Nanocrystalline Size Research Articles

Development of a novel fcc structure for an amorphous-nanocrystalline Ti-33Nb-4Mn (at.%) ternary alloy

In this work, a novel amorphous-nanocrystalline titanium‑niobium‑manganese solid solution ternary alloy with a Ti-33Nb-4Mn (at.%) nominal composition was developed by a High-Energy Mechanical Alloying. Nb and Mn were added to the elemental Ti as a β-phase (bcc) stabilizer and an amorphization promoter, respectively. The system evolved from the elemental Ti, Nb and Mn raw materials to a body centred cubic (bcc) TiNbMn alloy and, finally, to the formation of an original and stable face centred cubic (fcc) nanocrystalline TiNbMn alloy, not reported until now, at short milling time (20h). This alloy remains invariant until 120h. In turn, the partial amorphization of the system occurs and increases until at intermediate milling time (80h). The production of both original fcc and the amorphous TiNbMn alloy may be beneficial for reducing the Young's modulus and improving the mechanical strength pursued for the Ti alloy. The optimal milling time respect to the amorphization, nanocrystalline size and Fe mount from milling media was 60h and 80h (TiNbMn60h and TiNbMn80h), with >50wt% of an amorphous phase and a crystalline domain size of approximately 5nm.

Structural and optical characterization of p-type highly Fe-doped SnO2 thin films and tunneling transport on SnO2:Fe/p-Si heterojunction

Nanocrystalline highly Fe-doped SnO2 thin films were prepared using a new simple sol-gel method with iron amounts of 5, 10, 15 and 20%. The obtained gel offers a long durability and high quality allowing to reach a sub-5 nm nanocrystalline size with a good crystallinity. The films were structurally characterized through X-ray diffraction (XRD) that confirms the formation of rutile SnO2. High Resolution Transmission Electron Microscopy (HRTEM) images reveals the good crystallinity of the nanoparticles. Raman spectroscopy shows that the SnO2 rutile structure is maintained even for high iron concentration. The variation of the PL intensity with Fe concentration reveals that iron influences the distribution of oxygen vacancies in tin oxide. The optical transmittance results indicate a redshift of the SnO2 band gap when iron concentration increases. The above optical results lead us to assume the presence of a compensation phenomenon between oxygen vacancies and introduced holes following Fe doping. From current-voltage measurements, an inversion of the conduction type from n to p is strongly predicted to follow the iron addition. Electrical characterizations of SnO2:Fe/p-Si and SnO2:Fe/n-Si heterojunctions seem to be in accordance with this deduction. The quantum tunneling mechanism is expected to be important at high Fe doping level, which was confirmed by current-voltage measurements at different temperatures. Both optical and electrical properties of the elaborated films present a particularity for the same iron concentration and adopt similar tendencies with Fe amount, which strongly correlate the experimental observations. In order to evaluate the applicability of the elaborated films, we proceed to the fabrication of the SnO2:Fe/SnO2 homojunction for which we note a good rectifying behavior.

Effects of drug-oil properties on fabrication of drug nanocrystalline self-stabilizied Pickering emulsions

