Graphene Oxide TiO2 Research Articles

Photoelectrochemical properties of the composites based on TiO2 nanotubes, CdSe and graphene oxide

The photoelectrochemical properties of electrodes based on a nanocomposite consisting of TiO2 nanotubes and CdSe films modified with graphene oxide have been studied. It is shown that in such a nanocomposite, a good adhesion of the CdSe layer to the substrate is provided. In this nanocomposite, the cathodic dark leakage currents are lower, and the efficiency of photoelectrodes is higher. From studies of Raman spectra, in which 2LO and 3LO phonon lines were observed, the quality of the modified polycrystalline films of CdSe was concluded. The amount of graphene oxide in NT-TiO2/CdSe/GO composite was determined to be 1.16 mass%, which allows one to obtain optimal photosensitivity of electrodes. It was established that the introduction of graphene oxide into semiconductor electrodes leads to an increase in their photosensitivity which is associated with a decrease of the surface recombination rate. The efficiency of the investigated nanocomposites in the photoelectrochemical cell for hydrogen production was studied together with composites based on graphene materials.

Self-Assembled Reduced Graphene Oxide-TiO₂ Thin Film for the Enhanced Photocatalytic Reduction of Cr(VI) Under Simulated Solar Irradiation.

In this study, reduced graphene oxide-TiO₂ (RGO-TiO₂) thin film was prepared by a simple self-assembly method at the gas/liquid interface. The as-prepared thin films were characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), UV-visible-diffuse reflectance spectroscopy (UV-vis-DRS) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of TiO₂ and RGO-TiO₂ thin film were investigated via the reduction of Cr(VI) under simulated solar light and visible light (λ > 420 nm) irradiation. The results showed that the RGO-TiO₂ thin film exhibited remarkably enhanced activity for photoreduction of Cr(VI) under simulated sunlight or visible light irradiation, with a reaction rate constant of 5.7 times greater than that of pure TiO₂ thin film. The main reason for enhanced photocatalytic activity is that introduction of RGO can restrain the recombination of photogenerated electron-hole pairs and reduce the aggregation of TiO₂ NPs. The effects of different reaction parameters such as irradiation time, irradiation source, pH values, catalyst dosage and initial Cr(VI) concentration were investigated in detail. The highest photoreduction efficiency of Cr(VI) was achieved and the reduction rate constant k was 0.0189 min-1 during the reduction of 0.5 mg L-1 of Cr(VI) with 10 cm² RGO-TiO₂ thin film at pH 2.0 and 293 K. Moreover, different scavengers were also added in the photoreduction of Cr(VI) system to identify the reactive species. Based on the results of the present study, a possible mechanism of photoreduction on RGO-TiO₂ thin film under simulated solar light was proposed. Overall, this study provides a novel approach to efficiently photoreduction of Cr(VI) by RGO-TiO₂ thin film.

Corrosion resistance and photocatalytic activity evaluation of electrophoretically deposited TiO2-rGO nanocomposite on 316L stainless steel substrate

Abstract TiO2-rGO nanocomposite coatings were obtained by electrophoretic deposition (EPD) technique of TiO2 nanoparticles and graphene oxide (GO) on stainless steel substrate. First, GO particles were synthesized using a modified Hummers' method. GO was reduced electrochemically to form a coating in the presence of nano-sized TiO2 particles. The influences of different parameters such as GO concentration, coupling co-electro-deposition parameters (electrophoretic duration and voltage) on thickness, surface morphology and, corrosion behavior of the as-synthesized TiO2-rGO nanocomposite coatings were systematically surveyed. The morphology and microstructure were investigated by field emission scanning electron microscopy (FE-SEM), Raman spectra and X-ray diffraction (XRD) techniques. Atomic force microscopy (AFM) was harnessed to evaluate the topography of the as-prepared GO powder. The bonding characteristics of as-synthesized and as-reduced GO were examined after deposition, by Energy Dispersive Analysis of X-Ray (EDX) and Fourier-transform infrared spectroscopy (FT-IR). Corrosion behavior of coatings and that of the pure TiO2 layer were evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques (by applying potentiodynamic polarization spectroscopy (PDS)). Detailed SEM studies showed that increasing EPD voltage brings about a coating with increased porosity and microcracks with higher thickness. In addition to that, the presence of rGO reduced corrosion current density (icorr) and shifted corrosion potential (Ecorr) toward more noble values in 3.5% NaCl at room temperature. Also, Analyses revealed that the optimum electrophoretically synthesized coating was obtained at GO concentration of 1 g/L, 30 V and 30 min at room temperature. The corrosion current density of the corresponding coating was remediated up to 0.2 μA cm−2, which means an anti-corrosion ability of about 30 times compared to TiO2-coated and bare 316L stainless steel. The results of impedance spectroscopic studies demonstrated that this coating renders as a barrier layer and resistance increased from 2.95 KΩ cm2 for TiO2-coated layer to 10.49 KΩ cm2 for the optimized layer.

