Hitchhiking Nanoparticles: Mesenchymal Stem Cell-Mediated Delivery of Theranostic Nanoparticles

Nanotechnology has emerged as a promising solution to permanent elimination of cancer. However, nanoparticles themselves lack specificity to tumors. Due to enhanced migration to tumors, mesenchymal stem cells (MSCs) were suggested as cell-mediated delivery vehicles of nanoparticles. In this study, we have constructed a complex composed of photoluminescent quantum dots (QDs) and a photosensitizer chlorin e6 (Ce6) to obtain multifunctional nanoparticles, combining cancer diagnostic and therapeutic properties. QDs serve as energy donors-excited QDs transfer energy to the attached Ce6 via Förster resonance energy transfer, which in turn generates reactive oxygen species. Here, the physicochemical properties of the QD-Ce6 complex and singlet oxygen generation were measured, and the stability in protein-rich media was evaluated, showing that the complex remains the most stable in protein-free medium. In vitro studies on MSC and cancer cell response to the QD-Ce6 complex revealed the complex-loaded MSCs' potential to transport theranostic nanoparticles and induce cancer cell death. In vivo studies proved the therapeutic efficacy, as the survival of tumor-bearing mice was statistically significantly increased, while tumor progression and metastases were slowed down.

Three-dimensional dose-distribution measurement of therapeutic carbon-ion beams using a ZnS scintillator sheet

The accurate measurement of the 3D dose distribution of carbon-ion beams is essential for safe carbon-ion therapy. Although ionization chambers scanned in a water tank or air are conventionally used for this purpose, these measurement methods are time-consuming. We thus developed a rapid 3D dose-measurement tool that employs a silver-activated zinc sulfide (ZnS) scintillator with lower linear energy transfer (LET) dependence than gadolinium-based (Gd) scintillators; this tool enables the measurement of carbon-ion beams with small corrections. A ZnS scintillator sheet was placed vertical to the beam axis and installed in a shaded box. Scintillation images produced by incident carbon-ions were reflected with a mirror and captured with a charge-coupled device (CCD) camera. A 290 MeV/nucleon mono-energetic beam and spread-out Bragg peak (SOBP) carbon-ion passive beams were delivered at the Gunma University Heavy Ion Medical Center. A water tank was installed above the scintillator with the water level remotely adjusted to the measurement depth. Images were recorded at various water depths and stacked in the depth direction to create 3D scintillation images. Depth and lateral profiles were analyzed from the images. The ZnS-scintillator-measured depth profile agreed with the depth dose measured using an ionization chamber, outperforming the conventional Gd-based scintillator. Measurements were realized with smaller corrections for a carbon-ion beam with a higher LET than a proton. Lateral profiles at the entrance and the Bragg peak depths could be measured with this tool. The proposed method would make it possible to rapidly perform 3D dose-distribution measurements of carbon-ion beams with smaller quenching corrections.

Rolling circle amplification promoted magneto-controlled photoelectrochemical biosensor for organophosphorus pesticides based on dissolution of core-shell MnO2 nanoflower@CdS mediated by butyrylcholinesterase

A photoelectrochemical (PEC) aptasensing platform is devised for sensitive detection of an organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by thiocholine (TCh). TCH is produced from the butyrylcholinesterase-acetylthiocholine system, accompanied by target-triggered rolling circle amplification (RCA). The core-shell MnO₂ NF@CdS with excellent PEC performance was synthesized and employed as a photo-sensing platform. The target was detected on a functionalized magnetic probe with the corresponding aptamer. Upon malathion introduction, the aptamer was detached from the magnetic beads, while capture DNA (cDNA, with primer fragment) remained on the beads. The primer fragment in cDNA can trigger the RCA reaction to form a long single-stranded DNA (ssDNA). Furthermore, a large number of butyrylcholinesterase (BChE) were assembled on the long ssDNA strands through the hybridization with the S₂-Au-BChE probe. Thereafter, TCh generated from hydrolysis of ATCh by BChE can reduce MnO₂ NF (core) to Mn²⁺ and release the CdS nanoparticles (shell) from the platform electrode, significantly enhancing the PEC signal. Under optimal conditions, the proposed aptasensor exhibited high sensitivity for malathion with a low detection limit of 0.68 pg mL^-1. Meanwhile, it also presents outstanding specificity, reproducibility, and stability. Importantly, the sensing platform provides a new concept for detection of pesticide. Graphical abstract Herein, this work devised a photoelectrochemical (PEC) aptasensing platform for sensitive detection of organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by the as-produced thiocholine (TCh) from the butyrylcholinesterase-acetylthiocholine system, accompanying with the target-triggered rolling circle amplification (RCA).

Design and synthesis of robust Z-scheme ZnS-SnS2 n-n heterojunctions for highly efficient degradation of pharmaceutical pollutants: Performance, valence/conduction band offset photocatalytic mechanisms and toxicity evaluation

Petal-like ZnS-SnS₂ heterojunctions with Z-scheme band alignment were prepared by one-pot solvothermal strategy. The optimal (1:1) ZnS-SnS₂ can degrade 93.46 % of tetracycline and remove 73.9 % COD of pharmaceutical wastewater under visible-light irradiation due to the efficient production of H, O₂^-, h⁺ and OH. The toxicity evaluation by ECOSAR prediction and the growth of E. coli indicates efficient toxicity reduction of tetracycline by photocatalysis and the non-toxicity of ZnS-SnS₂. The attacked sites on tetracycline by reactive species were analyzed according to Fukui index, and two degradation pathways of tetracycline were inferred via the identification of intermediate products. Tetracycline degradation efficiency and the energy consumption in different water bodies were compared, and it was found that the electrical energy per order (EE/O) was the lowest in Ganjiang River. The valence band offset (ΔE_VBO) and conduction band offset (ΔE_CBO) of ZnS-SnS₂ were 1.02 eV and 0.22 eV, respectively. The probable photocatalytic mechanism of ZnS/SnS₂ heterojunctions with Z-scheme band alignment based on ΔE_VBO and ΔE_CBO was first presented.

Fabrication of vessel-like biochar-based heterojunction photocatalyst Bi2S3/BiOBr/BC for diclofenac removal under visible LED light irradiation: Mechanistic investigation and intermediates analysis

In this work, a novel, economical and effective vessel-like biochar-based photocatalyst Bi₂S₃/BiOBr/BC was synthesized by a facile one-pot solvothermal method for the first time. A series of characterization analyses demonstrated the successful preparation of photocatalyst Bi₂S₃/BiOBr/BC. Furthermore, diclofenac (DCF) as the target contaminant was applied to elucidate the enhanced photocatalytic performance (93.65%, 40 min) under energy-saving visible LED light irradiation. Comparison experiments among different photocatalysts and photoelectrochemical tests results illustrated that excellent photocatalytic performance of Bi₂S₃/BiOBr/BC 10% might be attributed to the electrons transfer of biochar and higher charge separation efficiency of heterojunction structure. Besides, lower electrical energy per order value indicated photocatalyst/visible LED light system was more energy-saving. Proper photocatalyst dosage (0.6 g/L) and relatively acidic water environment (pH = 5.0) would be beneficial to DCF photodegrdation by Bi₂S₃/BiOBr/BC. Good reusability and stability of Bi₂S₃/BiOBr/BC were verified via five consecutive recycle experiments. Furthermore, the role of active species was determined through trapping experiments and O₂- and h⁺ dominated the photodegradation reaction to mineralize DCF molecules. Eleven main intermediates and four possible photodegradation pathways were proposed by HRMS analysis. Accordingly, photocatalyst Bi₂S₃/BiOBr/BC would provide potential technical support for emerging pollutant removal in water matrix.

