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Single-site heterogeneous catalysts constructed with highly dispersed, spatially well-separated isolated species have attracted much attention due to their outstanding specific activity and selectivity attributable to the unsaturated surface coordination sites and unique local electronic structures. Furthermore, such single-site heterogeneous catalysts are considered to be attractive as models for the top surface of inorganic semiconducting materials. As catalysts and photocatalysts, they provide suitable reaction fields to investigate the relationship between the activity and local structure of the active sites. To obtain detailed information on the reaction mechanism at the molecular level, advanced characterization techniques such as X-ray absorption fine-structure spectroscopy (XAFS), FT-IR, UV–VIS, EPR, and photoluminescence spectroscopy were applied. Moreover, various solid materials such as silica, mesoporous materials including zeolites, and semiconducting materials offer applicable strategies to design unique single-site heterogeneous photocatalysts. In the present review, photocatalytic reactions on single-site heterogeneous catalysts constructed on semiconducting materials have been summarized. Special attention has been focused on photocatalytic reactions for clean energy such as the splitting of water, reduction of carbon dioxide with H2O, conversion of CH4, and fixation of nitrogen. Furthermore, the preparation of single-site heterogeneous catalysts, their characterizations, and the relationship between their local structures and photocatalytic activities are also discussed. The present review not only provides a systematic understanding of single-site heterogeneous photocatalysts but also an understanding of the reaction mechanisms of semiconducting photocatalysis at the atomic level as well as the design of high-performance catalytic and photocatalytic reaction systems. [ABSTRACT FROM AUTHOR]

A three-dimensionally macroporous-mesoporous lithium ion sieve (3DM-HTiO) was transformed from 3DM-LiTiO through washing with HCl solution, which was synthesized by a combination of hydrothermal and low-temperature calcination (600 °C) treatment, using polystyrene microarray as hard-template, and titanium isopropoxide and lithium acetate as co-precursors. The influence of HCl concentration and temperature on the deintercalation rate of Li and Ti from LiTiO was specifically explored to maximize the extraction ratio of Li/Ti. The acceleration of Li extraction and insertion in a porous structure was verified using nonporous LiTiO as a control. 3DM-HTiO showed superior Li adsorption performance (5.51 mmol/g) compared with its nonporous counterpart (1.12 mmol/g), which was ascribed to the reduced Li mass transfer resistance in the highly interconnected porous channel. The ion selectivity of the 3DM-HTiO lithium ion sieve followed the order of Li > Na ~ Ca > K > Mg. The adsorption performance could be maintained after six cycles. The high adsorption capacity, excellent selectivity, and good recyclability demonstrate the prosperous potential application of 3DM-HTiO. Graphical Abstract: [ABSTRACT FROM AUTHOR]

N-doped mesoporous carbon-capped MoO2 nanobelts (designated as MoO2@NC) were synthesized and applied to lithium-ion storage. Owing to the stable core-shell structural framework and conductive mesoporous carbon matrix, the as-prepared MoO2@NC shows a high specific capacity of around 700 mA h g−1 at a current of 0.5 A g−1, excellent cycling stability up to 100 cycles, and superior rate performance. The N-doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core-shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO2@NC to be a suitable and promising material for lithium ion battery. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-CN), as a kind of polymeric semiconductor that has unique electronic structure and excellent chemical stability, has attracted increasing attention of researchers. Moreover, the raw materials for the preparation of g-CN are various and easily accessible. All of these have provided favorable advantages for the fast development of g-CN. Compared to bulk g-CN, mesoporous g-CN has more prominent natures, such as high specific surface area, large pore volume, and the increased amount of surface active sites. Therefore, great efforts have been devoted to develop mesoporous g-CN (MCN). Up to now, many methods have been explored for the synthesis of MCN, such as hard-template method, soft-template method, template-free method, sol-gel method, and so on. Among these methods, the hard template method is used most widely. In this paper, the recent research on the synthesis of MCN was reviewed. In addition, the modifications to the obtained MCN, which lead to performance enhancement of the MCN for better applications, were also summarized. [ABSTRACT FROM AUTHOR]

