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The detection of toxic molecules has gained imperial attention to protect living organisms and their environment. The broadly explored sensor behaviour of triazine-based C3N4 reveals their ultra-high sensitivity towards numerous toxic molecules e.g., chemical welfare agents. However, another potential analogue of C3N4 composed of heptazine exhibits remarkable electrical and optical properties but has not been much explored in sensor technology, especially for toxic pollutants. Keeping this in mind, the sensing performance of heptazine-based g-C3N4 is explored for the detection of toxic amides by using First Principles calculations. In this context, acryloyl amide (C2H3CONH2), acryloyl chloride (C2H3COCl), fluoroacetic acid (C2H3FCOOH), flouroaceta amide (C2H2FONH2), flouroacetyl chloride (C2H2FOCl) are selected as toxic pollutants; herein, for the ease of understanding, these molecules are represented as AAM, ACl, FAAc, FAA, & FACl, respectively. The electrochemical sensitivity of g-C3N4 is determined via geometric, energetic, and electronic properties analysis, whereas the photochemical sensitivity is explored by UV–Vis absorption analysis based on TD-DFT calculations. The interaction energies of studied molecules on C3N4 range between − 9.09 and - 23.39 kcal/mol depending upon the type of interactions e.g., hydrogen bonding or dispersion, which are explained on the basis of Symmetry Adopted Perturbation Theory, Non-Covalent Interaction Index, and Quantum Theory of Atoms in Molecules analyses. The density of State analysis, Frontier Molecular Orbitals and NBO charge transfer characterized that the electronic behaviour of g-C3N4 can be an effective sensor material with a semiconducting nature and significant charge transfer. Lastly, UV–Vis absorption analysis confirms the photosensitivity of g-C3N4 upon interaction with toxic molecules. [ABSTRACT FROM AUTHOR]

Graphyne (GYN) has received immense attention in gas adsorption applications due to its large surface area. The adsorption of toxic ammonia and nitrogen halides gaseous molecules on graphyne has been theoretically studied at ωB97XD/6–31 + G(d, p) level of DFT. The counterpoise corrected interaction energies of NH3, NF3, NCl3, and NBr3 molecules with GYN are − 4.73, − 2.27, − 5.22, and − 7.19 kcal mol−1, respectively. Symmetry-adapted perturbation theory (SAPT0) and noncovalent interaction index (NCI) reveal that the noncovalent interaction between analytes and GYN is dominated by dispersion forces. The significant change in electronic behavior, i.e., energies of HOMO and LUMO orbitals and NBO charge transfer correspond to the pronounced sensitivity of GYN towards considered analytes, especially NBr3. Finally, TD-DFT calculation reveals a decrease in electronic transition energies and shifting of adsorption to a longer wavelength. The recovery time for NX3@GYN is observed in nanoseconds, which is many orders of magnitude smaller than the reported systems. The recovery time is further decreased with increasing temperature, indicating that the GYN benefits from a short recovery time as a chemical sensor. [ABSTRACT FROM AUTHOR]

Though the gas sensing applications of graphdiyne have widely reported; however, the biosensing utility of graphdiyne needs to be explored. This study deals with the sensitivity of graphdiyne nanoflake (GDY) towards the uric acid (UA) within the density functional framework. The uric acid is allowed to interact with graphdiyne nanoflake from all the possible orientations. Based on these interacting geometries, the complexes are differentiated with naming, i.e., UA1@GDY, UA2@GDY, UA3@GDY, and UA4@GDY (Fig. 1). The essence of interface interactions of UA on GDY is derived by computing geometric, energetic, electronic, and optical properties. The adsorbing affinity of complexes is evaluated at ωB97XD/6–31 + G(d, p) level of theory. The stabilities of the complexes are quantified through the interaction energies (Eint) with reasonable accuracy. The calculated Eint of the UA1@GDY, UA2@GDY, UA3@GDY, and UA4@GDY complexes are − 31.13, − 25.87, − 20.59, and − 16.54 kcal/mol, respectively. In comparison with geometries, it is revealed that the higher stability of complexes is facilitated by π-π stacking. Other energetic analyses including symmetry adopted perturbation theory (SAPT), noncovalent interaction index (NCI), and quantum theory of atoms in molecule (QTAIM) provide the evidence of dominating dispersion energy in stabilizing the resultant complexes. The HOMO–LUMO energies, NBO charge transfer, and UV–vis analysis justify the higher electronic transition in UA1@GDY, plays a role of higher sensitivity of GDY towards the π-stacked geometries over all other possible interaction orientations. The present findings bestow the higher sensitivity of GDY towards uric acid via π-stacking interactions. [ABSTRACT FROM AUTHOR]

