Carboxyl-rich carbon nanocomposite based on natural diatomite as adsorbent for efficient removal of Cr (VI)

Carboxyl-rich carbon nanocomposite based on natural diatomite was successfully synthesized as an effective adsorbent for removing Cr(VI) in aqueous solution in this work. The obtained carboxyl-rich carbon nanocomposites were comprehensively characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), N2 adsorption-desorption apparatus, zeta potential and Fourier transform infrared spectrometer (FTIR). After systematic and detailed study of the adsorption process, it is found that the initial pH of Cr(VI) aqueous solution has an important effect, and pH=1 should be the optimum condition for Cr(VI) adsorption at room temperature. It is proved that the introduction of carboxyl-containing functionalized groups was beneficial to improve the adsorption capacity. The adsorption process of Cr(VI) conforms to the pseudo-second-order kinetic model and Langmuir isotherm, and the adsorption behaviour is endothermic and spontaneous. Additionally, the maximal adsorption capacity towards Cr(VI) can reach to 142.857mg/g at 298.15K, which is significantly improved compared with the sample without carboxyl functionalization (19.4mg/g). Moreover, the prepared adsorbent can be recycled and reused at least four times after being washed by alkali solution. This study indicated that the carboxyl-rich carbon nanocomposite based on diatomite would be promising in removing heavy metal ions (Cr(VI)) from wastewater.