Liangguo Yan

Synthesis of amino functionalized magnetic graphenes composite material and its application to remove Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II) from contaminated water.

In the present study, a kind of graphenes magnetic material (Fe3O4-GS) was prepared by compositing graphene sheet with ferroferric oxide, and shown to be effective for removing Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II) ions from aqueous solution. The synthesized sorbent was characterized by SEM, TEM, FTIR, XRD, XPS and BET, respectively. The pHZPC value of the sorbent was estimated to be 3.5 by alkaline-titration methods. Fe3O4-GS can be simply recovered from water with magnetic separation at low magnetic field within one minute. The sorption capacities of the metals were 17.29, 27.95, 23.03, 27.83 and 22.07 mg g(-1) for Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II), respectively. Kinetic data showed good correlation with pseudo-second-order equation and the Freundlich model was found to fit for the isotherm data of all the heavy metal ions. It was found that the metals sorption was accomplished mainly via chelation or ion exchange. The results of thermodynamic studies illustrate that the adsorption process was endothermic and spontaneous in nature.

Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron-aluminum pillared bentonites.

Phosphorus removal is important for the control of eutrophication, and adsorption is an efficient treatment process. In this study, three modified inorganic-bentonites: hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron-aluminum pillared bentonite (Fe-Al-Bent), were prepared and characterized, and their phosphate adsorption capabilities were evaluated in batch experiments. The results showed a significant increase of interlayer spacing, BET surface area and total pore volume which were all beneficial to phosphate adsorption. Phosphate adsorption capacity followed the order: Al-Bent>Fe-Bent>Fe-Al-Bent. The adsorption rate of phosphate on the adsorbents fits pseudo-second-order kinetic models (R(2)=1.00, 0.99, 1.00, respectively). The Freundlich and Langmuir models both described the adsorption isotherm data well. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous in nature. Finally, phosphate adsorption on the inorganic pillared bentonites significantly raised the pH, indicating an anion/OH(-) exchange reaction.

Label-free immunosensor for the detection of kanamycin using Ag@Fe3O4 nanoparticles and thionine mixed graphene sheet

A highly sensitive label-free immunosensor for the detection of kanamycin had been developed using silver hybridized mesoporous ferroferric oxide nanoparticles (Ag@Fe₃O₄ NPs) and thionine mixed graphene sheet (TH-GS). TH was used as an electron transfer mediator. The electrical signal was greatly improved in the presence of GS due to its good electron-transfer ability. With the advantages of large specific surface area and excellent electrical conductivity, Ag@Fe₃O₄ NPs could immobilize more antibodies of kanamycin and promote the electron transfer. Cyclic voltammetry and square wave voltammetry were used to characterize the recognition of kanamycin. The proposed immunosensor showed good performances such as low detection limit (15 pg mL⁻¹), wide linear range (from 0.050 to 16 ng mL⁻¹), short analysis time (3 min), high stability, and good selectivity in the detection of kanamycin. The immunosensor was evaluated for pork meat sample, receiving satisfactory results.

Adsorption of Cd(II) by Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxides: Kinetic, isothermal, thermodynamic and mechanistic studies.

Understanding the adsorption mechanisms of metal cations on the surfaces of solids is important for determining the fate of these metals in water and wastewater treatment. The adsorption kinetic, isothermal, thermodynamic and mechanistic properties of cadmium (Cd(II)) in an aqueous solution containing Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxide (LDH) were studied. The results demonstrated that the adsorption kinetic and isotherm data followed the pseudo-second-order model and the Langmuir equation, respectively. The adsorption process of Cd(II) was feasible, spontaneous and endothermic in nature. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to explain the adsorption mechanisms. The characteristic XRD peaks and FTIR bands of CdCO3 emerged in the LDH spectra after Cd(II) adsorption, which indicated that the adsorption of Cd(II) by LDHs occurred mainly via CdCO3 precipitation, surface adsorption and surface complexation. Furthermore, the magnetic Fe3O4/Mg-Al-CO3-LDH can be quickly and easily separated using a magnet before and after the adsorption process.

