With superior optical and thermal properties, nanofluids represent an innovative approach for direct-absorption solar collectors. In this review, we discuss recent developments in the field of nanofluids utilized in direct absorption solar collectors in terms of their preparation techniques, optical behaviours, solar thermal energy conversion performance, as well as their physical and thermal stability, along with the experimental setups and calculation approaches used. (Nanomaterials 13, 2023, 1232).

We demonstrate the synthesis, full characterization and application of Cu-oxide nanoparticles with high optical absorption and long-term stability over many months. The synthesis method, based on a hybrid plasma-liquid non-equilibrium electrochemical process, ensures a very limited environmental impact as it relies on a solid metal precursor while avoiding the use of additional chemicals such as surfactants and other reducing agents. The results show that nanofluids produced with our Cu-oxide nanoparticles can achieve exceptional solar thermal conversion efficiencies close to ~90% and can provide a viable solution for an efficient solar thermal conversion technology. (Nano Energy 108, 2023, 108112).

Macroscopic ribbon-like assemblies of carbon nanotubes (CNTs) are functionalised using a simple direct-current-based plasma–liquid system, with oxygen and nitrogen functional groups being added. The ability to improve the wettability of the CNTs is of paramount importance for producing nanofluids, with relevance for a number of applications. Here, in particular, we investigate the efficacy of these samples as nanofluid additives for solar–thermal harvesting. (Nanomaterials 12, 2022, 2705).

Plasma direct exsolution at room temperature will enable improved sustainable synthetic routes, more control of catalysis microstructure as well as new application opportunities. Moreover, the factors that most affect the exsolution process are identified. It is shown that the surface defects produced initiate exsolution under a brief ion bombardment of an argon low-pressure and low temperature plasma. This results in controlled nanoparticles with diameters ≈19–22 nm with very high number densities thus creating a highly active catalytic material for CO oxidation which rivals traditionally created exsolved samples. (Advanced Energy Materials 12, 2022, 2201131).

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Nitrogen doping of carbon nanomaterials using a simple direct current-based plasma–liquid system enables rapid and high levels of functionalization with the atomic concentration of nitrogen reaching 22.5%, with amine groups, pyrrolic groups and graphitic nitrogen observed in the X-ray photoelectron spectra, the highest ever achieved. (Journal of Materials Science 57, 2022, 13314).

Nitrogen-doped carbon quantum dots are synthesized by a one-step atmospheric pressure microplasma process. The origin of the observed photoluminescence emission and its relationship with nitrogen doping is studied using a range of optical and chemical measurements along with verification by theoretical calculations (Carbon 183, 2021, 1).

We observe the extraction of carriers in a perovskite oxide with metallic behaviour and high conductivity, whilst also displaying broad absorption across the ultraviolet, visible, and near-infrared spectral regions, making it an attractive material for solar energy conversion. Furthermore, the optoelectronic properties of strontium niobate can easily be tuned by varying the Sr fraction or through doping (Nanoscale 21, 2021, 12271).

Plasma-electrochemistry has been successfully used to synthesize a range of metal–oxide nanoparticles and quantum dots (QDs). While nanoparticles and QDs can be an end to this process, they can also be viewed as ‘chemical probes’ that help understanding the underlying and progenitor chemical reactions. We have therefore studied plasma–ethanol interactions during the synthesis of CuO QDs (Green Chemistry 23, 2021, 3983).

Copper nanoparticles (Cu-NPs) represent a viable low-cost alternative to replace bulk copper or other more expensive NPs (e.g. gold or silver) in various applications. This study deals with the synthesis of well dispersed Cu-NPs by using an Ar + H2 microplasma using a solid copper precursor.The Cu-NPs were successfully deposited onto porous carbon nanotube ribbons; surface coverage and the penetration depth of the Cu-NPs inside the CNT ribbon structure were investigated as these can be beneficial for a number of applications (Nanoscale Advanced 3, 2021, 781).