Free radical destruction of beta-blockers in aqueous solution

Oxidation and mineralization rates of harmful organic chemicals in hydroxyl radical induced reactions

In most of advanced oxidation processes (AOPs) used to destroy harmful organic chemicals in water/wastewater hydroxyl radical (•OH) reactions oxidize (increasing the oxygen/carbon ratio in the molecules) and mineralize (transforming them to inorganic molecules, H2O, CO2, etc.) these contaminants. In this paper, we used the radiolysis of water to produce •OH and characterised the rate of oxidation and mineralization by the dose dependences of the Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) content values. Analysis of the dose dependences for 34 harmful organic compounds showed large differences in the oxidation and mineralization rates and these parameters are characteristic to the given group of chemicals. E.g., the rate of oxidation is relatively low for fluoroquinolone antibiotics; it is high for β-blocker medicines. Mineralization rates are low for both fluoroquinolones and β-blockers. The one-electron-oxidant •OH in most cases induces two - four-electron-oxidations. Most of the degradation takes place gradually, through several stable molecule intermediates. However, based on the results it is likely, that some part of the oxidation and mineralization takes place parallel. The organic radicals formed in •OH reactions react with several O2 molecules and release several inorganic fragments during the radical life cycle.

Insights into the efficient mineralization of antibiotic trimethoprim in aqueous media by Fe2+ catalytically enhanced vacuum-UV irradiation: Kinetics, mechanisms, and toxicity evaluation

The widespread existence of antibiotics in the environment has attracted growing concerns regarding the potential adverse effects on aquatic organisms, ecosystems, and human health even at low concentrations. Extensive efforts have been devoted to developing new methods for effective elimination of antibiotics from wastewater. Herein, a novel process of Fe2+ catalytically enhanced vacuum ultraviolet (VUV) irradiation was proposed as a promising approach for the removal of antibiotic trimethoprim (TMP) in water. Compared with UVC photolysis, VUV photolysis, and UVC/Fe2+, VUV/Fe2+ could increase the pseudo-first-order reaction rate constant of TMP removal by 6.6-38.4 times and the mineralization rate by 36.5%-59.9%. The excellent performance might originate from the synergistic effect of VUV and Fe2+, i.e., VUV irradiation could effectively split water and largely accelerate the Fe3+/Fe2+ cycle to generate more reactive oxygen species (ROS). EPR results indicated that •OH and O2•- were identified as the main ROS in the UVC/Fe2+ and VUV/Fe2+ processes, while •OH, O2•-, and 1O2 were involved in the VUV process. The operating parameters, such as Fe2+ dosage and initial TMP contents, were evaluated and optimized. Up to 8 aromatic intermediates derived from hydroxylation, demethylation, carbonylation, and methylene group cleavage were identified by UPLC-QTOF-MS/MS technique, the possible pathways of TMP degradation were proposed. Finally, the acute and chronic toxicity of intermediates formed during TMP degradation in the VUV/Fe2+ process were also evaluated.

Quantitative structure-activity relationships for the reaction kinetics of trace organic contaminants with one-electron oxidants

Understanding the reactivity between trace organic contaminants (TrOCs) and radicals involved in advanced oxidation processes (AOPs) is necessary for a good process design, but the experimentally determined rate constants (k values) are not sufficient for numerous artificial TrOCs. Thus, the development of quantitative structure-activity relationships (QSARs) for predicting k values may be an effective way to address this limitation. In this work, we developed QSARs for the reactions of TrOCs with AOP-related one-electron oxidants. Specifically, 15 QSARs using Hammett constants and 8 cross-correlations were developed based on the k values of over 400 reactions between TrOCs (most contain electron-rich moieties, such as phenol, aniline, and alkoxy benzene) and 5 one-electron oxidants (SO4˙-, Br˙, Br2˙-, Cl2˙-, and CO3˙-). Overall, the developed QSARs show a good predictive performance with 94% (237/251, for Hammett constant-based QSARs) and 80% (218/274, for cross-correlations) of the k values predicted within a factor of 3. All the Hammett constant-based QSARs show negative slope values and all cross-correlations show positive relationships, suggesting all 5 one-electron oxidants mainly share similar electrophilic mechanisms with the TrOCs highlighted in this work. Previous QSAR studies on the k values of one-electron oxidants were compared and integrated into their model analysis. Furthermore, k values predicted herein from the QSARs were used to evaluate the degradation of TrOCs during UV/persulfate and UV/chlorine treatment in multiple wastewater matrices, which were demonstrated to be useful. Finally, remarks on the use of the developed QSARs were presented.

Implementation of laser flash photolysis for radical-induced reactions and environmental implications

Confronted with the imperative crisis of water quality deterioration, the pursuit of state-of-the-art decontamination technologies for a sustainable future never stops. Fitting into the framework of suitability, advanced oxidation processes have been demonstrated as powerful technologies to produce highly reactive radicals for the degradation of toxic and refractory contaminants. Therefore, investigations on their radical-induced degradation have been the subject of scientistic and engineering interests for decades. To better understand the transient nature of these radical species and rapid degradation processes, laser flash photolysis (LFP) has been considered as a viable and powerful technique due to its high temporal resolution and rapid response. Although a number of studies exploited LFP for one (or one class of) specific reaction(s), reactions of many possible contaminants with radicals are largely unknown. Therefore, there is a pressing need to critically review its implementation for kinetic quantification and mechanism elucidation. Within this context, we introduce the development process and milestones of LFP with emphasis on compositions and operation principles. We then compare the specificity and suitability of different spectral modes for monitoring radicals and their decay kinetics. Radicals with high environmental relevance, namely hydroxyl radical, sulfate radical, and reactive chlorine species, are selected, and we discuss their generation, detection, and implications within the frame of LFP. Finally, we highlight remaining challenges and future perspectives. This review aims to advance our understandings of the implementation of LFP in radical-induced transient processes, and yield new insights for extrapolating this pump-probe technique to make significant strides in environmental implications.

