Zhenping Qin

Covalent crosslinked polyelectrolyte complex membrane with high negative charges towards anti-natural organic matter fouling nanofiltration

Removal of natural organic matter (NOM) from drinking water by membrane technology is attracting increasing attention. However, the fouling of the membrane by NOM is one of the biggest obstacles restricting its widespread application. Therefore an anti-NOM fouling polyelectrolyte complex (PEC) membrane was obtained by creating a negatively charged multilayer on a polyacrylonitrile (PAN) supporting membrane using a layer-by-layer assembly method. To improve the stability of the PEC membrane, the electrostatically assembled (poly(ethyleneimine)/poly(sodium 4-styrenesulfonate))n/PAN membranes were crosslinked by glutaraldehyde. It was found that the zeta potential of the membrane surface decreased after chemical crosslinking, which further improved the electrostatic repulsion to NOM and thus improved the anti-NOM fouling property. Results of a 30 day nanofiltration operation showed the crosslinked membrane had good stability and gave a higher rejection of NOM; the permeance of the crosslinked membrane was double that of the uncrosslinked membrane.

Self-cleaning and antifouling nanofiltration membranes—superhydrophilic multilayered polyelectrolyte/CSH composite films towards rejection of dyes

Superhydrophilic poly(ethyleneimine)/poly(sodium-4-styrenesulfonate) (PEI/PSS)–calcium silicate hydrate (CSH) multilayered membranes (PEI/PSS)2.0(PEI/PSS–CSH)n on polyacrylonitrile (PAN) substrate were prepared via layer-by-layer (LbL) assembly with in situ precipitation of consecutive Ca2+-integrated multilayered polyelectrolytes and sodium silicate. The surface structure and properties of these multilayered membranes (PEI/PSS)2.0(PEI/PSS–CSH)n were characterized by zeta potential, infrared resonance spectra, water contact angles, scanning electron microscopy, and atomic force microscopy, and the separation performances were evaluated by rejection of dyes, such as xylenol orange (XO) and rhodamine B (RB). The long term performance, self-cleaning and antifouling behaviors were investigated by retention of aqueous solutions of both dyes and bovine serum albumin (BSA) aqueous solution. The results indicated that the in situ incorporation of controlled CSH contents into PEI/PSS multilayers greatly improved the hydrophilicity of the multilayered membranes, resulting in the formation of a superhydrophilic (PEI/PSS–CSH)2.0 membrane with a water contact angle of 2.1° and the highest permeate fluxes of 191.5 and 183.5 L m−2 h−1 MPa−1 accompanied by the rejection of 94.0% and 91.2% for XO and RB aqueous solutions, respectively. When the number of assembled (PEI/PSS–CSH)n multilayers was higher than 2.0 bilayers, the rejection increased but the flux markedly decreased to XO and RB dyes, showing a characteristic trade-off phenomenon. Moreover, the superhydrophilic (PEI/PSS–CSH)2.0 membrane possessed a higher antifouling and self-cleaning behavior than the hydrophilic polyelectrolytes (PEI/PSS)2.0.

One-Step Transformation from Hierarchical-Structured Superhydrophilic NF Membrane into Superhydrophobic OSN Membrane with Improved Antifouling Effect

The hierarchical-structured superhydrophilic poly(ethylenimine)/poly(acrylic acid) (PEI/PAA)calcium silicate hydrate (CSH) multilayered membranes (PEI/PAA-CSH)n were prepared as aqueous nanofiltration (NF) membrane, and then they were transformed into superhydrophobic organic solvent nanofiltration (OSN) membranes by one-step modification of trimethylperfluorinatedsilane (PFTS). Investigation on surface structures and properties of these multilayered membranes (PEI/PAA-CSH)n indicated that the hierarchical-structured (PEI/PAA-CSH)n multilayered membrane produced by in situ incorporation of CSH aggregates into PEI/PAA multilayers facilitated its one-step transformation from superhydrophilicity into superhydrophobicity. Both of the superwetting membranes showed better nanofiltration performances for retention of dyes of water and ethanol solution, respectively. Moreover, the long-term performance and antifouling behaviors, investigated by retention of methyl blue (MB), bovine serum albumin (BSA), and humic acid (HA) aqueous water solution and nonaqueous ethanol solution indicated that both of the superhydrophilic and superhydrophobic membrane showed higher stability and excellent antifouling property.

