Plastic debris in lakes and reservoirs.

Plastic debris is thought to be widespread in freshwater ecosystems globally1. However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging2,3. Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 µm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris4. Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services.

Cobalt Impregnation on Titania Photocatalysts Enhances Vis Phenol Photodegradation.

One of the main challenges of photocatalysis is to find a stable and effective photocatalyst, that is active and effective under sunlight. Here, we discuss the photocatalytic degradation of phenol as a model pollutant in aqueous solution using NUV-Vis (>366 nm) and UV (254 nm) in the presence of TiO2-P25 impregnated with different concentrations of Co (0.1%, 0.3%, 0.5%, and 1%). The modification of the surface of the photocatalyst was performed by wet impregnation, and the obtained solids were characterized using X-ray diffraction, XPS, SEM, EDS, TEM, N2 physisorption, Raman and UV-Vis DRS, which revealed the structural and morphological stability of the modified material. BET isotherms are type IV, with slit-shaped pores formed by nonrigid aggregate particles and no pore networks and a small H3 loop near the maximum relative pressure. The doped samples show increased crystallite sizes and a lower band gap, extending visible light harvesting. All prepared catalysts showed band gaps in the interval 2.3-2.5 eV. The photocatalytic degradation of aqueous phenol over TiO2-P25 and Co(X%)/TiO2 was monitored using UV-Vis spectrophotometry: Co(0.1%)/TiO2 being the most effective with NUV-Vis irradiation. TOC analysis showed ca. 96% TOC removal with NUV-Vis radiation, while only 23% removal under UV radiation.

On the dissociation pathways of copper complexes relevant as PET imaging agents.

Several bifunctional chelators have been synthesized in the last years for the development of new 64Cu-based PET agents for in vivo imaging. When designing a metal-based PET probe, it is important to achieve high stability and kinetic inertness once the radioisotope is coordinated. Different competitive assays are commonly used to evaluate the possible dissociation mechanisms that may induce Cu(II) release in the body. Among them, acid-assisted dissociation tests or transchelation challenges employing EDTA or SOD are frequently used to evaluate both solution thermodynamics and the kinetic behavior of potential metal-based systems. Despite of this, the Cu(II)/Cu(I) bioreduction pathway that could be promoted by the presence of bioreductants still remains little explored. To fill this gap we present here a detailed spectroscopic study of the kinetic behavior of different macrocyclic Cu(II) complexes. The complexes investigated include the cross-bridge cyclam derivative [Cu(CB-TE1A)]+, whose structure was determined using single-crystal X-ray diffraction. The acid-assisted dissociation mechanism was investigated using HClO4 and HCl to analyse the effect of the counterion on the rate constants. The complexes were selected so that the effects of complex charge and coordination polyhedron could be assessed. Cyclic voltammetry experiments were conducted to investigate whether the reduction to Cu(I) falls within the window of common bioreducing agents. The most striking behavior concerns the [Cu(NO2Th)]2+ complex, a 1,4,7-triazacyclononane derivative containing two methylthiazolyl pendant arms. This complex is extremely inert with respect to dissociation following the acid-catalyzed mechanism, but dissociates rather quickly in the presence of a bioreductant like ascorbic acid.

Removal of the industrial azo dye crystal violet using a natural clay: Characterization, kinetic modeling, and RSM optimization.

Natural clay (NC) was employed as a natural adsorbent for the elimination of an azo dye Crystal Violet (CV) from aqueous media. The characterization of the clay was performed by X-ray diffractometry (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) equipped with an X-ray energy dispersion spectrometer (EDS) and Brunauer-Emmett-Teller (BET) specific surface area analysis. The Box-Behnken design (BBD) was used as a powerful tool to determine the stationary points of the main independent factors: initial CV concentration, initial pH, temperature, and adsorbent dose on the adsorption efficiency. The significance and adequacy of the model were investigated using analysis of variance (ANOVA). The obtained results indicated an optimal dye removal of 99.1% at pH = 3, initial CV concentration of 11.767 mg/L, adsorbent load of 3.075 g/L, and T = 298.0 K. The kinetic study was evaluated using three models: a pseudo-first-order (PFO), a pseudo-second-order (PSO), and an intraparticle diffusion model. The observed kinetics is in excellent agreement with the PSO kinetic model. Therefore, both isotherms Langmuir and Freundlich fitted well the adsorption equilibrium data. The thermodynamic study revealed that the main parameters including (ΔG°, ΔH°, and ΔS°) indicated that the adsorption of CV onto NC was an endothermic and spontaneous process.

