Effect of Carbonization Temperature on the Physicochemical and Sorption Properties of Coals from Plant Biomass for Removing Dyes from Solutions

This work is devoted to the synthesis and determination of physicochemical properties of biochars obtained by hydrothermal carbonization (HTC) of plant biomass, in particular, peach waste. The influence of material processing modes on the physicochemical properties of materials was assessed; namely, the features of changes in the crystal structure and chemical composition depending on the carbonization temperature of samples were determined. Scanning electron microscopy, energy-dispersive elemental analysis, IR Fourier spectroscopy, Raman spectroscopy, and X-ray phase analysis were used to analyze the physical, chemical and morphological characteristics. It is shown that, with an increase in the carbonization temperature, the concentration of elemental carbon in samples increases and the content of functional groups decreases. Sorption studies were carried out under static conditions on model solutions of organic dyes—methylene blue (MB) and Congo red (CR). It was found that carbonization increases the adsorption capacity of HTC coals by 2.5–3 times, but, in general, does not affect the sorption absorption rate. The equilibrium time for both dyes was 15 min.