1 Girma Gonfa, 1,2 Sintayehu Mekuria Hailegiorgis
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| 1. Introduction
Silica is a well-known material that is the most useful in- organic chemical compound for diferent industrial appli- cations, such as environmental, biomedical, agriculture, and even in chemical processing. Commonly, it is found on the earth’s crust and arises naturally as fint, sand, or quartz [1, 2]. Based on its structural characterization, silica gel has been found to be either amorphous or crystalline in ap- pearance, which is observed as an infexible 3-dimensional network of colloidal [3]. According to Kalapathy et al. [4], the structural character of the silica gel depends on its preparation method. Accordingly, it can also be categorized in aqua gel form, where the openings are occupied with water molecules in the xerogel aqueous phase, the openings are detached due to evaporation; besides, in the aerogel form, the solvent portion is detached by supercritical carbon dioxide. Biomass can be a potential source for the extraction of synthetic silica components such as silica gel. In such a way, biomass resources ash of rice husk [5], sorghum bagasse [6], tef straw [7], maize leaves [8], rice straw [9], wheat straw [10], sugarcane bagasse [11], sugarcane leaf [12], bamboo leaf [13] corn cob [14], and palm [1] are found to be potential feedstock. Sodium silicate is used in general to extract the silica from the residual ash of the feedstock [15]. Further, the produced silica is treated with diferent types of acid such as sulphuric acid [16], hydrochloric acid [17], nitric acid [18], and acetic acid [19] to turn it into gel. Several investigations have proven that the silica particles have numerous industrial applications, such as the synthesis of shear thickening fuid, as adsorbents, and inert material, even as potential catalyst [20–22]. Bageru and Srivastava [7] Hindawi Advances in Materials Science and Engineering Volume 2023, Article ID 4865273, 23 pages https://doi.org/10.1155/2023/4865273 and Mizer [5] have documented that the silica gel materials have a strong adsorption capacity due to its high surface area (700–800 m 2 /g) with appreciable other physical properties. In specifc, it exits excellent adsorption capacity on diferent organic compounds [23, 24]. Te soluble forms of silicates derived from silica have remarkable industrial applications, especially, in pharmaceuticals and construction areas. Te most common applications of liquid silicates are found in the development of ceramics [25, 26], concrete materials [27], glasses manufacturing [28], cement [29], delivery of biologically active ions [30], supercapacitors manufacturing [31], batteries [32], pharmaceuticals and cosmetics [33], detergents and adhesive agents [3, 4, 34]. Solid-state silica is used for various applications in the manufacturing of petroleum-derived products [35], fne-chemicals [36], bio- fuels [37], oil recovery [38], pollution abatement technol- ogies and optical materials [4, 39], catalyst support [40], microflters [41], thermal superinsulation [42], controlled release of drugs [23], and drug delivery systems for anti- biotics [34, 43]. Silica particles have also been demonstrated for their outstanding performance in infuencing plant metabolic ac- tivities [44]; it helps as a fertilizer to improve seedling growth rate, root development, and increase water retention [45] in plants. Moreover, silica gel exhibits several applications as adsorbent in chromatographic separation and removal of organic pollutants in water purifcation systems [46]. Commercially, silica can be produced from alkyl ortho- silicates ore using the appropriate catalysts, such as poly- ethlydiorthosilicate, tetraethyl ortothosilicate, and tetramethyl orthosilicate [7]. Silica gel is prepared by acid precipitation method using sodium silicate solution, quartz, and soda ash at the elevated temperature. So far, the conventional methods, namely, precipitation [47], electrocoagulation [48], alkaline fusion [49], chemical vapor deposition [50], sol-gel [3, 51], fuidized bed technology [52], and hydrothermal methods [3] are employed traditionally for the production of silica gel. However, high-temperature calcination that reaches up to 1710 ° C is found to be one of the major drawbacks for silica gel production in the traditional existing methods [3, 49]. High- temperature reaction leads to energy-intensive process that has an adverse efect on developing an economically sus- tainable process for silica gel production and its marketing as well [10]. Te conventional methods of producing silica gel limit its use in situations where product purity is not com- promised because they contain contaminants such as heavy metals [6]. In addition, large-scale production of crystalline silica nanoparticles may release toxic matters into the working environment that may create unsafe working condition which causes occupational diseases, such as lung cancer and pul- monary tuberculosis [53]. Silica gel can be produced from renewable sources of selected biomass such as palm tree [1], wheat straw [10], maize leaves [8], tef straw [7], sugarcane bagasse [11], rice husk and rice straw [5, 9], sugarcane leaf [12], oat husk [54], bamboo leaf [13], and corn cob [14]. At present, agricultural residues receive signifcant attention as feedstock to produce silica gel due to sustainability, economic and environmental concern. However, developing a process for silica gel production with low energy and cost requirements using agricultural biomass material is still challenging [5, 7]. So far, diferent approaches for preparing silica gel from agricultural residues have been carried out, such as hydrothermal technique, chemical vapor deposition, combustion synthesis, sol-gel processing [7, 55, 56], and precipitation methods [39]. Upon the potential importance of silica and silica gel, this comprehensive review has been narrated to provide the diferent techniques used for the synthesis and characterization of biobased silica and its current and prognostic applications. tải về 1.86 Mb. Chia sẻ với bạn bè của bạn:
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