Transition metal dichalcogenides (TMDCs) have shown tremendous potential for application in the field of optoelectronics owing to their extraordinary characteristics. The $\rm{WS_{2}/V_{0.25}W_{0.75}Se_{2}}$ van der Waals heterostructure was fabricated by layer transfer technique and its $I – V$ characteristic was measured at room temperature. The fabricated pn-junction heterostructure shows obvious current rectification with a rectification ratio of $\thicksim{39}$ at $\pm{1}$ V. The heterostructure was analysed in the dark and under polychromatic illumination. The noticeable rise in reverse current is observed at higher intensity of illumination. The photocurrent and photoresponsivity are found to be enhanced as intensity and bias voltage are increased. The higher value of the ideality factor of $\thicksim{2}$ is attributed to the inhomogeneity of the heterojunction.

Physicochemical adsorption and degradation of the azo dye, methylene blue (MB), when irradiated by visible and UV light in aqueous ZnO suspension have been investigated. The novelty of this work is to investigate the effect of dye concentration up to 200 mg/l, keeping the nanocatalysts’ concentration invariant as 1 g/l. The nanocatalysts before and after degradation process have been analysed to understand the mechanism of dye removal using X-ray diffractometer (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal gravimetric analyser(TGA). The results show that UV light degrades the dye to its intermediates through chemi-adsorption, whereas the visible light induces physisorption of dye molecules on ZnO nanocatalysts. The XRD pattern of the ZnO nanocatalysts revealed no changes in the internal structure of ZnO after the degradation process, confirming thereuse of catalysts.