Stability Of TiO2 Nanoparticles Research Articles

In situ growth and crystallization of TiO2 on polymeric membranes for the photocatalytic degradation of diclofenac and 17α-ethinylestradiol

TiO2in situ growth on three commercial membranes (polysulfone – PS, polyvinylidene fluoride – PVDF and polytetrafluoroethylene – PTFE) and its hydrothermal post-crystallization to transform TiO2 into a photocatalytically-active phase, were investigated under mild synthesis conditions to preserve the textural properties of the supports. The membranes were successfully prepared and characterized by scanning electron microscopy, thermogravimetry analysis, N2 physisorption, X-ray diffraction, and water contact angle measurements, among other techniques. Membrane supports with a more opened porosity and high hydrophilicity allowed to enhance the content and distribution of the anatase TiO2 nanoparticles on the membrane surface. The efficiency and the permeate flux of the developed membranes were investigated to simultaneously remove diclofenac (DCF) and 17α-ethinylestradiol (EE2) from water by adsorption and UV–LED (light-emitting diode) photocatalysis under continuous recirculating mode. All TiO2 membranes achieved removal efficiencies above 90% for both contaminants, EE2 being always preferentially adsorbed over DCF due to electrostatic repulsions between the DCF molecules and the surface of these membranes. The permeate flux of TiO2 membranes was enhanced after UV-LED exposure as a consequence of the degradation of the contaminants adsorbed on the membrane surface during the dark phase. Moreover, the stability of TiO2 nanoparticles on these membranes was studied by static tests under sonication and several consecutive reaction cycles. The TiO2 membrane prepared with PVDF was the most stable, also presenting a high photocatalytic activity.

A Study on the Stability of TiO2 Nanoparticles as an Electron Transport Layer in Quantum Dot Light-Emitting Diodes

We report highly efficient and robust quantum dot light-emitting diodes (QLEDs) with Li-doped TiO2 nanoparticles (NPs) as an electron transport layer (ETL). As core materials, ZnO-based inorganic NPs can enhance the performance of QLEDs due to their suitable energy level and solution processability. However, their fast electron mobility and instability in organic solvents are two main obstacles to practical display applications. The colloidal stability of TiO2 NPs in ethanol was confirmed after three day-storage, while ZnO NPs showed severe agglomeration. Inverted structure QLEDs using 3% Li-doped TiO2 NP were successfully fabricated and their optical/electrical properties were investigated. With 3% Li-doped TiO2 NPs, the charge balance in the emitting layer of the QLEDs was improved, which resulted in a maximum luminance of 159,840 cd/m<sup>2</sup> and external quantum efficiency (EQE) of 9.12%. These results were comparable to the performance of QLEDs with commonly used ZnO NPs. Moreover, the QLEDs with the Li-doped TiO2 NPs showed more stable characteristics than those with ZnO NPs after 7 days in ambient conditions. The EQE of the QLEDs with Li-doped TiO2 NPs was reduced by only 4.9%. These results indicate that Li-doped TiO2 NPs show great promise for use as a solution based inorganic ETL for QLEDs.

Effects of chlorella extracellular polymeric substances on the aggregation and stability of TiO2 nanoparticles as electrolytes

Effects of chlorella extracellular polymeric substances on the aggregation and stability of TiO2 nanoparticles as electrolytes

Ultrasonic effect on the photocatalytic degradation of Rhodamine 6G (Rh6G) dye by cotton fabrics loaded with TiO2

