Facile synthesis of water hyacinth stem derived activated carbon modified MnO2/Fe3O4 ternary composites for efficient photocatalytic degradation of methylene blue under visible light irradiation

Abstract

Nowadays environmental pollution, most dominantly water pollution caused by numerous point and non-point sources has been at alarming stage globally. Water pollution mostly facilitated by the expansion of industrialization, population size increment, threat of climate change, and urbanization. This global challenging problem needs global solutions and one of the effective and efficient protocols is fabrication of nano-sized advanced high porous catalysts. In the current findings, manganese oxide (MnO₂)-iron oxide (Fe₃O₄) modified with activated carbon (AC), (MnO₂/Fe₃O_4/AC) ternary composite catalysts were fabricated by adding 4 %, 8 %, and 12 % w/v of AC in the presence of Water Hyacinth (WH) leaf extract. Initially, AC was produced from stem of WH via modification using K₂CO₃ and KOH. Then, different amounts of AC was mixed with MnO₂/Fe₃O₄ nanocomposites (NCs) followed by characterization using thermal gravimetry coupled with differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled energy dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM/HRTEM with SAED), Brunauer-Emmett-Teller (BET), UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS) and Fourier Transform Infrared Spectroscopy (FTIR). The synthesized materials were used as high porous catalyst for the photocatalytic degradation of methylene blue (MB) dye under visible light irradiation. Synthesized materials were thermally stable above 400 °C. The morphology of the materials were spherical in morphology and highly porous. Percent of MB degradation using MnO₂, Fe₃O_4, MnO₂/Fe₃O_4, MnO₂/Fe₃O_4/4%AC_, MnO₂/Fe₃O_4/8%AC and MnO₂/Fe₃O_4/12 %AC were 82.0 %, 78.2 %, 78.3 %, 83.8 %, 87.2 % and 75.7 %, respectively. The MnO₂/Fe₃O_4/8%AC catalyst was most efficient and effective at pH 7, catalyst dose of 4 mg, and MB dye concentration of 10 ppm as compared to counterparts due to small crystalline size, large surface area, and porous size and enhanced light absorption behavior. AC was found to improve the surface area and so enhance the degradation of ability of MnO₂/Fe₃O₄ NCs.