Complexation Reactions Research Articles

The effect of autochthonous metal ions and humic substances on landfill leachate ozonation: Reactive oxygen species and 3D fluorescence analysis

This study investigated the ozonation process for landfill leachate treatment, focusing on the impact of autochthonous metal ions (Fe3+, Cu2+, Mn2+, Mg2+) and humic substances on the degradation of pollutants. Our findings revealed that the presence of these metal ions significantly enhanced the generation of hydroxyl radicals (OH), especially for Fe3+, demonstrating the highest catalytic activity. However, the humic substance attenuated the signals of reactive oxygen species (ROS), particularly the superoxide radical (O2−) in the presence of Cu2+ and Mn2+. These suggested that metal ions could complex with humic substances and further inhibit ROS production. Despite this inhibition, Fe3+ maintained its ROS-generating capacity even in the presence of humic substances, indicating its potential as a robust catalyst in landfill leachate. Batch tests further demonstrated that Fe3+ had the most positive effect on the degradation of sodium humate, as evidenced by a significant reduction in fluorescence regional integration (FRI) values. An integrated membrane bioreactor (MBR) and ozonation system were conducted, which firstly processed activated sludge treatment in the MBR and then pumped into the ozonation system via a peristaltic pump. After ozonation, the leachate overflowed back into the MBR for further treatment, creating a closed-loop system. It was observed that there was a significant reduction in humic substances, with a decrease of 96.31% in the FRI. Parallel factor analysis (PARAFAC) results corroborated these findings, which indicated a marked reduction in the abundance of humic-like substances C-BO-1 and C-BO-4 during the 17 days treatment period. This study revealed the pivotal role of microorganisms, ROS, metal ions, and humic substances in the treatment of landfill leachate. The metal ions presented in the leachate were confirmed to produce ROS during the ozonation process. However, a significant quantity of humic-like substances reduced the reactive ROS through complexation and consumption reactions. Simultaneously, microorganisms in the MBR system consumed humic substances such as C-BO-1 and C-BO-4, which promoted the degradation of contaminants in the landfill leachate. These insights provided implications for optimizing ozonation processes in leachate management, potentially leading to more efficient and environmentally sustainable waste disposal practices.

Ligand-engineered Fe(II)-metallo-supramolecular polymer with benzothiadiazole: Boosting electrochromic energy storage efficiency

The development of intelligent electrochromic energy storage devices that visually display color changes to indicate their charging and discharging status while offering high energy and power densities is gaining interest as a renewable energy solution. Our research engineered a bisterpyridine ligand (BTZ) with a benzothiadiazole spacer and its metallo-supramolecular polymer (Fe-BTZ) via Suzuki coupling and complexation reactions. Spectroscopic, morphological, and structural characterizations revealed nano-rod morphology due to higher aggregation of 1D Fe-BTZ metallo-supramolecular polymer. Quasi-solid-state electrochromic devices with Fe-BTZ as the active layer exhibited significant color changes (matte purple to dirty yellow), an optical contrast of 65.2 % at 567 nm, high coloration efficiency (518.2 cm2/C), quick coloration (0.5 s) and bleaching (1.8 s), and exceptional electrochromic durability compared with commonly used Poly-Fe metallo-supramolecular polymer. Conjugated ridged benzothiadiazole spacers enhanced electron mobility between the Fe-center during electrochemical transitions, increasing coloration efficiency, durability, and electrochromic speed. The Fe-BTZ and Prussian blue (PB)-based quasi-solid-state energy storage device also showed fast response times (1.1 s and 1.9 s), high CE (1077 cm2/C), 6500-cycle durability, high volumetric capacitance (70.1 ± 4 F/cm3) with a specific capacity of 10.96 mAh/g at 0.14 A/g current density and 74 % capacitance retention over 20,000 galvanostatic charge–discharge cycles. The device’s ability to power 18 red LEDs demonstrates its practical applicability.

