Abstract: In this work an aptamer-based biosensor is combined with a multisine electrochemical impedance spectroscopy sensing methodology into a novel and promising biosensing strategy. Employing a multisine instead of a traditional single sine measuring method allows the detection and quantification of parameters that provide information about the accuracy and reliability of the results, such as noise and distortions. This does not only lead to a shorter measurement time, but it also enables an easy and fast evaluation of the quality of the data and fitting, leading to more accurate results.

Abstract: It is a generally accepted idea that the particle size distribution strongly affects the optical spectra of colloidal plasmonic nanoparticles. It is often quoted as one of the main reasons while explaining the mismatch between the theoretical and experimental optical spectra of such nanoparticles. In this work, these aspects are critically analyzed by means of a bottom up statistical approach that considers variables such as mean, standard deviation and skewness of the nanoparticle size distribution independently from one another. By assuming normal and log-normal distributions of the particle size, the effect of the statistical parameters on the Mie analytical optical spectra of colloidal nanoparticles was studied. The effect of morphology was also studied numerically in order to understand to what extent it can play a role. It is our finding that the particle polydispersity, skewness and surface morphology in fact only weakly impact the optical spectra. While, the selection of suitable optical constants with regard to the crystallinity of the nanoparticles is a far more influential factor for correctly predicting both the plasmon band position and the plasmon bandwidth in theoretical simulations of the optical spectra. It is shown that the mean particle size can be correctly estimated directly from the plasmon band position, as it is the mean that determines the resonance wavelength. The standard deviation can on the other hand be estimated from the intensity distribution data obtained from dynamic light scattering experiments. The results reported herein clear the ambiguity around particle size distribution and optical response of colloidal plasmonic nanoparticles.

Abstract: This short review discusses recent developments related to the storage and release of hydrogen from liquid organic hydrogen carriers (LOHCs). It focusses on three areas of recent literature: the application and development of novel, alternative LOHC systems, process development and process integration in the storage and release of hydrogen from LOHCs, and the electrochemical conversion of LOHCs. For the novel LOHC systems, we briefly focus on reaction enthalpy and storage capacity as main KPIs for the comparison of those systems and discuss the technical availability on a relevant scale. In the field of process- and reactor development our emphasis lies on the power density of the chemical conversion units. The LOHC technology still requires further development to reach the necessary energy efficiency, flexibility and overall research maturity for market competitivity and commercial impact.

Abstract: The electrochemical detection of non-electroactive contaminants can be successfully faced via the use of indirect detection strategies. These strategies can provide sensitive and selective responses often coupled with portable and user-friendly analytical tools. Indirect detection strategies are usually based on the change in the signal of an electroactive probe, induced by the presence of the target molecule at a modified electrode. This critical review aims at addressing the developments in indirect electro-sensing strategies for non-electroactive contaminants in food and environmental analysis in the last years (2017-2019). Emphasis is given to the strategy design, the electrode modifiers used and the feasibility of technological transfer.

Abstract: The deployment of CCUS plants does not match the enormous requirements to meet the CO2 emission reductions fixed during the Paris agreement, and we must ask ourselves what is refraining the technology deployment, especially in light of the recent high CO2 prices. Owing to the higher costs than their fossil counterparts, Carbon Capture & Utilization represents a long-term solution. In addition to a gigantic scale-up effort even for the most mature Carbon Capture & Storage (CCS) technologies, various factors are responsible for the slow roll-out of CCS projects. Luckily, the financial sector and governments are playing their role. Support from the public is however key, and an open communication is required to convert social tolerance into social acceptance.

