TiO2 rGO Research Articles

Hybrid TiO2–RGO nanocomposite as high specific capacitance electrode for supercapacitor

This study describes the fabrication of composite electrodes comprising TiO2 and reduced graphene oxide layers using a moderate-temperature hydrothermal method. The morphology, crystalline structure, chemical composition, and optical features of the prepared composites were analyzed by FE-SEM, x-ray diffraction, FTIR, and UV–visible spectroscopy. The cyclic voltammetry (CV) and Nyquist plots were used to assess the electrochemical and impedance responses of the composite electrodes, respectively. The analysis revealed that the incorporation of RGO reduced the TiO2 bandgap to 3.87 eV 3.02 eV and improved the specific capacitance, enhancing the TiO2-RGO electrode’s supercapacitive performance. CV studies highlight that the TiO2-RGO composite has a high specific capacitance of 152 F g−1 at a substantially faster scan rate of 25 mV s−1 in a 1.0 M-KOH dilute electrolyte. These findings confirmed the applicability of the fabricated electrodes as prospective supercapacitor electrodes.

Facile synthesis of reduced graphene oxide and graphitic carbon nitride modified titanium dioxide nanospheres for photoanode of dye-sensitized solar cell

Titanium dioxide/reduced graphene oxide nanocomposites (TiO2/rGO NCs) have been broadly utilized as photoanode materials for dye-sensitized solar cell (DSSC). Nevertheless, photoelectric conversion efficiency (PCE) of DSSC is diminished due to recombination of charges takes place between photoanode and electrolyte interface. Herein, we have prepared a triplet structure nanocomposite composed of TiO2 nanospheres, rGO and graphitic carbon nitride (TiO2 NS/rGO/g-C3N4 NC) for photoanode of DSSC. The ternary TiO2 NS/rGO/g-C3N4 NC photoanode has enhanced dye absorption considerably and as a consequence, improved light harvesting efficiency. Besides, the introduction of rGO and g-C3N4 on the TiO2 NS has effectually speeded up the transport of electrons and minimized the recombination of photogenerated charges. Consequently, the DSSC integrated with ternary TiO2 NS/rGO/g-C3N4 NC photoanode has exhibited ∼41 % increment in the PCE of 5.77 % when compared to PCE of the pristine TiO2 NS photoanode (4.10 %). This finding has proposed a simplistic approach to advance photovoltaic performance of the DSSC.

Fabrication of photocatalytic PAN nanofiber membrane loading with TiO2@RGO by electro-spinning & electro-spraying

The new fibrous photocatalytic nanofiber membrane with both good photodegradation performance and mechanical property was developed. Here, TiO2@RGO (TR) which could disperse in PAN solution stably was prepared by solvothermal method with the help of acetic acid. Then the new photocatalytic PAN nanofiber membrane SS7.5-2.3 TR(A) was fabricated for the first time by electro-spinning & electro-spraying, where TR ruled as photocatalysts. Benefited from its novel triple structure, SS7.5-2.3 TR(A) had the best toughness when compared with S-0 (electro-spun dual-network structural membrane) and SS7.5 (control membrane without TR in electro-spraying solution). Moreover, the morphology and mechanical property of membrane was similar to that of original SS7.5-2.3 TR when it was used to photodegrade methyl orange solution five times later. Meanwhile, SS7.5-2.3 TR also had significant photocatalytic performance when applied to the degradation of other three dyes (rhodamine B, methylene blue and oil red) and silk dyeing wastewater, which indicated its potential in dyeing wastewater treatment.

