Short-period synthesis of ordered mesoporous silica SBA-15 using ultrasonic technique

Mesoporous silica SBA-15 was synthesized from rice husk ash via the ultrasonic technique in the hydrolysis-condensation stage. The effect of the time period in this stage on the mesoporous silica SBA-15 structure and physical properties was investigated and compared with those of the SBA-15 prepared by the conventional technique. It has been shown that the ultrasonic technique can be successfully applied for the synthesis of mesoporous silica SBA-15 with highly ordered hexagonal pore-arrangement and narrow PSD within the much shorter hydrolysis-condensation period. The SBA-15 products synthesized via the ultrasonic technique for the time period of 3 h have higher specific surface area, total pore volume, and microporosity than those prepared by the conventional technique for the time period of 24 h.     

Nature and reactivity of silica available in rice husk and its ashes

Scanning electron microscopy, reactivity and surface area measurements of rice husk and its ashes reveal the gradual formation of amorphous silica during ashing. The reactivity of the silica thus formed is found to be at its maximum for ashing temperatures between 400 and 600°C and hold-time from 6 to 12 h. The reactivity of the ash is found to decrease with increasing temperature (⩾ 600°C) and hold-time. IICT Communication No. 2375.     

Synthesis of mesoporous ZSM-5 from rice husk ash with ultrasound assisted alkali-treatment method used in catalytic cracking of light naphtha

A series of mesoporous ZSM-5 zeolite was synthesized with ultrasonic assisted alkali-treatment technique and their catalytic activity was investigated in catalytic cracking of light naphtha. ZSM-5 zeolite was synthesized from rice husk ash without using any organic template. Effect of alkali-treatment conditions on physicochemical properties of synthesized zeolite was investigated with XRD, FESEM, TEM, N2 adsorption-desorption isotherm, NH3-TPD and TGA technique. It was found that ultrasound energy facilitates the creation of hierarchical structure of ZSM-5 during alkali-treatment. According to XRD analysis, zeolite structure was preserved after 20 min ultrasonic assisted alkaline treatment. However, prolonged dessilication time led to the destruction of MFI zeolite structure. The synthesized ZSM-5 represented highly ordered hexagonal-shape morphology. With increasing alkali-treatment time, the plough land roughness appeared on the surface of zeolite. Comparison of the textural properties samples revealed that the mesopore surface area of alkali-treated samples increased considerably with the increase of ultrasonic assisted alkali-treatment time. Results from catalytic activity tests showed that ultrasound energy has great influence on the activity of ZSM-5. The sample had the highest activity after alkali-treated for 20 min in presence of ultrasound energy which was due to their appropriate hierarchical structure.     

Creep analysis of concrete containing rice husk ash

This paper presents an experimental study on the mechanical properties of concrete added with rice husk ash (RHA) as a supplementary cementitious material. The compressive strength, modulus of elasticity and creep were obtained experimentally from specimens with different RHA contents (0%, 10%, 15% and 20% of binder). The results show that the addition of RHA in concrete can improve both the compressive strength and modulus of elasticity and reduce the creep of concrete. The examination of pore micro-structure of hardened concrete using both the mercury intrusion porosimetry and scanning electron microscope techniques demonstrates that RHA particles can react with calcium hydroxide originated from cement hydration to produce additional C-S-H, which can fill voids and large pores and thus reduces the porosity related to capillary pores and voids. In addition, the release of absorbed water, which is retained in the small pores of RHA particles at early days, can improve cement hydration and thus reduce the porosity related to gel pores.     

Synthesis and surface characteristics of nanosilica produced from alkali-extracted rice husk ash

Rice husk is a form of agricultural biomass that provides an abundant silicon source. This study used rice husk as a raw material to prepare nanosilica without adding an extra surfactant. This work investigated a dissolution-precipitation technique as a function of acid treatment, sodium silicate concentration, gelation pH, aging temperature, and aging time to establish optimum conditions for preparing silica nanoparticles. Experimental results showed that silica produced by hydrochloric acid possesses higher surface area than that of sulfuric, oxalic, and citric acids. Surface characteristics of the sample depend mainly upon gelation pH. The highest surface area and pore volume of silica samples were 634 m²/g and 0.811 cm³/g. Pore diameters were controllable from 3 to 9 nm by adjusting the solution pH value. Particles had a uniform size of 5-30 nm. The objective of this study was to develop a method of nanosilica preparation that enhances the economic benefits of re-using rice husk waste.     

