Water depollution using metal-organic frameworks-catalyzed advanced oxidation processes: A review

Five naphthalene-amide-bridged Ni(ii) complexes: electrochemistry, bifunctional fluorescence responses, removal of contaminants and optimization by CVD

Five multifunctional Ni-CPs based on a new naphthalene-amide and different carboxylates were obtained and exhibited various properties. CNTs were synthesized from the precursors of CPs, showing selective removal of contaminants in water.

A comparative study in single- and binary-contaminant systems: the photodegradation of tetracycline and imidacloprid on flower-shaped Ag/AgBr/BiOBr under visible-light irradiation

A synergistic effect demonstrated in binary-contaminant systems is shown to be caused by the mutually complementary utilization of active species during photodegradation.

In situ growth of benzothiadiazole functionalized UiO-66-NH2 on carboxyl modified g-C3N4 for enhanced photocatalytic degradation of sulfamethoxazole under visible light

A newly-constructed hybrid photocatalyst with electron deficient units and an n–n heterojunction was synthesized to degrade antibiotics under visible light.

Iron-based metal-organic frameworks as novel platforms for catalytic ozonation of organic pollutant: Efficiency and mechanism

Developing new heterogeneous catalysts has attracted much attention and is of significant importance for the efficient catalytic ozonation of organic pollutant. Herein, for the first time, we explored four environmental-benign iron-based MOFs (Fe-MOFs) for the catalytic ozonation reaction. These Fe-MOFs were characterized by PXRD, FT-IR, SEM, XPS, N₂ sorption-desorption isotherms and chemisorbed-pyridine IR. All Fe-MOFs show high catalytic performances with their intrinsic Lewis acid sites (LAS). Furthermore, MIL-53(Fe) demonstrates the highest catalytic activity because of its largest amount of LAS and suitable porosity-derived attractive mass-transfer property. The Rhodamine B (RhB) degradation kinetic rate is calculated to be 5.76 min^-1 with MIL-53(Fe), while 1.82 min^-1 with MIL-88B(Fe), 1.40 min^-1 with MIL-101(Fe), 0.87 min^-1 with MIL-100(Fe) and 0.43 min^-1 of ozonation alone. The TOC removal in MIL-53(Fe)/O₃ system is 4 times higher than that of ozonation alone. MIL-53(Fe) displays acceptable reusability and stability after 5 cycles. Surface LAS of MIL-53(Fe) are the active sites for the ozone decomposition. Moreover, surface-adsorbed hydroxyl radical, superoxide radical and singlet oxygen are confirmed as the reactive oxygen species from ozone decomposition in MIL-53(Fe) suspension. This work offers new platforms for catalytic ozonation and may drive the development of MOFs-based catalytic ozonation for effective water treatment.

Cu@Co-MOFs as a novel catalyst of peroxymonosulfate for the efficient removal of methylene blue

In this study, for the first time, we describe the single step synthesis of a Cu particle-doped cobalt-based metal-organic framework (Cu@Co-MOF) using a hydrothermal method. The as-prepared materials were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy-energy disperse spectroscopy, thermogravimetry, and X-ray photoelectron spectroscopy, which confirmed the incorporation of zero-valent copper on the surface of the Co-MOFs. The heterogeneous catalytic activity of Cu@Co-MOFs was tested to activate peroxymonosulfate (PMS) for the removal of methylene blue (MB). The ratio of n(Cu)/n(Co) in the Cu@Co-MOFs showed a strong impact on the catalytic activity of the Cu@Co-MOFs, whereas a n(Cu)/n(Co) of 1 : 1 exhibited the best catalytic performance and obtained 100% MB removal within 30 min. The effects of initial pH, reaction temperature, PMS concentration, and catalyst dosages were investigated in this study. The stability and reusability of the Cu@Co-MOFs were also investigated. The results showed a low decline in the MB removal with the increase in cycle numbers, whereas 100% MB was removed by prolonging the reaction time. Heterogeneous reactions taking place in the pores and surface of the Cu@Co-MOFs played an important role in the generation of the sulfate radicals (SO4˙-) and hydroxyl radicals (·OH) that were the primary reactive species responsible for MB degradation.

