Search Results (17)

Lignocellulose is an important renewable biomass resource. However, at present, there is a lack of efficient and environmentally friendly catalytic systems that can selectively convert lignocellulose components into high-value sugars, and the value realization of agricultural waste (such as straw) remains challenging. Carbon-based solid acids are used in the valorization of biomass due to their simple preparation and excellent catalytic performance. In this study, the magnetic carbon microspheres catalyst was prepared using concentrated sulfuric acid and hydroxyethyl sulfonic acid as sulfonating agents. Two sulfonation catalysts were applied to the hydrolysis of typical agricultural waste (rice straw). The performance of catalyst conversion to reducing sugar was compared, and the glucose yield was lower than 30%. The sulfonation catalyst of hydroxyethyl sulfonic acid obtained a higher yield of pentose (76.67%) than that of concentrated sulfuric acid (74.25%) in 110 min. The optimal reaction conditions were found: substrate was 0.04 g straw, catalyst was 0.04 g, H₂O/γ-valerolactone ratio was 8:2 in the solvent, and the reaction time was 110 min at 140 °C. Under these conditions, the sulfonation properties of hydroxyethyl sulfonic acid as a green sulfonating agent are similar to those of concentrated sulfuric acid. Its excellent catalytic performance is attributed to the medium B/L acid density ratio on the catalyst surface. In addition, the prepared catalyst can be effectively separated from the reaction residue in the catalytic system. This work provides a green catalytic system for the high-value utilization of agricultural waste from renewable carbon sources. Full article

In this work, a closed-loop strategy for the management and valorization of winery waste was proposed. The exhausted pomace and grape stalks that are typically obtained from white wine industries were used as a source of simple sugars, namely, glucose and fructose, and of lignocellulosic feedstock for the preparation of selective catalysts for the 5-hydroxymethylfurfural (5-HMF) production from fructose. A novel synthetic procedure was developed for the synthesis of iron-sulfonated magnetic biochar catalysts (Fe-SMBCs). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), BET surface area, porous structure analysis and determination of total amount of acid sites were performed in order to characterize the physico-chemical properties of the synthesized systems. Then, these heterogeneous catalysts were successfully tested via the dehydration of simple sugars into 5-HMF by using methyl isobutyl ketone (MIBK) and gamma valerolactone (GVL) as co-solvents. The optimum 5-HMF yield of 40.9 ± 1.1%mol with a selectivity of 59.8 ± 2.6%mol was achieved by adopting the following optimized conditions: 0.1 g of catalyst, volume ratio of GVL to H₂O = 2 to 1, 403 K, 6 h. In addition, the catalyst was easily recycled using an external magnetic field and used for at least five reaction cycles without significant loss of catalytic activity. Full article

In this work, a novel sustainable approach was proposed for the integral valorisation of Arctium lappa (burdock) seeds and roots. Firstly, a preliminary recovery of bioactive compounds, including unsaturated fatty acids, was performed. Then, simple sugars (i.e., fructose and sucrose) and phenolic compounds were extracted by using compressed fluids (supercritical CO₂ and propane). Consequently, a complete characterisation of raw biomass and extraction residues was carried out to determine the starting chemical composition in terms of residual lipids, proteins, hemicellulose, cellulose, lignin, and ash content. Subsequently, three alternative ways to utilise extraction residues were proposed and successfully tested: (i) enzymatic hydrolysis operated by Cellulases (Thricoderma resei) of raw and residual biomass to glucose, (ii) direct ethanolysis to produce ethyl levulinate; and (iii) pyrolysis to obtain biochar to be used as supports for the synthesis of sulfonated magnetic iron-carbon catalysts (Fe-SMCC) to be applied in the dehydration of fructose for the synthesis of 5-hydroxymethylfurfural (5-HMF). The development of these advanced approaches enabled the full utilisation of this resource through the production of fine chemicals and value-added compounds in line with the principles of the circular economy. Full article

Sulfonated-silica-coated cobalt ferrite (CoFe₂O₄) magnetic nanoparticles (MNPs-SiCoFe-SO₃H) are efficient heterogeneous catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-one and octahydroquinazoline derivatives in the absence of solvent. The effects of solvent, temperature, and catalyst amount on the reaction are investigated. The easy separation, reusability of the catalyst, simplicity of the procedure, mild reaction conditions, and good yields (68–95%) within short reaction times (15–70 min) are the advantages of this method. The catalyst can be reused up to eight times with not much loss of activity. Scanning electron microscopy images, X-ray diffraction spectra, and elemental analysis of the recycled catalyst show that the catalyst is stable after the reaction. Full article

