Chemistry - Journal Articles
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Item Heterogeneous Fenton-type oxidative degradation of low-density polyethylene to valuable acid products using a nanostructured Fe–CeO2 solid solution catalyst(Royal Society of Chemistry, 2025-01-02) Breen, Rachel; Holmes, Justin D.; Collins, Gillian; Science Foundation IrelandThe chemical conversion of waste plastic polymers to useful commodity chemicals has become crucial to helping tackle the issue of global plastic waste today. Polyolefins maintain the highest production rate and lowest recycling rate worldwide due to their inert chemical structures. This work shows the synthesis of solid-solution Fe–CeO2 catalyst as an excellent heterogeneous catalyst for Fenton-type oxidative degradation of low-density polyethylene to achieve high yields of organic acids. The catalyst was synthesized in 3 molar ratios of Fe : Ce and it was found that the molar ratio of iron and cerium was crucial for catalytic performance with the Fe–CeO2 1 : 1 catalyst giving the highest yields of acid products. The catalyst achieved 91% mass loss and 71% organic acid at pH 7, with 1 wt% catalyst loading. The use of a multi-metal Fenton system resulted in a synergistic effect, displaying superior activity to systems with only one Fenton active metal. The heterogeneous nature of the catalyst allowed for easy recovery and demonstrated excellent recyclability in multiple cycles. The high recyclability performance was attributed to the stability of the solid solution structure.Item Pseudo molecular doping and ambipolarity tuning in Si junctionless nanowire transistors using gaseous nitrogen dioxide(John Wiley & Sons, Inc., 2024-11-19) Vardhan, Vaishali; Biswas, Subhajit; Ghosh, Sayantan; Tsetseris, Leonidas; Ghoshal, Tandra; Hellebust, Stig; Georgiev, Yordan M.; Holmes, Justin D.; Horizon 2020Ambipolar transistors facilitate concurrent transport of both positive (holes) and negative (electrons) charge carriers in the semiconducting channel. Effective manipulation of conduction symmetry and electrical characteristics in ambipolar silicon junctionless nanowire transistors (Si-JNTs) is demonstrated using gaseous nitrogen dioxide (NO2). This involves a dual reaction in both p- and n-type conduction, resulting in a significant decrease in the current in n-conduction mode and an increase in the p-conduction mode upon NO2 exposure. Various Si-JNT parameters, including “on”-current (Ion), threshold voltage (Vth), and mobility (µ) exhibit dynamic changes in both the p- and n-conduction modes of the ambipolar transistor upon interaction with NO2 (concentration between 2.5 – 50 ppm). Additionally, NO2 exposure to Si-JNTs with different surface morphologies, that is, unpassivated Si-JNTs with a native oxide or with a thermally grown oxide (10 nm), show distinct influences on Ion, Vth, and µ, highlighting the effect of surface oxide on NO2-mediated charge transfer. Interaction with NO2 alters the carrier concentration in the JNT channel, with NO2 acting as an electron acceptor and inducing holes, as supported by Density Functional Theory (DFT) calculations, providing a pathway for charge transfer and “pseudo” molecular doping in ambipolar Si-JNTs.Item Exfoliated molybdenum disulfide nanosheet networks as sensing materials for nitrogen dioxide detection(American Chemical Society, 2025-01-24) Urs, Kusuma; Carey, Tian; Tsetseris, Leonidas; Liu, Shixin; Synnatschke, Kevin; Sofer, Zdeněk; Coleman, Jonathan N.; Wenger, John Charles; Biswas, Subhajit; Holmes, Justin D.; Horizon 2020; European Commission; Deutsche Forschungs Gemeinschaft; Europen Research Council; European Regional Development FundNitrogen dioxide (NO2) is a gaseous air pollutant linked to respiratory and cardiovascular diseases and environmental problems such as acid rain and tropospheric ozone formation. Reference instruments for measuring NO2 are expensive, highlighting the need to develop low cost sensor technologies for wider scale monitoring of this critical pollutant. Here, we report the development of a scalable sensor using electrochemically exfoliated 2D molybdenum disulfide (MoS2) networks. The sensor can detect a wide range of NO2 concentrations at room temperature, with an experimental limit of detection (LOD) as low as 150 ppb and