Aggregation Of TiO2 Nanoparticles Research Articles

SiO2@TiO2 Core@Shell Nanoparticles Deposited on 2D-Layered ZnIn2S4 to Form a Ternary Heterostructure for Simultaneous Photocatalytic Hydrogen Production and Organic Pollutant Degradation.

It is challenging to design and prepare difunctional photocatalysts for simultaneous photocatalytic wastewater purification and hydrogen (H2) energy production. In this study, a novel ternary heterostructure pholocatalyst, ZnIn2S4@SiO2@TiO2 (ZIS@SiO2@TiO2) was successfully prepared by simple sol-gel and solvothermal methods. The SiO2 nanospheres were used as a support to prevent the aggregation of TiO2 nanoparticles efficiently. The SiO2@TiO2 nanoparticles were uniformly inserted into the 2D-layered flowerlike ZnIn2S4 to form a ternary heterostructure that can efficiently improve the separation and transportation of photoinduced electron-hole pairs. As expected, the 150%-ZIS@SiO2@TiO2 nanocomposite exhibited an excellent rate of H2 production under simulated sunlight (618.3 μmol g-1 h-1), which was 229 and 3.3 times higher than the binary SiO2@TiO2 nanoparticles and pure ZnIn2S4. Furthermore, the degradation efficiency of methylene blue reached 99.7% during the H2 production process. These findings provided possibilities to couple energy conversion with environmental restoration.

Preparation of sonoactivated TiO2-DVDMS nanocomposite for enhanced antibacterial activity.

Titanium dioxide (TiO2) nanoparticle has good photo-/sono-catalytic features, the reunion of this particle in solution-phase generally limits the extensive biomedical application. In the present study, the aggregation of TiO2 nanoparticles was alleviated by facile fabrication under different pH conditions. A novel TiO2 nanocomposite was further synthesized by properly conjugation with trace amount of DVDMS sensitizer (named DFT). The characterization, sonoactivity, as well as the antibacterial efficiency were specially evaluated. The results showed that the sonochemical activity of DFT was greatly improved as compared with the simple surface modification of TiO2 (F-TiO2) and free DVDMS, regarding to the hydroxyl radicals and singlet oxygen yields using the same ultrasound exposure. Moreover, ultrasonic stimulation of DFT exhibited excellent bacterial eradication, with up to 92.41% of killing efficiency in S. aureus. The flow cytometry analysis indicated an increased intracellular ROS and membrane disturbance by combination of DFT and ultrasound. The findings suggest that the proper fabrication and DVDMS incorporation greatly improved the sonocatalytic process of TiO2, and the ultrasound based biomedical applications of DFT deserve future deep investigation.

An antibacterial composite film based on cellulose acetate/TiO2 nanoparticles

The aims of this paper were: (1) prevent the aggregation of TiO2 nanoparticles and obtain a uniform suspension; (2) obtain homogeneous composite films through three simple steps; (3) evaluate the antibacterial properties of CA/TiO2 composite films against E. coli.

Molten Salt Hydrates in the Synthesis of TiO2 Flakes.

Herein, we present a method for the preparation of titanium dioxide with a relatively large surface area, mesoporosity, and good thermal stability. We show that by utilizing molten salt hydrates (MSH) as non-trivial synthesis media, we prepare materials with thin, flake-like morphology with a large aspect ratio. The thickness of the synthesized flakes can be controlled by adjusting the salt/water (always in the MSH regime) and/or the salt/precursor molar ratio. The TiO2 flakes appear to be formed via the aggregation of small TiO2 nanoparticles (typically around 7–8 nm) in an apparent 2D morphology. We hypothesize that the ordered structure of water molecules within the ions of the salt in conjunction with the fast hydrolysis/condensation rates occurring in the presence of water of the precursor used are responsible for this agglomeration. We also report that the purity of materials (anatase vs brookite crystalline phase) appears to be a function of the LiBr/water ratio which is hypothesized to arise either from pH variation or due to lattice matching of the relevant orthorhombic structures (brookite and LiBrx·3H2O). Discussion on the potential for scalability of the presented method is also highlighted in this article.

