Gold quantum clusters and plasmonic quantum nanoparticles were synthesized under femtosecond pulse laser irradiation in an aqueous gold precursor solution. The method produced gold clusters with average sizes of 0.6−1.6 nm after irradiation for 1−3 min, where a hydrated electron reacts as a reducer. As the irradiation is continued longer, plasmonic nanoparticles with larger sizes were produced. Both clusters and plasmonic nanoparticles exhibit fluorescence, indicating a quantum property, although it is not usually expected from conventional plasmonic gold nanoparticles. Thus, the femtosecond laser irradiation procedure can produce gold nanomaterials with the quantum and surface plasmon properties, being different from the chemical reduction. Zeolitic imidazolate framework-8 (ZIF-8) was incorporated as a holder during the synthesis of gold metal. The product, gold-encapsulated ZIF-8 (Au@ZIF-8), exhibits lesser plasmonic properties but stronger fluorescence than free particles due to rich quantum properties. Au@ZIF-8 has shown good catalytic properties on the reduction of 4-nitrophenol, and 100% catalytic reaction was obtained within 4 min for Au:ZIF-8 (0.4:1 wt/wt) catalyst, indicating that the larger amount of smaller-sized gold cluster formed in ZIF-8 is the better catalyst. Thus, the present study demonstrates a promising green synthesis approach in a capsule of the metal−organic framework, which is a physical bottom-up processing without additional chemicals and procedures and produces the stabilized quantum clusters with efficient catalytic performance.
The extraction of phytochemicals from Mimosa pudica Linn (MPL) using supercritical CO 2 has been studied and the results are presented in this paper. The significant variables affecting this extraction were investigated by DOE analysis. The effect of temperature and pressure on phytochemical yields was explored by measuring total phenolic compound (TPC), total flavonoid content (TFC), and total alkaloid compound (TAC).The maximum yield of TPC, TFC, and TAC extracted from MPL were 74.83 mg GAE/gram dry MPL, 30.93 mg QE/gram dry MPL and 14.23 mg HE/gram dry MPL, respectively. The work of Chrastil was used to correlate the experimental data. It was found that temperature and pressure greatly affected the yield of phytochemicals, whereas the effect of extraction time on the extraction yield diminished after 2h. Qualitative analysis of the phytochemicals extracted from MPL was performed by High Performance Liquid Chromatography (HPLC).The SC-CO 2 extraction was more selective than soxhlet extraction based on the HPLC spectra.
Environmental contextIndium is a metal increasingly used in high-technology industries, creating a demand for efficient recycling technology. We investigated extraction of indium from waste using a subcritical water extraction with organic acids. Compared with conventional methods employing concentrated mineral acids, the new method is less corrosive, more efficient and required shorter extraction times.
AbstractSubcritical water extraction (SWE) was applied to extract indium (In) from indium tin oxide (ITO) scrap. Four organic acids, acetic acid, gluconic acid, citric acid (CA) and etidronic acid (EA), were used at a solid-to-liquid ratio (S/L) of 10gL−1. Neither acetic acid nor gluconic acid yielded significant extraction of indium. A total of 70.71% and 96.93% of indium was extracted using 1M of CA and EA respectively at 150°C and a final pressure of 18–19 bar within 30min. The extraction efficiency of In was shown to increase with the increase in acid concentration and in temperature. Compared with conventional extraction methods, SWE was more effective using less concentrated acids and required a shorter reaction time.
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