Adsorption Structure Research Articles

A DFT study of dissolved gases generated of PD in converter transformer oil adsorbed on Ptn (n = 1 – 3) cluster doped MoS2 monolayer

The adsorption performances and sensing properties of Ptn (n = 1–3) MoS2 to three characteristic dissolved gases (CO2, CO, H2) generated of partial discharges in converter transformer oil was analyzed using DFT. The adsorption structure, band structure, charge transfer, adsorption energy, density of states, sensitivity and recovery time were utilized to explore the gas adsorption and sensing mechanism. The results demonstrate Ptn (n = 1–3) cluster greatly enhance weak adsorption ability and sensing property of pure MoS2 for CO2, CO, and H2. This paper provides the theoretical possibility to investigate a novel MoS2-based gas sensor.

Variations in the Photoexcitation Mechanism of an Adsorbed Molecule on a Gold Nanocluster Governed by Interfacial Contact.

We performed first-principles calculations on the optical response of a Au147-azobenzene complex to elucidate the role of the interfacial contact between Au147 and azobenzene. Our calculations of photoexcited electron dynamics for different configurations of azobenzene adsorbed on the Au147 nanocluster revealed that the optical properties of the azobenzene moiety change markedly by the interfacial contact, even if the electronic structure in the ground state is almost unchanged. The optical absorption measured for isolated azobenzene weakens when the Au147-azobenzene interaction increases, while the absorption measured using the light field along the Au147-azobenzene alignment strengthens. The electronic excitation analysis showed that the mechanism of the charge-transfer excitation between Au147 and azobenzene changes remarkably depending on the strength of the interfacial interaction. We revealed that the optical property can be governed by the atomic-scale difference in the adsorption structure of azobenzene on a Au147 nanocluster. This study affords novel insights that could enable the photoexcitation mechanism to be controlled by designing the interface between a metal nanoparticle and a molecule.

Adsorption properties of nCu2O-graphene (n = 1, 2, 3) for SOF2 and SO2F2 gas molecules

This study analyzed the adsorption and gas-sensing properties of nCu2O-graphene (n = 1, 2, 3) to SF6 characteristic decomposition products (SOF2 and SO2F2) based on the first-principles calculations. The interaction between the modified graphene monolayer and SOF2 or SO2F2 gas molecules was explored by analyzing adsorption structure, energy, distance, charge transfer, DOS, PDOS, and band gap. The results showed that Cu2O modification improved the conductivity and surface activity of the graphene substrate, and the gas sensitivity of nCu2O-graphene to SOF2 and SO2F2 enhanced. Except for the 2SO2F2/3Cu2O-graphene system, the conductivity of the other system decreased to different degrees. In contrast, the adsorption performance to SOF2 improved more, and the conductivity after the adsorption of SOF2 changed more obviously. Moreover, calculations showed that the recovery time of the SO2F2/Cu2O-graphene system is too short to build stable adsorption. Thus, Cu2O-graphene modified system was not suitable for SO2F2 gas detection. The other gas adoption systems can easily realize adsorption and desorption under suitable conditions. The study results provide a potential material for developing gas sensors using in Gas-insulated switchgear.

Beryllium oxide fullerene-like as a highly efficient sensor for formaldehyde: a DFT inspection

In tropospheric hydrocarbon oxidation triggered by the OH radical, formaldehyde (H2CO) is an essential reactive intermediate product. because of its toxicity and volatility, formaldehyde is harmful to human health. Therefore, formaldehyde removal is important for environmental pollution study. For multiple adsorption states, we present the adsorption energies, structures, energy gap (Eg), charge transfer, and electronic characteristics of formaldehyde (H2CO) on primary cations Li+, Li-, and two Li-encapsulated fullerene-like beryllium oxides (Be12O12, Li+@Be12O12, Li@Be12O12, and 2Li@Be12O12, respectively). By using DFT calculations, the results have been interpreted. The results show that the H2CO molecule weakly adsorbs to fullerene-like Be12O12, resulting in an energy release of around −0.38 to −0.14 eV and no substantial changes to its electrical characteristics. Compared to pure fullerene-like Be12O12, the H2CO adsorption properties of Li+@Be12O12, Li@Be12O12, and 2Li@Be12O12 are significantly improved. With the addition of H2CO, the most stable configuration energy gaps (Eg) shrank from 3.49 to 2.96 eV in the Li@Be12O12 and 2Li@Be12O12 samples. Additionally, it was demonstrated that following H2CO adsorption, the electrical conductance of Li@Be12O12 and 2Li@Be12O12 may be enhanced. The presence of H2CO molecules affects Li@Be12O12 and 2Li@Be12O12.

