Internal friction peaks due to interstitials in bcc alloys

Richter's and Snoek's original works established the existence of an anelastic relaxation produced by a stress-induced interstitial reorientation in bcc metals. This anelastic relaxation, now referred to as a Snoek peak, has been studied extensively and well characterized in the past for the interstitials carbon, nitrogen, and oxygen. The existence of a hydrogen Snoek peak in bcc metals has been a matter of some controversy, however. We have studied relaxation peaks in V, Nb, and V-Nb alloys recently. The alloys have complete mutual solubility and are of interest since they have an extremely high room temperature solid solubility for hydrogen. They also have, over a certain composition range, not shown any hydride phase precipitation at temperatures as low as 4K. Thus, if a hydrogen Snoek peak does exist, it should be found in such alloys. Indeed there is evidence now of a spectrum of hydrogen relaxation peaks below room temperature. Furthermore, there is a large misfit of V in Nb and Nb in V and, possibly, some chemical interaction such that trapping (or antitrapping) of the interstitials at the substitutional sites, causing solute-interstitial peaks, can be characterized. The present paper provides an overview of our observations regarding: the effect of hydrogen on the oxygen and nitrogen Snoek peaks in pure V and Nb, The oxygen relaxation peaks in V-Nb alloys, The hydrogen relaxation spectrum in V-Nb alloys, and the effect of oxygen on the hydrogen relaxation spectrum in V-Nb alloys. 52 refs., 13 figs., 3 tabs

New insights into heterogeneous generation and evolution processes of sulfate radicals for phenol degradation over one-dimensional alpha-MnO(2) nanostructures

Heterogeneous activation of peroxymonosulfate (PMS) has become an attractive approach for catalytic oxidation since it can not only provide sulfate radicals as an alternative to hydroxyl radicals, but also avoid the metal toxicity in homogeneous catalysis. In this study, three one-dimensional (1D) α-MnO₂ nanostructures, nanorods, nanotubes and nanowires, were fabricated by a one-pot hydrothermal method without addition of any surfactants. Shape-dependent performance of 1D α-MnO₂ was observed in catalytic degradation of phenol solutions. The phenol oxidation can be described by a first-order kinetic model and the activation energies of phenol oxidation on three α-MnO₂ materials were estimated to be 20.3, 39.3 and 87.1 kJ/mol on nanowires, nanorods, and nanotubes, respectively. Both electron paramagnetic resonance (EPR) spectra and competitive radical tests were applied to investigate the PMS activation processes and to differentiate the major reactive species dominating the catalytic oxidation. The processes of PMS activation, evolution of sulfate radicals, and phenol degradation pathways were clearly illustrated.Yuxian Wang, Stacey Indrawirawan, Xiaoguang Duan, Hongqi Sun, Ha Ming Ang, Moses O. Tadé, Shaobin Wan

Synergy of carbocatalytic and heat activation of persulfate for evolution of reactive radicals toward metal-free oxidation

Persulfate (or peroxydisulfate, PDS) is one of green and low-cost sources of sulfate radicals (SO4radical dot−) in advanced oxidation processes (AOPs) for in situ remediation of contaminated soil and water. The key in AOPs is to develop an effective technique for PDS activation. In this paper, nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were employed as a metal-free catalyst to activate PDS for oxidation of a diversity of organic contaminants such as nitrobenzene (NB), phenol, benzoquinone and sulfachlorpyridazine. For the first time, the coupling effects of carbocatalysis and heat were investigated in a range of 5–75 °C on PDS activation, which indicated that organic oxidation efficiency was enhanced at elevated temperatures. The presence of the carbocatalyst impressively decreased the PDS activation energy from 53.4 (by heat) to 10.3–22.5 kJ/mol (heat/carbocatalysis). Intriguingly, the mechanisms of heat-assisted carbocatalysis were temperature-dependant and the synergy of the heat/carbon integrated system appeared to be phenomenal at a high temperature region (55–75 °C). The thermal stimulation promoted PDS to generate hydroxyl radicals via heterogeneous water oxidation and mutual transformation from sulfate radicals, evidenced by the selective radical quenching and spin trapping techniques. The carbocatalyst boosted the radical production by simultaneously activating the reactants (PDS and organics) with the N-doped carbon atoms and facilitating the electron transport as a conductive substrate. Therefore, this study advances the understanding in the effect of reaction temperature on persulfate activation and unveils the synergy of carbocatalysis with heat for enhanced PDS activation.Xiaoguang Duan, Stacey Indrawirawan, Jian Kang, Wenjie Tian, Huayang Zhang, Xuezhi Duan, Xinggui Zhou, Hongqi Sun, Shaobin Wan

Adsorption

Removing of wastewater pollutants by novel adsorption techniques is urgent as they are continuously defiling the limited freshwater resources, seriously affecting the terrestrial, ecosystems, aquatic, and aerial flora and fauna. Emerging carbon nanotube (CNT)-based adsorbent materials are effective for efficient handling of wastewater pollutants. This chapter describes the mechanisms of CNT, and its forces to host the wastewater pollutants. Such details would help to considerably improve the performance of classical adsorbent technologies. Additionally, the functionalization of CNT and adsorption isotherms are considered as they have been significantly used for achieving maximum adsorption capacity and disclosing the adsorption phenomena of CNT, respectively. Some multifunctional CNT-based adsorbent are also discussed with reusability phenomena which need to be addressed before large-scale implementation of CNTs for water purification. Some suggestions and research clues are given to inform investigators of potentially disruptive CNT technologies and/or optimize the CNT sorption performances that have to be investigated in more detail

Nitrogen-Doped Graphene for Generation and Evolution of Reactive Radicals by Metal-Free Catalysis

N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8-11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700°C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the Ndoped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin-unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on Ndopedgraphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS activation processes and pathways of phenol degradation on nanocarbons. It was observed that both •OH and SO4 •- existed in the oxidation processes and played critical roles for phenol oxidation