Abstract:-RH-MCM-41 was synthesized by using silica from rice husk and further modified to increase acidity by adding Al with grafting method with Si/Al ratio of 75 and 25. The resulting materials were referred to as RH-AlMCM-41(75) and RH-AlMCM-41(25). The XRD spectra of all RH-AlMCM-41 confirmed a mesoporous structure of MCM-41. Surface areas of all RH-AlMCM-41 were in the range of 700-800 m 2 /g, lower than that of the parent RH-MCM-41, which was 1230 m 2 /g. After Al addition the Si/Al ratios of RHAlMCM-41(75) and … Show more
“…Several technological alternatives have been associated in the literature with the use of RH and RHA: production of silica and silicon carbide, using the ashes like filler in polymers, in concrete, production of silicates, zeolite synthesis (Chumee et al, 2009) and use as an adsorbent of heavy metals in synthetic wastewater (Srivastava et al, 2006;Naiya et al, 2009;Krishnani et al, 2008;Ye et al, 2010;Bhatnagar and Sillanpaa, 2010;Ahmaruzzaman, 2010).…”
-Heavy metal removal by adsorption using rice husks as a bioadsorbent was evaluated as an alternative for wastewater treatment. Batch equilibrium experiments and kinetic sorption studies were performed using monocomponent solutions of Ni(II), Cd(II), Zn(II), Pb(II) and Cu(II) in surface samples of in natura (RH) and calcined rice husks (RHA). RHA showed higher potential for removing lead and copper. Experimental data for adsorption isotherms of lead and copper were adjusted by Langmuir, Freundlich and Dubinin-Radushkevick (D-R) models, being better represented by the Langmuir model. The calcination of RH increased its surface area, improving its adsorption properties. From a morphological analysis obtained by SEM and diffraction patterns (XRD), a longitudinal fibrous and amorphous structure was observed for RH. TGA results indicated a total mass loss of around 60% for RH and 24.5% for RHA.
“…Several technological alternatives have been associated in the literature with the use of RH and RHA: production of silica and silicon carbide, using the ashes like filler in polymers, in concrete, production of silicates, zeolite synthesis (Chumee et al, 2009) and use as an adsorbent of heavy metals in synthetic wastewater (Srivastava et al, 2006;Naiya et al, 2009;Krishnani et al, 2008;Ye et al, 2010;Bhatnagar and Sillanpaa, 2010;Ahmaruzzaman, 2010).…”
-Heavy metal removal by adsorption using rice husks as a bioadsorbent was evaluated as an alternative for wastewater treatment. Batch equilibrium experiments and kinetic sorption studies were performed using monocomponent solutions of Ni(II), Cd(II), Zn(II), Pb(II) and Cu(II) in surface samples of in natura (RH) and calcined rice husks (RHA). RHA showed higher potential for removing lead and copper. Experimental data for adsorption isotherms of lead and copper were adjusted by Langmuir, Freundlich and Dubinin-Radushkevick (D-R) models, being better represented by the Langmuir model. The calcination of RH increased its surface area, improving its adsorption properties. From a morphological analysis obtained by SEM and diffraction patterns (XRD), a longitudinal fibrous and amorphous structure was observed for RH. TGA results indicated a total mass loss of around 60% for RH and 24.5% for RHA.
“…The XRD patterns of MCM-41 and Al-MCM-41 showed a decrease in intensity with a high amount of Fe added. In our previous work, the catalytic performances of bimetallic Pt-Fe catalysts with 5 wt.% Fe supported on RH-MCM-41 and Al-RH-MCM-41 were compared, and Pt-Fe/RH-MCM-41 gave a higher conversion [16]. Although it was expected that supports with higher acidity would be more active, the addition of Al resulted in a significant decrease in the surface area of MCM-41, which could explain the poorer performance.…”
Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum−iron catalysts Pt-Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was +3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H 2 O 2 as the oxidant at phenol : H 2 O 2 mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70• C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.
“…After calcination to eliminate the organics, metallic impurities such as oxides of alkali metals are removed by leaching with NaOH solution at temperatures between 100 and 200 o C for 1 h. Direct recovery of silica by precipitation from the basic solution is achieved by addition of drops of sulfuric acid to the hot basic solution, followed by thermal treatment at 110 o C [34]. Several products of commercial interest such as silicon carbide (SiC) used as semiconductors, pozzolan in cement manufacturing, and recently, sodium silicate in the preparation of silica-based mesoporous materials have been reported [35][36][37][38][39][40][41][42]. [42] demonstrated that RHA silica generated from biomass power plant can be used as silica framework for synthesis of MCM-41-type material with crystallinity characteristics and porosity similar to those synthesized from commercial silica.…”
Section: Utilization Of Silica Framework From Biomass Residuesmentioning
The synthesis of mesoporous silica materials was reviewed with a view to discuss the reaction mechanism and the various attempts made at enhancing the materials' properties by utilizing varieties of templating agents and silica frameworks from pure synthetic chemicals. This chapter also reviewed studies in which either the template or the framework was synthesized from benign reagents obtained from renewable sources, to achieve enhanced material properties. The view was to encourage the development of mesoporous silica materials in which both the template and the silica framework are from biomass origin. This approach may promote the large-scales synthesis of mesoporous silica for commercial purposes, which had previously been hampered by the toxic nature, cost of synthetic chemical reagents, and unsustainable synthetic routes.
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