Photocatalytic Activity Of Rutile TiO2 Research Articles

Development of Plasmonic Photocatalyst by Site‐selective Loading of Bimetallic Nanoparticles of Au and Ag on Titanium(IV) Oxide

AbstractMorphology‐controlled rutile titanium(IV) oxide (TiO2) and anatase TiO2 were prepared by a hydrothermal method and their surfaces were selectively loaded with Au, Ag and AuAg bimetallic nanoparticles (NPs) by photo‐deposition in order to obtain visible‐light responsive photocatalysts. With the help of local surface plasmon resonance (LSPR) of noble metal NPs, the photocatalytic activity of noble metal‐loaded TiO2 under visible‐light irradiation was improved compared to that of bare TiO2. The enhancement of LSPR on the photocatalytic activity of rutile TiO2 was larger than that of anatase TiO2 with optimum amount of Au or AuAg. In addition, the reusability (stability) of AuAg‐loaded TiO2 was much better than that of Ag‐loaded TiO2. Double‐beam photoacoustic results confirmed different trap energy level distribution lead to different electron transfer ways, resulting in different oxidizing capabilities and they gave one of important strategies for designing visible‐light responsive TiO2.

Improved photocatalytic activity of rutile TiO2 for organic oxidation through Ag nanoparticles and borate anions

Rutile TiO2 (RT) is usually used as photocatalyst for water oxidation, but seldom for organic oxidation, probably due to the slow reduction of O2. Herein we report a mutual effect of Ag nanoparticles and borate anions greatly increasing the photocatalytic activity of RT for phenol oxidation in neutral aqueous solution. RT was home-made, followed by calcination at 200―800 °C. With a given RT, the rates of phenol oxidation on the addition of Ag and borate were increased and decreased, respectively. In the presence of both Ag and borate, interestingly, the rate of phenol oxidation was larger than that in the presence of Ag. A (photo)electrochemical measurement revealed that Ag and borate, in contact with the irradiated RT, could catalyze O2 reduction and phenol oxidation, respectively. Since the electron and hole transfer processes would promote each other, the positive effect of Ag is further enhanced in the presence of borate. This work demonstrates that RT could be developed as a promising photocatalyst for organic oxidation through a surface co-catalyst.

Ag deposition effects on the photocatalytic activity of nanoparticulate TiO[formula omitted] — Comparison of gamma irradiation and UV irradiation methods

Rutile phase TiO2 nanoparticles were synthesized first by a modified polyol based sol–gel technique. One important aspect of this work is that the less common rutile phase of TiO2 could be synthesized under mild conditions of temperature and pH. Then these TiO2 nanoparticles were impregnated with Ag using radiation methods i.e. UV-radiation and γ-radiation. This resulted in the formation of Ag–TiO2 nanocomposites. The differences in structure, crystallinity and size of the Ag–TiO2 nanocomposites depends strongly on the reductive power of the reducing species involved as has been ascertained by TEM, XRD and XANES study. The weakly reducing free radicals generated from glycerol via the UV-irradiation method leads to formation of tetrapod precursor like composite nanoparticles of lower crystallinity. On the other hand, the strongly reducing hydrated electron (in the γ-irradiation method) leads to single crystalline, discrete and spherical Ag–TiO2 nanocomposites with traces of Ti2O3. We have been successful in preparing Ti2O3 which is a Magneli phase (MP) Ti sub-oxide, without calcination at very high temperatures. The photocatalytic efficiency of the composites is better than TiO2 itself. The photocatalytic efficiency of the nanocomposites depends on their structure and crystalline nature which can be ultimately correlated to the efficiency of production of active oxygen species like •OH. The presence of the narrow band gap Ti2O3 phase enhances photocatalytic activity of rutile TiO2.

Effects of S and Ta codoping on photocatalytic activity of rutile TiO2

In this study, pure titanium dioxide (TiO2), Ta-doped TiO2, S-doped TiO2, and Ta-S-codoped rutile TiO2 photocatalysts were prepared by a sol-gel method. To evaluate the properties of the synthesized samples, X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) were applied. XRD detection results showed that the samples contained rutile phase basically. Scanning electron microscope observation showed that the morphology of Ta-S-TiO2 was nearly spherical. Transmission electron microscope investigation indicated that Ta-S-TiO2 had a flower-shaped structure consisting of many nanorods. The measurement of Brunauer-Emmett-Teller (BET)-specific surface areas (SBET) showed that tantalum and sulfur codoping can effectively increase the SBET of TiO2. XPS results indicated that Ta was in the form of Ta5+ in the TiO2 structure. Finally, the photocatalytic activities of synthesized photocatalyst samples were measured for the degradation of methylene blue in ultraviolet and visible light irradiation. The results demonstrated that the Ta-S-codoped rutile TiO2 photocatalyst had better photocatalytic performance than pure rutile TiO2, Ta-doped rutile TiO2 and S-doped rutile TiO2 photocatalyst.

