Photoelectrocatalytic degradation of 4,4'-dibromobiphenyl in aqueous solution on TiO₂ and doped TiO₂ nanotube arrays

Polybrominated biphenyls have been widely used as flameretardants in textile and electronic industries, and additives in plastics. Over the past few decades, much attention has been given to polybrominated biphenyls in the environment and their effects on humans. In this paper, we studied on the degradation of 4,4′-dibromobiphenyl, a typical one of polybrominated biphenyls, through photoelectrocatalytic process with TiO₂, Zr/TiO₂ and Zr, N/TiO₂ nanotube arrays. The results showed that the photoelectrocatalytic process was more efficient than photocatalytic and electrolytic process alone. The results exhibited that the photoelectrocatalytic efficiency was significantly affected by the properties of the catalysts and bias potential, and the highest photoelectrocatalytic degradation rate was achieved with Zr, N/TiO₂ at 1 V and the order was Zr, N/TiO₂ > Zr/TiO₂ > TiO₂. The mechanism was also discussed by detecting the changes of pH value, bromine anion, total organic carbon and intermediates during the process.     

Aquatic photolysis of hydroxylated polybromodiphenyl ethers under direct UV irradiation: a case study of 2′-HO-BDE-68

Environmental Science and Pollution Research - Hydroxylated polyhalodiphenyl ethers (HO-PXDEs) have attracted considerable scientific interest as examples of emerging aquatic pollutants. However, a...     

Removal of Rhodamine B under visible irradiation in the presence of Fe⁰, H₂O₂, citrate and aeration at circumneutral pH

A new Vis-Fe⁰-H₂O₂-citrate-O₂ system comprising zero-valent iron, hydrogen peroxide, citrate anion and aeration at circumneutral pH under visible irradiation was studied. 21 μmol L⁻¹ of Rhodamine B (RhB) was chosen as the substrate to be tested. Experiments were conducted under conditions of 2.9 mmol L⁻¹ of H₂O₂, 12.6 g of Fe⁰ and 1.0 mmol L⁻¹ of citrate at pH 7.5. Results showed that, in 1 h reaction, 54% of RhB was removed with corresponding 26% of COD reduced. Meanwhile, the amount of released dissolved irons from Fe⁰ surface was found to be at a very low level as <5.4 μmol L⁻¹. Extinguishing tests with isopropanol suggested that RhB oxidation by hydroxyl radicals was the main process taken place in Vis-Fe⁰-H₂O₂-citrate-O₂ system, which accounted for 75% of substrate removal in 3 h reaction. Control and factor influencing experiments showed that the prohibitive extents of individual factor importance on RhB removal followed a decreasing order of Fe⁰ > H₂O₂ > citrate > Vis > O₂. This study showed an excellent system that could remove refractory organic compounds from water in laboratory researches, and also provided a good idea to reduce secondary contamination by dissolved irons in future investigations.     

Synergetic effects of Sr-doped CuBi<Subscript>2</Subscript>O<Subscript>4</Subscript> catalyst with enhanced photoactivity under UVA– light irradiation

Sr-doped CuBi₂O₄ micro-particles were successively synthesized via a solid-state technique and were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and UV–vis diffuse reflectance spectroscopy (UV–vis-DRS) techniques. Results show that Sr-doped CuBi₂O₄ was crystallized with a spinel-type structure and tetragonal crystal system, and the band gap energy was about 1.35 eV. The as-prepared Sr-doped CuBi₂O₄ treated at 573 °C for 12 h exhibited the highest efficiency, as a result of 97.22 % of CR degradation within 220 min, which is approximately 31 times greater than CR photodegradation when catalyzed by CuBi₂O₄ (3.13 %) and about 2.3 times superior than that catalyzed by the untreated Sr–doped CuBi₂O₄ sample (42.08 %). Pseudo-first-order kinetic model gave the best fit, with highest correlation coefficients (R ²?=?0.94–0.97). The Sr–doping and extending reaction time up to 12 h could be effective in producing Sr-doped CuBi₂O₄ materials that delay electron–hole recombination, thereby increasing the lifetime of the electron electron–hole separation and support the charge carrier transfer to the catalyst surface. On the basis of the calculated energy band positions, superoxide radical anions (O₂ ^?–) were the main oxidative species responsible for the photocatalytic degradation of CR dye solution.     

