Mesoporous Silicate Materials Research Articles

Synthesis and characterization of mesoporous silicas with dendritic and spongy-like structures: Potential supports for human lactate dehydrogenase-based microreactors aimed at anticancer inhibitor screening

Mesoporous silica are versatile materials with wide-ranging potential. Notably, they excel as enzyme supports. This work examines the influence of three distinct siliceous mesoporous materials used as supports for the enzyme human lactate dehydrogenase (hLDH-A). Drugs with inhibition effects have recently shown favorable effects on diminishing the proliferation of cancerous cells. The ultimate goal of this research is to produce a stable and effective biocatalyst suitable for being employed in a microreactor for the screening of hLDH-A inhibitors. The synthesized mesoporous silica exhibited distinctive structural features, including a quasi-mesocellular network, bent-channels structure, and a dendritic geometry with radial symmetry, as evidenced by FESEM and HR-TEM. These materials were functionalized with amino and aldehyde groups to covalently immobilize hLDH-A. Characterization of both pristine and functionalized materials involved a comprehensive examination of their physico-chemical properties. The CO dosing revealed Brønsted acidity characteristic of mesoporous silica, while FT-IR spectroscopy and N2 physisorption at 77 K confirmed their successful functionalization. Enzyme immobilization on the functionalized supports, performed with stabilizing agents such as PEG (0.05 mg mL−1) or trehalose (300 mM), produced promising results. The immobilization yield consistently exceeded 80 %, with retained activity reaching values as high as 15 %. The immobilization of the enzyme on mesoporous silica increased the stability of hLDH-A against alkaline and organic solutions. These findings hold significance for those exploring siliceous porous supports for enzyme immobilization, paving the way for the development of stable and active biocatalysts.

Silica extracts from fly ash modified via sol-gel methods and functionalized with CMPO for potential scavenging of rare earth elements La³⁺ and Ce³⁺

A mesoporous material was synthesized using silica extracts from fly ash and its properties were studied. Subsequently, it was functionalized with carbamoylmethylphosphine oxide (CMPO) to capture La3+ and Ce3+. The developed mesoporous material was obtained by the sol-gel method and was called Si-MMS (siliceous mesoporous materials), subsequently functionalized with APTMS (1-(2-aminoethyl)-3-aminopropyl trimethoxysilane) in a reflux system, which led to the synthesis of Si-MMS-APTMS. This derivative was modified with carbonyldiimidazole (CDI) and diethylphosphonoacetic acid, which finally resulted in the synthesis of Si-MMS-CMPO as the final product. The materials were characterized by DRIFT, XRD, SEM-EDS, TEM, XPS, elemental analysis and nitrogen isotherms at −196 °C, confirming that the synthesis and subsequent modification of the mesoporous structure was successful. Adsorption studies in batch systems indicated that the optimal pH for La3+ was 6, the Langmuir isotherm model and the non-linear Sips models were perfectly fitted and the best fitting kinetics is the Elovich model. For Ce3+ the optimal pH was 7.5, the non-linear Sips isotherm fit the best and the non-linear Pseudo-second order kinetics was the mechanism that best represents the adsorption. The maximum experimental adsorption capacity qe of La3+ was 17.00 mg g−1 and for Ce3+ was 30.09 mg g−1. In both cases, the rapid adsorption suggests an open porous matrix that facilitates the formation of chelates between the adsorbates and the phosphoryl group -PO32-.

Synthesis and characterization of surface-modified magnetic mesoporous silicate materials for phosphate adsorption.

