Abiotic and biotic degradation of five aromatic organosilicon compounds in aqueous media-Structure degradability relationships

Silicones have many applications and are produced in large quantities. Despite their potential toxicity, information on their environmental mineralisation is scarce. Therefore, we investigated a group of five organosilicon compounds (o-MeOC₆H₄SiMe₃ (1), p-MeOC₆H₄SiMe₃ (2), (p-MeOC₆H₄)₂SiMe₂ (3), o-Me₂NC₆H₄SiMe₃ (4) and p-Me₂NC₆H₄SiMe₃ (5)), recently developed to be 'benign by design' based on their readily degradable core structure. Five different degradability tests were performed, one assessing hydrolytic and two analysing biological and photolytic stability, respectively. All substances, except (p-MeOC₆H₄)₂SiMe₂ (3), hydrolysed within 24 h to 50% indicating that this is one of the major pathways of their primary elimination. In agreement with previous research, none of the substances was readily biodegradable. In contrast, 100% of p-Me₂NC₆H₄SiMe₃ (5) was primarily eliminated by photolytic and hydrolytic processes. The elimination rates of the other substances ranged from 7% to 64%. Irradiation at shorter wavelengths increased both the extent and speed of photodegradation. Eleven transformation products of p-Me₂NC₆H₄SiMe₃ (5) were detected, all of which were completely eliminated within 64 min of irradiation with a Hg lamp (200-400 nm). The insertion of an electron-donating group on the benzene ring like in p-Me₂NC₆H₄SiMe₃ (5) clearly enhanced photolytic degradability but further research is necessary to achieve truly biodegradable silicones.

Application of multivariate data techniques in photochemical study of polycyclic aromatic hydrocarbons (PAHs) and transformed PAH products in road dust

Road dust is a key repository for PAHs and transformed PAH products (TPPs) generated from natural and anthropogenic sources in the urban environment. Eventhough PAHs and TPPs are prone to post-emission photochemical processes, very limited studies exist on the subject for road dust. This knowledge gap is of particular concern since some of the resultant TPPs are notably more carcinogenic than their precursor PAHs. This study evaluated the role of 254 nm ultraviolet (UV) photons on the photochemistry of PAHs and TPPs in road dust. The findings show that UV irradiation had varying effects on the fate of analytes, particularly naphthalene (NAP), phenanthrene (PHE), 7, 12-dimethylbenz(a)anthracene (DMBA), 1-hydroxypyrene (HPY), 1-nitropyrene (1NPY), pyrene (PYR) and 5-nitroacenaphthene (5NAC). Photochemical relationship was identified between PYR, 1NPY and HPY, and DMBA and benzo(a)anthracene. Unlike carbonyl-PAHs, parent PAHs, nitro-PAHs and hydroxy-PAHs can originate from photolysis. Photon irradiation durations of 3, 6 and 7.5 h had the most intense influence on the photolytic process with 7.5 h as optimum. The photochemical rate at optimum irradiation duration shows an increasing trend of NAP < PHE < 1NPY < DMBA < 5NAC < HPY with respective estimates of 0.08, 0.11, 0.21, 0.22, 0.43, and 0.59 mg kg^-1 hr^-1. Physicochemical properties of analytes such as index of refraction and vapour pressure (in logarithmic form) had an inverse effect on photolysis. The knowledge generated is significant for the in-depth understanding of the fate of PAHs and TPPs on urban road surfaces and contributes to the greater protection of human health and the environment.

Investigation of the Potential Environmental Risks of Phthalate Derivatives Designed To Be Environmentally Friendly

Phthalate derivatives with low estrogenic activity, high infrared spectrum signals, high Raman characteristic vibration spectrum, high fluorescence intensity, and high ultraviolet sensitivity were selected as precursors from our previous studies, so that the changes in their toxicity and estrogenic activity during biological metabolism, ozone oxidation, photocatalytic degradation, photodegradation, and microbial degradation could be studied.The transformation pathways of these derivatives were simulated, and the reaction energy barriers were calculated. To determine the potential environmental risks of these phthalate derivatives, the pharmacophore models of biotoxicity and estrogen activity of phthalates were used to predict the biotoxicity and estrogen activity of the transformed products. The results showed an increase in the biotoxicity and estrogen activity of the biometabolites, ozonation products, photocatalytic degradation products, and microbial degradation products; the only products that did not follow this trend were the photodegradation products. Notably, the pathways that produced more potentially toxic compounds were the less favorable paths. Our results indicate that the transformation products of the designed environmentally friendly phthalate derivatives potentially pose environmental risks. To avoid such risks, the environmental transformation pathway of these derivatives should be simulated to screen for environmentally friendly phthalate molecules. Environ Toxicol Chem 2020;39:1138-1148. © 2020 SETAC.

Photodecomposition properties of brominated flame retardants (BFRs)

This study investigates the geometric and electronic properties of selected BFRs in their ground (S₀) and first singlet excited (S₁) states deploying methods of the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). We estimate the effect of the S₀→ S₁ transition on the elongations of the C-Br bond, identify the frontier molecular orbitals involved in the excitation process and compute partial atomic charges for the most photoreactive bromine atoms. The bromine atom attached to an ortho position in HBB (with regard to C-C bond; 2,2',4,4',6,6'-hexabromobiphenyl), TBBA (with respect to the hydroxyl group; 2,2',6,6'-tetrabromobisphenol A), HBDE and BTBPE (in reference to C-O linkage; 2,2',4,4',6,6'-hexabromodiphenylether and 1,2-bis(2,4,6-tribromophenoxy)ethane, respectively) bears the highest positive atomic charge. This suggests that, these positions undergo reductive debromination reactions to produce lower brominated molecules. Debromination reactions ensue primarily in the aromatic compounds substituted with the highest number of bromine atoms owing to the largest stretching of the C-Br bond in the first excited state. The analysis of the frontier molecular orbitals indicates that, excitations of BFRs proceed via π→π*, or π→σ* or n→σ* electronic transitions. The orbital analysis reveals that, the HOMO-LUMO energy gap (E^H-L) for all investigated bromine-substituted aromatic molecules falls lower (1.85-4.91 eV) than for their non-brominated analogues (3.39-8.07 eV), in both aqueous and gaseous media. The excitation energies correlate with the E^H-L values. The excitation energies and E^H-L values display a linear negative correlation with the number of bromine atoms attached to the molecule. Spectral analysis of the gaseous-phase systems reveals that, the highly brominated aromatics endure lower excitation energies and exhibit red shifts of their absorption bands in comparison to their lower brominated congeners. We attained a satisfactory agreement between the experimentally measured absorption peak (λ_max) and the theoretically predicted oscillator strength (λ_max) for the UV-Vis spectra. This study further confirms that, halogenated aromatics only absorb light in the UV spectral region and that effective photodegradation of these pollutants requires the presence of photocatalysts.

