Silica Aerogel Microparticles from Rice Husk Ash for Drug Delivery

Biopolymer-based beads for the adsorptive removal of organic pollutants from wastewater: Current state and future perspectives

Among biopolymer-based adsorbents, composites in the form of beads have shown promising results in terms of high adsorption capacity and ease of separation from the effluents. This review addresses the potential of biopolymer-based beads to remediate wastewaters polluted with emerging organic contaminants, for instance dyes, active pharmaceutical ingredients, pesticides, phenols, oils, polyaromatic hydrocarbons, and polychlorinated biphenyls. High adsorption capacities up to 2541.76 mg g-1 for dyes, 392 mg g-1 for pesticides and phenols, 1890.3 mg g-1 for pharmaceuticals, and 537 g g-1 for oils and organic solvents have been reported. The review also attempted to convey to its readers the significance of wastewater treatment through adsorption by providing an overview on decontamination technologies of organic water contaminants. Various preparation methods of biopolymer-based gel beads and adsorption mechanisms involved in the process of decontamination have been summarized and analyzed. Therefore, we believe there is an urge to discuss the current state of the application of biopolymer-based gel beads for the adsorption of organic pollutants from wastewater and future perspectives in this regard since it is imperative to treat wastewater before releasing into freshwater bodies.

pH-responsive on-demand release of eugenol from metal-organic frameworks for synergistic bacterial killing

Bacterial infections are a big challenge in clinical treatment, making it urgent to develop innovative antibacterial systems and therapies to combat bacterial infections. In this study, we developed a novel MOF-based synergistic antibacterial system (Eu@B-UiO-66/Zn) by loading a natural antibacterial substance (eugenol) with hierarchically porous MOF B-UiO-66 as a carrier and further complexing it with divalent zinc ions. Results indicate that the system achieved a controlled release of eugenol under pH responsive stimulation, with the complexation ability of eugenol and Zn2+ ions as a switch. Due to the destruction of a coordination bond between eugenol and Zn2+ ions by an acidic medium, the release of eugenol loaded in Eu@B-UiO-66/Zn reached 80% at pH 5.8, which was significantly higher than that under pH 8.0 (51%). Moreover, the inhibitory effect of Eu@B-UiO-66/Zn against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) after 24 h was 96.4% and 99.7%, respectively, owing to the synergistic antibacterial effect of eugenol and Zn2+ ions, which was significantly stronger than free eugenol and Eu@B-UiO-66. We hope that this strategy for constructing responsive MOF-based antibacterial carriers could have potential possibilities for the application of MOF materials in antibacterial fields.

Thermodynamics of Azo Dye Adsorption on a Newly Synthesized Titania-Doped Silica Aerogel by Cogelation: A Comparative Investigation with Silica Aerogels and Activated Charcoal

The adsorption isotherms of azo dyes on a newly synthesized titania-doped silica (TdS) aerogel compared to silica aerogels and activated charcoal (AC) are systematically investigated. Monolithic TdS aerogels were synthesized by the cogelation process followed by supercritical drying of tetraethyl orthosilicate (TEOS) as a gel precursor and titanium(IV) isopropoxide (TTIP) as a metal complex precursor for co-polymerization in ethanol solvent. An acid-base catalyst was used for the hydrolysis and condensation of TEOS and TTIP. The effect of Ti⁴⁺ doping in a silica aerogel on the mesoporous structure and the adsorption capacity of methylene blue (MB) and crystal violet (CV) dyes were evaluated from the UV-vis absorption spectra. In order to compare the adsorption isotherms, the surface areas of silica and TdS aerogels were first normalized with respect to AC, as adsorption is a surface phenomenon. The azo dye equilibrium adsorption data were analyzed using different isotherm equations and found to follow the Langmuir adsorption isotherm. The maximum monolayer adsorption capacities for the adsorbent TdS aerogel normalized with the AC of the Langmuir isotherm are 131.58 and 159.89 mg/g for MB and CV dyes, respectively. From the Langmuir curve fitting, the Q _max value of the TdS aerogel was found to increase by 1.22-fold compared to AC, while it increased 1.25-1.53-fold compared to the silica aerogel. After four cycles, regeneration efficiency values for MB and CV dyes are about 84 and 80%, respectively. The study demonstrates the excellent potential and recovery rate of silica and TdS aerogel adsorbents in removing dyes from wastewater. The pore volume and average pore size of the new aerogel, TdS, were found to be lower than those of the silica aerogel. Thus, a new TdS aerogel with a high capacity of adsorption of azo dyes is successfully achieved.

