Visible Light Photocatalytic Activity Of TiO2 Research Articles

Vitamin B5 copper conjugated triazine dendrimer improved the visible-light photocatalytic activity of TiO2 nanoparticles for aerobic homocoupling reactions

In this work, Cu-vitamin B5 (pantothenic acid) bonded to 2,4,6-trichloro-1,3,5-triazine produced a bioconjugated dendrimer giving rise to the visible-light photocatalytic activity of nanocrystalline TiO2. XPS spectra uncovered the coexistence of Cu(II)/Cu(I) oxidation states with a predominant contribution of Cu(I). The new heterogeneous bio-relevant Cu-photocatalyst (Cu(I) Cu(II) [PTAPA G2-B5] @TiO2) revealed a band gap value [Eg = (2.8 eV)] less than those of Cu free components [PTAPA G1-B5]@TiO2 (3.04) and [PTAPA G2-B5]@TiO2 (3.06) and particularly the bare TiO2 (3.15 eV). The reactions showed to be light-dependent with the best performance under room light bulbs. The photocatalytic efficiency of the as-prepared heterojunction photocatalyst was exploited in the aerobic Csp2–Csp2 homocoupling of phenylboronic acid and Csp–Csp homocoupling of phenyl acetylenes under visible-light irradiation to prepare structurally and electronically different biaryls. A radical pathway relying on the photogenerated e− and h+ and involving the Cu(I)–Cu(II) synergistic cooperation was postulated. The reusability and stability of the catalyst were verified by the recycling test, FT-IR spectra, and ICP-OES analysis.

Crystal strain engineering of AgBr/TiO2 for visible-light photocatalysis: Balancing light absorption and charge carrier kinetics

Addition of noble metals and/or their halides certainly improves the visible-light photocatalytic activity of TiO2, but whether this improvement is due to better photoabsorption capacity of the noble metal or enhanced photoelectrical properties of TiO2 itself, is still a subject of debate. Furthermore, the optimized load of noble metal halides at which best photocatalytic activity in TiO2 occurs hasn’t been explained in the literature consistently. Herein, we investigate the change in intrinsic lattice strain of TiO2 at different AgBr loadings which imparts selective optoelectronic properties turning AgBr/TiO2 system into a visible-light photocatalyst. XRD analysis reveals that beyond a maximum strain developed at an optimum AgBr loading level, the grain boundary interface can no longer withstand the increased strain at Ti—Ti, and Ti—O bonds and a chain of thermodynamically governed crystalline phase transformation within TiO2 begins. Faster dye degradation kinetics corroborate the hypothesis that the catalyst possessing maximum lattice strain shows superior photocatalytic properties. Photoelectrochemical studies was used to quantify the rate of charge transfer (kct) and rate of recombination (kr) of photogenerated electrons and holes. These studies revealed that although higher AgBr concentration may increase charge transfer through plasmon resonance but ultimately kr controls the total charge carrier flux that determines the photocatalytic efficicency of TiO2. Our work highlights methods in which the optimum loading of AgBr can be determined and presents fundamental insight into the role of lattice strain in balancing optical and electrical properties of TiO2 for constructing high-performance photocatalysts suitable for visible light application.

Visible-Light Photocatalytic Degradation of Aniline Blue by Stainless-Steel Foam Coated with TiO2 Grafted with Anthocyanins from a Maqui-Blackberry System

Anthocyanins from maqui (Aristotelia chilensis) and blackberry (Rubus glaucus) were used as light harvesters to improve the photocatalytic activity of titanium dioxide in visible light. Anthocyanins from both species were obtained using high-frequency ultrasound-assisted liquid-liquid extraction with methanol. Mixtures of anthocyanins were developed to study their effectiveness in the visible light/TiO2 reaction for the oxidation of aniline blue. For this purpose, stainless-steel foams were covered with TiO2 and anthocyanin and characterized by SEM. Different samples were fabricated by varying the ratio of the two anthocyanins in the mixture (100, 75, 50, 25 and 0 vol% of maqui-anthocyanin (delphinidin)). The mixtures of 25 vol% anthocyanin from maqui and 75 vol% anthocyanin from blackberry had higher total anthocyanin content and better photocatalytic activity in visible light: degradation of aniline blue was 40% at pH 7, 56% at pH 3 and 95% at pH 3 with the injection of oxygen for 2 h in comparison with TiO2-foam/UV light, which yielded values of 13% at pH 7 and 73% at pH 3 with and without the addition of oxygen. Natural dyes that are low-cost and environmentally friendly substances are shown to be capable of improving the visible-light photocatalytic activity of TiO2.

