Synthesis And Application Of Rice-like TiO₂/Graphene Composite Hydrogels

Graphene oxide?GO?was first prepared using the graphite as raw material through a modified Hummers method.Rice-like titanium oxide?TiO₂?/graphene hydrogel?RTGH?was then synthesized by a facile one-pot hydrothermal method using tetrabutyl titanate as the titanium source and sodium citrate?SC?as the structure-directing agent.During the hydrothermal process,rice-like TiO₂nanoparticles were formed with the induction of SC.Meanwhile,GO was reduced to reduced graphene oxide at high temperature.The structure and composition of the samples were characterized by a variety of test methods.The results showed that the as-prepared GO was monolayer,and the TiO₂ nanoparticles revealed the anatase-type structure with typical diameters of 15–40 nm and lengths of 40–100 nm.The synthesized graphene-based composite hydrogel is a black cylinder from the macroscopic point of view and a three-dimensional hierarchical pore structure from the microcosmic point of view.The pore size ranges from sub-micrometers to several micrometers,and pore walls are composed of graphene sheets stacked on each other.In order to investigate the dye adsorption properties of the materials,the prepared hydrogels were freeze-dried into aerogels?RTGA?and then immersed in the methylene blue?MB?solution for adsorption.UV-vis analysis showed that the resulting aerogel was a high-efficiency adsorbent,especially the sample RTGA3-12,which could complete the decolorization of the MB solution within 2 h.More importantly,the obtained graphene-based composite hydrogels were used as the electrodes for supercapacitors to test the electrochemical properties with using 1 mol L^-1 H₂SO₄ as the electrolyte.The three-electrode and two-electrode systems were both used.The results showed that RTGH exhibited more excellent electrochemical performance than pristine graphene hydrogel?GH?,P25/GH,and RTGH-blank.Obviously,the CV curves of RTGH exhibited a more quasi-rectangular shape,the Nyquist plots were closer to the imaginary axis,and the charge curves were more symmetrical with the discharge curves.Among these electrodes,the capacitance behavior of RTGH3-12 was the most remarkable.In the three-electrode system,the specific capacitance of RTGH3-12 was 372.3 F g^-1 at a current density of 0.2 A g^-1 and decreased to 294.4 F g^-1 when the current density increased to 32 A g^-1,indicating that RTGH3-12 has excellent rate performance.The cyclic stability of RTGH3-12 wastested at 8 A g^-1 with a specific capacitance retention of 98.3%after 2000charge/discharge cycles.Furthermore,the capacitance behavior of the assembled supercapacitors was not significantly reduced in a two-electrode system.The specific capacitance of RTGH3-12 was 332.6 F g^-1 at 0.2 A g^-1 and decreased to 256 F g^-1when the current density increased to 32 A g^-1.In addition,the stability test of RTGH3-12 was performed based on the conventional GCD test and floating technique at 4 A g^-1.The findings indicated that the RTGH3-12 had good stability with a capacitance retention ratio of 91.4%after 2000 charge/discharge cycles and 75.4%after 120 h of floating test.In short,the synergistic interaction between rice-like TiO₂nanoparticles and the graphene network with high specific surface greatly improved the adsorption and electrochemical performances of RTGHs.