Application of Cs/GO/TiO2 as Gas Sensor

Application of Cs/GO/TiO2 as Gas Sensor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Application of Cs/GO/TiO 2 as Gas Sensor Amged G. El-Srougy, Khaled S. Amin, Mohamed M. Mahmoud, Mahmoud S. Ghanem, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6321789/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Aug, 2025 Read the published version in Scientific Reports → Version 1 posted 14 You are reading this latest preprint version Abstract Chitosan a biodegradable, cheap polymer is a good choice for gas sensors. In this study, chitosan (Cs) was modified with graphene oxide (GO) and titanium dioxide (TiO 2 ), and its electronic properties were calculated using density functional theory (DFT) at B3LYP/LANL2DZ level. The calculated physical parameters includes total dipole moment (TDM), HOMO/LUMO energy gap (ΔE), global reactivity descriptors and density of states (DOS) and mapping the electrostatic potential (MESP). Results indicated Cs had significant modification such as enhanced ΔE from 6.908 to 2.197 eV and TDM from 5.884 to 14.432 Debye, global reactivity revealed enhanced reactivity with increased absolute softness and high electrophicility index. DOS show more available states and more localized HOMO/LUMO orbitals all enhance charge transfer. MESP shows reactivity and active sites for the interaction with its surrounding. The nanocomposite Cs/GO/TiO 2 is supposed to interact with three different gases; H 2 O, CO 2 , and CH 4 . The results exhibited changes in the ΔE and TDM, with Cs/GO/TiO 2 /CO 2 have the most pronounced changes. Partial density of states PDOS plots exhibited Ti atoms contribution in HOMO orbitals and LUMO with Cs/GO/TiO 2 /CO 2 having the most changes in its energy states. Adsorption energy E a was calculated and showed selectivity for CO 2 gas with − 0.104 eV indicating spontaneous interaction. Quantum theory of atoms in molecules confirmed the weak interaction with gases molecules and the enhanced stability via hydrogen bonding. The Cs/GO/TiO 2 nanocomposite was synthesized and FT-IR spectroscopy were conducted and compared with calculated IR to verify the models. Physical sciences/Materials science Physical sciences/Physics Chitosan GO DFT: B3LYP/LANL2DZ Gas Sensor TiO2 nanocomposite QTAIM Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction Biopolymers have garnered significant interest in sensor technology because of their environmentally friendly characteristics, availability, and straightforward processing [ 1 ]. Every year, around 100 billion tons of chitin is produced naturally on our planet by crustaceans, mollusks, insects, fungi, and similar organisms. At present, the extraction of chitin in industrial settings primarily depends on chemical techniques and the utilization of marine shell waste streams [ 2 ]. Chitosan (Cs), a random copolymer derived from chitin, demonstrates significant versatility. In acidic environments, the amino groups along its polymer chains become protonated, resulting in the polymer being cationic. This distinctive characteristic allows chitosan to engage with a wide variety of molecules, setting it apart as the sole cationic marine polysaccharide. The positive charge is thought to play a crucial role in its antimicrobial activity [ 3 ], considering its plentiful availability and remarkable functional characteristics including biocompatibility, bioactivity, biodegradability, and impressive mechanical strength [ 2 , 4 ]. The field of gas sensing is essential for identifying dangerous gases, keeping an eye on air quality, and guaranteeing environmental safety. While traditional gas sensors often utilize materials like metal oxides and semiconductors, there is a growing demand for sustainable, cost-effective, and environmentally friendly alternatives [ 5 ]. Chitosan, with its excellent film-forming ability and hydrophilic nature, has emerged as a promising candidate for gas sensing applications. Chitosan's gas-sensing capabilities can be further enhanced by incorporating other materials. For example, chitosan's responsiveness and reproducibility in detecting acetone gas are much improved when combined with metal oxides, like SnO 2 , leading to larger output voltages and improved performance [ 6 ]. Similarly, hybrid films created by blending chitosan with conductive polymers like polypyrrole (Ppy) or nanoparticles such as zinc oxide (ZnO) exhibit improved electrochemical properties. These hybrid materials demonstrate high selectivity and responsiveness toward specific gases, such as hydrogen [ 7 – 8 ]. Chitosan's abundance of hydroxyl (-OH) and amino (-NH 2 ) groups further enhances its hydrophilicity. The adsorption of water molecules is facilitated by these functional groups, increasing its sensitivity to variations in humidity and bolstering its potential for advanced environmental monitoring applications [ 9 ]. The incorporation of graphene oxide (GO) can enhances the performance of chitosan by providing high surface area, good electrical conductivity, and high oxygen-containing functional groups. Synergism between chitosan and GO causes a substantial improvement in the electrical and sensing properties of the composite material. incorporation of GO into chitosan not only changes the band gap but also enhances the charge transfer characteristics, which are extremely important for increased sensitivity and responsivity of the sensors [ 10 – 11 ]. In addition, GO/chitosan composites have been reported to greatly improve the mechanical stability and strength of the composite material and make the composite material stronger for diverse sensing purposes [ 12 ]. Furthermore, the oxygen-functional groups in GO enhance the interaction with target molecules, which makes sensors more sensitive and selective [ 13 – 14 ]. Titanium dioxide (TiO₂) is a prominent n-type semiconductor characterized by a band gap of around 3 eV. Its advantageous catalytic properties, durability, and environmental safety render it useful in a range of applications, such as gas sensors, solar cells, and photocatalytic processes [ 15 – 16 ]. TiO₂ is found in three primary crystalline forms: rutile, anatase, and brookite, with rutile being the most stable thermodynamically [ 17 ]. Gas sensors based on TiO₂ are extensively utilized for the detection of harmful gases, owing to their sensitivity, rapid response times, and affordability [ 18 ]. The incorporation of nanostructures significantly enhances the gas-sensing performance by increasing the surface-to-volume ratio, which facilitates the detection of various gases, including ozone, ethanol, acetone, hydrogen, and carbon monoxide [ 19 – 22 ]. Molecular modeling has been a powerful approach to elucidate electronic properties for many molecular systems. It became useful in studying the behavior and mechanism of interaction for sensors [ 23 – 24 ]. It was reported that, for gas sensing phenomena DFT could support the experimental findings and became an important tool in this filed [ 25 ]. The present work investigates the synthesis and modeling of a Cs/GO/TiO₂ nanocomposite utilizing density functional theory (DFT) for enhancement of biopolymer applications. DFT at B3LYP/LANL2DZ level was applied to evaluate physical parameters including the total dipole moment (TDM), the HOMO–LUMO and energy gap (ΔE). The density of states (DOS), HOMO-LUMO frontier orbitals, global reactivity descriptors, and molecular electrostatic potential (MESP) will clarify the active sites and charge transfer mechanisms involved in gas interactions. Moreover, Quantum theory of atoms in molecules (QTAIM) was conducted to investigate non-covalent interactions, and the adsorption energies to investigate selectivity. Finally, a comparison between theoretical predictions and Fourier-transform infrared (FT-IR) spectra was conducted to confirm the computational models. This computational strategy aims to create advanced nanocomposite that combine polymeric materials and metal oxides, utilizing the advantages of Cs, GO, and TiO 2 which enhance their properties, especially for gas sensing applications with improved selectivity and sensitivity. Calculation Details The models have been investigated using the G09 program [ 26 ]. The structures were computed at Molecular Modeling and Spectroscopy Laboratory, Centre for Excellence for Advanced Science, National Research. For the structural optimizations calculations, the Los Alamos National Laboratory 2 double ζ (LANL2DZ) basis set and the B3LYP functional (which combines Becke's three-parameter exchange functional with the Lee-Yang-Parr correlation functional) were used [ 27 – 29 ]. Utilizing consistent computational methodology, the total dipole moment (TDM), highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) were calculated. The energy gap (∆E), derived from HOMO-LUMO energy difference. TDM and ∆E provides critical insights into molecular interaction potential and reactivity. The molecular electrostatic potential (MESP) allows for the visualization of the active sites. The Density of States (DOS) was graphically represented to elucidate electronic behavior. Global reactivity descriptors, including fundamental quantum chemical parameters such as Ionization Potential (IE), Electronic Affinity (A), Chemical Potential (µ), Chemical Hardness (η), Absolute Softness (S), and Electrophilicity Index (ω) [ 30 – 32 ], were systematically calculated using the following formulas: \(\:IE=-{E}_{HOMO}\) (1) \(\:A=-{E}_{LUMO}\) (2) \(\:\mu\:=-\frac{IE\:+A}{2}\) (3) \(\:\eta\:=\frac{IE-A}{2}\) (4) \(\:S=\frac{1}{\eta\:}\) (5) \(\:{\omega\:}=\frac{{\mu\:}^{2}}{2\eta\:}\) (6) The adsorption energy E a for studied nanocomposites interacting with the adsorbed gases was calculated by the equation [ 33 ]: E a = − [E system − (E adsorbent + E adsorbate )] QTAIM topology analysis was conducted with the use of Multiwfn and visual molecular dynamics (VMD) software [ 34 – 35 ], to investigate the interaction with the adsorbed gases and the nature of the bonds formed as well as the stability of the nanocomposites. Finally, frequency calculations were performed to confirm that the structures correspond to true minima and to compare them with the FTIR data to validate the DFT level of methodology. Materials and Methods Materials and Instrumentation Chitosan deacetylation degree 90% ±5 purchased from Chitosan Egypt LLC. Sulfuric acid (96%) was obtained from Scharlau and hydrogen peroxide from PIOCHEM (30%). Sodium hydroxide and ethanol were purchased from El Nasr Pharmaceutical Chemicals Co., Cairo, Egypt. Titanium tetraisopropoxide Ti (OC 3 H 7 ) 4 termed as TTIP was purchased from Sigma Aldrich – Germany. Ethyl alcohol (C 2 H 5 OH), Polyethylene glycol PEG (M.W 6000), and Acetic acid (CH 3 COOH) were purchased from El-Nasr Pharmaceutical Company, Egypt. Citric acid (99.5%), and sodium hydroxide (≥ 97%), phosphoric acid (85%), potassium permanganate (99%), and graphite powder were obtained from Fisher Chemical. Distilled water and deionized (DI) Milli-Q water was used during the preparations of samples. The Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectra were obtained using an FT-IR spectrometer (Vertex 70, Bruker), which have a spectral range of 4000–400 cm − 1 and a spectral resolution of 4 cm − 1 . Preparation of TiO Nano titanium dioxide TiO 2 synthesis was carried out using precipitation technique. By dissolving titanium tetraisopropoxide into absolute ethanol (in ice bath), while stirring at low base, water was added to the solution. To control the grain growth duo to hydrolysis process, drops from Acetic acid and polyethylene glycol were added to the solution while stirred at high speed for 2 hours. The solution then left over night for precipitation to occur. Then two layers formed, the upper layer was the organic byproducts of the hydrolysis, and the lower layer was a TiO 2 precipitate. After that the TiO 2 precipitate was filtered and washed several times with distilled water, then dried overnight at 100°C. the yellow crystal blocks obtained were grounded into fine powder then calcinated for 3 hours at 500°C to get pure anatase nanoparticle of TiO 2 . Preparation of GO The modified Hummer’s method was used to synthesize GO. 3 g of graphite flakes were mixed with 360 ml of sulfuric acid and 40 ml of phosphoric acid, the mixture is in a 9:1 ration and is stirred continuously. The mixture was cooled in an ice bath, and then 18 g of KMnO₄ was slowly added. The color of the mixture change from black (graphite color) to a dark olive green, while temperature was regulated between 0 and 5°C in order to minimize exothermic reactions. After stirring the mixture at 40°C overnight, the mixture was mixed with 400 ml of iced deionized water containing 30% of H₂O₂. The color changed from buffer violet to light brown after this step. The mixture was filtered with centrifugation at 10,000 rpm and washed discarding the supernatant. The filtrate obtained was dried at 70°C for five hours using an oven. Preparation of Cs/GO/TiO Cs was mixed with GO and TiO₂ to form a nanocomposite. Specifically, 0.25 g of Cs was dissolved in 50 mL of deionized water (2% acetic acid) under continuous stirring. Two samples were prepared, pure Cs of 0.250 g (100%) and a mixture containing 0.225 g of Cs (90%), 0.0125 g of GO (5%), and 0.0125 g of TiO₂ (5%). The samples were stirred for 30 minutes at 70°C. The Cs/GO/TiO 2 mixture were followed by 2–3 minutes of sonication to ensure uniform dispersion of GO within the nanocomposite. The resulting solutions were then drop-cast onto petri dishes and left to dry at room temperature for five days to form the final composite film. Results and Discussion Building Module Molecules Before commencing the DFT calculations, we constructed molecular models of the structures. Figure (1) display the model structures where figure (1-a) shows three units of chitosan (Cs). Figure (1-b) shows Graphene oxide (GO) like structure with COOH, OH functional groups. Figure (1-c) shows Cs interacting weakly with GO through H atom of COOH and amine group of the Cs. Figure (1-d) the Cs/GO interacted weakly with TiO 2 through terminal OH of GO via Ti atom of TiO 2 . Calculated Physical Parameters The TDM provides valuable information about electronic charge distribution in molecules, hence has a crucial role in the establishment of molecular polarity. Such polarity notably influences the chemical properties and reactivity of the molecules as well as their interaction with the molecules that surround them. Elevated values of TDM may suggest that the structure exhibits heightened reactivity and enhanced capacity for interaction with surrounding molecules [36]. The HOMO–LUMO gap (ΔE) represents the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). ΔE helps in understanding a molecule's electronic properties and charge transport phenomena, providing insights into its stability and reactivity. Moreover, ΔE helps in understanding the electronic transport characteristics of molecular systems [37-38]. TDM and ΔE were calculated for the studied models using B3LYB/LANL2DZ method; the results are recorded in table (1). In the case of Cs, TDM and ΔE were found to be 5.884 Debye and 6.908 eV respectively. When Cs interacted with GO the TDM decrease a little to become 5.489 Debye but the ΔE significantly decreased to 2.748 eV. The addition of TiO 2 further improved the ΔE values and reach to 2.197 eV and enhanced the TDM which reaching to 14.432 Debye. This means that the composite Cs/GO/TiO 2 is more reactive than Cs or Cs/GO alone. Table 1. Calculated TDM in Debye and ΔE in eV for the studied structures. Structures TDM (Debye) ΔE (eV) Cs 5.884 6.908 GO 3.861 2.758 Cs/GO 5.489 2.748 Cs/GO/TiO 2 14.432 2.197 Global Reactivity Descriptors HOMO and LUMO values were calculated using B3LYB/LANL2DZ method, and Global reactivity IE, A, µ, η, S and ω can be defined and computed by the equations (1:6). The calculated global reactivity descriptors for Cs, GO, Cs/GO and Cs/GO/TiO 2 composite were recorded in table 2. Ionization energy (IE) value for the composite Cs/GO/TiO 2 shows lower value than Cs (from 5.931 to 5.614 eV). This means that a lower energy is required to remove an electron from the surface of the structure. Electron affinity (A) of Cs increased significantly from -0.977 to 3.147 eV as Cs interacted with GO/TiO 2 which indicates more energy when electron added to the system [30]. Hardness (η) and softness (S) values can be described as an indication of the inhibition of inter-molecule transfer of charge. The composite Cs/GO/TiO 2 display much lower value for hardness (η) (1.099 eV) in compered with the pure Cs (3.454). While softness (S) value of pure Cs displayed the lower value (0.290 eV) than the composite Cs/GO/TiO 2 (0.910 eV) which indicate the more reactivity of the composite Cs/GO/TiO 2 . The composite also shows higher values for µ and ω compering with pure Cs, which indicate that the composite structure has tendency to accept electrons and have better electrophilic characteristics. Table 2. Calculated global reactivity descriptors in eV for the studied structures. Structure IE A μ η S ω Cs 5.931 -0.977 -2.477 3.454 0.290 0.888 GO 5.426 2.669 -4.048 1.379 0.725 5.941 Cs/GO 5.370 2.622 -3.996 1.374 0.728 5.812 Cs/GO/TiO 2 5.614 3.417 -4.515 1.099 0.910 9.279 Mapping Molecular Electrostatic Potential MESP The molecular electrostatic potential MESP were calculated using B3LYB/LANL2DZ method. MESP can shows the reactivity of molecules by a color code and show the active sites [39]. The color range from red to blue where red represents negative region and blue is positive region of electrostatic potential, while green color is more neutral. Figure (2) shows the calculated MESP for the studied structures. In figure (2-a), MESP of pure Cs show red regions around the O atoms and blue regions around the H atom of OH. For Cs/GO/TiO 2 nanocomposite (figure (2-d)), the structure shows more red region around the O atoms of TiO 2 indicating a more reactive structure to surrounding molecules [40]. Frontier Molecular Orbitals The HOMO/LUMO frontier molecular orbitals were calculated using B3LYB/LANL2DZ method. HOMO and LUMO are the most essential parameters in quantum chemistry [41]. In chemistry, HOMO and LUMO are types of molecular orbitals. The acronyms stand for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively, and the difference between them is called the HOMO–LUMO gap. The calculation of HOMO and LUMO gives information on the transfer of charge within the molecule [42]. Figure (3) presents the distribution of HOMO and LUMO frontier orbitals where the red color denotes the positive phase and the green color denote to the negative phase. The HOMO–LUMO map of pure Cs and GO molecules are shown in Figure (3-a) and (3-b) respectively. When Cs interacts with GO as shown in Figure (3-c) all the electronic charge activity, HOMO-LUMO, shifted to the GO molecule. When TiO 2 molecule is added to the Cs/GO structure as shown in Figure (3-d), HOMO localized on TiO 2 and the LUMO on GO this localization enhance charge transfer interactions. This indicate enhancement in charge transfer and electron mobility. Density of States DOS The density of states (DOS) for the studied structures calculated using DFT: B3LYB/LANL2DZ method is displayed in figure (4). DOS represent the number of states per energy level, where the green lines represent occupied orbitals and the red lines correspond to the unoccupied (virtual) orbitals. In Figure (4-c) the nanocomposite Cs/GO exhibit a decrease in bandgap compared to Cs alone (figure (4-a)). After the incorporation of TiO 2 the bandgap decreased further and the number available unoccupied stated near the Fermi level increased as shown in Figure (4-d). This enhancement in available states facilitates charge transfer, as evidenced by the shifted virtual orbitals toward the Fermi level Gas Sensing The Cs/GO/TiO 2 nanocomposite was proposed to interact with three different gasses H 2 O, CO 2 and CH 4 , the gases models can be shown in figure (5). The structures were optimized at the same computational level. The optimized structures are recorded in figure (6), where figure (6-a) present Cs/GO/TiO 2 nanocomposite, figure (6-b) presents Cs/GO/TiO 2 interacting with H 2 O, figure (6-c) presents Cs/GO/TiO 2 interacting with CO 2 and figure (6-d) presents Cs/GO/TiO 2 interacting with CH 4 . In these models, the O atom of TiO 2 was supposed to interact weakly with the gases molecules. Electronic properties including total dipole moment (TDM) and HOMO-LUMO energy gap (ΔE) were calculated to quantify changes induced by gas adsorption. Table (3) displays the changes in TDM and ΔE values of the nanocomposite upon interaction with H 2 O, CO 2 , and CH 4 gases. Compared to the pristine nanocomposite TDM and ΔE values (14.432 Debye and 2.197 eV), significant changes in both parameters were observed upon interaction with H 2 O, CO 2 , and CH 4 gases. This indicates a sensitivity of the nanocomposite to these gases. The largest variation was observed with CO 2 interaction, where TDM increased from 14.432 Debye to 22.292 Debye, and ΔE decreased from 2.197 eV to 1.661 eV. This change in pristine nanocomposite values suggests strong interaction and high sensitivity towards CO 2 sensing. In contrast, the CH 4 interaction demonstrated the minimum change in TDM, which decreased to 7.887 Debye, and ΔE increased to 3.163 eV. The interaction with H 2 O shows moderate changes with TDM decreasing to 9.411 Debye and ΔE increasing to 3.958 eV. Table 3. Calculated TDM in Debye and ΔE in eV for the studied structures. Structures TDM (Debye) ΔE (eV) Cs/GO/TiO 2 14.432 2.197 Cs/GO/TiO 2 /H 2 O 9.411 3.958 Cs/GO/TiO 2 /CO 2 22.292 1.661 Cs/GO/TiO 2 /CH 4 7.887 3.163 MESP were calculated for Cs/GO/TiO 2 interacted with gas molecules and some changes in the charge distribution occurred, due to the interaction. The red regions around O atoms of TiO 2 in figure (7-a) disappeared for Cs/GO/TiO 2 /H 2 O and a neutral surface is dominant (figure (7-b)). The Cs/GO/TiO 2 interacting with CO 2 in figure (7-c), shows more spread reactive regions (red and blue) which indicate that the nanocomposite is susceptible to more interaction with the gas molecules. The Cs/GO/TiO 2 interacting with CH 4 exhibit less reactivity as shown in figure (7-d). These MESP changes align with observed trends in TDM and ΔE modulation. The HOMO-LUMO frontier orbitals of Cs/GO/TiO₂ were analyzed post-interaction with gases. In the pristine nanocomposite ( Figure (8-a) ), the HOMO localizes on TiO₂, while the LUMO resides on GO. Interaction with H₂O ( Figure (8-b )) shifts the HOMO to GO and distributes the LUMO across both GO and TiO₂. For CH₄ adsorption in figure (8-d) the HOMO and LUMO are distributed on GO and TiO 2 . For CO₂ adsorption ( Figure (8-c) ), the HOMO occupies the amine group of Cs, and the LUMO remains on GO/TiO₂. These orbital redistributions highlight analyte-specific electronic modulation, aligning with observed TDM and ΔE trends. Partial Density of States (PDOS) The projection of a specific atom's orbital on the density of states is provided by PDOS, where the total density of state (DOS), can be obtained by adding up all of the projections. PDOS plots for Cs/GO/ TiO 2 nanocompiste and its interaction with the gases is displayed in figure (9). The Ti atom contributes the most in both the unoccupied (virtual) and occupied orbitals, followed by O atoms. PDOS plot for Cs/GO/TiO 2 is shown in figure (9-a), there is some changes in DOS upon interaction with the gases. Figure (9-c) represent PDOS for Cs/GO/TiO 2 interacting with CO 2 , the changes in the states with the introduction of new states in the unoccupied orbitals (black lines), this make charge transfer easier to occur. The changes in the DOS are not as potent for the other gases as shown in figure (9-b) and figure (9-d). Adsorption Energy To investigate the selectivity of Cs/GO/TiO 2 nanocomposite for the studied gases, adsorption energy E a were calculated, the results are recorded in table (4). If E a is positive value that means the interaction need energy to occur and the interaction is endothermic. In contrast, if E a is negative value that indicates the interaction is spontaneous and release energy. Adsorption energy results showed significant selectivity for CO 2 adsorption where E a have a value of -0.104 eV for the adsorption of CO 2 onto Cs/GO/TiO 2 nanocomposite. While E a of the adsorption with H 2 O and CH 4 gases onto Cs/GO/TiO 2 nanocomposite were found to be 4.000 eV and 4.396 eV respectively. Table 4. Calculated adsorption energy E a as eV for the studied gases onto Cs/GO/TiO 2 nanocomposite. Structure Adsorption energy (eV) Cs/GO/TiO 2 /H 2 O 4.000 Cs/GO/TiO 2 /CO 2 -0.104 Cs/GO/TiO 2 /CH 4 4.396 QTAIM Analyses The Quantum Theory of Atoms in Molecules (QTAIM) provides a platform to analyze chemical bonding and intermolecular interaction, including non-covalent interactions. QTAIM utilizes electron density represented as ρ(r), which estimates the probability of an electron at any given point in space [43-45]. QTAIM maps ρ(r) and display regions of high and low electron density. By analyzing ρ(r), the Laplacian of electron density (∇²ρ) and the energy density H(r) at bond critical points (BCPs) and the type of bonding can be evaluated. Figure (10) illustrates the QTAIM topology for the nanocomposite and its interaction with the studied gases. The figure displaying the critical (CPs) and electron density paths, it shows the non-covalent interactions hydrogen bonding that stabilize the structures especially for figure (10-c) and (10-d). Upon investigating the BCPs between the Cs/GO/TiO 2 and the gases, the results of ρ(r) < 0.2 a.u. and the positive values of ∇²ρ(r) and H(r) it indicate a weak interaction as proposed. Calculated IR spectra The infrared (IR) frequencies provide fingerprint information and can identify functional groups and other characteristic bands. Therefore, the IR frequencies of Cs/GO/TiO 2 were calculated using DFT: B3LYP functional with LANL2DZ basis set and then compared to measured FT-IR data. Figure (11) depicts the absorbance FT-IR spectra for Cs/GO/TiO 2 nanocomposite and the recorded band assignment in table (5). For Cs IR spectra, the range 3350 – 3190 cm -1 is assigned to O–H and N–H stretching vibrations [46-47]. Symmetric/asymmetric CH 2 stretching appears at 2930 – 2870 cm -1 [46]. The C=O in amide I and N–H stretching (amide II) were observed at 1640 cm -1 and 1547 cm -1 respectively [48-49]. Additionally, stretching vibrations of carbodiimides CH 3 stretching corresponds to 1403 cm -1 [49], and 1065 cm -1 to C–O stretching at [50-51]. For GO bands the O–H stretching appears at 3350 – 3190 cm -1 [52]. At 1063 cm -1 , the C–O epoxide stretching [52], while the band C=C were observed at 1640 cm -1 [52]. The C=O and O–C–O stretching appears at 1735 cm -1 and 1065 cm -1 respectively [52]. The band C–H stretching observed at 898 cm -1 [53]. The characteristic band of Ti–O–Ti vibration fall within the range of 900 –400 cm −1 were observed at 640 –566 cm -1 and Ti–O stretching at 486 cm -1 within the same range [54-55]. Noticeably, the N–H stretching (amide II) band in the composite shifted from 1540 cm -1 (in pure Cs) to 1547 cm -1 , indicating some physical interactions in the composite. Then the Computed IR frequencies were compared with FT-IR measured results as in table (6). The 3764 – 3705 cm -1 of O–H stretching corresponds to 3350 – 3190 cm -1 in FT-IR while N–H stretching vibration appears at 3549 – 3455 cm -1 which correspond to the FT-IR range of 3350 – 3190 cm -1 . The CH 2 stretching was found at 3137 – 3039 cm -1 match the experimental 2930 – 2870 cm -1 . The N–H in amide II was found at 1597 cm -1 matching the 1547 cm -1 . The C=C stretching corresponds to 1664 – 1639 cm -1 which match the FT-IR of 1640 cm -1 . The Ti–O stretching was found at 997 – 990 cm -1 matching the experimental value in the range 900 – 400 cm -1 . The agreements between computed and experimental spectra validate the computational method. Table 5. The band assignment of FT-IR results for pure Cs and Cs/GO/TiO 2 nanocomposite. Structure FI-IR Assignment Ref Cs 3350 – 3190 O–H N–H 46 47 2930 – 2870 CH 2 46 1640 C=O in amide I 48 1547 N–H amide II 49 1403 CH 3 48 1065 C–O 50-51 GO 3350 – 3190 O–H 52 1063 C–O epoxide 1640 C=C 1735 C=O 1065 O–C–O 898 C–H 53 TiO 2 640 – 566 Ti–O–Ti 54 486 Ti–O 55 Table 6. Computed IR frequencies compared with FT-IR measured results for Cs/GO/TiO 2 . Computed IR FT-IR Assignment 3764~3705 3350 – 3190 O–H stretching 3549~3455 3350 – 3190 N–H stretching 3137~3039 2930 – 2870 CH 2 stretching 1597 1547 N–H amide II 1664~1639 1640 C=C stretching 1574~1569 1735 C=O stretching 997~990 900 – 400 Ti–O stretching C Conclusion DFT:B3LYP/LANL2DZ was utilized to model Cs/GO/TiO₂ composite, then its interaction with H 2 O, CO 2 and CH 4 gases and studied their electronic properties. TDM, ΔE, global reactivity and MESP results indicated that the composite have the ability to interact with its surrounding molecules. The Cs/GO/TiO₂/CO₂ system exhibits optimal sensing characteristics, with a significantly reduced HOMO-LUMO energy gap (ΔE = 1.661 eV) and enhanced polarity (TDM = 22.229 Debye), facilitating charge transfer and strong interaction. In contrast, Cs/GO/TiO₂/H₂O (ΔE = 3.958 eV, TDM = 9.411 Debye) and Cs/GO/TiO₂/CH₄ (ΔE = 3.163 eV, TDM = 7.887 Debye) show diminished sensitivity due to larger energy gaps and weaker dipole moments. The pronounced ΔE reduction and TDM increase for CO₂ align with its spontaneous adsorption energy (− 0.104 eV) and PDOS modifications, confirming selectivity. The values of ρ(r), ∇²ρ(r) and H(r) shows that, the bonds between the composite with the gases all are weak physical bonds which is good for sensing and reusability. The hydrogen bonds formed within the structural composite make the composite more stable. Cs/GO/TiO 2 was prepared and FT-IR characterization confirmed the functional groups, and then compared with computed IR for verification. The magnitude of the changes in physical parameters, particularly for CO 2 , suggests that Cs/GO/TiO 2 can be used for gas sensor applications requiring high sensitivity and reusability for CO 2 . Declarations Acknowledgements This paper is carried out during the 7th Spectroscopy Winter School (SWS-07), which conducted from December 2024 till February 2025 at Spectroscopy Department, National Research Centre, NRC., Egypt. Statement of Author Contributions The authors of this study have equally contributed to the work in hand for both writing and discussion. Conflict of Interest Statement The authors confirm that they have no competing interests to declare. Data availability The data supporting the findings of this study can be obtained from the corresponding author upon request, subject to reasonable conditions. References Singh, R., Shrivastava, A. & Bajpai, A. Biodegradable polymer nanocomposites for gas-sensing and bio-sensing applications: prospects and challenges. 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Ghanem","email":"","orcid":"","institution":"Al-Azhar University","correspondingAuthor":false,"prefix":"","firstName":"Mahmoud","middleName":"S.","lastName":"Ghanem","suffix":""},{"id":440105091,"identity":"e0a1c30d-1849-42ae-aebf-af94efd6335b","order_by":4,"name":"Hanan Elhaes","email":"","orcid":"","institution":"Ain Shams University","correspondingAuthor":false,"prefix":"","firstName":"Hanan","middleName":"","lastName":"Elhaes","suffix":""},{"id":440105092,"identity":"4251a16e-ee15-4fa5-be95-9933302dc631","order_by":5,"name":"Medhat A. Ibrahim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIie3PIQvCQBTA8ScPznJqfXLgPoEwORgGP8zJwCRiNMgUBC3D7Mo+y2CgZWA1KhaLYJIl8YbFIKc2wfu3F3689wBstt8MEaANVJ4+RvYhISCefE1IfXhVc5GgHI6pUY/O60sOgVMFTE8m4mUK/dWapBADPwohbc2B9dpGkihMOaNuLPpSX5goBtxzjWS71+RGk7ieFSTQpHY1k50+rDInJYgXBIstuDeTw0xWltSKwr4sha7+BZlnEvowPxX82nFok0nIR4HjLGbHi9FAafo0FE8gMDKTF+GbLTabzfZn3QGAsjo9QbUf+wAAAABJRU5ErkJggg==","orcid":"","institution":"National Research Centre","correspondingAuthor":true,"prefix":"","firstName":"Medhat","middleName":"A.","lastName":"Ibrahim","suffix":""}],"badges":[],"createdAt":"2025-03-27 15:23:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6321789/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6321789/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-14525-8","type":"published","date":"2025-08-25T15:57:44+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81032172,"identity":"4e216838-f3da-4b6f-ab22-b009bbcde91c","added_by":"auto","created_at":"2025-04-21 11:29:12","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":71854,"visible":true,"origin":"","legend":"\u003cp\u003eModule molecules structures for a- Chitosan (Cs), b- Graphene oxide (GO), c- Cs/GO and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/3b3d6f334cf6230576788a7e.jpg"},{"id":81029890,"identity":"f7feb70d-b9fe-4995-bb5f-e80f7ddec161","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82819,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated\u003cstrong\u003e \u003c/strong\u003eMESP for the modeled structure where a- Cs, b- GO, c- Cs/GO, and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/6fab51787ae4a327237c2098.jpg"},{"id":81029897,"identity":"c323a57f-23c8-4679-bd9d-6e14d8755009","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":89478,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated\u003cstrong\u003e \u003c/strong\u003eHOMO/LUMO