Dongyang Deng

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.

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.

Ag-Functionalized macro-/mesoporous AZO synthesized by solution combustion for VOCs gas sensing application

The aim of this paper is to develop easily manufactured and highly sensitive gas sensors for VOCs (volatile organic compounds) detection. Macro-/mesoporous 5 at% Al-doped ZnO (AZO) and Ag-AZO composite powders were prepared by a one-step solution combustion method and used to fabricate gas sensors. Both powders showed the same macro-/mesoporous morphology but have different grain sizes and separated silver phase due to the fast growth of ZnO and the reduction of Ag+. The capability of Ag-AZO was investigated for VOCs detection, including n-butanol, methanol, acetone, ethanol, isopropanol and formaldehyde. It is found that the added Ag greatly increases the gas response towards different VOCs. Particularly 2.5 at% Ag-AZO shows the most superior gas sensing performance to 100 ppm VOCs at an operating temperature of 240 °C, which is also the optimum operating temperature of other sensors. The results may be attributed to the synergistic effects of these doped and composite elements, the amount of adsorbed oxygen and the macro-/mesoporous morphology.

TiO 2 nanoparticles functionalized by Pd nanoparticles for gas-sensing application with enhanced butane response performances

Pd functionalized TiO2 nanoparticles were synthesized by a facile hydrothermal method. The structure, morphology, surface chemical states and surface area were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption isotherms, respectively. The as-synthesized pure and Pd functionalized TiO2 nanoparticles were used to fabricate indirect-heating gas sensor, and the gas-sensing characteristics towards butane were investigated. At the optimum temperature, the sensors possess good response, selectivity, response/recovery, repeatability as well as long-term stability. Especially for the high response, the response of 7.5 mol% Pd functionalized TiO2 nanoparticles based sensor reaches 33.93 towards 3000 ppm butane, which is about 9 times higher than that of pure TiO2 nanoparticles. The response and recovery time are 13 and 8 s, respectively. Those values demonstrate the potential of using as-synthesized Pd functionalized TiO2 nanoparticles as butane gas detection, particularly in the dynamic monitoring. Apart from these, a possible mechanism related to the enhanced sensing performance is also investigated.

Enhancing phosphate removal from water by using ordered mesoporous silica loaded with samarium oxide

A series of ordered mesoporous silica loaded with samarium oxide (Sm-MCM-41) were synthesized by a facile one-step sol–gel route using hexadecyltrimethylammonium bromide (CTAB) as the template, tetraethylorthosilicate (TEOS) as the silica source, and hexahydrated samarium chloride as the precursor. The as-synthesized materials with the Sm/Si molar ratio ranging from 0.2 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption–desorption measurements. All obtained compounds possess an ordered hexagonal mesoporous structure with a high surface area, a large pore volume, and uniform pore size. The mesoporous composites were used as the novel adsorbents for phosphate ion (H2PO4−) removal from synthetic aqueous solutions. The phosphate removal capacity of Sm-MCM-41 with a Sm/Si molar ratio of 0.6 was up to 20 mg P/g. The Sm functionalized mesoporous silica materials show a higher phosphate removal capacity compared to MCM-41 and Sm2O3 particles, making them promising candidates for water quality control and protection.