Antimicrobial activity of composite nanoparticles consisting of titania photocatalytic shell and nickel ferrite magnetic core

Reverse micelle and hydrolysis have been combined to synthesize composite nanoparticles consisting of anatase–titania photocatalytic shell and nickel ferrite magnetic core. The average particle size of the composite nanoparticles was in the range of 10–15 nm. The photocatalytic shell of titania is responsible for the photocatalytic and anti-microbial activity and nickel ferrite magnetic core is responsible for the magnetic behavior, studied by superconducting quantum interference device. The anatase TiO2 coated NiFe₂O₄ nanoparticles retains the magnetic characteristics of uncoated nanocrystalline nickel ferrites, superparamagnetism (absence of hysteresis, remanence and coercivity at 300 K) and non-saturation of magnetic moments at high field. The magnetic measurements results encourage their application as removable anti-microbial photocatalysts. Bacterial inactivation with UV light in the presence of titania-coated NiFe₂O₄ nanoparticles is faster than the action with UV light alone.     

Magnetically separable composite photocatalyst with enhanced photocatalytic activity

A novel magnetically separable composite photocatalyst, anatase titania-coated magnetic activated carbon (TMAC), was prepared in this article. In the synthesis, magnetic activated carbon (MAC) was firstly obtained by adsorbing magnetic Fe₃O₄ nanoparticles onto the activated carbon (AC), and then the obtained MAC was directly coated by anatase titania nanoparticles prepared at low temperature (i.e. 75 °C). The prepared samples were characterized by XRD, SEM and vibrating sample magnetometer (VSM). The composite photocatalyst can be easily separated from solution by a magnet, its photocatalytic activity in degradation of phenol in aqueous solution also has dramatic enhancement compared to that of the neat titania.     

Se and Te-modified titania for photocatalytic applications

Nanosized Se⁴⁺ and Te⁴⁺, respectively, doped titania was prepared by homogeneous hydrolysis of titanium oxo-sulfate with urea in aqueous solutions in the presence of amorphous selenium and tellurium. The prepared samples were annealing at temperature 200 and 400 °C. The structure of prepared samples was characterized by X-ray powder diffraction (XRD), selected area electron diffraction (SAED), surface area (BET), and porosity determination (BJH). The morphology and microstructure characteristics were obtained by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). The method of UV/Vis diffuse reflectance spectroscopy was employed to estimate band-gap energies of the Se and Te-doped titania. The photocatalytic activity of the prepared samples was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 and 400 nm wavelength. The best photocatalytic activity in UV and visible area exhibit the Se and Te-doped titania samples labeled TiSe3 (~11.5 wt% Se) and TiTe3 (~8.0% Te), respectively.     

Investigations on the photocatalytic activity of sol–gel derived plain and Fe/Nb-doped titania coatings on glass substrates

Plain and doped (Fe³⁺ and Nb⁵⁺) titania coatings were deposited by dip coating on soda lime glass substrates using titania sol synthesized by sol–gel route in combination with commercial nanoparticle dispersions. The dopant concentrations were fixed at 0.07 wt% and the coatings heat treated at 400 °C were characterized with respect to their thickness, phase composition, hydrophilicity/hydrophobicity and microstructure. Photocatalytic activity testing was carried out on the coatings by following up the degradation of methylene blue dye for up to 4 h at 1 h time intervals after exposure to sunlight. The effect of a trivalent and pentavalent doping of Ti⁴⁺ sites on photocatalytic activity of TiO₂ was investigated.     

An aqueous sol-gel synthesis of chromium(III) doped mesoporous titanium dioxide for visible light photocatalysis

Nanoparticles of titanium dioxide doped with Cr³⁺ ions have been prepared through an aqueous sol-gel method. The mesoporous nature of both pure and Cr³⁺ doped TiO₂ powders, with specific surface area of 7.4 and 6.6 m² g⁻¹, respectively, is maintained even at calcination temperature of 800 °C. The transformation of TiO₂ from the anatase to rutile phase is suppressed up to 800 °C by Cr³⁺ ion doping. Even though surface area values are decreased, the doped materials show improved photocatalytic activity, which may be due to increased crystallinity of the anatase phase without the formation of rutile. Doped materials have a red-shift in the band gap energy and hence, photoactivity under visible light. The rate of photodegradation of methylene blue dye for both pure and doped TiO₂ under visible light has been monitored in this study. The 0.25 mol% Cr(III) doped photocatalyst, calcined at 800 °C, shows the highest photocatalytic activity under visible light with a rate constant of ∼15.8 × 10⁻³ min⁻¹, which is nearly three times higher than that of commercially available Degussa P25 titania (5.8 × 10⁻³ min⁻¹).     