Hydrothermally synthesized self-assembled multi-dimensional TiO2/Graphene oxide composites with efficient charge transfer kinetics fabricated as novel photoanode for dye sensitized solar cell

The proposed work suggests the fabrication of hybrid TiO2/reduced graphene oxide composites with self-assembled multidimensional structure. The two step facile alkaline hydrothermal route is implemented using variable wt% of GO for the successful synthesis of multidimensional reduced graphene oxide TiO2 composites structure (MGTS). In the first step, TiO2 aggregates (TNA) were prepared by low temperature hydrothermal process. Subsequently, growth of multidimensional TiO2 on hGO sheet, as well as simultaneous reduction of GO is done and the as prepared MGTS is applied for dye sensitized solar cell (DSSC). Structural and surface morphology of the developed samples were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The X-ray photoelectron spectroscopy studies monitored the chemical composition and surface binding energy of TNA and MGTS samples. The current-voltage (J-V) and electrochemical impedance studies evaluates the performance of the TNA and MGTSs photoanodes in DSSC. The finest loading of GO in the TiO2 matrix assisted the accelerated electron transport channel within the TiO2 matrix resulting in superior photo conversion efficiency of 8.62% as compared with neat TiO2 which has an efficiency of 6.3%.

Conductivity of Composite Films Based on Conductive Polymer PEDOT:PSS, Graphene Oxide and Nanoparticles TiO2 for Contact Layers of Perovskite Photovoltaic Structures

The electrical properties of composite films based on conductive polymer PEDOT: PSS, graphene oxide (GO), and titanium dioxide nanoparticles (TiO2) (PEDOT: PSS– TiO2 and GO–TiO2) used as contact layers of organic and perovskite photovoltaic structures have been studied. As a result of the study of morphology by atomic force microscopy, it was found that the PEDOT: PSS–TiO2 and GO–TiO2 films have a globular structure with a grain size of ~200–300 nm. The current–voltage characteristics of the PEDOT: PSS–TiO2 and GO–TiO2 films are measured in the temperature range of 80–300 K, the dependences of the resistivity versus temperature, ρ(T), which have an activation character, are obtained. It is established that as the temperature decreases, the ρ(T) dependences show a transition from large values of the activation energy (570 meV and 329 meV) to lower values (25 meV and 2.2 meV) for the PEDOT: PSS–TiO2 and GO–TiO2 films, respectively. The mechanisms of transport of charge carriers in the materials studied are discussed.

Enhanced hydrophilic and antibacterial efficiencies by the synergetic effect TiO2 nanofiber and graphene oxide in cellulose acetate nanofibers.

In this study, a novel nanofiber with improved antibacterial efficiencies was created by introducing TiO2 nanofibers and graphene oxide (GO) sheets into cellulose acetate (CA) nanofibers using an efficient electrospinning process. The morphologies and chemical composition of above nanocomposite were fully measured by SEM, FTIR and XRD measurements. The results demonstrated that TiO2 nanofibers and GO sheets have a uniform distribution in the CA nanofibers and these two additives also could improve hydrophilicity. TiO2/GO/CA@cotton exhibited high antibacterial activity with an inhibition rate higher than 95% against B. subtilis and B. cereus bacteria. Therefore, the proposed nanofiber is promising for the large-scale production of antibacterial nanofiber/cotton hybrid yarns for biomedical and antibacterial textiles applications.