Rose bengal-decorated rice husk-derived silica nanoparticles enhanced singlet oxygen generation for antimicrobial photodynamic inactivation

Rice husks are well known for their high silica content, and the RH-derived silica nanoparticles (RH NPs) are amorphous and biocompatible; therefore, they are suitable raw materials for biomedical applications. In this study, rose bengal-impregnated rice husk nanoparticles (RB-RH NPs) were prepared for their potential photosensitization and ¹O₂ generation as antimicrobial photodynamic inactivation. RB is a halogen-xanthene type's photosensitizer showing high singlet oxygen efficiency, and the superior photophysical properties are desirable for RB in the antimicrobial photodynamic inactivation of bacteria. To enhance the binding of anionic RB to RH NPs, we conducted cationization for the RH NPs using polyethyleneimine (PEI). The control of the RB adsorption state on cationic PEI-modified RH NPs was essential for RB RH-NP photosensitizers to obtain efficient ¹O₂ generation. Minimizing RB aggregation allowed highly efficient ¹O₂ production from RB-RH NPs at the molar ratio of RB with the PEI, X_RB/PEI. = 0.1. The RB-RH NPs have significant antimicrobial activity against Streptococcus mutans compared to free RB after white light irradiation. The RB-RH NP-based antimicrobial photodynamic inactivation can be employed effectively in treating Streptococcus mutans for dental applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-023-08194-z.

Efficient Antibacterial Agent Delivery by Mesoporous Silica Aerogel

Bacterial infections still cause many health problems for human beings. Silica aerogels with a three-dimensional (3D) porous structure and a large surficial area are promising candidates for drug delivery, but they have rarely been investigated for antibacterial agent delivery. Herein, we study mesoporous silica aerogels as carriers for delivery of three slightly soluble antibacterial agents including cinnamaldehyde (CA, liquid), salicylic acid (SAA, solid), and sorbic acid (SOA, solid) under supercritical fluid carbon dioxide. Notably, all three antibacterial agents form uniform nanocrystals in the mesopores of silica aerogels and the loading efficiency reaches 56 wt %, which assists in overcoming the obstacles of low bioavailability of slightly soluble antibacterial agents. Benefiting from nanocrystallized antibacterial agents, the agent-loaded aerogels exhibit an inhibition rate of 99.99% against Escherichia coli during the initial release; notably, they still have a 95% inhibition rate even after ∼90% of CA is released. Importantly, the agent-loaded silica aerogels demonstrate good biocompatibility in vitro. This work indicates that mesoporous silica aerogels are a promising platform for antibacterial agent delivery.

Aerogels as promising materials for antibacterial applications: a mini-review

The increasing cases of bacterial infections originating from resistant bacteria are a serious problem globally and many approaches have been developed for different purposes to treat bacterial infections. Aerogels are a novel class of smart porous materials composed of three-dimensional networks. Recently, aerogels with the advantages of ultra-low density, high porosity, tunable particle and pore sizes, and biocompatibility have been regarded as promising carriers for the design of delivery systems. Recently, aerogels have also been provided with antibacterial activity through loading of antibacterial agents, incorporation of metal/metal oxides and via surface functionalization and coating with various functional groups. In this mini-review, the synthesis of aerogels from both conventional and low-cost precursors is reported and examples of aerogels displaying antibacterial properties are summarized. As a result, it is clear that the encouraging antibacterial performance of aerogels promotes their use in many antibacterial applications, especially in the food industry, pharmaceutics and medicine.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Mesoporous Silica Particles as Drug Delivery Systems-The State of the Art in Loading Methods and the Recent Progress in Analytical Techniques for Monitoring These Processes

