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1.
Red emitting Cr 3+ doped LiAl 5O 8 powder phosphor was prepared by combustion route using corresponding metal nitrates and urea in a single step. The prepared powder was characterized by X-ray diffraction and surface area measurements were carried out by Brunauer–Emmet–Teller adsorption isotherms. The electron paramagnetic resonance spectrum in the low field regions is typical for isolated Cr 3+ ions whereas the resonance signal in the high field region with g = 1.95 is due to exchange coupled Cr 3+–Cr 3+ pairs. The optical studies show two broad and intense bands characteristic of Cr 3+ ions in distorted octahedral symmetry. The photoluminescence spectrum gives a narrow red emission at 710 nm corresponding to 2E g → 4A 2g transition upon excitation of 562 nm. The crystal field parameter (Dq), Racah inter-electronic repulsion parameters ( B and C) and nephelauxetic parameters have been evaluated and discussed. 相似文献
2.
NaY zeolite particles with a high surface area of 723 m 2/g were synthesized by a hydrothermal method. Adsorption isotherms of pure gases CO 2 and N 2 on the synthesized NaY particles were measured at temperatures 303, 323, 348, 373, 398, 423, 448 and 473 K and pressures up to 100 kPa. It was found that the adsorption isotherm of CO 2 on the synthesized zeolite is higher than that on other porous media reported in the literature. All measured adsorption isotherms of CO 2 and N 2 were fitted to adsorption models Sips, Toth, and UNILAN in the measured temperature/pressure range and Henry’s law adsorption equilibrium constants were obtained for all three adsorption models. The adsorption isotherms measured in this work suggest that the NaY zeolite may be capable of capturing CO 2 from flue gas at high temperatures. In addition, isosteric heats of adsorption were calculated from these adsorption isotherms. It was found that temperature has little effect on N 2 adsorption, while it presents marked decrease for CO 2 with an increase of adsorbate loading, which suggests heterogeneous interactions between CO 2 and the zeolite cavity. 相似文献
3.
Commercial type X zeolites (Linde 13X) are nitrogen selective. Oxygen is the less abundant component in air; hence oxygen selective sorbents are desired for air separation. Mixed Na-Ce type X zeolites containing different ratios of Ce 3+/Na + ions are prepared by partial ion exchange of commercial X zeolite. The adsorption isotherms of nitrogen, oxygen and argon are measured and the pure-component selectivity ratios are compared and analyzed against commercial zeolites (13X) for air separation. Oxygen selectivity over nitrogen (1.5) and argon (4.0) are seen for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce 3+/Na + < 4.0) from Henry's constant determined from low pressure adsorption measurements. The oxygen and nitrogen isotherms cross over for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce 3+/Na + < 4.0), and the pressure at which cross they over increases as Ce 3+/Na + approaches 1. The oxygen selectivity as claimed in the patent by N.V. Choudary, R.V. Jasra, and S.G.T. Bhat (US Patent no. 6,087,289, 2000) is seen only at very low pressures in the volumetric adsorption measurement and the hydrogen treatment of the Ce-exchanged samples have no effect on the adsorption characteristics. 相似文献
4.
Well-ordered cubic zeolites 4A were synthesised using sol–gel process in the presence of different silica and aluminum sources. The aluminum and silica sources determined whether or not zeolites were formed at precise silica/alumina mole ratio. Zeolites were formed only when the aluminum source was sodium aluminate, the silica source was fumed silica, colloidal silica or sodium metasilicate. Our findings indicated that the type of zeolite invariably obtained was 4A and SEM images indicated that the produced zeolites are cubic shaped crystals with planar surfaces and well-defined edges and sharp crystals. In turn, synthesis parameters are seen to have a significant effect in maximizing heavy metals uptake (for example Cu 2+, Cr 3+, Cd 2+ and Ni 2+) by synthesized zeolites. Zeolite 4A gave better heavy metal uptakes than amorphous or non-zeolite crystalline materials. This was attributed to higher ion-exchange capacity and higher BET specific surface area 445 m 2/g and pore volume 0.141 cm 3/g. The latter attribute possibly translates to greater accessibility of ion-exchange sites and selectivity towards metal type by this zeolite followed the sequence: Cu 2+ > Cr 3+ ≥ Cd 2+ > Ni 2+. 相似文献
5.
