High Capacity Sorption Research Articles

High-capacity sorption of U(VI) from aqueous solution using a bio-based oxidized polymeric material

A novel bio-based oxidized polymeric material PAO-CIO was prepared, characterized and evaluated for its sorption toward U(VI) from aqueous solution. PAO-CIO was prepared using Cyclosorus interruptus as a novel supporter, which oxidized by sodium periodate and sodium chlorite, obtaining the oxidized particles, then surface-modified by γ-methacryloxypropyl trimethoxysilane, followed by a graft polymerization reaction and an amidoximation reaction. The SEM, TEM, XPS, FT-IR and XRD were used to characterize the adsorbent. Langmuir, Freundlich and Temkin models were appropriate for fitting the equilibrium data. According to the Langmuir model, the maximum sorption capacity (420.2mg/g) was achieved with pH 5.0, temperature 50°C. The sorption process was insensitive to the interference of other ions. A mixture desorption solution containing 5% NaCl (w/v) and 5% of HCl (v/v) could regenerate the U(VI)-loaded PAO-CIO completely. The sorption capacity only reduced 7.61% after six cycles compared to that of the fresh PAO-CIO. Therefore, PAO-CIO could serve as a cost-effective, efficient and novel adsorbent for U(VI) removal from aqueous solution.

Chemical Modifications of Cassava Peel as Adsorbent Material for Metals Ions from Wastewater

Residues from the processing of cassava roots (Manihot esculentaCrantz), or cassava peels, are evaluated as chemically modified adsorbents with H2O2, H2SO4, and NaOH, in the removal of metal ions Cd(II), Pb(II), and Cr(III) from contaminated water. Modified adsorbents were chemically characterized for their chemical composition andpHPZC(point of zero charge), while adsorption tests determined the best conditions of pH, adsorbent mass, and contact time between adsorbent and adsorbate in the process of removal of the metal ions. Isotherms obtained from the preliminary results were linearized by Langmuir’s and Freudlich’s models. The thermodynamic parameters, such asΔH,ΔG, andΔS, were also evaluated. The modifying solutions proposed were effective in the modification of adsorbents and resulted in high capacity sorption materials. Equilibrium time between adsorbent and adsorbate for the solutions contaminated with metals is about 40 minutes. The Langmuir model adjusted to most results, indicating monolayers adsorption of Cd(II), Pb(II), and Cr(III). The values obtained for LangmuirQmshow a higher adsorption capacity caused by chemical modifications, with values such as 19.54 mg Cd(II) per g of M. NaOH, 42.46 mg of Pb(II) per g of M. NaOH, and 43.97 mg of Cr(III) per g of M H2O2. Results showed that modified cassava peels are excellent adsorbent, renewable, high availability, and low-cost materials and a feasible alternative in the removal of metals in industries.

Paraquat and Diquat Sorption on Iron Oxide Coated Quartz Particles and the Effect of Phosphates

The covering of quartz particles (Q) with Fe oxides provides high capacity sorption and immobilization of both paraquat (PQ) and diquat (DQ) as well as phosphates (P), that can be used to remediate contaminated environments due to their persistence. Both PQ and DQ have higher sorption strength on crystalline iron oxide coated quartz particles (QFec) than on amorphous iron oxides (QFea), but the highest is for PQ, which might be due to its strongest interaction. The increasing addition of P contributes to the increase of quat maximum sorption on iron oxide coated quartz particles, because the cosorption of P causes the surface charge to become more negative, facilitating the sorption of positively charged quats, but this happens in a different way for both quats. It was also seen that the formation of phosphate−quat complexes has a lower affinity than P by the coated quartz particles. The characteristics of the coated quartz particles would allow increased sorption of these quaternary ammonium herbicide contaminants.

Simplified analysis of organic compounds in headspace and aqueous samples by high-capacity sample enrichment probe

A sample enrichment probe (SEP) consisting of a thin rod of an inert material and provided at one end with a short sleeve of polydimethylsilicone rubber was used for the high-capacity sample enrichment of analytes from gaseous and aqueous samples for analysis by gas chromatography (GC) and its hyphenated techniques. The silicone rubber was exposed to the analytical sample, after which the end of the rod carrying the silicone rubber was introduced into the injector and the analytes thermally desorbed and analysed by GC. This technique is similar to, but differs from, solid-phase microextraction (SPME) in that a much larger volume of the sorptive phase is employed, the sorptive phase is not introduced into the inlet of the GC via a needle and the injector is opened to the atmosphere for the introduction and removal of the SEP. In the determination of volatile and semi-volatile organic compounds in gaseous and aqueous media, the SEP technique gave results comparable with those obtained by the stir-bar-sorptive extraction (SBSE) and high-capacity sorption probe (HCSP) techniques. Implementation of the SEP technique requires only minor adaptations to the gas chromatograph and does not require any auxiliary thermal desorption and cryotrapping equipment.

