Al Adsorption Research Articles

First-Principles Study of Metal Adatom Adsorption on Black Phosphorene

We have investigated the structure, adsorption energy, growth mode, diffusion barrier, magnetic property, dipole moment, and work function of Li, Na, Mg, Al, Cr, Fe, Co, Ni, Mo, Pd, Pt, and Au adsorption on phosphorene using first-principles density-functional theory. We have found that all the adatoms favor the hollow site of hexagonal. It seems that the Mg, Cr, Mo, and Au adatoms may have three-dimensional (3D) growth mode on phosphorene substrate, whereas all other adatoms prefer two-dimensional (2D) growth mode. The metallic state is observed in Li, Na, Al, and Cr doped systems, and the Cr doped phosphorene displays magnetic state. The other eight metal doped systems still preserve semiconducting band gap. Among them, we obtained spin polarized band structures in Fe, Co, and Au doped systems with a band gap. In particular, the Fe doped phosphorene can be a potential candidate for dilute magnetic semiconductor material because no clustering problem will take place. We found a variation in dipole moment and work functions in each impurity doped layer. Both dipole moment and the shift of the Fermi level could account for the change of work function semiquantitatively.

Precipitates of Al(III), Sc(III), and La(III) at the muscovite-water interface.

The interaction of Al(III), Sc(III), and La(III) with muscovite-water interfaces was studied at pH 4 and 10 mM NaCl using second harmonic generation (SHG) and X-ray photoelectron spectroscopy (XPS). SHG data for Sc(III) and La(III) suggest complete and/or partial irreversible adsorption that is attributed by XPS to the growth of Sc(III) and La(III) hydroxides/oxides on the muscovite surface. Al(III) adsorption appears to coincide with the growth of gibbsite (Al(OH)3) deposits on the muscovite surface, as indicated by the magnitude of the interfacial potential computed from the SHG data. This interpretation of the data is consistent with previous studies reporting the epitaxial growth of gibbsite on the muscovite surface under similar conditions. The implication of our findings is that the surface charge density of mica may change (and in the case of Al(III), even flip sign from negative (mica) to positive (gibbsite)) when Al(III), Sc(III), or La(III) is present in aqueous phases in contact with heterogeneous geochemical media rich in mica-class minerals, even at subsaturation conditions.

Surface complexation of the phototrophic anoxygenic non-sulfur bacterium Rhodopseudomonas palustris

This work extends our knowledge of anoxygenic phototrophic bacteria (APB) interactions and contributes to the database of aquatic microorganism trace element adsorption parameters, such as heavy metal pollutants and limiting micronutrients. The surface properties of a phototrophic anaerobic non-sulfur bacterium (Rhodopseudomonas palustris KR-95p), which is often considered a model microorganism for Precambrian anoxygenic primary producers, were studied using potentiometric acid-base titration at various ionic strengths. The electrophoretic mobility of viable cells was measured as a function of pH and ionic strength, as well as cation (Zn, Cd, and Pb) and anion (Mo, W, and Cr) concentration. Zn, Cd, Sr, Pb, Cu, Cs, Al, Ga, Sb, As, Ge, Tl, W, and Mo adsorption was studied as a function of pH at a constant initial element concentration, yielding the pH-dependent adsorption edge. Zn, Cd, Sr, Cu and Pb adsorption was also studied as a function of metal concentration in solution at a constant pH, producing a “Langmuirian” adsorption isotherm. The non-electrostatic linear programming method (LPM) was used to fit the experimental data and assess the number of surface sites and adsorption reaction constants involved in heavy metal and anion binding to the cyanobacteria surface.The total H/OH binding site number (80–480μmol/gwet) for Rps. palustris encompasses the values reported for other APB (60–120μmol/gwet) and cyanobacteria (50–200μmol/gwet) examined using the same technique. For the cations, the adsorption edge follows the order Pb2+>Cu2+≫Cd2+≈Zn2+>Sr2+>Tl+>Cs+, which is similar to the element hydrolysis order. Trivalent hydrolysates (Al3+ and Ga3+) demonstrated increased adsorption with a pH increase at 2≤pH≤4 followed by desorption from the bacterial surface at pH>5–6 as negatively charged Al(OH)4− and Ga(OH)4−, similar to anions, such as MoO42− and WO42−. This behavior directly reflects the level of trace element complexation with two primary binding sites at the surface, carboxylate and phosphorylate, and certain electrostatic-like interactions between negatively charged anions and positive amine groups in acidic solutions. The main results of the present study are that the Rps. palustris exhibit trace element binding properties through their pH-dependence and overall adsorption capacity, which are similar to properties described earlier for other phototrophic bacteria, both anoxygenic bacteria and cyanobacteria. The absolute adsorption capacities for metal cations follow the order Rps. palustris<APB Rdb. blasticus<cyanobacteria Gloeocapsa sp, which presumably reflects a greater concentration of free metal cations in the external milieu for this species. Correspondingly, the adsorbed anion concentration is greatest for Rps. palustris, which therefore yields a higher proportion of positively charged amine groups or fewer negative charges overall due to a lower fraction of carboxylates and phosphorylates.

