Encapsulation of silver nanoparticles into graphite grafted with hyperbranched poly(amidoamine) dendrimer and their catalytic activity towards reduction of nitro aromatics

Ectopic expression of an Old Yellow Enzyme (OYE3) gene from Saccharomyces cerevisiae increases the tolerance and phytoremediation of 2-nitroaniline in rice

2-nitroaniline (2-NA) is an environmental pollutant and has been extensively used as intermediates in organic synthesis. The presence of 2-NA in the environment is not only harmful for aquatic life but also mutagenic for human beings. In this study, we constructed transgenic rice expressing an Old Yellow Enzyme gene, ScOYE3, from Saccharomyces cerevisiae. The ScOYE3 transgenic plants were comprehensively investigated for their biochemical responses to 2-NA treatment and their 2-NA phytoremediation capabilities. Our results showed that the rice seedlings exposed to 2-NA stress, showed growth inhibition and biomass reduction. However, the transgenic plants exhibited strong tolerance to 2-NA stress compared to wild-type plants. Ectopic expression of ScOYE3 could effectively protect transgenic plants against 2-NA damage, which resulted in less reactive oxygen species accumulation in transgenic plants than that in wild-type plants. Our phytoremediation assay revealed that transgenic plants could eliminate more 2-NA from the medium than wild-type plants. Moreover, omics analysis was performed in order to get a deeper insight into the mechanism of ScOYE3-mediated 2-NA transformation in rice. Altogether, the function of ScOYE3 during 2-NA detoxification was characterized for the first time, which serves as strong theoretical support for the phytoremediation potential of 2-NA by Old Yellow Enzyme genes.

Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

Pd nanoparticles decorated on Schiff base-modified chitosan/CeO2 as a heterogeneous and retriable nanocatalyst for Heck reactions and remediation of environmental pollutants

In this paper, we have developed a novel, highly active, eco-friendly, and versatile heterogeneous catalyst system in which Pd nanoparticles are decorated on Schiff base-modified chitosan‑cerium oxide particles (Pd@CS-CeO₂). In order to confirm the successful fabrication of Pd@CS-CeO₂, FTIR, XRD, SEM, TEM, BET, TG/DTG, and EDS analyses were performed, and its performance was evaluated as a heterogeneous nanocatalyst in Heck coupling reaction and reduction of nitro compounds. The catalytic tests showed that the desired Heck products were readily produced by Pd@CS-CeO₂ without being contaminated with the aryl iodides, bromides, and chlorides. Moreover, different nitro compounds were efficiently reduced to corresponding amino compounds by Pd@CS-CeO₂ within 95-160 s. Thanks to the heterogeneous nature of Pd@CS-CeO₂ catalyst, it was easily recovered via simple filtration and reused up to 5 successive runs by giving 88 % yield. Due to its good catalytic and reusability performance together with stability/durability, Pd@CS-CeO₂ is promising candidate as a catalyst for various catalytic or organic reactions.

Highly efficient and selective heterogeneous catalytic reduction of 2-nitroaniline by cerium oxide nanocatalyst under microwave irradiation

Efficient nanocatalyst with incredible performance is highly demanding in a heterogeneous catalysis system. Herein, we report the facile fabrication of uniform and highly stable Cerium Oxide nanoparticles (CeO₂ NPs), through chemical precipitation method using sodium hydroxide as reducing agent. The synthesized material is characterized through highly sophisticated techniques including UV-Visible, FT-IR, SEM, AFM, XRD, and Zeta Sizer- Potential to check the particle formation, surface morphology, topography, crystalline nature, size, and surface potential. The heterogeneous catalytic performance of CeO₂ NPs has been accomplished for the reduction of 2-nitroaniline from the aqueous media. The CeO₂ nanocatalyst displayed excellent reusability, while the reduction in several repetitive catalytic cycles against 2-nitroaniline under optimized conditions. The CeO₂ nanocatalyst shows 99.12% efficiency within 60s reaction time under a greener source of microwave radiation.

