Wai Han Mak

Surface modification offers a straightforward means to alter and enhance the properties and performance of materials, such as nanofiltration membranes for water softening. Herein, we demonstrate how a membrane’s surface charge can be altered by grafting different electrostatically varying copolymers onto commercial membrane surfaces using perfluorophenylazide (PFPA) photochemistry for enhanced ion separation performance. The native membrane’s performance—i.e., in terms of divalent cation separation—with copolymer coatings containing a positively charged quaternary ammonium (−N(Me)₃⁺), a negatively charged sulfonate (−SO₃^–), and an essentially neutral zwitterion (sulfobetaine, −N(Me)₂R₂⁺, and −SO₃^–), respectively, indicates that: (a) the sulfonated polymer induces robust Coulombic exclusion of divalent anions as compared to the negatively charged native membrane surface on account of its higher negative charge; (b) the positively charged ammonium coating induces exclusion of cations more effectively than the native membrane; and significantly, (c) the zwitterion polymer coating, which reduces the surface roughness and improves wettability, in spite of its near-neutral charge enhances exclusion of both divalent cations and anions on account of aperture sieving by the compact zwitterion polymer that arises from its ability to limit the size of ions that transport through the polymer along with dielectric exclusion. The outcomes thereby inform new pathways to achieve size- and charge-based exclusion of ionic, molecular, and other species contained in liquid streams.

Thin-film composite (TFC) membranes are favored for precise molecular sieving in liquid phase separations; they possess high permeability due to the minimal thickness of the active layer and the high porosity of the support layer. However, current TFC membrane fabrication techniques are limited by the available materials for the selective layer and do not demonstrate the level of structural control needed to substantially advance organic solvent nanofiltration (OSN) membrane technology. In this work, we employ the newly developed thin-film lift off (T-FLO) technique to fabricate polybenzimidazole (PBI) TFC membranes with porous support layers uniquely tailored to OSN. The drop-cast dense PBI selective layers endow the membranes with almost complete rejection of common small dye molecules. The polymeric support layer is optimized by a combinatorial approach using 4 different monomers that alter the cross-linking density and polymer chain flexibility of the final composite. These two properties substantially affect the porogen holding capacity of the reticular polymer network, leading to the formation of different macro-pore structures. With a 150 nm-thick PBI selective layer and fine-tuning of the support layer, the resulting membrane achieves stable and superior permeance of 14.0, 11.7, 16.4, 11.4, 17.1 and 19.7 L m-2 h-1 bar-1 for water, ethanol, methanol, isopropanol, THF and acetonitrile, respectively.

Graphene oxide (GO) membranes have great potential due to their low-friction water permeation combined with unique molecular sieving ability. However, the practical use of deposited GO membranes is limited by the inferior mechanical robustness in the composite structure derived from conventional deposition methods. Here, we report a nanostructured GO membrane that possesses great permeability and mechanical robustness. This composite membrane containing an ultrathin selective GO nanofilm (as low as 32 nm thick) and a post-synthesized macroporous support layer exhibits excellent stability in water and under practical permeability testing. With precise optimizations in both selective and support layers, unprecedented water permeability (47 liters m-2 hr-1 bar-1) and high retention (>98% of solutes with hydrated radii larger than 4.9 Å) were obtained.

Single-phase metal dodecaboride (MB₁₂) solid solutions, Zr_0.5Y_0.5B₁₂ and Zr_0.5U_0.5B₁₂ were prepared by arc melting from the pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and ¹⁰B and ¹¹B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr_1-xY_xB₁₂ were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as well as “templating” and patterning effects of the surface morphology. The hardness of the Zr_0.5Y_0.5B₁₂ phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ~17% higher than that of its parent compounds, ZrB₁₂ and YB₁₂, with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr_0.5U_0.5B₁₂ is ~54% higher than that of its UB₁₂ parent. The dodecaborides were confirmed to be metallic by band structure calculations, diffuse reflectance UV-vis and NMR spectroscopies. The nature of the dodecaboride colors – violet for ZrB₁₂ and blue for YB₁₂ – can be attributed to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y⁺3, Zr⁺⁴ and U^+5/+6. The superconducting transition temperatures (T_c) of the dodecaborides were determined to be 4.5 and 6.0 K for YB₁₂ and ZrB₁₂, respectively, as shown by resistivity and SQUID (superconducting quantum interference device) measurements. The T_c of the Zr_0.5Y_0.5B₁₂ solid solution was suppressed to 2.5 K.