Synthesis and properties of dense bulks for mesoporous silica SBA-15 by a modified hydrothermal method

Dense SBA-15 bulks with mesoporous structure as well as powdered SBA-15 were successfully synthesized by the modified hydrothermal method. These SBA-15 bulks have the higher density of 1.16 to 1.19 g/cm³, compared to green density of 0.68 g/cm³ for the pellet from SBA-15 powder. Obtained SBA-15 bulks possessed extremely high BET surface area of 467 m²/g and mesopore of 4.0 nm in diameter The possibility of densification for SBA-15 bulks using this method was confirmed.     

Properties of geopolymer with seeded fly ash and rice husk bark ash

In the present work, compressive strength of inorganic polymers (geopolymers) produced of seeded fly ash and rice husk bark ash has been investigated. Different specimens made from a mixture of fly ash and rice husk bark ash in fine and coarse form were subjected to compressive strength tests at 7 and 28 days of curing. The curing regime was different: one set of the specimens were cured at room temperature until reaching to 7 and 28 days and the other sets were oven cured for 36 h at the range of 40-90 °C and then cured at room temperature until 7 and 28 days. The results indicate that in both 7 and 28 days regimes, the highest strengths are related to the specimens by SiO₂/Al₂O₃ ratio equals 2.99 cured at 80 °C. For these specimens, those contained finer fly ash particles show more compressive strength. Thermogravimetric analysis and Fourier transform infrared spectroscopy both also are in agreement with the obtained results from compressive strength tests. In addition, SEM micrographs of the specimens show that the finer the particle size of the utilized ashes, the denser the microstructure which confirms the results obtained by the strength tests.     

Properties of autoclaved aerated concrete incorporating rice husk ash as partial replacement for fine aggregate

This study examines the effects of rice husk ash (RHA) on the physical, mechanical and microstructural properties of autoclaved aerated concrete (AAC) produced at a temperature of 180 °C for 8 h and 18 h. The RHA was used as an aggregate at various replacement ratios. The results demonstrated that RHA substitution for sand reduces compressive strength and unit weight. In terms of the microstructure, the highly reactive silica in RHA strongly affected the tobermorite transformation. At 8 h of autoclaving time, the lath-like and plate-like tobermorite formed in mixtures containing up to 50% RHA was replaced by a glass-like, silica-rich CSH structure at increased replacement ratios. However, extended processing had no significant effect on these properties, which indicates that the substitution of RHA for sand has a tendency to reduce the autoclaving time or autoclaving temperature required.     

Stabilization/solidification of lead-contaminated soil using cement and rice husk ash

This paper presents the findings of a study on solidification/stabilization (S/S) of lead-contaminated soil using ordinary Portland cement (OPC) and rice husk ash (RHA). The effects of varying lead concentrations (in the form of nitrates) in soil samples on the physical properties of their stabilized forms, namely unconfined compressive strength (UCS), setting times of early mixtures and changes in crystalline phases as well as chemical properties such as leachability of lead, pH and alkalinity of leachates are studied. Results have indicated that usage of OPC with RHA as an overall binder system for S/S of lead-contaminated soils is more favorable in reducing the leachability of lead from the treated samples than a binder system with standalone OPC. On the other hand, partial replacement of OPC with RHA in the binder system has reduced the UCS of solidified samples.     

Effects of calcination parameters on the silica phase of original and leached rice husk ash

This paper presents a contribution to the study of the effects of calcination parameters, including temperature and time, on the silica phase of original and leached rice husk ash. X-ray diffraction (XRD) analysis reveals the presence of totally crystalline silica in the original rice husk ash prepared at 800 °C. Fortunately, no indication of the presence in crystalline phase is found in the leached rice husk ash due to leaching. However, specific surface area analysis indicates that the high calcination temperature or the long calcination time renders the amorphous silica in the leached rice husk ash less activity. Therefore, the leaching procedure, the low calcination temperature and the short calcination time are proposed in order to prepare more active amorphous silica from the rice husk.     