To investigate the effects of drug and oil properties on the formation and stability of drug nanocrystalline self-stabilizied Pickering emulsions (NSSPE). Three insoluble Chinese medicine components (puerarin, tanshinone ⅡA and ferulic acid) were selected as model drugs, and Capmul C8, Fabrafil M 1944 CS, isopropyl myristate, Pzechwan Lovage Rhizome oil, and olive oil were used as oil phase. NSSPEs were developed by high pressure homogenization method and were evaluated for their appearance, centrifugal stability, droplet size and drug content changes in emulsion layer after storing at room temperature for 14 d. Then the properties of the oil (surface tension and viscosity) and properties of the drugs (surface energy, oil-water partition coefficient, size and Zeta potential of nanocrystalline and drug-water-oil contact angle) on the formation and stability of NSSPE were analyzed. The emulsification property and stability of five samples prepared with ferulic acid nanocrystals and different oils were significantly lower than those of puerarin and tanshinone ⅡA; the particle size of ferulic acid nanocrystals was 3.90 μm, extremely higher than 305 nm of puerarin and 406 nm of tanshinone ⅡA (P<0.05); the zeta potential of ferulic acid nanocrystals was -0.018 0 mV, significantly lower than －29.1 mV of puerarin and -42.6 mV of tanshinone ⅡA (P<0.05). Three samples prepared with isopropyl myristate and different drugs were not emulsions and the viscosity of isopropyl myristate was 4.67 mPa•s, significantly lower than that of the other oils (P<0.01). Puerarin-NSSPEs prepared with Pzechwan Lovage Rhizome oil showed best emulsification property and stability; the contact angle of puerarin in Pzechwan Lovage Rhizome oil-water was 69.7°, close to 90°, significantly higher than other contact angles. NSSPEs made by tanshinone ⅡA-Capmul C8-water, tanshinone ⅡA-Labrafil M 1944 CS-water showed highest stability, with a contact angle of 99.2° and 112° respectively, more close to 90° than other oils. The results indicated that viscosity, size and Zeta potential of nanocrystalline and three-phase contact angle had great influence on the formation and stability of NSSPE; surface tension of oil, surface energy of drug and oil-water partition coefficient may not be related to the construction of NSSPE.

Thermal stability of surface nano-crystallization layer in AZ91D magnesium alloy induced by laser shock peening

Thermal stability of surface nano-crystallization layer in AZ91D magnesium alloy induced by laser shock peening (LSP) was investigated in this paper. Transmission electron microscopy (TEM) and X-ray diffractometer (XRD) were employed to characterize the variation of microstructure and phase composition of AZ91D magnesium alloy after LSP with and without annealing. The enthalpy of the amorphous magnesium alloy after LSP was examined by differential scanning calorimeter (DSC). Results demonstrated that the average size of nano-crystalline on the surface of AZ91D alloy produced by LSP was 90–100nm. A mass of high density dislocations was observed in LSPed layer and gradually disappeared during the following annealing treatment. Recrystallization phenomenon, which was confirmed by analysis of TEM and XRD results, leads to a further reduction of crystal dimension. There is not enough time for recrystallized grain to grow up when annealing at 200°C–300°C. Meanwhile, amounts of precipitates exist in grain boundaries hindered the movement of dislocations, which indirectly impeded the growth of gains. When the annealing temperature exceeded 300°C, nano-grains became metastable and began to grow up dramatically in 20h, which can be attributed to the coarsening of precipitates and the disappearance of dislocation. Therefore, thermal stability of surface nano-crystallization layer mainly depends on the combined effect of high density dislocations, recrystallization, precipitates, and the uneven distribution of grains.

Structure, Mechanical and Tribological Properties of HVOF Sprayed (WC-Co+Al) Composite Coating on Ductile Cast Iron

The paper presents the results of examinations of WC-Co coating sprayed on ductile cast iron by high velocity oxygen fuel spray process (HVOF) with powder containing Al particles in an amount of 10%. The impact of Al particles added to the tungsten carbide coating on the structure, mechanical and tribological properties in the system of (WC-C)/ductile cast iron was examined. The microstructure of the thermal sprayed WC-Co+Al coating was characterized by light, scanning electron (SEM) and transmission electron (TEM) microscopes as well as the analysis of chemical and phase composition in micro areas (EDS, XRD). It was found that by supersonic thermal spraying with WC-Co powders with the addition of Al particles, the coatings of low porosity, high hardness, a very good adhesion to the substrate, compact structure with molten Al particles and finely fragmented WC particles embedded in a cobalt matrix, reaching the nanocrystalline sizes were obtained. Moreover, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (WC-Co+Al)/ductile cast iron as well as hardness and wear resistance of the coating. It was found that the addition of Al particles was significantly increase resistance to cracking and wear behaviour in the studied system

Two‐Step Fabrication of Li4Ti5O12‐Coated Carbon Nanofibers as a Flexible Film Electrode for High‐Power Lithium‐Ion Batteries

