Ag2S quantum dot-sensitized solar cells

We present a new photosensitizer – Ag₂S quantum dots (QDs) – for solar cells. The QDs were grown by the successive ionic layer adsorption and reaction deposition method. The assembled Ag₂S-QD solar cells yield a best power conversion efficiency of 1.70% and a short-circuit current of 1.54 mA/cm² under 10.8% sun. The solar cells have a maximal external quantum efficiency (EQE) of 50% at λ = 530 nm and an average EQE of ～ 42% over the spectral range of 400–1000 nm. The effective photovoltaic range covers the visible and near-infrared spectral regions and is ～ 2–4 times broader than that of the cadmium chalcogenide systems — CdS and CdSe. The results show that Ag₂S QDs can be used as a highly efficient and broadband sensitizer for solar cells.     

Photocatalytic activity of TiO2 nanotube layers loaded with Ag and Au nanoparticles

Ag and Au nanoparticles were found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotubular structures. The catalyst systems are demonstrated to be highly efficient for the UV-light induced photocatalytic decomposition of a model organic pollutant – Acid Orange 7. The metallic nanoparticles with a diameter of ∼10 ± 2 nm (Ag) and ∼28 ± 3 nm (Au) were attached to a nanotubular TiO₂ layer that consists of individual tubes of ∼100 nm of diameter, ∼2 μm in length and approx. 15 nm of wall thickness. Both metal particle catalyst systems enhance the photocatalytic decomposition significantly more on the nanotubes support than placed on a compact TiO₂ surface.     

Facile preparation of large aspect ratio ellipsoidal anatase TiO2 nanoparticles and their application to dye-sensitized solar cell

A simple one-step heat-treatment of peroxotitanate complex aqueous solution at around 100 °C was resulted in the formation of ellipsoidal anatase TiO₂ nanoparticles having a high aspect ratio with no branches. The length of these ellipsoidal TiO₂ falls in the range of 200–350 nm, depending on mole ratio of Ti⁴⁺/H₂O₂. Dye-sensitized solar cell based on these ellipsoidal nanocrystalline TiO₂ as photoanode was fabricated and characterized.     

Electrochemically synthesized CdS nanoparticle-modified TiO2 nanotube-array photoelectrodes: Preparation,characterization, and application to photoelectrochemical cells

A novel electrodeposited CdS nanoparticle-modified highly-ordered TiO₂ nanotube-array photoelectrode and its application to photoelectrochemical cells is reported. Results show formation of a thin, nanoparticulate CdS layer, comprised of sphere-like 10–20 nm diameter nanoparticles, on the anodic synthesized TiO₂ nanotube-array (inner diameter of 70 nm, wall thickness 25 nm and ca. 400 nm length) electrode. The resulting CdS–TiO₂ photoelectrode has an as-fabricated bandgap of 2.53, and 2.41 eV bandgap after sintering at 350 °C in N₂ ambient. Photoelectrochemical properties are described in detail.     

Dye-sensitized solar cells using anodic TiO2 mesosponge: Improved efficiency by TiCl4 treatment

In the present work, we produce 15 μm thick titania mesosponge layers (TMSL) by a Ti anodization/etching process and use the layers in dye-sensitized solar cells (DSCs). We show that the solar cell efficiency can considerably be improved by a TiCl₄ hydrolysis treatment (increase of approx. 40% to an overall value of 4.9% under AM 1.5 illumination). This beneficial effect is due to the decoration of the ～10 nm wide channels present in TMSL with TiO₂ nanoparticles of approx. 3 nm diameter, which allow for a significantly higher specific dye loading of the TMS structure.     

The performance of coupled (CdS:CdSe) quantum dot-sensitized TiO2 nanofibrous solar cells

Highly porous networks and reduced grain boundaries with one-dimensional (1-D) nanofibrous morphology offer enhanced charge transport in solar cells applications. Quantum dot (QDs) decorated TiO₂ nanofibrous electrodes, unlike organic dye sensitizers, can yield multiple carrier generations due to the quantum confinement effect. This paper describes the first attempt to combine these two novel approaches, in which CdS (～18 nm) and CdSe (～8 nm) QDs are sensitized onto electrospun TiO₂ nanofibrous (diameter ～80–100 nm) electrodes. The photovoltaic performances of single (CdS and CdSe) and coupled (CdS/CdSe) QDs-sensitized TiO₂ fibrous electrodes are demonstrated in sandwich-type solar cells using polysulfide electrolyte. The observed difficulties in charge injection and lesser spectral coverage of single QDs-sensitizers are solved by coupling (CdS:CdSe) two QDs-sensitizers, resulting in a enhanced open-circuit voltage (0.64 V) with 2.69% efficiency. These results suggest the versatility of fibrous electrodes in QDs-sensitized solar cell applications.     

