| In this work,A facile strategy was developed to fabricate net-like hematite nanoparticle/graphene oxide?GO?composite?NHG?,which involved two steps:?1?preparation of precursor?-FeOOH/graphene nano composite;?2?annealing the precursor in air atmosphere.After annealing,the product still remained graphene-like platform structure.By preparing control examples and characterization of intermediates in different temperature rising stages,we understand the formation mechanism and essential conditions of the net-like nanostructure.With the help of transmission electron microscopy?TEM?and X-ray spectroscopy?XPS?,the residual graphene in the composite was proven to be oxidized and transformed into graphene oxide after thermal annealing.What's more,in the composite,the degree of oxidization of graphene oxide could be controlled by simply changing annealing time.As a result,the band gap of graphene oxide can also be tuned correspondingly.In the photocatalytic water oxidation experiment,NHG with graphene oxide of appropriate oxidization degree and content exhibited much higher photocatalytic water oxidation rate(150?mol h–1g–1)than?-Fe2O3 nanorods(110?mol h–1g–1)and commercial?-Fe2O3(30?mol h–1g–1).Also,much better photoelectrochemical water splitting performance(0.86 mA cm-2at 1.6 V vs.reversible hydrogen electrode?RHE?,illumination intensity:AM 1.5G,100 mW/cm2)was achieved by NHG commercial?-Fe2O3 and?-Fe2O3 nanorods.The mechanism of this enhancement is discussed in detail.Combination of specific surface area analysis,surface chemical states analysis and energy level diagram of different components in the composite,the superiority is attributed to the fact that the photoinduced holes can be transferred from the valance band of?-Fe2O3 to that of GO,and GO replaces?-Fe2O3 as the reaction interface where holes inject into water to speed up the oxygen evolution rate.Fundamentally,the speed of the injection of holes into water is very slow for?-Fe2O3,but fast for GO.Moreover,due to the serious surface recombination,the lifetimes of photogenerated holes in?-Fe2O3 are extremely short,while relatively long in GO.What's more,GO prepared by annealing in air atmosphere is much different from that prepared by traditional Hummers method.GO obtained by annealing in air atmosphere is not readily reduced under illumination,for the photocatalytic water oxidation rate of NHGs did not showed any decreasing trend.So it is more stable than those obtained by Hummers method.GO aqueous solution prepared by Hummers method is easily reduced under illumination for 2 hours.In addition,the preparation method of photoanode film was described in detail,and essential steps in the method were highlighted.Photoanode films of different thickness were prepared,and corresponding absorption spectra were conducted and analysed to explore the influence of photoanode film on the optic property.Furthermore,the strategy presented here could be expanded as a general method to synthesize other types of net-like structured photocatalysts modified with GO for applications in water splitting. |
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