Dirac quantum spin liquid emerging in a kagome-lattice antiferromagnet

Emerging quasi-particles with Dirac dispersion in condensed matter physics are analogous to their cousins in high-energy physics in that both of them can be described by the Dirac equation for relativistic electrons. Recently, these Dirac fermions have been widely found in electronic systems, such as graphene and topological insulators. At the conceptual level, since the charge is not a prerequisite for Dirac fermions, the emergence of Dirac fermions without charge degree of freedom has been theoretically predicted to be realized in Dirac quantum spin liquids. In such case, the Dirac quasiparticles are charge-neutral and carry a spin of 1/2, known as spinons. Despite of theoretical aspirations, spectra evidence of Dirac spinons remains elusive. Here we show that the spin excitations of a kagome antiferromagnet, YCu$_3$(OD)$_6$Br$_2$[Br$_{x}$(OD)$_{1-x}$], are conical with a spin continuum inside, which are consistent with the convolution of two Dirac spinons. The spinon velocity obtained from the spin excitations also quantitatively reproduces the low-temperature specific heat of the sample. Interestingly, the locations of the conical spin excitations differ from those calculated by the nearest neighbor Heisenberg model, suggesting an unexpected origin of the Dirac spinons. Our results thus provide strong spectra evidence for the Dirac quantum-spin-liquid state emerging in this kagome-lattice antiferromagnet.Comment: 7 pages, 4 figure

Suspended anode-type microbial fuel cells for enhanced electricity generation

Electricity generation in microbial fuel cells can be restricted by a few factors, such as the effective area of the anode for biofilm attachment, diffusion limitation of substrates and internal resistance. In this paper, a suspended anode (carbon-based felt granule)-type microbial fuel cell was developed to make full use of the volume of the anode chamber and provide a larger surface area of the anode for the growth of exoelectrogenic bacteria. The current collector was rotated in the anodic chamber to contact with the suspended granules intermittently and achieve better mixing. The open-circuit voltage reached steady state at around 0.83 V. The maximum power density obtained from each scenario increased steadily with the increase in mixing rate. The internal resistance decreased when the rotational rate and the content of the carbon granules were increased. The maximum power density reached 951 +/- 14 mW m(-3) with a corresponding minimum internal resistance of 162.9 +/- 3.5 omega when the mass of carbon granules was 50 g and the rotational rate was 300 rpm. The suspended microbes made negligible contribution to the power density. The microbial fuel cell with a higher content of carbon granules had lower coulombic efficiency and lower relative abundance of exoelectrogenic bacteria

Abatement of sulfide generation in sewage by glutaraldehyde supplementation and the impact on the activated sludge accordingly

Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentrations of glutaraldehyde at 10, 15, 20, 30 and 40 mg·L−1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg·L−1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%–80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20 mg·L−1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around €3.7–4.6 S·kg−1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum “booster” dosage and the dosing frequency in situ accordingly.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Improvement of biological total phosphorus release and uptake by low electrical current application in lab-scale bio-electrochemical reactors

The overall process enhancement by different electrical current application on the biological phosphorus release and uptake have been investigated. Five reactors were constructed for three experiments and activated sludge was used as inoculums. In Exp.1 by comparing the control and the bio-electrochemical reactors, it was found that the overall phosphorus removal efficiency could be enhanced at lower electrical current applications of 5. mA and 10. mA, but were restrained at higher than 20. mA, although 20. mA could be a sensitive turning point. Moreover, the electrochemical effects of the cathodic and the anodic reactions on the phosphorus release and uptake, respectively, have been further evaluated separately under an electrical current application of 10. mA in Exp.2 and Exp.3, respectively. As observed, both of the biological release and uptake were improved by the cathodic reactions in the cathode reactor, but not by the anodic reactions in the anode reactor, and thus indicated that the cathodic reactions play an important role in the improvement of the biological phosphorus release and uptake. © 2012 Elsevier B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Graphite anodes activated by melamine, carbamide, ZnCl<inf>2</inf> and H<inf>3</inf>PO<inf>4</inf> in microbial fuel cells

