Interactions in MnCl2–Na2S–L-cysteine aqua system

Abstract

MnS nanoparticles find potential applications in advanced materials like energy storage, photocatalysis, biomedicine, etc. With the development of nanotechnology, research on the synthesis and properties of nanoscale MnS is intensifying . In this work, MnS nanoparticles stabilized by L-cysteine were synthesized at ambient temperatures by co-precipitation technique under a control of pH in acidic and basic aqueous media. The synthesis of the MnS/L-cysteine nanoparticles using typical precursors MnCl 2 and Na 2 S has been performed in two series by increasing the crystal-forming ions concentration by the order of magnitude . Control samples of Mn(OH) 2 and MnS were prepared using the same concentration of Mn 2+ as in the MnS/L-cysteine nanoparticles case. The possibility of Mn(OH) 2 nanoparticles formation as a result of the S 2- and Mn 2+ -ions interaction is discussed. Optical properties of the MnS/L-cysteine nanoparticles colloid solutions and various binary combinations of the three-component system were analyzed using UV-visible absorbance and photoluminescence (with an excitation wavelength of 405 nm) spectrophotometry. The critical concentration of L-cysteine in the system that demonstrates stabilizing action was determined . The conditions for the formation of MnS nanoparticles stabilized by L-cysteine or L-serine molecules and the dependence of the size of the obtained MnS nanoparticles on the increase in the concentration of crystal-forming ions are discussed. The effect of intensification of photoluminescence in the synthesis of nanoparticles MnS/L-Cys in the alkaline conditions was revealed. It is assumed that the products of the system components interaction are manganese sulfide nanoparticles stabilized by the L-cysteine and manganese hydroxide capable of being oxidized by atmospheric oxygen. Keywords: nanoparticles, manganese (II) sulphide, synthesis, absorption spectra, photoluminescence.