ab s t r ac tDiatomite and Mg(OH) 2 -modified diatomite (MMD) were employed as adsorbents for the removal of one cationic dye, Methylene Blue (MB), and two anionic dyes, Ramazol Golden Yellow (RGY) and Telon Blue (TB), from aqueous solution. Physical characteristics of the adsorbents were investigated using scanning electron microscope (SEM), energy dispersive X-rays (EDX), pH value of isoelectric point of zeta potential (pH IEP ) and Fourier transform infrared (FTIR) analyses. The Mg(OH) 2 content of MMD was found to be 13.45%, and three isoelectric points were observed around pH 2.0, 8.5 and 11.5 for MMD. The adsorption performance of dyes onto diatomite and MMD was studied using spectrophotometric analysis. It showed that the modification of diatomite enhanced removal of the anionic dyes from aqueous solution. The adsorption data were fitted to the Langmuir, Freundlich and Redlich-Peterson models. The results indicated that the Redlich-Peterson model was the best one in simulation of the adsorption isotherms, suggesting some heterogeneity in the surface or pores of the adsorbents. The adsorption of dyes onto diatomite and MMD may be attributed to electrostatic interaction, hydrogen bonding interaction, n-p interaction and Van Der Waals interaction.
Surface modification by grafting polymers on solid materials is an important strategy used to improve surface properties. This article reports that under appropriate conditions, very thin layers with desired morphologies may be constructed on a plasma-treated substrate by feeding a small quantity of a monomer with a mist stream carrying droplets produced from monomer solutions. We investigate the effects of process parameters that affect layer morphology, including exposure time to the mist stream, concentration of the monomer solution, and solvent selectivity. For a methyl methacrylate solution in ethanol, nanoparticles are uniformly grown with increasing monomer concentration or exposure time and finally form a porous layer at 3.65 mol L(-1) for 30 min. Decreasing solvent polarity not only affects surface morphology, but also increases hydrophobicity of the resulting surface. With 2,2,3,4,4,4-hexafluorobutyl methacrylate as the monomer, SEM and AFM micrographs indicated that mist polymerization results in numerous microspheres on the activated surface. These experimental results were interpreted by a mechanism in terms of an in situ polymerization accompanied by a phase transformation of the resulting polymer. Specifically, plasma treatment provides highly active cations and radicals to initiate very rapid polymerization, and the resulting polymers are consequently deposited from the liquid onto the surface under phase transition mechanisms.
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