for the modeled structure where a- Cs, b- GO, c- Cs/GO and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/d3fe4a696c84898ac1f682df.jpg"},{"id":81029908,"identity":"bee4b9d4-fef2-4643-a2c0-9bc8eb9b7a61","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":68437,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated\u003cstrong\u003e \u003c/strong\u003eDOS for the modeled structure where a- Cs, b- GO, c- Cs/GO, and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/13cb5b325f54baa6122daa8b.jpg"},{"id":81029895,"identity":"ff206c24-fac4-4ea7-b9b4-ba9f833ed81c","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":17537,"visible":true,"origin":"","legend":"\u003cp\u003eModule gas molecules structures whereas a- H\u003csub\u003e2\u003c/sub\u003eO, b- CO\u003csub\u003e2\u003c/sub\u003e and c- CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/73155d8767f2a7962db00ae7.jpg"},{"id":81029891,"identity":"e334f511-1271-4e23-806a-b8100cfe374c","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":82590,"visible":true,"origin":"","legend":"\u003cp\u003eThe physical interaction between Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003enanocomposite with the gas molecules\u003cstrong\u003e, \u003c/strong\u003ewhere; a- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e, b- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO, c- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/49ceba0c1f77ad334a74efbd.jpg"},{"id":81031025,"identity":"2bcfaa4a-e34b-4834-834a-4b0d04576f3f","added_by":"auto","created_at":"2025-04-21 11:21:12","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":87169,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated MESP for\u003cstrong\u003e \u003c/strong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003einteracted with gas molecules\u003cstrong\u003e, \u003c/strong\u003ewhere; a- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e, b- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO, c- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/0f37aa8c9873dcebb579646b.jpg"},{"id":81031022,"identity":"afb0b719-cf97-4002-a9a6-0ec7ac41bfeb","added_by":"auto","created_at":"2025-04-21 11:21:12","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":98828,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated HOMO/LUMO for\u003cstrong\u003e \u003c/strong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003einteracted with gas molecules\u003cstrong\u003e, \u003c/strong\u003ewhere; a- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e, b- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO, c- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/42cf21e3a8daa1d005b11794.jpg"},{"id":81029918,"identity":"5b61b18a-afca-4f8b-accb-122570ef2467","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":98203,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated PDOS for\u003cstrong\u003e \u003c/strong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003enanocomposite\u003cstrong\u003e \u003c/strong\u003eand the nanocomposite\u003cstrong\u003e \u003c/strong\u003einteracting with gas molecules\u003cstrong\u003e, \u003c/strong\u003ewhere; a- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e b- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO, c- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/a087239ce1d1578c58a29988.jpg"},{"id":81029906,"identity":"b4936e55-b462-4330-a70b-ee833884754c","added_by":"auto","created_at":"2025-04-21 11:13:12","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":87568,"visible":true,"origin":"","legend":"\u003cp\u003eCalculated\u003cstrong\u003e \u003c/strong\u003eQTAIM topology for Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite and the nanocompostie interacting with the gas molecules whereas; a- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e b- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO, c- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e and d- Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/f19ad28cbc164d47e39ddb80.jpg"},{"id":81032174,"identity":"f18d78b5-f9f9-4511-908d-5c04cad221bc","added_by":"auto","created_at":"2025-04-21 11:29:12","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":66676,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR absorbance spectra for pure Cs and Cs/GO/TiO\u003csub\u003e2 \u003c/sub\u003enanocomposite.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/844b50a0e54d4c0193bf9ca9.jpg"},{"id":90346017,"identity":"40522dcb-11e2-4438-9ba5-f1851b9be582","added_by":"auto","created_at":"2025-09-01 16:11:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1956634,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6321789/v1/847f4b7b-68d6-4c2c-a64e-ddca18798848.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eApplication of Cs/GO/TiO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e as Gas Sensor\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBiopolymers have garnered significant interest in sensor technology because of their environmentally friendly characteristics, availability, and straightforward processing [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Every year, around 100\u0026nbsp;billion tons of chitin is produced naturally on our planet by crustaceans, mollusks, insects, fungi, and similar organisms. At present, the extraction of chitin in industrial settings primarily depends on chemical techniques and the utilization of marine shell waste streams [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Chitosan (Cs), a random copolymer derived from chitin, demonstrates significant versatility. In acidic environments, the amino groups along its polymer chains become protonated, resulting in the polymer being cationic. This distinctive characteristic allows chitosan to engage with a wide variety of molecules, setting it apart as the sole cationic marine polysaccharide. The positive charge is thought to play a crucial role in its antimicrobial activity [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], considering its plentiful availability and remarkable functional characteristics including biocompatibility, bioactivity, biodegradability, and impressive mechanical strength [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The field of gas sensing is essential for identifying dangerous gases, keeping an eye on air quality, and guaranteeing environmental safety. While traditional gas sensors often utilize materials like metal oxides and semiconductors, there is a growing demand for sustainable, cost-effective, and environmentally friendly alternatives [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Chitosan, with its excellent film-forming ability and hydrophilic nature, has emerged as a promising candidate for gas sensing applications. Chitosan's gas-sensing capabilities can be further enhanced by incorporating other materials. For example, chitosan's responsiveness and reproducibility in detecting acetone gas are much improved when combined with metal oxides, like SnO\u003csub\u003e2\u003c/sub\u003e, leading to larger output voltages and improved performance [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Similarly, hybrid films created by blending chitosan with conductive polymers like polypyrrole (Ppy) or nanoparticles such as zinc oxide (ZnO) exhibit improved electrochemical properties. These hybrid materials demonstrate high selectivity and responsiveness toward specific gases, such as hydrogen [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Chitosan's abundance of hydroxyl (-OH) and amino (-NH\u003csub\u003e2\u003c/sub\u003e) groups further enhances its hydrophilicity. The adsorption of water molecules is facilitated by these functional groups, increasing its sensitivity to variations in humidity and bolstering its potential for advanced environmental monitoring applications [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The incorporation of graphene oxide (GO) can enhances the performance of chitosan by providing high surface area, good electrical conductivity, and high oxygen-containing functional groups. Synergism between chitosan and GO causes a substantial improvement in the electrical and sensing properties of the composite material. incorporation of GO into chitosan not only changes the band gap but also enhances the charge transfer characteristics, which are extremely important for increased sensitivity and responsivity of the sensors [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. In addition, GO/chitosan composites have been reported to greatly improve the mechanical stability and strength of the composite material and make the composite material stronger for diverse sensing purposes [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Furthermore, the oxygen-functional groups in GO enhance the interaction with target molecules, which makes sensors more sensitive and selective [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Titanium dioxide (TiO₂) is a prominent n-type semiconductor characterized by a band gap of around 3 eV. Its advantageous catalytic properties, durability, and environmental safety render it useful in a range of applications, such as gas sensors, solar cells, and photocatalytic processes [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. TiO₂ is found in three primary crystalline forms: rutile, anatase, and brookite, with rutile being the most stable thermodynamically [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Gas sensors based on TiO₂ are extensively utilized for the detection of harmful gases, owing to their sensitivity, rapid response times, and affordability [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The incorporation of nanostructures significantly enhances the gas-sensing performance by increasing the surface-to-volume ratio, which facilitates the detection of various gases, including ozone, ethanol, acetone, hydrogen, and carbon monoxide [\u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMolecular modeling has been a powerful approach to elucidate electronic properties for many molecular systems. It became useful in studying the behavior and mechanism of interaction for sensors [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. It was reported that, for gas sensing phenomena DFT could support the experimental findings and became an important tool in this filed [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe present work investigates the synthesis and modeling of a Cs/GO/TiO₂ nanocomposite utilizing density functional theory (DFT) for enhancement of biopolymer applications. DFT at B3LYP/LANL2DZ level was applied to evaluate physical parameters including the total dipole moment (TDM), the HOMO\u0026ndash;LUMO and energy gap (ΔE). The density of states (DOS), HOMO-LUMO frontier orbitals, global reactivity descriptors, and molecular electrostatic potential (MESP) will clarify the active sites and charge transfer mechanisms involved in gas interactions. Moreover, Quantum theory of atoms in molecules (QTAIM) was conducted to investigate non-covalent interactions, and the adsorption energies to investigate selectivity. Finally, a comparison between theoretical predictions and Fourier-transform infrared (FT-IR) spectra was conducted to confirm the computational models. This computational strategy aims to create advanced nanocomposite that combine polymeric materials and metal oxides, utilizing the advantages of Cs, GO, and TiO\u003csub\u003e2\u003c/sub\u003e which enhance their properties, especially for gas sensing applications with improved selectivity and sensitivity.