Promising sensor applications of graphdiyne for various gases and toxic molecules have extensively been studied; however, similar studies for the detection of chemical warfare agents (CWA) are not reported. Here, we report the adsorption of Lewisites (L1, L2, and L3), on graphdiyne nanoflake (GDY) using density functional theory (DFT) ωB97XD/6‐31+G (d,p) method. Our results show that Lewisite molecules are preferably physiosorbed at the triangular portion of GDY nanoflake. In particular, the binding of L3 (3‐chlorovinyl arsine) on GDY nanoflake is thermodynamically favorable than L1 (1‐chlorovinylarsonous dichloride) and L2 (2‐chlorovinylarsonous chloride). Symmetry adopted perturbation theory (SAPT0) analysis reveals that the least contribution of repulsive exchange component is present in case of L2@GDY complex. Further, the smallest HOMO‐LUMO energy gap, appreciable charge transfer (NBO), and largest red shift in ultraviolet‐visible (UV‐Vis) spectrum are also in accord with the higher %sensitivity of graphdiyne toward L2. Quantum theory of atom in molecule (QTAIM) analysis is performed to get insight into the noncovalent interactions. Therefore, it is predicted that the sensitivity of GDY nanoflake is potentially high for Lewisite especially for L2. [ABSTRACT FROM AUTHOR]

Linear conducting polymers are extensively studied as sensors for various analytes, whereas studies on cyclic analogues are limited. In this study, sensor applications of cyclic oligothiophenes (nCTs) have been explored by means of DFT (density functional theory) calculations. Three models, namely, five (5CT)-, six (6CT)- and seven (7CT)-membered cyclic oligothiophenes are evaluated against twelve different gaseous analytes. For optimization of geometries and interaction energies, the B3LYP method including Grimme's dispersion correction (B3LYP-D3) was applied with the 6-31++G(d,p) basis set. Chemical interactions of nCTs with NH3, CO, CO2, N2H4, HCN, H2O2, H2S, CH4, CH3OH, SO2, SO3 and H2O analytes are analyzed via interaction energies, Gibbs free energies, electronic properties and UV-Vis analysis. The interaction energies are quantitatively correlated with the volume of the cyclic oligothiophene (nCT). The electronic properties are calculated at the widely accepted B3LYP/6-31G(d) level of theory; however, the TD-B3LYP/6-31G(d) method is used for the UV-Vis analysis. Symmetry-adapted perturbation theory reveals that the 5CT system is highly sensitive towards analytes as compared to the 6CT and 7CT systems. This assumption is also strengthened by the HOMO–LUMO gaps and excited state properties. ESAPT, HOMO–LUMO gaps, NCI, and NBO charge transfer suggest that nCTs are highly sensitive towards SO3 followed by SO2. The density of state spectra shows the reasonable variation in the peaks of nCTs upon interaction with SO2 and SO3 analytes. The findings of this study suggest that cyclic oligothiophenes can effectively be used for the rational design of atmospheric sensors, which are superior to the conventional sensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption of hazardous CH 3 X (X = F, Cl & Br) molecules on C 4 H 4 NH, C 4 H 4 O, C 4 H 4 S and C 6 H 6 monomer units has been studied. • The adsorption behaviors are evaluated by the geometric conformations, adsorption energies, SAPT and QTAIM topological analyses. • The effect of fluorination on the adsorption behavior is quantified. • The increase in adsorption strength is observed for the fluorinated adsorbents. Despite the numerous publications describing the synthesis and electronic properties of fluorinated furan, thiophene and pyrrole, the systematic overview of their adsorption applications is still lacking. In this study, the effect of fluorination on the adsorption properties of furan (C 4 H 4 O), thiophene (C 4 H 4 S), pyrrole (C 4 H 4 NH) and benzene (C 6 H 6) are investigated with the help of density functional theory (DFT) calculations. Herein, the adsorption energies of CH 3 X (X = F, Cl & Br) on C 4 H 4 O, C 4 H 4 S, C 4 H 4 NH and C 6 H 6 and their fluorinated analogues are calculated using ωB97XD/6-31+G(d, p) level of theory. The results of the adsorption energies and symmetry adapted perturbation theory (SAPT0) reveal that the adsorption affinity of adsorbent is enhanced upon fluorination due to the increasing dispersion forces. To comprehensively investigate the variation in the electronic properties of nonfluorinated and fluorinated systems, the HOMO, LUMO orbitals and NBO charges are analyzed. The isosurfaces of orbitals show that the electron density is more localized onto the fluorinated adsorbents which are probably due to the presence of multiple electronegative fluorine atoms. Owing to the electron-withdrawing nature of fluorine, the electronic charges are transferred from CH 3 X to fluorinated adsorbents while the charges are shifted from nonfluorinated adsorbents to CH 3 X. Furthermore, the TD-DFT calculations reveal that the electronic transition energies are significantly decreased in most of the fluorinated complexes especially, CH 3 X@C 4 F 4 S and CH 3 X@C 4 F 4 NH. With these findings, it can be postulated that fluorine substitution can significantly surge the electronic and adsorption properties of sensor materials. [ABSTRACT FROM AUTHOR]

