Haoqin Zhang

Polydopamine-modified graphene oxide nanocomposite membrane for proton exchange membrane fuel cell under anhydrous conditions

A new approach to the facile preparation of anhydrous proton exchange membrane (PEM) enabled by artificial acid–base pairs is presented herein. Inspired by the bioadhesion of mussel, polydopamine-modified graphene oxide (DGO) sheets bearing –NH2 and –NH– groups are fabricated and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare the nanocomposite membrane. The DGO sheets are interconnected and homogeneously dispersed in SPEEK matrix, which provides unique rearrangement of the nanophase-separated structure and chain packing of nanocomposite membrane through interfacial electrostatic attractions. These attractions meanwhile induce the generation of acid–base pairs along the SPEEK–DGO interface, which then serve as long-range and low-energy-barrier pathways for proton hopping, imparting an enhanced proton transfer via the Grotthuss mechanism. In particular, under both hydrated and anhydrous conditions, the nanocomposite membrane exhibits much higher proton conductivity than the polymer control membrane. The enhanced proton conductivity results in the nanocomposite membrane having elevated cell performances under 120 °C and hydrous conditions, yielding a 47% increase in maximum current density and a 38% increase in maximum power density. Together with the stable conduction property, these results guarantee the nanocomposite membranes promising prospects in high-performance fuel cell under anhydrous and elevated temperature conditions.

Potent antibacterial activity of a novel silver nanoparticle-halloysite nanotube nanocomposite powder

Halloysite nanotubes (HNTs), natural nanotube, have been developed as a support for loading of antibacterial agents. Firstly, HNTs were modified by silane coupling agent (KH-792). And then, modified HNTs were immersed in silver nitrate solution and a complex reaction between the two amino groups of KH-792 and silver ions formed, leading to large clusters on the surface of HNTs. Finally, these silver containing clusters were converted into silver nanoparticles (Ag NPs) with about 5nm diameter by reduction process. A new antibacterial agent, Ag NPs/HNTs, was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy-energy dispersive X-ray analysis (STEM-EDX). The antibacterial test indicated that Ag NPs/HNTs showed good antibacterial performance against Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus).

Synthesis and antibacterial activity of copper-immobilized membrane comprising grafted poly(4-vinylpyridine) chains

Poly(4-vinylpyridine) (P4VP) brushes were grafted onto microporous polysulfone (PSF) membranes via surface-initiated atom transfer radical polymerization (SI-ATRP) and then immobilized copper (II) ions on the modified membrane. Copper-loaded membranes exhibited excellent antibacterial properties with the added advantage of repeated use. The chemical composition and surface morphology of the functionalized membrane was characterized by ATR-FTIR, XPS, SEM, and AFM. The results showed that P4VP brushes clustered to rod-shaped covering and the sub-layer of membrane maintained sponge-like structures at the same time. Additionally, the kinetic study of SI-ATRP reaction revealed that the chain length of P4VP brushes increased linearly as the polymerization time increased. The antibacterial effects of copper-loaded CMPSF-g-P4VP membrane against Escherichiacoli were examined and the antibacterial efficiency reached 100% when 2.49wt.% of copper (II) ions was immobilized on membrane. The presented results could serve as a good starting point for the fabrication of antibacterial CMPSF membranes for waste-water treatment applications.

Constructing Ionic Liquid-Filled Proton Transfer Channels within Nanocomposite Membrane by Using Functionalized Graphene Oxide

