1,721,231 research outputs found
Photocatalytic reductive and oxidative ability study of pristine ZnO and CeO2-ZnO heterojunction impregnated with Cu2O
Full text linkIn the present work the Cu2O-ZnO heterosystem and the novel Cu2O-CeO2-ZnO triphasic heterojunction were synthesized impregnating the ZnO and the CeO2-ZnO
system surfaces with 0.5% in weight of Cu2O, respectively. While X-ray powder diffraction (XRPD) evidenced any alteration in the matrix phases, the UV–vis and
electron paramagnetic resonance (EPR) spectroscopy highlighted a drastic change in the optical and electronic behaviour respect to the non-impregnated samples.
Deeply investigations allowed us identifying the photo-stability of the surface decorative Cu2O phase and the presence of additional copper species, namely Cu2+ and
Cu(0), coming as “waste” from the employed impregnation route. The presented outcomes brought us to suggest a beneficial impact of these species promoting the
overall photocatalytic process. Finally, both the oxidative and reductive photocatalytic activity of the produced materials has been evaluated by means the H2
generation from the water photosplitting process and through the photodegradation of the tolytriazol molecule, respectively, where the novel Cu2O-CeO2-ZnO
heterojunction exhibited the best performance upon UV–vis and purely visible irradiation
High-performance liquid chromatography/high-resolution mass spectrometry for the characterization of transformation products of ionic liquids
Full text linkRationaleIonic liquids (ILs) are a subject of active research in the field of alternative solvents. We studied the behaviour of a piperidine IL, 1-butyl-1-methylpiperidinium tetrafluoroborate (BMPA), through the elucidation of its transformation products (TPs) in water.MethodsThe transformation pathways of BMPA were investigated using high-performance liquid chromatography (HPLC) combined with a hybrid LTQ-Orbitrap instrument on the basis of mass defect filtering. TPs of BMPA were identified by fragmentation patterns and accurate mass measurements.ResultsThe separation and identification of 32 TPs was achieved. BMPA can be oxidized at different positions in the alkyl chains. The ultimate products corresponds to N-methyl-piperidinium and some byproducts involving ring-opening. Tests of acute toxicity, evaluated with Vibrio Fischeri bacteria, show that BMPA transformation proceeds through the formation of slightly harmful compounds.ConclusionsResults showed that the main transformation pathways of BMPA were alkyl chain hydroxylation/shortening and de-alkylation, and that HPLC/LTQ-Orbitrap can serve as an important analytical platform to gather the unknown TPs of ILs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Assessment of the photocatalytic transformation of pyridinium-based ionic liquids in water
Full text linkWe studied some ionic liquids (ILs) belonging to the pyridinium class under photocatalytic treatment. In particularly, we analysed how the length of the alkyl chain, the kind of inorganic ion and the type of substituents could influence the disappearance rate, the mineralization extent, the acute toxicity and the transformation mechanism. For such, we selected some pyridinium derivatives with different alkyl chain but the same anion, namely tetrafluoroborate (1-ethylpyridinium, 1-butylpyridinium, 1-hexylpyridinium), with two alkyl substituents (4-methyl-l-butylpyridinium) and with a different substituent (1-cyanopropylpyridinium). Then, on a selected IL (1-butylpyridinium), we evaluate the role of different inorganic anions (bromine and chlorine). The results show that irrespective to the alkyl chain or the number of substituents, the transformation involved an attack to the alkyl chain, proceeded through the formation of harmless compounds and the mineralization was easily achieved within 4 h. Nitrogen was mainly released as ammonium ion. When introducing a cyano group, the extent of nitrate ions and the number of possible transformation route increased. Conversely, the type of inorganic ion deeply affected the transformation pathways and the extent of mineralization. Actually, in the presence of bromide as anion, IL was only partially mineralized and the formation of highly persistent transformation products occurred. (C) 2017 Elsevier B.V. All rights reserved
Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review
Full text linkIn the last decades photocatalysis has become one of the most employed technologies
for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal
of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are
transition metal oxides, in which the band structure allows charge carrier separation upon solar
irradiation. The photoinduced charge carrier can thus cause oxidative and reductive redox reactions
at the surface, inducing the formation of the radical species able to initiate the AOPs. Despite the
great advantages of this process (non-toxic, cheap and environmentally clean), the main drawback
lies in the fact that the most efficient semiconductors are only able to absorb UV irradiation, which
accounts for only 5% of the total solar irradiation at the Earth’s surface and not enough to generate
the required amount of electron-hole pairs. On the other hand, many efforts have been devoted to
the sensitization of wide band gap transition metal oxides to visible light, which represents a higher
percentage (almost 45%) in the solar electromagnetic spectrum. Among all the strategies to sensitize
transition metal oxides to visible irradiation, doping with lanthanides has been less explored. In
this regard, lanthanides offer a unique electronic configuration, consisting in 4f orbitals shielded
by a 5s5p external shell. This occurrence, coupled with the different occupation of the localized
4f orbitals would provide an astounding opportunity to tune these materials’ properties. In this
review we will focus in depth on the modification of two promising photocatalytic transition metal
oxides, namely ZnO and ZrO2
, with cerium, europium and erbium atoms. The aim of the work
is to provide a comprehensive overview of the influence of lanthanides on the structural, optical
and electronic properties of the modified materials, emphasizing the effect of the different 4f orbital
