A review of common practices in gravimetric and volumetric adsorption kinetic experiments

The availability of commercial gravimetric and volumetric systems for the measurement of adsorption equilibrium has seen also a growth of the use of these instruments to measure adsorption kinetics. A review of publications from the past 20 years has been used to assess common practice in 180 cases. There are worrying trends observed, such as lack of information on the actual conditions used in the experiment and the fact that the analysis of the data is often based on models that do not apply to the experimental systems used. To provide guidance to users of these techniques this contribution is divided into two parts: a discussion of the appropriate models to describe diffusion in porous materials is presented for different gravimetric and volumetric systems, followed by a structured discussion of the main trends in common practice uncovered reviewing a large number of recent publications. We conclude with recommendations for best practice to avoid incorrect interpretation of these experiments.

Magnetic zeolite imidazole framework material-8 as an effective and recyclable adsorbent for removal of ceftazidime from aqueous solution

Zeolitic imidazolate framework-8 (ZIF-8) was synthesized by solvothermal method and the adsorption pore size was adjusted by changing the amount of template agent. The ZIF-8@SiO₂@Fe₃O₄ derived from self-assembly of ZIF-8 and SiO₂@Fe₃O₄ were then synthesized and used for ceftazidime (CAZ) removal. ZIF-8 was a regular dodecahedral particle with uniform particle size. The pore diameter was 6.47 nm and the specific surface area was 1182.5 m²·g^-1 in ZIF-8@SiO₂@Fe₃O₄. The adsorption of CAZ on ZIF-8@SiO₂@Fe₃O₄ as a function of adsorption temperature, contact time, ionic strength solution pH, and humic acid concentration were investigated. The error of equilibrium adsorption capacity between model fitting and actual experiments is only 1.19%. Kinetics for CAZ removal on ZIF-8@SiO₂@Fe₃O₄ was found to follow pseudo-second-order kinetics. Langmuir, Freundlich and Sips isotherm fitted the adsorption data well and gave similar correlation coefficients, suggesting a single layer adsorption of CAZ on ZIF-8@SiO₂@Fe₃O₄. The ZIF-8@SiO₂@Fe₃O₄ showed no apparent loss in CAZ adsorption after five cycles. These features indicate that the ZIF-8@SiO₂@Fe₃O₄ may be a promising adsorbent for CAZ removal from aqueous solution.

Magnetic ordered mesoporous carbon materials for adsorption of minocycline from aqueous solution: Preparation, characterization and adsorption mechanism

In this paper, the effect of cyanoguanidine (CNGE) for tailoring pore size during the soft-templating preparation of mesoporous carbon materials was studied. In consideration of cyclic utilization, the surface of the mesoporous carbon materials were doped with magnetic Fe₃O₄ particles. The characterization results (including TEM, XRD, BET, TGA and FT-IR) showed that adding CNGE did not destroy the ordered porous structure; instead, it changed the pore size from 2.98 nm to 9.42 nm. Besides, the mesoporous carbon materials exhibited a strong magnetic response owing to the dopant of Fe₃O₄ particles. With the increase in CNGE, some functional groups were added to the surface of the mesoporous carbon materials, which partly promoted the adsorption effect. The results indicated that adsorption approached equilibrium in the first 10 min and reached the maximum when the pore size was 5.89 nm. The kinetic of minocycline adsorption on magnetic ordered mesoporous carbon material could be interpreted by a pseudo-first-order model. The adsorption isotherms showed that the adsorption process was complex, combining physical and weak chemical adsorption, in good agreement with the Sips model.