Magnetic hydrogel based on xylan, poly (acrylic acid), and maghemite as adsorbent material for methylene blue adsorption: experimental design, kinetic, and isotherm.

A magnetic hydrogel based on xylan (X), poly (acrylic acid), and maghemite (γ-Fe2O3) named HXA-Fe2O3 was synthesized, characterized, and applied as an alternative material to remove methylene blue (MB) from aqueous media by adsorption. Maghemite was synthesized by coprecipitation method and later incorporated in the hydrogel matrix synthesized by free radical polymerization. The characterization studies included FTIR, DSC, XRD, VSM, Zeta Potential, TGA, SEM, TEM, and N2 adsorption isotherms (BET). The physicochemical characterization results confirmed the intended synthesis and showed the compositional, thermal, structural, morphological, textural, and magnetic profile of the materials. The adsorption studies included experimental design, kinetic, and isotherm. A full factorial design was employed considering the factors adsorbent dosage (g L-1), pH, and ionic strength (mmol L-1 of NaCl) for adsorption capacity and removal percentage responses. As ionic strength was not significant, a Doehlert design was employed with adsorbent dosage and pH, indicating the optimal adsorption conditions. The kinetics was well described by the PSO model, while the isotherm obeyed the Sips model. Equilibrium was attained at 60 min, and the maximum experimental adsorption capacity was up to 250.26 mg g-1 at pH 8.5, adsorbent dosage of 0.2 g L-1, and 298 K. These findings show that the magnetic hydrogel produced has great potential to be applied in the adsorption of basic molecules, such as MB.

Development of hydrogels based on xylan and poly (acrylic acid) for melamine adsorption in batch and continuous mode: experimental design, kinetics, isotherms, recyclability, and fixed-bed column.

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.

Improvement of activated carbon characteristics by sonication and its application for pharmaceutical contaminant adsorption.

Sonicated activated carbon (SAC) was developed and used to remove ibuprofen and ketoprofen from aqueous media by adsorption. A standard activated carbon sample (AC) was used as comparison. Both adsorbents were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption isotherms (Brunauer, Emmett, and Teller (BET)), helium gas pycnometry, and scanning electron microscopy (SEM). In the adsorption study, kinetics, equilibrium, and thermodynamics were evaluated. SAC presented better characteristics than AC. Pseudo-second-order model was adequate to predict the kinetic curves. The isotherm data obeyed the Sips model. Thermodynamic results revealed a spontaneous and endothermic process, where physisorption was involved. The maximum adsorption capacities of SAC were 134.5 and 89.2 mg g-1 for ibuprofen and ketoprofen, respectively. For AC, the maximum adsorption capacities were 115.1 and 79.1 mg g-1 for ibuprofen and ketoprofen, respectively. The sonication technique presented great potential to improve the AC characteristics, generating a promising material (SAC) for ibuprofen and ketoprofen adsorption.