Graphene Oxide TiO2 Nanocomposite Research Articles

Fluorine-functionalized reduced graphene oxide-TiO2 nanocomposites: A new application approach for efficient photocatalytic disinfection and algicidal effect

Using surface functionalization and related applications to 2D materials as innovative solutions to environmental pollution has gained considerable attention among researchers. Fluorinated graphene has derivative-based synergistic components with high thermal and chemical stability because of its structure and bonding. Fluorine-functionalized reduced graphene oxide (rFGO-TiO2) demonstrated enhanced hydrophilicity and wettability, highly efficient photocatalytic disinfection, and an algicidal effect. This study presents the hydrothermal synthesis of rFGO-TiO2 to realize antibacterial properties with high stability, which was conducted against the gram-negative bacteria Escherichia coli. To optimize antibacterial performance, the effects of multiple synthetic conditions were investigated. The antibacterial performance was optimized at an rFGO content of 1 wt%, hydrothermal temperature of 200 °C, and hydrothermal time of 1 h. The rFGO–TiO2 composite demonstrated an antibacterial efficiency of 5.76 log under ultraviolet A irradiation for 10 min and around 2 log under visible light. In the absence of light, rFGO–TiO2 took 6 h to reach an antibacterial efficiency of 6 log. Increasing the rFGO content and hydrothermal temperature beyond the optimal conditions reduced the antibacterial efficiency because of the excess rFGO and disruption of rFGO–TiO2 binding. Measurements with electron spin resonance spectroscopy confirmed that hydroxyl radicals and superoxide ions caused stress and damaged the membrane of a cell, which led to cell death.

Photocatalytic activity of graphene oxide-TiO2 nanocomposite on dichlorvos and malathion and assessment of toxicity changes due to photodegradation

Heterogeneous photocatalysis was used for the removal of two widely used organophosphorus pesticides, dichlorvos, and malathion from water. Graphene oxide-TiO2 nanocomposite (GOT) was synthesized and used as a photocatalyst for the removal of these pesticides. Batch studies for optimizing photocatalytic degradation and mineralization of pesticides over 80 min were conducted by varying the pH (2–10), catalyst dose (20 mg/L-200 mg/L), and initial pesticide concentration (0.5 mg/L-20 mg/L), and the irradiation source (125 W UV and visible lamp). Degradation kinetics for the pesticides were evaluated. Ellman assay was used to estimate the toxic effect of pesticides and evaluate toxicity reduction due to treatment. The highest degradation and mineralization of dichlorvos and malathion was observed at pH 6 and the optimum catalyst dose was 60 mg/L. Under UV irradiation, 80% and 90% degradation were observed for dichlorvos and malathion, respectively for 0.5 mg/L initial pesticide concentration. The photocatalytic degradation reaction followed Langmuir-Hinshelwood kinetics. A high degree of mineralization was achieved for both the pesticides. Analysis of the results revealed that the residual toxic effect after photocatalysis was primarily due to the residual parent compound. A comparative study revealed that GOT yielded better pesticide degradation compared to commercially available TiO2 under both UV and visible irradiation.

Enhanced photocatalytic activity of reduced graphene oxide-TiO2 nanocomposite for picric acid degradation

The rGO-TiO2 nanocomposite was synthesised via a hydrothermal method. Numerous analytical and spectroscopic techniques have been used to characterise rGO-TiO2. The findings indicate that TiO2 has a tetragonal rutile phase and that TiO2 nanoparticles were densely packed on the GO sheet. In this study, the photocatalytic degradation of organic pollutant (picric acid) with rGO-TiO2 nanocatalyst linked with Fenton reagent [Fe 2+/H2O2] at various pH levels (3, 7 and 10) was investigated using UV light (wavelengths 254,265 and 395 nm), visible light, and sunlight. Among the various light irradiation conditions, visible light and sun light demonstrated the highest degradation efficiency due to the presence of rGO-incorporated TiO2 catalyst (rGO-TiO2 nanocompsite). Photolysis of picric acid of 200 mg/L was completed in 15 min and 18 min at the optimal pH of 3 and FeSO4·7H2O concentration of 1 mM, as well as the catalyst dosage of 50 mg/L under visible light and sun light. The rGO-TiO2 nanocomposite catalyst's superior adsorption and degradation properties make it an ideal solar-driven catalyst for organic pollutant degradation.

