Suspensions Of TiO2 Nanoparticles Research Articles

Development of TiO2/PVA nanocomposites for application in solar cells

Thin films of TiO2/PVA nanocomposites were prepared by solvent casting method to be used as UV-masks for various applications and as anti-reflection coatings in solar cells. Doping of TiO2 nanoparticles into PVA matrix had effect on it’s semicrystallinity and electronic structure. In order to evaluate structural and optical properties of nanocomposite films, X-ray Diffractometer, UV-Vis Spectroscopy and Fourier Transform Infrared Spectroscopy were performed. XRD results of nanocomposite films were showing broadened peaks which were absent in that of the PVA.In absorption spectra, TiO2/PVA nanocomposite films were showing selective absorbance in UV region and no absorbance in visible region and intensity of absorbance was increased with increased wt% of TiO2 nanoparticles in TiO2/PVA nanocomposite.FTIR results confirmedformation of Ti-O-O bond which helps in suspension of TiO2 nanoparticles into PVA.Thermal stability of prepared nanocomposite films was determined using Differential Scanning Calorimetry (DSC). The presence of well-defined exothermic peak in nanocomposite films with 0.125 wt% and 0.062 wt% doping of TiO2 nanoparticles confirms crystalline nature of polymer nanocomposite films. Melting point temperature of TiO2/PVA nanocomposites was increased in compare to PVA.

Photoactivity of Titanium Dioxide Foams

TiO2 foams have been prepared by a simple mechanical stirring method. Short-chain amphiphilic molecules have been used to stabilize colloidal suspensions of TiO2 nanoparticles. TiO2 foams were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy, and scanning electron microscopy (SEM). The photoassisted oxidation of NO in the gas phase according to ISO 22197-1 has been used to compare the photoactivity of the newly prepared TiO2 foams to that of the original powders. The results showed that the photoactivity is increased up to about 135%. Foam structures seem to be a good means of improving the photoactivity of semiconductor materials and can readily be used for applications such as air purification devices.

Fabrication and photocatalytic activity of TiO2 composite membranes via simultaneous electrospinning and electrospraying process

In present study, a simultaneous electrospinning and electrospraying (SEE) process was employed to produce microclusters of TiO2 nanoparticles and interlock them in nanofibrous network. The photocatalytic composite membranes (PCMs) were fabricated by electrospraying TiO2 nanoparticle suspension into microcluster form that dispersed and entrapped within nylon-6 electrospun fiber membrane. Three PCMs membrane with TiO2 content of 52.0, 83.6, and 91.7wt.% were successfully fabricated. The membrane consisted of TiO2 microclusters, ranging in sizes from around 0.3 to 10μm, distributed uniformly within the nylon-6 nanofibrous network. PCMs photocatalytic activity against Methylene Blue (MB) in aqueous solution showed more than 98% MB removal efficiency after 120min of photocatalytic oxidation (PCO) for all PCMs. For PCM with the highest TiO2 content tested for 5 PCO cycles, it was found that most of their TiO2 content remained incorporated within the nanofibrous structure. The concept of nanoparticles clusters entrapment with SEE fabrication employed here provide a simple and effective method for reducing detachment of nanostructure phase from nanocomposite membrane.

The Effect of Solvents and Rare-Earth Element (Er, Yb) Doping on Suspension Stability of Sol-Gel Titania Nanoparticles.

