TiO2 Aggregates Research Articles

Distinct interactions of pig and cow manure-derived colloids with TiO2 nanoparticles and their impact on stability and transport

The application of livestock manure and aquaculture wastewater into agricultural soil introduces animal manure-derived colloids into the environment. These manure-derived colloids generally contain different organic matter components and may facilitate nanoparticle transport to the subsurface. This study investigated the interaction between manure-derived colloids (cow and pig manures) and titanium dioxide (TiO2) nanoparticles at neutral pH. The effect of this interaction on the stability, aggregation, and transport of TiO2 in a saturated porous media was studied. Our study found that cow manure-derived colloids have many humic-like substances, and pig manure-derived colloids contain many protein components and some humic-like substances. The interactions of different manure-derived colloids with TiO2 can affect the ζ-potential and aggregation status of TiO2 in the aqueous system. The results showed that cow manure-derived colloids slightly increased the TiO2 transport due to electrostatic repulsion, while pig manure-derived colloids substantially increased the TiO2 mobility in porous media because of both electrostatic repulsion and steric hindrance. Since both animal manure and TiO2 are ubiquitously present in the natural environment, manure-derived colloids can change the surface properties of TiO2 and facilitate TiO2 transport in the subsurface.

Ternary g-C3N4/TiO2/Ti3C2 MXene S-scheme heterojunction photocatalysts for NOx removal under visible light

Highly efficient composite photocatalysts were prepared through annealing partially oxidized Ti3C2 MXene with melamine under N2 flow. The two-dimensional Ti3C2 MXene was aforehand partially oxidized to form TiO2-Ti3C2 nanosheet by precisely controlling the oxidation conditions. Ternary g-C3N4/TiO2/Ti3C2 MXene photocatalyst was constructed by coating melamine derived g-C3N4 on TiO2-Ti3C2 nanosheet. The photogenerated electron-hole separation was significantly enhanced by the S-scheme heterojunction. Ti3C2 tightly bonded with TiO2 benefits transfer and aggregation of photo-induced holes. The composite material has an interconnected nanosheet structure, which increases the absorption of light and the reaction interface between gaseous reactant and photocatalysts. When evaluated as NOx purification photocatalysts, the fabricated composites get the high NO removal efficiency and low NO2 generation. Under visible light, NO removal efficiency of the composite photocatalyst can reach up to 66.3%, which is significantly better than the g-C3N4 or TiO2-Ti3C2. This work demonstrates that moderately oxidized Ti3C2 MXene is a good candidate for the construction of high-performance air purification photocatalysts.

Hydrothermal Synthesis of TiO2 Aggregates and Their Application as Negative Electrodes for Lithium-Ion Batteries: The Conflicting Effects of Specific Surface and Pore Size.

TiO2 aggregates of controlled size have been successfully prepared by hydrothermal synthesis using TiO2 nanoparticles of different sizes as a building unit. In this work, different techniques were used to characterize the as-prepared TiO2 aggregates, e.g., X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer, Emmett and Teller technique (BET), field emission gun scanning electron microscopy (FEGSEM), electrochemical measurements etc. The size of prepared TiO2 aggregates varied from 10–100 nm, and their pore size from around 5–12 nm; this size has been shown to depend on synthesis temperature. The mechanism of the aggregate formations was discussed in terms of efficiency of collision and coalescence processes. These newly synthetized TiO2 aggregates have been investigated as potential negative insertion electrode materials for lithium-ion batteries. The influence of specific surface areas and pore sizes on the improved capacity was discussed—and conflicting effects pointed out.

Large-Scale Synthesis Route of TiO2 Nanomaterials with Controlled Morphologies Using Hydrothermal Method and TiO2 Aggregates as Precursor.

TiO2 of controlled morphologies have been successfully prepared hydrothermally using TiO2 aggregates of different sizes. Different techniques were used to characterize the prepared TiO2 powder such as XRD, XPS, FEGSEM, EDS, and HRTEM. It was illustrated that the prepared TiO2 powders are of high crystallinity with different morphologies such as nanobelt, nanourchin, and nanotube depending on the synthesis conditions of temperature, time, and additives. The mechanism behind the formation of prepared morphologies is proposed involving nanosheet intermediate formation. Furthermore, it was found that the nanoparticle properties were governed by those of TiO2 nanoparticles aggregate used as a precursor. For example, the size of prepared nanobelts was proven to be influenced by the aggregates size used as a precursor for the synthesis.

