Underlying Adsorption Mechanism Research Articles

Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate

Chemical modification of agricultural waste biomass has proved to be an economy and effective approach to capture phosphate ions, except for that under acidic conditions and highly competitive ion systems. According to this, a new nanocomposite (HFO@St+) was fabricated by incorporating nano-sized hydrous Fe(III) oxides (HFO) within aminated wheat straw in order to overcome the bottleneck. The optimal pH of phosphate uptake by HFO@St+ was greatly broadened and observed over a wide pH range between 2.0 and 7.0. The binary exchange reaction indicated that phosphate was strongly and preferably adsorbed by HFO@St+ with the separation factor K of phosphate over nitrate increasing from 0.23–1 or 0.20–0.26 to 2.5–38 or 2.5–15 for near neutral or acidic pHs, respectively. The sorption selectivity for HFO@St+ followed the order of phosphate > nitrate > chloride under experimental conditions. The presence of inorganic and organic ligands (SO4 and HA) showed no significant effect on phosphate adsorption. XPS and FT-IR analyses were performed to explore the underlying mechanism of adsorption. The exhausted material could be regenerated with NaOH-NaCl solution for at least ten cycles, indicating that HFO@St+ can be used as a sustainable biomass product with excellent adsorption affinity for phosphate removal.

Simultaneous adsorption of Cd(II) and As(III) by a novel biochar-supported nanoscale zero-valent iron in aqueous systems

Biochar-supported nanoscale zero-valent iron (nZVI-BC) is a promising material for Cd(II) and As(III) removal from aqueous systems. In this study, simplified nZVI-BC composites were successfully synthesized and characterized via scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectroscopy (FTIR) to understand the underlying adsorption mechanism. SEM and FTIR confirmed that nZVI particles were distributed evenly on the biochar surface. XRD and XPS revealed that metal ions were separated from solutions via electrostatic adsorption, complexation, oxidation, precipitation/co-precipitation, and the formation of type B ternary surface complex. Batch experiments showed that nZVI-BC (1:1) had a high removal efficiency in a wide pH range of 5.0–8.0 for Cd(II) and 3.0–8.0 for As(III), the maximum Cd(II) and As(III) adsorption capacities were 33.81 and 148.5 mg/g within 2 and 1 h, respectively. Additionally, synergisticeffects considerably enhanced the adsorption capacity of nZVI-BC(1:1) in mixed adsorption systems, the adsorption capacities of Cd(II) and As(III) reached 179.9 and 158.5 mg/g, respectively. Hence, nZVI-BC(1:1) is an ideal candidate for Cd(II) and As(III) pollution treatment.

Novel polyazamacrocyclic receptor impregnated macroporous polymeric resins for highly efficient capture of palladium from nitric acid media

A novel composite resin C8-Cyclen/CG-71M, with the specific binding ability to palladium ions in HNO3 solution, was developed by impregnating tetraoctyl-substituted 1,4,7,10-tetraazacyclododecane (C8-Cyclen) receptor into the macroporous polymeric resins (Amberchrom CG-71M). The structure and morphology of obtained products were fully characterized. Study on the batch experiments revealed that C8-Cyclen/CG-71M resin exhibited rapid kinetics, favorable adsorption ability and high selectivity toward Pd(II) in a wide HNO3 concentration. The theoretical interpretation of the experimental data by employing kinetics models, Langmuir/Freundlich isotherms and thermodynamic equations were implemented to describe the adsorption behavior. The results showed that the adsorption process of Pd(II) by C8-Cyclen/CG-71M was comforted to a monolayer-coverage with the maximum adsorption capacity of 169.5 mg/g. Besides, the XPS analysis was performed to probe the underlying adsorption mechanism to Pd(II). A suggested mechanism involving the synergistic effect of four cyclic amines in C8-Cyclen receptors was proposed to describe the interaction manner between Pd(II) and C8-Cyclen/CG-71M. Furthermore, the resin was also applied to recovery Pd(II) from HCl media and similar results were obtained. Overall, due to the benign synthesis, efficient adsorption ability and facile operation, C8-Cyclen/CG-71M might be a promising resin material for Pd(II) selective capture from radioactive wastes, and other leaching solution of spent catalysts and electronic scraps.

Efficient removal of gaseous formaldehyde by amine-modified diatomite: a combined experimental and density functional theory study.

