9 Search Results

Carbon dioxide is a potentially valuable feedstock for carbon-based fuels or commodities but is only available in dilute streams. Many studies have focused on either the capture and concentration of CO₂ or the reduction of pure CO₂ streams. The direct reduction of sorbent-captured CO₂ in an integrated process would skip the energy-intensive CO₂ concentration and sorbent regeneration step. Herein, we report the electrocatalytic reduction of 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr·CO₂), which forms quantitatively from the reaction of sorbent 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with 10% and 0.04% CO₂ streams, by catalyst [Pt(dmpe)₂](PF₆)₂ (dmpe = 1,2-bis(dimethylphosphino)ethane) to formate with >70% Faradaic efficiencies. Unexpectedly, experimental studies indicate thatmore » the proton source phenol facilitates rapid decarboxylation of IPr·CO₂ to release CO₂, which is the substrate for reduction. Kinetic studies determined the rate of hydride transfer from a catalytic intermediate [HPt(dmpe)₂](PF₆) to form the C–H bond in formate to be 0.22 M^–1s^–1. Further details on the mechanism, transition state energy, and structure for hydride transfer to CO₂, a common step in CO₂ reduction, were explored using computational methods.« less

In the United States, many impoundments at coal-fired power plants contain elevated contaminants like arsenic, boron, barium, and selenium. Zeolites synthesized from fly ash show promise as sorbents for these contaminants. However, optimizing sorption capacity is challenging due to numerous possible topologies, silicon to aluminum (Si/Al) ratios, and cation types. In this study, molecular simulations are used to design cationic zeolites for boric acid adsorption. Force field models based on quantum mechanical calculations (PBE + D2) for Na-, Ca-, Mn-, and Fe-exchanged chabazite and LTA are presented. The new D2FF force fields reproduce DFT energies with about half the errormore » of UFF. Zeolite performance depends on Si/Al ratio and cation type, with low Si/Al ratio chabazite (CHA) and phillipsite (PHI) zeolite frameworks exchanged with Ca²⁺ or Na⁺/Ca²⁺ mixtures showing the highest adsorption. In conclusion, these findings suggest tailored fly ash-derived zeolites could provide effective boron removal from leachate ponds.« less

Carbon capture and utilization involve multiple energy- and cost-intensive steps. Dual-function materials (DFMs) can reduce these demands by coupling CO₂ adsorption and conversion into a single material with two functionalities: a sorbent phase and a metal for catalytic CO₂ conversion. The role of metal catalysts in the conversion process seems salient from previous work, but the underlying mechanisms remain elusive and deserve deeper investigation to achieve maximum utilization of the two phases. Here, for this work, preformed colloidal Ru nanoparticles were deposited onto a “NaOx”/Al₂O₃ sorbent to prepare prototypical DFMs with controlled phases for CO₂ capture and hydrogenation to CH₄.more » Ru addition was found to double the high-temperature CO₂ adsorption capacity by activating the “NaOx”/Al₂O₃ sorbent phase during a reductive pretreatment step. Most importantly, low Ru loadings were sufficient to ensure maximum CO₂ adsorption and conversion. This was attributed to the key role of the metal–sorbent interactions, wherein Ru was required to hydrogenate strongly bound CO₂ on the “NaO_x”/Al₂O₃ sorbent to CH₄ via the H₂ activated on Ru. This interaction facilitated rate-determining carbonate migration and subsequent hydrogenation at the metal–sorbent interface. Overall, Ru controlled the CO₂ hydrogenation reaction rate, while the “NaO_x”/Al₂O₃ sorbent dictated the CO₂ uptake capacity. By controlling metal–sorbent interactions at the molecular level, we demonstrate the critical role of the two phases and their synergy, facilitating the design of DFMs with maximum CO₂ capture and conversion efficiency.« less

Here this study reports energy-efficient and water-saving microwave-accelerated regeneration of sorbent (MARS) for dilute carbon capture from the ambient air. The experimental studies indicated that the CO₂ desorption rate from the chemisorbents increased with microwave output under near-isothermal conditions at near room temperature. The reduced activation energy of MARS, i.e., 20–28 kJ/mol, indicated enhanced CO₂ desorption kinetics by microwave-induced rotational–vibrational (rovibrational) coupling transitions, primarily due to the highly polarized feature of the carbamate (CO₂-PEI). The instant and selective delivery of microwave energy to the targeted polarized C–N bonds at room temperature is particularly advantageous for energy-efficient direct air capture. Themore » experimental results also demonstrated a good working capacity of 0.6–1.4 mmol of CO₂/g and a promising rapid MARS-DAC process with microwave swing. As it does not require steam regeneration and heat exchanger, a simple MARS process is attractive for CO₂ capture in water-stressed regions.« less

