Preparation of silica nanoparticles from semi-burned rice straw ash

Methods for the Preparation of Silica and Its Nanoparticles from Different Natural Sources

Silica (SiO2), a component of the earth's crust, has been in use for many nanotechnological applications. This review presents one of the newest methods for safer, more affordable, and more ecologically friendly production of silica and its nanoparticles from the ashes of agricultural wastes. The production of SiO2 nanoparticles (SiO2NPs) from different agricultural wastes, including rice husk, rice straw, maize cobs, and bagasse, was systematically and critically discussed. The review also emphasizes current issues and possibilities linked with contemporary technology to raise awareness and stimulate scholars' insight. Furthermore, the processes involved in isolating silica from agricultural wastes were explored in this work.

Rice straw based silicon nanoparticles improve morphological and nutrient profile of rice plants under salinity stress by triggering physiological and genetic repair mechanisms

The agricultural sector is facing numerous challenges worldwide, owing to global climate change and limited resources. Crop production is limited by numerous abiotic constraints. Among them, salinity stress as a combination of osmotic and ionic stress adversely influences the physiological and biochemical processes of the plant. Nanotechnology facilitates the production of crops either directly by eradicating the losses due to challenging environmental conditions or indirectly by improving tolerance against salinity stress. In this study, the protective role of silicon nanoparticles (SiNPs) was determined in two rice genotypes, N-22 and Super-Bas, differing in salinity tolerance. The SiNPs were confirmed through standard material characterization techniques, which showed the production of spherical-shaped crystalline SiNPs with a size in the range of 14.98-23.74 nm, respectively. Salinity stress adversely affected the morphological and physiological parameters of both varieties, with Super-Bas being more affected. Salt stress disturbed the ionic balance by minimizing the uptake of K+ and Ca2+ contents and increased the uptake of Na+ in plants. Exogenous SiNPs alleviated the toxic effects of salt stress and promoted the growth of both N-22 and Super-Bas, chlorophyll contents (16% and 13%), carotenoids (15% and 11%), total soluble protein contents (21% and 18%), and the activities of antioxidant enzymes. Expression analysis from quantitative real-time PCR showed that SiNPs relieved plants from oxidative bursts by triggering the expression of HKT genes. Overall, these findings demonstrate that SiNPs significantly alleviated salinity stress by triggering physiological and genetic repair mechanisms, offering a potential solution for food security.

Silica extraction from rice hull ash through the sol-gel process under ultrasound

Rice is among the main foods produced in the world and is part of the daily diet of most families. The main waste from rice processing is rice husk (RH), which has been used as biomass for energy generation through combustion. In this process, rice husk ash (RHA) is generated as a residue, and its silica (SiO₂) content varies from 85 to 98%. The present work describes the study of the extraction of silica from RHA by the ultrasound-assisted sol-gel method. An experimental design based on the response surface methodology (RSM) with the symmetrical, second-order rotational central composite design (RCCD) was applied to determine the best extraction conditions considering extraction time and molar ratio (n) as variables = n_NaOH/n_Silica). These optimal conditions were then applied to three ash samples, two obtained by the combustion process in a boiler furnace, with a mobile grate system (RHAC₁ and RHAC₂), and one obtained by the pyrolysis process (RHAP) carried out in a fixed bed reactor. Results showed that a molar ratio of 4.4, and an extraction time of 107 min were the best extraction conditions, leading to a yield of 73.3% for RHAP, 43.9% for RHAC₁, and 31.1% for RHAC₂. It was found that the extraction yield and textural properties of the silica obtained depend on the characteristics of the ash used. The silica extracted from RHAC₁ presented a surface area of 465 m².g^-1, mesopores of 4.69 nm, purity greater than 95%, and an ultra-fine granulometric distribution, reaching nanoparticle dimensions, characteristics comparable to commercially available silicas.

