Metal cocatalyst loading is one of the most widely explored strategies in promoting photocatalytic solar energy conversion. Engineering surface-active facets of metal cocatalyst and exploring how they modulate the reactivity is crucial for the further development of advanced photocatalysts. In this work, through controlled hybridization of two-dimensional (2D) TiO 2 nanosheets with well-designed Pd nanocube (Pd NC) with exposed {100} facet and Pd nano-octahedron (NO) with exposed {111} facet, we unravel the distinct crystal facet effect of Pd cocatalyst in promoting the selective hydrogenation of nitroarenes to amines of TiO 2 photocatalyst. The activity tests show that the Pd NO with {111} facet is a more efficient cocatalyst than the Pd NC with exposed {100} facet. The prepared TiO 2 -Pd NO composite displays a 900% enhancement of photocatalytic hydrogenation rate in comparison with bare TiO 2 , while the TiO 2 -Pd NC sample only shows a 200% photoactivity enhancement. Microscopic mechanism study discloses that the distinctive photoactivity improvement of Pd NO is ascribed to the concurrent modulation of the Schottky barrier height and enrichment of surface reactants: (i) the Pd NO with a lower Fermi level could result in steeper band bending of TiO 2 (i.e., higher Schottky barrier) than the Pd NC, which is more efficient in boosting interfacial separation and inhibiting the recombination of photoexcited charge pairs; and (ii) the {111} facet of Pd has higher nitroarenes adsorption ability and especially stronger hydrogen enrichment capability, thus accelerating the surface hydrogenation process and contributing to a higher reaction rate. This work emphasizes the rational facet control of cocatalysts for enhancing the photocatalytic hydrogenation performance.
The continuous rise in plastic waste raises serious concerns about the ensuing effects on the pollution of global environment and loss of valuable resources. Developing efficient approach to recycle the plastic has been an urgent demand for realizing a sustainable circular economy. Photocatalytic valorization directly utilizes solar energy to transform plastic pollutant into chemicals and fuels, which is hardly implemented by traditional mechanical recycling and incineration strategies, thus offering a promising approach to address the contemporary waste and energy challenges. Here, we focus on the recent advances in the high-value utilization of plastic waste through photocatalysis. The basic principle and different reaction pathways for the photocatalytic valorization of plastic waste are presented. Then, the developed representative photocatalyst systems and converted products are elaborately discussed. At last, the review closes with critical thoughts on research challenges along with some perspectives for further development of this emerging and fascinating filed.
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