Dr. Valdes-Morales, Hector

2018, Vega, Esther, Valdes-Morales, Hector

The influence of seven commercial activated carbons (ACs) to promote hydrogen peroxide decomposition and radical generation is assessed during four operating cycles. The amount of generated hydroxyl radicals is estimated from quenching experiments using methanol as a radical scavenger. The change in chemical surface composition of ACs upon contact with hydrogen peroxide after each operating cycle is measured by Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and by following the change in the value of the pH of the point of zero charge (pHPZC). Results reveal that when ACs are exposed to hydrogen peroxide for extended periods, their chemical surface composition is modified, reducing the capacity of these materials to promote hydrogen peroxide decomposition, and in turn decreasing the generation of hydroxyl radicals. Moreover, DRIFTS analyses show that ACs with an appreciable content of basic surface functionalities, such as chromene-type structures, would guarantee a continuous radical generation, reducing the loss of catalytic activity.

2021, Dr. Valdes-Morales, Hector, Vega, Esther

The efficiency of hydrogen peroxide in the regeneration of dimethyl sulphide (DMS) exhausted-activated carbons (ACs) is assessed in this study. Moreover, the influence of chemical surface composition is evaluated using six ACs (two commercial ACs and four chemically modified ACs) with different surface features. Chemical surface composition of ACs before and after different adsorption-regeneration cycles is assessed by temperature-programmed desorption coupled with mass spectroscopy (TPD-MS) and by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results reveal that up to a 60% of regeneration efficiency is attained, being more effective in the presence of ACs derived from Filtrasorb 300 AC sample. Experimental findings show that ACs with high content of basic oxygen–containing functional surface groups and mineral fraction are responsible to promote the catalytic decomposition of hydroxide peroxide, leading to a higher formation of hydroxyl radicals and to the observed increase in the regenerative oxidation of adsorbed DMS. However, a decrease in removal efficiency is related to an increase in the amounts of oxygen functionalities mainly in the form of strong acidic surface groups such as carboxylic acid anhydrides and carboxylic acids that shift the reaction mechanism from promoting the initiation of radical chain reactions to termination. Additionally, DRIFTS analyses indicate that after successive adsorption-regeneration cycles the fraction of organic molecules that remains adsorbed limits the access to active surface sites responsible for radical generation, reducing drastically the catalytic activity of ACs.