The application of silica gel synthesized from chemical bottle waste for zinc (II) adsorption using Response Surface Methodology (RSM)

The application of silica gel adsorbent synthesized from chemical bottle waste to remove zinc ions in the solution has been carried out. The synthesis of silica gel was carried out using alkaline fusion followed by sol-gel reactions. The chemical glass bottle container was made from borosilicate glass which was different from glass bottles for food and beverage that has been studied in previous studies. The Zn2+ adsorption was optimized using Box-Behnken Design (BBD). Box-Behnken Design was applied to study the optimum zinc ion removal and the input variables interaction. The input variables optimized were adsorbent dosage (1.0 - 2.0 g), initial zinc ion concentration in the solution (25 - 100 ppm), contact time (15 - 45 min), and pH (4 - 9). Response Surface Methodology (RSM) was applied to visualize the input variables' correlation to zinc ion removal. The optimum zinc ion removal was achieved at an adsorbent dosage of 2 g, initial concentration of 35 ppm, contact time of 45 min, and pH 8, which was 99.56%. The optimization of adsorption isotherm obtained that the adsorption follows the Langmuir isotherm model. The silica gel obtained was characterized using SEM-EDX and BET to obtain silica gel properties. The SEM-EDX showed a spherical shape of silica gel. Silica gel containing zinc (Zn) was observed from SEM-EDX after the adsorption process. A pore diameter of 42.098 nm and surface area of 297.083 m2/g were obtained from BET analysis of synthesized silica gel.

Facile Preparation and Characterization of Silica Nanoparticles from South Africa Fly Ash Using a Sol–Gel Hydrothermal Method

Silica nanoparticles (SNPs) consist of several applications which include lightweight aggregates, energy storage, and drug delivery. Nevertheless, the silica reagents used in SNP synthesis are both costly and hazardous. As a result, it is critical to look for other sources of silica. For this research, a simple sol–gel hydrothermal approach is used to make SNPs from South African fly ash (SAFA). SAFA is classified as fly ash class F according to X-ray fluorescence (XRF) analysis. The wide-angle X-ray diffraction (XRD) pattern reveals the structural composition of SAFA and the amorphous phase of extracted SNPs, while Fourier transform infrared (FTIR) examination reveals the presence of silanol and siloxane groups. Basic SNPs were generally spherical with diameters of about 60 nm, according to scanning electron microscopy (SEM) and transition electron microscope (TEM) studies. The presence of SiO2 is confirmed by energy-dispersive X-ray spectroscopy (EDX) spectrum analysis. Particle size assessment indicates particle sizes ranging from 48 nm to 87 nm in diameter, with a mean diameter of 67 nm. The application of SNPs in wastewater treatment demonstrated that they can be used to remove Cd2+ from an aqueous solution. This research offers new ideas for using South African fly ash in SNP manufacturing.

Structural, Optical, and Morphological Characterization of Silica Nanoparticles Prepared by Sol-Gel Process

In the current years, silica nanoparticles have become more favorable in various disciplines like medicine, nano-biotechnology, the food industry, and drug delivery due to their tunable physicochemical characteristics. In this paper, the silica nanoparticles were synthesized by hydrolysis and condensation of tetra-ethyl-ortho-silicate (TEOS) in an ethanolic medium using ammonia as a stimulator in the reaction. The chemical bond structures of silica nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) which confirmed the existence of the Si-O bonds according to the different absorption peaks of the samples. The amorphous structure of these nanoparticles was certified by finding the board peaks in the X-Ray Diffraction (XRD) patterns. The elemental chemical composition of silica nanoparticles was investigated by Energy Dispersive X-Ray Spectroscopy (EDX) where 61.48wt % of silicon and 23.48wt% of oxygen were found. Almost round-shaped spherical and uniform silica nanoparticles with smooth surfaces were investigated by Scanning Electron Microscopy (SEM) measurement. The different particle sizes of silica nanoparticles within the range of 95±5.59 to 280±7.8 nm were found by controlling the concentration of TEOS. The optical absorption spectra and band gap calculations were also analyzed by Ultraviolet-Visible (UV-Vis) spectrophotometry for the different concentrations of TEOS. The results revealed that with increasing the concentration of TEOS, the absorption spectra of silica nanoparticles increased and their optical bandgap decreased from 3.92 eV to 3.79 eV.

