UV-induced synthesis of polyaniline (PANI)-TiO2 composites : mechanistic insight and application as sorbent for wastewater remediation

In recent years, the application of PANI-based materials to pollutant abatement has been proposed owing to PANI environmental stability and excellent sorption capabilities1. However, conventional synthetic procedures of PANI-materials are based on toxic reagents and generate hazardous by-products and large amounts of inorganic waste. As an alternative to conventional PANI oxidative syntheses, we recently developed a green procedure starting from benign reactants ((N-(4-aminophenyl)aniline and H2O2) and initiated by light-irradiated titanium dioxide2. In order to unlock the full potential of this synthetic approach, we studied the relative roles of the oxide semiconductor and of H2O2 in this two step synthetic approach. Composites were synthesized by varying the TiO2 : H2O2 : aniline dimer molar ratios and were characterized from the compositional, structural, morphological, optical, and thermal point of view. Moreover, the reaction mechanism was investigated via a combination of spectroscopic and spectrometric techniques. We found that the first step is driven by TiO2 and UV irradiation and leads to the formation of oligomers at the oxide surface, promoting a higher polymer crystallinity in the final composite. The polymer chain growth requires the addition of H2O2 and the added amount has a crucial role on the reaction pathway. While stoichiometric H2O2 amounts promote the growth of oligomer chains adsorbed at the oxide surface, giving rise to highly porous, large surface area composites, an excess of H2O2 promotes homogenous phase reactions, leading to composites with higher PANI content and thermal stability, but more amorphous and with compact morphology. The composite properties can thus be tailored depending on the desired application. We tested the prepared composites towards the removal of wastewater pollutants, including both organic dyes and heavy metals. A fast and complete pollutant removal was achieved also in the presence of interferents. Consecutive tests with and without regeneration treatments showed promising results in terms of repeated usability, even in simulated drinking water matrix. References 1. C. Della Pina, M. A. De Gregorio, L. Clerici, P. Dellavedova, E. Falletta, J. Hazard. Mater. 2018, 344, 1 2. C. Cionti, C. Della Pina, D. Meroni, E. Falletta S. Ardizzone Chem. Commun. 2018, 54, 10702.