Selectively recovering rare earth elements with carboxyl immobilized metal-organic framework from ammonium-rich wastewater

The material with high adsorption capacity and selectivity is essential for recovering rare earth elements (REES) from ammonium (NH4+-N)-rich wastewater. Although the emerging metal-organic framework (MOF) has gained intensive attention in REES recovery, there are scientific difficulties unsolved regarding restricted adsorption capacity and selectivity, hindering its extensive engineering applications. In this work, a diethylenetriamine pentaacetic (DTPA)-modified MOF material (MIL-101(Cr)-NH-DTPA) was prepared through an amidation reaction. The MIL-101(Cr)-NH-DTPA showed enhanced adsorption capacity for La(III) (69.78 mg g−1), Eu(III) (103.01 mg g−1) and Er(III) (83.41 mg g−1). The adsorption isotherm and physical chemistry of materials indicated that the adsorption of REEs with MIL-101(Cr)-NH-DTPA was achieved via complexation instead of electrostatic adsorption. Such complexation reaction was principally governed by -COOH instead of -NH2 or -NO2. Meanwhile, the resulting material remained in its superior activity even after five cycles. Such a constructed adsorbent also exhibited excellent selective adsorption activity for La(III), Eu(III), and Er(III), with removal efficiency reaching 70% in NH4+-N concentrations ranging from 100 to 1500 mg L−1. This work offers underlying guidelines for exploitation an adsorbent for REEs recovery from wastewater.

Gold(III) complexes with chloride and cyanopyridines: Facilitated hydrolysis of nitrile ligand to amide and antibacterial activity

A range of novel simple gold(III) compounds has been synthesized in their monocrystalline form, including two previously unknown chloro-complexes of Au3+ with 2-cyanopyridine or 3-cyanopyridine, respectively. Our investigations have revealed the intricate nature of the reaction between 2-cyanopyridine and tetrachloroauric acid, yielding at least three distinct products. The main product, obtained in high yield, is a salt featuring a tetrachloroauric anion and a pyridinium cation stabilized by a hydrogen bond to a further 2-cyanopyridine molecule. Moreover, we observed the in-situ formation of a 2-cyanopyridine-AuCl3 complex, which undergoes hydrolysis of the nitrile bond to yield a picolinamide-Au(III) complex. The complexes were characterized by IR and Raman spectroscopies, NMR spectroscopy, and single-crystal XRD studies. Additional computational studies were conducted to explain unusual spectral features, the observed disparities in the complexation reactions of the three isomeric cyanopyridine ligands and the distinct reactivity of the complex with 2-cyanopyridine. Based on these studies, we propose a mechanism for the catalyzed hydrolysis of the nitrile bond within the Au(III) complex. Finally, we assessed the antimicrobial efficacy of the synthesized gold(III) complexes against a spectrum of bacteria and fungi.

Rapid precipitation of vanadium from solution using melamine as precipitant with high efficiency

AbstractBACKGROUNDSelective catalytic reduction (SCR) can effectively remove NOx from flue gas in a coal‐fired power plant. As the core of SCR technology, the catalyst has a limited lifespan. The process of reducing acid leaching and roasting water leaching can efficiently extract vanadium and tungsten from spent SCR catalyst. For vanadium recovery in solution, the traditional vanadium precipitation process by NH4Cl has the disadvantages of consuming high precipitant dosage and producing large amounts of waste water.RESULTSThis study focused on the vanadium precipitation process using a solution containing vanadium obtained from adopting some steps to handle the spent SCR catalyst. First, melamine was screened out as the vanadium precipitant. Then, the vanadium precipitation conditions were optimized as follows: solution pH value of 1.0, n(C3H6N6)/n(V) = 0.8, 110 °C and 30 min. Under the best precipitation conditions, the vanadium precipitation efficiency of melamine can reach 99.32%. Finally, the mechanisms of vanadium precipitation by NH4Cl and melamine were discussed, respectively.CONCLUSIONThe results showed that the vanadium precipitation process by NH4Cl followed the chemical reactions between NH4+ and vanadium ions, while the vanadium precipitation process by melamine followed the redox and complexation reactions which essentially belonged to the types of chemical adsorption. The vanadium precipitation product was roasted at 550 °C for 2 h to obtain the vanadium product. The main component of the vanadium product was V2O5, with a purity of 93.27 wt%. The total recovery efficiency of vanadium from spent SCR catalyst was 78.24%. © 2024 Society of Chemical Industry (SCI).

