Hard And Soft Acids And Bases Research Articles

Utilizing Solid Phase Sorbents with Various Functional Groups Based on the HASAB Principle for Recovering Platinum Group Metals from Secondary Sources

The study investigates the recovery of platinum-group metals (PGMs), Pd, Pt, and Rh, from secondary sources - spent catalytic converters, waste from a chemical industry, and a PGM refinery. Aquaregia was used to create leaching liquors and solid-phase extraction sorbents with different functional groups - DiOctyl Sulfide (DOS), Cyano (CN), Di-Ethylene Tetra-Amine (DETA), and strong anion exchanger (SAX) - were employed based on the "hard and soft acid and base (HASAB)" principles. The SAX-sorbent demonstrated the ability to retain PGMs in the presence of accompanying base metals selectively. In contrast, the DOS and CN sorbents were selective only for Pd, and the DETA sorbent displayed selectivity solely for Rh. Desorption experiments revealed that 3M HCl could effectively recover the PGMs from loaded solid-phase sorbents with significant HSE advantages. The study also noted the high stability of the sorbents, although improvements are needed, particularly in enhancing the reusability of the DETA-sorbent

Critical Evaluation of Childs Method for the NMR Spectroscopic Scaling of Effective Lewis Acidity: Limitations and Resolution of Earlier Discrepancies.

Quantifying Lewis acidity is essential for understanding and optimizing the performance of Lewis acids in diverse applications. Next to the widely accepted Gutmann-Beckett (GB) method, using triethyl phosphine oxide (TEPO) as a probe, the Childs method-employing trans-crotonaldehyde (TCA)-gained attention as an NMR-based technique for measuring effective Lewis acidity (eLA). Despite its steady use, the robustness of Childs method and its correlation with other measures remain underexplored. Previous comparisons between the GB and Childs scales revealed significant discrepancies, suggesting that hard and soft acid/base (HSAB) characteristics may be operative. In this study, we compare thermodynamic data for TCA binding to 117 Lewis acids (representing global Lewis acidity, gLA) with their corresponding NMR-induced chemical shifts in TCA. Our findings showcase notable deviations that reinforce key distinctions between eLA and gLA perspectives. Moreover, we identify significant limitations in the Childs method. First, the weak donor strength of TCA limits its applicability to only the strongest Lewis acids. Second, the exposed protons of TCA are prone to secondary interactions, obscuring the measurement of true Lewis acidity. Finally, our analysis reconciles discrepancies, refuting earlier assumptions that these arise from HSAB effects.

Modulating Confined Interlayer Environment By Hard Lewis Acid Cation for Enhancing Oxygen Evolution Reaction

