A novel strategy was reported for the fabrication of yolk–shell magnetic MFSVmS-Au nanocomposites (NCs) consisting of double-layered ellipsoidal mesoporous silica shells, numerous sub-4 nm Au nanoparticles (NPs), and magnetic Fe central cores. The hierarchical FSVmS NCs with ellipsoidal α-Fe2O3@mSiO2/mSiO2 as yolks/shells were first prepared through the facile sol–gel template-assisted method, and plenty of extremely stable ultrafine Au NPs were postencapsulated within interlayer cavities through the unique deposition–precipitation method mediated with Au(en)2Cl3 compounds. Notably, ethylenediamine ligands were used to synthesize the stable cationic complexes, [Au(en)2]3+, that readily underwent the deprotonation reaction to chemically modify negatively charged mesoporous silica under alkaline conditions. The subsequent two-stage programmed hydrogen annealing initiated the in situ formation of Au NPs and the reduction of α-Fe2O3 to magnetic Fe, where the synthesized Au NPs were highly resistant to harsh thermal sintering even at 700 °C. Given its structural superiority and magnetic nature, the MFSVmS-Au was demonstrated to be a highly efficient and recoverable nanocatalyst with superior activity and reusability toward the reduction of 4-nitrophenol to 4-aminophenol, and the pristine morphology was retained after six recycling tests.

The reactable polyelectrolyte, poly(allylamine hydrochloride), was used for the first time to fabricate BiOCl materials via an assisted solvothermal method. The influence of polyelectrolyte concentrations on the formation of BiOCl was systematically investigated. The samples were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 gas sorption, infrared spectroscopy (FT-IR), as well as ultraviolet–visible diffuse reflectance spectroscopy (DRS). The results showed that the polyelectrolyte, which acted as reactant, template, or structure-directing agent, had a great effect on the structure of as-fabricated BiOCl materials during the reactive process. The possible formation mechanism of the BiOCl materials has been studied. Moreover, the photocatalytic activity of the as-fabricated BiOCl was evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. Furthermore, the relationship between the structure of the BiOCl materials and the photocatalyic activity was studied in detail. The holes rather than •OH were the predominant active species in the photocatalytic process. Also, it can be supposed that the improved light harvesting, high surface area, O-vacancies, enhanced adsorption capability of dye, faster interfacial charge separation, and the special structure of BiOCl had contributed to the good photocatalytic activity and high photostability of BiOCl microspheres. This route preparing the BiOCl materials with special structure can be expected to be applicable to the preparation of other materials with novel morphologies and advanced properties in all kinds of fields, including photocatalysis and electrochemistry.Keywords: BiOCl; Photocatalytic; Polyelectrolyte; Visible light;

A novel strategy was described to construct Au-based yolk-shell SCVmS-Au nanocomposites (NCs), which combined the sol-gel template-assisted process for the assembly of hierarchical SCVmS NCs with modified CeO2/mSiO2 as yolks/shells, and the unique deposition-precipitation (DP) process mediated with Au(en)2Cl3 compounds for the synthesis of extremely stable supported Au nanoparticles (NPs). Characterization results indicated that the obtained SCVmS-Au NCs featured mesoporous silica shells, tunable interlayer voids, movable CeO2-modified cores and numerous sub-5 nm Au NPs. Notably, the Au(en)2Cl3 was employed as gold precursors to chemically modify into the modulated yolk-shell structure through the DP process and the subsequent low-temperature hydrogen reduction induced the in-situ formation of abundant supported Au NPs, bestowing these metal NPs with ultrafine grain size and outstanding sinter-resistant properties that endured harsh thermal conditions up to 750 °C. Benefiting from the structural advantages and enhanced synergy of CeO2-Au/mSiO2-Au yolks/shells, the SCVmS-Au was demonstrated as markedly efficient catalysts with superior activity and reusability in catalyzing the reduction of 4-nitrophenol to 4-aminophenol, and its pristine morphology still maintained after eight recycling tests.Schematic illustration of the preparation of yolk-shell SCVmS-Au and its reaction mechanism for catalytic reduction of 4-NP.

•The novel TiO2-SiO2 shell was constructed with TiO2 nanosheets and silica species.•The formation mechanism involves the growth of TiO2 and redeposition of silica.•The strategy could be applied in the synthesis of yolk@shell nanocatalyst.In this work, a novel strategy has been proposed to synthesize a hierarchical Pt@TiO2-mSiO2 yolk@shell nanocatalyst firstly. Inner active sites could be protected by the TiO2-mSiO2 shell. The formation mechanism involves the in-situ growth of TiO2 nanosheets and simultaneous redeposition of etch-released silica species. TEM images were employed to characterize each step of the synthesis process. During the hydrothermal process, original TiO2 layer can be converted into a hierarchical structure and the inner SiO2 sphere was etched out automatically. Furthermore, the reduction of 4-nitrophenol had been used to test the hierarchical Pt@TiO2-mSiO2 yolk@shell nanocatalyst. The mixed oxides shell was constructed with in-situ grown hierarchical TiO2 nanosheets and redeposited SiO2.

