Carboxylic acids are widely used in the production of fine chemicals. This study demonstrates rapid synthesis of carboxylic acids directly from alcohols in microdroplets by paper spray ionization under UV irradiation. Oxidation acceleration was contributed from paper substrate as a thin film format and microdroplets of smaller sizes by paper spray ionization. Yields can reach as high as 100% for all tested alcohols except 4-nitrobenzene alcohol (39%) in microdroplets compared to 1–10% for acids and 2–50% for aldehydes with methylbenzoate byproducts in bulk phase. Preparative paper spray ionization for scaling-up syntheses realized rates of 19 mg h–1. Paper spray-based synthesis not only possesses all merits of microvolume synthesis by electro- and sonic spray, but also owns unique properties of no need for phase-transfer catalysts, and high ease to salt deposition typically occurred at the capillary tips for the latter. All these merits indicate it is a high-efficiency green methodology.

The formation of amide bonds is one of the most valuable transformations in organic synthesis. Beckmann rearrangement is a well-known method for producing secondary amides from ketoximes. This study demonstrates the rapid synthesis of ketoximes and amides in microdroplets. Many factors are found to affect the yield, such as microdroplet generation devices, temperature, catalysts, and concentrations of reactants. In particular, the temperature has a great influence on the synthesis of amide, which is demonstrated by a sharp ascendance to the yield when the temperature was increased to 45 °C. The best amide yield (93.3%) can be obtained by using coaxial flowing devices, a sulfonyl chloride compound as a catalyst, and heating to 55 °C in microdroplets. The yields can reach 78.7–91.3% for benzoylaniline and 87.2–93.4% for benzophenone oximes in several seconds in microdroplets compared to 10.1–66.1% and 82.5–93.3% in several hours in the bulk phase. Apart from the dramatically decreased reaction time and enhanced reaction yields, the microdroplet synthesis is also free of severe reaction environments (anhydrous and anaerobic conditions). In addition, the synthesis in microdroplets also saves reactants and solvents and reduces the waste amounts. All of these merits indicate that the microdroplet synthesis is a high-efficiency green methodology.

A series of composite catalysts of C, N and P co-doped TiO2 were prepared by sol-gel method, using a biomass (soluble starch) dopant. The samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), fourier transform infrared (FTIR) spectroscopy. The results show that TiO2 is co-doped with C, N and P by one step. The resulting composite exhibited higher specific surface area, wider visible-light absorption band with respect to the pure TiO2. The sample calcined at 400∘C for 2[Formula: see text]h with a doping amount of 6[Formula: see text]g soluble starch showed the best electrochemical performance. The C, N and P co-doped TiO2 was also used for the degradation of methylene blue (MB) and degradation ratio was up to 98% in 80[Formula: see text]min under visible light irradiation.

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