Innovative microchannel-structured beads for microscale process intensification: A case study on water treatment for sulfamethoxazole abatement

This study focuses on the development of innovative microchannel-structured beads, designed to revolutionize diffusional mass transfer inside porous materials. Specifically, we created microchannel-structured alumina beads (AS0, 3 mm in diameter), using a combined phase-inversion and sintering process. This was followed by incorporating varying amounts of mesoporous γ-Al2O3 phase through a sol–gel process for the first time to enhance the internal specific surface area (SBET) of the AS0 beads, along with a 2 wt% cobalt catalytic phase applied via impregnation (2Co/ASx). A second approach for integrating cobalt-γ-Al2O3 inside the beads is a one-step co-impregnation process (2Co/ASx (co-imp.), x ranges from 0 to 4 with varying amounts of γ-Al2O3 sols). These samples were then subjected to the degradation of sulfamethoxazole (SMX) in the peroxymonosulfate (PMS)-activated AOPs system under mild reaction conditions. Experimental results demonstrated that the microchannel-structured beads with higher SBET displayed enhanced catalytic activity, with 2Co/ASx (co-imp.) achieving better catalytic efficiency compared to 2Co/ASx. This improvement was attributed to larger exposed open surface pores on the beads, which facilitated diffusional mass transfer of reactants and products. However, overloading γ-Al2O3 could reduce the accessibility of surface pores, increase mass transfer resistance at high pollutant concentrations (40 mg/L SMX), and consequently reduce SMX removal efficiency. More importantly, it is unexpected that the catalyst exhibited substantially higher performance after regeneration, achieving 96.32 % SMX removal in 20 min, compared to 95.75 % in 120 min for the fresh catalyst. This was attributed to the enhanced accessibility of open pores on the bead surface during regeneration, highlighting the significance of intensifying the diffusional transfer process to benefit catalytic reactions. Such benefits are highly transferable to a broader spectrum of heterogeneous catalysis applications.