Yanfeng Li

Preparation and Characterization of Magnetic Porous Carbon Microspheres for Removal of Methylene Blue by a Heterogeneous Fenton Reaction

High-specific-surface-area magnetic porous carbon microspheres (MPCMSs) were fabricated by annealing Fe(2+)-treated porous polystyrene (PS) microspheres, which were prepared using a two-step seed emulsion polymerization process. The resulting porous microspheres were then sulfonated, and Fe(2+) was loaded by ion exchange, followed by annealing at 250 °C for 1 h under an ambient atmosphere to obtain the PS-250 composite. The MPCMS-500 and MPCMS-800 composites were obtained by annealing PS-250 at 500 and 800 °C for 1 h, respectively. The iron oxide in MPCMS-500 mainly existed in the form of Fe3O4, which was concluded by characterization. The MPCMS-500 carbon microspheres were used as catalysts in heterogeneous Fenton reactions to remove methylene blue (MB) from wastewater with the help of H2O2 and NH2OH. The results indicated that this catalytic system has a good performance in terms of removal of MB; it could remove 40 mg L(-1) of MB within 40 min. After the reaction, the catalyst was conveniently separated from the media within several seconds using an external magnetic field, and the catalytic activity was still viable even after 10 removal cycles. The good catalytic performance of the composites could be attributed to synergy between the functions of the porous carbon support and the Fe3O4 nanoparticles embedded in the carrier. This work indicates that porous carbon spheres provide good support for the development of a highly efficient heterogeneous Fenton catalyst useful for environmental pollution cleanup.

Development of carbon nanotubes/CoFe2O4 magnetic hybrid material for removal of tetrabromobisphenol A and Pb(II).

Multi-walled carbon nanotubes (MWCNTs) coated with magnetic amino-modified CoFe2O4 (CoFe2O4-NH2) nanoparticles (denoted as MNP) were prepared via a simple one-pot polyol method. The MNP composite was further modified with chitosan (CTS) to obtain a chitosan-functionalized MWCNT/CoFe2O4-NH2 hybrid material (MNP-CTS). The obtained hybrid materials were characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectrogram (FT-IR) Analysis and X-ray Photoelectron Spectroscopy (XPS) Analysis, Vibrating Sample Magnetometer (VSM) Analysis and the Brunauer-Emmett-Teller (BET) surface area method, respectively. The composites were tested as adsorbents for tetrabromobisphenol A (TBBPA) and Pb(II), and were investigated using a pseudo-second-order model. The adsorption of TBBPA was well represented by the Freundlich isotherm; the Langmuir model better described Pb(II) absorption. MNP-CTS adsorbed both TBBPA and Pb(II) (maximum adsorption capacities of 42.48 and 140.1mgg(-1), respectively) better than did MNP without CTS. Magnetic composite particles with adsorbed TBBPA and Pb(II) could be regenerated using 0.2M NaOH solution and were separable from liquid media using a magnetic field.

Characterization and adsorption mechanism of Zn2+ removal by PVA/EDTA resin in polluted water.

Batch adsorption experiments were conducted using a PVA/EDTA resin as an adsorbent to adsorb Zn(II) ions from single component system in which experimental parameters were studied including solution pH, contact time, adsorbent dose and initial metal ions concentration. The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperatures. The results showed that the maximum removal of Zn(II) (99.8%) with 1 g L(-1) of sorbent was observed at 40 mg L(-1) at an initial pH value of 6. Removals of about 60-70% occurred in 15 min, and equilibrium was attained at around 30 min. The equilibrium data for the adsorption of Zn(II) on PVA/EDTA resin was tested with various adsorption isotherm models among which three models were found to be suitable for the Zn(II) adsorption. In addition, the kinetic adsorption fitted well to the pseudo-second-order model and the corresponding rate constants were obtained. Thermodynamic aspects of the adsorption process were also investigated. Furthermore a higher desorption efficiency of Zn(II) from the PVA/EDTA resin using acid treatment was available by more than 95%.

