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Pd supported on magnetic carbon coated halloysite as hydrogenation catalyst: Study of the contribution of carbon layer and magnetization to the catalytic activity

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Abstract

In this article, a magnetic carbon-coated halloysite nanoclay (Hal) was prepared through introduction of hydrothermally carbonized glucose (Glu) on Hal followed by the immobilization of magnetic nanoparticles (MNPs) and incorporation of resorcinol-formaldehyde polymeric shell (RF) and carbonization. The resulting composite was then successfully applied for the immobilization of Pd nanoparticles to afford [email protected]@Glu-Fe-C that could efficiently promote hydrogenation of nitroarenes in the aqueous media at low temperature. The catalyst exhibited high selectivity toward nitro group. Moreover, it was highly recyclable with low MNPs and Pd leaching. To elucidate the contribution of each component of the support to the catalysis, a precise study was carried out by preparing several control catalysts and comparing their catalytic activities with that of [email protected]@Glu-Fe-C. Furthermore, the effect of carbon source used for the formation of hydrothermally derived carbon -wrapped Hal and the order of incorporation of metallic nanoparticles on the catalytic activity of the final catalyst was investigated.

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... Accordingly, halloysite nanotubes have been developed as carriers for controlled release of active agents [19][20][21][22][23][24][25][26][27][28][29][30][31][32], as fillers for polymers [33][34][35][36][37][38][39] and for decontamination purposes [40][41][42][43][44][45]. Due to its high specific surface, halloysite was used as catalytic support for technological applications [46][47][48][49][50][51][52][53][54]. Recently, halloysite was successfully employed for the protective coating of hair [55,56]. ...
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In this work, we propose an easy strategy for the separation of halloysite/kaolinite mixtures in sucrose aqueous solution. Preliminarily, we investigated the influence of the sucrose addition on the colloidal stability of kaolinite nanoplates and halloysite nanotubes (HNTs) dispersed in water. Dynamic Light Scattering (DLS) measurements revealed that the HNTs aqueous mobility is dependent on the sucrose concentration, while the ζ-potential is negligibly affected by the addition of the carbohydrate in the aqueous solvent. On the other hand, any variations on the surface charge and dynamic behaviour of kaolinite were detected in the presence of sucrose. The obtained ζ-potential and DLS results were useful to interpret the sedimentation kinetics of kaolinite and halloysite dispersions. In particular, the peculiar sedimentation behaviour of halloysite were discussed by considering the screening effect of sucrose on the attractive interactions between the nanotubes. The latter was evaluated by the calculation of the corresponding Hamaker constants. On this basis, we estimated that the optimization of the separation between kaolinite and halloysite might be achieved in 10 wt% sucrose aqueous solution. This hypothesis was confirmed by the separation experiments, which exploited the different sedimentation behaviour of halloysite and kaolinite. Thermogravimetric experiments on the separated material and kaolinite/halloysite composites with variable composition allowed us to determine the efficiency of the separation protocol. To this purpose, the differential thermogravimetric curves were accurately analysed by using split Gaussian functions. In conclusion, this paper represents a further step in the purification of natural halloysite samples exploiting the ability of sucrose to control the attractive forces of the clay nanotubes as well as the colloidal stability of kaolinite nanoplates in aqueous solvent.
... To the best of our knowledge, there have not been any attempts to reduce, for example, iron in Fe-doped imogolite, in spite of the synthesis of this material having been successful. However, halloysite is frequently used as a traditional catalyst in conjunction with a metal [187][188][189][190][191], an oxide [192][193][194][195] or another type of NP [196]. ...
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The past two decades have been marked by an increased interest in the synthesis and the properties of geoinspired hydrosilicate nanoscrolls and nanotubes. The present review considers three main representatives of this group: halloysite, imogolite and chrysotile. These hydrosilicates have the ability of spontaneous curling (scrolling) due to a number of crystal structure features, including the size and chemical composition differences between the sheets, (or the void in the gibbsite sheet and SiO2 tetrahedron, in the case of imogolite). Mineral nanoscrolls and nanotubes consist of the most abundant elements, like magnesium, aluminium and silicon, accompanied by uncontrollable amounts of impurities (other elements and phases), which hinder their high technology applications. The development of a synthetic approach makes it possible to not only to overcome the purity issues, but also to enhance the chemical composition of the nanotubular particles by controllable cation doping. The first part of the review covers some principles of the cation doping approach and proposes joint criteria for the semiquantitative prediction of morphological changes that occur. The second part focuses on some doping-related properties and applications, such as morphological control, uptake and release, magnetic and mechanical properties, and catalysis.
... Considering the utility of these chemicals for the preparation of more complex organic compounds, such as pesticides, antioxidants, dyes and pigments as well as pharmaceuticals products [5][6][7], many research groups focused on the development of facile procedures for this reaction. Classically, hydrogenation of nitroarenes is achieved in the presence of metallic catalysts [8,9]. Among the reported catalysts, noble metals, such as Pt and Pd have been more focused [9]. ...
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In attempt to take advantages of naturally occurring compounds for the catalysis, a novel composite composed of β-cyclodextrin, dendrimer and bentonite clay is fabricated and utilized as a support for the stabilization of Pd nanoparticles. To prepare the support, bentonite is amino functionalized and then successively reacted with 2,4,6-trichloro-1,3,5-triazine and ethylenediamine to furnish a dendrimer of generation II on bentonite. Afterwards, the terminal functionalities of the dendrimer were adorned with cyclodextrin. Bentonite played role in the heterogenation of the catalyst and improvement of the stability of the composite while, cyclodextrins served as molecular shuttles and capping agent for the as-prepared Pd nanoparticles. Dendrimer with multi nitrogen atoms, on the other hand, improved Pd anchoring through electrostatic interactions. The catalyst was applied for the hydrogenation of nitroarenes under mild reaction condition in aqueous media in a selective manner. Notably, the catalyst could be recovered and reused repeatedly.
