Isomorphous Substitution Research Articles

Minerals with a palmierite-type structure. Part II. Nomenclature and classification of the palmierite supergroup.

AbstractThe palmierite supergroup, approved by the IMA-CNMNC, includes five mineral species characterised by the general crystal-chemical formula XIIM1XM22(IVTO4)2 (Z = 3). On the basis of the crystal-chemical arguments and heterovalent isomorphic substitution scheme M++T6+ ↔ M2++T5+, the palmierite supergroup can be formally divided into two groups: the palmierite group M12+M22+(T6+O4)2, and the tuite group M12+M222+(T5+O4)2. Currently, the palmierite group includes palmierite K2Pb(SO4)2, and kalistrontite K2Sr(SO4)2, whereas the tuite group combines tuite Ca3(PO4)2, mazorite Ba3(PO4)2, and gurimite Ba3(VO4)2. The isostructural supergroup members crystallise in space group R$\bar{3}$m (no. 166). The palmierite-type crystal structure is characterised by a sheet arrangement composed of layers formed by M1O12 and M2O10 polyhedra separated by TO4 tetrahedra perpendicular to the c axis. The abundance of distinct ions, which may be hosted at the M and T sites (M = K, Na, Ca, Sr, Ba, Sr, Pb, Rb, Zn, Tl, Cs, Bi, NH4 and REE; T = Si, P, V, As, S, Se, Mo, Cr and W) implies many possible combinations, resulting in potentially new mineral species. Minerals belonging to the palmierite supergroup are relatively rare and usually form under specific conditions, and their synthetic counterparts play a significant role in various industrial applications.

Enhancing the Immobilization of Hexavalent Chromium by the Interlayer Anion Adsorption of the Brucite-Transformed LDH in the Presence of Aluminum Ions

Current studies of chromium adsorption kinetics at the solid–liquid interface often neglect the influence of coexisting ions in complex wastewaters. Thus, it is critical to explore the hexavalent chromium Cr(VI) adsorption kinetics of solid-phase brucite (Mg(OH)2) in liquid-phase wastewater containing coexisting aluminum ions (Al(III)). This paper reveals that the presence of Al(III) significantly enhanced the Cr(VI) adsorption efficiency onto Mg(OH)2, with a peak of up to 91% compared to 5% for the absence of Al(III). The main reason for this enhancement was the initial surface ternary complexation of Mg(OH)2 and the cationic (Al(III)) isomorphic substitution to form Mg(II)-Al(III) layered double hydroxides (LDH), which also indicates a solid-phase transition on the surface of Mg(OH)2, which led to electrostatic adsorption in the gallery and made Cr(VI) immobilized and not readily released. Further calculation and analysis of the adsorption energy confirmed the mechanism of Cr(VI) adsorption. It was also concluded that Cr(VI) migration in Mg(OH)2-containing minerals was affected by the phase transformation of solids in the presence of Al(III). Hence, this study not only reveals the adsorption mechanism during the treatment of composite pollutant wastewater but also provides the methodological reference for brucite synergistic adsorption to remove heavy metal ions and purify and treat complex polluted wastewater.

Geochemical Characteristics of Garnet from Zinc–Copper Ore Bodies in the Changpo–Tongkeng Deposit and Its Geological Significance

The Changpo–Tongkeng tin polymetallic deposit in Dachang, Guangxi, is a world-class, superlarge, polymetallic tin deposit consisting of lower skarn zinc–copper ore bodies and upper tin polymetallic ore bodies. Garnet is the main gangue mineral in the skarn zinc–copper ore bodies and has a granular texture. Based on hand specimens and microscopic observations, the existing garnet can be divided into two generations: an early generation (Grt I) and a late generation (Grt II). The results of electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in situ microanalysis show that the contents of SiO2 and CaO in the garnets from the two generations present limited variations, while the FeOT and Al2O3 contents vary significantly, indicating the grossular–andradite solid solution series (Gro29–82And12–69). Compared with Grt I (Gro72And25), Grt II (Gro39And59) is Fe-enriched and oscillatory zoning is developed. The total rare earth element (REE) contents in the two generations of garnet are relatively low, showing light rare earth element (LREE) depletion and heavy rare earth element (HREE) enrichment patterns. Grt II has higher REE content than Grt I and exhibits significant negative Eu anomalies (δEu = 0.18–0.44). The contents and variation characteristics of the major and trace elements in the two generations of garnet suggest that there were variable redox conditions and water/rock ratios in the hydrothermal system during the crystallization process of garnet. In the early stage, skarnization was in a relatively closed and low-oxygen fugacity system, with hydrothermal diffusion metasomatism being dominant, forming homogeneous Grt I lacking well-developed zoning. In the late stage of skarnization, the oxygen fugacity of the ore-forming fluids increased, with infiltration metasomatism being dominant, forming Grt II with well-developed oscillatory zoning. The contents of Sn, As, W, In, and Ge in the garnets are relatively high and increase with the proportion of andradite. Sn in zinc–copper ore bodies mainly exists in the form of isomorphic substitution in garnet, which may be the main reason for the lack of tin ore bodies during the skarn stage. This paper compares the trace element contents in garnets from domestic skarn deposits. The results indicate that the Sn content and δEu in garnet can be used to evaluate the tin-forming potential of skarn deposits.

