Enhancement of Visible Light-Responsive Photocatalytic Efficiency by Using a Laccaic Acid-Modified Titanium Dioxide Photocatalyst

In this study, a laccaic acid-modified TiO2 photocatalyst (Lac-TiO2) was prepared via an impregnation method with 0.50, 1.00, 2.50, and 5.00 wt.% laccaic acid. The products’ physical properties were examined through X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoemission spectroscopy (XPS), UV-Vis diffused reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption/desorption, and photoluminescence (PL) spectroscopy. A possible photocatalytic mechanism was also proposed. XRD patterns revealed the anatase phase of TiO2 and Lac-TiO2 samples. High-magnification FE-SEM images showed that the TiO2 and Lac-TiO2 samples exhibited spherical-like structures. XPS results complementarily confirmed the presence of Ti, O, and C as the main elements of the Lac-TiO2 samples. Interestingly, the DRS spectra of the Lac-TiO2 samples extended into the visible region. FTIR spectra presented the characteristic bands of TiO2 and hydroxyl groups on the TiO2 surface. Instead of hydroxyl groups, the characteristic bands of laccaic acid were observed on the surface of the Lac-TiO2 samples. The photocatalytic properties of the Lac-TiO2 samples were evaluated in terms of methyl orange degradation under visible light irradiation. The Lac-TiO2 samples showed higher photocatalytic performance than the TiO2 sample.

Ag-Doped TiO2: Synthesis, Characterization and Photodegradation of 4BS Dye

Ag doped TiO2 nanoparticles with different metallic content (0.0, 0.1, 0.15 and 0.2 wt.%) were prepared by using EDTA-Glycol method. For the sake of comparison blank TiO2 sample is also prepared using same method. All the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). X-ray diffraction technique revealed that Ag-doped TiO2 has anatase structure and as the concentration of Ag increases the particle size will get decreases. The morphologies of TiO2 samples are influenced by doping Ag as shown by SEM images. The present work is mainly focused on the enhancement of photocatalytic reactivity of as synthesized samples by the photodegradation of 4BS under visible light irradiation using a LED lamp of (15 W) as a light source. A 96.3% of photodegradation of 4BS dye was achieved by utilizing 1 g/L of Ag-doped TiO2 at pH 6 for 100 min.

Photocatalytic degradation of Congo red dye using Fe-doped TiO2 nanocatalysts

Fe-doped TiO2 (2, 5, 10, 15 and 20% wt. of Fe) photocatalysts have been synthesized by sol-gel method using titanium aquacomplex precursor. The structure and morphology have been characterized by XRD, BET, SEM, and EDS analyses, Mossbauer and IR spectroscopies. XRD analysis confirmed the anatase structure. The introduction of ferric ions into the titania structure causes its amorphization. The crystallite sizes of obtained samples are around 3 nm. Fe-doped TiO2 samples possess mesoporous structure and high specific surface area (from 274 m2g-1 for 5Fe-TiO2 to 416.4 m2g-1 for 20Fe-TiO2). Mossbauer spectroscopy data confirms the incorporation of Fe3+ ions in the anatase structure. Photocatalytic degradation of Congo red dye using Fe-doped TiO2 photocatalysts was studied under the UV-A light. Optimized conditions for photocatalytic degradation of CR in the presence of hydrogen peroxide are obtained. It was found that the 2Fe-TiO2 sample in the presence of 20 mM H2O2 solution showed highest efficiency in dye photodegradation (99.4%) under UV-A light. The photodegradation kinetics was analyzed using a smartphone and fits well with first-order kinetics model.

