A broad-band,
environmentally friendly multijunction photocatalyst,
composed of mixed-phase ZnIn2S4 in situ grown
on TiO2 nanotree powders (NtPs), was prepared via a facile
hydrothermal method. The unique structure of the TiO2 NtPs
provided a large surface area for the easy growth of ZnIn2S4 and for the efficient adsorption of reactants. The
introduced ZnIn2S4, possessing a homojunction
structure enabled by two closely interlaced crystalline phases, endowed
the ZnIn2S4/TiO2 composite with an
enhanced visible-light response and boosted charge separation between
the two phases. Moreover, the in situ growth of ZnIn2S4 on TiO2, forming a heterojunction at the interface,
rendered an intimate contact and strong interaction, which was favorable
for the efficient charge transfer between the two components. These
advantages all together resulted in the significantly enhanced visible-light
photocatalytic activity in the degradation of methyl orange. The charge-transfer
dynamics and pathways were studied by performing photoluminescence
measurements and in situ irradiated X-ray photoelectron spectroscopy
analysis. The active species involved in photocatalysis were also
explored by carrying out trapping experiments. Based on these results,
the possible mechanism for the enhanced photocatalytic activity was
proposed and discussed. This work highlights the great potential of
developing broad-band and efficient ZnIn2S4-
and TiO2-based photocatalysts through simultaneously constructing
both a homojunction and a heterojunction for remediating environmental
pollution and provides a mechanistic understanding of photocatalysis
in a type-II, multijunction hybrid.