... Le et al. [18] used magnetic activated-carbon/clay composite for cationic Pb, Cu, and Ni adsorption, determining excellent adsorption properties (Pb > Cu > Ni). Sadjadi et al. [29] used a magnetic carbon-coated halloysite with the immobilization of Pd nanoparticles for hydrogenation of nitroarenes in aqueous media. Wang et al. [38] used natural attapulgite and cauliflower leaves as raw materials, determining that the synthesized material sorbed oxytetracycline efficiently. ...
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This work presents the synthesis and characterization of montmorillonite-Fe oxides (Mt-Mag) and Mt-Fe oxides-carbon (Mt-Mag-C) systems as adsorbent materials, prepared by efficient and low-cost procedures. Fe oxides were synthesized by alkaline oxidation in the presence of nitrates while carbonization was hydrothermally synthesized. The adsorption capacity of the synthesized materials was tested against different pollutants (norfloxacin, thiaben-dazole, thiophanate-methyl, oxytetracycline, P4R and Cr(VI)). Fe particles and carbon were not homogeneously distributed while Mt-Mag-C sample presented a lower specific surface area and porosity than Mt-Mag, related to carbon presence, while magnetic nanoparticles seem not to block Mt external pores. Both materials revealed negative surface charge, indicating that is dominated by montmorillonite. Besides, Mt structure seems to be modified by both Fe oxides and carbon synthesis. The magnetic response was higher in Mt-Mag-C than in Mt-Mag, indicating Fe phases modifications during carbonization. The principal identified Fe oxide was magnetite, with minor contributions of paramagnetic Fe 3 + , goethite, and paramagnetic relaxation, with a significantly increased of the spectral area of the latter in Mt-Mag-C. Fe concentration determined by Mössbauer spectroscopy resulted higher on Mt-Mag-C than Mt-Mag, indicating that Fe atoms located at the interlayer space of montmorillonite, that give not Mössbauer signal, are exposed by sonication and carbon synthesis, and new magnetite particles are formed through the reduction of Fe 3 + atoms in dextrose aqueous solution. The paramagnetic relaxation increase is related to new magnetite particles, that, because of carbon presence, cannot be magnetically coupled. A significant sorption capacity was found for cationic and zwitterionic compounds, revealing the relevance of electrostatic interaction. The magnetic response of Mt-Mag-C and the results of sorption tests for cationic and zwitterionic compounds, claims Mt-Mag-C as a promising sorbent material.
... Considering the environmental concerns and the fact that the features of the synthesized PAO is significantly affected by the used catalyst [50], development of efficient and environmentally benign catalytic system has been focused [38,48,51]. In the following of our research on the use of natural clays for the catalysis [31,52] and use of supported ILs [53] as heterogeneous catalysts and in attempt to develop a less-toxic procedure for oligomerization of α-olefins, herein we wish to report the utility of Hal-supported ILs-AlCl 3 catalytic systems with half content of AlCl 3 compared to classic AlCl 3 -catalyzed procedure for the synthesis of PAOs. The effects of these catalysts on the features of the as-prepared PAOs are investigated and compared with those of neat AlCl 3 . ...
Article
In attempt to reduce the use of toxic AlCl3 and develop more environmentally benign procedure for the oligomerization of 1-decene, three ionic liquids with different structures were supported on halloysite nano clay. The obtained supported ionic liquids, denoted as Hal-[MIM]⁺ Cl⁻, Hal-[BuIM]⁺ Cl⁻, Hal-[BeIM]⁺ Cl⁻, were then utilized along with AlCl3 with mass ratio of 1:1 as oligomerization catalysts. The used AlCl3 content in these systems was half of the catalyst amount in the classic AlCl3-catalyzed α-olefin oligomerizations. The features of the resultant polyalphaolefins were characterized via viscometry, ¹HNMR, ¹³CNMR, GC-Mass, and SimDis analyses and compared with those of polyalphaolefin derived from neat AlCl3. It was found that by using supported ionic liquids with almost half amount of AlCl3, PAOs with practically similar features to the one derived from AlCl3 can be obtained. Moreover, it was demonstrated that the nature of ionic liquid was also influential on the properties of the resulting PAO and in the case of Hal-[BuIM]⁺ Cl⁻, PAO with the lowest molecular weight, kinematic viscosity and polydispersity index and the highest viscosity index was obtained.
... Le et al. [18] used magnetic activated-carbon/clay composite for cationic Pb, Cu, and Ni adsorption, determining excellent adsorption properties (Pb > Cu > Ni). Sadjadi et al. [29] used a magnetic carbon-coated halloysite with the immobilization of Pd nanoparticles for hydrogenation of nitroarenes in aqueous media. Wang et al. [38] used natural attapulgite and cauliflower leaves as raw materials, determining that the synthesized material sorbed oxytetracycline efficiently. ...
... To solve this problem, a variety of supporting materials, such as polymers [2,4], metal oxides [15,16], clays [17,18] and carbon based materials have been widely employed to support and stabilize NPs. Among them, carbon-based materials that possess distinctive structural [19,20], chemical and electronic properties have been broadly investigated as alternative support materials [9,[21][22][23]. ...
