29Si NMR Research Articles

Unravelling the incorporation mechanisms of water in aluminous orthoenstatite: II. comprehensive 1H, 29Si and 27Al NMR measurements

AbstractAluminum has been shown to significantly enhance the water incorporation capacity of orthoenstatite (OEn), but the incorporation mechanisms remained to be clarified. We performed a comprehensive one- and two-dimensional 1H, 29Si and 27Al NMR study on four hydrous aluminous OEn samples containing 1–8 wt% Al2O3 synthesized at 1.5 GPa and 900 °C to clarify the issue. The combined 1H MAS and static (non-spinning) NMR, 1H double-quantum and triple-quantum MAS NMR, and 27Al→1H CP MAS NMR and HETCOR results, in particular, unambiguously revealed that a large part of the incorporated water are present as proton pairs in Mg vacancies adjacent to Al, with one proton of each pair for the dominant proton pairs exhibiting significantly weaker hydrogen bonding than those in Al-free OEn. Proton pairs in Mg vacancies remote from Al are minor or absent for samples with 4–8 wt% Al2O3, and more abundant for a sample with 1 wt% Al2O3. Isolated protons due to coupled substitutions of Al + H for 1Si and 2Mg (both with weak hydrogen bonding) were also detected, but are less abundant than hitherto considered. The observed NMR peaks match well with those predicted for the corresponding OH defect models from our first-principles calculations. Thus, the enhancement of water solubility by Al for OEn are due to not only coupled substitutions of Al + H for 1Si and 2Mg, but also interactions of Al with proton pairs in Mg vacancies. These mechanisms may also be important in other nominally anhydrous aluminous silicate minerals.

New Method for the Synthesis of 1,3-Diallyl-1,1,3,3-tetramethyldisiloxane

A new method for the synthesis of 1,3-diallyl-1,1,3,3-tetramethyldisiloxane is proposed that includes several steps: the synthesis of dicellosolvoxy(dimethyl)silane by the transesterification reaction followed by obtaining allyl(cellosolvoxy)dimethylsilane from it under the action of the Grignard reagent and its condensation. The resulting product was characterized by 1H, 13C, and 29Si NMR spectroscopy as well as gas-liquid chromatography. The yield of the product was more than 90%, its purity was 99%.

Wormhole Mesoporous Silica Framework with Enhanced Thiol Loading for Improved Hg2+ Sequestration.

Thiol-functionalized mesoporous silica and materials potentially dedicated to diverse applications of composite materials, metal colloids, and metal catalysts, etc. Here, we developed a new synthesis route for 3-methacryloxypropyl trimethoxy silane (MPTMS) functionalized mesoporous silica (KIT-6), achieving a 71.5 % enhancement in thiol functionalization on KIT-6 surfaces. Characterization using XRD, TEM, BET, FTIR, Raman, 29Si NMR, XPS, and ICP-OES revealed structural and morphological features. XRD, TEM, and BET confirmed the three-dimensional structural stabilization of mesoporous silica with ~4 nm pore diameter and a surface area of 1451 m2 g-1. FTIR, Raman, and 29Si NMR studies established the mechanism of thiol functionalization, the formation of a new wormhole chain structural framework (WCSF), and stabilization through hydrogen bonding within the mesopores. The 29Si NMR spectra showed characteristic peaks (T3, T2, Q4, Q3) indicating self-condensed functionalized thiols with siloxane networks. XPS analysis validated enhanced thiol functionalization, indicating a structurally homogeneous WCSF suitable for mercury adsorption. ICP-OES measured a mercury adsorption capacity of 3199.6 mg g-1 for KIT-6, with an Hg2+/S ratio of 1.8, corroborated by molecular structure and mechanism analysis. This innovative thiol functionalization approach enhances the efficacy of applications such as extracting Hg2+ from contaminated sources.

