In situ preparation of carbon/zeolite composite materials derived from coal gasification fine slag for removing malachite green: Performance evaluation and mechanism insight

Abstract

The stockpiling of coal gasification fine slag (CGFS) and the discharge of organic wastewater pose serious environmental threats. The complex synthesis process and limited pollutant removal capacity of CGFS-based adsorbents impede their efficient utilization in organic wastewater purification. In this work, carbon/zeolite composite materials (CZCM) derived from CGFS were prepared in situ using a one-pot method without further crystallization, achieving an ultra-high adsorption capacity (9705 mg/g) and excellent renewability for malachite green (MG). CZCM was identified as a typical mesoporous material with an abundant pore structure, facilitating the migration of MG within the material. Notably, various metal elements (e.g., iron and calcium) and chemical groups (e.g., carboxyl and hydroxyl) from CGFS were retained through this novel preparation method, providing additional adsorption sites and enhancing MG adsorption. The adsorption kinetics and thermodynamics results indicated that physisorption and multilayer adsorption were the primary adsorption modes of MG by CZCM, with the adsorption rate limited by internal diffusion. Furthermore, the adsorption process was found to be exothermic, spontaneous, and entropy-decreasing. Mechanistic investigations revealed that the exceptional adsorption performance of MG by CZCM was primarily attributed to electrostatic attraction and ion exchange, with hydrogen bonding and π-π interactions also playing significant roles. This study provides new insights into the development of CGFS-based adsorbents for organic wastewater treatment, promoting the efficient conversion and practical application of CGFS.