With the increasing demand for hydrogen energy, the non-noble metal catalysts in water splitting for hydrogen production are significant for addressing global environmental issues.[1] Among them, layered transition metal oxide/hydroxide (LTMO/LTMH) materials have drawn more attention for their high tunability of surface or bulk structural transformations after introducing different cations inside the interlayer, which could manifest OER activity.[2] Therefore, birnessite-layered manganese dioxide (MnO2) is considered a potential material for its ability to create a container for cation intercalation, which could significantly enhance its behavior in the oxygen evolution reaction (OER).[3] However, most of the investigations of its application in OER considered MnO2 layers as active sites, which may underestimate the function of intercalated cations and hence blur its real reaction active sites. Using the hard and soft acids and bases (HSAB) theory recently sheds new light and provides a new road for improving OER performance; hard Lewis acid captures hydroxyl and thus speeds up the cleavage of water molecules, generating a demanding local alkaline environment.[4-6] Herein, we grounded the perspective of the intercalated cations based on the HSAB theory, using layered MnO2 as the “container” for accommodating hard Lewis acid cations, achieving using Lewis acid cations for active sites, to enhance OER activity. We use the electrodeposition method to synthesize the precursor layered catalyst, TBA+/MnO2. With the ion exchange process, cations with different Lewis acidities (K+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) were intercalated inside this “nano-cell” (interlayer of layered MnO2) to discuss how they influenced the confined surrounding electrolyte environment and electron/mass transport. X-ray diffraction, Raman, and inductively coupled plasma verified the successful synthesis of layered MnO2 with different cations intercalated. The OER results of cation-intercalated MnO2 catalysts exhibited that intercalating the harder Lewis acid significantly influences the interlayer electrolyte environment, markedly accelerating and enhancing the reaction kinetics and OER activity. Furthermore, comparing the OER behavior of intercalated cations, free cations, and bulk metal foils, the intercalated hard Lewis acid cations showed superior reaction kinetics. This work thus provides a clear picture of the role of cations when intercalated into the MnO2 layers during OER and highlights a novel utilization of Lewis acid cations as active sites for enhancing OER activity. Reference [1] Wang, S.; Lu, A.; Zhong, C.-J. Hydrogen Production from Water Electrolysis: Role of Catalysts. Nano Converg. 2021, 8 (1), 4.[2] Kim, Y.; Choi, E.; Kim, S.; Byon, H. R. Layered Transition Metal Oxides (LTMO) for Oxygen Evolution Reactions and Aqueous Li-Ion Batteries. Chem. Sci. 2023, 14 (39), 10644–10663.[3] Ju, M.; Chen, Z.; Zhu, H.; Cai, R.; Lin, Z.; Chen, Y.; Wang, Y.; Gao, J.; Long, X.; Yang, S. Fe(III) Docking-Activated Sites in Layered Birnessite for Efficient Water Oxidation. J. Am. Chem. Soc. 2023, 145 (20), 11215–11226.[4] Pearson, R. G. Hard and Soft Acids and Bases. J. Am. Chem. Soc. 1963, 85 (22), 3533–3539.[5] Zhao, S.; Wang, Y.; Hao, Y.; Yin, L.; Kuo, C.-H.; Chen, H.-Y.; Li, L.; Peng, S. Lewis Acid Driving Asymmetric Interfacial Electron Distribution to Stabilize Active Species for Efficient Neutral Water Oxidation. Adv. Mater. 2024, 36 (7), 2308925.[6] Guo, J.; Zheng, Y.; Hu, Z.; Zheng, C.; Mao, J.; Du, K.; Jaroniec, M.; Qiao, S.-Z.; Ling, T. Direct Seawater Electrolysis by Adjusting the Local Reaction Environment of a Catalyst. Nat. Energy 2023, 8 (3), 264–272. Figure 1

(Invited) Enhancing Performance and Moisture Resistance of Solid Electrolyte in Sulfide-Based All-Solid-State Batteries via Oxygen Integration

Issues related to explosions and energy density constraints are presented by lithium-ion batteries (LIBs) employing organic electrolytes.1 The pursuit of overcoming these challenges has brought all-solid-state batteries (ASSBs), representing the next generation of batteries, to prominence as a viable solution. The interest has been directed towards sulfide-based solid electrolytes (SEs), recognized as a crucial component in ASSBs due to their elevated ionic conductivity. Nevertheless, challenges are encountered, encompassing the generation of hazardous hydrogen sulfide (H2S) attributed to the sulfide electrolytes' diminished chemical stability in the presence of moisture, which results in the degradation of cells.2 This necessitates the production of batteries in an environment devoid of reactive elements, thus imposing a hurdle for mass production. To address this issue, two strategies have been delineated: i) the integration of metal oxides such as Fe2O3, ZnO, and zeolite for the sequestration of H2S produced through hydrolysis; ii) the enhancement of SE's stability through doping with Bi, Sn, and Sb in alignment with the theory of hard and soft acids and bases (HSAB), or through replacement with oxides like Li2O and P2O5. The suppression of H2S generation might contribute to prolonged degradation of cells, as it entails the capture of H2S, a breakdown product of SEs. In contrast, the reinforcement of SE structures via the integration of oxygen derivatives is posited to provide the benefit of precluding the generation of H2S while preserving cell efficiency. Despite the notable influence of oxygen inclusion, the elucidation of its impact, anchored in dependable cell functionality and underlying mechanisms, has yet to be fully clarified.3,4 Thus, delving into the comprehension of structural reinforcement mechanisms facilitated by oxygen substitution and their implications is deemed of considerable importance for addressing the intrinsic challenges in SEs.In this study, a novel argyrodite composition incorporating a specified quantity of oxygen has been introduced to simultaneously augment its resistance to moisture and enhance its electrochemical performance without detracting from either attribute. The advantageous effects of oxygen substitution on structural reinforcement, resistance to moisture, and battery properties are delineated. The augmentation of the cathode/SE interface stability through oxygen substitution has been corroborated employing a high-capacity NCM811 (LiNi0.8Co0.1Mn0.1O2), and the decomposition behavior has been delineated through X-ray photoelectron spectroscopy (XPS). An evaluation and comparison of moisture stability have been conducted using transmission electron microscope-selected-area electron diffraction (TEM-SAED), and the sites of oxygen substitution have been meticulously identified utilizing Rietveld refinement and Raman spectroscopy. A mechanism positing the stabilization of the PS4 unit, pivotal for moisture resistance through oxygen-mediated structural evolution, is proposed. Furthermore, the significance of the SE in facilitating the commercial viability of sulfide-based ASSBs, accompanied by a substantial enhancement in battery performance, has been elucidated. References Janek and W. G. Zeier, Nature Energy, 2016, 1, 16141.Muramatsu, A. Hayashi, T. Ohtomo, S. Hama and M. Tatsumisago, Solid State Ionics, 2011, 182, 116-119.Sun, Y. Lai, N. Lv, Y. Hu, B. Li, L. Jiang, J. Wang, S. Yin, K. Li and F. Liu, ACS Appl Mater Interfaces, 2021, 13, 54924-54935.Hwang, Y.-J. Lee, S. R. Lee, Y.-C. Ha, M. Cho, S.-M. Lee and K. Cho, Journal of Materials Chemistry A, 2022, 10, 16908-16919.

