2.2.4. Conductive Substrate

Chang et al. studied the performance of Ni-doped ZnS/NiO/Ni foam photocatalysts [70]. Ni foam was decorated with doped ZnS to prepare the porous immobilized photocatalysts. The photocatalysts had an optimized activity of 2500 μmol/g−<sup>1</sup> h<sup>−</sup>1, resulting from their matched band structure, porous microstructure, and conductive Ni foam as substrate. The surface turned from hydrophobic to superhydrophilic after Ni-doped ZnS was grown on the surface of the Ni foam. In addition, the porous microstructure facilitated the transport of reactant and generated a large amount of surface active sites, and the conductive Ni foam aided in the separation of photoexcited carriers. Figure 5 shows a proposed mechanism, illustrating the band structure of the photocatalysts and the transport of photoexcited electrons. When the composite photocatalysts were irradiated with light, the photoexcited electrons were effectively separated by their transportation from ZnS to NiO. In addition, stainless-steel wire mesh is also a good candidate for the preparation of porous immobilized photocatalysts [71].

**Figure 5.** A possible mechanism for the photoexcitation and carrier transporting process of Ni-doped ZnS/NiO/Ni foam photocatalysts. Figure adapted from [70].