Effective graphene incorporation of strontium niobate–doped titanium oxide for photocatalytic hydrogen production

To meet the increasing global demand for clean energy and mitigate the impact of CO2 emissions on climate change, the production of photocatalytic hydrogen through water splitting is a compelling scientific and technological objective. Despite considerable efforts, the establishment of a reliable and highly efficient system for hydrogen generation powered by visible light remains challenging. In this study, we developed a solar-active strontium niobate-doped titanium oxide incorporated with graphene (Sr2Nb2O7–rGO–TiO2), characterized by various analytical techniques such as optical, morphological, HR-TEM, XPS, and XRD. Sr2Nb2O7–rGO–TiO2 demonstrated enhanced photocatalytic H2 evolution under solar irradiation without requiring precious-metal doping. The maximum H2 production performance rate of 1769 μmol/g/h was attained with the Sr2Nb2O7–rGO–TiO2 composites, significantly surpassing those of the bare (TiO2: 210 μmol/g/h, Sr2Nb2O7: 88 μmol/g/h) and binary (TiO2–rGO: 430 μmol/g/h, Sr2Nb2O7–rGO: 176 μmol/g/h, and Sr2Nb2O7–TiO2: 880 μmol/g/h) photocatalysts. The enhanced performance of the Sr2Nb2O7–rGO–TiO2 composite is attributable to the synergistic effect of rGO acting as an electron-transfer bridge. Thus, with the integration of rGO, absorption is attainable in an extended range up to 445 nm (2.90 eV), suggesting that the composite material could enable the catalyst to absorb more visible light. Additionally, the composite exhibited minor degradation after five consecutive cycles, demonstrating its excellent stability and reusability for hydrogen generation. Based on a comprehensive evaluation of the ESR and transient photocurrent response, a potential Z-scheme mechanism for the photocatalytic H2 generation activity over Sr2Nb2O7–rGO–TiO2 was suggested. The Z-scheme processability allows more electrons to contribute to the H2 evolution reduction. In this study, we developed a non-toxic, cost-effective, highly efficient, and recyclable photocatalyst for H2 production.

TiO2 nanowire formation and GO reduction through a hydrothermal reaction to improve the thermal conductivity of epoxy composites

AbstractThe thermal path must be properly configured to improve the thermal properties of polymer composites. Three‐dimensional (3D) thermally conductive networks can be used as an excellent means for building high‐speed conductive pathways in polymer composites. Titanium dioxide (TiO2) nanowire (NW)/reduced graphene oxide (rGO)/epoxy (EP) composite material has a 3D foam structure and focuses on TiO2 NW formation and rGO gelation through a hydrothermal process. The thermal conductivity of the synthetic composite material through filler loading at 50 wt.% and heat transfer path formation was 805% higher than that of pure EP, and the thermal conductivity was superior to that of the composite material with randomly dispersed fillers. Therefore, this work describes an advanced process to improve the thermal conductivity of polymer composites significantly.

A highly sensitive room temperature liquefied petroleum gas (LPG) sensor with fast response based on a titanium dioxide (TiO2)–reduced graphene oxide (r-GO) composite

The LPG sensing performance of TiO2–rGO composite is augmented due to the presence of a p–n junction with enhanced barrier width.

Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Graphene oxide (GO) obtained from coal-based graphite by the Hummers method was hydrothermally treated to obtain reduced GO (rGO). TiO2 was mixed with aqueous suspensions of GO and rGO and dried at 70 °C to obtain GO-TiO2 and rGO-TiO2 with 95 wt% TiO2. TiO2 was also combined with a GO suspension by hydrothermal treatment to obtain rGO-hTiO2 with 95 wt% TiO2. The three hybrids were used as catalysts for the photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO). Of the three materials, rGO-hTiO2 had the highest catalytic activity for the degradation of Rh B and MO under visible light irradiation. The reasons for having the best catalytic activity are that the incorporation of rGO into TiO2 helps increase its adsorption capacities for Rh B and MO as evidenced by adsorption in dark, and a narrowing of the TiO2 band gap as revealed by diffuse UV reflectance spectroscopy. This reduces the rate of recombination of electron-hole pairs by there being intimate contact between the TiO2 particles and rGO, forming Ti-O-C bonds as confirmed by XPS, with the TiO2 particles being uniformly decorated on the rGO sheets.

