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Hydrogen adsorption on Ru-decorated (8,0) zigzag single-walled carbon nanotube (SWCNT) was studied using density functional theory (DFT). Several decoration sites on the CNT surface were investigated before atomic or molecular hydrogen adsorption. The most stable location for a single Ru atom is above the hollow site, with an adsorption energy of E ads (Ru) = −2.133 eV. Ru decoration increases hydrogen adsorption energy nearly 46% compared to pristine CNT. When a hydrogen molecule is considered on Ru/SWCNT its adsorption is dissociative with an E ads (H 2 ) = −0.697 eV. The Ru-decorated SWCNT systems exhibit magnetic properties. Density of states (DOS) and overlap population density of states (OPDOS) were computed in order to study the evolution of the chemical bonding. C−C bonds interact with Ru and are weakened after adsorption. Strong Ru−H bonds are formed during hydrogen adsorption process at expenses of C−Ru bonds. The mains interactions include the Ru 5p z and 4d z 2 and C 2p z bands.

The adsorption of fully protonated tetracycline (TC) using Na-montmorillonite (Na-MMT) as an adsorbent is studied by DFT calculations. Geometric, electronic and magnetic properties are analyzed. To the best of our knowledge, this is the first theoretical DFT research about Na-MMT as an adsorbent of TC cationic specie. Two Na-MMT models are considered: dry and hydrated Na-MMT. The incorporation of four water molecules in the interlayer space results in the expansion of the d 001 parameter from 10.13 Å (dry) to 12.85 Å (hydrated). Finally, when TC molecule is adsorbed in the basal space of MMT, the increment of the d 001 parameter is about 10 Å respect to hydrated model. Dry and hydrated Na-MMT present a non-magnetic (µ = 0 µ B ) and semiconductor behavior. Nevertheless, the TC-MMT system becomes conductor, and presents a very important magnetic moment (µ = 10.60 µ B ). After TC adsorption in MMT a potential valley with a slight depth in the MMT interlayer is generated. For this reason, it is proposed that TC adsorption would provide active sites for the adsorption of new species (like Na ions and water molecules).