Jiasheng Fang

In-situ formation of supported Au nanoparticles in hierarchical yolk-shell CeO2/mSiO2 structures as highly reactive and sinter-resistant catalysts

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-5nm 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.

Synthesis and characterization of hollow ZrO2–TiO2/Au spheres as a highly thermal stability nanocatalyst

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 3-5nm 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.

Fabrication of Ellipsoidal Silica Yolk–Shell Magnetic Structures with Extremely Stable Au Nanoparticles as Highly Reactive and Recoverable Catalysts

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.

Synthesis of ordered mesoporous La2O3-ZrO2 composites with encapsulated Pt NPs and the effect of La-dopping on catalytic activity

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 1.48nm 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.

Double-Shelled TiO2 Hollow Spheres Assembled with TiO2 Nanosheets

High-quality double-shelled TiO2 hollow spheres (DHS-Ti) assembled with TiO2 nanosheets have been synthesized for the first time through a simple hydrothermal treatment of sSiO2 @TiO2 (TiO2 -coated solid SiO2 spheres). The double-shelled structure shows a high BET surface area up to 417.6 m2  g-1 . Anatase DHS-Ti of high crystallinity can be obtained without structural collapse by calcination treatment. The effects of cetyl trimethylammonium bromide (CTAB) concentration, pH, and hydrothermal reaction temperature have also been investigated with a series of contrast experiments. A formation mechanism involving the in situ growth of amorphous TiO2 nanosheets followed by the redeposition of dissolved silica species is proposed. Lastly, the DHS-Ti forming strategy can be extended as a general strategy to fabricate various morphological hollow nanostructures and double-shelled Pt nanocatalysts by rationally selecting functional sSiO2 nanoparticles as core materials. This work could open up a new strategy for controllable synthesis of complex hollow structures and other functional materials.

In situ doping of Pt active sites via Sn in double-shelled TiO2 hollow nanospheres with enhanced photocatalytic H2 production efficiency

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.

Self-assembly of hollow spherical nanocatalysts with encapsulated Pt NPs and the effect of Ce-dipping on catalytic activity

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.

A novel strategy to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst with enhanced thermal stability

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.

Dispersed gold nanoparticles supported in the pores of flower-like macrocellular siliceous foams based on an ionic liquid as catalysts for reduction

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.

Fabrication of sandwich-structured g-C3N4/Au/BiOCl Z-scheme photocatalyst with enhanced photocatalytic performance under visible light irradiation

A novel sandwich-structured g-C3N4/Au/BiOCl Z-scheme heterojunction with enhanced visible-light-driven photocatalytic activity was successfully fabricated using the reactable ionic liquid (1-methyl-3-[3’-(trimethoxysilyl) propyl] imidazolium chloride) as the template by a facile photoreduction followed by in situ deposition. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, scanning electron microscope and ultraviolet–visible diffuse reflectance spectroscopy. The role of Au in this system was discussed during the degradation of rhodamine B and tetracycline and photocatalytic hydrogen evolution under visible light irradiation. The influence of BiOCl dosage on the photocatalytic activity was also systematically investigated. The result found that the photocatalytic activity was improved using the as-fabricated CN/Au/BiOCl Z-scheme heterojunction than g-C3N4 or BiOCl. Besides, the fast separation rate of photogenerated electron–hole pairs and the improved light absorption in visible ranges of CN/Au/BiOCl samples might be related to the fact that the construction of Z-scheme could improve the optical and conductive properties and enhance the final photocatalytic property. From the free radicals trapping experiments, it was found that the photogenerated holes of BiOCl were the predominant active species in the photocatalytic process.