Bismuth sulfide Bi2S3 nanoparticles have gained significant attention for a wide range of energy and catalysis applications. This is because their high surface area and strong light absorption properties offer advantages in the development of transparent conductive films for photovoltaic devices, in the degradation of organic pollutants in wastewater treatment, and in the production of hydrogen fuel through water splitting.
Moreover, elongated Bi2S3 nanoparticles possess unique features that make them highly attractive for biomedical applications such as photothermal therapy, drug delivery, and computed tomography because of their biocompatibility, strong light absorption properties, and high X-Ray mass attenuation coefficient. However, realizing the full potential of these materials requires the development of new chemical methodologies that enable the modulation of particle morphology and functionalization.
The hot injection of organosulfur precursors has emerged as a promising approach to precisely tune the particle size and shape of a wide range of metal sulfide nanoparticles. Despite the numerous advantages of this approach, it has not been extensively explored for the rational design of elongated Bi2S3 nanoparticles. From a functionalization perspective, employing chelating functionalization agents that allow for further post-conjugation steps appears to be an interesting alternative for the surface engineering of particles. Dimercaptosuccinic acid (DMSA) is one such agent that holds promise, thanks to its two sulfhydryl groups that can be used for both grafting onto the particle surface and conjugation with targeting molecules.
On this account, the University of Barcelona researchers led by Professor Xavier Batlle: Dr. Mariona Escoda-Torroella, Dr. Carlos Moya, José A. Ruiz-Torres, Dr. Arantxa Fraile Rodríguez, and Professor Amílcar Labarta, investigated selective growth of Bi2S3 nanoparticles with adjustable optical properties. A two-step approach was adopted to synthesize and functionalize elongated Bi2S3 nanoparticles. The authors commenced their experimental work by investigating the role of reaction time and temperature in the hot injection of thioacetamide into a mixture of bismuth(III) neodecanoate, oleic acid, and oleylamine in 1-octadecene. The work is currently published in the peer-reviewed journal, Physical Chemistry Chemical Physics.
The research team reported the synthesis of Bi2S3 nanoparticles ranging from nanosphere to nanoneedle shapes with injection at 105°C with reaction times in the range 0 – 120 mins. On the other hand, highly crystalline nanorods were obtained by injecting at 165°C irrespective of the reaction time. Compared to bulk Bi2S3, the optical properties of both types of nanoparticles exhibited band gap enhancement. This was attributed to quantum confinement effects induced by small particle dimensions relative to typical exciton size as well as an improvement in the near-infrared absorption because of the anisotropic particle shape.
Furthermore, a ligand exchange approach based on DMSA was successfully used to transfer the elongated Bi2S3 nanoparticles to aqueous solutions by grafting this ligand onto the particle surface. Additionally, the particle stability was evaluated in several aqueous media as a function of the shape, ionic strength and pH. The as-prepared nanoparticles exhibited good stability in water and in phosphate-buffered saline solutions for a wide pH range.
In summary, the study demonstrated the controlled synthesis of Bi2S3 nanoparticles with robust stability in aqueous solutions. Results revealed larger optical absorption in the full spectrum of the elongated Bi2S3 nanoparticles than that of the nanosphere counterparts. Further, the increased absorbance in the near-infrared region could promote their exploitation in photothermal therapy experiments. In a statement to Advances in Engineering, Professor Xavier Batlle stated that elongated Bi2S3 nanoparticles have a wide range potential applications, and further research is needed to fully explore their capabilities. The study provided valuable insights that would contribute to advanced research on multi-compositional nanosystems that combine elongated Bi2S3 nanoparticles with magnetic or plasmonic materials.
Escoda-Torroella, M., Moya, C., Ruiz-Torres, J. A., Fraile Rodríguez, A., Labarta, A., & Batlle, X. (2023). Selective anisotropic growth of Bi2S3 nanoparticles with adjustable optical properties. Physical Chemistry Chemical Physics, 25(5), 3900-3911.