Volatile organic compound removal by post plasma-catalysis over porous TiO2 with enriched oxygen vacancies in a dielectric barrier discharge reactor.

Non-thermal plasma (NTP) degradation of volatile organic compounds (VOCs) into CO2 and H2O is a promising strategy for addressing ever-growing environment pollution. However, its practical implementation is hindered by low conversion efficiency and emissions of noxious by-products. Herein, an advanced low-oxygen-pressure calcination process is developed to fine-tune the oxygen vacancy concentration of MOF-derived TiO2 nanocrystals. Vo-poor and Vo-rich TiO2 catalysts were placed in the back of an NTP reactor to convert harmful ozone molecules into ROS that decompose VOCs via heterogeneous catalytic ozonation processes. The results indicate that Vo-TiO2-5/NTP with the highest Vo concentration exhibited superior catalytic activity in the degradation of toluene compared to NTP-only and TiO2/NTP, achieving a maximum 96% elimination efficiency and 76% COx selectivity at an SIE of 540 J L-1. Mechanistic analysis reveals that the 1O2, ˙O2- and ˙OH species derived from the activation of O3 molecules on Vo sites contribute to the decomposition of toluene over the Vo-rich TiO2 surface. With the aid of advanced characterization and density functional theory calculations, the roles of oxygen vacancies in manipulating the synergistic capability of post-NTP systems were explored, and were attributed to increased O3 adsorption ability and enhanced charge transfer dynamics. This work presents novel insights into the design of high-efficiency NTP catalysts structured with active Vo sites.

Defect-Engineered Graphene Films as Ozonation Catalysts for the Devastation of Sulfamethoxazole: Insights into the Active Sites and Oxidation Mechanism.

Graphene-based catalysts have been widely applied for catalytic ozonation. However, as it is difficult to obtain graphene with high structural precision, it is currently unfeasible to comprehend the relationships between the intrinsic structure of the layered carbon catalysts with its catalytic activities. Here, an advanced plasma-assisted etch strategy was used to fine tune the ozonation activity of monolayered graphene films by tailoring the defect types. Raman mapping indicated that the defects of the as-prepared monolayered graphene films were predominantly sp3, vacancy, and boundary-type defects, respectively. The roles and contributions of these active defects in manipulating the oxidative potential of monolayered graphene films were revealed by quenching experiments, electron paramagnetic resonance results, and density functional theory calculations. The catalytic results showed that the monolayered graphene films with boundary-like defects exhibited the best catalytic performance toward the degradation of sulfamethoxazole. This work contributes new insights into the design of high-efficiency carbonaceous catalysts by structuring additional defective sites.

Suitable Surface Oxygen Concentration on Copper Contributes to the Growth of Large Graphene Single Crystals.

In this Letter, we found that the growth of graphene on Cu oxide foil is significantly affected by the concentration of oxygen. The grain size of graphene grown on a Cu substrate with a relatively high oxygen concentration is much smaller than that on the substrate with lower oxygen concentration. By controlling the oxidation of the Cu substrate at a proper degree, we can obtain millimeter scale graphene single crystals at a growth temperature of 1050 °C. On the basis of our experimental observations, the dual role of oxygen in the CVD growth of graphene was revealed: (i) Oxygen on a Cu surface can contribute to the decomposition of hydrocarbon feedstock and decrease the graphene growth barrier, resulting in an increased growth rate and a larger grain size of graphene; (ii) excess oxygen in the Cu substrate leads to etching of the graphene edge. Our research provides insights to obtain large-area and single-crystalline graphene by choosing a proper Cu oxide substrate.

Observation of the transition state of domain wall displacement and GMI effect of FINEMET/graphene composite ribbons.

In this paper, the morphology, structure, and magnetic properties of FINEMET/graphene composite ribbons are systematically studied by SEM, Raman and static methods (hysteresis loops) and the dynamic method (giant magneto-impedance effect, GMI) respectively. It is revealed that with the increase of the number of graphene layers, the GMI effect of the FINEMET/graphene composite ribbons decreases, and the anisotropy field and the relaxation frequency of domain wall displacement of FINEMET/graphene composite ribbons increases. The result also confirmed that graphene does regulate the magnetic properties of FINEMET ribbon. Therefore, a comprehensive analysis of the influence of graphene on the magnetic properties of FINEMET ribbon is of important guiding significance in industrial applications.

Fabrication of porous graphene electrodes via CO2 activation for the enhancement of capacitive deionization.

