Preparation of metal organic frameworks modified chitosan composite with high capacity for Hg(II) adsorption.

In this study, a novel modified chitosan composite adsorbent (UNCS) was prepared by crosslinking between chitosan and metal organic frameworks (MOFs) material UiO-66-NH2 using epichlorohydrin as crosslinker. The influence of the prepared conditions was investigated. The structure and morphology of the composite were characterized by FT-IR, XRD, SEM, TGA, BET and zeta potential analysis. Effects of different variables for adsorption of Hg(II) on this adsorbent were explored. The kinetic studies indicated that the adsorption process followed the pseudo-second-order kinetic model and the adsorption equilibrium could be reached within 2 h. The adsorption was mainly controlled by chemical process. Adsorption isothermal studies illustrated that the adsorption fitted Langmuir isotherm model, implying the homogeneous adsorption on the surface of the adsorbent. The adsorbent exhibited high uptake and the maximum capacity from Langmuir model could reach 896.8 mg g-1 at pH 6. Thermodynamic studies showed the spontaneous nature and exothermic nature of the adsorption process. Additionally, the removal of Hg(II) on UNCS could achieve over 90 %. The adsorption-desorption cycled experiments indicated the appropriate reusability of the adsorbent. Hence, this adsorbent would be promising for the removal of Hg(II) from wastewater.

Preparation and characterization of polyethyleneimine functionalized magnetic graphene oxide as high uptake and fast removal for Hg (II).

Polyethyleneimine functionalized magnetic graphene oxide adsorbent (PEI-mGO) was synthesized by introducing polyethyleneimine onto Fe3O4/graphene oxide. The structures and morphologies of PEI-mGO was identified by using Fourier-tranform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) methods. Quantities of bar-like Fe3O4 nanoparticles were observed on the surfaces of PEI-mGO. The adsorption of PEI-mGO for Cu(II), Pb(II), Hg(II), Co(II) and Cd(II) was compared. The adsorption results indicated that PEI-mGO showed higher uptake for Hg(II) than the other ions. The influence of various variables for the adsorption of Hg(II) on PEI-mGO was explored. The adsorption kinetics and isotherm could be described well by the pseudo-second-order and Langmuir models. The maximal uptake of PEI-mGO for Hg(II) from Langmuir model was 857.3 mg g-1, which was higher than that reported previously. The adsorption removal was a fast and endothermic process governed by the chemical process. The uptake increased with increasing temperature. PEI-mGO showed an excellent performance for removal of Hg(II) with 93.3% removal efficiency from simulated wastewater. Adsorption-desorption cycled experiments indicated that PEI-mGO could be recycled. PEI-mGO could be easily separated from the adsorbed solution by using a magnet. Hence, this novel adsorbent would be promising for the removal of Hg(II) from wastewater.

Selective adsorption of Pb(II) and Hg(II) on melamine-grafted chitosan.

Amine groups can play significant roles in modified chitosans for adsorption of heavy metal ions. A novel chitosan modified adsorbent (GMCS) grafted with lots of amine groups was synthesized by using glutaraldehyde as a crosslinker between chitosan and melamine. The structure and morphology of GMCS was characterized using FT-IR, 13C NMR, elemental analysis, XRD, TGA, SEM, BET and zeta potential analysis. The adsorption of GMCS and chitosan for different heavy metal ions was compared. The results indicated that GMCS had higher selectivity and uptake for adsorption of Pb2+ and Hg2+ than chitosan. Effects of some variables for uptakes of Pb2+ and Hg2+ on GMCS were studied. The kinetic and isothermal results showed that the adsorption followed the pseudo-second-order kinetic and Langmuir isotherm models. The adsorbent had highest adsorption capacity of 618.2 mg/g and 490.7 mg/g at pH 5 and 6 for Pb2+ and Hg2+, respectively. The adsorption was an endothermic and spontaneous chemical process. Five cycled experiments of adsorption-desorption showed that the adsorbent could be efficiently regenerated.

