Photoremediation of methylene blue by biosynthesized ZnO/Fe3O4 nanocomposites using Callistemon viminalis leaves aqueous extract: A comparative study

This article reports a simple, cost-effective, and eco-friendly biosynthesis of ZnO/Fe3O4 nanocomposites using Callistemon viminalis leaves' water extract. For the first time, we used a green synthetic route via C. viminalis leaves' extract to prepare ZnO/Fe3O4 nanocomposites (NCs) using zinc acetate and ferric chloride as precursor materials. Fourier transform infrared (FTIR) spectroscopic results revealed polyphenolic compounds mainly phenolic acids present in the plant extract acted as both reducing and stabilizing agents to synthesize ZnO/Fe3O4 NCs. Outcomes of XRD and X-ray photoelectron spectroscopy confirmed the formation of ZnO-Fe3O4 heterojunction in ZnO/Fe3O4 NCs, with crystallite sizes of 45, 35, and 60 nm, respectively, according to Debye-Scherrer's formula. EDX confirmed Zn, Fe, and O in the ZnO/Fe3O4 nanocomposite. Scanning electron microscopy and transmission electron microscopy (TEM) analyses revealed the existence of both ZnO and Fe3O4 in the NCs with some agglomeration. The thermal stability of NCs was evaluated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) in a nitrogen atmosphere. In addition, as-prepared ZnO/Fe3O4 NCs along with biosynthesized ZnO and Fe3O4 (prepared by C. viminalis extract) nanoparticles were examined for photodegradation of methylene blue under visible light irradiation for 150 min. The result reveals that the photodegradation efficiency of ZnO/Fe3O4 NCs (99.09%) was higher compared to that of monometallic ZnO (84.7%) and Fe3O4 (37.1%) nanoparticles.

Automated summary

This study successfully synthesized ZnO/Fe3O4 nanocomposites using Callistemon viminalis leaves' water extract, forming ZnO-Fe3O4 heterojunctions. The photodegradation efficiency of the nanocomposites in degrading methylene blue was higher compared to monometallic ZnO and Fe3O4 nanoparticles.