A DFT-based analysis of adsorption of Cd2+, Cr3+, Cu2+, Hg2+, Pb2+, and Zn2+, on vanillin monomer: a study of the removal of metal ions from effluents

Theoretical study of the adsorption capacity of potentially toxic Cd2+, Pb2+, and Hg2+ ions in hemicellulose matrices

Hemicellulose is widely available in nature, is a sustainable resource and has a wide range of applications. Among them, adsorption stands out for the removal of potentially toxic ions. Thus, in the study, the adsorption of Cd2+, Pb2+ and Hg2+ ions in two hemicellulose matrices were elucidated through computational simulations using density functional theory. Molecular electrostatic potential and frontier molecular orbitals demonstrated whether the interactions could happen. Four interaction complexes were highlighted due to the interaction energy criteria, ΔEBind, ΔH and ΔG < 0.00 kcal mol-1, that is: Hm1… Pb (1); Hm2… Pb (3); Hm2…Cd (4) and Hm2…Hg (4) and the results show that they occur through physisorption. In structural parameter studies, interaction distances smaller than 3000 Å were identified, which ranged from 2.253 Å to 2.972 Å. From the analysis of the topological parameters of QTAIM, it was possible to characterize the intensities of the interactions, as well as their nature, which were partially covalent or electrostatic in nature. Finally, based on the theoretical results, it can be affirmed that the hemicellulose can interact with Cd2+, Pb2+ and Hg2+ ions, evidencing that this study can support further experimental essays to remove contaminants from effluents.

Effect of resolution enhancement using metal ion assisted strategy based on electrospray ionization-ion mobility spectrometry: A case study of carbendazim and thiabendazole in fruits

A method for the rapid and simultaneous determination of carbendazim and thiabendazole residues by electrospray ionization-ion mobility spectrometry (ESI-IMS) combined with a metal ion-assisted technique was developed and validated in different fruit matrices. The metal ion assisted strategy was performed instead of tedious pre-separation procedures to overcome the limitation of low resolution of IMS. Four transition metal cations, Co(II), Ni(II), Cu(II), and Zn(II), were screened and their interactions with carbendazim and thiabendazole were investigated. The injection flow rate and metal ion concentration were optimized. The Cu(II) assisted approach helped to achieve well-separated peaks with a peak-to-peak resolution of 3.61. This method was then applied to detect carbendazim and thiabendazole simultaneously in apples, pears, bananas, and mangoes. The limit of detection (LOD) were 0.03 mg kg-1 and 0.13 mg kg-1 for carbendazim and thiabendazole, respectively, while spiked recoveries were 61.5-122.0% and 83.5-119.8%, respectively, with RSDs less than 13.9%. These satisfactory evaluation parameters indicated that the approach was capable of performing quantitative analysis of multi-pesticide residues. In addition, the feasibility of using metal ion assisted-ESI-IMS for the simultaneous detection also was theoretically demonstrated through molecular electrostatic potential analysis and binding energy calculation based on density functional theory (DFT). Both experimental and theoretical results revealed the effectiveness of the metal ion assisted strategy in improving the resolution of ESI-IMS.

Computational Insights on the Chemical Reactivity of Functionalized and Crosslinked Polyketones to Cu2+ Ion for Wastewater Treatment

Today, the high concentrations of copper found in water resources result in an urgent problem to solve since human health and aquatic ecosystems have been affected. Functionalized crosslinked polyketone resins (XLPK) have demonstrated high performance for the uptake of heavy metals in water solutions. In addition, its green chemical synthesis makes these resins very attractive as sorbents for metal ions contained in wastewater. XLPK are not soluble in aqueous media and do not require any catalyst, solvent, or harsh conditions to carry out the uptake process. In this paper, a series of functionalized XLPK with pending amino-derivatives namely; butylamine (BA), amino 2-propanol (A2P), 4-(aminomethyl) benzoic acid (HAMC), 6-aminohexanoic acid (PAMBA), and 1,2 diamino propane (DAP) directly attached to the pyrrole backbone of the polymers and crosslinked by di-amine derivatives was investigated using Density Functional Theory (DFT) calculations. Our computational analysis revealed that dipole-dipole interactions played a crucial role in enhancing the adsorption of Cu2+ ions onto XLPKs. The negatively charged ketone moieties and functional groups within XLPKs were identified as key adsorption sites for the selective binding of Cu2+ ions. Additionally, we found that XLPKs exhibited strong electrostatic interactions primarily through the -NH2 and -C=O groups. Evaluation of the adsorption energies in XLPK-Cu(II) complexes showed that the DAP-Cu(II) complex exhibited the highest stability, attributed to strong Cu(II)-N binding facilitated by the amino moiety (-NH2). The remaining XLPKs displayed binding modes involving oxygen atoms (Cu(II)-O) within the ketone moieties in the polymer backbone. Furthermore, the complexation and thermochemical analysis emphasized the role of the coordinator atom (N or O) and the coordinating environment, in which higher entropic effects involved in the adsorption of Cu2+ ions onto XLPKs describes a lower spontaneity of the adsorption process. The adsorption reactions were favored at lower temperatures and higher pressures. These findings provide valuable insights into the reactivity and adsorption mechanisms of functionalized and crosslinked polyketones for Cu2+ uptake, facilitating the design of high-performance polymeric resins for water treatment applications.

