The overestimated role of singlet oxygen for pollutants degradation in some non-photochemical systems

Enhanced Oxidation of Organic Contaminants by Iron(II)-Activated Periodate: The Significance of High-Valent Iron–Oxo Species

“…Beyond expectation, a distinct signal of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO, g = 2.0006, α N = 17.1 G) was also detected using TEMP as the spin trapping agent (Figure d), which seemed to suggest the non-negligible role of 1 O 2 in the Fe­(II)/PI process (the weak TEMPO signal observed in TEMP control might be ascribed to the minor impurity in commercial TEMP). However, the degradation of SMX, 2,4,6-TCP (Figure S16), or PMSO (Figure S17) was not promoted in D 2 O, which was contradictory to the results of ESR spectroscopy, given that transferring an 1 O 2 -involved system into D 2 O would remarkably enhance organic oxidation due to the extended lifetime of 1 O 2 in D 2 O (22–70 μs) than that in H 2 O (2.9–4.6 μs). , As a matter of fact, the role of 1 O 2 in organic degradation is still quite controversial. , It has been documented that reactive species could oxidize TEMP to TEMP · + via direct electron transfer, followed by the deprotonation and O 2 addition that leads to the false detection of 1 O 2 (Figure S18), which well explained the phenomenon that the detected TEMPO signal was significantly suppressed under a N 2 atmosphere (Figure d). Moreover, by exploiting the characteristic phosphorescence emission of 1 O 2 at ∼1270 nm, , 1 O 2 was successfully identified in the H 2 O 2 /NaClO process in which the generation of 1 O 2 is widely accepted , but failed to be detected in the Fe­(II)/PI process (Figure S19).…”

“…50,51 As a matter of fact, the role of 1 O 2 in organic degradation is still quite controversial. 5,52 It has been documented that reactive species could oxidize TEMP to TEMP •+ via direct electron transfer, followed by the deprotonation and O 2 addition that leads to the false detection of 1 O 2 (Figure S18), 53 which well explained the phenomenon that the detected TEMPO signal was significantly suppressed under a N 2 atmosphere (Figure 4d). Moreover, by exploiting the characteristic phosphorescence emission of 1 O 2 at ∼1270 nm, 54,55 1 O 2 was successfully identified in the H 2 O 2 /NaClO process in which the generation of 1 O 2 is widely accepted 56,57 but failed to be detected in the Fe(II)/PI process (Figure S19).…”

Oxygen Vacancy-Induced Nonradical Degradation of Organics: Critical Trigger of Oxygen (O2) in the Fe–Co LDH/Peroxymonosulfate System

“…However, the catalytic mechanism of Vo for activating PMS remains ambiguous. The recent reports commonly reveal that the Vo-containing catalyst-induced PMS activation is mainly attributed to 1 O 2 and SO 4 •– / • OH, and 1 O 2 is claimed to play the dominant role, , while some studies have identified that 1 O 2 could not be the main reactive species for organics removal in neutral condition. , Nevertheless, Hu’s group recently proposed that the 1 O 2 was the side production formed from the decomposition of PMS by Vo, and made negligible contributions for organics removal in Vo/PMS system. It is still unclear why non-selective SO 4 •– / • OH formed but showed selective degradation of organics .…”

“…•− / • OH, and 1 O 2 is claimed to play the dominant role, 3,7 while some studies have identified that 1 O 2 could not be the main reactive species for organics removal in neutral condition. 13,14 Nevertheless, Hu's group recently proposed that the 1 O 2 was the side production formed from the decomposition of PMS by Vo, and made negligible contributions for organics removal in Vo/PMS system. It is still unclear why non-selective SO 4…”

Boosting the singlet oxygen production from H2O2 activation with highly dispersed Co–N-graphene for pollutant removal

“…Because quenching of 1 O 2 is solvent-dependent, it was reported that the rate constant is 16 times slower in D 2 O ( k D2O , 1.6 × 10 4 s −1 ) than in H 2 O ( k H 2 O , 2.5 × 10 5 s −1 ). 7 Since the fast quenching of 1 O 2 was decisive for the overall reaction, 40 the reaction rate constant of MB with 1 O 2 in a D 2 O and H 2 O mixed solvent ( k obs, mi x ) follows the equation below : 41 where k obs,H 2 O is the reaction rate constant of MB with 1 O 2 in H 2 O, and x H 2 O and x D2O are the molar proportions of H 2 O and D 2 O in the mixed solvent. In this study, 50% H 2 O was replaced by D 2 O, and a comparative kinetic study was carried out.…”