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Considering the eastern part of Hunan Province as the research area, 34 sampling sites were set up, 198 samples were collected from representative paddy soil, the distribution characteristics of antimony (Sb) were studied. The results showed that: (1) The content of Sb on the surface of paddy soil ranging from 0.07 to 11.00 mg/kg and the geometric mean was 1.56 mg/kg. (2) The distribution of contents of Sb in paddy soil in different areas was shown as Yueyang > Changsha > Zhuzhou > Xiangtan. (3) Sb showed a strong migration in paddy soil in the research area and its content increased initially and then decreased or gradually decreased with the increase of profile depth. (4) The content of Sb in the substratum was significantly affected by parent materials.

Concentrations of major and trace elements in sediments from the Xiangjiang and Yuanjiang River inlets to Dongting Lake (China) were analyzed using XRF and ICP-MS methods, respectively. The results show that sediments from both rivers show comparable major element compositions and a similar distribution of high strength field elements (Zr, Hf, Nb, Ta, Th and U), large ion lithophile elements (Ba, Sc, Ga, Ge, Rb, Y, Cs), and rare earth elements (REE). However, the distribution of heavy metals V, Cr, Co, Ni, Cu, Zn, Pb, Cd, Tl and Bi varies significantly in sediments between the two rivers. The Xiangjiang River sediments are characterized by having a distinctly higher enrichment of the heavy metals Cr, Mn, Ni, Cu, Zn, Pb, Tl, Bi and Cd, and they are mostly contaminated by these heavy metals. That leads to the formation of heavy-metal contaminated (HMC) sediments. Sediments from these two rivers can be coincidentally divided into three groups by their REE patterns and factor load plots of principle component analyzing on major elements of 173 samples. The HMC sediments can further be separated from those of less contaminated sediments by plots of (Eu/Eu)NS* against the synthetic enrichment index values, and the HMC sediments are found to be significantly higher enriched in the major elements Al2O3, Fe2O3, MnO, P2O5 and LOI, and depleted in SiO2 and Na2O. Therefore, the distribution of the major elements Al2O3, Fe2O3, MnO, CaO, P2O5, LOI, SiO2 and Na2O in the river sediments can be used as indicators for identifying the HMC sediments. Thus, the ‘aluminium–iron index’ (AF), the ‘silicate index’ (SI), the ‘grain size index,’ and the Al2O3/SiO2, Fe2O3/SiO2 and Al2O3/Na2O ratios are then established as chemical indices for the use of identifying the HMC sediments. River sediments that have values of AF > 25.6, SI < 67.5, Al2O3/SiO2 > 0.29, Fe2O3/SiO2 > 0.12 and Al2O3/Na2O > 43.0 are then identified to be the HMC sediments in the study area.

The measurement of pH has received great attention in diverse fields, such as clinical diagnostics, environmental protection, and food safety. Optical fiber sensors are widely used for pH sensing because of their great advantages. In this work, an optical fiber pH sensor is fabricated, by combining the merits of the multimode interference configuration and pH-sensitive polyaniline/polyacrylic acid (PAni/PAA) coatings, which was successfully in situ deposited on the no-core fiber (NCF) by the layer-by-layer (LBL) self-assembly method. The sensors’ performance was experimentally characterized when used for pH detection. It has a high sensitivity of 0.985 nm/pH and a great linear response in a universal pH range of 2–12. The response time and recovery time is measured to be less than 10 s. In addition, its temperature sensitivity is tested to be about 0.01 nm/°C with a low temperature crosstalk effect, which makes it promising for detecting pH in the liquid phase with temperature variation. The sensors also demonstrated easy fabrication, good stability, and repeatability, which are adapted to pH detection in most practical applications.

The catalysts employed in catalytic reactors greatly affect the reaction efficiency of the reaction system and the reactor’s performance. This work presents a rapid comparative study on three kinds of Fe-based materials integrated into an optofluidic Fenton reactor for water treatment. The Fe-based sheets (FeSiB, FeNbCuSiB, and FeNi) were respectively implanted into the reaction chamber to degrade the organic dyes with the assistance of H2O2. In the experiment, by adjusting the hydrogen peroxide concentration, flow rate, and light irradiation, the applicable conditions of the Fe-based materials for the dye degradation could be evaluated quickly to explore the optimal design of the Fenton reaction system. The results indicated that FeNi (1j85) exhibits excellent degradability in the microreactor, the reaction rate can reach 23.4%/s at the flow rate of 330 μL/min, but its weak corrosion resistance was definitely demonstrated. Although the initial degradability of the microreactor by using FeNbCuSiB (1k107) was not as good as that of 1j85, it increased after being reused several times instead, and the degradation efficiency reached >98% after being reused five times. However, the FeSiB (1k101) material shows the worst degradability and recycling. Therefore, in contrast, 1k107 has the greatest potential to be used in Fenton reactors for practical water treatment.