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1.
Andreas Othonos Emmanouil Lioudakis A. G. Nassiopoulou 《Nanoscale research letters》2008,3(9):315-320
We have studied ultrafast carrier dynamics in oxidized silicon nanocrystals (NCs) and the role that surface-related states
play in the various relaxation mechanisms over a broad range of photon excitation energy corresponding to energy levels below
and above the direct bandgap of the formed NCs. Transient photoinduced absorption techniques have been employed to investigate
the effects of surface-related states on the relaxation dynamics of photogenerated carriers in 2.8 nm oxidized silicon NCs.
Independent of the excitation photon energy, non-degenerate measurements reveal several distinct relaxation regions corresponding
to relaxation of photoexcited carriers from the initial excited states, the lowest indirect states and the surface-related
states. Furthermore, degenerate and non-degenerate measurements at difference excitation fluences reveal a linear dependence
of the maximum of the photoinduced absorption (PA) signal and an identical decay, suggesting that Auger recombination does
not play a significant role in these nanostructures even for fluence generating up to 20 carriers/NC. 相似文献
2.
The acid-base properties of -Al2O3 and alumina-supported B2O3, Ga2O3 and In2O3 have been determined by microcalorimetry of ammonia and sulfur dioxide adsorption. From the adsorption of NH3, it was found that the addition of B2O3 on alumina leads to an increase of the number of acid sites, while Ga2O3 and In2O3 additives caused a decrease in the acidity of alumina. Using SO2 as a probe molecule to study the basicity, the number of surface basic sites on alumina was found to be strongly decreased by the addition of boron oxide, while it was only slightly affected by the addition of gallium oxide and decreased by the addition of indium oxide. The differential heats of adsorption are discussed as a function of the coverage by the probe molecules. The electronic properties of the oxides are examined in order to explain the acid-base properties of the supported oxides. 相似文献
3.
We have studied femtosecond carrier dynamics in InN nanowires grown by reactive vapor transport. Transient differential absorption
measurements have been employed to investigate the relaxation dynamics of photogenerated carriers near and above the optical
absorption edge of InN NWs where an interplay of state filling, photoinduced absorption, and band-gap renormalization have
been observed. The interface between states filled by free carriers intrinsic to the InN NWs and empty states has been determined
to be at 1.35 eV using CW optical transmission measurements. Transient absorption measurements determined the absorption edge
at higher energy due to the additional injected photogenerated carriers following femtosecond pulse excitation. The non-degenerate
white light pump-probe measurements revealed that relaxation of the photogenerated carriers occurs on a single picosecond
timescale which appears to be carrier density dependent. This fast relaxation is attributed to the capture of the photogenerated
carriers by defect/surface related states. Furthermore, intensity dependent measurements revealed fast energy transfer from
the hot photogenerated carriers to the lattice with the onset of increased temperature occurring at approximately 2 ps after
pulse excitation. 相似文献
4.
Maniyazagan Munisamy Hyeon-Woo Yang Naveenkumar Perumal Nayoung Kang Woo Seung Kang Sun-Jae Kim 《International journal of molecular sciences》2022,23(8)
The most pressing concerns in environmental remediation are the design and development of catalysts with benign, low-cost, and efficient photocatalytic activity. The present study effectively generated a flower-like indium oxide (In2O3-MF) catalyst employing a convenient MOF-based solvothermal self-assembly technique. The In2O3-MF photocatalyst exhibits a flower-like structure, according to morphology and structural analysis. The enhanced photocatalytic activity of the In2O3-MF catalyst for 4-nitrophenol (4-NP) and methylene blue (MB) is likely due to its unique 3D structure, which includes a large surface area (486.95 m2 g−1), a wide spectrum response, and the prevention of electron–hole recombination compared to In2O3-MR (indium oxide-micro rod) and In2O3-MD (indium oxide-micro disc). In the presence of NaBH4 and visible light, the catalytic performances of the In2O3-MF, In2O3-MR, and In2O3-MD catalysts for the reduction of 4-NP and MB degradation were investigated. Using In2O3-MF as a catalyst, we were able to achieve a 99.32 percent reduction of 4-NP in 20 min and 99.2 percent degradation of MB in 3 min. Interestingly, the conversion rates of catalytic 4-NP and MB were still larger than 95 and 96 percent after five consecutive cycles of catalytic tests, suggesting that the In2O3-MF catalyst has outstanding catalytic performance and a high reutilization rate. 相似文献
5.