Where should Fenton go for the degradation of refractory organic contaminants in wastewater?

Fenton process has become a research hotspot due to the nonselective and efficient degradation of dissolved organic matter (DOM) by ·OH. However, there are still many challenges and bottlenecks for conventional Fenton (CF). This study provides the first comprehensive insight into the mechanisms of DOM degradation by the Fenton process, including the various subcategories of humic substances, emerging trace contaminants, including persistent organic pollutants, endocrine disrupting chemicals, and pharmaceuticals and personal care products, and the interference of humus and low molecular weight organic acids on the removal of trace contaminants. In addition, a statistical comparison of the economics of CF and three types of Fenton-like technologies (Photo-Fenton, Electro-Fenton, and Ultrasonic-Fenton) is conducted based on existing studies, which can be used as a reference for engineering applications. Moreover, a brief overview of the categories and characteristics of heterogeneous Fenton, which have been extensively studied in recent years, and a comparison of their catalysts are presented. In the end, the paper advances a possible future research direction.

Effects of the Water Matrix on the Degradation of Micropollutants by a Photocatalytic Ceramic Membrane

The consumption of pharmaceuticals has increased the presence of micropollutants (MPs) in the environment. The removal and degradation of pharmaceutical mixtures in different water matrices are thus of significant importance. The photocatalytic degradation of four micropollutants-diclofenac (DCF), iopamidol (INN), methylene blue (MB), and metoprolol (MTP)-have been analyzed in this study by using a photocatalytic ceramic membrane. We experimentally analyzed the degradation rate by using several water matrices by changing the feed composition of micropollutants in the mixture (from mg· L-1 to μg·L-1), adding different concentrations of inorganic compounds (NaHCO₃ and NaCl), and by using tap water. A maximum degradation of 97% for DCF and MTP, and 85% for INN was observed in a micropollutants (MPs) mixture in tap water at environmentally relevant feed concentrations [1-6 μg·L-1]o; and 86% for MB in an MPs mixture [1-3 mg·L-1]o with 100 mg·L-1 of NaCl. This work provides further insights into the applicability of photocatalytic membranes and illustrates the importance of the water matrix to the photocatalytic degradation of micropollutants.

Interaction of peracetic acid with chromium(III): Understanding degradation of coexisting organic pollutants in water

Peracetic acid (PAA, CH₃C(O)OOH) has gained significant attention for its use in wastewater disinfection. Wastewater usually contains both metal ions and organic pollutants and understanding reactions after adding PAA to such contaminated water is needed. This paper presents results regarding the effect of interactions between chromium(III) (Cr(III)) and PAA on the degradation of selected pharmaceuticals, mainly trimethoprim (TMP). The degradation of pharmaceuticals by PAA, PAA-Cr(III), and H₂O₂-Cr(III) under different conditions was examined (pH = 6.0-10.0 and molar ratios of PAA to Cr(III)). The degradation rate of TMP by PAA-Cr(III) was greater than by PAA and H₂O₂-Cr(III) under alkaline conditions. Degradation studies using quenching agents and probing molecules, and spectroscopic measurements (UV-visible and electron paramagnetic resonance) suggest ^•OH as the major radical species and Cr(IV)/Cr(V) as additional reactive species. The oxidized products of TMP by PAA-Cr(III) were identified and possible pathways proposed. Degradation of other pharmaceuticals having different molecular structures by PAA-Cr(III) and H₂O₂-Cr(III) systems were also investigated. Most of the pharmaceuticals degraded at faster rates by PAA-Cr(III) and H₂O₂-Cr(III) than by PAA alone, suggesting that co-present metal ions may play a significant role in PAA oxidation in water treatment.

Photocatalytic performance of heterojunction S-Tyr-NDI-Tyr/TiO2 formed by self-assembled naphthalimide derivatives and titanium dioxide

In this paper, a type of heterojunction photocatalyst S-Tyr-NDI-Tyr/TiO₂ was prepared by self-assembly of tyrosine-substituted naphthamide (NDA) and bonding with titanium dioxide. The self-assembly process and driving force of monomer M-Tyr-NDI-Tyr were simulated by theoretical calculation. Taking atenolol as the target pollutant, the photocatalytic performance of the heterojunction photocatalyst under visible light was studied, and the degradation products were analyzed by mass spectrometry. The environmental toxicity of photocatalytic process was evaluated by luminescent bacteria. The principle of high photocatalytic activity of S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst was proposed by analyzing the fluorescence spectrum, photocurrent density and resistance, electron paramagnetic resonance spectrum, free radical capture experiment and energy band position of S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst. In addition, the photocatalytic degradation of different pollutants by S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst was also studied. This work will provide a useful example for the further development of new and efficient organic supramolecular/inorganic semiconductor composite photocatalysts.

