The present study investigates the immobilization of Pb(II), Cd(II) and Ni(II) on clays (kaolinite and montmorillonite) in aqueous medium through the process of adsorption under a set of variables ...(concentration of metal ion, amount of clay, pH, time and temperature of interaction). Increasing pH favours the removal of metal ions till they are precipitated as the insoluble hydroxides. The uptake is rapid with maximum adsorption being observed within 180
min for Pb(II) and Ni(II) and 240
min for Cd(II). A number of available models like the Lagergren pseudo first-order kinetics, second-order kinetics, Elovich equation, liquid film diffusion and intra-particle diffusion are utilized to evaluate the kinetics and the mechanism of the immobilization interactions. Two isotherm equations due to Langmuir and Freundlich showed good fits with the experimental data. Kaolinite and montmorillonite have considerable Langmuir monolayer capacity with respect to Pb(II), Cd(II) and Ni(II), the values being in the range of 6.8–11.5
mg/g (kaolinite) and 21.1–31.1
mg/g (montmorillonite). The Freundlich adsorption capacity follows a similar order. The thermodynamics of the immobilization process indicates the same to be exothermic with Pb(II) and Ni(II), but endothermic with Cd(II). The interactions with Pb(II) and Ni(II) are accompanied by decrease in entropy and Gibbs energy while the endothermic immobilization of Cd(II) is supported by an increase in entropy and an appreciable decrease in Gibbs energy. The results have established good potentiality for kaolinite and montmorillonite to remove heavy metals like Pb(II), Cd(II) and Ni(II) from aqueous medium through adsorption-mediated immobilization.
Presence of dye molecules in water causes various harmful effects for both human and aquatic species. Herein, we tried to remove two cationic dyes, namely Crystal violet and Brilliant green, from ...water by kaolinite clay mineral. The kaolinite clay mineral is further treated with 0.25 M and 0.05 M H
2
SO
4
to increase its adsorption capacity. The structural changes due to acid treatment were analyzed by XRD, zeta potential, FTIR, SEM, cation exchange capacity, BET surface area, and pore volume measurements. Kinetic data were analyzed by using five different kinetic models and the data fitted best to pseudo-second-order model. Langmuir isotherm showed best fit to the adsorption of both Crystal violet and Brilliant green. Acid–treatment has slightly increased the adsorption capacities for both the dyes. The Langmuir monolayer adsorption capacity of raw kaolinite was found to be 47.17 and 25.70 mg g
−1
for Crystal violet and Brilliant green, respectively, which increased to 49.50 and 50.51 mg g
−1
for 0.25 M and 0.50 M acid-treated kaolinite in case of Crystal violet and to 26.45 and 26.88 mg g
−1
in case of Brilliant green at 303 K. Crystal violet adsorption was exothermic with increase in ∆
G
values, whereas Brilliant green adsorption was endothermic in nature with decrease in ∆
G
in the temperature range 293–323 K. Reusability study showed the adsorbents could be successfully used up to 3rd cycle without much loss of adsorption capacity.
A Vickers microhardness study has been carried out on (100) and (010) faces of solution-grown single crystals of magnesium sulphate hepta-hydrate (MgSO4·7H2O) over a load range of 10–80g. The Vickers ...hardness numbers (Hv) are found to decrease initially with increase in load and then appear to level-off. The (100) face is the softest one. The Meyer index ‘n’ of the two faces is less than 2 as expected theoretically if the particular crystal system belongs to the soft material category. Neither Kick's law nor Hays and Kendall's law can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to Li and Bradt's proportional specimen resistance (PSR) model. The elastic stiffness coefficient, c11, has also been calculated using Wooster's empirical relation from the hardness data and it shows reasonable agreement with a reported value. A hardness anisotropy for both planes has been observed in accordance with the orientation of the crystallographic planes.
An understanding of the kinetics and mechanism of the electrochemical oxidation of ethanol is of considerable interest for the optimization of the direct ethanol fuel cell. In this paper, the ...electro-oxidation of ethanol in sodium hydroxide solution has been studied over 70:30 CuNi alloy supported binary platinum electrocatalysts. These comprised mixed deposits of Pt with Ru or Mo. The electrodepositions were carried out under galvanostatic condition from a dilute suspension of polytetrafluoroethylene (PTFE) containing the respective metal salts. Characterization of the catalyst layers by scanning electron microscope (SEM)–energy dispersive X-ray (EDX) indicated that this preparation technique yields well-dispersed catalyst particles on the CuNi alloy substrate. Cyclic voltammetry, polarization study and electrochemical impedance spectroscopy were used to investigate the kinetics and mechanism of ethanol electro-oxidation over a range of NaOH and ethanol concentrations. The relevant parameters such as Tafel slope, charge transfer resistance and the reaction orders in respect of OH
− ions and ethanol were determined.
