Performance and mechanism of sulfite mediated oxidation of organic contaminants using iron(III) titanium oxide as catalyst

As sulfite has been employed currently in the catalytic degradation of various pollutants, the construction of more suitable and cheaper catalytic systems is required. Herein, a heterogeneous system for S(IV) activation by iron(III) titanium oxide (Fe2TiO5) was proposed to proceed the removal of acid orange 7 (AO7) and seven typical pharmaceutical and personal care products (PPCPs). Typically, the AO7 (10 mg L-1) can be degraded up to 67% within 60 min ([Fe2TiO5] = 0.8 g L-1, [S(IV)] = 2.0 mM, pH = 6.0). The effects of initial AO7 concentration, pH, Fe2TiO5 dosage, S(IV) concentration, and co-existing anions (HCO3- and H2PO4-) were examined to explore the application conditions and resistance of Fe2TiO5-S(IV) system. Moreover, the stability of Fe2TiO5-S(IV) system was tested by sequential runs, while XRD was also performed for the robustness evaluation of catalyst. The scavenging experiment showed that the active species in the system mainly include SO5 center dot-, HO center dot, and SO4 center dot-, while SO4 center dot-being the dominant one. Through the competitive experiments of EDTA, the density functional theory (DFT) computation and the XPS analysis, a sensible mechanism was proposed that the electron transfer within Fe (III)- SO32-complex and the Fe(III)-Fe(II)-Fe(III) redox process were crucial for the sulfite activation. Mean-while, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants (kobs) was established with a high significance (R2 = 0.991, p = 0.006) by using four descriptors. This work provides an innovative strategy of sulfate radical-based advanced oxidation processes (SR-AOPs) for organic contaminants degradation using metal oxide catalysts.