Post graduate dissertations (Theses) of Chemistry (Chy) http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/628 2026-04-05T13:07:39Z 2026-04-05T13:07:39Z Roksana Akter http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7228 2025-12-30T06:00:56Z 2025-05-14T00:00:00Z

Solvent free synthesis of Chalcones from Aldehydes and Ketones using Heterogeneous Niobic Acid catalyst Nurnobi Rashed, Dr. Md.; Roksana Akter; 0422032006; 541.395/ROK/2025 Chalcone, an important organic molecule featuring an α, β-unsaturated carbonyl framework, holds significant relevance in both organic synthesis and medicinal chemistry. It acts as a key intermediate in the production of polymers, fine chemicals, agrochemicals, and a range of pharmaceutical compounds due to its notable biological activities, including anti-inflammatory, anticancer, and antimicrobial properties. The synthesis of chalcones from aldehydes and ketones has traditionally relied on methods such as Claisen–Schmidt condensation, Meyer–Schuster rearrangement, Suzuki coupling, and Fries rearrangement. However, these approaches often demand elevated temperatures, prolonged reaction times, and substantial amounts of reagents or additives. While homogeneous acid catalysts like HCl, BF₃•Et₂O, and p-toluene sulfonic acid have been used in chalcone synthesis, they commonly yield low product output and pose challenges in catalyst separation and reuse. On the other hand, heterogeneous catalysts such as MgO, Fe₃O₄@MOF, supported BF₃, B₂O₃, LiNO₃ on natural phosphate, calcined hydrotalcites, and alkali-modified zeolites have also been explored. However, these systems often suffer from moderate yields, complex preparation procedures, harsh operating conditions, and environmental drawbacks.Moreover, in many cases, the Lewis acid sites of these catalysts become deactivated due to interaction with water generated during the reaction, leading to a decline in their catalytic performance. To overcome these obstacles, the development of a water-tolerant and efficient catalytic system is essential. Niobic acid (Nb₂O₅•nH₂O), a solid acid catalyst known for its water stability, offers a promising solution. Studies suggest that the Lewis acidic Nb⁵⁺ centers in niobic acid activate ketones by coordinating with their carbonyl groups, facilitating enol formation. Simultaneously, its Brønsted acid sites (–OH groups) enhance the electrophilicity of aldehydes by protonating their carbonyl oxygen. This dual activation by Lewis and Brønsted acid sites enables efficient carbon–carbon bond formation followed by dehydration, producing α, β-unsaturated chalcones under mild and eco-friendly conditions.Furthermore, the catalyst retains its activity over successive cycles, exhibiting minimal loss in performance upon reuse. This method supports a wide range of substrates, delivering high yields (up to 98%) with various aldehydes (e.g., 4-methylbenzaldehyde, 4-chlorobenzaldehyde) and ketones (e.g., 4-bromoacetophenone, tetralone). Therefore, this study aims to investigate the use of niobic acid (Nb₂O₅•nH₂O) as a sustainable, efficient, and recyclable catalyst for the synthesis of chalcones. Keywords: Chalcone, Nb2O5.nH2O, Lewis and Brønsted acid sites, water-tolerant

2025-05-14T00:00:00Z Afrina Hoque, Khondaker http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7227 2025-12-30T04:53:19Z 2025-06-30T00:00:00Z

Photocatalytic dye degradation and antimicrobial activities of CuO/ZnO/Co3O4 nanocomposites synthesized via green chemistry Chowdhury, Dr. Al-Nakib; Afrina Hoque, Khondaker; 0421033602F; 546.681/AFR/2025 The green synthesis of transition metal oxide nanocomposites using Litseaglutinosa leaf extract presents a environment friendly approach that eliminates the need for toxic chemicals, offering a promising solution to global issues such as non-biodegradable dye pollution and antibiotic resistance. In this study, binary (Co₃O₄/ZnO, ZnO/CuO, CuO/Co₃O₄) and ternary (CuO/ZnO/Co₃O₄) nanocomposites were synthesized via a green route and characterized using UV-Vis, FT-IR, XRD, and SEM-EDS techniques. The ternary CuO/ZnO/Co₃O₄ nanocomposite displayed a reduced band gap of 1.6-3.04 eV with dual absorption peaks at 271 nm and 523 nm, signifying enhanced visible light absorption. XRD confirmed the successful formation and crystalline nature of each composite, with crystallite sizes of 12.45 nm (ZnO/Co₃O₄), 8.93 nm (CuO/Co₃O₄), 26.53 nm (ZnO/CuO), and 21.61 nm (ZnO/CuO/Co₃O₄). SEM analysis revealed distinct morphologies, spherical-rod (ZnO/Co₃O₄), porous spongy (CuO/Co₃O₄), butterfly-like (ZnO/CuO), and irregular hybrid structures (ternary) while EDX confirmed the elemental purity and uniform distribution. Photocatalytic testing under direct sunlight (at 7 ppm dye, 0.6 mg catalyst, pH 11, and 180 min) demonstrated that CuO/ZnO/Co₃O₄ exhibited the highest MB degradation efficiency (95 %) and the fastest reaction rate (1.69×10⁻² min⁻¹), outperforming the binary composites. Antibacterial tests against E. coli showed moderate activity across all samples, with CuO/Co₃O₄ achieving the largest inhibition zones (8–16 mm). These findings indicate that the synthesized nanocomposites have potential for environmental remediation and antibacterial applications. Keywords:LitseaGlutinosa; Methylene blue; Nanocomposites; Photocatalytic activity; Antimicrobial activity; Dye degradation.

