Photoelectrochemical properties of TiO<Subscript>2</Subscript>/CdS heterostructures

The photoelectrochemical properties of TiO₂, CdS, and TiO₂/CdS anodes have been studied. The results demonstrate that, under illumination, CdS anodes are subject to photocorrosion, and Cd²⁺ ions pass into solution. Corrosion-resistant films of TiO₂ prevent CdS photocorrosion, and the CdS/TiO₂ system exhibits good photosensitivity in the visible range.     

CdS-sensitized ZnO nanorod arrays coated with TiO2 layer for visible light photoelectrocatalysis

A novel ZnO/CdS/TiO₂ nanorod array composite structure was fabricated by depositing CdS-sensitized layer onto ZnO nanorod arrays via chemical bathing deposition and subsequently coated by TiO₂ protection layer via a vacuum dip-coating process. The films were characterized by x-ray diffraction, field emission scanning electron microscopy, energy dispersive spectrum, and UV–Vis diffuse reflectance spectroscopy. For the films severed as the photoanodes, linear sweep voltammetry and transient photocurrent (i _ph) were investigated in a three-electrode system. The photoelectrocatalytic activity was evaluated by the degradation of methylene blue (MB) under visible light irradiation. The results show that the oriented ZnO nanorods are adhered by relatively uniform CdS-sensitized layer and coated with TiO₂ layer. Both the coated and uncoated CdS-sensitized ZnO nanorod arrays exhibit the visible light response and the photoelectrocatalytic activity on the degradation of MB under visible light irradiation. The ZnO/CdS/TiO₂ nanorod array film possesses stable and superior photoelectrocatalytic performance owing to the TiO₂ thin layer protecting the CdS from photocorrosion.     

Study of CdS-sensitized solar cells, prepared by ammonia-free chemical bath technique

In this study, cadmium sulfide (CdS)-sensitized solar cells have been fabricated, where nanoporous titanium oxide (TiO₂) photoelectrode of equal thickness has been prepared on SnO₂:F coated glass substrate using TiO₂ paste. Different amounts of CdS have been deposited by an ammonia-free chemical bath deposition technique with various deposition times. The CdS-sensitized TiO₂ photoelectrodes show polycrystalline nature. The optical measurement reveals that absorbance edge of the CdS-sensitized TiO₂ photoelectrode extends up to 540 nm and the amount of absorbance increases with the enhancement of CdS-deposition time. The CdS solar cell, with deposition time of 12 min, shows impressive photocurrent and moderate solar cell efficiency.     

Novel approach to control CdS morphology by simple microwave-solvothermal method

Nanosize CdS powders with different microstructures are prepared in different solvents by using rapid microwave irradiation. Effect of solvents and Cd²⁺ precursors are to be able to control the particle size, and microstructures of CdS have been investigated by X-ray diffraction and TEM. The different particle size and morphologies are observed using different Cd²⁺ precursors in different solvents. TEM micrographs clearly show multiarmed nanorods and spherical shape morphologies of CdS powders are obtained in polar solvent like water (H₂O), whereas non-polar polyol solvent like ethylene glycol (EG), prickle and cluster like morphologies of CdS are achieved with different Cd²⁺ precursors such as CdSO₄ and Cd (CH₃COO)₂. The spectroscopy studies of nanosize CdS are examined by photo-luminescence spectra. Band gap and the absorption co-efficient for nano CdS is also evaluated from optical absorption studies.     

