Search

International audience; The rise of emerging contaminants in waters challenges the scientific community and water treatment stakeholders to design remediation techniques that are simple, practical, inexpensive, effective, and environmentally friendly. Emerging contaminants include antibiotics, hormones, illicit drugs, endocrine disruptors, cosmetics, personal care products, pesticides, surfactants, industrial products, microplastics, nanoparticles, and nanomaterials. Removing those contaminants is not easy because classical wastewater treatment systems are not designed to handle emerging contaminants, and contaminants often occur as traces in complex organo-mineral mixtures. Here, we review advanced treatments for the removal of emerging contaminants in wastewater, with focus on adsorption-oriented processes using non-conventional adsorbents such as cyclo-dextrin polymers, metal-organic frameworks, molecularly imprinted polymers, chitosan, and nanocellulose. We describe biological-based technologies for the degradation and removal of emerging contaminants. Then, we present advanced oxidation processes as the most promising strategies because of their simplicity and efficiency.

En la presente investigación se prepararon sólidos porosos tipo carbón activado (CA) a partir de la activación química del cuesco de palma africana procedente de los cultivos de la región de la Guajira, Colombia, con soluciones de Fe(NO3)3 y Cu(NO3)2 con cambio en la concentración a dos diferentes temperaturas: 973 y 1073 K. Los sólidos adsorbentes preparados se caracterizaron para determinar sus propiedades fisicoquímicas y capacidades de adsorción de CO2. Los CA obtenidos presentan micro-mesoporosidad con áreas superficiales entre 5 y 1300 m2g-1. Los valores con respecto al contenido de carbono fijo se encuentran entre 47,1 y 78,4%; los resultados evidencian que el proceso de activación tiene efectos sobre los parámetros texturales, composición elemental y proximal de los sólidos obtenidos. También se realizó la caracterización morfológica de la superficie de los materiales con SEM evidenciando la formación de mayor rugosidad en las muestras activadas a 1073 K, específicamente, los carbones activados con el nitrato cúprico; además, mediante EDX se cuantificó la presencia de algunos elementos. Los valores obtenidos de la adsorción de CO2 a bajas presiones se encuentran entre 80 y 250 mg·g-1, evidenciándose una mayor afinidad hacia los sólidos adsorbentes (MCu3 y MFe5).

Mesostructured silica SBA-15 and amino-functionalized silica SBA-15-NH2 were synthesized, and then, characterization, adsorption capacity, and immersion enthalpies in caffeine and glyphosate on SBA-15 and SBA-15-NH2 were evaluated. The enthalpy parameter was determined using a local construction Tian-type heat conduction calorimeter. Calorimetric studies in caffeine solutions exhibit negative enthalpy values; exothermic process characteristics for SBA-15 were between -13.90 and -194.06 J g-1 and those for SBA-15-NH2 were between -7.22 and -60.34 J g-1, and the adsorption capacity of caffeine was better in SBA-15 than that in SBA-15-NH2. In contrast, the enthalpies of immersion in glyphosate solutions were -5.06 to -56.2 J g-1 and the immersion of SBA-15-NH2 in each solution generated enthalpy values of -9.06 to -41.2 J g-1, but the adsorption capacity of glyphosate was better in the amino-functionalized SBA-15. The results show that functionalization of SBA-15 produced differences in physicochemical characteristics of solids, since energy and affinity for the calorimetric liquids are related to the surface properties of solids as well as the chemical nature of the target molecule, immersion enthalpy, was different.

In this research, a calorimetric evaluation of activated carbon-type adsorbent solids prepared by chemical activation of African palm shells with solutions of Fe(NO3)3 and Cu (NO3)2 salts with change in concentration was carried out. In the investigation, the immersion calorimetry in porous carbon-type solids in water, dichloromethane, and benzene was determined. The solids were characterized by the nitrogen adsorption technique at 77 K and the determination of functional groups by Boehm titrations. The calorimetric evaluation showed that the immersion of porous materials generated immersion enthalpy values between −10.8 and −131 J g−1. The immersion calorimetry of these materials in the immersion liquids varied with respect to the change of chemical agents and to the change of concentrations at which these materials were prepared, showing variations in textural and chemical characteristics of porous solids. The BET areas obtained are between 120 and 1360 m2 g−1, and pore volumes are between 0.05 and 0.51 cm3 g−1; these parameters increased proportionally to the increase in the values of immersion enthalpies. The adsorbent solids obtained are used in the adsorption of CO2, in this investigation, the calorimetric study was carried out in solvents with different polarities, in order to correlate these enthalpic properties of the activated carbons with the surface area and the adsorption, which presented values between 88 and 218 mg g−1.

The methylparaben adsorption from aqueous solution onto activated carbon is a relevant topic because of the toxicity of this compound for human and environmental health. The physicochemical parameters allow us to evaluate the performance of the adsorption and the relationship between the surface chemistry and the adsorbed amount of methylparaben. The effect of the solution chemistry on the adsorption was also evaluated. In this work, the methylparaben adsorption on three activated carbons with different physicochemical properties, specifically different contents of oxygenated groups and total basicity, is presented. Kinetic, equilibrium, and calorimetry tests were conducted. The maximum adsorbed amount of methylparaben was achieved on an activated carbon with basic characteristics, Qmax = 1.64 mmol g–1; in the same activated carbon, the initial rate was 0.20 mmol g–1 h–1, and the value determined for the interaction enthalpy was −12.6 × 10–20 J molecules–1, and the Gibbs energy change was close to −14.96 kJ mol–1.