The effects of solvent on the suspension stability of titanium dioxide (TiO2) nanoparticle (NP)-doped rare-earth elements (Er and Yb) were evaluated. Pure and doped TiO2 NPs were successfully prepared by the sol-gel method under the supercritical drying conditions of ethanol. Doped nanopowders were prepared with 5 mol% Er or 5 mol% Yb concentration, and co-doped nanopowders were prepared with fixed 5 mol% Er concentration and various Yb concentrations of 5 and 10 mol%. TiO2 NP suspensions with diverse solvents, such as water, ethanol, methanol, and butanol, were prepared. The nanopowders were characterized by studying their structural and morphology properties. The NP size analysis revealed the average size of TiO2 as approximately around 7-12 nm. Suspensions of TiO2 NPs in different solvents were prepared by a two-step powder dispersion process using several ultrasonication methods. The aim of this paper was to prepare a stable suspension for a certain time period and then to produce doped and undoped TiO2 NP coatings for photovoltaic application. The effects of concentration, dopants, and solvents on the dispersibility and stability of TiO2 suspensions were evaluated. The UV-visible spectroscopy, zeta potential measurements, particle size distribution, SEM, and Hamaker 2 software confirm that the 5%Er-10%:TiO2 suspension exhibits a good stability and stable suspension improved by co-doped rare.

Photocatalytic degradation of lignocaine in aqueous suspension of TiO2 nanoparticles: Mechanism of degradation and mineralization

A detailed investigation on the photocatalytic degradation and mineralization of lignocaine, a local anesthetic, under UV irradiation has been carried out in this study. The dose of TiO2 was optimized initially and was found as 250mgL−1 for the degradation of 2mgL−1 concentration of lignocaine. The scavenging experiment using isopropanol and methanol revealed that the degradation is mainly controlled by hydroxyl radical. A fast disappearance of the parent compound (within 1h) and nearly 75% of mineralization (after 6hr) were observed using this method. The relatively low mineralization efficiency is due to the evolution of various transformation products during the degradation as identified by high-resolution mass spectrometry (LC-Q-TOF-MS). Ten well-separated product peaks were observed in the total ion chromatogram (TIC) for 30min irradiated sample of lignocaine. Based on the formation of these products, a degradation mechanism is proposed involving mainly hydroxylation, N-de-ethylation, and hydrogen abstraction. As part of mineralization study, the evolution of various inorganic ions was analyzed and the ammonium ion is found as the major inorganic species. A detailed mechanism is proposed for the inorganic ion release as well.

Minimizing structural deformation of gold nanorods in plasmon-enhanced dye-sensitized solar cells

Plasmonic metal nanoparticles have shown great promise in enhancing the light absorption of organic dyes and thus improving the performance of dye-sensitized solar cells (DSSCs). However, as the plasmon resonance of spherical nanoparticles is limited to a single wavelength maximum (e.g., ~ 520 nm for Au nanoparticles), we have here utilized silica-coated gold nanorods (Au@SiO2 NRs) to improve the performance at higher wavelengths as well. By adjusting the aspect ratio of the Au@SiO2 NRs, we can shift their absorption maxima to better match the absorption spectrum of the utilized dye (here we targeted the 600–800 nm range). The main challenge in utilizing anisotropic nanoparticles in DSSCs is their deformation during the heating step required to sinter the mesoporous TiO2 photoanode and we show that the Au@SiO2 NRs start to deform already at temperatures as low as 200 °C. In order to circumvent this problem, we incorporated the Au@SiO2 NRs in a TiO2 nanoparticle suspension that does not need high sintering temperatures to produce a functional photoanode. With various characterization methods, we observed that adding the plasmonic particles also affected the structure of the produced films. Nonetheless, utilizing this low-temperature processing protocol, we were able to minimize the structural deformation of the gold nanorods and preserve their characteristic plasmon peaks. This allowed us to see a clear redshift of the maximum in the incident photon-to-current efficiency spectra of the plasmonic devices (Δλ ~ 14 nm), which further proves the great potential of utilizing Au@SiO2 NRs in DSSCs.

Effect of Ions on Removal of TiO2Nanoparticles by Coagulation and Microfiltration

Abstract Removal of TiO2 nanoparticles (NPs) from water by coagulation and microfiltration (MF) was investigated at various ionic species and strengths. Appropriate coagulant doses were determined based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and coagulation with ferric chloride (FeCl3) at 0.1–0.2 mM or poly-aluminum chloride (PACl; [Al2(OH)nCl6-n]m) at 0.2–0.4 mM improved removal of TiO2 NPs to more than 90%, and, simultaneously, turbidity was significantly reduced. Using 0.2 mM FeCl3 as a coagulant, the mean particle size of suspended TiO2 NPs decreased from 145 to 43 nm after coagulation and sedimentation as a result of effective floc formation. Microfiltration (nominal pore size: 0.45 μm and 0.10 μm) of uncoagulated TiO2 NP suspensions produced lower NP concentrations in the filtrate than that in the filtrate of pre-coagulated water. This is because pre-coagulation and settling removed large NPs in the feed water that reduce the number of smaller particles than the pore sizes by cloggin...

