Carbon dots (CDs), as a revolutionary nanomaterial, exhibit unique advantages in terms of wastewater treatment, offering new opportunities for the development of water treatment technologies due to their simple synthesis methods, excellent biocompatibility, tunable optical properties, and favorable environmental performance. This review systematically discusses the synthesis methods, structural characteristics, and application progress of carbon dots in wastewater treatment, highlighting several key findings. (1) Excellent adsorption performance: CDs can effectively remove heavy metal ions, dyes, and organic pollutants from water. (2) Outstanding photocatalytic performance: Some carbon-dot-enhanced photocatalytic systems can efficiently remove pollutants under visible light. (3) Exceptional selective detection ability: CDs are capable of highly sensitive detection of heavy metals and organic pollutants in water, with the detection limits reaching the nanomolar level. (4) Enhanced membrane separation performance: The high water flux and excellent selectivity of carbon-dot-modified membranes make them suitable for efficient water treatment and water quality separation. (5) Enhancement of biological treatment: In biological treatment systems, CDs can significantly improve the microbial activity and electron transfer efficiency to enhance the efficiency of biological degradation processes. (6) Sustainable utilization of waste as a raw material and regeneration of CDs are conducive to reducing the cost of preparation of CDs. These findings indicate that CDs have broad application potential in wastewater treatment. Furthermore, this review looks ahead to the future development directions of CDs in wastewater treatment, proposing potential innovations in catalytic performance enhancement, cost control, and practical applications, aiming to provide important references and guidance for future research and industrial application of CDs in wastewater treatment.

Expansive clay is one of the most widely distributed soils in the world. Due to its rich content of strongly hydrophilic minerals—such as montmorillonite—expansive clay exhibits substantial swelling and shrinkage properties, and overconsolidation. The formation process of undisturbed expansive clay has a long and complicated geological history and innumerable drying–wetting cycles, resulting in the formation of special internal structures. In this study, the mud-to-natural-consolidation deposition process was simulated using a saturated mud-remolded sample preparation device, and then, mud-remolded soil under a certain consolidation pressure was prepared. Subsequently, the effects of the stress history and drying–wetting cycle on its mechanical properties and microstructure were examined through uniaxial consolidation compression experiments, K₀ consolidation experiments, and pressure plate experiments of undisturbed soil, mud-remolded soil, and a drying–wetting cycle sample. The results showed that the mud-remolded soil completely broke the natural structure of the undisturbed soil, with the structural characteristics of the remolded soil being restored to a certain extent after the drying–wetting cycle. This not only reduced the void ratio of the soil sample, but also changed its compressibility and water retention characteristics, revealing the role of atmospheric drying–wetting cycles in the natural overconsolidation state of expansive clay and providing a theoretical basis for understanding their overconsolidation characteristics.

Consolidated undrained triaxial shear tests were performed on undisturbed saturated structured clay at three unloading rates (0.1, 0.25, and 2.5 kPa/min) using a GDS triaxial system to determine the effects of different unloading rates and unloading stress paths on the stress–strain relationship, pore pressure variation, and failure strength characteristics of Zhanjiang structured clay. Microstructural changes in the clay were observed during shear tests at different unloading rates. Furthermore, the obtained stress–strain relationship indicates strain-softening under different unloading stress paths. Under the same axial strain, a larger unloading rate caused a larger deviatoric stress. Under the same conditions, the higher the confining pressure, the greater the peak pore pressure, the smaller the unloading rate, the greater the pore pressure development, and the greater the variation in the pore pressure. Moreover, the undrained shear strength increased with an increase in the unloading rate from 0.1 to 2.5 kPa/min. The change in the unloading rate had a greater effect on the undrained strength under the passive tensile path than that under the passive compression path. The microstructure of the Zhanjiang structured clay changed after shear tests at different unloading rates, exhibiting various degrees of adjustment in the particle arrangement, contact relations, pore sizes, and shapes.