Evaluation of Anti-microbial activity of graphene oxide-TiO2 nanocomposites with variable compositions

The anti-fungal activity towards the elimination of the fungus Candida albicans and Candida rugosa and anti-bacterial activity for the removal of gram-negative Escherichia coli, gram-positive Staphylococcus aurues bacteria were evaluated with the graphene oxide-TiO2 nanocomposites. These nanocomposites contain a fixed weight of titania with variable weight % of graphene oxide (1%, 5 %, 10 %, 15%). The photocatalytic activity of these composites has been evaluated earlier towards the degradation of different organic dyes. In the present work, their biological activity was determined. It was observed that the micro-organisms removal was higher in the presence of graphene oxide than with the bare nanotitania particles. Further, the removal has increased with increase in the wt.% of graphene oxide in the nanocomposites. Superior anti-microbial activity was shown by composite with 10 wt.% graphene oxide. In the studies, anti-bacterial performance was observed to be greater than the anti-fungal activity with the nanocomposites.

Robust self-cleaning effects of cotton fabrics coated with reduced graphene oxide (RGO)-titanium dioxide (TiO2) nanocomposites

The self-cleaning textiles coated with reduced graphene oxide-titanium dioxide (TiO2) nanocomposites have enhanced photocatalytic activities and could have great potential in practical applications. However, it is still problematic regarding how to avoid aggregation of reduced graphene oxide nanosheets in producing reduced graphene oxide-TiO2 nanocomposites. In this research article, we propose a new method to reduce the aggregation of reduced graphene oxide nanosheets in producing cotton fabrics coated with reduced graphene oxide-TiO2 nanocomposites by combining vibration-assisted ball milling and hydrothermal synthesis process. The microstructure and photocatalytic-related properties of the resultant reduced graphene oxide-TiO2 nanocomposites and their coating cotton fabrics were characterized by using a series of techniques including field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffraction spectroscopy (XRD), Raman, particle size distribution, Brunauer-Emmett-Teller,(BET), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS), diffuse reflectance spectra (DRS), ultraviolet photoelectron spectroscope (UPS), and photoluminescence (PL). It was indicated that the aggregation of reduced graphene oxide nanosheets in reduced graphene oxide-TiO2 nanocomposites was successfully avoided via ball milling in the presence of tetrabutyl titanate. After hydrothermal treatment, the resulting reduced graphene oxide-TiO2 nanocomposites were firmly immobilized on cotton fabric. It was demonstrated in the self-cleaning experiments that the resultant self-cleaning cotton fabrics are hydrophilic and could directly decompose color contaminants such as methylene blue, Congo red, and coffee stains under simulated sunlight irradiation due to the photo-degradation reactions of the reduced graphene oxide-TiO2 nanocomposite coating. The reduced graphene oxide-TiO2 nanocomposite-modified cotton fabric also exhibited excellent performance in both robust abrasion resistance and soap-washing resistance. The fabric photocatalytic self-cleaning capability was not found to decrease significantly after being repeatedly used for five times.

