Efficient solar-light-driven photoelectrochemical water oxidation of one-step in-situ synthesized Co-doped g-C3N4 nanolayers

Cobalt-doped g-C₃N₄ (Co-g-CN) nanolayers were prepared by a single-step thermal treatment with urea and cobalt nitrate. Different amounts of cobalt nitrate were tested to optimize the amount of cobalt dopant in the g-C₃N₄ (g-CN) matrix. Several characterization methods were used to explore the structural and optical properties along with the photoelectrochemical (PEC) performance. X-ray diffraction and Fourier transform infrared studies confirmed that g-CN nanolayers were successfully doped with cobalt without disturbing the basic 2-D structure and tris-triazine units of g-CN. Furthermore, microscopy images demonstrated that the cobalt effectively transformed the short nanosheets into long nanolayers. The cobalt-doping enhanced the visible absorption of g-CN and tuned the bandgap from 2.71 to 2.62 eV. An X-ray photoelectron spectroscopy (XPS) investigation discovered that cobalt entered into the g-CN network as Co²⁺ ions. XPS valence band spectra gave information on the modification in the valence and conduction band edge potentials due to cobalt doping. The photoluminescence intensity from the Co-g-CN samples was lesser than that from g-CN nanosheets, and the PEC activity of the Co-g-CN nanolayers was greater than that of as-prepared g-CN nanosheets. Co-g-CN samples prepared with 15 mg of cobalt nitrate hexahydrate showed a PEC performance of 3.2522 mA/cm², which was greater than that of g-CN nanosheets (1.9246 mA/cm²). The better PEC performance was ascribed to the synergistic consequence of the higher visible absorption obtained by tuning the bandgap and the host–guest interactions between cobalt and g-CN.     

Facile one-step synthesis of pellet-press-assisted saddle-curl-edge-like g-C3N4 nanosheets for improved visible-light photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) has attracted increasing interest as a visible-light-active photocatalyst. In this study, saddle-curl-edge-like g-C₃N₄ nanosheets were prepared using a pellet presser (referred to as g-CN P nanosheets). Urea was used as the precursor for the preparation of g-C₃N₄. Thermal polymerization of urea in a pellet form significantly affected the properties of g-C₃N₄. Systematic investigations were performed, and the results for the modified g-C₃N₄ nanosheets are presented herein. These results were compared with those for pristine g-C₃N₄ to identify the factors that affected the fundamental properties. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed a crystallinity improvement in the g-CN P nanosheets. Fourier-transform infrared spectroscopy provided clear information regarding the fundamental modes of g-C₃N₄, and X-ray photoelectron spectroscopy (XPS) peak-fitting investigations revealed the variations of C and N in detail. The light-harvesting property and separation efficiency of the photogenerated charge carriers were examined via optical absorption and photoluminescence studies. The valence band edge and conduction band edge potentials were calculated using XPS, and the results indicated a significant reduction in the bandgap for the g-CN P nanosheets. The Brunauer–Emmett–Teller surface area increased for the g-CN P nanosheets. The photocatalytic degradation performance of the g-CN P nanosheets was tested by applying a potential and using the classical dye Rhodamine B (RhB). The RhB dye solution was almost completely degraded within 28 min. The rate constant of the g-CN P nanosheets was increased by a factor of 3.8 compared with the pristine g-C₃N₄ nanosheets. The high crystallinity, enhanced light absorption, reduced bandgap, and increased surface area of the saddle-curl-edge-like morphology boosted the photocatalytic performance of the g-CN P nanosheets.     

Au and Co3O4 anchored Bi2WO6 with enhanced electron paramagnetic resonance,surface plasmon resonance,nonlinear and magnetic properties

The combination of surface plasmon resonance (SPR) effect with hetero-p–n structure shows promising benefits to optical linear and nonlinear properties. In this study, Au nanoparticles (NPs) decorated p–n hetero-structured Co₃O₄/Bi₂WO₆ composite was synthesized and characterized in terms of the optical linear and nonlinear and magnetic properties, morphology, electron transition, charge transfer, energy band gap, polarizability, SPR effect, and oxygen vacancies using scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Z-scan, ultraviolet–visible spectra, and vibrating sample magnetometer. The combination of Co₃O₄ provided active 3d electrons transition and charge transfer which increased carriers’ concentration and reduced the energy band gap. Au SPR enhanced the internal polarization and strengthened the built-in electric field, yielding strong nonlinear behavior. In addition, magnetic Co₃O₄ endowed sample with room-temperature ferromagnetism which was obviously strengthened by Au NPs. The obtained sample is promising for laser and photonics applications.     

