Nanocatalysis and prospects of green chemistry

Recent Advances in the Development of Greener Methodologies for the Synthesis of Benzothiazoles

The benzothiazole ring system has been recognised with crucial pharmacophoric features being present among various approved drugs and clinical and pre-clinical candidates. The medicinal importance of this privileged scaffold stimulated the interest of synthetic medicinal/ organic chemists for the synthesis of its derivatives due to their diverse biological applications. In most of the reports in the literature, benzothiazoles were synthesized by cyclocondensation of 2- aminothiophenol with either carboxylic acid and its derivatives or aldehydes. However, many of these procedures involve reaction conditions that are not in conformity with sustainable chemistry development. The negative impact of chemicals and their manufacturing processes on the environment, human health, and biodiversity raises safety concerns. On the other hand, the utilization of non-renewable energy sources, use of rare earth metals as catalysts, involvement of costly chemicals, prolonged reaction time at high temperatures, and considerable waste generation diminish the greener impact of these reaction methodologies and make them non-sustainable. In order to avoid such drawbacks of the non-sustainable practices in the synthesis of benzothiazoles, there have been continuous efforts to develop greener methodologies for the construction of this bioactive scaffold. This review aims to delve into the literature reports on the recent advancements in the development of greener methodologies for the synthesis of bioactive benzothiazoles.

3D Porous MoS2-Decorated Reduced Graphene Oxide Aerogel as a Heterogeneous Catalyst for Reductive Transformation Reactions

The MoS2-based reduced graphene oxide aerogel (MoS2-rGOA)-assisted organic transformation reactions are presented. MoS2-rGOA is used as a heterogeneous catalyst for the reduction of benzene derivatives such as benzaldehyde, nitrobenzene, and benzonitrile to benzyl alcohol, aniline, and benzamide and their derivatives, respectively, in green solvents (water/methanol) and green reducing agents (hydrazine hydrate having N2 and H2 as byproducts). The mechanistic features of the reduction pathway, substrate scope, and the best suitable conditions by varying the temperature, solvent, reducing agent, catalyst loading, time, etc. are optimized. All of the synthesized products are obtained in quantitative yield with purity and well characterized based on nuclear magnetic resonance analysis. Further, it is also observed that our catalyst is efficiently recyclable and works well checked up to 5 cycles.

Recent advances in the application of magnetic nanocatalysts in multicomponent reactions

Recently, the preparation and applications of magnetic nanostructures have attracted increasing attention in nanocatalysis studies, and magnetic nanoparticle (MNP) functionalized catalysts have been applied in important reactions such as Suzuki-Miyaura and Heck couplings. The modified nanocomposites demonstrate significant catalytic efficiency and excellent benefits in the context of catalyst recovery methods. This review discusses the recent modified magnetic nanocomposites in the field of catalytic applications along with the synthetic processes that are usually employed.

Non-Noble-Metal Mono and Bimetallic Composites for Efficient Electrocatalysis of Phosphine Oxide and Acetylene C-H/P-H Coupling under Mild Conditions

The present work describes an efficient reaction of electrochemical phosphorylation of phenylacetylene controlled by the composition of catalytic nanoparticles based on non-noble-metals. The sought-after products are produced via the simple synthetic protocol based on room temperature, atom-economical reactions, and silica nanoparticles (SNs) loaded by one or two d-metal ions as nanocatalysts. The redox and catalytic properties of SNs can be tuned with a range of parameters, such as compositions of the bimetallic systems, their preparation method, and morphology. Monometallic SNs give phosphorylated acetylene with retention of the triple bond, and bimetallic SNs give a bis-phosphorylation product. This is the first example of acetylene and phosphine oxide C-H/P-H coupling with a regenerable and recyclable catalyst.

Cu2O nanoparticle-catalyzed tandem reactions for the synthesis of robust polybenzoxazole

We report the synthesis of Cu₂O nanoparticles (NPs) by controlled oxidation of Cu NPs and the study of these NPs as a robust catalyst for ammonia borane dehydrogenation, nitroarene hydrogenation, and amine/aldehyde condensation into Schiff-base compounds. Upon investigation of the size-dependent catalysis for ammonia borane dehydrogenation and nitroarene hydrogenation using 8-18 nm Cu₂O NPs, we found 13 nm Cu₂O NPs to be especially active with quantitative conversion of nitro groups to amines. The 13 nm Cu₂O NPs also efficiently catalyze tandem reactions of ammonia borane, diisopropoxy-dinitrobenzene, and terephthalaldehyde, leading to a controlled polymerization and the facile synthesis of polybenzoxazole (PBO). The highly pure PBO (M_w = 19 kDa) shows much enhanced chemical stability than the commercial PBO against hydrolysis in boiling water or simulated seawater, demonstrating a great potential of using noble metal-free catalysts for green chemistry synthesis of PBO as a robust lightweight structural material for thermally and mechanically demanding applications.

