Comparative Study for Interactions of Sulfate Radical and Hydroxyl Radical with Phenol in the Presence of Nitrite

Abstract

Sulfate radical (SO4 •–)- and hydroxyl radical (HO•)-based advanced oxidation processes (AOPs) are effective for the removal of organic pollutants in water treatment. This study compared the interactions of SO4 •– and HO• for the transformation of phenol in UV/peroxydisulfate (PDS) and UV/H2O2 with the presence of NO2 –, which is widely present in aquatic environments and transforms SO4 •– and HO• to •NO2. By using laser flash photolysis, the products of phenol reacting with SO4 •– and HO• were demonstrated to be phenoxy radical and phenol-HO-adduct radical, respectively. This result, along with density functional theory (DFT) calculations, indicate that the predominant reaction mechanisms of phenol with SO4 •– and HO• with phenol are electron transfer and addition, respectively. The different mechanisms induced the much higher formation of nitrophenols by SO4 •– than HO• in the presence of NO2 – through the fast combination of phenoxy radicals and •NO2. The conversion yields of phenol to nitrophenols (including 2-nitrophenol and 4-nitrophenol), were 47.5% by SO4 •– versus 5.3% by HO• at the experimental conditions. Increasing PDS/H2O2 dosages from 0.2 to 1 mM resulted in a 61.9% increase of nitrophenol conversion yield in UV/PDS/NO2 – but a 35.4% decrease of that in UV/H2O2/NO2 –. In addition, the significant formation of phenoxy radicals by SO4 •– also induced many nitrated polymers in UV/PDS/NO2 –, while those induced in UV/H2O2/NO2 – were negligible. The significant formation of nitrophenols and nitrated polymers increased the mutagenicity by 860.5% when the removal rate of phenol was 98% by UV/PDS/NO2 –. This is the first study to demonstrate the different mechanisms of phenol transformation by SO4 •– and HO• in the presence of NO2 –.

Trace level nitrite sensitized photolysis of the antimicrobial agents parachlormetaxylenol and chlorophene in water

“…• generates 4-chloro-2-nitrocyclohexa-2,5-dienone ( Clewley et al, 1989 ). Such dienone is known to be unstable and undergoes rearrangement with the assistance of a H 2 O molecule, resulting in the formation of nitro-derivative ( Ji et al, 2017 ;Chen et al, 2020 ) (Scheme 3 of Fig. 3 ).…”

Deciphering Evolution Pathway of Supported NO3• Enabled via Radical Transfer from •OH to Surface NO3– Functionality for Oxidative Degradation of Aqueous Contaminants

“… 19 However, NO 2 • possesses moderate E 0 (1.0 V) and small t 1/2 (1.4 μs) and therefore cannot be as efficient as NO 3 • in degrading pollutants. 21 , 22 Interestingly, NO 2 – experiences further dissection into O •– and NO • . 19 Despite having a lengthy lifetime ( t 1/2 of 10 7 μs), NO • is inactive in degrading contaminants ( E 0 of −0.4 V).…”

“…It should be noted that NO 2 – functionalities can be radicalized via the • OH → NO 2 • SUP route ( Figure 1 B) yet cannot be desirable in decomposing contaminant due to the demerits of NO 2 • stated above. 19 , 21 , 22 , 40 Nevertheless, these can suggest the merits of Mn oxides in activating • OH → NO 3 • SUP and pose the necessity to select the Mn oxide suitable to disperse Mn n + /O α species with desired properties. Mn species are multivalent in nature (Mn 2+ /Mn 3+ /Mn 4+ ) and therefore offer a variety of architectures including MnO, Mn 3 O 4 , Mn 2 O 3 , and MnO 2 , among which MnO 2 was reported to provide the largest quantities of O α and/or Mn n + species, 41 , 42 thereby being chosen herein.…”

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…As part of the so-called “brown carbon”, nitroaromatic compounds play a role in the absorption of sunlight by airborne aerosols and, by so doing, they affect to a potentially significant extent the still-debated and insufficiently defined climate feedback of the aerosols [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Another reason for the recent interest towards photonitration is the acknowledgement of the important role it may play in photochemical processes for water treatment, which are gaining increasing attention and where the occurrence of nitrate and nitrite under technical UV irradiation might favour the formation of harmful compounds [ 17 , 18 , 19 , 20 , 21 ].…”