The effect of the presence of Ag nanoparticles on the photocatalytic degradation of oxalic acid adsorbed on TiO2 nanoparticles monitored by ATR-FTIR

Photocatalytic degradation of oxalic acid adsorbed on the Ag/P25 TiO₂ composite nanoparticle films were investigated using ATR-FTIR technique under UV irradiation. Ag/P25 TiO₂ composite nanoparticle films with various Ag content were tested. Topography and chemical structure/composition of the composite nanoparticle films were analyzed by AFM and XPS respectively. It was found that in the degradation reaction of the oxalic acid, the presence of only 2% Ag nanoparticles leads to six times more oxalic acid degradation compared to that degraded in the presence of pure P25 TiO₂ nanoparticles. The degradation rate of the oxalic acid is three times higher in the case of Ag/TiO₂ composite nanoparticle film than in the case of pure TiO₂ nanoparticles. It was observed that both the rate of oxalic acid degradation and the degraded amount of the oxalic acid were significantly affected by Ag incorporation.     

Fluoroalkylsilane treatment of TiO2 nanoparticles in difference pH values: Characterization and mechanism

In this research, TiO₂ nanoparticles were treated with hydrophobic 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (fluorosilane) in acidic, neutral and alkaline conditions. The treated nanoparticles were characterized using FTIR spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction spectroscopy. Reflectance spectra were obtained using UV–vis diffuse reflectance spectroscopy and band gap energy of the various nanoparticles was determined. Zeta potential measurements were used to evaluate colloidal stability of nanoparticles in aqueous media. The mechanism of fluorosilane adsorption on the surface of TiO₂ nanoparticles was investigated using ATR-FTIR spectroscopy and turbidimetric technique.The characterization results revealed that the amorphous fluorosilane adsorbs on the surface of TiO₂ nanoparticles in both neutral (pH 6) and alkaline (pH 11) solutions. The values of the band gap energy for all treated nanoparticles were almost the same, in the range of 3.10–3.18 eV. Zeta potential measurements showed that isoelectric point of the TiO₂ nanoparticles shifts from 6.8 for untreated TiO₂ to 4.4 for treated one. Based on the zeta potential measurement results, it is expected that treated TiO₂ nanoparticles in neutral or alkaline conditions have higher colloidal stability and better dispersion in the aqueous solutions. Hydrophobic character of fluoro specious on the surface of nanoparticles leads the treated nanoparticles migrate towards the suspension surface. Therefore, these treated nanoparticles may be useful for developing self-cleaning coatings with minimal destructive effect on the polymeric matrix.     

Decolorization of beads-milled TiO2 nanoparticles suspension in an organic solvent

In this paper, a new method is proposed for the decolorization of a yellow-hued suspension of rutile TiO₂ nanoparticles in an organic solvent (diethylene glycol dimethylether). The presence of color has always been undesirable in a suspension of nanoparticles filler used for industrial needs, particularly for optical applications.A colorless suspension was achieved by irradiating well-dispersed TiO₂ nanoparticles in an organic solvent with UV-light (λ = 254 nm) for 5 h. TiO₂ nanoparticles of 1 and 5 wt.% were dispersed using a beads mill method. Trimethoxytrifluor(propyl) silane was used as a dispersant to achieve stability. The effect of the UV-light irradiation on the TiO₂ nanosuspension was investigated by means of a Fourier transform nuclear magnetic resonance analyzer (FT-NMR). The dispersant was partially desorbed due to the interaction of UV light and the TiO₂/dispersant complex. Thus, an enhanced transparency and the absence of color were obtained for well-dispersed TiO₂ nanoparticles in an organic solvent.     

Preparation and dielectric properties of surface modified TiO2/silicone rubber nanocomposites

A TiO₂/silicone rubber (SR) nanocomposite was prepared via three-roll grinding followed compressive molding technology. The TiO₂ nanoparticles were chemically modified with silane couple agent and the modification effect on the dielectric and mechanical properties of the resultant composites was investigated. The results showed that the electrical breakdown strength and ultimate tensile strength of the modified TiO₂ (m-TiO₂)/SR nanocomposites enhanced significantly while the dielectric loss decreased relative to the naked TiO₂ (n-TiO₂)/SR nanocomposites. These results were well correlated to the uniform dispersion state of the m-TiO₂ as well as the remarkably enhanced interfacial interaction thanks to the presence of the silane couple agent.     