Electrophoretic kinetics of concentrated TiO2 nanoparticle suspensions in aprotic solvent

We studied the dependences of the concentration of additive and particle size on the electrophoretic mobility of TiO2 nanoparticles. A high concentration of TiO2 nanoparticles was dispersed in aprotic solvent, which is similar to the operating conditions of electrophoretic applications. Because spectroscopy has limits to measuring the electrophoretic mobility of concentrated suspensions in aprotic solvents, we developed a new measurement to determine the electrophoretic mobility of particles using the reflectance change according to the motion of the particles. TiO2 nanoparticles with sizes of 31 nm to 164 nm were synthesized by hydrolysis and were dispersed in cyclohexanone with a dye (Sudan Black B) for use in the new measurement method. In a concentrated suspension in aprotic solvent, the mobility of the particles was proportional to the dye concentration and was inversely proportional to the size of the particles. This infers that the particle size influences the drag force rather than the surface charge, and therefore, to increase the mobility by changing the surface charge, an additive is effective.

Studies on the performance of annular photo reactor (APR) for pharmaceutical wastewater treatment

Heterogeneous photocatalysis in presence of nanoparticles has become a promising pathway for treatment of wastewater containing pharmaceutical components. In the present research work, degradation of aqueous solution of chlorhexidine digluconate (CHD), an antibacterial drug, has been investigated using TiO2 nanoparticles suspension in the annular photo reactor (APR) under continuous mode having the provision of catalyst recovery. During the degradation of CHD, the effects of major influencing parameters, i.e., substrate to catalyst ratio, flow rate, recycle ratio and temperature on the performance of the photo reactor and its optimization has been performed using Response Surface Methodology (RSM). Moreover, the photocatalytic efficiency of the reactor has been validated by studying the degradation of other antibiotic drugs i.e. ibuprofen (IBP), atenolol (ATL) and carbamazepine (CBZ). The continuous mode operation in photo reactor has ensured the applicability of the present system in the large volume wastewater treatment. The percentage removal of drugs using such reactor having the facility of catalyst recovery is almost same as compared to typical batch photocatalytic system. Thus, the present developed system can be utilized for the treatment of wastewater containing pharmaceutical components which are photo catalytically degradable.

Electrophoretic impregnation of porous anodizing layer by synthesized TiO2 nanoparticles

This paper deals with the elaboration of a stable suspension of TiO2 nanoparticles and their incorporation by electrophoretic deposition into pores of an anodized 5754 aluminum alloy. The as-synthesized TiO2 nanopowder was characterized by the X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy and IR spectroscopy. During this work, both the transmission electron microscopy and particle analysis showed that the resulting particles had a narrow size distribution with a crystallite size of about 15 nm. The zeta potential and stability of TiO2 nanoparticles dispersed with poly(acrylic acid) in an aqueous solution were also measured. A porous anodic film was synthesized in the phosphoric acid-base electrolyte and then filled by 15 nm TiO2 particles via electrophoresis. In addition, the effect of poly(acrylic acid) and pH on the suspension stability has been investigated. It was also demonstrated that by adding glycine in buffered suspension gelating phenomenon can be avoided that inhibits the insertion of nanoparticles inside the pores of an anodic film. It was also noted that an applied electric field greatly influences the electrophoretic deposition process. The field emission gun-scanning electron microscopy observations showed that larger (125 nm in diameter) and linear (6 μm in length) pores are successfully filled in 5 min.

