Development of Aerosol Measurement and Synthesis Technology for Functional Materials

Nanomaterials are used widely for their improved material properties, compared to bulk, and there are multiple ways of manufacturing them. Aerosol methods are versatile and up-scalable, making them one of the most promising routes to produce contaminant free nanomaterials. As more sophisticated applications emerge, the precise control over the whole process becomes more necessary. The process steps are interlinked in the sense that altering the precursor can have profound effects on the performance of the final application and without measurements, it is hard to say what changes actually took place. This thesis considers the whole synthesis process of generating nanoparticles in gas phase and presents not only new results that improve different steps in this process, but also functionalized surfaces, prepared by depositing nanoparticles made with flame aerosol generation method. One big problem in nanoparticle synthesis, when spraying is involved, is the generation of residual particles that consume most of the produced mass, decreasing the number of nanoparticles produced. The generation process was optimized by tuning the precursor solution to increase the heat of combustion, which enables the evaporation of the residual particles. This process was characterized with aerosol instrumentation and the absence of residual particles verified with gravimetric analysis and electron microscopy. Structural information was gained by measuring the effective density of the generated particles. Building upon the usefulness of the density measurement, a new sensor-type instrument, density monitor (DENSMO) was developed. Here it is presented for synthesis monitoring purposes. The density of particles is monitored during synthesis to evaluate the stability of the system as well as characterize the shape of the generated particles. Further tuning of the produced nanoparticles’ morphology is conducted with real-time monitoring. Two kinds of surface functionalization were achieved with the deposition of nanoparticles: anti-icing and anti-bacterial. The anti-icing surface was accomplished with a slippery liquid-infused porous surface (SLIPS) structure, where a silicone oil is held on the surface by a porous nanoparticle layer. The wetting behavior of the surface can also be changed with this kind of coating. The produced SLIPS is shown to exhibit excellent anti-icing performance. The anti-bacterial coating is implemented on a fiber filter by the deposition of silver nanoparticles. The performance of the prepared material is tested against Staphylococcus aureus and Escherichia coli bacteria. Further optimization on the antibacterial property is required in order to eradicate the S. aureus bacteria, but the material here was quite effective against E. coli, showing the viability of the presented method. The utilized methods are tunable and scalable, therefore these results create a foundation for countless options for future materials and applications

Realtime monitoring of aerosol synthesis produced nanoparticles

Nanomateriaaleja on mahdollista tuottaa kaasufaasin kautta aerosolisynteesillä, jonka yhteydessä on tärkeää monitoroida tuotantoprosessia optimaalisen materiaalin tuottamiseksi. Aerosolihiukkasten pienten kokojen takia on monitorointiin käytettävä aerosolimittalaitteita. Kaupallisesti saatavat laitteet ovat kuitenkin kalliita tai ne eivät mittaa reaaliaikaisesti. Jos halutaan monitoroida aerosolihiukkasten rakennetta kuvaavaa efektiivistä tiheyttä on vielä käytettävä kahta eri laitetta, joiden tuloksista se voidaan laskea. Tässä työssä esitellään tämän ongelman ratkaisemiseksi reaaliaikainen monitorointilaite DENSMO. Teorialtaan DENSMO pohjautuu SMPS-ELPI tiheyssovitukseen, jossa aerosolihiukkasten sähköisen liikkuvuuskoon ja aerodynaamisen koon rinnakkain mittaamisella saadaan selville niiden efektiivinen tiheys. Laitteena DENSMO on yksinkertaistetumpi versio liikkuvuus-ELPI:stä, jossa ELPI:n ylimpien asteiden tilalle on sijoitettu liikkuvuusanalysaattori. DENSMO:ssa sähköistä liikkuvuuskokoa mitataan myös liikkuvuusanalysaattorilla ja aerodynaamista kokoa yhdellä alipaineimpaktorilla. Aerosolihiukkaset mitataan niiden mukanaan tuoman varauksen perusteella, joka niille saadaan aikaiseksi pienoiskoronavaraajalla. DENSMO:n toimintaa testattiin viidestä eri materiaalista tuotetuilla aerosolihiukkasilla, joista kaksi on nestemäisiä ja kolme kiinteitä huoneenlämpötilassa. Nestemäiset aerosolihiukkaset koostuivat dioktyylisebakaatista ja rikkihaposta. Kiinteät puolestaan natriumkloridista, titaniasta ja hopeasta. Näiden materiaalien avulla voitiin tuottaa aerosolihiukkasia, joiden tiheys on ~1 - 10 g/cm3 . Liikkuvuuskoon puolesta DENSMO:a testattiin noin 20 - 200 nm välisellä alueella. Referensseihin verrattuna DENSMO:n todettiin näyttävän koko mittausalueellaan keskimäärin liikkuvuuskoon 10 %, aerodynaamisen koon 27 %, efektiivisen tiheyden 29 % ja kokonaislukumääräpitoisuuden 36 % tarkkuudella