Interaction of Aluminum Ions with Fused Silica/Water Interfaces in the Presence of Oxalic Acid Tracked by Second Harmonic Generation

Second harmonic generation (SHG) and the χ(3) technique are used to investigate the effect of oxalic acid on the adsorption of aluminum [Al(III)] to the fused silica/water interface. Al(III) adsorption isotherms are measured in the presence and absence of oxalic acid and fit with the Diffuse Layer model to quantify thermodynamic binding parameters. The evolution of charge density throughout the adsorption process is analyzed and used to derive binding mechanisms at the molecular level. It is found that 0.5 mM oxalic acid irreversibly binds to and increases the negative surface charge on the fused silica surface −0.003 C/m2, corresponding to 1.9 × 1012 bound oxalate ions per cm2 under those conditions if oxalate were singly charged at the interface. Oxalic acid decreases the strength of the Al(III) adsorption interaction: the binding constant, Kads, decreases from 60 000 ± 10 000 to 1100 (200) M–1, corresponding to a reduction in the apparent adsorption free energy, ΔGads, from −37.2(4) to −27.3(5) kJ/mol, while surface charge densities at maximum metal coverage, σm, increase from 0.004(2) to 0.014(3) C/m2. Evidence is presented for a change in the dominant charge determining adsorption mechanism that corresponds with a change in Al(III) speciation. These results reveal important information about the surface activity and speciation of Al(III) in the presence of oxalic acid that have direct implications for the mobility, toxicity, and ultimate environmental fate of this metal pollutant.

Aluminum Affects Heterogeneous Fe(III) (Hydr)oxide Nucleation, Growth, and Ostwald Ripening

Heterogeneous coprecipitation of iron and aluminum oxides is an important process for pollutant immobilization and removal in natural and engineered aqueous environments. Here, using a synchrotron-based small-angle X-ray scattering technique, we studied heterogeneous nucleation and growth of Fe(III) (hydr)oxide on quartz under conditions found in acid mine drainage (at pH = 3.7 ± 0.2, [Fe(3+)] = 10(-4) M) with different initial aqueous Al/Fe ratios (0:1, 1:1, and 5:1). Interestingly, although the atomic ratios of Al/Fe in the newly formed Fe(III) (hydr)oxide precipitates were less than 1%, the in situ particle size and volume evolutions of the precipitates on quartz were significantly influenced by aqueous Al/Fe ratios. At the end of the 3 h experiments, with aqueous Al/Fe ratios of 0:1, 1:1, and 5:1, the average radii of gyration of particles on quartz were 5.7 ± 0.3, 4.6 ± 0.1, and 3.7 ± 0.3 nm, respectively, and the ratio of total particle volumes on quartz was 1.7:3.4:1.0. The Fe(III) (hydr)oxide precipitates were poorly crystallized, and were positively charged in all solutions. In the presence of Al(3+), Al(3+) adsorption onto quartz changed the surface charge of quartz from negative to positive, which caused the slower heterogeneous growth of Fe(III) (hydr)oxide on quartz. Furthermore, Al affected the amount of water included in the Fe(III) (hydr)oxides, which can influence their adsorption capacity. This study yielded important information usable for pollutant removal not only in natural environments, but also in engineered water treatment processes.

Preconcentration and determination of aluminum in water samples by inductively coupled plasma-atomic emission spectroscopy with brilliant green-based anion-exchange solid-phase extraction support

A new chelating resin is produced by coupling a dye brilliant green to Amberlite XAD-2 through an azo spacer. The resulting resin has been characterized by FT-IR, elemental analysis, thermogravimetric analysis, and scanning electron microscopy and studied for the preconcentration and determination of trace Al(III) from solution samples. The optimum pH value for sorption of the aluminate ions was nine. The sorption capacity of functionalized resin is 10.8 mg g−1. A recovery of 94% was obtained for Al(III) when eluted with 0.5M nitric acid. The equilibrium data of Al(III) adsorption on modified resin were analyzed using Langmuir, Freundlich, and Temkin models. The method was applied for Al(III) assay in environmental samples.

