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"Charge engineering" of semiconductor nanocrystals (NCs) through so-called electronic impurity doping is a long-standing challenge in colloidal chemistry and holds promise for ground-breaking advancements in many optoelectronic, photonic, and spin-based nanotechnologies. To date, our knowledge is limited to a few paradigmatic studies on a small number of model compounds and doping conditions, with important electronic dopants still unexplored in nanoscale systems. Equally importantly, fine-tuning of charge engineered NCs is hampered by the statistical limitations of traditional approaches. The resulting intrinsic doping inhomogeneity restricts fundamental studies to statistically averaged behaviors and complicates the realization of advanced device concepts based on their advantageous functionalities. Here we aim to address these issues by realizing the first example of II-VI NCs electronically doped with an exact number of heterovalent gold atoms, a known p-type acceptor impurity in bulk chalcogenides. Single-dopant accuracy across entire NC ensembles is obtained through a novel non-injection synthesis employing ligand-exchanged gold clusters as "quantized" dopant sources to seed the nucleation of CdSe NCs in organic media. Structural, spectroscopic, and magneto-optical investigations trace a comprehensive picture of the physical processes resulting from the exact doping level of the NCs. Gold atoms, doped here for the first time into II-VI NCs, are found to incorporate as nonmagnetic Au + species activating intense size-tunable intragap photoluminescence and artificially offsetting the hole occupancy of valence band states. Fundamentally, the transient conversion of Au + to paramagnetic Au 2+ (5d 9 configuration) under optical excitation results in strong photoinduced magnetism and diluted magnetic semiconductor behavior revealing the contribution of individual paramagnetic impurities to the macroscopic magnetism of the NCs. Altogether, our results demonstrate a new chemical approach toward NCs with physical functionalities tailored to the single impurity level and offer a versatile platform for future investigations and device exploitation of individual and collective impurity processes in quantum confined structures.

The development of Sn based anode materials for sodium ion batteries is mainly hindered by the limited understanding of sodiation/desodiation mechanisms inside the active material, which typically results in electrode damage. Herein, we report a post-mortem ex-situ scanning electron microscopic analysis of Sn thin film motivated by the intention to elucidate these structural mechanisms. Our results reveal for the first time that the surface of Sn electrode film becomes highly porous during sodiation with no presence of obvious cracks, a surprising result when compared to previous reports performed on Sn particles. Even more surprisingly, sequential ex-situ SEM observations demonstrate that, once the desodiation starts and reaches the second desodiation plateau (0.28 V), obvious cracks in the Sn film are instead observed along with porous islands of active material. These islands appear as aggregated particles which further split into smaller islands when the desodiation potential reaches its maximum value...

We studied the hysteresis and electric field effects on planar CH3NH3PbI3 perovskite devices, synthetized from laser-ablated precursors, by means of electrical characterizations at different scan rates and optical measurements. The aim of our investigation is to characterize the phenomena behind perovskite degradation under prolonged applied electric field. Using a perovskite more resistant to electric field induced degradation, we run long time characterizations that were not accomplishable before. Thus, we distinguished all the degradation-involved phenomena. The results point to the presence of ions migrating in the perovskite when the device is biased. Our data showed that ion migration degrades the interfaces with the consequent creation of degradation layers that limit the current injected in the device and the extracted photocurrent. These layers where detected also by means of optical Raman characterization. In order to explain the details of the mechanisms concurring to the observed behaviors, we presented a qualitative model. The observed phenomena exacerbated by the planar structure are even more destructive on standard solution processed perovskites to which the results of this work can be extended. Since, the same degradation dynamics occur on vertical devices, typical on perovskite solar cells, this work provides a useful in-depth analysis of the ionic migration effects.

Mercury (Hg) is a global highly toxic pollutant released by both anthropogenic and natural sources. Hg decontamination is of the utmost importance for human and ecosystem protection. Here, we propose a novel graphene-based membrane capable of performing rapid and highly selective Hg2+-rejection from water. Functionalized graphene flakes are produced by a non-oxidative, room-temperature and post processing-free “green” method to simultaneously exfoliate graphite into single-/few-layer graphene (SLG/FLG) flakes in water and functionalize them with cationic rhodamine 6G (R6G)viaa physisorption process (aromatic ring π–π stacking). The rhodamine 6G-functionalized graphene (R6G-FG) membrane shows a low-density (−3) packed laminar structure, where R6G molecules act as spacers between the SLG/FLG flakes. The presence of hydrophilic micro/nanodomains in this low-density structure results in a water permeation rate as high as 789.6 L m−2h−1bar−1(for an 80 μm-thick membrane, R6G-FG mass loading of 3.58 g m−2). Meanwhile, the R6G-FG complexes perform as ion-selective nano-traps for Hg2+, showing almost complete rejection (>99%) for a filtered solution volume normalized to the R6G-FG mass superior to 3 L g−1. The selective rejection capability of the R6G-FG membrane is ruled by competitive adsorption of metal ions and positively charged R6G molecules with different affinity onto the negatively charged graphene surface. Lastly, a washing treatment in alkaline conditions is also proposed for membrane regeneration and reuse. The rationalization of the working mechanism of the R6G-FG membrane is promising for eliminating the “permeability–selectivity trade-offs” often tackled by laminar two-dimensional material membranes.