Pyrene‐Functionalized Silicon Hybrid Porous Polymer for an Efficient Adsorption of Dyes

AbstractPyrene‐functionalized silicon hybrid porous polymer (TAPPy‐HPP). The hybrid polymer was successfully prepared via a Schiff base reaction using tetra(4‐aminophenyl)pyrene (TAPPy) and tetra(4‐formylphenyl)silane (TFS) as the building blocks.. This hybrid polymer was characterized using IR, solid‐state 13C and 29Si NMR, and elemental analysis. Its morphology was analyzed by PXRD and SEM. Thermal analysis using Thermal analysis using TGA shows that the synthetic polymer has greater thermal stability than its monomers at a temperature of 5 % weight loss (Td5 %) of 392 °C. Although TAPPy‐HPP has a Brunauer‐Emmet‐Teller surface area of 45.4 m2 g−1, it adsorbed dyes with high efficiency, particularly the anionic dye Congo Red (CR), with an adsorption capacity of up to 358 m2 g−1. Moreover, TAPPy‐HPP showed excellent recycling and regenerative properties. This polymer is a promising candidate for a fluorescent chemical sensor for the absorption of dyes due to its exceptional physiochemical stability and intense luminescence.

Sodium Alkyl(trimethylsilyl)amides: Substituent- and Solvent-dependent Solution Structures and Reactivities.

The preparation of sodium isopropyl(trimethylsilyl)amide (NaPTA), sodium (1-phenylethyl)(trimethylsilyl)amide (NaPETA), sodium tert-butyl(trimethylsilyl)amide (NaBTA), and isotopologues [15N]NaPTA and [15N]NaBTA are described. Solution structural studies using a combination of 29Si NMR spectroscopy, the Method of Continuous Variations, and density functional theory computations provided insights into aggregation and solvation in a range of solvents including toluene, N,N-dimethylethylamine, triethylamine, MTBE, THF, 1,2-dimethoxyethane (DME), diglyme, N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA). 12-crown-4, 15-crown-5, and 18-crown-6 revealed solvent- and substituent-dependent dimer-monomer mixtures with affiliated solvation numbers. Complexation of the three crown ethers documented both crown and substituent dependencies. Qualitative studies of reactivity showed a variety of reactions of NaPETA. Aminolysis of methyl benzoate with dialkylamines mediated by NaPTA afforded high yields of benzamides. Quantitative rate studies of aminolysis of methyl benzoate by NaPTA revealed a 47,000-fold range of rates. Detailed rate studies in toluene and THF showed dimer-based mechanisms. The role of primary- and secondary-shell solvation by THF is discussed, including nuances of methods used to separate the two contributions. PMDTA-solvated NaPTA monomer reacts as a monomer whereas bis-diglyme solvated monomer reacts as a dimer. Rate studies exploring the structure-reactivity correlations of the three crown ethers show mono- and bis-crown-based pathways in which 15-crown-5─the crown ether often said to be of choice for sodium─was decidedly inferior as an accelerant.

Microstructural characteristics of aluminosilicate minerals in cement clinker prepared from coal gangue, carbide slag, and desulfurization gypsum

Utilizing solid waste to prepare cement clinker with low-calcium minerals is crucial for the low-carbon evolution of cementitious materials. In this study, a belite-ye’elimite-ternesite cement clinker was prepared using coal gangue, carbide slag, and desulfurization gypsum instead of non-renewable resources. The evolution law of the silica-alumina mineral phase in cement clinker under different calcining temperatures was tested and analysed. The results show that the predominant mineral phases in cement clinker consist of belite, ye’elimite, and ternesite at 1200 °C to 1250 °C. The composition of cement clinker transforms into belite and ye’elimite as the calcination temperature increases to 1300–1400 °C. At 1400 ℃, the content of belite in cement clinker reaches a remarkable 85 %. The results of XPS and NMR spectra showed that the chemical binding energy and chemical shift of Al in the cement clinker changed after calcination, representing the transformation of the aluminate in kaolinite, with [AlO6], to ye’elimite, with [AlO4]. The peak fitting results of 29Si NMR spectra semi-quantitatively describe the transition process of the silicate mineral phase from kaolinite to ternesite and then to belite. Morphologically, the increase in calcination temperature leads to a significant enlargement of the grain size of belite in cement clinker. This study can provide a basis for research on the phase regulation of cement clinker composed mainly of low-calcium minerals.