Porphyrin and phthalocyanine heavy metal removal: overview of theoretical investigation for heterojunction organic solar cell applications

CONTEXT

Heavy metals are highly noxious, and their presence can cause diverse effects on living organisms and the environment. Crown ether porphyrins and phthalocyanines are known to effectively extract these pollutants and are also used in photovoltaic devices. This study aims to evaluate various factors that govern intramolecular charge transfer (ICT) and photo-injection processes, including maximum absorption wavelength (λ_max), density of states (DOS), charge transfer dipole (μ_CT), light harvesting efficiency (LHE), open-circuit voltage (V_oc), and free energy change of electron injection (ΔG_inj) in order to investigate the performance of different compounds designed from metalloporphyrins for bulk-heterojunction organic solar cell (BHJ-OSC) applications. The porphyrin complex showed the best optoelectronic properties, with remarkable LHE values and CT amounts compared to phthalocyanine derivatives. The central metal played a significant role in optimizing the optical properties of the materials for use in solar cells. HgPr4O and CdPr4O were found to have optimal V_oc values, resulting in effective injection, high electron, and hole mobilities, making them ideal materials for highly efficient BHJ-OSC devices.

METHODS

Density functional theory (DFT) approach was employed with the B3LYP functional and the def2TZVP basis set as implemented in the Gaussian 16 revision C.01 program to investigate the designed complexes and to compute geometrical parameters, frontier molecular orbitals (FMOs), and natural bond orbital (NBO). Furthermore, the time-dependent density functional theory (TD-DFT) method was used to analyze the optical properties and photovoltaic characteristics of selected metalloporphyrins by examining the UV-Vis spectra. In summary, the study presents a thorough description of the structural and electronic properties of the investigated complexes and provides insights into their potential use in photovoltaic applications.

Post-synthetic thiol modification of covalent organic frameworks for mercury(II) removal from water

Various materials have been developed for environmental remediation of mercury ion pollution. Among these materials, covalent organic frameworks (COFs) can efficiently adsorb Hg(II) from water. Herein, two thiol-modified COFs (COF-S-SH and COF-OH-SH) were prepared, through the reaction between 2,5-divinylterephthalaldehyde and 1,3,5-tris-(4-aminophenyl)benzene, followed by post-synthetic modification using bis(2-mercaptoethyl) sulfide and dithiothreitol, respectively. The modified COFs showed excellent Hg(II) adsorption abilities with maximum adsorption capacities of 586.3 and 535.5 mg g^-1 for COF-S-SH and COF-OH-SH, respectively. The prepared materials showed excellent selective absorbability for Hg(II) against multiple cationic metals in water. Unexpectedly, the experimental data showed that both co-existing toxic anionic diclofenac sodium (DCF) and Hg(II) performed positive effect for capturing another pollutant by these two modified COFs. Thus, a synergistic adsorption mechanism between Hg(II) and DCF on COFs was proposed. Moreover, density functional theory calculations revealed that synergistic adsorption occurred between Hg(II) and DCF, which resulted in a significant reduction in the adsorption system's energy. This work highlights a new direction for application of COFs to simultaneous removal of heavy metals and co-existing organic pollutants from water.

