Optimization of green synthesis process and characterization of metal oxide-based nano absorbents.

Every dairy plant has the same problem wastewater treatment generates sludge, and nobody knows what to do with it. Most of it just gets disposed of. This study asked a different question: could that sludge actually be useful
Specifically, could it work as a biological extract for making zinc oxide nanoparticles without any toxic chemicals involved Dairy sludge from Nandini Milk Factory, Mysuru was collected and tested against other dairy waste
fractions before being selected as the extract source. Zinc nitrate hexahydrate
served as the metal precursor and NaOH was used for pH control. The proteins,
phenolic acids, polysaccharides, and lipids naturally present in the sludge did
the job of both reducing the zinc ions and stabilizing the particles that formed
no synthetic reducing agents, no surfactants.
Four synthesis parameters were optimized using a Box-Behnken Design
precursor concentration, reaction temperature, reaction pH, and incubation time
across 30 experimental runs, with particle size and zeta potential as the
measured responses. What came out most clearly was that pH controls particle
size more than anything else. At pH 5.5 particles came out as small as 275 nm.
Push pH above 9 and the particles agglomerate badly, reaching over 2000 nm.
Temperature drove zeta potential more than any other single factor, with 80°C
giving the most stable colloidal suspension. The combined effect of temperature
and incubation time together turned out to be the strongest statistical term in the
entire zeta potential model neither factor alone tells the full story.
The final ZnO nanoparticles came out at 278 nm with a zeta potential of -48
mV. That zeta value puts the suspension firmly in the highly stable category.
Taken together these findings show dairy sludge works as a synthesis matrix for
green ZnO production and point clearly toward the parameter region worth
targeting in future work, particularly for antimicrobial and antioxidant testing