Mineralization of salicylic acid via catalytic ozonation with Fe-Cu@SiO2 core-shell catalyst: A two-stage first order reaction

Mesoporous Fe-Cu@SiO 2 core-shell catalyst was synthesized and assessed for its catalytic activity in the ozonation of salicylic acid (SA). The synthesized catalyst was characterized by XRD, TEM, SEM, XPS, H 2 -TPR, etc. Fe-Cu@SiO 2 exhibited a regular spherical shape and had the surface area at 1216 m 2  g −1 . The wrapping of metal components and their strong interaction prevented metal leaching. Fe-Cu@SiO 2 showed the highest activity for SA mineralization when compared with Fe@SiO 2 and Cu@SiO 2 . In Fe-Cu@SiO 2 /O 3 , 88% TOC was removed, which was 2.5 times as much as that in sole ozonation. SA degradation efficiency in Fe-Cu@SiO 2 /O 3 increased with initial pH. O 3 , ·OH and H 2 O 2 were the main reactive oxygen species accounting for SA mineralization. Due to their scavenging effect of ·OH, NH 4 + , NO 3 − and humic acids would inhibit the degradation efficiency of Fe-Cu@SiO 2 /O 3 . Acidic sites, oxygen vacancies and the Fe-Cu(I/II) electron transfer were responsible for ozone decomposition and ·OH generation. SA mineralization proceeded through the ·OH mechanism. Moreover, SA mineralization in O 3 and Fe-Cu@SiO 2 /O 3 both exhibited a two-stage pseudo first-order kinetics (stage I: 0–45 min; stage II: 45–120 min). The degradation intermediates were detected to investigate the reaction pathway. ORP and EEM were used to monitor the degradation process. Great difference was found for carboxylic acids accumulation in O 3 and Fe-Cu@SiO 2 /O 3 . The accelerated removal of oxalic acid and humic acid-like intermediates were responsible for the two-stage pseudo first-order kinetics.