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Mung bean is an important pulse crop. It is highly nutritive but is vulnerable to salinity stress. Therefore, the present study was aimed to investigate the protective effect of silicon (Si) against salt stress-induced damage to mung bean plants. Mung bean plants treated with NaCl (0, 50 and 100 mM) showed considerable declines in length and dry weights of shoots and roots. Chlorophyll-a (chl-a), chl-b, total chl, carotenoids and leaf relative water content (LRWC) decreased under NaCl stress. However, supplementation with Si in the form of sodium silicate (Na2SiO3) to NaCl-stressed plants ameliorated the adverse effects of NaCl on growth, biomass, pigment synthesis and leaf relative water content (LRWC). Silicon (Si)-supplemented plants exhibited enhanced chl-fluorescence and gas exchange parameters under normal (non-stress) as well as NaCl stress conditions. Salt-induced decline in the frequency of stomata and number of leaves per plant under salt stress was significantly recovered with Si supplementation. In addition, application of Si increased the levels of proline and glycine betaine in mung bean plants. Furthermore, histochemical staining tests showed that the levels of superoxide radicals and H2O2 increased with NaCl treatments, which thereby resulted in increased lipid peroxidation (LPO) and electrolyte leakage. Contrarily, decreased levels of H2O2, lipid peroxidation (measured as MDA content), and electrolyte leakage in Si-supplemented plants under NaCl stress indicated the stress mitigating role of Si. The activities of key antioxidant enzymes (SOD, CAT, APX and GR) under NaCl stress showed an increase under the NaCl regime. However, application of Si further boosted the activities of all four antioxidant enzymes in NaCl-stressed plants. The enhanced Na+ uptake and Na+/K+ ratio in mung bean plants accompanied by decreased K+ and Ca2+ uptake under NaCl stress were reversed with Si supplementation thereby resulting in enhanced accumulation of K+ and Ca2+ and decreased Na+. In conclusion, Si supplementation mitigated the negative effects of NaCl on mung bean plants through modifications in uptake of inorganic nutrients, osmolyte production and the antioxidant defence system.

Commercial sodium hydroxide (NaOH) and sodium silicate (SS) are commonly used as alkaline activators in geopolymer concrete production despite concerns about their availability and associated CO2 emissions. This study employs an alternative alkaline activator (AA) synthesized from a sodium silicate alternative (SSA) solution derived from rice husk ash (RHA) and a 10 M sodium hydroxide solution. The initial phase established an optimal water-to-binder (W/B) ratio of 0.50, balancing workability and structural performance. Subsequent investigations explored the influence of the alkali/precursor (A/P) ratio on geopolymer concrete properties. A control mix uses ordinary Portland cement (OPC), while ground granulated blast-furnace slag (GGBS)-based geopolymer concrete—GPC mixes (GPC1, GPC2, GPC3, GPC4) vary the A/P ratios (0.2, 0.4, 0.6, 0.8) with a 1:1 ratio of sodium silicate to sodium hydroxide (SS: SH). The engineering performance was evaluated through a slump test, and unconfined compressive strength (UCS) and tensile splitting (TS) tests in accordance with the appropriate standards. The geopolymer mixes, excluding GPC3, offer suitable workability; UCS and TS, though lower than the control mix, peak at an A/P ratio of 0.4. Despite lower mechanical strength than OPC, geopolymers’ environmental benefits make them a valuable alternative. GPC2, with a 0.4 A/P ratio and 0.5 W/B (water to binder) ratio, is recommended for balanced workability and structural performance. Future research should focus on enhancing the mechanical properties of geopolymer concrete for sustainable, high-performance mixtures.

