Liquid-solid Adsorption Research Articles

Energy-Efficient Separation of Xylene Isomers through Stacked 1-Aminopyrene Polymer Composite.

Developing high-performance adsorbents for energy-efficient separation of xylene isomers has important research and application value. Identification and separation of xylene isomers (PX, MX, and OX) at room temperature based on the different relative positions of two methyl groups on the benzene ring is an unprecedented attempt. Herein, 1-aminopyrene polymer (PAP) is designed and electro-synthesized composited with a supporting electrolyte as an adsorbent for the separation of xylene isomers using a multi-stage dispersed liquid-solid adsorption process at room temperature. Each -NH-pyrene-NH- unit can form a force field to identify and discriminate xylene isomer through π-π interaction combined with -CH3···-NH- interactions of different strength, thereby achieving separation of PX, MX, and OX isomers by amplifying the slight differences in the adsorption capacity and diffusion rates. The density functional theory (DFT) simulations provide a more quantitative analysis of the adsorbate-adsorbent interactions to illustrate PX > MX > OX order of adsorption selectivity. This study may offer an alternative strategy for the precise designing of energy-efficient and adsorption-based separation materials.

Valorization of Eggshell as Renewable Materials for Sustainable Biocomposite Adsorbents—An Overview

The production and buildup of eggshell waste represents a challenge and an opportunity. The challenge is that uncontrolled disposal of generated eggshell waste relates to a sustainability concern for the environment. The opportunity relates to utilization of this biomass resource via recycling for waste valorization, cleaner production, and development of a circular economy. This review explores the development of eggshell powder (ESP) from eggshell waste and a coverage of various ESP composite sorbents with an emphasis on their potential utility as adsorbent materials for model pollutants in solid–liquid systems. An overview of literature since 2014 outlines the development of eggshell powder (ESP) and ESP composite adsorbents for solid–liquid adsorption processes. The isolation and treatment of ESP in its pristine or modified forms by various thermal or chemical treatments, along with the preparation of ESP biocomposites is described. An overview of the physico-chemical characterization of ESP and its biocomposites include an assessment of the adsorption properties with various model pollutants (cations, anions, and organic dyes). A coverage of equilibrium and kinetic adsorption isotherm models is provided, along with relevant thermodynamic parameters that govern the adsorption process for ESP-based adsorbents. This review reveals that ESP biocomposite adsorbents represent an emerging class of sustainable materials with tailored properties via modular synthetic strategies. This review will serve to encourage the recycling and utilization of eggshell biomass waste and its valorization as potential adsorbent systems. The impact of such ESP biosorbents cover a diverse range of adsorption-based applications from environmental remediation to slow-release fertilizer carrier systems in agricultural production.

Simulation-based research on enhancing lubricity: investigating wettability and textured surfaces in alkane lubricants under boundary lubrication conditions.

Changing the wettability and surface texturing have a significant impact on lubrication. In this study, the researchers used the molecular dynamics (MD) method to investigate how adjusting the interaction between alkanes and the wall affects oil film morphology and frictional properties under boundary lubrication. The findings revealed that the bearing capacity was influenced by both the morphology of the oil film and the strength of solid-liquid adsorption. In cases where the walls had weak wettability, the alkanes formed clusters to effectively separate the walls, while in cases where the walls had strong wettability, the oil film spread and formed a strong adsorption film. The super oleophilic textured surface could enhance the oil film adsorption capacity and replenish the oil film to the friction area in time, and the super oleophobic smooth surface could further reduce the friction coefficient. Therefore, a composite surface consisting of a super oleophilic textured surface and a super oleophobic smooth surface can be designed to enhance the bearing capacity of the oil film and reduce friction.

Assessment of the Potential of Electrochemical Steps in Direct Air Capture through Techno-Economic Analysis.

