Advanced sanitation products infused with silver nanoparticles for viral protection and their ecological and environmental consequences.

The outbreak of coronavirus ailments (COVID-19) in 2019 resulted in public health crisis leading to global pandemonium. In response to the high prevalence of disease transmission, governments all around the globe implemented emergency measures in various routes (e.g., social distancing, personal hygiene, and disinfection of public/private places) to curb/contain COVID-19 infections. The social media infodemic, released as uncensored publishing and/or views/recommendations, also triggered large-scale behavior changes such as the overuse of advanced sanitation products (ASPs) containing nanomaterials. The majority of these ASPs contain silver nanoparticles (AgNPs) as an active ingredient to enhance their antimicrobial potential. Ecotoxicological concerns such as the transformation and degradation of these AgNP-infused products in terrestrial or aquatic environments are under the jurisdiction of the EPA. However, they are not considered in the FDA approval process. In light of excessive consumption of ASPs, it is time to consider their ecotoxicological screening prior to market approval jointly by the FDA and EPA, along with the implementation of post-market surveillance strategies. At the same time, efforts should be put into running awareness programs to prevent the overuse of ASPs.

Removal of gaseous benzene by a fixed-bed system packed with a highly porous metal-organic framework (MOF-199) coated glass beads.

The utility of nanomaterial adsorbents is often limited by their physical features, especially fine particle size. For example, a large bed-pressure drop is accompnied inevitably, if fine-particle sorbents are used in a packed bed system. To learn more about the effect of adsorbent morphology on uptake performance, we examined the adsorption efficiency of metal-organic framework 199 (MOF-199) in the pristine (fine powder) form and after its binding on to glass beads as an inert support. Most importantly, we investigated the effect of such coatings on adsorption of gaseous benzene (0.1-10 Pa) in a dry N2 stream, particularly as a function of the amount of MOF-199 loaded on glass beads (MOF-199@GB) (i.e., 0,% 1%, 3%, 10%, and 20%, w/w) at near-ambient conditions (298 K and 1 atm). A 1% MOF-199 load gave optimal performance against a 0.1 Pa benzene vapor stream in 1 atm of N2, with a two-to five-fold improvement (e.g., in terms of 10% breakthrough volume [BTV] (46 L atm [g.MOF-199)-1], partition coefficient at 100% BTV (3 mol [kg.MOF-199]-1 Pa-1), and adsorption capacity at 100% BTV (20 mg [g.MOF-199]-1 (areal capacity: 8.8 × 10-7 mol m-2) compared with those of 3%, 10%, and 20% loading. The relative performance of benzene adsorption was closely associated with the content of MOF-199@GB (e.g., 1% > 3% > 10% > 20%) and the surface availability (m2 [g.MOF-199]-1) such as 291 > 221 > 198 > 181, respectively. This study offers new insights into the strategies needed to expand the utility of finely powdered MOFs in various environmental applications.

Proof of concept for CUK family metal-organic frameworks as environmentally-friendly adsorbents for benzene vapor.

The utility of metal-organic frameworks (MOFs) such as the CUK family (CUK - Cambridge University-KRICT) has been explored intensively for adsorption/separation of airborne volatile organic compounds (VOCs). In this article, three M-CUK analogs (M = Mg, Co, or Ni) were synthesized hydrothermally under similar conditions to assess the effects of their isostructural properties and metal centers on adsorption of benzene vapor (0.05-1 Pa). A list of performance metrics (e.g., breakthrough volume (BTV) and partition coefficient (PC)) were used to assess the role of the metal type (in M-CUK-1s) in the adsorption of VOCs. Specifically, Co-CUK-1 (average pore size of 8.98 nm) showed 2-3 times greater performance (e.g., in terms of 10% BTV (2012 L atm g-1) and PC (6 mol kg-1 Pa-1)) over other analogs when exposed up to 0.05 Pa benzene vapor. The superiority of mesoporous Co-CUK-1 (e.g., enhanced adsorption diffusion mechanism through favorable metal-π and π- π interactions) can be attributed to the presence of cobalt metal centers (e.g., in reference to Mg- or Ni-CUK-1).

The effects of continuous- and stop-flow gas streams on adsorptive removal of benzene vapor using type - II covalent organic polymers.

Various materials have been investigated for the adsorptive removal of volatile organic compounds (VOCs, such as benzene). However, most materials proposed for the adsorptive removal of gaseous benzene (and other VOCs) perform relatively poorly (e.g., an impractically low-service 10% breakthrough volume [BTV10] at < 100 ppm). The adsorbent uptake rate (mg g-1 min-1) can also be assessed as a function of the gas-stream flow rate (or space velocity). The main aim of this study is to explore the effect of two different gas-stream supply modes - stopped flow (at a fixed stream flow rate of 330 mL atm min-1) vs. continuous flow (a variable-stream flow rate of 100, 200, or 330 mL atm min-1) on the adsorption metrics of gaseous benzene on 5 mg of two types of - II covalent organic polymers (COPs: CBAP-1 [DETA], CD; or CBAP-1 [EDA], CE). The sorbent tube outlet stream was sampled by two respective sampling methods (i.e., a large-volume injector [LVI] for stopped flow vs. syringe injection [SI] for continuous flow) for sample quantitation by gas chromatography flame-ionization detection (GC-FID). The observed BTV10 values in the two sampling modes were similar when tested using 10 ppm benzene, irrespective of sorbents: 56/60 (CD) vs. 620/624 L atm g-1 (CE). BTV10 values increased systematically with decreasing stream-flow rates to reflect the importance of space velocity in adsorptive removal of benzene. The overall assessment of adsorption performance between stopped flow (LVI) and continuous flow (SI) revealed that the performance of the adsorbent is independent of flow mode (e.g., when performance was compared at flow rate of 330 mL min-1).

Regeneration, degradation, and toxicity effect of MOFs: Opportunities and challenges.

Metal organic frameworks (MOFs) have been investigated extensively for separation, storage, catalysis, and sensing applications. Nonetheless, problems associated with their toxicity, recycling/reuse/regeneration, and degradation have yet to be addressed as one criterion to satisfy their commercialization. Here, the challenges associated with MOF-based technology have been explored to further expand their practical utility in various applications. We start a brief description of challenges associated with MOF-based technology followed by a critical evaluation of toxicity and need of technical options for regeneration of MOFs. Importantly, diverse techniques/process for reuse and regeneration of MOFs like activation of MOFs by heat, vacuum, solvent exchange, supercritical carbon dioxide (SCCO2) and other miscellaneous options have been discussed with recent examples. Afterward, we also present an economical aspect and future perspectives of MOFs for real world applications. All in all, we aimed to present opportunities and critical review of the current status of MOF technology with respect to their recycling/reuse/regeneration to consider their environmental impact.