Amphiphilic Janus Particles for Aerobic Alcohol Oxidation in Oil Foams

Abstract

Amphiphilic Janus silica particles, tunable with oleophobic-oleophilic properties and low fluorine content (8 wt % F), exhibited prominent foamability for a variety of aromatic alcohols at low particle concentrations (<1 wt %) compared to randomly functionalized silica particles. When selectively loaded with Pd nanoparticles on the oleophilic hemisphere, the particles displayed more than a 2-fold increase in catalytic activity for the aerobic oxidation of benzyl alcohol compared to nonfoam bulk catalysis under ambient O₂ pressure. The particles were conveniently recycled with high foamability and catalytic activity maintained for at least five consecutive runs.

Figure 1

(a) FT-IR and (b) PiFM spectra of pristine silica, JPs, and non-JPs. The green line indicates the location of the C–F stretching vibrations.

Figure 2

Topography, PiFM at 1145 cm^–1 and HR-TEM micrographs of (a1–a3) pristine silica, (b1–b3) Pd/JPs, and (c1–c3) Pd/non-JPs. The dark blue and green colors in a₂–c₂ refer to fluorocarbon chains and Si–O–Si moieties with bands at 1145 and 1085 cm^–1, respectively.

Figure 3

Contact angle and foamability of JPs and non-JPs with (a, d) BnOH, (b, e) mixture, and (c, f) o-xylene. Foaming conditions: 1.8 mL of solvent, 1 wt % particles, 1500 rpm, 100 °C, 1 h.

Figure 4

(a) Morphology and foamability of JPs in a BnOH–o-xylene (1:1 v/v) mixture at room temperature and variable JP loading. The bar size is 500 μm. (b) Evolution of the foam height (left ordinate axis) and average bubble (right ordinate axis) against the particle concentration. Foaming conditions: 0.8 mL of BnOH, 0.8 mL of o-xylene, 0.5–4.0 wt % JPs, 1500 rpm, 100 °C, 1 h.

Figure 5

(a) Morphology and foam stability of JPs in BnOH–o-xylene (1:1 v/v) mixture at room temperature and 1 wt % JP loading. The space bar size is 500 μm. (b) Time evolution of foam height and average bubble size. Foaming conditions: 0.8 mL of BnOH, 0.8 mL of o-xylene, 1 wt % JPs, 1500 rpm, 100 °C, 1 h, kept static at room temperature.

Figure 6

(a) Aerobic oxidation of BnOH over Pd/JPs and Pd/non-JPs. Reaction conditions: 0.8 mL of BnOH, 0.8 mL of o-xylene, O₂ balloon, 1 wt % particles, 1500 rpm, 100 °C, 1 h. (b) Kinetic profiles for the aerobic oxidation of BnOH over Pd/JPs and Pd/non-JPs. Reaction conditions: 0.8 mL of BnOH, 0.8 mL of o-xylene, an O₂ balloon, 1 wt % particles, 1000 and 1500 rpm, 100 °C, variable reaction time.

Figure 7

Recyclability and reuse of Pd/JPs for the aerobic oxidation of BnOH over five consecutive runs. Reaction conditions: 0.8 mL of BnOH, 0.8 mL of o-xylene, 1 wt % Pd/JPs, 1 bar O₂ balloon, 1500 rpm, 100 °C, 1 h.