Self-assembled reduced graphene oxide-TiO2 nanocomposites: Synthesis, DFTB+ calculations, and enhanced photocatalytic reduction of CO2 to methanol

A facile combined method, namely sonothermal-hydrothermal, was adopted to assemble titanium dioxide (TiO2) nanoparticles on the surface of reduced graphene oxide (RGO) to form nanocomposites. Characterization techniques confirm that RGO-TiO2 composite is well constituted. Enhanced photocatalytic CO2 reduction to methanol by the composites under UVA and visible irradiation suggests the modification in the band gap of the composite and promotion of the separation of photogenerated carriers, yielding methanol production rate of 2.33 mmol g−1 h−1. Theoretical investigation demonstrated that combining RGO with TiO2 resulted in an upward shift of TiO2 bands by 0.2 V due to the contribution of RGO electrons. Relatively strong adsorption of RGO over the (101) anatase surface with the binding energy of approximately 0.4 kcal mol−1 per carbon atom was observed. Consideration of orbitals of TiO2, RGO and RGO-TiO2 composite led to a conclusion that UVA photoreaction proceeds via the traditional mechanism of photogenerated electron transfer to RGO while visible light CO2 reduction proceeds as a result of charge transfer photoexcitation that directly produces electrons in RGO and holes in TiO2. Superior photocatalytic activity of RGO-TiO2 composite in the present study is attributed to the formation of tight contact between its constituents, which is required for efficient electron and charge transfer.

Optimizing the interface of C/titania@reduced graphene oxide nanofibers for improved photocatalytic activity

Photocatalysis has been proved a promising technology to alleviate the deterioration of environments by utilizing light energy. High efficiency and cycling stability are important for pollutant degradation in practical wastewater treatment. Herein we prepared C/titania@reduced graphene oxide nanofibers (C/TiO2@RGO NFs) by electrospun polyacrylonitrile/titania nanofibers (PAN/TiO2 NFs) wrapped with graphene oxide (GO)assisted with polydopamine, followed by one-step GO reduction, TiO2 crystallization and interface enhancing between anatase TiO2 and graphene by forming chemical bonding via heat treatment. The as-prepared C/TiO2@RGO NFs exhibited four times photocatalytic efficiency higher than commercial catalyst P25, and they also exhibited favorable cycling stability for methylene blue degradation under visible light illumination. The high photocatalytic efficiency is mainly attributed to the efficient charge separation and broadening visible light absorption originating from the interface enhancing between TiO2 and RGO. This work provides an insight to design more efficient graphene-based semiconductor photocatalysts for pollutant decomposition.

Photocatalytic activity of graphene oxide-TiO2 thin films sensitized by natural dyes extracted from Bactris guineensis.

This study synthesized and characterized composites of graphene oxide and TiO2 (GO–TiO2). GO–TiO2 thin films were deposited using the doctor blade technique. Subsequently, the thin films were sensitized with a natural dye extracted from a Colombian source (Bactris guineensis). Thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements were used for physico-chemical characterization. All the samples were polycrystalline in nature, and the diffraction signals corresponded to the TiO2 anatase crystalline phase. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) verified the synthesis of composite thin films, and the SEM analysis confirmed the TiO2 films morphological modification after the process of GO incorporation and sensitization. XPS results suggested a possibility of appearance of titanium (III) through the formation of oxygen vacancies (Ov). Furthermore, the optical results indicated that the presence of the natural sensitizer and GO improved the optical properties of TiO2 in the visible range. Finally, the photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution, and pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. These results indicated that the presence of GO has an important synergistic effect in conjunction with the natural sensitizer, reaching a photocatalytic yield of 33%.

