Transformation of graphene oxide by ferrous iron: Environmental implications.
Abiotic transformation of graphene oxide (GO) in aquatic environments can markedly affect the fate, transport, and effects of GO. The authors observed that ferrous iron (Fe[II])-an environmentally abundant, mild reductant-can significantly affect the physicochemical properties of GO (examined by treating aqueous GO suspensions with Fe(2+) at room temperature, with doses of 0.032 mM Fe(2+)  per mg/L, 0.08 mM Fe(2+)  per mg/L, and 0.32 mM Fe(2+)  per mg/L GO). Microscopy data showed stacking of GO nanosheets on Fe(2+) treatment. Spectroscopy evidence (X-ray diffraction, Fourier transform infrared transmission, Raman and X-ray photoelectron spectroscopy) showed significant changes in GO surface O-functionalities, in terms of loss of epoxy and carbonyl groups but increase of carboxyl group. The reduction mechanisms were verified by treating model organic molecules (styrene oxide, p-benzoquinone, and benzoic acid) resembling O-containing fragments of GO macromolecules with Fe(2+). With sedimentation and adsorption experiments (using bisphenol A as a model contaminant), the authors demonstrated that Fe(2+) reduced GOs still maintained relatively high colloidal stability, whereas their adsorption affinities were significantly enhanced. Thus, reduction of GO by mild reductants might be of greater environmental concerns than by stronger reducing agents (e.g., N2H4 and S(2-)), because the latter can result in too significant losses of surface O-functionalities and colloidal stability of GO. This interesting aspect should be given consideration in the risk assessment of GO.
College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin, China.
Fanfan
F
Wang
College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin, China.
Fang
F
Wang
College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin, China.
Guandao
G
Gao
College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin, China.
Wei
W
Chen
D000327:Adsorption; D019817:Benzoic Acid / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry; D003102:Colloids / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry / Q000648:ultrastructure; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013343:Styrenes / Q000737:chemistry; D014961:X-Ray Diffraction
D016227:Benzoquinones; D003102:Colloids; D005296:Ferrous Compounds; D010087:Oxides; D013343:Styrenes; C004532:quinone; D006108:Graphite; D019817:Benzoic Acid
Adsorption affinities; Colloidal stability; Ferrous iron reduction; Graphene oxide; Transformation