Octahedral Surface Research Articles

Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study

Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298K and 1atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na+) only while the other potassium cation (K+) and their concentrations were 3M and 5M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface.

Correction to ‘The geometry of structural equilibrium’

[This corrects the article DOI: 10.1098/rsos.160759.].

A molecular dynamics investigation into the adsorption behavior inside {001} kaolinite and {1014} calcite nano-scale channels: the case with confined hydrocarbon liquid, acid gases, and water

A set of molecular dynamics simulations was conducted, as the first comparative study of the adsorption behavior of liquid hydrocarbon/acid gases/water molecules over { 10bar{1}4} calcite surface and {001} octahedral kaolinite surface in nano-confined slit. According to atomic z-density profiles, hydrocarbon molecules have higher tendency towards the { 10bar{1}4} calcite surface than the {001} octahedral kaolinite surface. In addition, water molecules form stronger adsorption layer over calcite surface than kaolinite. In contrast, acid gas molecules have higher tendency towards kaolinite surface than calcite. This behavior was spotted within nanometer-sized slit pores. The results also point to reduction in self-diffusion coefficient of molecules with strong adsorption over mineral surfaces in nano-confined environment.

Structural studies of magnetic nanoparticles doped with rare-earth elements

Magnetic nanoparticles and those doped with rare-earth metal ions having spinel structure were synthesized, possessing the average particles size of 11.3-13.4 nm. According to Mossbauer spectroscopy data it can be concluded that prepared iron oxide nanoparticles are γ-Fe2O3. For materials containing rare-earth elements the decrease of octahedral component surface was observed in comparison to non-doped material, what can be explained by Eu3+, Sm3+ и Gd3+ ions occupying the octahedral position.

Configuration, Anion-Specific Effects, Diffusion, and Impact on Counterions for Adsorption of Salt Anions at the Interfaces of Clay Minerals

Interfacial interactions of clay minerals with salt solutions are ubiquitous and play a crucial role in a wide range of fields, where salt cations are the focus while anions are generally regarded as spectators. Here, molecular dynamics simulations show that the various anions are strongly adsorbed on the surfaces of clay minerals, and the resulting anion-specific effects are pronounced. Although constructing only H-bonds, anions form stable inner- and outer-sphere complexes with clay minerals, and F– and OH– can result in even more stable complexes than metal ions. The underlying anion-specific effects abide by the sequence OH– > F– > Cl– > I– and show apparent enhancements with increase of salt concentrations. OH– is particular at relatively high concentrations, forming clusters and capturing metal ions at octahedral AlO6 surfaces and approaching tetrahedral SiO4 surfaces with help of metal ions in addition to the monodispersive inner- and outer-sphere species at octahedral AlO6 surfaces that are simila...

Preparation of nacrite nanorolls and their reinforcing effect in LLDPE matrix

Nacrite nanorolls were prepared by the delamination and rolling of the platy nacrite particles and the nacrite nanorolls were melt‐compounded with LLDPE to prepare a novel Nacrite/LLDPE composite. In this method, hexylamine was intercalated into the interlayer space of methoxy‐modified nacrite precursor and the deintercalation of nacrite‐hexylamine intercalation complex in toluene resulted in the delamination and rolling of nacrite layers. The nacrite nanorolls were composed with linear low‐density polyethylene (LLDPE) to prepare a novel Nacrite/LLDPE composite. X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption–desorption test were used to evaluate the prepared nacrite nanorolls. The results showed that the interlayer octahedral surface of nacrite was grafted with methanol and the methoxy‐modified nacrite was intercalated with hexylamine. The deintercalation of nacrite‐hexylamine intercalation complex in toluene disturbed the orderly arrangement of nacrite layers, leading to a delamination of the layered particles and subsequent formation of aluminosilicate nanorolls. The specific surface area (SSA) and Vpor value of nacrite nanorolls reached 34.69 m2/g and 0.22 cm3/g (4.52 m2/g and 0.13 cm3/g for raw nacrite). Furthermore, the mechanical properties test confirmed that the introduction of nacrite nanorolls into LLDPE matrix could improve the tensile and tear strength. 6.4% and 6.8% higher tensile strength than the pure LLDPE were observed for Nacrite/LLDPE composite with 2 wt% and 4 wt% nacrite nanorolls filler. POLYM. COMPOS., 39:448–456, 2018. © 2016 Society of Plastics Engineers

