Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism

Important yet Overlooked HONO Source from Aqueous-phase Photochemical Oxidation of Nitrophenols

Nitrites (NO2-/HONO), as the primary source of hydroxyl radicals (•OH) in the atmosphere, play a key role in atmospheric chemistry. However, the current understanding of the source of NO2-/HONO is insufficient and therefore hinders the accurate quantification of atmospheric oxidation capacity. Herein, we highlighted an overlooked HONO source by the reaction between nitrophenols (NPs) and •OH in the aqueous phase and provided kinetic data to better evaluate the contribution of this process to atmospheric HONO. Three typical NPs, including 4-nitrophenol (4NP), 2-nitrophenol (2NP), and 4-nitrocatechol (4NC), underwent a denitration process to form aqueous NO2- and gaseous HONO through the •OH oxidation, with the yield of NO2-/HONO varied from 15.0 to 33.5%. According to chemical composition and structure analysis, the reaction pathway, where the ipso addition of •OH to the NO2 group on 4NP generated hydroquinone, can contribute to more than 61.9% of the NO2-/HONO formation. The aqueous photooxidation of NPs may account for HONO in the atmosphere, depending on the specific conditions. The results clearly suggest that the photooxidation of NPs should be considered in the field observation and calculation to better evaluate the HONO budget in the atmosphere.

MXene/ZnS/chitosan-cellulose composite with Schottky heterostructure for efficient removal of anionic dyes by synergistic effect of adsorption and photocatalytic degradation

Nowadays, dye water pollution is becoming increasingly severe. Composite of MXene, ZnS, and chitosan-cellulose material (MX/ZnS/CC) was developed to remove anionic dyes through the synergistic effect of adsorption and photocatalytic degradation. MXene was introduced as the cocatalyst to form Schottky heterostructure with ZnS for improving the separation efficiency of photocarriers and photocatalytic performance. Chitosan-cellulose material mainly served as the dye adsorbent, while also could improve material stability and assist in generation of free radicals for dye degradation. The physics and chemistry properties of MX/ZnS/CC composite were systematically inspected through various characterizations. MX/ZnS/CC composite exhibited good adsorption ability to anionic dyes with adsorption capacity up to 1.29 g/g, and excellent synergistic effects of adsorption and photodegradation with synergistic removal capacity up to 5.63 g/g. MX/ZnS/CC composite performed higher synergistic removal ability and better optical and electrical properties than pure MXene, ZnS, chitosan-cellulose material, and MXene/ZnS. After compounding, the synergistic removal percentage of dyes increased by a maximum of 309 %. MX/ZnS/CC composite mainly adsorbs anionic dyes through electrostatic interactions and catalyzes the generation of •O2-, h+, and •OH to degrade dyes, which has been successfully used to remove anionic dyes from environmental water, achieving a 100 % removal of 50 mg/L dye.

Photoreduction of Hg(II) by typical dissolved organic matter in paddy environments

The photochemical behavior of dissolved organic matter (DOM) in surface water and its effect on Hg(II) photoreduction has been extensively studied, but the contribution of DOM in paddy water to Hg(II) photoreduction is largely unknown. Herein, the effect of DOM from biochar (BC_DOM), rice straw (RS_DOM), and chicken manure (CM_DOM) on Hg(II) photoreduction were examined. The comparable reduction efficiency of Hg(II) suggested that DOM-like fraction (62.3-63.7%) contributes more than suspended particulate matter-like fraction (17.7-23.4%) and bacteria-like fraction (13.0-20.0%) in paddy water. Under irradiation, the typical DOM significantly promoted Hg(II) photoreduction, and the reduction efficiency of BC_DOM (65.5 ± 2.1%) was higher than that of CM_DOM (48.3 ± 2.6%) and RS_DOM (32.8 ± 2.4%) in 6 h. The quenching and kinetics experiments showed that superoxide anion (O₂^•-) was the main reactive species for Hg(II) photoreduction. Fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry revealed that DOM with a higher degree of lignin/carboxy-rich acyclic molecules, condensed aromatics structures, and phenolic compounds could promote the formation of O₂^•-. These findings highlight the importance of DOM in Hg(II) photoreduction and provide new ideas for regulating Hg cycling and bioavailability in paddy environments.

Rapid Redox Cycling of Fe(II)/Fe(III) in Microdroplets during Iron-Citric Acid Photochemistry

Fe(III) and carboxylic acids are common compositions in atmospheric microdroplet systems like clouds, fogs, and aerosols. Although photochemical processes of Fe(III)-carboxylate complexes have been extensively studied in bulk aqueous solution, relevant information on the dynamic microdroplet system, which may be largely different from the bulk phase, is rare. With the help of the custom-made ultrasonic-based dynamic microdroplet photochemical system, this study examines the photochemical process of Fe(III)-citric acid complexes in microdroplets for the first time. We find that when the degradation extent of citric acid is similar between the microdroplet system and the bulk solution, the significantly lower Fe(II) ratio is present in microdroplet samples due to the rapider reoxidation of photogenerated Fe(II). However, by replacing citric acid with benzoic acid, no much difference in the Fe(II) ratio between microdroplets and bulk solution is observed, which indicates distinct reoxidation pathways of Fe(II). Moreover, the presence of ^•OH scavenger, namely, methanol, greatly accelerates the reoxidation of photogenerated Fe(II) in both citric acid and benzoic acid situations. Further experiments reveal that the high availability of O₂ and the citric acid- or methanol-derived carbon-centered radicals are responsible for the rapider reoxidation of Fe(II) in iron-citric acid microdroplets by prolonging the length of HO₂^•- and H₂O₂-involved radical reaction chains. The results in this study may provide a new understanding about iron-citric acid photochemistry in atmospheric liquid particles, which can further influence the photoactivity of particles and the formation of secondary organic aerosols.

