TiO_2光催化降解氯酚类有机污染物的反应机理

氯酚类有机污染物具有较高毒性、难生物降解和强生物累积性等特点,成为较受关注的一类优先控制污染物.我们总结了氯酚TiO2光催化降解机理研究方面的最新进展,阐述了直接光解、·OH氧化、1O2氧化、O(3P)氧化、O2·氧化、导带电子还原和表面络合物电子转移等氯酚光降解途径与机理.重点讨论了O2在氯酚吸附、光催化降解乃至矿化过程中的重要作用.     

Investigation of the photochemical behaviour of pyrethroids lacking the cyclopropane ring by photo‐solid‐phase microextraction and gas chromatography/mass spectrometry

The characterization of by‐products arising from the UV photodegradation of two insecticide pyrethroids lacking the cyclopropane ring (flucythrinate and fenvalerate) has been investigated by gas chromatography coupled with mass spectrometry (GC/MS). Twenty photoproducts were tentatively identified mainly based on the interpretation of the experimental mass spectra or by using reference mass spectra. Some of these compounds had not previously been detected. Furthermore, the generation of some of the photoproducts might be a matter for concern due to their potential toxicity. The corresponding photodegradation routes, including postulation of the intermediate radicals, have also been proposed. These photodegradation studies were performed by photo‐solid‐phase microextraction (photo‐SPME) in which the SPME fibre was exposed to light after extraction of the target analytes from aqueous solutions. The degradation kinetics of the investigated pyrethroids and the photoformation‐photodegradation curves of the photoproducts generated in situ were also monitored through the ion chromatograms obtained for different irradiation times and the corresponding mass spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Confirming the Designed Thermal Degradation of a Polycarbonate by Tga/Ft-Ir

Abstract

Integrated thermogravimetric analysis/Fourier transform infrared spectroscopy (TGA/FT-IR) was applied to study the thermal degradation of an aliphatic polycarbonate based on 2,5-dimethyl-2,5-hexanediol and 1,4-cyclohexanediol. A single experiment confirms that the polymer decomposes as designed to the expected products. Carbon dioxide, 1,4-cyclohexanediol, and isomeric hexadienes were thus detected and identified by comparison of their vibrational spectra with those of pure compounds in the spectral library. Some mechanistic implications are discussed.     

A study of photodegradation of quetiapine by the use of LC-MS/MS method

Photodegradation of quetiapine under UVC irradiation in methanol solution was investigated and structural elucidation of its photodegradation products was performed with the use of the reversed phase UHPLC system coupled with accurate mass hybrid ESI-Q-TOF mass spectrometer. During one run all essential data for the determination of photodegradation kinetics and for the structural elucidation of the products was collected with the use of auto MS/MS mode. Five degradation products were found and their masses and formulas were obtained with high accuracy (0.26–5.02 ppm). For all the analyzed compounds, MS/MS fragmentation spectra were also obtained allowing structural elucidation of the unknown degradation products and indicating photodegradation pathways of quetiapine. The main photodegradation product was identified as 2-[2-[4-(5-oxidodibenzo[b,f][1,4]thiazepin-11-yl)-1-piperazinyl]ethoxy]-ethanol and the photodegradation reaction yields the first-order kinetics with the rate constant k = 0.1094 h⁻¹.     

Characterization of paliperidone photodegradation products by LC‐Q‐TOF multistage mass spectrometry

The photodegradation of paliperidone in aqueous and methanol media under UVA and UVC irradiation was investigated. The identification and structural elucidation of its photodegradation products were performed by the use of the reversed‐phase liquid chromatography coupled with accurate mass hybrid Q‐TOF mass spectrometry and an atmospheric pressure chemical ionization source. Five degradation products were found and their masses were obtained with high accuracy (1.10–5.26 ppm) based on the TOF (MS) spectra. For the structural elucidation of unknown degradation products MS/MS spectra were also registered. However, for the identification of the main photodegradation product (3‐{2‐[4‐(6‐fluoro‐1,3‐benzoxazol‐2‐yl)piperidin‐1‐yl]ethyl}‐9‐hydroxy‐2‐methyl‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐one) in‐source fragmentation connected with collision‐induced dissociation was used and MS³ spectra were finally performed. The photodegradation of paliperidone yields the first‐order kinetics in all tested conditions. The aqueous medium was in this case much less stable than the methanol solvent regardless of the irradiation source. Additionally, the toxicity of the analyzed photodegradation products was predicted by the use of ECOSAR software and comparable values of LC₅₀ for the main degradants and the parent compound were obtained. Copyright © 2015 John Wiley & Sons, Ltd.     