Abstract: We explorethepotentialofmicrowave(MW)-plasma-based in situ
utilizationoftheMartianatmospherewithafocusonthenovelpos-
sibilityoffixingN2 forfertilizerproduction. Conversioninasimulant
plasma (i.e.,
96% CO2,
2% N2, and
2% Ar),performedunderen-
ergyconditionssimilartothoseoftheMarsOxygen In Situ Resource
UtilizationExperiment(MOXIE),currentlyonboardNASA’sPerse-
verancerover,demonstratesthatO/O2 formedthroughCO2 dissociation
facilitatesthefixationoftheN2 fractionviaoxidationtoNOx.
PromisingproductionratesforO2, CO,andNOx of 47.0,76.1,and
1.25g/h,respectively,arerecordedwithcorrespondingenergy
costs of0.021,0.013,and0.79kWh/g,respectively.Notably,O2
productionratesare
30 timeshigherthanthosedemonstrated
by MOXIE,whiletheNOx production raterepresentsan
7% fixa-
tionoftheN2 fraction presentintheMartian atmosphere.MW-
plasma-basedconversionthereforeshowsgreatpotentialasan in
situ resourceutilization(ISRU)technologyonMarsinthatitsimulta-
neouslyfixesN2 and producesO2.

Abstract: High-rate activated sludge (HRAS) is an essential cornerstone of the pursuit towards energy positive sewage treatment through maximizing capture of organics. The capture efficiency heavily relies on the degree of solid separation achieved in the clarifiers. Limitations in the floc formation process commonly emerge in HRAS systems, with detrimental consequences for the capture of organics. This study pinpointed and overcame floc formation limitations present in full-scale HRAS reactors. Orthokinetic flocculation tests were performed with varying shear, sludge concentration, and coagulant or flocculant addition. These were analyzed with traditional and novel settling parameters and extracellular polymeric substances (EPS) measurements. HRAS was limited by insufficient collision efficiency and occurred because the solids retention time (SRT) was short and colloid loading was high. The limitation was predominantly caused by impaired flocculation rather than coagulation. In addition, the collision efficiency limitation was driven by EPS composition (low protein over polysaccharide ratio) instead of total EPS amount. Collision efficiency limitation was successfully overcome by bio-augmenting sludge from a biological nutrient removal reactor operating at long SRT which did not show any floc formation limitations. However, this action brought up a floc strength limitation. The latter was not correlated with EPS composition, but rather EPS amount and hindered settling parameters, which determined floc morphology. With this, an analysis toolkit was proposed that will enable design engineers and operators to tackle activated solid separation challenges found in HRAS systems and maximize the recovery potential of the process. (C) 2018 Elsevier Ltd. All rights reserved.

Abstract: Complete removal of estrogens such as estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2) in wastewater treatment is essential since their release and accumulation in natural water bodies are giving rise to environment and health issues. To improve our understanding towards the estrogen bioremediation process, a mathematical model was proposed for describing estrogen removal by nitrifying activated sludge. Four pathways were involved in the developed model: i) biosorption by activated sludge flocs; ii) cometabolic biodegradation linked to ammonia oxidizing bacteria (AOB) growth; iii) non growth biodegradation by AOB; and iv) biodegradation by heterotrophic bacteria (HB). The degradation kinetics was implemented into activated sludge model (ASM) framework with consideration of interactions between substrate update and microorganism growth as well as endogenous respiration. The model was calibrated and validated by fitting model predictions against two sets of batch experimental data under different conditions. The model could satisfactorily capture all the dynamics of nitrogen, organic matters (COD), and estrogens. Modeling results suggest that for El, E2 and EE2, AOB-linked biodegradation is dominant over biodegradation by HB at all investigated COD dosing levels. However, for E3, the increase of COD dosage triggers a shift of dominant pathway from AOB biodegradation to HB biodegradation. Adsorption becomes the main contributor to estrogen removal at high biomass concentrations. (C) 2018 Elsevier Ltd. All rights reserved.