The surface ligands on colloidal nanocrystals (NCs) play an important role in the performance of NCs based optoelectronic devices such as photovoltaic cells, photodetectors and light emitting diodes (LEDs). On one hand, the NC emission depends critically on the passivation of the surface to minimize trap states that can provide non-radiative recombination channels. On the other hand, the electrical properties of NC films are dominated by the ligands that constitute the barriers for charge transport from one NC to its neighbor. Therefore, surface modifications via ligandexchange have been employed to improve the conductance of NC films. However, in light emitting devices, such surface modifications are more critical due to their possible detrimental effects on the emission properties. In this work, we study the role of surface ligand modifications on the optical and electrical properties of CdSe/CdS dot-in-rods (DiRs) in films, and investigate their performance in all-solution processed LEDs. The DiR films maintain high PLQY, around 40-50%, and their electroluminescence in the LED preserves the excellent color purity of the PL. In the LEDs, the ligand-exchange boosted the luminance, reaching a four-fold increase from 2200 cd/m2 for native surfactants to 8500 cd/m2 for the exchanged aminoethanethiol ligands. Moreover, the efficiency roll-off, operational stability, and shelf life are significantly improved, and the external quantum efficiency is modestly increased from 5.1 % to 5.4 %. We relate these improvements to the increased conductivity of the emissive layer, and to the better charge balance of the electrically injected carriers. In this respect, we performed ultraviolet photoelectron spectroscopy (UPS) to obtain deeper insight in the band alignment of the LED structure., 26 pages, 4 figures

Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a highly anisotropic shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 {\deg}C and we obtain structures with a CdSe nanoplatelet core that is overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered., Comment: 26 pages, 6 figures, 1 table

Owing to the self-renewing reactive oxygen species scavenger capability of cerium oxide nanoparticles (nanoceria), we tested in vivo radioprotective effects on stem cells and tissue regeneration using low-dose irradiated planarians as model system. We treated planarians with nanoceria or gum Arabic, as control, and we analyzed the expression of stem cell molecular markers and tissue regeneration capability, as well as cell death and DNA damage in non-irradiated and in low-dose irradiated animals. Our findings show that nanoceria increase the number of stem cells and tissue regenerative capability, and reduce cell death and DNA damage after low-dose irradiation, suggesting a protective role on stem cells.

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 (n10) 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.

The intrinsic instability of lead halide perovskite materials in ambient atmosphere is one of the most critical issues that impede perovskite solar cell commercialization. To overcome it, the use of bulky organic spacers emerged as promising candidates for stable photovoltaics. The resulting perovskite thin films present complex morphologies, difficult to predict, which will directly affect the device efficiency. Here, by combining in-depth morphological and spectroscopic characterization, we show that both the ionic size and relative concentration of the organic cation drive the integration of bulky organic cations into the crystal unit cell and the thin film, inducing different perovskite phases and different vertical distribution, then causing a significant change in the final morphology. Based on such studies we propose a fine-engineered multi-phases perovskite by employing two different large cations, namely ethyl ammonium and butyl ammonium. The first one takes part to the 3D perovskite phase formation, the second one works as surface modifier by forming a passivating layer on top of the thin film. Together they lead to improved photovoltaic performance and device stability when tested in air under continuous illumination. Our findings propose a general approach to achieve reliability of perovskite-based optoelectronic devices.

Using wet chemistry synthesis methods we prepared nanodumbbell structures as a model oxide supported metal catalyst. In this peculiar configuration, a single metallic domain (M) is connected to a single metal oxide (MOx) one. The size, composition and morphology of each domain can be carefully controlled, allowing us to investigate the effects resulting from a hollow morphology of the MOx domains, while all other material’s properties were kept constant. We chose the CO oxidation as a model oxidation reaction and increasing the population of nanocrystals (NCs) with hollow oxide domains resulted in a decrease in catalytic activity. Despite the manipulation of oxide morphology affected the surface charge of the Au domain, the bulk oxide reducibility and the crystallinity of the nanosized oxide support, the rate limiting step of CO oxidation was not affected. The same apparent activation energy was indeed measured independently from the population of NCs with hollow oxide domains. The difference in catalytic performance was thus ascribed to a different number of interfacial active sites when the morphology evolved from full to hollow.

A novel WS2–graphite dual-ion battery (DIB) is developed by combining a conventional graphite cathode and a high-capacity few-layer WS2-flake anode. The WS2 flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows large-scale and free-material loss production (i.e., volume up to 8 L h−1 at concentration of 10 g L−1 and exfoliation yield of 100%) of few-layer WS2 flakes in dispersion. The WS2 anodes enable DIBs, based on hexafluorophosphate (PF6–) and lithium (Li+) ions, to achieve charge-specific capacities of 457, 438, 421, 403, 295, and 169 mAh g–1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0 A g–1, respectively, outperforming conventional DIBs. The WS2-based DIBs operate in the 0 to 4 V cell voltage range, thus extending the operating voltage window of conventional WS2-based Li-ion batteries (LIBs). These results demonstrate a new route toward the exploitation of WS2, and possibly other transition-metal dichalcogenides, for the development of next-generation energy-stor...

The electrocatalytic oxygen evolution reaction (OER) is an important half reaction in various technologies, such as metal air batteries and electrochemical water splitting. Transition metal chalcog...