Conventional administration of drugs is limited by poor water solubility, low permeability, and mediocre targeting. Safe and effective delivery of drugs and therapeutic agents remains a challenge, especially for complex therapies, such as cancer treatment, pain management, heart failure medication, among several others. Thus, delivery systems designed to improve the pharmacokinetics of loaded molecules, and allowing controlled release and target specific delivery, have received considerable attention in recent years. The last two decades have seen a growing interest among scientists and the pharmaceutical industry in mesoporous silica nanoparticles (MSNs) as drug delivery systems (DDS). This interest is due to the unique physicochemical properties, including high loading capacity, excellent biocompatibility, and easy functionalization. In this review, we discuss the current state of the art related to the preparation of drug-loaded MSNs and their analysis, focusing on the newest advancements, and highlighting the advantages and disadvantages of different methods. Finally, we provide a concise outlook for the remaining challenges in the field.

Inclusion of Hydrophobic Liquids in Silica Aerogel Microparticles in an Aqueous Process: Microencapsulation and Extra Pore Creation

Due to its extraordinary properties, silica aerogel has a high potential for a number of applications; however, the state-of-the-art technique of its production involves cost-intensive supercritical drying or solvent exchange with a nonpolar solvent. Here, we report on a pure aqueous process for the preparation of silica aerogel particles as well as silica hollow nanoparticles, which is based on the self-assembly of amphiphilic silica precursor polymers, PEGylated poly(ethoxysiloxanes) (PEG-PEOS), in water and subsequent conversion under basic conditions. Addition of a hydrophobic organic liquid to the aqueous dispersions of PEG-PEOS results in the spontaneous formation of oil-in-water emulsions, which resemble the self-assembled structures of PEG-PEOS in water swollen by the organic liquid. The products of basic conversion of the emulsions are silica aerogel particles as well as hollow nanocapsules loaded with organic liquid. Remarkably, the oil phase significantly increases the porosity of the aerogel particles by acting as a porogen; meanwhile, it only decreases the silica shell thickness of the hollow nanoparticles. During freeze-drying, the aerogel particles, acting as matrix-type microcapsules, can efficiently retain the encapsulated volatile hydrophobic liquid; at the same time, the liquid is completely evaporated from the hollow particles (core-shell-type microcapsules). The encapsulation efficiency of hydrophobic liquids in the aerogel particles can reach as high as 99% after drying. The barrier property of the aerogel particles is higher with PEG-PEOS of lower PEGylation degrees due to bigger particle size and higher meso- and microporosity. This work opens a new avenue to prepare particulate silica aerogel for different promising applications including microencapsulation.

Aerogels in drug delivery: From design to application

Aerogels are the lightest processed solid materials on Earth and with the largest empty volume fraction in their structure. Composition versatility, modularity, and feasibility of industrial scale manufacturing are behind the fast emergence of aerogels in the drug delivery field. Compared to other 3D materials, the high porosity (interconnected mesopores) and high specific surface area of aerogels may allow faster loading of small-molecule drugs, less constrained access to inner regions of the matrix, and more efficient interactions of the biological milieu with the polymer matrix. Processing in supercritical CO₂ medium for both aerogel production (drying) and drug loading (impregnation) has remarkable advantages such as absence of an oxidizing environment, clean manufacture, and easiness for the scale-up under good manufacturing practices. The aerogel solid skeleton dictates the chemical affinity to the different drugs, which in turn determines the loading efficiency and the release pattern. Aerogels can be used to increase the solubility of BCS Class II and IV drugs because the drug can be deposited in amorphous state onto the large surface area of the skeleton, which facilitates a rapid contact with the body fluids, dissolution, and release. Conversely, tuning the aerogel structure by functionalization with drug-binding moieties or stimuli-responsive components, application of coatings and incorporation of drug-loaded aerogels into other matrices may enable site-specific, stimuli-responsive, or prolonged drug release. The present review deals with last decade advances in aerogels for drug delivery. An special focus is paid first on the loading efficiency of active ingredients and release kinetics under biorelevant conditions. Subsequent sections deal with aerogels intended to address specific therapeutic demands. In addition to oral delivery, the physical properties of the aerogels appear to be very advantageous for mucosal administration routes, such as pulmonary, nasal, or transdermal. A specific section devoted to recent achievements in gene therapy and theranostics is also included. In the last section, scale up strategies and life cycle assessment are comprehensively addressed.

