Adsorption Of Br Research Articles

Removal of C.I. Basic Red 46 (BR 46) from contaminated water by adsorption onto hardened paste of Portland cement: Equilibrium isotherms and thermodynamic parameters study

The present study was carried out to investigate the potential of hardened paste of Portland cement (HPPC) as a low-cost adsorbent for the removal of Basic Red 46 (BR 46) from contaminated water by using batch adsorption studies. In this work, HPPC has been selected as adsorbent because of the main advantages such as high efficiency, simple separation of sludge, abundant availability and low-cost material. The removal of dye in aqueous medium through the process of adsorption with HPPC under a set of variables (contact time, adsorbent dosage, pH, temperature and adsorbent particles size) has been investigated. Results showed that removal of BR 46 increased over 80% with increasing adsorbent dosage, temperature, contact time, pH and adsorbent particle size decreasing.Also the equilibrium adsorption data were fitted well for Temkin isotherm. The adsorption of BR 46 was endothermic and spontaneous with ∆Hâ—¦ values of +5.452 kJ mol−1 and ∆Sâ—¦ values of 0.035 JK-1 mol-1. The free energy changes ∆Gâ—¦ was evaluated with temperature increasing. From the experimental results, it may be concluded that HPPC was an efficient and economical adsorbent for BR 46 removal. Key words: Adsorption, Basic Red 46 removal, hardened paste of Portland cement, kinetics, equilibrium isotherm, thermodynamic.

Reaction mechanism of direct H 2O 2 synthesis from H 2 and O 2 over Pd/C catalyst in water with H + and Br − ions

Kinetic analyses including mass transfer processes were applied for the title reaction and the H 2O 2 decomposition. Adsorption of Br − ion on the catalyst was also measured. A hydride-hydroperoxy species H-M-OOH (M, the metal surface) was proposed as the key intermediate in the H 2O 2 formation, the direct H 2O formation, and the H 2O 2 decomposition. The H + added would accelerate Br − adsorption, reductive elimination and β-elimination of the H-M-OOH species, and desorption of surface H 2O 2 species. Two types of metal surface sites were suggested, one of which had a high degree of coordinative unsaturation and catalyzed the direct H 2O formation and the H 2O 2 decomposition. Both reactions would be inhibited by adsorption of the Br − and H + pairs. Another had a low degree of unsaturation and was active for the H 2O 2 formation. Sulfur poisoning study revealed that several surface Pd atoms were inactivated at once by adsorption of a sulfur atom for H 2–O 2 reaction.

Synthesis of Pd−Pt Bimetallic Nanocrystals with a Concave Structure through a Bromide-Induced Galvanic Replacement Reaction

This article describes a systematic study of the galvanic replacement reaction between PtCl(6)(2-) ions and Pd nanocrystals with different shapes, including cubes, cuboctahedrons, and octahedrons. It was found that Br(-) ions played an important role in initiating, facilitating, and directing the replacement reaction. The presence of Br(-) ions led to the selective initiation of galvanic replacement from the {100} facets of Pd nanocrystals, likely due to the preferential adsorption of Br(-) ions on this crystallographic plane. The site-selective galvanic replacement resulted in the formation of Pd-Pt bimetallic nanocrystals with a concave structure owing to simultaneous dissolution of Pd atoms from the {100} facets and deposition of the resultant Pt atoms on the {111} facets. The Pd-Pt concave nanocubes with different weight percentages of Pt at 3.4, 10.4, 19.9, and 34.4 were also evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Significantly, the sample with a 3.4 wt.% of Pt exhibited the largest specific electrochemical surface area and was found to be four times as active as the commercial Pt/C catalyst for the ORR in terms of equivalent Pt mass.

Understanding 4-bromostyrene Adsorption on the Si(001)-(1 × 2) surface: A density functional theory study

Adsorption properties of 4-bromostyrene (Br–Sty) on the Si(001)-(1 × 2) surface are investigated by ab initio calculation based on density functional theory (DFT). For the adsorption of Br–Sty molecule on the Si(001)-(1 × 2) surface, we have assumed two possible cases within: (i) binding on the partially H-terminated surface and (ii) binding on the clean surface. For the first case, we have estimated two different binding sides: (i) Bromine-terminated bindings and (ii) Carbon-terminated binding. The adsorption energies of Br-terminated and C-terminated binding were found as 0.36 eV and 3.76 eV, respectively. In the same manner, we have also assumed two possible binding sides for the clean surface: (i) Br-terminated binding and (ii) ring-shaped binding. We have found adsorption energies for Br-terminated and ring-shaped binding as 0.14 eV and 1.10 eV on the clean surface, respectively. Moreover, the nudged elastic band method (NEB) was used to reveal the adsorption pathway of these binding models. These results serve to understand the possibility of the adsorption of Br–Sty molecules onto different kind of silicon surfaces into different reaction conditions.

