Enhanced visible light photocatalytic properties of Fe-doped TiO2 nanorod clusters and monodispersed nanoparticles

In order to get photocatalysts with desired morphologies and enhanced visible light responses, the Fe-doped TiO₂ nanorod clusters and monodispersed nanoparticles were prepared by modified hydrothermal and solvothermal method, respectively. The microstructures and morphologies of TiO₂ crystals can be controlled by restraining the hydrolytic reaction rates. The Fe-doped photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy (UV-vis), N₂ adsorption-desorption measurement (BET), and photoluminescence spectroscopy (PL). The refinements of the microstructures and morphologies result in the enhancement of the specific surface areas. The Fe³⁺-dopants in TiO₂ lattices not only lead to the significantly extending of the optical responses from UV to visible region but also diminish the recombination rates of the electrons and holes. The photocatalytic activities were evaluated by photocatalytic decomposition of formaldehyde in air under visible light illumination. Compared with P25 (TiO₂) and N-doped TiO₂ nanoparticles, the Fe-doped photocatalysts show high photocatalytic activities under visible light.     

Hydrothermal synthesis of well-dispersed ultrafine N-doped TiO2 nanoparticles with enhanced photocatalytic activity under visible light

Ultrafine nitrogen-doped TiO₂ nanoparticles with narrow particle size distribution, good dispersion, and high surface area were synthesized in the presence of urea and PEG-4000 via a hydrothermal procedure. TEM observation, N₂ adsorption, XRD, UV-vis spectroscopy, the Raman spectroscopy and XPS analysis were conducted to characterize the synthesized TiO₂ particles. The synthesized TiO₂ particles were a mixture of 49.5% anatase and 50.5% rutile with a size of around 5 nm. The photocatalytic activities were tested in the degradation of an aqueous solution of a reactive Brilliant Blue KN-R under both UV and visible light. The synthesized TiO₂ particles showed much higher photocatalytic activity than a commercial P25 TiO₂ powder under both UV and visible light irradiations. The high performance is associated to N doping, the reduced particle size, good dispersion, high surface area, and a quantum size effect.     

Sonodegradation and photodegradation of methyl orange by InVO4/TiO2 nanojunction composites under ultrasonic and visible light irradiation

The InVO₄/TiO₂ nanojunction composites with different weight ratio of 1:10, 1:25, 1:50 and 1:100 were successfully constructed using an ion impregnate method, followed by calcining temperature 400 °C for 2 h in Ar. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were evaluated through the degradation of methyl orange (MO) in aqueous solution under ultrasonic and visible light irradiation, respectively. The experimental results determined that the (1:50) InVO₄/TiO₂ nanojunction composite has exhibited the highest sonocatalytic activity. It can be ascribed to vectorial charge transfer at the co-excited InVO₄/TiO₂ interface under ultrasonic irradiation, results in the complete separation of electrons and holes. Interestingly, the (1:25) InVO₄/TiO₂ nanojunction composite displayed superior photocatalytic activity for MO degradation under visible light, indicating that InVO₄ as a narrow band gap sensitizer can expand photocatalytic activity of TiO₂ to visible region, and the charge transfer can be formed from high energy level of InVO₄ conduction band to the low energy level of TiO₂ conduction band in a present of excited InVO₄ alone under visible light irradiation. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were found to be dependent significantly on different InVO₄ contents, which can be explained by the influence of charge transfer on the basis of the work functions of different catalysis mechanism.     

Effect of hydrothermal temperature on photocatalytic properties of TiO2 nanotubes

This work presents a study on the effect of hydrothermal temperature and structure on the photocatalytic activity of TiO₂ nanotubes (TNT) prepared using commercially available TiO₂ nanoparticles (P25). From the results, it was found that a higher hydrothermal temperature led to an increase in the specific surface area, total pore volume, and the size of mesopores in TNT. Moreover, the TNTs synthesized by the hydrothermal method had a new structure, which was very different from the anatase and rutile structures found in P25. The TNTs synthesized at 150 °C had the highest specific surface area of 371 m²/g. However, the TNTs synthesized at 180 °C exhibited the best photocatalytic efficiency and dye adsorption capacity, as compared to other TNTs, resulting from their well-developed mesopores.     

Sonochemical and visible light induced photochemical and sonophotochemical degradation of dyes catalyzed by recoverable vanadium-containing polyphosphomolybdate immobilized on TiO2 nanoparticles

Na₅PV₂Mo₁₀O₄₀ supported on nanoporous anatase TiO₂ particles, TiO₂–PVMo, was used as an efficient photocatalyst for photocatalytic degradation of different dyes by visible light using oxygen as oxidant. This catalyst showed a good catalytic activity in the sonocatalytic and sonophotocatalytic decomposition of different dyes in aqueous solutions. The TiO₂–PVMo composite showed higher photocatalytic and sonocatalytic activity than pure polyoxometalate or pure TiO₂.     

