Magnesium-enriched poultry manure enhances phosphorus bioavailability in biochars.

Pyrolysis of calcium-rich feedstock (e.g., poultry manure) generates semi-crystalline and crystalline phosphorus (P) species, compromising its short-term availability to plants. However, enriching poultry manure with magnesium (Mg) before pyrolysis may improve the ability of biochar to supply P. This study investigated how increasing the Mg/Ca ratio and pyrolysis temperature of poultry manure affected its P availability and speciation. Mg enrichment by ∼2.1% increased P availability (extracted using 2% citric and formic acid) by 20% in Mg-biochar at pyrolysis temperatures up to 600 °C. Linear combination fitting of P K-edge XANES of biochar, and Mg/Ca stoichiometry, indicate that P species, mainly Ca-P and Mg-P, are altered after pyrolysis. At 300 °C, adding Mg as magnesium hydroxide [Mg(OH)2] created MgNH4PO4 (18%) and Mg3(PO4)2.8H2O (23%) in the biochar, while without addition of Mg Ca3(PO4)2 (11%) predominated, both differing only for pyrophosphate, 33 and 16%, respectively. Similarly, the P L2,3 edge XANES data of biochar made with Mg were indicative of either MgHPO4.3H2O or Mg3(PO4)2.8H2O, in comparison to CaHPO4.2H2O or Ca3(PO4)2 without Mg. More importantly, hydroxyapatite [Ca5(PO4)3(OH)] was not identified with Mg additions, while it was abundant in biochars produced without Mg both at 600 (12%) and 700 °C (32%). The presence of Mg formed Mg-P minerals that could enhance P mobility in soil more than Ca-P, and may have resulted in greater P availability in Mg-enriched biochars. Thus, a relatively low Mg enrichment can be an approach for designing and optimize biochar as a P fertilizer from P-rich excreta, with the potential to improve P availability and contribute to the sustainable use of organic residues.

Local Photothermal Control of Phase Transitions for On-Demand Room-Temperature Rewritable Magnetic Patterning.

The ability to make controlled patterns of magnetic structures within a nonmagnetic background is essential for several types of existing and proposed technologies. Such patterns provide the foundation of magnetic memory and logic devices, allow the creation of artificial spin-ice lattices, and enable the study of magnon propagation. Here, a novel approach for magnetic patterning that allows repeated creation and erasure of arbitrary shapes of thin-film ferromagnetic structures is reported. This strategy is enabled by epitaxial Fe0.52 Rh0.48 thin films designed so that both ferromagnetic and antiferromagnetic phases are bistable at room temperature. Starting with the film in a uniform antiferromagnetic state, the ability to write arbitrary patterns of the ferromagnetic phase is demonstrated by local heating with a focused laser. If desired, the results can then be erased by cooling below room temperature and the material repeatedly re-patterned.

Type-II core/shell CdS/ZnSe nanocrystals: synthesis, electronic structures, and spectroscopic properties.

We report a two-step synthesis of highly luminescent CdS/ZnSe core/shell nanocrystals (emission quantum yields up to 50%) that can produce efficient spatial separation of electrons and holes between the core and the shell (type-II localization regime). Our synthesis involves fabrication of cubic-singony CdS core particles that are subsequently overcoated with a layer of ZnSe in the presence of surfactant-ligands in a noncoordinating solvent. Studies of different growth regime of the ZnSe shell indicate that one approach to obtaining high emission efficiencies is through alloying the CdS/ZnSe interface with CdSe, which leads to the formation of an intermediate ZnCdSe layer with a graded composition. We perform theoretical modeling of these core/shell nanocrystals using effective mass approximation and applying first-order perturbation theory for treating both direct electron-hole coupling and the core/shell interface-polarization effects. Using this model we determine the range of geometrical parameters of the core/shell structures that result in a type-II localization regime. We further applied this model to evaluate the degree of electron-hole spatial separation (quantified in terms of the electron-hole overlap integral) based on measured emission wavelengths. We also discuss the potential applicability of these nanocrystals in lasing technologies and specifically the possibility of single-exciton optical gain in type-II nanostructures.