Next Article in Journal
Extensive CGMD Simulations of Atactic PS Providing Pseudo Experimental Data to Calibrate Nonlinear Inelastic Continuum Mechanical Constitutive Laws
Next Article in Special Issue
Single and Double-Stranded 1D-Coordination Polymers with 4′-(4-Alkyloxyphenyl)-3,2′:6′,3″-terpyridines and {Cu2(μ-OAc)4} or {Cu4(μ3-OH)2(μ-OAc)2(μ3-OAc)2(AcO-κO)2} Motifs
Previous Article in Journal
Design of Web-to-Web Spacing for the Reduced Pressure Drop and Effective Depth Filtration
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Polymers
Volume 11
Issue 11
10.3390/polym11111823
polymers-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Functional Metal Organic Framework/SiO2 Nanocomposites: From Versatile Synthesis to Advanced Applications

by
Mengyu Ma
,
Liangyu Lu
,
Hongwei Li
,
Yuzhu Xiong
and
Fuping Dong
*
Department of Polymer Materials and Engineering, Guizhou University, Guiyang 550025, China
*
Author to whom correspondence should be addressed.
Polymers 2019, 11(11), 1823; https://doi.org/10.3390/polym11111823
Submission received: 7 October 2019 / Revised: 3 November 2019 / Accepted: 4 November 2019 / Published: 6 November 2019
(This article belongs to the Special Issue Coordination Polymers: Properties and Applications)
Browse Figures
Versions Notes

Abstract

:
Metal organic frameworks (MOFs), also called porous coordination polymers, have attracted extensive attention as molecular-level organic-inorganic hybrid supramolecular solid materials bridged by metal ions/clusters and organic ligands. Given their advantages, such as their high specific surface area, high porosity, and open active metal sites, MOFs offer great potential for gas storage, adsorption, catalysis, pollute removal, and biomedicine. However, the relatively weak stability and poor mechanical property of most MOFs have limited the practical application of such materials. Recently, the combination of MOFs with inorganic materials has been found to provide a possible strategy to solve such limitations. Silica, which has excellent chemical stability and mechanical properties, shows great advantages in compounding with MOFs to improve their properties and performance. It not only provides structured support for MOF materials but also improves the stability of materials through hydrophobic interaction or covalent bonding. This review summarizes the fabrication strategy, structural characteristics, and applications of MOF/silica composites, focusing on their application in chromatographic column separation, catalysis, biomedicine, and adsorption. The challenges of the application of MOF/SiO2 composites are addressed, and future developments are prospected.

Graphical Abstract

1. Introduction

Metal organic frameworks (MOFs), also called porous coordination polymers (PCPs), as organic-inorganic hybrid materials with a 3D periodic grid structure formed by coordination bonds between metal ions or clusters and organic ligands, have developed rapidly in recent decades [1,2,3,4,5,6]. The structures of the originally prepared MOFs are not stable, and their skeletons easily collapse, limiting further research and application. In the 1990s, Yaghi et al. synthesized MOF-5, which retained the skeleton integrity after removing the guest molecules in the channel [7,8]. The successful synthesis of MOF-5 became a milestone in the development of MOFs. MOFs have the advantages of ultrahigh specific surface area, high and adjustable porosity, diverse structural composition, open metal sites, and chemical modifiability, which make them widely concerned in the fields of gas storage and separation, catalysis, energy, and drug-sustained release [9,10,11,12,13,14,15,16,17,18,19]. However, weak coordination bond composition results in the poor stability and low mechanical strength of many MOF materials, which greatly limit their application [20,21]. MOFs with higher stability can be obtained by synthesizing metal–nitrogen-containing MOFs with high bonding energy, by synthesizing MOFs with metals with high coordination numbers, or by post-synthetic modification using organic linkers [22,23,24]. Currently, in practical applications, especially in high-temperature and high-humidity industrial environments, enhancing the thermal stability, water stability, chemical stability, and mechanical strength of MOFs while maintaining high specific surface area and high activity remains a big challenge [23,25,26]. To solve this problem, researchers have attempted to compound MOFs with other materials to form MOF nanocomposites [27,28,29,30,31,32,33]. MOF composites are two-phase or multiphase composites based on MOFs as matrixes with polymers, metals, silica, graphene, or carbon nanotubes with different properties as the reinforcement phase [34,35,36,37,38,39,40,41,42,43,44]. Among them, silica, especially porous silica, is very suitable for the preparation of composite materials to improve the performance of MOFs due to its high stability and structural adjustability [45,46,47,48]. Silica not only provides structured support for MOFs but also improves the stability of materials through hydrophobic interaction or covalent bonding. The compound strategy of MOF/SiO2 composites generally includes an in situ method, where MOF crystals are grown on the prepared silica, and the sol–gel method, where a silica layer is coated on the synthesized MOF crystals [49].
MOF/silica composites demonstrate excellent performance in various applications. Especially, as the stationary phase of the chromatographic column, the highly uniform core–shell-structured MOF/silica composite could improve the uneven packing of MOF particles and greatly enhance the separation efficiency [50]. Silica has a guiding effect on the growth of MOF crystals and could effectively design and control the morphology of MOFs. The interaction between silanol groups on the silica precursor and metal center can cause structural changes in the material and lead to the increase in surface area and micropore volume, which will facilitate gas adsorption applications [51]. In addition, MOF/silica composites containing different open metal sites can not only act as catalysts but also support noble metal particles, which have great potential in the field of catalysis [52]. MOF/silica composites have also been utilized for drug delivery, angiography, diagnosis, treatment, and other biomedical fields [53]. Especially in the field of next-generation drug-sustained release, MOF materials have great advantages due to their organic-inorganic hybrid structure, molecular horizontal structure, designability/adjustable porosity, and easy chemical modification. After compounding with silica, the biological stability and structural diversity of MOF materials can be improved and become more suitable for biomedical applications [54]. As shown in Table 1, the synthesis strategy and the advanced applications of MOF/SiO2 nanocomposites have been summarized in detail. Even though people have reviewed some composite materials containing MOFs for some special applications [55,56,57,58,59], the review of the specific topic of MOF/SiO2 composite materials still seems necessary, due to the rapid development in this field. Herein, the fabrication and properties of MOF/silica composites reported in recent years are summarized. Especially, their applications in the fields of chromatographic column separation, catalysis, adsorption, and biomedicine, have been analyzed carefully. The problems and challenges in the application of MOF/silica composites are pointed out.

2. General Strategies for MOF/Silica Composite

Silica, which has excellent chemical stability and mechanical properties, shows great advantages in the compounding with MOFs to improve their properties and performance. It not only provides structured support for MOF materials but also improves the stability of materials through hydrophobic interaction and covalent bonding [60]. The structure, morphology, surface chemistry, and thermal stability of the MOF/silica composite could be characterized by the techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), etc. To fabricate MOF/SiO2 composites, three processes including in situ synthesis, sol–gel methods, and impregnation are usually utilized according to their application requirements.
For the in situ process of coating MOF layers on silica particles, silica seeds are prepared first, and then MOF are grown on them by the one-pot or layer-by-layer assembly method. As shown in Figure 1, Gao et al. first prepared carboxylate-terminated silica, which adsorbed the Zr4+ on the silica surface and finally reacted with 1,4-benzenedicarboxylic acid (H2BDC) to form UiO-66@SiO2 [61]. In this process, uniform-sized silica worked as a support and offered MOFs regular shape and narrow size distribution, which are very important for versatile applications.
In the sol-gel method, MOF crystals are first synthesized, and then the silica precursors are hydrolyzed, condensed, and gelled to form porous SiO2 shells in the presence of MOFs [79]. The silica coating prepared using this strategy not only maintains the intrinsic good performance of the MOFs but also improves the stability and mechanical properties of the MOF materials. As Figure 2 shows, a very thin shell of hydrophobic mesoporous silica was encapsulated on the prepared MIL-101(Cr) crystals by sol–gel and calcination processes [80]. The MIL-101(Cr)@SiO2 was utilized to catalyze the oxidation reaction of indene with H2O2 in acetonitrile, and the activity of MIL-101(Cr)@SiO2 was found obviously higher than that of the pure MIL-101(Cr) sample. The turnover frequency (TOF) value of the MIL-101(Cr)@SiO2 (95.2 mmol g−1 h−1) is 1.24 times higher than that of the MIL-101(Cr) (76.8 mmol g−1 h−1). Moreover, after 1 h, the conversion of indene with the MIL-101(Cr)@SiO2 sample is 95%, while the conversion with the MIL-101(Cr) is only 77%. The porous silica shell facilitates the diffusion of reactants, which will improve the catalytic performance and catalytic stability of the MOFs.
An impregnation approach could be utilized to grow MOFs confined in the pores of porous silica materials to well control the morphology of MOF/silica composites [81,82]. Abolghasemi et al. first fabricated mesoporous silica (SBA-15) with uniform large pores and then impregnated the silica into the MOF precursors with suitable solvent and grew MOFs only on the pore surfaces (Figure 3) [83]. The obtained MOF-5@SBA-15 nanocomposite shows an enhanced sorbent capacity of small molecules originating from the properties of the nanocomposites, including its porous structure, large surface area, and homogeneous morphology.

3. Application of MOF/Silica Composite

3.1. Application in Chromatographic Column Separation

Given the large specific surface area, adjustable pore structure, and large number of active metal sites, MOFs have great potential in separation applications, especially in chromatographic column separation [84,85,86,87,88]. However, the irregular shape and wide size distribution of MOF particles lead to the difficulty in column packing, low column efficiency, or high column pressure. Combining traditionally well-filled silica (which has excellent column-filling properties) with MOFs (which have excellent separation properties) is an excellent strategy to fabricate composites for the stationary phase of high-performance liquid chromatography (HPLC) [89,90,91,92]. The structure of the composite could greatly influence the separation ability of the materials. Exploring and optimizing the structure of MOF/SiO2 composites are important to improve the separation performance. Usually, MOF/SiO2 composites with a different structure for chromatographic column separation could be fabricated by impregnation, sol–gel or solvothermal process.

3.1.1. MOFs Grown on the Pores of Porous SiO2 Particles

To fabricate MOF/SiO2 composites for HPLC separation, porous silica particles are impregnated into the dispersion solution of MOF precursors and loaded with MOF nanocrystals in the pores after reaction to form the MOF/SiO2 composite. Ameloot et al. immersed porous silica beads in the precursor solution of HKUST-1, and after solvent evaporation, HKUST-1 crystals were grown in the pores of silica beads [93]. The obtained monodispersed MOF/SiO2 composite microspheres with a diameter of 3 µm showed high HPLC separation performance. Qu et al. also utilized carboxyl-modified mesoporous silica spheres as cores to grow a layer of HKUST-1 or ZIF-8 nanoscale films in the pores [62,94]. By adjusting the reaction condition, such as the volume of ethanol in the solvents, the formation of HKUST-1 crystals could be controllably coated only on the porous surface, and the thickness of the films could be controlled by changing the formation rate of nanocrystals (Figure 4). With the HKUST-1/SiO2 composite as a filler for the column of HPLC, a high separation efficiency as high as almost 140,000 plates per meter was achieved for the model analyte styrene.