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In attempt to develop low-cost biomass derived carbon materials with improved properties, herein we present a facile method for the fabrication of nitrogen doped carbon through carbonization of beet root, ZnCl2 and our developed cyano/nitrile-free ionic liquid. The resultant N-doped carbon possesses high specific surface area (1297 m2 g−1), abundant micropores and mesopores, an ideal pore size distribution and a partial graphite structure, and high nitrogen heteroatom doping. The nanosheet was then applied as a support for the immobilization of Pd nanoparticles to furnish an efficient and recyclable catalyst for the reduction of organic dyes, Rhodamine B and Methyl orange in the presence of NaBH4. A comparative study confirmed that introduction of ionic liquid could remarkably affect the properties of the catalyst in terms of Pd loading, nature of the formed carbon, textural properties and nitrogen content. The effects of the catalyst loading and the reaction temperature were elucidated. Moreover, the kinetic studies revealed that the activation energy, enthalpy, and entropy for the reduction of Methyl orange were as 30.3 kJ mol−1, 27.7 kJ mol−1, and -180.1 J mol−1 K−1, respectively. For Rhodamine B, these values were as follow: 44.8 kJ mol−1, 41.7 kJ mol−1, and -136 Jmol−1K−1, respectively.
... In this context, one of the most commonly used catalysts is heterogeneous silver species, prepared through stabilization of silver on a suitable support such as clays and carbon materials. [15,[21][22][23] In the continuation of our research on the development of catalysts using natural compounds, [24][25][26][27][28][29] we disclosed the use of novel plant extracts as reducing agents. [30,31] We have also reported the high efficiency of biochars as economic supports. ...
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In attempt to expand the use of natural compounds for waste treatment, a novel catalyst with the utility for dye reductive degradation is reported. In the catalyst synthesis procedure, the plant Echinops bannaticus was applied as a biosource and hydrothermally treated to furnish a hydrochar that served as a support. The latter was magnetized, vinyl functionalized, and then polymerized with copolymer of 2‐hydroxyethyl methacrylate and methacrylate polyhedral oligomeric silsesquioxane. Subsequently, Ag nanoparticles were stabilized on the resultant composite with the aid of Zinnia grandiflora extract as a natural reducing agent. The resulting catalyst displayed high catalytic activity for the reduction of methylene orange and rhodamine B dyes in aqueous media at room temperature. The effects of the reaction variables, including the reaction time and temperature, and the catalyst loading, were examined and the kinetic and thermodynamic terms for both reactions were evaluated. E a, ΔH #, and ΔS # values for the reduction of methyl orange were estimated as 50.0 kJ/mol, 51.50 kJ/mol, and −102.42 J mol⁻¹ K⁻¹, respectively. These values for rhodamine B were measured as 28.0 kJ/mol, 25.5 kJ/mol, and −187.56 J mol⁻¹ K⁻¹, respectively. The recyclability test also affirmed that the catalyst was recyclable for several runs with insignificant Ag leaching and decrement of its activity.
... Several methods have been identified as the promising approaches to improve the surface acidity such as functionalization of organic acids [24], isomorphous substitution of heteroatoms [25][26][27], dealumination [28,29], impregnation [30] and post-synthesis treatments [30,31]. In particular, grafting of metal chlorides (e.g., GaCl 3 , FeCl 3 , AlCl 3 ) on solid supports have found to be an effective approach to enhance the surface acidity of the solid catalysts [32][33][34][35][36]. However, the metal chloride salts tend to leach out from the support during the catalytic reactions as weak chemical interactions are involved [37]. ...
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Highly active metal chlorides grafted on silicoaluminophosphate number 5, MClx/SAPO-5 (M = Cu, Co, Sn, Fe and Zn) catalysts via simple grafting of respective metal chlorides (MClx) onto SAPO-5 are reported. The study shows that thermochemical treatment after grafting is essential to ensure the formation of chemical bondings between MClx and SAPO-5. In addition, the microscopy, XRD and nitrogen adsorption analyses reveal the homogeneous distribution of MClx species on the SAPO-5 surface. Furthermore, the elemental microanalysis confirms the formation of Si–O–M covalent bonds in ZnClx/SAPO-5, SnClx/SAPO-5 and FeClx/SAPO-5 whereas only dative bondings are formed in CoClx/SAPO-5 and CuClx/SAPO-5. The acidity of MClx/SAPO-5 is also affected by the type of metal chloride grafted. Thus, their catalytic behavior is evaluated in the acid-catalyzed acylation of 2-methylfuran under novel non-microwave instant heating conditions (90–110 °C, 0–20 min). ZnClx/SAPO-5, which has the largest amount of acidity (mainly Lewis acid sites), exhibits the best catalytic performance (94.5% conversion, 100% selective to 2-acetyl-5-methylfuran) among the MClx/SAPO-5 solids. Furthermore, the MClx/SAPO-5 solids, particularly SnClx/SAPO-5, FeClx/SAPO-5 and ZnClx/SAPO-5, also show more superior catalytic performance than common homogeneous acid catalysts (H2SO4, HNO3, CH3COOH, FeCl3, ZnCl2) with higher reactant conversion and catalyst reusability, thus offering a promising alternative for the replacement of hazardous homogeneous catalysts in Friedel–Crafts reactions.
... As the carriers for hydrogenation catalysts, natural clay nanotubes such as halloysite are of particular interest [16,[42][43][44][45]. Halloysite is a natural clay aluminosilicate nanotube from the kaolinite group named after the Belgian geologist Omalius d'Halloy who was the first to describe the mineral. ...
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Mesoporous ruthenium catalysts (0.74–3.06 wt%) based on ordered Mobil Composition of Matter No. 41 (MCM-41) silica arrays on aluminosilicate halloysite nanotubes (HNTs), as well as HNT-based counterparts, were synthesized and tested in benzene hydrogenation. The structure of HNT core-shell silica composite-supported Ru catalysts were investigated by transmission electron microscopy (TEM), X-ray fluorescence (XRF) and temperature-programmed reduction (TPR-H2). The textural characteristics were specified by low-temperature nitrogen adsorption/desorption. The catalytic evaluation of Ru nanoparticles supported on both the pristine HNTs and MCM-41/HNT composite in benzene hydrogenation was carried out in a Parr multiple reactor system with batch stirred reactors (autoclaves) at 80 °C, a hydrogen pressure of 3.0 MPa and a hydrogen/benzene molar ratio of 3.3. Due to its hierarchical structure and high specific surface area, the MCM-41/HNT composite provided the uniform distribution and stabilization of Ru nanoparticles (NPs) resulted in the higher specific activity and stability as compared with the HNT-based counterpart. The highest specific activity (5594 h−1) along with deep benzene hydrogenation to cyclohexane was achieved for the Ru/MCM-41/HNT catalyst with a low metal content.