Integration of plasmonic effect into MIL-125-NH2: An ultra-efficient photocatalyst for simultaneous removal of ternary system pollutants

Industrial effluents often contain mixed metal ions and dyes, and it is difficult to efficiently remove both types of contaminants simultaneously. Here, MIL-125-NH₂@Ag/AgCl composites were for the first time developed through a facile deposition-photoreduction method for simultaneously removing Cr(VI)/Rhodamine B (RhB)/Malachite Green (MG) ternary system pollutants under visible-light irradiation. The capacities of Cr(VI) reduction dramatically increased to 98.4% in the coexistence of RhB and MG compared to that of binary (Cr(VI)/RhB (69.6%) or Cr(VI)/MG (67.5%)) and single Cr(VI) (29%) systems. In the meantime, the degradation efficiencies of dyes especially RhB in the ternary system were also improved compared to that of their individual systems. On the grounds of all the experimental results, it can be concluded that the efficient light-harvesting and electrons migration in MIL-125-NH₂@Ag/AgCl and the synergistic effect of redox reactions between Cr(VI) and dyes hinder the recombination of photo-induced electron-hole pairs, which are responsible for their high photocatalytic activity to eliminate the mixed pollutants. This study provides a new route to construct high-performance photocatalysts for the practical treatment of wastewater containing mixed pollutants.

Photocatalytic degradation of paracetamol on Pd-BiVO4 under visible light irradiation

In this study, Pd-BiVO₄ bearing highly dispersed Pd nanoparticles was prepared from pure BiVO₄ using an impregnation method. The pure BiVO₄ and Pd-BiVO₄ catalysts were characterized by X-ray diffraction, scanning electron microscopy, UV-visible diffuse reflection, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results showed that the prepared catalysts had a monoclinic scheelite structure and exhibited a flake-like morphology. Pd-BiVO₄ showed a distinct response in the visible light region, with an extended absorption edge at 550 nm. According to the Scherrer formula, the nanocrystal particle sizes of the BiVO₄ and Pd-BiVO₄ catalysts were 35 and 28 nm, respectively. Highly dispersed Pd nanoparticles with sizes of 2.5 ± 0.5 nm were observed on the BiVO₄ surface. Two Pd valence states, Pd(II) and Pd(0), were identified in a 2:1 ratio. Pd-BiVO₄ exhibited excellent activity for paracetamol (PCT) degradation, with 100% removal achieved in 1 h under visible light irradiation. During degradation, the mineralization ratio reached up to 40% total organic carbon removal. Two highly active species, namely, hydroxyl and superoxide radicals, were determined by electron spin resonance (ESR). Furthermore, the potential degradation of PCT in this system was proposed based on intermediate information obtained using HPLC-MS and Gauss analysis. The high dispersion and small size of Pd nanoparticles might favor the removal of emerging contaminants using the Pd-BiVO₄ photocatalytic system.

Interactive Fe2O3/porous SiO2 nanospheres for photocatalytic degradation of organic pollutants: Kinetic and mechanistic approach

A uniformly distributed mesoporous silica nanospheres has been successfully synthesized. Silica nanospheres have been loaded with different content of Fe₂O₃ nanoparticles synthesized by the sol-gel process followed by calcination to form the Fe₂O₃ supported on silica nanospheres composite. The as-synthesized photocatalyst has been characterized for crystal structure, morphology, stability, surface area and also surface composition was determined. The photocatalytic oxidation ability of the composite photocatalyst was evaluated by degrading aqueous solutions of Methylene Blue and Congo red dyes under visible light having intense absorption in the wavelength range between 550 and 560 nm. The prime significance of silica is to act as catalyst support for uniform distribution of hematite particles for enhanced catalytic reactivity. Highest degradation has been achieved with 20 wt % loading of hematite nanoparticles indicating the less agglomeration and availability of more catalytic sites. Furthermore, colorless organic pollutants 2-chlorophenol and 2, 4-dichlorophenol have been degraded with high efficiency in the presence of H₂O₂ oxidizer. The scavenger experiments confirmed that hydroxyl radicals are the majorly participating species in this catalytic system. The composite system also shows good recyclability of the materials and advocates the promising nature of the designed system for multiple hazardous environmental contaminants.

Degradation of bisphenol a using peroxymonosulfate activated by WO3@MoS2/Ag hollow nanotubes photocatalyst

WO₃@MoS₂/Ag (HW@MA) hollow tubes were successfully engineered to photodegrade bisphenol A (BPA) combined with peroxymonosulfate (PMS) for the first time. XRD, XPS, TEM and SEM were conducted. The HW@MA tubes present excellent photocatalytic performance on the removal of BPA. The intermediate products of BPA were investigated by GC-MS analysis and the degradation pathway was proposed. To explore the transferred mechanism of photoproduced carriers, the electron paramagnetic resonance (EPR) technique was carried out. The results revealed that the superoxide radical (O₂^-), hydroxyl radical (OH), sulfate radical (SO₄^-) were the main active radicals. Moreover, the formed schottky junctions enhanced the separation efficiency of photoinduced electron-hole pairs. Besides, the effect of the photocatalysts' dosage, PMS concentration, pH of the initial solution and co-existing anions on the BPA degradation were investigated.

Updated and validated solar irradiance reference spectra for estimating environmental photodegradation rates

Irradiance reference spectra are used to calculate environmentally relevant photodegradation half-lives, but the currently used spectra were originally published in the 1980s with limited validation. The goal of this work is to provide updated irradiance reference spectra using the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS). The SMARTS irradiance spectra were validated against measurements from several high-resolution spectroradiometers, and the updated irradiance reference spectra use current measurements for atmospheric species that can affect the irradiance that reaches the Earth's surface. These updated irradiance spectra are provided in 1 nm increments from 280 to 800 nm for 0° to 70° latitude at 10° increments in both the northern and southern hemisphere. Lastly, the influence of the input parameters on the modeled irradiance spectra was investigated. This work will allow users to calculate more accurate photodegradation half-lives using the updated irradiance reference spectra, and it also provides insight for users to calculate their own location- and time-specific irradiance spectra using SMARTS.

Investigation of reactive oxygen species produced by microwave electrodeless discharge lamp on oxidation of dimethyl sulfide

Microwave electrodeless discharge lamp (MEDL) has been regarded as a powerful light source of photoreaction. Four kinds of chemicals, nitrogen (N₂), oxygen (O₂), water (H₂O) and dimethyl sulfide (DMS), were used as molecular probes to explore the generation process of reactive oxygen species (ROS) and their photo-oxidation performances on the photodegradation of organic pollutants with application of an exterior MEDL system. ROS such as O (³P), O₃, O (¹D) and ¹O₂ were generated via irradiation of O₂ and H₂O except dry N₂ by MEDL. They were transformed to other ROS including ·OH and H₂O₂ with increase of relative humidity. The ROS productivity was inhibited evidently by humidity and ·OH became the major active species at high humidity. An optimal mineralization rate of 23.6% for DMS photodegradation was reached in dry air compared with 8.74% at high humidity, which indicated that O (¹D) and ¹O₂ were more powerful oxidants than O₃ and OH. The results showed that the higher mineralization rate of organic pollutants was obtained by increasing the generation efficiency of ROS of O (¹D) and ¹O₂. Furthermore, the results provided an alternative to develop intensification technology on photodegadation of organic pollutants with MEDL system and an optimal operation process including photocatalyst and humidity.

