Arsenic ranks the 20th most abundant element in nature. It can have a valency of −3, 0, +3, or +5, depending on water chemistry. In natural waters, it exists as arsenate (AsO4)-3 and/or arsenite (AsO3)-3, also referred to as arsenic(V) and arsenic(III). The toxicity and mobility of arsenic are affected by its oxidation states. Arsenite is more toxic and mobile than arsenate in the aqueous environment. Arsenate primary exists in surface water, whereas arsenite dominates in ground water. The presence of arsenic in water is a serious threat to more than 100 million people in the world. There have been many documented incidents of arsenic contamination in ground water around the world, most notably in countries such as Taiwan, Chile, Argentina, Hungary, Bangladesh, India, Pakistan, Thailand, Vietnam, China, México (Zacatecas, San Luis Potosi, Chihuahua, Torreón, Durango) and the United States. In Mexico alone, it is estimated that 13 of the 31 states in Mexico suffer of arsenic contamination. It is known that Arsenic ingestion can lead to many adverse health effects, including skin lesions, diabetes mellitus, chronic bronchitis, cardiovascular disease, peripheral neuropathy, adverse reproductive outcomes, and hematological effects. Prolonged exposure to arsenic damages the central nervous system and results in diverse types of cancer in liver, lungs, bladder and skin. Arsenic poisoning has a great social cost since it affects children and adults alike. Due to these reasons is of great importance to provide cost-effective technologies capable of eliminating or reduce the levels of concentration of arsenic in drinking water, especially in rural and poor communities where access to costly or complex filtering systems is limited.
Arsenic removal from water is possible through different physicochemical processes which include coagulation, precipitation, ion exchange, membrane filtration, and sorption. Among them, sorption can have a good performance, ease in operation, and lower cost, which makes it attractive for its utilization.
Adsorption is limited by the surface area, active sites and lack of selectivity of the material used, however the arrival of nanomaterials has opened the opportunity to considerably increase the absorption capacity of materials. Furthermore, the possibility to carry out multiscale modeling of chemical systems (topic of research of this year Nobel laureates in Chemistry) can also be used to design molecules or materials with specific properties, for example the selectivity towards a specific chemical molecule or element.
At the CenERgy group in CINVESTAV-SALTILLO (Mexico), in collaboration with Dr. Joaquín Barroso Flores from the National Autonomous University of Mexico, we are combining computer modeling and experimentation to design and synthesize molecules and nanomaterials capable of eliminating arsenic more efficiently. For example, Figure 1 shows some computer models where the interaction between arsenic oxide and calix[n]arenos is being studied.