Search Results (123)

Based on the acid-sensitive characteristics of SBA-15 during synthesis, this study varied the acid types, pH values, and mixed acid ratios during SBA-15 preparation to enhance the performance of CaO/Cr-SBA-15 dual-functional materials (DFMs) in integrated CO₂ capture and utilization for oxidative dehydrogenation of ethane (ICCU-ODHE). It was found that the SBA-15 support synthesized in an H₂SO₄ environment exhibited a high specific surface area and abundant surface silanol groups, which facilitated the dispersion of Cr and increased the proportion of Cr⁶⁺ active sites, thereby achieving the highest ethane conversion. In contrast, the moderate surface acidity of the HCl-prepared support facilitated the selective dehydrogenation of ethane over Cr active sites, effectively inhibiting side reactions and maximizing ethylene selectivity. Further investigations into the effects of pH and mixed acids revealed that pH 1 is optimal for SBA-15 preparation. At this value, the support reached its maximum mesoporous ordering and specific surface area, allowing for optimal Cr dispersion. Consequently, the ethane conversion, ethylene selectivity, and DFM yield all reached their peak values. Any deviation from this pH led to degradation of the support structure and reduced Cr dispersion, resulting in a significant decline in catalytic performance. Among the tested materials, the CaO/Cr-SBA-15-Cl-S DFM synthesized with an HCl-H₂SO₄ mixed acid demonstrated the superior reactivity, achieving an ethylene yield of 33.95%. Long-term cycling tests indicated that the material possesses good stability, with its performance attenuation primarily attributed to coking and adsorbent sintering. Full article

Titanosilicates are Lewis acid catalysts widely applied in liquid-phase olefin epoxidation; however, in the presence of water, their performance is often limited by structural instability, active-site deactivation, and competing side reactions. This review critically examines hydrophobization strategies—based on controlled reduction in silanol groups or incorporation of organic functionalities—and discusses the experimental approaches used to evaluate surface hydrophobicity, including water adsorption measurements, infrared spectroscopy of silanols, contact angle analysis, and complementary spectroscopic methods. Although direct quantitative comparison among studies is hindered by differences in reaction systems and the lack of standardized catalytic metrics, consistent trends emerge. Lower silanol densities are generally associated with improved preservation of isolated tetrahedral Ti (IV) sites, higher H₂O₂ utilization efficiency, and reduced secondary epoxide ring-opening, leading to enhanced activity and selectivity under comparable conditions. These improvements are attributed to decreased local water activity, suppression of non-productive oxidant decomposition, and stabilization of Ti-peroxo intermediates responsible for direct epoxidation. Incorporation of organic groups produces a similar beneficial effect when introduced in moderate amounts, increasing surface hydrophobicity without significantly perturbing Ti coordination. However, beyond an optimal loading, catalytic performance declines due to pore blockage, diffusion limitations, and partial masking of active sites, revealing a threshold behavior. Fluoride also plays a dual role: when used during synthesis, it influences the insertion and distribution of framework Ti, whereas as a post-treatment, it primarily regulates silanol density and surface polarity while preserving active sites. Finally, hydrophobicity cannot be considered independently, as its impact depends on the solvent, oxidant, olefin nature, and active-site location, which collectively govern activity, selectivity, and catalyst stability. Full article

To enhance the early-age properties of steel slag cement mortar and promote the resource utilization of metallurgical solid waste, in this study, nano-SiO₂ (KH-NS) was modified using a KH550 silane coupling agent. The hydration kinetics and microstructure evolution were systematically analyzed by means of a macroscopic performance test (setting time and compressive strength) and multi-scale microscopic characterization (characterized by Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, X-ray Diffraction, Thermogravimetry-Differential Thermal Analysis, and isothermal calorimetry). The influence mechanism of its content on the early performance of the steel slag cement system was systematically studied. Research findings indicate that at a given dosage, increasing the proportion of KH-NS results in a shorter setting time for steel slag mortar. When the KH-NS dosage reaches 1.5%, the initial and final setting times of steel slag mortar decrease by 24.21% and 21.20%, respectively. The addition of KH-NS effectively enhances the compressive strength of mortar, with a particularly pronounced effect on early strength prior to 14 h of curing. At a KH-NS dosage of 1.5%, the onset of the accelerated phase of hydration heat release in steel slag cement mortar is advanced by 2.5 h. Mechanistic studies indicate that KH-NS accelerates cement hydration by promoting C₃S dissolution and C-S-H gel nucleation through interactions between surface silanol groups (Si-OH) and amino groups (-NH₂). Furthermore, KH-NS refines the pore structure via a micro-aggregate filling effect, reducing the number of harmful pores and improving the pore size distribution. KH-NS continuously consumes Ca(OH)₂ through pozzolanic reactions to generate C-S-H, with its reactivity increasing with higher dosage. Research confirms that KH-NS significantly enhances the early strength and density of steel slag mortar, providing both theoretical justification and technical support for developing low-carbon building materials based on solid waste with high dosage. Full article

