Hydroxyl radical production by a heterogeneous Fenton reaction supported in insoluble tannin from bark of Pinus radiata

Efficient Removal of Sulfamethoxazole in Electro-Oxidation System with Boron-Doped Diamond Anode and Electrolyte NaCl: Degradation Mechanisms

In recent years, the pollutant sulfamethoxazole (SMX) that is widely used in medical therapy has been frequently detected in different water systems. Thereby, it is necessary to develop green and effective advanced oxidation strategies, especially the electro-oxidation process. In this study, an electro-oxidation system featuring a boron-doped diamond (BDD) anode and NaCl as the supporting electrolyte was implemented to effectively remove sulfamethoxazole (SMX) without the addition of external oxidants. The operational parameters were optimized using the response surface methodology with a pH 7.5, current density of 4.44 mA/cm2, and NaCl concentration of 20 mmol/L. The optimization significantly enhanced the degradation efficiency of SMX to obtain 100% removal in 5 min. Results of scavenging and chemical probe experiments indicated the presence of hydroxyl radicals (•OH) and chlorine radicals (Cl•), with the latter primarily forming between the reaction of Cl- and •OH. A competition experiment further revealed the relative oxidative contribution of Cl• of 38.6%, highlighting its significant role in the degradation process. Additionally, ion chromatography analysis confirmed the presence of Cl• without the formation of harmful by-products such as ClO4-, affirming the environmentally friendly nature of the system. The toxicity of the degradation by-products was also assessed. The application of current was investigated to explore the influence of coexistence ions as well as repeatability. Overall, this work highlighted the effectiveness of the electro-oxidation system for the degradation of organic pollutants in saline wastewater, demonstrating the significance of optimization of operational parameters for efficient and sustainable environmental remediation.

A Review of Gallic Acid-Mediated Fenton Processes for Degrading Emerging Pollutants and Dyes

Diverse reducing mediators have often been used to increase the degradation of emerging pollutants (EPs) and dyes through the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + HO^● + HO^-). Adding reductants can minimize the accumulation of Fe³⁺ in a solution, leading to accelerated Fe²⁺ regeneration and the enhanced generation of reactive oxygen species, such as the HO^● radical. The present study consisted in reviewing the effects of gallic acid (GA), a plant-extracted reductant, on the Fenton-based oxidation of several EPs and dyes. It was verified that the pro-oxidant effect of GA was not only reported for soluble iron salts as a catalyst (homogeneous Fenton), but also iron-containing solid materials (heterogeneous Fenton). The most common molar proportion verified in the studies was catalyst:oxidant:GA equal to 1:10-20:1. This shows that the required amount of both catalyst and GA is quite low in comparison with the oxidant, which is generally H₂O₂. Interestingly, GA has proven to be an effective mediator at pH values well above the ideal range of 2.5-3.0 for Fenton processes. This allows treatments to be carried out at the natural pH of the wastewater. The use of plant extracts or wood barks containing GA and other reductants is suggested to make GA-mediated Fenton processes easier to apply for treating real wastewater.

A Short-Term Supplementation with a Polyphenol-Rich Extract from Radiata Pine Bark Improves Fatty Acid Profiles in Finishing Lambs

The aim of this study was to evaluate the effects of a short-term supplementation with a polyphenol-rich extract from radiata pine bark (PBE) on animal performance, blood parameters, and fatty acid (FA) profiles in finishing lambs. Twenty-seven Suffolk lambs (4 months old) fed a finishing diet were randomly assigned to one of the following treatments: diet without PBE or diet supplemented with PBE on a 1 or 2% dry matter (DM) basis, for 35 d (14 d adaptation and 21 d of experimental period). Data were compared using Tukey's test and orthogonal and polynomial contrasts. The results indicated that the supplementation with PBE increased (p = 0.008) relative growth rate (RGR) and improved (p = 0.003) protein conversion (CPC), whereas weight gain, carcass characteristic, and blood parameters were unaffected (p ≥ 0.106). Total mono- and polyunsaturated FAs, conjugated linoleic acid (CLA), and vaccenic and oleic acids were linearly increased (p ≤ 0.016) by PBE supplementation. In contrast, total saturated FAs (ΣSFA), Σn-6/Σn-3 ratio, atherogenicity index (AI), thrombogenic index (TI), and the proportion of elaidic acid were linearly decreased (p ≤ 0.018). In conclusion, the supplementation with 1 or 2% DM of PBE improves subcutaneous FA profiles by increasing CLA and reducing ΣSFA, Σn-6/Σn-3 ratio, AI, and TI. Additionally, PBE supplementation has the potential to improve RGR and CPC, with unaffected intake, growth performance, blood parameters, or carcass characteristics.

Assessment of a Fenton reaction driven by insoluble tannins from pine bark in treating an emergent contaminant

Iron ligands as 1,2-dihydroxybenzenes (1,2-DHBs) have been used to increase the oxidizing ability of Fenton systems. However, these kinds of ligands become toxic quinones in the process creating an environmental problem since these compounds cannot be easily separated from a solution. To avoid this problem, in the present work, water-insoluble tannins, obtained from Pinus radiata bark, were used as a source of 1,2-DHBs to promote the oxidizing ability of the Fenton process. The developed system was tested using atrazine, as a substrate, which is a toxic and recalcitrant compound, present in different sources of water. The best reaction conditions established by the experimental design were as follows: pH of 3.6; 2.4 mmol L^-1 of H₂O₂; 150 μmol L^-1 of Fe(III); and 800 mg L^-1 of tannins. A significant increase in the efficiency of the degradation of atrazine by the heterogeneous Fenton process was observed under these conditions. The repetitive use of the insoluble tannins for Fenton-like processes showed a similar oxidizing ability and did not produce the lixiviation of phenols or other aromatic compounds. Together, the results showed that insoluble tannins could be used safely at least five times to promote the reactivity of Fenton systems.

Roles of free radicals in NO oxidation by Fenton system and the enhancement on NO oxidation and H2O2 utilization efficiency

Low H₂O₂ utilization efficiency is the main problem when Fenton system was used to oxidize NO in flue gas. To understand the behaviour of the free radicals during NO oxidation process in Fenton system is crucial to solving this problem. The oxidation capacity of [Formula: see text] and [Formula: see text] on NO in Fenton system was compared and the useless consumption path of [Formula: see text] and [Formula: see text] that caused the low utilization efficiency of H₂O₂ were studied. A method to enhance the oxidation ability and H₂O₂ utilization efficiency by adding reducing additives in Fenton system was proposed. The results showed that both of [Formula: see text] and [Formula: see text] were active substances that oxidize NO. However, the oxidation ability of [Formula: see text] radicals was stronger. The vast majority of [Formula: see text] and [Formula: see text] was consumed by rapid reaction [Formula: see text] , which was the primary reason for the low utilization efficiency of H₂O₂ in Fenton system. Hydroxylamine hydrochloride and ascorbic acid could accelerate the conversion of Fe³⁺ to Fe²⁺, thereby increase the generation rate of ·OH and decrease the generation rate of [Formula: see text]. As a result, the oxidation ability and H₂O₂ utilization efficiency were enhanced.