Application of Hard and Soft Acid-base Theory to Construct Heterometallic Materials with Metal-oxo Clusters.

Heterometallic cluster-based materials offer the potential to incorporate multiple functionalities, leveraging the aggregation effects of clusters and translating this heterogeneity and complexity into unexpected properties that are more than just the sum of their components. However, the rational construction of heterometallic cluster-based materials remains challenging due to the complexity of metal cation coordination and structural unpredictability. This minireview provides insights into a general synthetic strategy based on Hard and Soft Acids and Bases (HSAB) theory, summarizing its advantages in the designed synthesis of discrete heterometallic clusters (intracluster assembly) and infinite heterometallic cluster-based materials (intercluster assembly). Furthermore, it emphasizes the potential to exploit the intrinsic properties of mixed components to achieve breakthroughs across a broad range of applications. The insights from this review are expected to drive the progress of heterometallic cluster-based materials in a controllable and predictable manner.

Application of Hard and Soft Acid‐base Theory to Construct Heterometallic Materials with Metal‐oxo Clusters

AbstractHeterometallic cluster‐based materials offer the potential to incorporate multiple functionalities, leveraging the aggregation effects of clusters and translating this heterogeneity and complexity into unexpected properties that are more than just the sum of their components. However, the rational construction of heterometallic cluster‐based materials remains challenging due to the complexity of metal cation coordination and structural unpredictability. This minireview provides insights into a general synthetic strategy based on Hard and Soft Acids and Bases (HSAB) theory, summarizing its advantages in the designed synthesis of discrete heterometallic clusters (intracluster assembly) and infinite heterometallic cluster‐based materials (intercluster assembly). Furthermore, it emphasizes the potential to exploit the intrinsic properties of mixed components to achieve breakthroughs across a broad range of applications. The insights from this review are expected to drive the progress of heterometallic cluster‐based materials in a controllable and predictable manner.

Electrolyte Reconfiguration by Cation/Anion Cross‐coordination for Highly Reversible and Facile Sodium Storage

AbstractHard carbon (HC) materials are promising anodes for sodium‐ion batteries (SIBs) owing to low cost, high specific capacity and low working potential. However, the poor compatibility of the electrolyte with HC leads to low initial coulombic efficiency (ICE) and sluggish Na+ transport kinetics. Here, we propose an electrolyte reconfiguration strategy based on the hard and soft acid and base (HSAB) theory by introducing methyltriphenylphosphonium bromide (MTPPB). MTPPB can realize a spontaneous cross‐coordination solvation structure with NaPF6 by selective affinity, synchronously optimizing the interfacial chemistry and sodium storage process. The advantages of the chemical π–π bridging of MTPP+‐HC and interaction of MTPP+‐PF6− contribute to preferential and oriented reduction of PF6−, forming a low‐resistance supramolecular SEI. Additionally, Na+‐Br− coordination weakens the Na+‐solvent interactions, facilitating Na+ de‐solvation kinetics. Consequently, the HC||Na cell achieves a superior ICE of 96.6 %, desirable rate capability under 25 °C and invisible capacity decay after 500 cycles at 1 C under −20 °C. The Na4Fe3(PO4)2P2O7||HC pouch battery displays a high ICE of 90.3 % and a 15 % increment of energy density under 25 °C. This work provides a guidance through electrolyte reconfiguration engineering for designing practical HC‐based SIBs with high energy/power density and long‐life span in the extended operating‐temperature range.