Selective and sensitive visible-light-prompt photoelectrochemical sensor of Cu2+ based on CdS nanorods modified with Au and graphene quantum dots

Nowadays, increasing the risk for copper leaching into the drinking water in homes, hotels and schools has become unresolved issues all around the countries such as Canada, the United States, and Malaysia. The leaching of copper in tap water is due to a combination of acidic water, damaged pipes, and corroded plumbing fixtures. To remedy this global problem, a triple interconnected structure of CdS/Au/GQDs was designed as a photo-to-electron conversion medium for a real time and selective visible-light-prompt photoelectrochemical (PEC) sensor for Cu²⁺ ions in real water samples. The synergistic interaction of the CdS/Au/GQDs enabled the smooth transportation of charge carriers to the charge collector and provided a channel to inhibit the charge recombination reaction. Thus, a detection limit of 2.27 nM was obtained, which is 10,000 fold lower than that of WHO's Guidelines for Drinking-water Quality (∼30 μM). The photocurrent reduction was negligible after 30 days of storage under ambient conditions, suggesting the high stability of photoelectrode. Moreover, the real-time monitoring of Cu²⁺ ions in real samples was performed with satisfactory results, confirming the capability of the investigated photoelectrode as the most practical detector for trace amounts of Cu²⁺ ions.

Performance optimization of CdS precipitated graphene oxide/polyacrylic acid composite for efficient photodegradation of chlortetracycline

Here a CdS embedded poly acrylic acid (PAA)/graphene oxide (GO) polymeric composite was prepared for the efficient degradation of chlortetracycline (CTC) driven by visible light irradiation. The structure-activity relationship of GO/PAA-CdS was confirmed through the photocatalytic evaluation of a series of samples prepared by varying GO concentration, molar ratio of Cd:S and the amount of crosslinking agent. Through the composition, morphology, photoelectrochemical characterizations and degradation kinetic studies, it could be confirmed that the enhanced photocatalytic activity is attributed to the controlled growth of CdS nanoparticles by polymer net structure and effective electron transfer along GO nanosheets. The photodegradation of CTC was confirmed to be mainly governed by O₂^- and OH radicals generated from GO/PAA-CdS. The degradation intermediates of CTC were confirmed by LC-MS, and possible degradation pathways were proposed based on the prediction of radical attacking sites according to Fukui function values obtained through Density Functional Theory (DFT). Moreover, it was found that the catalytic activity of the photocatalyst was maintained after several cycles confirming the enhanced anti-photocorrosion of GO/PAA-CdS. This research provided an efficient approach by a novel photocatalyst for the removal of CTC from wastewater.

Nitrofurazone degradation in the self-biased bio-photoelectrochemical system: g-C3N4/CdS photocathode characterization, degradation performance, mechanism and pathways

In this study, a self-biased bio-photoelectrochemical system (SB-BPES) was constructed using a bioanode and the g-C₃N₄/CdS heterojunction photocathode for nitrofurazone (NFZ) degradation under solar irradiation. The physio-chemical properties and optical performance of photocatalysts were characterized, and photo-electrochemical properties of various photocathodes were analyzed. Results showed that g-C₃N₄/CdS exhibited the broadest visible light absorption range (to 594 nm) and the most efficient e^--h⁺ separation; and its corresponding photocathode showed the highest photocurrent (9.8 μA), and the lowest charge transfer resistance (5.43 ☓ 10³ Ω). In the solar-illuminated SB-BPES with g-C₃N₄/CdS photocathode, about 80% of NFZ removal rate was achieved within 10 h. More importantly, TOC removal of 62.6% was achieved in 24 h, which was 1.8 times of that from the open circuit SB-BPES, and 4.3 folds of that from microbial degradation; also, about 1.5 times of those from SB-BPES with g-C₃N₄ and CdS photocathodes. Besides, reproducible current generations (∼1.0 mA) were produced. These verified that it was a self-sustained system for spontaneously pollutants degradation and electricity generation. Moreover, possible degradation mechanism and pathways were proposed according to the identified intermediates. This study provides inspiration for synchronic improving refractory organics degradation and net energy recovery.

Direct Z-scheme 1D/2D WO2.72/ZnIn2S4 hybrid photocatalysts with highly-efficient visible-light-driven photodegradation towards tetracycline hydrochloride removal

There are increasing environmental concerns of serious pollution from emission of antibiotic wastewater. Herein, a series of direct Z-scheme WO_2.72/ZnIn₂S₄ (WOZIS) hybrid photocatalysts composed of one-dimensional (1D) WO_2.72 (WO) nanorods and two-dimensional (2D) ZnIn₂S₄ (ZIS) nanosheets have been designed and constructed for tetracycline hydrochloride (TCH) degradation without presence of solid-state electron mediators. The crystalline phase, chemical composition, morphology, optical properties and photocatalytic activity of the as-prepared samples were characterized by the XRD, XPS, SEM, HRTEM, BET, UV-vis DRS, and PL. Obviously, all the WOZIS hybrid photocatalysts exhibited significantly enhanced photocatalytic activity towards TCH degradation. Meanwhile, WOZIS-1 sample with WO/ZIS molar ratio of 1:1 showed the highest photocatalytic activity. The significantly enhanced photoactivity of WOZIS hybrid photocatalyst was due to Z-scheme charge separation mechanism based on the build of tight interfacial contacts between WO nanorods and ZIS nanosheets, thereby driving efficient charge separation. Moreover, the high photocatalytic stability of as-prepared WOZIS-1 hybrid sample was revealed through seven successive cycling reactions.

One-step in situ hydrothermal fabrication of octahedral CdS/SnIn4S8 nano-heterojunction for highly efficient photocatalytic treatment of nitrophenol and real pharmaceutical wastewater

Octahedral CdS/SnIn₄S₈ nano-heterojunctions were fabricated by a facile and simple one-step in situ hydrothermal method, and the molar ratio of CdS to SnIn₄S₈ was optimized. The optimal (0.5:1)CdS/SnIn₄S₈ heterojunctions exhibit the highest visible-light photocatalytic activity with 97.1% degradation efficiency of 2-nitrophenol in 120min, which is much higher than those of individual CdS and SnIn₄S₈. The enhanced photocatalytic performance could be attributed to the effective separation and transfer of photogenerated charges originating from the well-matched band gap structures. Of special significance is that (0.5:1)CdS/SnIn₄S₈ can effectively mineralize 2-nitrophenol and real pharmaceutical wastewater. Moreover, CdS/SnIn₄S₈ nano-heterojunctions show excellent reusability in five cycles due to the stable surface composition and chemical valence state.

