Dual Stimulus Responsive GO-Modified Tb-MOF toward a Smart Coating for Corrosion Detection.

Smart-sensing coatings that exhibit multistimulus response, rapid indication, and reusability are in urgent need to effectively enhance the practicability of coatings while accurately detecting metal corrosion. In this work, a reusable corrosion self-reporting coating with multiple pH and Fe3+ stimulus responses was first constructed by the integration of a composite fluorescent probe into the resin matrix. This composite sensor was constructed by combining a lanthanide metal-organic framework (Ln-MOF) based on terbium and trimeric acid (H3BTC) with graphene oxide (GO) nanosheets (GO@Tb-BTC). The incorporation of GO formed a sea-urchin-like structure, thereby increasing the specific surface area and active sites of the probe. The coatings were characterized by using electrochemical impedance spectroscopy (EIS), visual observation, and fluorescence spectrophotometry. The surface morphology, wettability, and adhesion of the coating samples were analyzed using SEM, XPS, hydrostatic contact angle test, and an adhesion test. EIS measurements in 3.5 wt % NaCl solution for 72 h demonstrated the superior corrosion protection performance of the 0.3 wt %/GO@Tb-BTC/WEP coating compared to blank coating, with the charge-transfer resistance reaching 4.33 × 107 Ω·cm2, which was 9.5 times higher than that of the pure coating. The bright green fluorescence of GO@Tb-BTC/WEP coating exhibited a turn-off response when there was an excess of OH-/H+, but it demonstrated a reversible turn-on fluorescence when the ambient pH returned to neutral. Furthermore, such Fe3+-triggered fluorescence quenching responded to concentrations as low as 1 × 10-6 M. The fluorescence quenching rate of both intact and damaged coatings surpassed that of visual and EIS detection methods. Significantly, the fluorescence in scratches was effectively quenched within 25 min using 0.3 wt %/GO@Tb-BTC/WPU coating for visual observation. GO@Tb-BTC demonstrated exceptional corrosion self-reporting capabilities in both epoxy and polyurethane systems, making it a versatile option beyond single-coating applications.

[Determination of artemisinic acid in Artemisia annua at different growth stages based on spot area].

OBJECTIVE: Based on the important medicinal applications of artemisinic acid and the superiority of Thin Layer Chromagraphy (TLC), the spot area method of TLC was presented to determine the content changes of artemisinic acid of Artemisia annua at different growing stages. METHODS: The separation conditions including chromatographic solutions and chromogenic agent were optimized. The detection limit and the linear concentration range were analyzed. And the content changes of artemisinic acid of Artemisia annua at different growing stages were detected. RESULTS: The results showed that artemisinic acid extracted from Artemisia annua could be separated completely by the chromatographic solutions composed by petroleum ether,acetone and ethyl acetate (80: 19: 1). The artemisinic acid was clearly colored using the chromogenic agent consisting by ethanol, bromophenol blue and sulfuric acid. The detection limit of TLC was 0.05 mg/mL. The spot area of TLC had a good linear relationship within the range of 0.05-0.6 mg/mL, accorded with regression equation of y = 11.162 x + 0.0823. The results showed that the content of artemisinic acid at 0.041 mg/g in April which below the detection limit of TLC had no color spot. Contrarily, the spots of artemisinic acid were obvious in materials growing from May to September, and content was about 0.7, 1.2, 2.1, 2.4 and 2.7 mg/g, respectively corresponding to results by HPLC. CONCLUSION: The method can be applied to the quantitative analysis of artemisinic acid in Artemisia annua.

[Variation of content of artemisic acid in different growth stages of Artemisia annua].

OBJECTIVE: To study the variation of content of Artemisic acid of Artemisia annua from eight areas of four provinces around Wuling Mountain. METHODS: Artemisic acid of plants were extracted by organic solvent method. Qualitative and quantitative analysis of Artemisic acid were measured by thin layer chromatography (TLC) and high performance thin layer chromatography (HPLC), respectively. RESULTS: The results showed the average levels of Artemisic acid in May and August changed from 0.964 to 2.288 mg/g and from 1.837 to 3.737 mg/g, respectively. The average level in August was 1.5 times as that in May. The Artemisic acid in cultured plants was higher than the levels in wild plants, and Artemisic acid in plant collected below 300 m altitude was higher than that of the plant collected above 300 m altitude. CONCLUSION: The biosynthesis of Artemisic acid depends on the plant growth stage,which is mainly accumulated in plant at the mature stage.