Study on pH dependent ON/OFF fluorescent switching behaviour of hydrothermally synthesised vanadium disulphide quantum dots (VS2-QDs)

Abstract

It is fascinating to design and develop an inorganic quantum dot (QDs) which exhibit luminescence features with ion concentration, temperature, and pH sensitivity dependence. Vanadium disulphide (VS2) belongs to the family of transition metal dichalcogenides (TMDs), and is extensively studied owing to its layered characteristics features in sensing and filtrations technology, however, its fluorescence features have not been well studied so far. The current work describes a widely adopted eco-friendly hydrothermal approach for the synthesis of VS2-QDs. The average size of particles was determined to be ∼10 nm by transmission electron microscopy (TEM) and Zetasizer analysis. The synthetic approach adopted here facilitates in situ functionalization of QDs, which results in their high stability in aqueous medium and enhanced sensitivity towards their surroundings. As most of the QDs show the sensitivity towards pH, a thorough investigation of VS2 QDs for their pH dependent photoluminescence has been carried out. The VS2-QDs were discovered to exhibit a remarkable luminescence intensity that was found to be about 11 times higher in basic conditions (pH ∼ 13, QY = ∼4.80%) as compared to that in acidic conditions (pH ∼ 1, QY = ∼1.10%). The root cause of this ON/OFF florescence flipping may be related to the functional groups (such as −SO42−, −NH2, OH−, etc.) attached over the surface of QDs, acid etching, and protonation–deprotonation process. This paper highlights the pH dependent switching behaviour of VS2-QDs that could offer valuable information for designing a futuristic pH-based device for biomedical applications.