Theoretical study about effects of H2O and Na+ on adsorption of CO2 on kaolinite surfaces

The density functional theory(DFT) was used to investigate the adsorptions of carbon dioxide(CO2) on kaolinite surfaces and the influences of Na+ and H2O on the adsorption. Both cluster and periodic models of kaolinite were considered. The calculated results indicate that stable complexes can be formed between adsorbed CO2 and the surfaces of kaolinite in the presence or absence of sodium cation and water molecule. The Al―O octahedral surface has a larger adsorption affinity for CO2 than the Si―O tetrahedral surface of kaolinite because the hydroxyl groups of kaolinite Al―O surface present more activity than the basal O atoms of the Si―O tetrahedral surface in the intermolecular interactions. The existence of exchangeable sodium cations exerts the significant effect on the adsorption of CO2 with the dramatic increase of the adsorption energy, while the presence of water molecule decreases the adsorption strength insignificantly. The calculated Gibbs free energies of the adsorption reveal that the adsorptions of CO2 on all the investigated kaolinite surfaces are feasible thermodynamically in the gas phase. Surface free energy was calculated to provide the predictions of the surface stability as a function of temperature.

Reactive Oxygen Species on the (100) Facet of Cobalt Spinel Nanocatalyst and their Relevance in 16O2/18O2 Isotopic Exchange, deN2O, and deCH4 Processes—A Theoretical and Experimental Account

Periodic spin unrestricted, gradient corrected DFT calculations joined with atomistic thermodynamic modeling and experiment were used to study the structure and stability of various reactive oxygen species (ROS) and oxygen vacancies produced on the most stable terminations of the cobalt spinel (100) surface. The surface state diagram of oxygen in a wide range of pressures and temperatures was constructed for coverage varying from ΘO = 1.51 atom·nm–2 to ΘO = 6.04 atom·nm–2. A large variety of the unraveled surface ROS includes diatomic superoxo (CoO–O2––CoO), peroxo (CoT–O22––CoO), and spin paired (CoO–O2–CoO) adducts along with monatomic metal-oxo (CoT–O+, CoO–O2+) species, where CoT and CoO stand for the tetrahedral and octahedral cobalt surface centers, respectively. There are also two kinds of peroxo species associated with surface oxygen ions connected with 3CoO or 2CoO and 1CoT cations ((O2O,1T–O)2– and (O3O–O)2–), respectively). The results revealed that in the oxygen pressure range of typical catal...

The molecular structure of kaolinite–potassium acetate intercalation complexes: A combined experimental and molecular dynamic simulation study

The kaolinite (Kaol) intercalated with potassium acetate (Ac) was prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetry. Molecular dynamic simulation was performed to investigate the structure of Kaol–Ac intercalation complex and the hydrogen bonds between Kaol and intercalated Ac and water using INTERFACE forcefield. The acetate anions and water arranged in a bilayer structure in the interlayer space of Kaol. The potassium cations distributed in the interlayer space and strongly coordinated with acetate anions as well as water rather than keyed into the ditrigonal holes of tetrahedral surface of Kaol. Strong hydrogen bonds formed between the hydrogen atoms of hydroxyl on the octahedral surface and oxygen atoms of both acetate anions and water. The acetate anions and water also weakly bonded hydrogen to the silica tetrahedral surface through their hydrogen atoms with the oxygen atoms of silica tetrahedral surface.

Theoretical predictions of thermodynamic parameters of adsorption of nitrogen containing environmental contaminants on kaolinite.

