Jose Rene Rangel-Mendez

Chitosan selectivity for removing cadmium (II), copper (II), and lead (II) from aqueous phase: pH and organic matter effect

The aim of this study was to investigate the selectivity of chitosan for cadmium, copper and lead in the presence and absence of natural organic matter (NOM) in different pH solutions. Adsorption isotherms of one and three adsorbates at initial concentration of 5-100mg/L were carried out in batch reactors at pH 4, 5, or 7 and 25 degrees C in reactive and clarified water. The chitosan employed had a MW of 107.8 x 10(3)g/mol and degree of acetylation (DA) of 33.7%. The chitosan adsorption capacity at pH 4 in reactive water was 0.036, 0.016, 0.010mmol/g for Pb(2+), Cd(2+), and Cu(2+), respectively, and it decreased for Pb(2+) and Cd(2+) in clarified water. Conversely, experiments carried out in clarified water showed that the cadmium adsorption capacity of chitosan was enhanced about three times by the presence of NOM at pH 7: an adsorption mechanism was proposed. Furthermore, it was found that the biosorbent selectivity, in both reactive and clarified water at pH 4, was as follows Cu(2+)>Cd(2+)>Pb(2+). Finally, the preliminary desorption experiments of Cd(2+) conducted at pH 2 and 3 reported 68 and 44.8% of metal desorbed, which indicated that the adsorption mechanism occurred by electrostatic interactions and covalent bonds.

Zirconium-carbon hybrid sorbent for removal of fluoride from water: oxalic acid mediated Zr(IV) assembly and adsorption mechanism.

When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbents by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L(-1). The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS, and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis demonstrated that zirconium ions interact mainly with carboxylic groups on the activated carbon surfaces. Moreover, XPS analysis demonstrated that Zr(IV) interacts with oxalate ions, and the fluoride adsorption mechanism is likely to involve -OH(-) exchange from zirconyl oxalate complexes.

Adsorption kinetics of chromium(III) ions on agro-waste materials.

The objective of this research is to compare empirical (pseudo-first and pseudo-second order models) and diffusional models (film diffusion, film-pore-volume diffusion, and film-surface diffusion models) in predicting the adsorption kinetics of chromium(III) on water-washed agro-waste materials (sorghum straw, oats straw, and agave bagasse). Concentration decay curves can be predicted by using either empirical or diffusional kinetic models. However, the film diffusion model seems to be the most appropriated one based on the low reported deviation (0.45-4.09%), and the physical properties (low porosity 0.004-0.007, low surface area 0.6-1.2m(2)g(-1) and low pore volume 0.003-0.004cm(3)g(-1)) of the studied agro-waste materials, which support the idea that intraparticle diffusion may be neglected. Furthermore, the external mass transfer coefficient estimated with the film diffusion model has a physical meaning that helps to explain the diffusion of solutes across the film resistance in agro-waste biosorbents.

Arsenic removal by modified activated carbons with iron hydro(oxide) nanoparticles

Different activated carbons modified with iron hydro(oxide) nanoparticles were tested for their ability to adsorb arsenic from water. Adsorption isotherms were determined at As (V) concentrations < 1 ppm, with varying pH (6, 7, 8) and temperature (25 and 35 °C). Also, competition effect of anions on the As (V) adsorption capacity was evaluated using groundwater. The surface areas of the modified activated carbons ranged from 632 m(2) g(-1) to 1101 m(2) g(-1), and their maximum arsenic adsorption capacity varied from 370 μg g(-1) to 1250 μg g(-1). Temperature had no significant effect on arsenic adsorption; however, arsenic adsorption decreased 32% when the solution pH increased from 6 to 8. In addition, when groundwater was used in the experiments, the arsenic adsorption considerably decreased due to the presence of competing anions (mainly SO(4)(2-), Cl(-) and F(-)) for active sites. The data from kinetic studies fitted well to the pseudo-second-order model (r(2) = 0.98-0.99). The results indicated that sample CAZ-M had faster kinetics than the other two materials in the first 10 min. However, sample F400-M was only 5.5% slower than CAZ-M. The results of this study show that iron modified activated carbons are efficient adsorbents for arsenic at concentrations lower than 300 μg L(-1).

