Single layered Ti3C2(OH)2 nanosheets have been successfully fabricated by etching its Ti3AlC2 precursor with KOH in the presence of a small amount of water. The OH group replaced the Al layer within the Ti3AlC2 structure during etching, and Ti3C2(OH)2 nanosheets could be easily and efficiently achieved through a simple washing process. The delaminated single-layered nanosheets are clearly revealed by atomic force microscopy to be several micrometers in lateral size. Interestingly, the exfoliated Ti3C2(OH)2 nanosheets could be restacked to form a new layer-structured material after drying. When redispersing this restacked Ti3C2(OH)2 materials in water again, it could be re-delaminated easily only after shaking for several hours. The easy delamination and restacking properties, coupled with intrinsic metallic conductivity and hydrophilicity, make it an ideal two-dimensional building block for fabricating a wide variety of functional materials.

Porous Ni(OH)2 nanocubes were successfully fabricated by a simple self-sacrificial-template protocol using Ni–Co Prussian blue analogue (PBA) as precursor. When treated with NaOH, the simultaneous corrosion of Ni–Co PBA precursor and formation of amorphous Ni(OH)2 resulted in porous Ni(OH)2 nanocubes with uniform size of about 100 nm. Due to the large specific surface area and unique regular porous structure, the as-prepared materials showed large specific capacitance, relatively stable rate capability and long cycle stability when used as electrode materials for supercapacitors. With the voltage between 0.00 and 0.45 V versus Ag/AgCl, the specific capacitance can achieve 1842 F/g at a current density of 1 A/g.

Analysis the synergy among different components within graphene based asymmetric supercapacitor could help us to establish the criterion for construction the idea supercapacitor for real applications. For this purpose, 3D Networks for Fe2O3 and α- Ni(OH)2 individually/collectively decorated S-doped graphene composites were successfully synthesized. The electrochemical performances clearly indicate the multi-decorated composite possesses the largest specific capacitance, improved cycle stability and enhanced rate capability due to its efficient additive effect among the different components of supercapacitor. The pronounced high energy density, provided by redox-active transition mental oxide/hydroxide, combined with excellent conductivity, hydrophilia and efficient charge storage, originated from S-doped graphene, result in the excellent composite for asymmetric supercapacitor. Within the voltage range from 0 to 0.44 V versus Ag/AgCl, the specific capacitance of Fe2O3 and Ni(OH)2 co-decorated S-doped graphene composite can be achieved 2386 F g−1 at current density of 1 A g−1.The electrochemical performances clearly indicate the multi-decorated composite exhibits large specific capacitance, improved rate capability and long cycle stability due to its efficient additive effect among the different components of super-capacitor.Download high-res image (149KB)Download full-size image

Mesoporous C, N co-doped TiO2 was fabricated by a one pot pyrolysis method using ammonium titanyl oxalate as the precursor. When deposited with Au, the resulting materials possessed a relatively high surface area and highly dispersed gold nano-particles, exhibiting high catalytic activities for CO oxidation. The doping of C and N into meso-structured TiO2 increases the number of surface defect which could improve the absorption of oxygen, tune the metal-support interaction and promote the catalytic activities for CO oxidation.

A facile protocol for producing porous carbon spheres co-doped with nitrogen and sulfur is presented. Thiourea resorcinol-formaldehyde (RF) copolymerized resin microspheres were used as precursors. After only a simple calcination, the uniformly N, S co-doped graphitized carbon spheres could be obtained. Synergistic effects produced by the tunable content of N, S heteroatoms combined with the porous graphitized structures makes this one of the excellent non-platinum-based catalysts for the oxygen reduction reaction. When used in alkaline media, the materials exhibit high onset and half-wave potentials, high kinetic current density and a four-electron transfer pathway with low hydrogen peroxide yield, which is comparable to the commercial Pt/C catalyst. More importantly, the long-term durability test confirms its excellent stability for practical applications.

•Oxygen vacancy in CeO2 support plays an important role in CO oxidation process.•CeO2 nanocube, exposed by {100} facet, possesses much higher oxygen vacancy.•Pd loaded on CeO2 nanocube shows the highest activity compared with its counterpart.•The complete CO conversion temperature is only about 60 °C.Oxygen vacancy plays an important role in determine the catalytic activity of the supported noble metal catalyst during oxidation process. In this paper, CeO2 nanoparticles, single-crystalline nanorods and nanocubes with different exposed facets were synthesized as support through hydrothermal method. After loaded with Pd species, the structure effect of CeO2 support on CO oxidation process was studied. The experiment clearly shows that Pd loaded on CeO2 nanocubes, which are dominantly exposed by {100} facet, possesses the highest catalytic activity. The 50% CO conversion temperature is about 35 °C, much lower than that CeO2 nanorods (60 °C) and nanoparticles (90 °C), corresponding well with the order of the formation of oxygen vacancy on the different exposed facets of the CeO2 crystalline.

