Sorption Energy Research Articles

Surface water H-bonding network is key controller of selenate adsorption on [0 1 2] α-alumina: An Ab-initio study

Selenate adsorption onto metal oxide surfaces is a cost-effective method to remove the toxin from drinking water systems. However, the low selectivity of metal oxides requires frequent sorbent replacement. The design of selective adsorbents is stymied because the surface factors controlling selenate adsorption remain unknown. We calculate adsorption energies of selenate on the (012) α-Al2O3 surface using density functional theory to unravel the physics that controls adsorption. Our model is validated against experiment by correctly predicting selenate removal efficiency as a function pH. We find that the selenate adsorption energy on the anhydrous α-Al2O3 surface is surprisingly anti-correlated with the fully solvated adsorption energy; therefore, the direct interaction between adsorbate and sorbent is eliminated as the controlling mechanism. Rather, the change in number of surface hydrogen bonds after adsorption is the factor most correlated with the adsorption energy (R2 > 0.8); and is thus determined to be the factor controlling selenate adsorption. We find that pH affects adsorption by controlling the number of surface protons available for H-bonding to selenate. This work demonstrates that adsorption prediction should not be made based on gas phase sorption energies and suggests that surface engineering which increases surface protonation may be an effective strategy for increasing selenate sorption.

Surface coating of silica with amine functionalized calix[4]arene and its application in metal ion extraction

Calixarenes are known as fascinated macromolecules due to their flexible structure that can be cast into different fields of application. These macromolecules have been used as quick and highly selective functional material for the extraction and separation of metal ions. This study explores metal ion removal efficiency of new calixarene coated silica resin from aqueous environment through solid phase extraction. The calixarene-coated silica resin (CCS resin) was synthesized and characterized by FTIR, SEM, XRD, EDS and BET. Static and dynamic adsorption experiments were followed to check the removal efficiency of CCS resin. Adsorption experiment shows that, CCS resin has strong potential for the removal of divalent and trivalent metal ions as compare to monovalent metal ions. Adsorption data have been evaluated by applying Langmuir, Freundlich, D-R models and Thomas dynamic adsorption models. The adsorption isotherm of the CCS resin agreed well with the Langmuir adsorption equation with regression coefficient of 0.99 and good monolayer adsorption capacities such as 3.22, 2.95, 3.04, 3.11, 2.81 and 2.82 (mol.g−1) for Hg2+ Pb2+ La3+ Cr3+ Al3+ and Fe3+ respectively. The D-R isotherm model suggests that the adsorption process follow ion exchange mechanism with mean sorption energy falls in the range of 9.0–16 KJ.mol−1. Moreover, the exhaustion capacity of column was calculated by using the Thomas model, which shows very small qo value with good fit to data (R 2 =0.99). The thermodynamic and kinetic studies have also been performed, which reveals that the reaction is spontaneous and exothermic in nature and follows pseudo second-order kinetics.

Compression-assisted decomposition thermochemical sorption energy storage system for deep engine exhaust waste heat recovery

In the context of the stringent automobile emission legislations, this paper proposes a novel compression-assisted decomposition thermochemical sorption energy storage system for recovering engine exhaust waste heat, which is utilized to produce cooling capacity for a refrigerated vehicle. In this system, the desorption pressure of sorbent can be flexibly adjusted by changing the suction pressure of compressor embedded between the sorption bed and condenser, which ensures the stable operation of system even at relatively low exhaust temperatures. Simultaneously, the decomposition reaction increases suction pressure of compressor, so the coefficient of performance (COP) is thus greatly improved. Furthermore, the sorption bed can output cooling capacity for refrigerated compartment when the vehicle is parked. Currently, vehicle emission standards generally adopt World Harmonized Stationary Cycle test, and 13 engine operating points are selected. At an operating point 3 (a low engine load), i.e. 55% speed and 25% torque, the COP of the novel system at an evaporating temperature of −25 °C and a condensing temperature of 45 °C is 1.65, 1.5 times higher than that of conventional one. The weighted average COP under 13 operating points is still up to 1.48. Eventually, the novel system promotes the realization of low-carbon and low-cost refrigerated transportation.

Molecular Docking as a Tool to Examine Organic Cation Sorption to Organic Matter.