TiO2-SnS2 nanocomposites: solar-active photocatalytic materials for water treatment

The study is aimed at evaluating TiO₂-SnS₂ composites as effective solar-active photocatalysts for water treatment. Two strategies for the preparation of TiO₂-SnS₂ composites were examined: (i) in-situ chemical synthesis followed by immobilization on glass plates and (ii) binding of two components (TiO₂ and SnS₂) within the immobilization step. The as-prepared TiO₂-SnS₂ composites and their sole components (TiO₂ or SnS₂) were inspected for composition, crystallinity, and morphology using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analyses. Diffuse reflectance spectroscopy (DRS) was used to determine band gaps of immobilized TiO₂-SnS₂ and to establish the changes in comparison to respective sole components. The activity of immobilized TiO₂-SnS₂ composites was tested for the removal of diclofenac (DCF) in aqueous solution under simulated solar irradiation and compared with that of single component photocatalysts. In situ chemical synthesis yielded materials of high crystallinity, while their morphology and composition strongly depended on synthesis conditions applied. TiO₂-SnS₂ composites exhibited higher activity toward DCF removal and conversion in comparison to their sole components at acidic pH, while only in situ synthesized TiO₂-SnS₂ composites showed higher activity at neutral pH.

Toxicological impact of cadmium-based quantum dots towards aquatic biota: Effect of natural sunlight exposure

Cadmium-based quantum dots (QDs) are increasingly applied in existent and emerging technologies, especially in biological applications due to their exceptional photophysical and functionalization properties. However, they are very toxic compounds due to the high reactive and toxic cadmium core. The present study aimed to determine the toxicity of three different QDs (CdS 380, CdS 480 and CdSeS/ZnS) before and after the exposure of suspensions to sunlight, in order to assess the effect of environmentally relevant irradiation levels in their toxicity, which will act after their release to the environment. Therefore, a battery of ecotoxicological tests was performed with organisms that cover different functional and trophic levels, such as Vibrio fischeri, Raphidocelis subcapitata, Chlorella vulgaris and Daphnia magna. The results showed that core-shell type QDs showed lower toxic effects to V. fischeri in comparison to core type QDs before sunlight exposure. However, after sunlight exposure, there was a decrease of CdS 380 and CdS 480 QD toxicity to bacterium. Also, after sunlight exposure, an effective decrease of CdSeS/ZnS and CdS 480 toxicity for D. magna and R. subcapitata, and an evident increase in CdS 380 QD toxicity, at least for D. magna, were observed. The results of this study suggest that sunlight exposure has an effect in the aggregation and precipitation reactions of larger QDs, causing the degradation of functional groups and formation of larger bulks which may be less prone to photo-oxidation due to their diminished surface area. The same aggregation behaviour after sunlight exposure was observed for bare QDs. These results further emphasize that the shell of QDs seems to make them less harmful to aquatic biota, both under standard environmental conditions and after the exposure to a relevant abiotic factor like sunlight.

Hierarchical Layered WS2 /Graphene-Modified CdS Nanorods for Efficient Photocatalytic Hydrogen Evolution

Graphene-based ternary composite photocatalysts with genuine heterostructure constituents have attracted extensive attention in photocatalytic hydrogen evolution. Here we report a new graphene-based ternary composite consisting of CdS nanorods grown on hierarchical layered WS2 /graphene hybrid (WG) as a high-performance photocatalyst for hydrogen evolution under visible light irradiation. The optimal content of layered WG as a co-catalyst in the ternary CdS/WS2 /graphene composites was found to be 4.2 wt %, giving a visible light photocatalytic H2 -production rate of 1842 μmol h(-1)  g(-1) with an apparent quantum efficiency of 21.2 % at 420 nm. This high photocatalytic H2 -production activity is due to the deposition of CdS nanorods on layered WS2 /graphene sheets, which can efficiently suppress charge recombination, improve interfacial charge transfer, and provide reduction active sites. The proposed mechanism for the enhanced photocatalytic activity of CdS nanorods modified with hierarchical layered WG was further confirmed by transient photocurrent response. This work shows that a noble-metal-free hierarchical layered WS2 /graphene nanosheets hybrid can be used as an effective co-catalyst for photocatalytic water splitting.

Composition Directed Generation of Reactive Oxygen Species in Irradiated Mixed Metal Sulfides Correlated with Their Photocatalytic Activities

The ability of nanostructures to facilitate the generation of reactive oxygen species and charge carriers underlies many of their chemical and biological activities. Elucidating which factors are essential and how these influence the production of various active intermediates is fundamental to understanding potential applications of these nanostructures, as well as potential risks. Using electron spin resonance spectroscopy coupled with spin trapping and spin labeling techniques, we assessed 3 mixed metal sulfides of varying compositions for their abilities to generate reactive oxygen species, photogenerate electrons, and consume oxygen during photoirradiation. We found these irradiated mixed metal sulfides exhibited composition dependent generation of ROS: ZnIn2S4 can generate (•)OH, O2(-•) and (1)O2; CdIn2S4 can produce O2(-•) and (1)O2, while AgInS2 only produces O2(-•). Our characterizations of the reactivity of the photogenerated electrons and consumption of dissolved oxygen, performed using spin labeling, showed the same trend in activity: ZnIn2S4 > CdIn2S4 > AgInS2. These intrinsic abilities to generate ROS and the reactivity of charge carriers correlated closely with the photocatalytic degradation and photoassisted antibacterial activities of these nanomaterials.

Photocatalytic properties of zinc sulfide nanocrystals biofabricated by metal-reducing bacterium Shewanella oneidensis MR-1

Accumulation and utilization of heavy metals from wastewater by biological treatment system has aroused great interest. In the present study, a metal-reducing bacterium Shewanella oneidensis MR-1 was used to explore the biofabrication of ZnS nanocrystals from the artificial wastewater. The biogenic H2S produced via the reduction of thiosulfate precipitated the Zn(II) as sulfide extracellularly. Characterization by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscope (FESEM) confirmed the precipitates as ZnS nanocrystals. The biogenic ZnS nanocrystals appeared spherical in shape with an average diameter of 5 nm and mainly aggregated in the medium and cell surface of S. oneidensis MR-1. UV-vis DRS spectra showed ZnS nanoparticles appeared a strong absorption below 360 nm. Thus, the photocatalytic activity of ZnS was evaluated by the photodegradation of rhodamine B (RhB) under UV irradiation. The biogenic ZnS nanocrystals showed a high level of photodegradation efficiency to RhB coupled with a significant blue-shift of maximum adsorption peak. A detailed analysis indicated the photogenerated holes, rather than hydroxyl radicals, contributed to the photocatalytic decolorization of RhB. This approach of coupling biosynthesis of nanoparticles with heavy metal removal may offer a potential avenue for efficient bioremediation of heavy metal wastewater.

A superior photocatalytic performance of a novel Bi2SiO5 flower-like microsphere via a phase junction

A phase junction over a Bi(2)SiO(5) photocatalyst with the orthorhombic Bi(2)SiO(5) and the tetragonal Bi(2)SiO(5) structure was successfully synthesized via an ion exchange method using BiOBr solid microspheres as the sacrificial template. In the meantime, the as-prepared Bi(2)SiO(5) phase junction possesses a novel morphology of a flower-like microsphere with nanoparticles evenly embedded in its nano-petals. It was found that the Bi(2)SiO(5) phase junction not only showed a highly enhanced photocatalytic activity and excellent durability under UV or simulated solar irradiation, but also showed a remarkable visible-light activity for photo-degradation of phenol. Experimental results reveal that the tetragonal Bi(2)SiO(5) phase in this phase junction possesses a narrower band gap, thus leading to its extended light absorption. The efficient charge separation via a phase junction would make a great contribution to its highly enhanced photocatalytic activity under UV or simulated solar irradiation. The high efficiency in the degradation of organic pollutants makes the as-prepared photocatalyst a promising candidate for photocatalytic environmental purification.