Photocatalytic degradation of gaseous toluene over Ag-doping TiO₂ nanotube powder prepared by anodization coupled with impregnation method

In this work, Ag-doping TiO₂ nanotubes were prepared and employed as the photocatalyst for the degradation of toluene. The TiO₂ nanotube powder was produced by the rapid-breakdown potentiostatic anodization of Ti foil in chloride-containing electrolytes, and then doped with Ag through an incipient wetness impregnation method. The samples were characterized by scanning electron microscope, high-resolution transmission electron microscopy, X-ray diffraction, surface photovoltage measurements, X-ray photoelectron spectroscopy and N₂ adsorption. The nanotubular TiO₂ photocatalysts showed an outer diameter of approximately 40 nm, fine mesoporous structure and high specific surface area. The photocatalytic activity of Ag-doping TiO₂ nanotube powder was evaluated through photooxidation of gaseous toluene. The results indicated that the degradation efficiency of toluene could get 98% after 4 h reaction using the Ag-doping TiO₂ nanotubes as the photocatalyst under UV light illumination, which was higher than that of the pure TiO₂ nanotubes, Ag-doping P25 or P25. Benzaldehyde species could be observed during the photocatalytic oxidation monitored by in situ FTIR, and the formed benzaldehyde intermediate during reaction would be partially oxidized into CO₂ and H₂O.     

TiO₂ supported over SBA-15: an efficient photocatalyst for the pesticide degradation using solar light

Photocatalytic degradation and mineralization of pesticides are studied over TiO(2) supported mesoporous SBA-15 composite system using solar light. TiO(2) is immobilized over SBA-15 by solid sate dispersion method. The catalysts are characterized by XRD, surface area, UV-Vis diffused reflectance spectra, SEM and TEM. The detailed photocatalytic degradation studies are carried out over TiO(2), SBA-15 and different TiO(2) wt% supported SBA-15. The activity evaluation parameters such as catalyst amount, pH, and pollutant initial concentration are studied taking isoproturon as a model compound and established conditions for pesticide degradation. The optimum degradation is achieved over 10 wt% TiO(2)/SBA-15 within 30 min and the reaction is following pseudo-first order kinetics. The isoproturon mineralization is monitored with TOC reduction and it takes around 9h for disappearance. The commercial pesticide solutions containing imidacloprid and phosphamidon are also successfully degraded over these composites with the established conditions. The data indicates that 10 wt% TiO(2)/SBA-15 composite is an effective and highly active system for the pesticide degradations.     

Solar light–driven photocatalytic degradation and mineralization of beta blockers propranolol and atenolol by carbon dot/TiO2 composite

Herein improved solar light–driven photocatalytic degradation and mineralization of two emerging pollutants as well as recalcitrant beta blockers propranolol (PR) and atenolol (AT) have been demonstrated by metal-free carbon dot/TiO₂ (CDT) composite. Hydrothermally synthesized TiO₂ has been decorated with electrochemically synthesized carbon dots (CDs) and was well characterized by various analytical techniques viz. XRD, FTIR, Raman, XPS, UV–visible DRS, FESEM, and TEM. The optimized CDT composite, 2CDT (2 mL carbon dot/TiO₂), showed?~?3.45- and?~?1.75-fold enhancement in the photodegradation rate as compared to pristine TiO₂ for PR and AT respectively in 1 hour of irradiation along with complete degradation of PR and AT after 3 hours of irradiation. 2CDT exhibited 76% and 80% mineralization of PR and AT in contrast with 62% and 47% observed by pristine TiO₂. Further, the major reaction intermediates formed after degradation have been identified by HPLC/MS analysis, confirming more than 99% reduction of the parent compound for both PR and AT. Reusability of the optimized catalyst also showed successful degradation up to 3 cycles, showing reduction abilities of 97%, 95%, and 94% for 1st, 2nd, and 3rd cycle respectively. The enhanced degradation and mineralization efficiency of the 2CDT composite could be attributed to the excellent photosensitizer and electron reservoir properties of the CD along with upconverted photoluminescence behavior. The present study unlocks the possibility of using metal-free, facile CDT composite for effective degradation and mineralization of widely used beta blockers and other pharmaceuticals.

