Visible Light-induced Photocatalytic Activity Research Articles

Band gap engineered TiO2nanoparticles for visible light induced photoelectrochemical and photocatalytic studies

Visible light-active TiO2 (m-TiO2) nanoparticles were obtained by an electron beam treatment of commercial TiO2 (p-TiO2) nanoparticles. The m-TiO2 nanoparticles exhibited a distinct red-shift in the UV-visible absorption spectrum and a much narrower band gap (2.85 eV) due to defects as confirmed by diffuse reflectance spectroscopy (DRS), photoluminescence (PL), X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and linear scan voltammetry (LSV). The XPS revealed changes in the surface states, composition, Ti4+ to Ti3+ ratio, and oxygen deficiencies in the m-TiO2. The valence band XPS, DRS and PL results were carefully examined to understand the band gap reduction of m-TiO2. The visible light-responsive enhanced photocatalytic activity of m-TiO2 was demonstrated by degrading methylene blue and brilliant blue G. The EIS and LSV in the dark and under visible light irradiation further support the visible light-induced photocatalytic activities of the m-TiO2 due to a decrease in electron transfer resistance and an increase in photocurrent. This study confirms that m-TiO2 can be used effectively as a photocatalyst and photoelectrode material owing to its enhanced visible light-induced photocatalytic activity.

Facile synthesis of V(4+) self-doped, [010] oriented BiVO4 nanorods with highly efficient visible light-induced photocatalytic activity.

Monodispersed monoclinic BiVO4 nanorods grown along the [010] direction were prepared using a one-step low temperature hydrothermal method in the presence of the low-cost, nontoxic sodium oleate serving as a chelating agent. The BiVO4 nanorods with diameters of 15-20 nm possess a huge specific surface area as large as 28.2 m(2) g(-1), which can endow them with high photocatalytic activity and strong adsorption of reactants. Meanwhile, the specific [010] growth direction is capable of facilitating efficient electron-hole separation by accumulating electrons on {010} facets. Thus, the highly efficient photocatalytic activity of the as-prepared BiVO4 nanorods under visible light, which far surpasses that of commercial P25, is demonstrated by the degradation of rhodamine B and phenol. Plentiful V(4+) species, which can create oxygen vacancies, is detected implying that the as-obtained nanorods are self-doped BiVO4. Significantly, 61% of rhodamine B is adsorbed by the BiVO4 nanorods before irradiation owing to the appearance of plentiful O(2-) and OH(-) species on the surface adsorbed by oxygen vacancies. More excitingly, the excellent visible-light-driven photocatalytic activity of the as-obtained BiVO4 nanorods can be further elevated to an unprecedented level, roughly doubled, after applying a low temperature heat treatment process at 230 °C for 2 h and this improvement could primarily be ascribed to their optimized charge-carrier transport characteristics resulting from elevated crystallinity and decreased V(4+) species.

Preparation and visible light-induced photo-catalytic activity of H-PVA/TiO2 composite loaded on glass via sol–gel method

Sol–gel method was used to prepare polyvinyl alcohol/titanium dioxide (PVA/TiO2) composite films on glass slide, then the heat-treated polyvinyl alcohol/titanium dioxide (H-PVA/TiO2) composite loaded on glass and used as photo-catalyst was prepared by calcinating the precursor. Scanning electron microscopy (SEM), X-ray diffractionscopy (XRD), ultraviolet-visible diffuse reflection spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RAM) and fluorescence emission spectroscopy (FL) were used to characterize H-PVA/TiO2 composites. The visible light-induced photo-catalytic activities of the obtained composites prepared by different heat-treated temperature and different composition were examined through investigating the decolouration of rhodamine B (RhB) solution under visible light irradiation in the presence of the composites by means of UV–vis measurement. The results show that under the visible light irradiation, the H-PVA/TiO2 composite can make rhodamine B be degraded more efficiently than the PVA/TiO2 composite does, and the visible light photo-catalytic activity obviously depends on the heat-treated temperature and the composite composition. The 180°C of heat-treated temperature and the 16.7mass% of polymer content are beneficial for enhancing the efficiency of H-PVA/TiO2 of degrading RhB.

