Sodium Silicate Research Articles

Effect of Expanded Glass Lightweight Aggregate on the Performance of Geopolymer Mortar at Elevated Temperatures

AbstractThe greenhouse gas emissions associated with conventional concrete as a result of the cement industry have prompted scientists to search for eco-friendly alternatives. Among these promising alternatives is geopolymer concrete or mortar. This work studies the impact of using polyvinyl alcohol (PVA) fibers and lightweight expanded glass (EG) aggregate on the mechanical behaviour of lightweight geopolymer mortar (LWGM) at various temperatures (room temperature, 250 °C, and 500 °C). EG was utilized to partially replace the sand by 10 and 20%. Limited studies dealt with geopolymer mortar based on such composition at high temperatures. The geopolymer mortar was created using slag as the main precursor activated by a mixed solution of sodium hydroxide and sodium silicate. Various combinations were produced, and their behaviour was observed at room and high temperatures. Several tests such as workability, compressive and flexural strengths, density, stress-strain relationship, load-displacement behaviour, and uniaxial tensile strength were performed. The findings of the study indicate that the density and compressive strength of geopolymer mortar reduced with increasing the replacement level by the EG. However, the utilization of 10% EG can produce a lightweight mortar with a compressive strength of 17.9 at 28 days. Moreover, the use of 1% PVA significantly improves the mechanical performance. Furthermore, the mechanical characteristics of the materials were considerably altered when subjected to extreme temperatures of 500 °C as observed from experimental data.

Effects of elevated temperature on mechanical properties and microstructures of alkali-activated mortar made from low calcium fly ash-calcium carbide residue mixture

This research investigated the high-temperature resistance of alkali-activated mortar (AAM) using Class F fly ash (FA) blended with calcium carbide residue (CR) as a binder. The FA was blended with CR at 15 %, 30 %, and 45 % by weight. Sodium hydroxide (NaOH) and sodium silicate solution (Na2SiO3) was used as activator in the ratio of 2:1 by weight. The sodium hydroxide solution concentrations were 6, 8, and 10 M, the liquid-to-binder ratio was 0.85, and the binder-to-fine aggregate ratio was 1:2.75 by weight. The study assessed physical characteristics, compressive strength, weight loss, and microstructural analysis, subsequent to being subjected to 2-hour heating at 400, 600, and 800 °C. According to the findings, the highest compressive strength (prior heating) was recorded as 41.3 MPa after 28 days and this was observed in samples where 30 % of CR was combined with 70 % of FA. Meanwhile, when exposed to elevated temperatures, the compressive strength of all samples was decreased. The decomposition of Ca(OH)2, C-S-H, and C-A-S-H gel in the matrix as indicated by the microstructure result was conformed to the result of compressive strength loss. Nonetheless, when the samples were sintered at 800 °C, a new crystalline phase was formed, resulting in a slightly increase in compressive strength compared to samples sintered at 600 °C.

Performance of fly ash/GGBFS based geopolymer concrete with recycled fine and coarse aggregates at hot and ambient curing

The incorporation of recycled aggregates in geopolymer concrete (GPC) exhibits higher environmental sustainability due to its ability to utilize industrial by-products and construction and demolition (C&D) waste. This study investigates the combined effect of fine and coarse recycled aggregates on the behavior of GPC. In this research, fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as binder, whereas sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) were used as alkaline activators. Recycled fine aggregates (RFA) were used at 30%, 60% and 100% replacement of natural fine aggregates (NFA) and recycled coarse aggregates (RCA) were used at 0%, 50% and 100% replacement of natural coarse aggregates (NCA). To study the effect of curing temperature, two types of curing regimes, i.e. hot and ambient curing, were employed. Performance of developed GPC was evaluated in terms of workability, mechanical properties (compressive strength, splitting tensile strength, and flexural strength) and durability properties such as water absorption, sorptivity, resistance against acid attack, resistance against marine environment and electrical resistivity. It was found that the behavior of GPC is improved when the samples were cured at high temperature for 24 h, as compared to the samples cured under ambient curing conditions. Furthermore, NFA can be replaced up to 100% with NCA, and up to 60% in the presence of 50% RCA and up to 30% in the presence of 100% RCA. It was also found that with an increase in the percentage of recycled aggregates, durability performance gradually declined. The results showed that GPC can be developed with inclusion of both recycled fine and coarse aggregates, which can help to preserve valuable natural resources, reduce CO2 emission, and dispose C&D waste.