The magnetic mesoporous silica material, Mag-MCM-41, was synthesized by coating magnetite (Fe3O4) nanoparticles with a mesoporous material called MCM-41. Mag-MCM-41 and modified nanomaterials Mag-MCM-41-NN and Mag-MCM-41-NN-Fe+3 which were modified with aminopropyl functional groups. In water and wastewater, phosphate anions are considered significant contaminants due to their detrimental impact on the environment. They promote the growth of algae, leading to eutrophication. The purpose of this study is to investigate the removal of phosphate anions from aqueous solutions using modified magnetic silica particles. The Mag-MCM-41 material exhibits hexagonal properties and belongs to the class of "mesoporous" materials. It has a surface area of 923 m2.g-1, which was determined through N2 adsorption-desorption isotherms, FTIR, TEM, BET, and SAXS analysis. Kinetic and adsorption isotherm studies were conducted using Mag-MCM-41, Mag-MCM-41-NN, and Mag-MCM-41-NN-Fe+3 adsorbents to examine the behavior of phosphate anions. The kinetic and adsorption isotherm studies of phosphate anions revealed that the adsorption process on Mag-MCM-41, Mag-MCM-41-NN, and Mag-MCM-41-NN-Fe+3 adsorbents followed the chemical adsorption mechanism. Phosphate adsorption on all adsorbents occurred in a monolayer, and the MCM-41-NN-Fe+3 adsorbent exhibited the highest maximum adsorption capacity (qm) value of 112.87 mg.g-1 compared to the other adsorbents.

Regulation of Active ZnO Species on Si‐based Supports with Diverse Textural Properties for Efficient Propane Dehydrogenation

AbstractPropylene is deemed as a kind of key raw materials with significant value in industrial production. Highly dispersed Zn species are served as active sites in catalyzing propane dehydrogenation reaction (PDH). More importantly, the morphology and textural properties of Si‐based support exert the great influence on the formation of active Zn species. Herein, active Zn species were dispersed on macroporous commercial SiO2, mesoporous siliceous materials (SBA‐15, MCF, DMSN, KIT‐6), and microporous silicalite‐1 (S‐1), respectively. Characterization result indicated that the dispersed active ZnO species were prone to be formed on S‐1, which could be attributed to the confinement effect of micropores in S‐1 and the abundant Si‐OH groups interacted with Zn2+ species. As a result, the optimal ZnOA/S‐1 catalyst exhibited superior catalytic activity (propane conversion of 40.4 %, propylene selectivity of 96.0 %, 550 °C, WHSV=0.47 h−1) during PDH process. Furthermore, the relatively considerable performance of ZnOA/S‐1 catalysts could help to offer a guidance on the design of efficient and low‐cost catalysts for PDH reaction.

Novel copper desorption from a functionalized fly ash adsorbent using 1,1,1-trifluoro-2,4-pentanodione in ionic liquid [bmim][Tf2N]: Experimental and quantum chemistry calculations

In the context of the current environmental issues and the need to consolidate effective efforts according to the criteria of a circular economy, adsorption of copper from water with functionalized materials has shown high performance at low cost. However, desorption requires high amounts of acid and base to regenerate the functionalized material. In order to overcome this drawback, this work proposes an alternative desorbing phase based on a specific extractant for copper 1,1,1-trifluoro-2,4-pentanodione (TFA) dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. In this way, adsorption experiments were carried out using adsorbent fly ash, modified with a mesoporous siliceous material, and functionalized with 3-aminopropyl-triethoxysilane (APS). Under the operating conditions of this study, the best desorption performance was achieved using the lowest functionalization percentage of the absorbent material. The desorption percentage reached 45% after 200 min of contact with a stirred solution of TFA 0.2 [M] in IL. This percentage can be increased to around 70% through a second contact with fresh desorbing phase. Meanwhile, the conventional desorption technique with nitric acid showed faster kinetics and a slightly higher desorption percentage close to 50%. In turn, the final pH of the adsorbent slightly decreased when the proposed desorbing phase was used, representing an advantage over the use of acid. Additionally, it was possible to decrease the amount of desorbing phase allowing the concentration of copper. The COSMO-RS calculations indicate that a more hydrophobic IL could increase desorption percentage.

