UV Vis Diffuse Reflectance Absorption Spectra Research Articles

The synthesis, structures and characterizations of (C5H12NO)4Cd3Cl10·2H2O and (C5H12NO)2BiCl6·H5O2 crystals

Two new organic-inorganic hybrid crystals (C5H12NO)4Cd3Cl10·2H2O and (C5H12NO)2BiCl6·H5O2 were synthesized by solution method, and their basic physical properties, including structures, thermal stability analysis, UV–Vis diffuse reflectance absorption spectra and photoluminescent characteristic were characterized. The two crystals both crystallize in same monoclinic crystal system, but different P21/c and C2/c space group for (C5H12NO)4Cd3Cl10·2H2O and (C5H12NO)2BiCl6·H5O2, respectively. Their infrared, Raman and mass spectrometry were measured, with related characteristic peaks were identified. The Raman peaks at 249 and 88 cm−1 are ascribed to Cd-Cl stretching vibration and Cl-Cd-Cl deformation vibration, respectively. The mass spectra analysis confirm the existence of C5H12NO+ cation, [CdCl]+ and Na-(C5H12NO)2BiCl6·H4O2. A phase transition peak that respectively located at 378 and 403 K for (C5H12NO)4Cd3Cl10·2H2O and (C5H12NO)2BiCl6·H5O2 was detected by the synchronous thermal analysis, which is related with the loss of crystalline water in their structures. In addition, the maximum absorption peak at 230 and 240 nm, with corresponding band gap of 3.35 and 3.15 eV were fitted for (C5H12NO)4Cd3Cl10·2H2O and (C5H12NO)2BiCl6·H5O2, respectively. Furthermore, (C5H12NO)4Cd3Cl10·2H2O features a bluish white emission with the peak centering at 496 nm when it was excited at 380 nm by a Xenon lamp. This work extends the catalog of organic-inorganic hybrid metal halides and presents the potential application of (C5H12NO)4Cd3Cl10·2H2O in optical field.

A highly efficient In2S3/Ag2S/TiO2 NTAs photoelectrodes for photocathodic protection of Q235 carbon steel under visible light

A novel In2S3/Ag2S/TiO2 nanotube arrays (NTAs) was successfully fabricated by successive ionic layer adsorption and reaction method and electrochemical anodic oxidation method, and served as photoanode for photocathodic protection application. The micromorphologies, optical absorption properties, crystalline structure and elemental valence states of the composites were performed by field emission scanning electron microscopy, high resolution transmission electron microscope, UV–vis diffuse reflectance absorption spectra, x-ray diffractometer and x-ray photoelectron spectroscopy, respectively. The photocathodic protection performances of In2S3/Ag2S/TiO2 NTAs on the Q235 carbon steel (CS) were also studied. The In2S3/Ag2S/TiO2 nanocomposites show better photoelectrocatalytic and photocathodic protection performance than pure TiO2 NTAs. The photocurrent density of In2S3(9)/Ag2S(8)/TiO2 photoelectrode coupled with Q235 CS reach 211 μA cm−2, which is about 4.5 times higher than that of TiO2 NTAs. The photogenerated potential of Q235 CS coupled to In2S3(9)/Ag2S(8)/TiO2 under illumination shows a negative shift to −0.92 V versus SCE. Results indicate that the co-sensitization of In2S3 and Ag2S could extend the light absorption of TiO2 to the visible light range and enhance its photoelectric conversion efficiency.

Synthesis, structural and electrical conduction of some dual doped semiconductor oxides nanoparticles for photocatalytic degradation of Victoria blue-B and Brilliant yellow under solar light irradiation

