To achieve a rapid and facile quantitative evaluation of Sudan I illegally added in ketchup, fluorescent carbon quantum dots with excellent stability in acidic environments are required as the actual pH value of ketchup is close to 4.0. In this paper, we developed a green approach to prepare sulfur-doped carbon quantum dots (SCQDs) via hydrothermal treatment of lignin, isolated from pre-hydrolysis liquor, in sulfuric acid solution. The resultant SCQDs from lignin possessed sulfur-containing groups, which exhibited excellent fluorescence with a quantum yield up to 13.5% and good stability in acidic environments with a wide pH range of 0–5.0. Therefore, the SCQDs were successfully employed as a sensor to detect Sudan I in acidic solutions with excellent selectivity and sensitivity. The linear range for Sudan I was 0–40 μM, while the limit of detection was 0.12 μM. In addition, the fluorescent indicator paper functionalized with SCQDs also showed outstanding selectivity to Sudan I. The proposed SCQD sensing system not only displayed application potential for quantitative evaluation of Sudan I dye in practical samples, but also provided a way to convert lignin-based waste into highly valued nanoscale materials.

To delineate structural changes of lignin after SCEP, enzymatic hydrolysis lignin (EHL) in poplar chips, lignin in pretreated residues (SCEP-RL), lignin in liquors (SCEP-DL) were isolated and analyzed by GPC, ¹³ C-, ³¹ P-, 2D-HSQC-NMR and TGA.

Nowadays, afterglow materials with long-lifetime phosphorescence are mainly prepared from metal-containing substances. It is necessary and challenging to find a simple, green and feasible approach to generate afterglow materials with excellent phosphorescence from biomass materials. Herein, a facile strategy is proposed to construct afterglow materials via confining fluorescence carbon dots from lignin into silica (SiO₂). Specifically, a microwave-assisted carboxymethylation process was adopted for the lignin precursor, which endowed the lignin with abundant carboxyl groups (3.69 mmol g⁻¹) and maintained its benzene ring structure. Subsequently, N-doped lignin-based carbon dots (NL-CDs) with nanoscale size (6.07 nm) and excellent fluorescence (quantum yield = 30.6%) were prepared through the hydrothermal treatment of carboxymethylated lignin. Finally, the NL-CDs were confined in SiO₂ and the generated NL-CDs@SiO₂ exhibited excellent phosphorescence behavior in both solid-state and aqueous solution. The obtained afterglow materials achieved 5.97% of phosphorescence quantum yield and 834 ms of lifetime, which could be observed for 6 s by the naked eye. Meanwhile, a multi-modal information encryption strategy was designed based on the phosphorescence characteristics of the afterglow materials. The proposed strategy in this paper will pave the way to generate afterglow materials from lignin biomass and provide guidance for high-value utilization of lignin.

Waste newspaper is one of the most common cellulosic materials. Therefore, effective utilization of this commonly available biomass resource to prepare high-value carbon-based solid acid catalysts is an interesting and meaningful task. In this study we propose a new route for waste newspaper valorization, in which sulfonic-acid-functionalized carbon fiber can be directly produced from waste newspaper as a recyclable carbon based solid acid catalyst (WCSA) for the hydrolysis of cellulose. The as-prepared sulfonic-acid-functionalized carbon fiber contained –SO₃H, –COOH, and phenolic –OH groups and exhibited good catalytic activity for the hydrolysis of cellulose. WCSA prepared under sulfonation conditions at a temperature of 100 °C and for a duration of 10 h has a higher sulfonic acid content. A total reducing sugars (TRS) yield of 58.2% was obtained with a catalyst/microcrystalline cellulose (MCC) ratio of 4 at 150 °C using a reaction time of 6 h. The recycling performance of the WCSA catalyst indicated that the TRS remained almost stable for five cycles during the hydrolysis of cellulose.