Adaptable surfactant-mediated method for the preparation of anisotropic metal chalcogenide nanomaterials

The hot injection synthesis of nanomaterials is a highly diverse and fundamental field of chemical research, which has shown much success in the bottom up approach to nanomaterial design. Here we report a synthetic strategy for the production of anisotropic metal chalcogenide nanomaterials of different compositions and shapes, using an optimised hot injection approach. Its unique advantage compared to other hot injection routes is that it employs one chemical to act as many agents: high boiling point, viscous solvent, reducing agent, and surface coordinating ligand. It has been employed to produce a range of nanomaterials, such as CuS, Bi2S3, Cu2-xSe, FeSe2, and Bi4Se3, among others, with various structures including nanoplates and nanosheets. Overall, this article will highlight the excellent versatility of the method, which can be tuned to produce many different materials and shapes. In addition, due to the nature of the synthesis, 2D nanomaterial products are produced as monolayers without the need for exfoliation; a significant achievement towards future development of these materials.


General Metal Sulfide Synthesis:
A mixture of OAm (50 mL) and sulfur was degassed under vacuum at 80 o C for 30 min. The temperature was then raised to the reaction temperature under Ar, then rapid addition of the metal precursor, followed by stirring under Ar at the reaction temperature for varying amounts of time. Reactions were stopped by cooling the RBF under tap water, followed by methanol addition and centrifugation. Washings were performed by re-suspension with CHCl3 (1% OAm) and precipitation two times, followed by resuspension in CHCl3.

General Metal Selenide Synthesis:
A mixture of OAm (50 mL) and selenium was degassed under vacuum at 80 o C for 30 min, then the temperature was raised to 220 0 C under Ar until the Se(0) precursor was fully reduced to Se 2and dissolved. The temperature was then reduced to the reaction temperature, then rapid addition of the metal precursor, followed by stirring under Ar at the reaction temperature for varying amounts of time. Reaction stopped by cooling the RBF under tap water, followed by methanol addition and centrifugation. Washings were performed by re-suspension with CHCl3 (1% OAm) and precipitation two times, followed by resuspension in CHCl3.

Copper Sulfide I Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental sulfur (2 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 120 0 C. A solution was prepared of CuCl2.H2O (1 mmol) in NMP (5 mL). The copper solution was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 120 0 C. The reaction was stopped by cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation. Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product.

Copper Sulfide II Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental sulfur (3 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 180 0 C. A solution was prepared of CuCl2.H2O (1 mmol) in NMP (5 mL). The copper solution was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 180 0 C. The reaction was stopped by vii cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation. Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product.

Bismuth Sulfide Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental sulfur (3 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 180 0 C. A dispersion was prepared of BiCl3 (1 mmol) in NMP (5 mL). Note, this salt does not dissolve in NMP but forms a fine dispersion after sonication for 5 min. The bismuth dispersion was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 180 0 C. The reaction was stopped by cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation. Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product.

Copper Selenide Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental selenium (2 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 220 0 C. The reaction was stirred at 220 0 C until the Se was fully dissolved and reduced, as indication by the disappearance of black solid in the RBF. The temperature was then reduced to 180 0 C.
A solution was prepared of CuCl2.H2O (1 mmol) in NMP (5 mL). The copper solution was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 180 0 C. The reaction was stopped by cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation.
Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product. viii

Iron Selenide Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental selenium (3 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 220 0 C. The reaction was stirred at 220 0 C until the Se was fully dissolved and reduced, as indication by the disappearance of black solid in the RBF. The temperature was then reduced to 160 0 C A solution was prepared of FeCl2.4H2O (1 mmol) in NMP (5 mL). The copper solution was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 160 0 C. The reaction was stopped by cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation.
Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product.

Bismuth Selenide Synthesis
OAm (50 mL) was added to a RBF (100 mL) attached to a Schlenk line. The reaction was put under vacuum and the temperature was raised to 80 0 C. After 30min at 80 0 C the reaction was put under Ar, and then elemental selenium (3 mmol) was added to the reaction, under an Ar flow to avoid oxygen introduction into the RBF. The temperature was then raised to 220 0 C. The reaction was stirred at 220 0 C until the Se was fully dissolved and reduced, as indication by the disappearance of black solid in the RBF. The temperature was then reduced to 180 0 C A dispersion was prepared of BiCl3 (1 mmol) in NMP (5 mL). Note, this salt does not dissolve in NMP but forms a fine dispersion after sonication for 5 min. The bismuth dispersion was added to the reaction rapidly by syringe under an Ar flow. The reaction was then stirred for 30 mins at 180 0 C. The reaction was stopped by cooling the RBF in an ice bath followed by addition of MeOH (50 mL). The mixture was agitated briefly using a vortex, then separated into 4 centrifuge tubes for centrifugation to remove excess OAm and salts. The precipitated product was collected and the supernatant carefully removed and discarded. The product was then recombined into one centrifuge tube with a solution of OAm in CHCl3 (1%OAm, 20 mL). The dispersion was then mixed by vortex and then precipitated again by centrifugation. Washing with CHCl3 (1 % OAm) was repeated, then the precipitate was then dispersed in CHCl3 (20 mL) to yield the final product.