Modified TiO2 Photocatalysts Research Articles

Adjustment and Matching of Energy Band of TiO2-Based Photocatalysts by Metal Ions (Pd, Cu, Mn) for Photoreduction of CO2 into CH4

A series of the metal ions (Pd, Cu, and Mn) modified TiO2 photocatalysts are synthesized via simple sol–gel method. Characterized by X-ray diffraction, Raman, UV–vis absorption spectra, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, time-resolved photoluminescence (PL) decay curves, and PL, it was revealed these introduced metal ions existed as O–Me–O species (Me: Pd, Cu, and Mn) on the surface of TiO2. The corresponding theory calculation is used to investigate the electronic density of states and band structure of the metal ions (Pd, Cu, and Mn) modified TiO2. The modified TiO2 photocatalysts exhibit an improved photocatalytic performance on reduction of CO2 and H2O into methane (CH4), attributed to the contribution of surface species by enhancing the visible absorption efficiently, separating charge carriers, and matching of the redox potential on the photoreduction of CO2 into CH4. This article could provide a wider understanding about the adjustment and matching of the energy...

Comparative Study for Photodegradation of Remazol Red R by Different TiO2 Samples

Potassium dichromate modified TiO2 photocatalyst (MD-TiO2) was prepared and its photocatalytic activity was compared with that of ordinary commercial TiO2 (C-TiO2) and special Degussa P25 TiO2 (D-TiO2). An organic dye, remozol red R(RRR) was used as a substrate for photodegradation from aqueous solution into environmentally safe products such as water, carbon dioxide and mineral ions. The photodegradation of RRR was carried out by varying the concentration of different types of TiO2 suspension, initial concentrations of dyes between 0.5× 10-4 M and 2.5 ×10-4 M, pH between 2.0 and 6.0 and light sources which are UV, artificial visible and sunlight. With increasing the catalyst concentration, percent degradation was found to increase up to a concentration of 1.2 g/100 mL of C-TiO2, 0.12 g/ 100 mL of D-TiO2 and 0.10 g/100 mL of modified MD-TiO2 for a definite concentration of RRR. However, RRR shows adsorption on TiO2 samples except C-TiO2. Again, the photodegradation efficiency is inversely affected by the dye concentration. Thus, the removal efficiency was found to be influenced by all of the above parameters. The maximum removal efficiency is found at pH 3.0 under sunlight in the presence of modified MD-TiO2,which suggests that MD-TiO2 can be used as an effective material for the removal of RRR instead of C-TiO2 and D-TiO2.
 Dhaka Univ. J. Sci. 65(1): 49-54, 2017 (January)

功能材料rGO/TiO<sub>2</sub>复合光催化剂的合成与研究

本文设计采用碱性一步水热法低温下控制合成了不同石墨烯含量的rGO/TiO2复合材料(石墨烯质量分数为0%，1%，5%，10%，15%)。通过XRD，SEM，Raman，Nitrogen adsorption-desorption等表征手段和光催化降解亚甲基蓝溶液(MB)测试，研究了石墨烯及其含量对TiO2结构、形貌以及光催化活性的影响。结果表明：(1)强碱水热反应中GO被还原为薄片状石墨烯，用于修饰TiO2不改变其晶相结构；适量的石墨烯掺杂使复合物的粒径减小，比表面积增大，电子扩散、迁移阻抗减小。(2)适量的石墨烯不仅可增强污染物与光催化剂的有效接触，还可作为电子受体促进TiO2电子-空穴的分离，使TiO2的光催化活性提高。(3)但过量的石墨烯不光会覆盖TiO2的部分活性位点，还易于参与形成团聚产物，不利于TiO2光催化活性的提高。因此，当石墨烯含量为5%时，rGO/TiO2对MB的光催化活性提高到86.3%，光催化性能最佳。这为碳材料改性TiO2光催化剂的绿色开发提供了一种可靠途径。 In this paper, rGO/TiO2 composites with different amount of graphene were controllably synthesized by alkaline one-step hydrothermal method (the content of graphene is 0%, 1%, 5%, 10% and 15%). By XRD, SEM, Raman, Nitrogen adsorption-desorption and photocatalytic degradation of methylene blue solution (MB), we explored the effect of graphene and its contents on optimizing TiO2 structure, morphology and photocatalytic activity. The results indicated that: (1) GO was reduced to thin-flake graphene in the strong alkaline hydrothermal reaction. Besides, the doping of graphene did not change the crystalline phase structure of TiO2, but resulted in the decrease of particle size and increase of surface area when it comes to composites. Secondly, it also reduced the diffusion and transfer impedance of electrons. (2) Appropriate amount of graphene not only enhanced the effective contact between pollutants and photocatalysts, but also can be used as electron acceptor to promote the separation of electron-hole of TiO2, thus improving the photocatalytic activity of TiO2. (3) But excessive graphene would be able to covered partial ac-tive-sites of TiO2 and participated in the formation of agglomeration products, which was not conducive to the improvement of TiO2 photocatalytic activity. Therefore, rGO/TiO2 with 5% gra-phene revealed the best photocatalytic performance, and its photocatalytic activity to MB solution increased to 86.3%. This provides a reliable way for the ecological development of Carbon materials modified TiO2 photocatalyst.

