Bimetal oxalate‐derived synthesis of laponite‐decorated CoFe₂O₄ porous nanostructures for activation of peroxymonopersulfate towards degradation of rhodamine B

Abstract

BACKGROUND: Advanced oxidation processes based on sulfate radical have been widely employed for oxidation degradation of organic contaminants. Catalytic activation of peroxymonopersulfate (PMS) with transition metal oxides holds great promise for the generation of sulfate radical. In this work, laponite-decorated CoFe 2 O 4 porous nanostructures have been prepared through the thermal decomposition of laponite/oxalates, and evaluated as a magnetic catalyst to activate PMS for the oxidation of rhodamine B (RhB).RESULTS: The decoration of porous CoFe 2 O 4 microparticles with laponite was evidenced because of the presence of the vibration mode of Si O (at 1359 cm −1 ) in Fourier transform infrared spectra and the uniform distribution of Si and Mg elements from elemental mapping images. Decorating with laponite also resulted in an increase in amount of surface hydroxyl oxygen species, which facilitated the formation of Co OH complex for PMS activation. Furthermore, the enhanced activation of PMS with laponite-decorated CoFe 2 O 4 resulted in a faster removal (98.04%) of RhB as compared to undecorated CoFe 2 O 4 (79.62%) within 56 min. Meanwhile, the rate constant increased from 0.0288 (CoFe 2 O 4 ) to 0.0679 min −1 (laponite-decorated CoFe 2 O 4 ). The degradation rate of RhB progressively increased with reaction temperature and catalyst dosage. Scavenging and electron paramagnetic resonance tests manifested that the sulfate and superoxide radicals served as the major active species for the oxidation of RhB molecules. CONCLUSION:The above results demonstrated positive effects of laponite on the textural property, surface chemical states and catalytic activity of porous CoFe 2 O 4 microparticles. This study provides an insight into the promising role of laponite as an additive in improving PMS activation.

Alginate@ZnCO2O4for efficient peroxymonosulfate activation towards effective rhodamine B degradation: optimization using response surface methodology

“…In the same context the low degradation rate obtained at pH = 3.2 (44.92% with k obs = 0.0141 min −1 ) can be explained by the nature of RhB molecules which may have existed mostly as RhB + , as RhB has a dissociation constant (p K a ) of 3.7, which resulted in electrostatic repulsion and hindered the adsorption of RhB onto the catalyst surface. 50,58…”

“…At pH < 9.4, HSO 5 − ions dominate while SO 5 2− ions become dominant at higher pH. 50 The higher the alkalinity of the solution, the greater the electrostatic repulsion between the negative surface of the catalyst (ZnCo 2 O 4 /Alg) and PMS, resulting in lower activation of PMS on the catalyst surface, 62 and ultimately low catalytic activity at pH = 11. Additionally, under alkaline conditions, SO4˙ − radicals can combine with hydroxyl anions (OH − ) to form a less potent oxidant, HO˙, (SO 4 ˙ − + HO˙ − → SO 4 2− + HO˙).…”

“…The average value of crystallite size is founded to be 21.61 nm as well as the average calculated value for lattice parameters and cell volume (a = 8.079 A, V = 527.617 nm 3 ) are according to the theoretical values obtained of ZnCo 2 O 4 . 50 The XRD results for the alginate bead revealed the existence of a peak of 2q = 22°, 51 this peak was also found in the ZCO/Alg composite which indicates the incorporation of ZCO into the alginate matrix. These results are in good agreement with the infrared results.…”

“…In the same context the low degradation rate obtained at pH = 3.2 (44.92% with k obs = 0.0141 min −1 ) can be explained by the nature of RhB molecules which may have existed mostly as RhB + , as RhB has a dissociation constant (pK a ) of 3.7, which resulted in electrostatic repulsion and hindered the adsorption of RhB onto the catalyst surface. 50,58 This decrease may also be attributed to the H + ion scavenging effect for SOc − and OHc (eqn ( 5) and ( 6)), also a comparatively higher concentration of H + ions will restrict the dissociation of PMS and allow the formation of H 2 SO 5 that will partially substitute HSO 5 − , thus lowering the electrostatic attraction between positively charged ZnCo 2 O 4 /Alg and PMS. 23,59 SO 4 c − + H + + e − / HSO 4 c − (5)…”