Catalytic Neutralization of Water Pollutants Mediated by Dendritic Polymers

Radially polymerized dendritic compounds are nowadays an established polymer category next to their linear, branched, and cross-linked counterparts. Their uncommon tree-like architecture is characterized by adjustable internal cavities and external groups. They are therefore exceptional absorbents and this attainment of high concentrations in their interior renders them ideal reaction media. In this framework, they are applied in many environmentally benign implementations. One of the most important among them is water purification through pollutant decomposition. Simple and composite catalysts and photo-catalysts containing dendritic polymers and applied in water remediation will be discussed jointly with some unconventional solutions and prospects.

Highly stable silver nanoparticles containing guar gum modified dual network hydrogel for catalytic and biomedical applications

Although many preparation methods have been reported till date, it is still a great challenge to prepare silver nanoparticles (AgNPs) that simultaneously possess high stability and enhanced applicability. We report a rapid and efficient synthesis of AgNPs containing polyvinyl alcohol (PVA)-guar gum (GG) smart hydrogel composite, which exhibited pH-dependent swelling and enhanced mechanical strength. The AgNPs were synthesized in situ in the PVA-GG hydrogel from various concentrations of the AgNO₃ precursor solution in the presence of NaBH₄. Stable AgNPs (90 days) of 10-20 nm uniformly dispersed in PVA-GG hydrogel was obtained. Simultaneously, at the optimum concentration of AgNO₃ (0.01 M), the tensile strength and elongation at break were enhanced by 74 % and 11 %, and swelling capacity was increased by 18 % as compared to PVA-GG hydrogel (control). The PVA-GG-AgNPs hydrogel composite exhibited excellent catalytic activity and antibacterial property, which makes them a suitable candidate for industrial applications.

Optimization of sol-immobilized bimetallic Au-Pd/TiO2 catalysts: reduction of 4-nitrophenol to 4-aminophenol for wastewater remediation

A sol-immobilization method is used to synthesize a series of highly active and stable Au_xPd_1-x/TiO₂ catalysts (where x = 0, 0.13, 0.25, 0.5, 0.75, 0.87 and 1) for wastewater remediation. The catalytic performance of the materials was evaluated for the catalytic reduction of 4-nitrophenol, a model wastewater contaminant, using NaBH₄ as the reducing agent under mild reaction conditions. Reaction parameters such as substrate/metal and substrate/reducing agent molar ratios, reaction temperature and stirring rate were investigated. Structure-activity correlations were studied using a number of complementary techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The sol-immobilization route provides very small Au-Pd alloyed nanoparticles, with the highest catalytic performance shown by the Au_0.5Pd_0.5/TiO₂ catalyst. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Critical review on the chemical reduction of nitroaniline

Conversion of nitroaniline (NA), a highly toxic pollutant that has been released into aquatic systems due to unmanaged industrial development in recent years, into the less harmful or a useful counterpart is the need of the hour. Various methods for its conversion and removal have been explored. Owing to its nominal features of advanced effectiveness, the chemical reduction of 4-NA using various different nanocatalytic systems is one such approach that has attracted tremendous interest over the past few years. The academic literature has been confined to case studies involving silver (Ag) and gold (Au) nanoparticles, as these are the two most widely used materials for the synthesis of nanocatalytic assemblies. Focus has also been given to sodium borohydride (NaBH₄), which is used as a reductant during the chemical reduction of NA. This systematic review summarizes the fundamentals associated with the catalytic degradation of 4-NA, and presents a comprehensive and critical study of the latest modifications used in the synthesis of these catalytic systems. In addition, the kinetics, mechanisms, thermodynamics, as well as the future directions required for understanding this model reaction, have been provided in this particular study.

Schematic illustration of catalytic reduction of 4-NA in the presence of nanocatalysts and a reducing agent.

