Application of modified SBA-15 adsorbent with DABCO ligand for solid phase extraction of Cr(VI) ion from water environments

Trace detection of heavy metals and their effects is an important subject. Chromium is regarded as being one of the main pollutants in environmental samples. Chromium exists in the environment as Cr(III) and Cr(VI) oxidation states, but Cr(VI) can have acute and chronic toxic including carcinogenic effect. Cr(VI) ion is a well-known and widespread industrial contaminant which inflicts severe health problems to skin, mucous membranes, tooth and respiratory, etc. Meanwhile, the selective determination of Cr(VI) has been a longstanding analytical challenge and is of particular importance due to much higher level of toxicity compared to its counterpart (i.e., Cr(III)) [1-3]. The USEPA has set the concentration of 0.1 mg L−1 for total chromium in drinking water as “maximum contaminant level goals”, whilst the WHO has established the guideline value of 50 μg L−1 for Cr(VI) [4]. The crucial issue of the study is synthesis of novel nanocomposite suitable for sorption of selected species of chromium. Modified SBA-15 with 1,4-diazabicyclo[2.2.2]octane (DABCO) demonstrates selectivity toward chromium(VI) ions in the presence of Cr(III) at pH 5. The SBA/DABCO nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The nanocomposite was used as solid sorbent in preconcentration of Cr(VI) ions from water samples and their determination using flame atomic absorption spectrometry. The main factors affecting the extraction efficiency such as pH value, sample volume, eluent concentration and volume, amount of sorbent and coexisting ions have been investigated and established. In addition, under the optimal conditions the linear range, limit of detection, enrichment factor and relative standard deviation were found to be 2.0-400.0 μg/mL, 0.05 μg/mL, 83.3 and 2.68 %, respectively. The maximum adsorption capacity calculated based on the Langmuir adsorption model was 25  mg g−1. Finally, the method was successfully applied to the separation and preconcentration of Cr (VI) ion from tap, river and wastewater samples.