out by varying contact time, Hg²⁺ concentration, and system pH to study the adsorption equilibrium and kinetics. The Hg²⁺ ion-adsorption capacities of CBAP-1­(EDA) and CBAP-1­(AET) were 181 and 232 mg/g, respectively, at room temperature and pH 5, and the observed adsorption isotherms could be fitted well to the Langmuir model (correlation factor <i>R</i>² > 0.99). Under the optimum set of conditions, the adsorption equilibrium for CBAP-1­(AET) was reached within a contact time of 10 min; CBAP-1­(AET) exhibited an excellent distribution coefficient of greater than 2.41 × 10⁷ mL/g. The adsorption kinetics could be satisfactorily described by a pseudo-second-order model. Hg²⁺ recovery in the presence of commonly coexisting metal ions such as Na⁺, Ca²⁺, Mg²⁺, Pb²⁺, and Fe³⁺ was also investigated. CBAP-1­(AET) showed high Hg²⁺ selectivity against other ions except Pb²⁺. CBAP-1­(AET) was superior to CBAP-1­(EDA) in terms of overall performance; it could efficiently remove >96% of Hg²⁺ ions in 2 min from a 100 ppm of Hg²⁺ solution. The material could be reused for 10 consecutive runs with negligible loss in adsorption capacity