Transition Metal Series Research Articles

Investigation into the ability of langbeinite-type K2M2(SO4)3 (M = Mn, Fe, Co and Ni) materials to accommodate Na: The importance of the electronegativity of the framework cation

In this work we report a study of the langbeinite-type K2-xNaxM2(SO4)3 materials (M ​= ​Mn, Fe, Co and Ni) in order to evaluate the level of Na incorporation possible. The work showed that the level of Na incorporation decreased across the transition metal series, with the highest level of Na incorporation (up to x=1.3) observed for M=Mn. This trend does not appear to be related to the ionic radius of the transition metal, but rather its’ electronegativity. We illustrate this relationship with the inclusion of our prior work on K2-xNaxMg2(SO4)3 where even higher levels of Na were possible, and demonstrate that through co-doping with Mg, higher Na levels can be achieved for K2-xNaxM2(SO4)3 materials (M ​= ​Mn, Fe). The dependence on the electronegativity of the divalent cation is attributed to greater electronegativity leading to enhanced polarization of the framework, thus allowing for greater stabilization of the smaller Na cation as it ‘moves’ towards the edge of the framework cage to better fulfil its’ coordination requirements. Given the interest in related systems for Na ion battery applications, this work provides a new factor to consider when designing new materials for such applications.

Vital effect of sufficient vulcanization on the properties of Ni-Co-S/graphene composites for supercapacitor

Ni-Co-S/graphene-based composites have a broad prospect in the application of supercapacitors. Whether the vulcanization process is sufficiently performed seriously affect the performance of the composites. Here, a series of transition metal sulfide/graphene composites is synthesized through a two-step hydrothermal method by introducing different sulfur sources selected from organic (thiourea and thioacetamide) to inorganic (sodium sulfide and sodium thiosulfate). Both thioacetamide and sodium sulfide can vulcanize Ni-Co hydroxy-carbonate precursor to form the Ni-Co sulfide, but the other two cannot. And the Ni-Co-S/graphene composites synthesized by using sodium sulfide as sulfur source possess the best performance in asymmetric supercapacitor with an initial specific capacitance of 178.1 F g−1, and a capacitance retention of 89.47% after 10,000 cycles at 10 A g−1. The excellent stability is related to the ideal hollow structure with rich electrochemical active sites, and dispersed constituents of the Ni-Co-S on the surface of rGO.

Preparation of Mg-Al based solid base for the transesterification of propylene carbonate and methanol

A series of transition metals (Fe, Cu, Zr) modified Mg-Al solid bases were synthesized by co-precipitation method and characterized by XRD, N2 adsorption-desorption, FT-IR, XPS, CO2-TPD. The catalytic performances were investigated for the synthesis of dimethyl carbonate via transesterification of propylene carbonate (PC) and methanol. The results reveal that the surface basicity of the samples varies with the addition of different metals. The surface basic strength and density of the catalysts are the main factors affecting the catalytic activity. Among the catalysts studied, FeMgAl exhibits the highest surface basic density and thus shows the best catalytic performance. The conversion of PC can reach 66.2% under the temperature of 65°C, reaction time of 4 h, methanol/ester molar ratio of 10:1 and catalyst amount of 4% of the reactant.

Trends in transition metal solute diffusion in metals: The case of tungsten

The solute diffusion regulates many properties and phenomena of metal alloys. Decades of research has led to lots of knowledge of interrelationships between diffusion parameters and transition metal (TM) solutes properties in metals. But none has provided a universal relationship to elucidate the underlying physics of TM solute diffusion in metals. In this paper, we systematically study TM solutes diffusion in tungsten using the first-principles calculations coupled with harmonic transition state theory. We found the solute migration energies vary parabolically across the TM series reaching a maximum at V, Mo, and W for 3d, 4d, and 5d, respectively. The correlation factor is temperature-dependent in an Arrhenius-like way, whose fitted correlation energies and pre-factors are inversely proportional to the solute migration energies. Using the database of TM solute diffusion in tungsten developed here and other existing databases, we identify the role of the matrix metals on the law of solute diffusion. When the atomic radii of matrix metals are larger than TM solutes, the solute diffusion is dominated by metallic bonds between the solute and matrix atoms, whose solute migration energy follows a positive correlation to the melting point of the solute element. While for the reverse case, the solute diffusion is controlled by solute-induced lattice distortions and their solute migration energy shows a negative correlation with the solute radius.

