Graphite nanoparticles (GNPs), single-wall carbon nanotubes (SWCNTs) and graphene (GE) were dispersed into an ionic liquid (IL) to prepare nanofluids at different mass fractions, respectively. The thermo-physical characteristics, radiative properties, and photo-thermal conversion performance of the IL-based nanofluids containing the carbon nanomaterials with different morphologies were investigated in details. It is shown that all the nanofluids exhibit an increase in thermal conductivity and a decrease in viscosity as composed with the base liquid, and the enhancement and reduction ratios varied with their morphologies. The GE-dispersed nanofluids exhibit the highest thermal conductivity enhancement ratios as compared to the GNPs- and SWCNTs-dispersed ones at the same mass fractions. Among the nanofluids containing different carbon nanomaterials, the GE-dispersed nanofluids show the lowest transmittance and possess the highest extinction coefficients. It is revealed that the photo-thermal conversion performance of the IL has been enhanced by the addition of the carbon nanomterials, and the GE-dispersed nanofluids exhibit the highest photo-thermal conversion efficiency among the nanofluids containing different carbon nanomaterials. The superiorities in thermal conductivity, optical property and photo thermal conversion efficiency make the GE-dispersed nanofluids show great potential for use as high-performance HTFs in solar thermal systems such as working fluids for DASCs. (C) 2016 Elsevier Ltd. All rights reserved.