Atmospheric-Pressure Cold Plasma Activating Au/P25 for CO Oxidation: Effect of Working Gas

Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma

The performance of CO oxidation over plasmonic Au/TiO₂ photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO₂, an O₂ and Ar mixture gas as a discharge gas was employed to activate Au/TiO₂. The photocatalytic activity in CO oxidation over activated Au/TiO₂ was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O₂ content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO₂ rises rapidly at first and then remains constant at 75% when the O₂ content is above 50%. Compared with the discharge gas of 10% and 30% O₂/Ar, the sample activated by 50% O₂/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO₂ is discovered.

Plasma for Energy and Catalytic Nanomaterials

This Special Issue "Plasma for Energy and Catalytic Nanomaterials" of Nanomaterials is focused on advancements in synthesis and applications of energy and catalytic nanomaterials by plasma [...].

Diesel engine exhaust denitration using non-thermal plasma with activated carbon

A diesel engine de-NO_x system combining non-thermal plasma and activated carbon was set up. The de-NO_x efficiency reaches 91.8% and 92.5% for simulated gas and real exhaust gas, respectively. It has good potential to replace vanadium-based SCR.

Preparation of Pd/C by Atmospheric-Pressure Ethanol Cold Plasma and Its Preparation Mechanism

Treatment with atmospheric-pressure (AP) hydrogen cold plasma is an effective method for preparing highly active supported metal catalytic materials. However, this technique typically uses H₂ as working gas, which is explosive and difficult to transport. This study proposes the use of PdCl₂ as a Pd precursor and activated carbon as the support to fabricate Pd/C catalytic materials (Pd/C-EP-Ar) by using ethanol—which is renewable, easily stored, and safe—combined with AP cold plasma (AP ethanol cold plasma) followed by calcination in Ar gas at 550 °C for 2 h. Both Pd/C-EP and Pd/C-HP fabricated using AP ethanol and hydrogen cold plasma (without calcination in Ar gas) respectively, exhibit low CO oxidation reactivity. The activity of Pd/C-EP is lower than Pd/C-HP, which is mainly ascribed to the carbon layer formed by ethanol decomposition during plasma treatment. However, the 100% CO conversion temperature (T₁₀₀) of Pd/C-EP-Ar is 140 °C, which is similar to that of Pd/C-HP-Ar fabricated using AP hydrogen cold plasma (calcined in Ar gas at 550 °C for 2 h). The characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy indicated that the carbon layer formed by ethanol decomposition enhanced the interaction of metal nanoparticles to the support, and a high Pd/C atomic ratio was obtained. This was beneficial to the high CO oxidation performance. This work provides a safe method for synthesizing high-performance Pd/C catalytic materials avoiding the use of H₂, which is explosive and difficult to transport.

A Novel Route to Manufacture 2D Layer MoS2 and g-C3N4 by Atmospheric Plasma with Enhanced Visible-Light-Driven Photocatalysis

An atmospheric plasma treatment strategy was developed to prepare two-dimensional (2D) molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) nanosheets from (NH₄)₂MoS₄ and bulk g-C₃N₄, respectively. The moderate temperature of plasma is beneficial for exfoliating bulk materials to thinner nanosheets. The thicknesses of as-prepared MoS₂ and g-C₃N₄ nanosheets are 2-3 nm and 1.2 nm, respectively. They exhibited excellent photocatalytic activity on account of the nanosheet structure, larger surface area, more flexible photophysical properties, and longer charge carrier average lifetime. Under visible light irradiation, the hydrogen production rates of MoS₂ and g-C₃N₄ by plasma were 3.3 and 1.5 times higher than the corresponding bulk materials, respectively. And g-C₃N₄ by plasma exhibited 2.5 and 1.3 times degradation rates on bulk that for methyl orange and rhodamine B, respectively. The mechanism of plasma preparation was proposed on account of microstructure characterization and online mass spectroscopy, which indicated that gas etching, gas expansion, and the repulsive force of electron play the key roles in the plasma exfoliation. Plasma as an environmentally benign approach provides a general platform for fabricating ultrathin nanosheet materials with prospective applications as photocatalysts for pollutant degradation and water splitting.

The Preparation and Catalytic Properties of Nanoporous Pt/CeO2 Composites with Nanorod Framework Structures

Pt/CeO₂ catalysts with nanoporous structures were prepared by the facile dealloying of melt-spun Al_92-XCe₈Pt_X (X = 0.1; 0.3 and 0.5) ribbons followed by calcination. The phase compositions and structural parameters of the catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The specific surface area and pore size distribution were characterized by N₂ adsorption-desorption tests. The catalytic properties were evaluated by a three-way catalyst (TWC) measurement system. The results revealed that the dealloyed samples exhibited a nanorod framework structure. The Pt nanoparticles that formed in situ were supported and highly dispersed on the CeO₂ nanorod surface and had sizes in the range of 2-5 nm. For the catalyst prepared from the melt-spun Al_91.7Ce₈Pt_0.3 ribbons, the 50% CO conversion temperature (T₅₀) was 91 °C, and total CO could be converted when the temperature was increased to 113 °C. An X-ray photoelectron spectroscopy (XPS) test showed that the Pt_0.3/CeO₂ sample had a slightly richer oxygen vacancy; and a H₂ temperature-programmed reduction (H₂-TPR) test demonstrated its superior adsorption ability for reduction gas and high content of active oxygen species. The experiments indicated that the catalytic performance could be retained without any attenuation after 130 h when water and CO₂ were present in the reaction gas. The favorable catalytic activities were attributed to the high specific areas and small pore and Pt particle sizes as well as the strong interactions between the CeO₂ and Pt nanoparticles. The Pt nanoparticles were embedded in the surface of the CeO₂ nanorods, inhibiting growth. Therefore, the catalytic stability and water resistance were excellent.

Adhesive Hybrid SiO2.01C0.23Hx Nanoparticulate Coating on Polyethylene (PE) Separator by Roll-to-Roll Atmospheric Pressure Plasma

For the ever-increasing demand for highly safe lithium-ion batteries (LIBs), the common sol-gel process provides heat-resistance to separators with an inorganic coating, where the adhesion to the separator is the key to safety and stability. In this paper, we present a SiO2.01C0.23Hx-coated polyethylene (PE) separator through a roll-to-roll atmospheric plasma-enhanced chemical vapor deposition (R2R-APECVD) of hexamethyldisiloxane (HMDSO)/Ar/O2. The adhesion strength of SiO2.01C0.23Hx-coated PE was tested by peel-off test and found to be higher than that of the commercial Al2O3-coated separator (0.28 N/mm vs. 0.06 N/mm). Furthermore, the SiO2.01C0.23Hx-coated PE separator showed better electrochemical performance in C-rate and long term cycle tests. FTIR, SEM, and XPS analysis indicate that the increased adhesion and electrochemical performance are attributed to the inner hybrid SiO2.01C0.23Hx coating with organic and inorganic components.