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1.
Working temperature, sensitivity, and selectivity are some of the characteristics of the applied gas sensors. How to design and fabricate an ideal gas sensor working at room temperature is still challenging and attracting lots of interest. Two-dimensional (2D) materials with ultra-thin structure have been demonstrated as a family of ideal candidates to achieve this goal. Among them, Ti 3C 2T x MXene, a kind of layered sheet synthesized by selectively etching MAX phases materials, shows remarkable potential to be the sensitive materials solely or in a composite. However, their designing rules are still lacking critical thinking from the viewpoint of the intrinsic property of Ti 3C 2T x MXene based materials. In this article, two critical features, i.e., the thickness of the sensitive materials, and the scope of the analytes, are elaborated towards Ti 3C 2T x MXene based gas sensors after characterizing the performance of sensing reducing gases (NH 3 and CO) and oxidizing gas (NO 2). First, the thinner the Ti 3C 2T x MXene sensitive layer, the better the sensitivity. Second, the Ti 3C 2T x MXene based gas sensor is not suitable for strong and moderate oxidation gas due to its ease of oxidation. These two rules are demonstrated, and could be considered with priority both in the future researches and practical applications. 相似文献
2.
MXenes have attracted increasing research enthusiasm owing to their unique physical and chemical properties. Although MXenes exhibit exciting potential in cations adsorption due to their unique surface groups, the adsorption capacity is limited by the low specific surface area and undeveloped porosity. Our work aims at enhancing the adsorption performance of a well-known MXene, Ti 3C 2T x, for methylene blue (MB) by decorating tiny ZIF-8 nanoparticles in the interlayer. After the incorporation of ZIF-8, suitable interspace in the layers resulting from the distribution of tiny ZIF-8 appears. When employing in MB, the adsorption capacity of composites can reach up to 107 mg·g -1 while both ZIF-8 (3 mg·g -1) and Ti 3C 2T x (9 mg·g -1) show nearly no adsorption capacity. The adsorption mechanism was explored, and the good adsorption capacity is caused by the synergistic effect of ZIF-8 and Ti 3C 2T x, for neither of them is of suitable interspace or surface groups for MB adsorption. Our work might pave the way for constructing functional materials based on the introduction of nanoparticles into layered materials for various adsorption applications. 相似文献
3.
Two-dimensional (2D) titanium carbide MXene Ti 3C 2 has attracted significant research interest in energy storage applications. In this study, we prepared Chl@Ti 3C 2 composites by simply mixing a chlorophyll derivative (e.g., zinc methyl 3-devinyl-3-hydroxymethyl- pyropheophorbide a (Chl)) and Ti 3C 2 in tetrahydrofuran, where the Chl molecules were aggregated among the multi-layered Ti 3C 2 MXene or on its surface, increasing the interlayer space of Ti 3C 2. The as-prepared Chl@Ti 3C 2 was employed as the anode material in the lithium-ion battery (LIB) with lithium metal as the cathode. The resulting LIB exhibited a higher reversible capacity and longer cycle performance than those of LIB based on pure Ti 3C 2, and its specific discharge capacity continuously increased along with the increasing number of cycles, which can be attributed to the gradual activation of Chl@Ti 3C 2 accompanied by the electrochemical reactions. The discharge capacity of 1 wt-% Chl@Ti 3C 2 was recorded to be 325 mA·h·g –1 at the current density of 50 mA·g –1 with a Coulombic efficiency of 56% and a reversible discharge capacity of 173 mA·h·g –1 at the current density of 500 mA·g –1 after 800 cycles. This work provides a novel strategy for improving the energy storage performance of 2D MXene materials by expanding the layer distance with organic dye aggregates. 相似文献
4.