An Efficient and Eco-Friendly Recycling Route of Valuable Metals from Spent Ternary Li-Ion Batteries: Kinetics Evaluation of Chlorination Processes and Regeneration of LiNi0.8Co0.1Mn0.1O2 Cathode Materials.

The recycling of spent Li-ion batteries is urgent, and the effective recovery of valuable metals from spent cathode material is an economic and eco-friendly approach. In this study, Ni, Cu, Co, and Mn were extracted synchronously from spent LiNixCoyMn1-x-yO2 by chlorination and the complexation reaction of ammonium chloride at low temperatures. The kinetics of the chlorination process was investigated by nonisothermal thermal analysis to determine the rate equation of metal conversion, and the apparent activation energies were calculated to be 99.96 kJ·mol-1 for lithium and 146.70 kJ·mol-1 for nickel, cobalt, and manganese, respectively. The separation of valuable metals from polymetallic leaching solution and the regeneration of cathode materials were further investigated to promote the industrialization of the process. The recoveries of Ni, Co, Mn, and Li can reach 97.75, 99.99, 99.99, and 92.23%, respectively. The prepared LiNi0.8Co0.1Mn0.1O2 precursor is a multilayer spherical particle formed by stacking primary hexagonal nanosheets along the (010) crystal axis, the formation mechanism of which was discussed. The effect of temperature, time, and mixed lithium ratio on the performance of single crystal LiNi0.8Co0.1Mn0.1O2 cathode in the synthesis process was investigated to determine the optimum conditions. Compared with commercial materials, the prepared single crystal LiNi0.8Co0.1Mn0.1O2 cathode has a more regular crystal structure and higher initial discharge capacity (215.9 mAh·g-1 at 0.1 C).

Understanding the wettability alterations in carbonate reservoirs: Integrating experimental data and a surface complexation model for enhanced predictions

In this study, we developed a laboratory-based model to analyze wettability alteration in the oil–water-rock system. The selected Surface Complexation Model (SCM), based on experimental data, is refined through sensitivity analysis and comparison with experimental measurements, including zeta potential and contact angle. Our analysis indicates that, in addition to magnesium, calcium, and sulfate ions, the adsorption of sodium and chlorine on calcite surfaces, as well as sodium adsorption on oil surfaces, significantly affects electrostatic interactions and surface potential alterations. Consequently, the complexing reactions of these ions were incorporated into the model and adjusted based on sensitivity analysis. Moreover, surface complex reactions exhibit distinct behaviors in neutral, acidic, and alkaline environments. Therefore, different reactions were considered and sensitivity analyzed for oil and rock surfaces in neutral conditions. The model’s reliability was further validated by comparing predicted and experimental zeta potentials. Additionally, disjoining pressures were computed, and contact angles were simulated, demonstrating the model’s accuracy. Key findings include the successful modification of reaction parameters to achieve accurate results across different pH levels and ion concentrations. This confirms the applicability and reliability of the developed SCM for wettability alteration analysis, further supported by stability maps that consider varying ion concentrations and pH levels.

Efficient density functional theory directed identification of siderophores with increased selectivity towards indium and germanium

Siderophores are promising ligands for application in novel recycling and bioremediation technologies, as they can selectively complex a variety of metals. However, with over 250 known siderophores, the selection of suiting complexants in the wet lab is impractical. Thus, this study established a density functional theory (DFT) based approach to efficiently identify siderophores with increased selectivity towards target metals on the example of germanium and indium. Considering 239 structures, chemically similar siderophores were clustered, and their complexation reactions modeled utilizing DFT. The calculations revealed siderophores with, compared to the reference siderophore desferrioxamine B (DFOB), up to 128 % or 48 % higher selectivity for indium or germanium, respectively. Experimental validation of the method was conducted with fimsbactin A and agrobactin, demonstrating up to 40 % more selective indium binding and at least sevenfold better germanium binding than DFOB, respectively. The results generated in this study open the door for the utilization of siderophores in eco-friendly technologies for the recovery of many different critical metals from various industry waters and leachates or bioremediation approaches. This endeavor is greatly facilitated by applying the herein-created database of geometry-optimized siderophore structures as de novo modeling of the molecules can be omitted.