ABSTRACTTi3AlC2/Al2O3 composite materials were successfully fabricated from TiO2/TiC/Ti/Al powders by the in situ reactive hot pressed technique. The microstructure, mechanical and oxidation properties of the composites were investigated in the paper. Vickers hardness increased with the Al2O3 content. The relative density of Ti3AlC2/Al2O3 composites exhibits a declining tendency with Al2O3 content especially exceeds 10 vol.?%. The Ti3AlC2/Al2O3 composites show excellent electrical conductivity. The flexural strength and fracture toughness of Ti3AlC2/10 vol. % Al2O3 are 461 ± 20?MPa and 6.2?±?0.2?MPa m1/2, respectively. The cyclic oxidation behaviour of resistance of Ti3AlC2/10 vol. % Al2O3 composites at 800–1000°C generally obeys a parabolic law. The oxide scale of sample consists of a mass of α-Al2O3 and TiO2, forming a dense and adhesive protect layer. The result indicates that the Al2O3 can greatly improve the oxidation resistance of Ti3AlC2. 相似文献
6.
This research deals with the decolorization of synthetic wastewater, prepared with the acid 1:2 metal-complex textile dye C.I. Acid Blue 193, using the ozonation (O3) and H2O2/O3 processes. To minimize the number of experiments, they were performed using the 2k factorial design. Five influential parameters were examined: initial dye concentration, ozone flow rate, initial pH value, decolorization time and H2O2 addition. The decolorization efficiency was 95% in 20 minutes (pH = 7; O3 flow rate of 2 g/L.h) and a higher increase in the toxicity after the ozonation process (39%) indicates the formation of carcinogenic by-products. According to the variance test analysis, the initial dye concentration, the ozone flow rate, the initial pH value and the decolorization time and their first- and second-order interactions are significant, while the H2O2 addition was not important with respect to the discussed range. With the help of these significant factors a regression model was constructed and the adequacy of the model was checked. The obtained regression polynomial was used to model the relation between the absorbance and the influential parameters by fitting the response surface. This response surface may be used to predict the absorbance result from a set of influential parameters, or it can be rearranged in such a way as to predict the set of process decolorization parameters necessary to reduce the absorbance of wastewater with the given initial dye concentration, below the prescribed limit. It is also shown that the 2k factorial design can be suitable for predicting the operating expenses of the ozonation. 相似文献
7.
The mixed metal oxides TiO2-Fe2O3 and ZrO2-Fe2O3 were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO2-Fe2O3 catalysts. However, for TiO2-Fe2O3 catalysts, the surface area, the amount of acidic and basic sites and TiFe2O5 crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO2-Fe2O3 and ZrO2-Fe2O3 catalyst system and also for the TiO2-Fe2O3-ZrO2 system, i.e. the activities of these catalysts can be ranked in the following order: TiO2-Fe2O3-ZrO2>TiO2-Fe2O3 >ZrO2>Fe2O3>TiO2. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts. 相似文献
8.
Thomas Mathew Yusuke Yamada Atsushi Ueda Hiroshi Shioyama Tetsuhiko Kobayashi 《Catalysis Letters》2005,100(3-4):247-253
The steam reforming of dimethyl ether (DME) was performed on Ga2O3–Al2O3 mixed oxides prepared by sol–gel method. Ga2O3 significantly affects the catalytic performance with respect to the DME conversion and H2 yield. The catalytic activity increases with the Ga concentration in Ga2O3–Al2O3 mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga2O3 and Ga2O3 containing Al2O3 mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga2O3 for the production of H2 from DME and/or methanol. 相似文献
9.
An Fe2O3 (10 wt%)/Al2O3 (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce
styrene in the presence of CO2 instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO2 was considered to proceed both via a one-step pathway and via a two-step pathway. CO2 was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
The objective of the presented study was to test various oxidation processes with the aim being to reduce the concentration and toxicity of biocide wastewater from a Slovenian phytopharmaceutical factory. Laboratory-scale experiments employing two AOP processes – ozonation (O3) and peroxone (H2O2/O3) – were applied to reduce the concentration of the active components involved, i.e., methylisothiazolone (MI), chloromethylisothiazolone (CMI) and dichloromethylisothiazolone (DCMI). The reduction of the biocide wastewater load for the performed oxidation processes was evaluated using ecological parameters. The H2O2/O3 oxidation procedure using an O3 flow rate of 1g/L h, at a pH value of 10 and with the addition of 5 ml of H2O2 (0.3 M) proved to be the most effective treatment. The toxicity of the biocide-load wastewater with an initial EC50 = 0.38%, decreased to EC50 (24h) >100% and EC50 (48h) = 76%. 相似文献
11.
