Catalytic Reduction of p-Nitrophenol on MnO2/Zeolite -13X Prepared with Lawsonia inermis Extract as a Stabilizing and Capping Agent.

p-nitrophenol (pNP) is a highly toxic organic compound and is considered carcinogenic and mutagenic. It is a very stable compound with high resistance to chemical or biological degradation. As a result, the elimination of this pollutant has been very challenging for many researchers. Catalytic reduction is one of the most promising techniques, if a suitable catalyst is developed. Thus, this work aims to prepare an eco-friendly catalyst via a simple and low-cost route and apply it for the conversion of the toxic p-nitrophenol (pNP) into a non-toxic p-aminophenol (pAP) that is widely used in industry. Manganese oxide was prepared in an environmentally friendly manner with the aid of Lawsonia inermis (henna) extract as a stabilizing and capping agent and loaded on the surface of 13X molecular sieve zeolite. The UV-Vis spectrum, EDS, and XRD patterns confirmed the formation of the pure MnO2 loaded on the zeolite crystalline network. The TGA analysis showed that the samples prepared by loading MnO2 on zeolite (Mn2Z, Mn3Z, and Mn4Z) lost more mass than pure MnO2 (Mn) or zeolite (Z), which is mainly moisture adsorbed on the surface. This indicates a better dispersion of MnO2 on the surface of zeolite compared to pure MnO2, and thus a higher number of active adsorption sites. SEM images and EDS confirmed the dispersion of the MnO2 on the surface of the zeolite. Results showed a very fast reduction rate, following the order Mn2Z > Mn3Z > Mn4Z > Mn > Z. With sample Mn2Z, 96% reduction of pNP was achieved in 9 min and 100% in 30 min. For Mn3Z, Mn4Z, and Mn, 98% reduction was achieved in 20 min and 100% in 30 min. Zeolite was the slowest, with only a 40% reduction in 30 min. Increasing the amount of zeolite in the synthesis mixture resulted in lower reduction efficiency. The kinetic study indicated that the reduction of p-nitrophenol on the surface of the prepared nanocomposite follows the pseudo-first-order model. The results show that the proposed nanocomposite is very effective and very promising to be commercially applied in water treatment, due to its low cost, simple synthesis procedure, and reusability.

Nano-Silica Modified with Diamine for Capturing Azo Dye from Aqueous Solutions.

Nano-silica particles decorated with amine groups (S-DA) were prepared via a simple, one-pot method, and under very mild conditions in an attempt to improve the affinity of the silica nanoparticles toward capturing anionic organic dye, namely, methyl orange (MO). The prepared sample was characterized by different techniques such as XRD for crystallinity, SEM for morphological structure, TGA for thermal stability, BET surface area, and FTIR for surface functional groups. The prepared sample was tested for the removal of MO under different conditions including the mass of adsorbent, pH, initial concentration, and time. Results showed that the adsorption of MO was very fast with equilibrium achieved in less than 30 min and a maximum removal efficiency of 100% for a mass to volume ratio of 10 g/3 L, a pH of 2.5, initial concentration of 10 mgL-1, and under stagnant conditions. These results were compared with a bare nano-silica, which was not able to adsorb more than 3% after 24 h, indicating the important effect of amine groups. Furthermore, recycling the adsorbent was achieved by rinsing the MO-loaded adsorbent with a dilute solution of KOH. The adsorbent maintained 50% of its initial removal efficiency after four adsorption-desorption cycles.

Acacia nilotica Pods' Extract Assisted-Hydrothermal Synthesis and Characterization of ZnO-CuO Nanocomposites.

This work represents a novel combination between Acacia nilotica pods' extract and the hydrothermal method to prepare nanoparticles of pure zinc oxide and pure copper oxide and nanocomposites of both oxides in different ratios. Five samples were prepared with different ratios of zinc oxide and copper oxide; 100% ZnO (ZC0), 75% ZnO: 25% CuO (ZC25), 50% ZnO: 50% CuO (ZC50), 25% ZnO: 75% CuO (ZC75), and 100% CuO (ZC100). Several techniques have been applied to characterize the prepared powders as FTIR, XRD, SEM, and TEM. The XRD results confirm the formation of the hexagonal wurtzite phase of zinc oxide and the monoclinic tenorite phase of copper oxide. The microscopy results show the formation of a heterostructure of nanocomposites with an average particle size of 13-27 nm.

One-Pot Synthesis of Amine-Functionalized Nano-Silica via Sol-Gel Assisted by Reverse Micelle Microemulsion for Environmental Application.

Amine modified nano-silica was prepared via a one-pot route and under very mild conditions in water in oil microemulsion with a non-ionic surfactant to study the effect of changing the amount of N-[3-(Trimethoxysilyl)propyl]ethylenediamine (DA) added to the synthesis mixture on the characteristics of the obtained nanocomposite such as morphology, crystallinity, surface charge, particle size, surface area, and accordingly the effect of all of these factors on the efficiency of the nanocomposite for the removal of heavy metal ions, namely zinc, from aqueous solutions. XRD, SEM, TGA, BET, DLS, FTIR, and pH0 analysis were performed for samples and the results showed a strong effect for the amount of DA added to the synthesis mixture on the characteristics of the obtained nanocomposites. It was found that increasing the amount of DA added to the synthesis mixture increased the pH0, hydrodynamic particle size obtained by dynamic light scattering analysis, and the particle size obtained by SEM. Sample prepared without the addition of DA (SNP) and the samples prepared with 1.5 mL of DA (SNP-1.5DA) showed a better adsorption performance compared to the samples prepared with 0.5 and 1.0 mL of DA (SNP-0.5DA and SNP-1.0DA, respectively). The main factor affecting the adsorption efficiency was found to be the available surface area for each nanocomposite, which was directly related to the degree of crystallinity as obtained by XRD analysis.