Electrolyte Reconfiguration by Cation/Anion Cross-coordination for Highly Reversible and Facile Sodium Storage.

Hard carbon (HC) materials are promising anodes for sodium-ion batteries (SIBs) owing to low cost, high specific capacity and low working potential. However, the poor compatibility of the electrolyte with HC leads to low initial coulombic efficiency (ICE) and sluggish Na+ transport kinetics. Here, we propose an electrolyte reconfiguration strategy based on the hard and soft acid and base (HSAB) theory by introducing methyltriphenylphosphonium bromide (MTPPB). MTPPB can realize a spontaneous cross-coordination solvation structure with NaPF6 by selective affinity, synchronously optimizing the interfacial chemistry and sodium storage process. The advantages of the chemical π-π bridging of MTPP+-HC and interaction of MTPP+-PF6- contribute to preferential and oriented reduction of PF6-, forming a low-resistance supramolecular SEI. Additionally, Na+-Br- coordination weakens the Na+-solvent interactions, facilitating Na+ de-solvation kinetics. Consequently, the HC||Na cell achieves a superior ICE of 96.6%, desirable rate capability under 25 °C and invisible capacity decay after 500 cycles at 1 C under -20 °C. The Na4Fe3(PO4)2P2O7||HC pouch battery displays a high ICE of 90.3% and a 15% increment of energy density under 25 °C. This work provides a guidance through electrolyte reconfiguration engineering for designing practical HC-based SIBs with high energy/power density and long-life span in the extended operating-temperature range.

Dual Ligand Strategy for Efficient and Stable Ag–In–Ga–S Aqueous Quantum Dots

AbstractIn recent years, Ag−In−Ga−S (AIGS) quaternary quantum dots (QDs) have garnered significant attention as a novel class of environmentally friendly and non‐toxic QDs. However, the hydrothermal synthesis method for aqueous QDs has been plagued by issues such as inconsistent size, subpar crystallinity, and low photoluminescence quantum yield (PLQY). Herein, we developed a dual ligand strategy based on the hard and soft acids and bases (HSAB) theory to synthesize aqueous AIGS QDs with an impressive PLQY of up to 64.3 %, currently the highest value among hydrothermal‐synthesized uncoated I–III–VI QDs. The QDs exhibit better crystallinity, narrow size distribution (3.07±0.31 nm), and remarkable stability. The mechanism underlying this dual ligand strategy was further elucidated, shedding light on the distinct influences of different ligands on the growth of QDs. The high PLQY contributes to the further application of aqueous AIGS QDs in luminescent displays and the field of biology. Meanwhile, this ligand strategy has broad reference significance for efficient preparation of other water‐soluble QDs.

A Functional Air-Stable Li9.8GeP1.7Sb0.3S11.8I0.2 Superionic Conductor for High-Performance All-Solid-State Lithium Batteries.

Solid-state electrolytes (SSEs) based on sulfides have become a subject of great interest due to their superior Li-ion conductivity, low grain boundary resistance, and adequate mechanical strength. However, they grapple with chemical instability toward moisture hypersensitivity, which decreases their ionic conductivity, leading to more processing requirements. Herein, a Li9.8GeP1.7Sb0.3S11.8I0.2 (LGPSSI) superionic conductor is designed with a Li+ conductivity of 6.6 mS cm-1 and superior air stability based on hard and soft acids and bases (HSAB) theory. The introduction of optimal antimony (Sb) and iodine (I) into the Li10GeP2S12 (LGPS) structure facilitates fast Li-ion migration with low activation energy (Ea) of 20.33 kJ mol-1. The higher air stability of LGPSSI is credited to the strategic substitution of soft acid Sb into (Ge/P)S4 tetrahedral sites, examined by Raman and X-ray photoelectron spectroscopy techniques. Relatively lower acidity of Sb compared to phosphorus (P) realizes a stronger Sb-S bond, minimizing the evolution of toxic H2S (0.1728 cm3 g-1), which is ∼3 times lower than pristine LGPS when LGPSSI is exposed to moist air for 120 min. The NCA//Li-In full cell with a LGPSSI superionic conductor delivered the first discharge capacity of 209.1 mAh g-1 with 86.94% Coulombic efficiency at 0.1 mA cm-2. Furthermore, operating at a current density of 0.3 mA cm-2, LiNbO3@NCA/LGPSSI/Li-In cell demonstrated an exceptional reversible capacity of 117.70 mAh g-1, retaining 92.64% of its original capacity over 100 cycles.