Fast and effective sorption of radioactive Sr(II) onto mesoporous silicate

Abstract A mesoporous silicate material (MS) was effectively synthesized and applied as a solid sorbent for removal of radioactive Sr(II) ions from aqueous solution. MS was characterized using different tools including N2 adsorption-desorption analysis, FT-IR, XRD and SEM. The synthesized material has crystalline, porous nature and exhibited a large surface area of about 905.18 m2 g−1. The uptake of Sr(II) ions onto MS was investigated under different batch experimental conditions involving pH, equilibrium time, sample weight and initial concentration of Sr(II) ions. About 98 % of Sr(II) radionuclides were uptaken at pH 12 in the first minute. Different isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich and Temkin) were applied to analyze the obtained experimental sorption equilibrium data. The Langmuir isotherm model was aligned well with the sorption data. The maximum sorption capacity (Q max) of MS towards strontium ions attained the value 0.991 mmol/g. The parameters (ΔG°, ΔH° and ΔS°) were calculated from thermodynamic study and their values showed that sorption process of Sr(II) ions on MS is strong, take place spontaneously, and considered as endothermic process. The synthesized MS had the ability to efficiently remove Sr(II) radionuclides even in the presence of Na+ and Ca2+ as competing cations in aqueous solution. Among the studied desorbing agents, CaCl2 was the best one for desorbing Sr(II) radionuclides loaded onto MS. The synthesized MS was reused for sorption of strontium up to four cycles with acceptable efficiency.

Effect of nanoconfinement and pore geometry on point of zero charge in synthesized mesoporous siliceous materials

Effect of nanoconfinement and pore geometry on point of zero charge in synthesized mesoporous siliceous materials

In-situ synthesis of duster-like hollow mesoporous copper silicate composites for high-efficiency adsorption of aflatoxin B1 from water

Aflatoxin B1 (AFB1) is one of the pollutants widely distributed in wastewater, which easily causes serious harm to human health and ecosystem. Mesoporous silicate materials are often used as adsorbents attributed to their well-controlled structures and high surface area. Herein, copper silicate composites (MCSCs) with novel duster-like hollow mesoporous structure were synthesized in situ on an acid-etched sepiolite substrate, and used as adsorbents for removal of AFB1 from water. The resultant MCSCs exhibited high specific surface area (439 m2/g), consequently exposing abundant functional groups (e.g., Si–OH, Cu–OH and Si–O–Cu), which contributed to improved adsorption performance. As expected, the MCSCs showed excellent AFB1 adsorption capacity, and the maximum adsorption capacity, obtained from the Langmuir model, was 24.99 mg/g. Analyses of the kinetic data revealed that the adsorption process of AFB1 onto MCSCs were fitted well with the pseudo-second-order and Weber-Moris intra-particle diffusion models. The FTIR and XPS analysis confirmed that the adsorption mechanisms were mainly electron donor-acceptor interaction and hydrogen bonding. These results in this work will provide valuable information for the development of green and efficient strategy for synthesizing other silicate materials, which are expected to applied as highly efficient adsorbents to remove AFB1 from wastewater.

Removal of Zn2+ from Aqueous Solution Using Biomass Ash and Its Modified Product as Biosorbent.

To study the removal effect of bottom ash of biomass power plants and its modified products on zinc (Zn2+) in aqueous solution, a series of indoor experiments is carried out. The aim of this work is to explore a method to improve the ability of biomass ash to remove Zn2+ from aqueous solution and obtain its adsorption characteristics of Zn2+ in aqueous solution; on this basis, the feasibility of its application in the treatment of Zn2+-contaminated wastewater is analyzed. The mesoporous siliceous material is used to modify the biomass, and the modified material is functionalized with 3-aminopropyltriethoxysilane. The results show that the specific surface area of modified biomass ash is nine times that of the material before modification. The adsorption capacity of Zn2+ on the material increases with the increase of pH, and pH 6 is the optimum pH to remove Zn2+ from the aqueous solution. The Langmuir model and Freundlich model can show better fits for biomass ash and the modified material, respectively. Thermodynamic analysis results show that the adsorption of Zn2+ is spontaneous and endothermic in nature. The adsorption of Zn2+ onto biomass and modified biomass ash follow pseudo-first-order and pseudo-second-order kinetics, respectively.