A facile one-step co-precipitation method has been applied for the synthesis of a Pt decorated octahedral Fe3O4 catalyst. The simple addition of a Pt4+ and Fe2+ mixture into a KOH solution leads to the simultaneous formation of an octahedral Fe3O4 and in situ reduction of Pt4+. HAADF-STEM analysis demonstrates the good dispersion of the Pt species on the Fe3O4 (111) plane, and the resulting material exhibits excellent catalytic activity for CO oxidation under moisture conditions. The inevitably existing moisture contributes to the formation of reaction intermediate [COOH] and hence promotes the catalytic activity, which has been proved through in situ DRIFTS analysis.

A facile one-pot co-precipitation approach was applied to fabricate a meso-structured Pd–CeOx composite for low temperature CO oxidation. The as-prepared material had a much higher specific area and highly dispersed noble metal species, and thus showed excellent catalytic activity and stability for CO oxidation, especially under ambient conditions. Complete CO conversion could be achieved at as low as 25 °C for 5.9 wt% Pd doped catalyst, when 3.0 vol% H2O was introduced into the feed gas. The reaction mechanism on such a catalyst has been proposed through in situ DRIFTS and kinetic analysis.

A meso-structured Pd/NiO catalyst was successfully fabricated through a controlled pyrolysis and in situ reduction protocol. The resulting material possessed a relatively high surface area and highly dispersed palladium species. It showed much higher catalytic activity and stability for CO oxidation under ambient conditions. Complete CO conversion could be achieved at as low as −20 °C, when 1.2 vol% H2O was introduced into the feed gas. The catalyst exhibited no detectable deactivation even after 100 hours of reaction. The extraordinary catalytic activity and durability were attributed to the promotion of the water molecules and the synergetic effect between the Pd nanoparticles and meso-structured NiO support.

Spinel-type Co3O4 has been reported to be the only transition metal oxide to date, which exhibits excellent catalytic activity for low temperature CO oxidation. But unfortunately, it is quickly deactivated by moisture. Here we report a Fe-doped Co3O4 spinel catalyst which demonstrates high activity and excellent moisture resistance for low temperature CO oxidation, especially at a low CO concentration of around 100 ppm which mimics the situations in automobile road tunnels and indoor parks.

A series of mesoporous CeO2 supported noble metal (Pt, Pd, Au and Ag) catalysts, fabricated through a facial pyrolysis and in situ reduction protocol, were used for formaldehyde elimination under ambient conditions. The materials possessed relatively high specific surface area and uniformly dispersed noble metal nanoparticles, and showed very high catalytic activities for formaldehyde oxidation. For about 1 wt% noble metal loaded materials, Pt/CeO2, Pd/CeO2 and Au/CeO2 catalysts could completely catalytically oxidize HCHO at room temperature. Even for the low activity Ag/CeO2 catalyst, the complete conversion temperature could reach 100 °C, much lower than that reported before. Such good catalytic properties could be attributed to the strong synergetic interaction between the active component and CeO2 nano-crystalline aggregated support. The reaction mechanism over the noble-metal/CeO2 catalyst was also discussed through in situ DRIFTS analysis.

A simple, versatile and effective reverse micro-emulsion and pyrolysis protocol was presented for in situ growth of a PdO/Pt loaded mesoporous Al2O3 film. Noble metal (oxide) nanoparticles with a narrow size distribution were homogeneously dispersed throughout the Al2O3 support. Most importantly, the obtained worm-like catalyst network has both a high specific area and highly crystalline, which is favorable for application in methane catalytic combustion. When deposed on a micro-heater and used as a sensor element, the resulting micro-sensor demonstrated a short T90 response time, relatively high signal output, high enough signal/noise ratio and extraordinarily low power consumption for methane detection.

A series of meso-structured Pd/FeOx catalysts were successfully fabricated through a facile pyrolysis and in situ reduction strategy. The as-prepared materials possessed relatively high surface area and highly dispersed Pd species, and exhibited excellent low temperature CO oxidation properties under ambient conditions. Complete CO conversion could be achieved at as low as 0 °C, when 2.5 vol% H2O was introduced into the feed gas. In situ DRIFT analysis proved that these excellent catalytic properties can be attributed to the promotion of the water molecules and the synergetic effect between Pd nanoparticles and the meso-structured FeOx support.

A series of mesoporous PdCeOx solid solution with high specific area was successfully fabricated through a facile coprecipitation and low-temperature calcination strategy. The resulting materials possessed excellent catalytic activities for CO oxidation. The complete CO conversion could be achieved at as low as 20 °C. The doping of palladium increased the concentration of structural oxygen vacancy which is beneficial for the CO oxidation reaction process. The CO oxidation reaction mechanism over PdCeOx solid solution was proved through in situ DRIFTS analysis.

