Research on hydrophilicity and hydrophobicity of adsorption of NOM on metal oxide/ water interface in different pH values

The hydrophobicity before and after humic acid´s adsorption on Fe₂O₃ nanoparticles in various solution conditions was investigated with FTIR spectrum and thermogravimetric analysis methods. The results showed that, when the ionic strength was kept at 0, 0.005, 0.01 and 0.05mol/kg and pH value was changed from 7 to 12, the thermal weight loss of the complex, which formed after the adsorption of nano Fe₂O₃ and the dissolved humic acid molecules, decreased at first and then increased as the pH value increased. The hydrophilicity reduced and hydrophobicity enhanced when the pH value increased from 7 to 10, while the hydrophilicity enhanced and hydrophobicity reduced when the pH value increased from 10 to 12. When the ionic strength was 0.001mol/kg, and pH value was changed from 7 to 12, the thermal weight loss of the complex decreased as the pH value increased, which provided the evidence that the hydrophilicity reduced and hydrophobicity enhanced. The FTIR spectrum results indicated that the functional groups, which played a significant role in the hydrophilicity and hydrophobicity of the complex after adsorption process of nano Fe₂O₃ and the dissolved humic acid molecules, might be hydrophilic hydroxyl-OH, carbonyl C=0 and the hydrophobic alkane CH₂.