Preparation of TiO2 Nanoparticle Aggregates and Capsules by the ‘Two-Emulsion Method’

TiO2-based materials are of great practical interest in several technological areas. Both the size and the morphology of the TiO2 particles are of critical importance for their applications. The current study explores the effect of several factors on the outcome of the TiO2 particle synthesis via the so-called ‘two-emulsion method’. In this technique, two water-in-oil emulsions—each of them containing different reactant in the dispersed water drops—are mixed under well controlled conditions. Upon such mixing, partial coalescence of the water drops from the two emulsions leads to mixing of the drop content, with chemical reaction occurring within the drops, and to synthesis of Ti(OH)4 particles. Afterwards, the latter are transformed by emulsion heating into TiO2 particles and aggregates of predominantly anatase structure. Our results show that—depending on the precursor and surfactant concentrations, oil viscosity, emulsification time, and mixing speed—the obtained nanoparticles could aggregate either on the drop surface, forming capsules with a very smooth surface, or inside the water droplets, thus leading to hierarchically structured aggregates of micrometer size. The spherical smooth capsules are constructed of very small monodisperse TiO2 nanoparticles with size below 5 nm. The hierarchical bulk aggregates, on the other hand, are formed from bigger primary particles of sub-micrometer size. The obtained results show that one can obtain various TiO2 structures by controlling the conditions during the emulsion preparation and mixing

Occurrence Modes of Niobium in Kaolin Clay From Guizhou, China

Niobium in kaolin clay from the Late Permian sequences was reported in the range of several hundreds of micrograms per gram and was considered as a potential resource for its high concentrations and large areal distribution. Ti-bearing minerals associated with kaolin clay were identified as the main host phase for niobium in some case studies. However, the correlation between the concentration of niobium and titanium is poor, and the types of Ti-bearing minerals and modes of occurrence of niobium are not clear. Typical kaolin clay samples from the Late Permian sequences from southwest China were characterized, and the final products derived from kaolin clay sample were investigated using XRF, ICP-MS, XRD, SEM, and TEM (EDS). The results reveal that there were three types of TiO2 mineral phases in the clay samples: (a) massive TiO2 minerals and (b) aggregates of nano TiO2 minerals did not contain niobium while (c) granular TiO2 minerals were the source of niobium from the EDS analysis. The granular TiO2 minerals included anatase and rutile, both of which were the sources of niobium in kaolin clay in the current study. The findings are of great theoretical implication for source and origin study of Ti-bearing minerals and guidance for separation and recovery of niobium from kaolin clay.

Entropy-Driven Aggregation of Titanium Dioxide Nanoparticles in Aquatic Environments.

The aggregation process of engineered nanoparticles (ENPs) is important in assessing their fate and transport in the environment. Here, we present the application of isothermal titration calorimetry (ITC) in studying the thermodynamics of ENPs' aggregation in aqueous solutions containing monovalent (NaCl) and divalent (CaCl2) electrolytes, natural organic matter, and hematite natural NPs, which enables us to elucidate their interaction mechanism. The free energies for the aggregation of TiO2 at different solution conditions were dominated by large favorable entropy, presumably because of the expulsion of bound water molecules to the solution upon complexation. The copresence of humic acid and Ca2+ facilitated aggregation for both homo- and heterosystems through intra- or intermolecular bridging, leading to the formation of more compact aggregates. We believe that this ITC strategy can be successfully used to characterize the interaction details between ENPs and various environmental components in ambient water systems.

Synergistic effects of carbon doping and coating of TiO2 with exceptional photocurrent enhancement for high performance H2 production from water splitting

The “one pot” simultaneous carbon coating and doping of TiO2 materials by the hydrolysis of TiCl4 in fructose is reported. The synergistic effect of carbon doping and coating of TiO2 to significantly boost textural, optical and electronic properties and photocurrent of TiO2 for high performance visible light H2 production from water splitting has been comprehensively investigated. Carbon doping can significantly increase the thermal stability, thus inhibiting the phase transformation of the Titania material from anatase to rutile while carbon coating can suppress the grain aggregation of TiO2. The synergy of carbon doping and coating can not only ensure an enhanced narrowing effect of the electronic band gap of TiO2 thus extending the absorption of photocatalysts to the visible regions, but also promote dramatically the separation of electron-hole pairs. Owing to these synergistic effects, the carbon coated and doped TiO2 shows much superior photocatalytic activity for both degradation of organics and photocatalytic/photoelectrochemical (PEC) water splitting under simulated sunlight illumination. The photocatalytic activity of obtained materials can reach 5, 4 and 2 times higher than that of pristine TiO2, carbon doped TiO2 and carbon coated TiO2, respectively in the degradation of organic pollutants. The carbon coated and doped TiO2 materials exhibited more than 37 times and hundreds of times photocurrent enhancement under simulated sunlight and visible light, respectively compared to that of pristine TiO2. The present work providing new comprehensive understanding on carbon coating and doping effect could be very helpful for the development of advanced TiO2 materials for a large series of applications.

