Nonlinear evolution of two fast-particle-driven modes near the linear stability threshold

A system of two coupled integro-differential equations is derived and solved for the non-linear evolution of two waves excited by the resonant interaction with fast ions just above the linear instability threshold. The effects of a resonant particle source and classical relaxation processes represented by the Krook, diffusion, and dynamical friction collision operators are included in the model, which exhibits different nonlinear evolution regimes, mainly depending on the type of relaxation process that restores the unstable distribution function of fast ions. When the Krook collisions or diffusion dominate, the wave amplitude evolution is characterized by modulation and saturation. However, when the dynamical friction dominates, the wave amplitude is in the explosive regime. In addition, it is found that the finite separation in the phase velocities of the two modes weakens the interaction strength between the modes

Influence of phosphate buffer and proteins on the potentiometric response of a polymeric membrane-based solid-contact Pb(II) ion-selective electrode

In this work, the influence of phosphate buffer and proteins on the potentiometric response of a polymeric membrane-based solid-contact Pb2+-selective electrode (Pb2+-ISE) was studied. The effects of bovine serum albumin (BSA) adsorption at the surface of the ion-selective membrane combined with electrode conditioning in phosphate-buffered saline (PBS) solution was elucidated by potentiometry and electrochemical impedance spectroscopy. The adsorbed BSA at the surface of the Pb2+-ISE slightly lowered the detection limit but did not influence the selectivity of the Pb2+-ISE towards the interfering ions studied (Cu2+, Cd2+). Conditioning of the Pb2+-ISE in 0.01 mol dm–3 PBS resulted in a super-Nernstian response which was related to fixation/extraction of Pb2+ in the ion-selective membrane via precipitation of Pb3(PO4)2 by PO43– anions present in PBS. By conditioning of the Pb2+-ISE in 0.01 mol dm–3 PBS + 1 mg/ml BSA it was possible to extend the linear response range of the Pb2+-ISE towards lower analyte concentrations. The utilization of this conditioning procedure was validated by determination of Pb2+ concentrations down to ca 20 ppb in aqueous samples by Pb2+-ISEs and by comparing the results with those obtained by ICP-MS

The Effects of Washing Techniques on Thermal Combustion Properties of Sewage Sludge Chars

Sewage sludge chars were subjected to washing to produce a clean solid fuel of superior quality. First, sewage sludge was converted into chars at different carbonization temperatures (400–700 °C), and then the produced chars were washed with various washing techniques, i.e., water (W), hydrochloric acid (HCl), ethylenediamine tetraacetic acid (EDTA) and ultrasound-assisted water to further reduce ash and heavy metal contents. The washed chars were systematically characterized and their fuel properties were analyzed. The results indicated that all washing techniques decreased ash content of chars and improved their fuel ratio. The washed chars exhibited higher heating values, lower slagging and ash fouling indexes and higher combustion reactivity, indicating the better quality of the derived fuels. Among the washing techniques, HCl washing was the most efficient process as carbon content increased by 20%, while ash content decreased by 50%. The fuel ratio as well as slagging and ash fouling indexes were significantly improved. Furthermore, the combustion reactivity showed similar pattern to coal with high conversion rate suggesting the enhanced thermal stability of the fuel. In conclusion, pyrolysis as a single process seems inefficient to produce high quality chars; however, coupling pyrolysis with washing can yield chars with satisfactory fuel properties. Graphic abstract: [Figure not available: see fulltext.].acceptedVersionPeer reviewe

Ion selective electrodes for determination of low and ultra low concentrations of lead (II) in natural waters

