Direct Radiation Detection by a Semiconductive Metal–Organic Framework

Semiconductive metal–organic frameworks (MOFs) have attracted extraordinary research interest in recent years; however, electronic applications based on these emerging materials are still in their infancy. Herein, we show that a lanthanide-based semiconductive MOF (SCU-12) can effectively convert X-ray photons to electrical current signals under continuous hard X-ray radiation. The semiconductive MOF-based polycrystalline detection device presents a promising X-ray sensitivity with the value of 23.8 μC Gyair–1 cm–2 under 80 kVp X-ray exposure, competitive with the commercially available amorphous selenium (α-Se) detector. The lowest detectable X-ray dose rate is 0.705 μGy s–1, representing the record value among all X-ray detectors fabricated by polycrystalline materials. This work discloses the first demonstration of hard radiation detection by semiconductive MOFs, providing a horizon that can guide the synthesis of a new generation of radiation detection materials by taking the advantages of structural designability and property tunability in the MOF system

Unassisted Uranyl Photoreduction and Separation in a Donor–Acceptor Covalent Organic Framework

The donor–acceptor covalent organic framework (COF) TTT–DTDA (TTT = thieno­[3,2-b]­thiophene-2,5-dicarbaldehyde and DTDA = 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)­trianiline) was prepared and found to have long-lived excited states (>100 ms) characterized by transient absorption spectroscopy. These excited-state lifetimes were sufficient to perform the direct photoreduction of uranium at ppm concentration levels. The photoreduction of soluble uranyl species to insoluble reduced uranium products is an attractive separation for uranium, typically accomplished with sacrificial reagents and protective gases. In the case of TTT–DTDA, illumination in aqueous solutions containing only uranyl ions produced crystalline uranyl peroxide species ([UO2(O2)]) at the COF that were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy. The maximum absorption capacity of TTT–DTDA was found to be 123 mg U/g COF at pH 5 after 10 h of illumination in solutions devoid of sacrificial reagents or protective gases. The TTT–DTDA COF was recyclable and maintained high selectivity for uranium in competing ion experiments, which are necessary requirements for a practical uranium extraction strategy based on photochemical uranium reduction

Turn-up Luminescent Sensing of Ultraviolet Radiation by Lanthanide Metal–Organic Frameworks

Here, we report a series of two-dimensional lanthanide metal–organic frameworks Ln-DBTPA (where DBTPA = 2,5-dibromoterephthalic acid and Ln = Tb (1), Eu (2), or Gd (3)) showing a unique turn-up responsiveness toward ultraviolet (UV) radiation. The luminescence enhancement was derived from the accumulated radicals that can promote the intersystem crossing process. The compound 1 shows an ultralow detection limit of 9.1 × 10–9 J toward UV radiation, representing a new type of luminescent UV detectors

Reversible Amine-to-Imine Chemistry at a Covalent Organic Framework for Sustainable Uranium Redox Separation

The interconversion chemistry of amine-to-imine sites in a covalent organic framework (COF) was developed for the redox-based separation of uranium. Compared to traditional approaches using sacrificial reagents or material decomposition for the reduction and separation of uranium, amine-COF served as the electron donor and was regenerated repeatedly following the oxidation and uranium reduction/separation. The amine-COF, PI-3-AR, was formed from the sodium borohydride (NaBH4) reduction of the imine-linked COF, PI-3, prepared from the solvothermal synthesis of 1,3,5-triformyl benzene (TFB) and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)trianiline (TTA). PI-3-AR could be converted back to PI-3 via oxidative amination using an excess of the oxidant iodine, I2, or in the photochemical reduction of uranyl ions (UO22+). In consecutive photochemical uranium reduction and separation cycling experiments, the reduced amine COF, PI-3-AR, underwent: (i) oxidation alongside uranium photoreduction and deposition; (ii) acid treatment and uranium extraction; and (iii) NaBH4 reduction and material recovery. The COF, PI-3-AR, and novel separation process involving amine-to-imine interconversion effectively removed uranium (maximum adsorption = 278 mg U/g COF) and maintained >98% uranium recovery over five recycling steps at pH 4.0