A Strategical Improvement in the Performance of CO2/N2 Gas Permeation via Conjugation of L-Tyrosine onto Chitosan Membrane.

Rubbery polymeric membranes, containing amine carriers, have received much attention in CO2 separation because of their easy fabrication, low cost, and excellent separation performance. The present study focuses on the versatile aspects of covalent conjugation of L-tyrosine (Tyr) onto the high molecular weight chitosan (CS) accomplished by using carbodiimide as a coupling agent for CO2/N2 separation. The fabricated membrane was subjected to FTIR, XRD, TGA, AFM, FESEM, and moisture retention tests to examine the thermal and physicochemical properties. The defect-free dense layer of tyrosine-conjugated-chitosan, with active layer thickness within the range of ~600 nm, was cast and employed for mixed gas (CO2/N2) separation study in the temperature range of 25-115 °C in both dry and swollen conditions and compared to that of a neat CS membrane. An enhancement in the thermal stability and amorphousness was displayed by TGA and XRD spectra, respectively, for the prepared membranes. The fabricated membrane showed reasonably good CO2 permeance of around 103 GPU and CO2/N2 selectivity of 32 by maintaining a sweep/feed moisture flow rate of 0.05/0.03 mL/min, respectively, an operating temperature of 85 °C, and a feed pressure of 32 psi. The composite membrane demonstrated high permeance because of the chemical grafting compared to the bare chitosan. Additionally, the excellent moisture retention capacity of the fabricated membrane accelerates high CO2 uptake by amine carriers, owing to the reversible zwitterion reaction. All the features make this membrane a potential membrane material for CO2 capture.

A review on chitosan-based membranes for sustainable CO2 separation applications: Mechanism, issues, and the way forward.

Effective carbon dioxide (CO2) separation by nominal energy utilization is the factual attempt in the present era of energy scarcity and environmental calamity. In this perspective, the membrane- based gas separation technology is a budding endeavour owing to its cost -effectiveness, ease of operational maintenance and compact modular design. Among various membrane materials, bio-based polymers are of interest as they are abundant and can be obtained from renewable resources, and can also reduce our dependency on exhaustible fossil fuel-based sources. In this review, the structure-property relationship of chitosan and some of its film-forming derivatives has been critically studied for the first time in view of the fundamental properties required for gas separation applications. Various factors affecting the gas permeation performance of chitosan-based membranes have been highlighted along with prospects and propositions for the design of a few novel bio-based membranes based on the exhaustive analyses.

Graphene Quantum Dots-Doped Thin Film Nanocomposite Polyimide Membranes with Enhanced Solvent Resistance for Solvent-Resistant Nanofiltration.

The core of the organic solvent nanofiltration (OSN) technology is solvent-resistant nanofiltration (SRNF) membranes. Till now, relative poor performance of solvent resistance is still the bottleneck of industrial application of SRNF membranes. This work reports a novel polyimide (PI)-based thin-film nanocomposite (TFN) membrane which was embedded with graphene quantum dots (GQDs) and showed an improved solvent resistance for OSN application. This kind of SRNF membrane, termed (PI-GQDs/PI)XA, was synthesized via serial processes of interfacial polymerization (IP), imidization, cross-linking, and solvent activation. The IP process was performed between an aqueous m-phenylenediamine solution doped with GQDs, having an average size of 1.9 nm, and an 1,2,4,5-benzenetetracarboxylic acyl chloride n-hexane solution on the PI substrate surface. The prepared (PI-GQDs-50/PI)X SRNF membranes without organic solvent activation achieved an ethanol permeance of nearly 50% higher than those of the GQD-free membranes under the same preparation conditions, while no compromise of the dye rejection was observed. Further, after the solvent activation using N, N-dimethylformamide (DMF) at 80 °C for 30 min, the ethanol permeance achieved about an 8-folds increment, from 2.84 to 22.6 L m-2 h-1 MPa-1. Interestingly, the rejection of rhodamine B also increased from 97.8 to 98.6%. A long-term permeation test of more than 100 h using rose bengal (RB, 1017 Da)/DMF solution at room temperature demonstrated that the synthesized (PI-GQDs-50/PI)XA membranes could maintain the DMF permeance and the RB rejection as high as 18.3 L m-2 h-1 MPa-1 and 99.9%, respectively. Moreover, the immersion test of the prepared (PI-GQDs-50/PI)XA SRNF membranes in both DMF and ethanol at room temperature for about one year also demonstrated the long-term organic solvent stability, indicating their good potential for OSN application.

Graphene-Incorporated Biopolymeric Mixed-Matrix Membrane for Enhanced CO2 Separation by Regulating the Support Pore Filling.

The CO2 separation performance by a membrane is influenced essentially by film thickness, temperature, moisture, and pressure. Pore formation on the active layer and pore clogging of the membrane support are critical factors that impedes the CO2 separation performance. This study involves the development of a novel nanocomposite membrane (CS/SF/GNP) consisting of chitosan (CS), silk fibroin (SF), and graphene nanoparticles (GNP). The CS acts as the matrix, SF contributes to the CO2 facilitated transport by its inherent amines as carriers, and GNP helped in counteracting the support pore blockage during the gas separation test. The positive effect of GNP in the CS/SF/GNP was further apparent in the CO2 permeance inconsequential drop of ∼7% during the initial 12 h in the presence of moisture and pressure. The detailed characterizations including FESEM, AFM, and swelling were performed for the membranes. The effect of sweep water flow rate, temperature, and feed absolute pressure on CO2 separation performance from binary gas were performed. The CS/SF/GNP membrane exhibited CO2 permeance of 159 GPU and CO2/N2 selectivity of 93 at 90 °C and a feed absolute pressure of 2 bar having a sweep side water flow rate of 0.05 mL/min. Further, when CS/SF/GNP membrane was tested to separate CO2 from ternary gas mixture (CO2/N2/H2), it displayed excellent CO2 permeance of 126 GPU and selectivity for CO2/N2 and CO2/H2 as 104 and 52, respectively. The TGA isotherm and XPS analysis of CS/SF/GNP membrane suggested a thermal stability of the prepared membrane that establishes its suitability for the gas permeation at different temperature.