Kinetic, isotherm and thermodynamic investigations of phosphate adsorption onto core–shell Fe3O4@LDHs composites with easy magnetic separation assistance

In this study, three different magnetic core-shell Fe3O4@LDHs composites, Fe3O4@Zn-Al-, Fe3O4@Mg-Al-, and Fe3O4@Ni-Al-LDH were prepared via a rapid coprecipitation method for phosphate adsorptive removal. The composites were characterized by XRD, FTIR, TEM, VSM and BET analyses. Characterization results proved the successful synthesis of core-shell Fe3O4@LDHs composites with good superparamagnetisms. Batch experiments were conducted to study the adsorption efficiency of phosphate. Optimal conditions for the phosphate adsorption were obtained: 0.05 g of adsorbent, solution pH of 3, and contact time of 60 min. Proposed mechanisms for the removal of phosphate species onto Fe3O4@LDHs composites at different initial solution pH were showed. The kinetic data were described better by the pseudo-second-order kinetic equation and KASRA model. The adsorption isotherm curves showed a three-region behavior in the ARIAN model. It had a good fit with Langmuir model and the maximum adsorption capacity followed the order of Fe3O4@Zn-Al-LDH>Fe3O4@Mg-Al-LDH>Fe3O4@Ni-Al-LDH. Thermodynamic analyses indicated that the phosphate adsorption process was endothermic and spontaneous in nature. The three Fe3O4@LDHs composites could be easily separated from aqueous solution by the external magnetic field in 10s. These novel magnetic core-shell Fe3O4@LDHs adsorbents may offer a simple single step adsorption treatment option to remove phosphate from water without the requirement of pre-/post-treatment for current industrial practice.

Removal of mercury and methylene blue from aqueous solution by xanthate functionalized magnetic graphene oxide: Sorption kinetic and uptake mechanism.

Xanthate functionalized magnetic graphene oxide (Fe3O4-xGO) was successfully synthesized through linking xanthate groups to a kind of graphenes magnetic material (Fe3O4-GS). Fe3O4-xGO was found to be an ideal adsorbent for Hg(II) and methylene blue removal with a higher adsorption capacity. The synthesized adsorbent was characterized by SEM, TEM, FTIR, XRD, and BET respectively. Fe3O4-xGO can be simply recovered from water with magnetic separation at low magnetic field within only 1min. The adsorption capacity was found to be 118.55mg g(-1) for Hg(2+) (contact time for 180min, pH at 7 and temperature at 25°C) and 526.32mg g(-1) for methylene blue (contact time for 120min, pH at 5.5 and temperature at 25°C), respectively. Kinetic data showed good correlation with pseudo-second-order equation and the Langmuir model was found to fit for the isotherm data, which showed the contaminant sorption was accomplished mainly via chelation or ion exchange. The results of thermodynamic studies (ΔG<0, ΔH>0, ΔS>0) illustrate that the adsorption process was endothermic and spontaneous in nature. The experimental results suggest that Fe3O4-xGO has the potential applications in the environmental management.

Adsorption of benzoic acid from aqueous solution by three kinds of modified bentonites.

Benzoic acid removal is important for the water treatment, and adsorption is an efficient treatment process. Three kinds of modified bentonites, hydroxy-aluminum pillared bentonite (Al(OH)-Bent), octadecyl trimethyl ammonium chloride modified bentonite (OTMAC-Bent), and both octadecyl trimethyl ammonium chloride and hydroxy-aluminum modified bentonite (Al(OH)-OTMAC-Bent) were prepared and characterized by XRD, FTIR, and BET analysis. Experiments were conducted on the adsorption of benzoic acid by the prepared modified bentonites at different temperatures in batch experiments. The results show benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. Optimal conditions for the adsorption of benzoic acid on OTMAC-Bent and Al(OH)-OTMAC-Bent were as follows: pH of 3.5, 0.04 g/mL adsorbent, and contact time of 90 min. Increased adsorption with temperature indicates that the adsorptions of benzoic acid onto Al(OH)-OTMAC-Bent and OTMAC-Bent are spontaneous and endothermic. The adsorption data could be well interpreted by the Langmuir model and Temkin Equation. The adsorption efficiency was higher than 85%, suggesting that OTMAC-Bent and Al(OH)-OTMAC-Bent are excellent adsorbents for effective benzoic acid removal from water.

