Fabrication of Zn-MOF/ZnO nanocomposites for room temperature H2S removal: Adsorption, regeneration, and mechanism

A MOF-on-MOF heterostructure ratiometric/colorimetric dual-mode fluorescence sensor based on support vector machine for detecting tetracyclines in animal-derived foods

The misuse of tetracyclines in livestock production poses significant health risks. Thus, establishing convenient detection methods to replace complex laboratory tests for food safety is crucial. In this study, a heterostructure Zn-BTC/IRMOF-3 (denoted as ZBI) asynchronous response fluorescence sensor was developed for the qualitative and quantitative detection of tetracyclines in foods. The ZBI solution exhibited blue fluorescence under UV excitation; upon the introduction of tetracyclines, ZBI selectively recognized the tetracycline molecules through electron transfer, π-π stacking, and chelation, resulting in blue fluorescence quenching and green fluorescence enhancement. The ZBI sensor for tetracycline detection achieved recovery rates ranging from 93.91 to 111.91% in food samples, with a detection limit of as low as 0.086 μmol/L. Lastly, a portable sensing device using support vector classifier was constructed for detecting tetracyclines in real-life scenarios. Our findings introduce a new approach for fabricating fluorescence sensors and offer a novel method for detecting tetracyclines.

In Situ Generatable and Recyclable Oxygen Vacancy-Modified Fe2O3-Decorated WO3 Nanowires with Super Stability for ppb-Level H2S Sensing

Detecting hydrogen sulfide (H2S) odor gas in the environment at parts-per-billion-level concentrations is crucial. However, a significant challenge is the rapid deactivation caused by SO42- deposition. To address this issue, we developed a sensing material comprising Fe2O3-decorated WO3 nanowires (FWO) with strong interfacial interaction. During the H2S sensing process, important oxygen vacancies (OVs) are generated in situ and are recyclable on the surface of the Fe2O3 cluster. This sensor achieves a response of 140 (Ra/Rg) toward 50 ppm of H2S at 250 °C, with an experimentally measured detection limit of 1 ppb. It also exhibits remarkable stability, with no significant change observed over a long period of 150 days. Based on a combination of in situ DRIFT and DFT calculations, we have identified that the overactivation of O2 is the key step in the formation of SO42-. This overactivation can be partially modulated by the synergistic effect of Fe2O3 decoration and the in situ generated OVs, regulating the oxidation product to SO2 rather than the toxic SO42-. Furthermore, the continuous generation of OVs compensates for the loss of active sites pertaining to SO42- deposition, thereby contributing to the excellent stability of the sensor. This study underscores the beneficial impact of in situ OV generation in FWO for H2S sensing, offering a dynamic strategy to enhance sensor performance, particularly in terms of stability.

Rational Design and Synthesis of Fe-Doped Co-Based Coordination Polymer Composite Photocatalysts for the Degradation of Norfloxacin and Ciprofloxacin

The solar light-responsive Fe-doped Co-based coordination polymer (Fe@Co-CP) photocatalyst was synthesized under mild conditions. [Co(4-padpe)(1,3-BDC)]n (Co-CP) was first constructed using mixed ligands through the hydrothermal method. Then, Fe was introduced into the Co-CP framework to achieve the enhanced photocatalytic activity. The optimal Fe@Co-CP-2 exhibited excellent catalytic degradation performance for norfloxacin and ciprofloxacin under sunlight irradiation without auxiliary oxidants, and the degradation rates were 91.25 and 92.66% in 120 min. These excellent photocatalytic properties were ascribed to the generation of the Fe-O bond, which not only enhanced the light absorption intensity but also accelerated the separation efficiency of electrons and holes, and hence significantly improved the photocatalytic property of the composites. Meanwhile, Fe@Co-CP-2 displayed excellent stability and reusability. In addition, the degradation pathways and intermediates of antibiotic molecules were effectively analyzed. The free radical scavenging experiment and ESR results confirmed that •OH, •O2-, and h+ active species were involved in the catalytic degradation reaction; the corresponding mechanisms were deeply investigated. This study provides a fresh approach for constructing Fe-doped Co-CP-based composite materials as photocatalysts for degradation of antibiotic contaminants.