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO2 through an impregnation-hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO2 nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6 mm symmetry, a high specific surface area (446.27 m2 g−1), large pore volume (0.57 cm3 g−1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO2 nanocrystals are anchored to the carbon dot through TiON and TiOC bonds, as revealed by X-ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO2 is also verified by the formation of the TiN bond. This composite shows excellent adsorption capabilities for 2,4-dichlorophenol and acid orange 7, with an electron-deficient aromatic ring, through electron donor-acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible-light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible-light activity of TiO2. The adsorption capacity does not suffer any clear losses after being recycled three times. [ABSTRACT FROM AUTHOR]

A facile self-assembly synthetic procedure was exploited to fabricate mesoporous-silica-capped Fe3O4 mesoporous clusters, so-called bimodal mesoporous Fe3O4@SiO2 composites. Structural characterization demonstrated that the core of the Fe3O4 clusters is coated with a mesoporous silica shell of uniform size distribution. Moreover, unprecedentedly good tunability of the core size (180-1700 nm) and the shell thickness (20-75 nm) is achievable by changing the synthetic parameters. Application of the composite in the removal of the organic dye methylene blue (MB) from aqueous solution was examined. The composite exhibits excellent adsorption of methylene blue from aqueous solution (33.12 mg g-1) within 5 min and is easily regenerated by the photo-Fenton degradation reaction as a result of its high specific surface area, accessible pore channels, and good magnetic separation properties. This novel adsorbent promises extensive application in the practical removal of organic dyes. [ABSTRACT FROM AUTHOR]

Abstract: A layered mesoporous SAPO-34 with particle size of about 20μm was synthesized by using as-synthesized SBA-15 as silica source. For comparison, another three synthesis system were adopted to form SAPO-34 by using stoichiometric equivalence of calcined SBA-15, physical mixture of calcined SBA-15 and P123, and physical mixture of colloidal silica and P123 as initial reactants, respectively. The result shows that SAPO-34 can be prepared by all of the synthesis systems, however, only the sample prepared with as-synthesized SBA-15 shows mesoporous structure as revealed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Compared with SAPO-34 prepared with conventional and the above three contrasting systems, the specific surface area of this sample is considerably improved due to the existence of mesoporous structure. For the application as the catalyst for methanol to olefins (MTO) reaction, the layered mesoporous SAPO-34 presents the longest single life among all of samples. [Copyright &y& Elsevier]

Abstract: A novel floral mesoporous SAPO-34 was synthesized via conventional hydrothermal method in the presence of NaF with F/Si=0.02–0.2. X-ray diffraction (XRD) analysis shows that the crystallinity of SAPO-34 increases with the increasing F/Si ratio and reaches to the best at F/Si=0.1. Further increasing of F/Si ratio leads to the decrease of the crystallinity and the ultimate phase transformation to SAPO-5. Scanning electron microscopy (SEM) analysis shows that the addition of NaF leads to the formation of floral SAPO-34 while the addition of other salts including NH4F, NH4Cl and NaCl leads to the formation of traditional cubic SAPO-34. N2 sorption isotherm and NH3 temperature programmed desorption (NH3-TPD) analyses indicate that floral SAPO-34 has the largest pore volume but lowest strong acidity compared with other samples with traditional cubic morphology. When applied to methanol to olefin (MTO) reactions, floral SAPO-34 shows the comparable yields of propylene and butylenes to other samples but lowest overall olefin yield, which is attributed to the synergistic effect of the largest pore volume and lowest strong acidity. [Copyright &y& Elsevier]

Abstract: Mesoporous silica with thick pore wall (designated ECT) was synthesized in the presence of fluoride anions by using nonionic organosilicon surfactant (K903) as template. According to the results from XRD patterns and N2 adsorption–desorption analysis, the addition of fluoride has a strong effect on the pore diameter and pore wall thickness of the ECT samples. 29Si MAS NMR indicates that the degree of silicate condensation is greatly enhanced by adding fluoride ions. The hydrothermal stability of the mesoporous silica (ECT) synthesized in the presence of fluoride was found to be greatly improved compared to that of the sample without addition of fluoride ions. When F/Si=0.045, the mesostructure of the sample could still remain after refluxed in boiling water even for 20days. The ultra hydrothermal stability could be attributed to its thick pore wall, less defects in the silica framework and high degree of polymerization of silicate. Moreover, results from SEM reveal that the addition of fluoride anions also has great effect on the morphology structure of ECT sample. [Copyright &y& Elsevier]