Low-Temperature Synthesis of Anatase TiO2 Nanoparticles with Tunable Surface Charges for Enhancing Photocatalytic Activity

In this work, the positively or negatively charged anatase TiO2 nanoparticles were synthesized via a low temperature precipitation-peptization process (LTPPP) in the presence of poly(ethyleneimine) (PEI) and poly(sodium4- styrenesulfonate) (PSS). X-ray diffraction (XRD) pattern and high-resolution transmission electron microscope (HRTEM) confirmed the anatase crystalline phase. The charges of the prepared TiO2, PEI-TiO2 and PSS-TiO2 nanoparticles were investigated by zeta potentials. The results showed that the zeta potentials of PEI-TiO2 nanoparticles can be tuned from +39.47 mV to +95.46 mV, and that of PSS-TiO2 nanoparticles can be adjusted from −56.63 mV to −119.32 mV. In comparison with TiO2, PSS-TiO2 exhibited dramatic adsorption and degradation of dye molecules, while the PEI modified TiO2 nanoparticles showed lower photocatalytic activity. The photocatalytic performances of these charged nanoparticles were elucidated by the results of UV-vis diffuse reflectance spectra (DRS) and the photoluminescence (PL) spectra, which indicated that the PSS-TiO2 nanoparticles showed a lower recombination rate of electron-hole pairs than TiO2 and PEI-TiO2.

Hydrophilic modification of HDPE microfiltration membrane by corona-induced graft polymerization

Abstract Hydrophilic modification of high-density polyethylene membrane was performed with the introduction of peroxide onto the membrane surface by corona discharge treatment, followed by graft polymerization with acrylic acid. The surface graft polymerization was confirmed by attenuated total reflection-infrared and X-ray photo spectroscopy. Surface hydrophilicity was investigated by measuring the contact angles and moisture adsorption of the modified membrane. The results indicated that the modified membrane showed a significant increase in hydrophilicity. And water flux of the film increased from 102 L/m2 h of the virgin film to 200 L/m2 h of the grafted film, while the bovine serum albumin solution flux of the membrane increased from 43 L/m2 h of the virgin film to 98 L/m2 h of the modified membrane.

Preparation of Micro-porous Chitosan Membrane and Its Adsorption Property for Cr(VI) Ions

Chitosan (CS) micro-porous membranes were prepared by blending-phase inversion method using chitosan as film-forming polymer, polyethylene glycol (PEG) as porogen and glycerol as plasticizer. Adsorption experiments were conducted under varied Cr(VI) ions concentration, pH values, contact time and temperature. The results indicated that when the ratio of chitosan to polyethylene glycol and glycerol was 1:0.5:0.5 at pH of 2.79, the prepared CS membrane exhibited the highest adsorption capacity of 168.41 mg g−1 under Cr(VI) ions concentration of 100 mg L−1, contact time of 4 h, and membrane dosage of 10.0 mg. Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms at different Cr(VI) ions concentrations. The equilibrium data was found to be fitted well to the Langmuir isotherm. Pseudo-first-order and pseudo-second-order kinetics models were used to describe the membrane adsorption.

Adsorption of Cd(II) Ion on Aragonite Calcium Carbonate Crystals

Calcium carbonate was prepared with urea hydrolytic method, and was characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffract meter (XRD) and Ratio of surface area porosity analyzer. It is revealed that the Calcium carbonate obtained here is aragonite calcium carbonate crystals. The adsorption of Cd(II) ion onto aragonite calcium carbonate crystals were studied via investigating parameters as effect of contact time, dosage of aragonite calcium carbonate crystals and initial heavy metal concentration using static batch adsorption experiments. The results reveal that the removal rate of Cd(II) ion is 83% under the following conditions: temperature as 25 ℃, contact time as 120 min, initial concentration of the Cd(II) ion as 100 mg/L, and dosage of aragonite calcium carbonate crystals as 0.6 g/L. The adsorption capacity reaches 200 mg/g. Meanwhile the results suggest that the adsorption of the Cd(II) ion by the aragonite calcium carbonate crystals well follows the pseudo-second-order kinetics model, and the Langmuir isotherm model provides a good fit to the experimental data.