Arsenic and mercury are among the top five substances most hazardous to human health affecting millions of people worldwide. The main and probably only approach is to reduce their emissions into the environment and eliminate human exposure to contaminated water, food and other environmental and occupational hazards. A number of technologies for removing As and Hg from water, waste and contaminated land have been developed. Among them, novel selective adsorbents have shown high potential for deep and efficient decontamination of aqueous environment. Nanoporous activated carbon (AC) has shown significant adsorption capacity for both As and Hg species. despite being a non-selective adsorbent. However, AC is considered to be an expensive material even if it is made of agricultural by-products and novel adsorbents are being developed to achieve this goal. The adsorption efficiency of candidate materials for deep decontamination of water has been enhanced by using nanoparticulate adsorbents designed with high selectivity towards Hg or As. We have demonstrated high selectivity of composite adsorbents containing silica or fly ash as a matrix with immobilised silver nanoparticles (NPs) towards inorganic Hg. Nanosilver reacts with Hg forming an amalgam; size-controlled Ag NPs (of 11nm to 45nm size) immobilised on silica surface rapidly and effectively removed mercury from aqueous solution, with 1g of Ag capable of treating > 10,000 m3 of contaminated water (at environmentally-realistic ppb levels of Hg(II)). To solve the problem of high flow resistance of filtration devices packed with micro-/ nanoparticles, we explored two main routes: (i) make 3-D composites of supermacroporous (over 1 microm) polymer hydrogels with embedded target microand nanoparticles or entirely carbon 3D structures such as carbon aerogels. Metal nanoparticlepolymer/ hydrogel composites were produced by the embedding of reactive nanoparticles into porous gel scaffolds, in particular hydrogels or cryogels. The latter are macroporous gels produced by the polymerisation of water-soluble monomers under freezing temperatures, which are easy to manufacture, and offer controllable permeability, high mechanical strength, chemical stability and shape recovery. Haematite and magnetite nanoparticles embedded in the cryopolymer walls surrounding the macropores were used as adsorbents to remove As(III) from simulated environmental waters, and showed that despite physical embedding of the nanoparticles into the polymer, high nanoparticle reactivity was retained due to short diffusion pathways. Rapid and effective sorption of As(III) was achieved across a wide pH range, even in the presence of competing ions. Highly porous metal–organic frameworks (MOFs) have formed a new, novel and effective addition to technologies for capturing hazardous metal ion pollutants. The structure and functionality of MOFs can be modified to target particular contaminant types and groups. It has been shown that the As(III) uptake by a MIL-100(Fe) MOF (consisting of a porous carbon matrix bearing zero-valent iron magnetic core coated with an Fe-oxide layer and iron carbide) was 3- to 10-times higher than other adsorbent materials, such as graphite/graphite oxide, activated carbon, and pyrolytic carbon.