Post graduate dissertations (Theses) of Physics (PHY) http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/623 2026-04-08T12:26:10Z 2026-04-08T12:26:10Z Mahtabur Rahman, Md. http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7237 2026-01-21T04:13:57Z 2025-05-27T00:00:00Z

Carbon nanotube and PEDOT:PSS reinforced nanocomposite of cellulose nanocrystals for electrode materials Jellur Rahman, Dr. Mohammad; Mahtabur Rahman, Md.; 0422142511; 539/MAH/2025 In this study, cellulose nanocrystal (CNC)-based nanocomposites are synthesized using solution casting method. Varying amounts of carbon nanotubes and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) are integrated into the CNC matrix, which is derived from sugarcane bagasse (Saccharum officinarum), an agricultural waste product. The CNCs provided a sustainable and biodegradable platform, while the nanofillers enhanced the composite properties. Field emission scanning electron microscopy reveals a highly porous structure, and Brunauer-Emmett-Teller analysis confirms the mesoporosity of the nanocomposite with a specific surface area of 171.72 m2/g and an average pore diameter of 4.4 nm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy verify the interactions between the nanofillers and the polymer matrix. The nanocomposite exhibited excellent electrical conductivity (47 S/m) with high tensile strength (11.6 MPa) and remarkable flexibility when carbon nanotubes are incorporated in it and owing to the creation of conducting path. Electrochemical characterization using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy in a 0.5 M Na2SO4 electrolyte demonstrated a high specific capacitance of 572 F/g, an energy density of 28.5 Wh/kg, and a power density of 120 W/kg at a current density of 0.4 A/g. Furthermore, the material retained 98% of its capacitance after 5000 charge-discharge cycles. These CNC-based nanocomposites are expected to be promising for advanced supercapacitor and battery electrode materials, offering a sustainable, biodegradable, and high-performance alternative to conventional materials.

2025-05-27T00:00:00Z Jakaria Hosen, Md. http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7180 2025-08-30T04:08:39Z 2022-04-01T00:00:00Z

Structural, morphological, optical and electrical properties of MnO2/NiO bilayer thin films synthesized by spin coating method Sharmin, Dr. Mehnaz; Jakaria Hosen, Md.; 0422142507; 530.41/JAK/2025 Nickel oxide (NiO) and manganese dioxide (MnO2) are two technologically significant metal oxides showing p-type and n-type semiconducting behaviors, respectively. In this work, NiO thin films were deposited onto glass substrates using the sol-gel spin coating technique. NiO films were deposited at 3000, 3500, and 4000 rotation per minute (rpm). For the formation of MnO2/NiO bilayer composite films, MnO2 ¬films were deposited using the NiO thin films as the substrates. The as-deposited films were pre-heated at 250 ℃ for 10 min before annealing in the air at 600 ℃ for 1 hour. The film thickness was controlled via rpm variation during spin coating and the rpm was optimized observing the quality of the films. Field emission scanning electron microscopy analysis of NiO films revealed that the film surface contained agglomerated nanoparticles. The shape of the particles changed from spherical to uniformly distributed cubic particles in the MnO2/NiO film. Compositional analysis of NiO and MnO2/NiO was performed by the Energy dispersive X-ray analysis. From the X-ray photoelectron spectroscopy (XPS) investigation the oxidation state Ni2+ of NiO single-layer thin films and composite thin films Mn4+ and Ni2+ are identified by the survey analysis of XPS. The structure of the thin film was explored using X-ray diffraction (XRD) technique. The NiO film prepared at 3000 rpm showed XRD peaks for the (002) plane related to the hexagonal Ni2O3 structure. NiO films prepared at 3500 and 4000 rpm show peaks for (111), (200), and (220) planes related to face-centered cubic NiO structure. The MnO2/NiO film showed the existence of a (211) peak related to the α-MnO2 crystalline phase along with the (200) and (220) peaks for the NiO substrate. The crystallite size was found from 59 to 25 nm for NiO and from 60 to 15 nm for MnO2/NiO thin films, respectively. The least crystallite size was estimated for the films prepared at 4000 rpm. UV-vis spectroscopy analysis was carried out to record the transmittance data in the spectral range of 300 - 1100 nm. In the visible region of light, the maximum transmittance of the NiO films was found 98%, whereas the highest transmittance dropped to 54% for MnO2/NiO films in the NIR region. The optical band gap was estimated in the range of 3.73 to 3.77 eV for the NiO films and 2.56 to 2.70 eV for MnO2/NiO films. Photoluminescence spectra of NiO and MnO2/NiO films showed the peaks related to near-band-edge emission, green emission for oxygen vacancies or Ni interstitials, and yellow-orange emissions for the naturally deeper trap states. Room temperature electrical resistivity enhanced for the MnO2/NiO thin films in comparison with the NiO films. Activation energies were computed for NiO and MnO2/NiO thin films.

