Proton Adsorption Research Articles

Investigating the geochemical impact of burrowing animals: Proton and cadmium adsorption onto the mucus lining of Terebellid polychaete worms

Sediment–water interfaces are the sites of intense chemical activity in natural systems. Burrowing animals extend this interface, and at times coat it with mucous materials they secrete to line their burrows. However, the chemical reactivity of these burrow linings is poorly understood. In this study, we incubated burrowing terebellid worms ( Thelepus crispus) for the purposes of harvesting their mucus secretions and investigating its composition and metal adsorptive properties. The mucus was comprised of proteins, carbohydrates, and lipids in an approximate ratio of 200:50:1, and FTIR spectroscopy revealed abundant carboxyl, phosphoryl, hydroxyl, amino, and thiol functional groups typical of mucin-like material. Potentiometric titration data were best fit by a three-site surface complexation model, with a total ligand density of 11.26 ± 1.79 mmol per dry gram, which is relatively high compared to previously-studied humic substances and microbial biomass. Cd adsorption experiments demonstrated that the two most acidic ligands, inferred to represent carboxyl and phosphoryl functional groups, respectively, possessed cadmium stability constants that were comparable to analogous ligands inferred for bacterial surfaces. The third ligand, however, differed from bacterial surfaces in that it likely represents thiol functional groups, and displayed a higher Cd stability constant commensurate with the chalcophile nature of organic sulfur ligands. These results indicate that mucous burrow linings such as those produced by terebellid worms are geochemically important for driving metal adsorption and mineral nucleation reactions at the burrow–water interface.

Proton Charge and Adsorption of Humic Acid and Phosphate on Goethite

Little information is available about the changes of the proton charge of goethite in the presence of phosphate (P) and humic acid (HA). The objectives of this study were to systematically measure the proton charge of the ternary mixture and adsorption of HA and P on goethite. The potentiometric titration method was used to measure proton charges in single, binary, and ternary mixtures of goethite, HA, and P as a function of pH and ionic strengths. Results showed that proton charge in the ternary mixture became more negative with increasing pH and the loadings of HA and P. The point of zero charge (PZC) decreased linearly with the initial concentrations of HA and P. At low to intermediate pH, little variation was observed in adsorption of P on goethite in the presence of HA. A small reduction in the adsorption of P in the presence of HA was observed when compared with the control (without HA loading) at high pH. In 2008, Weng et al. developed a model describing the electrostatic interaction between HA and P at the 1‐plane of the compact part of the electrical double layer (EDL). In this study, Weng et al.'s model was used to interpret the effect of adsorbed HA on the adsorption of P on goethite as well as the nonsignificant interaction of PZC between HA and P.

Bridging oxygen as a site for proton adsorption on the vitreous silica surface

Molecular dynamics computer simulations were used to study the protonation of bridging oxygen (Si-O-Si) sites present on the vitreous silica surface in contact with water using a dissociative water potential. In contrast to first-principles calculations based on unconstrained molecular analogs, such as H(7)Si(2)O(7)(+) molecules, the very limited flexibility of neighboring SiO(4) tetrahedra when embedded in a solid surface means that there is a relatively minor geometric response to proton adsorption, requiring sites predisposed to adsorption. Simulation results indicate that protonation of bridging oxygen occurs at predisposed sites with bridging angles in the 125 degrees-135 degrees range, well below the bulk silica mean of approximately 150 degrees, consistent with various ab initio calculations, and that a small fraction of such sites are present in all ring sizes. The energy differences between dry and protonated bridges at various angles observed in the simulations coincide completely with quantum calculations over the entire range of bridging angles encountered in the vitreous silica surface. Those sites with bridging angles near 130 degrees support adsorbed protons more stably, resulting in the proton remaining adsorbed for longer periods of time. Vitreous silica has the necessary distribution of angular strain over all ring sizes to allow protons to adsorb onto bridging oxygen at the surface, forming acidic surface groups that serve as ideal intermediate steps in proton transfer near the surface. In addition to hydronium formation and water-assisted proton transfer in the liquid, protons can rapidly move across the water-silica interface via strained bridges that are predisposed to transient proton adsorption. Thus, an excess proton at any given location on a silica surface can move by either water-assisted or strained bridge-assisted diffusion depending on the local environment. The result of this would be net migration that is faster than it would be if only one mechanism is possible. These simulation results indicate the importance of performing large size and time scale simulations of the structurally heterogeneous vitreous silica exposed to water to describe proton transport at the interface between water and the silica surface.