Enhanced photocatalytic activity of three-dimensional TiO2/reduced graphene oxide aerogel by efficient interfacial charge transfer

TiO2 is one of the most widely used photocatalytic semiconductors. However, the rapid recombination of photogenerated electron-hole pairs severely weakens its photocatalytic activity. Herein, a three-dimensional TiO2/reduced graphene oxide (TiO2-rGO) aerogel with enhanced interfacial charge transfer was synthesized by a facile hydrothermal method, and its photocatalytic degradation of Methylene Blue (MB) and Reactive Red 24 (RR24) dyes was investigated. The photocatalytic results showed that TiO2–rGO aerogel possesses excellent photocatalytic activity, and its photocatalytic degradation rate towards dyes is more than 3.8 times that of pure TiO2 and more than 2.7 times that of TiO2-GO aerogel. Characterization results indicated that the significantly enhanced photocatalytic activity of TiO2-rGO aerogel could be attributed to the enhanced π–conjugated structure of rGO, which can effectively increase interfacial charge transfer and inhibit electron-hole pairs recombination. The mechanism suggested that OH and O2− are the active species in the photocatalytic degradation process. Our findings can provide an important reference for the preparation of high-performance TiO2-based photocatalysts.

Enhanced photodegradation toward graphene–based MgFe2O4–TiO2: Investigation and optimization

In this work, graphene–based MgFe2O4–TiO2 (MFO–TiO2@rGO) nanocomposite was synthesized and conducted an efficient photo–treatment with p–nitrophenol (PNP) as a well–known pollutant in water. The ternary material was characterized by modern analysis methods including Fourier transform infrared spectroscopy, X–ray diffraction, Raman spectroscopy, Transmission electron microscopy, Energy–dispersive X–ray spectroscopy, Selected area electron diffraction, and UV–vis spectroscopy. The simultaneous effects of the volume of H2O2, catalyst dosage, and pH on the photodegradation of p–nitrophenol were also examined by full factorial experimental design according to Box–Behnken designs. As a result, the characterization has confirmed the uniform bounding of MFO and TiO2 nanosizing from 4 to 6 nm on graphene with a high crystallinity degree. The photocatalysis of this material toward PNP can reach up to ∼99.44% in only 60 min reaction under UV control with 1.12 mL H2O2 added, 38.15 mg catalyst, and pH 9. Besides, in solar condition (directly under sun), the material also expressed a relatively impressive capability in degrade PNP from water. Furthermore, the ternary nanocomposite can be easily recycled and reused with an inconsiderable change in yield, represented by the elimination yield of recovered MFO–TiO2@rGO was significantly more than 90% after ten–run cycles. Indeed, the nanocomposite suggests an efficient pathway for treating organic contaminants in wastewater treatment.

TiO2–rGO nanocomposites with high rGO content and luminescence quenching through green redox synthesis

We developed TiO2–rGO nanocomposites with high exfoliated rGO content upto 47.1% (TG4) by weight hitherto not reported, through green redox synthesis. Progressive reduction of TiO2 nanocrystal size and their in situ intercalation occurred on increasing rGO via one pot synthesis, not reported previously and forming highly stable Ti–O–C bonds. With increase in rGO content, the exfoliation in the nanocomposite was also limited to single-few layered graphene oxide sheets through use of ascorbic acid avoiding restacking, and thereby the recombination of photogenerated carriers. TG4 showed 50% photoluminescence (PL) quenching indicating long-lived electron transfer state with rGO and apparent rate of nonradiative excited state decay of 1.15 × 108 s−1. Details of lattice orientation, Raman spectra, electronic states and PL lifetime decay are discussed to elucidate effective charge carrier separation in the nanocomposite. Near complete photodegradation of Alizarin Yellow GG azo dye, an industrial pollutant, could be obtained under direct sunlight using TG4 as catalyst.

