Nanostructural Design of ZnO Using an Agro-Waste Extract for a Sustainable Process and Its Photocatalytic Activity

The use of agro-waste extracts (AWEs) as a sustainable medium for developing cost-effective and ecologically friendly nanomaterials has piqued the interest of current researchers. Herein, waste extracts from papaya barks, banana peels, thumba plants, and snail shells were used for synthesizing ZnO nanostructures via a hydrothermal method, followed by calcination at 400 °C. The crystallinity and pure wurtzite phase formation of ZnO nanostructures were confirmed via X-ray diffraction. ZnO nanostructures with various morphologies such as tight sheet-like, spherical, porous sheet-like, and bracket-shaped, comprising small interconnected particles with a highly catalytically active exposed (0001) facet, were observed via field emission scanning electron microscopy and transmission electron microscopy. The formation mechanism of the various morphologies of the ZnO nanostructures was proposed. Ultraviolet-visible spectra showed different absorption band edges of ZnO nanostructures with a bandgap in the range of 3.17-3.27 eV. Photoluminescence studies showed the presence of various defect states such as oxygen and zinc vacancies and oxygen and zinc interstitials on ZnO nanostructures, which are usually observed in traditionally prepared ZnO. The photocatalytic activity of ZnO nanostructures was evaluated under direct sunlight using rhodamine B (RhB) and Congo red (CR) dyes as probe pollutants. Furthermore, prepared ZnO nanostructures could potentially adsorb anionic dyes (e.g., CR) in the absence of light. Superoxide and hydroxide radicals played a vital role in the photocatalytic activity of ZnO. The photocatalyst could be reused for up to three cycles, indicating its stability. Therefore, this study reports the diverse use of AWEs as cost-effective media for nanomaterial synthesis.

A Novel Utilization of Water Extract of Suaeda Salsa in the Pd/C Catalyzed Suzuki-Miyaura Coupling Reaction

Using biomass-derived solvents in various organic reactions is challenging for the fine chemicals industry. We herein report a Pd/C catalyzed Suzuki-Miyaura reaction in water extract of suaeda salsa (WES) without using external phosphine ligand, base, and organic solvent. The cross-coupling reactions were carried out in a basic WES medium with a broad substrate scope and wide functional group tolerance. Furthermore, the high purity of solid biaryl products can be obtained by column chromatography or filtration.

Synthesis, characterization, and photocatalytic activity of ZnO nanoparticles using water extract of waste coconut husk

The present work reports the use of natural alkaline extract from coconut husk ash as a precipitating agent for metal oxide nanoparticles synthesis. The abundance of K₂O and K₂CO₃ in it makes the extract highly basic and could be the alternative source of basic media in the laboratory. In this study, highly photoactive zinc oxide nanoparticles have been synthesized using water extract of waste coconut husk ash in a green approach which is considered as replacement of homogeneous base like NaOH and KOH. The formation of zinc oxide nanoparticles at different pH of the solution of coconut husk ash was confirmed through powder XRD, BET, SEM-EDX, UV-Vis, FTIR, and photoluminescence spectroscopy. The photocatalytic performance of the samples was evaluated through the degradation of methylene blue (MB) and methyl orange (MO) under solar irradiation which undergo degradation around 97% and 68% within 120 min, respectively. The high photocatalytic activity and rate constant could be attributed to the large surface area due to small particle size that could provide quicker photon absorption and reduction of charge carrier recombination. This current work introduces a new method to reduce energy consumption for the synthesis of highly photoactive low-cost zinc oxide nanoparticles.

Synthesis of bioactive scaffolds catalyzed by agro-waste-based solvent medium

The backbone of synthetic organic chemistry is the formation of carbon–carbon and carbon–heteroatom bonds. Scientists are actively working to develop new methods of bond-forming reactions because it is one of the most useful tools for the development of structurally diverse molecular entities. On the other hand, scientists are constantly discovering chemical processes to make them more sustainable in order to avoid the ever-increasing chemical emission associated with hazards to the environment. Thus, the development of greener catalytic reactions demonstrated a massive uptick in the ability to carry out carbon–carbon and carbon–heteroatom bond-forming reactions under environmentally friendly and simple reaction conditions. Various approaches are demonstrated, namely, solvent-free, microwave irradiation, ionic liquids, ball milling, ultrasound, one-pot, and aqueous-mediated methods under green chemistry protocol. Agro-waste is the postharvest part or agricultural residues derived from various agricultural activities, which has diverse scope and applications. The use of this agro-waste is an eco-friendly and cost-effective process of waste management. Appropriate and optimal utilization of these waste by-products is one of the major challenges in the present days. The recent trend around the globe is to transform waste into wealth concepts to achieve various applications. Agro-waste-derived ashes and extracted medium are successfully studied recently as a heterogeneous- or homogenous-based catalyst in various organic transformations. Agro-waste-derived catalysts are easily available, cost-effective, simple to prepare, nontoxic, easy to handle, biodegradable, and more environmentally benign. This article focuses more on a few instances of agro-waste-based homogeneous and heterogeneous organic synthesis, especially those used in the construction of bioactive molecule synthesis via C–C and C–X bond formation reactions are discussed. The compiled literature in this article is based on keywords used in the search engine on “agro-waste-based catalyst for organic transformations”, and review articles published on this topic, future scope, and summary are discussed.

