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Improving the perovskite/electron-transporting layer (ETL) interface is a crucial task to boost the performance of perovskite solar cells (PSCs). This is utterly fundamental in an inverted (p–i–n) configuration using fullerene-based ETLs. Here, we propose a scalable strategy to improve fullerene-based ETLs by incorporating high-quality few-layer graphene flakes (GFs), industrially produced through wet-jet milling exfoliation of graphite, into phenyl-C61-butyric acid methyl ester (PCBM). Our new composite ETL (GF:PCBM) can be processed into an ultrathin (∼10 nm), pinhole-free film atop the perovskite. We find that the presence of GFs in the PCBM matrix reduces defect-mediated recombination, while creating preferential paths for the extraction of electrons towards the current collector. The use of our GF-based composite ETL resulted in a significant enhancement in the open circuit voltage and fill factor of triple cation-based inverted PSCs, boosting the power conversion efficiency from ∼19% up to 20.8% upon the incorporation of GFs into the ETL. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of an active material for supercapacitors (SCs), namely α-Fe2O3/carbon composite (C-Fe2O3) made of elongated nanoparticles linearly connected into a worm-like morphology, by means of electrospinning followed by a calcination/carbonization process. The resulting active material powder can be directly processed in the form of slurry to produce SC electrodes with mass loadings higher than 1 mg cm−2 on practical flat current collectors, avoiding the need for bulky porous substrate, as often reported in the literature. In aqueous electrolyte (6 M KOH), the so-produced C-Fe2O3 electrodes display capacity as high as ~140 mAh g−1 at a scan rate of 2 mV s−1, while showing an optimal rate capability (capacity of 32.4 mAh g−1 at a scan rate of 400 mV s−1). Thanks to their poor catalytic activity towards water splitting reactions, the electrode can operate in a wide potential range (−1.6 V–0.3 V vs. Hg/HgO), enabling the realization of performant quasi-symmetric SCs based on electrodes with the same chemical composition (but different active material mass loadings), achieving energy density approaching 10 Wh kg−1 in aqueous electrolytes. [ABSTRACT FROM AUTHOR]

In the present study, we tackle the sustainable batteries topic by addressing its most defining aspects, namely what kind of waste material should be employed and its treatment for realizing performant battery anodes. In this regard, we focus on leather shaving waste (LSW), as it is an important waste element in many economies, resulting in an advantageous choice both from an environmental point of view and in terms of the circular economy. Herein, especially metal-free LSW is used to introduce an innovative kind of eco-friendly anode for lithium-ion batteries (LIBs). A pyrolysis process of the waste material is adopted to form biochar, followed by its texture engineering through either steam or CO2, both of them recognized as safe and environmentally friendly procedures. Indeed, these procedures develop hierarchical micro/mesopores in the biochar and modify the amount of oxygen-containing functional groups on its surface, which can lead to high-performance anodes. In this respect, when a water-based solvent and carboxymethyl cellulose (CMC) binder are employed, the fabricated electrode discloses high initial capacities and remarkable electrochemical stability in lithium-metal half-cells. In particular, the steam-activated electrode demonstrates a specific discharge capacity of 735 mA h g−1 after 1000 charge and discharge cycles at 0.5 A g−1. This anode electrode also secures an excellent initial capacity and acceptable cycling stability in full-cell LIBs where a high mass LiFePO4 loading cathode is employed. The results reported here represent a noticeable improvement with respect to the state of the art, hence demonstrating the enormous potential associated with the green re-use of waste materials in important sectors such as energy storage. [ABSTRACT FROM AUTHOR]

All‐inorganic metal halide perovskites are highly attractive materials for optoelectronics and are typically implemented as thin films, nanocrystals, and single crystals with macroscopic and millimeter‐size dimensions. Single crystals with regular shapes in the micrometer range are less explored and present an interesting alternative when a well‐defined and spatially localized response is desired. Here, CsPbBr3 microcrystals are fabricated by simple and fast drop‐casting of a precursor solution on several substrates that for the growth process are heated to temperatures in the range from 80 to 150 °C. The microcrystals have a cubic shape and feature a pyramidal cavity on their top surface that forms due to faster growth at the edges once the growing crystal is attached to the substrate. Distinct heterogeneity in the photoluminescence (PL) and conductivity of the different facets are measured by µ‐PL and conductive atomic force microscopy experiments. Toward device applications, the authors contact single microcrystals on conductive substrates mechanically with a micromanipulator tip. They observe diode‐like current–voltage curves and good photodetector functionality, obtaining a high responsivity of 150–300 A W−1 in the blue–green spectral region under forward bias, and a sharp detection band centered around 540 nm with peak responsivity close to 0.7 A W−1 under reverse bias. [ABSTRACT FROM AUTHOR]

