Aerosolized droplet mediated self-assembly of photosynthetic pigment analogues and deposition onto substrates

Reuse of Lignin to Synthesize High Surface Area Carbon Nanoparticles for Supercapacitors Using a Continuous and Single-Step Aerosol Method

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 retainment 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.

Rapid membrane surface functionalization with Ag nanoparticles via coupling electrospray and polymeric solvent bonding for enhanced antifouling and catalytic performance: Deposition and interfacial reaction mechanisms

Electrospray is an effective, fast, and potentially scalable approach for membrane surface functionalization using various engineered nanomaterials (ENMs). However, the lack of fundamental understandings of the deposition process hinders the controlled deposition, efficient utilization, and long-term stabilization of the ENMs, and thus the practical applications of the nanocomposite membranes. To bridge this critical knowledge gap, advanced online characterization techniques (laser diffraction size measurement and laser doppler velocimetry) coupled with mathematical aerosol modeling are utilized to understand the three key process parameters: droplet size, deposition velocity, and evaporation rate. After deposition, polymeric solvent bonding (i.e., interdiffusion and subsequent entanglement of polymers) was found to substantially stabilize the deposited Ag NPs. We further provide a comprehensive description of such interfacial reaction mechanisms. Our results show a consistency between theoretical predication and measurement of the droplet size or deposition velocity, whereas realistic droplet evaporation rate is lower than the theoretical value due to the addition of the polymer. Successful stabilization of Ag NPs via interfacial polymeric bonding occurs under the conditions of large material contact area, high material compatibility, proper temperature (e.g., 22 °C), and polymer-to-solvent ratio (e.g., 3-5%). Our coupled approach achieves superior Ag NP coverage with high stability within minutes. Despite some reduction in water permeance, the resultant membrane shows markedly improved catalytic and antimicrobial (antibiofouling) performance (>90% enhancement) and maintained rejection. Taken together, our findings provide fundamental insights into the coupled process of electrospray deposition and polymeric solvent bonding to enable additive manufacturing of novel nanocomposite membranes with diverse structures and multiple functions.

Graphene oxide microstructure control of electrosprayed thin films

The graphene oxide (GO) microstructure, in terms of flake distribution, folding, and crumpling, in thin films affects properties such as electrical conductivity and optical transparency after GO reduction. A thin film can be tailored to the user's application if the microstructure resulting from different deposition methods can be controlled. In this work, we compare the microstructures of GO coatings created through electrospray deposition (ESD) with random deposition processes. The comparisons include both MATLAB simulations and a dip coating process. The microstructure of ESD GO thin films can be altered by changing the distance between the nozzle and the substrate. We developed a semi-automatic image analysis script that analyzes scanning electron microscopy images to find effects of GO stacking or agglomeration, without the risk of human bias. A low nozzle to substrate distance creates structures of flat GO flakes, but solvent flooding the samples causes drying patterns. A high nozzle to substrate distance causes folding and crumpling of the GO flakes due to solvent evaporation, resulting in agglomerated GO on the substrate. For our ESD setup, a nozzle to substrate distance of 2-4 mm produced GO coatings with the lowest combined influence of drying effects and GO flake folding or crumpling.

Electrospray: More than just an ionization source

Electrospraying (ES) is a potential-driven process of liquid atomization, which is employed in the field of analytical chemistry, particularly as an ionization technique for mass spectrometric analyses of biomolecules. In this review, we demonstrate the extraordinary versatility of the electrospray by overviewing the specifics and advanced applications of ES-based processing of low molecular mass compounds, biomolecules, polymers, nanoparticles, and cells. Thus, under suitable experimental conditions, ES can be used as a powerful tool for highly controlled deposition of homogeneous films or various patterns, which may sometimes even be organized into 3D structures. We also emphasize its capacity to produce composite materials including encapsulation systems and polymeric fibers. Further, we present several other, less common ES-based applications. This review provides an insight into the remarkable potential of ES, which can be very useful in the designing of innovative and unique strategies.

Electrospraying preparation of metal germanate nanospheres for high-performance lithium-ion batteries and room-temperature gas sensors

Metal germanate nanospheres including Ca₂Ge₇O₁₆, Zn₂GeO₄ and SrGe₄O₉ were successfully synthesized by a direct and large-scale electrospraying method. As anodes for lithium ion batteries, the prepared metal germanate nanospheres showed high electrochemical lithium storage performance including excellent cycling stability and high rate capacity. Especially, the Ca₂Ge₇O₁₆ nanosphere anode delivered a high specific capacity of ∼ 670 mA h g^-1 at 0.2 A g^-1. The capacity retention was maintained around 71% even after 500 cycles. Moreover, when applied as room-temperature ammonia gas sensors, all three prepared germinate nanospheres showed significant sensing response values (6.04 for SrGe₄O₉, 2.73 for Zn₂GeO₄ and 1.70 for Ca₂Ge₇O₁₆), fast response-recovery time, excellent stability and outstanding selectivity.