Effect of coordination structure of aluminum on its activation from minerals and Oxisols during their acidification

The types and contents of phyllosilicate minerals in soils play an important role in soil acidification, as soil acid buffering capacity varies with the composition of the phyllosilicate minerals. In addition to aluminum-oxygen (Al-O) octahedrons, a certain number of Al-O tetrahedrons exist in phyllosilicate minerals due to the isomorphic substitution of silicon ion (Si4+) by aluminum ion (Al3+) in Si-O tetrahedrons of minerals. However, the effect of the two coordination structures of Al on the release of Al during mineral acidification has not yet been investigated. Therefore, the differences in Al activation in phyllosilicate minerals and soils with different Al coordination structures were investigated through constant-pH experiments and 27Al magic-angle spinning nuclear magnetic resonance (MAS-NMR) measurements. The results of 27Al MAS-NMR spectra showed that kaolinite contained Al-O octahedrons, phlogopite and illite contained Al-O tetrahedrons, and vermiculite composite contained both octahedral and tetrahedral Al. At pH < 5.1, the content of Al released from minerals during simulated acidification followed the order: illite > vermiculite composite > phlogopite > kaolinite, which was consistent with the orders of cation exchange capacity and content of tetrahedral Al of the minerals. According to the rate constants, the Al release rates were in the order of phlogopite > illite > vermiculite composite > kaolinite at pH 4.8. Except for phlogopite, the Al release rates in these minerals increased with decreasing suspension pH. Therefore, the Al release contents and rates were greater in phlogopite, illite, and vermiculite composite containing Al-O tetrahedrons than in kaolinite containing only Al-O octahedrons. Two Oxisols derived from basalt with different ages were selected for similar studies. The 27Al MAS-NMR spectra of the Oxisols showed that the 0.01-million-year (Ma) Oxisol contained both octahedral and tetrahedral Al, while the 1.33-Ma Oxisol contained only Al-O octahedrons. The contents of both exchangeable and soluble Al released from the 0.01-Ma Oxisol were greater than those from the 1.33-Ma Oxisol when the two soils were acidified to the same pH. The results from minerals and soils confirmed that Al was more readily released into solution and exchangeable sites as soluble and exchangeable Al in Al-O tetrahedrons than in Al-O octahedrons during the acidification of soils and minerals. The findings of this study will provide useful references for investigating the mechanisms of solid phase Al release and for mitigating soil acidification and inhibiting Al activation in different soil types.

Efficient lead removal from aquatic solution by (Co0.7Zn0.3)0.9Ni0.1Fe2O4 ferrite with tunable optical and magnetic properties.

A new material based on (Co0.7Zn0.3)0.9Ni0.1Fe2O4 ferrite was prepared by using a flash auto-combustion method. The characterization of XRD, SEM, EDX, FTIR, and VSM analysis presented that the (Co0.7Zn0.3)0.9Ni0.1Fe2O4 nanoferrite was prepared in single phase with crystallite size 32 nm and had dislocation density about 9.8 × 10−4 nm−2. EDS spectrum confirms the presence of constituting metal ions in (Co0.7Zn0.3)0.9Ni0.1Fe2O4 ferrite which is well-comparable with the standard stoichiometric ratios. VSM exhibits narrow loop with saturation magnetization about 67.076 emu/g, this is related to ferromagnetic and soft magnetic materials. Values of the energy band gap are 3.8 and 4.8 eV for the indirect and direct transition. The removal efficiency of the (Co0.7Zn0.3)0.9Ni0.1Fe2O4 nanoferrite was evaluated using adsorbing Pb(II) as typical heavy metals. Batch adsorption experiment was used to study the effects of pH of the aqueous solution, as well as contact time. Moreover, we examined the adsorption mechanism, isotherms, and kinetics. The removal efficiency of the (Co0.7Zn0.3)0.9Ni0.1Fe2O4 nanoferrite for Pb(II) adsorption was 99 % at pH 7 after 40 min, besides the isothermal data followed Langmuir isotherm model. While, kinetic data obeyed pseudo-second-order model. The (Co0.7Zn0.3)0.9Ni0.1Fe2O4 nanoferrite and heavy metal ions interacted by the following mechanisms: surface complexation, precipitation, and isomorphic substitution.