In this work, we report a feasible approach to synthesize a ternary nanocomposites, Pt/lanthanum doped mesoporous zirconium oxide (Pt/La2O3-ZrO2), via an effective two-step method. Ordered mesoporous La2O3-ZrO2 composites were firstly fabricated with mesoporous silica KIT-6 as a hard template. Subsequently, uniform Pt nanoparticles encapsulated by 4 hydroxyl-terminated poly (amidoamine) (G4-OH PAMAM) dendrimers were deposited on the La2O3-ZrO2 composites. The as-prepared samples were characterized by transmission electron microscope (TEM), N2 adsorption–desorption isotherm analysis, energy dispersion X-ray analysis (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (H2-TPR). The average size of PtDENs was found to be 1.48 nm in diameter. Furthermore, the introduction of La could improve the structure of the supports which was confirmed by XRD and H2-TPR analysis. The reduction of p-nitrophenol to p-aminophenol by NaBH4 was utilized to evaluate the catalytic performances of catalysts. Results indicated that the Pt/La2O3-ZrO2 catalyst calcined in nitrogen at 550 °C exhibited the highest catalytic performance and still kept the high catalytic activity even after six cycles. This phenomenon suggests that synergistic effect among Pt-Zr-La could enhance the catalytic efficiency. Finally, reaction mechanism was proposed for the reduction of p-nitrophenol.Download high-res image (61KB)Download full-size image

A Sn4+-doped double-shelled Pt/TiO2 hollow nanocatalyst (DHS-SnPt) with excellent photocatalytic H2 production efficiency was prepared successfully via a facile hydrothermal method. In the catalytic system, Pt active sites were in situ reduced by Sn2+ and showed an enhanced interaction with Sn species. The enhanced SnO2/Pt interface could accelerate the migration rate of e− from SnO2 to Pt, improving the charge separation efficiency of h+ and e−. The as prepared DHS-SnPt contained a very low Pt content (0.24 wt%) and showed the highest photocatalytic H2 production efficiency (ca. 18 496 μmol g−1 within 3 h), nearly 5.8 and 1.678 times as high as that of a pure double-shelled Pt/TiO2 hollow nanocatalyst and the traditional Sn4+ doped counterpart, respectively, demonstrating the significantly improved Pt atom utilization of DHS-SnPt in photocatalytic H2 evolution activity. On the basis of experimental results, a possible photocatalytic H2 production mechanism was proposed to explain the excellent H2 production efficiency of DHS-SnPt.

A Sn4+-doped double-shelled Pt/TiO2 hollow nanocatalyst (DHS-SnPt) with excellent photocatalytic H2 production efficiency was prepared successfully via a facile hydrothermal method. In the catalytic system, Pt active sites were in situ reduced by Sn2+ and showed an enhanced interaction with Sn species. The enhanced SnO2/Pt interface could accelerate the migration rate of e− from SnO2 to Pt, improving the charge separation efficiency of h+ and e−. The as prepared DHS-SnPt contained a very low Pt content (0.24 wt%) and showed the highest photocatalytic H2 production efficiency (ca. 18 496 μmol g−1 within 3 h), nearly 5.8 and 1.678 times as high as that of a pure double-shelled Pt/TiO2 hollow nanocatalyst and the traditional Sn4+ doped counterpart, respectively, demonstrating the significantly improved Pt atom utilization of DHS-SnPt in photocatalytic H2 evolution activity. On the basis of experimental results, a possible photocatalytic H2 production mechanism was proposed to explain the excellent H2 production efficiency of DHS-SnPt.

Herein, a novel combined strategy was developed for the preparation of double-shell hollow magnetic ultra-small Au-loaded ellipsoids (Fe@MO2–Au@H–SiO2) as powerful nanoreactors; these ellipsoids comprised double mesoporous shell structures, CeO2 or TiO2 inner active yolks, plenty of sub-3 nm Au nanoparticles (NPs), and magnetic Fe cores. The hierarchical yolk–shell architectures with ellipsoidal Fe2O3@MO2 (M: Ce or Ti)/mSiO2 as yolks/shells were fabricated first via a facile bottom-up assembly process based on sol–gel reactions. After this, encapsulation of numerous extremely stable Au NPs within the shell structures was accomplished via a two-stage reduction process based on the unique deposition–precipitation method mediated with Au(en)2Cl3 compounds; moreover, strong magnetism was integrated into the ellipsoids and inner voids were formed due to the transformation of Fe2O3 into smaller magnetic Fe. Note that ethylenediamine was used as a ligand to synthesize the stable gold precursors [Au(en)2]3+ that were chemically modified onto the double ellipsoidal shells under alkaline conditions. Due to their superior structural properties and enhanced composite synergy, the Fe@MO2–Au@H–SiO2 ellipsoids, especially Fe@CeO2–Au@SiO2, were shown as a highly efficient and recoverable nanocatalysts with outstanding activity and reusability in catalyzing the reduction of 4-nitrophenol to 4-aminophenol.

