A Hybrid {Silk@Zirconium MOF} Material as Highly Efficient AsIII-sponge

Abstract

Exposure of humans to Arsenic from groundwater drinking sources is an acute global public health problem, entailing the urgent need for highly efficient/low-cost Arsenite (As iii) up-taking materials. Herein we present an innovative hybrid-material, ZrMOF@SF d operating like an "As iii-sponge" with unprecedented efficiency of 1800 mg As iii gr −1. ZrMof@SF d consists of a neutral Zirconium Metal-Organic Framework [ZrMOF] covalently grafted on a natural silk-fiber (SF d). ZrMOF itself exhibits As iii adsorption of 2200 mg gr −1 , which supersedes any-so far-known As ΙΙΙ-sorbent. Using XPS, FTIR, BETporosimetry data, together with theoretical Surface-Complexation-Modeling (SCM), we show that the high-As ΙΙΙ-uptake is due to a sequence of two phenomena:[i] at low As iii-concentrations, surfacecomplexation of H 3 Aso 3 results in As iii-coated voids of ZrMOF, [ii] at increased As iii-concentrations, the As iii-coated voids of ZrMOF are filled-up by H 3 Aso 3 via a partitioning-like mechanism. in a more general context, the present research exemplifies a mind-changing concept, i.e. that a "partitioning-like" mechanism can be operating for adsorption of metalloids, such as H 3 Aso 3, by metal oxide materials. So far, such a mechanism has been conceptualized only for the uptake of non-polar organics by natural organic matter or synthetic polymers. Arsenic exposure through drinking water sourced from groundwater, is a global public health problem that is particularly devastating in certain highly populated countries 1,2. According to a 2000 to 2010 case study, 35 to 77 million people in areas of Bangladesh or India have been chronically exposed to arsenic in their drinking water in what described as the most significant mass poisoning in history 3. Arsenic is a naturally occurring metalloid, also released to the environment via anthropogenic activities. Arsenic strongly binds to proteins, so traces of this element can cause severe health problems to all life forms 4. The predominant forms of arsenic in the aquatic environment are As III (arsenite) and As V (arsenate). As III is more hazardous than As V , as it is more mobile/bioavailable, thus more toxic 5. This toxicity is due to its dominant H 3 AsO 3 form, i.e. the predominating species in a wide range of pH < 9 6 , typically encountered in natural waters. So far, traditional ion-exchange materials and sorbents, e.g. zeolites, clays, layered double hydroxides, resins have been used as arsenic adsorbends, however, with limited efficiency vs. As III 7,8. Given that As V , which exists as anion at pH > 2, is easier to adsorb on cationic surfaces, to overcome the low efficiency of As III uptake, an extra step of oxidation of As III to As V can be chosen before the application of various remediation technologies. Such oxidative pretreatment, however, suffers from the presence of multiple substances that interfere with As III oxidation 9,10. Therefore, it will be desirable to develop sorbents that could directly capture As III in natural pH conditions, without the need for ...

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