Bismuth vanadate-based semiconductor photocatalysts: a short critical review on the efficiency and the mechanism of photodegradation of organic pollutants

The number of publications on photocatalytic bismuth vanadate-based materials is constantly increasing. Indeed, bismuth vanadate is gaining stronger interest in the photochemical community since it is a solar-driven photocatalyst. However, the efficiency of BiVO₄-based photocatalyst under sunlight is questionable: in most of the studies investigating the photodegradation of organic pollutants, only few works identify the by-products and evaluate the real efficiency of BiVO₄-based materials. This short review aims to (i) present briefly the principles of photocatalysis and define the photocatalytic efficiency and (ii) discuss the formation of reactive species involved in the photocatalytic degradation process of pollutants and thus the corresponding photodegradation mechanism could be determined. All these points are developed in a comprehensive discussion by focusing especially on pure, doped, and composite BiVO₄. Therefore, this review exhibits a critical overview on different BiVO₄-based photocatalytic systems with their real efficiency. This is a necessary knowledge for potential implementation of BiVO₄ materials in environmental applications at larger scale than laboratory conditions.

Photodegradation of 2,4,4'-tribrominated diphenyl ether in various surfactant solutions: kinetics, mechanisms and intermediates

Currently, photodegradation has been proven to be an important way of eliminating polybrominated diphenyl ethers (PBDEs) from the environment. However, the mechanism of PBDE photodegradation in surfactants by UV light is still unclear. In this study, 2,4,4'-tribrominated diphenyl ether (BDE-28) was selected as the target pollutant to investigate the photodegradation of PBDEs in Triton X-100 (TX-100), sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) solutions. All photolysis experiments were performed above the critical micelle concentration (CMC). The results showed that photodebromination was the major pathway of BDE-28 photodestruction in different surfactants. From 1.5 CMC to 4 CMC, the photodegradation rates of BDE-28 increased as the concentration of TX-100 increased, and the increased concentration of SDBS has a negative effect on the photodegradation rate of BDE-28 due to the light barrier of SDBS. There was no obvious change in the case of CTAB. BDE-28 was debrominated to 4,4'-dibrominated diphenyl ether (BDE-15), 4-dibrominated diphenyl ether (BDE-3) and diphenyl ether (DE), subsequently. In addition, 2,8-dibrominated dibenzofuran (2,8-BDF), 2-monobrominated dibenzofuran (2-monoBDF), and dibenzofuran (DF) were produced via an intramolecular elimination of HBr from the PBDEs that had an ortho-bromine substituent. Moreover, DF can also be formed from DE and the generated amount of DF in CTAB was higher than that generated in SDBS and TX-100. We have also detected ortho-hydroxydiphenyl and para-hydroxydiphenyl during the photodegradation process.

Photoreactivity of graphene oxide in aqueous system: Reactive oxygen species formation and bisphenol A degradation

The phototransformation and environmental implications of graphene oxide (GO) have been widely studied in order to understand its implications upon release into the environment. However, very little is known about the formation of reactive oxygen species (ROS) by GO under solar irradiation. Currently there are no studies on the mechanism of ROS formation by GO or the amount of ROS catalyzed by the nanomaterials in the environment. In this study, we carefully investigated the different types and formation mechanisms of ROS generated by GO in the presence of simulated solar irradiation. The effect of GO's photoactivity on bisphenol A (BPA), a representative organic co-pollutant, was also studied. The conduction band electron (e_aq^-) of GO led to the formation of different ROS including OH, O₂^-, and ¹O₂. Among the three types of ROS investigated, O₂^- was the most abundant species generated during simulated solar irradiation of GO. BPA was degraded, mainly due to the oxidative potential of the valence band holes produced during solar irradiation of GO. This study advances understanding of the photoactivity of GO and its potential impact on other possible environmental co-pollutants.

Developing polyetherimide/graphitic carbon nitride floating photocatalyst with good photodegradation performance of methyl orange under light irradiation

Polyetherimide-graphitic carbon nitride (PEI-g-C₃N₄) floating photocatalyst has been synthesized by using polyetherimide (PEI) as linker to bind graphitic carbon nitride (g-C₃N₄) together. XRD and XPS analysis for PEI-g-C₃N₄ show that the interaction between PEI and g-C₃N₄ does not disturb the structure of g-C₃N₄. FTIR, TEM and theoretical results suggest that the long chain PEI binds g-C₃N₄ particles together to form PEI-g-C₃N₄ via hydrogen bonding interaction. Based on photodegradation results of methyl orange (MO), PEI can not photodegrade MO and just works as linker in PEI-g-C₃N₄, while the photodegradation performance of PEI-g-C₃N₄ is from the contribution of g-C₃N₄. Total organic carbon (TOC) analysis show that nearly 47% organic carbon has been converted into inorganic carbon after photodegradation, suggesting that PEI-g-C₃N₄ can destroy both NN bond and aromatic rings in MO under light irradiation. The photodegradation efficiency (91%) of MO by g-C₃N₄ is higher than that (80%) by PEI-g-C₃N₄ with stirring. But, the photodegradation efficiency (37%) of MO by g-C₃N₄ is lower than that (55%) by PEI-g-C₃N₄ without stirring. This is the advantage of floating photocatalyst with respect to the powder photocatalyst since the former can utilize more solar energy than the latter when stirring is not available.

Sequential Process Combination of Photocatalytic Oxidation and Dark Reduction for the Removal of Organic Pollutants and Cr(VI) using Ag/TiO2

We investigated a sequential photocatalysis-dark reaction, wherein organic pollutants were degraded on Ag/TiO₂ under UV irradiation and the dark reduction of hexavalent chromium (Cr(VI)) was subsequently followed. The photocatalytic oxidation of 4-chlorophenol (4-CP), a test organic substrate, induced the generation of degradation intermediates and the storage of electrons in Ag/TiO₂ which were then utilized for reducing Cr(VI) in the postirradiation period. The dark reduction efficiency of Cr(VI) was much higher with Ag/TiO₂ (87%), compared with bare TiO₂ (27%) and Pt/TiO₂ (22%). The Cr(VI) removal by Ag/TiO₂ (87%) was contributed by adsorption (31%), chemical reduction by intermediates of 4-CP degradation (26%), and reduction by electrons stored in Ag (30%). When formic acid, humic acid or ethanol was used as an alternative organic substrate, the electron storage effect was also observed. The postirradiation removal of Cr(VI) on Ag/TiO₂ continued for hours, which is consistent with the observation that a residual potential persisted on the Ag/TiO₂ electrode in the dark whereas little residual potential was observed on bare TiO₂ and Pt/TiO₂ electrodes. The stored electrons in Ag/TiO₂ and their transfer to Cr(VI) were also indicated by the UV-visible absorption spectral change. Moreover, the electrons stored in the preirradiated Ag/TiO₂ reacted with O₂ with showing a sign of low-level OH radical generation in the dark period.

Photo- and thermo-chemical transformation of AgCl and Ag2S in environmental matrices and its implication

AgCl and Ag₂S prevalently exist in the environment as minerals and/or the chlorination and sulfidation products of ionic silver and elemental silver nanoparticles (AgNPs). In this work, we investigated the chemical transformation of AgCl and Ag₂S under simulated sunlight (in water) and incineration (in sludge and simulated municipal solid waste, SMSW). In the presence of natural organic matter, AgCl in river water was observed to be transformed into AgNPs under simulated sunlight, while photo-reduction of Ag₂S could not take place under the same experimental conditions. During the course of incineration, pure Ag₂S was transformed into elemental silver while AgCl remained stable; however, both Ag₂S in sludge and AgCl in SMSW can be transformed to elemental silver under incineration, evident by the results of X-ray absorption spectroscopy and scanning electron microscopy measurements. Incineration temperature played an important role in the transformation of Ag₂S and AgCl into elemental silver. These results suggest that chemical transformations of Ag₂S and AgCl into elemental silver could be a possible source of naturally occurring or unintentionally produced AgNPs, affecting the fate, transport, bioavailability and toxicity of silver. Therefore, it is necessary to include the contributions of this transformation process when assessing the risk of ionic silver/AgNPs and the utilization and management of incineration residues.

