Surface-functionalized Silica Research Articles

Icephobic characteristics of organically functionalized silica surfaces

Icephobic characteristics of organically functionalized silica surfaces

Selective and high capacity recovery of aqueous Ag(I) by thiol functionalized mesoporous silica sorbent

A simplified sol–gel method was developed for the preparation of thiol functionalized porous silica particles using (3-mercaptopropyl)-trimethoxy-silane (MPTMS) for co-gelation in the presence of micellar templates. The resulting short range ordered porous silica microparticles are exceptionally effective sorbents of aqueous Ag(I). The binding of aqueous Ag(I) is almost stoichiometric in the broad pH range between 4.0 and 9.0 even at low Ag(I) concentrations until reaching the limiting 238 mg g−1 sorption capacity. The sorbent displays high selectivity towards Ag(I), which was tested in the simultaneous presence of several different metal compounds. The practically complete recovery of Ag(I) and the regeneration of the sorbent was achieved by washing with a 10 mM Na2S2O3 solution. X-ray photoelectron spectroscopy (XPS) revealed that silver is not reduced on the surface of the sorbent. The reason for the strong and selective binding of Ag(I) is the formation of layered thiolate coordination compounds on the functionalized silica surface that display characteristically high stability even in the presence of other competing metal ions.

Porphyrin-silica gel hybrids as effective and selective copper(II) adsorbents from industrial wastewater

Porphyrins are an important class of ligands with a tremendous ability to capture metal ions closely related to the rich coordination chemistry of porphyrins. Herein we use this characteristic to develop silica gel grafted derivatives for water remediation applications. Therefore, two porphyrin derivatives, one with three and the other with four mercaptopyridyl units were grafted on silica gel functionalized with 3-aminopropyltriethoxysilane. The new adsorbents Si3PyS and Si4PyS were characterized using a suitable set of techniques confirming the covalent attachment of the porphyrins to the silica surface. Additionally, microscopy and N2 adsorption analysis confirmed the structural integrity and preservation of the mesoporous structure of Si during surface modification. The results show that both hybrid materials exhibit good chemical and thermal stability and an outstanding Cu2+ removal capability, with a chemical adsorption capacity of 176.32 mg g–1 and 184.16 mg g–1, respectively. These materials have also been used in real water and industrial wastewater samples with minimal interference in their adsorption capabilities. Density Functional Theory calculations were performed to confirm the good performance of the hybrid materials Si3PyS and Si4PyS towards metal ions. The functionalization of silica surface with porphyrin-based ligands bearing additional binding motifs drastically improves the adsorption capability of the new hybrids towards metal ions. The presence of pyridyl units brings a meaningful advantage, since both porphyrin core and appended pyridyl groups are able of binding Cu2+ ions with high affinity, contributing to the enhancement of the chelating features of the adsorbents prepared when compared with other ligands supported in silica-based materials.

Revisiting Alkoxysilane Assembly on Silica Surfaces: Grafting versus Homo-Condensation in Solution

Silica surface functionalization is often done through the condensation of functional silanes on silanols, silica surfaces' terminal groups. APTES, aminopropyltriethoxysilane, is widely used due to its assumed high reactivity with silanols, kinetically promoted by the catalytic action of the terminal amine function. Here, we revisit, based on a quantitative analysis by solid-state 29Si NMR, the assembly of this silane on silica surfaces to investigate whether its presence results from grafting, i.e., hetero-condensation with silanol groups or from homo-condensation of silane molecules in solution leading to polycondensates physisorbed on silica. We investigate the interaction of APTES with a crystalline layered silicate, ilerite, and with amorphous nonporous silica. We also studied a second silane, cyanopropyltrichlorosilane (CPTCS), terminated with a nitrile group. Our results undoubtedly prove that while CPTCS is grafted on the silica surface, the presence of APTES on silica and silicate materials is only marginally associated with silanol consumption. The analysis of the signal related to silicon atoms from silanes (Tn species) and those from silica (Qn species) allowed for the accurate estimation of the extent of homo-condensation vs grafting based on the ratio of T-O-T/Q-O-T siloxane bridges. These findings deeply question the well-established certainties on APTES assembly on silica that should no longer be seen as grafting of alkoxysilane by hetero-condensation with silanol groups but more accurately as a homo-condensed network of silanes, predominantly physisorbed on the surface but including some sparse anchoring points to the surface involving less than 6% of the overall silanol groups.