Molecular docking simulations were performed to examine the structural effects of organic cations on their sorption to organic matter. A set of benzylamine compounds was used to assess the sorption trends arising from the systematic structural differences between ring or nitrogen substituents. Binding simulations were performed using AutoDock 4.2 with Schulten's proposed soil organic matter as a representative organic matter structure. The calculated binding energies for the sorbate compounds correlated strongly with the measured sorption energies for Pahokee peat, indicating that the simulated binding energies and their associated sorbate orientations were representative of the experimental conditions. Graphical docking orientations showed primary, secondary, and tertiary aminium compounds to form hydrogen-bond interactions with deprotonated carboxylic acid groups in a pocket of the organic matter structure. Quaternary ammonium compounds formed pi-pi or cation-pi interactions with the aromatic groups elsewhere in the same organic matter pocket. Ring substituents showed no clear trends in sorption energies with the substituent group type for primary aminium compounds. Rather, substituent groups altered the simulated van der Waals, electrostatic, hydrogen-bond, and desolvation energy contributions to the overall sorption energies, in part because of the variations in docking orientations between compounds. Increasing methyl substitution of the aminium nitrogen group was associated with an increase in van der Waals energy contributions and a decrease in electrostatic energy contributions to the overall compound sorption energies because of aminium charge delocalization into methyl substituents and steric hindrance from methyl substituents to form specific interactions. The findings illustrate how molecular docking can be used to explore the effects of organic cation structure on sorption interactions with organic matter.

Insight into the Sorption and Activation Energy Phenomenon of Kenaf Shive Sorbents in Crude Oil/Water Mixture

The secondary effect discovery of synthetic sorbents opened another research direction for many field of studies. However, the sorption parameters of lignocellulosic sorbents are rarely reported most importantly, kenaf shive. This paper centered at the sorption behavior of optimized kenaf shive sorbents using Response Surface Methodology (RSM) via surface deposit technique. Five-level Central Composite Design (CCD) experimental matrix was used to analyze the effect of particle sizes (125-1000 µm), stirring time (5-30min) and methyltrimethoxysilane (MTMS) concentration (5-20% v/v) as individual and combined variables process in the developed sorbents. The unmodified shive was compared with the modified, and it reveals a positive shift in the sorption capability. Instrumental analysis such as FTIR (Fourier Transform Infra-Red), DT-TGA (Differential Thermal-Thermogravimetric analysis) and BET (Brunaure-Emmett-Teller) were carried out on the optimized sorbent and the results were in conformity with the sorption results. The sorption behavior deployed fits the pseudo-first-order and Langmuir isotherm with regression coefficient R2=0.9496 and R2=0.9400. The sorption property was found to be spontaneous and exothermic, however, the activation energy studies shows physic-sorption phenomenon with 25.3 kJmol-1 and R2=0.9360.

Inherent Minerals Facilitated Bisphenol A Sorption by Biochar: A Key Force by Complexation

Biochar is a multiphase carbonaceous structure with inherent minerals. The role of minerals in organic sorption is essential for biochar application in environmental remediation. In this work, combined with X-ray diffraction (XRD) and 13C nuclear magnetic resonance (NMR) techniques, the composition of minerals and the sorption behavior of bisphenol A (BPA) were investigated. A demineralization treatment was applied to remove surface minerals containing silicon (Si), aluminum (Al), and calcium (Ca) elements, resulting in the exposure of micropores in aromatic carbon. These minerals could serve as vital sites to facilitate BPA sorption due to the complexation mechanism. The role of mineral elements in enhanced sorption could be in the sequence of Al mineral > Ca mineral > no mineral. Density functional theory (DFT) calculation confirmed the occurrence of complexation between minerals and BPA as evidenced by sorption energy. After demineralization, declined release ratio (RR) values implied that adsorbed BPA on demineralized biochars was more difficult to desorb than on original biochars owing to the restriction of micropores. The enhanced energy gap also verified that BPA molecules were more stable on demineralized biochars. This research casts new light on recognizing biochar minerals in relation to their underlying sorption mechanism for phenolic compounds.

