Hongfang Li

A Multifunctional 3D Ferroelectric and NLO-Active Porous Metal-Organic Framework

The tetracarboxylate organic linker and Zn(II) ions assemble into chiral building blocks for a porous metal-organic framework with ferroelectric and second-order nonlinear optical properties.

An efficient and reusable silica/dendrimer supported platinum catalyst for electron transfer reactions

A series of Pt nanoparticles (NPs) smaller than 3 nm were successfully encapsulated in dendrimer/SBA-15 organic and inorganic hybrid composite. The obtained catalysts were characterized by XPS, XRD and TEM. The results of XPS and XRD indicate the existence of Pt NPs in the hybrid matrix. TEM images display the Pt NPs with narrow size distribution are monodispersed in SBA-15 channels. Catalytic property of the supported Pt catalysts was investigated in inorganic (ferricyanide to ferrocyanide by thiosulfate) and organic (p-nitrophenol to p-aminophenol by sodium borohydride) electron transfer (redox) reactions. In both cases, the reduction reactions followed smoothly and the catalysts showed excellent catalytic activity. Moreover, the catalysts can be easily separated and reused several times preserving good catalytic performance.

Bifunctional composite prepared using layer-by-layer assembly of polyelectrolyte – gold nanoparticle films on Fe3O4 – silica core–shell microspheres

Layer-by-layer assembly of polyelectrolyte–gold nanoparticles (NPs) multilayer films on Fe3O4–silica core–shell microspheres provides a convenient method to design a bifunctional hybrid composite combining the catalytic and magnetic performance together. The Au NPs are effectively immobilized in the polyelectrolyte layer without blocking the catalytic sites. The obtained hybrid magnetic microspheres exhibit high catalytic performance in both organic and inorganic reduction reactions. The use of magnetic support for the immobilization of Au NPs guarantees facile, clean, fast and efficient separation of the catalyst at the end of the reaction cycle.

Synthesis and visible light photocatalytic properties of polyoxometalate–thionine composite films immobilized on porous TiO2 microspheres

Multilayer films (PW(12)-TH)(n) (PW(12)=PW(12)O(40)(3-), TH=thionine) were immobilized on porous anatase TiO(2) microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO(2) was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO(2) template particles had a round shape with an average diameter of 250 nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW(12)-TH)(n) composite films onto TiO(2) microspheres, and the growth of PW(12)-TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW(12)-TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO(2) became weaker when immobilized (PW(12)-TH)(n). The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO(2) and PW(12) showed an excellent photocatalytic performance. Both TH sensitization and PW(12) adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW(12)-TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.

Dark current characteristics of GaAs-based 2.6 µm InGaAs photodetectors on different types of InAlAs buffer layers

GaAs-based In0.83Ga0.17As photodetectors (PDs) with cut-off wavelengths up to 2.6 µm are demonstrated. The effects of continuously-graded or fixed-composition InAlAs buffers on the device performances are investigated. The dark current characteristics of the PDs at various temperatures are analysed in detail. The photocurrents are also measured at 300 K; the detectivity of the PDs is extracted. The two GaAs-based PDs with different buffer schemes show different temperature-dependent dark current behaviours. The around room temperature performances of the GaAs-based device on the fixed-composition buffer are not as good, but comparable to those of InP-based devices, revealing a promising candidate for the GaAs-based PDs and focal plane arrays for many low-end applications.

Zinc Porphyrin/Imidazolium Integrated Multivariate Zirconium Metal–Organic Frameworks for Transformation of CO2 into Cyclic Carbonates

The design and synthesis of metal-organic frameworks (MOFs) enclosed with multiple catalytic active sites is favorable for cooperative catalysis, but is is still challenging. Herein, we developed a sequential postsynthetic ionization and metalation strategy to prepare bifunctional multivariate Zr-MOFs incorporating zinc porphyrin and imidazolium functionalities. Using this facile strategy, tetratopic [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]zinc(II) (ZnTCPP) ligands were successfully installed into the cationic Zr-MOF to obtain ZnTCPP⊂(Br-)Etim-UiO-66. These MTV-MOFs, including TCPP⊂Im-UiO-66, TCPP⊂(Br-)Etim-UiO-66, and ZnTCPP⊂(Br-)Etim-UiO-66, were well characterized and used in CO2 capture and conversion into cyclic carbonate from allyl glycidyl ether and CO2 under cocatalyst-free and 1 bar CO2 pressure conditions. It was found that the structural features and CO2 affinity properties of these MTV-MOFs can be tuned by introducing imidazolium groups or doping zinc sites. Additionally, ZnTCPP⊂(Br-)Etim-UiO-66 exhibited enhanced catalytic activities compared to other MTV-MOFs herein for obtaining the 3-allyloxy-1,2-proplyene carbonate product, which was attributed to the cooperative effect of Zn2+ sites and Br- ions in this microporous ionic MTV-MOF. ZnTCPP⊂(Br-)Etim-UiO-66 can be recycled easily and used at least three times.

