Preparation of ZnS nanoparticles by electrospray pyrolysis

Zinc sulfide particles 20-40 nm in diameter were prepared by electrically d riven spray pyrolysis. Solutions of ethyl alcohol with zinc nitrate (Zn(NO3 )(2)) and thiourea (SC(NH2)(2)) at concentrations from 0.0025 to 0.2mol1(-1 ) and electrical conductivities between 10(-4) and 10(-1) Sm-1 were electro sprayed from steady cone-jets at flow rates from 0.05 to 0.16 ml h(-1), wit h positive and negative polarity. The initially highly charged drops formed were neutralized by bipolar ions from a radioactive source to increase the overall transmission efficiency through a reactor furnace. This process wa s made particularly effective by the innovation of placing the ion source d irectly within the electrospray chamber. The diameters of the final ZnS par ticles were measured on-line by a differential mobility analyzer and a cond ensation nucleus counter. In spite of ambiguities in the flow rate of liqui d through the cone-jet associated to solvent evaporation from the meniscus) , these diameters agree approximately with values expected from available s caling laws. Transmission electron micrographs also confirmed these results . Electrospray pyrolysis is hence able to generate non-agglomerated and sph erical ZnS nano;articles with geometrical standard deviation sigma(g) of ab out 1.3. (C) 1999 Elsevier Science Ltd. All rights reserved.