key: cord-0827430-y73wlhhh
authors: Prabha, S.; Durgalakshmi, D.; Rajendran, Saravanan; Lichtfouse, Eric
title: Plant-derived silica nanoparticles and composites for biosensors, bioimaging, drug delivery and supercapacitors: a review
date: 2020-11-12
journal: Environ Chem Lett
DOI: 10.1007/s10311-020-01123-5
sha: 4687be23400b6ffc630e3174ad768994846c0880
doc_id: 827430
cord_uid: y73wlhhh

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.

Silicon is a major element of earth's crust. Silica sand, the primary ore source of silicon, is abundant and easy to process. Silica minerals are referred by quartzite, tridymite, metamorphic rock, cristobalite and minerals such as polymorphs of silica. The combination of silicon and oxygen is called silicate, and 90% of earth's crust is made of silicate minerals. Clays and silica sand are silicate minerals that are used in applications such as making Portland cement in building mortar and modern stucco. Concrete made of silicates integrated within silica sand for making concrete is a major building material (Greenwood and Earnshaw 1997) . Silicones are used for various products such as moldrelease agents, molding compounds, waxes, waterproofing treatments, mechanical seals and high-temperature greases. Silica in the form of clay and sand is used in bricks and concrete. Glass silica obtained from sand is the major element in making various glass material with diverse properties. The silly putty contains also substantial amounts of silica, it is made by addition of boric acid to silicone oil. Liquid silicone is widely used as dry cleaning solvent and is an alternative for perchloro-ethylene solvents (Koch and Clément 2007) .

Silica is also used in biomedical applications such as contact lenses, breast implants, explosives and pyrotechnics.

Nanotechnology involves the development of nano-sized materials and devices. Notably, silica nanoparticles have occupied the prime position due to their facile synthesis, rich surface chemistry, low toxicity and controllable properties such as optoelectronic, mechanical and chemical stability (Rossi et al. 2005; Vivero-Escoto and Huang 2011) . These properties are not only extensively considered in biomedical field and but also for diverse applications such as agricultural, food industries, photovoltaic and energy storage applications (Liberman et al. 2014; Devi and Balachandran 2016) . Nanotechnology enables the extension of multifunctional medicine by integrating materials that allow multimodal imaging and theranostics applications (Bharti et al. 2015) . Notably, mesoporous silica nanoparticles have uniform pore size, hydrophilic surface property and high surface area. Such properties increase electrochemically active centers, thus enhancing electron transport and promoting electrolyte penetration, which meets the requirements of next-generation supercapacitors .

Silica nanoparticles have also been applied for fighting COVID-19. Here, a nanocomposite of silver nanocluster/ silica deposited on a FFP3 mask reduces the SARS-Cov-2 to zero (Balagna et al. 2020) . The nanocomposite also increases the life time of the mask and improves air filtering. Morevover, silica nanoparticles can be transformed to have a superhydrophilic surface which repels contaminated droplets (Meguid and Elzaabalawy 2020) .

Natural resources-based silica has garnered considerable interest in the materials science and biomedicine fields owing to its low cost, eco-friendliness, bioactivity and availability. Biomass is an alternative source for widely used organic precursors, namely tetraethyl orthosilicate (TEOS) and tetramethylorthosilicate. In biomedical applications, stability and biocompatibility are the prime issues. Therefore research if focussing on the development of biomass for preparing silica and implemented to theranostics applications.

Developed countries have followed the concept by which waste materials are not really waste but new sources for creating new materials. Developing countries have abundant agriculture-based resources and their by-products are used to produce various low-value products. In 2005, a bioenergy production project using municipal, animal, agricultural and industrial wastes was assigned by five countries: India, China, Sri Lanka, Philippines and Thailand. As a result, in 2010, bioenergy represented 45% of total energy in India, 17% in China, 33% in Sri Lanka, 34% in Philippines and 14% in Thailand. India is the major energy consumer in Asia. During 2011, biomass gasifier assignment of 0.5 MW power in Tamil Nadu and 1.20 MW in Gujarat were successfully installed (Pode and Reviews 2016) .

In India, 120 million tons of paddy rice is produced per annum, giving nearly 4.4 tons of rice husks (Giddel and Jivan 2007) . High silica content has been observed in biomass wastes (Oladeji 2010; Shen et al. 2014; Zemnukhova et al. 2015; Hossain et al. 2018; Dhinasekaran et al. 2020) . Rice husk ash contains 83-98% of silica (Saxena et al. 2009; Babaso and Sharanagouda 2017) . Corn is another major crop plant with 785 million tons produced annually in this world. India is the seventh largest producer of corn cob, with silica content as high as 60% in biomass (Kumar et al. 2010) . India produces an average of 500 million tons of crop residue per year, of which 140 million tons is surplus and 92 million tons is left as burned (Bhuvaneshwari et al. 2019) . Globally, uncontrolled burning of biomass wastes is causing environmental and health issues, thus calling for recycling options.

Recent research on silica has focused on nanoparticles. Silica nanoparticles can be prepared from either organic chemicals or biomass. Comparatively, the usage of biomass is less compared to synthetic organic precursors due to lack of a review and assessment on the importance of silica in biomass. Many reports have reviewed the preparation of silica nanoparticles from pure organic chemicals (Wu et al. 2013a, b; Bleta et al. 2018; Morin-Crini et al. 2019; Meena et al. 2020; Mahajan et al. 2020 ). Here we focus on silica nanoparticles from biomass for biosensors, bioimaging, drug delivery and supercapacitor applications.

Solid materials are generally crystalline, made of atoms, molecules and ions arranged in an orderly repeating pattern. In amorphous materials, atoms are not arranged in orderly repeating patterns. Silica has two types of structures: crystalline and amorphous. Silica occurs naturally as the solid amorphous phase of flint and opal and as the crystalline phase of cristobalite, quartz and tridymite. Amorphous phases can be transformed into crystalline phases by thermal treatments (Eq. (1)) (Waddell 2000) .

Quartz and sandstone are the impure forms of silica. The crystalline phases of silica are melanophlogopite, α-quartz, α-cristobalite, β-quartz, β-cristobalite, γ-tridymite, β-tridymite, α-tridymite, fasriges, chalcedon, keatite, moganite and stishovite. Amorphous phases of silica include hyalite opal, natural silica glass, sintered pearl, lechatelierite are amorphous phases of silica (Fanderlik 2013) . There are three polymorphic structures present in the silica, each structure having both low-temperature (α) and a high-temperature (1) (Douglas and Ho 2006) . In sediments, the transformation of amorphous silica opal-A into crystalline opal-CT (cristobalite-tridymite) with increasing burial, temperature and pressure has been correlated with an abrupt transformation of organic matter (Lichtfouse and Rullkötter 1994) . Figure 1 shows the structure of both crystalline and amorphous silica structures.

In 1800, Sir Humphry Davy thought that silica has to be a compound and not a single element. To test this hypothesis, in 1808 he did experiments to decompose of silex, alumine and glucine zircone, yet he failed to isolate the Si metal. In 1811, Louis-Jacques Thenard (1777-1857) and Louis-Joseph Gay-Lussac (1778-1850) explained that heating potassium with silicon tetrafluoride results in the formation of impure amorphous silicon. Silicon was discovered by Jakob Berzelius (1779-1848); in 1824, he prepared amorphous silicon successfully using earlier methods, and then, he removed fluorosilicates by repeated washing to get the purified product. The name silica is coming from the Latin word silex. Silica is the combination of silicon (Si) with oxygen (O 2 ) and the most plentiful compound in the earth's crust (Pauling 1957; Holden 2001) . The covalent network structure of SiO 2 is given in Fig. 2 .