In this study, the nanoparticles of undoped and dual (codoped) doped semiconductor oxides such as Bi2O3, Bi1.9Sm0.038Cu0.062O3; Co3O4, Co2.902Mn0.049Dy0.049O4; V2O5, V1.91Ni0.043Gd0.047O5; Cu2O, Cu1.927Mn0.036Yb0.037O; CeO2, and Ce0.938Ni0.028Zn0.034O2 were synthesized by tartarate and hydroxide coprecipitation method. The composition, structure, morphology, surface and optical properties of undoped and dual doped semiconductor oxides have been investigated by X-ray fluorescence spectroscopy (XRF), Energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analyzer and UV–Vis diffuse reflectance absorption spectra (UV–vis DRS). The XRD and SEM studies showcase monodispersion of undoped and dual (co-doped) doped semiconductor oxides in the average grain size range of 36–65 nm with a monoclinic structure for Bi2O3 and its doped oxide, cubic structure for Co3O4, Cu2O, CeO2 and their respective doped oxides and orthorhombic structure for V2O5 and its doped oxide. Rietveld refinements of XRD pattern and XPS results confirmed that the dual dopants exist in + 2 or + 3 states and successfully incorporated into the semiconductor oxide matrix. BET surface areas for these oxides were found in the range of 25.3–65.4 m2g−1. The band gap energy (Eg) of undoped and doped semiconductor had a direct transition to fall between 2.10 and 3.12 eV as estimated from the optical absorption data (UV–vis DRS) and found absorption band edge (λg) in the visible-light range. The d.c. electrical conductivity and thermo-electric power measurements for all compounds showed n-type semiconductor except undoped and doped Cu2O and Co3O4 compounds showed p-type semiconductivity. The photo catalytic activity of undoped and dual doped semiconductor oxides in the Victoria blue-B (VB) and Brilliant yellow (BY) solutions were studied in sunlight irradiation. A set of optimized conditions such as the amount of these oxides, initial dye concentration, pH, contact time and dopants on the photodegradation of these dyes were investigated in detail. The dual doped semiconductor oxides showed a noteworthy enhancement in the degradation of VB and BY dyes under exposure to sunlight. The enhanced photocatalytic activity can be attributed to the incorporation of multivalent dopants in semiconductor oxide matrix promoted the separation of photogenerated charges, inhibited the recombination of photogenerated carriers, and thus prolonged the charges lifetime to participate in the photocatalytic reaction. The kinetic measurements indicate the dominance of pseudo-first order rate constant for Victoria blue-B (VB) were higher than that of Brilliant yellow (BY) in all cases, indicating that the photocatalytic degradation of VB was easier and more rapid than BY dye during the adsorption and also ascribed to different molecular structure to these dyes. A tentative reaction mechanism has also been proposed for this photocatalytic reaction.

Fabrication, characterization and photoelectrochemical properties of CdS/CdSe nanofilm co-sensitized ZnO nanorod arrays on Zn foil substrate

The photoelectrochemical (PEC) performance of ZnO is restricted by its low light absorption ability and high recombination rate of photogenerated carriers. In order to overcome these drawbacks, ZnO/CdS/CdSe heterostructures are prepared on Zn foil substrate using facile three-step methods containing hydrothermal growth, successive ionic layer adsorption reaction (SILAR) and modified chemical bath deposition (CBD). The effects of process parameters containing the number of SILAR cycles of CdS, sensitization sequence of CdS and CdSe, and precursors of CdSe on PEC performance of ZnO/CdS/CdSe heterostructures, and ZnO NRAs on PEC performance of CdS/CdSe co-sensitizer have been scrutinized. Through CdS and CdSe co-sensitization, a layer of CdS/CdSe nanofilm is conformally deposited on ZnO nanorod arrays (NRAs) observed by transmission electron microscopy (TEM). Both the visible-light absorption ability and separation efficiency of photogenerated carriers of ZnO NRAs are significantly enhanced evidenced by UV–vis diffuse reflectance absorption spectra, photoluminescence (PL) spectra and electrochemical impedance spectra. Due to the synergistic effect of ZnO NRAs and CdS/CdSe co-sensitizer, the ZnO/CdS/CdSe heterostructures with five SILAR cycles and one modified CBD cycle (ZnO-CdS5-CdSe) show efficient PEC properties with photocurrent density of 6.244 mA/cm2 at −0.2 V vs Ag/AgCl under light illumination of 100 mW/cm2, which are 57.28 and 4.73 times higher than those of pristine ZnO NRAs and CdS/CdSe clusters, respectively. Moreover, the photoconversion efficiency and incident photon to current conversion efficiency (IPCE) of the ZnO-CdS5-CdSe photoanode reach 4.381% and 80.92%, respectively. The heterostructures based on Zn foil substrate in this study can be a promising candidate for practical PEC application and other applications such as photocatalytic degradation and solar cell due to its low manufacturing cost, large-scale production and efficient PEC ability.

