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The inverse-square decay law of the illuminance of a point light source with distance is a common notion of basic optics theory, which is readily demonstrated to be a direct consequence of the propagation of spherical wave fronts with the centre at the light source. It is far less common to address the experimental verification of this law and, even less, to study the illuminance decay with the distance of extended light sources, which somehow represent an unknown topic. We propose a scientific experiment where the light sensor of a smartphone is used to collect illuminance data as a function of the source-to-sensor distance and orientation. Through this procedure, students can realize the limit of validity of the inverse-square law and determine the luminance flux of the chosen point-like light source (e.g. the white LED flashlight of a smartphone). More interestingly, when dealing with extended sources (e.g. the LCD of a laptop displaying a white image) subtle characteristics of the decay trend emerge, particularly for distances lower that the source size. A detailed analysis of these characteristics is presented though a process allowing student engagement in a real scientific investigation, envisaging steps of data acquisition through experimental measurements, model construction on the basis of the observed patterns, and finally model testing. We provide a guided formulation for the general modelling of planar emitters, starting from the theoretical treatment of Lambertian sources. In this way, students are able to quantify the luminous emission also for extended sources and their deviation from a Lambertian behaviour.

Cross-coupling reactions are of great importance in chemistry due to their ability to facilitate the construction of complex organic molecules. Among these reactions, the Ullmann-type C−O coupling between phenols and aryl halides is particularly noteworthy and useful for preparing diarylethers. However, this reaction typically relies on homogeneous catalysts that rapidly deactivate under harsh reaction conditions. In this study, we introduce a novel heterogeneous catalyst for the Ullmann-type C−O coupling reaction, comprised of isolated Cu atoms chelated to a tetraethylenepentamine-pyrrole ligand that is immobilized on graphite nanoplatelets. The catalytic study reveals the recyclability of the material, and demonstrates the crucial role of the pyrrole linker in stabilizing the Cu sites. The work expands the potential of single-atom catalyst nanoarchitectures and underscores the significance of ligands in stabilizing metals in cationic forms, providing a novel, tailored catalyst for cross-coupling chemistries.

The water-mediated mineral carbonation represents a promising solution for the capture and the storage of atmospheric CO2. Even though this reaction might be spontaneous for a number of Mg- and Ca-rich mineral phases, it is characterized by considerable activation barriers. In order to make it effective, associated energy costs related to the achievement of adequate reaction conditions must be minimized. Microwave chemistry is known to provide for substantial increments of the reaction rate for several systems. We applied here microwave chemistry to the process of carbonation of aqueous slurries of brucite, a model system of Mg-rich mineral, subjected to partial pressures of CO2 as low as 6 bar and to no other additive. The temperature of the reactor was finely varied while the radiation power and the reactor pressure were monitored in real-time. The radiation power was used to estimate the radiation energy budget needed to complete the carbonation process, whereas the reactor pressure was used as a proxy of reaction progression. We show a detailed evolution of the carbonate products obtained in terms of mineral phases, morphological properties, and degree of crystallinity, both as precipitate and as solid residue in the exsiccated supernatant reaction liquid.

Electrochemical anion intercalation of highly oriented pyrolytic graphite in mineral acids (such as sulfuric, perchloric, etc.) represents a model system to study (i) the intercalation process of chemical compounds in stratified crystals; (ii) the evolution of gases at the surface and inside the sample and (iii) the evolution of swollen regions of graphite, called blisters. Although the explanation of the blister evolution mechanism can be dated back to the nineties of the last century, many chemical and physical properties have been explored only very recently. In particular, the mechanical properties of blisters on graphite are not widely discussed in the literature. Here, we employ in-situ atomic force microscopy (AFM) to characterize the blister stiffness. The same AFM tip is used to move mechanically the blister on the basal plane or even cut it. As a consequence of this operation, the entrapped gases (namely, CO, CO2 and O2) can deflate and the swollen graphite layers lay down to recompose the graphite basal plane.

Heat is an inexhaustible source of energy, and it can be exploited by thermoelectronics to produce electrical power or electrical responses. The search for a low-cost thermoelectric material that could achieve high efficiencies and can also be straightforwardly scalable has turned significant attention to the halide perovskite family. Here, we report the thermal voltage response of bismuth-based perovskite derivates and suggest a path to increase the electrical conductivity by applying chalcogenide doping. The films were produced by drop-casting or spin coating, and sulfur was introduced in the precursor solution using bismuth triethylxanthate. The physical-chemical analysis confirms the substitution. The sulfur introduction caused resistivity reduction by 2 orders of magnitude, and the thermal voltage exceeded 40 mV K-1 near 300 K in doped and undoped bismuth-based perovskite derivates. X-ray diffraction, Raman spectroscopy, and grazing-incidence wide-angle X-ray scattering were employed to confirm the structure. X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed to study the composition and morphology of the produced thin films. UV-visible absorbance, photoluminescence, inverse photoemission, and ultraviolet photoelectron spectroscopies have been used to investigate the energy band gap.

