Search Results (26)

Local temperature measurement is crucial for understanding nanoscale thermal transport and developing nanodevices for biomedical, photonic, and optoelectronic applications. The rise of photothermal therapy for cancer treatment has increased the demand for high-resolution nanothermometric techniques capable of non-contact intracellular temperature measurement and modification. Raman spectroscopy meets this need: the ratio of anti-Stokes to Stokes Raman intensities for a specific vibrational mode correlates with local temperature through the Boltzmann distribution. The present study proposes a novel photothermal therapy agent designed to advance the current state of the art while adhering to green chemistry principles, thereby favoring low-temperature synthesis involving limited energy consumption. A key challenge in this field is to achieve close contact between plasmonic nanosystems, which act as nanoheaters, and local temperature sensors. This is achieved by employing silver nanoparticles as a heat release agent, coated with anatase-phase titanium dioxide, as a local temperature sensor. The proposed synthesis, which combines refluxing and subcritical solvothermal treatments, enables direct anatase formation, despite its metastability under standard conditions, thus eliminating the need for a calcination step. Structural characterization through SAED-HRTEM and Raman spectroscopy confirms the successful crystallization of the desired phase. Moreover, the nanothermometry measurements conducted at various wavelengths ultimately demonstrate both the effectiveness of these nanomaterials as thermometric probes, with a relative sensitivity of about 0.24 K⁻¹%, and their capability as local heaters, with a release of a few tens of degrees. This work demonstrates a new synthetic strategy for these nanocomposites, which offers a promising pathway for the optimization of nanosystems in therapeutic applications. Full article

Titania-based materials are abundant in technological applications, as well as everyday products; however, many of its structure–property relationships are still unclear. In particular, its surface reactivity on the nanoscale has important consequences for fields such as nanotoxicity or (photo)catalysis. Raman spectroscopy has been used to characterize titania-based (nano)material surfaces, mainly based on empirical peak assignments. In the present work, we address the structural features responsible for the Raman spectra of pure, stoichiometric TiO₂ materials from a theoretical characterization. We determine a computational protocol to obtain accurate Raman response in a series of anatase TiO₂ models, namely, the bulk and three low-index terminations by periodic ab initio approaches. The origin of the Raman peaks is thoroughly analyzed and the structure–Raman mapping is performed to account for structural distortions, laser and temperature effects, surface orientation, and size. We address the appropriateness of previous experimental use of Raman to quantify the presence of distinct TiO₂ terminations, and provide guidelines to exploit the Raman spectrum based on accurate rooted calculations that could be used to characterize a variety of titania systems (e.g., single crystals, commercial catalysts, thin layered materials, facetted nanoparticles, etc.). Full article

Local temperature determination is essential to understand heat transport phenomena at the nanoscale and to design nanodevices for biomedical, photonic, and optoelectronic applications. In particular, the detection of the local temperature of the intracellular environment is interesting for photothermal therapy. In the present work, nanoparticles consisting of an Ag core, covered by a TiO₂ shell and Ag@TiO₂ core–shell, were suitably synthesized through a one-pot method. Silver nanoparticles synthesized in DMF were coated by controlled hydrolysis of titanium tetrabutoxide in the same reaction environment. The synthesis led to nanocomposites where AgNPs were covered by a diffuse layer of anatase. The nanocomposites were characterized using UV/Vis spectroscopy and Raman spectroscopy. The samples obtained proved to be good Raman nanothermometers with a sensitivity comparable to that of simple anatase nanoparticles. Full article

The primary objective of this research is to propose and compile a specific protocol for photocatalytic measurements of modified TiO₂ particles under visible-light irradiation. Nitrogen-modified titanium dioxide (N-TiO₂) powder was synthesized by the sol–gel method and characterized by X-ray Diffraction Analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy (micro-Raman), and Ultraviolet–visible Spectroscopy (UV-Vis). Photocatalytic tests were performed on a specially designed photocatalytic batch reactor to test the ability of the powder to degrade hazardous toxic compounds. Via the Taguchi method, nine experiments (L9) were compiled to examine the factors that affect the photocatalytic activity of the nano-sized powder. The N-TiO₂ particles were characterized by the dominance of the crystalline anatase phase, exhibiting crystals in the nano-scale. The Taguchi method was designed to control four selected parameters (pollutant selection among azo dyes, amount of catalyst to pollutant, distance of the photocatalytic cell from the radiation source, and time protocol) with three levels/options each. Conclusions were drawn regarding the way each parameter affects the final degradation of the pollutant. The parameter that proved to affect the degradation of the pollutant to a greater extent was the choice of pollutant, followed by the amount of catalyst. The other two factors almost slightly affect the process, with a similar percentage. Taking into account the abovementioned results, a photocatalytic protocol for testing TiO₂ nano-powder activity under visible light irradiation is proposed by using a batch, horizontal, rectangular, vis-LED equipped reactor with reflective walls. Full article

