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Gold and palladium are the most widely used precious metal materials in the field of electronic devices and industrial catalysis. How to realize the green recycling of gold and palladium is important and challenging. In this work, we found that gold and palladium in wastes, such as electronic devices and industrial catalysts, can be completely dissolved and recycled by photocatalysis. Gold and palladium are oxidized to the ionic state in water, which does not involve strong acids, strong alkalis, toxic cyanides, or an organic medium. More interestingly, the dissolution of gold and palladium in different halogen aqueous solutions has special selectivity, which depends on the coordination stability constants between gold and palladium with halide ions. Therefore, gold and palladium can be selectively dissolved in iodine ion solution and bromine ion solution, respectively, then gold and palladium can be obtained by a one-step reduction. This work opens up a new direction for optimizing the photocatalytic dissolution technology and promoting the green recycling of precious metals.

The gas–water interface plays an important role in the photocatalytic degradation of volatile organic compounds (VOCs). Herein, a novel photocatalytic reactor with a tunable gas–water interface was designed and utilized to investigate the performance of photocatalytic degradation of VOCs. The relationship between the key operating parameters of the reactor and VOCs mineralization was investigated in detail with toluene as a model pollutant. The results showed that a tunable gas–water interface was formed in the process of atomized spray photocatalytic oxidation. Furthermore, the photocatalyst was easily excited by light, generating more free radicals, which was conducive to improving the mineralization performance of toluene and the durability of the catalyst. The intermediates of the toluene reaction were analyzed by photoacoustic spectroscopy (PAS), total organic carbon (TOC), and electrospray ionization–ion trap mass spectrometry (ESI–MS). The results show that abundant hydroxyl radicals are formed at the gas–water interface, which is beneficial to the opening of the benzene ring and greatly reduces the formation of toxicity and byproducts. Simultaneously, we investigated the degradation performance of acetone, formaldehyde, and n-hexane in the reactor. This provides a new strategy for using photocatalytic technology to purify industrial flue gas and indoor air.

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