Att övervaka förekomsten av giftiga komponenter i naturliga vattendrag är nödvändigt för människans välmående. Eftersom halten av föroreningar i naturens ekosystem bör hållas möjligast låg, pågår en ständig jakt efter kemiska analysmetoder med allt lägre detektionsgränser. I dagens läge görs miljöanalyser med dyr och sofistikerad instrumentering som kräver mycket underhåll. Jonselektiva elektroder har flera goda egenskaper som t.ex. bärbarhet, låg energiförbrukning, och dessutom är de relativt kostnadseffektiva. Att använda jonselektiva elektroder vid miljöanalyser är möjligt om deras känslighetsområde kan utvidgas genom att sänka deras detektionsgränser. För att sänka detektionsgränsen för Pb(II)-selektiva elektroder undersöktes olika typer av jonselektiva membran som baserades på polyakrylat-kopolymerer, PVC och PbS/Ag2S. Fast-fas elektroder med membran av PbS/Ag2S är i allmänhet enklare och mer robusta än konventionella elektroder vid spårämnesanalys av joniska föroreningar. Fast-fas elektrodernas detektionsgräns sänktes i detta arbete med en nyutvecklad galvanostatisk polariseringsmetod och de kunde sedan framgångsrikt användas för kvantitativa bestämningar av bly(II)-halter i miljöprov som hade samlats in i den finska skärgården nära tidigare industriområden. Analysresultaten som erhölls med jonselektiva elektroder bekräftades med andra analytiska metoder. Att sänka detektionsgränsen m.hj.a. den nyutvecklade polariseringsmetoden möjliggör bestämning av låga och ultra-låga blyhalter som inte kunde nås med klassisk potentiometri. Den verkliga fördelen med att använda dessa blyselektiva elektroder är möjligheten att utföra mätningar i obehandlade miljöprov trots närvaron av fasta partiklar vilket inte är möjligt att göra med andra analysmetoder. Jag väntar mig att den nyutvecklade polariseringsmetoden kommer att sätta en trend i spårämnesanalys med jonselektiva elektroder.Yleisen hyvinvoinnin kannalta on tarpeen valvoa myrkyllisten aineiden esiintymistä luonnonvesissä. Koska luonnon ekosysteemissä haitallisten aineiden pitoisuuksien tulee pysyä alhaisina, etsitään jatkuvasti yhä herkempiä kemiallisia analyysimenetelmiä näiden aineiden määrittämiseksi. Ympäristöanalytiikassa joudutaan usein käyttämään kalliita ja monimutkaisia laitteita alhaisten pitoisuuksien määrityksessä. Nämä laitteet vaativat myös jatkuvaa huoltoa ja kunnossapitoa ja ovat tavallisesti melko kookkaita laboratoriolaitteita eivätkä siksi sovellu kenttäkäyttöön. Tässä työssä on kehitetty analyysimenetelmiä, missä määritykset on tehty potentiometrisesti ioniselektiivisillä elektrodeilla. Tämän analyysimenetelmän etuna on yksinkertainen käyttö ja mittalaitteiston pieni koko, mikä tekee menetelmästä erittäin sopivan käytettäväksi kenttäolosuhteissa. Nykyisin kaupallisesti saatavissa olevien ioniselektiivisten elektrodien mittaherkkyys ei aina riitä ympäristöanalytiikan kannalta merkittävien aineiden alhaisten pitoisuuksien määrittämiseen. Tutkimustyön tarkoituksena on ollut kehittää ioniselektiivisiä elektrodeja siten, että niillä on voitu määrittää ympäristön kannalta haitallisia aineita alhaisissa pitoisuuksissa. Lyijy on myrkyllinen raskasmetalli, jonka pitoisuuden luotettava määrittäminen vesitöissä on erittäin tärkeää. Tässä työssä on kehitetty erilaisia ioniselektiivisiä kalvoja, joilla on voitu parantaa nykyisin käytössä olevien elektrodien herkkyyttä, ts. on voitu määrittää erittäin alhaisia lyijypitoisuuksia. Kyseiset kalvot pohjautuvat polyakrylaatti-kopolymeereihin, PVC-pohjaiseen materiaaliin tai kiinteään suolasekoitukseen: PbS/Ag2S. Kiinteät elektrodit, joissa on PbS/Ag2S-kalvo ovat yleisesti kestävämpiä kuin polymeerikalvoihin perustuvat elektrodit. Kyseisten kiinteiden elektrodien määritysrajaa pystyttiin alentamaan