Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China.

Radium (Ra) isotopes are extensively used as geochemical tracers for studying water mass mixing and submarine groundwater discharge in marginal and coastal seas. However, river-borne particles and seafloor sediments are an important source of Ra in marine systems due to Ra desorption. Therefore, it is necessary to study the desorption behaviors of Ra isotopes in river sediment or suspended particles. Here, the desorption behaviors of four Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra) in the Zhangjiang River sediments were investigated by a series of designed variable-controlling experiments in the laboratory. Within the designed salinity range, desorption amounts of Ra isotopes increased with increasing salinity, and when the salinity was greater than 15 ppt, Ra desorption reached an equilibrium state. Overall, desorption of Ra isotopes increased with the decrease of particle grain size, however, the desorption fractions of 224Ra and 228Ra decreased with decreasing particle size due to the increase of original Ra activities in smaller sediment particles. In the experiments, we found that two sediment samples with similar mean grain size (3.8 µm and 3.3 µm) and similar grain size distributions had significantly different Ra desorption under the same conditions. The results of mineral composition analysis based on X-ray diffraction showed that these two samples had different percentages of kaolinite, quartz, and plagioclase, which indicated that the mineral composition of particles had an important effect on Ra isotope desorption. In conclusion, salinity, particle grain size, and mineral composition all had significant effects on Ra desorption behaviors of sediment particles. Based on the above desorption experiments, the desorbed fluxes of four Ra isotopes from river-borne sediments to the Dongshan Bay were estimated to be (5.95 ± 1.47) × 107 Bq yr-1 for 223Ra, (1.95 ± 0.27) × 109 Bq yr-1 for 224Ra, (2.73 ± 0.47) × 108 Bq yr-1 for 226Ra, and (1.26 ± 0.20) × 109 Bq yr-1 for 228Ra, respectively.

An effective method for the determination of 106Ru in seawater by γ-spectrometry.

106Ru is a product originating from the fission reactions of uranium (235U) and plutonium (239Pu). 106Ru represents a potential source of radioactive marine contamination since it makes up 70-90% of the total radioactivity of liquid effluents from fuel reprocessing plants; thus, it is important to effectively determine the quantity of 106Ru in the natural environment. In this study, a simple and effective method was developed for the determination of 106Ru in seawater by γ-spectrometry using NiS coprecipitation. In addition, the amounts of S2- and Ni2+ added, Ru3+ carrier addition, pH, salinity, and sample volume were tested, and accordingly, optimal conditions were proposed. With the optimized conditions, the recovery of 106Ru in seawater ranged from 85.3% to 92.3%, with an average of 88.1 ± 4.2%. The method proposed in the present study can also be applied to seawater samples with various salinities and volumes. For 20 L seawater and 24 h counting time on a γ-spectrometer, the limit of detection for 106Ru in seawater was 5.74 mBq/L. In contrast to the traditional CoS method, the usage of NiS does not require any heating process; thus, the pretreatment time is substantially reduced. In addition, by using our method, 106Ru can be determined in the presence of other radionuclides, further enhancing processing efficiency.

Preparation and Photocatalytic Properties of ZnO Deposited TiO2 Nanotube Arrays by Anodization.

ZnO doped TiO2 nanotube arrays (ZnO-TNTs) with an average diameter of 60~80 nm and an average length of 2~4 µm were prepared on the Ti substrate by a one-step anodizing method using NH4F/ethylene glycol as the electrolyte. The phase structure, morphology, chemical composition, photocatalytic property and mechanism of TNTs were studied by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectra, photoluminescence and photocatalytic degradation of methylene blue under visible light. The results showed that highly ordered ZnO doped TNTs were successfully prepared by anodization. ZnO nanoparticles were dispersively distributed inside the walls of TNTs. ZnO-TNTs having a different amount of ZnO was prepared by adjusting the concentration of Zn(NO3)2·6H2O in the electrolyte. It was found that by changing doping amount of ZnO, the width of the TiO2 band gap and the recombination rate of photo-generated electron-hole pairs also changed. The TNTs which doped with 1 mM ZnO showed the best degradation rate of methylene blue (MB). At the concentration of 1 cm²·mL-1 of ZnO-TNTs, the degradation rate reached at the level of 81.9% with 8 mg·L-1 methylene blue aqueous solution. Compared with undoped TNTs, the band gap of ZnO-TNTs reduced from 3.25 eV to 2.75 eV, and the recombination rate of photo-generated electron-hole pairs decreased significantly. The film of ZnO-TNTs prepared by the one-step anodizing method depicted excellent photocatalytic properties under visible light.

Cu2O/Ag co-deposited TiO2 nanotube array film prepared by pulse-reversing voltage and photocatalytic properties.

In this experiment, Cu2O/Ag co-deposition TiO2 nanotube array (Cu2O-Ag-TNT) film was prepared on pure Ti substrate with the method of combining anodic oxidation and electrodeposition by pulse-reversing voltage power supply in the electrolyte of NH4F, ethylene glycol, CuNO3 · 3H2O and AgNO3. The morphology, phase, chemical composition, photocatalytic property and mechanism of the nanotube array film were studied by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, UV-vis diffuse reflectance spectra, photoluminescence and photocatalytic degradation under visible light. The results showed that the depositional Cu2O and Ag existed in two forms, being the small-particle dispersion and large-particle sedimentary phase in the nanotube arrays: Cu2O-Ag-TNTs for different doping amounts of Ag could be prepared by adjusting the concentration of AgNO3 and the reverse voltages; with changing of the doping amount of Ag, the band gap and photo-generated electron-hole pair recombination rate also changed, and under the conditions of annealing and the optimized process parameter, the band gap of the nanotube arrays narrowed 0.49 eV and the rate of electron and pair recombination decreased noticeably; the nanotube array film for the concentration of 0.5 cm2 ml-1 degraded the methylene blue of 8 mg L-1, and the degradation rate reached above 98%. The co-deposition Cu2O-Ag-TNT film prepared by the one-step method performed well in the field of photocatalysis under visible light.