Heterotrophic anodic denitrification coupled with cathodic metals recovery from on-site smelting wastewater with a bioelectrochemical system inoculated with mixed Castellaniella species

Although Castellaniella species are crucial for denitrification, there is no report on their capacity to carry out denitrification and anode respiration simultaneously in a bioelectrochemical system (BES). Herein, the ability of a mixed inoculum of electricigenic Castellaniella species to perform simultaneous denitrification and anode respiration coupled with cathodic metals recovery was investigated in a BES. Results showed that 500 mg/L NO₃^--N significantly decreased power generation, whereas 100 and 250 mg/L NO₃^--N had a lesser impact. The single-chamber MFCs (SCMFCs) fed with 100 and 250 mg/L NO₃^--N concentrations achieved a removal efficiency higher than 90% in all cycles. In contrast, the removal efficiency in the SCMFCs declined dramatically at 500 mg/L NO₃^--N, which might be attributable to decreased microbial viability as revealed by SEM and CLSM. EPS protein content and enzymatic activities of the biofilms decreased significantly at this concentration. Cyclic voltammetry results revealed that the 500 mg/L NO₃^--N concentration decreased the redox activities of anodic biofilms, while electrochemical impedance spectroscopy showed that the internal resistance of the SCMFCs at this concentration increased significantly. In addition, BES inoculated with the Castellaniella species was able to simultaneously perform heterotrophic anodic denitrification and cathodic metals recovery from real wastewater. The BES attained Cu²⁺, Hg²⁺, Pb²⁺, and Zn²⁺ removal efficiencies of 99.86 ± 0.10%, 99.98 ± 0.014%, 99.98 ± 0.01%, and 99.17 ± 0.30%, respectively, from the real wastewater. Cu²⁺ was bio-electrochemically reduced to Cu⁰ and Cu₂O, whereas Hg⁰ and HgO constituted the Hg species recovered via bioelectrochemical reduction and chemical deposition, respectively. Furthermore, Pb²⁺ and Zn²⁺ were bio-electrochemically reduced to Pb⁰ and Zn⁰, respectively. Over 89% of NO₃^--N was removed from the BES anolyte during the recovery of the metals. This research reveals promising denitrifying exoelectrogens for enhanced power generation, NO₃^--N removal, and heavy metals recovery in BES.

Selective preconcentration separation of Hg(ii) and Cd(ii) from water, fish muscles, and cucumber samples using recycled aluminum adsorbents

Modified aluminum scrap waste was used in the selective extraction of Hg(ii), and Cd(ii) ions. The aluminum scraps were modified with dibenzoylmethane, or isatoic anhydride, or 5-(2-chloroacetamide)-2-hydroxybenzoic acid. The modified aluminum sorbents were characterized by FT-IR, SEM, XRD, XPS, TGA, and elemental analysis. Modes of chelation between adsorbents and target metal ions were deduced via DFT. The highest adsorption capacity was observed for benzo-amino aluminum (BAA) toward Hg(ii), which reached 234.56 mg g⁻¹, while other modified sorbents ranged from 135.28 mg g⁻¹ to 229.3 mg g⁻¹. Under the optimized conditions, the BAA adsorbent showed a lower limit of detection (1.1 mg L⁻¹) and limit of quantification (3.66 mg L⁻¹) for mercury ions than other sorbents. The prepared aluminum adsorbents also exhibited significant selectivities for Hg(ii) and Cd(ii) ions in the presence of competing metal ions.

Modified aluminum scrap waste was used in the selective extraction of Hg(ii), and Cd(ii) ions.

DFT study on the effect of functional groups of carbonaceous surface on ammonium adsorption from water

Density functional theory (DFT) was used to study the adsorption of ammonium ion on carbon materials. The effects of single and multiple adjacent functional groups of carbon structures on ammonium ion adsorption were emphasized. The electrostatic potential, adsorption energy, charge transfer, molecular orbital, and dipole moment of different configurations were analyzed. Results showed that the carbonyl group was more likely to adsorb ammonium ion than lactone, carboxyl, and hydroxyl. When the carbon material contained multiple adjacent functional groups at the same time, the adsorption of ammonium ion can be promoted or inhibited due to the interaction among functional groups. The effect of functional groups on the adsorption of π bond in carbon materials was related to the electronegativity of functional groups, i.e., greater electronegativity led to smaller adsorption energy of π bond. Carbon material itself is nonpolar and hydrophobic, so adding oxygen-containing functional groups can increase the dipole moment of carbon material molecules, thereby enhancing its polarity and adsorption capacity.