Silica-supported pyrolyzed lignin (pLG@silica) was investigated as a solid sorbent for the pre-concentration of rare earth elements (REE) from natural waters followed by inductively coupled plasma mass spectrometry (ICP-MS) analysis. The carbon-based material was easily prepared by pyrolytic treatment of lignin at 600 °C after its adsorption onto silica micro-particles. pLG@silica was characterized by scanning electron microscopy (SEM), surface area measurements (BET method), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), point of zero charge measurement, and X-ray photoelectron spectroscopy (XPS). The as-prepared material (50 mg) was tested as fixed-bed sorbent for the solid-phase extraction (SPE) of tap, river, and sea water samples spiked with REE in the 10–150 ng L−1 range, followed by ICP-MS analysis. A quantitative adsorption was observed for all REE with recoveries in the range of 72–118%. A suitable inter-day precision (RSDs 5–12%, n = 3) was obtained. Sample volumes up to 250 mL provided enrichment factors up to 100. The method detection and quantification limits (MDLs and MQLs) were in the range of 0.4–0.6 ng L−1 and 1–2 ng L−1, respectively. The batch-to-batch reproducibility was verified on four pLG@silica independent preparations. As remarkable advantages, pLG@silica proved to be of easy preparation using a waste material, inexpensive, and reusable for at least 20 SPE cycles.

[Image: see text] Current colloidal synthesis methods for CdSe nanoplatelets (NPLs) routinely yield samples that emit, in discrete steps, from 460 to 550 nm. A significant challenge lies with obtaining thicker NPLs, to further widen the emission range. This is at present typically achieved via colloidal atomic layer deposition onto CdSe cores, or by synthesizing NPL core/shell structures. Here, we demonstrate a novel reaction scheme, where we start from 4.5 monolayer (ML) NPLs and increase the thickness in a two-step reaction that switches from 2D to 3D growth. The key feature is the enhancement of the growth rate of basal facets by the addition of CdCl(2), resulting in a series of nearly monodisperse CdSe NPLs with thicknesses between 5.5 and 8.5 ML. Optical characterization yielded emission peaks from 554 nm up to 625 nm with a line width (fwhm) of 9–13 nm, making them one of the narrowest colloidal nanocrystal emitters currently available in this spectral range. The NPLs maintained a short emission lifetime of 5–11 ns. Finally, due to the increased red shift of the NPL band edge photoluminescence excitation spectra revealed several high-energy peaks. Calculation of the NPL band structure allowed us to identify these excited-state transitions, and spectral shifts are consistent with a significant mixing of light and split-off hole states. Clearly, chloride ions can add a new degree of freedom to the growth of 2D colloidal nanocrystals, yielding new insights into both the NPL synthesis as well as their optoelectronic properties.

Carbapenem-resistant Klebsiella pneumoniae (CP-Kp) is one of the most important opportunistic pathogens strongly associated with nosocomial infections. The capsule of CP-Kp not only contributes to its pathogenic potential but also ensures survival for bacteria in different environments and surfaces. Development of novel reactive nanomaterials can help to inhibit the survival of such microorganism and thereby their spreading in the hospital environment. In this work, the photocatalytic and antibacterial activities of PF-co-doped anatase TiO2 nanoparticles (NPs) were studied in details and related to the evolution of their structure and surface composition upon hydrothermal treatment at 250 °C for periods up to 12 h. Structural and morphological evolution were followed by X-ray diffraction, transmission electron microscopy while the surface composition was studied by X-ray photoelectron spectroscopy. Electron paramagnetic resonance measurements were carried out to reveal the formation of reactive oxygen species (ROS). Both OH and O2 − radicals as well as 1O2 were confirmed and quantitatively compared in different photoirradiated PF-TiO2 NPs dispersions. It was found that hydrothermal treatment increased the photocatalytic and antibacterial activity while PF-co-doping promoted the formation of OH radicals. By the application of PF-co-doping, the elevated level of OH led to rapid inactivation of CP-Kp.

Osteosarcoma is an aggressive form of bone cancer mostly affecting young people. To date, the most effective strategy for the treatment of osteosarcoma is the surgical removal of the tumor with or without combinational chemotherapy. In this study, we present the development of a pH-sensitive drug-delivery system in the form of microparticles, with increased chemotherapeutic action against the osteosarcoma cell line SAOS-2, and with reduced toxicity against the heart myoblastic cell line H9C2. The delivery system is composed of calcium carbonate and collagen type I, and is loaded with cerium dioxide (CeO2) nanoparticles (3-based therapeutic modulators (C-TherMods)), which corresponds to 6.4 μg/mL of encapsulated doxorubicin, can protect the H9C2 cells even after 120 h, since the percentage of viable cells at this time point is 65%. On the contrary, when H9C2 cells are treated with 0.5 μg/mL of free doxorubicin, 75% of the cells are dead only after 24 h. When SAOS-2 cells are treated with the same concentration of C-TherMods (250 μg/mL), the viability of SAOS-2 cells is 80% after 24 h, while it reduces to 50% after 120 h. At pH 6.0, the synergic effect of the pro-oxidant CeO2 nanoparticles and of the encapsulated doxorubicin leads to almost 100% of cell death, even at the lowest concentration of C-TherMods (50 μg/mL).

PbS nanocrystals are an important narrow-gap material for solar cells and photodetectors. Nevertheless, their application may be limited because device performance can be affected by atmospheric conditions. Indeed, the presence of oxygen and/or water can degrade the active layers, possibly leading to device failure. Strategies to address this issue are therefore actively explored. Here we report a solution-processed PbS quantum dot solar cell, consisting of a PbS-silane functionalized reduced graphene oxide (PbS-rGO) layer on top of the PbS absorber film, which enhances device stability, especially when the solar cells are exposed to moisture. Power conversion efficiency (PCE) measurements demonstrate a slower degradation under continuous illumination for solar cells with PbS-rGO. When storing the samples under saturated water vapor, differences are even more remarkable: with PbS-rGO the solar cells essentially maintain their initial PCE, while the PCE of the PbS reference devices is reduced by 50% after 5 days. Scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy reveal the damage to the PbS films and the formation of PbSOx crystals in the PbS reference devices. Such crystals are not observed in the PbS-rGO devices, further supporting the importance of the PbS-rGO barrier layer.

