Highly Sensitive Detection of UV Radiation Using a Uranium

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Highly Sensitive Detecting of UV Radiation using a Uranium Coordination Polymer Wei Liu, Xing Dai, Jian Xie, Mark Silver, Duo Zhang, Yanlong Wang, Yawen Cai, Juan Diwu, Jian Wang, Ruhong Zhou, Zhifang Chai, and Shuao Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17954 • Publication Date (Web): 08 Jan 2018 Downloaded from http://pubs.acs.org on January 8, 2018

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ACS Applied Materials & Interfaces

Highly Sensitive Detecting of UV Radiation using a Uranium Coordination Polymer Wei Liu,†§ Xing Dai,†§ Jian Xie,†§ Mark A. Silver,† Duo Zhang,† Yanlong Wang,† Yawen Cai,† Juan Diwu,† Jian Wang,‡ Ruhong Zhou,† Zhifang Chai,† Shuao Wang†* †

School for Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medi-

cine of Jiangsu Higher Education Institutions, Soochow University, 199 Ren’ai Road, Suzhou 215123, China ‡

Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun

130023, China KEYWORDS: Uranium coordination polymer; Photoluminescence; UV detection; Radical; DFT calculation ABSTRACT: The accurate detection of UV radiation are required in a wide range of chemical industries, environmental and biological related applications. Conventional methods taking advantage of semiconductor photodetectors surfer from several drawbacks such as sophisticated synthesis and manufacturing procedure, not being able to measure the accumulated UV dosage as well as high defect density in the material. Searching for new strategies or materials serving as precise UV dosage sensor with extremely low detection limit is still highly desirable. In this work, a radiation resistant uranium-organic framework [UO2(L)(DMF)] (L = 5Nitroisophthalic acid, DMF = N,N-Dimethylformamide, denoted as compound 1) was successfully synthesized through mild solvothermal method and investigated as a unique UV probe with the detection limit of 2.4 × 10-7 J. Based on the UV dosage dependent luminescence spectra, EPR analysis, single crystal structure investigation and the DFT calculation, the UV-induced radical quenching mechanism was confirmed. Importantly, the generated radicals are of significant stability which offers the opportunity for measuring the accumulated UV radiation dosage. Furthermore, the powder material of compound 1 was further upgraded into membrane material without loss in luminescence intensity to investigate the real application potentials. To the best of our knowledge, compound 1 represents the most sensitive coordination polymer based UV dosage probe reported up to date. extensive explorations owing to its rich structural chemistry INTRODUCTION and great application potential.22, 23 These materials could Ultraviolet radiation is widely used in chemical industries, readily be functionalized by tuning the organic linkers or metsuch as curing and photolithography, sterilization, surface al nodes that lead to distinctive host-guest chemistry. Particumodification technique and so forth,1-3 but can exhibit either larly, luminescent CPs or MOFs are emerging as a new class positive or negative impacts on human health. For instance, of luminescent platforms since the exploding development of UV radiation is crucial for assisting human skin to produce pure organic and inorganic luminescent materials has ocVitamin D that is necessary in physiological processes.4 Excurred.24, 25 These luminescent materials exhibit abundant discessive doses of UV radiation, however, impose great damage tinctive luminescence properties that could be viewed as a on the human body and may result in the development of cumajor innovation in the next generation of illumination and taneous malignant melanoma (CMM) and non-melanoma skin optical sensing or imaging materials.26-29 Among these are the 5 cancer (NMSC), leading to premature skin-aging and eye most widely studied MOF based chemical sensors for detectdisorders.6, 7 Besides these physical impacts, developing effiing heavy metal ions,30, 31 small molecules,32 toxic gases33 and cient UV photodetectors is also highly desirable in automotive, so forth, which are based on the pre-designed interaction beaerospace, environmental, and biological researches.7 Currenttween the adsorbed guest molecules and the framework. Two ly, various techniques have been developed to detect UV radimajor classes of luminescent CPs or MOFs are lanthanideation both qualitatively and quantitatively. The most develbased and d-block metal-bearing. The luminescence of these oped semiconductor photodetectors, including metalCPs or MOFs originates from either the transitions inside the semiconductor-metal (MSM) detectors,8 PIN photodiodes 4f shell of the lanthanide centers or the π-π*/n-π* transitions detectors,9 p-n junction diodes,10 and Schottky-barrier detecfrom the organic linkers. tors,11 often suffer from several disadvantages, such as sophisUranium, the most critical 5f element in the nuclear fuel cyticated synthesis and manufacturing procedure, not being able cle, is chosen in this work as the metal center based on the to measure the accumulated UV dosage as well as high defect following considerations. First, depleted uranium is an abundensity in the material. The latter greatly lowers the detection dant long-half-life radioactive by-product of the nuclear power sensitivity and efficiency.12 Luminescent methods show many industry that receives limited studies in luminescent coordinaadvantages over traditional detectors in terms of sensitivity, tion polymer systems compared with other metals. Secondly, 13 response time, and cost. However, this strategy was not welluranyl luminescence originating from the HOMO-LUMO developed until recently likely because of the shortage of UVtransition of hybridized molecular orbitals often exhibits responsive luminescent materials.14-21 brighter emission and more efficient absorption of UV light Coordination polymers or metal-organic frameworks (CPs than trivalent lanthanides owing to the non Laporte-forbidden or MOFs) are a class of crystalline materials which attract nature which greatly extends the detection limit.34 Thirdly,