Dipicolinamide functionalized titania for highly efficient sorption of tetra and hexavalent actinide

Dipicolinamide functionalized titania particles have been synthesized for efficient decontamination of uranyl and thorium ions from aqueous acidic waste solution. Langmuir isotherm was found to be predominating with maximum sorption capacity of 125 mg/g for Th and 111 mg/g for U, respectively. The sorption was found to follow pseudo 2nd order kinetics predominately, with rate constant 8.6E−04 mg g−1 min−1 for Th and 6.1E−04 mg g−1 min−1 for U, respectively. Up to 200 kGy of gamma irradiation, not much deterioration in extraction performance of sorbent material was observed. Three contacts of 0.1 M aqueous solutions of oxalic acid and sodium carbonate were found to be effective in quantitative elution of Th4+ and UO22+ from the loaded sorbent, respectively. The sorption of U and Th on dipicolinamide functionalized titania was evidenced by SEM images, elemental mapping and the EDX. Theoretical investigation revealed that, the solution phase free energy of sorption (ΔGsol) was higher for Th4+ (−114.1 kcal mol−1) compared to UO22+ (−80.41 kcal mol−1).

Uranium (VI) Adsorbate Structures on Portlandite [Ca(OH)2] Type Surfaces Determined by Computational Modelling and X-ray Absorption Spectroscopy

Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH)2] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO2(OH)n]2–n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.

Freundlich and Langmuir Isotherm Studies of Phosphorus Sorption unto Soils Derived from Basement Complex Rock, Alluvium, Coastal Plain Sand and Shale Parent Materials

To provide information on best model to predict Phosphorus (P) Sorption unto Soils derived from Basement Complex Rock, Alluvium, Coastal Plain Sand and Imo Shale Parent Materials in 3 states of Nigeria. Completely randomized design was used to collect surface soil samples in 3 replications from 4 locations in Nigeria.
 Samples were collected from Idanre, Koko, NIFOR and Uhonmora in Ondo, Delta and Edo states Nigeria, laboratory analysis was carried out in the Central analytical laboratory of Nigerian Institute for Oil-Palm Research (NIFOR) Benin City, Nigeria between march 2016 and September 2017.
 Soil samples were equilibrated in 25 ml of 0.01 M CaCl2 containing various concentration of P as KH2PO4 to give 0, 50, 100, 150, 200 and 250 mg/L P for 24 hours (h) at room temperature 25 ± 2oC. 3 drops of CHCl3 was added to inhibit P mineralization. The suspension was shaken for 24 h on a reciprocating mechanical shaker, centrifuged at 7000 rpm After equilibration, decanted and P determined using spectrophotometer. The sorption data were fitted to linear Freundlich and Langmuir sorption isotherm.
 Considering the Freundlich model, P adsorption capacity (a) and P sorption energy (n) was highest in soils B (1400 mg kg-1) and (2.806 L kg-1) respectively. The Freundlich model fitted better to the data obtained with average root mean square error (RMSE) and R2 value of 0.69 and 0.951 respectively, as against average RMSE and R2 value of 1.60 and 0.883 respectively obtained from Langmuir model.
 The sorption data fitted well to Freundlich and Langmuir isotherms of which Freundlich Adsorption model was found to be better based on lowest RMSE (0.69) and highest regression (R2 = 0.951) value. Freundlich model should be adopted to determine P sorption characteristics of the soils studied. These predictors, however, need further works to validate reliability.

Physicochemical Changes in Biomass Chars by Thermal Oxidation or Ambient Weathering and Their Impacts on Sorption of a Hydrophobic and a Cationic Compound.

This study examined conditions that mimic oxidative processes of biomass chars during formation and weathering in the environment. A maple char prepared at the single heat treatment temperature of 500 °C for 2 h was exposed to different thermal oxidation conditions or accelerated oxidative aging conditions prior to sorption of naphthalene or the dication paraquat. Strong chemical oxidation (SCO) was included for comparison. Thermal oxidation caused micropore reaming, with ambient oxidation and SCO much less so. All oxidative treatments incorporated O, acidity, and cation exchange capacity (CEC). Thermal incorporation of O was a function of headspace O2 concentration and reached a maximum at 350 °C due to the opposing process of burn-off. The CEC was linearly correlated with O/C, but the positive intercept together with nuclear magnetic resonance data signifies that, compared to O groups derived by anoxic pyrolysis, O acquired through oxidation by thermal or ambient routes contributes more to the CEC. Thermal oxidation increased the naphthalene sorption coefficient, the characteristic energy of sorption, and the uptake rate due to pore reaming. By contrast, ambient oxidation (and SCO) suppressed naphthalene sorption by creating a more hydrophilic surface. Paraquat sorption capacity was predicted by an equation that includes a CEC2 term due to bidentate interaction with pairs of charges, predominating over monodentate interaction, plus a term for the capacity of naphthalene as a reference representing nonspecific driving forces.

