Separation of Acetic Acid/Water Mixtures by Pervaporation through Poly(Vinyl Alcohol)–Sodium Alginate Blend Membranes

Yeast fermentation inspired Ca-alginate hydrogel membrane: lower transparency, hierarchical pore structure and higher hydrophobicity

With a fantastic combination of yeast fermentation and hydrogel membrane formation, a series of microorganism inspired porous hydrogel membranes (MIHM) with various mass ratios of yeast/sodium alginate (SA) were developed. The yeast cells were firstly activated by addition of glucose for generating byproduct carbon dioxide (CO₂), inducing the formation of porous structures. The ionic cross-linking between calcium chloride and SA was subsequently performed based on an egg-box model. It is of interest to note that the obtained MIHM hydrogel membranes exhibited decreased transparency and hierarchical porous structure with pore sizes varying from 2 nm to 1 mm, giving rise to significantly increased contact angle (CA) values from 63.65° to 107.83° and obviously decreased equilibrium swelling ratios from 79.72 to 18.05. Especially, the adsorption kinetics of crystal violet (CV) show that the MIHM hydrogel membrane exhibited an encouraging uptake capacity of 18.40 mg g⁻¹ at 10 mg g⁻¹ and the adsorption kinetics of CV could be well defined by a pseudo-first-order kinetic equation. Owing to great advantages in facile fabrication, high efficiency, low cost and desirable biocompatibility, the MIHM hydrogel membrane can be large-scale fabricated and used for industry and agriculture.

CO₂ from yeast fermentation was used to prepare a porous hydrogel membrane with decreased transparency, hierarchical pores and increased hydrophobicity.

Novel Swelling-Resistant Sodium Alginate Membrane Branching Modified by Glycogen for Highly Aqueous Ethanol Solution Pervaporation

A novel carbohydrate chain cross-linking method of sodium alginate (SA) is proposed in which glycogen with the branched-chain structure is utilized to cross-link with SA matrix by the bridging of glutaraldehyde (GA). The active layer of SA composite ceramic membrane modified by glycogen and GA for pervaporation (PV) demonstrates great advantages. The branched structure increases the chain density of the active layer, which compresses the free volume between the carbohydrate chains of SA. Large amounts of hydroxyl groups are consumed during the reaction with GA, which reduces the hydrogen bond formation between water molecules and the polysaccharide matrix. The two factors benefit the active layer with great improvement in swelling resistance, promoting the potential of the active layer for the dehydration of an ethanol-water solution containing high water content. Meanwhile, the modified active layer is loaded on the rigid α-Al₂O₃ ceramic membrane by dip-coating method with the enhancement of anti-deformation and controllable thickness of the active layer. Characterization techniques such as SEM, AFM, XRD, FTIR, XPS, and water contact angle are utilized to observe the composite structure and surface morphology of the composite membrane, to probe the free volume variation, and to determine the chemical composition and hydrophilicity difference of the active layer caused by the different glycogen additive amounts. The membrane containing 3% glycogen in the selective layer demonstrates the flux at 1250 g m^-2 h^-1 coupled with the separation factor of 187 in the 25 wt % water content feed solution at the operating temperature of 75 °C, reflecting superior pervaporation processing capacity compared with the general organic PV membranes in the same condition.