a theoretical LOD of 1.9 parts per quadrillion (ppq) in dry air. The sensor exhibited approximately 90% response to 1 ppm of NO2 within 10 min of exposure. UV irradiation significantly enhanced the sensor’s recovery time, reducing it from 20 min to less than 2 min. Evaluation of the sensor within a large (∼6.5 m3) atmospheric simulation chamber yielded a similar response and recovery time performance, opening the opportunity for further tests in the chamber under various conditions. Finally, using Density Functional Theory (DFT) calculations, we identified key atomic-scale structures and processes highlighting the importance of electrochemically exfoliated sulfur-deficient MoS2 for sensitive room temperature NO2 detection.Item Nitrogen dioxide detection with ambipolar silicon nanowire transistor sensors(American Chemical Society, 2025-01-31) Vardhan, Vaishali; Biswas, Subhajit; Ghosh, Sayantan; Tsetseris, Leonidas; Hellebust, Stig; Echresh, Ahmad; Georgiev, Yordan M.; Holmes, Justin D.; Horizon 2020Si nanowire transistors are ideal for the sensitive detection of atmospheric species due to their enhanced sensitivity to changes in the electrostatic potential at the channel surface. In this study, we present unique ambipolar Si junctionless nanowire transistors (Si-JNTs) that incorporate both n- and p-type conduction within a single device. These transistors enable scalable detection of nitrogen dioxide (NO2), a critical atmospheric oxidative pollutant, across a broad concentration range, from high levels (25–50 ppm) to low levels (250 ppb–2 ppm). Acting as an electron acceptor, NO2 generates holes and functions as a pseudodopant for Si-JNTs, altering the conductance and other device parameters. Consequently, ambipolar Si-JNTs exhibit a dual response at room temperature, reacting on both p- and n-conduction channels when exposed to gaseous NO2, thereby offering a larger parameter space compared to a unipolar device. Key characteristics of the Si-JNTs, including on-current (Ion), threshold voltage (Vth) and mobility (μ), were observed to dynamically change on both the p- and n-channels when exposed to NO2. The p-conduction channel showed superior performance across all parameters when compared to the device’s n-channel. For example, within the NO2 concentration range of 250 ppb to 2 ppm, the p-channel achieved a responsivity of 37%, significantly surpassing the n-channel’s 12.5%. Additionally, the simultaneous evolution of multiple parameters in this dual response space enhances the selectivity of Si-JNTs toward NO2 and improves their ability to distinguish between different pollutant gases, such as NO2, ammonia, sulfur dioxide and methane.Item A collaborative cocurricular undergraduate research experience on sustainable materials: analysis of biochar using the Boehm titration and spectroscopic techniques(American Chemical Society, 2025-02-06) Breen, Rachel; Goggin, Conor; Holmes, Justin D.; Collins, Gillian; Science Foundation IrelandThe use of renewable feedstocks such as biomass aligns with global priorities such as sustainability and climate change. Integrating these materials into experiments helps students understand the real-world relevance of chemistry to addressing environmental challenges. Here, we show that the use of biochar as a renewable feedstock provides an inquiry-based laboratory activity that gives students the opportunity to engage in an authentic investigative process. This activity describes a cocurricular summer workshop carried out with undergraduate students who had no prior research experience. The activity combined the Boehm titration as a chemical method for the analysis of biochar coupled with spectroscopic techniques. The workshop was designed to be collaborative in nature, where students collectively contributed to the overall experimental results and discussion. The motivation for the activity stems from a student undertaking a longer Undergraduate Research Experience (URE) in the form of a summer research placement and based on this work designing a research experience workshop that could be rolled out to benefit a larger number of students. We believe this approach of using longer or individual UREs to develop research-focused initiatives could be readily adopted by other UREs to promote and develop research skills.