A novel and an efficient 3-D high nitrogen doped graphene oxide adsorbent for the removal of Congo red from aqueous solutions

Abstract

The current study both synthesizes and uses four compounds of graphene oxide (GO), nitrogen doped graphene oxide (ND-GO), high nitrogen doped graphene oxide (HND-GO), and three dimensional high nitrogen doped graphene oxide (3D-HND-GO) in order to remove a model anionic dye, Congo red (CR) from wastewaters. It also compares their carbon nano-structure, with regard to removal efficiency and finds out that 3D-HNDG yields higher efficiency in removal of CR, especially at lower pHs. This is due to its better dispersibility and greater surface area. Also, batch adsorption technique has been utilized and all involved parameters that affect the removal efficiency, e.g. initial pH, adsorbent dosage, initial CR concentration, and contact time are examined. The study applies Central Composite Design (CCD) to figure out their efficacies, with the results showing the following optimum conditions for removal of 100 ppm of CR: 4 mg/mL of the adsorbent, pH = 3, and 25 min of contact time. Furthermore, it studies the adsorption activity of the synthesized adsorbent, including kinetics, isotherm, and desorption comprehensibly. The adsorption isotherm is well-fitted through the Langmuir model, exhibiting high CR adsorption capacity. Also, CR adsorption kinetics shows that it has obeyed a pseudo-second-order kinetic model, indicating that adsorption has made the ratelimiting step. In addition, the proposed adsorbent has successfully been applied to reduce the concentration of CR as hazardous dye materials in the water and wastewater samples.