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1.
In this study, cattail root was used to remove Congo Red (CR) from aqueous solution. The effects of operation variables, such as cattail root dosage, contact time, initial pH, ionic strength and temperature on the removal of CR were investigated using batch adsorption technique. Removal efficiency increased with increase of cattail root dosage and ionic strength, but decreased with increase of temperature. The equilibrium data fitted well to the Langmuir model (R2 > 0.98) and the adsorption kinetic followed the pseudo-second-order equation (R2 > 0.99). Thermodynamics parameters such as standard free energy change (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were analyzed. The values of ΔG° were between ?7.871 and ?4.702 kJ mol?1, of ΔH° was ?54.116 kJ mol?1, and of ΔS° was ?0.157 kJ mol?1 K?1, revealing that the removal of CR from aqueous solution by cattail root was a spontaneous and exothermic adsorption process. The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61 mg g?1 at 20, 30 and 40 °C, respectively. These results suggest that cattail root is a potential low-cost adsorbent for the dye removal from industrial wastewater.  相似文献   

2.
A type of ZrO2·nH2O was synthesized and its Cr(VI) removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The Cr(VI) adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model. The adsorption capacity increased from 61 to 66 mg g?1 when the temperature was increased from 298 to 338 K. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. The effective desorption of Cr(VI) on ZrO2·nH2O could be achieved using distilled water at pH 12.  相似文献   

3.
A new sensor for the determination of mercury at μg ml?1 levels is proposed based on the adsorption of mercury vapor on single-walled carbon nanotubes (SWCNTs). The changes in the impedance of SWCNTs were monitored upon adsorption of mercury vapor. The adsorption behaviour of mercury on SWCNTs was compared with that on multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs). Cold vapor of mercury was generated at 65 °C using Sn(II) solution as a reducing agent. The limit of detection was 0.64 μg ml?1 for Hg(II) species. The calibration curve for Hg(II) was linear from 1.0 to 30.0 μg ml?1. The relative standard deviation (RSD) of eight replicate analyses of 15 μg ml?1 of Hg(II) was 2.7%. The results showed no interfering effects from many foreign species and hydride forming elements. The system was successfully applied to the determination of the mercury content of different types of wastewater samples.  相似文献   

4.
Using zwitterionic hybrid polymers as adsorbent, the adsorption kinetics and isotherm, thermodynamic parameters of ΔG, ΔH and ΔS for the removal of Pb2+ from aqueous solution were investigated. It is indicated that the adsorption of Pb2+ ions on these zwitterionic hybrid polymers followed the Lagergren second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption process might be Langmuir monolayer adsorption. The negative values of ΔG and the positive values of ΔH evidence that Pb2+ adsorption on these zwitterionic hybrid polymers is spontaneous and endothermic process in nature. Moreover, the zwitterionic hybrid polymers produced reveal relatively higher desorption efficiency in 2 mol dm?3 aqueous HNO3 solution, indicating that they can be recycled in industrial processes. These findings suggest that these zwitterionic hybrid polymers are the promising adsorbents for Pb2+ removal and can be potentially applied in the separation and recovery of Pb2+ ions from the waste chemicals and contaminated water of lead-acid rechargeable battery.  相似文献   

5.
Biosorption of Pb(II) on bael leaves (Aegle marmelos) was investigated for the removal of Pb(II) from aqueous solution using different doses of adsorbent, initial pH, and contact time. The maximum Pb loading capacity of the bael leaves was 104 mg g?1 at 50 mg L?1 initial Pb(II) concentration at pH 5.1. SEM and FT-IR studies indicated that the adsorption of Pb(II) occurs inside the wall of the hollow tubes present in the bael leaves and carboxylic acid, thioester and sulphonamide groups are involved in the process. The sorption process was best described by pseudo second order kinetics. Among Freundlich and Langmuir isotherms, the latter had a better fit with the experimental data. The activation energy Ea confirmed that the nature of adsorption was physisorption. Bael leaves can selectively remove Pb(II) in the presence of other metal ions. This was demonstrated by removing Pb from the effluent of exhausted batteries.  相似文献   