Preparation and photocatalytic activity of Ag-modified GO-TiO2 mesocrystals under visible light irradiation

Nanosized metallic Ag particles modified graphene oxide-TiO2 mesocrystals (Ag/GO-TMCs) were successfully synthesized by photoreduction deposition method. The morphology, crystallization, structural features and chemical compositions of the as-prepared Ag/GO-TMCs catalysts were investigated using HRTEM, XRD, Raman spectra, XPS, UV–vis DRS, PLS, and N2 adsorption-desorption measurements. Ag nanoparticles were found to be evenly distributed on the surface of TiO2 mesocrystals (TMCs) and graphene oxide (GO). The Ag/GO-TMCs catalysts featured high crystallinity, abundant mesoporous structure, large surface area, and improved visible-light response. Photocatalytic applications of the catalysts for degradation of Rhodamine B (RhB) and dinitro butyl phenol (DNBP) under visible light irradiation were investigated. The results showed that the highly enhanced photocatalytic activity was obtained with Ag/GO-TMCs catalysts. The Ag/GO-TMCs photocatalyst with AgNO3/GO-TMCs mass ratio of 0.075:1 exhibited the highest photocatalytic degradation of RhB and DNBP under 3 h of visible light irradiation. The superior photocatalytic activity of Ag/GO-TMCs may be attributed to the higher visible-light absorbance ability and surface plasmon resonance (SPR) effect of Ag nanoparticles and GO. The Ag-GO/TMCs materials could be deemed as promising photocatalysts for organic contaminants removal under visible light irradiation, in assessing their high photocatalytic efficiency and good repeatability.

Проводимость композитных пленок на основе проводящего полимера PEDOT : PSS, оксида графена и наночастиц TiO-=SUB=-2-=/SUB=- для контактных слоев перовскитных фотовольтаических структур

AbstractThe electrical properties of composite films based on conductive polymer PEDOT: PSS, graphene oxide (GO), and titanium dioxide nanoparticles (TiO_2) (PEDOT: PSS– TiO_2 and GO–TiO_2) used as contact layers of organic and perovskite photovoltaic structures have been studied. As a result of the study of morphology by atomic force microscopy, it was found that the PEDOT: PSS–TiO_2 and GO–TiO_2 films have a globular structure with a grain size of ~200–300 nm. The current–voltage characteristics of the PEDOT: PSS–TiO_2 and GO–TiO_2 films are measured in the temperature range of 80–300 K, the dependences of the resistivity versus temperature, ρ( T ), which have an activation character, are obtained. It is established that as the temperature decreases, the ρ( T ) dependences show a transition from large values of the activation energy (570 meV and 329 meV) to lower values (25 meV and 2.2 meV) for the PEDOT: PSS–TiO_2 and GO–TiO_2 films, respectively. The mechanisms of transport of charge carriers in the materials studied are discussed.

A novel sensing layer based on metal–organic framework UiO-66 modified with TiO2–graphene oxide: application to rapid, sensitive and simultaneous determination of paraoxon and chlorpyrifos

Simultaneous electrochemical detection of paraoxon and chlorpyrifos based on metal–organic framework UiO-66 modified with TiO2–graphene oxide.

Correction: Graphene oxide–TiO2 composite: an efficient heterogeneous catalyst for the green synthesis of pyrazoles and pyridines

Correction for ‘Graphene oxide–TiO2 composite: an efficient heterogeneous catalyst for the green synthesis of pyrazoles and pyridines’ by Shweta Kumari et al., New J. Chem., 2016, 40, 5053–5060.

TiO2-Intercalated Graphene Oxides with Highly Efficient Photocatalytic Degradation for Methylene Blue