A series of novel dense mixed conducting ceramic membranes based on K 2NiF 4-type (La 1–xCa x) 2 (Ni 0.75Cu 0.25)O 4+δ was successfully prepared through a sol-gel route. Their chemical compatibility, oxygen permeability, CO and CO 2 tolerance, and long-term CO 2 resistance regarding phase composition and crystal structure at different atmospheres were studied. The results show that higher Ca contents in the material lead to the formation of CaCO 3. A constant oxygen permeation flux of about 0.63 mL·min −1·cm −2 at 1173 K through a 0.65 mm thick membrane was measured for (La 0.9Ca 0.1) 2 (Ni 0.75Cu 0.25)O 4+δ, using either helium or pure CO 2 as sweep gas. Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO 2 concentration. The membrane showed excellent chemical stability towards CO 2 for more than 1360 h and phase stability in presence of CO for 4 h at high temperature. In addition, this membrane did not deteriorate in a high-energy CO 2 plasma. The present work demonstrates that this (La 0.9Ca 0.1) 2(Ni 0.75Cu 0.25)O 4+δ membrane is a promising chemically robust candidate for oxygen separation applications. 相似文献
5.
Nanosized particles dispersed uniformly on Al 2O 3 particles were prepared from the decomposition of precursor Cr(CO) 6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr 2O 3, CrC 1−x, and C. A solid solution of Al 2O 3–Cr 2O 3 and an Al 2O 3–Cr 2O 3/Cr 3C 2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al 2O 3–Cr 2O 3/Cr-carbide (Cr 3C 2 and Cr 7C 3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr 3C 2 and Al 2O 3 is non-coherent, while the interface between Cr 7C 3 and Al 2O 3 is semi-coherent. 相似文献
6.
The effect of Al 2O 3 on mechanical properties of Ti 3SiC 2/Al 2O 3 composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti 3SiC 2/Al 2O 3 composite can reach 10.28 GPa, 50% higher than that of pure Ti 3SiC 2. However, slight decrease in the other mechanical properties was observed with Al 2O 3 addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al 2O 3 in the composite. 相似文献
7.
Unique self-assembled iron(II)molybdenum(IV)oxide(Fe 2Mo 3O 8)mesoporous hollow spheres have been facilely constructed via the bubble-template-assisted hydrothermal synthesis method combined with simple calcination.The compact assembly of small nanoparticles on the surface of the hollow spheres not only provides more active sites for the Fe 2Mo 3O 8,but also benefits the stability of the hollow structure,and thus improved the lithium storage properties of Fe2Mo3O8.The Fe 2Mo 3O 8 mesoporous hollow spheres exhibit high initial discharge and charge capacities of 1189 and 997 mA?h?g ?1 respectively,as well as good long-term cycling stability(866 mA?h?g ?1 over 70 cycles)when used as a lithium-ion battery anode.This feasible material synthesis strategy will inspire the variation of structural design in other ternary metal molybdates. 相似文献
8.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
9.
A process using metal-organic chemical vapor infiltration (MOCVI) conducted in fluidized bed was employed for the preparation of nano-sized ceramic composites. The Cr-species was infiltrated into Al 2O 3 granules by the pyrolysis of chromium carbonyl (Cr(CO) 6) at 300–450 °C. The granulated powder was pressureless sintered or hot-pressed to achieve high density. The results showed that the dominant factors influencing the Cr-carbide phases formation, either Cr 3C 2 or Cr 7C 3, in the composite powders during the sintering process were the temperature and oxygen partial pressure in the furnace. The coated Cr-phase either in agglomerated or dispersive condition was controlled by the use of colloidal dispersion. The microstructures showed that fine (20 –600 nm) Cr xC y grains (≤8 vol.%) located at Al 2O 3 grain boundaries hardly retarded the densification of Al 2O 3 matrix in sintering process. The tests on hardness, strength and toughness appeared that the composites with the inclusions (Cr 3C 2) had gained the advantages over those by the rule of mixture. Even 8 vol.% ultrafine inclusions have greatly improved the mechanical properties. The strengthening and toughening mechanisms of the composites were due to grain-size reduction, homogenous dispersion of hard inclusions, and crack deflection. 相似文献
10.
