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1. Carbon–titanium dioxide (C/TiO 2 ) nanofiber composites for chemical oxidation of emerging organic contaminants in reactive filtration applications

   https://doi.org/10.1039/D0EN00975J  

   Greenstein, Katherine E. ; Nagorzanski, Matthew R. ; Kelsay, Bailey ; Verdugo, Edgard M. ; Myung, Nosang V. ; Parkin, Gene F. ; Cwiertny, David M. ( March 2021 , Environmental Science: Nano)

   null (Ed.)

   The recalcitrance of some emerging organic contaminants through conventional water treatment systems may necessitate advanced technologies that use highly reactive, non-specific hydroxyl radicals. Here, polyacrylonitrile (PAN) nanofibers with embedded titanium dioxide (TiO 2 ) nanoparticles were synthesized via electrospinning and subsequently carbonized to produce mechanically stable carbon/TiO 2 (C/TiO 2 ) nanofiber composite filters. Nanofiber composites were optimized for reactivity in flow through treatment systems by varying their mass loading of TiO 2 , adding phthalic acid (PTA) as a dispersing agent for nanoparticles in electrospinning sol gels, comparing different types of commercially available TiO 2 nanoparticles (Aeroxide® P25 and 5 nm anatase nanoparticles) and through functionalization with gold (Au/TiO 2 ) as a co-catalyst. High bulk and surface TiO 2 concentrations correspond with enhanced nanofiber reactivity, while PTA as a dispersant makes it possible to fabricate materials at very high P25 loadings (∼80% wt%). The optimal composite formulation (50 wt% P25 with 2.5 wt% PTA) combining high reactivity and material stability was then tested across a range of variables relevant to filtration applications including filter thickness (300–1800 μm), permeate flux (from 540–2700 L m −2 h), incident light energy (UV-254 and simulated sunlight), flow configuration (dead-end and cross-flow filtration), presence of potentially interfering co-solutes (dissolved organic matter and carbonate alkalinity), and across a suite of eight organic micropollutants (atrazine, benzotriazole, caffeine, carbamazepine, DEET, metoprolol, naproxen, and sulfamethoxazole). During cross-flow recirculation under UV-irradiation, 300 μm thick filters (30 mg total mass) produced micropollutant half-lives ∼45 min, with 40–90% removal (from an initial 0.5 μM concentration) in a single pass through the filter. The initial reaction rate coefficients of micropollutant transformation did not clearly correlate with reported second order rate coefficients for reaction with hydroxyl radical ( k OH ), implying that processes other than reaction with photogenerated hydroxyl radical ( e.g. , surface sorption) may control the overall rate of transformation. The materials developed herein represent a promising next-generation filtration technology that integrates photocatalytic activity in a robust platform for nanomaterial-enabled water treatment. 

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2. Functionalized electrospun polymer nanofibers for treatment of water contaminated with uranium

   https://doi.org/10.1039/C9EW00834A  

   Johns, Adam ; Qian, Jiajie ; Carolan, Margaret E. ; Shaikh, Nabil ; Peroutka, Allison ; Seeger, Anna ; Cerrato, José M. ; Forbes, Tori Z. ; Cwiertny, David M. ( March 2020 , Environmental Science: Water Research & Technology)

   Uranium (U) contamination of drinking water often affects communities with limited resources, presenting unique technology challenges for U 6+ treatment. Here, we develop a suite of chemically functionalized polymer (polyacrylonitrile; PAN) nanofibers for low pressure reactive filtration applications for U 6+ removal. Binding agents with either nitrogen-containing or phosphorous-based ( e.g. , phosphonic acid) functionalities were blended (at 1–3 wt%) into PAN sol gels used for electrospinning, yielding functionalized nanofiber mats. For comparison, we also functionalized PAN nanofibers with amidoxime (AO) moieties, a group well-recognized for its specificity in U 6+ uptake. For optimal N-based (Aliquat® 336 or Aq) and P-containing [hexadecylphosphonic acid (HPDA) and bis(2-ethylhexyl)phosphate (HDEHP)] binding agents, we then explored their use for U 6+ removal across a range of pH values (pH 2–7), U 6+ concentrations (up to 10 μM), and in flow through systems simulating point of use (POU) water treatment. As expected from the use of quaternary ammonium groups in ion exchange, Aq-containing materials appear to sequester U 6+ by electrostatic interactions; while uptake by these materials is limited, it is greatest at circumneutral pH where positively charged N groups bind negatively charged U 6+ complexes. In contrast, HDPA and HDEHP perform best at acidic pH representative of mine drainage, where surface complexation of the uranyl cation likely drives uptake. Complexation by AO exhibited the best performance across all pH values, although U 6+ uptake via surface precipitation may also occur near circumneutral pH values and at high (10 μM) dissolved U 6+ concentrations. In simulated POU treatment studies using a dead-end filtration system, we observed U removal in AO-PAN systems that is insensitive to common co-solutes in groundwater ( e.g. , hardness and alkalinity). While more research is needed, our results suggest that only 80 g (about 0.2 lbs.) of AO-PAN filter material would be needed to treat an individual's water supply (contaminated at ten-times the U.S. EPA maximum contaminant level for U) for one year. 