Oxidative Degradation of Pharmaceutical Waste, Theophylline, from Natural Environment

The elimination of organic contaminants from natural resources is extremely important to ensure their (re-)usability. In this report, the degradation of a model pharmaceutical compound, theophylline, is compared between natural and laboratory-controlled environments. While the concentration of H2O2 variably affected the degradation efficiency (approximately from 8 to 20 min for complete degradation) in the photo-irradiation experiments, the inorganic compounds (NaNO3, KH2PO4 and ZnSO4) present in the medium seemed to affect the degradation by scavenging hydroxyl radicals (•OH). The end-product studies using high-resolution mass spectrometry (HRMS) ruled out the involvement of secondary radicals in the degradation mechanism. The quantitative calculation with the help of authentic standards pointed out the predominant role of hydroxylation pathways, especially in the initial stages. Although a noticeable decline in the degradation efficiency was observed in river water samples (complete degradation after 25 min with an approximately 20% total organic carbon (TOC) removal), appreciable TOC removal (70%) was eventually achieved after prolonged irradiation (1 h) and in the presence of additional H2O2 (5 times), revealing the potential of our technique. The results furnished in this report could be considered as a preliminary step for the construction of •OH-based wastewater treatment methodologies for the remediation of toxic pollutants from the real environment.

A novel Sm doped Cr2O3 sesquioxide-decorated MWCNTs heterostructured Fenton-like with sonophotocatalytic activities under visible light irradiation

Novel Sm doped Cr₂O₃ decorated MWCNTs nanocomposite photocatalyst was successfully prepared by a facile hydrothermal method for metoprolol (MET) degradation. A heterogeneous photo -Fenton like system was formed with the addition of H₂O₂ for ultrasonic irradiation (US), visible light irradiation (Vis) and dual irradiation (US/Vis) systems. The intrinsic characteristics of Sm doped Cr₂O₃ decorated MWCNTs nanocomposite was comprehensively performed using state-of-art characterization tools. Optical studies confirmed that Sm doping shifted the absorbance of Cr₂O₃ towards the visible-light region, further enhanced by MWCNTs incorporation. In this study, degradation of metoprolol (MET) was investigated in the presence of Cr₂O₃ nanoparticles, Sm doped Cr₂O₃ and Sm doped Cr₂O₃ decorated MWCNTs nanocomposites using sonocatalysis and photocatalysis and simultaneously. Several different experimental parameters, including irradiation time, H₂O₂ concentration, catalyst amount, initial concentration, and pH value, were optimized. The remarkably enhanced sonophotocatalytic activity of Sm doped Cr₂O₃ decorated MWCNTs could be attributed to the more formation of reactive radicals and the excellent electronical property of Sm doping and MWCNTs. The rate constant of degradation using sonophotocatalytic system was even higher than the sum of rates of individual systems due to its synergistic performance based on the kinetic data. A plausible mechanism for the degradation of MET over Sm-Cr₂O₃/MWCNTs is also demonstrated by using active species scavenger studies and EPR spectroscopy. Our findings imply that (^•OH), (h⁺) and (^•O₂^-) were the reactive species responsible for the degradation of MET based on the special three-way Fenton-like mechanism and the dissociation of H₂O₂. The durability and stability of the nanocomposite were also performed, and the obtained results revealed that the catalysts can endure the harsh sonophotocatalytic conditions even after fifth cycles. Mineralization experiments using the optimized parameters were evaluated as well. The kinetics and the reaction mechanism with the possible reasons for the synergistic effect were presented. Identification of degraded intermediates also investigated.

Evaluation of advanced oxidation processes for β-blockers degradation: a review

This study summarizes the results of scientific investigations on the removal of the three most often used β-blockers (atenolol, metoprolol and propranolol) by various advanced oxidation processes (AOP). The free radical chemistry, rate constants, degradation mechanism and elimination effectiveness of these compounds are discussed together with the technical details of experiments. In most AOP the degradation is predominantly initiated by hydroxyl radicals. In sulfate radical anion-based oxidation processes (SROP) both hydroxyl radicals and sulfate radical anions greatly contribute to the degradation. The rate constants of reactions with these two radicals are in the 10⁹-10¹⁰ M^-1 s^-1 range. The degradation products reflect ipso attack, hydroxylation on the aromatic ring and/or the amino moiety and cleavage of the side chain. Among AOP, photocatalysis and SROP are the most effective for degradation of the three β-blockers. The operating parameters have to be optimized to the most suitable effectiveness.

Rate Constants and Mechanisms for Reactions of Bromine Radicals with Trace Organic Contaminants

Bromine radicals can pose great impacts on the photochemical transformation of trace organic contaminants in natural and engineered waters. However, the reaction kinetics and mechanisms involved are barely known. In this work, second-order reaction rate constants with Br^• and Br₂^•- were determined for 70 common trace organic contaminants and for 17 model compounds using laser flash photolysis and steady-state competition kinetics. The k_Br^• values ranged from <10⁸ to (2.86 ± 0.31) × 10¹⁰ M^-1 s^-1 and the k_Br2^•- values from <10⁵ to (1.18 ± 0.09) × 10⁹ M^-1 s^-1 at pH 7.0. Six quantitative structure-activity relationships were developed, which allow predicting additional unknown k_Br^• and k_Br2^•- values. Single-electron transfer was shown to be a favored pathway for the reactions of Br^• and Br₂^•- with trace organic contaminants, and this was supported by transient spectroscopy and quantum chemical calculations. This study is essential in advancing the scientific understanding of halogen radical-involved chemistry in contaminant transformation.