Visible light-induced photocatalytic activity of SiO2/carbon cluster composite materials

Abstract A convenient – and quick to realize – approach for the synthesis of a novel nano-sized SiO2/carbon cluster composite photocatalyst is suggested. Since, the preparation of visible light sensitive SiO2/carbon cluster composite photocatalyst is hitherto unreported; we performed such investigations to develop a novel catalyst from insulating materials. The synthesized composite indeed show efficient photocatalytic activity by degrading the methylene blue under visible light-irradiation.

Visible-light-induced photodegradation of gas phase acetonitrile using aerosol-made transition metal (V, Cr, Fe, Co, Mn, Mo, Ni, Cu, Y, Ce, and Zr) doped TiO2

A series of semiconductor photocatalysts based on transition metals (M′=V, Cr, Fe, Co, Mn, Mo, Ni, Cu, Y, Ce, and Zr) incorporated TiO2 (Ti/M′=20 atomic ratio) materials have been synthesized by adopting a one-step liquid flame aerosol synthesis technique. The resulting materials were explored for the destruction of acetonitrile in gas phase under visible light irradiation at ambient conditions. Our H2-TPR studies revealed the formation of MeOTi bonds, which suggest the strong interaction of dopant metal-TiO2 in all the as-synthesized materials. The reduction peaks in Cr-doped TiO2 shifted to much lower temperatures, due to the increase in the reduction potential of titania and chromium. The strong interaction (formation of CrOTi bonds) is the main reason that the Cr/TiO2 is an active photocatalyst in visible light. Our XPS studies suggest that the relative atomic percentage value of Ti3+/Ti4+ characterized by XPS was significantly high for our flame-made Cr/TiO2 nanoparticles (Ti3+/Ti4+=0.89, 32.9%), whereas, other samples demonstrated poor atomic percentage value of Ti3+/Ti4+ (Ti3+/Ti4+=0.08–0.32). The existence of Ti3+ species with narrow band gap is highly beneficial for the promotion of visible light-induced photocatalytic activity. The position of the Cr 2p peaks shifted to lower binding energies in Cr-doped TiO2 nanoparticles. The electrons migrate from the TiO2 nanoparticles to chromium species, which reveals a strong interaction between Cr and TiO2 nanostructure in the interface of flame-made nanoparticles. Conversely, Mn3+ species combined with TiO2 because its surface metal dispersion was kept high after TiO2 loading. However, Mn3+ incorporated catalyst was inactive because of the small energy driving force for electrons to detrap from Mn2+. The UV–vis spectroscopy results of M′-doped TiO2 (M′=Fe, Cr, V, Co, Ce, and Ni) materials showed augmentation of light absorption in the visible range. The Cr, V and Fe (Ti:M′ atomic ratio=20:1) titania aerosol catalysts reduced the bandgap energy of TiO2 to 2.9eV under visible light irradiation. Among all of the catalysts we tested, the transition metals (M′=Cr, Fe, and V) incorporated materials have shown an impressive catalytic performance in visible light. Among all the catalyst tested, Cr-doped titania demonstrated a superior catalytic performance and the rate constant is about 8–19 times higher than the rest of the metal doped catalysts. Their catalytic performances are correlated with the UV–vis spectrum of each synthesized catalyst to reveal the specific role played by each metal ion.

Novel Bi2O3/NaBi(MoO4)2 heterojunction with enhanced photocatalytic activity under visible light irradiation

A novel Bi2O3/NaBi(MoO4)2 composite photocatalyst with nanostructured heterojunctions was prepared via a simple supercritical method. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–vis diffuse reflectance spectroscopy (DRS). The visible light-induced photocatalytic activities were evaluated. The activity of the composite catalyst was 5 and 13 times as much as that of pure NaBi(MoO4)2 and commercial Bi2O3, respectively. The catalyst could be reused more than five times without obvious deactivation. The enhanced photocatalytic performance was attributed to electric-field-assisted charge transfer at the heterojunction interfaces between Bi2O3 and NaBi(MoO4)2 with matching band potentials, which consequently favored an effective photoexcited electron and hole separation.