•ZnO/Ag2O heterostructures have been successfully fabricated by a photochemical route.•Ionic liquids were used as template for shape-controllable ZnO nanomaterials.•The type of ionic liquid played an important role in the growth of ZnO nanoparticles.•ZnO/Ag2O heterostructures had the enhanced photocatalytic ability.•Photocatalytic activity is a result of the combination of various factors.ZnO/Ag2O heterostructures have been successfully fabricated using ionic liquids (ILs) as templates by a simple photochemical route. The influence of the type of ionic liquid and synthetic method on the morphology of ZnO, as well as the photocatalytic activity for the degradation of Rhodamine B (RhB), tetracycline (TC) and ciprofloxacin (CIP) under ultraviolet and visible light irradiation was studied. The samples were characterized by XRD, SEM, TEM, PL and UV–vis DRS. The results established that the type of ionic liquid and synthetic method played an important role in the growth of ZnO nanoparticles. And as-fabricated ZnO/Ag2O materials exhibited self-assembled flower-like architecture whose size was about 3 μm. Moreover, as-prepared ZnO/Ag2O exhibited the enhanced photocatalytic activity than ZnO sample, which may be due to the special structure, heterojunction, enhanced adsorption capability of dye, the improved separation rate of photogenerated electron–hole pairs. According to the results of radical trapping experiments, it can be found that •OH and h+ were the main active species for the photocatalytic degradation of RhB. It is valuable to develop this facile route preparing the highly dispersive flower-like ZnO/Ag2O materials, which can be beneficial for environmental protection.Download high-res image (149KB)Download full-size image

••  Novel Fe2O3CeO2/carbon yolk-shell magentic architectures were designed.•Double-layered SiO2/RF composites were synthesized by extended Stöber route.•Sub-2 nm Au NPs were assembled by in-situ reduction combined with DP method.•Fe2O3CeO2/Au/H-mC displayed superior catalytic activity and reusability.We report herein the successful design of novel Au-assembled heterostructural yolk-shell magentic ellipsoids (Fe2O3CeO2/Au/H-mC) through a facile and rational synthetic strategy. These target products comprised magnetic Fe2O3CeO2 spindles, mesoporous carbon shells and well-dispersed sub-2 nm Au nanoparticles. Firstly, double-layered SiO2/polymer resin composites were uniformly coated on Fe2O3CeO2 spindles in a single step via the surfactant-free extended Stöber route. Subsequent carbonization-hydrothermal etching was conducted for the formation of movable magnetic hybrid metal-oxide cores within mesoporous carbon hollow shells to achieve hierarchical Fe2O3CeO2/carbon yolk-shell magnetic architectures. Finally, by inducing the low-temperature H2 reduction combined with the [Au(en)2]3+-mediated deposition-precipitation method, abundant ultrafine Au nanoparticles were in situ synthesized within these modulated ellipsoids, displaying incredible thermal stability and dispersibility due to the stabilization effect of capped ethylenediamine ligands. Impressively, taking advantages of unique heterostructural characteristics for strengthened composite synergies and electronic interactions, these Fe2O3CeO2/Au/H-mC ellipsoids as powerful nanoreactors manifested the merits of superior catalytic performance, feasible recovery and excellent reusability for efficient reduction of 4-nitrophenol and organic dyes under mild conditions. The synthetic protocol can be instructive for the creation of other high-efficiency nanocatalysts with complex multifunctional architectures.Synthetic for the preparation of heterostructural Fe2O3CeO2/Au/H-mC ellipsoids and their reaction mechanism.Download high-res image (169KB)Download full-size image

•A facile synthesis of Br-modified g-C3N4 with highly porous structure was developed.•Urea and ionic liquid were used as the precursors of Br-modified g-C3N4.•The ionic liquid content played a key role on the morphology of Br-modified g-C3N4.•Br-doping and porous structure improve the optical and conductive properties of CN.•The Br-modified g-C3N4 showed the higher H2 evolution rate than pure CN.Coping with the gradually increasing worldwide energy and environmental issues, it is urgent to develop efficient, cheap and visible-light-driven photocatalysts for hydrogen production. Here, we present a facile way to synthesize bromine doped graphitic carbon nitride (CN-BrX) with highly porous structure by using ionic liquid (1-butyl-3-vinylimidazolium bromide) as the Br source and soft-template for the first time, which applied in hydrogen evolution under visible light irradiation. A systematic study is conducted on the optimization in the doping amount. The results find that the as-fabricated CN-BrX photocatalysts possess a uniform porous network with thin walls due to the release of volatile domains and decomposition of ionic liquids. The highly porous structure with the large surface area (≤150 m2/g) benefits the exposure of active sites. Moreover, the bromine modification and porous structure can narrow the band gap, enhance the transportation capability of photogenerated electrons, improve the optical and conductive properties of CN, thus contribute to an outstanding H2 evolution rate under visible light irradiation (120 μmol h−1), which is about 3.6 times higher than pure CN. This work provides a new insight for designing the novel g-C3N4 based photocatalysts for hydrogen production, CO2 conversion and environmental remediation.Download high-res image (259KB)Download full-size image

