Recent progress of metal halide perovskite materials in heterogeneous photocatalytic organic reactions.

Photocatalytic technology is widely regarded as an important way to utilize solar energy and achieve carbon neutrality, which has attracted considerable attentions in various fields over the past decades. Metal halide perovskites (MHPs) are recognized as "superstar" materials due to their exceptional photoelectric properties, readily accessible and tunable structure, which made them intensively studied in solar cells, light-emitting diodes, and solar energy conversion fields. Since 2018, increased attention has been focused on applying the MHPs as a heterogeneous visible light photocatalyst in catalyzing organic synthesis reactions. In this review, we present an overview of photocatalytic technology and principles of heterogeneous photocatalysis before delving into the structural characteristics, stability, and classifications of MHPs. We then focus on recent developments of MHPs in photocatalyzing various organic synthesis reactions, such as oxidation, cyclization, C-C coupling etc., based on their classifications and reported reaction types. Finally, we discuss the main limitations and prospects regarding the application of metal halide perovskites in organic synthesis.

Open-Framework Vanadate as Efficient Ion Exchanger for Uranyl Removal.

The elimination of uranium from radioactive wastewater is crucial for the safe management and operation of environmental remediation. Here, we present a layered vanadate with high acid/base stability, [Me2NH2]V3O7, as an excellent ion exchanger capturing uranyl from highly complex aqueous solutions. The material possesses an indirect band gap, ferromagnetic characteristic and a flower-like morphology comprising parallel nanosheets. The layered structure of [Me2NH2]V3O7 is predominantly upheld by the H-bond interaction between anionic framework [V3O7]nn- and intercalated [Me2NH2]+. The [Me2NH2]+ within [Me2NH2]V3O7 can be readily exchanged with UO22+. [Me2NH2]V3O7 exhibits high exchange capacity (qm = 176.19 mg/g), fast kinetics (within 15 min), high removal efficiencies (>99%), and good selectivity against an excess of interfering ions. It also displays activity for UO22+ ion exchange over a wide pH range (2.00-7.12). More importantly, [Me2NH2]V3O7 has the capability to effectively remove low-concentration uranium, yielding a residual U concentration of 13 ppb, which falls below the EPA-defined acceptable limit of 30 ppb in typical drinking water. [Me2NH2]V3O7 can also efficiently separate UO22+ from Cs+ or Sr2+ achieving the highest separation factors (SFU/Cs of 589 and SFU/Sr of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO22+ and [V3O7]nn-, whereas the ion exchange rate is influenced by the mobility of UO22+ and [Me2NH2]+. Our experimental findings indicate that [Me2NH2]V3O7 can be considered as a promising uranium scavenger for environmental remediation. Additionally, the simulation results provide valuable mechanistic interpretations for ion exchange and serve as a reference for designing novel ion exchangers.

Modeling Uranyl Adsorption on MoS2/Mo2CTx Heterostructures Using DFT and BOMD Methods.

Uranium-bearing wastewaters exert a great threat to the ecological environment due to its high radiotoxicity level. The designing and fabrication of novel adsorption materials can be promoted for radionuclide elimination from wastewater. In this work, results from density functional theory and Born-Oppenheimer molecular dynamics simulations are reported for the uranyl adsorption behavior on the MoS2/Mo2CTx heterostructure in the gas phase and in an aqueous environment. Uranyl ions prefer to be adsorbed at deprotonated O sites on the Mo2COH surface and S sites on the MoS2 side of the heterojunctions, resulting in the formation of bidentate configurations. In addition to coordination interaction, H-bond and van der Waals interactions can also play an important role in binding configurations. More importantly, the oxidation state U(VI) can be reduced to U(V) and then to U(IV) caused by the strong reducibility of the Mo2COH surface at room temperature, whereas the uranyl complex can move freely on the MoS2 surface. However, the coordination number of U with respect to H2O in the first hydration shell on the Mo2COH surface remains unchanged and is found to be 3, which is similar to that on the MoS2 surface. This work provides novel nanosorbents for the removal of uranyl from wastewater. The present viewpoint provides valuable mechanistic interpretations for uranyl adsorption and will give a supplement to the experimental research.

Visible-Light Photocatalytic Aerobic C═C Bond Cleavage of Alkenes to Carbonyls by CsPbBr3 Nanocrystals.

Herein, we reported a facile and readily accessible visible-light-driven photocatalytic protocol to induce oxidative cleavage of C═C bonds to corresponding carbonyls using CsPbBr3 nanocrystals as photocatalysts. This catalytic system was applicable to a wide range of terminal and internal alkenes. Detailed mechanism studies indicated that a single-electron transfer (SET) process was involved in this transformation, wherein the superoxide radical (O2•-) and photogenerated holes played crucial roles. Additionally, DFT calculations revealed that the reaction was initiated by the addition of O2•- to the terminal carbon atom of the C═C bond and completed by releasing one molecular formaldehyde by the formed [2 + 2] intermediate; the latter conversion was a rate-determining process.

Accelerating Electrochemical Water Oxidation Activity by Tailoring Morphology and Electronic Structure of Nickel Organic Framework Nanoarrays with a Fe Etching Effect.