Role of extracellular polymeric substances in metal ion complexation on Shewanella oneidensis: Batch uptake, thermodynamic modeling, ATR-FTIR, and EXAFS study

The effect of cell wall-associated extracellular polymeric substances (EPS) of the Gram-negative bacterium Shewanella oneidensis strain MR-1 on proton, Zn(II), and Pb(II) adsorption was investigated using a combination of titration/batch uptake studies, surface complexation modeling, attenuated total reflectance – Fourier transform infrared (ATR-FTIR) spectroscopy, and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. Both unmodified (wild-type (WT) strain) and genetically modified cells with inhibited production of EPS (ΔEPS strain) were used. Three major types of functional groups (carboxyl, phosphoryl, and amide groups) were identified in both strains using ATR-FITR spectroscopy. Potentiometric titration data were fit using a constant capacitance model (FITEQL) that included these three functional groups. The fit results indicate less interaction of Zn(II) and Pb(II) with carboxyl and amide groups and a greater interaction with phosphoryl groups in the ΔEPS strain than in the WT strain. Results from Zn(II) and Pb(II) batch adsorption studies and surface complexation modeling, assuming carboxyl and phosphoryl functional groups, also indicate significantly lower Zn(II) and Pb(II) uptake and binding affinities for the ΔEPS strain. Results from Zn K-edge EXAFS spectroscopy show that Zn(II) bonds to phosphoryl and carboxyl ligands in both strains. Based on batch uptake and modeling results and EXAFS spectral analysis, we conclude that the greater amount of EPS in the WT strain enhances Zn(II) and Pb(II) uptake and hinders diffusion of Zn(II) to the cell walls relative to the ΔEPS strain.

In Situ STM Imaging of the Structures of Pentacene Molecules Adsorbed on Au(111)

In situ scanning tunneling microscope (STM) was used to examine the spatial structures of pentacene molecules adsorbed onto a Au(111) single-crystal electrode from a benzene dosing solution containing 16-400 microM pentacene. Molecular-resolution STM imaging conducted in 0.1 M HClO(4) revealed highly ordered pentacene structures of ( radical31 x radical31)R8.9 degrees , (3 x 10), ( radical31 x 10), and ( radical7 x 2 radical7)R19.1 degrees adsorbed on the reconstructed Au(111) electrode dosed with different pentacene solutions. These pentacene structures and the reconstructed Au(111) substrate were stable between 0.2 and 0.8 V [vs reversible hydrogen electrode, RHE]. Increasing the potential to E > 0.8 V lifted the reconstructed Au(111) surface and disrupted the ordered pentacene adlattices simultaneously. Ordered pentacene structures could be restored by applying potentials negative enough to reinforce the reconstructed Au(111). At potentials negative of 0.2 V, the adsorption of protons became increasingly important to displace adsorbed pentacene admolecules. Although the reconstructed Au(111) structure was not essential to produce ordered pentacene adlayers, it seemed to help the adsorption of pentacene molecules in a long-range ordered pattern. At room temperature (25 degrees C), approximately 100 pentacene molecules seen in STM images could rotate and align themselves to a neighboring domain in 10 s, suggesting that pentacene admolecules could be mobile on Au(111) under the STM imaging conditions of -150 mV in bias voltage and 1 nA in feedback current.

Calorimetric measurements of proton adsorption onto Pseudomonas putida

Having an understanding of the reactive nature of the bacterial surface is enhanced when its reactivity is considered in a thermodynamic framework. Towards this end, isothermal titration calorimetry was used to measure heats of proton adsorption onto Pseudomonas putida, a common Gram negative soil bacterium. Proton adsorption generated large exothermic heats and proton uptake continued down to pH 2.5. Applying a surface complexation model to the calorimetric data allowed for the derivation of site-specific enthalpies and entropies of proton adsorption. The 4-site non-electrostatic model of Borrok et al. [D.M. Borrok, J.B. Fein, J. Colloid Interface Sci. 286 (2005) 110] was chosen to describe proton adsorption and enabled derivation of site-specific enthalpies of −2.4 ± 0.3, −3.7 ± 0.2, −9.0 ± 0.6, and −36.0 ± 1.2 kJ/mol for Sites 1–4, respectively. Entropies of proton adsorption were calculated to be 51 ± 3, 75 ± 1, 91 ± 2, and 55 ± 4 J/mol K, for Sites 1–4, respectively. Enthalpies and entropies of Sites 1 and 3 are consistent with that of multifunctional organophosphonic acids, Site 2 is consistent with multifunctional carboxylic acids, and Site 4 is consistent with an amine. Temperature dependence of the acidity constants for Sites 1–3 is predicted to be minimal; however, Site 4 is predicted to more substantially affected by temperature.