Limestones coated with photocatalytic TiO2 to enhance building surface with self-cleaning and depolluting abilities

Natural stones with self-cleaning and depolluting abilities are appealing to preserve building façades in polluted urban sites and simultaneously to provide air-purification. Coating with photocatalytic Titanium dioxide is promising at this purpose; nonetheless, stone coating issues need better insights to support large-scale applications. In this paper, photocatalytic surfaces of two limestones having different roughnessess and porosities, are investigated by comparing coatings obtained from either water and alcohol based colloidal suspensions of TiO2 nanoparticles, which were synthetized by sol gel and hydrothermal process and sprayed with different loads on the stone surface. A commercial water-based TiO2 sol was also used. The study aims to assess the role of the substrates, the nature of the titania dispersions and the TiO2 loads, in determining characteristics and properties of the photocatalytic stone surfaces, in order to obtain suited coatings for real applications on buildings. Colorimetry detected negligible colour changes on both stone surfaces due to the coatings. A photodegradation test of Rhodamine B recorded a high self-cleaning efficiency on the coated surfaces, irrespective of the stones, the alcohol and water based suspensions, and their TiO2 loads. Conversely, the efficiency in a NOx abatement test was dependent on the porosity and roughness of the stones. ESEM-EDS on the applied coatings and XRD on the TiO2 nanopowders identified critical issues in the coating morphology and presence of by-products relating to the preparation of the sols, which may have implications in the durability performances.The overall results showed that all the obtained coatings were able to deliver photocatalytic surface of both limestones, which have a potential to be implemented as eco-efficient materials on buildings. Nonetheless, higher air purification ability issued for the limestone with higher porosity and roughness and the experimental TiO2 water-based sol performed better than the alcoholic and commercial ones as regards the coating morphology and absence of by-products.

Concurrent photocatalytic and filtration processes using doped TiO2 coated quartz fiber membranes in a photocatalytic membrane reactor

Titanium dioxide (TiO2) composite fiber membranes were prepared by means of sol-gel dip coating methods and were subsequently tested in a photocatalytic membrane reactor (PMR) experiment that incorporated two pollutant removal processes: dead-end filtration and photocatalytic degradation. TiO2 nanoparticle suspensions were initially prepared using the sol-gel synthesis. Quartz fiber filters were immediately dip coated with undoped and doped TiO2 sols producing three types of membranes: undoped, nitrogen-doped, and boron-doped TiO2. The synthesized composite filters were analyzed for their (i) morphology using scanning electron microscopy and (ii) crystal structure using Raman spectroscopy and X-ray diffraction. Chemical composition and chemical bonding of the membranes were determined using X-ray photoelectron spectroscopy. The permeability performance of the membranes was analyzed by measuring the flux using deionized water and the removal of a representative organic pollutant, acid orange 7 (dye), was measured. The experiments were conducted in the PMR under dark and ultraviolet illumination. The removal of dye was improved when undoped and doped TiO2 filters were used in place of a bare quartz fiber filter, except in the case when boron was used at a low doping concentration. The study demonstrates that optimization of doping parameters, such as the type of dopant (nitrogen or boron) and concentration, on TiO2 filters can improve the removal rates of model molecule using ultraviolet A irradiation.

Study of the Effects of SiO<sub>2</sub> Nanoparticles Concentration on the TiO<sub>2</sub> Nanoparticles Suspensions Stabilization

TiO2 nanoparticles (NPTiO2) suspensions are in several ecosystems and residue treatment processes or disposal systems due to their large industrial use and handling. The interactions of the NPTiO2 with NPSiO2 have special interest due to their strong ability to maintain high TiO2 nanoparticles concentration in suspension and promote nanoparticles clustering. These characteristics are used either in cleaning systems or in production of nanoparticles solution for several applications in the food industry or medicine. In this study, suspensions of NPTiO2 and NPSiO2 are synthetized and their stabilizations are discussed. A base TiO2 nanoparticles suspension was synthetized and the initial concentrations of SiO2 nanoparticles (NPSiO2) were changed in order to determine the effects of presence of SiO2 nanoparticles on the stabilization and clustering size. Zeta potential and concentrations measurements were carried out throughout the time and correlated with the initial concentrations of the base suspensions. In this study, the concentrations, zeta potential and pH are measured to estimate the stability of the suspensions. The clustering size, obtained by nanoparticle tracking analysis (NTA), are also monitored and discussed. Results of column soil experiments are discussed and compared under similar conditions with literature data.

