Dissolved organic matter (DOM) plays a significant role in the photochemical behavior of nano- and micro-plastic particles (NPs/MPs). We investigated the influence of DOM on the mechanism on the photoaging of NPs/MPs with different molecular structures under UV₃₆₅ irradiation in water. DOM components used in this study are mainly humic acid and fulvic acid. The results showed that DOM promoted the weathering of aliphatic NPs/MPs (polypropylene (PP)), but inhibited or had only a minor effect on the photoaging of aromatic NPs/MPs (polystyrene (PS) NPs/MPs, carboxyl-modified PS NPs, amino-modified PS NPs, and polycarbonate MPs). NPs with a large surface area may adsorb sufficient DOM on the particle surfaces through π-π interactions, which competes with NPs for photon absorption sites, thus, can delay the photoaging of PS NPs. Aromatic MPs may release phenolic compounds that quench •OH, thereby weakening the photoaging process. For aliphatic MPs, the detection of peracid, aldehyde, and ketone groups on the polymer surface indicated that DOM promoted weathering of PP MPs, which was primarily because the generation of •OH due to DOM photolysis may attack the polymer by C–C bond cleavage and hydrogen extraction reactions. This study provides insight into the UV irradiation weathering process of NPs/MPs of various compositions and structures, which are globally distributed in water.

Recently, hetero junction materials (p-n-p and n-p-n) have been developed for uplifting the visible light activity to destroy the harmful pollutants in wastewater. This manuscript presents a vivid description of novel n-p-n junction materials namely CeO₂-PPy-ZnO. This novel n-p-n junction was applied as the photocatalyst in drifting the mobility of charge carriers and hence obtaining the better photocatalytic activity when compared with p-n and pure system. Such catalyst's syntheses were successful via the copolymerization method. The structural, morphological and optical characterization techniques were applied to identify the physio-chemical properties of the prepared materials. Additionally, the superior performance of this n-p-n nanostructured material was demonstrated in the destruction of micro organic (chlorophenol) toxic wastes under visible light. The accomplished ability of the prepared catalysts (up to 92% degradation of chlorophenol after 180 min of irradiation) and their profound degradation mechanism was explained in detail.

The use of lanthanum-anchored zinc oxide distorted hexagon (La@ZnO DH) nanoclusters as an active material for the photodegradation of rhodamine B (Rh–B) dye via hydrogen bonding, electrostatic, and π-π interactions is examined herein. The active photocatalyst is derived from porous zeolite imidazole frameworks (ZIF-8) via a combined ultrasonication and calcination process. The distorted hexagon nanocluster morphology with controlled surface area is shown to provide excellent catalytic activity, chemical stability and demarcated pore volume. In addition, the low bandgap (3.57 eV) of La@ZnO DH is shown to expand the degradation of Rh–B under irradiation of UV light as compared to the pristine ZIF-8-derived ZnO photocatalyst due to inhibited recombination of electrons and holes. The outstanding physicochemical stability and enhanced performance of La@ZnO DH could be ascribed to the synergistic interaction among La3+ particles and the ZnO nanoclusters and provide a route for their utilization as a promising catalyst for the detoxification of Rh–B.

As the ubiquitous active components in aquatic environments, low molecular weight organic acids (LMWOAs) have a large influence on the environmental behaviors of contaminants. This research was focused on the effect of different LMWOAs including 11 aliphatic acids and 7 aromatic acids on the photodegradation kinetics of tetracycline (TC), and the development of quantitative structure-activity relationship (QSAR) model. Results showed that TC photodegradation in the presence of LMWOAs fitted pseudo-first-order photolysis kinetics, and the observed photolysis rate constant (kobs) varied from 0.077 to 0.331 h⁻¹. The QSAR model was developed by partial-least-squares (PLS) with using a sequential approach with 25 theoretical molecular descriptors. Four descriptors including ELUMO-EHOMO, ELUMO, CCR and Qmax were found to mechanistically and statistically affect kobs.The high cross validated regression coefficient (Qcum2, 0.898) and high correlation coefficient (R², 0.908) indicated significantly goodness-of-fit and high robustness of the model. The predicted and observed values with high agreement in the defined applicability domain featured accuracy and feasibility of model. This work provided a robust predictive method for estimating the TC photodegradation in the presence of different structures of LMWOAs.

