Amine-functionalized porous silica production via ex- and in-situ method using silicate precursors as a selective adsorbent for CO2 capture applications

A comparison of the amine-modified silica particle's characteristics via ex- and in-situ routes and their application as a CO2 gas adsorbent is reported. Modifying silica particles via ex-situ involves two separate steps: forming porous silica particles with sodium lauryl sulfate (SLS) as a template and impregnation using ultrasound assistance. In contrast to ex-situ modification, in-situ modification of silica particles is carried out in one step by mixing directly between the silica source and the modifying agent. Controlling the characteristics of modified silica particles via in-situ is carried out by adding an SLS template removed simultaneously with particle formation to increase the surface area and porosity. Increasing the SLS template concentration shows a linear relationship between increasing particle surface area and amine loading. However, two different modification routes exert a direct influence on aminopropyl distribution. Silanization via in-situ which involves a simultaneous condensation reaction produces a higher amine loading reaching 1.2845 mmol/g of silica than via ex-situ which is only 0.9610 mmol/g of silica. The amount of aminopropyl that can be grafted on the silica surface shows a linear relationship to the quantity of CO2 gas adsorption capacity. Amine-modified silica particles obtained the highest adsorption capability via the in-situ route with an SLS 3 CMC template of 2.32 mmol/g silica at an operating pressure of 6 bar.

Repurposing carbonate-based waste for producing an innovative binder: optimization and characterization

This study reports the full recycling of dolomite waste (DW) in the fabrication of a novel cementitious material through a facile and eco-efficient method. The proposed technique includes mixing different alkali-activators (i.e., NaOH and Na2SiO3) with DW powder, followed by curing at room temperature. Based on the alkali-activator type, sodium oxide concentration, and curing time, the formulated mixtures yield a wide range of compressive strengths. When DW powder is mixed with different contents of NaOH (2.5, 5, and 7.5 wt.% Na2O), the resulting hardened materials exhibited modest compressive strengths (less than 11 MPa) due to the formation of the gaylussite Na2CO3·CaCO3·5H2O phase. Concerning the other chemical activator (Na2SiO3), a significant improvement in the compressive strengths of the resulted hardened materials was detected. This was ascribed to the formation of calcium silicate hydrate, with a high binding capacity, through the exchange reaction between Na2SiO3 and CaCO3 inside DW. The sample activated with Na2SiO3 (silica modulus of 1.5) equivalent to Na2O of 7.5 wt.% offered the highest 90-day compressive strength (34 MPa). At silica modulus lower or higher than 1.5, a noticeable decrease in the performance of the hardened materials was observed, which could be attributed to the alter in binding phase composition. Overall, the present work presented a new approach in utilizing the available and low cost carbonate-based wastes as main precursors in the family of promising alkali-activated materials.

TL glow curve and kinetic analysis of Na2SiO3:Pr3+ under beta radiation effect

Ionizing radiation dosimetry with thermoluminescence (TL) materials based on silicon or glass can be interesting in its potential use in radiation monitoring as the solution to the constant looking of development of new radiation detectors. In this work, TL characteristics of sodium silicate exposed to beta radiation effects were studied. TL response beta irradiated exhibited a glow curve with two peaks centered at 398 K and 473 K. Samples showed linearity from 0.55 to 13.2 Gy. TL readings after 10 times showed a repeatability with an error of less than 1%. Remain information showed significant losses during the first 24 h, but its information was almost constant after 72 h of storage. The T_max-T_stop method exhibited three peaks which were mathematically analyzed with a general order deconvolution finding kinetic orders close to the second order for the first peak, meanwhile the kinetic order for the second peak and third peak are close to second order. Finally, the VHR method showed anomalous TL glow curve behavior with an increasing intensity TL as the heating rate increased.