Bismuth-modified rectorite with high visible light photocatalytic activity

Herein, we reported an ultrasonic-assisted synthesis of bismuth-modified rectorite with high visible light-induced photocatalytic activity. The as-synthesized samples were characterized by XRD, FT-IR, FESEM, TEM, BET, and UV–vis DRS techniques. Two toxic and nonbiodegradable organic compounds, Rhodamine B (RhB) and 2,4-dichlorophenol (DCP), were chosen as the target pollutants to characterize the adsorption performance and photocatalytic activity. The results showed that the prepared samples possessed strong adsorbility and exhibited high efficient photocatalytic activity under visible light irradiation. The excellent photocatalytic activity of bismuth-modified rectorite was ascribed to the strong adsorption ability, the interconnected heterojunction of Bi2O3 and Bi5O7NO3, and the produced OH. Finally, the possible mechanism was presented.

Fabrication and efficient visible light-induced photocatalytic activity of Bi2WO6/BiVO4 heterojunction

The Bi2WO6/BiVO4 photocatalyst with heterojunction structure was synthesized. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicated that Bi2WO6 nanoplate was loaded on the BiVO4 surface. UV–vis diffusion absorption spectra (DRS) displayed no obvious difference between the band gap absorption edges of the BiVO4 and Bi2WO6/BiVO4. It was found that the phenol degradation rate with Bi2WO6/BiVO4 was 2.55 times as great as that with the BiVO4 under visible light (λ > 400 nm) by the photocatalytic measurements. The enhanced photocatalytic performance of the Bi2WO6/BiVO4 sample was attributed to the improved separation efficiency of photogenerated hole–electron pairs generated by the heterojunction between Bi2WO6 and BiVO4.

One template approach to synthesize C-doped titania hollow spheres with high visible-light photocatalytic activity

Carbon-doped titania hollow spheres (THS) with unique hollow three-dimensional network structure were synthesized by a facile method using carbon spheres as template. The resultant samples, such as carbon spheres, carbon spheres coated with titania precursor, and final THS were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), Brunauer–Emmett–Teller (BET) and UV–vis absorption spectrum. Based on the results of these characterizations, a reasonable formation mechanism of the hollow three-dimensional network structure was proposed. The photocatalytic activity of as-prepared THS was evaluated by decoloration of methylene blue solution under visible light irradiation. Results indicated that THS possessed higher visible light-induced photocatalytic activity than commercial P25, which could be attributed to its visible light absorption characteristic created by C-doping and the unique hollow three-dimensional network structure.

Fabrication of carbon microspheres@PbMoO4 core–shell hybrid structures and its visible light-induced photocatalytic activity

PbMoO4-coated carbon microspheres ([email protected]4) were synthesized by a multistep method using CMSs as a support. In this synthesis dispersed CMSs were prepared by a hydrothermal method using glucose as a carbon source and used as an absorbent and support coated by PbMoO4 at room temperature. The as-prepared [email protected]4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The photocatalytic activity of the as-prepared sample was evaluated by degradation of Rhodamine B in aqueous solution under visible light irradiation. The [email protected]4 show effective photocatalytic activity. In addition, the photocatalytic mechanism of [email protected]4 was proposed.

Transformation of Indium Nanoparticles to β-Indium Sulfide: Digestive Ripening and Visible Light-Induced Photocatalytic Properties

We report the transformation of polydispersed dodecanethiol stabilized indium nanoparticles, obtained from bulk indium shot by evaporation/condensation solvated metal atom dispersion (SMAD) technique, into highly monodispersed partially alkyl thiolate-capped β-indiumsulfide (In(2)S(3)) by a postpreparative digestive ripening in high boiling point t-butyltoluene (190 °C) solvent. Upon digestive ripening, the as-prepared polydispersed black indium nanoparticles showed a characteristic color transition from black to cream, pale yellow, yellow, and finally to brown, indicating the transformation of the indium metal nanoparticles into intermediates composed of indium thiolates, sulfides, and polysulfides, and finally into the product In(2)S(3) nanoparticles whose surfaces are partially capped with thiolates. The transformed product (In(2)S(3)) was characterized with UV-vis, XRD, EDX, SEM, XPS, and TEM. From XRD and TEM measurements, the average size of the transformed In(2)S(3) nanoparticles is 5 nm. The optical absorbance of the as-prepared sample showed absorption peaks around 538 and 613 nm; upon digestive ripening these two peaks disappeared and stabilized at 375 nm, providing evidence of strong quantum confinement of excitons. The visible light-induced photocatalytic activity test with the In(2)S(3) nanoparticles showed that 95% of Rhodamine B (RhB) dye degraded after 100 min of irradiation with visible light.

