Activated carbon modified by Mo-doped CQDs: An efficient method to reduce the thermal hazard in toluene adsorption

Abstract

Activated carbon (AC) is one of the typical adsorbents for industrial treatment of VOCs, but AC itself has a high calorific value. When the heat generated by low-temperature oxidation cannot be released, it is easy to store heat and oxidize spontaneously, resulting in immeasurable harm. Therefore, it is important to study and improve the thermal stability of AC. In this study, Mo-doped carbon quantum dots (CQDs) was synthesized to enhance the safety of AC usage. The structure of AC before and after modification was characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD). On the modified Mo-doped CQDs/AC, there are more crystalline structures formed by Mo oxides on the surface, which makes the intermolecular force on the surface of AC increase. At the same time, Mo oxide has strong oxidation resistance, which can inhibit the thermal decomposition process of AC, and has stronger stability. The spontaneous combustion tendency and thermal hazard of AC before and after modification were greatly improved. The heat released in the toluene adsorption by the modified AC at different temperatures was significantly lower than the heat released by the unmodified AC. According to the Langmuir adsorption isotherm, the adsorption performance of Mo-doped CQDs (2.5 wt%) was 1.6 times higher than that of AC when the system was 25 °C. The results showed that Na2MoO4 CQDs modified AC could effectively improve the thermal stability and greatly reduce the spontaneous combustion tendency. A relative fire safety performance evaluation model was also established to comprehensively evaluate the fire risk of VOCs treatment by AC.