A facile synthetic strategy was developed for novel Au-loaded magnetic SiO2/carbon yolk-shell ellipsoids (Fe@SiO2-Au@H-C) composing of magnetic Fe@SiO2 yolks, mesoporous carbon shells and numerous sub-3 nm Au nanoparticles (NPs). The SiO2/polymer resin double-shell structures (Fe2O3@SiO2@RF) were prepared by the one-pot extended Stöber method, followed by carbonization-hydrothermal etching to attain hierarchical yolk-shell architectures (Fe2O3@SiO2@H-C) with mesoporous carbon shells. The H2 annealing reduction based on the unique deposition-precipitation method mediated with Au(en)2Cl3 compounds was post conducted to accomplish both the in-situ encapsulation of ultrasmall Au NPs and integration of inner entrapped Fe cores with strong magnetism. Hybrid formation of double-shell hollow structures and amorphous yolk structures was discernable in the yolk morphologies of Fe@SiO2-Au@H-C ellipsoids, and the embedded Au NPs displayed excellent dispersibility and enhanced thermal stability due to the protection of ethylenediamine stabilizer. With the merits of configural advantages and enhanced synergy of dual movable Au-embedded yolk/shell structures, the Fe@SiO2-Au@H-C ellipsoids as nanocatalysts were shown with outstanding activity and reusability toward the reduction of 4-nitrophenol and organic dyes, and appeared highly recoverable with well-preserved initial morphologies during the recycling processes.Schematic for the synthesis of ultrasmall Au-loaded magnetic SiO2/carbon yolk-shell ellipsoids.Download high-res image (235KB)Download full-size image

•Ionic liquid was used as template for dispersive bowknot-like ZnO microrods.•The bowknot-like ZnO consists of individual microrods whose size is about 1 μm.•The formation mechanism of the ZnO materials is tentatively elucidated.•The bowknot-like ZnO exhibited the high catalytic activity in the photodegradation.•Photocatalytic activity is a result of the combination of various factors.Here we present a facile method for the preparation of highly dispersive ZnO materials by using ionic liquid 1-methyl-3-[3′-(trimethoxysilyl) propyl] imidazolium chloride as the template. The influence of ionic liquid concentration and calcined atmosphere on the photoactivity is studied. The samples were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscope (SEM), N2 gas sorption and ultraviolet-visible diffuse reflectance spectroscopy. The results showed that the as-fabricated ZnO materials consisted of individual microrods with self-assembled bowknot-like architecture whose size was about 1 μm. The formation mechanism of the bowknot-like ZnO materials which is based on the self-assembly of ionic liquid is tentatively elucidated. Moreover, the ZnO-2.6N sample exhibited the higher activity for the photodegradation of MB than the photodegradation of MO and RhB. Furthermore, it was found that the ZnO materials calcined under air atmosphere showed the better photocatalytic activities than that of samples calcined under nitrogen atmosphere in the degradation of methylene blue (MB) under UV irradiation. And the special structure, surface area, adsorption capability of dye, the separation rate of photogenerated electron–hole pairs and band gap had effects on the photocatalytic activity of ZnO photocatalysts. O2 − was the main active species for the photocatalytic degradation of MB. It is valuable to develop this facile route preparing the highly dispersive bowknot-like ZnO materials and the ZnO materials can be beneficial for environmental protection.Download high-res image (156KB)Download full-size image

•Novel NiO-TiO2 hybrids/mSiO2 yolk-shell architectures were developed.•NiO-TiO2 p-n heterojunctions were constructed by NiO-doping hydrothermal route.•Supported Au NPs of sub–3 nm were synthesized by the DP method.•STNVS-Au NCs displayed remarkable catalytic activity and reusability.Novel NiO-TiO2 hybrids/mSiO2 yolk-shell architectures loaded with ultrasmall Au nanoparticles (STNVS-Au) were developed via the rational synthetic strategy. The hierarchical yolk-shell nanostructures (STNVS) with high surface areas were constructed by a facile “bottom-up” assembly process using SiO2 materials and polymer resins as cores/shells and sacrificial templates, accompanied by a simple hydrothermal incorporation of NiO into uniform amorphous TiO2 layers that were converted to NiO-anatase TiO2 p-n heterojunction hybrids. Then, numerous sub–3 nm Au nanoparticles were post encapsulated within STNVS nanostructures through the low-temperature hydrogen reduction based on the unique deposition-precipitation method with Au(en)2Cl3 compounds as gold precursors. The NiO-TiO2 hybrids alloying with Au nanoparticles were effectively protected and entrapped within STNVS architectures, and interacted with outer mSiO2-Au shells, which comprised the powerful STNVS-Au yolk-shell nanoreactors and produced stronger configural synergies in enhancing the heterogeneous catalysis. Into catalyzing the reduction of 4-nitrophenol to 4-aminophenol, the STNVS-Au was shown with outstanding activity and reusability, and its pristine morphology was well retained during the recycling process.Download high-res image (166KB)Download full-size imageSchematic for the reaction mechanism for STNVS-Au NCs in catalyzing the reduction of 4-NP.