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3. An Advanced Dual‐Function MnO 2 ‐Fabric Air Filter Combining Catalytic Oxidation of Formaldehyde and High‐Efficiency Fine Particulate Matter Removal

   https://doi.org/10.1002/adfm.202001488  

   Dai, Zijian ; Zhu, Jie ; Yan, Jiaqi ; Su, Jiafei ; Gao, Yunfei ; Zhang, Xing ; Ke, Qinfei ; Parsons, Gregory N. ( August 2020 , Advanced Functional Materials)

   Comprehensive treatment of indoor contaminants such as volatile organic compounds (VOCs) and fine particulate matter (PM_2.5) using transition metal oxide catalysts or functional fibrous filters has gained substantial attention recently. However, coupling VOC oxidation catalysts into high‐performance filter systems remains a challenge. Herein, an overall solution to strongly bind manganese dioxide (MnO₂) nanocrystals onto polypropylene (PP) nonwoven fabrics is provided. For the first time, uniform heterogeneous nucleation and growth of MnO₂onto PP nonwoven fabrics using intermediate inorganic nucleation films, including Al₂O₃, TiO₂, and ZnO, formed conformally on the fabrics via atomic layer deposition (ALD) are demonstrated. How different ALD thin films influence the crystallinity, morphology, surface area, and surface oxygen species of the MnO₂grown ALD‐coated PP fibers is further investigated. In addition to uniformity and integrity, ZnO thin films give rise to MnO₂crystals with the largest fraction of available surface oxygen, enabling 99.5% catalytic oxidation of formaldehyde within 60 min. Moreover, the metal oxide filters provide excellent PM removal efficiencies (ePM), achievingePM_2.590% andePM₁₀98%, respectively, making the approach an outstanding method to produce fully dual‐functional filtration media.

    

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4. Self-decontaminating nanofibrous filters for efficient particulate matter removal and airborne bacteria inactivation

   https://doi.org/10.1039/D0EN01230K  

   Zhu, Zan ; Zhang, Yu ; Bao, Liang ; Chen, Jianping ; Duan, Shun ; Chen, Sheng-Chieh ; Xu, Ping ; Wang, Wei-Ning ( April 2021 , Environmental Science: Nano)

   null (Ed.)

   With the increased bacteria-induced hospital-acquired infections (HAIs) caused by bio-contaminated surfaces, the requirement for a safer and more efficient antibacterial strategy in designing personal protective equipment (PPE) such as N95 respirators is rising with urgency. Herein, a self-decontaminating nanofibrous filter with a high particulate matter (PM) filtration efficiency was designed and fabricated via a facile electrospinning method. The fillers implemented in the electrospun nanofibers were constructed by grafting a layer of antibacterial polymeric quaternary ammonium compound (QAC), that is, poly[2-(dimethyl decyl ammonium) ethyl methacrylate] (PQDMAEMA), onto the surface of metal–organic framework (MOF, UiO-66-NH 2 as a model) to form the active composite UiO-PQDMAEMA. The UiO-PQDMAEMA filter demonstrates an excellent PM filtration efficiency (>95%) at the most penetrating particle size (MPPS) of 80 nm, which is comparable to that of the commercial N95 respirators. Besides, the UiO-PQDMAEMA filter is capable of efficiently killing both Gram-positive ( S. epidermidis ) and Gram-negative ( E. coli ) airborne bacteria. The strong electrostatic interactions between the anionic cell wall of the bacteria and positively charged nitrogen of UiO-PQDMAEMA are the main reasons for severe cell membrane disruption, which leads to the death of bacteria. The present work provides a new avenue for combating air contamination by using the QAC-modified MOF-based active filters. 

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5. Comparative life cycle assessment of graphitic carbon nitride synthesis routes

   https://doi.org/10.1111/jiec.13390  

   Aquino de Carvalho, Nathalia ; Gilbertson, Leanne M. ( April 2023 , Journal of Industrial Ecology)

   Graphitic carbon nitride (g‐C₃N₄) has gained great interest as a visible‐light‐activated photocatalyst. As an emerging nanomaterial for environmental applications, its competitive performance and environmentally responsible synthesis are critical to its success. A powerful tool for informing material development with reduced environmental impacts is life cycle assessment (LCA). In this study, LCA is used to evaluate the environmental impacts of g‐C₃N₄nanosheet produced via eight existing synthesis routes. The results reveal electricity as the main contributor to the cumulative impacts of all eight g‐C₃N₄syntheses. There are opportunities to reduce energy demand, and consequently the synthesis impacts, by revising synthesis procedures (i.e., removing or reducing time of use of a piece of equipment), optimizing the calcination step (i.e., faster heating rate, lower heating time, lower temperature), and moving to cleaner electricity sources. Further, benchmarking the environmental impacts of g‐C₃N₄nanosheets to a well‐established metal‐based photocatalyst, titanium dioxide nanoparticles (nano‐TiO₂), reveals mixed comparative results. The synthesis method substantially influences the comparative impacts. Considering use‐phase benefits of activating g‐C₃N₄with visible wavelength light emitting diodes compared to ultraviolet (UV) wavelengths for nano‐TiO₂results in a 52% energy demand reduction (in kWh). Performance of g‐C₃N₄compared to a high‐energy disinfection approach (i.e., conventional UV) reveals an inability to meet drinking water disinfection standards for viral load reduction (4‐log reduction) with any mass of g‐C₃N₄, given its high embodied resource footprint. This work establishes a foundation to inform and direct g‐C₃N₄nanosheets toward improved sustainable development.

    

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