Metal ions-based immunosensor for simultaneous determination of estradiol and diethylstilbestrol

Environmental estrogens (EEs) can cause various endocrine diseases. Herein, we designed an ultrasensitive electrochemical immunosensor for simultaneous detection of two typical EEs, estradiol and diethylstilbestrol. These two analytes were immobilized on graphene sheet (GS) modified glassy carbon electrode (GCE). Amino-group functionalized mesoporous Fe3O4 (Fe3O4-NH2) was loaded with Pb(2+) or Cd(2+), and then incubated with estradiol and diethylstilbestrol antibodies, respectively. Using an electrochemical analysis technique, two well-separated peaks were generated by the redox reaction of Pb(2+) or Cd(2+), making the simultaneous detection of two analytes on the electrode possible. Subsequently, square wave anodic stripping voltammetry (SWASV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behaviors of the immunosensor. Under optimized conditions, the SWASV peak currents were proportional to the concentrations of estradiol and diethylstilbestrol in the range from 0.050 pg mL(-1) to 100 ng mL(-1) and 1.0 pg mL(-1) to 100 ng mL(-1), respectively. The immunosensor exhibited highly sensitive response to estradiol with a detection limit of 0.015 pg mL(-1) and diethylstilbestrol with a detection limit of 0.38 pg mL(-1). Furthermore, the immunosensor was satisfactorily employed to detect estradiol and diethylstilbestrol simultaneously in water samples.

Adsorption of cadmium onto Al13-pillared acid-activated montmorillonite

The optimal preparation conditions for Al(13)-pillared acid-activated Na(+)-montmorillonite (Al(13)-PAAMt) were (1) an acid-activated Na(+)-montmorillonite (Na(+)-Mt) solution of pH 3.0, (2) a OH(-)/Al(3+) molar ratio of 2.4 and (3) Al(3+)/Na(+)-Mt ratio of 1.0 mmol g(-1). The effects of OH(-)/Al(3+) and Al(3+)/Na(+)-Mt ratios on the adsorption of Cd(2+) onto Al(13)-PAAMt were studied. A comparison of the adsorption of Cd(2+) onto Al(13)-PAAMt, Al(13)-pillared Na(+)-montmorillonite (Al(13)-PMt) and Na(+)-Mt suggested that Al(13)-PAAMt had higher adsorption affinity for Cd(2+) than the other two adsorbents. A pseudo-second-order model described the adsorption kinetics well. Cadmium adsorption followed the Langmuir two-site equation, while desorption was hysteretic.

The removal of lead ions from aqueous solution by using magnetic hydroxypropyl chitosan/oxidized multiwalled carbon nanotubes composites.

Magnetic hydroxypropyl chitosan/oxidized multiwalled carbon nanotubes (MHC/OMCNTs) composites were fabricated and applied as the adsorbent to study the adsorption characteristic of lead ions in aqueous solution. The results of Fourier transform infrared spectrum (FTIR), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) showed that the MHC/OMCNTs composites were synthesized successfully. The effects of the solution pH and the contact time were investigated, indicating that the optimal pH and contact time were pH 5.0 and 120min, respectively. The removal of lead ions was rather quick and the kinetic adsorption can be well described by pseudo-second-order model. The experimental results showed that the Sips model is more suitable than Langmuir, Freundlich and Dubinin-Radushkevich models. Furthermore, the parameters of the adsorption thermodynamic calculated in this research such as free energy (ΔG, -2.304 to -5.078kJmol(-1)), enthalpy (ΔH, 39.03kJmol(-1)) and entropy (ΔS, 138.7Jmol(-1)K(-1)) indicated that the adsorption process was endothermic and spontaneous. Therefore, the results in this research suggest that the MHC/OMCNTs composites are ideal adsorbent for the removal of lead ions in aqueous solution.