Safety‐by‐Design of Metal Oxide Nanoparticles Based on the Regulation of their Energy Edges

The safety of metal oxide (MOx) nanoparticles (NPs) has been highly concerned because of their wide application and potential toxicological injury. The safe-by-design strategy is usually developed to make safer MOx NPs based on regulation of their physicochemical properties. In the present study, manganese oxide (Mn3 O4 ) NPs, as a representative of insoluble toxic MOx NPs, are doped with a series of transition metal to regulate their conduction band energy (Ec ) out of biological redox potential range (BRPR) or Fermi energy (Ef ) far away from valence band energy (Ev ), aiming at completely eliminating the toxicity or significantly reducing the toxicity. It is found that all these M-doping cannot move Ec of Mn3 O4 NPs out of the BRPR but zinc (Zn)-, copper (Cu)-, and chromium (Cr)-doping do move Ef far away from Ev , where Zn-doping results in the largest |Ef - Ev | value. Various abiotic, in vitro and in vivo assessments reveal that Zn-, Cu-, and Cr-doped Mn3 O4 NPs can generate lower amount of •OH and trigger weaker injury than Mn3 O4 NPs, where Zn-doped Mn3 O4 NPs show the lowest toxicity. Regulating Ef far away from Ev becomes a feasible safe-by-design approach to achieve safe MOx NPs.

Transition-Metal Monofluorophosphate Ba2M2(PO3F)F6 (M = Mn, Co, and Ni): Varied One-Dimensional Transition-Metal Chains and Antiferromagnetism.

Four transition-metal monofluorophosphates, with a chemical formula of Ba2M2(PO3F)F6 (M = Mn, Co, Ni, and Cu), have been synthesized hydrothermally using phosphoric and fluorophosphoric acids. The structures of Ba2M2(PO3F)F6 were intensively investigated by single-crystal and powder X-ray diffraction. Their networks exhibited three-dimensional frameworks formed by cis-MO2F4 octahedra and PO3F tetrahedra. Ba2M2(PO3F)F6 (M = Mn, Co, and Cu) are isostructural, crystallizing in the monoclinic space group P21/c, while Ba2Ni2(PO3F)F6 adopted an unpredetermined structure, crystallizing in the monoclinic space group P21/n. The different arrangements of the same cis-MO2F4 moieties and PO3F groups within one-dimensional chains lead to different frameworks in this late-first-row transition-metal series. By a comparison of normalized bond lengths with their normal counterparts, the more elongated octahedral cis-MO2F4 units in Ba2Cu2(PO3F)F6 reveal the presence of static Jahn-Teller distortion, uncovering the puzzling reason for the exceptional structure of Ba2Ni2(PO3F)F6 in the series. Ba2M2(PO3F)F6 (M = Mn, Co, and Ni) forms spin chains of M2+ made of coupled dimers or tetramers, showing dominant antiferromagnetic behavior.

Molecular Docking Study of Biologically Active Ligand and the Insights of Synthesis, Characterization and In Vitro Studies of Derivatives of β-tubulin Polymerization Inhibitor as Antigout Agent

Background/objective: The aim of the study is to synthesize derivatives of colchicine, which is an anti-gout drug, and to enhance the antimicrobial activity of it. As it is observed in case study of drug– drug interaction, i.e. Colchicine and clarithromycin, which is known as antimicrobial drug has given fatal results, in consequence to that we have tried to enhance the antimicrobial activity of the drug itself, as there is always a need of antimicrobial drugs in the treatment of gout. In addition, to study the binding of protein and colchicine through molecular docking. Methods/analysis: In this work, the detailed molecular docking study of colchicine has been done and complexes of colchicine with Co (II), Ti(II), Ni (II) Fe (II) Zn(II) Cu(II) are synthesized and investigated by using IR, and antimicrobial antifungal screening. Findings/application: Docking shows the exact binding site of the ligand which is beta-tubulin inhibitor. It is also observed that first transition series metal forms stable complexes with this ligand specially and shows enhanced antimicrobial activity. Keywords: Colchicine Complexes, Molecular Docking, Gout, Beta Tubulin Inhibitor Antimicrobial Activity, IR.

