title: Biogenic modified silica as a sorbent of cadmium ions: preparation and characterization.
abstract: This work describes the preparation and characterization of biogenic modified silica from rice hull ash and its use as a sorbent of cadmium ions. Thus, an agro-industrial residue has been used to produce a new adsorbent product which is able to remove toxic elements. Mesoporous biogenic silica was obtained by alkaline extraction of sodium silicate by hydrolysis with the sol-gel process, and it was modified with salen using 1,2-dichloroethane as a spacer. The surface area of the silica was measured by nitrogen adsorption/desorption analysis. Surface modification was measured by Fourier transform infrared spectroscopy. The degree of functionalization was obtained by elemental analysis. This work showed that biogenic modified silica can be produced in aqueous media from rice hull ash using a simple method, providing an alternative method for adsorbent preparation. Thermogravimetric analysis showed that the salen-modified silica is stable up to 209 degrees C. The modified silica displays appropriate structural characteristics for an adsorbent. The cylindrical pores, open at both ends, allow free diffusion of cadmium ions to the adsorption sites on the silica surface. The surface modification increases cadmium adsorption on the silica surface 100-fold. The salen-modified silica showed specific adsorption for Cd(2+) of 44.52 mg/g SiO2 at cadmium concentration of 100 mg/l.
authors.affiliation: Department of Chemical Engineering, University of São Paulo, São Paulo, SP, Brazil. marcia_morais2004@yahoo.com.br
authors.forename: Márcia R M
authors.initials: MR
authors.lastname: Chaves
authors.forename: Edward R
authors.initials: ER
authors.lastname: Dockal
authors.forename: Rubem C R
authors.initials: RC
authors.lastname: Souza
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Büchler
mesh_terms: D000327:Adsorption; D000383:Agriculture; D018533:Biomass; D002104:Cadmium / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods; D005029:Ethylenediamines / Q000737:chemistry; D007220:Industrial Waste; D012275:Oryza / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013696:Temperature; D013818:Thermogravimetry; D014874:Water Pollutants, Chemical / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D005029:Ethylenediamines; D007220:Industrial Waste; D017640:Silicates; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D002104:Cadmium; D012822:Silicon Dioxide; C011452:disalicylaldehyde ethylenediamine; C005691:sodium silicate