Influence of agglomeration and aggregation on the photocatalytic activity of TiO2 nanoparticles

Particle aggregation and agglomeration influence the optical properties of materials and therefore their ability to absorb and scatter the incoming radiation, also affecting their photocatalytic activity [1–7]. We have studied the correlation between aggregation and photocatalytic activity for titanium dioxide by means of experimental measurements of extinction and photocatalytic activity and calculations of their optical properties (extinction, absorption and scattering cross-sections). This approach can be adopted to quantitatively assess the quantum yields of the heterogeneous photocatalytic systems. The study was performed on TiO2 PC105 Cristal ACTiV™, made of aggregated (and agglomerated) primary particles of anatase. The size of the aggregates has been reduced with ultra-sonication. Aqueous suspensions of the obtained materials were characterized by measuring the optical properties (UV–vis extinction), the sizing properties (DLS) and the photocatalytic activity (degradation of phenol under standard conditions). The extinction and absorption spectra of the suspensions were derived from the calculated coefficients, considering also the size distributions measured with DLS, and revealed that light absorption is maximized when particle aggregation and agglomeration are avoided, while diffusion of the incoming radiation dominates when large aggregates and agglomerates are present. The present paper represents a valuable approach to the accurate and reproducible measurement of the photocatalytic activity of TiO2 nanoparticles suspensions, thus allowing a more reliable comparison of the properties of different materials.

Quantitative biokinetics of titanium dioxide nanoparticles after intratracheal instillation in rats: Part 3

The biokinetics of a size-selected fraction (70 nm median size) of commercially available and 48V-radiolabeled [48V]TiO2 nanoparticles has been investigated in healthy adult female Wistar-Kyoto rats at retention time-points of 1 h, 4 h, 24 h, 7 d and 28 d after intratracheal instillation of a single dose of an aqueous [48V]TiO2-nanoparticle suspension. A completely balanced quantitative biodistribution in all organs and tissues was obtained by applying typical [48V]TiO2-nanoparticle doses in the range of 40–240 μg·kg−1 bodyweight and making use of the high sensitivity of the radiotracer technique. The [48V]TiO2-nanoparticle content was corrected for residual blood retained in organs and tissues after exsanguination and for 48V-ions not bound to TiO2-nanoparticles. About 4% of the initial peripheral lung dose passed through the air-blood-barrier after 1 h and were retained mainly in the carcass (4%); 0.3% after 28 d. Highest organ fractions of [48V]TiO2-nanoparticles present in liver and kidneys remained constant (0.03%). [48V]TiO2-nanoparticles which entered across the gut epithelium following fast and long-term clearance from the lungs via larynx increased from 5 to 20% of all translocated/absorbed [48V]TiO2-nanoparticles. This contribution may account for 1/5 of the nanoparticle retention in some organs. After normalizing the fractions of retained [48V]TiO2-nanoparticles to the fraction that reached systemic circulation, the biodistribution was compared with the biodistributions determined after IV-injection (Part 1) and gavage (GAV) (Part 2). The biokinetics patterns after IT-instillation and GAV were similar but both were distinctly different from the pattern after intravenous injection disproving the latter to be a suitable surrogate of the former applications. Considering that chronic occupational inhalation of relatively biopersistent TiO2-particles (including nanoparticles) and accumulation in secondary organs may pose long-term health risks, this issue should be scrutinized more comprehensively.

