The fabrication of supported noble metal nanocrystals (NCs) with well-controlled morphologies have been attracted considerable interests due to their merits in a wide variety of applications. Photodeposition is a facile and effective method to load metals over semiconductors in a simple slurry reactor under irradiation. By optimizing the photodeposition process, the size, chemical states, and the geometrical distribution of metal NCs have been successfully tuned. However, metal NCs with well-controlled shapes through the photodeposition process have not been reported until now. Here, we report our important advances in the controlled photodeposition process to load regular noble metal NCs. Reduced graphene oxide (rGO) is introduced as a reservoir for the fast transfer of photoelectrons to avoid the fast accumulation of photogenerated electrons on the noble metals which makes the growth process uncontrollable. Meanwhile, rGO also provides stable surface for the controlled nucleation and oriented growth. Noble metal NCs with regular morphologies are then evenly deposited on rGO. This strategy has been demonstrated feasible for different precious metals (Pd, Au, and Pt) and semiconductors (TiO2, ZnO, ZrO2, CeO2, and g-C3N4). In the prototype application of electrochemical hydrogen evolution reaction, regular Pd NCs with enclosed {111} facets showed much better performance compared with that of irregular Pd NCs.

Noble metal nanoclusters/oxides have been attracting close attention in heterogeneous catalysis due to their unique physical and chemical properties. However, due to the effect of the Schottky heterojunction, the deposited particles are easy to aggregate, and the size is difficult to control. In this work, we report a surface-confined photodeposition process to load ultrafine noble nanoclusters on semiconductor oxides, e.g., titanium oxide (TiO 2 ), in a fluidized bed (F method). Different from the traditional photodeposition in solution (L method), the metal precursors which are absorbed on the semiconductor are difficult to migrate via the F method, therefore effectively inhibiting the agglomeration of nanoparticles. Noble metal nanoclusters with a uniform size smaller than 2 nm are obtained. In the model reaction of the catalytic oxidation of formaldehyde (HCHO), Pt/ TiO 2 with an ultralow loading amount (0.08 wt% Pt) showed excellent performance for the catalytic oxidation of HCHO at room temperature, which is benefited from the small and uniform size of nanoclusters. This work brings an effective strategy in the fabrication of size-controlled noble metals on oxide supports for heterogeneous catalysis.

Tunable physicochemical properties of bimetallic core–shell heterostructured nanocrystals (HNCs) have shown enormous potential in electrocatalytic reactions. In many cases, HNCs are required to load on supports to inhibit catalyst aggregation. However, the introduction of supports during the process of growing core–shell HNCs makes the synthesis much more complicated and difficult to control precisely. Herein, we reported a universal photochemical synthetic strategy for the controlled synthesis of well-defined surfactant-free core–shell metal HNCs on a reduced graphene oxide (rGO) support, which was assisted by the fine control of photogenerated electrons directly transferring to the targeted metal seeds via rGO and the precisely tuned adsorption capacity of the added second metal precursors. The surface photovoltage microscopy (SPVM) platform proved that photogenerated electrons flowed through rGO to Pd particles under illumination. We have successfully synthesized 24 different core–shell metal HNCs, i.,e., MA@MB (MA = Pd, Au, and Pt; MB = Au, Ag, Pt, Pd, Ir, Ru, Rh, Ni and Cu), on the rGO supports. The as-prepared Pd@Cu core–shell HNCs showed outstanding performance in the electrocatalytic reduction of CO2 to CH4. This work could shed light on the controlled synthesis of more functional bimetallic nanostructured materials on diverse supports for various applications.

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