Palladium/graphene oxide nanocomposites with carbon nanotubes and/or magnetite for the reduction of nitrophenolic compounds

Graphene oxide (GO) was synthesised via the oxidation of graphite and was characterised using ATR FTIR, PXRD, SEM, TEM and TGA. These techniques confirmed the presence of characteristic oxygen-containing functional groups and the resulting increase in interlayer spacing in the nanostructure. GO is used as the support to form nanocomposites composed of combinations of the following: iron oxide nanoparticles (Fe₃O₄), carbon nanotubes (CNT) and palladium nanoparticles (Pd). The four final nanocomposites formed are: Pd/GO, Pd/Fe₃O₄/GO, Pd/CNT/GO, and Pd/CNT/Fe₃O₄/GO. Key intermediates were analysed using ATR FTIR for the confirmation of the modification. Additionally, all composites and their precursors underwent electron microscopic analysis to visually assess composite morphologies and the size distribution of deposited nanoparticles. The Fe₃O₄ and Pd nanoparticles were indistinguishable from each other in their spherical shape and particle diameters, which were no bigger than 32 nm. From the TGA, incorporation of Fe₃O₄, CNT and finally Pd into the nanocomposites increased total thermal stability in terms of mass percentage lost over the temperature programme. GO showed significant decomposition, with all nanocomposites remaining relatively stable up to 120 °C. ICP OES results showed total Pd content by mass percentage for each final composite, varied from 7.9% to 9.1% mass Pd/collective mass. XPS confirmed the expected elemental compositions of composites according to their structures and the Pd⁰ : Pd^II ratios are obtained. The nanocomposites were tested for the catalytic reduction of nitrophenols. Pd/CNT/Fe₃O₄/GO gave the highest TOF′ for the reduction of 4-NP and 2-NP. For the reduction of 3-NP, Pd/GO showed the highest TOF′. Nitrophenol's pK_a and catalyst TOF′ correlated in a direct proportional relationship for Pd/GO and Pd/Fe₃O₄/GO. It was found that Pd⁰ surpassed Pd^II in catalytic activity. Reduction of Pd^II to Pd⁰ took place during the first catalytic cycle.

Comparison of the catalytic activity for the reduction of nitrophenol over palladium-supported graphene oxide nanocomposites modified with iron oxide nanoparticles and/or carbon nanotubes.

A "One-Pot" Route for the Synthesis of Snowflake-like Dendritic CoNi Alloy-Reduced Graphene Oxide-Based Multifunctional Nanocomposites: An Efficient Magnetically Separable Versatile Catalyst and Electrode Material for High-Performance Supercapacitors

In this paper, a simple "one pot" methodology to synthesize snowflake-like dendritic CoNi alloy-reduced graphene oxide (RGO) nanocomposites has been reported. First-principles quantum mechanical calculations based on density functional theory (DFT) have been conducted to understand the electronic structures and properties of the interface between Co, Ni, and graphene. Detailed investigations have been conducted to evaluate the performance of CoNi alloy and CoNi-RGO nanocomposites for two different types of applications: (i) as the catalyst for the reduction reaction of 4-nitrophenol and Knoevenagel condensation reaction and (ii) as the active electrode material in the supercapacitor applications. Here, the influence of microstructures of CoNi alloy particles (spherical vs snowflake-like dendritic) and the effect of immobilization of CoNi alloy on the surface of RGO on the performance of CoNi-RGO nanocomposites have been demonstrated. CoNi alloy having a snowflake-like dendritic microstructure exhibited better performance than that of spherical CoNi alloy, and CoNi-RGO nanocomposites showed improved properties compared to CoNi alloy. The k app value of the (CoNiD)60RGO40-catalyzed reduction reaction of 4-nitrophenol is 20.55 × 10-3 s-1, which is comparable and, in some cases, superior to many RGO-based catalysts. The (CoNiD)60RGO40-catalyzed Knoevenagel condensation reaction showed the % yield of the products in the range of 80-93%. (CoNiD)60RGO40 showed a specific capacitance of 501 F g-1 (at 6 A g-1), 21.08 Wh kg-1 energy density at a power density of 1650 W kg-1, and a retention of ∼85% of capacitance after 4000 cycles. These results indicate that (CoNiD)60RGO40 could be considered as a promising electrode material for high-performance supercapacitors. The synergistic effect, derived from the hierarchical structure of CoNiD-RGO nanocomposites, is the origin for its superior performance. The easy synthetic methodology, high catalytic efficiency, and excellent supercapacitance performance make (CoNiD)60RGO40 an appealing multifunctional material.

