Activation of Periodate by Freezing for the Degradation of Aqueous Organic Pollutants

Abstract

A new strategy (i.e., freezing) for the activation of IO for the degradation of aqueous organic pollutants was developed and investigated. Although the degradation of furfuryl alcohol (FFA) by IO was negligible in water at 25 °C, it proceeded rapidly during freezing at -20 °C. The rapid degradation of FFA during freezing should be ascribed to the freeze concentration effect that provides a favorable site (i.e., liquid brine) for the proton-coupled degradation process by concentrating IO, FFA, and protons. The maximum absorption wavelength of cresol red (CR) was changed from 434 nm (monoprotonated CR) to 518 nm (diprotonated CR) after freezing, which confirms that the pH of the aqueous IO solution decreases by freezing. The degradation experiments with varying experimental parameters demonstrate that the degradation rate increases with increasing IO concentration and decreasing pH and freezing temperature. The application of the IO/freezing system is not restricted to FFA. The degradation of four other organic pollutants (i.e., tryptophan, phenol, 4-chlorophenol, and bisphenol A) by IO, which was negligible in water, proceeded during freezing. In addition, freezing significantly enhanced the IO-mediated degradation of cimetidine. The outdoor experiments performed on a cold winter night show that the IO/freezing system for water treatment can be operated without external electrical energy.

Unexpected bias of freeze-drying on the performance assessment of chemical oxidation of soils contaminated by polychlorinated biphenyls

“…As previously mentioned in Materials & Methods section, and to improve the freeze-drying process, the treated soil was rapidly pre-frozen in liquid nitrogen for 2 minutes and then transferred in freeze-dryer. In this case, the eutectic point is quickly reached and smaller ice crystals are expected to form (Choi 2018;. That also may stop the oxidation reaction in the soil containing oxidant during the kinetic assessment without adding a new chemical reagent in soil (Tang 2015;Rybnikova 2016).…”

“…To test how the freezing impacts the degradation extent, we perform oxidation tests in soil at -20 °C (a freezing temperature typically used in literature (Choi 2018;Jeong 2015;; Kim 2017; Min 2017)), and compare with those determined at room temperature (20°C) for the same reaction time (24 h). This freezing temperature (-20 °C) was also chosen because it is above the eutectic point of oxidant solution (supposed here as around -50 °C, as for a H 2 O 2 solution (Foley 1951; kim 2015)).…”

“…A further modification, which may occur during the freezing process, is pH change (Choi 2018). As the soil has an alkaline pH, an increase of OHconcentration with the freezing concentration effect may take place.…”

“…In the case of ferrate, a pH increase may affect the molecular speciation of ferrate(VI). At high pH, the dominant ferrate(VI) form is FeO 4 2-, which is the most stable species (Choi 2018;Sharma 2013;Sharma 2015). Figure 2.…”

“…The freezing effect is often associated to reactions, which occur in the cryosphere such as in upper stratosphere or polar regions (snowpack, freezing fogs, snowflakes) (O'Concubhair 2013). Several studies have already highlighted the effect of freezing to explain the oxidation of nitrites into nitrate in the permafrost or in polar regions Sun 2017;Takenaka 1992), the dissolution of iron oxides in atmospheric mineral dust (Jeong 2012;Jeong 2015), the reduction of chromate and A c c e p t e d M a n u s c r i p t bromate in frozen solution by organic compound as electron donor Kim 2011;Min 2017), or the activation of periodate in frozen solution for enhanced degradation of organic contaminants (Choi 2018). However, the freezing effect has never been investigated in the context of soil remediation where freezedrying is commonly used in the preparation of soil samples (Monfort 2019;Tang 2015;Rybnikova 2016).…”