Efficient photodegradation of azucryl red by copper-doped TiO2 nanoparticles-experimental and modeling studies

This research aims to investigate the effect of copper doping on the photocatalysis performance of TiO₂ nanoparticles for disposal wastewater from organic pollutants. X-ray diffraction analysis manifests the crystallization of a rutile phase for pure and copper-doped TiO₂ except for 2% resulting in a rutile-to-anatase phase transformation. The crystallite size is found less affected by Cu doping, i.e., ~30 nm. BET analysis indicates a decrease in the specific surface area as the doping loading increases. Scanning electron microscopy observations reveal spherical particles at the nanometer range for pure TiO₂ and then larger agglomerates of ultrafine particles with Cu doping. FTIR analysis notifies the existence of hydroxyl groups, which will promote the photocatalysis process. The photodegradation of azucryl red (AR) has been investigated under different conditions; i.e., Cu-loading, initial concentration of AR, and pH. The kinetics of the photodegradation process is further found to comply with the Lagergren kinetic law, regardless the experimental conditions. Nevertheless, the photodegradation process is not only controlled by the intra-particle diffusion mechanism, but also by mass transfer through a liquid film boundary. The maximum degradation of AR, i.e., 86%, has been achieved at pH = 5.0 during 60 min of contact time for the 2% Cu doping, with effective regeneration. The Freundlich model exhibits a better fitting for AR dye photodegradation equilibrium data, compared to Langmuir, Temkin, and Dubinin-Radushkevich.

Silica and Silica-Titania Xerogels Doped with Iron(III) for Total Antioxidant Capacity Determination

In order to design a sensor material for total antioxidant capacity determination we have prepared silica and silica-titania xerogels doped with iron(III) and modified with 1,10-phenanthroline. Titanium(IV) tetraethoxyde content in the precursors (titanium(IV) tetraethoxyde and tetraethyl orthosilicate) mixtures has been varied from 0 to 12.5% vol. Iron(III) concentrations in sol has been varied from 1 to 100 mM. The increase of titanium(IV) content has led to a decrease in BET surface area and average pore diameter and an increase of micropore surface area and volume, which has resulted in better iron(III) retention in the xerogels. Iron(III), immobilized in the xerogel matrix, retains its ability to form complexes with 1,10-phenanthroline and to be reduced to iron(II). Static capacities for 1,10-phenanthroline have been determined for all the iron(III) doped xerogels (0.207 mmol/g-0.239 mmol/g) and they are not dependent on the iron(III) content. Sensor materials-xerogels doped with iron(III) and modified with 1,10-phenanthroline-have been used for antioxidants (catechol, gallic and ascorbic acids, and sulphite) solid phase spectrophotometric determination. Limits of detection for catechol, gallic and ascorbic acids, and sulphite equal 7.8 × 10-6 M, 5.4 × 10-6 M, 1.2 × 10-5 M, and 3.1 × 10-4 M, respectively. The increase of titanium(IV) content in sensor material has led to an increase of the reaction rate and the sensitivity of determination. Proposed sensor materials have been applied for total antioxidant capacity (in gallic acid equivalents) determination in soft beverages, have demonstrated high stability, and can be stored up to 6 months at room temperature.

Electrochemical aptasensor for ultrasensitive detection of lipopolysaccharide using silver nanoparticles decorated titanium dioxide nanotube/functionalized reduced graphene oxide as a new redox nanoprobe

A novel and relatively simple signal-off electrochemical aptasensor was constructed for highly sensitive detection of lipopolysaccharide (LPS). For the first time, silver nanoparticles (AgNPs) decorated titanium dioxide nanotube (TNT) was conjugated with polydiallyldimethylammonium chloride (PDDA) functionalized reduced graphene oxide (rGO) to form a new nanohybrid of Ag-TNT/P-rGO. This nanohybrid with a large specific surface area exhibited excellent electrochemical activity, which not only served as the sensing platform to immobilize LPS binding aptamer (LBA) but was also employed as the redox probe to monitor the change of the electrochemical signal. The electrochemical signal responses were measured by cyclic voltammetry (CV) in the potential range -0.3 to 0.5 V at a scan rate of 0.1 V/s. The proposed aptasensor exhibited acceptable stability, reproducibility, and specificity for LPS detection with a wide linear range from 17 fg/mL to 100 ng/mL. The limit of detection (LOD) was 5 fg/mL. Furthermore, the prepared aptasensor showed acceptable recovery ranging from 96% to 103%, and the RSD varied between 1.4% and 8.5% for determining LPS in real samples.Graphical abstract.