Biosynthesis of waste pistachio shell supported silver nanoparticles for the catalytic reduction processes

Silver nanoparticles (NPs) are immobilised on pistachio shell surface by Cichorium intybus L. leaves extract as an antioxidant media. The Fourier transform infrared spectra, X-ray diffraction, field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and transmission electron microscope analyses confirmed the support of silver NPs on the pistachio shell (Ag NPs/pistachio shell). Ag NPs on the pistachio shell had a diameter basically in the 10-15 nm range. Reduction reactions of 4-nitrophenol (4-NP), and organic dyes at ambient condition were used in the investigation of the catalytic performance of the prepared catalyst. Through this research, the Ag NPs/pistachio shell shows a high activity and recyclability, and reusability without loss of its catalytic activity.

Simple and Practical Synthesis of Various New Nickel Boride-Based Nanocomposites and their Applications for the Green and Expeditious Reduction of Nitroarenes to Arylamines under Wet-Solvent-Free Mechanochemical Grinding

In this paper, we report a simple synthesis of four new nickel boride-based nanocomposites, namely Ni2B@ZrCl4, Ni2B@Cu2O, Ni2B@CuCl2 and Ni2B@FeCl3, from commercially available and cheap starting materials. All of the new Ni2B-based nanocomposites were well characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Further, the catalytic applications of these new nanocomposites were successfully evaluated in the wet-solvent-free reduction of aromatic nitro compounds to arylamines with sodium borohydride (NaBH4) at room temperature by a mechanochemical grinding technique. All the introduced catalytic systems provide excellent yields of arylamines in very short reaction times for a wide range of substrates. Also, recoverability and reusability of the new nanocomposites were investigated.

One-Pot Green Synthesis of Ag-Decorated SnO2 Microsphere: an Efficient and Reusable Catalyst for Reduction of 4-Nitrophenol

In this paper, hierarchical Ag-decorated SnO2 microspheres were synthesized by a facile one-pot hydrothermal method. The resulting composites were characterized by XRD, SEM, TEM, XPS, BET, and FTIR analysis. The catalytic performances of the samples were evaluated with the reduction of 4-nitrophenol to 4-aminophenol by potassium borohydride (KBH4) as a model reaction. Time-dependent experiments indicated that the hierarchical microspheres assembled from SnO2 and Ag nanoparticles can be formed when the react time is less than 10 h. With the increase of hydrothermal time, SnO2 nanoparticles will self-assemble into SnO2 nanosheets and Ag nanoparticles decorated SnO2 nanosheets were obtained. When evaluated as catalyst, the obtained Ag-decorated SnO2 microsphere prepared for 36 h exhibited excellent catalytic performance with normalized rate constant (κ nor) of 6.20 min-1g-1L, which is much better than that of some previous reported catalysts. Moreover, this Ag-decorated SnO2 microsphere demonstrates good reusability after the first five cycles. In addition, we speculate the formation mechanism of the hierarchical Ag-decorated SnO2 microsphere and discussed the possible origin of the excellent catalytic activity.

Catalytic reduction of 2-nitroaniline: a review

2-nitroaniline (2-NA) is highly toxic and environmental contaminant. It is reduced to less toxic and environmental benign product o-phenylenediamine by using different reducing agents like sodium borohydride, potassium borohydride, or hydrazine hydrate in the presence of various catalytic systems. These catalytic systems have various advantages and drawbacks. Silica-supported gold nanoparticles are frequently reported catalyst for the reduction of 2-nitroaniline in aqueous medium. In this review article, different catalytic systems reported for reduction of o-nitroaniline under various reaction conditions have been discussed. The critical review of the recent research progress for development of novel catalysts used for the reduction of 2-nitroaniline has been provided here.