Photoconductivity of n-type semiconductor nanoparticle-doped poly(N-vinylcarbazole) films

TiO₂, CdS and ZnS nanoparticles that disperse stably in organic solvents are synthesized. Poly(N-vinylcarbazole) films doped with the n-type semiconductor nanoparticles are prepared with a cast method. The films exhibit a transient photocurrent when irradiated by a light pulse and act such as a diode when AC voltage is applied under continuous illumination. The transient photocurrent response and diode-like properties are significantly different depending on the kind of the nanoparticles and their amounts. The films doped with TiO₂ and CdS nanoparticles increase the transient photocurrent at lower doped amounts, which is remarkable for TiO₂-doped films. Time of flight analysis of the transient photocurrent shows that mobility of hole in PVK increases with increase in the amount of CdS and TiO₂. From the studies on the diode-like properties, the current increase at lower dopant concentration is concluded to be due to increase in the amount of holes by an electron transfer from PVK to the photo-excited nanoparticles. At higher doping with CdS nanoparticles, main charge carrier of the films is found to change from holes to electrons.     

Surface modification and characterization for dispersion stability of inorganic nanometer-scaled particles in liquid media

Abstract

Inorganic nanoparticles are indispensable for science and technology as materials, pigments and cosmetics products. Improving the dispersion stability of nanoparticles in various liquids is essential for those applications. In this review, we discuss why it is difficult to control the stability of nanoparticles in liquids. We also overview the role of surface interaction between nanoparticles in their dispersion and characterization, e.g. by colloid probe atomic force microscopy (CP-AFM). Two types of surface modification concepts, post-synthesis and in situ modification, were investigated in many previous studies. Here, we focus on post-synthesis modification using adsorption of various kinds of polymer dispersants and surfactants on the particle surface, as well as surface chemical reactions of silane coupling agents. We discuss CP-AFM as a technique to analyze the surface interaction between nanoparticles and the effect of surface modification on the nanoparticle dispersion in liquids.     

Preparation and characterization of TiO2 bulk porous nanosolids

A novel TiO₂ bulk porous nanosolid (also called a “TiO₂ nanosponge”) was prepared by a solvothermal hot-press (SHP) technique, using TiO₂ nanoparticles (average particle size of 15 nm) and various solvents as the starting materials. The pore diameters of the nanosolids were rather uniform, and the maximum value of pore volume and specific surface area were 0.249 cm³/g and 59.455 m²/g, respectively. The pore volume and diameter of TiO₂ bulk porous nanosolid could be controlled by changing either the type or the amount of the solvent used in the experiment. No residual solvents could be detected by FTIR analysis, which means that the solvents had entirely escaped from the samples during the process of preparing TiO₂ bulk porous nanosolids.     

pH-Dependent gold nanoparticle self-organization on functionalized Si/SiO2 surfaces

The self-organization of citrate- and acrylate-stabilized gold nanoparticles onto SiO₂/hydroxyl-, amino- and nitro-terminated surfaces was investigated as a function of pH. Bare clean Si/SiO₂ substrates were used as the SiO₂/hydroxyl-terminated surfaces and self-assembled monolayers (SAM) of (3-aminopropyl)trimethoxysilane (APTMS) and 3-(4-nitrophenoxy)-propyltrimethoxysilane (NPPTMS) on Si/SiO₂ were employed as the amino- and nitro-terminated surfaces, respectively. All the surfaces were fully characterized by contact angle, atomic force microscopy (AFM), ellipsometry and X-ray photoelectron spectroscopy (XPS). Citrate- and acrylate-stabilized gold nanoparticle stability was also investigated as a function of pH by UV–visible absorption spectroscopy and Z-potentiometry. The gold nanoparticle surface coverage of the substrates was independently estimated by AFM and XPS. The results show that colloid deposition on bare SiO₂/OH surfaces and on NPPTMS monolayers is negligible with the exception of acrylate-stabilized gold nanoparticles which were found to be immobilized on nitro-terminated surfaces at pH lower than 3.5. Nevertheless, APTMS monolayers interact strongly with citrate- and acrylate-stabilized gold nanoparticles exhibiting a dependence of the surface coverage from the pH of the colloidal solution.     

