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HgBr crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Hg1+ is bonded in a distorted single-bond geometry to one Hg1+ and five equivalent Br1- atoms. The Hg–Hg bond length is 2.63 Å. There are one shorter (2.58 Å) and four longer (3.54 Å) Hg–Br bond lengths. Br1- is bonded in a distorted single-bond geometry to five equivalent Hg1+ atoms.
Mass spectrometry methods are currently under development by the atmospheric mercury (Hg) research community to elucidate the identity of atmospheric oxidized mercury (Hg II ) compounds. Due to high instrument detection limits, materials that can quantitatively preconcentrate atmospheric Hg II without facilitating compound-altering chemical reactions are needed to support these methods. Cation exchange membranes (CEM) and nylon membranes are currently used to preconcentrate ambient Hg II for concentration measurements and Hg II compound estimation, respectively. However, CEM and nylon membranes are poor candidates for observations by mass spectrometry methods due to release of interfering compounds upon heating; glasses do not have this problem. Here, three metal oxide glasses were explored as potential alternatives for Hg II preconcentration for future use with mass spectrometry methods: calcium phosphate (CaP), iron phosphate (FeP), and calcium aluminate (CaAl). The glasses demonstrated quantitative selective capture of HgBr 2 without capture of Hg 0 . Under ambient conditions, the CaP, FeP, and CaAl sorbed 36.4 ± 12.6% of the total HgII as the CEM. However, when Hg concentrations were normalized to surface area, CaP, FeP, and CaAl sorbed more HgBr 2 in the laboratory and ambient HgII compared to CEM. The CEM and CaP retained similar concentrations of HgBr 2 when preloaded samples were deployed in the field. Additionally, a permeation tube-based calibrator was used to load sorbents with HgBr 2 for investigation of HgII retention on CEM and thermal desorption profile changes on nylon membranes during active sampling. Nylon membranes were purchased from three vendors and used to compare HgBr 2 retention; a different HgBr 2 thermal desorption profile was achieved for each vendor’s nylon membrane.
Here we report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for low temperature plasma diagnostics. The system can measure gas species in solutions, with a detection limit (minimum detectable absorbance) of 9.1 × 10 -5 , which is equivalent to a detection limit of 0.04 parts per billion for measuring OH radicals in water at 308 nm. With higher reflectivity ringdown mirrors and improved design of a Brewster angle cell, the detection limit can potentially be up to 10 -6 or lower. In this exploratory study, the absorption cross sections of HgBr 2 and H 2 O 2 in the aqueous phase at 256 nm are measured to be (1.8 ± 0.1) × 10 -18 cm 2 and (5.2 ± 0.5) × 10 -20 cm 2 , respectively. Furthermore, temporal profiles of absorbance from distilled water, HgBr 2 , and H 2 O 2 solutions when interacting with a helium atmospheric plasma jet are individually characterized at different plasma powers, gas flow rates, and/or solute concentrations. The observed linear temporal profiles of absorbance from the plasma-interacted water suggest formation of H 2 O 2 from plasma-generated OH radicals, while the nonlinear temporal profiles from the plasma-treated HgBr 2 solutions reveal possible removal of HgBr 2 by OH radicals. Our results demonstrate that the new BA-CRDS system is a powerful tool for quantification of reactive plasma species in multiphases or other complex settings.
Anthropogenic mercury emission to the atmosphere adversely affects the environment, wildlife, and human health. Accordingly, the design and implementation of improved mercury-capture technologies have received increased attention. We present a computational chemistry-based screening study to guide the development of mercury-capture materials. We use density functional theory (DFT) to probe the efficacy of metal salts and metal oxides (NaCl, NaBr, KCl, KBr, CaCl 2 , CaBr 2 , NaNO 3 , and MgO) toward mercury capture and their ability to be regenerated for continued use. We focus on three primary sources of mercury emission as elemental gaseous mercury (Hg(0)) or oxidized gaseous mercury species (Hg(II); HgCl 2 or HgBr 2 ): (i) Hg(0) emission from artisanal Au production; (ii) Hg(II)/Hg(0) emission from inlet/outlet streams for flue-gas desulfurization (FGD) operation; and (iii) Hg(0) and Hg(II) emission from cement production. Our results suggest that CaCl 2 and CaBr 2 are good candidates for capturing Hg(0) in artisanal Au production. For FGD operation, KBr, MgO, CaCl 2 , and CaBr 2 are good candidates for capturing HgCl 2 and HgBr 2 , while CaBr 2 is the only studied material that can capture Hg(0) from the outlet FGD stream. For cement production, CaBr 2 is the only material of those studied that can capture Hg(0), HgCl 2 , and HgBr 2 . Furthermore, our DFT results can accelerate the development of cheap and regenerable mercury-capture materials, as well as better prevent the release of mercury to the environment.
