Unveiling the Dependence between Hydroxyl Radical Generation and Performance of Fenton Systems with Complexed Iron

Abstract

Humiclike substances (HLS) have been demonstrated to be useful auxiliaries to drive the (photo)-Fenton process at mild pH, by avoiding iron inactivation via formation of active complexes. However, the actual performance of the process is affected by a manifold of opposite processes. In this work, the generation of hydroxyl radical-like reactive species in the Fentonlike process has been investigated using electron paramagnetic resonance, employing 5,5-dimethyl-1-pyrroline-N-oxide as a probe molecule. The signal obtained with the Fe(II)–HLS–H2O2 system at pH = 5 was very intense but decreased with time, in line with the difficult reduction of the formed Fe(III) to Fe(II). On the contrary, the signal of the Fe(III)–HLS–H2O2 system was weak but stable. The most intense signal was observed at HLS concentration of ca. 30 mg/L. Interestingly, the performance of the Fenton system at pH = 5 to degrade caffeine followed the same trends, although caffeine removal was very low after 1 h of irradiation. The results were more evident in a solar simulated photo-Fenton process, where an increase in the abatement of caffeine was observed until an HLS concentration of 30 mg/L, where 98% removal was reached after 1 h.

Oxidative Inactivation of SARS-CoV-2 on Photoactive AgNPs@TiO2 Ceramic Tiles

“…The photocatalytic generation of • OH species to confirm the radical oxidation of the SARS-CoV-2 was checked by ESR analysis under similar solar light with UV light cut-off (400 nm) using DMPO as a trapping agent: the relevant spectra are reported in Figure 3. Unlike bare TiO 2 , the pattern of the typical signals of DMPO-• OH adduct [51] was notably detected in Ag@TiO 2 , confirming the high photonic synergism obtained in Ag-TiO 2 .…”

Humic-Like Substances as Auxiliaries to Enhance Advanced Oxidation Processes

“…This was attributed to the fact that once there is enough HLS to complex iron further addition of this substance only results in an inner filter effect or quenching of the reactive species by the excess of HLS. In fact, EPR measurements in the Fenton process in the presence of CVT230 showed a decrease in the signal attributed to ·OH in the presence of high amounts of this substance . Finally, addition of extra amounts of hydrogen peroxide is sometimes required, which might make the process unattractive under some experimental conditions …”

“…In fact, EPR measurements in the Fenton process in the presence of CVT230 showed a decrease in the signal attributed to •OH in the presence of high amounts of this substance. 35 Finally, addition of extra amounts of hydrogen peroxide is sometimes required, which might make the process unattractive under some experimental conditions. 25 A potentially interesting application of the HLS-driven photo-Fenton reaction is the treatment of scarcely soluble pollutants.…”

Enhancement of Iron-Based Photo-Driven Processes by the Presence of Catechol Moieties

“…By comparison with previous studies, similar trends have been observed when Humiclike Substances (HLS) are used as auxiliaries of the photo-Fenton reaction (Table 1). For instance, García-Ballesteros et al 2018 [18] and García-Negueroles et al 2019 [17] concluded that the degradation of caffeine (in a photo-Fenton system at pH = 5) was increased by the addition of different HLS in the range of 10-60 mg•L −1 . Moreover, Gomis et al 2014 [41], tested soluble bio-based substances (with the presence of phenolic carbon, phenoxy and carboxylic functional groups), obtaining an enhancement of the photo-Fenton reaction at pH 5.2.…”

“…Another interesting source of iron ligands are humic-like substances, which have been shown to be efficient for the enhancement of photo-Fenton processes (Table 1) [17][18][19]. Interestingly, a recent study suggests that iron chelated by humic substances is the major reservoir of Fe-complexed in oceans [20].…”