Effect of Fe(III)-bicarboxylic complexes in removal pollutant under UV and sunlight in aqueous solutions

In this study, we have applied Fe(III)-bi-carboxylic acid solutions containing citrate and oxalate ligands to degrade 3-méthylphénol (3MP) in aqueous solutions both under UV and sunlight. Under irradiation at 365 nm, the photodegradation of 3MP is markedly better in the presence of the Fe(III)Ox complex than in the Fe(III)Cit complex this fact is explained by an excess of H₂O₂ and Fe(II) generated by Fe(III)Ox photolysis creating the Fenton process. We mixtures were realized by varying the composition of the Fe(III)Cit and Fe(III)Ox in order to see the additives of the degradation efficiency of the pollutant. The results show that the addition of Fe(III)Ox to the Fe(III)Cit system evidently augmented the photodegradation rate at pH = 5.5. The Fe(III)Ox/Fe(III)Cit ratio is optimized at [Fe(III)Ox] (0.15/0.15)/[Fe(III)Cit] (0.15/0.6). Synergistic effect in the Fe(III)Ox/Fe(III)Cit binary system was confirmed. The addition of tertiobutanol (T-buOH) noticeably inhibited the photodegradation, indicating the involvement of ^•OH in the process. To verify the feasibility of photochemical processes in the environment, tests on the photodegradation of 3MP were performed under natural irradiation. The degradation was improved under excitation by sunlight in the presence of Fe(III)-bi-carboxylic acid solutions containing citrate and oxalate ligands. These results are very encouraging for the application of this system for the treatment of organic pollutants in aqueous solution.

Enhanced photocatalytic treatment using plasmonic Ag@Ag3PO4/Ag@AgCl nanophotocatalyst for simultaneous degradation of multiple parabens and UV-filters in various aquatic environments under visible light irradiation

In this study, simultaneous photocatalytic degradation of different parabens (methyl-, ethyl-, propyl-, and butyl paraben) and UV filters (benzophenone-3, 4-methylbenzylidene camphor, 2-ethylhexyl 4-(dimethylamino) benzoate, ethylhexyl methoxycinnamate and octocrylene) in water matrices was performed under visible light irradiation using novel double plasmonic Ag^@Ag₃PO₄/Ag^@AgCl nanophotocatalyst, synthesized by an easy and fast photochemical conversion and photo-reduction. It was found that the nanophotocatalyst with appropriate mole ratio of Ag^@Ag₃PO₄/Ag^@AgCl (1:3) showed superior photocatalytic activity than individual plasmonic nanoparticles. This is because there are two simultaneous surface plasmon resonances (SPR) generated by the metallic Ag nanoparticles, in addition to the hetero-junction structure formed at the interface between Ag^@Ag₃PO₄ and Ag^@AgCl. The structures of the synthesized photocatalysts were characterized, and the principal reactive oxygen species in the photocatalytic process were identified via a trapping experiment, confirming superoxide radicals (^∙O₂^-) as the key reactive species of the photocatalytic system. The process of photodegradation of the target pollutants was monitored using an optimized method that incorporated solid-phase extraction in combination with gas chromatography-mass spectrometry. The simultaneous photodegradation process was modeled and optimized using central composite design. The kinetic study revealed that the degradation process over Ag^@Ag₃PO_{4 (30%)}/Ag^@AgCl _(70%) under visible light followed a pseudo-first-order kinetic model. The simultaneous degradation of target compounds was further investigated in sewage treatment plant effluent as well as tap water. It was found that the matrix constituents can reduce the photodegradation efficiency, especially in the case of highly contaminated samples.

Photoinduced evolution of optical properties and compositions of methoxyphenols by Fe(III)-carboxylates complexes in atmospheric aqueous phase

The changes in optical properties and chemical compositions of methoxyphenols, which acted as an important aromatic compound from the biomass burning, were investigated in the presence of Fe(III)-carboxylates under aqueous phase conditions. The light was confirmed to be a key factor for stimulating the reaction of methoxyphenols and Fe(III)-carboxylates. The photoinduced evolution of optical properties of methoxyphenols was dependent on various factors, including irradiation intensity, types of carboxylates, dissolved oxygen and pH. The changes in the mass absorption efficiency at 306 nm (MAE₃₀₆) positively relied on irradiation intensity and dissolved oxygen. The acceleration effects of carboxylates on the decreases in MAE₃₀₆ of methoxyphenols followed the order of oxalate > citrate > malonate. The change amplitude of MAE₃₀₆ decreased with an increasing pH (3.5-9), while that of the mass absorption efficiency at 364 nm (MAE₃₆₄) increased with pH ranging from 3.5 to 7. The compositional evolutions of methoxyphenols by the photochemical aging were analyzed with the attenuated total reflection infrared spectroscopy (ATR-IR), confirming the decrease of CO groups and the increase of O-H and C-O groups. The photochemical reaction pathways of methoxyphenols with Fe(III)-carboxylates were proposed according to optical properties and compositions measurements.

Toxicity and removal of parabens from water: A critical review

Parabens are biocides used as preservatives in food, cosmetics and pharmaceuticals. They possess antibacterial and antifungal activity due to their ability to disrupt cell membrane and intracellular proteins, and cause changes in enzymatic activity of microbial cells. Water, one of our most valuable natural resource, has become a huge reservoir for parabens. Halogenated parabens from chlorination/ozonation of water contaminated with parabens have shown to be even more persistent in water than other types of parabens. Unfortunately, there is dearth of data on their (halogenated parabens) presence and fate in groundwater which serves as a major source of drinking water for a huge population in developing countries. An attempt to neglect the presence of parabens in water will expose man to it through ingestion of contaminated food and water. Although there are reviews on the occurrence, fate and behaviour of parabens in the environment, they largely omit toxicity and removal aspects. This review therefore, presents recent reports on the acute and chronic toxicity of parabens, their estrogenic agonistic and antagonistic activity and also their relationship with antimicrobial resistance. This article further X-rays several techniques that have been employed for the removal of parabens in water and their drawbacks including adsorption, biodegradation, membrane technology and advanced oxidation processes (AOPs). The heterogeneous photocatalytic process (one of the AOPs) appears to be more favoured for removal of parabens due to its ability to mineralize parabens in water. However, more work is needed to improve this ability of heterogeneous photocatalysts. Perspectives that will be relevant for future scientific studies and which will drive policy shift towards the presence of parabens in our drinking waters are also offered. It is hoped that this review will elicit some spontaneous actions from water professionals, scientists and policy makers alike that will provide more data, effective technologies, and adaptive policies that will address the growing threat of the presence of parabens in our environment with respect to human health.

