Degradation of methyl orange in water using RPB-prepared iron nanoparticles and persulfate

A rotating packed bed (RPB) with blade-packing and the liquid-phase reductive precipitation means were utilized to prepare iron nanoparticles. Methyl orange (MO) in water was degraded using the RPB-prepared iron nanoparticles as an activator of persulfate. The degradation of MO in the RPB-prepared iron nanoparticles/persulfate process was greatly fitted by the pseudo-first-order kinetics. The higher initial rate of degradation of MO was associated with lower pH, a larger dose of iron nanoparticles, or a higher sodium persulfate concentration. More MO was degraded at lower pH or a higher sodium persulfate concentration. Increasing the dose of iron nanoparticles from 0.007 g/L to 0.056 g/L enhanced the degree of degradation of MO in 20 min but further increasing the dose of iron nanoparticles to 0.112 g/L reduce the degree of degradation of MO in 20 min. According to radical quenching tests at pH 3, SO₄•⁻ contributed more than HO• to the degradation of MO in the RPB-prepared iron nanoparticle/persulfate process. At 25°C, pH 3, a dose of RPB-prepared iron nanoparticles of 0.028 g/L, a sodium persulfate concentration of 0.24 g/L, and an initial MO concentration of 10 mg/L, the degree of degradation of MO in 20 min was 93%, which markedly exceeded that (47%) achieved using iron nanoparticles that were prepared using a batch reactor with persulfate under the same operating conditions. Therefore, RPB-prepared iron nanoparticles with persulfate effectively degrade MO in water.