Cu2(OH)2CO3 clusters: Novel noble-metal-free cocatalysts for efficient photocatalytic hydrogen production from water splitting

Photocatalytic hydrogen evolution is a potential route for converting inexhaustible solar energy into available clean chemical energy. Herein, highly efficient and stable Cu2(OH)2CO3/TiO2 photocatalysts for hydrogen generation are prepared by incorporating Cu2(OH)2CO3 clusters onto the surface of TiO2 through a facile precipitation method. The obtained Cu2(OH)2CO3/TiO2 photocatalyst with optimal Cu2(OH)2CO3 content of 0.5mol% shows an outstanding photocatalytic H2-production rate of 6713μmolh−1g−1 (with apparent quantum efficiency of 15.4% at 365nm), which is comparable to the excellent Pt/TiO2 photocatalyst and more efficient than other copper specie modified TiO2 photocatalyst. The formation of Cu2(OH)2CO3/Cu+/Cu0 clusters essentially contribute to the enhanced H2-production activity by reducing the over-potential of water reduction and promoting the transfer of photogenerated electrons from the conduction band of TiO2 to the Cu2(OH)2CO3/Cu+/Cu0 clusters. A high stability of the Cu2(OH)2CO3/TiO2 photocatalyst is achieved due to the re-oxidation process of Cu+/Cu0 to Cu2(OH)2CO3 and structure confinement of Cu2(OH)2CO3 clusters in the mesopores of TiO2. This work brings in new insight in developing low-cost noble-metal-free photocatalytic system for solar-to-fuel conversion.

ChemInform Abstract: Selective Catalytic Reduction of NO by NH3 over Photocatalysts (Photo‐SCR): Mechanistic Investigations and Developments

AbstractReview: [differently modified TiO2 photocatalysts; 31 refs.

A mini-review on rare earth metal-doped TiO2 for photocatalytic remediation of wastewater.

Titanium dioxide (TiO2) has been considered a useful material for the treatment of wastewater due to its non-toxic character, chemical stability and excellent electrical and optical properties which contribute in its wide range of applications, particularly in environmental remediation technology. However, the wide band gap of TiO2 photocatalyst (anatase phase, 3.20eV) limits its photocatalytic activity to the ultraviolet region of light. Besides that, the electron-hole pair recombination has been found to reduce the efficiency of the photocatalyst. To overcome these problems, tailoring of TiO2 surface with rare earth metals to improve its surface, optical and photocatalytic properties has been investigated by many researchers. The surface modifications with rare earth metals proved to enhance the efficiency of TiO2 photocatalyts by way of reducing the band gap by shifting the working wavelength to the visible region and inhibiting the anatase-to-rutile phase transformations. This review paper summarises the attempts on modification of TiO2 using rare earth metals describing their effect on the photocatalytic activities of the modified TiO2 photocatalyst.

Developments in photocatalytic antibacterial activity of nano TiO2: A review

TiO2, which is one of the most explored materials, has emerged as an excellent photocatalyst material for environmental and energy fields, including air and water purification, self-cleaning surfaces, antibacterial and water splitting. This review summarizes recent research developments of TiO2-based photocatalyst used for photocatalytic antibacterial applications. Several strategies to enhance the efficiency of TiO2 photocatalyst are discussed, including doping with metal ions, noble metals, non-metals, and coupling with other materials. The mechanism of photocatalytic antibacterial activity in the presence of nano-sized TiO2 is also discussed. The modified TiO2 photocatalyst significantly inhibits the growth of bacterial cells in response to visible light illumination. TiO2 photocatalysis appears to be promising as a route of advanced oxidation process for environmental remediation.

