Evaluation of the Kinetic of Cu2+ Adsorption in the PVA Membranes Crosslinked with Sulfosuccinic and Citric Acids

Membrane of Poly (vinyl alcohol) (PVA) crosslinked with sulfosuccinic acid (SSA) and citric acid (CA) were characterized for the adsorption of copper ions (Cu2+). Usually the membranes used for this application have inorganic materials in their structure. However, when using only these acids, it was verified that the membrane containing SSA presents less swelling than the PVA and absorbs a higher content of Cu2+ when compared to the membrane containing CA. Therefore, it can be assumed that the membrane containing SSA can be used to cover soils that need protection against this type of ion. leaching. Kinetic models of diffusional and chemical control were used to understand the interaction phenomena of adsorption of ions and membranes. The mixed control kinetic model was also evaluated, in which it was possible to evaluate different parameters regarding the interaction ions and membranes. The obtained results indicated that the developed process has relevant utility. The kinetic modeling results contribute to a better understanding of heating phenomena of adsorption and also to the development of new cleaner technologies.

Synthesis of cation exchange membranes for capacitive deionization based on crosslinked polyvinyl alcohol with citric acid

Constructing new cation exchange membranes (CEM) has been regarded as an easy and effective approach to improving the capacitive deionization (CDI) system. In this study, a new method of fabrication of CEM was introduced by crosslinking sulfosuccinic acid (SSA) and citric acid (CA). The SSA and CA were crosslinked with polyvinyl alcohol (PVA) to fabricate CEMs in a series of conditions. The ion transference number for each fabricated membrane was tested to select the optimal recipe. The membrane fabricated by the selected method was then tested in the CDI system and the results show that the total percentage of SSA could be reduced from 5% to 1% by adding 5 g of non-toxic and inexpensive CA. The cost of preparing the membrane also decreased from US$0.18 per square meter to US$0.03. The adsorption capacity and the charge efficiency of membrane capacitive deionization system (MCDI) coated with a PVA/SSA/CA layer (mass ratio 10:1:5) was compared with the normal CDI and the MCDI coated with the original membrane (PVA:SSA = 19:5), which is named O-MCDI). The results show that with the modified membrane, the adsorption capacity and the charge efficiency can be enhanced by 18% and 28% compared with the CDI. In addition, although the cost is reduced, the desalination efficiency is still guaranteed. The adsorption capacity and charge efficiency are still increased by about 3% compared with the O-MCDI.

Chemically and Thermally Crosslinked PVA-Based Membranes: Effect on Swelling and Transport Behavior

The novel poly(vinyl alcohol) (PVA)-based membranes were prepared using the two-step crosslinking approach: the chemical crosslinking of PVA using sulfosuccinic acid (SSA) (0–50 wt.%) and the thermal treatment (120–160 °C). The membrane composition and crosslinking temperature were optimized in terms of the mechanical and transport properties. The FTIR-ATR analysis revealed that the increase of the SSA concentration and crosslinking temperature resulted in the rise of the ester bond bands intensity due to the esterification reaction between PVA and SSA. As a consequence, the PVA-based membrane with 50 wt % SSA and crosslinked at 140 °C showed the reduced Young’s modulus (from 1266.2 MPa to 1.4 MPa) and elongation at break (from 316% to 66%) in comparison with the pure PVA membrane. The studied swelling behavior of the obtained membranes revealed significantly higher water sorption than that in methanol and propal-2-ol whatever the crosslinking temperature. The performed studies provide a new way of tailoring the membrane physicochemical properties, in particular, the surface hydrophilicity. In addition, the obtained results are crucial for the design and elaboration of the polymer membranes for the pervaporative separation of the liquid-liquid mixtures, in particular, for the alcohol dehydration.

Crosslinked Sulfonated Poly(vinyl alcohol)/Graphene Oxide Electrospun Nanofibers as Polyelectrolytes

Taking advantage of the high functionalization capacity of poly(vinyl alcohol) (PVA), bead-free homogeneous nanofibrous mats were produced. The addition of functional groups by means of grafting strategies such as the sulfonation and the addition of nanoparticles such as graphene oxide (GO) were considered to bring new features to PVA. Two series of sulfonated and nonsulfonated composite nanofibers, with different compositions of GO, were prepared by electrospinning. The use of sulfosuccinic acid (SSA) allowed crosslinked and functionalized mats with controlled size and morphology to be obtained. The functionalization of the main chain of the PVA and the determination of the optimum composition of GO were analyzed in terms of the nanofibrous morphology, the chemical structure, the thermal properties, and conductivity. The crosslinking and the sulfonation treatment decreased the average fiber diameter of the nanofibers, which were electrical insulators regardless of the composition. The addition of small amounts of GO contributed to the retention of humidity, which significantly increased the proton conductivity. Although the single sulfonation of the polymer matrix produced a decrease in the proton conductivity, the combination of the sulfonation, the crosslinking, and the addition of GO enhanced the proton conductivity. The proposed nanofibers can be considered as good candidates for being exploited as valuable components for ionic polyelectrolyte membranes.