Undoped TiO2 Nanoparticles Research Articles

Enhanced Photocatalytic Activity by Tuning of Structural and Optoelectrical Properties of Cr(III) Incorporated TiO2 Nanoparticles

Polycrystalline undoped and chromium doped (2%, 4%, 6% and 8%) TiO2 nanoparticles (NPs) were synthesized using a simple acid-modified sol–gel method. Influence of chromium (Cr) doping on the microstructural, electrical, optical, and photocatalytic properties was studied using various analytical techniques viz. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), two-probe resistivity measurement and UV–visible absorption spectroscopy. Rietveld refinement of the XRD data reveals single phase, anatase crystal structure of the NPs in tetragonal symmetry with space group I41/amd. FTIR spectra demonstrate various functional groups and ensure anatase phase of all the samples. TEM images exhibit a significant change in the shape, size and morphology of the NPs on Cr incorporation in TiO2. Temperature-dependent resistivity measurements indicate the semiconducting nature of the samples and obey Arrhenius behaviour based on the mechanism of thermally activated conduction. A red shift in the UV–visible absorption spectra is noted on Cr doping, associated with the decrease in band gap from 3.1 eV for an undoped sample to 2.5 eV for an 8% Cr doped sample. Photoluminescence spectra signify that the dopant ions alter the density of oxygen vacancies that directly influence the electron–hole recombination rate. The photocatalytic performance is studied with regard to the degradation of chromophoric dyes, namely, rhodamine B and methylene blue under visible light illumination, revealing an increase in the photocatalytic activity with 82.2% and 73.4% degradation of the dyes after 120 min for the 6% Cr doped sample. This significant enhancement in the photocatalytic activity is attributed to the ease in the electron and hole separation by trapping sites produced due to Cr ions and oxygen vacancies. These observed results suggest that the Cr doped TiO2 NPs can be considered efficient photocatalysts with the advantage to tune the electronic structure and optical properties for possible applications in waste water treatment.

Drastic improvement in catalytic, optical and visible-Light photocatalytic behavior of cobalt and nickel doped TiO2 nanopowder

The titanium dioxide composites with cobalt (Co), nickel (Ni) and cobalt-nickel (Co-Ni) doped nanoparticles were synthesized using a sol-gel route. The structural, morphological, and physicochemical properties of mixed Co & Ni (3%) to TiO2 were characterized by XRD, FTIR, SEM, DSC-TGA, VSM, Raman and UV–vis spectroscopy. XRD pattern revealed TiO2 tetragonal-anatase phase and has confirmed a significant effect on crystallinity and particle size upon doping. The presence of strong chemical bonding and functional group at the interface of TiO2 nanoparticles was confirmed by FTIR. The increase in absorption range with different doped materials was recorded by UV–vis spectroscopy. The saturation magnetization (MS) was higher for TiO2 relative to doped materials. However, the thermal stability of the samples at high temperature (0 to 1000 °C) was monitored using DSC-TGA. The morphology of synthesized undoped and doped TiO2 nanoparticles showed agglomerations of nanomaterials was examined using SEM. The synthesized nanomaterials have been successfully applied as nanocatalyst in degradation of methylene blue. Co-Ni doped TiO2 nanoparticles an impressive catalytic performance in the presence of reducing agent NaBH4. This increase is attributed to augmentation of light absorption in the visible range with doping. Thus, Co:Ni:TiO2 in the presence of NaBH4 can be a promising photocatalyst in the field of wastewater treatment.

A new route for the synthesis of highly-active N-doped TiO2 nanoparticles for visible light photocatalysis using urea as nitrogen precursor