Preparation of aerogel beads and microspheres based on chitosan and cellulose for drug delivery: A review

Spherical aerogels are not easily broken during use and are easier to transport and store which can be used as templates for drug delivery. This review summarizes the possible approaches for the preparation of aerogel beads and microspheres based on chitosan and cellulose, an overview to the methods of manufacturing droplets is presented, afterwards, the transition mechanisms from sol to a spherical gel are reviewed in detail followed by different drying processes to obtain spherical aerogels with porous structures. Additionally, a specific focus is given to aerogel beads and microspheres to be regarded as drug delivery carriers. Furthermore, a core/shell architecture of aerogel beads and microspheres for controlled drug release is described and subjected to inspire readers to create novel drug release system. Finally, the conclusions and outlooks of aerogel beads and microspheres for drug delivery are summarized.

Drying Kinetics and Particle Formation from Dilute Colloidal Suspensions in Aerosol Droplets

Industrial processes such as spray drying of pharmaceutical and food products often involve the drying of aerosol droplets containing colloidal suspensions into powdered microparticles of desired properties. The morphology and surface properties of the final dry products/microparticles obtained after the drying process are strongly influenced by the parameters of the initial aerosol droplet composition and the drying conditions. In particular, the final dry microparticle morphology can be dependent on the dimensionless Péclet number (Pe), which expresses the relative competition between the diffusion of the dispersed particles within the droplet and the rate of solvent loss via evaporation. In this work, we examine how control over the gas phase drying conditions and initial aerosol droplet composition can be used to influence the aerosol droplet drying kinetics in the gas phase for a range of Péclet numbers. We used a single-particle levitation instrument, the electrodynamic balance, to measure the drying kinetics of colloidal silica droplets (0.10-0.60% v/v) under controlled gas phase drying conditions of temperature (263-326 K) and relative humidity (0-90%) and obtained Péclet numbers ranging from 4.05 to 184.5. We demonstrate that, for aerosol droplets with initially dilute feed colloid concentrations and within the constant evaporation regime, the starting composition does not strongly influence the solvent evaporation rate with the included nanoparticles (NPs) acting as spectators. However, the gas phase drying conditions, temperature, and relative humidity, directly influence the droplet temperature via evaporative cooling as well as the droplet drying kinetics and the final dry microparticle properties. With a priori knowledge of the droplet drying kinetics from the single droplet measurements, we further demonstrate the possibility of tailoring the morphology of the dried microparticles. Dried silica microparticles collected at Pe = 23.8 had dense spherical morphologies, while those at the highest Pe = 180.0 had crumpled surface morphologies with a transition in morphology between these limiting Pe values. Our results extend the fundamental understanding of the mechanisms controlling the drying of aerosol droplets in colloidal suspensions across a wide range of application areas extending from spray drying to the drying of respiratory fluid droplets containing bacteria and viruses and the drying of atmospheric aerosol droplets.

Engineering of Aerogel-Based Biomaterials for Biomedical Applications

Biomaterials with porous structure and high surface area attract growing interest in biomedical research and applications. Aerogel-based biomaterials, as highly porous materials that are made from different sources of macromolecules, inorganic materials, and composites, mimic the structures of the biological extracellular matrix (ECM), which is a three-dimensional network of natural macromolecules (e.g., collagen and glycoproteins), and provide structural support and exert biochemical effects to surrounding cells in tissues. In recent years, the higher requirements on biomaterials significantly promote the design and development of aerogel-based biomaterials with high biocompatibility and biological activity. These biomaterials with multilevel hierarchical structures display excellent biological functions by promoting cell adhesion, proliferation, and differentiation, which are critical for biomedical applications. This review highlights and discusses the recent progress in the preparation of aerogel-based biomaterials and their biomedical applications, including wound healing, bone regeneration, and drug delivery. Moreover, the current review provides different strategies for modulating the biological performance of aerogel-based biomaterials and further sheds light on the current status of these materials in biomedical research.