The chemical warfare agents (CWAs) are highly toxic for living systems and environment. These diverse effects of CWAs, especially blistering agents, need the development of highly selective sensors for their rapid and effective detection. Herein, by using density functional theory calculations, we explained the adsorption of nitrogen (NM) and sulphur mustard (SM) blistering agents on graphdiyne (GDY) sheet. The calculated adsorption energies illustrate the physisorption of blistering (SM & NM) agents on the graphdiyne surface. The symmetry adopted perturbation theory (SAPT) analysis predicts that the dispersion is a dominating component of interaction energy. Reduced density gradient (RDG) and quantum theory of atoms in molecules (QTAIM) analyses are performed to justify the nature of interactions. Based on QTAIM analysis, the interaction energies between graphdiyne and blistering agents are noncovalent in nature. Furthermore, RDG results reveals that the van der Waals interactions i.e., dispersion forces dominate in the complexes. The %sensitivity and average energy gap variations are illustrated by HOMO-LUMO gaps. The detection ability of graphdiyne is further studied using UV–Vis analysis, NBO charge transfer and density of state analysis. These properties depict the appreciable sensitivity of graphdiyne towards blistering agents (SM and NM). We believe that the results of this study are fruitful for experimentalist to design highly sensitive CWAs sensors using graphdiyne sheet. Unlabelled Image • The adsorption of blistering agents on GDY is studied by ωB97XD/6-31+G(d,p) method of DFT. • Adsorption behaviour is elucidated by SAPT, RDG and QTAIM analyses. • The dispersion forces dominate between BA-GDY complexes. • This study shows that GDY sheet has high sensitivity towards blistering agents. [ABSTRACT FROM AUTHOR]

Despite the numerous publications describing the photocatalytic and electronic properties of heptazine-based C 3 N 4 , the systematic study on the sensing behavior of pure heptazine-C 3 N 4 toward harmful chemical warfare agents (CWAs) is still lacking. Herein, we performed DFT calculations to investigate the adsorption behavior of C 3 N 4 toward various harmful and toxic CWAs including formaldehyde (OCH 2), thioformaldehyde (SCH 2), phosgene (OCCl 2), and thiophosgene (SCCl 2). ωB97XD functional of DFT along with 6–31G (d, p) basis set is used for all calculations for accurate estimation of noncovalent interactions. The CWAs are physiosorbed onto the C 3 N 4 having calculated interaction energy between −16.01 and −11.00 kcal/mol. Noncovalent interactions are further analyzed by symmetry-adapted perturbation theory (SAPT0), noncovalent interaction index (NCI), and quantum theory of atoms in molecules (QTAIM) analyses. The electronic behavior is characterized by the HOMO and LUMO energies, their energy gaps, and natural bond orbital (NBO) charge transfer. The charge transportation either donation or back donation is characterized by energy density difference (EDD) and charge decomposition analysis (CDA) analyses. The results demonstrate the trend of sensitivity of C 3 N 4 for toxic gases is OCH 2 @C 3 N 4 > SCH 2 @C 3 N 4 > OCCl 2 @C 3 N 4 > SCCl 2 @C 3 N 4. This theoretical work suggests that the C 3 N 4 can act as a good electrochemical sensor for a variety of toxic gaseous molecules. [Display omitted] • The sensing abilities of C 3 N 4 towards toxic molecules have been characterized by using ωB97XD/6-31G(d, p) level of DFT. • The sensing behavior of C 3 N 4 is studied through interaction geometries, energies, and electronic properties. • Among designed structures, OCH 2 @h-g-C 3 N 4 exhibits the strongest interaction due to electrostatic interactions. • C 3 N 4 exhibits significant sensitivity towards toxic molecules. [ABSTRACT FROM AUTHOR]