Degradation of Lignin Derivatives by Photocatalysts

Abstract

Photocatalytic degradation experiments were done with lignin sulfonate in a circulating reactor. Catalysts (TiO 2-P25-SiO 2 + Pt, TiO 2-P25-SiO 2, TiOSO 4 _30.6 wt%, ZnO + TiO 2-P25-SiO 2), synthesized via the sol-gel method, were immobilized on porous glass support material. A comparative study was done regarding morphology of coatings, degradation rates, reaction rates, dissolved carbon (DC), formation of peaks, and fluorescence of products formed from the photocatalytic degradation of lignin sulfonate obtained from a local paper plant. Through simultaneous reaction-extraction pathways applying dialysis filtration and highly porous polystyrene divinylbenzene adsorbent resin (HR-P) for solid-phase extraction (SPE), an attempt was been made to isolate smaller molecules produced from photocatalytic degradation. Moreover, relatively high lignin sulfonate (0.5 g/L) concentrations are used in the reactions. UV-Vis spectroscopy revealed a faster reduction in the concentration values for the aliphatic moiety compared to the aromatic moiety. Peaks were observed by both fluorescence spectroscopy and high-performance liquid chromotography (HPLC), suggesting the production of new substances and fluorophores.

Lignin Degradation Processes and the Purification of Valuable Products

“…These results have been confirmed in more recent studies [115,116,122,123]. The important role of oxygen in PLD was also confirmed [117,121].…”

“…This study confirmed the effective degradation of relatively high concentrations of lignosulfonates (500 mg/L) and indicated that potential high-value degradation products were formed, although these products were not identified or quantified [115]. The strategy of continuously isolating target products from the reaction mixture during photocatalytic degradation using a combination of solid-phase extraction and dialysis is an interesting approach for the production of aromatic products by PLD.…”

“…Band-gap energies are approximately 3.0 eV for rutile and 3.2 eV for anatase [114]. ZnO photocatalysts have also been used in several studies [115][116][117].…”

“…Potential disadvantages include the lower photocatalytic efficiency due to mass transfer limitations [130]. However, well-designed hydrodynamic operating conditions can address mass transfer limitations and restore high photocatalytic efficiency [115].…”

“…These operating conditions are cost efficient for two reasons: the immobilized catalyst removes the need for a downstream recovery step and the solar illumination is free, making such systems highly suitable for the treatment of wastewater produced by the pulp and paper industry. A comprehensive comparative analysis of TiO 2 coatings on sintered glass particles (grain size = 200-400 μm) packed in a borosilicate tube (26 cm long, 1 cm outer diameter, 6 mm internal diameter) was used to study the degradation of lignosulfonates supplied by a paper company [115]. The study compared several catalysts (TiO 2 -P25-SiO 2 + Pt, TiO 2 -P25-SiO 2 , ZnO + TiO 2 -P25-SiO 2 and TiOSO 4 _30.6 wt%) using established synthesis and coating procedures [131].…”