Photochemical mineralization of amoxicillin medicinal product by means of UV, hydrogen peroxide, titanium dioxide and iron

In the present study, the photochemical degradation of amoxicillin and total organic carbon (TOC) removal in pharmaceutical aqueous solutions was studied using UV irradiation, titanium dioxide, hydrogen peroxide and iron in a batch photoreactor operated for 120-150 min. The effect of the initial concentrations of the target compound, hydrogen peroxide and ferric ions and of their combination was examined. It was found that under direct UV photolysis, considerable TOC removals were obtained only when the initial concentration of amoxicillin (AM) was below 100 mg/L. For initial concentration of AM 250 mg/L, the TOC removals achieved were of no practical use (below 5%). The TOC removals achieved in the presence of TiO₂ were lower than 20% in all cases. In the presence of hydrogen peroxide in the range of 12.2-146.9 mmol/L and initial AM concentration 250 mg/L, for increasing H₂O₂ concentrations higher TOC removals were achieved up to the concentration of 73.4 mmol/L H₂O₂. The presence of even very small amounts of Fe(III) in the solution resulted in significantly increased TOC removals; 2.2 times higher than without Fe(III) after 120 min. Fe(III) presence accelerated dramatically the process during the first 60 min. The origin of Fe(III) ions was not important since practically the same results were obtained whether FeCl₃ or Fe(NO₃)₃ was used as source of ferric ions. Adjusting the initial concentrations of AM, Fe(III) and H₂O₂, TOC removals above 90% were achieved.

Degradation of moxifloxacin by ionizing radiation and toxicity assessment

The gamma ray induced degradation of moxifloxacin in aqueous media has been evaluated. The drug solutions (50 & 100 mg/L) were irradiated to absorbed doses of 0.3, 0.6, 0.9, 1.2, 1.5, 2, 3 and 4 kGy using Cs-137 gamma radiation source. The parameters such as drug initial concentration, oxidant (H2O2) concentration and gamma ray absorbed doses were optimized. The efficiency of Advanced oxidation processes (AOP) was evaluated on the basis of degradation, reduction in chemical oxygen demand (COD) and toxicity reduction of the drug. The maximum degradation of 94.01 and 88.30% was achieved when drug solutions were exposed to gamma irradiation absorbed dose of 4 kGy which enhanced to 100 and 99.06% in the presence of H2O2 (0.5 mL/L) for 50 and 100 mg/L respectively. A significant reduction in COD 72 and 75% for 50 mg/L while 65 and 69% in case of 100 mg/L was noted using gamma and gamma/H2O2 respectively at absorbed dose of 4 kGy. The parameters such as dose constant (k), removal efficiency (G-value), gamma ray absorbed doses required for 50, 90 and 99% degradation (D 0.50, D 0.90 and D 0.99) have been calculated. The radiolytic degradation was monitored by UV–Vis spectrophotometer and HPLC, FT-IR studies were performed to investigate the change in functional groups before and after treatment, while GC-MS analysis was carried out to monitor intermediates/degraded end-products. The FT-IR spectra has shown complete destruction of aromatic rings after radiation treatment but a minor peak appeared at 1216 cm−1 corresponding to CO stretching. The GC-MS study for the drug samples treated with gamma/H2O2 has shown no any significant peak which confirms the complete degradation. The cytotoxicity of treated samples was carried out by hemolytic assay and mutagenicity using Ames test before and after each treatment. The hemolytic test showed 73.92% hemolysis, while gamma/H2O2 treatment reduced the mutagenicity to 74.08 and 65.66% against TA98 and TA100 bacterial strains respectively. The response surface methodology (RSM) was employed to optimize the data. The obtained data elaborate that gamma/H2O2process is promising approach for the remediation of pharmaceutical waste effluent.

Efficient degradation of typical pharmaceuticals in water using a novel TiO2/ONLH nano-photocatalyst under natural sunlight

Photocatalytic degradation of typical pharmaceuticals in natural sunlight and in actual water is of great significance. In this study, the oxygen or nitrogen linked heptazine-base polymer (ONLH) was successfully incorporated with TiO₂ nanoparticles and formed a TiO₂/ONLH nanocomposite which was responded to the natural sunlight. Under natural sunlight, the TiO₂/ONLH can effectively degrade ten types of pharmaceuticals. In particular, fluoroquinolone containing N-piperazinyl, and cardiovascular drugs containing long aromatic side chains were easily degraded. The half-life of the best degradation performance of propranolol was less than 5 min. The rate constants of propranolol using the TiO₂/ONLH were approximately six- and eight-fold higher than those of pristine TiO₂ and ONLH, respectively. Two reactive species (OH and O₂^-) facilitated the rapid degradation of propranolol, which occurred primarily through the hydroxyl radical addition, ring-opening, and ipso substitution reactions. An acute toxicity test using luminescent bacteria indicated that the toxicity of the propranolol reaction solution gradually decreased with lower total organic carbon (TOC). According to the toxicity evaluation of monomer products, the TiO₂/ONLH also reduced the generation of toxic transformation products. The effects of actual water/wastewater have further shown the TiO₂/ONLH might be applied for the removal of pharmaceuticals in wastewater.