Nanocomposite electrodes based on pre-synthesized organically capped platinum nanoparticles and carbon nanotubes. Part I: Tuneable low platinum loadings, specific H upd feature and evidence for oxygen reduction

A bottom-up approach is used here to combine carbon nanotubes synthesized by CVD and organically capped platinum nanoparticles electrocatalyst exhibiting a direct electrochemical activity towards oxygen reduction. Both nano-objects are handled in liquid suspension and are associated together in a controlled way. The nanocomposite liquid dispersions can be precisely controlled in terms of platinum nanoparticles to carbon nanotubes weight ratios (NP/NT) which correspond to different coverages of nanotubes by nanoparticles. Electrodes with low to ultra-low platinum loadings can then be prepared on porous fuel cell carbon supports by filtration. The direct electrochemical activity towards aqueous oxygen reduction reaction (ORR) of electrodes with platinum loadings ranging from about 1 to 60 μg/cm 2 is reported without any activation step in order to keep the features of the nanoparticles intact. Before that, we studied the responses obtained when impregnating our hydrophobic electrodes by a voltamperometric gas consumption procedure. These responses are also dependent of the composition of our electrodes. Whereas our results are of particular interest with respect to the optimization of platinum loading in fuel cell electrodes, the specific behaviour of these capped platinum nanoparticles towards proton adsorption–desorption reveals the difficulty to determine reliable active surface area with related regard to the platinum loading and point to the necessity to determine other characteristic parameters for the electrodes.

Proton adsorption and acid-base properties of Tunisian illites in aqueous solution

Suspensions of illite clay minerals samples of three different origins (American illite from Montana, It(Mo), Tunisian glauconite from Gafsa, It(Ga), and Tunisian illite — chlorite mixed layer from El Hamma, It(Ha)) were prepared. The Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffractometry (XRD), Electron Scanning Microscopy (SEM) and surface area measurements were used to characterize the three illite samples having different extent of isomorphic substitution. The layers have a permanent negative charge due to isomorphic substitutions and pH dependent charges on the surface hydroxyls on the edges. Surface speciation of these samples was investigated using continuous potentiometric titration and mass titration curves between pH 4 and 11 at 0.001 M, 0.01 M, and 0.1 M NaCl solutions at ambient temperature. The two methods revealed point of zero charge (PZC) of the amphoteric edges sites approximately similar to the purified samples, in the range ∼7.5–8.5, ∼8.2–8.7, and ∼ 9.0–9.3 for It(Mo), It(Ha) and It(Ga), respectively. The PZCs of freshly prepared dispersions are higher than those reported in the literature indicating basic character of these samples (pH of equilibrium suspensions in distilled water were ∼7.9–9). In the present study, the focus was on the surface charge characteristics. A simple SCM model approach is presented to explain the illite H+ adsorption data. Surface weak acidic sites and surface ionization constants were calculated from titration data using regression methods. Sites with pKa1int values of 6–6.7; 5.4–5.8; 6.1–6.6 and sites at pKa2int values of 9.2–9.9; 10.2–10.4; 9.3–10 for It(Mo), It(Ga) and It(Ha), respectively, were assigned to amphoteric Al-OH and/or Fe-OH and Si-OH groups on the edges of illite samples.

Surface chemistry of K-montmorillonite: Ionic strength, temperature dependence and dissolution kinetics

The surface chemistry of K-montmorillonite was investigated by potentiometric titrations conducted at 25, 50 and 70 °C and at ionic strengths of 0.001, 0.01 and 0.1 M KNO 3. Proton adsorption decreases with electrolyte concentration at all pHs. The pH of zero net proton charge (PZNPC) decreases from 8.1 to 7.6 when the ionic strength increases from 0.001 to 0.1 M. Temperature has a very small effect on surface charge. A constant capacitance model that accounts for protonation/deprotonation of aluminol and silanol edge sites and basal plane H +/K + exchange is used to fit the experimental data. H + and OH − adsorption to specific surface sites appear to account for the pH-dependence of the K-montmorillonite dissolution.