Hydrogen inhibition of wet Al[sbnd]Li alloy dust collector systems using a composite green biopolymer inhibitor based on chitosan/sodium alginate: Experimental and theoretical studies

Aluminum‑lithium (AlLi) alloy polishing and grinding processes in wet dust collector systems could cause hydrogen fire and explosion. From the fundamental perspective of preventing hydrogen explosions, a safe, nontoxic, and sustainable modified green hydrogen inhibitor based on chitosan (CS) and sodium alginate (SA) was developed in this study and was used as a hydrogen evolution inhibitor for the processing of waste dust from AlLi alloys. The structure and elemental distribution of the synthesized material were characterized through characterization experiments. Hydrogen evolution experiments and a hydrolysis kinetic model were used to explore the inhibitory effect of modified CS/SA on AlLi alloy dust, and the results revealed that the inhibitory concentration of the hydrogen explosion lower limit was 0.40 wt%, with an inhibition efficiency of 91.93 %, indicating an 11.88–61.44 % improvement over that of CS and SA. As the inhibitor concentration increased and the temperature decreased, the hydrogen inhibition effect increased. Characterization experiments and density functional theory showed that CS/SA primarily formed a dense physical protective barrier on the dust surface through chemical adsorption and complexation reactions, interrupting the hydrogen evolution reaction between the metal and water. This study introduces a novel green modified hydrogen inhibitor that fundamentally addresses hydrogen generation and explosion.

Magneto-Luminescent Two-Dimensional Nanosheets of Gadolinium and Gold Nanocluster Assemblies with Surface Molecular Functionalization for White Light Emission.

We report the formation of photoluminescent two-dimensional (2D) crystalline nanosheet assemblies of gadolinium ions and ligand-stabilized gold nanoclusters (Gd-Au NCs). Transmission electron microscopy, selected area electron diffraction in conjunction with atomic force microscopy, and field-emission scanning electron microscopy analyses substantiated the 2D nature of Gd-Au NC nanosheets. The optical and magnetic properties of the nanosheets were investigated by photoluminescence measurements and vibrating-sample magnetometry analyses. The so-formed crystalline product was further utilized to generate a synchronous tricolor (orange, green, and blue) emission from a single excitation wavelength through an inorganic surface complexation reaction. The independent emissions were tunable after ligand functionalization by acetylsalicylic acid and fluorescein on the Gd-Au NC assembly. Interestingly, the assembled superstructure with augmented quantum yield led to white light emission at λexc ≈ 325 nm with CIE of (0.34, 0.33) and CRI value of >85 in the liquid phase. Furthermore, the ability to modulate the luminescence properties through the surface complexation of the 2D nanosheets of Au NCs may bring about new avenues toward applications in light-emitting devices, sensing, and biomedical imaging.

Integrated experiments and numerical simulations for chromium (VI) surface complexation in natural unconsolidated sediments

This study focuses on the adsorption and transport of Cr (VI) on natural sediments from Qiqihar, China. Through batch and column experiments, we assessed the adsorption capacities influenced by factors such as contact time, initial concentration, pH, ionic strength, solid-to-solution ratio, coexisting ions in groundwater, sediment characteristics and flow rate. The adsorption kinetics of Cr (VI) follow the pseudo-first-order model well, while the isotherms of all three sediments are accurately represented by the Freundlich model. The adsorption edges reveal a strong pH dependence in Cr (VI) adsorption: the stronger the acidity, the more favorable it is for adsorption. The adsorption capacity decreases with an increasing solid-to-solution ratio, stabilizing at higher ratios. Coexisting ions in groundwater reduce Cr (VI) adsorption in loam under neutral pH. Additionally, Fourier transform infrared spectroscopy (FTIR) results indicate that the hydroxyl group is the primary reactive functional group in all three sediments. X-ray photoelectron spectroscopy (XPS) results further show partial adsorbed Cr (VI) was reduced to Cr (III) by organic matters. However, surface complexation reactions dominate the removal of Cr (VI). On the base above, we introduced a surface complexation model, optimizing equilibrium complexation constants by fitting adsorption edges. Subsequently, reactive transport models incorporating both surface complexation and reduction processes for Cr (VI) were established to simulate column experiments. As the flow rate decreases, the adsorption capacity and the amount of reduction reaction for Cr (VI) increase, while the reduction rate decreases. Specifically, the reduction for Cr (VI) was found to be more significant in loam compared to sand, correlating with the organic matter content. The results emphasize the existence of surface complexation reactions and the role of organic matters in electron transfer. Our study provides significant information for understanding Cr (VI) adsorption and transport behavior in natural aquifer sediments.