Improved visible-light photocatalytic activity of TiO2 co-doped with copper and iodine

Cu-I-co-doped TiO2 photocatalysts active to visible light absorption were prepared by hydrothermal method and calcined at various temperatures (350 °C, 450 °C, and 550 °C). The co-doped powders at 350 °C displayed the highest experimental Brunauer–Emmett–Teller surface area and lowest photoluminescence intensity, which demonstrated that a decrease in electron–hole recombination process. The synthesis of co-doped TiO2 was performed at this optimized temperature. In the co-doped sample, the Cu2+ doped TiO2 lattice created a major “red-shift” in the absorption edge due to the presence of the 3d Cu states, whereas the amount of red-shift from the I5+ doping in the TiO2 lattice was minor. Interestingly, the presence of Cu2+ species also boosted the reduction of I5+ ions to the lower multi-valance state I− in the TiO2 lattice by trapping the photogenerated electrons, which resulted in effective separation of the photogenerated charges. The Cu-I-co-doped TiO2 was able to degrade methyl orange dye under visible-light irradiation with improved photocatalytic activity compared with the single metal-doped TiO2 and pure TiO2 because of the strong visible light absorption and effective separation of photogenerated charges caused by the synergistic effects of Cu and I co-dopants.

Enhanced visible-light photocatalytic activity of carbonate-doped anatase TiO2 based on the electron-withdrawing bidentate carboxylate linkage

Carbonate-doped anatase TiO2 photocatalysts were prepared by a conventional sol-gel method and subsequent xerogel carbonization process in hypoxic atmosphere. Acetic acid was used as the hydrolysis inhibitors of titanium butoxide (TBOT) and the carbon source was the organic species produced during the synthesis of TiO2 particles. Via a low-temperature (≤300°C) carbonization process, the carboxylate ligands from the chelated acetic acid molecules can be retained and transformed into the bidentate carboxylate linkage between the amorphous carbonate dopants and TiO2 lattice. The strong electron-withdrawing bidentate carboxylate ligands can induce valence band (VB) tail states to narrow the bandgap of TiO2, as confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonate dopants can serve as photosensitizer to absorb visible-light and help to promote the charge carriers’ separation through cooperation with bulk/surface defects of TiO2. The synergistic effects can significantly enhance the visible-light photocatalytic activities of TiO2 for phenol degradation (λ≥420nm). The band structure and possible photocatalytic mechanism of the carbonate-doped TiO2 were thus elucidated.

Significance of DCLK1 expression for pancreatic cancer

Visible-light-driven photocatalysis as a green technology has attracted a lot of attention due to its potential applications in environmental remediation. Although TiO2 is the most popular photocatalyst, the lack of visible light utilization and a low efficiency of electron-hole separation should be overcome. Therefore, Au nanoparticles (NPs) as cocatalyst were controllably loaded between the double-shell or into CeO2 shell (as photocatalyst and oxygen buffer) and then a novel visible-light-driven TiO2@CeO2 nanocomposite was prepared, using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The presence of TiO2 shell, Au NPs and CeO2 shell were confirmed by EDX and electron energy loss mapping analysis. Under visible-light irradiation, the photo-degradation rate constant k (min−1) was in the order of TiO2@[email protected]2 (0.026) > TiO2@CeO2/Au (0.021) > TiO2@CeO2 (0.014) > CeO2 (0.0091) > TiO2 (0.0046) > P25 (0.0034). Compared with P25, TiO2@CeO2, and TiO2@CeO2/Au, the visible-light photocatalytic activity of TiO2@[email protected]2 for the photo-degradation of organic pollutant and photo-reduction of Cr(VI) were the highest. This result was attributed to the combination of TiO2 and CeO2, the double-shelled and sandwiched nanostructure and the addition of Au NPs as electron trap site and surface plasmon resonance-sensitizer, which could reduce the recombination of the electron-hole and induce the visible light absorption. The major obstacle of heterogeneous photocatalysis could be resolved. The photo-degradation rate of 95% was achieved by TiO2@[email protected]2, which exhibited an increase of 63% compared to Degussa P25 TiO2. The photo-degradation activity of TiO2@CeO2/Au was improved by Au NPs loaded on outer shell of TiO2@CeO2/Au but limited by their stability. This work confirmed the importance of controllable location of the noble metals as cocatalysts.