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given the 5f/6d orbitals of uranyl are deeply involved in coordination, the luminescence is highly sensitive to the coordination environment, which affords more opportunities for developing detection ability (i.e. more efficient energy transfer).35 However, this system is substantially under-explored. The only two cases of uranyl-based compounds were reported for detection including our recent work on ionizing radiation detection and nitroaromatics detection based on a turn-off manner,36, 37 which initially confirmed the potential application of this class of luminescent materials in sensing. In this work, we introduce a uranyl-organic framework [UO2(5-NIPA)(DMF)] (5-NIPA = 5-Nitroisophthalic acid, DMF = N,N-Dimethylformamide, denoted as compound 1) to the application of UV radiation detection to be the first actinide material used in such aspect. Compound 1 exhibits great resistance to radioactivity which is not often observed in polymer materials.38 Interestingly, the luminescence of the material rapidly decreases when subjected to 365 nm UV light, the sensitivity of which can be witnessed from the detection limit of 2.4 × 10-7 J. This qualifies 1 to be the most sensitive coordination polymer based UV dosimeter.14-21, 39 The mechanism for this distinct luminescence behavior correlates with a radicalinduced quenching effect that empowers 1 with the ability to monitor UV radiation via photoluminescence as a result.

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iments were achieved using a RS-2000 Pro Biological Irradiator equipped with Cu Kα radiation at a dose rate of 72 Gy/hour. Synthesis: The material is synthesized based on our recently reported procedure.40 0.0502 g of UO2(NO3)2·6H2O, 0.0211 g H2L (L = 5-Nitroisophthalic acid, named as 5-NIPA), 0.0120 g H3BO3 and 5 ml mixed solvent (VH2O : VDMF (ml) = 2 : 3) were added into a 10 ml vials. The vials were then sealed and heated to 100 oC for 12 h and cooled to room temperature under ambient condition. Yellowish strip crystals were isolated as a pure product. Elemental analysis results: calculated C, 24.05 %; N, 5.34 %; H, 2.08 %; found C 24.03%; N, 5.27%; H, 1.92%. compound 1’, C, 19.00 %; N, 3.05 %; H, 1.69 %. X-ray Crystallography Studies: Single crystal X-ray diffraction data collection was accomplished on a Bruker D8-Venture diffractometer with a Turbo X-ray Source (Mo–Kα radiation, λ = 0.71073 Å) adopting the direct-drive rotating anode technique and a CMOS detector at 273 K. The data collection was carried out using the program APEX3 and processed using SAINT routine in APEX3. The structure of 1 was solved by direct methods and refined by the full-matrix least squares on F2 using the SHELXTL-2014 program. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms attached to carbon atoms were placed in geometrically idealized positions. Crystallographic data of 1 are summarized in Table S1 and S2. UV detection experiments: The UV detection experiment was carried out on a single crystal of compound 1. The luminescence spectra were collected after exposure the single crystal for various 365 nm UV dosage. DFT computational details: According to the experimentally obtained crystalline structure, we constructed a finite scale UO22+-2(C6H5COO-)-(CH3)2NCOH fragment, referred to as uranyl-5-NIPA-DMF, as the computational model. This model can reasonably simulate the local coordination environment of the uranyl center. As the chemical composition of the material was not changed before and after UV irradiation, we here considered the triplet DMF as the DMF• radical. The isolated ground state DMF (singlet), DMF• radical (triplet), the complexes of uranyl-5-NIPA-DMF (singlet), and uranyl-5NIPA-DMF• (triplet) were fully optimized at B3LYP/SDD~631G* level using Gaussian 09 program.41 The Becke three parameters hybrid exchange-correlation functional (B3LYP) was employed.42, 43 To consider the scalar relativistic effect, the Stuttgart/Dresden relativistic effective core potential (60 core electrons) and its corresponding valence basis set (32 valence electrons) were used for U atom.44, 45 The standard Gaussian-type 6-31G(d) basis set was used for C, N, O and H atoms.46 For accurately investigating the electronic structure, especially of the molecular orbital energy levels, of the two coordination complexes, higher precision single-point energy calculations based on the optimized geometries were performed using ADF program.47 In ADF calculations, the spinorbit relativistic effect was considered by zero order regular approximation (ZORA).48, 49 The statistical average of orbital potential (SAOP),50 an asymptotically correct exchangecorrelation potential) was employed for accurately calculating the energy levels. The all-electron relativistic triple-zeta with polarization (TZP) basis set was used for all atoms.51 Test strip development: A piece of adhesive tape was carefully clipped into 5 cm × 5 cm square and anchored to the