A novel strategy has been proposed to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst (LDH-Pt). The formation mechanism involves loading of Pt NPs on nanocarbon spheres (NCSs) and calcination of NCSs/Pt/Al2O3 to remove inner NCSs. Then, Ni–Al LDH nanosheets in situ grew from hollow Pt/Al2O3 nanoclusters via a hydrothermal process, eventually fabricating the hierarchical LDH-Pt nanocatalyst. TEM and SEM images were employed to characterize each step of the synthesis process. During the hydrothermal process, most of the Pt NPs in Al2O3 shells were inlaid in the in situ grown LDH nanosheets, exhibiting a higher thermal stability than traditional impregnated LDH catalysts. Lastly, the as-synthesized LDH-Pt was tested with a high temperature reaction (590 °C) of propane dehydrogenation to further demonstrate the enhanced thermal stability of LDH-Pt.

A novel strategy has been proposed to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst (LDH-Pt). The formation mechanism involves loading of Pt NPs on nanocarbon spheres (NCSs) and calcination of NCSs/Pt/Al2O3 to remove inner NCSs. Then, Ni–Al LDH nanosheets in situ grew from hollow Pt/Al2O3 nanoclusters via a hydrothermal process, eventually fabricating the hierarchical LDH-Pt nanocatalyst. TEM and SEM images were employed to characterize each step of the synthesis process. During the hydrothermal process, most of the Pt NPs in Al2O3 shells were inlaid in the in situ grown LDH nanosheets, exhibiting a higher thermal stability than traditional impregnated LDH catalysts. Lastly, the as-synthesized LDH-Pt was tested with a high temperature reaction (590 °C) of propane dehydrogenation to further demonstrate the enhanced thermal stability of LDH-Pt.

The design of micro/mesoporous silica materials with solid acid catalysts for the catalytic reactions can inject new vitality into the development of nanostructures. In this paper, zirconium was successfully incorporated into micro/mesoporous silica by the direct hydrothermal synthesis, employing P123 and protic ionic liquid as the structure-directing agent. The physico-chemical properties of the micro/mesoporous silica-zirconia were characterized by means of X-ray scattering, N2 gas sorption, scanning electron microscopy, transmission electron microscopy and NH3 desorbed TPD methods. The influence of Si/Zr ratio and different calcination temperature on the acidity and catalytic properties were discussed. Also, the catalytic activities of solid acid catalysts were evaluated by the alkylation of o-xylene with styrene. The results indicate that the heteroatom of zirconium has been successfully incorporated into the structure framework and the solid acid catalysts still possess hierarchically porous structure. The prepared catalytic materials contain moderate to strong acid sites, meanwhile, the amount of strong acid sites increases with a decrease of Si/Zr ratio. The SZ-10-SO42− (molar ratio of Si/Zr = 10) catalyst was found to be the most promising and gave the highest selectivity among all catalysts, which was due to the strong interaction between H2SO4 and micro/mesoporous materials in the presence of Zr, thus prevent H2SO4 leaching from the materials. It is worth noting that SZ-10-937 (calcined at 937 K) also has the higher yield of PXE, which maybe the enhancement of crystallization of tetragonal ZrO2 made the strong acid sites for SZ-973 sample be more than that of the other samples with the increase of calcination temperature.

We report a simple method for the fabrication of hierarchical silica-Pt nanotubes. In the system, initial Pt NPs can be obtained via the reduction of H2PtCl6 with trisodium citrate as reductant. The self-assembled SiO2@Pt@SiO2 spheres were stuck together and etched through the “surface-protected etching” strategy. Many vertically aligned silica branches in situ grew from the inlaid SiO2@Pt@SiO2 spheres, fabricating the hierarchical silica-Pt nanotubes automatically. TEM and SEM were conducted to monitor the morphological evolution. The effects of the PVP concentration and molar ratios of NH4OH to TEOS have also been investigated with a series of contrast experiments. Furthermore, in this work, several potential applications of HSNs have been investigated, such as the synthesis of Pt-CeO2 nanotubes and other single or double metal nanotubes. Besides, the hierarchical silica-Pt nanotubes exhibited a high thermal stability and excellent catalytic performance in the reaction of propane dehydrogenation, suggesting their potential application in various high-temperature reactions.Keywords: Catalyst; Hierarchical structure; Nanotubes; Pt; SiO2;

•A novel binary-metal-oxide-coated Au-HwFe3O4 nanocatalyst was prepared.•In situ fabrication of Au NPs on the surface of C/HwFe3O4 was achieved.•The nanocatalysts calcined at 750 °C still had excellent magnetism and reactivity.A novel method has been developed for the preparation of highly active and thermally stable Au nanocatalysts, including a ZrO2-TiO2 (hereafter referred to as ZT) mixed oxide layer, a moveable Hollow Fe3O4 (hereafter referred to as HwFe3O4) magnetic core and some Au NPs of 5–8 nm. This method involves the in situ reduction of Au NPs on the C/HwFe3O4 nanospheres by using the C layer as the reducing agents. SEM, TEM, EDX, and XRD were employed to characterize the prepared samples. The results showed the ZT layer could increase the thermal stability and reactivity. The reduction of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) was employed as a model reaction to test catalytic performance in this work. The results showed the ZT/Au/C/HwFe3O4 nanospheres calcined at 750 °C showed the highest catalytic activity, compared to the samples calcined at 550 °C and RT, respectively. Meanwhile, the sample (750 °C) still has certain of magnetism, suggesting the desired samples could be separated by magnet. Finally, the catalyst was reused for several cycles to reduce the nitrophenol.Figure optionsDownload full-size imageDownload as PowerPoint slide

