Three-dimensional Mesoporous Silica Research Articles

Sulfonated mesoporous TUD-1: An innovative environmentally friendly solid acid catalyst for various organic transformations

TUD-1, a novel sponge-like three-dimensional mesoporous silica material, was synthesized in one-step using a hydrothermal technique and triethanolamine as a template. To enhance its acidic properties, the TUD-1 material underwent sulfonation with varying amounts of sulfonic groups (1 and 3 wt%). Structural characteristics were determined using XRD, FTIR, Raman, BET analysis, HRTEM, SEM, and XPS. Surface acidities of the catalysts were evaluated through non-aqueous potentiometric titration and FTIR analysis of chemisorbed pyridine. The performance of catalysts was assessed in various reactions, including the Pechmann reaction, Friedel-Crafts acylation reaction, and Biginelli reaction for synthesis of 7-hydroxy-4-methyl-2H-chromen-2-one, aromatic ketones and 3, 4-dihydropyrimidin-2(1H)-one. The findings confirm that the TUD-1 mesoporous structure did not undergo any significant alteration post sulfonation. The sulfonated catalysts exhibited higher surface acidities than TUD-1. A correlation between surface acidity, particularly Brönsted acid sites, and catalytic efficiency in selected reactions was evident from both catalytic testing and characterization. Under moderate conditions, TUD-1-3SO3H exhibited outstanding catalytic performance and remarkable reusability across all selected reactions.

A green synthesis method of a mussel-inspired polyphenol-functionalized silica-based material and its highly efficient adsorption of gallium

Three-dimensional mesoporous silica is a distinctive nanomaterial celebrated for its unique structure, substantial specific surface area, enhanced utilization of active surfaces, and improved adsorption and catalytic reaction capabilities. Nevertheless, its limited surface functional groups often impede its effective ion adsorption capacity. Here, inspired by the mussel-adhesive phenomenon, in this study, we introduced a straightforward layer-by-layer assembly approach to fabricate a new series of KIT-6@x-catechol/polyethyleneimine composites, the catechol/polyethyleneimine is the shell and KIT-6 is the core. Importantly, catechol(CA) and polyethyleneimine(PEI) polymers as selective layers with dense structures and abundant cation exchange groups, resulting in outstanding adsorption performance for our material. At a pH of 3.0, Ga(III) exhibited a maximum adsorption capacity of 88.65 mg g−1 on the adsorbent. Furthermore, the adsorbent demonstrated selective adsorption capabilities for Ga(III) over Ge(IV), Al(III), Cu(II), Zn(II), and Co(II). The primary adsorption mechanism of KIT-6@x-CA/PEI is chelation that occurs through coordination between the O atom on the phenolic hydroxyl group of CA and Ga3+, Ga(OH)2+, Ga(OH)2+ under pH 3.0 conditions. In summary, the synthesized KIT-6@x-CA/PEI exhibits significant potential for water treatment containing Ga(III) through adsorption processes.

Green extraction of uranium (238U) from natural radioactive resources

Numerous strategies have been devised to effectively extract uranium (U[VI] or 238U) from raw materials because it is a significant energy source. This study focused on the highly selective extraction of 238U isotopes from altered granite rock (AGR) utilizing bio-absorbents/extracts from Three-dimensional mesoporous silica monoliths (MSMs), which have been successfully created from affordable and sustainable resources like rice husk (RH). The MSMs exhibited micrometric particle sizes, mesoscopic hexagonal geometry, and irregular nano/microspace voids and grooves along their surfaces. To establish specific binding sites for the extremely selective adsorption/trapping/capturing of ultratrace levels of 238U isotope at pH 3, the MSMs were modified with (2-diethylphosphatoethyl) triethoxy silane chelating agent. Considering that the spent adsorbent/extractor could be recycled/regenerated by using H2SO4 as a stripping agent, the recycled bio-adsorbents could be reused several times with high retention efficiency. The isotherm, kinetic models, and thermodynamic parameters of U(VI) extraction were investigated to describe the nature of adsorption between the bio-adsorbents/extractors and adsorbate species. Results indicated that the MSM and MMSM biosorbents were promising effective extractors for 238U isotopes due to (i) their natural sources; (ii) their contribution to the management of RH waste; (iii) their low cost and eco-friendliness; (iv) their high efficiency, sensitivity, selectivity, and capacity for the target ions; (v) their minimization of waste volume by enabling multiple reuse/cycles; (vi) and their retention of structural performance for several reuse/cycles that resulted in a cost-effective extraction/capture process. Our proposed natural, sustainable porous material and efficient approach might enable the efficient extraction of uranium species from different resources and the appropriate exploitation of natural/agro-waste for clean energy production.

Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by palladium(II) isatin Schiff base complex supported into three-dimensional mesoporous silica KIT-6

In this work, the catalytic activity of a palladium(II) isatin Schiff base complex immobilized into mesoporous silica KIT-6 (Pd-isatin Schiff base@KIT-6) was studied for the oxidation of different alcohols with tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as an oxidant under solvent-free conditions. To find the suitable reaction conditions, the effect of essential factors including the solvent, temperature, catalyst amount and kind of oxidant on the oxidation of benzyl alcohol was explored. The results showed that in this catalytic system, the corresponding aldehydes and ketones were obtained with high to excellent yields at 50 °C without the formation of carboxylic acids as by-products. The catalyst was easily recovered by simple filtration and reused in five subsequent reaction cycles without any significant loss in the catalytic activity. Moreover, the comparison of the Fourier transform infrared (FT-IR) spectrum, X-ray diffraction (XRD) pattern, scanning and transmission electron microscopy (SEM and TEM) images of the used catalyst with a fresh one showed that the structure of the Pd-isatin Schiff base@KIT-6 catalyst remained intact after five times of reuse.

One-pot synthesis of glycerol carbonate from glycerol using three-dimensional mesoporous silicates of K/TUD-1 under environmentally benign conditions

In the present study, a series of potassium (K) incorporated three-dimensional mesoporous silica material (K/TUD-1) has been synthesized for the one-pot synthesis of glycerol carbonate through transesterification of glycerol with dimethyl carbonate (DMC). The synthesized catalyst (K/TUD-1) has been characterized to confirm porosity by nitrogen adsorption-desorption isotherm, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Small-angle XRD revealed that TUD-1 is mesostructure in nature. Morphology study revealed that TUD-1 exhibited a 3D structure without any agglomeration. The surface area of bare TUD-1 significantly declined with the incorporation of active metal from 632 m2/g to 430 m2/g. However, the basicity of K/TUD-1 improved, which is a highly desired property for the transesterification reaction. Batch experimental results have been concluded that 7% K/TUD-1 has better catalytic activity for the conversion of glycerol to glycerol carbonate. Further investigation has been conducted on the influence of reaction parameters such as reaction temperature, reaction time, catalyst dosage, and DMC/glycerol molar ratio. Under optimized conditions the maximum glycerol carbonate yield (∼91.50 %) was observed with catalyst dose of 6 wt.% (of glycerol mass), DMC/glycerol molar ratio of 5, reaction temperature of 90 °C in 2.5 h. Further, catalyst feasibility was also conducted at optimized conditions, and it sustains activity up to 4 cycles. The kinetics of the reaction was studied using the ODE 15 s solver in MATLAB.

Efficient, selective and mild oxidation of sulfides and oxidative coupling of thiols catalyzed by Pd(II)-isatin Schiff base complex immobilized into three-dimensional mesoporous silica KIT-6

In this study, a palladium(II)-isatin Schiff base complex immobilized into three-dimensional (3D) mesoporous silica KIT-6 (Pd-isatin Schiff base@KIT-6) was synthesized and characterized by various techniques including inductively coupled plasma (ICP) and Fourier transform infrared (FT-IR) spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) technique and thermal gravimetric analysis (TGA). This new heterogeneous catalyst was successfully employed for the selective oxidation of sulfides to sulfoxides with tert-butyl hydroperoxide (tert-BuOOH) and oxidative coupling of thiols into corresponding disulfides using 30% H2O2 at room temperature. The products were obtained in good to excellent yields and no over-oxidation of sulfoxides and disulfides was observed. This catalytic system could also be applied for the chemo-selective oxidation of sulfides and thiols in the presence of other functional groups. The studied catalyst can be recovered easily by a simple filtration and reused five times in both oxidation reactions without a remarkable decrease in catalytic activity.

Improving the synthesis of Zn-Ta-TUD-1 for the Lebedev process using the Design of Experiments methodology

The synthesis method of a zinc-tantalum catalyst supported on three-dimensional mesoporous silica with high specific surface area was studied. Its activity in the conversion of ethanol to butadiene was optimized using the Design of Experiment approach. A Plackett-Burman screening design identified the important preparation parameters, notably the ratio of Zn to Ta. It was subsequently optimized using the Response Surface Methodology, affording a highly active catalyst.

Trimetallic Catalyst Supported Zirconium-Modified Three-Dimensional Mesoporous Silica Material and Its Hydrodesulfurization Performance of Dibenzothiophene and 4,6-Dimethydibenzothiophene

To prepare the highly active hydrodesulfurization (HDS) catalyst, modified Zr-KIT-5 materials were synthesized by in situ synthesis method and supported NiMoW trimetallic active phases for dibenzot...

