Laser processing of neat and gold-nanoparticle-functionalized ZnO and TiO2 nanoparticles by nanosecond-355-nm or picosecond-532-nm light enabled control of photocurrent generation under simulated sunlight irradiation in neutral aqueous electrolytes. We obtained more than twofold enhanced photoelectrochemical performance of TiO2 nanoparticles upon irradiation by picosecond-532-nm pulses that healed defects. Laser processing and gold nanoparticle functionalization of ZnO and TiO2 nanomaterials resulted in color changes that did not originate from optical bandgaps or crystal structures. Two-dimensional photoluminescence data allowed us to differentiate and quantify surface and bulk defects that play a critical yet oft-underappreciated role for photoelectrochemical performance as sites for detrimental carrier recombination. We developed a detailed mechanistic model of how surface and bulk defects were generated as a function of laser processing parameters and obtained key insights on how these defects affected photocurrent production. The controlled healing of defects by pulsed-laser processing may be useful in the design of solar fuels materials. Pulsed lasers are powerful tools for the time-efficient preparation and/or modification of functional materials. 14-21 Recent investigations have shown that laser-modified TiO2 particles can be used to improve the light-driven water splitting to form hydrogen 22 or

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Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of understanding the chemical processes that are triggered by the laser pulses, which may dictate the surface properties that are highly important in heterogeneous oxidation catalytic reactions. We observed the formation of radical oxygen species during LFL, which suggested that LFL is a physicochemical process that leads to particle size reductions and initiates oxidative processes. When the ionic strength in the nanoenvironment was increased, the oxidation of the first atomic layer saturated at 50%, whereby the surface charge density increases continuously. We found a correlation between the surface charge density after synthesis of colloidal nanoparticles and its behavior in catalysis. The properties of the laser-generated nanoparticles in the colloidal state appear to have predetermined the catalytic performance. We found that a smaller surface charge density of the usAu NPs was beneficial for the catalytic activity in CO and ethanol oxidation, while their peroxidase-like activity was affected less. The catalytic activity was 2 times higher for samples prepared by chloride-free LFL after ozone pretreatment compared to samples prepared in pure water.

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