Photodegradation of benzothiazole ionic liquids catalyzed by titanium dioxide and silver-loaded titanium dioxide

Abstract In recent years, ionic liquids (ILs) have been widely used in extraction, synthesis, electrochemistry and other fields. Meanwhile, the environmental impact of ILs has been attracting a lot of attention, and eco-friendly treatment for ILs is becoming a necessary subject. In this study, photocatalytic degradations of benzothiazole ILs catalyzed by titanium dioxide (TiO2) and silver-loaded titanium dioxide (Ag/TiO2) were studied for the first time. The degradation of benzothiazole hexafluorophosphate ([C4Bth]PF6) could reach more than 99% within 240 min with the catalysis of TiO2. To improve catalytic efficiency, Ag/TiO2 was synthesized and characterized by UV–Vis diffuse reflectance absorption spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The degradation of [C4Bth]PF6 could reach more than 99% within 120 min in the degradation catalyzed by Ag/TiO2. The photodegradation products of benzothiazole ILs are composed of inorganic substances or organic substances with simpler structures, which are easier to decompose and less toxic. The degradation system proposed by this study could provide a simple, green, safe, and economical method for the efficient treatment of benzothiazole ILs.

Template-free preparation of TiO2 microspheres for the photocatalytic degradation of organic dyes

TiO2 microspheres were successfully synthesised by simple solution phase method by using various amount of titanium butoxide as precursor. The prepared TiO2 were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance absorption spectra (UV-DRS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD analysis revealed that the as-synthesized TiO2 microsphere poses an anatase phase. The photocatalytic degradation experiments were carried out with three different dyes, such as methylene blue, brilliant black, reactive red-120 for four hours under UV light irradiation. The results show that TiO2 morphology had great influence on photocatalytic degradation of organic dyes. The experimental results of dye mineralization indicated the concentration was reduced by a high portion of up to 99% within 4 hours. On the basis of various characterization of the photocatalysts, the reactions involved to explain the photocatalytic activity enhancement due to the concentration of titanium butoxide and morphology include a better separation of photogenerated charge carriers and improved oxygen reduction inducing a higher extent of degradation of aromatics.

Synthesis and characterization of Zn/ZnO microspheres on indented sites of silicon substrate

Abstract Self-assembled Zn/ZnO microspheres have been accomplished on selected sites of boron doped P-type silicon substrates using hydrothermal approach. The high density Zn/ZnO microspheres were grown on the Si substrates by chemical treatment in mixed solution of zinc sulfate ZnSO4·7H2O and ammonium hydroxide NH4(OH) after uniform heating at 95 °C for 15 min. The Zn/ZnO microspheres had dimensions in the range of 1 μm to 20 μm and were created only on selected sites of silicon substrate. The crystal structure, chemical composition and morphology of as-prepared samples were studied by using scanning electron microscope SEM, X-ray diffraction XRD, energy dispersive X-ray spectroscopy EDS, Fourier transform infrared spectroscopy FT-IR and UV-Vis diffuse reflectance absorption spectra DRS. The energy band gap Eg of about 3.28 eV was obtained using Tauc plot. In summary, this study suggests that interfacial chemistry is responsible for the crystal growth on indented sites of silicon substrate and the hydrothermal based growth mechanism is proposed as a useful methodology for the formation of highly crystalline three dimensional (3-D) Zn/ZnO microspheres.

Remarkably enhanced photocatalytic hydrogen evolution over MoS2 nanosheets loaded on uniform CdS nanospheres

The MoS2/CdS composites with layered MoS2 loaded on uniform CdS nanospheres were synthesized by a two-step process combination hydrothermal and solvothermal treatments, and then applied in photocatalytic hydrogen evolution under visible light irradiation. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, UV–vis diffuse reflectance absorption spectra (UV-DRS), nitrogen adsorption-desorption measurement, photoluminescence spectra (PL) and photoelectrochemical tests. The effects of loading contents of MoS2 in the composites on the photocatalytic H2 evolution activity were comparatively investigated with 0.45molL−1 Na2S and 0.55molL−1 Na2SO3 as sacrificial agents. The results showed that the 5wt% MoS2/CdS composite could achieve the highest photocatalytic H2 evolution rate of 372μmolh−1 and apparent quantum efficiency (AQE) about 7.31% under 420nm monochromatic light irradiation. The remarkably enhanced photocatalytic activity of MoS2/CdS composite could be attributed to the effective transfer and separation of photogenerated charge carriers, and MoS2 being as a cocatalyst to facilitating photocatalytic H2 evolution reaction. A tentative mechanism of MoS2/CdS composites as photocatalysts for H2 evolution was proposed.