Photoassisted Anodic Oxidation of Bromide on an n-Type Titanium Dioxide Electrode in an Amide-Type Ionic Liquid

Photoassisted anodic oxidation of bromide (Br-) on an n-type titanium dioxide (n-TiO2) electrode has been investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing BMPBr at various concentrations. Photoassisted anodic oxidation of BMPTFSA was confirmed in the absence of BMPBr. A photoanodic current corresponding to the oxidation of Br- was observed under illumination of UV light. The onset potential of the photoanodic current was the function of the concentration of Br-, suggesting the flat band potential of the n-TiO2 electrode in the ionic liquid is related to the potential of zero charge, which is expected to be affected by the specific adsorption of Br- on the n-TiO2 electrode.

ChemInform Abstract: Kinetics of the Reaction of Silicon with Gaseous Bromine.

The chemical etching of intrinsic polycrystalline silicon has been studied at Br2 pressures between 0.05 and 30 Torr, and at temperatures ranging from 540 to 600 °C. In this temperature range, and at a pressure of 1 Torr and above, the etch rate is given by: Retch= 1010.2 ± 0.4 nm min–1 Torr–1/2 exp-[(132 ± 7 kJ mol–1)/RT]×P1/2– 109.8 ± 2.4 nm min–1 exp-[(140 ± 40 kJ mol–1)/RT]. Deviations from this rate law at low pressures were found to be consistent with a reaction mechanism which involves the dissociative adsorption of Br2 on the silicon surface. A kinetic analysis of the pressure and temperature dependences of the etch rate yields a value of 108.9 ± 1.3 nm min–1 Torr–1 exp-[(108 ± 22 kJ mol–1)/RT] for the first-order rate-controlling rate constant at low pressures and 1010.2 ± 0.4 nm min–1 Torr–1/2 exp-[(132 ± 7 kJ mol–1)/RT] for the half-order ‘composite’ rate constant which is observed at high pressures. The possibility that bromine atoms are produced in the gas phase, and that these species are responsible for the observed etch rates is also considered. The atom reaction and the molecule reaction proceed through the same intermediate, and the relative contribution from the two processes depends on how far the concentrations of these species are from their equilibrium values.

Organoclay particles as reinforcing agents in polysaccharide films

In this work an investigation is described on the use of organically modified montmorillonite clay particles as stabilizers of bioplastic films based on xylan. With the aim of facilitating the incorporation of the nanoparticles to the films, the former were treated with a non-ionic surfactant, inulin. In order to evaluate the possible role of electrostatic interactions in the formation of montmorillonite/xylan complexes, an exhaustive electrokinetic characterization of the modified montmorillonite was carried out. Because montmorillonite has been modified by adsorption of the cationic surfactant DSDMAC, the electrophoretic mobility of montmorillonite in the absence of inulin is positive in a wide range of concentration of NaCl and CaCl 2. On the contrary, addition of KBr provokes a charge inversion when the salt concentration is around 0.05 M, suggesting adsorption of Br − ions. In the presence of inulin, the positive electrophoretic mobility decreases with the concentration of this surfactant, and this can be explained by assuming that inulin adsorption is accompanied by simultaneous DSDMAC desorption, eventually producing charge inversion, particularly in the presence of bromide ions. A thorough characterization of the wettability of the xylan films demonstrated that it is dominated by acid–base interactions and that incorporation of inulin-coated montmorillonite leads to a considerable reduction of the hydrophilic character of the films.

