Photo-thermal conversion ability of PEG and H2O-based microfluids of sodium lignosulfonate and its carbonized form†

In the present work, colloidal systems of sodium lignosulfonate (lignin) and its carbonized form (C-lignin) in H₂O and polyethylene glycol (PEG) were synthesized and used for solar-thermal conversion. PEG and H₂O play the role of a dispersant of the suspended particles as the base fluids and an environment for transferring heat. Based on the results, PEG performs better as the base fluid than water. All the synthesized microfluids (MFs) were stable at an optimum concentration of 0.2 g/60 ml. The comparative studies show that the C-lignin/PEG has the best light-to-heat conversion efficiency. The C-lignin/PEG was used at high light intensities and for several heating/cooling cycles without losing its performance in heat generation. All the calculated thermo-physical parameters indicated that C-lignin/PEG is more eligible than lignin/PEG in photo-thermal conversion. The prepared C-lignin/PEG has several advantages: green, inexpensive and simplicity of the preparation procedure, not using a dispersant, high photo-thermal durability and heat-generation efficiency, and excellent ability to generate heat from sunlight.