The current situation in India regarding the COVID-19 pandemic is the worst since its first detection, in terms of the number of new cases per day, and it is now more than 10000 (as of June 16, ...2020). In addition to several precautionary steps being taken (social distancing, use of masks, sanitizing hands etc.), spraying disinfectants (NaOCl solution) over several residential, official and commercial buildings, open areas, markets, public road transports, railways etchas been occurring on a regular basis. It has also come to the world's attention that spraying of disinfectants has been especially used on people who are migrating from one part of the country to another. In this letter, I have made an attempt to discuss some major impacts of NaOCl on human health as well as atmospheric chemistry. NaOCl once emitted into the air reacts easily with the water vapor to form HOCl that further gets photo-dissociated into various reactive species. These reactive species have significant potentials to participate in various tropospheric chemistry of chlorine radical, ozone, S (IV) oxidation, hydrocarbon oxidation, modification of chloride salts etc. I have also recommended some important steps to be taken if spraying of NaOCl is deemed essential.
Bioremediation is traditionally carried out using ‘free’ bacterial cells; however, in recent years, utilization of ‘immobilized’ bacterial cells has gained attention as a promising technique due to ...multifarious benefits. This review collates a vast amount of existing literature on the myriad contaminants treated using immobilized bacteria. We also discuss various mechanistic aspects of using immobilized cells for environmental remediation applications, with special attention on cells encapsulated in hydrogels and their implementation in detoxifying harmful contaminants and environmental cleanup. We examine different methods/techniques for immobilizing viable bacterial cells in various supporting matrices, use of single- and multi-species bacterial communities, various growth substrates, and factors affecting the remediation process including mass transfer, kinetic processes and bioreactor configurations used in pilot and field-scale applications. The advantages and limitations associated with the use of immobilized bacteria in a bioreactor for contaminated water treatment are also discussed. From a sustainable futures perspective, resource recovery and retrieval of value-added products along with bioremediation could be an added benefit of the immobilized cell-based treatment system, making it a more cost-effective and viable treatment strategy as well as one that is amenable to the principles of circular economy.
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•Immobilized microbes for bioremediation have seen major advances in the last decade.•Myriad water contaminations have been treated using immobilized microbes.•Immobilization methods, materials, microbial species, substrates used are summarized.•Mass transfer, adsorption, kinetics, and reactor design considerations are discussed.•With high potential for resource recovery use of this technology is likely to grow.
Bimetallic nanoparticles (BNPs) often possess peculiar segregation behavior as the particle size, composition, shape, and temperature are varied. However, a thermodynamic model for this phenomenon ...has been lacking thus far. We show for the first time that the distribution of metal species within a nanoparticle can be adequately captured in terms of distribution coefficients calculated for the facets, facet edges, and bulk regions. Thermodynamic relations for the distribution coefficients are derived. Only m distribution coefficients from the m(m – 1) distribution coefficients are independent, where m denotes the number of regions. The theory is applied to AuPt, NiPt, and AuAg BNPs. Distribution coefficients are calculated at 400 and 600 K using Monte Carlo (MC) simulations of varying BNP sizes and compositions. A wide range of mixing behavior from alloying to partial or full segregation and core–shell to onion-like structures can be observed. A key finding is that the distribution coefficients are independent of the BNP size. The observed size-dependent segregation can be attributed to the relative availability of surface and bulk sites, i.e., the area-to-volume (A/V) ratio. This implies that two bimetallic nanostructures of different sizes and shapes but the same A/V ratio may exhibit nearly identical segregation behavior. Thus, nanothermodynamic segregation in bimetallic alloys may be described concisely using a handful of distribution coefficients.
Formation of complex 3-D nanoporous structures via selective dissolution of an electroactive component in a bulk material is commonly encountered in corrosion, electrochemistry and materials ...preparation. We report a characterization technique to rapidly calculate the size distribution of nanoporous ligaments and facets from molecular-scale models that reveal the evolution of nanoporous morphology reaching experimental timescales. The key feature of our approach is the use of connectivity lists for sites, which enables rapid quantification of several million-atom large nanoporous structures while being sufficiently versatile to handle non-cylindrical cross-sections, detachment of ligaments from the main structure, and crystal facet-related quantities. As an application of this characterization tool, we find that the alloy composition has a significant effect on the charge transfer and the structure whereas the starting shape (nanowires, nanocubes and nanoparticles of same size) has a subtle effect particularly at early-to-intermediate stages of nanoporosity evolution. These conclusions cannot be arrived at by visual examination of the simulated structures. Ascertaining differences in structural features upon changing synthesis conditions using our approach will be relevant to porous materials such as those encountered in corrosion, batteries and geological systems.
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Markov state models (MSMs) of biomolecular systems are often constructed using the molecular dynamics (MD) technique. Despite having very long MD trajectories, some states and pathways can be missing ...in the MD data, which may make the MSMs incomplete. Consequently, uncertainty quantification for the resulting MSM becomes important. Using deca-alanine as a prototype system, we demonstrate that rare-event acceleration techniques can be employed to greatly lower the MSM uncertainty with a high computational efficiency with the assumption that the rare-event acceleration technique is able to determine most pathways that are relevant to the dynamics. In particular, we explore applications of steered MD to construct MSMs. Upper and lower bounds for uncertainty in the resulting MSM are derived. Safeguards are built into our approach to handle scenarios where the rare-event acceleration technique is unable to discover some important pathways.
Several studies in the past have generated Markov State Models (MSMs), i.e., kinetic models, of biomolecular systems by post-analyzing long standard molecular dynamics (MD) calculations at the ...temperature of interest and focusing on the maximally ergodic subset of states. Questions related to goodness of these models, namely, importance of the missing states and kinetic pathways, and the time for which the kinetic model is valid, are generally left unanswered. We show that similar questions arise when we generate a room-temperature MSM (denoted MSM-A) for solvated alanine dipeptide using state-constrained MD calculations at higher temperatures and Arrhenius relation — the main advantage of such a procedure being a speed-up of several thousand times over standard MD-based MSM building procedures. Bounds for rate constants calculated using probability theory from state-constrained MD at room temperature help validate MSM-A. However, bounds for pathways possibly missing in MSM-A show that alternate kinetic models exist that produce the same dynamical behaviour at short time scales as MSM-A but diverge later. Even in the worst case scenario, MSM-A is found to be valid longer than the time required to generate it. Concepts introduced here can be straightforwardly extended to other MSM building techniques.
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