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Three-dimensional (3D) hybrid perovskites (HPs) are currently a key player in optoelectronic applications and, beyond the traditional photovoltaic applications, have also other great potentials as light-emitting diodes, lasers, photocatalysts, and photo- and X-ray detectors. However, despite the excellent performance of 3D HPs, certain HPs such as methylammonium lead iodide (CH3NH3PbI3named MAPbI3) lack long-term environmental stability because they are very sensitive to humidity and degrade under oxygen and light exposures. Moreover, MAPbI3films or single crystals or powders are mainly produced from precursor mixture methods and suffer some drawbacks such as the formation of intermediate phases with solvents affecting their performance. To face some of those problems, we have optimized the synthesis of MAPbI3via a green solvent-free mechanosynthesis process, which also provides large amounts of powders, and to enhance its chemical stability, we have mixed MAPbI3with graphite, which also granted the possibility to combine the different electronic properties of both components. The mechanosynthesis parameters have been optimized for both systems to minimize the defect amount, and their structural, optical, and electronic properties have been characterized. High-resolution transmission electron microscopy (HRTEM) and in situHRTEM highlighted common crystallographic orientations between MAPbI3nanograins (∼10 nm) in aggregates of mechanosynthesized (MS) powders. The band gap values and photoluminescence (PL) properties of mechanosynthesized MAPbI3are in good agreement with the ones reported for MAPbI3synthesized by chemical methods. A decrease in PL intensity related to the introduction of defects is observed with a longer grinding time, confirming that the selected grinding conditions were optimal. These mechanosynthesis conditions of MAPbI3were found also suitable to obtain MAPbI3@Graphite composites with different amounts of graphite. A homogeneous distribution of few-layer graphite within the MAPbI3matrix was noticed in powder-compacted wafers. Graphite-enhanced Raman scattering was observed with the composite with 5 wt % graphite showing its strong resistance to photodegradation and suggesting a charge transfer between graphite and MAPbI3. Such charge transfer is also in agreement with the quenching of the PL with an increasing amount of graphite. Further analysis of time-resolved PL decays confirmed, supported by X-ray detection results, that the presence of graphite impacted the charge transfer. The presence of graphite would induce a local modification of the Coulomb interaction, “attracting” the charge carriers at the graphite and MAPbI3interfaces and thus favoring the charge separation and transport. In addition, the composite with 5 wt % graphite exhibited promising photodetection properties with a photoresponsivity of 1.5 × 103A/W and an effective quantum effect of around 4.4 × 106% at 400 nm with a light power of 330 nW. This high photoconductive gain matches with the trapping of one type of charge carrier, while the other one is multiplied via injection from the contact electrodes, thus contributing even more to the photoconductivity. These results highlighted that the mechanosynthesis, which is green and efficient in providing large amounts of powders, is suitable to design homogeneous MAPbI3@Graphite composites with strong interactions between graphite and MAPbI3favoring an improved charge transfer and amplification of the photocurrent that will be very promising for photodetection applications.

Lead halide perovskites (LHPs) have emerged as promising candidates for a broad range of optoelectronic devices because of their unique physical properties. Methylammonium lead iodide (MAPI) perovskite has been the most commonly studied LHP due to its very promising optoelectronic properties. One of the main explored pathways for obtaining MAPI perovskites is the synthesis by ligand-assisted reprecipitation (LARP); however, this method is not totally understood from a phenomenological point of view. In this study, we took advantage of the development of a series of advanced in situtechniques to bring new insights into the pathway of this process that leads to MAPI perovskites from a precursor solution. First, we monitored the nucleation and growth processes of a solvated intermediate phase obtained viaLARP by correlating local information obtained by a direct visualization of the reaction medium using liquid-phase transmission electron microscopy (TEM) and more global information brought by synchrotron-based X-ray scattering measurements. This combined analysis, in real time and under representative conditions of the synthesis method, allowed us to decipher the structural evolution of the emerging phases, from amorphous and roughly spherical objects in the early stages of the process toward elongated ribbon-like morphology particles after a few seconds, through a crystallization process. Second, we followed in situthe transition of the as-obtained solvated intermediate phase toward the final phase of MAPI perovskite during a thermal treatment at 80 °C, using in this case a combination of gas-phase TEM, in image and diffraction modes, and temperature-resolved X-ray diffraction. We provided direct and unprecedented evidence of the fragmentation of the crystals, simultaneously to the occurrence of the structural transformation between the intermediate and final phases. Our approach, which involved also challenging development of new correlative methods, demonstrates the high interest of such an in situcorrelative study for a better understanding of the synthesis and properties of new emerging materials including LHPs.

Taking advantage of tungsten oxide inherent Brønsted–Lewis acidity, the first series of WO3–SiO2(HIPE) monolithic (MUB-104(x) series) catalysts bearing multiscale porosity have been designed through integrative chemistry. At the microscopic length scale, beyond X-ray diffraction (XRD) revealing the WO3monoclinic structure, local electron spin resonance (ESR) spectroscopy addresses g values clearly located at the frontier between extended WO3phases and polyanion clusters, in agreement with scanning transmission electron microscopy high-angle annular dark field (STEM-HAADF) investigations. NH3-TPD shows that when the tungsten loading is increased from 10 wt % for MUB-104(1) to 24 wt % for MUB-104(3), the amount of acidic sites significantly decreases from 0.35 to 0.08 mmol of NH3g–1, respectively, in agreement with the particle sizes. The MUB-104(x) series offers efficient cosolvent-less heterogeneous cycling catalysis toward both Friedel–Crafts alkylation and acylation syntheses. MUB-104(1) carries the highest turnover number (TON) of 121 and turnover frequency (TOF) of 20 h–1, while for acylation, MUB-104(1) carries the highest TON of 117 and TOF of 26 h–1. Besides, we find out that the catalysts offer good selectivity, where 30/70% of ortho- and para-substituted alkylated products are obtained. Considering the acylation reaction, the selectivity is even higher, reaching 100% toward the para-substituted acylated product. The catalyst, due to its intrinsic monolithic character, can be easily extracted from the reactive media, recycled, and re-employed further.