Charge Transfer Chemical Doping of Few Layer Graphenes: Charge Distribution and Band Gap Formation

The properties of few layer (one layer (1 L) to four layer (4 L)) graphenes doped by adsorption and intercalation of Br(2) and I(2) vapors are investigated. The Raman spectra of the graphene G vibrations are observed as a function of the number of layers. There is no evidence for chemical reaction disrupting the basal plane pi electron conjugation. Adsorption of bromine on 1 L graphene creates a high doped hole density, well beyond that achieved by electrical gating with an ionic polymer electrolyte. In addition, the 2D Raman band is completely quenched. The 2 L bilayer spectra indicate that the doping by adsorbed I(2) and Br(2) is symmetrical on the top and bottom layers. Br(2) intercalates into 3 L and 4 L graphenes. The combination of both surface and interior doping with Br(2) in 3 L and 4 L creates a relatively constant doping level per layer. In contrast, the G spectra of 3 L and 4 L with surface adsorbed I(2) indicate that the hole doping density is larger on the surface layers than on the interior layers and that I(2) does not intercalate into 3 L and 4 L. This adsorption-induced potential difference between surface and interior layers implies that a band gap opens in the bilayer type bands of 3 L and 4 L.

Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface‐enhanced Raman scattering spectroscopy

AbstractTwo kinds of room‐temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) and 1‐butyl‐3‐methylimidazolium tetrafluoroboride ([BMIM]BF4), were used as solvent, and the adsorption of the ionic liquids themselves and of N‐methylimidazole (NMIM) were investigated by electrochemical surface‐enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF4 liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br−, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)4Br]Br·H2O and [Cu(NMIM)4](BF4)2 were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright © 2009 John Wiley & Sons, Ltd.

Simultaneous scanning tunneling microscopy and stress measurements to elucidate the origins of surface forces

We have developed a new combined measurement system to investigate the underlying origins of forces on solid state surfaces from the viewpoint of atomic surface morphology. This system consists of two main parts: the measurements of force based on displacements and detailed atomic resolution observations of the surface morphology. The former involves a large sample cantilever and a capacitive detection method that provide sufficient resolution to detect changes of a few meV/atom or pN/atom at surfaces. For the latter, a scanning tunneling microscope was incorporated to observe structural changes occurring on the surface of the cantilever sample. Although this combined observation is not trivial, it was accomplished by carefully designing sample dimensions while suppressing the self-oscillation of the cantilever. To demonstrate the performance of this system a preliminary study of the room temperature adsorption of Br(2) on the clean Si(111)-7x7 surface is presented.

Influence of the Counterions of Cetyltrimetylammonium Salts on the Surfactant Adsorption onto Gold Surfaces and the Formation of Gold Nanoparticles

We report the effects of counterion species on the adsorption of cetyltrimetylammonium salts (C16TAX) onto gold surfaces and the subsequent formation of gold nanoparticles in the C16TAX surfactant solution. The surfactant adsorption onto gold surfaces was examined by using quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The counterion species (X) examined in this study were as follows: X = Br-, Cl-, NO3-, F-, OH-, and SO42-. The adsorption onto the gold surface depended on the counterion species of C16TAXthe frequency shift of QCM decreased in the following order: X = Br- > NO3- ≈ SO42- > Cl- > F- > OH-. The chemical reduction of gold(III) in the surfactant solutions of C16TAX with use of 2,2‘-iminodiethanol as a mild reducing agent produced anisotropic gold nanoparticles, depending on the surfactant counterion. The high-affinity adsorption of Br-, NO3-, and Cl- on gold surfaces produced anisotropic gold nanoparticles, while only spherical gold nanoparticles were obtained for weakly bound counterions such as SO42-, F-, and OH-. In contrast, the chemical reduction with hydrazine proceeded rapidly such that the shape of the gold nanoparticles was uncontrollable; this resulted in the formation of spherical gold nanoparticles, irrespective of the surfactant counterion.

Using Bromine Gas To Enhance Mercury Removal from Flue Gas of Coal-Fired Power Plants