Histopathological, biochemical and molecular studies on a model of systemic autoimmune disease induced by sodium silicate in non-genetically prone rats

Sodium silicate (Na2SiO₃) is an inorganic silica salt used in many products. Few studies reported autoimmune diseases (AIDs) due to Na2SiO₃ exposure. This study investigates the role of Na2SiO₃ exposure by different routes and doses in AID development in rats. We assigned 40 female rats to four groups: G1 control group, G2 rats were subcutaneously injected with 5 mg Na2SiO₃ suspension, and G3 and G4 rats were orally administered 5 mg and 7 mg Na2SiO₃ suspension, respectively. Na2SiO₃ was administered weekly for 20 weeks. Serum anti-nuclear antibodies (ANA) detection, histopathology of kidney, brain, lung, liver, and heart, oxidative stress biomarkers (MDA and GSH) in tissues, Matrix metalloproteinase activity in serum, TNF-α, and Bcl-2 expression in tissues were performed. ANA was significantly increased in silicate groups, especially G2. Creatinine was significantly increased in silicate groups. Histopathology revealed vasculitis and fibrinoid degeneration of blood vessels, a picture of immune-mediated glomerulonephritis in the kidneys, and chronic interstitial pneumonia with medial hypertrophy of pulmonary blood vessels. The activity of gelatinases (MMP-2 and MMP-9) and collagenase (MMP-13), which play role in inflammation, remodeling, and immune complex degradation, were significantly increased in the silicate-exposed groups. Bcl-2 was significantly decreased, indicating apoptosis. Therefore, oral administration and subcutaneous injection of Na2SiO₃ induced immune-mediated glomerulonephritis with elevated ANA levels and overexpression of TNF-α in rats.

Sodium silicate treatment accelerates biosynthesis and polymerization of suberin polyaliphatics monomers at wounds of muskmelon

Suberin polyaliphatics (SPA) is an important component of healing closing layer at fruit wounds. However, few study is available on the effect of sodium silicon treatment on SPA monomers biosynthesis and polymerization at muskmelon wounds. In this study, sodium silicate enhanced PLA₂ (Phospholipase A₂, PLA₂) expression and enzyme activity, increased oleic acid, linoleic acid, and linolenic acid contents, and degree of fatty acids unsaturation at wounds. Sodium silicate upregulated the expressions of LACS4 (Long chain acyl CoA synthetase, LACS), KCS10 (β-ketoacyl CoA synthase, KCS), CYP86B1 (Cytochrome P450 oxygenase, CYP), FAR3 (Fatty acyl CoA reductase, FAR), GPAT1 (Glycerol-3-phosphate acyltransferase, GPAT) and ABCG6 (ATP-binding cassette transporter), as well as their enzymes activities and ABC content. It is suggested that sodium silicate accelerates the deposition of SPA at muskmelon wounds by increasing the degree of fatty acids unsaturation, and promoting SPA monomers biosynthesis.

Immobilization of strontium in geopolymers activated by different concentrations of sodium silicate solutions

Sodium silicate is always used as an activator for the synthesis of geopolymer. However, the effect of sodium silicate concentration on the geopolymer used as adsorbent was still unclear. Therefore, the immobilization of Sr²⁺ in geopolymers activated by different concentrations of sodium silicate was studied through kinetic and isotherm modeling and solid characterizations including XRD, FTIR, TG, SEM-EDS, and N₂ adsorption-desorption isotherm. The adsorption amount of Sr²⁺ decreased with the sequence of S1, S2, and S3. According to the kinetic and isotherm modeling results, these sorption processes fitted better with pseudo-second-order, mainly governed by film diffusion. However, the diffusion mode was gradually closed to particle diffusion as for the sequence of S3, S2, and S1. Besides, the Langmuir model can be more befitting to sorption data than the Freundlich model, and the free energies decreased with the order of S1, S2, and S3. In addition, the specific surface areas did not change regularly with S1, S2, and S3. Thus, the distribution of Al tetrahedrons has a decisive role in the sorption process of Sr²⁺, even though the specific surface area is also a critical factor. More Al tetrahedrons can be formed under the activation of sodium silicate with higher concentration, leading to the low Si/Al molar ratio of the as-synthesized geopolymer.

