Photocatalytic Degradation of Methylene Blue by Using ZnO/Longan Seed Activated Carbon Under Visible-Light Region

In the present study, the synthesis of zinc oxide/longan seed activated carbon material (ZnO/LSAC) and its photocatalytic activity under the visible-light region are demonstrated. The pyrolysis of the carbonized material prepared from longan seeds and zinc acetate in the alkaline medium was conducted to manufacture ZnO/LSAC. The obtained material was characterized by using X-ray diffraction, Fourier transformation-infrared spectroscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray elemental mapping observation, nitrogen adsorption/desorption isotherms, ultraviolet-diffusive reflectance spectroscopy (DRS–UV–Vis), and photoluminescence spectra. The ZnO nanoparticles with 20–30 nm in diameter are highly dispersed on the LSAC matrix. The combination of ZnO with LSAC promotes visible-light absorption. The photocatalytic activities of the prepared composite were evaluated for the degradation of methylene blue (MB) under visible-light irradiation. The kinetics and mechanism for photodegradation were addressed. The kinetic data and equilibrium data fit the modified Langmuir–Hinshelwood model. Introducing C to ZnO lattice creates an intermediate energy level and narrows the absorption energy, which results in the visible-light-driven photocatalytic activity of ZnO/LSAC. Reusability studies show that the catalyst retains its original activity even after the third cycle of reuse. Besides MB, the present catalyst could catalyze the photodegradation of other dyes, such as rhodamine B, congo red, and methyl orange.