Covalent Immobilization of Aldehyde and Alcohol Dehydrogenases on Ordered Mesoporous Silicas

PurposeThis work studies the immobilization of two enzymes, the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (AldDH) both from Saccharomyces cerevisiae, which could be used to produce high value-added molecules from carboxylic acids embedded in anaerobic digestate.MethodsIn particular, three mesoporous siliceous materials, with different specific surface areas and pore sizes, (MSU-H, MSU-F and MCF0.75) were used as supports for covalent immobilization. The support materials were characterized by complementary techniques. Then, after a functionalization, creating a covalent bond between the enzyme and the support was performed. The specific activity and immobilization yield of the biocatalysts were then evaluated.ResultsThe best results were obtained with MSU-H and MSU-F, resulting in an immobilization yield greater than 50% in all cases, a specific activity of 0.13 IU/gsupp with the AldDH/MSU-H, 0.10 IU/gsupp with AldDH/MSU-F, 48.6 IU/gsupp with ADH/MSU-H and 12.6 IU/gsupp with ADH/MSU-H. These biocatalysts were then characterized by optimal pH and temperature and the stability factor was evaluated. With ADH/MSU-F no decrease in activity was observed after 120 h incubated at 50 °C. Finally, the biocatalysts AldDH/MSU-H and ADH/MSU-H were used to perform the reduction reaction and it was seen that after five reaction cycles the residual activity was greater than 20% in both cases.ConclusionThe ADH and AldDH enzymes have been successfully immobilized on mesoporous siliceous supports, considerably increasing their thermal stability and being able to reuse them for several reaction cycles. The use of this immobilization and these supports is adaptable to a wide variety of enzymes.Graphical

Inclusion and release of cytisine in mesoporous silicate materials: an agent for smoking cessation

Inclusion and release of cytisine in mesoporous silicate materials: an agent for smoking cessation

Cytostatic and Cytotoxic Effects of Hollow-Shell Mesoporous Silica Nanoparticles Containing Magnetic Iron Oxide.

Among the different types of nanoparticles used in biomedical applications, Fe nanoparticles and mesoporous siliceous materials have been extensively investigated because of their possible theranostic applications. Here, we present hollow-shell mesoporous silica nanoparticles that encapsulate iron oxide and that are prepared using a drug-structure-directing agent concept (DSDA), composed of the model drug tryptophan modified by carbon aliphatic hydrocarbon chains. The modified tryptophan can behave as an organic template that allows directing the hollow-shell mesoporous silica framework, as a result of its micellisation and subsequent assembly of the silica around it. The one-pot synthesis procedure facilitates the incorporation of hydrophobically stabilised iron oxide nanoparticles into the hollow internal silica cavities, with the model drug tryptophan in the shell pores, thus enabling the incorporation of different functionalities into the all-in-one nanoparticles named mesoporous silica nanoparticles containing magnetic iron oxide (Fe3O4@MSNs). Additionally, the drug loading capability and the release of tryptophan from the silica nanoparticles were examined, as well as the cytostaticity and cytotoxicity of the Fe3O4@MSNs in different colon cancer cell lines. The results indicate that Fe3O4@MSNs have great potential for drug loading and drug delivery into specific target cells, thereby overcoming the limitations associated with conventional drug formulations, which are unable to selectively reach the sites of interest.

Direct Synthesis of Mesoporous Siliceous Phosphotungstic Acid and Its Superior Catalytic Activity on the Cyclohexylation of Phenol

The synthesis of highly active and reusable mesoporous siliceous phosphotungstic acid materials (mPTA-Si) which are prepared through a simple self-assembly between phosphotungstic acid (PTA), the p...

Engineering and Performance of Ruthenium Complexes Immobilized on Mesoporous Siliceous Materials as Racemization Catalysts

Dynamic kinetic resolution (DKR) is one of the most attractive routes to enantioselective synthesis, and ruthenium complexes are often applied as racemization catalysts. Two substituted cyclopentadienyl ruthenium complexes were immobilized covalently and non-covalently on mesoporous silica of mesocellular foam (MCF) and Santa Barbara Amorphous (SBA)-15 type functionalized with a 3 carbon spacer and 4-(chloromethyl)-N-amidobenzoate moiety. The catalysts were studied in a model reaction of secondary alcohol racemization. The immobilization decreased catalyst activity, considerably more for SBA-15 than for MCFs, and complete racemization of 1-phenylethanol was achieved within 24 h with the MCF-supported catalyst. The catalyst could be recovered and reused, thus paving the way for further development of the DKR process. The synthesized materials were fully characterized by Fourier-transform infrared spectroscopy analysis, thermogravimetry analysis, inductively cou-pled plasma optical emission spectrometry, and nitrogen adsorption at 77 K.

