Aggregation Of TiO2 Nanoparticles Research Articles

Graphene‐Modified TiO2 Microspheres Synthesized by a Facile Spray‐Drying Route for Enhanced Sodium‐Ion Storage

A TiO2@reduced graphene oxide (TiO2@rGO) composite is synthesized successfully by a simple spray‐drying method. The structural and morphological characterizations reveal that the TiO2@rGO composite has a sphere‐like morphology with diameters of 5–15 µm, and each microsphere is actually a random aggregation of primary TiO2 nanoparticles, which are tightly covered by soft graphene sheets. The TiO2@rGO electrode exhibits enhanced electrochemical performance of high charge capacity (170 mA h g−1 at 0.1 C), long cycling life (87% of capacity retention after 300 cycles at 0.2 C), and high rate capability (55 mA h g−1 at 10 C). Compared with bare TiO2 microspheres, the improved electrochemical performance of the TiO2@rGO composite benefits from the introduction of graphene as a highly conductive, flexible, and large‐surface‐area scaffold to provide good electronic contact between active materials, suppress the aggregation of intermediate products, and alleviate the volume change during sodiation and desodiation. The encouraging experimental results suggest that the TiO2@rGO composite has great potential as a high‐capacity and high‐stability anode for the sodium‐ion batteries.

Synthesis, adsorption and photocatalytic property of halloysite-TiO2-Fe3O4 composites

Halloysite-TiO2-Fe3O4 composites were prepared by sequentially depositing anatase TiO2 and magnetic Fe3O4 particles on the halloysite nanotube (HNT) surfaces. HNT-TiO2 and HNT-TiO2-Fe3O4 composites were characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, specific surface analyzer, and X-ray diffraction. The surfaces of HNTs were attached with the aggregates of TiO2 and Fe3O4 nanoparticles, the contents of which were calculated to be about 15.2 and 1.5 wt% in HNT-TiO2-Fe3O4. The adsorption and photodegradation of methylene blue (MB) by HNT-TiO2 and HNT-TiO2-Fe3O4 were studied. HNT-TiO2-Fe3O4 exhibited the faster adsorption process than HNT-TiO2. The kinetic adsorption followed the pseudo-second-order model and the isotherm data fitted the Langmuir model well. The maximum adsorption capacities of MB were 28.07 and 27.27 mg/g for HNT-TiO2 and HNT-TiO2-Fe3O4, respectively. HNT-TiO2-Fe3O4 possessed the better removal capability of MB from the aqueous solution than HNT-TiO2. About 100% MB was removed for HNT-TiO2-Fe3O4 under UV light irradiation for 12 h, in contrast with about 80% MB removal for HNT-TiO2. HNT-TiO2-Fe3O4 exhibited higher photocatalytic activity for the persistent organic pollutant 4-nitrophenol than HNT-TiO2. HNT-TiO2-Fe3O4 and can be easily separated from the aqueous solution with the magnetic rather than the filtration or centrifugation.

Facile preparation of TiO2/C nanocomposites as anode materials for lithium-ion batteries

ABSTRACTTiO2/C nanospheres with diameter of 300–400 nm were synthesized by controlled thermal decomposition of titanium glycolate spheres in inert atmosphere. The effect of the calcination temperature and atmosphere on the structure and composition of the product are investigated. The products obtained by calcination of the precursor in nitrogen at 500°C consist of anatase and rutile nanoparticles, and amorphous carbon that is in situ generated from the organic components of glycolate precursor. When used as anode material for lithium-ion batteries, the as-prepared TiO2/C nanocomposite delivers a capacity of 166 mAh/g after 250 charge/discharge cycles at a current rate of 0.2 C and give a good rate capability. The native carbon not only improves the local conductivity but also prevents the aggregation and growth of TiO2 nanoparticles during calcination, allowing efficient electronic conductivity and Li ion diffusion.

Novel template-free synthesis of hollow@porous TiO2 superior anode materials for lithium ion battery

Template-free method is used to facilely synthesize TiO2 hollow microspheres via one-step hydrothermal method. Interestingly, the TiO2 hollow microspheres have porous shell with thickness of about 450 nm. The formation mechanism of the hollow@porous TiO2 microspheres involves the formation and aggregation of TiO2 nanoparticles followed by oriented growth, etching of HF, and then Ostwald ripening and transformation process. The prepared TiO2 microspheres show a reversible capacity of ~170 mAh g−1 after 150 cycles at a current density of 0.6 C and also exhibit a good rate capability of 40.8 mAh g−1 at a current density of 24 C due to the unique hollow@porous structure, which can offer more sites for the storage and insertion of Li ions, and accelerate electrolyte diffusion and Li ions transport. The results also indicate that the as-prepared TiO2 material possesses excellent electrochemical performances, which may be an ideal anode material for lithium ion battery.

