(507f) A Thermodynamics Study of Methylene Blue Adsorption on Hydrochars Produced from Orange Peel and Grape Skin

Hydrothermal carbonization (HTC) is a thermochemical process, where biomass is treated at subcritical water temperature under auto generous vapor pressure. Hydrochar, the solid product of HTC, is a carbon-dense material which contains oxygen functional groups on the surface. Among other process parameters, HTC temperature is the most dominant for hydrochar functional properties.

The surface functional groups on the surface of hydrochars play a vital role to use them as adsorbent. Recently, a qualitative analysis of functional groups for bio-waste (i.e., fruit peels) has been carried out to correlate the morphology of the hydrochars to their adsorption properties. In addition, analysis of surface functional groups have been carried out for hydrochars produced from model compound (i.e, cellulose) at different HTC temperature. However, studies on the surface functional groups of organic waste’s hydrochars are lacking including their applications. Investigation and characterization of surface functional groups of bio-waste hydrochars will possibly open up a new route for the production of low-cost adsorbents.

In this study, the acidic and basic functional groups on hydrochar surface produced from the orange peel and grape skin were quantified. A standard titration method (Boehm method) was used to measure functional groups on hydrochar surface. A batch adsorption study of methylene blue (MB) was carried out with variable adsorbate concentration, pH, and temperature. A possible mechanism of adsorption was suggested based on concurrently operating surface adsorption and surface functionality. Results showed that the MB adsorption decreases with the decrease of total acidic functional groups which also decreases with the increase of HTC temperature.