Catalytic application of silver nanoparticles immobilized to rice husk-SiO2-aminopropylsilane composite as recyclable catalyst in the aqueous reduction of nitroarenes

Magnetic yolk-shell structured periodic mesoporous organosilica supported palladium as a powerful and highly recoverable nanocatalyst for the reduction of nitrobenzenes

A novel palladium-loaded yolk-shell structured nanomaterial with magnetite core and phenylene-based periodic mesoporous organosilica (PMO) shell (Fe3O4@YS-Ph-PMO/Pd) nanocatalyst was synthesized for the reduction of nitrobenzenes. The Fe3O4@YS-Ph-PMO/Pd was prepared through cetyltrimethylammonium bromide (CTAB) directed condensation of 1,4-bis(triethoxysilyl)benzene (BTEB) around Fe3O4@silica nanoparticles followed by treatment with palladium acetate. This nanocatalyst was characterized by using Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), low-angle and wide-angle powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) analyses. These analyses showed a magnetic nanomaterial with high chemical and thermal stability for the designed composite. The Fe3O4@YS-Ph-PMO/Pd nanocomposite was employed as a powerful and highly recoverable catalyst in the green reduction of nitroarenes in H2O at room temperature. A variety of nitroarene derivatives were applied as substrate in the presence of 0.9 mol% of Fe3O4@YS-Ph-PMO/Pd catalyst. All nitroarenes were selectively converted to their corresponding amines with high to excellent yields (92-96%) within short reaction times (10-18 min). This catalyst was recovered and reused at least 11 times without significant decrease in efficiency and stability.

Recent Progress in Nanoparticles Based Sensors for the Detection of Mercury (II) Ions in Environmental and Biological Samples

To maintain a green and sustainable environment for human beings, rapid detection of potentially toxic heavy metals like mercury (Hg(II)) has attracted great attention. Recently, sensors have been designed which can selectively detect Hg(II) over other common available cations and give a naked eye or fluorometric response. In the last two decades, the trend is shifting from bulky organic chemosensors toward nanoparticles due to their rapid response, low cost, eco-friendly and easy synthesis. In this review, promising nanoparticles-based sensors for Hg(II) detection are discussed. The nano-sensors are functionalized with nucleotide or other suitable materials which coordinate with Hg(II) ions and give clear color or fluorescence change. The operational mechanisms are discussed focusing on its four basic types. The nanoparticles-based sensors are even able to detect Hg in three different oxidation states (Hg(II), Hg(I) and Hg(0)). Recently, the trend has been shifted from ordinary nanoparticles to magnetic nanoparticles to simultaneously detect and remove Hg(II) ions from environmental samples. Furthermore, the nano-sensors for Hg(II) are compared with each other and with the reported organic chemosensors.

Photocatalytic activity of silver nanoparticles@cellulose nanocomposites, from pistachio husk, in the toxic azo commercial dye degradation

In this work, an over-the-counter commercial dye, containing direct blue 151 in its composition, which is also discarded without any environmental regulation, was efficiency photodegraded using a green chemistry-synthesized nanocomposites type silver nanoparticles (AgNPs) supported on pistachio husk (PH). The green synthesis (GS) of the nanocomposites was carried out using the Anemopsis californica leaf extract (ExAc) as a reducing-stabilizing agent (AgNPs/ExAc-PH), for the first time. The presence of AgNPs on the nanocomposite surface was corroborated by field emission transmission electron microscope (FE-TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The synthesized AgNPs/ExAc-PH has a bimodal size of 24 and 25 nm (4.86 % each) and a 0.72 % of AgNPs on its surface. AgNPs were adhered to the PH surface, through secondary bonds between the Ag and the cellulose of the PH. The optimum conditions, for efficient photocatalytic degradation, were 5 mg of nanocomposite, 3.18 × 10-2 M of NaBH4, natural sunlight, and stirring; this results in a photodegradation efficiency of 100 % almost instantaneously. Furthermore, it was shown that the dye degradation process is primarily due to the photocatalytic degradation of the dye, which occurs almost instantaneously.

