RESUMO
Two hydrogels were synthesized, characterized, and applied as alternative materials to remove melamine (MEL) from aqueous media by adsorption. For the first time, a complete study of MEL adsorption is presented, including optimization, kinetics, isotherm, reuse, and column studies with these new materials. One hydrogel is based on xylan and poly (acrylic acid) and was named HXy, and the other is based on the same components functionalized with activated carbon and was named HXy-AC. The materials were synthesized by free radical polymerization and characterized by FTIR, XRD, TGA, DSC, SEM, zeta potential, point of zero charge, N2 adsorption isotherms (BET), helium gas pycnometry, Archimedes method, swelling analysis, and stability tests. The characterization results confirmed the intended synthesis and showed the thermal, morphological, textural, structural, and compositional profile, as well as the adsorption characteristics of the materials. The adsorption studies in batch process included experimental design, kinetics, isotherms, and recyclability, and in continuous mode, the studies included fixed-bed column experiments. The full factorial design showed that adsorbent dosage, pH, and ionic strength are significant for adsorption capacity and removal percentage responses. Doehlert design enabled the definition of the values of adsorbent dosage and pH that were most suitable for MEL adsorption into the materials, indicating the optimal adsorption conditions. The kinetics were well described by the pseudo-first-order model, with R2 above 0.9920 for both materials at all concentrations tested. The isotherm obeyed the Langmuir model, with R2 above 0.9939 for both materials at all temperatures tested. Equilibrium was attained at 180 min, and the maximum experimental adsorption capacity was up to 132.46 and 118.96 mg g-1 at pH 7, with adsorbent dosage of 0.5 g L-1, and 298 K for HXy and HXy-AC, respectively. Furthermore, HXy and HXy-AC materials maintained about 58 and 70% of their initial adsorption capacity at the end of five adsorption/desorption cycles, respectively. Breakthrough curves were described by the Yan model and presented a maximum adsorption capacity of 30.2 and 30.4 mg g-1, treating 3.4 and 6.1 L of influent until the breakthrough point of 0.5 mg L-1 with HXy-AC using 2.0 and 4.0 g of material, respectively. These findings show that the hydrogels produced present the potential to be applied in the adsorption of basic molecules, such as MEL.
Assuntos
Poluentes Químicos da Água , Xilanos , Adsorção , Projetos de Pesquisa , Hidrogéis/química , Cinética , Poluentes Químicos da Água/análise , Concentração de Íons de HidrogênioRESUMO
The lack of adequate treatment for the removal of pollutants from domestic, hospital and industrial effluents has caused great environmental concern. Therefore, there is a need to develop materials that have the capacity to treat these effluents. This work aims to develop and characterize an activated charcoal from olive pomace, which is an agro-industrial residue, for adsorption of Nimesulide in liquid effluent and to evaluate the adsorption kinetics and equilibrium using experimental design. The raw material was oven dried at 105 °C for 24 h, ground, chemically activated in a ratio of 1:0.8:0.2 of olive pomace, zinc chloride and calcium hydroxide and thermally activated by pyrolysis in a reactor of stainless steel at 550 °C for 30 min. The activated carbon was characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffractometry (XRD), Brunauer, Emmett and Teller (BET) method, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), density and zero charge potential analysis. The surface area obtained was 650.9 m2 g-1. The kinetic and isothermal mathematical models that best described the adsorption were PSO and Freundlich and the highest adsorption capacity obtained was 353.27 mg g-1. The results obtained showed the good performance of activated carbon produced from olive pomace as an adsorbent material and demonstrated great potential for removing emerging contaminants such as Nimesulide.