High-purity Silica Research Articles

Plant-derived silica nanoparticles and composites for biosensors, bioimaging, drug delivery and supercapacitors: a review.

Silica nanoparticles have rapidly found applications in medicine, supercapacitors, batteries, optical fibers and concrete materials, because silica nanoparticles have tunable physical, chemical, optical and mechanical properties. In most applications, high-purity silica comes from synthetic organic precursors, yet this approach could be costly, polluting and non-biocompatible. Alternatively, natural silica sources from biomass are often cheap and abundant, yet they contain impurities. Silica can be extracted from corn cob, coffee husk, rice husk, sugarcane bagasse and wheat husk wastes, which are often disposed of in rivers, lands and ponds. These wastes can be used to prepare homogenous silica nanoparticles. Here we review properties, preparation and applications of silica nanoparticles. Preparation includes chemical and biomass methods. Applications include biosensors, bioimaging, drug delivery and supercapacitors. In particular, to fight the COVID-19 pandemic, recent research has shown that silver nanocluster/silica deposited on a mask reduces SARS-Cov-2 infectivity to zero.

Quartz Ore Beneficiation by Reverse Flotation for Silicon Production

In this work the reverse flotation as beneficiation process for high-purity silica valorization from Draissa quartz deposits (Algeria) is studied as a potential raw material for photovoltaic silicon production and starting charge for crystal growth material for a large wide of applications such laser and scintillation. The samples are investigated by optical microscopy, secondary ion mass spectroscopy, X-ray fluorescence and Raman spectroscopy. The microscopic investigations detect solid impurities such as alkaline and plagioclase feldspars, micas and iron oxides. The analyzed silica shows well-developed crystals areas, delimited by microcrystalline regions. Impurities are predominantly located in low quartz granulometry (50-100 μm). The XRF results highlight 93.63 wt% SiO2, 0.16 wt%, Fe2O3, 0.171 wt% Cl, 0.15 wt% CaO, 5.74 wt% Al2O3, 0.074 wt% K2O, 0.001 wt% CdO, 0.006 wt% SnO2. However, these results remain insufficient for predestined use of this raw material. A preliminary enrichment using reverse flotation process improves the silica purity up to 99.6% and removes the major impurities, which is suitable intermediate technological product able for silicon production and optical application.

Ni mesostructured catalysts obtained from rice husk ashes by microwave-assisted synthesis for CO2 methanation

Abstract In this work, rice husk ashes were used to obtain a high purity silica precursor to synthesize mesoporous silica frameworks. A novel route for the synthesis of mesocellular silica foam (MCF) was developed using microwave irradiation during the hydrothermal treatment. Cyclohexane and cetyltrimethylammonium bromide were employed as swelling and structure-directing agents, respectively. Ni-based catalysts supported on MCM-41 and MCF mesostructured materials were obtained using two methods, one-pot and incipient wetness impregnation. The catalysts prepared for both methods presented noticeable differences in the metal-support interaction, which were observed by TEM, SAXRD, TPR and XPS. The impregnated catalysts showed preferentially Ni particles inside the pore structure of the support while the one-pot catalysts also showed Ni particles within the silica framework. The catalysts were evaluated in the CO2 methanation reaction between 200 and 500 °C at atmospheric pressure. The samples prepared by impregnation showed better catalytic performance than those prepared by the one-pot method. Thereby, the Ni particles highly distributed within the pore improved the CO2 methanation reaction. The Ni/MCF_ch_iwi presented the best catalytic performance reaching CO2 conversions and CH4 selectivities close to the reaction equilibrium, from 350 to 500 °C. The Ni/MCF_ch_iwi also showed high structure and catalytic stability, as well as coke resistance formation under reaction conditions.

