Preparation of Porous and Durable Metakaolin-Based Alkali-Activated Materials with Active Metal as Composites for Catalytic Wet Air Oxidation

Abstract

Novel porous and durable metakaolin-based alkali-activated materials (MK-AAMs) with active metal as composites were produced to degrade bisphenol A (BPA) in catalytic wet air oxidation (CWAO). Two composite producing processes were employed. The first process consisted of mixing metakaolin (MK), a foaming agent and active metal oxide (CuO, MnO2) in a strongly alkaline solution of K2SiO3 and KOH. Paste was cured under microwave radiation to produce porous CuO and MnO2 composites. A porous blank MK-AAM was produced as described above but without active metal and was used as a reference as well. Cu(OH)2 composite was produced by refluxing a blank MK-AAM in 0.5 M CuSO4 solution for 24 h. The specific surface area (SSA) of the reference, CuO, MnO2, and Cu(OH)2 composites were 36, 53, 61, 89 m2/g, respectively. Mechanical durability was determined in terms of compressive strength and 2.8, 3.4, 3.2, 3.6 MPa were received, respectively. The activity of the reference and the composites were tested in CWAO at 1 MPa and 150 °C for 5 h by using an aqueous model solution of BPA. Under the optimal conditions for CWAO (pressure: 1 MPa; temperature: 150 °C; initial pH 5–6; c[catalyst]: 4.0 g/L) with Cu(OH)2 composite, the BPA and total organic carbon (TOC) conversions of 100% and 53% were reached. During 5 h oxidation, the composites degraded due to the combined effect of erosion (1.5 wt%) and active metal (Cu, Mn) leaching (1.1 wt%, 3.6 wt%). It was proposed that BPA can be degraded energy-efficiently via CWAO into less harmful compounds under mild reaction conditions without losing the desired properties of the composites.