6.
A large LiBaB9O15 single crystal has been grown by the top-seeded solution growth (TSSG) method using a Li2Mo3O10 flux system. The crystal obtained exhibits (1 1 0), (1 1 3) and (1 0 2) faces. For the first time, thermal properties of the as-grown crystal, including thermal expansion, specific heat and thermal conductivity, have been investigated as a function of temperature. The specific heat of the LiBaB9O15 crystal was measured to be 0.663–1.110 J g?1 K?1 over the temperature range of 20–400 °C. The crystal exhibits thermal expansion along the a- and b-axis, coupled with thermal contraction along the c-axis, over the measured temperature range of 25–500 °C. The average thermal expansion coefficients along the a- and c-axis of the LiBaB9O15 crystal from 25 to 500 °C are calculated to be αa = 6.56 × 10?6 K?1 and αc = ?4.82 × 10?6 K?1, respectively.  相似文献   

7.
Low-cycle fatigue (LCF) tests are carried out on TP347H stainless steel at a strain rate of 8 × 10−3 s−1 with total strain amplitudes (Δεt/2) of ±0.4% and ±1.0%, at room temperature (RT) and 550 °C. It is found that the stress responses and dislocation structures under cyclic loading strongly depend on the value of strain amplitude at 550 °C. Compared with those at the same strain amplitude at RT, the material shows a rapid strain softening, and finally attains a stabilized state at Δεt/2 = ±0.4% and 550 °C, but the one presents an anomalous behavior, i.e., first a rapid hardening to the maximum stress, followed by a reducing softening at Δεt/2 = ±1.0% and 550 °C. More cells resulting from dislocation cross-slip and planar structures due to dynamic strain ageing (DSA) restricting cross-slip develop at low strain amplitude of ±0.4% at the first cycle. However, there are more complicated dislocation structures, such as cells, elongated cells, walls/channels and planar structures at Δεt/2 = ±1.0%. The observations of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) exclude the effects of martensitic transformation, creep, oxidation, and precipitations on these stress responses and microstructure evolutions, which result from DSA appearing at 550 °C.  相似文献   

8.
Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol–gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol–gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4–8, but the adsorbed nickel ion could be completely eluted using 2 mol L? 1 HNO3. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g? 1 and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol? 1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (Ea) was 25.291 kJ mol? 1 for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.  相似文献   

9.
The present work is an attempt to assess the drying kinetics of green pepper in a fluidized bed in a temperature range of 65–105 °C. The drying kinetics is modeled using several semi empirical models to estimate the kinetic parameters. Although the semi empirical model could fit the experimental data well within acceptable experimental error limits, the two parameter models such as Henderson Pabis model and Page Model are identified to predict the drying kinetics with lesser error. The kinetic parameter (k) is found to increase with the temperature for all the models. The activation energy (E) estimated using Arrhenius equation is found to be 30.3 kJ/mol, while the Arrhenius constant (ko) is found to be 0.09 s?1. The effective diffusivity coefficient is evaluated using Fick’s diffusion equation which is found increase with increase in temperature of the heating medium and to vary from 1.95 × 10?11 to 7 × 10?11 m2/s.  相似文献   

10.
Untreated Pinus halepensis sawdust has been investigated as an adsorbent for the removal of cadmium from aqueous solutions. Batch experiments were carried out to investigate the effect of pH, adsorbent dose, contact time, and metal concentration on sorption efficiency. The favorable pH for maximum cadmium adsorption was at 9.0. For the investigated cadmium concentrations (1–50 mg/L), maximum adsorption rates were achieved almost in the 10–20 min of contact. An adsorbent dose of 10 g/L was optimum for almost complete cadmium removal within 30 min from a 5 mg/L cadmium solution. For all contact times, an increase in cadmium concentration resulted in decrease in the percent cadmium removal (100–87%), and an increase in adsorption capacity (0.11–5.36 mg/g). The equilibrium adsorption data were best fitted with the Freundlich isotherm (R2 = 0.960). The kinetics of cadmium adsorption was very well described by the pseudo-second-order kinetic model (R2 > 0.999).  相似文献   

11.
High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG–DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (~203 kJ mol?1 and 280 kJ mol?1) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 °C and 1800 °C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (Ea  178 kJ mol?1; n = 1) even in oxidative atmosphere.  相似文献   

