Novel SPVA/g-C3N4-SA/PAN Pervaporation Membranes with Porous Catalytic Layers for Esterification Enhancement

A Comprehensive Review of Performance of Polyacrylonitrile-Based Membranes for Forward Osmosis Water Separation and Purification Process

Polyacrylonitrile (PAN), with its unique chemical, electrical, mechanical, and thermal properties, has become a crucial acrylic polymer for the industry. This polymer has been widely used to fabricate ultrafiltration, nanofiltration, and reverse osmosis membranes for water treatment applications. However, it recently started to be used to fabricate thin-film composite (TFC) and fiber-based forward osmosis (FO) membranes at a lab scale. Phase inversion and electrospinning methods were the most utilized techniques to fabricate PAN-based FO membranes. The PAN substrate layer could function as a good support layer to create TFC and fiber membranes with excellent performance under FO process conditions by selecting the proper modification techniques. The various modification techniques used to enhance PAN-based FO performance include interfacial polymerization, layer-by-layer assembly, simple coating, and incorporating nanofillers. Thus, the fabrication and modification techniques of PAN-based porous FO membranes have been highlighted in this work. Also, the performance of these FO membranes was investigated. Finally, perspectives and potential directions for further study on PAN-based FO membranes are presented in light of the developments in this area. This review is expected to aid the scientific community in creating novel effective porous FO polymeric membranes based on PAN polymer for various water and wastewater treatment applications.

Photo–Redox Properties of –SO3H Functionalized Metal-Free g-C3N4 and Its Application in the Photooxidation of Sunset Yellow FCF and Photoreduction of Cr (VI)

In this work, we synthesized a metal-free sulfonic functionalized graphitic carbon nitride using sulfuric acid through the wet impregnation technique. The functionalization of sulfonic groups (–SO3H) on g-C3N4 will promote a high surface charge density and charge separation owing to its high electronegativity. The g-C3N4–SO3H shows excellent optical/electronic and surface properties towards enhanced photo–redox reactions. The sulfonic groups also facilitate the availability of more separated charge carriers for photocatalytic oxidation and reduction reactions. The as-synthesized material has been characterized by different spectroscopic tools to confirm the presence of functionalized –SO3H groups and optoelectronic possessions. The photocatalytic responses of g-C3N4–SO3H result in 99.56% photoreduction of Cr (VI) and 99.61% photooxidation of Sunset Yellow FCF within 16 min and 20 min, respectively, of visible light irradiation. The g-C3N4–SO3H catalyst exhibits a high apparent rate constant (Kapp) towards the degradation of Cr (VI), and SSY, i.e., 0.783 min−1 and 0.706 min−1, respectively. The intense optical–electrochemical properties and potentially involved active species have been analyzed through transient photocurrent, electrochemical impedance, and scavenging studies. Consequently, the photocatalytic performances are studied under different reaction parameters, and the plausible photocatalytic mechanism is discussed based on the results.

Preparation and Characterization of Strongly Sulfonated Acid Block and Random Copolymer Membranes for Acetic Acid Esterification with 2-Propanol

In this paper, we report the synthesis of block and random copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and methyl methacrylate (MMA), with different AMPS feed ratios. These solution-processable copolymers with strongly sulfonated acid groups resulted in membranes with tunable ion exchange (IEC) and water absorption capacities. AFM images confirmed the microphase separation of PAMPS-b-PMMA-1:1 block copolymer membrane, annealed under the appropriate conditions. The resulting copolymers from the random combination of a 1:1 molar ratio of AMPS and MMA monomers are effective at enhancing the esterification conversion of acetic acid, when compared with a reaction catalyzed by PAMPS-b-PMMA block copolymers and the previously studied catalytic membranes. With the PAMPS-co-PMMA-1:1 membrane, the esterification reaction using acetic acid achieved 85% isopropyl acetate. These results are closely correlated with the increase in IEC (2.63 mmol H⁺g⁻¹) and the relationship between weight loss (20.3%) and swelling degree (68%) in 2-propanol.

Porous PVA-g-SPA/PVA-SA Catalytic Composite Membrane via Lyophilization for Esterification Enhancement

A catalytic composite membrane was developed for the enhancement of esterification by lyophilization for the first time. The catalytic composite membrane was composed of a poly(vinyl alcohol) (PVA)-sodium alginate (SA) separation layer and a spongy porous catalytic layer cross-linked by PVA and 4-sulfophthalic acid (SPA). Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results indicated the successful synthesis of the catalytic composite membrane. The membrane properties were evaluated by ethanol dehydration and esterification. The conversion rate of acetic acid reached 95.9% after 12 h. Compared with batch reactions, the conversion rate increased by 24.4%. After five cycles, the membrane still maintained outstanding catalytic activity. The resistance of mass transfer was analyzed, and the results showed that the porous structure reduced the catalytic layer resistance to total resistance from 70.27 to 32.88%. The composite membrane with a spongy porous catalytic layer exhibited superior dehydration and catalytic performance.