Fabrication of 10 nm diameter TiO2 nanotube arrays by titanium anodization

We report the fabrication of TiO₂ nanotube thin films using anodization method with HCl electrolyte and copper cathode. The process represents an alternative electrochemical approach using a non-noble metal cathode along with a safer electrolyte. In addition to the choice of electrolyte, the electrolyte concentration, anodization voltage, and anodization time all affect nanotube morphology. TiO₂ nanotubes with diameters as small as 10 nm were achieved.     

Physico-chemical, photoelectrochemical and photocatalytic properties of electrodeposited nanocrystalline titanium dioxide thin films

Crystal structure and microstructural properties of titanium dioxide (TiO₂) thin films prepared by cathodic electrodeposition on indium-tin-oxide coated glass substrates from aqueous peroxo-titanium complex solutions have been investigated. The electrodeposited TiO₂ thin film electrode exhibited anodic photocurrent upon visible light irradiation, indicating the typical behavior of n-type semiconductor. The photodecomposition of CH₃CHO by such thin films on exposure to ultraviolet light illumination was also observed.     

Preparation,characterization and photocatalytic activities of holmium-doped titanium dioxide nanoparticles

Holmium-doped TiO₂ nanoparticles with high photocatalytic activities were prepared by sol–gel method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, and surface area measurement by nitrogen adsorption in this study. Experimental results indicated holmium doping could increase the surface area of TiO₂ nanoparticles, and inhibit the growth of crystalline size and the anatase-to-rutile phase transformation. The results of photodegrading methyl orange showed holmium doping improved the photocatalytic activity of TiO₂, and the reasons could be attributed to the synergetic effects of large surface areas, small crystallite size, lattice distortion and more charge imbalance of holmium-doped TiO₂. In our experiment, the optimal doped amount was 0.3 mol.% for the maximum photocatalytic degradation ratio when holmium-doped TiO₂ was calcined at 500 °C, and the optimal calcined temperature was 600 °C when the doped amount was 0.5 mol.%.     

Sonochemical synthesis and photocatalytic activity of meso- and macro-porous TiO(2) for oxidation of toluene

Meso-and macro-porous TiO(2) were synthesized by ultrasonic induced solvothermal method. Octadecylamine as a soft template was used to direct the formation of porous structure. The as-prepared porous TiO(2) was characterized by low angle and wide angle X-ray diffraction, N(2) adsorption-desorption isotherms and BET surface area. The energy influence of ultrasound and heat and concentration of nitric acid for post extraction on formation of porous structure were investigated. The photocatalytic activities of TiO(2) were investigated by degrading toluene gas under UV light. The results revealed that proper energy facilitates the formation of porous structure and too low concentration of nitric acid cannot extract template from pores. The photocatalytic activities of TiO(2) with porous structure are higher than those of nonporous ones.     

Facile synthesis of Ag nanoparticles supported on TiO2 inverse opal with enhanced visible-light photocatalytic activity

TiO₂ inverse opal films loaded with silver nanoparticles (ATIO) were synthesized on glass substrates. TiO₂ inverse opal (TIO) films were prepared via a sol-gel process using self-assembly of SiO₂ colloidal crystal template and a facile wet chemical route featuring an AgNO₃ precursor solution to fabricate silver nanoparticles on the TIO films. The inverse opal structure and Ag deposition physically and chemically modify titania, respectively. The catalysts were characterized by Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectra, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The HRTEM results show that Ag nanoparticles measuring 5-10 nm were evenly distributed on TIO. Both the UV- and visible-light photocatalytic activities of the samples were evaluated by analyzing the degradation of methylene blue (MB) in aqueous solution. The results reveal that the apparent reaction rate constant (k_app) of MB degradation of the sample ATIO under UV-light irradiation is approximately 1.5 times that of the conventional Ag-loaded TiO₂ film (ATF) without an ordered porous structure at an AgNO₃ concentration of 5 mM in the precursor solution. At an AgNO₃ concentration of 10 mM, the sample exhibits a k_app value approximately 4.2 times that of ATF under visible-light irradiation. This enhanced visible-light photocatalytic performance can be attributed to the synergistic effect of optimized Ag nanoparticle deposition and an ordered macroporous TIO structure. Repeated cycling tests revealed that the samples showed stable photocatalytic activity, even after six repeated cycles.     

