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.
Many investigations focused on the capacity of ferrate for the oxidation of organic pollutant or adsorption of hazardous species, while little attention has been paid on the effect of ferrate resultant nanoparticles for the removal of organics. Removing organics could improve microbiological stability of treated water and control the formation of disinfection byproducts in following treatment procedures. Herein, we studied ferrate oxidation of p-arsanilic acid (p-ASA), an extensively used organoarsenic feed additive. p-ASA was oxidized into As(V), p-aminophenol (p-AP), and nitarsone in the reaction process. The released As(V) could be eliminated by in situ formed ferric (oxyhydr) oxides through surface adsorption, while p-AP can be further oxidized into 4,4′-(diazene-1,2-diyl) diphenol, p-nitrophenol, and NO 3 − . Nitarsone is resistant to ferrate oxidation, but mostly adsorbed (>85%) by ferrate resultant ferric (oxyhydr) oxides. Ferrate oxidation (ferrate/p-ASA = 20:1) eliminated 18% of total organic carbon (TOC), while ferrate resultant particles removed 40% of TOC in the system. TOC removal efficiency is 1.6 to 38 times higher in ferrate treatment group than those in O 3 , HClO, and permanganate treatment groups. Besides ferrate oxidation, adsorption of organic pollutants with ferrate resultant nanoparticles could also be an effective method for water treatment and environmental remediation.
The oxidation of the toxic heavy
metal thallium(I) (Tl(I)) is an
efficient way to enhance Tl removal from water and wastewater. However,
few studies have focused on the kinetics of Tl(I) oxidation in water,
especially at environmentally relevant pH values. Therefore, the kinetics
and mechanisms of Tl(I) oxidation by the common agents KMnO4 and HOCl under environmentally relevant pH condition were explored
in the present study. The results indicated that the pH-dependent
oxidation of Tl(I) by KMnO4 exhibited second-order kinetics
under alkaline conditions (pH 8–10) with the main active species
being TlOH, while the reaction could be characterized by autocatalysis
at pH 4–6, and Mn(III) might also play an essential role in
the MnO2 catalysis. Furthermore, a two-electron transfer
mechanism under alkaline conditions was preliminarily proposed by
using linear free energy relationships and X-ray photoelectron spectroscopy
(XPS) analysis. Distinctively, the reaction rate of Tl(I) oxidation
by HOCl decreased with increasing pH, and protonated chlorine might
be the main active species. Moreover, the Tl(I)-HOCl reaction could
be regarded as first order with respect to Tl(I), but the order with
respect to HOCl was variable. Significant catalysis by MnO2 could also be observed in the oxidation of Tl(I) by HOCl, mainly
due to the vacancies on MnO2 as active sites for sorbing
Tl. This study elucidates the oxidation characteristics of thallium
and establishes a theoretical foundation for the oxidation processes
in thallium removal.
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