Effects of Carbon Spacer Length on Conformational Transitions and Protein Adsorption of Polyzwitterions.

The properties of polyzwitterions are closely linked to their carbon spacer length (CSL) between oppositely charged groups. A thorough understanding of the effect of CSL on the properties of polyzwitterion-functionalized membranes is important for their fouling resistance and separation performances. In this work, polyzwitterion-functionalized membranes with different CSLs are prepared by coupling selective swelling-induced pore generation with zwitterionization, and the investigation is focused on comprehending the molecular mechanisms underlying protein resistance and conformational transitions within polyzwitterions under varying CSLs. The zwitterionized films show an enhancement in the surface negative potential with the increase of CSL, attributed to the negatively charged groups distanced from the positively charged groups. Quartz crystal microbalance with dissipation (QCM-D) demonstrates that zwitterionized films with different CSLs display distinct levels of resistance to protein adsorption. The trimethylamine N-oxide-derived polymer (PTMAO, CSL = 0) zwitterionized film shows the highest resistance compared to the poly(3-[dimethyl(2'-methacryloyloxyethyl] ammonio) ethanesulfonate (PMAES, CSL = 2) zwitterionized film and the poly(sulfobetaine methacrylate) (PSBMA, CSL = 3) zwitterionized film, owing to its electrical neutrality and pronounced hydrophilicity. Moreover, analysis of the anti-polyelectrolyte behaviors reveals that PTMAO does not undergo a significant conformation transition in deionized water and salt solutions, while the conformations of PMAES and PSBMA display to be more salt-dependent as the CSL increases, attributed to their increased polarization and dipole moment. As a result, the permeability of zwitterionized membranes exhibits enhanced salt responsiveness with the increase in CSL. The findings of this study are expected to facilitate the design of adsorption-resistant surfaces desired in diverse fields.

Absolute and Fast Removal of Viruses and Bacteria from Water by Spraying-Assembled Carbon-Nanotube Membranes.

Membrane separation is able to efficiently remove pathogens like bacteria and viruses from water based on size exclusion. However, absolute and fast removal of pathogens requires highly permeable but selective membranes. Herein, we report the preparation of such advanced membranes using carbon nanotubes (CNTs) as one-dimensional building blocks. We first disperse CNTs with the help of an amphiphilic block copolymer, poly(2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS, abbreviated as BCP). The PS blocks adsorb on the surface of CNTs via the π-π interaction, while the PDMAEMA blocks are solvated, thus forming homogeneous and stable CNT dispersions. We then spray the CNT dispersions on porous substrates, producing composite membranes with assembled CNT layers as the selective layers. We demonstrate that the optimized membrane shows 100% rejection to phage viruses and bacteria (Escherichia coli) while giving a water permeance up to ∼3300 L m-2 h-1 bar-1. The performance of the resultant BCP/CNT membrane outperforms that of state-of-the-art membranes and commercial membranes. The BCP/CNT membrane can be used for multiple runs and regenerated by water rinsing. Membrane modules assembled from large-area membrane sheets sustain the capability of absolute and fast removal of viruses and bacteria.

N-Doping Carbon-Nanotube Membrane Electrodes Derived from Covalent Organic Frameworks for Efficient Capacitive Deionization.

Capacitive deionization (CDI) is an energy-efficient and environmentally friendly electrochemical desalination technology which has attracted increasing attention in recent years. Electrodes are crucial to the performance of CDI processes, and utilizing a carbon-nanotubes (CNTs) membrane to fabricate electrodes is an attractive solution for advanced CDI processes. However, the strong hydrophobicity and low electrosorption capacity limit applications of CNTs membranes in CDI. To solve this problem, we introduce crystalline porous covalent organic frameworks (COFs) into CNTs membranes to fabricate N-doping carbon-nanotubes membrane electrodes (NCMEs). After solvothermal growth and carbonization, CNTs membranes are successfully coated with imine-based COFs and turned into integrated NCMEs. Comparing with the CNTs membranes, the NCMEs exhibit an ∼2.3 times higher electrosorption capacity and superior reusability. This study not only confirms that COFs can be used as high-quality carbon sources but also provides a new strategy to fabricate high-performance CDI electrodes.

Single-Layered Nanosheets of Covalent Triazine Frameworks (CTFs) by Mild Oxidation for Molecular-Sieving Membranes.

Covalent triazine framework (CTF) nanosheets featured with uniform intrinsic nanoporosity and excellent stability are promising building blocks for fast, selective membranes. However, it remains challenging to produce ultrathin CTF nanosheets, significantly hindering the development of CTF-based membranes. Herein, we develop a mild oxidation strategy to exfoliate CTFs, enabling the preparation of highly permeable membranes with stacked CTF nanosheets as the selective layers. The interlamellar spacing of CTF is effectively expanded following the mechanism of "proton donating-accepting" in which dimethyl sulfoxide (DMSO) works as a soft oxidant, leading to ultrathin CTF nanosheets with the assistance of ultrasonication. Furthermore, oxygen-containing functional groups are also introduced onto the CTF nanosheets through mild oxidation, improving surface hydrophilicity. The CTF nanosheet can be stacked onto porous substrates by vacuum filtration to form composite membranes with the thickness of the stacked CTF nanosheets down to ∼30 nm. Thus-obtained membranes exhibit impressive dye separation performances with both high water permeance and high rejection. This work provides not only an efficient method to synthesize ultrathin CTF nanosheets but also a process to prepare fast but selective membranes for molecular separations.

Silica nanotubes decorated by pH-responsive diblock copolymers for controlled drug release.

A novel nanocontainer, which has silica nanotube (SNT) core and pH-sensitive polymer shell attaching on the exterior surface of silica nanotube, is presented in this paper. Polymer nanorods, which are conveniently fabricated though polymerization-induced self-assembly and reorganization method, are used as templates for the deposition of silica to fabricate hybrid nanorods. Calcination of as-synthesized silica hybrid nanorods leads to hollow SNTs. SNTs are functionalized with reversible addition-fragmentation chain transfer (RAFT) agent, then surface RAFT polymerization is conducted to get poly(2-(diethylamino)ethyl methacrylate)-b-poly(oligo(ethylene glycol) methacrylate)-coated SNTs (SNT-PDEAEMA-b-POEGMA). Doxorubicin (DOX) can be encapsulated in SNT-PDEAEMA-b-POEGMA, and controlled release of loaded DOX is achieved by adjusting pH of the medium. In vitro cell viability and cellular internalization study confirm the potential application of this nanocontainer in drug and gene delivery.