Linalyl acetate is a key bioactive component of essential oils with notable calming and sedative effects; however, its high volatility severely limits stability and practical application. Herein, bimodal mesoporous silica (BMMs) was employed as an efficient carrier to encapsulate linalyl acetate using liquid- and gas-phase loading strategies, enabling high loading capacity and sustained release. Under optimized gas-phase conditions (600 mg·mL⁻¹, 85 °C, 2 h), a maximum loading capacity of 80.13% was achieved. The X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) patterns, scanning electron microscopy (SEM) images, N₂ adsorption–desorption isotherms, Fourier transform infrared (FT-IR) spectra, and thermogravimetric (TG) performances confirmed the successful confinement of linalyl acetate within the bimodal mesoporous channels. Particularly, the SAXS patterns revealed the pronounced fractal characteristics, whereas the increased mass-fractal dimension (D_m) values indicated the enhanced structural compactness, and higher surface-fractal dimension (D_s) values reflected increased surface roughness upon loading. Release experiments conducted in an open environment demonstrated an excellent sustained-release performance, with only 22.41% of linalyl acetate released from BMMs over 30 days, compared with 94.41% for the free compound. Molecular dynamics simulations further elucidated that the interactions between linalyl acetate molecules and surface silanol groups dominated the adsorption process and governed diffusion within the mesoporous channels. These findings suggested that BMMs provide a robust platform for stabilizing volatile fragrance compounds and achieving long-term controlled release. Full article

The inadequate biosafety of MRI contrast agents (CAs) remains a challenging issue. Both increasing the magnetic relaxivity of CAs and targeting them through conjugation with folates are promising approaches to addressing this issue. Silica nanoparticles (SNs) with Mn²⁺ ions specifically localized in the outer layer were selected as the target for further surface modification for the covalent attachment of folates. It was shown that when Mn-containing SNs are conjugated with folates via preliminary amino modification of the surface silanol groups, the folate-conjugated SNs suffer from colloidal instability. Thus, precoating Mn-containing SNs with unfolded BSA exposes surface amino groups that successfully conjugate with folates without loss of colloidal stability. Partial washout of surface-localized Mn²⁺ follows folate conjugation of Mn-containing SNs, although residual Mn²⁺ ions provide r₁₍₂₎ relaxivities of 62.1 (160.4) mM⁻¹s⁻¹ at 0.47 T. Full article

Colloidal solutions containing silica-coated silver nanoparticles (Ag@SiO₂) were synthesized through a two-step process integrating physical and chemical mechanisms. In the first step, laser ablation of a silicon target submerged in deionized water generated an H₂O–SiO₂ colloid, termed the as-cast colloid. This contained nanometric SiO₂ particles alongside micrometer-sized or larger silicon fragments produced by laser shockwave-induced target surface fragmentation. To refine particle size distribution and elevate nanometric SiO₂ concentration, the as-cast colloid underwent secondary laser irradiation, effectively fragmenting larger particles. The second step involved adding ionic silver to both as-cast and irradiated colloids, yielding Ag@SiO₂ nanoparticles. Structural properties were probed via XRD and TEM; optical characteristics via UV–Vis spectroscopy; and electrophoretic mobility via zeta potential measurements, both pre- and post-silver incorporation, to elucidate irradiation’s influence on synthesis. For controlled agglomeration, AlCl₃ was used to modify surface charge, neutralizing silanol groups on the silica shell and minimizing electrostatic repulsion through aluminum ion interactions. These findings demonstrate tunable Ag@SiO₂ colloids with precise surface properties for future development of advanced nanomaterials suitable for microbicidal applications. Full article