\u003c/p\u003e\n\u003ch3\u003eCalculation Details\u003c/h3\u003e\n\u003cp\u003eThe models have been investigated using the G09 program [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The structures were computed at Molecular Modeling and Spectroscopy Laboratory, Centre for Excellence for Advanced Science, National Research. For the structural optimizations calculations, the Los Alamos National Laboratory 2 double ζ (LANL2DZ) basis set and the B3LYP functional (which combines Becke's three-parameter exchange functional with the Lee-Yang-Parr correlation functional) were used [\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Utilizing consistent computational methodology, the total dipole moment (TDM), highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) were calculated. The energy gap (∆E), derived from HOMO-LUMO energy difference. TDM and ∆E provides critical insights into molecular interaction potential and reactivity. The molecular electrostatic potential (MESP) allows for the visualization of the active sites. The Density of States (DOS) was graphically represented to elucidate electronic behavior. Global reactivity descriptors, including fundamental quantum chemical parameters such as Ionization Potential (IE), Electronic Affinity (A), Chemical Potential (\u0026micro;), Chemical Hardness (η), Absolute Softness (S), and Electrophilicity Index (ω) [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], were systematically calculated using the following formulas:\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:IE=-{E}_{HOMO}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(1)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:A=-{E}_{LUMO}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:=-\\frac{IE\\:+A}{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\eta\\:=\\frac{IE-A}{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:S=\\frac{1}{\\eta\\:}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\omega\\:}=\\frac{{\\mu\\:}^{2}}{2\\eta\\:}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe adsorption energy E\u003csub\u003ea\u003c/sub\u003e for studied nanocomposites interacting with the adsorbed gases was calculated by the equation [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eE\u003csub\u003ea\u003c/sub\u003e = \u0026minus; [E\u003csub\u003esystem\u003c/sub\u003e \u0026minus; (E\u003csub\u003eadsorbent\u003c/sub\u003e + E\u003csub\u003eadsorbate\u003c/sub\u003e)]\u003c/p\u003e \u003cp\u003eQTAIM topology analysis was conducted with the use of Multiwfn and visual molecular dynamics (VMD) software [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], to investigate the interaction with the adsorbed gases and the nature of the bonds formed as well as the stability of the nanocomposites. Finally, frequency calculations were performed to confirm that the structures correspond to true minima and to compare them with the FTIR data to validate the DFT level of methodology.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eMaterials and Instrumentation\u003c/h2\u003e \u003cp\u003eChitosan deacetylation degree 90% \u0026plusmn;5 purchased from Chitosan Egypt LLC. Sulfuric acid (96%) was obtained from Scharlau and hydrogen peroxide from PIOCHEM (30%). Sodium hydroxide and ethanol were purchased from El Nasr Pharmaceutical Chemicals Co., Cairo, Egypt. Titanium tetraisopropoxide Ti (OC\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e termed as TTIP was purchased from Sigma Aldrich \u0026ndash; Germany. Ethyl alcohol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH), Polyethylene glycol PEG (M.W 6000), and Acetic acid (CH\u003csub\u003e3\u003c/sub\u003eCOOH) were purchased from El-Nasr Pharmaceutical Company, Egypt. Citric acid (99.5%), and sodium hydroxide (\u0026ge;\u0026thinsp;97%), phosphoric acid (85%), potassium permanganate (99%), and graphite powder were obtained from Fisher Chemical. Distilled water and deionized (DI) Milli-Q water was used during the preparations of samples. The Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectra were obtained using an FT-IR spectrometer (Vertex 70, Bruker), which have a spectral range of 4000\u0026ndash;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a spectral resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePreparation of TiO\u003c/h3\u003e\n\u003cp\u003eNano titanium dioxide TiO\u003csub\u003e2\u003c/sub\u003e synthesis was carried out using precipitation technique. By dissolving titanium tetraisopropoxide into absolute ethanol (in ice bath), while stirring at low base, water was added to the solution. To control the grain growth duo to hydrolysis process, drops from Acetic acid and polyethylene glycol were added to the solution while stirred at high speed for 2 hours. The solution then left over night for precipitation to occur. Then two layers formed, the upper layer was the organic byproducts of the hydrolysis, and the lower layer was a TiO\u003csub\u003e2\u003c/sub\u003e precipitate. After that the TiO\u003csub\u003e2\u003c/sub\u003e precipitate was filtered and washed several times with distilled water, then dried overnight at 100\u0026deg;C. the yellow crystal blocks obtained were grounded into fine powder then calcinated for 3 hours at 500\u0026deg;C to get pure anatase nanoparticle of TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003ch3\u003ePreparation of GO\u003c/h3\u003e\n\u003cp\u003eThe modified Hummer\u0026rsquo;s method was used to synthesize GO. 3 g of graphite flakes were mixed with 360 ml of sulfuric acid and 40 ml of phosphoric acid, the mixture is in a 9:1 ration and is stirred continuously. The mixture was cooled in an ice bath, and then 18 g of KMnO₄ was slowly added. The color of the mixture change from black (graphite color) to a dark olive green, while temperature was regulated between 0 and 5\u0026deg;C in order to minimize exothermic reactions. After stirring the mixture at 40\u0026deg;C overnight, the mixture was mixed with 400 ml of iced deionized water containing 30% of H₂O₂. The color changed from buffer violet to light brown after this step. The mixture was filtered with centrifugation at 10,000 rpm and washed discarding the supernatant. The filtrate obtained was dried at 70\u0026deg;C for five hours using an oven.\u003c/p\u003e\n\u003ch3\u003ePreparation of Cs/GO/TiO\u003c/h3\u003e\n\u003cp\u003eCs was mixed with GO and TiO₂ to form a nanocomposite. Specifically, 0.25 g of Cs was dissolved in 50 mL of deionized water (2% acetic acid) under continuous stirring. Two samples were prepared, pure Cs of 0.250 g (100%) and a mixture containing 0.225 g of Cs (90%), 0.0125 g of GO (5%), and 0.0125 g of TiO₂ (5%). The samples were stirred for 30 minutes at 70\u0026deg;C. The Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e mixture were followed by 2\u0026ndash;3 minutes of sonication to ensure uniform dispersion of GO within the nanocomposite. The resulting solutions were then drop-cast onto petri dishes and left to dry at room temperature for five days to form the final composite film.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003ch2\u003eBuilding Module Molecules\u003c/h2\u003e\n\u003cp\u003eBefore commencing the DFT calculations, we constructed molecular models of the structures. Figure (1) display the model structures where figure (1-a) shows three units of chitosan (Cs). Figure (1-b) shows Graphene oxide (GO) like structure with COOH, OH functional groups. Figure (1-c) shows Cs interacting weakly with GO through H atom of COOH and amine group of the Cs. Figure (1-d) the Cs/GO interacted weakly with TiO\u003csub\u003e2\u003c/sub\u003e through terminal OH of GO via Ti atom of TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003ch2\u003eCalculated Physical Parameters\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe TDM provides valuable information about electronic charge distribution in molecules, hence has a crucial role in the establishment of molecular polarity. Such polarity notably influences the chemical properties and reactivity of the molecules as well as their interaction with the molecules that surround them. Elevated values of TDM may suggest that the structure exhibits heightened reactivity and enhanced capacity for interaction with surrounding molecules [36].\u0026nbsp;The HOMO\u0026ndash;LUMO gap (\u0026Delta;E) represents the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).\u0026nbsp;\u0026Delta;E\u0026nbsp;helps in understanding a molecule\u0026apos;s electronic properties and charge transport phenomena, providing insights into its stability and reactivity. Moreover,\u0026nbsp;\u0026Delta;E helps in\u0026nbsp;understanding the electronic transport characteristics of molecular systems [37-38]. TDM and \u0026Delta;E were calculated for the studied models using B3LYB/LANL2DZ method; the results are recorded in table (1).\u0026nbsp;In the case of Cs, TDM and\u0026nbsp;\u0026Delta;E\u0026nbsp;were found to be 5.884 Debye and 6.908 eV respectively. When Cs interacted with GO the TDM decrease a little to become\u0026nbsp;5.489\u0026nbsp;Debye but the\u0026nbsp;\u0026Delta;E significantly\u0026nbsp;decreased to 2.748 eV. The addition of TiO\u003csub\u003e2\u003c/sub\u003e further improved the \u0026Delta;E values and reach to 2.197 eV and enhanced the TDM which reaching to 14.432 Debye. \u0026nbsp;This means that the composite Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e is more reactive than Cs or Cs/GO alone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u0026nbsp;\u003c/strong\u003eCalculated\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eTDM in Debye and \u0026Delta;E in eV for the studied structures.