Herein, nanocomposite membranes are fabricated based on functionalized graphene oxides (FGOs) and sulfonated poly(ether ether ketone) (SPEEK), followed by being impregnated with imidazole-type ionic liquid (IL). The functional groups (acidic group or basic group) on FGOs generate strong interfacial interactions with SPEEK chains and then adjust their motion and stacking. As a result, the nanocomposite membranes possess tunable interfacial domains as determined by its free volume characteristic, which provides regulated location for IL storage. The stored ILs act as hopping sites for water-free proton conduction along the FGO-constructed interfacial channels. The microstructure at SPEEK-FGO interface governs the IL uptake and distribution in nanocomposite membrane. Different from GO and vinyl imidazole functionalized GO (VGO), the presence of acidic (-SO3H) groups confers the p-styrenesulfonic acid functionalized GO (SGO) incorporated nanocomposite membrane loose interface and strong electrostatic attraction with imidazole-type IL, imparting an enhanced IL uptake and anhydrous proton conductivity. Nanocomposite membrane containing 7.5% SGO attains the maximum IL uptake of 73.7% and hence the anhydrous conductivity of 21.9 mS cm(-1) at 150 °C, more than 30 times that of SPEEK control membrane (0.69 mS cm(-1)). In addition, SGOs generate electrostatic attractions to the ILs confined within SGO-SPEEK interface, affording the nanocomposite membrane enhanced IL retention ability.

Synergistic proton transfer through nanofibrous composite membranes by suitably combining proton carriers from the nanofiber mat and pore-filling matrix

Proton carriers are essential for highly conductive polymer electrolyte membranes. Herein, a series of nanofibrous composite membranes (NFCMs) are prepared by facilely incorporating a polymer matrix (sulfonated poly(ether ether ketone) (SPEEK) or chitosan (CS)) into a PVA/SiO2-based nanofiber mat. By changing the functional groups (acid, base or neutral) on the nanofiber mat, three types of composite proton carriers (I-type: acid–neutral or base–neutral, II-type: acid–acid or base–base, III-type: acid–base or base–acid) are generated at the interfacial domains of NFCMs. These carriers construct continuous conductive pathways by means of the inter-lapped nanofibers and inter-connected polymer matrix. Through the investigation of proton conductivities under both hydrated and low humidity conditions, it is found that NFCMs with I-type proton carriers show low proton conduction properties due to the deficient proton hopping sites. By comparison, II-type carriers display an increase of carrier loading amount, thus affording enhanced proton transfer abilities to NFCMs. III-type proton carriers (acid–base pairs) exhibit a distinct induction effect, by which protonation and deprotonation are promoted, resulting in superior low-energy-barrier proton hopping pathways. Thus, it is reasonable to state that the carrier loading amount and the interactions within them are both crucial to proton migration. In addition, the superior proton conduction abilities of III-type proton carriers confer favorable fuel cell performances on the NFCMs.

Preparation and antibacterial property of SiO2–Ag/PES hybrid ultrafiltration membranes

ABSTRACT Polyethersulfone (PES) ultrafiltration membranes with antibacterial property were prepared by blending with SiO2–Ag composites via immersion precipitation phase inversion method. In this study, silica sol was prepared by tetraethoxysilane via hydrolysis and polymerization, then silica was mixed with AgNO3 solution, and silver nanoparticles were deposited on the surface of SiO2 via reduction reaction. FTIR spectra results showed that silica sol was prepared successfully. SiO2–Ag composites were characterized by transmission electron microscopy (TEM). The hybrid membranes were characterized by permeation properties testing, scanning electron microscopy (SEM), and antibacterial activity analysis. The permeation properties testing indicated that the modified membranes had higher pure water flux than the pure PES membrane. SEM results showed that the structure of membrane was not obviously affected by addition of SiO2–Ag composites. The antibacterial effect of the SiO2–Ag/PES hybrid membrane was assay...

Removal of Methyl Orange by Modified Halloysite Nanotubes

The halloysite nanotubes (HNTs) were modified with the surfactant of hexadecyltrimethylammonium bromide (HDTMA) to form a new adsorbent. The modified HNTs were characterized by the FTIR spectra and thermogravimetric analysis. The results showed that quaternary ammonium cations were grafted on the nanotubes surface successfully. The modified HNTs were used as adsorbent to remove anionic dye of methyl orange (MO) from aqueous solution. The effect of adsorbent dose, initial pH, contact time, initial concentration, ionic strength, and temperature were investigated. The adsorbent exhibited rapid adsorption rate and relatively high adsorption capacity of 91.74 mg/g for MO. The adsorption capacity of the adsorbent increased significantly with the increase of initial concentration, decreased with the increase of ionic strength, and varied little with temperature. Batch kinetic experiments showed that the adsorption fitted pseudo-second-order kinetic model well with correlation coefficients greater than 0.9999. The equilibrium isotherm data were well described by the Langmuir model. The regeneration of modified HNTs could be realized by eluents and the recovered adsorbent could be used again for MO removal. Due to its low cost, high adsorption capacity, and fast adsorption rate, HNTs could be used as an effective adsorbent for MO dye removal.

