Green Chemical Synthesis Research Articles

Green chemical synthesis of new chelating fiber and its mechanism for recovery gold from aqueous solution.

A novel environmentally-friendly polyacrylonitrile-2-amino-2-thiazoline chelating fiber (PANF-ATL) with good adsorption performance and thermal stability was synthesized in one step by nucleophilic addition reaction using water as a solvent. The optimum synthesis conditions for the chelating fibers are determined by controlling the synthesis temperature and the molar ratio of the reagents. The sulfur content and functional group capacity of the finally synthesized PANF-ATL were 3.82% and 1.19 mmol/g, respectively. PANF-ATL was characterized by elemental analysis, FTIR, TGA, SEM and XPS. Meanwhile, the adsorption characteristics and mechanism of PANF-ATL were evaluated. The Langmuir model and the pseudo-second-order model well described the adsorption of Au(Ⅲ) by PANF-ATL. The adsorption capacity of PANF-ATL obtained from Langmuir isotherm model towards Au(Ⅲ) was 130.58 mg/g (298 K). In addition, Au(Ⅲ) adsorbed on the fibers was completely eluted using a mixed solution of 4 mol/L HCl and 12% thiourea. It still has good adsorption performance after 5 adsorption-desorption cycles. Overall, PANF-ATL is a cost-effective adsorbent that can effectively adsorb Au(Ⅲ) in aqueous solution.

Metal-Free Photocatalysts for C-H Bond Oxygenation Reactions with Oxygen as the Oxidant.

Direct and selective oxygenation of C-H bonds to C-O bonds is regarded as an effective tool to generate high-value products. However, these reactions are still subject to challenges such as harsh reaction conditions, use of expensive transition metal catalysts, and involvement of stoichiometric oxidants. To avoid these, molecular oxygen would be ideal as oxidant, as the byproduct is water or hydrogen peroxide. Additionally, achieving these reactions by using metal-free catalysts would contribute to green and sustainable chemical synthesis. This Minireview summarizes recent reports on C-H oxygenation reactions with metal-free catalysts and molecular oxygen under visible-light conditions.

Paired Electrocatalytic Oxygenation and Hydrogenation of Organic Substrates with Water as the Oxygen and Hydrogen Source.

The use of water as an oxygen and hydrogen source for the paired oxygenation and hydrogenation of organic substrates to produce valuable chemicals is of utmost importance as a means of establishing green chemical syntheses. Inspired by the active Ni3+ intermediates involved in electrocatalytic water oxidation by nickel‐based materials, we prepared NiBx as a catalyst and used water as the oxygen source for the oxygenation of various organic compounds. NiBx was further employed as both an anode and a cathode in a paired electrosynthesis cell for the respective oxygenation and hydrogenation of organic compounds, with water as both the oxygen and hydrogen source. Conversion efficiency and selectivity of ≥99 % were observed during the oxygenation of 5‐hydroxymethylfurfural to 2,5‐furandicarboxylic acid and the simultaneous hydrogenation of p‐nitrophenol to p‐aminophenol. This paired electrosynthesis cell has also been coupled to a solar cell as a stand‐alone reactor in response to sunlight.

Preparation of novel mcl-PHA by green synthesis: influence of active small molecule via esterification effect on side chain

Microbial production of polyhydroxyalkanoic acid (PHA) with customized features has been attempted by humans through metabolic engineering. However, few studies have explored the green chemical synthesis of customized PHA using hydroxy fatty acids. In the present study, new mcl-PHA having C16-co-C16, blocked by esterification of hydroxy groups in the side chain, was synthesized by melt polycondensation using aleuritic acid (9, 10, 16-trihydroxyhexadecanoic acid) and lactic acid as long-chain fatty acid monomers and active blocking molecule, respectively. The results showed that when the two monomers reacted at 150 °C for 24 h, the properties of PHA were largely retained, along with free hydroxyl groups as much as possible. Comparison of the effect of different ratios of active small molecule (lactic acid) on the properties of new mcl-PHA revealed that copolymerization mainly happened between the long-chain monomers, and lactic acid served as a blocker by esterification in the side chain on the hydroxy groups of mcl-PHA. Further, the properties of side chain-esterified mcl-PHA (SCE-mcl-PHA) changed from rigid to soft with increasing ratio of active lactic acid monomer. The tensile strength of mcl-PHA was similar to that of commercially available products PLA and PHBV. The mechanical properties of SCE-mcl-PHA significantly changed by adding only 5 wt% lactic acid monomer. Besides, the cell proliferation analysis showed that the new PHA had minimum cytotoxicity, which was close to PLA and PHBV. Therefore, these new mcl-PHA and SCE-mcl-PHA have great potential for application in food, medicine, cosmetics, and other fields, and hence require further investigation.

