Revisiting carboxylic group functionalization of silica sol-gel materials

The carboxylic chemical group is a ubiquitous moiety present in amino acids, a ligand for transition metals, a colloidal stabilizer, and a weak acidic ion-exchanger in polymeric resins and given this property, it is attractive for responsive materials or nanopore-based gating applications. As the number of uses increases, subtle requirements are imposed on this molecular group when anchored to various platforms for the functioning of an integrated chemical system. In this context, silica stands as an inert and multipurpose platform that enables the anchoring of multiple chemical entities combined through several orthogonal synthesis methods on the interface. Surface chemical modification relies on the use of organoalkoxysilanes that must meet the demand of tuned chemical properties; this, in turn, urges for innovative approaches for having an improved, but simple, organic toolbox. Starting from commonly available molecular precursors, several approaches have emerged: hydrosilylation, click thiol-ene additions, the use of carbodiimides or the reaction between cyclic anhydrides and anchored amines. In this review, we analyze the importance of the COOH groups in the area of materials science and the commercial availability of COOH-based silanes and present new approaches for obtaining COOH-based organoalkoxide precursors. Undoubtedly, this will attract widespread interest for the ultimate design of highly integrated chemical platforms.

KIT-5 Structural and Textural Changes in Response to Different Methods of Functionalization with Sulfonic Groups

In this project, KIT-5 materials were effectively functionalized with sulfonic groups introduced by grafting or the co-condensation method and tested as heterogeneous solid acid catalyst. A co-condensation procedure leading to the stable, -SO₃H functionalized KIT-5 materials was successfully established. Moreover, the influence of both synthesis methods on the structural and textural parameters, as well as surface chemistry, morphology, and catalytic activity of -SO₃H/KIT-5 materials was thoroughly investigated. The syntheses with 3-mepkaptopropyltrimethoxysilane (MPTMS) acting as a modifying agent resulted in samples in which functional groups were introduced into the structure and/or onto the mesoporous silica surface. The oxidation stage of -SH to -SO₃H groups was carried out under mild conditions, using a "green" oxidant (H₂O₂). The application of different functionalization techniques and the introduction of different amounts of modifying agent allowed for an evaluation of the influence of these parameters on the ordering of the mesoporous structure of KIT-5 materials. The applied methods of assessment of the physicochemical parameters (XRD, low-temperature N₂ sorption, TEM) showed that, especially when the co-condensation method was applied, as the number of functional groups increased, the ordering of structure characteristic of KIT-5 decreased. On the other hand, the samples modified by grafting had a stable structure, regardless of the amount of introduced MPTMS. Test reactions carried out on the basis of Friedel-Crafts alkylation process showed that the synthesized materials can be considered promising acid catalysts in heterogeneous catalysis reactions.

Aspartic Acid- and Glycine-Functionalized Mesoporous Silica as an Effective Adsorbent to Remove Methylene Blue from Contaminated Water

In this work, aspartic acid- and glycine-functionalized mesoporous silica nanoparticles (Asp-MSNs and Gly-MSNs) were successfully prepared and applied as adsorbents for removal of methylene blue (MB) from contaminated water. The mesoporous structure of the fabricated nanomaterials was confirmed by nitrogen adsorption/desorption with specific surface area of ca. 700 m2/g and pore volume of 0.9 cm3/g for both Asp-MSNs and Gly-MSNs. The average size of the nanoadsorbents was estimated to be ca. 290 nm as characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The physical and chemical properties of the Asp-MSNs and Gly-MSNs were also characterized by Fourier transform infrared (FTIR) spectroscopy, zeta potential, and elemental analysis. Asp-MSNs and Gly-MSNs exhibited good adsorption performance for removal of cationic organic dyes (MB). The equilibrium adsorption capacity of Asp-MSNs and Gly-MSNs was found to be 55 mg·g−1 and 43 mg·g−1, respectively, under the optimal conditions. The Langmuir model and pseudo-second-order equation exhibited good correlation with the isotherm and adsorption kinetic data for MB, respectively.

Application of Non-Viral Vectors in Drug Delivery and Gene Therapy

Vectors and carriers play an indispensable role in gene therapy and drug delivery. Non-viral vectors are widely developed and applied in clinical practice due to their low immunogenicity, good biocompatibility, easy synthesis and modification, and low cost of production. This review summarized a variety of non-viral vectors and carriers including polymers, liposomes, gold nanoparticles, mesoporous silica nanoparticles and carbon nanotubes from the aspects of physicochemical characteristics, synthesis methods, functional modifications, and research applications. Notably, non-viral vectors can enhance the absorption of cargos, prolong the circulation time, improve therapeutic effects, and provide targeted delivery. Additional studies focused on recent innovation of novel synthesis techniques for vector materials. We also elaborated on the problems and future research directions in the development of non-viral vectors, which provided a theoretical basis for their broad applications.

Investigating Methylene Blue Removal from Aqueous Solution by Cysteine-Functionalized Mesoporous Silica

In this study, mesoporous silica nanoparticles (MSNs) were synthesised using the Stober method and functionalised with cysteine (MSN-Cys) for removal of Methylene Blue (MB) from aqueous solution using the batch method. The adsorbent nanoparticles were characterised by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), FTIR, BET, and TGA. Several influential factors on the adsorption of MB onto the surface of MSN-Cys particles were investigated, including pH, initial concentration, and contact time. The adsorption capacity of MB from aqueous solution increased from circa 70 mg/g MSN-Cys in acidic media to circa 140 mg/g MSN-Cys in basic media. Adsorption isotherms and kinetic models of adsorption were used to clarify the adsorption process. The measured adsorption isotherm was fitted with a Freundlich model for all solutions, and the kinetic model was determined to be pseudo-second-order.