Anchorage of iron hydro(oxide) nanoparticles onto activated carbon to remove As(V) from water

The adsorption of arsenic (V) by granular iron hydro(oxides) has been proven to be a reliable technique. However, due to the low mechanical properties of this material, it is difficult to apply it in full scale water treatment. Hence, the aim of this research is to develop a methodology to anchor iron hydro(oxide) nanoparticles onto activated carbon, in which the iron hydro(oxide) nanoparticles will give the activated carbon an elevated active surface area for arsenic adsorption and also help avoid the blockage of the activated carbon pores. Three activated carbons were modified by employing the thermal hydrolysis of iron as the anchorage procedure. The effects of hydrolysis temperature (60-120 °C), hydrolysis time (4-16 h), and FeCl(3) concentration (0.4-3 mol Fe/L) were studied by the surface response methodology. The iron content of the modified samples ranged from 0.73 to 5.27%, with the higher end of the range pertaining to the carbons with high oxygen content. The materials containing smaller iron hydro(oxide) particles exhibited an enhanced arsenic adsorption capacity. The best adsorbent material reported an arsenic adsorption capacity of 4.56 mg As/g at 1.5 ppm As at equilibrium and pH 7.

Immobilized redox mediator on metal-oxides nanoparticles and its catalytic effect in a reductive decolorization process.

Different metal-oxides nanoparticles (MONP) including α-Al(2)O(3), ZnO and Al(OH)(3), were utilized as adsorbents to immobilize anthraquinone-2,6-disulfonate (AQDS). Immobilized AQDS was subsequently tested as a solid-phase redox mediator (RMs) for the reductive decolorization of the azo dye, reactive red 2 (RR2), by anaerobic sludge. The highest adsorption capacity of AQDS was achieved on Al(OH)(3) nanoparticles, which was ∼0.16 mmol g(-1) at pH 4. Immobilized AQDS increased up to 7.5-fold the rate of decolorization of RR2 by anaerobic sludge as compared with sludge incubations lacking AQDS. Sterile controls including immobilized AQDS did not show significant (<3.5%) RR2 decolorization, suggesting that physical-chemical processes (e.g. adsorption or chemical reduction) were not responsible for the enhanced decolorization achieved. Immobilization of AQDS on MONP was very stable under the applied experimental conditions and spectrophotometric screening did not detect any detachment of AQDS during the reductive decolorization of RR2, confirming that immobilized AQDS served as an effective RMs. The present study constitutes the first demonstration that immobilized quinones on MONP can serve as effective RMs in the reductive decolorization of an azo dye. The immobilizing technique developed could be applied in anaerobic wastewater treatment systems to accelerate the redox biotransformation of recalcitrant pollutants.

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.

Hybrid photoactive materials from municipal sewage sludge for the photocatalytic degradation of methylene blue

To our knowledge this is the first manuscript describing a one step synthesis to produce an organic/inorganic hybrid material prepared by carbonization of municipal sewage sludge (ACRM) that shows photoactivity for the photocatalytic degradation of methylene blue (MB). The hybrid material (ACRM) exhibited a mesoporous texture while XRD and SEM-EDX showed Fe2O3 and Fe3C crystallites. Photodegradation of MB was studied under two different lamps and results were compared against those obtained with a commercial TiO2. The photocatalytic tests showed that the hybrid material is photoactive and the binary composite TiO2–ACRM showed higher apparent first-order rate constants for the degradation of MB than those obtained on pure TiO2. A synergy effect between TiO2 and ACRM was estimated at about 5 and 8 under lamps with UV-vis and almost pure visible light, respectively. It can be concluded that the photoactivity of TiO2–ACRM relative to neat TiO2 was up to one order of magnitude higher, suggesting that iron phases in the hybrid material photo-assist the TiO2 in the photodegradation of the methylene blue.

Studies of Adsorption of Heavy Metals onto Spent Coffee Ground: Equilibrium, Regeneration, and Dynamic Performance in a Fixed-Bed Column

Equilibrium and dynamic adsorption of heavy metals onto spent coffee ground (SCG) were studied. The equilibrium adsorption of Cd2