Design enhancement in hydroxide ion conductivity of viologen-bakelite organic frameworks for a flexible rechargeable zinc-air battery.

Quasi-solid-state rechargeable zinc-air batteries (ZABs) are suitable for the generation of portable clean energy due to their high energy and power density, safety, and cost-effectiveness. Compared to the typical alkaline aqueous electrolyte in a ZAB, polymer or gel-based electrolytes can suppress the dissolution of zinc, preventing the precipitation of undesirable irreversible zinc compounds. Their low electronic conductivity minimizes zinc dendrite formation. However, gel electrolytes suffer from capacity fade due to the loss of the volatile solvent, failing to deliver high-energy and high-power ZABs. Consequently, developing polymers with high hydroxide ion conductivity and chemical durability is paramount. We report cationic C-C bonded robust polymers with stoichiometrically controlled mobile hydroxide ions as solid-state hydroxide ion transporters. To boot, we increased the viologen-hydroxide-ion concentration through "by-design" monomers. The polymers constructed with these designer monomers exhibit a commensurate increase in their ionic conductivity. The polymer prepared with 4 OH- ion-containing monomer was superior to the one with 3 OH-. The conductivity increases from 7.30 × 10-4 S cm-1 (30 °C) to 2.96 × 10-3 S cm-1 (30 °C) at 95% RH for IISERP-POF12_OH (2_OH) and IISERP-POF13_OH (3_OH), respectively. A rechargeable ZAB (RZAB) constructed using 3_OH@PVA (polyvinyl alcohol) as the electrolyte membrane and Pt/C + RuO2 catalyst delivers a power density of 158 mW cm-2. In comparison, RZABs with a PVA interlayer provided only 72 mW cm-2. Notably, the device suffered an initial charge-discharge voltage gap of merely 0.55 V at 10 mA cm-2, which increased by only 2 mV after 50 hours of running. The battery operated at 10 mA cm-2 and worked steadily for 67 hours. We accomplished a flexible and rechargeable zinc-air battery (F-RZAB) exhibiting a maximum power density of 79 mW cm-2. This demonstration of a cationic viologen-bakelite polymer-based flexible secondary ZAB with versatile stochiometric hydroxide-ion tunability marks an important achievement in hydroxide-ion conducting solid-state electrolyte development.

Tailoring COFs: Transforming Nonconducting 2D Layered COF into a Conducting Quasi-3D Architecture via Interlayer Knitting with Polypyrrole.

Improving the electronic conductivity and the structural robustness of covalent organic frameworks (COFs) is paramount. Here, we covalently cross-link a 2D COF with polypyrrole (Ppy) chains to form a quasi-3D COF. The 3D COF shows well-defined reflections in the SAED patterns distinctly indexed to its modeled crystal structure. This knitting of 2D COF layers with conjugated polypyrrole units improves electronic conductivity from 10-9 to 10-2 S m-1. This conductivity boost is affirmed by the presence of density of states near the Fermi level in the 3D COF, and this elevates the COF's valence band maximum by 0.52 eV with respect to the parent 2D pyrrole-functionalized COF, which agrees well with the opto-electro band gaps. The extent of HOMO elevation suggests the predominant existence of a polaron state (radical cation), giving rise to a strong EPR signal, most likely sourced from the cross-linking polypyrrole chains. A supercapacitor devised with COF20-Ppy records a high areal capacitance of 377.6 mF cm-2, higher than that of the COF loaded with noncovalently linked polypyrrole chains. Thus, the polypyrrole acts as a "conjugation bridge" across the layers, lowering the band gap and providing polarons and additional conduction pathways. This marks a far-reaching approach to converting many 2D COFs into highly ordered and conducting 3D ones.

Ag Nanoparticles Supported on a Resorcinol-Phenylenediamine-Based Covalent Organic Framework for Chemical Fixation of CO2.

Covalent organic frameworks are a new class of crystalline organic polymers possessing a high surface area and ordered pores. Judicious selection of building blocks leads to strategic heteroatom inclusion into the COF structure. Owing to their high surface area, exceptional stability and molecular tunability, COFs are adopted for various potential applications. The heteroatoms lining in the pores of COF favor synergistic host-guest interaction to enhance a targeted property. In this report, we have synthesized a resorcinol-phenylenediamine-based COF which selectively adsorbs CO2 into its micropores (12 Å). The heat of adsorption value (32 kJ mol-1 ) obtained from the virial model at zero-loading of CO2 indicates its favorable interaction with the framework. Furthermore, we have anchored small-sized Ag nanoparticles (≈4-5 nm) on the COF and used the composite for chemical fixation of CO2 to alkylidene cyclic carbonates by reacting with propargyl alcohols under ambient conditions. Ag@COF catalyzes the reaction selectively with an excellent yield of 90 %. Recyclability of the catalyst has been demonstrated up to five consecutive cycles. The post-catalysis characterizations reveal the integrity of the catalyst even after five reaction cycles. This study emphasizes the ability of COF for simultaneous adsorption and chemical fixation of CO2 into corresponding cyclic carbonates.

Hyper-Cross-linked Porous Organic Frameworks with Ultramicropores for Selective Xenon Capture.

Exceptionally stable ultramicroporous C-C-bonded porous organic frameworks (IISERP-POF6, 7, 8) have been prepared using simple Friedel-Crafts reaction. These polymers exhibit permanent porosity with a Brunauer-Emmett-Teller surface area of 645-800 m2/g. Xe/Kr adsorptive separation has been carried out with these polymers, and they display selective Xe capture ( s(Xe/Kr) = 6.7, 6.3, and 6.3) at 298 K and 1 bar pressure. Interestingly, these polymers also show remarkable Xe/N2 ( s(Xe/N2) = 200, 180, and 160 at 298 K and 1 bar) and Xe/CO2 selectivity ( s(Xe/CO2) = 5.6, 7.4, and 5.6) for a 1:99 composition of Xe-N2/Xe-CO2. Selective removal of Xe at such low concentrations is extremely challenging; the observed selectivities are higher compared to those observed in porous carbons and metal-organic frameworks. Breakthrough studies were performed using the composition relevant to the nuclear off-gas mixture with the polymers, and we find that the polymers hold Xe for a longer time in the column, which illustrates the Xe/Kr separation performance under dynamic conditions.

Process optimization for the preparation of antioxidant rich ginger candy using beetroot pomace extract.

Now-a-days, there is an increased interest in fruits and vegetables processing by-products due to potential source of phytochemicals and pigments. Beetroot (Beta vulgaris) pomace extract is a rich source of betalain, phenolics and other bioactive components, which possess significant antioxidant activities. In the present study, process optimization was performed for developing ginger (Zingiber officinale) candy enriched with beetroot pomace extract using response surface methodology (RSM). The effect of two process variables: blanching time (0-10 min) and beetroot pomace extract (0-10%) was evaluated on physicochemical characteristics and phytochemicals content of the developed product. Maximum phytochemicals' activities were obtained under optimum conditions of 7.81 min blanching time and 9.24% beetroot pomace extract. FTIR analysis also confirmed the significant effect of beetroot pomace extract and it's blanching on the phytochemical potential of ginger candy. The study would be useful for developing similar novel and antioxidants rich food products supplemented with beetroot pomace extract.