Arsenic Surface Research Articles

Intrinsic and Stable Conjugation of Thiolated Mesoporous Silica Nanoparticles with Radioarsenic.

The development of new image-guided drug delivery tools to improve the therapeutic efficacy of chemotherapeutics remains an important goal in nanomedicine. Using labeling strategies that involve radioelements that have theranostic pairs of diagnostic positron-emitting isotopes and therapeutic electron-emitting isotopes has promise in achieving this goal and further enhancing drug performance through radiotherapeutic effects. The isotopes of radioarsenic offer such theranostic potential and would allow for the use of positron emission tomography (PET) for image-guided drug delivery studies of the arsenic-based chemotherapeutic arsenic trioxide (ATO). Thiolated mesoporous silica nanoparticles (MSN) are shown to effectively and stably bind cyclotron-produced radioarsenic. Labeling studies elucidate that this affinity is a result of specific binding between trivalent arsenic and nanoparticle thiol surface modification. Serial PET imaging of the in vivo murine biodistribution of radiolabeled silica nanoparticles shows very good stability toward dearsenylation that is directly proportional to silica porosity. Thiolated MSNs are found to have a macroscopic arsenic loading capacity of 20 mg of ATO per gram of MSN, sufficient for delivery of chemotherapeutic quantities of the drug. These results show the great potential of radioarsenic-labeled thiolated MSN for the preparation of theranostic radiopharmaceuticals and image-guided drug delivery of ATO-based chemotherapeutics.

Determining site-specific background level with geostatistics for remediation of heavy metals in neighborhood soils

The choice of a relevant, uncontaminated site for the determination of site-specific background concentrations for pollutants is critical for planning remediation of a contaminated site. The guidelines used to arrive at concentration levels vary from state to state, complicating this process. The residential neighborhood of Hickory Woods in Buffalo, NY is an area where heavy metal concentrations and spatial distributions were measured to plan remediation. A novel geostatistics based decision making framework that relies on maps generated from indicator kriging (IK) and indicator co-kriging (ICK) of samples from the contaminated site itself is shown to be a viable alternative to the traditional method of choosing a reference site for remediation planning. GIS based IK and ICK, and map based analysis are performed on lead and arsenic surface and subsurface datasets to determine site-specific background concentration levels were determined to be 50 μg/g for lead and 10 μg/g for arsenic. With these results, a remediation plan was proposed which identified regions of interest and maps were created to effectively communicate the results to the environmental agencies, residents and other interested parties.

Growth of arsenic doped ZnO films using a finite surface doping source by metal organic chemical vapor deposition

Arsenic doped ZnO films are prepared using a pre-deposited GaAs finite surface source on sapphire substrates by a MOCVD method. Their conductivity and optical properties are closely related to the annealing process. The as-grown ZnO film shows n-type conductivity with weak FA emission. The in situ annealed sample shows p-type conductivity. The AsZn–2VZn acceptor level is confirmed by low-temperature photoluminescence measurement. The post annealed ZnO film appears to be n-type, which is attributed to the arsenic surface enrichment and the compensation of introduced donor like defects. Our method could be widely used in fabricating arsenic doped p-type ZnO related photoelectric devices.

Structure and morphology of InSb epitaxial films in the AlAs matrix

We report the results of electron microscopy study of the structural and morphological features of epitaxial films in the AlAs matrix. The epitaxial films were grown in the matrix by deposition of indium and antimony from molecular flows onto the aluminum arsenide surface and subsequent deposition of aluminum and arsenic. The objects of study were (110) cross sections and (001) planar foils. Instead of the InSb binary compound, we found the InxAl1–xSbyAs1–y quaternary solid solution in the AlAs matrix in the form of a wetting layer with coherently conjugated and relaxed islands. The In and Sb contents in the solid solution were indirectly estimated. Misfit dislocations at the heterointerfaces of relaxed islands were analyzed using the geometric phase method. It was established that each misfit dislocation is formed by a pair of close 60° dislocations with the inclined Burgers vectors of the a/2〈110⟩ type. In this case, the resulting Burgers vector of each pair lies in the heterointerface plane.

Spatial Variation of Arsenic in Soil, Irrigation Water, and Plant Parts: A Microlevel Study.

