Carbon spheres/activated carbon composite materials with high Cr(VI) adsorption capacity prepared by a hydrothermal method.

Glucose and commercial activated carbon (AC) were used as starting materials to hydrothermally synthesize carbon spheres on the surface of AC, producing new carbon sphere-AC hybrid carbon materials. It was found that micrometer-sized carbon spheres, rich in oxygen-containing functional groups, can be effectively anchored to, and well-dispersed on, the surface and at the entrance to the macropores of AC. As the glucose concentration increased, the size and dispersion of carbon spheres changed, the porosity of the AC decreased, the number of oxygen-containing functional groups increased, and C--OH gradually became the dominant functional group. The carbon composites that were obtained exhibited a remarkably enhanced adsorption capacity for Cr(VI) per unit mass and per unit surface area. The highest adsorption capacity per unit mass achieved was 0.4834 mmol g(-1), about 4 times that of unmodified AC. The abundant surface oxygen-containing functional groups and relatively well-developed pore structure were the main causes of the high specific adsorption capacity of the carbon sphere/AC composites.