AbstractA self‐standing nonwoven flexible Li4Ti5O12/carbon nanofiber composite (denoted LTO/CNF) was synthesized by using a facile method involving the electrospinning fabrication of CNFs and chemical deposition of LTO over the CNF surface. Scanning electron microscopy and transmission electron microscopy analyses show that the LTO/CNF film is composed of 50±20 nm diameter LTO polycrystalline particles distributed over 300±50 nm diameter CNF nanofibers. The nitrogen sorption isotherm further reveals the existence of mesopores in the LTO/CNF film. The as‐prepared LTO/CNF composite exhibits attractive rate capability for lithium‐ion batteries (LIBs), delivering initial specific capacities of 158, 153, 146, 138, 131, 122, and 109 mA h g−1 at rates of 1, 5, 10, 20, 30, 40, and 50 C, respectively, and a very stable cycling performance during 500 charge and discharge cycles at 20 C, which superior to electrodes made of commercial coarse‐type LTO anodes. In addition, the electrochemical impedance is effectively reduced by fabricating the unique electrode architecture, which originates from the improved 3D conducting network and the nanocrystalline size of the LTO active phase. Electrospinning of CNFs and chemical deposition of a nanocrystalline LTO phase proves to be an effective and facile method to develop anodes for flexible LIBs with a wide range of potential applications.

Evolution of nanostructure in hydrogenated amorphous silicon thin films with substrate temperature studied by Raman mapping, Raman scattering and spectroscopic ellipsometry

Raman mapping and Raman scattering studies have been performed on hydrogenated silicon thin films deposited at different substrate temperature by rf-PECVD technique. In Raman mapping a clear difference in contrast, corresponding to different phases, was observed for films deposited at substrate temperature (Ts) ≥ 130 °C. The Raman spectra recorded at bright and dark spots in Raman image correspond to nanocrystalline and amorphous phase respectively. The fractional area of bright spots in Raman mapping was found to increase with increasing Ts. Also, the nanocrystalline fraction and size of nanocrystallites is found to increase with increasing Ts. These studies suggest that nucleation sites for the growth of nc-Si:H are formed at substrate temperature as low as 130 °C. With further increase in Ts more and more nucleation sites are formed which subsequently enhance crystallinity in these films. Films deposited at Ts ≥ 150 °C have larger band gap, higher roughness and higher photosensitivity and are of excellent device quality.

Application of Improved BP Neural Network in the Preparation Processing of the CaCO&lt;sub&gt;3&lt;/sub&gt; Nanocrystalline

A three-layer structure back-propagation network model based on the non-linear relationship between the size of the CaCO3 nanocrystalline and the technological factors, such as reaction time, reaction temperature, raw material adding amount of NaCO3 and CaCl2, was established. Moreover, in order to accelerate the converging rate and avoid the non-converging situation, the momentum terms are introduced. Besides, the variable learning speed is adopted. At the same time, the input variables were pretreated by using the main component analysis firstly. And the results show that the improved back propagation neural networks model is very efficient for predication of the CaCO3 nanocrystalline size.

Synthesis and photoluminescent properties of Dy3+ doped Y2O3 phosphor

In this report, structure, morphology and luminescent studies of Y2O3:Dy3+ phosphors prepared by solid sate reaction method are presented. With this simple and cost effective method, phosphor with desired phase composition can be obtained by mixing appropriate amounts of yttrium and dysprosium oxide. A set of samples is prepared with different Dy3+ concentrations in order to observe changes in luminescent properties. For all samples, XRD pattern showed that prepared phosphors have cubic structure,the crystallite size of the phosphors was calculated from the full width half maxima of the diffraction peaks by using Scherer formula equation and is approximated to be 143.1 nm. SEM analysis showed the nanocrystalline size of 110 nm. The SEM gives the agglomerated fluffy nature of prepared phosphor. FTIR confirms the characteristics vibrational mode Dy-O bonding. The variation of PL characteristics with varying concentration(0.5,1,1.5 and 2 mol%) of Dy3+ is analyzed .The optical absorption band spectra is measured in range 200 to 500 nm.