Hollow structures made of nanoscale building blocks are of great interest as catalysts for electrochemical water splitting. Here we report a solution-phase synthesis of yolk–shell Co3O4/Co1−xRuxO2 microspheres (MSs) having a shell made of Co1−xRuxO2 nanorods and the core of Co3O4. Benefiting from the peculiar morphology and the synergy between the different materials present in the MSs, the latter exhibit enhanced electrochemical oxygen evolution activity and long-term stability in acidic media. The catalyst achieves a catalytic current density of 10 mA cm−2 at an overpotential of only 240 mV, a small Tafel slope of 70 mV dec−1, and a high mass activity of 600 A g−1 and maintains its activity throughout a 24 h chronopotentiometry tests at constant current densities of 10 and 20 mA cm−2. [ABSTRACT FROM AUTHOR]

A synthesis of carbon nanoparticles from hydrothermal dissociation of sugars of different composition is proposed in the present experimental study. The process has been carried out in a stirred batch reactor at a fixed temperature, using precursors dissolved in aqueous solvent in the presence of NaOH. The use of surface passivation agents has been avoided in order to test how the competing kinetics of chemical reaction and of particle agglomeration may condition the properties of the final product. The carbon nanoparticles have been characterized in diameter by dynamic light scattering. It has been shown that the molecular structure of the precursor and the selected residence time have a basic role in determining the probability distribution function of the as-made nanoparticles diameters. When fructose and lactose are adopted as precursors, the process of sugar decomposition is active even at room temperature owing to the action of NaOH. The present method, thanks to its easy reproducibility and to the absence of noxious releases as a by product, may represent a first step towards a cost-effective and environmentally sound technique for the synthesis of carbon nanoparticles at a larger scale. Finally, such aspects are discussed and some applications of practical relevance are proposed. [ABSTRACT FROM AUTHOR]

The design of efficient and cost-effective catalysts for the hydrogen evolution reaction (HER) is the key for molecular hydrogen (H2) production from electrochemical water splitting. Transition metal dichalcogenides (MX2), most notably group-6 MX2 (e.g., MoS2 and WS2), are appealing catalysts for the HER alternative to the best, but highly expensive, Pt-group elements. However, their HER activity is typically restricted to their edge sites rather than their basal plane. Furthermore, their semiconducting properties hinder an efficient electron transfer to the catalytic sites, which impedes a high rate of H2 production. Herein, we exploit liquid-phase exfoliation-produced metallic (1H, 2H and 3R) NbS2 nanoflakes, belonging to the class of metallic layered group-5 MX2, to overcome the abovementioned limitations. Both chemical treatment with hygroscopic Li salt and electrochemical in operando self-nanostructuring are exploited to improve the NbS2 nanoflake HER activity. The combination of NbS2 with other MX2, in our case MoSe2, also provides heterogeneous catalysts accelerating the HER kinetics of the individual counterparts. The designed NbS2-based catalysts exhibit an overpotential at a cathodic current of 10 mA cm−2 (η10) as low as 0.10 and 0.22 V vs. RHE in 0.5 M H2SO4 and 1 M KOH, respectively. In 0.5 M H2SO4, the HER activity of the NbS2-based catalysts is also superior to those of the Pt/C benchmark at current densities higher than 80 mA cm−2. Our work provides general guidelines for a scalable and cost-effective exploitation of NbS2, as well as the entire MX2 portfolio, for attaining a viable H2 production through electrochemical routes. [ABSTRACT FROM AUTHOR]

Dry mechanochemical ball-milling of halide precursor salts is a promising route for the synthesis of high-purity halide perovskites in a fast and solvent-free manner. However, there is a lack of information on the process mechanisms, kinetics, and possible side-effects. Here, we investigated in detail the mechanochemical synthesis of fully-inorganic CsPbBr3 by ball-milling of stoichiometric CsBr and PbBr2. Detailed structural, morphological and optical analyses reveal several beneficial and detrimental effects of milling as a function of time. Three stages are identified during the process: (i) at short milling times (t < 5 min) different ternary compounds are formed, including stoichiometric CsPbBr3 as well as Cs4PbBr6, and to a lesser extent, CsPb2Br5. Photoluminescence from "nano" and "bulk" CsPbBr3 species is observed, centered at 525 nm and 545 nm, respectively. (ii) At the optimum time (around 5 min for the present case) the complete transformation of all reactants and byproducts into phase-pure CsPbBr3 has occurred. Photoluminescence corresponds to bulk CsPbBr3; (iii) at much longer milling times (up to 10 hours) eventually smaller quantum-confined CsPbBr3 NCs are exfoliated from the bulk product leading to a broad and blue-shifted emission. At this stage the photoluminescence intensity is strongly reduced which is ascribed to the formation of surface defects induced by ball-milling in dry conditions. [ABSTRACT FROM AUTHOR]

