Coating of TiO2 nanoparticles with PbS thin films and preparation of PbS nanoparticles using a one-pot sonochemical reaction under the multibubble sonoluminescence conditions

Preparations of PbS-coated titanium dioxide (TiO₂) and lead sulfide (PbS) nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) conditions were tested in water solutions. Under the optimal MBSL conditions (20 kHz and 220 W power input), PbS nanoparticles (diameter = 40-50 nm) were prepared by treating lead nitrate and thioacetamide for 20 min in water solutions. The size of PbS nanoparticles was found to be easily increased to about 90 nm in diameter by increasing the reactant concentration twice. A similar sonochemical reaction with TiO₂ nanoparticles (about 20-30 nm in diameter) gave rise to PbS-coated TiO₂ nanoparticles with a core/shell structure. The PbS thin film coating was quite uniform and the average coating depth of PbS on the TiO₂ nanoparticles was about 2-3 nm under the described conditions. It is interesting to note that the coating depth was found to be controlled to 2-10 nm range by increasing the amounts of reactants for Pb and S twice with a sonication time of 30 min.     

Fabrication of quantum dot-sensitized solar cells with multilayer TiO2/PbS(X)/CdS/CdSe/ZnS/SiO2 photoanode and optimization of the PbS nanocrystalline layer

In this work, two multilayer photoanode structures of TiO₂/PbS(X)/CdS/ZnS/SiO₂ and TiO₂/PbS(X)/CdS/CdSe/ZnS/SiO₂ were fabricated and applied in quantum dot-sensitized solar cells (QDSCs). Then, the effect of PbS QDs layer on the photovoltaic performance of corresponding cells was investigated. The sensitization was carried out by PbS and CdS QDs layers deposited on TiO₂ scaffold through successive ionic layer adsorption and reaction (SILAR) method. The CdSe QDs film was also formed by a fast, modified chemical bath deposition (CBD) approach. Two passivating ZnS and SiO₂ layers were finally deposited by SILAR and CBD methods, respectively. It was shown that the reference cell with TiO₂/CdS/ZnS/SiO₂ photoanode demonstrated a power conversion efficiency (PCE) of 3.0%. This efficiency was increased to 4.0% for the QDSC with TiO₂/PbS(2)/CdS/ZnS/SiO₂ photoelectrode. This was due to the co-absorption of incident light by low-bandgap PbS nanocrystalline film and also the CdS QDs layer and well transport of the charge carriers. For the CdSe included QDSCs, the PbS-free reference cell represented a PCE of 4.1%. This efficiency was improved to 5.1% for the optimized cell with TiO₂/PbS(2)/CdS/CdSe/ZnS/SiO₂ photoelectrode. The maximized efficiency was enhanced about 25% and 70% compared to the PbS-free reference cells with and without the CdSe QDs layer.

     

Effect of single-walled carbon nanotube in PbS/TiO2 quantum dots-sensitized solar cells

Single-walled carbon nanotubes (SWNTs) layers formed on indium-doped tin oxide (ITO) electrodes for enhanced photoconversion efficiency of PbS/TiO₂ quantum dots (Q dots)-sensitized photoelectrochemical solar cells (PECs). The short-circuit current of Q dots-sensitized PECs with SWNTs layers increased under illumination, and the dark current of the PECs was also reduced without illumination. Furthermore, the electron lifetimes of PbS/TiO₂/SWNTs in open-circuit voltage decay is higher than that of PbS/TiO₂ films at the same voltage. As a result, the power conversion efficiency of PbS/TiO₂ on ITO increased 35.6% in the presence of SWNTs due to the improved charge-collecting efficiency and reduced recombination process.     

PbS nanocrystals embedded in microstructures produced by micromoulding in capillaries

The study presents a new method to prepare PbS nanocrystals embedded in poly(acrylic acid) (PAA) microstructures by micromoulding in capillaries (MIMIC). The micropatterns were fabricated first from aqueous solution of acrylic acid lead monomer, and subsequently solidified by γ-ray polymerization. The resulting samples were treated with aqueous Na₂S solution to convert Pb precursor to PbS in the matrix. The final micropatterns of PAA embedded with PbS nanocrystals were of high resolution. The products were characterized by IR, XRD, TEM and SPM, respectively, and the results demonstrated that PbS embedded in PAA was nanocrystals.     