3.1.2. MOF Film on SiO2 Particles

To increase the packing efficiency and sorbent–solute contact time, a suitable approach is to coat MOFs on silica, which is cheap, has a high surface area, and functions as a support. Through a one-pot synthesis process, El-mehalmey et al. wrapped a layer of amino-modified MOF materials on the surface of silica particles (Figure 5) to prepare a UiO-66-NH2@silica composite material. The composite was used as a porous solid phase of ion exchange column to improve the filling efficiency of the column and increase the contact time of the adsorbent and solute [63]. The results showed that the composite has an excellent uptake capacity of Cr(VI) ions in the chromatographic column. Even under the interference of competing anions, such as chloride, bromide, nitrate, and sulfate, the ion exchange column could effectively eliminate Cr(VI) ions. Yan et al. prepared mesoporous composite materials of MOF crystals on silica particles with the aid of surfactant cetyltrimethylammonium bromide (CTAB) by the solvothermal method and utilized them as new stationary phases for liquid chromatography (LC) [64,95]. The results showed that the isomers could be separated quickly and efficiently. Tanaka et al. prepared chiral (R)-MOF–silica composites using chiral organic ligands and copper nitrate or zinc nitrate as raw materials in the presence of monodispersed silica spheres by a one-step solvothermal method [96,97]. As a stationary phase of enantiomers in HPLC, this chiral composite material has excellent selectivity and high separation efficiency for various chiral sulfoxides. In addition, using the sol–gel method and supercritical CO2 drying method, Nuzhdin et al. prepared an HKUST-1@SiO2 aerogel composite material and used it in the stationary phase of conventional LC to efficiently separate unsaturated hydrocarbon from saturated aliphatic hydrocarbon [98].

3.1.3. MOF Particles on SiO2 Particles

Recently, superficially porous particles with a solid core and porous shell as the stationary phase for separation columns exhibited higher separation performance compared with only solid or porous materials [99,100,101,102]. Ahmed et al. utilized silica microspheres modified with amino or carboxyl groups as the template core to synthesize copper-based HKUST-1 nanocrystals on them and finally obtained HKUST-1/SiO2 microspheres with regular morphology [103]. As the stationary phase for fast and HPLC (Figure 6), the composite materials combined the filling and supporting function of the silica with the large number of open active metal sites of MOFs, achieving a high-efficiency separation of HPLC, which can rapidly separate toluene/ethylbenzene/styrene in 1.5 min. The same group also prepared a ZIF-8/SiO2 composite with stable ZIF-8 as the shell, which demonstrated high column separation efficiency of the aromatic mixture up to 19,000 plates/m due to the large specific surface area and its π–π interaction with the aromatic compound [104].
The MOF/silica composite mainly combines the advantages of silica microspheres (stability and suitable morphology) and MOFs (large specific surface area, adjustable pore structure, modifiability, and a large number of active metal sites), indicating its high application potential for chromatographic column separation. To improve the separation performance, exploring and optimizing the structure of MOFs/SiO2 composites are important.

3.2. Application in Gas Adsorption

MOF materials have been widely used in the field of gas adsorption due to their high specific surface area, adjustable pore size, and pore surface, especially in the adsorption of carbon, sulfur, and nitrogen-containing gases [105,106,107]. The silica in the MOF/silica composites acts as a structure-directing agent to guide the growth of MOFs into a regular morphology and provides protection for MOFs to improve their stability [65]. The composite of porous/mesoporous silica and MOFs is expected to further reduce the mass transfer resistance of target molecules, such as gases, and accelerate the diffusion of target molecules, such as carbon dioxide. The synergistic effect between silicon dioxide and MOFs can also enhance the interaction between materials and gas molecules, thereby improving the gas adsorption efficiency of materials [108].

3.2.1. Carbon Dioxide Adsorption

For CO2 adsorption, porous/mesoporous silica materials are usually utilized as seeds, and MOF crystals are in situ synthesized on the seed to form MOF/SiO2 adsorbent [109]. As Sorribas et al. reported, the prepared mesoporous silica spheres (MSSs), MCM-41, reacts in situ with the precursors of Al(NO3)3·H2O and NH2-H2BDC to form the MOF/SiO2 composites through a layer-by-layer process (Figure 7) [110,111]. The adsorption amount of CO2 can reach 10 mmol/g when the materials are applied as a CO2 adsorbent due to the breathing behavior of the mesoporous silica core and microporous MOF shell. Through a hydrothermal process, MOF@SiO2 composites have also been reported by growing MOF nanocrystals on an SBA-15 or MCM-41 mesoporous silica matrix, which works as the structure-directing agent to guide the growth of MOFs [51,66]. As a CO2 adsorbent, the obtained composite material exhibits higher specific surface area than the original MOF material, and the material has a higher adsorption amount and a faster adsorption rate for CO2.
In other processes, MOF crystals as the core or dispersed phase are first prepared, and then silica is formed via a sol-gel process under the catalysis of acid and alkali to form MOFs/SiO2. Through a sol–gel process, Ulker et al. mixed the tetraethoxysilane (TEOS, SiO2 precursor) with the prepared HKUST-1 crystals to form an HKUST-1-doped and dispersed silica aerogel composite material [67]. Given the synergistic effect of MOFs and silica aerogel on gas adsorption, the composite has high CO2 adsorption capacity and can be used for carbon dioxide adsorption and the storage/separation of gas mixtures.

3.2.2. Adsorption of Water Vapor

Silica can be used to enhance the water stability of MOFs, and their composites can be used to adsorb water or other moist gases. Using a microwave-assisted sol-gel process, Uma et al. fabricated an MIL-101(Cr)-SiO2 composite with uniform mesopores; they found that the material has high adsorption efficiency to water vapor, and the water stability of the composite is significantly enhanced by the addition of silica [68]. Mazaj et al. first prepared amino-functionalized MOFs by modifying FDU-12 with aminopropyltriethoxysilane; then, the MOFs were immersed into a Cu2+ solution to obtain an HKUST-1@NH2-FDU-12 composite material with copper ions as ligands (Figure 8) [112]. In this composite, HKUST-1 is loaded into the pores of the silica matrix, and the hydrophobic silica provides a layer of protection for the MOFs, which significantly improves the structural stability and avoids the hydrolysis of pure HKUST-1 in direct contact with water. The large specific surface area of the MOFs and the structural stability of silica effectively increase the adsorption efficiency of the composite materials, which can be used to continuously capture humid gases.

3.2.3. Adsorption of Other Gases

In addition to the adsorption of carbon dioxide and water vapor, MOF/SiO2 composites can also be used for the adsorption and removal of sulfur-containing gases, such as H2S. Using an ultrasound-assisted in situ process, Saeedirad et al. grew ZIF-8 crystals on three kinds of mesoporous silica templates to form three kinds of composites, namely, MCM-41@ZIF-8, SBA-15@ZIF-8, and UVM-7@ZIF-8 [69]. The composite material performed well in the adsorption desulfurization of H2S and CH3CH2SH and had good recycling performance. Its absorption capacity was only reduced by approximately 10% after hydrogen sulfide and ethanethiol adsorption four times.

3.3. Application in the Field of Catalysis

As a kind of crystalline material containing metal or metal cluster junctions, metal–organic skeleton materials are expected to become heterogeneous catalysts or catalyst carriers [113,114,115,116,117,118,119,120]. MOF materials provide a highly tunable platform for structure and performance, integrating all the properties required for catalysis, including high surface area, high porosity, active metal sites, recyclability, and high crystallinity [55,121,122,123,124]. However, the active site of MOFs must be protected, especially in the high-temperature or high-oxidation environment of industrial catalysis, and the composite of silica/MOF material can effectively solve this problem [125]. Silica not only provides MOFs with thermal stability and structural integrity but also maintains the high availability of the active sites of MOFs.

3.3.1. MOFs/SiO2 as Direct Catalyst

MOF/silica composites for catalysis can be prepared by the in situ synthesis of MOF crystals in the pores of mesoporous silica. The macroscopic morphology and crystal defects greatly affect the catalytic performance of MOF composites. Karimi et al. obtained MOF-5 crystals with different morphologies by growing MOF-5 crystals on SBA-15 mesoporous silica at different concentrations [126]. Flower-like to nanorod-like MOF-5 crystals have been controllably fabricated by regulating the concentration of silica, which could guide the directional crystallization and growth of MOFs. Among them, nanorod-shaped MOF/silica composites were found to be highly selective to the ortho-products in the catalytic Friedel–Crafts alkylation reaction, showing superior catalytic performance to pure MOF-5 materials. Kou et al. first prepared SBA-15 mesoporous silica and then grew MOF crystals in silica nanopore in a double solvent containing hydrophobic solvent and a hydrophilic solution containing MOF precursors [70]. Based on a hydrophobic n-octane solvent and hydrophilic N,N-dimethylformamide (DMF) solvent containing MOF precursor, an MOF-5@SBA-15 composite was prepared (Figure 9). Contrary to the pure MOFs, the structure of the composites remained undamaged for 8 h in a humid environment, which indicated that the water stability of MOF-5 was significantly improved by the support and protection provided by mesoporous silica. With this material as the catalyst for the Friedel–Crafts alkylation reaction, the conversion of benzyl bromide reached up to 100% within 3 h, which is considerably higher than that of pure MOF-5. In addition, Song et al. soaked bulk silica in HKUST-1 precursor solution directly and obtained HKUST-1-SiO2 composite materials [71]. With the composite as catalyst, the oxidations of propylbenzene, 1,2,3,4-tetrahydronaphthalene, diphenyl methane, and fluorene were carried out, and the substrates, propylbenzene, and 1,2,3,4-tetrahydronaphthalene were oxidized to the respective ketones in >90% yields and >99% selectivity. The enhancement of the catalytic performance is thought to arise partially from the support of the silica monoliths. Furthermore, this type of HKUST-1-SiO2 is easily recovered by simple filtration and subsequently used in the successive 12 cycles without an obvious loss in conversion (from 95% to >99%), which presents the remarkable catalytic stability of the HKUST-1–SiO2 composite.
Another commonly used strategy for the preparation of MOF/silica composite catalyst materials is to first synthesize MOF materials and then grow a silica shell material on it by the sol–gel method. Ying et al. first prepared MIL-101(Cr) and then wrapped a very thin layer of mesoporous silica on the surface to fabricate a hydrophobic MIL-101(Cr)@mSiO2 composite and utilized it to catalyze the oxidation reaction of indene with H2O2 in acetonitrile [80]. Considering the reusability of the catalyst, 82% of the initial conversion is retained for MIL-101(Cr)@mSiO2 after three runs, while only 46% of the initial conversion is still present for MIL-101(Cr). Mesoporous silica not only enhances the stability of MOF materials because of its hydrophobicity but also shows improved catalytic activity and recyclability. Shalygin et al. mixed MOF powders and silica sol and then obtained an aerogel composite through a gelation of silica sol, separation, and a drying process [127]. This composite aerogel material has high selectivity in the reaction of the catalytic oxidation of styrene into phenylacetaldehyde and can be used as a catalytic flow reactor for the continuous preparation of styrene and phenylacetaldehyde.