Pesticide Residue Fast Screening Using Thermal Desorption Multi-Scheme Chemical Ionization Mass Spectrometry (TD-MION MS) with Selective Chemical Ionization

In this work, the detection characteristics of a large group of common pesticides were investigated using a multi-scheme chemical ionization inlet (MION) with a thermal desorption unit (Karsa Ltd.) connected to an Orbitrap (Velos Pro, Thermo Fisher Scientific) mass spectrometer. Standard pesticide mixtures, fruit extracts, untreated fruit juice, and whole fruit samples were inspected. The pesticide mixtures contained 1 ng of each individual target. Altogether, 115 pesticides were detected, with a set of different reagents (i.e., dibromomethane, acetonylacetone, and water) in different polarity modes. The measurement methodology presented was developed to minimize the common bottlenecks originating from sample pretreatments and nonetheless was able to retrieve 92% of the most common pesticides regularly analyzed with standardized UHPLC-MSMS (ultra-high-performance liquid chromatography with tandem mass spectrometry) procedures. The fraction of detected targets of two standard pesticide mixtures generally quantified by GC-MSMS (gas chromatography with tandem mass spectrometry) methodology was much less, equaling 45 and 34%. The pineapple swabbing experiment led to the detection of fludioxonil and diazinon below their respective maximum residue levels (MRLs), whereas measurements of untreated pineapple juice and other fruit extracts led to retrieval of dimethomorph, dinotefuran, imazalil, azoxystrobin, thiabendazole, fludioxonil, and diazinon, also below their MRL. The potential for mutual detection was investigated by mixing two standard solutions and by spiking an extract of fruit with a pesticide’s solution, and subsequently, individual compounds were simultaneously detected. For a selected subgroup of compounds, the bromide (Br-) chemical ionization characteristics were further inspected using quantum chemical computations to illustrate the structural features leading to their sensitive detection. Importantly, pesticides could be detected in actual extract and fruit samples, which demonstrates the potential of our fast screening method.Peer reviewe

Characterisation of gaseous iodine species detection using the multi-scheme chemical ionisation inlet 2 with bromide and nitrate chemical ionisation methods