As an emerging brominated flame retardant (BFR), tetrabromobisphenol S (TBBPS) has been frequently detected in the environmental media and organisms. Knowledges on the transformation and fate of TBBPS in both environment and engineering systems are essential to its ecological risk assessment. Herein, we reported the photochemical decomposition of TBBPS in aqueous solution upon 254 nm ultraviolet irradiation (UV₂₅₄). Results show that TBBPS was highly photoreactive, most likely due to the presence of four ortho-bromine substituents. The molar absorption coefficient and quantum yield of TBBPS were found to be pH-dependent, with the monoanionic form being most photoreactive. A series of photoproducts were identified by solid phase extraction (SPE) combined with liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI(+)-MS/MS. The photolysis of TBBPS likely proceeded through photonucleophilic substitution, photoreductive debromination, and β-scission reactions. A ketocarbene, possibly derived from the lower lying excited triplet state, was proposed to be involved in the photolysis of TBBPS. Ion chromatography analysis revealed that debromination occurred quickly, and the yield of bromide (Br⁻) approached 100% after 90 min irradiation. The presence of SRNOM and MRNOM inhibited the photodegradation rate of TBBPS, which is likely due to the light-screening and physical quenching effects of natural organic matter (NOM). Our results reveal that photolysis is an important process for the attenuation of TBBPS in aquatic system; however, naturally occurring species such as NOM can appreciably retard the decay of TBBPS.

A series of phosphorus containing ZnO (P–ZnO) photocatalysts with various percentages of phosphorus were successfully synthesized using the hydrothermal method. The structural, physical and optical properties of the obtained microparticles were investigated using diverse techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible diffusion reflectance spectroscopy (UV–Vis DRS), photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and N₂ adsorption-desorption analysis. The photocatalytic activities of the pure and P–ZnO samples were evaluated for the degradation of Rhodamine B (RhB) under visible light irradiation. The parameters such as pH, catalyst dosage, contaminant concentration and effect of persulfate as an oxidant were studied. It was found that the P–ZnO1.8% photocatalyst could destroy 99% of RhB (5 ppm) in 180 min at pH = 7; furthermore, it degraded ∼100% of 5 and 10 ppm of the RhB pollutant in 120 and 180 min, respectively, only by adding 0.01 g of persulfate into the reaction solution. To determine the photocatalytic mechanism, 2-propanol, benzoquinone and EDTA were used and it was indicated that hydroxyl radicals, superoxide ions and holes, all had major roles in the photocatalytic degradation but the hydroxyl radical effect was the most significant. The phenol degradation was also investigated using the P–ZnO1.8% optimum photocatalyst which could destroy 53% of the phenol (5 ppm) in 180 min. According to the reusability test, it was proved that after 5 cycles, the catalyst activity was not highly changed and it was potentially capable of pollutant degradation.

This study aims to use ultraviolet (UV) irradiation to decompose polybrominated diphenyl ethers (PBDEs) in the elutes and then reuse the surfactants. The results indicate that UV can remove 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) from surfactant eluents and Triton X series surfactants also can remove BDE-47 from the soil. Triton X-100 (TX-100) is the most promising surfactant during the washing and photodegradation processes. Quench experiments suggest that both ¹O₂ and OH• were involved in the TX-100 decomposition but only ¹O₂ is responsible for the degradation of BDE-47. In analysis of the photoproducts of BDE-47 by Gas Chromatography Mass Spectrum (GC-MS) and Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS), BDE-47 was mainly debrominated to the lower-brominated BDEs and then oxidized to ring-opening products. The little loss of TX-100 can mainly be attributed to the breakage of polyethylene oxide (PEO) chain. Nevertheless, the washing wastes treated by UV light can exhibit higher solubility for BDE-47 than before, indicating they can be reused for BDE-47 removal from soil. The toxicity assessment experiments were performed using Escherichia coli (E.coli) as an indicator. The results indicate that the removal of BDE-47 by UV irradiation can reduce the toxicity of eluent.

