Surface enriched nanofiber mats for efficient adsorption of Cr(VI) inspired by nature

Adsorption is a surface process. By evolution, nature has created design principles such as scaffolds that allow to carrying surface bound agents at high density. We used a nanofibrous pullulan/poly(vinyl alcohol)/poly(acrylic acid) (Pul/PVA/PAA) support to carry surface active PAMAM dendrimer similar to spores attached to mushroom gills. A monolayer of ceria (CeO2) nanoparticles served as the linker between PAMAM and the nanofiber. The nanocomposite was a highly effective Cr(VI) adsorbent and the maximum adsorption capacity q(max) = 847 mg g(-1) is the highest reported value for the same kind of materials so far. The materials was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FTIR), zeta potential and multipoint BET method to measure the specific surface area. Removal of Cr(VI) from aqueous media was tested under different batch and fixed bed column operation conditions such as pH, temperature and competing ions. Thermodynamic properties were determined based on a modified Langmuir adsorption isotherm and the adsorption kinetic was investigated. Positive entropy of adsorption and an endothermic adsorption process was found, while the rate-limiting step was pseudo second order which is associated with a chemisorption process. The nanocomposite was reusable and up to 95% of the adsorbed Cr(IV) ions were recovered by alkyne washing.