Commonly used alkali activation precursors such as blast furnace slag and fly ash will soon become less available due to resource competition, and may cease to be produced in certain regions. This limitation in future supply is a main driving force for the investigation of alternative precursor sources, such as non-blast furnace slags and non-ferrous slags, to produce alkali-activated binders. The current study investigates the incorporation of copper slag (CS) and stainless steel slag resulting from electric arc furnace operations (EAFSS) as partial replacements for ground granulated blast furnace slag (GGBFS) in producing alkali-activated materials (AAMs), at paste level. Five binary alkali-activated mixtures with different replacement levels of GGBFS with CS, and three ternary mixtures with both CS and EAFSS as partial and total replacements for GGBFS, are activated by a sodium silicate solution. Replacing GGBFS with CS and EAFSS retards the reaction kinetics, resulting in improved fresh-state properties of the investigated AAMs, better retention of workability and longer setting times. The reaction of alkali-activated 100% CS shows minimal initial exothermic activity until 3.5 h, when a single intense peak appears, representing delayed dissolution and subsequent polycondensation. X-ray diffraction (XRD) data indicate that the main crystalline phases of CS and EAFSS are stable in these alkaline systems; it is the glassy components that react. The use of CS and EAFSS in blended AAMs causes a minor increase in porosity of ~ 1–3% with respect to GGBFS only, and a small reduction in compressive and flexural strengths, although these reach 80 MPa and 8 MPa, respectively, after 28 days, even at a replacement level over 65 wt. %. Conversely, the 100% CS mixture exhibits a one-day compressive strength of 23 MPa, with a negligible increase thereafter. This result agrees with both FTIR and SEM analysis which highlight only minor changes in binder development after two days. It is believed that the unusual behaviour of CS in the investigated mixtures is related to the low availability of calcium in this precursor material.

Coal fires are global disasters, and China suffers the most serious coal fire disasters in the world. This paper introduces detailed detection and extinguishing methods for the wide range and complex coal fires at the No. 1 well in the Fukang mining area. First, the characteristics of the large and complex coal fire areas in the No. 1 well in the Fukang mining area are introduced, and 5 large fire areas are detected using the comprehensive detection range method, which detects fire areas before fire engineering practices are implemented. From the characteristics of this large-scale, complex coal fire, the zonal fire extinguishing scheme is formulated, designed, and applied, and the “shallow open fire stripping—construction of the boundary isolation zone—drilling and grouting in the deep fire area” series of events is utilized in the zonal fire extinguishing scheme. A new type of sodium silicate gel in compressive moisturizing plastic packing materials is used, an automatic grouting system is developed, and effective grouting processes are proposed, which can be adjusted according to the grouting effect analysis of the grouting parameters to determine the natural sedimentation and diffusion radius. After the construction was completed, the fire extinguishing effect was tested, revealing that the temperature in the fire zone cooled in a short time, and no subsequent heating phenomenon occurs. The method proposed in this paper provides guidance and a reference for other coal fires in the world.

A number of synthesis parameters directly influence the degree of reticulation/geopolymerisation of metakaolin exposed to alkaline solutions of sodium hydroxide and/or sodium silicate. In the latter case, a sodium silicate solution can be depolymerised by the introduction of an appropriate amount of NaOH. The effects of the ageing of the activator solution on the reticulation of metakaolin-based geopolymers are quantified for the first time in this work. We studied the anionic species of the sodium silicate solution with the addition of NaOH made just before the preparation of the paste, 24 h or 7 days before. These three ageing periods cause a significant difference in the Si-bearing species in solution, as demonstrated by nuclear magnetic resonance on 29 Si. The effect of these anionic species on the reticulation/polymerisation of metakaolin at room temperature was demonstrated by solid-state 27 Al and 29 Si MAS-NMR, the chemical stability in various solutions (deionised water, HCl, HNO 3 , H 2 SO 4 ), and X-ray diffraction on geopolymer powders before and after immersion in acids. Compressive strength before and after the immersion in acidic media was an additional measurement to assess the overall structural stability of the 3D polymerised network of the final dense ceramic-like product. Ageing of the activator solution affected the chemical stability of the hardened geopolymers accompanied by a slight to severe reduction in strength after leaching in HNO 3 or HCl and in H 2 SO 4 , respectively. The quantitative MAS-NMR description of the Si and Al coordination in the geopolymers was correlated with the chemical stability where the formulations with the higher number of Q4(0Al) and Q4(1Al) for the silicon species were more resistant (lower number of Na + compensating for Al +3 to be exchanged with H + ). The formulations with higher Al content in the structure, i.e. higher number of Q4(3Al) silicon species showed higher mechanical stability. These results show that the timing of the preparation of the alkaline activator is essential for a correct mix design.