Degradation of organic pollutants, especially organic dyes and antibiotics, by semiconductor photocatalysts is an efficient strategy for wastewater treatment. TiO₂ nanomaterials are considered to be promising photocatalysts due to their high chemical stability, high efficiency and availability. Anatase TiO₂ generally has superior photocatalytic activity to the rutile phase. However, the anatase phase can be irreversibly transformed to rutile phase when calcined at an elevated temperature. Methods to improve the stability of anatase are especially important for the TiO₂ gas sensors working at high temperatures. The addition of strong acids can effectively suppress this transformation process. However, these strong acids are relatively expensive, corrosive and environmentally unfriendly. Herein, oxalic acid (OA) as a natural acid was used to control the hydrolysis process of tetrabutyl titanate (TBOT), leading to controllable crystalline phase transformation and reduced crystalline size of TiO₂ on the nanoscale. What is more, the photocatalytic degradation performances were enhanced continuously when the molar ratio of OA to TBOT increased. The degradation reaction rate constants of CT650-R25 were about 10 times that of CT650-R0. The mechanism study shows that the enhanced photocatalytic activity can be attributed to the improved dispersibility, increased specific surface area and reduced recombination rates of photo-induced charge carriers and decreased energy bands as the concentration of OA increased. Thus, this work provides a simple, mild and effective method for controlling the crystalline forms of nano-TiO₂ with enhanced photocatalytic performance towards waste water treatment. Full article

Constructing surface topographies in the micro- or nanometer range is an effective way to improve the biocompatibility of biomaterials. For the present work, anatase coatings with controllable micro/nanoscale characteristics were successfully prepared on an MgZn alloy surface via solvothermal route, and their formation mechanisms are discussed. The features of the as-prepared coatings were characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM), an atomic force microscope (AFM), X-ray diffraction (XRD), and a contact angle goniometer. The corrosion behavior of the coatings was also evaluated by testing the open circuit potential (OCP) in SBF (Simulated Body Fluid). The results show that a gradual variation of the anatase coating morphologies was obtained through adjusting the solvothermal reaction conditions. With the increase of NH₄F concentration in the solution, the cross-combined anatase nanosheets became more dispersed. The micro/nanostructured anatase coatings provide the MgZn alloy with good corrosion resistance, which increased with the density of anatase nanosheets in the coatings. In addition, the coatings exhibit the inhibition of platelet aggregation, and the micro/nano structures can also adsorb endothelial cells. Full article

At the nanoscale, particle size affects the surface reactivity of anatase–water interfaces. Here, we investigate the effect of electrolyte media and particle size on the primary charging behavior of anatase nanoparticles. Macroscopic experiments, potentiometric titrations, were used to quantitatively evaluate surface charge of a suite of monodisperse nanometer sized (4, 20, and 40 nm) anatase samples in five aqueous electrolyte solutions. The electrolyte media included alkaline chloride solutions (LiCl, NaCl, KCl, and RCl) and Na-Trifluoromethanesulfonate (NaTr). Titrations were completed at 25 °C, as a function of pH (3–11) and ionic strength (from 0.005 to 0.3 m). At the molecular scale, density functional theory (DFT) simulations were used to evaluate the most stable cation surface species on the predominant (101) anatase surface. In all electrolyte media, primary charging increased with increasing particle size. At high ionic strength, the development of negative surface charge followed reverse lyotropic behavior: charge density increased in the order RbCl < KCl < NaCl < LiCl. Positive surface charge was greater in NaCl than in NaTr media. From the DFT simulations, all cations formed inner-sphere surface species, but the most stable coordination geometry varied. The specific inner-sphere adsorption geometries are dependent on the ionic radius. The experimental data were described using surface complexation modeling (SCM), constrained by the DFT results. The SCM used the charge distribution (CD) and multisite (MUSIC) models, with a two-layer (inner- and outer-Helmholtz planes) description of the electric double layer. Subtle charging differences between the smallest and larger anatase particles were the same in each electrolyte media. These results further our understanding of solid–aqueous solution interface reactivity of nanoparticles. Full article

