Zirconia enrichment in zircon sand by selective fungus-mediated bioleaching of silica

One of the important routes for the production of zirconia is by chemical treatment and removal of silica from zircon sand (ZrSixOy). We present here a completely green chemistry approach toward enrichment of zirconia in zircon sand; this is based on the reaction of the fungus Fusarium oxysporum with zircon sand by a process of selective extracellular bioleaching of silica nanoparticles. Since this reaction does not result in zirconia being simultaneously leached out from the sand, there is a consequent enrichment of the zirconia component in zircon sand. We believe that fungal enzymes specifically hydrolyze the silicates present in the sand to form silicic acid, which on condensation by certain other fungal enzymes results in room-temperature synthesis of silica nanoparticles. This fungus-mediated twofold approach might have vast commercial implications in low-cost, ecofriendly, room-temperature syntheses of technologically important oxide nanomaterials from potentially cheap naturally available raw materials like zircon sand.     

Synthesis of phthalazine compounds using heterogeneous base catalyst based on silica nanoparticles obtained from rice husk

Research on Chemical Intermediates - In this study, the nanoparticles of amorphous silica were easily extracted from low-cost rice husk ash. They were functionalized with 3-(chloropropyl)...     

Synthesis of MCM-22 zeolite using rice husk as a silica source under varying-temperature conditions

In this study, rice husk, an abundant agricultural byproduct, was utilized as an alternative silica source for the synthesis of MCM-22. The zeolite with high crystalline was synthesized using a three-stage varying-temperature hydrothermal method. The prepared silica and MCM-22 were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the duration required for zeolite crystallization was significantly decreased under varying-temperature conditions. The MCM-22 was in the form of thin platelet-like crystals, and no amorphous material existed in the framework of the MCM-22 after calcination and ammonium exchange. Cationic brilliant red 5GN, a basic dye used in the wool and blanket factories for fiber dyeing, was selected as the adsorptive to study the adsorption performance of the MCM-22. Adsorption experiments indicated that the maximum extent of adsorption was obtained at pH of 10, contact time of 60 min, and MCM-22 dose of 1.0 g/L. The adsorption kinetic has been described by first-order and pseudo-second-order models. It was observed that the rate of dye adsorption followed pseudo-second-order model.     

Extraction of biosilica from date palm biomass ash and its application in photocatalysis

There is an emerging trend in the valorization of biomass waste for the development of value-added products. Date palm biomass is an extensively available bioresource in Saudi Arabia. In date palm farms, the biomass residues are usually burnt, and a lot of ash is generated. Biomass ash is rich in silica, which is a valuable material used in a wide range of applications. This study explores the extraction of pure silica nanoparticles from date palm biomass ash (DPBA) and its application in photocatalysis. A chemical sol–gel method or thermal combustion method was employed for the extraction of silica. The extracted silica nanoparticles were characterized by EDX, FT-IR, XRD, SEM, BET, and TGA. FT-IR spectra of extracted biosilica samples displayed only the characteristic peaks corresponding to the silica functional groups. The chemically synthesized biosilica sample exhibited higher purity (98 %) and higher surface area (376 m²/g) compared to the thermally prepared biosilica samples. The SEM analysis revealed the presence of spherical-shaped silica particles of an average diameter of 93 nm in chemically extracted biosilica and 208 nm in thermally extracted biosilica. The newly extracted biosilica samples were tested for the photodegradation of the bromophenol blue dye in water. The dye degradation efficiency of chemically prepared biosilica sample was 82 % and that of thermally prepared biosilica sample was 74 %. The relatively higher degradation efficiency of BS-chemical could be due to its higher surface area and smaller particle size, and also due to the presence of lots of surface defects in this fully amorphous biosilica.     