Transition metal atom–doped monolayer MoS2 in a proton-exchange membrane electrolyzer

There has been a substantial research effort worldwide to develop non-noble metal catalysts for H2 production from water splitting using renewable energy sources, but most data were evaluated by voltammetry in laboratories. Here, exposed basal planes of MoS2 monolayer nanosheets with metal dopants across the first transition metal (TM) series in the periodic table (Fe, Co, Ni, Cu) are used as cathode catalysts for the proton-exchange membrane (PEM) water splitting in an electrolyzer under typical conditions of strong acidity with more negative applied voltage. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis and high-angle annular dark-field scanning transmission electron microscopy (HAADF–STEM) images show a direct proof on the single TM atoms residing at the surface basal sites, which subtly modify the electrocatalytic activity of the monolayer MoS2, depending on their electronic and metal-hydrogen binding ability. We report that Co-sMoS2 yields the highest current density in an electrolyzer with the hydrogen evolution reaction (HER) activity comparable with that of the commercial 20 wt% Pt/C under industrial applicable conditions. A general trend for the other TMs has also been established as evidenced by the change in TM effective nuclear charge across the periodic table, which perturbed the TM-Mo interaction and hence affects the HER activity.

Anti‐hepatocellular carcinoma, antioxidant, anti‐inflammation and antimicrobial investigation of some novel first and second transition metal complexes

New coordination compounds of some selected metal ions from the first and second transition metals series with a Schiff base were synthesized and characterized. The Schiff base is derived from 4‐Aminoantipyrine and 3‐(hydroxyimino) butan‐2‐one. The compounds were characterized by different analysis tools like; elemental analysis, mass spectra, Fourier transform infrared (FTIR) as well as electronic spectra, magnetic measurements, molar conductance and thermal analysis technique. All complexes were formed with 1:1 (metal: ligand) stoichiometry except Mn (II) where 1:2 (Mn: ligand) is formed. Schiff base ligand interacted as a tridentate ligand by using the nitrogen atoms of the imine and the oximato groups and the carbonyl oxygen atom as donor groups with all studied metal ions except copper (II) and manganese (II) where the carbonyl oxygen is not shared in the coordination. These complexes show various physicochemical properties. X‐ray powder diffraction shows different crystal systems; Cd (II) complex: hexagonal, Cu (II) complex: orthorhombic; and [Ni (II), Mn (II), Rh (III) & Pd (II)] complexes: monoclinic.All compounds showed potent cytotoxicity against the growth of human liver cancer cell lines. The square planar Pd (II) complex was more active than those of octahedral geometries of all other synthesized complexes. Cd (II) complex has the highest microbial growth inhibition than the rest of the prepared complexes. The docking active sites interactions were evaluated using the selected proteins EGFR tyrosine kinase and protein crystal structure of GlcN‐O‐P synthase. in vitro antioxidant assay revealed potent free radical scavenging activity of the three synthesized Cu (II), Pd (II) and Rh (III) complexes that exceeded the standard ascorbic acid. Pd (II) complex shows the most significant inhibition denaturation percent.

Where Is the Fluoro Wall?: A Quantum Chemical Investigation.

Despite their isoelectronic properties, fluoro and oxo ligands exhibit completely different chemical behavior. Formally speaking, the first is known to exclusively form single bonds, while the latter is generally observed to form double (or even triple) bonds. The biggest difference, however, lies in what is known among inorganic chemists as the Oxo Wall: the fact that six-coordinate tetragonal transition metal oxo complexes are not observed beyond group 7 elements. While the Oxo Wall was explained a few decades ago, some questions regarding the nature of the Oxo Wall remain unanswered. For example, why do group 8 oxo complexes with high oxidation states not violate the Oxo Wall? Moreover, why are transition metal fluoro complexes observed through the whole transition metal series? In order to understand how the small difference between these two isoelectronic ligands can give rise to such different chemical behaviors, we conducted an extensive computational analysis of the geometric and electronic properties of model fluoro and oxo complexes with metals around the Oxo Wall. Among many insights into the details of the Oxo Wall, we mostly learned that the oxygen 2p orbitals are prone to meaningfully interact with transition metal d orbitals, because they match not only spatially but also energetically, while for fluorine the p orbital energies are lower to an extent that interaction with transition metal d orbitals is much reduced. This in turn implies that in those instances where the metal d orbitals principally accessible for interaction are occupied, the oxygen 2p orbitals are too exposed to be stable.

