Adsorption of Pb2+, Cu2+ and Cd2+ by sulfhydryl modified chitosan beads.

A chitosan-based bead was synthesized by crosslinking as well as sulfhydryl modification reaction and its removal ability of Pb2+, Cu2+ and Cd2+ was investigated. The test results showed that the crystal structure of chitosan was destroyed completely and the specific surface area was greatly increased after modification. The adsorption of Pb2+, Cu2+ and Cd2+ by the beads was carried out at different pH, ionic strength, contact time and initial concentration and the maximum adsorption capacities were 273.7 mg/g, 163.3 mg/g and 183.1 mg/g, respectively. Furthermore, due to the large ion radius of Pb2+, its adsorption was seriously disturbed by other ions in the competitive adsorption process. Finally, the adsorption processes of Pb2+, Cu2+ and Cd2+ were well fitted by the Langmuir isotherm model and the pseudo second-order kinetics model, respectively. Combined with the results of X-ray photoelectron spectroscopy, chemical coordination is the main adsorption mechanism.

Preparation of Chitosan/Calcium Alginate/Bentonite Composite Hydrogel and Its Heavy Metal Ions Adsorption Properties.

In order to avoid the secondary pollution of the toxic residue of chemical crosslinking agent accompanied by chemical hydrogel adsorbent and enhance the adsorption performance of physical hydrogel, chitosan/calcium alginate/bentonite (CTS/CA/BT) composite physical hydrogel was constructed. The formation mechanism and structure of the composite hydrogel were determined by FTIR, XRD and SEM. Adsorption performances of the hydrogel toward Pb2+, Cu2+ and Cd2+ in water under different condition as well as multi-ion competitive sorption were investigated. The adsorption processes were described with the canonical adsorption kinetics and isotherms models. With the utilization of XPS analysis and adsorption thermodynamics analysis, it was found that the adsorptions were spontaneous physico-chemical adsorptions. The results showed that the maximum adsorption capacity of the hydrogel for Pb2+, Cu2+ and Cd2+ reached up to 434.89, 115.30 and 102.38 mg·g-1, respectively, better than those of other physical hydrogels or chitosan/bentonite composite. Moreover, the composite hydrogel improved the collectability of bentonite and showed a good reusability. The modification of bentonite and the formation of hydrogel were completed simultaneously, which greatly simplifies the operation process compared with the prior similar works. These suggest that the CTS/CA/BT composite hydrogel has promising application prospects for removal of heavy metal ions from water.

Preparation of a novel bio-adsorbent of sodium alginate grafted polyacrylamide/graphene oxide hydrogel for the adsorption of heavy metal ion.

A novel bio-adsorbent named SA-PAM/GO hydrogel composites was synthesized through free radical polymerization. The structure and performance were characterized and analyzed by BET, SEM-EDS, FTIR and TGA. After modification, the BET surface area increased more than tripled, which was consistent with SEM results. Under optimal conditions, the maximum adsorption capacity of Cu2+ and Pb2+ were 68.76 mg/g and 240.69 mg/g, respectively. In addition, the research of kinetics and isotherms displayed that the pseudo-second-order kinetic model and the Langmuir isotherm model fitted the data well. After further research, the different adsorption mechanism including physical adsorption, chemical adsorption and electrostatic interactions were discussed. The chemical adsorption accompanying the ion exchange process was confirmed as the staple adsorption mechanism. Furthermore, the adsorbent still maintained good adsorption capacity after 5 cycles of adsorption-regeneration. Therefore, the SA-PAM/GO hydrogel composites have potential to remove the heavy metal ions from water body effectively.

Preparation of acrylamide/acrylic acid cellulose hydrogels for the adsorption of heavy metal ions.

Modified cellulose hydrogels were prepared by blending and cross-linking with acrylamide and acrylic acid. The structure of hydrogels was characterized and analyzed with fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Under the optimized conditions, the maximum absorption capacity in modified cellulose hydrogels of Cu (II), Pb (II) and Cd (II) ions were 157.51, 393.28 and 289.97 mg/g, respectively. In addition, the metal ion adsorption process accorded with pseudo-second-order rate equation and Langmuir adsorption isotherm. Based on the microstructure analysis and adsorption kinetics, the adsorption mechanisms such as physical, chemical, and electrostatic interactions are discussed. The adsorption process was controlled by the ion-exchange mechanism.

Synthesis of recognition matrix from 4-methylamino-N-allylnaphthal-imide with fluorescent effect for the imprinting of creatinine.

4-Methylamino-N-allylnaphthalimide (4-MAANI), a functional monomer with fluorescent effect, was synthesized for the imprinting and specific uptake of creatinine, an important clinical marker for kidney function. 4-Methylamino-N-allylnaphthalimide was synthesized from the reaction of 4-bromo-1,8-naphthalic anhydride with allylamine to form 4-bromo-N-allylnaphthalimide and further to react with methylamine. Excitation and emission of the fluorescent monomer was investigated by both a three-dimensional plot of fluorescent intensity versus excited and emitted wavelengths and a corresponding contour plot. The photoluminescence properties of the as-prepared conjugated species were also studied. 4-Methylamino-N-allylnaphthalimide (4-MAANI) fluorescent monomer, methacrylic acid (MAA) functional monomer, ethylene glycol dimethylacrylate (EGDMA) cross-linker, and 2,2'-azobisisobutyronitrile (AIBN) initiator were then utilized in the presence of creatinine template for the processing of heat-induced polymerization. FT-IR analysis was used to confirm the successful synthesis of 4-MAANI. The specific recognition cavity for creatinine was then created from the polymer matrix after the removal of creatinine by proper solvent. The imprinting effect as well as selectivity from the creatinine containing mixture was also evaluated. The grouped clusters from the emitted fluorescent intensities of the imprinted and nonimprinted polymers before and after rebinding of creatinine were obtained and discussed. Serum spiked with a different concentration of creatinine was also used to confirm the feasibility of clinical applications in the future. Successful recognition of the creatinine molecule via the combined effect of molecular imprinting and photoluminescence of the imprinted polymeric material was thus confirmed in this work.