KIT-6 induced mesostructured TiO2 for photocatalytic degradation of methyl blue

In this study, titania/silica nanocomposite and mesoporous TiO₂ (m-TiO₂) photocatalysts are developed by KIT-6 template via a sol-gel approach. The synthesized photocatalysts are characterized by XRD, EDX, SEM, Raman, PL, and UV-vis DRS analysis techniques. The as-synthesized series revealed a high surface area, smaller size, a greater number of accessible active sites, and enhanced light-harvesting capability. The m-TiO₂ photocatalysts' charge recombination capability was curiously inferior to the rest of as-synthesized TiO₂/KIT-6 nanocomposite materials. The band-gap of as-synthesized materials were suitable for their activity in UV light irradiations. It was pragmatic that the photocatalytic degradation efficiency of m-TiO₂ photocatalysts was superior as compared to that of commercial TiO₂ photocatalyst under UV light irradiations, owing to the synergistic outcome of the anatase phase and a greater number of accessible active-sites availability as a result of high surface area. Moreover, the m-TiO₂ was critically evaluated by investigating various parameters affecting the photocatalytic degradation reaction of MB including the effect of irradiation time, pH, catalyst dosage, and dye concentration. The m-TiO₂, 45wt% composite material and commercial-TiO₂ exhibited 99.27, 91.20, and 84.67% degradation of methyl blue in 50 min, respectively. Finally, the m-TiO₂ exhibited excellent recyclability with negligible loss of activity performance.

Photogeneration of Reactive Species from Biochar-Derived Dissolved Black Carbon for the Degradation of Amine and Phenolic Pollutants

Due to agricultural waste combustion and large-scale biochar application, biochar-derived dissolved black carbon (DBC) is largely released into surface waters. The photogeneration of reactive species (RS) from DBC plays an important role in organic pollutant degradation. However, the mechanistic interactions between RS and pollutants are poorly understood. Here, we investigated the formation of DBC triplet states (³DBC*), singlet oxygen (¹O₂), and hydroxyl radical (^•OH) in straw biochar-derived DBC solutions and photodegradation of typical pharmaceuticals and personal care products (PPCPs). Laser flash photolysis and electron spin resonance spectrometry showed that DBC exhibited higher RS quantum yields than some well-studied dissolved organic matter. The RS caused rapid degradation of atenolol, diphenhydramine, and propylparaben, selected as target PPCPs in this study. The ³DBC* contributed primarily to the oxidation of selected PPCPs via one-electron-transfer interaction, with average reaction rate constants of 1.15 × 10⁹, 1.41 × 10⁹, and 0.51 × 10⁹ M^-1 s^-1, respectively. ^•OH also participated in the degradation and accounted for approximately 2.7, 2.5, and 18.0% of the total removal of atenolol, diphenhydramine, and propylparaben, respectively. Moreover, the photodegradation products were identified using high-resolution mass spectrometry, which further confirmed the electron transfer and ^•OH oxidation mechanisms. These findings suggest that DBC from the combustion process of agricultural biomass can efficiently induce the photodegradation of organic pollutants under sunlight in aquatic environments.

Degradation of aqueous methylparaben by non-thermal plasma combined with ZnFe2O4-rGO nanocomposites: Performance, multi-catalytic mechanism, influencing factors and degradation pathways

Non-thermal plasma (NTP) combined with zinc ferrite-reduced graphene oxide (ZnFe₂O₄-rGO) nanocomposites were used for the degradation of aqueous methylparaben (MeP). ZnFe₂O₄-rGO nanocomposites were prepared using the hydrothermal method, with the structure and photoelectric properties of nanocomposites then characterized. The effects of discharge power, initial MeP concentration, initial pH, and air flow rate on MeP degradation efficiency were investigated, and the multi-catalytic mechanism and MeP degradation pathways were established. Results showed that ZnFe₂O₄-rGO nanocomposites with a 10%:90% mass ratio of GO:ZnFe₂O₄ had an optimal catalytic effect. The MeP degradation efficiency of NTP combined with ZnFe₂O₄-rGO (10 wt%), was approximately 25% higher than that of NTP alone. Conditions favorable for MeP degradation included higher discharge power, lower MeP concentration, neutral pH value, and higher air flow rate. The degradation of MeP by NTP combined with ZnFe₂O₄-rGO nanocomposites followed pseudo-first-order kinetics. O₂^•-, •OH, H₂O_2, and O₃ were found to play important roles in the MeP degradation, as part of the multi-catalytic mechanism of NTP combined with ZnFe₂O₄-rGO nanocomposites. MeP degradation pathways were proposed based on the degradation intermediates detected by gas chromatography mass spectrometry, including demethylation, hydroxylation, carboxylation, ring-opening, and mineralization reactions. The prepared ZnFe₂O₄-rGO nanocomposites provide an approach for improved contaminant degradation efficiency, with reduced energy consumption in the NTP process.

Photooxidation mechanism of As(III) by straw-derived dissolved organic matter

Straw return-to-field is a common agronomic practice that would affect the physicochemical characteristics of the paddy soil and overlying water, but few studies have focused on the possible impacts of straw return on the conversion of pollutants. In this study, the photooxidation of As(III) in aqueous solution by straw-derived dissolved organic matter (S-DOM) was investigated. The results showed that dissolved organic matter derived from wheat straw (DOMws) and rape straw (DOMrs) exhibited good spectroscopic features and could efficiently oxidize As(III) under irradiation at pH 5.0, with the k_obs values of As(III) oxidation being 0.15 h^-1 and 0.17 h^-1 for DOMws and DOMrs, respectively. Quenching studies indicated that hydroxyl radical (OH) dominated the oxidation of As(III) for both types of dissolved organic matter (DOM), though singlet oxygen (¹O₂) also played a role in the DOMrs system. Since acidic conditions are favorable for the formation of OH, As(III) oxidation decreased with an increase of pH value. Additionally, the oxidation efficiency of As(III) was inhibited in the presence of NO₃^- (0.2-2 mM) while enhanced in the presence of Fe(III) (5-50 μM). This study is of great significance for understanding the removal/transformation behavior of pollutants in paddy fields that receive straw return.

