Adsorption Enthalpy ΔH Research Articles

Removal of Pb(II) from Aqueous Solutions by Adsorption Using Nano Mesoporous Silica MCF Adsorbent: Kinetic, Thermodynamic, Isotherm and Equilibrium Studies

Introduction: Pb2+ is a very toxic heavy metal and its pollution to environment is very harmful and to remove its pollution is a very important issue. Methods: In this work, nano Mesocellular Foams (MCF) silica material was synthesized by hydrothermal method in this research. Power X-ray diffraction and scanning electron miccroscopy, etc. were used to characterize the sample. In this paper, the adsorption of heavy metal ion Pb2+ by MCF was studied. Results: The sample showed spherical particles and the morphology was regular. Its average particle diameter was 2.2 μm. Transmission electron microscopic result showed that the structure of the MCF synthesized has honeycomb structure pore channels which are benefitial for adsorbing heavy metal ions. The nitrogen adsorption-desorption experimental results at low temperature of 77 K showed that the adsorption pore diameter of the MCF synthesized was 19.62 nm. The research results showed that when pH value was 4.5, temperature was 25 ± 1°C, the adsorbent material MCF was 0.2000 g:Pb2+ = 5 and the contact time was 40 min, the adsorption effect was the best and the adsorption rate reached 97.16 ± 0.03%, while the adsorption capacity reached 194.32 ± 0.13 mg/g. Conclusion: By studying, it has been found that the adsorption belongs to the quasi-second-order kinetic model, simultaneously, it also fits the Freundlich equation and in accordance with heterogeneous adsorption. The results of adsorption thermodynamics showed that when temperature is 25 ~ 45°C, the adsorption is a spontaneous exothermic reaction, ΔG° is less than zero, the adsorption enthalpy ΔH° is -31.856 kJ/mol and the adsorption entropy change ΔS° is -45.092 J/(mol·K).

Efficient Removal of Ni(II) and Co(II) Ions from Aqueous Solutions Using Silica-based Hybrid Materials Functionalized with PAMAM Dendrimers

ABSTRACT Many techniques of metal ions removal have been already implemented; however, there is still need for novel, efficient, and non-toxic adsorbents dedicated to heavy metals. In a recent study, the adsorptive properties of four hybrid materials consisting of silica platform surface grafted with poly(amidoamine) dendrimers (PAMAM) with different amino-terminal components, toward two heavy metal ions: Ni(II) and Co(II), were examined. The materials showed maximal scavenging properties at pH 5.4. To determine the adsorptive nature of the hybrid materials, experimental isotherms were fitted by the Langmuir, the Freundlich, and the Dubinin–Radushkevich models. All materials exhibited adsorption capability best described by the Langmuir model. The calculated adsorption capacities qm ranged between 86.7 and 116.6 mg g−1 for Ni(II) ions and 32.8 and 101.1 mg g−1 for Co(II) ions, which strictly indicate the influence of grafting agent structure on adsorptive properties of hybrid materials. The values of mean free energy E and adsorption enthalpy ΔH° jointly indicated the physical nature of adsorption processes. From the thermodynamic studies, the values of ΔH°, ΔS°, and ΔG° were obtained, indicating the spontaneous and endothermic character of investigated Ni(II)/Co(II) metal ions adsorption process on SiO2–dendrimer hybrid materials. Moreover, the materials exhibited selectivity toward Ni(II) ions.

Schiff-base reaction induced selective sensing of trace dopamine based on a Pt41Rh59 alloy/ZIF-90 nanocomposite

Zeolitic imidazole frameworks (ZIFs) are a new class of functional porous materials with attractive characters, such as gas storage, selective separation, catalysis, and drug delivery. We report herein using nanoscale ZIF-90 crystals with free aldehyde group of imidazole-2-carboxaldehyde (ICA) ligand for the selective electrochemical detection of dopamine. The averaged adsorption enthalpy ΔH (i.e., isosteric heat) of ZIF-90 to dopamine is estimated as 72 kJ mol−1 according to grand canonical Monte Carlo (GCMC) simulation. With further modification of a Pt41Rh59 alloy nanocatalyst, the electrochemical sensing performances towards dopamine are improved. The synergetic effect generated by a Pt41Rh59/ZIF-90 nanocomposite endows it a low detection limit of 1 nM and good specificity. The different anti-interference mechanisms to coexisting redox active species and amino analogues are also included in this work. The strategy demonstrated here may be extended to tune metal nodes as well as ligands of ZIFs crystals and further regulating their functionalities for different target molecules identification.