ChemInform Abstract: Challenges in Co‐Alloyed Titanium Oxynitrides, a Promising Class of Photochemically Active Materials.

AbstractReview: recent developments in modified TiO2 photocatalysts with emphasis on water splitting; 114 refs.

Photocatalytic Hydrogen Production from Glycerol-water over Metal Loaded and Non-metal Doped Titanium Oxide

Modifications of the TiO2 P25 photocatalyst with metals: Platinum (Pt), Copper (Cu) and nonmetal: Nitrogen (N) doping to produce Hydrogen (H2) from a glycerol-water mixture have been investigated. The metals (Cu and Pt) were loaded into Titanium Dioxide (TiO2 ) surface by employing an impregnation and Photo-Assisted Deposition (PAD) method, respectively. As prepared the metal doped TiO2 photocatalyst was then dispersed into an ammonia solution to obtain N-doped photocatalysts. The modified photocatalysts were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS). XRD patterns indicated that the modified TiO2 photocatalysts have a nano-size crystallite range of 16-23 nm, while the DRS analysis showed that the doping of both metal and non-metal into TiO2 photocatalysts could effectively shift photon absorption to the visible light region. The optimum Cu loading of Cu-N-TiO2 was found to be 5%, resulting in a 10 times higher H2 production improvement level when compared to unloaded TiO2, even though this is still considered to be inferior compared to that of a 1% Pt loading, which results in a 34 times higher level than an unmodified TiO2 photocatalyst. The effect of glycerol concentrations on hydrogen production has also been studied. This method offers a promising technology to find renewable and clean energy by using cheap materials and a simple technology.

Challenges in Co-Alloyed Titanium Oxynitrides, a Promising Class of Photochemically Active Materials

We present a perspective on recent developments in modified TiO2 photocatalysts for visible light-driven photochemistry with an emphasis on water splitting. We focus on doped and alloyed TiO2 and in particular address the synergistic effects observed in materials with both transition metal cations and nonmetal anions. Several reports have demonstrated absorption of longer wavelengths (λ = 500–600 nm) by codoped materials compared to the absorption edge of TiO2. We review these advances against the backdrop of well-established doped TiO2 research, suggesting on the basis of compositional analysis and wavelength-resolved measurements of photon conversion efficiency that the increase in visible light absorption is likely due to absorption between defect states rather than true band gap narrowing. We draw a distinction between codoped and co-alloyed materials, stressing the attractive electronic structure of the latter. In highlighting recent literature, data examining the rate of photochemical water splittin...

Photocatalytic activity and luminescence properties of RE3+–TiO2 nanocrystals prepared by sol–gel and hydrothermal methods

A series of Y3+, Pr3+, Er3+ and Eu3+ modified TiO2 photocatalysts were obtained via sol–gel (SG) and hydrothermal (HT) methods. Samples prepared this way were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission microscopy (STEM), BET surface area method and luminescence spectroscopy. The photocatalytic activity of the synthesized samples was evaluated by the degradation of phenol in aqueous solution under visible and ultraviolet light irradiations. Phenol in aqueous solutions was successfully decomposed under visible light (λ>420nm) using TiO2 modified with RE ions. Luminescence properties of the samples as well as XRD and XPS analyses, indicate that RE are rather in the form of their oxides than in the form of cations in the crystal structure of TiO2. Photocatalysts prepared by SG method possessed higher amount of RE2O3, fewer of OH− groups and Ti3+ species on the surface layer than powders obtained by HT method. Action spectra analysis showed that Pr3+-modified TiO2 could be excited under visible light in the 420–250nm range. Furthermore, photocatalysts obtained by HT method showed higher photocatalytic activity and lower intensity of luminescence emission than photocatalyst prepared by SG method.