Orbital energy mismatch engenders high-spin ground states in heterobimetallic complexes.

The spin state in heterobimetallic complexes heavily influences both reactivity and magnetism. Exerting control over spin states in main group-based heterobimetallics requires a different approach as the orbital interactions can differ substantially from that of classic coordination complexes. By deliberately engendering an energetic mismatch within the two metals in a bimetallic complex we can mimic the electronic structure of lanthanides. Towards this end, we report a new family of complexes, [Ph,MeTpMSnPh3] where M = Mn (3), Fe (4), Co (5), Ni (6), Zn (7), featuring unsupported bonding between a transition metal and Sn which represent an unusual high spin electronic structure. Analysis of the frontier orbitals reveal the desired orbital mismatch with Sn 5s/5p primarily interacting with 4s/4p M orbitals yielding localized, non-bonding d orbitals. This approach offers a mechanism to design and control spin states in bimetallic complexes.

Pressure-induced high-temperature superconductivity in hypothetical H3X (X=As, Se, Br, Sb, Te and I) in the H3S structure with [formula omitted] symmetry

The discovery of high critical temperature Tc superconductivity in highly compressed H3S has opened up the question of searching for strong electron–phonon coupling in the hydrides outside the transition metal series. The specific objective of this work is to explore the possibility of discovering a material that exceeds the superconducting transition temperature of H3S. Our study includes the materials H3X (X=As, Se, Br, Sb, Te, and I), is limited to the Im3¯m crystal structure. The procedure we adopt involves performing linearized augmented plane wave (LAPW) calculations for many different volumes to compute the electronic densities of states and their pressure variation. This is combined with Quantum-ESPRESSO (QE) calculations from which we obtain the phonon frequencies and the electron–phonon coupling constant λ, and followed by applying the multiple scattering-based theory of Gaspari and Gyorffy (GG) to obtain the Hopfield parameters and the McMillan–Allen–Dynes theory. It should be stressed that the GG approach decouples the electronic contribution to λ from the corresponding phonon contribution, and provides additional insights for the understanding of superconductivity in these materials. Based on our analysis, the hydrogen is the main contributor to the Tc in these materials as it makes up 75∼80 % of the total λ. Our calculations for H3Se and H3Br give a Tc∼100 K. For the other materials in our study we find that H3As is unstable and H3Sb, H3Te and H3I have small values of the McMillan–Hopfield parameters which makes it unlikely to give high Tc. However, according to both of our rigid band model and virtual crystal calculations, we predict a Tc∼150 K for H3Br with a small amount of hydrogen doping. Our basic conclusion is that the materials studied here could not reach very high Tc because the Hopfield parameters, which are the strongest contributor to high Tc, are not large enough.

Electronic and magnetic properties of 5d transition metal substitution doping monolayer antimonene: within GGA and GGA + U framework

The structure, electronic, and magnetic properties of 5d series transition metal atoms (TMs) (Hf to Hg) substitution doping antimonene are systematically investigated within the framework of the generalized gradient approximation density functional theory (DFT-GGA) calculations. Our results indicate that identical magnetic ground states are obtained both GGA and GGA with on-site Coulomb repulsion (GGA + U) methods, and the magnetic moment mainly arises from the localized 5d electrons of the 5d TMs. By selective doping different 5d TM atom, antimonene can be regulated from a spin non-polarized to spin-polarized semiconductor and metal. Interestingly, based on GGA + U level, we have demonstrated the spin-polarized semiconducting properties of Hf, Ta, W, Re, Os-substituted antimonene systems, and they can further transform into magnetic half-metallic by electronic or hole doping. Besides these, the weak magnetic coupling is found in the two identical TM impurity antimonene systems. The largest perpendicular magnetic anisotropy energy (MAE) manifests in Re@Sb, up to 18.33 meV in our research systems, and its physics origin of the large MAE is explored in detail in this article. These findings provide an efficient method to tune the physics properties of antimonene, supporting the potential application in the field of spintronics.