Sono and nano: A perfect synergy for eco-compatible Biginelli reaction

In this study, we evaluated the performance of nano-γ-Fe2O3–SO3H catalyst in the Biginelli reaction and synthesized 3,4-dihydropyrimidine-2-(1H)-ones. This reaction was carried out under solvent-free and ultrasonic irradiation conditions and belonged to one-pot multicomponent reactions (MCRs) with an adopted aromatic aldehyde, ethyl acetoacetate, and urea as starting materials for the beginning of the reaction. The synthesized materials were efficient in synthesizing 3,4-dihydropyrimidine-2-(1H)-ones via the Biginelli reaction under reaction conditions. Thus, the advantages of using nano-γ-Fe2O3–SO3H in the Biginelli reaction are short reaction time, high efficiency, green method, solvent free, and cost-effective. Furthermore, nano-γ-Fe2O3–SO3H as a heterogeneous catalyst can be recycled five times without significantly reducing catalytic activity.

Recent developments in green approaches for sustainable synthesis of indole-derived scaffolds

An important issue to discover biological structures is the design of sustainable, safe, clean, cost-effective, excellent efficient synthetic reactions, and minimal energy consumption to provide structural diversity compounds with interesting biological properties. Among five-membered nitrogen-containing heterocyclic compounds, indole-containing scaffolds are heterocyclic structures found in abundance in natural products and various synthetic compounds, which have received remarkable attention in recent years due to their therapeutic and pharmaceutical properties and valuable role in the process of drug discovery. Indoles can be synthesized by various procedures although most of these procedures have their own restrictions and drawbacks such as performing the reaction in a toxic solvent, need of transition-metal catalysts, and amount of waste solvents. Due to the medicinal importance of indole and the need for green methods of drug synthesis, this review highlights the latest green synthetic methods leading to the formation of indole-containing compounds focusing on the past 4 years with typical examples. This review is divided into two sections: green solvents and green techniques that lead to the synthesis of indole-derived scaffolds.

Element-specific contributions to improved magnetic heating of theranostic CoFe2O4 nanoparticles decorated with Pd

Decoration with Pd clusters increases the magnetic heating ability of cobalt ferrite (CFO) nanoparticles by a factor of two. The origin of this previous finding is unraveled by element-specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) combined with atomic multiplet simulations and density functional theory (DFT) calculations. While the comparison of XAS spectra with atomic multiplet simulations show that the inversion degree is not affected by Pd decoration and, thus, can be excluded as a reason for the improved heating performance, XMCD reveals two interrelated responsible sources: significantly larger Fe and Co magnetic moments verify an increased total magnetization which enhances the magnetic heating ability. This is accompanied by a remarkable change in the field-dependent magnetization particularly for Co ions which exhibit an increased low-field susceptibility and a reduced spin canting behavior in higher magnetic fields. Using DFT calculations, these findings are explained by reduced superexchange between ions on octahedral lattice sites via oxygen in close vicinity of Pd, which reinforces the dominating antiparallel superexchange interaction between ions on octahedral and tetrahedral lattice sites and thus reduces spin canting. The influence of the delocalized nature of Pd 4d electrons on the neighboring ions is discussed and the conclusions are illustrated with spin density isosurfaces of the involved ions. The presented results pave the way to design nanohybrids with tailored electronic structure and magnetic properties.

Noble-Metal-Free Multicomponent Nanointegration for Sustainable Energy Conversion

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO₂ reduction, and N₂ reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.

Magnetically recyclable silica-coated ferrite magnetite-K10 montmorillonite nanocatalyst and its applications in O, N, and S-acylation reaction under solvent-free conditions

Novel silica-coated ferrite nanoparticles supported with montmorillonite (K10) have been prepared successfully by using a simple impregnation method. Further, these nanoparticles were characterized by using different analytical methods like FT-IR, PXRD, EDS, and FE-SEM techniques. In addition, these nanoparticles have been explored for their catalytic activity for the O, N, and S-acylation reactions under solvent-free conditions which gave moderate to excellent yields in a much shorter reaction time. Moreover, these nanoparticles could easily be separated out from the reaction medium after the reaction completion by using an external magnetic field and have been re-used for 10 cycles without any significant loss of the catalytic activity.