Ear-like poly (acrylic acid)-activated carbon nanocomposite: A highly efficient adsorbent for removal of Cd(II) from aqueous solutions.

Poly (acrylic acid) modified activated carbon nanocomposite (PAA-AC) was synthesized. The structure and morphology of this nanocomposite were characterized by FTIR, SEM, TEM, XRD and Zeta potential. The adsorption of some heavy metal ions on PAA-AC was studied. The characterization results indicated that PAA-AC was a novel and ear-like nanosheet material with the thickness of about 40 nm and the diameter of about 300 nm. The adsorption results exhibited that the introduction of carboxyl groups into activated carbon evidently increased the uptake for heavy metal ions and the nanocomposite had maximum uptake for Cd(II). Various variables affecting adsorption of PAA-AC for Cd(II) were systematically explored. The maximum capacity and equilibrium time for adsorption of Cd(II) by PAA-AC were 473.2 mg g-1 and 15 min. Moreover, the removal of Cd(II) for real electroplating wastewater by PAA-AC could reach 98.5%. These meant that the removal of Cd(II) by PAA-AC was highly efficient and fast. The sorption kinetics and isotherm fitted well with the pseudo-second-order model and Langmuir model, respectively. The adsorption mainly was a chemical process by chelation. Thermodynamic studies revealed that the adsorption was a spontaneous and endothermic process. The results revealed that PAA-AC could be considered as a potential candidate for Cd(II) removal.

Preparation and characterization of poly (itaconic acid)-grafted crosslinked chitosan nanoadsorbent for high uptake of Hg2+ and Pb2.

A novel nanoadsorbent (PIACS) with average size of 52.6nm was prepared by controlling grafted polymerization of itaconic acid on chitosan to emulsion stage and then crosslinking with glutaraldehyde. The preparation conditions were optimized and PIACS was characterized by FT-IR, XRD, SEM, TEM and TGA. The adsorption of PIACS for some metal ions was studied. The adsorption results showed that PIACS for adsorption of Hg2+ and Pb2+ had higher uptakes than some reported adsorbents. Various variables for adsorption of Hg2+ and Pb2+ were systematically researched. The adsorption followed the pseudo-second-order kinetics and Langmuir isotherm models. The maximum uptakes of Hg2+ and Pb2+ from Langmuir model were 870.1mgg-1 and 1320mgg-1, respectively. Especially, the uptake of this nanoadsorbent for Pb2+ was 4 times of that of the macro-scale adsorbent with the similar structure reported. As temperature rising, uptake of Pb2+ decreased while uptake of Hg2+ almost had no change. In addition, the adsorbent could be regenerated with EDTA. Hence, this prepared method of nanomaterial might extend to the similar grafted polymerizing and crosslinking systems of polymers and PIACS would be a promising adsorbent in the removal of Hg2+ and Pb2+ from wastewaters.

Synthesis and characterization of poly(maleic acid)-grafted crosslinked chitosan nanomaterial with high uptake and selectivity for Hg(II) sorption.

Chitosan-poly(maleic acid) nanomaterial (PMACS) with the size of 400-900nm was synthesized by grafting poly(maleic acid) onto chitosan and then crosslinking with glutaraldehyde. The synthesis conditions were optimized. The structure and morphology of PMACS were characterized by FT-IR, XRD, SEM and TGA. PMACS was used to adsorb some heavy metal ions such as Hg(II), Pb(II), Cu(II), Cd(II), Co(II), and Zn(II). The results indicated that PMACS had selectivity for Hg(II) sorption. The effects of various variables for sorption of Hg(II) were further explored. The maximum capacity for Hg(II) sorption was found to be 1044mgg(-1) at pH 6.0, which could compare with the maximal value of the recently reported other sorbents. The sorption followed the pseudo-second-order kinetics and Langmuir isotherm models. The rising of temperature benefited the uptake and the sorption was a spontaneous chemical process. The sorbent could be reused with EDTA. Hence, the nanomaterial would be used as a selective and high uptake sorbent in the removal of Hg(II) from effluents.

