Graphene oxide stabilized carbon nanotube-water nanofluids for direct absorption solar collectors

Abstract

The utilization of solar thermal energy has shown remarkable growth recently. Due to the development of nanomaterials, suspensions of nanoparticles (nanofluids) have exhibited great performance in the solar thermal systems, especially in direct absorption solar collectors (DASC). The fundamental advantage of DASC by using nanofluids is the minimizing of solar energy transfer steps and reducing thermal losses in converting sunlight, as nanoparticles could harvest the solar energy directly and achieve good photothermal conversion properties. Carbon nanotube (CNT) based nanofluids showed great potential as a working fluid in DASC. Nevertheless, the stability of CNTs in suspensions is the main obstacle for the large use of CNT nanofluids. In this work, small amount of graphene oxide (GO) was introduced to stabilize CNT-water nanofluids without using any other organic surfactants. The GO stabilized CNT nanofluids exhibited long-term and high-temperature stability. The π-π interactions between the GO and CNT played a significant role for the good dispersion and stability of CNT in water. Furthermore, optical characterizations showed that the GO stabilized CNT nanofluids have widely absorbing over the solar spectrum which enabled highly efficient solar energy collections. Eventually, photothermal conversion performance of GO stabilized CNT nanofluids was tested under an irradiation of simulated solar light and the nanofluid demonstrated a high efficiency in DASC. The long-term stability coupled with broadband absorption properties of GO stabilized CNT nanofluids make them ideal candidates as photothermal conversion media for direct solar thermal collectors.