Abstract: Utilizing ammonia as a storage medium for hydrogen is currently receiving increased attention. A possible method to retrieve the hydrogen is by plasma-catalytic decomposition. In this work, we combined an experimental study, using a dielectric barrier discharge plasma reactor, with a plasma kinetic model, to get insights into the decomposition mechanism. The experimental results revealed a similar effect on the ammonia conversion when changing the flow rate and power, where increasing the specific energy input (higher power or lower flow rate) gave an increased conversion. A conversion as high as 82 % was achieved at a specific energy input of 18 kJ/Nl. Furthermore, when changing the discharge volume from 31 to 10 cm3, a change in the plasma distribution factor from 0.2 to 0.1 was needed in the model to best describe the conversions of the experiments. This means that a smaller plasma volume caused a higher transfer of energy through micro-discharges (non-uniform plasma), which was found to promote the decomposition of ammonia. These results indicate that it is the collisions between NH3 and the high-energy electrons that initiate the decomposition. Moreover, the rate of ammonia destruction was found by the model to be in the order of 1022 molecules/(cm3 s) during the micro-discharges, which is 5 to 6 orders of magnitude higher than in the afterglows. A considerable re-formation of ammonia was found to take place in the afterglows, limiting the overall conversion. In addition, the model revealed that implementation of packing material in the plasma introduced high concentrations of surface-bound hydrogen atoms, which introduced an additional ammonia re-formation pathway through an Eley-Rideal reaction with gas phase NH2. Furthermore, a more uniform plasma is predicted in the presence of MgAl2O4, which leads to a lower average electron energy during micro-discharges and a lower conversion (37 %) at a comparable residence time for the plasma alone (51 %).

Abstract: To support experimental research into gas conversion by warm plasmas, models should be developed to explain the experimental observations. These models need to describe all physical and chemical plasma properties in a coupled way. In this paper, we present a modelling approach to solve the complete set of assumed relevant equations, including gas flow, heat balance and species transport, coupled with a rather extensive chemistry set, consisting of 21 species, obtained by reduction of a more detailed chemistry set, consisting of 41 species. We apply this model to study the combined CO2 and CH4 conversion in the presence of O2, in a direct current atmospheric pressure glow discharge. Our model can predict the experimental trends, and can explain why higher O2 fractions result in higher CH4 conversion, namely due to the higher gas temperature, rather than just by additional chemical reactions. Indeed, our model predicts that when more O2 is added, the energy required to reach any set temperature (i.e., the enthalpy) drops, allowing the system to reach higher temperatures with similar amounts of energy. This is in turn related to the higher H2O fraction and lower H2 fraction formed in the plasma, as demonstrated by our model. Altogether, our new self-consistent model can capture the main physics and chemistry occurring in this warm plasma, which is an important step towards predictive modelling for plasma-based gas conversion.

Abstract: Warm plasma offers a promising route for CO2 splitting into valuable CO, yet recombination reactions of CO with oxygen, forming again CO2, have recently emerged as critical limitation. This study combines experiments and fluid dynamics + chemical kinetics modelling to comprehensively analyse the recombination reactions upon CO2 splitting in an atmospheric plasmatron. We introduce an innovative in-situ gas sampling technique, enabling 2D spatial mapping of gas product compositions and temperatures, experimentally confirming for the first time the substantial limiting effect of CO recombination reactions in the afterglow region. Our results show that the CO mole fraction at a 5 L/min flow rate drops significantly from 11.9 % at a vertical distance of z = 20 mm in the afterglow region to 8.6 % at z = 40 mm. We constructed a comprehensive 2D model that allows for spatial reaction rates analysis incorporating crucial reactions, and we validated it to kinetically elucidate this phenomenon. CO2 +M⇌O+CO+M and CO2 +O⇌CO+O2 are the dominant reactions, with the forward reactions prevailing in the plasma region and the backward reactions becoming prominent in the afterglow region. These results allow us to propose an afterglow quenching strategy for performance enhancement, which is further demonstrated through a meticulously developed plasmatron reactor with two-stage cooling. Our approach substantially increases the CO2 conversion (e.g., from 6.6 % to 19.5 % at 3 L/min flow rate) and energy efficiency (from 13.5 % to 28.5 %, again at 3 L/min) and significantly shortens the startup time (from ~ 150 s to 25 s). Our study underscores the critical role of inhibiting recombination reactions in plasma-based CO2 conversion and offers new avenues for performance enhancement.