Metal clusters with appropriate molecular ligands have been shown to be suitable subnanometer building blocks for supramolecular architectures with controlled secondary interactions, providing access to physical regimes not achievable with conventional intermolecular motifs. An example is the excimer photophysics exhibited by individual cluster-based superstructures produced by top-down etching of gold nanoparticles. Now, a supramolecular architecture of copper clusters is presented with controlled optical properties and efficient non-resonant luminescence produced via a novel bottom-up synthesis using mild green reductants followed by a ligand exchange reaction and spontaneous supramolecular assembly. Spectroscopic experiments confirm the formation of the intercluster network and reveal the permanent nature of their excimer-like behavior, thus extending the potential impact and applicability of metal cluster superstructures as efficient and stable non-resonant single-particle emitters.

We prepared 20–30 nm hollow CeO2 nanoparticles with 6–9-nm-thick porous shells by performing an easy, cost-effective, and water-based galvanic replacement on SiO2-supported Mn3O4 nanoparticles with Ce3+. The low-density, defected structure doped with residual Mn and the easily reducible surface makes the catalysts highly reactive for both CO oxidation and soot combustion reactions.

We utilize the solvent acidolysis crystallization technique to grow mixed dimethylammonium/methylammonium lead tribromide (DMA/MAPbBr3 ) crystals reaching the highest dimethylammonium incorporation of 44% while maintaining the 3D cubic perovskite phase. These mixed perovskite crystals show suppression of the orthorhombic phase and a lower tetragonal to cubic phase transition temperature compared to MAPbBr3 . We observe distinct behavior in the temperature-dependent photoluminescence properties of MAPbBr3 and mixed DMA/MAPbBr3 crystals due to the different organic cation dynamics governing the phase transition(s). Furthermore, we fabricate lateral photodetectors which show that, at room temperature, the mixed crystals possess higher detectivity compared to MAPbBr3 crystals caused by structural compression and reduced surface trap density. Remarkably, the mixed crystal devices exhibit large enhancement in their detectivity below the phase transition temperature (at 200K), while the MAPbBr3 devices demonstrate insignificant changes. The higher detectivity makes our devices attractive for visible light communication and for space applications. Our results highlight the importance of the synthetic technique for the halide perovskites compositional engineering that governs their structural and optoelectronic properties. This article is protected by copyright. All rights reserved.

We propose here a new colloidal approach for the synthesis of both all-inorganic and hybrid organic–inorganic lead halide perovskite nanocrystals (NCs). The main limitation of the protocols that are currently in use, such as the hot injection and the ligand-assisted reprecipitation routes, is that they employ PbX2 (X = Cl, Br, or I) salts as both lead and halide precursors. This imposes restrictions on being able to precisely tune the amount of reaction species and, consequently, on being able to regulate the composition of the final NCs. In order to overcome this issue, we show here that benzoyl halides can be efficiently used as halide sources to be injected in a solution of metal cations (mainly in the form of metal carboxylates) for the synthesis of APbX3 NCs (in which A = Cs+, CH3NH3+, or CH(NH2)2+). In this way, it is possible to independently tune the amount of both cations and halide precursors in the synthesis. The APbX3 NCs that were prepared with our protocol show excellent optical properties, such as high photoluminescence quantum yields, low amplified spontaneous emission thresholds, and enhanced stability in air. It is noteworthy that CsPbI3 NCs, which crystallize in the cubic α phase, are stable in air for weeks without any postsynthesis treatment. The improved properties of our CsPbX3 perovskite NCs can be ascribed to the formation of lead halide terminated surfaces, in which Cs cations are replaced by alkylammonium ions.

The aggregation and the photophysics of a water soluble perylenediimide (PDI) derivative that features two bromine substituents in the bay positions has been probed. Non-fluorescent aggregates were found to be present at concentrations of 1.0 × 10-5 M. In situ small-angle X-ray scattering (SAXS) measurements and complementary molecular modeling showed the presence of PDI aggregates. In their singlet excited states, the PDI aggregates are characterized by distinct transient fingerprints and rapid deactivation, as revealed by pump-probe experiments on the femto-, pico-, nano-, and microsecond timescales. The product of this deactivation is a PDI triplet excited state. The efficiency of the triplet formation depends on the concentration, and hence on the degree of aggregation. Notably, for PDI concentrations in the range of the critical micelle concentration, the efficiency of intersystem crossing is close to zero. In short, we have demonstrated, for the first time, aggregation-induced formation of triplet excited states for PDI derivatives.

Perfluorocarbons (PFCs) have proven to be very efficient in building up omniphobic surfaces because of the peculiar properties of fluorine atoms. However, due to their environmental impact and bioaccumulative potential, perfluorinated surfactants with chains longer than six carbon atoms have been banned, and other alternatives had to be found. Herein, we demonstrate the possibility to build omniphobic self-assembled monolayers (SAMs) using a multibranched fluorinated thiol (BRFT) bearing ultrashort fluorinated alkyl groups, surrounding a hydrocarbon polar core. This unique design allows us to multiply the number of fluorine atoms in the molecule (27 F atoms per molecule), affording a high fluorine density on the surface and a low surface free energy. Moreover, the presence of four ether bonds in the core may hasten molecular degradation in the environment because of the cleavage of such bonds in physiological conditions, thus overcoming bioaccumulation issues. BRFT may effectively represent a valuable sub...

