FeOOH was synthesized by ultrasound and

The photocatalytic degradation of MO was carried out in a XPA-7 photochemical reactor (Xujiang Electromechanical Plant, Nanjing, China). The schematic diagram has been shown in previous Ref. [33]. The temperature of reaction solutions was kept at 25 ± 2 °C by cooling water circulation. A medium-pressure Hg lamp (500, 300 and 100 W) with a maximum light intensity output at 365 nm was used as an irradiation source of ultraviolet light (UV). A 500 W xenon lamp was used as light source to mimic visible light (VL) at wavelengths from 300 to 800 nm. In general, the initial pH value of suspension was adjusted to 4.5 with 0.1 M sulfuric Spermine NONOate solution and sodium hydroxide solution. The initial concentration of MO was 80 mg L−1. All prepared β-FeOOH samples were dipped in MO solution and stirred in dark for 60 min to establish adsorption/desorption equilibrium between the dye and the catalysts before illumination. At given irradiation time intervals (20 min), a small quantity (2 mL) of the suspension was taken and centrifuged to separate the catalyst particles from the suspension. The concentration of MO was determined using a UV–vis spectrophotometer (Beijing Ruili Corp., UV-9100) at 464 nm. The degradation rate of methyl orange is dermis represented by (1 − Ct/C0), where C0 and Ct are the concentration of MO solution at initial time and after irradiated at t time, respectively.