Synthesis of TiO2/WO3 nanoparticles via sonochemical approach for the photocatalytic degradation of methylene blue under visible light illumination

Through an ultrasound assisted method, TiO₂/WO₃ nanoparticles were synthesized at room temperature. The XRD pattern of as-prepared TiO₂/WO₃ nanoparticles matches well with that of pure monoclinic WO₃ and rutile TiO₂ nanoparticles. TEM images show that the prepared TiO₂/WO₃ nanoparticles consist of mixed square and hexagonal shape particles about 8–12 nm in diameter. The photocatalytic activity of TiO₂/WO₃ nanoparticles was tested for the degradation of a wastewater containing methylene blue (MB) under visible light illumination. The TiO₂/WO₃ nanoparticles exhibits a higher degradation rate constant (6.72 × 10⁻⁴ s⁻¹) than bare TiO₂ nanoparticles (1.72 × 10⁻⁴ s⁻¹) under similar experimental conditions.     

Solid-phase photocatalytic degradation of polystyrene plastic with goethite modified by boron under UV-vis light irradiation

A novel photodegradable polyethylene-boron-goethite (PE-B-goethite) composite film was prepared by embedding the boron-doped goethite into the commercial polyethylene. The goethite catalyst was modified by boron in order to improve its photocatalytic efficiency under the ultraviolet and visible light irradiation. Solid-phase photocatalytic degradation of the PE-B-goethite composite film was carried out in an ambient air at room temperature under ultraviolet and visible light irradiation. The properties of composite films were compared with those of the pure PE films and the PE-goethite composite films through performing weight loss monitoring, scanning electron microscope (SEM) analysis, FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The photo-induced degradation of PE-B-goethite composite films was higher than that of the pure PE films and the PE-goethite composite films under the UV-irradiation, while there has been little change under the visible light irradiation. The weight loss of the PE-B-goethite (0.4 wt.%) composite film reached 12.6% under the UV-irradiation for 300 h. The photocatalytic degradation mechanism of the composite films was briefly discussed.     

Influence of MoS2 deposition time on the photocatalytic activity of MoS2/ V,N co-doped TiO2 heterostructure thin film in the visible light region

Electron-hole separation and a narrow band-gap are essential steps to obtain efficient photocatalysis, towards which the use of co-catalysts or co-doped-TiO₂ photocatalysts has become a widely used strategy. In this article, the combination of MoS₂ and co-doping of V, N is the goal to achieve high performance photocatalysts. We synthesized MoS₂/V, N co-doped TiO₂ heterostructure thin film by sol-gel and chemical bath deposition methods. Herein, we investigated the influence of deposition time of MoS₂ layer on visible-photocatalytic activity of the obtained samples. The thin films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy techniques. Visible-photocatalytic activity of these samples were evaluated on the removal of methylene blue (MB) under visible light irradiation. The results show that the aforementioned heterostructure thin films have better photocatalytic activities than those of TiO₂, MoS₂ and V, N co-doped TiO₂ counterparts in visible light region. The mechanism for increasing visible-photocatalytic property of the heterostructure thin films is discussed in detail. We find that MoS₂/V, N co-doped TiO₂ heterostructure thin film at MoS₂ deposition time of 45-min shows the highest photocatalytic performance in the visible light region with MB photodegradation rate about 99% for 150 min and the degradation rate constant is 2.06 times higher than that of V and N co-doped TiO₂ counterpart.     

Photocatalytic degradation of dyes using dioxygen activated by supported metallophthalocyanine under visible light irradiation

Zinc tetraaminophthalocyanine (Zn-TAPc) modified by cyanuric chloride was immobilized on silk fibers by covalent bond to obtain a supported photocatalyst (Zn-TDTAPc-SF). The photocatalytic degradation of acid orange II based on Zn-TDTAPc-SF/O₂ system was investigated under visible light irradiation (λ ≥ 400 nm). The results indicated that Zn-TDTAPc-SF exhibited excellent photocatalytic performance in the presence of O₂ under visible light irradiation. In 6 h, more than 93% of acid orange II (AO2) in Zn-TDTAPc-SF/O₂ system was eliminated at initial pH 5 under visible light irradiation, and Zn-TDTAPc-SF still remained effective in repetitive fives cycles. Furthermore, NaCl played a positive role in the catalytic reaction, different from the negative one observed in homogeneous catalysis, and the reaction can proceed in a more wide pH range from acidic to alkaline. Based on the analysis of FT-IR and Gas Chromatography/Mass Spectrometry (GC–MS), AO2 was mainly converted into some small molecular biodegradable aliphatic carboxylic compounds such as maleic acid, fumaric acid, succinic acid, etc. The photodegradation mechanism for the evolution of AO2 was proposed by Electron Paramagnetic Resonance (EPR) spectra.     