Perovskite-related Cs4PbBr6 nanocrystals present a “zero-dimensional” crystalline structure where adjacent [PbBr6]4– octahedra do not share any corners. We show in this work that these nanocrystals can be converted into “three-dimensional” CsPbBr3 perovskites by extraction of CsBr. This conversion drastically changes the optoelectronic properties of the nanocrystals that become highly photoluminescent. The extraction of CsBr can be achieved either by thermal annealing (physical approach) or by chemical reaction with Prussian Blue (chemical approach). The former approach can be simply carried out on a dried film without addition of any chemicals but does not yield a full transformation. Instead, reaction with Prussian Blue in solution achieves a full transformation into the perovskite phase. This transformation was also verified on the iodide counterpart (Cs4PbI6).

Nickel and cobalt-based chalcogenides are an interesting class of electrochemically active compounds. Herein we report a two-step synthesis of uniform hollow nickel cobalt perselenide nanostructured microparticles with a corrugated surface, randomly spaced pores, and a tunable composition. In the first step, we synthesized Ni–Co acetate hydroxide prism-shaped microparticles, which were subsequently used as templates for the selenization process at temperatures as low as 80 °C. The substitution of acetate and hydroxide anions with selenide anions at a low temperature eventually produced partially amorphous hollow microparticles due to the nanoscale Kirkendall effect. Thin films of the as-synthesized samples behaved as highly active catalysts for the electrochemical oxygen evolution reaction (OER). Among those, Ni0.88Co1.22Se4 hollow microparticles showed excellent performances, exhibiting a 10 mA/cm2 current density at a modest overpotential of 320 mV, a high turnover frequency of 0.146 S1–, and a long-ter...

We discuss the photoluminescence (PL) of quantum-confined CsPbBr3 colloidal nanocrystals of two different shapes (nanowires and nanoplatelets) at different concentrations in solution and in solid-state films. Upon increasing the nanocrystal concentration in solution, a constant drop in photoluminescence quantum yield is observed, accompanied by a significant PL red shift. This effect is reversible, and the original PL can be restored by diluting to the original concentration. We show that this effect can be in part attributed to self-absorption and partly to aggregation. In particular, for nanoplatelets, where the aggregation is mostly irreversible, while the self-absorption effect is reversible, the two contributions can be well separated. Finally, when dry solid-state films are prepared, the emission band is shifted into the green spectral region, close to the bulk CsPbBr3 band gap, thus preventing blue emission from such films.

CsPbBr3 nanocrystals passivated with short molecular ligands and deposited on a substrate were annealed from room temperature to 400 °C in inert atmosphere. Chemical, structural, and morphological transformations were monitored in situ and ex situ by different techniques, while optoelectronic properties of the film were also assessed. Annealing at 100 °C resulted in a 1 order of magnitude increase in photocurrent and photoresponse as a result of partial sintering of the NCs and residual solvent evaporation. Beyond 150 °C the original orthorhombic NCs were partially transformed into tetragonal CsPb2Br5 crystals, due to the desorption of weakly bound propionic acid ligands. The photocurrent increased moderately until 300 °C although the photoresponse became slower as a result of the formation of surface trap states. Eventually, annealing beyond 350 °C removed the strongly bound butylamine ligands and reversed the transition to the original orthorhombic phase, with a loss of photocurrent due to the numerous defects induced by the stripping of the passivating butylamine.

Cu

Silver benzeneselenolate [AgSePh]∞ is a coordination polymer that hosts a hybrid quantum well structure. The recent advancements in the study of its tightly bound excitons (∼300 meV) and photoconductive properties (recently employed in UV photodetection) make it an interesting representative of a material platform that is an environmentally stable alternative to 2D metal halide perovskites in terms of optoelectronic properties. To this aim, several challenges are to be addressed, among which is the lack of control over the metal-organic reaction process in the reported synthesis of the [AgSePh]∞ nanocrystal film (NC). This issue contributed to cast doubts over the origin of its intrabandgap electronic states. In this article we study all the steps to obtain phase pure [AgSePh]∞ NC films, from thin silver films deposition through its oxidation followed by a chemical vapor-solid reaction with benzeneselenol, by means of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopies are also employed to provide vibrational peaks assignment for the first time on this polymer. Our analysis supports an acid-base reaction scheme based on an acid attacking the metal oxide precursor, generating water as a byproduct of the polymeric synthesis, speeding up the reaction by solvating the PhSeH. The reaction readily goes to completion within 30 min in a supersaturated PhSeH/N2 atmosphere at 90 °C. Our analysis suggests the absence of the precursor's leftovers or oxidized species that could contribute to the intragap states. By tuning the reaction parameters, we gained control of film morphology to obtain substrate-parallel oriented microcrystals showing different excitonic absorption intensities. Finally, centimeter-size high-quality [AgSePh]∞ NC films could be obtained, enabling exploitation of their optoelectronic properties, such as UV photodetection, in large-area applications.