Synthesis and photochemical properties of Cu2+ doped layered hydrogen titanate

Cu²⁺ doped layered hydrogen titanate was prepared by the calcination of K₂CO₃, TiO₂ and CuO mixtures with the K₂CO₃:TiO₂:CuO molar ratio of 1:2.5(1−x):2.5x at 1200°C for 5 h followed by an ion-exchange reaction in 1 M HCl solution. The crystalline phase changed from monoclinic hydrogen tetratitanate to an orthorhombic lepidocrocite-type hydrogen titanate by increasing the amount of Cu²⁺ doped. Both compounds could be excited by visible light irradiation (λ>400 nm) and were capable of hydrogen gas evolution from an aqueous methanol solution, where the photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was slightly greater than that of Cu²⁺ doped lepidocrocite-type hydrogen titanate. The photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was enhanced by constructing Pt and TiO₂ pillars in the interlayer, and the incorporation of Pt in Cu²⁺ doped hydrogen tetratitanate enabled the cleavage of water into hydrogen and oxygen by irradiating visible light (λ>400 nm) without a sacrificial hole acceptor.     

Preparation of fine,uniform nitrogen- and sulfur-modified TiO2 nanoparticles from titania nanotubes

Abstract

TiO₂ nanoparticles modified with nitrogen and sulfur were prepared from titania nanotubes by a facile wet chemistry method. The samples synthesized with different thiourea/TiO₂ ratios showed a uniform nanoparticle size distribution centred at approximately 10 nm with a developed specific surface area of 246 m² g^-1. These modified nanosized photocatalysts exhibited higher photocatalytic activity for the degradation of gaseous isopropanol than unmodified titania nanotubes under visible illumination. This could be attributed to the synergistic effects of a large specific surface area, strong absorption in the visible region, a redshift in the adsorption edge, and surface adsorption modification induced by nitrogen and sulfur compounds.     

Preparation of magnetic photocatalyst nanoparticles—TiO2/SiO2/Mn–Zn ferrite—and its photocatalytic activity influenced by silica interlayer

A magnetic photocatalyst, TiO₂/SiO₂/Mn–Zn ferrite, was prepared by stepwise synthesis involving the co-precipitation of Mn–Zn ferrite as a magnetic core, followed by a coating of silica as the interlayer, and titania as the top layer. The particle size and distribution of magnetic nanoparticles were found to depend on the addition rate of reagent and dispersing rate of reaction. The X-ray diffractometer and transmission electron microscope were used to examine the crystal structures and the morphologies of the prepared composites. Vibrating sample magnetometer was also used to reveal their superparamagnetic property. The UV–Vis spectrophotometer was employed to monitor the decomposition of methylene blue in the photocatalytic efficient study. It was found that at least a minimum thickness of the silica interlayer around 20 nm was necessary for the inhibition of electron transference initiated by TiO₂ and Mn–Zn ferrite.     

Role of the synthesis procedure on the physicochemical properties of doped magnetite

The studies presented in this paper show the results of synthesis and physicochemical characterization of modified ferrite nanoparticles, which can be described by the general formula M_xFe_3-xO₄ (where x = 0.15 or 0.45) doped with Al³⁺, Cr³⁺, Cu²⁺ and Zn²⁺ ions. The nanoparticles were obtained through procedures using either water or organic environment. The aim of this study was to determine the influence of synthetic routine and doping on the quality of the obtained structure, morphology and magnetic properties of nanoparticles. Additionally, doping concentration of selected elements is a crucial influence on the crystallinity and magnetic properties of the obtained nanoparticles. Doped nanoparticles were synthesized by two chemical methods: co-precipitation of iron chlorides in a basic solution and thermal decomposition of iron(III) acetylacetonate in an organic high-boiling solvent. Obtained nanoparticles were characterized by transmission electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry, infrared spectroscopy and Mössbauer spectroscopy.     

