Nanostructured SiO2 material: synthesis advances and ...

Silica is a commercially significant material due to its extensive use in widespread applications and products. Synthetic amorphous silica (SAS) is a form of SiO 2 that is intentionally manufactured and has been produced and marketed for decades without significant changes in its physico-chemical properties. The industrial production of nanostructured SiO 2 is nowadays challenged by the expensive raw material use and high energy consumption. The search for non-petroleum-based fillers such as nanostructured SiO 2 , which are environmentally friendly, cheap, abundant, renewable, and efficient, has been initiated nowadays. Therefore, a large number of research activities have been carried out so far for the preparation of SAS from potential alternate precursors, i.e., synthetic chemicals, biogenic, and mineral ore resources. Reinforcement of rubbers with nanostructured SiO 2 fillers is a process of great practical and technological importance for improving their mechanical, dynamic, and thermal properties. The efficiencies of SiO 2 reinforcement correlate with different factors such as filler structure, surface area, rubber&#;filler interactions, and filler&#;filler interactions with their effects. This review paper discusses the recent synthesis advances of nanostructured SiO 2 from synthetic chemicals, biogenic and mineral ore resources, their physical characteristics, and applications in rubber reinforcement, overcoming challenges. Finally, summary and future work recommendations have been mentioned well for future researchers.

Please visit our website for more information on this topic.

1.&#;Introduction

With the rapid emergence of the field of nanotechnology, regulations specific to nanomaterials are under development. One of the key issues hindering regulation is a lack of agreement on the definition of what constitutes a nanomaterial. Currently, the most comprehensive and internationally recognized definition of nanomaterials is presented by the International Standards Organization (ISO). The ISO definition distinguishes between two subgroups, nano-objects and nanostructured materials, and defines them as:1 nano-objects are materials that exist in a defined singular form that have at least one dimension in the nano-scale (<100 nm), which includes nano-particles (3D in nano-scale), nanofibers (2D in nano-scale), and nano-plates (1D in nano scale). Nanostructured materials are materials that have structural features on the nano-scale but whose particle size is typically greater than 100 nm. Examples of these are materials that primarily exist in aggregated and/or agglomerated forms.

Silica is a commercially significant material due to its extensive use in widespread applications and products. The base unit of the structure of the macromolecular network nSiO2 is the [SiO4]4&#; tetrahedron. Synthetic amorphous silica (SAS) is a form of SiO2 that is intentionally manufactured and has been produced and marketed for decades without significant changes in its physico-chemical properties. SAS is in the form of white dry powders or dispersions of these powders are used in a multitude of industrial applications, i.e., an additive in rubber. It is also approved to be used in consumer products, i.e., food, cosmetics, and pharmaceuticals. To define, SAS in powder form is a nanostructured material according to the technical specification of ISO TS -1. The aggregate is the smallest indivisible unit upon dispersion. There are three types of synthetic amorphous SiO2 produced at the industrial scale: fumed SiO2, precipitated SiO2, and SiO2 gel. Of these three types of amorphous SiO2, precipitated SiO2, whose production started in the s, has the greatest commercial importance. Precipitated SiO2 is a finely divided white powder sparingly soluble in water and composed of aggregates up to approximately 1 mm in diameter.

The current commercial precipitated SiO2 is produced by a wet SiO2 production route or sol&#;gel process, in which an aqueous alkali metal silicate solution is neutralized with acid (e.g., H2SO4), releasing SiO2 and nH2O in a reaction tank to produce a slurry of SiO2. The most commonly used aqueous alkali silicate is water glass (Na2O·nSiO2; n = 2&#;4), which is produced by melting quartz sand with soda at about °C.2 Reaction conditions are manipulated according to the particle size required. Hydrogen bonding among particles will form clusters or aggregates, and these aggregates may loosely bond as agglomerates. Fumed silica (SiO2), also known as pyrogenic silica (SiO2), is mainly produced by reacting any SiO2 source with any carbon source in an electric arc furnace at approximately °C undergoing carbothermal reduction to metallurgical grade silicon, Si (met), which is then treated with HCl to produce SiCl4. The SiCl4, in turn, is combusted in a hydrogen&#;oxygen flame to produce fumed SiO2 plus byproduct HCl.3 Both synthetic amorphous silica commercial processes require expensive precursor use, corrosive, toxic and polluting side product generation, the need for tailoring properties of products, high-temperature and energy-intensive steps make production processes expensive in which further synthesis advancement has been the subject of much of the ongoing researches. Many researchers have devoted studies to replace the expensive source of synthetic silica with one that is cheaper and renewable, i.e., biogenic and mineral ore resources. In addition to this, researchers extensively worked on the promotion of widespread preparation methods with an emphasis on sol&#;gel synthesis parameter optimization to tailor the nanostructured SiO2 product physicochemical properties for specific applications, particularly for rubber reinforcement.