An investigation of the effects of pyrolysis parameters on gas separation properties of carbon materials

A significant extension of an earlier analysis of molecular sieving carbons formed from polymeric precursors is reported for separation of important gas pairs including O 2/N 2, CO 2/CH 4 and C 3H 6/C 3H 8. Previously, it was shown that changing the time or temperature of the pyrolysis protocol for a commercially available polyimide (Matrimid ®) altered the final properties of the carbons produced. Changing the precursor material was shown in this study to also affect the final carbon material obtained for a given final pyrolysis temperature. Analysis of low temperature carbon dioxide adsorption isotherms using density functional theory was employed to characterize the microporosity of the materials. Results are given here for a totally different packing-inhibited polyimide precursor (6FDA/BPDA-DAM). Sorption, permeation and diffusion data are compared with those obtained using the more densely packed commercial polyimide precursor Matrimid ® studied earlier. Thermal soak was also investigated and the effect on permeation properties determined for carbons using both precursors. The results indicate that carbons from both precursors have size-selective ultramicropores as well as larger nonselective micropores that provide high capacity sorption sites for penetrants. High permselectivities, combined with high permeabilities are found for some of the samples when compared with conventional polymer materials. A hypothetical ultramicropore size distribution is shown to be useful to relate transport data to results from more commonly used characterization techniques such as pore size distribution analysis.

Automated high-capacity sorption probe for extraction of organic compounds in aqueous samples followed by gas chromatographic analysis

An automated high-capacity sorption device for GC analysis of ultra trace components has been developed. The scope of the presented technique was to combine the simplicity of solid-phase microextraction (SPME) with the high extraction efficiency of the stir bar sorptive extraction technology. Sorptive extractions of water samples were performed using polydimethylsiloxane (PDMS) rubber tubing (120 μl) mounted onto a glass rod. The sampling procedure was carried out by a robotic autoinjector. Since the setup is fully automated, unattended and precise time-controlled extraction of samples is possible and makes quantitation with non-equilibrium extractions feasible. The sorption probes are easy to exchange, which facilitates off-line/in-field sampling. The system was evaluated with a test mixture of 44 environmentally hazardous compounds. Detection limits were found to be in the sub-ppt region. The performance of the system was demonstrated with the analysis of polycyclic aromatic hydrocarbons in urban snow.

Investigation of porosity of carbon materials and related effects on gas separation properties

Carbon molecular sieving membranes are chemically robust materials with tailorable gas transport properties for O 2/N 2, CO 2/CH 4 and C 3H 6/C 3H 8 separations. Such carbon materials were formed in this study by the pyrolysis of polyimide precursors. The final pyrolysis temperature was varied to alter the carbon structure, which changed the average pore size. Characterization of the porosity of these materials and how this feature changes when pyrolysis conditions are varied could guide the systematic control of these materials. However, the carbon is an amorphous, microporous material, which makes it difficult to characterize compared to crystalline materials. From separation studies of penetrants on these materials it appears that these materials have both ultramicropores (<7 Å) and larger micropores. The ultramicropores are believed to be mainly responsible for molecular sieving while the micropores provide negligible resistance to diffusion but provide high capacity sorption sites for penetrants. Techniques such as wide angle X-ray diffraction and the analysis of carbon dioxide adsorption isotherms using density functional theory were employed to characterize the microporosity of the material. The small dimensions of the key ultramicropores make accurate determination of their pore size distribution difficult. Therefore, to effectively discuss the differences in transport properties when different pyrolysis temperatures are used as well as penetrants with different dimensions, a hypothetical ultramicropore size distribution was used as a tool to discuss and interpret a combination of parameter effects and trends of separation properties.

Specificity of intermolecular action in systems including polyelectrolytes and ions of organic physiologically active substances

Abstract