Selectivity towards acetylene gas of flame-spray-made Nb-substituted SnO2 particulate thick films

0.1–2 wt% Nb-doped SnO2 nanoparticles were produced via flame spray pyrolysis (FSP) in a single step for the first time. The structural characterizations including X-ray diffraction, nitrogen sorption analysis, electron microscopy, energy dispersive and photoelectron X-ray spectroscopy revealed that Nb5+ species were substitutionally doped into the lattice of nanocrystalline tetragonal SnO2 nanoparticles (5–15 nm). The sensing layers produced by spin coating were tested towards 0.05–1 vol% C2H2 at 200–400 °C in air. Gas-sensing results indicated that the optimal Nb content of 0.5 wt% provided the best sensor response of ~776 with an excellent response time of 1.1 s to 1 vol% C2H2 at the optimal sensing temperature of 350 °C. Additionally, the optimal Nb-doped SnO2 sensor exhibited low humidity dependence, good long-term stability and high C2H2 selectivity relative to HCHO, CH3OH, C2H5OH, C3H6O, CH4, C2H4, C6H6, C7H8, C8H10, H2, NO2, NO and NH3. Moreover, low direct cross interferences were demonstrated against CH3OH and C8H10. The results were explained by the catalytic and electronic roles of n-type Nb dopants on C2H2 interaction. Thus, the Nb-doped SnO2 sensor is an attractive candidate for selective C2H2-sensing applications.

Defect-Rich Hierarchical Porous UiO-66(Zr) for Tunable Phosphate Removal.

The introduction of defects into hierarchical porous metal-organic frameworks (HP-MOFs) is of vital significance to boost their adsorption performance. Herein, an advanced template-assisted strategy has been developed to fine-tune the phosphate adsorption performance of HP-MOFs by dictating the type and number of defects in HP-UiO-66(Zr). To achieve this, monocarboxylic acids of varying chain lengths have been employed as template molecules to fabricate an array of defect-rich HP-UiO-66(Zr) derivatives following removal of the template. The as-prepared HP-UiO-66(Zr) exhibits a higher sorption capacity and faster sorption rate compared to the pristine UiO-66(Zr). Particularly, the octanoic acid-modulated UiO-66(Zr) exhibits a high adsorption capacity of 186.6 mg P/g and an intraparticle diffusion rate of 6.19 mg/g·min0.5, which are 4.8 times and 1.9 times higher than those of pristine UiO-66(Zr), respectively. The results reveal that defect sites play a critical role in boosting the phosphate uptake performance, which is further confirmed by various advanced characterizations. Density functional theory (DFT) calculations reveal the important role of defects in not only providing additional sorption sites but also reducing the sorption energy between HP-UiO-66(Zr) and phosphate. In addition, the hierarchical pores in HP-UiO-66(Zr) can accelerate the phosphate diffusion toward the active sorption sites. This work presents a promising route to tailor the adsorption performance of MOF-based adsorbents via defect engineering.

EXAFS investigation of Ni(Ⅱ) sorption at the palygorskite-solution interface: New insights into surface-induced precipitation phenomena