A comparative photocatalytic study of TiO2 loaded on three natural clays with different morphologies

In this work, a sol-gel method was used to load TiO2 nanoparticles on three clays (kaolinite, halloysite and palygorskite) with different morphologies (plates, tubes, and rods with micro tunnels), and then the photocatalytic performance of obtained clay-TiO2 composites for degradation of methyl orange was comparatively investigated. The results surprisingly show that the trend of photocatalytic performance of composites is opposite to that of special surface area of corresponding clays. By concentrated analysis of the loading status of TiO2, the lowest photocatalytic efficiency of palygorskite-TiO2 composite is mainly ascribed to (1) the aggregation of TiO2 nanoparticles on Pal surface, not the amount of TiO2 and (2) the relatively weak adsorption of Pal to methyl orange. The additional adsorption of hydroxyl surface of Kaol to methyl orange and little TiO2 in the lumen of Hal tube leads to the better photocatalytic performance of kaolinite-TiO2 composite than halloysite-TiO2 composite. Finally, kaolinite is proved to be an excellent carrier to support nano TiO2 resulting in a good photocatalytic performance and cycle stability, and the study can provide a direct guidance to select appropriate clay-photocatalyst composites for different practical applications.

Optical and Superhydrophilic Characteristics of TiO2 Coating with Subwavelength Surface Structure Consisting of Spherical Nanoparticle Aggregates

It is expected that the applications of photocatalytic coatings will continue to extend into many areas, so it is important to explore their potential for enhanced functionality and design flexibility. In this study, we investigated the effect of a subwavelength surface structure in a TiO2 coating on its optical and superhydrophilic characteristics. Using submicron-scale spherical aggregates of TiO2 nanoparticles, we fabricated a TiO2 film with a subwavelength surface structure. Optical examination showed the enhanced transmittance of visible light compared to that of a plain surface. This was considered to be a result of a graded refractive index at the air–TiO2 interface. The effect of the subwavelength surface structure on optical transmittance was also demonstrated by the numerical simulation of visible light propagation in which Maxwell’s equations were solved using the finite-difference time-domain method. In addition, superhydrophilic behavior without ultraviolet light illumination was observed for the subwavelength-structure film via the measurement of the contact angle of a water drop. Furthermore, it was confirmed that the photocatalytic activity of the proposed film was comparable with that of a standard TiO2 film. It was suggested that the control of the subwavelength surface structure of a TiO2 film could be utilized to achieve novel properties of photocatalytic coatings.

Synthesis of alginate/carbon nanotube/carbon dot/fluoroapatite/TiO2 beads for dye photocatalytic degradation under ultraviolet light

Fewer toxic and cost-effective catalysts such as organic-inorganic polymer composites are highly necessary for the water purification. This work describes the sono-assisted fabrication of photocatalyst including multi-walled carbon nanotubes (CNTs), carbon dots (Cdots), magnesium fluorohydroxyapatite (FA), and TiO2 nanoparticles (NPs) (CNT/Cdot/FA/TiO2) for methylene blue (MB) degradation in the water solution. This hybrid was employed for the reinforcement of crosslinked alginate (CAlg) and fabrication of CAlg/CNT/Cdot/FA/TiO2 composite. The photocatalytic behavior of this composite was examined for the MB degradation. To examine TiO2 NPs effect on the as- products, the mentioned samples were prepared without TiO2, as well. Photodegradation yields of the samples followed in the order of CNT/CD/FA/TiO2 > TiO2 NPs > CAlg/CNT/Cdot/FA/TiO2 composite > pure FA. The outcomes indicated that the TiO2 hybridization not only could postpone the recombination of photo-created electron-hole pairs but also prevented aggregation of TiO2 NPs, which led to enhancement in the photodegradation yield of MB.

Aggregation of TiO2 and Ag nanoparticles in soil solution – Effects of primary nanoparticle size and dissolved organic matter characteristics

The colloidal stability of nanoparticles NP in soil solution is important to assess their potential effects on ecosystems. The aim of this work was to elucidate the interactions between initial particle size di, particle number concentration (N0) as well as the characteristics of dissolved organic matter (DOM) for stabilizing Ag NP and TiO2 NP.In batch experiments using time-resolved dynamic light scattering (DLS), we investigated the aggregation of TiO2 NP (79 nm, 164 nm) and citrate-stabilised Ag NP (73 nm, 180 nm) in Ca2+ solution (2 mM) and two soil solutions, one extracted from a farmland and one from a floodplain soil (each containing 2 mM Ca2+).Our results demonstrate that the initial particle size and the particle number concentration affected aggregation more strongly in the presence of DOM than without DOM. The composition of DOM also affected aggregate size: NP formed larger aggregates in the presence of hydrophilic DOM than in the presence of hydrophobic DOM. Hydrophilic DOM showed a larger charge density than hydrophobic DOM. If Ca2+ is present, it may bridge DOM molecules, which may lead to greater NP destabilization. The results demonstrate that DOM interaction with NP may not only vary for different DOM characteristics (i.e. charge density) but may also be influenced by the presence of multivalent cations and different NP material; thus the effect of DOM on NP colloidal stability is not uniform.