Arsenic pollution became a great problem in the recent past in different countries including Bangladesh. The microlevel studies were conducted to see the spatial variation of arsenic in soils and plant parts contaminated through ground water irrigation. The study was performed in shallow tube well command areas in Sadar Upazila (subdistrict), Faridpur, Bangladesh, where both soil and irrigation water arsenic are high. Semivariogram models were computed to determine the spatial dependency of soil, water, grain, straw, and husk arsenic (As). An arsenic concentration surface was created spatially to describe the distribution of arsenic in soil, water, grain, straw, and husk. Command area map was digitized using Arcview GIS from the “mouza” map. Both arsenic contaminated irrigation water and the soils were responsible for accumulation of arsenic in rice straw, husk, and grain. The accumulation of arsenic was higher in water followed by soil, straw, husk, and grain. Arsenic concentration varied widely within command areas. The extent and propensity of arsenic concentration were higher in areas where high concentration of arsenic existed in groundwater and soils. Spherical model was a relatively better and appropriate model. Kriging method appeared to be more suitable in creating interpolated surface. The average arsenic content in grain was 0.08–0.45 mg/kg while in groundwater arsenic level it ranged from 138.0 to 191.3 ppb.

Adsorption of arsenic with struvite and hydroxylapatite in phosphate-bearing solutions.

Arsenic sorption at above neutral pH is relevant when considering contaminant mobility in alkaline, phosphorus-bearing wastewaters, and may be viable in the presence phosphate minerals. Arsenic adsorption on struvite (MgNH4PO4 · 6H2O, MAP) and hydroxylapatite (Ca5(PO4)3OH, HAP) was evaluated at pH 8-11 from solutions with 2.7-0.125 mM phosphate and 0.05 mM As(III) or As(V). Over 7 d, As(III) removal from solution was minimal, but As(V) removal increased with pH, and was higher in the presence of MAP compared to HAP with a maximum of 74% removal in pH 11 MAP-bearing solutions. X-ray absorption fine structure spectroscopy (XAFS) analysis of solids recovered from pH 10-11 solutions revealed different mechanisms of As(V) sorption with MAP and HAP. Arsenic forms monodentate mononuclear surface complexes with MAP through the formation of a Mg-O-As bond, but is incorporated at the near-surface of HAP forming a johnbaumite-like (Ca5(AsO4)3OH) structure. Experiments using radioactive (33)P at pH 10-11 revealed faster exchange of P at the HAP surface, which could promote more facile As incorporation. Near-surface incorporated As in HAP may be less susceptible to remobilization compared to surface adsorbates formed with MAP. Overall, both MAP and HAP may sorb As at high pH in the presence of phosphate. This is relevant to the fate of As in alkaline contaminated waters in contact with phosphate mineral phases.

Mechanism of arsenic poisoning on SCR catalyst of CeW/Ti and its novel efficient regeneration method with hydrogen

Deactivation and regeneration of arsenic are studied on novel CeO2–WO3/TiO2 for selective catalytic reduction (SCR) of NOx with NH3. It is found that the activity and N2 selectivity of poisoned catalyst are inhibited immensely at the entire temperature range. The fresh, poisoned and regenerated catalysts are characterized using XRD, BET, XPS, H2-TPR, NH3-TPD, NO+O2-TPD, in situ Raman and in situ DRIFTS. The characterization results indicate that the poisoning of arsenic decrease BET surface area, surface Ce3+ concentration and the amount of Lewis acid sites and adsorbed NOx species but increase the reducibility and number of chemisorbed oxygen species. According to the in situ DRIFTS investigations, the adsorption of surface-adsorbed NH3 and NOx species is suppressed at low temperature, while the reactivity between surface-adsorbed NH3 and NO is prohibited at high temperature. A novel H2 reduction regeneration not only effectively removes arsenic from the poisoned catalysts, but promotes surface Ce3+/Ce4+ ratio and form new NOx adsorptive sites. However, it also affects the chemical properties of catalyst such as crystalline Ce2(WO4)3 forming, surface active oxygen species raise and loss of Brønsted acid sites.