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 174px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructures\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTDM (Debye)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 164px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta;E (eV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 174px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cspan dir=\"LTR\"\u003eCs\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e5.884\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 164px;\"\u003e\n \u003cp\u003e6.908\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 174px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e3.861\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 164px;\"\u003e\n \u003cp\u003e2.758\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 174px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e5.489\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 164px;\"\u003e\n \u003cp\u003e2.748\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 174px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e14.432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 164px;\"\u003e\n \u003cp\u003e2.197\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch2\u003eGlobal Reactivity Descriptors\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eHOMO and LUMO values were calculated using B3LYB/LANL2DZ method, and Global reactivity IE, A, \u0026micro;,\u0026nbsp;\u0026eta;,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eS and \u0026omega; can be defined and computed by the equations (1:6). The calculated\u0026nbsp;global reactivity descriptors\u0026nbsp;for Cs, GO, Cs/GO and Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e composite were recorded in table 2. Ionization energy (IE) value for the composite Cs/GO/TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eshows lower value than Cs\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003e(from 5.931 to 5.614 eV). This means that a lower energy is required to remove an electron from the surface of the structure. Electron affinity (A) of Cs increased significantly from -0.977 to 3.147 eV as Cs interacted with\u0026nbsp;GO/TiO\u003csub\u003e2\u003c/sub\u003e which indicates more energy when electron added to the system [30]. Hardness (\u0026eta;) and softness (S) values can be described as an indication of the inhibition of inter-molecule transfer of charge. The composite Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e display much lower value for hardness (\u0026eta;) (1.099 eV) in compered with the pure Cs (3.454). While softness (S) value of pure Cs displayed the lower value (0.290 eV) than the composite Cs/GO/TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(0.910 eV) which indicate the more reactivity of the composite Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e. The composite also shows higher values for \u0026micro; and \u0026omega; compering with pure Cs, which indicate that the composite structure has tendency to accept electrons and have better electrophilic characteristics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003eCalculated global reactivity descriptors in eV for the studied structures.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"619\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructure\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026mu;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026eta;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026omega;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.931\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e-0.977\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e-2.477\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e3.454\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e0.290\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e0.888\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.426\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e2.669\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e-4.048\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e1.379\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e0.725\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.941\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.370\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e2.622\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e-3.996\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e1.374\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e0.728\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.812\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e5.614\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e3.417\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e-4.515\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e1.099\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e0.910\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e9.279\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch2\u003eMapping Molecular Electrostatic Potential MESP\u003c/h2\u003e\n\u003cp\u003eThe molecular electrostatic potential MESP were calculated using B3LYB/LANL2DZ method. MESP can shows the reactivity of molecules by a color code and show the active sites [39]. The color range from red to blue where red represents negative region and blue is positive region of electrostatic potential, while green color is more neutral. Figure (2) shows the calculated MESP for the studied structures. In figure (2-a), MESP of pure Cs show red regions around the O atoms and blue regions around the H atom of OH. For Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite (figure (2-d)), the structure shows more red region around the O atoms of TiO\u003csub\u003e2\u003c/sub\u003e indicating a more reactive structure to surrounding molecules [40].\u003c/p\u003e\n\u003ch2\u003eFrontier Molecular Orbitals\u003c/h2\u003e\n\u003cp\u003eThe HOMO/LUMO frontier molecular orbitals were calculated using B3LYB/LANL2DZ method. HOMO and LUMO are the most essential parameters in quantum chemistry [41]. In chemistry, HOMO and LUMO are types of molecular orbitals. The acronyms stand for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively, and the difference between them is called the HOMO\u0026ndash;LUMO gap. The calculation of HOMO and LUMO gives information on the transfer of charge within the molecule [42]. Figure (3) presents the distribution of HOMO and LUMO frontier orbitals where the red color denotes the positive phase and the green color denote to the negative phase. The HOMO\u0026ndash;LUMO map of pure Cs and GO molecules are shown in Figure (3-a) and (3-b) respectively. When Cs interacts with GO as shown in Figure (3-c) all the electronic charge activity, HOMO-LUMO, shifted to the GO molecule. When TiO\u003csub\u003e2\u003c/sub\u003e molecule is added to the Cs/GO structure as shown in Figure (3-d), HOMO localized on TiO\u003csub\u003e2\u003c/sub\u003e and the LUMO on GO this localization enhance charge transfer interactions. This indicate enhancement in charge transfer and electron mobility.\u003c/p\u003e\n\u003ch2\u003eDensity of States DOS\u003c/h2\u003e\n\u003cp\u003eThe density of states (DOS) for the studied structures calculated using DFT: B3LYB/LANL2DZ method is displayed in figure (4). DOS represent the number of states per energy level, where the green lines represent occupied orbitals and the red lines correspond to the unoccupied (virtual) orbitals. In Figure (4-c) the nanocomposite Cs/GO exhibit a decrease in bandgap compared to Cs alone (figure (4-a)). After the incorporation of TiO\u003csub\u003e2\u003c/sub\u003e the bandgap decreased further and the number available unoccupied stated near the Fermi level increased as shown in Figure (4-d). This enhancement in available states facilitates charge transfer, as evidenced by the shifted virtual orbitals toward the Fermi level\u003c/p\u003e\n\u003ch2\u003eGas Sensing\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite was proposed to interact with three different gasses H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e, the gases models can be shown in figure (5). The structures were optimized at the same computational level. The optimized structures are recorded in figure (6), where figure (6-a) present Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite, figure (6-b) presents Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with H\u003csub\u003e2\u003c/sub\u003eO, figure (6-c) presents Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with CO\u003csub\u003e2\u003c/sub\u003e and figure (6-d) presents Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with CH\u003csub\u003e4\u003c/sub\u003e. In these models, the O atom of TiO\u003csub\u003e2\u003c/sub\u003e was supposed to interact weakly with the gases molecules. Electronic properties including total dipole moment (TDM) and HOMO-LUMO energy gap (\u0026Delta;E) were calculated to quantify changes induced by gas adsorption.\u003c/p\u003e\n\u003cp\u003eTable (3) displays the changes in TDM and \u0026Delta;E values of the nanocomposite upon interaction with H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e, and CH\u003csub\u003e4\u003c/sub\u003e gases. Compared to the pristine nanocomposite TDM and \u0026Delta;E values (14.432 Debye and 2.197 eV), significant changes in both parameters were observed upon interaction with H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e, and CH\u003csub\u003e4\u003c/sub\u003e gases. This indicates a sensitivity of the nanocomposite to these gases. The largest variation was observed with CO\u003csub\u003e2\u003c/sub\u003e interaction, where TDM increased from 14.432 Debye to 22.292 Debye, and \u0026Delta;E decreased from 2.197 eV to 1.661 eV. This change in pristine nanocomposite values suggests strong interaction and high sensitivity towards CO\u003csub\u003e2\u003c/sub\u003e sensing. In contrast, the CH\u003csub\u003e4\u003c/sub\u003e interaction demonstrated the minimum change in TDM, which decreased to 7.887 Debye, and \u0026Delta;E increased to 3.163 eV. The interaction with H\u003csub\u003e2\u003c/sub\u003eO shows moderate changes with TDM decreasing to 9.411 Debye and \u0026Delta;E increasing to 3.958 eV. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u0026nbsp;\u003c/strong\u003eCalculated\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eTDM in Debye and \u0026Delta;E in eV for the studied structures.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructures\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTDM (Debye)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Delta;E (eV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp dir=\"RTL\"\u003e\u003cstrong\u003e\u003cspan dir=\"LTR\"\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e14.432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e2.197\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e9.411\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e3.958\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e22.292\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e1.661\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e7.887\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e3.163\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMESP were calculated for Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003einteracted with gas molecules and some changes in the charge distribution occurred, due to the interaction. The red regions around O atoms of TiO\u003csub\u003e2\u003c/sub\u003e in figure (7-a) disappeared for Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO and a neutral surface is dominant (figure (7-b)). The Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with CO\u003csub\u003e2\u003c/sub\u003e in figure (7-c), shows more spread reactive regions (red and blue) which indicate that the nanocomposite is susceptible to more interaction with the gas molecules. The Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with CH\u003csub\u003e4\u003c/sub\u003e exhibit less reactivity as shown in figure (7-d). These MESP changes align with observed trends in TDM and \u0026Delta;E modulation.