Sorption and photodegradation of tylosin and sulfamethazine by humic acid-coated goethite

Humic acid and mineral oxides are simultaneously present in soils and can form organomineral complexes. These complexes could influence the transport and fate of antibiotics in the environment. The objective of this study was to investigate the sorption and photodegradation of TYL and SMT on these complexes. The results showed that HA tended to interact with goethite via hydrophobic and pi-pi interactions. The sorption capacity and sorption rate gradually increased with the increasing concentrations of HA and the equilibrium time for TYL and SMT was 7 h and 24 h, respectively, on HA-goethite complexes. The sorption isotherms of TYL were more nonlinear and SMT were less nonlinear on HA-goethite complexes with the increasing concentrations of HA, which implies a more heterogeneous distribution of the sorption sites for TYL and more rigid and porous structures developed for SMT. The photodegradation of TYL and SMT by HA-goethite complexes increased with increasing the concentration of HA. An iron redox cycle couple should be a common phenomenon in the system, since both Fe(III) and HA are ubiquitous in the natural environment. The influence of HA and goethite on the fate of antibiotics in the environment is worth noting. This study is helpful in understanding the potential of toxic organic pollutants migration and transformation in the natural environment.