Utilization of agricultural and industrial waste as replacement of cement in pavement quality concrete: a review

Over the years, supplementary cementitious materials (SCM) have been successfully utilized in concrete buildings, but they have been rarely exploited in concrete pavements. In recent years, due to the growing importance of concrete pavements, researchers have begun studying the performance of various types of SCMs from pavement perspective. The overview herein assesses the existing research associated with utilizing different kinds of silica-rich waste as SCM. For this purpose, five agricultural waste (AW) comprising rice husk ash (RHA), rice straw ash (RSA), corn cob ash (CCA), palm oil fuel ash (POFA), sugarcane bagasse ash (SBA) and three industrial by-products (IB), i.e., fly ash (FA), ground granulated blast furnace slag (GGBFS) and microsilica (MS), were selected. Their effects on various properties of concrete were exhaustively reviewed. This study also furnishes reasons for limited literature on SCMs utilization in concrete pavements. Moreover, this review accentuates the previous studies' gaps, which require further research, such as the need for dedicated standard codes for AW utilization in concrete pavements. The guidance for future research to further enhance the properties of pavement quality concrete is also given.

Hydrothermal Extraction of Amorphous Silica from Locally Available Slate

Slate is a naturally available aluminous silicate based material and can be used as a good source for silica extraction. In the current investigation, the slate sample was passed through calcination and acid leaching processes to decrease alumina contents and other major constituents. Silica extraction was performed by alkaline hydrothermal treatment of a given slate sample followed by acidic precipitation. Different steps, including the effect of concentration of sodium hydroxide solution, reaction time, the ratio of the mass of sample to volume of alkaline solution, the temperature of dispersion, and pH of the filtrate, were investigated to extract the maximum amount of pure amorphous silica. The extracted silica was physicochemically analyzed through XRF, XRD, FT-IR spectroscopy, and SEM techniques. The amorphous nature of the extracted silica is evident from XRD and SEM studies, while FT-IR studies support its purity, showing peaks of only Si-O-Si bonds. The purity of the extracted silica was further confirmed via XRF spectroscopic analysis and a hydrofluoric acid test.

Cyclodextrin Stabilized Freeze-Dried Silica/Chitosan Nanoparticles for Improved Terconazole Ocular Bioavailability

This research assesses the beneficial effects of loading terconazole, a poorly water-soluble antifungal drug in silica/chitosan nanoparticles (SCNs) for ocular delivery. Nanoparticles were fabricated by the simple mixing of tetraethyl ortho silicate (TEOS) and chitosan HCl as sources of silica and nitrogen, respectively, along with alcoholic drug solution in different concentrations. Freeze-dried nanoparticles were fabricated using cyclodextrins as cryoprotectants. SCNs were assessed for their particle size, PDI, yield, drug loading and in vitro release studies. A 2³.3¹ full factorial experimental design was constructed to optimize the prepared SCNs. DSC, XRD, FTIR, in addition to morphological scanning were performed on the optimized nanoparticles followed by an investigation of their pharmacokinetic parameters after topical ocular application in male Albino rabbits. The results reveal that increasing the water content in the preparations causes an increase in the yield and size of nanoparticles. On the other hand, increasing the TEOS content in the preparations, caused a decrease in the yield and size of nanoparticles. The optimized formulation possessed excellent mucoadhesive properties with potential safety concerning the investigated rabbit eye tissues. The higher C_max and AUC_0–24 values coupled with a longer t_max value compared to the drug suspension in the rabbits’ eyes indicated the potential of SCNs as promising ocular carriers for poorly water-soluble drugs, such as terconazole.

