Amidoamine functionalized task specific carbon nanotube for efficient sorption of penta and hexavalent neptunium: Experimental and theoretical investigations

The present investigation demonstrated the efficient sorption of NpO2+ and NpO22+ on amidoamine functionalized multiwalled carbon nanotube via chemisorption following Langmuir isotherm. A pseudo second order kinetics were found to follow with the rate constant 5.13 x10(-4) and 3.85x10(-4)mg g(-1) min(-1) for NpO2+ and NpO22+, respectively. The radiolytic stability of the sorbent and the back extraction of the neptunium from the sorbent have been investigated. Computational study was also carried out to optimize the structure of the amidoamine functionalized carbon nanotube and its complex of NpO2+ and NpO22+. The amidoamine and all the nitrate anions are coordinated to the neptunyl centre in bidentate mode resulting to six-coordinated and octa-coordinated complex for NpO2+ and NpO22+, respectively. The theoretically calculated value of Delta G of NpO22+ sorption is found to be higher than that of NpO2+ which is in good congruence with the experimentally observed higher adsorption capacity for NpO22+ over NpO2+.