Effect of multi-walled carbon nanotubes loaded with Ag nanoparticles on the photocatalytic degradation of rhodamine B under visible light irradiation

Multi-walled carbon nanotubes loaded with Ag nanoparticles (Ag/MWNTs) were prepared by two methods (direct photoreduction and thermal decomposition). The photocatalytic activity of Ag/MWNTs for the degradation of rhodamine B (RhB) under visible light irradiation was investigated in detail. The adsorption and photocatalytic activity tests indicated that the MWNTs served as both an adsorbent and a visible light photocatalyst. The photocatalytic activity of MWNTs was remarkably enhanced when the Ag nanoparticles were loaded on the surface of MWNTs. Moreover, the visible light photocatalytic activity of Ag/MWNTs depended on the synthetic route. On the basis of the experimental results, a possible visible light photocatalytic degradation mechanism was discussed.     

Microemulsion synthesis, characterization of bismuth oxyiodine/titanium dioxide hybrid nanoparticles with outstanding photocatalytic performance under visible light irradiation

Reverse microemulsions, consisting of n-hexanol, Triton X-100, Cyclohexane and aqueous salt solutions, were used to synthesize BiOI, TiO₂ and BiOI/TiO₂ hybrid nanoparticles at room temperature. The particles had been characterized by X-ray powder diffraction, FT-IR spectra, TG-DSC analysis, nitrogen sorption, electron microscopy, and UV-vis diffuse reflectance spectroscopy. The photocatalytic properties of those particles were evaluated by degradation of methyl orange under visible light irradiation. The BiOI/TiO₂ composites showed about 5 times higher photocatalytic performances than BiOI when the mole ratio of BiOI to TiO₂ was 75%. The remarkable enhancement in the visible light photocatalytic activities of the BiOI/TiO₂ heterostructures could be first attributed to the effective electron-hole separations at the interfaces of the two semiconductors, which facilitated the transfer of the photoinduced carriers. Meanwhile, the heterojunction formed between BiOI and TiO₂ would further retard the recombination of photoinduced carriers. In addition, high degree of crystallization, bimodal porous structure, relative large specific surface area, and appropriate energy band gap have great contribution to the enhancement of photocatalytic performance.     

Rapid microwave-assisted synthesis of phase controlled BiVO<Subscript>4</Subscript> nanocrystals and research on photocatalytic properties under visible light irradiation

Pure tetragonal and monoclinic phases BiVO₄ were prepared from aqueous Bi (NO₃)₃ and NaVO₃ solutions by a rapid microwave-assisted method that employed accurate controlling of microwave irradiation time and power. The highly crystalline phase converted irreversibly from tetragonal to monoclinic BiVO₄ with gradually elongated irradiation time gradually, which is further proved by X-ray diffraction, UV–vis and Raman measurements. These variations of phase structures led to different photocatalytic properties under visible light.     

A novel Ce, C-codoped TiO2 nanoparticles and its photocatalytic activity under visible light

A novel photocatalyst (Ce, C-codoped titania) was synthesized through a modified sol-gel method under mild condition. The as-prepared sample was investigated by XRD, SEM, DRS and XPS. It was found that the as-prepared photocatalyst was composed of spheroidal particles, which were smaller than undoped ones. The absorbance spectrum of Ce, C-codoped TiO₂ exhibited significant red-shift to visible region. It can be ascribed to appearance of a new electronic state in the middle of the TiO₂ band-gap. Furthermore, cerium doping could slow the radiative recombination process of photogenerated electrons and holes in TiO₂. Accordingly, for degradation of dye Reactive Brillint Red X-3B (C.I. reactive red 2) under visible light, the photocatalytic activity of Ce, C-codoped TiO₂ improved much compared to other samples (C-doped TiO₂, undoped TiO₂ and P25).     

Effects of NiTiO3 nanoparticles supported by mesoporous MCM-41 on photoreduction of methylene blue under UV and visible light irradiation

In this work, we report the synthesis of nickel titanate nanoparticles loaded on nanomesoporous MCM-41 nanoparticles to determine the effect of MCM-41 nanoparticles on the photocatalytic activities of nickel titanate (NiTiO₃) nanoparticles by using simple solid-state dispersion (SSD) method. Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis diffuse reflectance spectra (DRS) analysis were used to characterize the size and morphology of the obtained nanocomposite. The photocatalytic activity (PA) of the as-prepared NiTiO₃ loaded on MCM-41 was evaluated by degradation of the methylene blue under irradiation of UV and visible light. The results showed that NiTiO₃ loaded on nanosize MCM-41 has higher photocatalytic activity than that of NiTiO₃ nanoparticles.     