Sorption reactions at the mineral/water interface control the fate and transport of trace metals in aqueous geochemical environments. While surface complexation theory is well established, understanding of surface induced precipitation at mineral/water interfaces is still limited. In this research, we employed a combination of macroscopic batch sorption studies, transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and extended X-ray absorption fine structure (EXAFS) spectroscopy to elucidate the sorption mechanisms of nickel (Ni) at palygorskite/solution interfaces. Compared to extensive studies focused on oxides and layer-structured clay minerals, research on chain-type clay minerals (e.g., palygorskite and sepiolite) is sparse. Thus, novel investigations using chain-type clay minerals can provide new insights into the metal sequestration mechanisms and improve equilibrium modeling. In this work, temperature-dependent kinetic experiments demonstrated that the activation reaction energy (Ea) for Ni sorption on palygorskite at pH 6.0 is 35.1 kJ mol−1, significantly lower than that of pH 7.5 (Ea = 102.1 kJ mol−1). These values indicated an adsorption reaction at low pH and a precipitation reaction at high pH. EXAFS analysis confirmed that below pH 6, Ni sorption was dominated by outer-sphere surface complexes at low ionic strength (I = 0.01 M) and inner-sphere surface complexation at high ionic strength (I = 0.1 M). Above pH 7.5, EXAFS data suggested the formation of Ni phyllosilicate precipitates, in agreement with its linear sorption isotherm. An important finding is that the precipitates can form at very low Ni concentrations (∼0.07 mM), with the sorption density of Γ = 0.09 μmol m−2, which corresponds to a 0.3% monolayer coverage for palygorskite. In contrast, at this low level of Ni concentration, surface precipitates did not form on γ-Al2O3. We propose that Ni can be directly induced to precipitate on the palygorskite surface in a process we term “continuous nucleation”. This is mechanistically different from the traditional adsorption-to-polymerization process on the γ-Al2O3 surface, which we term “staged nucleation”. Further testing revealed that a linear-shaped isotherm was also observed for Ni sorption on sepiolite, a clay mineral with similar structure and chemical composition to palygorskite, indicating a similar reactivity for both chain-structure phyllosilicates. This is distinct from the Langmuir-type sorption isotherm observed for Ni reaction with Al oxides and montmorillonite. The findings presented in this study improve not only the current understanding of metal sequestration and surface precipitation at mineral/water interfaces but also shed light on the large differences in the surface reactivities of clay minerals with chain structure versus layered structure.

Microstructure and catalytic properties of Fe3O4/BN, Fe3O4(Pt)/BN, and FePt/BN heterogeneous nanomaterials in CO2 hydrogenation reaction: Experimental and theoretical insights

Hexagonal boron nitride (h-BN) nanosheets are a promising material for various applications including catalysis. Herein, h-BN-supported Fe-based catalysts are characterised with respect to CO2 hydrogenation reaction. Heterogeneous Fe3O4/BN, Fe3O4(Pt)/BN, and FePt/BN nanostructures are obtained via polyol synthesis in ethylene glycol. The sizes of Fe3O4 nanoparticles and their distributions over h-BN surfaces depend on the amount of H2PtCl6 added to the synthesis media. Bimetallic FePt nanoparticles are formed when Pt content is high enough. In situ TEM analysis shows the formation of core–shell h-BN@FePt nanoparticles during heating that prevents FePt NPs from further sintering during the catalytic process. The mechanism of Fe and Pt interaction is elucidated based on the molecular dynamic simulations. The FePt/BN nanomaterials show significantly higher CO2 conversion rate compared to the Fe3O4/BN and Fe3O4(Pt)/BN heterogeneous nanomaterials and exhibit almost 100% selectivity to carbon monoxide. The Fe3O4/BN and Fe3O4(Pt)/BN nanomaterials show better selectivity to hydrocarbons. The possible reaction pathways are discussed based on the calculated sorption energies of all reactants, intermediate compounds, and reaction products. The study highlights pronounced catalytic properties of the developed system and reveals a unique interaction mechanism between its components increasing their stability.

A molecular investigation of urea and creatinine removal in the wearable dialysis device using Two-Dimensional materials

Urea and creatinine removal is considered challenging issues regarding the development of artificial kidneys. The present study was aimed at investigating the novel and tunable urea and creatinine adsorbents in the form of two-dimensional (2D) materials. To this end, various 2D materials were investigated. Moreover, the molecular dynamics (MD) and density functional theory (DFT) simulations were performed to assess urea and creatinine adsorption, interaction energies, and other adsorption properties of 2D materials. The validity of applied methods as well as results was confirmed by comparing them to relevant experimental studies. The results show 2D materials have high attraction energy for urea sorption. Twelve different types of 2D materials with high adsorption energies (up to −340.2 KJ/mol) can adsorb urea. These monolayers also can remove creatinine with stable adsorption (Gibbs free energies up to −17.23 KJ/mol). Accordingly, 2D materials can be suggested as promising adsorbents for artificial kidney applications. Besides, the COF, MXene, MoO3, and Bithmuthene monolayers exhibited greater urea and creatinine adsorption capacity, more enhanced adsorption energy, and excellent adsorption properties compared to other 2D materials. The functionalization of the surface with –COOH groups boasts the adsorption of urea and creatinine even further.