Integration of nickel doping with loading on graphene for enhanced adsorptive and catalytic properties of CdS nanoparticles towards visible light degradation of some antibiotics

Water dispersible, highly efficient nickel doped CdS nanoparticles anchored on graphene nanosheets as a photocatalyst for cephalexin and sulfamethoxazole photodegradation have been prepared in a facile microwave-furnace assisted method. Each one of the two modifications has played a critical role in nanocomposite functioning. Defects originated by dopant boosted the lifetime of carriers and thereupon graphene matrix transferred them to contribute effectively the photocatalytic process. Characterization results revealed the formation of monocrystalline hexagonal phase of all products and that both doping and loading on graphene have red-shifted the absorption edge of CdS towards the visible light region. Furthermore, FTIR confirmed the successful reduction of graphene oxide by the subsequent preparation steps. Adsorption isotherms revealed the role of graphene in enhancing substrate adsorption. Nevertheless, dissimilar pathways of catalytic degradation were observed on the doped composite as cephalexin oxidation was principally mediated by the hole-hydroxyl radical mechanism, sulfamethoxazole oxidation favored the superoxide radical mechanism. This composite has shown, however, a high photostability and minimized ions release of the composite.

Tetrabromobisphenol A photoelectrocatalytic degradation using reduced graphene oxide and cerium dioxide comodified TiO2 nanotube arrays as electrode under visible light

Tetrabromobisphenol A, one of the most important brominated retardants, is an typical persistent organic pollutant and it is of great value to develop rapid and effective degradation method. Present study established a photoelectrodegradation method with CeO₂ and reduced graphene oxide co-modified TiO₂ nanotube arrays (RGO-CeO₂-TiO₂ NAs), which were successfully synthesized and characterized with scanning electron microscopy (SEM) and Energy Dispersive X Ray Spectrometry (EDX). The SEM Images revealed that the nanotubes had a diameter of about 100 nm and an obvious layer of CeO₂ and RGO on the surface of TiO₂ nanotube arrays. The EDX data exhibited the presence of Ce element. The results demonstrated that TBBPA was degraded at a high degradation rate constant of 0.0191 min^-1, and photogenerated holes played a major role in the degradation reaction. Significant decrease of degradation efficiency was achieved with the presence of EDTA-2Na(hole scavenger), yet while the existence of t-BuOH(OH scavenger) resulted in less inhibition on the degradation. Besides, RGO-CeO₂-TiO₂ NAs exhibited good stability with rarely decline of degradation efficiency for ten reused runs. All these indicated that RGO-CeO₂-TiO₂ NAs were a good catalyst with extraordinary catalytic activity and stability for PEC degradation, and would have great potential in the control and removal of pollutants.

Distribution of free radicals and intermediates during the photodegradation of polychlorinated biphenyls strongly affected by cosolvents and TiO₂ catalyst

Polychlorinated biphenyls (PCBs) pose potential ecological risk because of their high toxicity and carcinogenicity. Photodegradation, which is an important process for the removal of PCBs, is greatly influenced by the cosolvent and catalyst. Hence, it is important to explore their effects on the photodegradation behavior of PCBs. In this study, 2,4,4'-trichlorobiphenyl (PCB28) was selected as a model compound, and the effects of two typical cosolvents, namely acetone and ethanol, and TiO2 catalyst on the distributions of free radicals and intermediates were investigated. Interestingly, the TiO2 catalyst did not promote PCB28 photodegradation. Moreover, the free radical distribution was greatly influenced in the presence of the TiO2 catalyst, while was only slightly affected in its absence by the cosolvent kinds. The main photodegradation pathways are proposed on the basis of the distribution of detected intermediates, which were significantly regulated by both the cosolvent and TiO2 catalyst. The results provide novel insights into the photodegradation of PCBs and may have important implications for choosing cosolvent in desorbing soil PCBs and consequently enhancing PCBs degradation.

Rapid reduction of lead leachate from hazardous fly ash using microwave treatment with acid combination

The novelty of this study is to rapidly reduce hazardous lead leachates from solid waste using microwave digestion treatment, which is an energy-saving and low greenhouse gas emission technology. The article presents the reduction of toxic characteristic leaching procedure-extractable lead concentration in the municipal solid waste incineration fly ash by the microwave digestion treatment in HNO3/H2SO4 combination, and focuses on the effects of treatment time and temperature. The results obtained from this study indicated a significant reduction efficiency of toxic characteristic leaching procedure-extractable lead concentration and showed sufficient reduction in leaching levels to render the treated fly ash safe in lead compound leaching characteristics. The reduction efficiency of toxic characteristic leaching procedure-extractable lead concentration can reach 98% in 15 minutes of treatment time. This is equivalent to the original toxic characteristic leaching procedure-extractable lead concentration of 46.2 mg L(-1) in raw fly ash being reduced down to less than 1.0 mg L(-1). Based on the experimental data obtained in this study, a useful correlation between reduction efficiency and treatment conditions is proposed. For engineering applications, the necessary minimum treatment time is solved using a graphic illustration method, by which the minimum treatment time (t(min)) is obtained if the desired reduction efficiency (η) and treatment temperature (T) are known. The effects of treatment time and temperature are discussed. Some problems caused by the microwave digestion treatment method are also delineated in this article.

Effect of low-molecular-weight organic acids on photo-degradation of phenanthrene catalyzed by Fe(III)-smectite under visible light

The photolysis of polycyclic aromatic hydrocarbons (PAHs) is potentially an important process for its transformation and fate on contaminated soil surfaces. In this study, phenanthrene is employed as a model to explore PAH photodegradation with the assistance of Fe(III)-smectite under visible-light while focusing on roles played by five low-molecular-weight organic acids (LMWOAs), i.e., malic acid, oxalic acid, citric acid, ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid. Our results show that oxalic acid is most effective in promoting the photodegradation of phenanthrene, while only a slight increase in the rate of phenanthrene photodegradation is observed in the presence of malic acid. Electron paramagnetic resonance experiments confirm the formation of CO2(-) radicals in the presence of malic and oxalic acid, which provides strong evidence for generating OH and subsequent photoreaction pathways. The presence of EDTA or nitrilotriacetic acid significantly inhibits both Fe(II) formation and phenanthrene photodegradation because these organic anions tend to chelate with Fe(III), leading to decreases in the electron-accepting potential of Fe(III)-smectite and a weakened interaction between phenanthrene and Fe(III)-smectite. These observations provide valuable insights into the transformation and fate of PAHs in the natural soil environment and demonstrate the potential for using some LMWOAs as additives for the remediation of contaminated soil.

Pd nanoparticles supported on MIL-101/reduced graphene oxide photocatalyst: an efficient and recyclable photocatalyst for triphenylmethane dye degradation

To improve the photocatalytic efficiency of chromium-based metal-organic framework (MIL-101) photocatalyst, Pd nanoparticles and reduced graphene oxide were used to modify the MIL-101 via a facile method. The resulting novel photocatalyst was characterized by UV-vis diffuse reflectance spectra (DRS), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was indicated that the photocatalyst afforded high photocatalytic efficiency for degradation of two triphenylmethane dyes, brilliant green and acid fuchsin, under exposure to visible light irradiation. Cyclic experiments demonstrated that the photocatalyst showed good reusability and stability for the dye degradation.