The multi-scheme chemical ionisation inlet 1 (MION1) enables rapid switching between the measurement of atmospheric ions without chemical ionisation and neutral molecules using various atmospheric pressure chemical ionisation methods. In this study, we introduce the upgraded version, the multi-scheme chemical ionisation inlet 2 (MION2). The new design incorporates enhanced ion optics, resulting in increased reagent ion concentration, ensuring a robust operation, and enabling the use of multiple chemical ionisation methods with the same ionisation time. In order to simplify the regular calibration of MION2, we developed an open-source flow reactor chemistry model called MARFORCE. This model enables quantification of the chemical production of sulfuric acid (H2SO4), hypoiodous acid (HOI), and hydroperoxyl radical (HO2). MARFORCE simulates the convection-diffusion-reaction processes occurring within typical cylindrical flow reactors with uniform inner diameters. The model also includes options to simulate chemical processes in the following two scenarios: (1) when two flow reactors with different inner diameters are connected and (2) when two flows are merged into one using a Y-shaped tee, although with reduced accuracy. Furthermore, the chemical mechanism files in the model are compatible with the widely used Master Chemical Mechanism (MCM), allowing for future adaptation to simulate other chemical processes in flow reactors. Furthermore, we conducted a comprehensive characterisation of the bromide (Br-) and nitrate (NO3-) chemical ionisation methods with different ionisation times. We performed calibration experiments for H2SO4, HOI, and HO2 by combining gas kinetic experiments with the MARFORCE model. The evaluation of sulfur dioxide (SO2), water (H2O), and molecular iodine (I2) involved dilution experiments from a gas cylinder (SO2), dew point mirror measurements (H2O), and a derivatisation approach combined with a high-performance liquid chromatography quantification (I2), respectively. Our findings indicate that the detection limit is inversely correlated with the fragmentation enthalpy of the analyte-reagent ion (Br-) cluster. In other words, stronger binding (resulting in a larger fragmentation enthalpy) leads to a lower detection limit. Additionally, a moderately longer ionisation time enhances the detection sensitivity, thereby reducing the detection limit. For instance, when using the Br- chemical ionisation method with a 300 ms ionisation time, the estimated detection limit for H2SO4 is 2.9×104 molec. cm-3. Notably, this detection limit is even superior to that achieved by the widely used Eisele-type chemical ionisation inlet (7.6×104 molec. cm-3), as revealed by direct comparisons. While the NO3- chemical ionisation method remains stable in the presence of high humidity, we have observed that the Br- chemical ionisation method (Br - MION2) is significantly affected by the air water content. Higher levels of air water lead to reduced sensitivity for HO2 and SO2 under the examined conditions. However, we have found that a sharp decline in sensitivity for H2SO4, HOI, and I2 occurs only when the dew point exceeds 0.5-10.5 °C (equivalent to 20 %-40 % RH; calculated at 25 °C throughout this paper). For future studies utilising the atmospheric pressure Br- chemical ionisation method, including Br - MION2, it is crucial to carefully consider the molecular-level effects of humidity. By combining approaches such as the water-insensitive NO3 - MION2 with Br - MION2, MION2 can offer more comprehensive insights into atmospheric composition than what can be achieved by either method alone. By employing instrument voltage scanning, chemical kinetic experiments, and quantum chemical calculations, we have conclusively established that the presence of iodine oxides does not interfere with the detection of HIO3. Our comprehensive analysis reveals that the ions IO3-, HIO3.NO3-, and HIO3.Br-, which are detected using the Br- and NO3- chemical ionisation methods, are primarily, if not exclusively, generated from gaseous HIO3 molecules within atmospherically relevant conditions.Peer reviewe

Liquid flame spray—a hydrogen-oxygen flame based method for nanoparticle synthesis and functional nanocoatings

In this review article, a specific flame spray pyrolysis method, Liquid Flame Spray (LFS), is introduced to produce nanoparticles using a coflow type hydrogen-oxygen flame utilizing pneumatically sprayed liquid precursor. This method has been widely used in several applications due to its characteristic features, from producing nanopowders and nanostructured functional coatings to colouring of art glass and generating test aerosols. These special characteristics will be described via the example applications where the LFS has been applied in the past 20 years.publishedVersionPeer reviewe

Soot particle agglomeration inlet (Spai) for enabling online chemical composition measurement of nanoparticles with the aerosol mass spectrometer

Nanoparticles are a topic of interest because of their effects on human health and the climate, but the current options for evaluating their chemical composition—one of the key properties that determine the mechanisms of these effects—remain very limited and often require long collection times. For example, the Soot Particle Aerosol Mass Spectrometer (SP-AMS) is an instrument that measures the chemical properties of particles in real time, but sampling loss fixes its lower particle size limit at 50 nm, thus excluding nanoparticles. Hence, we developed the Soot Particle Agglomeration Inlet (SPAI), an addition to the SP-AMS that enables it to detect and analyze nanoparticles by attaching them to the surfaces of artificially generated soot particles. We characterized and optimized the soot generation and the soot–nanoparticle agglomeration via laboratory testing and then assessed the SPAI’s performance using silver nanoparticles as the test aerosol. The SPAI increased the SP-AMS’s capability to detect the silver nanoparticles by 35 times, demonstrating its potential in resolving issues related to analyzing the chemical composition of nanoparticles, either as an enhancement of the SP-AMS or as an addition to other sample pretreatment systems.publishedVersionPeer reviewe

Measurement of the human respiratory tract deposited surface area of particles with an electrical low pressure impactor