Direct air capture (DAC) technologies are proposed to reduce the atmospheric CO2 concentration to mitigate climate change and simultaneously provide carbon as a feedstock independent of fossil resources. The currently high energy demand and cost of DAC technologies are challenging and could limit the significance of DAC processes. The present work estimates the potential energy demand and the levelized cost of capture (LCOC) of liquid solvent absorption and solid adsorption DAC processes in the long term. A consistent framework is applied to compare nonelectrochemical to electrochemical DAC processes and estimate the LCOC depending on the electricity price. We determine the equivalent cell voltage needed for the electrochemical steps to achieve comparable or lower energy demand than nonelectrochemical processes. The capital expenses (CapEx) of the electrochemical steps are estimated using analogies to processes that are similar in function. The results are calculated for a range of initial data of CapEx and energy demand to include uncertainties in the data.

Solidification of deep eutectic solvent containing fimasartan through wet impregnation and exploration of flow attributes by modified SeDeM-SLA expert system

The solidification of deep eutectic solvent (DES) through wet impregnation techniques on inert solid carriers is an interesting approach that offers better processing attributes and excellent stability. Herein, DES of Fimasartan (FS) was developed to improve its solubility and bioavailability. The selected DES-FS was solidified by wet impregnation method employing Nesulin US2 and Aerosil 200. The SeDeM-SLA (solid–liquid adsorption) system was employed to investigate flow attributes of solidified DES-FS. Further, the selected solidified DES-FS (A) was characterized by Fourier transforms infrared spectroscopy (FTIR), Powder X-ray diffraction (PXRD), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM). The DES comprising Choline Chloride (ChCl): Glycerol (Gly) (1:3) revealed maximum drug solubility (35.6 ± 2.2 mg/mL) and thus opted for solidification. Solidification through wet impregnation was employed using 1:0.5 ratios (DES-FS to carriers). The Index of Good Flow (IGF) value was calculated from the SeDeM-SLA expert system, which indicates the better flow characteristics of solidified DES-FS, particularly with Neusilin US2 [SDES-FS (A)]. The solid-state evaluation data of SDS-FS (A) suggested a transition of FS to an amorphous form, resulting in an increment in solubility and dissolution. A similar trend was reported in the in vivo pharmacokinetic study, which indicated a 2.9 folds increment in the oral bioavailability of FS. Furthermore, excellent stability, i.e., a shelf life of 28.44 months, reported by SDES-FS (A) in accelerated stability studies, suggests better formulation perspectives. In a nutshell, the present study evokes the potentiality of performing solidification through wet impregnation and successful implementation of the SeDeM-SLA expert model, which could find wide applications in pharmaceutical science.

Efficient removal of radioactive iodide from contaminated seawater by radiation-resistant Ag+-doping polypropylene nonwoven adsorbents

For the efficient removal of radioactive iodide ions from medium and low radioactive contaminated water, an Ag-doped adsorbent was designed via radiation grafting method and chemical modification and applied based on the solid–liquid adsorption method. The silver loading content in the adsorbents could be flexibly decided by adjusting the sulfhydryl content. SEM/EDS, ATR, XPS, and XRD characterization methods were used to determine the features of the new adsorbents. With the silver content 67.9 mg/g and 125.6 mg/g in the adsorbents PGM25%-Ag+ and PGM220%-Ag+ respectively, the maximum I− adsorption capacities were varied at 29.92 mg/g and 100.82 mg/g. In wide pH conditions (pH7-11), PGM25%-Ag+ was sufficient to achieve 131I removal efficiency of over 92 %, and the removal efficiency was almost unaffected in the coexistence of high concentration (10 mmol/L) of anions and complex real contaminated seawater, highlighting the applicability and selectivity of the adsorbent. The adsorption behavior conformed to the Langmuir isothermal model and pseudo-second-order kinetics model. XPS analysis confirmed that excellent adsorption capacity and selectivity were attributed to the chemical adsorption mechanism of ion exchange and complexation occurs between I− and Ag on the solid–liquid interface, where AgI precipitation formed. In addition, the Ag+-doping adsorbent withstood the harsh conditions of 200 kGy irradiation by observing the ATR structure, thermal stability, and 131I removal property. This study provides a feasible solution for the treatment of low and medium-radioactive contaminated seawater.

