Engineering the structure and the surface of anisotropic Bi2S3 Nanoparticles for Enhanced Optical Properties

Significance 

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.

Engineering the structure and the surface of anisotropic Bi2S3 Nanoparticles for Enhanced Optical Properties - Advances in Engineering

About the author

Dr. Carlos Moya is a Maria Zambrano postdoctoral researcher in the Department of Condensed Mattern at the University of Barcelona (UB, Spain). His research has focused on fundamental research paying special attention to the application of stimuli-responsive NPs for health and water remediation. After finishing his Ph.D. from UB in 2015, he has carried out several postdoctoral positions in public and private research institutions in Spain (Materials Institute of Barcelona), USA (Carnegie Mellon), and Belgium (University Libre of Brussels). His current research interests focused on the design and testing of anisotropic magneto-plasmonic nanoparticles as a new generation of theragnostic agents in preclinical assays.

About the author

Dr. Xavier Batlle is Full Professor and Head of the Department of Condensed Matter Physics of the University of Barcelona (UB).  He is co-leader of the Group of Magnetic Nanomaterials . He got his Bachelor and Master Degrees in Physics in 1987 and his PhD in Physics in 1990, all from UB. He has been visiting researcher for about 4 years in a number of international laboratories, including Lawrence Berkeley National Lab (CA, USA), University of California San Diego (CA, USA), CNRS and Institute Laue Langevin (Grenoble, France), and University of Cambridge (UK), among others. His work has aimed at the interplay among finite-size, surface, interface, interaction and proximity effects, and at the intimate correlation of the nanostructure (physical, chemical and magnetic) to the magnetic, electronic and electron transport properties of nanomaterials. At present, he is working in the potential applications of (magnetic) nanoparticles in biomedicine and arrays of plasmonic nanoelements for biosensing. He is Fellow of the American Physical Society (2012) ‘for his major, original contributions to the fundamental understanding of the magnetic properties of nanostructured materials and particle-like systems […].

Reference

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.

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