Phosphorus removal from water by the metal-organic frameworks (MOFs)-based adsorbents: A review for structure, mechanism, and current progress

Efficacious phosphate removal is essential for mitigating eutrophication in aquatic ecosystems and complying with increasingly stringent phosphate emission regulations. Chemical adsorption, characterized by simplicity, prominent treatment efficiency, and convenient recovery, is extensively employed for profound phosphorus removal. Metal-organic frameworks (MOFs)-derived metal/carbon composites, surpassing the limitations of separate components, exhibit synergistic effects, rendering them tremendously promising for environmental remediation. This comprehensive review systematically summarizes MOFs-based materials' properties and their structure-property relationships tailored for phosphate adsorption, thereby enhancing specificity towards phosphate. Furthermore, it elucidates the primary mechanisms influencing phosphate adsorption by MOFs-based composites. Additionally, the review introduces strategies for designing and synthesizing efficacious phosphorus capture and regeneration materials. Lastly, it discusses and illuminates future research challenges and prospects in this field. This summary provides novel insights for future research on superlative MOFs-based adsorbents for phosphate removal.

Laser-Driven Rapid Synthesis of Metal-Organic Frameworks and Investigation of UV-NIR Optical Absorption, Luminescence, Photocatalytic Degradation, and Gas and Ion Adsorption Properties

In this study, we designed a platform based on a laser-driven approach for fast, efficient, and controllable MOF synthesis. The laser irradiation method was performed for the first time to synthesize Zn-based MOFs in record production time (approximately one hour) compared to all known MOF production methods with comparable morphology. In addition to well-known structural properties, we revealed that the obtained ZnMOFs have a novel optical response, including photoluminescence behavior in the visible range with nanosecond relaxation time, which is also supported by first-principles calculations. Additionally, photocatalytic degradation of methylene blue with ZnMOF was achieved, degrading the 10 ppm methylene blue (MB) solution 83% during 1 min of irradiation time. The application of laser technology can inspire the development of a novel and competent platform for a fast MOF fabrication process and extend the possible applications of MOFs to miniaturized optoelectronic and photonic devices.

Dual-Functional Manganese-Doped ZnO-MOF Hybrid Material with Enhanced Hydrolytic Stability: A Fluorescent Photoinduced Electron Transfer Sensor for the Ultraselective Detection of Acetic Acid and Chromium (VI)

In recent years, the synthesis of metal-organic framework (MOF)─nanocomposites has received wide attention from the scientific fraternity due to the presence of a tunable hierarchical architecture and invasive versatility in applications. The present work focuses on the solvothermal synthesis of a novel hybrid MOF-nanocomposite through the impregnation of Mn-doped ZnO nanoparticles onto the matrix of a pioneer metal-organic framework that is composed of zinc metal connected with terephthalic acid linkers (MOF-5). The hierarchical arrangements of the prepared material were further assessed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM), UV-visible, photoluminescence (PL), and dynamic light scattering (DLS) measurements. The porosity analysis via nitrogen sorption measurements at 77 K showed that the material is porous with hierarchical micro-, wide micro-, and mesopores. The SAED pattern confirms the polycrystallinity of the material, which is in good agreement with the data obtained from PXRD analysis. Effective integration of Mn-doped ZnO onto the MOF structure was confirmed by XPS analysis, and the study further identified the oxidation state of the elements present. The synthesized analyte is an efficient fluorescent chemosensor for the detection of acetic acid, which can find further potential applications in intracellular imaging. Interestingly, the same compound also selectively detects the presence of Cr(VI) ions, thereby acting as a dual sensor, which finds applications in the sensing and removal of environmental contaminants. The material showed a sharp and intense emission at 569 nm at an excitation wavelength of 320 nm, and it exhibits high quenching efficiencies of 99.87 and 71.43% toward the sensing of μM level concentration of acetic acid and Cr2O72-, respectively. The highly efficient fluorescent sensing of pollutants, even at a shorter linear range, discarded the possibility of sensing the pollutants at higher concentration ranges. The Ksv value for the detection of acetic acid and Cr(VI) is found to be 3.7017 × 106 and 11.0324 × 106 M-1, respectively, which further confirms the higher sensing ability of the synthesized fluorophore. The mechanistic studies and density functional theory calculations of Mn-doped ZnO@MOF-5 reveal that photoinduced electron transfer plays a significant role in the turn-off response toward acetic acid and Cr2O72- ions. In the case of acetic acid, in addition to photoinduced electron transfer, hydrogen bonding interactions may also lead to fluorescence quenching. To the best of our knowledge, no precedent work has been reported for the sensing of acetic acid in the solution state. All other fluorescent sensing reports put forward the sensing and adsorption of acetic acid in the gaseous state, which makes this material a pioneer among others for the detection of acetic acid in the solution phase.