... In the continuation of our research on disclosing the catalytic utility of Hal 23,24 , recently we have reported facile recovery and high reusability of magnetic Hal 25,26 . On the other hand, our research on the catalytic activity of IL-Hal hybrid 27,28 showed that the presence of ILs on the Hal can efficiently improve anchoring of nanoparticles and suppressing their leaching. ...
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Using natural materials, i.e. halloysite nanoclay that is a biocompatible naturally occurring clay and Heracleum persicum extract that can serve as a green reducing agent, a novel magnetic catalyst, Fe3O4/Hal-Mel-TEA(IL)-Pd, has been designed and fabricated. To prepare the catalyst, halloysite was first magnetized (magnetic particles with mean diameter of 13.06 ± 3.1 nm) and then surface functionalized with melamine, 1,4 dibromobutane and triethanolamine to provide ionic liquid on the halloysite surface (5 wt%). The latter was then used as a support to immobilize Pd nanoparticles that were reduced by Heracleum persicum extract. The characterization of the catalyst established that the loading of Pd in Fe3O4/Hal-Mel-TEA(IL)-Pd was very low (0.93 wt%) and its specific surface area was 63 m²g⁻¹. Moreover, the catalyst showed magnetic property (Ms = 19.75 emu g⁻¹) and could be magnetically separated from the reaction. The catalytic performance of the magnetic catalyst for reductive degradation of methyl orange and rhodamine B in the presence of NaBH4 in aqueous media was investigated. The activation energy, enthalpy, and entropy for the reduction of methyl orange were estimated as 42.02 kJ mol⁻¹, 39.40 kJ mol⁻¹, and −139.06 J mol⁻¹ K⁻¹, respectively. These values for rhodamine B were calculated as 39.97 kJ mol⁻¹, 34.33 kJ mol⁻¹, and −155.18 Jmol⁻¹K⁻¹, respectively. Notably, Fe3O4/Hal-Mel-TEA(IL)-Pd could be reused for eight reaction runs with negligible loss of the catalytic activity (~3%) and Pd leaching (0.01 wt% of the initial loading).
... This class of hydrogenation reaction not only can be applied for the synthesis of fine chemicals, but is also applicable for environmental remediation. Similar to other hydrogenation reactions, reduction in nitro-compounds proceeds with the aid of a hydrogen source and a catalytic species [32,33]. The conventional catalyst for this process is supported Pd species. ...
Article
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A novel thermo-responsive catalyst for the hydrogenation of nitroarenes under mild reaction condition was devised. To prepare the catalyst, a thermo-responsive polymer was first synthesized through the co-polymerization of N-isopropylacrylamide and allylamine and then covalently grafted on the Cl-functionalized perlite. The resulting composite was subsequently utilized as a support for the stabilization of Pd nanoparticles. Investigation of the catalytic activity of the catalyst approved its high catalytic activity at a temperature above the lower critical solution temperature. More precisely, 0.03 g of the catalyst can promote the reaction of 1 mmol of nitro-compounds in H2O/EtOH (1:1) at 45 °C to furnish the corresponding products in 70–100% yields. This issue was assigned to the collapse of the polymeric component and formation of a hydrophobic environment that was beneficial for the mass-transfer of the hydrophobic nitroarenes. Notably, the catalytic activity of the catalyst was higher than that of palladated perlite and thermos-responsive polymer due to the synergistic effects between the perlite and polymeric moiety. Furthermore, the study of the substrate scope confirmed that a wide range of substrates with different steric and electronic properties could tolerate hydrogenation reaction. Moreover, the catalyst was highly selective toward hydrogenation of the nitro group and could be recycled up to seven runs with insignificant Pd leaching and loss of catalytic activity. The hot filtration test also confirmed the heterogeneous nature of the catalysis.
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A novel biochar-based graphitic carbon nitride was prepared through calcination of Zinnia grandiflora petals and urea. To provide acidic and ionic-liquid functionalities on the prepared carbon, the resultant biochar-based graphitic carbon nitride was vinyl functionalized and polymerized with 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylic acid and the as-prepared 1-vinyl-3-butylimidazolium chloride. The final catalytic system that benefits from both acidic (–COOH and –SO3H) and ionic-liquid functionalities was applied as a versatile, metal-free catalyst for promoting some model acid catalyzed reactions such as Knoevenagel condensation and Biginelli reaction in aqueous media under a very mild reaction condition. The results confirmed high activity of the catalyst. Broad substrate scope and recyclability and stability of the catalyst were other merits of the developed protocols. Comparative experiments also indicated that both acidic and ionic-liquid functionalities on the catalyst participated in the catalysis.
