Formation of uniform carrot-like Cu31S16–CuInS2 heteronanostructures assisted by citric acid at the oil/aqueous interface

Abstract

A simple two-phase strategy was developed to prepare Cu₃₁S₁₆–CuInS₂ heterostructures (HNS) at the oil/aqueous interface, in which the In(OH)₃ phase was often obtained in the products due to the reaction between indium ions and hydroxyl ions in the aqueous phase. To prevent the formation of the In(OH)₃ phase, citric acid was incorporated into the aqueous phase to assist in the synthesis of uniform carrot-like Cu₃₁S₁₆–CuInS₂ semiconductor HNS at the oil/aqueous interface for the first time. By manipulating the dosage of citric acid and Cu/In precursor ratios, the morphology of the Cu₃₁S₁₆–CuInS₂ HNS could be tailored from mushroom to carrot-like, and the presence of citric acid played a critical role in the synthesis of high-quality Cu₃₁S₁₆–CuInS₂ HNS, which inhibited the formation of the In(OH)₃ phase due to the formation of the indium(III)–citric acid complex. The formation mechanism was studied by monitoring the morphology and phase evolution of the Cu₃₁S₁₆–CuInS₂ HNS with reaction time, which revealed that the Cu₃₁S₁₆ seeds were first formed and then the cation-exchange reaction directed the subsequent anisotropic growth of the Cu₃₁S₁₆–CuInS₂ HNS.