Fe-mediated nickel organic framework nanoarrays (NiFe-MOFs NAs) on carbon cloth were successfully constructed from ultrathin nanosheets via an etching effect. This strategy also combined the dissolution and coordination effect of acidic ligand (2,6-naphthalenedicarboxylic acid, NDC) to a self-sacrificial template of Ni(OH)2 NAs. Benefiting from the strong Fe etching effect, dense and thick brick-like Ni-NDC nanoplates were tailored into loose and ultrathin NiFe-NDC nanosheets with abundant squamous nanostructures, which were still tightly attached to carbon cloth. As a consequence, more coordinatively unsaturated metal sites (CUMSs) that served as active centers were exposed to accelerate oxygen production. Meanwhile, the electronic structure of active Ni centers was modulated by the incorporation of Fe atoms. The charge density redistribution between Ni and Fe ultimately optimized the energy barrier of the adsorption/desorption of oxygenated intermediates, promoting the kinetics for water oxidation.

Introducing a Synergistic Ligand Containing an Exotic Metal in Metal-Organic Framework Nanoarrays Enabling Superior Electrocatalytic Water Oxidation Performance.

Designing and fabricating well-aligned metal-organic framework nanoarrays (MOF NAs) with high electrocatalytic activity and durability for water oxidation at large current density remain huge challenges. Here the vertical NiFc-MOF NAs constructed from agaric-like nanosheets were fabricated by introducing a ligand containing an exotic Fe atom to coordinate with Ni ion using Ni(OH)2 NAs as a self-sacrificing template. The NiFc-MOF NAs exhibited superior water oxidation performance with a very low overpotential of 161 mV at the current density of 10 mA cm-2. Chronoamperometry was tested at an overpotential of 250 mV, which delivered an initial industrial-grade current density of 702 mA cm-2 and still remained at 694 mA cm-2 after 24 h. Furthermore, it possessed fast reaction kinetics with a small Tafel slope of 29.5 mV dec-1. The superior electrocatalytic performance can be ascribed to the structural advantage of vertically grown agaric-like NAs and the synergistic electron coupling between Ni and Fe atoms, namely, electron transfer from Ni to Fe atoms in NiFc-MOF NAs. The exposed density and valence state of active Ni sites were synchronously increased. Furthermore, the energy barrier for the adsorption/desorption of oxygenated intermediates was ultimately optimized for water oxidation. This work provides a novelty orientation to accelerate electrocatalytic performance of MOF NAs by introducing self-sacrificing templates containing one metal and synergistic ligand containing dissimilar metal.

Significantly enhanced photoluminescence and thermal stability of La3Si8N11O4:Ce3+,Tb3+ via the Ce3+ → Tb3+ energy transfer: a blue-green phosphor for ultraviolet LEDs.

A series of Ce3+-, Tb3+- and Ce3+/Tb3+-doped La3Si8N11O4 phosphors were synthesized by gas-pressure sintering (GPS). The energy transfer between Ce3+ and Tb3+ occurred in the co-doped samples, leading to a tunable emission color from blue to green under the 360 nm excitation. The energy transfer mechanism was controlled by the dipole-dipole interaction. The Ce3+/Tb3+ co-doped sample had an external quantum efficiency of 46.7%, about 5.6 times higher than the Tb-doped La3Si8N11O4 phosphor (8.3%). The thermal quenching of the Tb3+ emission in La3Si8N11O4:Tb,Ce was greatly reduced from 74 to 30% at 250 °C, owing to the energy transfer from Ce3+ to Tb3+. The blue-green La3Si8N11O4:0.01Ce,0.05Tb phosphor was testified to fabricate a warm white LED that showed a high color rendering index of 90.2 and a correlated color temperature of 3570 K. The results suggested that the co-doped La3Si8N11O4:Ce,Tb phosphor could be a potential blue-green down-conversion luminescent material for use in UV-LED pumped wLEDs.

YScSi4N6C:Ce3+-A Broad Cyan-Emitting Phosphor To Weaken the Cyan Cavity in Full-Spectrum White Light-Emitting Diodes.

On the basis of a rough rule of thumb that the difference in ionic radius for the interstitial cationic pair may affect the structure of some nitride and carbonitride compounds, a novel carbonitride phosphor, YScSi4N6C:Ce3+, was successfully designed. The crystal structure (space group P63mc (No. 186), a = b = 5.9109(8) Å, c = 9.67701(9) Å, α = ß = 90°, γ = 120°) was characterized by single-crystal synchrotron X-ray diffraction and further confirmed by powder X-ray diffraction and refined with Rietveld methods. Ce3+-doped YScSi4N6C shows a broad excitation band ranging from 280 to 425 nm and a broad cyan emission band peaking at about 469 nm upon excitation by near-UV light (400 nm). The mechanism of thermal quenching for this phosphor was also investigated. In addition, a white light-emitting diode (w-LED) was prepared by coating a near-UV chip (λem = 405 nm) with YScSi4N6C:Ce3+, ß-sialon:Eu2+ (green), and CaAlSiN3:Eu2+ (red) phosphors. It emitted a well-distributed warm white light with high color rendering index (CRI) of 94.7 and a correlated color temperature (CCT) of 4159 K. The special color rendering index R12 of the obtained white light was as high as 88. All of the results indicate that this novel phosphor can compensate for the cyan cavity and has potential applications in the full-spectrum lighting field.