Evaluation and optimization of six adsorbents for removal of tetracycline from swine wastewater: Experiments and response surface analysis

The removal of tetracycline antibiotics using adsorbents is becoming an environmentally friendly and cost-effective method. This study systematically analyzed the stability, structure, morphology, and chemical properties of various adsorbents. Batch adsorption experiments (pH, time, temperature, tetracycline concentration, and adsorbent dosage) were conducted to compare the adsorption capacity of the six adsorbents (biochar, activated carbon, montmorillonite, zeolite, chitosan, and polymerized aluminum chloride) for tetracycline removal. The results indicated that montmorillonite had the highest adsorption efficiency, followed by biochar, with chitosan showing the lowest efficiency. At an adsorbent dose of 25 g/L and an initial tetracycline concentration of 120 mg/L, the removal rates of tetracycline by montmorillonite, biochar, and chitosan were 97.6%, 69.3%, and 12.2%, respectively. Furthermore, the removal rate of tetracycline by biochar, following the response surface methodology optimal mode, increased by 5.5%. The Elovich model was better suited to explain the adsorption process of tetracycline compared to the conventional pseudo-first kinetic model and second-order kinetic model. The isothermal adsorption model suggested that both chemisorption and physisorption occurred in all removal processes, in which chemisorption dominated. Tetracycline was efficiently adsorbed through the combined effects of pore filling, electrostatic attraction, π-π interactions, and complexation reactions of surface functional groups. Additionally, montmorillonite demonstrated superior performance as an adsorbent for tetracycline removal from swine wastewater compared to the other adsorbents studied.

Photodetachment photoelectron spectroscopy shows isomer-specific proton-coupled electron transfer reactions in phenolic nitrate complexes

The oxidation of phenolic compounds is one of the most important reactions prevalent in various biological processes, often explicitly coupled with proton transfers (PTs). Quantitative descriptions and molecular-level understanding of these proton-coupled electron transfer (PCET) reactions have been challenging. This work reports a direct observation of PCET in photodetachment (PD) photoelectron spectroscopy (PES) of hydrogen-bonded phenolic (ArOH) nitrate (NO3−) complexes, in which a much slower rising edge provides a spectroscopic signature to evidence PCET. Electronic structure calculations unveil the PCET processes to be isomer-specific, occurred only in those with their HOMOs localized on ArOH, leading to charge-separated transient states ArOH•+·NO3− triggered by ionizing phenols while simultaneously promoting PT from ArOH•+ to NO3−. Importantly, this study showcases that gas-phase PD-PES is a generic means enabling to identify PCET reactions with explicit structural and binding information.

(Invited) Two-Dimensional Metal–Organic Framework Acts As a Hydrogen Evolution Cocatalyst for Overall Photocatalytic Water Splitting

Water-splitting semiconductor photocatalysts require hydrogen evolution reaction (HER) cocatalysts, the majority of which are robust metals and metal oxides. Metal complexes feature designability and reaction selectivity. This feature should be appreciated in the application as HER cocatalysts by suppressing unfavorable back reactions; however, low stability hampers their application. In this research, we demonstrate that a fully π-conjugated and conductive two-dimensional metal–organic framework (2D MOF), which possesses both virtues of metals/metal oxides and metal complexes, serves as an ideal HER cocatalyst candidate. NiBHT, a kind of 2D MOF, is deposited on the photocatalyst SrTiO3:Al with CoO x as an oxygen evolution cocatalyst to show long-term overall one-step water splitting with an apparent quantum efficiency (AQE) of 6.5% at 350 nm. In comparison to Pt as a representative HER cocatalyst, NiBHT turns out to be a suppressor of back reactions related to oxygen reduction reactions, which is proven both experimentally and theoretically.