Behavior of Transition Metals Penetrating Silicon Substrate through SiO2 and Si3N4 Films by Arsenic Ion Implantation and Annealing

The behavior of metals penetrating the silicon substrate through a screen SiO2 or Si3N4 film by the collision of arsenic ion and surface metals are quantitatively demonstrated. We have found using silicon step etching followed by ICP-MS and SIMS that 0.1∼8% of surface metals (Fe, Cr, Ni, Cu, and W) penetrate silicon even when implanted through screen SiO2 film, depending on metal species and the film thickness. The surface metals on a CVD Si3N4 film can also penetrate into the silicon during ion implantation and/or subsequent annealing. W is most difficult to penetrate the thermally-grown SiO2 film, while W and Cr can easily penetrate a CVD Si3N4 films. We have also found using microwave photoconductive decay measurements that recombination centers are generated in silicon by low level metal penetration even when implanted through screen SiO2.

Surface states and charge accumulation states on reconstructed InAs(001) surfaces

Using angle-resolved photoelectron spectroscopy, we investigate the electronic structure of InAs(001) surfaces having different stoichiometries, i.e. the indium rich c(8×2)/4×2 surface and the arsenic-rich c(2×8)/2×4 surface. We also compare surfaces having the same reconstructions but prepared by different techniques; by ion bombardment and annealing and by wet chemical treatment. Moreover, the surfaces are prepared on nominally undoped and n-doped InAs samples.Occupied electronic states at the Fermi level are found in all investigated cases. For the arsenic rich surfaces a single pocket of the states is found close to the Γ¯1×1 point in the reciprocal space while for the indium-rich surfaces multiple pockets of states are seen close to the Γ¯4×2 points, i.e., in accordance with periodicity of the surface. It is concluded that these states have a character of charge accumulation states (CAS), however, in the case of the indium-rich surface, the CAS are in resonance with surface states.

Strain analysis of compositionally tailored interfaces in InAs/GaSb superlattices

The effect of interface composition control on interfacial strain distribution in InAs/GaSb superlattices on (100)-GaSb substrates is investigated by atomic resolution scanning transmission electron microscopy. The interface composition was controlled by either depositing InSb at each interface or soaking the GaSb-on-InAs interface under Sb2 atmosphere. The strain profiles reveal a distinct difference in the extent to which the superlattice strain is balanced using the two methods. In particular, they indicate that the degree of strain balance achievable with soaking is inherently limited by the arsenic surface coverage during GaSb-on-InAs interface formation, emphasizing the influence of V/III flux ratio at this interface. The results also explain observed X-ray diffraction profiles.

Publisher's Note: Evolution of the Fermi surface of arsenic through the rhombohedral to simple-cubic phase transition: A Wannier interpolation study [Phys. Rev. B88, 134103 (2013)

Publisher's Note: Evolution of the Fermi surface of arsenic through the rhombohedral to simple-cubic phase transition: A Wannier interpolation study [Phys. Rev. B<b>88</b>, 134103 (2013)

Evolution of the Fermi surface of arsenic through the rhombohedral to simple-cubic phase transition: A Wannier interpolation study

The pressure dependence of the Fermi surface of arsenic is examined using the technique of Wannier interpolation, enabling a dense sampling of the Brillouin zone and the ability to capture fine features within it. Focusing primarily on the A7 to simple-cubic phase transition, we find that this semimetal to metal transition is accompanied by the folding of Fermi surfaces. The pressure dependence of the density of states (DOS) of arsenic indicates that the onset of the Peierls-type cubic to rhombohedral distortion is signified by the appearance of emerging van Hove singularities in the DOS, especially around the Fermi level. As we noted in an earlier study, high levels of convergence are consequently required for an accurate description of this transition.

Nanoscale peculiarities of the thermally stimulated surface autosegregation of covalent crystals: Gallium arsenide

Nanoscale changes in the morphology and elemental composition of cleavage surfaces of gallium arsenide crystals, which arise due to thermally stimulated surface autosegregation, are investigated in detail and systematized. It is shown that, depending on the annealing conditions (temperature, duration, and evacuation), gallium arsenide dissociates, forming submicron nonstoichiometric layers on the surface or local phases of arsenic, gallium, and gallium oxide. The mechanism and nature of autosegregation are determined by the competing processes of arsenic sublimation and its surface diffusion with an activation energy of ∼31 kJ/mol. The migration of arsenic atoms is described with the help of a crystallochemical model. The nanomorphology of the surface phases includes arsenic and gallium nanoparticles with sizes of 10-200 nm, their agglomerates, and gallium oxide nano- and microcrystallites combined in plate- and chainlike configurations.