Robust synthesis of mono-dispersed spherical silica nanoparticle from rice husk for high definition latent fingermark development

Silica is one of the most functional metalloid oxides with a widespread application as semiconductor, fillers, silicone and ceramic primarily due to its structural versatility. In this work, a robust step-wise thermochemical treatment was successfully formulated for the controlled fabrication of high-purity mono-dispersed spherical silica nanoparticle from rice husk. The silica nanoparticle with the desired morphology was formed in two stages; thermal-assisted seed particle formation followed by particle growth through acidification of the solvent modified sodium silicate solution. The obtained powder was characterised, and the effectiveness of the powder for latent fingermark development across varied donors and surfaces was tested at the introductory level. The formed spherical particles were in the range of 200 to 400 nm, as confirmed by FESEM and HRTEM analysis. Minimising the degree of silica nanoparticle agglomeration notably affected their selectivity to fingermark residue. There was a striking improvement in the selectivity of the silica nanoparticle to fingermark residue. The improvement was attributed to the strong interaction between the silica nanoparticle and the lipid components in the fingermark residue, as compared to the commercial white powder that works solely based on mechanical adherence. Additionally, the size and morphology of the fabricated silica nanoparticle were optimised to enhance the clarity of the developed fingermark. Findings of this study could improve quality of fingermarks obtained in a crime scene due to considerably lower background interference without compromising the effectiveness of fingermark development.

Application of “Tissueoid Cell Culture System” Using a Silicate Fiber Scaffold for Cancer Research

Background: We developed a 3-dimensional (3D) culture system using a high-purity silica fiber scaffold of unwoven sheets called Cellbed^TM. Methods: We used adherent colon and esophagogastric junction adenocarcinoma cells, tongue squamous cell carcinoma (SqCC) cells, and nonadherent gastric cancer cells. These cells were subjected to staining with various substances and observed by electron microscopy. To evaluate the effects of extracellular matrix in carcinoma tissues, SqCC cells were cultured in Cellbed coated with collagens I, III, and IV. Results: Especially well-differentiated carcinoma cells cultured in this 3D system showed their own unique characteristics: luminal formation in adenocarcinoma cells and cell stratification and keratinization in SqCC cells. Scanning electron microscopy revealed the proliferation of cancer cells with cytoplasm entwined in Cellbed. Intercellular desmosomes in squamous epithelia were detected by transmission electron microscopy of vertical cross sections. SqCC cells cultured in Cellbed coated with collagen IV showed enhanced invasive and proliferative abilities. Conclusion: Because the morphology of cancer cells cultured in this 3D culture system is similar to that in living organisms, we called the system a “tissueoid cell culture system.” Coating with collagen IV enables the modification of cell-matrix interactions as well as recapitulation of the in vivo microenvironment.

Effect of Acid Leaching on Different State of Rice Husk

Rice husks (RH) are agricultural wastes available abundantly in rice producing country. A by-product obtained from combustion of rice husk is rice husk ash (RHA) which is rich in silica (SiO2) contents. This paper focused on the effect of acid leaching treatment on rice husk to produce high-purity silica. There are 4 different states of conditions involved; raw rice husk (RRH), treated rice husk (TRH), rice husk ash (RHA), and treated rice husk ash (TRHA). Citric acid; C6H8O7 was used as a leaching agent. TRH and TRHA was leached to see whether treated rice husk before combustion (TRH) or treated rice husk after combustion (TRHA) will produce more high-purity silica. Chemical composition analysis shows high amorphous silica content which is 98.47% with low metallic impurities at 1.0M C6H8O7, 70 oC for treated rice husk (TRH). X-ray diffraction (XRD) pattern shows the presence of amorphous silica in treated rice husk (TRH) and crystalline silica in treated rice husk ash (TRHA). Fragmentation of TRH into small pieces after acid leaching is seen where there is significant increase in the exposed surface areas. High-purity amorphous silica with more than 98% was prepared via citric acid leaching treatment and combustion process.

Obtaining Biogenic Silica from Sugarcane Bagasse and Leaf Ash

Besides mineral sources, silica can be found in plants, particularly in the epidermis, since during their growth plants absorb the mono-silicic acid present in the soil, storing it as a natural form of protection, insect pest control and transpiration regulator. Among the plants that present high levels of silica in their ashes, we can highlight sugarcane, with Brazil being the largest producer of sugarcane derived (sugar and bioethanol) in the world, accounting 615 million tons per year. Thus, the increasing of the international demand encourages an increase of the availability of sugarcane wastes, pushing its use for the generation of electric power, as for other purposes enabling a sustainable development. In this work, high purity silica nanoparticles (up to 95%) with predominantly amorphous microstructure were obtained after thermal (500 to 700 °C) and chemical treatments (1 molar hydrochloric acid solution, 10% volume) of sugarcane bagasse and leaves ashes. The obtained results indicate the possibility of using this silica in ceramics, glasses, refractory materials and construction applications, as well as in the cosmetic and pharmaceutical industry, molecular sieves and mesoporous membranes. The silica obtained in this research also proved to be suitable for obtaining porous silicon (using magnesiothermic reduction), where the experimental procedure employed is described elsewhere.

