Xinxin Xing

Ag–ZnO heterostructure nanoparticles with plasmon-enhanced catalytic degradation for Congo red under visible light

Ag–ZnO heterostructure nanoparticles were synthesized by a one-step solvothermal route from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), silver nitrate (AgNO3), potassium hydroxide (KOH) and methanol (CH3OH). The structure, morphology, component and optical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectroscopy and photoluminescence spectroscopy, respectively. The results show that highly crystalline wurtzite-type ZnO nanoparticles matrices with an average grain size of 7.4 nm are obtained. Highly crystalline metallic Ag nanoparticles are observed on the ZnO matrix with a good combination. The absorption spectra of the Ag–ZnO heterostructure nanoparticles show the existence of a special two-absorption-region (strong UV-light and weak visible-light at 421 nm). The intensities of photoluminescence in the visible light region have a regular decrease with the increase in the load amount of Ag. The photoactivity of the as-synthesized samples was tested by measuring the degradation of azo dye Congo red (CR) under visible light irradiation. And it is found that both ZnO nanoparticles and Ag–ZnO heterostructured nanoparticles have better photocatalytic efficiency than commercial TiO2 (P-25), and an appropriate loading amount of Ag nanoparticles can significantly enhance the photocatalytic efficiency. The photodegradation mechanism as well as enhancement of the photoactivity in the presence of silver nanoparticles is further investigated. The experimental results indicate the potential of using Ag–ZnO heterostructured nanoparticles for degradation of Congo red dye.

A general nonaqueous sol-gel route to g-C 3 N 4 -coupling photocatalysts: the case of Z-scheme g-C 3 N 4 /TiO 2 with enhanced photodegradation toward RhB under visible-light

The g-C3N4-coupling TiO2 photocatalysts with controllable particle size as well as the interface contact were prepared by a general nonaqueous sol-gel method. The structural and morphological features of g-C3N4/TiO2 were investigated through the X-ray diffraction, Fourier transformed infrared spectra, scanning electron microscopy and transmission electron microscopy, respectively. It is found the TiO2 nanoparticles with a size of 7.3 ± 1.6 nm are uniformly anchored on the surface of the g-C3N4 nanosheets in isolation. The photocatalytic properties of as-prepared g-C3N4/TiO2 were tested by degradation of Rhodamine B (RhB) under visible light, and an enhanced activity is observed. The mechanism of the enhanced activity was further investigated through N2 adsorption-desorption isotherms, UV-vis spectra, photoluminescence spectra, photoelectrochemical measurements, radical trapping experiments and X-ray photoelectron spectroscopy. Furthermore, the photocatalytic performances of obtained g-C3N4/TiO2 under sunlight were also evaluated in aspects of degradation efficiency and stability. The results indicate that the obtained g-C3N4/TiO2 is one promising photocatalyst for practical applications. The study of as-prepared g-C3N4/TiO2 also implies that the present method could be a general route of g-C3N4-coupling photocatalysts.

A high-performance n-butanol gas sensor based on ZnO nanoparticles synthesized by a low-temperature solvothermal route

ZnO nanoparticles with high crystallinity and several nanometers in size were synthesized by a low-temperature solvothermal route from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), potassium hydroxide (KOH) and methanol (CH3OH). The structural and the morphological characterizations of the ZnO nanoparticles were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption isotherms. The obtained nanoparticles are highly crystalline wurtzite-type ZnO with a uniform near-spherical shape and an average particle size estimated to be 8.4 ± 1.3 nm. Such a small particle size and slight agglomeration are attributed to the use of methanol, which acts as both a solvent and an inhibitor of growth and agglomeration. The as-synthesized ZnO nanoparticles were directly used as a gas sensing material toward n-butanol gas. Such a designed sensor device exhibits several advantages such as a high and fast response, short recovery time, and good stability toward n-butanol gas. At the optimal operating temperature (320 °C), its gas response toward 500 ppm n-butanol is 805 and the response and recovery times are 22 and 6 seconds, respectively.

