The photopolymerisation of methacrylic acid by colloidal semiconductors

Summary Methacrylic acid was photopolymerised using CdS and composite, CdS/HgS and CdS/TiO₂, colloidal semiconductor particles as initiators. The previously proposed photoinitiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO₂. The effect of pH on the course of the polymerisation was investigated and is discussed.     

Concentration dependence of the optical properties of glassy alloys in the HgS-Ga2S3-GeS2 system

The concentration dependences of the optical properties of glassy alloys in the HgS-Ga₂S₃-GeS₂ system have been investigated in the spectral range 2.0–2.9 eV. The energy gap E _g of glasses has been estimated, and the dependence of the energy gap on the content of HgS and Ga₂S₃ has been analyzed. The spectral dependences α(hν) for glasses in the system under investigation in the fundamental absorption range are described by the Urbach rule. The alloys containing ≥ 20 mol % (HgS + Ga₂S₃) are characterized by an ordering and a decrease in the energy gap E _g , which are explained by the changes in the short-range order in the arrangement of the atoms involved in the composition of alloys. It has been assumed that, at high concentrations of modifiers, there can arise microscopic inclusions, i.e., different defects, which can scatter light and decrease the transparency of glassy alloys.     

Foam Separation of Mercury(II) and Cadmium(II) from Aqueous Systems

Abstract

Mercury(II) and cadmium(II) were separated from aqueous systems by a number of batch-type precipitate flotation and adsorbing colloid flotation techniques. HgS, CdS, and Cd(OH)₂ were removed by precipitate flotation; Fe(OH)₃, Al(OH)₃, FeS, and CuS were used as adsorbing colloids. Sodium lauryl sulfate and hexadecyltrimethylammonium bromide (HTA) were used as collectors. Dependence of separation efficiency on pH and ionic strength was investigated. Floc foam flotation of both metals with CuS and HTA was found to be quite effective, resulting in residual Hg(II) levels as low as 5 ppb and residual Cd(II) levels as low as 20 ppb. Floc foam flotation of Cd(II) with FeS and HTA yielded residual Cd(II) levels as low as 10 ppb.     

Experimental study on ZnO-TiO<Subscript>2</Subscript> sorbents for the removal of elemental mercury

ZnO-TiO₂ sorbents synthesized by an impregnation method were characterized through XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and EDS (Energy dispersive spectrometer) analyses. An experiment concerning the adsorption of Hg⁰ by ZnO-TiO₂ under a simulated fuel gas atmosphere was then conducted in a bench-scale fixed-bed reactor. The effects of ZnO loading amounts and reaction temperatures on Hg⁰ removal performance were analyzed. The results showed that ZnO-TiO₂ sorbents exhibited excellent Hg⁰ removal capacity in the presence of H₂S at 150 °C and 200 °C; 95.2% and 91.2% of Hg⁰ was removed, respectively, under the experimental conditions. There are two possible causes for the H₂S reacting on the surface of ZnO-TiO₂: (1) H₂S directly reacted with ZnO to form ZnS, (2) H₂S was oxidized to elemental sulfur (S _ad ) by means of active oxygen on the sorbent surface, and then S _ad provided active absorption sites for Hg⁰ to form HgS. This study identifies three reasons why higher temperatures limit mercury removal. First, the reaction between Hg⁰ and H₂S is inhibited at high temperatures. Second, HgS, as the resulting product in the reaction of mercury removal, becomes unstable at high temperatures. Third, the desulfurization reaction strengthens at higher temperatures, and it is likely that H₂S directly reacts with ZnO, thus decreasing the S _ad on the sorbent surfaces.     