Application of a microbial siderophore desferrioxamine B in sunlight/Fe3+/persulfate system: from the radical formation to the degradation of atenolol at neutral pH

The present work reported a modified persulfate activation process with a microbial siderophore named desferrioxamine B (DFOB). DFOB was a natural complexing agent and could complex with Fe³⁺ strongly. The photochemical reactivity of Fe(III)-DFOB was studied. Fe²⁺ and HO^• were produced from Fe(III)-DFOB photolysis. Furthermore, the degradation of atenolol (ATL) was followed in light/persulfate (PS)/Fe(III)-DFOB system. The main oxidative radicals were SO₄^•- in this system. The results of pH effect showed that there was no obviously fluctuation on ATL degradation efficiency with the pH increased from 2.5 to 8.4. Moreover, k_SO4•-,DFOB was determined by laser flash photolysis (LFP) experiments. DFOB had positive effect on Fe²⁺ formation but negative effect on ATL degradation due to the high react rate constant between DFOB and SO₄^•-. The effects of chloride and carbonate ion were also investigated. The results in this study proposed the reaction mechanism of the modified persulfate activation process, and it could be applied in neutral and weak-alkaline pH range.

Degradation of methylparaben by sonocatalysis using a Co-Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo-first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near-neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.

Synergistic Adsorption for Parabens by an Amphiphilic Functionalized Polypropylene Fiber with Tunable Surface Microenvironment

A series of novel amphiphilic functionalized fibers with polarity tunable surface microenvironment were constructed by introducing hydrophilic polyamines and hydrophobic linear alkyl chain groups, aiming to selectively remove parabens from water. In addition, Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, etc. were employed to determine the successful preparation of amphiphilic functionalized fibers. The adsorption experimental data indicated that the amphiphilic fibers showed excellent selectivity for parabens. In the amphiphilic fibers, hydrogen bonding and hydrophobic interaction existing in one molecular unit can effectively act together to enhance the interaction between substrate and fibers. Kinetic studies illustrated that the adsorption process was a physical adsorption with chemical characteristics. The overall initial adsorption rate together with the stepwise adsorption rate was quantified, and it is inferred that the hydrophobic interaction plays a leading role in the first step of the adsorption process. Moreover, the Freundlich model well described the sorption process with a maximum adsorption of 138.4 mg/g. What's more, the fiber still keeps excellent adsorption capacity (>90%) even after 10 adsorption/desorption cycles, which certifies it is an excellent adsorbent and can be utilized to remove paraben in practice.

Decolorization of methylene blue using Fe(III)-citrate complex in a solar photo-Fenton process: impact of solar variability on process optimization

This study investigates the solar photo-Fenton based decolorization of a cationic dye methylene blue (MB) at circumneutral pH conditions. Water-soluble Fe(III)-citrate complex was used as a source of Fe(II) during the reaction by ligand-to-metal charge transfer under solar irradiation, and consequently, for the production of hydroxyl radicals. Solar decolorization of methylene blue was studied in sunny as well as cloudy weather, and further optimized using response surface methodology and Box-Behnken statistical experimental design. In this model, Fe(III) dose, citrate ion dose, and initial pH of the solution were used as independent parameters, and percentage decolorization of MB was used as a response. Better decolorization of MB was observed in sunny weather as compared to cloudy weather. A particular combination of parameters, i.e. pH of 7, Fe(III) of 0.5 mM, and citrate ion concentration of 10 mM, was found to achieve 89.19% and 51.22% decolorization in sunny and in cloudy weather respectively, which were the optimum/near-optimum performances for these weather conditions. Hence the process initiated with these parameters may potentially achieve better performance than any other parameter combination in all weathers, although the absolute removal would still depend on incident solar irradiation.

Microwave synthesis of iodine-doped bismuth oxychloride microspheres for the visible light photocatalytic removal of toxic hydroxyl-contained intermediates of parabens: catalyst synthesis, characterization, and mechanism insight

The iodine-doped bismuth oxychloride (I-doped BiOCl) microspheres are synthesized as the visible light photocatalysts for the photocatalytic removal of three toxic hydroxyl-contained intermediates of parabens. With the aid of the unique heating mode of microwave method, the I-doped BiOCl photocatalysts with tunable iodine contents and dispersed energy bands, instead of a mixture of BiOI and BiOCl or solid solution, are synthesized under the controllable conditions. Due to the stretched architectures, high specific surface area, and effective separation of photogenerated carriers, they exhibit high activity to the photocatalytic degradation of methyl 2,4-dihydroxybenzoate (MDB), methyl 3,4-dihydroxybenzoate (MDHB), and ethyl 2,4-dihydroxybenzoate (EDB). As a typical result, it is indicated that though MDB as the most difficult intermediate of parabens to be degraded, a 91.2% removal ratio can still be achieved over the I-doped BiOCl with an energy band of 2.79 eV within 60 min. In addition, it is also confirmed that these photocatalysts remain stable throughout the photocatalytic reaction and can be reused, and more importantly, the photogenerated h⁺ and •O₂^- are the key reactive species, while •OH plays a negligible role in the photocatalytic reaction. Resorcinol was identified as the main photodegraded intermediate. These results demonstrate that this photocatalytic system not only exhibit a high efficiency but also avoid the consequent secondary pollutions due to the no formation of complex hydroxyl derivatives.