Self-assembly of polyoxometalate–thionine multilayer films on magnetic microspheres as photocatalyst for methyl orange degradation under visible light irradiation

(PW(12)-TH)(n) multilayer films (PW(12)=PW(12)O(40)(3-), TH=thionine) were deposited successfully on core-shell structured Fe(3)O(4)@SiO(2) magnetic microspheres through layer-by-layer (LbL) self-assembly method. The physical and photocatalytic properties of such magnetic microspheres coated with (PW(12)-TH)(n) films have been characterized by SEM, FTIR, and UV-vis spectra. The microspheres exhibit better photocatalytic activity toward the degradation of methyl orange (MO) under visible light irradiation than the quartz slides support. In addition, the use of magnetic support guarantees facile, clean, fast, and efficient separation of the photocatalyst after the degradation of MO. Such catalysts can be reused several times and display good reproducibility by magnetic separation.

Cobalt coordination polymers regulated by in situ ligand transformation

A series of cobalt(II) coordination polymers {[Co(L1)2(H2O)2]·4H2O·2DMF}n (1; HL1 = 4-(3,5-(dicyano-2,6-dipyridyl)dihydropyridyl)benzoic acid; DMF = N,N-dimethylformamide), {[Co(L1a)2(H2O)2]·2H2O}n (2, HL1a = 4-(3,5-dicyano-terpyridyl)benzoic acid), and [Co3(μ3-OH)2(L1a)2(TP)(H2O)2]n (3, TPA = terephthalic acid) are reported, in which the conformation of the primary ligand L1− has been regulated by in situ oxidative dehydrogenation into L1a− in different solvent systems. Single crystal structural analyses reveal that compound 1 exhibits a 44-sql coordination layer structure constructed from cobalt centres and parent L1− ligands; compound 2 is constructed from Co2+ cations doubly connected by L1a− anions, which are generated in situ through oxidative dehydrogenation of L1−; while compound 3 features a rod-packing 3D network with a pcu-type topology, in which cobalt–oxygen chain units are interconnected by L1a− and TP2− mixed ligands. The formation mechanism of L1a− ligand via an in situ oxidative dehydrogenation reaction has been briefly discussed. This current study confirms that in situ ligand transformation is viable for controlled coordination polymer assembly, and is also adaptable to a more complexed ligand system.

Monodispersed Ag nanoparticles as catalyst: preparation based on crystalline supramolecular hybrid of decamethylcucurbit[5]uril and silver ions.

Monodispersed silver nanoparticles (Ag(0) NPs) have been first prepared on the basis of a postsynthesis via mild reduction from a new crystalline supramolecular hybrid solid assembled from Ag(+) ions and decamethylcucurbit[5]uril (Me10CB[5]). Uniform growth of nearly spherical Ag(0) NPs with an average size of ca. 4.4 nm was observed on the organic Me10CB[5] support to form Ag@Me10CB[5] composite material. The as-synthesized composite material was characterized by a range of physical measurements (PXRD, TGA, XPS, ICP, TEM, etc.) and was further exploited as a heterogeneous catalyst for the reduction of various nitrophenols in the presence of NaBH4. The kinetics of the reduction process was monitored under various experimental conditions. The Ag@Me10CB[5] composite material showed excellent catalytic performance over the reduction reactions and remained active after several consecutive cycles.

Controlled Synthesis of Noble Metallic Dimers and the Influence of Secondary Metals on the Catalytic Activity

To precisely discuss the influence of secondary metals on the whole nanosystem, two different types of Pd/Au dimers are constructed by reducing Au precursors with or without ascorbic acid. The number and size of gold nanoparticles attaching on larger Pd nanocrystals can be roughly controlled. Furthermore, based on electrocatalysis, we find that multidecorated dimers are generally more active than singly decorated ones. Meanwhile, the amount of Au precursor used in preparing multidecorated dimers is found to be very important to the catalytic activity of the as-prepared catalysts. The performance of the catalyst is enhanced with the increasing of Au precursor when the Au/Pd molar ratio is below 1:4, but hindered when the ratio climbs higher. Finally, this work provides a promising approach in forming hybrid nanocompositions to find an optimized amount of secondary metal, which is of significance in academic and economic fields.