Nitrogen-doped TiO2 nanoparticles with high specific surface area and photocatalytic activity under visible light were successfully produced using a modified sol-gel method with urea introduced as the nitrogen source. Different synthesis approaches and parameters such as doping temperature and urea to TiO2 molar ratio were tested to examine the best outcome regarding photocatalytic activity for both UV-A and visible light irradiation. UV–vis diffuse reflectance characterization revealed a decrease in band gap from 3.24 to a minimum of 2.79 eV with the N-doping process. The photocatalytic Methylene Blue dye degradation assays suggests that the introduction of nitrogen in the TiO2 lattice cell can provide a higher efficiency under both UV-A and visible irradiation. The maximum photocatalytic activity was achieved for the nitrogen-doped powders prepared with the lowest urea:TiO2 molar ratio (1.5) as it was the formulation that promoted an enhancement in N-doping and particle specific surface area to 182 m2 g−1, despite the fact that the highest specific surface area was registered for undoped TiO2 nanoparticles (228 m2 g−1). A synthesis step variation was performed to enhance the specific surface area of nanoparticles and consequently the photocatalytic activity. This modification promoted an increase in specific surface area by a factor of ∼5. XPS spectra confirmed a successful introduction of nitrogen in the TiO2 lattice up to 1.5 at.% for optimized powders, which is strongly dependant of the type of synthesis and the amount of dopant species added during the doping process.

Synthesis, Structural, Morphological and Optical Characterization of TiO2 and Nd3+ Doped TiO2 Nanoparticles by Sol Gel Method: A Comparative Study for Photovoltaic Application

Nano structured materials are currently receiving wide attention due their optical, electronic, magnetic, chemical, physical and mechanical properties. Semiconductor nano crystals have been widely studied for their fundamental properties. Pure and Nd3+ doped titanium dioxide nano powder was successfully synthesized by solgel method. The morphological and structural properties of as-prepared samples were characterized by X-ray diffraction (XRD), High resolution scanning electron microscope (HRSEM). The HRSEM analysis shows the partial crystalline nature of undoped, and doped TiO2 nanoparticles and it was performed to obtain the particles size. The energy dispersive X - ray (EDAX) technique was used to determine their elemental compositions. The optical properties of doped and undoped TiO2 nano particles were investigated by UV-Vis spectroscopy and Photoluminescence (PL). The band gap of the doped TiO2 nanoparticles was found to be less than un-doped TiO2 nanoparticles.

Dye sensitized solar cell based on environmental friendly eosin Y dye and Al doped titanium dioxide nano particles

Present communication deals with the development of cost effective dye sensitized solar cell (DSSC) with eco-friendly materials. Eco-friendly Eosin Y dye was used to sensitize photo anode which was fabricated using undoped and Aluminium doped titanium dioxide (TiO2) nanoparticles. Undoped and Aluminium doped TiO2 nanoparticles were synthesized by simple and cost effective sol-gel method. Aluminium doped and undoped TiO2 nanoparticles were characterized using UV-visible, FT-IR spectroscopy, x-ray Diffraction, and Scanning Electron Micrograph with EDX. The photo-voltaic activity of the cell was studied under light irradiation of 100 milliwatt cm−2. Aluminium doped TiO2 nanoparticle photo electrode exhibits more than 60% increase in cell efficiency as compared to the undoped TiO2 nanoparticle photo electrode.

Transition metals (Mn, Ni, Co) doping in TiO2 nanoparticles and their effect on degradation of diethyl phthalate

Transition metal-doped TiO2 nanoparticles are synthesized by sol–gel method. The as-prepared samples are characterized by various techniques to correlate structural and optical properties with chemical nature of dopants and their effect on photocatalytic degradation of diethyl phthalate esters. X-ray diffraction (XRD) reveals that all the samples are crystalline and exhibit anatase as a major phase. Chemical nature of dopants could not affect the formation of anatase and its volume fraction. The crystallite size of undoped and doped TiO2 nanoparticles varies between 10 and 12 nm as confirmed by XRD and transmission electron microscope. The lowest optical band gap observed is 2.47 eV in Mn-doped TiO2. Among all the samples, Ni-doped TiO2 sample shows better photocatalytic activity and degradation of diethyl phthalate due to its lower crystallite size and higher surface area than those of Mn- and Co-doped TiO2 samples.

