Enzymes, with high catalytic activities and substrate specificity,1, 2 are powerful environmentally friendly bio-catalysts. By the outstanding catalytic properties, natural enzymes are widely used in biology, chemistry, medicine, and industrial fields.3 Although promising, the complicated purification procedure, low operational stability, intrinsic environmental sensitivity, and difficulties in recycling and reusing has restricted the broad utilization of enzymes.3 Thus, it is urgent to seek alternatives.
Due to nano effect, there is surprising mutation from bulk to 2D nano-sized materials. When bulk Fe3O4 converted to Fe3O4 nanoparticles,4 they have enzyme-mimicking property. Since then, a bunch of studies on 2D artificial enzymes have rapidly developed.5, 6 These enzymes not only have low cost, better stability and robustness under extreme conditions, but also provides more possibilities in practical applications.7, 8 For example, V2O5 nanowires9 presents intrinsic catalytic activity towards classical peroxidase substrates in slightly acidic environments (pH about 4), such as 3,3,5,5-tetramethylbenzidine (TMB), in the presence of H2O2. Qu et al. used ultrathin graphitic carbon nitride (g-C3N4) as the template for in situ growth of AuNPs. The obtained g-C3N4@AuNPs, exhibiting remarkable enhanced peroxidase-like property, had a broad spectrum of antibacterial effects under a physiological level of H2O2.10 Due to the unique oxidase-like activities, Co4S3/Co(OH)2 nanotubes could transform resolved O2 to ·O2- in pH = 4 condition, avoiding the use of toxic H2O2.11 Yan’s group used Fe3O4 nanoparticles as peroxidase mimics to degrade pollutants in wastewater, such as phenols, methyl blues, rhodamine B, and other organic substances.12
Despite the constantly exploitation of nanozymes, the drastically affected by acid pH limits their scalable applications. Natural environments, such as sea water, river, and wastewater, cannot automatically provide acidic conditions, thereby most mimic enzymatic catalysts cannot work in such circumstances. How to avoid the extra addition of acid is highly desirable. If some nanozymes can use surrounding resources, by cleave H2O into H+, they can ensure their own working environments. As typical 2D materials, molybdenum disulfide (MoS2) is a promising candidate. The highly effective electron transfer from S-Mo-S bonds ensures their outstanding catalytic performance.13–15 It is reported that S vacancies (SVs) in MoS2 have strong adsorption energy,16 which might enable the absorb of H2O and produce H+. Thus, the exploration of MoS2 may bring new future for nanozymes.
In this work, using calculations and experiments, the possibility and mechanism of the cleavage of H2O induced by SVs in MoS2 nanosheets are systematically illustrated (Scheme. 1). The calculations suggest that SVs in MoS2 nanosheets can adsorb H2O and then yield H+ and ·OH. Regardless of outer environments, MoS2 nanosheets can create acidic conditions and permit their own peroxidase-like catalytic procedure. The results provide an in-depth insight into the nanozymes and will guide a new future for the design, synthesis and applications of 2D materials.