Effect of pH Variation on the Structural and Optoelectronic Properties of Zinc Sulfide Nanoparticles Capped with Sodium Carboxymethyl Cellulose

This work presents the required pH value for the synthesis of ZnS semiconductor nanocrystals capped with sodium carboxymethyl cellulose (CMC). The nanoparticles were synthesized using the precipitation technique. Structural, morphological and optical properties of nanoparticles synthesized at different pH values were investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and photoluminescence studies (PL). The structure of the nanoparticles is predominantly cubic zinc blende except for nanoparticles synthesized at pH 10 which is oxidized. All samples show agglomeration of particles with smooth surfaces. FTIR spectrum confirms the interaction of ZnS with CMC. The energy band gap shows stoke shift of 0.53-0.60 eV indicating quantum confinement effect. The obtained results show that nanoparticles stability is obtained at pH value of 4.0, 7.0 and 8.0 of precursor-surfactant mixture. These pH values maintain the viscosity of sodium carboxymethyl cellulose and hence the stability of nanoparticles over time. PL shows enhanced emission intensity for samples at these three pH values.