sähköisellä polarisaatiolla, jossa kalvon ja itse elektrodin läpi johdettiin pieni sähkövirta. Kehitetyllä menetelmällä pystyttiin määrittämään huomattavasti alhaisempia lyijypitoisuuksia kuin klassisella nolla-virta-potentiometritekniikalla. Menetelmää testattiin vesinäytteillä, jotka oli otettu Turun saaristossa olevan entisen teollisuusalueen läheltä. Saadut tulokset olivat vertailukelpoiset muilla analyysimenetelmillä saatuihin tuloksiin samoista näytteistä, ja siten osoittaen kehitetyn menetelmän käyttökelpoisuuden ja luotettavuuden. Lyijyselektiivisten elektrodien, kuten yleisesti ioniselektiivisten elektrodien, suurena etuna on, että määritykset voidaan tehdä myös käsittelemättömistä ympäristönäytteistä, joissa voi olla mukana kiintoainetta. Hyvin harva analyysimenetelmä sallii vastaavanlaisen, melko vähäisen näytteenkäsittelyn. Siksi uskon, että kehittämäni menetelmä tulee olemaan uudenlainen työkalu ympäristöanalytiikassa.Monitoring natural waters for toxic components is essential for human well-being. Since the content of pollutants occurring in natural ecosystems should be kept as low as possible, there is an ongoing search for analytical methods with ever lower detection limits. Nowadays, such analysis is realized by costly and sophisticated instrumentation which requires high maintenance. Owing to several advantages such as portability, low energy consumption, and relatively low cost, ion-selective electrodes (ISEs) may be considered useful in measurements of ionic pollutants. Such measurements are mainly possible when extending the sensitivity range of the ISEs by lowering the detection limit. In this work, in order to lower the detection limit of Pb2+-ISEs, polyacrylate co-polymer, PVC-based, and solid-state PbS/Ag2S ion selective membranes were used. Although the polyacrylate matrix was introduced to diminish transmembrane ion fluxes in conventional types of Pb2+-ISEs, no significant improvement in the detection limit was observed. Subsequently, a new conducting polymer material (polybenzopyrene doped with eriochrome black T) was applied as a sensing membrane/film. As a result it became possible to measure lead(II) easily down to 10–6 mol dm–3 Pb2+. A significant improvement in the detection limit was achieved by applying this electroactive film as an ion-to-electron transducer in solid-contact Pb2+-ISEs. In this way the lowering of the detection limit was achieved by concentration-time dependent conditioning and by the recovery of ISEs response at the nanomolar concentration range. The method was applied in the determination of Pb2+ in synthetic samples and was validated by the inductively coupled plasma mass spectrometry (ICP-MS) measurement. Another approach to lower the detection limit of Pb2+-ISEs was investigated with solidstate PbS/Ag2S membrane electrodes. After lowering the parasitic processes at the solidstate membrane two methods were applied to improve the low detection limit (LDL): the controlled adsorption of the analyte on the electrode surface after pre-treatment of the electrode (LDL~ 10–8 mol dm–3 Pb2+) and the tuned galvanostatic polarization of PbS/Ag2S membrane (LDL~ 10–9 mol dm–3 Pb2+). Due to the time limitations for a single measurement in the first method, the tuned galvanostatic polarization method was applied in measurements of Pb2+ in synthetic and environmental samples. PbS/Ag2S membrane electrodes were successfully applied and validated by other analytical techniques (ICPMS and differential pulse anodic stripping voltammetry; DPASV) in the quantitative determination of the lead(II) pollution in the environmental sample. In this thesis, novel approaches to lowering of the detection limit for measurements of low and ultra low analyte concentrations are presented