Adsorption and migration behaviors of heavy metals (As, Cd, and Cr) in single and binary systems in typical Chinese soils

In this study, the competitive adsorption and migration behaviors of arsenic (As), cadmium (Cd), and chromium (Cr) in typical Chinese soils were investigated. It was observed that Hainan, Shanxi, and Zhejiang Mengjiadai soils exhibited the highest adsorption capacities for As (563 μg/g), Cd (653 μg/g), and Cr (383 μg/g), respectively. Heavy metals (HMs) adsorption capacities were predicted by Extreme gradient boosting (XGBoost) models, and the Shapley additive explanation (SHAP) was employed to elucidate the effect of soil physicochemical properties on target values. Due to redox and complexation reaction, the primary factor affecting adsorption has changed from free state manganese (Mn) in single As system to antimony (Sb) in As/Cd and As/Cr systems. Furthermore, the maximum adsorption capacity (Qm) of As increased by 49.4 % with the addition of Cd into Heilongjiang soil. Finally, the migration process of HMs in Heilongjiang, Hebei, and Hainan soils was simulated by column experiments. With a relatively large dispersion coefficient (D = 29.630 cm2/h) and small retardation factor (Rh = 0.030), Cr penetrated fastest in Heilongjiang soil. This research demonstrates that both the types and coexistence of HMs may affect the HMs behaviors in soil.

Adsorption pathways of boron on clay and their implications for boron cycling on land and in the ocean

Reversible adsorption and isotope fractionation of boron on the surface of clay minerals is a key process that impacts boron isotope cycling in porewater, rivers and the ocean. However, the differences in boron isotope fractionation factors between various clay minerals and their dependence on fluid chemistry are not well known. We performed two sets of experiments, using solutions of pure water with added boron and seawater, to explore the isotope behavior during adsorption of boron onto kaolinite, smectite and illite. We found that the amount of sorbed boron increases with ionic strength of solutions and is proportional to the cation exchange capacity of a given clay mineral. Maximum adsorption is observed in alkaline seawater, which we attribute to the efficient fixation of magnesium-borate ion pairs onto negatively charged surface sites. Isotopic fractionation is modestly different between clays and demonstrates that clay surfaces preferentially sorb borate, even when the concentration of borate in solution is low. In both pure water and seawater, adsorbed complexes retain the isotopic composition of their dissolved precursors (borate or boric acid) with minimal isotopic fractionation. In other words, isotopic composition of adsorbed boron is set by the ability of clays to adsorb boron from an already fractionated boron pool rather than specific fractionation associated with the complexation reaction. Our experimental results allow us to provide revised constraints on the adsorbed boron being transported in terrestrial fluids and the ocean.

Exploring the Enhanced Oxidation Potential through Green Synthesis of Ofloxacin–Silver Complex: Investigating Silver and Ofloxacin Interaction at Varied Concentrations

The purpose for this work is to synthesize ofloxacin–Silver(I) complex with the highest oxidation potential in liquid state with green methodology. Initially, we investigated the complexation of the OFL ligand with silver ions using UV-visible spectrophotometry, differential pulse wave voltammetry, and electrochemical impedance spectroscopy. The UV-visible results indicated the interaction between OFL and Ag+ through a complexation reaction. Notably, the peak corresponding to OFL oxidation at 0.98 V showed a significant increase in the presence of silver, leading to an oxidation potential shift towards positive values attributed to the bond formation between the OFL and Ag+. In terms of structural characterization, various spectroscopic analyses were employed, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and scanning electron microscopy. The OFL–Ag+ complex formation was confirmed by the appearance of two distinct sharp bands at 547 and 950 cm−1 in the FTIR spectra. The average particle diameter of the OFL–Ag+ complex was determined to be 187.5 nm. This complex, synthesized as a brown solid powder soluble in water, exhibited the highest oxidation potential of 1.32 V. Hence, it holds promise for potential application in antibacterial activity.

