Studies of biosorption of Pb2+, Cd2+ and Cu2+ from aqueous solutions using Adansonia digitata root powders

The potentials of Adansonia digitata root powders (ADRP) for adsorption of Pb²⁺, Cd²⁺ and Cu²⁺ from aqueous solutions was investigated. Physico-chemical analysis of the adsorbent (ADRP) shows that hydroxyl, carbonyl and amino groups were predominant on the surface of the adsorbent. Scanning Electron Microscope (SEM) image revealed its high porosity and irregular pores in the adsorbent while the Energy Dispersive X-ray Spectrum showed the major element with 53.0% Nitrogen, 23.8% carbon, 9.1% calcium, 7.5% potassium and 6.6% magnesium present. The found optimal conditions were: initial concentration of the metal ions = 0.5 mg/L, pH = 5, contact time = 90 min, adsorbent dose = 0.4 g and particle size = 32 µm. Freundlich isotherm showed good fit for the adsorption of Pb²⁺, Cd²⁺ and Cu²⁺. Dubinin-Radushkevich isotherm revealed that the adsorption processes were physisorption Cd(II) and Cu(II) but chemisorption with respect to Pb(II) ions. The kinetics and thermodynamic studies showed that Pseudo-second order and chemisorptions provided the best fit to the experimental data of Pb (II) ions only. Batch desorption result show that desorption in the acidic media for the metal ions were more rapid and over 90% of the metal ions were recovered from the biomass.     

Investigating water and framework dynamics in pillared MOFs

In this work we highlight the use of molecular simulation to study the behaviour of water inside isostructural Zn-DMOF structures. Among the Zn-DMOF structures, the parent DMOF, and the DMOF-DM and DMOF-TF variants are known to be less stable than the DMOF-A and DMOF-TM structures in the presence of water. We apply tools such as radial distribution functions, rotational auto-correlation functions and the visualisation of adsorbate density distributions to investigate the differences in water behaviour within these structures. We also study properties that are inherent to the frameworks themselves such as thermal expansion and ligand flexibility. Our results indicate that water is only able to get 0.5 Å closer to the metal hydrolysis site in the water unstable structures than in the more water stable structures. The results can be somewhat sensitive to the details of the modelling of the electrostatic potential energy surface and, for dynamical properties, modelling of framework flexibility.