CeO2nanoparticles(NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 ℃/24 h(assigned as CeO2-80) and 500 ℃/2 h(assigned as CeO2-500). The as-prepar...CeO2nanoparticles(NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 ℃/24 h(assigned as CeO2-80) and 500 ℃/2 h(assigned as CeO2-500). The as-prepared materials and the commercial ceria(assigned as CeO2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV-vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye(CR) under UVAlight irradiation at various environmental key factors(e.g., reaction time and calcination temperature).Results reveal that CeO2compounds crystalize with cubic phase, CeO2-500 exhibits smaller crystallite size(9 nm vs 117 nm) than that of bare CeO2-com. SEM analysis shows that the materials are sphericallike in shape NPs with strong assembly of CeO2NPs observed in the CeO2-500 NPs. EDX analysis confirms the stoichiometry of CeO2NPs. UV-vis DRS measurement reveals that, CeO2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap(2.6 eV vs 3.20 eV) than that of bare CeO2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV(CeO2-com) to 0.17 eV(CeO2-500),highlighting an increase of crystalline size and internal microstrain in the CeO2-500 NPs sample. Zeta potential(IEP) of CeO2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO2-500 NPs at a rate constant of 10×10-3min-1, which is four times higher than that of CeO2-com(Kapp=2.4×10-3min-1) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO2-500 nano-catalyst can be ascribed to O2-, ’OH and R’+as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.展开更多
Land cover classification(LCC) in arid regions is of great significance to the assessment, prediction, and management of land desertification. Some studies have shown that the red-edge band of RapidE ye images was eff...Land cover classification(LCC) in arid regions is of great significance to the assessment, prediction, and management of land desertification. Some studies have shown that the red-edge band of RapidE ye images was effective for vegetation identification and could improve LCC accuracy. However, there has been no investigation of the effects of RapidE ye images' red-edge band and vegetation indices on LCC in arid regions where there are spectrally similar land covers mixed with very high or low vegetation coverage information and bare land. This study focused on a typical inland arid desert region located in Dunhuang Basin of northwestern China. First, five feature sets including or excluding the red-edge band and vegetation indices were constructed. Then, a land cover classification system involving plant communities was developed. Finally, random forest algorithm-based models with different feature sets were utilized for LCC. The conclusions drawn were as follows: 1) the red-edge band showed slight contribution to LCC accuracy; 2) vegetation indices had a significant positive effect on LCC; 3) simultaneous addition of the red-edge band and vegetation indices achieved a significant overall accuracy improvement(3.46% from 86.67%). In general, vegetation indices had larger effect than the red-edge band, and simultaneous addition of them significantly increased the accuracy of LCC in arid regions.展开更多
In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury...In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury intrusion porosimetry(MIP).The weakening coefficient and Weibull distribution function are introduced into the coupling model of mudstone moisture diffusion-swelling deformation-fracture based on finite-discrete element method(FDEM).The weakening effect of moisture on mudstone's mechanical parameters,as well as the heterogeneity of swelling deformation and stress distribution,is considered.The microcrack behavior and energy evolution of mudstone during hygroscopic swelling deformation under different vertical stresses are studied.The results show that the axial swelling strain of mudstone decreases with increase of the vertical stress.At low vertical stresses,moisture absorption in mudstone leads to formation of cracks caused by hydration-induced expansion.Under high vertical stresses,a muddy sealing zone forms on the mudstone surface,preventing further water infiltration.The simulation results of mudstone swelling deformation also demonstrate that it involves both swelling of the mudstone matrix and swelling caused by crack expansion.Notably,crack expansion plays a dominant role in mudstone swelling.With increasing vertical stress,the cracks in mudstone change from tensile cracks to shear cracks,resulting in a significant reduction in the total number of cracks.While the evolution of mudstone kinetic energy shows similarities under different vertical stresses,the evolution of strain energy varies significantly due to the presence of different types of cracks in the mudstone.The findings provide a theoretical basis for understanding the hygroscopic swelling deformation mechanism of red-bed mudstone at various depths.展开更多
The optical properties of Silicon-doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band-gap peak of InGaN is 437.0 nm and its full width ...The optical properties of Silicon-doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band-gap peak of InGaN is 437.0 nm and its full width of half-maximum (FWHM) is about 14.3 nm. The band-gap peak and FWHM for GaN are 364.4 nm and 9.5 nm, respectively. By changing the temperature from 20 K to 293 K, it is found that the PL intensity of samples decreases but the FWHM broadens with the increasing of the temperature. GaN sample shows red-shift, InGaN sample shows red-blue-red-shift. The temperature dependence of peak energy shift is studied and explained.展开更多
文摘CeO2nanoparticles(NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 ℃/24 h(assigned as CeO2-80) and 500 ℃/2 h(assigned as CeO2-500). The as-prepared materials and the commercial ceria(assigned as CeO2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV-vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye(CR) under UVAlight irradiation at various environmental key factors(e.g., reaction time and calcination temperature).Results reveal that CeO2compounds crystalize with cubic phase, CeO2-500 exhibits smaller crystallite size(9 nm vs 117 nm) than that of bare CeO2-com. SEM analysis shows that the materials are sphericallike in shape NPs with strong assembly of CeO2NPs observed in the CeO2-500 NPs. EDX analysis confirms the stoichiometry of CeO2NPs. UV-vis DRS measurement reveals that, CeO2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap(2.6 eV vs 3.20 eV) than that of bare CeO2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV(CeO2-com) to 0.17 eV(CeO2-500),highlighting an increase of crystalline size and internal microstrain in the CeO2-500 NPs sample. Zeta potential(IEP) of CeO2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO2-500 NPs at a rate constant of 10×10-3min-1, which is four times higher than that of CeO2-com(Kapp=2.4×10-3min-1) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO2-500 nano-catalyst can be ascribed to O2-, ’OH and R’+as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.
