Identifying the Nonradical Mechanism in the Peroxymonosulfate Activation Process: Singlet Oxygenation Versus Mediated Electron Transfer

Abstract

Select persulfate activation processes were demonstrated to initiate oxidation not reliant on sulfate radicals, although the underlying mechanism has yet to be identified. This study explored singlet oxygenation and mediated electron transfer as plausible nonradical mechanisms for organic degradation by carbon nanotube (CNT)-activated peroxymonosulfate (PMS). The degradation of furfuryl alcohol (FFA) as a singlet oxygen (1O2) indicator and the kinetic retardation of FFA oxidation in the presence of l-histidine and azide as 1O2 quenchers apparently supported a role of 1O2 in the CNT/PMS system. However, the 1O2 scavenging effect was ascribed to a rapid PMS depletion by l-histidine and azide. A comparison of CNT/PMS and photoexcited Rose Bengal (RB) excluded the possibility of singlet oxygenation during heterogeneous persulfate activation. In contrast to the case of excited RB, solvent exchange (H2O to D2O) did not enhance FFA degradation by CNT/PMS and the pH- and substrate-dependent reactivity of CNT/PMS did not reflect the selective nature of 1O2. Alternatively, concomitant PMS reduction and trichlorophenol oxidation were achieved when PMS and trichlorophenol were physically separated in two chambers using a conductive vertically aligned CNT membrane. This result suggested that CNT-mediated electron transfer from organics to persulfate was primarily responsible for the nonradical degradative route.

Carbonaceous composite materials from calcination of azo dye-adsorbed layered doubled hydroxide with enhanced photocatalytic efficiency for removal of Ibuprofen in water

“…As depicted in Fig. 6b, involvement of L-histidine, K 2 Cr O 7 and BQ distinctly hampered efficiency and rate of photodegradation, which reflected singlet oxygen, electron and superoxide radical were dominant radicals during photocatalytic process [45][46][47] . On the contrary, addition of EDTA-2Na and BuOH showed limited inhibiting effect, revealing photo-induced holes and hydroxyl radicals' attack on Ibuprofen was relatively weak [47][48] .…”

Vertically Aligned Carbon Nanotube Membranes: Water Purification and Beyond

“…In addition, CdSe quantum dots, which are photo-excitable, were placed on a VACNT membrane, thus forming a photoelectrochemical cell, in order to demonstrate the applicability of the VACNT membrane in solar energy production ( Figure 8 b). Electrical transport occurred through the surface of the CNTs with a conductivity of 495 mS cm −1 , whereas protons were transported through the inner pores of the VACNT membrane at a current of 5.84 × 10 −6 A. Yun et al utilized a VACNT membrane as an analytical system for the reduction of peroxymonosulfate (PMS) through the oxidation of 2,4,6-trichlorophenol (TCP) [ 129 ]. As the uncapped but hydrophobic VACNT membrane blocked the transport of H 2 O molecules and reactive oxygen species, the concomitant TCP oxidation and PMS reduction through the VACNT membrane offered a method which allowed the authors to identify the non-radical mechanism present in the PMS activation process ( Figure 8 c).…”

“…The red signal corresponds to the same experiment performed as a control on a VACNT membrane without quantum dots on the surface [ 77 ]. ( c ) Simultaneous 2,4,6-trichlorophenol (TCP) oxidation and peroxymonosulfate (PMS) reduction in the reaction system partitioned into two chambers by a VACNT membrane [ 129 ].…”

Carbonaceous composite materials from calcination of azo dye-adsorbed layered doubled hydroxide with enhanced photocatalytic efficiency for removal of Ibuprofen in water

“…As depicted in Fig. 6b, involvement of L-histidine, K 2 Cr 2 O 7 and BQ distinctly hampered efficiency and rate of photodegradation, which reflected singlet oxygen, electron and superoxide radical were dominant radicals during photocatalytic process [48][49][50] . On the contrary, addition of EDTA-2Na and BuOH showed limited inhibiting effect, revealing photo-induced holes and hydroxyl radicals' attack on Ibuprofen was relatively weak [50][51] .…”