Sonochemical degradation of benzenesulfonic acid in aqueous medium

Degradation of benzenesulfonic acid (BSA), the simplest aromatic sulfonic acid with extreme industrial importantance, by sonochemically generated hydroxyl radical (OH) have been thoroughly investigated. A reasonable reduction (∼50%) in the total organic carbon (TOC) was achieved only after prolonged irradiation (∼275 min, 350 kHz) of ultrasound, although a short irradiation of less than an hour is enough to degrade significant amount of BSA. The degradation efficiency of ultrasound has been reduced in lower and extremely higher frequencies, and upon increasing the pH. An irregular, but continuous, release of sulfate ions was also observed. Further, the release of protons upon the oxidation of BSA consistently reduces the experimental pH to nearly 2. High resolution mass spectrometric (HRMS) analyses reveals the formation of a number of aromatic intermediates, including three mono (I_a-c) and two di (II_a&b) hydroxylated BSA derivatives as the key products in the initial stages of the reaction. Pulse radiolysis studies revealed the generation of hydroxycyclohexadienyl-type radicals, characterized by absorption bands at 320 nm (k₂ = (7.16 ± 0.04) × 10⁹ M^-1 s^-1) and 380 nm, as the immediate intermediates of the reaction. The mechanism(s) leading to the degradation of BSA under sonolytic irradiation conditions along with the effect of various factors, such as the ultrasound frequency and reaction pH, have been explained in detail. The valuable mechanistic aspects obtained from our pulse radiolysis and HRMS studies are essential for the proper implementation of sonochemical techniques into real water purification process and, thus, receives extreme environmental relevance.

Preparation of TiO2-modified Biochar and its Characteristics of Photo-catalysis Degradation for Enrofloxacin

In order to solve the problem that the traditional biochar(BC) has insufficient removal ability of enrofloxacin and TiO₂ is difficult to recycle. In this study, TiO₂-modified biochar composites were prepared by impregnation method. Through characterization analysis, The BET specific surface area results indicated that after loading TiO₂, the specific surface area of TiO₂-biochar(Ti-BC), TiO₂-ironized biochar(Ti-FBC) and TiO₂-alkaline biochar(Ti-KBC) increased by 4.34, 10.43 and 11.52 times, respectively. The analysis results of SEM, EDS, FT-IR, XRD and XPS showed that TiO₂ was supported on biochar in the anatase state. The UV-vis DRS measurement showed that the band width of Ti-KBC was the smallest and the best catalytic activity. Under 15 W UV lamp (254 nm) irradiation, the photocatalytic degradation process of enrofloxacin by different biochar accords with the first-order kinetic equation. Ti-KBC showed best degradation effect under different initial concentrations of enrofloxacin. When the pH of the solution was 5.0 and the dosage of Ti-KBC was at 2.5 g·L⁻¹, the enrofloxacin degradation rate of 100 mg·L⁻¹ reached 85.25%. The quenching test confirmed that the active substance O₂•^— played a major role in the photocatalytic degradation process. After five cycles of the test, the degradation rate of Ti-KBC for enrofloxacin was 77.14%, which was still better than that of BC, Ti-BC and Ti-FBC.

Rate Constants and Mechanisms of the Reactions of Cl• and Cl2•- with Trace Organic Contaminants

Cl^• and Cl₂^•- radicals contribute to the degradation of trace organic contaminants (TrOCs) such as pharmaceutical and personal care products and endocrine-disrupting chemicals. However, little is known about their reaction rate constants and mechanisms. In this study, the reaction rate constants of Cl^• and Cl₂^•- with 88 target compounds were determined using laser flash photolysis. Decay kinetics, product buildup kinetics, and competition kinetics were applied to track the changes in their transient spectra. Cl^• exhibited quite high reactivity toward TrOCs with reaction rate constants ranging from 3.10 × 10⁹ to 4.08 × 10¹⁰ M^-1 s^-1. Cl₂^•- was less reactive but more selective, with reaction rate constants varying from <1 × 10⁶ to 2.78 × 10⁹ M^-1 s^-1. Three QSAR models were developed, which were capable of predicting the reaction rate constants of Cl₂^•- with TrOCs bearing phenol, alkoxy benzene, and aniline groups. The detection of Cl^•-adducts of many TrOCs suggested that Cl^• addition was an important reaction mechanism. Single electron transfer (SET) predominated in reactions of Cl^• with TrOCs bearing electron-rich moieties (e.g., sulfonamides), and their cation radicals were observed. Cl^• might also abstract hydrogen atoms from phenolic compounds to generate phenoxyl radicals. Moreover, Cl^• could react with TrOCs through multiple pathways since more than one transient intermediate was detected simultaneously. SET was the major reaction mechanism of Cl₂^•- reactions with TrOCs bearing phenols, alkoxy benzenes, and anilines groups. Cl₂^•- was found to play an important role in TrOC degradation, though it has been often neglected in previous studies. The results improve the understanding of halogen radical-involved chemistry in TrOC degradation.

BiOCl facilitated photocatalytic degradation of atenolol from water: Reaction kinetics, pathways and products

Atenolol (ATL), a kind of largely used beta-blockers, has been widely detected in the aquatic environment, which could cause adverse impact on human beings. In this study, bismuth oxychloride (BiOCl) photocatalyst was synthesized and applied to remove ATL in the aqueous system under simulated natural light. Emphasis was laid on the reaction kinetics and the impact of natural organic matter (NOM) (0-20 mg/L). Possible transformation pathways were systematically investigated based on identification of reaction products via liquid chromatography-mass spectrometry (LC-MS). As a consequence, BiOCl presents highly photocatalytic efficiency yielding up to nearly 100% ATL conversion after 60 min of interaction, together with fairly high photostability evidenced by considerably efficient removal of ATL after 10 catalytic cycles. Four kinds of possible products are detected using LC-MS in the process of reaction, indicating possible transformation ways of ATL photocatalysis. NOM has an inhibiting impact on the removal of ATL and influences the products distribution. This study provides an emerging nanocatalyst for ATL photodegradation and could eventually lead to development of novel methods to control pharmaceutical contamination in water.