The effect of sonication on the photodegradation of Rhodamine 6G (Rh6G, a fluorone dye) using woven cotton fabrics decorated with TiO2 nanoparticles (NPs) has been investigated. TiO2 NPs were synthesized in situ by sol–gel method in the presence of cotton textile and then hydrothermally treated. TiO2-loaded fabrics were treated ultrasonically to test adhesion to- and properties of the NPs on the fabrics. We demonstrate good adhesion and a good stability of the NPs of TiO2. Moreover, sonication substantially improved the distribution on the surfaces and hence enhanced the fabrics catalytic activity. Either under UV or simulated sunlight, ultrasonicated fabrics were found to have a high photocatalytic activity towards Rh6G, used as a model dye. SEM, XPS, UV–Vis and FTIR spectroscopy, as well as ground state diffuse reflectance and laser induced luminescence were used to characterize fabrics/TiO2 samples in terms of topography, surface composition, influence of hydrothermal treatment on photocatalytic activity, stability of TiO2 NPs, electro-optical properties of the modified fabrics, as well as the effect of ultrasonication on the photodegradation of Rh6G. This work paves the way to a larger scale improvement of the photocatalytic performances of TiO2-loaded cotton fabrics by post-sonication.

Fabrication and investigation of optical and optoelectrical properties of phenyltriethoxysilane-capped TiO2 nanoparticle/poly(N-vinylcarbazol) hybrids

A simple synthesis of organic–inorganic hybrids, using TiO2 nanoparticles and poly(N-vinylcarbazole), is carried out in the present work. The surface of TiO2 nanoparticles is modified by phenyltriethoxysilane (PhTES) to passivate it from aggregation and also improve its stability in organic solvents and compatibility in polymer matrices. Stabilization of TiO2 nanoparticles with PhTES is examined in both acid-catalyzed and basic media to choose an optimized procedure to avoid formation of inter-particle Si–O–Si bridges and prepare dispersed nanoparticles. X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy are applied to study the phase structures, surface morphologies, and structural properties of the samples. Ultraviolet (UV)–visible spectroscopy, photoluminescence spectroscopy, and current–voltage curves are used to characterize the optical and optoelectrical properties of the resulting samples. In addition, thermogravimetric analysis is used to investigate thermal stability of the samples. The photoluminescence quenching as a result of improved exciton dissociation, the formation of homogeneous hybrid layers, and the response of hybrid layers to UV light suggest that the resulting hybrids could be regarded as base compounds for fabricating high-performance UV photodetectors.

Removal of toluene vapors from the polluted air with modified natural zeolite and titanium dioxide nanoparticles.

Toluene is a colorless and flammab1le liquid with the same solubilizing capacity as benzene that is in many cases used as an alternative to benzene, because of the uncertainty of being carcinogens. Workers can be exposed to toluene by breathing the chemical. To avoid inhalation and dermal effects caused by exposure to toluene, solutions such as adsorption, thermal oxidation, membrane separation and photocatalytic processes are applied. In this study, removal of toluene vapors with modified natural zeolite and titanium dioxide nanoparticles was discussed. The natural zeolite was modified using chemical and thermal methods. The samples characterized by Brunauer-Emmet-Teller, Barrett-Joyner-Halenda, X-ray diffraction and scanning electron microscopy tests. After stabilization of TiO2 nanoparticles, the removal efficiency for the toluene vapors at a concentration of 50, 150 and 300 ppm were evaluated using a dynamic system. The results showed that the zeolite has a very porous surface and after modifying the context its specific surface area increased 2.54 times. The results of the adsorption capacity calculation and photocatalytic process showed that modified zeolite samples-TiO2 bed has greater efficiency in the adsorption capacity and better photocatalytic activity than a Ze-TiO2 bed. Ze-TiO2 bed was able to remove 26% of toluene vapors at the concentration of 50 ppm and inlet flow rate of 1 L/m, which was 1.26 times more than a bed Ze-TiO2. According to the results of this study, while modifying the natural zeolite increased desirable properties such as specific surface area and Si/Al ratio, but in comparison with similar studies with synthetic bed such as zeolite Y and ZSM-5, could not achieve desired results in a photocatalytic activity for its application in industry. However, because of its abundance in the world and Iran and therefore low cost of preparation and also due to its unique characteristics, it is recommended that more studies to be done about modifying and its application in photocatalytic processes.