Recovery Conditions,Impurity Composition,and Characteristics of Amorphous Silicon Dioxide from Wastes Formed in Rice Production

The conditions of recovery of amorphous and crystalline silicon dioxide from husk and straw of rice cultivated in various regions were studied. The dependence of the impurity composition and characteristics of amorphous silica on the plant strain, waste type, and procedures of waste processing was established. The optimum conditions of production of high-purity silicon dioxide were determined, and its characteristics were compared with those of commercial products.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 2, 2005, pp. 324–328.Original Russian Text Copyright © 2005 by Zemnukhova, Fedorishcheva, Egorov, Sergienko.     

One-pot and efficient synthesis of triazolo[1,2-a]indazole-triones via reaction of arylaldehydes with urazole and dimedone catalyzed by silica nanoparticles prepared from rice husk

A novel synthesis of triazolo[1,2-a]indazole-1,3,8-trione derivatives by reaction of urazole, dimedone and aromatic aldehydes under conventional heating and microwave irradiation and solvent-free conditions using silica nanoparticles prepared from rice husk ash as catalyst is described. The new method features high yields, multicomponent reactions and environmental friendliness.     

Zirconia Supported on Rice Husk Silica from Biowaste: A Novel,Efficient, and Recoverable Nanocatalyst for the Green Synthesis of Tetrahydro-1-benzopyrans

Russian Journal of Organic Chemistry - Zirconia supported silica from rice husk (an agricultural waste) has been utilized as a novel and efficient heterogeneous catalyst for the synthesis of...     

Green synthesis and physical properties of crystalline silica engineering nanomaterial from rice husk (agriculture waste) at different annealing temperatures for its varied applications

Crystalline nano silica (SiO₂) was synthesized using a cost-effective eco-friendly method from agricultural waste material like rice husk. Polymer nanocomposite has been prepared using the sol-gel technique from crystalline nano silica using PVA as a polymer binder. Thermal analysis measurement is employed to investigate thermal stability. The XRD analysis shows the crystalline nature of silica is revealed to have characteristic peaks of SiO₂. The particle size was evaluated using Schererr's formula and found to be in the range of 21–31 nm. FTIR measurement shows the presence of O–Si–O (silane) bond formation. The PL measurement shows broad excitation prominently in the visible region. In the XRD pattern, a major peak of the Nanocomposite is observed at an angular position of 19.5° degree, which is more prominent than that of the PVA with the addition of 0.2 wt percent Nano silica to the PVA composite. SEM provides information on homogeneous distribution. This could be beneficial in terms of higher mechanical qualities as well as multifunctional properties. By hydrogen bonding, the PVA molecules are strongly linked to each SiO₂ nanoparticle as measured by FTIR. The stability of materials is confirmed by Zeta Potential and DLS. In the photoluminescence property of SiO₂-PVA crystalline Nano silica composite is excited using a radiation wavelength of 200 nm. The indirect bandgap was determined to be 4.28 eV which could be attributed to the 1100 °C annealing temperature. Such materials may be used as a semiconductor material obtained from a direct natural source, rice husk. Thus, in the present research structural, physical, and optical properties of crystalline nano silica and its polymer composite are explored, which leads us to prepare technological grads material from agricultural waste for varied applications including Agriculture to medical science.     

Fluorescent dye-doped silica nanoparticles: new tools for bioapplications

The need to decipher various biological events has led to the elucidation of the molecular mechanisms underlying a number of disease processes. Consequently, the detection and simultaneous monitoring of chemical interactions between biological targets has become indispensable in medical diagnosis, targeted therapeutics, and molecular biology. Multiplexed applications employing nanomaterials, which represent the integration of nanotechnology and biology, have changed the bioanalytical outlook and provided various promising tools. Among these nanomaterials, fluorescent dye-doped silica nanoparticles have demonstrated excellent potential for use in advanced bioanalysis to facilitate deeper understanding of biology and medicine at the molecular level. In particular, silica nanoparticles have been applied to diagnostics and therapeutic applications in cancer and gene/drug delivery. This feature article summarizes recent developments in the synthesis, biocompatibility, and bioapplications of fluorescent dye-doped silica nanoparticles.     