Capacitive deionization (CDI) is a simple, cost-efficient and environmentally-friendly method for brackish water desalination. In order to improve the desalination performance, the inner structures of the porous electrodes should provide more space for ion storage and transportation. Therefore, we utilized an efficient method to synthesize porous graphene electrodes based on the technique of pressurized oxidation and CO2 activation. The prepared electrodes were characterized electrochemically by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy, and the desalination performance between different samples was compared as well. These results showed that AGE-30 had the highest electrosorption capacity (6.26 mg/g) among all samples, and this was attributed to its high specific surface area (898 m2/g), high pore volume (1.223 cm3/g), high specific capacitance (56.21F/g), and smaller inner resistance. Thus, the CO2 activation is confirmed to be a useful method for the enhancement of the graphene electrodes for CDI.

Epitaxial nucleation of CVD bilayer graphene on copper.

Bilayer graphene (BLG) has emerged as a promising candidate for next-generation electronic applications, especially when it exists in the Bernal-stacked form, but its large-scale production remains a challenge. Here we present an experimental and first-principles calculation study of the epitaxial chemical vapor deposition (CVD) nucleation process for Bernal-stacked BLG growth on Cu using ethanol as a precursor. Results show that a carefully adjusted flow rate of ethanol can yield a uniform BLG film with a surface coverage of nearly 90% and a Bernal-stacking ratio of nearly 100% on ordinary flat Cu substrates, and its epitaxial nucleation of the second layer is mainly due to the active CH3 radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this nucleation mechanism will help clarify the formation of BLG by the epitaxial CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.

The role of hydrogen in oxygen-assisted chemical vapor deposition growth of millimeter-sized graphene single crystals.

Involving oxygen in the traditional chemical vapor deposition (CVD) process has proven a promising approach to achieve large-scale graphene single crystals (GSCs), but its many relevant fundamental aspects are still not fully understood. Here we report a systematic study on the role of hydrogen in the growth of millimeter-sized GSCs using enclosure-like Cu structures via the oxygen-assisted CVD process. Results show that GSCs have different first layer growth behaviors on the inside and outside surfaces of a Cu enclosure when the H2 environment is varied, and these behaviors will consequently and strongly influence the adlayer formation in these GSCs, leading to two entirely different growth modes. Low H2 partial pressure (PH2) tends to result in fast growth of dendritically shaped GSCs with multiple small adlayers, but high PH2 can modify the GSC shape into hexagons with single large adlayer nuclei. This difference of adlayers is attributed to the different C diffusion paths determined by the shapes of their host GSCs. On the basis of these observations, we developed an isothermal two-step method to obtain GSCs with significantly improved growth rate and sample quality, in which low PH2 is first set to accelerate the growth rate followed by high PH2 to restrict the adlayer nuclei. Our results prove that the growth of GSCs can reach a reasonable optimization between their growth rates and sample quality by simply adjusting the CVD H2 environment, which we believe will lead to more improvements in graphene synthesis and fundamental insight into the related growth mechanisms.

Equilibrium chemical vapor deposition growth of Bernal-stacked bilayer graphene.

Using ethanol as the carbon source, self-limiting growth of AB-stacked bilayer graphene (BLG) has been achieved on Cu via an equilibrium chemical vapor deposition (CVD) process. We found that during this alcohol catalytic CVD (ACCVD) a source-gas pressure range exists to break the self-limitation of monolayer graphene on Cu, and at a certain equilibrium state it prefers to form uniform BLG with a high surface coverage of ∼94% and AB-stacking ratio of nearly 100%. More importantly, once the BLG is completed, this growth shows a self-limiting manner, and an extended ethanol flow time does not result in additional layers. We investigate the mechanism of this equilibrium BLG growth using isotopically labeled (13)C-ethanol and selective surface aryl functionalization, and results reveal that during the equilibrium ACCVD process a continuous substitution of graphene flakes occurs to the as-formed graphene and the BLG growth follows a layer-by-layer epitaxy mechanism. These phenomena are significantly in contrast to those observed for previously reported BLG growth using methane as precursor.

Synthesis, photophysical and photochemical properties of amphiphilic carboxyl phthalocyanine oligomers.

The synthesis and photochemical properties are reported for a series of novel amphiphilic carboxyl polymeric phthalocyanines, with zinc (3a), aluminum (3b), ytterbium (3c) and hydrogen (metal-free, 3d) as the substituted central atom, respectively. The synthesis routes included cyclotetramerization of tetra-phthalonitriles and subsequent hydrolysis of cyano to carboxyl in alkaline solution. All four molecules were verified to be oligomers by viscosity method. Specifically, 3c showed strongest fluorescent emission, which can be elevated by Triton X 100 and CTAB. The singlet oxygen quantum yield (Phi(Delta)) for 3a and 3b were larger than that of 3c and 3d. In the presence of surfactants, nearly 2 folds enhancement of Phi(Delta) was observed as 0.76 and 0.70 for 3a and 3b, respectively. The characteristic photochemical properties of these oligomers suggested potential applications in photodynamic therapy, photocatalysis and photodynamic diagnoses.