Effect of curing condition on mechanical properties and durability of alkali-activated slag mortar

While alkali-activated slag (AAS) has emerged as a promising alternative binder in construction engineering, a consensus on the optimal curing condition for this material has not been reached yet. It is well known that AAS can harden at ambient temperatures, but the influence of humidity on its properties remains poorly understood. Herein, we considered five curing conditions with different relative humidities (RH), including ambient/dry condition (RH=55%), sealed condition (RH=internal RH, decreasing from around 95% to 80%), fog condition (RH>95%), water immersion condition (RH=100%), and saturated limewater immersion condition (RH=100%). Various properties have been examined, including flexural and compressive strength, elastic modulus, shrinkage, pore structure, carbonation resistance, and freeze-thaw resistance of AAS mortars (AASM). Two types of commonly used activators, sodium hydroxide and sodium silicate (modulus at 1) solutions were used. The experimental results indicate that drying at early ages was detrimental to almost all the properties investigated. Sealed curing can deliver desirable mechanical properties and durability, but considerable shrinkage. Fog and water curings are highly effective at mitigating early-age shrinkage in AASM, but the problem of leaching adversely affects its long-term properties. Generally, limewater curing offers limited benefits compared to other high-humidity curing methods.

Preparation of Lightweight Porous Slag-based Geopolymer Highly Hydrophobic Materials for Efficient Oil-water Separation

Surface hydrophobic modification is a critical technology for enhancing the application properties of materials, crucial for the development of geopolymer materials in oil-water separation. in this study, a lightweight porous slag-based geopolymer highly hydrophobic materials (PSGHHMs) were successfully prepared in-situ using slag and liquid water glass by varying different influencing factors, such as the amount of water/foaming agent/polymethylhydrosiloxane (PMHS) and the curing temperature. The PSGHHMs exhibited high strength, large flux and excellent highly hydrophobic properties, with contact angle reaching 156.14° and a sliding angle of less than 2°. SEM-EDS, TG-DSC and FT-IR analysis reveal that the in-situ modification mechanism of PSGHHMs involves the hydrolysis of Si-H in PMHS under alkaline conditions to form Si-OH. This subsequently reacts with Ca-OH in C-S-H gel to produce Ca-O-Si. Consequently, the PSGHHMs retained their excellent highly hydrophobicity even after calcination at 450℃ for 2.5h. The PSGHHMs demonstrated robust resistance to acid/alkali/salt corrosion, as well as to friction, with the ability to quickly restore damaged highly hydrophobic properties. Additionally, the PSGHHMs could quickly absorb light/heavy oils, and achieving a desorption efficiency of over 99%. They were also capable of continuously separation of oil-in-water emulsions and oil-water mixtures. Given these properties, the PSGHHMs have broad potential applications in antifreezing, antifogging, drag reduction and oil-water separation.

Preparation of lightweight porous slag-based geopolymer highly hydrophobic materials for efficient oil-water separation

Surface hydrophobic modification is a critical technology for enhancing the application properties of materials, crucial for the development of geopolymer materials in oil-water separation. in this study, a lightweight porous slag-based geopolymer highly hydrophobic materials (PSGHHMs) were successfully prepared in-situ using slag and liquid water glass by varying different influencing factors, such as the amount of water/foaming agent/polymethylhydrosiloxane (PMHS) and the curing temperature. The PSGHHMs exhibited high strength, large flux and excellent highly hydrophobic properties, with contact angle reaching 156.14° and a sliding angle of less than 2°. SEM-EDS, TG-DSC and FT-IR analysis reveal that the in-situ modification mechanism of PSGHHMs involves the hydrolysis of Si-H in PMHS under alkaline conditions to form Si-OH. This subsequently reacts with Ca-OH in C-S-H gel to produce Ca-O-Si. Consequently, the PSGHHMs retained their excellent highly hydrophobicity even after calcination at 450℃ for 2.5 h. The PSGHHMs demonstrated robust resistance to acid/alkali/salt corrosion, as well as to friction, with the ability to quickly restore damaged highly hydrophobic properties. Additionally, the PSGHHMs could quickly absorb light/heavy oils, and achieving a desorption efficiency of over 99 %. They were also capable of continuously separation of oil-in-water emulsions and oil-water mixtures. Given these properties, the PSGHHMs have broad potential applications in antifreezing, antifogging, drag reduction and oil-water separation.

