UiO-66-NH2/Cu2O composite as an enhanced visible light photocatalyst for decomposition of organic pollutants

Highly Effective Generation of Singlet Oxygen by an Imidazole-Linked Robust Photosensitizing Covalent Organic Framework

Developing effective photosensitizers to initiate the generation of singlet oxygen (¹O₂) is of great significance in both chemistry and physiology. Herein, linking the photoactive porphyrin moieties by in situ-formed robust imidazole groups, a covalent organic framework (COF), PyPor-COF, was successfully designed and synthesized. Detailed characterizations reveal that it not only possesses high crystallinity, permanent porosity, and robust stability but also shows a semiconductive photoresponse activity. As demonstrated by electron paramagnetic resonance experiments, the COF can initiate the generation of ¹O₂ efficiently under visible-light irradiation, the efficiency of which is higher than that of the pristine porphyrin-based reactant and even higher than some commonly used commercially available photosensitizing agents. Anticancer experiments prove that it can efficiently trigger the production of ¹O₂ in a physiological environment. This work demonstrates that the imidazole-linked porphyrin-incorporated COF is a highly promising photosensitizer that can even be applied in photodynamic therapy.

Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

Green synthesis of MIL-100(Fe) derivatives and revealing their structure-activity relationship for 2,4-dichlorophenol photodegradation

MIL-100(Fe), a kind of iron-based metal-organic framework materials (MOFs), can be synthesized at room temperature or hydrothermal conditions, which are promising precursor materials for preparing photocatalysts to degrade some recalcitrant chlorophenols in industrial wastewater. However, the relationship between the structural characterization of MIL-100(Fe) derivatives and their photodegradation behavior of chlorophenol pollutants is still unclear. Thus, in this work, a porous Z-scheme α-Fe₂O₃/MIL-100(Fe) composite was successfully fabricated via partial-pyrolysis of MIL-100(Fe) precursor synthesized through green synthesis route, which was further used for degrading high-concentration of 2,4-dichlorophenol under visible-light illumination (λ > 420 nm). The effects of synthesis route and pyrolysis temperature of MIL-100(Fe) on the degradation efficiencies of as-derived materials for 2,4-dichlorophenol were investigated. The structure-activity relationship was illuminated in detail. Otherwise, the influence of several process factors, i.e., initial concentration and pH of the 2,4-dichlorophenol solution, catalyst dosage on the degradation efficiency of 2,4-dichlorophenol has also been performed. The removal efficiency of 2,4-dichlorophenol with the initial concentration of 100 mg L^-1 reached up to 87.65% under optimized conditions. Lastly, the possible mechanism was explored based on trapping experiments and some other characterization results. The study in this paper not only exhibited new insight into the modified α-Fe₂O₃ material with high photocatalytic activity but also provided a promising method for treating wastewater containing 2,4-dichlorophenol or other similar organic pollutants.

Applications of Metal-Organic Frameworks in Water Treatment: A Review

The ever-expanding scale of industry and agriculture has led to the gradual increase of pollutants (e.g., heavy metal ions, synthetic dyes, and antibiotics) in water resources, and the ecology and wastewater are grave problems that need to be solved urgently and has attracted widespread attention from the research community and industry in recent years. Metal-organic frameworks (MOFs) are a type of organic-inorganic hybrid material with a distinctive 3D network crystal structure. Lately, MOFs have made striking progress in the fields of adsorption, catalytic degradation, and biomedicine on account of their large specific surface and well-developed pore structure. This review summarizes the latest research achievements in the preparation of pristine MOFs, MOF composites, and MOF derivatives for various applications including the removal of heavy metal ions, organic dyes, and other harmful substances in sewage. Furthermore, the working mechanisms of utilizing adsorption, photocatalytic degradation, and membrane separation technologies are also briefly described for specific pollutants removal from sewage. It is expected that this review will provide inspiration and references for the synthesis of pristine MOFs as well as their composites and derivatives with excellent water treatment performance.

Visible Light Response Photocatalytic Performance of Z-Scheme Ag3PO4/GO/UiO-66-NH2 Photocatalysts for the Levofloxacin Hydrochloride

A Ag₃PO₄/GO/UiO-66-NH₂(AGU) composite photocatalyst was prepared by an ultrasonic-assisted in situ precipitation method. The optical property, structure, composition, and morphology of photocatalysts were investigated using UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive spectrometry, transmission electron microscopy, Fourier transform infrared spectroscopy, and charge flow tracking by photodeposition of Pt and PbO₂ nanoparticles. In comparison with Ag₃PO₄ and Ag₃PO₄/UiO-66-NH₂(AU), the AGU composite photocatalyst showed heightened photocatalytic performance for the degradation of levofloxacin hydrochloride (LVF). The AGU photocatalyst (dosage: 0.8 g/L) with 1% mass content of graphene oxide (GO), the mass ratio of Ag₃PO₄ and UiO-66-NH₂(U66N) reached 2:1, showed the highest photodegradation rate of 94.97% for 25 mg/L LVF after 60 min of visible light irradiation at pH = 6. The formation of a heterojunction and the addition of GO synergistically promote faster separation of electron-hole pairs, retain more active substances, and enhance the performance of the photocatalyst. Furthermore, the mechanism of the Z-scheme of the AGU composite photocatalytic is proposed.

High-sensitivity optical fiber hydrogen sensor based on the metal organic frameworks of UiO-66-NH2

A hydrogen sensor with high sensitivity was demonstrated by coating the metal organic frameworks of ${\rm{UiO}}\! -\! {\rm{66 \!-\! N}}{{\rm{H}}_2}$ on an optical fiber Mach-Zehnder interferometer (MZI). The MZI was made of a fiber mismatch structure by using a core-offset fusion splicing method. The effective refractive index of the ${\rm{UiO}}\! -\! {\rm{66\! -\! N}}{{\rm{H}}_2}$ film varied with the absorption and release of hydrogen, and the interference resonant dip wavelength and the intensity of the MZI changed with the variations of the concentration of hydrogen. The experimental results showed that the proposed sensor had a high hydrogen sensitivity of 8.78 dB/% in the range from 0% to 0.8%, which is almost seven times higher than the existing similar hydrogen sensor.