Bifacial illuminated PbS quantum dot-sensitized solar cells with translucent CuS counter electrodes

This paper reports the optimization of the TiO₂ photoanode and the fabrication of bifacial illuminated PbS quantum dot-sensitized solar cells (QDSSCs) with translucent CuS counter electrodes. TiO₂ photoanode is prepared by introducing a compact TiO₂ layer between FTO substrate and TiO₂ film with titanium diisopropoxide bis(acetylacetonate) in 1-butanol and post-treatment with TiCl₄ aqueous solution; then, PbS quantum dots (QDs) are deposited on the surface of TiO₂ film by successive ionic layer adsorption and reaction method; also, by means of control of the TiO₂ surface charge, QD density of TiO₂ film is improved by adding triethanolamine into the cationic precursor solution. Using this optimized TiO₂ photoanode and a translucent CuS counter electrode, a bifacial illuminated PbS QDSSC is fabricated. The preparation conditions are optimized and the surface morphology and electrochemical properties of TiO₂ photoanodes are characterized. The bifacial illuminated PbS QDSSC achieves a power conversion efficiency of 2.16 %, which is increased by 48.97 % compared with the single illuminated QDSSC.     

Design and development of electronic- and micro-structures for multi-functional working electrodes in dye-sensitized solar cells

This paper outlines a new strategy to optimize the performance of electrodes in dye-sensitized solar cells (DSSCs), through the engineering of electronic structures in conjunction with the micro-structures of the devices. We propose a simple hydrolysis method for the fabrication of a family of quasi-core–shell TiO₂ (hydrolysis)/PbS composites for working electrodes. Measurements confirm a shift in absorption from the UV to visible range. We also measured cell performance, including short-circuit photocurrent, open-circuit photovoltage, and the power conversion efficiency (η) of DSSCs. The obtained η of DSSC (6.05%) with a TiO₂ (P-25)/TiO₂ (hydrolysis) + 0.005 M PbS electrode is substantially higher than that of the conventional DSSC (5.11%) with a TiO₂ (P-25) electrode, due to improved p–n junctions, light-scattering, and light absorption. Finally, the shell of TiO₂ (hydrolysis) protected the core of PbS from the corrosive effects of electrolytes, thereby prolonging the life span of the DSSC. This novel approach to electrode design could lead to advances in DSSC as well as other energy applications including photo-catalysis technology.     

Structure and properties of lead and lead sulfide nanoparticles in natural zeolite

We have synthesized lead and lead sulfide nanoparticles embedded in a natural zeolite (clinoptilolite) matrix by a simple hydrothermal process. The process steps involve the partial removing of the natural cations in clinoptilolite, the ion-exchange process to enclose Pb ions and nanoparticles and finally a sulfuration process at different temperatures to obtain lead sulfide phases in the zeolite matrix. The samples were studied by X-ray diffraction, diffuse reflectance spectroscopy, energy dispersive X-ray spectroscopy, X-ray photon spectroscopy and transmission electron microscopy. The experimental results show the inclusion of three Pb species with different valence states after the Pb ion-exchange step, namely Pb²⁺, Pb⁴⁺, and Pb⁰. At the end of the process, two simultaneous lead sulfide crystalline phases, PbS (Galena) and PbS₂ (tetragonal) were synthesized in the clinoptilolite matrix. The optical absorption spectra of the samples show the exciton absorption peaks typical of colloidal PbS nanoparticles. The average size of the PbS nanoparticles was about 10 nm and their crystalline structure was determined from diffraction electron patterns. The high-pressure phase PbS₂ was also identified and its formation was attributed to the influence of the special conditions of clinoptilolite matrix as crystallization media to induce some selective nucleation process of this crystalline phase.     

Investigation of the microstructure and corrosion performance of a nanostructured titania-containing hybrid silicate film on mild steel

A pre-treatment system consisting of a nanostructured titania interlayer loaded with an inhibitor and a hybrid silicate film deposited on the TiO₂ layer is shown to provide protection against active corrosion of mild steel. A nanostructured TiO₂ interlayer was prepared on the mild steel surface via controllable hydrolysis of titanium alkoxide. To further improve this pre-treatment, the hybrid silicate film was synthesized from tetraethylorthosilicate and 3-glycidoxypropyltrimethoxysilane precursors. The morphology and structure of the titania interlayer and hybrid silicate film were characterized with atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. The corrosion performance of the coatings was examined using electrochemical techniques, including potentiodynamic scanning and electrochemical impedance spectroscopy. The TiO₂ nanostructure calcinated/inhibitor/hybrid silicate system shows enhanced corrosion performance, as confirmed by impedance and polarization measurements.     

