Photochemical Transformation of Graphene Oxide in Sunlight

Abstract

Graphene oxide (GO) is promising in scalable production and has useful properties that include semiconducting behavior, catalytic reactivity, and aqueous dispersibility. In this study, we investigated the photochemical fate of GO under environmentally relevant sunlight conditions. The results indicate that GO readily photoreacts under simulated sunlight with the potential involvement of electron-hole pair creation. GO was shown to photodisproportionate to CO2, reduced materials similar to reduced GO (rGO) that are fragmented compared to the starting material, and low molecular-weight (LMW) species. Kinetic studies show that the rate of the initially rapid photoreaction of GO is insensitive to the dissolved oxygen content. In contrast, at longer time points (>10 h), the presence of dissolved oxygen led to a greater production of CO2 than the same GO material under N2-saturated conditions. Regardless, the rGO species themselves persist after extended irradiation equivalent to 2 months in natural sunlight, even in the presence of dissolved oxygen. Overall, our findings indicate that GO phototransforms rapidly under sunlight exposure, resulting in chemically reduced and persistent photoproducts that are likely to exhibit transport and toxic properties unique from parent GO.

Photochlorination-induced transformation of graphene oxide: Mechanism and environmental fate

“…To date, only a few studies have focused on the transformation of GO in conditions similar and/or relevant to the natural environment Feng et al, 2015;Hou et al, 2015Hou et al, , 2016. Some of these studies have shown that sunlight is able to induce some physicochemical changes to the nanomaterials when present in aqueous media.…”

“…Concurrent or subsequent sunlight irradiation of chlorinated GO may result in further transformation, affecting further the physicochemical properties (and thus, environmental implications) of GO. This potential transformation of GO by photochlorination has not received much attention as most existing studies on the environmental fate of GO focused on its colloidal stability and sunlightinduced transformations (Chowdhury et al, 2013Wu et al, 2013;Hou et al, 2015).…”

Solar mediated reduction of graphene oxide

“…46 However, the experimental evidences have shown a reverse behaviour. Interestingly, sRGO has showed enhanced conductivity compared to RGO samples prepared through other routes.…”

Current applications of graphene oxide in nanomedicine

“…If this potential can then be coupled with the digitization and real-time monitoring of the cell sample (microdroplets), GO could be clinically exploited in the very near future. In our humble opinion, the great expectations fueling graphene-based research warrant a "digital shotgun" approach, thus clarifying any doubts regarding its efficacy and applicability not just in nanomedicine, but its future impact on environmental 181 and public health.…”