Ionic transport in AgI‐HgS‐As2S3 glasses: Critical percolation and modifier‐controlled domains

Electrical measurements, dc and ac, show that (AgI)_x(HgS)_0.5‐x/2(As₂S₃)_0.5‐x/2 glasses, 0.0 ≤  x ≤ 0.6, exhibit drastic changes in ionic conductivity σ_i with silver iodide additions. The ionic transport increases by 13 orders of magnitude with increasing silver content from ~0.002 to ~23 at.%, and the activation energy decreases from 1.05 to 0.35 eV. Two distinctly different ion transport regimes above the percolation threshold concentration, x_c ≈ 30 ppm, were distinguished. The critical percolation regime at low silver content (≤ 2‐5 at.% Ag) is characterized by a random distribution of silver‐related entities and obeys a power‐law composition dependence of σ_i. The ion transport parameters depend on the host network connectivity, represented by the average coordination number <n₀>, via the critical fictive temperature T₀; the calculated T₀ value is comparable to the glass transition temperature for the glassy (HgS)_0.5(As₂S₃)_0.5 host matrix. In contrast, in the modifier‐controlled domain, the silver‐related entities are nonrandomly distributed. The high Ag⁺ ionic mobility results from interconnected tetrahedral (AgI_2/2S_2/2)_n chains in the silver iodide content range 0.2 < x ≤ 0.5, and from 2D layers (Ag_3/3I_3/3)_n or 3D mixed tetrahedral subnetwork (AgI_3/3S_1/2) in the range x > 0.5.     

Speciation of mercury in fly ashes by temperature programmed decomposition

Mercury (Hg) is a toxic trace element which is emitted mostly in gas phase during coal combustion, although some Hg compounds may be retained in the fly ashes depending on the characteristics of the ashes and process conditions. To improve the retention of Hg in the fly ashes a good knowledge of the capture mechanism and Hg species present in the fly ashes is essential. The temperature programmed decomposition technique was chosen to identify the Hg species present in fly ashes obtained from two Pulverized Coal Combustion (PCC) plants and a Fluidized Bed Combustion (FBC) plant. The fly ashes were then used as Hg sorbents in a simulated flue gas of coal combustion and gasification. The Hg compounds found in the fly ash from the FBC plant after elemental mercury retention were mainly HgCl₂ and HgSO₄. The Hg species present in the two fly ashes from the two PCC plants were HgCl₂ and Hg⁰. The Hg species formed in the coal gasification atmosphere was HgS for all three fly ashes. The only Hg compound identified in the fly ashes after the retention of mercury chloride was HgCl₂.     

Characteristics of the removal of mercury vapor in coal derived fuel gas over iron oxide sorbents

The characteristics of a novel method for Hg removal using H₂S and sorbents containing iron oxide were studied. Previously, we have suggested that this method is based on the reaction of Hg and H₂S over the sorbents to form HgS. However, the reaction mechanism is not well understood. In this work, the characteristics of the Hg removal were studied to clarify the reaction mechanism. In laboratory made sorbents containing iron oxide were used as the sorbent to remove mercury vapor from simulated coal derived fuel gases having a composition of Hg (4.8 ppb), H₂S (400 ppm), CO (30%), H₂ (20%), H₂O (8%), and N₂ (balance gas). The following results were obtained: (1) The presence of H₂S was indispensable for the removal of Hg from coal derived fuel gas; (2) Hg was removed effectively by the sorbents containing iron oxide in the temperature range of 60-100 °C; (3) The presence of H₂O suppressed the Hg removal activity; (4) The presence of oxygen may play very important role in the Hg removal and; (5) Formation of elemental sulfur was observed upon heating of the used sample.     

Synthesis,structural and optical properties of ZnS,CdS and HgS nanoparticles from dithiocarbamato single molecule precursors

Dithiocarbamate complexes of Zn(II), Cd(II) and Hg(II) were synthesize and characterized by elemental analysis, thermogravimetric analysis, UV–Vis, FTIR, ¹H- and ¹³C-NMR spectroscopy. The complexes were thermolyzed at 180°C to prepare HDA-capped ZnS, CdS and HgS nanoparticles. The optical properties of the nanoparticles showed absorptions that are blue shifted with respect to the bulk and narrow emissions. The ZnS nanoparticles are in the cubic phase with average crystallite sizes of 3–5 nm. The CdS nanoparticles consist of a mixture of cubic and hexagonal phases with particle sizes of 8–22 nm, while the HgS nanoparticles are in the cubic phase with average crystallite sizes of 7–14 nm.     

Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80–150 °C using simulated flue gases having the composition of Hg⁰ (4.9 ppb), H₂S (0–20 ppm), SO₂ (0–487 ppm), CO₂ (10%), H₂O (0–15%), O₂ (0–5%), N₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80–100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S–SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S_ad+H₂O) and the Clause reaction (SO₂+2H₂S=3S_ad+2H₂O) may contribute to the Hg⁰ removal over activated carbon by the following reaction: S_ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.     

硫化汞溶解机理的研究

根据热力学平衡原理和设计的可逆电池反应,由 E~0(Hg~(2+)+S/HgS)数据,计算了 E~0(HgCl_4~(2+)+S/HgS+4Cl~-)数值,将其与 HNO_3的标准电极电位比较,定量地揭示了 HgS 溶于王水的原因在于该溶液中高浓度 Cl~-离子降低了 HgS 中硫的还原电位,从而提高了 HgS 的还原性所致,并非王水的氧化性比 HNO_3的更强。根据这个机理,作者进一步对有关电极反应的电极电位进行了计算和分析,预测并经实验验证了多种可以溶解 HgS 的普通化学试剂。     

Optical characterisation of anodic sulphide films on Hg1−xCdxTe (MCT) grown by the potential step method

The growth of native sulphide films on Hg_1−xCd_xTe (MCT) by potential steps to two different electrochemical growth regions has been studied by in-situ ellipsometry, photocurrent spectroscopy and second harmonic generation (SHG) rotational anisotropy. Films grown at −0.4 V versus SCE were porous and consisted mainly of cubic close packed (ccp) CdS. The photocurrent spectrum of the film exhibited a cut-off which closely conformed to the expected bandgap of CdS. The gradual increase in SH intensity as the sulphide film thickened was due to a contribution to the overall SH signal from the CdS film itself. No evidence of any hcp species was apparent in the rotational anisotropy patterns, with the four-fold pattern expected for the vicinal MCT surface being maintained even after film growth. When the potential was stepped to −0.3 V, the film grown absorbed the ellipsometer radiation once a thickness of 86 nm was reached. Photocurrent measurements showed a tail extending into the red region of the spectrum. These phenomena have been attributed to the incorporation of ccp HgS into the sulphide film as at this potential, the electrochemical reaction of the HgTe component of MCT can occur. SHG rotational anisotropy confirmed the four-fold symmetry of the ccp surface film.     

Mercury speciation in gypsums produced from flue gas desulfurization by temperature programmed decomposition

Temperature programmed decomposition was used to identify mercury (Hg) species in gypsum samples produced from flue gas desulfurization in two Spanish power stations (A and B). As stricter emission control/reduction policies, particularly those focusing on Hg, are being implemented, wet flue gas desulfurization (FGD) technologies used for the removal of SO₂ can result in the co-removal of highly-soluble oxidized Hg. The amount of Hg retained in FGD products may increase in the future if these units are optimized for co-capture. For this reason, it is important to identify the mercury species in FGD products not only to determine the potential risk when the wastes are finally disposed of, but also to understand the behaviour of mercury during combustion and therefore to improve the technologies for mercury removal. Different mercury species were identified in the gypsum samples. In power station A, HgS were the most probable Hg species, whereas in power station B the main compound was Hg halogenated compounds.     