Bayesian Spatial Design of Optimal Deep Tubewell Locations in Matlab, Bangladesh.

We introduce a method for statistically identifying the optimal locations of deep tubewells (dtws) to be installed in Matlab, Bangladesh. Dtw installations serve to mitigate exposure to naturally occurring arsenic found at groundwater depths less than 200 meters, a serious environmental health threat for the population of Bangladesh. We introduce an objective function, which incorporates both arsenic level and nearest town population size, to identify optimal locations for dtw placement. Assuming complete knowledge of the arsenic surface, we then demonstrate how minimizing the objective function over a domain favors dtws placed in areas with high arsenic values and close to largely populated regions. Given only a partial realization of the arsenic surface over a domain, we use a Bayesian spatial statistical model to predict the full arsenic surface and estimate the optimal dtw locations. The uncertainty associated with these estimated locations is correctly characterized as well. The new method is applied to a dataset from a village in Matlab and the estimated optimal locations are analyzed along with their respective 95% credible regions.

Assessment of Arsenic Surface Contamination in a Museum Anthropology Department

To assess potential arsenic (As) contamination of work surfaces to improve upon the control strategy at an anthropology department in a large natural history museum. Work practices were observed and control strategy reviewed to inform an occupational hygiene assessment strategy utilizing surface wipe sampling. A total of 35 sampling targets were identified, focusing on surfaces that receive high touch traffic, including workstations, artifact transport carts, and elevator buttons. Arsenic sampling and analysis were performed using reference method Occupational Safety and Health Administration ID-125G. Four of the sampling areas returned detectable levels of As, ranging from 0.052 to 0.350 μg/100 cm. Workplace observations and wipe sampling data enabled the development of recommendations to help to further reduce potential occupational exposure to As. Continuous reduction of surface contamination is prudent for known human carcinogens.

A process for the selective removal of arsenic from contaminated water using acetate functionalized zinc oxide nanomaterials

This research article deals with the uptake of arsenic from contaminated water using acetate functionalized zinc oxide (ZnO) nanomaterials. The ZnO nanomaterials of various sizes (6–60 nm) have been synthesized following different wet chemical routes. The arsenic removal efficacy of acetate functionalized ZnO nanomaterials was carried out at different pH and time interval. It has been concluded from the study that ZnO nanomaterials (&lt;60 nm) prepared by zinc acetate precursor effectively removes arsenic, while ZnO of same size prepared from zinc chloride, zinc nitrate, zinc sulphate precursor could not remove arsenic considerably. However, ZnO of same size synthesized using other than zinc acetate precursor and functionalized with acetate ions removes arsenic effectively. It is also proposed that acetate ions over the surface of ZnO adsorb arsenic by an oxo‐coordination mechanism and purifies water up to permissible limits of arsenic at pH 5.8–6.8. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1023–1029, 2013

Assessing Anthracene and Arsenic Contamination within Buffalo River Sediments

Anthracene and arsenic contamination concentrations at various depths in the Buffalo River were analyzed in this study. Anthracene is known to cause damage to human skin and arsenic has been linked to lung and liver cancer. The Buffalo River is labelled as an Area of Concern defined by the Great Lakes Water Quality Agreement between Canada and the United States. It has a long history of industrial activity located in its near vicinity that has contributed to its pollution. An ordinary kriging spatial interpolation technique was used to calculate estimates between sample locations for anthracene and arsenic at various depths. The results show that both anthracene and arsenic surface sediment (0–30 cm) is less contaminated than all subsurface depths. There is variability of pollution within the different subsurface levels (30–60 cm, 60–90 cm, 90–120 cm, 120–150 cm) and along the river course, but major clusters are identified throughout all depths for both anthracene and arsenic.