Elastomers or rubbers, whether natural or synthetic, are not usually used in their pure form due to insufficient practical physico-mechanical properties. Fillers are extensively used in the rubber industry to improve service efficiency and ease of processing, and their addition results in a fundamental change in the properties of rubber. According to the kinetic theory of elasticity, the rubber modulus (with no fillers) increases with the rise of temperature; the addition of fillers significantly changes the temperature coefficient of modulus and may even alter the sign of the coefficient, resulting in a decrease of the modulus with increasing temperature.

Fillers are classified based on chemical composition and their influence on rubber properties. Further, in rubber compounding, they can be divided primarily into three categories in accordance with their reinforcing effect: inactive, semi-active, and very active. The term active signifies the degree of reinforcement, i.e., the influence of the filler on the viscosity of the compound and the resulting mechanical properties. The main characteristics that determine the reinforcing effect of fillers are their structure and surface properties. Active fillers have a large relative surface area and high structure, providing strong physical and chemical interaction between the filler and polymer. However, a highly active filler surface leads to strong interparticle forces, which negatively influence the processing behavior as a result of the agglomeration of filler particles during mixing and storage.4 Common to composites' preparation and modification mechanisms, several factors influence the property profiles, which lie between those of pure rubber and filler or processability. These include volume fraction, particle dimension and geometry, dispersion quality, the interaction between rubber and fillers or among fillers, and, if applicable, the degree of orientation of fillers for anisotropic properties. These factors, in turn, affect one another, and synergy is achieved if an optimum balance is reached.5

The most common fillers used in the rubber industry are the carbon family of materials (carbon black, carbon fiber (CF), carbon nanotubes (CNTs), graphite and graphene), inorganic particles (nanoclays, polyhedral oligomeric silsesquioxane (POSS), SiO2, calcium carbonate (CaCO3), talc, zinc oxide (ZnO), titanium oxide (TiO2), alumina (Al2O3), halloysite), and biofillers (cellulose, husk, wood, coir).5&#;7 However, the large volume applications of rubber, certainly those involving high elasticity and mechanical properties, including stiffness, strength, toughness, abrasion resistance, anti-scratching property, or friction behavior, etc., are reinforced by carbon black and precipitated SiO2 as the dominant fillers. Even if both carbon black and nanostructured silica are the dominant fillers for rubbers, the search for non-petroleum based filler and a promising efficiency for reducing the rolling resistance of rubber nanocomposites in tire tread makes nanostructured silica an important and economical filler in the rubber industry. The potential of lowering the rolling resistance makes silica a promising reinforcement in the fabrication of green tire tread.8 Modern fuel-saving tire treads are commonly reinforced by silica due to the fact that this leads to lower rolling resistance and higher wet grip compared to carbon black-filled alternatives, which may have the potential to improve tire performance further.

Very limited review works have been reported yet on the synthesis advances of nanostructured SiO2 material from cheap, renewable potential precursors and characteristic features of SiO2 filler for rubber reinforcement. This paper highlights the synthesis advancement of nanostructured silica from potential precursors with emphasis on soft template based synthetic chemical precursors, biogenic, and mineral ore resources. The review also describes the reinforcement of rubber with nanostructured SiO2 fillers due to its mechanical, dynamic, and thermal properties and correlates with different factors like filler structure, surface area, filler&#;filler, and rubber&#;SiO2 filler interactions effects on SiO2 filled rubber nanocomposites with the overcoming challenges, which are reported in different works published so far.

Silica nanoparticles (SiNPs) or silicon dioxide are amorphous substances that have a spherical form. They can be produced in a variety of shapes and sizes, and the properties of their surfaces can be easily changed to suit several purposes. Silica nanoparticles are abrasive and absorbent in their nonporous form, but mesoporous silica nanoparticles with hexagonal pore structures have great potential in nanomedicine and drug applications.

Image Credit: jakkrit pimpru/Shutterstock.com

What are Silica Nanoparticles?

The most widely available materials of the Earth's crust include natural silica and silicates, which are primarily crystalline. Because of their excellent biocompatibility, heat resistance, low toxicity, simple synthetic approach, and massive synthetic supply, silicon dioxide nanoparticles, frequently referred to as silica nanoparticles, are attractive for biological applications. The size of the particles, porosity, crystallinity, and form of silica nanoparticles can all be carefully controlled, allowing them to be used in a wide range of industrial and research uses. Notably, the multiple surface changes accessible enable them to alter surface chemistry for drug loading, sturdy, and site-specific targeting.

This nanomaterial consistently features in research, though conflicting toxicity results have complicated its applications and necessitated further rigorous analysis. Still, substantial research into silica nanoparticles for therapeutic, diagnostic, and imaging reasons is ongoing; for example, hydrophilic medicines can be delivered to select tissues using silica nanoparticles.

