Conference Paper

Facile Synthesis of Anatase TiO2 Quantum Dot/ Graphene Nanosheet Composites with Enhanced Electrochemical Performance for Lithium-Ion Batteries

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1. Introduction With rising interest in green electrode materials for lithium-ion batteries (LIBs), increasing attention has been paid to titanium dioxide (TiO2) anode material in recent years because of its long cycle life, low cost, and minimum environmental impact. Moreover, the relatively high lithium insertion /extraction voltage of a TiO2 anode (higher than 1.5 V vs Li+/Li) can efficiently avoid the formation of SEI layers and lithium plating on the anode, which improves the safety of the batteries as compared with its carbon-based counterparts. However, many potential electrode materials (e.g., TiO2) in Li-ion batteries are limited by poor electron transport, slow Li-ion diffusion in electrodes, and increased resistance at the interface of electrode/electrolyte at high chargedischarge rates. Graphene, which has exceptional electrical, mechanical, optical, and surface properties, is widely utilized to prepare various hybrid materials. The graphene substrate itself can be contributory to the improved electrochemical performance because it may enhance the electronic conductivity of the overall electrode[1]. It is noteworthy, on the other hand, that the size and dispersion of nanoparticles on graphene are crucial factors for improving cell performance because small particle size plus good dispersion (e.g., down to several nanometers) can endow the composite electrode a superior high surface area to buffer the volume change of the particles, but it could also bring the required conductivity to individual nanoparticles and shorten the diffusion length for Li ions, which are beneficial for high lithium storage and rate capability, respectively. However, most metal oxide/graphene composites prepared so far have the high level of metal oxides accompanied with the partial aggregation of particles may also result in the rapid capacity loss and poor cycle performance. Therefore, it remains a challenge to develop a facile and general approach for the synthesis of well-dispersed MOx (e.g., TiO2) Quantum Dots/Graphene composites with favored structures for high-performance lithium-ion batteries (LIBs). 2. Experimental Section 2.1 Synthesis of graphene oxide (GO) The graphite oxide was synthesized from natural graphite flake (Alfa Aesar, 325 mesh) by a modified Hummers method. As-prepared graphite oxide was dispersed in water by ultrasonication for 30 min, followed by a low-speed centrifugation to get rid of any aggregated GO. 2.2 Preparation of TiO2 quantum dots /Graphene nanosheets (TiO2-QDs/GNs) Composites In a typical experimental procedure, 5.8 g of CTAB was dissolved in a mixture of 10 ml of n-pentanol and 60 ml of n-hexane; Then, the 10 ml GO aqueous dispersion (1 mg mL-1) was slowly poured and intensely stirred for 30 min at room temperature. Subsequently, with the formation of a golden water-in-oil emulsion. Then 0.8 ml of Titanium(III) chloride was added to golden water-in-oil emulsion while stirring. The achieved transparent microemulsions were poured into a Teflon-lined stainless steel autoclave (100 ml), and then placed in an oven maintaining 200°C for 6 h. The collected precipitates were treated under reduced pressure in a rotary evaporator to remove the volatile organic reagents and then repeatedly washed with water and ethanol to remove surfactants and other impurities. The final samples were dried at 80 °C for 2 h for further characterizations. 3. Results and Discussion In summary, we report a facile method to synthesize well-dispersed TiO2 quantum dots (6±2 nm) on graphene nanosheets (TiO2-QDs/GNs) in a water-in-oil (W/O) emulsion system (Figure 1). The prepared TiO2/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (190 mA h g-1 after 100 cycles), high Coulombic efficiency (over 96%), excellent cycling stability and high rate capability (as high as 144 mA h g-1 at 10 C, 135 mA h g-1 at 20 C, 124 mA h g-1 at 30 C and 101 mA h g-1 at 50 C, respectively). Very significantly, the preparation method employed can be easily adapted and may offer an attractive alternative approach for preparation of the highly dispersed nanosized graphene-based nanostructured composites as promising applications in various energy-storage devices high performance electrodes for various energy-storage devices. Figure 1 Electrochemical measurements of (a) TiO2-QDs/GNs and (b) TiO2-QDs electrodes. Inset in Fiure 1 is the Schematic of synthesis steps for TiO2-QDs/GNs composite. References [1] R. W. Mo, Y. Du, N. Q. Zhang, D. Rooney, K. N. Sun, Chem. Commun. 2013, 49, 9143.