Visible light photocatalytic performance of Co/Ag bimetallic coordination polymer catalysts designed from hard and soft acid-base theory

Heterometallic coordination polymers have promising applications in photocatalysis, and the design and selection of suitable organic ligands and coordination metals is the key to improve the catalytic activity of polymer photocatalysts. Herein, a novel Co/Ag bimetallic coordination photocatalyst, designed based on the hard and soft acid-base (HSAB) theory, has been successfully prepared by a stepwise method with Ag-S coordination as the main component and Co-N/Co-S as the complementary component. The obtained Co/Ag photocatalyst demonstrates excellent performance in the photocatalytic degradation (visible light) of halogenated phenolic pollutants. Degradation of 10 ppm of 4-chlorophenol could reach 100 % in 4 h, and 70 % degradation of 4-fluorophenol, which is even more difficult to degrade, could also be achieved. In addition, hydrogen production experiments conducted under visible light irradiation showed that the hydrogen production could reach 36.95 μmol h−1 g−1 for 6 h, which strongly demonstrated the excellent reduction ability of Co/Ag photocatalysts. The photocatalyst exhibits enhanced photocatalytic activity which is ascribed to the formation of Ag-S and Co-N/Co-S coordination, which greatly increases the charge density and facilitates charge transfer. Thus, the photogenerated electrons can induce both the conversion of O2 to •O2- for oxidation reactions, as well as the direct attack of the C-Cl bond for reduction reactions. This study demonstrates the successful design of the synergistic Co/Ag bimetallic coordination photocatalysts based on the HSAB theory, thereby offering a promising research avenue for the fabrication of heterometallic coordination photocatalysts.

Ag-Fe2O3 nanocomposites for synergistically enhanced antibacterial activity

Doping of metal or metal ions in the host lattice with good dopant distribution or forming a local contact boosts materials properties for specific applications. This work used the solution combustion approach (SCA) to synthesize Ag-Fe2O3 nanocomposites (SICs) following the single-source precursor doping strategy with good final material stoichiometry. The elemental distribution and composition, crystallinity, and morphology of SCA-based synthesized materials were analyzed using common techniques such as TEM, FESEM-EDS, and XRD. Even though the Lewis hard and soft acids and bases (HSAB) idea was precise for inclusion of Ag dopant in the Fe2O3 lattice, the formation of Schottky junctions between Ag and Fe2O3 is dominance as a result of dopant-host radii size differences. The independent peak for both Ag and Fe2O3 crystals on the XRD pattern analysis without peak shift confirms the dominance of Schottky junction formation. The presence of local contact between Ag and Fe2O3 was also confirmed by the HRTEM analysis, with d-spacing values of 0.22 and 0.36 nm, respectively. Compared to the bare Fe2O3, the antibacterial potential of the SIC is much greater, with a 23-mm zone of inhibition on Pseudomonas aeruginosa gram-negative bacteria, which confirms the presence of a synergistic effect.

Interaction mechanism of phytic acid functionalized graphene oxide with ionic dyes

Phytic acid functionalized graphene oxide (PA-GO) has fascinating application in environmental remediation. Herein, PA-GO was facilely prepared via hydrothermal method and utilized as adsorbent to remove aqueous Congo red (CR) and malachite green (MG). The adsorbent-adsorbate interaction mechanism was elaborately scrutinized based on the hard and soft acid base (HSAB) principle, spectroscopic analysis and adsorption fitting. Result shows, after five consecutive cycles, PA-GO maintains adsorption quantity 242.82 mg·g−1 and 117.53 mg·g−1 for CR and MG, respectively. The HSAB principle illuminates, primary interaction of PA-GO with both CR and MG is provided by phytic acid moiety (PA). For CR adsorption, electron of N atom in –NH2 group flows towards O atom in OH and O(-O-) of PA. While for MG adsorption, electron of N atom in (CH3)2N– group flows towards O atom in OH and O(-O-) of PA. FTIR, UV–Vis analyses supports the HSAB principle prediction. In brief, the hydroxyls and phosphoric groups introduced by PA functionalization enhance the adsorption affinity of GO. Adsorption of CR, MG by PA-GO under favorable pH is thermodynamically chemical but kinetically impelled by electrostatic interaction. This work may promote the development of efficient adsorbent based on PA-GO architecture for environmental remediation.

