3D-printed hybrid zirconia hydrogels for ultrahigh-efficiency phosphate adsorption

Phosphorus removal is a key technology to avoid water eutrophication. However, due to the relatively weak activity of phosphorous compounds, it is still a challenge to recycle them efficiently. In this paper, a 3D-printed acetylacetone-coordinating one-pot sol–gel strategy was proposed to prepare hybrid zirconia hydrogels with relatively high zeta potential (positive even when pH value reaches 8.0), high specific surface area (272.66 m² g⁻¹) and loose pore structure (average pore size is 5.97 nm). The adsorption experimental results showed that zirconia hydrogels had excellent phosphate adsorption performance, and the maximum adsorption capacity was 209.64 mg g⁻¹. The most valuable thing was that the hydrogels still maintained a very high adsorption capacity (142.00 mg g⁻¹) in a neutral environment. Zirconia hybrid hydrogel has higher surface potential (13.5 mV, pH = 6) and larger mesoporous structure (most probable pore size = 7.3 nm) than zirconia nanoparticles (5 mV, pH = 6; most probable pore size = 3.5 nm), which are beneficial to mass transfer, adsorption ability, and ultimately, excellent adsorption performance. Surprisingly, the zirconium-based hydrogel can realize 3D printing through ink direct writing technology, which endowed the block hydrogels with stable and macroscopical structure. The zirconia-based hydrogels constructed by 3D printing had a faster phosphate adsorption rate than the undesigned block hydrogels, and they were easier to recover than powdered adsorbents. The sol–gel and 3D printing strategy in this paper may provide a new idea for the optimal design of phosphate adsorbent for direct water treatment.

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