Properties of flyash-dolomite powder-mangalore tile waste powder based alkali-activated binder cured in ambient condition

AbstractThis research addresses the slower reaction rate of flyash based alkali activated binders by investigating the use of dolomite powder (DP) and Mangalore Tile waste powder (MTWP) to enhance the reaction rate and improve binder properties. The study evaluates the feasibility of combining these materials with flyash to develop effective alkali activated binders. Material characterization was performed to access their suitability as precursors in alkali activation. The proportions of these precursors were varied while maintaining a constant rate of alkali activators such as sodium hydroxide and sodium silicate. Tests for initial and final setting times, flowabilty, pH, electrical conductivity and compressive strength of the binders were conducted. Microanalysis supported the findings by providing detailed insights. Results indicate that the alkali activated FA-DP-MTWP binder exhibited faster setting and hardening with decreased flow ability. The pH of all FDT binder mixes provides necessary alkaline environment for forming stable reaction products like CSH, CASH, NASH and MSH, as identified by SEM, EDS, and XRD studies. This higher level of these activation products also lead to increased electrical conductivity. Optimal precursor utilization was achieved with 5% MTWP and 10% DP in the total binder, beyond which DP and MTWP acted only as fillers. Mechanical, mineralogical, and morphological analyses confirmed the binder's satisfactory performance and cementitious properties, demonstrating its potential value for construction applications. The study concludes that incorporating these materials can effectively enhance the properties of flyash based alkali activated binders. Graphical abstract

Performance and Microstructural Features of Sodium Silicate Shell Cured via Microfluidic Droplets of Citric Acid Solution

Performance and Microstructural Features of Sodium Silicate Shell Cured via Microfluidic Droplets of Citric Acid Solution

Autonomous Self-Healing Agents in Cementitious Materials: Parameters and Impacts on Mortar Properties

The concept of self-healing materials and the development of encapsulated curing agents represent a cutting-edge approach to enhancing the longevity and reducing the maintenance costs of cementitious structures. This systematic literature review aims to shed light on the parameters involved in the autonomous self-healing of cementitious materials, utilizing various encapsulated healing agents such as pellets, granules, and capsules. This review also identifies and selects studies that offer additional insights into the efficacy of the self-healing process in cementitious materials and the influence of these specific encapsulated healing agents on the physical mechanical properties of mortars. This comprehensive approach provides a deep understanding of the interplay between self-healing and the physical–mechanical properties of mortars containing these encapsulated healing agents. The main findings indicate that the cement-to-sand ratio, characteristics of fine aggregates, and encapsulation methods significantly impact crack control, self-healing efficiency, and properties of mortar in both fresh and hardened states. The content of encapsulated healing agents within the cementitious matrix affects both the initial workability or flow and subsequent mechanical properties. While pellets coated with PVA film typically reduce workability in the fresh state and compressive strength, capsules coated with Portland cement and sodium silicate mitigate these effects and improve crack sealing in fresh and hardened states without compromising the self-healing capacity of cracks. The three-point flexural test has emerged as the preferred method for a pre-crack assessment over 28 days, with variations depending on the type of healing agent used. As noted in the literature, water has been identified as the optimal environment for autonomous healing. These findings underscore the potential of encapsulation techniques to enhance self-healing capabilities through the controlled release of agents within the cementitious matrix, thereby advancing the research on and development of intelligent construction materials and increasing the durability of cement-based structures.

Performance of Fly ash/GGBFS based geopolymer concrete with recycled fine and coarse aggregates at hot and ambient curing

