TiO2-reduced Graphene Oxide Nanocomposites Research Articles

Reduced graphene oxide embedded titanium dioxide nanocomposite as novel photoanode material in natural dye-sensitized solar cells

Dye-sensitized solar cells were fabricated using the natural dye anthocyanin extracted from Nerium oleander, Ixora coccinea and Erythrina variegata flowers with sol–gel routed TiO2-reduced graphene oxide nanocomposite photoanode. X-ray diffraction analysis of TiO2-reduced graphene oxide nanocomposites proved the anatase phase titania. Scanning electron microscope analysis confirmed the incorporation of reduced graphene oxide in TiO2 matrix. Transmission electron microscopic analysis established the dispersion of reduced graphene oxide in TiO2 network. The influence of reduced graphene oxide on the band gap and life-time of electron–hole pair in TiO2-reduced graphene oxide nanocomposites was observed from ultra violet–visible and photoluminescence spectra respectively. Fourier transform infra-red analysis confirmed the expected interaction between TiO2 and reduced graphene oxide. An increase in electrical conductivity was observed in TiO2-redcued graphene oxide nanocomposites than the pristine TiO2. The optimized TiO2-redcued graphene oxide nanocomposite was used as an anode material in the construction of dye-sensitized solar cells and the performance was studied by photocurrent–voltage characteristics and electrochemical impedance spectroscopy. The solar cells with TiO2-redcued graphene oxide nanocomposite photo anode exhibited enhanced efficiency of 0.47–0.57%.

Comparison study on photocatalytic oxidation of pharmaceuticals by TiO2-Fe and TiO2-reduced graphene oxide nanocomposites immobilized on optical fibers

Incorporating reduced graphene oxide (rGO) or Fe3+ ions in TiO2 photocatalyst could enhance photocatalytic degradation of organic contaminants in aqueous solutions. This study characterized the photocatalytic activities of TiO2-Fe and TiO2-rGO nanocomposites immobilized on optical fibers synthesized by polymer assisted hydrothermal deposition method. The photocatalysts presented a mixture phase of anatase and rutile in the TiO2-rGO and TiO2-Fe nanocomposites. Doping Fe into TiO2 particles (2.40eV) could reduce more band gap energy than incorporating rGO (2.85eV), thereby enhancing utilization efficiency of visible light. Incorporating Fe and rGO in TiO2 decreased significantly the intensity of TiO2 photoluminescence signals and enhanced the separation rate of photo-induced charge carriers. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO exhibited higher photocatalytic activity for the degradation of pharmaceuticals under UV irradiation, while TiO2-Fe demonstrated more suitable for visible light oxidation. The results suggested that the enhanced photocatalytic performance of TiO2-rGO could be attributed to reduced recombination rate of photoexcited electrons-hole pairs, but for TiO2-Fe nanocomposite, narrower band gap would contribute to increased photocatalytic activity.

A gigantically increased ratio of electrical to thermal conductivity and synergistically enhanced thermoelectric properties in interface-controlled TiO2-RGO nanocomposites.

We report synergistically enhanced thermoelectric properties through the independently controlled charge and thermal transport properties in a TiO2-reduced graphene oxide (RGO) nanocomposite. By the consolidation of TiO2-RGO hybrid powder using spark plasma sintering, we prepared an interface-controlled TiO2-RGO nanocomposite where its grain boundaries are covered with the RGO network. Both the enhancement in electrical conductivity and the reduction in thermal conductivity were simultaneously achieved thanks to the beneficial effects of the RGO network, and detailed mechanisms are discussed. This led to the gigantic increase in the ratio of electrical to thermal conductivity by six orders of magnitude and also the synergistic enhancement in the thermoelectric figure of merit by two orders. Our results present a strategy for the realization of 'phonon-glass electron-crystals' through interface control using graphene in graphene hybrid thermoelectric materials.

TiO2-reduced graphene oxide nanocomposites by microwave-assisted forced hydrolysis as excellent insertion anode for Li-ion battery and capacitor

Abstract TiO2-reduced graphene oxide (rGO) nanocomposite (TiO2-rGO) is fabricated by microwave-assisted forced hydrolysis and examined as prospective electrode for energy storage applications, especially in Li-ion battery (LIB) and Li-ion capacitor (LIC). First, the uniformly distributed nanoscopic TiO2 particulates (∼3 nm) over rGO nanosheets is evaluated as anode in half-cell assembly to ascertain the Li-insertion behavior and found that ∼0.68 mol Li (∼227 mAh g−1) is reversible. Then, “rocking-chair” type LIB is fabricated with spinel LiMn2O4 cathode, and the LiMn2O4/TiO2-rGO assembly exhibits high capacity (∼120 mAh g−1 at 0.1 C rate), good rate capability (∼53 mAh g−1 at 1 C rate), and excellent cycleability (∼90% initial reversible capacity after 1000 cycle) as well. Similarly, the LIC is also constructed with activated carbon cathode, and such configuration delivered a maximum energy density of ∼50 Wh kg−1 with ∼82% retention after 4000 cycles. The synergistic effect of both rGO and anatase nanoparticles provides excellent energy efficiency and battery performance in different kind of Li-ion based energy storage devices.