Among all polymers, organic groups attached to a chain of inorganic atoms is a unique properties of silicone. Silicones are used in of electronics, paints, construction and beverages (Korzhinsky et al. 1995) . In medicine, silicone is used in artificial joints, antacids, implants of various notoriety and pacemakers (Korzhinsky et al. 1995) . Silicon dioxide (silica) occurs in the form of sand. Reduction of silica with carbon at high temperature was performed for manufacturing (2), Bell et al. 1968; Mozzi and Warren 1969; Gerber and Himmel 1986; Korzhinsky et al. 1995) .

The SiO 4 tetrahedron is the central functional component of both amorphous and crystalline of silica. The silicon

atom is placed at the center, and the four oxygen atoms are connected at each side of a tetrahedron (Fig. 3 , Henderson and Baker 2002) . According to various forms of silica, the tetrahedron depends on the angle (α) and bond length.

The energy of the Si-O bond is 4.5 eV (Devine et al. 2000) . Figure 4 shows the 3D silica structural parameters of bond length (d), polyhedron angle (φ) and inter-tetrahedral bond angle (α) (Lide 2004) .

In Raman spectra, bands correspond to Si-O − groups of various Q n units (n < 4). The band at 1050-1100 cm −1 is due to the symmetric stretching vibrations of the SiO 4 tetrahedra with one nonbridging oxygen (NBO) atom (Q 3 units); 920-950 cm −1 is due to the Si-O − stretching with two NBO (Q 2 units); 900 cm −1 is attributed to the stretching vibration of Q 1 units with three nonbridging oxygens; and 850 cm −1 is due to the symmetric stretching mode of Q 0 anions (McMillan 1984) . Figure 5a shows the infrared bands with vibrational modes. Nuclear magnetic resonance (NMR) study also predicts Q 0 , Q 1 , Q 2 , Q 3 , Q 4 notation in silica, and the numbers 0-4 denote the number of 'Si' units connected through the oxygen to the other single silicon atom. Q 0 , Q 1 , Q 2 , Q 3 are referred to as a silicon atom with zero, one, two Salh (2011) and Osipov et al. (2015) and three attachments of another silicon atom, respectively (Lunevich et al. 2016) . A schematic two-dimensional representation of the Q n species is shown in Fig. 5b .

Various preparation methods are available to synthesize silica nanoparticles, such as microemulsion processing (Finnie et al. 2007) , chemical vapor deposition (Rezaei et al. 2014) , combustion synthesis (Yermekova et al. 2010) , plasma synthesis (Saito et al. 2018) , hydrothermal techniques (Gu et al. 2012 ) and sol-gel processing (Prabha et al. 2019) . Major researches efforts have focused on controlling the size and morphology of nanoparticles (Brinker and Scherer 2013) . During chemical vapor condensation (CVC), inorganic precursors, e.g., silicon tetrachloride (SiCl 4 ), are decomposed by a high-temperature flame or react with hydrogen and oxygen to yield silica nanoparticles (Silva 2004; Vansant et al. 1995) . The main drawback of flame synthesis is the difficulty in controlling the phase composition, particle size and morphology (Klabunde 2001 ), yet flame synthesis is the major method for producing silica nanoparticles commercially in powder form. The different methods for silica nanoparticle preparation are presented in Table 1 .

The sol-gel technique has advantages of yielding pure, homogeneous materials, and enabling to obtain various forms of materials such as fibers, films, submicron powders and monoliths (Fardad 2000; Brinker and Scherer 2013) . The sol-gel process is defined as the chemical transformation from colloidal suspension of sol into a 3D interconnecting network of gel. In this process, a metal alkoxide undergoes hydrolysis and polymerization reactions to form the sol. Further, the sol allows to preparing the materials in various forms such as discrete particles or polymers. The reaction is controlled by the reactants such as alcohol, water and acid/base; the size of the particles is tuned by pH, precursor concentration and temperature (Burda et al. 2005; Yu et al. 2008; Singh et al. 2011a) .

Silica nanoparticles are synthesized by the sol-gelassisted, low-temperature Stöber method. In this process, the hydrolytic condensation reaction of Si-OH coupling occurs by replacement of an alkoxide group (-OR) with a hydroxyl group (-OH) (Kim et al. 2017 ). In the beginning, Stöber et al. prepared 1 μm of silica nanoparticles using 2Q n→ ↔ Q n−1 + Q n+1 (n = 1, 2, 3) the sol-gel method (Stöber et al. 1968 ). Then, a hundred nanometers to a few micrometers silica nanoparticles were obtained by controlling the concentration of the precursor during hydrolysis (Bogush et al. 1988 ). The Stöber method also allowed to synthesize various shapes of silica nanoparticles such as nanocubes and spheres. The cubic shape of silica nanoparticles is obtained by addition of tartaric acid during synthesis (Yu et al. 2005) , whereas monodisperse nanocubes of silica nanoparticles are prepared using ammonium tartrate as a surface-specific template in the sol-gel method (Yu et al. 2005) .

The influence of synthesis parameters on the size and shape of silica nanoparticles has been largely studied. The concentration of the precursor, e.g., tetraethylorthosilicate, and the alcohol, e.g., ethanol, both control the size and distribution of silica nanoparticles. Particle sizes of 1.5 nm and 20-1000 nm were obtained by tuning the concentrations of alcohol and the precursor (Shimura and Ogawa 2007; Wang et al. 2010) . Reaction temperature and time, and rotation per minute are also controlling the homogeneous distribution (Dabbaghian et al. 2010) . Particle sizes of 50-800 nm and 32-300 nm were obtained by varying the reaction temperature and time (Novak et al. 2010; Kim et al. 2017) . Narrow particles can be obtained by controlling the reaction parameters in the Stöber method.

In the wet chemical synthesis, the surfactant allows to tune the size of the particle and prevent agglomeration. Amorphous silica nanoparticles of 300-400 nm were prepared using polyvinyl pyrrolidone, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (Stanley and Nesaraj 2014) . Particle size of 9 nm was obtained using polyethylene glycol-100 as a surfactant (PEG 1000, Guo et al. 2017) . The properties of silica nanoparticles can be tuned also during sol-gel-assisted sonication. Particle size decreases with increased concentration of reagents, e.g., NH 3 , tetraethylorthosilicate, ethanol and water, by ultrasonication during the sol-gel process (Rao et al. 2005) . Further functionalization of silica nanoparticles allows applications in nanomedicine and the industry (Liberman et al. 2014; Dubey et al. 2015) .

