Reusability of OSNP for dye adsorption. (A) The OSNP can be reused
for phenol red adsorption (t = 5 min, pH = 2 treatment,
RT, 0.25 mg/mL or 0.66 mM phenol red, 2 mg of OSNP). Error bars represent
the standard deviation for 3 measurements. (B) The OSNP changed from
white to pink after addition to phenol red solutions and centrifugation
due to adsorption (Ads.), but they became white again after base treatment
due to dye desorption (Des.). (C) Change of zeta potential after dye
adsorption and recovery of zeta potential after dye desorption. NPs
represent the original OSNP; A1, A2, and A3 represent NPs after adsorption
in cycles 1, 2, and 3; D1, D2, and D3 represent NPs after desorption
in cycle 1, 2, and 3. (D) The accumulative loss of loss in the first
10 cycles. (E) The color of supernatant after desorption was more
intense than after adsorption indicating a high adsorption and desorption
efficiency.