Photocatalysis of dichlorvos using graphene oxide-TiO2 nanocomposite under visible irradiation: process optimization using response surface methodology

Graphene oxide-TiO2 nanocomposite (GOT) was used for degradation and mineralization of dichlorvos, an organophosphorus pesticide, from aqueous solution under visible irradiation. The nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, UV-DRS, Fourier-transform infrared spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. Anatase phase TiO2 nanoparticles (10–20 nm in diameter) were present in the nanocomposite. The nanoparticles were uniformly distributed on reduced GO sheets. A three-factor face-centered central composite design with response surface methodology was used for modeling and optimization of various variables that may potentially affect photodegradation, i.e. pH, catalyst loading, and initial dichlorvos concentration. A quadratic model was built to predict degradation, mineralization efficiency, and reaction rate constant. The experimental and predicted values depicted a good correlation and the utility of the models was confirmed by the high F-values observed for the degradation and mineralization models. High coefficient of determination (R 2) was obtained for the degradation (R 2 = 0.95) and mineralization (R 2 = 0.93) models. Pareto analysis was carried out to determine the effect of each variable on photocatalytic degradation and mineralization. The predicted results suggested that the optimum conditions for obtaining maximum degradation (69%) and mineralization (64%) were: initial dichlorvos concentration of 0.5 mg l−1 with a catalyst dose of 110 mg l−1 at pH 6.5. The main effect plots also suggested a significant influence of the variables used in the photocatalysis of dichlorvos by GOT.

Enhancing electron transport in perovskite solar cells by incorporating GO to the meso-structured TiO2 layer

In this study, the graphene oxide (GO)-TiO2 nanocomposite film prepared by the sol–gel method was used to optimize the photoelectric performance of the perovskite solar cells (PSCs), which structure is based on the carbon electrode and no hole transport layer. Through a series of scientific experiments, it has been proved that the GO–TiO2 nanocomposite film has excellent electrical properties. The electron transport layer which containing 1 wt% of GO makes the PSCs have the most excellent performance. Compared with the controlling PSCs, the photoelectric conversion efficiency of PSCs, which containing 1 wt% GO, increased by 9.3%, from 12.44 to 13.60%. Short-circuit current density (Jsc) increased by 5.99%, from 21.55 to 22.84 mA/cm2, and open circuit voltage remained basically unchanged. It can be seen from the measurement results that the trend of incident photon-to-electron conversion efficiency spectrum is consistent with J–V characteristics, indicating that the PSCs device containing 1 wt% GO has the best electron extraction and transfer performance. However, when too much GO is used, the increased surface charge trap state will lead to the acceleration of carrier recombination and the decrease of electron transport path, and the photovoltaic parameters show a downward trend.

Effect of the carbon loading on the structural and photocatalytic properties of reduced graphene oxide-TiO2 nanocomposites prepared by hydrothermal synthesis

This work deals with the preparation of reduced graphene oxide (RGO)-TiO2 composites by a one-step hydrothermal treatment. The effect of the RGO loading on both the structural properties and photocatalytic behavior of RGO-TiO2 is deeply addressed herein. The hydrothermal treatment promoted the reduction of graphene oxide, crystallization of TiO2 into anatase, and anchoring of TiO2 nanoparticles on RGO sheets. It was observed that the prepared anatase particles showed sizes below 10nm, whereas the RGO sheets displayed thicknesses smaller than 1nm. The use of RGO at concentrations up to 15wt% greatly increased the specific surface area of RGO-TiO2. It was demonstrated that the combination of RGO and TiO2 gives rise to materials with improved photocatalytic properties and tailored structural properties. The composite with the highest photoactivity was the one containing an RGO loading of 1wt%; this composite displayed a photocatalytic rate constant about 9.5 times higher than that evaluated for pure TiO2. This behavior may be related to the stacking of RGO nanosheets when its concentration is above 1wt%. Moreover, the addition of RGO in excess may prevent the activation of the TiO2 surface by UV light and also decrease the lifetime of the photogenerated electron-hole pairs. Therefore, it appears that 1wt% is the optimal loading of RGO to obtain a close interfacial contact between RGO and TiO2, leading to both an effective activation of TiO2 by UV radiation and an enhanced charge transfer between RGO and TiO2.

Photochemical degradation of toluene in gas-phase under UV/visible light graphene oxide-TiO2 nanocomposite: influential operating factors, optimization, and modeling.