Cu-based oxygen carriers for chemical looping processes: opportunities and challenges

Oxygen carrier (OC) material acting as the intermediate between reactors is key in a chemical looping process. Cu-based OCs are attractive candidates due to the superiority in reactivity, kinetics and capacity during the redox reactions with fuels. The ability of gaseous O2 release and the exothermic property for OC-fuel reaction provide more opportunities in chemical looping applications. This review illustrates the basic properties of Cu-based OCs and the opportunities in several chemical looping processes, including chemical looping combustion (CLC), chemical looping oxygen uncoupling (CLOU), chemical looping air separation (CLAS), chemical looping for syngas/H2 production, integrated CaO/CuO looping process and thermochemical energy storage (TCES). Besides, the technical challenges and the current strategies are discussed on agglomeration, attrition and ash accumulation. A perspective on the future research and development of Cu-based OCs is further discussed. This brief review may help with a better understanding and development for Cu-based OC design and the relevant chemical looping processes.National Research Foundation (NRF)Public Utilities Board (PUB)This research is supported by the National Research Foundation, Singapore, and PUB, Singapore’s National Water Agency under its RIE2025 Urban Solutions and Sustainability (USS) (Water) Centre of Excellence (CoE) Programme which provides funding to the Nanyang Environment & Water Research Institute (NEWRI) of the Nanyang Technological University, Singapore (NTU)

Inherently separated syngas production from plastic waste fast pyrolysis integrated with volatile chemical looping conversion with CO₂ splitting

To convert plastic waste into high-value products coupled with CO2 utilization, this study proposed a new concept to produce inherently separated syngas through fast pyrolysis integrated with volatile chemical looping CO2 splitting. Three conversion modes, i.e., redox, cracking and redox-cracking mixed modes, were evaluated using different catalyst, and found that cracking mode with Ni/Al2O3 or Ni/MgAl2O4 exhibited better fuel conversion and syngas separation performance than redox and mixed modes (using Ca2Fe2O5 and Ni/Ca2Fe2O5, respectively), achieving nearly full CO-H2 separation from the syngas product. Focusing on the cracking mode, higher temperature facilitated the fuel and coke conversion, due to the endothermic nature of both reaction stages. The syngas separation efficiency increased during 5 cycles and stabilized ∼95% while using Ni/MgAl2O4 catalyst. The redox between Ni0 and Ni2+ was inevitable for both cracking catalysts during multiple cycles due to the Ni-support interaction, limiting the full separation of syngas. The accumulation of low-reactive coke during multiple cycles was another important consideration. Ni/MgAl2O4 possessed weaker Ni-support interaction and less coke accumulation than Ni/Al2O3, thus performed better syngas separation efficiency. Therefore, it is crucial to minimize Ni-support interaction and the generation of high-graphitic coke for optimization.National Research Foundation (NRF)This research is supported by the National Research Foundation, Singapore, and PUB, Singapore’s National Water Agency under its RIE2025 Urban Solutions and Sustainability (USS) (Water) Centre of Excellence (CoE) Programme which provides funding to the Nanyang Environment & Water Research Institute (NEWRI) of the Nanyang Technological University, Singapore (NTU)

Physically tailoring ion fluxes by introducing foamlike structures into polymeric membranes of solid contact ion-selective electrodes

Transmembrane ion fluxes have earlier been identified as a source of potential instability in solid contact ion-selective electrodes (SC-ISEs). In this work, foamlike structures were intentionally introduced into a potassium-sensitive plasticized poly(vinyl chloride) ion-selective membrane (ISM) near the membrane|solid contact interface by controlling the temperature during membrane deposition. Foamlike structures in the ISM were shown to be effective at physically tailoring the transport of ions in the ion-selective membrane, greatly reducing the flux of interfering ions from the sample to the membrane|solid contact interface. The drifts during a conventional water layer test were hence able to be greatly mitigated, even with SC-ISEs incorporating a relatively hydrophilic poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) solid contact. In solutions with a high background concentration of interfering ions, equilibrated ion-selective electrodes with foamlike membranes were able to reproduce their initial potentials within 0.6 mV uncertainty (n = 3) from 0 to 18 h. This was achieved despite sensor exposure to solutions exceeding the selectivity limit of the ISEs in 3 h intervals, allowing improvement of the potential reproducibility of the sensors. Since the introduction of foamlike structures into ISM is linked to temperature-controlled membrane deposition, it is envisaged that the method is generally applicable to all solid contact ion-selective electrodes that are based on polymeric membranes and require membrane deposition from the cocktail solution.Economic Development Board (EDB)Nanyang Technological UniversityY.H.C. gratefully acknowledges funding from the Economic Development Board (EDB) of Singapore’s Industrial Postgraduate Program in support of this work. The authors thank NEWRI (Nanyang Technological University) and Singapore’s Economic Development Board (EDB) and Robert Bosch SEA for their financial support in this research