The low photocatalytic decomposition activity of TiO2 toward industrial pollutants at room temperature is one of the main obstacles for its practical application. TiO2-intercalated graphene oxide (GO) composites were prepared by in situ hydrolysis of butyl titanate in a GO aqueous solution, followed by hydrothermal reaction to improve their photoelectron separation efficiency. The in situ generated TiO2 nanocrystals could grow and adhere to the GO walls, thereby greatly improving the contact area and binding strength among them and resulting in low photoelectron transfer resistance. The photocatalytic activities of the as-prepared catalyst were evaluated via photodegradation of methylene blue (MB). The TiO2-intercalated GOs displayed much higher catalytic activity than GO, TiO2, and TiO2-adsorbed GOs. The degradation efficiency of MB by TiO2-intercalated GOs increased with increasing bath ratio of TiO2-intercalated GOs to MB solution, but it decreased with increasing initial concentration of MB. Degradation of MB by UV light was much faster than by simulated sunlight. The degradation time by sunlight was only 5% of degradation time by UV light. Cyclic catalytic experiments indicated that TiO2-intercalated GO maintained 99.97% degradation activity after repeated degradation (five times), thereby indicating the good decomposition durability.

Reduced Graphene Oxide–TiO2 Nanotube Composite: Comprehensive Study for Gas-Sensing Applications

Graphene oxide (GO) and reduced graphene oxide (RGO) have unique properties that can revolutionize the performances of functional devices. Graphene-based materials can be coupled with metal oxide nanomaterials for gas-sensing applications. In this work, we report the synthesis and gas-sensing properties of a composite material based on RGO-loaded TiO2 nanotubes. To properly tune the reduction of GO to RGO, we adopted a gas-phase process that can be applied in situ on each gas sensor device, allowing one to track the process effects through sensor conductance. We systematically investigated the gas-response dependence from the RGO loading and its reduction, showing the occurrence of an optimal RGO concentration arising from the interplay of these two parameters. Hence, these two factors should be considered in parallel to functionalize the metal oxide materials with GO for the fabrication of chemical sensor devices.

Gold-Palladium Nanoalloys Supported by Graphene Oxide and Lamellar TiO2 for Direct Synthesis of Hydrogen Peroxide.

Hybrid catalysts composed of gold-palladium nanoalloys that are sandwiched between layers of graphene oxide (GO) and lamellar TiO2 are synthesized via the deposition-reduction method. The resulting AuPd catalysts with different compositions of metal and support are fully characterized by a series of techniques, including X-ray diffraction, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. The catalysts are also optimized against Au, Pd, GO, and TiO2 contents and employed in the direct synthesis of hydrogen peroxide (DSHP) from H2 and O2. The sandwich-like AuPd nanoalloy comprising 1 wt % nanoparticle of an equimolar mixture of Au and Pd with 6 wt % GO and 93 wt % TiO2 supports shows a promising catalytic performance toward the DSHP reaction with H2O2 productivity and selectivity of 5.50 mol H2O2 gmetal-1 h-1 and 64%, respectively. The catalyst is found to be considerably more active than those reported in the literature. Furthermore, the H2O2 selectivity of the catalyst is found to improve considerably to 88% when the TiO2 support is pretreated by HNO3. It is found that the perimeter sites of the interface of AuPd alloy and TiO2 are deemed as catalytically active sites for the DSHP reactions and the acidic property of TiO2 can retard the other overreactions and the decomposition of yielded H2O2. Results of the present study may provide a design strategy for partially covered catalysts that are confined by 2D materials for selective reactions.

Enhanced photocatalytic New Coccine degradation and Pb(II) reduction over graphene oxide-TiO2 composite in the presence of aspartic acid-β-cyclodextrin

In this work, aspartic acid-β-cyclodextrin (ACD) was synthesized by the reaction of β-cyclodextrin with aspartic acid and epichlorohydrin, and graphene oxide-TiO2 (GO-TiO2) composite catalyst was prepared by a hydrothermal method. The complexation of ACD with New Coccine (NC) and Pb2+ was characterized with FT-IR and XPS, respectively, the results show that ACD can simultaneously complex NC and Pb2+. XRD analysis and SEM images of GO-TiO2 show that TiO2 platelets are well distributed on both sides of the graphene oxide sheets, and display a similar XRD pattern to the pure TiO2 nanoparticles with the typical diffraction peak of anatase phase. The effects of ACD on the photocatalytic degradation of NC and photocatalytic reduction of Pb2+ were investigated in the single pollution system, and the synergistic effects on the simultaneous photocatalytic NC degradation and Pb2+ reduction in the presence of ACD were also evaluated. The results showed that the presence of ACD was favorable to the acceleration of photocatalytic oxidation of NC and photocatalytic reduction of Pb2+ in the single pollution system, and the photocatalytic reaction rate constants of NC and Pb2+ in the presence of ACD increased 58% and 42%, respectively. For the combined pollution system, the synergistic effects on the simultaneous conversion of NC and Pb2+ in aqueous solutions were also further enhanced. ACD enhanced photocatalytic activity was attributed to the improvement of the electron transfer and mass transfer at the GO-TiO2 interface.

