CdS–SH/TiO₂ Heterojunction Photocatalyst Significantly Improves Selectivity for C–O Bond Breaking in Lignin Models

Abstract

The selective breaking of the Cβ–O bond has great potential for the conversion of lignin into high-value aromatic monomers. In the present work, we designed a CdS–SH/TiO2 heterojunction photocatalyst for the efficient selective breaking of the Cβ–O bond. The surface modification of CdS by –SH promoted close contact between the catalyst and lignin and further promoted the Fermi level matching with TiO2. A type-II heterojunction was constructed by CdS–SH and TiO2 nanosheets to enhance the light absorption range and further increase the separation of photogenerated electron–hole pairs, resulting in high catalytic activity. Finally, 85% phenol and 87% acetophenone yields were obtained under mild light irradiation using 2-phenoxy-1-phenylethanol as the model substrate. Several control experiments, along with DFT calculations, indicate that the reaction pathway is more likely to involve the oxidation of Cα–OH to form CαO initially, followed by the activation of Cβ–O, which is then reduced to further form aromatic monomers. This work achieves the efficient selectivity of lignin depolymerization and provides a reference for the design of heterojunction photocatalysts in the valorization of lignin.

Dispersing agglomerated Zn4In2S7 on g-C3N4 nanosheets to form a 2D/2D S-scheme heterojunction for highly selective photocatalytic cleavage of lignin models

“…With the optimized reaction conditions, other typical β-O-4 lignin model compounds were used as the research objects to explore the conversion of the model substance which are structurally closer to the real lignin by this catalyst (Table 5). 65 The catalyst exhibited a high conversion rate on 1b containing C γ –OH groups (entry 2). In contrast, the introduction of methoxy groups at the R 1 and R 3 positions significantly reduced the conversion of 1c under the same reaction conditions (entry 3).…”

Improved Lignin Conversion to High-Value Aromatic Monomers through Phase Junction CdS with Coexposed Hexagonal (100) and Cubic (220) Facets

“…For example, the conversion of PPP-ol generates acetophenone and acrylophenone as acetophenone-like products, and the conversion of DMP-ol generates DACE and DPE-one as acetophenone-like products. However, in previous works, as shown in Scheme S1, the conversion of PPP-ol and DMP-ol would typically generate hydroxypropiophenone (HPP) and 1-(3,4-dimethoxyphenyl)-3-hydroxypropan-1-one (DPH-one) as acetophenone-like products, respectively, both containing C γ –OH groups. ,,− In our reaction system, the generation of acetophenone and DACE are the products after the cleavage of C β -C γ bonds in HPP and DPH-one, respectively, as well as acrylophenone and DPE-one are generated after the dehydration of C γ –OH groups in HPP and DPH-one, respectively. Both cleavage of C β -C γ bonds and dehydration of C γ –OH groups in HPP and DPH-one to generate acetophenone-like products in our reaction system might be attributed the C γ –OH groups activation.…”

Revolutionizing lignin photovalorization: recent advances in TiO2-based materials and beyond in pursuit of optimal solutions for a sustainable future

“…Among various ongoing research activities, lignin conversion is achieved via different techniques, i.e., thermal catalytic, photocatalytic, and electrocatalytic. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] The traditional lignin depolymerization reaction is carried out by various thermochemical and catalytic techniques like acid/base hydrolysis, pyrolysis, oxidation, reduction, and hydrogenation. [35][36][37][38][39][40][41][42][43][44] However, these reactions are accompanied by intense reaction conditions that put a lot of strain on machinery and its operations, require a lot of energy, and bring harm to the environment.…”

“…The formation of a heterostructure or heterojunction holds multiple intrinsic advantages for heterogeneous photocatalysis in terms of increasing light absorption efficiency, exciton separation and transfer ability, and boosting surface redox reactions. In light of this, different TiO 2 -based heterostructures, such as TiO 2 -metal oxides, TiO 2 -metal suldes, TiO 2 -carbonbased materials, etc., 30,31,[90][91][92][93][94][95][96][97][98][99] have been developed and investigated for the lignin and lignin model compound conversion. For example, Hou et al 91 prepared TiO 2 nanotubes hydrothermally, and then developed a three-component CuO x /CeO 2 /TiO 2 nanotube catalyst by a wet-chemical deposition precipitation method that was capable of selectively catalyzing the C-C bond cleavage of b-1 models.…”

“…In light of this, different TiO 2 -based heterostructures, such as TiO 2 –metal oxides, TiO 2 –metal sulfides, TiO 2 –carbon-based materials, etc. , 30,31,90–99 have been developed and investigated for the lignin and lignin model compound conversion. For example, Hou et al 91 prepared TiO 2 nanotubes hydrothermally, and then developed a three-component CuO x /CeO 2 /TiO 2 nanotube catalyst by a wet-chemical deposition precipitation method that was capable of selectively catalyzing the C–C bond cleavage of β-1 models.…”