Current Nanoscience - Volume 11, Issue 4, 2015

Core-shell ZnO/SnO2 nanorods (NRs) were successfully synthesized via a facile two-step synthesis route. ZnO NRs (core) with the diameter about 300–800 nm and the length about 2-2.5 µm were first synthesized via a hydrothermal route, and then a continuous SnO2 layer (shell) with the thickness about 20-25 nm was easily coated on the ZnO NRs via a solvothermal route. Compared with pure ZnO NRs and SnO2 nanoparticles (NPs), the ZnO/SnO2 core-shell NRs show an obvious enhancement in gas sensing performance. The response of the sensor based on as-prepared ZnO/SnO2 core-shell NRs to 100 ppm ethanol is as high as 29.5 at 340 °C, and the response and recovery time are found to be about 18 s and 11 s, respectively. The gas sensing mechanism of the ZnO/SnO2 core-shell NRs was discussed in relation to ZnO/SnO2 heterojunctions.

Mesoporous modified red mud (MRM) was received by the acid digestion and alkali reprecipitation method modification of red mud (RM), and it was used as the support to prepare the CuO/MRM nanocatalysts via an impregnation approach. The asobtained nanocatalysts were characterized by the techniques of X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), transmission electron microscopy (TEM), and N2-sorption. The catalytic carbon monoxide oxidation properties were investigated by using the microreactor system with the gas chromatography (GC). TEM images and N2- sorption analysis results indicated that the as-prepared nanocatalysts possess the mesoporous structure, and which have high specific surface area and uniform pore-size. The catalytic activity test results revealed that the as-prepared mesoporous MRM supported CuO nanocatalysts were very active for catalytic carbon monoxide oxidation.

Ag-doped α-Fe2O3 nanoparticles were synthesized by the solid-state grinding method, and the as-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry-differential thermal analysis (TG-DTA), and X-ray photoelectron spectroscopy (XPS) techniques. The analysis results indicated that all the particles were of spherical morphology and their size was about 10 nm. The gas sensing properties of the sensors based on the as-prepared Ag/Fe2O3 nanoparticles to different gas were investigated in detail. Compared the gas sensing test results of the Ag-doped α-Fe2O3 with the α-Fe2O3 without doped, all of the sensors based on the Ag-doped α-Fe2O3 nanoparticles possess much better sensing behavior than that of pure α-Fe2O3. The sensor based on the 300 °C-calcined 3%-Ag/Fe2O3 materials displayed the maximum response to H2S at 150 °C, and to ethanol at 245 °C. This solid-state grinding method prepared Ag/α-Fe2O3 nanomaterials are promising candidate for low temperature H2S detection.

Monodispersed, uniform, and hierarchical calcium tungstate (CaWO4) microsphere structures were synthesized through a template-free hydrothermal synthesis using calcium chloride (CaCl2) and sodium tungstate dihydrate (Na2WO4•2H2O) as precursors, sodium phosphate dodecahydrate (Na3PO4•12H2O) was used as structure-directing agent. The obtained samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A possible formation mechanism of the spherical CaWO4 was proposed based on the experimental results. In addition, the fluorescence properties of the CaWO4 were studied. Experiment results indicated that the obtained CaWO4 microspheres were assembled by nanoparticles of 30-100 nm in diameter, PO4 3- played a crucial role in the self-assembly process of the hierarchical structure. Moreover, CaWO4 microspheres showed good fluorescence performance.

Tin sulfide hierarchical flower-like architectures were successfully prepared by a facile low temperature synthetic route. The as-prepared samples were characterized by the X-ray diffract ion (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM). The observation of FESEM and HRTEM showed that tin sulfide hierarchical flower-like architectures are of porous structure and composed of numerous nanoplates, which are randomly arranged and interconnected with each other. The photocatalytic activities of the as-prepared samples under visible light irradiation (λ>420 nm) were evaluated by the degradation of rhodamine B (RhB). The effect of heat-treatment temperatures on the photocatalytic efficiency of the as-prepared samples was investigated. The result showed that tin sulfide hierarchical flower-like architectures treated at the temprature of 90 °C exhibited the highest photocatalytic efficiency.

Leaf-like hierarchical γ-AlOOH was prepared by a facile template-free solvothermal method at 150°C for 6 h, using aluminum nitrate (Al (NO3)3˙9H2O) as aluminum source and a mixed water/ethanol solution as solvent. The obtained sample was characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption/ desorption technique. Experiment results indicated that the obtained leaf-like hierarchical γ-AlOOH exhibited a BET surface area of 190.3 m2/g and an average pore widths of 18.82 nm. The hierarchical γ-AlOOH showed excellent removal efficiency for Cr (VI), Methyl orange and Congo red with maximum adsorption capacity of 7.4 mg/g, 59.9 mg/g and 99.0 mg/g, respectively.

