Synthesis and characterization of graphene oxide-doped nano-hydroxyapatite and its adsorption performance of toxic diazo dyes from aqueous solution

In this study, graphene oxide-doped nano-hydroxyapatite (nHAp@GO) composite was synthesized via a simple in-situ one-pot method and was used as an adsorbent for the removal of toxic diazo dyes, Congo Red (CR) and Trypan Blue (TB), in water. A remarkable adsorption capacity for CR (48.5 mg/g) and TB (41.0 mg/g) were shown on the surface of nHAp@GO (2 g/L), respectively, and was much higher than those of bare nHAp or GO. After doping of GO on nHAp, the specific surface area of nHAp was increased by 2.5 times. The presence of sulphur peak in EDX spectrum and S–O stretching vibration peak in FTIR confirmed the adsorption of dyes on the surface of nHAp@GO composite. After the adsorption process, the shifting of d₍₁₀₀₎ spacing of nHAp confirmed the loading of bulky organic moieties on nHAp@GO composite. Maximum CR and TB dyes adsorption occurred in a wide range of initial pH between 3.0 and 10.0. The adsorption of both CR and TB dyes are due mainly to the electrostatic interaction, π − π stacking interaction, hydrophobic interaction, and hydrogen bonds between dyes and nHAp@GO composite. The nHAp@GO nanocomposite was recycled up to three times at the sustained efficiency after washing with ethanol solution. We believe that such multifunctional material developed in this study will be effectively used for the depollution of toxic diazo dyes in practical applications.