The Dependency of Kinetic Parameters as a Function of Initial Solute Concentration: New Insight from Adsorption of Dye and Heavy Metals onto Humic-Like Modified Adsorbents

Kinetics parameters are the essential issue in the design of water treatment systems for pollutants uptake. Though numerous studies have identified the boundary conditions that exert influence on the kinetics parameters, the influence of the dynamic initial solute concentration (C0) to the kinetic parameters generated from fitting kinetics model to experimental data has not been investigated thoroughly. This study revealed a change in the kinetics parameter value due to changes in the adsorption mechanism as an effect of dynamic C0. It was observed that at higher C0 the adsorbed solute at equilibrium (qe) increases and it takes longer time to reach equilibrium. As a result, the kinetics rate constant (k) calculated from adsorption reaction model (Lagergren, Ho, Santosa, and RBS) was decreased. In general, Ho model exhibit higher correlation coefficient value (R2) among the other model at low C0. At high C0, Ho’s R2 tend to decrease while the Lagergren and RBS’s R2 was increased. The amendment mechanism from external mass transport to intra-particle diffusion as a rate limiting step was evidenced by Boyd and Weber-Morris kinetics model. Further, the physicochemical properties of the adsorbent used in this work: chitin and Fe3O4 modified horse dung humic acid (HDHA-Fe3O4 and HDHA-Ch, respectively) with the solute: Pb(II), Methylene Blue (MB), and Ni(II) was deeply discussed in this paper. The outcomes of this work are of prime significance for effective and optimum design for pollutant uptake by adsorption equipment. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Production of Rosuvastatin Calcium Nanoparticles Using Gas Antisolvent Technique

The activity of pharmaceutical substances crucially depends on the bioavailability of the substances. The bioavailability of drugs in body and their rate of dissolution in the biological fluids are increased if the particle size is decreased. In the present paper, the Gas Anti-Solvent (GAS) method was used to lower the size of rosuvastatin particles. The effects of temperature (313–338 K), pressure (105–180 bar) and initial solute concentration (20–60 mg/ml) were evaluated by Response Surface Methodology (RSM). The optimum initial solute concentration, temperature and pressure were found to be 20 mg/ml, 313 K and 180 bar, respectively which resulted in the minimum particle size. Furthermore, the particles were characterized by Differential Scanning Calorimetry (DSC), Dynamic Light Scattering (DLS), Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-Ray Diffraction (XRD). The analyses showed that the rosuvastatin particles (60.3 nm) precipitated by GAS process become significantly smaller than the initial particles (45.8 µm).

Internal Flows in Microscopic Polymer Solution Droplets Evaporating on Flat Surfaces

To control the formation process of polymer thin films from polymer solution droplets using inkjet printings, internal flows of the droplets on substrates are studied. In our previous study [1], internal flow of polymer solution droplets receding on a lyophobic surface was experimentally visualized. It was found that the direction of the circulation flow in the droplet depended on the solvent and the initial solute concentration. In particular, the flow direction of polystyrene-anisole solution was reversed as the initial solute concentration increased. In this study, to clarify this reason, the conservation equations of momentum, energy and mass on two-dimensional cylindrical coordinate are numerically solved using a finite element method. The mathematical model considers the free convections derived by the dependencies of the density and surface tension on the solute concentration. As a result, the dependences of the calculated velocities on the initial solute concentration agree qualitatively with the experiments. The mathematical model predicts that double circulation flows appear after a single flow develops at high initial solute concentrations, while double circulations do not develop at low concentrations. It is concluded that the difference between the flow directions investigated experimentally is due to such a change of the flow structure. The distribution of the surface tension on the free surface is also discussed. When a local minimum of the surface tension appears on the free surface, the double circulations develop. According to the result for a low contact angle, the local minimum point shifts toward the axis of symmetry with a lapse of time, and finally erases the double circulations.

Effect of the Initial Solute Concentration on the Flow Pattern Inside an Evaporating Polymer Solution Droplet on a Substrate

The internal flow of an evaporating polymer solution droplet on a substrate is experimentally studied. The flow visualization is carried out. The effect of the initial polymer concentration is further investigated. A polystyrene-acetophenone (PS-Ap) and a polystyrene-anisole (PS-Ani) solution are employed as the droplet. A nylon powder is mixed with the droplet for the visualization by a YAG-laser sheet light. The droplet evaporates after the settlement on the substrate. Without the polymer dissolved in the solvent, complicated flow is observed in both droplets. For the cases with dissolved polymer, the flow pattern is rectified. In the PS-Ap droplet, the source flow is observed for the initial solute mass fraction c0 = 0.005 – 0.20. This convection becomes strong as c0 increases. The mechanism of the flow inside the PS-Ap droplet can be understood by the combination of the natural convection and Marangoni convection due to the differences of the temperature and the solute concentration. As for the PS-Ani droplet, the evaporation process and the flow pattern are affected by c0. For the dilute solution (0 < c0 < 0.03), the contact angle decreases during the contact line receding. The observed flow pattern becomes similar to that in the PS-Ap droplet. At c0 = 0.08 – 0.2, the decline of the contact angle is remarkable and the direction of the internal flow becomes inverse. This flow mechanism cannot be clarified, but it may have the relations with the decreasing contact angle.

Effect of Atomization Method on the Morphology of Spray-Generated Particles

Effect of various atomization methods and solute concentration on the morphology of spray dried magnesium sulphate particles is investigated. Four types of atomizers are characterized and tested including (i) a vibrating mesh nebulizer, (ii) a splash plate nozzle, (iii) an air mist atomizer, and (iv) a pressure atomizer. Several types of particle morphologies are identified in this research. Spray characteristics, such as droplet number density, droplet size, and velocity, and accompanying atomizing air have major influence on the drying and morphology of the particles. High initial solute concentrations result in the formation of thick-walled particles, and this prevents the particles to burst. It is found to be difficult to obtain fully filled magnesium sulphate particles, even for saturated solutions at room temperature because the solution equilibrium saturation changes substantially with temperature.