A Review on the Synthesis and Characterization of Metal Organic Frameworks for Photocatalytic Water Purification

This review analyzes the preparation and characterization of metal organic frameworks (MOFs) and their application as photocatalysts for water purification. The study begins by highlighting the problem of water scarcity and the different solutions for purification, including photocatalysis with semiconductors, such as MOFs. It also describes the different methodologies that can be used for the synthesis of MOFs, paying attention to the purification and activation steps. The characterization of MOFs and the different approaches that can be followed to learn the photocatalytic processes are also detailed. Finally, the work reviews literature focused on the degradation of contaminants from water using MOF-based photocatalysts under light irradiation.

Exploring Local Disorder within CAU-1 Frameworks Using Hyperpolarized 129Xe NMR Spectroscopy

The sorption properties of metal-organic frameworks (MOFs) can be influenced by introducing covalently attached functional side chains, which make this subclass of porous materials promising for applications as diverse as gas storage and separation, catalysis, and drug delivery. The incorporation of side groups usually comes along with disorder, as the synthesis procedures rarely allow for one specific position among a larger group of equivalent sites to be selected. For a series of isoreticular CAU-1 frameworks, chosen as model compounds, one out of four positions at every linker is modified with equal probability. Here, we investigate the influence of this disorder on Ar sorption and ¹²⁹Xe nuclear magnetic resonance spectroscopy using hyperpolarized ¹²⁹Xe gas. Models used for predicting the pore dimensions as well as their distributions were derived from the unfunctionalized framework by replacing one proton at every linker with either an amino, an acetamide, or a methyl urea functionality. The resulting structures were optimized using density functional theory (DFT) calculations. Results from void analyses and Monte Carlo force field simulations suggest that for available Ar nonlocal DFT (NLDFT) kernels, neither the pore dimensions nor the distributions induced by the side-chain disorder are well-reproduced. By contrast, we found the ¹²⁹Xe chemical shift analysis for the shift observed at high temperature to be well-suited to develop a detailed fingerprint of the porosity and side-chain disorder within the isoreticular CAU-1 series. After calibrating the ¹²⁹Xe limiting shift of the amino-functionalized framework with DFT calculations, the downfield shifts for the other two derivatives are an excellent measure for the reduction of the accessible pore space and reveal a strong preference for the side chains toward the octahedral voids for both cases. We expect that the strategy presented here can be commonly applied to disorder phenomena within MOFs in the future.

Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals

Anthropogenic climate change, principally induced by the large volume of carbon dioxide emission from the global economy driven by fossil fuels, has been observed and scientifically proven as a major threat to civilization. Meanwhile, fossil fuel depletion has been identified as a future challenge. Lignocellulosic biomass in the form of organic residues appears to be the most promising option as renewable feedstock for the generation of energy and platform chemicals. As of today, relatively little bioenergy comes from lignocellulosic biomass as compared to feedstock such as starch and sugarcane, primarily due to high cost of production involving pretreatment steps required to fragment biomass components via disruption of the natural recalcitrant structure of these rigid polymers; low efficiency of enzymatic hydrolysis of refractory feedstock presents a major challenge. The valorization of lignin and cellulose into energy products or chemical products is contingent on the effectiveness of selective depolymerization of the pretreatment regime which typically involve harsh pyrolytic and solvothermal processes assisted by corrosive acids or alkaline reagents. These unselective methods decompose lignin into many products that may not be energetically or chemically valuable, or even biologically inhibitory. Exploring milder, selective and greener processes, therefore, has become a critical subject of study for the valorization of these materials in the last decade. Efficient alternative activation processes such as microwave- and ultrasound irradiation are being explored as replacements for pyrolysis and hydrothermolysis, while milder options such as advanced oxidative and catalytic processes should be considered as choices to harsher acid and alkaline processes. Herein, we critically abridge the research on chemical oxidative techniques for the pretreatment of lignocellulosics with the explicit aim to rationalize the objectives of the biomass pretreatment step and the problems associated with the conventional processes. The mechanisms of reaction pathways, selectivity and efficiency of end-products obtained using greener processes such as ozonolysis, photocatalysis, oxidative catalysis, electrochemical oxidation, and Fenton or Fenton-like reactions, as applied to depolymerization of lignocellulosic biomass are summarized with deliberation on future prospects of biorefineries with greener pretreatment processes in the context of the life cycle assessment.

Highly-oriented one-dimensional MOF-semiconductor nanoarrays for efficient photodegradation of antibiotics

Highly-oriented one-dimensional MOF-semiconductor nanoarrays were developed for the efficient photodegradation of antibiotics.