Prompting direct single electron transfer to produce non-radical 1O2/H* by electro-activating peroxydisulfate process with core-shell cathode

Intensive investigation of the synergistic effects between electrocatalysis and peroxymonosulfate activation for efficient organic elimination

Hybrid systems combined eletrocatalysis and Fenton-like process attract a lot of attention due their outstanding performance and unique mechanism. Here, we proposed an efficient, cost-effective, and versatile electrochemical activation (ECA) system for efficient water purification, and intensively studied the synergistic effects between electrocatalysis and peroxymonosulfate (PMS)-based advanced oxidation. The ECA system achieved complete removal of 20 ppm tetracycline hydrochloride (TCH) in 15 min, with a rate constant of 0.338 min-1. Its performance was assessed across various operational parameters (PMS dosage, pH, applied voltage, electrode interval, temperature, co-existed ions, biomass, different oxidants), demonstrating its broad applicability and stability. Excellent degradation and mineralization for other 12 kinds of refractory organic pollutants were also achieved. The outstanding performance can be attributed to the synergistic effect in the system, in which electrocatalytic reduction of dissolved oxygen generated H2O2 and O2•-, boosting the number of reactive species, such as 1O2, by interacting with PMS. Furthermore, the presence of organic matter promotes electron transfer, amplifying the system's degradation capability. These findings not only highlight the ECA system's effectiveness in organic pollutant removal but also offer insights into the underlying degradation mechanisms, paving the way for future advancements in water purification technologies.

Insight into radical-nonradical coupling activation pathways of peroxymonosulfate by CuxO for antibiotics degradation

In this work, a heterogeneous catalyst of Cu_xO was rationally designed by using Cu-based metal organic frameworks (marked Cu-BDC) as the template, and was used to degrade tetracycline (TC) via activation of peroxymonosulfate (PMS). The optimal Cu_xO-350 showed excellent catalytic efficiency for TC degradation, and the reaction rate constant (0.104 min^-1) was 8 times higher than that (0.013 min^-1) of raw Cu-BDC. The characterization observations confirmed that Cu_xO-350 possessed multiple valence states (CuO and Cu₂O) and oxygen vacancies (O_v), both of which were favorable for the activation of PMS, resulting in promoting the generation of active species in the Cu_xO-350 + PMS system. Different from the free radical pathway in Cu-BDC + PMS system, a radical-nonradical coupling process was detected in the Cu_xO-350 + PMS system, which was confirmed by quenching experiments and EPR measurements. Moreover, the toxicity prediction showed that the toxicity of degradation intermediates declined compared with TC. This work not only opened up a new strategy for the rational design and preparation of high-efficient catalysts by employing metal organic frameworks precursors, but also offered an insight into the reaction mechanism of PMS activation through a radical-nonradical coupling process catalyzed by Cu_xO-350 derived from Cu-BDC.

Atomic Hydrogen in Electrocatalytic Systems: Generation, Identification, and Environmental Applications

Electrochemical reduction has emerged as a viable technology for the removal of a variety of organic contaminants from water. Atomic hydrogen (H*) is the primary species generated in electrochemical reduction processes. In this work, identification and quantification for H* are reviewed with a focus on methods used to generate H* at different positions. Additionally, we present recently developed proposals for the surface chemistry mechanisms of H* on the most commonly used cathodes as well as the use of H* in standard electrochemical reactors. The proposed reaction pathways in different H* systems for environmental applications are also discussed in detail. As shown in this review, the key hurdles facing H* reduction technologies are related to i) the establishment of systematic and practical synthetic methods; ii) the development of effective identification approaches with high specificity; and, iii) an in-depth exploration of the H* reaction mechanism to better understand the reaction process of H*.

In-situ fabrication of ionic liquids/MIL-68(In)-NH2 photocatalyst for improving visible-light photocatalytic degradation of doxycycline hydrochloride

Metal-organic framework (MOFs)-based composites have been popular in photocatalysis due to their outstanding physicochemical properties, such as large surface area, high activity and good transmission properties. Herein, a method of ionic liquids (ILs)-assisted synthesis of IL/MIL-68(In)-NH₂ composite materials were proposed, and composites were used for visible light catalytic degradation of doxycycline hydrochloride (DOXH). The effects of four kinds of ionic liquids on the structure and photocatalytic properties of the composites were explored, including diethylenetriamine acetate ([DETA][OAc]), diethylenetriamine hexafluorophosphate ([DETA][PF₆]), 1-ethyl-3-methylimidazole acetate ([EMIM][OAc]) and 1-ethyl-3-methylimidazole hexafluorophosphate ([EMIM][PF₆]). The results show that the introduction of different ionic liquids affects the grain growth of MOFs material and photocatalytic activity. Among them, IL_DAc/MIL-68(In)-NH₂ samples showed the highest photocatalytic activity. 92% removal rate of doxycycline hydrochloride and kinetic degradation constant (0.00918 min^-1) was observed under the optimal addition of IL_DAc (10 wt%), which was 4.6 times that of MIL-68(In)-NH₂. The enhancement was attributed to a combined effect of efficient adsorption at low concentration, an increase of active sites, and efficient charge transfer. In addition, the effects of pH and initial concentration were investigated. Finally, the photocatalytic mechanism of DOXH was elucidated, and the possible intermediate products and degradation pathways were discussed. Considering the excellent photostability and ultra-fast photodegradation of IL_DAc/MIL-68(In)-NH₂, this study opens up a new prospect for the preparation of ionic liquids functionalized MOFs with wide practical application value.

Electro-activating non-radical 1O2/H* via single atom manganese modified cathode: The indispensable role of metal active site Mn

As an alternative to noble-metal Pt based catalysts, metal-based single atomic catalytic (SACs) exhibited excellent atom efficiency and catalytic activity via exposing abundant single atomic active centers. Here, we synthesized the monatomic Mn ligands anchored on porous N, P, S- co-doped carbon framework (Mn content over 4.5 wt%) (denoted as Mn-SAC@PZS). The single atomic Mn exhibited super mass activity (11.58 m² g^-1) and kinetic current (1.122×10³ µA) with a much lower Tafel slope (4.25 mV dec^-1) at 0.792 V (vs. SCE). XANES and EXAFS revealed that the mononuclear Mn were inclined to coordinate with N and S rather than P to form the R space of Mn, in which the first coordination shells backscattered with Mn-N and Mn-S. RRDE revealed that one-electron ORR pathway (72 ~ 100%) dominated at the potential of 0.5 ~ 0.7 V, oxygen molecule was absorbed/activated on site Mn* to form O* intermediate, then further activated to ¹O₂ via one-electron ORR pathway, while H* was electro activated by non-metallic active sites (i.e. pyri-N, sp-N, -PN and SO). In addition, the Mn-SAC@PZS was capable of highly selectively capturing and effectively degrading CIP in the presence of HA. Fast and complete removal of CIP was achieved within 30 min in the Mn-SAC@PZS-EFLP system, and the apparent rate constant (k) was up to 0.25 min^-1. The energy consumption value was 0.453 kWh m^-3, much lower than non-single atomic catalyst MnxOy@PZS (0.655 kWh m^-3), which was comparable with the state-of-the-art advanced oxidation processes. These findings provided new insights into the maximum release of the atomic activity of the catalyst, and provides a possible way to selectively remove aromatics from multiple pollutants in complex water system.