Particle deposition in the human respiratory tract is considered to have negative effects on human health. The lung deposited surface area (LDSA) is an important metric developed to assess the negative health effects of particles deposited in the alveolar region of the human respiratory tract. The measurement of the LDSA is frequently based on the detection of the electrical current carried by diffusion charged particles. Various conversion factors can be used to convert the electric current into LDSA concentration with relatively good accuracy up to the size about 300-600 nm. In this study, we introduce stage-specific LDSA conversion factors for electrical low pressure impactor (ELPI+) data, which enable accurate and real time LDSA concentration and LDSA size distribution measurements in the particle size range from 6 nm to 10 µm. This wide size range covers most of the alveolar deposition of particles, which has not been possible previously by electrical methods. Also, the conversion factors for tracheobronchial and head airways particle surface area deposition were determined, and the stage-specific conversion factors were compared with the single-factor data conversion method. Furthermore, the stage-specific calibration was tested against real-world particle size distributions by simulations and against laboratory-generated aerosols. Particles larger than 300 nm were observed to significantly affect the total LDSA concentration. Stage-specific conversion factors are especially required while measuring aerosols containing larger particles or when considering the surface area deposition in the tracheobronchial region and head airways. The method and the conversion factors introduced in this study can be used to monitor LDSA concentrations reliably in various environments containing particles in different size ranges.acceptedVersionPeer reviewe

Controlling the phase of iron oxide nanoparticles fabricated from iron(III) nitrate by liquid flame spray

Iron oxide nanoparticles were synthesized in a liquid flame spray process from iron(III) nitrate. The choice of chemicals and all other process parameters affects the crystallographic phase composition and the quality of the material. Adjustment of the solvent composition and the gas flow rates was used to control the phase composition of the produced particles. All samples consisted of pure maghemite (γ‐Fe2O3) or a mixture of maghemite and hematite (α‐Fe2O3). When using pure alcohols as solvents, the maghemite/hematite phase ratio could be adjusted by changing the equivalence ratio that describes the oxidation conditions in the flame zone. A large residual particle mode formed in the size range of ~20‐700 nm along with a dominant very fine particle mode (2‐8 nm). Both phases seemed to contain large particles. A partial substitution of methanol with carboxylic acids turned the hematite phase into maghemite completely, even though some of particles were possibly not fully crystallized. Residual particles were still present, but their size and number could be decreased by raising the heat of combustion of the precursor solution. 30 vol‐% substitution of methanol with 2‐ethylhexanoic acid was adequate to mostly erase the large particles.publishedVersionPeer reviewe

Silver-Decorated TiO2 Inverse Opal Structure for Visible Light-Induced Photocatalytic Degradation of Organic Pollutants and Hydrogen Evolution

TiO2 inverse opal (TIO) structures were prepared by the conventional wet chemical method, resulting in well-formed structures for photocatalytic activity. The obtained structures were functionalized with liquid flame spray-deposited silver nanoparticles (AgNPs). The nanocomposites of TIO and AgNPs were extensively characterized by various spectroscopies such as UV, Raman, X-ray diffraction, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy combined with microscopic methods such as scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM. The characterization confirmed that high-quality heterostructures had been fabricated with evenly and uniformly distributed AgNPs. Fabrication of anatase TiO2 was confirmed, and formation of AgNPs was verified with surface plasmon resonant properties. The photocatalytic activity results measured in the gas phase showed that deposition of AgNPs increases photocatalytic activity both under UVA and visible light excitation; moreover, enhanced hydrogen evolution was demonstrated under visible light.acceptedVersionPeer reviewe

Atmospheric pressure thermal desorption chemical ionization mass spectrometry for ultra-sensitive explosive detection

Illegal explosives are a threat to aviation, transport sector, critical infrastructure and generally to public safety. Their detection requires extremely sensitive instruments with efficient workflows that allow large throughput of items. In this study, we built a trace explosives detection instrument that requires minimal sample treatment and reaches ultra-low picogram level detection limits for many common explosives. The instrument is based on thermal desorption of filters, which allows analysis of liquid and solid phase samples, and subsequent selective atmospheric pressure chemical ionization and detection with a mass spectrometer. We performed experiments to scope the optimal ionization chemistry for the system and selected Br− as the reagent ion, and measured the limit of detection for 14 different explosives that were generally in the picogram range. Finally, we demonstrate the usability of the system by sampling air to a filter from a storage room known to contain explosives, from which we detect four different explosives.</p