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4‐DiMe‐ImidH][Cr 7Ni IIF 8(O 2C tBu) 16] 1 (2,4‐DiMe‐ImidH=the cation of 2,4‐dimethylimidazole), [ImidH] 2[Cr 6Ni II2F 8(O 2CC tBu) 16] 2 (ImidH=the cation of imidazole), and [1‐Bz‐ImidH] 2 [Cr 7Ni II2F 9(O 2C tBu) 18] 3 (1‐Bz‐ImidH=the cation of 1‐benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3 . In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X‐ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J≈?5.8 cm ?1, and it is not possible to differentiate the exchange between two Cr III centers ( JCrCr) from the exchange between a Cr III and a Ni II center ( JCrNi). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present. 相似文献
6.
Removal of Cr 3+,Ca 2+,Mg 2+ and K + in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed
beds at 30 ∘C. The equilibrium selectivity was obtained as Cr +3 > Mg 2+ > Ca 2+≈K + for zeolite NaY and Ca 2 +≫Cr 3 + > Mg 2 +≈K + for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing
cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated.
Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that
chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a
higher affinity towards Cr 3+ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was
less retained in NaX due to the high selectivity towards calcium ions. 相似文献
7.
Studies on Oxide Catalysts. XLii. Redox Behaviour of Nickel in Zeolites NiNa? Y. 4. Influence of Composition on the Reducibility of Nickel in Zeolites NiNa? Y By chemical analysis (reaction with K 2Cr 2O 7) and ESCA investigations we determined the degree of reduction in reduced samples NiNa-Y as function of the mole ratio SiO 2/Al 2O 3 (module), of the Ni 2+ degree of exchange and the kind of the second cations. (NH 4+, Ca 2+, Co 2+, and Nd 3+) in the temperature region of 620–770 K. The degree of nickel reduction increases with increasing module, decreasing degree of exchange and decreasing number of Brönsted acidic centres. This behaviour is caused by the influence of the interaction between cations Ni 2+ and zeolite lattice on the reduction equilibrium. 相似文献
8.
The adsorption of naturally occurring radionuclides (UO 2
2+, Tl +, Pb 2+, Ra 2+, Bi 3+ and Ac 3+) onto zeolite (Z) and polyacrylamide-zeolite composite (PAA-Z) and its modified composition by phytic acid (Z-Phy and PAA-Z-Phy)
were investigated. Adsorption parameters were derived from the Langmuir and Freundlich fits to adsorption isotherms of the
ions studied. The adsorption isotherms were of L and H types. The adsorption capacity of Z decreased by PAA inclusion, but
the Phy modification of PAA-Z increased the capacity back to that of Z. The Phy modification made the adsorption spontaneity
at least ten times better than in the absence of Phy. This investigation showed that the zeolite, as one of the most abundant
natural materials and commonly used adsorbent can also be used for the removal of UO 2
2+ and, in the PAA-Z form, of the studied radionuclides. The usage of Z, as PAA-Z and its Phy modification provide research
materials which possess adequate practicality and effectiveness in studies of adsorption.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Adsorption isotherms of H 2S, CO 2, and CH 4 on the Si-CHA zeolite were measured over pressure range of 0–190 kPa and temperatures of 298, 323, and 348 K. Acid gases adsorption isotherms on this type of zeolite are reported for the first time. The isotherms follow a typical Type-I shape according to the Brunauer classification. Both Langmuir and Toth isotherms describe well the adsorption isotherms of methane and acid gases over the experimental conditions tested. At room temperature and pressure of 100 kPa, the amount of CO 2 adsorption for Si-CHA zeolite is 29 % greater than that reported elsewhere (van den Bergh et al. J Mem Sci 316:35–45 (2008); Surf Sci Catal 170:1021–1027 (2007)) for the pure silica DD3R zeolite while the amounts of CH 4 adsorption are reasonably the same. Si-CHA zeolite showed high ideal selectivities for acid gases over methane at 100 kPa (6.15 for H 2S and 4.06 for CO 2 at 298 K). Furthermore, H 2S adsorption mechanism was found to be physical, and hence, Si-CHA can be utilized in pressure swing adsorption processes. Due to higher amount of carbon dioxide adsorbed and lower heats of adsorption as well as three dimensional channels of Si-CHA pore structure, this zeolite can remove acid gases from methane in a kinetic based process such as zeolite membrane. 相似文献
10.