TiO2-Doped Electrospun Nanofibrous Membrane for Photocatalytic Water Treatment.

This work has been focused on the one-step fabrication by electrospinning of polyamide 6 (PA6) nanofibre membranes modified with titanium dioxide nanoparticles (TiO2), where these TiO2 nanoparticles aggregates could induce a photocatalytic activity. The main potential application of these membranes could be the purification of contaminated water. Thus, it is important to analyse the contaminant degradation capability since in these membranes this is based on their photocatalytic activity. In this work, the effect of the photocatalysis has been studied both on the degradation of an organic model contaminant and on the removal of Escherichia coli and other coliform bacteria. As a result, it was observed that these membranes present excellent photocatalytic activity when they are irradiated under UV light, allowing a 70% reduction of an organic model pollutant after 240 min. In addition, these membranes successfully removed Escherichia coli and other coliform bacteria in artificially inoculated water after 24 h of contact with them. Moreover, the stand-alone structure of the membranes allowed for the reusing of the immobilized catalyst. The experimental evidence indicated that developed nanofibre membranes are a fast and efficient solution for polluted water decontamination based on photocatalysis. Their use could contribute to guarantee a fresh water level and quality, mitigating the water scarcity problem worldwide.

Effects of interactions between humic acid and heavy metal ions on the aggregation of TiO2 nanoparticles in water environment

Nanoparticles (NPs), heavy metal and natural organic matter (NOM) may simultaneously exist in the aquatic environment, where they will affect the behavior of each other and may enhance their toxicities. Studies on the influences of interactions between NOM and heavy metal ions on the behavior of NPs are scarce. In this study, combined effects of Pb2+ and HA on the aggregation behavior of TiO2 NPs in water environment were investigated by Dynamic light scattering (DLS) and Nanoparticle tracking analysis (NTA). The results illustrated that interactions between Pb2+ and HA could case the aggregation of TiO2 NPs obviously. The concurrence of Pb2+ and HA resulted in decreased critical coagulation concentration (CCC) and increased attachment efficiencies. Meanwhile, we found that the addition sequences of HA and heavy metal clearly influenced the aggregation kinetics of TiO2 NPs. At different addition sequences, the complex reaction between Pb2+ and HA changed the surface charge of TiO2 NPs, and caused the different aggregation behavior which depended on the complex locations and complex sites. Furthermore, the excitation-emission-matrix (EEM) fluorescence spectra was used to verify the significant effects of the complex interactions between Pb2+ and HA on the aggregation of TiO2 NPs. Our results would be significant for interpreting TiO2 behavior in the complicated water system.The complexation between Pb2+ and HA promoted the aggregation of TiO2 NPs, meanwhile, complex locations and complex sites played an important role.

Few-layers of graphene modified TiO2/graphene composites with excellent electrochemical properties for lithium-ion battery

In this work, a simple, facile, and effective hydrothermal method toward TiO2/graphene composite has been developed by using tetrabutyl titanate and different layers of graphene oxide (GO) as the starting materials, exploring the influence of the layers of graphene on the lithium-ion battery composites. The structure and morphology were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Their electrochemistry performances were tested through galvanostatic charge–discharge, cyclic voltammetry (CV), and AC impedance (EIS). When used as anode material for lithium-ion batteries (LIBs), the reduced graphene oxide (rGO) can effectively prevent the aggregation of TiO2 nanoparticles and increase the electrical conductivity of the composites. The electrochemical tests indicate that the TiO2/rGO (few-layer) electrode exhibits higher electrochemical performance than that of TiO2/rGO (multi-layers) electrode regardless of the rate. At the current density of 100 mA g−1, the discharge capacity of TiO2/rGO (few-layers) can maintain 344.3 mAh g−1 after 100 cycles, which is higher than that of TiO2/rGO (multi-layers) 244.9 mAh g−1. TiO2/rGO (few-layers) showed reversible capacity values of 303.9 mAh g−1 and 245.6 mAh g−1 at current rates of 160 mA g−1 and 320 mA g−1, respectively, showing better rate performance. Our study demonstrates significant potential of few-layer graphene as anode materials for LIBs.