Role of concentration and hydrophobic nature of weak polyelectrolytes on adsorption structure and thermodynamics at oil-water interface: Study of several carboxylate polymers

Intermolecular structure, conformations, solvation and adsorption characteristics of four partially ionized polycarboxylic acids syndiotactic-poly(acrylic acid) (s-PAA), syndiotactic-poly(methacrylic acid) (s-PMA), isotactic-poly(methacrylic acid) (i-PMA) and atactic-poly(ethacrylic acid) (a-PEA) at oil (CCl4) - water interface is studied by molecular dynamics simulations over the range from dilute to monolayer coverage. Linearity and slope of Θ-Γ curves are correlated to conformational invariance and extent of adsorption (partial vs complete) respectively, within the range of concentration of study. Adsorption of i-PMA and a-PEA chains occurs deeper into the oil-side of interface region as driven by the greater hydrophobicity of these polymers. Higher tendency of highly extended s-PMA to desorb from the interface as compared to strong adsorption of compact coiled i-PMA is driven by their solvation behavior dictated by aspects of structural partitioning of chemical groups with respect to the solvents of the two phases. Hydrophobic side-group in the polyelectrolyte chain is responsible for the slower dynamics of the backbone. The observed variation in thickness of adsorbed layer and fractional interface coverage with concentration suggest partial adsorption of chain segments beyond saturation of interface rather than coiling of chains to accommodate additional chains. While a-PEA exhibits greater variation in interfacial tension, the change in electric potential difference across the interface indicates weak adsorption by s-PMA. The influence of the tacticity of PMA on dynamics and distribution of counter-ions is in agreement with experimental results. Results provide a significant advancement in our understanding of polyelectrolyte and polymer adsorption at oil-water liquid interface.

Density functional theory study on the interactions between H4POx (X = 6,7,8) groups and F,Si-doped reduced CeO1.979(111) surfaces

The structure of F,Si-doped reduced CeO1.979(111) surfaces were studied using DFT+U method, and the interaction between F,Si-doped CeO1.979(111) surfaces and H4POx (X = 6,7,8) groups on KDP surfaces was studied. The adsorption potential energy surface, bonding structure and electronic structure of stable adsorption of H4POx groups in the interaction systems were calculated and analyzed. The results indicate that the oxygen vacancy formation energy on the Ce0.979Si0.021O1.979(111) surface decreases by 1.396 eV, while on the CeO1.958F0.021(111) surface increases by 0.271 eV. The most stable adsorption sites of H4PO6, H4PO7, and H4PO8 groups have changed to the Cebri, Ot, and Ot sites on reduced surfaces. Two Si-O bonds and two Ce-O bonds on Ce0.979Si0.021O1.979(111) surface are broken to form a cavity. The number of Ce-O(H4POx) bonds and H bonds between Ce0.979Si0.021O1.979(111) surface and H4POx groups decreases by one. The number of Ce-O(H4POx) bonds and H bonds between the CeO1.958F0.021(111) surface and H4POx groups is still 3 and 2, but the bonding length is shortened. After the interaction between three reduced surfaces and H4POx groups, the band gaps all narrow and exhibit semi-metal properties. There was no charge transfer between Si and O(H4POx) in Si-doped system, while Bader charge transfer between O(H4POx) and Ce increase in F-doped system. The density of states of Ce0.979Si0.021O1.979(111) and CeO1.958F0.021(111) surfaces with H4POx groups move towards lower energy levels, and the latter moves more and is more stable.

A magnetically recyclable carboxyl-functionalized chitosan composite for efficiently removing methyl orange from wastewater: Isotherm, kinetics, thermodynamic, and adsorption mechanism