This article reports a facile and controllable one-step method to construct Pt@hollow mesoporous SiO2 (Pt@HMSiO2) nanoparticles (NPs). To enhance the catalytic activity, cerium species were impregnated into Pt@HMSiO2 NPs, fabricating highly reactive Pt–CeO2@HMSiO2 NPs. To verify the successful synthesis of the Pt@HMSiO2 and Pt–CeO2@HMSiO2 NPs, and study the influence of CeO2 species on the catalytic performance, the as-prepared NPs were characterized by several techniques, including SEM, TEM, EDX, FTIR, XRD, BET and UV-vis analyses. In this work, the reduction of 4-NP was employed as a model reaction to test the catalytic performance. Compared to Pt@HMSiO2, the Pt–CeO2@HMSiO2 NPs show higher catalytic activity, because of the co-catalysis of CeO2 NPs. However, the excess amount of CeO2 NPs would lead to a lower catalytic activity, due to the blocking of the catalyst pore. In addition, the Pt–CeO2@HMSiO2 NPs show a high thermal stability due to the protection of the SiO2 shell. Meanwhile, we have also used the reaction of propane dehydrogenation to further verify the excellent catalytic stability of Pt–CeO2@HMSiO2 NPs. This strategy is novel, albeit efficient, and can be extended to the preparation of other nanocatalysts.

Using mesoporous silica KIT-6 as a template, ordered mesoporous Co3O4–CeO2 composites with different contents of cobalt were prepared via the hard template method. Uniform Pt nanoparticles stabilized by polyamidoamine (PAMAM) dendrimers were immobilized on different Co3O4–CeO2 composites, resulting in Pt-based supported catalysts. The prepared materials were characterized by several techniques such as transmission electron microscopy (TEM), nitrogen physical adsorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDX). The results showed that the Co3O4–CeO2 composites have a regular pore structure and high crystallinity. Moreover, the specific surface area of Co3O4–CeO2 reached 135.04 m2 g−1 for 10 mol% of cobalt (Co/(Co + Ce)). The introduction of cobalt could improve the structure of the supports and enhance the catalytic efficiency for the prepared Pt-based supported catalysts. The catalytic performances were evaluated by the reduction of 4-nitrophenol as monitored by UV-Vis spectra. In a comparison of the catalysts with different cobalt contents, it was found that Pt/meso-CeO2Co10 possessed the highest catalytic performance as well as good reusability.

A facile method has been developed for the synthesis of a flower-like macrocellular siliceous foam with a large and uniform pore size, using P123 and protic ionic liquid as the co-templates under acidic conditions. The influence of the protic ionic liquid concentration and the hydrothermal temperature on the synthesis of the macrocellular siliceous foam is systematically investigated. The structures of all the composites were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis diffuse reflection spectroscopy, and N2 gas sorption. The results showed that the flower-like macrocellular siliceous foam possessed about 100 nm sized large pores, which was appropriate for it to be applied in catalytic reactions. Moreover, Au NPs were immobilized in the pores of the flower-like macrocellular siliceous foam through a self-assembly procedure. The obtained NH2-S-6-393/Au sample exhibited a remarkably higher catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4. The macrocellular siliceous foams are suitable supports for catalytic reactions on account of their special structure and can be highly beneficial for a wide range of applications.

A novel type of binary-metal-oxide-coated Au nanocatalyst, including a mixed oxide layer, a moveable magnetic Fe3O4 core and some Au NPs of 2–5 nm, has been synthesized successfully by a facile hydrothermal synthesis method. SEM, TEM, EDX, FTIR, XRD, and TGA were employed to characterize the prepared samples. The results showed the mSiO2–TiO2 layer could increase the thermal stability and reactivity of metal nanocatalysts compared to a pure TiO2 or SiO2 layer. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was employed as a model reaction to test catalytic performance in this work. The results showed that the binary-metal-oxide-coated nanocatalyst (550 °C) exhibited significantly enhanced catalytic performance compared with the pure SiO2 (550 °C) or TiO2 (550 °C). In particular, the mSiO2–TiO2/Au/C/Fe3O4 particles calcined at 550 °C showed the highest catalytic activity, compared to the samples calcined at 700 °C, 300 °C and RT. Meanwhile, because of C layer burning, the sample presented a few white spots between the Fe3O4 microsphere and the oxide layer, suggesting that the specific surface area was increased by calcination. The sample (550 °C) still has a certain degree of magnetism, suggesting the desired samples could be separated by magnet. Finally, to explain the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), a possible reaction mechanism was also proposed.

