Synthesis and characterizations of composite based on Cu2O ZnO-polyaniline for removal of Conco Red Dye

Abstract

In this study, ternary composite photocatalyst based on copper(I) oxide (Cu2O), zinc oxide (ZnO) and polyaniline (PANI) was synthesized using a facile one-pot solvothermal method and in-situ polymerization of aniline. At the initial stage, binary composites of Cu2O were prepared with titanium dioxide (TiO2) and ZnO where the loadings of both TiO2 and ZnO precursors were varied while keeping Cu2O precursor constant (0.045 mol). Preliminary photocatalytic activity testing and further characterizations of the samples showed that the sample containing equal precursor amount of Cu2O and ZnO (CZ(0.045-0.045)) has superior properties. This sample was then used to form a ternary nanocomposite with PANI by in-situ polymerization of aniline at room temperature (Cu2O/ZnO-PANI), while studying the effects of different oxidants and aniline loading. The Cu2O/ZnO-PANI (CZP) composite was first produced using ammonium persulfate (APS), and two composite oxidants comprising of a mixture of APS and potassium dichromate (K2Cr2O7) as well as potassium permanganate (KMnO4), under the same amount of aniline monomer to select the best one among the three oxidants. Composite oxidant comprising of APS and KMnO4 (APS/KMnO4) was found to be the best, therefore, the amount of aniline monomer was then varied (0.13, 0.1, 0.05, and 0.03 mL) while using APS/KMnO4 as the oxidant to produce the rest of the CZP composites. The composite produced using 0.1 mL aniline (CZP (0.1)) was found to have the best photocatalytic activity, so it was subjected to full characterizations as well as a photocatalytic test. Meanwhile, the amount of PANI on the optimised composite was quantified using thermogravimetric analysis (TGA) and found to be about 28%. Furthermore, the photodegradation of Congo Red (CR) dye was studied as a model reaction with the optimized catalyst (CZP (0.1)). The CZP (0.1) composite demonstrated outstanding adsorption properties, increased photocatalytic activity with a percentage degradation of 100% in less than 30 minutes, enhanced stability, and reusability on CR dye under visible-light irradiation. The reusability and stability studies were conducted by repeating the CR photodegradation experiment for five cycles, in which the recovered sample after the fifth cycle was subjected to X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses to see if there was a change in its structure and stability. The result revealed no significant change in all the analyses between the unused and five times reused samples. The photodegradation process of CR was further studied using in-situ capture, total organic carbon (TOC), and high performance liquid chromatography (HPLC) analyses. In-situ capture studies revealed that the holes (h+) and superoxide radicals (•O2-) were the main active species responsible for the degradation of CR using CZP (0.1), while the hydroxyl radical (•OH) plays a secondary role in the reaction. Likewise, the TOC studies revealed a removal of 90% after 30 min. Meanwhile, HPLC analysis also confirmed the degradation of CR by CZP (0.1) and revealed the formation of some possible intermediates as evident in the TOC analysis. Finally, the electron transfer mechanism was discussed and a double Z-scheme electron transfer mechanism is proposed for the CZP (0.1) composite system according to the experimental data, sample characterization, and band theory.