12.
We present a novel way of enhancing the utility of low cost readily available laterite by impregnating it with the α-MnO2 nanorods, thus making a composite material suitable for the removal of As(V) from aqueous media. The composites were synthesized by two methods: (i) ball-milling of a physical blend of laterite with pre-synthesized MnO2; and (ii) in situ formation of MnO2 in the presence of laterite. The BET surface area of composites prepared by both methods was markedly higher compared to un-modified laterite, and the presence of MnO2 in the composite was also confirmed by XRD analysis and TEM microscopy. The adsorption capacity for As(V) was found to be highly pH dependent and the adsorption kinetics followed a pseudo second-order kinetic model. The Langmuir adsorption isotherm was found to be the best model to describe the adsorption equilibrium of As(V) onto un-modified laterite as well both ball-milled and in situ formed composite. The adsorption capacities at room temperature and pH 7.0 were found to be 1.50 mg g?1, 8.93 mg g?1 and 9.70 mg g?1, for un-modified laterite, ball-milled and in situ formed composite, respectively.  相似文献   

13.
Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m?1 K?1 associated to a coefficient of thermal expansion of 12 × 10?6 °C?1 and a density of 6.6 g cm?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λCu = 400 W m?1 K?1, αCu = 17 × 10?6 °C?1, ρCu = 8.95 g cm?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.  相似文献   

14.
The adsorption of copper ions on Spirulina platensis was studied as a function of contact time, initial metal ion concentration, and initial pH regimes. Characterization of this adsorbent was confirmed by FTIR spectrum. Modified Gompertz and Logistic models have not been previously applied for the adsorption of copper. Logistic was the best model to describe experimental kinetic data. This adsorption could be explained by the intra-particle diffusion, which was composed of more than one sorption processes. Langmuir, Freundlich, and Redlich–Peterson were fitted to equilibrium data models. According to values of error functions and correlation coefficient, the Langmuir and Redlich–Peterson models were more appropriate to describe the adsorption of copper ions on S. platensis. The monolayer maximum adsorption capacity of copper ions was determined as 67.93 mg g?1. Results indicated that this adsorbent had a great potential for removing of copper as an eco-friendly process.  相似文献   

15.
A novel optode for determination of Hg(II) ions is developed based on immobilization of a recently synthesized ionophore, 7-(1H-imidazol-1-ylmethyl)-5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10 benzodioxatriaza cyclopentadecine-3,11(4H,12H)-dione, in a PVC membrane. Dioctyl sebacate was used as a plasticizer, sodium tetraphenylborate as an anionic additive and ETH5294 as a chromoionophore. The response of the optode was based on the complexation of Hg(II) with the ionophore in the membrane phase, resulting an ion exchange process between Hg(II) in the sample solution and H+ in the membrane. The effects of pH and amounts of the ionophore, chromoionophore, ionic additive and type of plasticizer on the optode response were investigated. The selectivity of the optode was studied in the present of several cations. The optode has a linear response to Hg(II) in the range of 7.2 × 10? 13–4.7 × 10? 4 mol L? 1 with detection limit of 0.18 pmol L? 1. The optode was successfully applied to the determination of Hg(II) in real samples.  相似文献   

16.
The results of studies on influence of 6 MeV electron irradiation on avalanche breakdown voltage (Ub) and on forward voltage (UF) at different values of direct current (IF) for the Mo Schottky diodes on epitaxial silicon of n-type conductivity are presented. It was found out that the avalanche breakdown voltage of the diodes is very sensitive to electron irradiation. A decrease in Ub was observed after electron irradiation with a fluence as low as 1 × 1011 cm?2. An increase in electron irradiation fluence from 1 × 1011 cm?2 to 5 × 1014 cm?2 resulted in 30% decrease in Ub, however, further increase in electron irradiation fluence from 5 × 1014 cm?2 to 3 × 1016 cm?2 led to some increase in the avalanche breakdown voltage. Monotonic increases in UF values at different IF with the increase in electron irradiation fluence were observed starting from a fluence of 5 × 1014 cm?2. Radiation-induced changes in Ub were unstable at room temperature and a significant recovery of Ub occurred after maintaining the irradiated diodes at room temperature for 30 days. Annealing at 120 °C for 20 min resulted in the almost complete recovery of Ub. Radiation-induced changes in UF values were stable up to 300 °C. Mechanisms of the observed radiation-induced changes in the Ub and UF values and defects responsible for the changes are discussed.  相似文献   