Ruthenium silicate (RS-1) zeolite: novel heterogeneous efficient catalyst for synthesis of 2-arylbenzothiazole derivatives

Mesoporous silicate and transition metal (Ru+3) containing mesoporous silicate materials or ruthenium silicate Ru+3/Si+4 where synthesis by using hydrothermal process. Mesoporous ruthenium silicate (RS-1) and zeolite catalyst have been successfully synthesized with variable molar ratio such as (a) Ru:Si 1:100, (b) Ru:Si 1:150, (c) Ru:Si 1:200. The elemental composition, structural morphology, crystal phase and properties and various parameters of the catalyst were examined by Fourier transform infrared spectroscopy, scanning electron microscopy, powder X-ray diffraction. Energy dispersive X-ray pattern/spectroscopy analysis EDX/EDS, where as the activity of obtained catalysts was tested in the Willgerodt–Kindler synthesis between 2-aminothiophenol and substituted aryl aldehyde (1:1 mol) to form a 2-arylbenzothiazole. The novelty of the presented work was the ruthenium (Ru+3) metal impregnations in silicate framework for the synthesis of novel ruthenium silicate (RS-1) zeolite as a catalyst and the investigation of the various parameters, role, its stability and catalytic activity in the Willgerodt–Kindler (combined both Knovenagel and Maichel addition reaction) synthesis. The developed protocol has several benefits such as short reaction time, mild reaction condition, and good reusability of catalyst.

Synthesis and mechanism of aluminum silicate mesoporous materials by F108 template

AbstractAluminosilicate mesoporous materials were synthesized using F108 template (polyethylene glycol-polypropylene glycolpolyethylene glycol) at a concentration of 0.034 g/ml and the molar ratio of Al2O3to SiO2was 0.09. The products were then characterized using nitrogen adsorption/desorption tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The effects of various crystallization temperatures as well as sodium hydroxide concentrations on the average diameter, pore volume, surface area, and morphology of the synthetic material were analyzed. Results showed that a sodium hydroxide concentration of 11 mol/L and a crystallization temperature of 130 °C produced a synthetic material with regular pore size and homogeneous arrangement including a specific surface area of 137.62 m2/g, an average pore volume of 0.27 cm3/g, along with an average pore size of 15.33 nm.

Propylsulfonic acid grafted on mesoporous siliceous FDU-5 material: A high TOF catalyst for the synthesis of coumarins via Pechmann condensation

Abstract Coumarins and their synthetic derivatives are extensively used as base chemicals in diverse industrial applications in the fields of pharmaceutics, cosmetics, and agrochemicals, among others. Due to the growing number of applications, the need for new methods of coumarins synthesis has gained importance worldwide. In this sense, the use of propylsulfonic acid supported in FDU-5 (FDU-5-Pr-SO3H) as a catalyst for the synthesis of coumarins via Pechmann condensation in solvent free medium was investigated. FDU-5-Pr-SO3H was synthesized by co-condensation of MPTES and TEOS. FDU-5-Pr-SO3H was used as catalyst for the synthesis of 7-hydroxy-4-methylcoumarin and reaction conditions were optimized. The optimization process involved the study of the influence of the catalyst load, Resorcinol:EAA molar ratio, reaction temperature and reaction time. The optimal conditions were: catalyst load of 1.65 mol %, reactants molar ratio of 1:1.5, temperature 130 °C and 60 min of reaction time. Under these conditions, the FDU-5-Pr-SO3H material showed excellent yield (96.5%) and turn over frequency (59 h−1). Finally, the synthetized material was assessed as a catalyst with other phenolic compounds with ethyl acetoacetate and with ethyl benzoylacetate. The obtained products were isolated and identified by comparison of their spectral data with those reported in literature; from these results can be concluded that the catalyst is active with a wide range of phenolic substrates.

