Table 3. Synthesis of nanoparticles for dye degradation with NaBH₄ as a co-catalyst.

Nanoparticles	Precursor	Condition	Size and shape	Application	References
FeNPs	(FeCl3·6H2O), Vernonia amygdalina leaf extract, ethanol	Room temperature	(1–4 µm) average particle size 2.31 µm	Catalytic degradation of methylene blue and crystal violet dye	69
AuNPs	AuCl3·HCl·4H2O, polyvinyl alcohol, polydopamine, sodium alginate, CaCl2-saturated boric acid, HCl, CaCO3, dopamine	Room temperature	Spherical in shape and diameter ranging from 5 to 60 nm	Degradation of rhodamine B	102
AgNPs	Imperata cylindrica, AgNO3	Heat (water bath) at 60 °C for 10 min	Average particle size was 31 nm	Degradation of methylene blue dye	103
Ag NPs, Ni NPs, Cu NPs	(CuCl2·2H2O), (NiCl2·6H2O), (AgNO3), (N2H4·H2O), PEG (biopolymer), PVP (synthetic polymer)	Wet chemical reduction method	Cu and Ag were spherical to cubic, uniform, and homogeneous in morphology, the Ni-NPs were polycrystalline 3–25 nm (Cu-NPs), 7–38 nm (Ni-NPs), and 4–45 nm (Ag-NPs)	Degradation of crystal violet, bromocresol green, and methylene blue	98
Ag NPs	Peltophorum pterocarpum leaves, NaOH pallets, AgNO3, nitric acid	80 °C for 45 min at pH 9	Spheres and ellipses with sizes in the range of 2–50 nm	Degradation of methylene blue dye	104