Environment friendly dual-frequency ultrasonic exfoliation of few-layer graphene

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

“…At the same time, the populated bubbly structure (increasing the temperature increases the tendency of more cloud formations due to higher vapour pressures ( Table 2 )) vigorously oscillates at the incident frequency and corresponding harmonics, synergistically promoting a gentle exfoliation of graphite, generating high quality graphene flakes. Results are in-line with our previous work, where we showed that a combination of high and low frequencies have the potential to alleviate the powerful SWs and populate the liquid with tiny bubbles that can also expedite the exfoliation process and produce high-quality flakes [13] . Hence, the key for successful and high-quality exfoliation is the control of temperature and power that will induce the right amount of acoustic energy to promote gentle exfoliation.…”

“…Although, exfoliating graphene in pure water is a challenging task, by optimising and controlling the input power and bulk temperature of water during ultrasonic processing, we can alleviate this problem to a great extent and produce flakes of high quality. In particular, our group recently developed a technique that generated high quality few layer graphene (FLG) flakes in a range of 3–5 layers (Ls) using a dual frequency approach in pure water [12] , [13] under controlled temperature. However, the particular temperature of 40 °C has been empirically chosen based on the existing literature without a solid scientific rationale behind this choice, and this what we aim to address in this work.…”

Direct Evidence of the Exfoliation Efficiency and Graphene Dispersibility of Green Solvents toward Sustainable Graphene Production

“…Typically, 1-methyl-2-pyrrolidone (NMP) or dimethylformamide (DMF) is used as a solvent in LPE since both are ideal for exfoliating graphite and producing stable dispersions of graphene . However, their toxicity and high boiling points, for example, 153 and 202 °C for DMF and NMP, respectively, are an issue in the context of sustainable graphene manufacturing, and therefore, alternative LPE solutions must be sought out. − High-boiling-point solvents are difficult to remove and result in major loss of the material, degradation of the material quality, and the generation of toxic waste. , Therefore, major significant efforts have gone into finding suitable and sustainable solvent alternatives, so-called green solvents. , Green solvents are eco-friendly solvents with low boiling points, for example, <100 °C, and low toxicity . Although previous work has shown that green solvents can indeed be used to produce graphene by means of LPE, it has not progressed much further.…”

“… 9 − 14 High-boiling-point solvents are difficult to remove and result in major loss of the material, degradation of the material quality, and the generation of toxic waste. 13 , 15 Therefore, major significant efforts have gone into finding suitable and sustainable solvent alternatives, so-called green solvents. 13 , 16 Green solvents are eco-friendly solvents with low boiling points, for example, <100 °C, and low toxicity.…”

Direct evidence of exfoliation efficiency and graphene dispersibility of green solvents towards sustainable graphene production

“…[9][10][11][12][13][14] High-boiling point solvents are difficult to remove and result in major loss of material, degradation of material quality and the generation of toxic waste. 13,15,16 Therefore, major significant efforts have gone into finding suitable and sustainable solvent alternatives, so-called green solvents. 13,17 Green solvents are eco-friendly solvents with low boiling points, e.g., < 100 ˚C, and low toxicity.…”