The photocatalytic interaction of Cr(VI) ions and phenol on polymer-modified TiO2 under visible light irradiation

To investigate the interaction of Cr(VI) and phenol in the photocatalytic process, the photocatalytic reaction of the mixed solution of these two pollutants was carried out using poly(fluorene-co-thiophene) modified TiO2 photocatalyst and visible light. In this mixed system, the removal efficiency in the presence of Cr(VI) and phenol were higher than that produced by individual systems, indicating a synergetic effect between the reduction of Cr(VI) and degradation of phenol. In the mixed system, Cr(VI) ions were reduced by the photo-generated electrons, and phenol was oxidized by photo-generated holes. In the presence of Cr(VI) ions, both the photocatalytic degradation and mineralization efficiency of phenol were promoted, but the promoting role was not the same. There was an optimum value of phenol/Cr(VI) molar ratio (1: 1) in the degradation process. If the ratio was less than 1 : 1, the promoting effect decreased slowly but was still fairly distinct. The mineralization efficiency of phenol increased gradually with the increasing concentration of Cr(VI) ions, but when phenol/Cr(VI) was less than 1 : 1, the rate of increase became slower.

Recent advances in rare-earth elements modification of inorganic semiconductor-based photocatalysts for efficient solar energy conversion: A review

This review focused on rare-earth elements containing inorganic semiconductor photocatalysts for efficient solar energy conversion. We also summarized the recent progress in the modification of the transition metal oxides and mixed oxides with rare earth ions. In the first section, we surveyed a variety of rare-earth elements modified TiO2 photocatalysts. Attributed to the modification with rare-earth elements, phase transformation of TiO2 from anatase to rutile was inhibited. Furthermore, the light-absorbing property of the TiO2 modified with rare-earth elements was also enhanced. In the second section, we summarized the effects of rare-earth elements on the modification of transition metal mixed oxides. It was believed that the corner-shared octahedral units in the form of networks, chains and slabs within the mixed oxide lattice were essential for the enhancement of the photocatalytic activity. In the last section, the strategy for the design of NIR or IR response upconversion composite photocatalysts was also discussed.

Octahedral rhenium K4[Re6S8(CN)6] and Cu(OH)2 cluster modified TiO2 for the photoreduction of CO2 under visible light irradiation

Octahedral hexacyano rhenium K4[Re6S8(CN)6] cluster complexes were grafted onto photoactive Cu(OH)2 cluster modified TiO2 {Cu(OH)2/TiO2} support. The rhenium and copper cluster modified TiO2 photocatalyst combines the advantages of heterogeneous catalyst (facile recovery, recycling ability of the catalyst) with the reactivity, selectivity of the soluble molecular catalyst. The synthesized heterogeneous catalyst was found to be highly efficient photoredox catalyst for the reduction of CO2 under visible light irradiation. Methanol was found to be the major liquid product with the formation of hydrogen as a by product as determined with GC-FID and GC-TCD, respectively. The methanol yield after 24h irradiation was found to be 149μmol/0.1g cat. for Re-cluster@Cu(OH)2/TiO2 photocatalyst that is much higher than 35μmol/0.1g cat. for Cu(OH)2/TiO2 and 75μmol/0.1g cat. for equimolar rhenium cluster in the presence of triethanolamine (TEOA) as a sacrificial donor. The quantum yields (ϕMeOH) of Re-cluster@Cu(OH)2/TiO2 and Cu(OH)2/TiO2 were found to be 0.018 and 0.004moleinstein−1, respectively. These values are much higher than those reported for other heterogeneous catalysts for six electron transfer reaction.

Cu(II) porphyrins modified TiO2 photocatalysts: Accumulated patterns of Cu(II) porphyrin molecules on the surface of TiO2 and influence on photocatalytic activity

The accumulated patterns of porphyrin molecules on the surface of TiO2 have an important effect on the photoactivity of porphyrin/TiO2 photocatalysts. Herein, two copper porphyrins containing flexible peripheral functional groups (meso-tetra(ester, carboxy)), Cu(II)5,10,15,20-tetrakis[4-(carboethoxymethyleneoxy)phenyl]porphyrin (CuPp(2a)) and Cu(II)5,10,15,20-tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin (CuPp(2b)), were synthesized and characterized spectroscopically. Their crystal structures were also determined by single crystal X-ray diffraction. The Cu(II) porphyrinTiO2 composites were also prepared and characterized. The accumulated patterns of synthesized copper porphyrins on the surface of TiO2 were proposed for the first time. The photoactivity of the composites was investigated by carrying out the degradation of 4-nitrophenol (4-NP) in aqueous solution under UV–visible light. The results indicated that the CuPp(2b)TiO2 showed the higher photocatalytic activity than that of CuPp(2a)TiO2. Above all, it can be concluded that the accumulated patterns of porphyrins on the surface of TiO2 is an important factor for the photocatalytic efficiency of porphyrin/TiO2.