Coupling of keratin with titanium surfaces is here realized both through thick coatings and molecular functionalization. This coupling has the final aim both of chemical and mechanical protection of the titanium surfaces and of improving interaction of titanium implants with soft tissues in transmucosal and percutaneous implants. Wool-derived keratin has been used and plasma decontamination/activation has been tested as possible strategy for the improvement of keratin grafting ability and adhesion. Coated/functionalized surfaces have been characterized by means of X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM), contact angle measurements X-Ray Diffraction (XRD), zeta potential and adhesion (tape and scratch) tests. These analyses evidenced that keratin was successfully coupled to titanium surfaces both in the form of molecular grafting and thick coating. In both cases, plasma surface activation improves keratin wetting and bonding ability for the substrates. The obtained coatings showed good adhesion and mechanical stability.

The nanoengineering of the structure of transition metal dichalcogenides (TMDs) is widely pursued to develop viable catalysts for the hydrogen evolution reaction (HER) alternative to the precious metallic ones. Metallic group-5 TMDs have been demonstrated to be effective catalysts for the HER in acidic media, making affordable real proton exchange membrane water electrolysers. Their key-plus relies on the fact that both their basal planes and edges are catalytically active for the HER. In this work, the 6R phase of TaS2 is "rediscovered" and engineered. A liquid-phase microwave treatment is used to modify the structural properties of the 6R-TaS2 nanoflakes produced by liquid-phase exfoliation. The fragmentation of the nanoflakes and their evolution from monocrystalline to partly polycrystalline structures improve the HER-activity, lowering the overpotential at cathodic current of 10 mA cm(-2) from 0.377 to 0.119 V. Furthermore, 6R-TaS2 nanoflakes act as ideal support to firmly trap Pt species, which achieve a mass activity (MA) up 10 000 A g(Pt)(-1) at overpotential of 50 mV (20 000 A g(Pt)(-1) at overpotentials of 72 mV), representing a 20-fold increase of the MA of Pt measured for the Pt/C reference, and approaching the state-of-the-art of the Pt mass activity.

The water dispersion of the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most used material precursors in organic electronics also thanks to its industrial production. There is a growing interest for conductive polymers that could be alternative surrogates or replace PEDOT:PSS in some applications. A recent study by our group compared electrodeposited PEDOT:Nafion vs PEDOT:PSS in the use for neural recordings. Here, we introduce an easy and reproducible synthetic protocol to prepare a water dispersion of PEDOT:Nafion. The conductivity of the pristine material is on the order of 2 S cm-1 and was improved up to ≈6 S cm-1 upon treatment with ethylene glycol. Faster ion transfer was assessed by electrochemical impedance spectroscopy (EIS), and, interestingly, an improved adhesion was observed for coatings of the new PEDOT:Nafion dispersion on glass substrates, even without the addition of the silane cross-linker needed for PEDOT:PSS. As proof of concept, we demonstrate the use of this novel water dispersion of PEDOT:Nafion in three different organic electronic device architectures, namely, an organic electrochemical transistor (OECT), a memristor, and an artificial synapse.

Ion migration is associated with hysteresis observed in halide perovskite-based solar cells and light-emitting diodes, however, it is crucial for their effective performance in memory devices. In the halide perovskites field, a direct link between the average/local structure and the preferred ion migration hopping pathway has yet to be established. Herein, we utilize the solvent acidolysis crystallization technique to grow various halide-deficient methylammonium copper halide crystals where perovskite-type layers are found. Through synchrotron X-ray powder diffraction (XRPD) and pair distribution function (PDF) analyses, we identify the halogen vacancy site in the copper halide octahedra, the octahedra tilting, and the thermal vibrations of the atoms around their average positions. We correlate the variations in these parameters to the hysteresis observed in the current-voltage curves and subsequently to the ON/OFF ratios of proof-of-concept memory devices fabricated using inert Pt electrodes. Furthermore, our best ON/OFF ratio of ~10 from our Pb-free devices compares well to the results obtained from two-dimensional Pb-based devices utilizing inert electrodes.

Plasmonic structures are renowned for their capability to efficiently convert light into heat at the nanoscale. However, despite the possibility to generate deep sub-wavelength electromagnetic hot spots, the formation of extremely localized thermal hot spots is an open challenge of research, simply because of the diffusive spread of heat along the whole metallic nanostructure. Here we tackle this challenge by exploiting single gold nanocones. We theoretically show how these structures can indeed realize extremely high temperature gradients within the metal, leading to deep sub-wavelength thermal hot spots, owing to their capability of concentrating light at the apex under resonant conditions even under continuous wave illumination. A three-dimensional Finite Element Method model is employed to study the electromagnetic field in the structure and subsequent thermoplasmonic behaviour, in terms of the three-dimensional temperature distribution. We show how the latter is affected by nanocone size, shape, and composition of the surrounding environment. Finally, we anticipate the use of photoinduced temperature gradients in nanocones for applications in optofluidics and thermoelectrics or for thermally induced nanofabrication.

Partial Hg2+ → Cd2+ cation exchange (CE) reactions were exploited to transform colloidal CdTe nanocrystals (NCs, 4-6 nm in size) into CdTe@HgTe core@shell nanostructures. This was achieved by working under a slow CE rate, which limited the exchange to the surface of the CdTe NCs. In such nanostructures, when annealed at mild temperatures (as low as 200 °C), the HgTe shell sublimated or melted and the NCs sintered together, with the concomitant desorption of their surface ligands. At the end of this process, the annealed samples consisted of ligand-free CdTe sintered films containing an amount of Hg2+ that was much lower than that of the starting CdTe@HgTe NCs. For example, the CdTe@HgTe NCs that initially contained 10% of Hg2+, after being annealed at 200 °C were transformed to CdTe sintered films containing only traces of Hg2+ (less than 1%). This procedure was then used to fabricate a proof-of-concept CdTe-based photodetector exhibiting a photoresponse of up to 0.5 A/W and a detectivity of ca. 9 × 104 Jones under blue light illumination. Our strategy suggests that CE protocols might be exploited to lower the overall costs of production of CdTe thin films employed in photovoltaic technology, which are currently fabricated at high temperatures (above 350 °C), using post-process ligand-stripping steps.