Abstract: The hydrothermally stable MCM-48 mesoporous molecular sieve was successfully prepared at extremely low cost of cetyltrimethylammonium bromide (CTAB) by carefully adjusting the synthesis conditions. The increasing of the crystallization temperature from 373K to 423K can dramatically reduce the CTAB surfactant amount for the preparation of MCM-48 from 0.65 to 0.1 of the CTAB/Si ratio. The effect of increasing crystallization temperature on the formation process of MCM-48 at low CTAB cost was carefully studied. The influences of OH−/Si ratio and fluoride addition to the structure stability of the MCM-48 material synthesized at CTAB/Si=0.1 and 423K were systematically studied by XRD patterns. Moreover, the combination of increasing crystallization temperature and adding small amount of fluoride ions can considerably improve the structure stability of MCM-48 when reducing the CTAB cost. [Copyright &y& Elsevier]

Incorporation of a dual-FRET dye pair into mesoporous silica nanoparticles yields sensitive and sensing-range tunable nanosensors with good reversibility that can be used for ratiometric pH measurements under a single-wavelength excitation. [ABSTRACT FROM AUTHOR]

Bright and colourful nanocomposites are easily fabricated by doping and fixing one or two kinds of oligosilicate fluorescent dots encapsulated with dye molecules into the pore channels of mesoporous silica nanoparticles, which can engender abundant fluorescent signals with a single excitation wavelength. [ABSTRACT FROM AUTHOR]

In this work, the Fe 2 O 3 -SiO 2 composite photo-Fenton catalyst was designed and synthesized as a photonic crystal with a hierarchical macro-mesoporous structure, which possesses a slow-light-effect region that overlaps with the absorption spectrum of methyl orange (MO). The prepared material exhibits remarkably high and stable photo-Fenton catalytic performance for the degradation of MO using only a low concentration of H 2 O 2 under visible light irradiation. The catalytic activity of the as-prepared material is better than that of the corresponding macroporous or mesoporous Fe 2 O 3 -SiO 2 composites as well as commercial Fe 2 O 3 or the homogenous photo-Fenton system of FeCl 3  · 6H 2 O. The efficient use of H 2 O 2 and the high catalytic activity are attributed to (i) the excellent adsorption of MO by the hierarchical macro-mesoporous structure and (ii) enhanced light harvesting from coupling the absorption spectrum of MO with the slow-light-effect region of the photonic crystal. This hierarchical macro-mesoporous Fe 2 O 3 -SiO 2 photonic crystal is expected to be a promising cost-effective photo-Fenton catalyst for degradation of a variety of dyes by deliberately tuning its slow-light-effect region, and opens up new perspectives for the development of highly efficient photo-Fenton catalysts for environmental remediation technology. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous ZSM-5 was synthesized by using dual templates and one step hydrothermal crystallization method under alkali conditions. Mesopores were created by using cetyltrimethylammonium bromide (CTAB) as the template and the crystallized pore wall framework was formed by using tetrapropylammonium bromide (TPAB) as the template. The specific influences of the polyethylene glycol (PEG) and ammonium fluoride (NH4F) addition, hydrothermal crystallization temperature, TPAB/Si and Al/Si ratio to the mesostructure and crystallinity of the obtained samples were carefully studied. In this system, PEG plays an important role in the maintenance of the mesoporous pore ordering and the zeolite crystallinity. Moreover, the study on the hydrothermal stability of the sample with best mesoporous pore ordering and zeolite crystallinity showed this kind mesoporous zeolite has extremely high hydrothermal stability in boiling water. [Copyright &y& Elsevier]

