Synthesis of electrically conducting composite adsorbents for wastewater treatment using adsorption & electrochemical regeneration

Electrically conducting adsorbent materials called Nyex™ 1000 & 2000 have already been reported with comparatively low adsorption capacity for various organic, biologically non-degradable and toxic compounds. Two composite adsorbents called CA1 & CA2 were synthesized using synthetic graphite-carbon black and expanded graphite-carbon black respectively. The aim of developing the new adsorbents was to increase the adsorption capacity along with good electrical properties. The developed adsorbents were characterized using N2 adsorption for specific surface area, Boehm surface titration for surface chemistry, bed electrical conductivity, laser size analyzer for average particle size, and scanning electron microscope (SEM) for particle morphology and shape. Then both the composite adsorbents were tested for the adsorption of acid violet 17 followed by an electrochemical regeneration. The adsorption study revealed that both the adsorbents had almost similar kinetic behavior with a significant increase in adsorption capacity for acid violet 17 (300 & 26 mg g−1 respectively) when compared with the adsorption capacity of previously developed electrically conducting materials called Nyex™ 1000 & 2000 (3.5 and 9 mg g−1 respectively). The composite adsorbent CA2 was successfully electrochemically regenerated by passing an electric charge of 138 C g−1 at a current density of 14 mA cm−2 for a treatment time of 60 min, whereas, the composite adsorbent CA1 could not be regenerated successfully. The regeneration efficiencies of CA2 were obtained at around 120% during five adsorption–regeneration cycles. The amount of actual charge passed of 138 C g−1 for achieving 100% regeneration efficiency was found to be similar with stoichiometrically calculated amount of charge. The amount of electrical energy required to oxidize each mg of adsorbed acid violet onto CA2 (24 J mg−1) was found to be significantly lower to that of Nyex™ 1000 & 2000 adsorbents (52 J mg−1 & 32 J mg−1 respectively).