Soft, Ecofriendly Functional cotton fabric using herbal oil incorporated with TiO2nano particles

Current research was undertaken to develop a new finishing formulation using titanium dioxide nanoparticles (TiO2) homogenously suspended in mixture of cationic softener and herbal oil. Its utilization as multifunctional finishing formulation to cotton based fabrics was investigated. The properties of the treated fabrics were monitored and compared with the untreated one. These properties were include the effect of cationic softener concentration, form of TiO2 nano particles (mixture of rutile and anatase), type of cotton fabrics (bleached or pre-carboxymethylated) and presence of herbal oil on the properties of the treated cotton fabrics were monitored. Moreover, stability of TiO2 nanoparticles in such finishing formulation was also determined. The effect of using eco-friendly herbal oil within the same finishing formulation on the antibacterial activities of the treated fabric was also evaluated. The treated fabrics were monitored for UV-protection, self-cleaning and antibacterial properties. Morphology and structure of TiO2 nanoparticles were characterized using XRD and TEM,. The antibacterial activities of the treated fabrics were evaluated against Staphylococcus aureus (gram-positive) strains and Escherichia coli (gram-negative), the results show significant antibacterial effect mainly against Staphylococcus aureus. In addition, the treated fabrics showed enhanced UV protection and self-cleaning properties with improving softness properties.

Thermophysical properties of TiO2-PVA/water nanofluids

Nanofluid, as an innovative cooling fluid, is a colloidal suspension with superior potential for enhancing the heat transfer performance of conventional fluids, however stability and durability are challenges for industrial applications. In attempts to investigate thermophysical properties (thermal conductivity and viscosity), many studies have been conducted, however no consensus has yet been reached. Thus, this work aims to investigate, experimentally, these properties including stability, by applying the technique of surface modification. The anatase structure of the titanium dioxide nanoparticle was synthesized by the hydrolysis of titanium isopropoxide. The surface modification of the nanoparticles was accomplished by treatment with PVA polymer (polyvinyl alcohol), with the aim of improving the stability of the nanofluids. The modified nanoparticles were used for the preparation of nanofluids with different volume percent loadings of nanoparticles in water ranging from 0.00125% to 0.1%. SEM, TEM, Raman, FTIR and XRD were used for the characterization of nanoparticles. Sedimentation photo capturing was applied to visualize the stability of the prepared nanofluids. A transient hot bridge (THB) apparatus was used for measuring the thermal conductivity of the nanofluids whereas the rotational viscometer was used to measure the viscosity of the nanofluids. Data were collected at temperatures ranging from 20°C to 50°C. The results showed that the measured viscosity and thermal conductivity of the nanofluids increased as the particle concentrations increased and were higher than the values of the base fluids. The results thus suggest that use of the surface modification technique has a significant effect on the stability of TiO2 nanoparticles.

Influence of wastewater type on the impact generated by TiO2 nanoparticles on the oxygen uptake rate in activated sludge process

Physicochemical characteristics of wastewater have a relationship with the stability of TiO2 nanoparticles (NPs). This in turn has an effect on the toxicity of TiO2 NPs in microorganisms. In this work, the effect of TiO2 NPs on activated sludge process was evaluated using three different types of wastewater: synthetic, raw, and filtered. The results showed that aggregate size of TiO2 NPs and their specific adsorption of substrates were influenced by the type of substrates and the presence of suspended solids in the wastewater. It was also shown that TiO2 NPs in raw wastewater severely inhibited oxygen uptake by microorganisms as compared to uptake in synthetic or filtered wastewater. The attachment of TiO2 NP aggregates on cell membranes was observed for all types of wastewater. However, the internalization of TiO2 NPs by microorganisms was observed only for raw and filtered wastewater. These results indicate that the effects caused by TiO2 NPs on activated sludge were different depending on the wastewater used for the experiment.

