Mesoporous TiO2-SiO2 Research Articles

Fixing Ni2+ onto mesoporous SiO2-TiO2 through amino silane and application as a catalyst for Kumada cross coupling reaction for 1,1′-biphenyl synthesis

Biphenyl synthesis through cross coupling reaction holds significant importance in organic synthesis. In this research, development of heterogeneous Ni(II) catalyst for Kumada cross coupling reaction to produce 1,1′-biphenyl compounds was studied. We used mesoporous SiO2-TiO2 as support material and functionalized it with 3-aminopropyltriethoxylsilane (APTES) as a binding site, and then introduced Ni(II) as a catalytically active species. The synthesized catalysts were comprehensively characterized. Based on the results, it was concluded that the catalysts were successfully synthesized with Ni(II) being bound to amino group in APTES. The catalysts effectively promoted the reaction and the maximum yield of 92% with almost 100% selectivity was achieved at 50 °C and 6 h. The catalyst was reusable without severe deactivation in first reuse. Every components in the catalyst were indispensable for the catalyst to show high catalytic performance. The catalyst developed in this study exhibited the performance comparable to those of previously investigated catalysts.

Block Copolymer and Cellulose Templated Mesoporous TiO2-SiO2 Nanocomposite as Superior Photocatalyst

A dual soft-templating method was developed to produce highly crystalline and mesoporous TiO2-SiO2 nanocomposites. Pluronic F127 as the structure-directing agent and pure cellulose as the surface area modifier were used as the templating media. While Pluronic F127 served as the sacrificing media for generating a mesoporous structure in an acidic pH, cellulose templating helped to increase the specific surface area without affecting the mesoporosity of the TiO2-SiO2 nanostructures. Calcination at elevated temperature removed all the organics and formed pure inorganic TiO2-SiO2 composites as revealed by TGA and FTIR analyses. An optimum amount of SiO2 insertion in the TiO2 matrix increased the thermal stability of the crystalline anatase phase. BET surface area measurement along with low angle XRD revealed the formation of a mesoporous structure in the composites. The photocatalytic activity was evaluated by the degradation of Rhodamine B, Methylene Blue, and 4-Nitrophenol as the model pollutants under solar light irradiation, where the superior photo-degradation activity of Pluronic F127/cellulose templated TiO2-SiO2 was observed compared to pure Pluronic templated composite and commercial Evonik P25 TiO2. The higher photocatalytic activity was achieved due to the higher thermal stability of the nanocrystalline anatase phase, the mesoporosity, and the higher specific surface area.

Self-Cleaning Characteristics of Mesoporous Nano-Crystalline TiO2–SiO2 Thin Films

Mesoporous TiO2–SiO2 films with remarkable self-cleaning capability were prepared by Sol–Gel methods and pressureless sintering. Here, the results show that the incorporation of 20 V% SiO2 onto the TiO2 films enhances the performance of anti-fog and self-cleaning. According to the SEM image, it is found that the TiO2 particles are dispersed by the SiO2, thus enlarging the specific surface area of the TiO2 particles. Therefore, super hydrophilicity and self-cleaning performance are promoted. Besides, the mesoporous structure is formed on the surface of the TiO2–SiO2 films after calcination. The mesoporous structure can improve the light utilization efficiency and the surface roughness of the films, thus promoting the performance of super hydrophilicity. Consequently, the mesoporous TiO2–SiO2 composite films as environmentally friendly coatings presented great potential in environmental governance.