     

Acute effects of Fe₂O₃, TiO₂, ZnO and CuO nanomaterials on Xenopus laevis

Metal oxide nanomaterials have exhibited toxicity to a variety of aquatic organisms, especially microbes and invertebrates. To date, few studies have evaluated the toxicity of metal oxide nanomaterials on aquatic vertebrates. Therefore, this study examined effects of ZnO, TiO₂, Fe₂O₃, and CuO nanomaterials (20-100 nm) on amphibians utilizing the Frog Embryo Teratogenesis Assay Xenopus (FETAX) protocol, a 96 h exposure with daily solution exchanges. Nanomaterials were dispersed in reconstituted moderately hard test medium. These exposures did not increase mortality in static renewal exposures containing up to 1000 mg L⁻¹ for TiO₂, Fe₂O₃, CuO, and ZnO, but did induce developmental abnormalities. Gastrointestinal, spinal, and other abnormalities were observed in CuO and ZnO nanomaterial exposures at concentrations as low as 3.16 mg L⁻¹ (ZnO). An EC₅₀ of 10.3 mg L⁻¹ ZnO was observed for total malformations. The minimum concentration to inhibit growth of tadpoles exposed to CuO or ZnO nanomaterials was 10 mg L⁻¹. The results indicate that select nanomaterials can negatively affect amphibians during development. Evaluation of nanomaterial exposure on vertebrate organisms are imperative to responsible production and introduction of nanomaterials in everyday products to ensure human and environmental safety.     

Experimental study on treatment of heavy metal–contaminated soil by manganese-oxidizing bacteria

Environmental Science and Pollution Research - There are many studies on the treatment of heavy metals by manganese-oxidizing bacteria and the reaction is good; the problem of compound pollution of...     

Bioremediation of heavy metal–polluted environments by non-living cells from rhizobial isolates

Environmental Science and Pollution Research - Rhizosphere bacteria, for example, rhizobia, can play several roles, and one of the most important, the protection of plant roots against toxic...     

UV–visible light-activated Ag-decorated,monodisperse TiO2 aggregates for treatment of the pharmaceutical oxytetracycline

Noble metal Ag-decorated, monodisperse TiO₂ aggregates were successfully synthesized by an ionic strength-assisted, simple sol–gel method and were used for the photocatalytic degradation of the antibiotic oxytetracycline (OTC) under both UV and visible light (UV–visible light) irradiation. The synthesized samples were characterized by X-ray diffraction analysis (XRD); UV–vis diffuse reflectance spectroscopy; environmental scanning electron microscopy (ESEM); transmission electron microscopy (TEM); high-resolution TEM (HR-TEM); micro-Raman, energy-dispersive X-ray spectroscopy (EDS); and inductively coupled plasma optical emission spectrometry (ICP-OES). The results showed that the uniformity of TiO₂ aggregates was finely tuned by the sol–gel method, and Ag was well decorated on the monodisperse TiO₂ aggregates. The absorption of the samples in the visible light region increased with increasing Ag loading that was proportional to the amount of Ag precursor added in the solution over the tested concentration range. The Brunauer, Emmett, and Teller (The BET) surface area slightly decreased with increasing Ag loading on the TiO₂ aggregates. Ag-decorated TiO₂ samples demonstrated enhanced photocatalytic activity for the degradation of OTC under UV–visible light illumination compared to that of pure TiO₂. The sample containing 1.9 wt% Ag showed the highest photocatalytic activity for the degradation of OTC under both UV–visible light and visible light illumination. During the experiments, the detected Ag leaching for the best TiO₂-Ag photocatalyst was much lower than the National Secondary Drinking Water Regulation for Ag limit (0.1 mg L^?1) issued by the US Environmental Protection Agency.     

Persulfate activation by ferrocene-based metal–organic framework microspheres for efficient oxidation of orange acid 7

Environmental Science and Pollution Research - Ferrocene-based metal–organic framework with different transition metals (M-Fc-MOFs, M?=?Fe, Mn, Co) was synthesized by a simple...     

