Enhanced antibacterial and algae inhibition performance by coral sand-supported nano-Ag composites†

Developing efficient, non-toxic (or low toxicity), low-cost, and long-lasting antibacterial and algae-inhibiting materials is an important issue closely related to human health. Coral sand, due to its porous and biologically residual nature, is an environmentally friendly pure natural material, and its application in the field of environment has attracted attention. This study used coral sand as a carrier to immobilize nano silver and obtained the composite material coral sand-Ag (CS-Ag), which could release nano silver in a slow-release manner to achieve the purpose of continuous sterilization and algae inhibition. The research results showed that 44.2% of silver ions could be sustained within one week, demonstrating a silver sustained release effect. There were obvious antibacterial circles around the CS-Ag composite material, with a diameter of 22.5 ± 0.1 mm for Staphylococcus aureus and 24.1 ± 0.1 mm for Escherichia coli. The bactericidal activity of silver-loaded coral sand was affected by environmental temperature and pH value. SEM observations showed that silver-loaded coral sand caused scars or holes on the surface of bacterial cells, which also confirmed its ability to damage bacterial cells. This material also had an inhibitory effect on single-cell algae. In the treatment group with a concentration of 1.0 g L⁻¹, the inhibition efficiency of CS-Ag on the growth of microalgae for 96 h can reach 89.7%. The addition of silver-loaded coral sand also affected the structural morphology of algal cells and the synthesis of chlorophyll a, thereby inhibiting photosynthesis and respiration, respectively. The high concentration of silver-loaded coral sand almost completely inhibited the photosynthesis and respiration of algal cells. Therefore, CS-Ag is expected to achieve the removal of bacteria and algae in intensive aquaculture water and achieve harmless disease control.