基金Under the auspices of Fundamental Research Funds for Central Universities,China University of Geosciences(Wuhan)(No.CUGL150417)National Natural Science Foundation of China(No.41274036,41301026)
文摘Land cover classification(LCC) in arid regions is of great significance to the assessment, prediction, and management of land desertification. Some studies have shown that the red-edge band of RapidE ye images was effective for vegetation identification and could improve LCC accuracy. However, there has been no investigation of the effects of RapidE ye images' red-edge band and vegetation indices on LCC in arid regions where there are spectrally similar land covers mixed with very high or low vegetation coverage information and bare land. This study focused on a typical inland arid desert region located in Dunhuang Basin of northwestern China. First, five feature sets including or excluding the red-edge band and vegetation indices were constructed. Then, a land cover classification system involving plant communities was developed. Finally, random forest algorithm-based models with different feature sets were utilized for LCC. The conclusions drawn were as follows: 1) the red-edge band showed slight contribution to LCC accuracy; 2) vegetation indices had a significant positive effect on LCC; 3) simultaneous addition of the red-edge band and vegetation indices achieved a significant overall accuracy improvement(3.46% from 86.67%). In general, vegetation indices had larger effect than the red-edge band, and simultaneous addition of them significantly increased the accuracy of LCC in arid regions.
基金funded by the National Natural Science Foundation of China(No.42172308)the Youth Innovation Promotion Association CAS(No.2022331).
文摘In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury intrusion porosimetry(MIP).The weakening coefficient and Weibull distribution function are introduced into the coupling model of mudstone moisture diffusion-swelling deformation-fracture based on finite-discrete element method(FDEM).The weakening effect of moisture on mudstone's mechanical parameters,as well as the heterogeneity of swelling deformation and stress distribution,is considered.The microcrack behavior and energy evolution of mudstone during hygroscopic swelling deformation under different vertical stresses are studied.The results show that the axial swelling strain of mudstone decreases with increase of the vertical stress.At low vertical stresses,moisture absorption in mudstone leads to formation of cracks caused by hydration-induced expansion.Under high vertical stresses,a muddy sealing zone forms on the mudstone surface,preventing further water infiltration.The simulation results of mudstone swelling deformation also demonstrate that it involves both swelling of the mudstone matrix and swelling caused by crack expansion.Notably,crack expansion plays a dominant role in mudstone swelling.With increasing vertical stress,the cracks in mudstone change from tensile cracks to shear cracks,resulting in a significant reduction in the total number of cracks.While the evolution of mudstone kinetic energy shows similarities under different vertical stresses,the evolution of strain energy varies significantly due to the presence of different types of cracks in the mudstone.The findings provide a theoretical basis for understanding the hygroscopic swelling deformation mechanism of red-bed mudstone at various depths.
文摘The optical properties of Silicon-doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band-gap peak of InGaN is 437.0 nm and its full width of half-maximum (FWHM) is about 14.3 nm. The band-gap peak and FWHM for GaN are 364.4 nm and 9.5 nm, respectively. By changing the temperature from 20 K to 293 K, it is found that the PL intensity of samples decreases but the FWHM broadens with the increasing of the temperature. GaN sample shows red-shift, InGaN sample shows red-blue-red-shift. The temperature dependence of peak energy shift is studied and explained.