Synthesis and characterization of bismuth phosphate nanoparticle in glass matrix

Glasses having composition 5Li2O–5ZnO– xBi2O3 –(90 − x) P2O5 (x = 5, 10, 15, 20 and 25 mol%) were prepared by the normal melt quenching technique. Nanocomposite glass containing bismuth phosphate BiPO4 nanocrystals was obtained, which can be attributed to homogeneous nucleation process. The formation of BiPO4 nanocrystals was confirmed and characterized by X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), differential scanning calorimetry, optical absorption (UV–Vis) and micro-hardness studies. The morphological analysis by XRD and TEM microscopy showed the formation of hexagonal BiPO4 nanocrystals, and its estimated nanocrystalline sizes were found to be varying from 5.35 to 11.53 nm depending on the Bi2O3 concentrations. The density (ρ) and molar volume (V m) were also determined and found to be in compositional dependence. Glass transition temperature (T g) and glass crystallization temperature (T c) were obtained and found to be increased (from 240.0 to 337.2 °C) with increasing Bi2O3 up to 20 mol% and then decreased (from 337.2 to 331.8 °C) due to the structural changes in the glass network. Effect of BiPO4 content on the optical properties had been investigated. From the UV–Vis spectra, it was observed that the fundamental absorption edge shifts toward lower wavelengths, i.e., blueshifts with increasing Bi2O3 mol% up to 20 mol%, and then shifts toward higher wavelengths, i.e., redshifts beyond 20 mol%. It was also observed that the obtained E opt (for indirect and direct transitions) increases with gradual increase in Bi2O3 content up to 20 mol% and then decreases beyond 20 mol%. This may be due to the introduction of Bi cations into the glass network as a network former up to 20 mol% causing a decrease in ΔE values, beyond 20 mol%, the introduction of Bi ions into the glass network interstitially leads to increase the values of ΔE. The optical properties of the present nanocrystallized glasses showed a quantum size dependence, in which the optical band gap energy (E opt) was changed as a function of BiPO4 nanocrystalline sizes.

Preparation and characterizations of CuO doped ZnO nano-structure for the photocatalytic degradation of 4-chlorophenol under visible light

In the present investigation, a ZnO nanostructure was synthesized by means of precipitation and sonochemical methods. The X-ray diffraction (XRD) pattern indicated that the wurtzite structure of ZnO had a hexagonal symmetry and there was no impurity. The average ZnO particles crystallite size was calculated at about 41 nm. The SEM and TEM images revealed nanostructure ZnO particles with a cauliflower-like and rod morphology with dimensions of 85, 79 and 117 nm. In order to investigate the increment of ZnO photoactivity under visible light, the CuO doped ZnO nanostructures were fabricated by a wet impregnation method using copper oxide as the copper source and ZnO as the precursor. The XRD analysis confirmed that the CuO phase was present in the as-prepared sample and the average size of nano crystalline decreased to about 36 nm. The DRS spectra indicated the extended absorption of CuO-ZnO to the visible range as a result of band gap reduction to 2.9 eV (in comparison of 3.2 eV in ZnO). In order to investigate the photocatalytic activity of the synthesized photocatalyst, the degradation of 4-Chlorophenol under visible light was performed. Sixteen experiments using full factorial were executed by adjusting four parameters (amount of catalyst, initial concentration of 4-Chlorophenol, pH, and time of irradiation). An empirical expression was proposed and successfully used to model the photocatalytic process with a high correlation, and an optimal experimental region was also obtained. According to the developed model for degradation and the subsequent ANOVA test using Design Expert software, the time of irradiation with a 46.57% effect played the most important role in the photocatalytic activity, while the influences of parameters on each other were negligible. Optimal experimental conditions for 4-Chlorophenol concentration (0.01 g/L) were found at an initial pH =8 and a catalyst loading of 0.07 g/L. The results indicated that CuO-ZnO can remove 95% of 4-chlorophenol from water under optimal conditions.