Toxicity of amorphous silica nanoparticles on eukaryotic cell model is determined by particle agglomeration and serum protein adsorption effects

Cell cultures form the basis of most biological assays conducted to assess the cytotoxicity of nanomaterials. Since the molecular environment of nanoparticles exerts influence on their physicochemical properties, it can have an impact on nanotoxicity. Here, toxicity of silica nanoparticles upon delivery by fluid-phase uptake is studied in a 3T3 fibroblast cell line. Based on XTT viability assay, cytotoxicity is shown to be a function of (1) particle concentration and (2) of fetal calf serum (FCS) content in the cell culture medium. Application of dynamic light scattering shows that both parameters affect particle agglomeration. The DLS experiments verify the stability of the nanoparticles in culture medium without FCS over a wide range of particle concentrations. The related toxicity can be mainly accounted for by single silica nanoparticles and small agglomerates. In contrast, agglomeration of silica nanoparticles in all FCS-containing media is observed, resulting in a decrease of the associated toxicity. This result has implications for the evaluation of the cytotoxic potential of silica nanoparticles and possibly also other nanomaterials in standard cell culture.     

Versatile biomimetic dendrimer templates used in the formation of TiO2 and GeO2

Biomimetic synthesis is emerging as an advantageous alternative to the harsh synthetic conditions traditionally used in metal oxide syntheses techniques. Silaffins, proteins from the C. fusiformis diatom, form silica in an aqueous environment under benign conditions. Amine terminated PAMAM and PPI dendrimers are effective mimics of silaffins and other silica precipitating polyamines. We have expanded the scope of dendrimer mediated metal oxide formation to include titanium dioxide, a photocatalyst, and germanium dioxide, a blue photoluminescent material. The nanoparticles were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (IR), and X-ray diffraction patterns (XRD). A variable temperature XRD analysis of TiO(2) nanoparticles was conducted to study the transition from anatase to rutile. TiO(2) nanoparticles synthesized in phosphate buffer showed a 200 degrees C decrease in the anatase to rutile transition temperature relative to TiO(2) templated in water. XRD analysis of GeO(2) nanoparticles in either water or phosphate buffer reveal crystalline alpha-phase germanium oxide. To our knowledge, this is the first report of the synthesis of crystalline GeO(2) under ambient conditions.     

Production of High Purity Amorphous Silica from Rice Husk

Combustion of the rice husk produces rice husk ash, which consists of mainly silica. High purity silica can be produced by controlled combustion after acid treatment. In this study, leaching of rice husk with hydrochloric acid and sulfuric acid were carried out prior to combustion to obtain purer silica. It was found that pre-treatment of the rice husk with sulfuric acid had accelerated the hydrolysis and decomposition of organic components as revealed by thermogravimetry (TG) and Scanning Electron Microscopy (SEM) analyses. In a systematic study, the combustion of un-leached, hydrochloric acid-leached and sulfuric acid-leached rice husks were performed in a muffle furnace at 500, 600, 700, 800 and 900^oC for 2 h. Results demonstrated that all the samples produced amorphous silica (SiO₂) and the average particle size were in the range of 0.50 to 0.70 μm. The effect of combustion at different temperatures between 500^oC and 900^oC on the silica production is very small, particularly at temperature above 600^oC. Thus, amorphous silica with purity above 99% as confirmed by X-Ray Fluorescence (XRF) analysis can be produced by hydrochloric and sulfuric acids leaching of the rice husk, followed by controlled combustion at 600^oC for 2 h. The BET surface area of the silica produced after leaching the rice husk with hydrochloric acid was higher (218 m²/g) than with sulfuric acid (209 m²/g). The silica obtained has potential application as filler in plastics and rubber compounding.     

