Using a bipolymer system consisting of polyvinylpyrrolidone (PVP) and poly(vinylidene fluoride) (PVDF), P25-TiO was immobilized into thin film mats of porous electrospun fibers. Pores were introduced by dissolving sacrificial PVP to increase surface area and enhance access to TiO. The highest photocatalytic activity was achieved using a PVDF:PVP weight ratio of 2:1. Methylene blue (MB) was used to visualize contaminant removal, assess the sorption capacity (5.93 ± 0.23 mg/g) and demonstrate stable removal kinetics ( k > 0.045 min) under UVA irradiation (3.64 × 10 einstein/cm/s) over 10 cycles. Treatment was also accomplished via sequential MB sorption in the dark and subsequent photocatalytic degradation under UVA irradiation, to illustrate that these processes could be uncoupled to overcome limited light penetration. The photocatalytic mat degraded bisphenol A and 17α-ethynylestradiol in secondary wastewater effluent (17 mg TOC/L), and (relative to TiO slurry) immobilization of TiO in the mat mitigated performance inhibition by co-occurring organics that scavenge oxidation capacity. This significantly lowered the electrical energy-per-order of reaction (EEO) needed to remove such endocrine disruptors in the presence of oxidant scavenging/inhibitory organics. Thus, effective TiO immobilization into polymers with affinity toward specific priority pollutants could both increase the efficiency and reduce energy requirements of photocatalytic water treatment.

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There is a growing need to mitigate the discharge of extracellular antibiotic resistance genes (ARGs) from municipal wastewater treatment systems. Here, molecularly-imprinted graphitic carbon nitride (MIP-C 3 N 4 ) nanosheets were synthesized for selective photocatalytic degradation of a plasmid-encoded ARG (bla NDM-1 , coding for multidrug resistance New Delhi metallo-β-lactamase-1) in secondary effluent. Molecular imprinting with guanine enhanced ARG adsorption, which improved the utilization of photogenerated oxidizing species to degrade bla NDM-1 rather than being scavenged by background nontarget constituents. Consequently, photocatalytic removal of bla NDM-1 in secondary effluent with MIP-C 3 N 4 (k = 0.111 ± 0.028 min −1 ) was 37 times faster than with bare graphitic carbon nitride (k = 0.003 ± 0.001 min −1 ) under UVA irradiation (365 nm, 3.64 × 10 −6 Einstein/L•s). MIP-C 3 N 4 can efficiently catalyze the fragmentation of bla NDM-1 , which decreased the potential for ARG repair by transformed bacteria. Molecular imprinting also changed the primary degradation pathway; electron holes (h + ) were the predominant oxidizing species responsible for bla NDM-1 removal with MIP-C 3 N 4 versus free radicals (i.e., •OH and O 2 − ) for coated but nonimprinted C 3 N 4 . Overall, MIP-C 3 N 4 efficiently removed bla NDM-1 from secondary effluent, demonstrating the potential for molecular imprinting to enhance the selectivity and efficacy of photocatalytic processes to mitigate dissemination of antibiotic resistance from sewage treatment systems.

Micrometer-sized titanium dioxide hierarchical spheres (TiO2-HS) were assembled from nanosheets to address two common limitations of photocatalytic water treatment: (1) inefficiency associated with scavenging of oxidation capacity by nontarget water constituents and (2) energy-intensive separation and recovery of the photocatalyst slurry. These micrometer-sized spheres are amenable to low-energy separation, and over 99% were recaptured from both batch and continuous flow reactors using microfiltration. Using nanosheets as building blocks resulted in a large specific surface area3 times larger than that of commercially available TiO2 powder (Evonik P25). Anchoring food-grade cyclodextrin onto TiO2-HS (i.e., CD-TiO2-HS) provided hydrophobic cavities to entrap organic contaminants for more effective utilization of photocatalytically generated reactive oxygen species. CD-TiO2-HS removed over 99% of various contaminants with dissimilar hydrophobicity (i.e., bisphenol A, bisphenol S, 2-naphthol, and 2,4-dichlorophenol) within 2 h under a low-intensity UVA input (3.64 × 10–6 einstein/L/s). As with other catalyst (including TiO2 slurry), periodic replacement or replenishment would be needed to maintain high treatment efficiency (e.g., we demonstrate full reactivation through simple reanchoring of CD). Nevertheless, this task would be offset by significant savings in photocatalyst separation. Thus, CD-TiO2-HS is an attractive candidate for photocatalytic water and wastewater treatment of recalcitrant organic pollutants.

Perfluorooctanoic acid (PFOA) is a widely distributed recalcitrant contaminant. In recent years, advanced oxidation processes have been explored for PFOA degradation, yet factors influencing their efficacy and degradation mechanism are not fully understood. Here, we resolve ambiguity in the literature regarding the role of superoxide in PFOA degradation (e.g., by nucleophilic attack) by considering three pure superoxideproducing systems: KO 2 in dimethyl sulfoxide, xanthine oxidase with hypoxanthine, and WO x /ZrO 2 catalyst with H 2 O 2 . Superoxide production was confirmed in all systems by electron paramagnetic resonance spectroscopy and by precipitation of nitroblue tetrazolium, a common superoxide probe. Positive control experiments showed that the produced superoxide degrades ∼48% of bisphenol A within 1 day, corroborating the fact that superoxide was sufficiently stable and available for reaction in the test systems. However, no PFOA degradation was observed, which was corroborated by the absence of fluoride and degradation byproducts in all three systems. Therefore, other reaction pathways should be explored for PFOA degradation.