Adsorption of Pb(II) cation from aqueous solutions by acid modified low-rank coal: An experimental study and simulation

An acid modified approach to enhance the adsorption capacity of low-rank coal (lignite) is proposed to reduce the risk of heavy metal ions within the wastewater. Adsorption kinetics, adsorption thermodynamics, adsorption coefficient and density functional theory DFT calculations were studied in this paper, respectively. The results indicate that the adsorption capacity of lignite was enlarged after HNO₃ modification, and pseudo-second order kinetics model and Langmuir isothermal adsorption model can be used to describe the adsorption process. The surface chemical properties of lignite play a dominant role rather than the specific surface area and total pore volume in the Pb(II) cation adsorption process, and it is suggested that the adsorption of Pb(II) cation by raw lignite (RL) and modified lignite (ML) is mainly completed by chemical adsorption. The Fourier transform infrared spectroscopy (FTIR) characterization showed that the surface oxygen functional groups of lignite increased after modification. The results of interaction energies between the model molecule and Pb(II) cation show that Pb(II) cation and -C-O-C are most easily combined, followed by -COOH, and -C = O is the weakest.

Computational study of the interaction of heavy metal ions, Cd(II), Hg(II), and Pb(II) on lignin matrices

Contamination by heavy metal ions, particularly in water resources, is a severe environmental problem. In this study, the interaction of metal ions, namely, Cadmium Cd(II), Mercury Hg(II), and Lead Pb(II), on lignin matrices was investigated based on theoretical calculations. Binding energy (ΔE_Bind) values proved that the Pb(II) interacted better with lignin matrices than Cd(II) or Hg(II), having energy values between -8.4 kcal mol^-1 to -20.2 kcal mol^-1. The Gibbs energy (ΔG) and enthalpy (ΔH) values for Pb(II) were <0, indicating that the process was spontaneous and released heat. However, the lignin matrices studied in this work did not interact efficiently with Cd(II) and Hg(II) ions because almost all ΔE_Bind, ΔG, and ΔH values were positive. The bond length of the interaction proved that the Pb ions yielded the smallest values, ratifying the values for the interaction energy. Analyses based on the quantum theory of atoms in molecules showed that the interactions between Pb(II) and the matrices were partially covalent, whereas the interactions of Cd(II) and Hg(II) were predominantly electrostatic, justifying the positive values of ΔE_Bind, ΔG, and ΔH. The natural bond orbital results showed that the ligand orbitals of the matrix interacted with the lone pair antibonding orbital (LP*) of the metal ions. The theoretical results of the study show the possibility of applying lignin to remove heavy metal ions, especially Pb, and providing information for research related to wastewater treatment.

Interaction of glyphosate in matrices of cellulose and diethylaminoethyl cellulose biopolymers: theoretical viewpoint of the adsorption process

Glyphosate is an herbicide widely used in agricultural activities causing contamination of soils and bodies of water and damage to the biodiversity of ecosystems. In this context, the present study aimed to theoretically study the adsorption potential of the biopolymer cellulose (CE) and its diethylaminoethyl cellulose derivative (DEAEC) with the herbicide glyphosate (GLY). Theoretical calculations were performed using the density functional theory. Molecular electrostatic potential and frontier molecular orbital analyses were performed, which allowed identifying the possible sites of interaction of biopolymers that were in the functional groups -OH and O- of cellulose and in the groups -O- and -NH+(CH2CH3)2 of the DEAEC. Reactivity indices chemical softness and hardness showed that both adsorbents could interact with adsorbate. Simulated IR indicated that the interactions could be evinced in experimental measurements by changes in the bands of glyphosate (ν(P = O), δ(P-O-H), δ(C-N-H)) or in the bands of CE and DEAEC (ν(C-O), ν(C-H), ν(N-H)). The binding energies showed that the GLY interacts more effectively with CE than DEAEC. The ΔH prove that all processes are exothermic and the CE-GLY1 interaction showed value of ΔG < 0. The topological results showed a greater number of interactions with electrostatic nature. The results found in the study show that the theoretical data provides useful information to support the use of biopolymers as matrices for glyphosate adsorption or other contaminants.

