Synthesis of Nanoparticles Using an Atmospheric Pressure Plasma Jet

Nanocrystalline N-doped ZnO, N-doped TiO2, and Li4Ti5O12 particles are synthesized by an atmospheric pressure plasma jet (APPJ). This APPJ is sustained using a repetitive pulse source with nitrogen or oxygen as the plasma gas. This system can sustain a stable plasma jet, allowing for a long treatment time. Nebulizer-generated precursor droplets are sprayed into the plasma jet, resulting in the fabrication of metal oxide particles within a very short time (ms).
This process is divided into three parts. First, Zn(NO3)2 solutions with NaNO3 are -sized droplets and fed into the downstream region of the APPJ. Salt solution droplets undergo vaporization and react to form solid particles in the downstream region of the jet. This process is a salt-assisted spray pyrolysis(SASP)-like process. During this SASP process, when the droplet temperature exceeds the melting point of the salt, the salts melt and act as high-temperature solvents and the particle size is about 50 nm from SEM images. The particles are collected using de-ionized water. The doping level is changed by controlling plasma flow rate.
Second, using the same system, N-TiO2 particles are synthesized by injecting the TTIP vapor into the plasma jet with a bubbler. The particle size, size distribution, and morphology are characterized by TEM, and particle composition is analyzed by XPS spectra.
Third, Li/Ti solution droplets undergo O2 and N2 plasma treatment and Li4Ti5O12 particles are synthesized using the same system. The as-prepared powder is crystallized Li4Ti5O12, as observed. The morphologies and particle size are controlled by simple system parameter (with/without pre-heater, carrier gas flow rate, concentration of precursor). We also propose a possible mechanism for the formation of particles with different morphologies.
As discussed in this thesis, the evolution of the particle upon entering the pre-heater followed by plasma treatment is sensitive to the carrier gas flow rate (resident time in pre-heater), the presence of the pre-heater, and the precursor concentration. In the plasma, the high temperature resulting solvent evaporation rate much higher than the solute diffusion rate resulting in hollow particles. In pre-heater(Tpre-heater < Tplasma),the solvent evaporate rate is nearly to the solute diffusion rate resulting in dense particles. The experiment of the morphology are summarized in this thesis.