Modeling alumina atomic layer deposition reaction kinetics during the trimethylaluminum exposure

A model describing the reaction kinetics and surface species dynamics for trimethylaluminum (TMA) half-reactions of alumina atomic layer deposition (ALD) is presented. The model is based on reaction energetics data taken from published quantum chemical computational studies; these data are used to determine kinetic parameters using statistical thermodynamics and absolute reaction rate theory. Four TMA half-reactions were modeled to account for TMA adsorption and subsequent reaction on a range of growth surfaces spanning bare to fully hydroxylated states. By coupling the reaction rate models with surface species conservation equations, we create a dynamic model useful for examining the relative rates of completing surface reactions. Numerical simulations performed with the model reveal that it is a combination of TMA adsorption on hydroxylated and bare surface oxygen sites that produces Al adsorption rates comparable with those found for saturating ALD growth of alumina.

Aluminum resistance and cell‐wall characteristics of pineapple root apices

AbstractPineapple (Ananas comosus [L.] Merrill) is one of the economically cultivated crops in Taiwan, which is grown mostly on acid soil. Aluminum (Al) is phytotoxic and sometimes inhibits root growth of crops in strongly acid soils. This study was conducted to evaluate the role in Al resistance of root‐apex cell walls of four important pineapple cultivars (Cayenne, Tainung No. 6, Tainung No. 13, and Tainung No. 17). The cell‐wall characteristics of root apices were determined using Fourier transform infrared spectroscopy (FTIR) and solid‐state 13C‐nuclear–magnetic resonance spectroscopy (13C‐NMR). The results show that the carboxylic and phenolic groups were highest in the cell wall of Tainung No.17 and lowest in that of Cayenne. Aluminum adsorption by cell wall could be described by Freundlich equation. The adsorption of Al by the cell wall of root apices was highest in Tainung No.17 and lowest in Cayenne. Tainung No.17 contained more carboxylic and phenolic groups in its cell wall of the root apices, causing more Al adsorption and so more damage to its root apices than that of the other three pineapple cultivars.

Dual Role of Biochars as Adsorbents for Aluminum: The Effects of Oxygen-Containing Organic Components and the Scattering of Silicate Particles

The adsorption of aluminum by biochars produced at different temperatures from rice straw (RS) and cattle manure (CM) was studied to determine the dual roles of biochar for aluminum adsorption. The compositional structures and surface charges of the biochars and ashes with and without Al loading were analyzed by Fourier-transform infrared spectroscopy, ζ-potential, scanning electron microscopy, and X-ray diffraction. The Al adsorption isotherms were fit well by the Langmuir model. The adsorption of Al to the biochars produced at 400 and 700 °C was much greater than the adsorption to the precursory materials and ashes. We found that the organic components and silicate particles within the biochars served as dual adsorptive sites for Al. The complexation of Al with organic hydroxyl and carboxyl groups and the surface adsorption and coprecipitation of Al with silicate particles (as KAlSi3O8) both contributed to the Al adsorption of the biochars. After the biochars were loaded with Al, the ζ-potentials of the biochars and ashes increased as a function of pH. The positive charge was maximized at pH 4.5, which is similar to the pH at which the maximum positive charge occurs for silica. The charge reversal was caused by the Stern-layer adsorption of hydrolyzed aluminum species (i.e., Al(OH)(2+) and Al(OH)2(+)) on the silicate surfaces via hydrogen bonds.

Comparative Study for Adsorption of Al(III) Ions from Aqueous Solutions with Series of Nano Functional Copolymers

High aluminum concentrations (3.6 to 6 mg/l) may precipitate as aluminum hydroxide affecting aquatic life. The present investigation aim is the sorption of Al3+ from aqueous solution using novel copolymers as an adsorbent. Nano chelating resins based on modified poly(styrene-alt-maleic anhydride) (SMA) with 2-aminopyridine, 3-aminobenzoic acid or p-sulfanilic acid were synthesized. These modified resins were further reacted by 1,2-diaminoethane or 1,3-diaminopropanefor preparation of nano tri-dimensional chelating resin in the presence of ultrasonic irradiations along with vigorous magnetic stirring. The synthesized copolymers were characterized by Fourier transform infrared (FT-IR), elemental analysis, XRD, SEM and thermal analysis (TGA/DTG). These polymeric resins, bearing O and N donor groups, had the advantage of being stable in basic and saline media. The adsorption of Al3+ ions by copolymers was investigated by atomic absorption spectroscopy (AAS). The sorption behavior of Al3+ ions at different pH values was examined with a batch equilibration technique and the results of Al(III) adsorption by different functionalized copolymers were compared. The maximum adsorption capacity was observed with copolymers at an optimal pH of 5.

