Preparation of photoactive nitrogen-doped rutile

An easy way of preparing highly N-doped rutile photocatalysts (N-TiO 2 /R) in tubular furnace in a constant ammonia (NH 3 ) flow at 800-1000 °C temperature range is presented. New materials were compared to TiO 2 samples prepared at the same temperatures in air atmosphere as well as to the starting material. Complete transformation of amorphous and anatase phases to rutile was confirmed by XRD method. Successful incorporation of relatively high amounts of nitrogen (up to 17% at.), in form of either TiO 2 (N), TiO x N y or TiN, on photocatalysts' surface and in their lattice was confirmed using XPS and XRD analysis. Also presence of Ti 3+ was revealed by EPR studies. In contrast to pristine TiO 2 , the UV-vis/DR absorption spectra of N-modified photocatalysts extended significantly into the visible light region. Whereas nitrogen concentration as well as visible light absorption were found to increase with increasing modification temperature, photocatalytic activity was, on the contrary decreasing. This may be due to the very high nitrogen concentration, obtained at higher modification temperature, as well as the presence of small amount of conductive TiN phase on the N-TiO 2 /1000 °C photocatalyst surface. The artificial solar light activity of new photocatalysts after thermal treatment in NH 3 increased in comparison to starting material, due to nitrogen modification and presence of Ti 3+ ions. Activity under UV(-vis) light, though, decreased after modification procedure, probably due to smaller surface areas of new photocatalysts and complete anatase to rutile transformation. © 2012 Elsevier B.V. All rights reserved

TiO2 modified by ammonia as a long lifetime photocatalyst for dyes decomposition

Ammonia-modified TiO2 (TiO2/N), prepared in a pressure reactor was used as the well- active and longlife photocatalyst for the azo dye (Reactive Red 198) decomposition. The effect of aeration and the different value of the pH of the reaction medium on the photocatalytic degradation of Reactive Red 198 in water has been investigated. It has been reported that the degradation is greatly influenced by the reaction pH and the faster decomposition of azo dye took place at pH 3.5. When the solution was acidic, a larger amount of azo dye on the positively charged surface of TiO2 photocatalysts was adsorbed. From the obtained results it can be seen that the effectiveness of the decolourisation of the solution was faster by using the nitrogen-modified TiO2

Influence of annealing and rinsing on magnetic and photocatalytic properties of TiO 2

Samples of TiO 2, calcined at 100 °C (type 1) and 200 °C (type 2), have been prepared without and with water rinsing. The crystallite sizes determined by XRD method were smaller than 15 nm for both types of samples. Magnetic resonance spectra of the obtained samples have been studied in 230-300 K temperature range. Before rinsing no magnetic spectra were observed but after rinsing the magnetic response appeared in form of a resonance line centered at g eff ∼ 2.54 with linewidth ΔH pp ∼ 460 G in type 1 samples and g eff ∼ 2.26 with linewidth ΔH pp ∼ 220 G in type 2 samples. The integrated intensity of the observed spectrum was two times greater in the type 1 sample. The resonance line could be attributed to the localized magnetic moments in the correlated spin system formed during rinsing. The rinsing resulted also in higher photocatalytic properties under UV-VIS irradiation. It is suggested that the number of oxygen vacancies increases after rinsing and as they are involved in the formation of low oxidation states of titanium ions, they could be responsible for the appearance of the observed magnetic properties. © 2011 Elsevier B.V. All rights reserved

Magnetic resonance study of annealed and rinsed N-doped TiO2 nanoparticles

Nanoparticles of nitrogen-modified TiO2 (N-doped TiO 2) calcined at 300 C and 350 C, have been prepared with and without water rinsing. Samples were characterized by x-ray diffractrometry (XRD) and optical spectroscopy. The electron paramagnetic resonance (EPR) spectra from centers involving oxygen vacancies were recorded for all samples. These could be attributed to paramagnetic surface centers of the hole type, for example to paramagnetic oxygen radicals O-, O2 - etc. The concentration of these centers increased after water rising and it further increased for samples annealed at higher temperature. Additionally, for samples calcined at 300 C, and calcined at 350 C and rinsed, the EPR spectra evidenced the presence of magnetic clusters of Ti3+ ions. The photocatalytic activity of samples was studied towards phenol decomposition under unltraviolet-visible (UV-Vis) irradiation. It was found that, in comparison to the starting materials, the rinsed materials showed increased photocatalytic activity towards phenol oxidation. The light absorption (UV-Vis/DRS) as well as surface Fourier transform infrared/diffuse reflectance spectroscopy (FTIR/DR) studies confirmed a significantly enhanced light absorption and the presence of nitrogen groups on the photocatalysts surfaces, respectively. A significant increase of concentration of paramagnetic centers connected with oxygen vacancies after water rising has had an essential influence on increasing their photocatalytic activity. © 2013 Versita Warsaw and Springer-Verlag Wien