Photoinduced Operation by Absorption of the Chalcogenide Nanocrystallite Containing Solar Cells

Abstract It is shown that for the solar cells containing chalcogenide nanocrystallites using external laser light, one can achieve some enhancement of the photovoltaic efficiency. Photoinduced treatment was carried out using two beams of splitted Er: glass laser operating at 1.54 μm. The light of the laser was incident at different angles and the angles between the beams also were varied. Also, the studies of nanocomposite effective structures have shown enhancement of effective nanocrystalline sizes during the laser treatment. Nanocrystallites of CuInS2 and CuZnSnS4 (CZTS) were used as chalcogenide materials. The optimization of the laser beam intensities and nanoparticle sizes were explored.

Morphological, Structural and Optical Properties of ZnO Thin Films Deposited by Dip Coating Method

Zinc oxide (ZnO) thin films were deposited on glass substrat by dip coating technique. The effects of sol aging time on the deposition of ZnO films was studied by using the field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and optical transmission techniques. The morphology of the films strongly depends on preparation route and deposition technique. It is noteworthy that films deposited from the freshly prepared solution feature indistinct characteristics; had relatively poor crystalline quality and low optical transmittance in the visible region. The increase in sol aging time resulted in a gradual improvement in crystallinity (in terms of peak sharpness and peak intensity) of the hexagonal phase for all diffraction peaks. Effect of sol aging on optical transparency is quite obvious through increased transmission with prolonged sol aging time. Interestingly, 72-168 h sol aging time was found to be optimal to achieve smooth surface morphology, good crystallinity and high optical transmittance which were attributed to an ideal stability of solution. These findings present a better-defined and more versatile procedure for production of clean ZnO sols of readily adjustable nanocrystalline size.

Mesoporous and Nanostructured TiO2 layer with Ultra-High Loading on Nitrogen-Doped Carbon Foams as Flexible and Free-Standing Electrodes for Lithium-Ion Batteries.

A simple and green method is developed for the preparation of nanostructured TiO2 supported on nitrogen-doped carbon foams (NCFs) as a free-standing and flexible electrode for lithium-ion batteries (LIBs), in which the TiO2 with 2.5-4 times higher loading than the conventional TiO2 -based flexible electrodes acts as the active material. In addition, the NCFs act as a flexible substrate and efficient conductive networks. The nanocrystalline TiO2 with a uniform size of ≈10 nm form a mesoporous layer covering the wall of the carbon foam. When used directly as a flexible electrode in a LIB, a capacity of 188 mA h g-1 is achieved at a current density of 200 mA g-1 for a potential window of 1.0-3.0 V, and a specific capacity of 149 mA h g-1 after 100 cycles at a current density of 1000 mA g-1 is maintained. The highly conductive NCF and flexible network, the mesoporous structure and nanocrystalline size of the TiO2 phase, the firm adhesion of TiO2 over the wall of the NCFs, the small volume change in the TiO2 during the charge/discharge processes, and the high cut-off potential contribute to the excellent capacity, rate capability, and cycling stability of the TiO2 /NCFs flexible electrode.

Deformation mechanisms of nanocrystalline alpha titanium in Ti-6Al-4V

The deformation mechanisms of alpha titanium with the hexagonal close-packed structure in Ti-6Al-4V subjected to severe plastic deformation were investigated. The fine-structure characteristics of alpha titanium with different nanocrystalline sizes were observed and analyzed via high-resolution transmission electron microscopy. The experimental results suggested that dislocation slip was the dominant deformation mechanism and the pyramidal 〈c+a〉-type dislocation slip was liberally activated as the nanocrystalline size was larger than 15nm. Meanwhile, twinning on {11¯01} plane contributed much less to the deformation. As the nanocrystalline size decreased to be smaller than 15nm, grain boundary sliding would accommodate the deformation.

Mechanical and Tribological Properties of HVOF-Sprayed (Cr3C2-NiCr+Ni) Composite Coating on Ductile Cast Iron

The aim of the investigations was to compare the microstructure, mechanical, and wear properties of Cr3C2-NiCr+Ni and Cr3C2-NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr 3 C 2 -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed Cr3C2-NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine Cr3C2 and Cr7C3 particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (Cr3C2-NiCr+Ni) in wear conditions.