Marine soft clay is characterized by a high water content and low strength, exhibiting pronounced creep deformation under long-term loading that threatens the serviceability and durability of coastal infrastructure. Accordingly, this study develops a creep constitutive model that combines elastic, plastic, and viscous effects and quantitatively evaluates time-dependent deformation under varying water contents and stress levels to provide reliable prediction tools for tunnel, excavation, and pile-foundation design. Cyclic creep tests were carried out on reconstituted marine soft clay with water contents of 40–60% and stress ratios of 0.4–1.2 using a pneumatic, fully digital, closed-loop triaxial apparatus. A “nonlinear spring–Bingham slider–dual viscous dashpot in parallel with a standard Kelvin dashpot” element assembly was proposed, and the complete stress–strain relationship was derived. Experimental data were fitted with Python to generate a creep-strain polynomial and verify the model accuracy. The predicted–measured creep difference remained within 10%, and the surface-fit coefficient of determination reached R² = 0.97, enabling rapid estimation of deformation for the given stress and time conditions. The findings offer an effective method for the precise long-term settlement prediction of marine soft clay and significantly enhance the reliability of the deformation assessments in coastal civil-engineering projects.

Occupation of land and damage to the surrounding ecosystem may occur due to the accumulation of dredged lake sediments. In order to solve the large amount of dredged lake sediments, industrial wastes (slag, desulfurization gypsum) and urban construction waste were used to solidify the lake substrate, obtained a new construction material. Water content, volumetric shrinkage, unconfined compressive strength and flexural strength parameters and hydraulic conductivity coefficients of the solidified sediment were obtained from water content determination tests, volumetric shrinkage tests, unconfined compressive strength tests, flexural tests and permeation tests. Mineralogical composition and microstructural characterization of the solidified sediment using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were obtained. The solidification mechanism of lake sediment under the coupling of industrial waste and urban construction waste was revealed. The water content of the specimens decreased rapidly, and shrinkage deformation occurred in curing for 7 d. The volumetric shrinkage of 28 d was eventually maintained at 1.27–5.19%. The trend of specimen strength changed with the extension of time in the overall increase state, the compressive strength and flexural strength within 28 d were 3.15–10.96 MPa and 0.64–2.69 MPa, respectively. The solidified sediment material showed excellent anti-seepage performance, the hydraulic conductivity reached stability at 1.22 × 10⁻⁸–55.4 × 10⁻⁸ cm/s. Gismondine, gypsum, calcite, scawtite and fibrous C-S-H phases were generated in the solidified material.

Landfills necessitate a liner barrier system to prevent the leakage of contaminants into the surrounding soil. However, the currently employed compacted clay liner (CCL) is insufficient to prevent the leakage of heavy metal ions. This study proposes a novel landfill liner system utilizing sludge-based activated carbon (SAC)-modified clay. The adsorption characteristics of SAC-modified clay liner (SAC-CCL) for Cd(II) or Cu(II) were evaluated through batch tests. The permeability coefficient and unconfined compressive strength of SAC-CCL were assessed through permeation and unconfined compression tests. The permeability coefficient of the SAC-modified clay ranged from 2.57 × 10⁻⁹ to 1.10 × 10⁻⁸ cm/s. The unconfined compressive strength of the SAC-CCL varied between 288 and 531 kPa. The migration of Cd(II) or Cu(II) within an 80 cm thick, full-scale SAC-CCL was simulated using soil column tests. The diffusion coefficient (D) was calculated by inversion using the one-dimensional solute migration equation. The diffusion coefficients (D) for Cd(II) and Cu(II) ranged from 1.9 × 10⁻¹⁰ to 13.5 × 10⁻¹⁰ m²/s. The retardant performance of SAC-CCL for Cd(II) and Cu(II) followed the order: 3% SAC-CCL > 1% SAC-CCL > CCL > 5% SAC-CCL, from strongest to weakest. Consequently, SAC-modified clay demonstrates significant potential as a landfill lining material. However, the migration behavior of heavy metal ions in SAC-CCLs under cyclic dry–wet conditions requires further investigation.