Evaluation of Dithiocarbamate-Modified Silica for Cisplatin Removal from Water

Despite the globally increasing use of platinum-based cytostatic drugs in the treatment of several types of cancer, only limited attention has been paid to developing a treatment for contaminated liquid samples originating from hospitals, laboratories and manufacturing facilities before and after their administration. In this work, we assess the efficiency of a low-cost adsorbent material, a dithiocarbamate-functionalized silica, in removing cisplatin from a solution containing it in the 0.5–150 mg L−1 concentration range. The advantage of having a surface-functionalized silica is that adsorption can occur by either non-covalent interaction or surface complexation. In the latter case platinum(II) is de-complexed and the original drug is no longer present. Adsorption occurs through a first rapid step, followed by a second slower process. This is likely due to the fact that in our operating conditions (0.9% w/v NaCl), only the original compound is present, for which ligand substitution is known to proceed slowly. The interesting performance, even at low metal concentration, and facile synthesis of the material mean it could be adapted for other applications where the recycling of platinum can be realized.

Amplified Fenton-Based Oxidative Stress Utilizing Ultraviolet Upconversion Luminescence-Fueled Nanoreactors for Apoptosis-Strengthened Ferroptosis Anticancer Therapy

As an emerging anticancer strategy, ferroptosis has recently been developed in combination with current therapeutic modalities to overcome the existing limitations of conventional therapies. Herein, an ultraviolet (UV) upconversion luminescence-fueled nanoreactor is explored to combine ferroptosis and apoptosis through the UV-catalyzed Fenton reaction of an iron supplement (ferric ammonium citrate) loaded in a mesoporous silica layer in addition to the support of a chemotherapeutic agent (cisplatin) attached on the functionalized silica surface for the treatment of triple negative breast cancer (TNBC). The nanoplatform can circumvent the low penetration depth typical of UV light by upconverting near-infrared irradiation and emitting UV photons that convert Fe3+ to Fe2+ to boost the generation of hydroxyl radicals (·OH), causing devastating lipid peroxidation. Apart from DNA damage-induced apoptosis, cisplatin can also catalyze Fenton-based therapy by its abundant production of hydrogen peroxide (H2O2). As a bioinspired lipid membrane, the folate receptor-targeted liposome as the coating layer offers high biocompatibility and colloidal stability for the upconversion nanoparticles, in addition to prevention of the premature release of encapsulated hydrophilic compounds, before driving the nanoformulation to the target tumor site. As a result, superior antitumor efficacy has been observed in a 4T1 tumor-bearing mouse model with negligible side effects, suggesting that such a nanoformulation could play a pivotal role in effective apoptosis-strengthened ferroptosis TNBC therapy.

The surface chemical functionality and diffusion mediated adsorption of organophosphates from their low concentration

The detection and removal of pesticides from their very low concentration solution are daunting tasks. The development of substrates leading to the adsorption of the pesticides requires a thorough understanding of the adsorption process. Here, we studied the interaction of two organophosphates, phorate, and malathion, on functionalized by using four different silane coupling agents, namely n-propyltrimethoxy silane (PTMS), octyltrimethoxy silane (OTMS), 3- (trimethoxysilyl) propyl methacrylate (TMSPMA) and 3- (triethoxysilyl) propionitrile (TESPN).Diffusion controlled kinetic model with a surface phase concept is developed. The concentration of the pesticides used in this work in the range of 1–20 mg/L. The model is fitted to the real-time adsorption data of phorate, and malathion over various substrates obtained using QCM-D. The results show that TMSPMA functionalized surface being more hydrophilic among all surfaces adsorbs hydrophobic pesticides molecules more uniformly. The monolayer adsorbed mass of pesticides obtained experimentally aligns with the theoretically calculated mass for TMSPMA functionalized silica surface. The adsorption is explained through molecular interactions. A reasonably strong binding with a possibility of reversible binding of phorate and malathion on TMSPMA functionalized surface is observed.