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Mesoporous materials are very attractive solids for the fabrication of confined nanoreactors since they overcome the problems of diffusion/deactivation shown by microporous structures. In this work, we present the fabrication of a confined nanoreactor obtained by functionalization with phosphoric acid of the empty lumen (diameter 10–15 nm) of halloysite nanotubes (Hal). Two different halloysite nanoreactors with phosphorylated catalytic sites were prepared by the wet impregnation method followed by thermal activation: 1) phosphate modified Hal (starting with pristine Hal), and 2) phosphate-modified etched Hal (starting with etched Hal obtained by soft-etching pristine Hal using sulphuric acid). The selective grafting of hydrogen phosphate groups onto the aluminol active sites was characterized by solid-state nuclear magnetic resonance (¹H, ²⁷Al, ²⁹Si HPDEC and ³¹P) and Fourier transform-infrared spectroscopies, and thermogravimetric and nitrogen physisorption analyses. Two different aluminum phosphate (AlOP) binding modes, monodentate (AlOPO(OH)2) and bidentate (AlO)2P(OH)2, with different distributions were observed in both phosphorylated-Hal nanoreactors. The selective functionalization of the internal lumen was confirmed because no interaction (due to SiOP binding mode) was detected between the outer surface of Hal and phosphoric acid. The confined nanoreactors prepared here preserved the main chemical structure and textural properties of Hal. The analysis of the specific surface area and mesopore size showed that, depending on the starting material, grafting the phosphate groups led to the formation of a monolayer or a polycondensation of phosphate moieties inside the tubular mesopore. However, in both prepared nanoreactors, phosphorylation did not result in saturating the material or pore blocking. These mesoporous materials could be used in catalysis and in situ nanoparticle synthesis.
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In this work, heterogeneous catalysts based on halloysite nanotubes (HNTs) were fabricated through mussel-inspired chemistry that could be used in situ to generate Fe3O4 nanoparticles on HNTs. HNT-based magnetic composites ([email protected]) were examined as catalysts for the Fenton reaction. The characterization results demonstrated that Fe3O4 nanoparticles could be well-dispersed on HNTs with polydopamine (PDA) as the linkage. Various experimental parameters, such as the concentrations of [email protected] and H2O2, reaction temperature and solution pH, of the degradation efficiencies were investigated in detail. The results demonstrated that the degradation efficiencies of methylene blue were greater than 97% under optimized conditions. Moreover, [email protected] also exhibited excellent degradation efficiencies for other organic dyes (such as rhodamine B, methyl orange, and Congo red). Electron spin-resonance spectroscopy suggested that free radicals such as •OH and •O2⁻ were generated during the Fenton reaction, which could destroy the structure of the organic dyes. Taken together, a biomimetic method based on the self-polymerization of dopamine and the in situ generation of Fe3O4 nanoparticles on HNTs is developed for the fabrication of [email protected] composites, which exhibit excellent degradation efficiencies towards different organic dyes through the Fenton reaction. This method can also be extended for the preparation of other multifunctional composites with potential for different applications.
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Heterogeneous catalysis benefits from some merits such as facile catalyst separation and recyclability. In this context, use of halloysite that is a naturally occurring clay with tubular morphology received growing attention and in recent decade many halloysite –based heterogeneous catalysts have been developed. Halloysite is a promising candidate for the formation of composites and hybrids. Mostly, halloysite preserved its structure in the course of hybridization and the properties of the resulting hybrids/composites depend on some factors such as the content of halloysite, preparation procedure and the hybrid/composite components. To date, halloysite based hybrids/composites have been applied for promoting various chemical and photochemical transformations. Mostly, this class of compounds exhibited promising catalytic performances that were superior to their individual components, suggesting the synergism between halloysite and the composite/hybrid component(s). Considering the outstanding catalytic performance of these composites/hybrids as catalysts or catalyst supports, this review article targets disclosing the catalytic utility of the halloysite nanocomposites/hybrids. The classification presented in this review is based on the types of the components that were hybridized with halloysite. In each section, it is tried to discuss the catalytic performance of the hybrid/composite and the effects of incorporation of halloysite on the catalysis.
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Acetalization of glycerol that is the by-product of biodiesel to fuel additives has received considerable attention. However, formation of a mixture of products in this acid-catalysed process is a challenging issue. In this research, a highly selective catalyst is devised that can selectively acetalize glycerol to solketal. To prepare the catalyst, bentonite clay was first decorated with an acidic polymer containing sulfonic acid and carboxylic acid functional groups. Then, the carboxylic acid groups of the polymer were changed to ionic liquids through reaction with triethanolamine. Finally, phosphotungstic acid was immobilized on the bentonite-polymer composite and the resultant catalyst was characterized. To achieve the highest catalytic activity, the catalyst amount and phosphotungstic acid loading have been optimized. It was found that 10 wt.% catalyst with 20 wt.% phosphotungstic acid loading led to 100% conversion and 99% yield to solketal under solvent-free condition at 55 °C. Moreover, the catalyst could be recycled up to four reaction runs without significant loss of its activity. Comparative studies with ionic liquid-free control catalyst approved that the presence of ionic liquid in the structure of the catalyst played an important role in the selectivity of the catalyst and ionic liquid-free counterpart led to less selectivity and formation of 2,2-dimethyl-1,3-dioxane-5-ol as by-product.
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Yolk-shell magnetic porous organic nanospheres (MPONs) supported Pd nanoparticles ([email protected]) were synthesized by encapsulating Fe3O4 and Pd nanoparticles in one cavity of hollow porous organic nanospheres (HPONs) using a continuous “ship-in-bottle” strategy. The obtained [email protected] possessed a hierarchically micro/mesoporous structure, high surface area (354 m²/g) and displayed excellent magnetic response (9 emu/g). They showed high catalytic performance in the oxidation of alcohols under mild conditions and the Heck-Mizoroki reaction, and brilliant magnetic recyclability, they can be removed rapidly from a reaction system using external magnetic fields without any catalytic activity decrease. Hence, the [email protected] are easily recoverable nanocatalysts which have practical significance in the future sustainable industry.
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Mixed metal oxides derived from layered double hydroxides (LDHs) present favorable characteristics, mainly linked to the homogeneous distribution of the Ni species inside the lattice of metal oxides, resulting in ultrafine Ni(0) nanocatalysts. Herein, we report on the preparation and characterization of Ni/NiMAlOx (M = Ca, Mg or Zn) catalyst derived from ternary LDHs. These Ni catalysts were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray spectrometer (EDX), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). For Ni/NiCaAlOx, the Ni particles were reduced in-situ and partially encapsulated by the NiCaAlOx support. The spatial confinement effects are beneficial to the metal-support interactions, which enhance the activity and catalytic stability of the Ni catalysts. The Ni/NiCaAlOx catalyst with strong basicity was highly active in phenol hydrogenation to cyclohexanol with a high TOF of 170 h⁻¹; also, this catalyst was recycled 8 times without apparent loss of activity, thus demonstrating its good activity and stability. The pivotal roles of the spatial confinement effects and basicity of the support derived from ternary LDHs provide a viable strategy for the manufacture of highly active and stable non-precious metal catalysts.
