A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic conversion of CO2 into value-added chemicals at low temperatures (<150 o C) and atmospheric pressure. The effect of specific energy density (SED) on the performance of the plasma process has been investigated. In the absence of a catalyst in the plasma, the maximum conversion of CO2 reaches 21.7 %. The synergistic effect from the combination of plasma with photocatalysts (BaTiO3 and TiO2) at low temperatures contributes to a significant enhancement of both CO2 conversion and energy efficiency by up to 250%. The synergy of plasma-catalysis for CO2 conversion can be attributed to both the physical effect induced by the presence of catalyst pellets in the discharge and the photocatalytic surface reaction driven by the plasma.

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Ammonia synthesis by plasma catalysis has emerged as an alternative process for decoupling nitrogen fixation from fossil fuels. Plasma activation can potentially circumvent the limitations of conventional thermocatalytic ammonia synthesis; however, the contribution of different reaction mechanisms to the production of ammonia at the catalyst surface remains unclear. Here, we identify the reaction intermediates adsorbed on γ-Al 2 O 3 -supported Ni and Fe catalysts during plasma-activated ammonia synthesis under various temperatures and reactor configurations using FTIR spectroscopy, steady-state flow reactor experiments, and computational kinetic modeling. Ammonia yield can be influenced by plasma-derived intermediates and their interactions with catalyst surfaces, which lead to different reaction pathways: Ni/γ-Al 2 O 3 enhances plasma-promoted NH 3 production and favors surface-adsorbed NH x species, while Fe/γ-Al 2 O 3 shows the presence of N 2 H y and a lower overall concentration of N-containing adsorbates. Plasma−catalyst interactions are probed to reveal that elevated temperature and plasma irradiation of the surfaces promote NH 3 desorption. The direct evidence of catalytic surface reactions occurring during a plasma-activated process provides mechanistic insight into plasma-activated ammonia synthesis.

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In this study, plasma-catalytic reforming of simulated biogas for the production of value-added fuels and chemicals (e.g., H 2 ) has been carried out in a coaxial dielectric barrier discharge (DBD) plasma reactor. The influence of four Ni catalysts (Ni/γ-Al 2 O 3 , Ni/MgO, Ni/SiO 2 , and Ni/TiO 2 ) on the plasma-catalytic biogas reforming has been investigated in terms of the conversion of reactants, the yield and selectivity of target products, the carbon deposition on the catalysts, and the energy efficiency of the plasma-catalytic process. The use of plasma combined with these Ni catalysts enhanced the performance of the biogas reforming. A maximum CO 2 conversion of 26.2% and CH 4 conversion of 44.1% were achieved when using the Ni/γ-Al 2 O 3 catalyst at a specific energy density (SED) of 72 kJ l −1 . Compared to other Ni catalysts, placing the Ni/γ-Al 2 O 3 catalyst in the DBD produced more syngas and C 3 ─C 4 hydrocarbons, but less C 2 H 6 . The lowest energy cost (EC) for biogas conversion and syngas production, as well as the highest energy efficiency and fuel production efficiency (FPE), were achieved when using the Ni/γ-Al 2 O 3 catalyst in the plasma process. The Ni/γ-Al 2 O 3 catalyst also showed the lowest surface carbon deposition of 3.8%, after catalysing the plasma biogas reforming process for 150 min at a SED of 60 kJ l −1 . Compared to other Ni catalysts, the enhanced performance of the Ni/γ-Al 2 O 3 catalyst can be attributed to its higher specific surface area, higher reducibility and more, stronger basic sites on the catalyst surface. K E Y W O R D Sbiogas reforming, dielectric barrier discharge, Ni catalysts, plasma-catalysis

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Digital transformation in manufacturing is one of the key megatrends in the development of global economy and society. Three-dimensional (3D) printing is a transformative digital technology poised to disrupt manufacturing and supply chains across major industries. Here we critically examine relevant insights into current and emerging applications of plasma nanotechnology in printing, including 3D printing. Plasma devices operated at atmospheric pressure coupled with printing processes may help strengthen 3D printing as an emerging fabrication technology that morphs diverse metal powders, polymers, plastics and other materials into digitally designed 3D shapes and patterns. We discuss how plasma applications may help overcome current limitations of 3D printing in various fields, e.g. limitations of sculpting composite materials, lack of mechanical strength and the need for postprocessing. Our key focus is on the challenges, opportunities and physical mechanisms of the use of 3D printing in nano-manufacturing, defined as the fabrication of nanoscale building blocks, such as nanoparticles and nanomaterials; their assembly into higher-order (micro-scale) structures; and the integration of these structures into larger (macro-) scale devices and systems by controlling energy and matter at nanoscale. Moreover, we discuss the physico-chemical mechanisms that result in highlyconformal deposition of nanostructured materials onto 3D surfaces with microscopic (and possibly nanoscale) control of textures and inter-layer cross-linking, without the need for additional heating. We further highlight the arising opportunities for plasma nanotechnology to synergize with the emerging digital transformation platforms in surface micro-and nano-structuring using polymers, metals, metallic alloys, and other materials. These new findings in plasma-digital nanoscale fabrication may lead to a new digital manufacturing platform suitable for a number of cutting-edge applications in electronic, sensing and energy devices.

Surface-enhanced Raman spectroscopy (SERS) technology is an attractive method for the prompt and accurate on-site screening of illicit drugs. As portable Raman systems are available for on-site screening, the readiness of SERS technology for sensing applications is predominantly dependent on the accuracy, stability and cost-effectiveness of the SERS strip. An atmospheric-pressure plasma-assisted chemical deposition process that can deposit an even distribution of nanogold particles in a one-step process has been developed. The process was used to print a nanogold film on a paper-based substrate using a HAuCl4 solution precursor. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the gold has been fully reduced and that subsequent plasma post-treatment decreases the carbon content of the film. Results for cocaine detection using this substrate were compared with two commercial SERS substrates, one based on nanogold on paper and the currently available best commercial SERS substrate based on an Ag pillar structure. A larger number of bands associated with cocaine was detected using the plasma-printed substrate than the commercial substrates across a range of cocaine concentrations from 1 to 5000 ng/mL. A detection limit as low as 1 ng/mL cocaine with high spatial uniformity was demonstrated with the plasma-printed substrate. It is shown that the plasma-printed substrate can be produced at a much lower cost than the price of the commercial substrate.