Dynamics of Charging of Muscovite Mica: Measurement and Modeling

The advent of a new method for measuring the zeta potential of planar surfaces, the rotating disk, allowed the investigation of the charging process of mica after immersion in water. The zeta potential of freshly cleaved muscovite mica was recorded within seconds of immersion of the sample and in fractions of a second thereafter. The zeta potential of mica in water at pH = 5.6 with no added potassium changed by 40-50 mV over approximately 1 min. A model of adsorption and desorption of potassium ions and protons captured this behavior and provided a framework for determination of surface adsorption rate constants. The charging of mica in alkaline KCl solutions of arbitrary concentration, however, was too fast for observation. The equilibrium zeta potential depended on the logarithm of salt concentration, in agreement with a model based on ion exchange reactions. The average values of the proton adsorption, proton desorption, potassium adsorption, and potassium desorption rate coefficients were 45 L/s +/- 15, 0.0014/s +/- 0.0006, 58 L/s +/- 5, and 0.14/s +/- 0.03, respectively. An equation giving the zeta potential as a function of the rate parameters and the concentrations of potassium ions and protons was derived. It is demonstrated that subtraction of zeta potentials, measured at different solution compositions within the same experiment, eliminates extrinsic factors and brings data from disparate measurements into agreement.

The Effect of UV‐Irradiation (under Short‐Circuit Condition) on Dye‐Sensitized Solar Cells Sensitized with a Ru‐Complex Dye Functionalized with a (diphenylamino)Styryl‐Thiophen Group

A new ruthenium complex, cis‐di(thiocyanato)(2,2′‐bipyridine‐4,4′‐dicarboxylic acid)(4,4′‐bis(2‐(5‐(2‐(4‐diphenylaminophenyl)ethenyl)‐thiophen‐2‐yl)ethenyl)‐2,2′‐bipyridine)ruthenium(II) (named E322) has been synthesized for use in dye‐sensitized solar cells (DSCs). Higher extinction coefficient and a broader absorption compared to the standard Ru‐dye, N719, were aimed. DSCs were fabricated with E322, and the efficiency was 0.12% initially. (4.06% for N719, as reference). The efficiency was enhanced to 1.83% by exposing the cell under simulated sunlight containing UV‐irradiation at short‐circuit condition. The reasons of this enhancement are (1) enhanceing electron injection from sensitizer to TiO2 following a shift toward positive potentials of the conduction band of TiO2 by the adsorption of protons or cations from the sensitizer, or from the redox electrolyte and (2) improving the regeneration reaction of the oxidized dye by the redox electrolyte by the dissolution of aggregated dye from the surface of TiO2 following the treatment.

Metal removal from silicon sawing waste using the electrokinetic method

Silicon feedstock supply for the photovoltaic industry can be increased by recycling sawing waste. Metal removal is an important step in recycling silicon from sawing waste. This study examined the feasibility of adopting the electrokinetic method to remove metal from sawing waste. Exactly how an applied electrical field and its duration affect metal removal efficiency was studied. The optimal operational parameters were analyzed based on a cost model. Analytical results show that metal removal depends on proton generation, adsorption exchange and electromigration. Increasing the electrical field and duration can reduce the residual iron in the kerf-loss slurry. When an electrical field of 2.0 V/cm was applied for 120 h, total residual iron percentage decreased to 0.42 wt.% in the slurry, and total removal efficiency was at least 92%. The local removal efficiency of iron could reach 98%.

Modeling the Effect of pH on Kinetics of Heavy Metal Ion Biosorption. A Theoretical Approach Based on the Statistical Rate Theory

The effect of pH is studied on the equilibrium and kinetics of heavy metal biosorption. A concept of an effective surface capacity is introduced to describe the equilibrium isotherms of metal ion adsorption. That effective surface capacity is controlled by adsorption of protons. The obtained simple theoretical expressions appear to be very efficient in correlating equilibrium isotherms of adsorption of two kinds of heavy metal ions on two kinds of biosorbents. Next, the statistical rate theory is applied to develop the related expressions for adsorption kinetics. These expressions appear to be very efficient in correlating kinetic isotherms measured at various pH values.