Diffusion of Resveratrol in Silica Alcogels

The trans-resveratrol (RSV)-loaded silica aerogel (RLSA) was prepared by the sol-gel method, adding the drug during the aging process, solvent replacement and freeze drying. A series of characterizations showed that RSV stays in the silica aerogel in two ways. First, RSV precipitates due to minimal solubility in water during the solvent replacement process. After freeze drying, the solvent evaporates and the RSV recrystallizes. It can be seen from scanning electron microscope (SEM) and transmission electron microscope (TEM) images that the recrystallized RSV with micron-sized long rod-shaped is integrated with the dense silica network skeleton. Second, from small-angle X-ray scattering (SAXS) results, a portion of the RSV molecules is not crystallized and the size is extremely small. This can be attached to the primary and secondary particles of silica to enhance its network structure and inhibit shrinkage, which is why the volume and pore size of RLSA is larger. In addition, the diffusion of RSV in silica alcogel was studied by a one-dimensional model. The apparent diffusion coefficients of inward diffusion, outward diffusion and internal diffusion were calculated by fitting the time- and position-dependent concentration data. It was found that the outward diffusion coefficient (5.25 × 10-10 m2/s) is larger than the inward (2.93 × 10-10 m2/s), which is probably due to the interface effect. The diffusion coefficients obtained for different concentrations in the same process (inward diffusion) are found to be different. This suggests that the apparent diffusion coefficient obtained is affected by molecular adsorption.

Uniformly Structured Methyltrimethoxysilane-Based Silica Aerogels with Enhanced Mechanical Property by Surfactant-Free Fabrication

The uniformity, elasticity and hydrophobicity of methyltrimethoxysilane (MTMS)-based silica aerogels, which were prepared by using dimethyl sulfoxide (DMSO) as the solvent, were investigated. The as-prepared silica aerogels were characterized by means of scanning electron microscope, Fourier transform infrared, contact angle/interface system and electronic universal testing machine. The hydrophobicity of the MTMS-based silica aerogels could be adjusted by tuning the MTMS/DMSO molar ratios. The water contact angle of the MTMS-based silica aerogels could be as high as 160.2∘, suggesting its superhydrophobic property. It was found that all the MTMS-based silica aerogels had the typical three-dimensional porous structure. The failure strain of MTMS-based silica aerogels could be as high as 66.14%.

Effect of Acidity Levels and Feed Rate on the Porosity of Aerogel Extracted from Rice Husk under Ambient Pressure

Silica aerogels have attracted tremendous interest due to their high specific surface area and the physical, chemical, and mechanical properties as promising materials for thermal insulation, chemical sensors, and energy storage devices. However, large-scale production of silica aerogels remains a challenge due to costly alkoxide precursors and energy-intensive supercritical drying processes. This paper analyzes the effect of acidity levels and feed rate on the porosity of rice husk aerogels with high specific surface area under ambient pressure. This synthetic approach is cost-effective, eco-friendly, and facilitates recycling. Rice husk ash, which consists of 92% amorphous pure silica, was produced by combustion. A process of solvent exchange and surface modification under ambient pressure at different pH levels was conducted for synthesis of the aerogel. The specific surface area of rice husk aerogel was confirmed as ranging from 385 to 861 m²/g under pH 1 to pH 9 and acid feed rate of 0.5 to 5.0 mL/min. The optimized aerogel had a specific surface area of 861 m²/g, a pore volume of 3.33 cm³/g, and an average pore diameter of 12 nm when synthesized at pH 1 and an acid feed rate of 2.5 mL/min. The aerogel was found to be highly hydrophobic, with a water contact angle of 156° up to about 340 °C.

