RESUMO
Electrocatalysts facilitating chlorine evolution reaction (ClER) play a vital role in chlor-alkali industries. Owing to a huge amount of chlorine consumed worldwide, inexpensive high-performing catalysts for Cl2 production are highly demanded. Here, a superb ClER catalyst fabricated through uniform dispersion of Pt single atoms (SAs) in C2 N2 moieties of N-doped graphene (denoted as Pt-1) is presented, which demonstrates near 100% exclusive ClER selectivity, long-term durability, extraordinary Cl2 production rate (3500 mmol h-1 gPt -1 ), and >140 000-fold increased mass activity over industrial electrodes in acidic medium. Excitingly, at the typical chlor-alkali industries' operating temperature (80 °C), Pt-1 supported on carbon paper electrode requires a near thermoneutral ultralow overpotential of 5 mV at 1 mA cm-2 current density to initiate the ClER, consistent with the predicted density functional theory (DFT) calculations. Altogether these results show the promising electrocatalyst of Pt-1 toward ClER.
RESUMO
Phytochemical study on the extract of Vietnamese medicinal plant Helicteres hirsuta Lour. has led to the isolation and structural elucidation of twelve secondary metabolites, 3-O-trans-caffeoylbetulinic acid (1), 3ß-benzoylbetulinic acid (2), betulinic acid methyl ester (3), betulinic acid (4), lupeol (5), 4-hydroxybenzoic acid (6), 3,4-dihydroxybenzoic acid methyl ester (7), 4-hydroxy-3,5-dimethoxybenzoic acid (8), 5,8-dihydroxy-7,4'-dimethoxyflavone (9), isoscutellarein 4'-methyl ether 8-O-ß-D-glucopyranoside (10), methyl caffeate (11) and stigmasterol (12). Especially, compound 2 was reported as a new natural product. Their structures were elucidated by a combination of 2D NMR and ESI-FT-ICR-MS spectroscopies. Furthermore, eight compounds were tested for their cytotoxicity against five cancer cell lines (Hela, HepG2, SK-LU-1, AGS and SK-MEL-2). The results showed that compounds (1, 3-5, 9) have moderate activities. This is the first study on the chemical constituents and their cytotoxicity of the Vietnamese Helicteres hirsuta L.