The properties of supercritical CO₂ (SCCO₂) and supercritical water (SCW) turn them into fluids with a great ability to remove organic adsorbates retained on solids. These properties were used herein to regenerate an activated carbon fiber (ACF) saturated with a pollutant usually contained in wastewater and drinking water, phenol. Severe regeneration conditions, up to 225 bar and 400 °C, had to be employed in SCCO₂ regeneration to break the strong interaction established between phenol and the ACF. Under suitable conditions (regeneration temperature, time, and pressure, and flow of SCCO₂) the adsorption capacity of the exhausted ACF was completely recovered, and even slightly increased. Most of the retained phenol was removed by thermal desorption, but the extra percentage removed by extraction allowed SCCO₂ regeneration to be significantly more efficient than the classical thermal regeneration methods. SCCO₂ regeneration and SCW regeneration were also compared for the first time. The use of SCW slightly improved regeneration, although SCW pressure was thrice SCCO₂ pressure. The pathways that controlled SCW regeneration were also investigated.

The reduction of CO₂ emissions and its elimination from the atmosphere has become one of the major problems worldwide, since CO₂ is the main cause of the greenhouse effect and climate change. In recent years, a great number of carbonaceous materials that can be used as CO₂ adsorbents have been synthesized. The strategy is usually to synthesize the materials and determine their adsorption capacity without studying previously the factors that influence this capacity. In this work, different properties of the adsorbents are analyzed to study their influence on the CO₂ adsorption capacity. For this purpose, 10 adsorbents have been synthesized using different strategies and characterized with X-ray photoelectron spectroscopy, X-ray diffraction, and micro-Raman spectroscopy. The percentage of sp² carbons, the position of the D + D′ peak of the second-order Raman spectrum, the micropore volume, and the grain size of the C sp² domains have been related to the amount of CO₂ adsorbed by the adsorbents. The results confirm a linear relationship between the volume of the micropores and the CO₂ uptake and it proves that CO₂ retention is favored in those materials that, in addition to having a high volume of micropores, also have low grain size of C.

Steam gasifies dodecane faster than supercritical water, but supercritical water is able to produce greater amounts of H₂.

High pressure supercritical water efficiently destroys and upgrades phenol by converting the pollutant into H₂ and CH₄.