Thermodynamic parameters of adsorption of 1,10-phenanthroline and 2,2′-bipyridyl on hematite, kaolinite and montmorillonites

Tetracycline Adsorption on Magnetic Sludge Biochar: Effects of pH, Humic Acid (HA), and Fulvic Acid (FA)

Natural organic matters (NOMs) are ubiquitous in the environment, but few systematic studies have examined the influence of NOMs on the sorption ability of magnetic sludge biochar. In this study, magnetic sludge biochar was synthesized, characterized, and used as a sorbent to remove tetracycline (TC) from aqueous solutions. The effects of pH, humic acid (HA), and fulvic acid (FA) on TC adsorption by magnetic sludge biochar were studied using batch experiments. Adding HA and FA can alter the adsorption behavior of TC, except for its pH dependency. The results of this study show that relatively low concentrations of dissolved HA (≤8 ppm) and FA (≤5 ppm) promote the adsorption capacity of TC, but higher concentrations compete against TC for sorption sites on the surface of magnetic sludge biochar. The results of this study promote a better understanding of the application of magnetic sludge biochar in real antibiotic wastewater.

Synthesis and characterisation of acid/basic modified adsorbents. Application for chlorophenols removal

A commercial activated carbon was modified with acid and basic reagents -an acidic one via treatment with sulphuric acid and a basic via treatment with pentaethylenehexamine- to yield adsorbents with different surface acid/base character. These modified adsorbents were characterised by elemental and immediate analysis, N₂ adsorption, XPS and point zero charge measurements. The new adsorbents were tested for chlorophenols removal in water (4-chlorophenol, 3,5-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) at different temperatures. Although the calculated process enthalpy was positive for all cases, indicating an endothermic process, the entropy was positive, resulting in a negative Gibbs free energy and spontaneous process. The adsorption capacity increases with temperature and decreases when the phenols' number of substituents increases. The modified acid-activated carbon demonstrated an exciting higher adsorbing capacity from 426.9 to 742.3 mg g^-1 for 2,4,6-trichlorophenol, whereas the adsorption capacity for the basic ranged between 142.9 and 238.0 mg g^-1. The Langmuir model satisfactorily fitted the adsorption equilibrium data for all chlorophenol contaminants.

Tetracycline adsorption on magnetic sludge biochar: size effect of the Fe3O4 nanoparticles

Activated sludge, which is difficult and expensive to treat and dispose of, is a key concern in wastewater treatment plants. In this study, magnetic sludge biochar containing activated sludge and different sizes (14.3, 40.2 and 90.5 nm) of Fe3O4 nanoparticles was investigated as an effective adsorbent for tetracycline (TC) adsorption. Magnetic sludge-based biochar was prepared by a facile cross-linking method and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and zeta potential analysis. The adsorption performances of TC on three kinds of adsorbents were investigated. Although 14.3 nm Fe3O4 nanoparticles could be inclined to aggregate and partially filled with pores of biochar, it turned out that magnetic sludge biochar with 14.3 nm Fe3O4 nanoparticles exhibited optimum performance for TC removal with adsorption capacity up to 184.5 mg g-1, due to the larger amounts of functional groups and the change of zeta potential. Furthermore, the adsorption kinetics of TC on three kinds of adsorbents were studied, which implied that the pseudo-second-order kinetic model exhibited the better fit for the entire sorption process.

Adsorption and co-adsorption of tetracycline and doxycycline by one-step synthesized iron loaded sludge biochar

Application of biochar as an adsorbent for wastewater treatment has obtained a tremendous research interest owning to their low cost and surface functionality. In this research, an iron loaded sludge biochar was successfully prepared through a simple and economical one-step modification hydrothermal method. The iron loaded sludge biochar possesses large amounts of surface organic functional groups (such as hydroxy, carboxyl and aromatic ring, etc.), smaller particle size (about 10 nm) as well as relative higher surface area (82.780 m² g^-1) than of the pristine one. The selective removal of two kinds of antibiotics by the prepared products was demonstrated. Experimental data was fitted to isotherm and kinetic models, and thermodynamic parameters were also calculated. In the single antibiotic system, the maximum adsorption amount of tetracycline (TC) and doxycycline (DOX) could reach 104.86 and 128.98 mg g^-1 at 293.15 K, respectively. In the binary antibiotics system, there was an antagonistic effect between TC and DOX. Furthermore, the adsorption of TC was much more inhibited than that of DOX owning to its deferent steric hindrance of molecular structure.

