Extensive use of per-and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the standard practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS molecules in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aqueous environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are (i) to investigate the role of physicochemical properties of PFAS on thermal regeneration, (ii) to assess the changes in regeneration yield as well as GAC physical and chemical structure upon thermal regeneration, and (iii) to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chemicals, while preserving the desired physicochemical properties of the valuable GAC adsorbent.
Photocontrolled
atom transfer radical polymerization-induced self-assembly
(PhotoATR-PISA) mediated by UV light (λ = 365 nm) was utilized
to obtain polymer nanostructures with variable morphologies, including
nanospheres, wormlike micelles, and vesicles, at ambient temperature
by using parts per million (ppm) levels (ca. < 20 ppm) of copper
catalyst. Using Cu(II)Br2/tris(pyridin-2-ylmethyl)amine
(TPMA) catalyst systems and functional ATRP initiators, we performed
PhotoATR-PISA all in one-pot via sequential chain extension starting
from solvophilic poly(oligo(ethylene glycol) methyl ether methacrylate)
(POEGMA) macroinitiator growth followed by PISA using different proportions
of glycidyl methacrylate (GMA) and/or benzyl methacrylate (BMA) core-forming
blocks forming alkyne-functional polymer nanoparticles. Remarkably,
multiple, iterative chain extensions were accomplished introducing
additional GMA and BMA monomers in multiple steps without additional
solvent leading to stable nanoparticle dispersions with record-high
final solid concentrations of 63 and 79 wt %, respectively. Core cross-linked
nanoparticles (CCL NPs) were synthesized by incorporating N,N-cystamine bismethacrylamide (CBMA)
cross-linkers in later stage chain extensions providing a route to
CCL nanoworms. Furthermore, introducing BMA and GMA in varying orders
sequentially allowed for the synthesis of sequence-controlled gradient
copolymers, though this had limited effects on nanoparticle morphology.
Finally, utilizing the copper(I)-catalyzed azide–alkyne cycloaddition
(CuAAC) click reactions between alkyne-functionalized NPs and bisazide,
telechelic poly(ethylene glycol) (PEG), nanostructured networks were
fabricated consisting of nanospherical, beaded worm, nanoworm, and
vesicle morphologies. The interstitial porosity of these ClickNP networks
allows them to be potent adsorbents with explored applications in
water treatment demonstrated via the rapid uptake of phenanthrene
pollutants from aqueous solutions.
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