Quantitative biokinetics of titanium dioxide nanoparticles after oral application in rats: Part 2

The biokinetics of a size-selected fraction (70 nm median size) of commercially available and 48V-radiolabeled [48V]TiO2 nanoparticles has been investigated in female Wistar-Kyoto rats at retention timepoints 1 h, 4 h, 24 h and 7 days after oral application of a single dose of an aqueous [48V]TiO2-nanoparticle suspension by intra-esophageal instillation. A completely balanced quantitative body clearance and biokinetics in all organs and tissues was obtained by applying typical [48V]TiO2-nanoparticle doses in the range of 30–80 μg•kg−1 bodyweight, making use of the high sensitivity of the radiotracer technique. The [48V]TiO2-nanoparticle content was corrected for nanoparticles in the residual blood retained in organs and tissue after exsanguination and for 48V-ions not bound to TiO2-nanoparticles. Beyond predominant fecal excretion about 0.6% of the administered dose passed the gastro-intestinal-barrier after one hour and about 0.05% were still distributed in the body after 7 days, with quantifiable [48V]TiO2-nanoparticle organ concentrations present in liver (0.09 ng•g−1), lungs (0.10 ng•g−1), kidneys (0.29 ng•g−1), brain (0.36 ng•g−1), spleen (0.45 ng•g−1), uterus (0.55 ng•g−1) and skeleton (0.98 ng•g−1). Since chronic, oral uptake of TiO2 particles (including a nano-fraction) by consumers has continuously increased in the past decades, the possibility of chronic accumulation of such biopersistent nanoparticles in secondary organs and the skeleton raises questions about the responsiveness of their defense capacities, and whether these could be leading to adverse health effects in the population at large. After normalizing the fractions of retained [48V]TiO2-nanoparticles to the fraction that passed the gastro-intestinal-barrier and reached systemic circulation, the biokinetics was compared to the biokinetics determined after IV-injection (Part 1). Since the biokinetics patterns differ largely, IV-injection is not an adequate surrogate for assessing the biokinetics after oral exposure to TiO2 nanoparticles.

Electrosprayed TiO2 nanoporous hemispheres for enhanced electron transport and device performance of formamidinium based perovskite solar cells.

Titanium dioxide (TiO2) nanoporous hemispheres (NHSs) with a radius of ∼200 nm are fabricated by electrospraying a hydrothermally synthesized TiO2 nanoparticle (NP) suspension solution. The resulting TiO2 NHSs are highly porous, which are beneficial to the infiltration of perovskites and provide a larger contact area, as building blocks to construct a mesoporous TiO2 layer for FA0.81MA0.15Pb(I0.836Br0.15)3 based perovskite solar cells (PSCs). By varying the TiO2 NHS collecting period (15 s, 30 s, 60 s and 90 s) during the electrospraying process, the performance of PSCs changes with different TiO2 NHS distribution densities. The optimized PSC employing TiO2 NHSs (60 s) exhibits a photovoltaic conversion efficiency (PCE) as high as 19.3% with a Jsc of 23.8 mA cm-2, a Voc of 1.14 V and a FF of 0.71. Furthermore, the PSC possesses a reproducible PCE value with little hysteresis in its current density-voltage (J-V) curves. The small perturbation transient photovoltage (TPV) measurement reveals a longer free carrier lifetime within the TiO2 NHS based PSC than that in the TiO2 NP based PSC, and the time of flight (TOF) photoconductivity measurement shows that charge mobilities in this system are also enhanced. These characteristics make TiO2 NHSs a promising electron transport material for efficient photovoltaic devices.

Accelerated Sedimentation Velocity Assessment for Nanowires Stabilized in a Non-Newtonian Fluid.