Zhaobin Wei Shaocong Jiang Qin Xin Shishan Sheng Guoxing Xieng 《Catalysis Letters》1991,11(3-6):365-374
The effect of TiO2 modified Al2O3 surface on the reducibility of MoO3 has been studied by TPR and XPS. The results show that Mo6+ in Mo/TiO2-Al2O3 can be reduced to much lower valency, especially at low Mo loading. The influence of the calcination temperature on the reduction of Mo6+ on Al2O3 and TiO2-Al2O3 carriers is different. The data reveals that the reducibility of Mo6+ on Al2O3 slightly decreased, while that on TiO2-Al2O3 increased when the calcination temperature was raised. It is suggested that the stronger tetrahedral site of the Al2O3 surface was first occupied by TiO2 and main octahedral Mo6+ in polymeric species-; and a small crystalline MoO3 formed on TiO2-Al2O3, whereas the formation of tetrahedral Mo6+ species and Al2(MoO4)3 phase was inhibited. 相似文献
12.
We have studied the optical properties and carrier dynamics in SnO2 nanowires (NWs) with an average radius of 50 nm that were grown via the vapor–liquid solid method. Transient differential
absorption measurements have been employed to investigate the ultrafast relaxation dynamics of photogenerated carriers in
the SnO2 NWs. Steady state transmission measurements revealed that the band gap of these NWs is 3.77 eV and contains two broad absorption
bands. The first is located below the band edge (shallow traps) and the second near the center of the band gap (deep traps).
Both of these absorption bands seem to play a crucial role in the relaxation of the photogenerated carriers. Time resolved
measurements suggest that the photogenerated carriers take a few picoseconds to move into the shallow trap states whereas
they take ~70 ps to move from the shallow to the deep trap states. Furthermore the recombination process of electrons in these
trap states with holes in the valence band takes ~2 ns. Auger recombination appears to be important at the highest fluence
used in this study (500 μJ/cm2); however, it has negligible effect for fluences below 50 μJ/cm2. The Auger coefficient for the SnO2 NWs was estimated to be 7.5 ± 2.5 × 10−31 cm6/s. 相似文献
13.
Sang-Woo Park Oh-Shim Joo Kwang-Deog Jung Hyo Kim Sung-Hwan Han 《Korean Journal of Chemical Engineering》2000,17(6):719-722
The stability and the activity of Fe2O3/Cr2O3 and ZnO/Cr2O3 catalysts were examined for a reverse-watergas-shift reaction (RWReaction). The initial activities of those catalysts were
quite high so that the conversion reached close to equilibrium. The activity of Fe2O3/Cr2O3 catalyst decreased from 33.5 to 29.8% during the RWReaction for 75 h at 873 K with GHSV (ml/gcat · h) of 100,000. Moreover,
the coke formation on the Fe2O3/Cr2O3 catalyst caused clogging in the RWReactor of the CAMERE process. On the other hand, the ZnO/Cr2O3 catalyst showed no coke formation and no deactivation for the RWReaction at 873 K with GHSV (ml/gcat · h) of 150,000. The
ZnO/Cr2O3 was a good catalyst for the RWReaction of the CAMERE process. 相似文献
14.
Yu-Jen Hsiao Chung-Hsin Lu Liang-Wen Ji Teen-Hang Meen Yan-Lung Chen Hsiao-Ping Chi 《Nanoscale research letters》2014,9(1):32
We demonstrate that heterojunction photovoltaics based on hydrothermal-grown In2S3 on p-Si were fabricated and characterized in the paper. An n-type In2S3 nanoflake-based film with unique ''cross-linked network’ structure was grown on the prepared p-type silicon substrate. It was found that the bandgap energy of such In2S3 film is 2.5 eV by optical absorption spectra. This unique nanostructure significantly enhances the surface area of the In2S3 films, leading to obtain lower reflectance spectra as the thickness of In2S3 film was increased. Additionally, such a nanostructure resulted in a closer spacing between the cross-linked In2S3 nanostructures and formed more direct conduction paths for electron transportation. Thus, the short-circuit current density (Jsc) was effectively improved by using a suitable thickness of In2S3. The power conversion efficiency (PCE, η) of the AZO/In2S3/textured p-Si heterojunction solar cell with 100-nm-thick In2S3 film was 2.39%. 相似文献
15.
Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al2O3, Pd/Al2O3, and PdO/Al2O3. Ethyl--13C alcohol (CH3
13CH2OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O2, A12O3 oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A12O3, decomposed much faster on Pd/A12O3 by diffusing to Pd and undergoing CO elimination to form CH4,13CO, H2, and surface carbon. On PdO/A12O3, the decomposition was slower than on Pd/A12O3 until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O2, Pd/Al2O3 was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A12O3 before it had significant oxidation activity. 相似文献
16.
Maria Wojciechowska Iwona Tomska-Foralewska Wiesław Przystajko Michał Zieliński 《Catalysis Letters》2005,104(3-4):121-128
Catalytic properties of Cr2O3 supported on MgF2 or Al2O3 have been modified by magnesium oxide. The catalysts have been obtained by the co-impregnation method and characterised by:
BET, XRD and TPR. As follows from the results, the oxides supported on magnesium fluorine react with each other already at
400 °C, leading to formation of an amorphous spinel-like phase. On the Al2O3 support such an MgCr2O4 spinel has appeared at much higher temperatures. The addition of magnesium oxide has a significant effect on the activity
and selectivity of the catalysts studied in the CO oxidation reaction at room temperature and in the reaction of cyclohexane
dehydrogenation. The magnesium–chromium catalysts supported on MgF2 have been found to show much higher activity and selectivity than the analogous systems supported on Al2O3. 相似文献
17.
《分离科学与技术》2012,47(16):2453-2464
The objectives of this study were to investigate the effects of ozone and the O3/H2O2 process on FeCl3 coagulation efficiency for the removal of the high content of natural organic matter (NOM) and arsenic (As) from groundwater (DOC = 9.27 ± 0.92 mg/L; 51.7 ± 16.4 µg As/L). Arsenic and NOM removal mechanisms during coagulation/flocculation are well investigated. However, data concerning arsenic removal in the presence of NOM, which is the subject of this article, are still insufficient. Laboratory and pilot plant test results have shown that the competition of NOM and As for adsorption sites on the coagulant surface have great influence on coagulation/flocculation efficiency for their removal. With both oxidation pre-treatments, arsenic content after the coagulation process was less than 2.0 µg/L in treated water. Application of ozone has a lower influence on coagulation efficacy in terms of DOC reduction, compared to the O3/H2O2 process with the same ozone dose. 相似文献
18.
A series of Mo/Al2O3 and Mo/TiO2-Al2O3 catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO2 on the sulfidability of molybdena was studied in detail. It is found that Mo/Al2O3 catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H2 to produce H2S. At 530–550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS2. When the surface of Al2O3 was covered by a monolayer of TiO2, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H2S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80–100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO2 loading. The function of TiO2 is explained by the weakened interaction between MoO3 and Al2O3 due to the coverage of the Al2O3 surface by TiO2. 相似文献
19.
HR Bahari HA Sidek FR Adikan WM Yunus MK Halimah 《International journal of molecular sciences》2012,13(7):8609-8614
Heavy metal oxide glasses, containing bismuth and/or lead in their glass structure are new alternatives for rare eart (RE) doped hosts. Hence, the study of the structure of these vitreous systems is of great interest for science and technology. In this research work, GeO(2)-PbO-Bi(2)O(3) glass host doped with Er(3+)/Yb(3+) ions was synthesized by a conventional melt quenching method. The Fourier transform infrared (FTIR) results showed that PbO and Bi(2)O(3) participate with PbO(4) tetragonal pyramids and strongly distort BiO(6) octahedral units in the glass network, which subsequently act as modifiers in glass structure. These results also confirmed the existence of both four and six coordination of germanium oxide in glass matrix. 相似文献
20.
《国际聚合物材料杂志》2012,61(6):547-556
Polymeric Si-Al sols were prepared from Al(OBus)3 and Si(OEt)4 (TEOS). Acetylacetone and isoeugenol were employed separately to chelate the Al precursor in order to slow down the chemical reactivity, avoiding precipitation. The characterization techniques were Fourier Transform Infrared Spectroscopy (FTIR), nitrogen sorption measurements, Thermal Gravimetric (TGA) and Differential Thermal Analyses (DTA). The Si-O-Al bond vibration was detected by FTIR in the 1056-1074 cmm1 region. From the N2 adsorption, isotherms the surface area results obtained range between 15.8 to 408.4 m2/g. Corresponding average pore diameter are 3.397 to 1.417 nm. It is found that the porous texture of the materials mainly depends to the chelating agent in the sols. A strong influence of the molecular structure of the chelating agents in the sols was observed in the oxides by TGA and DTA studies. 相似文献