Nano-sized quaternary CuGa2In3S8 as an efficient photocatalyst for solar hydrogen production

The synthesis of quaternary metal sulfide (QMS) nanocrystals is challenging because of the difficulty to control their stoichiometry and phase structure. Herein, quaternary CuGa2In3S8 photocatalysts with a primary particle size of ≈4 nm are synthesized using a facile hot-injection method by fine-tuning the sulfur source injection temperature and aging time. Characterization of the samples reveals that quaternary CuGa2In3S8 nanocrystals exhibit n-type semiconductor characteristics with a transition band gap of ≈1.8 eV. Their flatband potential is located at -0.56 V versus the standard hydrogen electrode at pH 6.0 and is shifted cathodically by 0.75 V in solutions with pH values greater than 12.0. Under optimized conditions, the 1.0 wt % Ru-loaded CuGa2In3S8 photocatalyst exhibits a photocatalytic H2 evolution response up to 700 nm and an apparent quantum efficiency of (6.9±0.5) % at 560 nm. These results indicate clearly that QMS nanocrystals have great potential as nano-photocatalysts for solar H2 production.

Near-infrared-emitting two-dimensional codes based on lattice-strained core/(doped) shell quantum dots with long fluorescence lifetime

Lattice-strained CdTe/CdS:Cu quantum dots (QDs) with a widely tunable near-infrared (NIR) fluorescence emission spectrum (700-910 nm) and long lifetime (up to 1 μs) are synthesized. Based on the multiemission and multi-lifetime of the well-defined QDs, NIR-emitting two-dimensional (2D) codes are achieved by embedding as-prepared QDs into agarose beads. This provides a new strategy for fluorescent 2D codes.

Adsorption and enhanced photocatalytic activity of the {0 0 0 1} faceted Sm-doped ZnIn2S4 microspheres

In this study, the doping effect of samarium on the structure, morphology, adsorption and photocatalytic performance of hexagonal ZnIn2S4 microspheres was studied. The photocatalytic activity of Sm-doped ZnIn2S4 microspheres was evaluated for the photodegradation of Rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The samples were characterized by XRD, SEM, XPS, UV-vis, TEM, and N2 adsorption-desorption analysis. The results show that the hexagonal ZnIn2S4 microspheres are composed of nanoplates growing along c-axis with the predominant negative-charged S plane. Compared with the photodegadation of MO dye, the negative-charged {0 0 0 1} facets not only are beneficial for the adsorption of RhB by -N(Et)2 groups but also can accumulate the separation of photogenerated electrons and holes, enhancing photodegradation efficiency by direct-hole photocatalysis. Moreover, Sm is partially substituted for In in the crystal lattice for forming the doping energy level which promotes the separation of photoinduced electron-hole pairs and enhances absorption of visible light. Hexagonal 2% Sm-doped ZnIn2S4 microspheres with exposed {0 0 0 1} facets resulted in higher photodegradation efficiency of RhB under visible light irradiation.

ESR dating of barite in sulphide deposits formed by the sea-floor hydrothermal activities

Barite is a mineral newly found to be practically useful for electron spin resonance (ESR) dating of sulphide deposits formed by the sea-floor hydrothermal activities. The recent studies for the properties of the ESR dating signal in barite are summarised in the present paper as well as the formulas for corrections for accurate dose-rate estimation are developed including the dose-rate conversion factors, shape correction for gamma-ray dose and decay of (226)Ra. Although development of the techniques for ESR dating of barite has been completed, further comparative studies with other dating techniques such as U-Th and (226)Ra-(210)Pb dating are necessary for the technique to be widely used.

Stimulated emission and lasing from CdSe/CdS/ZnS core-multi-shell quantum dots by simultaneous three-photon absorption

Three-photon pumped stimulated emission and coherent random lasing from colloidal CdSe/CdS/ZnS core-multishell quantum dots are achieved for the first time. These results can offer new possibilities in biology and photonics, as well as at their intersection of biophotonics.

Laser-induced photodynamic effects at silica nanocomposite based on cadmium sulphide quantum dots

In this paper we study the laser-induced modification of optical properties of nanocomposite based on cadmium sulphide quantum dots encapsulated into thiomalic acid shell which were embedded into a porous silica matrix. We found red shift of luminescence of the nanocomposite when exposed to laser radiation at λ = 405 nm. Using pump-probe method and Small-Angle X-ray Scattering technique it was found that laser radiation at λ = 405 nm also increases the absorption coefficient of the nanocomposite in 15 times due to agglomeration of quantum dots. The modification of absorption properties is fully reversible.

Determination of the photolysis rate coefficient of monochlorodimethyl sulfide (MClDMS) in the atmosphere and its implications for the enhancement of SO2 production from the DMS + Cl2 reaction

In this work, the photolysis rate coefficient of CH3SCH2Cl (MClDMS) in the lower atmosphere has been determined and has been used in a marine boundary layer (MBL) box model to determine the enhancement of SO2 production arising from the reaction DMS + Cl2. Absorption cross sections measured in the 28000-34000 cm(-1) region have been used to determine photolysis rate coefficients of MClDMS in the troposphere at 10 solar zenith angles (SZAs). These have been used to determine the lifetimes of MClDMS in the troposphere. At 0° SZA, a photolysis lifetime of 3-4 h has been obtained. The results show that the photolysis lifetime of MClDMS is significantly smaller than the lifetimes with respect to reaction with OH (≈ 4.6 days) and with Cl atoms (≈ 1.2 days). It has also been shown, using experimentally derived dissociation energies with supporting quantum-chemical calculations, that the dominant photodissocation route of MClDMS is dissociation of the C-S bond to give CH3S and CH2Cl. MBL box modeling calculations show that buildup of MClDMS at night from the Cl2 + DMS reaction leads to enhanced SO2 production during the day. The extra SO2 arises from photolysis of MClDMS to give CH3S and CH2Cl, followed by subsequent oxidation of CH3S.

Photocatalytic CO(2) reduction using non-titanium metal oxides and sulfides

Titanium dioxide (TiO2 ) is by far the most widely used photocatalyst both for the degradation of pollutants and in the field of renewable energies for the production of solar fuels. However, TiO2 has strong limitations in CO2 reduction, particularly under visible light irradiation. The flat-band potential of electrons in the conduction band of TiO2 is lower than that required for CO2 reduction and, therefore, it seems appropriate to develop and validate materials other than TiO2 . In addition, the photoresponse of TiO2 requires photons of wavelengths in the UV range shorter than 380 nm and strategies to implement a visible-light photoresponse on TiO2 by doping have not been completely satisfactory particularly because of problems in reproducibility and stability of the materials. For these reasons, we focus in this Review on semiconductors other than TiO2 that show photocatalytic activity in CO2 reduction. Attention has been paid to the irradiation conditions to put the productivity data into context. The role of co-catalyst and heterojunctions to increase the efficiency of charge separation is also discussed. Our aim is to describe the state of the art in the field of photocatalytic CO2 reduction using materials other than TiO2 , trying to trigger further research in this area.

Visible and near-infrared planar waveguide structure of polycrystalline zinc sulfide from C ions implantation

We report the fabrication of a planar waveguide in polycrystalline zinc sulfide by 6.0 MeV C ions implantation with a fluence of 5 × 10¹⁴ ion/cm² at room temperature. The near-field light intensity profiles in the visible and near-infrared bands are measured by the end-face coupling method with different laser sources. Investigation of the Raman spectra demonstrates that the microstructure of the polycrystalline zinc sulfide has no significant change after C ion implantation. The absorption spectra show that the implantation processes have no influence on the visible and infrared bands.

