Urchin-like Nb2O5 hollow microspheres enabling efficient and selective photocatalytic C–C bond cleavage in lignin models under ambient conditions

Z-scheme H5PMo10V2O40/g-C3N4 heterojunction with strong photooxidative capacity for promoting efficient cleavage of Cα-Cβ bond in lignin models and lignin

The efficient photocatalytic breakage of Cα-Cβ bonds has great significance for the valorization of lignin into value-added aromatic chemicals, but remains challenging owing to their demanding depolymerization conditions and high bond dissociation energies. In this study, the Z-scheme heterojunction H5PMo10V2O40/g-C3N4 (HPA/CN) photocatalyst was elaborately developed for the selective and efficient cleaving of Cα-Cβ bonds in real lignin and its β-O-4 models under mild conditions. The construction of Z-scheme heterojunction with irregular sheet micromorphology not only enhanced the charge separation and redox abilities, but also broadened the light absorption range and promoted charge-to-surface transfer in two redox components. Notably, 35 % HPA/CN could completely convert the 2-phenoxy-1-phenylethanol with Cα-Cβ bond cleavage selectivity of 97.4 %, achieving approximately 50.0- and 2.2-times higher conversion rates compared to HPA and CN, respectively. Meanwhile, this strategy also offered a wide substrate scope containing various β-O-4 model compounds and native lignin, leading to the generation of corresponding aromatics. The mechanism experiments revealed that photoinduced holes and superoxide radicals synergistically triggered the oxidative cleavage of Cα-Cβ bond. This study could provide a reference for photocatalytic production of value-added aromatic monomers by exploiting both renewable feedstocks and solar energy.

Visible-light-driven selective cleavage of lignin C-C bonds on the TiO2@g-C3N4heterostructured photocatalyst

The selective cleavage of lignin C-C bonds is a highly sought-after process with the goal of obtaining low-molecular-weight aromatic chemicals from renewable resources. However, it remains a challenging task to achieve under mild conditions. Photocatalysis is a potentially promising approach to address this issue, but the development of efficient photocatalysts is still in progress. In this study, we introduce the heterostructured TiO2@g-C3N4photocatalyst for the development of a visible light photocatalytic procedure for the selective cleavage of lignin C-C bonds under mild conditions. The photocatalyst displays favourable visible light absorption, efficient charge separation efficiency, and promising reusability. A typicalβ-O-4 dimer model, 2-phenoxy-1-phenylethanol, was effectively (96.0% conversion) and selectively (95.0 selectivity) cleaved under visible light at ambient conditions. This photocatalytic procedure was also effective when subjected to solar irradiation or other lignin dimer models withβ-O-4 orβ-1 linkages. This reaction occurred through a Cβ-centred radical intermediate and a six-membered transition state with photogenerated holes as the primary active species. The Cα-OH oxidative dehydrogenation of the substrate could also take place but was a relatively minor route. This study provides a new photocatalytic procedure for visible-light-driven lignin valorisation and sheds light on the design of high-performance nanocomposite photocatalysts for C-C bond cleavage.

Effect of hydrothermal pH values on the morphology of special microspheres of lignin-based porous carbon and the mechanism of carbon dioxide adsorption

The study reports the economic and sustainable syntheses of a lignin-based porous carbon (LPC) for CO2 capture application. The pH values of hydrothermal solution affected the polymerization and aromatization of spheroidization, with morphological changes from blocky to microsphere. In addition, the reliable mechanisms of CO2 adsorption were proposed by combining experiments with Gaussian16 simulations based on DFT. The electrostatic attraction of oxygen-containing functional groups and the diffusivity resistance of CO2 in the pores are the key factors for the CO2 adsorption. ​The carboxyl groups have the strongest electrostatic attraction to CO2. LPC-pH 1 has the highest carboxyl group content, possessing a CO2 adsorption capacity of up to 5.10 mmol/g at 0℃, 1 bar. Furthermore, CO2 diffusion resistance became a main factor as the adsorption temperature increases. The innovative combination of quantum chemical calculations and microscopic properties provides a viable pathway for an insight into the future control of lignin-based carbon formation.

Advances in surface properties characterization and modification for lignin

Renewed interests on lignin and its derivatives have led to increasingly more investigations due to the problems in environmental impact while with the great reuse possibilities for producing them-based new and advanced materials to reduce the petroleum achieving sustainable development. The related studies have shown more integrated database on the surface properties characterization and modification of those renewable materials. Based on numerous works did at our group and others reported elsewhere, this review covers the surface properties of lignin and its derivatives in relation to various methods and theories. In this work, the progress on the recent developments of advanced methods for lignin surface characterization and modification are also documented. Of this review, a perspective is finally presented.

Efficient Photocatalytic Cleavage of Lignin Models by a Soluble Perylene Diimide/Carbon Nitride S-Scheme Heterojunction

3,4,9,10-Perylenetetracarboxylic dianhydride (PDI) is one of the best n-type organic semiconductors and an ideal light-driven catalyst for lignin depolymerization. However, the charge localization effect and the excessively strong intermolecular aggregation trend in PDI result in rapid electron-hole (e- -h+ ) recombination, which limits photocatalytic performance. Herein, polymeric carbon nitride/polyhedral oligomeric silsesquioxane PDI (p-CN/P-PDI) S-scheme heterojunction photocatalyst was prepared by the solvent evaporation-deposition method for C-C bond selective cleavage of lignin β-O-4 model. Based on the material characterization results, the synergic role of polyhedral oligomeric silsesquioxane (POSS) and S-scheme heterojunction maintains appropriate aggregation domains, achieves better solar light utilization, faster charge-transfer efficiency, and greater redox capacity. Notably, the 3 % p-CN/P-PDI heterostructure exhibits a remarkable enhancement in cleavage conversion efficiency, achieving approximately 16.42 and 2.57 times higher conversion rates compared to polyhedral oligomeric silsesquioxane modified PDI (POSS-PDI) and polymeric carbon nitride (p-CN), respectively.