Crystal boron significantly enhances pollutants removal kinetics by Fe0/PMS system

Nano boron carbide effectively boost Fenton-like performance of hematite mediated systems: Roles of hematite exposed facets and synergistic catalysis between Fe and B

The inherent properties of exposed facets of iron minerals played key roles in heterogeneous reactions at the mineral interface, and the addition of co-catalysts has been elucidated to further enhance the reactions for contaminants degradation. Here, synergistic Fenton-like catalytic reactivity of different hematite dominant exposed facets ({001}, {012}, {100}, and {113}) with nano boron carbide (B4C) was revealed. In 5 h, as compared with the cumulative •OH in the B4C/H2O2 system (96.9 μM), while that in the {001}/B4C/H2O2 system was decreased by 19.6%, those in the {012}/B4C/H2O2, {100}/B4C/H2O2, and {113}/B4C/H2O2 systems were increased by 53.8%, 75.9%, and 84.0%, respectively. Significantly, {113}/B4C/H2O2 system exhibited strong capability for degradation of a broad spectrum of organic pollutants, including typical phenol, endocrine disruptor (bisphenol A), antibiotic (sulfanilamide), dyes (Rhodamine B and methylene blue), and pesticide (atrazine). During the Fenton-like reactions, higher synergy factor, Fe(III)/Fe(II) cycling rate, and amount of Fe-O-B bond in the {113}/B4C/H2O2 system were shown than those in other systems, thus exhibiting its desirable catalytic performance for •OH production and pollutants oxidation. Iron species and X-ray photoelectron spectroscopy (XPS) analyses indicated that B-B bond and interfacial suboxide boron (e.g., B-O) could provide electrons to facilitate Fe(III) reduction for boosting the Fe(III)/Fe(II) cycling. Density functional theory (DFT) results demonstrated the formation of Fe-O-B bond on hematite {113}, {100}, and {012} facets, which were beneficial to the breakage of O-O bond of bound H2O2 molecule and thus improved the generation of •OH. This study emphasized the essential role of B4C in developing tailored hematite facets as a contaminant remediation substrate, and provided important insights into the design of efficient heterogeneous Fenton-like systems.

Electro-enhanced metal-free peroxymonosulfate activator coupled with membrane-assisted process for simultaneous Ni-EDTA decomplexation and Ni ions recovery

Electro-enhanced metal-free boron/peroxymonosulfate (B/PMS) system has demonstrated potential for efficient metal-organic complexes degradation in an eco-friendly way. However, the efficiency and durability of the boron activator are limited by associated passivation effect. Additionally, the lack of suitable methods utilizing in-situ recovery of metal ions liberated from decomplexation causes huge resource waste. In this study, B/PMS coupled with a customized flow electrolysis membrane (FEM) system is proposed to address above challenges with Ni-EDTA used as the model contaminant. Electrolysis is confirmed to remarkably promote the activation performance of boron towards PMS to efficiently generate •OH which dominated Ni-EDTA decomplexation in the anode chamber. It is revealed that the acidification near the anode electrode improves the stability of boron by inhibiting passivation layer growth. Under optimal parameters (10 mM PMS, 0.5 g/L boron, initial pH = 2.3, current density = 68.87 A/m2), 91.8% of Ni-EDTA could be degraded in 40 min, with a kobs of 6.25 × 10-2 min-1. As the decomplexation proceeds, nickel ions are recovered in the cathode chamber with little interference from the concentration of co-existing cations. These findings provide a promising and sustainable strategy for simultaneous metal-organic complexes removal and metal resources recovery.

UV absorbance and electron donating capacity as surrogate parameters to indicate the abatement of micropollutants during the oxidation of Fe(II)/PMS and Mn(II)/NTA/PMS

In this study, the relative residual UV absorbance (UV₂₅₄) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes. In the Fe(II)/PMS process, due to the generation of SO₄^•- and •OH at acidic pH, UV₂₅₄ and EDC abatement was greater at pH 5. In the Mn(II)/NTA/PMS process, UV₂₅₄ abatement was greater at pH 7 and 9, while EDC abatement was greater at pH 5 and 7. This was attributed to the fact that MnO₂ was formed at alkaline pH to remove UV₂₅₄ by coagulation, and manganese intermediates (Mn(V)) were formed at acidic pH to remove EDC via electron transfer. Due to the strong oxidation capacity of SO₄^•-, •OH and Mn(V), the abatement of micropollutants increased with increasing dosages of oxidant in different waters in both processes. In the Fe(II)/PMS and Mn(II)/NTA/PMS processes, except for nitrobenzene (∼23% and 40%, respectively), the removal of other micropollutants was greater than 70% when the oxidant dosages were greater in different waters. The linear relationship between the relative residual UV₂₅₄, EDC and the removal of micropollutants was established in different waters, showing a one-phase or two-phase linear relationship. The differences of the slopes for one-phase linear correlation in the Fe(II)/PMS process (micropollutant-UV₂₅₄: 0.36-2.89, micropollutant-EDC: 0.26-1.75) were less than that in the Mn(II)/NTA/PMS process (micropollutant-UV₂₅₄: 0.40-13.16, micropollutant-EDC: 0.51-8.39). Overall, these results suggest that the relative residual UV₂₅₄ and EDC could truly reflect the removal of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes.

Removal of Bisphenol A via peroxymonosulfate activation over graphite carbon nitride supported NiCx nanoclusters catalyst: Synergistic oxidation of high-valent nickel-oxo species and singlet oxygen

In this work, a g-C₃N₄ supported NiCx nanoclusters catalyst (NiCx-CN) was developed, and its performance in activating peroxymonosulfate (PMS) was evaluated. Mechanism investigation stated that although singlet oxygen (¹O₂) was formed in the catalytic process, its contribution to BPA elimination was weeny. Interestingly, through the experiment with dimethyl sulfoxide as the probe, it was considered that the high-valent nickel-oxo species (Ni^&+=O), generated after the interaction of NiCx-CN and PMS, was the dominating reactive oxygen species (ROS). Theoretical calculations (DFT) implied that NiCx-CN might lose electrons to generate high-valent Ni, which was consistent with the detection of Ni³⁺ on the surface of the used NiCx-CN. Besides, the prepared NiCx-CN showed advantages in resisting the interference of inorganic anions. Meanwhile, three BPA degradation routes had been proposed based on the transformation intermediates. This study will establish a new protocol for PMS activation using heterogeneous Ni-based catalysts to efficiently degrade organic pollutants via a nonradical mechanism.