SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Cadmium pigments

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Over the past years a number of studies have described the instability of the pigment cadmium yellow (CdS). In a previous paper we have shown how cadmium sulfide on paintings by James Ensor oxidizes to CdSO(4)·H(2)O. The degradation process gives rise to the fading of the bright yellow color and the formation of disfiguring white crystals that are present on the paint surface in approximately 50 μm sized globular agglomerations. Here, we study cadmium yellow in the painting “Flowers in a blue vase” by Vincent van Gogh. This painting differs from the Ensor case in the fact that (a) a varnish was superimposed onto the degraded paint surface and (b) the CdS paint area is entirely covered with an opaque crust. The latter obscures the yellow color completely and thus presents a seemingly more advanced state of degradation. Analysis of a cross-sectioned and a crushed sample by combining scanning microscopic X-ray diffraction (μ-XRD), microscopic X-ray absorption near-edge spectroscopy (μ-XANES), microscopic X-ray fluorescence (μ-XRF) based chemical state mapping and scanning microscopic Fourier transform infrared (μ-FT-IR) spectrometry allowed unravelling the complex alteration pathway. Although no crystalline CdSO(4) compounds were identified on the Van Gogh paint samples, we conclude that the observed degradation was initially caused by oxidation of the original CdS pigment, similar as for the previous Ensor case. However, due to the presence of an overlying varnish containing lead-based driers and oxalate ions, secondary reactions took place. In particular, it appears that upon the photoinduced oxidation of its sulfidic counterion, the Cd(2+) ions reprecipitated at the paint/varnish interface after having formed a complex with oxalate ions that themselves are considered to be degradation products of the resin and/or oil in the varnish. The SO(4)(2-) anions, for their part, found a suitable reaction partner in Pb(2+) ions stemming from a dissolved lead-based siccative that was added to the varnish to promote its drying. The resulting opaque anglesite compound in the varnish, in combination with the underlying CdC(2)O(4) layer at the paint/varnish interface, account for the orange-gray crust that is disfiguring the painting on a macroscopic level. In this way, the results presented in this paper demonstrate how, through a judicious combined use of several microanalytical methods with speciation capabilities, many new insights can be obtained from two minute, but highly complex and heterogeneous paint samples.

Concepts: Spectroscopy, Cadmium, Pigment, Cadmium sulfide, Expressionism, Vincent van Gogh, Cadmium pigments, Les XX

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The optical properties of cadmium sulfide (CdS) nanoparticles in suspension are affected by morphology and suspending solvent. Time dependent stability of these properties is solvent dependent and is affected by illumination conditions under which the suspension is stored. Moreover, minute amounts of dissolved oxygen are sufficient in order to facilitate photodegradation.

Concepts: Oxygen, Colloid, Sulfur, Cadmium, Cadmium telluride, Cadmium sulfide, Cadmium pigments, Greenockite

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Visible-light irradiation (λ < 600 nm) of commercially-available CdS in alcohol successfully promotes hydrogenation of azobenzene to hydrazobenzene with more than 95% selectivity. This is promoted by strong adsorption of azobenzene to the photoformed zerovalent Cd species adjacent to the surface S vacancies on CdS; this leads to efficient reduction to hydrazobenzene.

Concepts: Zinc, Sulfur, Cadmium, Cadmium telluride, Cadmium sulfide, Cadmium oxide, Cadmium pigments, Greenockite

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Cadmium pigments are widely used in the polymer and ceramic industry. Their potential environmental risk is under debate, being the major barrier for appropriate regulation. We show that 83.0 ± 0.2 % of hazardous cadmium ion (Cd2+) was released from the commercial cadmium sulfoselenide pigment (i.e., cadmium red) in aqueous suspension within 24 h under simulated sunlit conditions. This photo-dissolution process also generated sub-20 nm pigment nanoparticles. Cd2+ release is attributed to the reactions between photogenerated holes and the pigment lattices. The photo-dissolution process can be activated by both ultraviolet and visible light in the solar spectrum. Irradiation under alkaline conditions or in the presence of phosphate and carbonate species resulted in reduced charge carrier energy or the formation of insoluble and photo-stable cadmium precipitates on pigment surfaces, mitigating photo-dissolution. Tannic acid inhibited the photo-dissolution process by light screening and scavenging photogenerated holes. The fast release of Cd2+ from the pigment was further confirmed in river water under natural sunlight, with 38.6 ± 0.1 % of the cadmium released within 4 h. Overall, this study underscores the importance to account for photochemical effects to inform risk assessments and regulations of cadmium pigments which are currently based on their low solubility.

Concepts: Ultraviolet, Light, Solubility, Sunlight, Cadmium, Pigment, Cadmium sulfide, Cadmium pigments

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Cadmium sulfide was popularly utilized as a light harvesting material for photoelectrochemical (PEC) water splitting, however, the drawback of poor durability limits its practical application. Herein, we show that a catalytically active and chemically inert cadmium indium sulfide (CdIn2S4) can improve the stability and even photocurrent of a CdS photoelectrode.

