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The aim of this study was to obtain indigenously the mesoporous silica (AMS) precursor to 3-aminopropyltriethoxysilane (APTES) and utilizing chitosan a templating natural biopolymer. The textural characteristics of AMS were obtained by the SEM (Scanning Electron Microscopy) and BET (Brunauer–Emmett–Teller) surface area measurements. AMS solid possessed specific surface area of 511.77 m 2 /g and having pore size and pore volume of 3.38 nm and 0.036 cm 3 /g, respectively. Further, the AMS was characterized by the XRD (X-ray Diffraction) and FT-IR (Fourier Transform- Infra Red) analyses. The mesoporous silica was employed for efficient removal of cadmium(II) and lead(II) from aqueous solutions. The influence of solution pH, initial cadmium(II)/or lead(II) concentrations, contact time, and background electrolyte concentrations were studied to deduce the mechanism involved at solid/solution interface. The equilibrium state adsorption data were utilized for the Langmuir and Freundlich adsorption isotherms and the Langmuir adsorption isotherm showed a good agreement with the experimental data. Uptake was found to be fairly fast and the kinetic modelling suggested that the adsorption of cadmium(II)/or lead(II) by AMS was occurred through fractal-like pseudo-second order kinetics. An increase in background electrolyte concentrations from 0.0001 to 0.01 mol/L NaNO 3 did not affect the removal of lead(II), whereas the cadmium(II) removal was slightly suppressed. The XPS (X-ray Photoelectron Spectroscopy) analysis indicated that removal of cadmium(II) or lead(II) occurred through the formation of a chemical bond with the oxygen atoms present with AMS solid. Furthermore, fixed-bed column adsorption was conducted and the loading capacity of cadmium(II) and lead(II) was found to be 11.54 and 8.59 mg/g, respectively. [ABSTRACT FROM AUTHOR]

The aim of this study is to synthesize the three different hybrid materials precursor to natural biopolymer chitosan. The silanes viz., 3-mercaptopropyl trimethoxysilane, trimethoxy(octyl) silane and 3-aminopropyl triethoxysilane were grafted with the chitosan network and were named as CHMS, CHTS and CHAS, respectively. The materials were characterized by the FT-IR spectrometry, SEM–EDX and XPS analyses. These solids were then employed in the efficient removal of Cr(VI) from aqueous solutions using batch and column reactor operations. The functionalized biomaterials possessed extremely high percent removal of Cr(VI) compared to bare chitosan at wide pH range i.e., pH ∼3.0 to 8.0. A fast uptake of Cr(VI) was occurred and high percentage removal was obtained at wide range of Cr(VI) initial concentrations (7.7–100.58 mg/L). The equilibrium state sorption data were utilized for the Langmuir and Freundlich adsorption isotherm studies. Similarly, an increase in background electrolyte concentrations from 0.0001 to 0.05 mol/L NaNO 3 was assessed for the uptake of Cr(VI) by these hybrid materials. Relatively a fast uptake of Cr(VI) by these hybrid materials were obtained and further the time dependence data were fitted well to the pseudo-second-order and fractal-like pseudo-second-order kinetic models rather a pseudo-first-order kinetic model. Furthermore, a detailed sorption mechanism was included with the help of FT-IR, TOC and XPS analyses. In addition, CHMS and CHTS were used for dynamic studies under column reactor operations. The breakthrough curves were then used for the non-linear fitting of the Thomas equation and the loading capacity of the column for Cr(VI) were estimated. [ABSTRACT FROM AUTHOR]

Chitosan is grafted with 3-aminopropyltriethoxysilane under inert atmosphere in acetic acid–ethanol solvent mixture. The materials are characterized by the SEM-EDX and FT-IR analyses. The successful grafting of silane with chitosan is confirmed by the EDX and FT-IR analytical data. The hybrid material is then employed in the remediation of aqueous solutions contaminated with As(V) under batch and column reactor operations. The sorption capacity of chitosan is tremendously increased with the incorporation of 3-aminopropyltriethoxysilane and the hybrid material showed high percent removal of As(V) within the pH ranges between pH 3.0–7.0. The equilibrium sorption is achieved within 120 min of contact and the kinetic data is best fitted to the pseudo first order kinetic model. Moreover, high percentage removal of As(V) is observed in a wide concentration range and the concentration dependence data fitted well to the Freundlich adsorption isotherm. On increasing the background electrolyte (NaNO 3 ) concentration by 100 times decreased significantly the removal of As(V); however, the presence of co-existing ions could not significantly affect the removal of As(V) using the synthesized hybrid material. Furthermore, the loading capacity of As(V) under the dynamic conditions using hybrid material packed column is estimated and found to be 2.576 mg/g. [ABSTRACT FROM AUTHOR]

Hypothesis Chitosan, naturally abundant biomaterial showed an insignificant affinity toward arsenate. The incorporation of organosilane could improve the physical and chemical properties of chitosan for the efficient removal of arsenate from aquatic environment. Experiment The hybrid materials were obtained by grafting the natural biopolymer chitosan with 3-mercaptopropyl trimethoxysilane (CHMS) and trimethoxy-octylsilane (CHTS). The hybrid materials along with bare chitosan were characterized with SEM–EDX, FT-IR and BET specific surface area analyses and the solid materials were further employed in the efficient remediation of aqueous solutions contaminated with As(V) under batch and column reactor operations. Findings The hybrid materials showed an extremely high percentage of As(V) removal compared to bare chitosan within a wide range of pH. As(V) was aggregated rapidly onto the solid surfaces and relatively high percent removal of As(V) was achieved in a wide range of As(V) initial concentrations. Moreover, As(V) was bound with, relatively, weaker forces and forming an ‘outer sphere complexes’ at the surface of solids. The presence of co-existing ions could not significantly affect the removal of As(V) from aqueous solutions. Furthermore, breakthrough data confirmed that these two hybrid materials possessed significantly high loading capacity of As(V) even under dynamic conditions. [ABSTRACT FROM AUTHOR]