Effect of the oxygen functional groups of activated carbon on its electrochemical performance for supercapacitors

The aim of this study is to investigate changes in microstructure and oxygen functional groups of liquefied wood activated carbon fibers using density functional theory, FTIR, X-ray photoelectron spectroscopy. Samples were immersed with hydrogen peroxide (H2O2) at three concentrations (15, 20, and 25 wt%), three temperatures (90, 70, and 50 °C) for three periods of time (1, 2, and 3 h). The results reveals that the pores average radius narrow, and micropores turn into mesopores or macropores with the increasing process, which brings about the surface area of treated samples decrease. Numerous oxygen functional groups are observed in the treated samples, and the ratios of oxygen and carbon increase from 3.2% before treated to 14.7% with H2O2 modification. The results confirm that the average pore radius and surface area decrease during treatment due to concentration and temperature. What is more, oxygen functional groups increase significantly with increasing treatment concentration.

Download Full-text

Role of Activated Carbon Precursor for Mercury Oxidation and Removal: Oxidized Surface and Carbene Site Interaction

Processes ◽

10.3390/pr9071190 ◽

2021 ◽

Vol 9 (7) ◽

pp. 1190

Author(s):

Regina Rodriguez ◽

Domenic Contrino ◽

David Mazyck

Keyword(s):

Activated Carbon ◽

Nitric Acid ◽

Gas Phase ◽

Functional Groups ◽

Bituminous Coal ◽

Activated Carbons ◽

Elemental Mercury ◽

Coconut Shell ◽

Mercury Removal ◽

Oxygen Functional Groups

Activated carbon (AC) is widely accepted for the removal of inorganic contaminants like mercury; however, the raw material used in the production of activated carbon is not always taken into consideration when evaluating its efficacy. Mercury oxidation and adsorption mechanisms governed by carbene sites are more likely to occur when graphitic-like activated carbons (such as those produced from high-ranking coals) are employed versus lignocellulosic-based ACs; this is likely due to the differences in carbon structures where lignocellulosic materials are less aromatic. In this research, the team studied bituminous coal-based ACs in comparison to coconut shell and wood-based (both less aromatic) ACs for elemental mercury removal. Nitric acid of 0.5 M, 1 M, and 5 M concentrations along with 10 M hydrogen peroxide were used to oxidize the surface of the ACs. Boehm titrations and FTIR analysis were used to quantify the addition of functional groups on the activated carbons. A trend was observed herein, resulting in increasing nitric acid molarity and an increased quantity of oxygen-containing functional groups. Gas-phase mercury removal mechanisms including physisorption, oxygen functional groups, and carbene sites were evaluated. The results showed significantly better elemental mercury removal in the gas phase with a bituminous coal-based AC embodying similar physical and chemical characteristics to that of its coconut shell-based counterpart. The ACs treated with various oxidizing agents to populate oxygen functional groups on the surface showed increased mercury removal. It is hypothesized that nitric acid treatment creates oxygen functional groups and carbene sites, with carbene sites being more responsible for mercury removal. Heat treatments post-oxidation with nitric acid showed remarkable results in mercury removal. This process created free carbene sites on the surface and shows that carbene sites are more reactive to mercury adsorption than oxygen. Overall, physisorption and oxygen functional groups were also dismissed as mercury removal mechanisms, leaving carbene-free sites as the most compelling mechanism.

Download Full-text