Boosting the catalytic activity of natural magnetite for wet peroxide oxidation

Abstract

This work explores the modification of naturally occurring magnetite by controlled oxidation (200-400 °C, air atmosphere) and reduction (300-600 °C, H atmosphere) treatments with the aim of boosting its activity in CWPO. The resulting materials were fully characterized by XRD, XPS, TGA, TPR, SEM, and magnetization measurements, allowing to confirm the development of core-shell type structures. The magnetite core of the solid remained unchanged upon the treatment whereas the Fe(II)/Fe(III) ratio of the shell was modified (e.g. 0.42, 0.11 and 0.63 values were calculated for pristine FeO, FeO-O400, and FeO-R400, respectively). The performance of the catalysts was tested in the CWPO of sulfamethoxazole (SMX) (5 mg L) under ambient conditions and circumneutral pH (pH = 5), using the stoichiometric dose of HO (25 mg L) and a catalyst load of 1 g L. The key role of the ferrous species on the mineral shell was evidenced. Whereas the oxidation of magnetite led to significantly slower degradation rates of the pollutant, its reduction gave rise to a dramatic increase, achieving the complete removal of SMX in 1.5 h reaction time with the optimum catalyst (FeO-R400) compared to the 3.5 h required with the pristine mineral. A reaction mechanism was proposed for SMX degradation, and a kinetic equation based on the Eley-Rideal model was accordingly developed. This model successfully fitted the experimental results. The stability of FeO-R400 was evaluated upon five sequential runs. Finally, the versatility of the catalytic system was proved in real environmentally relevant water matrices.

Degradation of widespread cyanotoxins with high impact in drinking water (microcystins, cylindrospermopsin, anatoxin-a and saxitoxin) by CWPO

“…The procedure followed for the preparation of Fe 3 O 4 -R400 has been previously reported (Álvarez-Torrellas et al, 2018). Briefly, powdered magnetite mineral was reduced at H 2 atmosphere (250 N mL min -1 of 25 vol.…”

“…% H 2 in N 2 ) for 3 h at 400 ºC. A detailed characterization of the catalyst, including XRD, textural properties, and magnetic measurements, can be found elsewhere (Álvarez-Torrellas et al, 2018;Serrano et al, 2018). Summarizing, the iron content was 73% wt., the specific surface area 7 m 2 g -1 and the particles showed a mean size of 0.2 m.…”

Oxidation of Cylindrospermopsin by Fenton Process: A Bench-Scale Study of the Effects of Dose and Ratio of H2O2 and Fe(II) and Kinetics

“…The results obtained by Munoz and co-workers [ 64 ] may be attributed to the nanocatalyst itself, which was specially designed and boosted for the heterogeneous Fenton-like oxidation [ 74 ]. As nanocatalysts have high surface areas and low diffusional resistance, they are more efficient than conventional heterogeneous catalysts [ 75 ].…”

Fast oxidation of the neonicotinoid pesticides listed in the EU Decision 2018/840 from aqueous solutions

“…In this work, the capability of dark heterogeneous Fenton oxidation, also known as catalytic wet peroxide oxidation (CWPO), for the elimination of the neonicotinoid pesticides listed in the EU Decision 2018/840 (ACT, CLT, IMD, THC and THM) has been investigated using the low-cost and environmentally-friendly system Fe 3 O 4 -R400/H 2 O 2 [30]. The kinetics of the reactions has been studied at 25 ºC, 1 atm and pH 0 = 5, using a representative concentration of the pesticides (1000 g L -1 ), a catalyst load of 1 g L -1 and the stoichiometric H 2 O 2 concentration for the total oxidation of the target pollutants (~4 -5 mg L -1 ).…”