Highly efficient CdSe quantum-dot-sensitized TiO2 photoelectrodes for solar cell applications

With 4.2 nm quantum-dots (QDs) as seeds on TiO₂ film, a highly efficient TiO₂ photoelectrode was prepared by a seed-growing process using chemical bath deposition technique, followed by a covering process with ZnS layer, and a post-sintering process at 400 °C. The assembled solar cells presented IPCE peak values of 73% and power conversion efficiency of 3.21% under AM 1.5 G irradiation.     

Structural evolution during the reaction of Li with nano-sized rutile type TiO2 at room temperature

Rutile type TiO₂ nanoparticles (10 nm × 200 nm in size) were prepared using a precipitation method in aqueous solution. Their lithium reactivities were followed using both classical galvanostatic insertion and in situ XRD measurements, and compared to that of a bulk and commercial nano-sized (50 nm) rutile TiO₂ sample so as to stress the interlink between Li insertion electrochemical capacity and crystallite size. For the highly divided material, we obtained a reversible capacity of 0.5 Li ion per formula unit after a first reduction step during which, the material is irreversibly transformed. Such a reduction step is shown to enlist two solid solution domains followed by the formation of a rocksalt type phase LiTiO₂. Such a specific reactivity of nano-sized rutile TiO₂ is explained in terms of better lattice strains accommodation during the insertion of lithium.     

Visible LED light photoelectrochemical sensor for detection of L-Dopa based on oxygen reduction on TiO2 sensitized with iron phthalocyanine

The present work describes the development of a new strategy to photoelectrochemical detection of L-Dopa at low potential based on oxygen reduction on TiO₂ sensitized with iron phthalocyanine (FePc/TiO₂). The FePc/TiO₂ composite shows a photocurrent 10-fold higher than that of pure TiO₂ nanoparticles and it was 4-fold higher than that of FePc exploiting visible light. The band gaps of pure TiO₂ nanoparticles, FePc and FePc/TiO₂, calculated according to the Kubelka–Munk equation, were 3.22 eV, 3.11 eV and 2.82 eV, respectively. The FePc/TiO₂ composite showed a low charge transfer resistance in comparison to the photoelectrode modified with FePc or TiO₂. Under optimized conditions, the photoelectrochemical sensor shows a linear response range from 20 up to 190 μmol L^− 1 with a sensitivity of 31.8 μA L mmol^− 1 and limit of detection of 1.5 μmol L^− 1 for the detection of L-Dopa.     

TiO2@CdS core–shell nanorods films: Fabrication and dramatically enhanced photoelectrochemical properties

In this paper, we prepared TiO₂@CdS core–shell nanorods films electrodes using a simple and low-cost chemical bath deposition method. The core–shell nanorods films electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrometry techniques. After applying these TiO₂@CdS core–shell nanorods electrodes in photovoltaic cells, we found that the photocurrent was dramatically enhanced, comparing with those of bare TiO₂ nanorods and CdS films electrodes. Moreover, TiO₂@CdS core–shell nanorods film electrode showed better cell performance than CdS nanoparticles deposited TiO₂ nanoparticles (P25) film electrode. A photocurrent of 1.31 mA/cm², a fill factor of 0.43, an open circuit photovoltage of 0.44 V, and a conversion efficiency of 0.8% were obtained under an illumination of 32 mW/cm², when the CdS nanoparticles deposited on TiO₂ nanorods film for about 20 min. The maximum quantum efficiency of 5.0% was obtained at an incident wavelength of 500 nm. We believe that TiO₂@CdS core–shell heterostructured nanorods are excellent candidates for studying some fundamental aspects on charge separation and transfer in the fields of photovoltaic cells and photocatalysis.     

