Magnetic poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) nanotubes modified with glacial acetic acid for removing methylene blue: Adsorption performance and mechanism

Adsorption kinetic models: Physical meanings, applications, and solving methods

Adsorption technology has been widely applied in water and wastewater treatment, due to its low cost and high efficiency. The adsorption kinetic models have been used to evaluate the performance of the adsorbent and to investigate the adsorption mass transfer mechanisms. However, the physical meanings and the solving methods of the kinetic models have not been well established. The proper interpretation of the physical meanings and the standard solving methods for the adsorption kinetic models are very important for the applications of the kinetic models. This paper mainly focused on the physical meanings, applications, as well as the solving methods of 16 adsorption kinetic models. Firstly, the mathematical derivations, physical meanings and applications of the adsorption reaction models, the empirical models, the diffusion models, and the models for adsorption onto active sites were analyzed and discussed in detail. Secondly, the model validity evaluation equations were summarized based on literature. Thirdly, a convenient user interface (UI) for solving the kinetic models was developed based on Excel software and provided in supplementary information, which is helpful for readers to simulate the adsorption kinetic process.

Synthesis and cationic dye biosorption properties of a novel low-cost adsorbent: coconut waste modified with acrylic and polyacrylic acids

Coconut waste (CW), a novel, low cost adsorbent, has been utilized for the removal of methylene blue (MB) dye from an aqueous solution. CW was chemically modified with acrylic (AcA) and polyacrylic acids (PAcA) using different modification methods, such as esterification with AcA, chemically grafting of PAcA, and plasma-enhanced chemical vapor deposition (PECVD) coating with PAcA. CW-based adsorbents were used in the experiments to study MB adsorption probability, and their activities were compared. The adsorption behavior of MB onto the adsorbents was investigated with respect to parameters such as sorbent dosage (0.5-4 g/L), pH (2-10), initial dye concentration (50-250 mg/L), and temperature (22-65 °C). The time taken of AcA modified CW (CW-AcA), PAcA-grafted CW (CW-PAcA_grafted), and PAcA-coated CW (CW-PAcA_coated) for the removal of 94.6%, 97.7%, and 91.0% of MB from 50 mg/L of dye solution is 180 min. Characterization of CW-based adsorbents was achieved using SEM, XRD, BET, XPS, and FT-IR analysis. The adsorption fitted the Langmuir model, and the adsorption kinetics were consistent with a pseudosecond-order kinetics model. The results obtained from the maximum adsorption capacity (q_max) for AcA-, PAcA_coated-, and PAcA_grafted-CWs were 138.88, 136.98, and 98.03 mg/g at adsorbent dose of 0.1 g/50 mL for initial dye concentration of 200 mg/L, 22 ± 1 °C, and pH 10:10:8.

Fabrication of core@shell structural Fe-Fe2O3@PHCP nanochains with high saturation magnetization and abundant amino groups for hexavalent chromium adsorption and reduction

The rational design of novel adsorption materials is imperative to remove toxic metal species from the polluted water. Herein, a core@shell structural Fe-Fe₂O₃@poly (hexachlorocyclotriphosphazene-co-polyethylenimine) (Fe-Fe₂O₃@PHCP) magnetic nanochain with high saturation magnetization was fabricated and used for effective adsorption and reduction of hexavalent chromium. The morphology and microstructure of Fe-Fe₂O₃@PHCP were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effects of concentration, pH, contact time, temperature and coexisting ions on Cr (VI) removal were studied. Four kinetic models (pseudo-first-order, pseudo-second-order, Bangham and intraparticle diffusion models) and two isotherm models (Freundlich and Langmuir) were used to fit experimental data. Results show the adsorption capacity of Fe-Fe₂O₃@PHCP for Cr (VI) is up to 229.0 mg g^-1. The excellent performance was ascribed to the favorable reduction of Cr (VI) to Cr (III), followed by the chelation of Cr (III) with imino groups. Meanwhile, the residual Cr (VI) were adsorbed on protonated amino and imino groups. The adsorption process is exothermic and spontaneous and nicely follows pseudo-second-order kinetics, intraparticle diffusion model and Langmuir isotherm model. These results indicated that easily separable Fe-Fe₂O₃@PHCP magnetic nanochains could be a promising adsorbent to remediate chromate wastewater.