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The adsorption mechanism of Cr(VI) onto different α-Fe2O3 crystal facets is chemisorption process through outer surface of doubly and triply coordinated hydroxyl groups.<br><br>Display Omitted<br>• 3D hierarchical α-Fe2O3 nanoparticles with different planes predominantly exposed were synthesized. • The Cr(VI) removal ability reach to 34.4 mg/g by flower-like α-Fe2O3 particles with (0 0 1) plane exposed. • The coordination between Cr(VI) and special doubly coordinated hydroxyl groups plays important role for adsorption.<br>Two kinds of 3D hierarchical α-Fe2O3 nanoparticles, flower-like structure with the (0 0 1) plane predominantly exposed on petals and urchin-like structure with nanorods grown along [0 0 1] direction, have been synthesized under the influence of glycerol by a facile hydrothermal method. It is proposed that the Fe(III)-glycerol micro-reaction units that selectively adsorb to (0 0 1) or other planes result in different morphologies. The adsorption of Cr(VI) from aqueous solution onto these α-Fe2O3 nanoparticles showed that the removal efficiency up to 98.5% and 88.8% in 25 mg/L Cr(VI) solution, and the adsorption capacity reaches to 34.4 mg/g and 26.0 mg/g without pH adjustment. The adsorption kinetic is well described by the pseudo-second-order model and the Cr(VI) adsorption on the adsorbent agrees well with the Langmuir model. Lower surface areas and more excellent adsorption property associates with the chemisorption of Cr(VI) onto α-Fe2O3 (0 0 1), which is achieved by coordination between Cr(VI) and doubly or triply coordinated hydroxyl groups on α-Fe2O3 surface.
A chemometrics-assisted excitation-emission matrix (EEM) fluorescence method is presented for simultaneous determination of umbelliferone and scopoletin in Tibetan medicine Saussurea laniceps (SL) and traditional Chinese medicine Radix angelicae pubescentis (RAP). Using the strategy of combining EEM fluorescence data with second-order calibration method based on the alternating trilinear decomposition (ATLD) algorithm, the simultaneous quantification of umbelliferone and scopoletin in the two different complex systems was achieved successfully, even in the presence of potential interferents. The pretreatment is simple due to the "second-order advantage" and the use of "mathematical separation" instead of awkward "physical or chemical separation". Satisfactory results have been achieved with the limits of detection (LODs) of umbelliferone and scopoletin being 0.06ngmL(-1) and 0.16ngmL(-1), respectively. The average spike recoveries of umbelliferone and scopoletin are 98.8±4.3% and 102.5±3.3%, respectively. Besides, HPLC-DAD method was used to further validate the presented strategy, and t-test indicates that prediction results of the two methods have no significant differences. Satisfactory experimental results imply that our method is fast, low-cost and sensitive when compared with HPLC-DAD method.