Highly-efficient and selective adsorption of phenols by GO-BT composite in the presence of rare earth elements

Recently, industrial activities have produced large quantities of wastewater containing metal ions (such as rare earth elements) or organic contaminants (such as phenols), which are difficult to be degraded or recycled. Carbon nanocomposites have been considered to be a kind of effective adsorbent for the separation/enrichment of organic substances or metal ions from aqueous solutions. To selectively adsorb/remove these contaminants, 2- bis(2-hydroxyethyl)amino-2-(hydroxymethyl)- 1,3-propanediolwas utilized as a functional component to modify graphene oxide (GO) by a facile one-step coupling method. The fabricated GO-BT composite was char-acterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, specific surface area analysis, thermogravimetric analysis and Zeta potential analysis. The equilibrium adsorption capacities of GO-BT composite for Y3+, Yb3+, Eu3+, Sm3+, Nd3+, La3+, Er3+, Pr3+, p-chlorophenol (PCP), p-methylphenol (PMP), phenol and aniline were tested to be 24.89, 28.13, 18.77, 57.46, 26.25, 33.12, 22.64, 6.529, 486.5, 391.8, 268.0 and 60.34 mu mol g-1, respectively. The selectivity coefficient of GO-BT composite toward Y3+ against phenol was 0.2999, confirming its excellent adsorption selectivity for organic phenols rather than rare earth elemental (REE) ions. After 10 times of adsorption-desorption cycles, GO-BT composite maintained 80% removal rate and considerable recycling per-formance. The adsorption process could be better described by the pseudo-second order kinetic model and the non-linear Langmuir isothermal model. Adsorption thermodynamic studies demonstrated a non-spontaneous and exothermic process with decreasing randomness. This work can provide some references for fabricating GO-based adsorbents for selective removal of organic reagents in the flotation separation of REE ores.