In situconstruction of BiOBr/Ag3PO4composites with enhanced visible light photocatalytic performances

Abstract

Synthesis of porous carbon-doped g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

The porous carbon-doped g-C3N4 nanosheets photocatalysts (NSs-APAM) were synthesized using anionic polyacrylamide (APAM) as the intercalator and carbon source via the thermal treatment method. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance absorption spectra (UV-DRS) and photoluminescence spectroscopy (PL). The results indicate that the APAM can effectively induce the formation of high-quality nanosheets (NSs) with narrowed bandgap. The specific surface area of NSs-APAM is 118.6m2/g, which is 5-fold larger than bulk g-C3N4. The carbon doping could narrow the bandgap, from 2.75eV of g-C3N4 NSs without carbon doping (NSs-Water) to 2.41eV of NSs-APAM. The two-dimensional NSs structure facilitates the charge separation by shortening the diffusion distance to the surface of photocatalysts. The synergic effects of the carbon doping and unique structural properties contributed to the superior photocatalytic activity of NSs-APAM with 95% degradation rate towards X–3B after 30min visible-light irradiation.

Facile Synthesis of Fluorine Doped Graphitic Carbon Nitride with Enhanced Visible Light Photocatalytic Activity

Fluorine doped graphitic carbon nitride (g-C3N4) was successfully synthesized by a convenient co-polycondensation of urea and ammonium fluoride (NH4F) mixtures, and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), UV-Vis diffuse reflectance absorption spectra (UV-DRS), nitrogen adsorption–desorption, photoelectrochemical measurement and photoluminescence (PL) spectra. The photocatalytic activities of fluorine doped g-C3N4 samples were evaluated by the degradation of Rhodamine B (RhB) solution under visible light irradiation. The results showed that the fluorine doped g-C3N4 had a better photocatalytic activity than that of undoped g-C3N4, which was attributed to the favorable textural, optical and electronic properties derived from the fluorine atoms substituting nitrogen atoms of g-C3N4 frameworks. The photoelectrochemical measurements confirmed that the charges separation efficiency was improved by fluorine doping g-C3N4. Moreover, the tests of radical scavengers demonstrated that the holes (h[Formula: see text]) and superoxide radicals ([Formula: see text]O[Formula: see text]) were the main active species for the degradation of RhB.

Fabrication of Cd0·5Zn0·5S nanoparticles decorated TiO2 nanotube arrays electrode and its enhanced photoelectrocatalytic performance

Cd0·5Zn0·5S nanoparticles modified TiO2 nanotube arrays composite electrodes (Cd0·5Zn0·5S/TiO2 NTAs) were successfully synthesized by the combination of electrochemical oxidation and hydrothermal process under various thiourea concentrations. The as-prepared electrodes were systematically characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance absorption spectra techniques. The influence of thiourea concentrations on the morphology structure, photoelectrochemical properties, and hydrogen production of Cd0·5Zn0·5S/TiO2 NTAs electrodes was systematically investigated. The Cd0·5Zn0·5S/TiO2 NTAs electrode fabricated at 8 mM thiourea concentration exhibits the highest hydrogen production rate of 523.1 μmol/(h∙cm2) and the maximum photocurrent density of 26.73 mA/cm2 under visible light illumination. The corresponding apparent quantum efficiency (QE) and visible-photoconversion efficiency are 55.2% and 11.97%, respectively. Electrochemical impedance spectroscopy (EIS) analysis of Cd0·5Zn0·5S/TiO2 NTAs electrode further demonstrates the enhanced photoelectrochemical performance, which can be attributed to the favorable microstructure and enhanced charge transfer.

Enhanced visible light photocatalytic degradation of Rhodamine B over phosphorus doped graphitic carbon nitride

Phosphorus doped graphitic carbon nitride (g-C3N4) was easily synthesized using ammonium hexafluorophosphate (NH4PF6) as phosphorus source, and ammonium thiocyanate (NH4SCN) as g-C3N4 precursor, through a direct thermal co-polycondensation procedure. The obtained phosphorus doped g-C3N4 was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), UV–vis diffuse reflectance absorption spectra (UV-DRS), photoelectrochemical measurement and photoluminescence spectra (PL). The photocatalytic activities of phosphorus doped g-C3N4 samples were evaluated by degradation of Rhodamine B (RhB) solution under visible light irradiation. The results showed that the phosphorus doped g-C3N4 had a superior photocatalytic activity than that of pristine g-C3N4, attributing to the phosphorus atoms substituting carbon atoms of g-C3N4 frameworks to result in light harvesting enhancement and delocalized π-conjugated system of this copolymer, beneficial for the increase of photocatalytic performance. The photoelectrochemical measurements also verified that the charge carrier separation efficiency was promoted by phosphorus doping g-C3N4. Moreover, the tests of radical scavengers demonstrated that the holes (h+) and superoxide radicals (O2−) were the main active species for the degradation of RhB.