Chemically activated nanoporous carbon adsorbents from waste plastic for CO2 capture: Breakthrough adsorption study

Abstract This paper describes the preparation of O-enriched porous carbonaceous adsorbents derived from low cost, abundantly available polyethylene terephthalate (PET) waste with high carbon content by directly carbonising at different temperatures (500–800 °C) and then chemically activating using variable impregnation ratios of KOH to carbon. The prepared carbon adsorbents were characterized for their textural and surface chemical properties using nitrogen sorption, CHN, FTIR, XRD, SEM, HRTEM, and XPS techniques. Further, to assess their CO2 adsorption-desorption performance under dynamic conditions, breakthrough experiments were conducted in a fixed-bed adsorption set up. Porous carbon obtained at 700 °C with KOH to carbon mass ratio of 3 (Act-3-700) exhibited best textural properties with BET surface area of 1690 m2g-1 and micropore volume of 0.78 cm3 g−1 and showed highest CO2 uptake of 1.31 mmol g−1 at 30 °C and 12.5% CO2 concentration. Four adsorption–desorption cycles establish the adsorbent's remarkable stability and regeneration. Furthermore, fractional order kinetic model explained the CO2 adsorption kinetics and Freundlich isotherm showed superior fit with the adsorption equilibrium data suggesting heterogeneous nature of the adsorbent surface. Negative values of Gibbs free energy ΔG° and adsorption enthalpy ΔH° indicate the spontaneous and exothermic nature of adsorption process.

The effect of temperature and concentration on the inhibition of acid corrosion of carbon steel by newly synthesized Schiff base

Inhibition effect of Schiff base namely 1-(2-hydroxybenzylidene)-3-(2,5-dioxoimidazolidin-4-yl) urea (ALS) was studied on carbon steel corrosion in 1.0M HCl by using the electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and linear polarization (LPR) and quantum chemical study. The values of activation energy (Ea), equilibrium constant (Kads), adsorption free energy ΔG°ads, adsorption enthalpy ΔH°ads and adsorption entropy ΔS°ads were discussed. The adsorption of inhibitor on metal followed Langmuir's adsorption isotherm. The thermodynamic parameters of adsorption reveal that there is a strong interaction between inhibitor and carbon steel. The highest inhibition efficiency was observed 5.0×10−4M ALS concentration at 318K. SEM and EDX observations confirmed the existence of protective inhibitor film on metal surface. Quantum chemical study supports the comparative inhibition effect of ALS.

Acetaldehyde and acetic acid adsorption on TiO2 under dry and humid conditions

Adsorption plays a key role in the volatile organic compound (VOC) photocatalytic oxidation performance and kinetic behavior. It can lead to VOC mixture sequential treatment or even photocatalyst deactivation. The aim of this work is to determine qualitative and quantitative data regarding VOC adsorption on P25 TiO2. Acetaldehyde and acetic acid adsorption on TiO2 have been studied under both dry and humid conditions. Three experimental methods have been used: breakthrough curves, room temperature desorptions and temperature-programmed desorptions. First, acetaldehyde and acetic acid adsorptions are studied individually. Dry and humid experiments provide complementary pieces of information to identify the adsorption modes, in accordance with literature. The Langmuir model parameters (adsorption constant (K), reversible and irreversible maximum adsorbed amounts (qm,rev and qm,irr), and adsorption enthalpy ΔH) are determined for each VOC. Based on experimental results, a model for acetaldehyde and water co-adsorption is proposed, taking into account the specific interaction between acetaldehyde and water molecule. Regarding acetic acid, a reactive adsorption pathway is proposed and a kinetic model is developed to describe the reactive adsorption. Finally, in order to understand multi-VOC interaction on TiO2 surface, the sequential adsorption of acetaldehyde and acetic acid is investigated and confronted with the single-VOC data. As a result, single VOC adsorption parameters are useful to understand and predict multi-VOC photocatalytic oxidation.

Synthesis, physical characteristics, and Cd2+ sorption studies of amorphous Fe(OH)3

This work investigates the physical characteristics of amorphous Fe(OH)3 synthesized by precipitation method for the sorption studies of Cd2+ ions. The exchange of surface protons was determined by potentiometric titration method. The particle size distribution shows the agglomeration of smaller particles and also the presence of nanoparticles. Batch sorption studies are performed with respect to concentration, pH, and temperature of the solution. The adsorption of Cd2+ ions is found to increase with increasing concentration and temperature of the solution. To interpret the sorption data, Langmuir and Freundlich models are used. The values of both the adsorption enthalpy ΔH and entropy ΔS are found to be positive, suggesting that sorption process is endothermic and spontaneous in nature. The Fe dissolved from the solid is found to be less than 1 mg/L, which proves the integrity of the adsorbent. Further, the mechanism of the sorption reaction is also explored.

Porosity of Pillared Clays Studied by Hyperpolarized 129Xe NMR Spectroscopy and Xe Adsorption Isotherms