Effect of ionizing radiation on human myeloperoxidase: Reaction with hydrated electrons.

Myeloperoxidase (MPO) is a myeloid-lineage restricted enzyme largely expressed in the azurophilic granules of neutrophils. It catalyses the formation of reactive oxygen species, mainly hypochlorous acid, contributing to anti-pathogenic defense. Disorders in the production or regulation of MPO may lead to a variety of health conditions, mainly of inflammatory origin, including autoimmune inflammation. We have studied the effect of ionizing radiation on the activity of MPO, as measured by the capacity retained by the enzyme to produce hypochlorous acid as reactive oxygen species after exposure to successive doses of solvated electrons, the strongest possible one-e- reducing agent in water. Chlorination activity was still present after a very high irradiation dose, indicating that radiation damage does not take place at the active site, hindered in the core of MPO structure. Decay kinetics show a dependence on the wavelength, supporting that the process must occur at peripheral functional groups situated on external and readily accessible locations of the enzyme. These results are relevant to understand the mechanism of resistance of our innate anti-pathogenic defense system and also to get insight into potential strategies to regulate MPO levels as a therapeutic target in autoimmune diseases.

Enhanced Photocatalytic Degradation of the Imidazolinone Herbicide Imazapyr upon UV/Vis Irradiation in the Presence of CaxMnOy-TiO2 Hetero-Nanostructures: Degradation Pathways and Reaction Intermediates.

The determination of reaction pathways and identification of products of pollutants degradation is central to photocatalytic environmental remediation. This work focuses on the photocatalytic degradation of the herbicide Imazapyr (2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid) under UV-Vis and visible-only irradiation of aqueous suspensions of CaxMnOy-TiO2, and on the identification of the corresponding degradation pathways and reaction intermediates. CaxMnOy-TiO2 was formed by mixing CaxMnOy and TiO2 by mechanical grinding followed by annealing at 500 °C. A complete structural characterization of CaxMnOy-TiO2 was carried out. The photocatalytic activity of the hetero-nanostructures was determined using phenol and Imazapyr herbicide as model pollutants in a stirred tank reactor under UV-Vis and visible-only irradiation. Using equivalent loadings, CaxMnOy-TiO2 showed a higher rate (10.6 µM·h-1) as compared to unmodified TiO2 (7.4 µM·h-1) for Imazapyr degradation under UV-Vis irradiation. The mineralization rate was 4.07 µM·h-1 for CaxMnOy-TiO2 and 1.21 µM·h-1 for TiO2. In the CaxMnOy-TiO2 system, the concentration of intermediate products reached a maximum at 180 min of irradiation that then decreased to a half in 120 min. For unmodified TiO2, the intermediates continuously increased with irradiation time with no decrease observed in their concentration. The enhanced efficiency of the CaxMnOy-TiO2 for the complete degradation of the Imazapyr and intermediates is attributed to an increased adsorption of polar species on the surface of CaxMnOy. Based on LC-MS, photocatalytic degradation pathways for Imazapyr under UV-Vis irradiation have been proposed. Some photocatalytic degradation was obtained under visible-only irradiation for CaxMnOy-TiO2. Hydroxyl radicals were found to be main reactive oxygen species responsible for the photocatalytic degradation through radical scavenger investigations.

Degradation of 2-mercaptobenzothizaole in microbial electrolysis cells: Intermediates, toxicity, and microbial communities.

The compound 2-mercaptobenzothizaole (MBT) has been frequently detected in wastewater and surface water and is a potential threat to both aquatic organisms and human health (its mutagenic potential has been demonstrated). This study investigated the degradation routes of MBT in the anode of a microbial electrolysis cell (MEC) and the involved microbial communities. The results indicated that graphene-modified anodes promoted the presence of more enriched, developed, and specific communities compared to bare anodes. Moreover, consecutive additions of the OH substituent to the benzene ring of MBT were only detected in the reactor equipped with the graphene-treated electrode. Both phenomena, together with the application of an external voltage, may be related to the larger reduction of biotoxicity observed in the MEC equipped with graphene-modified anodes (46.2 eqtox∙m-3 to 27.9 eqtox∙m-3).

Face-Fusion of Icosahedral Boron Hydride Increases Affinity to γ-Cyclodextrin: closo,closo-[B21 H18 ]- as an Anion with Very Low Free Energy of Dehydration.

