Preparation of a PANI/ZnO Composite for Efficient Photocatalytic Degradation of Acid Blue

Abstract

Polyaniline/zinc oxide (PANI/ZnO) composite photocatalysts were prepared from neutral media by in situ chemical oxidation of aniline (ANI) in the presence of different amounts of diethylene glycol (DEG). The PANI/ZnO composite photocatalysts were synthesized to efficiently remove organic dye (acid blue, AB25) from model wastewater. The PANI/ZnO composite photocatalysts were studied with the intention of efficient removal of organic dye (acid blue, AB25) from wastewater to obtain low-cost heterogeneous catalysts that offer high catalytic activity and stability. The conductive PANI polymer, which absorbs Vis irradiation, was used in this work as ZnO absorbs only ultraviolet (UV) irradiation; thus, the composite photocatalysts’ activity was broadened into the Vis region. Characterization of the composite photocatalysts was done by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, electric conductivity, UV-Vis spectroscopy, and by specific surface area (SBET) measurements. The composites’ photocatalytic activity under solar irradiation was validated by monitoring degradation of the AB25 dye. This study presented that it was possible both to prepare PANI and to prevent ZnO dissolution if in situ polymerization starts from neutral media with the addition of DEG. Additionally, efficient removal of AB25 dye, about 90% in 60 min, was achieved. The first-order rate constants of the photodegradation of AB25 by PANI/ZnO 0.02/0.024/0.04 DEG (and pure ZnO)) were computed to be 0.0272/0.0281/0.0325 (and 0.0062) min−1, indicating that the morphology and surface of the photocatalysts have significantly influenced the catalytic activity.

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.…”

“…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]).…”

“…To be precise, PANI salt should be synthesized in highly acidic conditions under which ZnO dissolves. In the previous work [10], we avoided ZnO dissolution by adding diethylene glycol (DEG). However, DEG additions also perturbed the PANI/ZnO composite's morphology.…”