Dielectric response and room temperature ferromagnetism in Cr doped anatase TiO2 nanoparticles

In the present work, nanocrystalline samples of Ti1−xCrxO2 (x=0, 0.02, 0.04, 0.06 and 0.08) were synthesized in anatase phase through simple and cost effective acid modified sol gel method. The influence of Cr doping on thermal, microstructural, electrical and magnetic properties was investigated in TiO2 host matrix. The surface morphology has revealed less agglomeration and considerable reduction in particle size in case of Cr doped TiO2 as compared to undoped TiO2 nanoparticles (NPs). Energy dispersive x-ray spectroscopy (EDS), Raman and X-ray photoelectron spectroscopy (XPS) established high purity, appropriate stoichiometry and oxidation states of the compositions. The dielectric properties of the nanoparticles were altered by the doping concentration, applied frequency as well as temperature variation. The variation in dielectric constant (ε′), dielectric loss (δ) and ac conductivity as a function of frequency and temperature at different doping concentration of Cr were interpreted in the light of Maxwell Wagner theory, space charge polarization mechanism and drift mobility of charge carriers. Both undoped and Cr doped TiO2 samples exhibit room temperature ferromagnetism (RTFM) that remarkably influenced by means of the Cr content. The significant enhancement in the magnetization was observed at 4% Cr doping. However, decrease in magnetization for higher doping signify antiferromagnetic interactions between Cr ions or superexchange mechanism. These results reveal that the oxygen vacancies play a crucial role to initiate the RTFM. Therefore, the present investigation suggests the potential applications of Cr doped TiO2 nanoparticles for spintronics application.

Effect of Nd3+ doping on structure, microstructure, lattice distortion and electronic properties of TiO2 nanoparticles

Doped and undoped TiO2 nanoparticles were prepared by Stöber method and thermally treated at 600 °C. The effect of Nd3+ ion on the structure and microstructure of anatase-phase TiO2 nanocrystals was studied by Rietveld refinement method using X-ray powder diffraction data. Bond lengths, bond angles, and edges distances were analyzed. The phase formation was confirmed by high-resolution transmission electron microscopy. The adjustment of Ti-O bond length induced by the addition of Nd3+ ions, reduced the octahedral distortion and altered the octahedral array in the anatase-phase TiO2 nanocrystal. The changes of structure and microstructure were mainly observed for TiO2 nanoparticles doped with 0.1 at.% of Nd3+ ions and attributed to the cationic substitution of Ti4+ ions which promoted changes in the density of states and gap band of TiO2. The dopant insertion resulted in a better structural stability of the nanocrystals that enhanced their charge transference and photocatalytic efficiency.

Principal component analysis of Raman spectra for TiO2 nanoparticle characterization

The Raman spectra of anatase/rutile mixed phases of Sn doped TiO2 nanoparticles and undoped TiO2 nanoparticles, synthesised by laser pyrolysis, with nanocrystallite dimensions varying from 8 to 28nm, was simultaneously processed with a self-written software that applies Principal Component Analysis (PCA) on the measured spectrum to verify the possibility of objective auto-characterization of nanoparticles from their vibrational modes. The photo-excited process of Raman scattering is very sensible to the material characteristics, especially in the case of nanomaterials, where more properties become relevant for the vibrational behaviour. We used PCA, a statistical procedure that performs eigenvalue decomposition of descriptive data covariance, to automatically analyse the sample’s measured Raman spectrum, and to interfere the correlation between nanoparticle dimensions, tin and carbon concentration, and their Principal Component values (PCs). This type of application can allow an approximation of the crystallite size, or tin concentration, only by measuring the Raman spectrum of the sample. The study of loadings of the principal components provides information of the way the vibrational modes are affected by the nanoparticle features and the spectral area relevant for the classification.

Synthesis and up-conversion properties of Ho3+-Yb3+-F− tri-doped TiO2 nanoparticles and their application in dye-sensitized solar cells

A series of Ho3+-Yb3+-F− tri-doped TiO2 nanoparticles (abbreviated as UP-F-TiO2 NPs) were prepared using a hydrosol−hydrothermal method, and their phase structure, morphology and luminescent properties were investigated. These nanoparticles were utilized to prepare a photoanode of dye-sensitized solar cells (DSSCs). Based on the up-conversion spectra of UP-F-TiO2 NPs, an up-conversion mechanism is proposed. The results indicate that the UP-F-TiO2 NPs were a mixture of anatase and rutile nanoparticles, and the mass fraction of the anatase phase first increases and then decreases with increasing incorporation of F− ions into UC-F-TiO2 NPs, while the un-doped TiO2 nanoparticles are in the rutile phase. The average sizes of the UP-F-TiO2 NPs are estimated to be 10nm. The HRTEM shows clear lattice fringes with spacings of 0.347nm and 0.323nm that correspond to the d spacings of the (101) facets in anatase TiO2 and the (110) facets in rutile TiO2, respectively. Under the excitation of 980nm NIR light, the UP-F-TiO2 NPs exhibit a stronger emission band centered at 543nm and two relatively weaker bands located at 667nm and 751nm. The DSSC assembled with a bilayer-structured UP-F-TiO2 NP photoanode has a 35.2% enhancement in conversion efficiency compared with DSSCs assembled with un-doped TiO2 photoanodes.