Hydrodeoxygenation of non-edible bio-lipids to renewable hydrocarbons over mesoporous SiO2-TiO2 supported NiMo bimetallic catalyst

Ni-catalysts are promising candidate for fatty acid hydrodeoxygenation (HDO), but are limited by their quite poor HDO selectivity. Herein, a mesoporous Ni-Mo/SiO2-TiO2 catalyst was prepared by precipitation and impregnation method and used for methyl laurate HDO, yielding 96.3% n-dodecane yield at full methyl laurate conversion. Non-edible bio-lipids such as jatropha oil and waste cooking oil also converted to n-C14+16+18 hydrocarbons with yields of 94.3% and 92.4%, respectively. Besides, Ni-Mo/SiO2-TiO2 shows strong chemoselectivity towards the HDO of ester groups. Experimental results showed that Mo-addition and Ti/Si molar ratio strongly influenced HDO selectivity. Oxygen vacancies formed on partial reduced TiO2 surface securely bond Ni NPs and activate CO/CO bonds, improving Ni NPs dispersion and promoting R–COOCH3→R–CHO reduction. Additional, Mo-addition switches reactant adsorption configuration from η1(C)-acyl to η2(C,O)-aldehyde, promoting the formation of R–CH2OH intermediate. Moreover, abundant Brønsted acidic sites (Mo4+–OH, Mo6+–OH, hydroxy groups) facilitate the HDO of R-CH2OH to R-CH3.

Mesoporous silica as a matrix for photocatalytic titanium dioxide nanoparticles: lipid membrane interactions.

In the present study, we investigate the combined interaction of mesoporous silica (SiO2) and photocatalytic titanium dioxide (TiO2) nanoparticles with lipid membranes, using neutron reflectometry (NR), cryo-transmission electron microscopy (cryo-TEM), fluorescence oxidation assays, dynamic light scattering (DLS), and ζ-potential measurements. Based on DLS, TiO2 nanoparticles were found to display strongly improved colloidal stability at physiological pH of skin (pH 5.4) after incorporation into either smooth or spiky ("virus-like") mesoporous silica nanoparticles at low pH, the latter demonstrated by cryo-TEM. At the same time, such matrix-bound TiO2 nanoparticles retain their ability to destabilize anionic bacteria-mimicking lipid membranes under UV-illumination. Quenching experiments indicated both hydroxyl and superoxide radicals to contribute to this, while NR showed that free TiO2 nanoparticles and TiO2 loaded into mesoporous silica nanoparticles induced comparable effects on supported lipid membranes, including membrane thinning, lipid removal, and formation of a partially disordered outer membrane leaflet. By comparing effects for smooth and virus-like mesoporous nanoparticles as matrices for TiO2 nanoparticles, the interplay between photocatalytic and direct membrane binding effects were elucidated. Taken together, the study outlines how photocatalytic nanoparticles can be readily incorporated into mesoporous silica nanoparticles for increased colloidal stability and yet retain most of their capacity for photocatalytic destabilization of lipid membranes, and with maintained mechanisms for oxidative membrane destabilization. As such, the study provides new mechanistic information to the widely employed, but poorly understood, practice of loading photocatalytic nanomaterials onto/into matrix materials for increased performance.

Plastic-free silica-titania-polyphenol heterojunction hybrids for efficient UV-to-blue light blocking and suppressed photochemical reactivity

The photocatalytic activity of ultraviolet (UV) filters, generating reactive oxygen species (ROS), must be minimized in skincare products to avoid adverse biological and chemical effects. Unfortunately, the screening effect of UV filters is intrinsically correlated with their photocatalytic activity in the presence of oxygen and water. Polymeric encapsulation has been widely employed to inhibit photochemical ROS generation; however, it can cause serious microplastic issues because UV filters act as photocatalysts under sunlight irradiation. Here we present plastic-free silica-titania-tannin (SiO2-TiO2-TA) heterojunction hybrids to increase UV-to-blue light blocking effects while suppressing UV-induced ROS generation by altering their photochemical routes. Mesoporous SiO2-TiO2 particles were prepared through the in situ synthesis of TiO2 nanocrystals within SiO2 particles, followed by the spontaneous deposition of TA via Ti-pyrogallol and Ti-catechol coordination. Ligand-to-metal charge transfer (LMCT) from TA to the conduction band of TiO2, demonstrated by theoretical calculations, extends the absorption spectrum of TiO2 over the blue wavelength regime, increasing a specific sun protection factor ∼ 1.8 times. The TA layer efficiently suppressed the UV-induced ROS generation: the SiO2-TiO2-TA produced only < 1 % hydroxyl radical ions compared to pristine TiO2 under simulated solar irradiation. Accordingly, the UV and blue light-induced cytotoxicity of fibroblasts was significantly alleviated by the ROS stabilization effect of TA complexed with TiO2, while pristine TiO2 exacerbated the cytotoxic effect via ROS generation in the cytoplasm. This work demonstrates that polyphenol coatings are a promising method to suppress the ROS generation by inorganic UV filters while increasing their screening effects through LMCT.

