Xiaoqing Fu

Surface accumulation conduction controlled sensing characteristic of p-type CuO nanorods induced by oxygen adsorption

P-type CuO nanorods were synthesized by a hydrothermal method and the ethanol-sensing properties of sensors based on CuO were investigated. The sensor resistance increased when it was exposed to ethanol and decreased in the air, which is contrary to the case for sensors realized from n-type semiconductor. The resistance of the CuO-based sensor was about 2 kΩ in air and 6 kΩ in ethanol vapour with concentration of 2000 ppm. Such a sensing property is attributed to surface accumulation conduction. Sensors based on CuO nanorods have potential applications in detecting ethanol in low concentration.

Fast humidity sensors based on CeO2 nanowires

Fast humidity sensors are reported that are based on CeO2 nanowires synthesized by a hydrothermal method. Both the response and recovery time are about 3 s, and are independent of the humidity. The sensitivity increases gradually as the humidity increases, and is up to 85 at 97% RH. The resistance decreases exponentially with increasing humidity, implying ion-type conductivity as the humidity sensing mechanism. A model based on the morphology and surface energy of the nanowires is given to explain these results further. Our experimental results indicate a pathway to improving the performance of humidity sensors.

Room-temperature oxygen sensitivity of ZnS nanobelts

Room-temperature oxygen sensing is realized from individual ZnS nanobelts. Under UV illumination the current through ZnS nanobelt increases from 0.265to2.26nA as the oxygen pressure decreases from 1×105to3×10−3Pa. The conductance of ZnS nanobelt exhibits a logarithmic dependence on oxygen pressure, which is in agreement with theoretical prediction. The sensing is based on the enhanced modulation of ZnS nanobelts conductance by adsorbed oxygen under illumination. These results demonstrate an approach to in situ precisely detect oxygen at room temperature.

Anomalous photoconductivity of CeO2 nanowires in air

The conductance of the CeO2 nanowire film is found to decrease by about two orders of magnitude in air under ultraviolet illumination. Such a drastic decrease in conductance is attributed to light-induced desorption of H2O from the nanowire’s surface. When exposed in air, the surface conductivity of the nanowire increases significantly due to the adsorption of H2O. Considering the large surface-to-volume ratio of the nanowire, the conductance of the nanowire film is mainly controlled by surface conduction. Upon ultraviolet illumination, desorption of H2O results in the decrease of the conductance of the nanowire film, thus leading to the anomalous photoconductivity.

Mitigating Nitrous Oxide Emissions from Tea Field Soil Using Bioaugmentation with a Trichoderma viride Biofertilizer

Land-use conversion from woodlands to tea fields in subtropical areas of central China leads to increased nitrous oxide (N2O) emissions, partly due to increased nitrogen fertilizer use. A field investigation of N2O using a static closed chamber-gas chromatography revealed that the average N2O fluxes in tea fields with 225 kg N ha−1 yr−1 fertilizer application were 9.4 ± 6.2 times higher than those of woodlands. Accordingly, it is urgent to develop practices for mitigating N2O emissions from tea fields. By liquid-state fermentation of sweet potato starch wastewater and solid-state fermentation of paddy straw with application of Trichoderma viride, we provided the tea plantation with biofertilizer containing 2.4 t C ha−1 and 58.7 kg N ha−1. Compared to use of synthetic N fertilizer, use of biofertilizer at 225 kg N ha−1 yr−1 significantly reduced N2O emissions by 33.3%–71.8% and increased the tea yield by 16.2%–62.2%. Therefore, the process of bioconversion/bioaugmentation tested in this study was found to be a cost-effective and feasible approach to reducing N2O emissions and can be considered the best management practice for tea fields.

Nitrous Oxide Emissions from Household Vegetable Fields in the Rural Residential Areas of Hilly Subtropical Central China

Nitrous oxide (N2O) emissions from a household vegetable field in a rural residential area of hilly subtropical central China were observed using a static chamber-gas chromatographic method from January 2010 to December 2011. The N2O fluxes exhibited seasonal dynamics and the accumulated N2O emissions during the wet seasons accounted for 83.5% of the total N2O emissions. Soil mineral nitrogen (N) contents were found not limiting factors because of the application of large amounts of human excreta. The daily N2O fluxes showed a significant, positive correlation with soil temperature, soil moisture and soil NO3 --N content, and soil denitrification may be the major pathway responsible for N2O emissions. High-frequency, intensive application of liquid excreta stimulated the N2O emission process. The average annual N2O emission rate was 12.1 ± 0.9 kg N ha-1 year-1 in the examined household vegetable field, and the total N2O emissions from household vegetable fields originating from the N source of human excreta in the studied Jinjing catchment (135 km2) were estimated as 1.58 ± 0.16 ton N year-1. Such emissions can be considered as N2O re-emissions of the N input into the ecosystem, and the emission factor of N2O re-emissions was estimated to be 0.57%. The findings indicated that under the present management practices, household vegetable fields in the subtropics of China provide a relevant contribution to greenhouse gas emissions and a responsive mitigation scheme at a household scale is needed to reduce N2O emissions.