Synthesis and Development of Metal Doped Quantum Dots for Environmental Remediation

Abstract

The main focus of the present research is the development of efficient catalysts for the degradation of wide range of pollutants present in different environmental compartments. For this purpose, two sets of compounds are synthesized. One class is designated as quantum dots and the second is sulphide based nanoparticles on the basis of particle size. The potential of these materials as candidates for environmental remediation is evaluated through degradation studies of dyes, polyaromatic hydrocarbons and pesticides. Quantum dots were synthesized to act as core (indium phosphide), shell (zinc sulphide) and (silver & copper) doped following the thermal decomposition process. Another series of compounds based on zinc and silver sulphide was attempted. The structure property relationship was assessed through a wide range of techniques including UV-Visible spectroscopy (UV-Vis), Photoluminescence spectrofluorometry (PL), X-ray Diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM) and Thermogravimetry (TGA). The particle size results obtained from TEM supported two ranges; 2.28-4.60 nm and 612 nm for quantum dots and sulphide based nanoparticles, respectively. Each material was spherical in shape with clear lattice fringes. The purity of the product was witnessed by the presence of main elements and doping was in proportion to concentration induced. XRD results of ZnS depicted lattice planes (111), (200), (220), (311), (400), and (331) in good agreement with cubic geometry. It was also found that doping stamped good thermal stability to the synthesized material. Each of the synthesized material was tested as potential photocatalyst candidate for the degradation of representative dyes (crystal violet, Congo red), polyaromatic hydrocarbons (phenanthrene, naphthalene and pyrene) and pesticide (deltamethrin). For this purpose, series of bench scale batch experiments were designed and photocatalytic activity under UV light irradiation was followed on UV-Visible, Gas chromatography coupled with Mass spectrometry, and High performance liquid chromatography.The degradation potential of QDs due to smaller particle size was higher than nanoparticles with optimum efficiency of 95% and 81%, respectively, for both cationic and anionic dyes. The results indicated that degradation of PAHs increased with increase in irradiation time as evident from the reduced intensity of molecular ion peaks at standard retention times. The fragment at m/z 149 represented formation of phthalic acid that is less hazardous than parent compound. The study concludes that each synthesized material can be employed as potential photocatalyst for the degradation of representative pollutants. It is recommended that environmental compartment with mix pollutants can conveniently be treated with a single material to an appreciable extent. The study offers economical and environment friendly remediation model.