Algal magnetic nickel oxide nanocatalyst in accelerated synthesis of pyridopyrimidine derivatives

This research presents a novel biological route for the biosynthesis of nickel oxide nanoparticles (NiO NPs) using marine macroalgae extract as a reducing and coating agent under optimized synthesis conditions. XRD and TEM analyses revealed that phytosynthesized NiO NPs are crystalline in nature with a spherical shape having a mean particle size of 32.64 nm. TGA results indicated the presence of marine-derived organic constituents on the surface of NiO NPs. It is found that biogenic NiO NPs with BET surface area of 45.59 m²g^-1 is a highly efficient catalyst for benign one-pot preparation of pyridopyrimidine derivatives using aqueous reaction conditions. This environmentally friendly procedure takes considerable advantages of shorter reaction times, excellent product yields (up to 96%), magnetically viable nanocatalyst (7 runs), low catalyst loadings, and free toxic chemical reagents.

Catalytic activity of synthesized 2D MoS2/graphene nanohybrids for the hydrodesulfurization of SRLGO: experimental and DFT study

Hydrodesulfurization (HDS) of straight run light gas oil (SRLGO) using novel highly active two-dimensional (2D) MoS₂/graphene (G) nanohybrid catalysts is a precursor technology for the production of clean heavy fuel. The aim of this research is the synthesis of 2D MoS₂/G nanohybrid catalysts by use of exfoliation method from commercial bulky MoS₂ and graphite using hydrothermal ball milling system, which is a low-cost, high-yield, and scalable method. These nanohybrid catalysts were characterized by XRD, Raman spectroscopy, XPS, SEM, TEM, STEM, ICP, BET surface, TPR, and TPD techniques. Also, catalytic activities of 2D MoS₂/G nanohybrid catalysts were evaluated under different operating conditions such as temperature, pressure, LHSV, and H₂/Feed (SRLGO) ratio in the HDS reaction. The conversion of the HDS of SRLGO with 14000 ppm sulfur showed a considerably higher activity of 2D MoS₂/G nanohybrid catalyst (99.95% HDS efficiency) compared with the Co-Mo/γAl₂O₃ as a commercial catalyst (90% HDS efficiency) in the operation condition (340 °C, 40 bars, LHSV: 1 h^-1and H₂/oil: 600 NL L^-1) which is economically valuable. Using density functional theory calculations, the detailed mechanism of the HDS process over MoS₂/G catalyst was explored. It was found that sulfur coverage on the Mo edge of MoS₂ plays an important role in the hydrogenation of sulfur components.

Biogenic synthesis of Pd-nanoparticles using Areca Nut Husk Extract: a greener approach to access α-keto imides and stilbenes

An eco-friendly green method for a one-step synthesis of palladium nanoparticles and their synthetic utility are reported.

Highly Active Ruthenium Catalyst Supported on Magnetically Separable Mesoporous Organosilica Nanoparticles

A facile and direct method for synthesizing magnetic periodic mesoporous organosilica nanoparticles from pure organosilane precursors is described. Magnetic ethylene- and phenylene-bridged periodic mesoporous organosilica nanoparticles (PMO NPs) were prepared by nanoemulsification techniques. For fabricating magnetic ethylene- or phenylene-bridged PMO NPs, hydrophobic magnetic nanoparticles in an oil-in-water (o/w) emulsion were prepared, followed by a sol–gel condensation of the incorporated bridged organosilane precursor (1,2 bis(triethoxysilyl)ethane or 1,4 bis(triethoxysilyl)benzene), respectively. The resulting materials were characterized using high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (XRD), solid-state NMR analysis, and nitrogen sorption analysis (N2-BET). The magnetic ethylene-bridged PMO NPs were successfully loaded using a ruthenium oxide catalyst by means of sonication and evaporation under mild conditions. The obtained catalytic system, termed Ru@M-Ethylene-PMO NPS, was applied in a reduction reaction of aromatic compounds. It exhibited very high catalytic behavior with easy separation from the reaction medium by applying an external magnetic field.

