Tourmaline synergized with persulfate for degradation of sulfadiazine: Influencing parameters and reaction mechanism

[Display omitted] •Tourmaline-PS system was developed for SDZ degradation at room temperature.•Tourmaline-PS could generate dominant OH and SO4− for degrading SDZ.•Spontaneous Fe(II)/Fe(III) conversion on TM was proved by Mössbauer spectra.•Mechanism and intermediates were proposed in Tourmaline-PS system.•Toxicity of SDZ and intermediate products was evaluated using Vibrio fischeri. Tourmaline (TM), a natural silicate mineral with spontaneous electric field was selected as an iron-source catalyst to activate ammonium persulfate (APS) for synergistic degradation of sulfadiazine (SDZ) at normal temperature. Firstly, TM was well characterized by combination of X-ray fluorescence spectrometer (XRF), Mössbauer spectroscopy, N2 adsorption–desorption isotherm, and scanning/transmission electron microscope (SEM/TEM). Then, TM-assisted APS system was utilized for SDZ degradation, and different parameters influencing the degradation efficiency were investigated. The optimized degradation efficiency of SDZ was 70.80% at pH = 3.0 in TM-APS system. After being reused for four times, TM-assisted APS system could still reach > 80% of the first degradation efficiency. The free radical scavenging and electron paramagnetic resonance experiments demonstrated that TM could assist APS to produce hydroxyl radicals and sulfate radicals for SDZ degradation. By combination of LC/MS spectra and Mössbauer spectroscopy, the degradation products, as well as the degradation mechanism, were proposed in heterogeneous TM-APS system. Finally, the acute toxicity of SDZ and the degradation products in TM-APS system was tentatively evaluated based on the luminescence inhibition of marine bacteria Vibrio fischeri. From this study, TM-assisted APS system shows higher degradation efficiency for SDZ at room temperature, and spontaneous cyclic conversion of Fe(II) and Fe(III) on TM surface ensures its good reusability, and accordingly, TM-APS system has good application potential for degradable removal of SDZ in water.