3.3.2. MOF/SiO2 Composite as Catalyst Support

Maintaining the catalytic activity of active metal/metal oxide nanoparticles and improving their stability are problems that need to be solved in the field of catalysis. Encapsulating the unstable catalyst particles into MOF materials is an effective approach that can address these problems [128]. MOFs were proven to be suitable carriers for noble metal nanoparticle catalysts due to their large specific surface area and abundant pores [129]. The MOF material has uniform micropores or mesopores, which can effectively prevent particle aggregation and facilitate the transfer and diffusion of guest molecules. Moreover, MOF materials are easy to be separated and can be reused, effectively extending the service life of catalyst and reducing environmental pollution. However, MOFs have limited thermal and mechanical stability [130], which could be enhanced by silica protection layer. Li et al. established a general method to “armorize” MOF materials by coating them with silica [72]. The first step of the method is to coat a layer of gel filamentous microporous silica shell on the surface of MOFs with the help of surfactant and then grow a layer of MOF shell on the surface to prepare a composite material with an MOF@mSiO2@MOF core–shell structure. This structure could improve the mechanical strength, hardness, and toughness of the MOF material. The prepared ZIF-8@mSiO2@ZIF-8 composite has been proven to have excellent catalytic performance in the catalytic reduction of 4-nitrophenol reaction by NaBH4 in water media after loading metal particles such as gold/copper. Similarly, Pascanu et al. fixed Pd metal onto the pores of the MIL-88B-NH2 material, coated the material surface with a layer of mesoporous silica coating, and finally fabricated Pd@MIL-88B-NH2@nano-SiO2 double-supported nano-Pd catalysts [73]. The materials exhibit high catalytic activity in the oxidation of benzyl alcohol without using any bubbling device under atmospheric pressure. Under continuous flow, the composite catalyst can withstand continuous operation at 110 °C for 7 days without deactivation. During this period, no metal leaching was observed, and the material maintained its structural integrity. To enhance the mechanical properties (hardness and toughness), Li et al. reported a general synthetic approach to coat microporous MOFs and their derivatives with an enforcing shell of mesoporous silica (mSiO2). With ZIF-8@Au and ZIF-8@Cu utilized as binary solid cores, meosporous silica layers were wrapped on them (Figure 10) [131]. The excellent accessibility of the porous silica-wrapped MOFs and their metal-containing nanocomposites showed excellent catalytic performance using the reduction of 4-nitrophenol as a model reaction with the reaction proceeded rapidly with a conversion over 99% in ca. 14 min.

3.3.3. MOF/SiO2 Composite-Derived Metal/Silica Catalyst

Using a ligand calcining or dissolving process, MOF/silica composites can directly derivatize metal/silica composites with good dispersibility and good catalytic activity [132,133]. Desai et al. loaded cobalt or cobalt–aluminum complexes onto the zirconium nodes of a zirconium-based MOF material NU-1000 using the osmotic method and then grew SiO2 in the voids of MOFs [134]. Finally, after removing the double organic ligands, the Co2-Zr6@SiO2 and AlCoZr6@SiO2 polymetallic site oxide cluster composites protected by silica carrier were prepared. The composite material was stable and firm, and its cobalt site exhibited high catalytic activity in the oxidation of benzyl alcohol to benzaldehyde. By calcining a ZIF-67/mesoporous silica composite, Zhou et al. prepared silica–Co/N carbon nanotube (CNT) composites [135]. The SiO2 shell not only prevented the rapid accumulation of Co nanoparticles in ZIF-67, but also provided a unique external “sieve” to induce the catalytic growth of CNTs. The prepared carbon nanotubes had a good 3D framework structure, good stability, and good solvent tolerance, and the composite exhibited excellent electrocatalytic performance, even exceeding some commercial catalysts.

3.4. Application in Biomedicine

Metal–organic matrix composites have attracted considerable attention in the fields of separation, adsorption, and catalysis; however, their application in biomedicine remains a challenge [136,137]. MOF composites have the advantages of flexible composition, adjustable pore size, and high crystallinity, and they have attracted considerable attention in biomedical fields, especially in drug delivery, angiography, diagnosis, and treatment [138,139,140]. The composite of silica shell and MOFs can provide several advantages, including enhancing the water dispersion and biocompatibility of the materials, and the condensation of organosilica precursors can further functionalize the MOF materials [141,142]. Rieter et al. first synthesized MOF nanorods with lanthanide metal ions and terephthalic acid; they then modified the nanorods with polyvinylpyrrolidone (PVP) and coated them with silica materials through a sol–gel process [143]. The obtained MOF/SiO2 composite materials showed good performance in drug sustained release and biomarkers.
For drug release, to avoid the rapid and uncontrolled release of the original drug, stimulus-responsive MOF composite materials have attracted interest. Zeolite imidazole MOFs, such as ZIF-8, synthesized from dimethylimidazole and zinc ions, have pH stimulation responsiveness. They are very stable under physiological conditions but dissociate under acidic conditions. Hence, the material is highly suitable for drug loading and targeted release. Jia et al. loaded the anticancer drug DOX into hollow mesoporous silica (HMS) and then wrapped ZIF-8 to obtain a DOX/HMS@ZIF-8 composite capsule (Figure 11) [74]. DOX in the HMS@ZIF-8 composite was not released under physiological conditions (pH 7.4); it was only released at low pH (4–6). HMS@ZIF-8 has excellent cell compatibility and can be used to assemble pH-responsive drug delivery systems. Zou et al. also fabricated a mesoporous layer on ZIF-8 particles with different morphologies and removed the ZIF-8 to obtain the HMS, which is suitable for drug delivery due to their excellent biocompatibility, large cavity, and controllable morphology [75].
The advantage of MOF/silica composites for biomedicine is that they combine the synergy of inorganic and organic chemistry, have high porosity and rich organic functional groups, and have biocompatibility and good stability. With carboxyl-functionalized silica beads as a matrix, Liu et al. prepared a SiO2@EuTTA composite by coating a layer of lanthanum with thiophene trifluoroacetone on the silica. After grafting a ZIF-8 shell on the composite, they prepared a SiO2@EuTTA@ZIF-8 core–shell composite [144]. The composite showed high selectivity and sensitivity to detect Cu2+ in environmental or biological solution systems.

3.5. Other Applications

MOFs/SiO2 have shown versatile applications by combining the high specific surface area, high porosity, and adjustable structure of MOFs and the high stability and functionality of SiO2. In addition to the above applications, the composite material could also be utilized as an electrode material. Its void structure can accommodate huge volume changes and maintain the structural integrity and long cycle stability of the electrode. Sun et al. synthesized a copper-based MOF material (Cu-MOF), which was coated with a layer of silica and finally carbonized at 700 °C to obtain a silica–copper–carbon nanocomposite electrode material [145]. For gas separation, porous silica provides a growing environment and support for MOF films, providing a new method for the preparation of gas-separated MOF films. Using a layer-by-layer process, Shekhah et al. fabricated MOF films with mesoporous silica foam as a template to form highly crystalline HKUST-1 and ZIF-8, which showed high performance for gas separation [76]. Lanthanide MOF materials have great potential in the fields of luminescent dopants, solid-state lighting, integrated optics, optical communication, and solar cells [146]. In the lanthanide MOF/SiO2 composite, lanthanide ions are connected to the Si–O network by covalent bonds, and the silica network provides uniform dispersion and luminescence stability for the lanthanide metal. Using a hydrothermal process, Lian et al. prepared SiO2@MOF composites (Figure 12) by coating lanthanide MOFs on carboxyl-modified silica spheres [77]. The obtained SiO2@MOF microspheres are suitable for a reliable sensing process for acetone and Cu2+. Moreover, the materials show excellent luminescent properties and have a potential applications in the development of white-light devices.
For water treatment, the addition of silica can improve the dispersion of MOFs in composite materials, which is extremely beneficial for the adsorption of pollutants in water and has great potential in the prevention and control of water pollution [147]. Han et al. synthesized a series of SiO2@Al–MOF(MIL-68) composites with different silica contents, which showed ultrafast aniline adsorption and high recyclability [78]. Given the good physical and chemical properties, MOF/SiO2 composites could be utilized in more applications.

4. Conclusions and Outlook

MOFs assembled by metal ions and organic ligands are a kind of newly crystallized porous material with ultrahigh porosity and very large specific surface area, and the addition of silica further improves the stability and availability of MOF materials. In Table 1, we summarized the synthesis and application of MOF/silica composite materials in chromatographic column separation, gas adsorption, catalysis, biomedicine, and other fields. A large number of readings in the literature have shown that MOF/silica materials show excellent properties that are rarely seen in other materials. By compounding with SiO2 material, the stability and mechanical properties of MOF material can not only be improved, but also the matrix structure of MOFs can be optimized by different SiO2 structures. In addition, the specific surface area and contact ability of the material can be improved.
The existing challenge lies in the structural control and the fabrication of composite materials with new structure. With new MOFs and their derivatives, the interface of MOFs and silica materials and the control of their morphology, including pores, will become prominent problems. A new preparation method for general MOF/SiO2 composites must be developed urgently. The key issues for future research are the regulation of the structure and morphology of MOFs/SiO2 materials and the surface modification and functionalization to obtain composites with stability, biocompatibility, and specific targeted functionality. MOF/silicon dioxide composites with high stability and structural controllability will have great application potential in the fields of environmental protection, biomedicine, and new energy.

Author Contributions

Conceptualization, M.M. and F.D.; writing—original draft preparation, M.M., L.L., H.L. and F.D.; writing—review and editing, M.M., Y.X. and F.D.