Synthesis and characterization of CoOx/BiVO4 photocatalysts for the degradation of propyl paraben

Cobalt-promoted bismuth vanadate photocatalysts of variable cobalt content (0-1.0 wt.%) were synthesized and characterized with various techniques including BET, XRD, DRS, XPS and TEM. BiVO₄ exists in the monoclinic scheelite structure, while cobalt addition improves the absorbance in the visible region although it does not affect the band gap energy of BiVO₄. Cobalt exists in the form of well-dispersed Co₃O₄ nanocrystallites, which are in intimate contact with the much larger BiVO₄ nanoparticles. Photocatalytic activity was evaluated for the degradation of propyl paraben (PP) under simulated solar radiation. The activity of pristine BiVO₄ is significantly improved adding small amounts of cobalt and is maximized for the catalyst containing 0.5 wt.% Co. PP degradation in ultrapure pure water increases with increasing photocatalyst loading (100 mg/L to 1.5 g/L), and decreasing PP concentration (1600-200 μg/L). Experiments in bottled water, as well as in pure water spiked with bicarbonate and chloride ions showed little effect of non-target inorganics on degradation. Conversely, degradation is severely impeded in secondary treated wastewater. The enhancement of the photocatalytic activity of the synthesized catalysts is attributed to efficient electron-hole separation, achieved at the p-n junction formed between the p-type Co₃O₄ and the n-type BiVO₄ semiconductors.

Intermittent light and microbial action of mixed endogenous source DOM affects degradation of 17β-estradiol day after day in a relatively deep natural anaerobic aqueous environment

All kinds of wastewaters containing steroid estrogens (SEs) and mixed endogenous source dissolved organic matter (DOM) enter natural water environments with intermittent illumination where microbial action occurs in a relatively deep natural aqueous environment. The role of mixed endogenous source DOM in SEs' biodegradation and photochemical degradation in such environments was studied using 17β-estradiol (E2) in laboratory experiments under anaerobic conditions. The experimental results show that microbial action can improve the optical properties and electron transfer capability of mixed endogenous source DOM, promoting photodegradation and biodegradation. Intermittent illumination attenuates DOM's electron transfer capacity and its chromophore groups, but it improves the bioavailability of low molecular weight dissolved organic matter which promotes microbial growth under anaerobic conditions. DOM-mediated co-degradation by light and microbial action over three days was better than either individually. The presence of Fe(III) promoted electron transfer, and Fe(III)-DOM complexes accelerated energy transfer under irradiation, enhancing photodegradation. Any remaining estrogens will continue to degrade, most effectively in well-aerated waters with sufficient illumination.

Photogeneration of hydroxyl radical in Fe(III)-citrate-oxalate system for the degradation of fluconazole: mechanism and products

The photochemical role of Fe(III)-citrate complex is significant in natural waters due to its ubiquitous existence and excellent photoreactivity at near neutral pH. Although there are many reports on the photoinduced degradation of pollutants in the Fe(III)-citrate system, the optimum pH for its photoreactivity is yet not clearly understood. Here, for the first time, we demonstrated that the optimum pH was 5.5 for the photoproduction of ^•OH in the Fe(III)-citrate system via kinetics modeling based on the steady-state approximation. According to the experimental results, the ^•OH photoproduction increased with increasing pH until 5.5 and then decreased in Fe(III)-citrate solution, which agreed well with the prediction trend of kinetic modeling. The effect of the common ligand oxalate on the photoreactivity of Fe(III)-citrate system was also investigated. The addition of oxalate promoted the photoproduction of ^•OH in Fe(III)-citrate solutions, and the measured [^•OH]_ss increased with oxalate concentration under a fixed Fe(III)-to-citrate ratio. Little synergistic effect exists in Fe(III)-citrate-oxalate system at pH 4.0-5.5. In contrast, an appreciable synergistic effect was observed at near neutral pH (6.0-8.0). Higher oxalate-to-citrate ratio facilitated the synergistic effect. Furthermore, antifungal drug fluconazole could be removed efficiently in the Fe(III)-citrate-oxalate system. The photodegradation kinetics also verified the optimum pH of Fe(III)-citrate system and synergistic effect of oxalate. By LC-ESI-MS/MS analyses, the photoproducts of fluconazole in the Fe(III)-citrate-oxalate system were identified and the reaction mechanism involving hydroxylation substitution and subsequent cleavage of heterocyclic amine was proposed. These findings suggest that Fe(III)-citrate exhibits best photoreactivity at pH 5.5, and the coexistence of reactive ligands will enhance its photoreactivity at circumneutral pH, indicating potential application in wastewater treatment via addition of appropriate citrate and co-ligands.

Photodegradation of amitriptyline in Fe(III)-citrate-oxalate binary system: Synergistic effect and mechanism

Fe(III) and carboxylic acids are ubiquitous in surface water and atmospheric water droplets. Numerous documents have reported the photochemistry of Fe(III)-carboxylate complexes, typically including Fe(III)-oxalate and Fe(III)-citrate. Our previous study preliminarily showed that oxalate enhances the photoreactivity of Fe(III)-citrate system. Here, we further investigate the synergistic effect of Fe(III)-citrate-oxalate binary system at different conditions with pharmaceutical amitriptyline (AMT) as the model pollutant. In the Fe(III)-oxalate system, the photodegradation of AMT decreased with increasing pH from 3.0 to 8.0. In the Fe(III)-citrate system, the optimal pH for AMT degradation is around 5.0 in the same pH range. For the Fe(III)-citrate-oxalate system, the photodegradation of AMT decreased with increasing pH, indicating the combined effect of both oxalate and citrate on the photoreactivity. The addition of oxalate to the Fe(III)-citrate system markedly accelerated the photodegradation of AMT. The Fe(III)-carboxylate binary system exhibited excellent photoreactivity and up to 90% AMT was removed after 30 min at pH 6.0 with Fe(III)/citrate/oxalate ratio of 10:150:500 (μM). Synergistic effect was observed in Fe(III)-citrate-oxalate binary system in the pH range of 5.0-8.0. The presence of oxalate promoted the depletion of citrate in the Fe(III)-citrate system. The higher concentration ratios of oxalate to citrate facilitated the synergistic effect in the Fe(III)-citrate-oxalate system. By LC-MS analyses, a possible pathway of AMT degradation was proposed based on hydroxyl radicals (OH) mechanism. This finding could be helpful for the better understanding of synergistic mechanism of Fe(III)-citrate-oxalate binary complexes, which will be of great potential application in environmental photocatalysis at near neutral pH.

