Abstract
A novel graphene-based composite, 5-methyl-1,3,4-thiadiazol-2-amine (MTA) covalently functionalized graphene oxide (GO-MTA), was rationally developed and used for the selective sorption of Ga(3+) from aqueous solutions, showing a higher adsorption capacity (48.20 mg g(-1)) toward Ga(3+) than In(3+) (15.41 mg g(-1)) and Sc(3+) (~0 mg g(-1)). The adsorption experiment's parameters, such as the contact time, temperature, initial Ga(3+) concentration, solution pH, and desorption solvent, were investigated. Under optimized conditions, the GO-MTA composite displayed the highest adsorption capacity of 55.6 mg g(-1) toward Ga(3+). Moreover, a possible adsorption mechanism was proposed using various characterization methods, including scanning electron microscopy (SEM) equipped with X-ray energy-dispersive spectroscopy (EDS), elemental mapping analysis, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Ga(3+) adsorption with the GO-MTA composite could be better described by the linear pseudo-second-order kinetic model (R(2) = 0.962), suggesting that the rate-limiting step may be chemical sorption or chemisorption through the sharing or exchange of electrons between the adsorbent and the adsorbate. Importantly, the calculated q(e) value (55.066 mg g(-1)) is closer to the experimental result (55.60 mg g(-1)). The well-fitted linear Langmuir isothermal model (R(2) = 0.972~0.997) confirmed that an interfacial monolayer and cooperative adsorption occur on a heterogeneous surface. The results showed that the GO-MTA composite might be a potential adsorbent for the enrichment and/or separation of Ga(3+) at low or ultra-low concentrations in aqueous solutions.