Amine-modified diatomite with remarkable formaldehyde (HCHO) removal efficiency was prepared by grafting 3-aminopropyltrimethoxysilane (APTMS) in this research. The interfacial properties and microstructures of the prepared adsorbents were characterized and analyzed. The HCHO adsorption properties of the amine modified diatomite were also systematically studied, and it has been proven to be effective adsorbent with better adsorption performance than activated carbon for the removal of gaseous HCHO. Furthermore, to better explain the experimental results, we performed density functional theory (DFT) study on the adsorption system and calculated the geometry, energy, and charge parameters based on first principles. Also, the underlying adsorption mechanism was proposed detailedly by combining experimentation with DFT calculation, suggesting that amine modified diatomite can be efficient adsorbent for the elimination of gaseous formaldehyde.

Combined adsorption/regeneration process for the removal of trace emulsified hydrocarbon contaminants

In this study a process of adsorption and electrochemical regeneration was evaluated for its efficiency in removing low concentrations of emulsified oil from produced water, which is generated as a by-product from the thermal in-situ production of heavy oil. Adsorption behavior was investigated using synthetic model emulsions and samples of produced water; theoretical models were applied to the adsorption equilibrium and kinetics. It was demonstrated that the rate of the adsorption process was controlled by external mass transport, with no contribution from intra-particle diffusion. The non-porous structure of the Graphite Intercalation Compound (GIC) adsorbent led to effective and fast adsorption of oil in less than 30 min. Based on the cryo-SEM imaging and EDX phase mapping, the underlying adsorption mechanism was envisioned in the frame of adhesion and spreading of the emulsified oil droplets on the surface of the predominately hydrophobic GIC surface. The adsorptive capacity of the GIC was 100% recoverable by electrochemical regeneration. Energy consumption for the adsorbent regeneration process was found to be 22 kWh per kg of COD removed for treatment of the synthetic emulsion and 36 kWh per kg of COD for produced water.

Carbon-based materials as adsorbent for antibiotics removal: Mechanisms and influencing factors

With the development of the removal of organic pollutants in the soil and water environment, antibiotics have been considered as emerging pollutants and received considerable attention among the scientific community. Thus, there is a need for an effective, economical, fast, operational feasible and environmental-friendly technology to remove antibiotics. Adsorption technology would be one of the most promising option on the basis that it best meets the criteria we set out above. From the most primitive activated carbon to the most innovative modified biochar, carbon-based materials have played a significant role in the adsorption process of antibiotics all the time. This paper reviews the adsorption behavior of some representative antibiotics (e.g., chloramphenicols, sulfonamides, tetracyclines, flouroquinolones) over various carbonaceous materials (i.e., activated carbon, carbon nanotubes, graphene, and biochar). Nevertheless, in addition to the structural characteristics and adsorption capacities of carbon-based materials, a special emphasis was placed on the underlying adsorption mechanisms and roles of different influencing factors in the adsorption process. Moreover, the knowledge gaps and research challenges have been highlighted, including design and optimization of the carbonaceous materials for antibiotics adsorption.

Experimental study of the kinetics of the adsorption of nitrogen by coal containing different amounts of water.

Useful insight can be gained into the underlying adsorption mechanism by studying the adsorption of nitrogen by primary structure coal with different water content. In this work, a coal-adsorption gas experimental system is used to investigate the adsorption of nitrogen by coal samples containing different amounts of water ( 2.894%, 1.871%, 0.897%, and 0%) and different pressures (0.7, 1.2, 1.7, 2.2, 2.7, 3.2, and 3.7MPa). The adsorption rates under the different conditions were calculated using a volume method, and the adsorption kinetics investigated using a kinetic model. The results show that an adsorption model based on an opposing process characterizes the adsorption behavior better than the pseudo-first order kinetic model and pseudo-second order kinetic model. The adsorption rate constant, k, reflects the rate at which the gas can get into the pores of different sizes in the coal a greater k value, implies a greater increment in the rate. The k value is found to decrease when the initial pressure is increased for the same moisture content. Also, the greater the water content, the smaller the value of k for a given initial pressure. As the moisture content continues to increase, the k value tends to a certain value. The results presented can provide an experimental basis for the study of the mechanism responsible for the adsorption of nitrogen by primary structure coal with different moisture content.