Preparation and characterization of vinyl-functionalized mesoporous SBA-15 silica by a direct synthesis method

Vinyl groups were used to functionalize the pore channels of mesoporous SBA-15 materials by the co-condensation of tetraethyl orthosilicate (TEOS) and triethoxyvinylsilane (TEVS) in the presence of poly(ethylene glycol)-B-poly(propylene glycol)-B-poly(ethylene glycol) (P123) surfactants under acidic conditions. The final materials were investigated in detail by means of FT-IR, XRD, TEM, solid state NMR and N₂ adsorption, in order to study the effect of vinyl concentration on their mesoscopic order and pore structure. The results show that vinyl groups are attached covalently to the pore wall of SBA-15 after modification. The mesoscopic architecture almost remains intact upon functionalization, with only a minor decrease of the intensity of (110) diffractions for the 20 mol% TEVS-functionalized samples, which still preserve a desirable pore structure, with a surface area of 883.7 m²/g, a pore volume of 0.98 cm³/g and a mean pore size of 4.4 nm.     

pH值敏感介孔纳米复合材料SBA-15/PAA的制备与性能研究

通过浸渍吸附的方法将pH值敏感的功能单体-丙烯酸引入到介孔二氧化硅SBA-15的孔道内,经自由基聚合使丙烯酸(AA)在孔道内聚合,成功合成了pH值敏感的SBA-15/聚丙烯酸(PAA)纳米复合材料,所得纳米复合材料的结构通过XRD、TEM、氮气吸附/脱附、TG、FT-IR等手段进行了表征,并进行了pH敏感性能研究.结果表明,当聚合物(PAA)的量达到20%左右时,复合材料仍然具有较大的孔体积0.5203cm3/g和较高的比表面积334.5m2/g.聚合反应的发生没有破坏SBA-15的有序介孔结构,这种纳米复合材料初步显示出了pH敏感性.这种具有高比表面的pH值响应介孔纳米复合材料,有望在药物缓释领域得到应用.     

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.     

Synthesis and characterization of ordered mesoporous silica by using polystyrene microemulsion as templates

A simple room temperature synthesis of pure mesoporous silica by using a homemade and functional template: polystyrene microemulsion is reported. The process consists of HCl-catalysed sol-gel reactions of tetraethyl orthosilicate (TEOS) in polystyrene microemulsion, followed by removal of the template via solvent extraction or calcining. X-ray diffraction, Transmission Electron Microscope and N₂ adsorption-desorption isotherms are then used to characterize the mesostructure. The results indicate that the synthesized mesoporous silica has a large BET surface area with more than 900 m²/g, large pore volume with more than 0.8 cm³/g and ordered mesopore-structure. This provides a possible way to control the meso-structure and pore size of mesoporous materials via potential functional templates.     

纳米颗粒磁增强SBA-15介孔复合材料的制备及磁性能

利用浸渍法合成了Co₃O₄/SBA-15和CoFe₂O₄/SBA-15介孔纳米磁性材料, 并利用X射线粉末衍射(XRD)、 透射电子显微镜(TEM)、 场发射扫描电子显微镜(FESEM)及振动样品磁强计(VSM)对样品的微观结构和磁性能进行了分析。结果显示, Co₃O₄及CoFe₂O₄纳米颗粒分布在SBA-15介孔材料的孔道中, 可有效提高SBA-15介孔材料的磁性能。研究发现, SBA-15介孔纳米磁性材料的磁特性由掺杂的纳米磁性颗粒的性质决定, 其磁性能随Co₃O₄及CoFe₂O₄含量的增加而升高, 矫顽力可达400Oe, 饱和磁化强度达9emu/g。      

Short-period synthesis of high specific surface area silica from rice husk char

Porous silica with high specific surface areas is prepared from rice husk char within a short period by avoiding the commonly used hydrothermal treatment step and using polyethylene glycol (PEG, molecular weight = 20,000) as a template. The preparation process mainly involves sodium silicate production, precipitation with ortho-phosphoric acid, and calcination. The amount of used PEG significantly affects the silica textural properties like the specific surface area, total pore volume and mesopore volume. The reason should be attributed to the amount of PEG removed from the PEG-silica composites by calcination. By varying the PEG dosage from 100 to 176 mg, porous silica with specific surface areas ranging from 709 to 936 m²/g could be successfully prepared within 10 h.     