Laser cooling of ytterbium-doped silica glass

Laser cooling of a solid is achieved when a coherent laser illuminates the material in the red tail of its absorption spectrum, and the heat is carried out by anti-Stokes fluorescence of the blue-shifted photons. Solid-state laser cooling has been successfully demonstrated in several materials, including rare-earth-doped crystals and glasses. Here we show the net cooling of high-purity Yb-doped silica glass samples that are fabricated with low impurities to reduce their parasitic background loss for fiber laser applications. The non-radiative decay rate of the excited state in Yb ions is very small in these glasses due to the low level of impurities, resulting in near-unity quantum efficiency. We report the measurement of the cooling efficiency as a function of the laser wavelength, from which the quantum efficiency of the Yb-doped silica is calculated.

Study on chemical kinetics and characterization of nanosilica from rice husk and rice straw in the fixed-bed pyrolysis process

Rice husk (RH) and rice straw (RS) are important by-products from the rice industry. When RH and RS are subjected to pyrolysis, the products include char, tar, and a gaseous mixture containing syngas. In this study, silica was obtained by subjecting char to alkaline extraction. The obtained silica was modified to fit sophisticated industrial applications by adding alcohol and water during extraction in an optimized silicate:alcohol:water ratio. Methanol (MeOH), ethanol (EtOH), and propanol (PrOH) were used as particle size modifiers. The silica obtained were characterized through methods such as Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), and field emission scanning electron microscope (FESEM). The obtained silica had an average particle size of 20–170 nm, a high average BET-specific surface area of 328 m2/g, and a high purity of 98.26%, which enhanced its favorability in the pharmaceutical and food-packaging sectors. FTIR analysis confirmed the presence of Si–O–Si, Si–OH, and Si–O bonds in the silica. A higher purity of silica was obtained from RS than from RH. To obtain high-purity silica, nitrogen should be used as the pyrolyzing agent and acid leaching of the extracted silica should be conducted. To facilitate the design, operation, and economic study of industrial process plant, the clear understanding on kinetics of RH and RS plays a very important role. The kinetic parameters for RH and RS char were estimated through Gaussian distribution of the activation energy model (DAEM).

Study of Algerian sand from Zemmouri deposits

As the largest country in Africa and home to a variety of topographies and geologies, Algeria is rich in substantial mineral reserves. But unfortunately, these minerals are currently underutilized, as the mining sector attracted a little investment and researches. High-purity silica sand for several applications is currently sourced but just from a few locations in Algeria (Beddiaf Chihi and Leghrieb J Afr Earth Sci 106:129–133, 2015; Anas Boussaa et al. A Phys Pol A 129:129–133, 2016a; Anas Boussaa et al. Rev Energ Renouv 19(N°3):481–486, 2016b; Anas Boussaa et al. OpenChem 16:1227–1232, 2018; Zouaouid and Gheriani Silicon 11:1537, 2019; Bendida et al. Energy Procedia 36:825–833, 2013; Maazouzi et al. Silicon 6(3):149–154, 2014; Meftah and Mahboub Silicon. 12:2019–2153, 2019). The grow demand for this material by the industries is expecting, so more silica sand sources are required to be found, and for successful high-purity silica sand resource identification, detailed characterization properties is essential. To our knowledge, no research concerning Zemmouri silica sand characterization has been reported up to now. It is therefore important to investigate the capacity of this vast silica sand deposit for its potential uses and to enable the economic development of this region. This study seeks to determine the various textural parameters and chemico-physical properties of sand located in Zemmouri (Algeria) for its future industrial utilization. The result of this study using XRF indicates that Zemmouri sand has got a very good purity (99.3% silica). The value of densities was determined, agreeing with the actual values required by the standard. According to the granular analysis, different granular parameters were determined and the sand was found as well-graded medium sand and as poorly fair sand. The optical observations were carried out, and the micrograph observations indicated the presence of different shapes of sand grain, some rounded whereas others are angular edged or elongated.