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P, Se-codoped g-C3N4 (PSeCN) nanosheet was in situ prepared by facile thermal polymerization of melamine, phosphonitrilic chloride trimer, and selenium black powder as the precursors. It was found as a suitable support for the immobilization of silver nanoparticles (Ag NPs). The prepared nanocatalyst was fully characterized via standard analysis methods including EDX, ICP-OES, XRD, FT-IR, SEM, TEM, and BET. This PSeCN/Ag nanocatalyst with a higher specific surface area compared with CN, showed excellent catalytic activity towards the reduction of several nitroaromatic compounds using sodium borohydride (NaBH4) in short reaction times with high efficiency and good selectivity in water as a green solvent. Significantly, the above-mentioned nanocomposite could be reused six times without appreciable loss of its catalytic activity.
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A novel metal-organic framework-based nanocomposite has been designed and synthesized via a two-step procedure. First, CoFe2O4@TiO2 nanoparticles have been prepared through initial formation of CoFe2O4 nanoparticles, followed by introduction of TiO2 by using titanium tetraisopropoxide. Subsequently, HKUST-1 metal-organic framework has been formed through self-assembly of Cu(NO3)2·3H2O and trimesic acid in the presence of CoFe2O4@TiO2 nanoparticles. The properties of the resultant nanocomposite, CoFe2O4@TiO2@HKUST-1, have been analyzed via XRD, TGA, TEM, SEM, BET, VSM and FTIR and compared with those of HKUST-1, CoFe2O4@TiO2 and CoFe2O4. It was found that the nanocomposite showed lower specific surface area compared to HKUST-1. Moreover, incorporation of CoFe2O4@TiO2 resulted in significant morphological change. VSM analysis implied that the magnetic properties of CoFe2O4@TiO2 and the nanocomposite were lower than that of CoFe2O4. However, they could be magnetically separated by using an external magnet.
Chapter
The “Heck reaction” (also called the Mizoroki–Heck reaction) is the chemical reaction of an unsaturated halide (triflate) with an activated alkene in the presence of a base and a palladium (Pd) species as catalyst to generate a substituted alkene. One of the benefits of the Heck reaction is its outstanding trans-selectivity. The Heck reaction is a Pd-catalyzed carbon–carbon cross-coupling reaction that takes place between aryl halides or vinyl halides and activated alkenes in the presence of a base. Recent developments in catalysts and reaction conditions have resulted in a much broader range of donors and acceptors that are amenable to the Heck reaction. In this chapter, we try to follow and cover, the total synthesis of alkaloids using Heck reaction.
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Natural clay nanotube-metal based core/shell catalysts for hydroprocesses: structural design, synthesis, applications.
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In attempt to develop green protocols for organic transformations, a novel catalyst is prepared by combination of the features of metal-organic frameworks and polymers of cyclic carbohydrates. In detail, cyclodextrin nanosponge was synthesized from β-cyclodextrin that is a cyclic carbohydrate with capability of formation of inclusion complex and then hybridized with the as-prepared iron based metal-organic framework. The composite was then palladated to furnish a catalyst for hydrogenation of nitroarenes in aqueous media at ambient temperature. It was postulated that cyclodextrin nanosponge in the catalyst backbone can act as a nanoreactor to encapsulate and transfer nitroarenes in aqueous media and control the growth of Pd nanoparticles by acting as a capping agent. The results approved high efficiency of the catalyst, superior to the palladated CDNS and metal-organic framework. Using this catalyst, steric substrates with low solubility in water as well as substrates with competing functionalities could efficiently be hydrogenated. Moreover, the catalyst could be recycled several times with low Pd leaching and loss of activity.
Article
In attempt to develop green protocols for organic transformations, a novel catalyst is prepared by combination of the features of metal-organic frameworks and polymers of cyclic carbohydrates. In detail, cyclodextrin nanosponge was synthesized from β-cyclodextrin that is a cyclic carbohydrate with capability of formation of inclusion complex and then hybridized with the as-prepared iron based metal-organic framework. The composite was then palladated to furnish a catalyst for hydrogenation of nitroarenes in aqueous media at ambient temperature. It was postulated that cyclodextrin nanosponge in the catalyst backbone can act as a nanoreactor to encapsulate and transfer nitroarenes in aqueous media and control the growth of Pd nanoparticles by acting as a capping agent. The results approved high efficiency of the catalyst, superior to the palladated CDNS and metal-organic framework. Using this catalyst, steric substrates with low solubility in water as well as substrates with competing functionalities could efficiently be hydrogenated. Moreover, the catalyst could be recycled several times with low Pd leaching and loss of activity.
Article
A composite adsorbent composed of metallic copper (Cu), polypyrrole (PPy), halloysite nanotubes (HNTs) and magnetite nanoparticles (Fe3O4) was developed to extract and enrich sulfonamides by dispersive magnetic solid phase extraction. The composite could adsorb sulfonamides via hydrogen bonding and hydrophobic, π-π and π-electron-metal interactions. The extraction conditions were optimized and the developed composite adsorbent was characterized and provided a large surface area that enhanced extraction efficiency for sulfonamides. Coupled with high performance liquid chromatography, the adsorbent was used to quantitatively determine sulfonamides found in milk samples. The response of the developed method exhibited linearity from 5.0 to 150.0 μg kg⁻¹ for sulfathiazole, and from 2.5 to 100.0 μg kg⁻¹ for sulfamerazine, sulfamonomethoxine and sulfadimethoxine. Limits of detection were between 2.5 and 5.0 μg kg⁻¹. Recoveries of sulfonamides in milk samples ranged from 83.0 to 99.2% with RSDs lower than 6%. The developed composite adsorbent showed good reproducibility and reusability.