Enhanced photocatalytic activity of anatase-TiO2 nanoparticles by fullerene modification: A theoretical and experimental study

A series of fullerene (C60)-modified anatase TiO2 (a-TiO2) nanocomposites with different weight loadings of C60 were successfully synthesized by a simple solution phase method. The as-prepared C60@a-TiO2 nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET), UV–vis diffuse reflectance absorption spectra (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The photocatalytic degradation of methylene blue (MB) by the neat a-TiO2 and C60@a-TiO2 nanocomposites was investigated under UV-A light irradiation, demonstrating that C60 effectively enhances the photocatalytic activity of a-TiO2 nanoparticles with an optimal amount of 2.0wt%. By combining with the density functional theory (DFT) calculations, we investigated the electronic structures of C60@a-TiO2 hetero-interfaces to reveal the underlying principle of the C60 loading on the photocatalytic activity. It was found that the incorporation of C60 on the a-TiO2 surface not only narrowed the band gap, but also introduced an additional doping state between the valance and conduction band. Therefore, the presence of intermediate electronic state will in turn contribute to the efficient charge separation and enhanced light adsorption for the C60@a-TiO2 nanocomposites, resulting in an improved photocatalytic performance.

Sonochemical Synthesis of CdS/C3N4 Composites with Efficient Photocatalytic Performance Under Visible Light Irradiation.

The CdS/C3N4 composites with efficient photocatalytic performance under visible light irradiation were synthesized by a facile sonochemical route. The as-prepared CdS/C3N4 composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution trans- mission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), fourier transform infrared spectroscopy (FTIR) and photoluminescence spectra (PL). The photocatalytic degradation of rhodamine B (RhB) by the CdS/C3N4 composites was explored and optimized, suggesting the optimal amount of CdS in the composites was 50 wt%. The significantly enhanced photocatalytic activity of CdS/C3N4 composites could be attributed to the effectively interfacial transfer of photogenerated charge carriers between CdS and C3N4, which restrained the recombination of electron-hole pairs.

Facile synthesis of Ag3PO4/C3N4 composites with improved visible light photocatalytic activity

Abstract

Enhanced photoelectrochemical performance of PbS sensitized Sb–SnO2/TiO2 nanotube arrays electrode under visible light illumination

The novel PbS sensitized Sb–SnO2/TiO2 nanotube arrays (NTAs) composite electrode (PbS/Sb–SnO2/TiO2 NTAs) was fabricated by microwave combined with sonication-assisted successive ionic layer adsorption and reaction technique (S-SILAR). The obtained electrodes were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance absorption spectra techniques. Enhanced photocurrent (15.52mA/cm2) of the PbS/Sb–SnO2/TiO2 NTAs electrode was observed and can be attributed to the facile photo-generated electrons transfer and enhanced charge separation efficiency. Furthermore, the PbS/Sb–SnO2/TiO2 NTAs composite electrode shows a higher H2 production rate than the Sb–SnO2/TiO2 NTAs electrode and PbS/TiO2 NTAs electrode. The results indicate that the PbS/Sb–SnO2/TiO2 NTAs electrode is a promising photoanode in visible photocatalytic water splitting.

Facile ion-exchange synthesis of BiOI/Bi2O2CO3 heterostructure for efficient photocatalytic activity under visible light irradiation

The BiOI/Bi2O2CO3 heterostructural photocatalysts were synthesized by a facile ion-exchange route between Bi2O2CO3 precursor and KI with ultrasonic reaction. The as-prepared BiOI/Bi2O2CO3 heterostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance absorption spectra (DRS), fourier transform infrared spectroscopy (FTIR) and photoluminescence spectra (PL). The BiOI/Bi2O2CO3 heterostructures exhibited much higher photocatalytic activities than those of single Bi2O2CO3 and BiOI for the degradation of Rhodamine B (RhB) under visible light irradiation. The significantly enhanced photocatalytic activity of BiOI/Bi2O2CO3 heterostructures could be attributed to the formation of p–n heterojunction between p-type BiOI and n-type Bi2O2CO3, which effectively separated the photogenerated electron–hole pairs. The possible mechanism of BiOI/Bi2O2CO3 heterostructures as photocatalysts was proposed.