Immobilization of nanoscale Fe0 in and on PVA microspheres for nitrobenzene reduction

In this study, nanoscale Fe(0) was immobilized in and on poly(vinyl alcohol) (PVA) microspheres by the inverse suspension crosslinked method. Two different sizes of Fe(0)/PVA microspheres were synthesized in the presence and absence of dispersant. The chelating action between Fe(2+) and PVA was identified by Fourier transform infrared and X-ray photoelectron spectroscopy. The morphology and distribution of the obtained Fe(0)/PVA microspheres were characterized by environmental scanning electron microscope, energy-dispersive X-ray spectrometry, and X-ray diffraction. Nanoscale Fe(0) particles were mostly dispersed over the surface of the microspheres. They were distributed more homogeneously on the surfaces of Fe(0)/PVA microspheres with diameter of 600-700 microm than those with diameter of 10-12 microm. The nitrobenzene (NB) reduction reactions followed pseudo-first-order kinetics. The normalized surface rate constants (k(SA)) values were determined to be 0.162 L h(-1)m(-2) for L-Fe(0)/PVA microspheres, 0.098 L h(-1)m(-2) for S-Fe(0)/PVA microspheres, and 0.023 L h(-1)m(-2) for nanoscale Fe(0) particles. Furthermore, with the analysis of the products by GC/MS, possible reductive pathways of NB by Fe(0)/PVA microspheres were suggested. The recovery rates of iron in microspheres were determined to be 81.17% for large Fe(0)/PVA and 60.31% for small Fe(0)/PVA.

Use of microorganisms immobilized on composite polyurethane foam to remove Cu(II) from aqueous solution

Composite polyurethane (PU) foams were made via the polymerization of toluene diisocyanate (TDI) and polyether polyol with activated carbon fiber, and immobilized microorganisms on polyurethane (IPU) foam were prepared by cultivating the microbe B350 in a mixture of culture medium and PU. We used batch adsorption techniques to study the removal of Cu(II) ions from aqueous solutions via PU and IPU. Moreover, the effects of pH, temperature, carrier amount, and biosorption time on the removal rate of Cu(II), adsorption equilibrium, and adsorption kinetics were investigated in detail. The IPU showed an excellent removal rate for Cu(II). The adsorption kinetics data were in good agreement with the pseudo-second-order rate model, and the adsorption isotherms could be adequately described by the Langmuir equation. For synthetic wastewater containing Cu(II), the removal rates for Cu(II) and COD after 4h treatment were 85% and 80%, respectively.

Preparation of Superparamagnetic Fe3O4@Alginate/Chitosan Nanospheres for Candida rugosa lipase Immobilization and Utilization of Layer-by-Layer Assembly to Enhance the Stability of Immobilized Lipase

Superparamagnetic alginate nanospheres with diameter of 50 nm were prepared by self-assembly of alginate in the Ca(2+) solution; and then superparamagnetic alginate/chitosan nanospheres, which have positive charge and could adsorb lipase directly, were obtained with a following assembly of chitosan based on the electrostatic interaction between alginate and chitosan. Subsequently, oxidic poly (ethylene glycol) was used to functionalize the magnetic alginate/chitosan nanospheres. Thus, the magnetic nanospheres with aldehyde groups and a brushlike structure were formed. With various characterizations, it was verified that the magnetic alginate/chitosan nanospheres held small diameters (around 60 nm) and displayed superparamagnetism with high saturation magnetization. The Candida rugosa lipase (CRL), meanwhile, was immobilized onto the magnetic alginate/chitosan nanospheres by electrostatic adsorption and covalent bonding, respectively. Afterward, a layer-by-layer (LBL) assembly process was utilized to coat the immobilized CRL (ICRL) with covering layers made up of alginate and chitosan. After studying the properties of ICRL such as activity, kinetic behaviors, stability and reusability, it was proved that the ICRL prepared with two methods displayed more excellent properties than that prepared with electrostatic adsorption only. Additionally, coating ICRL with covering layers showed good effect on improving the stability of ICRL.

Preparation and characterization of a novel nano-absorbent based on multi-cyanoguanidine modified magnetic chitosan and its highly effective recovery for Hg(II) in aqueous phase.

