Background: Acacia arabica tree is a moderate-sized, short-trunked, and almost evergreen tree mostly found in drier areas. The aqueous stem bark extract of this plant contains phenolic, condensed tannin which acts as a reducing and capping agent in green synthesized ZnO NPs, making it the least toxic semiconductor photocatalyst for the treatments of wastewater containing dye effluents, with moderate bandgap energy.

Methodology: At the initial stage, a 40 mL aqueous leaf extract of Acacia arabica wascombined with 460 mL of 4.36M (CH₃COO)₂Zn.2H₂O and heated at 60°C while stirring, after which the obtained precipitate was filtered. Next, 30 mL of NH₄OH solution was added dropwise to 500 mL of the filtrate obtained from the initial reaction stage with constant stirring for 20 minutes at room temperature, and then stirred at 60°C for 4 h. The resulting chemo-green ZnO NPs were filtered and washed with ethyl alcohol, followed by calcination at 450⁰C for 2.5 h, then again washed with ethyl alcohol and dried in an oven at 100⁰C. XRD, zeta potential, and FTIR and DRS, measurements were carried out to examine the crystallinity, surface charge, and optical properties of chemo-green synthesized ZnO NPs. For photocatalytic testing, a 10 mg/L aqueous solution of malachite green dyes and 1 g/L ZnO NPs was stirred in the dark, followed by irradiation in sunlight.

Results and Discussion: Here, chemo-green synthesized ZnO NPs have direct band gap energies equivalent to ZnO NPs from the chemical and green method; they had negatively charged surfaces and good dye degradation in 160 minutes, which suggests the reutilization of unused filtrate obtained from the green method for further high-yield synthesis of ZnO NPs with scant use of ammonium hydroxide, stimulating sustainability and lightening the economic burden; they can be used for the demineralization of dyes coming from wastewater from the textile industry.