Taguchi optimization of geopolymer concrete produced with rice husk ash and ceramic dust

Metakaolin, fly ash, and mostly granulated blast furnace slag (GBFS) are traditionally used in the production of geopolymer. This study, adding to the knowledge base on geopolymer concretes as an alternative to cement mixtures, explored an experimental approach that investigates the use of ceramic dust (CD) and rice husk ash (RHA) with high SiO content instead of GBFS in the production of geopolymers. For this purpose, instead of GBFS, RHA at proportions of 0, 5%, 10%, and 15% and CD at proportions of 0, 10%, 20%, and 30% were used in the production of geopolymer concrete. In addition, groups were determined with a Taguchi L16 matrix with NaOH (an important material in geopolymer production) at 12, 14, 16, and 18 molality. Varying combinations of flow diameter, density, porosity, and water absorption rate were used, and their performance under high temperatures in terms of compressive strength was evaluated. The use of RHA in geopolymer concretes produced using CD and RHA had a negative effect on the flow and water absorption rates. However, the use of CD had a positive effect, and geopolymer concretes with high density and porosity were obtained. In addition, it was determined that strengths > 70 MPa could only be obtained if 5-20% CD were used at 14-16 molality. The resistance of geopolymer concretes to high temperatures is lower than normal concretes. However, when comparing RHA and CD, it was determined that the use of CD would be more effective on geopolymer materials, and special measures should be taken at temperatures > 450 °C.

A high value utilization process for coal gasification slag: Preparation of high modulus sodium silicate by mechano-chemical synergistic activation

Coal gasification coarse slag (CGCS) is solid waste generated during coal gasification. The mainly treatment method of CGCS is storage and landfill, which causes severe environmental pollution and waste of land resources. Sodium silicate can be synthesized using CGCS after impurities are removed for the high content of amorphous silica. In this work, a novel method of acid activation depolymerization-dilute alkali dissociation is proposed to synthesize high-modulus, low-impurity sodium silicate using CGCS under mild conditions. In the acid activation depolymerization process, the content of impurities such as CaO and Fe₂O₃ can be reduced from over 30% to below 3%. SiO₂ composition can be enriched from 35.75% to 60.60%. The SiOAl bond is broken, the coordination structures of Q⁴(2Al) and Q⁴(3Al) are depolymerized, and the reactive Q⁴(0Al) and Q³(0Al) coordination structures of amorphous silica are formed. Numerous defects appear in the aluminosilicate structure, exposing a large number of active SiOH bonds. Efficient desilicated ratio is increased from 7.59% to 73.45%. During the process of dilute alkali dissociation, a large number of reactive SiOSi bonds with network structure defects are broken with the destruction of hydroxyl groups, while SiO and SiOH bonds are formed. Amorphous silica is leached into the liquid phase in the form of oligomers, and high-modulus sodium silicate can be obtained. Under optimal conditions, the removal ratio of amorphous silica and modulus of sodium silicate can reach 80% and 3.53, respectively. The synthesized sodium silicate can be used to produce hydrated silica, adhesives and surface coatings. This process not only reduces pollution, but also alleviates the shortage of high-purity quartz sand resources and promotes the clean development of coal chemical enterprises.

Synthesis of sodium silicate using industrial by-products glauber's salt and microsilica: Effective reuse of the waste

Large amounts of by-products, including glauber's salt (GS) and microsilica (MS), are accumulated from chlor-alkali industry and ferrosilicon industry development, which not only wastes precious resources, but also causes serious environmental problems. In order to recycle and reuse these industrial by-products, solid sodium silicate was synthesized using GS and MS as the main raw materials, and semi-coke (SC) as the reducing agent. The effects of melting parameters including GS/SC and MS/GS molar ratio, heating rate, temperature, reaction time, and SC particle size on the conversion efficiency and modulus of solid sodium silicate were investigated and optimized. Under optimal conditions, the maximum conversion efficiency of 94.91% was obtained with modulus of 2.5. Characterization analysis of the products indicated that the amorphous silicate sodium was successfully synthesized. Moreover, the reaction mechanism was investigated, which focused on the thermal behavior and phase transformation using thermo-gravimetric and differential scanning calorimetric (TG-DSC) and in-situ X-ray diffraction. Additionally, the causes and suppression measures of "glauber's salt water" (GSW) during the experiment were summarized. This work not only creates resource utilization of GS and MS, but also provides the foundation for the synthesis of sodium silicate with GS.

