Dissolved organic matter isolates obtained by solid phase extraction exhibit higher absorption and lower photo-reactivity: Effect of components.

Notable differences in photo-physical and chemical properties were found between bulk water and solid phase extraction (SPE) isolates for dissolved organic matter (DOM). The moieties extracted using modified styrene divinylbenzene cartridges, which predominantly consist of conjugated aromatic molecules like humic acids, contribute mainly to light absorption but exhibit lower quantum yields of fluorescence and photo-produced reactive intermediates (PPRIs). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed lignin as the moieties displaying most significant variance in abundance. In Van Krevelen-Spearman plot, we observed molecules positively or negatively correlated with DOM's optical and photochemical properties (including SUVA254, steady-state concentrations of ·OH, 1O2 quantum yield, etc.) were confined to specific regions, which can be delineated using a threshold modified aromaticity index (AImod) of 0.3. Based on the relationships between optical properties and PPRI production, it is suggested that the energy gap between ground state and excited singlet state (△ES1→S0), governing the inner conversion rate, serves as a determinant for apparent quantum yield of PPRIs in DOM, with intra-molecular charge transfer (CT) interactions potentially playing a pivotal role. Regarding DOM's photoreactivity with pollutants, this study has revealed, for the first time, that protein/amino sugars/amino acids could act as antioxidant groups in addition to phenols on the photolysis of sulfadiazine. These findings provide valuable insights into DOM photochemistry and are expected to stimulate further research in this area.

Characterization of microplastic-derived dissolved organic matter in freshwater: Effects of light irradiation and polymer types.

This study investigated the impacts of light irradiation and polymer types on the leaching behavior of dissolved organic matter (DOM) from microplastics (MPs) in freshwater. Polypropylene had the highest leaching capacity of DOM after photoaging, followed by polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET). While similarly low levels of DOM were observed in the remaining 5 MP suspensions under UV irradiation and in almost all MP suspensions (except PA) under darkness. These suggest that the photooxidation of some buoyant plastics may influence the carbon cycling of nature waters. Among 9 MP-derived leachates, PET leachates had the highest chromophoric DOM concentration and aromaticity, probably owing to the special benzene rings and carbonyl groups in PET structures and its fast degradation rate. Protein-like substances were the primary fluorescent DOM in MP suspensions (except PS), especially in darkness no other fluorescent substances were found. Considering the bio-labile properties of proteins together, MPs regardless of floating or suspended in an aquatic environment may have prevalent long-term effects on microbial activities. Besides, from monomers to hexamers with newly formed chemical bonds were identified in UV-irradiated MP suspensions. These results will contribute to a deep insight into the potential ecological effects related to MP degradation.

Analysis on the attenuation characteristics of PPCPs in surface water and their influencing factors based on a compilation of literature data.

The attenuation characteristics of PPCPs play an important part in predicting their environmental concentrations. However, considerable uncertainty remains in reported laboratory data on the attenuation characteristics of PPCPs. In this analysis, we compile information on laboratory-observed photodegradation half-lives (t1/2), biodegradation t1/2, the organic carbon normalized adsorption constant (KOC) and field-observed overall attenuation t1/2 for PPCPs in water bodies from more than 200 peer-reviewed studies. To mitigate the effects of such uncertainty, we derive representative values (RV) for PPCP degradability from these records to better compare the characteristics of different PPCPs. We further examine the influence of experimental conditions and environmental drivers on the determination of t1/2 using difference analysis and correlation analysis. The results indicate that for laboratory photodegradation tests, different light sources, initial concentration and volume significantly affect t1/2, whereas there is no significant difference between values obtained from tests conducted in pure water and natural water. For biodegradation, laboratory-measured t1/2 values in batch, flume and column studies gradually decrease, marking the controlling role of experimental setup. Redox condition, initial concentration and volume are also recognized as important influencing factors. For adsorption, water-sediment ratio is the primary reaction parameter. As two frequently investigated factors, however, pH and temperature are not significant factors in almost all cases. In field observations, the persistence of carbamazepine, typically used as a tracer, is in doubt. Water depth and latitude are the most correlated drivers of t1/2, indicating the predominant status of photodegradation in the overall attenuation rates. These findings call for caution when selecting experimental parameters and environmental drivers in determining PPCP's attenuation rates and establishing PPCP fate models in the field.

Quantitative structure-activity relationship models for the reaction rate coefficients between dissolved organic matter and PPCPs.

To predict PPCPs' photolysis rate in natural aquatic environment, it is essential to grasp the reaction rates between DOM and PPCPs, yet there are few measured data and no prediction models for this important photochemical parameter. To address this, a reaction rate coefficient (αDOM) was defined to describe the apparent rate of DOM-involved photoreaction for PPCPs. The measured αDOM values for 40 PPCPs in 9 DOM samples varied dramatically, ranging from (-2.1 ± 0.1)× 1010 to (2.2 ± 0.1)× 1011 M-1 s-1. Then the quantitative structure-activity relationship (QSAR) models were developed using chemical and water quality descriptors via the random forest method. We initially separated positive and negative values by a classifier with an AUC value of 0.965, followed by the construction of regression models for positive and negative values, respectively, using a regressor. Positive models achieved satisfactory goodness-of-fit and predictive ability (R2adj=0.92 and Q2ext=0.86), while negative models demonstrated acceptable performance (R2adj=0.71 and Q2ext=0.70). Finally, a comprehensive photolysis model that incorporates the QSAR models for αDOM was established and the significance of water quality parameters was emphasized through sensitive analysis. This model enables more elaborate predictions of PPCPs' photolysis rates in various water samples, providing valuable assistance for forecasting PPCPs' environmental fate.