Removal of radionuclides by layered double hydroxides materials

Layered double hydroxides (LDHs), one of the most important two-dimensional layered compounds, have enabled massive developments in effective pollution treatments. Over the past few decades, their derivative materials have also applied to the efficient removal of radionuclides owing to the intrinsic advantages of their low cost, easy preparation, large surface areas, topological transformation, and environment-friendly. In this review, we give an overview of the recent advances in LDH-based nanomaterials, from a brief introduction to their preparation and modification methods to an overview of their application in the removal of radionuclides and an exploration of their underlying adsorption mechanisms. In the end, a summary and outlook are also briefly addressed. This review intends to provide deep insight into the design of high-performance LDH-based materials for the potential elimination of radionuclides from aqueous solutions during environmental pollution cleanup.

Effects of the preassembly of benzohydroxamic acid with Fe (III) ions on its adsorption on cassiterite surface

Metal ions are widely used as activators in the flotation of oxidised minerals. At the same dosage of collector, the recovery of target minerals (cassiterite, scheelite, wolframite and ilmenite) can be evidently improved with the addition of metal ion activator. Adsorption of metal ions and their hydroxides can provide attractive sites for collector attachment, contrary to bare minerals that exhibit considerably low affinity towards the collector. Iron complexes of benzohydroxamic acid (BHA) are formed during the reaction of ferric chloride with BHA in the solution. These complexes also exhibit strong collecting ability towards cassiterite in the flotation, which contradicted the classical theory that the activator must be added before the collector. However, the major active component and the underlying adsorption mechanism of the Fe-BHA complexes are still unknown. In this study, the solution chemistry calculation has been used to identify the major active components of the Fe-BHA complexes. Accordingly, a preferred adsorption model of the Fe-BHA complexes onto the cassiterite surface has been proposed and proven effective, through first-principles calculations based on density functional theory, flotation experiments and adsorption tests. Our results might shed new light on the activation mechanism of metal ions in mineral flotation.

Adsorption of Lead on Sulfur-Doped Graphitic Carbon Nitride Nanosheets: Experimental and Theoretical Calculation Study

Two-dimensional (2D) layered materials for environmental remediation require abundant functional groups and high affinity for target pollutions. In this work, a heteroatom sulfur-doped graphitic carbon nitride (S3.9%-g-C3N4) material had been fabricated by pyrolysis for S- and N-rich supramolecular polymer precursor. A hierarchically porous structure with multimodal pore size distribution can facilitate Pb(II) ions’ diffusion from wastewater to the S3.9%-g-C3N4 surface. Batch adsorption experiments revealed that the resulting S-doped conjugated system of g-C3N4 exhibited enhanced adsorption capacity (52.63 mg g–1) as compared with that of individual g-C3N4 (31.25 mg g–1) at pH = 4.5. Accordingly, the higher adsorption ability for S3.9%-g-C3N4 was on account of its binding sites (i.e., soft S ligand) for coordination with Pb(II) than g-C3N4. Significantly, thermodynamic parameters demonstrated that the adsorption of Pb(II) on S3.9%-g-C3N4 was a spontaneous and endothermic process, and the kinetic experiments suggested that the chemisorption governed the adsorption process. Additionally, all geometries of (S-g-C3N4)–Pb(II) systems were thoughtfully constructed to explore the optimized structure, and these results were combined with the results of Density Functional Theory calculations to show that the enrichment of Pb(II) on S3.9%-g-C3N4 was energetically favored in C3N4–S–N3—the monosubstituted system with high Ead value (4.75 eV), in which the chemical binding sites of S–Pb and N–Pb were further evidenced by XPS analysis. The presented results not only demonstrated a facile and environmentally friendly strategy to synthesize porous S3.9%-g-C3N4 nanosheets with preferable Pb(II) adsorption ability, but also revealed the underlying adsorption mechanism for Pb(II) by experiments and theory simulation.

Progress in the Physisorption Characterization of Nanoporous Gas Storage Materials

Abstract Assessing the adsorption properties of nanoporous materials and determining their structural characterization is critical for progressing the use of such materials for many applications, including gas storage. Gas adsorption can be used for this characterization because it assesses a broad range of pore sizes, from micropore to mesopore. In the past 20 years, key developments have been achieved both in the knowledge of the adsorption and phase behavior of fluids in ordered nanoporous materials and in the creation and advancement of state-of-the-art approaches based on statistical mechanics, such as molecular simulation and density functional theory. Together with high-resolution experimental procedures for the adsorption of subcritical and supercritical fluids, this has led to significant advances in physical adsorption textural characterization. In this short, selective review paper, we discuss a few important and central features of the underlying adsorption mechanisms of fluids in a variety of nanoporous materials with well-defined pore structure. The significance of these features for advancing physical adsorption characterization and gas storage applications is also discussed.