Phyto-Assisted Assembly of Metal Nanoparticles in Chitosan Matrix Using S. argel Leaf Extract and Its Application for Catalytic Oxidation of Benzyl Alcohol.

The design and synthesis of eco-friendly solid-supported metal nanoparticles with remarkable stability and catalytic performance have gained much attention for both industrial and environmental applications. This study provides a novel, low-cost, simple, and eco-friendly approach for decorating cross-linked chitosan with gold nanoparticles (AuNPs), greenly prepared with Solenostemma argel (S. argel) leaf extract under mild conditions. Glutaraldehyde-modified chitosan beads were used to coordinate with Au(III) ions and act as stabilizing agents, and S. argel leaf extract was used as a cost-effective phyto-reducing agent to reduce gold ions to elemental Au nanoparticles. The successful cross-linking of chitosan with glutaraldehyde, the coordination of Au(III) ions into the chitosan matrix, and the phytochemical reduction of Au(III) to Au nanoparticles were investigated via FT-IR spectroscopy. The obtained Au nanoparticles have a uniform spherical shape and size <10 nm, as confirmed by both X-ray diffraction (XRD) (~8.8 nm) and TEM (6.0 ± 3 nm). The uniformity of the AuNPs' size was confirmed by Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM). The powder X-ray diffraction technique showed crystalline AuNPs with a face-centered cubic structure. The elemental analysis and the Energy Dispersive Spectroscopy (EDS) analysis both confirmed the successful integration of Au nanoparticles with the chitosan network. The catalytic activity of this highly stable nanocomposite was systematically investigated via the selective oxidation of benzyl alcohol to benzaldehyde. Results showed a remarkable conversion (97%) and excellent selectivity (99%) in the formation of benzaldehyde over other side products.

Green Synthesis of an Activated Carbon-Supported Ag and ZnO Nanocomposite for Photocatalytic Degradation and Its Antibacterial Activities.

In this study Ag nanoparticles (AgNPs), ZnO nanoparticles (ZnONPs), and Ag/ZnO nanocomposites were greenly synthesized and loaded on activated carbon via three different routes: simple impregnation, successive precipitation, and co-precipitation. Neem leaf extract was used as a reducing and stabilizing agent. The morphological and structural properties of the synthesized nanocomposites have been examined using different analytical techniques such as XRD, SEM, FTIR, and UV. The antibacterial and catalytic activity of the synthesized nanocomposites were examined and compared. The results showed that AgNPs loaded on activated carbon (Ag/AC) has the best catalytic activity compared to the other nanocomposites, which is attributed to the good dispersal of AgNPs on the surface of activated carbon. Furthermore, AgNPs showed the best antibacterial effect on eight out of 16 tested pathogens. Results also showed that the order of precipitation is an important factor, as both antibacterial activities and photodegradation activities were higher for ZnO/Ag/AC than Ag/ZnO/AC. Furthermore, the co-precipitation method was shown to be better than the successive precipitation method for 4-nitrophenol photodegradation and 14 out of the 16 antibacterial tests performed.

Experimental Design Modeling of the Effect of Hexagonal Wurtzite-ZnO Synthesis Conditions on Its Characteristics and Performance as a Cationic and Anionic Adsorbent.

Surface composite design was used to study the effect of the ZnO synthesis conditions on its adsorption of methyl orange (MO) and methylene blue (MB). The ZnO was prepared via hydrothermal treatment under different conditions including temperature (T), precursor concentration (C), pH, and reaction time (t). Models were built using four Design expert-11 software-based responses: the point of zero charge (pHzc), MO and MB removal efficiencies (RMO, RMB), MO and MB adsorption capacities (qMO, qMB), and hydrodynamic diameter of ZnO particles (Dh). ZnO was characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, UV/VIS spectroscopy, thermal gravimetric analysis (TGA), and dynamic light scattering (DLS). The formation of ZnO was confirmed by the XRD, UV, and FTIR spectra. Results showed a very high efficiency for most of the samples for adsorption of MB, and more than 90% removal efficiency was achieved by 8 samples among 33 samples. For MO, more than 90% removal efficiency was achieved by 2 samples among 33 samples. Overall, 26 of 31 samples showed higher MB adsorption capacity than that of MO. RMB was found to depend only on the synthesis temperature while RMO depends on temperature, pH, and reaction time. pHzc was found to be affected by the synthesis pH only while Dh depends on the synthesis pH and precursor concentration.

CO2 deactivation of supported amines: does the nature of amine matter?

Adsorption of CO(2) was investigated on a series of primary, secondary, and tertiary monoamine-grafted pore-expanded mesoporous MCM-41 silicas, referred to as pMONO, sMONO, and tMONO, respectively. The pMONO adsorbent showed the highest CO(2) adsorption capacity, followed by sMONO, whereas tMONO exhibited hardly any CO(2) uptake. As for the stability in the presence of dry CO(2), we showed in a previous contribution [J. Am. Chem. Soc.2010, 132, 6312-6314] that amine-supported materials deactivate in the presence of dry CO(2) via the formation of urea linkages. Here, we showed that only primary amines suffered extensive loss in CO(2) uptake, whereas secondary and tertiary amines were stable even at temperature as high as 200 °C. The difference in the stability of primary vs secondary and tertiary amines was associated with the occurrence of isocyanate as intermediate species toward the formation of urea groups, since only primary amines can be precursors to isocyanate in the presence of CO(2). However, using a grafted propyldiethylenetriamine containing both primary and secondary amines, we demonstrated that while primary amines gave rise to isocyanate, the latter can react with either primary or secondary amines to generate di- and trisubstituted ureas, leading to deactivation of secondary amines as well.