Deciphering photocatalytic degradation of methylene blue by surface-tailored nitrogen-doped carbon quantum dots derived from Kraft lignin.

Lignin in black liquor can be used to manufacture carbon nanomaterials on a large scale. However, the effect of nitrogen doping on the physicochemical properties and photocatalytic performance of carbon quantum dots (NCQDs) remains to be explored. In this study, NCQDs with different properties were prepared hydrothermally by using kraft lignin as the raw material and EDA as a nitrogen dopant. The amount of EDA added affects the carbonization reaction and surface state of NCQDs. Raman spectroscopy showed that the surface defects increased from 0.74 to 0.84. Photoluminescence spectroscopy (PL) showed that NCQDs had different intensities of fluorescence emission at 300-420 nm and 600-900 nm. Meanwhile, NCQDs can photo-catalytically degrade 96 % of MB under simulated sunlight irradiation within 300 min. After three months of storage, the fluorescence intensity of NCQDs remained above 94 %, showing remarkable fluorescence stability. After four times of recycling, the photo-degradation rate of NCQDs was maintained above 90 %, confirming its outstanding stability. As a result, a clear understanding of the design of carbon-based photo-catalyst fabricated from the waste of the paper-making industry has been gained.

Enzymatic Synthesis of a Polyol Ester from Levulinic Acid and Trimethylolpropane and Its Tribological Behavior as Potential Biolubricant Basestock.

In this study, a polyol ester from levulinic acid (LA) and trimethylolpropane (TMP) was synthesized by enzymatic catalysis in a solvent-free system. The total conversion of TMP reached up to 84% on average after lipase recycling for five times. The produced ester showed excellent lubrication properties, such as high viscosities at 40 °C (86.53 mm2/s) and 100 °C (8.91 mm2/s), a good viscosity index (49), a low pour point (-27 °C), and a high flash point (223 °C). The frictional wear behavior was evaluated on a four-ball test machine (FTM) by adding the ester into a reference mineral oil. The blend with 10% ester showed a smaller wear scar diameter (WSD) (0.62 mm) when compared with that of pure mineral oil (0.78 mm). The results demonstrated that the obtained ester has huge potential as biolubricant basestock.