Controllable Preparation Of Functional Inorganic Nanoparticles And Process Intensification

Microreactor technology is an emerging technology in the 21st century. With a special micro-nano structure, the mass transfer and mixing efficiencies can be greatly intensified in the microreactor. In recent years, microreactor technology has become a research hot spot in the chemical engineering field. Microporous tube-in-tube micro-channel reactor (MTMCR) is a a novel microreactor with large throughput capacity. Therefore, the MTMCR is especially suitable for the mass production of nano materials.Inorganic nanomaterials exhibit many excellent properties, such as good activity, quantum effect, etc., and show a broad application prospect. In this work, the MTMCR was adopted as a reactor to prepare quantum dots and calcium carbonate nanoparticles. The work includes the controllable synthesis of CdTe quantum dots in aqueous phase, synthesis of CdS quantum dots in the presence of erythorbic acid (EA), synthesis of CdS quantum dots in the MTMCR and controllable preparation of calcium carbonate nanoparticles in the MTMCR. The research content is as follows:1. Investigate the effect of EA on the aqueous formation of CdS quantum dots (QDs) at room temperature. The CdS QDs were prepared in water by a one-pot non-hot-injection process at room temperature without N2 protection. The Cd and S sources were CdCl2 and Na2S, respectively, together with 3-mercapto-propionic acid (MPA) as the passivating ligand. The experimental results indicated that the use of the oxygen scavenger, i.e. EA, was an important factor for the formation of the CdS QDs with good optical properties. The effects of operating conditions such as pH, MPA/Cd molar ratios and reactant concentrations on the optical properties of QDs were investigated to determine the optimum operating conditions. NMR, FT-IR, in situ absorption, and photoemission studies indicated that the high quality of the as-prepared CdS QDs was due to the reducibility of EA and the passivation of QDs surface (particularly in alkaline environment). This study indicated that the use of EA could be a reasible means to enable the formation of QDs in water at room temperature.2. Investigate EA promoted preparation of CdS QDs and the intensification of the preparation process in an MTMCR. The effects of the micropore size of the MTMCR, liquid mixing time in the MTMCR, liquid flow rate, and reactant concentration on the size and size distribution of CdS QDs were investigated. It was found that the size and size distribution of CdS QDs can be controlled in the MTMCR, and the reaction was intensified in the MTMCR. A combination of EA promoted formation technique with the MTMCR for mass production of nanoparticles may be a promising pathway for controllable preparation of QDs.3. Synthesis and optimization of CdTe QDs with the auxiliary of EA and ethanol. Without N2 protection, the CdTe QDs was prepared with CdCl2 and NaHTe as Cd source and Te source respectively, together with EA and MPA as the co-passivating ligand. The experimental results indicated that the use of the oxygen scavenger, i.e. EA, was an important factor for the formation of the CdTe QDs with good optical properties. The fluorescence intensity was improved in the presence of ethanol in the synthesis process. Effects of experimental parameters such as molar ratio of MPA/Cd, temperature, pH, reaction time and NaBH4 dosage on the optical properties of QDs was investigated. The high quality of the as-prepared CdTe QDs were due to the reducibility of EA and the passivation of QDs surface. This study indicated that the use of EA and ethanol could be a practical method to promote the optical properties of CdTe.4. Study on controllable preparation of nano-CaCO3 particles and process intensification in the MTMCR. Nano-CaCO3 particles with tunable size were synthesized via CO2/Ca(OH)2 precipitation reaction in an MTMCR with a throughput capacity up to 400 L/h for CO2 and 76.14 L/h for liquid. The overall volumetric mass-transfer coefficient (KLa) of CO2 in the MTMCR was deduced and analyzed. The effects of operating conditions including gas volumetric flow rate, initial Ca(OH)2 content, liquid volumetric flow rate, annular channel width and micropore size on particle size were investigated. The results indicated that the mass transfer in the MTMCR can be greatly intensified in contrast with a stirred tank reactor (STR), and the particle size can be well controlled by tuning the operating conditions. The as-prepared nano-CaC03 particles have an average size of 28 nm and a calcite crystal structure.