Ordered mesoporous ceria (meso-CeO2) was fabricated by nanocasting employing Ia3d mesoporous silica KIT-6 as the template. For comparison, ceria nanoparticles (nano-CeO2) with non-ordered mesoporous were also synthesized via a sol–gel method. Polyamidoamine (PAMAM) dendrimers were used as stabilizing agents to prepare a dispersed Pt nanoparticle colloidal solution. Afterward, the obtained well-dispersed Pt nanoparticles were immobilized on meso-CeO2 and nano-CeO2, respectively. The prepared samples were characterized through several techniques, such as X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy dispersion X-ray analysis (EDX) with mapping. The results revealed that the as-prepared meso-CeO2 has high crystallinity, a relatively small crystalline size, a well-ordered mesoporous structure and high surface area of 115.3 m2 g−1. In addition, the Pt/meso-CeO2 catalyst showed relatively uniform distribution of Pt nanoparticles with small sizes (∼4 nm). The catalytic performances of the as-synthesized catalysts were evaluated relying on the reduction of 4-nitrophenol monitored by UV-vis spectra. It was found that Pt/meso-CeO2 exhibited better catalytic activity compared with Pt/nano-CeO2. Besides, Pt/meso-CeO2 possessed good reusability and maintained a conversion of no less than 90% even after five cycles.

•Protic ionic liquid (butylamine acetate) was used as template for core-shell structured mesoporous silica spheres.•Silica spheres possessed smaller pores in the shell and larger mesopores in the core.•The ionic liquid content played a key role on the morphology of the silica sphere.Core-shell structured mesoporous silica spheres were successfully fabricated by utilizing cetyltrimethyl ammonium bromide (CTAB) and protic ionic liquid (butylamine acetate) as the co-templates. The obtained samples were characterized by N2 gas sorption, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results established that silica spheres possessed smaller pores in the shell and larger mesopores in the core. The formation mechanism of the silica sphere which is based on the interaction between protic ionic liquid (PIL) and CTAB is tentatively elucidated. And it is valuable to develop this facile route and the mesoporous silica spheres can be beneficial for a wide range of applications.Postulated mechanism of the core-shell structured mesoporous silica spheres.

Uniform ceria hollow nanospheres composed of ceria nanocrystals have been synthesized via a simple one-step hydrothermal method without using any template. Afterwards, these hollow materials were used as support to prepare the Au/CeO2 catalyst for the reduction of 4-nitrophenol (4-NP). It was found that the obtained porous CeO2 hollow nanospheres were morphologically uniform, with an average diameter of 210 nm and high specific surface area of 167 m2 g−1. According to the basis of a time-dependent experiment, a self-assembly process coupled with an Ostwald ripening mechanism was proposed to explain the evolution of CeO2 hollow nanospheres. In comparison with the commercial CeO2 powder supported sample, the synthesized hollow Au/CeO2 nanospheres catalyst exhibited significantly enhanced catalytic activity. In addition, the results of cyclic stability of the catalyst indicated that similar catalytic performance without visible reduction could be found after 7 repeated cycles. As for this catalyst system, the unique porosity structures of the support, uniform distribution of metallic particles together with the high thermal stability of Au NPs were all responsible for the improved reaction properties.

Uniform hierarchical SiO2/Au/CeO2 rod-like nanostructures were successfully fabricated by combining three individual synthesis steps, in which sub-5 nm gold nanoparticles (Au NPs) were coated with a mesoporous CeO2 shell. This method involves preparation of rod-like silica particles, deposition of Au NPs through a self-assembly procedure and then sequential deposition of CeO2 layers. To investigate the catalytic structure, the obtained sample was characterized by several techniques, including transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N2 adsorption–desorption isotherms (BET), and UV-vis diffuse reflection spectroscopy. It was found that SiO2/Au/CeO2 possessed an integral core shell structure including encapsulated Au NPs as core and mesoporous CeO2 as shell. Meantime, the inner silica plays an important role in the morphology control and improvement of the catalyst mechanical strength. The sample shows unique features such as uniform rod-like morphology, well dispersed Au NPs, and large specific surface area. The results of reaction performance indicate that the synthesized SiO2/Au/CeO2 catalysts exhibit significantly enhanced catalytic activity. Moreover, the catalytic activity of our as-prepared nanocomposite catalysts was well maintained even after 8 repeated cycles. It is clear that the core–shell composites can be used as effective nanoreactors with superior catalytic activity and recyclability due to their unique structural features.

A novel hollow tubular SiO2–Au catalyst with a mesoporous structure (HTMS) was successfully fabricated by a combination of the sol–gel and calcination processes. This method involves the preparation of modified MWCNTs, the sequential deposition of Au and then silica layers through the sol–gel processes, and finally the calcination at the desired temperature to remove the MWCNTs. The obtained samples were characterized by several techniques, such as N2 adsorption–desorption isotherms, transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, UV-Vis spectra, X-ray diffraction and Thermogravimetric Analysis (TGA). The results established that a different calcination temperature has an obvious influence on the morphology and structure of the final hollow tubular. When the temperature is 550 °C, the obtained materials exhibit the distinctly tubular structure because of the decomposition of MWCNTs and the preservation of hollow tubes. Furthermore, in the catalyst system, the mesoporous silica layer can act as the physical barrier to resist the agglomeration and sintering of Au nanoparticles even after being subjected to harsh treatments up to 650 °C. In our experiments, the catalytic activities of HTMS SiO2–Au were investigated by photometrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH4. It was found that the prepared HTMS SiO2–Au catalysts exhibited a high catalytic activity and this sample could be easily recycled without a decrease of the catalytic activities in the reaction.

