Adsorptive removal of p-nitroaniline from aqueous solution by bamboo charcoal: kinetics, isotherms, thermodynamics, and mechanisms

The characteristics of commercial bamboo charcoal and adsorptive removal of p-nitroaniline (PNA) from aqueous solution by this bamboo charcoal were studied intensively. The effects of adsorbent grain size and solution pH value on the adsorption were investigated by conducting a series of batch adsorption experiments. The results showed that bamboo charcoal with grain size of 80-100mesh was optimal for the adsorption, and the removal efficiency kept decreasing with the increase of solution pH value, the acidic solution environment was generally optimal for this adsorption. The adsorption amount decreased with increasing solution temperature, and the maximum adsorption amount of PNA (C-0=400mg/L) was found to be 176.92mg/L (278K), 170.10mg/L (298K), and 154.93mg/L (308K), respectively. The kinetic rates were modeled by using the pseudo-first and pseudo-second-order equations, and the pseudo-second-order equation could explain the adsorption kinetics most effectively. The equilibrium data were fitted with the Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich models, and the result showed it followed the Redlich-Peterson model very well, which suggested the co-existence of single-layer adsorption and heterogeneity of adsorption mechanisms. The thermodynamic data showed the adsorption was a spontaneous and exothermic process. The entropy of the adsorption was greater than zero, which suggested the net increase of system randomness.