Adsorption of p-nitroaniline by phenolic hydroxyl groups modified hyper-cross-linked polymeric adsorbent and XAD-4: A comparative study

Phenolic hydroxyl groups modified hyper-cross-linked polymeric adsorbent HJ-02 was prepared and it was applied to remove p-nitroaniline in aqueous solution as compared with Amberlite XAD-4. The results indicated that the adsorption at the solution pH of 3.7–7.8 was efficient for HJ-02 resin while that at the solution pH higher than 4.1 was favorable for XAD-4. The ionic strength affected the adsorption slightly and NaCl at a low concentration (<10%) had a positive effect. The adsorption kinetic curves obeyed the pseudo-second-order rate equation and HJ-02 resin had lower rate constant than XAD-4. The adsorption isotherms could be fitted by Langmuir isotherm and the adsorption capacity onto HJ-02 resin was much larger than that onto XAD-4. The adsorption enthalpy, adsorption free energy, and adsorption entropy onto HJ-02 resin were a little more negative than those onto XAD-4. Analysis of the adsorption mechanism suggested that the phenolic hydroxyl groups uploaded on HJ-02 resin and the predominant mesopores (2–5 nm) were the main reasons for its much larger adsorption capacity.