UVA-LED-Assisted Activation of the Ferrate(VI) Process for Enhanced Micropollutant Degradation: Important Role of Ferrate(IV) and Ferrate(V)

Abstract

This paper investigated ultraviolet A light-emitting diode (UVA-LED) irradiation to activate Fe­(VI) for the degradation of micropollutants (e.g., sulfamethoxazole (SMX), enrofloxacin, and trimethoprim). UVA-LED/Fe­(VI) could significantly promote the degradation of micropollutants, with rates that were 2.6–7.2-fold faster than for Fe­(VI) alone. Comparatively, UVA-LED alone hardly degraded selected micropollutants. The degradation performance was further evaluated in SMX degradation via different wavelengths (365–405 nm), light intensity, and pH. Increased wavelengths led to linearly decreased SMX degradation rates because Fe­(VI) has a lower molar absorption coefficient at higher wavelengths. Higher light intensity caused faster SMX degradation, owing to the enhanced level of reactive species by stronger photolysis of Fe­(VI). Significantly, SMX degradation was gradually suppressed from pH 7.0 to 9.0 due to the changing speciation of Fe­(VI). Scavenging and probing experiments for identifying oxidative species indicated that high-valent iron species (Fe­(V)/Fe­(IV)) were responsible for the enhanced degradation. A kinetic model involving target compound (TC) degradation by Fe­(VI), Fe­(V), and Fe­(IV) was employed to fit the TC degradation kinetics by UVA-LED/Fe­(VI). The fitted results revealed that Fe­(IV) and Fe­(V) primarily contributed to TC degradation in this system. In addition, transformation products of SMX degradation by Fe­(VI) and UVA-LED/Fe­(VI) were identified and the possible pathways included hydroxylation, self-coupling, bond cleavage, and oxidation reactions. Removal of SMX in real water also showed remarkable promotion by UVA-LED/Fe­(VI). Overall, these findings could shed light on the understanding and application of UVA-LED/Fe­(VI) for eliminating micropollutants in water treatments.

Photochemical and Photophysical Dynamics of the Aqueous Ferrate(VI) Ion

“…23,24 Improved transformation of TOCs can be achieved through "activation" of ferrate(VI)�the addition of aqueous-phase reductants, 25−27 acids, 28,29 carbonaceous materials, 30,31 or UV light. 18,32,33 The improvement in effectiveness can be attributed to the formation of Fe(V) (perferryl) and Fe(IV) (ferryl) intermediates, 25,26,34 than the parent Fe(VI) ion toward target compounds. 9,35,36 Since the Fe(V) species are known to have higher reduction potentials, most proposed mechanisms for either direct oxidation of TOCs or generation of intermediary oxidizing species (e.g., hydroxyl radicals) with activated ferrate invoke a pentavalent iron intermediate, 9,18,33−35 though recent studies have suggested that Fe(IV) species likely play a significant role as well.…”

Preferential Destruction of Micropollutants in Water through a Self-Purification Process with Dissolved Organic Carbon Polar Complexation

“…9−11 However, complete removal is still not feasible (9−99%) 7,12 due to the competition of mg-level DOC in water for oxidants. 13 promoting its utilization by planktonic bacterivores, 19 suggesting that the formed particles may have greater electron polarity than HA. Therefore, investigating the interaction mode between the self-organized complex and micropollutants may be key to developing technologies for the preferential removal of micropollutants.…”

“…The increasing complex-mixture micropollution in aquatic systems with thousands of industrial chemical compounds has received great attention due to its potential to cause undesirable effects on aquatic life and human health . Especially, pesticides, pharmaceuticals, personal care products, endocrine disrupting chemicals, and so on were widely detected in municipal wastewater, raw drinking water, and reclaimed wastewater, with the trace levels ranging from ng/L to μg/L, − even in filtered water and tap water. , Therefore, removing these micropollutants from water is very important and urgent to avoid long-term human and biological exposure.…”

“…Over the past few decades, a wide range of advanced treatment methods has been investigated for the removal of micropollutants from different waters. For drinking-water treatment, physical methods including adsorption and membrane filtration could mitigate micropollutants availably by 15–95 and 70–98%, respectively, due to the interference of primary dissolved organic carbon (DOC). , To remove micropollutants from large quantities of raw drinking water, municipal wastewater, and reclaimed wastewater, these processes often require the assistance of reactive oxidants. − However, complete removal is still not feasible (9–99%) , due to the competition of mg-level DOC in water for oxidants …”

Oxidation Towards Enrofloxacin Degradation Over Nanoscale Zero-Valent Copper: Mechanism and Products

“…In the end, the loss of CO would be formed and generate an amine species group (P7, m/z = 263). It should be mentioned that m/z = 263 was the most generally reported intermediate product in ENR oxidative degradation such as electrochemical degradation(Wang et al 2017), peroxymonosulfate(Zhou et al 2018b;Nihemaiti et al 2020), and ferrate(Yang et al 2016(Yang et al , 2022a. A possible reaction mechanism for ENR degradation has been suggested, based on the chromatogram and mass spectrum obtained in conjunction with the current literature.…”