Ultraviolet absorption redshift induced direct photodegradation of halogenated parabens under simulated sunlight

As disinfection by-products of parabens, halogenated parabens are frequently detected in aquatic environments and exhibit higher persistence and toxicity than parabens themselves. An interesting phenomenon was found that UV absorption redshift (∼45 nm) occurs after halogenation of parabens at circumneutral pH, leading to overlap with the spectrum of terrestrial sunlight. This work presents the first evidence on the direct photodegradation of seven chlorinated and brominated parabens under simulated sunlight. These halogenated parabens underwent rapid direct photodegradation, distinguished from the negligible degradation of the parent compounds. The photodegradation rate depended on their forms and substituents. The deprotonation of halogenated parabens facilitated the direct photodegradation. Brominated parabens exhibited higher degradation efficiency than chlorinated parabens, and mono-halogenated parabens had higher degradation than di-halogenated parabens. The pseudo-first-order rate constants (k_obs) for brominated parabens (0.075-0.120 min^-1) were approximately 7-fold higher than those of chlorinated parabens (0.011-0.017 min^-1). A quantitative structure-activity relationship (QSAR) model suggested that the photodegradation was linearly correlated with the C-X bond energies, electronic and steric effects of halogen substituents. The photodegradation products were identified using QTOF-MS analyses and a degradation pathway was proposed. The yeast two-hybrid estrogenicity assay revealed that the estrogenic activities of the photoproducts were negligible. These findings are important for the removal of halogenated parabens and predictions of their fate and potential impacts in surface waters.

Efficient degradation of imipramine by iron oxychloride-activated peroxymonosulfate process

Synthesized iron oxychloride (FeOCl) was firstly applied to activate peroxymonosulfate (PMS) to degrade imipramine (IMI), a tricyclic antidepressant. Compared to some other Fe-based materials including zero valent iron, Fe₂O₃, Fe₃O₄ and ferric ions, FeOCl presented an impressive catalytic activity on PMS at near-neutral condition due to its unique structure containing abundant unsaturated iron atoms and oxo-bridged configuration. With an increase of FeOCl dose, PMS dose or initial pH in ranges of 0.02 - 0.5 g/L, 0.1 - 2.5 mM and 4.0 - 8.0, the degradation efficiency of IMI was effectively raised by 64.0%, 48.5% and 50.6%, respectively. The presence of either bicarbonate or chloride stimulated the removal of IMI. Moreover, 70.4% of IMI was degraded under the background of real water with 2 mM PMS. The possible reactive species were identified as sulfate and hydroxyl radicals. The formed hypochlorite through the reaction of PMS and the released chloride ions may also contribute to the degradation of IMI. Among the oxidants, sulfate radical was proven to be the dominate one in the system. Additionally, the FeOCl/PMS system can overall effectively degrade six other organic compounds including amitriptyline, desipramine, propranolol, nitrobenzene, methyl-paraben and ethyl-paraben, further suggesting the possible application of this system in treatment of vast aquatic micro-organic pollutants.

Photo-Oxidation of Bisphenol A in Aqueous Solutions at Near Neutral pH by a Fe(III)-Carboxylate Complex with Oxalacetic Acid as a Benign Molecule

The photo-oxidation of organic pollutants as induced by ferric-carboxylate complexes was known to be a photo-Fenton-like process. The use of a carboxylate ligand with higher efficiency and lower toxicity at near neutral pH is of high interest to researchers. In this work, photo-oxidation of bisphenol A (BPA) induced by a ferric-oxalacetic acid complex in aqueous solutions was investigated under 395 nm LED lamps. The results showed that the rate of BPA degradation increased in the order pH 10.0 << 8.0 < 6.5 < 4.0 within the first 10 min. More than 90% of BPA was successfully oxidized with Fe(III)/oxalacetic acid with a ratio of 1:5 at pH 6.5, which was primarily attributed to the generated hydroxyl radical. Iron in the Fe(III)-oxalacetic acid system was reused by simple addition of oxalacetic acid to the reaction mixture. Compared to common carboxylate ligands (pyruvic acid, oxalic acid, and citric acid), oxalacetic acid is more efficient and environmentally friendly for the Fe(III)-carboxylate complex-based photo-Fenton-like process at near neutral pH.

The photosensitized oxidation of mixture of parabens in aqueous solution

The work presents results of studies on the photosensitized oxidation of mixture of five parabens (methyl-, ethyl-, propyl-, n-butyl-, and benzylparaben) in aqueous solution. Aluminum phthalocyanine chloride tetrasulfonic acid and xenon lamp simulating solar radiation were used as a photosensitizer and a light source, respectively. The purpose was to investigate the influence of inhibitory effect compounds present in the mixture on the reaction rate. The influence of the addition of second photosensitizer on the parabens degradation rate was investigated. The effect of additives: tert-butanol - hydroxyl radical scavenger and sodium azide - singlet oxygen scavenger on reaction course was also determined. The transformation products formed during the photosensitized oxidation process were analyzed by UPLC-MS/MS. The efficiency of photosensitized oxidation of parabens with natural sunlight irradiation in the central Poland was checked.

Thermoactivated persulfate oxidation of pesticide chlorpyrifos in aquatic system: kinetic and mechanistic investigations

The widespread occurrence of organophosphorus pesticides (OPPs) in the environment poses risks to both ecologic system as well as human health. This study investigated the oxidation kinetics of chlorpyrifos (CP), one of the typical OPPs, by thermoactivated persulfate (PS) oxidation process, and evaluated the influence of key kinetic factors, such as PS concentrations, pH, temperature, bicarbonate, and chloride ions. The reaction pathways and mechanisms were also proposed based on products identification by LC-MS techniques. Our results revealed that increasing initial PS concentration and temperature favored the decomposition of CP, whereas the oxidation efficiency was not affected by pH change ranging from 3 to 11. Bicarbonate was found to play a detrimental role on CP removal rates, while chloride showed no effect. The oxidation pathways including initial oxidation of P=S bond to P=O, dechlorination, dealkylation, and the dechlorination-hydroxylation were proposed, and the detailed underlying mechanisms were also discussed. Molecular orbital (MO) calculations indicated that P=S bond was the most favored oxidation site of the molecule. The toxicity of reaction solution was believed to increase due to the formation of products with P=O structures. This work demonstrates that OPPs can readily react with SO₄^·- and provides important information for further research on the oxidation of these contaminants.