Controlling lead release due to uniform and galvanic corrosion - An evaluation of silicate-based inhibitors

Silicates have been added to drinking water for decades, both to sequester iron/manganese and as a corrosion control treatment for lead. But the mechanisms by which they might act to limit lead release are not well understood. We evaluated the effects of two silicate formulations on lead release due to uniform and galvanic corrosion over a wide range of pH and dissolved inorganic carbon concentrations. We compared these results to better-characterized systems, with added ortho- or polyphosphate and in an inhibitor-free control. Independent of pH, silicates did not consistently mitigate lead release due to either uniform or galvanic corrosion. Furthermore, lead carbonates appeared to determine lead solubility in the presence of sodium silicate. While silicate treatment did promote the formation of a nanometer-thick silicon layer on lead and a decrease in crystallite size at the scale surface, these changes did not inhibit lead release. But unlike polyphosphate-which is known to form soluble complexes with lead and disperse particulate metals-high ratio silicate did not exacerbate lead release. Metasilicate did exacerbate lead release, especially at pH 7 and 5 mg DIC/L; this suggests that silicate formulation may have an important effect on the dispersion of lead-rich particles.

Effect of sodium silicate on lead release from lead service lines

The effect of sodium silicate addition on lead release from lead service lines (LSLs) was investigated using laboratory-based pipe loop experiments with LSLs harvested from a water utility that has one of the Great Lakes as its source water. The LSLs were first conditioned with a synthetic water similar to that of Buffalo Water that matched the major water chemistry that the pipes had experienced in the field; the one exception was the absence of dissolved organic carbon in the synthetic water. After conditioning, the LSLs were used in tests with the same synthetic water and with sodium silicate added to the water for half of the LSLs. In one test sodium silicate addition was performed with adjustment of the pH to maintain it at the same value (pH 7.7) as before addition. In this test sodium silicate effectively reduced the dissolved and particulate lead concentrations in the water within six weeks of treatment. Periodic assessments of the corrosion scales in the pipes found that sodium silicate accumulated throughout the scale thickness and gradually decreased the lead release. In the other test the pH was allowed to increase from 7.7 to 8.8 upon addition of 20 mg/L as SiO₂ sodium silicates, and parallel control experiments were performed with the same pH increase made using sodium hydroxide addition. In these tests the lead concentrations decreased in both the silicate-treated and control pipes, and the decreases were not significantly different between the silicate-treated and control pipes.

A novel industrial-scale strategy to prevent degradation and caking of ammonium nitrate

Several research studies have been performed to minimise the hygroscopicity of ammonium nitrate for increasing its commercial value and decreasing the nitrogen content. In this study, the hygroscopicity of ammonium nitrate was reduced using silicic acid, calcium lignosulfonate, and sodium silicate in the two-stage vacuum ammonium nitrate production process. Degradation of ammonium nitrate was observed after two years of storage, which is considered a standard by the European Fertilizer Manufacturers Association.

