Biofragmentation of Polystyrene Microplastics: A Silent Process Performed by Chironomus sancticaroli Larvae.

Polystyrene (PS) is one of the main synthetic polymers produced around the world, and it is present in the composition of a wide variety of single-use objects. When released into the environment, these materials are degraded by environmental factors, resulting in microplastics. We investigated the ability of Chironomus sancticaroli (Diptera, Chironomidae) to promote the fragmentation of PS microspheres (24.5 ± 2.9 µm) and the toxic effects associated with exposure to this polymer. C. sancticaroli larvae were exposed to 3 different concentrations of PS (67.5, 135, and 270 particles g-1 of dry sediment) for 144 h. Significant lethality was observed only at the highest concentration. A significant reduction in PS particle size as well as evidence of deterioration on the surface of the spheres, such as grooves and cracks, was observed. In addition, changes in oxidative stress biomarkers (SOD, CAT, MDA, and GST) were also observed. This is the first study to report the ability of Chironomus sp. to promote the biofragmentation of microplastics. The information obtained demonstrates that the macroinvertebrate community can play a key role in the degradation of plastic particles present in the sediment of freshwater environments and can also be threatened by such particle pollution.

Mechanochemical hydroquinone regeneration promotes gold salt reduction in sub-stoichiometric conditions of the reducing agent.

Bottom-up mechanochemical synthesis (BUMS) has been demonstrated to be an efficient approach for the preparation of metal nanoparticles (NPs), protected by surface agents or anchored on solid supports. However, there are limitations, such as precise size and morphological control, due to a lack of knowledge about the mechanically induced processes of NP formation under milling. In this article, we further investigate the BUMS of AuNPs. Using SiO2 as a solid support, we studied the effect of typical reducing agents, namely NaBH4, L-ascorbic acid, and hydroquinone (HQ), on the conversion of a AuIII source. XANES showed that HQ is the strongest reducing agent under our experimental conditions, leading to the quantitative conversion of gold salt in a few minutes. Interestingly, even when HQ was used in sub-stoichiometric amounts, AuIII could be reduced to ratios higher than 85% after two minutes of milling. Investigations into the byproducts by 1H NMR and GC-FID/MS enabled the identification HQ regeneration and the formation of its derivatives. We mainly focused on benzoquinone (BQ), which is the product of the oxidation of HQ as it reduces the gold salt. We could demonstrate that HQ is regenerated from BQ exclusively under milling and acidic conditions. The regenerated HQ and other HQ-chlorinated molecules could then reduce gold-oxidized species, leading to higher conversions and economy of reactants. Our study highlights the intriguing and complex mechanisms of mechanochemical systems, in addition to fostering the atom and energy economy side of mechanochemical means to produce metal nanoparticles.

An Overview on the Development of Electrochemical Capacitors and Batteries - part II.

In the second part of the review on electrochemical energy storage, the devolvement of batteries is explored. First, fundamental aspects of battery operation will be given, then, different materials and chemistry of rechargeable batteries will be explored, including each component of the cell. In negative electrodes, metallic, intercalation and transformation materials will be addressed. Examples are Li or Na metal batteries, graphite and other carbonaceous materials (such as graphene) for intercalation of metal-ions and transition metal oxides and silicon for transformation. In the positive electrode section, materials for intercalation and transformation will be reviewed. The state-of-the-art on intercalation as lithium cobalt oxide and nickel containing oxides will be approached for intercalation materials, whereas sulfur and metal-air will also be explored for transformation. Alongside, the role of electrolyte will be discussed concerning performance and safety, with examples for the next generation devices. Finally, a general future perspective will address both electrochemical capacitors and batteries.

An Overview on the Development of Electrochemical Capacitors and Batteries - Part I.

The Nobel Prize in Chemistry 2019 recognized the importance of Li-ion batteries and the revolution they allowed to happen during the past three decades. They are part of a broader class of electrochemical energy storage devices, which are employed where electrical energy is needed on demand and so, the electrochemical energy is converted into electrical energy as required by the application. This opens a variety of possibilities on the utilization of energy storage devices, beyond the well-known mobile applications, assisting on the decarbonization of energy production and distribution. In this series of reviews in two parts, two main types of energy storage devices will be explored: electrochemical capacitors (part I) and rechargeable batteries (part II). More specifically, we will discuss about the materials used in each type of device, their main role in the energy storage process, their advantages and drawbacks and, especially, strategies to improve their performance. In the present part, electrochemical capacitors will be addressed. Their fundamental difference to batteries is explained considering the process at the electrode/electrolyte surface and the impact in performance. Materials used in electrochemical capacitors, including double layer capacitors and pseudocapacitive materials will be reviewed, highlighting the importance of electrolytes. As an important part of these strategies, synthetic routes for the production of nanoparticles will also be approached (part I).

