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Carbon dots (CDs) have excellent uorescence properties and can be used in many research elds. In this paper, carbon dots were prepared by microwave-assisted pyrolysis of citric acid and urea, characterized by transmission electron microscope (TEM), X-ray diffractometer (XRD), 13 C-NMR spectrum, zeta potential, Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) absorption and uorescence spectra, and detected the Hg 2+ and ascorbic acid (AA) sequentially. It showed that carbon dots were hollow, spherical particles and less than 10 nm, photoluminescence quantum yield of carbon dots was about 15%. The CDs were selective and sensitive to Hg 2+ and AA based on the "on-off-on" uorescence behavior. The detection limits of CDs for Hg 2+ and AA were 0.138 µM and 0.212 µM, respectively. Fluorescence response mechanism of CDs was also discussed.

Ca-looping is an effective way to capture CO2 from coal-fired power plants. However, there are still issues that require further study. One of these issues is the effect of steam on the Ca-looping process. In this paper, a self-madethermogravimetric analyzer that can achieve rapid heating and cooling is used to measure the change of sample weight under constant temperature conditions. The parameters of the Ca-looping are studied in detail, including the addition of water vapor alone in the calcination or carbonation stage and the calcination/carbonation reaction temperatures for both calcination and carbonation stages with water vapor. Steam has a positive overall effect on CO2 capture in the Ca-looping process. When steam is present in both calcination and carbonation processes, it increases the decomposition rate of CaCO3 and enhances the subsequent carbonation conversion of CaO. However, when steam was present only in the calcination process, there was lower CaO carbonation conversion in the following carbonation process. In contrast, when steam was present in the carbonation stage, CO2 capture was improved. Sample characterizations after the reaction showed that although water vapor had a negative effect on the pore structure, adding water vapor increased the diffusion coefficient of CO2 and the carbonation conversion rate of CaO.

Fe-based chemical looping gasification is a clean biomass technology, which has the advantage of reducing CO2 emissions and the potential of self-sustaining operation without supplemental heating. A novel process combining Fe-based chemical looping and biomass pyrolysis was proposed and simulated using Aspen Plus. The biomass was first subjected to pyrolysis to coproduce biochar, bio-oil and pyrolysis gas; the pyrolysis gas was subjected to an Fe looping process to obtain high-purity hydrogen and carbon dioxide. The influences of the pyrolysis reactor operating temperature and fuel reactor operation temperature, and the steam reactor and air reactor on the process performance are researched. The results showed that, under the operating condition of the established process, 23.07 kg/h of bio-oil, 24.18 kg/h of biochar, 3.35 kg/h of hydrogen and a net electricity of 3 kW can be generated from 100 kg/h of rice straw, and the outlet CO2 concentration of the fuel reactor was as high as 80%. Moreover, the whole exergy efficiency and total exergy loss of the proposed process was 58.98% and 221 kW, respectively. Additionally, compared to biomass direct chemical looping hydrogen generation technology, the new process in this paper, using biomass pyrolysis gas as a reactant in the chemical looping hydrogen generation process, can enhance the efficiency of hydrogen generation.

Recently, carbon dots (CDs) have exhibited promising applications in the fluorescence detection of various ions and biomolecules. This work synthesized a new type of nitrogen-doped CDs (N-CDs), characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR), UV-vis absorption spectra, and fluorescence spectra. The results show that the spherical and uniform N-CDs (quantum yield: 60.2%) have remarkable fluorescence properties and photostability, which makes N-CDs can be utilized as an "on-off-on" sensor for Hg2+ and glutathione (GSH). In addition, the pH-sensitive behavior of N-CDs makes it also applicable to H+ detection under acid conditions (pKa = 3.53). The linear range of the "turn-off" sensor detecting Hg2+ was 0 - 50 μM, with a 0.014 μM limit of detection (LOD). GSH was detected by the fluorescence "turn-on" method with a linear range of 0 - 60 μM and a LOD of 0.125 μM. The outstanding performance of N-CDs makes it potential applications in ecological pollution and biomolecule visualization monitoring.