Hansheng Li

Vapor diffusion synthesis of CoFe2O4 hollow sphere/graphene composites as absorbing materials

Novel CoFe2O4 hollow sphere/graphene composites were synthesized by a facile vapor diffusion method in combination with calcination at 550 °C. The structure and morphology of as-prepared hybrid materials were characterized by electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Uniform CoFe2O4 hollow spheres with a diameter of about 500 nm and a shell thickness of approximately 50 nm were homogeneously distributed on graphene sheets. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss of −18.5 dB was observed at 12.9 GHz for the CoFe2O4 hollow sphere/graphene composites with a thickness of 2 mm, and the effective absorption frequency ranged from 11.3 to 15.0 GHz. The CoFe2O4 hollow sphere/graphene composites exhibited better microwave absorbing performance than the CoFe2O4 hollow spheres. A possible formation mechanism for CoFe2O4 hollow sphere/graphene composites was proposed.

Study on nanomagnets supported TiO2 photocatalysts prepared by a sol-gel process in reverse microemulsion combining with solvent-thermal technique.

A sol-gel process in reverse microemulsion combined with solvent-thermal technique was developed for synthesizing a series of nanomagnets supported TiO(2) (TiO(2)/NMs) photocatalysts in this study. The structure of TiO(2)/NMs photocatalysts was characterized by Fourier transform infrared (FTIR), TG-DSC, X-ray diffraction (XRD), Raman spectrometry, TEM, BET, and VSM. The influence of CoFe(2)O(4) dosage on the photocatalytic activity and magnetism of TiO(2)/NMs photocatalysts was investigated. The results showed that nanosized anatase TiO(2) were uniformly coated on spinel CoFe(2)O(4) in the prepared TiO(2)/NMs photocatalysts. They possessed typical ferromagnetic hysteresis and performed better photocatalytic activity in degradation of methylene blue than TiO(2) prepared by the same method. The existence of CoFe(2)O(4) nanomagnets played an important role on the crystalline grain size of TiO(2) and the specific surface area of the prepared TiO(2)/NMs photocatalysts, thus had an important influence on its photocatalytic performance and magnetism. The photocatalytic performance of TiO(2)/NMs photocatalysts is related to their specific surface area, crystalline grain sizes of TiO(2) and particle size, as well as the doping effect of Fe(3+). The highest photocatalytic activity in degradation of methylene blue for TiO(2)/NMs photocatalysts at the CoFe(2)O(4) content of 20wt.% was achieved, with k(p) 28.32% higher than that of pure TiO(2) photocatalyst. Moreover, the experiments on recycled use of TiO(2)/NMs photocatalyst demonstrated a good repeatability of the photocatalytic activity.

Preparation of rugby-shaped CoFe2O4 particles and their microwave absorbing properties

Porous rugby-shaped CoFe2O4 particles were synthesized using a vapor diffusion method in combination with calcination. The morphologies and structures of the as-prepared CoFe2O4 particles were characterized by field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, and N2 adsorption–desorption measurement. Results showed that uniform CoFe2O4 rugbies were about 1.1 μm in length and 500 nm in width at the widest point. Rugby-shaped CoFe2O4 nanoparticles were assembled by the layers of nanoparticles and exhibit porous structures. The magnetic and electromagnetic parameters were measured using a vibrating sample magnetometer and a vector network analyzer, respectively. The obtained rugby-shaped products exhibited a saturation magnetization of 73.4 emu g−1 and a coercivity of 2218.7 Oe at room temperature. A minimum reflection loss of −34.1 dB was observed at 13.4 GHz for the sample with a thickness of 2.5 mm, and the effective absorption frequency (RL < −10 dB) ranged from 12.3 to 14.9 GHz, indicating the excellent microwave absorption performance of the novel products. The absorbing performance of the CoFe2O4 rugbies was better than that of the CoFe2O4 nanoparticles.

Catalytic performance of hierarchical H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether

Abstract Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as the source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N2 adsorption-desorption measurement and NH3 temperature-programmed desorption. The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated. Among these catalysts, H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80% methanol conversion and 100% dimethyl ether selectivity in a wide temperature range of 170–300 °C, and H-ZSM-5/MCM-41 prepared with nNa/nSi = 0.47 showed constant methanol conversion of about 88.7%, 100% dimethyl ether selectivity and excellent lifetime at 220 °C. The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves. The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.

Catalytic performance of acidic ionic liquid-functionalized silica in biodiesel production

Abstract Acidic ionic liquid ([BsAIm][OTf]) was immobilized on sulfhydryl-group-modified SiO 2 (MPS-SiO 2 ) via free radical addition reaction. The [BsAIm][OTf] loading on acidic ionic liquid-functionalized silica ([BsAIm][OTf]/SiO 2 ) was controlled through tuning the sulfydryl (SH) content of MPS-SiO 2 . All the samples were characterized by FT-IR, elemental analysis, N 2 adsorption-desorption measurements and TG-DTA. The catalytic performance of [BsAIm][OTf]/SiO 2 in the esterification of oleic acid and the transesterification of glycerol trioleate for biodiesel production was investigated. The results showed that with the increase of [BsAIm][OTf] loading on SiO 2 the specific surface area and pore volume of [BsAIm][OTf]/SiO 2 decreased, and the pore diameter of [BsAIm][OTf]/SiO 2 narrowed. In the esterificaiton of oleic acid, the oleic acid conversion increased with the increasing [BsAIm][OTf] loading. In the transesterification of glycerol trioleate, with the increasing [BsAIm][OTf] loading the glycerol trioleate conversion decreased and the selectivities to glycerol monooleate and methyl oleate increased.