Drugs are considered emerging pollutants from water sources and are therefore considered to be of high toxicological risk to aquatic fauna. Activated carbon adsorption is one of the methods approved by the Word Health Organization to remove pharmaceutical compounds from water in treatment plants due to its cost and easy implementation. This study presents the modification of a commercial activated carbon by heat treatment at 1073, 1173, and 1273 K. The impact of the physicochemical changes of the adsorbent on the adsorption capacity of salicylic acid and methylparaben, compounds derived from phenol, was studied. Finally, the adsorbate-adsorbent interactions are evaluated through immersion calorimetry. It is observed that at 1173 K, activated carbon increases its surface area by 29%. At higher temperatures, the surface area drops to 21%. In the activated carbon subjected to heat treatment at 1173 K, it increases the adsorption capacity of salicylic acid and methylparaben by 24 and 34%, respectively, compared to activated carbons subjected to higher temperatures. The interaction enthalpies (adsorbate-adsorbent interaction) have values between -12 and 5 J g-1.

In this investigation, adsorption heats were determined using a direct method (adsorption calorimetry, Ad-Cal) and an indirect method (in which adsorption isotherms are measured at different levels...

Activated carbons were prepared from a lignocellulosic material, African palm shells (Elaeis guineensis), by chemical impregnation of the precursor with solutions of 1-7% w/v Cu(NO3)2 at five different concentrations. These were carbonized in a carbon dioxide atmosphere at 1073 K to obtain different carbons. Their textural properties were characterized by nitrogen and carbon dioxide adsorption isotherms in order to evaluate the pore-size distribution. The immersion enthalpies of the activated carbons in benzene, dichloromethane, and water were determined. The CO2 adsorption capacities of the materials at 273 K under low-pressure conditions were also determined. Chemical characterization was performed by mass spectrometry, Fourier transform infrared spectroscopy, and temperature-programmed reduction. With this method of preparation under the concentrations described, activated micro-mesoporous carbons were obtained, with the formation of highly mesoporous solids that favored the process of diffusion of molecules of CO2 into the material. Here, we show that activated carbons were obtained with different textural characteristics: surface Brunauer-Emmett-Teller areas varied between 473 and 1361 m2 g-1 and micropore volume between 0.18 and 0.51 cm3 g-1. The activated carbon with the highest values of textural parameters was ACCu5-1073. Micro-mesoporous solids were obtained with the methodology used. This is important as it may help the entry of CO2 molecules into the pores. The adsorption of CO2 in the materials prepared presented values between 103 and 217 mg CO2 g-1; the values of volume of narrow microporosity obtained were between 0.16 and 0.45 cm3 g-1. The solid with the greatest capacity for adsorption of CO2 and volume of narrow microporosity was ACCu3-1073. The use of these solids is of importance for future practical and industrial applications. The adsorption kinetic of CO2 in the activated carbons prepared with metallic salt of copper is in good accordance with the intraparticle diffusion model, for which diffusion is the rate-limiting step. The adsorption of CO2 in the prepared activated carbons is favorable from the energy and kinetic point of view, as these accompanied by the presence of wide micro-mesoporosity favor the entry of CO2 into the micropores.

Nanoporous carbons have been prepared from mangosteen peels-derived chars by physical activation under CO2 flow as a function of temperature. As an example of circular bioeconomy, these sustainable adsorbents were used to remove atrazine, a common pesticide from the agroindustry. Several adsorption models such as Langmuir (two parameter), Sips and Redlich-Peterson (three parameters) were applied to verify the influence of carbon's properties on the uptake of atrazine. Additional kinetic models (pseudo-first order, pseudo-second order and Avrami's) allowed to establish that a mixture of physisorption and chemisorption describes the interaction between the nanoporous carbons and atrazine. As a general fact, an important diffusion of atrazine from the bulk of solution to the surface of carbons was observed. All samples were able to remove atrazine, but the highest uptake was found in the carbon with the highest contribution of micropores to the total pore of volume and with the lowest content of basic surface groups. Several correlations between the kinetic and equilibrium parameters for the atrazine adsorption were found as a function of the textural properties and surface chemistry. Based on the kinetics and equilibrium parameters, the present work proposes a mechanism for the atrazine adsorption on nanoporous carbons contributing to the understanding of the interactions between pollutant molecules and the surface functional groups on nanoporous carbons in the liquid-solid interface.

Metal adatoms play a key role in surface diffusion, adsorption conformation, and self-assembly of porphyrin molecules on metal surfaces. Herein, we study the specific influence of coadsorption of F...