Onsite paper-type colorimetric detector with enhanced sensitivity for alkali ion via polydiacetylene-nanoporous rice husk silica composites

A paper-type colorimetric detector for identifying the degree of alkali ion concentration with the naked eye was fabricated using polydiacetylene/nanoporous rice husk silica (PDA/NP-SiO₂) nanocomposites as a potentially effective, rapid, and facile approach to detect alkali ion in aqueous solution. This study is worth investigating because it has the advantage of visually confirming the alkaline ion in aqueous solution without the aid of other analytical instruments directly at on-site as if pH indicator analysis. The concept of this study is the facile synthetic route of PDA and NP-SiO₂. Nanoporous rice husk silica (NP-SiO₂) with a high specific surface area 450 m²/g was extracted from leached rice husk ash via a sol-gel process and utilized for efficient absorption of alkali ion. PDA was used as a material to differentiate the degree of alkali ion drawing using only the change of color. By compositing these two materials on the surface of filter paper using the spray drying method, the resulting PDA/NP-SiO₂ composites with NP-SiO₂ of the different specific surface areas showed a different change of color indicated by the degree of alkali ions even at a low concentration of less than 122 μm. The composite was further analyzed by UV spectroscopy for a change of color and images for screening depending on the alkali ion concentrations. The color response percentage of the PDA/NP-SiO₂ composites (PDA/449S; S_BET 449.9213 m²/g) was 23.39% at 0.122 mM of NH₄OH. Consequently, the result from this study showed the possibility of sensitively distinguishing the alkali ions ranging from pH 9.86 to pH 11.38 using only the naked eye, brought potential features that can be used as a convenient and facile primary water testing kit in practical applications.

Sol-gel derived flexible silica aerogel as selective adsorbent for water decontamination from crude oil

Oil spills are the most important threat to the sea ecosystem. The present study is an attempt to investigate the effects of sol-gel parameters on seawater decontamination from crude oil by use of flexible silica aerogel. To this goal, methyltrimethoxysilane (MTMS) based silica aerogels were prepared by two-step acid-base catalyzed sol-gel process, involving ambient pressure drying (APD) method. To investigate the effects of sol-gel parameters, the aerogels were prepared under two different acidic and basic pH values (i.e. 4 and 8) and varied ethanol/MTMS molar ratios from 5 to 15. The adsorption capacity of the prepared aerogels was evaluated for two heavy and light commercial crude oils under multiple adsorption-desorption cycles. To reduce process time, desorption cycles were carried out by using roll milling for the first time. At optimum condition, silica aerogels are able to uptake heavy and light crude oils with the order of 16.7 and 13.7, respectively.

Organic–inorganic hybridization for the synthesis of robust in situ hydrophobic polypropylsilsesquioxane aerogels with fast oil absorption properties

In situ hydrophobic polypropylsilsesquioxane aerogels (PSAs) were successfully synthesized via an organic–inorganic hybridization method by a sol–gel process, in which propyltriethoxysilane (PTES) and tetraethylorthosilicate (TEOS) were used as co-precursors. ²⁹Si NMR and FTIR analyses indicated the high degree of condensation of the precursors and proved the attachment of propyl (–C₃H₇) groups in PSAs, respectively. By means of incorporating propyl groups, both mechanical robustness and in situ hydrophobicity were obtained. Meanwhile, the mechanical strength, contact angle and density obviously increased with the increase in propyl groups. Under optimized conditions, as-prepared PSA could endure up to a 70% maximum linear compression with few cracks. Benefiting from the robust structure and in situ hydrophobicity, PSAs showed high absorption capacities (8–10 times that of its own weight) and fast absorption properties (<20 s) for a wide range of organic solvents and could be reused at least 5 times.

In situ hydrophobic and mechanically robust polypropylsilsesquioxane aerogels (PSAs) were successfully synthesized via an organic–inorganic hybridization method by a sol–gel process.

