Carbon from Recycled Materials for Solar Thermal Evaporation and Oil Absorption

This study investigated the carbonization of recycled materials for solar thermal evaporation and oil absorption. Cotton fabric, cardboard, and wood were carbonized and treated with acidic substances (lemon juice, sulfuric acid, hydrochloric acid) to modify the carbon surface. The effectiveness of the recycled carbon in solar thermal evaporation and oil adsorption was analyzed. Results showed that untreated carbon showed higher efficiency in solar thermal evaporation due to its larger solar interface, while acid-treated carbon was less effective in the solar steam generation because of the changed surface properties. Quantitative thermal analysis revealed significant weight loss in wood between 285-350°C, with an exothermic peak at 345°C. Wood-derived carbon was 30% more efficient in solar water desalination and sewage purification compared to commercial activated carbon. For oil absorption, lemon juice-treated carbon outperformed others by 40%, except for commercial activated carbon, which was 1.5 times more effective due to its high porosity. This is because the lemon juice containing citric acid, hydroxy groups, vitamin C, and other organic molecules can modify the surface conditions of carbon. Lemon juice as an availability of natural resource for carbon surface property modification has practical application in many subtropical and/or tropical areas. It is believed that using squeezed lemon juice is a more sustainable practice than using concentrated hydrochloric acid or pure citric acid considering that using concentrated acids introduces more complex synthesizing steps and incurring high cost. The average solar thermal evaporation rate of typical recycled carbon reached 1.93 kg/(m2∙h).