EXPERIMENTAL SECTION Materials and instrumentations: All reagents and solvents were purchased from commercial suppliers and used as received without further purification. The elemental analyses (C, H, and N) were carried with a Vario EL CHNOS elemental analyzer. Powder X-ray diffraction (PXRD) data were collected from 5° to 50° with a step of 0.02° and data collection time of 0.2 s on a Bruker D8 Advance diffractometer with Cu Kα radiation (λ=1.54056 Å) and a Lynxeye one-Dimensional detector. The ATR-FTIR spectra of the samples without KBr were recorded in the range of 3000-400 cm-1 by a Thermo Nicolet iS 50 spectrometer. Scanning electron microscopy images and energy-dispersive spectroscopy data (SEM/EDS) were recorded on a FEI Quanta 200FEG Scanning Electron Microscope with the energy of the electron beam being 30 keV. Samples were mounted directly on the carbon conductive tape with Au coating. The single crystal solid-state photoluminescence and UV-vis absorption spectra were recorded on a Craic Technologoes microspectrophotometer. Crystals were placed on quartz slide, and data was collected after auto-set optimization. When the 365 nm excitation light was selected, an optical filter masking signal below 420 nm was applied in order to mask the interference of excitation light. The photoluminescence spectra bulk samples were collected on FLS 980 Spectrometer. Thermalgravimetric (TG-DSC) analysis was carried out on a NETZSCH STA 449 F3 Jupiter instrument in the range of 30 - 900 °C under a nitrogen flow at a heating rate of 10 °C/ min. The electron paramagnetic resonance (EPR) data was characterized on a Bruker EMX-10/12 analyzer for compound 1 in the range of 300-500 mT at 100 K. Large dose γ-ray irradiation experiments were conducted using a 60Co irradiation source (60000 curie) with a dose rate of 1.2 kGy/hour. Low dose γ-ray irradiation experiments were performed using a 137Cs irradiator (Gammacell 1000 Elite/3000 Elan) with a dose rate of 285 Gy/hour. X-ray irradiation exper-


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ACS Applied Materials & Interfaces glass plane. Then, 30 mg of the finely ground powder of compound 1 was painted to the adhesive tape uniformly. Another piece of adhesive tape was used to cover the exposed powder of 1. The double layered strip was then peeled from the glass matrix and moved to a pressure device under 15 kg/cm2 for 10 hours. The resulting strips were reserved in a lucifuge vessel.