The incorporation of recycled aggregates in geopolymer concrete (GPC) exhibits higher environmental sustainability due to its ability to utilize industrial by-products and construction and demolition (C&D) waste. This study investigates the combined effect of fine and coarse recycled aggregates on the behavior of GPC. In this research, fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as binder, whereas sodium silicate (Na2SiO3)and sodium hydroxide (NaOH) were used as alkaline activators. Recycled fine aggregates (RFA) were used at 30%, 60% and 100% replacement of natural fine aggregates (NFA) and recycled coarse aggregates (RCA) were used at0%,50% and 100% replacement of natural coarse aggregates (NCA). To study the effect of curing temperature, two types of curing regimes, i.e. hot and ambient curing, were employed. Performance of developed GPC was evaluated in terms of workability, mechanical properties (compressive strength, splitting tensile strength, and flexural strength) and durability properties such as water absorption, sorptivity, resistance against acid attack, resistance against marine environment and electrical resistivity. It was found that the behavior of GPC is improved when the samples were cured at high temperature for 24 hours, as compared to the samples cured under ambient curing conditions. Furthermore, NFA can be replaced up to 100% with NCA, and up to60%in the presence of 50% RCA and up to 30% in the presence of 100% RCA. It was also found that with an increase in the percentage of recycled aggregates, durability performance gradually declined. The results showed that GPC can be developed with inclusion of both recycled fine and coarse aggregates, which can help to preserve valuable natural resources, reduce CO2emission, and dispose C&D waste.

Compressive Strength of Geopolymer Mortar Reinforced with Rice Husk Fibers

Geopolymer concrete has been proposed to minimize carbon dioxide emissions related to the cement production industry. This environmentally friendly material consists of industry waste materials activated chemically by an activation solution. In this study, the geopolymer mortar has been designed with 70% fly ash and 30% metakaolin. Hydroxide sodium in 14 molar concentrations blended with sodium silicate in a 2.5:1 ratio was used as the activation solution. Rice husk fibers were added as reinforcement in (1%, 1.5%, and 2%), and waste paper (paper pulp and paper ash) was added in (1%, 2%, and 5%) by volume of cementitious material. The geopolymer mortar samples underwent a curing process through exposure to a temperature of 60°C in an oven for 24 hours. The findings indicate that the samples reinforced with 2% rice husk fibers exhibited the most significant improvement in compressive strength, with 59% and 55% increases after 7 and 28 days of curing, respectively. In general, using waste paper and rice husk fibers significantly enhanced the compressive strength of geopolymer mortar.

Lanthanum-loaded geopolymer for phosphate removal from agricultural runoff

The removal of phosphate from agricultural runoff is of great importance to mitigate an overabundance of nutrients discharging into receiving water bodies, which are susceptible to eutrophication. In this study, a La-loaded geopolymer was produced by adding metakaolin within an alkaline medium, consisting of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The ratio of Na2SiO3:NaOH within the geopolymer slurry was manipulated to evaluate its effect on phosphate adsorption capacity. The 1.54 ratio yielded the highest adsorption capacity of 33.65 mg g−1. However, due to structural strength, safety, and economic considerations, the 2.0 ratio was used for the isotherm and kinetic adsorption testing. The La-loaded geopolymer exhibited higher phosphate removal in batch adsorption experiments at an acidic level (pH 4) and elevated temperature (40 °C). Moreover, ionic strength (3.5–20 mM) had a negligible impact on phosphate removal, indicating inner-sphere complexation as the main mechanism of adsorption. Additionally, bicarbonate and humic acid increased phosphate removal, whereas sulfate slightly decreased adsorption capacity. The La-loaded geopolymer was further evaluated using a synthetic agricultural solution, which yielded a Type III adsorption isotherm, demonstrating unrestricted multilayer phosphate adsorption. Results from this study verified the La-loaded geopolymer is a promising adsorbent for phosphate removal from agricultural runoff and underlined the importance of matrix effects on treatment performance.

Experimental Study and Analytical Modeling of Tensile Performance of Ultra-High-Performance Concrete Incorporating Modified Recycled Aggregates

Incorporating recycled aggregates (RA) into Ultra-High-Performance Concrete (UHPC) is pivotal for the sustainable development of high-performance construction materials. This study investigates the enhancement of RA through two methods: low-concentration acid treatment and sodium silicate treatment, focusing on improving physical properties and microstructural integrity. Experimental designs encompassed varying types of modified RA (URA, T1RA, T2RA), RA replacement rates (0%, 25%, 50%, 100%), and two steel fiber shapes (SSF and HSF), resulting in twenty-one distinct axial tensile specimen formulations. The study reveals substantial improvements in modified RA's physical properties, effectively mitigating internal microcracks and pores. Modified RA significantly bolstered UHPC-RA's tensile strength, notably when chemically strengthened, underscoring its efficacy in enhancing RA quality. However, escalating RA content correlated with diminished mechanical indices like tensile strength and toughness, attributed to reduced specimen quality. Digital Image Correlation (DIC) accurately forecasted crack locations, highlighting the minimal influence of modified RA and fiber bridging on specimen failure modes. Digital Image Correlation (DIC) technology successfully predicted crack locations, with modified RA and fiber bridging behavior slightly impacting specimen failure modes. A comprehensive theoretical model incorporating RA deterioration and hooked steel fiber anchorage predicted tensile behaviour, offering vital insights for designing UHPC-RA systems.

