Abstract
Polycyclic aromatic hydrocarbon (PAHs) is classified as persistent hazardous organic priority
pollutants produced by anthropogenic as well as natural activities. The present study
investigates the kinetics, isotherm, and thermodynamic behavior of five PAHs (fluorene,
phenanthrene, anthracene, fluoranthene and benzo[k]fluoranthene) for their adsorption onto
a Nigerian bentonite clay modified with hexadecylpyridinium bromide. Kinetic models of
pseudo-first order (Lagergren) and pseudo-second order (Ho–McKay) were evaluated for the
kinetic studies and intra-particle diffusion (Weber and Morris) model was applied for the
adsorption mechanism. The results suggest the better applicability of pseudo-second order
model (> 0.99) and the mechanism of the adsorption was found to be intra-particle diffusion
with occurrence of some other mass transfer mechanisms. Among the isotherms, Langmuir,
Freundlich and Temkin models were used for the equilibrium studies, Langmuir isotherm
models exhibited the best fit (> 0.80). The calculated values of RL and n were between 0-1 and
n > 1 respectively, indicating the favorability of the adsorption process. The thermodynamic
parameters: Gibb’s free energy change, ΔG was found to be negative, indicating that the
adsorption process was spontaneous and feasible. The positive values of the enthalpy ΔH and
entropy ΔS changes indicate the endothermic nature of the adsorption process and increase in
the degree of randomness at the solid–liquid interface as well as good affinity of PAHs towards
the adsorbents.