The coordinatively unsaturated chromium(II)-based Cr 3[(Cr 4Cl) 3(BTT) 8] 2 (Cr−BTT; BTT 3−=1,3,5-benzenetristetrazolate) metal–organic framework (MOF) has been shown to exhibit exceptional selectivity towards adsorption of O 2 over N 2/H 2. Using periodic density functional theory (DFT) calculations, we attempted to decipher the origin of this puzzling selectivity. By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas-bound MOFs [(Cr 4(X) 4Cl) 3(BTT) 8] 3− (X=O 2, N 2, and H 2), we unequivocally established the role of spin states and spin coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The binding of O 2 to the MOF follows an electron-transfer mechanism resulting in a Cr III superoxo species (O 2.−) with a very strong antiferromagnetic coupling between the two centers, whereas N 2/H 2 are found to weakly interact with the metal center and hence only slightly perturb the associated coupling constants. Although the gas-bound and unbound MOFs have an S=0 ground state (GS), the nature of spin the configurations and the associated magnetic exchanges are dramatically different. The binding energy and the number of oxygen molecules that can favorably bind to the Cr center were found to vary with respect to the spin state, with a significant energy margin (47.6 kJ mol −1). This study offers a hitherto unknown strategy of using spin state/spin couplings to control gas adsorption selectivity in MOFs. 相似文献
11.
The efficiency of activated carbons prepared from corncob, to remove asphaltenes from toluene modeled solutions, has been studied in this work. The activating agent effect over carbonaceous solid preparation , and also temperature effect on the asphaltenes adsorption on the prepared activated carbons, was studied. The asphaltene adsorption isotherms were determined, and the experimental data were analyzed applying the Langmuir, Freundlich, Redlich–Peterson, Toth and Radke–Prausnitz and Sips models. Redlich–Peterson model described the asphaltenes isotherm on the activated carbons better. The asphaltenes adsorption capacities at 25° for activated carbons were: 1305 mg g?1, 1654 mg g?1 and 559.1 mg g?1 for GACKOH, GACKP and GACH3PO4, respectively. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also evaluated from the adsorption isotherms in asphaltene solutions from toluene solutions, and it was found that the adsorption process was spontaneous and exothermic in nature. Kinetic parameters, reaction rate constant and equilibrium adsorption capacities were evaluated and correlated for each kinetic model. The results show that asphaltene adsorption is described by pseudo-second-order kinetics, suggesting that the adsorption process is chemisorption. The adsorption calorimetry was used to analyze the type of interaction between the asphaltenes and the activated carbons prepared in this work, and their values were compared with the enthalpic values obtained from the Clausius–Clapeyron equation. 相似文献
12.
Zn‐Fe layered double hydroxide with chloride intercalation (ZFCL) was synthesized by a coprecipitation method at room temperature. ZFCL was characterized by N 2 adsorption‐desorption isotherms, X‐ray diffraction, scanning electron microscope, Zeta‐sizer analyzer, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The results showed that ZFCL had large surface area and layered structure. The maximum adsorption capacity of ZFCL was 150.6 mg/g at 25°C. That was higher than most other adsorbent which were reported. The kinetic data were described better by the pseudo‐second‐order adsorption kinetic rate model. The adsorption isotherm on the adsorbent was described by Langmuir, Freundlich, and Sips models at pH 6 and followed the fitting order: Sips >Freundlich>Langmuir. Thermodynamic analyses indicated that the phosphate adsorption on ZFCL was endothermic and spontaneous in nature. The sequence of coexisting cations and anions competing with phosphate was Ca 2+ > Mg 2+ > Na + and SO 42− > NO 3− > Cl −. ZFCL can be regenerated by the sequential use of NaOH and ZnCl 2. The adsorption capacity remained high as 108.6 mg/g after regeneration of 3 times. The results of zeta potential, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy analyses indicated that the phosphate adsorption mechanisms involved ion exchange, Zn 3(PO 4) 2 precipitation, and the formation of inner‐sphere complex via replacement of surface hydroxyl groups by phosphate. 相似文献
13.
Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeO x/IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N 2 adsorption isotherms and temperature programmed reduction (TPR). Cu 2+, Co 2+, and Cr 4+/Cr 3+ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeO x/IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO 2. However, MeO x/IM catalysts had a low performance in styrene production (activity less than 15 × 10 ?3 mmol h ?1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni 2+ or Fe 3+ coordinated with the MCM-41 framework, as well as NiO x and Fe 2O 3 extra-framework species, is continuously oxidized by the CO 2 to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe 3+ species produced active sp 2 carbon compounds, which are removed by CO 2; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni 2+ and Ni 0 species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO 2 plays a role in furnishing the lattice oxygen to maintain the Fe 3+ active sites in the dehydrogenation of ethylbenzene to form styrene. 相似文献
14.
Biosorption of metal ions with Penicillium chrysogenum mycelium is described in this article. Alkaline pretreatment was used to remove proteins and nucleic acids from cells, and
this treatment increased the adsorption capacities, for Cr 3+ from 18.6 mg g −1 to 27.2 mg g −1, for Ni 2+ from 13.2 mg g −1 to 19.2 mg g −1, for Zn 2+ from 6.8 mg g −1 to 24.5 mg g −1. The adsorption of metal ions was strongly pH dependent. The mycelium could beused for large-scale removal of Cr 3+ from tannery wastewater. The results show that this inexpensive mycelium adsorbent has potential in industry because of its
high adsorption capacity. The main chelating sites are amino groups (−NH 2) of chitosan in the mycelium. A new model is established, which describes the relation of adsorption of metal ions on pH
according to amino group chelating with metal ions and H +. The relative errors of simulation for Cu 2+, Ni 2+, Zn 2+, and Cr 3+ are 4.66%, 5.45%, 11.55%, and 1.69%, respectively. 相似文献
15.
Ion-exchange experiments were conducted at 25°C between the zeolite mineral clinoptilolite and aqueous solutions of Na +/Sr 2+ (0.005, 0.05, and 0.5 N), K +/Sr 2+ (0.05 N), and K +/Ca 2+ (0.05 N). The isotherm data were used to derive equilibrium constants and Gibbs energies for the ion-exchange reactions and Margules parameters for the zeolite solid solution. The Margules model, in combination with the Pitzer equations for activity coefficients of aqueous ions, was used to predict isotherms for ion exchange involving clinoptilolite and aqueous solutions of Na +/Sr 2+, K +/Sr 2+, and K +/Ca 2+ over wide ranges of solution composition and concentration. The ion-exchange isotherms are strongly dependent on the total solution concentration. For Na +/Sr 2+ ion exchange, isotherm values at 0.005 and 0.5 N predicted using thermodynamic parameters derived from the 0.05 N data showed excellent agreement with measured values. The model was also applied to calculations of aqueous composition based on the chemistry of coexisting zeolite phases. The results show that the aqueous composition can be predicted well from the composition of the zeolite, at least for systems that involved binary (two-cation) exchange. Because the thermodynamic model can be easily extended to ternary and more complicated mixtures, it may be useful for modeling ion-exchange equilibria in multicomponent systems. 相似文献
16.
Various contents of Li +, Ni 2+ or Cu 2+ were introduced in zeolite NaA by conventional cation exchange. Crystal damages are observed on samples having suffered the lower pH. The heat of adsorption of CO 2 and C 2H 4 was determined by isothermal calorimetry. Very high initial heats (100–120 kJ mol ?1) are found in NaA as well as in Li + exchanged samples, perhaps due to chemisorption on alkaline cations; they vanish when Ni 2+ or Cu 2+ replaces more than 20% of Na +, in like manner with Co 2+ or ZnI 2+. For the adsorption of C 2H 4, high initial heats are absent in the case of NaA, but gradually appear when divalent cations are introduced. Apart from these strong initial values, the heats of adsorption present a plateau vs. the adsorbed amount. Abnormal low values at the plateau are indicative of crystal damages. 相似文献
17.