Impact of shaping optical fiber preforms based on grinding and a CO2 laser on the inner-cladding losses of shaped double-clad fibers.

We experimentally compared for the first time, two techniques of optical fiber preform shaping based on the mechanical grinding and thermal CO2 laser processing from the point of the inner-cladding losses. The shaped preforms were fabricated of coreless pure silica technical rods as well as high purity silica Heraeus F300 rods and drawn them into coreless multimode fibers with various inner-cladding geometries coated with a low index fluorinated polymers. The background losses of the fibers were measured via the cut-back method and compared to the losses of the unshaped fibers with a circular cross-section. Results show that both preform-shaping techniques would induce additional losses in the inner-cladding. High surface scattering losses were observed in the mechanically-grinded fibers. On the other hand, the mechanical grinding retains the advantage of a significant reduction of attenuation peaks attributed to OH-groups that penetrated into the preform surface during the preform collapse. On the contrary, CO2 laser thermal-shaping provides the advantage of quick, fully automated shaping with smooth surface finish and induces much lower scattering losses, but it is not so effective in removing water penetrated surface layer of the preform so that OH-groups diffuse deeper towards the preform center. Additionally, laser thermal-shaping allows processing the preform to complex shapes which are more effective in scrambling cladding modes. Some of the absorption peaks of OH-groups and fluorinated polymers may be rather close to common pumping wavelengths and this should be considered in the design of the double-clad fibers and selection of proper shaping technology.

Performance Comparison of Four Portable FTIR Instruments for Direct-on-Filter Measurement of Respirable Crystalline Silica.

Exposure to dusts containing respirable crystalline silica is a recognized hazard affecting various occupational groups such as miners. Inhalation of respirable crystalline silica can lead to silicosis, which is a potentially fatal lung disease. Currently, miners' exposure to respirable crystalline silica is assessed by collecting filter samples that are sent for laboratory analysis. A more timely field-based silica monitoring method using direct-on-filter (DoF) analysis is being developed by researchers at the National Institute for Occupational Safety and Health (NIOSH) to provide mine operators with the option to evaluate miners' exposure at the mine. This field-based silica monitoring technique involves the use of portable Fourier transform infrared (FTIR) instruments. As a step in the development of this new analytical technique, four commercially available portable FTIR instruments were evaluated for their ability to provide reproducible measurements from filter samples containing respirable crystalline silica. Reported testing indicates that measurements varied within ±4.1% between instruments for filter samples that contained high-purity respirable crystalline silica. Measurements varied within ±3.0% between instruments for filter samples that contained varying mineral composition. Filter samples were repeatedly analyzed by the same instrument over short and extended periods of time, and mean coefficients of variation did not exceed ±1.6 and ±2.4%, respectively. Mixed model analysis revealed that there was no statistically significant (P < 0.05) change in average measurements made over an extended period of time for all instruments. Results suggest that each of the four FTIR instruments evaluated in this study were able to generate precise and reproducible DoF analysis results of respirable dust samples.

Preparation of Polycrystalline Silicon from Rice Husk by Thermal Decomposition and Aluminothermic Reduction

Polycrystalline silicon was extracted from rice husk by thermal decomposition and aluminothermic methods. Rice husk was thermally decomposed under various heat treatments and acid purifications. High purity silica of 99.81% was obtained by subsequent rice husk washing, pressure cooking in mixed chloride acid peroxide solution, and burning at 500oC for one hour. Aluminothermic reduction of silica was conducted at various calcination temperatures. It is found that 78.6% of silica was converted to silicon for calcination temperature of 800oC. Leaching the reduction product with strong hydrochloric and hydrofluoric acids produced silicon polycrystalline with a purity of 99.91%.