Correlation between structural and optical properties of 30 nm and 60 nm lead sulfide nanowires

PbS nanowires with 30 nm and 60 nm diameter fabricated under the same condition of electrochemical deposition with sulfuric and oxalic anodic alumina membranes (AAM), respectively, have been successfully prepared in order to study their optical properties in relation to their size. Scanning electron microscopy indicates that the 60 nm PbS nanowire arrays have the same shape with the 30 nm. X-ray diffraction result shows that 60 nm PbS nanowires are crystalline and have a highly (200) preferential orientation like 30 nm ones. UV spectrum considers the nanowire size decrease as the absorption peak shifts to the blue. The quantum confinement effects compared between 30 nm and 60 nm PbS nanowire arrays were observed by the measurements of ultraviolet-visible absorption spectroscopy (UV-vis).     

Optical and magnetic properties of 30 and 60 nm Ni nanowires

Ni nanowire arrays of high aspect ratio with the diameters of about 30 nm and 60 nm were prepared by DC applied AC electrodeposition. We observe the different preferred orientation and various magnetic behaviors of 30 and 60 nm diameter nanowires. In addition, the coercivity H_c(||), squareness S(||) and the ratio H_c(||)/H_c(⊥) where the applied field is parallel (||) and perpendicular (⊥) to the long axis of nanowires increase with decreasing wire diameter. This is the first time that optical results of Ni nanowires were presented.     

Preparation of boron-doped TiO2 films by autoclaved-sol method at low temperature and study on their photocatalytic activity

A series of uniform and transparent boron-doped TiO₂ films were synthesized from autoclaved-sol without organic solvent at low temperature. As-prepared B-TiO₂ films with two layers were characterized by XRD, DRS, XPS and AFM. The photocatalytic characteristics were measured based on the degradation of Rhodamine B (RhB) solution under visible or UV light. The results indicated that the anatase phase was the main crystal form of the films, containing a small amount of brookite. The presence of boron caused a red shift in the absorption band of TiO₂ films. The doped boron was mainly presented in the form of B₂O₃, O-Ti-B and O-Ti-B bonds, confirming that autoclaved-sol synthesis at low temperature allowed for incorporation of boron atoms into the TiO₂ matrix. Transmission of the films was about 90% in the visible region. The 10% (atom) B-TiO₂ film exhibited the best photocatalytic activity both in visible and UV light.     

Synthesis of sub-5 nm Co-doped SnO2 nanoparticles and their structural,microstructural, optical and photocatalytic properties

A swift chemical route to synthesize Co-doped SnO₂ nanopowders is described. Pure and highly stable Sn_1−xCo_xO_2−δ (0 ≤ x ≤ 0.15) crystalline nanoparticles were synthesized, with mean grain sizes <5 nm and the dopant element homogeneously distributed in the SnO₂ matrix. The UV–visible diffuse reflectance spectra of the Sn_1−xCo_xO_2−δ samples reveal red shifts, the optical bandgap energies decreasing with increasing Co concentration. The samples' Urbach energies were calculated and correlated with their bandgap energies. The photocatalytic activity of the Sn_1−xCo_xO_2−δ samples was investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02% (w/w) of Sn_0.95Co_0.05O_2−δ nanoparticles in 60 min of irradiation.     

Inexpensive synthesis of anatase TiO2 nanowires by a novel method and its electrochemical characterization

We demonstrate a simple, rapid, inexpensive and novel approach for the synthesis of a kind of anatase TiO₂ nanowires. The method is based on a hydrothermal method under normal atmosphere without using the complex Teflon-lined autoclave, high concentrations NaOH solution and long reaction time. The as-prepared materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The obtained anatase TiO₂ nanowires show excellent performance. The initial Li insertion/extraction capacity is 260 and 224 mA h g^− 1 at 20 mA g^− 1, respectively. In the 20th cycle, the reversible capacity still remains about 216 mA h g^− 1, exhibiting excellent cycling stability. The discharging capacity is about 159 mA h g^− 1 in the 20th cycle at 200 mA g^− 1, demonstrating a good high-rate performance. Anatase TiO₂ nanowires might be a promising anode material for lithium-ion batteries.     

Titanium dioxide thin films, their structure and its effect on their photoactivity and photocatalytic properties

Atomic Layer Deposition has been used to deposit titanium dioxide thin films on soda-lime glass substrates. A series of films with thicknesses from 2.6 to 260 nm has been created and the film structure has been studied with X-ray diffraction. It has been observed that at a reaction temperature of 350 °C, titanium dioxide thin films initially grow as anatase but after a certain thickness, growth continues as rutile. The photoactivity and photocatalytic activity of the films have been found to reach their maximum at a film thickness of 15 nm. At this thickness, the film structure shows a small fraction of rutile crystallites in a largely anatase matrix indicating that both crystal phases are necessary for the maximum activity.     

