Magnetically recoverable β-Ni(OH)2/γ-Fe2O3/NiFe-LDH composites; isotherm, thermodynamic and kinetic studies of synthetic dye adsorption and photocatalytic activity

Abstract NiFe layered double hydroxides were prepared by co-precipitation from nickel(II) nitrate hexahydrate and iron(III) nitrate nonahydrate at a pH range from 8 to 12 and subsequent hydrothermal treatment at 150 °C for 24 h. The X-ray diffraction patterns revealed that β-Ni(OH)2 and γ-Fe2O3 co-existed with a NiFe-layered double hydroxide, when prepared at pH 10, 11 and 12. The absorption band at 565 nm of the products prepared at pH 10–12 was observed together with the increase of the saturated magnetization from 0.96 emu·g−1 for NiFe-layered double hydroxide prepared at pH 8 to 12.99 emu·g−1 for NiFe-layered double hydroxide prepared at pH 12, corresponding to the formation of γ-Fe2O3. The layered double hydroxide samples possessed high adsorption capacities of Congo Red (98.6–142.4 mg·g−1) and Rhodamine 6G (46.1–97.0 mg·g−1). The adsorption of both dyes followed a Langmuir isotherm and the processes were endothermic for Congo Red and exothermic for Rhodamine 6G removals. Among the tested samples, NiFe-layered double hydroxide prepared at pH 11 exhibited the best photocatalytic degradation for Congo Red (removal of 91.1%, 10 ppm) and Rhodamine 6G (removal of 90.7%, 10 ppm) under the visible light irradiation for 5 h. According to high specific surface area (72 m2·g−1), magnetic property and stability, the β-Ni(OH)2/γ-Fe2O3/NiFe-layered double hydroxide composite could be reused as an efficient adsorbent and a photocatalyst that easily collected from the reaction.