General trends in Horiuti-Polanyi mechanism vs non-Horiuti-Polanyi mechanism for water formation on transition metal surfaces

It is generally acknowledged in heterogeneous catalysis that hydrogenation follows the so-called Horiuti-Polanyi (HP) mechanism. In this work, a thorough investigation of the mechanism of hydrogenation of hydroxyl groups and O catalyzed by a series of transition metals was carried out through density functional theory calculations, as surface hydroxyls and O are very common species in many catalytic systems. It is found that different metal catalysts exhibit different mechanisms. On some metal catalysts, the non-HP mechanism is preferred, whereas the classic HP mechanism is favored on other catalysts. Detailed analyses of the metal-dependent mechanism shows that the activity toward the dissociation of H2 decides which mechanism is preferred. On active catalysts, such as Ni and Pt, H2 prefers to dissociate with strong H adsorption energies, which lead to the classic HP mechanism being favored. On inactive surfaces, on the other hand, the adsorption of H is weak, which results in the non-HP mechanism being preferred. The parameter η, which is a structural descriptor, was defined to understand the different mechanisms.

Exclusively catalytic oxidation of toluene to benzaldehyde in an O/W emulsion stabilized by hexadecylphosphate acid terminated mixed-oxide nanoparticles

A series of hexadecylphosphate acid (HDPA) terminated mixed-oxide nanoparticles have been investigated to catalyze the oxidation of toluene exclusive to benzaldehyde under mild conditions in an emulsion of toluene/water with the catalysts as stabilizers. With the HDPA-Fe2O3/Al2O3 as the basic catalyst, a series of transition metals, such as Mn, Co, Ni, Cu, Cr, Mo, V, and Ti, was respectively doped to the basic catalyst to modify the performance of the catalytic system, in expectation of influencing the mobility of the lattice oxygen species in the oxide catalysts. Under normally working conditions of the catalytic system, the nanoparticles of catalysts located themselves at the interface between the oil and water phases, constituting the Pickering emulsion. Both the doped iron oxide and its surface adsorbed hexadecylphosphate molecules were essential to the catalytic system for excellent performances with high toluene conversions as well as the exclusive selectivity to benzaldehyde. Under optimal conditions, ∼83% of toluene conversion and >99% selectivity to benzaldehyde were obtained, using molecular oxygen as oxidant and HDPA-(Fe2O3-NiO)/Al2O3 as the catalyst. This process is green and low cost to produce high quality benzaldehyde from O2 oxidation of toluene.

In vitro leishmanicidal activity of copper (II) 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine complex and analogous transition metal series

A series of triazolopyrimidine transition metals complexes have been synthesized by the reaction between the derivative 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) with M(NO3)2·XH2O (M = Cu(II), Co(II), Ni(II) and Zn(II)). These four compounds have been characterized by spectroscopic and thermal analysis and the crystal structure of the Cu(II) one has been solved by X-ray diffraction methods. The in vitro antiparasitic activity of these complexes against four leishmania spp. strands and their toxicity against macrophage host cells have also been studied, in order to elucidate the influence of different metal centres in the leishmanicidal effect to fight neglected tropical diseases.

A novel generalized metal dissolution approach for the synthesis of mixed valent mesoporous metal oxides

A novel approach is introduced to synthesize multivalent, mesoporous metal oxides with high surface area using zero oxidation state precursors. Herein, the synthesis and comprehensive characterization of the metal oxides of s block, p block, transition metal, and lanthanide series elements are reported. Some of the synthesized metal oxides showed mixed phases at relatively low temperatures which is advantageous over single-phase materials. The initial metal dissolution process allows this method to be extended to any metal in the periodic table and metal alloys. A green and highly efficient catalytic sp2-sp2 C–C coupling reaction is carried out using high surface area MoO3 (142 m2/g) where complete conversion is observed within one hour.