The influence of the layer charge on the microstructure was studied for a series of three hybrid pillared interlayered clays based on the organic dication Me(2)DABCO(2+) and charge reduced synthetic fluorohectorites. To get a detailed picture of the local arrangements within the interlayer space, multinuclear solid-state NMR spectroscopy was performed in conjunction with high-resolution (129)Xe MAS NMR, temperature-dependent wide-line 1D and 2D (129)Xe NMR, and Ar/Ar(l) and Xe/Xe(l) physisorption measurements. The resulting layer charge (x) for the three samples are 0.48, 0.44, and 0.39 per formula unit (pfu). The samples exhibit BET equivalent surfaces between 150 and 220 m(2)/g and pore volumes which increase from 0.06 to 0.11 cm(3)/g while the layer charge reduces. 1D and 2D (1)H, (13)C, (19)F, and (29)Si MAS data reveal that the postsynthetic charge reduction induces regions with higher defect concentrations within the silicate layers. Although the pillars tend to avoid these defect-rich regions, a homogeneous and regular spacing of the Me(2)DABCO(2+) pillars is established. Both the Ar/Ar(l) physisorption and (129)Xe NMR measurements reveal comparable pore dimensions. The trend of the temperature-dependent wide-line (129)Xe spectra as well as the exchange in the EXSY spectra is typical for a narrow 2D pore system. (129)Xe high-resolution experiments allow for a detailed description of the microstructure. For x = 0.48 a bimodal distribution with pore diameters between 5.9 and 6.4 Å is observed. Reducing the layer charge leads to a more homogeneous pore structure with a mean diameter of 6.6 Å (x = 0.39). The adsorption enthalpies ΔH(ads) determined from the temperature-dependent (129)Xe chemical shift data fit well to the ones derived from the Xe/Xe(l) physisorption measurements in the high-pressure limit while the magnitude of ΔH(ads) in the low-pressure limit is significantly larger. Thus, the (129)Xe data are influenced by adsorbate-adsorbent as well as adsorbate-adsorbate interactions.

Immobilisation of lead(II) ions from aqueous solutions on natural coal

The immobilisation of lead(II) ions from aqueous solutions on natural coal was investigated to compare calculated and measured adsorption enthalpies. For this purpose, adsorption isotherms were measured at temperatures of 303, 333 and 353 K. Adsorption enthalpy ΔH was evaluated from temperature dependence of the equilibrium constant of adsorption using the van‘t Hoff equation. Thus, the value of ΔH = 27 kJ mol−1 was obtained manifesting endothermic effect of lead(II) immobilisation on the coal. However, based on the flow and immersion calorimetric measurements, the exothermic character of lead(II) adsorption on the studied coal was proven with a value of about −7 kJ mol−1.

Adsorption Performance for Ag(І) of an Ethoxycarbonyl Thiourea Chelating Resin

Effects of initial concentration of Ag(І), concentration of HNO3, contact time and adsorption temperature on adsorption capacities of a novel polystyrene modified ethoxycarbonyl thiourea resin were investigated, and the maximum adsorption capacity of Ag(І) reached 4.11 mmol·g-1. The adsorption kinetics was well fitted Boyd’s diffusion equation of liq·uid film, so the adsorption was controlled by liquid film diffusion. The experimental date fitted Langmuir equation, and the correlation coefficient was close to 1. The positive value of adsorption enthalpy ΔH is indicative of an endothermic process. FT-IR characteristic peaks of ethoxycarbonyl and thiourea groups changed obviously fore-and-aft adsorption, which means that the corresponding functional groups coordinate with Ag during the adsorption process.

Inhibition Effect of Nitrotetrazolium Blue Chloride on the Corrosion of Steel in Hydrochloric Acid Solution

The inhibition effect of nitrotetrazolium blue chloride (NTBC) on the corrosion of cold rolled steel (CRS) in 1.0-5.0 mol·L - 1 HCl solution was investigated by weight loss method, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that NTBC is a good inhibitor for CRS in 1.0 mol·L - 1 HCl solution and the adsorption of NTBC on the CRS surface obeys the Langmuir adsorption isotherm. Inhibition efficiency increases with inhibitor concentration while it decreases with hydrochloric acid concentration and temperature. The adsorption thermodynamic parameters (adsorption free energy ΔG 0 , adsorption enthalpy ΔH 0 , adsorption entropy ΔS 0 ) and corrosion kinetic parameters (corrosion rate constant k, kinetic reaction constant B) were also calculated. Based on these parameters the inhibitive mechanism is discussed. Potentiodynamic polarization curves show that NTBC acts a mixed-type inhibitor. EIS spectra exhibit one capacitive loop at high frequency and this is followed by a small inductive loop at low frequency, and the charge transfer resistance increases with inhibitor concentrations. SEM clearly shows that the addition of NTBC can drastically retard the corrosion of steel in hydrochloric acid media.

Investigation of performances and mechanism of fluoride removal by Fe (III)-loaded ligand exchange cotton cellulose adsorbent

Novel adsorbent, Fe(III)-loaded ligand exchange cotton cellulose adsorbent [Fe(III)LECCA], was used to investigate the adsorption performances and mechanism of fluoride removal from aqueous solutions. The adsorbent was found to adsorb fluoride rapidly and effectively. The fluoride removal was influenced by pH. Adsorption model followed first-order reaction at different temperature, theapparent adsorption activated energyE, was 6.37 kJ·mol−1, and adsorption enthalpy ΔH was 5.35 kJ·mol−1. The adsorption capacity of fluoride on adsorbent was 3.2 mmol·g−1 (dry weight). The maximal integer coordination ratio of fluoride with Fe(III) LECCA was 3∶1. The ligand exchange mechanism of adsorption was elucidated through chemical methods and IR spectral analysis.