Improvement of epoxy resin properties by incorporation of TiO2 nanoparticles surface modified with gallic acid esters

Epoxy resin/titanium dioxide (epoxy/TiO₂) nanocomposites were obtained by incorporation of TiO₂ nanoparticles surface modified with gallic acid esters in epoxy resin. TiO₂ nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO₂ nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO₂ nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO₂ nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO₂ nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO₂ nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO₂ nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO₂ nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO₂ nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.     

Mass-synthesized anatase titania nanocrystals with tunable size and shape via sol-gel in organic solvents with adsorbing ligands

High-quality anatase titania (TiO₂) nanoparticles, nanowires, and nanorods have been mass-synthesized by the modified sol-gel method in the saturated fatty alcohol, acid, and amine systems with adsorbing ligands, respectively. These obtained quasi-spherical TiO₂ nanoparticles showed the mean size of 16.5 nm with a narrow size-distribution. These resulting TiO₂ nanowires had the uniform diameter of 3.8 nm with the length range of 80-180 nm, and TiO₂ nanorods had the uniform diameter of 7.5 nm with the length range of 40-70 nm, respectively. We demonstrated that the shapes, sizes and morphology of these anatase TiO₂ nanocrystals could be controlled systematically by adjusting certain reaction parameters, such as the kind of organic solvents, the alkyl length of organic solvents, and the reaction time. It has been found that the shape of the products was primarily determined by the kind of organic solvents. However, their sizes, size-distributions, and morphology could be controlled by adjusting the alkyl length of organic solvents and the reaction time. Based on the analysis of all experiment results, we have investigated the growth mechanism of these TiO₂ nanocrystals with the different shape. Meanwhile, this synthetic method can be extended further for the preparation of other oxides nanocrystals.     

Supercritical fluid mediated synthesis of poly(2-hydroxyethyl methacrylate)/Fe3O4 hybrid nanocomposite

Poly(2-hydroxyethyl methacrylate) (PHEMA) and magnetic nanoparticle (Fe₃O₄) hybrid nanocomposite was synthesized by dispersion polymerization in supercritical carbon dioxide (scCO₂) using a copolymeric stabilizer, poly[(2-dimethylamino)ethyl methacrylate-co-1H,1H-perfluorooctyl methacrylate] (PDMAEMA-co-PFOMA). Fe₃O₄ nanoparticles were first surface-modified with a silane coupling agent methacryloxypropyltrimethoxysilane (MPTMS), which provides a reactive CC bond and can copolymerize with 2-hydroxyethyl methacrylate (HEMA). After immobilization of the silane coupling agent, polymer chains were successfully grafted onto the surface of Fe₃O₄, resulting in the formation of core-shell nanostructure. FE-TEM pictures showed that the nanoparticles were well dispersed in the polymer matrix. The incorporation of Fe₃O₄ in the nanocomposite was confirmed by FT-IR, XRD and XPS. Thermal stability and magnetic property increase with the increasing amount of Fe₃O₄ nanoparticles in the composite. This new environmentally benign green synthetic route may offer advantages of easy separation and solvent removal.     

Influence of surface modified TiO2 nanoparticles on dielectric properties of PVdF–HFP nanocomposites

Polyvinylidene fluoride-co-hexaflouropropylene (PVdF–HFP)/TiO₂ hybrid nanocomposites membranes for electrical applications have been prepared using a solvent casting technique. The interface between PVdF–HFP and TiO₂ was modified using aminopropyltrimethoxysilane (APS) coupling agent. The silane linkages on the TiO₂ surface have been confirmed using Fourier transform infra red spectroscopy. WAXD and DSC analysis has been employed to estimate the variation in crystallinity within the membrane as a function of the incorporation of both untreated and APS treated TiO₂. The dispersion of both nanoparticles in the PVdF–HFP matrix were characterized by atomic force microscopy and differences were observed in the images of APS treated and untreated. Variation in electrical properties such as conductivity, dielectric constant, dielectric loss and electric modulus of the hybrid composite films were studied employing AC impedance spectroscopy over a range of frequency from 1 kHz to 1 MHz at room temperature. Theoretical models like Maxwell, Faruka, Rayleigh and Lichtenecker were employed to calculate the effective dielectric constant of hybrid nanocomposite membranes and the estimated values were compared with the experimental data. Further, the variation in thermal stability of PVdF–HFP membrane as a function of untreated and silane treated TiO₂ reinforcement has been estimated using thermogravimetric analysis.     