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Amines can be applied in the synthesis of various important compounds such as dyes, drugs, polymers, pharmaceutical products, and biologically active materials. The significant subject in the preparation of amines is the selection of the most effective heterogeneous catalyst to get the best catalytic efficiency, stability, recoverability, and reusability. For this target, we prepared new alginate magnetically recoverable nanocatalyst by stabilization of Ag nanoparticles on the surface of the halloysite (HS) [HS-Alginate-Ag/Fe3O4]. Several detection methods confirmed the production of HS-Alginate-Ag/Fe3O4 nanocatalyst and the results obtained were well explained in the context. HS-Alginate-Ag/Fe3O4 presented good catalytic performance for the hydrogenation of nitro compounds using NaBH4 as the reducing agent and hydrogen donor. The good activity and durability of this catalyst can be attributed to the good dispersion and nano-sized particle of silver nanoparticles.
Article
In this study, a new hollow nanotube material, 30% Co–CHNTs was prepared by the impregnation–chemical reduction–calcination method. This material can be used as a peroxymonosulfate (PMS) activator to catalyse the degradation of sulfamethoxazole (SMX). The best reaction conditions that correspond to the degradation rate of SMX, up to 97.5%, are as follows: the concentration of SMX is 10 mg L⁻¹, the amount of catalyst is 0.20 g L⁻¹, the dosage is 1.625 mM, and the solution pH is 6.00. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometry (ICP-OES) show that the calcined composites mainly stimulate an increase in the content of bivalent cobalt in PMS and reduce the leaching of cobalt ions after the reaction. Additionally, the 30% Co–CHNTs + PMS reaction system exhibits a reasonable SMX degradation rate in a natural organic matter solution and excellent stability after three repeated experiments. Furthermore, the possible degradation mechanism in the 30% Co–CHNTs + PMS reaction system was analysed through electron paramagnetic resonance (EPR) and free-radical capture experiments, and it was observed that the non-radical degradation of ¹O2 plays a leading role in SMX degradation. Finally, according to the nine degradation intermediates detected by liquid chromatography-mass spectrometry (LC–MS), four possible SMX degradation routes were proposed. This study proved that a 30% Co–CHNTs heterogeneous catalyst is easily prepared, inexpensive, and environmentally friendly and has potential application in antibiotic wastewater treatment.
Article
Copper Schiff base complex with allyl functionality was prepared and reacted with amino-functionalized halloysite. The resultant compound was then reacted successively with melamine and the as-prepared copper Schiff base complex to furnish a polymeric moiety with multi copper Schiff base complex on the halloysite outer surface. The latter was then characterized by EDS, FTIR, TGA, ICP, TEM, XRD, VSM and elemental mapping analysis and subsequently applied as a catalyst for promoting one-pot reaction of aldehydes and dimedone to synthesize xanthene derivatives. The catalyst showed high catalytic activity under mild reaction condition and could be easily recovered and efficiently recycled with low Cu leaching. Notably, this protocol could be generalized to various aldehydes with different electron densities.
Article
A novel composite of metal-organic framework and perlite is prepared through hydrothermal treatment of terephthalic acid and Cu(NO3)2.3H2O in the presence of perlite. The resulting composite was then utilized as a support for the immobilization of Pd nanoparticles. The obtained compound was characterized via XRD, TGA, ICP, FTIR, TEM, FE-SEM/EDS and elemental mapping analysis and applied as a catalyst for the hydrogenation of nitroarenes under mild reaction condition. The results approved that the catalyst could efficiently promote hydrogenation of various nitroarenes with different electronic densities and steric properties. Moreover, the catalyst showed high selectivity towards hydrogenation of nitro groups. Hot filtration test affirmed heterogeneous nature of catalysis. Furthermore, the present catalytic composite was highly recyclable with low Pd leaching. A comparative study also approved superior activity of the composite compared to palladated perlite and metal-organic framework.
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In this article, halloysite nanoclay (Hal) was used as porogen for the synthesis of nitrogen doped porous carbon material with high specific surface area and pore volume. To this purpose, polymerization of melamine and terephthalaldehyde (MT) was performed in the presence of amine-functionalized carbon coated Hal (Hal@Glu-2N) that was prepared from hydrothermal treatment of Hal and glucose. Then, the prepared nanocomposite was palladated and carbonized to afford Pd@Hal@C. To further improve the textural properties of the nanocomposite, and introduce more pores in its structure, Hal nanotubes were etched. The characterization of the resulting compound, Pd@C, and comparing it with Pd@Hal@C, showed that etching of Hal significantly increased the specific surface area and pore volume in Pd@C. Pd@C was successfully used as a heterogeneous catalyst for promoting hydrogenation of nitroarens in aqueous media using hydrogen with atmospheric pressure as a reducing agent. The comparison of the structural features and catalytic activity of the catalyst with some control catalysts, including, Pd@Hal, Pd@Hal@Glu, Pd@Hal@Glu-MT and Pd@Hal@C confirmed that nitrogen groups in C could improve the Pd anchoring and suppress its leaching, while etching of Hal and introduction of more pores could enhance the catalytic activity through facilitating the mass transfer.