Controllable synthesis of copper-organic frameworks via ligand adjustment for enhanced photo-Fenton-like catalysis

The efficient heterogeneous photo-Fenton-like catalysts based on two secondary ligand-induced Cu(II) metal-organic frameworks (Cu-MOF-1 and Cu-MOF-2) were constructed for the first time and investigated for the degradation of multiple antibiotics. Herein, two novel Cu-MOFs were prepared using mixed ligands by a facile hydrothermal method. The one-dimensional (1D) nanotube-like structure could be obtained by using V-shaped, long and rigid 4,4'-bis(3-pyridylformamide)diphenylether (3-padpe) ligand in Cu-MOF-1, while polynuclear Cu cluster could be prepared more easily by using short and small isonicotinic acid (HIA) ligand in Cu-MOF-2. Their photocatalytic performances were measured by degradation of multiple antibiotics in Fenton-like system. Comparatively, Cu-MOF-2 exhibited superior photo-Fenton-like performance under visible light irradiation. The outstanding catalytic performance of Cu-MOF-2 was ascribed to the tetranuclear Cu cluster configuration and excellent ability of photoinduced charge transfer and hole separation thus improved the photo-Fenton activity. In addition, Cu-MOF-2 showed high photo-Fenton activity in wide pH working range 3-10 and maintained wonderful stability after five cyclic experiments. The degradation intermediates and pathways were deeply studied. The main active species h⁺, O₂^- and OH worked together in photo-Fenton-like system and possible degradation mechanism was proposed. This study provided a new approach to design the Cu-based MOFs Fenton-like catalysts.

Adsorption of hydrogen sulfide by iron-based adsorbent derived from fly ash and iron slag

In this article, an innovative sorbent (Fe-FA) is prepared from fly ash; ferrous sulfate-containing waste slag (FSS), which are industrial wastes; and NaOH by a hydrothermal method at 100 °C. As a result, in comparison to several conventional sorbents, such as ZnO, Fe₂O₃, 13X zeolite, and activated carbon, Fe-FA had the best adsorption performance for H₂S adsorption. Fe-FA had not only a higher adsorption capacity (near 150 mg/g) but also a longer breakthrough time (near 400 min) when gas hourly space velocity was 8000 h^-1. Then, characterizations of XRD, BET, NH₃-TPD, FTIR, and XPS analyzed basic properties of Fe-FA and revealed reasons for the excellent adsorption performance. In general, the excellent adsorption performance of Fe-FA for H₂S is mainly due to the high content of iron species (almost 50%) and suitable mesoporous structure in the Fe-FA.