Magnetic characteristics and optical band alignments of rare earth (Sm+3, Nd+3) doped garnet ferrite nanoparticles (NPs)

Yttrium iron garnet (YIG) nanoparticles (NPs) doped with rare earth (RE) metal ions (Y_2.5Sm_0.5Fe₅O₁₂, Y_2.5Nd_0.5Fe₅O₁₂) were successfully synthesized by sol-gel auto combustion approach. The cubic crystalline structure and morphology of the prepared garnet ferrite NPs were analyzed by X-ray diffractometer (XRD) and field emission scanning electron microscopy (FESEM). The cubic crystalline garnet phase of the synthesized YIG, Sm-YIG and Nd-YIG samples was successfully achieved at 950 °C sintering temperature. The force constant and absorption bands were estimated by using Fourier transform infrared spectroscopy (FTIR). The doping effect of RE metal ions on the chemical states of YIG were examined by x-ray photoelectron microscopy (XPS). The valence band (from 12.63 eV to 13.22 eV), conduction band (from 10.89 eV to 11.34 eV) edges and optical bandgap values of RE doped YIG samples were calculated using UV–Vis spectroscopy and ultraviolet photo electron spectroscopy (UPS). The magnetic analysis of the prepared NPs was studied using vibrating sample magnetometer (VSM). The XPS analysis of RE doped YIG samples exhibit the existence of RE (Sm⁺³, Nd⁺³) contents on the surface of YIG ferrite by decreasing the oxygen lattice in garnet structure. The optical bandgap (from 1.74 eV to 1.88 eV) explains the semiconducting nature of the synthesized NPs. The UPS results confirm the valence band position of YIG doped samples. The saturation magnetization and remanence of RE doped garnet ferrite samples increased from 13.45 to 18.83 emu/g and 4.06–6.53 emu/g, respectively.     

Electropolymerized bioresistant coatings of OEGylated dendron carbazoles: Design parameters and protein resistance SPR studies

The electrografting of oligoethylene glycol or (OEG)ylated carbazole linear dendrons and their protein adsorption resistance properties have been investigated by surface plasmon resonance (SPR) spectroscopy. A series of the carbazole dendron generations, G₀, G₁, G₂ were synthesized and electrodeposited by cyclic voltammetry (CV) on Au-glass substrate which also served as a surface for evanescent waveguide excitation in SPR. In addition, the films were characterized by in-situ electrochemical SPR (EC-SPR), static water contact angle, and X-ray photoelectron spectroscopy (XPS) measurements. It was observed that electropolymerized films prepared from the higher generation linear-dendron G₂, is most effective in preventing non-specific protein adsorption as observed by SPR kinetic measurements using fibrinogen as model protein. Film thickness also played a critical role in protein adsorption resistance - electrodeposition approaching monolayer thickness gave the highest protein resistance. In addition, the films were evaluated for non-specific protein binding against the smaller proteins, lysozyme and bovine serum albumin (BSA). The study provides insight to manipulating the architecture and composition of protein resistant materials deposited on metals and semi-conducting substrates and their possible use in biomedical applications.     

Modeling gold/iron oxide interface system

The effect of gold particle size and Au/FeO _x interface on the electronic properties and catalytic activity using samples of Au/SiO₂/Si(100), Au/FeO _x /SiO₂/Si(100), FeO _x /Au/SiO₂/Si(100) has been modelled. Nanosize gold particles of varying size were fabricated by deposition of a 10 nm thick gold film onto SiO₂/Si(100) substrate by electron beam evaporation followed by modification using low energy Ar⁺ ion bombardment or Ar⁺ ion implantation. These modifications formed Au islands of decreasing size accompanied by the strong redistribution of the Au 5d valence band structure determined by ultraviolet and X-ray photoelectron spectroscopy (UPS, XPS) and increased activity in catalytic CO oxidation. The gold/iron oxide interface was prepared by deposition of iron oxide using pulsed laser deposition (PLD). The structural properties of gold and iron oxide were characterized by XPS, atomic force microscopy (AFM), transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS). Generally, the formation of gold/iron oxide interface increases the catalytic activity in CO oxidation regardless of the sequence of deposition, namely either Au/FeO _x /SiO₂/Si(100) or FeO _x /Au/SiO₂/Si(100) is formed. Furthermore, the interface formed is operative in determining the catalytic activity even if gold is not exposed to the surface, but it is located underneath the iron oxide layer. This is a promoting effect of the Au nanoparticles, which is more efficient than that of the bulk like Au films.     