Degrading aquatic organic pollutants efficiently is very important but strongly relied on the design of photocatalysts. Porous graphene could increase photocatalytic performance of ZnO nanoparticles by promoting the effective charge separation of electron-hole pairs if they can be composited. Herein, porous graphene, ZnO nanoparticles and porous graphene/ZnO nanocomposite were prepared by fine tuning of partial combustion, which graphene oxide imperfectly covered by the layered Zn salt was combusted under muffle furnace within few minutes. Resulting ZnO nanoparticles (32–72 nm) are dispersed uniformly on the surface of graphene sheets, the pore sizes of porous graphene are in the range from ∼3 to ∼52 nm. The synthesized porous graphene/ZnO nanocomposite was confirmed to show enhanced efficiency under natural sunlight irradiation compared with pure ZnO nanoparticles. Using porous graphene/ZnO nanocomposite, 100% degradation of methyl orange can be achieved within 150 min. The synergetic effect of photocatalysis and adsorption is main reason for excellent MO degradation of PG/ZnO nanocomposite. This work may offer a new route to accurately prepare porous graphene-based nanocomposite and open a door of their applications.

Removal of toxic formaldehyde from environmental waters is crucial to maintain ecosystem sustainability and human health. In this work, MIL-100(Fe) as a heterogeneous Fenton-like photocatalyst was used for the treatment of formaldehyde-contaminated water. The MIL-100(Fe) was synthesized via a facile solvothermal method and fully characterized using different spectroscopic and microscopic techniques. Based on the results, the formation of highly porous, crystalline, and stable visible light-responsive MIL-100(Fe) was confirmed. The Fenton-like photocatalytic efficiency of the MIL-100(Fe) toward the degradation of formaldehyde was then studied under visible light irradiation. For this purpose, the effect of initial concentration of formaldehyde, photocatalyst dose, H₂O₂ concentration, solution pH, and contact time on the removal efficiency of the MIL-100(Fe) was investigated using central composite design. The obtained results showed that the removal efficiency of the MIL-100(Fe) is significantly affected by the initial concentration of formaldehyde. A second-order model with R² = 0.93 was developed for the system that was able to adequately predict the percentage removal of formaldehyde by the MIL-100(Fe) under different experimental conditions. According to the numerical optimization results, by using 1.13 g L⁻¹ photocatalyst and 0.055 mol L⁻¹ H₂O₂, 93% of formaldehyde can be removed after 119 min from an aqueous solution containing 700 mg L⁻¹ of formaldehyde at pH 6.54.

In this study, the synthesis of Fe₃O₄@GO@g-C₃N₄ ternary nanocomposite for enhanced photocatalytic degradation of phenol has been investigated. The surface modification of Fe₃O₄ was performed through layer-by-layer electrostatic deposition meanwhile the heterojunction structure of ternary nanocomposite was obtained through sonicated assisted hydrothermal method. The photocatalysts were characterized for their crystallinity, surface morphology, chemical functionalities, and band gap energy. The Fe₃O₄@GO@g-C₃N₄ ternary nanocomposite achieved phenol degradation of ∼97%, which was significantly higher than that of Fe₃O₄@GO (∼75%) and Fe₃O₄ (∼62%). The enhanced photoactivity was due to the efficient charge carrier separation and desired band structure. The photocatalytic performance was further enhanced with the addition of hydrogen peroxide, in which phenol degradation up to 100% was achieved in 2 h irradiation time. The findings revealed that operating parameters have significant influences on the photocatalytic activities. It was found that lower phenol concentration promoted higher activity. In this study, 0.3 g of Fe₃O₄@GO@g-C₃N₄ was found to be the optimized photocatalyst for phenol degradation. At the optimized condition, the reaction rate constant was reported as 6.96 × 10⁻³ min⁻¹. The ternary photocatalyst showed excellent recyclability in three consecutive cycles, which confirmed the stability of this ternary nanocomposite for degradation applications.