Synthesis,characterization and electrochemical properties of a compact titanium dioxide layer

In this paper, we report on the synthesis, characterization, and electrochemical properties of a compact titanium dioxide layer as well as its application in dye-sensitized solar cells (DSCs). The compact TiO₂ layer, which was prepared via a facile approach by the hydrolysis of TiCl₄ aqueous solution, has been characterized by XRD, SEM, UV–vis absorption spectroscopy, voltammetry, and electrochemical impedance spectroscopy (EIS). Experimental results show that the compact TiO₂ layer with the thickness of about 100 nm is composed of anatase-phase nanoparticles with the particle size of 10–15 nm. Impedance measurements display that the compact layer of TiO₂ can prevent the back reaction of electrons with tri-iodide ions under low applied potentials, increase the open circuit voltage (V_oc) and fill factor (FF), and finally improve the conversion efficiency (η) for the DSCs from 7.5 to 8.1%.     

Photoelectrochemical solar cell properties of heteropolytungstic acid-incorporated TiO2 nanodisc thin films

Thin film of heteropolytungstic acid (HPA)-incorporated TiO₂ nanodisc was fabricated, and its photovoltaic performances were observed as a function of irradiation wavelength from 400 nm to 750 nm. Its incident photon-to-current efficiency (IPCE) was determined to be 18.6% around 500 nm, with energy conversion efficiency of 6.9%, which were observed to be further enhanced to 23% and 9%, respectively, by adsorption of ruthenium or porphyrin dyes. Complementary electron transports from both HPA and dyes to TiO₂ nanodisc seems to avoid most of the backward electron or hole transfer reactions to enhance the photoelectrochemical efficiencies of dye-sensitized solar cells.     

Layer-by-layer nanoparticle coatings on lignocellulose wood microfibers

The layer-by-layer (LbL) self-assembly technique was applied to deposit organized multilayers of TiO₂ or SiO₂ nanoparticles of 30–80 nm diameter, and 50-nm diameter halloysite clay nanotubes on softwood fibers. Fluorescent and scanning electron microscopy images showed complete nanoparticle coating on these fibers. The thickness of the two-layer coating was estimated as 46, 58, and 115 nm for TiO₂, SiO₂, and halloysite tubules, respectively, which corresponds to ca. 1 wt% nanoparticle loading of the fibers. The brightness test of paper handsheets prepared from nanocoated fibers showed that TiO₂ nanoparticle coating gave handsheet reflectance of 84% at 450 nm, which is 4% higher than the brightness of the control sample from virgin fibers. The paper handsheets prepared with nanoparticle-coated fibers had 30–50% higher porosity with tensile strength index retained close to the control sample.     

Thermal plasma synthesis of nanotitania and its characterization

Titanium dioxide (TiO₂) nanoparticles were prepared by the thermal plasma synthesis; which give a highly crystalline product. Their morphological studies are carried out by using techniques like SEM, EDAX, TEM and SEAD. Crystal size was calculated by XRD using Scherrer equation; which is observed at two current amperes; at 80 A size ranges between 25 and 30 nm and at 120 A size ranges between 30 and 42 nm. Composition analysis was done by TEM–EDAX, FTIR and Fast Fourier Transform techniques. The FTIR peaks clearly show that synthesized TiO₂ nanoparticles are in anatase phase; this phase is generally preferred because of its high photocatalytic activity, since it has a more negative conduction band edge potential (higher potential energy of photogenerated electrons), high specific area, nontoxic, photochemically stable and relatively in expensive.     

Spectral broadening in quantum dots-sensitized photoelectrochemical solar cells based on CdSe and Mg-doped CdSe nanocrystals

In order to absorb a broad spectrum in visible region, a co-sensitized TiO₂ electrode was prepared by CdSe and Mg-doped CdSe quantum dots (Q dots). The power conversion efficiency of the co-sensitized Q dots photoelectrochemical solar cells (PECs) showed 1.03% under air mass 1.5 condition (I = 100 mW/cm²), which is higher than that of individual Q dots-sensitized PECs. The incident-photon-to-current conversion efficiency of the co-sensitized PECs showed absorption peaks at 541 and 578 nm corresponding to the two Q dots and displayed a broad spectral response over the entire visible spectrum in the 500–600 nm wavelength domains.     

Small diameter TiO2 nanotubes with enhanced photoresponsivity

We report ultraviolet (UV) light detection of thin wall TiO₂ nanotubes (TNTs) with open diameter ~ 20 nm obtained by a two anodization procedure. This small diameter nanotubular geometry shows significant enhancement of the photoresponsivity and results in a large increase of photocurrent. The photocurrent is one order higher than that of classical nanotubes with diameter of 140 nm at − 1.0 V bias. We attribute this improvement to the modulation of hole carrier density as a result of field effects from the diameter-dependent population of the surface-trapped electrons. This finding demonstrates inherent size effects of internal gain in semiconductor nanotubes.     