Strong effect of light scattering by distribution of TiO2 particle aggregates on photocatalytic efficiency in aqueous suspensions

This work examines the important role of light power absorbed by TiO2 on the photocatalytic degradation of dichloroacetic acid (DCA) in a semi-continuous slurry photoreactor with UV–Vis radiation. This system is an excellent model for understanding the light matter interaction, because DCA is transparent and the acid pH of the solution prevents the formation of large TiO2 aggregates. Under these conditions, the light power absorbed by four different commercial Titania photocatalysts, along the whole volume of the reactor, has been quantitatively calculated by assuming a Mie scattering model on a distribution of different particle sizes. Although the different chemical nature of the four considered samples (three of them provided by the Evonik Company, P25, P25/20 and P90, together with Hombikat UV 100), and the different catalytic efficiency based on weight, we have found that all the catalytic responses are fundamentally controlled by the absorbed radiation in the four samples. Therefore, in the studied samples, any difference in the catalytic behavior is only due to the light-matter interaction being of lesser importance other mechanisms, as space-charge blocking.

Ultrasound-activated TiO2/GO-based bifunctional photoreactive adsorbents for detoxification of chemical warfare agent surrogate vapors

Commercial TiO2 (P25), alone or in the presence of graphite oxide (GO), was exposed to ultrasound treatment (US) with the objective to modify the surface of nanoparticles through introducing defects and chemical heterogeneity, and to build the composite with GO of synergistic features. The obtained materials were extensively characterized using XRD, HR-TEM, TA-MS, FTIR, XPS, potentiometric titration, adsorption of nitrogen, and UV/Vis diffuse reflectance techniques. The results showed that the US treatment/activation led to the formation of defects on the surface of the TiO2 nanoparticles, which were associated with an increase in the amount of terminal hydroxy groups, and which resulted in narrowing of the band gap energy. The composite formed upon the ultrasonic activation contained partially reduced GO particles deposited on the surface of TiO2 aggregates and bonded with the titania phase through its carboxylic groups existing at the edges of small defectous graphene particles, leading to a high volume of mesopores formed between the particles/aggregates of the nanoparticles. The US-treated materials showed a superior bifunctional detoxification performance, to adsorb and photocatalytically decompose vapors of a chemical warfare agent surrogate, as a result of the surface alteration/activation and an increase in the porosity.

A density gradient centrifugation method for rapid separation of nanoTiO2 and TiO2 aggregates from microalgal cells in complex mixtures with mercury

In natural environment, the microorganisms are exposed to complex mixtures of contaminants, including manufactured nanoparticles and their aggregates. Evaluation of the toxicant accumulation in biota exposed to such cocktails is a challenging task because the microorganisms need to be separated from nanomaterial aggregates often of a comparable size. We propose a method for separation of TiO2 aggregates from green microalga Chlamydomonas reinhardtii and subsequent determination of cellular Hg concentration in algae exposed to mixture of Hg with nanoTiO2, known also to adsorb Hg. The method is based on differences in specific weight of algae and TiO2 aggregates, using medium speed centrifugation on a step gradient of sucrose. The efficiency of the separation method was tested with nanoTiO2 of three different primary sizes at four concentrations: 2, 20, 100 and 200 mg L−1. The method gives a possibility to separate nanoTiO2 and their aggregates from the algae with a mean recovery of 83.3% of algal cells, thus allowing a reliable determination of Hg accumulation by microalgae when co-exposed to Hg and nanoTiO2.• A rapid and reliable method to separate algal cells and nanoparticle aggregates of comparable size.• A method to measure the cellular amount of Hg in green alga co-exposed to Hg and nanoTiO2.