Controllable synthesis and change of emission color from green to orange of ZnO quantum dots using different solvents

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.

The xylene sensing performance of WO3 decorated anatase TiO2 nanoparticles as a sensing material for a gas sensor at a low operating temperature

Here, pristine and WO3 decorated TiO2 nanoparticles were synthesized by a one-step hydrothermal method without the use of a surfactant or template and used to fabricate gas sensors. Various techniques were employed for the characterization of the structure and morphology of the as-prepared products. The gas-sensing characteristics of the fabricated sensors were investigated for various concentrations of xylene at different temperatures. At a low operation temperature of 160 °C, the sensors possess an excellent gas response, selectivity, linear dependence, low detection limitation, and repeatability as well as long-term stability. In particular, for the high gas response of the 10.0 mol% WO3 decorated TiO2 nanoparticles based sensor, its response reaches 92.53 for 10 ppm xylene, which is much higher than that of the pristine TiO2 based sensor. And the detection limit is 1 ppm. Those values demonstrate the potential of using WO3 decorated TiO2 nanoparticles for xylene gas detection, particularly with low concentration xylene. Apart from this, the mechanism related to the advanced properties was also investigated and presented.

A one-step nonaqueous sol–gel route to mixed-phase TiO2 with enhanced photocatalytic degradation of Rhodamine B under visible light

Anatase–rutile mixed-phase TiO2 is proved to have better photocatalytic activity than pure anatase TiO2, but the preparation of the mixed-phase TiO2 usually needs thermal treatments at more than 500 °C. In this study, we present a one-step nonaqueous sol–gel route to form mixed-phase TiO2 at relatively low temperatures from 160 to 220 °C. The structure, morphology and surface chemical state were examined with X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The influence of the preparation temperature on the structural characteristics including grain size and phase content were investigated using the Rietveld refinement. Through TEM, the evolution from sphere-like anatase nanoparticle to hexagonal rutile single-crystal was investigated. The photocatalytic activities of the obtained anatase and anatase-rutile TiO2 were evaluated by degradation of Rhodamine B under visible light, and a distinct enhanced activity was observed. Through the UV-vis spectrum and mass spectrum, the pathway of RhB degradation caused by the mixed-phase TiO2 with visible light was studied. At the same time, the mechanism of the enhanced photocatalytic properties was presented. The mechanisms were verified with UV-vis measurements. It is believed that the obtained mixed-phase TiO2 is one promising candidate for wastewater treatment.

Enhanced formaldehyde sensing properties of SnO2 nanorods coupled with Zn2SnO4

Ternary oxide Zn2SnO4 was introduced to a rod-like nanostructured SnO2 gas sensor for formaldehyde detection by a facile one-step hydrothermal synthesis. The effects of the Zn2SnO4 additive on the structure, morphology and gas-sensing property of SnO2 were investigated in this study. It was confirmed that control of the Zn amounts in the precursor solution was effective in realizing well-developed one- and two-dimensional coexisting structured SnO2–Zn2SnO4 (SnZn) nanocomposites. The gas sensing properties of the resulting SnZn composites to HCHO vapor were tested. The results showed that the presence of Zn2SnO4 species in SnO2 powders could effectively enhance electrical conductivity, reduce optimal operating temperature and improve the gas response of the sensors. The composite exhibited the highest response towards HCHO in the case of 35 at% Zn2SnO4 nanoplates coupling with hierarchical branched structures of SnO2 nanorods (SnZn35) at a relatively lower operating temperature of 162 °C. The good gas-sensing performance of the SnZn35 composite can be ascribed to the smaller particle size, the larger surface area and the more absorbed Ox− species, which all are favorable for gas diffusion and sensing reactions. This work renders great potential in the fabrication of gas sensors using a binary–ternary oxide composite, which can be further applied in indoor pollution detection.

