  Two-dimensional (2D) Janus transitional metal dichalcogenides (TMDCs) have
great potential for photocatalytic water splitting due to their novel
properties induced by the unique out-of-plane asymmetric structures. Here, we
systematically investigate the geometric, electronic and optical properties of
2D Janus MoSSe with titanium doping and vacancies to explore their synergistic
effects on photocatalytic activity. We find that there are effective
attractions between the substituted or adsorbed Ti atoms and S/Se vacancies.
The Ti adatoms dramatically extend the light absorption range to infrared
region. The S/Se vacancies coexisting with Ti adatoms will modulate the
transition of photo-excited electrons, thereby enhancing the sunlight
absorption. The Ti adatoms either existing alone or coexisting with vacancies
introduce smaller lattice distortion compared to substituted Ti atoms and these
Ti adatoms induce smaller effective mass of charge carriers. The configuration
of S vacancy coexisting with Ti adatoms on Se-surface exhibits the most
significant synergistic effects and best overall photocatalytic performance.
Our work reveals the mechanism and effects induced by doping and vacancies
coexisting in 2D Janus TMDCs, also propose a new practical strategy to improve
the performance of 2D photocatalysts.