Lack of vibrations on fresh concrete negatively influences the compaction and thus the quality of concrete. This is particularly concerning with geopolymer concrete (GPC) containing sodium silicate (Na 2 SiO 3 ), which is viscous in nature. In this study, self-compacting geopolymer concrete (SCGC) containing fly ash (FA) and ultrafine slag (UFS) with copper slag aggregates (CSA) was proposed and investigated. CSA were used as a substitute to sand (by weight) in SCGC at different percentages up to 60%. In the fresh state, slump, T500 slump flow, V-funnel, L-box, U-box, and sieve aggregation ratio tests were performed to investigate flowability, passing ability, and viscosity. At the hardened state, the compressive strength, water absorption, chloride ion resistance and sorptivity tests were examined. The flowability of SCGC improved when CSA were added, and the highest slump of 735 mm was achieved for the mix with 60% CSA. Substitution of up to 20% of CSA enhanced the properties of SCGC at all ages. Mix having 20% CSA (20CSA-SCGC) was superior to other mixes, exhibiting the highest compressive strength (47 MPa) at 365 days while possessing the lowest water absorption, sorptivity, and the highest chloride ion resistance. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses also confirmed the improved microstructure of Mix 20CSA-SCGC. Meanwhile, X-ray diffraction (XRD) analysis confirmed the presence of quartz and calcium silicate hydrate (CSH) products, which were the main contributors to properties enhancement.

Natural diatomite, an amorphous siliceous rock, was used as a source of silica for the synthesis of a silicate gel to replace commercial sodium silicate gel in the synthesis of geopolymers from blast furnace slag at room temperature. Nine diatomite gels were synthesized by varying the diatomite content in the gel by 0, 10, and 15% and the NaOH molarity by 6 M, 8 M, and 10 M. The chemico-mineralogical and microstructural characterization results of the elaborated geopolymers showed that the blast furnace slag activation by diatomite gel under optimal conditions (8 M NaOH molarity and 10% diatomite) leads to a good dissolution and polycondensation of the precursor by forming amorphous gels of C-A-S–H type, as well as the mineral phase hydrotalcite, which are the same geopolymerization products detected in the case of the use of conventional silicate gel, and consequently, the obtaining of a geopolymer with interesting physical–mechanical characteristics: compressive strength of 42 MPa, density of 1. 61 g/cm 3 , ultrasonic pulse velocity of 3855 m/s. Thus, this new approach used in this work proved to be successful in reducing the cost and environmental impact of geopolymers.

In the tropics, warm temperatures and high rainfall contribute to acidic soil formation because of the significant leaching of base cations (K+, Ca2+, Mg2+, and Na+), followed by the replacement of the base cations with Al3+, Fe2+, and H+ ions at the soil adsorption sites. The pH buffering capacity of highly weathered acid soils is generally low because of their low pH which negatively impacts soil and crop productivity. Thus, there is a need to amend these soils with the right amount of inorganic liming materials which have relatively high neutralizing values and reactivity to overcome the aforementioned problems. Soil leaching and the pH buffering capacity studies were conducted to determine whether the co-application or co-amendment of a calcium carbonate product (Calciprill) and sodium silicate can improve soil nutrient retention and pH buffering capacity of the Bekenu series (Typic Paleudults). A 30 day soil leaching experiment was carried out using a completely randomized design with 16 treatments and 3 replications after which the leached soil samples were used for a pH buffering capacity study. The Calciprill and sodium silicate treatments significantly improved soil pH, exchangeable NH4+, available P, exchangeable base cations, Effective Cation Exchange Capacity (ECEC), and pH buffering capacity in comparison with the untreated soil. The improvements were attributed to the alkalinity of Calciprill and sodium silicate due to their high inherent K+, Ca2+, Mg2+, and Na+ contents. The neutralizing effects of the amendments impeded the hydrolysis of Al3+ (96.5%), Fe2+ (70.4%), and Mn2+ (25.3%) ions resulting in fewer H+ ions being produced. The co-application of Calciprill and sodium silicate reduced the leaching of Ca2+ (58.7%) and NO3− (74.8%) from the amended soils. This was due to the ability of sodium silicate to reduce soil permeability and protect the Calciprill and available NO3− from being leached. This also improved the longevity of Calciprill to enhance the soil pH buffering capacity. However, the amounts of NH4+, P, and base cations leached from the amended soils were higher compared with the un-amended soils. This was due to the high solubility of sodium silicate. The most suitable combination amendment was 7.01 g Calciprill and 9.26 g sodium silicate (C2S5) per kilogram soil. It is possible for farmers to adopt the combined use Calciprill and sodium silicate to regulate soil nutrient retention and improve the soil pH buffering capacity of highly weathered acidic soils. This will enhance soil and crop productivity.

