One of the most promising techniques of recent research is adsorption. This technique attracts great attention in environmental technology, especially in the decontamination of water and wastewaters. A “hidden” point of the above is the cost of adsorbents. As can be easily observed in the literature, there is not any mention about the synthesis cost of adsorbents. What are the basic criteria with which an industry can select an adsorbent? What is the synthesis (recipe) cost? What is the energy demand to synthesize an efficient material? All of these are questions which have not been answered, until now. The reason for this is that the estimation of adsorbents’ cost is relatively difficult, because too many cost factors are involved (labor cost, raw materials cost, energy cost, tax cost, etc.). In this work, the first estimation cost of adsorbents is presented, taking into consideration all of the major factors which influence the final value. To be more comparable, the adsorbents used are from a list of polymeric materials which are already synthesized and tested in our laboratory. All of them are polymeric materials with chitosan as a substrate, which is efficiently used for the removal of heavy metal ions.

Chitin is mentioned as the second most abundant and important natural biopolymer in worldwide scale. The main sources for the extraction and exploitation of this natural polysaccharide polymer are crabs and shrimps. Chitosan (poly-β-(1 → 4)-2-amino-2-deoxy-d-glucose) is the most important derivative of chitin and can be used in a wide variety of applications including cosmetics, pharmaceutical and biomedical applications, food, etc., giving this substance high value-added applications. Moreover, chitosan has applications in adsorption because it contains amino and hydroxyl groups in its molecules, and can thus contribute to many possible adsorption interactions between chitosan and pollutants (pharmaceuticals/drugs, metals, phenols, pesticides, etc.). However, it must be noted that one of the most important techniques of decontamination is considered to be adsorption because it is simple, low-cost, and fast. This review emphasizes on recently published research papers (2013–2021) and briefly describes the chemical modifications of chitosan (grafting, cross-linking, etc.), for the adsorption of a variety of emerging contaminants from aqueous solutions, and characterization results. Finally, tables are depicted from selected chitosan synthetic routes and the pH effects are discussed, along with the best-fitting isotherm and kinetic models.

The compound of chitin is the second most important and abundant natural biopolymer in the world. The main extraction and exploitation sources of this natural polysaccharide polymer are mainly crustaceans species, such as shrimps and crabs. Chitosan (CS) (poly-β-(1 → 4)-2-amino-2-deoxy-d-glucose) can be derived from chitin and can be mentioned as a compound that has high value-added applications due to its wide variety of uses, including pharmaceutical, biomedical, and cosmetics applications, food etc. Furthermore, chitosan is a biopolymer that can be used for adsorption applications because it contains amino and hydroxyl groups in its chemical structure (molecules), resulting in possible interactions of adsorption between chitosan and pollutants (uranium, mercury, rare earth elements (REEs), phenols, etc.). However, adsorption is a very effective, fast, simple, and low-cost process. This review article places emphasis on recent demonstrated research papers (2014–2020) where the chemical modifications of CS are explained briefly (grafting, cross-linking etc.) for the uptake of uranium, mercury, and REEs in synthesized aqueous solutions. Finally, figures and tables from selected synthetic routes of CS are presented and the effects of pH and the best mathematical fitting of isotherm and kinetic equations are discussed. In addition, the adsorption mechanisms are discussed.

In this experimental study, the use of 5-hydroxymethyl-furfural (HMF) organic compound as a grafting agent to chitosan natural polymer (CS) was examined. One optimized chitosan derivative was synthesized, and then tested (CS-HMF), in order to uptake nickel, mercury, and barium metal ions from single- and triple-component (multi-component) aqueous solutions. The characterization of the material before and after the metal uptake was achieved by scanning electron microscopy (SEM). The ability of the adsorption of CS-HMF was tested at pH = 6. The adjusting of temperature from 25 to 65 °C caused the increase in the adsorption capacity. The equilibrium data were fitted to the models of Langmuir and Freundlich, while the data from kinetic experiments were fitted to pseudo-1st and pseudo-2nd order models. The best fitting was achieved for the Langmuir model (higher R²). The adsorption capacity for nickel, mercury, and barium removal at 25 °C (single component) was 147, 107, and 64 (mg/g), respectively. However, the total adsorption capacity for the multi-component was 204 mg/g. A thermodynamic study was also done, and the values of ΔG⁰, ΔH⁰, and ΔS⁰ were evaluated.

The aim of the present study is the synthesis of activated carbon (AC) from different agricultural wastes such as tea and plane tree leaves in order to use them for the removal of pramipexole dihydrochloride (PRM) from aqueous solutions. Two different carbonization and synthetic activation protocols were followed, with the herein-proposed ultrasound-assisted two-step protocol leading to better-performing carbon, especially for the tea-leaf-derived material (TEA(char)-AC). Physicochemical characterizations were performed by Fourier-transform infrared spectroscopy (FTIR), N₂ physisorption, and scanning electron microscopy (SEM). TEA(char)-AC presented the highest surface area (1151 m²/g) and volume of micro and small mesopores. Maximum capacity was found at 112 mg/g for TEA(char)-AC at an optimum pH equal to 3, with the Langmuir isotherm model presenting a better fitting. The removal efficiency of TEA(char)-AC is higher than other biomass-derived carbons and closer to benchmark commercial carbons.

The aim of the present study was to synthesize various samples of activated carbon (AC) from different agricultural sources as precursors, like orange peels, tea stalks, and kiwi peels, as well as sucrose. The synthesis of AC was achieved with chemical activation using H₃PO₄ and KOH. The produced AC samples were tested as adsorbents for the removal of a pharmaceutical model compound, pramipexole dihydrochloride (PRM), from synthetic aqueous synthetic solutions. The produced-from-sucrose AC presented the higher yield of synthesis (~58%). The physicochemical features of the materials were analyzed by FTIR spectroscopy, N₂ physisorption, and SEM imaging. More specifically, the AC sample derived from sucrose (SG-AC) had the highest specific surface area (1977 m²/g) with the total pores volume, mesopores volume, and external surface area being 1.382 cm³/g, 0.819 cm³/g, and 751 m²/g, respectively. The effect of the initial pH and PRM concentration were studied, while the equilibrium results (isotherms) were fitted to Langmuir and Freundlich models. The maximum adsorption capacities were found to be 213, 190, 155, and 115 mg/g for AC samples produced from sucrose, kiwi peels, orange peels, and tea stalks, respectively.