Mesoporous Spherical Aggregates Consisted of Nb-Doped Anatase TiO2Nanoparticles for Li and Na Storage Materials

Mesoporous spherical aggregates of Nb-doped anatase TiO2 nanoparticles were synthesized by a simple one-pot solvothermal method in supercritical methanol and were evaluated as anode materials for L...

Influence of the Heat Treatment on the Particles Size and on the Crystalline Phase of TiO₂ Synthesized by the Sol-Gel Method.

Titanium biomaterials’ response has been recognized to be affected by particles size, crystal structure, and surface properties. Chemical and structural properties of these nanoparticle materials are important, but their size is the key aspect. The aim of this study is the synthesis of TiO2 nanoparticles by the sol-gel method, which is an ideal technique to prepare nanomaterials at low temperature. The heat treatment can affect the structure of the final product and consequently its biological properties. For this reason, the chemical structure of the TiO2 nanoparticles synthesized was investigated after each heat treatment, in order to evaluate the presence of different phases formed among the nanoparticles. FTIR spectroscopy and XRD have been used to evaluate the different structures. The results of these analyses suggest that an increase of the calcination temperature induces the formation of mixed-crystalline-phases with different content of anatase and rutile phases. The results obtained by SEM measurements suggest that an increase in the particles size accompanied by a noticeable aggregation of TiO2 nanoparticles is due to high temperatures achieved during the thermal treatments and confirmed the presence of different content of the two crystalline phases of titanium dioxide.

Tuning Texture and Morphology of Mesoporous TiO₂ by Non-Hydrolytic Sol-Gel Syntheses.

The development of powerful synthetic methodologies is paramount in the design of advanced nanostructured materials. Owing to its remarkable properties and low cost, nanostructured TiO2 is widely investigated for applications such as photocatalysis, energy conversion or energy storage. In this article we report the synthesis of mesoporous TiO2 by three different non-hydrolytic sol-gel routes, and we investigate the influence of the synthetic route and of the presence and nature of the solvent on the structure, texture and morphology of the materials. The first route is the well-known ether route, based on the reaction of TiCl4 with iPr2O. The second and third routes, which have not been previously described for the synthesis of mesoporous TiO2, involve the reaction of Ti(OiPr)4 with stoichiometric amounts of acetophenone and benzoic anhydride, respectively. All materials are characterized by XRD, N2 physisorption and SEM. By playing with the non-hydrolytic route used and the reaction conditions (presence of a solvent, nature of the solvent, calcination), it is possible to tune the morphology and texture of the TiO2. Depending on the reaction conditions, a large variety of mesoporous TiO2 nanostructures could be obtained, resulting from the spontaneous aggregation of TiO2 nanoparticles, either rounded nanoparticles, platelets or nanorods. These nanoparticle networks exhibited a specific surface area up to 250 m2 g−1 before calcination, or up to 110 m2 g−1 after calcination.

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

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

Secondary Particle Formation during the Nonaqueous Synthesis of Metal Oxide Nanocrystals.

This study aims to elucidate the aggregation and agglomeration behavior of TiO2 and ZrO2 nanoparticles during the nonaqueous synthesis. We found that zirconia nanoparticles immediately form spherical-like aggregates after nucleation with a homogeneous size of 200 nm, which can be related to the metastable state of the nuclei and the reduction of surface free energy. These aggregates further agglomerate, following a diffusion-limited colloid agglomeration mechanism that is additionally supported by the high fractal dimension of the resulting agglomerates. In contrast, TiO2 nanoparticles randomly orient and follow a reaction-limited colloid agglomeration mechanism that leads to a dense network of particles throughout the entire reaction volume. We performed in situ laser light transmission measurements and showed that particle formation starts earlier than previously reported. A complex population balance equation model was developed that is able to simulate particle aggregation as well as agglomeration, which eventually allowed us to distinguish between both phenomena. Hence, we were able to investigate the respective agglomeration kinetics with great agreement to our experimental data.

