Degradation of Perfluorooctanoic Acid with Hydrated Electron by a Heterogeneous Catalytic System

Abstract

Hydrated electron (eaq –)-induced reduction protocols have bright prospects for the decomposition of recalcitrant organic pollutants. However, traditional eaq – production involves homogeneous sulfite photolysis, which has a pH-dependent reaction activity and might have potential secondary pollution risks. In this study, a heterogeneous UV/diamond catalytic system was proposed to decompose of a typical persistent organic pollutant, perfluorooctanoic acid (PFOA). In contrast to the rate constant of the advanced reduction process (ARP) of a UV/SO3 2–, the k obs of PFOA decomposition in the UV/diamond system showed only minor pH dependence, ranging from 0.01823 ± 0.0014 min–1 to 0.02208 ± 0.0013 min–1 (pH 2 to pH 11). As suggested by the electron affinity (EA) and electron configuration of the diamond catalyst, the diamond catalyst yields facile energetic photogenerated electron emission into water without a high energy barrier after photoexcitation, thus inducing eaq – production. The impact of radical scavengers, electron spin resonance (ESR), and transient absorption (TA) measurements verified the formation of eaq – in the UV/diamond system. The investigation of diamond for ejection of energetic photoelectrons into a water matrix represents a new paradigm for ARPs and would facilitate future applications of heterogeneous catalytic processes for efficient recalcitrant pollutant removal by eaq –.

Integrated Photocatalytic Reduction and Oxidation of Perfluorooctanoic Acid by Metal–Organic Frameworks: Key Insights into the Degradation Mechanisms

“…Based on the fluoride (F – ) concentration in the supernatant, the calculated overall defluorination rate (overall deF%) using eq reached 66.7%, where [F – ] is the measured fluoride ion concentration in the supernatant, [PFAS] 0 is the initial PFAS concentration, and N C–F is the total number of C–F bonds in the parent PFAS molecule. The overall deF% in this system was comparable to other e aq – -based systems. ,,, It is important to note that the reactivity of e aq - is generally higher under alkaline conditions (e.g., pH ≈ 10.0), presumably because the quenching effect of e aq – by H + to form less reactive hydrogen radical (H • , E 0 = −2.3 V NHE ) under acidic conditions becomes significant. ,,, With the use of glucose in this study, the solution pH was maintained in the range of 4.6–5.8 throughout the experiment. Although the degradation efficiency of PFOA could be compromised by the scavenging effect of H + , this pH range is closer to that of wastewater, and our results demonstrated the effectiveness of MIL-125-NH 2 at this pH range.…”

“…24,47,48,52 It is important to note that the reactivity of e aq is generally higher under alkaline conditions (e.g., pH ≈ 10.0), presumably because the quenching effect of e aq − by H + to form less reactive hydrogen radical (H • , E 0 = −2.3 V NHE ) under acidic conditions becomes significant. 26,48,53,54 With the use of glucose in this study, the solution pH was maintained in the range of 4.6−5.8 throughout the experiment. Although the degradation efficiency of PFOA could be compromised by the scavenging effect of H + , this pH range is closer to that of wastewater, and our results demonstrated the effectiveness of MIL-125-NH 2 at this pH range.…”

“…50 Notably, the presence of H + could be important in the additional reaction steps of our proposed mechanisms, which matches well with the slightly acidic pH in this experiment. Nevertheless, previous studies were mostly performed under alkaline conditions, 24,47,48,53,54 and additional efforts are needed to elucidate the thermodynamically favorable reaction mechanisms under those conditions. Overall, our results showcased the effectiveness of a photocatalytic system with integrated reductive and oxidative reactive species and provided new insights into the underlying reaction mechanisms of PFOA degradation.…”

New Indole Derivative Heterogeneous System for the Synergistic Reduction and Oxidation of Various Per-/Polyfluoroalkyl Substances: Insights into the Degradation/Defluorination Mechanism

“…26 Under acidic conditions, H + would quench e aq − to form hydrogen radicals ( • H) with relatively lower reductivity (∼ −2.3 V vs SHE). 33,47 As the DIHA system is at neutral to acidic pH conditions, it is Here, we also studied the perfluoroheptane compound (CF 3 -(CF 2 ) 5 -CF 3 ) without a charged headgroup, and it could achieve 46.5% defluorination (Figure S11), close to the F-ratio of −CF 2 -in perfluoroheptane (10/16). Therefore, hydrodefluorination on the −CF 2 -chain comprised a very important degradation/defluorination mechanism in the DIHA system, which guarantees a high degradation/defluorination rate toward various poly-/perfluorinated compounds.…”

Electronic manipulating in hydrated electron simulation of the carbon-halogen bond reductive cleavage

“…In recent years, its increasing application in per uorinated compounds treatments suggests that its reduction capacity for the strong covalent bond has begun to be noticed (Gu et al, 2017;Chen et al, 2020;Liu et al, 2022b). The reaction pathway and product identi cation were comprehensively inspected for mechanisms with many experimental techniques, e.g., electron paramagnetic resonance (Liu et al, 2022a) or comparing the kinetics over different chemical groups (Mezyk et al, 2012), or by in situ surface-enhanced Raman spectroscopy (Jiang et al, 2019). However, e − (aq) solvation structure and evolution remains enigmatic due to its short lifetime and relatively low concentration (Reitmeier et al, 2006;Siefermann et al, 2010).…”