In this work, the long-term stability of titanium oxide nanowire suspensions was accessed by an accelerated sedimentation with centrifugal forces. Titanium oxide (TiO2) nanoparticle (NP) and nanowire (NW) dispersions were prepared, and their sizes were carefully characterized. To replace the time-consuming visual observation, sedimentation velocities of the TiO2 NP and NW suspensions were measured using an analytical centrifuge. For an aqueous TiO2 NP suspension, the measured sedimentation velocities were linearly dependent on the relative centrifugal forces (RCF), as predicted by the classical Stokes law. A similar linear relationship was also found in the case of TiO2 NW aqueous suspensions. However, NWs preferred to settle parallel to the centrifugal direction under high RCF because of the lower flow resistance along the long axis. Thus, the extrapolated sedimentation velocity under regular gravity can be overestimated. Finally, a stable TiO2 NW suspension was formulated with a shear thinning fluid and showed great stability for weeks using visual observation. A theoretical analysis was deduced with rheological shear-thinning parameters to describe the nonlinear power-law dependence between the measured sedimentation velocities and RCF. The good agreement between the theoretical predictions and measurements suggested that the sedimentation velocity can be properly extrapolated to regular gravity. In summary, this accelerated assessment on a theoretical basis can yield quantitative information about long-term stability within a short time (a few hours) and can be further extended to other suspension systems.

Directional solidification of aqueous TiO2 suspensions under reduced gravity

Porous materials exhibiting aligned, elongated pore structures can be created by directional solidification of aqueous suspensions—where particles are rejected from a propagating ice front and form interdendritic, particle-packed walls—followed by sublimation of the ice, and sintering of the particle walls. Theoretical models that predict dendritic lamellae spacing—and thus wall and pore width in the final materials—are currently limited due to an inability to account for gravity-driven convective effects during solidification. Here, aqueous suspensions of 10–30 nm TiO2 nanoparticles are solidified on parabolic flights under micro-, lunar (∼0.17 g; gl = 1.62 m/s2), and Martian (∼0.38 g; gm = 3.71 m/s2) gravity and compared to terrestrially-solidified samples. After ice sublimation and sintering, all resulting TiO2 materials exhibit elongated lamellar pores replicating the ice dendrites. Increasing the TiO2 fraction in the suspensions leads to decreased lamellar spacing in all samples, regardless of gravitational acceleration. Consistent with previous studies of microgravity solidification of binary metallic alloys, lamellar spacing decreases with increasing gravitational acceleration. Mean lamellar spacing for 20 wt% TiO2 nanoparticles suspensions under micro-, lunar, Martian, and terrestrial gravity are, respectively: 50 ± 8, 34 ± 11, 30 ± 6, and 23 ± 9 μm, indicating that gravity-driven convection strongly affects lamellae spacing under terrestrial gravity conditions. Gravitational effects on lamellar spacing are highest at low TiO2 fractions in the suspension; for 5 wt% TiO2 suspensions, the microgravity lamellar spacing is more than twice that under terrestrial gravity (182 ± 21 vs. 81 ± 23 μm). Results of this study are in good agreement with previous studies of binary metallic alloy solidification where primary dendrite spacing increases under microgravity. Literature data from ice-templating systems are used to discuss a dependence on lamellae spacing of the density ratio of particles and fluid.

Properties of TiO2/Au nanocomposite produced by pulsed laser irradiation of mixture of individual colloids

TiO2/Au nanocomposite was produced by irradiating the mixture of Au and TiO2 nanoparticle suspensions with the second harmonic beam of Nd:YAG pulsed laser. TiO2 and Au nanoparticles were produced by laser ablation method separately. Titanium dioxide and gold nanoparticles were prepared by ablation of a high purity titanium and gold plates in deionized water, respectively. The fundamental wavelength of a Nd:YAG laser operating at 1064 nm with pulse width of 7 ns and 10 Hz repetition rate was employed to produce nanoparticles. Targets was placed on the bottom of water contain. The synthesized Au and TiO2 colloidal solutions were mixed in equal volumetric ratio and irradiated with the 532 nm laser. The laser spot size was 6 mm on the solution surface, and the laser fluence during the post-irradiation was at 2 J/cm2. Irradiation was done using 5000 pulses at 10 Hz repetition rate and 7 ns pulse width. Results show that the absorption spectrum of nanocomposite is similar to TiO2 spectrum with a surface plasmonic absorption peak at about 530 nm. Both lattice structure of TiO2 and Au nanoparticles appears in the lattice structure of nanocomposite.