Efficient Removal of Hexavalent Chromium and Congo Red by Graphene Oxide/Silica Nanosheets with Multistage Pores

Graphene oxide (GO)/silica nanosheets (GO/MS@HBP) were synthesized through in situ hydrolysis of tetraethoxysilane (TEOS) on graphene oxide (GO) nanosheets, followed by modification of hyperbranched polymer (HBP) to remove multiple pollutants (Cr(VI) and Congo red (CR)). Characterization methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric-differential scanning calorimetry (TG-DSC), Raman, N2 adsorption/desorption, and X-ray photoelectron spectroscopy (XPS), etc. were adopted. The results of Brunauer–Emmett–Teller (BET) analysis revealed that the prepared GO/MS@HBP has a multistage pore structure with a specific surface area of 345.7176 m2·g–1. The factors of adsorbent dosage, adsorption time, initial solution concentration, pH, etc. that influence adsorption were studied. The maximum adsorption quantities of Cr(VI) and CR at room temperate were 92.2510 and 416.6667 mg·g–1, respectively, and the removal could still be over 90% after three cycles for Cr(VI). Pseudo-second-order kinetic and Langmuir isotherms were more suitable to describe the adsorption process. A possible adsorption mechanism was also proposed. It could be considered as a promising adsorbent because of its good adsorption effect and reproducible property.