Wurtzite CuInS₂ and CuInxGa₁-xS₂ nanoribbons: synthesis, optical and photoelectrical properties

Single crystalline wurtzite ternary and quaternary semiconductor nanoribbons (CuInS(2), CuIn(x)Ga(1-x)S(2)) were synthesized through a solution-based method. The structure and composition of the nanoribbons were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), the corresponding fast Fourier transform (FFT) and nanoscale-resolved elemental mapping. Detailed investigation of the growth mechanism by monitoring the structures and morphologies of the nanoribbons during the growth indicates that Cu(1.75)S nanocrystals are formed first and act as a catalyst for the further growth of the nanoribbons. The high mobility of Cu(+) promotes the generation of Cu(+) vacancies in Cu(1.75)S, which will facilitate the diffusion of Cu, In or Ga species from solution into Cu(1.75)S to reach supersaturated states. The supersaturated species in the Cu(1.75)S catalyst, Cu-In-S and Cu-In-Ga-S species, start to condense and crystallize to form wurtzite CuInS(2) or CuIn(x)Ga(1-x)S(2) phases, firstly resulting in two-sided nanoparticles. Successive crystallizations gradually impel the Cu(1.75)S catalyst head forward and prolong the length of the CuInS(2) or CuIn(x)Ga(1-x)S(2) body, forming heterostructured nanorods and thus nanoribbons. The optical band gaps of CuIn(x)Ga(1-x)S(2) nanoribbons can be continuously adjusted between 1.44 eV and 1.91 eV, depending on the Ga concentration in nanoribbons. The successful preparation of those ternary and quaternary semiconductor nanoribbons provide us an opportunity to study their photovoltaic properties. The primary photoresponsive current measurements demonstrate that wurtzite CuIn(x)Ga(1-x)S(2) nanoribbons are excellent photoactive materials. Furthermore, this facile method could open a new way to synthesize other various nano-structured ternary and quaternary semiconductors, such as CuInSe(2) and CuIn(x)Ga(1-x)Se(2), for applications in solar cells and other fields.

In situ photo-assisted deposition of MoS₂ electrocatalyst onto zinc cadmium sulphide nanoparticle surfaces to construct an efficient photocatalyst for hydrogen generation

We reported herein a facile and scalable preparation process for MoS(2)-decorated Zn(x)Cd(1-x)S hybrid photocatalysts for hydrogen generation. Zn(x)Cd(1-x)S nanopowder was first prepared from commercially available precursors employing a solution based process. MoS(2) hydrogen evolution reaction catalyst was then loaded onto the Zn(x)Cd(1-x)S nanopowder via a photo-assisted deposition process which employed mild conditions (room temperature, atmospheric pressure and visible light illumination). Thus, this process represents an important advantage in the large scale production of semiconductor/MoS(2) hybrid photocatalysts in comparison to the conventional method relying on thermal decomposition of (NH(4))(2)[MoS(4)] precursor at high temperature and under H(2)S pressure. The best Zn(0.2)Cd(0.8)S/MoS(2) 3% showed two hundred-and-ten times (210 times) faster hydrogen generation rate on visible light illumination compared with that obtained for un-treated Zn(0.2)Cd(0.8)S. That was the most impressive catalytic enhancement ever recorded for a semiconductor photocatalyst decorated with a noble metal free electrocatalyst.

Contrasting behaviour of the co-activators in the luminescence spectra of Y2O2S:Tb3+,Er3+ nanometre sized particles under UV and red light excitation

Nanometre sized particles of terbium and erbium co-doped yttrium oxysulfide up-converting phosphors were prepared by a urea homogeneous-precipitation method. Results from X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. Upconversion emission was observed from the Er(3+) cations when particles were excited with laser light of 632.8 nm wavelength. Under these conditions no interactions between the Er(3+) cations and the Tb(3+) cations were observed. In contrast there was evidence from the Stokes emission of the Er(3+) cations under 254 nm excitation for an interaction between the Er(3+) and Tb(3+) cations reducing intensity of the latter's blue and green emission bands by cross relaxation processes.

ZnO/TiO2 nanocable structured photoelectrodes for CdS/CdSe quantum dot co-sensitized solar cells

Photoelectrode made of nanocable structure of ZnO nanorods (NR) coated with TiO(2) nanosheets (NSs) was investigated for CdS/CdSe quantum dot co-sensitized solar cells. ZnO NRs prepared solution reaction at 60 °C served as the backbone for direct electron transport in view of the single crystallinity of the ZnO NRs and the high electron mobility of ZnO semiconductor. Anatase TiO(2) NSs with the thickness of ∼10 nm and the length of ∼100 nm were assembled onto the surface of ZnO NRs via a solvothermal method. It was found that the thin shell of TiO(2) might have remarkable influence on the quantum dot sensitized solar cells (QDSCs) through (a) increasing the surface area of ZnO NRs to allow for adsorbing more quantum dots (QDs), which led to high short current density, (b) forming an energy barrier that hindered the electrons in the ZnO from being back to the electrolyte and QDs, and thus, reduced the charge recombination rate, resulting in prolonged electron lifetime and enhanced open voltage. In comparison with the case of ZnO NRs, the short-circuit current density, open-circuit voltage, fill factor and charge recombination resistance of ZnO/TiO(2) nanocable photoelectrode increase by 3%, 44%, 48% and 220%, respectively. As a result, a power conversion efficiency of 2.7% of QDSCs with core-shell structural nanocable photoelectrode has been obtained, which is as much as 230% of that of 1.2% obtained for ZnO NR photoelectrode.

Adsorptional photocatalytic degradation of methylene blue onto pectin-CuS nanocomposite under solar light

This study describes the effect of adsorption on methylene blue degradation using pectin-CuS nanocomposite (PCSNC). The nanocomposite was synthesized using co-precipitation methods followed by direct encapsulation with pectin. The synthesized nanocomposite was characterized by SEM, TEM, XRD, FTIR and UV-vis spectral technique. The adsorption and photocatalytic efficiencies of PCSNC were compared with copper sulphide nanoparticle (CSNP). The dye removal was studied under different reaction conditions. The adsorption capacity of pectin based nanocomposite was higher due to other free functional group on pectin surface after connecting to nanoparticles. The simultaneous adsorption and photodegradation process (A+P) was the most efficient process due to rapid destruction of adsorbed dye molecules. The complete COD removal was attained in 10h using PCSNC/A+P process. On comparing with CSNP, pectin-CuS nano composite showed more degradation efficiency and reusability for MB degradation.

Iron pyrite nanocubes: size and shape considerations for photovoltaic application

Multiple lines of recent research indicate that iron pyrite (FeS(2)) requires a {100}-terminated crystal morphology in order to maintain semiconducting properties. Additionally, the large absorption coefficient of pyrite allows for the near complete absorption of above band gap radiation in <50 nm layers. However, to our knowledge <50 nm pyrite nanocubes have yet to be isolated. Herein, we demonstrate the synthesis of ~37 nm phase pure pyrite nanocubes by manipulating the sulfur chemical potential and ligand environment of the system. Ultraviolet-visible (UV-vis) absorption spectroscopy gives a signal of resonant light scattering indicating strong electronic coupling between nanocubes, which may allow for nanocube films with superior electron mobility. The absorption spectroscopies of cubic and irregular nanocrystals are contrasted and compared with recent theoretical work in order to investigate the effect of shape on electronic properties. Specifically, nanocubes have been found to have absorption characteristics closer to theory as compared to irregular nanocrystals, especially for UV radiation: 250-350 nm. Pyrite nanocubes display an indirect band gap at ~1.1 eV in addition to two direct transitions at ~1.9 and ~3.0 eV, correlating well to theoretical values.