Methylparaben removal using heterogeneous photocatalysis: effect of operational parameters and mineralization/biodegradability studies

Methylparaben (MePB) is an organic compound employed mainly in the manufacture of different personal care products. However, it has been recently listed as a potential endocrine disrupter chemical. Therefore, the main objective of this work was to evaluate the degradation of MePB in aqueous solutions using heterogeneous photocatalysis with TiO₂ and hydrogen peroxide. In this way, effects of pH and the initial concentrations of catalyst, H₂O₂, and pollutant on treatment were analyzed. A face centered, central composite design was used for determination of the influence of each parameter in the process and the conditions under which the pollutant suffers the highest rates of degradation were selected. In general, results indicate that combination TiO₂/H₂O₂/light irradiation leads to ∼90 % of substrate removal after 30 min of reaction and that hydroxyl free radicals are the main specie responsible for organic matter elimination. Finally, in terms of mineralization and biodegradability, experimental results indicated that part of the organic matter was transformed into CO₂ and water and the photo-treatment promoted an increase in samples biodegradability.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m²/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500μg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

On the capacity of ozonation to remove antimicrobial compounds, resistant bacteria and toxicity from urban wastewater effluents

The degradation of erythromycin (ERY) and ethylparaben (EtP) in urban wastewater effluents at low concentration level during ozonation was investigated under different experimental conditions. Both substrates were rapidly eliminated within 2min at low ozone dose of 0.3mgL^-1 and the experimental data were well fitted in the pseudo-first-order kinetic model. The ratio of HO- and O₃-exposure (R_ct) at the inherent pH was found to be 1.9×10^-8. The degradation of ERY and EtP was pronounced at pH 8 compared to acidic pH conditions, while the degradation rate of both substrates was found to be matrix-depended. It was also shown that both O₃- and HO-mediated pathways are involved in the degradation of EtP, whereas the saturated-rich structure of ERY renders it O₃-recalcitrant. Under the optimum O₃ dose, the BrO₃^- concentration was found to be lower than 10μgL^-1. Five and fifteen transformation products were elucidated during ERY and EtP oxidation, respectively. The root and shoot inhibition can be attributed to the oxidation products formed upon dissolved effluent organic matter transformation. Escherichia coli harbouring resistance to ERY survived ozonation better than EtP-resistant E. coli. However, neither ERY- nor EtP-resistant E. coli were detected after 15min of ozonation.

Degradation of ethyl paraben by heat-activated persulfate oxidation: statistical evaluation of operating factors and transformation pathways

A factorial design methodology was implemented to evaluate the importance of ethyl paraben (EP) concentration (500-1500 μg/L), sodium persulfate concentration (400-500 mg/L), temperature (40-60 °C), reaction time (2-30 min), water matrix (pure water or secondary treated wastewater), and initial solution pH (3-9) on EP removal by heat-activated persulfate oxidation. All individual effects, except the solution pH, were statistically significant and so were the second-order interactions of ethyl paraben concentration with temperature or the reaction time. The influence of the water matrix was crucial, and the efficiency of the process was lower in secondary treated wastewater due to the presence of natural organic matter and inorganic salts that compete with ethyl paraben for the reactive oxygen species. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to identify major transformation by-products (TBPs); 13 compounds were detected as TBPs of EP. Degradation occurred through (i) hydroxylation, (ii) dealkylation, and (iii) oligomerization reactions leading to TBPs with ether and biphenyl structures. Oligomerization reactions were found to be the dominant pathway during the first steps of the reaction. The toxicity of 500 μg/L EP in secondary treated wastewater was tested against marine bacteria Vibrio fischeri; toxicity increased during the first minutes due to the production of several TBPs, but it consistently decreased thereafter.

Mechanisms of Sb(III) Photooxidation by the Excitation of Organic Fe(III) Complexes

Organic Fe(III) complexes are widely distributed in the aqueous environment, which can efficiently generate free radicals under light illumination, playing a significant role in heavy metal speciation. However, the potential importance of the photooxidation of Sb(III) by organic Fe(III) complexes remains unclear. Therefore, the photooxidation mechanisms of Sb(III) were comprehensively investigated in Fe(III)-oxalate, Fe(III)-citrate and Fe(III)-fulvic acid (FA) solutions by kinetic measurements and modeling. Rapid photooxidation of Sb(III) was observed in an Fe(III)-oxalate solution over the pH range of 3 to 7. The addition of tert-butyl alcohol (TBA) as an ·OH scavenger quenched the Sb(III) oxidation, suggesting that ·OH is an important oxidant for Sb(III). However, the incomplete quenching of Sb(III) oxidation indicated the existence of other oxidants, presumably an Fe(IV) species in irradiated Fe(III)-oxalate solution. In acidic solutions, ·OH may be formed by the reaction of Fe(II)(C2O4) with H2O2, but a hypothetical Fe(IV) species may be generated by the reaction of Fe(II)(C2O4)2(2-) with H2O2 at higher pH. Kinetic modeling provides a quantitative explanation of the results. Evidence for the existence of ·OH and hypothetical Fe(IV) was also observed in an irradiated Fe(III)-citrate and Fe(III)-FA system. This study demonstrated an important pathway of Sb(III) oxidation in surface waters.

Sonochemical degradation of ethyl paraben in environmental samples: Statistically important parameters determining kinetics, by-products and pathways

The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250-1250 μg/L, ultrasound (US) density 20-60 W/L, reaction time up to 120 min, initial pH 3-8 and sodium persulfate 0-100mg/L, either in ultrapure water or secondary treated wastewater. A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration)×(US density), (EP concentration)×(pHo) and (EP concentration)×(time). Experiments at an increased EP concentration of 3.5mg/L were also performed to identify degradation by-products. LC-TOF-MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound.

