Ti(IV)-exchanged nano-ZIF-8 and nano-ZIF-67 for Enhanced Photocatalytic Oxidation of Hydroquinone

Abstract The metal centres of nano-ZIF-8(Zn) and nano-ZIF-67(Co) were partially exchanged with titanium centres to form bimetallic nZIF-8(Zn/Ti) (52% Ti4+) and nZIF-67(Co/Ti) (38% Ti4+) respectively, for enhanced photocatalytic performance. A morphological and structural analysis by SEM, EDS-Mapping and PXRD showed that the particle size, distribution, and the structural integrity of the Sodalite frameworks of the parent ZIFs were retained during the exchange process to form the new bimetallic Ti-ZIFs. FTIR confirmed that no additional chemical bonds were formed during the process. XPS binding energies confirmed the preservation of the Zn(II), Co(II) and Ti(IV) oxidation states, as well as the Ti-content, consistent with ICP-OES and EDS measurements. The Ti-exchanged ZIFs showed higher activity during the photocatalytic oxidation of hydroquinone in comparison with their parent ZIFs. Their kinetic rates were nearly five times faster than those of the parent ZIFs, with the first-order rate constants k = 0.189 min-1 for nZIF-8(Zn/Ti) and k = 0.139 min-1 for nZIF-67(Co/Ti). These catalysts are efficient, stable, and reusable for three photocatalytic cycles without a significant loss of catalytic activity.