Continuous solvothermal synthesis of copper nanoparticles in supercritical ethanol

Continuous supercritical solvothermal synthesis of copper nanoparticles is of great interest due to its enormous potential in energy sustainability. In this study, supercritical methanol and ethanol were used as reaction solvents, copper nitrate [Cu(NO3)2] and copper acetate [Cu(CH3COO)2] were used as representative inorganic and organic copper precursors. Finally, macromolecular organic polymers [polyvinylpyrrolidone, PVP, (C6H9NO)n] and long-chain fatty acids [decanoic acid, CH3(CH2)8COOH] were used as ligands to study cooper nanocrystals' formation mechanism. The results showed that a higher conversion rate of Cu2+ and smaller crystals were obtained when supercritical ethanol acted as solvent due to the variation of hydrogen bonding degree. Compared with NO3−, more thorough conversion and faster nucleation can be realized when CH3COO− acts as precursor anion. These arise from the diverse chemical bonding degree and functional group. Moreover, with the addition of macromolecular PVP, the dispersibility of obtained copper nanoparticles was significantly better than with the reaction of decanoic acid addition. Moreover, with increase in the PVP concentration, the morphology of the product became more and more regular, the distribution became more and more even, which was caused by inconsistent growth rates of each crystal surface under different PVP concentrations. This research provides deep insight into the supercritical solvothermal black box and lays the foundation for industrial application of this technology.