The Influence of Conditions of Polycondensation in Acid Medium on the Structure of Oligosilsesquioxanes with a Novel Eugenol-Containing Substituent.

Eugenol-containing oligoorganosilsesquioxanes were synthesized by the method of hydrolytic polycondensation in an active medium under various reaction conditions. The obtained products were characterized by 29Si NMR spectroscopy and MALDI-TOF spectrometry. It was shown that factors such as the reaction temperature, polycondensation duration, and molar ratio between the initial alkoxysilane monomer and acetic acid may affect the molecular weight characteristics and molecular structure of the formed oligomer, like the content of stressed cyclic units (T3, DTT, TDT) and unstressed silsesquioxane units TnDm. In particular, an increase in the ratio of the initial reagents led to an increase in the content of silsesquioxane Tn fragments from 28.2%mol to 41.7%mol, while the number of strained cyclic structures decreased by more than two times. An increase in the synthesis time is of no particular practical value since it was found that the composition of the oligomers synthesized for 6 h and 12 h was practically identical, as was that of the oligomers synthesized for 24 h and 48 h. A noticeable transition in the oligomer composition was observed only when the synthesis time was changed from 12 h to 24 h. Finally, it was shown that the choice of synthesis temperature had the strongest effect on the oligomer composition. The oligomer synthesized at 95 °C contained the highest amount of silsesquioxane Tn fragments, >77%mol, while a Tn fragment content of ~42%mol was observed during the synthesis at 117 °C. It was shown that silsesquioxanes are devitrified at room temperature (Tg from -6.4 to -10.6 °C), and their thermal stability in an inert atmosphere is 300 °C. The synthesized oligomers, due to the presence of hydroxyl-containing eugenol units, may be promising binders and additives for functional epoxy-silicone paints and coating materials.

Hybrid Dendrimer Network based on Silsesquioxane and Glycidyl Methacrylate for Enhanced Adsorption of Iodine and Dyes in Environmental Remediation.

A novel hybrid network was synthesized in two steps: the first step involved the attachment of glycidyl methacrylate (GMA) to octa(aminophenyl) silsesquioxane (OAPS) through a ring-opening reaction, forming a hybrid dendrimer structure, and the second step involved the cross-linking of hybrid dendrimer using an azobisisobutyronitrile initiator to create the final hybrid network of OAPS-GMA. The synthesized hybrid material was comprehensively characterized using fourier transform infrared Spectroscopy (FTIR), nuclear magnetic resonance ((1H, 13C, and 29Si NMR) spectroscopy, thermogravimetric Analysis (TGA), and scanning electron microscopy (SEM). The BET surface area was found to be 25.44 m2/g, and significant 2.341 cm3/g of total pore volume was observed. The TGA analysis shows that the material is highly stable up to 450 °C. The synthesized network demonstrated remarkable adsorption capacities for iodine and dyes. It exhibited an iodine adsorption capacity of 3.4 g/g from vapors and 874 mg/g from solution. Additionally, it showed significant adsorption capacities for Rhodamine B and Congo red, with values of 762 mg/g and 517 mg/g, respectively. This study not only provides a novel method for preparing GMA-functionalized silsesquioxane-based porous hybrid polymers but also contributes to advancing solutions for environmental pollution issues.