Mechanochemical Synthesis and Biological Evaluation of Novel Isoniazid Derivatives with Potent Antitubercular Activity.

A series of isoniazid derivatives bearing a phenolic or heteroaromatic coupled frame were obtained by mechanochemical means. Their pH stability and their structural (conformer/isomer) analysis were checked. The activity of prepared derivatives against Mycobacterium tuberculosis cell growth was evaluated. Some compounds such as phenolic hydrazine 1a and almost all heteroaromatic ones, especially 2, 5 and 7, are more active than isoniazid, and their activity against some M. tuberculosis MDR clinical isolates was determined. Compounds 1a and 7 present a selectivity index >1400 evaluated on MRC5 human fibroblast cells. The mechanism of action of selected hydrazones was demonstrated to block mycolic acid synthesis due to InhA inhibition inside the mycobacterial cell.

Triple Play of Band Gap, Interband, and Plasmonic Excitations for Enhanced Catalytic Activity in Pd/HxMoO3 Nanoparticles in the Visible Region.

Plasmonic photocatalysis has been limited by the high cost and scalability of plasmonic materials, such as Ag and Au. By focusing on earth-abundant photocatalyst/plasmonic materials (HxMoO3) and Pd as a catalyst, we addressed these challenges by developing a solventless mechanochemical synthesis of Pd/HxMoO3 and optimizing photocatalytic activities in the visible range. We investigated the effect of HxMoO3 band gap excitation (at 427 nm), Pd interband transitions (at 427 nm), and HxMoO3 localized surface plasmon resonance (LSPR) excitation (at 640 nm) over photocatalytic activities toward the hydrogen evolution and phenylacetylene hydrogenation as model reactions. Although both excitation wavelengths led to comparable photoenhancements, a 110% increase was achieved under dual excitation conditions (427 + 640 nm). This was assigned to a synergistic effect of optical excitations that optimized the generation of energetic electrons at the catalytic sites. These results are important for the development of visible-light photocatalysts based on earth-abundant components.

Solvent-Free Aerobic Oxidative Cleavage of Methyl Oleate to Biobased Aldehydes over Mechanochemically Synthesized Supported AgAu Nanoparticles.

The performance of mechanochemically synthesized supported bimetallic AgAu nanoalloy catalysts was evaluated in the oxidative cleavage of methyl oleate, a commonly available unsaturated bio-derived raw material. An extensive screening of supports (SiO2 , C, ZrO2 , Al2 O3 ), metallic ratios (Ag : Au), reaction times, temperatures, and use of solvents was carried out. The performance was optimized towards productivity and selectivity for the primary cleavage products (aldehydes and oxoesters). The optimal conditions were achieved in the absence of solvent, using Ag8 Au92 /SiO2 as catalyst, at 80 °C, reaction time of 1 h, substrate to catalyst=555 and 10 bar of molecular oxygen. A strong support effect was observed: the selectivity to aldehydes was best with silica as support, and to esters was best using zirconia. This shows not only that mechanochemical preparation of bimetallic catalysts is a powerful tool to generate useful catalyst compositions, but also that a safe, green, solventless synthesis of bio-derived products can be achieved by aerobic oxidative cleavage.

Mechanochemical Strategies for the Preparation of SiO2-Supported AgAu Nanoalloy Catalysts.

Silver-gold nanoalloys were prepared from their metal salts precursors through bottom-up mechanochemical synthesis, using one-pot or galvanic replacement reaction strategies. The nanostructures were prepared over amorphous SiO2 as an inert supporting material, facilitating their stabilization without the use of any stabilizing agent. The nanomaterials were extensively characterized, confirming the formation of the bimetallic nanostructures. The nanoalloys were tested as catalysts in the hydrogenation of 2-nitroaniline and exhibited up to 4-fold the rate constant and up to 37% increased conversion compared to the respective single metal nanoparticles. Our approach is advantageous to produce nanoparticles with clean surfaces with available catalytic sites, directly in the solid-state and in an environmentally friendly manner.

Tandem X-ray absorption spectroscopy and scattering for in situ time-resolved monitoring of gold nanoparticle mechanosynthesis.

Current time-resolved in situ approaches limit the scope of mechanochemical investigations possible. Here we develop a new, general approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy (XAS) and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au micro and nanoparticles in the presence of three different reducing agents, hydroquinone, sodium citrate, and NaBH4. Moreover, we show how XAS offers new insight into the early stage generation of growth species (e.g. monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.

A mechano-colloidal approach for the controlled synthesis of metal nanoparticles.

A mechano-colloidal approach was developed to produce Au nanotadpoles. It comprises the generation of seeds by ball-milling from a solid mixture containing a precursor, reductant, and capping agent, followed by the dispersion of this mixture in water leading to seeded-growth to generate the target nanoparticle morphology.