HgBrHg7(O2Br)2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of two HgBr ribbons oriented in the (0, 1, 0) direction and two Hg7(O2Br)2 sheets oriented in the (0, 0, 1) direction. In each HgBr ribbon, Hg+1.38+ is bonded in a 2-coordinate geometry to one Hg+1.38+ and two equivalent Br1- atoms. The Hg–Hg bond length is 2.64 Å. There are one shorter (2.58 Å) and one longer (3.01 Å) Hg–Br bond lengths. Br1- is bonded in an L-shaped geometry to two equivalent Hg+1.38+ atoms. In each Hg7(O2Br)2 sheet, there are seven inequivalent Hg+1.38+ sites. In the first Hg+1.38+ site, Hg+1.38+ is bonded in a distorted see-saw-like geometry to two O2- and two Br1- atoms. There are one shorter (2.18 Å) and one longer (2.39 Å) Hg–O bond lengths. There are one shorter (2.66 Å) and one longer (2.90 Å) Hg–Br bond lengths. In the second Hg+1.38+ site, Hg+1.38+ is bonded in a 4-coordinate geometry to three O2- and one Br1- atom. There are a spread of Hg–O bond distances ranging from 2.18–2.52 Å. The Hg–Br bond length is 2.88 Å. In the third Hg+1.38+ site, Hg+1.38+ is bonded in an L-shaped geometry to two O2- atoms. There are one shorter (2.39 Å) and one longer (2.41 Å) Hg–O bond lengths. In the fourth Hg+1.38+ site, Hg+1.38+ is bonded in a 1-coordinate geometry to three O2- and one Br1- atom. There are a spread of Hg–O bond distances ranging from 2.54–2.92 Å. The Hg–Br bond length is 3.48 Å. In the fifth Hg+1.38+ site, Hg+1.38+ is bonded in a distorted linear geometry to two O2- and one Br1- atom. There are one shorter (2.03 Å) and one longer (2.08 Å) Hg–O bond lengths. The Hg–Br bond length is 3.13 Å. In the sixth Hg+1.38+ site, Hg+1.38+ is bonded in a distorted single-bond geometry to one O2- and three Br1- atoms. The Hg–O bond length is 2.20 Å. There are a spread of Hg–Br bond distances ranging from 3.25–3.33 Å. In the seventh Hg+1.38+ site, Hg+1.38+ is bonded in a trigonal planar geometry to three O2- and one Br1- atom. There are a spread of Hg–O bond distances ranging from 2.22–2.29 Å. The Hg–Br bond length is 3.30 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to four Hg+1.38+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to four Hg+1.38+ atoms. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Hg+1.38+ atoms. In the fourth O2- site, O2- is bonded to four Hg+1.38+ atoms to form distorted corner-sharing OHg4 tetrahedra. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 1-coordinate geometry to four Hg+1.38+ atoms. In the second Br1- site, Br1- is bonded in a 2-coordinate geometry to five Hg+1.38+ atoms.
HgHgBrHg4O3BrHg2OBr crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four mercury molecules; four Hg2OBr clusters; two HgBr ribbons oriented in the (0, 1, 0) direction; and two Hg4O3Br sheets oriented in the (0, 0, 1) direction. In each Hg2OBr cluster, there are two inequivalent Hg+1.38+ sites. In the first Hg+1.38+ site, Hg+1.38+ is bonded in a 1-coordinate geometry to one Br1- atom. The Hg–Br bond length is 3.10 Å. In the second Hg+1.38+ site, Hg+1.38+ is bonded in a single-bond geometry to one O2- atom. The Hg–O bond length is 2.29 Å. O2- is bonded in a bent 120 degrees geometry to one Hg+1.38+ and one Br1- atom. The O–Br bond length is 1.79 Å. Br1- is bonded in a distorted L-shaped geometry to one Hg+1.38+ and one O2- atom. In each HgBr ribbon, Hg+1.38+ is bonded in a 2-coordinate geometry to one Hg+1.38+ and two equivalent Br1- atoms. The Hg–Hg bond length is 2.63 Å. There are one shorter (2.55 Å) and one longer (3.14 Å) Hg–Br bond lengths. Br1- is bonded in an L-shaped geometry to two equivalent Hg+1.38+ atoms. In each Hg4O3Br sheet, there are four inequivalent Hg+1.38+ sites. In the first Hg+1.38+ site, Hg+1.38+ is bonded in a distorted linear geometry to two O2- and three equivalent Br1- atoms. Both Hg–O bond lengths are 2.11 Å. There are a spread of Hg–Br bond distances ranging from 3.21–3.27 Å. In the second Hg+1.38+ site, Hg+1.38+ is bonded in a 2-coordinate geometry to two O2- and one Br1- atom. Both Hg–O bond lengths are 2.47 Å. The Hg–Br bond length is 3.02 Å. In the third Hg+1.38+ site, Hg+1.38+ is bonded in a distorted single-bond geometry to one O2- atom. The Hg–O bond length is 2.90 Å. In the fourth Hg+1.38+ site, Hg+1.38+ is bonded to three O2- and one Br1- atom to form distorted corner-sharing HgBrO3 trigonal pyramids. There are a spread of Hg–O bond distances ranging from 2.29–2.34 Å. The Hg–Br bond length is 2.92 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four Hg+1.38+ atoms to form corner-sharing OHg4 tetrahedra. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Hg+1.38+ and one O2- atom. The O–O bond length is 1.40 Å. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Hg+1.38+ and one O2- atom. Br1- is bonded in a 5-coordinate geometry to five Hg+1.38+ atoms.