Facile synthesis of two 2-anthracene ammonium-based magnetic ionic liquids (MILs), 2-anthracene ammonium tetrachloroferrate (III) ([2A-A]FeCl 4) and 2-anthracene ammonium trichlorocobaltate (II) ([2A-A]CoCl 3) was performed by protonation of 2-aminoanthracene, followed complexation with FeCl 3/CoCl 2. The MILs were tested in the adsorptive removal of Cd 2+, As 3+, Pb 2+ and Cr 3+ from water sources. Upon treatment with 10 mg dosage of MILs in 10 mL aqueous solution of 50 ppm each of Cd 2+, As 3+, Pb 2+ and Cr 3+, adsorption capacity (mg/g) in the range of 5.73–55.5 and 23.6–56.8 for [2A-A]FeCl 4 and [2A-A]CoCl 3 respectively were recorded. Thus, the optimization, kinetic and isotherms studies were conducted using the [2A-A]CoCl 3 adsorbent. The [2A-A]CoCl 3 was more effective in pH 7–9, and equilibrium adsorption was achieved after 60 min contact time. The adsorption process proceeded via the Pseudo-second order pathway and the Langmuir isotherm model is the best fit for the adsorption process (with q max = 227 – 357 mg/g) of all the targeted metal ions. The [2A-A]CoCl 3 adsorbent demonstrated practicality with large distribution and selectivity coefficients of the targeted ions, and up to six times regeneration. 相似文献
18.
The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated
adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption
kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of
BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m 2⋅g −1 and 487 m 2⋅g −1 for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape.
For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a
Langmuir model. Adsorption equilibrium constant K
i,L
calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g −1 and more than twice as high as obtained from Henry’s law with K
i
is 26.8 mL⋅g −1. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K
i
is 17.1 mL⋅g −1. Adsorption enthalpy Δ h
Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol −1 for extrudates and −29.6 kJ⋅mol −1 for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion
rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes
faster than desorption. 相似文献
19.
Zeolite A and A + X mixtures were prepared from coal-fly ash procured from China by using an alkali fusion method. X-ray diffraction
showed that both the materials were crystalline and reproducible. Scanning Microscopy revealed that pure zeolite A particles
have cubic morphology while the mixture shows intergrowth of cubic and pyramidal crystals. The surface area for A + X mixture
was around 330 m 2/g which is higher than zeolite A, however, lower than typical X zeolite. CO 2 and N 2 adsorption isotherms were measured and the data was fitted by the Dual Site Langmuir equation. These zeolites were then tested
for CO 2 capture at different temperatures in a process with a nine step cycle. When compared with 13X zeolites at higher temperature
(∼90 °C), both the zeolite A + X mixture and zeolite A prepared from fly ash showed better performance in CO 2 capture from flue gas because they have higher selectivity of CO 2 over N 2. 相似文献
20.
Two series of zeolite X/activated carbon composites with different ratios of zeolite and activated carbon were prepared through a combination process of CO 2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution. An additional surface modification was achieved in diluted NH 4Cl solution. CO 2 and N 2 uptakes on the composites before and after modification were determined for pressures up to 101?kPa at 273 and 298?K, respectively. Langmuir-Freundlich and Toth adsorption models were used to describe the adsorption isotherms of CO 2 and the corresponding heats of adsorption were estimated with the Clausius-Clapeyron equation. Both before and after modification, all composites exhibited a remarkable preferential adsorption of CO 2 compared to N 2, with the modified composites showing a higher adsorption selectivity to CO 2 over N 2 than the unmodified composites. With an increasing ratio of zeolite in the composites, adsorption capacity and adsorption heat of CO 2 on the composites increased simultaneously. Lower adsorption heat was observed both before and after modification especially at the low-loading region and when there was less energetic heterogeneity on the surface of the modified composites. The results may be attributed to the elimination of strong basic sites on the modified composites, which is favorable for desorption of CO 2 on the adsorbents and application in pressure swing adsorption processes. 相似文献
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