Electrosynthesis of Hydrogen Peroxide Synergistically Catalyzed by Atomic Co-Nx -C Sites and Oxygen Functional Groups in Noble-Metal-Free Electrocatalysts.

Hydrogen peroxide (H2 O2 ) is a green oxidizer widely involved in a vast number of chemical reactions. Electrochemical reduction of oxygen to H2 O2 constitutes an environmentally friendly synthetic route. However, the oxygen reduction reaction (ORR) is kinetically sluggish and undesired water serves as the main product on most electrocatalysts. Therefore, electrocatalysts with high reactivity and selectivity are highly required for H2 O2 electrosynthesis. In this work, a synergistic strategy is proposed for the preparation of H2 O2 electrocatalysts with high ORR reactivity and high H2 O2 selectivity. A Co-Nx -C site and oxygen functional group comodified carbon-based electrocatalyst (named as Co-POC-O) is synthesized. The Co-POC-O electrocatalyst exhibits excellent catalytic performance for H2 O2 electrosynthesis in O2 -saturated 0.10 m KOH with a high selectivity over 80% as well as very high reactivity with an ORR potential at 1 mA cm-2 of 0.79 V versus the reversible hydrogen electrode (RHE). Further mechanism study identifies that the Co-Nx -C sites and oxygen functional groups contribute to the reactivity and selectivity for H2 O2 electrogeneration, respectively. This work affords not only an emerging strategy to design H2 O2 electrosynthesis catalysts with remarkable performance, but also the principles of rational combination of multiple active sites for green and sustainable synthesis of chemicals through electrochemical processes.

Highly Stable Dual‐Phase Membrane Based on Ce0.9Gd0.1O2–δ—La2NiO4+δ for Oxygen Permeation under Pure CO2 Atmosphere

Dense oxygen ion–conducting ceramic membranes with CO2 resistance can promote many advanced applications such as membrane reactors for green chemical synthesis and oxy‐fuel combustion for clean energy delivery. The state‐of‐the‐art perovskite oxide membranes are characterized by their high O2 flux but low stability in a CO2‐containing atmosphere. To solve this problem, dual‐phase membranes have captured the imagination of researchers. Herein, a novel dual‐phase hollow fiber membrane with a composition of 40 wt% Ce0.9Gd0.1O2–δ (GDC)–60 wt% La2NiO4+δ (LNO) is developed via a combined phase inversion sintering process. During the high temperature treatment, La‐doping behavior is observed with La leaching out from the LNO phase and diffusing into the GDC phase. This dual phase membrane displays the O2 flux of 1.47 at 950 °C, which is reduced by 10% to 1.31 mL min−1 cm−2 when the sweep gas is switched from helium to pure CO2. Such minor O2 flux reduction is due to the strong CO2 adsorption on membrane surface occupying the O2 vacancies without permanent membrane damage, which is fully eliminated by an inert gas purge. Such a robust dual‐phase membrane exhibits the potential to overcome the low stability problem under the CO2‐containing atmosphere.

Effect of the Immobilization Strategy on the Efficiency and Recyclability of the Versatile Lipase from Ophiostoma piceae.

The recombinant lipase from Ophiostoma piceae OPEr has demonstrated to have catalytic properties superior to those of many commercial enzymes. Enzymatic crudes with OPEr were immobilized onto magnetite nanoparticles by hydrophobicity (SiMAG-Octyl) and by two procedures that involve covalent attachment of the protein (mCLEAs and AMNP-GA), giving three nanobiocatalysts with different specific activity in hydrolysis of p-nitrophenyl butyrate (pNPB) and good storage stability at 4 °C over a period of 4 months. Free OPEr and the different nanobiocatalysts were compared for the synthesis of butyl esters of volatile fatty acids C4 to C7 in reactions containing the same lipase activity. The esterification yields and the reaction rates obtained with AMNP-GA-OPEr were in general higher or similar to those observed for the free enzyme, the mCLEAs-OPEr, and the non-covalent preparation SiMAG-Octyl-OPEr. The time course of the esterification of the acids C4 to C6 catalyzed by AMNP-GA-OPEr was comparable. The synthesis of the C7 ester was slower but very efficient, admitting concentrations of heptanoic acid up to 1 M. The best 1-butanol: acid molar ratio was 2:1 for all the acids tested. Depending on the substrate, this covalent preparation of OPEr maintained 80–96% activity over 7 cycles, revealing its excellent properties, easy recovery and recycling, and its potential to catalyze the green synthesis of chemicals of industrial interest.