Interfacial Microstructure and Enhanced Mechanical Properties of Carbon Fiber Composites Caused by Growing Generation 1-4 Dendritic Poly(amidoamine) on a Fiber Surface

In an attempt to improve the mechanical properties of carbon fiber composites, propagation of poly(amidoamine) (PAMAM) dendrimers by in situ polymerization on a carbon fiber surface was performed. During polymerization processes, PAMAM was grafted on carbon fiber by repeated Michael addition and amidation reactions. The changes in surface microstructure and the chemical composition of carbon fibers before and after modification were investigated by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. All the results indicated that PAMAM was successfully grown on the carbon fiber surface. Such propagation could significantly increase the surface roughness and introduce sufficient polar groups onto the carbon fiber surface, enhancing the surface wettability of carbon fiber. The fractured surface of carbon fiber-reinforced composites showed a great enhancement of interfacial adhesion. Compared with those of desized fiber composites, the interlaminar shear strength and interfacial shear strength of PAMAM/fiber-reinforced composites showed increases of 55.49 and 110.94%, respectively.

Effects of grafting low-generation poly(amido amine) onto carbon fiber surface by in situ polymerization on the mechanical properties of fiber composites

Low-generation poly(amido amine) (PAMAM)-grafted carbon fibers (CFs) emerged as a new reinforcement for improving the mechanical properties of fiber composites. In this work, hybrid reinforcement, which could greatly enhance the surface roughness and wettability of CF, was prepared via growing PAMAM onto fiber surface by in situ polymerization.The modified surface morphology and chemical composition were investigated by scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis test, and X-ray photoelectron spectroscopy. Experimental results indicated PAMAM dendrimers grown on the CF significantly enhanced interfacial properties of the resulting composites. In addition, compared with the desized CF composites, the CF grafted with PAMAM composites exhibited 34.65% enhancement in the interfacial shear strength.

Designing versatile heterogeneous catalysts based on Ag and Au nanoparticles decorated on chitosan functionalized graphene oxide

Herein we report the covalent grafting of chitosan on graphene oxide (GO) followed by a simple approach for anchoring silver (AgNPs) and gold (AuNPs) nanoparticles onto a chitosan grafted graphene oxide surface by a NaBH4 reduction method. Catalytic activity of prepared heterogeneous GO grafted chitosan stabilized silver and gold nanocatalysts (GO-Chit-Ag/AuNPs) was explored for the reduction of aromatic nitroarenes and degradation of hazardous azo dyes in the presence of NaBH4. Both catalysts were found to exhibit excellent catalytic activity towards the reduction of aromatic nitroarenes and azo dyes degradation. Furthermore, the nanocatalysts were found to be selective towards the reduction of nitro groups in halonitroarenes without any dehalogenation under mild conditions.

Nanosilver as a new generation of silver catalysts in organic transformations for efficient synthesis of fine chemicals

Silver nanoparticles catalysis has been of great interest in organic synthesis and has expanded rapidly in the past ten years because of nanosilver catalysts' unique reactivity and selectivity, stability, as well as recyclability in catalytic reactions.

Advancement in methodologies for reduction of nitroarenes

Recent advancement in reduction methods of nitroarenes are reviewed. The different methods are classified based on the source of hydrogen utilized during reduction and the mechanism involved in the reduction process.

Simple and rapid hydrogenation of p-nitrophenol with aqueous formic acid in catalytic flow reactors

The inner surface of a metallic tube (i.d. 0.5 mm) was coated with a palladium (Pd)-based thin metallic layer by flow electroless plating. Simultaneous plating of Pd and silver (Ag) from their electroless-plating solution produced a mixed distributed bimetallic layer. Preferential acid leaching of Ag from the Pd–Ag layer produced a porous Pd surface. Hydrogenation of p-nitrophenol was examined in the presence of formic acid simply by passing the reaction solution through the catalytic tubular reactors. p-Aminophenol was the sole product of hydrogenation. No side reaction occurred. Reaction conversion with respect to p-nitrophenol was dependent on the catalyst layer type, the temperature, pH, amount of formic acid, and the residence time. A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined. p-Nitrophenol was converted quantitatively to p-aminophenol within 15 s of residence time in the porous PdO reactor at 40 °C. Evolution of carbon dioxide (CO₂) was observed during the reaction, although hydrogen (H₂) was not found in the gas phase. Dehydrogenation of formic acid did not occur to any practical degree in the absence of p-nitrophenol. Consequently, the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid.