The economic feasibility of electrocatalytic carbon dioxide reduction reaction (CO2RR) relies on developing highly selective and efficient catalysts operating at a high current density. Herein, we explore a ligand-engineering strategy involving the use of metal–organic frameworks (MOFs) and combining the desirable features of homogeneous and heterogeneous catalysts for boosting the activity of CO2RR. Zn-based MOFs involving two different azolate functional ligands, i.e., 1,2,4-triazole (Calgary Framework 20, CALF20) and 2-methylimidazole (zeolitic imidazolate framework-8, ZIF-8), were investigated for CO2RR in an alkaline flow cell electrolyzer. The highest CO partial current density of −53.2 mA/cm2 was observed for a Zn-based MOF (CALF20). CALF20 showed the highest reported Faradaic efficiency of Zn-based MOFs for CO production (∼94% at −0.97 V versus reversible hydrogen electrode, RHE), with a turnover frequency (TOF) of 1360.8 h–1 and a partial current density of −32.8 mA/cm2. Experimental and density functional theory (DFT) results indicate that the sp2 carbon atoms in azole ligands coordinated with the metal center in MOFs are the active sites for CO2RR due to the fully occupied 3d orbital of Zn­(II) centers. Ab initio investigation shows that both azolate frameworks in CALF20 and ZIF-8 have the most favorable adsorption sites at the N–sp2 C. Adopting the triazole ligand in CALF20 enhances the charge transfer (as compared with the diazole group in ZIF-8), which induces more electrons in the adjacent active sites at the azole ligand and facilitates *COOH formation, boosting current density and Faradaic efficiency toward CO production. This study suggests that ligand engineering in MOFs could be a viable approach to design a highly efficient CO2RR catalyst.

Using Quinolin-65 (Q-65) as a model-adsorbing compound for polar heavy hydrocarbons, the nanosize effect of NiO nanoparticles on the adsorption of Q-65 was investigated. Different-sized NiO nanoparticles with sizes between 5 and 80 nm were prepared by the controlled thermal dehydroxylation of Ni(OH)2. The properties of the nanoparticles were characterized using XRD, BET, FTIR, HRTEM and TGA. The effects of the nanosize on the textural properties, the shape and the morphology were studied. The adsorption of Q-65 molecules onto different-sized nanoparticles was tested in toluene-based solutions. On a normalized surface area basis, the number of Q-65 molecules adsorbed per nm(2) of the NiO surface was the highest for NiO nanoparticles of size 80 nm, while that for 5 nm sized NiO nanoparticles was the lowest. Excitingly, the adsorption capacity of other NiO sizes varied from loading suggesting different adsorption behavior, which exhibits the significance of textural properties during the adsorption of Q-65. Computational modeling of the interaction between the Q-65 molecule and the NiO nanoparticle surface was carried out to get more understanding of its adsorption behavior. A number of factors contributing to the enhanced adsorption capacity of nanoscale NiO were determined. These include surface reactivity, topology, morphology and textural properties.

Please cite this article in press as: Nassar, N.N., et al., Treatment of olive mill based wastewater by means of magnetic nanoparticles: Decolourization, dephenolization and COD removal. Environ. Nanotechnol. Monit. Manag. (2014), http://dx. a b s t r a c tOlive mill wastewater (OMW) is an environmental concern that has been highlighted as a serious environmental problem in the Mediterranean basin countries because of its high organic load and phytotoxic and antibacterial phenolic compounds, which resist biological degradation. Consequently, this type of wastewater represents a huge challenge for the conventional wastewater treatment techniques as it can impact the lifetime of bacteria needed for the treatment. Iron-oxide nanoparticles are attractive for wastewater treatment for two important reasons. First, nanoparticles can remove pollutants from wastewater rapidly. Second, this magnetic type of nanoparticles could be separated easily using a magnet after finishing treatment process. In this study, we aimed at investigating the effectiveness of the magnetic iron oxide nanoparticles in the removal of large organic contaminants from OMW. Batch and continuous mode processes were applied on OMW treatment to determine the effect of contact time, solution pH, coexisting contaminants and the adsorption isotherm.The results showed that the adsorption was fast and the adsorption reached equilibrium within less than 30 min. The adsorption equilibrium data fit very well to the Brunauer-Emmett-Teller (BET) Model, indicating multi-layers adsorption. The adsorption of major pollutants was associated to an efficient removal of coexisting contaminants such as heavy metals and free ions. The adsorption of OMW pollutants was dependent on pH of the solution. Finally, continuous-mode process was tested successfully using a packed bed column that combined sand filtration with magnetic nanoparticles to decolourize OMW effluent. This study will provide valuable insight on the effect of nanoparticles toward the treatment and recyclability of olive mill wastewater, which is crucial for the local olive mill industry. After seeing the successful achievement of integrating nanoparticles with fixed bed filtration, a preliminary process description and cost estimation of stand-alone plant (with a capacity of 4 m 3 /h) for OMW treatment were considered in this study. Process capital and annual operating costs were estimated to be $12,306 and $476/year, respectively.

