Graphene oxide wrapped copper-benzene-1,3,5-tricarboxylate metal organic framework as efficient absorbent for gaseous toluene under ambient conditions

CuBTC Metal-Organic Framework Decorated with FeBTC Nanoparticles with Enhance Water Stability for Environmental Remediation Applications

Metal-organic frameworks (MOFs) based on Cu-benzene tricarboxylate (CuBTC) are widely used for gas storage and removal applications. However, they readily lose their crystal structures under humid conditions, limiting their practical applications. This structural decomposition reduces the specific surface area, gas adsorption capability, and recyclability of CuBTC considerably. In this study, a stable MOF against water exposure was designed based on FeBTC nanoparticle-covered CuBTC (FeCuBTC). A simple one-pot solvothermal process that enables the epitaxial growth of FeBTC on the CuBTC surface was proposed. Structural and morphological analyses after water exposure revealed that the water stability of FeCuBTC was better than that of CuBTC, which completely lost its crystallinity. This observed improvement in the water stability of the synthesized MOF proved to be beneficial for the adsorption of formaldehyde under humid conditions. The proposed strategy herein is simple yet highly effective in the design of hetero-bimetallic MOFs with considerably improved water resistance and extended applicability for environmental remediation processes.

Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough".

Graphene-based porous nanohybrid architectures for adsorptive and photocatalytic abatement of volatile organic compounds

Volatile organic compounds (VOCs) represent a considerable threat to humans and ecosystems. Strategic remediation techniques for the abatement of VOCs are immensely important and immediately needed. Given a unique set of optical, mechanical, electrical, and thermal characteristics, inimitable surface functionalities, porous structure, and substantial specific surface area, graphene and derived nanohybrid composites have emerged as exciting candidates for abating environmental pollutants through photocatalytic degradation and adsorptive removal. Graphene oxide (GO) and reduced graphene oxide (rGO) containing oxygenated function entities, i.e., carbonyl, hydroxyl, and carboxylic groups, provide anchor and dispersibility of their surface photocatalytic nanoscale particles and adsorptive sites for VOCs. Therefore, it is meaningful to recapitulate current state-of-the-art research advancements in graphene-derived nanostructures as prospective platforms for VOCs degradation. Considering this necessity, this work provides a comprehensive and valuable insight into research progress on applying graphene-based nanohybrid composites for adsorptive and photocatalytic abatement of VOCs in the aqueous media. First, we present a portrayal of graphene-based nanohybrid based on their structural attributes (i.e., pore size, specific surface area, and other surface features to adsorb VOCs) and structure-assisted performance for VOCs abatement by graphene-based nanocomposites. The adsorptive and photocatalytic potentialities of graphene-based nanohybrids for VOCs are discussed with suitable examples. In addition to regeneration, reusability, and environmental toxicity aspects, the challenges and possible future directions of graphene-based nanostructures are also outlined towards the end of the review to promote large-scale applications of this fascinating technology.

Antibacterial properties of recoverable CuZnO@Fe3O4@GO composites in water treatment

The growth of bacteria will lead to water quality deterioration and equipment damage. Therefore, it is necessary to control the growth and reproduction of microorganisms in water treatment. A new type of magnetic recoverable CuZnO@Fe3O4@GO composites was prepared by ultrasonic method, and the composites were characterized and analyzed by SEM, TEM, XPS, and other methods. The optimum mass ratio of composites was determined by orthogonal experiment, and the antibacterial properties and mechanism of the composite were investigated by gram-positive bacteria Staphylococcus aureus and gram-negative bacteria Escherichia coli. Finally, the antibacterial properties of the composites in the effluent of the secondary sedimentation tank were researched. It was shown that the optimum mass ratio of the composites was GO:Fe3O4:CuZnO =1:2:3. When the dosage of composites was 180 mg L-1 and the action time was 100 min, the antibacterial rate against S. aureus and E. coli reached more than 99.5%. The composites could destroy the cell structure of two kinds of bacteria, increase the content of active oxygen in bacteria cells, and enhance the leakage rate of protein by more than 9 times in 150 min, thereby causing the death of the bacteria. And the antibacterial rate of the composites in effluent of the secondary sedimentation tank could reach 99%, and the magnetic recovery rate could reach more than 98%. After 5 cycles of use, the antibacterial rate could still exceed 90%.