Sulfonated polymer-based materials, among heterogeneous catalysts, are frequently utilized in chemical transformations due to their outstanding chemical and physical durability. In this regard, a magnetic sulfonated melamine–formaldehyde resin (MSMF) catalyst was successfully prepared from a mixture of sulfonated melamine–formaldehyde and Fe₃O₄ nanoparticles in two steps. MSMF was used as a heterogeneous catalyst for the one-pot, three-component condensation of benzyl pyrazolyl naphthoquinones in water as a green solvent and 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones. The antimicrobial and antioxidant activities of catalyst, benzyl pyrazolyl naphthoquinones, and 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones were evaluated using agar disk-diffusion and DPPH assays, respectively. The antioxidant activity of the catalyst and 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones was found to be 75% and 90%, respectively. Furthermore, catalyst, benzyl pyrazolyl naphthoquinones, and 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones exhibited antimicrobial activity against Staphylococcus aureus and Escherichia coli. In conclusion, MSMF is a superior catalyst for green chemical processes, owing to its high catalytic activity, stability, and reusability. Full article

Chloroaluminate ionic liquid bound on magnetic nanoparticles (Fe₃O₄@O₂Si[PrMIM]Cl·AlCl₃) was prepared and used as a heterogenous Lewis acidic catalyst for the Friedel–Crafts sulfonylation of aromatic compounds with sulfonyl chlorides or p-toluenesulfonic anhydride. The catalyst’s stability, efficiency, easy recovery, and high recyclability without considerable loss of catalytic capability after four recycles were evidence of its advantages. Furthermore, the stoichiometry, wide substrate scope, short reaction time, high yield of sulfones, and solvent-free reaction condition also made this procedure practical, ecofriendly, and economical. Full article

A heterogeneous solid acid catalyst was synthesized using tire polymer waste (TPW) for the esterification of waste chicken fat (CF) enriched with fatty acids. The TPW was carbonized and functionalized with concentrated sulfuric acid under various sulfonation conditions to obtain a sulfonated tire polymer char (TPC-SO₃H) catalyst. The TPC-SO₃H catalyst was further characterized via acid-base titration (to ascertain the total concentration of acid), X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Brunauer–Emmett–Teller (BET) analysis. The esterification reaction conditions of extracted chicken fat with methanol and the viability of catalyst reuse were also investigated. The composition of the free fatty acid (FFA) decreased to below 1% under optimum reaction conditions of 5% TPC-SO₃H catalyst, the methanol-to-CF molar-ratio of 15:1, and a reaction time of 120 min at 70 °C. The catalyst preserved its conversion efficiency above 90%, even after three cycles. The results demonstrate that the catalyst is applicable and efficient in the esterification of raw materials containing various fatty acid compositions since different carbonized materials have distinct abilities to combine acid groups. Furthermore, after de-acidification of CF-FFA by the as-prepared TPC-SO₃H catalyst, the neutral CF was transesterified completely to biodiesel and characterized via Fourier Transform Infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H NMR) spectroscopy and physicochemical analysis. This work unveils a promising technique for utilizing tire waste generated in large quantities for the development of a novel heterogeneous acid catalyst for biodiesel production. Full article

With the increase in global demand for biodiesel, first generation feedstock has drawn the attention of governmental institutions due to the correlation with large land farming areas. The second and third feedstock generations are greener feedstock sources, nevertheless, they require different catalytic conditions if compared with first generation feedstock. In this work, we present the synthesis and characterization of oligoesters matrices and their functionalization to act as a pseudo-homogeneous acid catalyst for biodiesel production, named Oligocat. The main advantage of Oligocat is given due to its reactional medium interaction. Initially, oligocat is a solid catalyst soluble in the alcoholic phase, acting as a homogeneous catalyst, providing better mass transfer of the catalytic groups to the reaction medium, and as the course of the reaction happens, Oligocat migrates to the glycerol phase, also providing the advantage of easy separation of the biodiesel. Oligocat was synthesized through polymerization of aromatic hydroxy acids, followed by a chemical functionalization applying the sulfonation technique. Characterization of the catalysts was carried out by infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). The synthesized oligomers presented 5357 g·mol⁻¹ (Mw) and 3909 g·mol⁻¹ (Mn), with a moderate thermal resistance of approximately 175 °C. By sulfonation reaction, it was possible to obtain a high content of sulphonic groups of nearly 70 mol%, which provided the catalytic activity to the oligomeric matrix. With the mentioned physical–chemical properties, Oligocat is chemically designed to convert second generation feedstock to biodiesel efficiently. Preliminary investigation using Oligocat for biodiesel production resulted in conversion rates higher than 96.5 wt.%. Full article