Among the large family of transition metal dichalcogenides, recently ReS

Metallic two-dimensional transition-metal dichalcogenides (TMDs) of the group 5 metals are emerging as catalysts for an efficient hydrogen evolution reaction (HER). The HER activity of the group 5 TMDs originates from the unsaturated chalcogen edges and the highly active surface basal planes, whereas the HER activity of the widely studied group 6 TMDs originates solely from the chalcogen- or metal-unsaturated edges. However, the batch production of such nanomaterials and their scalable processing into high-performance electrocatalysts is still challenging. Herein, we report the liquid-phase exfoliation of the 2H-TaS2 crystals by using 2-propanol to produce single/few-layer (1H/2H) flakes, which are afterward deposited as catalytic films. A thermal treatment-aided texturization of the catalytic films is used to increase their porosity, promoting the ion access to the basal planes of the flakes, as well as the number of catalytic edges of the flakes. The hybridization of the H-TaS2 flakes and H-TaSe2 flakes tunes the Gibbs free energy of the adsorbed atomic hydrogen onto the H-TaS2 basal planes to the optimal thermo-neutral value. In 0.5 M H2SO4, the heterogeneous catalysts exhibit a low overpotential (versus RHE, reversible hydrogen electrode) at the cathodic current of 10 mA cm–2 (η10) of 120 mV and high mass activity of 314 A g–1 at an overpotential of 200 mV. In 1 M KOH, they show a η10 of 230 mV and a mass activity of 220 A g–1 at an overpotential of 300 mV. Our results provide new insight into the usage of the metallic group 5 TMDs for the HER through scalable material preparation and electrode processing.

Microelectrode arrays are used for recording and stimulation in neurosciences both in vitro and in vivo. The electrodeposition of conductive polymers, such as poly(3,4-ethylene dioxythiophene) (PEDOT), is widely adopted to improve both the in vivo recording and the charge injection limit of metallic microelectrodes. The workhorse of conductive polymers in the neurosciences is PEDOT:PSS, where PSS represents polystyrene-sulfonate. In this paper, the counterion is the fluorinated polymer Nafion, so the composite PEDOT:Nafion is deposited onto a flexible neural microelectrode array. PEDOT:Nafion coated electrodes exhibit comparable in vivo recording capability to the reference PEDOT:PSS, providing a large signal-to-noise ratio in a murine animal model. Importantly, PEDOT:Nafion exhibits a minimized polarization during electrical stimulation, thereby resulting in an improved charge injection limit equal to 4.4 mC cm-2 , almost 80% larger than the 2.5 mC cm-2 that is observed for PEDOT:PSS.

Phonons are quantized lattice vibrations that represent a major energy dissipation channel in solid-state systems [1], both at the macro- and at the nano-scale. Although the phonon response of a specific nanomaterial is usually considered as its intrinsic fingerprint, here we show how it can be altered by exploiting the unique properties of terahertz (THz) plasmonic nanocavities [2]. Specifically, we obtained such nanocavities from the end-to-end coupling (30-nm gap size) of few-μm-long plasmonic gold nanoantennas. We fabricated a series of plasmonic arrays featuring different nanoantenna lengths, spanning from 4.75 μm to 6.75 μm, thus tuning their resonances between approximately 7 and 9 THz. We tested our approach on cadmium sulphide (CdS) nanocrystals (NCs), spin-coated over the array surfaces (Fig. 1a), since these NCs feature a dipole-active (Frohlich) phonon mode at 7.85 THz. We performed THz transmission measurements using a Fourier-transform THz microscope coupled to synchrotron light (ELETTRA, Trieste), showing the splitting of the nanoantenna resonance into two new vibro-polariton bands, as shown in Fig. 1b. This anti-crossing behaviour represents a distinctive signature of the strong coupling between the plasmon and phonon modes, the splitting (Rabi) at the crossing point being directly related to the coupling strength. More intriguingly, we also observed the phonon resonance modification without any THz illumination, just exploiting the vacuum electric field of the nanocavities [3] (estimated to be as high as 4.6× 105 V/m). To this end, we performed a series of micro-Raman measurements on individual nanocavity areas, finding evidence of the two new hybrid states (P− and P+ in Fig. 1c) even in THz "dark" conditions. The evidence of phonon mode splitting both in THz and Raman characterizations confirms the possibility of altering the intrinsic phonon response of a nanomaterial using properly tailored plasmonic resonators, which could open new avenues for the manipulation of energy dissipation in nanodevices. Novel cavity geometries that promise to further boost the strong vibrational coupling in these systems will be presented on site.

We present a fast and sensitive nanosensor that can detect organic mercury, exploiting the combination of the catalytic and plasmonic properties of gold nanoparticles (AuNPs). The method is one-step and completely instrument-free, and has a colorimetric readout clearly detectable by simple visual inspection. The AuNPs catalyze efficient organic mercury reduction to the metallic form (Hg0 ), allowing its nucleation and amalgam formation on particle surface, with consequent aggregation-induced plasmon shift. This leads to very rapid (1 min) and specific colorimetric detection of mercury species. The achieved limit of detection (20 ppb) is compliant with current regulatory limits in food.

