A carbon nanotube/polyaniline/graphene (MWCNT–PANI–G) composite as sulfur host has been prepared by a simple self-assembly approach with potential application for lithium–sulfur (Li–S) batteries. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the microstructures and morphology of the as-prepared samples. It is demonstrated that the sulfur can be evenly impregnated into the MWCNT–PANI–G composite with strong chemical bonding. The resultant S@MWCNT–PANI–G composite with a sulfur content of 68 wt% shows excellent electrochemical performance as cathode for Li–S batteries. It delivers a high initial discharge capacity up to 1290 mA h g−1, good capacity retention of 784 mA h g−1 after 100 cycles of charge/discharge at the current density of 330 mA g−1, and good rate capability of 663 mA h g−1 and 548 mA h g−1 at 1.65 and 3.3 A g−1, respectively. The remarkable electrochemical performances are mainly attributed to the unique architecture of MWCNT–PANI–G with an enhanced electronic and ionic conductivity. Furthermore, this special architecture can provide strong physical and chemical confinement to the active materials and the soluble lithium polysulphides. Therefore, our study demonstrates a facile and low-cost approach to fabricate cathode materials for high-performance Li–S batteries.

•Novel SnO2 quantum dots/graphene has been prepared via microwave irradiation.•Uniform SnO2 quantum dots of about 1–5 nm are homogeneously dispersed on graphene.•The composite shows an enhanced lithium-storage performance.•The enhancement is attributed to the quantum and size effects and the synergistic effects.SnO2 quantum dots/reduced graphene oxide (SnO2/rGO) composite has been successfully prepared by a rapid microwave-irradiation process and subsequent annealing treatment. SEM and TEM results reveal that SnO2 quantum dots with the sizes of 1–5 nm are uniformly anchored on rGO nanosheets. The SnO2/rGO composite as an anode material presents a high initial discharge capacity of 1628 mAh/g and maintains a reversible capacity of 797 mAh/g after 100 cycles. After being cycled at various rates for 100 cycles, the capacity can recover to 777 mAh/g at 100 mA/g. The high reversible capacity, long cycling life and good rate performance can be attributed to the size effect of SnO2 quantum dots and the synergistic effect from rGO nanosheets.

The Keggin-structured heteropolyacid H4PMo11VO40 and its triethylamine-modified derivative [(C2H5)3NH]4PMo11VO40 were prepared and characterized by FT-IR and UV–visible spectrometry, and elemental analysis. Direct hydroxylation of benzene to phenol by H2O2 over these two catalysts was then compared. The effect of the triethylamine in [(C2H5)3NH]4PMo11VO40 on the catalytic hydroxylation of benzene was investigated in detail. The results showed that although the triethylamine-modified catalyst is not significantly more active than the parent heteropolyacid catalyst, its reaction-controlled phase-transfer characteristics enable easy separation of the catalyst from the reaction medium, and its reuse, suggesting its potential for application to the hydroxylation of benzene to phenol with H2O2.

The sulfoxy or sulfonic acid-functionalized MIL-101 catalyst was prepared by either post-functionalization or pre-modification of the organic linkers with the functionalized ligands, respectively, the latter is the so-called one-pot synthesis method. These catalysts were systemically characterized by XRD, N2 adsorption, acid–base titration, and FT-IR techniques and applied in the liquid-phase esterification of monocarboxylic acids with monohydric alcohols. The results show that the sulfonic acid-functionalized MIL-101 (S-MIL-101) prepared by the one-pot synthesis method possesses a higher catalytic activity in the esterification than its counterpart the sulfoxy acid-functionalized MIL-101 (S/MIL-101) prepared by the post-functionalized method, due to the fact that S-MIL101 has a higher acid loading and a high utilization efficiency of the functionalized acid sites. Moreover, S-MIL-101 is stable to leaching, behaves as a true heterogeneous catalyst, can be easily recovered by filtration, and can be reused five times in succession without any loss of its catalytic activity.