Efficient adsorption of Mn(II) by layered double hydroxides intercalated with diethylenetriaminepentaacetic acid and the mechanistic study

In this study, greatly enhanced Mn(II) adsorption was achieved by as-synthesized diethylenetriaminepentaacetate acid intercalated Mg/Al layered double hydroxides (LDHs-DTPA). The adsorption capacity of LDHs-DTPA was 83.5 mg/g, which is much higher than that of LDHs-EDTA (44.4 mg/g), LDHs-Oxalate (21.6 mg/g) and LDHs (28.8 mg/g). The adsorption data of aqueous Mn(II) using LDHs-DTPA could be well described by the pseudo-second order kinetics and Langmuir isotherm model. Thermodynamics study results also showed that the adsorption process of Mn(II) by LDHs-DTPA was exothermic as indicated by the negative ΔH value. Furthermore, based on the structural, morphological and thermostable features, as well as FT-IR and XPS characterizations of LDHs-DTPA and the pristine LDHs, the adsorption mechanism of Mn(II) was proposed. The carboxyl groups of DTPA were proposed to be the main binding sites for Mn(II), and the hydroxyl groups of LDHs also played a minor role in the adsorption process. Among the three common regeneration reagents, 0.1 mol/L Na₂CO₃ was the best for reusing LDHs-DTPA in Mn(II) adsorption. Besides, the Mn(II) adsorption performance could be hindered in the presence of typical inorganic ions, especially cations. Further specific modifications of LDHs-DTPA are suggested to get more selective adsorption of Mn(II) in practical applications.

Treatment of Contaminated Groundwater via Arsenate Removal Using Chitosan-Coated Bentonite

In the present research, treatment of contaminated groundwater via adsorption of As(V) with an initial concentration of 50.99 µg/L using chitosan-coated bentonite (CCB) was investigated. The effect of adsorbent mass (0.001 to 2.0 g), temperature (298 to 328 K), and contact time (1 to 180 min) on the removal efficiency was examined. Adsorption data was evaluated using isotherm models such as Langmuir, Freundlich, and Dubinin-Radushkevich. Isotherm study showed that the Langmuir (R2 > 0.9899; χ2 ≤ 0.91; RMSE ≤ 4.87) model best correlates with the experimental data. Kinetics studies revealed that pseudo-second order equation adequately describes the experimental data (R2 ≥ 0.9951; χ2 ≤ 0.8.33; RMSE ≤ 4.31) where equilibrium was attained after 60 min. Thermodynamics study shows that the As(V) adsorption is non-spontaneous (ΔG0 ≥ 0) and endothermic (ΔH0 = 8.31 J/mol) that would result in an increase in randomness (ΔS0 = 29.10 kJ/mol•K) within the CCB-solution interface. FT-IR analysis reveals that hydroxyl and amino groups are involved in the adsorption of As(V) from groundwater. Results of the present research serve as a tool to determine whether CCB is an environmentally safe and cost effective material that could be utilized in a permeable reactive barrier system for the remediation of As(V) from contaminated groundwater.

Adsorption of Mn2+ from aqueous solution using Fe and Mn oxide-coated sand

The adsorption of Mn2+ onto immobilized Mn-oxide and Fe-oxide adsorbent such as manganese oxide-coated sandl (MOCS1), manganese oxide-coated sand2 (MOCS2), iron oxide-coated sand2 (IOCS2), and manganese and iron oxide-coated sand (MIOCS) was investigated. The effects of pH (5.5 to 8.0) and temperature (25 to 45 degrees C) on the equilibrium capacity were examined. Equilibrium studies showed that there is a good fit with both Freundlich and Langmuir isotherm, which indicates surface heterogeneity and monolayer adsorption of the adsorbents. Kinetic data showed high correlation with the pseudo second-order model, which signifies a chemisorption-controlled mechanism. The activation energies, activation parameters (deltaG, deltaH, deltaS), and thermodynamic parameters (deltaG0, deltaH0, deltaS0) confirmed that adsorption with MIOCS was endothermic and more spontaneous at higher temperature while an opposite trend was observed for the other adsorbents. Thermodynamic studies showed that adsorption involved formation of activated complex, where MOCS 1 and MIOCS follow a physical-chemical mechanism, while MOCS2 and IOCS2 follows purely chemical mechanism.

