2.1 Materials
Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was bought from Tianjin Fengchuan Co., Ltd. Potassium permanganate (KMnO4, ≥99.5%) was obtained from Luoyang Haohua Co., Ltd. Methyl orange (C14H14N3SO3Na, AR), Pyrrole (C4H5N, ≥99%), and Iron chloride hexahydrate (FeCl3·6H2O, AR) were purchased from Shanghai Aladdin Co., Ltd. Commercial sulphuric acid (H2SO4) 99.9%, and ethanol were used as received which were purchased from China National Pharmaceutical Group Co., Ltd. All aqueous solutions are formulated with deionized (DI) water, and the chemicals can be used without any further purification.