Funding

This research was financially supported by National Natural Science Foundation of China (NSFC No. 51663003) and the Science and Technology Department of Guizhou Province ((2019)1092, 2016123, and GZU201625).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zhang, Y.; Yang, L.; Yan, L.; Wang, G.; Liu, A. Recent advances in the synthesis of spherical and nanomof-derived multifunctional porous carbon for nanomedicine applications. Coord. Chem. Rev. 2019, 391, 69–89. [Google Scholar] [CrossRef]
  2. Yue, Y.; Fulvio, P.F.; Dai, S. Hierarchical metal-organic framework hybrids: Perturbation-assisted nanofusion synthesis. Acc. Chem. Res. 2015, 48, 3044–3052. [Google Scholar] [CrossRef] [PubMed]
  3. Salunkhe, R.R.; Kaneti, Y.V.; Kim, J.; Kim, J.H.; Yamauchi, Y. Nanoarchitectures for metal-organic framework-derived nanoporous carbons toward supercapacitor applications. Acc. Chem. Res. 2016, 49, 2796–2806. [Google Scholar] [CrossRef]
  4. Cai, W.; Wang, J.; Chu, C.; Chen, W.; Wu, C.; Liu, G. Metal organic framework-based stimuli-responsive systems for drug delivery. Adv. Sci. 2019, 6, 1801526. [Google Scholar] [CrossRef]
  5. Duan, J.; Jin, W.; Kitagawa, S. Water-resistant porous coordination polymers for gas separation. Coord. Chem. Rev. 2017, 332, 48–74. [Google Scholar] [CrossRef]
  6. Masoomi, M.Y.; Morsali, A. Applications of metal-organic coordination polymers as precursors for preparation of nano-materials. Coord. Chem. Rev. 2012, 256, 2921–2943. [Google Scholar] [CrossRef]
  7. Yaghi, O.M.; O’Keeffe, M.; Ockwig, N.W.; Chae, H.K.; Eddaoudi, M.; Kim, J. Reticular synthesis and the design of new materials. Nature (London U.K.) 2003, 423, 705–714. [Google Scholar] [CrossRef]
  8. Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O.M. Design and synthesis of an exceptionally stable and highly porous metal-organic framework. Nature 1999, 402, 276. [Google Scholar] [CrossRef]
  9. Zhong, M.; Kong, L.; Li, N.; Liu, Y.-Y.; Zhu, J.; Bu, X.-H. Synthesis of MOF-derived nanostructures and their applications as anodes in lithium and sodium ion batteries. Coord. Chem. Rev. 2019, 388, 172–201. [Google Scholar] [CrossRef]
  10. Yan, B. Photofunctional mof-based hybrid materials for the chemical sensing of biomarkers. J. Mater. Chem. C 2019, 7, 8155–8175. [Google Scholar] [CrossRef]
  11. Xie, Y.; Deng, C. Designed synthesis of a “one for two” hydrophilic magnetic amino-functionalized metal-organic framework for highly efficient enrichment of glycopeptides and phosphopeptides. Sci. Rep. 2017, 7, 1162. [Google Scholar] [CrossRef] [PubMed]
  12. Kirchon, A.; Feng, L.; Drake, H.F.; Joseph, E.A.; Zhou, H.-C. From fundamentals to applications: A toolbox for robust and multifunctional mof materials. Chem. Soc. Rev. 2018, 47, 8611–8638. [Google Scholar] [CrossRef] [PubMed]
  13. He, L.; Liu, Y.; Lau, J.; Fan, W.; Li, Q.; Zhang, C.; Huang, P.; Chen, X. Recent progress in nanoscale metal-organic frameworks for drug release and cancer therapy. Nanomedicine 2019, 14, 1343–1365. [Google Scholar] [CrossRef] [PubMed]
  14. Elsayed, A.; Elsayed, E.; Al-Dadah, R.; Mahmoud, S.; Elshaer, A.; Kaialy, W. Thermal energy storage using metal-organic framework materials. Appl. Energy 2017, 186, 509–519. [Google Scholar] [CrossRef]
  15. Ding, M.; Flaig, R.W.; Jiang, H.-L.; Yaghi, O.M. Carbon capture and conversion using metal-organic frameworks and mof-based materials. Chem. Soc. Rev. 2019, 48, 2783–2828. [Google Scholar] [CrossRef]
  16. Cirujano, F.G.; Luz, I.; Soukri, M.; Van Goethem, C.; Vankelecom, I.F.J.; Lail, M.; De Vos, D.E. Boosting the catalytic performance of metal-organic frameworks for steroid transformations by confinement within a mesoporous scaffold. Angew. Chem.-Int. Ed. 2017, 56, 13302–13306. [Google Scholar] [CrossRef]
  17. Chowdhury, M.A. Metal-organic-frameworks for biomedical applications in drug delivery, and as mri contrast agents. J. Biomed. Mater. Res. Part A 2017, 105, 1184–1194. [Google Scholar] [CrossRef]
  18. Adatoz, E.; Avci, A.K.; Keskin, S. Opportunities and challenges of MOF-based membranes in gas separations. Sep. Purif. Technol. 2015, 152, 207–237. [Google Scholar] [CrossRef]
  19. Jiao, L.; Wang, Y.; Jiang, H.-L.; Xu, Q. Metal-organic frameworks as platforms for catalytic applications. Adv. Mater. 2018, 30, 1703663. [Google Scholar] [CrossRef]
  20. Yuan, S.; Feng, L.; Wang, K.; Pang, J.; Bosch, M.; Lollar, C.; Sun, Y.; Qin, J.; Yang, X.; Zhang, P.; et al. Stable metal-organic frameworks: Design, synthesis, and applications. Adv. Mater. 2018, 30, 1704303. [Google Scholar] [CrossRef]
  21. Cavka, J.H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K.P. A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. J. Am. Chem. Soc. 2008, 130, 13850–13851. [Google Scholar] [CrossRef] [PubMed]
  22. Wen, Y.; Chen, Y.; Wu, Z.; Liu, M.; Wang, Z. Thin-film nanocomposite membranes incorporated with water stable metal-organic framework cubttri for mitigating biofouling. J. Membr. Sci. 2019, 582, 289–297. [Google Scholar] [CrossRef]
  23. Wang, S.; Serre, C. Toward green production of water-stable metal-organic frameworks based on high-valence metals with low toxicities. Acs Sustain. Chem. Eng. 2019, 7, 11911–11927. [Google Scholar] [CrossRef]
  24. McGuire, C.V.; Forgan, R.S. The surface chemistry of metal-organic frameworks. Chem. Commun. 2015, 51, 5199–5217. [Google Scholar] [CrossRef]
  25. Wei, J.-H.; Yi, J.-W.; Han, M.-L.; Li, B.; Liu, S.; Wu, Y.-P.; Ma, L.-F.; Li, D.-S. A water-stable terbium(iii)-organic framework as a chemosensor for inorganic ions, nitro-containing compounds and antibiotics in aqueous solutions. Chem.-An Asian J. 2019, 14, 3694–3701. [Google Scholar] [CrossRef]
  26. Wang, L.; Xu, H.; Gao, J.; Yao, J.; Zhang, Q. Recent progress in metal-organic frameworks-based hydrogels and aerogels and their applications. Coord. Chem. Rev. 2019, 398, 213016. [Google Scholar] [CrossRef]
  27. Zhu, Q.-L.; Xu, Q. Metal-organic framework composites. Chem. Soc. Rev. 2014, 43, 5468–5512. [Google Scholar] [CrossRef]
  28. Zhang, J.; Bai, H.-J.; Ren, Q.; Luo, H.-B.; Ren, X.-M.; Tian, Z.-F.; Lu, S. Extra water- and acid-stable MOF-801 with high proton conductivity and its composite membrane for proton-exchange membrane. Acs Appl. Mater. Interfaces 2018, 10, 28656–28663. [Google Scholar] [CrossRef]
  29. Xie, W.; He, W.-W.; Du, D.-Y.; Li, S.-L.; Qin, J.-S.; Su, Z.-M.; Sun, C.-Y.; Lan, Y.-Q. A stable ALQ3@MOF composite for white-light emission. Chem. Commun. 2016, 52, 3288–3291. [Google Scholar] [CrossRef]
  30. Qi, P.; Han, Y.; Zhou, J.; Fu, X.; Li, S.; Zhao, J.; Wang, L.; Fan, X.; Feng, X.; Wang, B. MOF derived composites for cathode protection: Coatings of licoo2 from uio-66 and mil-53 as ultra-stable cathodes. Chem. Commun. 2015, 51, 12391–12394. [Google Scholar] [CrossRef]
  31. Liu, Y.; Liu, Z.; Huang, D.; Cheng, M.; Zeng, G.; Lai, C.; Zhang, C.; Zhou, C.; Wang, W.; Jiang, D.; et al. Metal or metal-containing nanoparticle@mof nanocomposites as a promising type of photocatalyst. Coord. Chem. Rev. 2019, 388, 63–78. [Google Scholar] [CrossRef]
  32. Gao, X.; Zhai, Q.; Hu, M.; Li, S.; Song, J.; Jiang, Y. Design and preparation of stable CPO/HRP@h-MOF(zr) composites for efficient bio-catalytic degradation of organic toxicants in wastewater. J. Chem. Technol. BioTechnol. 2019, 94, 1249–1258. [Google Scholar] [CrossRef]
  33. Chatterjee, A.; Hu, X.; Lam, F.L.-Y. A dual acidic hydrothermally stable mof-composite for upgrading xylose to furfural. Appl. Catal. A Gen. 2018, 566, 130–139. [Google Scholar] [CrossRef]
  34. Zhang, F.; Liu, L.; Tan, X.; Sang, X.; Zhang, J.; Liu, C.; Zhang, B.; Han, B.; Yang, G. Pickering emulsions stabilized by a metal-organic framework (MOF) and graphene oxide (go) for producing mof/go composites. Soft Matter 2017, 13, 7365–7370. [Google Scholar] [CrossRef]
  35. Yang, P.; Liu, Q.; Liu, J.; Zhang, H.; Li, Z.; Li, R.; Liu, L.; Wang, J. Interfacial growth of a metal-organic framework (uio-66) on functionalized graphene oxide (GO) as a suitable seawater adsorbent for extraction of uranium(vi). J. Mater. Chem. A 2017, 5, 17933–17942. [Google Scholar] [CrossRef]
  36. Wu, Q.; Wang, J.; Jin, H.; Yan, T.; Yi, G.; Su, X.; Dai, W.; Wang, X. Mof-derived rambutan-like nanoporous carbon/nanotubes/co composites with efficient microwave absorption property. Mater. Lett. 2019, 244, 138–141. [Google Scholar] [CrossRef]
  37. Rao, Z.; Feng, K.; Tang, B.; Wu, P. Surface decoration of amino-functionalized metal organic framework/graphene oxide composite onto polydopamine-coated membrane substrate for highly efficient heavy metal removal. ACS Appl. Mater. Interfaces 2017, 9, 2594–2605. [Google Scholar] [CrossRef]
  38. Qi, X.-L.; Zhou, D.-D.; Zhang, J.; Hu, S.; Haranczyk, M.; Wang, D.-Y. Simultaneous improvement of mechanical and fire-safety properties of polymer composites with phosphonate-loaded mof additives. Acs Appl. Mater. Interfaces 2019, 11, 20325–20332. [Google Scholar] [CrossRef]
  39. Peng, L.; Yang, S.; Sun, D.T.; Asgari, M.; Queen, W.L. MOF/polymer composite synthesized using a double solvent method offers enhanced water and co2 adsorption properties. Chem. Commun. 2018, 54, 10602–10605. [Google Scholar] [CrossRef]