2025-06-30T00:00:00Z Sabikun Nahar Munna http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7212 2025-12-07T09:07:03Z 2024-04-02T00:00:00Z

Investigation of the adhesive behavior of graphene oxide based crosslinked hydrogels Roy, Dr. Chanchal Kumar; Sabikun Nahar Munna; 0419032703F; 546.681/SAB/2024 Strong adhesion of hydrogels remains a challenge due to the large amount of water in hydrogels. Hydrogel adhesion is primarily influenced by bond chemistries, network topologies, and energy dissipation mechanisms. Hydrogel based adhesive materials have a lot of promise because of their softness, antifouling ability, shock-absorbing capacity, and compatibility with living tissues. However, majority of traditional hydrogels have shown poor adhesion properties to different substrates, including different gel surface. In this study, a new strategy has been developed for making adhesive hydrogel by using graphene oxide based crosslinker (GOBC). The GOBC has multifunctional crosslinking ability to enhance adhesive behavior in hydrogel. Polyacrylic acid (PAA) and polyacrylamide (PAM) hydrogels were prepared by the incorporation of different composition of GOBC. The adhesive test has been performed to compare the adhesive strength of prepared adhesive hydrogels. The mechanical test also has been performed to compare the mechanical properties of adhesive hydrogels. The adhesive properties of GOBC crosslinked polyacrylic acid (PAA-GOBC) hydrogels and GOBC crosslinked polyacrylamide (PAM-GOBC) hydrogels were observed by adhesive force-displacement behavior. From the FC vs √(A/C) plot (FC is maximum force capacity, A is area of contact, C is compliance) the GC (energy release rate) values of PAA-GOBC and PAM-GOBC have been calculated. By comparing these values with polydimetylsiloxane (PDMS) has been gotten the proper conclusion of adhesive property of PAA-GOBC and PAM-GOBC hydrogels. This modification of GOBC hydrogels with good adhesive properties are expected to broaden the application of the adhesive hydrogels in biomedical engineering.

2024-04-02T00:00:00Z Kamrul Hasan http://lib.buet.ac.bd;localhosthttp://:8080/xmlui/handle/123456789/7205 2025-12-03T04:28:11Z 2025-01-05T00:00:00Z

Controllable nanochannel formation in double network hydrogel based electrolytes for enhanced supercapacitor performance Dr. Abu Bin Imran; Kamrul Hasan; 0422032008; 541.392/KAM/2025 Hydrogel materials have gained significant research attention due to their unique three-dimensional polymeric network structure, which not only retains large volumes of water but also enables the incorporation of various functional guest molecules within their tunable porous architecture. In developing stretchable energy storage devices, hydrogels' high-water content and softness properties make them ideal candidates for flexible electronics, particularly in applications like supercapacitors and rechargeable batteries. In this study, we used a double-network hydrogel where the first network, composed of a copolymer of 2-(acryloyloxy) ethyl trimethyl ammonium chloride and acrylic acid (AAc), forms a rigid, brittle matrix. The second network, made of polyvinyl alcohol (PVA), interpenetrates this structure, transforming it into a soft, ductile matrix with enhanced mechanical strength due to the flexibility of PVA. The electrochemical performance was evaluated by a two-electrode system under various scan rates of cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Here, we have reported the formation of controllable nanochannels in double network hydrogel-based electrolytes, which improved ion transport and boosted supercapacitor performance. The 100 nm (7%) porous double-network hydrogel-based electrolyte achieved an ionic conductivity of 12.6 mS/cm and a specific capacitance of 189.3 mF/cm² at a current density of 0.1 mA/cm². In comparison, the non-porous double-network hydrogel-based electrolyte had an ionic conductivity of 2.5 mS/cm and a specific capacitance of 74.7 mF/cm². Additionally, the pores generated by 300 nm (7%) and 500 nm (5%) porous DN hydrogel electrolyte displayed a specific capacitance of 183.3 mF/cm² and 159.0 mF/cm², respectively, at a current density of 0.1 mA/cm². Whereas filter paper as a separator instead of 100 nm (7%) porous DN hydrogel electrolyte has a specific capacitance of 81.77 mF/cm² at a current density of 0.1 mA/cm² and ionic conductivity of 0.89 mS/cm. These findings highlighted that nanochannel formation within double-network hydrogels significantly enhances capacitive performance and positions them as promising materials for supercapacitor applications. Keywords: Double network hydrogel, electrolyte, nanochannel, silica nanoparticle, supercapacitor

2025-01-05T00:00:00Z