Candle soot particles-modified macroporous monoliths for efficient separation of floating oil/water and stable emulsions

Abstract

Separation of floating oil/water and stable emulsions is important for the oil industries and the environment for profitability and environmental protection. In the present work, we report a simple method of making macroporous monoliths by ice-templating, followed by their surface hydrophobization by the adsorption of candle soot particles (CSPs). With an increase in the loading of nano-sized CSPs (average diameter 55 nm) on monoliths, their surface coverage by CSPs increased gradually. This resulted in an increase in water contact angle from 0º to ~130º, revealing increased and controllable hydrophobicity. Thus, hydrophilic, omniphilic, oleophilic, and elastic monoliths were easily obtained and used as sponges. Pristine monolith (S0) has its maximum absorption capacity of 30, 5, 6, and 7.5 times its weight for water, heptane, paraffin oil, and toluene, respectively. This suggested that although S0 is a good absorbent, it lacks selectivity for emulsion separation. In contrast, the one with complete and uniform surface coverage by CSPs (S5) showed its maximum absorption capacity of 2, 10, 12, 13 times its weight for water, heptane, paraffin oil, and toluene, respectively. Further, S5 was used for the separation of stable water-in-gasoline and water-in-toluene emulsions with separation efficiency of 95% of gasoline and 98% of toluene, respectively. This superior performance of S5 is attributed to its macroporous structure with uniform and complete surface coverage by CSPs.