Improving the photocatalytic activity of polyaniline and a porphyrin via oxidation to obtain a salt and a charge-transfer complex

Abstract

Environmental problems caused by organic dyes have led to the development of efficient methods for their treatment. Photocatalytic degradation has proved to be a viable technique to decompose these pollutants into less dangerous compounds. In this study, the photocatalytic activity of a polyaniline salt and a porphyrin was improved by preparing a hybrid of both components, i.e., a polyaniline-sulfate-5,10,15,20-tetrakis(4-hydroxy phenyl)-21H,23H porphine salt (PANI–H₂SO₄–TKHP). This salt was synthesized by a chemical oxidative polymerization pathway and used as a photocatalyst for the degradation of RhB dye. The formation of this salt was confirmed by FT-IR, XRD and UV-vis spectroscopy. Oxidation of aniline in the presence of TKHP by ammonium persulfate results in the formation of both the polyaniline salt (PANI–H₂SO₄–TKHP) and a charge-transfer complex between PANI and TKHP via π–π stacking. PANI–H₂SO₄–TKHP was observed in a nanotube morphology (which was confirmed by SEM and TEM) with a reasonably good yield (88 wt%), conductivity (1.2 ohm⁻¹ cm⁻¹) and thermal stability (200 °C). The photocatalytic performance of PANI–H₂SO₄–TKHP was compared with its individual components of PANI–H₂SO₄ and TKHP under visible light irradiation. PANI–H₂SO₄–TKHP exhibited an effective photocatalytic activity (78% dye degradation), and a plausible mechanism for photocatalytic degradation was proposed in terms of the HOMO and LUMO levels of the components.