Photocatalytic Performances of Ag3PO4 Polypods for Degradation of Dye Pollutant under Natural Indoor Weak Light Irradiation

It is still a big challenge for Ag3PO4 to be applied in practice mainly because of its low stability resistant to photo corrosion, although it is an efficient photocatalyst. Herein, we have mainly investigated its activity and stability under indoor weak light for the degradation of dye pollutants. It is amazing that under indoor weak light irradiation, rhodamine B (RhB) can be completely degraded by Ag3PO4 polypods after 36 h, but only 18% of RhB by N-doped TiO2 after 120 h. It is found that under indoor weak light irradiation, the degradation rate (0.08099 h(-1)) of RhB over Ag3PO4 polypods are 46 times higher than that (0.00173 h(-1)) of N-doped TiO2. The high activity of Ag3PO4 polypods are mainly attributed to the three-dimensional branched nanostructure and high-energy {110} facets exposed. After three cycles, surprisingly, Ag3PO4 polypods show a high stability under indoor weak light irradiation, whereas Ag3PO4 have been decomposed into Ag under visible light irradiation with an artificial Xe light source. This natural weak light irradiation strategy could be a promising method for the other unstable photocatalysts in the degradation of environmental pollutants.

Photochemical and microbial transformation of emerging flame retardants: cause for concern?

Among anthropogenic chemicals, flame retardants have attracted mounting environmental concerns. In recent years, an increasing number of studies have been conducted worldwide to investigate flame-retardant sources, environmental distribution, wildlife and human exposure, and toxicity. Data generated have demonstrated that some flame-retardant substances such as polybrominated diphenyl ethers (PBDE) are persistent, bioaccumulative, and toxic to exposed organisms. However, comparatively much less attention has been paid to the mechanisms and products of environmental transformation of flame retardants. This lack of information undermines our understanding of the environmental behavior and fate of flame retardants, as well as the associated risks to environmental and human health. Photochemical and microbial transformation of flame retardants in various matrices and environmental compartments can elevate the toxicological significance of flame retardant exposure, via the formation of, for example, lesser halogenated but more bioaccumulative degradation products and toxic radicals. Such pathways raise concerns related to the environmental safety of some alternative flame retardants that are presumably safe and used to replace PBDEs. To fully assess the environmental risks, more research is needed to investigate the environmental transformation potential of emerging flame retardants including polymeric flame retardants. Enhanced analytical efforts are needed to better characterize transformation products and transient radicals. Additional mesocosm and field studies are needed to elucidate transformation kinetics and consequences under environmentally relevant conditions.

A review of photochemical approaches for the treatment of a wide range of pesticides

Pesticides are renowned as some of the most pernicious chemicals known to humankind. Nine out of twelve most hazardous and persistent organic chemicals on planet have been identified as pesticides and their derivatives. Because of their strong recalcitrant nature, it often becomes a difficult task to treat them by conventional approaches. It is well perceived that many factors can interfere with the degradation of pesticides under ambient conditions, e.g., media, light intensity, humic content, and other biological components. However, for the effective treatment of pesticides, photochemical methods are viewed as having clear and perceivable advantages. In this article, we provide a review of the fundamental characteristics of photochemical approaches for pesticide treatment and the factors governing their capacity and potential in such a process.

ZnO nanocrystals anchored graphene: in situ solvothermal synthesis and enhanced photocatalytic performance

ZnO nanocrystals anchored graphene composite (ZnO/G) was synthesized by a facile in situ solvothermal route. The nanocomposite was characterized by X-ray diffraction (XRD), scanning electron spectroscopy (SEM), transmission electron microscopy (TEM) and Raman spectra (RS). The results indicated that the ZnO particles with an average diameter of ca. 12.6 nm were well-dispersed on the surface of the graphene nanosheets. The optical properties were investigated by fluorescence (PL) and UV diffuse reflectance (UV-VIS). It showed that the nanocomposite displayed a fluorescence quenching property. Furthermore, the nanocomposite showed a remarkably enhanced photocatalytic activity to degrade organic pollutants (MB, MO, Rh-B) under visible light irradiation, with a percentage degradation of MB reaching as high as 99.8% in 60 min.

Controllable synthesis of Cu2O/Cu composites with stable photocatalytic properties

Here we reported a facile approach to synthesize Cu2O/Cu composite particles by one-step sono-chemical process. The content of Cu in the Cu2O/Cu composites can be easily controlled by adjusting the synthesis time. Phase, morphology and optical properties of the products were carried out by X-ray diffraction (XRD), field-emission scanning electron microscopy (FSEM), transmission electron microscope (TEM), ultraviolet-visible (UV-vis) spectroscopy and nitrogen adsorption apparatus. Using photocatalytic degradation of Methyl orange (MeO) dye under visible-light illumination, we have investigated the influence of Cu on the photocatalytic activity of Cu2O, to find out its potential application in waste water treatment. Especially, the stability of the photocatalyst was confirmed using reclaimed Cu2O/Cu in ten successive runs. Results demonstrated clearly that Cu2O/Cu were stable and resistant to photocorrosion during the photocatalytic oxidation of organic compounds, indicating that these Cu2O/Cu composites are promising candidates for pollutant processing.

Ferric ion mediated photodecomposition of aqueous perfluorooctane sulfonate (PFOS) under UV irradiation and its mechanism

Perfluorooctane sulfonate (PFOS) recently has received much attention due to its global distribution, environmental persistence and bioaccumulation. The methods for PFOS decomposition are very limited due to its inertness. In this report we first found the photodecomposition of PFOS under UV was greatly accelerated by addition of ferric ions. In the presence of ferric ion (100 μM), PFOS (20 μM) decreased to below the detection limit within 48 h, with the rate constant of 1.67 d(-1), which was 50 times higher than that by direct photolysis (0.033 d(-1)). Besides fluoride and sulfate ions, C2-C8 perfluorocarboxylic acids (PFCAs) were identified as the main intermediates. It was found that addition of PFOS into the FeCl3 aqueous solution led to reduction of UV absorption, and the presence of ferric ion reduced the response of PFOS as analyzed by UPLC-MS/MS, which indicated that PFOS formed a complex with ferric ion. The ESR detection indicated that the electronic state of Fe(3+)-PFOS complex changed during reaction. And the role of oxygen and hydroxyl radical on the defluorination of PFOS was investigated. Accordingly the mechanism for PFOS photodecomposition in the presence of ferric ion was proposed.

Graphitic-C(3)N(4)-hybridized TiO(2) nanosheets with reactive {001} facets to enhance the UV- and visible-light photocatalytic activity

AnataseTiO(2)nanosheets with dominant {001} facets were hybridized with graphitic carbon nitride (g-C(3)N(4)) using a facile solvent evaporation method. On top of the superior photocatalytic performance of highly reactive {001} facets, the hybridization with g-C(3)N(4) is confirmed to further improve the reactivity through degrading a series of organic molecules under both UV- and visible-light irradiation. It is proposed that an effective charge separation between g-C(3)N(4) and TiO2 exists in the photocatalytic process, i.e., the transferring of photogenerated holes from the valence band (VB) of TiO(2) to the highest occupied molecular orbital (HOMO) of g-C(3)N(4), and the injecting of electrons from the lowest unoccupied molecular orbital (LUMO) of g-C(3)N(4) to the conduction band (CB) of TiO(2). Due to this synergistic effect, the enhancement of UV- and visible-light photoactivity over the hybrid is achieved. Furthermore, it has been revealed that holes were the main factor for the improved photoactivity under UV-light, while the OH radicals gained the predominance for degrading organic molecules under visible-light. Overall, this work would be significant for fabricating efficient UV-/visible-photocatalysts and providing deeper insight into the enhanced mechanisms of π-conjugated molecules hybridized semiconductors.

