Supplementary Material
Effect of cationic surfactant head groups on synthesis, growth and agglomeration behaviour of ZnS nanoparticles
S.K. Mehta*, Sanjay Kumar, Savita Chaudhary and K.K. Bhasin
Department of Chemistry and Centre for Advanced Studies in Chemistry,
Panjab University, Chandigarh-160014, India
Scanning Electron Microscopy (SEM): SEM images of powdered sample were taken using JEOL (JSM-6100) scanning microscope. The samples for SEM analysis were prepared by washing the powder obtained after solvent evaporation with water at least twice to remove excess surfactant. Then this washed sample was again washed with ethanol and dried at 60C. this powdered sample was now sprinkled on the metal grids for gold coating and SEM anlalysis.
Fig. S1. SEM images of dried ZnS nanopowder separated from (a) CTAC and (b) CPyC.
Effect of UV-radiations of two different wavelengths on ZnS nanoparticles: These studies were carried out to confirm the degradation of synthesized ZnS nanoparticles by UV-light. The as prepared ZnS nanoparticles in presence aqueous micellar solution of CTAC and CPyC (10 ml each) were taken in glass flasks and kept inside the UV-cabinet (Popular India). The samples were then irradiated with UV-light of wavelength 254 nm for two hours. The samples were then taken out and immediately transferred into Quartz cuvette of 1 cm path length to record UV-vis spectra with a Jasco-530V spectrophotometer. Similar procedure was followed for the irradiation of samples at 365 nm.
Fig. S2. Absorption spectra of ZnS nanoparticles prepared in (a) CPyC (b) CTAC; before (solid lines) and after UV-irradiation for two hours (dotted lines) at 254nm and 365nm (shown in inset)
Growth induced shift in UV-vis spectra of ZnS nanoparticles as a function of time: Fig. S3 represents change in UV-visible spectra of ZnS nanodispersion in aqueous CPyC and CTAC as a function of time. In these studies, the particles were produced by quickly adding the aqueous surfactant solutions containing Zn2+ in to the other containing S2- ions. The solution was then immediately transferred in to quartz cuvette for UV-visible spectroscopy. The mixing time was about 40-45 s before taking the spectra. The spectra were then taken at an interval of 2 minutes. As can be seen, the typical shoulder due to ZnS in the wavelength range of 260-300 nm is progressibly red shifted with time and became almost constant after nearly 20 minutes.
Fig. S3. Change in UV-vis absorption spectra of ZnS nanoparticles as a function of time in aqueous micellar solution of (a) CPyC (b) CTAC. Magnified views of Absorption shoulder are shown as insets.
Effect of ZnS nanoparticle concentration on UV-vis spectra: To prepare different concentration of ZnS nanoparticles, the aqueous micellar solution containing Zn(OAc)2 was added dropwise to another containing Na2S with constant stirring. The solution was then allowed to stand for about two hours for stabilization at room temperature. The concentrations of Zn(OAc)2 in aqueous micellar solution were varied between 0.1-0.5 mM. As mention in result and discussion section, in excess of sulfide ions, the concentration of ZnS nanoparticles can be taken directly proportional to that of Zn2+ ions.
Fig. S4: UV-vis absorption spectra of different ZnS nanoparticles concentrations prepared in fixed 3 mM aqueous CPyC and CTAC. [ZnS]: (1) 0.5 mM, (2) 0.4 mM, (3) 0.3 mM, (4) 0.2 mM, (5) 0.1 mM
The ZnS nanoparticles in aqueous micellar media were then subjected to UV-vis spectroscopic measurements.Therepresentative UV-visible spectra of ZnS nanodispersion in 3 mM aqueous CPyC and CTAC as a function of [ZnS] (0.1 mM – 0.5 mM) are shown in Fig. S4. The increase in absorbance of spectra with increasing salt concentration reflects formation of more ZnS nanoparticles in accordance with Lambert-beer law of absorbance. Therefore, we can infer that smaller the number absorbing species lesser is the absorbance of the UV-vis spectra.
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