Catalytic activity for CO oxidation of Cu–CeO2 composite nanoparticles synthesized by a hydrothermal method

A facile hydrothermal method has been developed for the synthesis of nanosized Cu–CeO2 composites with various Cu contents. The obtained catalysts, with a Cu/CeO2 atomic ratio in the range of 0–40%, were characterized as to their structure, morphology, and redox features by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 physisorption, and temperature programmed reduction with hydrogen. The experimental results show that the particles are highly crystalline CeO2 nanopowders of 5–8 nm primary particle size and the Cu nanoparticles indeed coexist with the CeO2 nanoparticles (cubic fluorite CeO2). The influence of Cu contents on their catalytic performance for CO oxidation was also studied. As for the catalytic reactivity, nanosized Cu–CeO2 composites have a higher catalytic activity than CeO2 in CO oxidation. It is ascribed to the effect between the cycle transition of Ce4+/Ce3+, oxygen vacancies and surface area, which are induced by copper. The catalytic activity of the Cu–CeO2 composites exhibits Cu content dependence where the best catalytic activity occurs at a Cu/CeO2 atomic ratio of 30%. In addition, nanosized Cu–CeO2 composites also show high catalytic activity for selective oxidation of CO in excess H2 at relatively low temperature.

Enhanced methanol sensing properties of SnO2 microspheres in a composite with Pt nanoparticles

SnO2 microspheres in a composite with Pt nanoparticles (0, 0.5, 1.5, 2.5, 5.0 mol% Pt loading) were synthesized by a solvothermal method. The crystal structure, morphology, and specific surface area were thoroughly characterized. It is found that the Pt–SnO2 nanocomposites consist of a large amount of small spheres with average diameters up to hundreds of nanometers, and every small sphere is composed of numerous primary nanocrystallites with an average size of about 8 nm. Compared with the pristine SnO2, the presence of Pt nanoparticles has no influence on the growth behavior of the SnO2 microspheres. The gas sensors based SnO2 microspheres in a composite with Pt nanoparticles not only show a lower operating temperature and immensely enhanced responses, but also exhibit a faster response and recovery speeds and remarkable stability to methanol, especially the 5.0 mol% Pt–SnO2 nanocomposite. The gas sensor based on the 5.0 mol% Pt–SnO2 nanocomposite exhibits a response value of 190.88 to 100 ppm methanol at a low operating temperature of 80 °C, while the gas sensor based on pristine SnO2 only displayed a response value of 19.38 at an operating temperature of 200 °C. The reasonable explanation of the gas-sensing performance enhancement for the gas sensors based on Pt–SnO2 nanocomposites is attributed to the strong spillover effect of the Pt nanoparticles and the electronic interaction between Pt nanoparticles and SnO2 microspheres, both of which promoted the low temperature gas-sensing performance.

NiO nanosheets assembled into hollow microspheres for highly sensitive and fast-responding VOC sensors

Uniform, hollow NiO microspheres constituted from nanosheets were synthesized by a simple water bath method through a SiO2 spheres template-assisted approach and applied in an efficient gas sensor towards volatile organic compound (VOC) vapors. The structural characterizations reveal that sub-micrometer NiO hollow microspheres (350–400 nm) were formed by assembling NiO nanosheets of 20–40 nm thickness. The gas responses to the five reductive gases, including isopropanol, acetone, methanol, ethanol and formaldehyde, at a low concentration of 50 ppm are 11.3, 9.9, 8.2, 7.7 and 5.0, respectively. NiO hollow microspheres showed higher responses for VOCs compared to other NiO nanostructures previously reported in the literature. The gas sensor based on NiO hollow microspheres shows a high response and fast response and recovery towards VOCs, making it a promising candidate for a practical detector of VOCs. The improved performance of NiO hollow microspheres was attributed to hollow spaces that offer a high surface-to-volume ratio and an intrinsically large specific surface area of 167.31 m2 g−1, leading to an improved surface activity. It was suggested that a layer of adsorbed oxygen over the NiO surface possibly decreases the thickness of the space charge layer in VOC gases and leads to an increase in resistance and therefore response.