Grafting polysiloxane onto ultrafiltration membranes to optimize surface energy and mitigate fouling.

Conventional approaches to mitigate fouling of membrane surfaces impart hydrophilicity to the membrane surface, which increases the water of hydration and fluidity near the surface. By contrast, we demonstrate here that tuning the membrane surface energy close to that of the dispersive component of water surface tension (21.8 mN m-1) can also improve the antifouling properties of the membrane. Specifically, ultrafiltration (UF) membranes were first modified using polydopamine (PDA) followed by grafting of amine-terminated polysiloxane (PSi-NH2). For example, with 2 g L-1 PSi-NH2 coating solution, the obtained coating layer contains 53% by mass fraction PSi-NH2 and exhibits a total surface energy of 21 mN m-1, decreasing the adsorption of bovine serum albumin by 44% compared to the unmodified membrane. When challenged with 1 g L-1 sodium alginate in a constant-flux crossflow system, the PSi-NH2-grafted membrane exhibits a 70% lower fouling rate than the pristine membrane at a water flux of 110 L (m2 h)-1 and good stability when cleaned with NaOH solutions.

Rightsizing Nanochannels in Reduced Graphene Oxide Membranes by Solvating for Dye Desalination.

Membranes with high water permeance, near-zero rejection to inorganic salts (such as NaCl and Na2SO4), and almost 100% rejection to organic dyes are of great interest for the dye desalination (the separation of dyes and salts) of textile wastewater. Herein, we prepared reduced graphene oxide membranes in a solvation state (S-rGO) with nanochannel sizes rightly between the salt ions and dye molecules. The S-rGO membrane rejects >99.0% of Direct Red 80 (DR 80) and has almost zero rejection for Na2SO4. By contrast, conventional GO or rGO membranes often have channel sizes smaller than divalent ions (such as SO42-) and thus high rejection for Na2SO4. More interestingly, high salinity in typical dye solutions decreases the channel size in the S-rGO membranes and thus increases the dye rejection, while the Na2SO4 rejection decreases because of the negatively charged surface on GO and the salt screening effect. The membranes also show pure water permeance as high as 80 L m-2 h-1 bar-1, which is about 8 times that of commercial NF 90 membrane and 2 times that of a commercial ultrafiltration membrane (with a molecular weight cutoff of 2000 Da), rendering their promise for practical dye desalination.

Structure-Function Assessment of Mannosylated Poly(ß-amino esters) upon Targeted Antigen Presenting Cell Gene Delivery.

Antigen presenting cell (APC) gene delivery is a promising avenue for modulating immunological outcomes toward a desired state. Recently, our group developed a delivery methodology to elicit targeted and elevated levels of APC-mediated gene delivery. During these initial studies, we observed APC-specific structure-function relationships with the vectors used during gene delivery that differ from current non-APC cell lines, thus, emphasizing a need to re-evaluate vector-associated parameters in the context of APC gene transfer. Thus, we describe the synthesis and characterization of a second-generation mannosylated poly(ß-amino ester) library stratified by molecular weight. To better understand the APC-specific structure-function relationships governing polymeric gene delivery, the library was systematically characterized by (1) polymer molecular weight, (2) relative mannose content, (3) polyplex biophysical properties, and (4) gene delivery efficacy. In this library, polymers with the lowest molecular weight and highest relative mannose content possessed gene delivery transfection efficiencies as good as or better than commercial controls. Among this group, the most effective polymers formed the smallest polymer-plasmid DNA complexes (∼300 nm) with moderate charge densities (<10 mV). This convergence in polymer structure and polyplex biophysical properties suggests a unique mode of action and provides a framework within which future APC-targeting polymers can be designed.

Modeling the transport of neutral disinfection byproducts in forward osmosis: Roles of reverse salt flux.

The rejection of disinfection byproducts (DBPs) is an important consideration for the application of forward osmosis (FO) in wastewater recycling. However, the transport of organic compounds in FO is not well predicted by existing models, partially because these models have not incorporated the effect of reverse salt flux, a phenomenon previously shown to influence the transport of pharmaceutical compounds. In this study, we investigated the effects of reverse salt flux on DBP transport in FO and the corresponding mechanisms. We used a commercial Aquaporin membrane and tested sixteen DBPs relevant to wastewater recycling. Using draw solutions constituted by NaCl, MgSO4, or glucose in a bench-scale FO system, we first confirmed that higher reverse salt flux resulted in lower DBP permeance. By integrating results from the bench-scale FO system and those from diffusion cell tests, we showed that two mechanisms contributed to the hindered DBP transport: the steric hindrance in the active layer caused by the presence of the draw solute and the retarded diffusion of DBPs in the support layer via a "salting-out" effect. Lastly, we developed a modified solution-diffusion model incorporating these two mechanisms by accounting for the free volume occupied by draw solute molecules in the active layer and by introducing the Setschenow constant, respectively. The modified model significantly improved the prediction of permeance for halogenated DBPs, and revealed the relative importance of steric hindrance (dominant for large DBPs) and retarded diffusion (dominant for hydrophobic DBPs). The modified model did not accurately predict the permeance of nitrosamines, attributable to their extremely high hydrophilicity or large size.

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.