Adsorption of azo dye Congo red on the Sn-doped TiO2 surface

In this paper, the effect of SnO2 impurity on the surface charge and adsorption properties of TiO2 samples is investigated. The experimental value of the zero charge point for TiO2 with 3%, 6% and 12% of SnO2 equals 3.53, 3.97 and 3.2, respectively. The adsorption activity of the samples was studied on model solutions of the anionic dye – Congo red. The maximum adsorption capacity (qexp) equals 24.6 mg/g for 3Sn/TiO2, 25.0 mg/g for 6Sn/TiO2 and 39.1 mg/g for 12Sn/TiO2. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to describe the adsorption mechanism of Congo red dye on the surface of Sn/TiO2 samples. Based on the results of the studies of Congo red adsorption by the surface of titanium dioxide doped with Sn, all samples agree best with the Langmuir model. The correlation coefficients for the Langmuir isotherms are in the range of 0.9927 - 0.9996, while the values ​​of R2 for the Freundlich and Dubinin-Radushkevich isotherms are in the range of 0.721 - 0.8329 and 0.8283 - 0.9433, respectively. Experimental data obtained from adsorption isotherms show that the TiO2 sample containing 12% SnO2 is the most active. The best result of Congo red removal occurred at a concentration of Co = 5 mg/l (% of removed dye ≈ 83% for 12Sn/TiO2; 81% for 6Sn/TiO2 and 71% for 3Sn/TiO2). Therefore, the studied samples of TiO2 doped with SnO2 can be used as effective adsorbents of Congo red from aqueous solutions.

Effect of Urea Addition on Anatase Phase Enrichment and Nitrogen Doping of TiO2 for Photocatalytic Abatement of Methylene Blue

TiO2-based materials are commonly employed as photocatalysts for industrial wastewater treatment. The primary reasons of employing TiO2 include cost effectiveness, ready availability, eco-friendliness, non-toxic behavior, and exceptional resistance towards photo-corrosion. However, the wider band gap of pure TiO2 restricts its performance because of its optical absorption of solar light to the ultraviolet (UV) region only, and to some extent of photo-excited charge recombination. In the present work an attempt is made to develop a facile synthesis approach by using urea, a cheap chemical precursor, to form nitrogen doped TiO2 with the key objective of extended light absorption and thus enhanced photocatalytic performance. It was also observed that the urea-induced anatase phase enrichment of TiO2 is another key factor in promoting the photocatalytic performance. The photocatalysts prepared by varying the amount of urea as a nitrogen dopant precursor, are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) to evaluate their crystallinity, morphology, functional groups, and charge separation properties, respectively. Moreover, the surface area was also estimated by physicochemical adsorption. The maximum nitrogen-doped sample yielded >99% photodegradation efficiency of methylene blue (MB) dye-simulated wastewater as compared to a pure TiO2 sample which exhibited 6.46% efficiency. The results show that the simultaneous factors of nitrogen doping and anatase phase enhancement contributes significantly towards the improvement of photocatalytic performance.

Photocatalytic Degradation of Thiacloprid Using Tri-Doped TiO2 Photocatalysts: A Preliminary Comparative Study

Different tri-doped TiO2 photocatalysts (Fe-N-P/TiO2, Fe-N-S/TiO2, Fe-Pr-N/TiO2, Pr-N-S/TiO2, and P-N-S/TiO2) were successfully prepared and tested in the photocatalytic removal of thiacloprid (THI) under UV-A, visible, and direct solar light irradiation. The physical-chemical properties of the prepared catalysts were analyzed by different characterization techniques, revealing that dopants are effectively incorporated into the anatase TiO2 lattice, resulting in a decrease of the energy band gap. The reduction of photoluminescence intensity indicates a lower combination rate and longer lifespan of photogenerated carriers of all doped samples in comparison with the un-doped TiO2. The doped photocatalysts not only significantly promote the photodegradation under UV-A light irradiation but also extend the optical response of TiO2 to visible light region, and consequently improve the visible light degradation of THI. Fe-N-P tri-doped TiO2 sample exhibits the highest THI photodegradation degree (64% under UV-A light, 29% under visible light and 73% under solar light).

Optical Sensing of Molecular Oxygen (O2) via Metal Oxide Photoluminescence: A Comparative Study of TiO2, SnO2 and ZnO

A comparative study is presented on the photoluminescence (PL) response toward molecular oxygen (O2) in tin dioxide (SnO2), zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles. The findings show that both PL enhancement and PL quenching can be observed on different materials, arguably depending on the spatial localization of the defects responsible for the PL emission in each different oxide. No significant results are evidenced for SnO2 nanoparticles. ZnO with red/orange emission shown an O2-induced PL enhancement, suggesting that the radiative emission involves holes trapped in surface vacancy oxygen centers. While the ZnO results are scientifically interesting, its performances are inferior to the ones shown by TiO2, which exhibits the most interesting response in terms of sensitivity and versatility of the response. In particular, O2 concentrations in the range of few percent and in the range of a few tenths of a part per million are both detectable through the same mixed-phase TiO2 sample, whose rutile phase gives a reversible and fast response to larger (0.4–2%) O2 concentration while its anatase phase is usable for detection in the 25–75 ppm range. The data for rutile TiO2 suggest that its surfaces host deeply trapped electrons at large densities, allowing good sensitivities and, more notably, a relatively unsaturated response at large concentrations. Future work is expected to improve the understanding and modeling of the photophysical framework that lies behind the observations.