A novel supported catalyst with various oxide shells (SiO2, TiO2, ZnO) assembled on Au nanoparticles with carbon nanotubes as support has been successfully fabricated. This process involves preparation of modified MWCNTs, sequential deposition of Au and then oxide shells, and finally calcination at high temperature to remove the organics. The obtained samples were characterized by several techniques, including N2 adsorption–desorption isotherms, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), UV-Vis spectra, X-ray diffraction and thermogravimetric analysis (TGA). The results established that all the oxide shells could serve as effective barriers to prevent the migration and aggregation of Au NPs during calcination. Moreover, different oxide layers have an obvious influence on the distribution of Au nanoparticles. Additionally, the prepared catalyst exhibited a mesoporous structure because of the preservation of carbon nanotubes. In our experiments, the catalytic activities of MOx/Au/CNTs were investigated by photo-metrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH4. It was found that the prepared TiO2/Au/CNTs catalyst revealed excellent catalytic activity and the sample could be easily recycled without a decrease of the catalytic activity in the reaction.

•The mechanism involves the growth of TiO2 and simultaneous redeposition of silica.•The redeposited mSiO2 provides a physical barrier to prevent Pt NPs from sintering.•The hierarchical TiO2 nanostructure shows an obvious co-catalysis effect.A novel hierarchical TiO2@Pt@mSiO2 hollow nanocatalyst with enhanced thermal stability has been synthesized successfully. The formation procedure involves a facile synthesis of SiO2@TiO2@Pt nanospheres and a subsequent solvothermal process. During the hydrothermal process, original TiO2 layer was transformed into a hierarchical nanostructure and, meanwhile, etch-released silica species redeposited on the surface of the in-situ grown TiO2 nanoplatelets. In the catalytic system, the in-situ grown TiO2 nanoplatelets were buried in the redeposited mSiO2 layers and the Pt NPs dispersed uniformly between TiO2 nanoplatelets and mSiO2 layers. Importantly, the redeposited mSiO2 layer provides a physical barrier to prevent Pt NPs from sintering up to 550 °C and the hierarchical TiO2 nanostructure shows an obvious co-catalysis effect in the reduction of 4-NP. Besides, the mSiO2 layer could also control the rapid crystallization process of TiO2 nanoplatelets effectively. In the high temperature reaction of propane dehydrogenation, HHN exhibits a lower deactivation parameter, indicating the excellent thermal stability.

A novel binary-metal-oxide-coated hollow microspheres-titanium dioxide-zirconium dioxide-coated Au nanocatalyst was prepared via a facile hydrothermal synthesis method. SEM, TEM, EDX, FTIR, XRD, UV–vis and XPS analyses were employed to characterize the composition, structure, and morphology of ZrO2–TiO2 hollow spheres. The size of Au nanoparticles was found to be 3–5 nm in diameter before being immobilized on the aforementioned mesoporous ZrO2–TiO2 layer and used as catalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. Compared with TiO2/Au and ZrO2/Au, ZrO2–TiO2/Au NPs showed a higher catalytic activity because of due to mixed oxide synergistic effect. Besides, the sample gets the highest thermal stability and reactivity at 550 °C, after calcining the hollow ZT/Au NPs at 550 °C, 300 °C and room temperature, respectively. Finally, a possible reaction mechanism was also proposed to explain the reduction of 4-nitrophenol to 4-aminophenol over ZrO2–TiO2/Au catalyst.Schematic illustration for the preparation of a novel ZT/Au hollow catalyst.

A novel hollow tubular SiO2–Au catalyst with a mesoporous structure (HTMS) was successfully fabricated by a combination of the sol–gel and calcination processes. This method involves the preparation of modified MWCNTs, the sequential deposition of Au and then silica layers through the sol–gel processes, and finally the calcination at the desired temperature to remove the MWCNTs. The obtained samples were characterized by several techniques, such as N2 adsorption–desorption isotherms, transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, UV-Vis spectra, X-ray diffraction and Thermogravimetric Analysis (TGA). The results established that a different calcination temperature has an obvious influence on the morphology and structure of the final hollow tubular. When the temperature is 550 °C, the obtained materials exhibit the distinctly tubular structure because of the decomposition of MWCNTs and the preservation of hollow tubes. Furthermore, in the catalyst system, the mesoporous silica layer can act as the physical barrier to resist the agglomeration and sintering of Au nanoparticles even after being subjected to harsh treatments up to 650 °C. In our experiments, the catalytic activities of HTMS SiO2–Au were investigated by photometrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH4. It was found that the prepared HTMS SiO2–Au catalysts exhibited a high catalytic activity and this sample could be easily recycled without a decrease of the catalytic activities in the reaction.