A new approach for synthesis of well-crystallized Y zeolite from bentonite and rice husk ash used in Ni-Mo/Al2O3-Y hybrid nanocatalyst for hydrocracking of heavy oil

A series of Ni-Mo/Al₂O₃-Y hybrid nanocatalysts were synthesized for hydrocracking of heavy oil. The well crystallized Y zeolite was synthesized from mineral bentonite and rice husk ash by a two-step synthesis method. The solution combustion method was applied to develop a fast and simple technique for preparing of alumina-supported NiMo catalyst with high hydrodesulfurization activity. Such activity may be due to the morphological and textural modification as a consequence of the release of a high amount of exhaust gases during the combustion process. The XRD analysis revealed that the P zeolite was a competitive phase presented in the obtained product that could be eliminated using a two-step synthesis method. Compared to a one-step method, the pore volume and external surface area of the synthesized zeolite by the two-step method increased by 74 and 62%, respectively. The hydrocracking results illustrated that the synthesized zeolite was able to convert 66% of heavy oil to lighter products and reduce the viscosity up to 60%. Furthermore, the amount of sulfur removal was found to be 58%. The spent catalyst characterization suggested that the type of deposited coke was hard coke with the unsaturated aromatic ring which could be responsible for the pores blockage after the cracking reaction.     

Effect of grinding of low-carbon rice husk ash on the microstructure and performance properties of blended cement concrete

The effectiveness of unground low-carbon rice husk ash (URHA) as a pozzolan and the effect of grinding the URHA to finer fractions for use in portland cement system were investigated. The properties investigated include the setting time and calcium hydroxide depletion of rice husk ash (RHA) pastes; microstructure and flow behavior of RHA mortars; strength and durability of RHA concretes. Results from this investigation suggested that the URHA and ground RHA (GRHA) mixtures performed better than the control mixtures in all tests conducted except water demand and setting time. The URHA mixture revealed denser microstructure compared to the control mixture. The internal porosity created by the coarse RHA grains in the matrix and their inability to completely participate in pozzolanic reaction may be the reasons for the poorer performance of the URHA mixture than compared to the GRHA mixture. The effect of grinding the RHA to finer fractions either substantially or slightly improved all properties except final setting time. With the performance of the GRHA concrete somewhat similar to that of the SF concrete, the use of ground RHA can be concluded to provide acceptable performance in portland cement systems.     

Synthesis and characterization of a novel neighboring dicarboxyl-modified SBA-15 via the Diels-Alder reaction

A novel neighboring dicarboxyl-modified SBA-15 (SBA-15-(COOH)₂) has been synthesized by the Diels-Alder reaction of cyclopentadienyl-modified SBA-15 (SBA-15-Cp), which was synthesized by co-condensation of (2-(cyclopenta-1,3-dienyl) ethyl) triethoxysilane and tetraethoxyorthosilicate in the presence of P123 as structure directing agent, with maleic anhydride and hydrolysis in dilute sulfuric acid. This novel material was characterized by N₂ sorption, X-ray diffraction and transmission electron microscopy. The results showed that the ordered mesoporous structure of SBA-15-Cp has been preserved after the Diels-Alder reaction and hydrolysis. Fourier transformed infrared spectroscopy investigation indicated that neighboring dicarboxyl groups were successfully incorporated in SBA-15. The acidity capacity and the dissociation constant for SBA-15-(COOH)₂ were ca. 0.54 mmol/g and 4.84 respectively.     

Preparation and characterization of silica aerogels from oil shale ash

The silica aerogels were successfully synthesized using oil shale ash which is a by-product of oil shale processing via ambient pressure drying. The physical and textural properties of the silica aerogels have been investigated and discussed. The results showed that the organic modification of hydrogels was a crucial step during the processing which preserved mesopores in ambient pressure drying. The unmodified hydrogel underwent tremendous shrinkage during the drying and yielded microporous silica aerogel. Using this novel route, it could produce silica aerogel with low tapping density of 0.074 g/cm³, high specific surface (909 m²/g) and cumulative pore volume of 2.54 cm³/g. From the industrial point of view, the present process is quite suitable for a large scale production of powdered silica aerogel. Furthermore, it provides a new way to solve the problem of oil shale ash pollution.