Synthesis of hollow Fe3O4 microboxes guided by the hard and soft acid-base principle for enhanced electromagnetic wave absorption

A novel strategy based on the hard and soft acid-base (HSAB) principle to synthesize high-quality Fe3O4 microboxes was investigated. Initially, an Fe3O4 thin shell was generated on the surface of Cu2O cubic templates by meticulously regulating the hydrolysis kinetics of Fe3+. The Cu2O templates were then selectively dissolved using NH4Cl as an etchant, in conjunction with the reduction of Fe3+, yielding the hollow architectures of Fe3O4 microboxes. Capitalizing on the inherent merits of the hollow microstructures, the Fe3O4 microboxes exhibited superior electromagnetic wave (EMW) absorption efficiency. The Fe3O4 microboxes/paraffin composites demonstrated remarkable EMW absorption performance. A sample with 60 wt% loading and 1.16 mm thickness achieved the minimum reflection loss (RLmin) of − 35.9 dB at 16.2 GHz, with an effective absorption bandwidth (EAB) of 3.5 GHz.

Using a Metaverse to Teach Students to Predict the Interaction of Acids and Bases Using Hard and Soft Acids and Bases (HSAB) Theory

Using a Metaverse to Teach Students to Predict the Interaction of Acids and Bases Using Hard and Soft Acids and Bases (HSAB) Theory

Elucidating the Role of Chalcogenide‐Based Interface Passivators in Enhancing the Stability of Perovskite Solar Cells

AbstractChalcogenide‐based Lewis bases are widely used in perovskite solar cells (PSCs) due to their effectiveness in passivating Pb2+ and Pb0‐related defects. However, the underlying principles governing their defect passivation and the relative efficacy of different chalcogen elements remain poorly understood. This study evaluates the effectiveness of oxygen, sulfur, and selenium‐based interface passivator molecules in enhancing the stability and power conversion efficiency (PCE) of perovskite solar cell devices. The hard and soft acid and base (HSAB) principle has been utilized here to gain insights into the defect passivation behavior of chalcogenide‐based molecules. The photoluminescence, ideality factor, and trap density measurements reveal that the sulfide and selenide‐passivated devices exhibit superior defect passivation compared to the oxide‐passivated control device. In terms of stability, the average T75 lifetime (time at which 75% of the initial PCE is retained) of the oxide, sulfide, and selenide passivated samples is 6%, 30%, and 50% higher compared to their un‐passivated counterparts. This enhanced stability with the sulfide and selenide‐based passivators can be attributed to their soft Lewis base nature, which resulted in stronger interaction with the Pb‐related defects, as evidenced by the density‐functional theory calculations and X‐Ray photoelectron spectroscopy study.

Adsorption of Pd(II) ions by electrospun fibers with effective adsorption sites constructed by N, O atoms with a particular spatial configuration: Mechanism and practical applications

The separation and recovery of palladium from electronic waste (e-waste) are of great significance as they can alleviate environmental pollution and avoid resource loss. Herein, a novel nanofiber modified by 8-hydroxyquinoline (8-HQ-Nanofiber) with adsorption sites co-constructed by N and O atoms of hard bases was fabricated, which has good affinity properties for the Pd(II) ions belonging to soft acid in the leachate of e-waste. The adsorption mechanism of 8-HQ-Nanofiber for Pd(II) ions was revealed from the perspective of molecular level relied on a series of characterizations, such as FT-IR, ss-NMR, Zeta potential, XPS, BET, SEM and DFT. The adsorption of Pd(II) ions on 8-HQ-Nanofiber reached equilibrium within 30 min and the maximum uptake capacity was 281 mg/g at 318.15 K. The adsorption behavior of Pd(II) ions by 8-HQ-Nanofiber was described by the pseudo-second-order and Langmuir isotherm models. The 8-HQ-Nanofiber exhibited relatively good adsorption performance after 15 times of column adsorption. Finally, based on hard and soft acids and bases (HSAB) theory, a strategy to regulate the Lewis alkalinity of adsorption sites by specific spatial structures is proposed, which provides a new direction for the design of adsorption sites.

