Metal-free catalysis of persulfate activation and organic-pollutant degradation by nitrogen-doped graphene and aminated graphene

Abstract

We evaluated three types of functionalized, graphene-based materials for activating persulfate (PS) and removing (i.e., sorption and oxidation) sulfamethoxazole (SMX) as a model emerging contaminant. Although advanced oxidative water treatment requires PS activation, activation requires energy or chemical inputs, and toxic substances are contained in many catalysts. Graphene-based materials were examined herein as an alternative to metal-based catalysts. Results show that nitrogen-doped graphene (N-GP) and aminated graphene (NH2-GP) can effectively activate PS. Overall, PS activation by graphene oxide was not observed in this study. N-GP (50 mg L(-1)) can rapidly activate PS (1 mM) to remove >99.9% SMX within 3 h, and NH2-GP (50 mg L(-1)) activated PS (1 mM) can also remove 50% SMX within 10 h. SMX sorption and total removal was greater for N-GP, which suggests oxidation was enhanced by increasing proximity to PS activation sites. Increasing pH enhanced the N-GP catalytic ability, and >99.9% SMX removal time decreased from 3 h to 1 h when pH increased from 3 to 9. However, the PS catalytic ability was inhibited at pH 9 for NH2-GP. Increases in ionic strength (100 mM NaCl or Na2SO4) and addition of radical scavengers (500 mM ethanol) both had negligible impacts on SMX removal. With bicarbonate addition (100 mM), while the catalytic ability of N-GP remained unaltered, NH2-GP catalytic ability was inhibited completely. Humic acid (250 mg L(-1)) was partially effective in inhibiting SMX removal in both N-GP and NH2-GP systems. These results have implications for elucidating oxidant catalysis mechanisms, and they quantify the ability of functionalization of graphene with hetero-atom doping to effectively catalyze PS for water treatment of organic pollutants including emerging contaminants.

Biochar‐mediated oxidation of phenol by persulfate activated with zero‐valent iron

“…Persulfate activated by dimensional‐structured nanocarbons can reportedly remove nearly 100% of phenols after 30 min . In addition, oxidative degradation of sulfamethoxazole reached 99.9% removal by persulfate activated with nitrogen‐doped or aminated graphene after 3 h …”

“…Previous studies have showed that persulfate can be induced through various methods to emit sulfate radicals (SO 4 − ·) ( E o = 2.6 V), relatively strong oxidants with a voltage only slightly lower than that of the hydroxyl radical (·OH) ( E o = 2.7 V) . Activation methods include heat, ultraviolet light, transition metals, and metal‐free carbon catalysts …”

A magnetic CoFe2O4–CNS nanocomposite as an efficient, recyclable catalyst for peroxymonosulfate activation and pollutant degradation

“…5(a)), but was decreased only by 22% (within 5 min) with TBA addition. Therefore, the key role of SO 4 c À in the SA degradation can be conrmed.…”

“…Advanced oxidation processes (AOP) based on the sulfate radical (SO 4 c À ) are promising alternatives to those based on hydroxyl radicals for water treatment and environmental remediation applications, with advantages such as high redox potential (2.5-3.1 V), 1 relatively long lifetime and wide pH range.…”

Ultra-sustainable Fe78Si9B13 metallic glass as a catalyst for activation of persulfate on methylene blue degradation under UV-Vis light

“…Because of the strong redox potential and stability, persulfate (S 2 O 8 2− , E o  = 2.01 V19) is a promising source of SO 4 ∙ − . The established methods for easily activating S 2 O 8 2− to SO 4 ∙ − are sole activation by UV20 or heat21, and catalytic activation by metal-free catalyst22 or metal-based catalyst232425. Among these methods, the production rate of homogeneous activation of SO 4 ∙ − by heat ( k  = 1.0 × 10 −7  M −1 s −1  19) is relatively lower compared to catalytic activation.…”