The supramolecular recognition of closo,closo-[B21 H18 ]- by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass-spectrometric measurements and computations, which indicated the formation and stability of CD ⋅ B21 H18- complexes in the gas phase. The thermodynamic signature of solution-phase binding is exceptional, the association constant for the γ-CD complex with B21 H18- reaches 1.8×106  M-1 , which is on the same order of magnitude as the so far highest observed value for the complex between γ-CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum-mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B21 H18- anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.

Photo-immobilization of proteins on carbons.

The photofunctionalization of three different carbons with two proteins was studied at room temperature. Water solutions of bovine serum albumin, BSA, and α-amylase, AA, were photolyzed at 21 °C in the presence of graphite microparticles (6.20 µm), MPG, graphene oxide, MPGO, and graphene oxide modified with SO2, mMPGO. The insertion of BSA on carbon matrixes occurred with a deoxygenation reaction, most likely due to a dehydration step of a water molecule. XPS, TOC and TGA, showed that the BSA photo-insertion on MPG was highly efficient with 34.9% of the weight of MPG after photolysis, with an initial concentration of 1 g∙L-1 of BSA. A high yield of AA photoinsertion on the carbons was also obtained. The calculated weight of AA inserted on MPG and MPGO after photolysis was 22.30% and 18.08%, respectively, with respect to the initial weight of carbon, when the initial concentration of AA was 60 mg∙L-1. AA immobilized on MPG was active while the enzyme on MPGO showed a smaller activity, within the experimental error. Although a certain extent of denaturalization of both proteins was observed during photolysis, the molecular weight and composition changed very little during the photolysis, which would produce mainly conformational changes and isomerization reactions.

Photolytic insertion of albumin on activated carbon modified with ozone.

254nm photolyses of bovine serum albumin [BSA] in aqueous solutions, were carried out in the presence of activated carbons modified by reaction with ozone. The photolyses were monitored by fluorescence spectroscopy and UV spectrophotometry, and the products were characterized by elemental analysis, FTIR, TGA, total organic carbon analyses [TOC], and XPS. The ozonation reaction was carried out at room temperature with O3 under dry and wet conditions. The carbon characterization showed that the reaction increased the amount of epoxide and carbonyl groups on the carbon matrix. The activated carbon modified with dry O3 exhibited higher concentration of oxidized groups in its surface, smaller surface area and lower thermal stability. Characterization of the photolysis of ozonized carbons pointed to a small release of carbon organic groups during the reaction with elimination of epoxide groups and increase of carbonyl groups without change of thermal stability. Photolysis of BSA in aqueous solution occurred with fluorescence quenching due to changes of the local microenvironment and/or macromolecular conformational changes. Absorbance increase of the UV spectrum indicated a hyperchromic effect due to albumin structure modifications during photolysis. TGA analysis of the photolysed activated carbons in the presence of BSA suggested that ozonized carbon samples underwent insertion of BSA upon photolysis, in particular the sample ozonized under dry conditions. The changes observed for the FTIR and elemental analysis agreed with this conclusion, which was further supported by 13C SS-NMR, fluorescence emission and XPS.

Effect of the calcination temperature on the photocatalytic efficiency of acidic sol-gel synthesized TiO2 nanoparticles in the degradation of alprazolam.

We report a comparative study on the photodegradation of the widely used benzodiazepine psychoactive drug alprazolam (8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine, ALP) using direct photolysis, and titanium dioxide photocatalyzed reaction. Titanium dioxide photocatalysts were prepared as nanoparticles by acidic sol-gel methods, calcined at two different temperatures, and their behavior compared with P25 (Degussa type) TiO2. Efficient photodegradation was observed in the photocatalytic process, with over 90% degradation after 90 minutes under optimized conditions. Triazolaminoquinoline, 5-chloro-(5-methyl-4H-1,2,4-triazol-4-yl)benzophenone, triazolbenzophenone, and α-hydroxyalprazolam were identified as the degradation products by fluorescence spectroscopy and HPLC-MS. A comparison with the literature suggests that 8H-alprazolam may also be formed. Good mineralization was observed with TiO2 photocatalysts. ALP photodegradation with TiO2 follows pseudo-first order kinetics, with rates depending on the photocatalyst used. The effects of the quantity of the photocatalyst and concentration of alprazolam were studied.

Photolysis of phenylalanine in the presence of oxidized carbon nanotubes.