Crack-Free and Thickness-Controllable Deposition of TiO2–rGO Thin Films for Solar Harnessing Devices

The use of thin films consisting of TiO2 and reduced graphene oxide (TiO2–rGO) in solar harnessing devices is gaining momentum thanks to improved charge-transporting characteristics. In this report, we propose a facile spin-coating methodology for the deposition of crack-free and thickness-controllable TiO2–rGO thin films. A range of characterization techniques were utilized to confirm the formation of the TiO2–rGO thin film. Improved charge-transporting properties of TiO2–rGO composite thin films were confirmed by measuring their photoelectrochemical (PEC) activity under simulated solar light illumination. In particular, it was found that the TiO2–rGO composite thin film yielded a better photocurrent response (~151.3 µA/cm2) than the bare TiO2 thin film (~71.6 µA/cm2) at 1.23 eV vs. the reversible hydrogen electrode (RHE). The obtained results suggested that rGO addition remarkably improves the charge-transporting properties in TiO2 films.

In-depth understanding of the photoreduction of graphene oxide to reduced-graphene oxide on TiO2 surface: Statistical analysis of X-ray photoelectron and Raman spectroscopy data

In UV-assisted photoreduction of graphene oxide (GO) using TiO2, TiO2 supplies photogenerated electrons to reduce GO, which exhibits enhanced electrical conductivity, and induce a chemical interaction between TiO2 and reduced-GO (rGO) for improved charge separation. Here, we investigated the photosynthesis of the TiO2–rGO composite with varying the UV irradiation time, TiO2 source (TiO2-D or –HT, commonly employed in dye-sensitized solar cells), and light power. The final products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy. Most importantly, the chemical interaction between the rGO matrix and TiO2 was confirmed by X-ray photoelectron spectroscopy (XPS), whereas the carbon defects were studied by Raman spectroscopy. As expected, the chemical interaction between the rGO matrix and TiO2 was confirmed by the formation of Ti–O–C and Ti–C bonds. Moreover, during UV irradiation, the concentration of carbon defects increased evenly, implying that the photodegradation occurred simultaneously with the photoreduction of GO. The XPS and Raman data were further subjected to statistical analyses, including principal component analysis, multivariate linear regression and analysis of variance (ANOVA), and ANOVA–simultaneous component analysis. The results indicated that the irradiation time and TiO2 source had the highest impacts on the final products.

Photocatalytic Degradation of Alachlor over Titania-Reduced Graphene Oxide Nanocomposite: Intrinsic Kinetic Model and Reaction Pathways

An intrinsic kinetic model based on a proposed reaction photomechanism explicitly dependent on the volumetric rate of photon absorption (VRPA) has been performed and analyzed for the photocatalytic degradation of alachlor in water. A titania-reduced graphene oxide nanocomposite (HBK TiO2–rGO) was used as the photocatalyst. The proposed degradation pathway was elucidated addressing H* – abstraction, HO* substitution, C–C scission, C–N bond scission, and dealkylation reactions. A suitable kinetic model has successfully been validated by fitting the obtained experimental data to reproduce the evolution of alachlor photodegradation at different HBK-rGO loadings. After simplification, the proposed kinetics were adjusted to a reasoned simplified model of 1–2 parameters, showing very good fitting between predicted and experimental values, as denoted by the resulting lower root-square-mean errors. Finally, the synthesized nanocomposite addressed very good stability and durability applied to the degradation of alachlor by photo-oxidation along six consecutive cycles of reuse.

TiO2-rGO Composite for Photocatalytic Decolorization of Methylene Blue Under the Visible Light Illumination

Titanium dioxide-reduced graphene oxide (TiO2-rGO) was synthesized by hydrothermal method using TiO2 powder and rGO precursor from graphite rod by modified Marcano Method. The obtained TiO2-rGO photocatalyst was characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), and Diffuse reflectance UV (DRUV). Based on XRD diffractogram, it is known that TiO2 has an anatase crystal phase. In the FTIR spectrum, it was observed that there was an absorption peak at the wavenumber of 1630 cm-1 from the vibration (C=C) as an indication that the C atom was incorporated into the TiO2 structure. The incorporation of C atoms into the TiO2 structure to form TiO2-rGO causes the bandgap energy to decrease from 3.29 eV to 3.20 eV. The photocatalytic activity was tested against decolorization of methylene blue solution for 180 minutes under visible light illumination from a 50 watt LED lamp. Every 10 minutes, absorbance was measured using a UV-Vis spectrophotometer at a wavelength of 664 nm. TiO2-rGO photocatalyst has better photocatalytic activity with %D of 96.39% under UV light and 84.32% under visible light illumination, while TiO2 is only able to degrade 93.87% and 36.55%, respectively.