Silicate nanoparticles occur in various astrophysical environments where they experience substantial processing due to events such as grain-grain collisions and irradiation. However, the structure and chemical evolution together with the origin of these grains are still poorly understood and intensively debated. For this purpose, we performed liquid-phase nanosecond pulsed laser ablation on olivine single crystals to (i) simulate space weathering in a water environment (e.g., hydrous or volatile-rich bodies) and (ii) study the chemical and structural evolution of both the target surface and the ablated material. In particular, optical spectroscopy analyses have been performed on the ablated material and correlated with high-resolution transmission electron microscopy and diffraction, whereas compositional variations of the ablated target surface were determined by X-ray photoelectron spectroscopy. Our results show that the target material is enriched in Fe and depleted in Mg after the ablation process, with the water environment triggering the oxidation of Fe2+ into Fe3+ in a region confined at the solid-liquid interface and thus promoting the formation of magnetite on the sample surface. On the other hand, in the ablated material we find olivine crystalline fragments with shock features together with Mg-rich crystalline nanoparticles. Notably, no metallic iron nanoparticles have been detected in the ablated material. Our simulation of space weathering in the water environment revealed structural and chemical changes which are expected to give rise to distinctive features in the reflectance spectra when compared to those from airless bodies of the inner solar system.

The formation of stable and insoluble Mg- and Ca-carbonates and/or hydroxy-carbonate hydrates, through water-mediated reaction of Mg(OH)2 (brucite) and Ca(OH)2 (portlandite) with carbon dioxide, is referred to as mineral carbonation (MC). MC is among the most promising potential solutions for long-term carbon capture and storage (CCS), since it is spontaneous under a wide range of conditions. However, kinetic barriers pose severe limitations to the practical exploitation of MC, implying energy requirements to reach sufficiently high reaction rates. Trying to overcome these hindrances, we show here the application of microwave (MW)-assisted processes for the carbonation of brucite, used as a model system for the carbonation occurring in a number of widely diffused minerals, such as serpentine. The mechanism, kinetics, and energy costs of the reaction, together with the chemical characteristics of the products obtained, are inferred by a combined study, carried out by both a MW synthesizer on bulk brucite water slurries and a purposedly developed microscopy platform, working on nano-scale regions of the surface of brucite single crystals.

Mineral Carbonation (MC) is included among the most promising potential solutions for long-term carbon capture and storage (CCS). This mineral treatment consists in the water-mediated reaction of the CaO and MgO components of minerals with carbon dioxide, with formation of stable and insoluble Ca- and Mg-carbonates and/or hydroxy-carbonate hydrates. Noteworthy, these latter compounds constitute also valuable secondary raw materials employed, e.g., in the construction sector. Despite the carbonation reaction is spontaneous under a wide range of conditions, kinetic barriers pose sever limitations for its practical exploitation. High fractions of MgO are available in serpentine minerals, characterized by alternated layers of silica [SiO2] and brucite [Mg(OH)2], quarried in a number of sites in Europe, with a relevant role played by Italy. This industrial activity is characterized by the production of a fraction as large as 50% of waste in the form of serpentine pebble and powder, representing potential reservoirs for fixing a quantity as large as 20 ktons of CO2 per site/per year in the form of re-utilizable Mg-carbonates. With the scope to contribute in making this possibility a reality, we show here the application of microwave (MW)-assisted processes for the in-depth study of the carbonation of brucite, representing a model systems for the reactive component of serpentine. MW reactors allow for a fine tuning of the temperature, pressure and irradiation energy, enabling us to infer the mechanism, kinetics, and energy costs of the reaction and to identify the chemical characteristics of the products.