continuous exposure to light at 365 nm, the luminescence of 1 began to dramatically decrease in intensity, as depicted in Figure 2a. In order to quantitatively investigate this UVquenching process, we calculate the quenching ratio in 1 [denoted as (I0-I)/I0 %, where I0 is the initial luminescence intensity, I is the luminescence intensity after irradiation by UV light and the UV radiation dosage]. The luminescence intensity of 1 was reduced to approx. 22.4% of the original intensity when exposed to a ca. 1.1 × 10-2 mJ of UV radiation (Figure 2b). Emission was almost completely quenched upon exposure of 3.3 × 10-2 mJ of UV light. Quenching in 1 could even be observed with the naked eye as shown in Figure 2c. These results provide evidence that 1 may be used as a hypersensitive detection material. The limit of the detection in 1 can be determined by the following equations: DT = 3σ/k (1) σ = 100 × (ISE/I0) (2) where the detection limit noted as DT; ISE represents the standard error of the luminescence intensity (as determined by the baseline measurement of blank samples monitored at λExc = 512 nm); I0 is the measured initial luminescence intensity of 1; k is the slope obtained from the linear fit in the lower dosage range of the dosage-dependent luminescence intensity calibration curve. Based on the acquired data, the detection limit was determined to be 2.4 × 10-7 J which indicates the powerful detection capacity of 1.53

RESULTS AND DISCUSSIONS Structure elucidation. Single crystal X-ray diffraction studies revealed that 1 crystallizes in the triclinic space group, P 1 . As shown in Figure 1, the overall structure can be described as a series of stacked neutral 1D chains. Each uranium(VI) cation in 1 adopts a typical seven-coordinate pentagonal bipyramids, where five equatorial oxygen atoms come from one DMF, one bidentate L2-, and two monodentate L2- molecules. The asymmetric unit contains one crystallographically unique UO22+ unit, one L2- and one DMF molecule (Figure 1a and b). The U−O bond lengths are in the range of 2.31-2.45 Å and the axial U=O bond distances are 1.746 and 1.768 Å which correspond well with previously reported metrics for seven-coordinate uranyl(VI) materials.52 L2- ligand pairs bridge two UO22+ cations into a dimer, while chelation of a third UO22+ cation extends infinite neutral uranyl-L chains down the [101] axis. DMF molecules coordinate on either edge of the chains (Figure 1d). The distance between two adjacent chains is about 3.41 Å based on the inward facing benzene rings. Significant parallel πstacking results between aromatic rings of L2- ligands from nearby chains forming flat sheets, as shown in the Figure 1d. These sheets then stack on each other to form a pseudolayered structure.

Figure 2. a) UV dosage dependent luminescence spectra of 1 performed on a single crystal to showing the quenching effect under 365 nm UV light. b) The correlation between the quenching ratio and radiation dosage. Inset is the corelation between D/[(I0I)/I0%] and the UV dosage c) is the corresponding luminescence photographs of a single crystal after received continuous UV radiation.

Figure 1. Crystal structure depictions of 1, hydrogen atoms are omitted for clarity: a) Coordination environment of uranium(VI). b) Asymmetric unit of [UO2(L)(DMF)]. c) The 1D metal-organic chain of 1 composed by 5-Nitroisophthalic acid linked asymmetric units. d) The pseudo-layered structure comprising 1D chains coalescing due to π···π interactions. Atom colors: U = green, O = red, C = black, N = blue.

In fact, the phenomenon of photoluminescence quenching induced by UV light is rarely reported in CPs or MOFs systems, especially for uranium-bearing materials. We were further motivated to determine if different kinds of radiation with higher energy (e.g. X-ray and γ-ray) could cause similar

UV dosage dependent luminescence spectra. The ability to detect UV radiation was initially observed when collecting the photoluminescence spectrum of a single crystal of 1. After



quenching of the luminescence in 1. In sharp contrast to our recently reported uranyl-based MOF sensor that can respond to UV, X-, and γ-ray radiations, the photoluminescence of 1 remained unaffected by low dose X- and γ-ray radiations (Figure S1 and Figure S2). As shown in Figure S3 and S4, only when the radiation dose reached between 100 Gy and 100 kGy of either X- or γ-ray was there any observable decrease in luminescence intensity. This selective quenching property is best understood as a function of the ability of 1 to absorb these different kinds of radiation.35 Additionally, the n→π* and π→π* transitions in the carbonyl groups and benzene ring, respectively, largely contribute to the absorption of UV light (Figure S10). The efficiency to generate radicals is enhanced under UV radiation in 1, which directly results in the different quenching features observed for these ionizing radiations.