2022-04-01T00:00:00Z Hossan Shahid Shohrawardy, Mohammed http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7169 2025-08-26T08:47:37Z 2024-12-07T00:00:00Z

Effect of chemical treatment and gamma-ray irradiation on the performances of sunn hemp and okra hessian cloth-reinforced thermoplastic composites Mina, Dr. Md. Forhad; Hossan Shahid Shohrawardy, Mohammed; 1015144001P; 539.7524/HOS/2024 Untreated sunn hemp hessian cloth and okra hessian cloth reinforced high-density polyethylene (HDPE) composites with 40, 45, 50, 55, 60, and 65 wt% cloth contents were separately prepared by compression molding methods at 190 ℃ and 5-ton pressure. The optimized cloth content for both types of composites was observed to be 55 wt%, as determined by their better mechanical properties. Then, both types of hessian cloths were treated with 5, 10, and 15 wt% concentrations of alkali (NaOH) solutions. With these treated hessian cloths, two series of 55 wt% cloth content reinforced HDPE composites were fabricated. Then, the optimum treatment concentration of alkali was found to be 10 wt%, as evaluated by their superior mechanical properties. 55 wt% cloth content reinforced composite with both untreated and optimum alkali-treated cloths were irradiated under gamma-ray at doses 2.5, 5, and 7.5 kGy at the rate of 6 kGy/h and the optimum dose was found to be 5 kGy. Untreated and alkali-treated sunn hemp and okra cloths reinforced composites as well as their gamma-ray irradiated composites were subsequently characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), physical property test, mechanical test, differential scanning calorimetry, and thermo-gravimetric analyses. From the FTIR analyses new bonds of C‒O, C=C, and ‒CH were observed between sunn hemp or okra fibers and HDPE matrix due to gamma-ray irradiation, showing network structure in the irradiated samples. FESEM of their gamma-ray irradiated composites reveals improved fiber-to-matrix adhesion. From the XRD analysis, only the alkali-treated cloth-reinforced composite shows higher crystallinity than all other samples. The water intake properties of 5 kGy dose gamma-ray irradiated sunn hemp hessian cloth composite was obtained as 10.1%, which is 37 and 14% more hydrophobic in nature than that of merely untreated, and alkali-treated cloth-reinforced composites. The tensile strength of the gamma-ray irradiated sunn hemp cloth-reinforced composite is 68 MPa, which is 42% greater than that of untreated cloth reinforced composite. The Young’s modulus of irradiated sunn hemp cloth-reinforced composite is 1.97 GPa, which is 28% higher than that of untreated cloth-reinforced composites, respectively. The melting and degradation temperatures of gamma-ray irradiated sunn hemp composite are 151 ℃ and 331 ℃, respectively. These results are higher than that of other composites of the same kind. Similar tendencies of the results of water intake, mechanical, and thermal properties were observed for untreated, alkali-treated, and gamma-ray irradiated okra hessian cloth-reinforced composites.

2024-12-07T00:00:00Z Anisur Rahman, Md. http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7065 2025-04-23T03:55:06Z 2024-11-10T00:00:00Z

Growth and characterization of amino acid based organic and semi-organic single crystals for nonlinear optical applications Podder, Dr. Jiban; Anisur Rahman, Md.; 0418144002 P; 537.6/ANS/2024 Novel semiorganic and organic crystals have been grown by natural slow evaporation process. To grow semiorganic crystals, organic materials L-asparagine monohydrate (LAM) and L-alanine (LA) have been doped with inorganic compounds potassium dihydrogen phosphate (KDP), as well as LAM has been doped with magnesium sulphate heptahydrate (MSHH) and zinc sulphate heptahydrate (ZSHH). This work also covers the growth of organic single crystals of LAM and LA. The different doping concentrations were 0.2, 0.4, 0.8, and 1.0 mol% of LAM and LA. The solubility, metastable zone width (MSZW) and different nucleation kinetics parameters like energy of formation of the critical nucleus (ΔG*), interfacial energy (σ) have been measured. From FT-IR spectroscopy, various functional groups have been identified and bond lengths of the groups have been observed to increase with doping concentration. Strong and sharp x-ray diffraction peaks validate the formation of good crystalline structure. The calculated strain and crystallite size have been observed to enhance with doping concentration. Surface morphology of the grown crystals has been studied by SEM images after etching. From energy dispersive x-ray (EDX) analysis, the constituent elements of the grown crystals have been identified. From microhardness study, the hardness values are observed to reduce with increasing doping level and the doped crystals have been specified as soft category materials. From thermogravimetric analysis (TGA), different stages of thermal decomposition have been observed and the corresponding kinetic and thermodynamic parameters reveal spontaneous reaction mechanism. The different decomposition stages have been confirmed by the negative differential scanning calorimetry (DSC) peak. From dielectric studies, the obtained dielectric loss and dielectric constant indicate normal dielectric behavior of the crystals. From DC conductivity study, an increase in conductivity is observed for the doped samples. UV-Vis spectral analysis reveals enhanced optical transparency for the doped crystals. The optical linear susceptibility χ(1), third order nonlinear susceptibility χ(3) and nonlinear refractive index n2 have been detected to increase with doping concentration. From quantum computational analysis, the frontier molecular orbitals have been drawn and NLO properties were determined by density functional theory (DFT) which are observed to increase for the doped crystals. All findings demonstrate that the semi-organic crystals possess good photo response and favorable nonlinear optical properties.

2024-11-10T00:00:00Z