Position£ºhomepage ¡ú Academic Achivements
Primary Academic Achivements
1. Species¡¯ tranport and catalyzed water-splitting in multi-layered bipolar membranes

    Several theoretical voltage drop models have been put forward for the bipolar membranes of some conventional physical configurations and effective methods have been founded for reducing water-splitting voltage on the basis of analysis on the models. Much attention was paid to the mechanism study on the water-splitting catalyzed by amphoteric hydroxides and polymer weak acids or alkalis, and it was found that the catalysis could be ascribed to the increase in water dissociation constants in free aqueous solutions. Accordingly, we presented a principle for selecting catalyst to enhance the water-splitting in bipolar membranes(Science in China, Ser.B 1999,42(6):589-598£»Desalination£¬2002£¬in press£»Chinese J Chem Eng., 2001,9(2):179-185£»Chem Res Chin Uni., 2001,17(4):457-464)¡£

    Beside the mechanism study on the water-splitting in bipolar membranes, the application of this technology has been undergoing. We have successful applied the water-splitting to organic acid preparation and ion separation in ocean chemical industry. In particular, 1 M or so citric acid can be prepared from sodium citrate. This result, most likely, will be used to reform the current processes of organic acid production, and thus attracted much attention of the experts on organic acid production. Invited by international craft brothers and recommended by the president of European Membrane Society, we submitted two reviews to Desalination and Resources Recycle, Recovery, and gained more attention from the world. Dr. A J B Kemperman (Twente University, the Netherlands; chief editor of Handbook of bipolar membrane technology, and organizer of European Bipolar Membrane Process) wrote to us many times to show his agreement on our ideas and willingness to cooperate with us or exchange students). Many scholars from Japan, Russia, Spain and Singapore also expressed their interests in our reviews. Prof. Vicente Montiel Leguey (Universidad de Alicante, Spain) thought of our review as a great work for scholars and teachers in the field of electrodialysis.

    Guided by the water-splitting model, many catalysts were tested and its catalytic effects were also summarized. One of the catalysts is PEG, which can enhance water-splitting, and its catalytic effect increases with its molecular weight. The corresponding paper was accepted by J. Colloid Interface Sci., and the reviewer commented as follows: "Although catalysis of metal ions and amines on water splitting in BPM has been reported, approach to the modification of BPM interface using PEG is very unique and very impressive. Actually, this study will prove to be valuable for researchers in the field of membrane science and technology, and fundamental studies on water dissociation mechanism at the BPM interface". In view of the current theories, amphoteric molecules should catalyze the water-splitting, and then we studied the sorption behaviors of BSA on polymer membranes and its catalytic effect as the interface of bipolar membranes. The results indicated that BSA was fastened to the membrane surface and thus was qualified as an interface material (JCIS170; AICHE J 08068 Version 1). However, it could suppress the water-splitting under some conditions, which went against the current theories. Correspondingly, we put forward a new mechanism¡ªinterfacial repulsion and molecular denaturation, and it could explain why there was an increase in the voltage drop for water-splitting.

2£®Homogenous ion-exchange membrane and corresponding processes

    To obtain a series of charged, especially positively-charged, membranes, the strategy we adopted to modify linear polymer is methyl-substitution, benzyl-substitution, and chemical cross-linking. The experimental results has proved that (1) methyl-substitution can lead to an increase in membrane electrical conductance and thus favors the application in electrodialysis, (2)benzyl-substitution can decrease membrane water uptake and enhance membrane permselectivity, and thus is favorable for dialysis, and (3) chemical cross-linking can improve membrane thermal stability and mechanical strength. All these conclusions have laid a good theoretical foundation for practical application of these membranes.

