Controllable synthesis of silver nanoparticles using a multi-stage microfluidic reactor driven by two valveless piezoelectric pumps

Combining microfluidics and piezoelectric drive technology, a controllable synthesis method of silver nanoparticles (AgNPs) is proposed, which uses a multi-stage microfluidic reactor driven by two valveless piezoelectric pumps. First, the liquid-phase synthesis mechanism of AgNPs and the working principle of the reactor were analyzed. Then, in order to investigate the influence of working parameters, reductant concentration, and polyvinylpyrrolidone (PVP) addition or not on the synthesis of AgNPs, a series of related experiments were carried out. The synthesized AgNPs were characterized by UV-spectrometer and transmission electron microscope (TEM). Experimental results show that the operating parameters of the reactor have an effect on the particle size, concentration, and homogeneity of the synthesized AgNPs. Among them, the mixing reaction performance of this reactor is gradually enhanced during the driving voltage increase from 30 Vpp to 120 Vpp. During this period, the average particle size of AgNPs in colloids increase from 24.67 nm to 25.93 nm and the concentration increase from 0.541 to 1.602. while the particle size deviation decreases from 7.03 nm to 4.15 nm, that is, the homogeneity gradually became better. As the concentration ratio of reductant to precursor increases from 0.5:1–4:1, the average particle size of AgNPs synthesized in the colloid gradually increases from 21.35 nm to 28.19 nm. However, the concentration of AgNPs in the colloid increases and then decreases, and the homogeneity becomes better and then worse. Especially, when the concentration ratio of reductant to precursor is 2:1, the synthesized AgNPs have higher concentration and smaller particle size deviation. Adding a reasonable amount of protectant (mPVP/mAg=1.5) can effectively inhibit the agglomeration of the synthesized AgNPs, and can ensure the preparation of AgNPs with good homogeneity and monodispersity. The related research shows that the proposed multi-state microfluidic reactor driven by two valveless piezoelectric pumps has good mixing reaction performance, and can be applied to the controllable synthesis of high-quality AgNPs under suitable conditions.