Hydroquinone

C₃N₄ nanosheets were synthesized
using a previously reported procedure by heating 10 g of urea (>99%,
Wako Pure Chemicals Co.) at 823 K in air for 2 h in a crucible in
a muffle furnace.^{29 (link)} Plasma treatment of
C₃N₄ was conducted in a hydroquinone-containing
aqueous solution using a previously reported setup.^{52 (link),53 (link)} Nonequilibrium plasma was generated in a NaCl solution (0.1 g L⁻¹) containing 1 wt % C₃N₄ and
4 wt % hydroquinone (>99%, Wako Pure Chemicals Co.) in 100 mL of
deionized
water and dispersed using a magnetic stirrer. A bipolar pulse with
an amplitude of 1.6 kV, a current of 6 A, a repetition frequency of
80 kHz, and a pulse width of 0.4 ms was applied to tungsten rods (diameter:
1 mm) separated by a 2 mm gap, and the plasma was maintained for 1
h. Figure S1 shows the voltage–current
characteristics, optical emission spectrum, and a photograph of the
plasma. After plasma treatment, the remaining hydroquinone and byproducts
were removed using water, methanol, DMA, and acetone, and the washed
plasma-C₃N₄ was dried overnight under a vacuum.

The deoxyArbutin was obtained from Denjelly Co., Ltd. (Miaoli, Taiwan, R.O.C) and arbutin was purchased from Alfa Aesar (Ward Hill, MA, USA). Hydroquinone was purchased from Wako Pure Chemical Industries (Osaka, Japan). Propylene glycol (PG), sodium hydroxide (NaOH), sodium dodecyl sulfate (SDS), and other chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA). Dulbecco’s modified Eagle’s medium (DMEM), α-modified essential medium (α-MEM), fetal bovine serum (FBS), trypsin-EDTA, penicillin, and streptomycin were purchased from Gibco BRL/Invitrogen (Carlsbad, CA, USA). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was purchased from USB Affymetrix (Cleveland, OH, USA). The Caspases-3 assay kit with subtracts Asp-Glu-Val-Asp p-nitroanilide (DEVD-pNA) and anti-caspase-3 antibody was purchased from BioVision, Inc. (Milpitas, CA, USA). Deionized distilled water (ddH₂O) for solutions and buffers was produced by the Milli-Q system (Millipore, Bedford, MA, USA).

Na ion-exchanged Y-type zeolite (Na-Y) with SiO₂/Al₂O₃ = 5.5 was supplied by Tosoh Co. The following chemicals were used as received: FeSO₄∙7H₂O (Wako, > 99%), sodium nitrate (Wako, 99.0%), ethylenediaminetetraacetate acid (TCI, 98.0%), ethylenediaminetetraacetate acid disodium salt (Wako, 99.5%), sodium hydroxide (Wako, 93%), 2,2′;6′,2″-terpyridine (TCI, 98.0%), methanol (Wako, 99.8%), 30% aqueous hydrogen peroxide (Wako, 30–35.5%), benzene (Wako, 99.5%), phenol (Wako, 99.0%), catechol (Wako, 99.0%), hydroquinone (Wako, 99.0%), o-dichlorobenzene (Wako, 98.0%), and acetonitrile (Wako, 99.5%).
ICP-AES and CHN elemental analyses of all catalysts were carried out after the sample was dissolved into a HF solution. The powder XRD patterns of the catalysts were collected on a Rigaku MiniFlex II diffractometer using CuKα radiation. The Brunauer–Emmet–Teller (BET) surface area measurements were conducted to determine the specific surface areas and pore diameters of the samples by performing N₂ adsorption experiments at 77 K using a BEL Japan Bellsorp-max instrument. The UV-vis spectra were recorded on a Hitachi U-4000 spectrometer for solid samples. Gas chromatography (GC, Shimadzu GC-2014) was performed using a flame ionization detector equipped with a DB-1MS capillary column (internal diameter = 0.25 mm and length = 30 m) at the nature of the non-polar liquid phase.