Efficiency and mechanism of atenolol decomposition in Co-FeOOH catalytic ozonation

Co-incorporated α-FeOOH nanocrystal (Co-FeOOH) was synthesized and applied for the ozonation of atenolol (ATL) in water. The compound was characterized and recognized as a transitional structure from FeOOH to CoFeO₄. The presence of Co-FeOOH was observed to support the formation of •OH by promoting ozone decomposition, and the degradation of ATL and TOC was significantly improved during the catalytic ozonation. Catalytic reactions were rationally designed in different water matrices, efficient and simultaneous removal of ATL and natural organic contaminants was achieved. It was found that the reactions kinetics depend strongly on the solution pH which could alter the surface properties of catalyst and influence the ozone-decomposition. Based on the 19 organic intermediates identified by UPLC/Q-TOF-mass spectrometry, possible reaction pathways were accordingly proposed to elucidate the mechanism of atenolol degradation by ozone molecular and •OH. Three positions of ATL structure were concluded as the most vulnerable sites to be attacked by oxygen species to initiate the degradation path.

Enhanced degradation of organic contaminants by zero-valent iron/sulfite process under simulated sunlight irradiation

Degradation of propranolol (PrP) by a combined zero-valent iron and sulfite system under simulated sunlight irradiation (ZVI/sulfite/photo) was investigated. Simulated sunlight irradiation enhanced the degradation of PrP by accelerating the decomposition of ferric sulfite complex as a result to producing sulfite radical (SO₃^•-). As bubbles would block the transport of photons in the reaction solution, mechanical aeration rather than purging air was suggested to sustain the essential dissolved oxygen. The degradation of PrP increased with the elevation of initial ZVI concentration from 0.05 to 0.5 mM, but decreased a little with further increasing ZVI concentration to 1.0 mM. The degradation of PrP raised from 68.5% to 98.7% while sulfite dose increased from 0.1 to 2.0 mM. High removal efficiencies were always achieved when the initial PrP concentration ranged from 10 to 40 μM. As HSO₃^- which can efficiently complex Fe(II) and transfer Fe(III) to Fe(II) is the dominant species of sulfite at pH 4.0-6.0, the highest removal of PrP was achieved at pH 4.0-6.0. The presence of bicarbonate and humic acid significantly retarded the removal of PrP, while chloride ions could promote the removal of PrP to some extent. SO₄^•-, HO^• and SO₅^•- were suggested to account for PrP removal, while SO₄^•- was evidenced to be the dominant radicals. Good reuse of ZVI in the system was also achieved as the removal of PrP kept higher than 80% after repeatedly used for 5 times. Possible degradation pathways of PrP in the ZVI/sulfite/photo system were accordingly proposed based on LC-MS and density functional theory calculation. The removal of amitriptyline, nitrobenzene, imipramine and methylparaben in the ZVI/sulfite/photo system was also evaluated. As a reducing agent, sulfite is expected to consume the possible formed bromine-containing intermediates as a result to inhibiting the formation of bromate, which is better than the activated persulfate system.

Activation of peroxymonosulfate by BiOCl@Fe3O4 catalyst for the degradation of atenolol: Kinetics, parameters, products and mechanism

BiOCl@Fe₃O₄ photocatalyst was synthesized to activate peroxymonosulfate (PMS) for atenolol (ATL) degradation under simulated sunlight irradiation in present study. XRD, SEM, adsorbability and pore size distribution of BiOCl@Fe₃O₄ were analyzed. Magnetic BiOCl performed high activity in PMS activation and could be easily solid-liquid separation by applying an external magnetic field. Many parameters were inspected, including scavengers, PMS concentration, catalyst dosage, pH, anions (Cl^- and CO₃^-). h⁺, SO₄^-, HO, O₂^-, SO₅^- were involved in ATL degradation in BiOCl@Fe₃O₄/PMS/sunlight system. The second-order rate constant of the reaction between ATL and SO₄^- (k_ATL, _SO4-) was estimated via laser flash photolysis experiments. Moreover, ATL mineralization was followed by TOC analyzer. Twelve possible intermediate products were identified through LC-QTOF-MS analysis, and six ATL degradation pathways were concluded. This type of magnetic photocatalyst is characterized by ease of separation, high activation and good reusability. It may have application potential in refractory organic pollutants degradation.

Comparative study on degradation of propranolol and formation of oxidation products by UV/H2O2 and UV/persulfate (PDS)

The frequent detection of propranolol, a widely used β-blocker, in wastewater effluents and surface waters has raised serious concern, due to its adverse effects on organisms. UV/hydrogen peroxide (UV/H₂O₂) and UV/persulfate (UV/PDS) processes are efficient in eliminating propranolol in various waters, but the formation of oxidation products in these processes, as well as the assessment of their toxicity, has not been systematically addressed. In this study, we identified and compared transformation products of propranolol produced by hydroxyl radical (^•OH) and sulfate radical (SO₄^•-). The electrostatic attraction enhances the reaction between SO₄^•- and the protonated form of propranolol, while ^•OH shows non-selectivity toward both protonated and neutral propranolol species. The hydroxylation of propranolol by ^•OH occurs at either amine moiety or naphthalene group while SO₄^•- favors the oxidation of the electron-rich naphthalene group. Further oxidation by ^•OH and SO₄^•- results in ring-opening products. Bicarbonate and chloride exert no effect on propranolol degradation. The generation of CO₃^•- and Cl-containing radicals is favorable to oxidizing naphthalene group. The acute toxicity assay of Vibrio fischeri suggests that SO₄^•- generates more toxic products than ^•OH, while CO₃^•- and Cl-containing radicals produce similar toxicity as SO₄^•-. High concentrations of bicarbonate in UV/H₂O₂ increase the toxicity of treated solution.