Atomic layer epitaxy (ALE), a technique relying on saturating gas–solid reactions, was applied in the preparation of CrO x/Al 2O 3 catalysts using Cr(acac) 3 vapor and air as source materials for CrO x. Vaporized Cr(acac) 3 was reacted with preheated Al 2O 3, and the surface complex formed was treated with air to remove the ligand residues. The Cr loading increased from 1.3 to 12.5 wt.% as the number of saturating Cr(acac) 3 and air reactions was increased from one to 10. CrO x/Al 2O 3 catalysts were also prepared from solution by incipient wetness impregnation (0.3–21 wt.%). XPS and UV–VIS measurements of the catalysts revealed the presence of both Cr 6+ and Cr 3+. Although the oxidation state distribution was similar, H 2-temperature programmed reduction (TPR) and solubility measurements indicated that Cr 6+ surface sites were in stronger interaction with Al 2O 3 and more uniformly distributed in the catalysts prepared by ALE than by impregnation. On the basis of the activity of the catalysts in the dehydrogenation of i-butane, we propose that the dehydrogenation reaction uses both reduced Cr 6+, i.e. redox Cr 3+, and exposed non-redox Cr 3+ sites. Furthermore, the dehydrogenation reaction must be insensitive to the size of the CrO x ensembles since activities were similar for the catalysts prepared by ALE and impregnation. The decay of the dehydrogenation activity in successive prereduction–reaction–regeneration cycles was attributed to a decrease in the number of redox Cr 3+ sites. 相似文献
11.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
12.
For high performance supercapacitors, novel hierarchical yolk-shell a-Ni(OH) 2/Mn 2O 3 microspheres were controllably synthesized using a facile two-step method based on the solvothermal treatment. The unique a-Ni(OH) 2 based yolk-shell microstructures decorated with numerous interconnected nanosheets and the hetero-composition features can synergistically enhance reactive site exposure and electron conduction within the microspheres, facilitate charge transfer between electrolyte and electrode materials, and release structural stress during OH − chemisorption/desorption. Moreover, the Mn 2O 3 sediments distributed over the a-Ni(OH) 2 microspheres can serve as an effective protective layer for electrochemical reactions. Consequently, when tested in 1 mol·L −1 KOH aqueous electrolyte for supercapacitors, the yolk-shell a-Ni(OH) 2/Mn 2O 3 microspheres exhibited a considerably high specific capacitance of 2228.6 F·g −1 at 1 A·g −1 and an impressive capacitance retention of 77.7% after 3000 cycles at 10 A·g −1. The proposed a-Ni(OH) 2/Mn 2O 3 microspheres with hetero-composition and unique hierarchical yolk-shell microstructures are highly promising to be used as electrode materials in supercapacitors and other energy storage devices. 相似文献
13.
Al 2O 3 hollow fibre membranes were prepared by a combined phase-inversion and sintering method. An organic binder solution (dope) containing suspended aluminium oxide (Al 2O 3) powders, either in mono size or a distributed size, is spun to a hollow fibre precursor, which is then sintered at elevated temperatures. In spinning the hollow fibre precursor, polyethersulfone (PESf), N-methyl-2-pyrrolidone (NMP) and polyvinyl pyrrolidone (PVP) were used as a polymer binder, a solvent and an additive, respectively. The Al 2O 3 hollow fibre membranes prepared were characterized using a scanning electron microscope (SEM) and gas permeation techniques. Effects of Al 2O 3 particle size and size distribution, the sintering temperature and Al 2O 3/PESf ratio on the structure and performance of the resulting membranes were studied extensively. The prepared Al 2O 3 hollow fibre membranes retains its asymmetric structure (mainly resulted from the phase inversion technique) even after the sintering process. Preparation of the Al 2O 3 hollow fibre membrane with a high mechanical strength and moderate permeation characteristics is feasible if the Al 2O 3 powders with a distributed particle size in the spinning (dope) solution is employed. 相似文献
14.