Natural Feedstock in Catalysis: A Sustainable Route Towards Organic Transformations

Catalysts are the jewel in the crown of the chemical industry, accelerating reaction kinetics and augmenting the efficiency of desired reaction paths. Natural feedstock is a renewable resource capable of providing valuable functional products; in addition, it confers an opportunity to create catalysts. As an alternative to stoichiometric reagents, and as a part of a sustainable approach, the implications of using natural feedstocks as a source of new catalysts has attracted considerable interest. Natural feedstock-derived catalysts can promote chemical transformations more efficiently. Recent reports have highlighted the significant role of these biogenic, cost-effective, innocuous, biodegradable materials as catalysts in many biologically and pharmacologically important protocols. This review outlines the decisive organic transformations for which feedstock-derived catalysts have been employed effectively and successfully, along with their economic and environmental benefits over traditional catalytic systems.

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.

Glycolysis of Poly(Ethylene Terephthalate) Using Biomass-Waste Derived Recyclable Heterogeneous Catalyst

Plastic production has increased by almost 200-fold annually from 2 million metric tons per year in 1950s to 359 million metric tons in 2018. With this rapidly increasing production, plastic pollution has become one of the most demanding environmental issues and tremendous efforts have been initiated by the research community for its disposal. In this present study, we reported for the first time, a biomass-waste-derived heterogeneous catalyst prepared from waste orange peel for the depolymerisation of poly(ethylene terephthalate) (PET) to its monomer, bis(2-hydroxyethyl terephthalate) (BHET). The prepared orange peel ash (OPA) catalyst was well-characterised using techniques such as IR, inductively coupled plasma (ICP)-OES (Optical Emission Spectrometry), XRD, X-ray fluorescence (XRF), SEM, energy-dispersive X-ray spectroscopy (EDX), TEM, BET (Brunauer-Emmett-Teller) and TGA. The catalyst was found to be composed of basic sites, high surface area, and a notable type-IV N₂ adsorption–desorption isotherm indicating the mesoporous nature of the catalyst, which might have eventually enhanced the rate of the reaction as well as the yield of the product. The catalyst completely depolymerises PET within 90 min, producing 79% of recrystallised BHET. The ability of reusing the catalysts for 5 consecutive runs without significant depreciation in the catalytic activity and its eco- and environmental-friendliness endorses this protocol as a greener route for PET recycling.

Pawpaw (Carica papaya) Peel Waste as a Novel Green Heterogeneous Catalyst for Moringa Oil Methyl Esters Synthesis: Process Optimization and Kinetic Study

This study evaluated pawpaw (Carica papaya) peel ash as a green solid base catalyst for Moringa oleifera oil methyl esters (MOOME) production. Taguchi orthogonal array approach was used to examine the impact of vital process input variables (calcined pawpaw peel (CPP) loading, reaction temperature, methanol-to-M. oleifera oil (MeOH:MOO) molar ratio and reaction time) on the MOOME yield. Catalytic potency potential of the CPP was evaluated by Fourier transform infrared (FTIR), Barrett-Joyner-Halenda (BJH), Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) methods. The results obtained indicate that the CPP consists of nanoparticles and alkaline elements K (23.89 wt.%), Ca (2.86 wt.%) and Mg (1.00 wt.%). The high values of coefficient of determination, R2 (0.9992) and adjusted R2 (0.9968) as well as the low value of the coefficient of variation (0.31%) for the model developed indicate it can be used to sufficiently describe the transesterification process. MOOME yield of 96.43 ± 0.10 wt.% was achieved at the optimum values of 3.5 wt.% CPP loading, 9:1 MeOH:MOO molar ratio, 35 °C reaction temperature and 40 min reaction time. The kinetic modeling of the transesterification process determined the reaction rate constant and overall reaction order as 0.20465 L·mol−1·s−1 and 2, respectively. The results of this study demonstrate both CPP and MOO are feasible renewable resources for MOOME production. The kinetic data generated may be useful in reactor design for the transesterification process.

Pd-based nanoparticles: Plant-assisted biosynthesis, characterization, mechanism, stability, catalytic and antimicrobial activities

Among various metal nanoparticles, palladium nanoparticles (Pd NPs) are one of the most important and fascinating nanomaterials. An important concern about the preparation of Pd NPs is the formation of toxic by-products, dangerous wastes and harmful pollutants. The best solution to exclude and/or minimize these toxic substances is plant mediated biosynthesis of Pd NPs. Biogenic Pd-based NPs from plant extracts have been identified as valuable nanocatalysts in various catalytic reactions because of their excellent activities and selectivity. They have captured the attention of researchers owing to their economical, sustainable, green and eco-friendly nature. This review attempts to cover the recent progresses in the fabrication, characterization and broad applications of biogenic Pd NPs in environmental and catalytic systems. In addition, the stability of biosynthesized Pd NPs and mechanism of their formation are investigated.