In the present investigation, an efficient heterogeneous catalyst system made of a polyaniline-derived polymer (Poly [anthranilic acid]-[N-(1′,3′-phenylenediamino) −3-butane sulfonate]) and iron oxide nanoparticles (Fe₃O₄ NPs) is presented. Firstly, this novel catalytic system (Fe₃O₄@Polyaniline-SO₃H) has been fabricated via a convenience method and magnetized via an in situ process. The as-prepared solid acid catalyst was also carefully analyzed by Fourier transfer infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDX). It has been suitably applied for the one-pot multicomponent synthesis of acridinediones as an important class of heterocyclic compounds. The first and foremost advantage of this catalytic system is that the (Fe₃O₄@Polyaniline-SO₃H) is magnetically separated from the reaction mixture through their high paramagnetic behavior. The main attractive characteristics of the presented green protocol are very short reaction times, excellent yields, and the avoidance of hazardous or toxic reagents and solvents. Easy separation, high reusability, cost-effective and mild catalyst are important advantages of the new catalyst in comparison to other catalysts for the synthesis of acridinedione derivatives via one-pot four-component reaction. Full article

Acid catalysis is widely used in the chemical industry, and nowadays many efforts are being focused on replacing the more common homogeneous catalysts with heterogeneous ones in order to make greener the industrial processes. In this perspective, sulfonic solid acid materials represent a valid alternative to the homogenous mineral acid in several acid catalyzed reactions. In this minireview, an overview of the recent advances on the preparation, stability and application of these materials is reported. Special attention is addressed to the sustainability of the considered processes, starting from the catalyst’s preparation, the use of green solvents and reducing the possible reaction steps. Ways to tackle the main drawback represented by easy leaching of acid groups are described. For an easy catalyst recovery, the use of a magnetic core in a catalyst particle, with the related synthetic approaches, is also illustrated. Finally, a section is dedicated to the principal characterization techniques to identify the structural properties of the catalysts. Full article

A series of polydodecylmethylsilsesquioxane (PDMSQ) nanocomposite latexes were prepared via emulsion polymerization of methyltriethoxysilane (MTES) and dodecyltrimethoxysilane (DTMS) and sodium hydroxide as the catalyst, and sodium dodecyl benzene sulfonate/Tween 80 as the mixed emulsifiers. Effects of the emulsifier doses, the reaction temperature, the catalyst concentration and the oil/water ratio on the particle size and distribution of the PDMSQ nanoparticles were discussed. Particle size and micromorphology, structure, thermal stability, crystallinity and hydrophobicity of PDMSQ nanoparticles (PDMSQ NPs) were investigated by dynamic laser scattering (DLS), Fourier transform infrared spectroscopy (FTIR), silicon-nuclear magnetic resonance (²⁸Si-NMR), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and contact angle tester. Results showed that a series of PDMSQ NPs could be obtained with an average particle size of less than 80 nm and narrow distribution as well as spherical structure under the optimal process conditions. PDMSQ NPs exhibited excellent thermal stability and were mainly amorphous but also contained some crystal structures. Importantly, the static water contact angles (WCAs) on its latex films were larger than 150° and the WCAs hysteresis were less than 10°, thus those PDMSQ nanocomposite latexes show potential in the field of superhydrophobic coatings. Full article

