“Fish gill” -shaped ordered porous PVA@CNNS hybrid hydrogels with fast charge separation and low resistance for effectively photocatalytic synthesis of lactic acid from biomass-derived sugars

Abstract

The development of hydrogel-based photocatalysts with three-dimensional ordered porous structure, fast charge separation, and low resistance is significantly in photocatalytic biorefinery but nonetheless poses certain challenges. Herein, we introduced a novel strategy to prepare “Fish gill”-shaped hydrogel-based photocatalysts via freezing-induced encapsulation of ultra-thin carbon nitride nanosheets into a three-dimensional ordered porous polyvinyl alcohol matrix (name as FG-s-PVA@CNNSx). The encapsulation of CNNS in FG-s-PVA@CNNS3 posed no effects on the absorption of visible light but accelerated the transfer/migration of photo-induced charge and reduced the resistance. For photocatalysis, the ordered porous structure of FG-s-PVA@CNNS3 proved to be conducive to the reactants adsorption and mass transfer while the lactic acid yield achieved 92.6%. FG-s-PVA@CNNS3 exhibited excellent stability and reusability, in which the yield of the 10th cycle well reached 95.6% of its first cycle. FG-s-PVA@CNNS3 also displayed exceptional universality wherein the lactic acid yields were 92.6% (glucose), 89.1% (fructose), 88.6% (mannose), 56.0% (rhamnose), 71.1% (arabinose), and 70.9% (xylose). In addition, the effects of various oxidative species on the photocatalytic reaction were systematically discussed, among which ·O2- played a pertinent role. Overall, the construct of hydrogel-based photocatalysts and their application provide a strategy for photocatalytic biorefinery.