جذب انتخابی رنگ های کاتیونی از محلول آبی با کامپوزیت چارچوب آلی – فلزی مبتنی بر پلی آکسومتالات Selective adsorption of cationic dyes from aqueous solution by polyoxometalate-based metal–organic framework composite

With the rapid industrial development, the pollution of water is becoming more and more serious resulting in the shortage in water supply [1]. Dyes are color organic compounds and widely used in the synthesis, textile, cosmetic, leather, printing, paper, food and other industries [2–۴]. So far, more than 7 × ۱۰۵ t year−۱ and 10,000 different types of dyes are produced all over the world. To be sure, 10% to 15% of the dye is discharged due to washing operations and incomplete exhaustion of coloring materials during the dyeing process [5], which poses a significant threat to environment and human health because of their toxicity, potential mutagenicity, and even carcinogenicity without reasonably processing [6–۸]. Moreover, the discharge of the dyes without treatment into the rivers is easily noticed since dyes are highly visible, which is commonly harmful to aquatic life [9,10]. Therefore, it is necessary to  find appropriate treatment strategies for efficient removal of dyes from waste-water system before their discharge. So far, there are many techniques which have been reported on the effective elimination of hazardous substances from aqueous solutions such as biological methods, physical, chemical, electrocoagulation, photocatalytic degradation, oxidation and so on [11–۱۵]. Among the proposed techniques, adsorption is the procedure of choice and can reach good results as it is highly efficient, inexpensive and simple in operation [16–۱۸]. This has encouraged the exploration of adsorbents with abundant availability and good economy. Nowadays a huge amount of low cost adsorbents are investigated including the common adsorbents, products of industrial or agricultural origin such as activated carbon [19], carbon nanotubes [20], activated slag, sugarcane, wood dust,fruit peel[21], tea waste ash, rice husk [22], metal–organic frameworks(MOFs) [23,24] and so on. However, there is still a great need to explore some kinds of new and low cost adsorbents with high adsorption capacity, even high selectivity and short contact time towards specific dyes [25]. Recently, the adsorbents with a high selectivity towards targeted dyes have attracted more and more researchers’ interests due to their huge potentiality in the controlled separation of dye mixtures and chemicals during treating industrial wastewater, as well as making sensors for the detection and identification of certain types of dyes [26]. MOFs fabricated by metal ions or metallic clusters connected through organic ligands by strong bonds are a new class of porous crystalline organic-inorganic hybrid materials [27]. Compared with conventional inorganic porous materials, MOFs have some unique features such as ultrahigh porosity, incredibly large BET surface area, multiple coordination sites, big pore volume and structural adaptivity, which brings many various potential applications such as gas separation and storage, sensors, energy storage, pollutant removal, catalysis, drug delivery and so on [28,29]. So many researches have been aimed at designing new MOFs structures and studying their various applications during the past two decades [30]. However, MOFs also exhibit several weak points such as the relative low stability in solution and brittleness or lack of flexibility hampering their realistic applications. It is necessary to introduce a new functionality for enhancing their realistic properties.