Sodium silicate prime defense responses in harvested muskmelon by regulating mitochondrial energy metabolism and reactive oxygen species production

The effects of postharvest treatment with sodium silicate (Si) (100 mM) on mitochondrial ROS production and energy metabolism of the muskmelon fruits (cv. Yujinxiang) on development of defense responses to Trichothecium roseum were studied. Si treatment decreased decay severity of inoculated muskmelons, enhanced the activities of energy metabolism of key enzymes and kept the intracellular ATP at a higher level; meanwhile, Si also induced the mtROS accumulation such as H₂O₂ and superoxide anion. TMT-based quantitative proteomics analysis revealed that a total of 24 proteins with significant differences in abundance involved in energy metabolism, defense and stress responses, glycolytic and TCA cycle, and oxidation-reduction process. It is suggested by our study that melon fruit mitochondria, when induced by Si treatments, play a key role in priming of host resistance against T. roseum infection through the regulation of energy metabolism and ROS production in the pathogen infected muskmelon fruits.

Waterglass impregnation of municipal solid waste incineration bottom ash applied as sand replacement in mortars

Incineration has been recognized as one of the most applied strategies for the processing of the municipal solid waste (MSW). The primary output from the incineration of the MSW is Bottom Ash (BA), whose particles are highly porous and contaminated with heavy metals, chlorides, and sulphates, limiting its application in concrete. For improving the applicability as aggregates, many porous materials are impregnated with a pozzolanic solution, easing their use as building materials. However, this treatment has never been applied to by-products like BA, and therefore the influence of a coating on the leaching behaviour of the by-products has never been investigated. This study analyses the effect of an impregnation treatment based on different sodium silicate amounts on BA particles between 1 and 2 mm. The application of the coating lowers the pore volume of BA by 2.5 times, allowing a sand replacement up to 100% and improving the rheological behaviour of mortars till 38%, compared to uncoated samples. Replacing 50 vol.% of coated BA achieves 22% higher flexural and comparable compressive strength than the uncoated BA samples, thanks to the reduction of the Ca/Si ratio in the reaction products. Finally, in the presence of the coating, the leaching of the following contaminants Cl, Ba, Cu, Zn is reduced by 88, 98, 94 and 97%, respectively, compared to the uncoated BA application. Therefore, the impregnation treatment not only favours the application of higher amounts of BA, but it also improves the final performances of the product both mechanically and environmentally.

Comparison of silicon nanoparticles and silicate treatments in fenugreek

Silicon (Si) fertilization improves crop cultivation and is commonly added in the form of soluble silicates. However, most natural plant-available Si originates from plant formed amorphous SiO₂ particles, phytoliths, similar to SiO₂-nanoparticles (SiNP). In this work we, therefore, compared the effect by sodium silicate and that of SiNP on Si accumulation, activity of antioxidative stress enzymes catalase, peroxidase, superoxide dismutase, lignification of xylem cell walls and activity of phenylalanine ammonia-lyase (PAL) as well as expression of genes for the putative silicon transporter (PST), defensive (Tfgd 1) and phosphoenolpyruvate carboxykinase (PEPCK) and protein in fenugreek (Trigonella foenum-graecum L.) grown in hydroponics. The results showed that Si was taken up from both silicate and SiNP treatments and increasing sodium silicate addition increased the translocation of Si to the shoot, while this was not shown with increasing SiNP addition. The silicon transporter PST was upregulated at a greater level when sodium silicate was added compared with SiNP addition. There were no differences in effects between sodium silicate and SiNP treatments on the other parameters measured. Both treatments increased the uptake and accumulation of Si, xylem cell wall lignification, cell wall thickness, PAL activity and protein concentration in seedlings, while there was no effect on antioxidative enzyme activity. Tfgd 1 expression was strongly downregulated in leaves at Si addition. The similarity in effects by silicate and SiNP would be due to that SiNP releases silicate, which may be taken up, shown by a decrease in SiNP particle size with time in the medium.