Core–shell nanostructure supported Pt catalyst with improved electrocatalytic stability in oxygen reduction reaction

Core–shell nanostructure electrode (TiO₂@C) for oxygen reduction reaction is prepared with TiO₂ nanoparticles at 900 °C in a methane atmosphere. The TiO₂@C supported Pt catalyst (Pt/TiO₂@C) contains Pt nanoparticles on TiO₂@C nanostructure electrodes consisting of TiO₂ as a core and carbon as a shell. In the accelerated stability test, the Pt/TiO₂@C exhibits a superior ORR stability to conventional carbon supported Pt catalyst. It is likely that the enhanced catalytic properties of the nanostructure supported Pt catalyst may be due to graphite-like carbon and an improved electronic conductivity of the core–shell nanostructure.     

Microstructure, Magnetic and Electronic Transport Properties of Co–TiO2 Nanocomposite Films in Metal Matrix

In this work, Co–TiO₂ metallic composite films with a novel nanostructure have been electrodeposited in potentiostatic regime onto copper substrates, from a solution based on cobalt sulfate containing suspended TiO₂ nanoparticles, with magnetic stirring of the electrolyte. The effect of deposited film thickness on the morphology, microstructure, and composition of the films was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Functional properties (magnetic and electronic transport) of films with different thicknesses were studied in a view to find out the possibility for some technological applications. Nanocomposite Co–TiO₂ films contain three main phases: hcp Co crystalline grains (9–10 nm average size), TiO₂ nanoparticles (28 nm average diameter) embedded in Co metallic matrix and Co(OH)₂ adsorbed on the crystallite frontiers. The films display hysteresis (coercive field of 7.8÷11.9 kA/m) and significant values of magnetoresistance (with a maximum of ?59 % in the case of 0.07 μm film thickness). These properties can be qualitatively explained both by the elastic spin-dependent scattering of the conduction electrons at the interface between the magnetic Co matrix grains and the nonmagnetic regions, and by occurrence of antiferromagnetic coupling between Co crystallites, favored by inclusion in film of TiO₂ nanoparticles.     

Control of the quantum size effect of TiO2-SiO2 hybrid particles

This paper describes the control of the quantum size effect by controlling the coating layer thickness in TiO₂-SiO₂ core-shell hybrid particles obtained by the liquid phase deposition (LPD) method. The coating layer thickness of TiO₂ on SiO₂ nano-particles was controlled by changing the [Ti]/[Si] ratio. The titania coating thickness and crystallite size were estimated by transmission electron microscope (TEM) and X-ray diffraction (XRD), respectively. The quantum size effect of the obtained nano-hybrid particles was estimated by the band gap energy shift, using ultraviolet-visible spectroscopy (UV-vis). As a result, we successfully controlled the degree of the quantum size effect by controlling the coating layer thickness in core-shell TiO₂-SiO₂ hybrid particles.     

Photoinduced properties of nanocrystalline TiO<Subscript>2</Subscript> sol-gel derived thin films

In this paper, nanostructure TiO₂ thin films were deposited on glass substrates by sol-gel dip coating technique. X-ray diffraction and Fourier transform infrared spectroscopy were used to determine film behaviour. The super-hydrophilicity was assessed by contact angle measurement. Photocatalytic properties of these films were evaluated by degradation of methylene blue under UV irradiation. The XRD pattern of TiO₂ powder samples confirmed the presence of polycrystalline anatase phase with a crystal size of 17 nm. The results indicated that UV light irradiation had significant effect on super-hydrophilic and photocatalytic properties of TiO₂ thin films.     

Novel Structure for High Performance UV Photodetector Based on BiOCl/ZnO Hybrid Film

A novel type of high performance ultraviolet (UV) photodetector (PD) based on a ZnO film has been prepared by incorporating a BiOCl nanostructure into the film. The responsivity of the BiOCl/ZnO hybrid film PD in UV region can reach 182.87 mA W^?1, which is about 2.72 and 6.87 times for that of TiO₂/ZnO hybrid film PD and pure ZnO film PD. The rise/decay time of BiOCl/ZnO hybrid film PD is 25.83/11.25 s, which is much shorter than that of TiO₂/ZnO hybrid film PD (51.94/26.05 s) and pure ZnO film PD (69.34/>120 s). The BiOCl nanostructure can inject photogenerated electrons into the ZnO film under UV light illumination, leading to the increase of photocurrent, and forms barriers to block the straight transmission of electrons between electrodes, resulting in the decrease of decay time. The results of control experiment show that the transfer path of photogenerated electrons formed by p–n junction will be cut off after depositing gold nanoparticles on the film surface, which means this hybrid film is a unique and novel structure to improve the optoelectronic performance of photodetectors. This novel BiOCl/ZnO hybrid structure paves new route for the development of film PDs based on ZnO film.     