Heat is an inexhaustible source of energy and stimuli. Thermoelectric generators and thermal sensors can produce power or an electrical signal, harvesting the waste heat. The search for a material that could be low cost, guarantee high efficiencies and be directly scalable has drawn attention to the family of halide perovskites. Here, we report bismuth-based perovskite-derivates to be used in thermal harvesting applications and suggest a path to increase the electrical conductivity by applying the mixed-anion approach, where the halide was partially substituted with sulphur to reduce the electrical resistivity. The layers were produced by drop-casting or spin coating; bismuth tri-ethylxanthate has been successfully used as a sulphur source. The Seebeck coefficients measured were higher than 40 mV K-1 in doped and undoped bismuth-based perovskite-derivates. Here, we present an extensive result discussion, based on Raman spectroscopy, X-ray diffraction, UV–visible characterization, ultra-violet, X-ray and inverse photoemission spectroscopies, SEM and EDS analysis. The significant Seebeck coefficient and the micrometre-sized sample dimensions make these compounds highly attractive for heat-flow sensing applications and, above all, for those technologies requiring miniaturised and flexible devices.

Porphyrins are ubiquitous organic molecules having a pivotal role in biological processes and as active layers in thin-film based advanced technological devices. Free-base porphyrins and porphyrinic compounds are subjected to tautomerism, i.e. the reversible prototropic formation of two isomers differing only in the position of the H-atoms bonded to the pyrrole N-atoms inside the molecular cavity. Different tautomers may have substantially different molecular conformation, conferring an anisotropic character to the system. Tautomerism characterizes the isolated porphyrin molecules and is generally also active in solid state aggregates [1]. The accomplishment of a frozen tautomeric form in monomolecular aggregates of porphyrins represented the basis for the exploitation of an intra-molecular mechanism for the development of single-molecule optoelectronic devices. Here, we show the results of growth methods, which ensure at room temperature: i) the nucleation of a pure porphyrin 2D phase on a substrate without the simultaneous growth of 3D crystals; ii) the selection of a single tautomeric form; iii) the prediction of the tautomer orientation of the deposited molecules; iv) the generation of an electronically correlated 2D layer of molecules giving rise to two stable states (the two orientations of the tautomers) to be exploited in logic devices. The successful iso-orientation at room temperature of tautomers in monomolecular domains of free-base tetraphenyl porphyrin (H2TPP) was accomplished onto exfoliated HOPG(0001) [2,3]. However, the six-fold symmetry of HOPG(0001) generates an overall isotropic distribution of such domains, hindering the possibility to scale the physical properties from multidomains of the molecular film down to the single molecule. Moreover, HOPG is a conductive substrate, which represents an obstacle for the integration of the assembly into devices. These issues were recently solved by using as a substrate the triclinic and chiral cleavage sur

The possibility of following electrochemical processes in situ and in real time using optical techniques is important in view of shining a light on the chemical processes at the surface. The interest grows if the optical apparatus is compact and can be employed in industrial quality-check protocols. Here, we show how graphite anion intercalation–an important chemical process to massively produce graphene flakes–can be monitored by a UV-vis spectrometer when the graphite works as an electrode immersed inside the electrochemical cell. Important information on the reversibility or quasi-reversibility of the reaction shows a clear visualization in optical color maps.

Surface differential reflectivity (SDR) and reflectance anisotropy spectroscopy (RAS) [sometimes known as reflectance difference spectroscopy] are two well-known optical spectroscopies used in the investigation of surfaces and interfaces. Their adaptability on different experimental conditions (vacuum, controlled atmosphere and liquid environment) allows for the investigation not only of surface states and/or ultra-thin films but also of more complex interfaces. In these circumstances, the analysis of the sample with both techniques is decisive in view of obtaining a correct picture of the sample optical properties. In this work, we show a microelectronic hardware solution useful to control both a SDR and a RAS apparatus. We describe an electronic architecture that can be easily replicated, and we applied it to a representative sample where the interpretation of the optical properties requires an analysis by both SDR and RAS.

Thin organic films are widely used in sensors, solar cells, and optical devices due to their intense absorption in the visible/near-infrared (IR) region. Shifting, quenching, or reshaping of some spectral features can be achieved by chemical functionalization of the molecules, whereas an anisotropic fingerprint due to preferential molecular alignment can be induced via a proper design and/or preparation of the substrate. Recently, we investigated the optical response of thin films of porphycene to acidification. With respect to the well-known and closely related tetraphenyl porphyrin, porphycene has the clear advantage of being optically active in the full visible range, and this makes visible by naked eye the immediate change of the film from brilliant blue-turquoise to green when exposed to HCl vapors. In this work, by exploiting a homemade reflectance anisotropy spectroscopy (RAS) apparatus, we explore possible optical anisotropies in the visible spectral range of porphycene films and relate them to the film morphology analyzed by atomic force microscopy (AFM).