Effect of N and Fe codoping on the electronic structure and optical properties of TiO2 from first-principles study**Project supported by the National Natural Science Foundation of China (No. 11005050) and the Graduate Innovation Project of Jiangsu Province (No. SJLX_0517).

The electronic structure and optical properties of N and Fe codoping TiO2 have been investigated by first-principles calculations based on density functional theory. The calculated results indicate that the stability of N and Fe codoping TiO2 will change at different substitutional sites of N and Fe. The mechanism of band gap narrowing of doping TiO2 is discussed by investigating the density of state. The different substitutional site of N and Fe in codoping TiO2 influences the visible-light absorption. An increased visible-light absorption for doping TiO2 results from the synergistic effect of N and Fe codoping. Therefore, N and Fe codoping may enhance the visible-light photocatalytic activity of TiO2.

Photonic, and photocatalytic behavior of TiO2 mediated by Fe, CO, Ni, N doping and co-doping

Fe, Co, Ni, or N addition could modulate the photonic and catalytic responses of TiO2 for photocatalysts applications. Their morphologies, structures, compositions and photocatalytic performance in the degradation of methylene blue were characterized by scanning electron microscopy, X-ray diffraction, UV–vis absorption spectroscopy, Raman spectra and X-ray photoelectron spectroscopy. The results showed that dopants affect the electronic transition energies by changing the optical band gap and the impurity absorption peaks of the specimens. Especially, co-doping enhances the visible-light photocatalytic activity of TiO2 by 4–10 times that of pure TiO2, and the Co and N co-doping derives 10-fold photocatalytic activity.

Immobilization of S, N-codoped TiO2 nanoparticles on glass beads for photocatalytic degradation of methyl orange by fixed bed photoreactor under visible and sunlight irradiation

This research focused on photodegradation of organic compound by a fixed bed photoreactor. The photoreactor consists of a cylindrical glass tube, was filled by TiO2 coated glass beads codoped with sulfur and nitrogen (S, N). The photoactive layer of TiO2 was deposited on glass beads using the sol–gel dip-coating technique. The S, N-codoped TiO2 film after thermal treatment at 500°C for 1h, was characterized by XRD, XPS, SEM and EDX analyses. The XRD analyses exhibited an anatase structure of TiO2 with particle size about 35nm. The photocatalytic activity was determined by degradation of methyl orange (MO) (7mg/L, pH 2). The effective parameters of photocatalyst efficiency were investigated in laboratory and large volume scales under visible and sun light irradiations. The results showed that visible-light photocatalytic activity of TiO2 was extremely increased through adding thiourea (Tu) as a source of nitrogen and sulfur into TiO2 sol, which conducted to degradation of MO solution up to 95% in sunlight irradiation after only 2h. Overall, the photoreactor of immobilized S, N-codoped TiO2 on glass beads was found to be a promising technology for water treatment.

Study of Synergistic Effect of Ce- and S-Codoping on the Enhancement of Visible-Light Photocatalytic Activity of TiO2

Study of Synergistic Effect of Ce- and S-Codoping on the Enhancement of Visible-Light Photocatalytic Activity of TiO₂

Enhancing the visible-light photocatalytic activity of TiO2 by heat treatments in reducing environments

Abstract Following a series of recent studies that demonstrated enhanced visible-light photocatalytic activities of TiO2 by annealing in reducing atmospheres, a systematic investigation was conducted, in which TiO2 nanoparticles were annealed in various controlled atmospheres with the estimated oxygen partial pressure being varied from ∼10−1 to ∼10−25 atm and presence of other species (Ar, H2, N2, vacuum or hydrocarbon); subsequently, photocatalytic activities were tested. The results suggest that the oxygen partial pressure during annealing is not the dominant controlling factor. Furthermore, the use of vacuum environments or the presence of hydrocarbon species during annealing is effective in enhancing the photocatalytic activity, but the presence of H2 at a partial pressure of 0.05 atm does not show an appreciable beneficial effect. HRTEM suggested that the enhanced photocatalytic activity of vacuum-activated TiO2 may be related to subnanometer-thick disordered surface layers.