Photodegradation of antibiotics under simulated solar radiation: implications for their environmental fate

Roxithromycin, erythromycin, ciprofloxacin and sulfamethoxazole are frequently detected antibiotics in environmental waters. Direct and indirect photolysis of these problematic antibiotics were investigated in pure and natural waters (fresh and salt water) under irradiation of different light sources. Fundamental photolysis parameters such as molar absorption coefficient, quantum yield and first order rate constants are reported and discussed. The antibiotics are degraded fastest under ultraviolet 254 nm, followed by 350 nm and simulated solar radiation. The composition of the matrix (pH, dissolved organic content, chloride ion concentration) played a significant role in the observed photodegradation. Under simulated solar radiation, ciprofloxacin and sulfamethoxazole degrade relatively quickly with half-lives of 0.5 and 1.5h, respectively. However, roxithromycin and erythromycin, macrolides are persistent (half-life: 2.4-10 days) under solar simulation. The transformation products (15) of the targeted antibiotics produced under irradiation experiments were identified using high resolution mass spectrometry and degradation pathways were proposed.

Preparation and characterization of Pd doped ceria-ZnO nanocomposite catalyst for methyl tert-butyl ether (MTBE) photodegradation

A series of binary oxide catalysts (ceria-ZnO) were prepared and doped with different amounts of palladium in the range of 0.5%-1.5%. The prepared catalysts were characterized by SEM, TEM, XRD and XPS, as well as by N2 sorptiometry study. The XPS results confirmed the structure of the Pd CeO2-x-ZnO. The photocatalytic activity of these catalysts was evaluated for degradation of MTBE in water. These photocatalyst efficiently degrade a 100ppm aqueous solution of MTBE upon UV irradiation for 5h in the presence of 100mg of each of these photocatalysts. The removal of 99.6% of the MTBE was achieved with the ceria-ZnO catalyst doped with 1% Pd. In addition to the Pd loading, the N2 sorptiometry study introduced other factors that might affect the catalytic efficiency is the catalyst average pore sizes. The photoreaction was determined to be a first order reaction.

Microwave/H2O2 efficiency in pentachlorophenol removal from aqueous solutions

BACKGROUND

Pentachlorophenol (PCP) is one of the most fungicides and pesticides. Acute and chronic poisoning from PCP may be occurred by dermal absorption, and respiration or ingestion. With respect to health and environmental effects of PCP, many methods were considered regarding its removal. Microwave assisted other methods are environmental friendly, safety, and economical method, consequently, in this study; microwave assisted with hydrogen peroxide (MW/H2O2) was used for PCP removal from aquatic solutions.

METHODS

The possible of PCP removal was considered by application of a modified domestic microwave. PCP removal rate was considered under different factors such as H2O2 dose (0.01, 0.02, 0.1, 0.2, 0.3 mol/L), PCP concentration (100,200, 300, 400, 500, 750, 1000 mg/L), pH (3, 7, 11), energy intensity (180,450, 600 W), COD (344 mg/L), and scavenger testes (0.02 mol/L from each of Tert- butyl alcohol (TBA), NaCl, NaHCO3, and Na2CO3). The concentration changes of PCP were determined using spectrophotometer and HPLC spectra, respectively.

RESULTS

The best PCP removal was obtained in condition of pH 11, 0.2 mol/L H2O2, and 600 W energy intensity. Moreover, COD removal in this condition was 83%. Results obtained from radical scavengers indicated that OH° had only an initiator role, and had not a dominant role, and order reaction was in first order.

CONCLUSIONS

The results of microwave/H2O2 application showed that this process is suitable for removal of PCP and other chlorinated organic compounds in alkaline pH.

Photo-Fenton effect of 4-chlorophenol in ice

The photoconversion of 4-chlorophenol (4-CP) in a simulated sunlight-Fenton system was investigated in ice and aqueous solution. It was found that the hydroxyl radical (OH) had an important effect on the photoconversion of 4-CP in both phases, but the effects of Cl(-), SO4(2-), NO3(-), and HCO3(-) were different. In aqueous solution, the photoconversion efficiency of 4-CP was proportional to the OH concentration, and hence, Cl(-) and HCO3(-) as OH scavengers prohibited the photoconversion; SO4(2-) had little effect; NO3(-) promoted the process under certain conditions owing to OH being generated by the photolysis of NO3(-). In ice, however, the photoconversion efficiency of 4-CP was not proportional to the concentration of OH. The photoconversion efficiency of 4-CP increased with increasing concentrations of all ions, although the OH remained almost constant, only increasing or decreasing slightly. This provides new evidence for the presence of a quasi-liquid layer (QLL). Hydroxylation products were detected in both phases. All photoproducts in aqueous solution contained only a single benzene ring, whereas in ice, dimers were also detected.

Response surface methodology (RSM) analysis of photodegradation of sulfonated diazo dye Reactive Green 19 by UV/H2O2 process

A central composite design was used to investigate the influence of the main process parameters on the degradation of Reactive Green 19 (RG19) azo dye by the UV/H2O2 treatment. The combined use of UV radiation and H2O2 resulted in the decolorization and dearomatization of the dye. They were monitored by measuring the spectral changes occurring, respectively, in the visible and UV regions of the dye spectrum. RG19 degradation was found to be practically complete over a time of 15-60 min, for decolorization, and 50-200 min, for dearomatization, depending on the applied conditions. Both processes followed apparent first-order kinetics. The associated rate constants were used as the response variables and their dependence on initial dye and H2O2 concentrations, pH and reaction time was investigated by the response surface methodology. Response surface plots for the decolorization and dearomatization processes were very similar in shape. For both processes, the initial dye and H2O2 concentrations were the key factors controlling dye degradation.

Structuring β-Ga2O3 photonic crystal photocatalyst for efficient degradation of organic pollutants

Coupling photocatalysts with photonic crystals structure is based on the unique property of photonic crystals in confining, controlling, and manipulating the incident photons. This combination enhances the light absorption in photocatalysts and thus greatly improves their photocatalytic performance. In this study, Ga2O3 photonic crystals with well-arranged skeleton structures were prepared via a dip-coating infiltration method. The positions of the electronic band absorption for Ga2O3 photonic crystals could be made to locate on the red edge, on the blue edge, and away from the edge of their photonic band gaps by changing the pore sizes of the samples, respectively. Particularly, the electronic band absorption of the Ga2O3 photonic crystal with a pore size of 135 nm was enhanced more than other samples by making it locate on the red edge of its photonic band gap, which was confirmed by the higher instantaneous photocurrent and photocatalytic activity for the degradation of various organic pollutants under ultraviolet light irradiation. Furthermore, the degradation mechanism over Ga2O3 photonic crystals was discussed. The design of Ga2O3 photonic crystals presents a prospective application of photonic crystals in photocatalysis to address light harvesting and quantum efficiency problems through manipulating photons or constructing photonic crystal structure as groundwork.