Here we evaluated the graphite anodes activated by melamine, carbamide, ZnCl2 and H3PO4 in microbial fuel cells (MFCs). Results indicated that the graphite activated by melamine, carbamide and zinc chloride, respectively, could improve the voltage output and power densities, as well as decrease the internal resistances. MFCs with graphite activated by melamine as anode achieved the highest maximum power generation (0.442W/m3), 26.8% greater than the untreated graphite. The reason for improved performance is the introduction of nitrogen-containing functional groups on the electrode that can increase the efficiency of electron transfer from the bacteria to the anode surface, enhance surface wettability and improve bacterial adhesion. The chemical activation processes are the most cost-effective because of simply immersion, no heating, no electrochemical process and no expensive chemicals.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Effect of the chemical oxidation demand to sulfide ratio on sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater

This work focused on studying the effect of the chemical oxidation demand to sulfide ratio (COD/S) on power generation and sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater containing organic contaminants. The maximum power density achieved was 20±1 W m -3 V Anode and the Coulombic yield was 20±2%. The COD/S of influent played an important role in elemental sulfur and sulfate production because of competition between acetate oxidation and element sulfur oxidation to sulfate in the anode. When the COD/S was 12.50/1, more than 74.0% of sulfide was converted into elemental sulfur after 24 hours of operation. The effect of the COD/S on power generation was negligible when the COD/S ranged between 4.85/1 and 18.53/1. After 24 hours, the COD removals were 110±6, 213±9, 375±8 and 410±10 mg l -1 when the COD/S was 4.85/1, 8.9/1, 12.5/1 and 18.53/1, respectively. The COD removal increased with the increasing COD of the influent, which fitted to the model of first-order reaction kinetics. © 2013 Copyright Taylor and Francis Group, LLC.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Recovering platinum from wastewater by charring biofilm of microbial fuel cells (MFCs)

Reduction in and recovery of precious metals are research hotspots in the environmental engineering field. In this study, we investigated the transformation and distribution of platinum in microbial fuel cells (MFCs) and demonstrated a feasible approach to recover platinum (Pt) from wastewater with less than 16.88 mg/L platinum through charring biofilms in MFCs and generate Pt/C catalyst. The optimal reaction condition was identified, and charred biofilms were analyzed via SEM-EDS, XRD and XPS. Results showed that less than 10% of Pt was in MFC effluents, and less than 0.5% was in the cathode chamber when the influent concentration was below 16.88 mg/L. Close to 40% of Pt could be recovered. The recovery efficiency could be higher should the reactions run longer. SEM-EDS and XRD results indicated that the metallic form Pt0 is one of the reduction products in MFCs. XPS results induced that Pt (IV) was reduced to Pt (II) and Pt0. Keywords: Microbial fuel cells, Platinum, Bio-reduction, Recovery, Sludg

Chemically activated graphite enhanced oxygen reduction and power output in catalyst-free microbial fuel cells

In search of a cost effective cathode material for microbial fuel cells (MFCs), graphite was chemically treated with H3PO4, HNO3, ZnCl2, urea or melamine, and the effect of chemical activations on the oxygen reduction reaction (ORR) was examined. The performance of MFCs with activated graphite as the catalyst-free cathodes was then compared to those with untreated graphite. Results suggested that H3PO4 and HNO3 activations could improved ORR, showing the highest ORR activity in graphite treated with 14.62 M H3PO4 for 12 h at 30-50 °C. MFCs with H3PO4 and HNO3 activated graphite cathodes generated maximum power densities (7.9 W/m3 and 6.5 W/m3, respectively) 2.4 and 1.8 times higher than that of the untreated control. The chemical activation process involves just a simple immersion step, and it does not require heating, electrochemical process or expensive chemicals. Therefore, it is a highly cost-effective approach to improve the performance of MFCs. We recommend an in-situ modification of graphite cathodes in scale-up MFCs with either H3PO4 or HNO3 to optimize MFCs' various industrial applications.SCOPUS: ar.jinfo:eu-repo/semantics/publishe