Zepeng Zhang

Copper-catalyzed N-formylation of amines with CO2 under ambient conditions

We carried out work on N-formylation of amines with CO2 and PhSiH3 to produce formamides catalyzed by a copper complex. It was found that the Cu(OAc)2–bis(diphenylphosphino)ethane (dppe) catalytic system was very efficient for these kind of reactions at room temperature and 1 atm CO2 with only 0.1 mol% catalyst loading.

Layer-by-layer reduced graphene oxide (rGO)/gold nanosheets (AuNSs) hybrid films: significantly enhanced photothermal transition effect compared with rGO or AuNSs films

Photothermal materials prepared from graphene and Au nanoparticles have received increasing attentions in various fields ranging from smart devices to advanced medical therapies. In this report, we studied the photothermal transition effects of LbL AuNS/rGO (AuNS: Au nanosheets) films under laser irradiation at 940 nm and comparisons were made with the film of rGO or AuNSs, wherein a single type of photothermal effective species exists. The results indicate that the hybrid LbL AuNS/rGO films displayed enhanced photothermal effects compared with the rGO or AuNSs films. The photothermal performance of the hybrid AuNS/rGO films deteriorated over repeated use or long-term laser irradiation, but the ultimate performance after irradiation was still better than that of the rGO or AuNS films. The hybrid film was able to load the model drug methylene blue (MB), and release MB 4 times faster with NIR irradiation than without, suggesting potential application in the combined chemical and thermal therapies. Thus, the hybrid film of AuNS/rGO is recommended when short-term or few-cycle photothermal applications are required. In comparison, rGO multilayered film better suits long-term or repeated photothermal applications, wherein stable photothermal performance is required.

Effects of variables on the dispersion of cationic–anionic organomontmorillonites and characteristics of Pickering emulsion

In this study, montmorillonites modified with different amounts of cationic and anionic surfactants by variable steps were used as research objects; physicochemical properties, dispersion of cationic–anionic organomontmorillonites and characteristics of Pickering emulsion were further investigated. XRD diffraction studies of organomontmorillonites showed that basal spacings of organomontmorillonites increased first and then dropped with the increasing amount of cationic surfactants used in the process of modification. Contact angles and swell indices showed that organic matter in the interlayer of organomontmorillonites had a more profound effect than the surface polarity on the dispersion of organomontmorillonites. The micro-macro morphology, thixotropy and volume of emulsion of the Pickering emulsion at elevated temperatures were further tested. The results illustrated that organomontmorillonites modified by three steps with a certain range of surfactants, and surface coated by cationic surfactants were weakly flocculated and had uniform dispersion in a 90u2006:u200610 oil–water ratio Pickering emulsion. The resulting emulsion had preferable stability and thixotropy. Cationic–anionic organomontmorillonites can be widely applied in the drilling industry and cosmetic industry as stable and cost-effective lipophilic colloid.

Influence of different exchangeable cations (Li+, Na+ and Ca2+) on the modification effects and properties of organomontmorillonites used in oil-based drilling fluids/muds

Montmorillonite with different exchangeable cations (Li+, Na+ and Ca2+) in the inter spaces were modified using a combination of cationic and anionic surfactants, to prepare cationic–anionic organomontmorillonites (Li-organomontmorillonite, Na-organomontmorillonite and Ca-organomontmorillonite). The prepared organomontmorillonites were used in oil-based drilling fluids. Structure and properties of the cationic–anionic organomontmorillonites were studied using X-ray diffraction, thermogravimetry and contact angles. The properties of different oil–water ratios of oil-based drilling fluids/muds with added organomontmorillonite at room and high temperatures were studied using a rotary viscometer, filtration loss apparatus and a six-speed viscometer. The results showed that exchangeable cations in the inter-spaces of montmorillonite had an obvious impact on the structure and properties of the cationic–anionic organomontmorillonites. Of the three kinds of cationic–anionic organomontmorillonite, the cationic–anionic organomontmorillonite prepared from Li-montmorillonite had the largest basal spacing, best thermal stability and highest surface polarity which was followed by Na-montmorillonite and Ca-montmorillonite successively. Application of the research to oil-based drilling fluids/muds through adding different organomontmorillonites showed that Li-organomontmorillonite showed the best applied properties in full oil-based drilling fluids/muds at 180 °C. Na-organomontmorillonite showed the best applied properties in 80u2006:u200620/90u2006:u200610 oil–water ratio oil-based drilling fluids/muds at 180 °C. The oil-based drilling fluids/muds with added Ca-organomontmorillonite had the worst applied properties at 180 °C.

A comparative study performance of cationic organic montmorillonite prepared by different methods

Abstract In this paper, cationic organic montmorillonites (OMts) were prepared by dry, semi-dry, and wet methods. The structures and properties of these OMts according to the modification methods were studied. By the characterization of XRD, TG-DTA, lipophilicity, and thixotropy, the results showed that cationic OMt prepared by wet method with sufficient surfactants had better properties, including contact angle, swelling capacity, thixotropic loop area, and thermal stability compared with cationic OMt prepared by dry and semi-dry methods. Attention should be paid that with low ratio amount of surfactants used, cationic OMt prepared by the semi-dry method had favorable properties compared with cationic OMt prepared by wet method, and it had the potential to be applied in industrial field due to its environment-friendly and modification efficiency characteristics.

Effect of Emulsification Processes on the Stability of Pickering Emulsions Stabilized by Organomontmorillonites

ABSTRACT In this paper, effect of emulsification processes on the properties of Pickering emulsions stabilized by organomontmorillonites (OMts) was studied. Results of micro-morphology and X-ray diffraction showed that the structure of OMt in emulsion depended on the emulsification processes and had an effect on the stability of emulsion. We propose a schematic diagram to reveal the relationship between emulsification processes-OMt laminates structure-stability of Pickering emulsion. In emulsion prepared by ultrasonic, OMt showed uniform dispersion, loose structure, and irregular crystalline. In emulsion prepared by vortex mixing method, OMt illustrated stacking and coagulation structure. In emulsion prepared by microwave method, OMt showed interacting structure and had a little interaction with oil/water interface, and thus the properties of emulsion prepared by microwave was weakly related to oil/water ratios. Emulsification processes had a profound effect on the structure of OMt and stability of Pickering emulsion, which can be used as a trigger to prepare emulsion for various applications. GRAPHICAL ABSTRACT

Structure and performance of anionic–cationic-organo-montmorillonite in different organic solvents

Montmorillonite (Mt) was modified in aqueous solution by cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfonate (SDS) under ultrasonic conditions at 60 °C. Anionic–cationic-organo-montmorillonite (ACOMt) was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle measurement. The results indicated that ACOMt was prepared successfully, and the polar property of ACOMt was higher than that of cationic-organo-montmorillonite (COMt). The results of SEM proved that there were great amounts of loose and thin platelets of ACOMt. In addition, the properties of ACOMt in three organic solvents were investigated using XRD, SEM, optical microscopy and viscometry, etc. The results of the XRD patterns demonstrated that the basal spacing of ACOMt became small because of parts of the surfactants getting out of the interlayer after being dispersed in the organic solvents. Moreover, with the increase in the solvent polarity, the amounts of surfactants getting out of the interlayer increased. The results of optical microscopy revealed that, with the increase of surfactants and the polar property, the dispersibility of powdery samples in the organic solvents improved and ACOMt in a highly polar solvent showed the best dispersibility. However, the results of SEM indicated that the morphology of ACOMt dispersed in three organic solvents was not significantly different. Meanwhile, dispersion of ACOMt in xylene exhibited the best thixotropic properties and apparent viscosity.