Characterization and stability of TiO2 nanoparticles in industrial dye stuff effluent

ABSTRACTStability studies were conducted in different solutions (deionized water (DI), NaCl, CaCl2, and MgCl2) at different pH. Agglomeration and zeta potential were influenced by ionic strength, type of electrolyte, and the presence of dye stuff. The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to analyze the stability and/or agglomeration of the nanoparticles in the different solutions. Repulsive or attractive forces stipulated by the DLVO theory were used to quantitatively discuss the results. The increase in ionic strength increased agglomeration which was linked to pHpzc, as there were minimal electrostatic repulsions at the pzc, yet the attractive van der Waals forces were dominant. Addition of the dye stuff significantly decreased the agglomeration as the dye stuff changed the overall zeta potential of TiO2 nanoparticles to negative across the entire pH which improved stability as there were particle–particle repulsions. Monovalent and divalent cations were compared and Ca2+ increased the mean diameter of nanoparticles as it effectively decreased the EDL of the nanoparticles, thus enhancing agglomeration. The DLVO theory was successful at explaining, in terms of the interaction energies between nanoparticles, the phenomena that caused either agglomeration or stability of the as-synthesized TiO2 nanoparticles in the different solutions.

Surface speciation of myo-inositol hexakisphosphate adsorbed on TiO2 nanoparticles and its impact on their colloidal stability in aqueous suspension: A comparative study with orthophosphate

Despite extensive research demonstrating the influence of organic matter and inorganic phosphate on the stability of TiO2 nanoparticles (NPs), far less research has assessed the impact of myo-inositol hexakisphosphate (IHP), a common organic phosphate widely present in the environment. In this study, the adsorption of IHP on TiO2 NPs and its impact on their colloidal stability were investigated using batch experiments, dynamic light scattering (DLS) techniques, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. Inorganic orthophosphate (Pi) adsorption was run for comparison. The ratio of the Pi/IHP adsorption density (1.528: 0.453) at pH5.0 suggested that IHP may complex on the TiO2 surface through three of its six phosphate groups. Zeta potential measurements, ATR-FTIR and NMR spectra indicated that IHP/Pi adsorbed onto TiO2 NPs by forming inner-sphere complexes and modified the surface charge of these NPs, which exerted a great impact on their colloidal stability. Interactions between NPs measured by sedimentation and aggregation size highly depended on the pH, surface phosphorus coverage, and surface phosphorus species. The impact of IHP on the aggregation and dispersion of TiO2 NPs was significantly larger than that of Pi, in agreement with the calculation from the DLVO theory. This study highlighted the impact of IHP relative to Pi on the colloidal stability of TiO2 NPs in phosphorus-enriched environments.

Effect of electrolyte valency, alginate concentration and pH on engineered TiO2 nanoparticle stability in aqueous solution

Agglomeration and disagglomeration processes are expected to play a key role on the fate of engineered nanoparticles in natural aquatic systems. These processes are investigated here in detail by studying first the stability of TiO2 nanoparticles in the presence of monovalent and divalent electrolytes at different pHs (below and above the point of zero charge of TiO2) and discussing the importance of specific divalent cation adsorption with the help of the DLVO theory as well as the importance of the nature of the counterions. Then the impact of one polysaccharide (alginate) on the stability of agglomerates formed under pH and water hardness representative of Lake Geneva environmental conditions is investigated. In these conditions the large TiO2 agglomerates (diameter>1μm) are positively charged due to Ca2+ and Mg2+ specific adsorption and alginate, which is negatively charged, adsorbs onto the agglomerate surface. Our results indicate that the presence of alginate at typical natural organic matter concentration (1–10mgL−1) strongly modifies the TiO2 agglomerate (50mgL−1) stability by inducing their partial and rapid disagglomeration. The importance of disagglomeration is found dependent on the alginate concentration with maximum of disagglomeration obtained for alginate concentration ≥8mgL−1 and leading to 400nm fragments. From an environmental point of view partial restabilization of TiO2 agglomerates in the presence of alginate constitutes an important outcome. Disagglomeration will enhance their transport and residence time in aquatic systems which is an important step in the current knowledge on risk assessment associated to engineered nanoparticles.

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.