Preparation of TiO2 from ilmenite using sulfuric acid decomposition of the titania residue combined with separation of Fe3+ with EDTA during hydrolysis

A new process of “mechanical activation–hydrochloric acid leaching–concentrated sulfuric acid decomposition–water leaching–separation of Fe³⁺ with EDTA during hydrolysis” was proposed to prepare high-purity TiO₂ from Panzhihua ilmenite. The hydrolyzed titania residue prepared from mechanically activated Panzhihua ilmenite leached by hydrochloric acid was decomposed by concentrated sulfuric acid and subsequently dissolved in water yielding titanium sulfate solution. In order to improve the purity of the precursor during the hydrolysis of TiO²⁺, EDTA was investigated as an additive to restrain the hydrolysis of Fe³⁺. The effects of sulfuric acid concentration, acid-to-titania residue mass ratio in the process of acid digestion and the significant effects of water leaching time, leaching temperature and liquid-to-solid mass ratios on the recovery of Ti from the residue were studied in this paper. The recovery of Ti was above 98% under optimal conditions. Well-crystallized anatase TiO₂ and rutile TiO₂ could be obtained through calcining at different temperatures and no impurity can be detected by EDS in titanium dioxide. The results demonstrated that the process is inexpensive, environment friendly and promising in preparing high-purity TiO₂ from ilmenite with a high content of gangues like Panzhihua ilmenite.     

Enhanced optical and hydrophilic properties of Si and Cd co-doped TiO<Subscript>2</Subscript> thin films

In this study, preparation of Si and Cd co doped (5 mol% Si and 5–20 mol% Cd) TiO₂ dip-coated thin films on glass substrates via sol–gel process have been investigated. The samples were characterized by X-ray diffraction (XRD) and Scanning electron microscopy analysis after heat treatments. XRD results suggested that adding dopants has a great effect on crystallinity and particle size of TiO₂. Titania rutile phase formation was inhibited by Si⁴⁺ and promoted by Cd²⁺ doping. But the effect of Cd doped appeared at high concentration. Accordingly, the thin films showed various water contact angles. The water contact angles changed from 69.0° to 9.6° by changing the content of Cd doped.     

Chemically deposited TiO2/CdS bilayer system for photoelectrochemical properties

In the present investigation, TiO₂, CdS and TiO₂/CdS bilayer system have been deposited on the fluorine doped tin oxide (FTO) coated glass substrate by chemical methods. Nanograined TiO₂ was deposited on FTO coated glass substrates by successive ionic layers adsorption and reaction (SILAR) method. Chemical bath deposition (CBD) method was employed to deposit CdS thin film on pre-deposited TiO₂ film. A further study has been made for structural, surface morphological, optical and photoelectrochemical (PEC) properties of FTO/TiO₂, FTO/CdS and FTO/TiO₂/CdS bilayers system. PEC behaviour of FTO/TiO₂/CdS bilayers was studied and compared with FTO/CdS single system. FTO/TiO₂/CdS bilayers system showed improved performance of PEC properties over individual FTO/CdS thin films.     

Interfacial assembly of sandwich mixed (Phthalocyaninato)(Porphyrinato) rare earth triple-decker complexes: Effect of in situ coordination

Interfacial assembly of sandwich mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes [(Pc)Eu(Pc)Eu(TPyP)] (1) and [(TPyP)Sm(Pc)Sm(TPyP)] (2) (Pc = phthalocyaninate, TPyP = meso-tetrakis(4-pyridyl)porphyrinate) has been comparatively studied at the air/pure water and the air/CdCl₂ aqueous solution subphase interfaces. Surface pressure-area isotherms revealed the remarkable increase of limiting mean molecular area of the triple-deckers with the presence of Cd²⁺, suggesting the occurrence of in situ interfacial coordination. The formation of coordination bonds between the pyridyl groups of TPyP macrocycles in the triple-deckers and Cd²⁺ ions from the subphase was further supported by FT-IR spectroscopic data. Electronic absorption measurements showed the formation of J-aggregates of the triple-decker molecules in the interfacial assembled films.     