Due to the growing number of people infected with the new coronavirus globally, which weakens immunity, there has been an increase in bacterial infections. Hence, knowledge about simple and low-cost synthesis methods of materials with good structural and antimicrobial properties is of great importance. A material obtained through the combination of a nanoscale hydroxyapatite material (with good biocompatibility) and titanium dioxide (with good degradation properties of organic molecules) can absorb and decompose bacteria. In this investigation, three different synthesis routes used to prepare hydroxyapatite/titanium dioxide nanomaterials are examined. The morphology and semiquantitative chemical composition are characterized by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX). The obtained materials’ phase and structural characterization are determined using the X-ray powder diffraction method (XRD). The crystallite sizes of the obtained materials are in the range of 8 nm to 15 nm. Based on XRD peak positions, the hexagonal hydroxyapatite phases are formed in all samples along with TiO₂ anatase and rutile phases. According to SEM and TEM analyses, the morphology of the prepared samples differs depending on the synthesis route. The EDX analysis confirmed the presence of Ti, Ca, P, and O in the obtained materials. The IR spectroscopy verified the vibration bands characteristic for HAp and titanium. The investigated materials show excellent antimicrobial and photocatalytic properties. Full article

We propose obtaining TiO₂ films by ICPCVD for the fabrication of low-loss waveguides. The challenge is to produce a dense and homogeneous layer with a high refractive index and low absorption in the visible range. Crystallized layers with features such as grains and amorphous layers have a rather low index for the application targeted, so we aimed for an intermediate state. We investigated the influence of plasma power, pressure, deposition time and annealing temperature on the structural, crystalline, and optical properties in order to tailor them. We showed that crystallization into rutile at the nanoscale occurred during deposition and under wisely chosen conditions, we reached a refractive index of 2.5 at 630 nm without creating interfaces or inhomogeneity in the layer depth. Annealing permits one to further increase the index, up to 2.6. TEM analysis on one sample before and after annealing confirmed the nano-polycrystallization and presence of both anatase and rutile phases and we considered that this intermediate state of crystallization was the best compromise for guided optics. Full article

TiO₂ nanoparticles (TiO₂-NPs) have a wide range of industrial applications (paintings, sunscreens, food and cosmetics) and is one of the most intensively used nanomaterials worldwide. Leaching from commercial products TiO₂-NPs are predicted to significantly accumulate in wastewater sludges, which are then often used as soil amendment. In this work, sludge samples from four wastewater treatment plants of the Chihuahua State in Mexico were obtained during spring and summer (2017). A comprehensive characterization study was performed by X-ray based (laboratory and synchrotron) techniques and electron microscopy. Ti was detected in all sludge samples (1810–2760 mg/kg) mainly as TiO₂ particles ranging from 40 nm up to hundreds of nm. Micro-XANES data was analyzed by principal component analysis and linear combination fitting enabling the identification of three predominant Ti species: anatase, rutile and ilmenite. Micro-XANES from the smaller Ti particles was predominantly anatase (68% + 32% rutile), suggesting these TiO₂-NPs originate from paintings and cosmetics. TEM imaging confirmed the presence of nanoscale Ti with smooth surface morphologies resembling engineered TiO₂-NPs. The size and crystalline phase of TiO₂-NPs in the sludge from this region suggest increased reactivity and potential toxicity to agro-systems. Further studies should be dedicated to evaluating this. Full article

HZSM-5 (MFI type) of composition (H_x)[Al³⁺_xSi_12−xO₂₄] × wH₂O and nanocomposites NA/HZSM-5, NA:M/HZSM-5 (NA—nanoscale anatase; M = V, Ni, Ag) with Si/Al = 12, 25, 40, 300 (sp.gr. Pnma or P2₁/n; z = 8), as well as zeolites [(Ti⁴⁺_xSi_12−xO₂₄] × wH₂O (TS) with Si/Ti = 47, 53, 73.5 (sp.gr. Pnma) were studied by XRPD, XAS, FTIR-spectroscopy, BET, XPS, SEM, EDX, TPD, UV–VIS-spectroscopy, UV–DRS, and chemiluminescence methods. The results obtained together with photocatalytic, adsorption, antimicrobial, catalytic properties were analyzed using crystallochemical concepts and literature data. It was shown that NA or NA:M introduction into HZSM-5 leads, respectively, to the photodegradation of MeO dye in the UV region or difenoconazole in the visible range, and contributes to the appearance in the dark of adsorption (almost complete extraction of P(V), As(V), and Se(V) from aquatic environment) and bacteriostatic properties in respect to Staphylococcus epidermidis, Bacillus antracoides, and Escherichia coli for NA:Ag/HZSM-5(40, 300). The presence of titanium ions in NA nanoparticles on the HZSM-5 surface improves the catalytic activity in ethanol and propane (the best performance for NA/HZSM-5(25) and NA/HZSM-5(40), respectively) conversion. Determination of the composition (surface and bulk) and structure (statistical and local) of TS zeolites together with the found correlations made it possible to propose new catalysts in the reactions of propane, ethanol, and allyl chloride conversion. Full article