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... The capacity is higher than the TiO 2 /reduced-GO anode reported previously, e.g. 190 mAh g −1 at 320 mA g −1 [313], 161 mAh g −1 at 170 mA g −1 [314], 200 mAh g −1 at 100 mA g −1 [315] or 175 mAh g −1 at 100 mA g −1 [316]. This is attributed by the authors to the high-capacity Fe 3 O 4 as an auxiliary active material, and also the choice of pristine graphene rather than reduced graphene oxide (r-GO), because the electronic properties of r-GO are damaged during the oxidation-reduction process needed to prepare it. ...
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Presently, the negative electrodes of lithium-ion batteries (LIBs) is constituted by carbon-based materials that exhibit a limited specific capacity 372 mAh g−1 associated with the cycle between C and LiC6. Therefore, many efforts are currently made towards the technological development nanostructured materials in which the electrochemical processes occurs as intercalation, alloying or conversion reactions with a good accommodation of dilatation/contraction during cycling. In this review, attention is focused on advanced anode composite materials based on carbon, silicon, germanium, tin, titanium and conversion anode composite based on transition-metal oxides.
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Conformal structured TiO2-reduced graphene oxide composite nanosheets (TiO2@rGO CNS) have been synthesized by a one-step hydrothermal method. The prepared TiO2 composite features a two-dimensional (2D) structure with an ultra-large specific surface area of 269 m2 g–1 and homogeneous TiO2 nanoparticles directly grown on the surface of reduced graphene oxide (rGO) sheets. With this special architecture of 2D sheet, it gives rise to improve light-harvesting and photo-to-electron conversion efficiency. When the TiO2@rGO CNS incorporated into the photoanode, it exhibits a greatly enhanced absorption in the visible range and low charge transfer resistance of 10.16 Ω compared with that of bare TiO2-based electrode (15.22 Ω). When the rGO content in TiO2@rGO CNS is 0.8 wt%, the fabricated solar cell obtains a remarkably enhanced power conversion efficiency (up to 7.05%), compared with that of the bare TiO2-based solar cell (4.36%), where the short-circuit current density, open-circuit voltage, and fill factor of the device are 13.63 mA cm– 2, 0.712 V, and 0.69, respectively. With the above-mentioned merits, this work supplies a feasible approach for the functionalization of 2D materials decorated with controlled metal oxide nanoparticles, which is expected as a promising material in high-performance photovoltaic devices for practical applications.
The photo-Fenton process is one of the most important advanced oxidation technologies in environmental remediation. However, the poor recovery of catalysts from treated water impedes the commercialization of this process. Herein, we propose a novel approach for the preparation of TiO 2 -graphene oxide (GO)-Fe 3 O 4 with high photo-Fenton catalytic performance and capability of magnetic recovery. To realize the recovery of the catalysts, the combination of a submerged magnetic separation membrane photocatalytic reactor (SMSMPR) and TiO 2 -GO-Fe 3 O 4 was applied to degrade the refractory antibiotic organic compounds in aqueous solution. The results indicate that GO can induce better cycle and catalytic performance of the catalysts. Fe 3 O 4 can not only enhance the heterogeneous Fenton degradation of organic compounds but also provide magnetism of the photocatalyst for magnetic separation from treated water. As a result, the TiO 2 -GO-Fe 3 O 4 composite in the SMSMPR exhibits excellent photo-Fenton catalytic performance and stability for amoxicillin (AMX) degradation. Both backwashing treatment and magnetic separation in the SMSMPR could enhance the photo-Fenton catalytic activity, durability, and separation properties, promoting practical application of this approach for wastewater treatment. Two possible pathways for AMX photodegradation in the SMSMPR were analyzed by means of a Q-TOF LC/MS system, with most of the intermediates finally mineralized to CO 2 , water and inorganic ions.
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