Sorption equilibrium prediction of competitive adsorption of herbicides 2,4-D and MCPA from aqueous solution on activated carbon using ANN

The simultaneous adsorption of two herbicides—2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)—from their aqueous binary mixtures onto granular activated carbon was studied. The quantities adsorbed were determined by HPLC with UV detection. The experimental data were analysed using the Freundlich adsorption isotherm. The high correlation coefficients indicated that the adsorption equilibrium fitted the Freundlich isotherm well. A multilayer perceptron (MLP) (an artificial neural network model—ANN) was applied to describe the adsorption equilibrium in multicomponent systems. This enabled sorption isotherms to be predicted for all possible combinations of the two herbicides. The experimental results and the calculated data obtained from MLP for the solutions of the individual components and their mixtures suggest that MCPA is better adsorbed onto activated carbon than 2,4-D.     

Effects of dissolved metal chlorides on the behavior of silica nanoparticles in aqueous media

Effects of chlorides of univalent (LiCl, NaCl, KCl), bivalent (MgCl₂, BaCl₂) and trivalent (AlCl₃) metals at different concentration (0.001–0.1 M) on the behavior of nanosilica A-200 (0.5–5 wt.%) in aqueous media are analyzed using photon correlation spectroscopy (particle size distribution, PSD), electrophoresis (zeta potential ζ), potentiometric titration (surface charge density), and estimation of screening length of primary particles and their aggregates. The zeta potential and the PSD are affected by silica content, pH, and concentration and type of dissolved salts. Smaller but more strongly hydrated Li⁺ cations caused stronger nonlinear dependences of the zeta potential on pH and salt content than Na⁺ or K⁺. This nonlinearity is much stronger at a lower content of silica (0.5–1 wt.%) than at C _A-200 = 2.5 or 5 wt.%. At a high concentration of nanosilica (5 wt.%) the effect of K⁺ ions causes stronger diminution of the negative value of the zeta potential due to better adsorption of larger cations. Therefore, the influence of K⁺ on increasing screening length is stronger than that of Na⁺ for both primary nanoparticles and their aggregates. A similar difference in the ζ values is observed for different in size cations Ba²⁺ and Mg²⁺.      

Modeling of sorption kinetics: the pseudo-second order equation and the sorbate intraparticle diffusivity

The applicability of the pseudo-second order equation (PSOE) has been explained on the ground of the model assuming that the overall sorption rate is limited by the rate of sorbate diffusion in the pores of sorbent (intraparticle diffusion model). Mathematical expressions have been proposed in order to describe the dependence of the pseudo-second order constant on such parameters as the initial sorbate concentration, the progress of the sorption process and the solid/solution ratio. Further, it has been shown that equilibrium sorption capacities estimated by using PSOE may be much lower than the actual ones: it depends mainly on how the sorption system is close to equilibrium. The values of parameters applied in calculations were taken from the literature and correspond to the biosorption systems designed to remove the heavy metals from the aqueous solution.     

Highly excited alpha-cluster states in 34S

The elastic-scattering reaction ³⁰Si + $ \alpha$ was studied using the Thick Target Inverse Kinematics technique. Data were taken at a ³⁰Si beam energy of 150MeV in a reaction chamber filled with ⁴He gas, corresponding to the excitation region of 12-24MeV in ³⁴S . The data were treated in the framework of a simplified R -matrix approach, and energies, widths and spin assignments were obtained for 111 resonances in an approximative manner. The structure is discussed within the concept of $ \alpha$ -cluster structure in the quasi-continuum of ³⁴S and is compared to recent data for ³²S .     

Insights into the retention mechanism on an octadecylsiloxane-bonded silica stationary phase (HyPURITY C18) in reversed-phase liquid chromatography

Plots of the retention factor against mobile phase composition were used to organize a varied group of solutes into three categories according to their retention mechanism on an octadecylsiloxane-bonded silica stationary phase HyPURITY C18 with methanol-water and acetonitrile-water mobile phase compositions containing 10-70% (v/v) organic solvent. The solutes in category 1 could be fit to a general retention model, Eq. (2), and exhibited normal retention behavior for the full composition range. The solutes in category 2 exhibited normal retention behavior at high organic solvent composition with a discontinuity at low organic solvent compositions. The solutes in category 3 exhibited a pronounced step or plateau in the middle region of the retention plots with a retention mechanism similar to category 1 solutes at mobile phase compositions after the discontinuity and a different retention mechanism before the discontinuity. Selecting solutes and appropriate composition ranges from the three categories where a single retention mechanism was operative allowed modeling of the experimental retention factors using the solvation parameter model. These models were then used to predict retention factors for solutes not included in the models. The overwhelming number of residual values [log k (experimental) - log k (model predicted)] were negative and could be explained by contributions from steric repulsion, defined as the inability of the solute to insert itself fully into the stationary phase because of its bulkiness (i.e., volume and/or shape). Steric repulsion is shown to strongly depend on the mobile phase composition and was more significant for mobile phases with a low volume fraction of organic solvent in general and for mobile phases containing methanol rather than acetonitrile. For mobile phases containing less than about 20 % (v/v) organic solvent the mobile phase was unable to completely wet the stationary phase resulting in a significant change in the phase ratio and for acetonitrile (but less so methanol) changes in the solvation environment indicated by a discontinuity in the system maps.     

Neutron Structure of the Ground State of 7He

JETP Letters - A study of the neutron structure of the ground state of 7He has been performed by means of registration and analysis of the decay channels of the residual nuclei following absorption...     

Correlations in ternary fission

An experiment investigating correlations in ternary fission of²³³U induced by cold polarized neutrons was performed at the high flux reactor of the ILL in Grenoble (France). With the experimental setup, Left—Right and time reversal symmetry violating and conserving correlations between neutron spin $\hat \sigma $ , neutron momentum $\hat p_n $ , momenta of fission fragments $\hat p_f $ and ternary particles $\hat p_t $ could be investigated.