Abstract: An unbiased photo-fuel cell (PFC) is a device that integrates the functions of a photoanode and a cathode to achieve simultaneous light-driven oxidation and dark reduction reactions. As such, it generates electricity while degrading pollutants like volatile organic compounds (VOCs). The photoanode is excited by light to generate electron-hole pairs, which give rise to a photocurrent, and are utilized to oxidise organic pollutants simultaneously. Here we have systematically studied various TiO2/WO3 photoanodes towards their photocatalytic soot degradation performance, PFC performance in the presence of VOCs, and the combination of both. The latter thus mimics an urban environment where VOCs and soot are present simultaneously. The formation of a type-II heterojunction after the addition of a thin TiO2 top layer over a dense WO3 bottom layer, improved both soot oxidation efficiency as well as photocurrent generation, thus paving the way towards low-cost PFC technology for energy recovery from real polluted air.

Abstract: The effect of pore size on plasma catalysis is crucial but still unclear. Studies have shown plasma cannot enter micropores and mesopores, so catalysts for traditional thermocatalysis may not fit plasma catalysis. Here, 3D porous Cu and CuO with different pore sizes were prepared using uniform silica particles (10–2000 nm) as templates, and compared in plasma-catalytic dry reforming. In most cases, the smaller the pore size, the higher the conversion of CH4 and CO2. Large pores reachable by more electrons did not improve the reaction efficiency. We attribute this to the small surface area and large crystallite size, as indicated by N2-sorption, mercury intrusion and XRD. While the smaller pores might not be reachable by electrons, due to the sheath formed in front of them, as predicted by modeling, they can still be reached by radicals formed in the plasma, and ions can even be attracted into these pores. An exception are the samples synthesized from 1 μm silica, which show better performance. We believe this is due to the electric field enhancement for pore sizes close to the Debye length. The performances of CuO and Cu with different pore sizes can provide references for future research on oxide supports and metal components of plasma catalysts.

Abstract: We present a zero-dimensional kinetic model to characterise specifically the gas-phase dynamics of methane
conversion in a nanosecond pulsed discharge (NPD) plasma reactor. The model includes a systematic approach to
capture the nanoscale power discharges and the rapid ensuing changes in electric field, gas and electron temperature,
as well as species densities. The effects of gas temperature and reactor pressure on gas conversion and
product selectivity are extensively investigated and validated against experimental work. We discuss the
important reaction pathways and provide an analysis of the dynamics of the heating and cooling mechanisms. H
radicals are found to be the most populous plasma species and they participate in hydrogenation and dehydrogenation
reactions, which are the dominant recombination reactions leading to C2H4 and C2H2 as main
products (depending on the pressure).

Abstract: Given the ecological problems associated to the CO2 emissions of fossil fuels, plasma technology has gained
interest for conversion of CO2 into value-added products. Microwave plasmas operating at atmospheric pressure
have proven to be especially interesting, due to the high gas temperatures inside the reactor (i.e. up to 6000 K)
allowing for efficient thermal dissociation of CO2 into CO and O2. However, the performance of these high
temperature plasmas is limited by recombination of CO back into CO2 once the gas cools down in the afterglow.
In this work, we computationally investigated several quenching nozzles, developed and experimentally tested
by Hecimovic et al., [1] for their ability to quickly cool the gas after the plasma, thereby quenching the CO
recombination reactions. Using a 3D computational fluid dynamics model and a quasi-1D chemical kinetics
model, we reveal that a reactor without nozzle lacks gas mixing between hot gas in the center and cold gas near
the reactor walls. Especially at low flow rates, where there is an inherent lack of convective cooling due to the
low gas flow velocity, the temperature in the afterglow remains high (between 2000 and 3000 K) for a relatively
long time (in the 0.1 s range). As shown by our quasi-1D chemical kinetics model, this results in a important loss
of CO due to recombination reactions. Attaching a nozzle in the effluent of the reactor induces fast gas quenching
right after the plasma. Indeed, it introduces (i) more convective cooling by forcing cool gas near the walls to mix
with hot gas in the center of the reactor, as well as (ii) more conductive cooling through the water-cooled walls of
the nozzle. Our model shows that gas quenching and the suppression of recombination reactions have more
impact at low flow rates, where recombination is the most limiting factor in the conversion process.