Bromine gas was evaluated for converting elemental mercury (Hg0) to oxidized mercury, a form that can readily be captured by the existing air pollution control device. The gas-phase oxidation rates of Hg0 by Br2 decreased with increasing temperatures. SO2, CO, HCl, and H2O had insignificant effect, while NO exhibited a reverse course of effect on the Hg0 oxidation: promotion at low NO concentrations and inhibition at high NO concentrations. A reaction mechanism involving the formation of van der Waals clusters is proposed to accountfor NO's reverse effect. The apparent gas-phase oxidation rate constant, obtained under conditions simulating a flue gas without flyash, was 3.61 x 10(-17) cm3 x molecule(-1) x s(-1) at 410 K corresponding to a 50% Hg0 oxidation using 52 ppm Br2 in a reaction time of 15 s. Flyash in flue gas significantly promoted the oxidation of Hg0 by Br2, and the unburned carbon component played a major role in the promotion primarily through the rapid adsorption of Br2 which effectively removed Hg0 from the gas phase. At a typical flue gas temperature, SO2 slightly inhibited the flyash-induced Hg0 removal. Conversely, NO slightly promoted the flyash induced Hg0 removal by Br2. Norit Darco-Hg-LH and Darco-Hg powder activated carbons, which have been demonstrated in field tests, were inferred for estimating the flyash induced Hg0 oxidation by Br2. Approximately 60% of Hg0 is estimated to be oxidized with the addition of 0.4 ppm of gaseous Br2 into full scale power plant flue gas.

Thermodynamic studies of bromide adsorption at the Pt(111) electrode surface perchloric acid solutions: Comparison with other anions

The thermodynamics of the so-called perfectly polarizable electrode was employed to analyze the voltammograms of a Pt(1 1 1) electrode in KBr solutions with an excess of a supporting electrolyte (0.1 M HClO4 and 0.1 M KClO4 + 10?3 M HClO4 + xM KBr where x varied between 5 × 10?4 and 1 × 10?2). The surface Gibbs excess, the Gibbs energy of adsorption and the charge number at a constant electrode potential and a constant chemical potential have been determined. The effect of pH on the magnitude of these parameters has been evaluated. The thermodynamic parameters for bromide have been compared to the parameters determined from previous thermodynamic studies of (bi)sulfate, chloride and OH adsorption at the Pt(1 1 1) electrode surface. As expected, bromide adsorption is stronger than for the other anions and halide adsorption seems to be limited by close packing of the adlayer. The calculated charge number values suggest that Br adsorption involves a full charge transfer, as in the case of chloride

Adsorption of Dodecyltrimethylammonium Bromide and Sodium Bromide on Gold Studied by Liquid Chromatography and Flow Adsorption Microcalorimetry

Here, we report on a new aspect of the adsorption of Br- on the surface of gold. The adsorption of dodecyltrimethylammonium bromide (C12TABr) from aqueous solutions onto macroporous gold particles was studied by continuous flow frontal analysis solid/liquid chromatography and flow adsorption microcalorimetry. The material balance and enthalpy balance of adsorption and the change in the solution pH were measured simultaneously. Initially, Br- is irreversibly bound to high-affinity surface sites counterbalanced by the adsorption of H+ from the aqueous phase. The surface speciation is accompanied by the formation of C12TAOH, which in turn results in a significant pH increase in the bulk solution. The net process was found to be strongly exothermic (-280 kJ.mol(-1)), which is indicative of the occurrence of chemisorption. The specific adsorption of Br- is followed by the reversible adsorption of C12TABr to produce a firmly bound monolayer in a head-to-surface arrangement (-53 kJ.mol(-1)). In a relatively narrow range of the surface coverage, various composite structures may develop on the top layer and eventually transform to full-cylindrical surface aggregates. The surface aggregation was found to be reversible, with an enthalpy change of -11 kJ.mol(-1). The importance of the specific binding of Br- to the surface of gold was confirmed by measurement of the initial adsorption of NaBr on the microparticles. The initial adsorption was found to be irreversible, with an enthalpy change of approximately -240 kJ.mol(-1). This process involved the formation of an AuBr-/H+ electric double layer at the gold/water interface, accompanied by a dramatic increase in the solution pH due to the release of a copious amount of OH- in the bulk liquid phase.

An off-lattice model for Br electrodeposition on Au(100): from DFT to experiment

Since Br adsorption on Au(100) displays an incommensurate ordered phase, a lattice-gas treatment of the adlayer configurations is not reliable. We therefore use density functional theory slab calculations to determine the parameters necessary for the construction of an off-lattice model. We compute and analyze the total energy and electron density as the lateral Br position and coverage are varied. This allows the calculation of the corrugation potential, the short-range lateral interactions, the dipole moment (long-range interactions), and the residence charge. From these parameters, we construct an off-lattice model with no freely adjustable parameters. The simulation results compare remarkably well with experimental results.