In this study, a kind of magnetically recyclable adsorbent for dyes was synthesized by grafting diethylenetriamine pentaacetate acid (DTPA) to the composite of Fe3O4 microspheres and crosslinked chitosan (CS). The microstructures, molecular structure, crystal structure, and magnetic hysteresis loops of the chitosan matrix adsorbent before and after grafting was characterized. The results suggested that DTPA was covalent bonded with the composite of Fe3O4 microspheres and chitosan. The modified composite has larger specific surface area and can realize rapid solid-liquid separation. Batch experiments were conducted to optimize the parameters affecting the adsorption of methyl orange (MO). The adsorption process could be better described by pseudo-second-order kinetics model and Langmuir isotherm equation, and its saturated adsorption capacity of the modified adsorbents was 1541.5 mg·g−1 at 25 °C, which was 1.40 times of that the unmodified adsorbent (1104.1 mg·g−1). The obtained values of the thermodynamic parameters indicated that the adsorption was a spontaneous process. The regeneration experiment proved the stability and reproducibility of the adsorbent even after five cycles of adsorption-desorption. The primary adsorption mechanism was electrostatic interaction and hydrogen bonding. The adsorbent could be potentially applied for removing dyes from wastewater in wide pH of range, especially acid wastewater.

Fabrication of MgO powder through ultrasound-assisted precipitation for uptake of reactive dyes from wastewater: Change in porous structure for efficient adsorption

Fabrication of MgO powder through ultrasound-assisted precipitation for uptake of reactive dyes from wastewater: Change in porous structure for efficient adsorption

Engineering of Stable Anionic/Neutral MOFs with Zinc-Adeninate Building Units for Efficient C2H2/CO2 Separation.

Using adenine and metal ions to form secondary building units (SBUs), further connected by a highly symmetrical multicarboxylic linker to construct an amino-modified porous framework with high porosity, is an effective strategy. By regulating the deprotonation and hydrolysis capacity of the synthesized solvent, it is possible to obtain different charged frameworks. In this work, two stable anionic/neutral MOFs, (Et2NH2)[Zn3(TCPE)(adenine)2CH3COO]·DEF·3H2O (1) and [Zn3.5(adenine)(TCPE)1.5(DMA)(H2O)0.5]·2DMA·2H2O (2), have been synthesized based on zinc-adeninate building units and symmetric tetrakis(4-carboxyphenyl)ethylene (H4TCPE) in N,N-diethylformamide (DEF) and N,N-dimethylacetamide (DMA) reaction systems, respectively. 1 is an anionic framework based on 1D rod zinc-adeninate SBU, containing 1D rectangular (14.3 × 6.3 Å2) and square (14.3 × 14.3 Å2) channels. While 2 is a neutral framework built from isolated zinc-adeninate SBU, it contains hexagonal cages with a dimension of 5.5 Å in the structure. Both of them have high porosity (61.6% for 1 and 46.3% for 2) and high stability in a wide range of pH. 1 and 2 show high C2H2 adsorption capacity at 298 K (48.1 and 70.1 cm3 g-1, respectively) and selective capacity for C2H2/CO2 mixtures, which was confirmed by the breakthrough experiments. Furthermore, the interaction between the frameworks and gas molecules has also been explained by theoretical calculation. This work provides a good example of the design and regulation of porous structures for adsorption and separation functions.

Sensing properties of SF6 decomposition gas sensor based on Rh doped α-AsP monolayer

The detection of decomposition components of SF6 insulating gas in gas-insulated switchgear (GIS) is of great significance to evaluating GIS's operating state and ensuring the equipment's safety. In order to detect and diagnose the main decomposition gases SO2, SOF2, and SO2F2 of SF6, this work systematically analyses the intrinsic α-AsP monolayer and two Rh-modified α-AsP monolayers. Specifically, the adsorption structure, energy, charge transfer and deformed charge density, the total density of states, the partial density of states, and recovery time were discussed and calculated in detail, and the internal mechanism of the entire adsorption process was clarified. Meanwhile, the results show that Rh adsorbed on α-AsP monolayer (Rh-AsP-O) has a good adsorption effect on SO2, SOF2, and SO2F2 gases. From the sensor's perspective, the Rh-AsP-O monolayer has potential applications in the gas-sensing field of SO2, SOF2, and SO2F2.

Prism rather than tetrahedron: low-energy structures for gaseous gold clusters Au10(O2)n + by density functional calculations

