Jiandong Zhuang

Hierarchical porous TiO2@C hollow microspheres: one-pot synthesis and enhanced visible-light photocatalysis

Hierarchical porous TiO2-carbon hybrid composites with a hollow structure were successfully fabricated by a one-pot low-temperature solvothermal approach in the presence of dodecylamine. The growth mechanism of the hierarchical hollow spheres was demonstrated to include the condensation of a carbon source and the co-instantaneous in situ hydrolysis of Ti-alkoxide, and the consequent assembly of TiO2@C hybrid nanoparticles on a self-conglobated template. As compared with the TiO2@C solid spheres (86%), the hierarchical TiO2@C hybrid hollow spheres exhibited an enhanced photocatalytic efficiency (97%) for the visible-light photooxidation of rhodamine B. Investigations demonstrated that the enhancement can be attributed to the hierarchical porous hollow structure. Moreover, the superoxide radical was detected as the main active species generated in the oxidation reaction of RhB over TiO2@C photocatalysts. A corresponding mechanism was also proposed for the photocatalysis process.

Influence of spatial configurations on electromagnetic interference shielding of ordered mesoporous carbon/ordered mesoporous silica/silica composites

Ordered mesoporous carbons (OMCs), obtained by nanocasting using ordered mesoporous silicas (OMSs) as hard templates, exhibit unique arrangements of ordered regular nanopore/nanowire mesostructures. Here, we used nanocasting combined with hot-pressing to prepare 10 wt% OMC/OMS/SiO2 ternary composites possessing various carbon mesostructure configurations of different dimensionalities (1D isolated CS41 carbon nanowires, 2D hexagonal CMK-3 carbon, and 3D cubic CMK-1 carbon). The electric/dielectric properties and electromagnetic interference (EMI) shielding efficiency (SE) of the composites were influenced by spatial configurations of carbon networks. The complex permittivity and the EMI SE of the composites in the X-band frequency range decreased for the carbon mesostructures in the following order: CMK-3-filled > CMK-1-filled > CS41-filled. Our study provides technical directions for designing and preparing high-performance EMI shielding materials. Our OMC-based silica composites can be used for EMI shielding, especially in high-temperature or corrosive environments, owing to the high stability of the OMC/OMS fillers and the SiO2 matrix. Related shielding mechanisms are also discussed.

Synthesis and electromagnetic interference shielding effectiveness of ordered mesoporous carbon filled poly(methyl methacrylate) composite films

Thin films of ordered mesoporous carbon (OMC) with various mass fractions (0–40 wt%) composited with poly(methyl methacrylate) (PMMA) have been fabricated via a solvent casting method for electromagnetic interference (EMI) shielding materials. The OMC (actually CMK-3) embedded inside the polymer matrix endows the composite films with high electric conductivity which goes up with the increase of the OMC mass fraction. Through a four-probe method, it has been found that this novel composite film has a typical percolation threshold of 12.8 wt% CMK-3. Furthermore, the measured EMI shielding efficiency (SE) in 8.0–12.0 GHz (X-band) of the OMC/PMMA composite films has a strong dependence on the OMC content. The contribution of the absorption to total EMI SE of the system is larger than that of the reflection, that is, the absorption is more than 70%. For the composite film with 40 wt% OMC (0.4 mm in thickness), the mean EMI SE reaches 18.5 dB, indicating its promising application in EMI shielding.

Preparation and luminescence properties of SiO2/Lu2Si2O7:Ce composite starting from mesopore template

A chemical processing method has been developed for preparing the nanosized phosphors of Lu2Si2O7:Ce3+ (LPS:Ce) by choosing mesoporous template SBA-15 as Si source. Accordingly, the luminescent ceramic composite of SiO2/LPS:Ce has also been densified by hot pressing at elevated temperatures using composited powders with the prepared LPS:Ce phosphor particles embedded in SiO2 matrix. XRD analysis and TEM observation have been carried out for both the prepared LPS:Ce phosphors and the final SiO2/LPS:Ce ceramics, indicating complete crystallization and a well distribution of LPS:Ce nanoparticles in SiO2 component. The ultra-violet fluorescence spectra, X-ray excited luminescence spectra, and decay time of the resultant SiO2/LPS:Ce ceramic composite have also been measured, showing a blue emission from Ce3+ and a fast decay time of about 37 ns. Experimental results show that an attractive strategy has been successfully developed for producing translucent or even transparent ceramics with phosphor nanoparticles embedded in matrix. The specific route can provide an effective control of reaction channels and a uniform distribution of phosphor particles in matrix by the template guiding role from ordered mesoporous SiO2. The fabrication method thus developed could be employed in other kinds of composited ceramics.

Preparation and Luminescence Properties of

Bi4Si3O12:Zn2+(BSO:Zn) polycrystalline powders were successfully prepared by sol-gel method. X-ray diffraction measurements confirm that the Zn2+-doped materials are all monophasic solid solution powders. The influences of doping concentration on the photoluminescence and radioluminescence characteristics have been investigated and discussed. The Zn2+ doped material shows a better light yield than that of undoped material under X-ray excitation. The fluorescence decay time of the optimal material, excited by UV has been aslso measured. The results show that the Zn2+ ion doping has a positive effect on the light yield of BSO. But the crystal growth and characterizations of BSO:Zn polycrystalline powders prepared deserve further investigations.