Influence of Controlled Aggregation on Thermal Conductivity of Nanofluids

Nanoparticles aggregation is considered, by the heat transfer community, as one of the main factors responsible for the observed enhancement in the thermal conductivity of nanofluids. To gain a better insight into the veracity of this claim, we experimentally investigated the influence of nanoparticles aggregation induced by changing the pH value or imposing a magnetic field on the thermal conductivity of water-based nanofluids. The results showed that the enhancement in thermal conductivity of TiO2–water nanofluid, due to pH-induced aggregation of TiO2 nanoparticles, fell within the ±10% of the mixture theory, while applying an external magnetic force on Fe3O4–water nanofluid led to thermal conductivity enhancements of up to 167%. It is believed that the observed low enhancement in thermal conductivity of TiO2–water nanofluid is because, near the isoelectric point (IEP), the nanoparticles could settle out of the suspension in the form of large aggregates making the suspension rather unstable. The magnetic field however could provide a finer control over the aggregate size and growth direction without compromising the stability of the nanofluid, and hence significantly enhancing the thermal conductivity of the nanofluid.

Formation of rod-like nanostructure by aggregation of TiO2 nanoparticles with improved performances

To improve the performance of titanium dioxide (TiO2)-based devices, many efforts have been made to prepare nanostructures with composite of TiO2 nanoparticles and nanorods. In this work, a novel rod-like TiO2 nanostructure was obtained via a controllable hydrolysis process. Morphology and structure analysis showed that the rod-like nanostructure was a well-aligned aggregate of nearly spherical TiO2 nanoparticles. Rod-like TiO2 nanoparticle aggregates were fabricated on a primary TiO2 nanoparticle-based layer without the use of template, and formed a hierarchical TiO2 composite film together. The photocatalytic activity of the TiO2 film with rod-like nanoparticle aggregates was evaluated by the degradation of methylene blue. The antibacterial activity of fabricated hierarchical TiO2 film was assessed against Staphylococcus aureus. The photoelectrochemical property of this film as the photoanode in assemble dye-sensitized solar cell was also tested. Compared with randomly distributed nanoparticle-based TiO2 film, the hierarchical TiO2 film exhibited improved performance of photocatalysis, antibacterial activity and photoelectric conversion.

The diverse toxic effect of SiO2 and TiO2 nanoparticles toward the marine microalgae Dunaliella tertiolecta

Nanoparticles (NPs) are widely used in many industrial applications. NP fate and behavior in seawater are a very important issue for the assessment of their environmental impact and potential toxicity. In this study, the toxic effects of two nanomaterials, silicon dioxide (SiO2) and titanium dioxide (TiO2) NPs with similar primary size (~20 nm), on marine microalgae Dunaliella tertiolecta were investigated and compared. The dispersion behavior of SiO2 and TiO2 NPs in seawater matrix was investigated together with the relative trend of the exposed algal population growth. SiO2 aggregates rapidly reached a constant size (600 nm) irrespective of the concentration while TiO2 NP aggregates grew up to 4 ± 5 μm. The dose-response curve and population growth rate alteration of marine alga D. tertiolecta were evaluated showing that the algal population was clearly affected by the presence of TiO2 NPs. These particles showed effects on 50 % of the population at 24.10 [19.38-25.43] mg L(-1) (EC50) and a no observed effect concentration (NOEC) at 7.5 mg L(-1). The 1 % effect concentration (EC1) value was nearly above the actual estimated environmental concentration in the aquatic environment. SiO2 NPs were less toxic than TiO2 for D. tertiolecta, with EC50 and NOEC values one order of magnitude higher. The overall toxic action seemed due to the contact between aggregates and cell surfaces, but while for SiO2 a direct action upon membrane integrity could be observed after the third day of exposure, TiO2 seemed to exert its toxic action in the first hours of exposure, mostly via cell entrapment and agglomeration.

Ultrasmall TiO2 Nanoparticles in Situ Growth on Graphene Hybrid as Superior Anode Material for Sodium/Lithium Ion Batteries.