Single and multicomponent adsorption of amoxicillin, ciprofloxacin, and sulfamethoxazole on chitosan-carbon nanotubes hydrogel beads from aqueous solutions: Kinetics, isotherms, and thermodynamic parameters

The removal of antibiotics in water receiving bodies is an integral part in eradicating antimicrobial resistance which has become a major threat to public health. Solid-liquid adsorption has demonstrated to be an effective technique in the removal of antibiotics from aqueous environments. Herein, chitosan-carbon nanotube (chitosan-CNT) hydrogel beads were synthesised for the adsorption of amoxicillin (AMX), ciprofloxacin (CIP) and sulfamethoxazole (SMX) from aqueous solution. Adsorption kinetics, isotherms and thermodynamic parameters were systematically investigated at a solution pH of 7. Single adsorption kinetics findings suggest that experimental data for AMX, CIP and SMX was better fitted by the nonlinear pseudo-first order model with calculated maximum adsorption capacities of 23.1 mg.g−1, 23.7 mg.g−1 and 25.17 mg.g−1, respectively. Moreover, findings from the Weber-Morris kinetic model suggest that multiple processes were limiting the overall adsorption rate of AMX, CIP and SMX on chitosan-CNT. Adsorption isotherm results indicated that single adsorption experimental data was better fitted by the nonlinear Freundlich isotherm model, while binary and ternary system experimental data were better fitted by the nonlinear competitive extended Sips adsorption isotherm models. Moreover, results for binary and ternary adsorption showed that multicomponent adsorption systems exhibited both antagonistic and synergistic adsorption of AMX, CIP and SMX. From the thermodynamics fundings, it was evident that the adsorption of AMX, CIP and SMX from solution is an endothermic process governed by both physical and chemical adsorption mechanisms. Based on the findings of the current study, it was concluded that chitosan-CNT has potential as a green technology for the removal of antibiotics from solution.

Phenomenological‐based model of direct blue 2 adsorption on corncob in a fixed‐bed

AbstractThis work presents a phenomenologically based semi‐physical model (PBSM) for the liquid–solid adsorption process, which has been experimentally validated. Two modes of operation of adsorption of direct blue 2 dye (DB2) on corn cobs in a fixed bed are discussed by applying the PBSM. The first mode of operation is the typical continuous liquid flow, whereas the second is a semicontinuous mode with the recirculation of liquid leaving the column. These modes of operation were used to illustrate different ways in which the system reaches equilibrium conditions. The equilibrium distribution curve (EDC) for low DB2 concentration was reached with the best fit using the Langmuir–Freundlich model (). The local mass transfer coefficient for the solid phase was evaluated by the PBSM deduction, and subsequently, the diffusivity of the surface solid was experimentally evaluated through comparison in terms of the PBSM. Regardless of the mode of operation, surface diffusion is associated with only the nature of the adsorbent material rather than the concentration of the liquid phase. In addition, the PBSM exhibited liquid and solid concentration changes at different points in the column. Moreover, different operating curves of the process were constructed and validated, exhibiting similar results when comparing the predictions of the model and the experimental data. These findings support the strength of the constructed model, enabling its extension to other adsorbent–dye systems.

Development of an interval double-stochastic carbon-neutral electric power system planning model: A case study of Fujian province, China