The determination and prediction of the apparent reaction rates between excited triplet-state DOM and selected PPCPs.

To determine and predict the reaction rate between 3DOM* and PPCPs in various water bodies, this study defines a reaction rate coefficient ( [Formula: see text] ) to describe the reaction between 3DOM* and PPCPs. As the values also included the inhibition effect of DOM's antioxidant moieties, the calculation of [Formula: see text] is inconsistent with that of a bimolecular rate constant via the steady-state kinetic method. The [Formula: see text] values of 12 selected PPCPs were determined in two DOM solutions and ten DOM-containing water samples collected from typical surface water bodies in Beijing. The Pearson coefficients between nine predictors including the absorbance ratio (E2/E3), specific absorption coefficient at 254 nm (SUVA254), fluorescence index (FI), biological index (BIX), humification index (HIX), pH, total organic carbon (TOC), total fluorescence intensity (TFI) and TOC normalized TFI (TFI/TOC) and [Formula: see text] were examined. Correlation patterns for sulfonamides, ß-blockers and diclofenac supported the electron transfer pathway, and was distinctly different from those appeared for FQs where quenching effect played a main part. TFI and TFI/TOC were recognized as the most useful surrogates in empirically predicting [Formula: see text] . For PPCPs that went through the electron transfer pathway, [Formula: see text] could be well fit to the Rehm-Weller model assuming a proportional relationship between TFI and △Get. For FQs, [Formula: see text] was found to linearly correlated with TFI/TOC. The [Formula: see text] values determined in this study enrich the database of PPCPs photolysis parameters, and the correlation analysis provides reference for forecasting PPCPs fate in the aquatic environment.

FeOCl-confined activated carbon for improving intraparticle Fenton-like oxidation regeneration.

Highly efficient oxidation, as non-thermal regeneration technology, is a promising method to solve the regeneration problem of spent activated carbon (AC) in wastewater treatment. In this study, FeOCl was confined into activated carbon (FeOCl/AC) for catalytic oxidation of contaminants on AC during the regeneration process. The characterization results of FeOCl/AC showed that amorphous FeOCl was distributed in micropores, mesopores and macropores of AC. The methylene blue (MB)-adsorbed FeOCl/AC had a regeneration efficiency of 93.7 % at neutral pH in the presence of H2O2, much higher than 46.9 % by Fenton oxidation and 33.7 % by H2O2 oxidation. Meanwhile, the spent FeOCl/AC after the adsorption of atrazine, 2,4-dichlorophenol, and ofloxacin had the regeneration efficiencies of 71.5 %, 86.4 %, and 100 %, respectively. Moreover, the regeneration efficiency still reached 87 % in the fifth adsorption-regeneration cycle, and was linearly decreased with the increase of adsorbed amounts of MB. During 6 h regeneration of spent FeOCl/AC, 97 % of adsorbed MB was degraded. Electron paramagnetic resonance and radical trapping experiments indicated that both superoxide and hydroxyl radicals were involved in MB oxidation during the regeneration process.

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.

The degradation of enrofloxacin by a non-metallic heptazine-based OCN polymer: Kinetics, mechanism and effect of water constituents.

Antibiotics are widespread in the environment with notable ecological risk, for which efficient and green removal technologies are demanded. As a kind of g-C3N4-based material with remarkable photocatalytic property, OCN is an oxygen- and nitrogen-linked carbon nitride organic polymer which can be synthesized through a single-step thermal polymerization method. In this study, OCN was applied for the visible-light-driven photocatalytic degradation of a typical fluoroquinolone (FQ) antibiotics enrofloxacin (ENR). The photocatalysis process achieved over 97% ENR removal within 60 min with 0.4 mg/L OCN and 4 mg/L ENR at pH 8.2. The photocatalytic mechanism of OCN at different pH was studied for the first time. It was shown that O2⋅-, 1O2 and h+ made contributions at neutral or basic pH and 1O2 contributes the most (57.6% at pH 8.2), while ⋅OH played a role only under acidic condition with a contribution rate of 23.8% at pH 3.2. The cleavage of the piperazine ring and the quinolone ring were two main degradation pathways. The common water constituents humic acid and NO3- showed a dual effect, but HCO3- and Cl- inhibited the degradation. The effect of different water matrices was tested under natural sunlight and it was only a tiny disturbance to the degradation rates. The biotoxicity test conducted using Vibrio fischeri indicated that the toxicity of degradation products became negligible after 3 h. This study demonstrated that OCN is a promising candidate for the advanced treatment and in-situ remediation.