Xiang Zhang

Toward 3D graphene oxide gels based adsorbents for high-efficient water treatment via the promotion of biopolymers.

Recent studies showed that graphene oxide (GO) presented high adsorption capacities to various water contaminants. However, the needed centrifugation after adsorption and the potential biological toxicity of GO restricted its applications in wastewater treatment. In this study, a facile method is provided by using biopolymers to mediate and synthesize 3D GO based gels. The obtained hybrid gels present well-defined and interconnected 3D porous network, which allows the adsorbate molecules to diffuse easily into the adsorbent. The adsorption experiments indicate that the obtained porous GO-biopolymer gels can efficiently remove cationic dyes and heavy metal ions from wastewater. Methylene blue (MB) and methyl violet (MV), two cationic dyes, are chosen as model adsorbates to investigate the adsorption capability and desorption ratio; meanwhile, the influence of contacting time, initial concentration, and pH value on the adsorption capacity of the prepared GO-biopolymer gels are also studied. The GO-biopolymer gels displayed an adsorption capacity as high as 1100 mg/g for MB dye and 1350 mg/g for MV dye, respectively. Furthermore, the adsorption kinetics and isotherms of the MB were studied in details. The experimental data of MB adsorption fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm, and the results indicated that the adsorption process was controlled by the intraparticle diffusion. Moreover, the adsorption data revealed that the porous GO-biopolymer gels showed good selective adsorbability to cationic dyes and metal ions.

Graphene oxide-based polymeric membranes for broad water pollutant removal

Graphene oxide (GO) and its derivatives display excellent removal abilities of water contaminants; however, the complex preparation process of GO-based adsorbents and difficult collection of GO sheets during the adsorption process limit their practical applications. Hence, three kinds of GO-based polymeric membranes with specific adsorption characteristics were fabricated by a facile blending method, including GO/PES membrane, reduced GO (RGO)/PES membrane, and polyethyleneimine (PEI) coated GO membrane of GO@PEI/PES membrane. The GO/PES membrane exhibited selective adsorption for cationic dyes, the RGO/PES membrane exhibited selective adsorption for endocrine disruptors, and the GO@PEI/PES membrane exhibited selective adsorption for anionic dyes. The adsorption data fitted the pseudo-second-order kinetic model and the Langmuir isotherm well, and the adsorption process was controlled by the interparticle diffusion. The thermodynamic studies indicated that the adsorption reactions were spontaneous and exothermic processes. The dynamic adsorption results indicated that the prepared membranes could be used in wastewater filtration. The study indicated that GO-based polymeric membranes with broad water pollutant removal could be fabricated by facile strategies, and the problem of difficult collection of GO sheets during and after adsorption process was solved.

Integrating zwitterionic polymer and Ag nanoparticles on polymeric membrane surface to prepare antifouling and bactericidal surface via Schiff-based layer-by-layer assembly

Development of antibacterial membranes is strongly desired for biomedical applications. Herein, we integrated antifouling and bactericidal properties on polymeric membrane surface via Schiff-based layer-by-layer (LbL) assembly. Zwitterionic polymers bearing plentiful amino groups (based on polyethylenimine (PEI) and sulfobetaine methacrylate (SBMA), and termed as PEI-SBMA) were utilized to prepare an antifouling membrane surface; then robust wide-spectrum bactericidal Ag nanoparticles (Ag NPs) were in situ generated on the surface. The as-prepared zwitterionic polymer surface showed excellent resistance to protein adsorption and bacterial adhesion. The Ag NPs could be tightly and uniformly distributed on the membrane surface by the chelation of PEI-SBMA, and endowed the membrane with bactericidal activity. Meanwhile, the Ag NPs loaded membrane could effectively resist bacterial attachment for a long time, even though the bactericidal activity lost. The proposed bactericidal and antifouling membrane was flexible, versatile and could be large-scale preparation; and this strategy would have great potential to be widely used to avoid undesired bacterial contamination of biomedical implants or biological devices.