To inhibit the aggregation of TiO2 nanoparticles and to improve the electrochemical kinetics of TiO2 electrode, a hybrid material of ultrasmall TiO2 nanoparticles in situ grown on rGO nanosheets was obtained by ultraphonic and reflux methods. The size of the TiO2 particles was controlled about 10 nm, and these particles were evenly distributed across the rGO nanosheets. When used for the anode of a sodium ion battery, the electrochemical performance of this hybrid TiO2@rGO was much improved. A capacity of 186.6 mAh g(-1) was obtained after 100 cycles at 0.1 A g(-1), and 112.2 mAh g(-1) could be maintained at 1.0 A g(-1), showing a high capacity and good rate capability. On the basis of the analysis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the achieved excellent electrochemical performance was mainly attributed to the synergetic effect of well-dispersed ultrasmall TiO2 nanoparticles and conductive graphene network and the improved electrochemical kinetics. The superior electrochemical performance of this hybrid material on lithium storage further confirmed the positive effect of rGO.

Heteroaggregation of engineered nanoparticles and kaolin clays in aqueous environments

The increasing and wide use of nanoparticles (NPs), including TiO2 and Ag NPs, have raised concerns due to their potential toxicity and environmental impacts. Kaolin is a very common mineral in aquatic systems, and there is a very high probability that nanoparticles (NPs) will interact with these clay minerals. We studied the effect of kaolin particles on the aggregation of NPs under different conditions, including the role of pH, ionic strength (IS), and humic acid (HA). We show that kaolin reduces the energy barrier and the Critical Coagulation Concentration (CCC) at pH 4. At pH 8, even though the energy barrier of the system without kaolin increases, kaolin promotes NP aggregation via heteroaggregation. When IS is equal to or greater than the CCC, on the one hand HA promotes aggregation of TiO2 NPs, but on the other hand HA decreases the rate of Ag NP aggregation because the existence of a surface coating may limit the adsorption of HA on these Ag NPs. In addition, the presence of HA increases the energy barrier and the CCC of the binary system (kaolin + NPs). Thus, the complex interactions of clay, NPs, IS, pH, and HA concentration determine the colloidal stability of the NPs. We find that kaolin is a potential coagulant for removal of NPs that behave like Ag and TiO2.

TiO2 incorporated in magnetic mesoporous SBA-15 by a facile inner-pore hydrolysis process toward enhanced adsorption–photocatalysis performances for As(III)

A facile inner-pore hydrolysis combining solvent evaporation method was used to decorate mesoporous silica, in which γ-Fe2O3 nanoparticles was preloaded onto mesoporous SBA-15 followed by decoration of TiO2 nanoparticles. This decoration process exploited the homogeneous dispersivity of γ-Fe2O3 and TiO2 nanoparticles in/on SBA-15 and inhibit aggregation of γ-Fe2O3 and TiO2 nanoparticles, which in turn leaded to a synergistic photocatalytic oxidation and adsorption of As(III). It was found that the prepared nanocomposites had mesoporous structure, large specific surface area, high pore volume and superparamagetism according to SEM/TEM, N2 adsorption–desorption isotherms, XRD and VSM analysis. Experimental results show that SBA-15/γ-Fe2O3–TiO2 can oxidize As(III) to As(V) efficiently in the photocatalysis reaction. At the same time, As(V) is effectively removed through adsorption by the composites. In addition, with the treatment of alkali solution, As(V) can be easily desorbed from SBA-15/γ-Fe2O3–TiO2. After reusage for 5 times, the composites still retain comparable catalysis and adsorption performance compared with that of first use, revealing the excellent stability of the composites.

Titanium dioxide nanoparticles exacerbate pneumonia in respiratory syncytial virus (RSV)-infected mice

To reveal the effects of TiO2 nanoparticles, used in cosmetics and building materials, on the immune response, a respiratory syncytial virus (RSV) infection mouse model was used. BALB/c mice were exposed once intranasally to TiO2 at 0.5mg/kg and infected intranasally with RSV five days later. The levels of IFN-γ and chemokine CCL5, representative markers of pneumonia, in the bronchoalveolar lavage fluids of RSV-infected mice had increased significantly in TiO2-exposed mice compared with the control on day 5 post-infection, but not in uninfected mice. While pulmonary viral titers were not affected by TiO2 exposure, an increase in the infiltration of lymphocytes into the alveolar septa in lung tissues was observed. Immunohistochemical analysis revealed aggregation of TiO2 nanoparticles near inflammatory cells in the severely affected region. Thus, a single exposure to TiO2 nanoparticles affected the immune system and exacerbated pneumonia in RSV-infected mice.

