Wei Feng

Synthesis of graphene oxide functionalized surface-imprinted polymer for the preconcentration of tetracycline antibiotics

In this work, we synthesized graphene oxide functionalized a surface-imprinted polymer based on the self-polymerization of dopamine to generate the imprinted cavity. Using minocycline as the template molecule, effects of experimental conditions in the imprinting procedure such as γ-MAPS@GO percentage, template concentration, and self-polymerization time of dopamine on the selectivity and performance of the prepared molecularly imprinted polymers were investigated. The characteristics of the prepared surface-imprinted polymer were determined by scanning electron microscope, transmission electron microscope, energy dispersive spectroscopy, Fourier-transformed infrared spectra, X-ray photoelectron spectroscopy, thermal gravimetric analysis, atomic force microscope, and water contact angle. The prepared graphene oxide functionalized surface-imprinted polymer showed good recognition capacity and enrichment performance for tetracycline antibiotics and was successfully applied to the detection of the target analytes in milk samples.

Water film inside graphene nanosheets: electron transfer reversal between water and graphene via tight nano-confinement

Based on quantum dynamics simulations using the density functional tight-binding (DFTB) method, we provide a detailed geometric and electronic structure characterization of a nano-confined water film within two parallel graphene sheets. We find that, when the distance between the graphene bilayer is reduced to 4.5 A, the O–H bonds of the water molecules become almost parallel to the bilayer; however, further reducing the distance to 4.0 A induces an abnormal phenomenon characterized by several O–H bonds pointing to the graphene surface. Electronic structure analyses revealed that the charge transfers of these nano-confined water molecules are opposite in these two situations. In the former scenario, the electron loss of each water molecule in the confined aqueous monolayer is approximately 0.008 e, with electrons migrating to graphene from the p orbitals of water oxygen atoms; however, in the latter case, the electron transfer is reversed, with the water monolayer gaining electrons from graphene in excess of 0.017 e per water molecule. This reversed behavior arises as a result of the empty 1s orbitals of H atoms, which are disturbed by the delocalized π orbitals formed by the p electrons of the carbon atoms. Our current study highlights the importance of the nano-confinement on the electronic structures of interfacial water, which can be very sensitive to small changes in physical confinement such as a small reduction in the graphene interlayer distance, and may have implications in de novo design of graphene nano-channels with unique water transport properties for nanofluidic applications.

HYPERCONJUGATION EFFECT ON THE STRUCTURAL STABILITY OF A TERT-BUTYL AND ITS DERIVED C4Hn(n = 4–10) ISOMERS

The hyperconjugation effect on molecular structural stability is studied by performing first-principles calculations on the tert-butyl and its derived C4Hn(n = 4–10) isomer structures. Four of the isomer structures with n = 7–10 were found to show hyperconjugation similar to that in the tert-butyl, with hyperconjugation orbital energies decreasing with the increase of the number of hydrogen atoms participating in the hyperconjugation (PIH). The distribution of charge carried by the PIH hydrogen atoms is uniform, which reveals a delocalization character in the electronic structures; and the PIH hydrogen atoms are found responsible for the main IR spectrum peak relating to C-H stretching vibration.

Enhanced visible-active photochromism of a polyoxometalates/TiO2 composite film by combining Bi2O3 nanoparticles

A novel photochromic hybrid film was successfully synthesized by introducing Bi2O3 into a phosphomolybdic acid (PMoA)/TiO2 system as a visible light sensitizer. The influence of Bi2O3 addition on microstructure and photochromic properties was studied via transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). The results revealed that the Keggin geometry of PMoA and basic structure of Bi2O3 were preserved in the obtained film, and the interaction between PMoA and TiO2 was strengthened after combining Bi2O3. Upon visible light irradiation, the composite films changed from colorless to blue and showed reversible photochromism in the presence of oxygen. Moreover, the photochromic performance of the Bi2O3/PMoA/TiO2 film was better than that of PMoA/TiO2 film. The amount of PMoA participating in the photo-reductive reaction increased after adding Bi2O3 into the PMoA/TiO2 composite, which resulted in photochromic efficiencies enhancing.

The theoretical chemical calculations clarify the mechanism of beta-alkylation of 1-phenylethanol with benzyl alcohol catalyzed by iron(II) acetylacetonate methods

Iron(II) acetylacetonate was suggested to be a better catalyst of the β-alkylation of 1-phenylethanol with benzyl alcohol to form 1,3-diphenyl-1-propanol. DFT calculations have been performed to study the internal mechanism, the structures of intermediates and transition states, and the exchange of electronic density in detail. The energetic results show that this β-alkylation reaction proceeds via the hydrogen autotransfer mechanism and the catalytic cycle includes three sequential stages: (1) alcohol oxidation to produce aldehyde associated with hydride anion transfer, (2) cross-aldol condensation to form a chalcone and (3) chalcone reduction with multi-step hydrogenation. In order to study whether the only by-product, water, has clearly influenced the reaction, eight catalyst hydrogenation pathways and four catalyst dehydrogenation pathways have been studied. We are delighted to find that the presence of the only by-product, water, can significantly increase the reduction energy barrier of dihydrochalcone. The energy barrier of the catalysts hydrogenation is less than 6 kcal mol−1. Our calculation results are fundamentally coincident with the experimental detections, and suggest that the crossing-coupling reaction occurs through a reliable mechanism. Two dihydrochalcone catalysts were designed on the basis of how the β-alkylation reaction proceeds.

