Carbon nitride 2-D surface as a highly selective electrochemical sensor for V-series nerve agents

Recent advances in sensing toxic nerve agents through DMMP model simulant using diverse nanomaterials-based chemical sensors

Recent terrorist assaults have demonstrated the need for the exploration and design of sustainable and stable chemical sensors with quick reaction times combined with great sensitivity. Among several classes of chemical warfare agents, nerve agents have been proven to be the most hazardous. Even short-term exposure to them can result in severe toxic effects. Human beings inadvertently face the after-effects of these chemicals even several years after these chemicals were used. Due to the extreme toxicity and difficulty in handling, dimethyl methylphosphonate (DMMP), a simulant of nerve agents with much lesser toxicity, is frequently used in laboratories as a substitute. Having a chemical structure almost identical to those of nerve agents, DMMP can mimic the properties of nerve agents. Through this paper, authors have attempted to introduce the evolution of several chemical sensors used to detect DMMP in recent years, including field-effect transistors, chemicapacitors, chemiresistors, and mass-sensitive sensors. A detailed discussion of the role of nanomaterials as chemical sensors in the detection of DMMP has been the main focus of the work through a comprehensive overview of the research on gas sensors that have been reported making use of the properties of a wide range of nanomaterials.

A-agents, misleadingly known as "Novichoks": a narrative review

"Novichok" refers to a new group of nerve agents called the A-series agents. Their existence came to light in 2018 after incidents in the UK and again in 2020 in Russia. They are unique organophosphorus-based compounds developed during the Cold War in a program called Foliant in the USSR. This review is based on original chemical entities from Mirzayanov's memoirs published in 2008. Due to classified research, a considerable debate arose about their structures, and hence, various structural moieties were speculated. For this reason, the scientific literature is highly incomplete and, in some cases, contradictory. This review critically assesses the information published to date on this class of compounds. The scope of this work is to summarize all the available and relevant information, including the physicochemical properties, chemical synthesis, mechanism of action, toxicity, pharmacokinetics, and medical countermeasures used to date. The environmental stability of A-series agents, the lack of environmentally safe decontamination, their high toxicity, and the scarcity of information on post-contamination treatment pose a challenge for managing possible incidents.

Transition Metal Sensing with Nitrogenated Holey Graphene: A First-Principles Investigation

The toxicity of transition metals, including copper(II), manganese(II), iron(II), zinc(II), hexavalent chromium, and cobalt(II), at elevated concentrations presents a significant threat to living organisms. Thus, the development of efficient sensors capable of detecting these metals is of utmost importance. This study explores the utilization of two-dimensional nitrogenated holey graphene (C₂N) nanosheet as a sensor for toxic transition metals. The C₂N nanosheet's periodic shape and standard pore size render it well suited for adsorbing transition metals. The interaction energies between transition metals and C₂N nanosheets were calculated in both gas and solvent phases and were found to primarily result from physisorption, except for manganese and iron which exhibited chemisorption. To assess the interactions, we employed NCI, SAPT0, and QTAIM analyses, as well as FMO and NBO analysis, to examine the electronic properties of the TM@C₂N system. Our results indicated that the adsorption of copper and chromium significantly reduced the HOMO-LUMO energy gap of C₂N and significantly increased its electrical conductivity, confirming the high sensitivity of C₂N towards copper and chromium. The sensitivity test further confirmed the superior sensitivity and selectivity of C₂N towards copper. These findings offer valuable insight into the design and development of sensors for the detection of toxic transition metals.

