Comparison of UV/H2O2, UV/PMS, and UV/PDS in Destruction of Different Reactivity Compounds and Formation of Bromate and Chlorate

Synergistically piezocatalytic and Fenton-like activation of H2O2 by a ferroelectric Bi12(Bi0.5Fe0.5)O19.5 catalyst to boost degradation of polyethylene terephthalate microplastic (PET-MPs)

Pollution of microplastics (MPs) has been drastically threating human health, however, whose elimination from the environment by current approaches is inefficient due to their high molecular weight, stronghydrophobicity and stable covalent bonds. Herein, we report a novel and highly-efficient route to degrade MPs contaminants through synergistically piezocatalytic and Fenton-like activation of H2O2 by a ferroelectric Bi12(Bi0.5Fe0.5)O19.5 catalyst under ultrasound treatment. For 10 g/L polyethylene terephthalate microplastics (PET-MPs), the synergistic strategy reached a 28.9 % removal rate in 72 h, which is greatly enhanced in comparison to the individual piezocatalysis and Fenton (Fenton-like) activation. By optimizing the types of oxidants (H2O2, peroxymonosulfate and peroxydisulfate) and bismuth ferrite catalysts (non-piezoelectric Bi2Fe4O9 and piezoelectric BiFeO3/Bi12(Bi0.5Fe0.5)O19.5), it was revealed that H2O2 is the best oxidant, and the piezoelectric Bi12(Bi0.5Fe0.5)O19.5 with a high aspect-ratio morphology showed higher activity than the Bi2Fe4O9 and BiFeO3. The catalyst dosage and H2O2 concentration were further optimized, and the good durability of the catalyst was also demonstrated through multiple uses. Different characterization technologies demonstrated the occurrence of PET-MPs oxidation and fragmentation during the treatment process. The plausible mechanism of synergistically piezocatalytic and Fenton-like H2O2 activation was proposed based on measurements of band structure, piezoelectric property and reactive oxygen species generation. Finally, we detected the intermediates and determined a possible degradation route of PET-MPs. The toxicity assessment indicated that the produced intermediates have low toxicity and potential risks to the environment.

Application of machine learning algorithms for the prediction of metformin removal with hydroxyl radical-based photochemical oxidation and optimization of process parameters

This study investigated the effectiveness of hydroxyl radical-based photochemical oxidation processes on metformin (METF) removal, and the experimental data were modeled by machine learning (ML) algorithms. Hydrogen peroxide (HP), sodium percarbonate (PC), and peracetic acid (PAA) were used as hydroxyl radicals sources. Modeling was conducted using ML algorithms with the integration of additional experiments. Under optimum conditions (UV/PC: pH 5, PC 6 mM, UV/HP: pH 3, HP 6 mM, UV/PAA: pH 9, PAA 6 mM), the METF removal efficiency was 74.1 %, 40.7 %, and 47.9 % with UV/PC, UV/HP, and UV/PAA, respectively. The scavenging experiments revealed that hydroxyl and singlet oxygen radicals were dominant in UV/PC and hydroxyl radicals were predominant in UV/HP and UV/PAA. Nitrate negatively affected UV/HP, UV/PC, and UV/PAA, whereas chlorine had a positive impact. The EE/O were 0.682, 1.75, and 1.41 kWh/L for UV/PC, UV/HP, and UV/PAA, respectively. The experimental results were successfully modeled by ML models with high R2 values and low MAE and RMSE values. XGBoost models effectively represent data with generalization by avoiding overfitting. Using ML algorithms to model hydroxyl radical-based photochemical oxidation processes is considered an effective and practical method for future research.