Effect of graphene oxide loading on TiO2: Morphological, optical, interfacial charge dynamics-A combined experimental and theoretical study

Reduced graphene oxide (rGO)TiO2 composites are prepared using photo-reduction method by varying GO to TiO2 weight ratio from low (rGOT-0.001, 0.01, & 0.1) to high (rGOT-1, 3 & 10) range and its effect on morphological, optical and mechanism of fast charge dynamics at the interface are investigated. Experimental analysis confirm that reduction process improves as TiO2 amount increases in rGO-TiO2 but leads to aggregation of TiO2 nanoparticles. rGOT-3 composite displayed the highest photocatalytic activity for degradation of phenols compared to TiO2, GO and other composites. This was achieved due to uniform dispersion of TiO2 nanoparticles over rGO surface, which enables distinct formation of TiOC bond between each TiO2 nanoparticle and rGO surface, and results in slight red shift in the band edge. This TiOC bond facilitates fast electron transfer from TiO2 to rGO and reduces recombination rate as revealed by photoluminescence and time resolved photoluminescence spectroscopy. The experimental findings were further investigated using density functional theory simulations. Band structure calculation confirms high mobility states induced within the band gap due to formation of TiOC bond in rGO-TiO2 model which assists in fast electron transfer from TiO2 to rGO during the photocatalytic process and hence reduces recombination rate.

Facile fabrication of TiO2-graphene nanocomposites (TGNCs) for the efficient photocatalytic oxidation of perfluorooctanoic acid (PFOA)

The present work describes the facile synthesis of the TiO2-graphene nanocomposites (TGNCs) graphene oxide-TiO2 and reduced graphene oxide-TiO2 and evaluates their photocatalytic performance and mechanism in the decomposition of intractable perfluorooctanoic acid (PFOA). More than 90% photocatalytic PFOA decomposition was achieved by the TGNCs (200 mg/L), while only 16% of the initial 12 μM PFOA was decomposed by the commercial TiO2. The presence of graphene provided surface enhancement effects and limited the recombination of electron-hole pairs during photocatalytic decomposition. The effect of quenching agents, isopropyl alcohol and sodium persulfate, in the photocatalytic system gave insight into understanding the mechanism of decomposition.

Heterogeneous Activation of Persulfate by Graphene Oxide-TiO2 Nanosheet for Oxidation of Diclofenac: Optimization by Central Composite Design

In this study, the performance of oxidation with actived persulfate (PS) by graphene oxide-TiO2 nanosheet (GO-TiO2) was investigated for diclofenac (DCF) removal, an anti-inflammatory analgesic being widely used in human health care and veterinary treatment. GO-TiO2 containing oxygen functional groups is employed as an activator for the activation of PS used as the oxidizing agent. Modeling and optimization of the process were performed by central composite design (CCD) as a response surface methodology (RSM). The effects of various factors, including PS concentration, GO-TiO2 amount, initial pH of DCF solution, and reaction time on DCF oxidation, were evaluated. When the estimated values of the full quadratic model obtained with CCD were compared with the actual experimental results, a strong agreement was obtained with an R2 value of 0.9553. Besides, the model consistency was verified by analysis of variance (ANOVA) with a value of 20.17 of F value and P value of less than 0.05. After the optimization run, maximum DCF removal of 93.06% occurred with contact time of 14 min, pH of 5.54, PS concentration of 10 g/L, and 0.1 g of GO-TiO2 as optimal variable values.