Photocatalytic effects of plasma-heated TiO2−x particles under visible light irradiation

The photocatalytic characteristics of partially reduced TiO2 (TiO2−x ) by plasma treatment and plasma-heated treatment were investigated in the visible-light region. For the visible-light photocatalytic activity of TiO2−x , plasmaheated treatment shows stronger than plasma treatment significantly. The TiO2−x by plasma-heated treatment shows broader red-shifted absorption bands than one by plasma treatment in the visible-light region. The surface color of TiO2−x by plasma treatment and plasma-heated treatment changed from white to sky blue, and to navy, respectively. After exposure to air, the surface color of TiO2−x changed from sky blue to white for plasma treatment and from navy to beige for plasma-heated treatment.

An enhanced visible-light photocatalytic activity of TiO2 by nitrogen and nickel–chlorine modification

A series of nitrogen and nickel–chlorine co-modified TiO2 photocatalysts (TiO2-N–x%Ni) with visible-light response have been synthesized by a sol–gel method. The results of photocatalytic degradation of 4-chlorophenol (4-CP) suggest that TiO2-N–x%Ni photocatalyst shows a higher activity than both pure TiO2 and nitrogen doped TiO2 (TiO2-N) under visible-light irradiation. The structure and properties of the photocatalysts have been investigated by XRD, XPS, UV–vis diffuse reflectance spectra (DRS), and photoluminescence (PL) spectra. It was found that unique chemical species, such as N–Ox and O–Ni–Cl, existed on the surface of TiO2-N–x%Ni. The energy levels of N–Ox and O–Ni–Cl surface states locate above the valence band and below the conduction band of TiO2, respectively. This could lead to strong visible-light absorption and an enhanced charge carrier separation compared with both pure and TiO2-N. Our results offer a paradigm for preparation of photocatalyst with a high visible-light activity by simultaneously doping TiO2 with two or more different elements.

Synthesis, characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins

Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH3, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO2–SiO2, ZnPP–TiO2–SiO2 and ZnCP–TiO2–SiO2, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO2–SiO2 samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO2–SiO2 under visible light irradiation and follow the order of ZnMP–TiO2–SiO2 > ZnPP–TiO2–SiO2 > ZnCP–TiO2–SiO2.

One-step preparation, characterization and visible-light photocatalytic activity of Cr-doped TiO2 with anatase and rutile bicrystalline phases

Cr-doped TiO2 (Cr-TiO2) nanoparticles with anatase and rutile bicrystalline phases were synthesized by a simple one-step flame spray pyrolysis (FSP) technique. The influences of chromium doping on the phase composition, microstructures, and optical properties of Cr-TiO2 were analyzed by the methods of XRD, TEM, EPR, XPS, UV–vis diffuse reflectance spectroscopy, and nitrogen adsorption–desorption. It was revealed that Cr3+ doping not only extends the visible light response of TiO2 but also increases the content of rutile in the bicrystalline TiO2. XPS results confirmed that Cr3+ can effectively promote the formation of oxygen vacancy which is contributed to the anatase-to-rutile transformation. EPR analysis indicated that the existing state of Cr in Cr-TiO2 is closely relative to the Cr content: Cr is mainly incorporated into the crystal lattice of TiO2 when the Cr content is lower than 1at.%, while higher Cr content is favorable to the formation of Cr2O3 clusters. The photocatalytic activities of different Cr-TiO2 photocatalytsts were evaluated in terms of the photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) under visible light irradiation. Appropriate Cr3+ doping can significantly enhance the visible-light photocatalytic activity of TiO2, which is attributed to the improvement of visible light response as well as the suitable anatase-to-rutile ratio. Excess Cr3+ doping is detrimental to the improvement of visible light photocatalytic activity, which is relative to the formation of Cr2O3 clusters as well as too high rutile content.