4-Aminoacetophenone Intercalated CoAl Layered Double Hydroxides: Synthesis, Characterization and Adsorptive Removal of Cd(II) ions from Water Samples

In the present study, CoAl-NO3 Layered Double Hydroxides (CoAl-NO3-LDH) was synthesized and an enolate anion of 4-Aminoacetophenone (AAP) was intercalated into LDH following the reconstruction approach. The CoAl-NO3-LDH and CoAl-AAP-LDH were characterized by Fourier-Transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analyses. CoAl-AAP-LDH worked well for adsorption of Cd(II) ions from aqueous samples at optimum pH 7, adsorbent dosage 25 mg, concentration of Cd(II) ions 25 mg L-1 and shaking time 20 min at 25 °C. Different isotherms such as Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms fitted well to adsorption data with correlation coefficient (R2) of 0.998, 0.982 and 0.992, respectively. Monolayered (Qm) and multi-layered (KF) capacities of CoAl-AAP-LDH for adsorption of Cd(II) ions were calculated and found to be 34.40 and 19.44 mg g-1, respectively. Sorption energy was calculated and found to be 9.13 kJ mol-1, indicating chemisorption or ion exchange sorption mechanism. The method worked well for the adsorption of Cd(II) ions from wastewater samples.

Sorption isotherms and thermodynamic properties of wheat malt under storage conditions

AbstractThe growing use of wheat malt in food applications has boosted studies regarding suitable conditions for processing and storage. Because water sorption during storage may affect the malt functionality, sorption isotherms of wheat malt were determined aiming at covering a wide range of temperatures (10–40°C) and relative humidity (5.80–98.18%). Different theoretical models were fitted to the experimental data. Thermodynamic properties as heat of sorption, enthalpy, entropy, and Gibbs free energy were evaluated. Equilibrium moisture content tended to increase with increasing water activity and decreasing temperature. Henderson and GAB models showed the best fit for wheat malt isotherms. Isosteric heat of sorption increased as the moisture content decreased. Differential enthalpy (−1,071.82 to −36.95 kJ/kg) and entropy (2.29 to 0.12 kJ/k/K) values were linearly dependent, meeting the requirements to confirm the compensation theory. Water adsorption of wheat malt was considered as an enthalpy‐driven (ΔH < 0) and spontaneous process (−324.13 kJ/kg< ΔG < −0.13 kJ/kg). Reported data can be useful for designing adequate storage conditions of wheat malt.Practical ApplicationsWheat malt has been widely used together with or in replacement of barley malt in many food applications, from brewing to ingredient industries. As a consequence of the seasonality, wheat malt should be stored for long periods to ensure the supply chain over the year. As seen as the storage conditions may affect the quality and shelf‐life of wheat malt, this work aimed at: reporting experimental conditions to better preserve the malt quality and make viable its long‐term usage in different food applications; determining and evaluating its water sorption properties in a range of temperatures and relative humidity; providing mathematical models and thermodynamic analysis for designing adequate storage conditions.

Synthesis of new functionalized Calix[4]arene modified silica resin for the adsorption of metal ions: Equilibrium, thermodynamic and kinetic modeling studies

In this study, a new efficient resin-based material has been synthesized through the surface modification of silica by functionalized calix[4]arene and applied for the adsorption of metal ions from aqueous media. The synthesis of functionalized calix[4]arene modified silica (FCMS) resin was characterized by FTIR, CHNS, BET surface area, SEM analyses. The FCMS resin has high thermal and chemical stabilities that were checked by the thermogravimetric analysis and various acidic/basic conditions. The efficiency of the FCMS resin was checked by performing a set of batch experiments under optimized parameters such as concentration of the metal solution, pH, resin dosage, time, temperature, and competitive adsorption in mixed solutions. The results showed that better adsorption has been achieved at pH 7, with 25 mg adsorbent dosage and 10 min contact time. The equilibrium kinetic study showed that the metal adsorption follows the pseudo 2nd order kinetic model with quite high coefficients of determination values (R2 > 0.99). The experimental data have been validated by applying three adsorption isotherm models and the results revealed that the Freundlich isotherm model (R2 > 0.99) was the best fit for the adsorption of Cu2+, Pb2+, and Cd2+ ions. However, the sorption energy calculated from the D-R isotherm model for Cu2+, Pb2+, and Cd2+ ions suggested that an ion-exchange mechanism is involved on the surface of the FCMS resin. The thermodynamic data demonstrated that the reaction is spontaneous and endothermic. The FCMS resin was also applied on real wastewater samples and the results demonstrated that the resin has a good ability to treat metal-contaminated wastewater.

