Identifying the chloroperoxyl radical in acidified sodium chlorite solution

Area of Science:

• Analytical Chemistry
• Environmental Chemistry
• Physical Chemistry

Background:

• Acidic sodium chlorite solutions are used in water disinfection.
• The active radical species responsible for its efficacy have not been definitively identified.
• Understanding these species is crucial for optimizing water treatment processes.

Purpose of the Study:

• To identify the active radical species in acidic sodium chlorite solutions.
• To investigate the feasibility of quantifying these species using the diethylphenylenediamine (DPD) method.
• To characterize the properties of the identified radical species.

Main Methods:

• Electron spin resonance (ESR) spectroscopy was employed to detect and identify radical species.
• Quantum chemical calculations were performed to determine the stability of potential radical structures.
• UV-visible spectroscopy was used to obtain the spectrum of the identified radical.
• The diethylphenylenediamine (DPD) method was used to quantify free chlorine concentrations.

Main Results:

• A long-lived, thermodynamically stable radical species, termed the chloroperoxyl radical (Cl-O-O●), was directly observed via ESR spectroscopy.
• The observed ESR parameters did not match known chlorine or chlorine dioxide radicals.
• Quantum chemical calculations confirmed the superior stability of the chloroperoxyl radical compared to the chlorine dioxide radical.
• The chloroperoxyl radical exhibited maximum UV-visible absorbance at 354 nm, linearly correlated with ESR signal intensity.
• DPD method measurements showed a linear relationship with the 354 nm absorbance and ESR signal intensity.

Conclusions:

• The chloroperoxyl radical (Cl-O-O●) is identified as the active species in acidic sodium chlorite solutions.
• The DPD method is a feasible technique for quantifying chloroperoxyl radicals.
• This research provides a method for monitoring active species in water treatment applications.