▎ 摘　　要

NOVELTY - A composite material comprises a carbon nanotube and ferrihydrite particles, where the carbon nanotube has an outer surface and the ferrihydrite particles are disposed on the outer surface of the carbon nanotube. The composite material has a specific surface area and a specific capacitance. The composite material comprises the ferrihydrite particles and carbon nanotube in a weight ratio of 5:95-95:5. The weight ratio is selected such that the composite material has a desired balance between the specific surface area and the specific capacitance. USE - A composite material for use in filter for separating a component from a fluid stream (claimed). ADVANTAGE - Nanofiltration offers a lower energy and cost, produces less waste waters, and works at higher pH. The composite filters have a reduced potential for biofouling; can remove both elemental hazards and organic contaminants from water to improve its potability; can have improved adsorption of contaminants via use of carbon nanotubes rather than graphene or other nanoformulations of carbon; and can have improved water transport over other carbon-based filters. The method allows for precise control of the proportion of carbon nanotubes to ferrihydrite in the resulting composite, thus, allowing precise control of the surface area and surface charge. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) filter for separating a component from a fluid stream, comprising a composite material, where the fluid stream comprises liquid water or an aqueous solution; (2) method of use of the filter which involves using the filter in a separation to separate the component from the fluid stream, where the method comprises water purification, environmental remediation, and/or solid phase extraction; (3) method of making the composite material which involves contacting the carbon nanotube with an amount of iron nitrate to form a mixture, where the amount of iron nitrate relative to the carbon nanotube determines the weight ratio of the ferrihydrite particles and the carbon nanotube in the composite material; and contacting the mixture with a base to adjust the pH of the mixture to induce precipitation of the ferrihydrite particles onto the outer surface of the carbon nanotube; and forming the composite material; and (4) method which involves making a set of composite materials, where each composite material comprises a carbon nanotube and ferrihydrite particles in a weight ratio, the carbon nanotube having an outer surface and the ferrihydrite particles being disposed on the outer surface of the carbon nanotube, and the weight ratio of the ferrihydrite particles and the carbon nanotube is different for each composite material; determining the specific surface area and the specific capacitance of each composite material in the composite materials; comparing the specific surface area and specific surface capacitance for the composite materials to determine the weight ratio of the ferrihydrite particles and carbon nanotube at which the composite material has a desired balance between the specific surface area and the specific capacitance.