Green chemistry synthesis of biocompatible ZnS quantum dots (QDs): their application as potential thin films and antibacterial agent

We are presenting here the synthesis of quantum dots (QDs) of direct band gap semiconductor, cubic ZnS through modified green chemistry-mediated chemical precipitation reaction. Green chemistry-synthesized (GCS) ZnS QDs were characterized using powder X-ray diffraction and high-resolution transmission electron microscope techniques. Analysis of results, revealed by both the techniques for the synthesized QDs, is complementary as far as the size range (2–6 nm) of ZnS QDs is concerned. UV–Vis spectrophotometric spectrum (λmax = 314 nm) showed a conspicuous blue shift than the bulk. The Fourier-transformed infrared spectra convincingly reported a Zn–S bond stretching frequency at 649 cm−1. The characterized QDs were subjected to the preparation of thin films over SiO2 template (57 nm thickness) using photoresist spin coating technique at the ambient condition. The surface topology of nanoscale-thick films was studied by atomic force microscope (roughness parameter—33.28 nm, rms; for a scan area of 3.48 × 3.48 μm2). The symmetrical (skewness = 1.68) and random distribution (kurtosis = 2.93) of the peaks and valleys revealed the nanoscale-thick films of ZnS QDs. Zeta potential (− 9.2 mV) fairly proved stable existence of ZnS QDs. The GCS QDs were found to be non-toxic toward L929 mouse fibroblastic cells and human erythrocytes. However, they demonstrated significant inhibitory effects against seven bacterial pathogens with an average zone of inhibition of 1.5 cm at 100 μg/ml concentration. The minimum inhibitory concentrations determined were in the range of 75 to 125 μg/ml for gram-positive and 100 to 150 μg/ml for gram-negative bacterial pathogens.

Studies on interaction of green silver nanoparticles with whole bacteria by surface characterization techniques

The use of silver nanoparticles (AgNPs) with their novel and distinct physical, chemical, and biological properties, has proven to be an alternative for the development of new antibacterial agents. In particular, the possibility to generate AgNPs coated with novel capping agents, such as phytomolecules obtained via a green synthesis (G-AgNPs), is attracting great attention in scientific research.Recently, we showed that membrane interactions seem to be involved in the antibacterial activity of AgNPs obtained via a green chemical synthesis using the aqueous leaf extract of chicory (Cichorium intybus L.). Furthermore, we observed that these G-AgNPs exhibited higher antibacterial activity than those obtained by chemical synthesis.In order to achieve the green AgNPs mode of action as well as their cellular target, we aimed to study the antibacterial activity of this novel green AgNPs against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The effect of the G-AgNPs on the bacterial surface was first evaluated by zeta potential measurements and correlated with direct plate count agar method. Afterwards, atomic force microscopy was applied to directly unravel the effects of these G-AgNPs on bacterial envelopes.Overall, the data obtained in this study seems correlate with a multi-step mechanism by which G-AgNPs-lipid membrane interactions is the first step prior to membrane disruption, resulting in antibacterial activity.

Green Synthesis of Zwitterion-Functionalized Nano-Octahedral Ceria for Enhanced Intracellular Delivery and Cancer Therapy

The present work reports a new method for the green chemical synthesis of biomaterials using an integrated, room-temperature, aqueous, chemical technique involving surfactant-free precipitation of ...

Bio-inspired synthesis of aqueous nanoapatite liquid crystals

The macroscopically ordered structure of rod-like nanoapatites within the collagen matrix is of great significance for the mechanical performance of bones and teeth. However, the synthesis of macroscopically ordered nanoapatite remains a challenge. Inspired by the effect of citrate molecules on apatite crystals in natural bone and the similarities between these ordered rod-like nanoapatites and the nematic phase of inorganic liquid crystals (LCs), we synthesized aqueous liquid crystal from rod-like nanoapatites with the aid of sodium citrate. Following a similar procedure, aqueous Mg(OH)2 and Mg3(PO4)2 LCs were also prepared. These findings lay the foundation for the fabrication of macroscopically assembled nanoapatite-based functional materials for biomedical applications and offer a green chemical synthesis platform for the development of new types of inorganic LCs. This process may reduce the difficulties in synthesizing large quantities of inorganic LCs so that they can be applied to the fabrication of functional materials.

The styrene monooxygenase system.