Immobilized TiO2-reduced graphene oxide nanocomposites on optical fibers as high performance photocatalysts for degradation of pharmaceuticals

A series of TiO2-reduced graphene oxide (rGO) coated side-glowing optical fibers (SOFs) were synthesized by polymer assisted hydrothermal deposition method (PAHD), and characterized by crystallographic and spectroscopic methods. Fourier transform infrared spectroscopy showed that the mixed graphene dioxide (GO) was reduced during PAHD coating of TiO2-GO nanocomposites. X-ray diffraction patterns revealed TiO2 presented as a mixture phase of anatase, rutile and brookite in the TiO2-rGO nanocomposites. UV–vis absorption spectra of TiO2-rGO nanocomposites indicated that mixing rGO into TiO2 particles could reduce band gap energy, thereby enhancing utilization efficiency of visible light. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO nanocomposites exhibited significantly higher photocatalytic activities as compared to pure TiO2, and were strongly affected by the amount of rGO in the catalysts. While photocatalysis with 2.7% rGO achieved 54% degradation of carbamazepine, 81% of ibuprofen, and 92% of sulfamethoxazole after 180min UV irradiation, the mineralization rates of the pharmaceuticals were similar between 52% and 59%. The photocatalytic oxidation of pharmaceuticals by the prepared nanocomposites followed the Langmuir–Hinshelwood kinetic model. There was an obvious positive correlation between degradation rate constant and quantum flux for both UV and visible light, with correlation coefficient of 0.991. In addition, long-term photoactivity testing of TiO2-rGO coated SOFs demonstrated the durability of the immobilized TiO2-rGO nanocomposites on optical fibers for water treatment.

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO2–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO2 crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO2 was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO2–RGO nanocomposite modified electrode was also highly improved.

Synthesis of TiO2–Reduced Graphene Oxide Nanocomposites for Efficient Adsorption and Photodegradation of Herbicides

The elimination of herbicides in aquatic environment is influenced by various biotic or abiotic factors. Thus, efficient, more applicable, and flexible methods are in demand. Photodegradation has been applied to remove three main types of herbicides, phenylurea, triazine, and chloroacetanilide, from water, based on a series of TiO2–reduced graphene oxide nanocomposites. Experimental results showed that the three types of herbicides could be mostly removed under simulated sunlight irradiation for 5 h with the as-prepared photocatalyst. Compared with pure TiO2 or P25, the photodegradation efficiency has been markedly increased. Thus, the present work could promote a new strategy dealing with the pollution of herbicides in aquatic ecosystems.

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

TiO2/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03g RGO, x=0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO2 on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite.

Photocatalytic degradation of bisphenol A by TiO2-reduced graphene oxide nanocomposites

TiO2-reduced graphene oxide (RGO) nanocomposites were prepared via hydrothermal synthesis. The prepared hybrid materials were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The results indicated that P25 nanoparticles with size of 20–30 nm were dispersed on RGO sheets after the hydrothermal process. The photocatalytic activity of TiO2-RGO was evaluated by degrading bisphenol A (BPA) under UV light illumination. The photocatalytic degradation process was fitted well by the pseudo-first order reaction model. The degradation rate constants were strongly affected by the mass ratio of RGO in the hybrid materials and the optimal mass ratio of RGO to commercial TiO2 (P25) was 3.0 wt%. Under the optimal degradation conditions, the rate constant of BPA over P25–3RGO (−0.0132 min−1) was 2.93 times of that over P25 (−0.00451 min−1). The results indicated that the introduction of RGO in P25 not only can enhance the adsorption ability for BPA, but also improve the photocatalytic activity of P25 for degradation of BPA greatly.