In this study, bone chars were obtained from an alien aquatic species “devilfish” bones by pyrolysis of 500–800 °C. Bone chars were evaluated as a sustainable adsorbent of fluoride, and it was found pyrolyzed bone char at 500 °C adsorbed the most amount of fluoride. Thermodynamic parameters of fluoride adsorption on devilfish bone chars were estimated as ΔH° = 7.213 kJ mol−1, ΔG° = 23.61 kJ mol−1, and ΔS° = 103.4 J mol−1 K−1 indicating that adsorption is endothermic, spontaneous, and with a great affinity of fluoride on bone char. The fluoride desorption study showed that fluoride is desorbed from the material of 0.24 to 20.06%, so the adsorption is considered to be partly reversible. The regeneration of the bone char at 400, 500, and 600 °C was studied, and it was noted that its adsorption capacity decreases slightly, so it could be considered appropriate for the use in water treatment technologies. Adsorption of fluorides from drinking well water of a rural community with dental fluorosis problems and high levels of fluoride in water revealed that by increasing the amount of the bone char of 0.05 to 0.8 g, the disposal of fluoride increases from 69.1 to 98.7%. Lastly, it was established that the bone char synthesized from devilfish is a low-cost, viable, sustainable material to remove fluorides from water and represents an environmental management strategy of this alien species.

Immersion enthalpies of activated carbons modified on their chemical surface were determined in benzene, cyclohexane, hexane, ethanol and water. Three samples of activated carbons were used: the starting sample and two samples subjected to modifications with nitric acid and heat treatment at 750 °C, respectively, in order to modify their textural properties, but mainly their surface chemistry. Subsequently, textural characterization and surface chemistry were performed by N2 adsorption isotherms, Boehm titrations and the determination of the pHpzc. For the chemical characterization, phenolic groups predominated in the starting sample as well as a greater total acidity with respect to the sample that was subjected to heat treatment, in which the amount of oxygenated groups decreased and the total basicity increased. For the modification with nitric acid, the presence of the oxygenated groups increased. The enthalpies of immersion were exothermic (between − 21.23 and − 128.8 J g−1). Benzene was the non-polar compound with the greatest enthalpy, followed by cyclohexane and hexane, due to its atomic disposition and the interaction with the surface groups of activated carbon. For polar compounds, ethanol had higher values for the enthalpy of immersion with respect to water, due to the ability to interact with the polar and non-polar part of the molecule, to its interaction with different oxygenated groups and finally to the formation of clusters which favor an increase in solid-solvent energy interactions.

Adsorption isotherms of benzene, cyclohexane, and hexane were determined from the gas phase on microporous activated carbons with Brunauer–Emmett–Teller areas between 816 and 996 m2 g–1. The Dubinin–Radushkevich equation was used to calculate the parameters of characteristic energy Eo and micropore volume Wo. Also, immersion enthalpies of activated carbons in solvents were obtained (benzene: −95.0 to −145.1 J g–1; cyclohexane: −21.2 to −91.7 J g–1; and hexane: −16.4 to −66.1 J g–1), and they were used to calculate the product EoWo with the Stoeckli and Kraehenbuehl equations. Subsequently, values of EoWo from the two techniques (between 512 and 2223 J cm3 mol–1 g–1 for the adsorption isotherms; between 1204 and 12008 J cm3 mol–1 g–1 for immersion enthalpies) were correlated with some characteristics of the adsorbate such as molecular size, the molar volume, and the dielectric constant. It was found that modifying the activated carbon affected the adsorption process, being favored by temperature changes and restricted by oxidation processes. The adsorbate, which showed the highest values for EoWo, was benzene, because it had a smaller molecular size and a higher dielectric constant.

In the present work, the synthesis of aerogels was carried out from a mixture of resorcinol–formaldehyde as the precursors. The synthesis conditions used were those adjusted to obtain micropore mat...

In this work Ni(II) and Cr(III) adsorption on Durvillaea antarctica surface were studied, optimal condition of pH, adsorption time is achieved at pH 5.0, with contact times of 240 and 420 minutes for a maximum adsorption capacity of 32.85 and 102.72 mg g-1 for Ni(II) and Cr(III), respectively. The changes in the vibration intensity of the functional groups detected in the starting material by Fourier transform infrared spectroscopy and the opening of the cavities after the biosorption process detected by scanning electron microscopy images suggested the interaction of the metal ions with the surface and the changes in the chemical behavior of the solid. The heavy metal adsorption equilibrium data fitted well to the Sips model. The effect of competitive ions on adsorption equilibrium was also evaluated, and the results showed that the two metals compete for the same active sites of the biosorbent; the increase of the Ni(II) initial concentration increases its adsorption capacity but decreases the adsorption capacity of Cr(III).

Adsorption of Triton X-100 non-ionic surfactant in aqueous solution on activated carbon was performed. The activated carbon was prepared from waste tires by chemical impregnation at 10, 20, 30, and 40% w·w−1 of potassium hydroxide. Two carbonization temperatures, 700 and 900° C were used with a heating rate of 2 °C·min−1 and a 3 h retention time in N2 flow of 100 mL·min−1. The carbons obtained were characterized by N2 adsorption at − 196 °C, scanning electron microscopy, infrared microscopy, thermogravimetric analysis, and titration of functional groups. In adsorption studies of Triton X-100, the amount of adsorbed Triton X-100 was characterized by High-performance Liquid Chromatography and Langmuir, Freundlich, Toth, and Redlich-Peterson models were evaluated. The solids showed an area between 42 and 528 m2·g−1 with characteristic isotherms of micro-mesoporous solids, and a pore distribution of 7.0 to 8.0 A by Dubinin-Astakov with a chemical surface having acid and basic groups. The carbon that adsorbed the most Triton X-100 was QK409 with Q0 220 mg·g−1.