Effect of cobalt isomorphic substitution on the properties of goethite and the adsorption of lead

Iron oxides are ubiquitous in the environment and often contain impurities because of their substitution by Al, Mn, Co, and other metals. However, few studies have focused on Co substitution and subsequent Pb(II) adsorption on its surfaces. Herein, the effect of the isomorphic substitution of Co on the physiochemical properties of goethite and the atomic-level mechanisms of lead sorption in relation to structural changes were investigated in this work. The results showed that Co substitution reduced the unit cell parameters and crystallinity of goethite. More Fe-OH groups on the surface were exposed with Co substitution, leading to the preferential sorption of Pb. The DFT calculations further revealed that the valence band was shortened and the total density of states was more biased towards the Fermi level in Co-substituted goethite, making the surface electrons more active. In addition, both Pb2+ and Pb(OH)+ were adsorbed by goethite, forming a tridentate complex with three oxygen atoms. In this process, sp3 hybridization mainly occurred. These results provide a new perspective for studying the properties of Co-substituted goethite and its reaction with lead, helping to expand the application of DFT calculations to simulate and predict the fixation and mobilization of heavy metals in goethite-rich soils/sediments.

Atomic Arrangement, Hydrogen Bonding and Structural Complexity of Alunogen, Al2(SO4)3·17H2O, from Kamchatka Geothermal Field, Russia

Alunogen, Al2(SO4)3·17H2O, occurs as an efflorescent in acid mine drainage, low-temperature fumarolic or pseudofumarolic (such as with coal fires) terrestrial environments. It is considered to be one of the main Al-sulphates of Martian soils, demanding comprehensive crystal-chemical data of natural terrestrial samples. Structural studies of natural alunogen were carried out in the 1970s without localization of H atoms and have not been previously performed for samples from geothermal fields, despite the fact that these environments are considered to be proxies of the Martian conditions. The studied alunogen sample comes from Verkhne–Koshelevsky geothermal field (Koshelev volcano, Kamchatka, Russia). Its chemical formula is somewhat dehydrated, Al2(SO4)3·15.8H2O. The crystal structure was solved and refined to R1 = 0.068 based on 5112 unique observed reflections with I &gt; 2σ(I). Alunogen crystalizes in the P-1 space group, a = 7.4194(3), b = 26.9763(9), c = 6.0549(2) Å, α = 90.043(3), β = 97.703(3), γ = 91.673(3) °, V = 1200.41(7) Å3, Z = 2. The crystal structure consists of isolated SO4 tetrahedra, Al(H2O)6 octahedra and H2O molecules connected by hydrogen bonds. The structure refinement includes Al, S and O positions that are similar to previous structure determinations and thirty-four H positions localized for the natural sample first. The study also shows the absence of isomorphic substitutions in the composition of alunogen despite the iron-enriched environment of mineral crystallization. The variability of the alunogen crystal structure is reflected in the number of the “zeolite” H2O molecules and their splitting. The structural complexity of alunogen and its modifications ranges from 333–346 bits/cell for models with non-localized H atoms to 783–828 bits/cell for models with localized H atoms. The higher values correspond to the higher hydration state of alunogen.