In situ synthesis of transparent TiO2 nanoparticle/polymer hybrid

Transparent TiO₂ nanoparticle/polymer hybrids were synthesized from titanium isopropoxy methacrylate via hydrolysis and polymerization in 2-methoxymethanol. Crystalline TiO₂ nanoparticles were uniformly dispersed in the polymer matrix. A highly transparent free-standing TiO₂ nanoparticle/polymer hybrid film was synthesized. The refractive index (RI) of the hybrid films on Si substrates could be controlled by varying the concentration of TiO₂ nanoparticles: the RI increased with increase in Ti content. A further increase in the RI was achieved upon irradiation with ultraviolet light. A TiO₂ nanoparticle/PMMA hybrid without the silica component exhibited an RI of 1.717 and an Abbe number of 21.6.     

Hybrid Organic–Inorganic Colloidal Composite ‘Sponges’ via Internal Crosslinking

An effective method for the generation of hybrid organic–inorganic nanocomposite microparticles featuring controlled size and high structural stability is presented. In this process, an oil‐in‐water Pickering emulsion is formed using hydrophilic amine‐functionalized silica nanoparticles. Covalent modification using a hydrophobic maleic anhydride copolymer then alters nanoparticle wettability during crosslinking, causing a core‐shell to nanocomposite structural reorganization of the assemblies. The resulting porous nanocomposites maintain discrete microparticle structures and retain payloads in their oil phase even when incubated in competitive solvents such as ethanol.     

Organic solvent based TiO<Subscript>2</Subscript> dispersion paste for dye-sensitized solar cells prepared by industrial production level procedure

In order to prepare the TiO₂ liquid dispersions for the electrodes of dye-sensitized solar cells with industrial mass production level at a reasonable cost, the present study investigates the preparation of TiO₂ liquid dispersions by a general industrial dispersion technique using readily available P25. To determine the TiO₂ dispersion offering the best light–electricity energy conversion efficiency, the suitability of various types of solvents and resins for use in TiO₂ dispersion are tested. In general, organic solvent based TiO₂ dispersions are found to allow the formation of more uniform thin films in comparison with water-based dispersions. A preparation using ethyl cellulose as the resin and the terpineol as the solvent is found to exhibit the best conversion efficiency. We have also found that using two kinds of resins of different molecular weights gave rise to better efficiency. Among 26 metal compounds tested in this study, the best metal dopant was Ag. XRD and XPS measurements confirm that the Ag exists as metal Ag and silver oxide.     

Controlled preparation of titania nanofilm by a template of polydopamine film and its reversible wettability

Titanium oxide (TiO₂) nanofilm was prepared by a simple method of sol-gel deposition on the glass substrate, which was pre-modified with a polydopamine (PDA) film. The as-prepared TiO₂ nanofilm was analyzed by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The thickness of TiO₂ film can be controlled by the thickness of PDA film, which was dependent on the polymerization time. The mechanism of wettability conversion on TiO₂ film was investigated by means of contact angle measurements in different experimental conditions. The results demonstrated that humidity was the major factor for converting the hydrophobic surface of TiO₂ film into hydrophilic surface under ultra-violet (UV) irradiation. And atmospheric oxygen played dominant role in reconverting the hydrophilic surface of TiO₂ film into hydrophobic surface when it was stored in the dark. The TiO₂ nanofilm showed reversible hydrophobic/hydrophilic conversion in the condition of alternating between UV irradiation and storage in the dark.     

A novel hydrophobic adsorbent of electrospun SiO<Subscript>2</Subscript>@MUF/PAN nanofibrous membrane and its adsorption behaviour for oil and organic solvents

