Removal of Cesium from Aqueous Solution by Using Newly Developed Adsorbents and Comparative Study

2014【要旨

Influence of Ga-doping on the thermoelectric properties of Bi(2−x)GaxTe2.7Se0.3 alloy

Bi(2−x)GaxTe2.7Se0.3 (x=0, 0.04, 0.08, 0.12) alloys were fabricated by vacuum melting and hot pressing technique. The structure of the samples was evaluated by means of X-ray diffraction. The peak shift toward higher angle can be observed by Ga-doping. The effects of Ga substitution for Bi on the electrical and thermal transport properties were investigated in the temperature range of 300–500 K. The power factor values of the Ga-doped samples are obviously improved in the temperature range of 300–440 K. Among all the samples, the Bi(2−x)GaxTe2.7Se0.3 (x=0.04) sample showed the lowest thermal conductivity near room temperature and the maximum ZT value reached 0.82 at 400 K

Enhanced microbial chromate reduction using hydrogen and methane as joint electron donors

Hydrogen and methane commonly co-exist in aquifer. Either hydrogen or methane has been individually utilized as electron donor for bio-reducing chromate. However, little is known whether microbial chromate reduction would be suppressed or promoted when both hydrogen and methane are simultaneously supplied as joint electron donors. This study for the first time demonstrated microbial chromate reduction rate could be accelerated by both hydrogen and methane donating electrons. The maximum chromate reduction rate (4.70 ± 0.03 mg/L·d) with a volume ratio of hydrogen to methane at 1:1 was significantly higher than that with pure hydrogen (2.53 ± 0.02 mg/L·d) or pure methane (2.01 ± 0.02 mg/L·d) as the sole electron donor (p < 0.01). High-throughput 16S rRNA gene amplicon sequencing detected potential chromate reducers (e.g., Spirochaetaceae, Delftia and Azonexus) and hydrogenotrophic bacteria (e.g., Acetoanaerobium) and methane-metabolizing microorganisms (e.g., Methanobacterium), indicating that these microorganisms might play important roles on microbial chromate reduction using both hydrogen and methane as electron donors. Abundant hupL and mcrA genes responsible for hydrogen oxidation and methane conversion were harbored, together with chrA gene for chromate reduction. More abundant extracellular cytochrome c and intracellular NADH were detected with joint electron donors, suggesting more active electron transfers

Cobalt-based coordination polymers as heterogeneous catalysts for activating Oxone to degrade organic contaminants in water: A comparative study

While Co represents the most efficient metal for activating Oxone to degrade organic contaminants, it is still highly desired to develop reusable and easy-to-recover heterogeneous Co-based catalysts. As chemistry of metal coordination compounds advances, a special class of organometallic polymers, so-called “coordination polymers” (CPs), has been developed. CPs contain repeated and cross-linked coordination entities to afford hierarchical structures with evenly-distributed Co moieties, making CPs attractive for activating Oxone. In this study, three CoCPs are particularly developed for the first time as heterogeneous catalysts to activate Oxone. Specifically, three organic ligands, including cyanuric acid (CA), trithiocyanuric acid (TTA), and pyridinedicarboxylic acid (PDA), were employed to investigate the effect of ligand on physical and chemical properties of the resulting CoCPs. More importantly, their catalytic activities for activating Oxone are compared and studied through investigating their distinct characteristics. As decolorization of Acid Red (AR) is employed as a model test for evaluating Oxone activation, these CoCPs outperform conventional Co3O4 nanoparticles (NPs) for activating Oxone. Among these CoCPs, CoCA exhibits the highest catalytic activity, followed by CoTTA and CoPDA, because CoCA possesses a much higher surface area and pore volume as well as a higher fraction of Co content. These CoCPs also remain effective under weakly acidic and basic as well as saline conditions for activating Oxone to decolorize AR. CoCPs are reusable to activate Oxone over multiple cycles and maintained regeneration efficiencies >90%. These features validate that CoCPs can be promising alterative catalysts for activating Oxone to degrade organic contaminants

Spontaneous FeIII/FeII redox cycling in single-atom catalysts: Conjugation effect and electron delocalization

Summary: The mechanism of spontaneous FeIII/FeII redox cycling in iron-centered single-atom catalysts (I-SACs) is often overlooked. Consequently, pathways for continuous SO4·-/HO⋅ generation during peroxymonosulfate (PMS) activation by I-SACs remain unclear. Herein, the evolution of the iron center and ligand in I-SACs was comprehensively investigated. I-SACs could be considered as a coordination complex created by iron and a heteroatom N-doped carbonaceous ligand. The ligand-field theory could well explain the electronic behavior of the complex, whereby electrons delocalized by the conjugation effect of the ligand were confirmed to be responsible for the FeIII/FeII redox cycle. The possible pyridinic ligand in I-SACs was demonstrably weaker than the pyrrolic ligand in FeIII reduction due to its shielding effect on delocalized π orbitals by local lone-pair electrons. The results of this study significantly advance our understanding of the mechanism of spontaneous FeIII/FeII redox cycling and radical generation pathways in the I-SACs/PMS process

Nickel Oxide Grafted Andic Soil for Efficient Cesium Removal from Aqueous Solution: Adsorption Behavior and Mechanisms

An andic soil, akadama clay, was modified with nickel oxide and tested for its potential application in the removal of cesium from aqueous solution. Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and powder X-ray diffraction (XRD) results revealed the nickel oxide was successfully grafted into akadama clay. N₂ adsorption–desorption isotherms indicated the surface area decreased remarkably after modification while the portion of mesopores increased greatly. Thermogravimetric-differential thermal analysis (TG-DTA) showed the modified akadama clay had better thermostability than the pristine akadama clay. Decreases in cation exchange capacity (CEC) and ζ-potential were also detected after the modification. Adsorption kinetic and isotherm studies indicated the adsorption of Cs⁺ on the modified akadama clay was a monolayer adsorption process. Adsorption capacity was greatly enhanced for the modified akadama clay probably due to the increase in negative surface charge caused by the modification. The adsorption of Cs⁺ on the modified akadama clay was dominated by an electrostatic adsorption process. Results of this work are of great significance for the application of akadama clay as a promising adsorbent material for cesium removal from aqueous solutions