Effects of donor doping and acceptor doping on rutile TiO2 particles for photocatalytic O2 evolution by water oxidation

Crystalline defects of photocatalyst particles may be considered to be the recombination center of photoexcited electrons and holes. In this study, we investigated the photocatalytic activity of cation-doped rutile TiO2 photocatalysts for O2 evolution from an aqueous silver nitrate solution under ultraviolet light irradiation. The photocatalytic activity of rutile TiO2 was enhanced by donor doping of Ta5+ and Nb5+ with a valence higher than that of Ti4+, regardless of increased density of electrons and Ti3+ species (an electron trapped in Ti4+ sites). Conversely, acceptor doping of lower valence cations such as In3+ and Ga3+ decreased photocatalytic activity for O2 evolution by water oxidation. The doping of equal valence cations such as Sn4+ and Ge4+ hardly changed the activity of non-doped TiO2. This study demonstrates that Ti3+ species, which is a crystalline defect, enhanced the photocatalytic activity of semiconductor oxides, for example rutile TiO2 with large crystalline size.

Influence of surface metallic silver deposit and surface fluorination on the photocatalytic activity of rutile TiO2 for the degradation of crystal violet a cationic dye under UV light irradiation

Silver metallization and fluorination on the surface of rutile TiO2 (SRT and FRT) was carried out by photochemical reduction and wet impregnation methods respectively. TiO2, SRT and FRT were characterized by various analytical techniques like PXRD, SEM, EDX, FTIR, PL, UV–vis absorbance and XPS. The photocatalytic degradation of crystal violet (CV) was carried out at three different pH conditions. Acidic pH was found to be more favorable for the degradation, in spite of low adsorption of cationic CV molecules on the catalyst surface. The electrostatic repulsion at this pH drives the CV molecules into the bulk of the solution suggesting the involvement of bulk hydroxyl radicals rather than surface adsorbed hydroxyl radicals. The degradation efficiency can be represented by the following order SRT>FRT>TiO2. The Ti-peroxo (Ti-OO-Ti) complex species formed in presence of H2O2 by the combination of two trapped holes (Ti–O) in aqueous medium is predicted to enhance the rate of generation of hydroxyl radicals. The exciton mobility is dependent on the polaron effective mass which is higher for rutile TiO2 accounting for its lower activity. The bulk charge carrier transport which is less in bare rutile TiO2 is enhanced in the surface modified TiO2. Effective trapping of photogenerated excitons/electrons by F-/Ag0 can facilitate their migration and increase the activity by tenfolds. The rate of degradation of CV followed two reaction pathways, slower N-demethylation in basic conditions and rapid aromatic cleavage at the central carbon atom in the acidic pH conditions.

Site-Selective Binary Alloy Nanoparticles Deposition on TiO2 Nanorod for Acetic Acid Oxidative Decomposition Under UV-Vis Irradiation

Alloy nanoparticles (NPs) loaded TiO2 photocatalysts have attracted considerable attention in recent years as a promoter of highly active photocatalysts under ultraviolet (UV) irradiation [1]. Many synthetic techniques have been utilized in preparation of binary alloy NPs loaded TiO2. However, control of deposition site for alloy NPs on TiO2 is one of a challenging theme in TiO2 study. Herein, we present that site-selective Pt-Pb NPs deposition on rutile TiO2 nanorod by successive reduction of metal ions, photo-reduction of Pt4+ and followed by microwave assisted polyol reduction of Pb2+ (2-step method). The Pt-Pb NPs were site-selectively deposited on the reduction site on (110) surface of the rutile TiO2 nanorod. The photocatalytic activity of rutile TiO2 was significantly enhanced after Pt-Pb NPs loading for oxidative decomposition of AcOH in aqueous phase as shown in following figure. The AcOH was completely oxide to CO2 and the CO2 evolution of the site-selectively Pt-Pb NPs deposited TiO2 was nearly six times higher than that of a bare rutile TiO2 and three times higher than randomly Pt-Pb NPs deposited TiO2. The well mating of the reduction reaction site on photocatalyst, TiO2, and deposition site for co-catalyst, Pt-Pb NPs, induces efficient electron injection from photocatalyst TiO2 to co-catalyst Pt-Pb NPs, promoting oxygen reduction reaction, reduction process of AcOH oxidative decomposition. The accelerated electron consumption in reduction process leads to smooth oxidative decomposition of AcOH at oxidation site. These findings suggest that the site-selective deposition of alloy NPs is a predominant way to bring out catalytic performance of co-catalyst alloy NPs on TiO2. [1] T. Gunji, A. J. Jeevagan, M. Hashimoto, T. Nozawa, T. Tanabe, S. Kaneko, M. Miyauchi, F. Matsumoto, Appl. Catal B 181 (2016) 475-480. Figure 1