\u003c/p\u003e\n\u003cp\u003eThe HOMO-LUMO frontier orbitals of Cs/GO/TiO₂ were analyzed post-interaction with gases. In the pristine nanocomposite (\u003cstrong\u003eFigure (8-a)\u003c/strong\u003e), the HOMO localizes on TiO₂, while the LUMO resides on GO. Interaction with H₂O (\u003cstrong\u003eFigure (8-b\u003c/strong\u003e)) shifts the HOMO to GO and distributes the LUMO across both GO and TiO₂. For CH₄ adsorption in figure (8-d) the HOMO and LUMO are distributed on GO and TiO\u003csub\u003e2\u003c/sub\u003e. For CO₂ adsorption (\u003cstrong\u003eFigure (8-c)\u003c/strong\u003e), the HOMO occupies the amine group of Cs, and the LUMO remains on GO/TiO₂. These orbital redistributions highlight analyte-specific electronic modulation, aligning with observed TDM and \u0026Delta;E trends.\u003c/p\u003e\n\u003ch3\u003ePartial Density of States (PDOS)\u003c/h3\u003e\n\u003cp\u003eThe projection of a specific atom\u0026apos;s orbital on the density of states is provided by PDOS, where the total density of state (DOS), can be obtained by adding up all of the projections. PDOS plots for Cs/GO/ TiO\u003csub\u003e2\u003c/sub\u003e nanocompiste and its interaction with the gases is displayed in figure (9). The Ti atom contributes the most in both the unoccupied (virtual) and occupied orbitals, followed by O atoms. PDOS plot for Cs/GO/TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eis shown in figure (9-a), there is some changes in DOS upon interaction with the gases. Figure (9-c) represent PDOS for Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e interacting with CO\u003csub\u003e2\u003c/sub\u003e, the changes in the states with the introduction of new states in the unoccupied orbitals (black lines), this make charge transfer easier to occur. The changes in the DOS are not as potent for the other gases as shown in figure (9-b) and figure (9-d).\u003c/p\u003e\n\u003ch3\u003eAdsorption Energy\u003c/h3\u003e\n\u003cp\u003eTo investigate the selectivity of Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite for the studied gases, adsorption energy E\u003csub\u003ea\u003c/sub\u003e were calculated, the results are recorded in table (4). If E\u003csub\u003ea\u003c/sub\u003e is positive value that means the interaction need energy to occur and the interaction is endothermic. In contrast, if E\u003csub\u003ea\u003c/sub\u003e is negative value that indicates the interaction is spontaneous and release energy. Adsorption energy results showed significant selectivity for CO\u003csub\u003e2\u003c/sub\u003e adsorption where E\u003csub\u003ea\u003c/sub\u003e have a value of -0.104 eV for the adsorption of CO\u003csub\u003e2\u003c/sub\u003e onto Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite. While E\u003csub\u003ea\u003c/sub\u003e of the adsorption with H\u003csub\u003e2\u003c/sub\u003eO and CH\u003csub\u003e4\u003c/sub\u003e gases onto Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite were found to be 4.000 eV and 4.396 eV respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4.\u003c/strong\u003e Calculated adsorption energy E\u003csub\u003ea\u003c/sub\u003e as eV for the studied gases onto\u0026nbsp;Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 309px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructure\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 294px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdsorption energy (eV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 309px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 294px;\"\u003e\n \u003cp\u003e4.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 309px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 294px;\"\u003e\n \u003cp\u003e-0.104\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 309px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CH\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 294px;\"\u003e\n \u003cp\u003e4.396\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch3\u003eQTAIM Analyses\u003c/h3\u003e\n\u003cp\u003eThe Quantum Theory of Atoms in Molecules (QTAIM) provides a platform to analyze chemical bonding and intermolecular interaction, including non-covalent interactions. QTAIM utilizes electron density represented as \u0026rho;(r), which estimates the probability of an electron at any given point in space [43-45]. QTAIM maps \u0026rho;(r) and display regions of high and low electron density. By analyzing \u0026rho;(r), the Laplacian of electron density (\u0026nabla;\u0026sup2;\u0026rho;) and the energy density H(r) at bond critical points (BCPs) and the type of bonding can be evaluated. Figure (10) illustrates the QTAIM topology for the nanocomposite and its interaction with the studied gases. The figure displaying the critical (CPs) and electron density paths, it shows the non-covalent interactions hydrogen bonding that stabilize the structures especially for figure (10-c) and (10-d). Upon investigating the BCPs between the Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e and the gases, the results of \u0026rho;(r) \u0026lt; 0.2 a.u. and the positive values of \u0026nabla;\u0026sup2;\u0026rho;(r) and H(r) it indicate a weak interaction as proposed.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eCalculated IR spectra\u003c/h2\u003e\n\u003cp\u003eThe infrared (IR) frequencies provide fingerprint information and can identify functional groups and other characteristic bands. Therefore, the IR frequencies of Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e were calculated using DFT: B3LYP functional with LANL2DZ basis set and then compared to measured FT-IR data. Figure (11) depicts the absorbance FT-IR spectra for Cs/GO/TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003enanocomposite and the recorded band assignment in table (5). For Cs IR spectra, the range 3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190 cm\u003csup\u003e-1\u003c/sup\u003e is assigned to O\u0026ndash;H and N\u0026ndash;H stretching vibrations [46-47]. Symmetric/asymmetric CH\u003csub\u003e2\u003c/sub\u003e stretching appears at 2930\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e2870 cm\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003e[46]. The C=O in amide I and N\u0026ndash;H stretching (amide II) were observed at 1640 cm\u003csup\u003e-1\u003c/sup\u003e and 1547 cm\u003csup\u003e-1\u003c/sup\u003e respectively [48-49]. Additionally, stretching vibrations of carbodiimides CH\u003csub\u003e3\u003c/sub\u003e stretching corresponds to 1403 cm\u003csup\u003e-1\u003c/sup\u003e [49], and 1065 cm\u003csup\u003e-1\u003c/sup\u003e to C\u0026ndash;O stretching at [50-51]. For GO bands the O\u0026ndash;H stretching appears at 3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190 cm\u003csup\u003e-1\u003c/sup\u003e [52]. At 1063 cm\u003csup\u003e-1\u003c/sup\u003e, the C\u0026ndash;O epoxide stretching [52], while the band C=C were observed at 1640 cm\u003csup\u003e-1\u003c/sup\u003e [52]. The C=O and O\u0026ndash;C\u0026ndash;O stretching appears at 1735 cm\u003csup\u003e-1\u003c/sup\u003e and 1065 cm\u003csup\u003e-1\u003c/sup\u003e respectively [52]. The band C\u0026ndash;H stretching observed at 898 cm\u003csup\u003e-1\u003c/sup\u003e [53]. The characteristic band of Ti\u0026ndash;O\u0026ndash;Ti vibration fall within the range of 900\u003cstrong\u003e\u0026ndash;400\u003c/strong\u003e\u0026thinsp;cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e were observed at 640\u003cstrong\u003e\u0026ndash;566\u003c/strong\u003e cm\u003csup\u003e-1\u003c/sup\u003e and Ti\u0026ndash;O stretching at 486 cm\u003csup\u003e-1\u003c/sup\u003e within the same range [54-55]. Noticeably, the N\u0026ndash;H stretching (amide II) band in the composite shifted from 1540 cm\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003e(in pure Cs) to 1547 cm\u003csup\u003e-1\u003c/sup\u003e, indicating some physical interactions in the composite. Then the Computed IR frequencies were compared with FT-IR measured results as in table (6). The 3764\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3705 cm\u003csup\u003e-1\u003c/sup\u003e of O\u0026ndash;H stretching corresponds to 3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190 cm\u003csup\u003e-1\u003c/sup\u003e in FT-IR while N\u0026ndash;H stretching vibration appears at 3549\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3455 cm\u003csup\u003e-1\u003c/sup\u003e which correspond to the FT-IR range of 3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190 cm\u003csup\u003e-1\u003c/sup\u003e. The CH\u003csub\u003e2\u003c/sub\u003e stretching was found at 3137\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3039 cm\u003csup\u003e-1\u003c/sup\u003e match the experimental 2930\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e2870 cm\u003csup\u003e-1\u003c/sup\u003e. The N\u0026ndash;H in amide II was found at 1597 cm\u003csup\u003e-1\u003c/sup\u003e matching the 1547 cm\u003csup\u003e-1\u003c/sup\u003e. The C=C stretching corresponds to 1664\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e1639 cm\u003csup\u003e-1\u003c/sup\u003e which match the FT-IR of 1640 cm\u003csup\u003e-1\u003c/sup\u003e. The Ti\u0026ndash;O stretching was found at 997\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e990 cm\u003csup\u003e-1\u003c/sup\u003e matching the experimental value in the range 900\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e400 cm\u003csup\u003e-1\u003c/sup\u003e. The agreements\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ebetween computed and experimental spectra validate the computational method.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5.\u003c/strong\u003e The band assignment of FT-IR results for pure Cs and Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStructure\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFI-IR\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAssignment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRef\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"6\" valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCs\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eO\u0026ndash;H\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eN\u0026ndash;H\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e46\u003c/p\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e2930\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e2870\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eCH\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e46\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1640\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eC=O in amide I\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1547\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eN\u0026ndash;H amide II\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1403\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eCH\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eC\u0026ndash;O\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e50-51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"6\" valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eO\u0026ndash;H\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"5\" valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e52\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1063\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eC\u0026ndash;O epoxide\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1640\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eC=C\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1735\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eC=O\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e1065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eO\u0026ndash;C\u0026ndash;O\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e898\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp dir=\"RTL\"\u003e\u003cspan dir=\"LTR\"\u003eC\u0026ndash;H\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e640\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e566\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eTi\u0026ndash;O\u0026ndash;Ti\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 126px;\"\u003e\n \u003cp\u003e486\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 162px;\"\u003e\n \u003cp\u003eTi\u0026ndash;O\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 260px;\"\u003e\n \u003cp\u003e55\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 6.