Biosolids containing per- and polyfluoroalkyl substances (PFAS) could contaminate the receiving environments once they are land applied. In this report, we evaluated the feasibility of controlling the bioavailability of PFAS in biosolids to timothy-grass through stabilization or mobilization approaches. Stabilization was accomplished by adding a sorbent (i.e. granular activated carbon (GAC), RemBind, biochar) to biosolids, while mobilization was achieved by adding a surfactant, sodium dodecyl sulphate (SDS), to biosolids. The results showed that the ΣPFAS concentration in grass shoots grown in biosolids amended soil treated by GAC or RemBind at 2% was only 2.77% and 3.35% of the ΣPFAS concentrationmore » detected in shoots grown in biosolids amended soil without a sorbent, respectively, indicating the effectiveness of GAC and RemBind for stabilizing PFAS and reduce their bioavailability. On the other hand, mobilization by adding SDS to biosolids at a dose range of 10–100 mg/kg significantly increased the plant uptake of ΣPFAS by 15.48%–108.57%. Thus, mobilization by adding SDS could be a valuable approach for enhancing the PFAS removal if phytoremediation is applied. Moreover, higher rate of PFAS uptake took place after grass cutting was observed in this study. Thus, proper mowing and regrowth of timothy-grass could lead to efficient and cost-effective removal of PFAS from biosolids amended soil through phytoremediation and leave the site clean to be used for other purposes.« less

Global water stress and challenges for producing sufficient supplies of fit-for-purpose water are amplifying. Atomically engineered interfaces are emerging as a powerful tool in the fabrication of advanced water treatment materials. Atomic layer deposition (ALD) and recently developed related methods, such as sequential infiltration synthesis (SIS), offer a tremendously diverse library of chemistries for interface functionalization. Thickness, stoichiometry, and physicochemical properties can be manipulated with precision. We review their fundamental physical chemistry and processing factors. ALD/SIS engineering strategies, including direct deposition, growth with intermediate layers, and secondary treatment are presented with realization of efficient water treatment. We lay out amore » pathway to establishing an ALD/SIS-based universal functionalization platform for water treatment, including sensitization strategies, in situ regulation, secondary reactions, and simulation/machine learning. Furthermore, we also provide a perspective on ALD/SIS-based interface engineering via synergy with other widely used interface engineering techniques to develop facile, versatile, and energy-efficient strategies for tackling increasingly complex water challenges.« less

Chemical looping air separation (CLAS) represents a promising approach for efficient O₂ production from the air. This present study aims at optimizing the absorber/desorber operations and the separation process with extensive experimental validation. Specifically, a one-dimensional packed bed model was developed to investigate the CLAS operation with a Sr_0.8Ca_0.2Fe_0.9Co_0.1O_3-δ perovskite sorbent. The redox thermodynamics of perovskite sorbent was measured by TGA and then incorporated into a linear driving force model to describe the O₂ absorption and desorption rates. Both 4-step and 5-step air separation cycle configurations, with various cyclic structures, were performed in a subpilot-scale packed bed. The model predictedmore » O2 purity and productivity were consistent with experimental results, supporting its accuracy and applicability. Parametric analysis and multi-objective optimization were further carried out to assess the performance of CLAS. Both O₂ purity and recovery increased monotonically with the cycle time, airflow rate, steam flow rate, and absorption pressure. Meanwhile, optimal O₂ productivity and power consumption can only be achieved by specific combinations of these parameters. The optimized results showed that CLAS can be highly competitive when compared to conventional pressure swing adsorption (PSA) or cryogenic distillation. The 5-step cycle configuration achieved a minimum power consumption of 118 kW·h for producing 1 ton O₂ with ≥ 95% purity. The maximum O₂ productivity reached 0.0932 g_O2/(g_sorbent·h) with 390 kW·h/ton O₂ of energy consumption (95% pure). The optimization results also indicate that CLAS can potentially be more efficient than cryogenic distillation even when the required O₂ purity is above 99%.« less

Existing CO₂-mediated oxidative dehydrogenation (CO₂-ODH) of ethane has yet to demonstrate >60% single-pass CO yield due to the intrinsic equilibrium limitations. We report a unique approach with mixed molten carbonates as a reaction medium for CO₂-ODH, which strategically partitions the CO₂-ODH reactions into gas and molten-salt phases and facilitates integrated CO₂ capture from power plant flue gases. An 89% CO yield was achieved at 770°C, doubling the equilibrium limitation of conventional CO₂-ODH. The high CO yield in turn enhances ethylene formation. Further characterizations confirmed that molten-salt mediated ODH (MM-ODH) proceeds through a gas-phase cracking and molten-salt mediated reverse water-gas-shift reactionmore » pathway. Based on this understanding, thermodynamic analysis and ab initio molecular dynamics simulations were conducted to develop general principles to optimize the molten-salt reaction medium. Process analyses confirm that MM-ODH has the potential to be significantly more efficient for CO₂ capture and utilization than conventional CO₂-ODH.« less

Aerogels have much potential in both research and industrial applications due to their high surface area, low density, and fine pore size distribution. Here we report a thorough structural study of three-dimensional aerogels composed of highly crystalline sp²-bonded boron nitride (BN) layers synthesized by a carbothermic reduction process. The structure, crystallinity and bonding of the as-prepared BN aerogels are elucidated by X-ray diffraction, ¹¹B nuclear magnetic resonance, transmission electron microscopy, and resonant soft X-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of ~155° and exhibit high oil uptake capacity (upmore » to 1500 wt%). In conclusion, the oil can be removed from the BN aerogel by oxidizing in air without damaging the crystalline porous structure of the aerogel or diminishing its oil absorption capacity.« less