Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: An XPS investigation of mechanism

Thermodynamics and mechanism studies on electrochemical removal of cesium ions from aqueous solution using a nanoparticle film of copper hexacyanoferrate

Nanoparticle (NPs) film of copper hexacyanoferrate (CuHCF(III)) was developed for electrochemically cesium separation from wastewater. Different form the electro- or chemical deposited films, CuHCF(III) NPs were firstly covered with ferrocyanide anions, so that they can be well dispersed in water and formed ink. Then CuHCF(III) NPs can be uniformly coated by simple wet printing methods, so it is feasible to prepare NPs film of any sizes, or any patterns at low cost. This process provided a promising technology for preparing large scale electrodes for sequential removal of Cs from wastewater in the columns. Cs separation can be controlled by an electrically switched ion exchange (ESIX) system. Effect of temperatures, and ionic strength on Cs removal was investigated. Thermodynamics results showed that Cs adsorption process was exothermic in nature and favored at low temperature. Ionic strength study indicated the CuHCF(III) film can selectively separate Cs in wide ionic strength range from 1 × 10(-4) to 1 × 10(-1) M Na(+). XPS results demonstrated that the electrochemical oxidation-reduction of Fe (II/III) made contributions to Cs separation.

Mercury(II) removal with modified magnetic chitosan adsorbents

Two modified chitosan derivatives were prepared in order to compare their adsorption properties for Hg(II) removal from aqueous solutions. The one chitosan adsorbent (CS) is only cross–linked with glutaraldehyde, while the other (CSm), which is magnetic, is cross-linked with glutaraldehyde and functionalized with magnetic nanoparticles (Fe₃O₄). Many possible interactions between materials and Hg(II) were observed after adsorption and explained via characterization with various techniques (SEM/EDAX, FTIR, XRD, DTG, DTA, VSM, swelling tests). The adsorption evaluation was done studying various parameters as the effect of pH (optimum value 5 for adsorption and 2 for desorption), contact time (fitting to pseudo–first, –second order and Elovich equations), temperature (isotherms at 25, 45, 65 °C), in line with a brief thermodynamic analysis (ΔG⁰ < 0, ΔH⁰ > 0, ΔS⁰ > 0). The maximum adsorption capacity (fitting with Langmuir and Freundlich model) of CS and CSm at 25 °C was 145 and 152 mg/g, respectively. The reuse ability of the adsorbents prepared was confirmed with sequential cycles of adsorption-desorption.

Highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex: process and mechanism studies

Metal-biopolymer complexes has recently gained significant attention as an effective adsorbent used for the removal of Cr(VI) from water. Unfortunately, despite increasing research efforts in the field of removal efficiency, whether this kind of complex can reduce Cr(VI) to less-toxic Cr(III) and what are the mechanisms of detoxification processes are still unknown. In this study, despite the highly adsorption efficiency (maximum adsorption capacity of 173.1 mg/g in 10 min), the significant improvement of Cr(VI) reduction by chitosan-Fe(III) complex compared with normal crosslinked chitoan has been demonstrated. In addition, the structure of chitosan-Fe(III) complex and its functional groups concerned with Cr(VI) detoxification have been characterized by the powerful spectroscopic techniques X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). The XPS spectra indicated that the primary alcoholic function on C-6 served as an electron donor during Cr(VI) reduction and was oxidized to a carbonyl group. The X-ray adsorption near edge spectra (XANES) of the Cr(VI)-treated chitosan-Fe(III) complex revealed the similar geometrical arrangement of Cr species as that in Cr(III)-bound chitosan-Fe(III). Overall, a possible process and mechanism for highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex has been elucidate.

Polyurethane-Keratin Membranes: Structural Changes by Isocyanate and pH, and the Repercussion on Cr(VI) Removal

Keratin has the capacity to interact with metal ions. In order to take advantage of this potential, a novel membrane with polyurethane and keratin has been developed and studied for removal of Cr(VI) from aqueous solution. Physicochemical and morphological properties of these hybrid membranes were studied, varying synthesis parameters such as the type of isocyanate and pH in keratin solution. The effects of using diphenyl-methane-diisocyanate or toluene-diisocyanate and modifying the pH in keratin solutions were evaluated by scanning electron microscopy, Fourier transform infrared spectroscopy, and dynamical mechanical analysis. Results show that pH has a strong influence on morphology and on Cr(VI) removal efficiency. When pH in keratin solution is low (2.5), the protein separates from water, and a more closed cell in the membrane is obtained affecting its mechanical properties. The removal efficiency of Cr(VI) was also assessed at different pH values of chromium solutions. These results show that when pH of the Cr solution is acidic (at 1.5), the Cr(VI) removal percentages increase significantly, reaching up to a 58%. Thus this paper demonstrates the successful combination of synthetic and natural polymers depending on the process parameters to be applied in the critical purpose of remediation of Cr(VI) contamination.