Application of polyionic magnetic nanoparticles as a catalyst for the synthesis of carbonitriles with both indole and triazole moieties via a cooperative geminal-vinylogous anomeric-based oxidation

Three-component reaction of aldehydes with 3-(1H-indol-3-yl)-3-oxopropanenitrile and 1H-1,2,4-triazol-5-amine under the solvent-free condition at 70 °C was effectively performed in the presence of 2 mg of polyionic magnetic nanoparticles with pyrazine bridge [Fe₃O₄@SiO₂@(CH₂)₃]₂-Pyrazinium-[TCM]₂ as a catalyst for the synthesis of 7-aryl-5-(1H-indol-3-yl)-[1,2,4]triazolo[1,5-a]pyrimidine-6-carbonitriles via a cooperative anomeric-based oxidation. The polyionic magnetic nanoparticles catalyst was simply recovered and reused four successive runs. The morphology and structure of MNPs catalyst were investigated by numerous techniques such as XRD, FT-IR, EDX, WDX, FE-SEM, TEM, TGA, DTA, and VSM. The obtained products are reported for the first time that were identified by various analyses techniques such as melting point, FT-IR, ¹H NMR, ¹³C NMR, and elemental analysis (CHN). A term entitled a cooperative geminal-vinylogous anomeric-based oxidation was introduced for the latter step of the reaction mechanism for the first time. Synthesis of 7-aryl-5-(1H-indol-3-yl)-[1,2,4]triazolo[1,5-a]pyrimidine-6-carbonitriles by using [Fe₃O₄@SiO₂@(CH₂)₃]₂-Pyrazinium-[TCM]₂ MNPs as a catalyst.

Rice husk-SiO2 supported bimetallic Fe-Ni nanoparticles: as a new, powerful magnetic nanocomposite for the aqueous reduction of nitro compounds to amines

This paper reports a novel green procedure for immobilization of bimetallic Fe/Ni on amorphous silica nanoparticles extracted from rice husk (RH-SiO2). The heterogeneous nanocomposite (Fe/Ni@RH-SiO2) was identified using SEM, EDX, TEM, BET, H2-TPR, TGA, XRD, VSM, ICP-OES, and FT-IR analyses. The Fe/Ni@RH-SiO2 nanocomposite was applied as a powerful catalyst for the reduction of structurally diverse nitro compounds with sodium borohydride (NaBH4) in green conditions. This procedure suggests some benefits such as green chemistry-based properties, short reaction times, non-explosive materials, easy to handle, fast separation and simple work-up method. The catalyst was separated by an external magnet from the reaction mixture and was reused for 9 successive cycles with no detectable changes of its catalytic efficiency.

Atmospheric pulsed laser deposition and thermal annealing of plasmonic silver nanoparticle films

A new method for pulsed laser deposition of plasmonic silver nanoparticle (NP) films in flowing gas at atmospheric pressure is described. The ablation was done using an excimer laser at 248 nm. Fast optical imaging shows that the ablation plume is captured by the flowing gas, and is expected to form a NP aerosol, which is carried 5-20 mm to the substrate. The dependence of the deposition rate on laser fluence, gas flow velocity, and target-substrate distance was investigated using electron microscopy and absorption spectroscopy of the deposited films. The NP films were annealed in argon and hydrogen at 400 °C, and in air for temperatures in the range 200 °C-900 °C, leading to strong enhancement, and narrowing of the surface plasmon resonance. The films were used for surface enhanced Raman spectroscopy of a 10^-5 molar solution of Rhodamine 6G; films annealed in air at 400 °C were five times more sensitive than the as-deposited films.

A nano silver-xerogel (Ag nps@modified TEOS) as a newly developed nanocatalyst in the synthesis of benzopyranopyrimidines (with secondary and primary amines) and gem-bisamides

Silver nanoparticles have been prepared from a chemical reduction approach and supported on modified TEOS (tetraethylorthosilicate) xerogel to be studied as a nanocatalyst.