A novel one-step preparation of sonochemical method was applied to synthesize Co/Zn co-doped TiO₂ nanoparticles using a sonicator of 750 W, 20 kHz for 30 min at room temperature. The formation of the anatase TiO₂ phase for all as-prepared samples was observed from XRD results with a crystalline size in nanoscale. The use of ultrasound allowed for the successful doping of both Co and Zn into the TiO₂ lattice, which was confirmed by Synchrotron light including X-ray near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) spectroscopy. Ti K-edge, Co K-edge, and Zn K-edge XANES spectra exhibited the dominating +4, +2, and +2 valence state of Ti, Co, and Zn in as-prepared samples, respectively. A detailed XANES and EXAFS data analysis give strong evidence that the Co/Zn dopants partially replace the Ti atom of the TiO₂ host. The Co/Zn co-doping extends the light absorption of the host to the visible region and restricts the e⁺/h⁺ recombination. The photocatalytic activity of samples was tested for degradation of Rhodamine B dye solution under visible light irradiation. The as-synthesized of the co-doped catalyst was presented as highly efficient, with 2.5 and 5 times dye degradation compared with single-doped and bare TiO₂. Full article

Induction heating treatment (IHT) has recently been used to improve the bioactivity and biocompatibility of titanium and its alloys, greatly related to the formation of the nanoscale oxide coating. In this work, the effect of ultrasonic on the IHT oxidation behavior of pure titanium has been investigated. Ultrasonic-assisted IHT of pure titanium was carried out for 13, 20 and 25 s. Submicro-/nano-scale morphological coatings with rutile and anatase TiO₂ were prepared on the surface of titanium substrates subjected to ultrasonic-assisted IHT. In particular, the TiO₂ crystals were significantly refined by ultrasonic impact. An improvement in hydrophilicity and hardness of the oxide film was achieved by ultrasonic-assisted IHT. The refinement of TiO₂ crystals is suggested to be caused by ultrasonic induced changes of energy, defect density and their correlation with diffusion of oxygen. The present study provides a potential method to refine the nanoscale oxide films on titanium substrates, which is promising for improving the wear resistance and bioactivity of titanium and its alloys. Full article

The determination of local temperature at the nanoscale is a key point to govern physical, chemical and biological processes, strongly influenced by temperature. Since a wide range of applications, from nanomedicine to nano- or micro-electronics, requires a precise determination of the local temperature, significant efforts have to be devoted to nanothermometry. The identification of efficient materials and the implementation of detection techniques are still a hot topic in nanothermometry. Many strategies have been already investigated and applied to real cases, but there is an urgent need to develop new protocols allowing for accurate and sensitive temperature determination. The focus of this work is the investigation of efficient optical thermometers, with potential applications in the biological field. Among the different optical techniques, Raman spectroscopy is currently emerging as a very interesting tool. Its main advantages rely on the possibility of carrying out non-destructive and non-contact measurements with high spatial resolution, reaching even the nanoscale. Temperature variations can be determined by following the changes in intensity, frequency position and width of one or more bands. Concerning the materials, Titanium dioxide has been chosen as Raman active material because of its intense cross-section and its biocompatibility, as already demonstrated in literature. Raman measurements have been performed on commercial anatase powder, with a crystallite dimension of hundreds of nm, using 488.0, 514.5, 568.2 and 647.1 nm excitation lines of the CW Ar⁺/Kr⁺ ion laser. The laser beam was focalized through a microscope on the sample, kept at defined temperature using a temperature controller, and the temperature was varied in the range of 283–323 K. The Stokes and anti-Stokes scattered light was analyzed through a triple monochromator and detected by a liquid nitrogen-cooled CCD camera. Raw data have been analyzed with Matlab, and Raman spectrum parameters—such as area, intensity, frequency position and width of the peak—have been calculated using a Lorentz fitting curve. Results obtained, calculating the anti-Stokes/Stokes area ratio, demonstrate that the Raman modes of anatase, in particular the E_g one at 143 cm⁻¹, are excellent candidates for the local temperature detection in the visible range. Full article

Ti6Al4V samples, obtained by selective laser melting (SLM), were subjected to successive treatments: acid etching, chemical oxidation in hydrogen peroxide solution and thermochemical processing. The effect of temperature and time of acid etching on the surface roughness, morphology, topography and chemical and phase composition after the thermochemical treatment was studied. The surfaces were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and contact profilometry. The temperature used in the acid etching had a greater influence on the surface features of the samples than the time. Acid etching provided the original SLM surface with a new topography prior to oxidation and thermochemical treatments. A nanostructure was observed on the surfaces after the full process, both on their protrusions and pores previously formed during the acid etching. After the thermochemical treatment, the samples etched at 40 °C showed macrostructures with additional submicro and nanoscale topographies. When a temperature of 80 °C was used, the presence of micropores and a thicker anatase layer, detectable by X-ray diffraction, were also observed. These surfaces are expected to generate greater levels of bioactivity and high biomechanics fixation of implants as well as better resistance to fatigue. Full article