The
widespread environmental occurrence of per- and polyfluoroalkyl substances
(PFAS) has attracted significant regulatory, research, and media attention
because of their toxicity, recalcitrance, and ability to bioaccumulate.
Perfluorooctane sulfonate (PFOS) is a particularly troublesome member
of the PFAS family due to its immunity to biological remediation and
radical-based oxidation. In the present study, we present a heterogeneous
reductive degradation process that couples direct electron transfer
(ET) from surface-modified carbon nanotube electrodes (under low potential
conditions) to sorbed PFOS molecules using UV-generated hydrated electrons
without any further chemical addition. We demonstrate that the ET
process dramatically increases the PFOS defluorination rate while
yielding shorter chain (C3–C7) perfluorinated
acids and present both experimental and ab initio evidence of the
synergistic relationship between electron addition to sorbed molecules
and their ability to react with reductive hydrated electrons. Because
of the low energy consumption associated with the ET process, the
use of standard medium-pressure UV lamps and no further chemical addition,
this reductive degradation process is a promising method for the destruction
of persistent organic pollutants, including PFAS and other recalcitrant
halogenated organic compounds.
Per and polyfluoroalkyl substances (PFAS), legacy chemicals used in firefighting and the manufacturing of many industrial and consumer goods, are widely found in groundwater resources, along with other regulated compounds, such as chlorinated solvents. Due to their strong C− F bonds, these molecules are extremely recalcitrant, requiring advanced treatment methods for effective remediation, with hydrated electrons shown to be able to defluorinated these compounds. A combined photo/ electrochemical method has been demonstrated to dramatically increase defluorination rates, where PFAS molecules sorbed onto appropriately functionalized cathodes charged to low cell potentials (−0.58 V vs Ag/ AgCl) undergo a transient electron transfer event from the electrode, which "primes" the molecule by reducing the C−F bond strength and enables the bond's dissociation upon the absorption of a hydrated electron. In this work, we explore the impact of headgroup and chain length on the performance of this two-electron process and extend this technique to chlorinated solvents. We use isotopically labeled PFAS molecules to take advantage of the kinetic isotope effect and demonstrate that indeed PFAS defluorination is likely driven by a twoelectron process. We also present density functional theory calculations to illustrate that the externally applied potential resulted in an increased rate of electron transfer, which ultimately increased the measured defluorination rate.
Besides its poor dissolution rate, the bitterness of quercetin also poses a challenge for further development. Using carnauba wax, shellac or zein as the shell-forming excipient, this work aimed to microencapsulate quercetin by hot-melt extrusion for taste-masking. In comparison with non-encapsulated quercetin, the microencapsulated powders exhibited significantly reduced dissolution in the simulated salivary pH 6.8 medium indicative of their potentially good taste-masking efficiency in the order of zein > carnauba wax > shellac. In vitro bitterness analysis by electronic tongue confirmed the good taste-masking efficiency of the microencapsulated powders. In vitro digestion results showed that carnauba wax and shellac-microencapsulated powders presented comparable dissolution rate with the pure quercetin in pH 1.0 (gastric) and 6.8 (intestine) medium; while zein-microencapsulated powders exhibited a remarkably slower dissolution rate. Crystallinity of quercetin was slightly reduced after microencapsulation while its chemical structure remained unchanged. Hot-melt extrusion microencapsulation could thus be an attractive technique to produce taste-masked bioactive powders.
Recovery of nutrients, such as ammonia, from wastewater offers an attractive approach to increase the overall sustainability of waste management practices.
The
growth of mineral crystals on surfaces is a challenge across
multiple industrial processes. Membrane-based desalination processes,
in particular, are plagued by crystal growth (known as scaling), which
restricts the flow of water through the membrane, can cause membrane
wetting in membrane distillation, and can lead to the physical destruction
of the membrane material. Scaling occurs when supersaturated conditions
develop along the membrane surface due to the passage of water through
the membrane, a process known as concentration polarization. To reduce
scaling, concentration polarization is minimized by encouraging turbulent
conditions and by reducing the amount of water recovered from the
saline feed. In addition, antiscaling chemicals can be used to reduce
the availability of cations. Here, we report on an energy-efficient
electrophoretic mixing method capable of nearly eliminating CaSO4 and silicate scaling on electrically conducting membrane
distillation (ECMD) membranes. The ECMD membrane material is composed
of a percolating layer of carbon nanotubes deposited on porous polypropylene
support and cross-linked by poly(vinyl alcohol). The application of
low alternating potentials (2 Vpp,1Hz) had a dramatic impact
on scale formation, with the impact highly dependent on the frequency
of the applied signal, and in the case of silicate, on the pH of the
solution.
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