Surface-Plasmon-Induced Visible Light Photocatalytic Activity of TiO2 Nanospheres Decorated by Au Nanoparticles with Controlled Configuration

This work is focused on the development of a surface plasmon-induced visible light active photocatalyst system composed of silica–titania core–shell (SiO2@TiO2) nanostructures decorated with Au nanoparticles (Au NPs). The influence of size and distribution of Au NPs on photocatalysis, its fabrication methods, and exploration of the mechanism of visible light activity were investigated. A favorable architecture of SiO2 beads with a thin layer of TiO2 was decorated with Au NP arrays having different size and areal density. Surface modification of SiO2@TiO2 leads to a viable and homogeneous loading of Au NPs on the surface of TiO2, which renders visible light-induced photocatalytic activity on the whole TiO2 surface. An optimized system employing Au NP arrays with 15 nm size and 700/μm2 density showed best catalytic efficiency due to a synergistic effect of the firm contact between Au NPs and TiO2 and efficiently coupled SPR excitation. A brief mechanism relating the electron transfer from surface-plasmon-st...

Efficient and Stable Photocatalytic Activity of CeVO<sub>4</sub>/TiO<sub>2</sub> Nanocrystalline Heterojunction under Visible Light Irradiation

A visible-light-driven CeVO4/TiO2 photocatalyst with nanostructured heterojunction has been successfully prepared by a simple coupled method. The catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and spin-trapping electron paramagnetic resonance (EPR). The visible light-induced photocatalytic activities were evaluated by decomposing benzene in gas phase. The result showed that the prepared catalyst exhibited efficient photocatalytic activities with high photochemical stability under visible light irradiation.

Solution combustion synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl 2O 4 nanopowders

Mixed amorphous and crystalline MgAl 2O 4 nanopowders with visible light-induced photocatalytic activity were prepared via a simple solution combustion method using glycine and urea as fuel mixtures. The obtained samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, Brunauer–Emmett–Teller (BET) surface area, thermogravimetry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV–Vis diffuse reflection spectrum. The results showed that the combustion was almost complete, the crystallinity and crystallite size of MgAl 2O 4 increased with the increase of fuels, and there was N atoms doped in the catalysts. The MgAl 2O 4 containing amorphism had photo-absorption ability in visible light region. The photocatalytic results for degradation of methylene blue (MB) indicated that the combustion-synthesized samples had photocatalytic activity, whereas the annealed well crystalline MgAl 2O 4 nanopowders had none. The MgAl 2O 4 sample containing about 45.6% crystalline and 55.4% amorphous materials showed the highest photocatalytic activity, with a 99.5% MB removal in 100 min under visible light irradiation. The fluorescence spectra verified that the greater the formation rate of OH radicals, the higher the photocatalytic activity achieved.

Investigating the antifungal activity of TiO2 nanoparticles deposited on branched carbon nanotube arrays

Branched carbon nanotube (CNT) arrays were synthesized by plasma-enhanced chemical vapour deposition on a silicon substrate. Ni was used as the catalyst and played an important role in the realization of branches in vertically aligned nanotubes. TiO2 nanoparticles on the branched CNTs were produced by atmospheric pressure chemical vapour deposition followed by a 500 °C annealing step. Transmission and scanning electron microscopic techniques were used to study the morphology of the TiO2/branched CNT structures while x-ray diffraction and Raman spectroscopy were used to verify the characteristics of the prepared nanostructures. Their antifungal effect on Candida albicans biofilms under visible light was investigated and compared with the activity of TiO2/CNT arrays and thin films of TiO2. The TiO2/branched CNTs showed a highly improved photocatalytic antifungal activity in comparison with the TiO2/CNTs and TiO2 film. The excellent visible light-induced photocatalytic antifungal activity of the TiO2/branched CNTs was attributed to the generation of electron–hole pairs by visible light excitation with a low recombination rate, in addition to the high surface area provided for the interaction between the cells and the nanostructures. Scanning electron microscopy was used to observe the resulting morphological changes in the cell body of the biofilms existing on the antifungal samples.