Phototoxicity of TiO2 nanoparticles to zebrafish (Danio rerio) is dependent on life stage

Zebrafish embryos have been used increasingly to evaluate nanomaterial toxicity. The present study compared phototoxicity of TiO2 nanoparticles with zebrafish at 4 life stages (embryos, yolk-sac larvae, free-swimming larvae, and juvenile) under simulated sunlight using the 96-h standard toxicity assay. Yolk-sac larvae were found to be the most sensitive to TiO2 phototoxicity, suggesting that the widely used zebrafish embryo test may not fully or accurately predict hazard and risk of these nanoparticles to small fish.

How redox conditions and irradiation affect sorption of PAHs by dispersed fullerenes (nC60)

Surface properties, dispersion state, and sorption behavior of carbon-based nanomaterials will change after being released into the environment. To study these processes, five different scenarios were considered to probe the impact of changes in surface properties of dispersed fullerenes (nC60) on their sorption potential due to irradiation and presence of oxygen. Sorption isotherms of pyrene by nC60 were determined at environmentally relevant concentrations applying a passive sampling method. Isotherms of all dispersion scenarios were best fit with the Dubinin-Ashthakov model. Sorption was strongest for nC60 kept under anoxic condition. Both the presence of oxygen and irradiation significantly decreased the sorption capacity of nC60, while commercially available polyhydroxy fullerenes had the smallest sorption. In addition, competition for sorption sites was never observed in multiple sorbate experiments with four polycyclic aromatic hydrocarbons at small concentration. A strong relationship between sorption coefficients and hydrophobic properties of sorbates suggests that hydrophobic interactions are of major importance. The results emphasize that aging of released fullerenes results in a reduced strength of interactions with nonpolar compounds and, thus, reduces the impact on the environmental transport of hydrophobic pollutants.

Visible light photocatalytic activity of Fe(3+)-doped ZnO nanoparticle prepared via sol-gel technique

The optical properties of a ZnO photocatalyst were enhanced with various dopant concentrations of Fe(3+). Doped ZnO nanoparticles were synthesized via a sol-gel method without the use of capping agents or surfactants and was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. The results showed that ZnO has a wurtzite, hexagonal structure and that the Fe(3+) ions were well incorporated into the ZnO crystal lattice. As the Fe(3+) concentration increased from 0.25 wt.% to 1 wt.%, the crystal size decreased in comparison with the undoped ZnO. The spectral absorption shifts of the visible light region (red shift) and the band gap decreases for each Fe-ZnO sample were investigated. The photocatalytic activities of the ZnO and Fe-ZnO samples were evaluated based on the degradation of 2-chlorophenol in aqueous solution under solar radiation. The samples with a small concentration of Fe(3+) ions showed enhanced photocatalytic activity with an optimal maximum performance at 0.5 wt.%. The results indicated that toxicity removal of 2-chlorophenol at same line of degradation efficiency. Small crystallite size and low band gap were attributed to high activities of Fe-ZnO samples under various concentrations of Fe(3+) ions compared to undoped ZnO.

Singlet oxygen mediated apoptosis by anthrone involving lysosomes and mitochondria at ambient UV exposure

Anthrone a tricyclic aromatic hydrocarbon which is toxic environmental pollutant comes in the environment through photooxidation of anthracene. We have studied the photomodification of anthrone under environmental conditions. Anthrone generates reactive oxygen species (ROS) like (1)O2 through Type-II photodynamic reaction. Significant intracellular ROS generation was measured through dichlorohydrofluorescein fluorescence intensity. The generation of (1)O2 was further substantiated by using specific quencher like sodium azide. UV induced photodegradation of 2-deoxyguanosine and photoperoxidation of linoleic acid accorded the involvement of (1)O2 in the manifestation of anthrone phototoxicity. Phototoxicity of anthrone was done on human keratinocytes (HaCaT) through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and neutral red uptake assays. Anthrone induced cell cycle arrest (G2/M-phase) and DNA damage in a concentration dependent manner. We found apoptosis as a pattern of cell death which was confirmed through sub-G1 fraction, morphological changes, caspase-3 activation, acridine orange/ethidium bromide staining and phosphatidylserine translocation. Mitochondrial depolarization and lysosomal destabilization was parallel to apoptotic process. Our RT-PCR results strongly supports our view point of apoptotic cell death through up-regulation of pro-apoptotic genes p21 and Bax, and down regulation of anti-apoptotic gene Bcl2. Therefore, much attention should be paid to concomitant exposure of anthrone and UV-R for its total environmental impact.

Photocatalytic CO(2) reduction using non-titanium metal oxides and sulfides

Titanium dioxide (TiO2 ) is by far the most widely used photocatalyst both for the degradation of pollutants and in the field of renewable energies for the production of solar fuels. However, TiO2 has strong limitations in CO2 reduction, particularly under visible light irradiation. The flat-band potential of electrons in the conduction band of TiO2 is lower than that required for CO2 reduction and, therefore, it seems appropriate to develop and validate materials other than TiO2 . In addition, the photoresponse of TiO2 requires photons of wavelengths in the UV range shorter than 380 nm and strategies to implement a visible-light photoresponse on TiO2 by doping have not been completely satisfactory particularly because of problems in reproducibility and stability of the materials. For these reasons, we focus in this Review on semiconductors other than TiO2 that show photocatalytic activity in CO2 reduction. Attention has been paid to the irradiation conditions to put the productivity data into context. The role of co-catalyst and heterojunctions to increase the efficiency of charge separation is also discussed. Our aim is to describe the state of the art in the field of photocatalytic CO2 reduction using materials other than TiO2 , trying to trigger further research in this area.

UVA photoirradiation of nitro-polycyclic aromatic hydrocarbons-induction of reactive oxygen species and formation of lipid peroxides

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are a class of genotoxic environmental contaminants. We have long been interested in determining the mechanisms by which nitro-PAHs induce genotoxicity. Although the metabolic activation of nitro-PAHs leading to toxicological activities has been well studied, the photo-induced activation of nitro-PAHs has seldom been reported. In this paper, we report photo-induced lipid peroxidation by 19 nitro-PAHs. The results indicated that all but two of the nitro-PAHs can induce lipid peroxidation. Mechanistic studies suggest that lipid peroxidation by nitro-PAHs is mediated by free radicals generated in the reaction. There was no structural correlation between the nitro-PAHs and their ability to induce lipid peroxidation upon UVA irradiation, or between the HOMO-LUMO gap and the ability to cause lipid peroxidation. Most of the nitro-PAHs are less potent in terms of causing lipid peroxidation than their parent PAHs. The lack of correlation is attributed to the complex photophysics and photochemistry of the nitro-PAHs and the yield of reactive oxygen species (ROS) and other factors.

