Spiral-template from waste tea-leaf to design hierarchical dispersed zinc oxide nanocatalyst for boosting their photocatalytic carbon dioxide reduction

The utilization of cellulose-based templates to enhance the dispersion of zinc oxide (ZnO) nanoparticles represents an effective approach for enhancing their photocatalytic carbon dioxide (CO2) reduction activity. However, the limited availability of surface active sites on linear cellulose fiber has posed a significant challenge for loading ZnO nanoparticles. The present study introduces a technique for segregating spiral vessel (SV) from waste tea-leaves and employing them as templates for in-situ self-assembled ZnO nanoparticles. Due to the inherent three-dimensional (3D) stability of the spiral structure, ZnO nanoparticles exhibit excellent dispersion and maintain a stable hierarchical spiral morphology even after template removal. With the help of a field emission scanning electron microscope (FE-SEM), it could be observed that SV-loaded ZnO nanospheres extracted from waste Pu 'er tea-leaves retained the best spiral morphology after removing the template. The photocatalytic CO2 conversion over spheroidal ZnO with SV as templates (ZnOSS) significantly enhanced yields of CO and CH4, reaching 6.700 and 1.666 mu mol.g(-1) h(-1), respectively, surpassing those of other synthesized catalysts. The results obtained from the free radical scavenging experiment and electron paramagnetic resonance (EPR) test demonstrate the pivotal involvement of superoxide radicals (center dot O-2(-)) and hydroxyl radicals (center dot OH) in the photocatalytic reduction of CO2. Quantum mechanical simulation further verified that the ZnO (0 0 2) crystal face was the best reaction interface with CO2. The design of a cellulose-based spiral template not only facilitates the valorization of waste biomass but also offers a novel perspective for the synthesis of efficient photocatalysts.