Nanoporous composite of carbon nanosheets and functional titania nanoparticles formed by reassembling of exfoliated graphite oxides with colloidal titania

Reassembling of exfoliated graphite oxide (GO) layers by contacting with titania clear sol gives a novel nanoporous composite of carbon nanosheets and functional titania nanoparticles, in which titania particles with an evident brookite structure or a mixed phases of anatase and brookite are encapsulated on the basal plane of and in between the inner surfaces of carbon nanosheets without aggregating together or depositing only on the edges of carbon nanosheets. These composites successfully combine properties of carbon nanosheets and titania nanoparticles, exhibiting an enhanced adsorptivity and a good photocatalytic activity toward organic dyes due to its unique structure, better porosity, and compatible surface affinity.     

Synthesis and photocatalytic activity of mesoporous cerium doped TiO2 as visible light sensitive photocatalyst

Cerium doped titania materials were synthesized varying the cerium concentration from 0 to 10 wt%. Materials are characterised by XRD, TEM, XPS and N₂ adsorption desorption method. Surface area and visible light absorption substantially increases and crystallite size decreases with the increasing cerium content. Cerium doping stabilizes the anatase phase and surface area even at 600 °C calcination. Photocatalytic activity towards methylene blue decomposition and selenium (IV) reduction is found to increase with the cerium content up to 5 wt% and then decreases. Materials calcined at 600 °C shows better activity than that calcined at 400 °C, even though surface area decreases. Anatase crystallinity mostly decides the photocatalytic activity rather than only surface area. It can be concluded that the optimum visible light absorption and oxygen vacancy with 5% cerium doping enhances the photocatalytic activity. In addition photocatalytic performance is found to depend on the presence of Ce⁴⁺/Ce³⁺ rather than only visible light absorption.     

Low-temperature synthesis of magnetically recoverable,superparamagnetic, photocatalytic,nanocomposite particles

A new, simple, low-temperature method for the synthesis of superparamagnetic, photocatalytic, nanocomposite particles for applications in the decomposition of pollutants in water is presented. The method is based on the coating of clusters of superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles with a photocatalytic anatase layer using the hydrolysis of aqueous TiOSO₄. The clusters of an appropriate size between 100 and 200 nm form by the simultaneous agglomeration of the aminopropyl-triethoxy-silane-grafted maghemite nanoparticles with a size of approximately 15 nm in a suspension of diluted TiOSO₄. During a sudden increase of pH with the addition of NaOH the titania is heterogeneously nucleated at the cluster surfaces. If the hydrolysis was conducted at an elevated temperature of 90 °C, the titania layer was nanocrystalline anatase. The composition of the nanocomposite particles, i.e., the thickness of the anatase layer, can be controlled simply by changing the starting TiOSO₄/Fe₂O₃ ratio for low titania contents, and by multiple coatings to get high titania contents. The photocatalytic activity of the nanocomposites was evaluated in the photocatalytic decomposition of formic acid. The activity seems to increase with an increase in the thickness and the crystallinity of the anatase coating, whereas it decreased after the calcination of the as-synthesized nanocomposite. The coating of the maghemite nanoparticles with a thin layer of insulating silica also slightly improves the photocatalytic activity.     

Preparation, characterization and photocatalytic performance of Nd-doped titania nanoparticles with mesostructure

Nd³⁺-doped titania nanoparticles with mesostructures were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as directing and pore-forming agent. The obtained materials were characterized by XRD, nitrogen adsorption-desorption, TEM and DRS. The existence of neodymium ion affect significantly the phase transition of the amorphous to anatase, and the band-gap energy was reduced because of the defect energy level induced by the 4f atomic orbital of Nd³⁺ with the optimal content of 1.5 at.% Nd. Density functional theory calculations can explain the band-gap narrowing. The maximum photocatalytic activity corresponds to the 0.5 at.% Nd³⁺-doped anatase nanopowders with mesostructures, which is higher than that of undoped samples.     