Efficient Detection of Nerve Agents through Carbon Nitride Quantum Dots: A DFT Approach

V-series nerve agents are very lethal to health and cause the inactivation of acetylcholinesterase which leads to neuromuscular paralysis and, finally, death. Therefore, rapid detection and elimination of V-series nerve agents are very important. Herein, we have carried out a theoretical investigation of carbon nitride quantum dots (C₂N) as an electrochemical sensor for the detection of V-series nerve agents, including VX, VS, VE, VG, and VM. Adsorption of V-series nerve agents on C₂N quantum dots is explored at M05-2X/6-31++G(d,p) level of theory. The level of theory chosen is quite adequate in systems describing non-bonding interactions. The adsorption behavior of nerve agents is characterized by interaction energy, non-covalent interaction (NCI), Bader's quantum theory of atoms in molecules (QTAIM), frontier molecular orbital (FMO), electron density difference (EDD), and charge transfer analysis. The computed adsorption energies of the studied complexes are in the range of -12.93 to -17.81 kcal/mol, which indicates the nerve agents are physiosorbed onto C₂N surface through non-covalent interactions. The non-covalent interactions between V-series and C₂N are confirmed through NCI and QTAIM analysis. EDD analysis is carried out to understand electron density shifting, which is further validated by natural bond orbital (NBO) analysis. FMO analysis is used to estimate the changes in energy gap of C₂N on complexation through HOMO-LUMO energies. These findings suggest that C₂N surface is highly selective toward VX, and it might be a promising candidate for the detection of V-series nerve agents.

Effective Degradation of Novichok Nerve Agents by the Zirconium Metal-Organic Framework MOF-808

Novichoks are a novel class of nerve agents (also referred to as the A-series) that were employed in several poisonings over the last few years. This calls for the development of novel countermeasures that can be applied in protective concepts (e.g., protective clothing) or in decontamination methods. The Zr metal-organic framework MOF-808 has recently emerged as a promising catalyst in the hydrolysis of the V- and G-series of nerve agents as well as their simulants. In this paper, we report a detailed study of the degradation of three Novichok agents by MOF-808 in buffers with varying pH. MOF-808 is revealed to be a highly efficient and regenerable catalyst for Novichok agent hydrolysis under basic conditions. In contrast to the V- and G-series of agents, degradation of Novichoks is demonstrated to proceed in two consecutive hydrolysis steps. Initial extremely rapid P-F bond breaking is followed by MOF-catalyzed removal of the amidine group from the intermediate product. The intermediate thus acted as a competitive substrate that was rate-determining for the whole two-step degradation route. Under acidic conditions, the amidine group in Novichok A-230 is more rapidly hydrolyzed than the P-F bond, giving rise to another moderately toxic intermediate. This intermediate could in turn be efficiently hydrolyzed by MOF-808 under basic conditions. These experimental observations were corroborated by density functional theory calculations to shed light on molecular mechanisms.

Computational investigation of a covalent triazine framework (CTF-0) as an efficient electrochemical sensor

In the current study, a covalent triazine framework (CTF-0) was evaluated as an electrochemical sensor against industrial pollutants i.e., O₃, NO, SO₂, SO₃, and CO₂. The deep understanding of analytes@CTF-0 complexation was acquired by interaction energy, NCI, QTAIM, SAPT0, EDD, NBO and FMO analyses. The outcome of interaction energy analyses clearly indicates that all the analytes are physiosorbed onto the CTF-0 surface. NCI and QTAIM analysis were employed to understand the nature of the non-covalent interactions. Furthermore, SAPT0 analysis revealed that dispersion has the highest contribution towards total SAPT0 energy. In NBO analysis, the highest charge transfer is obtained in the case of SO₃@CTF-0 (−0.167 e⁻) whereas the lowest charge transfer is observed in CO₂@CTF-0. The results of NBO charge transfer are also verified through EDD analysis. FMO analysis revealed that the highest reduction in the HOMO–LUMO energy gap is observed in the case of O₃ (5.03 eV) adsorption onto the CTF-0 surface, which indicates the sensitivity of CTF-0 for O₃ analytes. We strongly believe that these results might be productive for experimentalists to tailor a highly sensitive electrochemical sensor using covalent triazine-based frameworks (CTFs).

In the current study, a covalent triazine framework (CTF-0) was evaluated as an electrochemical sensor against industrial pollutants i.e., O₃, NO, SO₂, SO₃, and CO₂.