To address the challenges of difficult recovery, significant environmental hazards associated with homogeneous catalysts, and insufficient catalytic activity of heterogeneous supports in the catalytic dehydration of fructose to produce 5-hydroxymethylfurfural (5-HMF), this study employs a straightforward nitric acid modification method to prepare an acid-activated silica gel catalyst for application in this reaction system. Through systematic investigation of the influence of modification conditions on catalyst performance and economic benefits, optimal reaction conditions were determined: DMSO as the solvent, nitric acid-modified silica gel as the catalyst, a reaction temperature of 120 °C, a solid–liquid ratio of 1:30 (g∙mL⁻¹), and a fructose-to-catalyst mass ratio of 1:1. Under these conditions, the maximum 5-HMF yield reached 91.6%. Characterization via specific surface area, pore size analysis, and acid/base site characterization (NH₃-TPD) revealed that nitric acid modification preserved the silica gel’s pore structure. Through oxidative cleaning, etching to expose silanol groups, and inducing surface defects, this process significantly increased the number of acid sites on the silica gel surface, thereby enhancing catalytic activity. This study presents a low-cost, easily recoverable, and environmentally friendly heterogeneous catalytic strategy for the efficient conversion of fructose into 5-HMF. It also provides experimental guidance for the targeted functionalization of silica-based catalytic materials, holding significant implications for advancing the high-value utilization of biomass resources. Full article

This study investigates the effect of sodium-silicate-based chemical surface modification of polypropylene (PP) fibers on the mechanical and fresh-state properties of cementitious composites. The proposed method introduces silanol and siloxane groups onto the PP surface through a radical-assisted chlorination route, aiming to enhance fiber–matrix interfacial bonding. Modified fibers increased the polycarboxylate ether (PCE) demand by 100% compared to the control mixture, while unmodified PP fibers caused a 58% increase at equivalent workability. The incorporation of PP fibers resulted in limited changes in compressive strength (1-7%), whereas silicate-modified fibers led to notable late-age flexural strength gains of 10% (28 days) and 17% (56 days). Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed successful surface functionalization, while the heterogeneous silicate deposition still contributed positively to interfacial transition zone (ITZ) performance. Overall, sodium-silicate-modified PP fibers improve flexural behavior and interfacial bonding in cement-based systems, offering a promising approach for enhanced mechanical performance and sustainability. Full article

The contamination of water bodies by dye effluents from micro-scale in-house denim laundries remains a significant environmental concern in central México, particularly in the Atoyac River, where conventional treatment methods are not economically viable. This study develops and evaluates Nylon-6/pumice powder (PPw) nonwoven composites as hybrid adsorptive membranes for the removal of methylene blue (MB) from aqueous solutions. Pumice, a locally abundant siliceous mineral, was incorporated into Nylon-6 through melt-compounding and melt-blown fiber processing at 1 wt% and 5 wt% loadings. SEM, XRD, and TGA confirmed even filler distribution, structural stability, and the development of a porous, layered structure. Batch adsorption tests revealed a rapid initial dye adsorption, followed by a slower diffusion-controlled phase, with equilibrium achieved within 15 min for PPw and within 30 min for the composites. The data fitted both Langmuir and Freundlich isotherms, indicating that MB adsorption involved a combined mechanism: monolayer adsorption on uniform silanol/aluminol sites and multilayer physical adsorption at the polymer–mineral interfaces. Higher PPw content increased adsorption capacity (q_max = 1.1460 mg/g) and surface uniformity, resulting in favorable Freundlich exponents (n = 2). Finally, it was found that adsorption proceeds via chemisorption, where the pumice powder provides reactive sites. These findings demonstrate that Nylon-6/PPw nonwoven composites combine the strength of a synthetic material with the surface reactivity of a natural mineral, providing an effective and scalable Nature-Based Solution for decentralized dye removal, aligned with Sustainable Development Goals 6 and 12. Full article

