Department of Chemistry

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Author: search.filters.author.Dr. Mazhar Amjad GilaniSubject: search.filters.subject.FA19

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    A First Principle Study on Sensing Properties of Twisted Nanographenes Towards Phosgene, Thiophosgene and Formaldehyde
    (Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Naila Sattar; FA19-R06-007; Dr. Mazhar Amjad Gilani; LHR TP 7324
    The harmful chemicals like chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) are extremely pernicious to the climate and living systems. The efficient detection and removal of these noxious chemicals in limited time span is essential for the human health and environmental security. Twisted nanographenes have great applications in the fields of energy storage and optoelectronics, but their applications as sensors are rarely described. Therefore, we have explored theoretically the sensitivity and selectivity of twisted nanographenes C32H16, C64H32 towards the harmful chemicals like phosgene, thiophosgene and formaldehyde. Here, we elaborate the phenomena of adsorption of the selected toxic chemicals on twisted nanographenes' surface within the framework of density functional theory (DFT). Adsorption interpretation is depending upon the optimized geometries, adsorption energies, NBO (natural bond orbital) charge transfer, frontier molecular orbital (FMO), absorption (UV-Vis), NCI (non-covalent interaction) and QTAIM (quantum theory of atoms in molecules) analyses. Results of interaction energies reveal the physiosorption of the toxic chemicals on the twisted nanographenes surface, which mainly arise due to the non-covalent interactions. The non-covalent nature of adsorption of toxic chemicals on twisted nanographenes surface is also ascribed by the NCI and QTAIM analyses. Most favorable adsorptions of the selected toxic chemicals occur at the edges of the distorted moiety (central ring). The average band gap changes (%Eg) and %sensitivity is quantitatively determined by the molecular orbital analysis, to evaluate the sensitivity of twisted nanographenes. Among the selected chemicals, the sensing of thiophosgene (ThP) is prominent on the twisted nanographenes surface, having interaction energies of -8.19 and -12.14 kcal mol-1 (in case of C32H16 and C64H32 tNGs), respectively. Therefore, it is concluded that twisted nanographenes can be applied as a potential sensing agent for the detection of toxic chemicals, especially thiophosgene. This x research will help the experimentalists to devise novel sensors based on twisted nanographenes.
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    Theoretical Prediction of Nocturnal/Diurnal and Seasonal Real World Absorption Spectra of Polycyclic Aromatic Hydrocarbons and their Derivatives in Two Chinese Polluted Cities
    (Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Sahiba Fareed; FA19-R06-014; Dr. Mazhar Amjad Gilani; LHR TP 7320
    Brown carbon (BrC) is an organic aerosol, released during combustion of organic matter. It strongly absorbs solar radiations hence, plays an important role in radiative forcing. Neglecting brown carbon from climate models leads to difference between theoretical and experimental works. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are the major constituents of the BrC and they are persistent environmental pollutants. Their study is the need of hour as they are ubiquitous in atmosphere and carcinogenic in nature. Our strategy here is to utilize time dependent-density functional theory (TD-DFT) to model the absorption spectra of PAHs and their derivatives in two Chinese industrial sites: Qingcheng district (site A) and Longtang town of Qingyuan (site B). These data are corrected for “Real-world” experimental concentrations of PAHs over these cities. For the first time, nocturnal/diurnal and seasonal variations of PAHs are being studied at a time in these Chinese regions. These findings show that most relevant absorption regions for climate forcing are ~320nm, ~380nm and ~430nm. Moreover, almost all the absorption at site A and B takes place mainly due to PAHs while OPAHs and NPAHs play a very negligible part in absorption. Site A is highly affected by climate forcing caused by these PAHs. Absorption in winter is higher as compared to that of in summer. Furthermore, this model infers that relevant contributors to absorption at ~320nm are PAHs and OPAHs while absorption at ~380nm is attributed only to PAHs. Absorption at ~430nm is mainly explained by PAHs and NPAHs. Most of the absorption takes place in UVA and visible regions of the electromagnetic spectrum. More specifically, from the 35 studied PAHs and their derivatives, the major contributors towards radiative forcing are DBA (dibenzo[ah]anthracene), BaA (benz[a]anthracene) and BkF (benzo[k]fluoranthene) (PAHs). While among OPAHs and NPAHs, major contributors are Bpone (6H-benzo[c,d]pyrene-6-one), Bzdion (Benzo[a]anthracene-7,12-dione) and 7NBaA (7-nitrobenz[a]anthracene). Thus, our x theoretical modeling approach remarkably identifies the most relevant PAHs, OPAHs and NPAHs for climate forcing in this Chinese region.