Significant reduction in the optical band-gap and defect assisted magnetic response in Fe-doped anatase TiO2 nanocrystals as dilute magnetic semiconductors

The nature of BMPs, whether overlapped or isolated, determines the magnetic behavior of Fe-doped TiO₂.

Ultrathin-Film Titania Photocatalyst on Nanocavity for CO2 Reduction with Boosted Catalytic Efficiencies

Photocatalytic CO₂ reduction with water to hydrocarbons represents a viable and sustainable process toward greenhouse gas reduction and fuel/chemical production. Development of more efficient catalysts is the key to mitigate the limits in photocatalytic processes. Here, a novel ultrathin-film photocatalytic light absorber (UFPLA) with TiO₂ films to design efficient photocatalytic CO₂ conversion processes is created. The UFPLA structure conquers the intrinsic trade-off between optical absorption and charge carrier extraction efficiency, that is, a solar absorber should be thick enough to absorb majority of the light allowable by its bandgap but thin enough to allow charge carrier extraction for reactions. The as-obtained structures significantly improve TiO₂ photocatalytic activity and selectivity to oxygenated hydrocarbons than the benchmark photocatalyst (Aeroxide P25). Remarkably, UFPLAs with 2-nm-thick TiO₂ films result in hydrocarbon formation rates of 0.967 mmol g^-1 h^-1, corresponding to 1145 times higher activity than Aeroxide P25. This observation is confirmed by femtosecond transient absorption spectroscopic experiments where longer charge carrier lifetimes are recorded for the thinner films. The current work demonstrates a powerful strategy to control light absorption and catalysis in CO₂ conversion and, therefore, creates new and transformative ways of converting solar energy and greenhouse gas to alcohol fuels/chemicals.

Effect of TiO2 morphology on the benzyl alcohol oxidation activity of Fe2O3–TiO2 nanomaterials

Three series of Fe loaded (1, 3, 5 and 7 mol% Fe) TiO₂ anatase nanomaterials with different morphologies; nanoparticles, nanotubes and nanofibers were synthesized and used as catalysts for oxidation of benzyl alcohol.

Nanotubes with anatase nanoparticulate walls obtained from NH4TiOF3 nanotubes prepared by anodizing Ti

In this work, titanium dioxide nanoparticulate nanotubes (NP-NT) in anatase phase from ammonium oxyfluorotitanate nanotubes (NT NH₄TiOF₃) are shown.

In-situX-ray diffraction activation study on an Fe/TiO2pre-catalyst

This study focuses on the use ofin situpowder X-ray diffraction (PXRD) and quantitative phase analysis using the Rietveld method to monitor the structural properties of a titania-supported iron (10% Fe/TiO2) pre-catalyst during calcination (oxidation) and activation (reduction) in the temperature range 25–900°C. The TiO2oxidation study revealed an increase in anatase particle size before the anatase to rutile phase transformation, lending credibility to the bridging mechanism proposed by Kimet al.[(2007),Mater. Sci. Forum,534–536, 65–68]. Pre-catalyst oxidation experiments allowed for the determination of a suitable calcination temperature (450°C) of the pre-catalyst in terms of maximum hematite concentration and appropriate particle size. These experiments also confirmed that the anatase to rutile phase transformation occurred at higher temperatures after Fe addition and that anatase was the sole donor of Ti4+ions, which are known to migrate into hematite (Gennariet al., 1998), during the formation of pseudobrookite (Fe2TiO5) at temperatures above 690°C. Using the results from the oxidation experiments, two pre-catalyst samples were calcined at different temperatures; one to represent the preferred case and one to represent a case where the pre-catalyst had been excessively heated. Samples of the excessively heated catalysts were exposed to different reducing gas atmospheres (5, 10 and 100% H2/N2) and heated in thein situPXRD reactor, so that diffraction data could be collected during the activation process. The results show that reduction with gases containing low concentrations of H2(5 and 10%) led to the formation of ilmenite (FeTiO3) and we were able to show that both anatase and rutile are consumed in the reaction. Higher concentrations of H2led to the formation of magnetite (Fe3O4) and metallic iron (Fe0). We also noted a decrease in the anatase to rutile transformation temperature under reducing atmospheres when compared with the pre-catalyst heat-treatment experiment. A reduced calcination temperature prior to reduction allowed more facile Fe reduction.

