Enhanced adsorption of micropollutants on oxygen plasma-modified carbon nanotubes (O-CNTs) under electrochemical assistance

The engineering of electro-assisted adsorption reactors provides potential perspectives to cooperate electrochemical technology and adsorption process for valid elimination of emerging micropollutants in wastewater. Herein, electro-responsive adsorbent is prepared through oxygen plasma-modification of carbon nanotubes (OCNTs), followed by molding with epoxy resin and carbonization subsequently. The surface and chemical properties of pristine and modified CNTs are characterized by TEM imaging, XPS analysis, Raman, and FTIR spectroscopy, which indicate the successful introduction of oxygen-containing functional groups on CNTs. The electrically enhanced adsorption performance of organic pollutants on O-CNTs is investigated under different external electric potentials, electrolyte concentrations, and pH values. At the applied potential of +0.6 V, the adsorption capacitive of O-CNTs for aniline and phenol are boosted by 2.6 and 3.3 times than that under open circuit (OC) condition, which has an excellent electro-adsorption capacity of 42.12 mg/g for phenol and 41.58 mg/g for aniline, respectively. The adsorption mechanisms of aniline and phenol on pristine CNTs and O-CNTs are evaluated through the modeling fitting of adsorption behavior. The pi-pi interaction is supposed to be enhanced between the pi-electrons of the oxygen-free Lewis basic sites on the graphite layer of O-CNTs and the free electrons on the aromatic rings of the aniline and phenol molecules. This work provides a practical synthetization of electro-responsive O-CNTs adsorbent through plasma technology and the corresponding electrically-enhanced elimination process of micropollutants. More significantly, this finding offers an electroregulation strategy for CNT-based adsorption material to achieve both high adsorption capacity and high efficiency in contaminated-water treatment.