Enhanced adsorption of mercury ions on thiol derivatized single wall carbon nanotubes.

Thiol-derivatized single walled carbon nanotube (SWCNT-SH) powders were synthesized by reacting acid-cut SWCNTs with cysteamine hydrochloride using carbodiimide coupling. Infrared (IR) spectroscopy, Raman spectroscopy and thermogravimetric analysis confirmed the successful functionalization of the SWCNTs. SWCNT-SH powders exhibited a threefold higher adsorption capacity for Hg(II) ions compared to pristine SWCNTs, and a fourfold higher adsorption capacity compared to activated carbon. The influence of adsorption time, pH, initial metal concentration and adsorbent dose on Hg(II) ion removal was investigated. The maximum adsorption capacity of the SWCNT-SH powders was estimated by using equilibrium isotherms, such as Freundlich and Langmuir, and the maximum adsorption capacity of the SWCNT-SH powder was found to be 131 mg/g. A first-order rate model was employed to describe the kinetic adsorption process of Hg(II) ions onto the SWCNT-SH powders. Desorption studies revealed that Hg(II) ions could be easily removed from the SWCNT-SH powders by altering the pH. Further, the adsorption efficiency of recovered SWCNT-SH powders was retained up to 91%, even after 5 adsorption/desorption cycles.

Alginate-graphene oxide hybrid gel beads: an efficient copper adsorbent material.

Here we report on the adsorption performance of calcium alginate (Ca-Alg2) and Ca-Alg2 with encapsulated graphene oxide (Ca-Alg2/GO) gel bead adsorbents for the successful removal of Cu(2+) ions from aqueous solution. Different adsorbent doses, Cu(2+) concentrations and contact times were investigated using equilibrium and kinetic studies. The adsorbents were characterized using Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and focussed ion beam scanning electron microscopy (FIB/SEM). The equilibrium adsorption data were fitted to Langmuir isotherms and the maximum adsorption capacities of the Ca-Alg2 and Ca-Alg2/GO gel beads were found to be 42.7 mg g(-1) and 60.2 mg g(-1), respectively. The equilibrium adsorption data were fitted to a pseudo-second-order kinetic equation showing that the Ca-Alg2 gel beads had a higher kinetic adsorption rate at 0.0425 g mg(-1)min(-1) compared to Ca-Alg2/GO at 0.0179 g mg(-1)min(-1).

Beta-cyclodextrin decorated nanostructured SERS substrates facilitate selective detection of endocrine disruptor chemicals.

We demonstrate the selective detection of endocrine disruptor chemicals (EDCs) from river water using surface enhanced Raman scattering (SERS). By means of nanosphere lithography, the SERS substrate was prepared via the initial deposition of a monolayer of silica nanospheres (with diameter of ∼330 nm) on a silicon substrate as the template. Subsequently, a 180 nm thick layer of silver followed by a 20 nm layer of gold was deposited. This surface was modified with mono-6-deoxy-6-((2-mercaptoethyl)amino)-beta-cyclodextrin (ß-CD) in order to produce a selective capture surface suitable for EDC capture and their detection by means of SERS. We show that EDC model compounds, including 3-amino-2-naphthoic acid (NAPH), potassium hydrogen phthalate (PHTH) and the EDC ß-estradiol (ESTR), were captured by the ß-CD decorated surface. This surface facilitated SERS detection with limits of detection of 3.0 µM (NAPH), 10 µM (PHTH) and 300 nM (ESTR), all 10-100 times lower than that without the surface modification with ß-CD. Individual and simultaneous detection of NAPH and PHTH from their mixture was achieved as evidenced using the bianalyte Raman technique.

Synthesis and biological evaluation of mannose-6-phosphate-coated multivalent dendritic cluster glycosides.

The synthesis of multivalent dendritic cluster glycosides of mannopyranosyl-6-phosphate is presented. Poly(amido amine)-based dendrimers of 0.5-3.5 generations, containing carboxylic acid peripheral functionalities, were utilized so as to install 4, 8, 16 and 32 mannopyranosyl-6-phosphate residues at the peripheries of the dendrimers. Amide bond formation between an amine-tethered mannopyranosyl-6-phosphate monomer unit and carboxylic acid-functionalized dendrimers was conducted to synthesize the dendritic cluster glycosides. The constitutions of the Man-6-P-containing dendrimers were assessed by 1H, 13C and 31P NMR spectroscopies and the sugar content analysis by a resorcinol assay. Preliminary biological studies with few newly synthesized Man-6-P-containing dendrimers showed that these compounds could bind the purified goat liver mannose 6-phosphate receptor (MPR 300) protein.

Synthesis and Langmuir studies of bivalent and monovalent alpha-D-mannopyranosides with lectin Con A.

Highly avid interaction between carbohydrate ligands and lectin receptors nominally requires the ligand presentation in a clustered form. We present herein an approach involving Langmuir monolayer formation of the sugar ligands and the assessment of their lectin binding at the air-water interface. Bivalent alpha-D-mannopyranoside containing the glycolipid ligand was used to study its binding profiles with lectin Con A, in comparison to the corresponding monovalent glycolipid. In addition to the bivalent and monovalent nature of the glycolipid ligands at the molecular level, the ligand densities at the monolayer level were varied with the aid of a nonsugar lipid molecule so as to obtain mixed monolayers with various sugar-nonsugar ratios. Lectin binding of bivalent and monovalent ligands at different ratios was monitored by differential changes in the surface area per molecule of the mixed monolayer, with and without the lectin. The present study shows that maximal binding of the lectin to the bivalent ligand occurs at lower sugar densities at the interface ( approximately 10% sugar in the mixed monolayer) than for that of the monovalent ligand ( approximately 20% sugar in the mixed monolayer). It is observed that complete coverage of the monolayer with only the sugar ligands does not allow all of the sugars to be functionally active.