Montmorillonite surface properties and sorption characteristics for heavy metal removal from aqueous solutions

Surface properties of montmorillonite (MMT) and its adsorption characteristics for heavy metals have been investigated with nickel and copper as sorbate from aqueous solutions. Employing the potentiometric and mass titration techniques in batch experimental methods, the point of zero charge (PZC) and point of zero net proton charge (PZNPC) of MMT edges at different ionic strengths present pH PZC and pH PZNPC to be 3.4 ± 0.2. A crossing point was observed for the proton adsorption vs. pH curves at different ionic strengths of KCl electrolyte and in investigating MMT remediation potentialities as sorbent for heavy metals polluted waters, the effects of heavy metal concentration, pH, MMT dosage, reaction time and temperature for Cu 2+ and Ni 2+ uptake were studied. The sorption of metal ions by MMT was pH dependent and the adsorption kinetics revealed sorption rate could be well fitted by the pseudo-second-order rate model. The data according to mass transfer and intraparticle diffusion models confirmed diffusion of solutes inside the clay particles as the rate-controlling step and more important for the adsorption rate than the external mass transfer. Adsorption isotherms showed that the uptake of Cu 2+ and Ni 2+ could be described by the Langmuir model and from calculations on thermodynamic parameters, the positive Δ G° values at different temperatures suggest that the sorption of both metal ions were non-spontaneous. Change in enthalpy (Δ H°) for Ni 2+ and Cu 2+ were 28.9 and 13.27 kJ/mol K respectively, hence an endothermic diffusion process, as ion uptake increased with increase in temperature. Values of Δ S° indicate low randomness at the solid/solution interface during the uptake of both Cu 2+ and Ni 2+ by MMT. Montmorillonite has a considerable potential for the removal of heavy metal cationic species from aqueous solution and wastewater.

Electrolytic Deposition Behaviors of Ni-SiC Composite Coatings Containing Submicron-Sized SiC Particles

Submicron-sized SiC particles (130 nm mean diameter) were codeposited with nickel by electrolytic plating in a nickel sulfamate bath to from Ni−SiC composite coatings. The effects of plating parameters, such as pH of the plating bath, SiC content in the plating bath, stirring rate, and current density on the deposition behaviors of Ni−SiC composite coatings were investigated. Results revealed that zeta potential decreased with increasing pH; the iso-electric point was measured to be }7.0 in pH. The codeposition of SiC increased with increasing pH, and the deposition rate increased with increasing SiC content in the plating bath. This may be due to the increased flux of approaching SiC particle towards the cathode due to enhanced SiC content in the plating bath. The codeposition of SiC exhibited a maximum at the stirring rate of 100 rpm. This can be explained by hydrodynamic effects and particle characteristics. The deposition rate increased with increasing current density. The codeposition of SiC increased up to a maximum of 15 A/dm2 and then decreased This can be explained by electrophoretic movement of the SiC particles due to the adsorption of nickel ions and protons in the plating bath on the SiC particle surface. Submicron-sized SiC particles provided for a rough plating surface. This effect may be attributable to the strong tendency of submicron-sized SiC particles to agglomerate in the plating bath.

Self-organization of Copper Secondary Nodules by the Second Micro-MHD Effect

In copper electrodeposition under a magnetic field parallel to an electrode surface, at the initial stage, 3D nucleation is suppressed, yielding a flat surface (the first micro-MHD effect). However, after long-term deposition with proton adsorption, characteristic secondary nodules emerge from 2D nucleation, which is called the second micro-MHD effect. From the instability analysis of non-equilibrium fluctuations, at the initial stage, the 2D nuclei are self-organized at a negative overpotential of the double layer, whereas for the secondary nodule formation, a positive overpotential of the double layer is required. Therefore, it is concluded that the adsorption of proton changes the polarity of the double layer overpotential from negative to positive, the secondary nodules are self-organized.