A Study on the thermal destruction of rice husk in air and nitrogen atmosphere

The methods of X-ray analysis, infrared spectroscopy, differential thermal analysis and scanning electron microscopy were used in this study. The objects of the experiments were rice husk obtained during processing of rice, variety Krasnodarski 424. The rice husk was burnt in air and in non-oxygen medium at several burning temperatures. The color of the oxidized product was stipulated by the burning temperature. The X-ray analysis showed that the amorphous SiO₂ present in the rice husk begins to crystallize in the form of α-cristobalite at 850°C. Using differential thermal analysis, the thermal destruction of rice husk was studied in air and nitrogen media and the initial and final temperatures of the process were determined. The silica distribution was examined by scanning electron microscopy and infrared spectroscopic techniques.     

Model studies of colloidal silica precipitation using biosilica extracts from<Emphasis Type="Italic"> Equisetum telmateia</Emphasis>

Structural materials containing silicon are produced in single celled organisms through to higher plants and animals. Hydrated amorphous silica is a colloidal mineral of infinite functionality that is formed into structures with microscopic and macroscopic form. Proteins and proteoglycans are suggested to play a critical role in the catalysis of silica polycondensation and in structure direction during the formation of these magnificent structures. This article extends knowledge on the effect of protein containing biosilica extracts from Equisetum telmateia on the kinetics of silica formation and structure regulation. Utilising potassium silicon catecholate as the source of soluble silicon, bioextracts obtained from plant silica by dissolution of the siliceous phase with aqueous HF following extensive acid digestion of the plant cell wall were found to modify the kinetic rate constants for the formation of small silicic acid oligomers under circumneutral pH conditions and to modify the solubility of silicic acid in solution. Addition of the bioextracts at ca. 1 wt% to the reaction medium reduced the sizes and range of sizes of the fundamental silica particles formed and led to the formation of crystalline polymorphs of silica under conditions of ca. neutral pH, room temperature and in the absence of multiply charged cations, conditions assumed to be relevant to the biological mineralization environment. The ability of biological organisms to regulate the formation of silica structures with prevention of crystallinity is discussed as are the implications of this study in terms of the generation of new materials with specific form and function for industrial application.     

Synthesis and properties of water-soluble silica nanoparticles

Methods for synthesis and optimum conditions of the formation of stable water-soluble silica nanoparticles are presented. The silica nanoparticles were synthesized by the hydrolytic polycondensation of tetraethoxysilane using two methods: under alkaline conditions (Stöber´s method) or in an acetic acid medium followed by the modification by grafting triethylene oxide moieties on the particle surface. The structure of the modified silica nanoparticles was confirmed by the data of IR and NMR spectroscopy. Polydispersity was evaluated by gel permeation chromatography and dynamic light scattering. The formation and stability of Langmuir monolayers of the silica nanoparticles modified by triethylene oxide moieties were studied.     

Determination of crystalline silica in silica fume

Silica fume is formed as a by-product in the manufacture of silicon from quartzite. This paper describes an analytical method for the determination of crystalline silica in silica fume. The crystalline silica was determined after removal of amorphous silica from the fume. A gravimetric method was developed for the determination of the total crystalline silica in the fume, while the cascade impactor technique was used to determine the crystalline content in the -10 microm fraction. X-Ray diffraction, scanning electron microscopy and particle size distributions were used to validate the steps in the analytical procedure. The total crystalline silica content was found to vary from 2.7 to 8.6% with an RSD of +/-2%, while the crystalline silica content of the -10 microm fraction was 0.23 to 0.55% with an RSD of +/-10%. A knowledge of the crystalline silica content of silica fume is of great importance in the area of Occupational Health and Safety. The samples surveyed were shown to have levels of crystalline silica in the respirable fraction well within the draft guidelines for silica fume. It is proposed that this method be accepted as a standard method for the determination of crystalline silica in silica fume.     

