Mesoporous silica-carbon composites fabricated by a universal strategy of hydrothermal carbonization: controllable synthesis and applications

Interesterification of Glyceryl Trioctanoate Catalyzed by Sulfonic Silica-Based Materials: Insight into the Role of Catalysts on the Reaction Mechanism

In the present work, the acid-catalyzed interesterification of glyceryl trioctanoate (GTO) with ethyl acetate was investigated as a model reaction for the one-step production of biofuel and its additives. The activity of heterogeneous acid catalysts, such as silica-based propyl-sulfonic ones, was evaluated. Propyl-sulfonic groups were grafted on both amorphous and mesoporous silica oxide (SBA-15, KIT-6) using different functionalization processes and characterized by N₂ adsorpion-desorption isotherm (BET), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and potentiometric titration. During the optimization of the reaction conditions with the most active catalyst (Am-Pr-SO₃H), it was shown that the addition of ethanol allowed a total conversion of GTO together with 89% and 56% yield of ethyl octanoate and triacetin, respectively. The catalytic performance is strictly correlated to the catalyst features, in terms of both the acid capacity and the porous structure. Moreover, the catalytic performance is also affected by a synergistic mechanism between silanols and Pr-SO₃H groups towards the 'silanolysis' of ethyl acetate. The overall results show that the presence of ethanol, the reaction time, and the amount of catalyst shifts the reaction towards the formation of the biofuel mixture composed by ethyl octanoate and triacetin.

Stability of mesoporous silica using ricinoleic methyl ester as a template with the addition of HCl and application of Cd2+ adsorption optimized by Box-Behnken design

Mesoporous silica is restricted to organic solvents or other acidic media. The application of mesoporous silica depends on the medium's chemical stability and mechanical properties. It is necessary to stabilize the mesoporous silica material under acidic conditions. The results of the nitrogen adsorption characterization show that MS-50 has a large surface area and porosity, resulting in good mesoporous silica. Using variance analysis (ANOVA) to compare the collected data, the best conditions were found at a pH of 6.32, a Cd²⁺ concentration of 25.30 ppm, an adsorbent dose of 0.06 g, and a time of 70.44 min. The Cd²⁺ adsorption experiment data best fit the Langmuir isotherm model with the maximum amount of Cd²⁺ that MS-50 could absorb being 103.10 mg g^-1.

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly.

Sulfonated Mesoporous Silica-Carbon Composite Derived from a Silicate-Polyethylene Glycol Gel and Its Application as Solid Acid Catalysts

Solid acid catalyst is a promising alternative to the counterpart homogeneous acid for esterification reaction from the viewpoint of reusability and environmental concerns. This work aims to develop sulfonated mesoporous silica-carbon composite as solid acid catalyst for the esterification. The catalyst was synthesized from sodium silicate as the silica precursor and polyethylene glycol (PEG) as both carbon precursor and template via a sol-gel route in an aqueous system. Then, it was carbonized to produce mesoporous silica-carbon composite. Using the proposed method, the surface area of the silica-carbon composite could reach as high as 1074.21 m2/g. Although the surface area decreased to 614.02 m²/g when it was functionalized with sulfonate groups, the composite had a high ionic capacity of 5.3 mEq/g and exhibited high catalytic activity for esterification reaction of acetic acid with ethanol. At a reaction temperature of 80 °C, the acetic acid conversion reached 76.55% in 4 h. In addition, the catalyst had good reusability, which can be comparable with the commercial catalyst Foltrol F-007. It appears that the sulfonated silica-carbon composite prepared from sodium silicate using PEG as the carbon source a promising candidate as catalyst for esterification and the related area. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Hydrothermal carbons/ferrihydrite heterogeneous Fenton catalysts with low H2O2 consumption and the effect of graphitization degrees

As the heterogeneous Fenton reactions are always restricted by the unsatisfied reduction efficiency of Fe(III) and ineffective consumption of H₂O₂, many strategies have been developed. In this work, we prepared hydrothermal carbons (HTC) with different graphitization degrees using glucose under different hydrothermal times, and then they were combined with ferrihydrite (Fh). Interestingly, although 30%HTC/Fh has much better BPA degradation efficiency than Fh (26 times larger of calculated degradation rate constants), the decomposition rate of H₂O₂ in the former system is lower. The generated Fe(II) of HTC/Fh is much higher than that of Fh during the heterogeneous Fenton reactions, and the degradation of BPA is almost unaffected by p-benzoquinone (scavenger of superoxide radicals (O₂^•-)) while greatly inhibited by isopropanol (scavenger of hydroxyl radicals (HO^•)). These results indicate that HTC act as electron donors due to the abundant carbon-centered persistent free radicals (PFRs) to directly reduce Fe(III) to Fe(II) and therefore decrease the H₂O₂ consumption by Fe(III), which subsequently inhibits the generation of less active O₂^•- and promote the utilization efficiency of H₂O₂. HTC with a low graphitization degree contain more PFRs for Fe(III) reducing, significantly enhancing the Fenton catalytic activity of Fh.

One-pot hydrothermal cross-linking preparation of poly(vinylpyrrolidone) immobilized silica stationary phase for hydrophilic interaction chromatography

Hydrothermally cross-linked polyvinylpyrrolidone (PVP) immobilized SiO₂ stationary phase (CPVP-Sil) was prepared via a green and facile one-pot method which was demonstrated for hydrophilic interaction liquid chromatography (HILIC) as well as reverse phase chromatography(RP). A water or organic solvent-insoluble permanent CPVP immobilizing on the silica particle surface can be formed simply by dipping silica particles into PVP solution and low temperature hydrothermal treatment. The cross-linked PVP network coating on SiO₂ endow it ring lactam functional groups which exhibited excellent separation ability of polar compounds by a typical HILIC retention mechanism at higher organic solvent contents (>55% ACN) and additionally polyvinyl groups for separation of alkylbenzenes in RP mode(<25% ACN). A high column efficiency of about 7 × 10⁴ plates per meter was obtained for the test catechol compound. Remarkably, the CPVP-Sil packing materials showed good stability in acid (at pH 3.5) or basic (at pH 9.5) conditions, with 5400-fold column volumes and 3500-fold column volumes respectively.