Herein, novel ternary kaolin/CeO₂/g-C₃N₄ composite was prepared by sol-gel method followed by hydrothermal treatment. The self-assembled 3D “sandwich” structure consisting of kaolin, CeO₂ and g-C₃N₄ nanosheets, was systematically characterized by appropriate techniques to assess its physicochemical properties. In the prerequisite of visible-light irradiation, the removal efficiency of ciprofloxacin (CIP) over the kaolin/CeO₂/g-C₃N₄ composite was about 90% within 150 min, 2-folds higher than those of pristine CeO₂ and g-C₃N₄. The enhanced photocatalytic activity was attributed to the improved photo-induced charge separation efficiency and the large specific surface area, which was determined by electrochemical measurements and N₂ physisorption methods, respectively. The synergistic effect between the kaolin and CeO₂/g-C₃N₄ heterostructure improved the photocatalytic performance of the final solid. The trapping and electron paramagnetic resonance (EPR) experiments demonstrated that the hole (h⁺) and superoxide radicals (•O₂⁻) played an important role in the photocatalytic process. The photocatalytic mechanism for CIP degradation was also proposed based on experimental results. The obtained results revealed that the kaolin/CeO₂/g-C₃N₄ composite is a promising solid catalyst for environmental remediation.

The geomorphology of river basin is complex, and its soil sedimentary characteristics are poorly defined. To study the spatial variability of soil structure in different sedimentary environments at the basin scale, 356 sets of soil samples were collected from five typical sedimentary environments in the Yellow River Basin and the Haihe River Basin, including the upper and lower reaches of the rivers, mountain-front plains, central alluvial plains and eastern coastal plains. The particle size distribution (PSD) of the soil samples was obtained using a laser particle size analyzer, and the fractal dimension (D) of the soil structure was derived by applying fractal theory. The PSD, D and the correlation between them were analyzed by the Pearson correlation method for typical sedimentary environments in two basins. The results show that: (1) The main soil types in the typical geological environments in the basin are sand, loamy sand, sandy loam, silty loam, and silty soil. The soil particle size in the upper and lower reaches of the rivers was higher than that in the plain areas. (2) In the plane, The D value descended in different regions in the following order: the mountain-front plain > the eastern coastal plain > the upper Yellow River > the central alluvial plain > the lower Yellow River. In the vertical direction for both rivers, the D value showed a decreasing trend with increasing burial depth. (3) The model results showed a cubic polynomial correlation between D values and PSD, which was closely related to the non-uniformity of particle size during sorting and deposition. The soil PSD and fractal characteristics are effective tools for the quantitative evaluation of soil structure in various sedimentary environments in the basin.

With the implementation of the policy of ecological protection and high-quality development of the Yellow River Basin, the Guohe River Basin, which is close to the middle reaches of the Yellow River Basin, is also an important part of future development. Mathematical statistics, the Piper diagram, ion proportion coefficient method, Gibbs diagram and reverse hydrogeochemical simulation are used to analyze the chemical characteristics and evolution of groundwater in the Guohe River Basin (Henan Section). The dominant ions in the study area are HCO₃⁻ and Na⁺, and the three-layer aquifer has obvious zoning characteristics. The results show that the chemical types of shallow groundwater in this area are HCO₃−Na • Mg • Ca, intermediate HCO₃-Na and deep HCO₃−Na. Using the ion proportion coefficient method, it is found that Na⁺, Ca^2+, and Mg²⁺ in the groundwater aquifer undergo cation exchange in the aquifer. According to the reverse hydrogeochemical simulation, gypsum in the three aquifers is in a dissolved state, carbonate and sulfide ores in the shallow layer are dissolved, dolomite and halite in the intermediate layer are dissolved, calcite and sulfide ores are precipitated and carbonate, halite and sulfide ores in the deep layer are precipitated; the hydrogeochemical evolution model is established to find that Ca²⁺ in groundwater displaces Na⁺ in the aqueous medium. This research can provide a scientific basis for the rational development and utilization of groundwater and ecological protection in the Yellow River Basin.