Fabrication and evaluation of properties of modified epoxidized natural rubber hybrid films by the incorporation of amine‐functionalized nanosilica

ABSTRACT The study presented in this paper focuses upon the preparation, characterization, and properties of novel epoxidized natural rubber/functionalized SiO2 nanocomposites (ENR/f-SiO2 NCs) through the incorporation of surface-functionalized silica nanoparticles (f-SiO2 NPs). Initially, ENR latex (epoxide content of 38%) as a matrix modifier was produced by epoxidation of natural rubber using in situ formed performic acid by mixing formic acid with hydrogen peroxide at 40°C for 24 hours. In order to prevent accumulation and obtain homogeneous dispersion of SiO2 NPs into the ENR latex, 3‐aminopropyltriethoxysilane (APS) was grafted onto the silica surface to form f-SiO2 nanoparticles. Then, f-SiO2 nanoparticles with various contents (0, 5, 10, 15, 20, and 25 wt.%) were embedded into the ENR matrix by ultrasonication technique for the fabrication of ENR/f-SiO2 NCs. The effect of f-SiO2 on the structural, morphological, and thermal properties of ENR was studied by infrared spectroscopy (IR), scanning electron microscopy (SEM), thermo-gravimetric analyses (TGA), x-ray diffraction (XRD).

Silane-Based SAMs Deposited by Spin Coating as a Versatile Alternative Process to Solution Immersion.

Functionalization of silica surfaces with silane-based self-assembled monolayers (SAMs) is widely used in material sciences to tune surface properties and introduce terminal functional groups enabling subsequent chemical surface reactions and immobilization of (bio)molecules. Here, we report on the synthesis of four organotrimethoxysilanes with various molecular structures and we compare their grafting by spin coating with the one performed by the conventional solution immersion method. Strikingly, this study clearly demonstrates that the spin coating technique is a versatile, fast, and more convenient alternative process to prepare robust, smooth, and homogeneous SAMs with similar properties and quality as those deposited via immersion. SAMs were characterized by PM-IRRAS, AFM, and wettability measurements. SAMs can undergo several chemical surface modifications, and the reactivity of amine-terminated SAM was confirmed by PM-IRRAS and fluorescence measurements.

A Review on Synthesis, Properties, and Applications of Polylactic Acid/Silica Composites.

Polylactic acid (PLA)/silica composites as multifunctional high-performance materials have been extensively examined in the past few years by virtue of their outstanding properties relative to neat PLA. The fabrication methods, such as melt-mixing, sol–gel, and in situ polymerization, as well as the surface functionalization of silica, used to improve the dispersion of silica in the polymer matrix are outlined. The rheological, thermal, mechanical, and biodegradation properties of PLA/silica nanocomposites are highlighted. The potential applications arising from the addition of silica nanoparticles into the PLA matrix are also described. Finally, we believe that a better understanding of the role of silica additive with current improvement strategies in the dispersion of this additive in the polymer matrix is the key for successful utilization of PLA/silica nanocomposites and to maximize their fit with industrial applications needs.

Spectral and structural investigation of silica aerogels properties synthesized through several techniques

The paper presents fairly coverage for the made-up and characteristics of most different forms of aerogels progressed from the original systems of silica-based. The aerogels structural and spectral properties can be tailored through synthesizing techniques providing the requirements of the desired application. present a comparative investigation of the spectral and structural properties for silica aerogels derived from different preparation techniques. Seven samples synthesized through the sol-gel polymerization of tetraethylorthosilicate, tetramethylorthosilicate, and sodium silicate precursor, were tested. Some of these samples were hydrophobized using trimethylchlorosilane. The precursors were adopted independently in the preparation process. Supercritical carbon dioxide, ambient pressure, and freeze-drying techniques had been followed separately as drying techniques. The silica aerogels physical properties are examined through Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption-desorption, and scanning electron microscope (SEM) tests. Identically, surface-functionalized silica aerogels were acquired from a variety of aerogels, consequently, comparing their chemical structures. The recorded FTIR spectra pointed out chemically analogous existence of silica networks with some differences, commonly, due to the additive incorporated and the synthesizing techniques. The results show that; pore-size, morphology, and the hydrophobic tendency could be controlled through the selection of the starting precursor, drying technique, and starting pH.