Enhancement of photocatalytic degradation of polyethylene plastic with CuPc modified TiO2 photocatalyst under solar light irradiation

Solid-phase photocatalytic degradation of polyethylene (PE) plastic, one of the most common commercial plastic, over copper phthalocyanine (CuPc) modified TiO₂ (TiO₂/CuPc) photocatalyst was investigated in the ambient air under solar light irradiation. Higher PE weight loss rate, greater texture change; more amount of generated CO₂, which is the main product of the photocatalytic degradation of the composite PEC plastic can be achieved in the system of PE-(TiO₂/CuPc) in comparison with PE-TiO₂ system. The CuPc promoted charge separation of TiO₂ and enhanced the photocatalytic degradation of PE based on the analysis of surface photovoltage spectroscopy (SPS). During the photodegradation of PE plastic, the reactive oxygen species generated on TiO₂ or TiO₂/CuPc particle surfaces play important roles. The present study demonstrates that the combination of polymer plastic with TiO₂/CuPc composite photocatalyst in the form of thin film is a practical and useful way to photodegrade plastic contaminants under solar light irradiation.     

Enhanced photocatalytic performance of ultrasound treated GO/TiO2 composite for photocatalytic degradation of salicylic acid under sunlight illumination

The current research work deals with the preparation of TiO₂ and GO/TiO₂ composite by simple, chemical, cost effective hydrothermal method. Graphene oxide (GO) is prepared by modified Hummer’s method. Dispersion of GO is achieved by an ultrasonic cleaning bath for 1 h. using a power of 200 W and at a frequency of 40 kHz. The prepared catalyst material is characterized by different characterization techniques. XRD study confirms the prepared material is polycrystalline in nature. The synthesized TiO₂ and GO/TiO₂ photocatalyst materials are used to study the photocatalytic degradation of salicylic acid under sunlight illumination. GO/TiO₂ composite shows superior photocatalytic activity than TiO₂. GO/TiO₂ composite shows 57% degradation of salicylic acid. Mineralization of salicylic acid is studied using chemical oxygen demand.     

Synthesis and photochemical properties of HTaWO6/ (Pt,TiO2) nanocomposite under visible light irradiation

A new layered nanocomposite, HTaWO₆/(Pt, TiO₂) was synthesized using n-type semi-conductor HTaWO₆ as a host material. HTaWO₆ and HTaWO₆/TiO₂were white, while both HTaWO₆/Pt and HTaWO₆/(Pt, TiO₂) were yellow. The yellow color might be attributed to H_1-xTaWO_6-x/2 formed by the photo-induced phase transformation promoted by Pt. Although HTaWO₆/Pt showed absorption in visible light region (λ > 400 nm), the hydrogen evolution activity was negligibly small. On the other hand HTaWO₆/(Pt, TiO₂) showed excellent photocatalytic activities even under visible light irradiation. The sample containing rutile type titania such as TiO₂(P-25) also showed hydrogen evolution activity, but the activity was smaller than that of HTaWO₆/(Pt, TiO₂). These results suggested that rutile type titania, which can be excited by visible light of wavelength less than 413 nm, played an important role in the visible light-induced photocatalytic activity. The improvement of the hydrogen evolution activity of rutile type titania by intercalating into HTaWO₆/Pt may be due to the depression of the recombination of photoinduced electrons and holes by the heterogeneous electron transfer from rutile type TiO₂ to HTaWO₆/Pt.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Carbon-nanodot-coverage-dependent photocatalytic performance of carbon nanodot/TiO_2 nanocomposites under visible light

Carbon nanodots(CDs) with visible absorption band and TiO_2 are integrated to enhance the photosensitivity of TiO_2.The CD/TiO_2 nanocomposites show obvious CD-coverage-dependent photocatalytic performance. The CD/TiO_2 nanocomposites with moderate CD coverge exhibit the highest photocatalytic activity after being irradiated with visible light, which is more excellent than that of TiO_2. Too little CD coverage could result in poor visible light absorption, which limits the photocatalytic performance of CD/TiO_2 nanocomposites. While, too much CD coverage weakens the photocatalytic activity of CD/TiO_2 nanocomposites by restraining the extraction of conduction band electrons within TiO_2 to generate active oxygen radicals and the electron transfer(ET) process from CDs to TiO_2. These results indicate that rational regulation of CD coverage and the realization of efficient ET process are important means to optimize the photocatalytic performance of CD/TiO_2 nanocomposites.