Mesostructured Mn3O4-supported Pd catalyst was successfully fabricated through a facile template-assisted pyrolysis and impregnation strategy. The resulting materials displayed large surface area and high dispersion of palladium species, and showed much enhanced catalytic activities for CO oxidation especially under moisture condition. For 2.7 wt% Pd-loaded catalyst, temperatures for 100% and 50% CO conversions were measured to be as low as 22 °C and 0 °C (4.0 vol% H2O), respectively. More importantly, the material showed excellent catalytic stability, and no activity loss was found even after the reaction for 30 hours. This unique catalytic durability under moisture condition was assigned to the synergetic effect between Pd nanoparticles and Mn3O4 support.

In order to get a methane catalytic combustion micro-sensor, two different catalytic systems used in traditional methane catalytic combustion sensors were fabricated into a mesoporous structure and their catalytic activities were investigated. In comparison, the Rh2O3–Al2O3 system can form more a uniform mesoporous structure and has a much higher specific surface area. Even more importantly, it has relatively higher catalytic activity and stability for the methane catalytic combustion reaction. After being coated on a microelectro-mechanical system (MEMS) micro-heater, a catalytic combustion type methane micro-sensor was fabricated. The meso-structured Rh2O3–Al2O3 hybrid based MEMS sensor demonstrated a short T90 response time, relatively high signal output, high enough signal/noise ratio for practical detecting and strong anti-poison properties.

Polycrystalline mesoporous C–N-codoped anatase TiO2 has been successfully fabricated using a simple but efficient controlled thermal decomposition approach and their photo-degradation properties were evaluated. In such a synthesis, ammonium titanyl oxalate was first prepared and used as precursor. The C–N-codoped anatase TiO2 was then directly generated via the pyrolysis of the ammonium titanyl oxalate precursor and the resultant nano-sized crystallites connected together to form a mesoporous structure. The as-prepared material by calcination at 300 °C at a heating rate of 0.5 °C min−1 possessed a high surface area and showed extraordinarily high photocatalytic degradation properties under visible irradiation.

Uniform mesoporous rhodium oxide/alumina hybrid have been prepared following a facile one-pot self-assembly approach using P123 as template. Such hybrid nanomaterials display a high dispersion of both the noble metal oxide and the alumina within mesoporous structure in a broad Rh/Al mole ratio up to 8:1, which makes them attractive materials for catalytic applications. After coating on MEMS micro-heater, a catalytic combustion type methane gas micro-sensor was fabricated and investigated for its sensing performance. The mesostructure-based sensor demonstrated a short T90 response time, relatively high signal output, high enough signal/noise ratio and extraordinarily low power consumption.

A LDH confined Au nano-catalyst has been successfully synthesized through a flocculation and in-situ reduction method. In this composite, Au nano-colloids were evenly dispersed in LDH gallery and its particle size was less than 1 nm. The highly dispersed gold nano-colloids in layered Mg―Al double hydroxide support were found to be a high performance catalyst for CO lower temperature oxidation. The catalytic experiments indicated that the CO oxidation reaction could be initiated at lower than − 30 °C and almost a 100% conversion can be achieved at 0 °C. The catalyst stability studies show that after 12 h reaction at 0 °C; the CO conversion has not any apparent decrease.Download full-size imageHighlights► The Au&LDH composite was fabricated with flocculation method. ► It was found to be a high performance catalyst for CO lower temperature oxidation. ► The CO oxidation reaction could be initiated at lower than – 30 °C. ► Almost a 100% conversion can be achieved at 0 °C.

Single-layered g-C3N4 nanosheets have been fabricated by delaminating directly its bulk counterpart in an alkaline solution. According to the theoretical modeling, the interaction of OH− with terminal NH2 or bridged NH group of the triazine units within bulk g-C3N4 crystal structure could result in decreased bonding energy between layers and promote the total delamination. The resulting g-C3N4 nanosheets colloid has a relatively high concentration (12 g/L) compared with the traditional ultrasonic assistant exfoliation method. The delaminated nanosheets are revealed by atomic force microscopy to show a lateral size of a hundred nanometers and a thickness of about 0.4 nm, which provides a direct evidence for the total exfoliation of g-C3N4 crystals into their single sheets. More importantly, the X-ray diffraction measurement confirms that the g-C3N4 nanosheets could be re-assembled with well-preserved original crystal structure. The exfoliation mechanism was also confirmed by the DFT calculation.

Uniform mesoporous rhodium oxide/alumina hybrid have been prepared following a facile one-pot self-assembly approach using P123 as template. Such hybrid nanomaterials display a high dispersion of both the noble metal oxide and the alumina within mesoporous structure in a broad Rh/Al mole ratio up to 8 : 1, which makes them attractive materials for catalytic applications. After coating on MEMS micro-heater, a catalytic combustion type methane gas micro-sensor was fabricated and investigated for its sensing performance. The mesostructure-based sensor demonstrated a short T90 response time, relatively high signal output, high enough signal/noise ratio and extraordinarily low power consumption.