Effects of the Chemical and Structural Properties of Silane Monolayers on the Organization of Water Molecules and Ions at Interfaces, from Molecular Dynamics Simulations.

Understanding the organization of the hydration layer at functionalized silica surfaces is relevant for a large range of biosensing applications or surface phenomena such as biomolecule adsorption. Silane monolayers are widely used to functionalize silica surfaces. Using molecular dynamics simulations, we have investigated the role of silane molecule head-group charge, alkyl chain length, and surface coverage in the structural organization and dynamic properties of Na+ ions, Cl- ions, and water molecules at the interface. The silane molecules studied are 3-aminopropyldimethylethoxysilane, n-propyldimethylmethoxysilane, octadecyldimethylmethoxysilane, and (dimethylamino)dimethylsilylundecanoate. Our results suggest that the distribution of interfacial ions is sensitive to the 2D dispersion of the silane-charged head groups. Also, while charged silane monolayers show a strong orientation of interfacial water molecules, which leads to a rupture in the hydrogen bond network and disturbs their tetrahedral organization, the arrangement of water molecules at the interface with uncharged silane monolayers seems to be related to the surface roughness and to alkyl chain length. In line with these results, the diffusion of ions and water molecules is higher at the CH3 long monolayer interface than at the CH3 short monolayer interface and at the charged monolayer interfaces. Also, whatever the silane molecules studied, bulk properties are recovered around 0.7 nm above the interface. The interfacial water organization is known to impact biomolecule adsorption. Therefore, these results could further help in optimizing the functionalization layers to capture analytes.

Molecular Interactions of Silica Nanoparticles and Biomolecule-Functionalized Silica Nanoparticles with Bixa orellana L. Plant DNA

Surface functionalization of silica nanoparticles (SiNPs) with biomolecules, such as amino acids, amino sugars and carbohydrates was performed to produce surface-functionalized silica nanoparticles (f-SiNPs) through physical adsorption on the surface of colloidal SiNPs. The structural and physicochemical properties of the SiNPs and f-SiNPs were determined using SEM, FTIR, UV, DLS and NMR spectroscopy. The size of the functionalized-silica nanoparticles is found in the range of ~28.0 to 141.0 nm while the surface charge of the nanoparticles was observed to be negative except for f-SiNPs-Met, f-SiNPs-Glu and f-SiNPs-Gly. The SEM images of surface morphology of f-SiNPs described the differences from the SEM images of SiNPs that corroborated the silica nanoparticles’ functionalization. The synthesized SiNPs and f-SiNPs with biomolecules have been used for interaction with plant DNA isolated from the Bixa orellana L. plant. DNA interaction was quantified using agarose gel electrophoresis, visualized with a marker, and the purity was examined by the absorption ratio of A260: A280 (1.81) of isolated DNA and the quantity of the estimated dsDNA was found to be 1495 μg/mL. Interaction of DNA with alanine-SiNPs have shown greater intercalation properties due to its hydrophobic nature that protected the action of DNA molecules, whereas lysine-encapsulated nanoparticles have revealed DNA de-naturalization or replication.

Schiff-base silver nanocomplexes formation on natural biopolymer coated mesoporous silica contributed to the improved curative effect on infectious microbes

