Nitumani Das

The potential to produce high-purity C₂H₄ has made ethylene-selective adsorbents for ethane (C₂H₆)/ethylene (C₂H₄) gas mixture separation appealing as viable substitutes for traditional cryogenic distillation. In this aspect, porous organic polymers (POPs) are anticipated to become the next-generation potential adsorbent due to their easily customizable functions and functional sites suitable for gas separation. This article reports the selective C₂H₄ adsorption over C₂H₆ using microporous copper(I)-coordinated POP (Cu@Di-POP) via fine-tuning of the π complexation and pore size. The specially designed adsorbent has the ideal pore size and coordinated Cu(I) ions to form π-complexation with C₂H₄ molecules, which enabled it to adsorb C₂H₄ (at 1 bar, 24.9, 18.9, and 13.4 cm³ g^-1 at 273, 298, and 323 K, respectively) while significantly reducing C₂H₆ adsorption (at 1 bar, 16.9, 12.7, and 8.8 cm³ g^-1 at 273, 298, and 323 K, respectively). At 1 bar, Cu@Di-POP exhibited IAST selectivities of 6.09, 5.60, and 4.13 for C₂H₄/C₂H₆ at 273, 298, and 323 K, respectively, suggesting its C₂H₄ selective behavior, which was further confirmed from the experimental breakthrough measurement. Furthermore, the computational studies carried out with density functional theory highlighted an enhanced charge distribution leading to dπ-pπ conjugation between C₂H₄ π-electrons and Cu d-electrons, thereby showing a relatively higher interaction energy of -37.23 kcal/mol with C₂H₄ as compared to -16.06 kcal/mol with C₂H₆ gas molecules.

Development of crystalline porous materials for selective CO₂ adsorption and storage is in high demand to boost the carbon capture and storage (CCS) technology. In this regard, we have developed a β-keto enamine-based covalent organic framework (VM-COF) via the Schiff base polycondensation technique. The as-synthesized VM-COF exhibited excellent thermal and chemical stability along with a very high surface area (1258 m² g^-1) and a high CO₂ adsorption capacity (3.58 mmol g^-1) at room temperature (298 K). The CO₂/CH₄ and CO₂/H₂ selectivities by the IAST method were calculated to be 10.9 and 881.7, respectively, which were further experimentally supported by breakthrough analysis. Moreover, theoretical investigations revealed that the carbonyl-rich sites in a polymeric backbone have higher CO₂ binding affinity along with very high binding energy (-39.44 KJ mol^-1) compared to other aromatic carbon-rich sites. Intrigued by the best CO₂ adsorption capacity and high CO₂ selectivity, we have utilized the VM-COF for biogas purification produced by the biofermentation of municipal waste. Compared with the commercially available activated carbon, VM-COF exhibited much better purification ability. This opens up a new opportunity for the creation of functionalized nanoporous materials for the large-scale purification of waste-generated biogases to address the challenges associated with energy and the environment.

In this work, we illustrated the design and development of a metal-coordinated porous organic polymer (POP) namely VO@TPA-POP via a post-synthetic metalation strategy to incorporate oxo-vanadium sites in a pristine polymer (TPA-POP) having acetylacetonate (acac) as anchoring moiety. The as-synthesized VO@TPA-POP exhibited highly robust and porous framework, which has been utilized for thioanisole (TA) oxidation to its corresponding sulfoxide. The catalyst demonstrated notable stability and recyclability by maintaining its catalytic activity over multiple reaction cycles without any significant loss in activity. The X-ray absorption spectroscopy (XAS) and density functional theory (DFT) analysis establish the existence of V(+4) oxidation state along with the VO(O)₄ active sites into the porous network and the most energetically feasible mechanistic pathway involved in the TA oxidation, respectively, indicating the role of electron density associated with vanadium center during the catalytic transformation. Thus, this work aims at the demonstration of versatility and potential of VO@TPA-POP as a porous heterogeneous catalyst for the TA oxidation followed by decontamination of sulfur mustards (HD's) to their corresponding less toxic sulfoxides in a more efficient and greener way.

Herein, we have designed and synthesized two heteroatom (N, O) rich covalent organic frameworks (COF), PD‐COF and TF‐COF, respectively, to demonstrate their relative effect on CO₂ adsorption capacity and also CO₂/N₂ selectivity. Compared to the non‐fluorinated PD‐COF (BET surface area 805 m² g⁻¹, total pore volume 0.3647 ccg⁻¹), a decrease in BET surface area and also pore volume have been observed for fluorinated TF‐COF due to the incorporation of fluorine to the porous framework (BET surface area 451 m² g⁻¹, total pore volume 0.2978 ccg⁻¹). This fact leads to an enormous decrease in the CO₂ adsorption capacity and CO₂/N₂ selectivity of TF‐COF, though it shows stronger affinity towards CO₂ with a Qst of 37.76 KJ/mol. The more CO₂ adsorption capacity by PD‐COF can be attributed to the large specific surface area with considerable amount of micropore volume compared to the TF‐COF. Further, PD‐COF exhibited CO₂/N₂ selectivity of 16.8, higher than that of TF‐COF (CO₂/N₂ selectivity 13.4).

This Feature Article represents the existing research activities about diverse synthetic approaches with possible modification of functionality of POPs (COFs, CTFs and some amorphous POPs) and their exciting applications (photocatalytic CO₂ reduction, bio-mass upgradation & water splitting) as next generation nanoreactors.