Remarkable adsorption of hydroquinone as an anion contaminant by using the magnetic supported bimetallic (NiCu-MOF@MAC) nanocomposites in aqueous solutions

The purposes of this work were to synthesize the core-shell magnetic and nonmagnetic supported bimetallic metal-organic frameworks (MOFs) on the walnut-based activated carbon by the facile preparation method to investigate the feasibility of the performance adsorption of hydroquinone in the aqueous solutions. Activated carbon as a substrate and nickel, copper, and trimesic acid were employed in the structure of the prepared MOFs. The adsorbents were characterized by XRD, FTIR, FESEM, EDX, TEM, BET, and VSM analysis. The goethite and magnetite phases were detected in the morphology of the magnetic adsorbent as confirmed by the XRD pattern. Increases in the pH value from 6 and the adsorption temperature led to a lower adsorption capacity of the samples. The maximum adsorption capacity for the well-dispersed nanoparticles of magnetic (NiCu-MOF@MAC and nonmagnetic (NiCu-MOF@AC) was calculated to be 303.03 and 454.54 mg/g by using linear Langmuir isotherm as an appropriate model, respectively. The achievements from the reusability evaluation illustrated that the magnetic bimetallic MOF nanocomposite could successfully be applied to remove hydroquinone from the wastewater on an industrial scale. The kinetic experimental data was in good agreement with the pseudo-second-order model.

Effect of Small Molecular Organic Acids on the Structure and Catalytic Performance of Sol–Gel Prepared Cobalt Cerium Oxides towards Toluene Combustion

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and tartaric acid (TA), were selected. The effect of organic acids on the composition, structure, morphology and catalytic performance of metal oxides is discussed in details. The cobalt cerium oxides catalysts were characterized by various techniques, including TG–DSC, XRD, SEM–EDS, N2–adsorption and desorption, XPS, and H2–TPR analyses. The results show that the nature of organic acids influenced the hydrolysis, condensation and calcination processes, as well as strongly affected the textural and physicochemical properties of the metal oxides synthesized. The best catalytic activity was obtained with the CoCe–MA catalyst, and the toluene conversion reached 90% at 242 °C. This outstanding catalytic activity could be related to its textural, redox properties and unique surface compositions and oxidation states. In addition, the CoCe–MA catalyst also showed excellent stability in long–time activity test.

Modeling, optimization and experimental studies of supported nano-bimetallic catalyst for simultaneous total conversion of toluene and cyclohexane in air using a hybrid intelligent algorithm

This study reveals the simultaneous deep oxidation of toluene and cyclohexane over optimal supported bimetallic catalysts over almond shell based activated carbon. To the best of our knowledge, this study is the first to construct a hybrid intelligent model to predict and determine an optimal supported bimetallic catalyst to oxidize aromatic and aliphatic compounds in air. The effects of preparation and operating parameters, including oxidation temperature, initial concentration of VOCs, structure of the catalyst and metal oxide content, on VOCs conversion were studied by modeling a database containing 50 data points derived from our previously published study, by an artificial neural network (ANN). Reported experimental data were predicted by a feed-forward network with 11 neurons and tansig function in the hidden layer. The non-linear network demonstrated stronger influence of oxidation temperature and cobalt content on the complete conversion of toluene and cyclohexane in the mixture. A hybrid model containing a genetic algorithm (GA) and an ANN were employed to realize the optimum catalyst at constant operating conditions for the complete conversion of toluene and cyclohexane in air. A well dispersed optimal alloy catalyst with 8 wt% metal oxide content (2.5 wt% copper oxide and 5.5 wt% cobalt oxide) over activated carbon was synthesized by heterogeneous deposition–precipitation for the complete conversion of toluene (model = 95.50%, experimental = 96%) and cyclohexane (model = 91.88% and experimental = 91%), simultaneously. Characterizations of the optimal catalyst were carried out by XRD, TEM, ICP, FESEM and BET analyses to justify its highest performance.

This study reveals the simultaneous deep oxidation of toluene and cyclohexane over optimal supported bimetallic catalysts over almond shell based activated carbon.

Oxidation of toluene in humid air by metal oxides supported on γ-alumina

Monometallic and bimetallic supported metal oxides catalysts on γ-alumina were prepared by heterogeneous deposition-precipitation. The γ-alumina used as a support was synthesized by the sol-gel and the co-precipitation methods. Supports and catalysts were characterized by Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The performance of the prepared catalysts was studied for total oxidation of toluene in air at different relative humidity and oxidation temperatures. Efficiency of bimetallic catalysts for deep oxidation of toluene was higher than copper oxide supported on γ-alumina. Although increasing the lanthanum, cobalt, and nickel loading on the support led to a modified catalyst surface and morphology, the catalytic activity of bimetallic catalysts decreased with increasing lanthanum, cobalt, and nickel content due to the reduced amount of copper oxide which has a higher activity for oxidation of volatile organic compounds. The γ-alumina prepared by the sol-gel method using ethanol as a solvent (AlSE) was the best support and La-Cu/AlSE had the best performance (toluene removal efficiency >90%). In addition, the presence of water vapor in the feed had a negative effect on toluene conversion.

Adsorption properties of regenerative materials for removal of low concentration of toluene

A specific type of material, activated carbon fiber (ACF), was modified by SiO₂, and the final products ACF-x were obtained as ACF-12.5, ACF-20, ACF-40, and ACF-80 according to different dosages of tetraethoxysilane (TEOS). The modified material on the ACF surface had a significant and smooth cover layer with low content of silica from scanning electron microscope (SEM) image. The modified ACF-x showed the stronger hydrophobicity, thermal stability, and adsorption capacity, which had almost no effect in the presence of water vapor and no destruction in multiple cycles. ACF-20 was proven as the most efficient adsorbent in humid conditions. The dual-function system composed of the regenerative adsorbents and the combustion catalyst would be efficient in consecutive toluene adsorption/oxidation cycles, in which the combustion catalyst was prepared by the displacement reaction of H₂PtCl₆ with foam Ni. Therefore, the adsorption/catalytic oxidation could be a promising technique in the indoor air purification, especially in the case of very low volatile organic compound (VOC; toluene) concentration levels.

IMPLICATIONS

Exploring highly effective adsorptive materials with less expensive costs becomes an urgent issue in the indoor air protection. ACF-20 modified by SiO₂ with Pt/Ni catalysts shows stronger hydrophobicity, thermal stability, and adsorption capacity. This dual-function system composed of the regenerative materials and the combustion catalyst would be a promising technique in the indoor air purification, especially in the case of removal of very low concentration of toluene.

Novel Co–Ni–graphene composite electrodes for hydrogen production

A novel, highly efficient composite electrode containing earth-abundant elements (Co–Ni) and graphene has been developed for the electrocatalytic hydrogen evolution reaction in an alkaline medium.