Accurate Insulating Oil Breakdown Voltage Model Associated with Different Barrier Effects

In modern power systems, power transformers are considered vital components that can ensure the grid’s continuous operation. In this regard, studying the breakdown in the transformer becomes necessary, especially its insulating system. Hence, in this study, Box–Behnken design (BBD) was used to introduce a prediction model of the breakdown voltage (VBD) for the transformer insulating oil in the presence of different barrier effects for point/plane gap arrangement with alternating current (AC) voltage. Interestingly, the BBD reduces the required number of experiments and their costs to examine the barrier parameter effect on the existing insulating oil VBD. The investigated variables were the barrier location in the gap space (a/d)%, the relative permittivity of the barrier materials (εr), the hole radius in the barrier (hr), the barrier thickness (th), and the barrier inclined angle (θ). Then, only 46 experiment runs are required to build the BBD model for the five barrier variables. The BBD prediction model was verified based on the statistical study and some other experiment runs. Results explained the influence of the inclined angle of the barrier and its thickness on the VBD. The obtained results indicated that the designed BBD model provides less than a 5% residual percentage between the measured and predicted VBD. The findings illustrated the high accuracy and robustness of the proposed insulating oil breakdown voltage predictive model linked with diverse barrier effects.

When Silicon Materials Meet Natural Sources: Opportunities and Challenges for Low-Cost Lithium Storage

The manipulation of progressive lithium-ion batteries (LIBs) with high energy density, low cost, and long-term cycling stability is of high priority to meet the growing demands for next-generation energy storage devices. Silicon (Si) has been receiving marvelous attention as a promising anode material for rechargeable LIBs, due to its high theoretical gravimetric capacity and low cost. Si is the second most abundant element in the earth crust in the form of silicates, so it is the most cost-effective element as an anode material in next-generation LIBs. In this review, different natural sources such as rice husk, sugar cane bagasse, bamboo, reed plant, sand, halloysite, and different waste sources such as waste of the solar power industry, fly ash, straw ash, and other industrial waste that can give rise to different nanostructured Si are systematically summarized. In addition, different synthesis methods of fabricating nanostructured Si are reviewed as well as including magnesiothermic reduction, etching methods, ball milling, and chemical vapor deposition. The advantages and disadvantages of these kind of synthesis methods are discussed as well. Furthermore, the opportunities and challenges of nano-Si are also discussed.

The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw

Difficulties in the production of lignin from rice straw because of high silica content in the recovered lignin reduce its recovery yield and applications as bio-fuel and aromatic chemicals. Therefore, the objective of this study is to develop a novel method to reduce the silica content in lignin from rice straw more effectively and selectively. The method is established by monitoring the precipitation behavior as well as the chemical structure of precipitate by single-stage acidification at different pH values of black liquor collected from the alkaline treatment of rice straw. The result illustrates the significant influence of pH on the physical and chemical properties of the precipitate and the supernatant. The simple two-step acidification of the black liquor at pilot-scale by sulfuric acid 20w/v% is applied to recover lignin at pH 9 and pH 3 and gives a percentage of silica removal as high as 94.38%. Following the developed process, the high-quality lignin could be produced from abundant rice straw at the industrial-scale.

Production and characterization of silica nanoparticles from fly ash: conversion of agro-waste into resource

A chemical method to synthesize amorphous silica nanoparticles from the incinerated paddy straw has been introduced. The synthesis was conducted through the hydrolysis by alkaline-acidic treatments. As a result, silica particles produced with the sizes were ranging at 60-90 nm, determined by high-resolution microscopy. The crystallinity was confirmed by surface area electron diffraction. Apart from that, chemical and diffraction analyses for both rice straw ash and synthesized silica nanoparticles were conducted by X-ray diffraction and Fourier-transform infrared spectroscopy. The percentage of silica from the incinerated straw was calculated to be 28.3. The prominent surface chemical bonding on the generated silica nanoparticles was with Si-O-Si, stretch of Si-O and symmetric Si-O bonds at peaks of 1090, 471, and 780 cm^-1, respectively. To confirm the impurities of the elements in the produced silica, were analyzed using X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The stability of silica nanoparticles was investigated using thermogravimetric analysis and zeta potential. The measured size from zeta potential analysis was 411.3-493 nm and the stability of mass reduction was located at 200 °C with final amount of mass reduced ∼88% and an average polydispersity Index was 0.195-0.224.

