Sensitive hydrocarbon detection by CdSe NRs; impact of surfactants on quenching process

Abstract

Cadmium Selenide (CdSe) nanostructures are fluorescent in nature with a bandgap of 1.74 eV at room temperature. The article depicts synthesis of cadmium selenide nanorods (CdSe NRs) through the solvothermal method. The protocol involves the use of surfactant CTAB, Ascorbic acid and Ethylenediamine under same conditions of temperature and duration, the effect of which is understood on morphology and absorption. The water-soluble precursors Na₂SeO₃ and CdCl₂ for Se and Cd, respectively were used and heated in a Teflon lined autoclave for 5 h at 180 °C. There are numerous methods reported for the synthesis of CdSe NRs but we opted to use solvothermal wet chemical technique to understand the influence of different types of surfactants on various features [1-2].  The detection of hydrocarbons by CdSe nanorods is demonstrated through UV-visible absorption quenching technique and analysed through stern-vomer plots. The morphology and structural features of the NRs are examined through Field emission scanning electron microscope, X-ray diffraction and Raman spectroscopy techniques. The micrographs of nanorods are illustrated in fig. 1 and 2, which shows difference in the structure of nanorods due to the impact of different surfactants with rest of the conditions similar. All the diffraction peaks in XRD plot can be indexed as pure hexagonal wurtzite CdSe structure as shown in fig. 3. In contrast, the Raman peaks at 206, 413 and 621 cm⁻¹ observed at the excitation energy of 2.41 eV correspond to the 1LO, 2LO and 3LO phonons of the CdSe NRs. Instead of using conventional organic dye molecules and QDs, we wish to investigate NRs in this field of optical detection as QDs tend to agglomerate at the time of wet-dry process [3].

Organic solvent like benzene possesses wide industrial applications but are volatile in nature. It easily vaporizes at room temperature (RT) and exposure to them may have dangerous health effects.  Therefore, it is of utmost importance to develop an efficient, sensitive and swift technique plus materials for the measurement of these organic vapours in the health sector. There are diversified strategies available for monitoring the hazardous molecules, which include electrical, optical and quartz crystal microbalance. Luminescent semiconductor nanostructures exhibit size dependent spectral properties like narrow and tuneable emission peaks and broad absorption bands that has been used in spectroscopic research and applications. Moreover, the resistance to photobleaching, chemical stability and water solubility make them more interesting fluorescent probes than traditional organic dyes for chemo/biosensing/drug delivery applications.  

This technique of absorption spectroscopy to sense aromatic hydrocarbons proved to be more precise, sensitive, reversible and easy to use.  The molecules like benzene, toluene and xylene are tested under real samples (water) in a wide range of 100-1000 ppm, under liquid form. The intensity of the absorption maxima decreases with a red shift on increasing the concentration of hydrocarbons through a fixed amount of CdSe NRs. The purpose to carry out this research is to explore 1D nanostructures and the material CdSe in the field of organic molecule detection. To the best of our knowledge, this report is scarcely reported in literature with lowest detection limits.