Trash to Treasure: Eco-Friendly and Practical Synthesis of Amides by Nitriles Hydrolysis in WEPPA

The hydration of nitriles to amides in a water extract of pomelo peel ash (WEPPA) was realized with moderate to excellent yields without using external transition metals, bases or organic solvents. This reaction features a broad substrate scope, wide functional group tolerance, prominent chemoselectivity, and good reusability. Notably, a magnification experiment in this bio-based solvent at 100 mmol further demonstrated its practicability.

A Microwave Accelerated Sustainable Approach for the Synthesis of 2-amino-4H-chromenes Catalysed by WEPPA: A Green Strategy

Background:

The agricultural wastes as a source offer an excellent alternative to replace many toxic and environmentally hazardous catalysts, due to their least toxicity, ease of biodegradability, and ability to act as a greener catalytic medium. Some of the agro-waste based catalysts reported are BFE, WERSA, WEB, and WEPBA. 2-Amino-4H-chromene derivatives are promising biologically potent heterocyclic compounds, due to their medicinal applications such as antimicrobial, anti-inflammatory, antibacterial, antiviral, anticancer, antidiuretic, anticoagulant and antianaphylactic activities. The present work describes a microwave accelerated, efficient, eco-friendly and economical approach for the synthesis of 2-amino-4H-chromenes through condensation of substituted arylaldehyde, malononitrile and resorcinol/naphthol catalyzed water extract of pomegranate peel ash (WEPPA) under microwave irradiation. The reaction completed within 3-6 min with good to excellent yield of product isolation. The final product isolated by simple filtration and recrystallization gave a spectroscopically pure form of product and did not require further purification.

Methods:

The pomegranate peel ash water extract as an agro-waste derived catalyst was employed under microwave irradiation for the economical synthesis of 2-amino-4H-chromene derivatives.

Results:

The reported agro-waste based catalyst was obtained in the absence of external base, additives and solvent-free synthesis of 2-amino-4H-chromene using aryl aldehyde, malononitrile and resorcinol/ naphthol under microwave irradiation. WEPPA acts as a solvent media and catalyst, as it plays a dual role in the synthesis of 2-amino-4H-chromenes.

Conclusion:

We established an efficient, simple, agro-waste based catalytic approach for the synthesis of 2-amino-4H-chromene derivatives from the condensation of arylaldehyde, malononitrile and resorcinol/α-naphthol/β-naphthol employing WEPPA as an efficient catalyst under microwave synthesis. The method has found to be a greener, economic and eco-friendly approach for the synthesis of chromene scaffolds. The advantages of the present approach are solvent-free, no external metal, chemical base free, short reaction time and isolated product in good to excellent yields. The catalyst is agro-waste derived, which has abundant natural sources available, thus making the present approach a greener one.

WEPA: a bio-derived medium for added base, π-acid and ligand free Ullmann coupling of aryl halides using Pd(OAc)2

A bio-derived sustainable medium based on water extract of pomegranate ash (WEPA) has, for the first time, been developed for the homocoupling of aryl halides under palladium-assistance. Avoiding the requirement of an external base, ligand and π-acid, the use of the proposed renewable medium offers remarkable attributes like wide substrate scope, good to nearly quantitative yields of biphenyls with exceptional chemoselectivity and scale up viability.

Biogenic synthesis of palladium nanoparticles and their applications as catalyst and antimicrobial agent

This paper describes a simple in-situ process of synthesizing highly dispersed palladium nanoparticles (PdNPs) using aqueous leaf extract of GarciniapedunculataRoxb as bio-reductant and starch (0.3%) as bio-stabilizer. The PdNPs are characterized by techniques like FTIR, TEM, SEM-EDX, XRD and XPS analysis. It is worthnoting thatwhen the synthesis of nanoparticles was carried out in absence of starch, agglomeration of particles has been noticed.The starch-assisted PdNPs showed excellent aqueous-phase catalytic activities for three important reactions: the Suzuki-Miyaura cross-coupling reactions of aryl halides (aryl bromides and iodides) with arylboronic acids; selective oxidations of alcohols to corresponding carbonyl compounds; and reduction of toxic Cr(VI) to nontoxic Cr(III). Our catalyst could be reused up to four cycles without much compromising with its activity. Furthermore, the material also demonstrated excellent antimicrobial and anti-biofilm activities against a novel multidrug resistant clinical bacterial isolate Cronobactersakazakii strain AMD04. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PdNPswere found to be 0.06 and 0.12 mM respectively.

Metformin as a versatile ligand for recyclable palladium-catalyzed cross-coupling reactions in neat water

We present the high catalytic activity of an in situ generated palladium(ii)/metformin complex in neat water for the Suzuki–Miyaura and Sonogashira cross-coupling reactions.