# Facile Preparation of Graphene Oxide-MIL-101(Fe) Composite for the Efficient Capture of Uranium
## 2 Materials and Methods
### Batch Sorption Experiments  
The adsorption properties of composite samples were studied by batch experiments. Stock dispersions of adsorbents including MIL-101(Fe) and the GO10(15, 18, 20)-MIL-101(Fe) composites were prepared with a concentration of 1.2 g L\({}^{-1}\). U (VI) stock solution (0.2 g L\({}^{-1}\)) was also prepared. Adsorption suspensions to perform adsorption experiment with different conditions were prepared by diluting the stock adsorbent suspension and U(VI) solution with distilled water. The adsorbent concentration in the adsorption suspension was 0.20 g L\({}^{-1}\) except for the adsorption experiment with different adsorbent doses. The initial U concentration of 10 mg L\({}^{-1}\) is selected to study the adsorption behavior of the GO-Fe MOF composite towards U(VI), which simulated the example of industrial effluents with a relatively high U concentration. The effect of pH on the adsorption efficiency was investigated by tuning the solution pH with a different concentration of HNO\({}_{3}\) or NaOH (0.01 mM\(\sim\)0.1 M), which guaranteed that the added amount of HNO\({}_{3}\) or NaOH was almost negligible in comparison with the volume of the adsorption solution. The pH modulation process was monitored by a pH meter. The adsorption efficiency of GO15-MIL-101(Fe) under different initial U concentrations (0.035 mg L\({}^{-1}\), 1.3 mg L\({}^{-1}\), 3 mg L\({}^{-1}\)) was also tested (pH = 5.5, T = 298 K). These concentrations took reference from a previous study [6]. The adsorption isotherms were achieved by performing adsorption experiment under different initial U(VI) concentrations (5 mg L\({}^{-1}\)-70 mg L\({}^{-1}\) with 5 mg L\({}^{-1}\) intervals) under pH = 5.5 at different temperatures (298 K, 313 K, 328 K). The pH of the adsorption suspensions was tuned to 5.5 at 298 K and then the adsorption solutions were placed in a shaker under different temperatures. Adsorption kinetics were performed at ambient temperature (pH = 5.5). The influence of coexisting ions (cations from NaNO\({}_{3}\), KNO\({}_{3}\), Mg(NO\({}_{3}\))\({}_{2}\), Ca(NO\({}_{3}\))\({}_{2}\) and anions from NaNO\({}_{3}\), NaCl, Na(SO\({}_{4}\))\({}_{2}\), and Na(CO\({}_{3}\))\({}_{2}\), the concentration was 0.01 M) towards the adsorption performance was further investigated. Particularly, the removal efficiency of U(VI) on GO15-MIL-101(Fe) and MIL-101(Fe) was compared in simulated surface water and groundwaterThe pH, composition, and related ion concentrations were determined based on previous studies (Table S1) [44]. The suspension was agitated for over 24 h to achieve equilibrium. The concentration of uranyl ions under equilibrium was confirmed by the Arsenazo III based colorimetric method. U (VI) can form a binary complex with Arsenazo III. The uranyl ion content was determined by measuring the absorbance of the complex at 656 nm. Samples with U(VI) concentration in ppb level were tested via inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. The adsorption percentage (Adsorption, %) and adsorption capacity (\(q_{e}\), mg g\({}^{-1}\)) can be obtained based on the following equations:  
\[\text{Adsorption = \frac{(C_{0}-C_{e})}{C_{0}}\times 100\%} \tag{1}\]  
\[q_{e}\ =\ \frac{(C_{0}-C_{e})\times V}{m} \tag{2}\]  
where, \(C_{0}\) (mg L\({}^{-1}\)) and \(C_{e}\) (mg L\({}^{-1}\)) correspond to the U(VI) concentration of the adsorption suspension at the beginning and equilibrium, respectively. \(V\) (mL) and \(m\) (g) are the solution volume and adsorbent dosage, respectively. Triplicate measurements showed that the relative errors were within 5%.