Synthesis of Mesoporous Silica Incorporated with Low Iron Concentration and Gelatin Co-Template via The Ultrasonication Method and Its Methylene Blue Photodegradation Performance

In this work, low iron concentration incorporated on mesoporous silica with gelatin co-template (Fe2O3/GSBA-15) has been successfully synthesized via the ultrasonication method. The physical, chemical, and structural properties of the samples were investigated with X-Ray Diffraction (XRD), Scanning Electron Microscope- Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infra-Red (FTIR), and N2 adsorption-desorption. Results showed good distribution of low concentration of iron oxide on the gelatin mesoporous silica GSBA-15. Elemental and surface analysis presented that iron oxide incorporation with higher concentration exhibited lower surface area due to the blocking pore. The highest photocatalytic activity on the methylene blue dye degradation was achieved at 10% Fe2O3/GSBA-15 with ~80% efficiency. The results revealed that the photocatalytic activity of Fe2O3/GSBA-15 enhanced with the presence of iron oxide. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Synthesis and characterization of ZnBTC-based MOFs: effect of solvents and salt

In this work, we studied the optimization of synthetic approaches to creating structurally modified metal-organic frameworks under various synthesis conditions. We investigated the influence of the various solvents and zinc salts on the structural characteristics of the metal-organic framework based on benzene-1,3,5-tricarboxylic acid (H3BTC). The results indicate that the variation of the types of both solvent and salt is a parameter affecting the crystallinity, phase purity, and morphology of the metal-organic framework. This was confirmed by comprehensive structural characterization (SEM, EDX, PXRD).

Enhanced degradation of sulfamethoxazole by non-radical-dominated peroxymonosulfate activation with Co/Zn co-doped carbonaceous catalyst: Synergy between Co and Zn

Bimetallic catalysts are often used for peroxymonosulfate (PMS) activation in recent years due to the synergistic effects between two different metal species. However, the synergy between Zn and other transition metal in PMS activation are rarely studied because of the ease of evaporation of Zn species at high temperature. In this work, a Co/Zn co-doped carbonaceous catalyst derived from ZIF-67@ZIF-8 (Z67@8D) was prepared successfully by the core-shell replacement strategy, and used to activate PMS for sulfamethoxazole (SMX) degradation. Due to the co-existence of Co/Zn species (e.g., Co/Zn-N site), Z67@8D showed a much higher catalytic activity than that of Z8D, Z67D, and several commercial oxides. Importantly, the CoZn synergy was deeply revealed by combining experiments and density functional theory (DFT) calculations, in which Zn could adjust the electron distribution of Co, reducing the PMS adsorption energy and thus enhancing PMS decomposition and singlet oxygen (¹O₂) formation. Moreover, formed ZnO and graphitic structure of Z67@8D could also promote the catalytic activity. In addition, the good stability and reusability, universal applicability, and high environmental robustness of Z67@8D were demonstrated. Our findings may provide a new insight into the Zn-based bimetallic catalysts for PMS activation and pollutant degradation.

Fabrication of HKUST-1/ZnO/SA nanocomposite for Doxycycline and Naproxen adsorption from contaminated water

Doxycycline and Naproxen are among the most widely used drugs in the therapy of CoVID 19 disease found in surface water. Water scarcity in recent years has led to research to treat polluted water. One of the easy and low-cost methods for treatment is adsorption. The utilize of Metal-Organic Frameworks (MOFs) to evacuate pharmaceutical contaminants from water sources has been considered by researchers in the last decade. In this research, HKUST-1/ZnO/SA composite with high adsorption capacity, chemical and water stability, recovery, and reuse properties has been synthesized and investigated. By adding 10 wt% of ZnO and 50 wt% of sodium alginate to HKUST-1, at 25 °C and pH = 7, the specific surface area is reduced by 60%. The parameters of drugs concentration C₀ =(5,80) mg/L, time=(15,240) min, and pH= (2,12) were investigated, and the results showed that the HKUST-1/ZnO/SA is stable in water for 14 days and it can be used in 10 cycles with 80% removal efficiency. The maximum Adsorption loading of doxycycline and Naproxen upon HKUST-1/ZnO/SA is 97.58 and 80.04 mg/g, respectively. Based on the correlation coefficient (R²), the pseudo-second-order and the Langmuir isotherm models were selected for drug adsorption. The proposed mechanism of drug uptake is by MOFs, hydrogen bonding, electrostatic bonding, and acid-base interaction.