The change in the thermodynamic properties of triclosan adsorption on three activated carbons with the different surface chemistry was studied through immersion calorimetry and equilibrium data; the amount adsorbed of triclosan (Q) during calorimetry was determined and correlated with the energy associated with adsorbate–adsorbent interactions in the adsorption process. It was noted that triclosan adsorption capacity decreases with an increase in oxygenated surface groups. For an activated carbon oxidized with HNO3 (OxAC), the amount adsorbed was 8.50 × 10−3 mmol g−1, for a activated carbon without modification (GAC) Q = 10.3 × 10−3 mmol g−1 and for a activated carbon heated at 1073 K (RAC1073) Q = 11.4 × 10−3 mmol g−1. The adsorbed amounts were determined by adjusting the isotherms to the Sips model. For the activated carbon RAC1073, the immersion enthalpy (ΔHimm) was greater than those of the other two activated carbons due to the formation of interactions with the solvent (ΔHimmOxAC = − 27.3 J g−1

The interaction between binary mixtures of benzene/cyclohexane and toluene/cyclohexane into three activated carbons with different physical and chemical properties was determined by means of immersion enthalpy. The solids had areas between 935 and 816 m2 g−1 and pore volumes between 0.32 and 0.35 cm3 g−1. A cyclic chain aliphatic compound and two aromatic compounds were used, one of them with an aliphatic substitution of a carbon; the above, to verify the influence of the components of the mixture with different molar compositions in the process of interaction between the adsorbent and the adsorbate. For wetting liquids, the energy of interaction is higher in the aromatic compounds (benzene: between − 145.10 and − 94.98 J g−1; toluene: − 126.10 and − 59.06 J g−1) than with cyclohexane (− 91.71 and − 21.23 J g−1). For the mixtures, the values are between − 34.22 and − 109.52 J g−1. The contributions of each of the components of the mixture to the adsorbate–porous solid interaction were also determined. It was found that the decrease in surface groups favors the interaction with the compounds of interest and the activated carbon, since the solid that showed the highest interaction for both the wetting liquids separately and for the mixtures is the modified activated carbon at the highest activation temperature (750 °C); on the other hand, the sample with the highest content of oxygenated surface groups presented the least interaction with each of the components and with the mixtures.

The adsorption of phenol, salicylic acid and methylparaben on activated carbon is carried out using solvents with different pH, the adsorption and calorimetric data are analyzed in order to determine the effect of the substituent on the adsorption capacity. The adsorption isotherms were adjusted to the Langmuir model, which allows to assume the formation of specific adsorbate–adsorbent interactions between groups present in the adsorbate molecules, the substituents of the aromatic ring, and chemical groups on the activated carbon. According to the Lagmuir model the formation of specific interactions generates the monolayer adsorption so it is possible to correlate the adsorption capacity with changes in the interactions present in the system. It was determined that the adsorption process is disadvantaged at extremes pH values. From the Langmuir model it was calculated that the maximum adsorbed capacity of phenol and methylparaben in activated carbon granular activated carbon using water as solvent was 3.11 and 1.58 mmol g−1 respectively. The adsorption process of salicylic acid does not adjust to the Langmuir model due to the presence of different interactions that includes repulsion forces. From thermodynamic calculations and calorimetric data, it was determined that the immersion enthalpies vary between − 8.33 and − 59.3 J g−1, while the change in the enthalpy associated with interactions substituents-activated carbon is between − 15.1 and 6.40 J g−1 for the carboxylic acid and between − 0.50 and 20.0 J g−1 for the ester group.

International audience; Water pollution by emerging contaminants has become a major source of concern and a priority for society and public authorities. Emerging contaminants are a group of natural and synthetic chemicals and biological agents that are not routinely monitored or regulated in the environment and may have known or suspected adverse effects on the environment and human health. The list of these substances is particularly long and includes pharmaceuticals, personal care products and cosmetics, pesticides, surfactants, industrial products and additives, nanoparticles and nanomaterials, and pathogens. Many emerging contaminants are released continuously into the environment and can cause chronic toxicity even at low concentrations, endocrine disruption in humans and aquatic life, and the development of antibiotic resistant bacteria. It is therefore necessary to mobilize efforts to protect human health and biodiversity.Two of the main sources of emerging contaminants are wastewater treatment discharges and agricultural practices. However, conventional wastewater treatment plants have not been designed to remove such contaminants. It is therefore important to develop effective treatment methods capable of eliminating the parent emerging molecules and their metabolites. This is a difficult and challenging task because most of emerging contaminants are recalcitrant substances. The methods must also target not only water chemicals but also water microbiols in order to reduce and eliminate the toxicity and impact of the treated wastewater. During the past two decades, several physical, chemical and biological technologies have been proposed for emerging contaminant removal. Each technology has its own advantages and constraints not only in terms of cost, but also in terms of efficiency, feasibility, and environmental impact. However, among the various treatment processes currently cited for wastewater treatment, only few are commonly employed by the industrial sector for technological and economic reasons. Extensive research on this topic highlights the growing interest of scientists in developing treatment systems that are increasingly effective in removing mixtures of trace pollutants, simple to implement from a technological point of view, economically viable and environmentally friendly, with little or no impact on the environment.The objective of this chapter is to present the recent state of knowledge on the advanced treatments proposed for the removal of emerging contaminants in wastewater when they are present in trace amounts in wastewater. After generalconsiderations on wastewater treatment plant, the first part is focused on adsorption-oriented processes using conventional (activated carbon, clays) or non-conventional (cyclodextrin polymers, metal-organic frameworks, molecularly imprinted polymers, chitosan, nanocellulose) adsorbents. Biosorbents such as cyclodextrin bead polymers have great potential in environmental applications although they are still at the laboratory study stage. The second part presents examples of biological-based technologies for the degradation and elimination of emerging contaminants. Selected biological approaches include constructed wetlands, biomembrane reactors, strategies based on the use of algae, fungi and bacteria, and enzymatic degradation. The third part briefly presents the membrane filtration strategy that is already used as a tertiary treatment. The final part is focused on advanced oxidation processes that also represent one of the most promising strategies because of their simplicity and efficiency.