The purpose of this study is to reveal the adsorption mechanism of oxygen molecules on gold clusters. density functional theory is employed to investigate the low-energy structure of multiple O2 adsorption on the Au10 + cluster and findings are compared with IR spectra. The nature of bonding of the O2 molecule and Au10 + cluster has been characterised through several metrics like binding energy, dissociation energy, bond length, and vibrational frequencies. The result shows that the lowest-energy structures are prism-shaped rather than tetrahedron-shaped, where only one O2 is chemically adsorbed while others are physically adsorbed. Chemically adsorbed η2-O2 behaves like free O2 –, forming a single electron π bond with Au10 +, while physically adsorbed η1-O2 does not result in an effective chemical bond and behaves like free O2. This study provides insights into the mechanism of oxygen molecule adsorption on gold clusters and can contribute to further research on the catalytic mechanism of gold clusters. Highlights Lowest energy structures are prism-shaped rather than tetrahedron-shaped, which is supported by IR spectrum and chemical hardness. Chemically adsorbed O2 is activated and displays structural and spectral features of free O2 –, while physically adsorbed O2 is close to free O2 in vibrational frequency and bond length. Chemical adsorption is equivalent to a single electron π bond while physical adsorption forms no effective chemical bond due to the lack of electronic pairing between Au10 + and O2.

Derivatives Based on Cyclodextrin Structure for Adsorption of Heavy Metal Ions and Organic Pollutants in Wastewater

AbstractThis study provides a solution for the treatment of heavy metal ions as well as common organic pollutants in water by adsorption, which contributes to the achievement of sustainable development goals. In this work, a new adsorption material, β‐cyclodextrin‐acrylic acid‐acrylamide (CD‐AA‐AM‐MBA), is synthesized. The structure of the materials is characterized and analyzed using fourier transform infrared spectroscopy (FT‐IR), Xray diffraction spectroscopy(XRD), scanning electron microscopy(SEM) and thermogravimetric analysis(TGA). The effects of initial ion concentration, contact time, and different pH values on the adsorption performance are studied. Under the optimized conditions, the adsorption capacity in CD‐AA‐AM‐MBA of Cu2+, Pb2+, Cd2+, Methylene Blue(MB), Methyl Orange(MO), phenol, m‐cresol and p‐cresol are 58.66, 326, 48.5, 58.27, 51.34, 6.63, 3.7 and 5.91 mg g−1.

Sustainable hybrid biocomposite adsorbents for anion-selective or concerted removal of ionic pollutants: Organic dyes to arsenate

The controlled removal of hazardous ionizable compounds ranging from organic dyes from the textile industry to inorganic anions such as fluoride, sulfate or arsenate in aqueous media presents challenges to this day. This study devised a synthetic strategy to enable anion selective or simultaneous adsorption of anionic and cationic species. Therefore, versatile ternary metal composites (TMCs) were prepared with variable aluminum salt precursors: TMC-S for Al2(SO4)3 and TMC-N for Al(NO3)3 with variable Al3+ content from high to low values (S1>S2>S3>S4; N1≫N3) for the respective TMCs. Characterization was achieved through complementary methods: pHPZC, TGA, PXRD, XPS, 27Al/13C NMR and IR spectroscopy. The TMC surface properties were assessed via dye adsorption with methylene blue (MB) as a model cation, whereas methyl orange (MO) and reactive Black 5 (RB5) served as model anion systems. Sulfate, fluoride and arsenate represented a variety of inorganic anion target pollutant species.The maximum equilibrium adsorption capacity of MO decreased (TMC-S1 to TMC-S4; 0.67 to 0.41 mmol/g), whereas the MB adsorption capacity increased from 0.03 to 0.47 mmol/g. The arsenate adsorption capacity also decreased with decreased aluminum concentration during synthesis from 0.71 mmol/g (TMC-S1) to 0.46 mmol/g (TMC-S4). Arsenate and fluoride were chemisorbed onto the Al-centers, in contrast to the dye probes, which undergo physisorption. Additionally, arsenate was selectively removed from saline samples of groundwater with up to 6000 mg/L sulfate species, which contributes to salinity without altering the adsorption properties. This study hereby highlights the unique role of variable aluminum salt during synthesis to enable facile tailoring of the adsorbent structure and selective anion adsorption (TMC-S1) versus a more general (less selective) adsorption of ionic species (TMC-S4) for multi-component pollutant removal.

