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Abstract
Single-layer MoS2-MoO3-x heterojunction nanosheets with visible-light-sensitive band gap energy and average lateral dimensions of ~70 nm were synthesized by using a two-step combined exfoliation method. The exfoliation was initiated from pristine MoS2, while some sulfur sites in expanded MoS2 sheets during exfoliating were substituted by ambient non-thermal oxygen, resulting in formation of α-MoO3-x crystalline domains. The morphological features, crystalline structure, phase formation, number of layers, and optical properties of the MoS2-MoO3-x nanosheets were determined by atomic force microscopy; X-ray diffraction; field emission electron microscopy; transmission electron microscopy; and Raman, UV–visible–NIR, diffuse transmittance, and photoluminescence spectroscopies. The produced α-MoO3-x domains displayed a narrower indirect band gap energy (~1.95 eV) than that of stoichiometric MoO3 (~3 eV), and a broad light absorption range from visible to near-infrared region can act as a plasmonic material facilitating the separation of the photoinduced carriers and enhancing the photocatalytic activity of the MoS2 domain, having ~1.75(2.16) eV indirect (direct) band gap energy. In this regard, the MoS2-MoO3-x heterojunction nanosheets showed single-layer-based excitation-dependent luminescence emissions and visible-light-induced photocatalytic features, at the same time. This study can contribute to promising applications of sheet-like nanomaterials for purposes requiring simultaneous photoluminescence and photocatalytic features, such as in-vivo monitoring and targeting.
Highlights
Photocatalytic materials have attracted increasing attention in various scientific fields [1]and for various technological applications [2,3] since 1972 [4]
MoS2 nanosheets have been applied as effective photocatalysts, because of their excellent optical and chemical properties [5,16,17] and having a more suitable and direct band gap energy of about 1.9 eV
It should be clarified that the main goal of this work is indicating the ability to form 2D MoS2 -MoO3-x heterojunctions working as a photocatalyst, without any attempt at optimization
Summary
Photocatalytic materials have attracted increasing attention in various scientific fields [1]and for various technological applications [2,3] since 1972 [4]. TiO2 [12] and ZnO [13], as efficient photocatalysts, are mostly applicable in common processes, but TiO2 ’s wide band gap in pure state (~3.2 eV) is considered a barrier to its use due to having an excitation wavelength in the UV region [5]. This problem can be overcome by addition and/or cooperation of metallic [14] or carbon-based [15] nanomaterials. The high catalytic activity of ultrathin MoS2 nanosheets (especially 1T-MoS2 ) is due to the number of active edge sites for catalysis [22,23]
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