Site-selective deposition of binary Pt–Pb alloy nanoparticles on TiO2 nanorod for acetic acid oxidative decomposition

Alloy nanoparticles (NPs) loaded TiO2 photocatalysts have attracted considerable attention in the recent years as a promoter of highly active photocatalysts under ultraviolet (UV) irradiation. Many synthetic techniques have been utilized in preparation of binary alloy NPs loaded TiO2. However, control of deposition site for alloy NPs on TiO2 is one of the challenging themes in TiO2 study. Herein, we present that site-selective Pt–Pb NPs deposition on rutile TiO2 nanorod by successive reduction in metal ions, photo-reduction of Pt4+ and followed by microwave assisted polyol reduction of Pb2+ (2-step method). The Pt–Pb NPs were site-selectively deposited on the reduction site on (110) surface of the rutile TiO2 nanorod. The photocatalytic activity of rutile TiO2 was significantly enhanced after Pt–Pb NPs loading for oxidative decomposition of AcOH in aqueous phase. The AcOH was completely oxide to CO2 and the CO2 evolution of the site-selectively Pt–Pb NPs deposited TiO2 was nearly six times higher than that of a bare rutile TiO2 and three times higher than randomly Pt–Pb NPs deposited TiO2. The well mating of the reduction reaction site on photocatalyst, TiO2, and deposition site for co-catalyst, Pt–Pb NPs, induces efficient electron injection from photocatalyst TiO2 to co-catalyst Pt–Pb NPs, promoting oxygen reduction reaction and reduction process of AcOH oxidative decomposition. The accelerated electron consumption in reduction process leads to smooth oxidative decomposition of AcOH at oxidation site. These findings suggest that the site-selective deposition of alloy NPs is a predominant way to bring out catalytic performance of co-catalyst alloy NPs on TiO2.

In situ loading of CuS nanoflowers on rutile TiO2 surface and their improved photocatalytic performance

CuS nanoflowers, fabricated by an element-direct-reaction route using copper and sulfur powder, were loaded on rutile TiO2 (CuS/TiO2) at low temperature. CuS/TiO2 composites were utilized as the photocatalysts for the degradation of Methylene Blue (MB) and 4-chlorophenol (4-CP). X-ray diffraction (XRD), UV Raman spectroscopy, transmission electron microscopy (TEM), XPS, and UV-visible diffuse reflectance spectra were used to characterize the crystalline phase, morphology, particle size, and the optical properties of CuS/TiO2 samples. It is found that CuS/TiO2 photocatalyst, which CuS are loaded on the surface of rutile TiO2, exhibited enhanced photocatalytic degradation of MB (or 4-CP) than TiO2 or CuS. This indicates that CuS can enhance effectively the photocatalytic activity of rutile TiO2 by forming heterojunction between CuS and rutile TiO2, which is confirmed by photoluminescence (PL) spectra and TEM. Moreover, CuS content has a significant influence on photocatalytic activity and 2wt% CuS/TiO2 showed the maximum photocatalytic activity for degradation of MB.

Structural, Elastic and Optical Properties of Ag-Doped Rutile TiO<sub>2 </sub>

The structural, elastic and optical properties of Ag-doped rutile TiO2 are studied using the first principles calculations method. Four different functionals are employed using the ultrasoft pseudopotentials (USPs) on a supercell of size 2a × 2b × 1c. The band gaps of un-doped TiO2 obtained using PBE, RPBE, PW91 and LDA-CA-PZ are 1.861, 1.873, 1.857 and 1.854 eVs respectively. However, after Ag substitution in the supercell, the band gaps are reduced for all of the functionals. After substitution, in the region near to the Fermi level, some new electronic states are observed. The calculated elastic constants show that the structure is mechanically stable. The obtained values of the B, G and elastic constants of un-doped TiO2 are consistent with prior published experimental findings. For Ag-doped supercell, implementing PW91, B and G are 119 and 62 GPa. For the same size of supercell, using LDA-CA-PZ, B and G are 152 and 70 GPa. Besides, the results of the optical properties show that the major absorption peaks for all of the functionals locate away from the visible region. This shows poor absorption of visible light and weak photocatalytic activity of rutile TiO2.

