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In this paper, a convenient solution combustion method to synthesis hierarchically porous Ag-loaded ZnO heterojunction nanocomposites with various Ag contents was reported. The analysis of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption were conducted to characterize the ingredients, microstructure and surface morphology. Ag and ZnO show separate phases due to the reduction of Ag + and the faster crystallization rate of ZnO. The as-synthesized powders were used as gas sensing materials to fabricate gas sensors. The gas-sensing performance was tested towards 100 ppm formaldehyde at an optimum operating temperature of 240 °C and Ag-loaded ZnO (with the different Ag atomic ratio) based gas sensors showed a superior gas-sensing performance comparing with pure ZnO. Especially 1 at% Ag-loaded ZnO has the highest gas response as 170.42. The possible gas-sensing mechanism was discussed in this paper. For example, the influence of surface area, the formation of heterostructure, Ag elements, adsorbed oxygen and so on. [ABSTRACT FROM AUTHOR]

Beta-manganese dioxide (β-MnO) microrods were hydrothermally synthesized from ammonium persulfate [(NH)SO] solution using manganese sulfate (MnSO) as reductant at 180 °C for 3 h. The characterizations, including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, showed that the crystallinity and morphology of the as-synthesized samples were well-defined β-MnO microrods with the diameters of about 100 nm and lengths of about 2-4 μm. To explore the optimal degradation conditions, the as-synthesized β-MnO microrods were employed into the degradation of methyl orange dye solution with the concentration of 20 mg/L in the presence of H with pH values equalling 1.0, 1.5, 2.0, 3.0, 5.0, and 7.0, respectively. The results indicate that the degradation efficiency could reach 98% after 9 min at the pH value of 1.0 or 2.0. Also, the lower the pH value, the higher the degradation efficiency. Based on these experimental results, a proper mechanism of the degradation process of methyl orange is proposed and the rationality of the mechanism is further investigated through the scientific control tests. [ABSTRACT FROM AUTHOR]

A facile, cost-effective, template-free chemical method was developed for the synthesis of β -Co(OH) 2 nanoplatelets under the different preparation conditions. The morphology and microstructure of as-synthesized samples were examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS), respectively. The observations revealed the formation of a single phase of the hexagonal brucite-like β -Co(OH) 2 , which had an irregular hexagonal disk with angles of adjacent edges of 120°, edge lengths ranging from 200 to 300 nm, and thicknesses of 20–40 nm. When investigated as catalyst for CO oxidation, the β -Co(OH) 2 nanoplatelets exhibited good catalytic activity for CO. Among β -Co(OH) 2 nanoplatelets, the sample prepared at 100 °C for 8 h performed the best, giving the T 100% (the temperature required for achieving a CO of 100%) of 120 °C for the oxidation of CO. There are good correlations of Co 3+ /Co 2+ , the absorbed O x − ions and surface OH group with catalytic activity of the samples for CO oxidation. [ABSTRACT FROM AUTHOR]

Hollow CuO fibers were successfully fabricated using a facile solution combustion method by incorporating cotton fibers as biotemplate. XRD patterns along with Rietveld refinement confirm the formation of CuO with monoclinic phase. The length of the as-synthesized CuO fibers is at micrometer scale, and the average fiber diameter ranges from several nanometers up to order of micrometers. After combustion reaction, a large amount of coalescent particles left on the surface of the cotton fibers to form porous walls of CuO. By totally removing cotton body at 600 °C, hollow CuO fibers were obtained. A possible growth mechanism of hollow CuO fibers using cotton fibers as templates was given based on experimental data. When used as a sensing material in gas sensor, it exhibited a superior sensitivity and good selectivity toward low-ppm-level (1–100 ppm) n -propanol. Theses findings not only provide a novel approach to fabricate hollow CuO fibers via a solution combustion route, but also explore a promising gas sensor toward n -propanol. [ABSTRACT FROM AUTHOR]