Ti-MWW synthesis via acid-modulated isomorphous substitution of ERB-1 for efficient ethylene oxidative hydration to ethylene glycol

Although the oxidative hydration of ethylene with hydrogen peroxide (H2O2) to ethylene glycol (EG) over Ti-MWW zeolites take advantages of step-saving and facile operation, both H2O2 utilization efficiency and EG yield are relatively low, because some extra-framework octahedral Ti species are usually formed in the Ti-MWW zeolites synthesized by prevailing methods, which are detrimental to selective oxidation. In the present work, an acid-modulated isomorphous substitution method, i.e., layered borosilicate MWW-type zeolite (ERB-1) treated with HNO3 aqueous solution containing tetrabutyl orthotitanate (TBOT), is developed to synthesize a Ti-MWW zeolite without extra-framework octahedral Ti species under the optimized synthesis conditions. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that in the zeolite prepared by the currently developed synthesis method there are more open Ti(OSi)3OH sites formed, resulting in the stronger Lewis acidity that is very helpful to EG production from the oxidative hydration of ethylene with H2O2, compared to the one synthesized by the prevailing method. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by calcination at high temperatures. Therefore, it is anticipated that the currently developed Ti-MWW might be industrially applicable in the one-pot synthesis of EG from ethylene with H2O2.

Sulfidation of Ni-bearing goethites to pyrite: The effects of Ni and implications for its migration between iron phases

Goethite and pyrite are common iron minerals in oxic or anoxic environments, respectively, both minerals being major reservoirs for Nickel, a bio-essential element. Mineral transformation between goethite and pyrite is frequent owing to the alternation of oxic and anoxic conditions in sulfate-rich environments. This mineral transformation has been amply studied, but the effect of Ni on this transformation and its fate along it remain poorly understood. Sulfidation of Ni-free and Ni-containing (through adsorption or isomorphic substitution) goethites was thus studied experimentally by reacting goethite with dissolved S(-II) (molar Fe:S≈1:1). X-ray diffraction and associated Rietveld refinement, thermogravimetric analysis, scanning/transmission electron microscopy, X-ray absorption spectroscopy, and wet chemistry were used to monitor mineralogical evolutions and unravel Ni association with reaction products. After 44 days of sulfidation, about half of initial goethite converted to iron sulfides: thermodynamically stable pyrite (67%–93%) with minor contents of mackinawite (2%–15%) and greigite (5%–25%). Although the overall content of iron sulfides formed was essentially independent of Ni presence, Ni hampered the conversion from metastable iron sulfides (i.e., mackinawite and greigite) to pyrite (67%–78% vs. 93%, in the presence and absence of Ni, respectively). Pyrite formation from metastable sulfide precursors yielded a uniform Ni distribution in newly formed pyrite, regardless of the initial Ni association with goethite. Although no Ni was released to solution during pyrite formation, Ni incorporation to pyrite results in an increased risk of release to the environment as iron sulfides will be oxidized when exposed to air and water in supergene environments, leading to highly acidic conditions favoring Ni solubility and mobility.

Origin of Fe-rich clay minerals in Early Devonian volcanic rocks of the Northern Minusa basin, Eastern Siberia

The formation of clay minerals in volcanic successions follows various evolutionary trends, the understanding of which is crucial for estimating the age of volcanism and the prospecting clay deposits. Early Devonian volcanics within the Byskar Series of the Minusa Depression (Khakassia) are variably altered to a range of phyllosilicate mineral assemblages. This study highlights the origin and formational conditions of the clay minerals, including illite, glauconite, smectite (saponite) and chlorite. Detailed mineralogical and chemical investigation identifies the predominant phyllosilicates, including 1 M illite, illite-smectite (R = 3), 1 M glauconite, smectite, chlorite and kaolinite within trachyandesite, trachyte, and rhyodacite. The phyllosilicates formed by the diagenetic transformation of volcanics after eruptive phases. Evolution trends of phyllosilicates depend largely on the composition of the volcanic substrate. The smectite to illite trend developed due to the dissolution of felsic volcanics and the alteration of smectites into illites with the K+, Al3+ and Mg2+ dominating the mineral formation system. The illites evolved by the substitution of Fe2+ and Mg2+ for Al3+ in the octahedral sheets of smectites. The K+, which was released due to devitrification of felsic substances, was introduced into the interlayer sites for compensating the layer charge originated by the isomorphic substitution in tetrahedral and octahedral sheets. The smectite to glauconite transition trend corresponds to the devitrification and dissolution of alkaline intermediate-felsic volcanics. Early formed dioctahedral smectites evolved into glauconite probably with the predominance of K+ and Fe2+/3+ ions in the formation environment. The substitution of Fe2+/3+ to Al3+ and Mg2+ in the octahedral sheets of smectite contributed to the formation of a layer charge and the entry of exchangeable K+ into the interlayers of glauconite. The third trend involved the formation of smectites (saponites) or chlorites within the intermediate volcanics possibly with Mg-rich but K-poor mineral system.