Enhanced photocatalytic,antibacterial, and electrochemical properties of CdO-based nanostructures by transition metals co-doping

In the present work, single Ni-doped and Co, Cr, Cu co-doped CdO nanostructures via sol-gel approach were fabricated. The XRD diffractograms have confirmed the successful doping and co-doping in CdO lattice without any impurity phase generation. FTIR and Raman spectra have further confirmed the metal-oxygen bonding vibration and optical phonon modes related to CdO. FE-SEM images exhibited nanobelt type morphology varied with the type of dopant and EDX evident the presence of dopants along with Cd, and O. PL and IV results exhibited that the charge carrier recombination hinders and electrical conductivity has improved by co-doping. UV–vis absorbance spectra have shown redshift in energy bandgap by co-doping. The CV, EIS, and GCD tests suggested the superior electrochemical capacitive characteristic of co-doped CdO and can serve as efficient electrode materials. The photocatalytic activity results exhibited increased photodegradation performance by co-doping, and the highest was achieved for Ni/Cr co-doped samples. The antimicrobial activity results have shown a higher zone of inhibition against Escherichia coli and Staphylococcus aureus bacterial strains. The narrow energy bandgap, lower recombination, and low charge transfer resistance are responsible for boosting the properties of CdO by co-doping and making it a prospective candidate as effective photocatalysts, antibiotic-resistant agents, and supercapacitor electrode materials.     

Radiation-induced luminescence from TiO2 by 10 keV O, N and Ar ion irradiation

Radiation-induced luminescence (RIL) produced by 10 keV O⁺, N⁺ and Ar⁺ irradiation at room temperature has been used to study energy transfer in titanium dioxide (TiO₂) targets. RIL spectra in the UV-visible region show numerous atomic lines and three bands. Two visible bands by crystalline defects and an UV band at 3.9 eV originating from radiation transitions between the Ti³⁺ 3d and O²⁻ 2 s states in the TiO₂ crystal are observed. The experimental results suggest that the excitations were not mainly produced by transitions from the ground state to excited states but by cascade radiations from higher excited states.     

Microstructure and optical properties of photoactive TiO2:N thin films

In this work, we have chosen oxidation of TiN thin films as a feasible method for preparation of nitrogen-doped titanium dioxide thin films, TiO₂:N, for photocatalytic applications. DC reactive magnetron sputtering with the plasma emission control was used for deposition of stoichiometric TiN thin films. The microstructure and chemical composition of films before and after oxidation were investigated by means of RBS, X-ray diffraction (XRD) in grazing incidence diffraction (GID) configuration, AFM and XPS techniques. The electrical conductivity was measured by the van der Pauw method as a function of the oxidation temperature. The optical transmittance and reflectance spectra of the films were measured over the visible and UV ranges of the light spectrum. GID diffraction patterns of as-sputtered TiN thin films and those after oxidation indicate that TiO₂ rutile is formed at around 300 °C. Nitrogen is still present as indicated by XPS studies even when XRD detects the rutile only. Optical absorption of thin films oxidized at 450 °C is shifted towards the visible range of the light spectrum.     

Quantification of silver ion release, in vitro cytotoxicity and antibacterial properties of nanostuctured Ag doped TiO2 coatings on stainless steel deposited by RF magnetron sputtering

Surface treatments on biomaterials using several methods have greatly reduced the in vivo bacterial attachment, surface colonization and formation of biofilm. In this study, the effect of silver (Ag) ion release against in vitro antibacterial activity and cytotoxicity of 1-4wt% Ag doped titania (TiO₂) thin film coatings were evaluated. These coatings were deposited for 1-6 h onto stainless steel substrate (SS) using (radio frequency) RF magnetron sputtering technique. The coatings predominantly in the crystalline anatase phase were configured using X-ray Diffraction (XRD). Scanning electron microscopy (SEM) observation showed the presence of Ag-TiO₂ nanoparticles of less than 100 nm in all the coated surfaces confirming the formation of nanostructured coatings. An initial rapid release, followed by a sustained lower release of Ag ion concentration was measured between 0.45 and 122 ppb when all the coated substrates immersed in Phosphate Buffered Saline (PBS) for 1-10 days. The obtained concentration was less than the maximum toxic concentration for human cells; yet achieved antibacterial concentration, sufficient to kill or inhibit the growth of bacteria. In vitro cytotoxicity results have indicated that 1-4 wt% of Ag doped TiO₂ coatings had no adverse effect on mouse fibroblast proliferation, confirming its cytocompatibility. The antibacterial assessment was performed on 1 and 2 wt% Ag-TiO₂ coatings using Staphylococcus aureus (S. aureus) whereby significant antibacterial activity was observed in 2 wt% Ag-TiO₂ coatings.     