Silica Nanoparticles for Drug Delivery

Silica nanoparticles utilized in improvement for nano theranostics purposes are characterized as porous or nonporous based on their morphological and, to some degree, functional characteristics. The enhanced properties between porous and nonporous silica nanoparticles, although identical in composition, are considerable, with significant consequences for their implementation and biocompatibility.

Because of their biocompatibility and ease of manufacturing, which allows surface modification, silica nanoparticles are the most distinctive feature for drug administration. Mesoporous silica, for instance, has many empty pores, which allows vast quantities of the active moiety to be enclosed.

A porous variation, known as mesoporous silica nanoparticles or MSN, adds features such as variable pore volume and size, resulting in a high encapsulation efficiency. In the case of bacterial infestations, SiNPs and their derivatives can be a useful tool for delivering antimicrobials to specific locations, thereby decreasing the impact of high medication doses and associated adverse effects.

There have been several positive studies of mesoporous silica nanoparticles containing medicines for cancer treatment. MSN have gained popularity as a drug delivery method because of their porous nature. This property enables them to hold a lot of medications with low water solubility. Encapsulated medicines are protected from enzymatic breakdown by the silica matrix.

It has also been shown that mesoporous silica nanoparticles can cause vascular endothelial malfunction, causing oxidative stress and significantly increasing procoagulant and proinflammatory responses.

With competitive price and timely delivery, Hebei Silicon Research Electronic Materials Co., L sincerely hope to be your supplier and partner.

Papule tactics also prevent medications from being released prematurely. By adding a targeted ligand to silica-based nanoparticles, they may be directed to sick cells while reducing detrimental effects in normal tissue. When silica nanoparticles are infused, they come into contact with blood cells and proteinases.

Reduction of Acute Inflammatory Effects of Fumed Silica Nanoparticles

Video Credit: American Chemical Society/YouTube.com

Challenges with Silica Nanoparticles

Increased interest in SiNPs for drug delivery applications has led to the requirement of a step-by-step modification of their compositions to eliminate or minimize known toxic features. Many parameters, including shape, dose, size, type of cell in the research, treatment period, surface area, and material particular, have been identified to influence silica nanoparticle cytotoxicity.

However, hemolysis and caseation are common problems for drug delivery applications since they limit effectiveness and jeopardize safety. As a result, hemocompatibility screening for nano-drug carriers is required.

Synthesis Techniques

A number of different methods may be used to make SiNPs, which can vary in size from 10 to 500 nm and have various morphologies and physicochemical features. The Stober's procedure and the microemulsion technique are the two most widely used synthesis techniques.

Silica nanoparticles constitute silica mesopores (2&#;50 nm diameter of pores) with distinct physicochemical features. Nanohelices, nanozigzags, nanotubes, and nanoribbons are examples of nanocarriers that may be made in various sizes and forms. These nanoparticles are used in catalytic reactions, adsorption, PDT, diagnosing sensors, separation, and medicinal drug delivery because of their adjustable electrical, optical, and mechanical capabilities.

In drug delivery, a challenge for silica nanoparticles is the surface of mesoporous silica with a significant amount of hydroxyl groups, making it particularly susceptible to aggregation. As a result, the researchers attempted to alter the surface to lower its surface energy and enhance its dispersibility and usage efficiency.

Surface physical modifications and chemical alteration are the most common approaches used today.

Future Outlooks for Silica Nanoparticles

The future of silica nanoparticles is bright. MSNs have fascinated researchers as a promising nanocarrier for nano-based tumor detection and cancer treatment among several nanostructures created. MSNs have also shown considerable promise as a biotherapeutics tool.

Silica nanoparticles applications also play an essential function in improving seed germination in plants. Silica nanoparticle is a 'quasi-essential' essential plant nutrient, regulating various physiological functions such as fertilization, germinative development, photosynthesis, and drought tolerance. As a result, assessing the impact of silica nanoparticles on different physiological processes is critical.

Continue reading: Developing Fingerprints Using Silica Nanoparticles.

References and Further Reading 

Abbasi, M., et al. () Mesoporous silica nanoparticle: Heralding a brighter future in cancer nanomedicine. Available at: https://doi.org/10./j.micromeso..

Chen, L., et al. () The toxicity of silica nanoparticles to the immune system. Available at: https://doi.org/10./nnm--

Karaman, D., and Helene, K. () Chapter 1 - Silica-based nanoparticles as drug delivery systems: Chances and challenges. Available at: https://doi.org/10./B978-0-12--4.-8

Selvarajan, V., et al. () Silica Nanoparticles&#;A Versatile Tool for the Treatment of Bacterial Infections. Available at: https://doi.org/10./fchem..

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Nanostructured SiO2 material: synthesis advances and ...

What are Silica Nanoparticles?