Highly Efficient Degradation of Tartrazine with a Benzoic Acid/TiO2 System

The roles of benzoic acid and its derivatives in the photocatalytic degradation of tartrazine (TZ) by titanium dioxide have been studied. A series of comparative experiments were carried out, such as the experimental comparisons of concentrations, pH values, effects on the para-position of benzoic acid, gas atmospheres, and different target pollutants. It should be noted that the degradation rate of TZ solution without benzoic acid and benzoic acid after degradation for 90 min was 28.69 and 99.08%, respectively. The reason for the above results is that benzoic acid acts as an electron donor to react with photogenerated holes, suppressing the recombination of photogenerated holes and electrons, and thus causing a significant increase in the degradation rate. Moreover, the degradation process is mainly induced by O₂ ^•- and photogenerated holes (h⁺). It is the first time that the benzoic acid/TiO₂ system has been used to degrade the TZ dye. In addition, the benzoic acid/TiO₂ system is also suitable for the degradation of other organic dyes such as methyl orange, rhodamine B, methylene blue, and methyl violet.

Degradation of atenolol via heterogeneous activation of persulfate by using BiOCl@Fe3O4 catalyst under simulated solar light irradiation

Efficient oxidative degradation of pharmaceutical pollutants in aquatic environments is of great importance. This study used magnetic BiOCl@Fe₃O₄ catalyst to activate persulfate (PS) under simulated solar light irradiation. This degradation system was evaluated using atenolol (ATL) as target pollutant. Four reactive species were identified in the sunlight/BiOCl@Fe₃O₄/PS system. The decreasing order of the contribution of each reactive species on ATL degradation was as follows: h⁺ ≈ HO^· > O₂^·- > SO₄^·-. pH significantly influenced ATL degradation, and an acidic condition favored the reaction. High degradation efficiencies were obtained at pH 2.3-5.5. ATL degradation rate increased with increased catalyst and PS contents. Moreover, ATL mineralization was higher in the sunlight/BiOCl@Fe₃O₄/PS system than in the sunlight/BiOCl@Fe₃O₄ or sunlight/PS system. Nine possible intermediate products were identified through LC-MS analysis, and a degradation pathway for ATL was proposed. The BiOCl@Fe₃O₄ nanomagnetic composite catalyst was synthesized in this work. This catalyst was easily separated and recovered from a treated solution by using a magnet, and it demonstrated a high catalytic activity. Increased amount of the BiOCl@Fe₃O₄ catalyst obviously accelerated the efficiency of ATL degradation, and the reusability of the catalyst allowed the addition of a large dosage of BiOCl@Fe₃O₄ to improve the degradation efficiency.

Degradation of acetaminophen in aqueous solution under visible light irradiation by Bi-modified titanate nanomaterials: morphology effect, kinetics and mechanism

Three morphologies of Bi-modified titanate nanomaterials were prepared using the hydrothermal method and controlled parameters to degrade acetaminophen.

Influence of Peroxide Impurities in Povidone on the Stability of Selected β-Blockers with the Help of HPLC

A present study was conducted to investigate compatibility of β-blocker drugs( like atenolol, labetalol hydrochloride, bisoprolol fumarate, metoprolol succinate, carvedilol and propranolol hydrochloride) with the pharmaceutical excipient povidone. To check the influence of peroxide impurity present in povidone on the stability of β-blockers, a binary mixture technique has been adopted. The binary mixtures (1:1) of β-blockers with povidone excipient were stored for the duration of 6 months at accelerated conditions (40°C and 75% RH) and analyzed with the technique of high-performance liquid chromatography (HPLC). On analysis, HPLC results shows that, the percentage of total impurity for atenolol-2.15%, bisoprolol fumarate-3.55%, carvedilol-2.19%, and labetalol hydrochloride-1.89%, with respect to povidone. To verify the interaction of H₂O₂ present in povidone as an impurity, oxidative degradation of selected active pharmaceutical ingredients were performed and degradation profile were compared with that of degradation impurities generated in drug-excipient mixture at accelerated conditions. The relative retention time (RRT) of impurities generated in accelerated stability study samples resembles the RRT of degradation products generated by oxidative degradation of pure drugs. Thus, it confirms that degradation of β-blockers with povidone was mediated by organic peroxides present as an impurity in povidone.

Ozonation as a pretreatment process for nanofiltration brines: Monitoring of transformation products and toxicity evaluation

Considerable interest has been given to using nanofiltration (NF) in lieu of reverse osmosis for water reclamation schemes due to lower energy consumption, higher flux rates while ensuring good micropollutants rejection. The application NF results in the generation of a large concentrated waste stream. Treatment of the concentrate is a major hurdle for the implementation of membrane technologies since the concentrate is usually unusable due to a large pollutants content. This work focuses on the application of ozonation as pretreatment of urban NF concentrates, the generation of transformation products and their relative toxicity. Three pharmaceutical micropollutants largely encountered in water cycle were selected as target molecules: acetaminophen, carbamazepine and atenolol. Through accurate-mass Q-TOF LC-MS/MS analyses, more than twenty ozonation products were detected, structure proposals and formation pathways were elaborated. Attempts were made to understand the correlation between the transformation products and acute toxicity on Vibrio fischeri strain. It is the first time that an integrated study reported on the ozonation of pharmaceuticals in urban membrane concentrates, in terms of transformation products, kinetics, degradation mechanisms, as well as toxicity assessment.

