Photoelectrochemical generation of hydrogen from water is considered to be the most appealing solution for the replacement of fossil fuels as a source of energy. For this reason, the study of novel and affordable materials with high energy conversion efficiencies is currently a crucial objective for the scientific community. Chemical modification of two-dimensional (2D) and layered materials, such as fluorination, can play a decisive role in tuning the properties for energy-related applications, as it was documented in the past by fluorination of graphite and graphene. MAX phases (MAX) are a class of layered ternary compounds that is well known for their interesting physical properties but still underexplored as a photoelectrocatalyst for energy conversion. Herein, a set of MAX, namely, Ta2AlC, Cr2AlC, Ti2AlC, and Ti3AlC2, was exposed to fluorine gas in a controlled environment and their photoelectrocatalytic properties were tested for the hydrogen evolution reaction with illumination by a visible light source of 660 nm wavelength. All of the mentioned compounds showed excellent hydrogen evolution performances under illumination, in particular after the fluorination process. Fluorinated Cr2AlC is the phase that showed the lowest overpotential, and fluorinated Ti2AlC and Ti3AlC2 showed the most prominent photoelectrocatalytic enhancement upon fluorination. The fluorinated MAX phases should find broad applications to photoelectrochemistry, as their fluorinated graphene counterparts did in the past.

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Cyclopentyl methyl ether and 2-methyltetrahydrofuran, low impact ethereal solvents forming a positive azeotrope with water, were successfully employed as solvents in the synthesis of a variety of acetals carried out under Dean–Stark conditions in the presence of heterogeneous acidic catalysts. Under these conditions, ammonium salts, either as such or supported on SiO2, performed better or equally well than widely employed homogeneous and heterogeneous acidic catalysts such as p-toluenesulfonic acid, Amberlyst 15®, or Montmorillonite K10. Several examples highlight the advantage of tuning the relative acidities of ammonium salts by appropriately selecting the counterion. Within one of these examples, our protocol clearly outweighs the classic p-toluenesulfonic acid/toluene protocol in terms of chemoselectivity. Silica-supported catalysts were characterized by SEM, TEM, and FTIR spectroscopies, as well as by N2 physisorption. Such a characterization reveals an even distribution of ammonium salts on silica, thus confirming the formation of expected catalytic supports.