금속물질로 개질된 광촉매를 이용한 톨루엔 광분해특성 연구

In photocatalysis, the addition of metal matter to TiO2 can alter the surface properties. As such, the metal can increase the rate of the photodegradation reaction. In this study, a range of modified TiO2 photocatalysts were prepared and tested to improve the activity of photodegradation at a batch-typed photoreactor. To obtain a good sol solution of the TiO2 photocatalyst, several types of dispersion agents and stabilizers were investigated. The photocatalyst solutions were modified with isoproply alcohol as the dispersion agent and sodium silicate as the stabilizer. The effects of various metallic elements on enhancing the photocatalytic activity of TiO2 on the degradation of toluene were examined. Palladium-added TiO2 was found to be the best, whereas copper or tungsten-added also showed good results. In the case of palladium addition, the increase in removal efficiency was 25%. On the other hand, Fe-added TiO2 showed a notable decrease in photocatalytic degradation. Additional doping of copper or tungsten on the Pd/TiO2 had no positive effect on the photodegradation activity.

Photocatalytic Degradation of Diisopropanolamine in Heterogeneous Photo-Fenton System

Photodegradation of 100 ppm diisopropanolamine (DIPA) was studied employing heterogeneous photo-Fenton system using iron modified TiO2 photocatalyst. A series of Fe/TiO2 photocatalysts were prepared via hydrolysis-hydrothermal and wet impregnation methods. Photocatalysts prepared using wet impregnation method was found to have similar activity under both UV and visible light. Addition of H2O2 during the photodegradation study obviously promoted the COD removal efficiency. When stoichiometric concentration of H2O2 was added, as high as 80% of COD was removed within 1.5 h reaction. Further modification is required to increase the photocatalyst performance in photodegradation of DIPA.

PCBM supported on titania used as an efficient photocatalyst under visible light

A [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-modified TiO2 photocatalyst was prepared by a simple facile chemisorption approach.

Engineering the TiO2 outermost layers using magnesium for carbon dioxide photoreduction

Magnesium modified TiO2 photocatalyst has been found to improve the CO2 photoreduction reaction, with a high selectivity towards CH4. Thus, Mg–TiO2 has been synthesized with different compositions up to 2.0wt%. Unlike the bare TiO2, the surface reorganization originated by the presence of Mg enhances the formation of methane by a factor of 4.5, corroborating that complete reduction of CO2 is achieved. It was found that the enhancement of the overall photocatalytic activity towards carbon dioxide reduction can be increased by a factor of 3, revealing a straightforward correlation with the surface states induced by the presence of the doping element. Finally, the evolution of the selectivity versus methane formation against hydrogen is discussed for the different magnesium loadings.

Quantum yield with platinum modified TiO2 photocatalyst for hydrogen production

The present study reports quantum yields for hydrogen production using a Pt modified titanium dioxide (DP25) photocatalyst in a slurry medium, under near-UV irradiation. The photocatalyst was prepared using the incipient wetness impregnation method. The modified photocatalyst exhibited a reduced energy band of 2.73eV upon Pt addition. Experiments were performed in a Photo CREC Water II Reactor. This unit allows the establishment of macroscopic radiation balances. These irradiation balances showed a maximum LVREA (local volumetric rate of energy absorption) of 0.15g/L. Regarding hydrogen formation via H radicals, the addition of a 2vol.% ethanol scavenger allowed achieving significant amounts of hydrogen free of oxygen. It was noticed that the rate of hydrogen formation in the presence of ethanol is a function of the pH of the water solution. It was also observed that the calculated 7.8% quantum efficiency showed good degree of photon utilization and confirmed the value of the Pt modified TiO2 photocatalyst and Photo CREC Water II Unit set up for hydrogen production, via water splitting.