Stability and Synergistic Effect of Polyaniline/TiO2 Photocatalysts in Degradation of Azo Dye in Wastewater

Abstract

The polyaniline/TiO2 (PANI/TiO2) composite photocatalysts were prepared by the in situ chemical oxidation of aniline (An) in the presence of TiO2 particles. For this purpose, photocatalysts with different amounts of PANI polymer were prepared and analysed. Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis indicated successful synthesis of the PANI polymer and its conductivity was also determined. The micrographs of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to explain the impact of the aniline amount on the aggregation process during the synthesis of the composites. The smallest size of aggregates was obtained for the photocatalysts with 15% of PANI (15PANI/TiO2) due to the formation of homogenous PANI. The photocatalytic activity of studied PANI/TiO2 photocatalysts was validated by monitoring the discoloration and mineralization of Reactive Red azo dye (RR45) in wastewater. The 15PANI/TiO2 sample presented the highest photocatalytic efficiency under ultraviolet A (UVA) irradiation, in comparison to pure TiO2. This was explained by the formation of uniformly dispersed PANI on the TiO2 particles, which was responsible for the synergistic PANI-TiO2 effect.

The Impact of In Situ Polymerization Conditions on the Structures and Properties of PANI/ZnO-Based Multiphase Composite Photocatalysts

“…The PANI/ZnO weight loss was monitored from 25 to 600 °C (Figure 3). According to Figure 3, there are three distinguishing temperature regions that occur frequently when investigating PANI/ZnO (and TiO2 [11,33]) composites [10]. The first temperature region (0-120 °C), i.e., the first maximum, can be attributed to the water removal, which is expected, as several papers reported ingress of water during PANI oxidation [29,34] and water incorporated in zinc salts.…”

“…To be precise, exposure of PANI/ZnO to the solar irradiation produces radicals that degrade the dye (Scheme 1), but they also could degrade PANI in the composites. However, in our previous work [11], we used TG to analyze the PANI-based photocatalyst composite and we showed that the radicals (obtained during solar treatment) did not degrade PANI in the composite. This specific property of PANI-based photocatalyst composite was assigned to the high chemical stability of PANI; and thus, this kind of test was not conducted in this work.…”

“…Thermogravimetric (TG) analysis is a very suitable technique to examine the amount and stability of PANI in the prepared PANI/ZnO composites (see, e.g., [10,11]). In order to obtain a more detailed insight, TG measurements were conducted in a nitrogen atmosphere.…”

“…The photocatalytic efficiency of ZnO and PANI/ZnO catalyst samples (1 g/L) was evaluated by monitoring the concentration of AB 25 dye (30 mg/L) in water during simulated solar irradiation. The AB 25 concentration value used here is the one which is routinely employed in this kind of investigation; and thus, we have continuously applied it in our studies [10,11]. The whole procedure was described in detail when PANI/ZnO and PANI/TiO 2 composite photocatalysts were investigated [10,11].…”

“…ZnO photocatalytic properties are hindered by relatively high bandgap energy (≈> 3 eV). Scheme was adapted from [10] (also see [11,12]).…”