One dimensional Mn–Ce–O x composite nanomaterials with various Mn contents were synthesized successfully by a hydrothermal method. The impacts of Mn contents on their morphologies and physical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The analysis reveals that the obtained composites are one-dimensional (1D) rod-like nanostructures. The catalytic behaviors of Mn–Ce–O x nanomaterials were investigated for CO oxidation. The Mn–Ce–O x catalysts were found to be more active than catalysts based on ceria alone. The catalytic activities of all one dimensional Mn–Ce–O x materials for CO conversion are quite high (142< T 50% <229 °C). Among the obtained nanocatalysts, the Mn–Ce–O x composite nanomaterials with 40 wt% Mn exhibit the best catalytic activity and the 50% CO conversion can be reached at 142 °C. The presence of transition metal element Mn can promote the production of oxygen vacancies and improve oxygen mobility, which result in enhancing the oxygen-storage capacity of the one dimensional Mn–Ce–O x materials and its catalytic performance for CO conversion. [ABSTRACT FROM AUTHOR]

ZnO quantum dots (QDs), a few nanometers in size, were synthesized by a sol–gel method using different solvents (methanol, ethanol and hexanol). The structural, morphological and photoluminescent properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence spectrometry, and UV-vis spectroscopy. The results indicated that ZnO QDs with good dispersion, ranging in size from 3.3 nm to 7.7 nm, could be controlled easily by the solvents. The ZnO QDs exhibited strong visible emission from green to orange. The reasons for the change in emission color are believed to be the quantum size effect and the change in defect concentration due to the different solvents used in their preparation. A possible mechanism for the photoluminescence of ZnO QDs is also presented. [ABSTRACT FROM AUTHOR]

Cobalt ion (Co 2+ ) is known to be harmful for human beings, and effectively portable sensor is one of the key for its prophylaxis and treatment. In this work, Zn(CH 3 COO) 2 ·2H 2 O, Na 2 S·9H 2 O and thioglycolic acid were used to prepare ZnS quantum dots through a facile water-bath method. The structure and morphology of the ZnS quantum dots were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Scanning electron microscope (SEM) was also used to observe the surface morphology of the test paper prepared by a simple dipping-drying process. The Co 2+ sensing properties of as-prepared test paper were investigated. And it was found that the color of as-fabricated test paper could change from white to brown within 1 min with addition of Co 2+ aqueous solution, which makes it possible for qualitative detection of Co 2+ through naked eyes. In this mode, a widely detectable range from 10 to 1000 mg L −1 is reached by the test paper. In addition, through measuring the grey level of the test paper by ordinary smart phone and laptop, a semi-quantitative function of the test paper is realized. Moreover, the as-fabricated paper sensor can resist the interference of a serious cations and anions, and suits for a wide pH surrounding from 1.08 to 9.65, which makes it a promising Co 2+ sensor for practical use. In addition, through X-ray diffraction and UV–vis spectra, the sensing properties of as-fabricated test paper are attributed to the chemical reaction between as-prepared ZnS quantum dots and Co 2+ ions. And the formation of CoS 2 should be responsible for the color change from white to brown. [ABSTRACT FROM AUTHOR]

3D macro-/nanoporous spinel MCo 2 O 4 (M = Zn, Ni, Cu and Fe) have been successfully fabricated by means of an untemplate and flash synthesis via self-sustained decomposition of metal-organic complexes The effects of the combustion agent to metal nitrate ratio on the combustion behavior, phase and morphology of the products were studied. Pure cobaltites with the hierarchically porous morphology were obtained directly through the combustion of the precursors under fuel-lean conditions in one-step without further heat treatment. The samples were characterized by X-ray diffraction, SEM/TEM imaging, mercury intrusion porosimetry, which indicate that the products possess hierarchical porous structure. A possible forming mechanism was given based on the series of experimental data. [ABSTRACT FROM AUTHOR]