Concepts: Sulfur, Cadmium, Cadmium telluride, Sulfides, Cadmium sulfide, Cadmium oxide, Cadmium pigments, Greenockite

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A macroscopic urea-functionalized CdS (CdS-U) is synthesized for the first time. The CdS-U material is formed through the interaction between NH2/NH groups on urea and COO(-) groups on sodium oleate-capped CdS nanoparticles (CdS-So NPs). The CdS-U material exhibites excellent visible light photocatalytic activity and plasticity and has the potential to be produced as rewritable papers. It is convenience to produce a large-scale film by CdS-U. Letters can be written on the CdS-U film and disappear through a dissolution-irradiation process, and then the CdS-U film can be recycled by drying. This novel CdS-U material might be of interest and provide a new chance to advance the application of visible light photocatalyst on rewritable papers.

Concepts: Sulfur, Cadmium, Photocatalysis, Visible spectrum, Cadmium telluride, Cadmium sulfide, Cadmium pigments, Greenockite

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Optoelectronic properties of nanoparticles are intimately coupled to the complex physiochemical interplay between the inorganic core and the organic ligand shell. Magic-sized clusters, which are predominately surface atoms, provide a promising avenue to clarify these critical surface interactions. Whereas these interactions impact the surface of both nanoparticles and magic-sized clusters, we show here that only clusters manifest a shift in the excitonic peak by up to 0.4 eV upon solvent or ligand treatment. These results highlight the utility of the clusters as a probe of ligand-surface interactions.

Concepts: Oxygen, Chemistry, Sociology, Organic compound, Inorganic chemistry, Cadmium, Cadmium pigments, Micromeritics

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It is fascinating and challenging to endow conventional materials with unprecedented properties. For instance, cadmium sulfide (CdS) is an important semiconductor with excellent light response; however, its potential in gas-sensing was underestimated owing to relatively low chemical activity and poor electrical conductivity. Herein, we demonstrate that an ideal architecture, ultrathin nanoflake arrays (NFAs), can improve significantly gas-sensing properties of CdS material. The CdS NFAs are grown directly on the interdigitated electrode to expose large surface area. Their thickness is reduced below the double Debye length of CdS, permitting to achieve a full depletion of carriers. Particularly, the prepared CdS nanoflakes are enclosed with high-energy {0001} facets exposed, which provides more active sites for gas adsorption. Moreover, the NFAs exhibit the light-trapping effect, which further enhances their gas sensitivity. As a result, the as-prepared CdS NFAs demonstrate excellent gas-sensing and light-response properties, thus being capable of dual gas and light detection.

Concepts: Electrochemistry, Adsorption, Cadmium, Electrical conductivity, Surface area, Cadmium telluride, Cadmium sulfide, Cadmium pigments

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Chemically modified graphenes (CMGs) offer a means to tune a wide variety of graphene’s exceptional properties. Critically, CMGs can be transferred onto a variety of substrates, thereby imparting functionalities to those substrates that would not be obtainable through conventional functionalization. One such application of CMGs is enabling and controlling the subsequent growth of inorganic thin films. In the current study, we demonstrated that CMGs enhance the growth of inorganic films on inert surfaces with poor growth properties. Fluorinated graphene transferred onto polyethylene enabled the dense and homogeneous deposition of cadmium sulfide (CdS) film grown via chemical bath deposition (CBD). We showed the coverage of CdS film can be controlled by the degree of fluorination from less than 20% to complete coverage of the film. The approach can also be applied to other technologically important materials such as ZnO. Finally, we demonstrated that an electron beam SF6 plasma could pattern fluorine onto a graphene/PE sample to selectively grow CdS films on the fluorinated region. Therefore, CMG coatings can tailor the surface properties of polymers and control the growth of inorganic thin films on polymers for the development of flexible electronics.

Concepts: Sulfur, Cadmium, Fluorine, Control, Cadmium sulfide, Cadmium pigments, Inorganic compounds

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The effects of uniconazole (S-3307) appliation on the growth and cadmium (Cd) accumulation of accumulator plant Malachium aquaticum (L.) Fries. were studied through a pot experiment. The application of S-3307 increased the biomass and photosynthetic pigment content of M. aquaticum under Cd-contaminated soil, and also improved the SOD and POD activities in M. aquaticum. Applying S-3307 increased Cd content in shoots and decreased Cd content in roots of M. aquaticum, but the translocation factor (TF) of M. aquaticum increased with the increase of S-3307 concentration. For phytoextraction, the application of S-3307 increased Cd extractions by roots, shoots and whole plants of M. aquaticum, and the maxima were obtained at 75 mg L(-1) S-3307, which increased by 22.07%, 37.79% and 29.07% respectively, compared with their respective controls. Therefore, S-3307 can be used for enhancing the Cd extraction ability of M. aquaticum, and 75 mg L(-1) S-3307 was the optimal dose.

Concepts: Photosynthesis, Plant, Botany, Cadmium, Pigment, Extraction, Phytoremediation, Cadmium pigments