Electrospray Functionalization of Titanium Dioxide Nanoparticles with Transferrin for Cerenkov Radiation Induced Cancer Therapy

Titanium dioxide (TiO₂) nanoparticles have shown success as photosensitizers in the form of light-based cancer therapy called Cerenkov radiation induced therapy (CRIT). While TiO₂ nanoparticles have been reported to be an effective therapeutic agent, there has been little work to control their functionalization and stability in aqueous suspension. In this work, the controlled coating of 25 nm diameter TiO₂ nanoparticles with the glycoprotein transferrin (Tf) for application in CRIT was demonstrated using an electrospray system. Monodisperse nanoscale droplets containing TiO₂ and Tf were dried during flight, coating the proteins on the surface of the metal oxide nanoparticles. Real-time scanning mobility particle sizing, dynamic light scattering, and transmission electron microscopy show efficient control of the Tf coating thickness when varying the droplet size and the ratio of Tf to TiO₂ in the electrospray precursor suspension. Further, the functionality of Tf-coated TiO₂ nanoparticles was demonstrated, and these particles were found to have enhanced targeting activity of Tf to the Tf receptor after electrospray processing. The electrospray-coated Tf/TiO₂ particles were also found to be more effective at killing the multiple myeloma cell line MM1.S than that of nanoparticles prepared by other reported functionalization methods. In summary, this investigation not only provides a single-step functionalization technique for nanomaterials used in Cerenkov radiation induced therapy but also elucidates an electrospray coating technique for nanomaterials that can be used for a wide range of drug design and delivery purposes.

Directed assembly of the thylakoid membrane on nanostructured TiO2 for a photo-electrochemical cell

The thylakoid membrane mainly consists of photosystem I (PSI), photosystem II (PSII) and the cytochrome b6f embedded in a lipid bilayer. PSI and PSII have the ability to capture sunlight and create an electron-hole pair. The study aims at utilizing these properties by using the thylakoid membrane to construct a photo-electrochemical cell. A controlled aerosol technique, electrohydrodynamic atomization, allows a systematic study by the fabrication of different cell configurations based on the surfactant concentration without any linker, sacrificial electron donor and mediator. The maximum photocurrent density observed is 6.7 mA cm(-2) under UV and visible light, and 12 μA cm(-2) under visible light illumination. The electron transfer occurs from PSII to PSI via cytochrome b6f and the electron at PSII is regenerated by water oxidation, similar to the z-scheme of photosynthesis. This work shows that re-engineering the natural photosynthesis circuit by the novel technique of electrospray deposition can result in an environmentally friendly method of harvesting sunlight.

Energy transfer in aggregates of bacteriochlorophyll c self-assembled with azulene derivatives

Bacteriochlorophyll (BChl) c is the main light-harvesting pigment of certain photosynthetic bacteria. It is found in the form of self-assembled aggregates in the so-called chlorosomes. Here we report the results of co-aggregation experiments of BChl c with azulene and its tailored derivatives. We have performed spectroscopic and quantum chemical characterization of the azulenes, followed by self-assembly experiments. The results show that only azulenes with sufficient hydrophobicity are able to induce aggregation of BChl c. Interestingly, only azulene derivatives possessing a conjugated phenyl ring were capable of efficient (∼50%) excitation energy transfer to BChl molecules. These aggregates represent an artificial light-harvesting complex with enhanced absorption between 220 and 350 nm compared to aggregates of pure BChl c. The results provide insight into the principles of self-assembly of BChl aggregates and suggest an important role of the π-π interactions in efficient energy transfer.

Linker-free deposition and adhesion of Photosystem I onto nanostructured TiO2 for biohybrid photoelectrochemical cells

Photosystem I (PSI) from oxygenic photosynthetic organisms is an attractive sensitizer for nano-biohybrid solar cells as it has a combined light-harvesting and reaction center in one protein complex and operates at a quantum yield close to one in biological systems. Using a linker-free deposition technique enabled by an electrospray system, PSI was coupled to 1-D nanostructured titanium dioxide thin films to fabricate an electrode for a photoelectrochemical cell. After deposition, the surfactant in the PSI aggregate was dissolved in the surfactant-free electrolyte, ensuring that partly hydrophobic PSI was not resuspended and stayed in contact with titanium dioxide. A maximum current density of 4.15 mA cm(-2) was measured after 10 min of electrospray deposition, and this is the highest current density reported so far for PSI-based photoelectrochemical cells. The high current is attributed to 1D nanostructure of titanium dioxide and orientation of the PSI onto the surface, which allows easy transfer of electrons.