Influence of Pore-Size/Porosity on Ion Transport and Static BSA Fouling for TiO2-Covered Nanoporous Alumina Membranes

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO2 layer by the atomic layer deposition technique (Sf-NPAM/TiO2 and Ox-NPAM/TiO2 samples) was analyzed by membrane potential and electrochemical impedance spectroscopy measurements. The results showed the significant effect of pore radii (10 nm for Sf-NPAM/TiO2 and 13 nm for Ox-NPAM/TiO2) when compared with porosity (9% and 6%, respectively). Both electrochemical techniques were also used for estimation of protein (bovine serum albumin or BSA) static fouling, and the results seem to indicate deposition of a BSA layer on the Sf-NPAM/TiO2 fouled membrane surface but pore-wall deposition in the case of the fouled Ox-NPAM/TiO2 sample. Moreover, a typical and simple optical technique such as light transmission/reflection (wavelength ranging between 0 and 2000 nm) was also used for membrane analysis, showing only slight transmittance differences in the visible region when both clean membranes were compared. However, a rather significant transmittance reduction (~18%) was observed for the fouled Sf-NPAM/TiO2 sample compared to the fouled Ox-NPAM/TiO2 sample, and was associated with BSA deposition on the membrane surface, thus supporting the electrochemical analysis results.

Photocatalytic and UV-VIS Optical Properties of Titanium-Silver Doped Composite Synthesized by Hydrothermal Method

Titanium (TiO2) has been studied and proved to be the most ideal photocatalyst due to several aspects such as high photoactivity, thermal and chemical stability, relatively inexpensive and non-toxicity. As the problem statement, the photoactivity and optical stability are the crucial aspects to synthesize an ideal photocatalyst. These aspects can be improved through the synthesize method to enhance its nanocrystal crystallinity. The purpose of this research is to synthesize the high crystalline silver-titanium (AgTiO2) nanoparticles and study its photoactivity and optical properties. The Ag-TiO2 was synthesized through the modification of caustic hydrothermal method and molten salt doping process to dope the silver nitrate (AgNO3) as a dopant agent. The photoactivity performance of high grade TiO2 and high crystallinity Ag-TiO2 were examine via a Methylene Blue Degradation (MBD) testing under both visible light and UV light. The optical properties were measured through the Surface Area BET (SBET) and UV-Vis-NIR spectrophotometer (UV-Vis). The UV-Vis results show that the 0.01%-Ag-TiO2 sample has a lowest band gap with 2.6eV compared to the commercial TiO2 (P25) and other samples. The SBET analysation shows that, the biggest surface area was formed in 0.05%-Ag-TiO2 followed by 0.01%-Ag-TiO2, un-doped TiO2 and 0.03%-Ag-TiO2. For the MBD-testing, the high crystalline Ag-TiO2 was performed a better photoactivity compared to the high grade TiO2. The 0.05%-Ag-TiO2 has the best crystallinity and morphology growth compared to 0.01%-Ag-TiO2 and 0.03%-Ag-TiO2 doping samples. The results obtained proves that, the presence of silver dopants was successfully improved the nanocrystal crystallinity of Ag-TiO2 and influenced its photoactivity performance.

SYNTHESIS OF SM3+ DOPED WITH TIO2 NANOPARTICLES POWDER AS MID-IR OPTICAL FILTER

Samarium ions doped TiO2 nanoparticles were prepared successfully via Sol-Gel Technique with varying conditions. Effects of Sm3+ doping concentrations on the optical properties in the mid-infrared region was studied. FTIR spectra for pure and doped samples after annealing process show a single transition peak at wave number around 1109 cm-1 and 1116 cm-1 respectively, the wave number of the single transition peak depends on the Sm+3 doping ratio. By Comparing with wavelength of the high transition ratio of the pure TiO2 sample, slightly decries shift on the peak wavelength occur with an increment of doping concentration ratio. The FTIR spectrum gives a good indication the direction of synthesis of optical band-pass filter at a wavelength around 8.964µm (~1116 Cm-1).