N-Nitrosodimethylamine (NDMA) is a disinfection byproduct of concern because of its carcinogenicity and toxicity at low concentrations. The efficient removal of NDMA from water is challenging due to its polarity and high miscibility with water. In this study, coconut shell activated carbon (AC) was modified by heat treatment at 800 degrees C (AC800) to obtain an efficient sorbent for the adsorption of NDMA in water. Results revealed a more than 50% increase in NDMA adsorption upon heat treatment. The heat treatment improved the surface area of AC from 984 to 1,124 m2/g. The elemental analysis revealed that AC’s carbon content (%C) improved (from 86% to 91%), whilst oxygen content (%O) decreased (from 11% to 6%) upon heat treatment. Similar trends were observed on the surface of AC (92% C and 7% O) and AC800 (94% C and 5% O), as shown by the X-ray photoelectron spectroscopy (XPS). AC800 surface became more hydrophobic and less polar due to lower oxygen content. It is hypothesized that NDMA adsorption occurs through hydrogen bonding of the N-nitroso group (N=O) of NDMA with oxygen-containing functional groups of AC and hydrophobic-hydrophobic interactions between methyl groups of NDMA and AC surface. The significant improvement of NDMA adsorption upon heat treatment suggested that hydrophobic interactions dominate polar interactions. Our results revealed that chemisorption plays a significant role in NDMA adsorption. These mechanistic insights were applied to improve NDMA extraction through SPE cartridges for trace-level analysis of NDMA in water and synthetic wastewater effluents, where more than 100% recoveries were observed by using AC800. Additionally, a continuous column study conducted for 25 days using AC and AC800 showed significantly higher bed adsorption capacity for 10% breakthrough of AC800 (1.21 ug/g) than that of AC (0.48 ug/g). Our results revealed an efficient and economical method of extracting NDMA from water.

Thermally modified coconut shell activated carbon as efficient adsorbent for N-nitrosodimethylamine

ACS Fall 2021

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