Preparation of poly(sodium acrylate-acrylamide) superabsorbent nanocomposites incorporating graphene oxide and halloysite nanotubes

To investigate the synergistic effect of multi-nanofillers in a superabsorbent nanocomposite, a poly (sodium acrylate–acrylamide) superabsorbent nanocomposite incorporating graphene oxide and halloysite nanotubes (PAA-AAm–HNT–GO) was synthesized via the inverse suspension polymerization method. Graphene oxide (GO) was prepared by an improved method and halloysite nanotubes (HNTs) were modified by grafting carboxyl groups. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were carried out to examine the structure and morphology of the resulting superabsorbent nanocomposite. It was found that HNTs, GO and poly(sodium acrylate-acrylamide) (PAA-AAm) copolymers combine well with each other during the polymerization process. Meanwhile, the particle sizes of the resulting superabsorbent nanocomposite reduced to about one-tenth of the original size after the introduction of HNTs and GO. The PAA-AAm–HNT–GO superabsorbent nanocomposite exhibited a significant improvement in its water absorption and water retention abilities, due to the synergistic effect of the HNTs and GO, compared with controls, which may make it suitable for use in some special applications that demand a higher water absorption and retention capacity.

Ammonium removal from aqueous solutions by zeolite adsorption together with chemical precipitation

The aim of this study was to remove ammonium from aqueous solution and recycle ammonium. Ammonium removal from aqueous solution by natural and pretreated zeolites, breakthrough curve, chemical regeneration of pretreated zeolite, ammonium removal from regeneration solution by chemical precipitation and NH(4) (+) adsorption isotherms were investigated by conducting a series of batch and continuous experiments in this study. Morphologies and structures of zeolites were analyzed by Surface Area and Pore Size analysis, Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy. The NH(4) (+)-N removal efficiencies by natural and NaCl-treated zeolite were 30.73% and 85.55% respectively at an initial concentration of 100 mg/L. Breakthrough and exhaustion capacities for adsorption of ammonium ions were 3.36 and 4.26 mg /g (NH(4) (+)-N/zeolite), respectively. After chemical regeneration, NH(4) (+)-N removal efficiency by NaCl-treated zeolite only reduced 9.95% than previously. NH(4) (+)-N concentration of the regeneration solution was reduced from 460 to 74.55 mg/L by chemical precipitation. The Freundlich isotherm provided a slightly more consistent fit to the experimental data of ammonium adsorption on NaCl-treated zeolite than Langmuir. Based on the results, it was concluded that the objective of this study had been well achieved.

Preparation and antibacterial property of PES/AgNO3 three-bore hollow fiber ultrafiltration membranes

In this study, a three-bore polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with antibacterial properties was prepared by phase inversion, using PES as the membrane material, N,N-dimethylacetamide (DMAC) as solvent, polyvinylpyrrolidone (PVP) and AgNO3 as additives. The silver particles were detected by X-ray photoelectron spectroscopy. The effect of AgNO3 content on the antibacterial properties and separation performance was studied in detail. The membranes showed good antibacterial activity against Escherichia coli after adding AgNO3 and the antibacterial rate of PES/AgNO3 UF membrane with AgNO3 content of 1 wt% could reach 99.9% after running for 48 hours. Moreover, the bovine serum albumin solution filtration results indicated that the PES/AgNO3 membranes had a certain degree of antifouling performance. Therefore, three-bore PES/AgNO3 membranes have a potential application to reduce both bacterial and organic fouling in water treatment.