Leveraging metal alloy-hybrid support interaction to enhance oxygen evolution kinetics and stability in proton exchange membrane water electrolyzers

This study presents the unprecedented high OER performance of binary iridium (Ir) and ruthenium (Ru) nanoparticles on TiO2-oxide-decorated reduced graphene oxide (rGO) in acidic media. IrRu alloy electrocatalysts supported on TiO2-rGO (denoted as IrRu/TG) were prepared via ultrasonic spray pyrolysis, followed by the polyol method. TiO2-rGO (TG) support is used not only to disperse IrRu nanoparticles effectively but also to induce the electronic modulation of Ir by downshifting its d-band center compared to unsupported catalysts. IrRu/TG exhibits optimal OER performances and high stability when the weight ratio of TiO2:rGO is 90:10 (i.e., T90G10). The successfully synthesized IrRu/T90G10 exhibits remarkable OER activity, requiring a low overpotential of 254 mV to reach 10 mA cm−2 compare with the unsupported IrRuOx (372 mV), IrRu/rGO (325 mV), and commercial Ir black (340 mV). Moreover, TiO2-rGO (TG) support inhibits the aggregation and oxidative dissolution of IrRu species, thereby enhancing the stability in acidic media. In proton exchange membrane water electrolyzer (PEMWE) tests using membrane electrode assemblies (MEAs), IrRu/T90G10 shows more than twice the mass activity of commercial IrO2.

Tailoring hierarchical porous TiO2 based ternary rGO/NiO/TiO2 photocatalyst for efficient hydrogen production and degradation of Rhodamine B

This study reports a facile and cost effective approach for synthesizing a ternary photocatalyst rGO/NiO/TiO2 (RGNPT) based on three-dimensionally hierarchical porous TiO2 (PT) particles, rGO and NiO as a cocatalyst for efficient photocatalytic hydrogen generation. The efficient junction architecture of RGNPT was observed from the TEM study. The composite's morphology was tuned by varying the weight ratio variation of graphene oxide (5, 7.5, and 10 Wt%). The obtained material showed impressive photocatalytic efficiency for H2 production in aqueous methanol suspension. The p-n junction hybrid composite RGNPT-7.5Wt% showed superior activity towards H2 production yield 8,215 µmolg−1 after 4 h of light irradiation and apparent quantum yield efficiency 9.19%. The photocatalyst shows promising results of 88% of photo-degradation efficiency to Rhodamine B (Rh-B) dye. The RGNPT-7.5Wt% demonstrated the higher current density 0.16 µAcm−2 whereas NiO-porous TiO2 (NPT) showed ten folds lower of 0.017 µAcm−2 using Ag/AgCl electrode. The electron impedance spectroscopic results of RGNPT-7.5Wt% heterostructure exhibited higher photocurrent response and lower charge transfer resistance and significantly accelerate the electrons transfers across the NPT and NiO. Photoluminescence lifetime of RGNPT-7.5Wt% (τ = 3.21 ns) is 16 times higher than porous TiO2 (τ = 0.10 ns). This work manifestates that hierarchical porous TiO2 and rGO graphene plays a vital role in the electron transfer pathway, which is further considered an excellent strategy for synthesizing the ternary composites and enhancing photocatalytic hydrogen production.

