Mechanism of Sulfate Radical Formation on Activation of Persulfate Using Doped Metal Oxide and Its Role in Degradation of Tartrazine Dye in an Aqueous Solution
Fetcia Jackulin, P. Senthil Kumar, Chitra Boobalan, R. Gayathri
Abstract
Degradation of tartrazine dye (TZD) was performed in this study using sulfate radicals (SO 4 •– ) generated from the activated sodium persulfate (SPS) using Fe 3 O 4 @PDA nanoparticles (NPs). The NPs were characterized by Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX). The average particle size of the NPs was 17.49 nm from XRD analysis. The presence of the C–N group at 1129 cm –1 in FTIR and 2.54% of the nitrogen element identified from the EDX plot was evidence of successful doping of polydopamine (PDA). Superparamagnetic nature with a decrease in the M s value to 42.015 emu/g after doping was determined. Doping was further confirmed by XPS analysis with binding energies at 399.68 and 400.99 eV. The average particle size from HRTEM analysis was 21.47 nm with a lattice spacing of 0.30 nm. Turnover number (TON) and turnover frequency (TOF) values for Fe 3 O 4 @PDA were determined to be 3.72 and 0.0248 min –1 with respect to different systems, respectively. Optimum conditions for the Fe 3 O 4 @PDA/SPS system were 50 ppm TZD, 0.9 g/L catalyst, 12 mM SPS, and pH 4 with 94.68% efficiency in 150 min. The inhibition effect of ions in TZD degradation followed the order humic acid <NO 3 – < Cl – < CO 3 2 . The kinetic model fitting the Fe 3 O 4 @PDA/SPS system has pseudo-second-order kinetics. Excess formation of SO 4 •– produced hydroxyl radicals ( • OH) that were identified by a scavenging test. Reusability of the NPs was performed for five cycles and showed acceptable degradation performance up to 82.47%. The intermediates identified from gas chromatography–mass spectrometry (GCMS) proved the cleavage of azo and sulfonate groups of TZD with the formation of nontoxic intermediates. Finally, the phytotoxicity assessment was studied using Vigna radiata (Green grams). The % decrease of the root, shoot, and seedling length for the degraded dye solution was negligible. Hence, this study proved that the Fe 3 O 4 @PDA/SPS system could effectively degrade TZD with nontoxic intermediate formation.