In this work, we presented the paracetamol-activated carbon interactions and their effect on the adsorption capacity. We evaluated kinetic, equilibrium, and calorimetric data using different solvents (water, HCl 0.1 M, and NaCl 0.1 M) to evaluate the changes in the adsorbent-adsorbate interaction. In addition, the commercial activated carbon (AC) was modified through thermal (ACTT) and chemical (ACNA) methods to change the physicochemical properties of the adsorbents. The relative kinetic constants decrease with the content of basic groups on the activated carbon, indicating a lower influence of diffusion on the adsorption rate when the chemical interactions increase (0.1 ACNA >0.09 AC >0.03 ACTT mmol g−1). The adsorption capacity for AC at acidic pH increases slightly compared to tests carried out in the water. Under this condition, the adsorbed amount of paracetamol was 1.31 mmol g−1. However, the maximum adsorption capacity was achieved on ACTT using water as solvent (1.57 mmol g−1). The paracetamol adsorbed decreases in NaCl (osmotic, ionic strength) on all activated carbons by around 20%. The interaction enthalpy of the paracetamol-activated carbon interaction presents values between − 18.0 and 2.3 J per molecule adsorbed. The Gibbs energy released during the adsorption process is between − 33.1 and − 29.8 kJ mol−1.

In this study, bone chars were obtained from an alien acuatic species “devilfish” bones by pyrolysis of 500–800°C. Bone chars were evaluated as a sustainable adsorbent of fluoride, it was found pyrolysed bone char at 500°C adsorbed the most amount of fluoride. The effect of pH indicated that the adsorption capacity increased as the pH decreased. Thermodynamic parameters of fluoride adsorption on devilfish bone chars were estimated as ΔH°= 7.213 kJ mol− 1, ΔG°= 23.61 kJ mol− 1 and ΔS° = 103.4 J mol− 1 K− 1 indicating that adsorption is endothermic, spontaneous and with great affinity of fluoride on bone char from devilfish. The fluoride desorption study showed that fluoride is desorbed from the material of 0.24 to 20.06 %, so the adsorption is considered to be partly reversible. The regeneration of the bone char at 400, 500 and 600°C was studied and it was noted that its adsorption capacity decreases slightly so it could be considered appropriate for the use in water treatment technologies. Adsorption of fluorides from drinking well water of a rural community with dental fluorosis problems and high levels of fluoride in water, revealed that by increasing the amount of the bone char of 0.05 to 0.8 g, the disposal of fluoride increases from 69.1 to 98.7 %. Lastly, it was established that the bone char synthesized from devilfish is a low-cost, viable a sustainable material to remove fluorides from water and represents an environmental management strategy of this alien species.

Residues of analgesics compounds are generated daily polluting the environment including drinking water. Currently, analgesics are considered emerging pollutants of high impact due to their toxic effect on aquatic animals. Different methods have been tested that allow the decontamination of water of these compounds including adsorption, which has a high effectiveness and low cost. However, the performance of the process depends on the type of adsorbent, its physicochemical properties, as well as the characteristics of the adsorbate and the solution. This text compiles the theoretical aspects applied to the adsorption of drugs from aqueous solution on activated carbon, one of the most-used adsorbents in water treatment plants. Additionally, the main results published in the literature on this subject are included, focusing on three important pollutants: paracetamol and diclofenac. According to the literature for the analgesics analyzed in this review, the most-used activated carbons were made from lignocellulosic materials and commercial adsorbents. Other options are activated carbons made from waste as polyethylen. The surface areas of adsorbents used for adsorption are between 184 and 2794 m2 g−1, the maximum adsorption capacity reported in the literature evaluated for acetaminophen is 2794 mg g−1 and for diclofenac 1801 mg g−1. Not all studies report thermodynamic data, however the values found for the change in Gibbs adsorption energy are similar for both analgesics, and is around −25 KJ mol−1.

