Physicochemical and catalytic properties of Au nanorods micro-assembled in solvents of varying dipole moment and refractive index

• Physicochemical activities of Au nanorods in water largely differ from organic solvents.
• Au nanorods agglomeration increased with dipole moments of different polar solvents.
• Refractive indexes of Au nanorods dispersion in various polar solvents are enhanced.
• Electrokinetics significantly altered depending on agglomerated size of Au nanorods.
• Catalysis or co-catalysis activity is varied as per the extent of Au nanorods coagulation.

This paper deals with the impact of dipole moment (1.66–3.96 D) and refractive index (1.333–1.422) of the dispersion solvent on the plasmon absorption, surface charge, zeta potential, and adsorption properties of Au nanorods (AuNRs). AuNRs (length ≈ 53 nm and width ≈ 20 nm) undergo agglomeration (size 50–180 nm) with increase in the dipole moment of solvent (iPrOH < MeOH < DMF <  DMSO). Whereas, no such coagulation occurs in H2O and CCl4 suspension as confirmed by DLS and TEM size distribution. The electrostatic interaction of AuNRs with its surface adsorbed solvent dipoles leads to alteration of the their ionic state, absolute electronic charge and zeta potential (+49.79 mV in H2O, +8.99 mV in DMF and −4.65 mV in MeOH dispersion) to a greater extent. This interaction distinctly modifies the adsorption behavior of polar molecules like p-nitrophenol and salicylic acid on AuNRs surface, as evidenced by the measured changes in their electro-kinetic parameters. As a result, we observe a substantial difference in catalytic and co-catalytic activities of AuNRs dispersed in various solvents as mentioned above because the catalytic properties of AuNRs are strongly dependent on the type of solvent in which they are dispersed.

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