Comprehensive investigation of CO2 adsorption on Mg–Al–CO3 LDH-derived mixed metal oxides

Layered double hydroxides (LDHs) have been intensively studied for high-temperature CO2 capture. However, big differences in the CO2 capture capacity, ranging from 0.28 to 0.6 mmol g−1, have often been reported for the same Mg–Al–CO3 LDH. Furthermore, how the active Mg–O species that are responsible for CO2 adsorption are formed is still unclear. In this work, we have performed a comprehensive investigation on the CO2 adsorption characteristics of Mg–Al–CO3 LDH-derived mixed metal oxides. Based on these results we proposed the possible adsorption sites and the mechanisms for CO2 adsorption. Initially, the effects of synthesis method, Mg : Al ratio, pretreatment conditions, adsorption conditions, and thermal stability on the CO2 adsorption capacity were systematically studied. By carefully examining the structural changes during thermal treatment using X-ray diffraction and solid state NMR, we suggest that the active Mg–O species could be induced either by the substitution of Mg2+ by Al3+ in the periclase MgO lattice, or by the diffusion of Al3+ out of the octahedral brucite layers. This work not only suggests the optimal testing conditions for LDH-derived CO2 adsorbents, but also provides a clearer understanding of the CO2 adsorption sites and mechanisms on LDH-derived mixed oxides and sheds light on the synthesis and utilization of LDH-derived high-temperature CO2 adsorption materials.

ADSORPTION OF PHOSPHATE FROM AQUEOUS SOLUTIONS BY THERMALLY MODIFIED PALYGORSKITE

In this study, palygorskite clay calcinated at different temperatures from 200 to 900 C was used as adsorbent to remove phosphate from aqueous solutions. The crystal structure and the surface property of the thermally modified material was investigated to determinate the relationship between the adsorption capacity of the adsorbent and the changes of the crystal structure and surface property. The results indicate that palygorskite clay calcinated at 700 C had the highest adsorption capacity. Complete dehydroxylation destroyed the crystal structure and Al coordination was changed from octahedral to tetrahedral and further to a small amount of penta-coordination. The thermally modified adsorbent material was amorphous. All these structure changes enhanced the activity of Al and phosphate adsorption.

Ab Initio Studies of Al and Ga Adsorption on 4H-SiC{0001} Surfaces

Changes in the atomic and electronic structure of Siand C-terminated 4H-SiC{0001} surfaces resulting from aluminium and gallium adsorption have been studied within density functional theory framework. Al and Ga coverages ranging from a submonolayer to one monolayer were considered. Our results show that Al binds more strongly to both surfaces than Ga. The binding is stronger to the C-terminated surface for both metals. The sites occupied by Al and Ga atoms at 1 monolayer are di erent and it is due to a di erent charge transfer from metal to the substrate.

Dissociation and reconstruction of O2 on Al (1 1 1) studied by First-principles

The dissociative adsorption and reconstruction of oxygen molecule on Al (111) surface have been investigated by Density Functional Theory (DFT) with the generalized gradient approximation using structure optimization and a supercell approach. Four vertical and eight parallel sites of O2 adsorption on Al (111) surface were calculated corresponding to oxygen coverages of 0.22, 0.5 and 1 ML (monolayer). It is found that different surface geometries are formed after oxygen molecule dissociation on different sites of Al (111) surface, which is determined by oxygen original adsorption sites as well as oxygen coverage. The oxygen atoms coming from oxygen molecule dissociation tend to occupy the most stable adsorption sites of the Al (111) surface. When oxygen coverage is 1 ML, the dissociation of oxygen molecule is related to both its original adsorption site and the interaction between oxygen molecules. The correlation of surface reconstruction of Al (111) surface, adsorption site, adsorption energy and oxygen coverage is discussed in detail. The steering effect plays an important role in the oxygen molecule dissociative process.