Brownian Dynamic Study of the Aggregation Process of TiO2 Nanoparticles in Aqueous Suspensions

Abstract To fully comprehend the aggregation process of TiO2 nanoparticles in aqueous suspensions, one must quantitatively characterize the size distribution and the number of aggregates during the aggregation process. A Brownian dynamics approach was applied to simulate the aggregation of TiO2 nanoparticles in aqueous suspension. The well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was utilized to describe the particle–particle interaction. The effect of particle size (10, 20, and 30 nm), pH (5.5, 7.0, and 9.0), and ionic strength (0.001, 0.01, and 0.1 M) on aggregation process was characterized using the number of aggregates, single TiO2 nanoparticles, and size distribution of aggregates. Results indicated that aggregate size and degree of aggregation decreased with increase of pH, and increased with the increase of ionic strength. In comparison with pH and ionic strength, primary particle size probably played a critical role in the aggregation of the TiO2 nanoparticles in aqueous suspension. T...

Prompting Charge Injection in Aqueous Mesoscopic Photoelectrochemical Cells

Despite high efficiencies have been achieved, conventional mesoscopic dye-sensitized solar cells using organic solvents based electrolytes that generally have the disadvantages of high vapour pressure against reliable encapsulation, and most importantly, are not environmentally friendly. Electrolytes based on water, a cheap, earth-abundant, non-toxic and non-flammable solvent, therefore, attracted considerable research interests. Water based electrolyte would negatively shift the conduction band of TiO2 as the water molecules irreversibly change the interfacial properties of the sensitized TiO2 film. In our work, tungsten doped mesoporous TiO2 nanoparticle aggregates (TNA) possessing high surface area and superior scattering effect, were developed to induce positive shift of the TiO2 conduction band, enhancing the driving force for electron injection and collection efficiencies. The electrochemical impedance spectra indicate a retarded charge recombination and increased electron diffusion length after W-doping. By fine-tuning the W-doping concentration to 0.25 %, aqueous DSCs produced a significant improved open circuit voltage of 712 mV and a short circuit current of 7.05 mA cm-2, leading to an overall increased power conversion efficiency of 3.40 % at 1000 W m-2 simulated irradiation, which is roughly 25 % enhancement compared to that without W-doping photoanode.

Effects of the adsorption of NOM model molecules on the aggregation of TiO2 nanoparticles in aqueous suspensions

Interaction of synthetic TiO2 (anatase) nanoparticles in aqueous suspension at pH 5 was investigated as a function of time in the presence of various organic molecules in terms of adsorption and aggregation behaviour. ζ-potential and average particle diameter were determined with electrophoretic and dynamic light scattering, respectively, while batch adsorption experiments were used to quantify the amount of organic ligand adsorbed to the TiO2 NP. An IR spectroscopic study was carried out at pH 2.8 and 5 to gain information about the interactions of the adsorbed molecules with the TiO2 surface on the molecular level. Furthermore, DLVO calculations provided information about the interaction energies between particles and their tendency to aggregate under some experimental conditions. Colloidal stability of TiO2 NPs in the presence of organic molecules was studied during a time period of up to 90 days. Results showed that ligands with different functional groups may interact differently with the surface depending on the type and position of available surface sites, the molecular structure of the ligand and suspension pH. Adsorption, hydrodynamic diameter and ζ-potential were affected by the ligand concentration in all tested systems. Increased concentration gave rise to increased adsorption, while ζ-potential decreased and charge inversion was observed for all tested molecules at pH 5. IR spectroscopic study showed the formation of inner sphere and/or outer sphere complexes depending on pH and type of organic ligand. According to DLVO calculations, the critical coagulation concentration (CCC) indicated a trend of increasing colloidal stability with increased concentration of SRFA at pH 5, which was in agreement with the experimental data.

Titania/mesoporous silica nanotubes with efficient photocatalytic properties

Abstract Ordered nanocrystalline titania-mesoporous silica nanotube structures are synthesized by hydrolysis of the titania precursor inside pours silica shell. Silica coating surrounding carbon nanotubes was further removed by thermal reduction. The proposed method of functionalization silica channels with the titania nanoparticles preclude aggregation of TiO2 nanoparticles. The nanocrystalline silica/titania (mt-SiO2/TiO2) nanotubes were prepared according to the describe method has high specific surface area and possesses excellent photocatalytic properties capable of decomposing phenol and methylene blue in a short time. Since the nanocrystalline TiO2 is produced in the wall of the mesoporous silica tube, phenol or dye molecules can react with TiO2 nanoparticles from both the inside and outside.