Engineering a lignin-based hollow carbon with opening structure for highly improving the photocatalytic activity and recyclability of ZnO

Enzymatic hydrolysis lignin (EHL), an industrial waste, is mainly used as a low-grade combustible energy source. Design and preparation of high value-added materials with EHL is still a challenge. Demonstrated here in was the first application of EHL as the precursor for preparing a lignin-based hollow carbon (LHC) with opening structure based on a facial self-assembly and carbonization process. ZnO nanoparticles can be uniformly immobilized on the exterior and interior surface of LHC due to rich oxygen-containing functional groups and opening structure, and composite (ZnO/LHC) was obtained. The ZnO/LHC presented high photocatalytic degradation rate of ciprofloxacin and photocatalytic H-2 evolution rate, which were about 2.0 times and 1.8 times that of pure ZnO, respectively. The enhancement can be attributed to the electronic interaction between ZnO and LHC, endowing ZnO extended photoabsorption region and enhanced separation of hole-electron pairs. Moreover, the hollow and opening structure offered photocatalyst fast substance transfer, abundant active sites and high light-harvesting. Besides, the recyclability of ZnO was also improved after the introduction of LHC. Our study not only opens up new avenues for the high value-added application of EHL, but also offers a simple strategy to promote the practical use of ZnO photocatalyst.