The structure and mechanical properties of the stomatopod dactyl club have been studied extensively for its extreme impact tolerance, but a systematic in situ investigation on the multiscale ...mechanical responses under high‐speed impact has not been reported. Here the full dynamic deformation and crack evolution process within projectile‐impacted dactyl using combined fast 2D X‐ray imaging and high‐resolution ex situ tomography are revealed. The results show that hydration states can lead to significantly different toughening mechanisms inside dactyl under dynamic loading. A previously unreported 3D interlocking structural design in the impact surface and impact region is reported using nano X‐ray tomography. Experimental results and dynamic finite‐element modeling suggest this unique structure plays an important role in resisting catastrophic structural damage and hindering crack propagation. This work is a contribution to understanding the key toughening strategies of biological materials and provides valuable information for biomimetic manufacturing of impact‐resistant materials in general.
Multiscale structural and mechanical characterization of stomatopod cuticle under in situ spherical projectile penetrating loadings. In this work the full dynamic crack evolutionary process and other toughening mechanisms inside the dactyl club under high‐speed impact were uncovered.
Abstract Platelet adhesion, activation and fibrinogen-mediated aggregation are primary events in vascular thrombosis and occlusion. An injectable delivery system that can carry thrombolytics ...selectively to the sites of active platelet aggregation has immense potential in minimally invasive targeted therapy of vascular occlusion. To this end we are studying liposomes surface-modified by fibrinogen-mimetic RGD motifs that can selectively target and bind integrin GPIIb–IIIa on activated platelets. Here we report liposome surface-modification with a conformationally constrained high affinity cyclic RGD motif to modulate the GPIIb–IIIa-binding capability of the liposomes. Such affinity enhancement is important for practical in vivo applications to compete with native fibrinogen towards binding GPIIb–IIIa. The platelet-binding of RGD-modified liposomes was studied by fluorescence and scanning electron microscopy, and flow cytometry, in vitro . Binding of RGD-modified liposomes was also tested in vivo in a rat carotid injury model and analyzed ex vivo by fluorescence microscopy. The results from all experiments show that cyclic RGD-liposomes bind activated platelets significantly higher compared to linear RGD-liposomes. Hence, the results establish the feasibility of modulating the platelet-targeting and binding ability of vascularly targeted liposomes by manipulating the affinity of surface-modifying ligands.
Kaolinite, montmorillonite and their poly(oxo zirconium) and tetrabutylammonium derivatives have been used in this work for removing Cd(II) from aqueous solution. Batch adsorption studies were ...carried out under various Cd(II) concentrations, amount of clay adsorbents, pH, interaction time and temperature. The uptake of the metal was initially very fast, but gradually slowed down indicating diffusion into the interior of the adsorbent particles. The adsorption processes were more akin towards second order reaction mechanism. The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir and Freundlich isotherms, which gave good fits with both isotherms. Adsorption was poor in strongly acidic solution but was improved in alkaline medium and continuously increased with rise in pH. The values of the thermodynamic parameters, Δ
H, Δ
S and Δ
G, indicated the interactions to be thermodynamically favourable.
Pb(II) adsorption was studied under different conditions (pH, time, metal ion concentration, clay amount, temperature) on kaolinite, montmorillonite, and their poly(hydroxo)zirconium (ZrO–kaolinite, ...ZrO–montmorillonite) and tetrabutylammonium (TBA–kaolinite, TBA–montmorillonite) derivatives. All samples were calcined (ZrO-derivatives at 773 K, TBA-derivatives at 973 K) before using as adsorbents. The data were interpreted assuming first- and second-order kinetics. The rate constants including the pore diffusion rate constant are reported. The adsorption data could be fitted with Freundlich and Langmuir isotherms, and the coefficients indicated favorable adsorption of Pb(II) on the clays. Determination of the thermodynamic parameters, ΔH, ΔS, and ΔG showed the adsorption to be exothermic accompanied by decrease in entropy and Gibbs energy.
Polarimetry has widespread applications within atmospheric sensing, telecommunications, biomedical imaging, and target detection. Several existing methods of imaging polarimetry trade off the ...sensor's spatial resolution for polarimetric resolution, and often have some form of spatial registration error. To mitigate these issues, we have developed a system using oriented polymer-based organic photovoltaics (OPVs) that can preferentially absorb linearly polarized light. Additionally, the OPV cells can be made semitransparent, enabling multiple detectors to be cascaded along the same optical axis. Since each device performs a partial polarization measurement of the same incident beam, high temporal resolution is maintained with the potential for inherent spatial registration. In this paper, a Mueller matrix model of the stacked OPV design is provided. Based on this model, a calibration technique is developed and presented. This calibration technique and model are validated with experimental data, taken with a cascaded three cell OPV Stokes polarimeter, capable of measuring incident linear polarization states. Our results indicate polarization measurement error of 1.2% RMS and an average absolute radiometric accuracy of 2.2% for the demonstrated polarimeter.
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