  40. Ma, B.; Guo, H.; Wang, M.; Li, L.; Jia, X.; Chen, H.; Xue, R.; Yang, W. Electrocatalysis of Cu-MOF/graphene composite and its sensing application for electrochemical simultaneous determination of dopamine and paracetamol. Electroanalysis 2019, 31, 1002–1008. [Google Scholar] [CrossRef]
  41. He, S.; Wang, H.; Zhang, C.; Zhang, S.; Yu, Y.; Lee, Y.; Li, T. A generalizable method for the construction of MOF@polymer functional composites through surface-initiated atom transfer radical polymerization. Chem. Sci. 2019, 10, 1816–1822. [Google Scholar] [CrossRef] [PubMed]
  42. Gu, J.; Fan, H.; Li, C.; Caro, J.; Meng, H. Robust superhydrophobic/superoleophilic wrinkled microspherical mof@rgo composites for efficient oil-water separation. Angew. Chem.-Int. Ed. 2019, 58, 5297–5301. [Google Scholar] [CrossRef] [PubMed]
  43. Ehrling, S.; Kutzscher, C.; Freund, P.; Mueller, P.; Senkovska, I.; Kaskel, S. MOF@SiO2 core-shell composites as stationary phase in high performance liquid chromatography. Microporous Mesoporous Mater. 2018, 263, 268–274. [Google Scholar] [CrossRef]
  44. Cai, J.; Lu, J.-Y.; Chen, Q.-Y.; Qu, L.-L.; Lu, Y.-Q.; Gao, G.-F. Eu-based MOF/graphene oxide composite: A novel photocatalyst for the oxidation of benzyl alcohol using water as oxygen source. New J. Chem. 2017, 41, 3882–3886. [Google Scholar] [CrossRef]
  45. Prabhu, A.; Al Shoaibi, A.; Srinivasakannan, C. Preparation and characterization of silica aerogel-zif-8 hybrid materials. Mater. Lett. 2015, 146, 43–46. [Google Scholar] [CrossRef]
  46. Lajevardi, A.; Sadr, M.H.; Yaraki, M.T.; Badiei, A.; Armaghan, M. A ph-responsive and magnetic Fe3O4@silica@mil-100(Fe)/beta-cd nanocomposite as a drug nanocarrier: Loading and release study of cephalexin. New J. Chem. 2018, 42, 9690–9701. [Google Scholar] [CrossRef]
  47. Kesse, S.; Boakye-Yiadom, K.O.; Ochete, B.O.; Opoku-Damoah, Y.; Akhtar, F.; Filli, M.S.; Farooq, M.A.; Aquib, M.; Mily, B.J.M.; Murtaza, G.; et al. Mesoporous silica nanomaterials: Versatile nanocarriers for cancer theranostics and drug and gene delivery. Pharmaceutics 2019, 11, 77. [Google Scholar] [CrossRef]
  48. Laskowski, L.; Laskowska, M.; Vila, N.; Schabikowski, M.; Walcarius, A. Mesoporous silica-based materials for electronics-oriented applications. Molecules 2019, 24, 2395. [Google Scholar] [CrossRef]
  49. Cahill, J.F.; Fei, H.; Cohen, S.M.; Prather, K.A. Characterization of core-shell mof particles by depth profiling experiments using on-line single particle mass spectrometry. Analyst 2015, 140, 1510–1515. [Google Scholar] [CrossRef]
  50. Arrua, R.D.; Peristyy, A.; Nesterenko, P.N.; Das, A.; D’Alessandro, D.M.; Hilder, E.F. Uio-66@ sio2 core-shell microparticles as stationary phases for the separation of small organic molecules. Analyst 2017, 142, 517–524. [Google Scholar] [CrossRef]
  51. Chen, C.; Li, B.; Zhou, L.; Xia, Z.; Feng, N.; Ding, J.; Wang, L.; Wan, H.; Guan, G. Synthesis of hierarchically structured hybrid materials by controlled self-assembly of metal organic framework with mesoporous silica for co2 adsorption. ACS Appl. Mater. Interfaces 2017, 9, 23060–23071. [Google Scholar] [CrossRef] [PubMed]
  52. Yang, H.; Li, J.; Zhang, H.; Lv, Y.; Gao, S. Facile synthesis of POM@MOF embedded in sba-15 as a steady catalyst for the hydroxylation of benzene. Microporous Mesoporous Mater. 2014, 195, 87–91. [Google Scholar] [CrossRef]
  53. Li, H.; Lv, N.; Li, X.; Liu, B.; Feng, J.; Ren, X.; Guo, T.; Chen, D.; Stoddart, J.F.; Gref, R.; et al. Composite cd-mof nanocrystals-containing microspheres for sustained drug delivery. Nanoscale 2017, 9, 7454–7463. [Google Scholar] [CrossRef] [PubMed]
  54. Zheng, H.; Zhang, Y.; Liu, L.; Wan, W.; Guo, P.; Nystrom, A.M.; Zou, X. One-pot synthesis of metal organic frameworks with encapsulated target molecules and their applications for controlled drug delivery. J. Am. Chem. Soc. 2016, 138, 962–968. [Google Scholar] [CrossRef]
  55. Zhan, G.; Zeng, H.C. Integrated nanocatalysts with mesoporous silica/silicate and microporous mof materials. Coord. Chem. Rev. 2016, 320, 181–192. [Google Scholar] [CrossRef]
  56. Wen, M.; Li, G.; Liu, H.; Chen, J.; An, T.; Yamashita, H. Metal-organic framework-based nanomaterials for adsorption and photocatalytic degradation of gaseous pollutants: Recent progress and challenges. Environ. Sci.-Nano 2019, 6, 1006–1025. [Google Scholar] [CrossRef]
  57. Perez, E.V.; Karunaweera, C.; Musselman, I.H.; Balkus, K.J., Jr.; Ferraris, J.P. Origins and evolution of inorganic-based and mof-based mixed-matrix membranes for gas separations. Processes 2016, 4, 32. [Google Scholar] [CrossRef]
  58. Maya, F.; Palomino Cabello, C.; Figuerola, A.; Turnes Palomino, G.; Cerda, V. Immobilization of metal-organic frameworks on supports for sample preparation and chromatographic separation. Chromatographia 2019, 82, 361–375. [Google Scholar] [CrossRef]
  59. Elrasheedy, A.; Nady, N.; Bassyouni, M.; El-Shazly, A. Metal organic framework based polymer mixed matrix membranes: Review on applications in water purification. Membranes 2019, 9, 88. [Google Scholar] [CrossRef]
  60. Hu, X.; Yan, X.; Zhou, M.; Komarneni, S. One-step synthesis of nanostructured mesoporous ZIF-8/silica composites. Microporous Mesoporous Mater. 2016, 219, 311–316. [Google Scholar] [CrossRef]
  61. Gao, B.; Huang, M.; Zhang, Z.; Yang, Q.; Su, B.; Yang, Y.; Ren, Q.; Bao, Z. Hybridization of metal-organic framework and monodisperse spherical silica for chromatographic separation of xylene isomers. Chin. J. Chem. Eng. 2019, 27, 818–826. [Google Scholar] [CrossRef]
  62. Qu, Q.; Xuan, H.; Zhang, K.; Chen, X.; Ding, Y.; Feng, S.; Xu, Q. Core-shell silica particles with dendritic pore channels impregnated with zeolite imidazolate framework-8 for high performance liquid chromatography separation. J. Chromatogr. A 2017, 1505, 63–68. [Google Scholar] [CrossRef] [PubMed]
  63. El-Mehalmey, W.A.; Ibrahim, A.H.; Abugable, A.A.; Hassan, M.H.; Haikal, R.R.; Karakalos, S.G.; Zaki, O.; Alkordi, M.H. Metal-organic framework@silica as a stationary phase sorbent for rapid and cost-effective removal of hexavalent chromium. J. Mater. Chem. A 2018, 6, 2742–2751. [Google Scholar] [CrossRef]
  64. Yan, X.; Hu, X.; Komarneni, S. Facile synthesis of mesoporous mof/silica composites. RSC Adv. 2014, 4, 57501–57504. [Google Scholar] [CrossRef]
  65. Tari, N.E.; Tadjarodi, A.; Tamnanloo, J.; Fatemi, S. One pot microwave synthesis of mcm-41/cu based mof composite with improved co2 adsorption and selectivity. Microporous Mesoporous Mater. 2016, 231, 154–162. [Google Scholar] [CrossRef]
  66. Chen, C.; Feng, N.; Guo, Q.; Li, Z.; Li, X.; Ding, J.; Wang, L.; Wan, H.; Guan, G. Template-directed fabrication of mil-101(Cr)/mesoporous silica composite: Layer-packed structure and enhanced performance for co2 capture. J. Colloid Interface Sci. 2018, 513, 891–902. [Google Scholar] [CrossRef]
  67. Ulker, Z.; Erucar, I.; Keskin, S.; Erkey, C. Novel nanostructured composites of silica aerogels with a metal organic framework. Microporous Mesoporous Mater. 2013, 170, 352–358. [Google Scholar] [CrossRef]
  68. Uma, K.; Pan, G.-T.; Yang, T.C.K. The preparation of porous sol-gel silica with metal organic framework mil-101(Cr) by microwave-assisted hydrothermal method for adsorption chillers. Materials 2017, 10, 610. [Google Scholar] [CrossRef]
  69. Saeedirad, R.; Ganjali, S.T.; Bazmi, M.; Rashidi, A. Effective mesoporous silica-ZIF-8 nano-adsorbents for adsorptive desulfurization of gas stream. J. Taiwan Inst. Chem. Eng. 2018, 82, 10–22. [Google Scholar] [CrossRef]
  70. Kou, J.; Sun, L.-B. Fabrication of metal-organic frameworks inside silica nanopores with significantly enhanced hydrostability and catalytic activity. ACS Appl. Mater. Interfaces 2018, 10, 12051–12059. [Google Scholar] [CrossRef]
  71. Song, G.-Q.; Lu, Y.-X.; Zhang, Q.; Wang, F.; Ma, X.-K.; Huang, X.-F.; Zhang, Z.-H. Porous Cu-BTC silica monoliths as efficient heterogeneous catalysts for the selective oxidation of alkylbenzenes. Rsc Adv. 2014, 4, 30221–30224. [Google Scholar] [CrossRef]
  72. Li, Z.; Zeng, H.C. Armored mofs: Enforcing soft microporous mof nanocrystals with hard mesoporous silica. J. Am. Chem. Soc. 2014, 136, 5631–5639. [Google Scholar] [CrossRef] [PubMed]
  73. Pascanu, V.; Gomez, A.B.; Ayats, C.; Platero-Prats, A.E.; Carson, F.; Su, J.; Yao, Q.; Pericas, M.A.; Zou, X.; Martin-Matute, B. Double-supported silica-metal-organic framework palladium nanocatalyst for the aerobic oxidation of alcohols under batch and continuous flow regimes. ACS Catal. 2015, 5, 472–479. [Google Scholar] [CrossRef]
  74. Jia, X.; Yang, Z.; Wang, Y.; Chen, Y.; Yuan, H.; Chen, H.; Xu, X.; Gao, X.; Liang, Z.; Sun, Y.; et al. Hollow mesoporous silica@metal-organic framework and applications for pH-responsive drug delivery. Chemmedchem 2018, 13, 400–405. [Google Scholar] [CrossRef]
  75. Zou, Z.; Li, S.; He, D.; He, X.; Wang, K.; Li, L.; Yang, X.; Li, H. A versatile stimulus-responsive metal-organic framework for size/morphology tunable hollow mesoporous silica and pH-triggered drug delivery. J. Mater. Chem. B 2017, 5, 2126–2132. [Google Scholar] [CrossRef]
