As the largest container and resource of metals, sediment has a special role in the fate of metals. Factors influencing bioavailability of heavy metals in sediment have never been comprehensively considered and the sediment properties still fail to understand and even controversial. In this review, the mechanisms of sediment properties such as acid-volatile sulfides (AVS), organic matter, texture (clay, silt or sand) and geology, organism behaviors as well as those influencing the bioavailability of metals were analyzed. Under anoxic condition, AVS mainly reduce the solubility and toxicity of metals, while organic matters, Fe-Mn oxides, clay or silt can stabilize heavy metals in elevated oxidative-reductive potential (ORP). Other factors including the variation of pH, redox potential, aging as well as nutrition and the behavior of benthic organism in sediment also largely alter metals mobility and distribution. These factors are often inter-related, and various toxicity assessment methods used to evaluate the bioavailability of trace metals have been also discussed. Additionally, we expect that some novel synthetic materials like polysulfides, nano-materials, provide the substantial amendments for metals pollution in sediment.

Carbon nanomaterials (CNMs) are novel nanomaterials with excellent physicochemical properties, which are widely used in biomedicine, energy and sensing. Besides, CNMs also play an important role in environmental pollution control, which can absorb heavy metals, antibiotics and harmful gases. However, CNMs are inevitably entering the environment while they are rapidly developing. They are harmful to living organisms in the environment and are difficult to degrade under natural conditions. Here, we systematically describe the toxicity of carbon nanotubes (CNTs), graphene (GRA) and C₆₀ to cells, animals, humans, and microorganisms. According to the current research results, the toxicity mechanism is summarized, including oxidative stress response, mechanical damage and effects on biological enzymes. In addition, according to the latest research progress, we focus on the two major degradation methods of chemical degradation and biodegradation of CNTs, GRA and C₆₀. Meanwhile, the reaction conditions and degradation mechanisms of degradation are respectively stated. Moreover, we have prospects for the limitations of CNM degradation under non-experimental conditions and their potential application.

Advanced oxidation processes (AOPs) have attracted special attention owing to the high removal efficiency of recalcitrant organic contaminants. Recently, the use of layered double hydroxides (LDHs) or LDH composites as catalysts for AOPs (photocatalysis, Fenton reaction methods, and sulfate radical (SO₄˙⁻)-mediated oxidations) has received increasing attention and has become a new research hotspot. This is due to their layered structure, flexible tunability, electronic properties, and high physicochemical stability. Herein, we provide a comprehensive review on the development and progress in the synthesis of pristine LDH and modified LDH catalysts for AOPs. Special attention has been paid to the design strategies of high-performance LDHs, including (1) rational design of pristine LDHs, such as binary and ternary LDHs, (2) calcination of LDHs at an appropriate temperature, (3) modification of LDHs with a semiconductor or metal as a cocatalyst, (4) changing the compensating anions, and (5) controlling the LDH morphology. Finally, some valuable perspectives on the challenges and future research directions in LDH-based AOPs are discussed.

This review introduces briefly the use of LDH materials as adsorbents and catalysts for the decontamination of dyes wastewater.