Selective dealumination of large pore Zeolite Beta for effective Brønsted acid site utilization

Tuning of Al sites through spatial and geometric distribution is a novel pursuit for deterministic catalytic performance. To design an efficient Zeolite Beta for phenol alkylation with optimal physicochemical attributes, we conducted a systematic study with a series of dicarboxylic acids to selectively extract the framework and/or non-framework Aluminium. Herein, the post-synthetic treatment resulted in dealuminated catalysts of silicon-to-aluminum ratio ∼15–53. Extensive Al and Si NMR studies glean the selective extraction of aluminum from the zeolitic framework along with recomposition in T sites. The potency study alludes to the convoluted role of pH, chelating ability, and/or site accessibility for complexation. The differentiated Al extraction results in the emergence of unique super-strong acid sites. The novelty of our approach was established using phenol alkylation with cyclohexanol wherein we observed the highest conversion and desired CC alkylated product formation for the malonic acid-treated Zeolite Beta.

Synthesis of Carbosilane Dendrimers with an Amine-Containing Shell Using CuAAC

A new synthetic approach to carbosilane dendrimers bearing amino-containing functional groups in the shell is proposed based on the Cu-catalyzed azide–alkyne cycloaddition. The structures of the resulting compounds are confirmed using 1H, 13C, and 29Si NMR spectroscopy, as well as gel permeation chromatography.

Synergic Effects of Ordered Mesoporous Bifunctional Ionic Liquid: A Recyclable Catalyst to Access Chemoselective N-Protected Indoline-2,3-dione Analogous

SBA-15 and organic ionic liquid were incorporated in a post-grafting technique for generating a bifunctional ionic liquid embedded mesoporous SBA-15. The prepared heterogeneous catalyst was employed for the first time to synthesize N-alkylated indoline-2,3-dione at mild conditions to afford excellent yields in a short reaction time. The synthesized DABCOIL@SBA-15 catalyst was meticulously characterized by various techniques, such as FT-IR, solid-state 13C NMR, solid-state 29Si NMR, small-angle X-ray diffraction (XRD), and N2 adsorption–desorption. Further, the morphological behavior of the catalyst was studied by SEM and TEM. The thermal stability and number of active sites were determined by thermogravimetric analysis (TGA). The Hammett equation was used to analyze the synergetic effect of the catalyst and substituent effects on the N-alkylated products of 5-substituted isatin derivatives, which resulted in a negative slope. This negative slope indicates a positive charge in the transition state. Notably, the DABCOIL@SBA-15 catalyst demonstrated its practicality by being reused for seven cycles with consistently high catalytic activity.

An influence of geothermal water, temperature and pressure on the hydration of multicomponent cement binders

Cement pastes of different compositions were hydrated in a geothermal solution with the simultaneous action of high temperature (150 °C) and pressure (18 MPa) for 7 days. The influence of solution on phase composition and compressive strength of pastes was investigated based on the comparison with hydration in water and using TGA, XRD, FTIR, 29Si, and 27Al NMR. The geothermal solution accelerated hydration and pozzolanic reactions. A higher amount of more thermally stable products was formed. Undesired transformation to crystalline α-C2SH in the samples with the highest C/S ratio was restricted. The uptake of carbonates from the solution led to an increased amount of calcite. As a result, increased compressive strength values were determined. Preferential incorporation of Al3+ into the structure of C-(A-)S-H or hydrogrossular phases depended on the composition of cement pastes.

Catalytic Application of POSS–COF-[(Co(acetate)2] for Selective Reduction of Nitriles to Amines

We report the reticular synthesis and structural investigations through the spectroscopic analysis of a novel polyhedral oligomeric silsesquioxane (POSS)-modified framework, hereby ascribed as a catalyst for the selective reduction of aryl nitriles to amines. The integration of the unique features of the polyhedral oligomeric silsesquioxane with 2,2′-Bipyridine-4,4′-dicarboxaldehyde and subsequently coordination to cobalt acetate manifests a distinctive feature, which is a stable covalent bond between Co and the functionalized POSS, effectively preventing catalyst leaching. The cobalt acetate-modified POSS–COF, synthesized with this approach, underwent a comprehensive characterization employing various analytical techniques including FTIR, XRD, SEM, XPS, TGA, and 29Si NMR. This thorough characterization provides a detailed insight into the structural and chemical attributes of the catalyst. Our catalyst, with its exceptional catalytic efficiency in catalyzing reduction reactions compared to its homogeneous counterparts, and its distinctive three-dimensional metalated POSS system, shows outstanding catalytic performance attributed to its diverse coordination interactions with ligands. Moreover, this catalyst presents additional merits, such as facile recovery and recyclability, making it a promising candidate for sustainable and efficient catalytic processes and thus instilling hope for a greener future.