The method of electrospinning was used to create nanofibers made of cellulose acetate (CA) and essential oils (EOs). CA polymer at 15% w/v was dissolved in acetone and then 1% or 5% v/v of EOs was added to the polymer solution. The utilized essential oils were rosemary and oregano oils. Then, the CA/EOs in acetone solution were electrospun, creating micro/nanofibers, approximately 700-1500 nm in diameter. Raman spectroscopy was used to detect the attachment of the EOs in the CA electrospun fibers (ESFs). Scanning electron microscopy was used to study the morphology, topography and dimensions of the ESFs. The formed CA/EOs ESFs are found to have good antimicrobial properties against three common microbial species, frequently found in difficult to treat infections: Bacteria species Staphylococcus aureus, Escherichia coli and the yeast Candida albicans. ESFs with 5% v/v oregano oil with respect to the initial solution, showed the best antimicrobial and anti-biofilm effects due to the potency of this EO against bacteria and fungi, especially for Escherichia coli and Candida albicans. This work describes an effective and simple method to prepare CA/EOs ESFs and opens up many new applications of micro/nanofibers such as improved antimicrobial wound dressings, anti-biofilm surfaces, sensors and packaging alternatives. [ABSTRACT FROM AUTHOR]

Copper nanoparticles have been synthesized in ethylene glycol (EG) using copper sulphate as a precursor and vanadium sulfate as an atypical reductant being active at room temperature. We have described a technique for a relatively simple preparation of such a reagent, which has been electrolytically produced without using standard procedures requiring an inert atmosphere and a mercury cathode. Several stabilizing agents have been tested and cationic capping agents have been discarded owing to the formation of complex compounds with copper ions leading to insoluble phases contaminating the metallic nanoparticles. The elemental copper nanoparticles, stabilized with polyvinylpyrrolidone (PVP) and sodium dodecyl sulphate (SDS), have been characterized for composition by energy dispersive X-ray spectroscopy (EDS), and for size by dynamic light scattering (DLS), and transmission electron microscopy (TEM), giving a size distribution in the range of 40-50 nm for both stabilizing agents. From a methodological point of view, the process described here may represent an alternative to other wet-chemical techniques for metal nanoparticle synthesis in non-aqueous media based on conventional organic or inorganic reductants. [ABSTRACT FROM AUTHOR]

Titanium dioxide nanocrystals (TiO2 NCs), through their photocatalytic activity, are able to generate charge carriers and induce the formation of various reactive oxygen species (ROS) in the presence of O2 and H2O. This special feature makes TiO2 an important and promising material in several industrial applications. Under appropriate antioxidant balancing, the presence of ROS is crucial in plant growth and development, therefore, the regulated ROS production through the photocatalytic activity of TiO2 NCs may be also exploited in the agricultural sector. However, the effects of TiO2 NCs on plants are not fully understood and/or phase-pure TiO2 NCs are rarely used in plant experiments. In this work, we present a phase-selective synthesis of TiO2 NCs with anatase and rutile crystal phases. The nanomaterials obtained were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance UV-Vis spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). In field experiments, Vitis vinifera cv. Cabernet Sauvignon leaves developed under natural sunlight were treated with aqueous dispersions of TiO2 NCs at concentrations of 0.001, 0.01, 0.1, and 1 w/v%. The effect of the applied nanocrystals was characterized via leaf photochemistry, mineral nutrient contents, and pyridoxine levels. We found that stress responses of grapevine to anatase and rutile NCs treatments are different, which can be related to the different ROS profiles of the two polymorphs. Our results indicate that TiO2 NCs may be utilized not only for direct pathogen inactivation but also for eliciting plant defense mechanisms. [ABSTRACT FROM AUTHOR]

A versatile and straightforward route to produce polymer foams with functional surface through their decoration with gold and palladium nanoparticles is proposed. Melamine foams, used as polymeric porous substrates, are first covered with a uniform coating of polydimethylsiloxane, thin enough to assure the preservation of their original porous structure. The polydimethylsiloxane layer allows the facile in-situ formation of metallic Au and Pd nanoparticles with sizes of tens of nanometers directly on the surface of the struts of the foam by the direct immersion of the foams into gold or palladium precursor solutions. The effect of the gold and palladium precursor concentration, as well as the reaction time with the foams, to the amount and sizes of the nanoparticles synthesized on the foams, was studied and the ideal conditions for an optimized functionalization were defined. Gold and palladium contents of about 1 wt.% were achieved, while the nanoparticles were proven to be stably adhered to the foam, avoiding potential risks related to their accidental release. [ABSTRACT FROM AUTHOR]

