The XRD patterns of pristine UiO-66-NH2 and UA composite are indicated in Fig. 1(a). The pristine UiO-66-NH2 exhibits characteristic peaks at the 7.3°, 8.3° and 25.6° which are in consistent with the early report, showing the successful synthesis of UiO-66-NH2 and its high crystallization [4]. These characteristic peaks also appear in the XRD pattern of UA composite, showing the existence of crystal UiO-66-NH2 in the UA nanocomposite.
FT-IR spectra of UiO-66-NH2 and UA are indicated in Fig. 1(b). As to UiO-66-NH2, the peaks at 1580 and 1420 cm-1 are attributed to C-O bonding and C-C vibrational modes in carboxylates, respectively [5]. 1258 and 1385 cm-1 are ascribed to the C-N stretching of aromatic amines [6]. The adsorption bands at 764 and 659 cm-1 are ascribed to Zr-O as longitudinal and transverse modes [7]. The bands located 3475 and 3352 cm-1 are designated to the asymmetric and symmetric vibrations of N-H bond in NH2, respectively [8, 9]. These characteristic bands are in consistence with early literatures, confirming the successful synthesis of UiO-66-NH2. As to CPA-MA, the band located 1676 cm-1 is ascribed to the stretching of C=O [10]. It can be found that the typical bands of UiO-66-NH2 and CPA-MA appear in the spectrum of UA, indicating the well incorporation of UiO-66-NH2 and CPA-MA, furthermore, peaks related to the NH2 of UiO-66-NH2 (3475 and 3352 cm-1), and the peak related to the C=O of CPA-MA (1676 cm-1) are all significantly weakened in the spectrum of UA, showing the NH2 groups in UiO-66-NH2 have condensed with the C=O groups in CPA-MA to form the composite of UA.
As shown in Fig. 1 (c)-(e), the SEM and TEM imagines show that the UA nanocomposites exhibits a morphology of cube with the sizes of around 60-80 nm. The chemical composition of UA was further determined by the mapping and EDX analysis (Fig. 1 (f), (g)). It can be seen that the elements of Zr, N, C, Cl, O, P and S exist and uniformly distribute in UA composite. These results confirm that UiO-66-NH2 was successfully incorporated with CPA-MA to form the composite of UA.
To investigate the effects of adsorbent dosage toward Ce4+ capture, dosage of UA was set from 0.5 to 2 g/L, and the related adsorption capacities are indicated in Fig. S1. As one can see that the highest unit adsorption capacity appears when the dosage is 0.5 g/L, so 0.5 g/L was determined as the optimal dosage. The kinetic process of UA adsorbing Ce4+ was investigated (Fig. S2 (a)). Results showed that the adsorption course was more preferably described by the pseudo-second-order kinetic model (Fig. S2 (b), (c) and Table S1). The adsorption capacity of UA was compared with other previously reported Ce4+ adsorbents, the results are shown in Table S2, indicating it being among the top Ce4+ adsorbents.
In order to test the response of UA toward Ce4+, the adsorptions were conducted with Ce4+ concentration, and the related diffuse reflectance spectra reflecting were recorded with a visible light spectrophotometer. The results indicate that the adsorbent can change its color as capturing Ce4+ ions with different concentration. The color of crude UA is olive drab. In the testing Ce4+concentration range, the Ce4+ load UA shows light cyan, and the chroma of UA decrease with the increase of Ce4+ concentration (insert in Fig. 2 (a)), which can be testified by the intensity decrease at λ=454 nm with the increase of Ce4+ concentration (Fig. 2 (a)). Furthermore, as plot the Ce4+ concentration vs. intensity value at 454 nm, it can be found that the intensity changing have linear relationship with the Ce4+ concentration, as shown in Fig. 2 (b). The high coefficience (R2) values of 0.9700 exhibits the high linear dependence, indicating that Ce4+ concentration can be measured by chroma changing of UA.
The limits of detection (LOD) is 3.24 mg/L, which can be calculated by follows:
![](https://myfiles.space/user_files/58894_9946feeafa4c1df7/58894_custom_files/img1628846929.JPG)
where M refers to the standard deviation obtained in the blank, and S refers to the slope of the linear range in the calibration graph.
So as to study the anti-interference ability, the adsorption capacities of UA toward Ce4+ were tested with several co-existing ions (Mg2+, Zn2+ and Cu2+). In the experiments, 100 mg/L Ce4+ was paired with 0, 100, 150, 200, 250, or 300 mg/L the competing ion, respectively. It can be seen in Fig. 3 (a), the existence of competing ions can affect the adsorption of Ce4+ on the nanocomposite in different level, depending on the species. Cu2+ shows the least competitiveness, the nanocomposite removal rate can be retained ~87%. In the presence of Zn2+, which is the most competitive, the nanocomposite removal rate can be retained ~80%. These consequences show that UA has a relatively high anti-interference capacity as adsorbing Ce4+.
The crude UA is olive drab. When UA captures 10 mg/L Ce4+, its color quickly changes to be pale green in seconds. When UA was added to the solution containing other metal ions such as Mg2+, Zn2+ and Cu2+, even their concentrations are 30 times higher than that of Ce4+, they can not change UA’ color a bit. The results are shown in Fig. 3 (b), which indicates that Ce4+ can be qualitatively detect even by naked-eye according to UA’s color.