Over the last few years, nanoparticles have been used as thermal enhancement agents in many heat transfer based fluids to improve the thermal conductivity of the fluids.

Industrial activities lead to a substantial share of current anthropogenic CO 2 emissions and are some of the most challenging to abate. Direct utilization of industrial flue gases to produce fuels or value-added chemicals is challenging due to the presence of impurities and low concentrations of CO 2 . Herein, we demonstrate a rational assembly of a permselective gas diffusion electrode (PGDE) for direct CO 2 conversion from quasi flue gas (i.e., 10−15% CO 2 , 4% O 2 , and N 2 balance at 100% relative humidity). The electrode design consists of a metal−organic framework (MOF) based mixed matrix membrane (MMM) that enables the selective permeation of CO 2 to a silver electrocatalyst. The MOF is CALF-20, notable for the ability to physisorb CO 2 in wet gas streams. Applying this approach, we convert N 2 -diluted CO 2 streams to CO at a faradaic efficiency of 95% compared to 58% for the nonmodified counterpart electrode with MMM. The PGDE retained its electrochemical performance when introducing O 2 by preventing ∼84% loss of current toward parasitic oxygen reduction reaction (ORR) and reported 30 mA cm −2 CO partial current density. Further, wetting the gas stream showed a negligible effect on the MOF and the electrochemical performance. Using our PDGE, we report nearly constant CO selectivity over 19 h in a membrane electrode assembly electrolyzer. This approach offers the potential for direct utilization of low-concentration CO 2 while avoiding the economic and environmental costs of obtaining purified CO 2 feedstocks.

The nanosize effects of NiO nanosorbcats on adsorption and post‐adsorption catalytic thermo‐oxidative decomposition of vacuum residue (VR) n‐C5 asphaltenes was investigated using a UV‐vis spectrophotometer and thermogravimetric analyzer coupled with a mass spectrometer. Sizes between 5 and 80 nm of different‐sized NiO nanosorbcats were employed. Batch adsorption experiments were carried out for the considered asphaltenes in toluene solutions, monitored via UV‐vis spectrophotometry. The macroscopic adsorption isotherms were described by implementing the solid‐liquid equilibrium (SLE) model. The findings showed that thermally cracked vacuum residue (VR) n‐C5 asphaltenes interact to different extents with different‐sized NiO nanosorbcats. A normalized surface area basis was used for the amount of VR n‐C5 asphaltene adsorbed per nm2 of NiO surface, which was the highest for NiO nanoparticles of size 80 nm, with 5 nm size being the lowest. Thermogravimetric analysis of VR n‐C5 asphaltenes was also achieved and the reaction products were explored by a mass spectrometer. The Kissinger‐Akahira‐Sunose (KAS) isoconversional model was used to describe the reaction mechanism and to confirm the validity of the catalytic role of the different particle sizes of NiO nanosorbcats. The highest catalytic activity was for smallest NiO when compared to the highest NiO nanosorbcats. Furthermore, the results of thermodynamic transition state parameters of activation; changes in Gibbs free energy (ΔG‡), entropy (ΔS‡), and enthalpy (ΔH‡) highlighted the catalytic activity of NiO nanosorbcats towards VR n‐C5 asphaltenes oxidation. These findings exhibit the significance of textural properties and nanosize of nanoparticles during adsorption and thermal catalytic processing of asphaltenes.

Magnetic iron-oxide nanoparticles exhibit high efficiency in wastewater treatment for many important reasons, including that they can remove contaminants from wastewater rapidly owing to their high external surface area/unit mass and interstice reactivity. Additionally, this type of iron oxide can easily be separated using a magnet after finishing the treatment process, can be used as a catalyst for the decomposition of adsorbed contaminants and thus reduce sludge formation, and can cost-effectively meet the environmental regulations for wastewater treatment since it can be prepared in situ where treatment is needed via various techniques. In this study, we use magnetic iron oxide nanoparticles for dye removal from synthetic and real textile wastewater for the first time. The effects of different experimental parameters on dye removal, such as contact time, initial concentration, solution pH, and coexisting ions, were investigated. Computational modelling of the interaction of different dye molecules with different surfaces of g-Fe 2 O 3 nanoparticles is performed to obtain more mechanistic insights on the adsorption behaviour. The results showed that dye adsorption was fast, as external adsorption was dominated. The adsorption equilibrium data fit very closely to the Langmuir adsorption isotherm model, confirming monolayer adsorption, which is supported by the adsorption computational calculations. The adsorption was spontaneous, endothermic, and physical in nature.

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