X-ray absorption near edge structure and X-ray photoelectron spectroscopy studies of chloride in passive oxide films

X-ray absorption near edge structure (XANES), utilizing both electron yield and X-ray fluorescence detectors, and X-ray photoelectron spectroscopy (XPS) were used to follow chloride uptake by oxide-covered aluminum in 0.1 M NaCl solutions. The aluminum samples were polarized at selected potentials below (less positive than) the pitting potential. The electron yield XANES and XPS showed multiple peaks. The XPS chloride spectra showed two distinct sets of doublets. One doublet is related to chloride on the surface and the second is related to chloride incorporated in the oxide film. The XANES results also showed two peaks which are attributed to chloride on the surface and in the bulk of the oxide.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

Rare-earth-doped tungsten oxide microspheres with highly enhanced photocatalytic activites

Rare-earth-doped WO_2.72 microspheres (RE-WO_2.72 MSs) have been successfully synthesized by using a facile solvothermal route with tungsten salt as precursor, RE (RE=Ce, La, and Y) metal salts as dopants, and ethanol as solvent. Results of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and energy dispersive spectroscopy (EDS) showed that the solvothermal process allowed for the homogeneous doping of WO_2.72 while maintaining the original crystal structure. The RE doping could effectively engineer the bandgap of WO_2.72, which could not only enhance the light-harvesting ability but also deduce up-shift of both the conduction band and valence band. Compared to the undoped WO_2.72 nanorods (NRs), the RE-WO_2.72 MSs exhibited highly enhanced photocatalytic properties for the degradation of methylene blue (MB) under full spectrum light irradiation. This work provides a versatile strategy for the synthesis of RE-doped tungsten oxides and can be extended to the doping of other oxide semiconductors.     

Deposition of Au colloids on plasmachemically modified carbon nanofibers

The surface properties of fishbone (FB) carbon nanofibers (CNFs) were altered. This was achieved by H₂O-plasma treatment (FB-plasma) and oxidation in HNO₃ (FB-HNO₃). By zeta-potential measurements, the surfaces of as-grown and acid treated CNFs were found to be negatively charged at all pHs. Meanwhile, basic entities were introduced by H₂O-plasma treatment, indicated by an isoelectric point of pH 4.6. Ultraviolet-visible measurements indicated the successful deposition of negatively charged Au colloids on FB-plasma, and incomplete deposition on FB-HNO₃. The nature of the basic sites accommodating colloid deposition is discussed based on X-ray photoelectron spectroscopy (XPS) results. The XPS study indicated significant differences in the type and amount of surface groups. Also, a variation in the fraction of defect and/or edge sites was found. The possible sites responsible for colloid immobilization are discussed based on the XPS results. Plasma treatment is demonstrated as a simple and effective procedure for altering the surface characteristics of CNFs.     

Surface,interface and electronic properties of F8:F8BT polymeric thin films used for organic light‐emitting diode applications

Ultrathin polymeric films consisting of poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (F8) blended with poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) grown onto PEDOT:PSS/ITO/PET were investigated by X‐ray photoelectron spectroscopy (XPS), depth‐profiling XPS, reflection electron energy loss spectroscopy (REELS) and angle‐dependent X‐ray absorption spectroscopy (XAS) to gain information on the films' electronic, order and interface properties. AFM studies provide valuable information on the films' nanotopographical properties and homogeneity. Spectroscopic ellipsometry and photoluminescence spectroscopy were used also to obtain information on the optoelectronic properties. Well‐ordered films were observed from the XAS analysis, measured at the sulfur K absorption edge. XPS measurements demonstrated that the surface composition of the polymer thin films prepared by a spin‐coating wet‐chemical deposition method matches the expected F8:F8BT blend stoichiometry. The interfacial properties were studied through an argon ion sputtering process coupled to the XPS acquisition, showing an enhancement of oxygen components at the interface. The films' inhomogeneity was verified by AFM images and analysis. We obtained a value of 3.1 eV as the electronic bandgap of the F8:F8BT film from REELS data, whereas analysis of the spectroscopic ellipsometry spectra revealed that the optical bandgap of F8:F8BT has a value of 2.4 eV. A strong green emission was obtained for the produced films, which is in agreement with the expected emission due to the 1:19 ratio of the F8 and F8BT blended polymers. © 2018 Society of Chemical Industry     

Effect of the titania morphology on the Au/TiO2-catalyzed aerobic epoxidation of stilbene