Carrier transport and shielding properties of rod-like mesoporous TiO2–SiO2 nanocomposite

Synthesizing material candidates having both high ultraviolet (UV) absorbing capacity and low photoactivity is a paramount challenge. The present study reports the sonosynthesis of titanium oxide (TiO2) - silicon dioxide (SiO2) nanocomposite that possesses good UV screening efficacy but reduced photoactivity. It was observed that the synthesized TiO2–SiO2 (TS11) composite with a 1:1 M ratio of TiO2 and SiO2 precursors showed lower photoactivity (25.91% pollutant degradation in 300 min) while maintaining its UV shielding properties (20% UV transmittance in 200–400 nm region). The surface area and average pore diameter of TS11 nanocomposite was found to be 2 m2g-1 and 18.8 nm as per Barrett- Joyner- Halenda (BJH) analysis. Low photoactivity could be accounted to the reduced surface area and unique rod-like morphology of the TS11 composite that probably trapped the photoactive TiO2 particles within the SiO2 rods. The TS11 nanocomposite showed tunable band gap in comparison to that of bare TiO2 and SiO2 which is desirable for optoelectronic applications. The carrier transport properties were evaluated by fabricating an ITO/TS11/Al based Schottky diode. Lower carrier mobility, diffusion length and higher transit time under illumination in comparison to other TiO2 composites appears consistent with reduced photoactivity.

Distributed Bragg reflectors from colloidal trilayer flake solutions

The fabrication of highly reflective inorganic distributed Bragg reflectors (DBRs) from aqueous solutions of colloidal flakes is demonstrated. Our approach involves the deposition of compact or mesoporous TiO2–SiO2–TiO2 trilayers onto a patterned sacrificial layer. A subsequent etch-release of the patterned flakes into water results in a colloidal flake solution. Drops of this flake-containing solution are then deposited onto another substrate, where they self-assemble into stacks upon solvent evaporation. This method gives rise to high quality DBRs in a much quicker fabrication process compared to previously established methods and produces ordered DBRs of high reflectivity. Changing compact for mesoporous assemblies, the produced DBRs can be used for environmental refractive index sensing. The presented approach may open the way for the on-demand integration of stimuli-responsive DBRs into microfluidic and fiber-end sensing applications or allow the integration of highly reflective colloidal flakes with light emission and detection technologies.

Low-Temperature Synthesis of Micro–Mesoporous TiO2–SiO2 Composite Film Containing Fe–N Co-Doped Anatase Nanocrystals for Photocatalytic NO Removal

A simple low-temperature (< 100 °C) hot-water treatment was used to synthesize Fe–N co-doped anatase nanocrystals which were uniformly dispersed in micro–mesoporous SiO2 host film for the first time. The Fe–N co-doped TiO2–SiO2 (FNTS) film exhibited stable photocatalytic activities. A NO removal efficiency of 56.1% was achieved under simulated solar light irradiation without any obvious inactivation in 30 min. The transient photocurrent response of FNTS film is approximately six times higher than that of non-doped TiO2–SiO2 film, indicating the superior charge separation of photo-generated electron–hole pairs. Electron spin resonance analysis showed that the ·OH and ·O2− radicals were key species to remove NO. Combined with quantitative reaction intermediates, the possible photocatalytic degradation mechanism of NO over FNTS film was proposed. In addition, the FNTS thin films exhibited intrinsic super-hydrophilicity and durable self-cleaning property even after 6 months of storage in the dark. This work provides a facile method to load the catalyst on thermal labile substrates, such as soda–lime glass and organic polymer for more practical applications. A simple low-temperature (< 100 °C) hot-water treatment was used to synthesize micro–mesoporous TiO2–SiO2 composite film, which shows good self-cleaning ability and superior photodegradation activity for NO removal under solar light.