Styrene monooxygenases are soluble two-component flavoproteins that catalyze the NADH and FAD-dependent enantioselective epoxidation of styrene to styrene oxide in the aqueous phase. These enzymes present interesting mechanistic features and potential as catalysts in biotechnological applications ranging from green chemical synthesis to bioremediation. This chapter presents approaches for the expression of the reductase (SMOB, StyB) and epoxidase (SMOA, StyA) components of SMO from pET-vectors as native or N-terminally histidine-tagged proteins in commercial strains of E. coli. The two-component structure of SMO and hydrophobic nature of styrene substrate requires some special consideration in evaluating the mechanism of this enzyme. The modular composition of the enzyme allows the flavin-reduction reaction of SMOB and styrene epoxidation reaction of SMOA to be evaluated both independently and as a composite catalytic system. The freedom to independently study the reductase and epoxidase components of SMO significantly simplifies studies of equilibrium-binding and the coupling of the free energy of ligand binding to the electrochemical potential of bound FAD. In this chapter, methods of steady-state and pre-steady-state kinetic assay, experimental approaches to equilibrium-binding reactions of flavin and substrate, and determination of the electrochemical midpoint potential of FAD bound to the reductase and epoxidase components of SMO are presented. This presentation focuses on approaches that have been successfully used in the study of the wild-type styrene monooxygenase system recovered from Pseudomonas putida (S12), but similar approaches may be effective in the characterization of related two-component enzyme systems.

Facile Green Chemistry Synthesis of Ag Nanoparticles Using Areca Catechu Extracts for the Antimicrobial Activity and Photocatalytic Degradation of Methylene Blue Dye

Green synthesis of silver nanoparticles (Ag NPs) using Areca catechu extract as reducing agent was investigated. The bioreduction of silver ions into silver nanoparticles was monitored using UV-visible spectrophotometry. The synthesized Ag NPs were studied by Fourier transform infra-red spectroscopy (FTIR), UV–visible spectroscopy, Transmission electron microscopy (TEM) analysis, Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. The photocatalytic degradation of methylene blue was estimated spectrophotometrically using the green synthesized silver (Ag) as nanocatalyst. Disc diffusion method was used to investigate the antimicrobial properties of the Ag NPs against the tested bacterial strains

Photocatalysis as an advanced reduction process (ARP): The reduction of 4-nitrophenol using titania nanotubes-ferrite nanocomposites.

TiO2 photocatalysis is an advanced process, employed worldwide for the oxidation of organic compounds, that leads to significant technological applications in the fields of health and environment. The use of the photocatalytic approach in reduction reactions seems very promising and can open new horizons for green chemistry synthesis. For this purpose, titanium dioxide nanotubes (TNTs) were developed in autoclave conditions using TiO2 P25 as a precursor material. Based on these nanotubular substrates, TiO2/CoFe2O4 (TCF) nanocomposites were further obtained by wet impregnation method. The materials were thoroughly characterized and their structural, textural, vibrational, optoelectronic and magnetic properties were determined. The composite materials combine absorbance in the visible optical range and high BET surface area values (˜100 m2/g), showing extremely high yield in the photocatalytic reduction of 4-nitrophenol (4-NP), exceeding 94% within short illumination time (only 35 min). The developed nanocomposites were successfully reused in consecutive photocatalytic experiments and were easily removed from the reaction medium using magnets. Both remarkable recycling ability and high-performance stability in the photocatalytic reduction of nitrophenol were observed, thus justifying the significant economic potential and industrial perspectives for this advanced reduction process.

Green chemical synthesis of Pd nanoparticles for use as efficient catalyst in Suzuki‐Miyaura cross‐coupling reaction

Herein, we report the synthesis of tiny spherical Pd nanoparticles (NPs) by green chemical method under ambient conditions using flower extract of Lantana camara plant. The size of the Pd NPs is tunable from 4.7 to 6.3 nm by systematically controlling the concentration of either metal ions or plant extract. The synthesized Pd NPs were well characterized by different spectroscopic, microscopic and diffractometric techniques. The Pd NPs offered good size‐dependent catalytic activity in the Suzuki‐Miyaura C‐C coupling reaction under mild reaction conditions in (1: 1) water‐ethanol mixture. The catalyst is stable and exhibited excellent reusability up to three cycles of coupling reaction after which the catalytic activity decreases.

Biocatalysis Using Immobilized Enzymes in Continuous Flow for the Synthesis of Fine Chemicals

Biocatalysis has emerged as one of the most promising technologies to enable green synthesis of important chemicals, due to the ambient conditions generally applied for these reactions. Nonetheless, a general uptake of enzymatic transformations has been hindered by the perceived high cost of recombinant proteins. Recent interest in continuous flow from the synthetic chemistry community has now begun to spread to biotransformations, with protein immobilization playing a key part. As a consequence, continuous biotransformations using immobilized enzymes are becoming more accessible to nonexperts. This review will discuss several recent examples of continuous biotransformations that use immobilization, with a focus on examples involving fine chemical synthesis. It will also examine some of the issues that the community has as a whole, most importantly a lack of unified reporting tools to allow comparison and assessment of the different techniques.

