Size Effects of NiO Nanoparticles on the Competitive Adsorption of Quinolin-65 and Violanthrone-79: Implications for Oil Upgrading and Recovery

Using
Quinolin-65 (Q-65) and Violantrone (V-79) as model molecules
for polar heavy hydrocarbons and resins, the nanosize effects of NiO
nanoparticles on the competitive molecular adsorption on nanoparticles
were conducted using multiwavelength UV–visible derivative
spectrophotometry method. This is important for understanding the
role of nanoparticles in oil upgrading and recovery processes. Computer
simulations were also carried out to validate the experimental findings
and provide more insights on the interactions between the Q-65 and/or
V79 molecules and the NiO nanoparticle surface. Different-sized NiO
nanoparticles (5, 40, and >100 nm) were synthesized by controlled
thermal dehydroxylation of Ni­(OH)2. Nanoparticles were
characterized using XRD, BET, FTIR, and XPS. Macroscopic adsorption
isotherms of Q-65 and V-79 molecules over 5 and 40 nm NiO nanoparticles
were evaluated in toluene-based solutions as individual and binary
solutions. On a normalized surface area basis, the number of Q-65
and V-79 molecules adsorbed per nm2 of the NiO surface
was the highest for 40 nm NiO nanoparticles and lowest for 5 nm NiO.
Results also indicated that NiO nanoparticles were more prone to adsorb
V-79 than Q-65. Equilibrium binding constants for V-79 and Q-65, determined
by the Langmuir adsorption model, showed the binding affinity for
V-79 is size dependent. Simultaneous competitive adsorption between
V-79 and Q-65 showed that V-79 concentration is an important factor
influencing the uptake of both V-79 and Q-65, whereas the concentration
of Q-65 affects only Q-65 uptake. Computational modeling results were
consistent with the experimental results, confirming our conclusions
about the adsorption process in this binary system.