Synthesis of Titanium Nitride Nanoparticles by Pulsed Laser Ablation in Different Aqueous and Organic Solutions

Abstract

Owing to a strong photothermal response in the near-IR spectral range and very low toxicity, titanium nitride (TiN) nanoparticles (NPs) synthesized by pulsed laser ablation in liquids (PLAL) present a novel appealing object for photo-induced therapy of cancer, but the properties of these NPs still require detailed investigation. Here, we have elaborated methods of femtosecond laser ablation from the TiN target in a variety of liquid solutions, including acetonitrile, dimethylformamide, acetone, water, and H₂O₂, to synthesize TiN NPs and clarify the effect of liquid type on the composition and properties of the formed NPs. The ablation in all solvents led to the formation of spherical NPs with a mean size depending on the liquid type, while the composition of the NPs ranged from partly oxidized TiN to almost pure TiO₂, which conditioned variations of plasmonic peak in the region of relative tissue transparency (670-700 nm). The degree of NP oxidation depended on the solvent, with much stronger oxidation for NPs prepared in aqueous solutions (especially in H₂O₂), while the ablation in organic solvents resulted in a partial formation of titanium carbides as by-products. The obtained results contribute to better understanding of the processes in reactive PLAL and can be used to design TiN NPs with desired properties for biomedical applications.

Keywords: EDX; XPS; laser ablation in aqueous and organic solutions; pulsed laser ablation in liquids; titanium nitride nanoparticles.

Figure 1

SEM characterization of NPs prepared by PLAL of TiN target in different liquids. (A–E) size histograms of H₂O₂-TiN, W-TiN, DMF-TiN, A-TiN, and AN-TiN NPs, respectively. Black curves are lognormal data fits. Insets demonstrate characteristic SEM images of the NPs. (F) Mode size of the lognormal fits of size distribution of NPs prepared in different liquids. Error bars represent distribution widths.

Figure 2

EDX characterization of synthesized TiN-based NPs. (A) Averaged background corrected EDX spectra (black line—AN-TiN NPs, red line—DMF-TiN NPs, blue line—A-TiN NPs, green line—W-TiN NPs, purple line—H₂O₂-TiN NPs, brown line—TiN ablation target). All spectra are normalized to titanium and averaged over all data points, measured on each sample. (B) Nitrogen and (C) oxygen content of synthesized NPs normalized to titanium. Values are calculated as the intensity of nitrogen peak at 0.39 keV or oxygen peak at 0.52 keV, divided by intensity of the Ti peak at 4.5 keV, respectively. (D) Ratio of nitrogen content to oxygen content in the NPs. Data in (B–D) are represented as mean ± standard deviation. At least seven different data points were measured on each sample.

Figure 3

XPS characterization of the synthesized NPs. (A) Ti 2p, (B) N 1s, (C) O 1s, and (D) C 1s electronic levels of H₂O₂-TiN (purple), W-TiN (green), A-TiN (blue), DMF-TiN (red), and AN-TiN (black) NPs.

Figure 4

Optical extinction spectra of H₂O₂-TiN (purple), W-TiN (green), A-TiN (blue), DMF-TiN (red), and AN-TiN (black) NPs measured in 10 mm optical cuvettes and normalized to mass concentration of Ti in ug/mL.