Lithium Bond Impact on Lithium Polysulfide Adsorption with Functionalized Carbon Fiber Paper Interlayers for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are of great interest as a promising energy storage device because of their high theoretical capacity and energy density. However, they exhibit poor discharge capacity and capacity retention during long-term cycling because of their inherent drawbacks including the poor conductivity of sulfur and lithium sulfide, the shuttle effect of lithium polysulfides (LiPSs), and the large volume expansion of sulfur to lithium sulfide. An effective approach that can solve these problems is to use an interlayer inserted between the separator and the cathode. Nevertheless, the underlying adsorption mechanism of LiPSs on the interlayer has not yet been widely investigated. Herein, the effect of lithium bond chemistry on the adsorption of LiPSs on the functionalized carbon fiber paper (CFP) interlayer containing hydroxyl, carboxyl, or amide functional groups is investigated by a density functional theory approach. It is found that the functionalized CFP exhibits a strong lithium bond inter...

Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence.

We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basis.

Metal-Modified Cu-BTC Acid for Highly Enhanced Adsorption of Organosulfur Species

In this study, we provide an approach to the tunable metal modification on Cu-BTC (BTC= 1,3,5-benzenetricarboxylic acid) in order to achieve a highly enhanced adsorption affinity toward organosulfur species. We propose a strategy to regulate the metal compositions via the well-controlled reduction of Cu(II) to Cu(I) in Cu-BTC using ethanol as the reducing agent coupled with loaded Ag as catalyst under mild conditions. Applying scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), we confirmed the successful modification and explored their structural changes. The quantitative relationship between metal compositions of Cu-BTC samples and their adsorption capacities for organosulfur compounds including dimethyl disulfide (DMDS), ethyl sulfide, and 1-propanethiol were highlighted, and the underlying adsorption mechanism was elucidated. Present resu...

Study of the removal mechanism of aquatic emergent pollutants by new bio-based chars.

This work is dedicated to study the potential application of char byproducts obtained in the gasification of rice husk (RG char) and rice husk blended with corn cob (RCG char) as removal agents of two emergent aquatic contaminants: tetracycline and caffeine. The chars presented high ash contents (59.5-81.5%), being their mineral content mainly composed of silicon (as silica) and potassium. The samples presented a strong basic character, which was related to its higher mineral oxides content. RCG char presented better textural properties with a higher apparent surface area (144m2g-1) and higher micropore content (V micro=0.05cm3g-1). The alkaline character of both chars promoted high ecotoxicity levels on their aqueous eluates; however, the ecotoxic behaviour was eliminated after pH correction. Adsorption experiments showed that RG char presented higher uptake capacity for both tetracycline (12.9mgg-1) and caffeine (8.0mgg-1), indicating that textural properties did not play a major role in the adsorption process. For tetracycline, the underlying adsorption mechanism was complexation or ion exchange reactions with the mineral elements of chars. The higher affinity of RG char to caffeine was associated with the higher alkaline character presented by this char.

Born-Oppenheimer molecular dynamics simulation of pentanoic acid adsorption on α-Al2O3

Adsorption of a single pentanoic acid (C5H10O2) molecule on (0001) α-Al2O3 in a vacuum was explored with the aid of Born-Oppenheimer molecular dynamics simulations. Computer simulations were carried out considering two different situations, namely a clean Al/O-terminated surface and, also, a (0001) α-Al2O3 surface saturated with doubly-coordinated, isolated hydroxyls. In the first case, pentanoic acid adsorbs dissociatively, with the creation of an isolated surface hydroxyl, while the oxygen from the molecule's former carbonyl makes a bond to a nearby surface Al. On the other hand, pentanoic acid adsorbs on hydroxylated alumina by making a strong hydrogen bond to a surface oxygen, with the molecule aligning itself nearly parallel to the surface after full relaxation. For each case (i.e., pentanoic acid adsorption on Al/O-terminated or hydroxylated corundum surface), the different adsorption mechanism has a marked impact on the respective calculated infrared absorption spectrum, which can be of further use as an analytical tool to determine the underlying adsorption mechanism in actual experiments.