Biosynthesis of Copper Oxide Nanoparticles with Potential Biomedical Applications

Introduction

In recent years, the use of cost-effective, multifunctional, environmentally friendly and simple prepared nanomaterials/nanoparticles have been emerged considerably. In this manner, different synthesizing methods were reported and optimized, but there is still lack of a comprehensive method with multifunctional properties.

Materials and Methods

In this study, we aim to synthesis the copper oxide nanoparticles using Achillea millefolium leaf extracts for the first time. Catalytic activity was investigated by in situ azide alkyne cycloaddition click and also A³ coupling reaction, and optimized in terms of temperature, solvent, and time of the reaction. Furthermore, the photocatalytic activity of the synthesized nanoparticles was screened in terms of degradation methylene blue dye. Biological activity of the synthesized nanoparticles was evaluated in terms of antibacterial and anti-fungal assessments against Staphylococcus aureus, M. tuberculosis, E. coli, K. pneumoniae, P. mirabili, C. diphtheriae and S. pyogenes bacteria's and G. albicans, A. flavus, M. canis and G. glabrata fungus. In the next step, the biosynthesized CuO-NPs were screened by MTT and NTU assays.

Results

Based on our knowledge, this is a comprehensive study on the catalytic and biological activity of copper oxide nanoparticles synthesizing from Achillea millefolium, which presents great and significant results (in both catalytic and biological activities) based on a simple and green procedure.

Conclusion

Comprehensive biomedical and catalytic investigation of the biosynthesized CuO-NPs showed the mentioned method leads to synthesis of more eco-friendly nanoparticles. The in vitro studies showed promising and considerable results, and due to the great stability of these nanoparticles in a green media, effective biological activity considered as an advantageous.

ZnO-nanorods Promoted Synthesis of α-amino Nitrile Benzofuran Derivatives using One-pot Multicomponent Reaction of Isocyanides

AIMS AND OBJECTIVE

In this work ZnO-nanorod (ZnO-NR) as reusable catalyst promoted Strecker-type reaction of 2,4-dihydroxyacetophenone, isopropenylacetylene, trimethylsilyl cyanide (TMSCN), primary amines and isocyanides at ambient temperature under solvent-free conditions and produced α-amino nitriles benzofuran derivatives in high yields. These synthesized compounds may have antioxidant ability.

MATERIALS AND METHODS

ZnO-NRs in these reactions were prepared according to reported article. 2,4-dihydroxyacetophenone 1 (2 mmol) and isopropenylacetylene 2 (2 mmol) were mixed and stirred for 30 min in the presence of ZnO-NR (10 mol%) under solvent-free conditions at room temperature. After 30 min, primary amine 3 (2 mmol) was added to the mixture gently and the mixture was stirred for 15 min. After this time TMSCN 4 (2 mmol) was added to the mixture and stirred for 15 min. After completion of the reaction, as indicated by TLC, isocyanides 5 was added to mixture in the presence of catalyst.

RESULTS

In the first step of this research, the reaction of 2,4-dihydroxyacetophenone 1, isopropenylacetylene 2, methyl amine 3a, trimethylsilyle cyanide 4 and tert-butyl isocyanides 5a was used as a sample reaction to attain the best reaction conditions. The results showed this reaction performed with catalyst and did not have any product without catalyst after 12 h.

CONCLUSION

In conclusion, we investigate multicomponent reaction of 2,4-dihydroxyacetophenone 1, isopropenylacetylene 2, primary amines 3, trimethylsilyl cyanide 4 and isocyanides along with ZnO-NRs as reusable catalyst at room temperature under solvent-free conditions which generates α-amino nitrile benzofuran derivatives in high yields. The advantages of our method are high atom economy, green reaction conditions, higher yield, shorter reaction times, and easy work-up, which are in good agreement with some principles of green chemistry. The compounds 8c exhibit excellent DPPH radical scavenging activity and FRAP compared to synthetic antioxidants BHT and TBHQ.

Bimetallic BaMoO4 nanoparticles for the C–S cross-coupling of thiols with haloarenes

The C–S cross-coupling of alkyl/aryl thiols with haloarenes using BaMoO₄ nanoparticles was accomplished with high yields, and good functional group tolerance and selectivity. Unactivated bromo and 4-acetyl fluoroarenes can afford thioethers in high yields.

Reactivity triggered by an organic microcrystal interface: a case study involving an environmentally benign, aromatic boric acid reaction

At a self-assembled {002} crystal-solution interface, inactive 9-anthracene boric acid was transformed into a highly active state, for catalyst-free aromatic substitution and oxidation.

