MnOx@N-doped carbon nanosheets derived from Mn-MOFs and g-C3N4 for peroxymonosulfate activation: Electron-rich Mn center induced by N doping

Single-atom Mn-embedded carbon nitride as highly efficient peroxymonosulfate catalyst for the harmful algal blooms control

In recent years, water quality deterioration caused by harmful algal blooms (HABs) has become one of the global drinking water safety issues, and sulfate radical driven heterogeneous advanced oxidation technology has been widely used for algae removal. However, the shortages of low active site exposure, metal leaching, and secondary contamination limit its further application. Therefore, the single-atom Mn anchored on inorganic carbon nitride was constructed to enhance the oxidation and coagulation of algal cells while maintaining cell integrity in this study. The removal efficiency of Microcystis aeruginosa was as high as 100 % within 30 min under the optimal conditions of 400 mg/L single-atom Mn-embedded g-C3N4 (SA-MCN) and 0.32 mM peroxymonosulfate (PMS). Importantly, the K+ release, malondialdehyde concentration, floccules morphology and variation of algal organic matters further showed that the algal cells still maintained high integrity without severe rupture during the catalytic reaction. Furthermore, the catalytic mechanisms of algae removal by moderate oxidation and simultaneous coagulation in this system were explored by quenching experiments, EPR analysis, theoretical calculation, and Zeta potential. In brief, this study highlighted the single-atom heterogeneous catalyst with high-efficiency and environmental-friendliness in harmful algal blooms control.

CuFeS2 supported on dendritic mesoporous silica-titania for persulfate-assisted degradation of sulfamethoxazole under visible light

Sulfamethoxazole (SMX) is a prevalent sulfonamide antibiotic found in the environment, and it has a variety of detrimental effects on environmental sustainability and water safety. Recently, the combination of photocatalysis and sulfate radical-based advanced oxidation processes (SR-AOPs) has attracted a lot of interest as a viable technique for degradation of refractory pollutants. In this study, a visible light active CuFeS2 supported on dendritic mesoporous silica-titania (CuFeS2-DMST) photocatalyst was synthesized to improve the ability of TiO2 to activate persulfate (PS) by introducing CuFeS2 (Fe2+/Fe3+, Cu+/Cu2+ redox cycles). The CuFeS2-DMST/PS/Vis system demonstrated superior SMX degradation efficiency (88.9%, 0.0146 min-1) than TiO2 because of reduced e-/h+ recombination, excellent charge separation and mobility, and a greater surface area than TiO2. Furthermore, after four consecutive photocatalytic cycles, the system demonstrated moderate stability. From chemical quenching tests, O2●-, h+, 1O2, SO4●- and ●OH were found to be the main reactive oxidizing species. The formed intermediates during the degradation process were identified, and degradation mechanisms were proposed. This study proposes a viable technique for activating PS using a low-cost, stable, and high-surface-area TiO2-based photocatalyst, and this concept can be applied to design photocatalysts for water treatment.

Starch of oat derived nanostructured Fe/Mn bimetallic carbon materials for sulfamethoxazole degradation via peroxymonosulfate activation

Fe/Mn bimetallic carbon materials were synthesized by combining oat and urea, followed by and carbonization processes, the activity and mechanism of the obtained materials in activating peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation were determined. Data suggested that the obtained material (CN@FeMn-10-800) showed the optimal performance for SMX degradation under the1:8:0.05:0.05 mass ratios of oat/urea/Fe/Mn. Around 91.2 % SMX (10 mg L-1) was removed under the conditions of 0.15 g L-1 CN@FeMn-10-800 and 0.20 g L-1 PMS. The CN@FeMn-10-800 showed great adaptability under different conditions, satisfactory activation repeatability and versatility. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that core-shell structure with rich porous of CN@FeMn-10-800 was achieved. Quenching test and electron paramagnetic resonance (EPR) indicated that surface bound oxygen and singlet oxygen (1O2) were the dominate reactive groups in this system. X-ray photoelectron spectroscopy (XPS) suggested that graphite N, Fe0, Fe3C and Mn(II) were the dominant active sites. Through the work, a simple strategy could be found to make high-value use of biomass and use it to effectively purified wastewater.