Efficient Adsorption Capacity of MgFe-Layered Double Hydroxide Loaded on Pomelo Peel Biochar for Cd (II) from Aqueous Solutions: Adsorption Behaviour and Mechanism.

A novel pomelo peel biochar/MgFe-layered double hydroxide composite (PPBC/MgFe-LDH) was synthesised using a facile coprecipitation approach and applied to remove cadmium ions (Cd (II)). The adsorption isotherm demonstrated that the Cd (II) adsorption by the PPBC/MgFe-LDH composite fit the Langmuir model well, and the adsorption behaviour was a monolayer chemisorption. The maximum adsorption capacity of Cd (II) was determined to be 448.961 (±12.3) mg·g-1 from the Langmuir model, which was close to the actual experimental adsorption capacity 448.302 (±1.41) mg·g-1. The results also demonstrated that the chemical adsorption controlled the rate of reaction in the Cd (II) adsorption process of PPBC/MgFe-LDH. Piecewise fitting of the intra-particle diffusion model revealed multi-linearity during the adsorption process. Through associative characterization analysis, the adsorption mechanism of Cd (II) of PPBC/MgFe-LDH involved (i) hydroxide formation or carbonate precipitation; (ii) an isomorphic substitution of Fe (III) by Cd (II); (iii) surface complexation of Cd (II) by functional groups (-OH); and (iv) electrostatic attraction. The PPBC/MgFe-LDH composite demonstrated great potential for removing Cd (II) from wastewater, with the advantages of facile synthesis and excellent adsorption capacity.

Removal, recycle and reutilization of multiple heavy metal ions from electroplating wastewater using super-stable mineralizer Ca-based layered double hydroxides

From an environmental and resource management perspective, it is preferable to recover and reuse heavy metal ions found in electroplating wastewater. The discharge of electroplating wastewater has caused serious environmental pollution and resource waste. Ca-based layered double hydroxides (LDHs) stabilizers are designed, which show a rapid, effective, and adequate capacity exceeding 400 mg/g against solutions of Cu2+, Zn2+, Co2+, and Ni2+ ions through an isomorphous substitution mechanism. The needs of plant development were met by the use of CaAl-LDH in soil remediation. While Cu resources can be recovered from the CuAl-LDH products by electrolysis, the final mineralization products from Ni2+ and Zn2+ ions showed exceptional performance in visible-light-induced photocatalytic reduction of CO2 with excellent selectivity (98.7% toward CO and CH4) and the removal of arsenite ions (99.97%). The results of this investigation revealed a feasible new approach to the removal, recycling, and reutilization of heavy metal ions.

Simultaneously enhanced aromatics selectivity and catalyst lifetime in methanol aromatization over [Zn, Al]-ZSM-5 via isomorphous substitution with optimized acidic properties and pore structure

Zinc-modified HZSM-5 zeolites as efficient catalysts have been widely applied in methanol to aromatics (MTA) reactions, however, the relationship between aromatics selectivity and catalytic stability in traditionally loaded catalysts seems to be a stubborn trade-off. To improve both catalytic indicators simultaneously and reveal the relation of the states of introduced Zn species to the consequential influence in physiochemical properties, a series of [Zn, Al]-Z5 zeolites with different Zn contents were prepared via isomorphous substitution under a fixed Si/Me (Me = Al or Al and Zn) ratio. Results revealed that there were three possible states of the introduced Zn species, namely the highly-dispersed ZnO phase, the Zn(OH)+ occupying the ion-exchange sites, and the tetra-coordinated ZnO42- integrated into the zeolite framework. A portion of Zn was successfully integrated into the five-membered rings of zeolite in the form of Si-O(H)-Zn, which played the role of strong Brönsted acid sites and led to the formation of hierarchical structures aside from the intrinsic micropores. Besides, extra-framework Zn(OH)+ was formed by the interaction between dissociate Zn species and the Si-O(H)-Al structure, giving rise to larger proportions of Lewis acid sites. Benefitting from the optimized acidic properties and pore structure, 0.5[Zn, Al]-Z5 exhibited higher aromatics selectivity and longer catalyst lifetime (26.0% and 132 h) than [Al]-Z5 without Zn addition (19.6% and 52 h) in methanol aromatization. Overall, our findings opened a new way to improve the efficiency of MTA reaction and broadened the method to obtain metal-modified zeolite catalysts.

Synthesis and Characterization of Biphasic Calcium Phosphate Substituted Cerium as a Potential Osteoporotic Bone Filler

Biphasic calcium phosphate substituted cerium (BCP/Ce) is a potential material for osteoporotic bone filler. Synthesis of BCP/Ce was conducted by the sol-gel method. This work aimed to study the influence of cerium as a precursor on the crystal structures, surface properties, and agglomeration of BCP/Ce. A series of samples were prepared by various Ce percentages (0.5–16%) and a constant molar ratio of (Ca + Ce)/P = 1.2. A structural study by Rietveld refinement calculation confirmed that synthesis without Ce produced BCP that contained hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) at a ratio of 93:7. The presence of Ce increased β-TCP content to 73% for the use of Ce 8%. None of Ca in the HA structure was replaced by Ce. Otherwise, Ce replaced Ca in β-TCP structure by isomorphic substitution at the Wyckoff site of 6a (0,0,-0.085) or Ca (4) position. As the maximum occupancy of Ca (4) = 43%, about 17% of that was substituted by Ce for the use of 14% Ce. Ce was found in two states as Ce3+ and Ce4+ ions with Ce3+/Ce4+ ratio &gt; 1. The presence of Ce on the particle surface caused a change in the particle shape, from plate-like to spherical. The particle size decreased to &lt;100 nm with the increase of Ce content. The rise of Ce content in BCP decreased the luminescent property due to the increase of oxygen vacancies. The negative value of Zeta potential confirms that BCP/Ce surface can accommodate bone cell proliferation.

Insight into the Mechanism of Cd2+ Removal by MgAl Layered Double Hydroxides with Different Host-Guest Interactions.

Layered double hydroxides (LDHs) have shown great potential as adsorbents for the removal of heavy metals. Nevertheless, how the host-guest interactions of LDHs affect the removal mechanism remains to be less explored. Herein, CO3 2- /NO3 - /SO4 2- /Cl- intercalated MgAl-LDHs with different host-guest interactions were fabricated and their removal mechanism for Cd2+ was investigated. The removal capacity increased in the order of MgAl-CO3 (127.3 mg/g)<MgAl-SO4 (173.3 mg/g)<MgAl-NO3 (305.0 mg/g)≈MgAl-Cl (312.5 mg/g). The quasi-in-situ XRD and XAS demonstrated that Cd2+ was removed as CdCO3 for MgAl-CO3 , while for MgAl-Cl/NO3 /SO4 , Cd2+ was removed as CdAl-LDHs by an isomorphic substitution mechanism. DFT calculations revealed that compared to the CdAl-LDHs formation the Gibbs free energy of the CdCO3 formation was lower, which made it easier to remove Cd2+ as CdCO3 on MgAl-CO3 . Conversely, isomorphic substitution of MgAl-NO3 to obtain CdAl-LDHs was a free energy reduction process.

Эластопроводимость германеновых нанолент с изоморфными дефектами замещения

The results of the theoretical study of the impurity germanium nanoribbons piezoresistance are demonstrated in this article. The nanomaterial contains point isomorphic substitution defects of different concentrations of two types of isomorphic atoms of group IV: silicon (Si) and tin (Sn). The functions of the dependence of the longitudinal component of the elastic conductivity tensor on the magnitude of the strain of tension (compression), types and concentrations of defects are presented to study the characteristics of the piezoresistance effect. The results of the calculations show a qualitative agreement of the behavior of the piezoresistance constant of germanene nanoribbons for two types of isomorphic defects and with the literature data. Quantitative analysis allows us to conclude that the longitudinal component is higher in modulus in nanofilms with tin impurities, which indicates a more pronounced piezoresistance of the material. Conclusions are showed, that the impurity germanene with the tin atoms manifested more pronounced piezoresistance properties. It was be explained by high the electron mobility of the valence shell of this element compared to the germanium atom. This shell of the atom turns out to be more sensitive to deformations of the structure. Such material can be more effectively integrated as a basic element of semiconductor electronics devices due to the high susceptibility of its properties to the effects of deformations and the concentration of structural defects in accordance with this factor.

Efficient and Superstable Mineralization of Toxic Cd2+ Ions through Defect Engineering in Layered Double Hydroxide Nanosheets

Water and soil pollution caused by toxic cadmium ions (Cd2+) is a serious threat to animals, plants, and human health. Discovering low-cost mineralizers which can efficiently and stably immobilize Cd2+ ions is therefore imperative for wastewater treatment and soil remediation. In this work, we report the successful development of a novel mineralizer for Cd2+ ion capture. A magnesium–aluminum layered double hydroxide (MgAl-LDH) with a monolayer structure (MgAl-mono) was first prepared and then calcined at 350 °C for 4 h to produce a defective MgAl-mono-350. MgAl-mono-350 offered a very high Cd2+ removal capacity (1385.5 mg/g at 25 °C) and the ability to reduce the concentration of Cd2+ in aqueous solution from 100 ppm to less than 50 ppb in 15 min (meeting the discharge standard of industrial wastewater). Detailed characterization and computational studies revealed that MgAl-mono-350 possessed abundant oxygen defects, thereby enabling superstable mineralization of Cd2+ via isomorphous substitution process,and the Cd2+ ions are immobilized in the generated CdAl-LDH structure. MgAl-mono-350 also offered outstanding selectivity for Cd2+ ions over other common ions. This work demonstrates the potential of defect-engineered LDH materials for the selective removal of heavy metals from polluted water.

Chemical speciation of phosphorus in farmland soils and soil aggregates around mining areas

Phosphorus (P) speciation determines its bioavailability, mobility, and environmental risk in soils. Farmland soils around mining areas are worldwide distributed, yet the P speciation in such soils remains poorly understood. In this study, we determined the P speciation in the farmland soils and soil aggregates around mining areas from China and evaluated their relationship with soil pH and Fe/Al fractions using chemical extraction, P K-edge X-ray absorption near-edge (XANES) spectroscopy, and correlation analysis. Chemical extraction revealed that soil P was dominated by inorganic P (Pi) (68.0 – 82.5%) largely associated with pedogenic Fe/Al oxides (43.4% – 94.8%). The P was mainly adsorbed and occluded by Fe/Al oxides in acidic soils, while predominantly existed as Ca-P and occluded species in alkaline soils. The presence of heavy metals appeared to have no significant effect on P speciation in these soils. Compared with the macroaggregates, the available P, total P, and their ratio all increased dramatically in the soil colloids (< 0.002 mm) due to the accumulation of Fe/Al oxides. The XANES analysis indicated that the P speciation in the acidic soils and soil aggregates was dominated by Fe-P, followed by Al-P, and little Ca-P; in contrast, the proportions of Ca-P increased but Fe-P decreased in the alkaline soils and soil aggregates. Compared with the macroaggregates, the proportions of Fe-P increased while Ca-P decreased in the soil colloids. Correlation analysis indicated that amorphous Al and isomorphic substitution Al played critical roles in P immobilization by pedogenic Fe/Al oxides. These new insights into the P speciation are essential for environmental risk assessment and efficient utilization of P in the farmland soils.

Spectral and quantum mechanical investigation of calcium apatites isomorphically substituted in the anionic sublattice

The evolution of the valence band, the charge states of atoms, and the optical and vibrational spectra in Ca10(PO4)x(VO4)y(AsO4)z(OH)2 (x + y + z = 6) compound with three different types of oxygen tetrahedra have been studied by XPS, IR, and optical spectroscopy with the use of quantum mechanical calculation methods in the DFT approximation. It is shown that the occupied part of the valence band of compounds with three different types of tetrahedra has a pronounced band character with varying lengths of individual subbands. Two structural regions separated by energy are observed: the valence band's upper part and the valence band's lower part (subvalent states). The structure of the valence band's middle part, the region of valence states with energies from ∼ 13.0–19.0 eV, is weakly expressed. The sublattice of oxygen tetrahedra is decisive in forming the shape and the main features of the total density of electronic states of the compounds under study. The vibrations anharmonicity in the crystal lattice of such compounds can vary depending on the concentration of tetrahedra of a specific type. Such changes are local, and with the help of directed substitutions, it is possible to create the required spatial distribution of the anharmonic component over the crystal.The design of the calcium apatites structure by the method of isomorphic substitutions of (XO4) tetrahedra with tetrahedra of various types and with different ratios makes it possible to control the energy band gap width.

Effect of Isomorphous Substitutions in Calcium Triphosphate, Ca3(PO4)2, on the Microstructural and Chemical Properties of Phosphate Cements Prepared from It

Effect of Isomorphous Substitutions in Calcium Triphosphate, Ca3(PO4)2, on the Microstructural and Chemical Properties of Phosphate Cements Prepared from It