Hydroxymethyl-Functionalized Polymer Nanospheres with a Hollow Mesopore Structure for Efficient Acteoside Adsorption

Hydroxymethyl-Functionalized Polymer Nanospheres with a Hollow Mesopore Structure for Efficient Acteoside Adsorption

Ion solvation as a predictor of lanthanide adsorption structures and energetics in alumina nanopores

Adsorption reactions at solid-water interfaces define elemental fate and transport and enable contaminant clean-up, water purification, and chemical separations. For nanoparticles and nanopores, nanoconfinement may lead to unexpected and hard-to-predict products and energetics of adsorption, compared to analogous unconfined surfaces. Here we use X-ray absorption fine structure spectroscopy and operando flow microcalorimetry to determine nanoconfinement effects on the energetics and local coordination environment of trivalent lanthanides adsorbed on Al2O3 surfaces. We show that the nanoconfinement effects on adsorption become more pronounced as the hydration free energy, ΔGhydr, of a lanthanide decreases. Neodymium (Nd3+) has the least exothermic ΔGhydr (−3336 kJ·mol−1) and forms mostly outer-sphere complexes on unconfined Al2O3 surfaces but shifts to inner-sphere complexes within the 4 nm Al2O3 pores. Lutetium (Lu3+) has the most exothermic ΔGhydr (−3589 kJ·mol−1) and forms inner-sphere adsorption complexes regardless of whether Al2O3 surfaces are nanoconfined. Importantly, the energetics of adsorption is exothermic in nanopores only, and becomes endothermic with increasing surface coverage. Changes to the energetics and products of adsorption in nanopores are ion-specific, even within chemically similar trivalent lanthanide series, and can be predicted by considering the hydration energies of adsorbing ions.

Micro-characterization of the adhesion properties and mechanisms at the asphalt-silica aggregate interface under combined thermal-oxygen aging and chloride salt erosion

In this investigation, various Atomic Force Microscopy (AFM) probes were used to characterize changes in the adhesion properties of aged asphalt under different concentrations of chloride salt. The characterization included analyzing the surface morphology, roughness parameters, height-height correlation function (HHCF), and force-distance curves of the asphalt. Additionally, Molecular Dynamics (MD) simulation was employed to reveal the underlying mechanisms that govern changes in adhesion properties between aged asphalt and aggregate when subjected to chloride salt erosion. Interfacial erosion and internal erosion models were constructed to facilitate a comprehensive analysis from multiple perspectives. The results demonstrate that chloride salts interact with the interface between asphalt and silica aggregates, engaging in competitive adsorption with the asphalt. The strength of this competitive adsorption is influenced by the constituents of the asphalt and the concentration gradient of chloride salts both within and outside the asphalt matrix. Under this concentration gradient, polar components are attracted to the asphalt surface by chloride ions, forming triangular adsorption structures with water molecules and aggregates such as asphaltene. Components with lower polarity exhibit distinct distributions and diffusion states due to variations in molecular weight and spatial configuration. As the concentration of chloride salts increases, the concentration gradient intensifies, resulting in enhanced transformations, migrations, and dissolutions of asphalt components. Consequently, the micro-morphology of the asphalt tends to smoothen, the HHCF undergoes significant modifications, roughness decreases, and the adhesion performance between asphalt and aggregate weakens. Moreover, at higher concentrations, the formation of precipitated chloride salt crystals disrupts the continuity of the asphalt, further compromising interfacial adhesion performance. This study is expected to provide theoretical guidance for the modification of asphalt and the improvement of asphalt pavement lifespan in complex service environments.

Cerium(IV) chitosan-based hydrogel composite for efficient adsorptive removal of phosphates(V) from aqueous solutions

The excess presence of phosphate(V) ions in the biosphere is one of the most serious problems that negatively affect aqueous biocenosis. Thus, phosphates(V) separation is considered to be important for sustainable development. In the presented study, an original cerium(IV)-modified chitosan-based hydrogel (Ce-CTS) was developed using the chemical co-precipitation method and then used as an adsorbent for efficient removal of phosphate(V) ions from their aqueous solutions. From the scientific point of view, it represents a completely new physicochemical system. It was found that the adsorptive removal of phosphate(V) anions by the Ce-CTS adsorbent exceeded 98% efficiency which is ca. 4-times higher compared with the chitosan-based hydrogel without any modification (non-cross-linked CTS). The best result of the adsorption capacity of phosphates(V) on the Ce-CTS adsorbent, equal to 71.6 mg/g, was a result of adsorption from a solution with an initial phosphate(V) concentration 9.76 mg/dm3 and pH 7, an adsorbent dose of 1 g/dm3, temperature 20 °C. The equilibrium interphase distribution data for the Ce-CTS adsorbent and aqueous solution of phosphates(V) agreed with the theoretical Redlich-Peterson and Hill adsorption isotherm models. From the kinetic point of view, the pseudo-second-order model explained the phosphates(V) adsorption rate for Ce-CTS adsorbent the best. The specific effect of porous structure of adsorbent influencing the diffusional mass transfer resistances was identified using Weber-Morris kinetic model. The thermodynamic study showed that the process was exothermic and the adsorption ran spontaneously. Modification of CTS with cerium(IV) resulted in the significant enhancement of the chitosan properties towards both physical adsorption (an increase of the point of zero charge of adsorbent), and chemical adsorption (through the presence of Ce(IV) that demonstrates a chemical affinity for phosphate(V) anions). The elaborated and experimentally verified highly effective adsorbent can be successfully applied to uptake phosphates(V) from aqueous systems. The Ce-CTS adsorbent is stable in the conditions of the adsorption process, no changes in the adsorbent structure or leaching of the inorganic filling were observed.