A New Organic Dye Cordia sebestena Sensitized Solar Cell with Current-Voltage Characteristics

Titanium dioxide nanoparticles have been synthesized by a novel modified sol-gel for the fabrication of natural dye sensitized solar cells. The natural photo sensitizer extracted from Cordia sebestena flower was mixed with the precursor solution. The flower dye has put the effort of a surfactant which has resulted colourized TiO2 instead of white TiO2. Whencompared to the conventional sol-gel method, this modified process has enhanced the properties of TiO2 like, morphology, uniformity in dye absorption. It has reduced the agglomeration of TiO2 and dye aggregation significantly. The optimized molecular geometry of sebestenoid D, the major pigment of Cordia sebestena and HOMO-LUMO plot are found using density functional theory. The TiO2 nanoparticles were subjected to structural, optical, spectral and morphological studies which showed improved properties in modified sol-gel process. Ecofriendly and low-cost natural dye sensitized solar cells (DSSC) were fabricated using conventional and pre-dye treated TiO2 sensitized by Cordia sebestena flower extract. The I-V studies showed the solar light photon to electron conversion efficiencies of 0.87 and 1.28 % for sol-gel and modified sol-gel methods, respectively. There has been an enhancement in efficiency by 47 % in modified sol-gel method which is very much promising in terms of efficiency for natural dye sensitized solar cells.

Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structural properties

Photocatalytic properties of titanium dioxide (TiO2) have been widely studied. However, its tendency to aggregation in biopolymer-based nanocomposites limits its application for food packaging and has been few studied. The aim of this work was to study the dispersion of TiO2 (0–2 wt%) incorporated in the hydroxypropyl methylcellulose (HPMC-TiO2) and gelatin (gelatin-TiO2) film forming solutions. Particle size and zeta potential of TiO2 nanoparticles were investigated. Nanocomposite films were characterized as to the thickness, moisture content, solubility, color, absorption to the light, relative opacity, morphology, chemical composition, crystallinity, thermal and mechanical properties and water vapor permeability (WVP). TiO2 nanoparticles showed better dispersion in acid medium than water. Moisture content, water solubility and WVP of the gelatin-TiO2 films were influenced by the incorporation of TiO2, while HPMC-TiO2 films were not. The increase of relative opacity of the films as TiO2 was more attenuated for the gelatin-TiO2 films due to lower TiO2 aggregation in gelatin. Morphology, chemical composition, crystallinity and thermal properties of the films evidenced that TiO2 was better dispersed in both matrices at 1 wt%. It was also concluded that TiO2 aggregation generated more biphasic regions in HPMC than generated in gelatin, which caused a microstructural reorganization in the matrices.

Preparation of concentrated multilayer graphene dispersions and TiO2-graphene composites for enhanced hydrogen production

Photocatalytic hydrogen (H2) production is an attractive hydrogen production technology. It is initiated by charge-separation in titanium (IV) dioxide (TiO2) upon photoexcitation. Electrons reduce water to generate H2 while holes oxidize hydroxide to generate hydroxyl radicals. TiO2 is widely used because it is inexpensive, chemically stable, nontoxic, and environmentally friendly. The activity of TiO2 is limited, but adding a supporting noble metal nanoparticle such as platinum greatly enhances it. Due to resource risks and cost issues, we consider using graphene as an alternative to noble metal nanoparticles. Herein we report a new method to prepare a concentrated multilayer graphene solution and hydrogen production from an aqueous methanol solution. When we used graphene with different sheet sizes or improved the aggregation of TiO2 (TIO-9), the H2 evolution rate is 1.6 times higher than that of pristine TIO-9. The contact state and the dispersed state of graphene and TiO2 play important roles in improving the activity.

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.

Hydrothermally synthesized self-assembled multi-dimensional TiO2/Graphene oxide composites with efficient charge transfer kinetics fabricated as novel photoanode for dye sensitized solar cell

The proposed work suggests the fabrication of hybrid TiO2/reduced graphene oxide composites with self-assembled multidimensional structure. The two step facile alkaline hydrothermal route is implemented using variable wt% of GO for the successful synthesis of multidimensional reduced graphene oxide TiO2 composites structure (MGTS). In the first step, TiO2 aggregates (TNA) were prepared by low temperature hydrothermal process. Subsequently, growth of multidimensional TiO2 on hGO sheet, as well as simultaneous reduction of GO is done and the as prepared MGTS is applied for dye sensitized solar cell (DSSC). Structural and surface morphology of the developed samples were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The X-ray photoelectron spectroscopy studies monitored the chemical composition and surface binding energy of TNA and MGTS samples. The current-voltage (J-V) and electrochemical impedance studies evaluates the performance of the TNA and MGTSs photoanodes in DSSC. The finest loading of GO in the TiO2 matrix assisted the accelerated electron transport channel within the TiO2 matrix resulting in superior photo conversion efficiency of 8.62% as compared with neat TiO2 which has an efficiency of 6.3%.

