Investigation of the effectiveness of waste nut shell–based hydrochars in water treatment: a model study for the adsorption of methylene blue

Abstract

Thousands of tons of walnut and pistachio green outer shells emerge as waste sources. Recycling such wastes in environmental applications is of great importance. In this study, the efciency of waste walnut and pistachio shell–based hydrochars in removing methylene blue (MB), which represents hazardous chemicals, from the water was investigated. Outer green pistachio shell–based hydrochar (PH) and outer green walnut shell–based hydrochar (WH) were characterized by FT-IR, SEM, EDX, TG–DTA, and BET analyses. The adsorption of MB was carried out at diferent concentrations and temperatures using WH and PH, and the adsorption parameters of Langmuir and Freundlich were investigated. The R2 values of PH were calculated as 0.9963, 0.9974, and 0.9950 and of WH adsorbent were calculated as 0.9759, 0.9939, and 0.9981 for the MB adsorption at 298 K, 313 K, and 323 K, respectively. The separation factor (RL) values for WH and PH were calculated as 0.1650≥RL≥0.103, 0.1108≥RL≥0.0177, respectively. Both adsorbents ft the Langmuir model. The ΔH° values of the WH and PH adsorbents were found to be 37.0940 and 22.2493, respectively. Positive ΔH° values indicated that the adsorption was endothermic. The negative ΔG° values of both adsorbents indicated a spontaneous adsorption process. It was shown that waste nut shell–based hydrochars can be used efectively in water treatment.