Synergic adoption of diverse measures and consideration of multiple uncertainties are essential for electric power systems to achieve carbon neutrality. To fill the research gap, an interval double-stochastic carbon-neutral electric power system planning (abbreviated as IDS-CEP) model is developed. In the IDS-CEP model, reduction measures include electricity mix improvement, CO2 capture, transport, and storage (including monoethanolamine absorption and membrane separation), CO2 direct air capture (containing solid adsorption technique and liquid adsorption technique), ecosystem carbon sinks (forest, farmland, and ocean); uncertainties involve stochastic electricity demand, CO2 emission allowance, CO2 emission coefficient, and other interval parameters, which are quantified as forty-five scenarios and three levels. Through the application in Fujian province (China), results disclose that: (i) combination of the reduction measures would help Fujian achieve carbon neutrality with minimized system cost by 2060, their contributions could averagely be ranked as electricity mix improvement (70.75%) > forest (6.03%) > monoethanolamine absorption (5.98%) > farmland (4.53%) > solid adsorption technique (3.83%) > membrane separation (3.45%) > ocean (3.35%) > liquid adsorption technique (2.08%); (ii) to guarantee electricity supply, total installed capacity should be expanded to [156.16, 197.78]GW, where low-carbon electricity (especially nuclear, wind and photovoltaic electricity) installed capacity would occupy [74.68, 76.66]% by conducting electricity mix improvement to reduce CO2 emission; (iii) the changes in electricity mix structure would lead to decreased water utilization (by [48.57, 61.54]%) and pollutant emissions (by [77.00, 87.35]%); (iv) uncertainties would significantly affect decisions about electricity generation and CO2-emission reduction, resulting in varied system costs (in a wide interval of [6.07, 9.16] × 1012 RMB¥). Authorities can choose appropriate schemes according to their risk attitudes towards uncertainties. Results provide scientific planning support for Fujian's electricity generation sector; meanwhile, the IDS-CEP model can also be used in other regions by updating data information.

Formulation, characterization, pharmacokinetics and antioxidant activity of phloretin oral granules

Phloretin (PHL), a flavonoid of the dihydrogen chalcone class, is reported to have low oral bioavailability due to its poor solubility and absorption. A common approach to enhance the solubility of such flavonoids is solubilization in a polymeric or lipidic matrix which would help in enhance dissolution rate and solubility. Accordingly, in the current study PHL was dissolved in Gelucire® 44/14 by melt-fusion technique and the viscous semisolid melt was adsorbed on a solid carrier to obtain free flowing granules. SeDeM-SLA (Solid-Liquid Adsorption) expert system was employed to select the most suitable carrier. This study achieved positive outcomes through the successful development of formulated oral PHL granules. The granules exhibited good stability, and favourable pharmacokinetic properties. In addition, the selected carrier effectively retained the antioxidant properties of PHL.

Lysozyme–Mineral Clay Systems: Comparison of Interaction for Controlled Release in Feed Application

A synthetic approach to bond lysozyme (LY) to commercial natural carriers, namely clay minerals (bentonite, BN; and sepiolite, SP) and commercial zeolite (Phil 75®, PH), already in use in feed formulation, is proposed. The synthetic route, which implies solid–liquid adsorption, is a simple and effective way for preparing hybrid materials characterized by LY loadings up to 37 mgLY/gcarrier. By operating at pH 4.3, initial LY content of 37.5 mgLY/gcarrier, and reaction time of 90 min, hybrid materials with LY loadings of 37, 35, and 12 mgLY/gcarrier for LY-SP, LY-BN, and LY-PH, respectively were obtained. The LY initial concentration and pH, as well as the physico-chemical properties of the carries were found to be the parameters that govern the synthesis of the materials. The driving force for an effective LY adsorption and interaction is the combined Zero Point Charge (ZPC) of the carriers, always negative (in the range between −4 and −170 mV) and the positive ZPC of LY, as well as the carrier morphology, characterized by mesoporosity (pore dimensions in the range of 5–12 nm). However, it is the interaction of charges of opposite sign that mainly affects LY loadings and bond strength. Based on SEM-EDX analysis, LY molecules are quite homogeneously spread onto the carriers’ surface. TG-DTG analyses showed that the LY–carrier interaction in the hybrid materials is stronger than that in a simple mechanical mixture of the components. Specifically, in the hybrid materials, the phenomenon at 300 °C, associated to LY decomposition, is broadened and slightly shifted towards higher temperatures (320–350 °C), whereas in a mechanical mixture of the same composition, it occurs at temperatures closer to those of free LY, as if there were no or very weak interactions. At pH 3, a very little LY release, 0.03 and 0.01 mgLY/gcarrier, was found for LY-BN and LY-PH, respectively. The latter became larger at pH 7, 0.06 mgLY/gcarrier for both BN and PH carriers, suggesting that BN and PH are better modulators of LY release. The paper provides insights for the study and the development of new optimized feed formulations for the targeted delivery of natural compounds with antimicrobial activity, alternatives to antibiotics, and vaccinal antigens.