The surface modification of coal fly ash (CFA) with silane coupling agents improves its compatibility with polymer matrices and supports its use as a sustainable filler in composite materials. This study examined the effects of the solvent system, reaction temperature, and pH on the grafting of 3-aminopropyltriethoxysilane (APTES) onto CFA surfaces. Functionalization was assessed by Fourier-transform infrared spectroscopy (FTIR), focusing on the CH₂ symmetric and asymmetric stretching bands of pure APTES at 2919 and 2957 cm⁻¹, noting that a slight shift in these bands can be expected following the change in the local chemical environment upon grafting. Solvent mixtures containing water (ethanol/water, acetone/water, and sulfuric acid/water) produced stronger coupling than the toluene solvent, which indicated the importance of water for APTES hydrolysis and silanol formation. Coupling efficiency increased with temperature and reached a maximum at 80 °C, where the balance between hydrolysis and condensation favored the formation of stable Si–O–Si bonds. The highest degree of functionalization was observed at pH 9, which corresponds to the point of zero charge of alumina in CFA, where neutral surface hydroxyl groups were available to react with silanols. These results define the optimal conditions for APTES grafting onto CFA and demonstrate its potential as a silane-modified filler in polymer composites. Atomic force microscopy (AFM) provided direct visual evidence of significant surface texture modifications induced by APTES treatment in the ethanol/water solvent system. Full article

Late-Archean seawater functioned as a vast, redox-tuned colloidal system for which its kinetics were largely governed by the surface chemistry of silica–iron nanoparticles. By reproducing Archean seawater (≈0.7 M ionic strength, 25 °C) in laboratory anoxic-to-mildly oxic reactors, the ζ potential (zeta-potential(ζ)) of silica–iron nanoparticles was investigated, and we tracked how transient O₂ pulses (≤9 mg L⁻¹) regulated it. The zeta (ζ) potential was applied as the key diagnostic parameter to quantify both the sign of the ζ potential and the colloidal stability of simulated silica–iron particles in dispersion. Under strictly anoxic conditions, silica colloids (SiO₂(aq)) exhibit a persistently negative ζ potential (ζ ≈ −25 mV) in the simulated seawater (pH 6.5), arising from deprotonated silanol groups (≡Si–O⁻). Upon the addition of Fe²⁺, the inner-sphere complexation of ferrous ions on SiO₂ colloids partially replaces ≡Si–O⁻ with ≡Si–O–Fe⁺/≡Si–O–Fe–OH sites; the net negative charge density at the outer Stern plane nevertheless increases, and the ζ potential shifts from −25 mV to −30 mV. As the simulated seawater was oxygenated, the dissolved and surface-bound Fe²⁺ ions were oxidized to Fe³⁺, causing the ζ potential to exceed −30 mV. This study demonstrates that Fe²⁺–silica interactions generate electrostatic destabilization, suspending micron-scale aggregates and thus modulating the solubility and speciation of SiO₂ in early oceans. Also, transient micro-oxic pulses are shown to shift silica–iron colloids between metastable aggregation and dispersion by modulating their ζ potential. Subsequently, AFM and TEM were used to characterize the morphological changes in the colloidal particles from the liquid state to the dry state. Furthermore, infrared and XPS analyses were conducted on the colloidal samples. These findings provide certain reference significance for reconstructing the chemical evolution process of seawater in the Late-Archean period and for understanding the factors influencing the silicon–iron cycle of seawater in the Late-Archean era. Full article

In this study, four types of Fe₃O₄-based magnetic nanospheres were functionalized with distinct surface groups to examine how surface chemistry influences their co-transport with tetracycline (TC) in porous media. The functional groups investigated are carboxyl (−COOH), epoxy (−EPOXY), silanol (−SiOH), and amino (−NH₂). Particles bearing −COOH, −EPOXY, or −SiOH are negatively charged, facilitating their transport through porous media, whereas −NH₂-modified particles acquire a positive charge, leading to strong electrostatic attraction to the negatively charged TC and quartz sand, and consequently substantial retention with reduced mobility. Adsorption of TC onto Fe₃O₄-MNPs is predominantly chemisorptive, driven by ligand exchange and the formation of coordination complexes between the ionizable carboxyl and amino groups of TC and the surface hydroxyls of Fe₃O₄-MNPs. Additional contributions arise from electrostatic interactions, hydrogen bonding, hydrophobic effects, and cation–π interactions. Moreover, the carboxylate moiety of TC can coordinate to surface Fe centers via its oxygen atoms. Molecular dynamics simulations reveal a hierarchy of adsorption energies for TC on the differently modified surfaces: Fe₃O₄-NH₂ > Fe₃O₄-EPOXY > Fe₃O₄-COOH > Fe₃O₄-SiOH, consistent with experimental findings. The results underscore that tailoring the surface properties of engineered nanoparticles substantially modulates their environmental fate and interactions, offering insights into the potential ecological risks associated with these nanomaterials. Full article