Visible-light responsive zinc ferrite doped titania photocatalyst for methyl orange degradation

Visible-light responsive zinc ferrite doped titania (ZFDT) photocatalysts were prepared by sol-gel method. Diffuse Reflectance Spectroscopy (DRS) result shows that the absorption edge of ZFDT has moved to the visible spectrum range and a very large redshift occurs in comparison with the undoped titania. X-ray diffraction (XRD) results show that zinc ferrite can prevent the transformation of titania from anatase to rutile when the content of zinc ferrite is above 1.5%; while the phase transformation is promoted when its content is below 1.5%. In the latter case, zinc ferrite was assumed to exist as separate zinc and ferric cations in the lattice of titania in the form of oxides, both of which promote the phase transformation as previously reported in other literatures. Field emission scanning electron micrography (FE-SEM) shows that the average particle size of 1.5%ZnFe₂O₄/TiO₂ calcined at 500 °C is about 70 nm. The photocatalytic experimental results exhibit that ZFDT powders can effectively photodegrade methyl orange under visible light irradiation and the maxium photoactivity is achieved when the amount of zinc ferrite is 1.5%.     

Synthesis, characterization and in vitro cytotoxicity of self-regulating magnetic implant material for hyperthermia application

Gd-substituted zinc ferrite nanoparticles with low Curie temperatures (T_c) were synthesized by a chemical co-precipitation method. The magnetic properties and heat generation characteristics of these magnetic nanoparticles were investigated. The T_c of ZnGd_xFe_2 − xO₄ nanoparticles increased with increasing Gd³⁺ substitution, and was ~ 318 K at x = 0.02, which was a suitable Curie temperature for thermal seeds implanted in human body. The study on heat generation ability under external alternating magnetic field showed that the temperatures of these nanoparticles could be safely controlled around T_c without the temperature probe and controller. Furthermore, in vitro cytotoxicity of the ferrite nanoparticles was assessed using MTT assay. The results demonstrated that exposure to the bare ferrite nanoparticles for 48 h resulted in concentration-dependent toxicity. Cell growth inhabitation was observed when 4.0 mg/ml of bare ferrite nanoparticles was used. In contrast, PEG-capped nanoparticles had no significant effect on cell viability at any of the concentrations tested.     

Synthesis and performance of novel magnetically separable nanospheres of titanium dioxide photocatalyst with egg-like structure

A magnetically separable photocatalyst TiO(2)/SiO(2)/NiFe(2)O(4) (TSN) nanosphere with egg-like structure was prepared by a unique process that combined a liquid catalytic phase transformation method, reverse micelle technique and chemical precipitation means. The prepared photocatalyst shows high photocatalytic activity for the degradation of methyl orange in water. The magnetic property measurements indicate that the photocatalyst possesses a superparamagnetic nature. It can be separated from water when an external magnetic field is added and redispersed into water solution after the external magnetic field is eliminated. It is one of the promising photocatalysts for wastewater treatment. A transmission electron microscope (TEM) and an x-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that nickel ferrite core nanoparticles were completely encapsulated into monodisperse silica nanospheres as carrier, and titania nanoparticle aggregates were coated onto the surface of SN nanospheres, forming an imperfect TiO(2) shell for photocatalysis. The SiO(2) layer between the NiFe(2)O(4) core and the TiO(2) shell effectively prevents the injection of charges from TiO(2) particles to NiFe(2)O(4), which gives rise to an increase in photocatalytic activity. Moreover, the recycled TSN exhibits good repeatability of the photocatalytic activity.     

Ultrasonic-assisted synthesis and solar photoactivity investigation of Ce,B co-modified TiO2 nanoparticles

In this study, Ce and B co-modified TiO₂ nanoparticles were prepared using an ultrasonic-assisted sol–gel method. The prepared sample was characterized by X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy and BET analysis. In order to detect the effect of dopants on the titania, the photocatalytic activity of these as-prepared titania nanoparticles was determined by following the degradation of the reactive dye methylene blue under solar light irradiation. The activity was compared to that of pure titania. It was revealed that the photocatalytic activity of the Ce and B co-modified titania nanoparticles produced a significant enhancement compared to pure titania. The apparent rate constant of the as-prepared co-modified titania was 3 times higher than that of pure titania.     

