Faizal Soyekwo

Nickel hydroxide nanosheet membranes with fast water and organics transport for molecular separation

Two-dimensional nanosheets of late show great promise as novel materials for size-selective separation membranes of high efficiency. Herein, we demonstrate a novel laminated nanofiltration membrane for fast water purification and organic solvent nanofiltration using the 1 nm-thick and 50 nm-wide nickel hydroxide nanosheets that are facilely prepared by a green chemistry method. The resulting membranes exhibit uniform and flectional two-dimensional laminated structure. With about 1 nm high laminated channels, they allow super-fast transport of water and organic solvents. The water and organic fluxes are three orders of magnitude higher than commercially available polymeric nanofiltration membranes. In addition, the membranes have high retention for organic dyes in aqueous and organic solutions. Typically, the 3.18 μm-thick membrane with the molecular weight cut-off of 328 g mol-1 has an outstanding pure water flux of 99 L m-2 h-1 bar-1 and up to 97% rejection for direct yellow dye molecules. The newly developed nickel hydroxide nanosheets and the subsequent membranes have great potential application in water purification, organic solvent filtration and electronic devices.

Metal in situ surface functionalization of polymer-grafted-carbon nanotube composite membranes for fast efficient nanofiltration

The development of inorganic functionalized membranes with the capacity to effectively separate molecules or ions in solutions based on the size or electrostatic interactions is pivotal to purification and separation applications. Herein, we demonstrate a novel green strategy utilizing a completely aqueous process to construct an asymmetrically structured metal surface functionalized polymer–matrix nanocomposite nanofiltration membrane. Crosslinked polyethyleneimine (PEI) is grafted on a carboxylated carbon nanotube intermediate layer incorporated into the macroporous cellulose acetate substrate to form the composite membrane. The resulting membrane is subsequently inorganically modified via an in situ surface reaction of zinc nitrate with excess ammonium hydroxide to produce the hydrophilic and positively charged membrane. Crosslinking enhances the polymer interaction with the carbon nanotube interlayer which in turn endows it with mechanical strength and sustains the membrane pore structure during pressure driven filtration. The functionalized membrane displays outstanding pure water flux of 16.5 ± 1.3 L m−2 h−1 bar−1 while exhibiting good nanofiltration performance of bivalent cations, which is ascribed to the electrostatic repulsion via the Donnan exclusion effect. Meanwhile the membranes exhibit excellent separation of organic molecules and long-term filtration stability. This newly developed approach presents a promising route for the construction of highly permeable nanofiltration membranes for fast purification and separation applications.

LBL assembled polyelectrolyte nanofiltration membranes with tunable surface charges and high permeation by employing a nanosheet sacrificial layer

Polyelectrolyte membranes provide a highly promising platform for an efficient and sustainable nanofiltration (NF) process. The challenge is to prepare polyelectrolyte NF membranes with high permeation. Herein, we report a novel strategy to fabricate a polyelectrolyte membrane via a layer-by-layer (LBL) self-assembly technique with a Ni(OH)2 nanosheet sacrificial layer for a fast NF process. The sacrificial layer helps to deposit a LBL assembled polyelectrolyte layer directly on a microfiltration (MF) substrate and thus results in the formation of a membrane with tiny filtration resistance. Meanwhile, the surface charges and thickness of the membranes can be adjusted facilely by the number of assembled layers. The resultant membranes show excellent NF performances with a high water flux of up to 466 L m−2 h−1 bar−1, perfect rejection for organic dye molecules and moderate salt rejection (88.2% MgSO4). Typically, the 570 nm-thick membrane has the water flux of 198 L m−2 h−1 bar−1, 98% rejection for dyes (Mw 373.9) and 81.3% rejection for MgCl2. Furthermore, the membrane has a good rejection and anti-fouling ability for organic molecules with similar charges. The newly developed strategy has wide application in the fabrication of highly permeable polyelectrolyte membranes.

Imidazolium-functionalized anion exchange membranes using poly(ether sulfone)s as macrocrosslinkers for fuel cells

A series of novel macrocrosslinked imidazolium-based anion exchange membranes (AEMs) with high hydroxide conductivity and dimensional stability were synthesized by crosslinking a poly(vinyl imidazole) ionic liquid with bromide-terminated poly(ether sulfone) via Menshutkin reaction. Fourier transform infrared (FT-IR) and energy dispersive spectrometry (EDS) were used to confirm the chemical structure and successful crosslinking of the AEMs. The contiguous imidazolium cations along the polyolefin backbone are found to aggregate and connect to form continuous hydroxide transport microchannels by the introduction of long hydrophobic poly(ether sulfone) chain as evidenced by atomic force microscopy (AFM). As a consequence, a high hydroxide conductivity of 78.5 mS cm−1 was achieved for the crosslinked PES/PVIIL-0.4 membrane at 80 °C. A single cell test using the PES/PVIIL-0.4 membrane exhibits an open circuit voltage of 1.039 V and peak power density of 109.5 mW cm−2 at the current density of 190 mA cm−2 at 60 °C. This newly developed strategy holds great promise to prevent fuel crossover in alkaline fuel cells.

Multi-cation crosslinked anion exchange membranes from microporous Tröger's base copolymers

Polymers of intrinsic microporosity (PIMs) represent a novel class of membrane materials attracting much attention over the past decade. But challenges still exist in the preparation of anion exchange membranes (AEMs) due to their poor solubility and brittleness. Here we present a new strategy to synthesize soluble PIMs for high performance AEMs. By combining merits of two Trogers base units, the synthesized copolymer exhibits good solubility as well as excellent mechanical properties. The copolymer has good solubility in dimethylsulfoxide (DMSO) after little quaternization and thus permits crosslinking with a long-flexible multi-cation agent. The resulting membrane has good dimensional stability (20.8% swelling ratio at 60 °C) and excellent alkaline resistance. Subsequently, this membrane exhibits a high hydroxide conductivity of 103.9 mS cm−1 (80 °C) at a low ion exchange capacity (IEC) of 1.67 meq g−1. Moreover, this membrane achieves a peak power density of 158 mW cm−2 in a single fuel cell at a current density of 330 mA cm−2 at 60 °C. The presented approach is beneficial for developing high performance PIM-based AEMs and highlights the tremendous potential of multi-cation cross-linked Trogers base AEMs for wide application in energy and separation fields.