Huixian Wang

Recent advances in halloysite nanotube derived composites for water treatment

Halloysite nanotubes (HNTs) are naturally occurring clay mineral with nanotubular structures and have found increasing potential applications in industrial fields. Here, after a brief introduction of the general structure, main properties and newly emerging applications of HNTs, particular attention is paid to HNT-derived applications in water treatment. We mainly review the recent progress in applications of HNT-derived nanocomposites in heavy metal ion, dye or organic pollutant removal from wastewater and HNT-containing membranes for water filtration. The HNT-derived composites exhibit superior properties for water treatment in various ways and are promising to be used in practical applications. Finally, we summarize the predominant mechanisms acting in the applications of water treatment and future prospects are discussed.

MoS2 Nanosheets Functionalized Composite Mixed Matrix Membrane for Enhanced CO2 Capture via Surface Drop-Coating Method.

Molybdenum disulfide (MoS2) is a graphene-like two-dimensional inorganic material, which has been used for the first time as an inorganic nanofiller to prepare a composite mixed matrix membrane to separate CO2 and N2. Polysulfone (PSf) was used as a support substrate and poly(dimethylsiloxane) (PDMS) was used as the gutter layer. The selective layer was prepared by mixing a CO2-philic copolymer Pebax 1657 with MoS2 nanosheets to enhance CO2 permeance. In addition, a simple drop-coating and evaporation method was developed to prepare the selective layer. Both permeability and selectivity of the MoS2-Pebax membrane have exceeded the pristine Pebax membrane. The permeability and selectivity reached to the maximum values of 64 Barrer and 93, respectively, at 0.15 wt % MoS2 nanosheets loadings. This result has been on the Robesons upper bound line. The membrane also showed higher stability. The separation mechanism of the membrane is based on the well-known solution-diffusion mechanism. In addition, the stronger adsorption energy of MoS2 nanosheets to CO2 than N2 also provides the enhancement of gas selectivity.

Preparation and antibacterial activity of copper nanoparticle/halloysite nanotube nanocomposites via reverse atom transfer radical polymerization

Copper nanoparticle supported halloysite nanotubes with a 15 nm lumen and 30 nm external diameter via surface initiation reverse atom transfer radical polymerization were fabricated and showed good antibacterial activity against Escherichia coli (E. coli).

Enzyme-embedded metal–organic framework membranes on polymeric substrates for efficient CO2 capture

In this work, carbonic anhydrase (CA) molecules were embedded into metal–organic frameworks (MOFs) via physical absorption and chemical bonds, which could overcome the enzymatic inactivation and the poor separation property of pristine MOF materials. And then, these nanocomposites (enzyme-embedded MOFs) as the crystal seeds were in situ grown on oriented halloysite nanotube layers to develop novel biocatalytic composite membranes. These membranes exhibited optimal separation performance with a CO2/N2 selectivity of 165.5, about 20.9 fold higher than that of the membrane without embedded CA molecules, surpassing the Robeson upper bound (2008). At the same time, the CO2 permeance increased about 3.2 fold (from 7.6 GPU to 24.16 GPU). Importantly, the biocatalytic composite membranes showed good stability and mechanical properties and were easily scalable, which could be extended to industrial applications.

Three-dimensional self-assembled graphene oxide/enzyme in the presence of copper phosphate

Self-assembly of two-dimensional graphene nanosheets is an important strategy for obtaining graphene architectures for practical applications. However, construction of graphene self-assembled architecture in the presence of protein and copper salts has never been realized. In this paper, a one-pot facile, self-assembled graphene oxide (GO) with tremella-like structure in the presence of lysozyme and copper phosphate was reported. Compared with individual free lysozyme, GO, and even copper phosphate, GO/lysozyme nanocomposites showed excellent antibacterial activity against Escherichia coli, which is about ten-fold higher than that of the free enzyme. This study could provide a new method of three-dimensional self-assembled graphene oxide in the presence of protein and copper phosphate.

Biomimetic material functionalized mixed matrix membranes for enhanced carbon dioxide capture

Carbonic anhydrase (CA) has been widely used in gas separation membranes because of its high affinity for CO2 molecules. In this work, a novel biomimetic material (Co-2,6-bis(2-benzimidazolyl)pyridine, CoBBP) which has a similar molecular structure to the CA enzyme but with higher stability and a lower price was successfully synthesized. The excellent thermal stability, dispersibility and high CO2 selectivity make CoBBP a promising alternative to CA. Then, a series of Pebax–CoBBP mixed matrix membranes were constructed to explore their capability for CO2/N2 separation. Compared to the pristine Pebax-1657, the Pebax–CoBBP mixed matrix membrane with the optimized 1.33 wt% CoBBP loading showed an improved CO2 permeability of 675.5 barrer and a CO2/N2 selectivity of 62, surpassing the Robeson upper bound (2008). Furthermore, the hydrogen bonds between CoBBP and polyamide chains improved the chain stiffness of the linear glassy polymer, ensuring good operational mechanical stability. In short, this work could provide a promising method to exploit alternatives to the CA enzyme and to fabricate biomimetic membranes.