The photoelectrochemistry of transition metal-ion-doped TiO2 nanocrystalline electrodes and higher solar cell conversion efficiency based on Zn2+-doped TiO2 electrode

Metal-ion-doped TiO₂ nanoparticles were prepared with hydrothermal method. The change of photocurrents at different electrode potentials and wavelengths of incident light showed two different characteristics for various transition metal-ion-doped TiO₂ electrodes. In Zn²⁺ and Cd²⁺-doped TiO₂ electrodes, a characteristic of n-type semiconductor was observed and the incident photon to conversion efficiency (IPCE) were larger than that of pure TiO₂ electrode at the thickness of electrode film of 0.5 m when the content of doped metal ion was less than 0.5%. The effect of the thickness of films on IPCE was also investigated. The IPCE of pure TiO₂ electrode was strongly dependent on the thickness of films. The change tendency of the IPCE for Zn²⁺-doped TiO₂ (0.5% Zn²⁺) electrodes with its thickness was different from that of pure TiO₂. In Fe³⁺, Co²⁺, Ni²⁺, Cr³⁺ and V⁵⁺-doped TiO₂ electrodes, a phenomenon of p-n conversion was observed. The difference of photoresponse and the value of photocurrents are dependent on the doping method and concentration of the doped metal ions. The maximum conversion efficiency of RuL₂(SCN)₂-sensitized Zn²⁺-doped TiO₂ solar cell (1.01%) was larger than that of RuL₂(SCN)₂-sensitized pure TiO₂ solar cell (0.82%) at the same conditions when 0.5 mol·l^–1 (CH₃)₄N·I+0.05 mol·l^–1 I₂ in propylene carbonate solution was used as electrolyte.     

The gas sensitivity of nano TiO2-SnO2 film doped with Cd(II) ion

The nanocomposite oxide (0.2TiO₂-0.8SnO₂) doped with Cd²⁺ powder have been prepared and characterized by XRD and their gas-sensing sensitivity were characterized using gas sensing measurement. Experimental results show that, bicomponent nano anatase TiO₂ and rutile SnO₂ particulate thick film doped with Cd²⁺ behaves with good sensitivity to formaldehyde gas of 200 ppm in the air, and the optimum sensing temperature was reduced from 360 °C to 320 °C compared with the undoped Cd²⁺ thick film. The gas sensing thick films doped with Cd²⁺ also show good selectivity to formaldehyde among benzene, toluene, xylene and ammonia as disturbed gas and could be effectively used as an indoor formaldehyde sensor.     

Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue)

Lanthanide ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, and Yb³⁺)/doped TiO₂ nanoparticles were successfully synthesized by sol–gel method. Their photocatalytic activities were evaluated using Direct Blue dye (DB53) as a decomposition objective. The structural features of TiO₂ and lanthanide ions/TiO₂ were investigated by XRD, SEM, UV-diffuse reflectance, and nitrogen adsorption measurements. Our findings indicated that XRD data characteristic anatase phase reflections and also XRD analysis showed that lanthanides phase was not observed on Lanthanide ions/TiO₂. The results indicated that Gd³⁺/TiO₂ has the lowest bandgap and particle size and also the highest surface area and pore volume (V_p) as well. Lanthanide ions can enhance the photocatalytic activity of TiO₂ to some extent as compared with pure TiO₂ and it was found that Gd³⁺/TiO₂ is the most effective photocatalyst. The photocatalytic tests indicate that at the optimum conditions; illumination time 40 min, pH ∼4, 0.3 g/L photocatalyst loading and 100 ppm DB53; the dye removal efficiency was 100%. Details of the synthesis procedure and results of the characterization studies of the produced lanthanide ions/TiO₂ are presented in this paper.     

Boron implantation effects in CdS thin films grown by chemical synthesis

CdS thin films grown on ITO/glass substrates by using chemical bath (CB) were boron-implanted employing 100 keV beam of boron ions (B⁺) with fluences in the range 1.0×10¹⁵–1.0×10¹⁶ ions/cm². The B doping was successfully carried out, as was proved by the major carrier density introduced in the range 0.8×10¹⁸–5.4×10¹⁸ cm⁻³, which was calculated from thermo power measurements. Raman spectroscopy results support the assumption that triply ionized boron (B³⁺) enters into the CdS lattice occupying Cd²⁺ sites, which create shallow donor levels in the forbidden energy band gap.     