Synthesis of SiO2 nanostructures from Pennisetum glaucum and their effect on osteogenic differentiation for bone tissue engineering applications

Silica nanostructures were fabricated from Pennisetum glaucum (pearl millet) seed husk by acid-pretreatment and calcination. The fabricated silica nanostructure (SN) functional groups, crystalline nature, surface morphology, and particle size were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. Additionally, the cytocompatibility of SNs was analyzed on human mesenchymal stem cells (hMSCs) in an MTT assay, propidium iodine (PI) staining, and acridine orange/ethidium bromide (AO/EB) staining. We observed peaks at 1090 and 800 cm^-1, which were assigned to symmetric, asymmetric, and bending vibrations of O-Si-O. The SNs showed an amorphous nature with a spherical shape and were 20-60 nm in diameter. The MTT assay results indicated that SNs exhibited cytocompatibility in hMSCs. The PI staining and AO/EB staining results suggested that SNs do not affect nuclear morphology at up to 400 μg/mL. Furthermore, SNs effect on osteogenic differentiation in hMSCs was studied. These results indicate that SNs induced osteogenic differentiation in hMSCs by upregulation of ALP, BSP, ON and RUNX2 genes. Our process could valorize the Pennisetum glaucum agricultural residues to high value products for bone tissue engineering applications.

Characterization of Polypropylene Green Composites Reinforced by Cellulose Fibers Extracted from Rice Straw

Polypropylene (PP) based green composites containing 10, 20, 30, 40 and 50 wt% of cellulose fibers (CFs) which were extracted from rice straw were successfully prepared by melt blend method. The CFs washed with H2O2 after alkaline extraction showed lower water absorption than that not washed with H2O2. The thermal, mechanical, and biodegradation properties of composites were also investigated. The 10% weight loss temperature of the composites was decreased with the increasing CFs content, but all the composites showed over 300°C. Young’s modulus and flexural properties of PP were improved by blending PP with CFs. The pure PP showed no degradability, but the PP/CFs composites degraded from about 3 to 23 wt%, depending on CFs content after being buried in soil for 50 days. These PP/CFs composites with high thermal, mechanical properties and biodegradability may be useful as green composite materials for various environmental fields.

An overview of chitin or chitosan/nano ceramic composite scaffolds for bone tissue engineering

Chitin and chitosan based nanocomposite scaffolds have been widely used for bone tissue engineering. These chitin and chitosan based scaffolds were reinforced with nanocomponents viz Hydroxyapatite (HAp), Bioglass ceramic (BGC), Silicon dioxide (SiO₂), Titanium dioxide (TiO₂) and Zirconium oxide (ZrO₂) to develop nanocomposite scaffolds. Plenty of works have been reported on the applications and characteristics of the nanoceramic composites however, compiling the work done in this field and presenting it in a single article is a thrust area. This review is written with an aim to fill this gap and focus on the preparations and applications of chitin or chitosan/nHAp, chitin or chitosan/nBGC, chitin or chitosan/nSiO₂, chitin or chitosan/nTiO₂ and chitin or chitosan/nZrO₂ in the field of bone tissue engineering in detail. Many reports so far exemplify the importance of ceramics in bone regeneration. The effect of nanoceramics over native ceramics in developing composites, its role in osteogenesis etc. are the gist of this review.

Simultaneous preparation of nano silica and iron oxide from palm oil fuel ash and thermokinetics of template removal

This work reports a method for simultaneous synthesis of nano silica and iron oxide from POFA.

Analytical analysis of synthesized biosilica from bioresidues

Rice straw and maize stalk are major residues of agriculture field. These residues were utilized to synthesis nano-biosilica by sol-gel route. The structural properties of rice straw ash, maize stalks ash and biosilica were characterized by X-ray diffraction and FTIR. Morphology evaluation by SEM confirms the formation of nano-biosilica of spherical shape.