Activated carbon obtained from cardboard tube waste of immersion thermocouple and adsorption of methylene blue

Thermocouple sensors which use cardboard tubes are used as thermal insulators to measure the temperature of liquid steel. After its use, the material is discarded, causing high waste of the cardboard tube of the immersion thermocouple (CTW). Thus, this study aimed to use it as a precursor for the production of activated carbon (AC-CTW) by activation with H3PO4. A CHN analyzer estimated the carbon, hydrogen, and nitrogen contents of CTW. CTW and AC-CTW were characterized by FTIR, XRD, TGA, and SEM. Besides, AC-CTW was also characterized by XRF, zeta potential, and BET. The batch adsorption of MB onto AC-CTW was tested at various times of contact, temperature, adsorbent dosage, solution pH, and initial solution concentrations. Adsorption mechanisms were investigated using kinetic models, isothermal models, and thermodynamic studies. Elementary CTW analysis showed carbon content of 39.29%, and FTIR, XRD, SEM, and TGA revealed the predominantly cellulosic nature of the CTW. The characterizations of AC-CTW showed a material with an amorphous structure, good thermal stability, potential zeta negative, irregular and porous surface, and BET surface area of 468.9 m2 g−1. The optimum parameters of adsorption were determined as contact time of 90 min, 55 °C, pH 6, and AC-CTW dosage of 0.16 g. The Langmuir isotherm and pseudo-first-order kinetic models fitted better with experimental tests. The AC-CTW showed a maximum adsorption capacity of 182.481 mg g−1. According to the thermodynamic study, the adsorption was spontaneous and endothermic. Thereby, CTW is a potential raw material for producing activated carbon.