Cd adsorption onto Pseudomonas putida in the presence and absence of extracellular polymeric substances

The role of bacterial extracellular polymeric substances (EPS) in metal adsorption was determined by studying Cd adsorption onto the gram-negative bacterial species Pseudomonas putida with and without enzymatic removal of EPS from the biomass material. A range of experimental approaches were used to characterize the Cd adsorption reactions, including bulk proton and Cd adsorption measurements, FTIR spectroscopy, and fluorescence microscopy. The proton-reactivities of the biomass samples with EPS are not significantly different from those obtained for EPS-free biomass. Similarly, the presence of EPS does not significantly affect the extent of Cd removal from solution by the biomass on a mass-normalized basis, based on bulk Cd adsorption measurements conducted as a function of pH, nor does it appear to strongly affect the Cd-binding groups as observed by FTIR. However, fluorescence microscopy indicates that Cd, although concentrated on cell walls, is also bound to some extent to EPS. Together, the results from this study suggest that the P. putida EPS can bind significant concentrations of Cd from solution, and that the nature and mass-normalized extent of the binding is similar to that of the cell wall. Therefore, the EPS-bearing systems do not exhibit enhanced mass-normalized removal of Cd from solution relative to the EPS-free systems. The presence of the EPS effectively increases the viability of cells exposed to aqueous Cd, likely due to sequestration of the Cd away from the cells due to Cd-EPS binding.

An X-ray absorption study of the dissolution of siderite at 300 bar between 50 °C and 100 °C

Dissolution of siderite has been monitored in a small size batch reactor at a constant pressure of 300 bar and temperatures of 50 °C, 75 °C, and 100 °C, in acidic conditions. The technique, based on X-ray absorption spectroscopy measurements, allows simultaneous measurements of aqueous iron concentration and speciation as a function of time under in situ high pressure and high temperature conditions. Far from equilibrium, dissolution can be described by r + = k H+ a H+ where a H+ stands for aqueous proton activity and k H+ is the dissolution rate constant normalized to geometric surface area. The values of the rate constant obtained in this study are 4.5 × 10 − 9 mol cm − 2 s − 1 , 4 × 10 − 8 mol cm − 2 s − 1 , and 1.7 × 10 − 7 mol cm − 2 s − 1 , at 50 °C, 75 °C, and 100 °C, respectively. The corresponding activation energy, Δ E = 73 kJ mol − 1 , suggests a dissolution process controlled by chemical reaction, i.e., proton adsorption at the siderite surface. A NaCl molality of 1 mol kg − 1 is shown to strongly slow down the dissolution process. Speciation of Fe 2+ in solution is dominated by hexahydrated octahedral species with some significant contribution (about 25%) of the chlorinated species only in 1 mol kg − 1 NaCl, in good agreement with recorded X-ray absorption spectra. No Fe 3+ was detected. These results are found to be consistent with those obtained in previous siderite dissolution studies carried out under constant chemical affinity using the rotating disc technique. This agreement opens up interesting perspectives for retrieving, from batch micro-reactor experiments, kinetic parameters which are essential for the modelling of fluid-rock interactions in storage conditions.

Potential of zero charge as a sensitive probe for the titration of ionizable self-assembled monolayers

Potential of zero charge and interfacial capacitance values of ω-mercaptoalkanoic acid monolayers deposited on Au(1 1 1) are derived from immersion current transients, and are applied to the analysis of their acid properties. Potential of zero charge and capacitance titration curves extend over six pH units, and exhibit apparent pK 1/2 values that vary with electrolyte concentration. Electrostatic adsorption of protons at the monolayer-solution boundary provides a quantitative explanation of these observations, and leads to a diffuse layer corrected p K a value of 4.3, which is independent of the thiol chain-length.

Goethite surface reactivity: A macroscopic investigation unifying proton, chromate, carbonate, and lead(II) adsorption

The goethite surface structure has been extensively studied, but no convincing quantitative description of its highly variable surface reactivity as inversely related to its specific surface area (SSA) has been found. The present study adds experimental evidence and provides a unified macroscopic explanation to this anomalous behavior from differences in average adsorption capacities, and not in average adsorption affinities. We investigated the chromate anion and lead(II) cation adsorption behavior onto three different goethites with SSA varying from 50 to 94 m 2/g, and analyzed an extensive set of published anion adsorption and proton charging data for variable SSA goethites. Maximum chromate adsorption was found to occupy on average from 3.1 to 9.7 sites/nm 2, inversely related to SSA. Congruency of oxyanion and Pb(II) adsorption behavior based on fractional site occupancy using these values, and a site density analysis suggest that: (i) ion binding occurs to singly and doubly coordinated sites, (ii) proton binding occurs to singly and triply coordinated sites (ranging from 6.2 to 8 total sites/nm 2, in most cases), and (iii) a predominance of (210) and/or (010) faces explains the high reactivity of low SSA goethites. The results imply that the macroscopic goethite adsorption behavior may be predicted without a need to investigate extensive structural details of each specific goethite of interest.