An improved method for the production of high purity silica from sugarcane bagasse ash obtained from a bioethanol plant boiler

In most tropical countries where sugarcane is grown at a commercial scale, there are substantial quantities of sugarcane bagasse ash rich in amorphous silica. A simple, low-cost chemical method for the extraction of pure silica from the boiler collected ash is of importance. In this study, sol–gel coupled with adsorption using activated carbon was used to extract high-purity amorphous silica from sugarcane bagasse ash. Physicochemical characteristics of the extracted silica samples were checked using X-ray fluorescence spectrometer, X-ray powder diffraction, Fourier-transform infrared spectroscopy, nitrogen (N2) adsorption–desorption method, scanning electron microscope and transmission electron microscopy. Most metal impurities that include iron, manganese, magnesium, calcium, potassium, titanium and chromium were adsorbed by the activated carbon due to its large specific surface area of 1308 m2/g, which enhances the physical adsorption of dissolved or dispersed substances from the solution. Amorphous nano-silica of 98.92% purity and particle size range of 6–24 nm was obtained. From the N2 adsorption–desorption analysis, the silica powder showed the following properties 240 m2/g for specific surface area, 0.58 cm3/g average pore volume and 10 nm for average pore diameter.

Analisis Silika (SiO2) Hasil Kopresipitasi Berbasis Bahan Alam menggunakan Uji XRF dan XRD

Synthesis process of silica (SiO 2 ) from Bancar sand has been carried out by coprecipitation method using NaOH. This study tried to obtain high purity silica from the natural resources by analyzing it using the Rietveld method. Experiments are conducted with different training. Study of X-ray Fluorescence (XRF) analysis showed that Bancar sand was used containing a silica composition weight of 81.7%. X-ray Diffraction (XRD) pattern proves that the synthesized SiO 2 formed is amorphous silica, but is still a crystal structure, so that amorphous silica has not yet been formed as a whole. SiO 2 content obtained showed high purity using the Rietveld method proved by GoF < 4%. By using MAUD software was obtained silica from coprecipitation methods have particle size were 98.4 ± 57.7 nm.

High purity and amorphous silica (SiO2) prepared from oil palm frond (OPF) through sol–gel method

Malaysia is known as the second largest oil palm producer in the world which subsequently also producing abundant of oil palm biomass either from milling site or plantation site. Oil palm frond (OPF) is one such oil palm biomass that usually produced abundantly in oil palm plantation site and thus it has potential for research of its application and used. This study aims to establish the utilization of OPF in silica synthesis through sol–gel method and its possibility in producing high purity and amorphous silica. To achieve this, OPF processed via several stages of combustion, acid leaching treatment with citric acid and finally silica synthesis via modified sol–gel method. The results obtained shown that from per kg of OPF, ∼3.5% or about 34.7 g of ash was produced that later subjected to acid leaching treatment and managed to recover approximately 18.7 g of acid leached oil palm frond ash (OPFA) or ∼53.9%. From this amount, 68.4% of silica or about 12.8 g of silica successfully produced from the acid leached OPFA. The synthesized silica then characterized using FTIR and presented almost identical spectra with commercial silica specifically at peak at peak 3350–3390 cm−1, 1600–1640 cm−1 and 1040–1100 cm−1 which represent Si-OH bond and Si-O-Si asymmetric bond respectively. The lack of peak at 622 cm−1 indicate that the silica is amorphous in nature and with the acid leaching treatment performed prior sol–gel, possible high purity silica was successfully produced.

Extraction of high-purity silica from rice husk via hydrochloric acid leachingtreatment

The present paper aimed at the investigation of the effect of preliminary acid treatment on the structure and purity of extracted silica. In this study, the acid leaching of rice husk (RH) in 2 M hydrochloric acid solution before the calcination process at 600 $^{\circ}$C was proposed to achieve completely white silica with high specific surface area and low content of impurities. RH, selected from the Almaty Region, Kyzylorda Region, and Turkestan Region was used as the main silica source. The results confirmed that the highest purity (98.2%-99.7%) amorphous silica with a specific surface area between 120 and 980 m$^{2}$ g$^{-1}$ could be extracted during acid treatment and controlled calcination. The structure is amorphous, porosity diameter decreased from 26.4 nm to 0.9 nm, and specific pore volume increased from 0.5 to 1.2 cm$^{3}$ g$^{-1}$.