One-Step Synthesis of Ag@TiO₂ Nanoparticles for Enhanced Photocatalytic Performance.

Polyamide network polymers (PNP) modified TiO2 nanoparticles (NPs) were decorated with Ag NPs in hydrothermal gel method, forming one-step synthesized photocatalysts, Ag@TiO2 NPs. The effect of PNP and the amount of Ag NPs added were investigated in this work. PNP acted as a nanocage to prevent TiO2 aggregation and capture Ag accurately, which could effectively control product sizes and improve dispersibility in solvents. Simultaneously, TiO2 NPs modified with Ag NPs exhibited remarkable photocatalytic effects. One-step synthesis simplified the experimental process and avoided the agglomeration of silver ions during the secondary reaction, achieving the purpose of uniform distribution at a specific location of TiO2 NPs. The prepared Ag@TiO2 NPs-0.5 could remove 79.49% of Methyl Orange (MO) after 3 h of ultraviolet light irradiation, which was 2.7 times higher than the reaction rate of pure TiO2 NPs. It also exhibited good photoactivity under Visible light conditions. Moreover, the mineralization rate of MO over the Ag@TiO2 NPs-0.5 could be up to 72.32% under UV light and 47.08% under Visible light irradiation, which revealed that the prepared catalysts could effectively degrade most of the MO to CO2 and H2O. The samples also demonstrated the excellent stability and easy recyclability with over 90% of the original catalytic level for MO degradation. The photocatalysts studied also exerted broad application prospects such as photovoltaic hydrogen production, electronic sensors and biomedicine.

Underwater superoleophobic mesh with transformable micro-nano structure for ultrafast oil/water separation

Oil/water separation with superwetting mesh is an emerging method for removing oil from wastewater, but the adopted meshes at present are not reliable in practical applications due to their poor pressure-bearing capacity. A TiO2-deposited and coated mesh (TDCM) with underwater superoleophobicity and transformable micro-nano structure is reported to separate oil/water mixtures with efficiencies >99%. Due to the compactness of deposited porous TiO2 aggregates triggered by pressure, the TDCM can bear applied pressures of ≥12.6 kPa dependent on oil types and achieve ultrafast water transportation driven by retentate accumulation or other applied pressure without oil breaking through. The feature of the pressure-induced surface structure transformation will not damage the surface wettability and oil/water separation performance of the TDCM and is demonstrated effectively in mitigating the theoretical trade-off between water flux and pressure-bearing capacity. Furthermore, the TDCM has good self-cleaning performances for particulate and organic pollutants before and after surface structure transformation with the aid of oil and ultraviolet illumination. As a novel mesh for oil/water separation, the TDCM shows great potential in real applications and provides a brand-new perspective of developing advanced materials for oil removal from water in complicated situations.

Compaction-induced restructuring of aggregated nanoparticle films using the discrete element method

Aggregated nanoparticle films find application in many fields such as gas sensing, solar cells and batteries. These films are characterized by size distributions of polydisperse primary particles and sintered particle aggregates that dictate both the response to external load and functional properties such as heat or charge transport. Mechanical compaction of the films strongly affects these properties in a way that can be quantified by the change of porosity and pore size distributions on the applied compacting pressure. The exact restructuring mechanisms of the aggregate architecture, however, remain unknown. Here, we apply Discrete Element Method (DEM) simulations to gain access to such restructuring mechanisms in TiO2 nanoparticle films synthesized by flame-spray pyrolysis. The ability of the sintered TiO2 aggregates to rearrange via mutual detachment, rolling or sliding events dictated by non-covalent, humidity-dependent interactions are known to be crucial to predict the correct response to compaction. In this work, the importance of elastic deformation of aggregates according to a novel sinter bridge model is elucidated. The best match between DEM simulations and experiments is obtained for bridges with a tensile and bending strengths substantially larger than bulk TiO2, consistently with a low probability of critical fracture initiation in nanometer-scale structures.

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.