Degradation of diuron by persulfate activated with ferrous ion

The degradation of diuron by persulfate (S2O82−, PS) activated with ferrous ion (Fe2+) was investigated. The PS–Fe2+ system achieved high levels of reduction of diuron (90%). The optimal PS/Fe2+ molar ratio for diuron reduction was found to be 1:1. A chelating agent, sodium citrate, was used to control the amount of Fe2+ in solution for activation of the oxidant, with the optimum results obtained when the molar ratio of citrate and Fe2+ was 1:1. A reductive chemical, hydroxylamine, was also applied into the PS–Fe2+ system, and the hydroxylamine/Fe2+ molar ratio of 2:1 significantly increased the degradation of diuron due to enhancement of redox of Fe3+ to Fe2+. The main degradation product of diuron was 1-(3,4-Dichlorophenyl)-3-methylurea(DCPMU); SO4− attack did not cause the opening of the aromatic ring of diuron.

The fast stage of PS–Fe2+ system depends on the initial Fe2+ concentration, and it is the rate-limiting step. The slower stage is due to the accumulation of Fe3+ and the poor recovery of Fe2+, which is pH-dependent. There is a need to slow down the precipitation rate of iron at neutral pH to make the PS–Fe2+ system more practical for environmental remediation applications. To our knowledge, this is the first study on introducing the common reductive chemical, hydroxylamine (NH2OH), to accelerate the redox of Fe3+ to Fe2+ in PS–Fe2+ and combine the citrate and hydroxylamine together to slow down the precipitation rate of iron. The promising results demonstrate that hydroxylamine is a new and effective catalyst to improve activate reaction efficiency under neutral pH and the degradation efficiency depends upon the oxidant dose. Effect of initial Fe2+ dosage in the PS–Fe2+ system on diuron degradation. Conditions: [Diuron]0 = 0.05 mM; [PS]0 = 1.0 mM; [Fe2+]0 = 0.05–1.0 mM; initial pH = 7.0; reaction time = 240 min.Figure optionsDownload as PowerPoint slideHighlights
► The optimal dosage ratio of PS-to-Fe2+ was 1:1 and better degradation at lower pH3.
► Sodium citrate or hydroxylamine (HA) improved diuron degradation at neutral pH.
► Fe2+:citrate ratio = 1:1 was the best ratio and Fe2+:HA ratio = 1:2 was the best ratio.
► 1-(3,4-Dichlorophenyl)-3-methylurea is main degradation product by SO4− oxidation.