As is well known, hydrotalcite-like compounds, such as layered-double-hydroxide (LDH) materials, have shown great potential applications in many fields owing to their unique characteristics, including a higher anion exchange capacity, a structure memory effect, low costs, and remarkable recyclability. While the lower surface area and leaching of metal ions from LDH composites reduce the process efficiency of the catalyst, combining LDH materials with other materials can improve the surface properties of the composites and enhance the catalytic performance. Among organic compounds, carbon materials can be used as synergistic materials to overcome the defects of LDHs and provide better performance for environmental functional materials, including adsorption materials, electrode materials, photocatalytic materials, and separation materials. Therefore, this article comprehensively reviews recent works on the preparation and application of layered double-hydroxide-based carbon (LDH–C) composites as synergistic materials in the field of environmental remediation. In addition, their corresponding mechanisms are discussed in depth. Finally, some perspectives are proposed for further research directions on exploring efficient and low-cost clay composite materials.

As algae are extremely sensitive to heavy-metal ions and can be critical biological indicators in the heavy-metal toxicity analyses conducted by environmental health researchers, this paper explores the sensitivity to temporal toxicity of three species of green algae: Scenedesmus obliquus, Chlorella pyrenoidosa, and Selenastrum capricornutum. The method of time-dependent microplate toxicity analysis was used to systematically investigate the changes in the toxicities of the three green-algae species induced by different concentrations of cadmium (Cd). The chlorophyll a content, antioxidant enzyme activity, and malondialdehyde (MDA) content in the algae were analyzed to explore the mechanism of Cd toxicity after 96 h of exposure. The results showed that the toxic effects of Cd on the three algae species were time-dependent. By comparing the toxic effect of Cd, indicated by pEC₅₀ (the negative logarithm of EC₅₀), on the algae species at four durations of exposure (24, 48, 72, and 96 h), this study found that the indicator organisms had different sensitivities to Cd. The order of sensitivity was C. pyrenoidosa > S. obliquus > S. capricornutum. Cd exposure had significant effects on the chlorophyll a and MDA content and on the enzyme activity of superoxide dismutase (SOD) and catalase (CAT) in the algae species. The chlorophyll a content in the cells of the algae decreased with increasing Cd concentration. The enzyme activity of CAT and content of MDA increased with increasing Cd concentration, which indicated that Cd had an oxidative stress effect on the three algae species.

A novel pomelo peel biochar/MgFe-layered double hydroxide composite (PPBC/MgFe-LDH) was synthesised using a facile coprecipitation approach and applied to remove cadmium ions (Cd (II)). The adsorption isotherm demonstrated that the Cd (II) adsorption by the PPBC/MgFe-LDH composite fit the Langmuir model well, and the adsorption behaviour was a monolayer chemisorption. The maximum adsorption capacity of Cd (II) was determined to be 448.961 (±12.3) mg·g⁻¹ from the Langmuir model, which was close to the actual experimental adsorption capacity 448.302 (±1.41) mg·g⁻¹. The results also demonstrated that the chemical adsorption controlled the rate of reaction in the Cd (II) adsorption process of PPBC/MgFe-LDH. Piecewise fitting of the intra-particle diffusion model revealed multi-linearity during the adsorption process. Through associative characterization analysis, the adsorption mechanism of Cd (II) of PPBC/MgFe-LDH involved (i) hydroxide formation or carbonate precipitation; (ii) an isomorphic substitution of Fe (III) by Cd (II); (iii) surface complexation of Cd (II) by functional groups (-OH); and (iv) electrostatic attraction. The PPBC/MgFe-LDH composite demonstrated great potential for removing Cd (II) from wastewater, with the advantages of facile synthesis and excellent adsorption capacity.

Three degradation strains that can utilize β-Hexachlorocyclohexanes (β-HCH) as the sole carbon source were isolated from the soil substrate of constructed wetland under long-term β-HCH stress, and they were named A1, J1, and M1. Strains A1 and M1 were identified as Ochrobactrum sp. and strain J1 was identified as Microbacterium oxydans sp. by 16S rRNA gene sequence analysis. The optimum conditions for degradation with these three strains, A1, J1, and M1, were pH = 7, 30 °C, and 5% inoculum amount, and the degradation rates of 50 μg/L β-HCH under these conditions were 58.33%, 51.96%, and 50.28%, respectively. Degradation characteristics experiments showed that root exudates could increase the degradation effects of A1 and M1 on β-HCH by 6.95% and 5.82%, respectively. In addition, the degradation bacteria A1 and J1 mixed in a ratio of 1:1 had the highest degradation rate of β-HCH, which was 69.57%. An experiment on simulated soil remediation showed that the compound bacteria AJ had the best effect on promoting the degradation of β-HCH in soil within 98 d, and the degradation rate of β-HCH in soil without root exudates was 60.22%, whereas it reached 75.02% in the presence of root exudates. The addition of degradation bacteria or degradation bacteria-root exudates during soil remediation led to dramatic changes in the community structure of the soil microorganisms, as well as a significant increase in the proportion of aerobic and Gram-negative bacterial groups. This study can enrich the resources of β-HCH degrading strains and provided a theoretical basis for the on-site engineering treatment of β-HCH contamination.

In recent years, β-Hexachlorocyclohexane (β-HCH) has been detected frequently in water, seriously threatening human health and ecological balance. To explore the effects of different treatment groups on the removal of β-HCH in experimental water and the response of microbial community structure in the system, three strains of β-HCH-degrading bacteria—Ochrobactrum sp. (Och1, Och2) and Pseudomonas sp. (Pse1)—combined with Canna were selected for microbial, plant, and microbe–plant repair hydroponic experiments, respectively. Solid-phase extraction combined with GC-ECD and high-throughput sequencing determined the β-HCH content and bacterial community in water and Canna tissues. The results showed that when β-HCH stress concentrations were 10 μg·L⁻¹ and 100 μg·L⁻¹, Och1 and Pse1 showed the best degradation performance (33.49% and 60.02%, respectively). Following this, the three degrading strains were combined with Canna. Under the two β-HCH stress concentrations, the combination of Och1–Canna showed the highest β-HCH removal efficiency (96.74% and 99.06%). At the same time, we measured the concentration of β-HCH in Canna tissues and found that Och1 had a better removal effect on β-HCH in water and that the addition of Pse1 may significantly improve the absorption capacity of β-HCH in Canna roots. In addition, the relative abundance of Methophilic bacteria in experimental water and Canna root samples increased significantly after the inoculation of degrading bacteria, suggesting that Methophilic bacteria may be vital in degrading benzene-ring-containing substances. The results of this research can provide a theoretical basis and technical support for the prevention and control of the non-point source pollution of organic pesticides.