Synthesis, Structural Elucidation, Density Functional Theory Calculations, In Vitro Antimicrobial, Anti‐Inflammatory and Anticancer Activities of Novel Zn (II)‐Group Fourteen Heterobimetallic Complexes Derived From Schiff Base Ligand

ABSTRACTIn the present work, new heterobimetallic complexes with the general formula [Zn(C16H32N8)M2(R)4Cl2], where M = Sn (IV) and Si (IV) and R = ‐CH3 and ‐C6H5, were synthesized by reacting the methanolic solution of the monometallic complex [Zn(C16H36N8)Cl2] with group 14 organometallic dichloride [(CH3)2SnCl2/(C6H5)2SnCl2/(CH3)2SiCl2/(C6H5)2SiCl2]. The structures of the synthesized complexes were determined using several spectrometric techniques, including FT‐IR, 1H NMR, 13C NMR, 119Sn NMR, 29Si NMR, ESI‐MS, PXRD, and molar conductivity measurements. Density functional theory (DFT) calculations were carried out to investigate the quantum chemical characteristics of the newly synthesized Zn (II) complexes. The antimicrobial potential of the monometallic and heterobimetallic complexes was evaluated against two Gram‐positive bacteria (Bacillus subtilis and Bacillus cereus), two Gram‐negative bacteria (Xanthomonas campestris and Pseudomonas aeruginosa), and two fungal strains (Aspergillus flavus and Fusarium oxysporum) by the agar well diffusion method, with heterobimetallic complex [Zn(C16H32N8)Sn2(C6H5)4Cl2] as the most potent complex against microbes. The complex [Zn(C16H32N8)Sn2(C6H5)4Cl2] exhibited significant potential in inhibiting inflammation, demonstrating an IC50 value of 9.75 μg/mL, which closely rivals that of the standard drug sodium diclofenac (IC50 = 4.59 μg/mL). Furthermore, all the synthesized compounds were assessed for their anticancer potential against three cancer cell lines (HCT‐116, MCF‐7, and HeLa) by the MTT assay. The results indicated that the complex [Zn(C16H32N8)Sn2(C6H5)4Cl2] exhibited the most pronounced cytotoxic effects, with values of 4.25 ± 0.15 μM, 4.90 ± 0.18 μM, and 5.20 ± 0.24 μM observed for HCT‐116, MCF‐7, and HeLa cancer cell lines, respectively.

Pharmacologically significant penta, hexa, and heptacoordinate mono organosilicon (IV) Schiff base complexes derived from phenyl alanine: Synthesis, spectral characterization, antimicrobial, antioxidant, anti-inflammatory, and anti-diabetic studies

Mono organosiliocn (IV) Schiff base complexes 1a-2c derived from phenyl alanine were prepared and characterized. Six new complexes were evaluated in vitro against different bacteria; besides their antioxidant, anti-inflammatory and antidiabetic properties were also tested. Combination of infrared and multinuclear NMR (1H NMR, 13C NMR and 29Si NMR) techniques evidenced the formation of penta, hexa, and heptacoordinated species. The in-vitro antileishmanial study for complexes 1a and 2b against the amastigote stage of the parasite, a mouse macrophage cell line infected with promastigotes expressing luciferase, the IC50 for all tested complexes was lower than that of the miltefosine (standard drug). In antibacterial activity, with the increase in the concentration the zone of inhibition increased. 2c showed the maximum percent inhibition for most number of bacteria which are E. coli (87.50 ± 4.17 %), S. typhi (85.96 ± 3.04 %), S. aureus (70.71 ± 1.75 %), K. pneumonia (7.97 ± 1.26 %) and while 2a and 2b only showed maximum percent inhibition of 77.78 ± 1.92 % and 66.67 ± 2.31 for the bacterium B. subtilis and S. abony respectively at a concentration of 10 mg/ml. Also the methyl silicon (IV) Schiff base complexes showed less antibacterial activity than the ethyl silicon (IV) Schiff base complexes. Pharmacological activities of mono organosilicon (IV) complexes increase with an increase in the number of organo group as well as ligands. 2c possessed the best antioxidant, anti-inflammatory, and anti-diabetic activities.