The intercalation of graphite by electrochemical methods is an efficient strategy to produce massive graphene flakes. In fact, when graphite is biased inside an acidic solution, anions enter inside the stratified structure of the electrode and reduce the layer-to-layer interaction. Consequently, a gentle sonication is sufficient to disperse the graphene flakes inside the electrolyte. In view of an optimisation of the production protocol, a detailed analysis of the intercalation mechanism at the molecular length scale is mandatory. In the last 30 years, electrochemical (EC) scanning probe microscopies (e.g. EC-STM and in situ AFM) have been widely exploited in this research topic. In fact, these techniques have the possibility of combining the EC characterisation (e.g. cyclic-voltammetry, CV) with mechanical characterisation (e.g. adhesion and friction) and topography acquisition with high (molecular) lateral resolution. In this work, we investigate the tribological properties of the basal surface of graphite before and after the anion intercalation. By comparing the results acquired after the extraction of the graphite electrode from the EC cell with those collected inside the EC cell during the CV by an in situ AFM, we show how some features deriving from anisotropic friction can be exploited to unveil the very early stage of graphite exfoliation.

The development of novel protocols and techniques for waste treatment represents the state of the art in the “green conversion”. Chemical wastes deriving from industrial and power‐station processes, which involve organic crystals, can be hazardous for the environment. Studying their dissolution mechanism, both theoretically and experimentally, represents a mandatory step in the critical task of their disposal. Surprisingly, most of the studies are focused on millimeter scale length, from which one could estimate/learn/acknowledge the crystal dissolution rate. In these studies, where no information about the dissolution mechanism on a molecular scale is provided, etch‐pit formation is recognized as the ultimate mechanism of crystal dissolution.In this work, we show the morphological evolution of organic nanocrystals in a reactive dissolution process controlled by pH. This approach allows us to explore ranges of high undersaturation, whereby crystal dissolution occurs even though etch‐pit formation is suppressed. Adopting different surface and bulk‐sensitive techniques (atomic force microscopy, time‐of‐flight secondary ion mass spectroscopy and X‐ray/electron diffraction, Raman spectroscopy, respectively), we investigate the dissolution process of porphyrin thin films deposited on the basal plane of highly oriented pyrolytic graphite, proving that such films constitute a model system to unveil the dissolution mechanism of organic nanocrystals.

The functionality of low dimensional phases of porphyrins in optical, chemical, electrical, and multimodal combinational devices is strictly related to the control of molecular orientation within the produced solid layers. A promising strategy to drive the growth of adlayers with predictable structural properties relies on the template effect exerted by the substrate. Tetraphenyl porphyrins, being disc-shaped objects, can be adsorbed on a crystal surface by taking on different geometries. An edge-on configuration is adopted when the interactions among molecules overtake those between molecules and substrate, whereas a flat-on configuration is adopted when molecule-substrate interaction is dominant, with the weaker intermolecular interaction driving a close-packed geometry in the adlayer. For this latter reason, square and/or hexagonal lattice symmetries of physisorbed porphyrin layers are disclosed on highly interacting metal substrates such as Au(111). Unfortunately, metal substrates modify the intrinsic properties of porphyrins by suppressing many of their functionalities. To overcome this drawback, here we report the selective growth of porphyrins in a flat-on arrangement on the chiral (110) cleavage surface of the mixed molecular organic crystal formed by 2,5-diketopiperazine and fumaric acid in a 1:1 mole ratio. The energetic advantage ensured by the interaction with the insulating substrate drives the prevalent formation of domains with a square symmetry, which is retained from monolayer to multilayers. However, rare domains with a hexagonal symmetry are revealed and analyzed by high-resolution scanning probe microscopic techniques. The experimental structural analysis performed at the nanoscale, combined with ab initio calculations, allowed us to demonstrate that the molecular architectures we found arise from the simultaneous fulfillment of site adsorption energy maximization driven by peculiar molecular motifs of the selected substrate, close-packing criter

Nano‐sensor materials, especially if they target biological purposes, require a fine control and tooling of the properties at the molecular scale when intra‐molecular properties have to be exploited, e. g., in optical sensors. By means of optical spectroscopies (namely, spectrophotometry, spectrofluorimetry, and surface differential reflectivity), we unveil that thin films of porphycene show a spectacular chromatic change when exposed to acid vapors (namely, to hydrochloric acid). After the exposure, the original optical properties of porphycene films are recovered in few seconds and without any thermal annealing. In addition, since clear spectroscopic signatures are observed both in absorption and in reflectivity, the porphycene reveals to be suitable even for deposition of films onto opaque substrates. These findings are of significant interest in view of a potential engineering of the molecules and an implementation in devices.