A new kind of nano-absorbent with the entirely novel structure, nano-absorbent of multi-cyanogunidine modified magnetic chitosan (CG-MCS nano-absorbent), has been firstly synthesized by using the functionalized chitosan and cross-linking agent with cyanoguanidine group simultaneously. The resulting nano-absorbent was characterized by means of the Fourier transform infrared spectra (FT-IR), transmission electron microscope (TEM), X-ray diffraction (XRD), elemental analysis and vibrating sample magnetometer (VSM). The resulting nano-absorbent basen on multi-cyanoguanidine modified magnetic chitosan has been demonstrated holding highly effective recovery for mercury ions, in other words, it showed both the extraordinary adsorption capacity for Hg(II) at high initial concentration and the strong removal ability for it at low concentration, the maximum adsorption capacity was up to 285 mg g(-1) and the removal percentage could reach 96% at low concentration. Meanwhile, the resulting CG-MCS nano-absorbent also showed a high selectivity adsorption for Hg(II) among coexisting heavy metals and the good regeneration performance.

Novel magnetic beads based on sodium alginate gel crosslinked by zirconium(IV) and their effective removal for Pb2+ in aqueous solutions by using a batch and continuous systems

Novel magnetic sodium alginate gel beads (Fe3O4@SA-Zr) were successfully prepared by using zirconium(IV) as crosslinking ions, and used as adsorbent for removal of Pb(2+) ions from aqueous solutions in batch and fixed-bed column systems. Fe3O4@SA-Zr was characterized by SEM, FT-IR, XRD and VSM. Fe3O4@SA-Zr had the macroporous structure, exhibited greater stability and possessed a sensitive magnetic response. More importantly, Fe3O4@SA-Zr exhibited high adsorption capacity, fast kinetics and high selectivity towards Pb(2+) ions. Experimental data was well described by Langmuir isotherm with a maximum adsorption capacity of 333.33 mg/g. FTIR and XPS indicated that the carboxyl and hydroxyl groups of SA and hydroxyl groups binding to Fe and Zr species were involved in Pb(2+) adsorption. Fixed-bed column packed with Fe3O4@SA-Zr exhibited higher removal efficiency for Pb(2+)ions. Consequently, Fe3O4@SA-Zr with excellent absorbability, stability and reusability could be used as a promising adsorbent for Pb(2+) removal in wastewaters.

Reversible immobilization of glucoamylase onto magnetic chitosan nanocarriers.

A simple preparation process for the monodispersed pH-sensitive core-shell magnetic microspheres was carried out consisting of chitosan self-assembled on magnetic iron oxide nanoparticles. Meanwhile, glucoamylase was immobilized as a model enzyme on this carrier of Fe3O4/CS microspheres by ionic adsorption. The morphology, inner structure, and high magnetic sensitivity of the resulting magnetic chitosan microspheres were studied, respectively, with a field emission scanning electron microscope (SEM), transmission electron microscope (TEM), FT-IR spectroscopy, thermogravimetric analysis (TGA), and a vibrating sample magnetometer (VSM). Subsequently, the properties of glucoamylase immobilized on the regenerated supports were also investigated by determining storage stability, pH stability, reusability, magnetic response, and regeneration of supports. The results from characterization and determination remarkably indicated that the immobilized glucoamylase obtained presents excellent storage stability, pH stability, reusability, magnetic response, and regeneration of supports. Therefore, this kind of magnetic Fe3O4/CS microspheres with perfect monodispersity should be an ideal support for enzyme immobilization.

Preparation and adsorption performance of a novel bipolar PS-EDTA resin in aqueous phase.

A novel chelating resin containing many amino and carboxyl functional groups, PS-EDTA resin, was prepared from chloromethylated polystyrene bead by reacting with ethylenediamine and chloroacetate in aqueous phase in sequence. The structure of PS-EDTA resin was characterized by means of infrared spectroscopy, scanning electron microscopy, surface area analysis and thermogravimetry. Adsorption behavior of the resin for Ag (I) ions in aqueous solutions was investigated by batch experiments. The results indicated that the adsorption removal of PS-EDTA resin for Ag (I) could achieve more than 99.9% at pH values of 5.0 with an initial Ag (I) concentration of 60.0mg/L within 2h. The maximum removal capacity of PS-EDTA toward Ag (I) was found to be almost 3314.97 mg/g at 25 degrees C. In addition, adsorption kinetic data were described by pseudo-second-order equation and the equilibrium data fitted very well with the Freundlich model. It was found that the PS-EDTA resin had excellent adsorption properties for Ag (I), so it should be a promising composite adsorbent with application in the recovery of Ag (I) ions from aqueous environment.