In this study thermodynamic parameters of adsorption of nitrogen containing environmental contaminants (NCCs, 2,4,6, trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dinitroanisole (DNAN), and 3-one-1,2,4-triazol-5-one (NTO)) interacting with the tetrahedral and octahedral surfaces of kaolinite were predicted. Adsorption complexes were investigated using a density functional theory and both periodic and cluster approach. The complexes, modeled using the periodic boundary conditions approach, were fully optimized at the BLYP-D2 level to obtain the structures and adsorption energies. The relaxed kaolinite-NCCs structures were used to prepare cluster models to calculate thermodynamic parameters and partition coefficients at the M06-2X-D3 and BLYP-D2 levels from the gas phase. The entropy effect on the Gibbs free energies of adsorption of NCCS on kaolinite was also studied and compared with available experimental data. The results showed that in all calculated models, the NCCs molecules are physisorbed and they favor a parallel orientation toward both kaolinite surfaces. It was found that all calculated NCCs compounds are more stable on the octahedral than on the tetrahedral surface of kaolinite. The Gibbs free energies and partition coefficients were also predicted for interactions of NCCs with Na-kaolinite from aqueous solution. Calculations revealed adsorption of NCCs is effective from the gas phase on both cation free kaolinite surfaces and on Na-kaolinite from aqueous solution at room temperature. Theoretical data were validated against experimental results, and the reasons for small differences between calculated and measured partition coefficients are discussed.

Combined experimental and theoretical investigation of interactions between kaolinite inner surface and intercalated dimethyl sulfoxide

Kaolinite intercalation complex with dimethyl sulfoxide (DMSO) was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetry–differential scanning calorimetry (TG–DSC) combined with molecular dynamics simulation. The bands assigned to the OH stretching of inner surface of kaolinite were significantly perturbed after intercalation of DMSO into kaolinite. Additionally, the bands attributed to the vibration of gibbsite-like layers of kaolinite shifted to the lower wave number, indicating that the intercalated DMSO were strongly hydrogen bonded to the alumina octahedral surface of kaolinite. The slightly decreased intensity of 1031cm−1 and 1016cm−1 band due to the in-plane vibration of SiO of kaolinite revealed that some DMSO molecules formed weak hydrogen bonds with the silicon tetrahedral surface of kaolinite. Based on the TG result of kaolinite–DMSO intercalation complex, the formula of A12Si2O5(OH)4(DMSO)0.7 was obtained, with which the kaolinite–DMSO complex model was constructed. The molecular dynamics simulation of kaolinite–DMSO complex directly confirmed the monolayer structure of DMSO in interlayer space of kaolinite, where the DMSO arranged almost parallel with kaolinite basal surface with all methyl groups being distributed near the interlayer midplane and oxygen atoms orienting toward to the alumina octahedral surface. The radial distribution function between kaolinite and intercalated DMSO verified the strong hydrogen bonds forming between hydroxyl hydrogen atoms of alumina octahedral surface and oxygen atoms of DMSO. Moreover, some methyl groups of DMSO were weakly hydrogen bonded to the oxygen atoms of silicon tetrahedral surface through the hydrogen atoms. The mean square displacement of DMSO oxygen atoms and hydrogen atoms in z direction kept unchanged during the simulation time because of the hydrogen-bond interaction between inner surface of kaolinite and DMSO, which constrained the mobility of intercalated DMSO in the direction normal to the kaolinite basal surface.

Surface Effects and Adsorption of Methoxy Anchors on Hybrid Lead Iodide Perovskites: Insights for Spiro-MeOTAD Attachment

Despite the intense study that has been carried out on hybrid organic–inorganic perovskites, motivated by the breakthrough of perovskite solar cells, the surface properties of the methylammonium (MA) lead halide perovskites still remain vastly unexplored. The polar structure of the hybrid perovskites suggests that their surface properties are important to the operation of the photovoltaic devices. To gain insight into these properties, we have investigated the (001) the surfaces of the hybrid CH3NH3PbI3 perovskite by a combination of ab initio methods that include the surface relaxation and the molecular dynamics simulations. We also investigated the binding modes of the methoxybenzene (anisole molecule, CH3OC6H5) on the perovskite surface, with the goal of clarifying the perovskite/spiro-MeOTAD attachment mechanisms. It is found that the methoxybenzene can adsorb on the (001) octahedral surface of the MAPbI3 perovskite depleted of the methylammonium cation, where the methoxy group finds a stable minimum of ∼38.6 kJ/mol in the interstice of the corner-sharing PbI6 octahedra. However, there is no stable attachment site for the methoxybenzene on the PbI2 flat (001) surface of the perovskite. The attachment mechanism is governed by the electrostatic interaction of the methoxy group with the surface, which is repulsive with the iodides and attractive with the Pb(II) ion.