Surfactant-dependent photoluminescence of CdTe/CdS nanocrystals

ABSTRACT

The photoluminescence of aqueously synthesised core/shell CdTe/CdS quantum dots (QDs) was investigated. Two molar ratios (2.4 and 1.3) of thioglycolic acid (TGA) to Cd²⁺ were compared to determine the best synthesis conditions for high photoluminescent quantum yield (PLQY) and photostability. A difference in the PLQY of the CdTe/CdS QDs was observed when CdS shells were grown with different TGA/Cd²⁺ ratios. The difference in the observed PLQY was attributed to the quality of the passivation of the CdTe during the CdS shell growth. At TGA/Cd²⁺ ratio of 1.3, the CdS shell forms through homogeneous nucleation, which is limited by diffusion of growth material from the solution onto the QDs surface. Due to the lattice mismatch of CdTe and CdS, the core will experience coherence strain resulting in dislocation sites and surface defects between nucleation sites which can result in non-radiative trap states. When the TGA/Cd²⁺ ratio is 2.0, the CdS shell grows epitaxially, minimising the number of surface trap states. Finally, we observed that the fluorescence intermittency was supressed for CdTe QDs after UV light illumination, attributed to annealing of deep surface trap states by UV light.     

Synthesis of CdS-Au2S-Au hybrid dendritic nanostructures

The hybrid CdS-Au₂S-Au dendritic nanocrystals were synthesized in toluene solution at 70 °C. UV-vis and photoluminescence (PL) spectra recorded the optical properties of hybrid nanostructures, which showed an obvious blue shift relative to the absorption peak of CdS dendritic nanocrystals. The initial CdS dendritic nanocrystals exhibited band gap and trap state emission, both of which were quenched by Au parts. Analysis of the hybrid nanostructures by XRD shows the presence of appreciable amounts of Au₂S, indicating that the chemical process involving cation exchanges between Au⁺ ions and Cd²⁺ ions was found.     

Electrodepositions of CdS,ZnS and Cd1-xZnxS films

Thin films of CdS, ZnS and Cd_1-xZn_xS, (0< x<1) have been electrodeposited from acidic bath using CdSO₄, ZnSO₄ and Na₂S₂O₃ at pH between 2 to 2.5 onto different substrates. The structural and optical properties of these films have been studied. It was found that CdS, ZnS and Cd_1-x Zn_x S film could be electrodeposited from acidic bath. The XRD patterns showed that the films consist of mixed phases of CdS and ZnS with presence of free Cd, Zn and S. The optical properties showed that bandgaps of CdS and ZnS are 2.4 and 3.55 eV respectively. The bandgaps of Cd_1-x Zn_x S films varied between 2.4 to 3.55 eV, depending upon Zn content in the film.     

Synthesis and environmental applications of cellulose/ZrO2 nanohybrid as a selective adsorbent for nickel ion

Cellulose/ZrO₂ nanohybrid has been synthesized by simple growth of ZrO₂ on cellulose matrix and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Interestingly, FESEM showed nanoparticles with an average size of 50 nm. The analytical potential of the newly prepared nanohybrid was studied for a selective extraction of nickel prior to its determination by inductively coupled plasma-optical emission spectrometry. The selectivity of nanohybrid was investigated toward eight metal ions, including Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Ni²⁺, Zn²⁺ and Zr⁴⁺. Data obtained from the selectivity study showed that nanohybrid was the most selective toward Ni²⁺. The uptake capacity for Ni²⁺ was experimentally calculated and found to be 79 mg g⁻¹. Moreover, adsorption isotherm data of Ni²⁺ on nanohybrid was well fit with the Langmuir adsorption isotherm, strongly supporting that the adsorption process was mainly monolayer on homogeneous adsorbent surfaces. Finally, data of Ni²⁺ adsorption on nanohybrid as a function of contact time displayed that equilibrium kinetics are very fast.     

