A 3D Porous Structured Cellulose Nanofibrils-Based Hydrogel with Carbon Dots-Enhanced Synergetic Effects of Adsorption and Photocatalysis for Effective Cr(VI) Removal

Increasing chromium pollution poses a significant threat to the global environment and human health, and it is critical to remove hexavalent chromium (Cr(VI)) from water. Hence, a three-dimensional (3D) porous structured cellulose nanofibrils-based hydrogel (CNH) was synthesised using cellulose nanofibrils (CNs), carbon dots (CDs) and alpha-FeOOH, with CDs-enhanced synergetic effects of adsorption and photocatalysis for removing Cr(VI). In the CNH, CNs were conducted as a natural frame to construct a 3D porous structure increasing the specific surface area and providing additional active sites, CDs enhanced the amino group-induced adsorption for Cr(VI) and facilitated the transfer of photogenerated electron from alpha-FeOOH, and alpha-FeOOH was nanosized photocatalyst for generating photogenerated electron. A series of adsorption and photocatalysis experiments showed the superior adsorption-photocatalytic performance, as demonstrated by the large adsorption capacity and high kinetic constant of 115.98 mg/g and 0.06380, respectively, which was about 8 and 26 times as high as that of alpha-FeOOH. This superior removal performance was due to the mechanism of CDs-enhanced adsorption-photocatalysis synergy. This study not only provided a novel strategy for preparing green and efficient bifunctional materials for high-efficient Cr(VI) removal but also proposed a corresponding novel mechanism for CDs-enhanced synergetic effect of adsorption and photocatalysis.