Bêhounekite, U(SO4)2(H2O)4, from Jáchymov (St Joachimsthal), Czech Republic: the first natural U4+sulphate

AbstractBêhounekite, orthorhombic U(SO4)2(H2O)4, is the first natural sulphate of U4+. It was found in the Geschieber vein, Jáchymov (St Joachimsthal) ore district, Western Bohemia, Czech Republic, crystallized on the altered surface of arsenic and associated with kaatialaite, arsenolite, claudetite, unnamed phase UM1997-20-AsO:HU and gypsum. Bêhounekite most commonly forms short-prismatic to tabular green crystals, rarely up to 0.5 mm long. The crystals have a strong vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and have very good cleavage along ﹛100﹜. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Bêhounekite is moderately pleochroic, α∼β is pale emerald green and γ is emerald green, and is optically biaxial (+) withα =1.590(2), β = 1.618(4), γ = 1.659(2) (590 nm), 2V (calc.) = 81°, birefringence 0.069. The empirical formula of bêhounekite (based on 12 O atoms, from an average of five point analyses) is (U0.99Y0.03)Σ1.02(SO4)1.97(H2O)4. The simplified formula is U(SO4)2(H2O)4, which requires UO253.77. SO331.88, H2O 14.35, total 100.00 wt.%. Bêhounekite is orthorhombic, space groupPnma, a =14.6464(3),b =11.0786(3), c = 5.6910(14) Å,V =923.43(4) Å3,Z =4, Dcalc= 3.62 g cm–3. The seven strongest diffraction peaks in the X-ray powder diffraction pattern are[dobsin Å (I)(hid)]:7.330 (100) (200), 6.112 (54) (210), 5.538 (21) (020), 4.787 (42) (111), 3.663 (17) (400), 3.478 (20) (410), 3.080 (41) (321). The crystal structure of bêhounekite has been solved by the charge-flipping method from single-crystal X-ray diffraction data and refined toR1=2.10 % with aGOF =1.51, based on 912 unique observed diffractions. The crystal structure consists of layers built up from [8]-coordinate uranium atoms and sulphate tetrahedra. The eight ligands include four oxygen atoms from the sulphate groups and four oxygen atoms from the H2O molecules. Each uranium coordination polyhedron is connected via sulphate tetrahedra with other uranium polyhedra and through hydrogen bonds to the apices of sulphate tetrahedra. The dominant features of the Raman and infrared spectra of bêhounekite are related to stretching vibrations of SO4tetrahedra (∼1200–950 cm–1), O-H stretching modes (∼3400–3000 cm–1) and H—O—H bending modes (∼1650 cm–1). The mineral is named in honour of František Bêhounek, a well known Czech nuclear physicist.

A Monte Carlo investigation of Gallium and Arsenic migration on GaAs(100) surface

We perform an atomic scale simulation of GaAs/GaAs(100) growth, using the Kinetic Monte Carlo (KMC) technique, to investigate some aspects of Gallium and Arsenic surface migration. We show that the interlayer migration rate is smaller for Arsenic than for Gallium. Results suggest that upward diffusion is thermally activated while downward diffusion is kinetically controlled. We also find an oscillatory behavior of the surface diffusion rates during the growth, in close relation to the roughening of the substrate. The surface migration rates are governed by the temperature, but mostly by the Arsenic to Gallium flux ratio. The Gallium average diffusion lengths are estimated to be ~440 nm at 620°C and ~130 nm at 530°C, in agreement with experimental data.

Adsorptive removal of As(III) by biogenic schwertmannite from simulated As-contaminated groundwater

This study investigates synthesis of biogenic schwertmannite by Acidithiobacillus ferrooxidans and its role and mechanism in adsorption of As(III) from water. Results indicate that schwertmannite particles formed through oxidation of ferrous sulfate by A. ferrooxidans cells for different times vary greatly in size and in morphology. The hedge-hog like schwertmannite formed after reaction for 72 h are aggregative spheroid particles with a diameter of approximately 2.5 μm and its chemical formula can be expressed as Fe 8O 8(OH) 4.42(SO 4) 1.79. Batche studies show that both Freundlich and Langmuir model are suitable for describing the adsorption behavior of As(III) on schwertmannite at pH 7.5 and As(III) in simulated groundwater can be effectively removed by biogenic schwertmannite with a maximum adsorption capacity of 113.9 mg As(III) g −1 and the optimal pH is in the range of 7–10. The arsenic removal is hardly affected by the competing anions often observed in groundwater unless the mole concentration of PO 4 3 - and SO 4 2 - in groundwater are 75 or 750 times higher than As(III), respectively. The mechanism of As(III) adsorption on biogenic schwertmannite involves ligand exchanges between arsenic species and surface hydroxyl group and sulfate. In addition, experiments show that As(III)-sorbed biogenic schwertmannite aged in deionized water at 25 °C exhibits no mineralogy phase changes even after ageing at pH 6.0 and 8.5 for 90 d.