Formation of Cd particles by UV laser irradiation

Formation of the metal particles of Cd has been studied by nanosecond laser flash photolysis using an ArF excimer laser with the oscillation wavelength of 193 nm. The sample was a 10% methanol solution of CdCl₂. The solvated electron, e_aq⁻, was generated by the excitation of charge transfer bands of Cl⁻ to solvent. The e_aq⁻ efficiently reduced Cd²⁺ to Cd⁺ during a laser pulse of 30 ns (FWHM). The Cd particles were produced by the reaction between Cd⁺ and Cd⁺. In the air saturated solution, the Cd⁺ was easily oxidized by dissolved oxygen. The concentration of the Cd particles formed in the degassed solution was approximately twice of that in the air saturated solution.     

Varied crystalline orientation of anatase TiO<Subscript>2</Subscript> nanotubes from [101] to [001] promoted by TiF<Subscript>6</Subscript><Superscript>2−</Superscript> ions and their enhanced photoelectrochemical performance

Herein, we report an ionic cross-linkage process of synthesizing [001] preferred oriented anatase TiO₂ nanowires and nanotubes hybrid structure (TWTs) based on anodization method wherein varied amounts of TiF₆ ^2? ions are added in synthetic process. We show how the TiF₆ ^2? ions switch the growth direction of TWTs from [101] to [001] (denoted as T₁₀₁WTs and T₀₀₁WTs, respectively) and change their geometrical morphologies, i.e., small ionic radii TiF₆ ^2? ions migrate and partly replace the TiO₆ ^2? octahedra under electric field, which separate out and leave vacancies during annealing process, resulting in a reconstruction of TiO₂. Importantly, absorption property and photoelectrochemical (PEC) performance of T₀₀₁WTs exceed those of T₁₀₁WTs. Furthermore, CdS QDs are assembled onto TWTs photoelectrodes by successive ionic layer adsorption and reaction technique. Likewise, T₀₀₁WT/CdS presents superior absorption capability and enhanced PEC performance to those of T₁₀₁WT/CdS. This could be attributed to their preponderances of improved light absorption capability and decreased electron recombination.     

Growth of CdS nanoparticles in Y- and Z-type Langmuir–Blodgett thin film using 1,3-bis-(p-iminobenzoic acid)indane

Cadmium sulphide (CdS) nanoparticles were formed in 1,3-bis-(p-iminobenzoic acid)indane by exposing Cd²⁺ doped Y- and Z-type multilayered Langmuir–Blodgett (LB) films to H₂S gas. The growth of CdS nanoparticles were monitored by UV–visible spectroscopy measurements. It was observed that CdS nanoparticles in both Y- and Z-type LB films cause a blue-shift in absorption spectra. The surface morphology of LB films were characterized with atomic force microscopy DC electrical measurements were carried out for these LB films grown in a metal/LB film/metal sandwich structures with and without CdS nanoparticles. By analyzing I–V curves and assuming Schottky conduction mechanism the barrier height was found to be as 1.25 and 1.17?eV for Y-type unexposed and exposed samples; 1.18 and 1.25?eV for Z-type unexposed and exposed samples, respectively.     

Synthesis,characterization and optical properties of CdS nanoparticles confined in SBA-15

A novel and dexterous in situ method is introduced to load CdS nanocrystals into SBA-15, which uses the acid–base reaction of mercaptoacetic acid with 3-aminopropyltriethoxysilane, the modifier of internal surface of mesoporous materials to facilitate loading of sulfur precursor, followed by adsorption of Cd²⁺ and calcination at 300 °C in N₂ atmosphere for 2 h. XRD, N₂ adsorption–desorption isotherms, HRTEM, EDS, FT-IR, UV–vis absorption spectrum and PL spectrum were used to characterize the composite material. It was found that the CdS nanocrystals were confined in the channel of SBA-15 with an average size of 6 nm. The mesoporous silica-supported CdS composites showed a room temperature photoluminescence property.