Abstract: Human activities are rapidly depleting phosphate reserves and dispersing diluted phosphorus (P) into the environment through municipal and industrial wastewater, underscoring the need to recover P from waste streams. Herein, we demonstrate an air-cathode-based electrochemical approach for the rapid, one-step P recovery from synthetic human urine. This approach enables 99.97% recovery of P from urine (748 mg P/L) and significantly reduces processing time to ~ 10 min, compared with the hours required by alternative techniques that report similar recovery. Moreover, the resulting effluent meets typical U.S. discharge limits (< 1 mg P/L). We also systematically investigate the P capture mechanism using X-ray Absorption Spectroscopy and evaluate the application of the recovered P as a fertilizer. A cost analysis based on the scaled-up design of the electrochemical approach estimates P recovery at $18.8/kg P. Overall, the fast kinetics, high capture efficiency, and cost-effective processing indicate the potential for scalable P recovery. 

Abstract: The size and morphology of nanosized aggregates play a crucial role in determining their performance in several applications, including healthcare, energy storage, and catalysis. Both the size and morphology are impacted by several aerosol mechanisms, including sintering. Studies have reported the role of sintering combined with other aerosol mechanisms, such as collisional growth. Many systems in which sintering occurs also have a concomitant chemical reaction. In this study, a novel geometric model (GM) is developed to predict the evolution in size and morphology of multiparticle aggregates under simultaneous sintering and chemical reaction. A furnace aerosol reactor system is then used to study the evolution of lignin nanoparticles that are impacted by sintering and reaction. Using the developed model, kinetic parameters for sintering and reaction are determined by comparing GM to the experimental results. The kinetic parameters for lignin reaction agreed well with literature-reported values. The kinetic parameters for lignin sintering, which are the pre-exponential factor and activation energy, were estimated as 6.6x10−8 s.nm−1 and 116.4 kJ.mol−1, respectively. The lignin sintering rate parameters were effectively used to establish the impact on the synthesis of lignin-based high-value products, specifically nanomaterials and bio-oil. The developed GM is simple and generalizable to investigate the size and morphology changes of other materials that undergo reactions with sintering.

Abstract: Lignin, a constituent of biomass, is a byproduct waste of the pulp and paper industry that may have several potential applications in nanoparticle form. Conventional synthesis of lignin nanoparticles (LNPs) involves physicochemical batch and multistep processes. We report here a continuous and single-step process for the synthesis of LNPs in a furnace aerosol reactor (FuAR) starting from bulk powders with minimal use of solvents. The synthesized LNPs were analyzed for their size distribution and functional group composition. Based on the changes in functional groups, the maximum temperature in the FuAR for obtaining LNPs without significant chemical degradation was found to be around 300 °C at a residence time of 5.8 s. The as-produced LNPs had a geometric mean diameter between 50 and 68 nm. Furthermore, the bulk and as-synthesized LNPs were tested for UV protection applications. The observed improvement in UV protection with a decrease in lignin particle size is systematically investigated using the optical absorption parameter, which provides a quantitative correlation for the effect of lignin particle size and mass concentration on UV protection performance. Overall, this study contributes to advancing lignin valorization by demonstrating the synthesis of LNPs using the scalable FuAR method and providing a novel quantitative correlation for the design of high-performance lignin-based UV protection materials.

Abstract: There is a growing demand for the synthesis of high surface area carbons, also known as carbon nanoparticles (CNPs). Existing synthesis methods for high surface area carbons have limited environmental benignity and economic viability due to the requirement of multistep and batch processes and harsh activating and/or templating chemicals. Herein, we demonstrate the synthesis of high surface area CNPs from lignin, a waste byproduct, through a single-step, continuous gas phase aerosol technique without the use of activating or templating chemicals. This continuous approach requires significantly less time for synthesis: on the order of seconds in comparison to hours for conventional methods. Properties of carbon materials synthesized from lignin are controlled by temperature and residence time, and the role of these parameters inside the aerosol reactor on carbon nanoparticle size, morphology, molecular structure, and surface area is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance, and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retention of over 98% after 10,000 cycles. This is a clear demonstration of their superior performance compared with supercapacitors synthesized earlier from lignin. Overall, the simple (single-step, continuous, and rapid) operation and the avoidance of the use of activating/templating chemicals make the aerosol technique a promising candidate for the scalable and sustainable synthesis of CNPs from lignin.

Abstract: A key aspect of circular economies is using sustainable pathways for processing advanced materials. While significant advances have been made in the discovery of novel materials that have innovative functionalities, rarely is attention provided to a holistic analysis to ensure that processes are sustainable. Rigorous analysis methodologies must be used to compare alternative processing methods. In this study, a comprehensive life cycle assessment (LCA) is conducted to evaluate a continuous and single-step aerosol synthesis approach in comparison to conventional batch pyrolysis methods for producing high-surface-area (porous) carbon materials. First, porous carbon nanoparticles (CNPs) are synthesized using a lab-scale aerosol reactor, and LCA is conducted to identify the key processing parameters contributing to their environmental impact. These results are then successfully used to guide the design of an optimized scaled-up aerosol reactor, achieving up to 75% reduction in global warming potential compared to conventional scaled-up batch pyrolysis techniques. Finally, the role of particle size and pyrolysis energy source in the environmental impact of CNP synthesis is systematically investigated. Overall, the simple (single-step, continuous, and rapid) operation and promising sustainability of the aerosol technique highlight its significant potential for the scalable synthesis of carbon nanomaterials from lignin.

Abstract: There is a growing demand for advanced functional materials, such as carbon composites, and their scalable synthesis requires environmentally sustainable and economically viable approaches. Carbon-silicon (C–Si) composites are particularly promising anode materials for high-capacity Li-ion batteries. However, their conventional synthesis approaches often involve two-step solvothermal batch processes that require several hours (~10 h) and rely on chemical additives to facilitate encapsulation. A single-step and continuous aerosol approach for synthesizing C–Si composites is demonstrated in this work. The aerosol approach significantly reduces synthesis time to as low as ~4 s, utilizes lignin (a waste byproduct of the pulping industry) as a carbon precursor, and enables additive-free encapsulation of silicon nanoparticles (NPs) in carbon. The role of processing temperatures (23-1050 ◦C) inside the aerosol reactor on the composite properties, including morphology, molecular structure, porosity, electrical conductivity, and elastic modulus, is systematically investigated, providing mechanistic insights into silicon NPs encapsulation. Furthermore, the suitability of as-synthesized C–Si composites for Li-ion battery anodes is evaluated. The composites exhibited significantly improved cyclic stability compared to bare silicon NPs, and their performance is correlated to physicochemical properties. Overall, the rapid and additive-free encapsulation of silicon NPs and the use of lignin as a sustainable carbon precursor highlight the potential of the aerosol route for the scalable production of carbon composites.