Preparation and modification of hierarchical nanostructuredBi2WO6 with high visible light-induced photocatalytic activity

Hierarchical nanostructured Bi2WO6 micro-clews were synthesized by a solvothermal process with mixed solvents and formaldehyde. The hierarchicalBi2WO6 micro-clews, with anaverage diameter of ca. 1.0 µm, consisted of nano-sheets assembled in a special fashion and the formation process mainlywent through an Ostwald ripening-anisotropic growth and self-assembling process. TheBi2WO6 micro-clews werefurther modified by Bi2O3 to fabricate heterojunction photocatalysts, whereBi2O3 nanoparticles were uniformly assembled on the surface ofBi2WO6 nano-sheets.Compared with pure Bi2WO6 and Bi2O3, the composite photocatalyst exhibits higher photocatalytic activity for the degradationof rhodamine B under visible light. On the basis of characterization by x-raydiffraction, photoluminescence and UV–vis diffuse reflectance spectroscopies, amechanism was proposed to account for the enhanced photocatalytic activity of theBi2O3/Bi2WO6 heterojunction.

Visible light-induced photocatalytic activity of Ag-containing TiO 2/carbon nanofibers composites

TiO 2/carbon nanofiber (CNF) composites containing Ag nanoparticles (Ag–TiO 2/CNF) were prepared and their photocatalytic degradation ability upon visible light irradiation assessed. The reduction of methylene blue (MB) adsorption in an aqueous solution by the photocatalysts occurred due to the combined effects of MB adsorption in the pores of CNFs and decomposition by the photocatalysts throughout the process. The Ag–TiO 2/CNF photocatalyst degraded MB 17 times faster than the TiO 2/CNF composites with no Ag nanoparticles after 3 h under visible light illuminations.

Synthesis, characterization and photocatalytic performance of VDyO x composite under visible light irradiation

A VDyO x (V 2O 5/DyVO 4) composite photocatalyst was prepared using a simple solution method. The powders were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Visible light-induced photocatalytic activities of the powders were evaluated by the degradation of acetone. Results generally show that the binary semiconductors V 2O 5/DyVO 4 with matching band potentials exhibit better photocatalytic properties compared with those of the single phase V 2O 5 or DyVO 4. An acetone conversion of 91.6% was achieved over V 1.5Dy 1O x composite photocatalyst under visible light irradiation. Effective electron–hole separation in the two semiconductors is believed to be mainly responsible for the increased photocatalytic performance of composites. The performance of the VDyO x composite catalyst can be further improved by loading a small amount of Pt. In addition, the Pt doped V 1.5Dy 1O x catalyst was also proven to be efficient in the photodegradation of 2-propanol and benzene.

Hydrothermal synthesis and highly visible light-induced photocatalytic activity of zinc-doped cadmium selenide photocatalysts

Novel Zn-doped CdSe photocatalysts were synthesized by a mild hydrothermal route. The as-prepared products were characterized by X-ray powder diffraction (XRD), UV–vis absorption spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis. The as-synthesized photocatalysts efficiently catalyzed the photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation, exhibiting higher photocatalytic activity than commercially available photocatalysts such as P25 and CdSe. The effects of the treatment temperature of the photocatalysts, the different zinc contents, the quantity of the photocatalysts, and the concentration of MB on photocatalytic performance were also investigated.

Photochemical synthesis and photocatalytic activity in simulated solar light of nanosized Ag doped TiO2 nanoparticle composite

We have investigated photochemical synthesis and visible light induced catalytic activity of nanosized silver (Ag) doped titania (TiO2). Synthesis of the composite was achieved by photochemical reduction of a mixture of P25 Degussa TiO2 and silver nitrate (AgNO3) solution under ultraviolet (UV) irradiation. Ag nanoparticles less than 3nm in diameters were well dispersed on the surface of TiO2. The resulting photocatalytic material was characterized by various analytical techniques and their photocatalytic activity was evaluated by decomposition of methylene blue (MB) dye solution under visible light irradiation. The composite nanoparticles exhibited enhanced visible light-induced photocatalytic activity compared to that of pure TiO2. The enhanced activity is attributed to simultaneous effects of nano-Ag deposits by increasing the absorption capacity in visible region and acting as electron trappers to promote charge separation of photoinduced electrons (e−) and holes (h+).