The main parameters controlling the size and shape of silica nanoparticles are concentrations of tetraethylorthosilicate (TEOS), ammonia hydroxide (NH 4 OH)/ammonia (NH 3 ), water, ethanol and reaction temperature (Bogush et al. 1988; Rao et al. 2005) . Table 2 presents factors controlling particle size. Overall, particle size increases with tetraethylorthosilicate concentration (Sumathi and Thenmozhi 2016) , ethanol concentration (Singh et al. 2014a ), pH of the reaction (Singh et al. 2011a ) and reaction temperature (Zainala et al. 2013) . Particle size also increases with increasing concentration of H 2 O, yet as H 2 O concentration increases the size of some particles decreases. This is because H 2 O accelerates tetraethylorthosilicate hydrolysis; and H 2 O dilute oligomers in the reaction, which helps to produce larger particles and smaller particle, respectively ). Finally, a narrow distribution of particle size is obtained at high concentrations of ammonia (Zeng et al. 2015) . While the mechanism corresponding to the nucleation and growth of silica nanoparticles still needs to be explained, a well understanding of the impact of synthesis parameters on the resultant particle size and shape is gradually developing. Table 3 shows chemical methods of silica nanoparticle preparation. The influence of the chemical reagents on particle size, distribution and morphology is given as scanning electron microscopy and transmission electron microscopy images in Figs. 6 and 7, respectively. Mono-dispersed mesoporous silica nanoparticles obtained using polymer lattices, metal oxides and silica colloids Polymer latex-templating Selective functional groups activated by surface activation for silicification Functional groups activation achieved by layer-by-layer deposition through electrostatic attraction Metal or metal oxide nanoparticles Cetyltrimethylammonium bromide (CTAB) acts both as stabilizer and mesostructural directing agent Thickness of mesoporous silica shells tuned by varying the ratio of surfactant and silica precursor Core-shell silica Core is coated with non-toxic material to make nanoparticles biocompatible Shell layer reduces toxicity and enhances the properties of the core material

To prepare silica nanoparticles, most investigations use organic precursors of alkoxysilane such as tetraethylorthosilicate (TEOS) and tetramethylorthosilicate (Bosio et al. 2013 ). Nonetheless, silica from natural resources is used in biomedical and materials fields due to low cost, eco-friendliness and availability. Silica can be successfully extracted from biomass such as sugarcane bagasse, rice husk, corn cob, coffee husk and wheat husk. Rice husk is an abundant (2017) Stober method-silica nanoparticles with a high concentration.Tetraethylorthosilicate (TEOS) as a starting material.

10 nm of 4% of silica nanoparticle through reaction condition. By removing solvent, particle concentration increased up to 15 wt.% without aggregation Tadanaga et al. (2013) TEOS, ammonia (NH 3 ), H 2 O controls the reaction rate and particle size. NH 3 and H 2 O concentrations control the hydrolysis and the condensation processes.

Monodisperse spherical silica nanoparticles at 20 nm Beganskienė et al. (2004) Stober method A series of nanoparticles with controllable size from 20 to 100 nm Silica nanoparticles influence as a function of the temperature, precursor, water and catalyst

Particle size is independent of the concentration of the precursor and depends on the concentration of the ammonia solution. But it is inversely proportional to the reaction temperature The average size of silica nanoparticles depends on the reactants and reaction temperature. The particle sizes of 28.91 nm-113.22 nm through varying the temperature of the reaction. 2-butanol as a solvent Hajarul et al. (2011) silicon source, and contains about 75-90% of cellulose, hemicellulose and lignin totaling and 17-20% of ash content (Azmi et al. 2016 ). The ash contains more than 90% of silica and few metallic impurities. Sugarcane bagasse ash, a major by-product of the sugarcane industry, contains 40-50% of silica; acid pretreatment allows to increase amount of silica up to 80% (Ganesan et al. 2007; Singh and All Jawald 2013) . Corn cobs, obtained from maize corn, contain more than 60% of silica (Owoeye et al.) . Wheat husk ash contains up to 90% silica (Naqvi et al. 2011) , which is close to that of dry silica sand, of 99.4%. Bamboo leaf ash also has a large silica content of 75.90-82.86 wt.% (Silviana and Bayu 2018) . Raw teff straw contains about 52% of silica, which can be increased to 97% after thermal treatment (Wassie and Srivastava 2017) .

Examples of silica-rich biomass are shown in Fig. 8 . Extraction of silica from biomass, preparation and characterization of silica nanoparticles are discussed below.

Corn is one of the most frequently grown food crops in the world; it is extracted from maize (corn). Corn cob ash contains more than 60% of silica and few metallic elements (Adesanya and Raheem 2009) . Corn cob is grounded to a fine powder that is used to produce silica, silicates and silica nanoparticles. Corn cob is used for enzymes, absorbents (Tsai et al. 2001) , proteins ), fuel Table 4 (Okoronkwo et al. 2013) .

Nanosilica is prepared from corn cob ash by precipitation (Mohanraj et al. 2012) . The 50-60% of silica in corn cob ash must be purified to remove of impurities. Silica aquagel from corn cob ash is prepared by alkaline extraction and acid . NH 4 OH concentration controls the density of the silica particles. The narrow distribution of particle size obtained at higher ammonia concentration and H 2 O could accelerate TEOS hydrolysis and helps to produce larger particles . Silica can be isolated from corn cob by varying pH (7-10) using the sol-gel method . The results show a 99.50% purity, larger surface area, high reactivity and 98.50% amorphous state. Scanning electron microscopic (SEM) images of corn cob and silica nanoparticles are displayed in Fig. 9 .

Silica nanoparticles from corn cob extracts are also prepared by precipitation. Here, soluble sodium silicate solution from corn cob ash is used as a source of silica, and concentrated sodium hydroxide (NaOH) is used as a source of soda. Various parameters such as specific gravity, pH value, viscosity and electrical conductivity were studied (Ajayi and Owoeye 2015) . Silica nanoparticles prepared from corn cob yield amorphous silica with large surface area.

Rice husk has been studied for energy and for production of silica (Liu et al. 2016a, b) . For instance, rice husk ash is a precursor for silica gel synthesis by the sol-gel method: here sodium silicate is prepared first then converted into a gel by acid treatment (Geetha et al. 2016) . Acid and thermal treatments yield a white color silica with high surface area (Della et al. 2002) . Rice husk has about 20% of minerals (Carmona et al. 2013) . Organic compounds include cellulose, hemicellulose and lignin. Minerals contains 94% of silica and 6% of Al 2 O 3, K 2 O, MgO, CaO and P 2 O 5 . Composition varies depending on soil type, fertilizers and weather conditions (De Souza et al. 2002) . The chemical composition of rice husk is shown in Table 5 .

For optimal production of nanosilica from rice husk, the effect of the acid leaching, concentration of sodium silicate solution, reaction temperature and time of aging and gelation, pH on synthesizing silica nanoparticle, were studied (Liou and Yang 2011) . Research also focused on morphology of rich husk ash, which displays a porous structure after washing, acid treatment and sintering (Madrid et al. 2012) . As a consequence, rich husk ash shows promising 

applications for construction materials and technical ceramics due to the high reactivity of the porous structure. Extraction and characterization of silica from a different rice husks such as agulhinha and cateto were analyzed (Carmona et al. 2013) . Highly pure silica nanoparticles with high specific area and an average size of 25 nm were prepared by alkali extraction, followed by acid precipitation (Yuvakkumar et al. 2014) . Research has also focused on 'waste in valuable product manufacture' using silica, revealing good performance and simple industrial implementation as anti-sticking agents, filter in rubber products and paper (Todkar et al. 2016) . Silica nanocomposite can be prepared with rice husk ash, which is used as a nanofiller in epoxy-silica nanocomposites; products display good tensile strength, uniform distribution and no agglomeration (Moosa and Saddam 2017) . To synthesize high surface area silica aerogel from rice husk ash, the water extract of rice husk is used as a precursor in the sol-gel process (Feng et al. 2018) . The image of rice husk, after acid leach of rice husk, and the morphology of rice husk ash and silica nanoparticles are shown in Fig. 10 . Overall, rice husk silica can be used to develop valuable products, thus solving the disposal issue (Tyagi et al. 2017 ).

India has the second largest manufacture of sugarcane in the world. Bagasse is the residue of sugarcane; bagasse is obtained industrially by milling. India produces 10 million tons of sugarcane bagasse ash as a waste material (Goyal et al. 2007 ). Silica is abundant in sugarcane bagasse ash (Aigbodion et al. 2010; Faria et al. 2012) . Mesoporous silica nanoparticles prepared from sugarcane bagasse are applied in biomedical and industrial fields (Rahman et al. 2015) . Sugarcane bagasse is considered as a better option (Prabha et al. 2019) than wood fibers in producing textiles, paper, pressed wood materials and other products (Mandal and Chakrabarty 2011) . Silica extracted from sugarcane is suitable as additive for membrane fabrication (Mokhtar et al. 2016 ).