\u003c/strong\u003e Computed IR frequencies compared with FT-IR measured results for Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"650\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eComputed IR\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFT-IR\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAssignment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e3764~3705\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eO\u0026ndash;H stretching\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e3549~3455\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e3350\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e3190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eN\u0026ndash;H stretching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e3137~3039\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e2930\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e2870\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eCH\u003csub\u003e2\u003c/sub\u003e stretching\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e1597\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e1547\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eN\u0026ndash;H amide II\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e1664~1639\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e1640\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eC=C stretching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e1574~1569\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e1735\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eC=O stretching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003e997~990\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 209px;\"\u003e\n \u003cp\u003e900\u003cstrong\u003e\u0026ndash;\u003c/strong\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 213px;\"\u003e\n \u003cp\u003eTi\u0026ndash;O stretching\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eC\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eDFT:B3LYP/LANL2DZ was utilized to model Cs/GO/TiO₂ composite, then its interaction with H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e gases and studied their electronic properties. TDM, ΔE, global reactivity and MESP results indicated that the composite have the ability to interact with its surrounding molecules. The Cs/GO/TiO₂/CO₂ system exhibits optimal sensing characteristics, with a significantly reduced HOMO-LUMO energy gap (ΔE\u0026thinsp;=\u0026thinsp;1.661 eV) and enhanced polarity (TDM\u0026thinsp;=\u0026thinsp;22.229 Debye), facilitating charge transfer and strong interaction. In contrast, Cs/GO/TiO₂/H₂O (ΔE\u0026thinsp;=\u0026thinsp;3.958 eV, TDM\u0026thinsp;=\u0026thinsp;9.411 Debye) and Cs/GO/TiO₂/CH₄ (ΔE\u0026thinsp;=\u0026thinsp;3.163 eV, TDM\u0026thinsp;=\u0026thinsp;7.887 Debye) show diminished sensitivity due to larger energy gaps and weaker dipole moments. The pronounced ΔE reduction and TDM increase for CO₂ align with its spontaneous adsorption energy (\u0026minus;\u0026thinsp;0.104 eV) and PDOS modifications, confirming selectivity. The values of ρ(r), \u0026nabla;\u0026sup2;ρ(r) and H(r) shows that, the bonds between the composite with the gases all are weak physical bonds which is good for sensing and reusability. The hydrogen bonds formed within the structural composite make the composite more stable. Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e was prepared and FT-IR characterization confirmed the functional groups, and then compared with computed IR for verification. The magnitude of the changes in physical parameters, particularly for CO\u003csub\u003e2\u003c/sub\u003e, suggests that Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e can be used for gas sensor applications requiring high sensitivity and reusability for CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThis paper is carried out during the 7th Spectroscopy Winter School (SWS-07), which conducted from December 2024 till February 2025 at Spectroscopy Department, National Research Centre, NRC., Egypt.\u003c/p\u003e\n\u003cp\u003eStatement of Author Contributions\u003c/p\u003e\n\u003cp\u003eThe authors of this study have equally contributed to the work in hand for both writing and discussion.\u003c/p\u003e\n\u003cp\u003eConflict of Interest Statement\u003c/p\u003e\n\u003cp\u003eThe authors confirm that they have no competing interests to declare.\u003c/p\u003e\n\u003cp\u003eData availability\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe data supporting the findings of this study can be obtained from the corresponding author upon request, subject to reasonable conditions.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSingh, R., Shrivastava, A. \u0026amp; Bajpai, A. 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Titanium dioxide nanoparticles (TiO₂ NPs) promote growth and ameliorate salinity stress effects on essential oil profile and biochemical attributes of Dracocephalum moldavica. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e(1) (2020); https://doi.org/10.1038/s41598-020-57794-1.\u003c/li\u003e\n\u003cli\u003eChougala, L. S., Yatnatti, M. S., Linganagoudar, R. K., Kamble, R. R. \u0026amp; Kadadevarmath, J. S. A simple approach on synthesis of TiO₂ nanoparticles and its application in dye sensitized solar cells. \u003cem\u003eJ. Nanoelectron. Phys.\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e(4), 04005\u0026ndash;04006 (2017); https://doi.org/10.21272/jnep.9(4).04005.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Chitosan, GO, DFT: B3LYP/LANL2DZ, Gas Sensor, TiO2, nanocomposite, QTAIM","lastPublishedDoi":"10.21203/rs.3.rs-6321789/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6321789/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eChitosan a biodegradable, cheap polymer is a good choice for gas sensors. In this study, chitosan (Cs) was modified with graphene oxide (GO) and titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e), and its electronic properties were calculated using density functional theory (DFT) at B3LYP/LANL2DZ level. The calculated physical parameters includes total dipole moment (TDM), HOMO/LUMO energy gap (ΔE), global reactivity descriptors and density of states (DOS) and mapping the electrostatic potential (MESP). Results indicated Cs had significant modification such as enhanced ΔE from 6.908 to 2.197 eV and TDM from 5.884 to 14.432 Debye, global reactivity revealed enhanced reactivity with increased absolute softness and high electrophicility index. DOS show more available states and more localized HOMO/LUMO orbitals all enhance charge transfer. MESP shows reactivity and active sites for the interaction with its surrounding. The nanocomposite Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e is supposed to interact with three different gases; H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e, and CH\u003csub\u003e4\u003c/sub\u003e. The results exhibited changes in the ΔE and TDM, with Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e have the most pronounced changes. Partial density of states PDOS plots exhibited Ti atoms contribution in HOMO orbitals and LUMO with Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e/CO\u003csub\u003e2\u003c/sub\u003e having the most changes in its energy states. Adsorption energy E\u003csub\u003ea\u003c/sub\u003e was calculated and showed selectivity for CO\u003csub\u003e2\u003c/sub\u003e gas with \u0026minus;\u0026thinsp;0.104 eV indicating spontaneous interaction. Quantum theory of atoms in molecules confirmed the weak interaction with gases molecules and the enhanced stability via hydrogen bonding. The Cs/GO/TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite was synthesized and FT-IR spectroscopy were conducted and compared with calculated IR to verify the models.\u003c/p\u003e","manuscriptTitle":"Application of Cs/GO/TiO2 as Gas Sensor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-21 11:13:07","doi":"10.21203/rs.3.rs-6321789/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-05T08:59:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-05T03:59:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"236151949655873573371019969598757881184","date":"2025-05-26T06:33:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-17T05:11:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"121568689718370473644641562955231994889","date":"2025-05-08T11:22:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"156502793588828419943579122732568274416","date":"2025-05-07T14:44:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-08T12:51:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"173502023225034501802915807233292752985","date":"2025-03-31T11:55:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"161479748107833601448242405622832250814","date":"2025-03-31T11:07:39+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-31T11:01:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-31T11:01:05+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-03-31T10:46:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-28T15:29:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-03-27T15:08:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0693046c-5d5c-445a-bfd7-9fe1c76a553b","owner":[],"postedDate":"April 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47444836,"name":"Physical sciences/Materials science"},{"id":47444837,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2025-09-01T16:10:02+00:00","versionOfRecord":{"articleIdentity":"rs-6321789","link":"https://doi.org/10.1038/s41598-025-14525-8","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-08-25 15:57:44","publishedOnDateReadable":"August 25th, 2025"},"versionCreatedAt":"2025-04-21 11:13:07","video":"","vorDoi":"10.1038/s41598-025-14525-8","vorDoiUrl":"https://doi.org/10.1038/s41598-025-14525-8","workflowStages":[]},"version":"v1","identity":"rs-6321789","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6321789","identity":"rs-6321789","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}