Exploring Metal Nanocluster Catalysts for Ammonia Synthesis Using Informatics Methods: A Concerted Effort of Bayesian Optimization, Swarm Intelligence, and First-Principles Computation.

This paper details the use of computational and informatics methods to design metal nanocluster catalysts for efficient ammonia synthesis. Three main problems are tackled: defining a measure of catalytic activity, choosing the best candidate from a large number of possibilities, and identifying the thermodynamically stable cluster catalyst structure. First-principles calculations, Bayesian optimization, and particle swarm optimization are used to obtain a Ti8 nanocluster as a catalyst candidate. The N2 adsorption structure on Ti8 indicates substantial activation of the N2 molecule, while the NH3 adsorption structure suggests that NH3 is likely to undergo easy desorption. The study also reveals several cluster catalyst candidates that break the general trade-off that surfaces that strongly adsorb reactants also strongly adsorb products.

Stability of Single Gold Atoms on Defective and Doped Diamond Surfaces.

Polycrystalline boron-doped diamond (BDD) is widely used as a working electrode material in electrochemistry, and its properties, such as its stability, make it an appealing support material for nanostructures in electrocatalytic applications. Recent experiments have shown that electrodeposition can lead to the creation of stable small nanoclusters and even single gold adatoms on the BDD surfaces. We investigate the adsorption energy and kinetic stability of single gold atoms adsorbed onto an atomistic model of BDD surfaces by using density functional theory. The surface model is constructed using hybrid quantum mechanics/molecular mechanics embedding techniques and is based on an oxygen-terminated diamond (110) surface. We use the hybrid quantum mechanics/molecular mechanics method to assess the ability of different density functional approximations to predict the adsorption structure, energy, and barrier for diffusion on pristine and defective surfaces. We find that surface defects (vacancies and surface dopants) strongly anchor adatoms on vacancy sites. We further investigated the thermal stability of gold adatoms, which reveals high barriers associated with lateral diffusion away from the vacancy site. The result provides an explanation for the high stability of experimentally imaged single gold adatoms on BDD and a starting point to investigate the early stages of nucleation during metal surface deposition.

Adsorption features of pigments onto iron oxides: Co-effect of the molecular structure of adsorbates and the varied surface properties of minerals

The knowledge about the adsorption properties of pigments onto different iron oxide minerals is still limited. The adsorption behaviors of three typical pigments, including amaranth (AR), tartrazine (TA), and brilliant blue (BB), onto three iron oxides (ferrihydrite, goethite, and hematite) were investigated. The primary mechanism of their interactions was the electrostatic attraction. The affinities of iron oxides toward any pigment were generally in the sequence of ferrihydrite > goethite > hematite (e.g., the maximum adsorption amounts (qmax) of AR onto the three iron oxides were 35.5 mg/g, 11.6 mg/g, and 4.2 mg/g, respectively), which was related to the differences in physicochemical properties of minerals (e.g., specific surface area, surface hydroxyl density, and crystal structure). Interestingly, for a given iron oxide, the pigment-binding capacity of the mineral was in the order of AR > TA > BB. This effect was attributed to variations in pigment molecular sizes and electrostatic interactions between pigments and minerals. The pigment-binding capabilities of iron oxides changed as the solution pH varied. Hydrogen-bonding and electrostatic interactions were the main mechanisms below and above pH > pHPZC (pH value at zero point charge), respectively. Furthermore, adding Cu2+ facilitated pigment adsorption, mainly stemming from the surface-bridging effect. Pigments also enhanced Cu2+ adsorption onto iron oxides due to the decreasing electrostatic repulsion between Cu2+ and particles as well as the complexion between Cu2+ with pigment molecules adsorbed on mineral surfaces. The insightful information demonstrates that ubiquitous iron oxide minerals can affect the fate of pigments in natural environments.