Dispersion and stability of titanium dioxide nanoparticles in aqueous suspension: effects of ultrasonication and concentration

The increasing applications of titanium dioxide (TiO(2)) nanoparticles raise concerns about their potential environmental impacts. To investigate the fate and transport of TiO(2) nanoparticles in aqueous suspension, ultrasonication is widely used for the dispersion of TiO(2) nanoparticles in laboratory-scale studies. There is a pressing need for detailed information on the dispersion and stability of TiO(2) nanoparticles. This study investigated the change of size, zeta potential, and pH of TiO(2) nanoparticles aqueous suspension under different conditions of ultrasonication and concentrations. It was found that the hydrodynamic diameter of TiO(2) nanoparticles decreased with increasing suspension concentration and remained stable for more than 1 hour after sonication, which is enough for experimental research. The pH decreased with increasing nanoparticles concentration. Ultrasonication remarkably improved zeta potential to be above 15 mV for all the samples. Therefore, 20 minutes of ultrasonication (180 W) is sufficient for the dispersion of this rutile TiO(2) nanoparticles suspension, which can remain stable for more than 1 hour. However, the optimum sonication time for TiO(2) nanoparticles dispersion is influenced by many factors, such as TiO(2) nanoparticles concentration, solution chemistry, and sonicator parameters.

The effect of inorganic ions on the aggregation kinetics of lab-made TiO2 nanoparticles in water

Metal oxide nanoparticles released from nanotechnology-based industries have attracted more attention recently because of their potentially hazardous effect to humans and the ecosystem. The aggregation of nanoparticles has a great influence on their fate in the environment and is relevant to their potential toxicities. In this study, we synthesized stable TiO2 nanoparticle suspension and investigated their distinct aggregation kinetics in the presence of various inorganic ions. Different concentrations of salts (NaCl, CaCl2 and Na2SO4) were chosen to represent various environmental solutions. The particle size of TiO2 nanoparticles increased when ionic concentrations went up. The stability of TiO2 nanoparticles in water is also affected by combinations of salts and ionic strength. For our lab-made TiO2 nanoparticles, it was easier to form aggregates in the presence of anions than in the presence of cations. Furthermore, divalent ions were better than monovalent ions in promoting aggregation formation. The attachment efficiencies of TiO2 aggregates were constructed based upon the aggregation kinetics. The critical coagulation concentration values for our lab-made TiO2 nanoparticles were higher than previously reported. The aggregation kinetics fit the Derjaguin–Landau–Verwey–Overbeek theory well; that is, divalent anions neutralized the nanoparticle surface charge and promoted aggregate formation more efficiently than the monovalent ones did. Our results indicated that the ionic concentration and ionic type required for the aggregation of TiO2 NPs are critical. These factors should be taken into account for interpreting the behavior of NPs and for developing strategies to remove NPs from the aquatic environment.

Stability Analysis of Nano-Sized Titanium Dioxide in Aqueous Environment

Nano-sized titanium dioxide in aquatic environment poses potential impact on environment and human health. In this research, the impact of pH value, humic acid (HA) and divalent cations (Ca2+) on the stability of titanium dioxide nanoparticles(NPs) in the aqueous enviorment was investigated using a batch test. The results showed that the particle size of TiO2 NPs was not sensitive to the pH value but presented inversely proportional to zeta potential. The TiO2 NPs become more stable along with surface zeta potential, accompany with small particle size and high dispersion. In the presence of HA, the particle size was smaller and TiO2 NPs could be stabilized. This might be synergistic effect of the ligand exchange and electrostatic force. Meanwhile, NPs particle size increased with the addition of Ca2+ and the stability of TiO2 NPs became decreased.

Preparation of thermostable highly dispersed titanium dioxide from stable hydrosols

A large set of stable nanodispersed TiO2 hydrosols differing in particle structure and dispersion medium composition was synthesized. For highly dispersed TiO2 samples obtained by calcination of dried sols at 500°C phase compositions, sizes of primary crystallites, and specific surface areas were found. The factors affecting thermal stability of TiO2 nanoparticles were analyzed. The sol containing the most thermostable nanoparticles was used to produce a highly efficient catalyst for cyclohexanone ammoximation.