Well-dispersed Fe 3 O 4 @Ag@mSiO 2 nanoparticle was fabricated by encapsulating Ag into yolk-shell structured Fe 3 O 4 @mSiO 2 composed of superparamagnetic Fe 3 O 4 core and mesoporous SiO 2 shell with bi-solvent nanocasting technique using AgNO 3 as the precursor. Ag can dwell in both the cavity between Fe 3 O 4 and mesoporous SiO 2 as an asymmetric shell and the mesoporous channel, or exclusively fill the cavity through increasing the reduction temperature of AgNO 3 from 350 to 550 °C. The asymmetric Ag shell proves to be high SERS-sensitive for the detection of methyl blue dispersed in ethanol solution as assisted by magnetically separation, with an enhanced factor of 5.02 × 10 4 . The SERS self-monitoring NaBH 4 reduction of p-nitrothiophenol catalyzed by Ag nanoclusters in the pore channel was further in situ and real-time achieved with an excellent recyclability. [ABSTRACT FROM AUTHOR]

A fluorescent resonance energy transfer (FRET) system was built for ratiometric sensing of Hg 2+ in water with periodic mesoporous organosilica (PMO) nanoparticles (NPs) as the scaffold. The silylated rhodamine 6G with a spiro-ring (R6G) as the energy acceptor was covalently attached on the pore walls of anthracene (Anth) encapsulated PMO NPs, which played the role of energy donor. In the presence of Hg 2+ , the fluorescence emission from R6G in the pore channel was observed by exciting Anth in the framework, which means the emission energy of Anth can effectively funnel into R6G and excite it. The successful FRET from Anth to R6G should be attributed to the shortened distance between them attributed to the nanometer-sized pore system of PMO matrix, which finally leads to the emission of original colorless R6G through a Hg 2+ -promoted ring-opening process of R6G derivative. An extremely low detection limit for Hg 2+ (6 × 10 −9 M) can be achieved. These results demonstrate that fluorescent PMOs have great potential as supporting materials for enhanced fluorescence chemosensors. [ABSTRACT FROM AUTHOR]

Hierarchical macro–mesoporous silica materials co-incorporated with Cr and Ti were directly synthesized by adopting close-packed array of polystyrene microsphere as hard template for macropore through a simple soaking-calcination way, where Si/Ti ratio was fixed at 200 and Si/Cr ratio was set between 200 and 10. Ti specie is highly dispersed in porous matrix and Cr specie mainly exists as tetra-coordinated CrO 3 at higher Si/Cr ratio (Si/Cr ≥ 50), which transforms to a mixture of CrO 3 and crystallized hexa-coordinated Cr 2 O 3 when Si/Cr ratio is below 50. This highly interconnected porous material co-incorporated with Cr and Ti presents highest visible-light driven photocatalytic activity at Si/Cr = 20 toward degradation of AO7. Moreover, macro–mesoporous photocatalyst presents higher activity than those of macroporous and mesoporous ones at the same Si/Cr ratio. The improved visible light driven catalytic activity is mainly attributed to effective metal to metal charge transfer from Cr(VI) to Ti(IV) benefitted from the uniform dispersion of these two species in hierarchical porous silica matrix. [ABSTRACT FROM AUTHOR]

Abstract: Monodisperse mesoporous silica nanosphere (MSN) modified with anthracene derivative, 2-(3-(triethoxysilyl) propylamino)-N-(9-anthryl methyl) acetamide (SGAAn) has been fabricated as a fluorescent sensor (SGAAn-MSN) for the detection of metal ions, which shows an exclusive selectivity to Cu2+. Compared with SGAAn, SGAAn-MSN presents a higher sensitivity to Cu2+. The loading amount of SGAAn in MSN has a great influence on the detection sensitivity of SGAAn-MSN, which varies with the local concentration and accessibility of SGAAn in the pore channel of MSN. Interference studies indicate that the addition of other metal ions such as Ag+, Cd2+ and Pb2+ has a negligible effect on the selectivity of SGAAn-MSN to Cu2+. The possible mechanism for the sensing behavior of SGAAn-MSN to Cu2+ is proposed based on the relation between fluorescence quench degree and Cu2+ concentration. [Copyright &y& Elsevier]