Effect of Temperature and Acoustic Pressure During Ultrasound Liquid-Phase Processing of Graphite in Water

Abstract

Ultrasound-assisted liquid-phase exfoliation is a promising method for manufacturing two-dimensional materials. Understanding the effect of ultrasonication parameters such as the temperature and input power on the developed pressure field is pivotal for optimization of the process. Limited research has been carried out to determine the optimal temperature for exfoliation, with some data generating disputed results. Simply maximizing the sonication power does not necessarily produce a higher yield because of shielding. In this study, a high-temperature calibrated cavitometer was used to measure the acoustic pressure generated in different graphite solutions in deionized water at various temperatures (from 10°C to 70°C) and input power conditions (from 20% to 100%). In addition, high-speed optical imaging provided insight on the shock wave generation from transient bubble collapses under different sonication conditions. The optimal sono-exfoliation parameters were determined to be 20% input power at 10°C for graphite flake solution, and 100% input power at 40°C to 50°C for graphite powder solution.

Temperature as a key parameter for graphene sono-exfoliation in water

“…The enhancement in graphene exfoliation with temperature (as discussed previously in section 3.1) can also be explained using the schematic presented in Fig. 7 and in line with our previous work in [22] . The arrows shown in the figure indicate the quantity of SWs and bubbles/bubbly clouds in the bulk liquid.…”

“…In most cases, we see a solution temperature of 40 °C registering the largest acoustic pressure, correlating with the characterisation of the produced graphene samples, indicating that larger pressures facilitate exfoliation. As previously discussed, despite 10 °C solutions generating the largest pressures in some cases (and also demonstrated elsewhere [22] ), the dispersion of the bulk graphite is hindered at this low temperature (see Fig. 2 (d)), in addition to the increased surface tension in the solution (see Table 2 for physical properties of water), which decreases the efficiency of graphene exfoliation.…”

“…1 shows the schematic diagram of our low-frequency experimental setup used for performing ULPE of graphene. The series of ULPE experiments were performed using a Heilscher UP400St piezo-electric transducer (a titanium sonotrode tip diameter of 22 mm, operating at a frequency of 24 kHz) in DIW at different temperatures 10 ± 1 °C, 20 ± 1 °C, 40 ± 1 °C and 60 ± 1 °C (verified with an RS 52 digital thermometer) for 50 % (peak-to-peak amplitude, 23 μm) based on our previous work [22] and 60 % (for close comparison) input generator powers (peak-to-peak amplitude, 27 μm). The calculated values of acoustic energy and sonication energy for different temperatures are listed in Table 1 .…”

“…We considered acoustic energy to be a more relevant quantification parameter for these particular experiments, where the temperature of the solution is controlled by the recirculating chiller. It is also a common practice in sono-studies to use acoustic input energy or probe displacement (peak-to-peak amplitude) facilitating direct comparison with other works in the field [22] , [46] , [47] . The probe tip was immersed 10 mm below the liquid surface for all the experiments.…”

“…For this reason, this article is specifically aimed at finding the one-step facile ULPE route for producing graphene in DIW at an optimum solution temperature based on the role of cavitation dynamics and following our previous work in [22] , which opens the way for its exploitation in a wide spectrum of applications where graphene in pure water is the first choice.…”