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the most possible mechanism that results in optical emission quenching should be the energy transfer from the uranyl center to nearby generated radicals in the structure. Solvent exchange experiments were conducted to understand the aforementioned energy transfer mechanism. Preparing a DMF-free sample (1’) was achieved by immersing the crystals of 1 in methanol for three days with agitation. The FT-IR sprectum shown in Figure S6 displays the absence of stretching bands at 1,654.3 cm-1 (the C=O stretch),56 indicating that successful exchange had occured. Corroborative conclusions can be drawn from elemental analysis results show that the molar ratio of nitrogen in 1’ was reduced compared to that of 1 (7.1% residual N atoms attributed to DMF molecules). Subsequent irradiation experiments reveal that 1’ exhibits less sensitivity toward UV radiation. The initial emission intensity in 1’ was quenched by 15.4%, compared to 77.6% in 1, after recieving 1.1 × 10-2 mJ of UV radiation (Figure S8). This slight quench of the photoluminescence in 1’ could be induced by the residual DMF molecules in the framework which were not completely exchanged. On the other hand, the generated radicals exhibit stable characteristic in the framework as can be confirmed by the time-dependent luminenescence intenisty meaurments, which is important for indicating the accumulated UV dose (Figure S9). Identification of the role of DMF radicals (DMF•) in this energy transfer mechanism may provide impactful evidence for other areas of chemistry outside of our own.

Figure 3. a) PXRD patterns for samples irradiated with UV, 100 Gy X-ray and 100 kGy γ-ray radiation. b) The EPR spectra of 1 before and after UV, 100 Gy X-ray, 100 kGy γ-ray radiations.

Figure 4. a) The optimized geometry structure and bond parameters of ground state DMF molecule. b) The optimized geometry structure, bond parameters (left) and net spin density (right) of triplet DMF• radical. c) and d) The simulated radicalfree and radical-bearing coordination structures of the fragment, named as uranyl-5-NIPA-DMF and uranyl-5-NIPA-DMF•, respectively. Bond parameters are labeled below each structures.

Investigation of the quenching mechanism. The ability for the higher energy radiation to degrade the framework is an additional phenomenon that was speculated to occur in 1. However, PXRD data and FT-IR and Raman spectra illustrate the integrity of the framework remains intact throughout these radiation experiments. The quenching process is by no means an effect of the collapse of the structure (Figure 3a and Figure S5 - S7). Hence, the radical quenching mechanism was taken into consideration based on recent findings on photochromic MOFs.35, 54 EPR analysis (Figure 3b) confirms the presence of the radicals in those samples irradiated with high doses of either UV, X-, or γ-ray radiation.16, 55 Therefore,

DFT calculation. Computational analyses were employed to explain the radical-induced energy transfer mechanism that occurs in irradiated samples of 1. To do so, the ground state structures of both DMF and DMF• were investigated using DFT in order to understand how this change affects the quench-inducing molecule. In the ground state (Figure 4a), the calculated C1-O3 bond distance in DMF is about 1.220 Å


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ACS Applied Materials & Interfaces by coordination ligand.53 When the uranyl ions are coordinated by 5-NIPA and DMF ligands, the energy gap between HOMO and LUMO increased to about 4.60 eV (Figure 5b). In consequence, the location of the uranyl emission peaks will exhibit a blue shift requiring greater energy to promote the transitions. The generated DMF• radical can only slightly influence the energy gap between HOMO and LUMO (4.56 eV, Figure 5c). This can explain why the emission peak position of uranyl doesn’t change in 1 before and after irradiation, since the energy requirements of electronic transitions are closer. However, the difference comes from the appearance of four impurity energy levels near the LUMO, including two single electron occupied states and two single electron unoccupied states. These four impurity energy levels actually are the two single occupied orbitals and two unoccupied orbitals of the DMF• radical. Hence, we can reasonably conclude here that these impurity energy levels could disturb or even prevent electronic excitation and back-moving between HOMO and LUMO, and thus quench the luminescence of uranyl. This quenching effect will increase with the accumulation of DMF• radicals in the structure, thereby decreasing the luminescence intensity in proportion to the dosage of UV radiation.