  76. Shekhah, O.; Fu, L.; Sougrat, R.; Belmabkhout, Y.; Cairns, A.J.; Giannelis, E.P.; Eddaoudi, M. Successful implementation of the stepwise layer-by-layer growth of mof thin films on confined surfaces: Mesoporous silica foam as a first case study. Chem. Commun. 2012, 48, 11434–11436. [Google Scholar] [CrossRef]
  77. Lian, X.; Yan, B. Novel core-shell structure microspheres based on lanthanide complexes for white-light emission and fluorescence sensing. Dalton Trans. 2016, 45, 2666–2673. [Google Scholar] [CrossRef]
  78. Han, T.; Li, C.; Guo, X.; Huang, H.; Liu, D.; Zhong, C. In-situ synthesis of SiO2@MOF composites for high-efficiency removal of aniline from aqueous solution. Appl. Surf. Sci. 2016, 390, 506–512. [Google Scholar] [CrossRef]
  79. He, L.; Li, L.; Zhang, L.; Xing, S.; Wang, T.; Li, G.; Wu, X.; Su, Z.; Wang, C. ZIF-8 templated fabrication of rhombic dodecahedron-shaped ZnO@SiO2, ZIF-8@SiO2 yolk-shell and sio2 hollow nanoparticles. Crystengcomm 2014, 16, 6534–6537. [Google Scholar] [CrossRef]
  80. Ying, J.; Herbst, A.; Xiao, Y.-X.; Wei, H.; Tian, G.; Li, Z.; Yang, X.-Y.; Su, B.-L.; Janiak, C. Nanocoating of hydrophobic mesoporous silica around mil-101cr for enhanced catalytic activity and stability. Inorg. Chem. 2018, 57, 899–902. [Google Scholar] [CrossRef]
  81. Ma, M.-M.; Li, M.; Ke, F.-S. Fabrication and properties of metal-organic framework@mesoporous composites. Chin. J. Inorg. Chem. 2018, 34, 1663–1669. [Google Scholar]
  82. Luz, I.; Soukri, M.; Lail, M. Confining metal-organic framework nanocrystals within mesoporous materials: A general approach via “solid-state” synthesis. Chem. Mater. 2017, 29, 9628–9638. [Google Scholar] [CrossRef]
  83. Abolghasemi, M.M.; Yousefi, V.; Piryaei, M. Synthesis of a metal-organic framework confined in periodic mesoporous silica with enhanced hydrostability as a novel fiber coating for solid-phase microextraction. J. Sep. Sci. 2015, 38, 1187–1193. [Google Scholar] [CrossRef] [PubMed]
  84. Bahrani, S.; Ghaedi, M.; Dashtian, K.; Ostovan, A.; Mansoorkhani, M.J.K.; Salehi, A. MOF-5(Zn)-Fe2O4 nanocomposite based magnetic solid-phase microextraction followed by HPLC-UV for efficient enrichment of colchicine in root of colchicium extracts and plasma samples. J. Chromatogr. B 2017, 1067, 45–52. [Google Scholar] [CrossRef] [PubMed]
  85. Chen, Z.; Yu, C.; Xi, J.; Tang, S.; Bao, T.; Zhang, J. A hybrid material prepared by controlled growth of a covalent organic framework on amino-modified mil-68 for pipette tip solid-phase extraction of sulfonamides prior to their determination by hplc. Microchim. Acta 2019, 186, 393. [Google Scholar] [CrossRef] [PubMed]
  86. Li, Y.; Zhu, N.; Chen, T.; Ma, Y.; Li, Q. A green cyclodextrin metal-organic framework as solid-phase extraction medium for enrichment of sulfonamides before their hplc determination. MicroChem. J. 2018, 138, 401–407. [Google Scholar] [CrossRef]
  87. Muench, A.S.; Lohse, M.S.; Hausdorf, S.; Schreiber, G.; Zacher, D.; Fischer, R.A.; Mertens, F.O.R.L. Room temperature preparation method for thin MOF-5 films on metal and fused silica surfaces using the controlled sbu approach. Microporous Mesoporous Mater. 2012, 159, 132–138. [Google Scholar] [CrossRef]
  88. Zhang, J.-H.; Nong, R.-Y.; Xie, S.-M.; Wang, B.-J.; Ai, P.; Yuan, L.-M. Homochiral metal-organic frameworks based on amino acid ligands for hplc separation of enantiomers. Electrophoresis 2017, 38, 2513–2520. [Google Scholar] [CrossRef]
  89. Fu, Y.-Y.; Yang, C.-X.; Yan, X.-P. Fabrication of ZIF-8@ SiO2 core-shell microspheres as the stationary phase for high-performance liquid chromatography. Chem. A Eur. J. 2013, 19, 13484–13491. [Google Scholar] [CrossRef]
  90. Sun, J.-K.; Yang, X.-D.; Yang, G.-Y.; Zhang, J. Bipyridinium derivative-based coordination polymers: From synthesis to materials applications. Coord. Chem. Rev. 2019, 378, 533–560. [Google Scholar] [CrossRef]
  91. Zhang, X.; Han, Q.; Ding, M. One-pot synthesis of uio-66@sio2 shell-core microspheres as stationary phase for high performance liquid chromatography. RSC Adv. 2015, 5, 1043–1050. [Google Scholar] [CrossRef]
  92. Moradi, Z.; Dil, E.A.; Asfaram, A. Dispersive micro-solid phase extraction based on Fe3O4@ SiO2@TI-MOF as a magnetic nanocomposite sorbent for the trace analysis of caffeic acid in the medical extracts of plants and water samples prior to hplc-uv analysis. Analyst 2019, 144, 4351–4361. [Google Scholar] [CrossRef] [PubMed]
  93. Ameloot, R.; Liekens, A.; Alaerts, L.; Maes, M.; Galarneau, A.; Coq, B.; Desmet, G.; Sels, B.F.; Denayer, J.F.M.; De Vos, D.E. Silica-mof composites as a stationary phase in liquid chromatography. Eur. J. Inorg. Chem. 2010, 2010, 3735–3738. [Google Scholar] [CrossRef]
  94. Qu, Q.; Si, Y.; Xuan, H.; Zhang, K.; Chen, X.; Ding, Y.; Feng, S.; Yu, H.-Q. A nanocrystalline metal organic framework confined in the fibrous pores of core-shell silica particles for improved hplc separation. Microchim. Acta 2017, 184, 4099–4106. [Google Scholar] [CrossRef]
  95. Yan, Z.; Zheng, J.; Chen, J.; Tong, P.; Lu, M.; Lin, Z.; Zhang, L. Preparation and evaluation of silica-uio-66 composite as liquid chromatographic stationary phase for fast and efficient separation. J. Chromatogr. A 2014, 1366, 45–53. [Google Scholar] [CrossRef] [PubMed]
  96. Tanaka, K.; Muraoka, T.; Hirayama, D.; Ohnish, A. Highly efficient chromatographic resolution of sulfoxides using a new homochiral mof-silica composite. Chem. Commun. 2012, 48, 8577–8579. [Google Scholar] [CrossRef] [PubMed]
  97. Tanaka, K.; Muraoka, T.; Otubo, Y.; Takahashi, H.; Ohnishi, A. Hplc enantioseparation on a homochiral mof-silica composite as a novel chiral stationary phase. RSC Adv. 2016, 6, 21293–21301. [Google Scholar] [CrossRef]
  98. Nuzhdin, A.L.; Shalygin, A.S.; Artiukha, E.A.; Chibiryaev, A.M.; Bukhtiyarova, G.A.; Martyanov, O.N. Hkust-1 silica aerogel composites: Novel materials for the separation of saturated and unsaturated hydrocarbons by conventional liquid chromatography. RSC Adv. 2016, 6, 62501–62507. [Google Scholar] [CrossRef]
  99. Ahmed, A.; Skinley, K.; Herodotou, S.; Zhang, H. Core-shell microspheres with porous nanostructured shells for liquid chromatography. J. Sep. Sci. 2018, 41, 99–124. [Google Scholar] [CrossRef]
  100. Gumustas, M.; Zalewski, P.; Ozkan, S.A.; Uslu, B. The history of the core-shell particles and applications in active pharmaceutical ingredients via liquid chromatography. Chromatographia 2019, 82, 17–48. [Google Scholar] [CrossRef]
  101. Wan, G.; Xia, H.; Wang, J.; Liu, J.; Song, B.; Yang, Y.; Bai, Q. Synthesis of SiO2@ SiO2 core-shell microspheres using urea-formaldehyde polymers as the templates for fast separation of small solutes and proteins. Chin. Chem. Lett. 2018, 29, 213–216. [Google Scholar] [CrossRef]
  102. Xia, H.; Wang, J.; Chen, G.; Liu, J.; Wan, G.; Bai, Q. One-pot synthesis of SiO2@ SiO2 core-shell microspheres with controllable mesopore size as a new stationary phase for fast hplc separation of alkyl benzenes and -agonists. Microchim. Acta 2019, 186, 125. [Google Scholar] [CrossRef]
  103. Ahmed, A.; Forster, M.; Clowes, R.; Bradshaw, D.; Myers, P.; Zhang, H. Silica SOS@HKUST-1 composite microspheres as easily packed stationary phases for fast separation. J. Mater. Chem. A 2013, 1, 3276–3286. [Google Scholar] [CrossRef]
  104. Ahmed, A.; Forster, M.; Jin, J.; Myers, P.; Zhang, H. Tuning morphology of nanostructured zif-8 on silica microspheres and applications in liquid chromatography and dye degradation. Acs Appl. Mater. Interfaces 2015, 7, 18054–18063. [Google Scholar] [CrossRef] [PubMed]
  105. Castro-Gonzales, L.; Kimmerle, K.; Schippert, E.; Fickinger, D. Finding and evaluating of adequate adsorbents for the adsorption of co2 from humid gas streams. Chem. Sel. 2016, 1, 2834–2841. [Google Scholar]
  106. Kim, Y.K.; Hyun, S.-m.; Lee, J.H.; Kim, T.K.; Moon, D.; Moon, H.R. Crystal-size effects on carbon dioxide capture of a covalently alkylamine-tethered metal-organic framework constructed by a one-step self-assembly. Sci. Rep. 2016, 6, 19337. [Google Scholar] [CrossRef]
  107. Kondo, A.; Takanashi, S.; Maeda, K. New insight into mesoporous silica for nano metal-organic framework. J. Colloid Interface Sci. 2012, 384, 110–115. [Google Scholar] [CrossRef] [PubMed]
  108. Lu, G.; Farha, O.K.; Kreno, L.E.; Schoenecker, P.M.; Walton, K.S.; Van Duyne, R.P.; Hupp, J.T. Fabrication of metal-organic framework-containing silica-colloidal crystals for vapor sensing. Adv. Mater. 2011, 23, 4449–4452. [Google Scholar] [CrossRef]
  109. Chakraborty, A.; Maji, T.K. Mg-MOF-74@SBA-15 hybrids: Synthesis, characterization, and adsorption properties. APL Mater. 2014, 2, 124107. [Google Scholar] [CrossRef]
  110. Sorribas, S.; Zornoza, B.; Serra-Crespo, P.; Gascon, J.; Kapteijn, F.; Tellez, C.; Coronas, J. Synthesis and gas adsorption properties of mesoporous Silica-NH2-MIL-53(AL) core-shell spheres. Microporous Mesoporous Mater. 2016, 225, 116–121. [Google Scholar] [CrossRef]