The Catalytic Reduction of Carboxylic Acid Derivatives and CO2 by Metal Nanoparticles on Lewis-Acidic Supports.

The development of heterogeneous catalysts for green chemical synthesis is currently a growing area in catalysis and sustainable chemistry. Especially the use of renewable carbon resources such as carbon dioxide (CO2 ) and biomass-derived compounds (e. g. carboxylic acids, esters, and amides) represent highly attractive research targets. As these substances reside in a high oxidation state, efficient reduction processes are required in order to convert these substrates into useful and value-added chemicals. Moreover, in the interest of mass production, these substrates should be reduced by molecular H2 and a heterogeneous catalyst. In this context, our group has developed advanced catalysts and established design guidelines for catalysts that promote the reductive transformations of carboxylic acid derivatives and CO2 . Our studies show that cooperative catalysis between Lewis-acidic sites on the catalyst support and supported metal nanoparticles are crucial for the success of these challenging hydrogenations. In this review, we summarize the results of our recent studies on the direct synthesis of value-added chemicals from CO2 and carboxylic acid derivatives using supported transition-metal catalysts, and we propose a design concept for heterogeneous catalysts that promote these processes.

Green Chemistry Synthesis of Five-Membered Heterocylic Derivatives (1, 3, 4-oxadizoles) by Using Grinding Technique

Green Chemistry Synthesis of Five-Membered Heterocylic Derivatives (1, 3, 4-oxadizoles) by Using Grinding Technique

Single-atom catalyst: a rising star for green synthesis of fine chemicals

Abstract The green synthesis of fine chemicals calls for a new generation of efficient and robust catalysts. Single-atom catalysts (SACs), in which all metal species are atomically dispersed on a solid support, and which often consist of well-defined mononuclear active sites, are expected to bridge homogeneous and heterogeneous catalysts for liquid-phase organic transformations. This review summarizes major advances in the SAC-catalysed green synthesis of fine chemicals in the past several years, with a focus on the catalytic activity, selectivity and reusability of SACs in various organic reactions. The relationship between catalytic performance and the active site structure is discussed in terms of the valence state, coordination environment and anchoring chemistry of single atoms to the support, in an effort to guide the rational design of SACs in this special area, which has traditionally been dominated by homogeneous catalysis. Finally, the challenges remaining in this research area are discussed and possible future research directions are proposed.

CO2 erosion of BaCo0.85Bi0.05Zr0.1O3-δ perovskite membranes under oxygen permeating conditions

Abstract CO2-resistant oxygen selective ceramic membranes have wide applications in clean energy delivery and green chemical synthesis. In this work, CO2 erosion and O2 permeation behavior of BaCo0.85Bi0.05Zr0.1O3-δ (BCBZ) perovskite hollow fibre membranes are investigated. The BCBZ hollow fibre was fabricated by a combined phase-inversion and sintering technique. Experimental results indicate that the O2 permeation flux can reach 3.07 mL cm−2 min−1 at 1000 °C under the air/Ar gradient whereas the O2 flux reduced significantly in CO2 presence depending on the CO2 concentration in the feed gas or sweep gas. The deteriorating effect of CO2 on the membrane performance in the feed side was more significant than when it was present in the permeate side. One of the BCBZ hollow fibre samples had been tested for more than 190 h; undergoing six thermal cycles from 700 to 1000 °C in different CO2-containing gas streams. With high CO2 concentrations up to 10 vol.% in both feed and permeate sides, no permeation was observed due to the strong CO2 adsorption on the membrane surface; however, the O2 flux can be completely recovered once the CO2 became absent in the gas atmosphere. When the membrane test was continued up to 180 h, the O2 flux value cannot be fully recovered and 9.6% of the original flux value was lost due to the carbonate salt formation. To get the quantitative information on the erosion rate, more membrane samples had been tested from 1 to −8 days in 10 vol.% CO2 at 900 °C under the oxygen permeating conditions. We found that the erosion rate was relatively fast at the beginning stage with corrosion depth up to 3 µm for the first 3 days but slowed down to 1 µm depth for the subsequent 5 days. The significantly reduced erosion rate is due to the higher O2 concentration in the locally uncontaminated membrane area (without the carbonate deposition). Inspired by such findings, one future strategy to protect the membrane is to deposit the membrane surface using more robust ion-conducting layer like Sm0.2Ce0.8O1.9.