Configurational disorder effects on adatom mobilities on Ti1−xAlxN(001) surfaces from first principles

We use metastable NaCl-structure Ti0.5Al0.5N alloys to probe effects of configurational disorder on adatom surface diffusion dynamics which control phase stability and nanostructural evolution during film growth. First-principles calculations were employed to obtain potential energy maps of Ti and Al adsorption on an ordered TiN(001) reference surface and a disordered Ti0.5Al0.5N(001) solid-solution surface. The energetics of adatom migration on these surfaces are determined and compared in order to isolate effects of configurational disorder. The results show that alloy surface disorder dramatically reduces Ti adatom mobilities. Al adatoms, in sharp contrast, experience only small disorder-induced differences in migration dynamics.

The structure and electronic properties of AlN/SrTiO3 (1 1 1) interfaces

The specific adsorption sites at the initial growth stage and the atomic structure of AlN on the SrTiO3 (111) substrate have been systematically investigated. The Al adsorption atoms are more favorable than the N atoms for the SrTiO3 (111) surface. The abnormal Al/SrO3 interface is energetically favorable among the atomic arrangements of the AlN/SrTiO3 (111) interfaces. Oxygen vacancies at the abnormal Al/SrO3 interface weaken the stability and induce the occupied states.

Surface Charge Transfer Induced Ferromagnetism in Nanostructured ZnO/Al

The present study reports on the origins of room temperature ferromagnetism in zinc oxide (ZnO)-Al nanoparticles using a combination of X-ray absorption near edge structure (XANES) experiments and density functional theory (DFT) simulations. Our findings reveal that the spontaneous magnetization observed in these systems originates from the adsorption of Al on surfaces of ZnO nanoparticles. Our DFT simulations have identified unique configurations for Al adsorption on ZnO surfaces that lead to a spin-polarized charge transfer to O 2p states in surface and subsurface layers. XANES spectra of the magnetic ZnO/Al nanoparticles provide the necessary experimental evidence for the charge transfer to ZnO surfaces and confirm the origin of ferromagnetic behavior. Our results illustrate a complex interplay between the atomic level interfacial structure and the resulting ferromagnetic ordering in metal-coated semiconductor oxide nanostructures.

Protective role of mucilage against Al toxicity to root apex of pea (Pisum sativum)

Mucilage can strongly bind Al in the rhizosphere. Although there are still debates about the role of mucilage in protection of the root apex from Al toxicity, we considered that it might be associated with the characteristics of Al adsorption in mucilage. When the mucilage was kept intact, the accumulation of Al and induction of callose in root tips of pea (Pisum sativum) remained lower; thus root elongation was less inhibited than when mucilage was removed under Al exposure in mist culture. Size exclusion chromatography showed both a high and a low molecular weight polysaccharide fraction from root mucilage. Aluminum was predominately detected in high molecular weight polysaccharides, which strongly bound cations. The results indicate that the persistence of mucilage does protect the root apex from Al toxicity by immobilizing Al in high molecular weight polysaccharides.

Metal (Li, Al, Ca and Ti) Absorbed Graphene with Defects for Hydrogen Storage: First-Principles Calculations

The characteristics of Li, Al, Ca and Ti metal adsorption on graphene with boron substitution and various vacancy defects are investigated using density functional theory calculation. Hydrogen adsorption characteristics and electronic structure of H2/metal adsorbed graphene were also calculated. It was found that Li, Al, Ca and Ti metal atoms are well dispersed on the graphene and can form a (2 x 2) pattern because clustering of metal atoms is hindered by the repulsive Coulomb interaction between the metal adatoms and the strong bonding force between the dispersed metal atom and graphene. Ca and Ti metal adatom show strong binding energy with the graphene in the cases of B substitution and specific vacancy, respectively. Ca and Ti were also found to be able to 8H2 molecules on the double side of the boron substituted graphene. This allows for a storage capacity of a 8.5 and 7.9 wt% hydrogen for Ca and Ti adatom, respectively.

DFT study of the coverage effects for Al adsorption on Si(1 1 1) surfaces

Density functional theory (DFT) calculations have been carried out to investigate the interactions between the Si(1 1 1) surface and the Al adatoms. Different adsorption sites and coverage effects have been considered. For low Al coverage, the threefold-filled adsorption site is the most energy favored site. With the increase of Al coverage, adatom–adatom interactions become increasingly important and Al atomic chains or clusters are formed. With the clean Si(1 1 1) surface of metallic feature, we found that 1/3 ML Al adsorption leads to a semiconducting surface. The results for the electronic behavior suggest the formation of the polarized covalent bonding between the Al adatom and the Si(1 1 1) surface.