Polythiophene-functionalized magnetic carbon nanotube-supported copper(I) complex: a novel and retrievable heterogeneous catalyst for the "Phosphine- and Palladium-Free" Suzuki-Miyaura cross-coupling reaction

A simple preparation of catalysts with high catalytic activity and superior cycling stability is very desirable. In this contribution, magnetic carbon nanotube functionalized by polythiophene (CNT-Fe₃O₄-PTh) acts as an efficient and retrievable host for copper nanoparticles to prepare CNT-Fe₃O₄-PTh-Cu(I) as a nontoxic and inexpensive catalyst. FT-IR, TGA, EDX, VSM, XRD, FE-SEM, TEM, and AAS techniques were employed to characterize the structure of the synthesized magnetic heterogeneous nanocomposite. Thereafter, the catalytic application of the catalyst was evaluated for the phosphine- and palladium-free Suzuki-Miyaura cross-coupling reaction in water/ethanol as a green media in short reaction times with good to excellent yields. Various derivatives of biaryl compounds were synthesized by reaction of aryl halides and phenylboronic acid. Simple methodology and easy workup, short reaction times, elimination of volatile and toxic solvents, biocompatible reaction conditions, and high yields are some advantages of this protocol. Moreover, the catalyst showed a good reusability owing to its magnetic properties and was recycled several times without appreciable decrease in its catalytic efficiency. Copper(I) nanoparticles supported on magnetic carbon nanotube functionalized by polythiophene (CNT-Fe₃O₄-PTh-Cu(I)), was prepared and used for ligand- and palladiumfree Suzuki-Miyaura cross-coupling reaction in water/ethanol as a green media in short reaction times with good to excellent yields. Reusability and stability tests demonstrated that the as prepared catalyst can be recycled with a negligible loss of its activity.

Non-biodegradable polymeric waste pyrolysis for energy recovery

Nowadays, increasing population, widespread urbanization, rise in living standards together with versatile use of polymers have caused non-biodegradable polymeric wastes affecting the environment a chronic global problem, simultaneously, the existing high energy demand in our society is a matter of great concern. Hence forth, this review article provides an insight into the technological approach of pyrolysis emphasizing catalytic pyrolysis for conversion of polymeric wastes into energy products and presents an alternative waste management technique which is a leap towards developing sustainable environment. Pyrolysis of waste non-biodegradable polymer materials involves controlled thermal decomposition in the absence of oxygen, cracking their macromolecules into lower molecular weight ones, resulting into the formation of a wide range of products from hydrogen, hydrocarbons to coke. Nanocatalyzed pyrolysis is a recommended solution to the low thermal conductivity of polymers, promoting faster reactions in breaking the C-C bonds at lower temperatures, denoting less energy consumption and enabling enhancement in the process selectivity, whereby higher value added products are generated with increased yield. Nanotechnology plays an indispensable role in academic research as well as in industrial applications. Existing reviews illustrate that one of the oldest application field of nanotechnology is in the arena of nanocatalysis. Nanocatalysis closes the gap between homo and heterogeneous catalyses while combines their advantageous characteristics and positive aspects, reducing the respective drawbacks. During the current nanohype, nanostructured catalysts are esteemed materials and their exploration provide promising solutions for challenges from the perspective of cost and factors influencing catalytic activity, due to their featured high surface area to volume ratio which render enhanced properties with respect to the bulk catalyst.

Copper iodide and ZnO nanoparticles catalyzed multicomponent synthesis of 1,3-cyclopentadiene: study of antioxidant activity

Zinc oxide (ZnO) nanoparticles, as a simple and recyclable catalyst, were easily synthesized and used for the synthesis of 1,3-cyclopentadiene derivatives by a four-component reaction of terminal alkynes, sulfonyl azides, activated acetylenic compounds, and isocyanides in the presence of copper iodide in acetonitrile at room temperature. In these reactions, 1,3-cyclopentadiene derivatives were obtained in good yield and in a short reaction time. In this research, antioxidant activity was investigated for the some newly synthesized compounds such as 5a–5d using the DPPH radical trapping and reducing potential tests of ferric ion and comparing results with synthetic antioxidants (TBHQ and BHT). In this study, compounds 5a–5d show good DPPH radical trapping and excellent reducing power of ferric ion.