Reduction of Nitroarenes into Aryl Amines and N-Aryl hydroxylamines via Activation of NaBH₄ and Ammonia-Borane Complexes by Ag/TiO₂ Catalyst

In this study, we report the fabrication of mesoporous assemblies of silver and TiO₂ nanoparticles (Ag/MTA) and demonstrate their catalytic efficiency for the selective reduction of nitroarenes. The Ag/TiO₂ assemblies, which show large surface areas (119–128 m²·g⁻¹) and narrow-sized mesopores (ca. 7.1–7.4 nm), perform as highly active catalysts for the reduction of nitroarenes, giving the corresponding aryl amines and N-aryl hydroxylamines with NaBH₄ and ammonia-borane (NH₃BH₃), respectively, in moderate to high yields, even in large scale reactions (up to 5 mmol). Kinetic studies indicate that nitroarenes substituted with electron-withdrawing groups reduced faster than those with electron-donating groups. The measured positive ρ values from the formal Hammett-type kinetic analysis of X-substituted nitroarenes are consistent with the proposed mechanism that include the formation of possible [Ag]-H hybrid species, which are responsible for the reduction process. Because of the high observed chemo selectivities and the clean reaction processes, the present catalytic systems, i.e., Ag/MTA-NaBH₄ and Ag/MTA-NH₃BH₃, show promise for the efficient synthesis of aryl amines and N-aryl hydroxylamines at industrial levels.

Poly(amic acid) salt-stabilized silver nanoparticles as efficient and recyclable quasi-homogeneous catalysts for the aqueous hydration of nitriles to amides

The reversible pH-response of the Ag–PAAS catalyst allows it to catalyze the selective hydration of various nitriles quasi-homogeneously in water and to be easily recovered by simply adjusting the pH value of the solution.

Multifunctional Fe3O4@nSiO2@mSiO2/Pr-Imi-NH2·Ag core–shell microspheres as highly efficient catalysts in the aqueous reduction of nitroarenes: improved catalytic activity and facile catalyst recovery

Core@shell nanoparticles with a superparamagnetic iron oxide core, a middle nonporous silica shell, and an outer organo functionalized mesoporous silica shell were synthesized and evaluated for immobilizing Ag nanoparticles.

Nitroarene reduction: a trusted model reaction to test nanoparticle catalysts

Nitrophenol reduction to aminophenol with a reducing agent is conveniently carried out in aqueous medium mainly with a metal or metal oxide catalyst. This reduction is presently considered as a benchmark reaction to test a catalyst nanoparticle. Thousands of original reports have enriched this field of nanoparticle catalyzed reaction. Synthesis of different metal and metal oxide nanoparticles and their composites along with their role as catalysts for nitrophenol reduction with varying reducing agents have been elucidated here. The progress of the reaction is conveniently monitored by UV-visible spectrophotometry and hence it becomes a universally accepted model reaction. In this review we have discussed the reaction kinetics considering its elegance and importance enlightening the long known Langmuir-Hinshelwood mechanism and Eley-Rideal mechanism at length, along with a few other mechanisms recently reported. A brief description of the synthetic procedures of various nanoparticles and their respective catalytic behaviour towards nitroarene reduction has also been accounted here.

A green procedure for direct oxidation of organic halides to aldehydes and ketones catalyzed by a molybdate-based catalyst

The direct oxidation of various primary and secondary halides to the corresponding aldehydes and ketones using 30% H₂O₂ as a green oxidant has been investigated using a molybdate-based heterogeneous magnetic catalyst.

Single-step preparation of recyclable silver nanoparticle immobilized porous glass filters for the catalytic reduction of nitroarenes

A single step preparation of recyclable silver nanocatalysts for catalytic reduction of nitroarenes with high efficiency.

A magnetic supported iron complex for selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide at room temperature

Selective oxidation of sulfides to corresponding sulfoxides using H₂O₂ as a green oxidant at room temperature have been investigated by a magnetic supported iron (iron(ii) acetylacetonate) as an efficient and recyclable heterogeneous catalyst with excellent sulfide conversion and good sulfoxide selectivity.