The current study aimed to investigate the removal efficiency of toluene using synthesized titanium dioxide-graphene oxide composites under visible light and UV irradiation. The characterization of synthesized composites was examined by field emission scanning electron microscope equipped with energy dispersive, X-ray diffraction and fourier transforms infrared. In order to find the optimum of the main experimental parameters affecting the removal efficiency of toluene including the length of the reactor, initial concentration, and flow rates, central composite design together with response surface methodology with R software was used. The initial concentration of toluene in the inlet of the reactor as well as its concentration in the outlet was measured using gas chromatography with the flame ionization detector. Analysis of variance results for the quadratic model showed that the highly significant and simple linear regression was established as a predicting model. Multiple and adjusted R2 were 0.965 and 0.974 for UV irradiation GO-TiO2 model and 0.951 and 0.959 for visible light GO-TiO2 model, respectively. As such, the differences less than 0.2 between multiple and adjusted R2 in two models indicate that two examined models were fitted well. The highest removal efficiency of toluene using UV irradiation GO-TiO2 and visible light GO-TiO2 was obtained at optimum condition; length of reactor 40cm, initial concentration of 0.1ppm, and flow rate equal to 1lmin-1, with 97.7 and 77.2%, respectively. The results indicated that the removal efficiency of toluene increased considerably with rising the length of the reactor, decreasing flow rates, and initial concentration.

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.

Memory Devices: Photocatalytic Reduction of Graphene Oxide-TiO2 Nanocomposites for Improving Resistive-Switching Memory Behaviors (Small 29/2018)

Memory Devices: Photocatalytic Reduction of Graphene Oxide-TiO₂ Nanocomposites for Improving Resistive-Switching Memory Behaviors (Small 29/2018)

Photocatalytic Reduction of Graphene Oxide-TiO2 Nanocomposites for Improving Resistive-Switching Memory Behaviors.

Graphene oxide (GO)-based resistive-switching (RS) memories offer the promise of low-temperature solution-processability and high mechanical flexibility, making them ideally suited for future flexible electronic devices. The RS of GO can be recognized as electric-field-induced connection/disconnection of nanoscale reduced graphene oxide (RGO) conducting filaments (CFs). Instead of operating an electrical FORMING process, which generally results in high randomness of RGO CFs due to current overshoot, a TiO2 -assisted photocatalytic reduction method is used to generate RGO-domains locally through controlling the UV irradiation time and TiO2 concentration. The elimination of the FORMING process successfully suppresses the RGO overgrowth and improved RS memory characteristics are achieved in graphene oxide-TiO2 (Go-TiO2 ) nanocomposites, including reduced SET voltage, improved switching variability, and increased switching speed. Furthermore, the room-temperature process of this method is compatible with flexible plastic substrates and the memory cells exhibit excellent flexibility. Experimental results evidence that the combined advantages of reducing the oxygen-migration barrier and enhancing the local-electric-field with RGO-manipulation are responsible for the improved RS behaviors. These results offer valuable insight into the role of RGO-domains in GO memory devices, and also, this mild photoreduction method can be extended to the development of carbon-based flexible electronics.

Graphene Oxide–TiO2 Nanocomposite Films for Electron Transport Applications

Graphene oxide–titanium dioxide (GO–TiO2) nanocomposite thin films were prepared for application as the window layer of perovskite solar cells. Graphene oxide (GO) was prepared by a modified Hummer’s method, and titanium dioxide (TiO2) nanoparticles were synthesized by hydrothermal solution method. Thin films of GO–TiO2 nanocomposite were prepared with different wt.% of GO by spin coating on indium tin oxide (ITO) substrate followed by annealing at 150°C. X-ray diffraction analysis revealed rutile phase of TiO2 nanostructures. The bandgap of the pure TiO2 thin film was found to be 3.5 eV, reducing to 2.9 eV for the GO–TiO2 nanocomposites with a red-shift towards higher wavelength. Furthermore, thermal postannealing at 400°C improved the transparency in the visible region and decreased the sheet resistance. Morphological and elemental analysis was performed by scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The current–voltage characteristic of the GO–TiO2 nanocomposites indicated Ohmic contact with the ITO substrate. The chemical composition of the as-synthesized GO–TiO2 nanocomposites was investigated by x-ray photoelectron spectroscopy (XPS). The results presented herein demonstrate a new, low-temperature solution-processing approach to obtain rGO–TiO2 composite material for use as the electron transport layer of perovskite solar cells.