With increasing oil spill accidents, the development of effective and low-cost adsorbents with good hydrophobicity is highly desirable. To cope with the clean-up of oil spill, a hydrophobic adsorbent was synthesized by electrospinning using inexpensive raw materials. By ingeniously combining melamine with polyacrylonitrile (PAN) as well as SiO₂ nanoparticles, a novel composite nanoadsorbent named SiO₂@MUF/PAN nanofibrous membrane was prepared and characterized. The adsorbents were conducted based on uniform nanofibre networks and were abundant with narrow slit-like pores, which are significant for the retention of oil and organic solvents. The hydrophobicity of the as-prepared membranes was enhanced with an increasing amount of SiO₂, and the highest water contact angle was 128.3°. Furthermore, the combination of SiO₂ and melamine increased the thermal stability of the membranes. With the unique pore structures and hydrophobicity, the membranes were able to selectively remove not only oil but also organic solvents from water surface. The adsorption capacities of the membranes with SiO₂ nanoparticles (0.9 wt%) were the highest and that for peanut oil, diesel, pump oil and engine oil were 19.09, 13.12, 18.48 and 22.67 g g^?1, respectively, while that for organic solvents ranged from 12.92 to 22.16 g g^?1. After 10 adsorption–regeneration cycles, the adsorption capacity was still around 35% of the initial value. Due to its high oil adsorption capacity, excellent reusability and the cost-effective hydrophobic, SiO₂@MUF/PAN have a great potential for oil spill clean-up.     

Enhanced Photocatalytic Performances of CeO2/TiO2 Nanobelt Heterostructures

CeO₂/TiO₂ nanobelt heterostructures are synthesized via a cost‐effective hydrothermal method. The as‐prepared nanocomposites consist of CeO₂ nanoparticles assembled on the rough surface of TiO₂ nanobelts. In comparison with P25 TiO₂ colloids, surface‐coarsened TiO₂ nanobelts, and CeO₂ nanoparticles, the CeO₂/TiO₂ nanobelt heterostructures exhibit a markedly enhanced photocatalytic activity in the degradation of organic pollutants such as methyl orange (MO) under either UV or visible light irradiation. The enhanced photocatalytic performance is attributed to a novel capture–photodegradation–release mechanism. During the photocatalytic process, MO molecules are captured by CeO₂ nanoparticles, degraded by photogenerated free radicals, and then released to the solution. With its high degradation efficiency, broad active light wavelength, and good stability, the CeO₂/TiO₂ nanobelt heterostructures represent a new effective photocatalyst that is low‐cost, recyclable, and will have wide application in photodegradation of various organic pollutants. The new capture–photodegradation–release mechanism for improved photocatalysis properties is of importance in the rational design and synthesis of new photocatalysts.     

Improvement of impact toughness of AWS E6010 weld metal by adding TiO2 nanoparticles to the electrode coating

The effect of TiO₂ nanoparticles in the electrode coating on the impact toughness of three weld metals prepared by the shielded metal arc welding process was investigated and the main factors affecting the impact toughness were discussed. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. When the content of TiO₂ nanoparticles in the composition of electrode coating is increased, the morphology of ferrite in the microstructure of columnar zone will change from Widmanstätten ferrite to acicular ferrite. This finally changes to allotriomorphic ferrite when the amount of TiO₂ nanoparticles in the electrode coating goes relatively high. Furthermore, the addition of TiO₂ nanoparticles is effective in refining the ferrite grain size of the reheated microstructures of weld metals. This effect is attributed to the increased number of nucleation sites on the oxide nanoparticles. The impact toughness of the weld metal was improved by adding TiO₂ nanoparticles, especially when a medium TiO₂ nanoparticle content was used in the electrode coating. A significant increase in the impact toughness of weld metal was shown to be due to the increased percentage of acicular ferrite and refinement of microstructure.     

Effect of addition of TiO2 nanoparticles on the microstructure,microhardness and interfacial reactions of Sn3.5AgXCu solder

In this work, TiO₂ nanoparticles were successfully incorporated into Sn3.5Ag and Sn3.5Ag0.7Cu solder, to synthesize novel lead-free composite solders. Effects of the TiO₂ nanoparticle addition on the microstructure, melting property, microhardness, and the interfacial reactions between Sn3.5AgXCu and Cu have been investigated. Experimental results revealed that the addition of 0.5 wt.% TiO₂ nanoparticles in Sn3.5AgXCu composite solders resulted in a finely dispersed submicro Ag₃Sn phase. This apparently provides classical dispersion strengthening and thereby enhances the shear strength of composite solder joints. After soldering, the interfacial overall intermetallic compounds (IMC) layer of the Sn3.5AgXCu lead-free solder joint was observed to have grown more significantly than that of the Sn3.5AgXCu composite solder joints, indicating that the Sn3.5AgXCu composite solder joints had a lower diffusion coefficient. This signified that the presence of TiO₂ nanoparticles was effective in retarding the growth of the overall IMC layer.