Akira Takahashi

Recovering nitrogen and potassium from agricultural wastewater is crucial for sustainable resource circulation. However, potassium has rarely been treated as a recoverable nutrient. In this study, we developed an electrochemical adsorption method using nickel Prussian blue analog electrodes to simultaneously recover potassium (K+) and ammonium (NH4+) from synthetic agricultural wastewater containing sodium (Na+) as a competing ion. Under high-concentration conditions (ca. 1000–2000 mg L–1), both NH4+ and K+ were efficiently recovered with recovery efficiencies of ∼70%, whereas Na+ uptake remained negligible. By optimizing the constant current operation at low concentrations (ca. 100 mg L–1), stable adsorption was achieved, enabling selective recovery of NH4+ and K+ with efficiencies of ∼40%. Desorption experiments confirmed that the captured ions were effectively released and concentrated by more than one order of magnitude. Apparent selectivity coefficients of NH4+ and K+ relative to Na+ were similar across conditions, indicating that electrochemical separation performance was governed primarily by ion transport limitations. The electrodes demonstrated stable performance over 10 cycles. These findings demonstrate a practical electrochemical approach for the co-recovery and concentration of nitrogen and potassium, highlighting the potential of potassium recovery as a valuable resource-recovery strategy for agricultural wastewater treatment.

This study explores the behavior of crystalline water during the adsorption of Na ⁺ , K ⁺ , and NH ₄ ⁺ ions onto layered zirconium phosphate (ZrP) using powder X‐ray diffraction (XRD) and thermogravimetric analysis (TG). Cation uptake proceeded via two discrete adsorption steps, each accompanied by distinct structural transformations and water‐related phenomena. For Na ⁺ , water molecules were incorporated into the interlayer region during the second adsorption stage. In contrast, adsorption of K ⁺ and NH ₄ ⁺ involved the release of crystalline water during the first stage, followed by water incorporation in the second stage. Notably, ZrP exhibited no measurable dissolution under the analytical conditions employed even under strongly alkaline conditions (pH ≈ 12). Furthermore, acid‐induced desorption followed by readsorption confirmed that the layered structure of ZrP remained intact and fully regenerable. These findings demonstrate that ion‐dependent migration of crystalline water plays a critical role in the adsorption mechanism and indicate that the dynamic behavior of interlayer water must be considered in the rational design of layered inorganic materials.

A small archived dataset, interpreted through objective-focused machine learning, enables prioritisation and experimental validation of thermally robust Prussian blue analogues.

Mn₃[Fe(CN)₆]₂ (MnHCF) selectively adsorbs methanol from water with a distribution coefficient of 11 mL g⁻¹, which is 3–11 times that of activated carbons and zeolites. MnHCF exhibits an adsorption capacity of 0.36 mmol g⁻¹ and can adsorb 1000 mg MeOH per L in aqueous solution, demonstrating its effectiveness for treating methanol-contaminated wastewater.

Surface-modified Prussian blue shows 10² times higher bulk proton conductivity (0.018 S cm⁻¹) than that of unmodified Prussian blue.

Conventional methanol recovery and purification processes are highly energy-intensive; processes using selective adsorbents that consume low energy are preferable. However, conventional adsorbents have low methanol selectivity under humid conditions. In this study, we develop a selective methanol adsorbent, manganese hexacyanocobaltate (MnHCC), which enables the efficient removal of methanol from waste gas and its subsequent reuse. MnHCC adsorbs 4.8 mmol-methanol/g-adsorbent at 25 degrees C in a humid gas containing 5000 ppmv of methanol, which is five times higher than the adsorption capacity of activated carbon (0.86 mmol/ g). Although MnHCC exhibits the simultaneous adsorption of methanol and water, it has a higher adsorption enthalpy for methanol. Thus, pure methanol (95%) was recovered via thermal desorption at 150 degrees C after dehydration. The estimated energy of this recovery was 18.9 MJ/kg-methanol, approximately half that of existing mass production methods. MnHCC is reusable and stable even after 10 cyclic experiments. Consequently, MnHCC has the potential to contribute to both the recycling of methanol from waste gas and its lowcost purification.

Ammonia adsorbents effective even in trace concentration are keys of the countermeasure for air pollution of particulate matter caused by ammonia emission from agriculture sectors. We revealed that Prussian blue (PB) and its analogues (PBAs), one of the porous coordination polymers, have higher ammonia adsorption capacity in 10 ppmv of ammonia (part per mil-lion in volume, 10 ppmv = 0.0001 volume percent), ≥ 8 times that of conventional adsorbents. Moreover, these compounds can be recycled only through water flushing. The adsorption capacity of PBA was restricted to 10 cycles of adsorption/desorption, and the air sample for the experiment was collected from the composting equipment present in a swine farm. Despite the presence of saturated water vapor in the exhaust gas, the adsorbents showed excellent selectivity in the removal of the ammonia from the sample.

Well-defined K ₂ Zn ₃ [Fe(CN) ₆ ] ₂ -nanoparticles (NPs) synthesized with a micromixer showed robust redox reaction cyclability.