Graphene oxide functionalized chitosan-magnetite nanocomposite for removal of Cu(II) and Cr(VI) from waste water.

A novel adsorbent material for removal of metal ions from aqueous solution was made by modifying chitosan. The schiff base prepared from reaction of chitosan with 3-(p-anisyl)-4-formylsydnone was further functionalized with graphene oxide. Finally Fe3O4 nanoparticles were incorporated into the modified chitosan to obtain a novel adsorbent material. The nanocomposite made was characterized using FTIR, TGA, SEM, EDS and XRD techniques and evaluated for adsorptive removal of Cu(II) and Cr(VI) ions from aqueous solutions. The maximum adsorption capacities of the adsorbent for Cu(II) and Cr(VI) ions were found to be 111.11 and 142.85 mgg-1 respectively. The adsorption data fitted well with Langmuir isotherm model and followed pseudo second order kinetic model. Thermodynamic parameters indicated the adsorption to be spontaneous and endothermic. The desorption studies revealed the efficient recovery of adsorbate species and possible reusability of the adsorbent material.

Paper based field deployable sensor for naked eye monitoring of copper (II) ions; elucidation of binding mechanism by DFT studies.

The study demonstrates the fabrication of test strips made from newly synthesized ortho-Vanillin based colorimetric chemosensor (probe P) that could be employed as field deployable tool for rapid and naked eye detection of Cu2+. Upon addition of Cu2+ to the chemosensor, it exhibits rapid pink color from colorless and can be easily seen through the naked eye. This probe exhibits a remarkable colorimetric "ON" response and the absorbance intensity of the probe enhances significantly in presence of Cu2+. The sensing mechanism has been deduced using FTIR, XPS, LCMS and DFT studies. The binding mechanism of the probe to Cu2+ was substantiated by DFT studies. HOMO of the probe suggests that a high electronic density resides on O, N atoms and thus these are the favorable binding site for the metal ions. Study revealed that the P + Cu2+ complex is -35.64 eV more stable than individual reactants. The Cu2+ binds to the probe in 1:1 stoichiometry with a binding constant of 2.6 × 104 M-1 as calculated by Job's plot and Benesi-Hildebrand plot. The chemosensor shows 1.8 × 10-8 M detection limit, which is considerably lesser than that of the WHO admissible limit of [Cu2+] in drinking water. Possible interfering ions namely Ca2+, Mg2+, Fe2+, Co2+, Ni2+, Cd2+, Hg2+, Mn2+, Al3+ and Cr3+ do not show any appreciable interference in the colorimetric response of the probe towards Cu2+. Particularly, the colorimetric "ON-OFF-ON" responses are proved to be repeated over 5 times by the sequential inclusion of Cu2+ and S2-. Sensitivity of the probe in real-time water and blood samples is found at par with results with AAS and ICP-OES techniques. Further, the reversibility of the probe and the easy fabrication of deployable strips for real-field naked eye detection of Cu2+ suggest importance of synthesized probe.

Synthesis and metal ion adsorption characteristics of graphene oxide incorporated chitosan Schiff base.

The work reports the development of a novel adsorbent material based on modified chitosan for removal of Cu (II) and Cr (VI) ions from aqueous solution. Heterocyclic modification of chitosan has been achieved by the reaction of chitosan with 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde resulting in a Schiff base. This was further modified by incorporation of graphene oxide at the C6 position through ester linkage. This modification results in increase in the number of binding sites like donor nitrogens, OH and COOH groups. The modified polymer was characterized using FTIR, TGA, SEM, EDS and XRD techniques. The adsorption capacity exhibited by the modified chitosan towards Cu (II) and Cr (VI) were 111.11 and 76.92 mg/g respectively which is a significant improvement compared to chitosan. The adsorption data fitted well with Langmuir isotherm model and pseudo second order kinetic model. The thermodynamic analysis of adsorption data indicated endothermic and spontaneous nature of adsorption. A high desorption of over 80% was achieved for Cu (II) in acidic solution and for Cr (VI) in basic solution indicating efficient recovery of adsorbate species.