Continuous synthesis of functional silver nanoparticles using microreactor: Effect of surfactant and process parameters

In this work an attempt was made to intensify the process of nanoparticles synthesis in microreactor. Main objective of the work was to investigate the intensification of silver nanoparticles synthesis using surfactants and to study the effect of associated process parameters in microreactor such as concentration and flow rate of precursor. Reduction reaction was carried out using silver nitrate and sodium borohydride. Two surfactants namely sodium dodecyl sulfate (SDS) and N-cetyl N,N,N,trimethyl ammonium bromide (CTAB) were used to evaluate the effect on particle size by controlling nucleation and growth mechanism. Results of microreactor synthesis were compared with batch process. m parameters such as flow rates, concentrations of reactants/surfactants were determined to obtain nanosize silver colloidal particles in continuous microreactor. Results show that use of 0.02 g/mL SDS with 1 mL/min (0.001 M) AgNO3 and 3 mL/min (0.003 M) NaBH4 flow rate shows minimum particle size of 4.8 nm. From residence time distribution (RTD) data, it is found that the Peax number was highest 0.39 at Re number 67 (flow rate of 7 mL/min), which signifies the less axial dispersion. The increase in the particle size with an increase in the CTAB loading is due to the agglomeration effect that cationic CTAB, which has positive charge on head, leads to aggregation. SDS favors the reduction in particle size of silver nanoparticle.