Paola E. Diaz-Flores

Simultaneous adsorption of Cd2+ and phenol on modified N-doped carbon nanotubes: experimental and DFT studies.

Carbon nanotubes are novel materials that have been investigated for diverse applications, but only a few studies have been focused on environmental issues. In this work, we report on the efficient adsorption of phenol and cadmium ions on N-doped carbon nanotubes (CNx), which have been modified in air at different temperatures. The pristine and modified CNx nanotubes were characterized by SEM, TGA, elemental analysis and their surface areas were also determined. The adsorption experiments of toxic pollutants were carried out in batch reactors at 25 degrees C. The characterization of modified CNx by these techniques showed an increase in oxygen content and surface area in comparison with the pristine CNx tubes. The individual adsorption capacity was 0.10 and 0.07 mmol/g for phenol and Cd(2+), respectively. The experimental data of the competitive adsorption of phenol and Cd(2+) revealed that the cadmium removal was favored as the phenol concentration increased, whereas the phenol adsorption capacity was slightly affected at any cadmium concentration. These results suggest that modified CNx tubes have a great potential in environmental applications as adsorbents of organic and inorganic compounds in aqueous phases. In addition, first-principles calculations were carried out in order to elucidate the mechanism of Cd(2+) adsorption on CNx.

Fluoride removal in water by a hybrid adsorbent lanthanum–carbon

Various health problems associated with drinking water containing high fluoride levels, have motivated researchers to develop more efficient adsorbents to remove fluoride from water for beneficial concentrations to human health. The objective of this research was to anchor lanthanum oxyhydroxides on a commercial granular activated carbon (GAC) to remove fluoride from water considering the effect of the solution pH, and the presence of co-existing anions and organic matter. The activated carbon was modified with lanthanum oxyhydroxides by impregnation. SEM and XRD were performed in order to determine the crystal structure and morphology of the La(III) particles anchored on the GAC surface. FT-IR and pK(a)s distribution were determined in order to elucidate both the possible mechanism of the lanthanum anchorage on the activated carbon surface and the fluoride adsorption mechanism on the modified material. The results showed that lanthanum ions prefer binding to carboxyl and phenolic groups on the activated carbon surface. Potentiometric titrations revealed that the modified carbon (GAC-La) possesses positive charge at a pH lower than 9. The adsorption capacity of the modified GAC increased five times in contrast to an unmodified GAC adsorption capacity at an initial F(-) concentration of 20 mg L(-1). Moreover, the presence of co-existing anions had no effect on the fluoride adsorption capacity at concentrations below 30 mg L(-1), that indicated high F(-) affinity by the modified adsorbent material (GAG-La).

The adsorption kinetics of cadmium by three different types of carbon nanotubes.

Oxidized nitrogen-doped multiwall carbon nanotubes (ox-N-MWCNTs), oxidized multiwall carbon nanotubes (ox-MWCNTs), and oxidized single-wall carbon nanotubes (ox-SWCNTs) were evaluated via batch adsorption kinetic experiments to determine the effect of nanotube morphology on the adsorption rate of cadmium. The nanotubes were characterized by HRTEM, XRD and Raman spectroscopy. Cadmium adsorption isotherms were determined at pH 6. Analyses of the kinetic data with an external mass transport model and an intraparticle diffusion model considered two cases: (1) single nanotubes suspended in aqueous solution and (2) agglomerates of nanotubes suspended in aqueous solution. The intraparticle diffusion model produced the best fit to the experimental data. However, only the diffusivity coefficients for single nanotubes suspended in solution were similar to literature values: about 4×10(-9), 1×10(-9) and 2.4×10(-11) cm(2)/s for ox-N-MWCNTs, ox-MWCNTs and ox-SWCNTs, respectively. The morphology of the various carbon nanotubes might determine cadmium diffusivity. The high amount of sidewall pores observed in the single-walled carbon nanotubes could limit cadmium diffusion and account for the slow diffusion rate of 180 min. Conversely, the short length, small surface area and bamboo-type morphology observed with nitrogen-doped multiwall carbon nanotubes may account for the relatively fast adsorption rate of 15 min as this morphology prevents cadmium diffusion through the internal tubular space of these nanotubes.

Adsorption of Cadmium(II) from an Aqueous Solution onto Activated Carbon Cloth

Abstract The effects of surface properties and solution pH and temperature on the adsorption of cadmium(II) onto activated carbon fiber cloth (ACC) made from polyacrylonitrile (PAN) were investigated in this work. The ACC was oxidized with HNO3 solution and the concentration of acidic sites increased during oxidation whereas that of basic ones diminished. The adsorption capacity of the oxidized ACC was higher than that of ACC without oxidation because the ACC contained greater concentration of acidic sites. It was found that the maximum adsorption took place at pH 8 and the adsorption capacity increased near 22 times, augmenting the pH from 2 to 8. The adsorption capacity diminished on the average twofold, increasing the temperature from 15 to 35°C. Cd(II) adsorbed on ACC at pH 6 can be almost completely desorbed by reducing the solution pH to 2. The adsorption capacity is considerably dependent upon the characteristics of the ACC surface and temperature and pH of the solution.

Erratum to: Biosorption of Cu(II) and Pb(II) from aqueous solutions by chemically modified spent coffee grains

The original version of this article unfortunately contained mistakes. The presentations of Figs. 1 and 2 were incorrect. The correct versions of the figures are given in following page.