A mean field model, for storage and desorption of NO x in a Pt/BaO/Al 2O 3 catalyst is developed using data from flow reactor experiments. This relatively complex system is divided into five smaller sub-systems and the model is divided into the following steps: (i) NO oxidation on Pt/Al 2O 3; (ii) NO oxidation on Pt/BaO/Al 2O 3; (iii) NO x storage on BaO/Al 2O 3; (iv) NO x storage on Pt/BaO/Al 2O 3 with thermal regeneration and (v) NO x storage on Pt/BaO/Al 2O 3 with regeneration using C 3H 6. In this paper, we focus on the last sub-system. The kinetic model for NO x storage on Pt/BaO/Al 2O 3 was constructed with kinetic parameters obtained from the NO oxidation model together with a NO x storage model on BaO/Al 2O 3. This model was not sufficient to describe the NO x storage experiments for the Pt/BaO/Al 2O 3, because the NO x desorption in TPD experiments was larger for Pt/BaO/Al 2O 3, compared to BaO/Al 2O 3. The model was therefore modified by adding a reversible spill-over step. Further, the model was validated with additional experiments, which showed that NO significantly promoted desorption of NO x from Pt/BaO/Al 2O 3. To this NO x storage model, additional steps were added to describe the reduction by hydrocarbon in experiments with NO 2 and C 3H 6. The main reactions for continuous reduction of NO x occurs on Pt by reactions between hydrocarbon species and NO in the model. The model is also able to describe the reduction phase, the storage and NO breakthrough peaks, observed in experiments. 相似文献
15.
Mesostructured MnO x–Cs 2O–Al 2O 3 nanocomposites have been synthesized by reverse microemulsion method combined with hydrothermal treatment and then applied to the catalytic combustion of methane. Compared to impregnation-derived conventional MnO x/Cs 2O/Com-Al 2O 3 catalyst, the microemulsion-derived catalyst showed higher activity and stability for methane combustion. The T10% of the fresh and of the 72 h aged Mn xO–Cs 2O–Al 2O 3 were 475 and 490 °C, respectively, recommending it as a potential candidate catalyst for application in hybrid gas turbines. The homogeneous composition of the microemulsion-derived nanocomposite catalyst can hinder the loss of Cs + and accelerate the formation of Cs–β-alumina phase, ensuring thus higher activity and stability for methane combustion. 相似文献
16.
Pd/Nb 2O 5/Al 2O 3 catalysts were investigated on propane oxidation. Diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) analysis suggested that monolayer coverage was attained between 10 and 20 wt.% of Nb 2O 5. Temperature programmed reduction (TPR) evidenced the partial reduction of niobium oxide. The maximum propane conversion observed on the Pd/10% Nb 2O 5/Al 2O 3 corresponded to the maximum Nb/Al surface ratio. The presence of NbO x polymeric structures near to the monolayer could favor the ideal Pd 0/Pd 2+ surface ratio to the propane oxidation which could explain the promoting effect of niobium oxide. 相似文献
17.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
18.
A series of the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts ( x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H 2-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts the surface phase structure were the Ce 1−xCu xO 2−x solid solution, -Al 2O 3 and γ-Al 2O 3. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce 1−xCu xO 2−x solid solution. The Cu component of the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce 1−xCu xO 2−x solid solution and the Al 2O 3 washcoats and the FeCrAl support. 相似文献
19.
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO x adsorber catalyst, Pt/K/Al 2O 3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al 2O 3 phase with associated hydroxyl groups at the surface, and an alkalized-Al 2O 3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al 2O 3 and 65% for the alkalized-Al 2O 3. NO 2 and CO 2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al 2O 3 adsorbs 0.087 μmol CO 2/m 2and 2.0 μmol NO 2/m 2, and Pt/K/Al 2O 3 adsorbs 2.0 μmol CO 2/m 2and 6.4 μmol NO 2/m 2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al 2O 3 during both lean and rich periods of the NO x adsorber catalyst cycle. 相似文献
20.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, had a turnover frequency at 700°C of 0.05 s −1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO =4 to the latter Sr-promoted La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
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