Effective and selective removal of organic pollutants from aqueous solutions using 1D hydroxyapatite-decorated 2D reduced graphene oxide nanocomposite

The efficient and selective removal of toxic dye molecules from water/surface water remains a problematic task, owing to their high water solubility and low biodegradability. We fabricated the hydroxyapatite-decorated reduced graphene oxide (HA@rGO) nanocomposites via a simple hydrothermal process and used them as efficient adsorbents for the diazo dyes removal. In the batch experiments, the resultant HA@rGO nanocomposites exhibited fast and excellent removal performance for Trypan blue and Congo red dye molecules in a wide pH range and the maximum adsorption efficiencies of 146.51 and 150.09 mg/g, respectively. Several characterization analysis results demonstrated that the removal performance of the HA@rGO nanocomposites for the toxic dyes was mainly driven by electrostatic, hydrophobic, π–π interactions, and H-bonding between the adsorbents and dye molecules in the aqueous solution. Ubiquitous co-anions have significant influence on the dye removal performance of the HA@rGO nanocomposites because of the higher ionic radius and electronegativity. After adsorption, the exhausted HA@rGO nanocomposites could be regenerated in alkaline solution and reused throughout five successive adsorption–desorption cycles. We believe that the adsorbent fabricated in this work can be effectively used to remove toxic diazo dye molecules from aqueous media.