Rapid Synthesis of Cerium-UiO-66 MOF Nanoparticles for Photocatalytic Dye Degradation

An unprecedented synthesis method is used to form a series of Ce-UiO-66-X (X = NH2, OH, H, NO2, COOH) metal-organic frameworks by precipitation from mixed solvents, with instantaneous crystallisation on combining separate solutions of ligands and metal precursors. This allows the first direct synthesis of Ce-UiO-66-OH. Powder X-ray diffraction (PXRD) shows that all materials are pure phase with a broadened profile that indicates nano-scale crystallite domain size. The effect of different functional groups on the benzene-1,4-dicarboxylate linker within the UiO-66 structure has been investigated on degradation of two cationic (methylene blue and rhodamine B) and two anionic (Congo red, and Alizarin red S) dyes under UV and visible light irradiation at room temperature. Analysis of the dye adsorption in the absence of light is accounted for using pseudo-first order kinetics, and the Ce-UiO-66-NH2, Ce-UiO-66-OH, and Ce-UiO-66-H materials display a considerable photocatalytic activity to degrade Alizarin red S and Congo red rapidly between 1 and 3 minutes. The materials show excellent photostability and recyclability under UV and visible light, with no loss of crystallinity seen by PXRD and activity maintained over 5 cycles, with 16 hours photostability for Ce-UiO-66-NH2.

The chemical formula of the materials can be written as: Ce6O4(OH)4(BDC-X)6-N(OH)2N(H2O)2N(solvent)x Where solvent = DMF and water, and the ligand defects are charge balanced by hydroxide ions with additional water to complete the coordination sphere of Ce.
This can be written as: The UiO-66 mass loss to ~ 350°C is the elimination of the water and other solvent trapped in the pores and dehydroxylation of the clusters.
This assumes the charge is balanced by some retained oxide taking the place of linker defects, and the other oxygen sites are vacant.Upon continued heating the remaining hydroxide and the ligand is lost to yield CeO2 above 500 C.Note that continued heating gives further loss of oxygen to yield CeO2-x.
Thus, irrespective of the amount of solvent present initially the unknown value n can be determined from the mass losses at each step: the results are shown in Table 4 of the main text.4 of the main paper.
TOC analysis was performed using a Shimadzu analyzer.The clear solution remaining after photocatalytic degradation of 15 mg of Congo Red in 200 mL water using 25 mg of the material Ce-UiO-66-NH2 was analysed.
The initial carbon content of the Congo Red solution was equivalent to 8.27 mg in 200 mL (CR contains 55 % carbon by mass).
160 mL of the product solution was diluted with 800 mL deionised water for TOC analysis, and this gave a result of 1.66 ppm.
Therefore around 25 % of the original carbon is present in solution as soluble carbon species.The remainder may have been lost as CO2, or have been adsorbed by the MOF.

Figure S10 :
Figure S10: Thermogravimetric analysis of Ce-UiO-66-X materials measured in air (heating rate 10 o C min -1 ) with observed % mass losses indicated.The results of analysis are shown inTable 4 of the main paper.

Table S1a :
Details of the deconvolution of XPS spectra of Ce-BDC-NH2.

Table S1b :
Details of the deconvolution of XPS spectra of Ce-BDC-OH.

Table S1c :
Details of the deconvolution of XPS spectra of Ce-BDC-H

Table S1d :
Details of the deconvolution of XPS spectra of Ce-BDC-NO2

Table S1e :
Details of the deconvolution of XPS spectra of Ce-BDC-COOH

Table S2 :
Kinetic parameters of adsorption of cationic and anionic dyes by Ce-UiO-66-X.