cost-effective removal of cr(vi) ions from wastewater using supported melamine-based covalent organic framework

Nowadays, environmental pollution with metal ions is one of the challenges in human societies. heavy metals, which are inherently toxic, can be found naturally or through human activities in different hydrology and water sources, which may cause serious damage to the environment and require close monitoring of these species due to lack of treatment. among heavy metal ions, chromium and its compounds enter the wastewater from many industries like metal plating, tanning, metal cleaning, dyeing, textile and refractory materials. chromium (iii) exists naturally in animal cells and is a vital element for maintaining the metabolism of glucose, lipids and proteins effective in mammals, whereas, it is well-known that cr(vi) is a very dangerous metal pollutant with non-biodegradable and carcinogenic properties. accumulation of cr(vi) in the human body lead to various health consequences, therefore its removal before release into the environment using a suitable adsorbents is a necessity [1]. covalent organic frameworks (cofs) are a class of materials that form two- or three- dimensional structures through reactions between organic precursors resulting in strong, covalent bonds to afford porous, stable, and crystalline materials. cofs have demonstrated a great potential in the removal of heavy metals due to its high adsorption capacity, large surface area, tunable porosity, porous structure, and recyclability. these features give cofs advantages over traditional adsorbents [2-3].the aim of this work was to develop a new adsorbent for the removal of cr(vi) ions from wastewater. in this regard, an amino acid supported melamine-based covalent organic framework was synthesized through a facile hydrothermal method. the structure and morphology of the synthesized cof-based adsorbent were characterized by different technique. the maximum adsorption capacity of the prepared adsorbent is 157.2 mg g-1 for removing cr(vi) ions at ambient temperature and an optimum ph of 2.5. it was found that the adsorption data can be well fitted to the linear langmuir model (r2 = 0.996). the adsorption kinetics can also be well described by the linear pseudo-second-order model. to make a portable, highly sensitive, and low-cost device for in situ sensing of trace amounts of cr(vi) ions, the smartphone colorimeter platform was developed using accessible equipment. the ability of suggested method with portable device can become an alternative to the conventional methods in field-analysis.