Preparation, characterization and application of TiO2 nanoparticles surface-modified by DDAT

DDAT(S-1-Dodecyl-S′-(α, α′-dimethyl-α″-acetic acid) trithiocarbonate) modified TiO₂ photocatalysts were prepared by hydrothermal treatment before TiO₂ crystallization. The adsorption of DDAT onto the surface of titania nanoparticles led the shifting of the onset wavelength of the optical absorption in the visible range corresponding to ligand-to-metal charge transfer transition within the surface-modified complex. The interaction of TiO₂ nanoparticles with DDAT was investigated by infrared spectra. The XRD indicated that the modification process could not influence the crystallite phase of TiO₂. The photocatalytic studies suggested that the DDAT modified TiO₂ photocatalysts showed enhanced photocatalytic efficiency of photodegradation of 2,4-dichlorophenol compared with the as-prepared TiO₂ under visible-light irradiation.     

Comparative photocatalytic study of two selected pesticide derivatives, indole-3-acetic acid and indole-3-butyric acid in aqueous suspensions of titanium dioxide

Heterogeneous photocatalysed degradation of two selected pesticide derivatives such as indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) has been investigated in aqueous suspensions of titanium dioxide by monitoring the change in substrate concentration employing UV spectroscopic analysis technique and depletion in total organic carbon (TOC) content as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, types of TiO_2, substrate and catalyst concentration, and in the presence of electron acceptor such as hydrogen peroxide (H₂O₂) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 showed comparatively highest photocatalytics. The pesticide derivative, indole-3-acetic acid was found to degrade slightly faster than indole-3-butyric acid.     

Deposition of photocatalytic TiO2 layers by pulse magnetron sputtering and by plasma-activated evaporation

Crystalline TiO₂ thin films, especially layers with predominantly anatase phase, exhibit photocatalytic activities resulting in photoinduced hydrophilic, self-cleaning and antifogging properties. In this paper, a comparison of the photocatalytic properties of layers deposited with two different PVD techniques is given.On one hand, a reactive pulse magnetron sputtering (PMS) system has been used to obtain TiO₂ films at dynamic deposition rates from 8 to 50 nm m/min. On the other hand, TiO₂ layers were deposited by reactive electron beam evaporation at very high deposition rates between 500 and 1000 nm m/min. An additional spotless arc discharge (Spotless arc Activated Deposition—SAD process) was used for plasma activation to improve layer properties. Photoinduced hydrophilicity was investigated by measuring the decrease of the water contact angle during UV-A irradiation.     

Multifunctional dual Z-scheme heterostructured Sm2O3-WO3-La2O3 nanocomposite: Enhanced electrochemical,photocatalytic, and antibacterial properties

In this study, heterostructured dual Z-scheme Sm₂O₃-WO₃-La₂O₃ nanocomposite (NC) and bare Sm₂O₃, WO₃, and La₂O₃ nanostructured (NSs) were prepared using a co-precipitation approach. The comparative electrochemical, photocatalytic, and antimicrobial properties of NC and NSs were studied. The XRD spectrum exhibits the formation of bare NSs and NC having cubic-Sm₂O₃, monoclinic-WO₃, and hexagonal-La₂O₃ phases. FESEM results showed mesoporous morphology of NC. The higher electrical conductivity 261.33 mho-cm⁻¹ and lower optical energy bandgap 2.55 eV were obtained for NC. The photodegradation tests exhibited that NC photocatalyst has degraded 99% (methylene blue), 96% (Methyl orange), 99% (safranin-O), 48% (p-nitroaniline), and 98% (methyl red) dyes pollutants in 40 min sunlight radiation and showed strong inhibition activity against E. coli, K. pneumoniae, S. aureus, P. Vulgaris, and P. aeruginosa bacterial strains with zones of inhibition (ZOI) 31 mm, 30 mm, 30 mm, 28 mm, and 31 mm, respectively. Electrochemical studies revealed the excellent capacitive characteristics of NC with a specific capacitance 532F/g at a scan rate 5 mV/s, energy density 48.0278 W h Kg⁻¹, and power density 0.3782 KW Kg⁻¹ at 0.006 A/cm² current density. Furthermore, the present study revealed a novel composition for environmental remediation and energy storage applications.     

Controlled synthesis and characterization of 10 nm thick Al2O3 nanowires

α-Al₂O₃ nanowires, with diameter around 10 nm, were synthesized in bulk quantity by heating the mixture of pure aluminum and graphite powders at 900 °C. Scarcity of oxygen is regarded as the reason for the growth of the small diameter α-Al₂O₃ nanowires at relatively low temperature. The product was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The Oxygen vacancies in the nanowires lead to the strong photoluminescence in the wavelength range of 400-700 nm with its peak at 527 nm.