Synthesis of polyoxymethylene dimethyl ethers from methylal and trioxane catalyzed by Brønsted acid ionic liquids with different alkyl groups

Bronsted acid ionic liquids with different alkyl group carbon chain lengths and an alkane sulfonic acid group were synthesized through bromoalkane, imidazole and 1,4-butane sultone as raw materials. The structures and properties of the ionic liquids were experimentally characterized. Catalytic reaction of methylal (DMM) with trioxane (TOX) for preparation of polyoxymethylene dimethyl ethers (PODMEn, CH3O(CH2O)nCH3, where n > 1) was investigated in various Bronsted acid ionic liquids with different carbon chain length of alkyl groups. The carbon chain length of alkyl groups and activity correlation for the ionic liquids was studied. It was found that the structures of ionic liquids were consistent with the designed structure and their purities were high. They possessed high thermal stability and wide liquid range. The hydrophobicity of ionic liquids became stronger with the increase of carbon chain length. With increasing the carbon chain length of ionic liquids, the selectivity of PODME3–8 is increased at first and then decreased. Among all the ionic liquids, [C6ImBS][HSO4] shows the best catalytic performance and the selectivity of PODME3–8 is 57.85%.

Targeted imaging of brain gliomas using multifunctional Fe3O4/MnO nanoparticles

Integrating T1- and T2-components of magnetic resonance (MR) imaging into a single particle has been demonstrated to be effective for improving the diagnostic accuracy. However, a T1–T2 dual modal MR contrast agent with glioma targeting ability remains unexplored. In this study, we prepared gourd-shaped Fe3O4/MnO hybrid NPs with a size of 25 nm through a thermal decomposition method. The water dispersibility was then obtained via a ligand exchange process with carboxylic acid-terminated silane. The sequential conjugation of chlorotoxin (CTX) and Cy5.5 on the carboxyl groups of attached silane endowed Fe3O4/MnO hybrid NPs with near-infrared fluorescence and glioma-targeting characteristics. The in vitro studies confirmed the targeting ability of Fe3O4/MnO–Cy5.5–CTX NPs toward C6 glioma cells. The in vivo T1–T2 dual modal MR imaging of glioma-bearing brain verified that the CTX conjugation led to a better contrast enhancement of the tumour tissue from the normal tissue both in T1 and T2 imaging, comparing to unconjugated NPs, which could enable more accurate diagnosis of gliomas.

Basic polymerized imidazolide-based ionic liquid: an efficient catalyst for aqueous Knoevenagel condensation

A novel basic polymerized ionic liquid (BPIL): polymeric 1-[(4-ethenylphenyl)methyl]-3-propylimidazolium imidazolide was synthesized and characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR) and electron spray ionization mass spectrometry (ESI-MS). The BPIL was used as an efficient catalyst for aqueous Knoevenagel condensations with extended substrates. In comparison with common base catalysts, the BPIL showed high catalytic activity, which was ascribed to the cooperation between the strong basicity and the high surface activity. Moreover, the BPIL with high molecular weight has high surface activity and low catalytic activity. In addition, the BPIL was easily recovered and maintained high catalytic activity after five cycles of use in the system using benzaldehyde and malononitrile as substrates.

Graphitic carbon nitride quantum dot decorated three-dimensional graphene as an efficient metal-free electrocatalyst for triiodide reduction

We demonstrate a new strategy for the development of graphitic carbon nitride quantum dots decorated on three-dimensional graphene as an efficient electrocatalyst for triiodide reduction. The special architecture of these hybrids endows them with an abundance of exposed sites and multiple pathways of charge and mass transport, resulting in synergistically enhanced electrochemical performance.

Synthesis of methylal from methanol and formaldehyde catalyzed by Brønsted acid ionic liquids with different alkyl groups

The catalytic reaction of methanol with formaldehyde for the preparation of methylal was investigated in various Bronsted acid ionic liquids with different carbon chain length of alkyl groups. The structures, acidities, and properties of ionic liquids were experimentally characterized and theoretically analyzed. The Bronsted acidity–viscosity–activity correlation for the ionic liquids was studied. Among all these ionic liquids, [C6ImBS][HSO4] exhibited the best catalytic performance, which was ascribed to its strong Bronsted acidity and low viscosity. The catalytic activity of the ionic liquid was near that of concentrated sulfuric acid. The influences of ionic liquid dosage, reaction temperature and molar ratio of methanol to formaldehyde were explored using [C6ImBS]HSO4 as the catalyst. Under the optimal conditions of n(methanol) : n(formaldehyde) : n(ILs) = 2.5 : 1 : 0.0258, 60 °C, and 4 h, the conversion of formaldehyde can reach 63.37%. The ionic liquid [C6ImBS]HSO4 could be reused.