Visible light responsive noble metal-free nanocomposite of V-doped TiO2 nanorod with highly reduced graphene oxide for enhanced solar H2 production

The visible light responsive nanocomposite of vanadium-doped TiO2 nanorod anchoring on highly reduced graphene oxide (RGO) has been successfully synthesized using a simple one step low temperature hydrothermal method. The nanoparticles, loaded on RGO, were intentionally fabricated as nanorods to enhance their contact with the RGO sheets. Compared to undoped TiO2 and non-composited V-TiO2 nanoparticles, the nanocomposite exhibited enhanced H2 evolution under visible light illumination. Density Functional Theory (DFT) computation also confirms the bandgap narrowing of TiO2 by doping vanadium. Furthermore, the photogenerated electrons could be effectively trapped by the conducting RGO sheets, thereby suppressing electron–hole recombination. This noble metal-free nanocomposite material composed of highly conducting sheets also offers promise for other energy applications such as lithium ion batteries.

Sonocatalytic degradation of humic acid by N-doped TiO2 nano-particle in aqueous solution

BackgroundUn-doped and N-doped TiO2 nano-particles with different nitrogen contents were successfully synthesized by a simple sol–gel method, and were characterized by X-ray diffraction, field emission scanning electron microscopy, Energy dispersive X-ray analysis and UV–visible diffuse reflectance spectra techniques. Then enhancement of sonocatalytic degradation of humic acid by un-doped and N-doped TiO2 nano-particles in aqueous environment was investigated. The effects of various parameters such as initial concentration of humic acid, N-doping, and the degradation kinetics were investigated.ResultsThe results of characterization techniques affirmed that the synthesis of un-doped and N-doped TiO2 nano-particles was successful. Degradation of humic acid by using different nano-particles obeyed the first-order kinetic. Among various nano-particles, N-doped TiO2 with molar doping ratio of 6 % and band gap of 2.92 eV, exhibited the highest sonocatalytic degradation with an apparent-first-order rate constant of 1.56 × 10-2 min−1.ConclusionsThe high degradation rate was associated with the lower band gap energy and well-formed anatase phase. The addition of nano-catalysts could enhance the degradation efficiency of humic acid as well as N-doped TiO2 with a molar ratio of 6 %N/Ti was found the best nano-catalyst among the investigated catalysts. The sonocatalytic degradation with nitrogen doped semiconductors could be a suitable oxidation process for removal of refractory pollutants such as humic acid from aqueous solution.Electronic supplementary materialThe online version of this article (doi:10.1186/s40201-016-0242-2) contains supplementary material, which is available to authorized users.

Visible –Light Induced Photocatalytic Degradation of Fungicide with Fe and Si Doped TiO2 Nanoparticles

Iron (Fe) and Silica (Si) doped TiO2 nanoparticles were synthesized by surface impregnation method. The concentration of dopants, Fe (1%, 2%, 3% and 4%) and Si (3%, 5%, 7% and 9%) were varied for the preparation of doped TiO2 which were characterized by XRD, FESEM and TEM analysis. The TEM measurement shows that the particle size is in the range of 25- 35nm for Fe and Si doped TiO2. With the optimum dopant concentration i.e. 2% for Fe and 5% for Si, doped TiO2 showed nearly 98% degradation of fungicide carbendazim under sunlight. Optical measurements indicate that the absorption band edge of Fe and Si dopants were shifted towards visible wavelength. Band gap of doped and undoped TiO2 nanoparticles was measured by UV-Vis spectroscopy. Fe and Si doped TiO2 degrades fungicide much faster than the undoped TiO2 at optimum catalyst loading of 1g L-1. Result signifies that doped TiO2 (Fe, Si) have remarkable efficiency to degrade complex fungicide into smaller molecules, in the presence of sunlight.