  111. Sorribas, S.; Zornoza, B.; Tellez, C.; Coronas, J. Ordered mesoporous Silica-(ZIF-8) core-shell spheres. Chem. Commun. 2012, 48, 9388–9390. [Google Scholar] [CrossRef] [PubMed]
  112. Mazaj, M.; Cendak, T.; Buscarino, G.; Todaro, M.; Logar, N.Z. Confined crystallization of a hkust-1 metal-organic framework within mesostructured silica with enhanced structural resistance towards water. J. Mater. Chem. A 2017, 5, 22305–22315. [Google Scholar] [CrossRef]
  113. Ji, P.; Feng, X.; Oliveres, P.; Li, Z.; Murakami, A.; Wang, C.; Lin, W. Strongly lewis acidic metal-organic frameworks for continuous flow catalysis. J. Am. Chem. Soc. 2019, 141, 14878–14888. [Google Scholar] [CrossRef]
  114. Chen, Y.; Ma, S. Biomimetic catalysis of metal-organic frameworks. Dalton Trans. 2016, 45, 9744–9753. [Google Scholar] [CrossRef]
  115. Xu, C.; Fang, R.; Luque, R.; Chen, L.; Li, Y. Functional metal-organic frameworks for catalytic applications. Coord. Chem. Rev. 2019, 388, 268–292. [Google Scholar] [CrossRef]
  116. Li, B.; Zeng, H.C. Synthetic chemistry and multifunctionality of an amorphous Ni-MOF-74 shell on a Ni/SiO2 hollow catalyst for efficient tandem reactions. Chem. Mater. 2019, 31, 5320–5330. [Google Scholar] [CrossRef]
  117. He, W.; Guo, X.; Zheng, J.; Xu, J.; Hayat, T.; Alharbi, N.S.; Zhang, M. Structural evolution and compositional modulation of zif-8-derived hybrids comprised of metallic ni nanoparticles and silica as interlayer. Inorg. Chem. 2019, 58, 7255–7266. [Google Scholar] [CrossRef]
  118. Dhakshinamoorth, A.; Asiri, A.M.; Garcia, H. 2D metal-organic frameworks as multifunctional materials in heterogeneous catalysis and electro/photocatalysis. Adv. Mater. 2019, 31, 1900617. [Google Scholar] [CrossRef]
  119. Masoomi, M.Y.; Morsali, A.; Dhakshinamoorthy, A.; Garcia, H. Mixed-metal mofs: Unique opportunities in metal-organic framework (mof) functionality and design. Angew. Chem.-Int. Ed. 2019, 58, 15188–15205. [Google Scholar] [CrossRef]
  120. Dhakshinamoorthy, A.; Garcia, H. Metal-organic frameworks as solid catalysts for the synthesis of nitrogen-containing heterocycles. Chem. Soc. Rev. 2014, 43, 5750–5765. [Google Scholar] [CrossRef]
  121. Xi, B.; Tan, Y.C.; Zeng, H.C. A general synthetic approach for integrated nanocatalysts of metal-silica@zifs. Chem. Mater. 2016, 28, 326–336. [Google Scholar] [CrossRef]
  122. Dhakshinamoorthy, A.; Asiri, A.M.; Garcia, H. Metal-organic framework (mof) compounds: Photocatalysts for redox reactions and solar fuel production. Angew. Chem.-Int. Ed. 2016, 55, 5414–5445. [Google Scholar] [CrossRef] [PubMed]
  123. Dhakshinamoorthy, A.; Asiri, A.M.; Garcia, H. Metal-organic frameworks catalyzed c-c and c-heteroatom coupling reactions. Chem. Soc. Rev. 2015, 44, 1922–1947. [Google Scholar] [CrossRef] [PubMed]
  124. Dhakshinamoorthy, A.; Li, Z.; Garcia, H. Catalysis and photocatalysis by metal organic frameworks. Chem. Soc. Rev. 2018, 47, 8134–8172. [Google Scholar] [CrossRef]
  125. Lee, S.; Kim, J.; Kim, J.; Lee, D. Zeolitic imidazolate framework membrane with marked thermochemical stability for high-temperature catalytic processes. Chem. Mater. 2018, 30, 447–455. [Google Scholar] [CrossRef]
  126. Karimi, Z.; Morsali, A. Modulated formation of metal-organic frameworks by oriented growth over mesoporous silica. J. Mater. Chem. A 2013, 1, 3047–3054. [Google Scholar] [CrossRef]
  127. Shalygin, A.S.; Nuzhdin, A.L.; Bukhtiyarova, G.A.; Martyanov, O.N. Preparation of hkust-1@silica aerogel composite for continuous flow catalysis. J. Sol-Gel Sci. Technol. 2017, 84, 446–452. [Google Scholar] [CrossRef]
  128. Sun, C.-Y.; To, W.-P.; Wang, X.-L.; Chan, K.-T.; Su, Z.-M.; Che, C.-M. Metal-organic framework composites with luminescent gold(iii) complexes. Strongly emissive and long-lived excited states in open air and photo-catalysis. Chem. Sci. 2015, 6, 7105–7111. [Google Scholar] [CrossRef]
  129. Zhou, W.; Zou, B.; Zhang, W.; Tian, D.; Huang, W.; Huo, F. Synthesis of stable heterogeneous catalysts by supporting carbon-stabilized palladium nanoparticles on mofs. Nanoscale 2015, 7, 8720–8724. [Google Scholar] [CrossRef]
  130. Ohhashi, T.; Tsuruoka, T.; Inoue, K.; Takashima, Y.; Horike, S.; Akamatsu, K. An integrated function system using metal nanoparticle@mesoporous silica@metal-organic framework hybrids. Microporous Mesoporous Mater. 2017, 245, 104–108. [Google Scholar] [CrossRef]
  131. Li, B.; Ma, J.-G.; Cheng, P. Silica-protection-assisted encapsulation of cu2o nanocubes into a metal-organic framework (ZIF-8) to provide a composite catalyst. Angew. Chem.-Int. Ed. 2018, 57, 6834–6837. [Google Scholar] [CrossRef] [PubMed]
  132. Zhang, M.; Wang, C.; Liu, C.; Luo, R.; Li, J.; Sun, X.; Shen, J.; Han, W.; Wang, L. Metal-organic framework derived co3o4/c@sio2 yolk-shell nanoreactors with enhanced catalytic performance. J. Mater. Chem. A 2018, 6, 11226–11235. [Google Scholar] [CrossRef]
  133. Zhang, S.; Han, A.; Zhai, Y.; Zhang, J.; Cheong, W.-C.; Wang, D.; Li, Y. Zif-derived porous carbon supported pd nanoparticles within mesoporous silica shells: Sintering- and leaching-resistant core-shell nanocatalysts. Chem. Commun. 2017, 53, 9490–9493. [Google Scholar] [CrossRef] [PubMed]
  134. Desai, S.P.; Malonzo, C.D.; Webber, T.; Duan, J.; Thompson, A.B.; Tereniak, S.J.; DeStefano, M.R.; Buru, C.T.; Li, Z.; Penn, R.L.; et al. Assembly of dicobalt and cobalt-aluminum oxide clusters on metal-organic framework and nanocast silica supports. Faraday Discuss. 2017, 201, 299–314. [Google Scholar] [CrossRef] [PubMed]
  135. Zhou, H.; He, D.; Saana, A.I.; Yang, J.; Wang, Z.; Zhang, J.; Liang, Q.; Yuan, S.; Zhu, J.; Mu, S. Mesoporous-silica induced doped carbon nanotube growth from metal-organic frameworks. Nanoscale 2018, 10, 6147–6154. [Google Scholar] [CrossRef]
  136. Wang, X.-G.; Dong, Z.-Y.; Cheng, H.; Wan, S.-S.; Chen, W.-H.; Zou, M.-Z.; Huo, J.-W.; Deng, H.-X.; Zhang, X.-Z. A multifunctional metal-organic framework based tumor targeting drug delivery system for cancer therapy. Nanoscale 2015, 7, 16061–16070. [Google Scholar] [CrossRef]
  137. Novio, F.; Simmchen, J.; Vazquez-Mera, N.; Amorin-Ferre, L.; Ruiz-Molina, D. Coordination polymer nanoparticles in medicine. Coord. Chem. Rev. 2013, 257, 2839–2847. [Google Scholar] [CrossRef] [Green Version]
  138. Wang, X.; Shi, J.; Zhang, S.; Wu, H.; Jiang, Z.; Yang, C.; Wang, Y.; Tang, L.; Yan, A. Mof-templated rough, ultrathin inorganic microcapsules for enzyme immobilization. J. Mater. Chem. B 2015, 3, 6587–6598. [Google Scholar] [CrossRef]
  139. Zhao, H.; Shu, G.; Zhu, J.; Fu, Y.; Gu, Z.; Yang, D. Persistent luminescent metal-organic frameworks with long-lasting near infrared emission for tumor site activated imaging and drug delivery. BioMaterials 2019, 217, 119332. [Google Scholar] [CrossRef]
  140. Wang, D.; Wu, H.; Lim, W.Q.; Phua, S.Z.F.; Xu, P.; Chen, Q.; Guo, Z.; Zhao, Y. A mesoporous nanoenzyme derived from metal-organic frameworks with endogenous oxygen generation to alleviate tumor hypoxia for significantly enhanced photodynamic therapy. Adv. Mater. 2019, 31, 1901893. [Google Scholar] [CrossRef]
  141. Adhikari, C.; Mishra, A.; Nayak, D.; Chakraborty, A. Metal organic frameworks modified mesoporous silica nanoparticles (MSN): A nano-composite system to inhibit uncontrolled chemotherapeutic drug delivery from bare-msn. J. Drug Deliv. Sci. Technol. 2018, 47, 1–11. [Google Scholar] [CrossRef]
  142. Deng, K.; Hou, Z.; Li, X.; Li, C.; Zhang, Y.; Deng, X.; Cheng, Z.; Lin, J. Aptamer-mediated up-conversion core/mof shell nanocomposites for targeted drug delivery and cell imaging. Sci. Rep. 2015, 5, 7851. [Google Scholar] [CrossRef] [PubMed]
  143. Rieter, W.J.; Taylor, K.M.L.; Lin, W. Surface modification and functionalization of nanoscale metal-organic frameworks for controlled release and luminescence sensing. J. Am. Chem. Soc. 2007, 129, 9852–9853. [Google Scholar] [CrossRef] [PubMed]
  144. Liu, C.; Yan, B. Highly effective chemosensor of a luminescent silica@lanthanide complex@mof heterostructured composite for metal ion sensing. Rsc Adv. 2015, 5, 101982–101988. [Google Scholar] [CrossRef]
  145. Sun, Z.; Xin, F.; Cao, C.; Zhao, C.; Shen, C.; Han, W.-Q. Hollow silica-copper-carbon anodes using copper metal-organic frameworks as skeletons. Nanoscale 2015, 7, 20426–20434. [Google Scholar] [CrossRef]
  146. Michaelides, A.; Aravia, M.; Siskos, M.G.; Skoulika, S. Photochemical reactivity of a lamellar lanthanum mof. Crystengcomm 2015, 17, 124–131. [Google Scholar] [CrossRef]
  147. Tang, Y.; Dubbeldam, D.; Guo, X.; Rothenberg, G.; Tanase, S. Efficient separation of ethanol-methanol and ethanol-water mixtures using ZIF-8 supported on a hierarchical porous mixed-oxide substrate. Acs Appl. Mater. Interfaces 2019, 11, 21126–21136. [Google Scholar] [CrossRef]
Polymers 11 01823 g001 550
Figure 1. Synthetic procedure of UiO-66@SiO2 shell-core composites via in situ coating process. Reproduced from [61], with permission from Elsevier, 2019.
Figure 1. Synthetic procedure of UiO-66@SiO2 shell-core composites via in situ coating process. Reproduced from [61], with permission from Elsevier, 2019.