Infectious microbes that spread easily in healthcare facilities remain as the severe threat for the public health, especially among immunocompromised populations. Given the intricate problem of dramatic increase in resistance to common biocides, the development of safe and efficient biocide formulated agents to alleviate drug resistance is highly demanding. In this study, Schiff-base ligands were successfully formed on natural biopolymer of epsilon-poly-L-lysine (e-PL) decorated aldehyde functionalized mesoporous silica SBA-15 (CHO-SBA-15) for the selective coordination of silver ions, which was affirmed by various physicochemical methods. Besides the identified broad-spectrum antibacterial activities, the as-prepared Schiff-base silver nanocomplex (CHO-SBA-15/e-PL/Ag, CLA-1) exhibited an improved inhibitory effect on infectious pathogen growth typified by Escherichia coli and Staphylococcus aureus in comparison with two control silver complexes without Schiff-base conjugates, SBA-15/e-PL/Ag and CHO-SBA-15/Ag, respectively. In addition, CLA-1 remarkably inhibited the growth of Mycobacterium tuberculosis due to the excellent antimicrobial activity of silver species. Significantly, CLA-1 kills Candida albicans cells, inhibits biofilm formation, and eliminates preformed biofilms, with no development of resistance during continuous serial passaging. The antifungal activity is connected to disruption of bacterial cell membranes and increased levels of intracellular reactive oxygen species. In mouse models of multidrug-resistant C. albicans infection, CLA-1 exhibited efficient in vivo fungicidal efficacy superior to two antifungal drugs, amphotericin B and fluconazole. Moreover, CLA-1 treatment induces negligible toxicity against normal tissues with safety. Therefore, this study reveals the pivotal role of the molecular design of Schiff-base silver nanocomplex formation on biopolymer surface-functionalized silica mesopores as a green and efficient nanoplatform to tackle infectious microbes.

Core Size-Dependent Proton Conductivity of Silica Filler-Functionalized Polymer Electrolyte Membrane

Polymer electrolyte fuel cells (PEFC) are expected as next energy generation systems, and their performance is strongly dependent upon the polymer electrolyte membrane (PEM). We have suggested a new model of PEM with a three-dimensional proton conduction passways structure using the filler method, particularly focused on the functionalization of filler particles. The polymer surface-functionalized silica nanoparticles (NPs) with three different particle sizes were prepared by the reversible addition–fragmentation chain transfer polymerization with particles (RAFT PwP) method that we developed. Silica NPs coated with an in situ polymerized block copolymer consisted of a proton conductive polymer and a protective polymer. We confirmed that the proton conductivity increased and the activation energy decreased as the core particle size became smaller because of enlarging the total interface area between each particle and increasing the proton conduction passways.

Chemoenzymatic Epoxidation of Limonene Using a Novel Surface-Functionalized Silica Catalyst Derived from Agricultural Waste.

Limonene is one of the most important terpenes having wide applications in food and fragrance industries. The epoxide of limonene, limonene oxide, finds important applications as a versatile synthetic intermediate in the chemical industry. Therefore, attempts have been made to synthesize limonene oxide using eco-friendly processes because of stringent regulations on its production. In this regard, we have attempted to synthesize it using a cost-effective and eco-friendly process. Chemoenzymatic epoxidation of limonene to limonene oxide was carried out using in situ generation of peroxy octanoic acid from octanoic acid and H2O2. In this study, agricultural-waste rice husk ash (RHA)-derived silica was surface-functionalized using (3-aminopropyl) triethoxysilane (APTS), which was cross-linked using glutaraldehyde for immobilization of Candida antarctica lipase B. Furthermore, the immobilized enzyme was entrapped in calcium alginate beads to avoid enzyme leaching. Thus, limonene oxide was prepared using this catalyst under conventional and microwave heating. The microwave irradiation intensifies the process, reducing the reaction time under the same conditions. Maximum conversion of limonene to limonene oxide of 75.35 ± 0.98% was obtained in 2 h at 50 °C using a microwave power of 50 W. In the absence of microwave irradiation, the conventional heating gave 44.6 ± 1.14% conversion in 12 h. The reaction mechanism was studied using the Lineweaver–Burk plot, which follows a ternary complex mechanism with inhibition due to peroxyoctanoic acid (in other words H2O2). The prepared catalyst shows high reusability and operational stability up to four cycles.

Hybrid-Supported Bilayers Formed with Mixed-Charge Surfactants on C18-Functionalized Silica Surfaces.

