Morphology-Controlled CaCO3 Nanostructures by Modified Co-Precipitation in Pulsed Mode

Calcium carbonate nanoparticles and nanorods were synthesized by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions through co precipitation method. A new rout of synthesis was done by both using pulsed mixing method and controlling the addition of calcium nitrate. The effect of the agitation speed, and the temperature on particle size and morphology were investigated. Particles were characterized using X-ray Microanalysis, X-ray analysis (XRD) and scanning electron microscopy (SEM). The results indicated that increasing the mixer rotation speed from 3425 to 15900 (rpm) decreases the average particle size to 64±7 nm. A rapid nucleation then aggregation induced by excessive shear force phenomena could explain this observation. Moreover, by increasing the reaction temperature, the products were converted from nanoparticle to nanorods. The maximum attainable aspect ratio was 6.23 at temperature of 75°C and rotation speed of 3425. Generally, temperature raise promoted a significant homoepitaxial growth in one direction toward the formation of calcite nanorods. Overall, this study can open new avenues to control the morphology of the calcium carbonate nanostructures.

Continuous Flow Controlled Synthesis of Gold Nanoparticles Using Pulsed Mixing Microfluidic System

To prepare the gold nanoparticles (AuNPs) with uniform sizes, fine morphology, and good monodispersity, a pulsed mixing microfluidic system based on PZT actuation was presented. The system includes PZT micropump and Y type micromixer. By adjusting voltage (entrance flow rate), pulsed frequency, phase, and other parameters, a variety of mixing modes can be achieved, so as to realize the controllable synthesis of nanoparticles in a certain range. By numerical simulation and analysis, the channel section size, entrance angle, and pulse frequency were optimized. Based on the optimized structure and working parameters, the test prototype has been manufactured in lab, and the related synthesis tests of AuNPs were carried out. The test results indicate that AuNPs with uniform morphology and good monodispersity can be synthesized using the system with the section size (0.4 mm × 0.4 mm), the entrance channel angle (60°) under condition of the pulsed frequency (300 Hz), and the entrance flow rate (4 mL/min). The average diameter and its standard deviation of AuNPs synthesized were 21.6 nm, 4.83 nm, respectively. The research work above can be applied to the fields such as the controlled synthesis of noble metal nanoparticles, biomedicine, and microchemical system.

High-Speed Pulsed Mixing With High-Frequency Switching of Pumping From Three Micropumps

In this study, we proposed a novel mixing method using alternate pulsed flows from three inlet channels using three piezoelectric valveless micropumps. Two solutions are assigned into one micropump and the other two micropumps, respectively. The fabricated microfluidic device consists of a cross-shaped mixing channel with three inlet microchannels and three valveless micropumps. According to the experimental results, it was confirmed that the pulsed mixing using three inlet microchannels increased mixing speed with increasing the switching frequency of the micropump driving up to 200 Hz. The proposed method solved the problem of a bias of concentration ratio near the sidewalls which has happened in the previous pulsed mixing method using T- or Y-shaped microchannel with two inlet microchannels. Furthermore, by controlling a solution flow at the confluent area utilizing a reverse flow of the micropump, the mixing speed dramatically increased and the mixing time of 3.6 ms for 90% mixing ratio was achieved at the micropumps switching of 400 Hz.