A generalized Drucker–Prager viscoplastic yield surface model for asphalt concrete

A generalized Drucker–Prager (GD–P) viscoplastic yield surface model was developed and validated for asphalt concrete. The GD–P model was formulated based on fabric tensor modified stresses to consider the material inherent anisotropy. A smooth and convex octahedral yield surface function was developed in the GD–P model to characterize the full range of the internal friction angles from 0° to 90°. In contrast, the existing Extended Drucker–Prager (ED–P) was demonstrated to be applicable only for a material that has an internal friction angle less than 22°. Laboratory tests were performed to evaluate the anisotropic effect and to validate the GD–P model. Results indicated that (1) the yield stresses of an isotropic yield surface model are greater in compression and less in extension than that of an anisotropic model, which can result in an under-prediction of the viscoplastic deformation; and (2) the yield stresses predicted by the GD–P model matched well with the experimental results of the octahedral shear strength tests at different normal and confining stresses. By contrast, the ED–P model over-predicted the octahedral yield stresses, which can lead to an under-prediction of the permanent deformation. In summary, the rutting depth of an asphalt pavement would be underestimated without considering anisotropy and convexity of the yield surface for asphalt concrete. The proposed GD–P model was demonstrated to be capable of overcoming these limitations of the existing yield surface models for the asphalt concrete.

Effects of water molecules on rearrangements of formamide on the kaolinite basal (001) surface.

The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) were investigated using periodic density functional theory in conjunction with pseudopotential plane-wave approach. Surface hydroxyl groups covering the octahedral surface of kaolinite were found to play the role of catalysts in the transformations of FM. They induce a reduction of 31 kcal/mol on the energy barrier for formation of its isomer aminohydroxymethylene (AHM), which is close to the reduction amount calculated for water-catalyzed reactions. This suggests that the kaolinite octahedral surface exerts a catalytic effect similar to that of the water molecule. As the tetrahedral surface does not contain catalytic surface hydroxyl groups, only water-assisted FM transformation was therefore studied on this surface whose energy barrier amounts to ∼17 kcal/mol. The combined effect of both water and kaolinite on FM rearrangements via triple hydrogen transfer reactions does not significantly lower the energy barriers, as compared to those of double hydrogen transfer reactions. The triple hydrogen transfer energy barriers amount to ∼20 and ∼36 kcal/mol, and the double ones are ∼21 and ∼40 kcal/mol for formation of formimic acid and AHM isomers, respectively. However, the energies of the systems in water-catalyzed channels lie below the available energies of the original reactants, and thus these channels are more favored than the water-free ones. With its multiple functions as both a supporting plate-form and a catalyst for FM reactions, kaolinite can thus be regarded as an important natural catalyst for prebiotic synthesis.

Theoretical study of adsorption of nitrogen-containing environmental contaminants on kaolinite surfaces.