Enhanced Olefin and CO2 Permeance Through Mesopore-Confined Ionic Liquid Membrane

Nanocomposites of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4), in three-dimensional mesoporous silica (KIT-6) were fabricated and utilized as mesopore-confined ionic liquid membranes for Olefin and CO2 Separation. Compared to neat BmimBF4, the fabricated membrane showed 10-times-enhanced gas permeation property for olefin separation, and 5-times-enhanced gas permeation property for CO2 separation with gas-selectivity remaining unchanged. Moreover, the enhanced diffusion-limited current density of the electrochemical cell involving I-/I3- redox couple in BmimBF4/KIT-6 nanocomposite was observed. This implies that mesoporous KIT-6 can be used as an effective additive in nanocomposite membranes for enhanced olefin and CO2 permeance.

Three-dimensional mesoporous silica networks with improved diffusion and interference-abating properties for electrochemical sensing

One of the key issues of electrochemical sensing in complex matrices is the presence of interferents which can foul the electrode and block the access to the active surface. A possible strategy to promote selectivity is based on the use of interference-abating layers, which can however significantly hamper the sensor response by limiting the analyte diffusion. Here, hard template mesoporous silica films with pore size in the 20–75 nm range and tuneable thickness, deposited onto conductive ITO substrates, were prepared and studied from the physicochemical (FE-SEM, SEM, AFM, water contact angle determinations, UV–vis spectroscopy) and the electrochemical (CV, EIS) point of view. Pore size dependent diffusion phenomena were observed, giving rise to enhanced electrochemical performance for 20–40 nm pores despite the presence of an insulating layer at the electrode surface. The tuneable morphology of the samples together with the wetting properties were found to be pivotal for the understanding of the electrochemical behaviour. The best performance was obtained for the samples with the 20-nm porosity and the highest film thickness. These results were also confirmed by EIS data elaboration, able to provide quantitative measurements about the mass transport resistance of the pores. The modified electrodes were tested for dopamine detection in the presence of a large interfering protein (mucin). The porous and charged network allowed the interfering macromolecule to be excluded, preventing the electrode biofouling and enhancing the performances of the device towards dopamine detection.

Development of Ca/KIT-6 adsorbents for high temperature CO2 capture

The incorporation of CaO into an inert porous solid support has been identified as an effective approach to improve the stability of adsorbents for CO2 capture. In this work, we focus on enhancing the capacity of carbon capture and cyclic stability of CaO by impregnating CaO particles into a three-dimensional mesoporous silica (KIT-6) support. At a low CaO loading, the three-dimensional mesoporous support was filled with CaO nano-particles. The further increase of CaO loading resulted in the aggregation of CaO particles on the external surface of the support material, as identified by electron microscopy analysis. These CaO/KIT-6 adsorbents show excellent high-temperature CO2 carbonation/calcination stability over multiple cycles of CaO carbonation and calcination. The enhancement of the performance of carbon capture is attributed to the interaction between CaO and the silica skeleton of KIT-6 through the formation of interfacial CaSiO3 and Ca2SiO4 which enhanced the resistance of CaO sintering.

Nanostructured TiO2/KIT-6 catalysts for improved photocatalytic reduction of CO2 to tunable energy products

Nanostructured TiO2/KIT-6 catalysts with different concentrations of incorporated TiO2, have been synthesized, characterized, and examined in order to improve the photocatalytic reduction of carbon dioxide (CO2) feedstock with water vapor (H2O) to produce tunable value-added energy products. Nanostructured TiO2, dispersed on KIT-6 (three-dimensional mesoporous silica), was found to be present in both the silica framework and on the surface, where it produced large surface area photocatalysts with enhanced adsorption capability of the reactants to photocatalytically convert into CH4, CH3OH (hydrocarbons) and CO, H2 (similar to syngas). The formed products were influenced directly by the dispersed TiO2 concentration as well as by the calcination temperature. Hydrocarbon and CO formation as well as the reaction kinetics improved as the TiO2 concentration was increased from 1 to 20wt%. However, a further increase in TiO2 loadings (to 90%) decreased the hydrocarbon and CO, and increased H2 formation. The highest optimization toward hydrocabon selectivity was shown by 20wt% TiO2, while a 90wt% TiO2 loading was more selective for H2 formation. This was likely due to the uniform dispersion and stabilization of the anatase TiO2 with 20wt% on KIT-6, which in turn allowed more CO2 adsorption and a better light penetration than 90% TiO2/KIT-6 in which it showed a bulk phase and large agglomerates with light penetration limitations that were more favorable for H2O adsorption. A reaction mechanism, which has helped to understand these findings, has been proposed. Moreover, a 24h activity test with the optimized 20wt% TiO2/KIT-6 showed an increase in the product yield but only a minor, gradual decrease in the reaction rate, which points out that these photocatalysts could be promising for turning CO2 greenhouse gas feedstock into selective renewable energy products.