Ulexite-galena intermediate-weight concrete as a novel design for overcoming space and weight limitations in the construction of efficient shields against neutrons and photons

Recently, due to space and weight limitations, scientists have tried to design and produce concrete shields with increased attenuation of radiation but not increased mass density. Over the past years, the authors' had focused on the production of heavy concrete for radiation shielding, but this is the first experience of producing intermediate-weight concrete. In this study, ulexite (hydrated sodium calcium borate hydroxide) and galena (lead ore) have been used for the production of a special intermediate-weight concrete. Shielding properties of this intermediate-weight concrete against photons have been investigated by exposing the samples to narrow and broad beams of gamma rays emitted from a ⁶⁰Co radiotherapy unit. Densities of the intermediate-weight concrete samples ranged 3.64-3.90 g cm⁻³, based on the proportion of the ulexite in the mix design. The narrow-beam half-value layer (HVL) of the ulexite-galena concrete samples for 1.25 MeV ⁶⁰Co gamma rays was 2.84 cm, much less than that of ordinary concrete (6.0 cm). The Monte Carlo (MC) code MCNP4C was also used to model the attenuation of ⁶⁰Co gamma-ray photons and Am-Be neutrons of the ulexite-galena concrete with different thicknesses. The ⁶⁰Co HVL calculated by MCNP simulation was 2.87 cm, indicating a good agreement between experimental measurements and MC simulation. Furthermore, MC-calculated results showed that thick ulexite-galena concrete shields (60-cm thickness) had a 7.22 times (722 %) greater neutron attenuation compared with ordinary concrete. The intermediate-weight ulexite-galena concrete manufactured in this study may have many important applications in the construction of radiation shields with weight limitations such as the swing or sliding doors that are currently used for radiotherapy treatment rooms.

Direct laser pruning of CdS(x)Se1-x nanobelts en route to a multicolored pattern with controlled functionalities

CdS(x)Se(1-x) nanobelts are interesting nanostructured materials with a tunable band gap from 1.7 to 2.4 eV depending on the nanobelts' stoichiometry. On the basis of their chemical compositions, these nanobelts give out strong photoluminescence with unique color. In this work, we demonstrate that a direct focused laser beam irradiation was able to achieve localized modification of the chemical composition of the nanobelts. As a result, we could locally change the optical properties of these nanobelts. With a scanning laser beam, micropatterns with a wide range of fluorescence color could be created on a substrate covered with ternary nanobelts without a prepatterned mask. The laser modified nanobelts showed higher resistance to acid corrosion and these nanobelts exhibited more superior photoconductivity. The construction of micropatterns with functionality/color control within the sample would provide greater building blocks for photoelectronic applications.

Enhanced photocatalytic performance of ZnS for reversible amination of α-oxo acids by hydrothermal treatment

To understand how life could have originated on early Earth, it is essential to know what biomolecules and metabolic pathways are shared by extant organisms and what organic compounds and their chemical reaction channels were likely to have been primordially available during the initial phase of the formation of prebiotic metabolism. In a previous study, we demonstrated for the first time the reversible amination of α-oxo acids on the surface of photo-illuminated ZnS. The sulfide mineral is a typical component at the periphery of submarine hydrothermal vents which has been frequently argued as a very attractive venue for the origin of life. In this work, in order to simulate more closely the precipitation environments of ZnS in the vent systems, we treated newly-precipitated ZnS with hydrothermal conditions and found that its photocatalytic power was significantly enhanced because the relative crystallinity of the treated sample was markedly increased with increasing temperature. Since the reported experimental conditions are believed to have been prevalent in shallow-water hydrothermal vents of early Earth and the reversible amination of α-oxo acids is a key metabolic pathway in all extant life forms, the results of this work provide a prototypical model of the prebiotic amino acid redox metabolism. The amino acid dehydrogenase-like chemistry on photo-irradiated ZnS surfaces may advance our understanding of the establishment of archaic non-enzymatic metabolic systems.

CFD modeling of a UV-LED photocatalytic odor abatement process in a continuous reactor

This paper presents a model study of a UV light-emitting-diode (UV-LED) based photocatalytic odor abatement process. It integrated computational fluid dynamics (CFD) modeling of the gas flow in the reactor with LED-array radiation field calculation and Langmuir-Hinshelwood reaction kinetics. It was applied to simulate the photocatalytic degradation of dimethyl sulfide (DMS) in a UV-LED reactor based on experimentally determined chemical kinetic parameters. A non-linear power law relating reaction rate to irradiation intensity was adopted. The model could predict the steady state DMS concentration profiles by calculating the advection, diffusion and Langmuir-Hinshelwood reaction kinetics. By affecting the radiation intensity and uniformity, the position of the LED array relative to the catalyst appeared to be a critical parameter determining DMS removal efficiency. Too small distances might yield low quantum efficiency and consequently poor abatement performance. This study provided an example of LED-based photocatalytic process modeling and gave insights into the optimization of light source design for photocatalytic applications.

Selective oxidation with nanoporous silica supported sensitizers: an environment friendly process using air and visible light

Transparent and porous silica xerogels containing various grafted photosensitizers (PSs) such as anthraquinone derivatives, Neutral Red, Acridine Yellow and a laboratory-made dicyano aromatics (DBTP) were prepared. In most cases, the xerogels were shown to be mainly microporous by porosimetry. The PSs were characterized in the powdered monoliths (form, aggregation, concentration) by electronic spectroscopy which also proved to be a useful tool for monitoring the material evolution after irradiation. These nanoporous xerogels were used as microreactors for gas/solid solvent-free photo-oxygenation of dimethylsulfide (DMS) using visible light and air as the sole reactant. All these PSs containing monoliths were efficient for gas-solid DMS oxidation, leading to sulfoxide and sulfone in varying ratios. As these polar oxidation products remained strongly adsorbed on the silica matrix, the gaseous flow at the outlet of the reactor was totally free of sulfide and odorless. The best results in term of yield and initial rate of degradation of DMS were obtained with DBTP containing xerogels. Moreover, as these materials were reusable without loss of efficiency and sensitizer photobleaching after a washing regeneration step, the concept of recyclable sensitizing materials was approved, opening the way to green process.

Room-temperature synthesis of Zn(0.80)Cd(0.20)S solid solution with a high visible-light photocatalytic activity for hydrogen evolution

Visible light photocatalytic H(2) production from water splitting is of great significance for its potential applications in converting solar energy into chemical energy. In this study, a series of Zn(1-x)Cd(x)S solid solutions with a nanoporous structure were successfully synthesized via a facile template-free method at room temperature. The obtained solid solutions were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and N(2) adsorption-desorption analysis. The solid solutions show efficient photocatalytic activity for H(2) evolution from aqueous solutions containing sacrificial reagents S(2-) and SO(3)(2-) under visible-light irradiation without a Pt cocatalyst, and loading of the Pt cocatalyst further improves the visible-light photocatalytic activity. The optimal photocatalyst with x = 0.20 prepared at pH = 7.3 displays the highest activity for H(2) evolution. The bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S nanoparticles exhibit a high H(2) evolution rate of 193 μmol h(-1) and 458 μmol h(-1) under visible-light irradiation (λ ≥ 420 nm), respectively. In addition, the bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S catalysts show a high H(2) evolution rate of 252 and 640 μmol h(-1) under simulated solar light irradiation, respectively. Moreover, the Zn(0.80)Cd(0.20)S catalyst displays a high photocatalytic stability for H(2) evolution under long-term light irradiation. The incorporation of Cd in the solid solution leads to the visible light absorption, and the high content of Zn in the solid solution results in a relatively negative conduction band, a modulated band gap and a rather wide valence bandwidth, which are responsible for the excellent photocatalytic performance of H(2) production and for the high photostability.