    In particular, the advantage of this strategy is that membrane preparation does not need chloromethylation, in which chloromethylmethylether, a hazardous chemical, is often used. More details were published in the international journal J. Membr. Sci. (J Membr Sci., 2001,190/2:159-166; 2001,183/2:193-200.;2002,199(1-2):203-210£»2002,203/1-2:145-153), and the reviewers thought highly of the research, and considered the strategy economical, effective, easy for industrial scaling-up and capable of protecting environment from the danger of chloromethylmethylether.

    Another interesting section of our work is the research on charged particles¡¯ transport in charged membranes. After examining the microcosmic ¡°percolation theory¡± and macroscopic ¡°3-phase model¡±, we established a new model for the diffusion of charged particles in a charged membrane ¨Cshaped medium. The corresponding paper was accepted by Chem. Eng. Sci., and the value of this model is like a touchstone to tell conductor from insulator, and further tell pass from blockage when charged particles diffuse in the membrane phase. The model is expected to be brought to practice in membrane preparation and such separation processes as nanofiltration and reverse osmosis.

3. Inorganic-organic composite/hybrid membranes and other membranes

    Organic membranes have been used on a large scale because of good flexibility, easy membrane formation, diversity, and adaptability. However, their application is limited in some fields due to their low mechanical strength, poor thermal and chemical stability, liability to blockage, and difficulty in cleansing.

    In comparison, inorganic membranes have high mechanical strength, good thermal and biochemical stability, long lifetime, and ease in cleansing and sterilizing, so they have good perspectives in the application of separation and membrane reaction. However, they are fragile, difficult to process and transport, less diverse, hard to be charged, and liable to membrane fouling. To overcome the disadvantages of organic and inorganic membranes, we started the research on preparation of organic-inorganic composite/hybrid membranes by sol-gel method.

Laboratory-developed method for preparation of positively-charged organic-inorganic hybrid membranes Journal of Membrane Science, 2003, 216(1-2), 269-278

Laboratory-developed method for preparation of negatively-charged organic-inorganic hybrid membranes Journal of Membrane Science, 2003, revised for publication

4£®Controlled release of biologically active reagents

    Another research interest is controllable release of pharmaceuticals, and the subjects we investigated include 5-fluoracilum/ethylene-vinyl alcohol copolymer (5-Fu/EVAL) and levonorgestrel (LNG, a contraceptive). Based on the in-vitro release kinetics of those subjects, we established membrane-phase diffusion model, pore diffusion model, and membrane-pore double-diffusion model, and initiated a procedure to identify the diffusion style by percolation threshold method. A success was achieved when applying the method to explain why the tortuousity is extremely large in some diffusion-determined controlled release systems, which can not explained by the precious theories. According to our research results, the reason is that the local condition is not sufficient for pore diffusion, and membrane phase diffusion is the main diffusion style. More details were published continually in domestic and international journals (Inter J. Pharm.Sci, 2000,197(1-2):23-34; 1998,170(2):139-149), and have earned many citations.

5£®Adsorption of proteins and membrane fouling

    According to the adsorption behavior of proteins onto commercial polymer membranes, we came to the opinion that proteins were adsorbed in congregates and its adsorption style depended on not only coverage but also time and concentration. At the same coverage, protein adsorption at higher concentrations and after a short time was different from the one at lower concentrations and after a long time. The former had such characteristics as easier congregation and desorption and less deformation, but the latter was conventional adsorption and had more irreversible processes. This new opinion modified the originally admitted theory that adsorption style is only determined by coverage. The corresponding FTIR-mapping and AFM micrographs have confirmed our opinion (J. Colloid Interface Sci., 2003, 262/2:342-350).

    On the basis of the preliminary examination on protein adsorption, we furthered the research by investigating the competitive adsorption between proteins and put forward expensive proteins can have larger recovery by sacrificing one kind of cheap protein in the process of biochemical filtration.

Adsorption Model

FTIR-mapping suggests that proteins diffused from outside to inside

The AFM micrographs (before and after adsorption, and after desorption) confirms the congregation of proteins at high concentration when being adsorbed.