Synergetic Hydroxyl Radical Oxidation with Atomic Hydrogen Reduction Lowers the Organochlorine Conversion Barrier and Potentiates Effective Contaminant Mineralization

Abstract

For effective treatment and reuse of wastewater, removal of organochlorines is an important consideration. Oxidation or reduction of these compounds by one-component free radicals is difficult because of the high-energy barrier. Theoretical calculations predict that redox synergy can significantly lower the energy barriers. Hence, we developed an energy-efficient dual photoelectrode photoelectrochemical system wherein the oxidized and reduced radicals coexist. Taking p-chloroaniline as an example, the atomic hydrogen first initiates nucleophilic hydrodechlorination to form a critical intermediate followed by the electrophilic oxidation of the hydroxyl radical; the process shows stable free-energy changes. Compared to oxidation alone, the reaction rate and mineralization in the redox synergy system were ∼4.5 and ∼2.1 times higher, respectively. Nitrogen was also completely removed via this system. The full life cycle assessment with power consumption as the boundary showed that the proposed system was sustainable and highly energy efficient, ensuring its application in organochlorine wastewater treatment.

Electrochemical Reduction and Oxidation of Chlorinated Aromatic Compounds Enhanced by the Fe-ZSM-5 Catalyst: Kinetics and Mechanisms

“…At 30 mA/cm 2 and 0.5 g/L Fe-ZSM-5, the EC value at hour 8 (77.9% TOC removal) was 1.2 kW h (g TOC) −1 , which was higher than the value (0.74 kW h (g TOC) −1 ) at 20 mA/cm 2 (70.5% TOC removal). The EC values (<1.2 kW h (g TOC) −1 ) were much lower than those reported. , Our results are similar to the recent studies that redox synergy between H* and • OH effectively lowered energy consumption and improved the degradation of persistent refractory chlorinated organic compounds. , In addition, the reusability of catalysts is crucial for practical application. To evaluate the reusability of Fe-ZSM-5, experiments were conducted by repeatedly spiking lindane to the same solution (Figure S8), and the content of Fe in ZSM-5 decreased from 0.98 to 0.56%.…”

“… 12 , 13 Our results are similar to the recent studies that redox synergy between H* and • OH effectively lowered energy consumption and improved the degradation of persistent refractory chlorinated organic compounds. 26 , 84 In addition, the reusability of catalysts is crucial for practical application. To evaluate the reusability of Fe-ZSM-5, experiments were conducted by repeatedly spiking lindane to the same solution ( Figure S8 ), and the content of Fe in ZSM-5 decreased from 0.98 to 0.56%.…”

Incorporating Oxygen Atoms in a SnS2 Atomic Layer to Simultaneously Stabilize Atomic Hydrogen and Accelerate the Generation of Hydroxyl Radicals for Water Decontamination

“…and refractory organic contaminants (e.g., phenol, 4-nitrophenol, 4-chlorophenol, and 2,4,6-trichlorophenol), which are discharged in natural waters, pose a threat to human health and ecosystem stability. − Photoelectrocatalysis (PEC) has been considered an efficient method for the reduction of heavy metal ions and oxidation of contaminants . In terms of the PEC process, considerable progress had been made in achieving the reduction of heavy metal ions at the photocathode and oxidation of organic molecules at the photoanode based on the e – –h + pair. , The efficiency of synchronous reduction and oxidation reactions depends on the strong reducing and oxidizing active species generated in situ on the photoelectrode surface, including electrons (e – ), surface-adsorbed atomic hydrogen (H*), hydroxyl radical (•OH), super oxygen radical (•O 2 – ), and singlet oxygen ( 1 O 2 ). , …”

“…4 In terms of the PEC process, considerable progress had been made in achieving the reduction of heavy metal ions at the photocathode and oxidation of organic molecules at the photoanode based on the e − −h + pair. 5,6 The efficiency of synchronous reduction and oxidation reactions depends on the strong reducing and oxidizing active species generated in situ on the photoelectrode surface, including electrons (e − ), surface-adsorbed atomic hydrogen (H*), hydroxyl radical (•OH), super oxygen radical (•O 2 − ), and singlet oxygen ( 1 O 2 ). 7,8 The photocathode is regarded as the primary location for the reduction reaction in the PEC systems.…”

Direct Electron Transfer Coordinated by Oxygen Vacancies Boosts Selective Nitrate Reduction to N2 on a Co–CuOx Electroactive Filter

“…While the residual adsorbed H* could not be directly captured by DMPO, the ESR characterization is still expected to be capable of assessing the total yield with regard to the rapid surface–interface equilibrium of H*. , Figure S24 shows that the peak intensity of DMPO-H for Co–CuO x is significantly weaker than those for CuO x and Co 3 O 4 –CuO, suggesting the less contribution of H* to nitrate reduction on Co–CuO x . We then conducted the scavenger-quenching experiments to investigate the effect of tertiary butanol (TBA), that is, a reported scavenger of H*, on nitrate reduction. As expected, the percentage removal of nitrate showed a relatively small decline after the introduction of TBA (Figure S25).…”