CdS/CdSe quantum dot co-sensitized graphene nanocomposites via polymer brush templated synthesis for potential photovoltaic applications

CdS/CdSe quantum dot (QDs) co-sensitized graphene sheets have been obtained via polymer brush templated synthesis. Firstly, the anionic functional polymer (polymethacrylate cadmium) was grafted via the surface initiated atomic transfer radical polymerization (ATRP) using a macromolecular initiator, which contains polymerized pyrene units for chemical anchoring on graphene surface and alkyl bromines to initiate ATRP. Then, the coordinated cadmium in the polymer chains can act as a source precursor for QDs. After reaction, polymer brushes can be recovered and act as the nanoreactor via the absorption of cadmium ions by carboxylate groups. So, high density QDs can be multiply uploaded onto the graphene surface by repeated steps. The as-prepared composite materials exhibited significantly enhanced visible light response compared to plain graphene, and have potential applications as the platform to build solar cell assembles.

Sonochemistry synthesis and enhanced photocatalytic H2-production activity of nanocrystals embedded in CdS/ZnS/In2S3 microspheres

ZnS and CdS nanocrystals with a size of 5-10 nm embedded in CdS/ZnS/In(2)S(3) microspheres have been successfully synthesized by a sonochemistry method at room temperature and normal pressure without the use of templates or surfactants. The as-prepared products have been characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), EDX line spectrum, high-angle annular dark-field imaging (HAADF), UV-visible diffuse reflectance spectra (UV-vis) and photoluminescence (PL) spectra. The reaction process in the solution under ultrasonic irradiation was investigated by gas chromatography-mass spectrometry (GC-MS). The mechanisms of phase formation and morphology control of CdS/ZnS/In(2)S(3) microspheres are proposed and discussed in detail. Furthermore, the photocatalytic activity of CdS/ZnS/In(2)S(3) for water splitting was investigated under visible-light irradiation (λ > 400 nm) and an especially high photocatalytic activity (apparent yield is 40.9% at 420 nm) was achieved in the absence of co-catalysts.

Air stable, photosensitive, phase pure iron pyrite nanocrystal thin films for photovoltaic application

Iron pyrite (FeS(2)) is a naturally abundant and nontoxic photovoltaic material that can potentially make devices as efficient as silicon-based ones; however existing iron pyrite photovoltaic devices contain thermodynamically unstable FeS(2) film surfaces that lead to low open circuit voltages. We report the rational synthesis of phase pure, highly crystalline cubic FeS(2) nanocrystals (NCs) using a trioctylphosphine oxide (TOPO) assisted hot-injection method. The synthesized pyrite NC films have excellent air stability over one year. In contrast, obvious surface decomposition was observed on the surface of FeS(2) NCs synthesized without TOPO. A high carrier mobility of 80 cm(2)/(V s) and a strong photoconductivity were observed for the first time for pyrite films at room temperature. Our results indicate that TOPO passivates both iron and sulfur atoms on FeS(2) NC surfaces, efficiently inhibiting surface decomposition.

CdS microspheres composed of nanocrystals and their photocatalytic activity

A simple and template-free solution phase synthesis method has been developed for the preparation of novel CdS hollow microspheres using cadmium nitrate and thioacetamide precursors. In this manuscript, we demonstrate that process parameters such as the reaction time, precursor ratio, and reaction temperature strongly influence the morphology of the final product. The synthesized products have been characterized by a variety of methods, including X-ray powder diffraction (XRD), Raman spectroscopy, high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray diffraction (EDX) analysis, X-ray photoelectron spectroscopy (XPS), and UV-visible diffused reflectance spectroscopy (UV-DRS). XRD analysis confirmed the cubic structure of the CdS microspheres, which has also been further supported by Raman spectroscopy. The HR-SEM measurements revealed the spherical morphology of the CdS microspheres which has been evolved by the oriented aggregation of the primary CdS nanocrystals. The TEM measurements confirmed the hollow shell-like structure of the spheres; the formation of their hollow interiors can be explained by the Ostwald ripening mechanism. UV-DRS studies showed that the band gap of the CdS microspheres increased with increasing cadmium-nitrate-to-thioacetamide ratio. Furthermore, studies of photocatalytic activity revealed that the synthesized CdS hollow microspheres exhibit an excellent photocatalytic performance in rapidly degrading methyl tert-butyl ether (MTBE) in aqueous solution under visible-light illumination. These results suggest that CdS microspheres will be an interesting candidate for photocatalytic detoxification studies under visible light radiation.

Synthesis of single crystalline CdS nanocombs and their application in photo-sensitive field emission switches

Single crystalline CdS nanocombs were synthesized by a thermal evaporation route. The photo-sensitive field emission current shows a reproducible switching behavior, with a rise in current level of nearly five times the initial preset value of ∼1 μA. An ultra low turn-on field, required to draw an emission current density of ∼0.1 μA cm(-2) (100 nA), is found to be ∼0.26 V μm(-1) (260 V), which is much lower than the reported values for various other CdS nanostructures. Upon illumination with visible light the CdS nanocombs act as a photo field emission switch. At an applied field of ∼0.65 V μm(-1) the current densities are observed to be ∼14.6 μA cm(-2) and ∼26.9 μA cm(-2), without and with light illumination, respectively. The average emission current is seen to be stable over the duration of measurement for two preset values. The high sensitivity and fast response in the visible range indicates that the CdS nanocombs can be used as a photo-sensitive field emitting switch in device applications, and also in pulsed electron beam technology.

Electric field dependent photocurrent decay length in single lead sulfide nanowire field effect transistors

We determined the minority carrier diffusion length to be ∼1 μm in single PbS nanowire field effect transistors by scanning photocurrent microscopy. PbS nanowires grown by the vapor-liquid-solid method were p-type with hole mobilities up to 49 cm(2)/(V s). We measured a photoresponse time faster than 14 μs with near-unity charge separation efficiency at the contacts. For the first time, we also observed a field-dependent photocurrent decay length, indicating a drift dominant carrier transport at high bias.

Potential particulate pollution derived from UV-induced degradation of odorous dimethyl sulfide

UV-induced degradation of odorous dimethyl sulfide (DMS) was carried out in a static White cell chamber with UV irradiation. The combination of in situ Fourier transform infrared (FT-IR) spectrometer, gas chromatograph-mass spectrometer (GC-MS), wide-range particle spectrometer (WPS) technique, filter sampling and ion chromatographic (IC) analysis was used to monitor the gaseous and potential particulate products. During 240 min of UV irradiation, the degradation efficiency of DMS attained 20.9%, and partially oxidized sulfur-containing gaseous products, such as sulfur dioxide (SO2), carbonyl sulfide (OCS), dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2) and dimethyl disulfide (DMDS) were identified by in situ FT-IR and GC-MS analysis, respectively. Accompanying with the oxidation of DMS, suspended particles were directly detected to be formed by WPS techniques. These particles were measured mainly in the size range of accumulation mode, and increased their count median diameter throughout the whole removal process. IC analysis of the filter samples revealed that methanesulfonic acid (MSA), sulfuric acid (H2SO4) and other unidentified chemicals accounted for the major non-refractory compositions of these particles. Based on products analysis and possible intermediates formed, the degradation pathways of DMS were proposed as the combination of the O(1D)- and the OH- initiated oxidation mechanisms. A plausible formation mechanism of the suspended particles was also analyzed. It is concluded that UV-induced degradation of odorous DMS is potentially a source of particulate pollutants in the atmosphere.