Synthesis of amorphous mesoporous TiO2-SiO2 and its excellent catalytic performance in oxidative desulfurization

Amorphous mesoporous TiO2-SiO2 composites have been prepared by introducing n-propyltriethoxysilane (PTES) into the synthesis system of titanium silicalite-1 (TS-1). The hydrolysate of PTES can participate in the condensation between ‘Si(OH)4’ and ‘Ti(OH)4’, and generate the isolated ‘alkyl-rich regions’ and ‘inorganic TiO2-SiO2 regions’. Proper amount of ‘alkyl rich regions’ can highly separate titania–silica species and seriously retard the crystal growth, thereby producing the amorphous mesoporous structure. As the PTES/Si molar ratio is between 0.1 and 0.2, the resulting samples have plenty of three-dimensional connected mesopores, and they display outstanding catalytic performance in the oxidative desulfurization of bulky sulfur compounds.

Integrated fast-mass transfer and high Ti-sites utilization into hybrid amphiphilic TS@PMO catalyst towards efficient solvent-free methyl oleate epoxidation

For solvent-free catalytic oxidations, low efficiency resulted from poor mass transfer and insufficient utilization of active centers remains a tough problem. Herein, we demonstrate a novel hybrid core-shell catalyst (TS@PMO) with an amphiphilic shell and a Ti-surface-enriched mesoporous TiO2-SiO2 (TS) core to address this challenge. Such TS@PMO realizes its amphiphilicity via an ex situ formed periodic mesoporous organosilica (PMO) shell. Simultaneously, by a unique etching effect induced by organic precursor growth on [SiO4] tetrahedra in TS core, active Ti sites are facilely enriched in near-surface layer of core and extra mesoporous cavities are introduced for substrate reservation. When applied for solvent-free epoxidation of methyl oleate (MO) with H2O2, TS@PMO exhibits remarkably boosted catalytic activity (X = 90.2%) and epoxide selectivity (S = 70.2%), overwhelming the unmodified titanosilicate (X = 63.7%, S = 49.2%) and Ti-containing organosilica (X = 39.8%, S = 25.0%). Such result benefits from an evidently enhanced interphase mass transfer and sufficiently accessible active Ti sites in TS@PMO. On the one hand, amphiphilic PMO shell can efficiently collect hydrophobic substrate and H2O2, while abundant mesopores in the shell offer open-path for them to access active sites in the core; on the other hand, an increased framework Ti (IV) density and their surface-enrichment in TS core greatly improve the utilization of active Ti sites. This study effectively makes up for the deficiencies of slow mass transfer and insufficient utilization of conventional titanosilicates in biphasic reactions, which paves a new avenue to exploit other hybrid catalysts for high-efficiency solvent-free catalysis.

Flexible Mesoporous Membranes with Revivability and Superwettability for Sustainable Oil–Water Separation

Separating emulsified oil–water emulsions is still a significant challenge owing to the serious fouling and low permeation flux of the membrane. Here, a flexible mesoporous TiO2-SiO2 composite memb...

Mesoporous Titania-Silica nanocomposite as an effective material for the degradation of Bisphenol A under visible light

A simple and very effective method is proposed for the removal of Bisphenol A (BPA) under visible light using mesoporous TiO2-SiO2 nanocomposite. The material was characterized using FTIR, XRD, DRS, XPS, FESEM, HRTEM, and BET techniques. The photo degradation efficiency of TiO2-SiO2 compared with bare TiO2. The effect of calcination temperature on the photo-degradation of the materials is also studied. The radical intermediates formed during the degradation of BPA were followed with different radical scavengers. The solution after reaction is subjected to TOC (Total Organic Carbon content) and LCMS analysis to determine the mineralization rate and degradation products exist in the solution. Kinetic studies were revealed that the degradation process follow pseudo first order kinetics.