Ordered macroporous silica particles as a photomaterial transparent solid matrix were synthesized from sodium silicate (Na 2 SiO 3 ) as a silica source and sodium lauryl sulfate (SLS, an anionic surfactant), as a template to form pores via the consecutive sol–gel spray drying. The investigation is carried out in two stages, (1) controlling the particle morphology to obtain a spherical shape and (2) controlling the pore structure. The concentrations of the SiO 2 precursor, carrier gas flow rate, feeding rate, and drying temperature were varied to identify their effects on particle morphology. Spherical and donut-shaped particle morphologies are more prominent when these parameters are used. On the other hand, the addition of SLS to the SiO 2 precursor resulted in controlled macroporous silica particles, depending on the SLS concentration. The deposition of ZnO quantum dots (QDs) on the silica surface stabilizes the optical properties of ZnO by increasing the intensity of photoluminescence (PL) emission and demonstrating excitation-wavelength-dependent photoluminescence. The ZnO/SiO 2 composite particles demonstrated the highest PL intensity with the use of 1 CMC SLS addition and a ZnO concentration of 25% mol, which was almost 30,000 times greater than that of pure ZnO particles. Therefore, an even distribution of ZnO QDs on the silica surface, which is influenced by the silica morphology and its ZnO concentration ratio, can minimize ZnO QDs agglomeration, directly reducing its functional characteristics as a photomaterial.

Background Diatoms, which can accumulate large amounts of carotenoids, are a major group of microalgae and the dominant primary producer in marine environments. Phaeodactylum tricornutum , a model diatom species, acquires little silicon for its growth although silicon is known to contribute to gene regulation and play an important role in diatom intracellular metabolism. In this study, we explored the effects of artificial high-silicate medium (i.e. 3.0 mM sodium metasilicate) and LED illumination conditions on the growth rate and pigment accumulation in P. tricornutum , which is the only known species so far that can grow without silicate. It’s well known that light-emitting diodes (LEDs) as novel illuminants are emerging to be superior monochromatic light sources for algal cultivation with defined and efficient red and blue lights. Results Firstly, we cultivated P. tricornutum in a synthetic medium supplemented with either 0.3 mM or 3.0 mM silicate. The morphology and size of diatom cells were examined: the proportion of the oval and triradiate cells decreased while the fusiform cells increased with more silicate addition in high-silicate medium; the average length of fusiform cells also slightly changed from 14.33 µm in 0.3 mM silicate medium to 12.20 µm in 3.0 mM silicate medium. Then we cultivated P. tricornutum under various intensities of red light in combination with the two different levels of silicate in the medium. Higher biomass productivity also achieved in 3.0 mM silicate medium than in 0.3 mM silicate medium under red LED light irradiation at 128 μmol/m 2 /s or higher light intensity. Increasing silicate reversed the down-regulation of fucoxanthin and chlorophyll a under high red-light illumination (i.e. 255 μmol/m 2 /s). When doubling the light intensity, fucoxanthin content decreased under red light but increased under combined red and blue (50:50) lights while chlorophyll a content reduced under both conditions. Fucoxanthin accumulation and biomass productivity increased with enhanced red and blue (50:50) lights. Conclusion High-silicate medium and blue light increased biomass and fucoxanthin production in P. tricornutum under high light conditions and this strategy may be beneficial for large-scale production of fucoxanthin in diatoms.