Light emitting diodes (LED) based on halide perovskite nanocrystals (NC) have received widespread attention in recent years. In particular, LEDs based on CsPbBr3 NCs were the object of special interest. Here, we report for the first time green LED based on CsPbBr3 NCs treated with ammonium thiocyanate solution before purification with polar solvent. The champion device fabricated based on the treated CsPbBr3 NCs showed high efficiency and high stability during operation as well as during storage. A study on morphology and current distribution of NC films under applied voltages was carried out by conductive atomic force microscopy, giving a hint on efficiency roll-off. The current work provides a facile way to treat sensitive perovskite NCs and to fabricate perovskite NC-based LED with high stability. Moreover, the results shed new light on the relation between film morphology and device performance and on the possible mechanism of efficiency roll-off in NC LED. [ABSTRACT FROM AUTHOR]

An innovative approach for the fabrication of hybrid photocatalysts on a solid porous polymeric system for the heterogeneous photocatalytic degradation of organic pollutants is herein presented. Specifically, gold/zinc oxide (Au/ZnO)-based porous nanocomposites are formed in situ by a two-step process. In the first step, branched ZnO nanostructures fixed on poly(methyl methacrylate) (PMMA) fibers are obtained upon the thermal conversion of zinc acetate-loaded PMMA electrospun mats. Subsequently, Au nanoparticles (NPs) are directly formed on the surface of the ZnO through an adsorption dipping process and thermal treatment. The effect of different concentrations of the Au ion solutions to the formation of Au/ZnO hybrids is investigated, proving that for 1 wt % of Au NPs with respect to the composite there is an effective metal–semiconductor interfacial interaction. As a result, a significant improvement of the photocatalytic performance of the ZnO/PMMA electrospun nanocomposite for the degradation of methylene blue (MB) and bisphenol A (BPA) under UV light is observed. Therefore, the proposed method can be used to prepare flexible fibrous composites characterized by a high surface area, flexibility, and light weight. These can be used for heterogeneous photocatalytic applications in water treatment, without the need of post treatment steps for their removal from the treated water which may restrict their wide applicability and cause secondary pollution. [ABSTRACT FROM AUTHOR]

Abstract A two-pot bismuth nanoparticle synthesis based on a combination of a bottom-up method and a disaggregation technique is proposed. These steps are sequential in time and are operated in an aqueous and organic solvent, respectively. In the first phase, a cementation process with aluminium and zinc as sacrificial metals in compact form is carried out using mannitol, saponin and maltodextrin as eco-friendly capping agents for bismuth nanoparticles. In the second phase, a wet ball-stirring process allows obtaining a primary particles release in propylene glycol with a satisfactory stability. The products are characterized by dynamic light scattering and transmission electron microscopy for the size and by X-ray diffraction for both size and chemical composition. The diameters of bismuth nanoparticles obtained using both zinc and aluminium as reductants lie in the range of 10–120 nm independently of the capping agents. With respect to conventional one-pot processes using sacrificial metals in powder, this technique allows obtaining a high purity metallic bismuth at the end of the cementation step without requiring further purification treatments, thus avoiding a waste of chemical reagents in view of a cleaner production and sustainability. All stages of preparation are carried out at room temperature for a better energy saving and safety management. This process may represent a valid alternative to standard techniques based on noxious reductants or high temperature synthesis, thus promoting a shift towards a green nanoparticle synthesis. [ABSTRACT FROM AUTHOR]

The fabrication of pectin-cellulose nanocrystal (CNC) biocomposites has been systematically investigated by blending both polysaccharides at different relative concentrations. Circular free-standing films with a diameter of 9 cm were prepared by simple solution of these carbohydrates in water followed by drop-casting and solvent evaporation. The addition of pectin allows to finely tune the properties of the biocomposites. Textural characterization by AFM showed fibrous morphology and an increase in fiber diameter with pectin content. XRD analysis demonstrated that pectin incorporation also reduced the degree of crystallinity though no specific interaction between both polysaccharides was detected, by ATR-FTIR spectroscopy. The optical properties of these biocomposites were characterized for the first time and it was found that pectin in the blend reduced the reflectance of visible light and increased UV absorbance. Thermal stability, analyzed by TGA, was improved with the incorporation of pectin. Finally, pectin-cellulose nanocrystal biocomposites showed a good biodegradability in seawater, comparable to other common bioplastics such as cellulose and low-molecular weight polylactide, among others. • Pectin and CNC have been blended at different proportions to form biocomposites. • No interaction between both polysaccharides was detected by ATR-FTIR spectroscopy. • Pectin modifies morphology, crystallinity, physical properties, and biodegradation. [ABSTRACT FROM AUTHOR]