Interaction between chlorophenols in the adsorption process on corn straw biochar

Abstract

The treatment of effluents containing emerging contaminants, such as chlorophenols (CPs), by bio-char adsorption has been a hotspot topic. However, the interaction between CPs in the adsorption process on biochar is still unknown at present. In this paper, two kinds of biochar were prepared from corn straw under pyrolysis of 300°C and 600°C, labeled as BC300 and BC600, respectively, and were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The adsorption process and mechanism of biochar on CPs, including phenol (PHE), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP), were investigated using the batch equilibrium experimental method in a single component system (SCS) and multi-component system (MCS), respectively. The adsorption regularity of CPs on biochars in the MCS resembles that in the SCS. In the MCS, the pseudo-second-order kinetic model is fitted better for the adsorption process of CPs on biochar (R2 ≥ 0.938). The maximum adsorption capacity (qm) of PHE, 4-CP and 2,4-DCP is 28.16, 32.54 and 36.04 mg/g, respectively. The isotherm adsorption process is fitted more consistent with Langmuir–Freundlich model (R2 ≥ 0.913). The qm of PHE, 4-CP and 2,4-DCP in the MCS is 43.02, 60.85 and 96.48 mg/g, but the qm of PHE, 4-CP and 2,4-DCP in the SCS is 63.91, 121.03 and 145.09 mg/g, respectively. The pH value of solution is a key factor influencing the adsorption of CPs on the biochar. At pH < 9, the adsorption capacity (qe) of CPs on biochar almost remains con-stant as increase of pH values. By way of the contrast, at pH > 9, the qe of CPs decreases rapidly with increasing pH values. However, there is an interaction between CPs in the adsorption process on biochar in the MCS compared with that in the SCS, that is, one or two of three co-existing pollutants can inhibit the adsorption of each of CPs on biochar. Furthermore, the adsorption capacity of CPs on biochar increases with the number of chlorine atoms in CPs, that is, the more chlorine atoms in CPs, the easier it is to be adsorbed on biochar.