In the nineteenth century, silica was found in plants, and then, silica is generally accepted as a sustainable polymer compound (Hariharan and Sivakumar 2013) . The chemical composition of sugarcane bagasse ash is shown in Table 6 ( Chusilp et al. 2009 ). The effect of calcination temperature and alkali concentration on silica structure have been studied (Rahmat et al. 2016; Athinarayanan et al. 2017) . HCl is used for washing, and NaOH was for silica extraction. Acid pretreatment in autoclave removes metal ions and induces the hydrolysis of organic substances. Bagasse ash filler treated with HCl/ NH 4 F gives silica of 77%-97% purity (Huabcharoen et al. 2017) . SEM images of the sugarcane bagasse, bagasse ash and silica nanoparticles from sugarcane bagasse are shown in Fig. 11 .

Porosity is classified according to pore size (Table 7 , Barrabino 2011) . Porosity is defined as the periodic arrangements with uniform size mesopores integrated within the amorphous silica matrix.

Mesoporous silica material was discovered in 1992 by the Mobil Oil corporation and is known as the M41S phase having pore diameters from about 2 to 10 nm (Hoffmann et al. 2006) . The materials are often referred to as Mobil composition of matter (MCM) (Caras 2011) , and the most popular MCM materials are MCM-41 and MCM-48, displaying 2D hexagonal and 3D cubic arrangement of pores, respectively (Tzankov et al. 2014) . Mesoporous silica got high interest due to tunable particle size (10-1000 nm) and pore diameter (2-30 nm), large surface area and pore volume, flexible morphology, surface functionalization and uniform mesoporosity, tunable and narrow pore size distribution, and excellent biocompatibility and biodegradation. Mesoporous silica nanoparticles (MSNPs) have been developed for inorganic delivery (Caras 2011) . Mesoporous silica nanoparticles have sizes ranging from 50 to 500 nm in diameter with pores ranging from 2 to 20 nm; these pores are mainly cylindrical . Pores act as vehicles and reservoirs in a wide range of fields such as drug delivery, adsorption and heterogeneous catalysis. Applications include drug delivery of therapeutic agents (Thomas et al. 2010; Trewyn et al. 2007 ). Microscopic images of mesoporous silica obtained by various methods are shown in Fig. 12 . Mesoporous silica nanoparticles are prepared using amphiphilic molecules as templates for their internal structure. Two different structures can be obtained by changing the synthesis conditions, the two-dimensional hexagonal structure known as MCM-41 Kresge et al. 1992 ) and the tridimensional cubic structure MCM-48 (Hoffmann et al. 2006) . Mesoporous silica materials were first synthesized for catalytic applications (Yanagisawa et al. 1990; Kresge et al. 1992) . To increase biocompatibility, smaller sizes and homogeneous morphology are required. For instance, submicrometer MCM-41 particles were prepared in 1997 by a modified Stober method (Grün et al. 1997) . Later, 100 nm MCM-41 silica particles were synthesized using a dilute surfactant solution (Cai et al. 2001) , and then, less than 50 nm particles were prepared by dialysis (Suzuki et al. 2004) . Overall, mesoporous silica nanoparticles have large pore volume and surface area and can be functionalized with versatile functional groups for theranostic applications.

Core-shell nanoparticles refer as inner material coated with another material on the surface (Law et al. 2008 ). Core-shell nanoparticles have numerous advantages over conventional nanoparticles in biological applications because these particles display high dispersibility and low cytotoxicity, bio-and cytocompatibility, better conjugation with other bioactive molecules, and increased thermal and chemical stability (Sounderya and Zhang 2008) . The core is coated with non-toxic material to make nanoparticles biocompatible. The shell layer reduces the toxic layer and (Chatterjee et al. 2014) . Core-shell nanoparticles are mainly designed to increase the binding affinity with ligands, drugs and receptors in biomedical applications (Sahoo and Labhasetwar 2003; Gilmore et al. 2008; Chen et al. 2010) . The thickness of the shell can be tuned to improve contrast agents, targeted drug delivery, specific binding and biosensing (Pinho et al. 2010) . Microscopic images of silica nanoparticles with a core-shell structure are shown in Fig. 13 . Tables 8 and 9 present core-shell silica nanoparticles for biosensor and bioimaging applications. Fig. 13 Transmission electron microscopy. a Silica-gadolinium particle, reprinted with permission from Kobayashi et al. (2007) . b Silver-silica with silica shell thickness of 8 ± 2 nm . Core-shell of polystyrene-silica composites (PSC), c silica: styrene 1:10, d silica:styrene 1.5:10, reprinted with permission from Ding et al. (2004) . Core-shell of gold-silica at various scales: e 500 nm, f 20 nm. Gold-silica with template of 0.1 g cetyltrimethylammonium bromide (CTAB) at various scales: g 200 nm, h 10 nm, reprinted with permission from Vu et al. 

Silica nanoparticles are used in many fields such as biomedical, electrical, textile and rubber sectors, yet nowadays research is moving toward the biomedical field. Here silica nanoparticles are used in diagnosis and to control diseases by identifying and correcting the genetic disorders, as a theranostics agent. In addition, some applications such as biosensor, bioimaging, drug delivery and supercapacitor are briefly discussed. Applications of silica nanoparticles are shown in Fig. 14 and Table 10 .

Sensors are the analytical device that consists of an active sensing material with a signal transducer (Kuswandi 2019) .

In general, sensors can be categorized into two types: biosensors and chemical sensors. This classification is based on sensing aspects, where the biosensors can sense biochemical compounds such as enzymes (Verma 2017) , antibodies, nucleic acids, cells and tissues (Yogeswaran and Chen 2008) . Biosensors typically consist of two intimately associated elements: a bioreceptor and a transducer. Based on the transducing mechanism, biosensors are further classified as (i) optical-detection biosensors, (ii) resonant biosensors, (iii) thermal detection biosensors, (iv) ion-sensitive field-effect transistor-based biosensors and (v) electrochemical biosensors (Chaubey and Malhotra 2002) . Numerous electrochemical biosensors have been developed for determining various substances such as glucose (Saei et al. 2013) , cholesterol (Hui et al. 2015) , dopamine (Huang et al. 2015) , hydrazine (Liu et al. 2016a, b) , hydrogen peroxide (Ju and Chen 2015) , kanamycin (Qin et al. 2016 ) and cysteine (Amiri et al. 2017) .

Optical biosensors are applicable in environmental monitoring, biomedical research, pharmaceuticals, healthcare, homeland security and the battlefield due to powerful detection and analysis tools (Amiri et al. 2017) . For non-enzymatic detection of hydrogen peroxide (H 2 O 2 ), graphene oxide was composited with silica nanoparticles (Huang and Li 2013) . Amperometric studies show that composites of graphene oxide and silica nanoparticles enhance the electrochemical activity of hydrogen peroxide detection in alkaline medium, with a low detection limit of 2.6 μM and high reproducibility. Functionalized mesoporous silica is used for detection of H 2 O 2 and controlled treatment of heart failure (Tan et al. 2017 ). Here, the H 2 O 2 -sensitive probe is attached to the surface of a mesoporous silica nanoparticles (MSNP), and captopril, a drug for heart failure, is loaded inside the pores of nanoparticles. A MSNP-based system of high loading efficiency and releasing capacity was developed and combined with detection by chemiluminescence of luminol / hydrogen peroxide . For dengue RNA detection, 3-aminopropyltriethoxysilane (APTES)-functionalized graphene oxide was enclosed in silica nanoparticles (Jin et al. . Results showed better selectivity and lower detection limit than graphene oxide without enclosed silica.