Adsorption mechanism and removal efficiency of magnetic graphene oxide-chitosan hybrid on aqueous Zn(II)

Magnetic architecture incorporating graphene-chitosan has demonstrated encouraging application in wastewater purification. Herein, a ternary hybrid based on Fe3O4-graphene oxide-chitosan (MGOCS) was fabricated and employed as adsorbent to remove aqueous Zn(II). The adsorption mechanism was intensively inspected based on the hard and soft acid base (HSAB) theory. Results present, MGOCS removes 96.73 % of Zn(II) in 38 min, with adsorption quantity 386.92 mg·g−1. Electron transfer and energy lowering determined by the HSAB theory illuminate the plausible adsorption sites in each component of MGOCS: O2− in Fe3O4, -C(=O)NH-, -NH2 in chitosan and -OH in graphene oxide. The exploration was upheld by spectroscopic analyses. Thereby, following adsorption mechanism was proposed. (1) ZnO bond was formed featured by electron donation. (2) The -C(=O)NH- group formed via amidation between graphene oxide and chitosan contributes to Zn(Π) uptake. This work may inspire the development of efficient adsorbent based on magnetic graphene-chitosan for wastewater remediation.

Unraveling Bonding Mechanisms and Electronic Structure of Pyridine Oximes on Fe(110) Surface: Deeper Insights from DFT, Molecular Dynamics and SCC-DFT Tight Binding Simulations.

The development of corrosion inhibitors with outstanding performance is a never-ending and complex process engaged in by researchers, engineers and practitioners. The computational assessment of organic corrosion inhibitors' performance is a crucial step towards the design of new task-specific materials. Herein, the electronic features, adsorption characteristics and bonding mechanisms of two pyridine oximes, namely 2-pyridylaldoxime (2POH) and 3-pyridylaldoxime (3POH), with the iron surface were investigated using molecular dynamics (MD), and self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations. SCC-DFTB simulations revealed that the 3POH molecule can form covalent bonds with iron atoms in its neutral and protonated states, while the 2POH molecule can only bond with iron through its protonated form, resulting in interaction energies of -2.534, -2.007, -1.897, and -0.007 eV for 3POH, 3POH+, 2POH+, and 2POH, respectively. Projected density of states (PDOSs) analysis of pyridines-Fe(110) interactions indicated that pyridine molecules were chemically adsorbed on the iron surface. Quantum chemical calculations (QCCs) revealed that the energy gap and Hard and Soft Acids and Bases (HSAB) principles were efficient in predicting the bonding trend of the molecules investigated with an iron surface. 3POH had the lowest energy gap of 1.706 eV, followed by 3POH+ (2.806 eV), 2POH+ (3.121 eV), and 2POH (3.431 eV). In the presence of a simulated solution, MD simulation showed that the neutral and protonated forms of molecules exhibited a parallel adsorption mode on an iron surface. The excellent adsorption properties and corrosion inhibition performance of 3POH may be attributed to its low stability compared to 2POH molecules.

Titanium Sulfonate-Based Metal–Organic Frameworks

Titanium-based metal–organic frameworks (Ti-MOFs) are one of the most active fields of MOFs due to their intriguing catalytic properties; however, the fast reaction between the widely used carboxylate-based ligand (hard base) and Ti4+ ion (hard acid) makes the syntheses of Ti-MOFs extremely challenging. In this work, we propose a new strategy by adopting sulfonic acid (soft base) as organic ligands to synthesize Ti-MOFs based on hard and soft acid and base (HSAB) theory. As an example of this strategy, seven titanium sulfonate metal–organic frameworks have been synthesized from 1,5-naphthalenedisulfonic acid (H2nds) and titanium isopropoxide and their structures are determined by single-crystal X-ray diffraction. These compounds exhibit permanent porosity, solvent stability, and light adsorption ability with a narrow band gap (2.67 eV). This work demonstrates a powerful method for the single-crystal syntheses of new Ti-MOFs, which will greatly promote the development of Ti-MOFs.