Enhanced activation of peroxymonosulfate with metal-substituted hollow MxCo3-xS4 polyhedrons for superfast degradation of sulfamethazine

Developing catalysts with high efficiency is a long-term goal of the sulfate radical-based advanced oxidation processes (SR-AOPs) for emerging contaminant degradations. In this work, a series of transition metal (Mn, Ni, Cu, Zn)-substituted hollow cobalt-based bimetallic sulfide polyhedrons (MxCo3-xS4) were fabricated using MOF-templated sulfuration strategy. The hollow structure supplied a highly reactive shell containing abundant exposed active sites while density functional theory (DFT) calculation revealed that metal substitution increased positive charge density of Co atoms and facilitated PMS adsorption on catalyst surface. The as-synthesized polyhedrons exhibited superior catalytic activities for sulfamethazine (SMT) degradation over a broad pH range (pH = 2–11). Mn0.3Co2.7S4 polyhedrons were selected as the target catalysts for the best performance with nearly 97% SMT was removed within 8 min with the apparent rate constant of 0.363 min−1, which was higher than those of reported researches by 3–4 times. Multiple reactive oxygen species including sulfate radical (SO4−·), superoxide radical (O2·−) and singlet oxygen (1O2) were determined to work by quenching test and electron paramagnetic resonance (EPR). Furthermore, the catalysts showed good reusability for SMT degradation in the presence of PMS over five runs. This work shed new light on the feasibility and superiority of metal substitution in synergistically improving the catalytic activity of cobalt sulfides, and provided a novel class of Co-based catalysts for recalcitrant contaminants degradation by SR-AOPs.

Multimetallic metal-organic frameworks derived transition metal doped iron selenide arrays for efficient oxygen evolution reaction

A feasible and general strategy based multimetallic metal-organic frameworks template is developed to fabricate hierarchical structured multimetallic selenide. The obtained series of transition metal doped iron selenide exhibit high performance for oxygen evolution reaction (OER). Especially, the Cu-doped FeSe2 electrocatalyst shows the lowest overpotential of 193 mV at a current density of 10 mA cm−2 which outperforms previously reported selenide-based electrocatalysts. The experimental results and theoretical simulations demonstrate that the doping of substitutional Cu in the host lattice of FeSe2 optimizes the electronic structure, being favorable for accelerating the electron transfer and boosting reaction kinetic. Meanwhile, the special structure design enables the electrocatalyst with hierarchical structures, affording rich exposed active sites for efficient OER. Therefore, this work provides a feasible strategy for fabricating hierarchical structured metal selenides for potential electrochemical energy storage and conversion.

Chemical weathering of garnet in Banded Iron Formation: Implications for the mechanism and sequence of secondary mineral formation and mobility of elements

Abstract The chemical weathering of rocks and minerals on the Earth’s surface leads to the mobilization and redistribution of elements and has (a) significant control on the chemistry of the soil-hydrosphere-atmosphere system, (b) a profound effect on the bioavailability and toxic effects of elements, and (c) applications in mineral exploration among others. In this study, we describe the sequential weathering of spessartine- and pyrope-bearing almandine garnet in metamorphosed banded magnetite quartzite from the Khetri Copper Belt, western India. Based on detailed microtextural relations the following sequence of garnet weathering is proposed: garnet → alumo-goethite1 → alumo-goethite2 → kaolinite ± (monazite + xenotime ± thorite) → haematite. Our study thus reports for the first time the presence of alumo-goethite, kaolinite, monazite, xenotime, and thorite in weathering assemblage of garnet. The sequential chemical weathering of garnet was both grain boundary-controlled and fracture-controlled. Tectonic fractures (developed during exhumation), reaction-induced fractures (developed due to volume expansion), and secondary porosity (developed due to volume reduction) collectively controlled the propagation of weathering. Integrating multiple lines of evidence, e.g., corrugated contact between the weathering phases, presence of pores, relative molar volume changes, and high mobility of most elements it is argued that the weathering progressed through an interface-coupled dissolution-precipitation process. In situ major and trace element measurements and mass balance calculations show that several major (Fe, Na, K, P) and trace elements (Cl, F, alkalis, alkaline earth elements, and first series transition and base metals) were added while Si, Al, Ca, Mg and Mn were lost during the garnet to alumo-goethite transformation. During kaolinitization, all the major elements except Si and Al were lost to the weathering fluid. The alkali and alkaline earth, first series transition elements, base metals excepting Cr were lost during this weathering stage. Phosphorous, REEs, and Th were locally immobilized as monazite, xenotime, and thorite. In the more advanced stages of weathering, kaolinite was replaced by haematite. This stage involved re-addition of several major (except Al and Si) and trace elements. It is seen that although alumo-goethite, kaolinite, and haematite can host significant quantities of several trace elements, alumo-goethite and haematite have a much better potential of immobilizing most trace elements including toxic ones compared to kaolinite in the weathering profile.