Rationally designed magnetic nanoparticles as anticoagulants for blood purification

Heparin-based anticoagulant drugs are widely used for the prevention of blood clotting during extracorporeal circuit (bloodlines or cassette system) and surgical procedures as well as for the treatment of thromboembolic events. However, these anticoagulants are associated with bleeding risks that demand continuous monitoring and neutralization with antidotes. We explore the possibility of utilizing anticoagulants for blood clotting prevention, then removing them before transfusing the blood back to body, thus avoid bleeding risks. Here, we report on the strength of a strategy to solve problems with bleeding risks by rationally designing and using superparamagnetic iron oxide nanoparticles (SPIONs) with layer-by-layer self-assembled heparin. The morphology of these SPIONs was investigated by using dynamic light scattering and transmission electron microscopy. In vitro assays demonstrated superior efficacy and safety profiles and significantly mitigated conventional heparin-induced bleeding risks. In addition, the in vivo assay in a model animal (dog) proved that it is possible to use magnetic anticoagulant (MAC) in blood purification. The new magnetic anticoagulant drugs may benefit patients undergoing high-risk surgical procedures and may overcome anticoagulant-related bleeding problems to a great extent.

Anion-responsive poly(ionic liquid)s gating membranes with tunable hydrodynamic permeability

Novel anion-responsive intelligent membranes with functional gates are fabricated by filling polyethersulfone microporous membranes with poly(ionic liquid)s (PILs) gels. The wetting properties of the PILs could be controlled by changing their counteranions (CAs), and thus, the filled PILs gel gates in the membrane pores could spontaneously switch from the closed state to the open one by recognizing the hydrophilic CAs in the environment and vice versa. As a result, the fluxes of the intelligent membranes could be tuned from a very low level (0 mL/m2·mmHg for Cl-, Br-, and BF4-) to a relatively high one (430 mL/m2·mmHg for TFSI). The anion-responsive gating behavior of the PILs filled membranes is fast, reversible, and reproducible. In addition, the intelligent membranes are sensitive to contact time and ion concentrations of the hydrophobic CA species. The proposed anion-responsive intelligent membranes are highly attractive for ion-recognizable chemical/biomedical separations and purifications.

Graphene oxide-based polyethersulfone core–shell particles for dye uptake

Graphene oxide (GO), a graphene nanomaterial with great application potential, possesses promising adsorption abilities towards various water contaminants due to the ultra-large surface area and the nature of electric charge on the surface. However, ultrahigh centrifugation for a prolonged time is strongly needed to collect the highly dispersed GO in the recovery process. In this study, a GO-based polymeric composite particle with core–shell structure was fabricated by a facile method. Polyethersulfone (PES) was chosen as the shell to enwrap GO through a liquid–liquid phase inversion process, since the PES shell presented high porosity, good mechanical property and easily modified ability. Methylene blue (MB), a cationic dye, was chosen as the adsorbate to investigate the adsorption capabilities, kinetics and isotherms of the prepared particles. The PES@GO core–shell particles displayed an adsorption capacity as high as 352.11 mg g−1 for MB dye, and the adsorption rates could be improved by modifying the PES shells with hydrophilic fillers. The MB adsorption behavior fitted the pseudo-second-order kinetic model and the Langmuir isotherm very well, and the adsorption process was controlled by the intra-particle diffusion. In addition, a particle column was used to further study the removal ability of environmental toxins, and the results revealed that the composite particles had great potential to remove cationic dyes for wastewater treatment on an industrial scale.

Design of Robust Thermal and Anion Dual-Responsive Membranes with Switchable Response Temperature

In this study, poly(ionic liquids/ N-isopropylacrylamide) (PIL/NIPAM) modified poly(ether sulfone) microporous membranes were prepared using a pore-filling method. Due to the anion-sensitive wettability of the PIL and the thermal-sensitive phase transformation of PNIPAM, the permeability of the modified membranes showed robust anion and thermal dual-responsive behaviors. In addition, the response temperature of the membranes could be adjusted precisely from 30 to 55 °C by anion exchange, which was attributed to the cooperative interaction of the PIL and PNIPAM. The switchable response temperature and the dual-responsive performances of the membranes were demonstrated by measuring the water fluxes under various conditions. The results indicated that the membrane permeabilities increased when exchanging the counteranions (CAs) from hydrophilic to hydrophobic ones; the thermal response behaviors were also obvious, and the sensitivity increased when increasing the hydrophobicity of the CA (the fluxes could be adjusted from 0 to 3800 mL/m2 mmHgh by controlling the temperature and CAs). At last, filtration tests were designed with the membranes, and the results indicated that by controlling the temperature and/or CA species, three different poly(ethylene glycol) molecules could be easily separated according to their molecule sizes in a single step.