Mixtures of cationic-anionic surfactants have been shown to spontaneously form ordered monolayers at hydrophobic-hydrophilic boundaries, including air-water and oil-water interfaces. In this work, confocal Raman microscopy is used to investigate the structure of hybrid-supported surfactant bilayers (HSSBs) formed by deposition of a distal leaflet of mixed cationic-anionic surfactants onto a proximal leaflet of n-alkane (C18) chains on the interior surfaces of chromatographic silica particles. The surface coverage of the two surfactants in a hybrid bilayer was determined from carbon analysis and the relative Raman scattering of their respective head-groups. Within the measurement uncertainty, the stoichiometric ratio of the two surfactants is one-to-one, equivalent to mixed-charge-surfactant monolayers at air-water and oil-water interfaces and consistent with the role of the head-group electrostatic interactions in their formation. When self-assembled on the hydrophobic surface, pairs of oppositely charged n-alkyl chain surfactants resemble a phospholipid (phosphatidylcholine) molecule, with its zwitterionic head-group and two hydrophobic acyl chain tails. Indeed, the structure of these hybrid-supported surfactant bilayers on C18-modified silica surfaces is similar to that of hybrid-supported lipid bilayers (HSLBs) on the same supports, but with denser and more-ordered n-alkyl chains. Hybrid-supported surfactant bilayers exhibit a melting phase transition (gel to liquid-crystalline phase) with structural and energetic characteristics similar to those of hybrid-supported bilayers prepared from a zwitterionic phospholipid of the same alkyl chain length. These mixed-charge surfactants on n-alkane-modified silica are stable in water over time (months), results that suggest the potential use of these hybrid bilayers for generating supported lipid-bilayer-like surfaces or for separation applications.

Effect of functionalized silica nanoparticles on the mass transfer process in active PLA nanocomposite films obtained by supercritical impregnation for sustainable food packaging

Nanocomposite films based on PLA with 1.0 % w/w silica nanoparticles (NP) and surface-functionalized silica nanoparticles with lactic acid (NP-LA), respectively, were obtained by extrusion process. Subsequently, cinnamaldehyde (ci) was incorporated through supercritical impregnation in the films at a pressure of 12 MPa, 40 °C temperature and 1.0 MPa min−1 depressurization rate. The developed materials were characterized on their thermal-mechanical, structural and barrier properties. Simultaneously, a phenomenological mass transfer was used to describe the release of cinnamaldehyde from the bionanocomposite in an aqueous food simulant (ethanol 10 % v/v solution). A 44 % decrease in oxygen permeability concerning the material without nanoparticles was checked as well as the plasticizing effect of cinnamaldehyde. Regarding the release of the active compound, the incorporation of functionalized nanoparticles NP-LA decreased the diffusion coefficient from 3.5·10−14 to 0.9·10−14 (m2/s), obtaining the filling effect of the silica nanoparticles, delaying the active compound release.

Functionalized silica surfaces as carriers for monoclonal antibodies in targeted drug delivery systems: Accelerated molecular dynamics study

We perform accelerated molecular dynamics simulations to study the adsorption process of trastuzumab monoclonal antibodies on silicon and several functionalized – hydroxylated, methylated and thiolated – silica surfaces. We find that surface chemistry plays an important role on the adsorption and the conformational changes of the adsorbed antibody. The hydroxylated silica surface leads to the smallest adsorption energy and keeps the tertiary protein structure almost unchanged; adsorption at this surface will hence allow trastuzumab to continue binding to the antigen HER2, as required for its use in cancer therapy. Adsorption on the other surfaces leads to strong protein denaturation.

α-Aminophosphonate derivatives of triethoxysilane for the synthesis of surface-modified silica

A convenient synthetic route for the preparation of α-aminophosphonate derivatives of triethoxysilane, attractive precursors for silica surface functionalization, was developed. The condensation of commercially available APTES with carbonyl compounds followed by Pudovik reaction of imines with diethyl phosphite yielded desired N-phosphonomethyl functionalized (3-aminopropyl)triethoxysilanes in high yields without further purification. The chemical structures of obtained products were undoubtedly proved by 1H, 13C and 31P NMR spectroscopy, elemental analysis and mass spectrometry.