Environmental perspectives of recycling various combustion ashes in cement production – a review

Recycling different types of ashes for cement production has gained increasing attentions worldwide in a bid to close the waste loop. It minimizes waste landfilling and meanwhile produces useful secondary materials with reduced costs. Ascribed to the presence of elevated metal concentrations, however, it also receives negative inclination for their reuse. Herein, recycling various combustion ashes, such as municipal solid waste incineration fly ashes (MSWI FA), municipal solid waste incineration bottom ashes (MSWI BA), coal fly ashes (CFA), coal bottom ashes (CBA), blast furnace slags (BFS), biomass ashes (BIOA), sewage sludge ashes (SSA) and different co-combustion ashes (CCA), were comprehensively reviewed, from environmental perspectives combined with statistical data analysis (e.g. bulk components, trace metals, leaching potential, and etc.), to quantitatively explore their feasibility during cement production. It was unveiled that pozzolanic contents were predominant which highly fluctuated in their composition based on the ash type, limiting the replacement at maximum of 5–10 wt%. Considering total metal criteria, heavy metal contents posed challenges as secondary raw materials for blended cements. However, in consideration of metal leaching criteria, exothermic pozzolanic reactions in the second phase of blended cement would sufficiently alleviate their leaching potential, ensuring the environmental feasibility. Apart from the above, treatment costs have to be evaluated in nexus of multiple factors, whereas government policies play significant roles in valorization of recycling ashes. From sustainability perspective, life cycle assessment promises the overall strategy on ash utilization in cement industry.Accepted versio

Facile synthesis of electrocatalytically active bismuth oxide nanosheets for detection of palladium traces in pharmaceutical wastewater

Current synthesis routes of bismuth oxide nanosheets (BiONS) are relatively complicated, requiring the use of halogens or metalloids. Herein, a facile method to synthesize BiONS without the addition of halogens or other metalloids was developed. The synthesized BiONS were identified to have flake-shaped structures (300-1000 nm in width) with the thickness of 6-10 nm, which were predominantly made of β-Bi2O3. Such BiONS were applied to modify the surface of screen-printed carbon electrodes (BiONS-SPCEs) for the development of a robust palladium (Pd2+) sensor. After optimizing the electrochemical parameters of the sensor, it was found that the linear sensor response range and limit of detection for Pd2+ were 40-400 and 1.4 ppb, respectively. The electrocatalytic activity of the Pd2+-sensor was validated in the competing environment of other metal and metalloid ions. Real samples collected during a Pd recovery process from pharmaceutical wastewater were used to verify the application of BiONS-SPCEs in control of palladium recovery process. The quantitative results of post recovery palladium concentrations obtained using BiONS-SPCEs in treated pharmaceutical wastewater samples were in good agreement with those obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES). Thus, such Pd2+-sensor provided the possibility of on-site process control of complex industrial samples for obtaining near-instant information that would lead to better management of resources used in the process, and same time assure environmental standards for both recovered products and processed discharge.National Environmental Agency (NEA)This work was supported by the National Environment Agency (NEA) of Singapore under the Urban Solutions and Sustainability (USS) Integration Fund [Project Reference No.: NEA/ETD/R&DPROJ/CTWL-2018-4D-03]