Visible-light photocatalytic activity of TiO2−x by heat treatment and plasma-heat treatment

The partial reduction of TiO2 was attempted by heat treatment and plasma-heat treatment and it was carried out to investigate the photocatalytic characteristics of partially reduced TiO2 (TiO2−x) in the visible-light region. As a result, the plasma-heat treatment shows significantly stronger than the heat treatment for the visible-light photocatalytic activity of TiO2. The red-shifted absorption bands in the visible-light region of TiO2−x by plasma-heat treatment gave broader than one by heat treatment. The TiO2−x by heat treatment and plasma-heat treatment was changed white to beige color, and white to navy, respectively.

Improved visible-light photocatalytic activity of titania activated by nitrogen and indium modification

Nitrogen and indium co-modified TiO2 was prepared by a simple sol–gel method. Under visible-light irradiation, the modified catalysts exhibited much higher photocatalytic activity for 4-chlorophenol photodegradation than both the as-prepared TiO2 and nitrogen-doped TiO2. The structure and properties of the resultant catalysts were characterized by XRD, BET, XPS, UV-vis DRS and PL techniques. It was found that unique chemical species, such as N–O and O–In–Clx (x = 1 or 2), existed on the surface of the nitrogen and indium co-modified TiO2. The surface-state energy levels introduced by these surface species were located close to the valence and conduction bands, respectively, which could lead to significant absorption in the visible-light region and facilitate the separation of photogenerated electrons and holes. Thus, the visible-light photocatalytic activity of TiO2 can be greatly improved by nitrogen and indium modification. We envision the opportunities for using such a method to develop TiO2-based visible-light photocatalysts suitable for practical applications.

Visible-light photocatalytic activity of anatase TiO 2 treated with argon plasma

We examined the partial reduction of anatase-type TiO 2 by argon (Ar) plasma treatment and hydrogen (H 2) plasma treatment to investigate the differences in catalyst characteristics in the visible-light region. The partially reduced TiO 2 samples prepared by Ar plasma treatment and H 2 plasma treatment gave broader, red-shifted absorption bands in the visible-light region and showed evidence of visible-light absorption due to oxygen defects. For the visible-light photocatalytic activity of TiO 2 − x , Ar plasma treatment appears to have an effect similar to that of H 2 plasma treatment with respect to high-discharge input power.

Synergetic effects of nitrogen doping and Au loading on enhancing the visible-light photocatalytic activity of nano-TiO2

Abstract Nitrogen-doped together with gold-loaded TiO 2 (Au/N–TiO 2 ) nanoparticles were prepared by a simple wet-chemical method. The samples were characterized by XRD, TEM, XPS, UV–vis diffuse reflectance spectroscopy, and photoluminescence (PL) spectroscopy. It reveals that Au was loaded on the surface of TiO 2 in the form of metallic Au, and nitrogen is introduced into TiO 2 matrix in the form of substitutional nitrogen and interstitial nitrogen. Au/N–TiO 2 exhibits much higher visible-light photocatalytic activity when compared with single N-doped or Au-loaded TiO 2 . A synergetic effect was proposed to explain the effects of nitrogen doping and Au loading on enhancing the visible-light photocatalytic activity of TiO 2 .

Visible-light photocatalytic activity of TiO 2/ZnS nanocomposites prepared by homogeneous hydrolysis

Photocatalytic active TiO 2/ZnS composites were prepared by homogeneous hydrolysis of mixture of titanium oxo-sulphate and zinc sulphate in aqueous solutions with thioacetamide. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HRTEM) and electron diffraction (ED). The nitrogen adsorption–desorption was used for surface area (BET) and porosity determination. Diffuse reflectance UV/VIS spectra for evaluation of photophysical properties were recorded in the diffuse reflectance mode (R100) and transformed to an absorption spectra through the Kubelka–Munk function. The method of UV/VIS diffuse reflectance spectroscopy was employed to estimate band-gap energies of the prepared TiO 2/ZnS nanocomposites. The photoactivity of the prepared TiO 2/ZnS nanocomposites was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry under irradiation of 255 nm, 365 nm and 400 nm wavelength. Under the same conditions, the photocatalytic activity of the commercially available photocatalyst (Degussa P25), the pure anatase TiO 2 and sphalerite ZnS were also examined. The composite sample having the highest catalytic activity was obtained by hydrolysis of mixture solutions 0.63 M TiOSO 4 and 0.08 M ZnSO 4 · 7H 2O.