Tungstate/titanate composite nanorod as an efficient visible light photo catalyst

The fabrication of tungstate/titanate composite nanorods is studied with the effect of calcination temperatures. The composites contain agglomerates in as prepared form which transformed to nanorods at higher calcination temperature. As prepared agglomerates begin to transform into nanorods morphology at 600 °C and acquires the nanorods morphology completely at 800 °C. Tetrahedral tungstate ions with subsequent calcination result in fabrication and growth of one dimensional geometry. The fabrication and growth of the nanorods are illustrated by scanning and transmission electron microscopy. Presence of W inhibits the anatase phase transformation to rutile which shows thermally stability of the composite up to 800 °C. The composite nanorods exhibit higher photo activity as compared to pure sample, Degussa P-25 and WO(3) in degradation of Rhodamine B under visible and UV light. The highest photo catalytic activity of the composite at 800 °C is due to retention of anatase form, unique structural characteristics, high surface area and tungsten incorporation. The new composite material extends the spectral response from UV to the visible region and reduces electron-hole recombination.

Spectrophotometric studies of visible light induced photocatalytic degradation of methyl orange using phthalocyanine-modified Fe-doped TiO2 nanocrystals

In this paper, preparation and visible light induced photocatalytic activity of phthalocyanine-modified Fe-doped TiO(2) nanocrystals (Pc/Fe-TiO(2)) with different Fe doping content (0, 0.05, 0.5 and 3.0 mol% Fe) as photocatalysts for the degradation of methyl orange have been reported. The study carried out using XRD, FT-IR, EDX, BET, DRS, UV-Vis, SEM and TEM techniques. Results revealed that modified TiO(2) nanocrystals possessed only the anatase phase with crystal sizes of about 10-23 nm and high surface areas of 2.8-37.3 m(2)/g. It can be seen phthalocyanine and Fe(3+) ion exist in photocatalysts based on analysis of FT-IR and EDX. The doping amount of Fe remarkably affects the activity of modified TiO(2) nanocrystals as catalysts. The 0.5 mol% Fe doping exhibited enhanced photocatalytic activity in this work. It was found that phthalocyanine and Fe induced a shift in the energy band gap to lower energies, which changes from 3.26 to 2.26 eV for pure TiO(2) and Pc/3% Fe-TiO(2) nanocrystals, respectively. Results of the degradation of methyl orange revealed that modified TiO(2) nanocrystals showed much more photocatalytic activity than pure TiO(2) under visible light which makes the applicability of TiO(2) photocatalysts even more versatile.

Deposition of anatase titania onto carbon encapsulated magnetite nanoparticles

A novel magnetically separable photocatalyst (titania-coated carbon encapsulated magnetite: TCCEF) was prepared. The prepared composite photocatalyst was characterized with an x-ray diffractometer (XRD), a transmission electron microscope (TEM), a Fourier transform infrared spectrometer (FT-IR) and a vibrating sample magnetometer (VSM). The photocatalytic activity of the samples was determined by degrading model contaminated water, a phenol aqueous solution. The results were compared with single-phase titania (pure titania and Degussa P25) and Fe(3)O(4)/TiO(2), and enhanced photocatalytic activity was obtained. It is suggested that the enhanced photocatalytic activity is ascribed to two major factors. First, the encapsulation of magnetite into the carbon layer may inhibit the direct electrical contact of titania and magnetite, hence preventing the photodissolution of the iron oxide phase. Second, the enhanced hydroxyl groups on TCCEF may inhibit the recombination of electron-hole pairs. On the other hand, the magnetic photocatalyst can be easily recovered from a slurry with the application of an external magnetic field.