Enhanced Catalytic Performance of Three-Dimensional Ordered Mesoporous Transition Metal (Co, Cu, Fe)-Doped CeO2 Catalysts for CO Catalytic Oxidation

Transition metal (Co, Cu, Fe)-doped CeO2 catalysts with three-dimensional mesoporous channels had been synthesized through a nanocasting route using three-dimensional mesoporous silica KIT-6 as the template. All four catalysts exhibited high surface area (>120 m2 g−1) and ordered mesopore. The research results showed that Co3O4, CuO, Fe2O3 crystallites in catalysts were encapsulated by nanosized CeO2, respectively, and a small fraction of Co, Cu, Fe ions were exposing on the surface and strongly interacting with CeO2. These ions (Co, Cu, Fe) maximized interaction with Ce ion in three-dimensional mesoporous structure, resulting in unique redox properties. The research results showed that the introduction of promoter (Co, Cu and Fe species) could effectively enhance the chemisorbed oxygen and oxygen vacancy concentration on the surface of metal-doped CeO2 catalysts. Compared with Co and Fe species, the Cu species had an obvious enhancement. The characteristic was relatively conducive to the catalytic oxidation of CO. The catalysts were evaluated for the catalytic oxidation CO reaction. The Cu-doped CeO2 catalyst exhibited the highest catalytic activity, and complete conversion temperature (T100) was about 50 °C for CO oxidation.

The First Example of ortho-Arylation of Benzamides over Pd/Mesoporous Silica: A Novel Approach for Direct sp2 C–H Bond Activation

Three-dimensional mesoporous silica with a highly dispersed palladium nanoparticles composite (PS-3) catalyst has been prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, nitrogen sorption, and high resolution transmission electron microscopy. The PS-3 catalyst utilized for the first time as an efficient and reusable catalyst in the ortho-arylation of benzamides by aryl iodides has been demonstrated with the simplest amide CONH2 as a directing group. It can be successfully applied to various benzamides and aryl iodides with both electron donating and withdrawing groups. The catalyst can be simply recovered and reused several times without significant loss in catalytic activity.

Synthesis of highly active nanostructured PtRu electrocatalyst with three-dimensional mesoporous silica template

Nanostructured PtRu material has been successively synthesized via chemical co-reduction of hexachloroplatinic acid and ruthenium trichloride using three-dimensional (3D) hexagonal mesoporous SBA-12 silica as a solid template, and has been studied as an electrocatalyst toward methanol electro-oxidation. The ordered nanostructure of the PtRu particles has been disclosed by transmission electron micrographs and is characterized by regular pores of ca. 3.0 ± 0.3 nm in diameter separated by walls of ca. 3.0 ± 0.3 nm thick. X-ray diffraction and energy dispersive X-ray spectroscope studies indicate that the PtRu material comprises of complicated phases rather than a single alloy phase of Pt and Ru. The specific electrochemical surface area of the nanostructured powder measured using both CO and underpotential deposited Cu stripping techniques is 74–78 m 2 g –1, higher than that of unsupported precious metal catalysts prepared using standard techniques. The combination of high surface area and periodic nanostructure of the templated PtRu makes it an interesting promising fuel cell electrocatalyst. This has been demonstrated by the high activity of the templated PtRu towards the methanol electrooxidation. Therefore the solid template route based on 3D mesoporous silica with controlled pore size and high pore interconnectivity provides an interesting alternative to produce promising high-surface-area electrode materials.

Microemulsion Liquid Crystal Templates for Highly Ordered Three-Dimensional Mesoporous Silica Monoliths with Controllable Mesopore Structures

Nanostructure composite silica monoliths (HOM-n) with three-dimensional (3-D) structures and controllable pore size were fabricated by using microemulsion lyotropic liquid crystal mesophase as templates under acidic conditions. By addition of alkanes with different molecular size (C6-C19 alkyl chains) into the primary lyotropic liquid crystal mesophase of Brij 56 (C16EO10), quaternary microemulsion liquid crystal phases formed and the mesophase topology of the surfactant was significantly enhanced with 3-D structures. Hydrocarbon molecular size and the degree of solubilization significantly influenced the amphiphilic phase behavior and the mesopore morphological structure. The phase transitions between the different cubic symmetries could be controlled by using a different solubilizing agent in the microemulsion phases of Brij 56 amphiphile. Thereby, the phase transition of primary liquid crystal mesophases in the microemulsion systems were used to fabricate well-defined highly ordered mesoporous silica m...