Radiation-induced degradation of 4-chloroaniline in aqueous solution

The radiation-induced decomposition of 4-chloroaniline (4-ClA) was studied under steady-state conditions using aqueous solutions saturated with air, pure oxygen, N₂O, argon and argon in the presence of t-Butanol. Using HPLC-method, the initial G-values of the substrate degradation as well as of a number of radiolytic products were determined. The formation of aminophenols, chlorophenols, aniline and phenol in addition to chloride, ammonia, formaldehyde and mixture of aldehydes as well as carboxylic acids was studied as a function of absorbed dose. Based on the experimental data, probable reaction mechanisms for the degradation of 4-ClA by γ-rays and the formation of the identified products are presented.     

Photodegradation and by-products identification of commercial extractant Cyanex 302

The photodegradation of the organothiophosphorous extractant Cyanex 302 and purified bis(2,4,4-trimethylpentyl)monothiophosphinic acid dissolved in toluene was carried out in photoreactor using UV–Vis light irradiation. Possible degradation products were identified with the assistance of FT-IR, LC/MS/MS and GC/MS. The catalytic influence of zinc(II), copper(II) and cobalt(II) ions and the presence of trace values of water and aqueous solutions of sulphuric acids on the photodecomposition of Cyanex 302 were studied. The results demonstrated that the presence of trace amounts of water causes mainly the degradation of bis(2,4,4-trimethylpentyl)monothiophosphinic acid with the simultaneously fourfold increase in bis(2,4,4-trimethylpentyl)phosphinic acid concentration. The shaking with aqueous solution of sulphuric acids results in the decrease in the photodegradation probably by blocking of OH radical. Metal ions also affect the degradation causing the increase in bis(2,4,4-trimethylpentyl)phosphinic acid concentration. The photodegradation was also carried out in open atmosphere under sunlight and the obtained results were compared with those obtained in a Heraeus photoreactor.     

ZnO-rich CdS-ZIF-8 catalyst for enhanced visible-light photocatalytic degradation of methylene blue

CdS-ZIF-8 photocatalyst was prepared by introducing a ZnO-rich zeolitic imidazolate framework-8 (ZIF-8) during synthesis of CdS by a facile solvothermal method, using ZnO-rich ZIF-8 and cadmium acetate [Cd(Ac)₂] as support and CdS precursor, respectively. The introduction of ZnO-rich ZIF-8 and the photodegradation performance of the catalyst for methylene blue (MB) organic dye were systemically investigated. The CdS-ZIF-8 catalysts were also characterized using X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy, N₂ adsorption–desorption measurements, Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy. The results indicated that CdS-ZIF-8 contained ZIF-8, CdS, and ZnO phases. The CdS in CdS-ZIF-8 catalysts exhibited smaller particle size compared with pure CdS. Furthermore, compared with pure CdS, CdS-ZIF-8-30 with introduction of ZnO-rich ZIF-8 exhibited higher surface area (77.3 m²/g) and pore volume (0.103 cm³/g). EDX and FT-IR results suggested that a CdS/ZnO heterostructure was formed, which effectively reduced recombination of photogenerated electron–hole pairs. Radical trapping experimental data and band edge position analysis revealed that Z-scheme behavior also played a role in the system. Relying on the combined effect of their structure, the photodegradation efficiency of all the CdS-ZIF-8 catalysts was obviously superior to that of pure CdS for degradation of MB under visible-light irradiation. Photodegradation results illustrated that CdS-ZIF-8 with introduction of 30 mg ZnO-rich ZIF-8 (denoted as CdS-ZIF-8-30) exhibited optimal photodegradation activity.     

Identification of degradation products of indigoids by tandem mass spectrometry

The study concerns identification of photodegradation products of indigotin, indirubin and isoindigo. Experimental methodology consists of degradation of standard solutions of indigoids in a solar box and analysis of samples taken at different aging time by using capillary high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometric and spectrophotometric detectors. Identification of the formed compounds was based on careful interpretation of the electrospray ionization MS/MS spectra. Apart from the well‐known degradation products of indigoids: isatin, isatoic anhydride and anthranilic acid, another seven species were also identified, and their proposed structures were confirmed by high‐resolution molecular masses measurements; according to the best knowledge of authors, they have not been reported so far. The obtained results formed the basis for postulating mechanism of the process. Moreover, the MRM (Multiple Reaction Monitoring) method was developed for the identification of natural dyes and their degradation products in textiles of historical value. Apart from such colorants as indigotin and flavonoids, also presence of degradation products of indigoids was confirmed. Copyright © 2015 John Wiley & Sons, Ltd.     