Selective adsorption of lead on grafted and crosslinked chitosan nanoparticles prepared by using Pb(2+) as template.

Poly(acrylic acid) grafted and glutaraldehyde-crosslinked chitosan nano adsorbent (PAACS) was synthesized by using Pb(2+) as a template ion. The structure and morphology of PAACS were characterized by FT-IR, XRD, SEM and elemental analyses. The adsorption of PAACS for different heavy metal ions was compared and the effects of various variables for adsorption of Pb(2+) were systematically studied. The results indicated that the PAACS was the aggregates of nanoparticles with the diameter of about 50-200 nm and had selectivity for Pb(2+) adsorption. The adsorption for Pb(2+) showed a maximum adsorption capacity of 734.3 mg g(-1) at pH 5.0 and 303 K, which was higher than in a study previously reported on ion-imprinted adsorbents. The adsorption followed the pseudo-second-order kinetics and Langmuir isotherm models. The adsorption was spontaneous and changed from chemical process into physical process when the temperature exceeded 303 K. The adsorbent could be recycled with EDTA. Therefore, PAACS would be useful as a selective and high uptake nano adsorbent in the removal of Pb(2+) from effluents.

Microwave preparation of triethylenetetramine modified graphene oxide/chitosan composite for adsorption of Cr(VI).

A novel triethylenetetramine modified graphene oxide/chitosan composite (TGOCS) was successfully synthesized by microwave irradiation (MW) method and compared with one prepared by conventional heating. This composite was characterized by FTIR, XRD, SEM, BET and elemental analysis. Adsorption of Cr(VI) on the composite was studied. The experimental results indicated that the product obtained by MW had higher yield and uptake than one obtained by the conventional and uptake of TGOCS for Cr(VI) was higher than that of the recently reported adsorbents. The effects of various variables on adsorption of Cr(VI) by TGOCS were further researched. The highest adsorption capacity of 219.5mg g(-1) was obtained at pH 2. Adsorption followed pseudo-second-order kinetic model and Langmuir isotherm. The capacity increased as increasing temperature. The adsorbent could be recyclable. These results have important implications for the application expansion of microwave preparation and the design of new effective composites for Cr(VI) removal in effluents.

Thermal preparation of chitosan-acrylic acid superabsorbent: optimization, characteristic and water absorbency.

Chitosan-acrylic acid superabsorbent polymer was successfully prepared by the thermal reaction without using initiator and crosslinker in air. The effects of some reaction variables on the water absorbency of this polymer were investigated by orthogonal tests, and the optimal conditions were described. The influences of temperature, time, ratio of the reactants and neutralization degree of acrylic acid on the reaction were further studied. These polymers were also prepared in nitrogen atmosphere and by using a radical initiator and compared against thermal reaction obtained polymers. The structures of the polymers were characterized by FT-IR, TGA, XRD, (13)C NMR and elemental analyses. The results showed that the thermal reaction product of acrylic acid with chitosan might form N-carboxyethyl grafted and amide-linked polymer and this product could absorb water 644 times its own dry weight. The possible mechanism for the thermal reaction was further suggested. The purpose of this research was to explore the friendly synthesized method of the superabsorbent.

Preparation of carboxymethyl chitosan in aqueous solution under microwave irradiation.

Carboxymethyl chitosan was prepared by reacting chitosan with chloroacetic acid in water under microwave irradiation. The effect of the reaction conditions was investigated and optimal conditions were identified. The influence of mass ratio of chloroacetic acid to chitosan, microwave power and pH on the degree of substitution or intrinsic viscosity were further studied. The degree of substitution of the carboxymethyl chitosan synthesized exceeded 0.85.