A multi-integrated approach on toxicity effects of engineered TiO2 nanoparticles

The new properties of engineered nanoparticles drive the need for new knowledge on the safety, fate, behavior and biologic effects of these particles on organisms and ecosystems. Titanium dioxide nanoparticles have been used extensively for a wide range of applications, e.g, self-cleaning surface coatings, solar cells, water treatment agents, topical sunscreens. Within this scenario increased environmental exposure can be expected but data on the ecotoxicological evaluation of nanoparticles are still scarce. The main purpose of this work was the evaluation of effects of TiO2 nanoparticles in several organisms, covering different trophic levels, using a battery of aquatic assays. Using fish as a vertebrate model organism tissue histological and ultrastructural observations and the stress enzyme activity were also studied. TiO2 nanoparticles (Aeroxide® P25), two phase composition of anatase (65%) and rutile (35%) with an average particle size value of 27.6±11 nm were used. Results on the EC50 for the tested aquatic organisms showed toxicity for the bacteria, the algae and the crustacean, being the algae the most sensitive tested organism. The aquatic plant Lemna minor showed no effect on growth. The fish Carassius auratus showed no effect on a 21 day survival test, though at a biochemical level the cytosolic Glutathione-S-Transferase total activity, in intestines, showed a general significant decrease (p<0.05) after 14 days of exposure for all tested concentrations. The presence of TiO2 nanoparticles aggregates were observed in the intestine lumen but their internalization by intestine cells could not be confirmed.

Graphene TiO2 nanocomposites with high photocatalytic activity for the degradation of sodium pentachlorophenol

A series of graphene–TiO2 photocatalysts was synthesized by doping TiO2 with graphene oxide via hydrothermal treatment. The photocatalytic capability of the catalysts under ultraviolet irradiation was evaluated in terms of sodium pentachlorophenol (PCP-Na) decomposition and mineralization. The structural and physicochemical properties of these nanocomposites were characterized by X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy, scanning electron microscopy, Ultraviolet–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectra, and Fourier-transform infrared spectroscopy. The graphene–TiO2 nanocomposites exhibited higher photocatalytic efficiency than commercial P25 for the degradation of PCP-Na, and 63.4% to 82.9% of the total organic carbon was fully mineralized. The improved photocatalytic activity may be attributed to the accelerated interfacial electron-transfer process and the significantly prolonged lifetime of electron-hole pairs imparted by graphene sheets in the nanocomposites. However, excessive graphene and the inhomogeneous aggregation of TiO2 nanoparticles may decrease photodegradation efficiency.

Mechanism of TiO2 nanoparticle-induced neurotoxicity in zebrafish (Danio rerio).

Zebrafish (Danio rerio) has been used historically for evaluating the toxicity of environmental and aqueous toxicants, and there is an emerging literature reporting toxic effects of manufactured nanoparticles (NPs) in zebrafish embryos. Few researches, however, are focused on the neurotoxicity on adult zebrafish after subchronic exposure to TiO2 NPs. This study was designed to evaluate the morphological changes, alterations of neurochemical contents, and expressions of memory behavior-related genes in zebrafish brains caused by exposures to 5, 10, 20, and 40 μg/L TiO2 NPs for 45 consecutive days. Our data indicated that spatial recognition memory and levels of norepinephrine, dopamine, and 5-hydroxytryptamine were significantly decreased and NO levels were markedly elevated, and over proliferation of glial cells, neuron apoptosis, and TiO2 NP aggregation were observed after low dose exposures of TiO2 NPs. Furthermore, the low dose exposures of TiO2 NPs significantly activated expressions of C-fos, C-jun, and BDNF genes, and suppressed expressions of p38, NGF, CREB, NR1, NR2ab, and GluR2 genes. These findings imply that low dose exposures of TiO2 NPs may result in the brain damages in zebrafish, provide a developmental basis for evaluating the neurotoxicity of subchronic exposure, and raise the caution of aquatic application of TiO2 NPs.

Fabrication of TiO2/SiO2 hybrid fibers with tunable internal porous structures

TiO2 nanoparticles are easily aggregated, which greatly hinders their application to be utilized as photocatalysts. One of the effective routes is to make the TiO2 nanoparticles assembled on/in a solid carrier. In current work we report the fabrication of hybrid TiO2/SiO2 fibers with tunable internal porous structures via a capillary electrospinning technique combined with subsequent high-temperature pyrolysis treatment, in which the porous SiO2 fiber frameworks could offer a platform to assemble the TiO2 nanoparticles with a uniform spatial distribution. The resultant fibers were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). It is found that the introduced concentration of tetrabutyl titanate (TBOT) plays a profound effect on the formation of the hybrid TiO2/SiO2 fibers. The experimental results suggest that tailoring the concentrations of raw material in the precursor solutions could permit the formation of internal structures with solid, hollow and hierarchically porous shapes, enabling the fabrication of hybrid TiO2/SiO2 fibers with tunable structures. Present work could provide a facile strategy for limiting the aggregation of TiO2 nanoparticles, which could give them a promising high photocatalysis performance.