Physical and chemical surface modification of carbon nanotubes for adsorptive desulfurization of aromatic impurities in diesel fuel

Due to some environmental problems of sulfur compounds, it is necessary to eliminate these impurities from hydrocarbon fuels. To achieve effective removal of aromatic sulfur compounds such as benzothiophene and dibenzothiophene, different surface modification of carbon nanostructures, physical and chemical surface modifications, were utilized to reach the adsorptive desulfurization and oxidative desulfurization processes. The acid treatment by H₂SO₄/HNO₃ and polymer-wrapping technique by polyethylene glycol were used for chemical and physical surface modification, respectively. Additionally, we tried to control the intensity and types of functional groups on the surface of carbon nanotubes. Besides, the efficiency of sulfur removal was measured. Both single-walled and multi-walled carbon nanotubes were utilized, and prepared samples have been investigated by FTIR, UV-Visible, TEM, Raman, and TGA techniques. The adsorption capacity values of each sample were evaluated by the temperature, time, and concentration parameters. The result shows that this surface modification can significantly improve the impurity removal of hydrocarbon fuel. Polymer-coated complexes showed higher removal values due to better dispersion than surface-oxidized carbon nanotubes. It was demonstrated that 90% of sulfur impurities with aromatic structure could be removed using an insignificant amount of the synthesized complex at moderate conditions. Besides, a comparison of laboratory data by conventional adsorption isotherms was investigated, and finally, the best operating conditions for maximum adsorbent performance were evaluated.

ZnO@MOF-5 as a Fluorescence "Turn-Off" Sensor for Ultrasensitive Detection as well as Probing of Copper(II) Ions

Recently, the synthesis, characterization, and structural evaluation of metal-organic framework (MOF) nanocomposites gain more attention due to the versatility in their applications. In the present work, the fluorescent active ZnO@MOF-5 composite was synthesized by encapsulating ZnO nanoparticles into the zinc terephthalate metal-organic framework (MOF-5). ZnO nanoparticles were prepared by a green method using the leaf extract of Annona muricata. Incorporation of ZnO nanoparticles onto the framework structure (ZnO@MOF-5) was done by a solvothermal method. The new composite material was characterized by Fourier transform infrared spectroscopy, Powder X-ray diffraction, Ultraviolet-visible spectroscopy, Transmission Electron Microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, Dynamic light scattering, Thermogravimetry-Differential Thermal analysis, and Photoluminescence spectroscopy. The material displayed blue fluorescence with a peak at 402 nm upon excitation at 282.46 nm. ZnO@MOF-5 showed a good fluorescence sensing efficiency toward the detection as well as probing of Cu(II) ions in aqueous solution. Sensing experiments performed revealed that as the concentration of copper ions in the solution increases, the quenching efficiency of the composite also increases. A quenching efficiency of 96.20% was achieved on reaching a concentration of 5 μM. The limit of detection for the sensing of Cu²⁺ ions was calculated to be 0.185 μM.

Synthesis of Nano-ZnO/Diatomite Composite and Research on Photoelectric Application

The key to the commercialization of sustainable energy conversion technologies is the development of high-performance catalysts. The discovery of a stable, efficient, and low-cost multi-function catalysts is the key. We used a simple green precipitation method to load nanozinc oxide particles onto a diatomite substrate. The ZnO is nano-sized. This precipitation method produces ZnO nanoparticles in situ on diatomite. The catalysts degraded 90% of Methylene blue solution and also degraded gaseous benzene and gaseous acetone. Not only can the catalysts be used for the organic degradation of wastewater, but it also has the potential to degrade volatile organic compounds. Photocatalytic efficiency is closely related to the generation and separation of photogenerated electrons and holes. The effective suppression of the recombination rate of photoliving carriers and thus improvement of the photocatalytic activity, has become a key research area. At present, photocatalysis is an effective technology to inhibit photogenerated carrier recombination, which is often studied in sewage treatment. Photoelectrochemical decomposition of water reduces the recombination of photogenerated electrons and holes by applying an external bias, thus improving the quantum efficiency for the complete mineralization of organic pollutants. The composite catalysts were used for oxygen and hydrogen extraction reactions, and a comparison of the catalysts with various loading ratios showed that the photoelectrochemical decomposition of water activity of the composite catalysts are due to pure ZnO, and the efficiency is highest when the loading ratio is 10%. This work provides new methods for the design and further optimization of the preparation of photoelectrochemical decomposition of water catalysts.