Mechanisms of interaction between metal-organic framework-based material and persulfate in degradation of organic contaminants (OCs): Activation, reactive oxygen generation, conversion, and oxidation

Metal-organic frameworks (MOFs)-based materials have been of great public interest in persulfate (PS)-based catalytic oxidation for wastewater purification, because of their excellent performance and selectiveness in organic contaminants (OCs) removal in complex water environments. The formation, fountainhead and reaction mechanism of reactive oxygen species (ROSs) in PS-based catalytic oxidation are crucial for understanding the principles of PS activation and the degradation mechanism of OCs. In the paper, we presented the quantitative structure-activity relationship (QSAR) of MOFs-based materials for PS activation, including the relationship of structure and removal efficiency, active sites and ROSs as well as OCs. In various MOFs-based materials, there are many factors will affect their performances. We discussed how various surface modification projects affected the characteristics of MOFs-based materials used in PS activation. Moreover, we revealed the process of ROSs generation by active sites and the oxidation of OCs by ROSs from the micro level. At the end of this review, we putted forward an outlook on the development trends and faced challenges of MOFs for PS-based catalytic oxidation. Generally, this review aims to clarify the formation mechanisms of ROSs via the active sites on the MOFs and the reaction mechanism between ROSs and OCs, which is helpful for reader to better understand the QSAR in various MOFs/PS systems.

Highly Efficient Copper Doping LaFeO3 Perovskite for Bisphenol A Removal by Activating Peroxymonosulfate

A series of copper doping LaFeO3 perovskite (LaCuxFe1−xO3, LCFO, x = 0.1, 0.4, 0.5, 0.6, 0.9) are successfully synthesized by the sol-gel method under mild conditions. In this study, it is applied for the activation of peroxymonosulfate (PMS) for bisphenol A (BPA) removal. More than 92.6% of BPA was degraded within 30 min at 0.7 g/L of LCFO and 10.0 mM of PMS over a wide pH range with limited leaching of copper and iron ions. The physical–chemical properties of the catalysts were demonstrated by using X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Furthermore, the effects of catalyst dosage, PMS concentration, initial pH value, and inorganic anions on the LCFO/PMS system were fully investigated. Quenching experiments were performed to verify the formation of reactive oxidant species, which showed that the radical reaction and mechanisms play a great role in the catalytic degradation of BPA. The perovskite LCFO is considered a stable, easy to synthesize, and efficient catalyst for the activation of PMS for wastewater treatment.

Thermal effect on sulfamethoxazole degradation in a trivalent copper involved peroxymonosulfate system

Persulfate (PS) activated by thermal or homogeneous metals can generate reactive oxygen species (ROS) and high-valence-state metals for contaminants degradation, showing great potential for applications. However, thermal effect in peroxymonosulfate (PMS) system with high-valence-state metal is still ambiguous. In this study, divalent copper (Cu(II)) catalysis was taken to explore thermal effect on PMS performance. Results showed that the Sulfamethoxazole (SMX) removal efficiency in the Cu(II)/PMS system at 60 min increased by only 5.9% with temperature increase from 30 °C to 60 °C. Moreover, SMX removal efficiency was excellent at neutral or basic pH, best with PMS concentration of 2.4 mM, and slightly affected by Cu(II) concentration. The singlet oxygen (¹O₂) was identified as main active species at low temperature while sulfate radicals (SO₄^-) was more effective at high temperature with Cu(II) co-activation. Also, trivalent copper (Cu(III)) was an important active species. The higher Cu(III) content, the better SMX removal efficiency, but the stronger intermediates toxicity. In combination with removal efficiency and intermediates toxicity at different temperatures, 30 °C was the optimal reaction temperature. Overall, this study provides new perspective on utilization of waste heat and high-valence-state metal for organic wastewater treatment in PMS systems.