Universal “Plug and Play” Real-Time Entire Automotive Exhaust Effluents, Industry Vents and Flue Gas Emissions Liquefiers: The Game Changer Approach-Phase Two Category

Universal “Plug and Play” Real-Time Entire Automotive Exhaust Effluents, Industry Vents and Flue Gas Emissions Liquefiers: The Game Changer Approach-Phase Two Category

Toward a mechanistic understanding of adsorption behavior of phenol onto a novel activated carbon composite

In this research, the solid–liquid adsorption systems for MSAC (PbFe2O4 spinel-activated carbon)-phenol and pristine activated carbon-phenol were scrutinized from the thermodynamics and statistical physics (sta-phy) viewpoints. Experimental results indicated that MSAC composite outperformed pristine AC for the uptake of phenol from waste streams. By increasing the process temperature, the amount of phenol adsorbed onto both adsorbents, MSAC composite and pristine AC, decreased. Thermodynamic evaluations for MSAC demonstrated the spontaneous and exothermic characteristics of the adsorption process, while positive values of ΔG for pristine AC indicated a non-spontaneous process of phenol adsorption in all temperatures. In a mechanistic investigation, statistical physics modeling was applied to explore the responsible mechanism for phenol adsorption onto the MSAC composite and pristine AC. The single-layer model with one energy was the best model to describe the experimental data for both adsorbents. The adsorption energies of phenol onto both adsorbents were relatively smaller than 20 kJ/mol, indicating physical interactions. By increasing temperature from 298 to 358 K, the value of the absorbed amount of phenol onto the MSAC composite and pristine AC at saturation (Qsat) decreased from 158.94 and 138.91 to 115.23 and 112.34 mg/g, respectively. Mechanistic studies confirm the significant role of metallic hydroxides in MSAC to facilitate the removal of phenol through a strong interaction with phenol molecules, as compared with pristine activated carbon.

Adsorption of the hydrophobic organic pollutant hexachlorobenzene to phyllosilicate minerals

Hexachlorobenzene (HCB), a representative of hydrophobic organic chemicals (HOC), belongs to the group of persistent organic pollutants (POPs) that can have harmful effects on humans and other biota. Sorption processes in soils and sediments largely determine the fate of HCB and the risks arising from the compound in the environment. In this context, especially HOC–organic matter interactions are intensively studied, whereas knowledge of HOC adsorption to mineral phases (e.g., clay minerals) is comparatively limited. In this work, we performed batch adsorption experiments of HCB on a set of twelve phyllosilicate mineral sorbents that comprised several smectites, kaolinite, hectorite, chlorite, vermiculite, and illite. The effect of charge and size of exchangeable cations on HCB adsorption was studied using the source clay montmorillonite STx-1b after treatment with nine types of alkali (M+: Li, K, Na, Rb, Cs) and alkaline earth metal cations (M2+: Mg, Ca, Sr, Ba). Molecular modeling simulations based on density functional theory (DFT) calculations to reveal the effect of different cations on the adsorption energy in a selected HCB-clay mineral system accompanied this study. Results for HCB adsorption to minerals showed a large variation of solid–liquid adsorption constants Kd over four orders of magnitude (log Kd 0.9–3.3). Experiments with cation-modified montmorillonite resulted in increasing HCB adsorption with decreasing hydrated radii of exchangeable cations (log Kd 1.3–3.8 for M+ and 1.3–1.4 for M2+). DFT calculations predicted (gas phase) adsorption energies (− 76 to − 24 kJ mol−1 for M+ and − 96 to − 71 kJ mol−1 for M2+) showing a good correlation with Kd values for M2+-modified montmorillonite, whereas a discrepancy was observed for M+-modified montmorillonite. Supported by further calculations, this indicated that the solvent effect plays a relevant role in the adsorption process. Our results provide insight into the influence of minerals on HOC adsorption using HCB as an example and support the relevance of minerals for the environmental fate of HOCs such as for long-term source/sink phenomena in soils and sediments.