Polymers 11 01823 g001
Polymers 11 01823 g002 550
Figure 2. Schematic representation of the synthesis of MIL-101(Cr)@mSiO2 sample via a sol–gel process to grow silica layer on MOF crystal. (a) MIL-101Cr; (b) as-synthesized MIL-101(Cr)@mSiO2; (c) final MIL-101(Cr)@mSiO2. Reproduced from [80], with permission from American Chemical Society, 2018.
Figure 2. Schematic representation of the synthesis of MIL-101(Cr)@mSiO2 sample via a sol–gel process to grow silica layer on MOF crystal. (a) MIL-101Cr; (b) as-synthesized MIL-101(Cr)@mSiO2; (c) final MIL-101(Cr)@mSiO2. Reproduced from [80], with permission from American Chemical Society, 2018.
Polymers 11 01823 g002
Polymers 11 01823 g003 550
Figure 3. Synthesis of MOF-5@SBA-15 hybrid nanomaterial via an impregnation approach to grow MOFs only in the pores of porous silica materials. Reproduced from [83], with permission from Wiley-VCH, 2018.
Figure 3. Synthesis of MOF-5@SBA-15 hybrid nanomaterial via an impregnation approach to grow MOFs only in the pores of porous silica materials. Reproduced from [83], with permission from Wiley-VCH, 2018.
Polymers 11 01823 g003
Polymers 11 01823 g004 550
Figure 4. A schematic pathway for the modification of core-shell silica particles with HKUST-1 crystals. Reproduced from from [94], with permission from Springer, 2014.
Figure 4. A schematic pathway for the modification of core-shell silica particles with HKUST-1 crystals. Reproduced from from [94], with permission from Springer, 2014.
Polymers 11 01823 g004
Polymers 11 01823 g005 550
Figure 5. Hierarchical buildup of the UiO-66-NH2@silica and the column packing for (Cr2O7)2− removal. Reproduced from [63], with permission from the Royal Society of Chemistry, 2018.
Figure 5. Hierarchical buildup of the UiO-66-NH2@silica and the column packing for (Cr2O7)2− removal. Reproduced from [63], with permission from the Royal Society of Chemistry, 2018.
Polymers 11 01823 g005
Polymers 11 01823 g006 550
Figure 6. SEM images of (a) as-prepared spheres-on-sphere (SOS) silica particles particles and (b) HKUST-1@SOS-SiO2 particles. Reproduced from [103], with permission from the Royal Society of Chemistry, 2013.
Figure 6. SEM images of (a) as-prepared spheres-on-sphere (SOS) silica particles particles and (b) HKUST-1@SOS-SiO2 particles. Reproduced from [103], with permission from the Royal Society of Chemistry, 2013.
Polymers 11 01823 g006
Polymers 11 01823 g007 550
Figure 7. SEM images of SiO2 coated with NH2-MIL-53(Al) crystals by (a) an ex situ seeding process with mesoporous silica spheres (MSSs) added into NH2-MIL-53(Al) seeds in N,N-dimethylformamide (DMF), or by (b) in situ seeding with MSSs were added to the synthesis gel of NH2-MIL-53(Al) seeds. (c) Adsorption–desorption isotherms of N2 at −196 °C for SiO2, NH2-MIL-53(Al), seeds and SiO2-NH2MIL53(Al) samples. (d) Adsorption–desorption isotherms of CO2 at 0 °C for SiO2, NH2-MIL-53(Al), and SiO2-NH2MIL53(Al) samples. Solid and open symbols correspond to adsorption and desorption, respectively. Reproduced from [110], with permission from Elsevier, 2016.
Figure 7. SEM images of SiO2 coated with NH2-MIL-53(Al) crystals by (a) an ex situ seeding process with mesoporous silica spheres (MSSs) added into NH2-MIL-53(Al) seeds in N,N-dimethylformamide (DMF), or by (b) in situ seeding with MSSs were added to the synthesis gel of NH2-MIL-53(Al) seeds. (c) Adsorption–desorption isotherms of N2 at −196 °C for SiO2, NH2-MIL-53(Al), seeds and SiO2-NH2MIL53(Al) samples. (d) Adsorption–desorption isotherms of CO2 at 0 °C for SiO2, NH2-MIL-53(Al), and SiO2-NH2MIL53(Al) samples. Solid and open symbols correspond to adsorption and desorption, respectively. Reproduced from [110], with permission from Elsevier, 2016.
Polymers 11 01823 g007
Polymers 11 01823 g008 550
Figure 8. HRTEM micrographs of (a,b) NH2-FDU-12 silica matrix and (c,d) HKUST-1/FDU-12 composite viewed at lower (a,c) and higher (b,d) magnifications. Reproduced from [112], with permission from the Royal Society of Chemistry, 2017.
Figure 8. HRTEM micrographs of (a,b) NH2-FDU-12 silica matrix and (c,d) HKUST-1/FDU-12 composite viewed at lower (a,c) and higher (b,d) magnifications. Reproduced from [112], with permission from the Royal Society of Chemistry, 2017.
Polymers 11 01823 g008
Polymers 11 01823 g009 550
Figure 9. (a) Dispersion of mesoporous silica (SBA-15) in hydrophobic n-octane; (b) addition of the hydrophilic N,N-dimethylformamide (DMF) solution containing MOF precursors (metal ions and ligands); (c) formation of MOFs at 120 °C for 24 h. Reproduced from [70], with permission from American Chemical Society, 2018.
Figure 9. (a) Dispersion of mesoporous silica (SBA-15) in hydrophobic n-octane; (b) addition of the hydrophilic N,N-dimethylformamide (DMF) solution containing MOF precursors (metal ions and ligands); (c) formation of MOFs at 120 °C for 24 h. Reproduced from [70], with permission from American Chemical Society, 2018.
Polymers 11 01823 g009
Polymers 11 01823 g010 550
Figure 10. TEM images for (a) ZIF-8@Au after calcination, (b) ZIF-8@Au@mSiO2 before calcination, (c) ZIF-8@Au@mSiO2 after calcination, (d) ZIF-8@Au@mSiO2@ZIF-8, (e) ZIF-8@Cu after calcination, (f) ZIF-8@Cu@mSiO2 before calcination, (g) ZIF-8@Cu@mSiO2 after calcination, and (h) ZIF-8@Cu@mSiO2@ZIF-8. Reproduced from [72], with permission from American Chemical Society, 2014.
Figure 10. TEM images for (a) ZIF-8@Au after calcination, (b) ZIF-8@Au@mSiO2 before calcination, (c) ZIF-8@Au@mSiO2 after calcination, (d) ZIF-8@Au@mSiO2@ZIF-8, (e) ZIF-8@Cu after calcination, (f) ZIF-8@Cu@mSiO2 before calcination, (g) ZIF-8@Cu@mSiO2 after calcination, and (h) ZIF-8@Cu@mSiO2@ZIF-8. Reproduced from [72], with permission from American Chemical Society, 2014.
Polymers 11 01823 g010
Polymers 11 01823 g011 550
Figure 11. Synthesis of hollow mesoporous silica (HMS)/MOFs with encapsulated anticancer drug molecules. Reproduced from [74], with permission from Wiley-VCH, 2018.
Figure 11. Synthesis of hollow mesoporous silica (HMS)/MOFs with encapsulated anticancer drug molecules. Reproduced from [74], with permission from Wiley-VCH, 2018.
Polymers 11 01823 g011
Polymers 11 01823 g012 550
Figure 12. Schematic of synthesis and sensing process of SiO2@Ln-dpa core–shell microspheres. Reproduced from [77], with permission from the Royal Society of Chemistry, 2016.
Figure 12. Schematic of synthesis and sensing process of SiO2@Ln-dpa core–shell microspheres. Reproduced from [77], with permission from the Royal Society of Chemistry, 2016.
Polymers 11 01823 g012
Table
Table 1. Synthesis strategy and advanced applications of MOF/SiO2 nanocomposites. MOF: metal organic framework.
Table 1. Synthesis strategy and advanced applications of MOF/SiO2 nanocomposites. MOF: metal organic framework.
MOF/SiO2Synthesis StrategyApplicationRef.
UiO-66@SiO2Solvothermal process to coat UiO-66 on silica coreStationary phase for HPLC[61]
HKUST-1-SiO2Synthesis of MOFs in the mesoporous silica poresStationary phase for HPLC[62]
UiO-66-NH2@SiO2One pot synthesis of UiO-66-NH2 and silica gelStationary phase for HPLC[63]
HKUST-1-SiO2MOFs were incorporated in situ into mesoporous silica poresStationary phase for HPLC[64]
Cu(BDC)-SiO2MOFs nanocrystals grown in the pores of mesoporous silicaCO2 adsorption[65]
MIL-101(Cr)-SiO2In situ hydrothermal method CO2 adsorption[66]
HKUST-1-SiO2Sol–gel methodCO2 adsorption[67]
MIL-101(Cr)-SiO2Microwave-assisted hydrothermalWater vapor adsorption[68]
ZIF-8@SiO2Ultrasound-assisted in situ processH2S adsorption[69]
MOF-5@SiO2Double-solvent strategy to grow MOFs inside silica poresCatalyst[70]
HKUST-1-SiO2In situ synthesis of MOFs in porous silica monolithsCatalyst[71]
ZIF-8@ SiO2
ZIF-7@ SiO2
UiO-66@ SiO2
HKUST-1@ SiO2		Sol-gel process to coat silica on MOFsCatalyst support[72]
MIL-88B-NH2@ SiO2Sol-gel process to coat silica on MOFsCatalyst support[73]
ZIF-8@ SiO2Drug DOX loaded into hollow mesoporous silica and then wrapped ZIF-8Drug Delivery[74]
SiO2@ZIF-8Mesoporous silica layer on ZIF-8 particlesDrug Delivery[75]
HKUST-1-SiO2
ZIF-8-SiO2		Layer-by-layer grown of MOFs on silica foamGas separation[76]
SiO2@Eu-dpaSolvothermal process to grow MOFs on silica spheres Fluorescence sensing[77]
SiO2@MIL-68MIL-68(Al) grow and nucleate on the surface of silica nanoparticlesPollute removal[78]

Share and Cite

MDPI and ACS Style

Ma, M.; Lu, L.; Li, H.; Xiong, Y.; Dong, F. Functional Metal Organic Framework/SiO2 Nanocomposites: From Versatile Synthesis to Advanced Applications. Polymers 2019, 11, 1823. https://doi.org/10.3390/polym11111823

AMA Style

Ma M, Lu L, Li H, Xiong Y, Dong F. Functional Metal Organic Framework/SiO2 Nanocomposites: From Versatile Synthesis to Advanced Applications. Polymers. 2019; 11(11):1823. https://doi.org/10.3390/polym11111823

Chicago/Turabian Style

Ma, Mengyu, Liangyu Lu, Hongwei Li, Yuzhu Xiong, and Fuping Dong. 2019. "Functional Metal Organic Framework/SiO2 Nanocomposites: From Versatile Synthesis to Advanced Applications" Polymers 11, no. 11: 1823. https://doi.org/10.3390/polym11111823

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop