Substitutional Adsorption Research Articles

Pb2+ and Cd2+ ion adsorption capability of a novel hydrotalcite-like absorbent FeMnNi-LTH in water

This paper discusses the application of a layered triple hydroxide (FeMnNi-LTH) in removing Pb2+ and Cd2+ ions from aqueous solutions. The material was synthesized via co-precipitation, adhering to a molar ratio of 1:1:2 (Fe:Mn:Ni). It was characterized using FTIR, XRD, SEM and TEM. The results indicate that the synthesized material is classified as a hydrotalcite and exhibits a well-defined layered structure. Batch experiments were conducted to investigate the adsorption of Pb2+ and Cd2+ by FeMnNi-LTH, taking into account various factors such as coexisting ions, pH, temperature, adsorbent dosage, and contact time. The experimental results showed that the adsorption capacity of this material for Pb2+ and Cd2+ was 253.89 mg/g and 56.90 mg/g at 25 °C, respectively. Moreover, it exhibits a consistent high adsorption capacity across a broad pH range (pH 3–5.5). When cations coexist, they compete for adsorption sites in the following order: Zn2+ > Ca2+ > Mg2+ > Cd2+/Pb2+. Based on the calculated thermodynamic parameters, it is inferred that the adsorption process is endothermic and spontaneous. The adsorption mechanism, as analyzed by modeling and characterization, involves isomorphic substitution, surface complexation, precipitation, electrostatic attraction, and physical adsorption. The quantitative analysis of the adsorption mechanism revealed that FeMnNi-LTH primarily adsorbs Pb2+ and Cd2+ via precipitation and surface complexation. It was revealed by comparison with other adsorbents that the synthesized FeMnNi-LTH can be used for remediation of heavy metal pollution in water.

Employing dolomite as magnesium source to prepare calcined layered double hydroxides for chromium contaminated soil treatment: Exploring the influence of temperature, bioavailability, and microbial diversity

Layered double hydroxides (LDH-D) and their calcined counterparts, using dolomite as a source of magnesium, were utilized for the immobilization of chromium (Cr(VI)) in soil. The results indicate that LDH-D, both with and without varying calcination temperatures, can effectively immobilize Cr(VI) in soil. Among the different calcination temperatures tested, LDH-D subjected to calcination at 500 °C (LDH-D-500) showed particularly high efficacy. Long-term TCLP experiments demonstrated the inhibition of soil-to-plant transmission of Cr(VI), thereby highlighting the long-lasting immobilization capacity of LDH-D and its calcined derivatives. Furthermore, the analysis of the microbial community's adaptation in post-remediation soil confirmed the durability and bioavailability of LDH-D-500 for Cr immobilization. Examination of the material's morphology and structure after immobilization shed light on the mechanism of immobilization in soil. The results revealed that interlayer anion exchange and surface adsorption were the main factors responsible for the effective immobilization of LDH-D and LDH-D-300. On the other hand, LDH-D-900, with a dominant spinel (MgAl2O4) structure, faced challenges in returning to its original layered configuration, making surface adsorption the primary mechanism for immobilization. LDH-D-500 primarily relied on the structure memory effects of LDHs to immobilize Cr(VI) through structural recovery processes, facilitated by electrostatic attraction and surface adsorption. It is also important to note that CaCO3 plays an important role in adsorption. Additionally, a portion of Cr(VI) was converted to Cr(III) through phenomena such as isomer substitution and complexation adsorption. The proficiency of LDH-D-500 in immobilizing Cr, its ability for instantaneous separation, and the potential for regeneration make it a promising material for remediation of heavy metal-contaminated soil. The investigations suggest that the use of dolomite to create hydrotalcite and calcining it at 500 °C could effectively render environmental Cr inactive, thereby optimizing resource utilization.

Developed Recyclable CaFe-Layered Double Hydroxide for Efficient Cadmium Immobilization in Soil: Performance and Bioavailability

Powdered layered double hydroxide (CaFe-LDH) was synthesized via hydrothermal co-precipitation, demonstrating successful preparation upon characterization. Subsequently, experiments were conducted to assess its efficacy in immobilizing divalent cadmium (Cd(II)). The findings substantiated the effectiveness of CaFe-LDH in immobilizing Cd(II) within soil. Various influencing factors, including LDH dosage, pH, and soil heavy metal concentration, were systematically investigated, revealing CaFe-LDH’s superiority in Cd(II) immobilization. Notably, the leaching concentration of Cd(II) was notably reduced from 142.30 mg/L to 32.99 mg/L, with a maximum adsorption capacity of 31.10 mg/L, underscoring the significant role of CaFe-LDH in Cd(II) removal. Furthermore, the stability of CaFe-LDH was confirmed via toxicity characteristic leaching procedure (TCLP) experiments and plant potting tests. In-depth analysis of the immobilization mechanism through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) elucidated isomorphous substitution and surface adsorption as the primary mechanisms responsible for Cd(II) immobilization in contaminated soils. Additionally, isomorphic substitution and adsorption onto oxygen-containing functional groups were observed. This comprehensive study underscores the promising potential of CaFe-LDH in immobilizing Cd(II) in contaminated soil. With its commendable immobilization properties and recyclability, CaFe-LDH emerges as a promising solution for remediating heavy-metal-contaminated soils.

Non-Metal Doping as a First-Principles Study for Promoting the Hydrogen Evolution of Two-Dimensional Electride Y2C Electrocatalysts

The two-dimensional electrochemical Y2C’s low work function and strong charge transfer qualities limit its applicability in catalysis due to its poor catalytic activity. In this paper, based on density functional theory calculations, we use two techniques to increase the HER catalytic activity of the Y2C monolayer: substitution doping (XC) and adsorption doping (XT) of non-metal (X = N, P, O, S, and F). The results showed that the absolute values of hydrogen free energies (ΔGH*) of the substitutional dopants of PC, SC and adsorptive dopants of NT, OT, ST, and PT had increased catalytic activity compared with those of the pristine Y2C monolayer (−0.673 eV). It was highlighted that the adsorption doping of PT can further reduce the adsorption free energy of the pristine Y2C monolayer to −0.19 eV, which is close to the optimal zero value, and the binding energy of the hydrogen atoms on the Y2C surface significantly increased from −0.913 to −0.438 eV, which is more favorable for the desorption of hydrogen atoms. These results demonstrate that the doping of non-metals activates the adsorption of hydrogen atoms on monolayer Y2C and provides a feasible method for hydrogen generation.

Quantum-mechanical study of the optimal phosphorus atoms arrangement on silicene

Manufacturing precise quantum computers with small errors in quantum operations, long coherence times, and low power consumption is the most important challenge in modern nanoelectronics. To understand the operating modes of such calculators in detail, both the optimal arrangement of the qubit system within the structure and changes in its magnetic properties must be comprehensively investigated. In this paper, the behaviour of one and two phosphorus atoms on the surface of silicene is studied using quantum mechanical non-collinear calculations, which consider spin–orbit coupling. The magnetization and ion charge on phosphorus atoms for substitution and different adsorption positions are determined. The optimal positions, binding energies, and activation barriers for the diffusion of adsorbed phosphorus in the presence and absence of a primary adsorbed or substituting phosphorus atom are also established. Overall, the results of this work have important implications for researchers and technologists in the manufacture of Si:P based quantum computers.

π–π stack driven competitive /complementary adsorption of aromatic compounds on MIL-53(Al)

In this study, the selective adsorption of aromatic compounds on mesoporous MIL-53(Al) was investigated, and followed the order: Biphenyl (Biph) > Triclosan (TCS) > Bisphenol A (BPA) > Pyrogallol (Pyro) > Catechol (Cate) > Phenol (Phen), and exhibited high selectivity toward TCS in binary compounds. In addition to hydrophobicity and hydrogen bonding, π–π interaction/stacking predominated, and more evidently with double benzene rings. TCS-containing halogens could increase π interaction on the benzene rings via forming Cl–π stacking with MIL-53(Al). Moreover, site energy distribution confirmed that complementary adsorption mainly occurred in the Phen/TCS system, as evidenced by ΔQpri (the decreased solid-phase TCS concentration of the primary adsorbate) < Qsec (the solid-phase concentrations of the competitor (Phen)). In contrast, competitive sorption occurred in the BPA/TCS and Biph/TCS systems within 30 min due to ΔQpri = Qsec, followed by substitution adsorption in the BPA/TCS system, but not for the Biph/TCS system, likely attributed to the magnitude of energy gaps (Eg) and bond energy of TCS (1.80 eV, 362 kJ/mol) fallen between BPA (1.74 eV, 332 kJ/mol) and Biph (1.99 eV, 518 kJ/mol) according to the density-functional theory of Gaussian models. Biph with a more stable electronic homeostasis than TCS lead to the occurrence of substitution adsorption in the TCS/BPA system, but not in the TCS/Biph system. This study provides insight into the mechanisms of different aromatic compounds on MIL-53(Al).

Efficient removal of alkali and alkaline earth metals from biodiesel using Ion-exchange resin: Performance and mechanism

Raw materials, production process, and other factors cause several metal ions to exist in biodiesel. Furthermore, the existence of alkali and alkaline earth metals seriously affects the quality and performance of biodiesel. To improve fuel quality, a 732 ion-exchange resin was used to reduce the contents of alkali and alkaline earth metal ions in Jatropha biodiesel. The adsorption efficiency of the ion-exchange resin for alkali and alkaline earth metal ions in biodiesel was evaluated using ion chromatography, while the adsorption mechanism of ion change resin on alkali and alkaline earth metal ions in biodiesel was elucidated via FTIR and XPS. In addition, the effects of ion-exchange resin on several key physiochemical properties of biodiesel, including oxidation stability, corrosivity, heat value and kinematic viscosity, were also explored. The results showed that the total content of alkali and alkaline earth metal ions in biodiesel was reduced by 88.19%, and the K+, Na+, Mg2+, and Ca2+ contents were reduced to 0.11 mg/kg, 0.89 mg/kg, 0.53 mg/kg, and 0.78 mg/kg, respectively, after removing the ion-exchange resin. In the removal process, the hydroxyl group of sulfonic acid group on the ion-exchange resin is broken, and the substitution adsorption reaction between H+ and the alkali and alkaline earth metal ions in biodiesel is carried out. Moreover, the oxidation induction period of biodiesel was prolonged by 40.8% owing to the reduction in the content of alkali and alkaline earth metal ions, which significantly blocked the decomposition pathways of unstable oxidation intermediates in biodiesel. The degree of copper corrosion in biodiesel did not change significantly before and after ion-exchange resin adsorption during short-term corrosion (3 h); however, the copper corrosion grade decreased from 2c to 1b after ion-exchange resin adsorption during long term corrosion (240 h). Nevertheless, the heat value and kinematic viscosity of biodiesel were observed to be independent of the ionic metal content.

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.

Enhanced Gas Adsorption on Cu3(BTC)2 Metal-Organic Framework by Post-Synthetic Cation Exchange and Computational Analysis.

Increased gas adsorption in a series of post-synthetically modified metal-organic frameworks (MOFs) of the type HKUST-1 was achieved by the partial cation exchange process. Manipulation of post-synthetic conditions demonstrates high tunability in the site substitution and gas adsorption properties during the dynamic equilibrium process. In this work, post-synthetic modification of Cu3(BTC)2 is carried on by exposure to TM2+ solutions (TM = Mn, Fe, Co, Ni) at different time intervals. The crystal structure, composition, and morphology were studied by powder X-ray diffraction, Fourier-transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, and scanning electron microscopy. Structural analysis supports the retention of the crystal structure and partial substitution of the Cu metal nodes within the framework. A linear increase in the transmetalation process is observed with Fe and Co with a maximum percentage of 39 and 18%, respectively. Conversely, relatively low cation exchange is observed with Mn having a maximum percentage of 2.40% and Ni with only 2.02%. Gas adsorption measurements and surface area analysis were determined for each species. Interestingly, (Cu/Mn)3(BTC)2 revealed the highest CO2 adsorption capacity of 5.47 mmol/g, compared to 3.08 mmol/g for Cu3(BTC)2. The overall increased gas adsorption can be attributed to the formation of defects in the crystal structure during the cation exchange process. These results demonstrate the outstanding potential of post-synthetic ion exchange as a general approach to fine-tuning the physical properties of existing MOF architectures.

Preparing of layered double hydroxide- alginate microspheres for Cr(VI)-contaminated soil remediation

The powdered layered double hydroxide(LDH) synthesized by hydrothermal coprecipitation was compounded with sodium alginate to form microspheres(LDH-AL). The characterizations of the LDH-AL show that the microspheres were successfully prepared. Then the immobilization experiments of hexavalent chromium(Cr(VI)) were investigated. The results have proved the effectiveness of microspheres in the immobilization of Cr(VI) in soil. Other limiting factors including LDH percentage, the effects of pH, LDH-AL dosage, interlayer ions, and initial heavy metal concentration were also explored. The LDH-AL showed advantages and its maximum adsorption capacity is 17.0 mg/g. LDH contained in the materials plays a main role in the removal process. In addition, the toxicity characteristic leaching procedure (TCLP) experiment, plant potting tests, and simulation of natural aging processes were used to verify the stability of microspheres. While a series of characterization investigated the adsorption mechanism, the interlayer ion exchange and surface adsorption are the main reasons for Cr(VI) immobilization in contaminated soil. There are also isomer substitution and complexation adsorption phenomena. This study demonstrated the potential application of LDH-AL microspheres in the immobilization of Cr(VI) from contaminated soil.

Selective recovery of glyphosine from glyphosate mother liquor using a modified biosorbent: Competitive substitution adsorption

Here, an easy to prepare, environmentally friendly, and highly efficient biosorbent was synthesized for the selective recovery of glyphosine from glyphosate mother liquor. Batch adsorption and continuous fixed-bed column experiments were conducted to determine its adsorption properties and evaluate its potential towards practical applications. The results showed that the biosorbent exhibited a fast adsorption rate and high adsorption capacity (296.1 mg/g) toward glyphosine. Further, the biosorbent performed better under acidic conditions, and was easily regenerated using an alkaline solution, maintaining a high removal efficiency even after 5 adsorption-desorption cycles. Competitive adsorption experiments in binary and ternary systems revealed that the biosorbent showed a higher adsorption affinity toward the target glyphosine compared with glyphosate and phosphorous acid (which are the other main constituents of glyphosate mother liquor), enabling the selective recycling of glyphosine. These observations were further supported through density functional theory (DFT) calculations of the adsorption energy. Moreover, fixed-bed column experiments showed that the prepared biosorbent could maintain its high performance in actual glyphosate mother liquor. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses revealed that the adsorption mechanism is strongly associated with electrostatic attraction and hydrogen bonding between –NH3+ and glyphosine. Overall, the prepared biosorbent can be considered as an excellent candidate for the selective recovery of glyphosine from complicated industrial wastewater systems.

Remediation of Cu and As contaminated water and soil utilizing biochar supported layered double hydroxide: Mechanisms and soil environment altering

Preparing materials for simultaneous remediation of anionic and cationic heavy metals contamination has always been the focus of research. Herein a biochar supported FeMnMg layered double hydroxide (LDH) composites (LB) for simultaneous remediation of copper and arsenic contamination in water and soil has been assembled by a facile co-precipitation approach. Both adsorption isotherm and kinetics studies of heavy metals removal by LB were applied to look into the adsorption performance of adsorbents in water. Moreover, the adsorption mechanisms of Cu and As by LB were investigated, showing that Cu in aqueous solution was removed by the isomorphic substitution, precipitation and electrostatic adsorption while As was removed by complexation. In addition, the availability of Cu and As in the soil incubation experiments was reduced by 35.54%–63.00% and 8.39%–29.04%, respectively by using LB. Meanwhile, the addition of LB increased the activities of urease and sucrase by 93.78%–374.35% and 84.35%–520.04%, respectively, of which 1% of the dosage was the best. A phenomenon was found that the richness and structure of microbial community became vigorous within 1% dosage of LB, which indirectly enhanced the passivation and stabilization of heavy metals. These results indicated that the soil environment was significantly improved by LB. This research demonstrates that LB would be an imaginably forceful material for the remediation of anionic and cationic heavy metals in contaminated water and soil.

Study of Substitutional Adsorption of an Iron Film on a Silver Surface

Study of Substitutional Adsorption of an Iron Film on a Silver Surface

Selective Recovery of Glyphosine from Glyphosate Mother Liquor by a Modified Biosorbent: Competitive Substitution Adsorption

Selective Recovery of Glyphosine from Glyphosate Mother Liquor by a Modified Biosorbent: Competitive Substitution Adsorption

Structural and electronic effects of adsorbed Bi on the metallic atomic chains in Au/Si(111)5 [formula omitted] 2

Changes in the structural and electronic properties of the quasi-one-dimensional metal-chain Au/Si(111)5 × 2 reconstruction induced by Bi adsorption were investigated using scanning tunneling microscopy observations, angle-resolved photoelectron spectroscopy measurements and density-functional theory calculations. It was found that Bi atoms substitute the Au atoms in the edge rows of the four-atomic-row Au ridge of the Au/Si(111)5 × 2 reconstruction. The Au/Si(111)5 × 2 surface, which is originally highly heterogenous in its electronic properties, becomes still more heterogeneous upon Bi substitutional adsorption. The overall effect of Bi adsorption resides in the increase of the system Fermi energy due to the electron donation from the Bi atoms to the reconstructed surface. This provides a possibility to tune the metallic properties of the system via controlled Bi dosing.

Formation of BN-covered silicene on ZrB2/Si(111) by adsorption of NO and thermal processes.

We have investigated the adsorption and thermal reaction processes of NO with silicene spontaneously formed on the ZrB2/Si(111) substrate using synchrotron radiation x-ray photoelectron spectroscopy (XPS) and density-functional theory calculations. NO is dissociatively adsorbed on the silicene surface at 300 K. An atomic nitrogen is bonded to three Si atoms most probably by a substitutional adsorption with a Si atom of silicene (N≡Si3). An atomic oxygen is inserted between two Si atoms of the silicene (Si-O-Si). With increasing NO exposure, the two-dimensional honeycomb silicene structure gets destroyed, judging from the decay of typical Si 2p spectra for silicene. After a large amount of NO exposure, the oxidation state of Si becomes Si4+ predominantly, and the intensity of the XPS peaks of the ZrB2 substrate decreases, indicating that complicated silicon oxinitride species have developed three-dimensionally. By heating above 900 K, the oxide species start to desorb from the surface, but nitrogen-bonded species still exist. After flashing at 1053 K, no oxygen species is observed on the surface; SiN species are temporally formed as a metastable species and BN species also start to develop. In addition, the silicene structure is restored on the ZrB2/Si(111) substrate. After prolonged heating at 1053 K, most of nitrogen atoms are bonded to B atoms to form a BN layer at the topmost surface. Thus, BN-covered silicene is formed on the ZrB2/Si(111) substrate by the adsorption of NO at 300 K and prolonged heating at 1053 K.

Effect of 3d transition metal substitutional dopants and adatoms on mono layer TcS2 ab initio insights

Abstract Within the spin polarized density functional theory formalism, the properties (structural, magnetic, electronic and optical) of transition metal (TM) substitutional doping as well as adsorption on monolayer TcS2 has been investigated. The TMs considered in this study were Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn. TM substitutional doping was found to be energetically favored under S-rich conditions compared to Tc-rich conditions. This suggests that it might be possible for substitutional doping to be realized experimentally. The calculated adsorption energies were negative in the case of Sc, Ti, V, Cr, Mn, Ni and Cu adsorption indicating the likelihood of adsorbing these TMs on mono layer TcS2. Both TM substitutional doping and adsorption were found to; induce a net magnetization, induce states within the band gap of the host and also modify the optical absorption spectra of TcS2. Magnetic ground states arising from transition metal doping and adsorption make these systems ideal candidates for magnetic and spintronic applications. Optical anisotropy was observed in the case of electric field parallel E‖z and perpendicular EꞱz to the z-axis.

Electrochemical studies of prothioconazole as a novel corrosion inhibitor for copper in acidic solutions.

Prothioconazole is a fungicide that has a wide number of applications in agriculture, and it can ensure the safety of crops, users, and the environment. Prothioconazole, as a suppressor of copper dissolution in 0.5 M H2SO4 solution, has been evaluated using electrochemical experiments, weight loss tests, quantum chemical calculations, and scanning electron microscopy (SEM). The electrochemical test results showed that prothioconazole was an excellent inhibitor, and the anticorrosion ability increased with the inhibitor concentration. The interaction of prothioconazole with copper is a spontaneous adsorption process accompanied by typical chemisorption. The number of water molecules (X) displaced by one prothioconazole molecule was obtained using diverse substitutional adsorption models based on electrochemical impedance spectroscopy (EIS) data. In addition, the Fukui functions indicate that the triazole and benzene rings and the –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> S atoms were the main active sites for the adsorption process.

First-principles investigation of the effect of substitution and surface adsorption on the magnetostrictive performance of Fe-Ga alloys

Materials with large magnetostriction are widely used in sensors, actuators, micro electromechanical systems, and energy-harvesters. Binary Fe-Ga alloys (Galfenol) are the most promising rare-earth-free candidates combining numerous advantages such as low saturation magnetic field (~200 Oe), excellent ductility and low cost, while further improving their performance is imperative for practical applications. Using density functional theory calculation, we report results of the effect of substituting small amount of additional elements X (eg. X = Ag, Pd and Cu) on magnetostriction of Fe-Ga alloys, and find that it may double the magnetostriction with a substitutional percentage of only 1.6%. Moreover, adsorbents with high chemical activity (eg. O or Os atoms) may affect the surface energy of different face-orientations of Fe-Ga alloys, indicating proper surface treatments are necessary to tune the alignment of Fe-Ga grains to achieve better performance. These results may be helpful to further optimize the magnetostrictive properties of Fe-Ga alloys for device applications.

Kinetics of small molecule adsorption studied using precision ellipsometry

On the basis of a miniature polarisation modulator, a precision ellipsometry system has been made, enabling real‐time measurement of subnanometre thin layers on reflecting substrates. This system monitored the kinetics of adsorption and desorption of propanol, or ethanol, or methanol on oxidised Si substrates. While adsorption of propanol and ethanol increased the thickness, adsorption of methanol showed surprising kinetics: the thickness first increased, then decreased. To explain this, a model of substitutional (or competitive) adsorption has been used, where the target molecule is adsorbed only when it substitutes another one leaving an adsorption site. The model fits the experimental data quantitatively and can predict processes involving several components on solid surfaces. Precision ellipsometry demonstrated its high analytical potential in investigation of surfaces at molecular level.