Modeling of adsorption isotherm of freeze‐dried mahaleb powder using artificial neural network and calculation of thermodynamic sorption properties

AbstractIn this study, adsorption isotherms of freeze‐dried mahaleb powder were obtained using gravimetric method at four different temperatures (5, 25, 35, and 60°C). Experimental adsorption data were modeled using empirical models and artificial neural network. The GAB model gave the best fit among the empirical models with high R2 (0.9908–0.9982) and low P% (4.71–8.40%) values. However, artificial neural network (ANN) model having 10 hidden neurons optimized using Lavenberg‐Marquardth training algorithm was superior to the empirical models with the highest R2 (0.9965–0.9999) and lowest P% (0.74–8.52%) values. The ANN model explained the adsorption behavior of mahaleb powder ideally at all temperatures. In addition to the adsorption kinetics of mahaleb powder, thermodynamic properties such as isosteric heat of sorption, differential entropy and Gibbs free energy were also determined. Isosteric heat of sorption values were high when moisture contents of the powders were low. Also, differential entropy values followed the same trend which indicated that the adsorption process was driven by enthalpy. Gibbs free energy at the isokinetic temperature of 458.48 K was determined as −306.7 J/mol. Gibbs free energy values were below zero at all different temperatures. The results showed that ANN model can be suitable for predictive control systems in the food industry and the data obtained for thermodynamic properties can be useful for the storage of mahaleb powder in industrial scale.Practical ApplicationsAn intelligent model, which is artificial neural network was used for modeling of adsorption behavior of freeze‐dried mahaleb powder and it predicted the adsorption data better than empirical models. Thermodynamic properties which are mostly important for the prediction of energy consumption of a process were also determined. The data of the freeze‐dried mahaleb powder can be significant for the food industry in terms of prediction of shelf‐life and energy requirements.

Equilibrium and thermodynamic investigation of biosorption of nickel from water by activated carbon made from palm kernel chaff

Novel biosorbents were derived from a waste product of palm kernel oil extraction known as palm kernel chaff (PKC). One portion of the PKC was carbonized in a furnace and then activated chemically, while the other half was activated without carbonization. Both were designated as CPKC and UPKC, respectively. The two biosorbents so produced were then used to conduct batch equilibrium and kinetic sorption studies at 30 °C, 35 °C and 40 °C and pH 3.0 and 9.0 for an agitation period of 5, 10, 20, 40, 60, 90, and 120 min. The Koble-Corrigan, Dubinin-Radushkevich, and the Freundlich isotherms fitted the experimental data very well with R2 values of 0.97 to 1.0, 0.95 to 1.0, and 0.96 to 1.0, respectively. The linear type II Langmuir isotherm performed much better (0.96 ≤ R2 ≤ 1.0) than the nonlinear isotherm. The maximum sorption capacity was obtained as 120.6 mg/g using CPKC at pH 9.0 and 35 °C. The Langmuir separation coefficient values (0.022 ≤ RL ≤ 0.926) show that the sorption of nickel to PKC is favorable. The most favorable sorption condition was found for CPKC at pH 9 and temperature of 40 °C. The values of sorption energy (8.21 ≤ E ≤ 14.27) and the isosteric heat of sorption (−133.09 ≤ ∆Hx ≤ −17.92) indicate that the mode of sorption is mostly ion exchange. Thermodynamic parameters also show that the process is exothermic and entropy-driven. The pseudo-second-order kinetic model shows the best correlation compared to the other kinetic models. The coefficient of correlation for the pseudo-second-order model was mostly within the range of 0.999–1.000 for 90% of all kinetic studies carried out.