Feasibility of photocatalytic degradation of an organophosphorus pesticide using graphene oxide-TiO2 nanocomposite

Feasibility of photocatalytic degradation of an organophosphorus pesticide using graphene oxide-TiO2 nanocomposite

Crumpling of graphene oxide through evaporative confinement in nanodroplets produced by electrohydrodynamic aerosolization

Restacking of graphene oxide (GO) nanosheets results in loss of surface area and creates limitations in its widespread use for applications. Previously, two-dimensional (2D) GO sheets have been crumpled into 3D structures to prevent restacking using different techniques. However, synthesis of nanometer size crumpled graphene particles and their direct deposition onto a substrate have not been demonstrated under room temperature condition so far. In this work, the evaporative crumpling of GO sheets into very small size (<100 nm) crumpled structures using an electrohydrodynamic atomization technique is described. Systematic study of the effect of different electrohydrodynamic atomization parameters, such as (1) substrate-to-needle distance, (2) GO concentration in the precursor solution, and (3) flow rate (droplet size) on the GO crumpling, is explored. Crumpled GO (CGO) particles are characterized online using a scanning mobility particle sizer (SMPS) and off-line using electron microscopy. The relation between the confinement force and the factors affecting the crumpled structure is established. Furthermore, to expand the application horizons of the structure, crumpled GO–TiO2 nanocomposites are synthesized. The method described here allows a simple and controlled production of graphene-based particles/composites with direct deposition onto any kind of substrate for a variety of applications.

Graphene oxide-TiO2 and reduced graphene oxide-TiO2 nanocomposites: Insight in charge-carrier lifetime measurements

A hybrid nanocomposites containing nanocrystalline TiO2 and graphene related materials (graphene oxide and reduced graphene oxide) were successfully prepared elevated pressure using hydrothermal method. The structural and textural properties as well as the presence of different carbonaceous structures on the surface of obtained nanocomposites have been characterized by means of XRD, FTIR/DRS and Raman spectroscopy. FTIR/DRS analysis allowed to find characteristic peaks of graphene oxide: epoxy stretching at 1229cm−1 and alkoxy stretching vibration at 1059cm−1. In the spectrum of nanocomposites containing rGO, all the bands decreased or even disappear. It can be indicated that GO was successfully reduced to rGO. SEM studies showed difference between graphene oxide (aggregated, crumpled, non-transparent) and reduced graphene oxide (thin and transparent) flakes. The Time Resolved Microwave Conductivity analysis have been utilized to investigate the excess of charge-carrier lifetimes in TiO2-graphene oxide and TiO2-reduced graphene oxide hybrid nanocomposites. It was generally concluded that modification of starting TiO2 with carbonaceous precursors leads to the slight increase of intensity of the TRMC signals, indicating that more electrons are induced in the conduction band of hybrid nanocomposites. It is also worth mentioning that the decay of studied signals of modified powders depends on added carbon precursor, indicating that the type of deposited species may affect the slight or significant suppression of recombination or charge-carriers trapping.