Cobalt Phthalocyanine Tetracarboxylic Acid Functionalized Polymer Monolith for Selective Enrichment of Glycopeptides and Glycans

In this study, poly(glycidyl methacrylate‐ethyleneglycol dimethacrylate) monolith functionalized with cobalt phthalocyanine tetracarboxylic acid is prepared. The polymer monolithic material is used for glycopeptides enrichment coupled with MALDI–TOF MS. By taking advantage of cobalt phthalocyanine including hydrogen bonds between isoindole subunits of phthalocyanine and glycans, coordination interaction between cobalt and glycopeptides, the monolithic material is successfully applied to the enrichment of glycopeptides efficiently and selectively. With IgG and horse radish peroxidase as the model glycoproteins, 28 and 17 glycopeptides could be identified respectively after enrichment with the monolith, only four and three glycopeptides could be obtained for direct analysis. The monolith is also employed to the digests mixture of BSA and IgG (50:1, m/m), indicating the high enrichment selectivity of glycopeptides even in the presence of a large interference ratio. The detection limit is determined to be 6.7 fmol, implying that the present method had great potential for trace sample analysis. In addition, the monolith was successfully applied to the enrichment of N‐linked glycans in human serum samples, demonstrating its great potential for the analysis of glycoproteins.

Effect of Chain Conformation on the Single-Molecule Melting Force in Polymer Single Crystals: Steered Molecular Dynamics Simulations Study

Understanding the relationship between polymer chain conformation as well as the chain composition within the single crystal and the mechanical properties of the corresponding single polymer chain will facilitate the rational design of high performance polymer materials. Here three model systems of polymer single crystals, namely poly(ethylene oxide) (PEO), polyethylene (PE), and nylon-66 (PA66) have been chosen to study the effects of chain conformation, helical (PEO) versus planar zigzag conformation (PE, PA66), and chain composition (PE versus PA66) on the mechanical properties of a single polymer chain. To do that, steered molecular dynamics simulations were performed on those polymer single crystals by pulling individual polymer chains out of the crystals. Our results show that the patterns of force-extension curve as well as the chain moving mode are closely related to the conformation of the polymer chain in the single crystal. In addition, hydrogen bonds can enhance greatly the force required to stretch the polymer chain out of the single crystal. The dynamic breaking and reformation of multivalent hydrogen bonds have been observed for the first time in PA66 at the single molecule level.

Cloud point extraction of rare earths and zinc using 1,10-phenanthroline and Triton X-114 coupled with microwave plasma torch-atomic emission spectrometry

In the present work, cloud point extraction (CPE) of rare earths and zinc coupled with microwave plasma torch-atomic emission spectrometry (MPT-AES) was studied with 1,10-phenanthroline as the chelating agent and polyethylene glycol tert-octylphenyl ether (Triton X-114) as the surfactant. The experimental parameters affecting the cloud point extraction, such as the aqueous phase pH, Triton X-114 concentration, 1,10-phenanthroline concentration, ionic strength, and equilibration time, were systematically studied and optimized. Effects of common coexisting ions on the determinations were also investigated. Under the optimum conditions, the calibration curves were linear over the concentration range of 0.005–5 μg mL−1. The limits of detection (3σ) were determined in the range of 0.3–1.0 μg L−1 with a relative standard deviation range of 2.4–4.1% (n = 7). The developed CPE-MPT-AES method was successfully validated by the recovery studies in real water and human urine and serum samples.

A Study of Adsorption Behavior of Single Water Molecule on the Surface of Polyhedral Oligomeric Silsesquioxanes

The adsorption of a water molecule on the surface of polyhedral oligomeric silsesquioxanes (POSS, (HSiO3/2)n, nxa0=xa04, 6, 8, 10 and 12) with cage structures was studied using the density functional tight-binding method with the inclusion of an empirical dispersion term in total energy. The results revealed that water molecule is favor to adsorb on the ring surfaces which are formed by Si–O–Si bonds of various cage structures. With the increase of the ring size in the same cage, both the adsorption energy and charge transfer increase, while the hydrogen bond length decreases. For all the cage structures, the presence of a single water molecule causes only negligible charge transfer (no more than 0.01xa0e) from the cages to the water molecule, indicating that the adsorption of a single water molecule has no significant effects on the electronic properties of POSS. Comparing to the large energy gaps (about 8.27–8.63xa0eV) between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, the water adsorption can only cause slight reductions (within 0.15xa0eV) in the energy gap. Hence, the energy gap of the systems are primarily determined by the characteristics of POSS, instead of the energy transfer.

Enhanced Visible-active Performance of Bi2O3 Catalyst by ZnFe2O4 Combination

Abstract ZnFe2O4/Bi2O3 composites with different molar ratios of ZnFe2O4 and Bi2O3 were successfully synthesized. The prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and UV-Vis diffuse reflectance spectroscopy (UV-DRS). The result showed that Zn-O-Bi was formed between the interface of ZnFe2O4 and Bi2O3 without destroying the structures of ZnFe2O4 and Bi2O3. The photocatalytic activity was tested by methyl orange degradation under visible light and the probable reason for the activity enhancement was also investigated compared with pure Bi2O3 and ZnFe2O4. The photodegradation rate increased with the increase of the combination amount of ZnFe2O4, and reached peak value of 0.167 when molar ratio of ZnFe2O4:Bi2O3 came to 0.067, and then decreased with the further increase of the amount of ZnFe2O4 under the same condition. The synergistic effect of the crystal on the photocatalytic activity of ZnFe2O4/Bi2O3 composites were proposed. The higher photocatalytic activity of ZnFe2O4/Bi2O3 composite can be closely related to photosensitization of ZnFe2O4 rooted in the Zn-O-Bi formed between the interface of ZnFe2O4 and Bi2O3.