Serving as shape control agent, polyvinyl pyrrolidone (PVP) has been widely used in chemical synthesis of metal nanoparticles. However, the role of molecular weight (MW) of PVP has been rarely concerned. In this study, we show a facile method to control the shapes of silver nanocrystals using PVP with different MWs. PVP_MW=8,000, PVP_MW=29,000, PVP_MW=40,000, and PVP_MW=1,300,000 are compared in the present study. Surprisingly, high-yield silver rodlike nanostructures, nanospheres, and nanowires can be obtained under the same growth environment and reactant concentrations by simply changing the MW of PVP. The mechanism studies of the role of PVP with different MWs in the growth process were carried out systemically using the morphology and spectroscopic measurement, FT-IR spectrum analysis, and seed crystallization monitoring. The results indicate that the MW of PVP plays a determinant role in the morphology and optical property control of the silver nanocrystals. Meantime, the concentration of PVP was found to be an assistant factor to further improve the shape and the yield of the synthesized nanocrystals.

The shape of plasmonic nanostructures such as silver and gold is vital to their physical and chemical properties and potential applications. Recently, preparation of complex nanostructures with rich function by chemical multistep methods is the hotspot of research. In this review we introduce three typical multistep methods to prepare silver nanostructures with well-controlled shapes, including the double reductant method, etching technique and construction of core-shell nanostructures. The growth mechanism of double the reductant method is that different favorable facets of silver nanocrystals are produced in different reductants, which can be used to prepare complex nanostructures such as nanoflags with ultranarrow resonant band bandwidth or some silver nanostructures which are difficult to prepare using other methods. The etching technique can selectively remove nanoparticles to achieve the aim of shape control and is widely used for the synthesis of nanoflowers and hollow nanostructures. Construction of core-shell nanostructures is another tool to control shape and size. The three methods can not only prepare various silver nanostructures with well-controlled shapes, which exhibit unique optical properties, such as strong surface-enhanced Raman scattering (SERS) signal and localized surface plasmon resonance (LSPR) effect, but also have potential application in many areas.

The effect of plasmon-induced hot carriers (HCs) enables the possibility of applying semiconductors with wide band gaps to visible light catalysis, which becomes an emerging research field in environmental protections. Continued efforts have been made for an efficient heterostructure photocatalytic process with controllable behaviors of HCs. Recently, it has been discovered that the improvement of the utilization of HCs by band engineering is a promising strategy for an enhanced catalytic process, and relevant works have emerged for such a purpose. In this review, we give an overview of the recent progress relating to optimized methods for designing efficient photocatalysts by considering the intrinsic essence of HCs. First, the basic mechanism of the heterostructure photocatalytic process is discussed, including the formation of the Schokkty barrier and the process of photocatalysis. Then, the latest studies for improving the utilization efficiency of HCs in two aspects, the generation and extraction of HCs, are introduced. Based on this, the applications of such heterostructure photocatalysts, such as water/air treatments and organic transformations, are briefly illustrated. Finally, we conclude by discussing the remaining bottlenecks and future directions in this field.