Precious metals such as gold and platinum are valued materials for a variety of important applications, but their scarcity poses a risk of supply interruption. However, the dissolution and recovery of precious metals using the current methods are limited by associated serious environmental pollution and high energy consumption. Here, we show a photocatalytic process that allows one to selective retrieve 7 kinds of precious metal elements (Ag, Au, Pd, Pt, Ru, Rh and Ir) (with dissolution efficiency of 99%) from waste circuit boards, ternary automotive catalysts and even ores. Precious metals is recovered with high purity (≥98%) through a simple reductive method. The whole process only needs light and catalyst without strong acid, strong base and highly toxic cyanide. It has an environmentally friendly, scalable and efficient way, in which the catalyst has been recycled more than 100 times under normal temperature and pressure without performance degradation. It has successfully realized the scale of dissolution from grams to kilograms, and it is expected to realize large-scale recovery of precious metals in industrial application. This general approach provides an unprecedent technology for recycling resources on earth.
The status of defects of TiO 2 are of fundamental importance in determining its physicochemical properties. Here we report a simple chemical deposition method for controllable synthesis of defective anatase TiO 2 nanocrystals under various calcination atmospheres. XPS and ESR analysis reveals that both the oxygen vacancies (V O ) and the trivalent titanium (Ti 3+ ) defects exist in TiO 2 after N 2 treatment (N-TiO 2 ). Meanwhile, mainly V O defects can be obtained in TiO 2 with air calcination (A-TiO 2 ). ESR spectra for reactive oxygen species determination, clearly show that the visible light catalytic activity is mainly caused by the efficient activation of oxygen molecules to •O 2− species for A-TiO 2 , which play an important role in hindering the accumulation of intermediates during p-chlorophenol (4-CP) photodegradation process. However, the oxygen molecules cannot be activated for N-TiO 2 even with superior visible light absorption and thus the photogenerated electron are reductant, which participated in the transformation of BQ to HQ via electron shuttle mechanism. Moreover, A-TiO 2 exhibits higher separation efficiency of photogenerated carriers than that of N-TiO 2 , showing the critical role of V O with a suitable concentration in transferring photogenerated charges.
High sensitivity strain sensors have been fabricated by depositing chromium (Cr) nanoparticles between silver interdigital electrodes coated on the substrate of a flexible plastic material like polyethylene terephthalate. A gas phase cluster beam deposition system was used for the preparation of the nanoparticle arrays with a well-defined conductance. We demonstrate that the conductance of the nanoparticle arrays is dominated by the quantum transport between the closely spaced nanoparticles. Compared to the traditional metallic foil or semiconductor strain sensors, this kind of strain sensor demonstrates both a higher gauge factor, which can be as large as the order of 100, and a wider dynamic range, with a workable maximum applied strain beyond 3%.
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