Zr-UiO-66, ionic liquid (HMIM+TFSI−), and electrospun nanofibers (polyacrylonitrile): All in one as a piezo-photocatalyst for degradation of organic dye

The synergistic effect provided by combining piezocatalysis and photocatalysis can assure the future of water cleaning. The Zr-UiO-66 (ZrU) piezo-photocatalyst was first synthesized through the solvothermal process and then followed by the incorporation with the liquid-based piezocatalyst of HMIM+TFSI− at three different concentrations to provide ZrU@ILs, which were subsequently incorporated into the piezocatalytic matrix of polyacrylonitrile (PAN). The solution of ZrU@IL/PAN was then subjected to electrospinning to fabricate the ZrU@IL/PAN nanofibers (NFs). Among the three dye models, Rhodamine B (RhB) was more degraded and the order of ZrU@IL/PAN NFs > ZrU/PAN NFs > ZrU@IL > IL/PAN NFs > pure PAN NFs > ZrU > HMIM+TFSI− was observed for its degradation in exposure to both ultrasonic (US) vibration and light radiation, approving the boosted influence of the three catalytic components of ZrU, HMIM+TFSI−, and PAN NFs in the degradation of RhB and more effectiveness of the fibrous form of catalysts compared to their corresponding catalytic powders. A synergistic effect was detected in the piezo-photodegradation efficiencies of RhB (2.2 %-95.4 %) compared to the individual photodegradation (0.0 %-21.3 %) and individual piezodegradation efficiencies (2.3 %-84.2 %). The ZrU@IL-1/PAN NFs as the optimal piezo-photocatalyst displayed high recycling after four cycles of usage, RhB mineralization percentage of 67 % within 40 min, and a pseudo-first-order kinetic rate constant being 1.67 and 12.8 times higher than that of individual piezocatalysis and individual photocatalysis. Tauc plots and Mott-Schottky measurements in agreement with the radical trapping experiments suggested the main role of O2•- and HO• species in the RhB degradation mechanism. LC-MS-MS was applied to clarify the intermediates generated during the RhB piezo-photodegradation process.