Study of photocatalytic degradation of environmentally harmful phthalate esters using Ni-doped TiO2 nanoparticles

Undoped and Ni-doped TiO2 nanoparticles are synthesized using sol–gel technique. The physical, structural, optical and thermal properties of the samples are investigated using X-ray powder diffraction, Fourier transform infrared spectroscopy, transmittance electron microscopy, UV–visible diffuse reflectance and thermogravimetric analysis. The photocatalytic activity of the samples is investigated by the photocatalytic degradation of phthalate esters. Phthalate esters have been considered as endocrine disrupting compounds. Ni-doped TiO2 samples show better photocatalytic activity as compared to undoped TiO2 sample. The greater photocatalytic activity of doped samples as compared to undoped TiO2 can be attributed to the production of more number of electron–hole pairs in doped samples.

Rapid photo- and photo-Fenton-like catalytic removals of malachite green in aqueous solution on undoped and doped TiO2 nanotubes

Undoped and Fe-doped TiO2 nanotubes with Fe content of 0–3.86 at.% were fabricated by hydrothermally treating sol–gel-derived undoped and Fe-doped TiO2 nanoparticles in NaOH aqueous solution. The Fe doping narrowed the optical band gap of the nanotubes from 3.17 to ~2.76 eV as the increase in Fe-doping content from 0 to 3.86 at.%. The nanotubes showed a large specific surface area of ~274–303 m2 g−1, which increased as the increase of Fe content. The sunlight-excited degradation experiments of malachite green in the water indicated that the nanotubes had a high photocatalytic activity. The Fe doping further enhanced the photocatalytic activity of the nanotubes, increased as increasing Fe-doping content. Moreover, the photodegradation of the dye became more fast as H2O2 was used, showing remarkable Fenton-like photocatalytic activity. This Fenton-like reaction also enhanced as increasing Fe content. An optimal H2O2 dosage was also observed. The quasi-kinetic first-order rate constant of the photodegradation of the malachite green aqueous solution with the concentrations of 1 × 10−6 and 1×10−5 mol l−1 were in the range of ~1.61–2.03 and ~0.41–0.65 min−1, respectively. These constants further increased to ~2.81–3.51 and ~1.71–2.04 min−1 as the H2O2 with a concentration of 10 ml l−1 is used.

High power TiO2 and high capacity Sn-doped TiO2 nanomaterial anodes for lithium-ion batteries

A range of phase-pure anatase TiO2 (∼5 nm) and Sn-doped TiO2 nanoparticles with the formula Ti1-xSnxO2 (where x = 0, 0.06, 0.11 and 0.15) were synthesized using a continuous hydrothermal flow synthesis (CHFS) reactor. Charge/discharge cycling tests were carried out in two different potential ranges of 3 to 1 V and also a wider range of 3 to 0.05 V vs Li/Li+. In the narrower potential range, the undoped TiO2 nanoparticles display superior electrochemical performance to all the Sn-doped titania crystallites. In the wider potential range, the Sn-doped samples perform better than undoped TiO2. The sample with composition Ti0.85Sn0.15O2, shows a capacity of ca. 350 mAh g−1 at an applied constant current of 100 mA g−1 and a capacity of 192.3 mAh g−1 at a current rate of 1500 mA g−1. After 500 charge/discharge cycles (at a high constant current rate of 382 mA g−1), the same nanomaterial anode retains a relatively high specific capacity of 240 mAh g−1. The performance of these nanomaterials is notable, particularly as they are processed into electrodes, directly from the CHFS process (after drying) without any post-synthesis heat-treatment, and they are made without any conductive surface coating.

