Abstarct: The synthesis of 1,4-disubstituted 1,2,3-triazoles through copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has gained much attention due to its versatility and broad range of applications. In this section, two novel heterogeneous copper catalysts baxsed on dehydroacetic acid chitosan Schiff baxse (DCSB) are reported for the CuAAC reaction in water. The DCSB was synthesized through the condensation reaction of dehydroacetic acid and chitosan, and was subsequently used to support Cu(II) ions and CuO nanoparticles (CuO NPs). The structural and spectral properties of the prepared compounds (DCSB-Cu and DCSB-CuO) were investigated by FT-IR, XRD, FE-SEM, EDX, BET, and TGA analyses. Subsequently, their catalytic activity was evaluated in a model reaction involving the 1,3-dipolar cycloaddition reaction of benzyl chloride, phenylacetylene, and sodium azide in the presence of sodium ascorbate. After optimizing the reaction conditions, the synthesis of other 1,2,3-triazole derivatives was investigated in the presence of these catalysts. Moreover, the recyclability of the catalysts in the CuAAC reaction was examined over four consecutive cycles. A new composite, AgI-loaded CoFe2O4-tobermorite (CFO-Tbm-N-AgI), was synthesized and characterized using FT-IR, EDX, XRD, SEM, UV-Vis DRS, and VSM techniques. The band gap energy for the CFO-Tbm-N-AgI and CFO-Tbm composites was determined to be 2.41 and 2.63 eV, respectively. The mesoporous nature of the composite was confirmed by BET measurements. It effectively degraded the highly toxic Rhodamine B (RhB) dye under visible light irradiation, achieving a degradation efficiency of 96.01%. The effect of various parameters, including initial dye concentration, photocatalyst dosage, and pH, on dye degradation was investigated. The degradation process followed a pseudo-first-order kinetics model with a rate constant (k) of 0.0145 min-1. LC-MS analysis identified N-de-ethylated species as the most probable intermediates formed during RhB degradation. The photo-generated holes (h⁺) were the major species responsible for the photocatalytic degradation of RhB dye, as confirmed through radical scavenging experiments. Furthermore, the reusability of the CFO-Tbm-N-AgI composite was successfully tested over three cycles. In recent years, silver nanoparticles have attracted significant attention as efficient catalysts for the reduction of nitroaromatic compounds using sodium borohydride (NaBH4). In this section, a novel nanocomposite containing magnetic calcium silicate hydrate modified with silver nanoparticles (Fe3O4/CSH/NH2/Ag) was prepared and characterized by FT-IR, EDX, XRD, SEM, and VSM analyses. The catalytic activity of this composite was investigated in the reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4 as a hydrogen source. Moreover, the reduction reactions of other nitroaromatic compounds, including 2-nitroaniline (2-NA), 3-nitroaniline (3-NA), and 4-nitroaniline (4-NA), were successfully tested in the presence of this catalyst. Additionally, the antibacterial activity of Fe3O4/CSH/NH2/Ag and Fe3O4/CSH composites against S. aureus and E. coli strains was measured using the agar well diffusion method. In this section, a new cobalt(II) complex, [Co(L)(NCS)2], containing a bis(aryl imino)pyridine Schiff baxse ligand (L) and two auxiliary thiocyanate (SCN-) ligands, was prepared and its crystal structure was determined. X-ray crystallographic data revealed that the complex crystallizes in the monoclinic space group C2/c, exhibiting a neutral mononuclear [Co(L)(NCS)2] molecule with a distorted square pyramidal coordination geometry. The catalytic activity of this complex was investigated in the aerobic epoxidation of cis-cyclooctene using isobutyraldehyde as a model reaction. Various factors affecting the epoxide yield, including solvent, catalyst loading, reaction time, and temperature, were optimized. Subsequently, the epoxidation of other alkenes such as cyclohexene, 1-octene, and styrene was successfully tested in the presence of this catalyst under optimized conditions. Furthermore, the radical trapping experiments were performed to determine the reaction mechanism.