BiVO4/MIL-101 composite having the synergistically enhanced visible light photocatalytic activity

The BiVO4/MIL-101 composite and pure materials were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, UV-vis diffuse reflectance absorption spectra and photoluminescence emission spectra.

CdS-TiO2 photoelectrodes Formed through Pulsed Electrodeposition of Cadmium on TiO2 Nanotube Films and Treatment with H2s for Application in Solar Cells

TiO2 nanotubes films (TNAs), compared with classic nanocrystalline photoanodes, can accelerate electron transport and diminish the recombination probability, making it suitable for use as a photoelectrode in solar cells [1]. However, one of the critical drawbacks of TiO2 is its wide band gap (3.0 and 3.2 eV for the rutile and anatase phases, respectively). That means, only ultraviolet region of the solar spectrum (about 7%) can be utilized by pure TiO2. Therefore, different methods were developed to extend the light harvesting region of TiO2, including dye sensitization and coupling with low band gap semiconductors. Coupled CdS/TNAs photoelectrode has been considered to be an important technique because CdS has a narrow band gap (2.4 eV) and its conduction band level is higher than that of TiO2. Upon illumination, the excited electrons from CdS can be rapidly transferred to TNAs, arriving at the electron collectors through the nanotube microstructure [1]. Different methods have been reported to couple CdS with TNAs, being the most commonly used: sequential chemical bath deposition (SCBD) and electrochemical deposition. However, with these methods the CdS is obtained for precipitation reactions between ions Cd2+ and S2- located in the interface electrode-electrolyte, therefore, no direct contact is ensured among CdS and TNAs. In this way, to guarantee direct contact between CdS and TNAs, an electrochemical/chemical (E/C) process was proposed in this work. This process is similar as that developed by Penner and his group to deposit CdS nanocrystals on HOPG substrates. TiO2 nanotube films were grown by potentiostatic anodization of titanium foils at 30 V during 2 hours in 0.05 M NH4F in ethylene glycol (10% water) electrolyte [2]. As-prepared films were rinsed with ethanol and water, left to air dry, and heat treated in ambient air at 450º C for 30 min (slope rate 10 ºCmin-1). E/C method consists of three steps [3]: (1) Cd nanoparticles were deposited in heat treated TNAs by pulsed electrodeposition to different reduction potentials [4] and varying on and off times; (2) the modified films were annealing at 400ºC for 30 min (slope rate 10 ºCmin-1) to form CdO/TNAs; (3) finally, the CdO/TNAs were heated in H2S atmosphere at 300º C for 30 min (slope rate 10 ºCmin-1) to convert CdO into CdS. The CdS/TNAs photoelectrodes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-Vis diffuse reflectance absorption spectra (DRS). We also investigated the photoelectrochemical behavior of the CdS/TNAs photoelectrodes under visible illumination. Acknowledgements.The authors are indebted to the CONACyT (Mexico) for their financial support to carry out this work (Projects CB-2008/105655 and INFR-2011-1-163250). J.E. Carrera-Crespo is grateful to CONACyT for the PhD fellowship granted. The authors thank to LDRX (T 128) UAM-I for XRD measurements. References. [1] X. Ma, Y. Shen, G. Wu, Q. Wu, B. Pei, M. Cao, F. Gu, “Sonication-assisted sequential chemical bath deposition of CdS nanoparticles into TiO2 nanotube arrays for application in solar cells”, J Alloy Compd (2012) 538: 61-65 [2] P. Acevedo-Peña, L. Lartundo-Rojas, I. González, “Effect of water and fluoride content on morphology and barrier layer properties of TiO2 nanotubes grown in ethylene glycol-based electrolytes”, J Solid State Electr (2013) 17: 2939-2947 [3] R. M. Penner, “Hybrid electrochemical/chemical synthesis of quantum dots”, Acc Chem Res (2000) 33: 78-86 [4] J. E. Carrera-Crespo, P. Acevedo-Peña, M. Miranda-Hernández, I. González, “Electrocrystallization of cadmium on anodically formed titanium oxide”, J Solid State Electr (2013) 17: 445-457