occupation in the three considered doping atoms. Moreover, a large portion of the discussion will be
devoted to the structural-properties relationships evidencing the improved light absorption working
mechanism of each system and the resulting enhanced photocatalytic performance in the abatement
of contaminants in aqueous environments
Beyond TiO2: Cerium-Doped Zinc Oxide as a New Photocatalyst for the Photodegradation of Persistent Pollutants
Full text linkWe prepared via hydrothermal synthesis zinc oxide samples doped with cerium. The samples were characterized via powder X-Ray Diffraction measurements, Diffuse Reflectance UV Vis spectroscopy, Scanning Electron Microscopy and Transmission Electron Microscopy with EDX (Energy Dispersive X-Ray spectroscopy) analysis, and BET (Brunauer-Emmett-Teller) surface area analysis. XRD measurements reveal the formation of highly crystalline materials; wurtzite is the most important. All materials were tested using phenol as model molecule and their performances were compared with TiO2 P25. The material showing the best performance, namely Ce-doped ZnO, was then used to abate some emerging pollutants. We chose three iodinated X-ray contrast agent (ICM), iopromide, iopamidol and diatrizoate, known to be recalcitrant to traditional advanced oxidation processes. In the presence of TiO2 P25, all ICM exhibited a slow degradation, with t(1/2) ranging from 30 min (iopamidol) to 120 min (diatrizoate) and several hours are required for their complete disappearance. The employment of Ce-doped ZnO leads to a sharp increase in their disappearance, with t(1/2) obtained within 15 min (iopamidol) or 25 min (diatrizoate) and the complete abatement is achieved within 2 h
Ternary systems based on ZnO/CeO2/Cu2O for the degradation of phenol and carbamazepine
Full text linkIn this paper we prepared via different synthetic processes, two ternary systems based on ZnO, CeO2 and Cu2O for the abatement of organic pollutants. The system ZnO/CeO2 was already known to be efficient in the degradation of emergent contaminants, the addition of cuprous oxides allows also to enhance reductive properties to the material thanks to its specific potential. The mixed oxides were characterized via power X Ray Diffraction, UV visible Diffuse Reflectance and Electron Paramagnetic Resonance. The materials obtained through hydrothermal synthesis shown better performances in the abatement of phenol and carbamazepine
Chitosan, Gelatine, and Cellulose Based Hydrogels for the Removal of Potentially Toxic Elements from Aquaculture Water: A Comparative Study
Full text linkSince aquaculture is playing an increasingly important role in food supply, ensuring the healthiness of aquatic environments is a fundamental issue. Anthropogenic activities are often a source of contamination for water and, among the pollutants released, potentially toxic elements (PTEs) represent a well-known hazard to human health and ecosystem safety. In this study, carboxymethylcellulose-alginate (HY-ACMC), methacrylated-chitosan (HY-MCHI), and methacrylated-gelatine (HY-MGEL) hydrogels are synthesized, characterized, and tested as sorbents for PTEs removal. The removal efficiency is significantly affected by pH and contaminants' concentration. Furthermore, experiments in real aquaculture samples from Italy and Denmark farms are carried out to evaluate the matrix effect. Finally, hydrogel regeneration is optimized and sorbent efficiency for multiple cycles of water remediation treatment is investigated. All tested materials show promising removal capabilities even in real water. HY-ACMC has proven to be the most effective for single-cycle remediation treatments thanks to its high performance in all the studied conditions, although it is unstable to regeneration. On the other hand, regeneration with Na2EDTA improves HY-MCHI efficiency, granting its prolonged employment over time. Considering both performances in real water samples and reusability results, HY-MGEL seems to be the most reliable material for multiple cycles of water remediation treatments
Study of the Photoinduced Fate of Selected Contaminants in Surface Waters by HPLC‐HRMS
Full text linkRationale: Photoinduced transformation of contaminants of emerging concern (CECs) can occur in aquatic environment and could lead to the formation of transformation products (TPs) of greater concern than the parent compounds. For such, the fate of epoxiconazole, hymecromone, and coumarin in water was investigated by simulating photoinduced abiotic transformations to assess the toxicity of their TPs and which CEC may be of greatest concern. Methods: Heterogeneous photocatalysis with TiO2 and direct photolysis of selected CECs were exploited to simulate their TPs. The TPs were assessed by means of HPLC coupled with an Orbitrap MS analyser in ESI positive mode, while their toxicity was evaluated through a Vibrio fischeri bioluminescence assay, and ECOSAR tool. Results: The formation of numerous TPs via different photoinduced pathways was noticed (27 for epoxiconazole, 6 for coumarin, and 8 for hymecromone, some of which are in the form of structural isomers). Toxicity assessment via V. fischeri assay showed that, unlike coumarin species, epoxiconazole transformation proceeds through the formation of toxic compounds. By means of ECOSAR software, the formation of predominant more noxious TPs of epoxiconazole was proved than the parent compound for both acute and chronic toxicities. Instead, most TPs of coumarin and hymecromone generally exhibited "harmful" and "toxic" levels of acute and chronic toxicities. Conclusions: A probable structural identification was assigned to the monitored TPs via HPLC-HRMS to recognize the several transformation pathways, of which the hydroxylation reaction was predominant, and which compound may be more hazardous in the aquatic system due to its TPs. Epoxiconazole transformation brought to potentially toxic TPs, whereas photoinduced degradation of coumarin and hymecromone resulted in less hazardous TPs. The most significant aspect of this work is the ability of this overall approach to identify the formation of photoinduced TPs that are potentially more toxic than the original CEC
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