Carbon nitride-doped melamine-silver adsorbents with peroxidase-like catalysis and visible-light photocatalysis: Colorimetric detection and detoxification removal of total mercury

Mesoporous melamine-silver (MA-Ag) nanocomposites doped with carbon nitride quantum dots (CN_QDs) were fabricated simply by the controlled supramolecular self-assembly. It was discovered that the resulting nanoflower-like CN_QDs@MA-Ag nanocomposites could exhibit the peroxidase-like catalysis, which could be specifically enhanced by Hg²⁺ by forming Ag@Hg alloys. A double catalysis-based colorimetric method was thereby developed for the fast detecting of Hg²⁺ and Hg⁰ in wastewater samples, with the levels down to 0.050 nM and 18.3 nM, respectively. Moreover, strong visible-light-driven photocatalysis of the nanocomposites was demonstrated for oxidizing Hg⁰ into Hg²⁺ through photocatalytic H₂O₂ production so as to realize the detoxification of Hg⁰ in the environmental wastewater. Besides, the fabricated mesoporous CN_QDs@MA-Ag nanocomposites with large specific surface areas might facilitate the high Hg adsorption through the powerful MA-Hg chelate interaction, showing the efficient adsorption and/or removal of total Hg. The catalysis-selective colorimetric analysis and photocatalysis-based detoxification removal of total mercury may promise for wide applications in the environmental monitoring and wastewater treatment of toxic heavy metals of mercury.

Computational study of phosphate adsorption on Mg/Ca modified biochar structure in aqueous solution

Phosphate removal in water using biochar is widely investigated. Density functional theory was used to study the adsorption of phosphate (H₂PO₄^-) on biochar in water after metal modification. Two types of metals, Mg and Ca, were used to modify the biochar structure, and the edge and metal adsorptions of H₂PO₄^- were investigated on the modified biochar structure. Results were analyzed from the aspects of structural stability, adsorption energy, change in dipole moment, density of electronic states, and atoms in molecules analysis. The overall effect of metal-modified biochar materials on phosphate adsorption was stronger than that of unmodified biochar materials in terms of molecular level. The stability of the metal-modified structure by adding metal was low, and adsorption was prone to occur in this situation. The Ca-modified biochar showed better phosphate adsorption than the Mg-modified structure. Metal adsorption performed better than edge adsorption, proving that the modified metal in the biochar structure played a leading role in H₂PO₄^- adsorption. Metal adsorption was mainly caused by electrostatic attraction, and edge adsorption was mainly caused by covalent bonding.

A DFT study on the adsorption of nucleobases with Au20

The interactions of nucleobase with Au₂₀ cluster were studied utilizing density functional theory (DFT). We find that the nucleobases were attached with Au₂₀ through Au-N or Au-O bonds. The orders of calculated adsorption energy are cytosine > adenine > guanine > thymine. The maximum adsorption energy is - 0.787 eV which belongs to the adsorption of cytosine on Au₂₀ cluster. Our calculations show that the HOMO-LUMO gaps of Au₂₀ are significantly decreased by the nucleobase adsorption, suggesting the potential detection for nucleobases. The interactions between Au₂₀ and nucleobases are revealed through the QTAIM analysis. The NBO analysis was investigated for the electron transfer of donor-acceptor of all types of complexes. The IR and UV-vis spectra were simulated for the further identification in the experiment.

Adsorption Properties of Hydrated Cr3+ Ions on Schiff-base Covalent Organic Frameworks: A DFT Study

Considering the superior physiochemical property, increasing efforts have been devoted to exploiting the covalent organic frameworks (COFs) materials on the environmental remediation of heavy metal ions. Water pollution caused by Cr³⁺ metal ions is of special concern for scientists and engineers. Notwithstanding all the former efforts made, it is surprising that very little is known about the interaction mechanisms between the hydrated Cr³⁺ metal ions and COF materials. In present context, density functional theory (DFT) method is used to elucidate geometric and electronic properties with the purpose of putting into theoretical perspective the application values and interaction mechanisms for COF materials on Cr³⁺ capture. The results showed that all the five selected Schiff-base COFs materials displayed good adsorption performance on Cr³⁺ removal while the phenazine-linked and imine-COFs possessed the most favorable adsorption capacity due to the optimal chemical units and frameworks. The hydration effect was found to play a two-side role in the adsorption process and interaction mechanisms, involving coordination, hydrogen bonds, as well as weak non-covalent interactions, have been illuminated to explain the observed different adsorption behaviors. This study provides a general guidance for the design and selection of efficient COF materials as high-capacity Cr³⁺ adsorbents.