Defect engineering-induced porosity in graphene quantum dots embedded metal-organic frameworks for enhanced benzene and toluene adsorption.

The emerging environmental issues necessitate the engineering of novel and well-designed nanoadsorbents for advanced separation and purification applications. Despite recent advances, the facile synthesis of hierarchical micro-mesoporous metal-organic frameworks (MOFs) with tuned structures has remained a challenge. Herein, we report a simple defect engineering approach to manipulate the framework, induce mesoporosity, and crease large pore volumes in MIL-101(Cr) by embedding graphene quantum dots (GQDs) during its self-assembly process. For instance, MIL-101@GQD-3 (Vmeso: 0.68 and Vtot: 1.87 cm3/g) exhibited 300.0% and 53.3% more meso and total pore volume compared to those of the conventional MIL-101 (Vmeso: 0.17 and Vtot: 1.22 cm3/g), respectively, resulting in 1.7 and 2.8 times greater benzene and toluene loading at 1 bar and 25 °C. In addition, we found that MIL-101@GQD-3 retained its superiority over a wide range of VOC concentrations and operating temperature (25-55 °C) with great cyclic capacity and energy-efficient regeneration. Considering the simplicity of the adopted technique to induce mesoporosity and tune the nanoporous structure of MOFs, the presented GQD incorporation technique is expected to provide a new pathway for the facile synthesis of advanced materials for environmental applications.

Ultrasonication-assisted synthesis of 2D porous MoS2/GO nanocomposite catalysts as high-performance hydrodesulfurization catalysts of vacuum gasoil: Experimental and DFT study.

In this study, a novel, simple, high yield, and scalable method is proposed to synthesize highly porous MoS2/graphene oxide (M-GO) nanocomposites by reacting the GO and co-exfoliation of bulky MoS2 in the presence of polyvinyl pyrrolidone (PVP) under different condition of ultrasonication. Also, the effect of ultrasonic output power on the particle size distribution of metal cluster on the surface of nanocatalysts is studied. It is found that the use of the ultrasonication method can reduce the particle size and increase the specific surface area of M-GO nanocomposite catalysts which leads to HDS activity is increased. These nanocomposite catalysts are characterized by XRD, Raman spectroscopy, SEM, STEM, HR-TEM, AFM, XPS, ICP, BET surface, TPR and TPD techniques. The effects of physicochemical properties of the M-GO nanocomposites on the hydrodesulfurization (HDS) reactions of vacuum gas oil (VGO) has been also studied. Catalytic activities of MoS2-GO nanocomposite are investigated by different operating conditions. M9-GO nanocatalyst with high surface area (324 m2/g) and large pore size (110.3 Å), have the best catalytic performance (99.95%) compared with Co-Mo/γAl2O3 (97.91%). Density functional theory (DFT) calculations were also used to elucidate the HDS mechanism over the M-GO catalyst. It is found that the GO substrate can stabilize MoS2 layers through weak van der Waals interactions between carbon atoms of the GO and S atoms of MoS2. At both Mo- and S-edges, the direct desulfurization (DDS) is found as the main reaction pathway for the hydrodesulfurization of DBT molecules.

Adsorption of cadmium using modified zeolite-supported nanoscale zero-valent iron composites as a reactive material for PRBs.

The main challenge in utilizing permeable reactive barriers (PRB) for remediation of metals-contaminated groundwater is determination of a proper low-cost reactive medium that can remove the desired contaminants simultaneously. In this study, the performance of different zeolite materials and nZVI-based adsorbents for cadmium (Cd) removal was compared. Further, a composite of the best nZVI and zeolite samples was synthesized with the removal efficiency of 20.6 g/kg and selected as the proposed adsorbent. Moreover, the characteristics of the composite were analyzed through different techniques (BET, XRF, XRD, FT-IR, FE-SEM and EDX). In addition, through kinetic and thermodynamic studies, the effect of temperature, pH, ionic strength and presence of other metal ions on Cd removal efficiency was investigated. According to the results, since sodium zeolite (NaZ) provides a large number of specific ion-exchange sites for decoration with nZVI, stabilizes nZVI, and prevents its aggregation and further leaching in the harsh environment, the NaZ-nZVI composite is capable of removing Cd by adsorption and is applicable in PRBs, and thus it seems that the aforementioned composite is a proper candidate for groundwater remediation from a wide range of metal ions.

A novel highly sensitive and selective H2S gas sensor at low temperatures based on SnO2 quantum dots-C60 nanohybrid: Experimental and theory study.

In this study, SnO2 quantum dots-fullerene (SnO2 QDs-C60) nanohybrid as novel sensing material was synthesized by a simple hydrothermal method. The structure and morphology of the synthesized sample were studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The prepared hybrid was used as gas sensors for detection of different gasses including 70 ppm H2S, 1% methane, and 1% propane at low temperatures of 100-200 °C. The results indicated that the SnO2 QDs-C60 nanohybrid has high response and high selectivity to 70 ppm H2S, 1% methane, and 1% propane gasses at low temperatures. The highest response (Rair/Rgas) of 66.0 and 5.4-70 ppm H2S and 1% methane gasses at 150 °C and the response of 2.7-1% propane at 200 °C were observed for the prepared nanohybrid gas sensor. Moreover, the prepared sensor showed a good selectivity toward H2S gas. Also, DFT calculations were used for studying the interaction of these gases with SnO2-C60. DFT results showed that H2S has the strongest interaction and the highest effect on band-gap variation which is in a good agreement with experimental results.

Facile synthesis of a SnO2@rGO nanohybrid and optimization of its methane-sensing parameters.

Stannic oxide nanoparticles and various compositions of SnO2@rGO (reduced graphene oxide) nanohybrids were synthesized by a facile hydrothermal method and utilized as chemiresistive methane gas sensors. To characterize the synthesized nanohybrids, BET (Brunauer-Emmett-Teller), XRD, FESEM, TEM, FTIR, and Raman techniques were used. Sensing elements were tested using a U-tube flow chamber with temperature control. To obtain the best sensor performance, i.e., the highest signal and the fastest response and recovery times, the sensing element composition, operating temperature, and gas flow rate were optimized. The highest response (change in resistance) of 47.6% for 1000 ± 5ppm methane was obtained with the SnO2@rGO1% nanohybrid at 150°C and a flow rate of 160sccm; the response and recovery times were 61s and 5min, respectively. A sensing mechanism was suggested, based on the experiments.