Dependence of Activity of Rutile Titanium(IV) Oxide Powder for Photocatalytic Overall Water Splitting on Structural Properties

Rutile TiO2 powder having a band gap of 3.0 eV was studied as a photocatalyst for overall water splitting with respect to structural properties. The structures of rutile TiO2 samples were characterized by means of X-ray diffraction, scanning electron microscopy, photoacoustic spectroscopy, and a photoelectrochemical technique. It was found that rutile TiO2 particles that are photocatalytically active for the reaction exhibit a lower density of surface trapping states that slow water oxidation kinetics, as well as spatially separated reduction/oxidation sites at exposed crystal faces. This study also demonstrated that the photocatalytic activity of rutile TiO2 for overall water splitting, even when the material was well crystallized, was sensitive to defects that exist in (or near) the surface rather than in the bulk crystal.

Photocatalytic Performance of Nitrogen, Osmium Co-Doped TiO<SUB>2</SUB> for Removal of Eosin Yellow in Water Under Simulated Solar Radiation

Nitrogen, osmium co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using ammonia as the nitrogen source and osmium tetroxide as the source of osmium. The role of rutile phase OsO2 in enhancing the photocatalytic activity of rutile TiO2 towards the degradation of Eosin Yellow was investigated. The materials were characterised by various techniques that include FTIR, Raman, XRD, SEM, EDS, TEM, TGA and DRUV-Vis. The amorphous, oven dried sample was transformed to the anatase and then the rutile phase with increasing calcination temperature. DRUV-Vis analysis revealed a red shift in absorption with increasing calcination temperature, confirmed by a decrease in the band gap of the material. The photocatalytic activity of N, Os co-doped TiO2 was evaluated using eosin yellow degradation and activity increased with increase in calcination temperature under simulated solar irradiation. The rutile phase of the co-doped TiO2 was found to be more effective in degrading the dye (k(a) = 1.84 x 10(-2) min(-1)) compared to the anatase co-doped phase (k(a) = 9.90 x 10(-3) min(-1)). The enhanced photocatalytic activity was ascribed to the synergistic effects of rutile TiO2 and rutile OsO2 in the N, Os co-doped TiO2.

Preparation and photocatalytic activity of rutile TiO2 and goethite composite photocatalysts

Rutile TiO 2 and goethite (α-FeOOH) composite photocatalysts were fabricated by hydrolysis and precipitation using titanium tetrachloride as a precursor and α-FeOOH as a support. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results show that at lower temperature, rutile TiO 2 particles coat on the surface of α-FeOOH particles to form rutile TiO 2 -α-FeOOH composite photocatalyst. At higher temperature, iron ions are doped into the rutile TiO 2 lattice to form iron-doped rutile TiO 2 tubes; at medium temperature, the sample is a mixture with both composite and iron-doped structures. The photocatalytic activity of the samples is estimated by their ability to degrade methyl orange under irradiation with ultraviolet-visible light (200–800 nm) at ambient temperature. The photocatalytic activities of the samples are improved compared with that of pure rutile TiO 2 and α-FeOOH. The sample containing a mixture of composite and iron-doped structures shows the highest photocatalytic activity of that investigated. As a result, the photocatalytic activity of Ti 2 O could be improved effectively by combining with α-FeOOH or doping iron. 以四氯化钛为钛源, 针铁矿(帽-FeOOH)为载体, 采用水解沉淀法制备了金红石相二氧化钛(Ti 2 O)与帽-FeOOH的复合光催化材料, 并采用X射线衍射/扫描电子显微镜/透射电子显微镜/X射线能量散射谱和X射线光电子能谱对样品进行了表征. 结果表明, 低温下, 金红石相Ti 2 O包覆于帽-FeOOH表面, 并形成复合结构; 较高温下, 铁离子进入金红石相Ti 2 O晶格, 并形成铁掺杂金红石相Ti 2 O纳米管; 中温下, 样品兼有复合和掺杂两者特征. 在室温下以甲基橙为降解对象, 采用钨灯+氘灯(波长200–800 nm)为光源, 对样品的光催化活性进行了测试. 结果表明, 样品对甲基橙的光催化降解效果良好; 与纯帽-FeOOH和金红石相Ti 2 O相比, 不同结构样品的光催化活性均有所提高, 其中, 复合兼掺杂型样品的光催化活性最高. 由此可见, 与帽-FeOOH复合和铁掺杂是提高Ti 2 O光催化活性的有效途径. The structure of rutile TiO 2 and α-FeOOH composite photocatalysts can be controlled by adjusting reaction temperature, and their photocatalytic activity is maximized when they possess a core-shell structure with Fe 3+ doping.