Toxicological aspects of photocatalytic degradation of selected xenobiotics with nano-sized Mn-doped TiO2

The toxic effects of two selected xenobiotics, bisphenol A (BPA) and atrazine (ATZ), were evaluated after photocatalytic degradation using nano-sized, Mn-doped TiO2. Undoped and Mn-doped TiO2 nanoparticles were synthesized. The samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), UV–vis-diffuse reflectance spectra (DRS), X-ray fluorescence spectroscopy (XRF), and BET surface area. The photocatalytic efficiency of the undoped and Mn-doped TiO2 was evaluated for BPA and ATZ. The toxicity of the synthesized photocatalysts and photocatalytic by-products of BPA and ATZ was determined using frog embryos and tadpoles, zebrafish embryos, and bioluminescent bacteria. Possible toxic effects were also evaluated using selected enzyme biomarkers. The results showed that Mn-doped TiO2 nanoparticles did not cause significant lethality in Xenopus laevis embryos and tadpoles, but nonfiltered samples caused lethality in zebrafish. Furthermore, Mn-doping of TiO2 increased the photocatalytic degradation capability of nanoparticles, and it successfully degraded BPA and AZT, but degradation of AZT caused an increase of the lethal effects on both tadpoles and fish embryos. Degradation of BPA caused a significant reduction of lethal effects, especially after 2–4h of degradation. However, biochemical assays showed that both Mn-doped TiO2 and the degradation by-products caused a significant change of selected biomarkers on X. laevis tadpoles; thus, the ecological risks of Mn-doped TiO2 should be considered due to nanomaterial applications and for spilled nanoparticles in an aquatic ecosystem. Also, the risk of nanoparticles should be considered using indicator reference biochemical markers to verify the environmental health impacts.

Enhanced photo-catalytic activity of Sr and Ag co-doped TiO2 nanoparticles for the degradation of Direct Green-6 and Reactive Blue-160 under UV & visible light

This work is focused on sol–gel synthesis of silver and strontium co-doped TiO2 nanoparticles and their utilization as photo-catalysts in degradation of two textile dyes. Effect of pH, intensity of light, amount of photo-catalyst, concentration of dye, sensitizers, etc., were studied to optimize conditions for obtaining enhanced photo-catalytic activity of synthesized nanoparticles. XRD, BET, HR-TEM, EDAX and UV–Vis (diffused reflectance mode) techniques were used to characterize the nanoparticles. Interestingly, band gap of Sr and Ag co-doped TiO2 nanoparticles showed considerable narrowing (2.6eV) when compared to Ag doped TiO2 (2.7eV) and undoped TiO2 (3.17eV) nanoparticles. Incorporation of Ag and Sr in the lattice of TiO2 could bring isolated energy levels near conduction and valence bands thus narrowing band gap. The XRD analysis shows that both Ag and Sr nanoparticles are finely dispersed on the surface of titania framework, without disturbing its crystalline structure. TEM images indicate that representative grain sizes of Ag-doped TiO2 & Sr and Ag co-doped TiO2 nanoparticles are in the range of 8–20nm and 11–25nm, respectively. Effective degradation of Direct Green-6 (DG-6) and Reactive Blue-160 (RB-160) under UV and visible light has been achieved using the photo-catalysts. Sr and Ag co-doped TiO2 photo-catalysts showed higher catalytic activity during degradation process in visible region when compared to Ag-doped and undoped TiO2 nanoparticles which could be attributed to the interactive effect caused by band gap narrowing and enhancement in charge separation. For confirming degradation of the dyes, total organic carbon (TOC) content was monitored periodically.

Effect of Cr incorporation on the properties of TiO2 nanoparticles synthesized by microwave technique

The present work focus on the development of an effective process for the production of undoped and Cr doped TiO2 nano powders by microwave technique. The influence of Cr doping on the structure, phase, vibrational bands and optical properties of TiO2 were discussed. The X-ray diffraction patterns of the nanoparticles revealed preferentially oriented (101) anatase phase for TiO2. Fourier transform infrared spectral analysis confirmed the presence of anatase phase for both pure and Cr Doped TiO2. The UV–Visible spectra revealed the increase in absorption band with Cr doping when compared with undoped TiO2 nano particles, and optical band gap decreased slightly with Cr doping. SEM micrographs show spherical shaped grains of TiO2 with high homogeneity, with a subsequent reduction in agglomeration of particles with Cr doping suggesting its potential application for better photo catalytic activity.

Exceptional thermal stability of undoped anatase TiO2 photocatalysts prepared by a solvent-exchange method

A new solvent-exchange method for preparation of undoped anatase TiO2 nanoparticles with unprecedented thermal stability has been presented.