Silica nanoparticles can be easily utilized for molecular imaging techniques, such as optical imaging, e.g., fluorescence and bioluminescence, magnetic resonance imaging (MRI), radionuclide imaging, e.g., positron emission tomography (PET) and single-photon emission computed tomography (SPECT), computed tomography (CT), ultrasound, photoacoustic imaging and Raman imaging (Tang and Cheng 2013) . Silica nanoparticles are used as contrast agents in medical imaging to encapsulate contrast agent particles such as an iron oxide (Lee et al. 2009 ), gold (Viarbitskaya et al. 2011 ), silver (Gong et al. 2007) , organic dyes (Yuan et al. 2005 ) and quantum dots (Hagura et al. 2011 ). The 20-30 nm silica-coated fluorophore is photostable, and brightness is 20 times higher than composing fluorophores (Ow et al. 2005) . The outer silica shell allows target specific cells and tissues by silica surface functionalization (Ow et al. 2005) . Computed tomography is mostly used in diagnosis due to the limited depth of tissue penetration . A hybrid of silica with gold nanoparticles and fluorescein isothiocyanate dyes display a strong fluorescence signal at 520 nm under 490 nm excitation (Feng et al. 2014) . Silica-coated gold nanospheres can be coated with fluorescent quantum dots, yet further coating with silica is needed to reduce the defects of quantum dots . This composite was used for contrast-enhanced computed tomography and fluorescence imaging. The probe of -oxidized-glucose oxidase on gold nanoparticlesmesoporous silica. Modified gold electrode with 2-aminoethanethiol as a cross-linker (Bai et al. 2007) Hollow silica spheres DNA Biosensor Depositing gold nanoparticle/hollow silica spheres on a screen-printed carbon paste electrode for the detection of E.coli DNA. Using glutaraldehyde bifunctional cross-linker, an aminated DNA probe is coupled to the aminated hollow silica spheres and deposited onto the electrode of gold nanoparticle-modified screen-printed carbon paste (Ariffin et al. 2018 ) TAT (cell penetrating peptide) conjugated with fluorescein isothiocyanate and doped silica nanoparticles Bioimaging Human lung adenocarcinoma (A549) cells (in vitro) and rat brain tissue (in vivo) tagged with nanoparticles. Endovascular approach targets brain blood vessels to study blood-brain barrier (Santra et al. 2004 ) Carbon dots inserted in a silica shell around polylactide-polyethylene-glycol conjugated silica core Bioimaging Fluorescence induced by incorporation of carbon dots into silica nanoparticle shell. Carbon dots with silane groups on the silica shell using a one-pot reaction. For cellular uptake, silica-loaded core are incubated with A549 cells line and studied for drug release and bioimaging Silica core-shell material proved promising materials for both bioimaging and anticancer drug delivery (Mehdi et al. 2018 Uniform hollow-core mesoporous shell carbon nanospheres fabricated by a surface co-assembly of monodisperse silica nanospheres method. This strategy is easier compared to other methods. 2.0 M sulfuric acid solution as the electrolyte: working electrode is hollowcore mesoporous shell carbon nanospheres coated glass carbon electrode, platinum electrode used as a counter. Good sustainability of capacitance (You et al. 2011) in vivo gastric cancer cells using folic acid-conjugated silica coated with gold nanoclusters of about 58 nm size was used for computed tomography and fluorescence imaging (Zhou et al. 2013) . Magnetic resonance imaging is mostly used for noninvasive diagnostic techniques (Viswanathan et al. 2010 ). Silica-coated gadolinium nanoparticles co-doped with europium (Eu 3+ ) and terbium (Tb 3+ ) were used for magnetic resonance and fluorescence imaging. Gadolinium carbonate particles are often used in magnetic resonance imaging. To increase biocompatibility, biomass-derived silica nanoparticles were conjugated with a fluorescent material and used for biological imaging application (Pandey et al. 2014 ). Here, meso-silica nanoparticles derived from rice husk were composited with green fluorescent carbon dots by hot injection. The complex shows high drug loading efficiency and stronger fluorescence compared to carbon dots alone. Thus, this complex material can be used for theranostic applications. Rice husk-derived silica composite with rare earth elements, europium/gadolinium ions were prepared by microwave-assisted combustion (Araichimani et al. 2020) . Europium ions and gadolinium ions in the silica matrix exhibited potential of fluorescence imaging and T1-weighted magnetic resonance imaging, respectively. Thus, rice husk silica nanoparticles with rare earth ions are a good alternative for developing cost-effective bioimaging contrast agents.

Drug delivery systems based on silica nanoparticles are fastdeveloping in nanomedicine, yet it requires the analysis of toxicity, biodistribution, clearance and immune response of silica and modified silica (Biju 2014) . Mesoporous silica nanoparticles are widely used for drug delivery application (Chowdhury 2018) . Owing to the presence of surface silanol groups, they can be functionalized to tune the load and release of drugs (Vallet-Regí et al. 2007 ). Amine-functionalized mesoporous silica nanoparticles are widely used (Vallet-Regí et al. 2011) . High drug loading and slow drug release are observed (Chowdhury, 2016) . A such approach has been used for various drugs, e.g., heparin (Wan et al. 2012) , hydrocortisone (Lopez et al. 2009 ), metoprolol (Guo et al. 2010) , salidroside (Peng et al. 2013) , venlafaxine (Tang et al. 2011) , vancomycin (Lai et al. 2003) , methotrexate (Carino et al. 2007 ), sophoridine (Dong et al. 2014) insulin and cyclic adenosine monophosphate (cAMP, Zhao et al. 2010) , and anticancer drugs such as doxorubicin and 5-fluorouracil (Singh et al. 2011b; Mei et al. 2012; Wu et al. 2013a, b; Hwang et al. 2015) .

Magnetic carbon nanotubes composited with mesoporous silica shows a high loading capacity for therapeutic molecules such as protein cytochrome C and drug gentamicin (Singh et al. 2014b) . Small interfering RNA (siRNA) was loaded and then released over a days to a week. Transferrin was grafted on the surfaces of mesoporous silica nanoparticles by a redox-cleavable disulfide bond, then was used as capping agent and targeting ligand (Chen et al. 2017) . To examine the redox-responsive and burst release of doxorubicin, transferrin was integrated into mesoporous silica nanoparticles with the presence and absence of glutathione. Here, the presence of glutathione has perfect capping efficiency of transferrin and also enhanced the biocompatibility.

Nanocarriers of amine-modified mesoporous silica-iron oxide functionalized with 2, 3-dimercaptosuccinic acid via chemical amidation show that a negligible amount of the drug is released in the absence of a magnetic field . Upon application of a magnetic field, nanocaps are removed by chemical bond breaking, which induces high drug release. This material is also applicable for molecular imaging by T 2 -weighted magnetic resonance contrast influencing agents. Composites of rice husk-derived silica nanoparticles and polycaprolactone nanofibers are used for drug delivery of drugs such as allantoin (Ke et al. 2016) . To reduce cost and increase biocompatibility, 5-fluorouracil was fixed to chitosan-coated biomass silica nanoparticles (Dhinasekaran et al. 2020) . The results showed that potential in targeting the cancer cell lines MCF-7 and A549.