Synthesis of ordered mesoporous silica with various pore structures using high-purity silica extracted from rice husk

Rice husk is a promising abundant bioresource for the production of high value-added silica materials because it has the highest SiO2 content among all plant-based resources. In this study, ordered mesoporous silica with various pore structures are synthesized from rice husk by combining acid leaching, chemical dissolution, and co-assembly with additional surfactants. Depending upon the type of the surfactant used and the co-assembly conditions, various mesoporous silica that have controlled pore structures (mesocellular forms and hexagonal nanochannel structures), pore sizes (3–60nm), large surface areas (297–895 m2g−1), and pore volumes (0.81–1.77cm3g−1) are successfully synthesized from a sodium silicate solution, which was made from high-purity silica (99.8%) extracted from rice husk. The synthesis of high value-added silica from an abundant bioresource can open up new avenues for sustainable and environment-friendly industrial development.

FOAM STABILITY PERFORMANCE ENHANCED WITH RICE HUSK ASH NANOPARTICLES

Rice husk ash (RHA) has been recently used as a source of silica (SiO2) production due to its high silica content. Besides, high purity silica nano-powder has been successfully synthesized from RHA and employed in various industries including electronic component manufacturing and fillers in polymers. Meanwhile, silica nanoparticles has been widely used in the application of Enhanced Oil Recovery (EOR). This is due to its ability in enhancing the foam stability besides modifying the wettability of the rocks in the formation. However, the synthesis of silica nanoparticles from RHA for the application in big scale operation such as EOR using conventional method is energy and time consuming. Therefore, the objective of this work is to study the effectiveness of using nano-sized rice husk ash (nano-RHA) as an additive to stabilize normal gas generated surfactant foam used in EOR. In order to decrease the size of the RHA into nano range, planetary ball mill was used in both dry grinding and wet grinding. Different surfactants including anionic and non-ionic were then used to study the polydispersity index of the dispersion and the hydrodynamic diameter using dynamic light scattering in dilute suspension. Besides, the nano-RHA was also characterized using FESEM, EDX, XRD and the change in specific area after grinding process was studied using BET. The foamability of different surfactants were then studied using minor concentration of nano-RHA. Next, the concentration of the nano-RHA was varied from 0.1wt% to 0.9wt% in normal gas bulk foam stability test using the suitable surfactant, the texture of foam was observed as well. Apart from that, the effect of oil on bulk foam was also studied. Finally, the result was compared using pure silica nanoparticles as the foam addictive at the same variation of concentrations. Dispersion stability tests showed that both anionic and non-ionic surfactants can be used to disperse nano-RHA in water. Moreover, in the presence of 0.9wt% of nano-RHA concentration, the bulk foam stability test results revealed that the sodium dodecyl sulfate (SDS) bulk foam half-life increased by 17.9% without the presence of oil, and gave an increment of 20.7% half-life in the presence of oil. Therefore, the study showed a potential of utilizing nano-RHA in stabilizing bulk foam.

System Maps for the Retention of Neutral Compounds on an Electrostatic-Shielded Reversed-Phase Column

The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral compounds on an octadecylsiloxane-bonded positive shield porous silica stationary phase (Luna Omega PS C18) for aqueous mobile phases containing 10–70% (v/v) methanol or acetonitrile. Electrostatic interactions (cation exchange) for weak bases were observed using acetonitrile–water but not methanol–water mobile phases at a similar level to a sterically shielded octadecylsiloxane-bonded silica column (Kinetex XB-C18). The system constants of the solvation parameter model and retention factor correlation plots for varied compounds indicated that the Luna Omega PS C18 stationary phase was (near) selectivity equivalent to the diisobutyloctadecylsiloxane-bonded superficially porous silica column Kinetex XB-C18. No specific interactions related to the embedded charged/chargeable functional group were observed compared with other high-purity type-B silica octadecylsiloxane-bonded stationary phases for typical reversed-phase separation conditions with unbuffered mobile phases.