We use a colloidal deposition method to prepare gold nanoparticles with similar size distributions centered at 3 nm over various anatase titania supports. All UV100, PC500 and AK350 titanias are loaded with similar amount of gold (1.0 ± 0.2 wt.%) which is in similar electronic and optical environments, as shown by X-ray photoelectron spectroscopy (XPS) and UV–vis. This allows us to assess the effect of the titania crystallization, morphology and chemical composition on the catalytic properties of gold in the aerobic epoxidation of trans-stilbene. We find that Au/UV100 is more active than Au/PC500 and Au/AK350 but that selectivities are similar on all materials. Epoxide yields on the other hand critically depend on the support functionalization and surface composition. TG–DTA characterization of the bare titania powders reveals indeed that AK350, which leads to the least active catalyst, is slightly less hydroxylated than PC500 and UV100. This indicates that surface titanol groups might be involved in the epoxidation of trans-stilbene. The presence of boron oxide on Au/UV100 (XPS), due to reaction of UV100 with the NaBH₄ reductant during the synthesis, is also thought to promote the epoxide-forming mechanism. This chemical promotion effect appears to compensate for the specific and beneficial gold–P25 interaction. As a result, Au/UV100 is more efficient than the reference Au/P25 catalyst for this reaction.     

Preparation and characterization of TiO2 photocatalysts by Fe doping together with Au deposition for the degradation of organic pollutants

Fe³⁺ doped TiO₂ deposited with Au (Au/Fe–TiO₂) was successfully prepared with an attempt to extend light absorption of TiO₂ into the visible region and reduce the rapid recombination of electrons and holes. The samples were characterized by X-ray diffraction (XRD), N₂ physical adsorption, Raman spectroscopy, atomic absorption flame emission spectroscopy (AAS), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The photocatalytic activities of the samples were evaluated for the degradation of 2,4-chlorophenol in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. The results of XRD, XPS and high-resolution transmission electron microscopy (HRTEM) analysis indicated that Fe³⁺ substituted for Ti⁴⁺ in the lattice of TiO₂, Au existed as Au⁰ on the surface of the photocatalyst and the mean particle size of Au was 8 nm. Diffuse reflectance measurements showed an extension of light absorption into the visible region for Au/Fe–TiO₂, and PL analysis indicated that the electron–hole recombination rate has been effectively inhibited when Au deposited on the surface of Fe-doped TiO₂. Compared with Fe doped TiO₂ sample and Au deposited TiO₂ sample, the Au/Fe–TiO₂ photocatalyst exhibited excellent visible light and UV light activity and the synergistic effects of Fe³⁺ and Au was responsible for improving the photocatalytic activity.     

Core–Shell Heterostructured BiVO<Subscript>4</Subscript>/BiVO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> with Improved Photocatalytic Activity

To enhance the photocatalytic activity of monoclinic scheelite (ms) BiVO₄ for dye degradation, the heterostructured core (BiVO₄)/shell (BiVO₄:Eu³⁺) samples were synthesized by sol–gel method. The samples were characterized by UV–Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The results reveal that as-synthesized photocatalysts are characteristic of ms core/shell structure, responsive to visible light. The XPS spectra confirm that the doped Eu³⁺ mainly distributed in the outside layer of BiVO₄ particle. The valence band (VB) spectra indicate the shell (BiVO₄:Eu³⁺) exhibits a high carrier mobility. The core/shell photocatalysts showed higher photocatalytic activity than pure BiVO₄ through degrading Rhodamine B and Methylene blue. The better performance of core/shell heterojunction mainly results from that the Eu³⁺ ions selectively present on shell layer, increasing the VB value of shell layer (forming a interface electric field with core) and carrier mobility. It is considered that the half-filled 7f–electron configuration of Eu³⁺ can improve the electron trapping and transfer. Besides, the low PL intensity and high S_BET of BiVO₄/BiVO₄:Eu³⁺ contribute to enhanced photocatalytic performances.     

On the reduction potential of cation-exchanged heteropolyacids (HPAs)

UV-Visible spectroscopy and scanning tunneling microscopy (STM) studies were performed to explore reduction potentials of cation-exchanged Keggin-type heteropolyacid (HPA) catalysts. Absorption band edge and negative differential resistance (NDR) peak voltage of cation-exchanged HPA samples determined by UV-Visible spectroscopy and STM, respectively, were colsely related to their reduction potentials. It was observed that HPAs with higher reduction potentials showed absorption band edges at longer wave lengths and exhibited NDR peak voltages at less negative applied values. The reduction potentials of cation-exchanged HPA catalysts could also be correlated with the electronegativities of counter-cations. Substitution of more electronegative counter-cations increased reduction potentials of the HPAs. The NDR peak voltage and the absorption band edge of HPAs could be utilized as a correlating parameter for their reduction potentials.     

