Lateral size reduction of graphene oxide preserving its electronic properties and chemical functionality

Abstract

A simple and effective approach to control the lateral size of graphene oxide maintaining its characteristics while enhancing its applications.

High-Yield Production of Nano-Lateral Size Graphene Oxide by High-Power Ultrasonication

“…It is noticeable that most of the lateral dimensions reduction occurs in the first 2 h (Figure 4B). This fast initial effect was also reported in the abovementioned work by Méndez-Romero and coworkers [10]. The initially large concentration of defects in graphene oxide's basal plane (lower dissociation energy related to sp 3 bonding) facilitates sheet breakup caused by the high-shear forces associated with ultrasound's acoustic cavitation.…”

“…As previously mentioned, the higher energy applied during contact the high-power sonication probe in multiple recirculation cycles, could have contributed for a slight reduction of GOn. Similarly, Méndez-Romero and coworkers reported a slight increase in C/O ratio, ranging from 1.95 to 2.01, for their GOn exposed to increasing times of high-power ultrasonication [10]. It is important to notice that, in our method, we produce GOn directly from GtO, contrary to the previously mentioned work, where previously exfoliated GO (not GtO) is size reduced.…”

“…Even more striking is the fact that the dispersion concentration was significantly higher for GOn than for GO (7.5 mg mL -1 and 1 mg mL -1 , respectively). Méndez-Romero and coworkers reported that zeta potential did not tend to change with lateral size for their GOn produced by high-power ultrasonication, however, they did not evaluate colloidal stability [10]. Generally, smaller average particle size and coefficient of variation (ratio of the standard deviation to the mean particle size), together with lower zeta potential values, have been identified as critical parameters to demonstrate dispersion stability of GO materials, thus favoring the production of homogeneous GO dispersions at larger scales and with improved product quality [14,15].…”

“…Ultrasonication is actually already used in combination with the Hummers or Marcano methods of GO production, in order to achieve the final exfoliation and dispersion of GO flakes in liquid medium, albeit most often using low-power bath immersion systems and therefore not inducing significant changes in lateral dimensions [9]. The first use of high-power ultrasound treatment for effective reduction of GO's lateral dimensions was recently reported by Méndez-Romero and coworkers [10]. GO was first produced by the modified Hummers method, having been exfoliated for 1 hour in a low-power ultrasonic bath in the last step.…”

Methods to Scale Down Graphene Oxide Size and Size Implication in Anti-cancer Applications

“…The product that is obtained is a reduced graphene oxide, rGO, in which sp 2 domains restored by reduction and residual oxygenated functional groups coexist. Mèndez-Romero et al have recently reported a simple but highly effective approach to prepare GO around 100 nm in lateral dimension and high concentration by ultrasound in low-temperature conditions, without alteration of electronic properties and excellent solubility in water ( Méndez-Romero et al, 2020 ). Their procedure consists of sonicating an aqueous dispersion of GO (3mg mL –1 ) with an ultrasonic probe operating at a 40% amplitude while keeping the temperature strictly controlled at 18°C for 4 h. The dynamic light scattering (DLS) analysis of the samples taken at regular time intervals (every 30 min for a total of 4 h) shows that the lateral size of the flakes decreases significantly in the first 2 h of the process from 500 nm to about 100 nm, reached 100 nm, the size decreases more slowly as the time of sonication increases.…”