*2.1. Materials*

Rice straw was harvested at the South China Agricultural University in 2016. Benzene (99.5%, AR, Damao Chemical Reagent Factory, Tianjin, China), ethanol (99.7%, AR, Guangzhou Chemical Reagent Factory, Guangzhou, China), sodium chlorite (NaClO2, 80%, Aladdin), acetic acid glacial (CH3COOH, 99.5%, AR, Guangzhou Chemical Reagent Factory), potassium hydroxide (KOH, 85%, AR, Shanghai RichJoint Chemical Reagents, Shanghai, China), hydrochloric acid (HCl, 1 N, certified, Guangzhou Chemical Reagent Factory), sodium hydroxide (NaOH, 96%, Guangzhou Chemical Reagent Factory), sodium hypochlorite (NaClO, 8.0%, AR, Damao Chemical Reagent Factory), 2,2,6,6-tetramethylpyperdine-1-oxyl (TEMPO, 98%, Aladdin), sodium bromide (NaBr, 99.9%, AR, Tianjin Fuchen Chemical Reagent Factory, Tianjin, China), methylene blue (MB, AR, Tianjin Fuchen Chemical Reagent Factory), Congo red (CR, Tianjin Fuchen Chemical Reagent Factory), graphene nanoplates (GnPs, Aldrich, grade C-750, thickness: a few nm, particle size: <2 μm, specific surface area: 750 m2 g−1), and OH-functionalized multi-walled carbon nanotubes (CNTs, Cheap Tubes, external diameter: 50–80 nm, internal diameter: 5–10 nm, length: 10–20 μm, OH content: 5.5%, specific surface area: 60 m2 g−<sup>1</sup> [30]) were used as received. The chemical formula, maximum absorption wavelength and electrical property under neutral pH of MB and CR are shown in Table S1. The deionized (DI) water used was purified by an AIKE Advanced-II-OS water purification system (Cheng Du Kangning Science and Technology Development Company, Chengdu, China).