Heavy metal halides and selenides have unique properties which make them excellent materials for chemical, biological and radiological sensors. Recently it has been shown that selenohalides are even better materials than halides or selenides for gamma-ray detection. These materials also meet the strong needs of a wide band imaging technology to cover ultra-violet (UV), midwave infrared wavelength (MWIR) to very long wavelength infrared (VLWIR) region for hyperspectral imager components such as etalon filters and acousto-optic tunable filters (AO). In fact AOTF based imagers based on these materials have some superiority than imagers based on liquid crystals, FTIR, Fabry-Perot, grating, etalon, electro-optic modulation, piezoelectric and several other concepts. For example, broadband spectral and imagers have problems of processing large amount of information during real-time observation. Acousto-Optic Tunable Filter (AOTF) imagers are being developed to fill the need of reducing processing time of data, low cost operation and key to achieving the goal of covering long-wave infrared (LWIR). At the present time spectral imaging systems are based on the use of diffraction gratings are typically used in a pushbroom or whiskbroom mode. They are mostly used in systems and acquire large amounts of hyperspectral data that is processed off-line later. In contrast, acousto-optic tunable filter spectral imagers require very little image processing, providing new strategies for object recognition and tracking. They are ideally suited for tactical situations requiring immediate real-time image processing. But the performance of these imagers depends on the quality and homogeneity of acousto-optic materials. In addition for many systems requirements are so demanding that crystals up to sizes of 10 cm length are desired. We have studied several selenides and halide crystals for laser and AO imagers for MWIR and LWIR wavelength regions. We have grown and fabricated crystals of several materials such as mercurous chloride, mercurous bromide, mercurous iodide, lead chloride lead bromide, lead iodide, thallium arsenic selenide, gallium selenide, zince sulfide zinc selenide and several crystals into devices. We have used both Bridgman and physical vapor transport (PVT) crystal growth methods. In the past have examined PVT growth numerically for conditions where the boundary of the enclosure is subjected to a nonlinear thermal profile. Since past few months we have been working on binary and ternary materials such as selenoiodides, doped zinc sulfides and mercurous chloro bromide and mercurous bromoiodides. In the doped and ternary materials thermal and solutal convection play extremely important role during the growth. Very commonly striations and banding is observed. Our experiments have indicated that even in highly purified source materials, homogeneity in 1-g environment is very difficult. Some of our previous numerical studies have indicated that gravity level less than 10-4 (-g) helps in controlling the thermosolutal convection. We will discuss the ground based growth results of HgClxBr(1-x) and ZnSe growth results for the mm thick to large cm size crystals. These results will be compared with our microgravity experiments performed with this class of materials. For both HgCl-HgBr and ZnS-ZnSe the lattice parameters of the mixtures obey Vagard's law in the studied composition range. The study demonstrates that properties are very anisotropic with crystal orientation, and performance achievement requires extremely careful fabrication to utilize highest figure of merit. In addition, some parameters such as crystal growth fabrication, processing time, resolution, field of view and efficiency will be described based on novel solid solution materials. It was predicted that very similar to the pure compounds solid solutions also have very large anisotropy, and very precise oriented and homogeneous bulk and thin film crystals is required to achieve maximum performance of laser or imagers. Some of the parameters controlling the homogeneity such as thermos-solutal convection driven forces can be controlled in microgravity environments to utilize the benefits of these unique materials.