Oxygen-enriched activated carbons (ACs) for electrochemical capacitors (ECs) were prepared from coal-based humic acids (HAs) by zinc chloride (ZnCl2) activation. The effects of ZnCl2/HAs ratio and activation temperature on the characteristics of ACs were investigated by nitrogen adsorption at 77K, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The electrochemical performances of ECs with ACs as electrode in a 3M KOH aqueous solution were evaluated by galvanostatic charge-discharge, cyclic voltammetry and Nyquist impedance spectroscopy. The results indicate that the optimum conditions for preparing ACs from coal-based HAs are ZnCl2/HAs ratio of 2.0 and activation temperature of 500 °C. The AC as electrode for ECs prepared under these conditions presents a high specific capacitance of 226 F/g at a high current density of 5 A/g, and exhibits good cycling stability and minimal resistance. The excellent electrochemical performances of ACs are attributed to three aspects: the well-developed porosity with moderate specific surface area, three-dimensional interconnected pore structure and the oxygen-enriched functional groups in carbon network.

The N doped TiO2 (N-TiO2) photocatalyst was prepared by a sol-gel method using ammonium nitrate (NH4NO3) as solid substrates and doping source. The thermal dissociation of NH4NO3 during heat treatment process of dried gel can introduce N element to TiO2 promoting the crystal transformation and adjusting the band structure. Meanwhile, the N-TiO2 samples have large specific surface area and well mesoporous structure. The doped N element narrow the band gap of TiO2 and its light absorption edge has been broadened to visible region. The photocatalytic degradation measurement exhibit that the N-TiO2 sample show high photocatalytic activities in decolorisation of RhB under visible light irradiation. The kinetic calculations reveal that photocatalytic reaction rate constant for N-TiO2 is approximately 3 times higher than that for pure TiO2.

Recently, AgI and BiOI semiconductors (or their composites) have been widely investigated and demonstrated to be novel and efficient visible-light photocatalytic materials, while seldom investigations about the AgI-BiOI solid solutions with adjustable band gap and band edge have been reported. In this study, Agx(BiO)1-xI spherical solid-solution photocatalysts with controllable band structure were prepared by the combination of in situ ion-exchange route and a following low-temperature calcination process by using BiOI microspheres as the precursor. The influence of AgI amount on the microstructures and photocatalytic performance of AgI-BiOI solid solutions was discussed. It was found that the structure stability of BiOI could be greatly enhanced after the formation of AgI-BiOI solid solution, and the resultant samples show a controllable band gap in the range of 1.76-2.19 eV. Experimental results showed that the prepared Agx(BiO)1-xI solid solution exhibited a much better visible-light photocatalytic activity and stability than the pure BiOI. When the AgI amount was 1 at.%, the resultant Agx(BiO)1-xI (x = 0.01) solid solution showed the best photocatalytic activity, and its rate constant (k = 0.039 min-1) was about 3 times that of the pure BiOI even after 4 cycles of photocatalytic reaction. Considering its facile preparation from aqueous solutions, the present synthesized method of Agx(BiO)1-xI solid-solution photocatalyst can provide new insight for the development of other visible-light photocatalytic materials.

The construction of Z-scheme photocatalyst has been verified to be an effective route to develop high-efficiency visible-light composite photocatalysts. In this study, we designed a highly efficient Z-scheme Cu2O-rGO-CuO composite photocatalyst by using rGO as a solid electron mediator. The Cu2O-rGO-CuO composites were synthesized via a facile two-step method, including the initial grafting of rGO on the Cu2O surface and then in situ deposition of CuO nanoparticles on the Cu2OrGO surface. It was found that all the resulted Cu2O-rGO-CuO photocatalysts showed a much higher photocatalytic activity than the single-component (Cu2O) or two-component (such as Cu2O-rGO and Cu2O-CuO) photocatalysts, and the Cu2O-rGO-CuO (0.5 wt%) showed the highest performance (k = 0.033 min-1), obviously higher than that of Cu2O-rGO (0.014 min-1) and Cu2O-CuO (0.010 min-1) photocatalysts. Based on the experimental results and energy band structures of Cu2O and CuO, a possible mechanism of Z-scheme Cu2O-rGO-CuO photocatalytic system was proposed to account for their enhanced photocatalytic performance. The enhanced photocatalytic activity can be ascribed the efficient electron transfer in Cu2O-rGO-CuO Z-scheme system via rGO as a new and effective electron mediator. Compared with the wellknown electron mediators such as Au, Ag, and Pt, the present promising graphene nanosheets with large specific surface area and high electroconductivity can be regarded as an ideal solid-state electron mediator for the design and development of various Z-scheme photocatalysts.

