Dyes Adsorption onto Fe₃O₄-Bis(trimethoxysilylpropyl)amine Composite Particles: Effects of pH and Ionic Strength on Electrostatic Interactions

Hydrophobic, electrostatic interactions, and hydrogen bonding play important roles in dyes adsorption. Solution pH and ionic strength of aqueous solutions are important factors affecting dye adsorption by influencing the aforementioned interactions. In order to understand adsorption mechanism of dye on the mesoporous particles, Fe₃O₄-bis(trimethoxysilylpropyl)amine (Fe₃O₄-TSPA) composite particles were used to adsorb methyl orange (MO), methyl blue (MB), and neutral red (NR) from aqueous solutions. Fe₃O₄-TSPA particles were found to be effective in removing acidic dyes at pH < 8.5. The adsorption amount of MB was nearly 0.047 mmol/g at pH 2. The adsorptions of MO and MB were found to be significantly influenced by electrostatic interactions. Based on the effect of NaCl on the adsorption, it was concluded that the electrostatic attraction was suppressed by high ionic strength, but suppression was less significant when electrostatic attraction was strong.