Conjugated polyaniline has shown anticorrosive, hydrophilic, antibacterial, pH-responsive, and pseudocapacitive properties making it of interest in many fields. However, in situ grafting of polyaniline without harsh chemical treatments is challenging. In this study, we report a simple, fast, and non-destructive surface modification method for grafting tetraaniline (TANI), the smallest conjugated repeat unit of polyaniline, onto several materials via perfluorophenylazide photochemistry. The new materials are characterized by nuclear magnetic resonance (NMR) and electrospray ionization (ESI) mass spectroscopy. TANI is shown to be covalently bonded to important carbon materials including graphite, carbon nanotubes (CNTs), and reduced graphene oxide (rGO), as confirmed by transmission electron microscopy (TEM). Furthermore, large area modifications on polyethylene terephthalate (PET) films through dip-coating or spray-coating demonstrate the potential applicability in biomedical applications where high transparency, patternability, and low bio-adhesion are needed. Another important application is preventing biofouling in membranes for water purification. Here we report the first oligoaniline grafted water filtration membranes by modifying commercially available polyethersulfone (PES) ultrafiltration (UF) membranes. The modified membranes are hydrophilic as demonstrated by captive bubble experiments and exhibit extraordinarily low bovine serum albumin (BSA) and Escherichia coli adhesions. Superior membrane performance in terms of flux, BSA rejection and flux recovery after biofouling are demonstrated using a cross-flow system and dead-end cells, showing excellent fouling resistance produced by the in situ modification.

2D nanomaterials are finding numerous applications in next‐generation electronics, consumer goods, energy generation and storage, and healthcare. The rapid rise of utility and applications for 2D nanomaterials necessitates developing means for their mass production. This study details a new compressible flow exfoliation method for producing 2D nanomaterials using a multiphase flow of 2D layered materials suspended in a high‐pressure gas undergoing expansion. The expanded gas–solid mixture is sprayed in a suitable solvent, where a significant portion (up to 10% yield) of the initial hexagonal boron nitride material is found to be exfoliated with a mean thickness of 4.2 nm. The exfoliation is attributed to the high shear rates ( > 10⁵ s⁻¹) generated by supersonic flow of compressible gases inside narrow orifices and converging‐diverging channels. This method has significant advantages over current 2D material exfoliation methods, such as chemical intercalation and exfoliation, as well as liquid phase shear exfoliation, with the most obvious benefit being the fast, continuous nature of the process. Other advantages include environmentally friendly processing, reduced occurrence of defects, and the versatility to be applied to any 2D layered material using any gaseous medium. Scaling this process to industrial production has a strong possibility of reducing the cost of creating 2D nanomaterials.

Because the transition from oxidative phosphorylation to anaerobic glycolytic metabolism is a hallmark of cancer progression, approaches to identify single living cancer cells by their unique glucose metabolic signature would be useful. Here, we present nanopipettes specifically developed to measure glucose levels in single cells with temporal and spatial resolution, and we use this technology to verify the hypothesis that individual cancer cells can indeed display higher intracellular glucose levels. The nanopipettes were functionalized as glucose nanosensors by immobilizing glucose oxidase (GOx) covalently to the tip so that the interaction of glucose with GOx resulted in a catalytic oxidation of β-d-glucose to d-gluconic acid, which was measured as a change in impedance due to drop in pH of the medium at the nanopipette tip. Calibration studies showed a direct relationship between impedance changes at the tip and glucose concentration in solution. The glucose nanosensor quantified single cell intracellular glucose levels in human fibroblasts and the metastatic breast cancer lines MDA-MB-231 and MCF7 and revealed that the cancer cells expressed reproducible and reliable increases in glucose levels compared to the nonmalignant cells. Nanopipettes allow repeated sampling of the same cell, as cells remain viable during and after measurements. Therefore, nanopipette-based glucose sensors provide an approach to compare changes in glucose levels with changes in proliferative or metastatic state. The platform has great promise for mechanistic investigations, as a diagnostic tool to distinguish cancer cells from nonmalignant cells in heterogeneous tissue biopsies, as well as a tool for monitoring cancer progression in situ.

In this report, we demonstrate a hand-held wireless voltage-clamp amplifier for current measurement of nanopore sensors. This amplifier interfaces a sensing probe and connects wirelessly with a computer or smartphone for the required stimulus input, data processing, and storage. To test the proposed signal transduction by ion nanogating (STING) wireless amplifier, in the current study the system was tested with a nano-pH sensor to measure pH of standard buffer solutions and the performance was compared against the commercial voltage-clamp amplifier. To the best of our knowledge, STING amplifier is the first miniaturized wireless voltage-clamp platform operated with a customized smartphone application (app).