More and more liters of water are demanded to supply the needs of the world’s population. However, many of the human activities generate water pollution. Some of the emerging pollutants, as pharmaceuticals, are hazardous for the environmental and human health. The adsorption on activated carbon is used as tertiary treatment in wastewater plants, in this step the emerging pollutants are removed when the molecules are resistant to other techniques. The immersion calorimetry is a technique used to determine the energy exchange during the formation of pollutant-activated carbon interactions, there are the most important interaction on the adsorption because the amount of pollutant adsorbed depends to the affinity with the adsorbent surface. In this work we using the immersion calorimetry to determine the affinity between the activated carbon and a pharmaceutical compound (pollutant) and its correlation with the adsorbate uptake. The tests were carried out on three activated carbons with different content of oxygenated groups and aqueous solutions of paracetamol and methylparaben. A deep thermodynamic study of the adsorbate-adsorbent interactions was carried out by calculation of two enthalpies: The immersion and interaction enthalpy. The first determines the energy associated with the formation of solvent-adsorbent and adsorbate-adsorbent interaction while the second, only evaluates the energy exchanges during adsorbate-adsorbent interaction. The values obtained for immersion enthalpy are between −38.9 and −69.5 J g−1 at solutions 6.62 mmol L−1. The interaction enthalpy has values in the range of −19.2 and 48.8 J g−1. The endothermic enthalpies are associated with a highest affinity solvent-activated carbon.

It is evident that high consumption of several kind of products around the world increases the presence of pollutants in different water sources. For example, caffeine is an alkaloid widely used in foods, beverages, and commercial analgesic medicines as a central nervous system stimulant. Caffeine is an anthropogenic pollutant, and it is part of emergent contaminants. In addition, nickel (II) has been found in industrial effluents such as mining, oil refining, mineral processing, electroplating, silver refining, paint formulation, battery manufacturing, and steam electric power plants. This metal is toxic and it bio-accumulates, thus it has been classified as a priority pollutant. Thus, it is necessary to use innovative techniques to remove pollutants of water. In this sense, adsorption is an option to deal with this problem; therefore, carbonaceous materials could be a good alternative. Moreover, magnetic carbon composites obtained from carbonaceous materials have been widely studied for environmental applications, as it makes easy the process of separation from aqueous solutions.

Mercury and its compounds are toxic substances, whose uncontrolled presence in the environment represents a danger to ecosystems and the organisms that inhabit in it. For this reason, in this work, we carried out a study of mercury [Hg(II)] adsorption from aqueous solution on functionalized activated carbon. The activated carbons were prepared by chemical activation of a mango seed with solutions of CaCl2 and H2SO4 at different concentrations, later, the carbonaceous materials were functionalized with Na2S, with the aim of increasing the sulfur content in the carbonaceous matrix and its affinity to mercury. The materials were characterized using: proximal analysis, scanning electron microscopy, Boehm titrations, point zero charge (pHPZC), and infrared spectroscopy. Additionally, immersion calorimetries were performed in the mercury solution. The results of textural and chemical characterization show materials with low Brunauer-Emmett-Teller (BET) surface areas between 2 and 33 m2·g-1 and low pore volumes. However, they had a rich surface chemistry of oxygenated groups. The enthalpies of immersion in the mercury solutions are between -31.71 and -77.31 J·g-1, showing a correlation between the magnitude of the enthalpic data and the adsorption capacity of the materials. It was evidenced that the functionalization process produces a decrease in the surface area and pore volume of the activated carbons, and an increase in the sulfur content of the carbonaceous matrix. It was evidenced that the functionalization process generated an increase in the mercury [Hg(II)] adsorption capacity between 21 and 49% compared to those of the nonfunctionalized materials, reaching a maximum adsorption capacity of 85.6 mgHg2+g-1.

The increase in CO2 concentrations in the atmosphere in recent years, has evidenced the need to find technological alternatives to remove this pollutant from the environment. In this sense, adsorption has been positioned as a promising option for CO2 removal, using porous materials such as activated carbon. In order to contribute to the production of adsorbent solids for the capture of CO2, in this work an activated carbon was prepared using as a lignocellulosic precursor African palm stone (Elaeis guineensis) by chemical activation with CaCl2 and H3PO4. Additionally the material obtained was subjected to a chemical modification with HNO3 and NH4OH, in order to study the influence that these treatments have on the CO2 adsorption capacity of the prepared porous material. The carbonaceous materials were characterized by physical adsorption of N2 at 77K, CO2 at 273K, proximate analysis, Boehm titrations and immersion calorimetry in water and benzene. Activated carbons have a BET area between 634 m2g-1 and 865 m2g-1, with a micropore volume between 0.25 cm3g-1 and 0.34 cm3g-1. The experimental results indicated that the modification of activated carbon with HNO3 and NH4OH generates a decrease in the surface area and pore volume of the material, as well as an increase in surface groups that favor the adsorption of CO2, which was evidenced by an increase in the adsorption capacity of this gas.

Activated carbons with different chemical and textural properties were used to carry out the adsorption of toluene and hexane from gas phase and from liquid phase for toluene-hexane solutions where toluene was used as a solute and hexane as the solvent, complementing the process with the evaluation of the immersion enthalpy for the pure components and toluene-hexane mixtures at different molar fractions. The adsorption capacities for the gas phase were between 3.40 mmol g-1 and 0.05 mmol g-1, being higher for toluene because of the π-π interaction with the solid; when evaluating the liquid phase, the adsorption capacities were 0.24 and 0.74 mmol g-1, where the adsorption of toluene decreased compared to the gas phase because of the solute-solute, solvent-solvent, solute-solvent interaction. The immersion enthalpies for the pure solvents were between -40.87 J g-1 and -126.10 J g-1 being higher also for toluene confirming a greater interaction compared to hexane; for the mixtures, immersion enthalpy was higher than hexane enthalpies, but lower than toluene enthalpies with values between -59.79 J g-1 and -107.95 J g-1. It was found that there was a greater interaction between the sample with a lower content of acid groups and a greater surface area with toluene due to the high electron density of carbon and London-type as π- π interactions with the aromatic compound. For mixtures, hexane decreased the adsorption capacity and interaction with respect to toluene because there was competition for adsorption sites and subsequent displacement of hexane molecules when the amount of toluene on the surface increased.