Comprehensive description of the photodegradation of bromophenols using chromatographic monitoring and chemometric tools

A general procedure for the study of complex photodegradation processes of environmental pollutants based on chromatographic monitoring and chemometric method is proposed. The procedure consists of multiset data analysis of aliquots collected at different reaction times and injected in High-Performance Liquid Chromatography coupled to diode array detection and mass spectrometry (HPLC-DAD-MS). In this study, photodegradation of six bromophenols with different degrees of bromination has been investigated in order to find out their photodegradation pathways and kinetics and to show the potential of the procedure proposed. Multivariate curve resolution-alternating least squares (MCR-ALS) has been used to resolve chromatographic elution profiles and pure spectra of species involved in the photodegradation process and, hence, to elucidate the photodegradation mechanism and to propose the chemical structure of the main photoproducts. This study shows that chromatographic monitoring is the preferred option when photochemical systems with large number of components with similar spectra and kinetic evolution are analyzed. This work reveals the advantages of the double DAD and MS detection to provide mechanistic and structural information about these complex photodegradation processes.     

Preparation of PANI-TiO2 nanocomposites and their solid-phase photocatalytic degradation

A series of polyaniline-anatase TiO₂ (PANI-TiO₂) nanocomposite powders with different PANI:TiO₂ ratios were prepared by ‘in-situ’ deposition oxidative polymerization of aniline hydrochloride using ammonium persulfate (APS) as oxidant in the presence of ultrafine grade powder of anatase TiO₂ cooled in an ice bath. And the solid-phase photocatalytic degradation of PANI-TiO₂ nanocomposites was investigated under the ambient air in order to assess the feasibility of developing photodegradable polymers. The photodegradation of the composite powders was compared with that of pure PANI powders by performing weight loss monitoring, elemental analysis, FT-IR and UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The PANI-TiO₂ nanocomposite powders showed highly enhanced photodegradation and the photodegradation increased with decreasing ratios of PANI:TiO₂. A weight loss of about 6.8% was found for the PANI-TiO₂ (1:3) nanocomposite; however, the weight loss of the PANI-HCl powder was only 0.3% after being irradiated for 60 h under air. The photocatalytic degradation of the nanocomposite powders accompanied the peak intensity decrease in the FT-IR spectra at 1235 cm⁻¹, attributed to C-N stretching mode for benzenoid unit, and the depigmentation of the powders due to the visible light scattering from growing cavities. The elemental analysis and XPS analysis of the composite showed that the bulk and surface concentrations of N decreased with irradiation. A possible mechanism for the photocatalytical oxidative degradation was also mentioned.     

Photocatalytic mineralization of chlorinated organic pollutants in water by polyoxometallates. Determination of intermediates and final degradation products

Homogeneous aqueous solutions of organochlorine pesticides and chlorophenols, namely, lindane, hexachlorobenzene and 2,4-dichlorophenol (2,4DCP), undergo effective photodegradation upon photolysis with UV and near visible light in the presence of a characteristic polyoxometallate catalyst PW₁₂O₄₀ ³⁻. These substrates remained, practically, intact (lindane, HCB) or underwent minor degradation under similar conditions in absence of catalyst. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometallate with H₂O. The system compares with the widely published TiO₂. Chlorohydroquinone (ClHQ), hydroquinone (HQ), chlorobenzoquinone (ClBQ), benzoquinone (BQ), 3,5-dichlorocatechol (3,5DCC) and 4-chlorocatechol (4CC), among others, were identified as the main aromatic intermediates in the photodegradation of 2,4DCP. Acetic acid was detected as ring cleavage product. In all cases the final photodegradation leads to complete mineralization of substrates to CO₂ and HCl.     

Separation and Identification of Photolysis Products of Clothianidin by Ultra-Performance Liquid Tandem Mass Spectrometry

Photolysis of clothianidin by Xenon lamp was investigated by Ultra-Performance Liquid Chromatography Electrospray Ionization tandem mass spectrometry (UPLC-ESI/MS/MS). Quantitative study on the photodegradation of clothianidin found that the photodegradation obeyed first order kinetics (C = 9.9917e – 0.187^t, R² = 0.994). The half-life was about 3.6 hours. Qualitative study on photolysis products of clothianidin were taken by checking all total ion spectra of different sample time. A total of eight products was found in this study. The structure of each product was determined by the total ion spectrometry spectrum and daughter-scan spectrum. The mechanism of photodegradation of this pesticide included radical denitration, nucleophilic substitution, and rearrangement, ring-open, and ring-close. Through the analysis of the change of every product and the mass information, the photolysis pathway was drawn. From this study, products of V, VI, and VII seemed more stable than clothianidin.     