Contributions of Abiotic and Biotic Processes to the Aerobic Removal of Phenolic Endocrine-Disrupting Chemicals in a Simulated Estuarine Aquatic Environment

The contributions of abiotic and biotic processes in an estuarine aquatic environment to the removal of four phenolic endocrine-disrupting chemicals (EDCs) were evaluated through simulated batch reactors containing water-only or water-sediment collected from an estuary in South China. More than 90% of the free forms of all four spiked EDCs were removed from these reactors at the end of 28 days under aerobic conditions, with the half-life of 17α-ethynylestradiol (EE2) longer than those of propylparaben (PP), nonylphenol (NP) and 17β-estradiol (E2). The interaction with dissolved oxygen contributed to NP removal and was enhanced by aeration. The PP and E2 removal was positively influenced by adsorption on suspended particles initially, whereas abiotic transformation by estuarine-dissolved matter contributed to their complete removal. Biotic processes, including degradation by active aquatic microorganisms, had significant effects on the removal of EE2. Sedimentary inorganic and organic matter posed a positive effect only when EE2 biodegradation was inhibited. Estrone (E1), the oxidizing product of E2, was detected, proving that E2 was removed by the naturally occurring oxidizers in the estuarine water matrixes. These results revealed that the estuarine aquatic environment was effective in removing free EDCs, and the contributions of abiotic and biotic processes to their removal were compound specific.

Flower-like Bi4O5I2/Bi5O7I nanocomposite: facile hydrothermal synthesis and efficient photocatalytic degradation of propylparaben under visible-light irradiation

A novel nonstoichiometric inter-bismuth oxyiodides heterostructure photocatalyst are synthesized and exhibited high potential for applications in visible-light photocatalytic environmental cleaning.

A new combined process for efficient removal of Cu(II) organic complexes from wastewater: Fe(III) displacement/UV degradation/alkaline precipitation

Efficient removal of heavy metals complexed with organic ligands from water is still an important but challenging task now. Herein, a novel combined process, i.e., Fe(III)-displacement/UV degradation/alkaline precipitation (abbreviated as Fe(III)/UV/OH) was developed to remove copper-organic complexes from synthetic solution and real electroplating effluent, and other processes including alkaline precipitation, Fe(III)/OH, UV/OH were employed for comparison. By using the Fe(III)/UV/OH process, some typical Cu(II) complexes, such as Cu(II)-ethylenediaminetetraacetic acid (EDTA), Cu(II)-nitrilotriacetic acid (NTA), Cu(II)-citrate, Cu(II)-tartrate, and Cu(II)-sorbate, each at 19.2 mg Cu/L initially, were efficiently removed from synthetic solution with the residual Cu below 1 mg/L. Simultaneously, 30-48% of total organic carbon was eliminated with exception of Cu(II)-sorbate. Comparatively, the efficiency of other processes was much lower than the Fe(III)/UV/OH process. With Cu(II)-citrate as the model complex, the optimal conditions for the combined process were obtained as: initial pH for Fe(III) displacement, 1.8-5.4; molar ratio of [Fe]/[Cu], 4:1; UV irradiation, 10 min; precipitation pH, 6.6-13. The mechanism responsible for the process involved the liberation of Cu(II) ions from organic complexes as a result of Fe(III) displacement, decarboxylation of Fe(III)-ligand complexes subjected to UV irradiation, and final coprecipitation of Cu(II) and Fe(II)/Fe(III) ions. Up to 338.1 mg/L of Cu(II) in the electroplating effluent could be efficiently removed by the process with the residual Cu(II) below 1 mg/L and the removal efficiency of ∼99.8%, whereas direct precipitation by using NaOH could only result in total Cu(II) removal of ∼8.6%. In addition, sunlight could take the place of UV to achieve similar removal efficiency with longer irradiation time (90 min).

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10(-4) E/(m(2) s). Six nitrogen-doped titania catalysts synthesized by annealing a sol-gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450-800 °C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600 °C) was used for further tests. Experiments were performed at EP concentrations between 150 and 900 μg/L, catalyst loadings between 100 and 1000 mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100 mg/L. For EP concentrations up to 300 μg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750 mg/L and hydrogen peroxide up to 100 mg/L. Near-neutral (pH = 6.5-7.5) and alkaline conditions (pH = 9) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10-20 mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices. UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration-time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.

Oxidative photodegradation of herbicide fenuron in aqueous solution by natural iron oxide α-Fe2O3, influence of polycarboxylic acids

The photodegradation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by using a natural iron oxide (NIO), α-Fe2O3, in aqueous solution at acidic pH has been undertaken. The NIO was characterized by the Raman spectroscopy method. The degradation pathways and the formation of degradation products were studied. A high-pressure mercury lamp and sunlight were employed as light source. Fenuron photodegradation using NIO with oxalic acid followed the pseudo-first-order kinetics, the optimal experimental conditions were [oxalic acid]0 = 10(-3) M and [NIO] = 0.1 g L(-1) at pH 3. A UVA/NIO/oxalic acid system led to a low fenuron half-life (60 min). The results were even better when solar light is used (30 min). The variables studied were the doses of iron oxide, of carboxylic acids, the solution pH and the effect of sunlight irradiation. The effects of four carboxylic acids, oxalic, citric, tartaric and malic acids, on the fenuron photodegradation with NIO have been investigated, oxalic acid was the most effective carboxylic acid used at pH 3. A similar trend was observed for the removal of total organic carbon (TOC), 75% of TOC was removed. The analytical study showed many aromatic intermediates, short-chain carboxylic acids and inorganic ion.

One-pot synthesis of micro/nano structured β-Bi2O3 with tunable morphology for highly efficient photocatalytic degradation of methylparaben under visible-light irradiation

Micro/nanostructures β-Bi₂O₃ with tunable morphologies were synthesized via an one-pot solvothermal–calcining route for efficient visible-light photocatalytic removal of methylparaben from water.