The aim of this study was to evaluate and compare the adsorption and photocatalytic activity of activated carbon-based photocatalysts. Titanium dioxide (TiO2) and zinc oxide (ZnO) were chosen as semiconductors to prepare composites with activated carbon by the wet impregnation method. Activated carbon was prepared using as starting material onion leaves (Allium fistulosum) and as activating agent phosphoric acid (H3PO4). Photooxidation and batch adsorption of phenol was studied to compare the efficiency of the materials prepared. The results showed that the composite AC–TiO2 has a greater photocatalytic activity and a better adsorption capacity compared to AC–ZnO composite.

In the adsorption literature, the Van't Hoff equation is used in different manners without any criteria about the concepts of physical-chemistry of equilibrium for calculation of thermodynamic parameters of adsorption. Indeed, the equilibrium constant (K) should be dimensionless for being used in the Van't Hoff equation. However, this is not a simple adjustment of units, as being spread in the literature, to become K dimensionless. In this paper, it will be calculated the equilibrium constants using numeric examples and show the flaws of the thermodynamics calculations, when the value of K is wrongly calculated, and what are the expected results of the changes in enthalpy (ΔH°) and changes in the entropy (ΔS°) that are spread in the literature.

Amino functionalized solids were obtained by anchoring ethoxysilane and ethylenediaminetetraacetic groups onto the surface of a mesostructured silica SBA-15. The materials were characterized by nitrogen adsorptiondesorption, Fourier transform infrared spectroscopy (FTIR), and potentiometric titration. The samples SBA-15, SBA-15 -NH2 and SBA-15-EDTA were tested in the simple and competitive adsorption of Co (II) and Ni (II) ions from aqueous solutions. The equilibrium data were analyzed using the Langmuir isotherm by nonlinear regression analysis. The influence of textural and chemical characteristics of the three different silicas on Co (II) and Ni (II) removal was also studied. A complementary study based on density functional theory was performed. Adsorption isotherms of Ni and Co fitted well with Langmuir model, exhibiting high adsorption capacity of 47.7 and 27.4 mg of metal/g of SBA-15, 62.9 and 59.7 mg of metal/g of SBA-15-NH2 and 74 and 67.7 mg of metal/g of SBA-15-EDTA, respectively, in simple adsorption tests. In the case of adsorption from binary solutions, both cations compete for the same active sites, a preferential Ni adsorption being shown. A detailed data analysis demonstrated that EDTA functionalization allows the best retention efficiency of both heavy metals from their corresponding aqueous solution. Fil: Rodríguez Estupiñán, Paola. Universidad de los Andes; Colombia Fil: Legnoverde, María Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina Fil: Simonetti, Sandra Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Díaz Compañy, Andres Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Giraldo, Liliana. Universidad Nacional de Colombia; Colombia Fil: Moreno Piraján, Juan Carlos. Universidad de los Andes; Colombia Fil: Basaldella, Elena Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina

The presence of phenol in water bodies exists due to the discharge of wastewater from industrial, agricultural and domestic activities. Its presence in water is associated with a decrease in the quality of drinking water because its change the taste and odour [1]. The adsorption process is one of the most used treatments to remove the phenol of waters and the activated carbon is an appropriate adsorbent due to its high surface area, porosity and low cost.The studies about the adsorption process are addressed by different views of point such as equilibrium and thermodynamic data. In this work, the adsorption isotherms of phenol on five activated carbons with different physicochemical properties in aqueous solution are presented. In addition, the immersion enthalpies, the interaction enthalpies, the Gibbs energy and the entropy changes are included.The isotherms data are adjusted to the Freundlich and Sips models. The immersion enthalpy values are between −7.670 and −57.0 J g−1, the interaction enthalpies are between 48.00 and −11.70 J g−1, the Gibbs energy change are between −5337 and −12322 J mol−1 K−1 and finally, the entropy change values are between 18.10 and 39.70 J K−1. Keywords: Adsorption, Entropy, Gibbs energy, Immersion enthalpy, Interaction enthalpy, Phenol

Caffeine and diclofenac are molecules with high human intake, and both belong to the &lsquo, emergent&rsquo, class of contaminants. These compounds have been found at different concentrations in many sources of water worldwide and have several negative impacts on aquatic life systems, that is why the search for new alternatives for their removal from aqueous media is of transcendental importance. In this sense, adsorption processes are an option to attack this problem and for this reason, biochar could be a good alternative. In this regard, were prepared six different biochar from fique bagasse (FB), a useless agroindustry by-product from fique processing. The six biochar preparations were characterized through several physicochemical procedures, while for the adsorption processes, pH, adsorption time and concentration of caffeine and diclofenac were evaluated. Results showed that the biochar obtained by pyrolysis at 850 &deg, C and residence time of 3 h, labeled as FB850-3, was the material with the highest adsorbent capacity with values of 40.2 mg g&minus, 1 and 5.40 mg g&minus, 1 for caffeine and diclofenac, respectively. It was also shown that the experimental data from FB850-3 fitted very well the Redlich&ndash, Peterson isotherm model and followed a pseudo-first and pseudo-second-order kinetic for caffeine and diclofenac, respectively.