N掺杂TiO_2纳米粉体的制备及其可见光催化性能

首次以钛酸纳米管(NTA)为Ti的前驱体,以尿素为N源,采用水热法制备N掺杂TiO2纳米微粒,并用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、紫外-可见漫反射光谱仪(UV-Vis DRS)、透射电镜(TEM)、傅立叶变换红外光谱(FT-IR)等技术对不同条件下制备的产物进行了表征.探讨了尿素的掺杂量、水热温度对N掺杂TiO2形貌和结构的影响,并以亚甲基蓝为模型反应物考察了其在可见光下的催化性能,结果表明样品UN-130-1/2催化活性最高.     

Photodegradation of 2-nitrophenol catalyzed by CoO, CoS and CoO/CoS nanoparticles

The nanoparticles of CoO, CoS and CoO/CoS composite are synthesized using precipitation method. The X-ray diffraction, UV–Vis absorption spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and FT-IR spectroscopy are used to characterize the prepared nanoparticles. The EDX analysis shows the formation of CoO_0.67S_0.33 composite. The XRD pattern indicates the hexagonal structure for nanocomposite. The formation of Co–O and Co–S bonds is confirmed by FT-IR spectra. The band-gap energies of 2.97, 3.06 and 2.91 eV are obtained from UV–Vis spectra of CoO, CoS and CoO/CoS nanoparticles, respectively. The results of photodegradation of 2-nitrophenol show that the photoreactivity order of nanocatalysts is CoO/CoS > CoO > CoS. The pseudo first-order kinetic rate constants of 6.4 × 10^?3, 4.3 × 10^?3 and 12.2 × 10^?3 min^?1 are obtained for CoO, CoS and CoO/CoS nanoparticles, respectively, at photodegradation reaction conditions of pH 10, 30 mg/L of 2-NP and 1.3 g/L of the catalyst. The proposed nanocomposite shows an acceptable reusability and stability against photocorrosion in four-cycle photodegradation experiments.     

Photodegradation of substituted stilbene compounds: what colors aging paper yellow?

Photodegradation of lignin is one of the major postprocessing problems in paper production, as this renders yellowing of the paper and reduced paper quality. In this study, we have explored the photochemical properties of substituted stilbene derivatives believed to be key chromophores in the photodegradation of lignin derived from cinnamyl alcohol. In particular, the present work focuses on the computation of UV/vis electronic absorption spectra for different methoxylated stilbenes and their proposed photodegradation products. All calculations were performed using the time-dependent formalism of density functional theory (TD-DFT) and the B3LYP hybrid functional. It is concluded that the methodology employed is capable of reproducing not only the overall spectra, but also subtle features owing to the effects of different substitution patterns. For the strongly absorbing first excited singlet state (HOMO --> LUMO excitation) of the methoxylated stilbenes, the calculated transition energies are, albeit somewhat fortuitously, in excellent agreement with experimental data. The light-induced yellowing indirectly caused by the presence of stilbenes can be rationalized in terms of the absorption spectra of the resulting photodegraded o-quinones, for which distinct transitions in the 420-500 nm region of the visible spectrum lacking prior to degradation are observed.     

Application of solid-phase microextraction to the study of the photochemical behaviour of five priority pesticides: "on-fiber" and aqueous photodegradation

Solid-phase microextraction (SPME) is applied to study the photochemical degradation of five priority pesticides: atrazine, alachlor, aldrin, dieldrin, endrin. Analyses were carried out by gas chromatography-mass spectrometry. The possibility of studying the photochemical degradation of the target compounds in solid-phase microextraction fibers, "photo-SPME", is evaluated employing different SPME coatings. The target analytes were extracted from aqueous solutions using different commercial coatings and then, the fibers were exposed to UV light. Results indicated that on-fiber photodegradation takes place in a considerably major extent using PDMS coating for an irradiation time of 30min. On-fiber photodegradation kinetics of each analyte were determined by UV irradiation of the PDMS for different times. A large number of photoproducts were generated and they were tentatively identified by means of their mass spectra and with the aid of literature. In this way, main photodegradation mechanisms could be postulated. Aqueous photodegradation studies followed by SPME were performed and compared with photo-SPME. All the photoproducts detected in the aqueous experiments were previously found in the photo-SPME experiments. This study shows the potential of photo-SPME to evaluate the photo-transformation of organic pollutants.     