The ionic crosslinked 2-acrylamido-2-methylpropane sulfonic acid-co-acrylic acid hydrogel, AMPS/AA and its Ag and Fe₃O₄ composites were synthesized using an in situ technique. The surface charge, particle sizes, morphology, and thermal stability of the prepared AMPS/AA-Ag and AMPS/AA-Fe₃O₄ composites were evaluated using different analytical techniques and their adsorption characteristics were evaluated to remove the methylene blue cationic dye, MB, from their aqueous solutions at optimum conditions. Also, the same monomers were used to synthesize AMPS/AA microgel and its Ag and Fe₃O₄ nanocomposites, which were synthesized using the same technique. The AMPS/AA-Fe₃O₄ nanocomposite was selected as conventional iron-supported catalyst due to the presence of both Fe(II) and Fe(III) species besides its magnetic properties that allow their easy, fast, and inexpensive separation from the aqueous solution. It was then evaluated as a heterogeneous catalyst for complete MB degradation from aqueous solution by heterogeneous Fenton oxidation. It achieved a high rate of degradation, degrading 100 mg L⁻¹ of MB during a short time of 35 min as compared with the reported literature. Full article

Herein, we report the synthesis of nanoporous polytriphenylamine polymers (PPTPA) by a simple one-step oxidative polymerization pathway and the materials were sulfonated with chlorosulfonic acid to introduce acidic sulfonic groups to the polymers to form solid acid catalysts (SPPTPA). Magnetic properties were added to SPPTPA catalysts by depositing Fe₃O₄ nanoparticles to develop (FeSPPTPA) solid acid catalysts, for performing dehydration of fructose to 5-hydroxymethylfurfural (HMF), which is regarded as a sustainable source for liquid fuels and commodity chemicals. XRD, FTIR spectroscopy, SEM, TGA, and N₂ sorption techniques were used to characterize synthesized materials. The FeSPPTPA80 nanocatalyst showed superior catalytic activities in comparison to other catalysts due to the nanorods that formed after sulfonation of the PPTPA polymeric material which gave the catalyst enough catalytic centers for dehydration reaction of fructose. The recyclability tests revealed that the magnetic solid acid catalysts could be reused for four consecutive catalytic runs, which made FeSPPTPA a potential nanocatalyst for production of HMF. Full article

Conversion of biorenewable feedstocks into transportation fuels or chemicals likely necessitates the development of novel heterogeneous catalysts with good hydrothermal stability, due to the nature of highly oxygenated biomass compounds and the prevalence of water as a processing solvent. The use of carbon-based materials, derived from sugars as catalyst precursors, can achieve hydrothermal stability while simultaneously realizing the goal of sustainability. In this work, the simultaneous pyrolysis of glucose and taurine in the presence of multi-walled carbon nanotubes (MWCNTs), to obtain versatile solid acids, has been demonstrated. Structural and textural properties of the catalysts have been characterized by TEM, TGA, and XPS. Additionally, solid state nuclear magnetic resonance (ssNMR) spectroscopy has been exploited to elucidate the chemical nature of carbon species deposited on the surface of MWCNTs. Al(OTf)₃, a model Lewis acidic metal salt, has been successfully supported on sulfonic groups tethered to MWCNTs. This catalyst has been tested for C₆ sugar dehydration for the production of HMF in a tetrahydrofuran (THF)/water solvent system with good recyclability. Full article

To improve the reactivity of the soda lignin, an acid ionic liquid 1-butyl-3-mthylimidazolium chloride ([BMIM]Cl) was used as the catalyst and solvent to degrade the soda lignin through hydrogenolysis. Structural elucidation of the lignin samples was conducted by using a combination of analytical methods including chemical analysis, ultraviolet spectrophotometry (UV spectrophotometry), Fourier transform infrared spectroscopy (FT-IR spectra), two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) techniques, and gel permeation chromatography (GPC). The antioxidant activities of the lignin samples were evaluated using the diammonium 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS⁺) radical scavenging and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging methods. The degradation mechanism was proposed based on the characterization results. The optimal reaction condition was as follows: the concentration of [BMIM]Cl in the solution was 10 wt %, the hydrogen initial pressure was 3 MPa, and the solution was heated for 4 h at 90 °C. After the reaction, the total hydroxyl content of the soda lignin increased by 81.3%, while the phenolic hydroxyl content increased by 23.1%. At the same time, the weight-average molar mass of the soda lignin sample decreased from 8220 to 6450 g/mol with an improved antioxidant activity. In addition, approximately 56.7% of the β-O-4 linkages were degraded in the lreaction. The main effect of the acid ionic liquid [BMIM]C1 was related to the cleavage of β-O-4 linkages. This study has shown the potential of using the catalyzed soda lignin as a natural polymer antioxidant. Full article