Magnetic porous carbons derived from metal-organic frameworks for effective adsorption of tetracycline

Recovery of adsorbent from solid-liquid adsorption system is important for the application of adsorption technique. Due to high efficiency and low cost, separation induced by external magnetic field has attracted large attentions. In this work, we prepared a series of cobalt-doped magnetic porous carbons (Co-PC) via using Co-benzimidazole (Co-PhIm) as the precursor. In the green synthesis of Co-PhIm, water was used to partly substitute the organic solvent that was applied in previous reports. Interestingly, upon the addition of water, the porosity was boosted and the magnetism was not weakened obviously. Among the prepared porous carbons, the optimized Co-PC-C exhibited a large adsorption capacity (998.3 ​mg ​g−1) for tetracycline (TC) and rapid equilibrium time (30 ​min) at low concentrations. Co-existing ions had almost ignorable interferences and the optimized pH was found near the neutral environment. Furthermore, this material can be well regenerated through a simple elution method. Therefore, our work provides an effective adsorbent for TC antibiotic and proposes a guideline to enhance the porosity of adsorbent.

Experimental analysis of a high-performance open sorption thermal storage system with absorption-crystallization-adsorption processes

Sorption thermal energy storage is one of the promising solar thermal energy storage considering its long-term storage ability. Since the common sorption thermal storage suffers from low sorption capacity, a high energy storage density enhancement mechanism is always essential for a cost-effective and compact storage system. With three-phase sorption thermal storage, high energy storage density from the crystallization sorption process can be achieved. However, such a sorption process brings significant challenges, including crystal blockage issues in absorption system or solution leakage handling problems in adsorption system, which need to be resolved. Here, we showed a high-performance sorption thermal storage that can attain high energy storage density via a full liquid-to-solid state sorption process. Such a process is achieved by adopting moist air as heat and mass transfer media, which enables liquid absorption, crystallization, and solid adsorption in a simple configuration simultaneously. The lab-scale model achieved high energy storage density in the range of 333–405 kWh/m3 resulting from the heat of absorption and crystallization of LiCl, which is the record value for liquid absorption systems. The energy storage density obtained from the dual liquid and solid sorption processes is enhanced by 278 % compared with that of the conventional cycle at 70 % RH (relative humidity) and temperature lift of 10 °C. With simple construction and high energy storage density, the proposed system has great potential in real applications.

Prediction of breakthrough curves for multicomponent adsorption in a fixed-bed column using logistic and Gompertz functions

In order to facilely predict the multicomponent breakthrough curves and avoid the complicated numerical solution, this work proposes two empirical models based on the logistic and Gompertz functions. The S-shaped and bell-like curves correspond to the adsorption and displacement processes respectively. The equilibrium loading of each component can be calculated by integration of the measured breakthrough curves. The effects of the model parameters on the breakthrough curves are investigated. The applicability of the two empirical models is validated by three binary and four ternary adsorption systems, including the gas–solid and liquid–solid adsorption. The residual plot and coefficient of determination ( R 2 ) are used to evaluate their fitting quality. The results indicate that the fitting curves agree well with the experimental data and all of the residuals are distributed randomly. The five model parameters ( k , τ , k *, τ * and c ) are easily obtained by the nonlinear regression. For example, the fitting results are k = 1.37 × 10 −2 min −1 , τ = 292 min, k * = 1.25 × 10 −2 min −1 , τ * = 453 min and c = 85.3 for adsorption of n -butyl acetate and p -xylene on granular activated carbon. On the whole, the Gompertz model is superior to the logistic model in terms of the fitting accuracy. The significance of this work is to provide a simple and practical method for prediction of the multicomponent breakthrough curves.