Influence of Silica Modulus on the Activation of Amorphous Wollastonitic Hydraulic Binders with Different Alumina Content: Study of Hydration Reaction and Paste Performance.

This study investigates how different sodium silicate SiO2/Na2O MS ratios (0.75, 0.9, and 1.2) affect the hydration behavior of amorphous wollastonitic hydraulic (AWH) binders containing various amounts of Al2O3 content (4, 7, 10, and 12%wt). The effects of and interaction between the MS ratio of the activator and the Al2O3 content of the sample on the hydration reaction and paste performance were investigated. The reaction was followed by calorimetry, and the pastes' compressive strength performances were tested at different curing times (2, 7, and 28 days). The hydrated pastes were characterized by FTIR, thermogravimetry analysis, and X-ray diffraction. The calorimetric results show that a higher Al2O3 cContent and a higher MS ratio result in a longer induction period. In terms of paste performance, an increase of the Al2O3 coupled with an activation with a 1.2 MS ratio results in a lower compressive strength after 28 days of hydration; the results range from 76 to 52 MPa. A decrease of the MS ratio to 0.9 allowed the obtention of a narrower range of results, from 76 to 69 MPa. Even though a decrease of the MS ratio to 0.75 led to higher hydration kinetics and high compressive strength results at early ages, at 28 days of curing, a decrease in compressive strength was observed. This may be a consequence of the fast kinetic of the mixture, since the rapid growth of hydration products may inhibit the dissolution at later ages and increase the porosity of the paste. Moreover, the high Al intake in the hydration product, facilitated by the high sodium content of the activator, promotes the formation of a higher number of calcium aluminate silicate hydrate structures (C-A-S-H) to the detriment of calcium silicate hydrate structures (C-S-H), decreasing the compressive strength of the samples. The TGA results indicate that the samples hydrated with the MS075 solution resulted in a higher number of hydrated products at early ages, while the samples hydrated with the MS09 and MS1.2 solutions exhibit a steady increase with curing time. Hence, an equilibrium in the hydration kinetic promoted by Si saturation-undersaturation appears to be fundamental in this system, which is influenced by both the MS ratio and the Al(OH)4- content in solution. The results of this study suggest that for this type of binder, optimal performance can be achieved by decreasing the MS ratio to 0.9. This composition allows for a controlled kinetic and overall higher compressive strength results in pastes produced with this AWH precursor.

Silica extraction from sodium silicate for wollastonite synthesis at low temperatures

In this study, ceramic wollastonite was prepared at low temperatures by using amorphous silica and calcium oxide powders. The amorphous silica was extracted from sodium silicate, while calcium oxide (CaO) was obtained through the calcination of calcium carbonate (CaCO3) particles. The effect of reaction temperature on the formation of wollastonite was systematically investigated. The synthesized powders were analyzed using various characterization techniques, including X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results indicate that the synthesized silica nanopowders exhibit a notable surface area, with specific surface area (SSA) values reaching 148 m²/g for samples subjected to calcination at 600°C. Furthermore, based on XRD and differential scanning calorimetry (DSC) analyses, it is evident that β-CaSiO3 forms at approximately 780°C and subsequently undergoes complete transformation into α-CaSiO3 at 1200°C. Notably, this study underscores that the utilization of amorphous silica expedites wollastonite formation at lower temperatures compared to those reported in existing literature.

A Novel Intumescent MCA-Modified Sodium Silicate/Acrylic Flame-Retardant Coating to Improve the Flame Retardancy of Wood.