Green Removal of Toxic Th(IV) by Amino-Functionalized Mesoporous TiO2-SiO2 Nanocomposite

Mesoporous TiO2-SiO2 nanocomposite (TS) was synthesized via sol-gel method and Amino-functionalized using 3-(aminopropyl) triethoxysilane. prepared amino-functionalized TiO2-SiO2 (NH2TS) was evaluated for eliminating radioactive Th(IV) ion in comparison with (TS). The prepared nanocomposites were characterized using FT-IR, XRD, DSC-TGA, SEM, EDS, BET, and BJH analyses. DSC and TGA analyses revealed that the total organic content of the NH2TS was at about 4%. According to the XRD patterns, synthesized nanocomposites exhibited only the crystalline anatase phase, and the sizes of the anatase crystallites in the prepared TS and NH2TS calculated to be 10.4 and 14.1nm, respectively. Moreover, the pore diameters of TS and NH2TS estimated to be 4.65 and 3.632 nm according to their BJH plot. The kinetic data of Th(IV) uptake process on both of two nanocomposites corresponded well to the pseudo-second-order equation. Adsorption thermodynamic parameters including the standard enthalpy, entropy, and Gibbs free energy revealed that the ion exchange reactions on both of NH2TS and TS nanocomposites were endothermic and spontaneous processes. The results indicated that NH2TS exhibited higher adsorption affinity toward Th(IV) compared to TS. Moreover, based on the Langmuir model, the maximum adsorption capacity of NH2TS nanocomposite towards the Th (IV) was found to be 1000 mg/g.

Green and facile sol-gel synthesis of the mesoporous SiO2-TiO2 catalyst by four different activation modes.

The most environmentally friendly protocol for obtaining mesoporous SiO2–TiO2 catalysts has been sought. Water has been employed as a green solvent, the energy input has been minimized, and three further principles (1, 3, and 12) of Green Chemistry have been considered. Four different modes for promoting the reaction have been comparatively evaluated, namely near-infrared and microwave electromagnetic irradiations, ultrasound, and traditional mantle heating. Brunauer–Emmett–Teller (BET) analyses of the catalysts produced revealed that the non-conventional activation modes afforded both large surface areas (335–441 m2 g−1) and smaller crystal sizes (7.2–15.3 nm) than the mantle heating process. These modes also generated the catalysts in shorter reaction times than traditional mantle heating, 10–30 min versus 3 h, with anatase as the sole crystalline phase. The photocatalytic degradation of 4-chlorophenol has been carried out to assess the catalytic efficiencies of the hybrid materials. The catalyst synthesized with microwave assistance showed the best mineralization activity (97%), followed by those prepared with ultrasound, near-infrared, and mantle heating. The materials have been extensively characterized by FTIR, XRD, DRS-UV/Vis, SEM, 29Si MAS NMR, and BET analyses. To the best of our knowledge, this is the first such comparative assessment of green energetic alternatives in developing a sol–gel process.

Fabrication of flexible TiO2-SiO2 composite nanofibers with variable structure as efficient adsorbent

As inorganic oxides become increasingly popular in practical applications, variable structure, superior softness and large specific surface area of inorganic oxides play an increasingly vital role. In this work, hierarchical and flexible TiO2-SiO2 nanofibrous mats were fabricated by sol-gel combined with calcination. This method thoroughly eliminated the complicated spinneret and unstable efflux compared with coaxial and multifluidic electrospinning. Interestingly, the interior structure of TiO2-SiO2 composite nanofibers was variable, which was tuned via changing the ratio of continuous phase and oil phase, varying from mesoporous, multi-channel to hollow. The specific surface area of mesoporous TiO2-SiO2 nanofibers was as large as 674.6 m2 g-1. It was confirmed that TiO2-SiO2 nanofibrous mats could maintain integrated morphology after bending to curvature which the radius is 0.6 mm, indicating the brittleness of inorganic oxides was successfully overcome. Flexible TiO2-SiO2 composite nanofibers as adsorbent showed superior adsorption efficiency and recyclable performances.