TiO2-reduced graphene oxide nanocomposite for high-rate application of lithium ion batteries

TiO2-reduced graphene oxide nanocomposite has been synthesized by a facile hydrothermal process. The structure and morphology have been characterized by X-ray diffraction and scanning electron microscopy. The result shows that a unique nanocomposite has been obtained with the TiO2 nanoparticle homogenously dispersed onto the reduced graphene oxide sheets. The electrochemistry performance has been tested through cyclic voltammetry, constant current discharge/charge tests, and electrochemical impedance techniques. The initial lithium ion storage capacity is 368 mAhg−1 at the rate of 10 mAg−1, which exceeds the theoretical capacity value of the anatase TiO2 (335 mAhg−1). The nanocomposite exhibits good high-rate capacity of 136.1 mAhg−1 at rate of 1,000 mAg−1, and, after 100 cycles, the coulombic efficiency is still maintained as high as 98.6 %. The high specific capacity and good stability can be attributed to the unique structures and make the nanocomposite a promising substitute of the current commercial graphite anode in high-power, high-rate application of lithium ion batteries.

Photo-less catalysis of TiO2-reduced graphene oxides

A series of TiO2-reduced graphene oxide (RGO) nanocomposites were prepared by a green one-pot hydrothermal reactions using P25 as the titania precursor and graphene oxide (GO). Our method provides the notable advantages of a one-step reaction without employing toxic solvents, thereby providing a green, simple and quick synthetic route to produce TiO2-RGO nanocomposites. The synthesized nanocomposites showed enhanced photocatalytic activity compared to P25 under UV–vis illumination, it even can degrade the Rhodamine (Rh) B in the dark conditions.

Hydrothermal synthesis of mixed crystal phases TiO2–reduced graphene oxide nanocomposites with small particle size for lithium ion batteries

A rutile and anatase mixed crystal phase of nano-rod TiO2 and TiO2–reduced graphene oxide (TiO2–RGO) nanocomposites with small particle size were prepared via a facile hydrothermal approach with titanium tetrabutoxide and graphene oxide as the precursor. Hydrolysis of titanium tetrabutoxide and mild reduction of graphene oxide were simultaneously carried out. Compared with traditional multistep methods, a novel green synthetic route to produce TiO2–RGO without toxic solvents or reducing agents was employed. TiO2–RGO as anode of lithium ion batteries was characterized by extensive measurements. The nanocomposites exhibited notable improvement in lithium ion insertion/extraction behavior compared with TiO2, indicating an initial irreversible capacity and a reversible capacity of 295.4 and 112.3 mA h g−1 for TiO2–RGO after 100 cycles at a high charge rate of 10 C. The enhanced electrochemical performance is attributed to increased conductivity in presence of reduced graphene oxide in TiO2–RGO, a rutile and anatase mixed crystal phase of nano-rod TiO2/GNS composites, small size of TiO2 particles in nanocomposites, and enlarged electrode–electrolyte contact area, leading to more electroactive sites in TiO2–RGO.

Photocatalytic Synthesis of TiO2 and Reduced Graphene Oxide Nanocomposite for Lithium Ion Battery

In this work, we synthesized graphene oxide (GO) using the improved Hummers' oxidation method. TiO2 nanoparticles can be anchored on the GO sheets via the abundant oxygen-containing functional groups such as epoxy, hydroxyl, carbonyl, and carboxyl groups on the GO sheets. Using the TiO2 photocatalyst, the GO was photocatalytically reduced under UV illumination, leading to the production of TiO2-reduced graphene oxide (TiO2-RGO) nanocomposite. The as-prepared TiO2, TiO2-GO, and TiO2-RGO nanocomposite were used to fabricate lithium ion batteries (LIBs) as the active anode materials and their corresponding lithium ion insertion/extraction performance was evaluated. The resultant LIBs of the TiO2-RGO nanocomposite possesses more stable cyclic performance, larger reversible capacity, and better rate capability, compared with that of the pure TiO2 and TiO2-GO samples. The electrochemical and materials characterization suggest that the graphene network provides efficient pathways for electron transfer, and the TiO2 nanoparticles prevent the restacking of the graphene nanosheets, resulting in the improvement in both electric conductivity and specific capacity, respectively. This work suggests that the TiO2 based photocatalytic method could be a simple, low-cost, and efficient approach for large-scale production of anode materials for lithium ion batteries.

One-pot polyelectrolyte assisted hydrothermal synthesis of TiO2-reduced graphene oxide nanocomposite

We demonstrated a facile and efficient strategy for the fabrication of poly(diallyldimethylammonium chloride) (PDDA)-assisted reduced graphene oxide (RGO) sheets–titanium dioxide (TiO2) in the absence of any seeds and surfactants. PDDA is used as both a reducing agent and a stabilizer to prepare the colloidal suspension of graphene nanosheets. The incorporation of PDDA successfully turns graphene nanosheets into general platforms for in situ growth of TiO2. The prepared TiO2–RGO has been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy) and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy and transmission electron microscopy) have been employed to probe the morphological structures as well as to investigate the exfoliation of RGO sheets. It is interesting to see that the TiO2–RGO composites exhibited excellent photocatalytic activity to hydrogen evolution.