Synthesis of silica nanoparticles using biomimetic mineralization with polyallylamine hydrochloride

To synthesize silica particles under mild conditions, we proposed a biomimetic synthesis method. The synthesis process was carried out based on a biphasic sol-gel synthesis method using TEOS (tetraethyl orthosilicate) as a silica source and PAH (polyallylamine) as a substitute for proteins of marine microorganisms for biosilicification. The function and activity of the PAH, used as a replacement for bioactive substances, were confirmed through comparisons between control experiments and designed experiments. The PAH exhibited the ability accelerate condensation with hydrolyzed TEOS in aqueous solutions. The PAH also exhibited high condensation activity in acidic and neutral conditions to produce silica particles. Moreover, PAH also created the nuclei of the silica particles, and the number of nuclei could be controlled by the concentration of PAH. In addition to exhibiting these unique capabilities, PAH did not generate any complexes or composites with the silica species. Depending on the synthesis conditions, the synthesized silica particles exhibited various shapes, such as sponge-like, self-assembled, irregular spherical and completely spherical shapes. The sizes of the primary particles were diverse, with a range from 10nm to 50nm. In particular, by adjusting the PAH concentration, it was possible to obtain nearly perfect spherical-shaped silica nanoparticles with uniform sizes, which has rarely been reported. Above all, using this paper, we can get closer to understanding the principles of silica formation using PAH as a replacement for the bioactive proteins of microorganisms.

Rice Husk Silica-Derived Nanomaterials for Battery Applications: A Literature Review

Silica-rich rice husk (RH) is an abundant and sustainable agricultural waste. The recovery of value-added products from RH or its ash to explore an economic way for the valorization of agricultural wastes has attracted wide attention. For instance, RH can be converted to biofuels and biochars simultaneously via thermochemical processes. In general, the applications of RH biochars include soil remediation, pollutant removal, silicon battery materials, and so forth. This review concludes recent progress in the synthesis of RH-derived silicon materials for lithium-ion battery (LIB) applications. Silica nanomaterials produced from RH are initially discussed. RH amorphous silica can also be fabricated to crystal silicon used for battery materials via widely used magnesiothermic reduction. However, the RH-derived Si nanoparticles suffer from a low Coulombic efficiency in the initial charge/discharge and limited cycle life as anode materials due to high surface reactions and low thermodynamic stability. The synthesis of Si materials with nano/microhierarchical structure would be an ideal way to improve their electrochemical performances. Embedding nano-Si into 3D conductive matrix is an effective way to improve the structural stability. Among the Si/carbon composite materials, carbon nanotubdes (CNTs) are a promising matrix due to the wired morphology, high electronic conductivity, and robust structure. Additionally, CNTs can easily form 3D cross-linked conducting networks, ensuring effective electron transportation among active particles. Si nanomaterials with microhierarchical structures in which CNTs are tightly intertwined between the RH-derived Si nanoparticles have been proven to be ideal LIB anode materials.

Achieving low dielectric, surface free energy and UV shielding green nanocomposites via reinforcing bio-silica aerogel with polybenzoxazine

Silica aerogel (SA) derived from rice husk ash was functionalized using benzoxazine terminated silane (FSA) and was used as a nanoreinforcement for industrial valuable resin polybenzoxazine (PBZ) in order to achieve low dielectric, to improve the surface as hydrophobic and to enhance the UV shielding behavior of the resulting nanocomposites.

Synthesis and biomedical applications of aerogels: Possibilities and challenges

Aerogels are an exceptional group of nanoporous materials with outstanding physicochemical properties. Due to their unique physical, chemical, and mechanical properties, aerogels are recognized as promising candidates for diverse applications including, thermal insulation, catalysis, environmental cleaning up, chemical sensors, acoustic transducers, energy storage devices, metal casting molds and water repellant coatings. Here, we have provided a comprehensive overview on the synthesis, processing and drying methods of the mostly investigated types of aerogels used in the biological and biomedical contexts, including silica aerogels, silica-polymer composites, polymeric and biopolymer aerogels. In addition, the very recent challenges on these aerogels with regard to their applicability in biomedical field as well as for personalized medicine applications are considered and explained in detail.

Preparation of SiO2 aerogel from rice husk ash

Silica was leached from rice husk ash as sodium silicate by NaOH treatment.