Supercapacitors have attracted interest owing to their extended cycle life performance, high charge/discharge rates and high power density (Miller and Simon 2008; Liu et al. 2010; Simon and Gogotsi 2010) . Supercapacitors are considered as a very promising energy storage device to complement or eventually replace the batteries of wearable and portable electronics, and electrical and hybrid vehicles (Kaempgen et al. 2009 ). Supercapacitors can be classified into two main categories according to the energy storage mechanisms: electric double-layer capacitors (EDLC) and pseudocapacitors (Winter and Brodd 2004) . Mesoporous silica nanoparticles with conducting polyaniline wires wrapped with graphene oxide were found to expand the surface area and allow the movement of ions and charge transfer (Javed et al. 2018) . Manganese dioxide/mesoporous nanocomposite are obtained by facile chemical synthesis and then used as electrode material for supercapacitor applications, thus displayed superior electrochemical performance ). Rice-derived silicon was composited with carbon (SiO x /C) for Li-ion batteries by one-step pyrolysis exhibiting SiO x /C anode specific capacity of 654 mAh g −1 after 1000 cycles, with higher capacity up to 920 mAh g −1 (Huang et al. 2019) . To use rice husk for energy storage, tin oxide was decorated on huskderived silica nanoparticles by facile microwave combustion (Vijayan et al. 2020) . Here, the presence tin oxide on silica nanosphere provides reactive surfaces for charges adsorption and desorption.

Silica nanoparticles are not only used in the biomedical field but also used in various fields such as material packing, textile (Riaz et al. 2019) , agriculture and food (Rastogi et al. 2019) , adsorbents in the removal of organic and inorganic pollutants (Morin-Crini et al. 2019), rubber field (Peng et al. 2007) , water treatment (Demadis and Mavredaki 2005) , concrete and construction and photocatalytic degradation (Alaoui et al. 2009 and Batista et al. 2010 ).

Silica nanoparticles are promising material for medical and electronics applications. Because of its optoelectronic properties, silicon (Si) is extensively used in photovoltaic and energy storage applications. Recently, the application of silica is also explored in biomedical fields in the form of silica nanoparticles as bioimaging, biosensors and drug delivery, due to its biocompatibility, biodegradability and low toxicity. The silica nanoparticles can be prepared by different methods and most of the researchers used the well-known Stober method to get monodispersed particles with narrow size distribution. Compared to silica nanoparticles prepared using tetraethylorthosilicate as a precursor, silica nanoparticles from biomass are exhibiting good properties at low cost. Silica sources can also be obtainable from rice husk, sugarcane bagasse, corn cob and wheat husk.

Development of corn cob ash blended cement

Potential utilization of solid waste (bagasse ash)

Extraction of soluble sodium silicate using corn cob ash as a silica source

Preparation and characterization of a new TiO 2/SiO2.composite catalyst for photocatalytic degradation of indigo carmin

A gold@ silica core-shell nanoparticlebased surface-enhanced Raman scattering biosensor for labelfree glucose detection

A magnetic CoFe 2 O 4/SiO 2 nanocomposite fabricated by the sol-gel method for electrocatalytic oxidation and determination of L-cysteine

Rare-earth ions integrated silica nanoparticles derived from rice husk via microwave-assisted combustion method for bioimaging applications

Effect of varying corn cob and rice husk ashes on properties of moulding sand

An ultrasensitive hollow-silica-based biosensor for pathogenic Escherichia coli DNA detection

Multicolor nanoprobes based on silica-coated gadolinium oxide nanoparticles with highly reduced toxicity

Synthesis and biocompatibility assessment of sugarcane bagassederived biogenic silica nanoparticles for biomedical applications

Synthesis of SiO2 nanostructures using sol-gel method

Characterisation of silica derived from rice husk

Rice husk and its applications

Fluorescent dye-doped silica nanoparticles: new tools for bioapplications

Gold nanoparticlesmesoporous silica composite used as an enzyme immobilization matrix for amperometric glucose biosensor construction

Virucidal effect against coronavirus SARS-CoV-2 of a silver nanocluster/silica composite sputtered coating

Mesoporous silica for drug delivery: Interactions with model fluorescent lipid vesicles and live cells

Synthesis of mesoporous silica particles with control of both pore diameter and particle size

A new family of mesoporous molecular sieves prepared with liquid crystal templates

FTIR, TEM and NMR investigations of Stöber silica nanoparticles

The vibrational spectra of vitreous silica, germania and beryllium fluoride

Mesoporous silica nanoparticles in target drug delivery system: a review

Chemical modifications and bioconjugate reactions of nanomaterials for sensing, imaging, drug delivery and therapy

Crop residue burning in India: policy challenges and potential solutions

Cyclodextrin-based supramolecular assemblies: a versatile toolbox for the preparation of functional porous materials

Preparation of monodisperse silica particles: control of size and mass fraction

A new method to inertize incinerator toxic fly ash with silica from rice husk ash. Environ

Sol-gel science: the physics and chemistry of sol-gel processing

Dilute solution routes to various controllable morphologies of MCM-41 silica with a basic medium

Glucan particle delivery of mesoporous silicadrug nanoparticles

Silica-based mesoporous materials as drug delivery system for methotrexate release

Nanosilica from rice husk: extraction and characterization

Multibranched gold-mesoporous silica nanoparticles coated with a molecularly imprinted polymer for label-free antibiotic surface-enhanced Raman scattering analysis

Review processing, properties and applications of reactive silica from rice husk-an overview

Core/shell nanoparticles in biomedical applications

Mediated biosensors

Enzymatic hydrolysis of corncob and ethanol production from cellulosic hydrolysate

Multifunctional magnetically removable nanogated lids of Fe 3 O 4-capped mesoporous silica nanoparticles for intracellular controlled release and MR imaging

Engineered biocompatible nanoparticles for in vivo imaging applications

Transferrin gated mesoporous silica nanoparticles for redox-responsive and targeted drug delivery

Stimulus-response mesoporous silica nanoparticlebased chemiluminescence biosensor for cocaine determination

The controlled release of drugs and bioactive compounds from mesoporous silica nanoparticles

Silica materials for biomedical applications in drug delivery, bone treatmentor regeneration, and MRI contrast agent

Effects of LOI of ground bagasse ash on the compressive strength and sulfate resistance of mortars

Multifunctional magnetic-fluorescent nanocomposites for biomedical applications

Photocracking silica: tuning the plasmonic photothermal degradation of mesoporous silica encapsulating gold nanoparticles for Cargo release

A parametric study of the synthesis of silica nanoparticles via sol-gel precipitation method

Silica derived from burned rice hulls

Rice husk ash as an alternate source for active silica production

Green additives to enhance silica dissolution during water treatment

A review on synthesis, characterization and applications of silica particles international journal of advanced

Silica nanoparticles encapsulated by polystyrene via surface grafting and in situ emulsion polymerization

Thermally and magnetically dual-responsive mesoporous silica nanospheres: preparation, characterization, and properties for the controlled release of sophoridine

Crystal structures of silica and metal silicates

Synthesis and characterization of SiO2 nanoparticles via sol-gel method for industrial applications

Chitosan mediated 5-Fluorouracil functionalized silica nanoparticle from rice husk for anticancer activity

Core-shell monodisperse spherical mSiO 2/Gd 2 O 3: Eu 3+@ mSiO 2 particles as potential multifunctional theranostic agents

Amsterdam Fardad M (2000) Catalysts and the structure of SiO2 sol-gel films

Recycling of sugarcane bagasse ash waste in the production of clay bricks

A FITC-doped silica coated gold nanocomposite for both in vivo X-ray CT and fluorescence dual modal imaging

