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 (O-CNTs), 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 π-π interaction is supposed to be enhanced between the π-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 electro-regulation strategy for CNT-based adsorption material to achieve both high adsorption capacity and high efficiency in contaminated-water treatment.