with a bond order of 1.83. This corresponds to a C=O bond comprising one σ bond and one π bond. In contrast, the C1-O3 bond distance in DMF• increased to about 1.314 Å resulting in a bond order of 1.14 (Figure 4b, left), which is more characteristic of a C–O bond. Spin density analysis (Figure 4b, right) revealed the presence of spin-polarized p-electrons on both C1 and O3 atoms that supports the division of the C1-O3 π bond. In this condition, the oxygen atom greatly activated and atypical behavior is accessible. As comparison to the DFT calculation results, we investigated the crystal structure of the same single crystal before and after radiation. Interestingly, C1-O3 bond length increased from 1.253 to 1.268 after 100 kGy of γ radiation which corresponds to the increasing effect observed by DFT calculation. These results indicate that the radical is generated on the C-O bond in DMF molecules. The calculated O3-U coordination length in the simulated radical-free fragment (uranyl-5-NIPA-DMF, Figure 4c) is 2.456 Å. As expected, the coordination distance of O3-U containing the activated O3 in DMF• radical shortened to 2.366 Å in the simulated radical-bearing fragment (uranyl-5-NIPA-DMF•, Figure 4d), indicating the stronger interaction between the DMF• radical and uranyl center.

Figure 6. Luminescence photographs of the test strips made from 1 showing the space resolution recognition of UV radiation. a) Left to right: the original strip under daylight, under low energy UV light, after partially receiving 1.2 J of UV radiation. b) Left to right: the original strip under daylight, under UV light, after being partially exposed to sunlight for 1 hour.

According to these interesting features, the bulk powder material of 1 was further developed into testing strips to explore the potential application under real environments. As depicted in Figure 6a, the initial strips exhibit light yellow color under daylight while uniform green luminescence under UV radiation. However, when the selected circle area received accumulated UV radiation for 3 minutes, a dark speckle appeared which is indicative of the quenching effect of 1 by UV light. On the other hand, another piece of test strip was used to detect UV radiation from sunlight. As shown in Figure 6b, after exposure under sunlight for an hour, the selected exposure area exhibits a similar quenching phenomenon as of that under UV light, which further illustrates that 1 is highly sensitive and can be used to monitor UV radiation at very low dose levels.

Figure 5. Density of states (DOS) of a) the isolated uranyl molecule, b) the uranyl-5-NIPA-DMF complex and c) the uranyl5-NIPA-DMF• complex. The gray-filled and empty areas below DOS curves indicate the occupied and unoccupied states, respectively. For each DOS, the lowest unoccupied U(5f) orbital is normalized at 0 eV for convenience.

In order to further understand how the DMF radicals influence the luminescence property of 1, the electronic structures of the isolated uranyl molecule (UO22+), the simulated radicalfree and radical-bearing skeletons were investigated by density of states (DOS) analyses and are shown in Figure 5 (the lowest unoccupied U(5f) orbital is normalized into 0 eV). As for the isolated uranyl, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LOMO) shown are the U-O σ bond and U(5f) empty orbital (Figure 5a), respectively, which is in agreement with the previous reported values.53 The calculated HOMO-LUMO energy gap of the isolated uranyl is about 3.01 eV. Generally, the origin of luminescence of uranyl is recognized as the electronic transitions between HOMO and LUMO and rarely affected

CONCLUSIONS

In summary, a highly stable uranium-organic framework was successfully synthesized through solvothermal method that exhibits superior sensing property. The intrinsic luminescence of 1 could be quenched by UV which makes it suitable for monitoring UV radiation. The radical-induced quenching



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mechanism confirmed by EPR, X-ray crystallography, and DFT calculations studies corroborate this property of 1. Importantly, these radicals exhibit great stability which makes it possible for this property of 1 to persist despite receiving a significant dose of radiation. At last, powder of 1 was also developed into a membrane material without any loss in luminescence intensity or character which further confirms the applicability of this material to UV detection. This work provides us new opportunity for searching powerful UV responsive materials by taking advantage of efficient UV light asbsorber (uranyl) as metal center. We further noticed that many other uranyl hybrid materials constructed from different types of ligands and solvents may enxibit similar properties, which can be therefore fine tuned by varying uranyl coordiation enviorments, crystal structures, and chemical constituents (e.g. light sensitizer), and the systematic investigations are in progress. We also believe this work offers new insight into methods in which depleted uranium may be reused for beneficial purposes.

ASSOCIATED CONTENT Supporting Information Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]

Notes The authors declare no competing financial interest.

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. §The first three authors contributed equally.

ACKNOWLEDGMENT This work was supported by grants from the National Science Foundation of China (21422704, 21790370, 21790374, 21761132019, and U1532259), the Science Challenge Project (JCKY2016212A504), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and "Young Thousand Talented Program" in China.

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