Synthesis of high specific surface area silica aerogel from rice husk ash via ambient pressure drying

Formation of silica nanoparticles in microemulsions

Evaluation of bagasse ash as supplementary cementitious material

Preparation and characterization of silica material from rice husk ash-an economically viable method

The potential advantages of nanoparticle drug delivery systems in chemotherapy of tuberculosis

The structure of silica glass

Waste to wealth, potential of rice husk in India a literature review

Novel nanomaterials for clinical neuroscience

Ag/SiO2 core-shell nanoparticle-based surfaceenhanced Raman probes for immunoassay of cancer marker using silica-coated magnetic nanoparticles as separation tools

Controlling particle size in the Stöber process and incorporation of calcium

Chemistry of the elements

The synthesis of micrometerand submicrometer-size spheres of ordered mesoporous oxide MCM-41

One-pot hydrothermal synthesis of mesoporous silica nanoparticles using formaldehyde as growth suppressant

Synthesis of disperse amorphous SiO2 nanoparticles via sol-gel process

Enantioselectively controlled release of chiral drug (metoprolol) using chiral mesoporous silica materials

Highly luminescent silica-coated ZnO nanoparticles dispersed in an aqueous medium

Properties of amorphous silica entrapped isoniazid drug delivery system

Studies on synthesized nanosilica obtained from bagasse ash

Synchrotron radiation: earth, environmental and materials sciences applications

Silica-based mesoporous organic-inorganic hybrid materials

History of the origin of the chemical elements and their discoverers

Rice husk/rice husk ash as an alternative source of silica in ceramics: a review

Solid polymer electrolyte based on ionic bond or covalent bond functionalized silica nanoparticles

Fluorescein isothiocyanate embedded silica spheres in gadolinium carbonate shells as novel magnetic resonance imaging and fluorescence bi-modal contrast agents

Purification and characterization of silica from sugarcane Bagasse ash as a reinforcing filler in natural rubber composites

Evaporation-induced coating of hydrous Ruthenium oxide on mesoporous silica nanoparticles to develop highperformance supercapacitors

A high performance electrochemical biosensor based on Cu 2 O-carbon dots for selective and sensitive determination of dopamine in human serum

Electrocatalytic performance of silica nanoparticles on graphene oxide sheets for hydrogen peroxide sensing

Synthesis and characterization of MnO2/Hollow mesoporous silica nanocomposite as electrode materials for application in supercapacitors

Engineering rice husk into a high-performance electrode material through an ecofriendly process and assessing its application for lithium-ion sulfur batteries

Nickel nanoparticles modified conducting polymer composite of reduced graphene oxide doped poly (3, 4-ethylenedioxythiophene) for enhanced nonenzymatic glucose sensing

Functional nanovalves on protein-coated nanoparticles for in vitro and in vivo controlled drug delivery

Preparation of spherical silica nanoparticles: Stober silica

Fluorescent dye labeled iron oxide/ silica core/shell nanoparticle as a multimodal imaging probe

Mesoporous silica wrapped with graphene oxide-conducting PANI nanowires as a novel hybrid electrode for supercapacitor

Impedimetric dengue biosensor based on functionalized graphene oxide wrapped silica particles

Evaluating the effects of sugar cane bagasse ash (SCBA) and nanosilica on the mechanical and durability properties of mortar

In situ growth of surfactant-free gold nanoparticles on nitrogen-doped graphene quantum dots for electrochemical detection of hydrogen peroxide in biological environments

Printable thin film supercapacitors using single-walled carbon nanotubes

Densification characteristics of corn cobs

Allantoin-loaded porous silica nanoparticles/ polycaprolactone nanofiber composites: fabrication, characterization, and drug release properties

Synthesis of size controlled spherical silica nanoparticles via sol-gel process within hydrophilic solvent

Introduction to the nanoworld

Preparation of multilayered silica-Gd-silica core-shell particles and their magnetic resonance images

Fabrication of quantum dot/silica core-shell particles immobilizing Au nanoparticles and their dual imaging functions

Special materials in pyrotechnics: VI. Silicon-an old fuel with new perspectives. Propellants Explosives

Native Al and Si formation

Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism

Preparation of nanoparticles from corn cobs by chemical treatment methods

Nanobiosensor approaches for pollutant monitoring

A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drug molecules

Optically and magnetically doped organically modified silica nanoparticles as efficient magnetically guided biomarkers for two-photon imaging of live cancer cells. The Journal of

Magnetic resonance imaging of macrophage activity in atherosclerotic plaques of apolipoprotein E-deficient mice by using polyethylene glycolated magnetic fluorescent silica-coated nanoparticles

Synthesis and surface functionalization of silica nanoparticles for nanomedicine

Accelerated transformation of organic matter below the silica transition zone in immature sediments from the Japan Sea

Handbook of chemistry and physics

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

Advanced materials for energy storage

A review on recent advances in the comprehensive application of rice husk ash

Nanoparticulate X-ray computed tomography contrast agents: from design validation to in vivo applications

An ultrasensitive electrochemical sensor for hydrazine based on AuPd nanorod alloy nanochains

Cortisol controlled release by mesoporous silica

Silica scale formation and effect of sodium and aluminium ions-29 Si NMR study

Discovery of nano-sized gold particles in natural plant tissues

Production and characterisation of amorphous silica from rice husk waste, WasteEng' 2012

Carbon-based solid acids: a review. Environ

Isolation of nanocellulose from waste sugarcane bagasse (SCB) and its characterization

Studies on MCM-41 mesoporous silica for drug delivery: effect of particle morphology and amine functionalization

Structural studies of silicate glasses and meltsapplications and limitations of Raman spectroscopy

Inorganic nanoparticles for natural product delivery: a review

Potential of combating transmission of COVID-19 using novel self-cleaning superhydrophobic surfaces: part I-protection strategies against fomites

Multifunctional core-shell silica microspheres and their performance in self-carrier decomposition, sustained drug release and fluorescent bioimaging

Hollow mesoporous silica nanoparticles conjugated with pH-sensitive amphiphilic diblock polymer for controlled drug release

Electrochemical capacitors for energy management

Preparation and characterization of nano SiO2 from corn cob ash by precipitation method

Characterization on silica from waste sugarcane bagasse for membrane fabrication

Synthesis and characterization of nanosilica from rice husk with applications to polymer composites

X-ray imaging of newlydeveloped gadolinium compound/silica core-shell particles

Synthesis of silica materials containing cyclodextrin and their applications in wastewater treatment

The structure of vitreous silica

Precipitated silica from wheat husk

Redox-active silica nanoparticles. Part 4. Synthesis, size distribution, and electrochemical adsorption behavior of ferrocene-and (diamine) (diphosphine)-ruthenium (II)-modified Stöber silica colloidal particles

Extraction and characterization of amorphous silica from corn cob ash by sol-gel method

Development of silica nanoparticle from corn cob ash

Fuel characterization of briquettes produced from corncob and rice husk resides

Raman spectroscopy and statistical analysis of the silicate species and group connectivity in cesium silicate glass forming system

Bright and stable core-shell fluorescent silica nanoparticles

Effect of temperature, time and atmospheric condition on active silica extraction from Corn Cob ash

Synthesis of mesoporous silica oxide/C-dot complex (meso-SiO 2/C-dots) using pyrolysed rice husk and its application in bioimaging

Discovery of the elements

A pH-responsive nano-carrier with mesoporous silica nanoparticles cores and poly (acrylic acid) shell-layers: fabrication, characterization and properties for controlled release of salidroside

Fine tuning of the relaxometry of γ-Fe2O3@ SiO2 nanoparticles by tweaking the silica coating thickness