The performance and mechanism of sulfidated nano-zero-valent iron for the simultaneous stabilization of arsenic and cadmium

Co-contamination of soil and groundwater with arsenic (As) and cadmium (Cd) is widespread. Sulfidized Nanoscale Zero-Valent Iron (S-nZVI) is effective in removing As and Cd from contaminated environments. However, the mechanisms governing As and Cd removal from systems containing both species are still unclear. This study investigated the effectiveness of S-nZVI in the simultaneous removal of Cd(II) and As(III) from contaminated solutions and their interaction mechanisms. Adsorption experiments were conducted under aerobic conditions to investigate the effect of Cd(II) and As(III) on their co-immobilisation at different As(III) and Cd(II) concentrations. S-nZVI was characterised before and after the reaction to elucidate the mechanism of its simultaneous immobilisation of As(III) and Cd(II). Batch experiments revealed that the presence of Cd(II) and As(III) together considerably promotes the passivation of S-nZVI. The adsorption of Cd(II) at Cd:As = 1:3 was 198.37 mg/g, which was 27.6 % higher than that in Cd(II)-only systems, and the adsorption of As(III) at As:Cd = 1:3 was 204.05 mg/g, which was 175 % higher than that in As(III)-only systems. The results of X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that the removal of Cd(II) and As(III) by S-nZVI involves electrostatic adsorption, complexation and oxidation reactions, amongst which electrostatic adsorption and ternary-complex generation are responsible for the synergistic effect. As and Cd ions can form two types of surface complexes with FeOH or FeS on the outer layer of S-nZVI: anionic bridging to form Fe–As–Cd and cationic bridging to form Fe–Cd–As. This investigation elucidates the synergistic action of Cd(II) and As(III) during their removal using S-nZVI. Thus, S-nZVI is a promising material for the combined removal of Cd(II) and As(III), which can mitigate environmental pollution.

Multicomponent and Surface Charge Effects on PFOS Sorption and Transport in Goethite-Coated Porous Media under Variable Hydrochemical Conditions.

Perfluorooctanesulfonate (PFOS), a toxic anionic perfluorinated surfactant, exhibits variable electrostatic adsorption mechanisms on charge-regulated minerals depending on solution hydrochemistry. This work explores the interplay of multicomponent interactions and surface charge effects on PFOS adsorption to goethite surfaces under flow-through conditions. We conducted a series of column experiments in saturated goethite-coated porous media subjected to dynamic hydrochemical conditions triggered by step changes in the electrolyte concentration of the injected solutions. Measurements of pH and PFOS breakthrough curves at the outlet allowed tracking the propagation of multicomponent reactive fronts. We performed process-based reactive transport simulations incorporating a mechanistic network of surface complexation reactions to quantitatively interpret the geochemical processes. The experimental and modeling outcomes reveal that the coupled spatio-temporal evolution of pH and electrolyte fronts, driven by the electrostatic properties of the mineral, exerts a key control on PFOS mobility by determining its adsorption and speciation reactions on goethite surfaces. These results illuminate the important influence of multicomponent transport processes and surface charge effects on PFOS mobility, emphasizing the need for mechanistic adsorption models in reactive transport simulations of ionizable PFAS compounds to determine their environmental fate and to perform accurate risk assessment.

Control of Iron(II)-Tris(2,2'-Bipyridine) Light-Induced Excited-State Trapping via External Electromagnetic Fields.

Light-induced excited spin-state trapping reactions in iron pyridinic complexes allow the iron's low-to-high spin transition in a sub-picosecond timescale. Employing a recently developed model for [Fe(2,2'-bipyridine)3]2+ photochemical spin-crossover reaction in conjunction with quantum wavepacket dynamics, we explore the possibility of controlling the reaction through external electromagnetic fields, aiming at stabilizing the initial metal-to-ligand charge transfer states. We show that simple Gaussian-shaped electromagnetic fields have a minor effect on the population kinetics. However, introducing vibrationally excited initial wavepacket representations allows for maintaining the population trapped in the metal-to-ligand charge transfer states. Using optimal control theory, we propose an electromagnetic field shape that increases the lifetime of metal-to-ligand charge transfer states. These results open the route for controlling the iron photochemistry through the action of external electric fields.