Photoelectro-Fenton treatment of pesticide triclopyr at neutral pH using Fe(III)–EDDS under UVA light or sunlight

Environmental Science and Pollution Research - One of the main challenges of electrochemical Fenton-based processes is the treatment of organic pollutants at near-neutral pH. As a potential...     

Novel two-step vapor-phase synthesis of UV–Vis light active Fe2O3/WO3 nanocomposites for phenol degradation

Supported Fe₂O₃/WO₃ nanocomposites were fabricated by an original vapor phase approach, involving the chemical vapor deposition (CVD) of Fe₂O₃ on Ti sheets and the subsequent radio frequency (RF)-sputtering of WO₃. Particular attention was dedicated to the control of the W/Fe ratio, in order to tailor the composition of the resulting materials. The target systems were analyzed by the joint use of complementary techniques, that is, X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and optical absorption spectroscopy. The results showed the uniform decoration of α-Fe₂O₃ (hematite) globular particles by tiny WO₃ aggregates, whose content could be controlled by modulations of the sole sputtering time. The photocatalytic degradation of phenol in the liquid phase was selected as a test reaction for a preliminary investigation of the system behavior in wastewater treatment applications. The system activity under both UV and Vis light illumination may open doors for further material optimization in view of real-world end-uses.

     

The key role of hydrophobicity in the determination of pharmaceuticals by liquid chromatography–electrospray ionization-mass spectrometry under the interference of natural organic matter

Environmental Science and Pollution Research - The determination of trace-level pharmaceuticals in water is generally performed using liquid chromatography combined with mass spectrometry, which is...     

Removal of toxic heavy metal ions from waste water by functionalized magnetic core–zeolitic shell nanocomposites as adsorbents

Functionalized magnetic core–zeolitic shell nanocomposites were prepared via hydrothermal and precipitation methods. The products were characterized by vibrating sample magnetometer, X-ray powder diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, and transmission electron microscopy analysis. The growth of mordenite nanocrystals on the outer surface of silica-coated magnetic nanoparticles at the presence of organic templates was well approved. The removal performance and the selectivity of mixed metal ions (Pb²⁺ and Cd²⁺) in aqueous solution were investigated via the sorption process. The batch method was employed to study the sorption kinetic, sorption isotherms, and pH effect. The removal mechanism of metal ions was done by chem–phys sorption and ion exchange processes through the zeolitic channels and pores. The experimental data were well fitted by the appropriate kinetic models. The sorption rate and sorption capacity of metal ions could be significantly improved by optimizing the parameter values.     

Enhanced photocatalytic activity of efficient magnetically recyclable core-shell nanocomposites on 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) degradation under UV-LED irradiation

Environmental Science and Pollution Research - The congener polychlorinated biphenyls (PCBs) are one of the of persistent organic pollutant compounds that increase lifestyle-related diseases, such...     

Changes in heavy metal contents in an acidic forest soil affected by depletion of soil organic matter within the time span 1969–93

Measurements of heavy metal content (Pb, Cd, Zn) were made in the period 1969–93 in a forested ecosystem near Möhlin (north-western part of Switzerland). Some distinct changes were found in the soil, especially in the subsoil (30–35 cm). The main and most likely driving force of the induced changes in the subsoil can be traced back to the observed decomposition of organic matter which strongly influenced the behaviour of major and minor chemical constituents of the soil. These changes are presumably mostly due to incidents that occurred in the past caused by the nearby aluminium industry. Generally, the observed changes in soil chemistry increase with decreasing distance to the aluminium plant in the time span 1969–93. The influence, if any, of the vegetation type and the forest management on the changes in the subsoil could not be figured out. Changes in the Pb content primarily correlate with soil organic matter (with a significant decrease in the subsoil). Good correlations are also found with Fe and partially with Al and Mn. Cd correlates well with pH, (earth)alkali ions, and generally to a lower degree with Mn, Fe and Al, but almost no correlation was found with the organic matter of the soil. Zn holds an intermediate position: significant correlations with organic C, (earth)alkali ions, Fe, Al and Mn were found but pH correlated only very weakly. The main transportation mechanism of Pb in the subsoil is believed to be primarily in colloidal form. Colloid release mechanisms are hypothesised to be due to the humus disintegration and the consequent reaction chain. In contrast to Pb, the elements Cd and Zn have, presumably, been translocated to a great extent as aqueous species.