The incompatibility between inorganic flame retardants and organic acrylic coatings represents a significant challenge that requires resolution. This work selected environmentally friendly organic aqueous acrylic coatings as the substrate, sodium silicate hydrate as the inorganic flame retardant, and melamine cyanurate (MCA) as the flame-retardant modifier and the flame-retardant co-modifier, with the objective of improving the dispersion and flame-retardant properties of sodium silicate hydrate in the aqueous acrylic coatings. Subsequently, the sodium silicate/MCA/waterborne acrylic acid flame-retardant coating was prepared. The flame-retardant treatment was then applied to poplar veneer in order to create a flame-retardant poplar veneer. The dispersion of the flame-retardant coating was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and X-ray diffractometry (XRD). Furthermore, the flame-retardant properties of the flame-retardant poplar veneer were analyzed by thermogravimetry (TG), limiting oxygen index (LOI), and cone calorimeter. The results demonstrated that the MCA-modified sodium silicate flame retardant was well dispersed in aqueous acrylic coatings. The results of the flame-retardant properties of the poplar veneer indicated that the ignition time of the 9% flame retardant-treated poplar veneer was increased by 122.7%, the limiting oxygen index value was increased by 43.0%, and the peak heat release rate (pHRR), the peak total heat release rate (pTHR), and the peak mass loss rate were decreased by 19.9%, 10.8%, and 27.2%, respectively, in comparison to the non-flame retardant-treated poplar veneer. Furthermore, the residual char mass increased by 14.4%, and the residual char exhibited enhanced thickness, density, and regularity. The results demonstrated that MCA was an effective promoter of sodium silicate dispersion in acrylic coatings. Furthermore, the sodium silicate/MCA/waterborne acrylic flame-retardant coating significantly enhance the flame retardancy of wood, and its flame retardant mechanism was consistent with the synergistic silicone-nitrogen expansion flame-retardant mechanism. This work presents a novel approach to enhancing the dispersion of inorganic flame retardants in organic coatings, offering a valuable contribution to the advancement of research and application in the domains of innovative flame retardant coatings and flame retardant wood.

Nuclear waste glass alteration under the influence of iron, claystone, and cementitious grout: An integral study

To prepare for the future deep geological disposal of high-level waste, the alteration of two inactive nuclear glasses was studied in the presence of claystone, iron, and cementitious grout at 50 °C for a period of 4 years. The materials were immersed together in a synthetic water representative of claystone solution composition. Blank experiments were also carried out to study the independent behaviors of iron and glass in the synthetic water. The evolution of the solutions’ chemistry was monitored. At the end of the experiments, the glass and iron, as well as the neoformed phases, were characterized. Results showed that Si, Ca, Mg, and Fe are key elements. A competition exists between the retention/integration of species into glass gels and clay-like neoformations. Magnesium tends to be leached from glasses and form Mg-silicates. It would only integrate into the gel if it was widely available in the solution. Furthermore, iron could form Fe-silicates. Whether for Mg or Fe, the formation of silicates was detrimental to the glass since it involved the creation of a silicon sink and thus the conservation of a high alteration rate. Concerning calcium, in these experiments it appeared that this species tends to be integrated/retained within the gels. In the pH conditions existing here, it seems that there is no competition with a neoformation. The specific impact of the cementitious grout was also studied, and the results showed that the presence of this material in the system had a beneficial effect on glass alteration due to a significant Si supply in the solution, enabling a reduction in the glass alteration rate.

Eco-Friendly Fungal Chitosan-Silica Dual-Shell Microcapsules with Tailored Mechanical and Barrier Properties for Potential Consumer Product Applications.

Commercial perfume microcapsules are becoming popular across the globe to fulfill consumers' demands. However, most of microcapsules rely on synthetic polymers and/or animal-sourced ingredients to form the shells. Therefore, replacement of the shell materials is imperative to minimize environmental microplastic pollution, as well as to meeting peoples' needs, religious beliefs, and lifestyles. Herein, we report a methodology to fabricate environmentally benign dual-shell (fungal chitosan-SiO2) microcapsules laden with fragrance oil (hexyl salicylate). Anionically stabilized oil droplets were coated with fungal chitosan via interfacial electrostatic interactions at pH 2, which were then covered by an inorganic coating of SiO2 produced via external alkaline mineralization of sodium silicate. Core-shell microcapsules with a spherical morphology were achieved. Under compression, dual-shell chitosan-SiO2 microcapsules yielded a mean nominal rupture stress of 3.0 ± 0.2 MPa, which was significantly higher than that of single-shell microcapsules (1.7 ± 0.2 MPa). After 20 days in neutral pH water, only ∼2.5% of the oil was released from dual-shell microcapsules, while single-shell microcapsules cumulatively released more than 10%. These findings showed that the additional SiO2 coating significantly enhanced both mechanical and barrier properties of microcapsules, which may be appealing for multiple commercial applications, including cosmetics and detergents.