Fabrication and photoelectrochemical characteristics of the patterned CdS microarrays on indium tin oxide substrates

In an effort to investigate the extraordinary photoelectrochemical characteristics of nanostructured CdS thin films in promising photovoltaic device applications, the patterned CdS microarrays with different feature sizes (50, 130, and 250 μm in diameter) were successfully fabricated on indium tin oxide (ITO) glass substrates using the chemical bath deposition method. The ultraviolet lithography process was employed for fabricating patterned octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) as the functional organic thin layer template. The results show that the regular and compact patterned CdS microarrays had been deposited onto ITO glass surfaces, with clear edges demarcating the boundaries between the patterned CdS region and substrate under an optimal depositing condition. The microarrays consisted of pure nanocrystalline CdS with average crystallite size of about 10.7 nm. The photocurrent response and the optical adsorption of the patterned CdS microarray thin films increased with the decrease of the feature size, which was due to the increased CdS surface area, as well as the increased optical path length within the patterned CdS thin films, resulting from multiple reflection of incident light. The resistivity values increase with the increase of feature size, due to the increase of the relative amount of gaps between CdS microarrays with increasing the feature size of patterned CdS microarrays.

Applicability of a continuous-flow system inner-coated with S-doped titania for the photocatalysis of dimethyl sulfide at low concentrations

The present study investigated the photocatalytic activity of an S-doped TiO(2) photocatalyst with regards to dimethyl sulfide degradation under visible-light irradiation, along with its deactivation and reactivation. The dimethyl sulfide conversion was between 85% and 93% for the lowest relative humidity range (10-20%) and close to 100% for the two higher relative humidity ranges (45-55% and 80-90%). The conversion was also close to 100% for the two lowest input concentrations (0.039 and 0.195 ppm), while it was between 91% and 96% at 3.9 ppm and between 85% and 90% at 7.9 ppm. In contrast to the input concentration dependences on conversion, the calculated degradation rates increased as input concentrations increased. The dimethyl sulfide conversion at low concentrations (<or=0.39 ppm), which are associated with non-occupational inn occurring. However, catalyst deactivations were observed during the photocatalytic process whdoor air quality issues, was up to nearly 100% for long time periods (at least 603 h), without any significant catalyst deactivatioen higher concentrations (3.9 and 7.8 ppm) were used. The photocatalyst, reactivated by using two types of air (dried and humidified) under visible-light irradiation, did not regain all of its initial activities. Sulfate groups were qualitatively identified as the reaction products on the photocatalyst surface. In addition, gaseous byproducts, quantitatively determined, included dimethyl disulfide, methanol, and SO(2). It is noteworthy that the peak concentration of dimethyl disulfide (0.79 ppm = 790 ppb), generated over the photocatalytic process with the highest dimethyl sulfide input concentration, exceeded the odor threshold value of 0.1-3.6 ppb for dimethyl disulfide.

Dynamics of the hysteretic voltage-induced torsional strain in tantalum trisulfide

We have studied how the hysteretic voltage-induced torsional strain, associated with charge-density-wave (CDW) depinning, in orthorhombic tantalum trisulfide depends on square-wave and triangle-wave voltages of different frequencies and amplitudes. The strains are measured by placing the sample, with a wire glued to the center as a transducer, in a radio frequency cavity and measuring the modulated response of the cavity. From the triangle waves, we map out the time dependence of the hysteresis loops, and find that the hysteresis loops broaden for waves with periods less than 30 s. The square-wave response shows that the dynamic responses to positive and negative voltages can be quite different. The overall frequency dependence is relaxational, but with multiple relaxation times which typically decrease with increasing voltage. The detailed dynamic response is very sample dependent, suggesting that it depends in detail on interactions of the CDW with sample defects.

Dramatically enhanced photoresponse of reduced graphene oxide with linker-free anchored CdSe nanoparticles

A linker-free connected reduced graphene oxide/CdSe nanoparticle (R-GO/CdSe NP) nanocomposite was produced by directly anchoring CdSe NPs onto R-GO. The morphological and structural characterizations evidence that the single-crystal CdSe NPs with the size of a few tens of nanometers can be efficiently decorated on the R-GO. The photoresponse of this nanocomposite is drastically enhanced compared with that of the pure CdSe NPs, the bare R-GO, and the physically mixed R-GO/CdSe NPs, while the photoluminescence of the CdSe NPs in the composite is much quenched, indicating that the photoinduced carriers generated from the CdSe NPs can be transferred to the R-GO effectively and separately. This ability makes the R-GO/CdSe NP nanocomposite a great promise for wide potential applications in optoelectronics.

A sonochemical method for the preparation of cadmium sulfide and cadmium selenide nanoparticles in aqueous solutions

Sonochemistry is a branch of chemistry where sound energy in the form of ultrasound is used to influence the course of reactions. A short-term, local increase in temperature occurs when the solutions and suspensions are irradiated by ultrasound. This happens because the substance absorbs the ultrasound waves. The purpose of this research was the synthesis of CdS and CdSe nanoparticles. We used cadmium sulfate hydrate (CdSO(4).8/3H(2)O), elemental S and Se. Aqueous solutions of NaOH, Na(2)SO(3) and EDTA were used as the solvents. During the syntheses, we used a direct immersion ultrasound probe by vibracell. The device operates with a constant frequency of 20 kHz, with the possibility to change the amplitude and with it the input of energy to the time unit. The products were characterized by X-ray powder diffraction (XRD), thermal analyses (TGA, SDTA) and TEM analyses.

The heat annealing effect on the performance of CdS/CdSe-sensitized TiO2 photoelectrodes in photochemical hydrogen generation

Heat treatment was utilized to anneal the semiconductor sensitizers (CdS, CdSe and CdS/CdSe) assembled on mesoporous TiO(2) films to enhance the performance of the photoelectrodes in a process of photoelectrochemical hydrogen generation. Various annealing temperatures (150, 300 and 400 degrees C) were employed and the results show that appropriately elevating the temperature (to approx. 300 degrees C) can increase the crystallinity of the CdS and CdSe, improve the charge transport characteristic of a photoelectrode and, therefore, lead to a higher performance of the TiO(2) /CdS and TiO(2) /CdSe electrodes. However, an over-annealing temperature (400 degrees C) may cause serious oxidation and/or decomposition of the sensitizers which is unfavorable to the photoelectrode. For the co-sensitized electrode, counter-diffusion of CdS and CdSe happens at the CdS/CdSe interface when the TiO(2) /CdS/CdSe electrode was co-annealed at 300 degrees C, which significantly decreases the performance of the co-sensitized electrode. This problem was solved by annealing first a TiO(2) /CdS electrode at 300 degrees C, followed by CdSe assembly and a second annealing at 150 degrees C. This electrode appears to have better performance than the others.