Gold nanoparticles decorated biguanidine modified mesoporous silica KIT-5 as recoverable heterogeneous catalyst for the reductive degradation of environmental contaminants

This current study involves the novel synthesis of Au nanoparticles (Au NPs) decorated biguanidine modified mesoporous silica KIT-5 following post-functionalization approach. The tiny Au NPs were being stabilized over the in situ prepared biguanidine ligand. The high surface area material was characterized using analytical techniques like Fourier Transformed infrared (FT-IR) spectroscopy, N2-adsorption-desorption isotherm, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction study (XRD). Our material was found to be an efficient catalyst in the reductive degradation of harmful water contaminating organic dyes like Methylene blue (MB), Methyl Orange (MO) and Rhodamin B (RhB) in presence of NaBH4 at room temperature. The whole procedure was followed up with the help of time dependant UV-Vis spectroscopy. All the reactions followed pseudo-unimolecular kinetics and corresponding rate constant were determined. The reduction rate becomes high in presence of higher load of catalysts.

Delivery of Natural Agents by Means of Mesoporous Silica Nanospheres as a Promising Anticancer Strategy

Natural prodrugs derived from different natural origins (e.g., medicinal plants, microbes, animals) have a long history in traditional medicine. They exhibit a broad range of pharmacological activities, including anticancer effects in vitro and in vivo. They have potential as safe, cost-effective treatments with few side effects, but are lacking in solubility, bioavailability, specific targeting and have short half-lives. These are barriers to clinical application. Nanomedicine has the potential to offer solutions to circumvent these limitations and allow the use of natural pro-drugs in cancer therapy. Mesoporous silica nanoparticles (MSNs) of various morphology have attracted considerable attention in the search for targeted drug delivery systems. MSNs are characterized by chemical stability, easy synthesis and functionalization, large surface area, tunable pore sizes and volumes, good biocompatibility, controlled drug release under different conditions, and high drug-loading capacity, enabling multifunctional purposes. In vivo pre-clinical evaluations, a significant majority of results indicate the safety profile of MSNs if they are synthesized in an optimized way. Here, we present an overview of synthesis methods, possible surface functionalization, cellular uptake, biodistribution, toxicity, loading strategies, delivery designs with controlled release, and cancer targeting and discuss the future of anticancer nanotechnology-based natural prodrug delivery systems.

Acid-functionalized Mesoporous Silicate (KIT-5-Pr-SO3H) Synthesized as an Efficient and Nanocatalyst for Green Multicomponent

Materials and Methods:

All reagents were purchased from Aldrich and Merck with high-grade quality and used as received. The structural characteristics of the KIT-5 which was obtained, using three-dimensional large cage type face-centered cubic Fm3m mesoporous silica materials (KIT-5) nanocages were obtained according to the procedure described by Kleitz et al. </P><P> Results: The purpose of this study is developing a new acid-functionalized mesoporous catalyst. Initially, (KIT-5) nanocages were obtained according to the procedure described by Kleitz et al. Then, KIT-5-Pr-SH was prepared by Mercaptopropyltriethoxysilane as illustrated in Scheme 1. In the next step, the solid product was oxidized with H2O2. </P><P> The full characterization for proving the structure of the nano-size particles was achieved using FT-IR, TGA, TEM, SEM, and EDX analysis.

Conclusion:

Acid-functionalized mesoporous silica has been proved to act as an effective catalyst in various organic reactions. In this project, for the first time, KIT-5 was functionalized by propyl-sulfonic acid as a heterogeneous solid acid catalyst. Sulfonic acid functionalized KIT-5 (KIT-5-Pr-SO3H) performs as an organicinorganic hybrid catalyst, whereas Brønsted acid sites have been selectively generated. In this regard, the catalytic activities of this novel heterogeneous catalyst were successfully examined by the one-pot multicomponent reaction.

Functionalization of cubic mesoporous silica SBA-16 with carboxylic acid via one-pot synthesis route for effective removal of cationic dyes

In this work, we demonstrate that a high density of −COOH groups loading, up to 60 mol% based on silica, is successfully incorporated into SBA-16 via a one-pot synthesis route, which involves co-condensation of carboxyethylsilanetriol sodium salt (CES) and tetraethylorthosilicate (TEOS) templated by Pluronic F127 and P123 in an acidic medium. A variety of characterization techniques are performed to confirm quantitative incorporation of carboxylic groups into ordered cubic mesostructures. These functionalized materials are used to effectively remove two cationic dyes methylene blue (MB) and phenosafranine (PF) with the maximum adsorption capacities of 561 and 519 mg g(-1), respectively, at pH 9. The zeta potential results reveal that the electrostatic interactions between cationic dye molecule and negatively charged surface of the adsorbent play a crucial role in their high adsorption capacities. For a binary component system consisting of MB and PF, competitive adsorption of these two dyes is observed with adsorption capacity values slightly lower than those of the corresponding single dye systems. The dye adsorbed material can be easily regenerated by simple acid washing and be reused for five times with MB removal efficiency still up to 98.6%, showing its great potentials in environmental remediation.

One-step preparation of CdS-modified mesoporous titanate nanobelts and their application as high-performance cationic dye adsorbents

CdS-modified mesoporous titanate nanobelts (CTNS) were prepared successfully by one step, using TiO₂ nanobelts and CdS quantum dots, and applied as an adsorbent for the first time for the removal of typical cationic dyes.

Facile one pot synthesis of mesoporous organic–inorganic hybrid aluminosilicate spheres with ultra-high aluminium contents and their enhanced adsorption behavior for methylene blue

An facile approach to synthesize mesoporous organo-aluminosilicate spheres with high aluminium content has been developed under static conditions.