Improving pH buffering capacity of an acid soil to regulate nutrient retention and mitigate water pollution using Calciprill and sodium silicate

In the tropics, high rainfalls and hot temperatures cause the formation of highly weathered acid soils with low pH buffering capacity (pHBC). Such soils are prone to nutrient losses via leaching, surface runoff, and volatilization. The poor nutrient retention of the highly weathered soils can cause environmental pollution in water bodies and detrimentally affect aquatic ecosystem. A preliminary study was conducted by mixing an acid soil (Bekenu series, Typic Paleudults) with Calciprill (80 %, 90 %, and 100 % Ca saturation) and sodium silicate (90, 105, 120, 135, and 150 kg ha−1) to determine the effects of the amendments on pH and pHBC of Bekenu series. Furthermore, a soil incubation study was carried out to determine the relationship between pH, pHBC, and effective cation exchange capacity (ECEC) after the soil was applied with Calciprill and sodium silicate and incubated for 40, 80, and 120 days. After the soil was harvested, the relationship between pHBC with soil exchangeable ammonium (NH4+), available nitrate (NO3-), and available phosphorus (P) to determine whether the combined use of Calciprill and sodium silicate is able to mitigate N and P losses through surface runoff and leaching to contaminate the surface and underground water bodies. The results from the studies showed that Calciprill and sodium silicate significantly increased soil pH and pHBC of Bekenu series. Notably, in the soil incubation study, the treatments with Calciprill and sodium silicate consistently improved pHBC compared with the soil without these amendments, suggesting that C2S4 (Calciprill at 90 % Ca saturation and sodium silicate at 135 kg ha−1) is the minimum amount of the amendments required to improve the pHBC of Bekenu series. The significant positive correlation between pH, pHBC, and ECEC throughout the soil incubation study indicates that the amendments are capable of improving pHBC of the Bekenu series when the pH and ECEC increase because of their alkalinity in addition to the presence of carbonate and silicate minerals. The significant positive correlations between pHBC with exchangeable NH4+ and available P at 40 and 80 DAI suggest that the Calciprill and sodium silicate can improve NH4+ and P availability for crop uptake. On the contrary, the significant negative correlation between pHBC and available NO3- at 80 DAI also suggests that the combined use of amendments can significantly reduce the NO3- contamination in water bodies because of improved pHBC. The most suitable combination for improving soil pH, ECEC, and pHBC is C2S4 (Calciprill at 90 % Ca saturation and sodium silicate at 135 kg ha−1) and it is possible to co-apply Calciprill and sodium silicate to mitigate NO3- contamination in water bodies. To further validate the findings of this study, greenhouse study is recommended to elucidate the plant-soil interactions.

Modification of Coal Fly Ash Waste into Manganese-Oxide-Coated-Zeolite (MOCZ) to Adsorb Heavy Metal Ions Ni2+

High consumption of coal as a source of electrical energy in Indonesia has resulted in piles of waste from coal burning, namely fly ash, which can damage the environment and harm health. Fly ash contains main oxides, namely silica (SiO2) and alumina (Al2O3), whose components are similar to zeolite, so they can be synthesized into zeolite-like material (ZLM) which can be used as an adsorbent for heavy metal Ni2+. Therefore, this research discussed the characterization of manganese-oxide-coated-zeolite (MOCZ) from fly ash waste as a heavy metal adsorbent. The research procedure consisted of preparation, purification, and activation stage of fly ash to obtain fly ash that is free from impurities, the stage of making sodium silicate and sodium aluminate, and zeolite synthesis. The resulting zeolite was then coated with manganese oxide to expand the surface area of the zeolite and increase the ability of zeolite to adsorb heavy metal Ni2+. The research results showed that fly ash waste that was coated with manganese oxide can adsorb heavy metal Ni2+. The adsorption of the Ni2+ metal ion solution by zeolite with MOCZ modification is in line with the pseudo-second-order kinetic and Langmuir isotherm.