Constructing a Photocatalyst for Selective Oxidation of Benzyl Alcohol to Benzaldehyde by Photo-Fenton-like Catalysis

A photoactive metal-organic framework (MOF), [K(H₂O)][Cu(DPNDI)][Cu(DPNDI)(CH₃CN)(H₂O)] [Cu_1.5(DPNDI)_1.5H_1.5P₂W₁₈O₆₂]·2H₂O (Cu(Ι)W-DPNDI), was prepared by combining a functional photosensitizer N, N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI), copper(I) ions, and an oxidation catalyst [P₂W₁₈O₆₂]^6- into a single framework via a hydrothermal process. Cu(Ι)W-DPNDI exhibited a stable structure, strong light absorption capacity, a suitable band gap, and photoelectric properties, which provided favorable conditions for photocatalysis. In the confined space, the well-aligned Cu(I) ions and POM polyanions played a synergetic effect in the electron-transfer process and reactive oxygen species generation. By coupling photocatalysis and heterogeneous Fenton-like catalysis, Cu(Ι)W-DPNDI displayed high efficiency for the selective oxidation of aromatic alcohols, with up to >99% selectivity and 75% yield.

Comparison of ribavirin degradation in the UV/H2O2 and UV/PDS systems: Reaction mechanism, operational parameter and toxicity evaluation

Residues in surface water of ribavirin, which used extensively during the COVID-19 pandemic, have become an emerging issue due to its adverse impact on the environment and human health. UV/H2O2 and UV/peroxydisulfate (PDS) have different degradation effects on ribavirin, and the same operational parameter have different effects on the two processes. In this study, the reaction mechanism and degradation efficiency for ribavirin were studied to compare the differences under UV/H2O2 and UV/PDS processes. We calculated the total rate constants of ribavirin with HO• and SO4 •- in the liquid phase as 2.73 × 108 and 9.39 × 105 M-1s-1. The density functional theory (DFT) calculation results showed that HO• and SO4 •- react more readily with ribavirin via H-abstraction (HAA). The nitrogen-containing heterocyclic ring is difficult to undergo ring-opening degradation. The UV/PDS process was more stable and performed better than the UV/H2O2 for the ribavirin degradation when the same molar oxidant dosage was applied. HO• plays an extremely important role in the degradation of ribavirin by UV/PDS. The reason for this phenomenon is the combination of the higher yield of HO• produced in the UV/PDS process and the faster reaction rate of ribavirin with HO•. The UV/H2O2 process is more sensitive to pH than UV/PDS. Alkaline condition can significantly inhibit the ribavirin degradation. The effects of natural organic matter (NOM) and ribavirin concentration were also compared. Eventually, the toxicity prediction of the product showed that the opening-ring products were more toxic than the parent compound.

Chloride-Mediated Enhancement in Heat-Induced Activation of Peroxymonosulfate: New Reaction Pathways for Oxidizing Radical Production

This study is the first to demonstrate the capability of Cl^- to markedly accelerate organic oxidation using thermally activated peroxymonosulfate (PMS) under acidic conditions. The treatment efficiency gain allowed heat-activated PMS to surpass heat-activated peroxydisulfate (PDS). During thermal PMS activation at excess Cl^-, accelerated oxidation of 4-chlorophenol (susceptible to oxidation by hypochlorous acid (HOCl)) was observed along with significant degradation of benzoic acid and ClO₃^- occurrence, which involved oxidants with low substrate specificity. This indicated that heat facilitated HOCl formation via nucleophilic Cl^- addition to PMS and enabled free chlorine conversion into less selective oxidizing radicals. HOCl acted as a key intermediate in the major oxidant transition based on temperature-dependent variation in HOCl concentration profiles, kinetically retarded organic oxidation upon NH₄⁺ addition, and enabled rapid organic oxidation in heated PMS/HOCl mixtures. Chlorine atom that formed via the one-electron oxidation of Cl^- by the sulfate radical served as the primary oxidant and was involved in hydroxyl radical production. This was corroborated by the quenching effects of alcohols and bicarbonates, reactivity toward multiple organics, and electron paramagnetic resonance spectral features. PMS outperformed PDS in degrading benzoic acid during thermal activation operated in reverse osmosis concentrate, which was in conflict with the well-established superiority of heat-activated PDS.