Solvothermal synthesis of visible light responsive nitrogen-doped titania nanocrystals

Nitrogen ion-doped titania nanoparticles were obtained by the homogeneous precipitation in hexamethylenetetramine-titanium trichloride mixed solution followed by heat treatment in the solution at desired temperatures. After that the sample powders obtained were calcined in air at desired temperatures. Various phases of titania such as anatase, rutile and brookite were obtained depending on the reaction condition. Crystallite size, specific surface area and color also greatly changed as 5-50 nm, 20--200 m²·g^-1 and light gray-yellow, respectively, depending on the solvent, pH, etc. The products after calcination around 400°C were yellow indicating doping with nitrogen ion. Photocatalytic activity for the oxidative decomposition of NO in air atmosphere was also evaluated by using a continuous flow system with 1 ppm NO gas, where the high pressure mercury arcs filtered using various filters were irradiated. All colored titania nanoparticles showed photocatalytic activity under visible light irradiation for the oxidative decomposition of nitrogen monoxide in air. Especially, the nanoparticles of anatase type nitrogen-doped titania obtained by the homogeneous precipitation using hexamethylenetetramine-methanol aqueous solution around 200°C showed excellent photocatalytic activity under visible light irradiation.     

Preparation of doped TiO2 nanofiber membranes through electrospinning and their application for photocatalytic degradation of malachite green

Fe³⁺ doped TiO₂ composite nanofiber membranes and pure TiO₂ nanofiber membranes were prepared through electrospinning, and were applied to the photocatalytic degradation of malachite green (MG) in aqueous solutions under simulated sunlight. The effects of ferric ion content, initial concentration of MG, photocatalyst loading, and recycling behavior were studied. Microscopic characterization showed that the products have fiber morphology with bent property and favorable continuity. The degradation results showed that TiO₂ nanofiber membranes containing 0.8 mol% Fe³⁺ performed the best photocatalytic activity against MG under identical light irradiation. The TiO₂:Fe³⁺ composite nanofiber membranes maintained their photocatalytic efficiency through seven recycling processes.     

Optimization of CdO nanoparticles by Zr<Superscript>4+</Superscript> doping for better photocatalytic activity

Chemically controlled co-precipitation method has been adopted for the fabrication of pure and different wt% Zr doped CdO photocatalysts. Conventionally, the crystallite size and crystalline phase of CdO are in the midst of the parameters involved in the control of the photocatalytic activity. Aiming utterly at the size effect that modifies other attributes which are important to assess the photocatalytic activity of nanometric CdO, it was explored to synthesize CdO nanoparticles with controlled size, highly comparable morphology and analogous phase. The crystal structure and the crystallite size were estimated from the X-ray diffraction patterns and were confirmed through transmission electron microscope. The degree of crystallinity varied on Zr doping and the calculated crystallite sizes were in the range of 16–81 nm. The dopant ion Zr⁴⁺ have been detected through X-ray photoelectron spectroscopy (XPS) analysis signifying the dopant to substitute for cadmium (Cd²⁺) in the lattice of CdO. Particle size dependent optical band gaps calculated in the range 2.02–2.57 eV informed the viability of the materials to initiate photocatalytic reaction in the visible light region. Lesser recombination rate of the generated electrons and holes under light irradiation produced low intense photoluminescence peaks that displayed the appropriateness as photocatalysts. Zr⁴⁺ doping resulted in the enhancement of photocatalytic activity, evaluated by monitoring the degradation of methylene blue solution. 0.5 wt% Zr doped CdO nanoarticles calcined at 400 °C exhibited the highest photocatalytic activity with better percentage of color abatement (80.95%). The pseudo-first-order reaction rate became faster on Zr doping such that the rate constant is ~?0.4–0.5 h^?1 for Zr doped CdO while that for pure CdO is ~?0.3 h^?1.