Biochar sulfonic acid immobilized chlorozincate ionic liquid: an efficiently biomimetic and reusable catalyst for hydrolysis of cellulose and bamboo under microwave irradiation

A chlorozincate ionic liquid-functionalized biochar sulfonic acid (BC-SO₃H-IL-Zn) was designed and conveniently prepared via multistep processes, involving the syntheses of biochar sulfonic acid (BC-SO₃H) and 1-trimethoxysilylpropyl-3-methylimidazolium chloride (IL)-ZnCl₂ (IL-Zn), followed by grafting the IL-Zn onto BC-SO₃H. The proposed catalyst was found to show a much higher turnover number (TON, 5.91 for cellulose and 1.78 for bamboo) for the microwave-assisted hydrolysis of cellulose and bamboo to reducing sugars (RSs) in water compared to the corresponding IL-functionalized BC-SO₃H (BC-SO₃H-IL, TON, 3.23 for cellulose and 0.46 for bamboo) and BC-SO₃H (TON, 1.51 for cellulose and 0.15 for bamboo). Furthermore, it, like BC-SO₃H-IL, possessed an excellent repeatability for cellulose hydrolysis. The excellent catalytic performance of BC-SO₃H-IL-Zn is likely due to the following reasons: Firstly, the introduction of ZnCl₂ bestows the catalyst with a delignification function. Secondly, in comparison with the OH groups of BC-SO₃H, the IL and especially IL-Zn groups flexibly bound to BC-SO₃H, like cellulose binding domain of cellulose, show an stronger affinity for cellulose molecules, on the other hand, they play a better synergistic role and improved acidity in the SO₃H groups (as a catalysis domain of cellulase) catalyzing cleavage of the β-1,4-glycosidic bonds of cellulose, as supported by the adsorption experiments of catalysts to oligosaccharides, their thermogravimetric analysis and catalytic reaction results.

Chlorozincate ionic liquid functionalized biochar sulfonic acid (BC-SO₃H-IL-Zn) proposed by us was found to be an efficiently biomimetic catalyst for the heterogeneous hydrolysis of cellulose and lignocelluloses to RSs and 5-hydroxymethyl furfural (5-HMF) under microwave irradiation.