L ascorbic acid l aa

Polyallylamine hydrochloride (PAH, weight-average molecular weight 150 000) was supplied by Nitto Boseki Co., Ltd. (Tokyo, Japan). l-Ascorbic acid (l-AA) and ammonia solution (NH₃·H₂O) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Methotrexate (MTX) was purchased from Huzhou Prospect Pharmaceutical Co. (Zhejiang, CN). Dialysis membrane (molecular weight cut-off = 8000–14 000 Da) was purchased from Shanghai Green Bird Technology development Co., Ltd. Human lung adenocarcinoma cells (A549) were purchased from Shanghai Cell bank (Shanghai, CN). All reagents were of analytical grade and used without further purification. All the aqueous solutions were prepared using Milli-Q water with a resistivity of 18.2 MΩ (Purelab Classic Corp., USA).

Natural graphite powder (200 mesh, 99.9% purity), cupric chloride, concentrated sulphuric acid (98%), potassium permanganate, hydrogen peroxide (30%), hydrochloric acid, hydrazine hydrate (80%) and ammonia solution (30%) were purchased from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). L-Ascorbic acid (L-AA) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). All chemicals were of analytical grade and used as received without further purification. Deionized water was prepared in a Milli-Q Plus system (Millipore, Milford, MA, USA).