Desulfurization reactions of thiophene and cyclohexane over Zn and Nb modified zeolites in FCC process

In refineries, one of the most important production units is Fluid Catalytic Cracking (FCC). In them, the incorporation of additives to the catalyst is a very interesting option to reduce the sulfur content of gasoline, and thus obtain commercial fuel specifications. In this study, the transformation of thiophene into a cyclohexane (HC) stream for its in-situ desulfurization has been investigated, using catalysts based on niobium or zinc (6 wt%) incorporated into three types of zeolites: HUSY, HBeta and HZSM-5. Catalytic tests were carried out at 773 K in an automatically controlled fixed-bed tubular reactor. The reaction products were analyzed online by gas chromatography, with FID detector for hydrocarbons and SCD for sulfur compounds, and the catalysts were characterized by XRD, FTIR, N2 adsorption isotherms, HRTEM, XRF, 29Si and 27Al solid state NMR, NH3-TPD and FTIR-pyridine techniques. The results indicate that the addition of metals did not significantly alter the textural and structural properties of the zeolites, and that the Nb/HB and Nb/HY catalysts were the most effective in the conversion of thiophene, and selective toward paraffins and H2S mainly. The performance of these materials was attributed to the existence of an optimal balance between the Brønsted and Lewis acid sites, which increased the hydrogen transfer coefficient (HTC) during the cyclohexane transformation, resulting in higher desulfurization activity. The addition of zinc drastically increased the density of the Lewis acid sites and decreased the HTC, favoring the production of aromatics and thiophene condensation reactions, thus transferring sulfur to the gasoline streams. In general, the catalysts investigated are of significant interest as additives for sulfur reduction in FCC gasoline streams, either by producing easily removable H2S or by transferring sulfur to heavier fractions.

Exploring the reinforcing mechanism of graphene oxide in cementitious materials through microstructural analysis of synthesised calcium silicate hydrate

Graphene oxide (GO) has been shown to enhance the mechanical properties and durability of cementitious materials, although the exact reinforcement mechanism is not fully understood. Given the critical role of calcium silicate hydrate (CSH) in determining these materials' properties, this study investigates the microstructural changes in CSH with the incorporation of GO. Using a co-precipitation method, CSH samples with and without GO were synthesised and characterised through thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and nuclear magnetic resonance (29Si NMR and 1H NMR). The results demonstrated that GO incorporation enhances the polymerisation and crystallinity of CSH, as evidenced by TGA and XRD. FTIR and SEM analyses indicated that the CSH structures became more ordered and denser with GO addition. NMR analysis further confirmed improved structural order and reduced interlayer spacing. Overall, incorporating GO into CSH significantly increases crystallite size and promotes a more ordered CSH structure. These effects collectively result in enhanced load transfer, improved crystal interlocking, and a synergistic improvement in the mechanical properties and durability of cementitious materials.