Resilient mesoporous TiO2/graphene nanocomposite for high rate performance lithium-ion batteries

Abstract Mesoporous TiO2/graphene composite is synthesized using graphene oxide (GO) and cheap TiOSO4 as precursors via a facile one-step hydrothermal route. In this process, Ti(OH)4, the hydrolysis product of TiOSO4 in acidic environment reacts with functional groups (epoxy bridges, hydroxyl groups, carboxyl groups) on the GO sheets, which establishes strong Ti–O–C chemical bonds that link in situ formed TiO2 nanoparticles and graphene sheets together. Fourier transform infrared (FT-IR), Raman and X-ray photoelectron spectroscopy (XPS) confirms the existence of the Ti–O–C chemical bond in the resultant composite. Such kind of chemical bond could prevent the aggregation of TiO2 nanoparticles, avoid the restacking of graphene sheets, facilitate the fast transport of the Li-ions, enhance electronic conductivity, offer a high tap density, maintain the structural integrity during charge/discharge process, and consequently achieve excellent cycle stability and high rate capability in Li-ion batteries. At the current density of 5000 mA g−1, the discharge capacity of the composite can be readily retained at 141.7 mAh g−1 after 100 cycles, which is outstanding among the TiO2 composites in the literature.

Morphological evolution of hierarchical nickel titanates by elevation of the solvothermal temperature

In this study, the morphological evolution of hierarchical nickel titanates was first-ever investigated by simply raising the solvothermal temperature. At room temperature, irregular aggregates of anatase TiO2 nanoparticles were reluctantly formed. Increasing the temperature to 100°C resulted in the assembly of 3D drum-shaped nickel titanate clusters where the three-dimensional geometry was constructed via coalescent nanoparticles with a mean size of 126.8nm. An intermediate stage containing circular cylinders and irregular prisms was obtained at intermediate temperatures. Further elevation of the solvothermal temperature to 160°C and 180°C gave 1D uniform hexagonal nanoprisms of nickel titanates. Increasing the solvothermal temperature accelerates the nucleation rate, which drastically promotes crystallization and self-assembly, thereby evolving to the hierarchical structure of NiTiO3.

Contact behavior of size fractionated TiO2 nanoparticle agglomerates and aggregates

The size dependent contact behavior of nanoparticle agglomerates was studied. Size fractionated TiO2 nanoparticle agglomerates were synthesized with a combination of a flame spray reactor and a differential mobility analyzer resulting in four different agglomerate sizes (median values from 78 to 161nm). Contact behavior of the fractionated agglomerates was investigated using atomic force microscopy. A model of the contact behavior of agglomerates under tensile stress was established in which the aggregates within the agglomerates rearrange and form chains before breakage. Force curves show that the length of the chains and the amount of rearrangements depend on the agglomerate sizes. Larger agglomerates require more work for their aggregate rearrangement before the final breakage is induced.

Synthesis of TiO2 with controllable ratio of anatase to rutile

Dual-phase TiO2 photocatalysts with controllable ratio of anatase to rutile were synthesized, and evaluated using the degradation of Rhodamine B (RhB) under UV light irradiation. The TiO2 samples prepared by one-pot redox reactions in the presence of graphene oxide (GO) were characterized by X-ray diffraction, physical adsorption–desorption of nitrogen, and scanning/transmission electron microscope techniques. Results showed that the weight percentage of anatase and rutile in the resulting TiO2 samples linearly changed with the starting mass ratio of TiCl3 over GO (RTiCl3/GO). The formed reduced GO (rGO) was completely removed by calcination at 450 °C, leaving behind pure crystallized TiO2 materials. The two-dimensional rGO sheet inhibited the aggregation of TiO2 nanoparticles, and the oxygen functional groups benefitted the formation of the anatase phase especially at low RTiCl3/GO. TiO2 with 55% of anatase and 45% of rutile displayed the highest photoactivity due to its unique hierarchical structures, including anisotropically shaped structure of rutile nanorods, intimate interfacial contact between anatase and rutile, and the dense interconnections among anatase particles, which retarded the electron–hole recombination and enhanced the photocatalytic performance.

TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability

The behavior of manufactured TiO2 nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO2 nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO2 nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO2 nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO2 nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO2 nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO2 nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO2 nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO2 nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO2 nanoparticles.