Single and ternary nanocomposite electrodes of Mn3O4/TiO2/rGO for supercapacitors

Graphene (G) and ternary nanocomposites of Mn3O4, TiO2, and reduced graphene oxide(rGO) electrodes have been prepared for supercapacitor applications. The as-synthesized samples were characterized using several techniques including XRD, SEM, TEM, XPS, and Raman spectroscopy. Electrochemical characterizations were studied via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). XRD patterns of TiO2 and Mn3O4 showed the formation of anatase and hausmannite tetragonal nanoparticles, respectively, whereas rGO and G showed an amorphous structure. The TEM analysis showed spherical shaped particles with less than 50 nm sizes for Mn3O4, nanotube for TiO2, fiber structure for rGO, and layered structure for graphene. The Mn3O4/TiO2/rGO ternary nanocomposite electrode presented a much higher specific capacitance than its single individual constituents. The ternary nanocomposite has a specific capacitance of 356 F g−1 in 6 M KOH aqueous electrolyte and respectable cycling performance, with 91% capacitance retained over 3000 cycles referring to its suitability for supercapacitor applications. An asymmetric supercapacitor (ASC) was constructed using a Mn3O4–TiO2–rGO (MTrGO) as a positive electrode and G as a negative electrode. The organized (ASC) works steadily under the potential window of 0–1.8 V and provides a high-energy density of 31.95 Wh kg−1 at a power density of 7188 W kg−1 complemented by satisfactory cycle stability with 87% capacitance retention over 1000 cycles.

Effect mechanism of copper ions on photocatalytic activity of TiO2/graphene oxide composites for phenol-4-sulfonic acid photodegradation

Organic pollutants in electroplating wastewater can be removed by photodegradation, however the effect mechanism of heavy metal ions on photocatalytic activity still remains unknown. Herein, we firstly reported the self-assembly synthesis of titanium dioxide/reduced graphene oxide (TiO2/rGO) composites for phenol-4-sulfonic acid (PSA) removal, and investigated the effects of Cu2+ ions on photocatalytic efficiency. During the self-assemble process, rGO nanosheets were connected together to form network macropores, and simultaneously induced the deposition of hierarchically nanostructured TiO2 microspheres. The synergetic effects of TiO2 microspheres and rGO nanosheets improved the photocatalytic activity by enhancing light adsorption ability, stabilizing electron-hole separation and decreasing band gap energy. The Cu2+ ions in wastewater showed positive and negative effects on PSA photodegradation. In the photocatalytic reaction, the electron-induced reduction reaction of Cu(II) into Cu(0) or Cu(I) took place, which inhibited electron-hole recombination and thus enhanced photocatalytic activity. However, the high chemical stability of PSA-Cu(II) complex compounds held back PSA photodegradation. The appropriate concentrations of Cu2+ ions at around 25 mg/L accelerated PSA photodegradation over TiO2/rGO composites. The PSA degradation into CO2 and H2O was performed by using hydroquinone, benzoquinone and maleic acid as degradation intermediates. Hence, TiO2/rGO composites are novel multifunctional photocatalysts to purify electroplating wastewater.

TiO2 Nanosheet-Redox Graphene Oxide/Sulphur Cathode for High-Performance Lithium-Sulphur Batteries

Lithium-sulphur batteries are considered as some of the most potent secondary-battery systems. These batteries are expected to have extensive applications in fields requiring high-energy density. However, such applications are hindered by some serious intrinsic obstacles. Herein, TiO₂ nanosheets-rGO/sulphur (TiO₂ NS-rGO/S) composites were fabricated through a two-process hydrothermal method. TiO₂ nanosheets served as active sites for polysulphide absorption, whereas rGO offered space for sulphur improvement and TiO₂ NS-rGO/S composites. The TiO₂ NS-rGO/S composite exhibited high discharge capacity of 1099 mAh·g-1 at 0.2 C rate and retained a capacity of 690 mAh·g-1 after 100 cycles, with high sulphur loading of 3 mg·cm-2. The high initial specific discharge capacity and improved cyclic stability were attributed to the synergistic effects of TiO₂ nanosheets and rGO. These results indicated that the simple, low-cost and scalable method provides a novel perspective on practical utilisation of lithium-sulphur batteries.

TiO2–rGO nanocomposite as an efficient catalyst to photodegrade formalin in aquaculture's waters, under solar light

A solar photocatalytic process, using TiO2–rGO as photocatalyst, is proposed to degrade the formalin disinfectant. This process can treat aquaculture freshwater before its discharge or recirculation, promoting sustainable water.