A series of polyoxometalate (POM)-based amphiphilic catalysts were prepared via functionalization of the V-containing Keggin POM H4PMo11VO40 by cationic surfactants with different carbon-chain lengths. These prepared catalysts were systematically characterized by Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), thermogravimetric (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, and X-ray diffraction (XRD) techniques as well as by the elemental analysis. Their catalytic activities were evaluated in the selective oxidation of benzyl alcohol to benzaldehyde by H2O2 under organic solvent-free conditions. Among the catalysts investigated, the amphiphilic (ODA)4PMo11VO40 (ODA: octadecylmethylammonium) shows the highest catalytic efficiency for the selective oxidation. The high activity and selectivity of the prepared (ODA)4PMo11VO40 are probably related to its amphiphilic property. A maximum conversion of benzyl alcohol is 60.6% with a selectivity of 99% for benzaldehyde under the optimized reaction conditions over (ODA)4PMo11VO40, which offers excellent reusability, confirmed by the recycling of the used catalyst.

Various catalysts, including the heteropolyacid (HPA) H4PMo11VO40, its cesium salts, and inorganic–organic dual modified HPA catalyst, were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (13C NMR), N2 adsorption, acid–base titration, electron spin resonance (ESR) and X-ray diffraction (XRD) techniques as well as elemental analysis. These prepared catalysts were used in the hydroxylation of benzene to phenol by H2O2 as oxidant. The inorganic–organic dual modified HPA Cs2.5(MIMPS)1.5PMo11VO40, prepared by partially exchanging Cs+ with protons in H4PMo11VO40 and followed by the immobilization of 3-(1-methylimidazolium-3-yl)propane-1-sulfonate (MIMPS), led to a liquid–solid biphasic catalysis system in the hydroxylation, which showed the best catalytic performance in terms of reusability and catalytic activity. The high reusability of Cs2.5(MIMPS)1.5PMo11VO40 in the heterogeneous hydroxylation was probably due to its high resistance in leaching of bulk HPA into the reaction medium. The slightly enhanced catalytic activity for the catalyst was due to the acid sites available from MIMPS beneficial to the hydroxylation.The inorganic–organic dual modified heteropolyacid Cs2.5(MIMPS)1.5PMo11VO40, prepared by partially exchanging Cs+ with protons in H4PMo11VO40 and followed by the immobilization of 3-(1-methylimidazolium-3-yl)propane-1-sulfonate (MIMPS), led to a liquid–solid biphasic reaction system for hydroxylation of benzene with H2O2, which showed the best catalytic performance in terms of reusability and catalytic activity. The high reusability of Cs2.5(MIMPS)1.5PMo11VO40 in the heterogeneous hydroxylation was probably due to its high resistance of leaching of bulk heteropolyacid into the reaction medium. The slightly enhanced catalytic activity for the catalyst was due to the acid sites available from MIMPS beneficial to the hydroxylation.Download full-size image

The sulfoxy or sulfonic acid-functionalized MIL-101 catalyst was prepared by either post-functionalization or pre-modification of the organic linkers with the functionalized ligands, respectively, the latter is the so-called one-pot synthesis method. These catalysts were systemically characterized by XRD, N2 adsorption, acid–base titration, and FT-IR techniques and applied in the liquid-phase esterification of monocarboxylic acids with monohydric alcohols. The results show that the sulfonic acid-functionalized MIL-101 (S-MIL-101) prepared by the one-pot synthesis method possesses a higher catalytic activity in the esterification than its counterpart the sulfoxy acid-functionalized MIL-101 (S/MIL-101) prepared by the post-functionalized method, due to the fact that S-MIL101 has a higher acid loading and a high utilization efficiency of the functionalized acid sites. Moreover, S-MIL-101 is stable to leaching, behaves as a true heterogeneous catalyst, can be easily recovered by filtration, and can be reused five times in succession without any loss of its catalytic activity.