This work proposes a new methodology to determine the adsorption mechanism for salicylic acid and paracetamol on activated carbon based on the physicochemical characteristics of adsorbent and adsorbates. The methodology is divided into two parts: the determination of adsorption kinetics (order and mechanism) and the study of the chemical interactions (adsorbate-adsorbent and solvent-adsorbent) using calorimetry tests. Then, the results obtained in both techniques were correlated with the amount of drug adsorbed. The adsorption kinetics of salicylic acid and paracetamol on activated carbons with different oxygen contents could be described with widely kinetic models such as intraparticle, pseudo-first-order, pseudo-second-order, Avrami, and Elovich models; different information about the adsorption mechanism are offered by each of them. The results indicated that the pseudo-first-order rate constant decreases with the molecular size of analgesics and the carboxylic acid groups on the adsorbent surface; the rate constant values are between 0.12 and 2.31 h−1. The adsorbed amount of analgesics and the adsorption rate are greatest on activated carbons with basic characteristics (QRAC 0.45 > 0.24 > 0.21 mmol g−1 for phenol, salicylic acid, and paracetamol, respectively). The enthalpy changes follow the same trend in all activated carbons; for RAC, the results were ΔHimmPHEN = − 33.4 J g−1, ΔHimmSA = − 35.9 J g−1, and ΔHimmPAR = − 45.4 J g−1. The analgesic diffusion rate in the boundary layer increases with the formation of adsorbate-adsorbent interactions (exothermic process).

Se analizaron los cambios entálpicos y entrópicos derivados del proceso de adsorción de acetaminofén sobre carbones activados con química superficial modificada. Se realizó, además, una variación del pH para determinar los cambios en las propiedades termodinámicas cuando existen cargas en el adsorbato y en el adsorbente. Se encontró que la máxima capacidad de adsorción (1,172 mmoles g -1) corresponde al proceso llevado a cabo en el carbón activado denominado CAR en este estudio a pH 7; los valores de las funciones termodinámicas de entalpía de inmersión y entropía de adsorción fueron -36,02 J g-1 y 0,123 J g-1 K-1, respectivamente. Así, el cambio de entropía de adsorción para el acetaminofén en los carbones activados estudiados dependió del pH. Se encontró que esta función termodinámica varía en el siguiente orden pH 2 pH 11 pH 7. Este comportamiento se relaciona con el número de especies presentes en la solución capaces de interactuar con la superficie del carbón activado. The enthalpic and entropic changes resulting from the process of acetaminophen adsorption on activated carbons with modified surface chemistry were studied. A pH variation was performed to determine the changes in the thermodynamic properties when there are charges in the adsorbate and adsorbent. It was found that the maximum adsorption capacity (1.172 mmoles g -1)corresponds to the process carried out in the activated charcoal labeled as CAR in this study at pH 7; the values of the thermodynamic functions immersion enthalpy and entropy of adsorption were -36.02 J g -1 and 0.123 J g -1 K-1, respectively. Thus, the adsorption entropy change for the acetaminophen on the activated carbons depended on the pH. It was found that this thermodynamic function varies in the following order pH 2 pH 11 pH 7. This behavior is related to the number of species present in the solution capable of interact with the activated carbon surface. Foram analisadas as mudanças entrópicas e entalpicas resultantes do processo de adsorção de acetaminofeno sobre carvões activados com superfície química modificada. Além disso, foi realizada uma variação do pH para determinar as alterações nas propriedades termodinâmicas quando existem cargas no adsorbato e no adsorvente. Foi encontrado que a máxima capacidade de adsorção (1.172 mmol g -1) corresponde ao processo realizado no carvão ativado chamado CAR neste estudo em pH 7; os valores das funções termodinâmicas de entalpia de imersão e entropia de adsorção foram -36,02 J g -1 e 0,123 J g -1 K-1 respectivamente. As mudança da entropia de adsorção para o acetaminofeno nos carvões activados dependeu do pH. Foi encontrado que esta função termodinâmica varia na seguinte ordem pH 2 pH 11 pH 7. Este comportamento está relacionado ao número de espécies presentes na solução capaz de interagir com a superfície de carvão activado.

The chemical surface of Santa Barbara Amorphous-15 (SBA-15) was functionalized with polyaniline (SBA-15/PA) and was prepared using aniline and ammonium persulfate as the modifying agent and oxidant. The samples were characterized by N2 physical adsorption at 77 K. SBA-15’s surface area was 654.5 m2 g−1, changing to 254.6 m2 g−1. The total acidity and basicity were determined using a modified Boehm’s method, and the point of zero charge pH (pHpzc) was determined. Immersion calorimetry in water, benzene, and NaOH, HCl, and phenol (100 mg L−1) solutions was performed, producing values ranging from −15.1 to −174.1 J g−1 related to the chemical surface, pHpzc, and acid and base group values. Finally, the phenol adsorption capacity was found to be higher for the modified polyaniline silica, at 138 mg g−1.