Comparison of three corrosion inhibitors in simulated partial lead service line replacements

Partial lead service line replacements (PLSLR) were simulated using five recirculating pipe loops treated with either zinc orthophosphate (1mg/L as P), orthophosphate (1mg/L as P) or sodium silicate (10mg/L). Two pipe loops served as ⿿inhibitor-free⿿ (Pb-Cu) and ⿿galvanic free⿿ (Pb-PVC) controls. Changes in water quality (CSMR [0.2 or 1], conductivity [⿿330mS/cm or ⿿560mS/cm], chlorine [1.4mg/L]) were not observed to provide a significant impact on lead or copper release, although galvanic corrosion was shown to be a driving factor. Generally, both orthophosphate and zinc orthophosphate provided better corrosion control for both total and dissolved lead (30min, 6h, 65h) and copper (30min, 6h), when compared to either the inhibitor-free control or the sodium silicate treated system. This work highlights the importance of understanding the complex interplay of corrosion inhibitors on particulate and dissolved species when considering both lead and copper.

Investigation of sodium silicate-derived gels as encapsulants for hazardous materials--the case of scorodite

High content arsenic waste generated in the metallurgical industry can be converted into a synthetic mineral, scorodite, FeAsO4·2H2O, and deposited into a landfill site. Scorodite is most stable in weakly acidic to neutral pH range under oxic conditions. A novel way to enhance the range of stability for scorodite is to encapsulate it with an inert material. In this work, silicate gel is developed and investigated as a possible encapsulating material for scorodite. The initial method of gel formation in this study produced a silicate gel with high alkalinity (pH 10) that was incompatible with scorodite. A reverse titration method was developed producing a gel with optimum pH profile (5-6.5). This technique proved to have only marginal effect on scorodite stabilization prompting an investigation of different ageing techniques (drying; 22, 44°C and hydrothermal treatment; 110, 160°C) as a means of producing silica-like coatings with better stabilization potential. Interestingly most of these measures proved counterproductive as aged scorogels showed a higher release of As than scorodite alone. Through surface-sensitive depth profile analysis (XPS), and molecular-sensitive analysis (Raman and FTIR mapping), it was discovered that the silicate engaged into an "ion-exchange" type reaction on the surface of scorodite by bonding to iron, hence the observed release of arsenic. Development of a hydrothermally-induced iron silicate layer may lead to an effective encapsulant.

A vibrational spectroscopic study of the silicate mineral analcime - Na2(Al4SiO4O12)·2H2O - a natural zeolite

We have studied the mineral analcime using a combination of scanning electron microscopy with energy dispersive spectroscopy and vibrational spectroscopy. The mineral analcime Na2(Al4SiO4O12)·2H2O is a crystalline sodium silicate. Chemical analysis shows the mineral contains a range of elements including Na, Al, Fe(2+) and Si. The mineral is characterized by intense Raman bands observed at 1052, 1096 and 1125cm(-1). The infrared bands are broad; nevertheless bands may be resolved at 1006 and 1119cm(-1). These bands are assigned to SiO stretching vibrational modes. Intense Raman band at 484cm(-1) is attributed to OSiO bending modes. Raman bands observed at 2501, 3542, 3558 and 3600cm(-1) are assigned to the stretching vibrations of water. Low intensity infrared bands are noted at 3373, 3529 and 3608cm(-1). The observation of multiple water bands indicate that water is involved in the structure of analcime with differing hydrogen bond strengths. This concept is supported by the number of bands in the water bending region. Vibrational spectroscopy assists with the characterization of the mineral analcime.

Zeolite materials prepared using silicate waste from template synthesis of ordered mesoporous carbon

Significant amount of silica waste is generated in the preparation of porous carbon materials using template synthesis. Industrial production of such porous carbon not only creates waste chemicals, but also poses significant environmental concerns and high waste treatment cost. Recycling is proposed as the best solution for tackling such chemical wastes. In this study, etched silica waste released from template synthesis of mesoporous carbon is recycled to produce precious functional microporous zeolite materials. The solid silica template is etched out with NaOH solution to produce silica-free mesoporous carbon. The collected silica waste is recycled to generate zeolites such as LTA and MFI type silica materials. The formation of zeolites is confirmed by FT-IR, XRD, (29)Si NMR, (27)Al NMR, and SEM. This straight forward green chemistry route not only recycles the waste chemicals, but also decreases environmental pollution for better improvement of our living.