From MOF-199 Microrods to CuO Nanoparticles for Room-Temperature Desulfurization: Regeneration and Repurposing Spent Adsorbents as Sustainable Approaches

MOF-199 is one of the well-studied metal-organic frameworks (MOFs) for the capture of small gas molecules. In this study, we have investigated the thermal transformation of MOF-199 microrods to CuO nanoparticles by various microscopic and spectroscopic techniques. The growth of oxide was initiated by the formation of ∼2.5 nm particles at 200 °C, which ended up as CuO nanoparticles of ∼100-250 nm size at 550 °C. An intermediate presence of Cu2O along with CuO was recorded at 280 °C. The MOF and calcined products were tested for the room-temperature desulfurization process. MOF-199 showed the maximum adsorption capacity for H2S gas (77.1 mg g-1) among all adsorbents studied. Also, MOF-199 showed a better regeneration efficiency than the derived oxide. For a sustainable process, the exhausted adsorbents were used for the photocatalytic degradation of methylene blue. The exhausted materials showed better degradation efficiencies than the fresh materials. This study reports new sustainable approaches for MOF-199 application in air and water decontamination.

Metal organic framework derived NaCoxOy for room temperature hydrogen sulfide removal

Novel NaCoxOy adsorbents were fabricated by air calcination of (Na,Co)-organic frameworks at 700 °C. The NaCoxOy crystallized as hexagonal microsheets of 100-200 nm thickness with the presence of some polyhedral nanocrystals. The surface area was in the range of 1.15-1.90 m2 g-1. X-ray photoelectron spectroscopy (XPS) analysis confirmed Co2+ and Co3+ sites in MOFs, which were preserved in NaCoxOy. The synthesized adsorbents were studied for room-temperature H2S removal in both dry and moist conditions. NaCoxOy adsorbents were found ~ 80 times better than the MOF precursors. The maximum adsorption capacity of 168.2 mg g-1 was recorded for a 500 ppm H2S concentration flowing at a rate of 0.1 L min-1. The adsorption capacity decreased in the moist condition due to the competitive nature of water molecules for the H2S-binding sites. The PXRD analysis predicted Co3S4, CoSO4, Co3O4, and Co(OH)2 in the H2S-exposed sample. The XPS analysis confirmed the formation of sulfide, sulfur, and sulfate as the products of H2S oxidation at room temperature. The work reported here is the first study on the use of NaCoxOy type materials for H2S remediation.

Terephthalate and trimesate metal-organic frameworks of Mn, Co, and Ni: exploring photostability by spectroscopy

We report a rapid synthesis for the fabrication of terephthalate and trimesate metal-organic frameworks (MOFs) of Mn, Co, and Ni by ultrasonication of organic linkers with freshly prepared metal hydroxides. The MOFs were characterized by various microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. MOFs with low bandgap energy (1.88-2.73 eV) showed strong absorbance in the UV-visible range. MOFs were exposed to UV irradiation for 40 h to understand their photostability. The MOFs showed decreased surface area and porosity with CoBTC as an exception. PXRD was less convincing for exploring functional changes in the UV-irradiated MOFs. XPS predicted changes in the oxidation states of metal nodes, the degradation of the organic linkers, and decarboxylation process in many of the transition MOFs. The study predicted terephthalate-based MOFs as more photostable than corresponding trimesate-based MOFs. This study is one of the first attempts in exploring photostability of MOFs with Mn, Co, and Ni as nodes.