Access to clean water is fundamental to maintain the basic standards of public health. The World Bank is estimating over a billion individuals lacking access to potable water, causing millions of deaths annually. Only few point-of-use technologies are available providing efficient removal of pollutants and pathogens. Hence there is a critical need to develop low-cost, sustainable and highly effective filtration technologies essential for undeveloped countries lacking water treatment infrastructures.

Since the Middle Ages, people have been using charcoal to filter water because of its exceptional ability to adsorb contaminants. With the advent of nanotechnology, new forms of carbon have been discovered (i.e. carbon nanotubes, CNTs), which have demonstrated impressive sorption capacities, and more spectacularly, have found to be able to efficiently remove viruses and bacteria from water. Unfortunately, methods need to be developed to organize CNTs into highly structured and well-understood materials for safe and efficient implementation in filtration devices.

Herein we report an unprecedented sequential engineering of the architecture of CNT materials by combining emulsification methods with colloidal self-assembly. This approach allows preparation of well-defined spherical CNT supraparticles, which upon assembly, give rise to a filter whose porosity and density can be precisely engineered, allowing full exploitation of the impressive decontaminating action of CNTs.