Removal of methylene blue by Polyaniline/TiO ₂ hydrate: Adsorption kinetic, isotherm and mechanism studies

Polyaniline/TiO ₂ (PANI/TiO ₂ ), as a promising adsorbent, was synthesized and applied in the adsorption of methylene blue (MB) to evaluate the adsorption performance of PANI/TiO ₂ for cationic dye. The effects of dosage, pH, temperature and ionic strength on the adsorption efficiency were investigated in details. The adsorption isotherm and kinetic studies were conducted and the results revealed that the adsorption of MB on PANI/TiO ₂ was mainly controlled by chemical adsorption, membrane diffusion and intraparticle diffusion. The maximum adsorption capacity was 458.10 mg/g. HCl solution (0.1 mol/L) was used as stripping agent to study the regeneration stability of PANI/TiO ₂ , and the adsorption efficiency can be maintained over 99% after 10 cycles. The N ₂ adsorption-desorption and Fourier Transform Infrared Spectroscopy of PANI/TiO ₂ before and after adsorption were compared and analyzed to obtain the information of adsorption mechanisms. The adsorption of MB by TiO ₂ mainly occurred on the surface hydroxyl and carboxyl groups, and was mainly heterogeneous multilayer physisorption. However, the adsorption of MB on PANI part occurred mainly on amino groups by hydrogen bonding and electrostatic interaction, and on benzene ring by π-π stacking and hydrophobic interaction, and was assigned to heterogeneous multilayer chemical adsorption by comparing the theoretical monolayer adsorption capacity and the actual adsorption capacity. After composition, PANI and TiO ₂ cooperated in the adsorption process of MB and exhibited their respective advantages. The PANI/TiO ₂ was an excellent adsorbent for organic cation dyes and was expected to be a kind of universal adsorbent for multiple pollutants.