Isotherm, kinetic, and thermodynamic studies for dynamic adsorption of toluene in gas phase onto porous Fe-MIL-101/OAC composite

In the present paper, micro-mesoporous Fe-MIL-101/OAC composite using in situ incorporation of Fe-MIL-101 into oxidized activated carbon was synthesized and characterized by XRD, FT-IR, SEM, EDS, and BET techniques. The adsorption performances of toluene onto adsorbents in the gas phase were studied using a laboratory-scale dynamic adsorption system under moist ambience. The toluene adsorption capacity of Fe-MIL-101/OAC composite and Fe-MIL-101 were 127 and 97.6 mg g^-1, severally. Results revealed that the larger pores in micro-mesoporous Fe-MIL-101/OAC enhanced the molecular diffusion rate. The findings indicated that micro-mesoporous structures played key roles in the capture of toluene molecules. The initial toluene concentration positively affected on toluene adsorption capacity while temperature and humidity negatively affected on toluene adsorption capacity. The Langmuir model and the pseudo-second-order kinetics model described better adsorption process of Fe-MIL-101/OAC composite. Thermodynamic findings determined that toluene adsorption over Fe-MIL-101/OAC was spontaneous, exothermic physisorption. The regeneration of the composite was still up to 72.6% after six cycles. The micro-mesoporous Fe-MIL-101/OAC composite proposes a promising support for the high toluene removal for future. Graphical abstract.

MOFs-carbon hybrid nanocomposites in environmental protection applications

The demand for green engineering environmentally friendly nanomaterials had made carbon nanotube a suitable material to keep metal-organic frameworks (MOFs) in the application of wastewater treatment and air pollution monitoring systems. This review summarizes many of the recent research accomplishments in the synthesis of MOFs and MOFs-carbon hybrid nanocomposites for various applications such as wastewater treatment and removal of hazardous gases (CO, SO₂, H₂S and NH₃) with emphasis on MOF/CNTs composites. This review focuses on the efficient removal of pollutants from the environment using adsorption techniques. Another important application of MOFs composite discussed in this review is sensor materials for environmental pollution.

Synergetic effect between adsorption and photodegradation on rGO/TiO2/ACF composites for dynamic toluene gaseous removal

The toluene poses a serious threat to the atmospheric environment and human health. Herein, the reduced graphene oxide (rGO)/TiO₂ immobilized on the activated carbon fiber (ACF) are fabricated by ultrasonic assisted sol-gel impregnation method to photodegrade dynamic toluene. Characterizations of rGO/TiO₂/ACF composites reveal that the majority of graphene oxide (GO) is reduced to rGO and rGO/TiO₂ is evenly loaded onto the ACF surface in the form of a smooth film. Furthermore, the photoelectrochemical experiments demonstrate both rGO and ACF can enhance significantly the separation efficiency of electron-hole pairs. The maximum removal efficiency of rGO/TiO₂/ACF-0.75% can be up to 85% under ultraviolet irradiation. The rGO/TiO₂/ACF exhibits more excellent adsorption and photodegradation activity for dynamic toluene than both rGO/TiO₂ and ACF due to the synergetic effect rather than a simple linear combination of the rGO/TiO₂ and ACF for toluene conversion. The possible photodegradation pathway is proposed according to intermediates measured by GC-MS, and adsorption coupling photocatalytic mechanisms are discussed.

Synthesis and application of Cu-BTC@ZSM-5 composites as effective adsorbents for removal of toluene gas under moist ambience: kinetics, thermodynamics, and mechanism studies

Metal organic frameworks (MOFs) are excellent adsorbents that provide abundant specific surface area, adjustable pore structure, and rich active sites. The purpose of this study was to prepare composites with hydrophobic and high microporous specific surface area and to adsorb toluene gas in moist ambience. An ethanol activation-assisted hydrothermal method was proposed to synthesize copper-benzene-1,3,5-tricarboxylic acid (Cu-BTC) metal-organic framework, Cu-BTC, and ZSM-5 molecular sieve composites (Cu-BTC@ZSM-5). The dynamic adsorption process of toluene on different adsorbents was investigated, and the results showed that the toluene adsorption capacity of Cu-BTC@ZSM-5 (158.6 mg/g) was 2.53 times higher than Cu-BTC (62.7 mg/g), when the ZSM-5 content is 5% and the humidity is 30%RH. Compared with other factors, the humidity inhibited the adsorption of toluene on Cu-BTC@ZSM-5. Langmuir model and the pseudo-second kinetics model can better describe the adsorption behavior of Cu-BTC@ZSM-5. The thermodynamic results showed the adsorption process was a spontaneous exothermic process at low temperature and mainly physical adsorption. The relative regenerability can still up to 80.4% after six cycles. The adsorption mechanisms of Cu-BTC@ZSM-5 were pore-filling adsorption, π-π interaction, cation-π bonding, and hydrophobic interactions. This study will help to design a systematic route to evaluate the adsorption performance of Cu-BTC@ZSM-5 for toluene.