Heavy metal contamination in lake sediments is a serious problem, particularly in developing countries such as China. To evaluate heavy metal pollution and risk of contamination in lake sediments on a national scale in China, we collated available data in the literature of the last 10 years on lake sediments polluted with heavy metals from 24 provinces in China. Based on these data, we used sediment quality guidelines, geoaccumulation index, and potential ecological risk index to assess potential ecological risk levels. The results showed that approximately 20.6% of the lakes studied exceeded grade II level in Chinese soil quality standards for As, 31.3% for Cd, 4.6% for Cu, 20.8% for Ni, 2.8% for Zn, and 11.1% for Hg, respectively. Besides, the mean concentrations for As in 10.3% of lakes, Hg in 11.9% of lakes, and Ni in 31.3% of lakes surpassed the probable effect level. The potential ecological risk for toxic metals decreased in the order of Cd > Hg > As > Cu > Pb > Ni > Cr > Zn, and there were 21.8% of the lakes studied in the state of moderate risk, 10.9% in high risk, and 12.7% in very high risk. It can be concluded that Chinese lake sediments are polluted by heavy metals to varying degrees. In order to provide key management targets for relevant administrative agencies, based on the results of the pollution and ecological risk assessments, Cd, Hg, As, Cu, and Ni were selected as the priority control heavy metals, and the eastern coastal provinces and Hunan province were selected as the priority control provinces. This article, therefore, provides a comprehensive assessment of heavy metal pollution in lake sediments in China, while providing a reference for the development of lake sediment quality standards.

Metal-free graphitic carbon nitride (CN) is one of the promising semiconductor candidates for photocatalytic application, but mostly only shows moderate activity, owing to the fast recombination of photoinduced electron–hole pairs due to the huge Coulomb interaction between them. The targeted relaxation of photoinduced excitons into free charge carriers is an effective strategy to enhance photocatalytic activity but still very challenging. Here, by using CN as a model, we propose that the grafting of tunable L-cysteine units in porous ultrathin tubular CN (TCN-Lc) can effectively relax photoinduced excitons into electrons and holes and then accelerate charge transfer from CN to active sites for an improved photocatalytic reaction (denoted as the edge effect), and the porous ultrathin tubular structure in CN also enlarges the specific surface area and enhances visible-light absorption ability to thus improve photocatalytic activity. The optimized TCN-Lc10 shows impressive photocatalytic performance for degrading various contaminants such as colored dye and antibiotics and for H₂ evolution (6468 μmol h⁻¹ g⁻¹) with an apparent quantum yield of up to 13.4% at 420 nm under visible light irradiation. The density functional theory (DFT) calculations also reveal that the edge effect via grafting of tunable cysteine units on the CN surface can disrupt the intrinsic electronic state distribution to form energy disordered interfaces and facilitate directional transfer of electrons to the surface. This study offers a new insight to regulate exciton dissociation and charge transfer in semiconductor photocatalysts for contaminant degradation and energy conversion.