A sorbent with a high enough capacity for NH 4 + could serve as an oral binder to lower urea levels in end-stage kidney disease (ESKD) patients. A hydrogen-loaded cation exchanger such as zirconium phosphate Zr(HPO 4 ) 2 •H 2 O (ZrP) is a promising candidate for this application. However, the NH 4 + binding selectivity versus other ions must be improved. Here, we have developed a gas-permeable and hydrophobic surface coating on an amorphous form of ZrP using tetraethyl orthosilicate and methoxy-terminated polydimethylsiloxane. The hydrophobic coating serves as a barrier to ions in water solution from reaching the ion-exchanger's surface. Meanwhile, its gas-permeable nature allows for gaseous ammonia transfer to the cation exchanger. In vitro studies were designed to replicate the small intestine's expected ion concentrations and exposure time to the sorbent. The effectiveness of the coating was measured with NH 4 + and Ca 2+ solutions and uncoated ZrP as the negative control. X-ray photoelectron spectroscopy and scanning electron microscopy measurements show that the coating successfully modifies the surface of the cation exchanger�ZrP. Water contact angle studies indicate that coated ZrP is hydrophobic with an angle of (149.8 ± 2.5°). Simulated small intestine solution studies show that the coated ZrP will bind 94% (±11%) more NH 4 + than uncoated ZrP in the presence of Ca 2+ . Meanwhile, Ca 2+ binding decreases by 64% (±6%). The nearly fourfold increase in NH 4 + selectivity can be attributed to the gas-permeable and hydrophobic coating applied on the ZrP surface. This work suggests a novel pathway to develop a selective cation exchanger for treating ESKD patients.

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Because electric fields are both invisible and three dimensional, they can be quite difficult to introduce to students. Simple diagrams are unable to convey the complexity or depth of the field, and computer simulations in isolation do not provide a familiar spatial context for students to understand what they see. Through “immersing” the classroom in an imaginary electric field, we propose an activity to engage the students in both visualizing and computing the electric field generated by a distribution of charges. This activity provides the opportunity for active learning within classrooms of all sizes, whether they utilize a traditional lecture format or a reformed learning environment.

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