高分子保护水热法制备高分散硫化汞纳米颗粒

以聚乙烯吡咯烷酮为保护剂,以硝酸汞和硫代乙酰胺为原料,采用水热法合成了高分散的硫化汞(HgS)纳米颗粒,并通过TEM、XRD、XPS对其进行了表征。结果表明:水热法有利于提高HgS纳米颗粒的结晶性能;所制备的HgS为立方结构的β-HgS纳米颗粒,颗粒粒径小,平均粒径约为11.5nm,粒径分布范围窄,分散性能好,纯度高。     

Material and diagnostic characterization of 17th century mural paintings by spectra‐colorimetry and SEM‐EDS: An insight look at José de Escovar Workshop at the CONVENT of Na Sra da Saudação (Southern Portugal)

The early 17th century mural paintings set from the low‐choir of the extinct Dominican Convent of Nossa Senhora da Saudação in the town of Montemor‐o‐novo were analyzed by a setup comprising visible spectra‐colorimetry and scanning electron microscopy coupled with energy dispersive X‐ray spectrometry (SEM‐EDS) complemented with optical microscopy (OM), micro X‐ray diffraction, micro FTIR, and micro Raman spectroscopy. The main goals were material and diagnostic characterization of the paint layers and pictorial techniques used by Jose de Escovar workshop, one of the most active and controversial easel and mural painters of Evora Archiepiscopate between 1585 and 1622. The results show a differentiate use of red, blue, and green pigments in an alkaline environment. Stable mercury sulfide (HgS) was identified in almost all red areas in the latest scenes while, in the first ones, red ochre (Fe₂O₃) is the predominant pigment. Faded smalt (a co‐potassium silicate glass) is present pure in the sky background or mixed with red ochre in the garments at the beginning of the low‐choir but less at the end. Five kinds of copper‐based materials, with different degrees of color alteration, were found, namely malachite and azurite, copper chlorides, copper sulfates (e.g., posjnakite), and pseudomalachite. Another curious feature is the uneven use of a limewash made with slaked calcitic lime in the carnations. Lack of material, internal organization strategies, or technical differences within the team are probably the most likely causes. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 288–306, 2014; Published Online 5 February 2013 in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/col.21792     

多孔Al2O3-ZrO2陶瓷的微观结构

以Al₂O₃、ZrO₂陶瓷粉体为溶质,以莰烯为溶剂,以Texaphor963作为添加剂,制备出低粘度高稳定性的陶瓷浆料,采用冷冻注模工艺制备出具有较高强度的陶瓷坯体,采用无压烧结工艺,得到了多孔Al₂O₃-ZrO₂陶瓷制品,并对其微观结构进行了研究。     

Preparation and properties of transparent PMMA/ZrO2 nanocomposites using 2-hydroxyethyl methacrylate as a coupling agent

Transparent PMMA/ZrO₂ nanocomposites were prepared by in-situ bulk polymerization of methyl methacrylate (MMA)/ZrO₂ dispersions that were firstly synthesized using nonaqueous synthesized ZrO₂ nanocrystals and the function monomer, 2-hydroxyethyl methacrylate (HEMA), as the ligand. The dispersion behavior of ZrO₂ nanoparticles in MMA, structure, mechanical and thermal properties of the PMMA/ZrO₂ nanocomposites were investigated comprehensively. It was found that ZrO₂ nanoparticles were well dispersed in MMA with HEMA ligand, but the MMA/ZrO₂ dispersions easily destabilized in air as well as at elevated temperatures. The destabilization temperature of the dispersion is raised by increasing the molar ratio of HEMA/ZrO₂ to match the bulk polymerization temperature. The PMMA/ZrO₂ nanocomposites showed an interesting chemical structure (namely, highly cross-linked structure even at ZrO₂ content as low as 0.8 wt% and hydrogen bonding interaction between polymer matrix and ZrO₂ nanoparticles), with enhanced rigidity without loss of the toughness and improved thermal stability. The relationship between the structure and the properties of the PMMA/ZrO₂ nanocomposites based on the HEMA coupling agent was discussed.     

