Sustainably-derived sulfonated pinecone-based hydrochar catalyst for carbohydrate dehydration

Waste pinecones are a forest resource that have not been widely utilized as feedstocks for producing catalytic materials. By combining waste pinecones with l-cysteine, they can be transformed into Brønsted acid hydrochars through three sequential mild treatment processes: (i) mix ball-milling of pinecones with l-cysteine, (ii) low-temperature hydrothermal treatment (200 °C, 18 h) and (iii) oxidation with H2O2. The as-prepared sulfonated materials denoted as PbmC-SO3H were applied as catalysts to study the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF), where it was found that 5-HMF yields as high as 96.4 % were obtained at 85 °C in 1.5 h reaction time over PbmC-SO3H in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) ionic liquid reaction solvent. The PbmC-SO3H material had high adsorption capacity for fructose (96.1 mg/g) and low adsorption capacity for 5-HMF (38.1 mg/g) in water compared with non-functionalized or non-oxidized experimental blanks. Spectroscopy of adsorbed fructose on the carbon materials and DFT calculations confirmed cooperative adsorption behavior of COOH, OH and –SO3H groups. Forest management strategies can utilize waste pinecones with bio-derived l-cysteine to produce sulfonated carbon catalysts and chemicals via low energy and sustainable processes.