Changes Of Chemical Structure And Performance Of Graphene Oxide Exposed To Oxidation Environment

Owing to their superior properties,graphene-family nanomaterials have been applied in various fields.Their release into environment seems an inevitable consequence of the massive future application of these carbonaceous materials.The increasing production of graphene oxide(GO)has raised concerns about its potential health and ecological risks since the early 2010 s,which calls for immediate attention on its efficient removal technology.However,most of the existing literatures on water treatment often regard GO as a photocatalyst,adsorbent and catalyst support,rather than a potential contaminant.Here we report that GO can be oxidized by UV/H2O2 and UV/persulfate(PS).Their changes in chemical structure and performance are studied.Main original conclusions are:(1)The overall oxygen-containing functionalities of GO dramatically declined after oxidation by UV/H2O2 and UV/PS system.After radicals attack,sheet-like GO was destructed into lots of flakes.The extent of mineralization of GO was 81.2% and 13.8% in UV/PS and UV/H2O2 system,respectively.Therefore,UV/PS system is capable to be an efficient removal technology of GO.In addition,this study indicates GO can be destructed upon the radicals attack when it is used as a support or catalyst in producing sulfate radicals from PS or peroxymonosulfate(PMS)activation.Therefore,special attention on GO stability should be given while GO-based nanocomposites are used in advanced oxidation processes where highly reactive radicals are abundant.(2)Given that GO structure would be changed in advanced oxidation processes,their removal efficiency of methylene blue(MB)is investigated.Results indicated that after the oxidation,the functional groups on GOs began to decrease after the first one hour.Pseudo-second-order kinetic model can better describe kinetics of adsorption with R2 > 0.999.The adsorption data fitted well the Langmuir model with the maximum adsorption amount(samples after 1,2,4 h oxidation in UV/H2O2 and UV/PS system)of 580.26,591.80,598.63,521.77,554.91 and 568.00 mg/g,respectively.The adsorption nature of GOs decreased particularly in UV/PS system with an increase of oxidation time.