Driven by the exceptional optoelectronic performance and prospective applications of organic−inorganic hybrid perovskites (HPs), an array of methods to synthesize and process HPs has been developed. Although most studies focus on solution processing, a number of reports have examined vapor-phase effects, such as the unusual liquefaction of HP films when exposed to methylamine (MA 0 ) vapor. Here, using in situ spectroscopy and microscopy, we examine the thermodynamics and kinetics of the liquefaction and recrystallization of methylammonium lead iodide (MAPbI 3 ) films with MA 0 and find that the phenomena are best described as amino-deliquescence and amino-efflorescence, respectively. By constructing a quantitative phase diagram, we show that aminodeliquescence is driven by the highly exothermic dissolution of MAPbI 3 by MA 0 with a heat of solution of approximately −96 kJ mol −1 , which drives the condensation of MA 0 at a pressure more than two orders of magnitude below the equilibrium vapor pressure. Surprisingly, the dissolution is accompanied by a decrease in entropy of ∼173 J mol −1 K −1 , suggesting the formation of a liquid state with the semi-ordered MA 0 solvent. Kinetic analysis of aminoefflorescence reveals nucleation and growth rates that decrease and increase, respectively, with increasing temperature, which together yield thin-film grain sizes that increase exponentially with temperature to produce millimeter-sized grains. The findings reveal amino-deliquescence as a highly driven thermodynamic process that is potentially a general effect for HP materials in the presence of amines. The apparently ordered nature of the liquid and large grain size after amino-efflorescence may provide a further pathway for control over morphology, crystallinity, and composition of HP systems.

Motivated by the extraordinary physical properties and potential optoelectronic applications of organic–inorganic hybrid perovskites (HPs), a variety of methods to synthesize and design high-quality HP structures has been developed. Nevertheless, the soft, organic nature of HP materials such as methylammonium lead iodide (MAPbI3) poses limitations to existing techniques, particularly for patterning the materials. Here, we demonstrate a hybrid top-down/bottom-up approach to patterning single-crystal HP microstructures. First, top-down lithography and chemical surface functionalization are used to prepare patterns with specific surface characteristics. Next, solid MAPbI3 powder is deposited on the patterns and liquefied by amino-deliquescence with methylamine (MA0) vapor, causing liquid MA0(MAPbI3) n to flow into the patterns while dewetting the remaining substrate. Lastly, MAPbI3 recrystallizes in the patterns by amino-efflorescence. By controlling the nucleation and growth conditions during amino-efflorescence, the characteristic grain size during recrystallization is orders of magnitude larger than the feature sizes of the patterns, thus causing the patterned microstructures to be single crystals. Contact angle measurements between liquid MA0(MAPbI3) n and a variety of organic and inorganic surfaces with and without chemical functionalization show that the wettability of surfaces can be tuned over a large range, providing flexibility in the choice of substrate and lithographic resist. The microstructures are free of exogenous solvents and suitable for optoelectronic device integration. As proof of concept, we demonstrate a photodetector that exhibits performance metrics consistent with single-crystal MAPbI3. The results provide a process for photonic and optoelectronic device design that can likely be extended to other potentially amino-deliquescent HP materials.

This paper presents an experimental lab designed for undergraduate students which focuses on soil science and chemistry. Students perform a series of tests to classify soil's phosphate retaining characteristics, texture, pH, organic matter content, and permeability with the addition of a novel soil amendment, Al Mg biochar. This lab has minimal cost as most chemicals are inexpensive and a soil column is crafted from a used water bottle, filter paper, and masking tape. Students apply their measurements to understand how agriculture plays a role in ocean and watershed health and how soil-testing, soil amendments, and responsible farming practices can minimize agriculture's footprint. It is important for agriculturally focused students to understand how soil chemistry relates to crop yields, and the importance of responsible agricultural practices. Learning outcomes and student attitudes from this experiment were assessed to evaluate the experiment.

In situ mid-infrared spectroscopy is a powerful technique for understanding the mechanism of CO2 reduction (CO2R) catalysts because it enables the direct detection of catalytic intermediates and products. Moreover, spectroelectrochemistry (SEC), the coupling of spectroscopy with electrochemistry, allows spectroscopic changes to be correlated with applied potentials to reveal potential-dependent intermediates that are often relevant to photoelectrochemical reactions. Hybrid photoelectrodes, composed of a narrow bandgap semiconductor, like silicon (Si), with a covalently linked molecular catalyst, are a promising platform for sunlight-driven catalysis, but characterization of the catalytic mechanism(s) is challenging under photoelectrochemical conditions, particularly when the catalyst is present in monolayer or less concentrations. Here, we have developed a new strategy to use multiple-reflection attenuated total reflectance IR spectroscopy (ATR-IR) coupled with electrochemistry to characterize catalysts directly integrated with a semiconductor surface under applied potential. We show that by surface-proximal n-type or p-type doping of the top ∼100 to 200 nm of the crystal surface, Si ATR crystals can be used simultaneously as the internal reflection element and semiconductor working electrode for ATR-IR-SEC measurements. The surface-proximal doping strategy yields a quasi-equipotential surface with excellent infrared transparency that would have been compromised by free carrier absorption if the crystal was uniformly doped. This approach permits the catalytically active functionalized surface to be directly probed without modification and overcomes signal-to-noise limitations of other strategies that use separately deposited working electrodes on Si ATR crystals. Proof-of-concept ATR-IR-SEC spectra were collected during the reduction and oxidation of monolayers of Re- and Ru-based transition-metal carbonyl complexes, respectively, verifying the viability of the technique to probe redox processes associated with CO2R catalysts on Si electrode surfaces with high sensitivity.

Slag and Al/Mg oxide modified Douglas fir biochar (AMOB) were compared for their phosphate adsorbing abilities for use individually or in combination for simulated agriculture run-off remediation in wetlands. Aqueous batch and column sorption experiments were performed for both low-cost materials. AMOB was prepared in bulk using a novel green method. Material analyses included XRD, elemental analysis, SEM, EDX, and BET. Biochar and slag have different phosphate removal mechanisms. In short residence times (≤2 h), adsorption phenomena dominate for both adsorbents. Surface area likely plays a role in adsorption performance; slag was measured to be 4.1 m2/g while biochar’s surface area was 364.1 m2/g. In longer residence times (>2 h), the slow leaching of metals (Ca, Al, and Mg) from slag continue to remove phosphate through the precipitation of metal phosphates. In 24 h, slag removed more free phosphate from the solution than AMOB. Preliminary fixed bed column adsorption of slag or AMOB alone and in tandem was performed adopting a scaled-up model that can be used to remediate agricultural runoff with high phosphate content. Additionally, a desorption study was performed to analyze the efficiency of material regeneration. While AMOB does not release any adsorbed phosphates, slag slowly releases 5.7% adsorbed phosphate over seven days.