Enhanced catalytic performance of Nb doping Ce supported on ordered mesoporous TiO2-SiO2 catalysts for catalytic elimination of 1,2-dichlorobenzene

Ordered mesoporous TiO2-SiO2 materials with high specific area were synthesized by evaporation–induced self–assembly (EISA) method. CeNb/TiSi catalysts were prepared via impregnation method and evaluated for catalytic elimination of 1,2-dichlorobenzene (o-DCB). The structures and properties of CeNb/TiSi were controlled by adjusting Ti/Si and Ce/Nb molar ratios and characterized by N2 adsorption-desorption, XRD, TEM, Raman, XPS and temperature-programmed technology. Results showed that Ce and Nb oxides were highly dispersed on the surface of TiO2-SiO2 carriers due to its high specific surface area. Nb oxides was not only contributed to moderate and strong acid sites but also conducive to the catalytic elimination of o-DCB. Weak acid sites mainly derived from hydroxyl on the surface of Si. The catalyst without Si exhibited an optimum elimination efficacy of o-DCB but bad stability due to the deposition of Cl−, while the sample with high content of Si had excellent stability on account of the preferable chlorine-resistant ability of Si in catalytic elimination reaction o-DCB. Furthermore, the reaction mechanism of o-DCB catalytic elimination was proposed, in which surface lattice oxygen played a role of redox sites.

Mesoporous SiO2 nanostructure: Light-induced adsorption enhancement and its application in photocatalytic degradation of organic dye

Mesoporous SiO2 nanostructure was synthesized by a simple controlled hydrolysis process. The obtained mesoporous SiO2 nanostructure was composed of amorphous silica nanoparticles and exhibits significant light-induced adsorption performance. The light-induced adsorption enhancement may be caused by exchanging adsorption between hydroxyl groups and dye molecules because the adsorption process under light irradiation exhibits significant chemical adsorption property. Combining this mesoporous SiO2 and rutile TiO2 materials, the obtained hybrid photocatalyst displays superior photocatalytic degradation performance of RhB dye due to the excellent adsorption performance and the increase of surface defects on the surface of TiO2 nanostructure. These results provide novelty route for the further design and development of high performance photocatalyst in actual application.

G-C3N4 quantum dots-modified mesoporous TiO2–SiO2 for enhanced photocatalysis

The utilization of TiO2-based photocatalysts for an efficient removal of dye pollutants is limited due to their low surface area, high recombination rate of the photo-generated electrons and holes and an insufficient absorption of sunlight with only 3–4% use of solar energy. Based on this background, we have successfully fabricated a carbon nitride quantum dots (CNQDs)-modified mesoporous TiO2–SiO2 (Me-TSCN) via a simple calcination method since the mesoporous structure is expected to induce a great increase in the specific surface area by carbon nitride quantum dots, being favorable for the adsorption of the reactant molecules and the mass transfer of the reaction products. Furthermore, such CNQD modification facilitates the separation of photo-generated electrons and holes. As a result, the composite's modification with structural design could significantly improve the photocatalytic activity of TiO2-based catalysts, achieving outstanding photocatalytic activity in the degradation of dye pollutants such as rhodamine B.

Research progress of photocatalysis based on highly dispersed titanium in mesoporous SiO2

With the development of the human economy and green chemistry, people pay much more attention to environmental safety. Correspondingly, mesoporous TiO2 and its correlated photocatalysts are able to help people seek for better life. In this review, first of all, we briefly introduce the preparations and applications of mesoporous TiO2-SiO2 materials, which exhibit excellent performance in pollutants decomposition and H2 evolution in photocatalysis. Then, we review the mesoporous composites of Ti-SiO2 materials, which are ideal materials used in the photoreduction of air pollutants such as CO2, NO and NO2. It is powerfully evident from the literature surveys that these TiO2 based mesoporous photocatalysts possess a large potential in environment and energy development.