A significant improvement in adsorption behavior of mesoporous TUD-1 silica through neodymium incorporation

Neodymium was incorporated into the three-dimensional mesoporous siliceous material TUD-1. In order to understand the chemical and morphological structure of the prepared material, several characterization techniques were performed. The characterization results show the formation of highly distributed isolated Nd3+ ions incorporated in the silica matrix in tetrahedrally coordinated structure, moreover no aggregation of separate phase(s) was/were observed. The prepared material was investigated as an adsorbent for methyl green (MG) dye in aqueous solution as a model cationic dye. The results show higher adsorption capacity for Nd-TUD-1 by almost 24 times higher than the neat parent TUD-1 material and more than 100 times higher than bulky Nd2O3 under neutral pH. The adsorption results were fitted perfectly with pseudo-second-order model. Moreover, the adsorption isotherms were perfectly fitted with Freundlich isotherm model which indicates the formation of a multilayer of the dye molecules onto the Nd-TUD-1 surface as a physisorption with endothermic nature.

Synthesis and functionalization of cauliflower-like mesoporous siliceous foam materials from oil shale waste for post-combustion carbon capture

In this work, meso-structured siliceous form materials (SFM) were synthesized from oil shale ash via a green and time-saving microemulsion templating method and modified with polyethleneimine (PEI) for post-combustion carbon capture. The effects of preparation conditions, such as P123/TMB ratio, aging temperature and pH values, on sample morphology and pore structure were studied to understand the characteristics of inorganic silica precursors. Results show that the SFMs possess 3-dimensional porous framework with a large surface area of 901.3 m3/g and a pore volume of 2.0 cm3/g. The CO2 adsorption behaviour of PEI-impregnated SFMs were investigated in terms of CO2 adsorption capacity and temperature swing adsorption (TSA) cycling stability under a simulated flue gas condition (75 °C and 15% CO2/N2). The results show that pore-expanded SFMs with 50 wt% PEI loading exhibited higher CO2 uptake (109 mg/g-adsorbent) compared to non-pore-expended materials (50 mg/g-adsorbent) and no appreciable reduction in CO2 uptake was observed in the first 10 cycles. However, the DRIFTS spectra of CO2-evacuated adsorbents revealed the presence of alkylammonium carbamates residuals and formations of urea species. This could explain the reduction in CO2 adsorption capacity after 10 cycles.

Highly dispersed metal incorporated hexagonal mesoporous silicates for catalytic cyclohexanone oxidation to adipic acid

Abstract Adipic acid is a dicarboxylic acid of great industrial importance, mainly used in the production of nylon-6,6 and polyurethane. The use of nitric acid as an oxidant in the industrial production of adipic acid poses significant carbon footprint to the environment. Clean adipic acid synthesis methods using a heterogeneous catalyst with H2O2 as oxidant and water as solvent have potential advantages of low catalyst cost, easy synthesis and recovery, cleanness and environmental protection. In this work, hexagonal mesoporous silicate materials were synthesized by a sol–gel method and evaluated for cyclohexanol/cyclohexanone oxidation to adipic acid. The physical and chemical properties of Fe-HMS were characterized by XRD, HR-TEM, BET and UV–Vis. The experimental results showed that Fe-HMS materials show pore sizes ranging from 2–3 nm. W- and Mo-based polyoxometalates were also evaluated and compared to the Fe-based HMS catalysts. To improve the adipic acid yield, the influence of the transition metal as well as the effect of metal loading, reaction temperature and catalyst amount on the catalytic performances of Fe-HMS have been investigated in details. When Si/Fe atomic ratio = 100, Fe-HMS catalyst shows the highest activity, with a cyclohexanone conversion of 92.3% and adipic acid selectivity of 29.4%. The reaction pathway of cyclohexanone oxidation was further proposed based on experimental data.