Postsynthesis ligand exchange has been employed extensively on lead halide perovskite (LHP) nanocrystals (NCs), but the complex ligand shell composition of the starting NCs prevented a clear understanding of the exchange process, and the surface chemistry of the final NCs remained poorly characterized. Here, we describe a ligand exchange strategy involving the displacement of both cationic and anionic ligands on native model systems of CsPbBr 3 NCs, which are exclusively coated with Cs-oleate. These ligands are exchanged with various quaternary ammonium bromides (R 4 NBr), and complete exchange is confirmed by nuclear magnetic resonance (NMR) spectroscopy analysis. The displacement of the native Cs-oleate ligands with proton-free R 4 NBr delivers NCs with excellent colloidal stability and near-unity PLQY, which is preserved after washing with polar solvents, over 3 weeks of storage in air, and after heating a solution of NCs to 80 °C, as confirmed by NMR analysis. The results, together with density functional theory calculations, suggest that the higher stability of quaternary ammonium capped NCs is not due to a stronger binding interaction to the surface but rather to weaker solvent-ligand interactions of R 4 NBr compared to Cs-oleate, driving the former to the surface of the NCs.

Single- and few-layered InSe flakes are produced by the liquid-phase exfoliation of beta-InSe single crystals in 2-propanol, obtaining stable dispersions with a concentration as high as 0.11 g/L. Ultracentrifugation is used to tune the morphology, i.e., the lateral size and thickness of the as-produced InSe flakes. We demonstrate that the obtained InSe flakes have maximum lateral sizes ranging from 30 nm to a few um, and thicknesses ranging from 1 to 20 nm, with a max population centred at ~ 5 nm, corresponding to 4 Se-In-In-Se quaternary layers. We also show that no formation of further InSe-based compounds (such as In2Se3) or oxides occurs during the exfoliation process. The potential of these exfoliated-InSe few-layer flakes as a catalyst for hydrogen evolution reaction (HER) is tested in hybrid single-walled carbon nanotubes/InSe heterostructures. We highlight the dependence of the InSe flakes morphologies, i.e., surface area and thickness, on the HER performances achieving best efficiencies with small flakes offering predominant edge effects. Our theoretical model unveils the origin of the catalytic efficiency of InSe flakes, and correlates the catalytic activity to the Se vacancies at the edge of the flakes., 39 pages

The design of cost-effective and efficient electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is pivotal for the molecular hydrogen (H

The unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of organoammonium molecules are exploited to engineer the optical emission and robustness of a new set of Ruddlesden-Popper metal-halide layered perovskites. It is shown that the type of molecule regulates the number of hydrogen bonds that it forms with the edge-sharing [PbBr6 ]4- octahedra layers, leading to strong differences in the material emission and tunability of the color coordinates, from deep-blue to pure-white. Also, the emission intensity strongly depends on the length of the molecules, thereby providing an additional parameter to optimize their emission efficiency. The combined experimental and computational study provides a detailed understanding of the impact of lattice distortions, compositional defects, and the anisotropic crystal structure on the emission of such layered materials. It is foreseen that this rational design can be extended to other types of organic linkers, providing a yet unexplored path to tailor the optical and mechanical properties of these materials and to unlock new functionalities.

The wide interest in developing green energy technologies stimulates the scientific community to seek, for devices, new substitute material platforms with a low environmental impact, ease of production and processing and long-term stability. The synthesis of metal oxide (MO) semiconductors fulfils these requirements and efforts are addressed towards optimizing their functional properties through the improvement of charge mobility or energy level alignment. Two MOs have rising perspectives for application in light harvesting devices, mainly for the role of charge selective layers but also as light absorbers, namely MoO3(an electron blocking layer) and Co3O4(a small band gap semiconductor). The need to achieve better charge transport has prompted us to explore strategies for the doping of MoO3and Co3O4with vanadium (V) ions that, when combined with oxygen in V2O5, produce a high work function MO. We report on subcritical hydrothermal synthesis of V-doped mesostructures of MoO3and of Co3O4, in which a tight control of the doping is exerted by tuning the relative amounts of reactants. We accomplished a full analytical characterization of these V-doped MOs that unambiguously demonstrates the incorporation of the vanadium ions in the host material, as well as the effects on the optical properties and work function. We foresee a promising future use of these materials as charge selective materials in energy devices based on multilayer structures

All-inorganic lead halide perovskite nanocrystals exhibit excellent optical properties, which make them promising for optoelectronic devices. However, the insulating organic ligands at the nanocrystals’ surface represent a major issue in their effective application in devices. To decrease the effect of the ligands on carrier transport in perovskite nanocrystal-based films, several post-synthesis treatment methods have been reported, but in most of the cases the nanocrystals tend to degrade over long term storage. To address these concerns, herein we develop a novel surface treatment procedure based on the combination of ammonium thiocyanate and benzoyl bromide for CsPbBr3 nanocrystals. The morphological, optical and structural characterizations were carried out to investigate the evolution of both as-prepared and surface-treated nanocrystals in spin-coated films, over ageing under ambient conditions. It was found that films based on the treated nanocrystals present higher stability, providing a promising path for fabricating optoelectronic devices based on these materials.