Hydrocoal synthesis by hydrothermal carbonization method, modifications and investigation of their catalytic effects

The seeds of the loquat (Eriobotrya japonica), which has an important place in meeting the fruit needs of our country, remain as waste after consumption. It is an important issue to evaluate such biomass wastes, which occur in large quantities, and to transform them into products that will create added value. In this study, the adsorption properties and photocatalytic activities of hydrochars obtained by hydrothermal carbonization process using waste biomass loquat seeds and the composite materials of these hydrochars prepared with BiOI were investigated. Using the seeds of loquat fruit obtained from the Mersin-Erdemli region, hydrothermal carbonization (HTC) method was used to produce hydrochar at 150°C, 200°C, and 250°C temperatures for 2, 4, and 6 hours. The surface properties and characterizations of the obtained hydrochars were determined by BET, SEM, XRD and FTIR analyses. The hydrochar obtained as a result of HTC for 2 h at 250°C has the highest surface area with 13.80 m2/g according to BET analysis. Acid (H3PO4) and base (KOH) activation processes were carried out in order to improve the hydrochars surface properties. As a result of acid pre-activation (AHK), the surface area of hydrochar increased, while the basic activation (BHK) decreased. However, the ability to adsorb the methylene blue dye of the BHK structure obtained as a result of base activation reached 100%. Composite BiOI@AHK and BiOI@BHK catalysts obtained with bismuth oxyiodide (BiOI) and activated hydrochar samples by solvothermal method were synthesized and their characterizations were carried out and their effectiveness in methylene blue adsorption and photocatalytic oxidation were investigated. Methylene blue (MM) adsorption was determined as 1.65%, 4.55%, 99.66% and 35.22% for 0.5 g/L hydrochar, acid-activated hydrochar, base-activated hydrochar and BiOI, respectively. It was determined that both adsorption and photocatalytic oxidation properties of the prepared BiOI@AHK(160) and BiOI@BHK(160) composite structures were superior to the BiOI catalyst. It was observed that composite photocatalysts with synergistic effect facilitated the MM reaction with the hole (h+) structures formed on the surface of BiOI by providing MM adsorption on the surface. In addition, it was determined that the electro/void junction was prevented by the HK in the structure of the composite BiOI@AHK(160) and BiOI@BHK(160) catalysts and the MM degradation increased by 91.7% and 98.4%, respectively, due to the adsorption / photocatalysis synergistic effect.