Benchmarking Micropollutant Removal by Activated Carbon and Porous β-Cyclodextrin Polymers under Environmentally Relevant Scenarios

Abstract

The cost-effective and energy-efficient removal of organic micropollutants (MPs) from water and wastewater is challenging. The objective of this research was to evaluate the performance of porous β-cyclodextrin polymers (P-CDP) as adsorbents of MPs in aquatic matrixes. Adsorption kinetics and MP removal were measured in batch and flow-through experiments for a mixture of 83 MPs at environmentally relevant concentrations (1 μg L) and across gradients of pH, ionic strength, and natural organic matter (NOM) concentrations. Performance was benchmarked against a coconut-shell activated carbon (CCAC). Data reveal pseudo-second-order rate constants for most MPs ranging between 1.5 and 40 g mg min for CCAC and 30 and 40000 g mg min for P-CDP. The extent of MP removal demonstrates slower but more uniform uptake on CCAC and faster but more selective uptake on P-CDP. Increasing ionic strength and the presence of NOM had a negative effect on the adsorption of MPs to CCAC but had almost no effect on adsorption of MPs to P-CDP. P-CDP performed particularly well for positively charged MPs and neutral or negatively charged MPs with McGowan volumes greater than 1.7 (cm mol)/100. These data highlight advantages of P-CDP adsorbents relevant to MP removal during water and wastewater treatment.

Reduction of a Tetrafluoroterephthalonitrile‐β‐Cyclodextrin Polymer to Remove Anionic Micropollutants and Perfluorinated Alkyl Substances from Water

“…We found that 1 exhibited relatively high log K D values for cationic MPs,a long with neutral compounds that bind to CDs well, which is consistent with previous reports [16,32] and observations (Figure 3). [13,17] All 18 cationic substances exhibited log K D values greater than 2on polymer 1.Incontrast, 21 of 25 anionic substances and all 10 anionic PFASs exhibited relatively low log K D values between À0.5 and 1.0 on polymer 1.These low affinities make polymer 1 an ineffective adsorbent for most anionic MPs at environmentally relevant concentrations and economically reasonable doses of 1.Incontrast, polymer 2 strongly binds anionic substances,with 21 of 25 exhibiting log K D values > 2.6 and all ten anionic PFASs exhibiting log K D values between 2.8-4.0. However,p olymer 2 binds cationic MPs more weakly with log K D values for 16 of 18 cationic MPs between À0.5-1.5.…”

“…[1,2] Concerns about their negative effects on human health [3][4][5][6][7] and the environment [8][9][10] motivate the development of technologies that remove MPs more effectively. [11][12][13][14][15][16] These efforts are complicated by the broad range of physiochemical properties of MPs,i ncluding charge,s ize,h ydrophobicity,a nd their diverse chemical functionality. b-cyclodextrin (b-CD)-based polymers (CDPs) with aromatic crosslinkers have shown promise to remove MPs from water.…”

“…b-cyclodextrin (b-CD)-based polymers (CDPs) with aromatic crosslinkers have shown promise to remove MPs from water. [11,12,14,16] Forexample,aCDP crosslinked by tetrafluoroterephthalonitrile (TFN), was formed as apermanently porous network (1,F igure 1) that rapidly removes many MPs from water, [11] resists fouling by natural organic matter, [13,14] and can be regenerated. [17] Astudy of the binding of 83 MPs under environmentally relevant concentrations revealed that 1 rapidly removes many cationic and neutral MPs but shows poor affinity for most anionic MPs.…”

“…[17] Astudy of the binding of 83 MPs under environmentally relevant concentrations revealed that 1 rapidly removes many cationic and neutral MPs but shows poor affinity for most anionic MPs. [13] This selectivity for cations was later attributed to anionic phenolate groups introduced to the TFN crosslinkers during the polymerization. [16] Thei nability of 1 to bind anionic micropollutants,i ncluding anionic perfluorinated alkyl substances (PFASs), [13,16] is am ajor limitation to its broad utility and technological promise.…”

“…Then itriles of 1 were reduced to primary amines using excess BH 3 ·S(CH 3 ) 2 in THF at reflux for 40 hours,u sing conditions modified from those used to reduce TFN-based polymers of intrinsic microporosity. [28] After reduction, insoluble polymer 2 was subjected to an acidic workup followed by treatment with base.T he reduction was characterized by FT-IR, cross-polarized magic angle spinning (CP-MAS) solid-state 13 CNMR, ac hloranil test for amines, combustion analysis,a nd zeta potential measurements.F T-IR was consistent with partial reduction of the nitriles,asthe spectrum of 2 shows as trongly attenuated nitrile stretch at 2238 cm À1 relative to that of 1 when each spectrum was normalized at the CÀOstretch at 1020 cm À1 .The spectrum of 2 also shows an N À Hbending signal at 1580 cm À1 (Figure 2a). In the CP-MAS 13 C-NMR, the nitrile carbons of 1 resonate at 94.44 ppm.…”