Photocatalytic microreactor using TiO2/Ti plates: Formation of TiO2 nanostructure and separation of oxidation/reduction into different channels

TiO₂ is the most popular and promising high-activity photocatalyst and has many applications. Recently, photocatalysis in microreactors has attracted attention due to its effective light irradiation and short diffusion distance. This article introduces our study on the fabrication of TiO₂/Ti bilayer plates and their application in a photocatalytic microreactor. First, TiO₂ layers with controlled nanostructures were fabricated via the direct oxidation of Ti plates. A network-like and flake-like nanostructure of TiO₂ was formed on the surface of Ti plates by alkaline treatment. TiO₂ nanotube arrays were formed by anodization of the Ti plate. These TiO₂/Ti plates exhibited high photocatalytic performance in the microreactor, which was enhanced by developing the nanostructure. Second, we developed a new photocatalytic microreactor with stacked channels for oxidation and reduction employing the charge separation effect of the TiO₂/Ti plate. The UV irradiation of the TiO₂-side channel generates pairs of holes and electrons, which are separated by the TiO₂/Ti plate and contribute to oxidation and reduction in the different channels. We confirmed the feasibility of this microreactor and demonstrated that the pH difference in the two channels was the important factor enhancing the reduction induced by transferred electrons.     

New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum

New processes for the preparation of nanostructure on glass surfaces have been developed through anodic oxidation of sputtered aluminum. Aluminum thin film sputtered on a tin doped indium oxide (ITO) thin film on a glass surface was converted into alumina by anodic oxidation. The anodic alumina gave nanometer size pore array standing vertically on the glass surface. Kinds of acids used in the anodic oxidation changed the pore size drastically. The employment of phosphoric acid solution gave several tens nanometer size pores. Oxalic acid cases produced a few tens nanometer size pores and sulfuric acid solution provided a few nanometer size pores. The number of pores in a unit area could be changed with varying the applied voltage in the anodization and the pore sizes could be increased by phosphoric acid etching. The specimen consisting of a glass substrate with the alumina nanostructures on the surface could transmit UV and visible light. An etched specimen was dipped in a TiO₂ sol solution, resulting in the impregnation of TiO₂ sol into the pores of alumina layer. The TiO₂ sol was heated at ∼400 °C for 2 h, converting into anatase phase TiO₂. The specimens possessing TiO₂ film on the pore wall were transparent to the light in UV–Visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on the glass surface. The removal of the barrier layer alumina at the bottom of the pores was necessary to attain smooth electro deposition of Ni. The photo catalytic function of the specimens possessing TiO₂ nanotube array was investigated in the decomposition of acetaldehyde gas under the irradiation of UV light, showing that the rate of the decomposition was quite large.     

Aerosol route synthesis of Ni-CeO2-Al2O3 hybrid nanoparticle cluster for catalysis of reductive amination of polypropylene glycol

We demonstrated an aerosol-based approach to synthesize Ni-CeO₂-Al₂O₃ hybrid nanostructure as a potent nanopowder catalyst for the production of polyetheramine via reductive amination of polypropylene glycol. The method combines a gas-phase evaporation-induced self-assembly with two-stage thermal treatments of the aerosol particles. The hybrid Ni-CeO₂ nanoparticles (NPs) composed of ultrafine, homogeneously-distributed nanocrystallites of metallic Ni and ceria were shown to uniformly decorate on the surface of Al₂O₃ nanoparticle cluster (NPC). The composition, physical size and surface state of the hybrid nanostructure were tunable by design. It was found that hybridization with Al₂O₃ or CeO₂ enhanced catalytic activity of the Ni catalyst. A high yield of ≈77% of the desired PEA and a high selectivity to primary amine (≈100%) achieved simultaneously. The surface nitridation of Ni catalyst was effectively suppressed via the incorporation with CeO₂ NPs. An enhanced operation stability was observed by using the Ni-CeO₂-Al₂O₃ hybrid nanostructure as catalyst in comparison to the Ni-only NP. The work demonstrated a facile route for controlled gas-phase synthesis of hybrid nanopowder catalysts using Al₂O₃ NPC as the support matrix and CeO₂ NP as the promoter to further enhance the performance of Ni catalyst toward reductive amination.     

