Table 1.

Effective variables and their working ranges for Box-Behnken design.

Factors	Lower level (− 1)	Center point (0)	Higher level (+ 1)
A: nozzle size (do), mm	0.46	0.57	0.68
B: NPs fraction ($\omega$), wt.%	0.01	0.055	0.10
C: contact time ($\tau$), s	150	300	450