Insights into Si/Al ratios for enhanced performance of β-zeolites in thermocatalytic cracking of crude oil to light olefins

The escalating demand for key petrochemicals, particularly ethylene and propylene, underscores the critical need for proficient catalysts in crude oil conversion processes. Attaining high propylene selectivity necessitates catalysts with superior adsorption capacity, thermal stability, moderate surface acidity, and pores large enough to facilitate the diffusion of larger crude oil molecules. In the present study, three different BEA Zeolites (β-zeolite) catalysts were successfully synthesized by hydrothermal method and used for catalytic cracking of Arabian Light crude oil to produce valuable petrochemical products, such as propylene, ethylene, and naphtha. The catalysts were characterized using 27Al and 29Si NMR, NH3-TPD, BET, XRD, TGA, FTIR, XRF, and FE-SEM. The thermocatalytic cracking of Arabian Light crude oil was evaluated in a fixed-bed microactivity test (MAT) unit between 550 and 600 °C. The as-prepared β-zeolite with a Si/Al ratio of 50 exhibited better catalytic activity in the catalytic cracking of Arabian Light crude oil compared to counterparts with Si/Al ratios of 35 and 65, This superiority can be attributed to its optimal combination of surface acid site distribution, textural properties, surface morphology, and high adsorption capacity. The highest feed conversion (83.4 %) and selectivity to propylene (16.11 %) were attained using β-zeolite with a Si/Al ratio of 50 at 600 °C. Importantly, our findings suggest that these catalysts hold significant potential, rivalling primary MFI catalysts like ZSM-5 commonly employed in similar reactions. This underscores their promise as catalysts of choice in the realm of catalytic cracking processes, paving the way for advancements in petrochemical production.

Effect of temperature and superplasticizer on hydration of C3S and carbonation products of C-S-H

This study investigated the effect of different C3S hydration temperatures and the addition of superplasticizer on the microstructure of C-S-H and the polymorphy of subsequent carbonation products. Various analytical methods, including XRD, TG, 29Si NMR, and SEM, were employed. The results showed that increasing the hydration temperature elevated the polymerization degree of C-S-H and altered its morphology. This change consequently influenced the polymorphy of carbonation products, primarily calcium carbonates (calcite, aragonite, and vaterite) generated in the subsequent carbonation process. The amount of aragonite and vaterite increased from 5.20 % to 13.39 % as the hydration temperature rose from 20 ℃ to 85 ℃. The addition of naphthalene sulfonate gormaldehyde condensate (NSF) also elevated the polymerization degree of C-S-H and increased the amount of aragonite and vaterite by 4.8–7.35 %. Hydration temperature and NSF are found to be responsible for the different morphology of C-S-H and its carbonation products. Fiber-like C-S-H gels formed at high temperatures are more likely to produce aragonite and vaterite, while foil-like C-S-H gels formed at normal or low temperatures are more likely to generate calcite during carbonation.

Inhibiting efflorescence of alkali-activated slag mortar by improving its hydrophobicity with methyl-terminated polydimethylsiloxane (PDMS): Evidences showing the remained PDMS

This paper proposes to prepare hydrophobic alkali-activated slag (AAS) mortars with methyl-terminated polydimethylsiloxane (PDMS), a hydrophobic polymer with low surface energy, to minimize its water sorptivity and efflorescence. To depict the efflorescence process of PDMS-modified AAS mortars, visual inspections of efflorescence features, the leaching behavior of sodium ions, water absorption characteristics of mortars and contact angle tests were conducted. Additionally, the hydration process, microscopic morphology, and chemical structure of PDMS-modified AAS mortars and pastes were examined by compressive strength, isothermal calorimetry, TEM, SEM, FT-IR, 29Si NMR, enabling the explanation of PDMS working mechanisms. The results demonstrated that the addition of PDMS successfully mitigated esthetic issues and the spalling of mortars caused by efflorescence. Furthermore, PDMS reduced the risk of long-term durability issues of AAS mortars by restricting the loss of sodium ions after efflorescence. At the same time, the introduction of PDMS with dosage below 5 % did not significant retarder the hydration reaction process or the development of strength of AAS. However, it did alter the micromorphology and chemical structure of the hydration product. PDMS linked to the hydration products through covalent bonds and acted as a bridging role to alter the micromorphology of the hydration products. The resulting multi-structured material exhibited micropapillary and nano-coating layers with hydrophobic methyl functional groups, imparting hydrophobicity to the PDMS-AAS hydration product.