Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

The development of highly efficient and rapid photoinitiating systems for free radical photopolymerization under the irradiation of visible light has attracted increasing attention due to their widespread potential applications in, for example, 3D printing or dental polymers. Unfortunately, currently available visible-light-sensitive photoinitiators are not efficient enough for 3D printing applications suffering from low printing speeds. Here we describe a series of photoinitiating systems consisting of disubstituted aminoanthraquinone derivatives (i.e., 1-amino-4-hydroxyanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone) and various additives (e.g., tertiary amine and phenacyl bromide) toward the free radical photopolymerization of various acrylate monomers (such as commercial 3D resin) under the irradiation of blue to red LEDs. It is shown that the type and position of substituents of the aminoanthraquinone derivative can significantly affect its photoinitiation properties. The most efficient disubstituted aminoanthraquinone derivativebased photoinitiating system was selected and used for the 3D printing of a commercial 3D resin in a 3D printer with polychromatic visible light as the irradiation source. It is shown that its printing speed was dramatically enhanced compared to a commercial photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO).

We reveal a unique mechanism by which pure water can be dissociated to form free radicals without requiring catalysts, electrolytes, or electrode contact by means of high-frequency nanometer-amplitude electromechanical surface vibrations in the form of surface acoustic waves (SAWs) generated on a piezoelectric substrate. The physical undulations associated with these mechanical waves, in concert with the evanescent electric field arising from the piezoelectric coupling, constitute half-wavelength “nanoelectrochemical cells” in which liquid is trapped within the SAW potential minima with vertical dimensions defined by the wave amplitude (∼10 nm), thereby forming highly confined polarized regions with intense electric field strengths that enable the breakdown of water. The ions and free radicals that are generated rapidly electromigrate under the high field intensity in addition to being convectively transported away from the cells by the bulk liquid recirculation generated by the acoustic excitation, thereby overcoming mass transport limitations that lead to ion recombination.

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