Can radiation chemistry supply a highly efficient AO(R)P process for organics removal from drinking and waste water? A review

The increasing role of chemistry in industrial production and its direct and indirect impacts in everyday life create the need for continuous search and efficiency improvement of new methods for decomposition/removal of different classes of waterborne anthropogenic pollutants. This review paper addresses a highly promising class of water treatment solutions, aimed at tackling the pressing problem of emerging contaminants in natural and drinking waters and wastewater discharges. Radiation processing, a technology originating from radiation chemistry studies, has shown encouraging results in the treatment of (mainly) organic water pollution. Radiation ("high energy") processing is an additive-free technology using short-lived reactive species formed by the radiolysis of water, both oxidative and reducing, to carry out decomposition of organic pollutants. The paper illustrates the basic principles of radiolytic treatment of organic pollutants in water and wastewaters and specifically of one of its most practical implementations (electron beam processing). Application examples, highlighting the technology's strong points and operational conditions are described, and a discussion on the possible future of this technology follows.

Indirect photodegradation of the lampricides TFM and niclosamide

3-Trifluromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide) are lampricides used in tributaries of the Great Lakes to kill the invasive parasitic sea lamprey (Petromyzon marinus). Although the lampricides have been applied since the late 1950s, their photochemical behavior in natural environments is still not well understood. This study examines the indirect photodegradation of these two compounds and the resulting yields of organic and inorganic photoproducts in water samples collected from five tributaries of Lake Michigan. The tributaries were selected to span the length of Lake Michigan and its natural carbonate geologic gradient. In the presence of dissolved organic matter (DOM), the niclosamide photodegradation rate triples, while the rate of TFM photodegradation is unchanged. Additionally, the yield of lampricide organic products is influenced by DOM because many of the organic photoproducts themselves are prone to DOM-mediated indirect photodegradation. The indirect photodegradation of niclosamide is primarily mediated by reaction with singlet oxygen, which accounts for more than 50% of the increased photodegradation rate. Additionally, hydroxyl radicals and carbonate radicals (CO₃^-˙) influence niclosamide indirect photolysis, and their contribution is dependent on the specific river water chemistry. For example, CO₃^-˙ contribution to niclosamide photodegradation, while small, is greater in southern tributaries where there is higher carbonate alkalinity.

Application of ozonation for pharmaceuticals and personal care products removal from water

Due to the shortening on natural water resources, reclaimed wastewater will be an important water supply source. However, suitable technologies must be available to guaranty its proper detoxification with special concern for the emerging pharmaceutical and personal care products that are continuously reaching municipal wastewater treatment plants. While conventional biological systems are not suitable to remove these compounds, ozone, due to its interesting features involving molecular ozone oxidation and the possibility of generating unselective hydroxyl radicals, has a wider range of action on micropollutants removal and water disinfection. This paper aims to review the studies dealing with ozone based processes for water reuse by considering municipal wastewater reclamation as well as natural and drinking water treatment. A comparison with alternative technologies is given. The main drawback of ozonation is related with the low mineralization achieved that may lead to the production of reaction intermediates with toxic features. The use of hydrogen peroxide and light aided systems enhance ozone action over pollutants. Moreover, scientific community is focused on the development of solid catalysts able to improve the mineralization level achieved by ozone. Special interest is now being given to solar light catalytic ozonation systems with interesting results both for chemical and biological contaminants abatement. Nowadays the integration between ozonation and sand biofiltration seems to be the most interesting cost effective methodology for water treatment. However, further studies must be performed to optimize this system by understanding the biofiltration mechanisms.

Kinetic Study of Hydroxyl and Sulfate Radical-Mediated Oxidation of Pharmaceuticals in Wastewater Effluents

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO^•)- and sulfate radical (SO₄^•-)-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO^•- and SO₄^•--mediated oxidation. In the UV/H₂O₂ process, a simplified kinetic model involving only steady state concentrations of HO^• and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO^• in the removal of PPCPs. In the UV/K₂S₂O₈ process, the calculated steady state concentrations of CO₃^•- and bromine radicals (Br^•, Br₂^•- and BrCl^•-) were 600-fold and 1-2 orders of magnitude higher than the concentrations of SO₄^•-, respectively. The kinetic model, involving both SO₄^•- and CO₃^•- as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO₄^•- could lead to overestimations of the removal efficiencies of the SO₄^•--mediated oxidation of nitroimidazoles in wastewater effluents.

Environmental photochemical fate of selected pharmaceutical compounds in natural and reconstituted Suwannee River water: Role of reactive species in indirect photolysis

This study reports the impact of two reactive species, hydroxyl radical and singlet oxygen, on the photochemical degradation of three selected pharmaceutical compounds in natural and reconstituted solutions of Suwannee River water. Absolute bimolecular rate constants (M^-1s^-1) were determined for the reaction of hydroxyl radical and singlet oxygen with danofloxacin ((6.15±0.11)×10⁹; (7.50±0.13)×10⁴), fluvastatin ((6.96±0.16)×10⁹; (1.64±0.18)×10⁸), and paroxetine ((8.65±0.12)×10⁹, (1.18±0.13)×10⁸), respectively. For all three pharmaceutical compounds, the rate constants for reactions with the hydroxyl radical were similar; however, those for singlet oxygen varied by three orders of magnitude. In the waters studied, the steady-state concentration of the hydroxyl radical was on the order of 10^-17-10^-18M, and for singlet oxygen, 10^-12-10^-14M. The percent contribution of each species to the degradation of each pharmaceutical in each water matrix was calculated, and several trends were identified enabling a better understanding of the role of these reactive species.