Preparation and characterization of low fouling novel hybrid ultrafiltration membranes based on the blends of GO−TiO2 nanocomposite and polysulfone for humic acid removal

In this work, graphene oxide (GO)−TiO2 nanocomposite was synthesized by in situ sol−gel reaction at pH=2 using GO nanosheets suspension and titanium isopropoxide precursor. The synthesized GO−TiO2 nanocomposite was explored as a filler to fabricate improved antifouling novel hybrid ultrafiltration membranes for removal of humic acid from aqueous solution. Membranes were fabricated from polymer blend solutions containing polysulfone and GO−TiO2 with varied loading amount (0–5wt%) by the non-solvent induced phase separation (NIPS) method. Contact angle, atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and outer surface zeta potential studies were conducted in order to characterise the membranes in terms of roughness, structure, surface properties and charge. The porous hydrophilic hybrid membranes were shown to have an asymmetric structure with improved surface roughness. The water permeability and antifouling capacity of hybrid membranes with 10ppm HA solution were dependent on the loading amount of GO–TiO2. Incorporation of GO–TiO2 nanocomposite was found to improve the antifouling characteristics of the membranes when challenged with HA solutions. Irreversible HA fouling was substantially reduced with increased loading of GO−TiO2 nanocomposite (wt%). The lowest irreversible fouling ratio (3.2%) was obtained for the membrane containing 5wt% nanocomposite (to total wt% of PSf, MG−5). Ultrafiltration of HA solutions of varied concentrations using hybrid membranes was studied at pH=7 and 1bar feed pressure. The removal efficiency of hybrid membranes for HA was controlled by the membrane surface charge concentration, porosity and HA exclusion. The membrane MG−5 had the highest HA removal efficiency for 10ppm HA solution at pH=7.

Synthesis of graphene oxide-TiO2 nanocomposite as an adsorbent for the enrichment and determination of rutin

Objective(s): This paper describes synthesizing of magnetic nanocomposite with co-precipitation method. Materials and Methods: Magnetic ZnxFe3-xO4 nanoparticles with 0-14% zinc doping (x=0, 0.025, 0.05, 0.075, 0.1 and 0.125) were successfully synthesized by co-precipitation method. The prepared zinc-doped Fe3O4 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and UV-Vis spectroscopy. Results: results obtained from X-ray diffraction pattern have revealed the formation of single phase nanoparticles with cubic inverse spinal structures which size varies from 11.13 to 12.81 nm. The prepared nanoparticles have also possessed superparamagnetic properties at room temperature and high level of saturation magnetization with the maximum level of 74.60 emu/g for x=0.075. Ms changing in pure magnetite nanoparticles after impurities addition were explained based on two factors of “particles size” and “exchange interactions”. Optical studies results revealed that band gaps in all Zn-doped NPs are higher than pure Fe3O4. As doping percent increases, band gap value decreases from 1.26 eV to 0.43 eV. Conclusion: these magnetic nanocomposite structures since having superparamagnetic property offer a high potential for biosensing and biomedical application.

Reduced graphene oxide-TiO2 nanocomposite as a promising visible-light-active photocatalyst for the conversion of carbon dioxide

Photocatalytic reduction of carbon dioxide (CO2) into hydrocarbon fuels such as methane is an attractive strategy for simultaneously harvesting solar energy and capturing this major greenhouse gas. Incessant research interest has been devoted to preparing graphene-based semiconductor nanocomposites as photocatalysts for a variety of applications. In this work, reduced graphene oxide (rGO)-TiO2 hybrid nanocrystals were fabricated through a novel and simple solvothermal synthetic route. Anatase TiO2 particles with an average diameter of 12 nm were uniformly dispersed on the rGO sheet. Slow hydrolysis reaction was successfully attained through the use of ethylene glycol and acetic acid mixed solvents coupled with an additional cooling step. The prepared rGO-TiO2 nanocomposites exhibited superior photocatalytic activity (0.135 μmol gcat−1 h−1) in the reduction of CO2 over graphite oxide and pure anatase. The intimate contact between TiO2 and rGO was proposed to accelerate the transfer of photogenerated electrons on TiO2 to rGO, leading to an effective charge anti-recombination and thus enhancing the photocatalytic activity. Furthermore, our photocatalysts were found to be active even under the irradiation of low-power energy-saving light bulbs, which renders the entire process economically and practically feasible.