The design of electrocatalysts capable of selectively reducing nitrate to ammonia is gaining interest as a means of transforming waste into fertilizers. However, most prior investigations of prototypical electrocatalysts, such as polycrystalline Pd and Pt, have focused on unraveling the mechanisms responsible for the selective reduction of nitrate to nitrogen gas. Such polycrystalline noble metals demonstrate notoriously low activity for nitrate reduction (nitrate to nitrite) and high activity for nitrite reduction (nitrite to nitrogen). Here, we aim to elucidate the effect Pd surface structure has on nitrate and nitrite reduction and to determine what role catalyst structural design can play in enabling selective reduction of nitrate to ammonia. Through synthesizing nanocatalysts with controlled facets (e.g., nanocubes, cuboctahedrons, octahedrons, and concave nanocubes), we demonstrate that Pd(111) > Pd(100) > Pd­(hk0) for nitrate reduction activity and Pd(100) > Pd­(hk0) > Pd(111) for nitrite reduction activity in an alkaline electrolyte. Octahedrons without Pd (100) facets exhibited nearly selective production of NO2 – with little to no measurable NH3 or N2. However, nanocubes that expose only the Pd(100) facet exhibited high activity for NO2 – reduction to NH3. Cuboctahedrons that expose both Pd(111) and Pd(100) facets demonstrated the highest production of ammonia (306.8 μg h–1 mgPd –1) with a faradaic efficiency of 35%. Density functional theory (DFT) simulations reveal that *NO3 dissociation to *NO2 + O* is more favorable on Pd(111) than Pd(100), explaining the faster nitrate reduction kinetics on the Pd(111) facet observed in the experiments. The simulations also show that *NO2 binds less strongly to Pd(111) compared to Pd(100). Thus, nitrite formed via nitrate dissociation readily desorbs from the Pd(111) surface, which explains why Pd(111) selectively reduces nitrate to nitrite. The results show that cuboctahedron is bifunctional in nature, with the (111) facet catalyzing the conversion of NO3 – to NO2 – and the (100) facet catalyzing the conversion of NO2 – to NH3.

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An array of homogeneous glycans representing all the major carbohydrate structures present in the cell wall of the human pathogen Mycobacterium tuberculosis and other mycobacteria has been probed with a panel of glycan-binding receptors expressed on cells of the mammalian innate immune system. The results provide an overview of interactions between mycobacterial glycans and receptors that mediate uptake and survival in macrophages, dendritic cells, and sinusoidal endothelial cells. A subset of the wide variety of glycan structures present on mycobacterial surfaces interact with cells of the innate immune system through the receptors tested. Endocytic receptors, including the mannose receptor, DC-SIGN, langerin, and DC-SIGNR (L-SIGN), interact predominantly with mannose-containing caps found on the mycobacterial polysaccharide lipoarabinomannan. Some of these receptors also interact with phosphatidyl-myo-inositol mannosides and mannose-containing phenolic glycolipids. Many glycans are ligands for overlapping sets of receptors, suggesting multiple, redundant routes by which mycobacteria can enter cells. Receptors with signaling capability interact with two distinct sets of mycobacterial glycans: targets for dectin-2 overlap with ligands for the mannose-binding endocytic receptors, while mincle binds exclusively to trehalose-containing structures such as trehalose dimycolate. None of the receptors surveyed bind furanose residues, which often form part of the epitopes recognized by antibodies to mycobacteria. Thus, the innate and adaptive immune systems can target different sets of mycobacterial glycans. This array, the first of its kind, represents an important new tool for probing, at a molecular level, biological roles of a broad range of mycobacterial glycans, a task that has not previously been possible.

Electrode materials are a crucial component for achieving high desalination performance via capacitive deionization (CDI). In the present work, we have successfully fabricated a manganese dioxide (MnO2)/activated carbon (AC) composite electrode using an anodic electrodeposition technique. Surface characterization confirms the presence of electrodeposited MnO2 on the AC surface with an amorphous structure and improved wetting behavior. Cyclic voltammetry and galvanostatic charge/discharge measurements indicate that the MnO2/AC composite electrode exhibits a high specific capacitance (77.6 F g–1 at 5 mV s–1), rate capability, and excellent cycling reversibility for capacitive charge storage. Furthermore, the salt electrosorption capacity is investigated using batch mode experiments at a working voltage of 1.0 V in a 0.01 M NaCl solution. The MnO2/AC composite electrode presents a superior electrosorption capacity of 9.3 mg g–1, which is approximately 1.6-fold higher than that of the pure AC electrode (5.7 mg g–1). This significant improvement can be attributed to the mixed capacitive-Faradaic process, corresponding to the combination of the double-layer charging of the high specific surface area (625 m2 g–1) and the pseudocapacitive redox reaction of MnO2. Therefore, the electrodeposited MnO2/AC composite is a potential electrode material for high-performance CDI.

Environmentally friendly and energy-efficient ways to produce ammonia are essential to meet global food demands. Here, a new approach for ammonia production at nominally ambient conditions is introduced. As proof of concept, ammonia is synthesized mechanocatalytically by ball milling titanium in a continuous gas flow. The ammonia synthesis reaction is proposed to follow a transient Mars− van Krevelen mechanism under mechanically activated conditions, where molecular nitrogen incorporation into the titanium lattice and titanium nitride hydrogenation occur in thermodynamically distinct environments. X-ray powder diffraction and X-ray absorption spectroscopy confirm the formation of titanium nitride from titanium and N 2 . The reactivity of nitrided titanium supports that lattice nitrogen plays a role in ammonia formation. The in situ formed titanium nitride is catalytically active, and the nitride regeneration reaction is determined to be the ratelimiting step. A preliminary technoeconomic analysis shows that this approach could be feasible for distributed ammonia production.

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Pseudocapacitive electrode materials that involve a Faradaic process are being used in capacitive deionization (CDI). In the present work, manganese dioxide was electrodeposited onto a carbon nanotube-chitosan composite to create a pseudocapacitive electrode (denoted MnO 2 /CNT−CS) for an enhanced desalination performance. The benefits of coupling MnO 2 with the CNT−CS matrix are attributed to the mesoporosity to facilitate ion transport, hydrophilicity to increase the electrochemical contact, and good electrical conductivity to improve the Faradaic chargetransfer of MnO 2 . The electrochemical properties were investigated by electrochemical impedance, galvanostatic charge−discharge and cyclic voltammetry studies. Considering its low specific surface area (89.8 m 2 g −1 ), the MnO 2 /CNT−CS composite electrode exhibited pseudocapacitive-like behaviors with a high specific capacitance (42.3 F g −1 at 5 mV s −1 ) and good rate capability. Furthermore, when the MnO 2 /CNT−CS electrode served as a cathode in batch-mode CDI at 1.2 V, the salt adsorption capacity was 6.01 mg g −1 for 1 mM NaCl, which is higher than that of most MnO 2 -coated carbon electrodes. The improved sorption capacity was ascribed to the intercalation of Na + ions via the Mn redox reaction between +4 and +3 oxidation states. The cycling performance was further tested over 15 charge− discharge cycles. Consequently, the pseudocapacitive MnO 2 /CNT−CS electrode is a promising cathode material for highperformance desalination. These results also suggest a promising approach for using redox-active MnO 2 in CDI.

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.