Adsorption studies of azotetrazolate and 3,6-dihydrazinotetrazine on peat

The objective of our studies was the evaluation of the adsorption process of two high-nitrogen compounds-dihydrazinotetrazine (DHTz) and azotetrazolate ion (AZ)-on a chosen peat. The experiments were performed using a static method at three different temperatures (283, 298, and 333 K). The adsorption process of DHTz and AZ on peat was characterized by isotherms according to the Freundlich and Langmuir models. The obtained correlations between adsorption and equilibrium concentration were in good accordance with the Freundlich and Langmuir models, as confirmed by high values of the correlation coefficients (0.97-0.99). Adsorption of AZ on peat was less efficient than that of DHTz, and this inference was experimentally proven. The maximum surface coverages of peat particles with adsorbate according to the Langmuir model were calculated as 0.02 and 0.17 mol kg(-1) (at 298 K) for AZ and DHTz, respectively. The determined adsorption equilibrium constants confirmed greater adsorption of DHTz on the investigated peat. It can be concluded that adsorption of AZ occurred to a much lesser extent compared to that of DHTz, pointing to a potentially greater threat of migration of soluble azotetrazolates in soil. Standard enthalpies of adsorption estimated for AZ and DHTz were -11.1 and -23.7 kJ mol(-1), respectively. Based on these adsorption enthalpy values, it can be stated that both investigated compounds are adsorbed on peat by a physisorption process.

Nitrate removal from aqueous solution by Arundo donax L. reed based anion exchange resin

Arundo donax L. reed based anion exchange resin (ALR-AE resin) was prepared by the amination reaction for the adsorption of nitrate from aqueous solution. The physicochemical properties of the ALR-AE resin as well as its adsorption properties for nitrate were measured. Results indicated that large amounts of amine groups have been grafted onto the structure of the resin. The FTIR and Raman spectra validated the ion exchange mechanism for nitrate adsorption by ALR-AE resin. The adsorption data showed an exothermic nature for the adsorption of nitrate by ALR-AE resin, and the equilibrium time for the adsorption process was about 10 min. The maximum adsorption capacity (Q(max)) for nitrate was 44.61 mg/g. The saturated adsorption capacity of ALR-AE resin in column was about 38.9 mg/g, which accounted for about 87.2% of the resin's Q(max). The preferential adsorption capacity of the ALR-AE resin followed the order as: SO(4)(2-)>NO(3)(-) ≈ PO(4)(3-)>NO(2)(-). In addition, the utilization of the resin in actual water samples indicated that the ALR-AE resin could be used for the treatment of many ionic polluted wastewaters.

From the Cover: Implications for complex cognition from the hafting of tools with compound adhesives in the Middle Stone Age, South Africa

Compound adhesives made from red ochre mixed with plant gum were used in the Middle Stone Age (MSA), South Africa. Replications reported here suggest that early artisans did not merely color their glues red; they deliberately effected physical transformations involving chemical changes from acidic to less acidic pH, dehydration of the adhesive near wood fires, and changes to mechanical workability and electrostatic forces. Some of the steps required for making compound adhesive seem impossible without multitasking and abstract thought. This ability suggests overlap between the cognitive abilities of modern people and people in the MSA. Our multidisciplinary analysis provides a new way to recognize complex cognition in the MSA without necessarily invoking the concept of symbolism.

Removal of copper from aqueous solution using newspaper pulp as an adsorbent

Newspaper pulp was found to be a potential adsorbent for removal of copper from aqueous medium. Detail adsorption study of Cu on newspaper pulp was investigated. Batch adsorption study was carried out as a function of contact time, adsorbent dose, temperature (303-323 K). The experimental data was analyzed using Freundlich, Langmuir, Dubinin-Radushkevich (D-R) and Redlich-Peterson (R-P) isotherm models. It was found that Freundlich, Langmuir and R-P models fitted well. pH variation study revealed that the adsorption increased with increase in pH of the solution. Maximum loading capacity was found to be 30 mg g(-1) at 20 mg L(-1) of initial Cu concentration. Adsorption data were analyzed using two kinetic models, Lagergren first order and pseudo second order. It was observed that pseudo second order represented the best correlation. Langmuir isotherm was used to obtain the thermodynamic parameters such as free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) of adsorption. The negative value of free energy and positive value of enthalpy change indicate that the adsorption of Cu on newspaper pulp is a spontaneous process and endothermic. The results of activation energy also confirmed that the adsorption of Cu on newspaper pulp is physical in nature. Present investigation emphasized that newspaper pulp may be utilized as a low cost adsorbent for copper removal.