The Stability of the Adsorption of Some Anions on Chemical Manganese Dioxide

AbstractThe stability of the adsorption of three anions (nitrate, bromide, and chloride) on chemical manganese dioxide (CMD) was studied using a two‐variable, two level factorial design. The two variables were the concentration and pH of the solutions of the sodium salt of the anions. The concentration CMD was varied from 1 M–0.001 M and the pH from 3.5–2.5. 84, 67, and 54 % variations in the adsorption of Br–, NO3–, and Cl– on CMD, respectively, were obtained. Independently, the concentration and pH affected the electric surface charge. However, their combined influence has a negative and low effect. The surface response plots of the model equations, which did not show the optimum values for concentration and pH, reinforced this observation. The highest stability of the anions was observed when concentration and pH were at their minimum values of 0.001 M and 2.5, respectively.

Reactivity of halogens on a Si(111) surface studied by surface differential reflectivity

The adsorption of Br on a $\mathrm{Si}(111)7\ifmmode\times\else\texttimes\fi{}7$ surface at room temperature and the isothermal desorption of silicon bromides from a Br-terminated Si(111) rest atom surface at about 900 K have been investigated by means of in situ real-time surface differential reflectivity (SDR) spectroscopy in order to elucidate the fundamental processes of Br-etching. The present results are compared with those of previous SDR studies on chlorine adsorption and chloride desorption. In the adsorption process, both the sticking probability on adatom dangling bonds and the breaking probability of adatom back bonds are larger than those for Cl adsorption. In the desorption process, the activation energy for bromide desorption (1.8 eV) is smaller than that for chloride desorption. The experimental results can be well interpreted in terms of larger repulsive interaction between Br adsorbates. The activation energy for the formation of the dimer-adatom-stacking fault structure (3.5 eV) is larger than that for the surface after chloride desorption.

A density functional study of Br on Cu( [formula omitted]) at low coverages

Density functional theory has been used to study the adsorption of Br on Cu(1 0 0) at low coverages. As expected, the most stable binding site for Br atoms is the fourfold hollow site. The barrier for Br hopping between adjacent hollow sites along 〈0 1 1〉 directions via twofold saddle points is estimated to be 0.23 eV, whereas the barrier for hopping along 〈0 1 0〉 directions via an on-top site is 0.37 eV. The low barriers for motion between hollow sites indicate that it should not be possible to image low coverages of Br on Cu(1 0 0) at room temperature in scanning tunnelling microscopy. It is suggested that features previously attributed to Br atoms in hollow sites should in fact be assigned to Br bound in surface copper vacancy sites.

Ab initiocalculations for bromine adlayers on the Ag(100) and Au(100) surfaces: Thec(2×2)structure

Ab initio total-energy density-functional methods with supercell models have been employed to calculate the c(2x2) structure of the Br-adsorbed Ag(100) and Au(100) surfaces. The atomic geometries of the surfaces and the preferred bonding sites of the bromine have been determined. The bonding character of bromine with the substrates has also been studied by analyzing the electronic density of states and the charge transfer. The calculations show that while the four-fold hollow-site configuration is more stable than the two-fold bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on the Au(100) surface. The one-fold on-top configuration is the least stable configuration on both surfaces. It is also observed that the second layer of the Ag substrate undergoes a small buckling as a consequence of the adsorption of Br. Our results provide a theoretical explanation for the experimental observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces results in different bonding configurations.

Identification of Surface Allenyl and Its Transformation into Propargyl with C3H3Br Adsorption by RAIRS on Ag(111)

Chemisorbed allenyl/propargyl (two possible C3H3 isomers) intermediates on Ag(111) were isolated and identified by reflection−absorption infrared spectroscopy (RAIRS). Following the adsorption of propargyl bromide at 110 K, surface heating resulted in the cleavage of the CBr bond at 200 K (confirmed by X-ray photoelectron spectroscopy) and surface hydrocarbon species bearing the characteristic CCC stretching vibration in RAIRS, indicative of the surface-bound allenyl. This assignment was supported by the same experiment using bromopropadiene (allenyl bromide) as the precursor, in which the identical spectral change was observed. A distinct molecular transformation occurred around 300 K featuring the appearance of new IR bands, particularly the C⋮C stretch mode, suggesting that surface propargyl was formed. This propargylic intermediate remained thermally stable to 450 K before further decomposition and reactions on the surface.