Optical properties of porous silicon coated with ultrathin gold film by RF-magnetron sputtering

Optical properties of porous silicon (PS) with ultrathin gold (Au) coatings were investigated. The gold films were deposited by using an RF-sputter-deposition technique on PS prepared by electrochemical anodization of P-type (1 0 0) Si. Photoluminescence (PL) spectroscopy and UV/VIS photospectroscopy analyses were performed to investigate the PL and optical transmittance properties of the Au-coated PS samples. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron emission spectroscopy (XPS) analyses were also performed to investigate the origin of the PL enhancement by Au deposition. The PL intensity of PS is 6.4% increased by depositing 5.3 nm Au film using an RF-sputtering technique, but it is decreased 28.4% by postannealing. FTIR, spectrophotometry and XPS analysis results suggest that the PL enhancement by Au film deposition is attributed to the oxidation inhibiting effect of the Au film. However, it is not desirable to deposit an Au film thicker than 5.3 nm on PS as the PL intensity is decreased rather than increased owing to a significant decrease in the transmittance. Deterioration in the PL of the Au-coated PS by postannealing is ascribed to oxidation of the PS layer occurring at the high annealing temperature in spite of the Au passivation.     

Development of growth cycle for antimony telluride film on Au (1 1 1) disk by electrochemical atomic layer epitaxy

Electrochemical deposition of Sb₂Te₃ thin film on Au (1 1 1) disk via the route of electrochemical atomic layer epitaxy (ECALE) is described in this paper. Electrochemical aspects of Te and Sb on Au, Te on Sb-covered Au, and Sb on Te-covered Au were studied by means of cyclic voltammetry and coulometry. The apparent variation of coverage for Te or Sb on hetero-covered substrate is explained by considering the thermodynamic process of compound formation. A steady ECALE deposition for Sb₂Te₃ compound could be attained after negatively adjusting the underpotential deposition (UPD) potentials of Sb and Te on Au in steps over the initial 40 cycles, and the potentials could be kept constant for the following deposition. A 200-cycle deposit, which was grown with the steady deposition potentials, was proved to be a single phase Sb₂Te₃ compound by X-ray diffraction analysis. The 2:3 stoichiometric ratio of the deposit was further verified by energy dispersive X-ray (EDX) quantitative analysis. The p-type semiconductive property was demonstrated by measurements of the Seebeck coefficient and the electrical resistivity with a value of 145 μV/K and 9.37 μΩm, respectively. The morphologies of deposits with various growth cycle numbers were observed with FE-SEM. The evolvement mechanism of the morphology was investigated. The results show that the morphology of deposit has changed after initial potential adjustment and numberless thin sheets appeared and grew uprightly during the continuous cycle process. Fourier transform infrared spectroscopy (FTIR) absorption measurements suggested a band gap of 0.26 eV in very good agreement with literature reports for Sb₂Te₃ single crystals.     

Modeling heterogeneous catalysts: metal clusters on planar oxide supports

Model catalysts consisting of Au and Ag clusters of varying size have been prepared on single crystal TiO₂(110) and ultra-thin films of TiO₂, SiO₂ and Al₂O₃. The morphology, electronic structure, and catalytic properties of these Au and Ag clusters have been investigated using low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) and spectroscopy (STS) with emphasis on the unique properties of clusters <5.0 nm in size. Motivating this work is the recent literature report that gold supported on TiO₂ is active for various reactions including low-temperature CO oxidation and the selective oxidation of propylene. These studies illustrate the novel and unique physical and chemical properties of nanosized supported metal clusters.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Visible light active Au:TiO2 nanocomposite photoanodes for water splitting: Sol–gel vs. sputtering

In this study, pure TiO₂ and Au:TiO₂ nanocomposite thin films are both synthesized using sol–gel and RF reactive co-sputtering methods. Physical and photoelectrochemical properties of the thin films deposited by each method are compared. The optical density spectra and scanning electron microscopy images of the Au:TiO₂ films reveal formation of gold nanoparticles in the all nanocomposite films synthesized by two methods. Moreover, the optical bandgap energy of the thin films decreases with addition of Au nanoparticles. X-ray photoelectron spectroscopy indicates that the presence of gold in metallic state and the formation of TiO₂ is stoichiometric. The photoelectrochemical properties of the TiO₂ and Au:TiO₂ thin films are characterized by using a compartment cell containing KOH solution as electrolyte. It is found that in the pure systems, TiO₂ sputtered films shows a higher photocurrent under visible light illumination while a reverse result is obtained for the Au:TiO₂ systems. In addition, photoirradiation on electrode/electrolyte (EE) and substrate/electrode (SE) interfaces for the sputtered samples reveals the EE illumination enhances the photoresponse of the layers as compared to SE case.