17.
A reliable and effective method for the determination of trace molybdenum in effluents is proposed. Molybdenum (VI) is analyzed by Microwave Plasma Torch Optical Emission Spectrometry (MPT-OES) based on the adsorption collection onto microcrystalline anthracene modified with 8-hydroxyquinoline. The possible reaction mechanism was discussed in detail and the optimum conditions for adsorption of Mo (VI) were confirmed. The experimental data were fitted well with the pseudo-second-order kinetic model and Langmuir model at all studied temperatures. The calculated thermodynamic parameters (ΔG?, ΔH? and ΔS?) showed that the adsorption of molybdenum onto microcrystalline anthracene was feasible, spontaneous and endothermic at 280–320 K. The recovery of this method is in the range of 96.5%–103.3% with preconcentration factor of 100 and the limit detection after preconcentration is 0.078 μg L? 1. The proposed method has been successfully applied to the determination of trace Mo (VI) in environmental water samples with satisfactory results.  相似文献   

18.
In the present study, we report the formation of transparent glass-ceramics containing BaGdF5 nanocrystals under optimum ceramization of SiO2–BaF2–K2O–Sb2O3–GdF3–Eu2O3 based oxyfluoride glass and the energy transfer mechanisms in Eu2+  Eu3+ and Gd3+  Eu3+ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu3+ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature (Tg), the crystallization onset temperature (Tx), and crystallization peak temperature (Tp) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF5 phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5–15 nm in size. The emission transitions from the higher excited sates (5DJ, J = 1, 2, and 3) as well as lowered asymmetry ratio of the 5D0  7F2 transition (forced electric dipole transition) to that of the 5D0  7F1 transition (magnetic dipole) of Eu3+ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu3+ ions into the cubic BaGdF5 nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu2+ ions and Gd3+ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu3+ by monitoring emission at 614 nm indicated energy transfer from (Eu2+  Eu3+) and (Gd3+  Eu3+) in both glass and glass-ceramics samples.  相似文献   

19.
CO reducing strategy to control the morphologies of palladium nanocrystals was investigated. By using CO as a reducing agent, uniform and well-defined concave tetrahedral Pd nanocrystals with a mean size of about 55 ± 2 nm were readily synthesized with Pd(acac)2 as a precursor and PVP as a stabilizer. The structures of the as-prepared Pd nanocrystals were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), ultraviolet–visible (UV–vis) absorption spectroscopy and electrochemical measurements. The results demonstrated that CO was the most essential for the formation of the concave tetrahedral Pd nanostructures. The morphologies and sizes of the final products can be well controlled by adjusting the flow rate of CO. The most appropriate CO flow rate, temperature and time for the formation of the ideal concave tetrahedral Pd nanocrystals was 0.033 mL s?1, 100 °C and 3 h, respectively.  相似文献   

20.
Electrochemical and impedance experiments were carried out to evaluate the corrosion behavior of copper in aerated 0.1 mol L? 1 H2SO4 solutions in the presence of three xanthine derivatives with similar chemical structures. The corrosion rate of copper was found to increase in the presence of theophylline and theobromine and decrease in the presence of caffeine. The adsorption and inhibitory effect of caffeine on copper surfaces in aerated 0.1 mol L? 1 H2SO4 solutions were then investigated in detail by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), contact angle measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and fluorescence experiments. The data obtained indicate that caffeine behaves as a cathodic-type inhibitor adsorbing onto the copper surface according to the Temkin isotherm, with the negative ?G°ads value of ? 31.1 kJ mol? 1 signifying a spontaneous adsorption process. The corrosion inhibition efficiency increased with caffeine concentration in the range of 1.0–10.0 mmol L? 1. Furthermore, the EIS results obtained at the open-circuit potential and surface analysis (SEM, EDS and fluorescence) clearly demonstrated the adsorption of the organic compound onto the copper electrode. The contact angle measurements revealed the formation of a hydrophobic protective film. This film covers up to 72% of the total active surface, acts as a protective barrier and prevents interaction between the metal, water and oxygen molecules.  相似文献   

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