Photolyses at 254 nm of phenylalanine (Phe) in aqueous solutions, were carried out in the presence of oxidized carbon nanotubes modified by the reaction with SO2 (mNTO). Kinetics of the photolyses were followed by UV spectrophotometry at 220 nm, and the products were characterized by HPLC, XPS, and (13)C-SSNMR. The ratio of the initial rates of photolysis in the presence and absence of mNTO, k*/ko*, showed a systematic decrease. The photolytic decay of Phe occurs with minor formation of tyrosine. The mass of nanotubes produced an exponential attenuation of the photolytic decomposition of Phe. Total carbon analyses (TCA) showed no inorganic carbon formation after the photolyses. The first-order rate constant of photofunctionalization of mNTO by the insertion of phenylalanine onto the nanotube matrix was calculated from TCA to be kin = 30.1 min(-1). Comparison of the XPS spectra of the mNTO before and after the photolysis, using the atom inventory technique, suggests the insertion of Phe along with the extrusion of a sulfide radical anion ((•)S(-)) which undergo subsequent oxidation to SO4(2-). The obtained results show the effects of mNTO on the photolysis of Phe and provide a new method of photofunctionalization of carbon materials, modified by the intermediates of the reduction of SO2, with an organic moiety.

Selective insertion of sulfur dioxide reduction intermediates on graphene oxide.

Graphite microparticles (d50 6.20 µm) were oxidized by strong acids, and the resultant graphite oxide was thermally exfoliated to graphene oxide sheets (MPGO, C/O 1.53). Graphene oxide was treated with nonthermal plasma under a SO2 atmosphere at room temperature. The XPS spectrum showed that SO2 was inserted only as the oxidized intermediate at 168.7 eV in the S 2p region. Short thermal shocks at 600 and 400 °C, under an Ar atmosphere, produced reduced sulfur and carbon dioxide as shown by the XPS spectrum and TGA analysis coupled to FTIR. MPGO was also submitted to thermal reaction with SO2 at 630 °C, and the XPS spectrum in the S 2p region at 164.0 eV showed that this time only the nonoxidized episulfide intermediate was inserted. Plasma and thermal treatment produced a partial reduction of MPGO. The sequence of thermal reaction followed by plasma treatment inserted both sulfur intermediates. Because oxidized and nonoxidized intermediates have different reactivities, this selective insertion would allow the addition of selective types of organic fragments to the surface of graphene oxide.

Photochemical and photocatalytic degradation of trans-resveratrol.

Photochemical and photocatalytic degradation of the emerging pollutant trans-resveratrol has been studied under different irradiation wavelengths and using different TiO2 catalysts. trans-Resveratrol was more easily degraded when irradiated using the whole spectral range (UV-Vis) rather than with UV and near-UV to visible irradiation. The main intermediate of trans-resveratrol phototransformation was identified as its isomer cis-resveratrol. Different TiO2 catalysts were used to carry out the photocatalytic degradation of trans-resveratrol. Catalysts properties such as crystallite dimensions, surface area and presence of hydroxy surface groups are shown to be crucial to the photocatalytic efficiency of the materials tested. From the point of view of trans-resveratrol abatement, the photocatalytic process was more efficient than the pure photochemical one resulting in higher degradation rates and higher organic content removal. Six photoproducts of trans-resveratrol phototransformation were identified mainly resulting from the attack of the hydroxyl radical to the organic molecule.

Understanding the mechanism of base-assisted decomposition of (N-halo),N-alkylalcoholamines.

The base-assisted decomposition of (N-X),N-methylethanolamine (X = Cl, Br) takes place mainly through two concurrent processes: a fragmentation and an intramolecular elimination. The global process follows second order kinetics, first order relative to both (N-X),N-methylethanolamine and base. Interaction of the base with the ionizable hydroxylic hydrogen triggers the reaction. The intramolecular elimination pathway leads to formaldehyde and 2-aminoethanol as reaction products via base-assisted proton transfer from the methyl to the partially unprotonated hydroxylic oxygen, with loss of halide. Meanwhile, the fragmentation pathway leads to methylamine and two equivalents of formaldehyde via bimolecular base-promoted concerted breakage of the molecule into formaldehyde, halide ion and N-methylmethanimine. Kinetic evidences allow a crude estimation of the concertedness and characterization of the transition structure for both processes, which are slightly asynchronous, the proton transfer to the base taking place ahead of the rest of the molecular events. The degree of asynchroneity increases as the bases become weaker. Electronic structure calculations, at the B3LYP/6-31++G** level, on the fragmentation pathway support the proposed mechanism.