Weak Acid–Base Interaction Induced Assembly for the Synthesis of Diverse Hollow Nanospheres

We have established a novel and generalizable hydrothermal synthesis for diverse hollow nanospheres, which cover polymer, carbon, graphitic carbon, and metal-doped carbon hollow nanospheres. The synthesis principle is based on the weak acid–base interaction (−COO^–/NH₄⁺/–COO^–) induced assembly. That is, the ammonium cations from the reactant ammonia act as a trigger for the assembly of COO^– group-containing polymer around surfactant oleic acid micelles through the weak interaction between carboxylate anion and ammonium ion. Consequently, hollow polymer nanospheres (HPSs) with diameters ranging from 100 to 200 nm and hollow core sizes ranging from 30 to 80 nm can be synthesized. It was determined that approximately 61% of the added amount of NH₃ participates is retained in the HPS product. Taking these HPSs as the precursor, hollow carbon nanospheres (HCSs) with tunable surface areas can be obtained by varying the preparation conditions. More importantly, owing to the presence of the COO^– functional groups, a wide range of metal cations (e.g., Fe³⁺ and Ag⁺) can be successfully introduced into these HPSs, so that they can then be converted to hollow graphitized nanospheres and Ag-doped catalytically active HCSs.