Magnetic properties of co-modified Fe,N-TiO2 nanocomposites

Iron and nitrogen co-modified titanium dioxide nanocomposites, nFe,N-TiO2 (where n = 1, 5 and 10 wt% of Fe), were investigated by detailed dc susceptibility and magnetization measurements. Different kinds of magnetic interactions were evidenced depending essentially on iron loading of TiO2. The coexistence of superparamagnetic, paramagnetic and ferromagnetic phases was identified at high temperatures. Strong antiferromagnetic interactions were observed below 50 K, where some part of the nanocomposite entered into a long range antiferromagnetic ordering. Antiferromagnetic interactions were attributed to the magnetic agglomerates of iron-based and trivalent iron ions in FeTiO3 phase,whereas ferromagnetic interactions stemmed from the F-center mediated bound magnetic polarons. © N. Guskos et al. 2015

Magnetic resonance study of co-modified (Co,N)-TiO2 nanocomposites

Three nCo,N-TiO2 nanocomposites (where cobalt concentration index n = 1, 5 and 10 wt %) were prepared and investigated by magnetic resonance spectroscopy at room temperature. Ferromagnetic resonance (FMR) lines of magnetic cobalt agglomerated nanoparticle were dominant in all registered spectra. The relaxation processes and magnetic anisotropy of the investigated spin system essentially depended on the concentration of cobalt ions. It is suggested that the samples contained two magnetic types of sublattices forming a strongly correlated spin system. It is suggested that the existence of strongly correlated magnetic system has an essential influence of the photocatalytic properties of the studied nanocomposites

EPR, spectroscopic and photocatalytic properties of N-modified TiO 2 prepared by different annealing and water-rinsing processes

Samples of TiO 2, calcined at 350 °C, 400 °C, 450 °C and 500 °C, have been prepared without and with water rinsing. The crystallite sizes were determined to be below 32 nm for all types of samples. Temperature dependence of magnetic resonance spectra of the obtained samples has been investigated. The electron paramagnetic resonance (EPR) spectra of free radicals were recorded for all samples, non-rinsed and water-rinsed, centered between g eff = 2.0027(3) and g eff = 2.0032(3) with linewidths ΔH pp = 5(1) G and ΔH pp = 8(1) G. The temperature dependence of the EPR integrated intensities has shown the presence of different relaxation processes operating in high temperature range, which could have arisen due to different concentrations of conducting electrons. For the water-rinsed sample annealed at 400 °C the ferromagnetic resonance (FMR) spectrum of magnetic agglomerates was recorded. Very intense reorientation processes of a correlated spin system have been observed in different temperature ranges. The EPR spectra of trivalent titanium ions were registered in all samples. The number of oxygen vacancies could have increased, possibly involving complexes and agglomerates containing trivalent titanium ions. © 2012 Elsevier B.V. All rights reserved

Enhancement of the Photoelectrochemical Performance of CuWO₄ Thin Films for Solar Water Splitting by Plasmonic Nanoparticle Functionalization

The effect of plasmonic nanoparticles (NPs) on the photoelectrochemical water splitting performance of CuWO₄ is studied here for the first time. CuWO₄ thin films were functionalized with well-defined Au NPs in two composite configurations: with the NPs (I) at the CuWO₄–electrolyte interface and (II) at the CuWO₄ back contact. In both cases, the incident photon to current conversion efficiency of the film was increased (∼6-fold and ∼1.2-fold for configurations I and II (at λ = 390 nm), respectively). Two important advantages of placing the NPs on the CuWO₄–electrolyte interface are identified: (1) Au NPs, coated with a 2 nm TiO₂ layer, are found to significantly enhance the surface catalysis of the film, decreasing the surface charge recombination from ∼60% to ∼10%, and (2) the NP’s near-field can promote additional charge carriers within the space charge layer region, where they undergo field-assisted transport, essentially avoiding recombination. Our study shows that Au NPs, coated with a 2 nm TiO₂ layer, can significantly mitigate the catalytic and optical photoelectrochemical (PEC) limitations of CuWO₄. An increase from 0.03 to 0.1 mA cm^–2 in the water-splitting photocurrent was measured for a 200 nm film under simulated solar irradiation at 1.23 V vs RHE