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Results for “acid-base nucleation”

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DOE OSTI2022

The missing base molecules in atmospheric acid–base nucleation

Abstract Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2024

Tailoring the Interfacial Interactions of Porous Polymer Membranes to Accelerate Atomic Layer Deposition: The Latent Path to Antifouling Membranes

Atomic layer deposition (ALD) is a powerful strategy to engineer hybrid organic-inorganic membranes with emergent functionalities. The combination of atomic-level thickness control, a wide materials palette, and unprecedented conformality allows the physiochemical properties (e.g., hydrophilicity) of mesoporous polymer membranes to be precisely tuned. The nucleation of ALD material growth on polymer surfaces relies on Lewis acid-base interactions and remains an overlooked motif with tremendous potential to accelerate ALD nucleation and growth. Strategies to enhance these interactions could enable desirable properties such as antifouling behavior to be imparted on inert polymer surfaces that lack the necessary functional groups for ALD nucleation. Here, in this study, we demonstrate that the reactivity of polyacrylonitrile (PAN) membranes toward ALD metal oxide (MO) precursors with Lewis acid characteristics is enhanced by introducing strong Lewis base functional groups (amidoxime: Am) on the PAN backbone (Am-PAN). The resulting Lewis acid-base interactions accelerate the MO nucleation in Am-PAN and reduce the number of deposition cycles required to achieve hydrophilicity compared with the untreated PAN membrane. Unveiling the reaction mechanism, in situ Fourier transform infrared (FTIR) spectroscopy measurements established enhanced interaction dynamics between the ALD MO precursors and the Am-PAN membrane, unlike the PAN membrane. Spectroscopic ellipsometry and thermogravimetric analysis measurements revealed higher MO loadings in Am-PAN membranes compared to PAN membranes for the same number of ALD cycles. We found that strong Lewis acid-base interactions accelerated the ALD for a range of materials including Al 2 O 3 , TiO 2 , SnO 2 , and ZnO. More broadly, our work demonstrates that tailoring metal-precursor-polymer interactions is a powerful strategy to accelerate and modulate the ALD. We used this design strategy to fabricate Al 2 O 3 -Am-PAN hybrid membranes that showed 2-fold higher antifouling capability compared to pristine PAN membranes prepared with an equivalent number of Al 2 O 3 ALD cycles. Our approach expands the scope of design options for fouling-resistant porous hybrid inorganic-organic membranes and may ultimately reduce the operational costs of water treatment.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Generalized Synthesis of Highly-Dispersed, Ultrafine Transition Metal Nanoparticles on Silica Spheres for Enhanced Optical Absorption

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5 nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. Here, this work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiO x NSs) by forming a uniform coating of metal oxyhydroxide [MO y (OH) z ] through preferred surface acid–base reactions and ii) thermally reducing MO y (OH) z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiO x NSs. The capability of this synthesis strategy is verified by loading ufMNPs of various transition metals and bimetallic combinations onto the SiO x NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiO x NSs, which generate intense electric fields near the surface of the SiO x NSs. The SiO x NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiO x -NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Descriptor-Based Analysis of Atomic Layer Deposition Mechanisms on Spinel LiMn 2 O 4 Lithium-Ion Battery Cathodes

Protective coatings have been shown to effectively suppress Mn ion dissolution from the spinel LiMn 2 O 4 lithium-ion battery cathode by stabilizing the surface against undesired side reactions with the electrolyte. In spite of extensive study, however, there remains a lack of atomic-scale understanding of how such coatings are deposited, and no molecular-level descriptor to predict trends in deposition mechanisms has been identified. We have recently shown that Al 2 O 3 coatings grown by atomic layer deposition (ALD) with alternating trimethylaluminum (TMA) and water exposures exhibit submonolayer growth because of precursor decomposition on the lithium manganate spinel (LMO) surface during early ALD pulses. In the present work, we elucidate the underlying mechanisms of this Al 2 O 3 ALD process using density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) experiments, and we introduce a generalized descriptor-based framework to understand the resulting trends across a spectrum of surface structures and functionalities. We demonstrate that all decomposition products, including CH 3 -aluminum adducts and dissociated CH 3 groups, are Lewis bases and are coordinated to oxygen atoms on the LMO surface, leading to charge transfer to Lewis acidic Mn 3d states. Inert-transfer XPS supports these theoretical predictions, showing an increase in near-surface Mn 3+ content following TMA exposure and shifts in C is spectra consistent with C-O bond formation. We extend the DFT studies to various low- and high-index LMO surface facets, as a proxy for tuning the Lewis acid-base interactions between surface-bound CH 3 * and near-surface Mn ions. The thermochemistry for TMA reactions on these chemically distinct LMO surfaces demonstrates that ALD is structure-sensitive and that there is higher reactivity for TMA decomposition and Al 2 O 3 nucleation near LMO steps and defects. Motivated by the Lewis basic character of the decomposition products, we introduce the oxygen vacancy formation energy as a descriptor for decomposition energetics, and we demonstrate that all energetics are correlated to this quantity through the number of electrons that are transferred along the reaction coordinate. Finally, based on these findings, we hypothesize that improved electrochemical cycling with only 1-2 ALD cycles may be due to selective passivation of defect sites on the LMO surface that are more susceptible to Mn dissolution, and we suggest that similar descriptor-based analyses could be useful for the study of other ALD coatings on oxide substrates.

25 ENERGY STORAGE↗

DOE OSTI2020

CsI-Antisolvent Adduct Formation in All-Inorganic Metal Halide Perovskites

The excellent optoelectronic properties shown by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, high-performance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the lead-halide precursor salts. These adduct-based precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in all-inorganic perovskites such as CsPbI 3 . In this work, inorganic perovskite composition CsPbI 3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other A-site cation salts. These CsI adducts control nucleation more so than the PbI 2 -dimethyl sulfoxide (DMSO) adduct and demonstrate how the A-site plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsI-MeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.

14 SOLAR ENERGY↗