Nano-porous C4N as a toxic pesticide's scavenger: A quantum chemical approach

The sensing affinity of C₄N is the most fascinating topic of research due to its excellent chemical and electronic properties. Moreover, owing to the highly active porous cavity, C₄N can easily accommodate foreign molecules. Herein, we studied the adsorption properties of carbamate insecticides (CMs) namely, Dimetalin (DMT), Carbanolate (CBT), Isolan (ISO) and Propoxur (PRO) using density functional theory calculations. All the results are calculated at widely accepted ωB97XD functional along with 6-31G(d, p) basis set. The calculated counterpoise corrected interaction energy of the reported complexes ranges between -20.05 and -27.04 kcal/mol, however, the interaction distances are found to be higher than 2.00 Å. The values of interacting parameters depict that the carbamate molecules are physisorbed via noncovalent interactions that can easily be reversible. Moreover, the binding of selected insecticides notably changes the electronic structure of C₄N. The electronic changes are characterized by the energies of HOMO & LUMO, their energy gaps and CHELPG charge transfer. The charge density difference between C₄N surface and carbamate pesticides are characterized by EDD and CDA analysis. Moreover, the ab initio molecular dynamic study reveals that the complexes are stable even at 500 K. The photochemical sensing properties of C₄N are estimated by time dependent UV-Vis calculations. The high sensitivity of C₄N towards considered analytes enable it to act as a promising sensor for toxic pesticides.

Adsorption, Gas-Sensing, and Optical Properties of Molecules on a Diazine Monolayer: A First-Principles Study

Using first-principles calculations, the structural, electronic, and optical properties of CO2, CO, N2O, CH4, H2, N2, O2, NH3, acetone, and ethanol molecules adsorbed on a diazine monolayer were studied to develop the application potential of the diazine monolayer as a room-temperature gas sensor for detecting acetone, ethanol, and NH3. We found that these molecules are all physically adsorbed on the diazine monolayer with weak adsorption strength and charge transfer between the molecules and the monolayer, but the physisorption of only NH3, acetone, and ethanol remarkably modified the electronic properties of the diazine monolayer, especially for the obvious change in electric conductivity, showing that the diazine monolayer is highly sensitive to acetone, NH3, and ethanol. Further, the adsorption of NH3, acetone, and ethanol molecules remarkably modifies, in varying degrees, the optical properties of the diazine monolayer, such as work function, absorption coefficient, and the reflectivity, whereas adsorption of other molecules has infinitesimal influence. The different adsorption behaviors and influences of the electronic and optical properties of molecules on the monolayer show that the diazine monolayer has high selectivity to NH3, acetone, and ethanol. The recovery time of NH3, acetone, and ethanol molecules is, respectively, 1.2 μs, 7.7 μs, and 0.11 ms at 300 K. Thus, the diazine monolayer has a high application potential as a room-temperature acetone, ethanol, and NH3 sensor with high performance (high selectivity and sensitivity, and rapid recovery time).

Effective adsorption of A-series chemical warfare agents on graphdiyne nanoflake: a DFT study

Chemical warfare agents (CWAs) are highly poisonous and their presence may cause diverse effects not only on living organisms but also on environment. Therefore, their detection and removal in a short time span is very important. In this regard, here the utility of graphdiyne (GDY) nanoflake is studied theoretically as an electrochemical sensor material for the hazardous CWAs including A-230, A-232, and A-234. Herein, we explain the phenomenon of adsorption of A-series CWAs on GDY nanoflake within the density functional theory (DFT) framework. The characterisation of adsorption is based on optimised geometries, BSSE-corrected energies, SAPT0, RDG, FMO, CHELPG charge transfer, QTAIM and UV-Vis analyses. The calculated counterpoise adsorption energies for reported complexes range from - 13.70 to - 17.19 kcal mol^-1. These adsorption energies show that analytes are physiosorbed onto GDY which usually takes place through noncovalent interactions. The noncovalent adsorption of CWAs on GDY is also attributed by the SAPT0, RDG and QTAIM analyses. These properties also reveal that dispersion factors dominate in the complexes among many noncovalent components (exchange, induction, electrostatic, steric and repulsion). In order to estimate the sensitivity of GDY, the %sensitivity and average energy gap variations are quantitatively measured by energies of HOMO and LUMO orbitals. In terms of adsorption affinity of GDY, UV-Vis analysis, CHELPG charge transfer and DOS analyses depict an appreciable response towards these toxic CWAs. Graphical abstract.

