## 5 Conclusions and Perspectives  
In the past several years, with the development of advanced materials and microscopy, substantial progress has been realized to make deep insights into the kinetics of HCs in PMH based photocatalysts. The efforts for the design of high-performance PMH, including the compositions, morphology, and band structures between metals and semiconductors and the external EM field, have been sufficiently developed for the effective harvesting and transferring of photons. In this review, we presented the progress in the rational design of photocatalysts based on PMH in recent years. The \"hot spots\" structures, plasmonic cavity and hollow structures for obtaining photon trapping in a broad spectrum are introduced. To realize a fast transfer of HCs, some reliable methods, including clearer interfacial regions, the rational design of electrical transporting channel, a specific contact of the crystal face and the polarization of incident light, are individually detailed. In addition, the typical applications for  
Figure 12: Membrane based PMH photocatalysts for water/air purifications. (**a**) The scheme of the fabrication of a bifunctional membrane and (**b**) the synergistic effects in the steam generation and pollutants decomposition. (**c**) The rates of degradation of RhB in Au-AAO, TiO\({}_{2}\)-AAO and TiO\({}_{2}\)-Au-AAO. (**a–c**) Reproduced with permission. [114] Copyright 2016, American Chemical Society. (**d**) The scheme for designing Ag@CNTs/Al\({}_{2}\)O\({}_{3}\) filters by chemical vapor deposition and a polyol process. (**e**) The antimicrobial rates and (**f**) degradation rates of volatile organic compounds (VOCs) in different purification filters. (**d–f**) Reproduced with permission. [124] Copyright 2017, the Royal Society of Chemistry. environmental protections are also listed in order to give a brief framework for researchers to focus on in the present. There are also some points to consider for future investigations. First, the exact physical model for the process relating to the generation, transportation and injections of HCs needs to be built up. There are arguments that the dominating contributions of electrons (interband transitions with a relatively low energy of electrons or intraband transitions induced by SPs) from photoexcited metals is the improvement of catalytic reactivity, and some works have given different opinions [134; 135]. The distinguishing of non-thermal effects (HCs effects) and thermal effects, which allows us to quantify each contribution for the enhancement of the process of photocatalysis, is also of great importance for designing specific structures with different purposes [136; 137; 138]. Second, in the past years, although numerable technologies on the optimization and design of the rational employment of PMH have emerged [139; 140; 141; 142; 143], the crystal growth mechanisms and hetero-assembly techniques still need to be revealed clearly. Furthermore, the optical characteristics of PMH are studied mainly on a macroscopic level; for example, the absorption and reflection in self-assembly films, and the optical phenomena we observed, are integrated effects with millions of nanostructures. Additionally, the microscopic evidence of a single structure must be presented urgently for a comprehensive understanding of light-matter interactions [144; 145; 146]. In this regard, the in situ characterization technique must be further developed to help solve these limits. Practically, for rich functional systems, the cost, biocompatibility, stability and ease to integrate into other platforms must also be considered. [PERSON] and [PERSON] drafted the main parts of manuscript. [PERSON]-[PERSON], [PERSON], [PERSON], [PERSON]-[PERSON], [PERSON] and [PERSON] participated in the draft preparation. All authors read and approved the final manuscript.