Rice Husk‐derived Hierarchical Micro/Mesoporous Carbon–Silica Nanocomposite as Superior Filler for Green Electronic Packaging Material

In this study, a carbon‐controllable hierarchical micro/mesoporous carbon–silica material derived from agricultural waste rice husk was easily synthesized and utilized as filler in an epoxy matrix for electronic packaging applications. Scanning electron microscopy, thermogravimetric analysis, and N₂ adsorption/desorption isotherms were used to characterize the morphology, thermal stability, carbon content, and porous structural properties, respectively, of the as‐obtained carbon–silica material, namely rice husk char (RHC ). As a filler material, the uniformly dispersed RHC filler in the epoxy/RHC composite was easily prepared through hydrogen bonding of the silanol group of silica with the epoxy matrix. For electronic packaging applications, the thermal conductivity and thermomechanical properties (storage modulus and coefficient of thermal expansion) of the epoxy/RHC composites improved with increasing carbon content. Moreover, loading of the 40% RHC filler substantially enhanced the storage modulus of the epoxy/RHC composite (5735 MPa ) compared to the epoxy with 40% commercial silica filler (3681 MPa ). Considerable commercial potential is expected for the carbon–silica composite because of the simple synthesis process and outstanding performance of the prepared packaging material.     

Understanding rice hull ash as fillers in polymers: A review

The polymer industry has a newfound interest in fillers from industrial by-products and other waste materials having potential recyclability. This new class of fillers includes fillers from natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husks) and a recent entry in the form of silica ash – an industrial waste material –obtained by burning rice husks. Rice hulls possess an unusually high percentage of `opaline silica'. Its annual worldwide output is more than 80 million tons, which corresponds to 3.2 million tons of silica. Silanol groups present on the surface of rice hull ash can positively influence its reinforcing character ash as a filler, however, being hydrophilic, it suffers fromfiller-aggregation and moisture absorption. Present article reviews the performance of rice husk ash, or silica ash, in polymeric composites. This paper emphasizes the need for better characterization of silica ash to obtain an in-depth understanding of its behaviour with the view to identifying suitable modifications to improve its performance as a filler. It is emphasized that poor understanding of silica ash as a filler is linked to the lack of surface characterization, since its behaviour is significantly linked to its surface properties. Based on this analysis, a new approach to silica ash modification is proposed.     

High-performance CO<Subscript>2</Subscript> capture on amine-functionalized hierarchically porous silica nanoparticles prepared by a simple template-free method

The adsorption of CO₂ on polyethyleneimine (PEI)-functionalized hierarchically porous silica nanoparticles (PSNs), prepared by using rice husk as a silica source via a simple template-free method, was reported in this study. Compared with traditional alkaline fusion and surfactant-templating methods for preparing waste-derived porous silica materials as CO₂ adsorbents, this method holds specific important advantages in being an inexpensive, and energy-saving process with faster production rate. The results revealed that the (NH₄)₂SiF₆ salt formed during the synthetic process served as an effective porogen, which can be readily removed by washing with water. Additionally, the total pore volumes of PSNs materials were strongly correlated to the amount of (NH₄)₂SiF₆. When evaluated as a support of PEI for CO₂ adsorption, 55PEI/PSNs(12/14) could reach 159 mg/g at 75 °C under 15 % CO₂, which was remarkably superior to those using waste silicate precursors reported in the previous literature. It was demonstrated that both PEI loading, and total pore volume of the PEI/silica composite sorbents, played key roles on CO₂ adsorption. Besides, 55PEI/PSNs(12/14) also showed high stability during 20 cycles of adsorption–desorption operation, implying its high potential in post-combustion CO₂ capture.     

Effect of removing silica in rice husk for the preparation of activated carbon for supercapacitor applications

The significant influence of silica inside rice husk in the preparation and electrochemical performances of activated carbon are investigated. The removing of silica results in high mesoporous ratio and good rate capability.