Self-assembled natural rubber/silica nanocomposites: its preparation and characterization

Potential applications of rice husk ash waste from rice husk biomass power plant

Influence of the parameters in the preparation of silica nanoparticles from biomass and chemical silica precursors towards bioimaging application

Size regulation and prediction of the SiO2 nanoparticles prepared via Stöber process

A novel signal amplification strategy of an electrochemical aptasensor for kanamycin, based on thionine functionalized graphene and hierarchical nanoporous PtCu

Synthesis of mesoporous silica with controlled pore structure from bagasse ash as a silica source

Study of calcination temperature and concentration of NaOH effect on crystallinity of silica from sugarcane Bagasse Ash (SCBA)

Properties of concrete containing rice husk ash under sodium chloride subjected to wetting and drying

A novel method for synthesis of silica nanoparticles

Application of silicon nanoparticles in agriculture

A version of Stöber synthesis enabling the facile prediction of silica nanospheres size for the fabrication of opal photonic crystals

Onestep chemical vapor deposition and modification of silica nanoparticles at the lowest possible temperature and superhydrophobic surface fabrication

Modification of silica nanoparticles to develop highly durable superhydrophobic and antibacterial cotton fabrics

Recent applications of starch derivatives in nanodrug delivery

Stöber synthesis of monodispersed luminescent silica nanoparticles for bioanalytical assays

Electrochemical biosensors for glucose based on metal nanoparticles

Nanotech approaches to drug delivery and imaging

Solutionplasma-mediated synthesis of Si nanoparticles for anode material of lithium-ion batteries

Defect related luminescence in silicon dioxide network: a review

TAT conjugated, FITC doped silica nanoparticles for bioimaging applications

Multienzymatic Cholesterol Nanobiosensor Using Core-Shell Nanoparticles Incorporated Silica Nanocomposite

Biomass-based energy fuel through biochemical routes: a review

Corn cob as a potential feedstock for slow pyrolysis of biomass

Extraction and physical characterization of amorphous silica made from corn cob ash at variable pH conditions via sol gel processing

Agro-residue-based renewable energy technologies for rural development

Introduction to nanotechnology and its applications to medicine

Silicon conversion from bamboo leaf silica by magnesiothermic reduction for development of Li-ion baterry anode, MATEC Web of Conferences'

Materials for electrochemical capacitors

Preparation of silica nanoparticles and its beneficial role in cementitious materials

Sol-Gel processing of silica nanoparticles and their applications

Bioresponsive mesoporous silica nanoparticles for triggered drug release

Multifunctional hybrid nanocarrier: magnetic CNTs ensheathed with mesoporous silica for drug delivery and imaging system

Utilization of sugarcane bagasse ash (SCBA) as pozzolanic material in concrete. A review

Composite silica coated gold nanosphere and quantum dots nanoparticles for X-ray CT and fluorescence bimodal imaging

A fluorescent aptasensor for amplified label-free detection of adenosine triphosphate based on core-shell Ag@ SiO2 nanoparticles

Use of core/shell structured nanoparticles for biomedical applications

Porous silica and carbon derived materials from rice husk pyrolysis char

Preparation of surfactant templated nanoporous silica spherical particles by the Stöber method. Effect of solvent composition on the particle size

A sensitive optical sensor based on DNAlabelled Si@SiO2 core-shell nanoparticle for the detection of Hg2+ ions in environmental water samples

Effect of surfactants on the wet chemical synthesis of silica nanoparticles

Synthesis and characterization of nanoparticles, consisting of a gadolinium paramagnetic core and a mesoporous silica shell, for controlled delivery of hydrophobic drugs

Controlled growth of monodisperse silica spheres in the micron size range

Preparation of spherical silica nanoparticles by Sol-Gel method, II

Synthesis of silica nanoparticles having a well-ordered mesostructureusing a double surfactant system

Synthesis of monodispersed silica nanoparticles with high concentration by the Stöber process

Responsive mesoporous silica nanoparticles for sensing of hydrogen peroxide and simultaneous treatment toward heart failure

Poly (lactic acid)-coated mesoporous silica nanosphere for controlled release of venlafaxine

Nonporous silica nanoparticles for nanomedicine application

Inclusion of poorly soluble drugs in highly ordered mesoporous silica nanoparticles

Extraction of silica from rice husk

Synthesis and functionalization of a mesoporous silica nanoparticle based on the sol-gel process and applications in controlled release

Cleaner production of carbon adsorbents by utilizing agricultural waste corn cob

Extraction and characterization of silica from rice husk for use in food industries

Mesoporous silica nanoparticles as drug carriers

Medical applications of organic-inorganic hybrid materials within the field of silicabased bioceramics

Mesoporous materials for drug delivery

Characterization and chemical modification of the silica surface

Synthesis of mesoporous silica nanoparticles by sol-gel as nanocontainer for future drug delivery applications. Boletín de la Sociedad Española de Cerámica y Vidrio

Extraction, characterization, and catalytic potential of amorphous silica from corn cobs by sol-gel method

Nanobiotechnology advances in enzymatic biosensors for the agri-food industry

Luminescence enhancement from silica-coated gold nanoparticle agglomerates following multi-photon excitation

Microwave combustion synthesis of tin oxidedecorated silica nanostructure using rice husk template for supercapacitor applications

Alternatives to gadolinium-based metal chelates for magnetic resonance imaging

Inorganic-organic hybrid nanomaterials for therapeutic and diagnostic imaging applications

Gold@ silica catalyst: porosity of silica shells switches catalytic reactions

Silica, amorphous. Kirk-Othmer Encycl Chem Technol

Sustained release of heparin on enlarged-pore and functionalized MCM-41

Preparation of spherical silica particles by Stöber process with high concentration of tetra-ethyl-orthosilicate

Synthesis and characterization of Nano-Silica from Teff Straw

What are batteries, fuel cells, and supercapacitors?

Synthesis of highly monodispersed teardrop-shaped core-shell SiO2/TiO2 nanoparticles and their photocatalytic activities

pH and thermo dual-stimuli-responsive drug carrier based on mesoporous silica nanoparticles encapsulated in a copolymerlipid bilayer

Synthesis of mesoporous silica nanoparticles

The preparation of alkyltriinethylaininonium-kaneinite complexes and their conversion to microporous materials

Combustion synthesis of silicon nanopowders

A review on the electrochemical sensors and biosensors composed of nanowires as sensing material

Easy synthesis of hollow core, bimodal mesoporous shell carbon nanospheres and their application in supercapacitor

Chemical methods for preparation of nanoparticles in solution

Synthesis of silica nanocubes by sol-gel method

Impact of silica nanoparticle design on cellular toxicity and hemolytic activity

Encapsulation of organic pigment particles with silica via sol-gel process

Highpurity nano silica powder from rice husk using a simple chemical method

Study on the effect of synthesis parameters of silica nanoparticles entrapped with rifampicin

Abdul K Production of silica nanoparticles entrapped with Rifampicin: effect of surfactant, stirring rate and water content

Effect of ammonia concentration on silica spheres morphology and solution hydroxyl concentration in Stober process

Biomass derived silica containing products for removal of microorganisms from water

High efficiency reductive degradation of a wide range of azo dyes by SiO2-Co core-shell nanoparticles

Capped mesoporous silica nanoparticles as stimuli-responsive controlled release systems for intracellular drug/gene delivery

Folic acid-conjugated silica capped gold nanoclusters for targeted fluorescence/X-ray computed tomography imaging

A novel SERS nanoprobe based on the use of core-shell nanoparticles with embedded reporter molecule to detect E. coli O157: H7 with high sensitivity