Remarkable enhancement in sensor ability of polyaniline upon composite formation with ZnO for industrial effluents

Polyaniline emeraldine salt and Polyaniline Zinc Oxide composite are comprehensively studied to compare their sensing ability towards ammonia, acetone, methanol and ethanol. Sensing ability is evaluated through thermodynamic, geometric and electronic parameters. A number of orientations are evaluated in search for the lowest energy structure. The comparison of thermodynamic, geometric and electronic parameters of simple and composite sensors confirmed that composite sensor shows better sensing ability than simple PANI. Composite formation between polyaniline and zinc oxide is a thermodynamically feasible process with interaction energy of -42.8 kcal/mol. Both sensor shows highest interaction energy for ethanol among four analytes. Composite sensor shows almost twice the interaction with ethanol, methanol and acetone while 1.5 times the interaction energy for ammonia. The results of run simulations and subsequent calculations showed that in composite sensors, zinc oxide not only enhances the binding power of conducting polymer with analytes but also interacts directly with analytes. Strong hydrogen bonding as well as weak dispersion forces of attraction are responsible for the stability of composite and all complexes, as revealed by non-covalent interaction (NCI) studies. Acetone shows a different behaviour in composite sensor complex than other analytes.

The C2N surface as a highly selective sensor for the detection of nitrogen iodide from a mixture of NX3 (X = Cl, Br, I) explosives

Explosives are quite toxic and destructive; therefore, it is necessary to not only detect them but also remove them. The adsorption behavior of NX₃ analytes (NCl₃, NBr₃ and NI₃) over the microporous C₂N surface was evaluated by DFT calculations. The nature of interactions between NX₃ and C₂N was characterized by adsorption energy, NCI, QTAIM, SAPT0, NBO, EDD and FMO analysis. The interaction energies of NX₃ with C₂N are in the range of −10.85 to −16.31 kcal mol⁻¹ and follow the order of NCl₃@C₂N > NBr₃@C₂N > NI₃@C₂N, respectively. The 3D isosurfaces and 2D-RGD graph of NCI analysis qualitatively confirmed the existence of halogen bonding interactions among the studied systems. Halogen bonding was quantified by SAPT0 component energy analysis. The SAPT0 results revealed that ΔE_disp (56.75%) is the dominant contributor towards interaction energy, whereas contributions from ΔE_elst and ΔE_ind are 29.41% and 14.34%, respectively. The QTAIM analysis also confirmed the presence of halogen bonding between atoms of NX₃ and C₂N surface. EDD analysis also validated NCI, QTAIM and NBO analysis. FMO analysis revealed that the adsorption of NI₃ on the C₂N surface caused the highest change in the E_HOMO–LUMO gap (from 5.71 to 4.15 eV), and resulted in high sensitivity and selectivity of the C₂N surface towards NI₃, as compared to other analytes. It is worth mentioning that in all complexes, a significant difference in the E_HOMO–LUMO gap was seen when electronic transitions occurred from the analyte to the C₂N surface.

Explosives are quite toxic and destructive; therefore, it is necessary to not only detect them but also remove them.

Superhalogen doping: a new and effective approach to design materials with excellent static and dynamic NLO responses

The first-ever example where superhalogen doping alone is introduced as a new and effective approach to impart large NLO responses.