Extraction of biosilica from date palm biomass ash and its application in photocatalysis

There is an emerging trend in the valorization of biomass waste for the development of value-added products. Date palm biomass is an extensively available bioresource in Saudi Arabia. In date palm farms, the biomass residues are usually burnt, and a lot of ash is generated. Biomass ash is rich in silica, which is a valuable material used in a wide range of applications. This study explores the extraction of pure silica nanoparticles from date palm biomass ash (DPBA) and its application in photocatalysis. A chemical sol–gel method or thermal combustion method was employed for the extraction of silica. The extracted silica nanoparticles were characterized by EDX, FT-IR, XRD, SEM, BET, and TGA. FT-IR spectra of extracted biosilica samples displayed only the characteristic peaks corresponding to the silica functional groups. The chemically synthesized biosilica sample exhibited higher purity (98 %) and higher surface area (376 m²/g) compared to the thermally prepared biosilica samples. The SEM analysis revealed the presence of spherical-shaped silica particles of an average diameter of 93 nm in chemically extracted biosilica and 208 nm in thermally extracted biosilica. The newly extracted biosilica samples were tested for the photodegradation of the bromophenol blue dye in water. The dye degradation efficiency of chemically prepared biosilica sample was 82 % and that of thermally prepared biosilica sample was 74 %. The relatively higher degradation efficiency of BS-chemical could be due to its higher surface area and smaller particle size, and also due to the presence of lots of surface defects in this fully amorphous biosilica.     

Photostability and toxicity of finasteride,diclofenac and naproxen under simulating sunlight exposure: evaluation of the toxicity trend and of the packaging photoprotection

Background

Drugs photostability plays two different opposite roles; a real advantage arises considering the longer expiration time of the drugs while the consequent persistence in the environment involves an obvious negative effect bound to their harmfulness.On this basis we tested the photostability and toxicity of three pharmaceutical active principles: Finasteride, Diclofenac and Naproxen. The pure active principles, as well as commercial drugs containing them, were considered; for the last, the protective effect of the packaging was also evaluated. Samples were irradiated according to the ICH Guidelines for photostability testing (The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use); a simulating sunlight source (a mercury-vapor lamp coupled to a tungsten filament one) was used to cover the wavelength range 300–2000 nm; Temperature, Relative Humidity, Irradiance and Illuminance were maintained constant during the photodegradation. The concentrations of the pharmaceutical active principles during the photodegradation were monitored by HPLC with UV/Vis detector. Toxicity tests were performed by means of an amperometric biosensor based on suspended yeast cells. Since the products obtained by the photodegradation process can result as toxic or more toxic than the original molecules, tests were performed first and after the photodegadation.

Results

After 90 hours of exposure the concentration resulted lowered by 42.9%, 88.4% and 91% for Finasteride, Naproxen and Diclofenac respectively. Toxicity of the pure active principles follows the same order of the photostability. After photodegradation a contribute of the reaction products was evidenced.

Conclusions

The simple and cheap analytical procedure here proposed, allowed to obtain not only data on photostability and toxicity of the pure active principles but, even if roughly, also useful information on the reactions kinetic and toxicity of the photodegradation products.

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漂浮型BiFeO3/膨胀珍珠岩的制备及其可见光催化性能

利用水热法制备了新颖的、漂浮型的膨胀珍珠岩(EP)负载BiFeO₃(BiFeO₃/EP)复合光催化材料。采用X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱仪(XPS)和紫外可见漫反射(UV-Vis-DRS)对制备的复合材料进行了表征与分析。SEM和TEM结果清楚地表明BiFeO₃纳米粒子已被负载到EP表面。与纯BiFeO₃相比,BiFeO₃/EP复合材料明显提高了对可见光的吸收能力,减小了带隙宽度,在可见光下对亚甲基蓝(MB)的降解表现出更强的光催化活性。其中,70%BiFeO₃/EP复合材料对MB染料废水的光催化活性最高,其光催化反应一级速率常数是纯BiFeO₃的2.2倍。由于质轻中空的特点,制备的BiFeO₃/EP颗粒漂浮在液面上,有利于相分离和反应后光催化剂的回收。材料的重复性试验表明,复合材料在MB光降解过程中是相当稳定的。