The adsorption of nitrogen-containing compounds (NCCs) including 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dinitroanisole (DNAN), and 3-nitro-1,2,4-triazol-5-one (NTO) on kaolinite surfaces was investigated. The M06-2X and M06-2X-D3 density functionals were applied with the cluster approximation. Several different positions of NCCs relative to the adsorption sites of kaolinite were examined, including NCCs in perpendicular and parallel orientation toward both surface models of kaolinite. The binding between the target molecules and kaolinite surfaces was analyzed and bond energies were calculated applying the atoms in molecules (AIM) method. All NCCs were found to prefer a parallel orientation toward both kaolinite surfaces, and were bound more strongly to the octahedral than to the tetrahedral site. TNT exhibited the strongest interaction with the octahedral surface and DNAN with the tetrahedral surface of kaolinite. Hydrogen bonding was shown to be the dominant non-covalent interaction for NCCs interacting with the octahedral surface of kaolinite with a small stabilizing effect of dispersion interactions. In the case of adsorption on the tetrahedral surface, kaolonite-NCC binding was shown to be governed by the balance between hydrogen bonds and dispersion forces. The presence of water as a solvent leads to a significant decrease in the adsorption strength for all studied NCCs interacting with both kaolinite surfaces.

Modification of kaolinite by Grafting of siderophilic ligands to the external octahedral surface

The modification of the external octahedral surface of kaolinite (Kaol) was investigated using two siderophilic ligands (SL): 3,4-dihydroxybenzophenone (DBP) and quercetin (Qu). These SL have a 1,2-dihydroxyphenyl group that forms chelate-complexes with aluminum cations. Adsorption isotherms were obtained colorimetrically. PXRD patterns proved that the adsorption was attributed only to the external surfaces. Furthermore, adsorption of fluoride ions was applied to quantify the non-μ-hydroxy groups of the edges and derive the surface area of edges.Comparing maximum adsorption capacities with surface area of edges, it can be safely concluded that SL are indeed capable to coordinate to the aluminol basal surface of Kaol. This conclusion is corroborated by significant bathochromic shifts upon adsorption of the ligands that indicate the formation of a surface complex with exposed Al3+. Thus even small amounts of adsorbed SL changed the surface tension of Kaol significantly. Consequently, forced sedimentation experiments showed that the modified Kaol is rendered hydrophobic enough to form stable dispersions in organic solvents fostering preparation of clay polymer nanocomposites (CPN).

The DFT study of adsorption of 2,4-dinitrotoluene on kaolinite surfaces

Volatile organic compounds can be adsorbed on the surfaces of clay minerals, but the mechanisms and interactions between adsorbate and clay surface are still not well understood. In this paper, the adsorption of 2,4-Dinitrotoluene (2,4-DNT) molecule on the kaolinite surface has been studied at the B3LYP/6-31G(d) level. The cluster models of Si13O37H22 and Al6O24H30 for tetrahedral (Si–O) and octahedral (Al–O) surfaces of kaolinite were constructed, and various gas state properties (including electron density, adsorption energies (AE), hydrogen bonds (both primary hydrogen bonds and secondary hydrogen bonds), vibration frequencies, electrostatic potential, and so on) were explored. The results suggest that the adsorption of 2,4-DNT on kaolinite is due to the formation of hydrogen bonds. Simultaneously, 2,4-DNT molecule is preferentially adsorbed on the Al–O surface. The structures and energies of the absorption of 2,4-DNT molecule on the kaolinite surfaces present an intuitive view for future experimental studies on these atmospheric pollutants.

Characterization of kaolinite intercalation compounds with benzylalkylammonium chlorides using XRD, TGA/DTA and CHNS elemental analysis

Kaolinite of high structural order was intercalated with selected ammonium salts containing a benzyl group: benzyltrimethylammonium (B1), benzyltributylammonium (B2), benzalkonium (B3), benzyldimethyltetradecylammonium (B4) and benzyldimethylhexadecylammonium (B5) chlorides. As a precursor, a methoxy-kaolinite was used which had OCH3 methoxyl groups attached to the octahedral sheet. Such change of the octahedral surface character enabled intercalation of the salts which was not possible using other precursors (e.g. kaolinite–dimethyl sulfoxide). The new intercalation compounds were characterized using XRD (X-ray diffraction), thermal analysis (TGA/DTA) and CHNS elemental analysis. The XRD revealed a significant shift of the kaolinite basal reflection to higher values range from ~14Å (B1 salt) to ~38Å (B5 salt) which confirmed the intercalation. The d values depended on the type of used salt as well as on its initial concentration. The estimated space occupied by each molecule enabled to calculate the maximal molar capacity of the kaolinite in relation to the salts. The results were compared with the chemical formulas of the materials calculated on the basis of CHNS measurements. The TGA/DTA analyses were helpful to confirm the successful intercalation of the selected salts as the thermal decomposition of the kaolinite derivatives took place at higher temperatures as compared to appropriate physical mixtures.