Hollow Cu2O spheres with highly porous shells were synthesized via a facile one-pot solution route at low temperature. The resultant Cu2O spheres were characterized by means of XRD, SEM, TEM and BET techniques. The results show that the typical diameters of the prepared Cu2O hollow spheres are 100-300 nm. Each Cu2O sphere is constructed of small nanoparticles. Electrochemical tests reveal that the hollow Cu2O spheres have very high and stable lithium ion (Li +) storage capacities of 412.5 mAh g-1 at 0.5C after 100 cycles. The superior Li storage performance of the Cu2O spheres is due to their highly porous nanostructure and fine spherical morphology. The prepared Cu2O spheres show great promise for use as high performance anode materials for lithium ion batteries (LIBs).

The C, N and S co-doped TiO2 (C-N-S-TiO2) photocatalyst was prepared by sol-gel method using titanium n-butoxide [Ti(OC4H9)4] and acetic acid (HAc) as raw materials and modifier, thiourea (H2N(CS)NH2) as solid substrates and doping source. The X-ray diffraction, transmission electron microscope, N2 adsorption-desorption measurements, X-ray photoelectron spectroscopy and UV-visible diffuse reflectance spectroscopy were used to characterize as-prepared samples. The results indicated that the thermal dissociation process of H2N(CS)NH2 could introduce doping elements to adjust the band structure and promote the crystal transformation. The C-N-S-TiO2 photocatalyst showed highly photocatalytic activity under visible light irradiation, and the surface reaction rate constant was approximately 4 times higher than pure TiO2 sample.

White fungus-like In2S3 microspheres and In2S3/Cu1.8Se composites were successfully synthesized via a facile ultrasound-assisted microwave method. The reaction temperature could be as low as 70 °C and the reaction time was very short. The In2S3 microspheres were constructed by nanoflakes and many cavities existed in the microspheres. In2S3/Cu1.8Se composite was synthesized using the asprepared In2S3 microspheres as the template. Introducing Cu1.8Se compound did not changed the basic morphology of the template. Through doctor blade coating-rapid sintering method, CuIn(S, Se)2 film was further fabricated. The as-prepared film was demonstrated to be flat and compact, which could be applied as chalcopyrite solar cell thin film.

We report here the world’s first large size plastic monolithic dye-sensitized solar cells (DSCs) with size of 1cmx10cm. A novel printable metal-carbon/graphite composite was used as the counter electrode. By transferring this counter electrode on top of working electrode through a cold isostatic pressing technology, flexible monolithic DSC was successfully fabricated. Our results show that charge transfer resistance of carbon/graphite counter electrode was reduced to about 0.2 Ω.cm2 after being reinforced with magnetron sputtering coated Pt nano particles, which is comparable with sandwich structure plastic DSC with commercial Pt/ITO-PET substrates.

Perovskite based solar cells without the hole conducting material and the evaporated metal electrode would reduce the materials cost of the photovoltaic technology. In this study, we report fully printable, organic-inorganic metal-halide perovskite solar cells with conversion efficiencies exceeding 7%. These fully printable devices were fabricated in a planar structure by directly printing a graphite film on top of an underlying CH3NH3PbI3 perovskite layer. This fabrication method is attractive for making low cost perovskite solar cells as no precious metals and expensive hole conducting materials are required. Both planar and mesoscopic architectures were compared, with the planar structure better compatible to the graphite electrode. Using the planar structure, it was found that a pure graphite layer of approximately 20 µm produced good device performance.

As an ideal visible light responsive photocatalyst, BiVO4 has attracted much attention recently. However, the performance of BiVO4 is decided not only by its crystal structures, but also by its shapes. In this work, monoclinic BiVO4 hollow nanoplates were synthesized by a facile hydrothermal method with the assistance of NH4Cl. The obtained products were composed of numerous uniform circular nanoplates with a diameter of ~5 µm and a thickness of ~500 nm. These nanoplates have an improved crystallinity and a (004) plane dominated XRD diffraction. Notably, hollow nanostructures generated in the center of these nanoplates. Thus, the BiVO4 hollow nanoplates exhibited enhanced photocatalytic water oxidation performance compared with that of the BiVO4 nanorods. This work may provide new insights into the nanostructured engineering of semiconductors as well as opportunities for the development of other photocatalytic materials.

Titanium dioxide (TiO2) nanoparticles were successfully attached to the outer surface of one dimensional oxidized multi-walled carbon nanotubes (MWCNTs) via sol-gel technique. It was well-established that calcination temperature played a critical role in controlling the crystallinity and phase of MWCNTs/TiO2 composites. Thus, the effects of calcination temperature on the resulting MWCNTs/TiO2 were illustrated. The phase transition of MWCNTs/TiO2 composites was determined using XRD analysis. The photocatalytic activity evaluation of MWCNTs/TiO2 composites was conducted under degradation of organic dye (methyl orange solution). The results revealed that annealed MWCNTs/TiO2 composites showed significantly enhanced photocatalytic activity due to the highly crystalline anatase TiO2 structures.