The contamination of water resources with heavy metals creates problems for using it as a source of drinking water. Adsorption is one of the most promising methods for heavy metal ion removal from natural and wastewater. The process of removing copper (II) from aqueous solutions using SiO₂ xerogel as an adsorbent has been studied. The xerogel was thoroughly characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and argon adsorption–desorption isotherms, revealing an amorphous structure with a high surface area (~347 m²/g) and uniform mesoporosity (2–14 nm pore size). The surface chemistry, dominated by silanol groups, was confirmed by XPS analysis. The adsorption process is influenced by electrostatic interactions between the positively charged Cu(II) ions and the negatively charged surface groups, with the optimal performance near neutral pH. Batch adsorption experiments demonstrated that the silica xerogel effectively removes Cu(II) ions from aqueous solutions, with removal efficiency exceeding 99% at pH values above 4.0. The maximum adsorption capacity of copper (II) ions on SiO₂ xerogel is 67.5 mg/L. Full article

Two nitrogen-modified mesoporous MCM-41-type silicas were synthesized by the sol–gel route and post-grafting surface modification procedure, obtaining an aminopropyl-modified MCM-41 (denoted MCM-41-N) and an aminoethyl-aminopropyl-modified MCM-41 (denoted MCM-41-NN). Hexavalent chromium removal from acidified water by adsorption and reduction to Cr(III) on the solid mesophases was analyzed. The modified silicas were characterized by powder X-ray diffraction (XRD), Fourier transformed infrared spectra (FT-IR), nitrogen adsorption–desorption measurements at −196 °C, X-ray photoelectron spectroscopy (XPS), ²⁹Si solid state Nuclear Magnetic Resonance (²⁹Si-RMN), and thermogravimetric analysis (TGA). Both samples exhibited very high capacities for decreasing Cr(VI) concentrations in water, according to the Langmuir isotherm model: 129.9 mg·g⁻¹ for MCM-41-N and 133.3 mg·g⁻¹ for MCM-41-NN. The chromium speciation in the supernatant after 24 h indicates that MCM-41-N had a higher capacity to reduce Cr(VI) to the less toxic Cr(III) species than MCM-41-NN: 92.9% vs. 72.5% when the initial Cr(VI) concentration was 10 mg·g⁻¹. These differences were related to the different capacity of nitrogen atoms in MCM-41-N and MCM-41-NN to interact with the surrounding surface silanols which are required for the chemical reduction in the hexavalent species to take place, as evidenced by FT-IR and XPS analysis. Also, the Cr(III)/Cr(VI) atomic ratios on the solid’s surfaces were higher for MCM-41-N. These results highlight the characteristics that nitrogen atoms incorporated into silica matrices must possess in order to maximize the transformation of Cr(VI) into the trivalent species, thereby reducing the generation of toxic waste harmful to living organisms. Full article

The selective dehydrogenation of ethanol to acetaldehyde is an efficient alternative to biomass valorization. Herein, a series of Cu catalysts supported on Silicalite-1 zeolites with tunable contents of surface silanols and the same Cu loading of 3 wt% were synthesized by an impregnation method. The parent Silicalite-1 supports and as-synthesized Cu/S-1 catalysts were characterized by N₂ adsorption, XRD, SEM, TEM, TGA, DRIFT, ²⁹Si MAS NMR, XPS, and TPR. The Cu dispersion and Cu species distribution of Cu/S-1 catalysts can be modulated by engineering the amount of silanol groups on the support. More silanols present on the surfaces of parent Silicalite-1 supports can promote the Cu dispersion, and lead to a higher Cu⁺/Cu⁰ molar ratio arising from strong interfacial interaction between Cu species and silanols on the Silicalite-1 support via the formation of Si-O-Cu bonds. Thus, higher catalytic activity is achieved. Full article