The reduction process of phytic acid–silver ion system: A pulse radiolysis study

Reduction of silver ion in a silver–phytic acid (1:1 ratio) system has been studied using pulse radiolysis technique. Time-resolved transformation of the intermediates, Ag⁺→Ag⁰→Ag₂⁺→Ag₃²⁺, has been clearly observed in the reduction of silver–phytic acid (1:1) system. The effect of phytic acid on the formation and decay of initial silver clusters has been also studied. The surface plasmon absorption band of stable silver nanoparticle (410 nm) and dynamic light scattering technique has been used to characterize the nanoparticles and measure the average size (R_av=100 nm).     

Photocatalytic activity of nitrogen and copper doped TiO2 nanoparticles prepared by microwave-assisted sol-gel process

Cu and N-doped TiO₂ photocatalysts were synthesized from titanium (IV) isopropoxide via a microwave-assisted sol-gel method. The synthesized materials were characterized by X-ray diffraction, UV-vis diffuse reflectance, photoluminescence (PL) spectroscopy, SEM, TEM, FT-IR, Raman spectroscopy, photocurrent measurement technique, and nitrogen adsorption–desorption isotherms. Raman spectra and XRD showed an anatase phase structure. The SEM and TEM images revealed the formation of an almost spheroid mono disperse TiO₂ with particle sizes in the range of 9-17 nm. Analysis of N₂ isotherm measurements showed that all investigated TiO₂ samples have mesoporous structures with high surface areas. The optical absorption edge for the doped TiO₂ was significantly shifted to the visible light region. The photocurrent and photocatalytic activity of pure and doped TiO₂ were evaluated with the degradation of methyl orange (MO) and methylene blue (MB) solution under both UV and visible light illumination. The doped TiO₂ nanoparticles exhibit higher catalytic activity under each of visible light and UV irradiation in contrast to pure TiO₂. The photocatalytic activity and photocurrent ability of TiO₂ have been enhanced by doping of the titania in the following order: (Cu, N) - codoped TiO₂ > N-doped TiO₂ > Cu-doped TiO₂ > TiO₂. COD result for (Cu, N)-codoped TiO₂ reveals ∼92% mineralization of the MO dye on six h of visible light irradiation.     

Enhanced electrochemical performance of carbon-coated TiO2 nanobarbed fibers as anode material for lithium-ion batteries

We report the electrochemical performance of carbon-coated TiO₂ nanobarbed fibers (TiO₂@C NBFs) as anode material for lithium-ion batteries. The TiO₂@C NBFs are composed of TiO₂ nanorods grown on TiO₂ nanofibers as a core, coated with a carbon shell. These nanostructures form a conductive network showing high capacity and C-rate performance due to fast lithium-ion diffusion and effective electron transfer. The TiO₂@C NBFs show a specific reversible capacity of approximately 170 mAh g^− 1 after 200 cycles at a 0.5 A g^− 1 current density, and exhibit a discharge rate capability of 4 A g^− 1 while retaining a capacity of about 70 mAh g^− 1. The uniformly coated amorphous carbon layer plays an important role to improve the electrical conductivity during the lithiation–delithiation process.     

Synthesis of silver nanoparticles supported on silica aerogel using gamma radiolysis

Silver clusters on SiO₂ support have been synthesized using ⁶⁰Co gamma radiation. The irradiation of Ag⁺ in aqueous suspension of SiO₂ in the presence of 0.2 mol dm⁻³ isopropanol resulted in the formation of yellow suspension. The absorption spectrum showed a band at 408 nm corresponding to typical characteristic surface plasmon resonance of Ag nanoparticles. The effect of Ag⁺ concentration on the formation of Ag cluster indicated that the size of Ag clusters vary with Ag⁺ concentration, which was varied from 4×10⁻⁴ to 5×10⁻³ mol dm⁻³. The results showed that Ag clusters are stable in the pH range of 2–9 and start agglomerating in the alkaline region at pH above 9. The effect of radiation dose rate and ratio of Ag⁺/SiO₂ on the formation of Ag clusters have also been investigated. The prepared clusters have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed the particle size of Ag clusters to be in the range of 10–20 nm.