Room temperature synthesis of ultra-small, near-unity single-sized lead halide perovskite quantum dots with wide color emission tunability, high color purity and high brightness

Phosphor with extremely narrow emission line widths, high brightness, and wide color emission tunability in visible regions is required for display and lighting applications, yet none has been reported in the literature so far. In the present study, single-sized lead halide perovskite (APbX3; A = CH3NH3 and Cs; X = Cl, Br, and I) nanocrystalline (NC) phosphors were achieved for the first time in a one-pot reaction at room temperature (25 °C). The size-dependent samples, which included four families of CsPbBr3 NCs and exhibited sharp excitonic absorption peaks and pure band gap emission, were directly obtained by simply varying the concentration of ligands. The continuity of the optical spectrum can be successively tuned over the entire UV–visible spectral region (360–610 nm) by preparing CsPbCl3, CsPbI3, and CsPb(Y/Br)3 (Y = Cl and I) NCs with the use of CsPbBr3 NCs as templates by anion exchange while maintaining the size of NCs and high quantum yields of up to 80%. Notably, an emission line width of 10–24 nm, which is completely consistent with that of their single particles, indicates the formation of single-sized NCs. The versatility of the synthetic strategy was validated by extending it to the synthesis of single-sized CH3NH3PbX3 NCs by simply replacing the cesium precursor by the CH3NH3X precursor.

Grain size and lattice parameter's influence on band gap of SnS thin nano-crystalline films

Tin sulphide nano-crystalline thin films were fabricated on glass and Indium Tin Oxide (ITO) substrates by thermal evaporation method. The crystal structure orientation of the films was found to be dependent on the substrate. Residual stress existed in the films due to these orientations. This stress led to variation in lattice parameter. The nano-crystalline grain size was also found to vary with film thickness. A plot of band-gap with grain size or with lattice parameter showed the existence of a family of curves. This implied that band-gap of SnS films in the preview of the present study depends on two parameters, lattice parameter and grain size. The band-gap relation with grain size is well known in the nano regime. Experimental data fitted well with this relation for the given lattice constants. The manuscript uses theoretical structure calculations for different lattice constants and shows that the experimental data follows the trend. Thus, confirming that the band gap has a two variable dependency.

High-Yielding Green Hydrothermal Synthesis of Ruthenium Nanoparticles and Their Characterization.

Using hydrothermal techniques, a novel synthetic approach to prepare ruthenium nanoparticles has been developed. At 180 degrees C and under autogenous pressure, starting from an aqueous solution of ruthenium trichloride, the method yielded nanoparticles whose form and size both depended on the reducing agent: sodium citrate (hexagonal shaped nanocrystals, 1-20 nm), ascorbic acid (spherical nanoparticles, 3-5 nm) and succinic acid (spherical nanoparticles, 1-120 nm). Depending on the reaction variables, the nature and concentration of partially reduced species determines the characteristics of the final products. HRTEM image analysis along with the simulation techniques were stabilized preferential growth of nanoparticles on specific directions. Ruthenium samples have been investigated by Temperature-Programmed Reduction (TPR) showing that the reduction temperature of nanoparticles is correlated to their nanocrystalline size.

Photocatalytic degradation of indigo carmine using Nd-doped TiO2-decorated graphene oxide nanocomposites

A series of neodymium-doped titanium dioxide (Nd–TiO2) decorated on graphene oxide (GO) were synthesized by sol–gel method. The structures, morphologies and optical properties of the nanocomposites (Nd–TiO2–GO) were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. The photocatalytic study of Nd–TiO2–GO nanocomposites was evaluated via the degradation of indigo carmine under simulated solar light. Results demonstrated that the photodegradation efficiency of indigo carmine solutions irradiated by solar simulated light for 3 h with the nanocomposites used as a catalyst reached a level of 92 % (0.6 % Nd). This high photocatalytic degradation of indigo carmine solutions by the Nd–TiO2–GO nanocomposites is ascribed to the spherical nanocrystalline size of TiO2.