Zirconium 4 oxide

Dead leaves of red maple (Acer rubrum) were collected from the ground in Houghton, Michigan, in October 2021. The leaves were thoroughly washed with pure water, laid out to dry at room temperature, and then ground into powders (≤300 μm). Three other types of dead leaves, namely, those of the Cercis canadensis, Quercus rubra, and Acer platanoides, were collected and treated in the same manner. Choline chloride (≥98%), oxalic acid dihydrate (98%), calcium oxalate monohydrate (99%), hydrochloric acid (36% solution), nitric acid (68-70% solution), and hydrogen peroxide (30% solution) were purchased from Thermo Fisher Scientific. Sodium sulfate (≥99%), sodium sulfite (≥98%), sodium hydroxide (≥97%), sodium chlorite (80%), sulfuric acid (95-98%), acetic acid (≥99.7%), tetracycline (98.0-102.0%), methanol (≥ 99.9%), chloroform (≥99.8%), magnesium oxide (97%), chloroplatinic acid hexahydrate (≥37.50% Pt basis), zinc oxide (99.99%), titanium (IV) oxide (P25, ≥99.5%), tungsten (VI) oxide (<100 nm particle size), cerium (IV) oxide (99.95%), zirconium (IV) oxide (99%), gallium (III) oxide (≥99.99%), molybdenum (IV) sulfide (99%), and tungsten (IV) sulfide (99%) were acquired from Sigma Aldrich.