The photoconversion of gamma-hexachlorocyclohexane under UV irradiation in water, snow and ice

The photochemistry of organic pollutants has received increasing attention in ice and snow. In this work, the photoconversion of gamma-hexachlorocyclohexane (γ-HCH) under UV irradiation was investigated in water, snow and ice. The photoconversion rate, products and mechanisms were inspected, and the effect of inorganic ions (NO2(-), NO3(-), HCO3(-) and Fe(2+)) was discussed. The results showed that γ-HCH could be photoconverted in water, snow and ice, with the photoconversion rate being fastest in snow, and slowest in ice. All photoconversion could be described by the first-order kinetics model. In water, snow and ice, the common photoproducts of γ-HCH were alpha-hexachlorocyclohexane (α-HCH) and pentachlorocyclohexene. α-HCH was generated by a change in the bonding of a chlorine atom in γ-HCH; pentachlorocyclohexene was generated by the removal of a molecule of chlorine hydride from a molecule of γ-HCH. Different concentrations of NO2(-), NO3(-) and HCO3(-) all inhibited the photoconversion of γ-HCH, and the inhibition effect decreased with increasing concentrations of NO2(-) and NO3(-), but increased with the increasing concentrations of HCO3(-). Different concentrations of Fe(2+) promoted the photoconversion of γ-HCH in water and ice, but had little effect in snow.

Sequential reduction-oxidation for photocatalytic degradation of tetrabromobisphenol A: kinetics and intermediates

C-Br bond cleavage is considered as a key step to reduce their toxicities and increase degradation rates for most brominated organic pollutants. Here a sequential reduction/oxidation strategy (i.e. debromination followed by photocatalytic oxidation) for photocatalytic degradation of tetrabromobisphenol A (TBBPA), one of the most frequently used brominated flame retardants, was proposed on the basis of kinetic analysis and intermediates identification. The results demonstrated that the rates of debromination and even photodegradation of TBBPA strongly depended on the atmospheres, initial TBBPA concentrations, pH of the reaction solution, hydrogen donors, and electron acceptors. These kinetic data and byproducts identification obtained by GC-MS measurement indicated that reductive debromination reaction by photo-induced electrons dominated under N(2)-saturated condition, while oxidation reaction by photoexcited holes or hydroxyl radicals played a leading role when air was saturated. It also suggested that the reaction might be further optimized for pretreatment of TBBPA-contaminated wastewater by a two-stage reductive debromination/subsequent oxidative decomposition process in the UV-TiO(2) system by changing the reaction atmospheres.

Enhanced visible-light induced degradation of benzene on Mg-ferrite/hematite/PANI nanospheres: in situ FTIR investigation

The dramatic enhanced visible-light photocatalytic activity of Mg-ferrite/hematite nanospheres photocatalysts on benzene were obtained after hybridized by polyaniline (PANI) using the chemisorption method. The samples were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectra and UV-Vis diffuse reflectance spectroscopy. The enhancement of photocatalytic degradation of benzene under visible-light irradiation was mainly ascribed to the high efficiency of charge separation induced by the hybrid effect of PANI and Mg-ferrite/hematite. By using the in situ FTIR technique, ethyl acetate, carboxylic acid and aldehyde could be regarded as the intermediate products, and CO(2) is determined as the final product during the reaction process.

Photocatalytic debromination of preloaded decabromodiphenyl ether on the TiO(2) surface in aqueous system

There have been serious concerns about polybromodiphenyl ethers (PBDEs) in the environment because of their global distribution and bioaccumulation. Owing to strong hydrophobicity of PBDEs, the regular photocatalytic system, in which the substrate is solvated in the bulk solution, is not applicable to the removal of the PBDEs in water. In this work, the photocatalytic reduction degradation of decabromodiphenyl ether (BDE209), the most-used PBDEs, was investigated in aqueous system, by pre-adsorbing it on the surface of photocatalyst. It was found that the preloaded BDE209 underwent efficient reductive debromination in aqueous system under irradiation with wavelength larger than 360 nm in the presence of electron donors such as methanol. Our experiments further show that such a preloaded system exhibits different characteristics from that in the organic solution. The meta-debrominated intermediate is predominant in the present system, while the ortho-debrominated one is the main nona-BDE products in the organic solution. In addition, different from other photocatalytic system, the pH has little effect on the photocatalytic reaction. We propose that these differences are originated from the formation of overlayer of hydrophobic BDE209 to limit the motion of BDE209 and the access of water and H(+)/OH(-) to the TiO(2) surface.

Ultrasonic degradation of butadiene, styrene and their copolymers

Ultrasonic degradation of commercially important polymers, styrene-butadiene (SBR) rubber, acrylonitrile-butadiene (NBR) rubber, styrene-acrylonitrile (SAN), polybutadiene rubber and polystyrene were investigated. The molecular weight distributions were measured using gel permeation chromatography (GPC). A model based on continuous distribution kinetics approach was used to study the time evolution of molecular weight distribution for these polymers during degradation. The effect of solvent properties and ultrasound intensity on the degradation of SBR rubber was investigated using different pure solvents and mixed solvents of varying volatility and different ultrasonic intensities.

A survey of photocatalytic materials for environmental remediation

Heterogeneous photocatalysis is an advanced oxidation process which has been the subject of a huge amount of studies related to air cleaning and water purification. All these processes have been carried out mainly by using TiO(2)-based materials as the photocatalysts and ca. 75% of the articles published in the last 3 years is related to them. This review illustrates the efforts in the search of alternative photocatalysts that are not based on TiO(2), with some exceptions concerning particularly innovative modifications as nanoassembled TiO(2) or TiO(2) composites with active carbon, graphite and fullerene. Papers reporting preparation, characterization and testing of binary, ternary and quaternary compounds, have been reviewed. Despite many of these photocatalysts being effective for the photodecomposition of many pollutants, most of them do not allow a complete mineralization of the starting compounds, differently from TiO(2).

Removal of persistent organic pollutant hexachlorocyclohexane isomers by advanced oxidation process

Organochlorine insecticide Lindane (gamma-Hexachlorocyclohexane) and its isomers (alpha, beta, delta-HCH) are recalcitrant and toxic compounds. They were progressively banished in most of the countries, because of their persistence and toxicity. Due to their nonselective production process and widespread use, they are still occurring in the environment. These insecticides and isomers were detected in all media like soil, ground water, sediments, vegetables and even in human tissues. In this study, UV, H2O2, UV+H2O2, Fenton's reagent, UV+Fenton's reagent, Advanced Oxidation Process (AOP) have been applied for degradation of HCH isomers (a, beta, gamma and delta-HCH). The results revealed that the UV+H2O2 treatment was most effective, which could do 99% degradation of all isomers of HCH within 75 minutes. The results in detail are presented and discussed in this paper.

Synthesis of surface sulfated BiWO with enhanced photocatalytic performance

Sulfated BiWO (SBiWO) was synthesized by an impregnation method to enhance the visible-light-driven photoactivities of BiWO (BiWO). The characterization results verified that sulfate anion mainly anchored on the catalyst surface greatly extended the visible-light-responsive range without destroying the crystal lattice. Moreover, the SBiWO-based photoactivities were evaluated with the removal of Malachite Green (MG) under UV-Vis irradiation emitted from two microwave-powered electrodeless discharge lamps (MPEDL2) and under visible light (lamda > 420 nm). The results demonstrated that the kinetic constant was increased 2.25 times, varying from 0.1478 (BiWO) to 0.3328 min(-1) (SBiWO-1). Similar results were also obtained for the visible light-driven reaction. Furthermore, radical scavengers such as t-butanol restricted the visible-light induced degradation of MG over BiWO and SBiWO-1. This indicated that the sulfating process increased the generation of reactive oxygen species, which was further verified by molecular probe with salicylic acid. Thus, more blue-shifting at lam = 618 nm was observed over SBiWO. On the basis of the above results, the photocatalytic mechanism over the sulfated catalyst was also discussed.