NMR and IR study of kaolinite intercalation compounds with benzylalkylammonium chlorides

Novel intercalation compounds of kaolinite with selected benzylalkylammonium chlorides, obtained using methoxy-kaolinite as a precursor, were characterized by 13C, 27Al, and 29Si solid-state NMR and infrared (FTIR) spectroscopy. The analyses allowed the confirmation of both the formation and structure of precursors (kaolinite-dimethyl sulfoxide and methoxy-kaolinite), as well as the intercalation compounds. According to the 13C CP-MAS NMR spectra of the derivatives with benzyltrimethylammonium chloride (B1), the methyl groups of the molecules, arranged in a monolayer, were keyed into the ditrigonal holes of the kaolinite tetrahedral sheet. The local environment of internal carbons of benzyltributylammonium chloride (B2) butyl chains was mostly perturbed during intercalation. In turn, the structure of the benzyldimethylhexadecylammonium chloride (B5) after intercalation was changed from the solid-like to liquid-like conformation with an increase of gauche conformers, which was attested both by 13C CP-MAS NMR and FTIR. The 13C CP-MAS NMR analysis confirmed that the methoxyl groups attached to the octahedral surface of methoxy-kaolinite were not affected by intercalation. The 27Al and 29Si MAS NMR did not show any significant distortion of the Al-octahedra and Si-tetrahedra after intercalation of the organic salts. The IR analyses indicated an increased amount of intercalated water with the increase of initial salt concentration.

Trace element partitioning in mixed-habit diamonds

Mixed-habit diamonds are a special type of crystal that form by simultaneous growth by two different mechanisms; octahedral and cuboid growth. This type of crystal growth is known to preferentially partition nitrogen into the octahedral growth sectors during growth. To identify if this fractionation occurs for any other trace element, this study applies in situ laser ablation mass spectrometry to a well-studied collection of mixed-habit diamonds. The results show high concentrations of nickel (3.6–36.4ppm) and cobalt (0.108–1.25ppm) in the cuboid sectors, whereas the octahedral sectors contain only <0.05–0.35ppm nickel and <0.014–0.03ppm cobalt. The relative enrichment of nickel in the cuboid sectors varies between 10 and 460 times. For cobalt, where the concentrations in the octahedral sector are commonly below the limit of quantification, the enrichment is estimated to be in the range of 10–100 times. There appears to be a rough linear relationship between the concentrations of the two elements in the cuboid sectors, with nickel concentrations approximately 27 times that of cobalt. This finding of nickel fractionation into the cuboid sectors is the opposite of what is seen in synthetic diamonds grown from FeNi solvents, where Ni is only found in the octahedral growth sectors. We propose that this is because the inherent lattice strain in the rough cuboid diamond growth of natural mixed-habit diamonds is greater than that in the smooth octahedral growth, making it easier to fit the large Ni and Co ions into a divacancy. In diamonds grown from metal solvents (i.e. industrial synthetic diamonds), the cube face is a smooth one, therefore the partitioning of trace elements is simply a result of the octahedral surface offering more bonding opportunities than the cube surface.Due to the extremely low concentrations of trace elements in these gem quality diamonds, many of the elements are commonly below the limit of quantification (LOQ). While we are confident that Pr, Sr, Pb, Zr, V, Cr and Zn are not fractionated by the crystal growth mechanisms of mixed-habit diamonds that affect Ni and Co, this remains to be proven for the remaining trace elements analysed. Data on the fractionation of copper are inconclusive, with 75% of data from the cuboid sectors above the LOQ and all data from the octahedral sectors below the LOQ. However, the values of the LOQ for the octahedral data are often higher than those of the cuboid data, so further investigation of Cu is necessary to confirm its behaviour.