How solid–liquid adsorption affects the liquid–vapor interface in pores

AbstractThe augmented Young–Laplace (AYL) equation has been widely used to describe the liquid–vapor interfaces affected by capillarity and adsorption, particularly in nanoporous or clay minerals where strong adsorptive interaction prevails. Still, how adsorption ultimately shapes the liquid–vapor interface in pores remains elusive. All current forms of the AYL equation only consider the attractive van der Waals interaction for complete wetting surface and are mostly an extension of the general equation based on thermodynamic principles without rigorous derivation. In this paper, closed forms of the AYL equations are derived by variational calculus method for two typical pore models considering effects of capillarity and adsorption, based on the minimization of free energy for the equilibrium system. The van der Waals, electrical, and structural forces are incorporated as disjoining pressure into the proposed AYL equations to quantify effects of both attractive and repulsive interactions (hence complete and partial wetting conditions) on interfacial geometry and equilibrium matric potential. Numerical calculation algorithms are established to solve the interfacial geometric profiles and characteristics. The proposed model illustrates a transition region on the interface where geometry and physical characteristics are drastically altered under adsorption compared with sole capillarity. Different surface wettabilities are examined for interface profiles and curvature distributions. An apparent contact angle on the partial wetting surface is identified that is approaching complete wetting as the adsorption dominates when pore size reduces. Water retention and interparticle force demonstrate clear distinctions in their evolution, with different particle sizes and varying half‐filling angles under adsorptive conditions as water volume changes.

Revealing the adsorption mechanism of copper on hemp-based materials through EDX, nano-CT, XPS, FTIR, Raman, and XANES characterization techniques

Hemp-based materials have been recently proposed as adsorbents for metals present in aqueous solutions using adsorption-oriented processes. This study aims to reveal the adsorption mechanism of materials prepared from hemp shives as co-products of the hemp industry, namely sodium carbonate-activated (SHI-C) and polycarboxylic agent-grafted (SHI-BTCA) hemp shives. The interactions between copper and two hemp-based materials were characterized by different microscopic and spectroscopic techniques such as energy-disperse X-ray (EDX) spectroscopy, computed nano-tomography (nano-CT), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. The results showed remarkable different mechanisms for copper adsorption onto the SHI-C and SHI-BTCA hemp shives. Namely, copper surface adsorption and diffusion in the structure of the SHI-C material were predominant, whereas the adsorption of copper onto SHI-BTCA was due to a chemisorption phenomenon and ion-exchange involving the adsorbent carboxylate groups. The combination of the abovementioned complementary microscopic and spectroscopic techniques allowed us to characterize and distinguish the type of interactions involved in the liquid-solid adsorption phenomena.

Improper Estimation of Thermodynamic Parameters in Adsorption Studies with Distribution Coefficient KD (qe/Ce) or Freundlich Constant (KF): Considerations from the Derivation of Dimensionless Thermodynamic Equilibrium Constant and Suggestions

Adsorption processes often include three important components: kinetics, isotherm, and thermodynamics. In the study of solid–liquid adsorption, “standard” thermodynamic equilibrium constant [Formula: see text]; dimensionless) plays an essential role in accurately calculating three thermodynamic parameters: the standard Gibbs energy change (∆ G°; kJ/mol), the standard change in enthalpy (∆ H°; kJ/mol), and the standard change in entropy [∆ S°; J/(mol × K)] of an adsorption process. Misconception of the derivation of the [Formula: see text] constant that can cause calculative errors in values (magnitude and sign) of the thermodynamic parameters has been intensively reflected through certain kinds of papers (i.e., letters to editor, discussions, short communications, and correspondence like comment/rebuttal). The distribution coefficient ( K D) and Freundlich constant ( K F) have been intensively applied for calculating the thermodynamic parameters. However, a critical question is whether K D or K F is equal to [Formula: see text]. This paper gives (1) thorough discussion on the derivation of thermodynamic equilibrium constant of solid–liquid adsorption process, (2) reasonable explanation on the inconsistency of (direct and indirect) application of K D or K F for calculating the thermodynamic parameters based on the derivation of [Formula: see text], and (3) helpful suggestions for improving the quality of papers published in this field.