Synthesis of Hydrophilic and Hydrophobic Carbon Nanoparticles from Benzene/Water Bilayer Solution with Femtosecond Laser Generated Plasma Filaments in Water

Abstract

We synthesized hydrophilic and hydrophobic carbon nanoparticles (CNPs) by femtosecond laser (0.8¯m, 40 fs) irradiation of the water layer of an aerated benzene/water (B/W) bilayer solution. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species such as hydroxyl radicals in a well-confined volume; i.e., plasma filament. The properties of the particle surface were controlled simply by adjusting the laser focusing position, the duration between the preparation of B/W bilayer solution and the laser irradiation. The hydrophobic CNPs appeared to be nearly identical in size and morphology to hydrophilic CNPs. Raman spectroscopy revealed that both particles had a graphitic and disordered structure; however, IR spectroscopy clearly showed that the hydroxy group is the origin of the hydrophilicity. The time evolution of particle formation, products in water, and benzene dissolution behavior in water reveals that the surface properties are determined by the concentration of benzene in water. The diluted aqueous benzene solution gave hydrophilic particles; however, the density of particles was much smaller than that formed in B/W bilayer solution. We concluded that the production of denser hydrophilic CNPs in B/W bilayer was achieved by limiting the concentration of benzene in water layer by B/W interface, and by continuously supplying benzene into water layer through B/W interface. We discuss the subsequent reaction mechanism leading to CNPs of different surface characters.

Synthesis of Fluorine‐Doped Hydrophilic Carbon Nanoparticles from Hexafluorobenzene by Femtosecond Laser Pulses

“…In addition, our procedurew orks at room temperature, at aqueous, and aeratedconditions without any harsh reagents. [17] We concluded that the productiono f dense CNPs in B/W bilayer solution was due to the continuous supply of benzene into water layer through the B/W interface. Those particles did not show hydrophilicity at all:t he particles did not move to the water layer (upper layer,F igure 1d)b ut stayed in the HFB layer (lower layer) after the addition of water followed by shaking.…”

“…The atomic composition of fluorine in the CNPs as wella so nt heir surface was highert han in previously reported methods. [17] In addition, the yield of CNPs were enhanced by using benzene/water (B/W) bilayer solution. The HFB turned dark yellow upon femtosecond laser irradiation and was accompanied by black particles (Figure 1a).…”

“…The HFB turned dark yellow upon femtosecond laser irradiation and was accompanied by black particles (Figure 1a). [17] Furthermore, we investigated that the affinity of CNPs to water was determined by the concentration of benzene in water. It was noted that no particles appeared from benzene, [16] whereas CNPs were formed from aqueous benzene under the same experimental conditions.…”

“…Those particles did not show hydrophilicity at all:t he particles did not move to the water layer (upper layer,F igure 1d)b ut stayed in the HFB layer (lower layer) after the addition of water followed by shaking. [17] Therefore, we preparedw ater/HFB( W/HFB) bilayer solutionsw ith different concentrations of HFB in the water layer.A si nt he case of B/W bilayer solution, [17] hydrophilic CNPs were formed when the concentration of HFB in water was low,t hat is, the water layer was exposed to laser pulses immediately after the preparation of W/HFBb ilayer solution: [17] In addition, the yield of CNPs were enhanced by using benzene/water (B/W) bilayer solution.…”

“…[14] In contrast, the CNPs(HFB) seemed to be highly aggregated (Figure 2a,F igure S1b), and none of the particles were isolatede ven after 100-fold dilution with HFB (Figure S1d). [19] Unlike the case of hydrophilic CNPs produced from B/W bilayer solution, [17] CNPs(W)d id not have ah ydrophilic group such as OH. [19] Unlike the case of hydrophilic CNPs produced from B/W bilayer solution, [17] CNPs(W)d id not have ah ydrophilic group such as OH.…”