New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum

New processes for the preparation of nanostructure on glass surfaces have been developed through anodic oxidation of sputtered aluminum. Aluminum thin film sputtered on a tin doped indium oxide (ITO) thin film on a glass surface was converted into alumina by anodic oxidation. The anodic alumina gave nanometer size pore array standing vertically on the glass surface. Kinds of acids used in the anodic oxidation changed the pore size drastically. The employment of phosphoric acid solution gave several tens nanometer size pores. Oxalic acid cases produced a few tens nanometer size pores and sulfuric acid solution provided a few nanometer size pores. The number of pores in a unit area could be changed with varying the applied voltage in the anodization and the pore sizes could be increased by phosphoric acid etching. The specimen consisting of a glass substrate with the alumina nanostructures on the surface could transmit UV and visible light. An etched specimen was dipped in a TiO₂ sol solution, resulting in the impregnation of TiO₂ sol into the pores of alumina layer. The TiO₂ sol was heated at ~400 °C for 2 h, converting into anatase phase TiO₂. The specimens possessing TiO₂ film on the pore wall were transparent to the light in UV–Visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on theglass surface. The removal of the barrier layer alumina at the bottom of the pores was necessary to attain smooth electro deposition of Ni. The photo catalytic function of the specimens possessing TiO₂ nanotube array was investigatedin the decomposition of acetaldehyde gas under the irradiation of UV light, showing that the rate of the decomposition was quite large.     

Magnetic properties of the highly iron-doped rutile TiO2 nano crystals

The highly iron-doping to the rutile TiO₂ nano-crystals up to Fe/Ti = 0.2 (Ti_0.833Fe_0.167O_2−δ) was investigated by magnetic and high-pressure annealing study. The magnetic data clearly confirmed the substitution and absence of ferromagnetic order. Instead, presence of anti-ferromagnetic interactions was detected. The high-pressure annealed pellets were revealed highly electrically insulating, reflecting electrical nature of the doped crystals. The result provides a great contrast to what was observed for the thin film form of the doped ferromagnetic TiO₂.     

TiO<Subscript>2</Subscript> nanocrystals grown on graphene as advanced photocatalytic hybrid materials

A graphene/TiO₂ nanocrystals hybrid has been successfully prepared by directly growing TiO₂ nanocrystals on graphene oxide (GO) sheets. The direct growth of the nanocrystals on GO sheets was achieved by a two-step method, in which TiO₂ was first coated on GO sheets by hydrolysis and crystallized into anatase nanocrystals by hydrothermal treatment in the second step. Slow hydrolysis induced by the use of EtOH/H₂O mixed solvent and addition of H₂SO₄ facilitates the selective growth of TiO₂ on GO and suppresses growth of free TiO₂ in solution. The method offers easy access to the GO/TiO₂ nanocrystals hybrid with a uniform coating and strong interactions between TiO₂ and the underlying GO sheets. The strong coupling gives advanced hybrid materials with various applications including photocatalysis. The prepared graphene/TiO₂ nanocrystals hybrid has superior photocatalytic activity to other TiO₂ materials in the degradation of rhodamine B, showing an impressive three-fold photocatalytic enhancement over P25. It is expected that the hybrid material could also be promising for various other applications including lithium ion batteries, where strong electrical coupling to TiO₂ nanoparticles is essential.     

Preparation of micro-nano-composites of TiO2/carbon nanostructures,C-CNT macroscopic shaping and their applications

Micro-nano-composites of TiO₂/carbon were synthesised using a collage of carbon nanostructures (carbon nanotubes (CNTs) and carbon nanofibers (CNFs)) on a TiO₂ surface through a TiO₂ sol-gel layer. C-CNT macroscopic shaping (C-CNT composites) were produced using CNTs as a starting material and a phenol-formaldehyde (PF) or polystyrene (PS) polymer as an adhesive. The morphologies of the composites were characterised by scanning electron microscopy (SEM). The collage of carbon nanostructures on the surface of TiO₂ in the composite was observed by transmission electronic microscopy (TEM). The superhydrophobicity of the C-CNT macroscopic shapes was demonstrated by contact angle measurements using AutoCAD software. The photoactivity of the composites was examined by the conversion of methylene blue (MB) in aqueous solution under irradiation from high-pressure mercury lamp. Higher photoactivity was observed using the TiO₂/carbon nanostructure composites than with TiO₂ alone.