Electronic structures and optical properties of transition metals (Fe, Co, Ni, Zn) doped rutile TiO2

The geometric structures of transition metals (Fe, Co, Ni and Zn) doped rutile TiO2 are studied using the first-principles method based on the density functional theory. The lattice parameters, the electronic energy band structure, and the optical properties are calculated and discussed. The results show that the errors between calculated and experimental values of lattice parameters are less than 3.6%. Appropriate dopants of transition metal ions not only influence the band structure of rutile TiO2 system and broaden the scope of light absorption, but also play an important role in trapping electrons, improving the effective separation of electronic-hole pair and enhancing light absorption ability. The optimum Fe, Co, Ni, Zn doped rutile TiO2 systems in theory are Ti0.75Fe0.25O2, Ti0.75Co0.25O2, Ti0.75Ni0.25O2, Ti0.17Zn0.17O2, respectively. The 3d orbits of Fe, Co, Ni split into two groups of energy bands, t2g and eg states contribute to the higher level of valence band and the lower level of conduction band, respectively, which is conducive to the generation of electronic-hole pair and the enhancement of photocatalytic performance of rutile TiO2. Zn 3d orbit is completely filled with electrons, and the electrons are hardly excited, so the photocatalytic activity of rutile TiO2 is not obviously improved.

Origin of Low Photocatalytic Activity of Rutile TiO2

Rutile TiO2 nanoparticles were synthesized using the colloidal sol-gel process and their photocatalytic properties were characterized in comparison with anatase TiO2 nanoparticles. The synthesized rutile nanoparticles were found to possess higher surfaces area than the anatase nanoparticles and to exhibit lower photocatalytic activities, demonstrating that rutile TiO2 has intrinsically low photocatalytic properties. The photoluminescence (PL) study suggested that the inferior photocatalytic activity of rutile nanoparticles is correlated with the intrinsic recombination of photogenerated electron-hole pairs.

Enhanced photocatalytic activity of rutile TiO2 prepared by anodic oxidation in a high concentration sulfuric acid electrolyte

The photocatalytic characteristics of TiO2 prepared by anodic oxidation in an electrolyte with a high concentration of sulfuric acid were investigated, focusing on the crystallinity and microstructure of the oxide. The predominant phase in the anodic oxide changes from anatase to rutile with the sulfuric acid concentration; the change appears when this concentration is 0.4M. Nanosized pores appear in the oxide when the concentration of sulfuric acid is greater than 0.1M, and the surface area increases with the sulfuric acid concentration. Structural analysis revealed that the inhomogeneous lattice strain in both anatase and rutile is reduced to almost zero, implying that the oxide contains a small number of recombination sites; as a result, the probability of the extinction of the photogenerated charges is low. The methylene blue (MB) bleaching test shows that the photocatalytic activity improves as the concentration of sulfuric acid increases and that the characteristics of rutile are better than those of anatase. It is concluded that rutile-structured TiO2 exhibits the best photocatalytic activity among the investigated oxides, due to its high crystallinity and porous microstructure.

Photocatalytic dehydrogenation of aliphatic alcohols by aqueous suspensions of platinized titanium dioxide

Photoirradiation (λex > 300 nm) of Ar-purged aqueous propan-2-ol solution gave hydrogen and acetone in the presence of platinum- and/or ruthenium dioxide-loaded TiO2. The photocatalytic activity of anatase TiO2 depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide. The photocatalytic activity of rutile TiO2 was negligible even when loaded with platinum black. The effective wavelengths for the photocatalytic dehydrogenation of propan-2-ol were below ca. 390 nm, in agreement with the u.v. absorption spectrum of anatase TiO2. In a similar way primary, secondary and tertiary aliphatic alcohols underwent photocatalytic oxidation, accompanied by hydrogen liberation, by the platinized TiO2. The primary and secondary alcohols gave the corresponding carbonyl derivatives, while 2-methylpropan-2-ol and acetone gave dimeric products accompanied by stoichiometric hydrogen evolution. The initial rate of dehydrogenation in these photocatalytic systems was in proportion to the rate constants of hydrogen abstraction by hydroxyl radical in the homogeneous systems.