Catechin can effectively prevent the occurrence of cancers due to its strong antioxidant capacity. In this study, the catechin contents of black teas from 12 different regions of south China were investigated using fluorescence spectroscopy. Herein, the catechin contents of various black teas with constant concentration were determined at the optimal excitation and emission wavelength combining the standard addition method and fluorescence spectroscopy. The results indicated that there was a linear relationship between the obtained concentration and fluorescence intensity, where the R values were all greater than 0.99 and the limit of quantification (LOQ) was 0.02 μg/mL. Furthermore, the content of catechin monomer in the chlorophyll environment was measured under the same experimental conditions to demonstrate the correctness of the above experimental methods. It revealed that the experimental error was about 1.14% compared with the actual content. The current work was proved to be an efficient way to detect fluorescence spectrum through diluting the concentration of tea samples, thereby increasing the determination limit of catechin.

A series of Auloaded porous gC 3 N 4 nanosheets were prepared by anchoring Au nanoparticles onto gC 3 N 4 surfaces. The asprepared samples were characterized via xray powder diffraction, Fourier transform infrared, transmission electron microscopy, Brunauer-Emmett-Teller, photoluminescence, and ultraviolet-visible measurements, respectively. The activities of Au/gC 3 N 4 composites were evaluated by the photocatalytic degradation of gaseous isopropyl (IPA) under visiblelight illumination. The results indicated that 2% Au/gC 3 N 4 exhibited the highest photocatalytic efficiency of gaseous IPA oxidation (11.51 ppm min −1 ), which was 2.4 times higher than that of pure gC 3 N 4 nanosheets. The remarkable improved photodegradation efficiency derived from the promoted photoinduced carriers separation and larger specific surface area. For one thing, the ultrathin mesoporous gC 3 N 4 nanosheets provided abundant reactive sites and facilitated electron diffusion. For another, the localized surface plasmon resonance and electron-sink effect of Au particles significantly suppress the recombination of the photoinduced holes and electrons. Therefore, the deposition of Au nanoparticles with porous gC 3 N 4 nanosheets could be regarded as an efficient way to enhance the photocatalytic activity of gaseous IPA pollutant removal.

A rapid, selective and sensitive method for the detection of caffeine in tea infusion and tea beverages are proposed by using 3,5-diaminobenzoic acid as a fluorescent probe. The 3,5-diaminobenzoic acid emits strong fluorescence around 410 nm under the excitation of light at 280 nm. Both the molecular electrostatic potential analysis and fluorescent lifetime measurement proved that the existence of caffeine can quench the fluorescence of 3,5-diaminobenzoic acid. Under the optimal experimental parameters, the 3,5-diaminobenzoic acid was used as a fluorescent probe to detect the caffeine aqueous solution. There exists a good linear relationship between the fluorescence quenching of the fluorescent probe and the concentration of caffeine in the range of 0.1–100 μM, with recovery within 96.0 to 106.2%, while the limit of detection of caffeine is 0.03 μM. This method shows a high selectivity for caffeine. The caffeine content in different tea infusions and tea beverages has been determined and compared with the results from HPLC measurement.

Surface-enhanced Raman spectroscopy (SERS) was used to simply and sensitively detect the artificial sweetener aspartame added to purified water. In this paper, a cavity formed spontaneously by silver ion droplets, and liquid polydimethylsiloxane (PDMS) is used as an SERS substrate to integrate plasma nanoparticles into optical devices. Firstly, Raman spectral characteristics of aspartame powder and aspartame aqueous solution were analyzed. Secondly, the effect of aspartame content in purified water on SERS intensity was investigated by using the prepared PDMS plasma cavity to test the samples. Thirdly, the SERS calibration curve was established by using the characteristic peak intensity of aspartame, and a good linearity relationship between the concentration of aspartame added in purified water and the characteristic peak intensity of 1588(±5) cm-1 was obtained. The linear regression equation and correlation coefficient (r) were y = 11412.73874 x + 107.36722 and 0.99593, respectively. The average recovery of aspartame in purified water was 101–106%, and the relative standard deviation (RSD) was 0.121–0.496%. The experimental results show that using this method can detect aspartame in purified water correctly, which is expected to be used in the identification and detection of sweeteners in purified water.