Kinetics, equilibrium and thermodynamics studies on biosorption of Rhodamine B from aqueous solution by earthworm manure derived biochar

Earthworm manure (EM) largely produced as vermicomposting is being widely disposed as organic solid waste. In this study, EM was pyrolyzed at 400–600 °C to prepare a series of biochar samples (EMCs). The physicochemical properties and adsorption capability to Rhodamine B (RB) using the EMCs as well as the underlying adsorption mechanism were thoroughly investigated. N2 adsorption/desorption isotherms and scanning electron microscopy (SEM) analysis indicated that the specific surface area and porosity structure of the EMCs were significantly promoted compared with the raw EM. Also, abundant oxygen-containing surface functional groups like hydroxyl (-OH) and carboxyl (-COOH) were retained and aromatic C=C groups were largely generated in the EMCs after pyrolysis process, as evidenced by Fourier transform infrared spectroscopy (FTIR). The adsorption results showed that the EMCs were effective for RB adsorption. The equilibrium adsorption data could be well fitted by Langmuir isotherm model with a maximum adsorption capacity of 14.49–21.60 mg g−1, whereas the adsorption kinetics followed the pseudo-second-order model. Thermodynamic analysis revealed that the adsorption was assigned to a spontaneous and endothermic process. Ion exchange, hydrogen bonding, electrostatic interaction and π-π stacking interaction driven by oxygen-containing surface functional groups and aromatic C=C of EMCs were found to be responsible for RB adsorption.

Organic dye removal from aqueous solutions by hierarchical calcined Ni-Fe layered double hydroxide: Isotherm, kinetic and mechanism studies

Hierarchically porous nickel–iron-layered double hydroxide (NiFe-LDH) with a Ni2+/Fe3+ molar ratio of 3 was successfully synthesised through a simple hydrothermal route. After calcination at 400°C, NiFe-LDH transformed into nickel–iron-layered double oxides (NiFe-LDO). The as-prepared samples were characterised through X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption. The calcined and uncalcined NiFe-LDH was used as adsorbents to remove Congo red (CR) dye in an aqueous solution. The equilibrium adsorption data of NiFe-LDH and NiFe-LDO samples were well fitted to Langmuir model and were characterised by excellent adsorption capacities of 205 and 330mg/g, respectively. Pseudo-second-order kinetic and intra-particle diffusion models indicated that CR was well adsorbed on the adsorbent. The underlying adsorption mechanism was investigated and observed as anion exchange and reconstruction.

Underlying Adsorption Mechanisms of Water in Hydrophobic and Hydrophilic Zeolite Imidazolate Frameworks: ZIF-71 and ZIF-90

The hydration of porous materials is relevant for separation, transport, and catalysis purposes, among others. In this respect, zeolitic imidazolate frameworks (ZIFs) have received considerable attention since they have shown remarkable resistance to water as well as to other organic solvents. Studies on water adsorption in ZIFs are however relatively scarce and primarily focused on the effect of the host composition and porosity on their hydrophobic or hydrophilic nature. In this work, we explore the underlying adsorption mechanisms of water in ZIF-71 and ZIF-90, which are experimentally known structures. These ZIFs have been reported hydrophobic and hydrophilic, respectively. We conducted Monte Carlo simulations using previously validated models and force fields to compute the adsorption isotherms of water in both ZIFs at room temperature. Although the polar functional group in ZIF-90 leads to adsorption in the gas phase, a following rapid cage filling occurs as in ZIF-71. A consistent description of th...

Fingerprints of energy dissipation for exothermic surface chemical reactions: O2 on Pd(100).

We present first-principles calculations of the sticking coefficient of O2 at Pd(100) to assess the effect of phononic energy dissipation on this kinetic parameter. For this, we augment dynamical simulations on six-dimensional potential energy surfaces (PESs) representing the molecular degrees of freedom with various effective accounts of surface mobility. In comparison to the prevalent frozen-surface approach, energy dissipation is found to qualitatively affect the calculated sticking curves. At the level of a generalized Langevin oscillator model, we achieve good agreement with experimental data. The agreement is similarly reached for PESs based on two different semi-local density-functional theory functionals. This robustness of the simulated sticking curve does not extend to the underlying adsorption mechanism, which is predominantly directly dissociative for one functional or molecularly trapped for the other. Completely different adsorption mechanisms therewith lead to rather similar sticking curves that agree equally well with the experimental data. This highlights the danger of the prevalent practice to extract corresponding mechanistic details from simple fingerprints of measured sticking data for such exothermic surface reactions.