Zinc acetate zn ch3coo 2

Zinc acetate (Zn (CH₃COO)₂) as a precursor for zinc oxide nanoparticles was purchased from Sigma Aldrich Co, Dresden, Germany. Meanwhile, sodium hydroxide, and sodium alginate were purchased from Across Co., St. Louis, MO, USA. Streptozotocin (STZ) and homocysteine standard were purchased from Sigma Chemical Co., St. Louis, MO, USA. Deionized water was used for dilution, analysis, and application. All other chemicals are of analytical grade and were used as received without further purification or modification.

Before coating with zinc oxide, the surface of the ball resonator optical fibers was cleaned in 20 mL of Piranha solution (H₂SO₄:H₂O₂ = 4:1) for 20 min to remove organic impurities and increase -OH groups. Then, the sensors were washed with distilled water and dried with nitrogen gas, followed by silanization in a 5% solution of (3-aminopropyl) trimethoxysilane (APTMS) in methanol solution for 30 min. Next, the optical fibers were heat treated for 60 min at 100 °C and then coated with a layer of zinc oxide using the sol–gel method [41 (link)]. The sol was deposited by dissolving 0.4 g of zinc acetate Zn(CH₃COO)₂ (purity 98%, Sigma-Aldrich, St. Louis, MO, USA) in 10 mL of ethanol at room temperature with vigorous stirring on a magnetic stirrer for 1 h. Afterwards, the sol solution was uniformly applied to surface of the ball resonator by dip-coating technique and dried in a muffle furnace at 100 °C for 10 min. Subsequent annealing at 250 °C for 60 min resulted in the formation of a uniform ZnO thin layer on the surface of the spherical tip. The ZnO immobilization on the surface of the ball resonator optical fiber was verified by scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

The zinc–air battery tests were performed by the home-made liquid zinc–air battery which was assembled using a polished Zn foil (0.25 mm thickness) as the metal electrode and the semiconductor photoelectrode (i.e., BiVO₄ or α-Fe₂O₃) as the air electrode. The electrolyte used was 1 M KOH with 0.03 M zinc acetate (Zn(CH₃COO)₂, 99.99%, Sigma-Aldrich) (dissolved in KOH to form zincate, $\mathrm{Zn}{\left(\mathrm{OH}\right)}_4^{2\mathrm{-}}$ ) to ensure reversible Zn electrochemical reactions at the Zn electrode. For comparison, the performance of sunlight-promoted rechargeable zinc–air batteries was tested under the same conditions as traditional zinc–air batteries except the illumination on the photoelectrode. The galvanostatic discharge–charge cycling tests (20 min discharge followed by 20 min charge) were performed by Land-CT2001A battery-testing system (Wuhan LAND Electronic Co., Ltd, China) in the dark and under illumination, respectively. The specific capacity (mAh g⁻¹) and the energy density (mWh g⁻¹) based on the weight of consumed Zn are calculated according to Eqs. 15 and 16: $\mathrm{Specific}\mathrm{capacity}=\frac{\mathrm{Discharge}\mathrm{current}\times \mathrm{Service}\mathrm{hours}}{\mathrm{the}\mathrm{weight}\mathrm{of}\mathrm{consumed}\mathrm{Zn}}$ $\mathrm{Energy}\mathrm{density}=\frac{\mathrm{Discharge}\mathrm{current}\times \mathrm{Service}\mathrm{hours}\times \mathrm{Average}\mathrm{discharge}\mathrm{voltage}}{\mathrm{the}\mathrm{weight}\mathrm{of}\mathrm{consumed}\mathrm{Zn}}$