Fine-sized BaMgAl10O17:Eu phosphor powders prepared by spray pyrolysis from the spray solution with BaF2 flux

Fine-sized BaMgAl₁₀O₁₇:Eu²⁺ phosphor powders with plate-like morphology were prepared by spray pyrolysis process. The effects of ratio of BaF₂ and Ba(NO₃)₂ used as the source materials of Ba component on the morphological and optical properties of the BaMgAl₁₀O₁₇:Eu²⁺ phosphor powders were investigated. BaF₂ was used as the flux material as well as the source material of Ba component. The phosphor powders prepared from the spray solution with the same mole concentrations of BaF₂ and Ba(NO₃)₂ had fine size, plate-like morphology and narrow size distribution. The addition of BaF₂ as the source material of Ba component increased the photoluminescence intensities of the phosphor powders. The phosphor powders prepared from the spray solution with the ratios of BaF₂ and Ba(NO₃)₂ larger than 1 had the similar photoluminescence intensities to that of the commercial product.     

Reactions of dinitrogen pentoxide and nitrogen dioxide with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine

The reactions of gaseous dinitrogen pentoxide (N₂O₅) and nitrogen dioxide (NO₂) with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) coated on the inside surface of a glass reaction cell were studied at 298 K. Unsaturated phosphatidylcholines are significant components of pulmonary surfactant in the alveolar region of the lung and hence serve as a simple model to examine reactions of pulmonary surfactant with these oxidant air pollutants. Using high-performance liquid chromatography (HPLC), Fourier transform infrared and fast atom bombardment mass spectroscopy, the major products of reactions of POPC with N₂O₅ and NO₂ were separated and identified. In the POPC-N₂O₅ reaction using either air or helium as a buffer gas, the nitronitrate, vinyl nitro and allylic nitro derivatives, as well as a small amount of thetrans-isomer of the starting material, were obtained. The nature of the products obtained from the POPC-NO₂ reaction depends on the concentration of NO₂ as well as whether air is present. At low NO₂ concentrations (P_{NO 2}/_{N 2}O₄≤3.8 Torr) in air or in helium, thetrans-isomer of POPC was formed almost exclusively. At higher NO₂ concentrations (P_{NO 2}/N₂O₄≥20 Torr) in helium, the dinitro, vinyl nitro and nitro alcohol derivatives were formed. In the presence of air (or 24%¹⁸O₂ in helium), a nitronitrate and a dinitronitrate were additional products. Mechanisms for the formation of the observed products and implications for the inhalation of oxides of nitrogen are discussed.     

Synthesis of Novel Solid Base of MgO Covered with Metal Oxides

The solid base catalysts of MgO covered with SiO₂, Al₂O₃, TiO₂, and ZrO₂ were prepared by decomposition of the corresponding alkoxide over an Mg(OH)₂ surface in ethyl acetate solution followed by thermal decomposition. The acid-base properties of the prepared catalysts were estimated using 2-propanol decomposition activity and selectivity. The stability of catalysts for the aldol reaction of acetone against H₂O was examined. The acid sites were generated on the MgO surface by covering with metal oxides. Base sites were formed when the MgO was covered with Al₂O₃. Catalysts made of MgO covered with more than 7 mol% Al₂O₃ showed sufficient stability against H₂O as well as reusability.     

Synthesis of ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript> Hierarchical Nanostructure by Au Catalysts Induced Thermal Evaporation

In this paper, ZnGa₂O₄ hierarchical nanostructures with comb-like morphology are fabricated by a simple two-step chemical vapor deposition (CVD) method: first, the Ga₂O₃ nanowires were synthesized and employed as templates for the growth of ZnGa₂O₄ nanocombs; then, the as-prepared Ga₂O₃ nanowires were reacted with ZnO vapor to form ZnGa₂O₄ nanocombs. Before the reaction, the Au nanoparticles were deposited on the surfaces of Ga₂O₃ nanowires and used as catalysts to control the teeth growth of ZnGa₂O₄ nanocombs. The as-prepared ZnGa₂O₄ nanocombs were highly crystallized with cubic spinel structure. From the photoluminescence (PL) spectrum, a broad band emission in the visible light region was observed of as-prepared ZnGa₂O₄ nanocombs, which make it promising application as an optical material.