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Taking advantage of computational chemistry, the best diamine for the synthesis of a multi‐dentate ligand from the reaction with 3‐(trimethoxysilyl) propylisocyanate (TEPI) was selected. Actually, predictive Density Functional Theory (DFT) calculations provided the right diamino chain, i.e. ethylenediamine, capable to sequester a palladium atom, together with the relatively polar solvent toluene, and then undergo the experiments as a selective catalytic agent. The ligand was then prepared and applied for the decoration of the halloysite (Hal) outer surface to furnish an efficient support for the immobilization of Pd nanoparticles. The resulting catalyst exhibited high catalytic activity for hydrogenation of nitroarenes. Moreover, it showed high selectivity towards nitro functional group. The study of the catalyst recyclability confirmed that the catalyst could be recycled for several reaction runs with only slight loss of the catalytic activity and Pd leaching. Hot filtration test also proved the heterogeneous nature of the catalysis. Using computational chemistry, the best diamine, ethylenediamine, for the synthesis of a multi‐dentate ligand from the reaction with 3‐(trimethoxysilyl)propylisocyanate was selected. The ligand was then synthesized and applied for the decoration of the halloysite to furnish an efficient support for the immobilization of Pd nanoparticles. The catalyst exhibited high catalytic activity y for hydrogenation of nitroarenes.
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Considering the excellent performance of halloysite as a catalyst support and in an attempt to benefit from the concept of nanoreactors in the catalysis, an innovative catalytic system has been designed, in which acrylamide and bis‐acrylamide were photo‐polymerized in the presence of palladated halloysite. The novel precipitation photo‐polymerization method avoided the formation of an extended polymeric network, but led to the formation of co‐polymer on the halloysite periphery. The co‐polymer exhibited good swellability in aqueous media and formed hydrogel. This hydrophilic environment around catalytic palladated halloysite can be considered as a nanoreactor that can concentrate the substrate and bring them into the vicinity of the palladated halloysite. This catalytic system was used for promoting hydrogenation of hydrophobic nitro arenes in aqueous media. To avoid immiscibility of hydrophobic substrates and hydrophilic nature of the nanoreactor, that emerged from swelling of hydrogel, β‐cyclodextrin (CD) was utilized as phase transfer agent. The results confirmed high catalytic activity of this catalytic system. Even highly hydrophobic substrates could tolerate hydrogenation under this protocol to furnish the corresponding product in high yield. Finally, the contribution of both CD and hydrogel to the catalysis was confirmed. Moreover, studying the recyclability of the catalyst as well as Pd leaching proved the high recyclability of the catalyst and low leaching of Pd nanoparticles.
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For the first time, a hybrid system, composed of halloysite (Hal), cyclodextrin modified melamine-based polymer is developed and employed for immobilization of Pd(0) nanoparticles. The resulting catalytic hybrid system, Pd@HTMC, was then applied as a heterogeneous catalyst for hydrogenation of nitroarenes to the corresponding anilines. The results established that Pd@HTMC could promote hydrogenation under very mild reaction conditions and relatively short time. Moreover, investigation of sterically demanding substrate, nitro-naphthalene, as well as substrate with competing functional group, 4-nitroacetophenone, confirmed that the catalyst is capable of hydrogenation of sterically demanding substrate, while selectively hydrogenates nitro functional group over keto-functionality. The recyclability experiment proved that the catalyst was recyclable up to six reaction runs with slight loss of the catalytic activity and Pd leaching. Moreover, hot filtration test confirmed the heterogeneous nature of the catalyst. Finally, the contribution of cyclodextrin modified melamine-based polymer to the catalysis was confirmed by comparison of the catalytic activity of Pd@HTMC with control catalysts.
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In this study, Au–Ag and Pt–Ag bimetallic nanocages were loaded on natural halloysite nanotubes (HNTs) via galvanic exchange based on Ag@HNT. By changing the ratio of Au to Ag or Pt to Ag in exchange processes, Au–Ag@HNT and Pt–Ag@HNT with different nanostructures were generated. Both Au–Ag@HNT and Pt–Ag@HNT systems showed significantly improved efficiency as peroxidase-like catalysts in the oxidation of o-phenylenediamine compared with monometallic Au@HNT and Pt@HNT, although inert Ag is dominant in the composition of both Au–Ag and Pt–Ag nanocages. On the other hand, loading on HNTs enhanced the thermal stability for every system, whether monometallic Ag nanoparticles, bimetallic Au–Ag or Pt–Ag nanocages. Ag@HNT sustained thermal treatment at 400 °C in nitrogen with improved catalytic performance, while Au–Ag@HNT and Pt–Ag@HNT maintained or even had slightly enhanced catalytic efficiency after thermal treatment at 200 °C in nitrogen. This study demonstrated that natural halloysite nanotubes are a good support for various metallic nanoparticles, improving their catalytic efficiency and thermal stability.
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Palladium nanoparticles stabilized by lightly cross-linked phosphine-decorated polymer immobilized ionic liquids (PIIL) and their PEGylated counterparts (PEGPIIL) are highly effective catalysts for the aqueous phase hydrogenation and sodium borohydride-based reduction of a wide range of nitroaromatic and heteroaromatic compounds under mild conditions with low catalyst loadings. Introduction of extensive cross-linking with tris(4-vinylphenyl)phosphine to isolate the phosphine-based heteroatom and limit the number of surface Pd----P interactions did not have a significant influence on catalyst performance. Comparative testing revealed PdNPs immobilized on lightly cross-linked phsophine-decoarted PEGylated polymer to be a highly efficient catalyst for the aqueous phase reduction of nitroarenes with a TON of 36,000 (TOF = 2,580 h-1) for hydrogenation and a TON of 274,000 (TOF = 17,125 h-1) for transfer hydrogenation. Even though these reactions occur under diffusion control due the poor solubility of the substrate these values are the highest to be reported for the room temperature aqueous phase reduction of nitroarenes catalyzed by a nanoparticle-based system. A continuous flow reduction of nitrobenzene in a packed bed reactor operated over a period of 250 min with no sign of catalyst deactivation and the corresponding space-time-yield of 0.738 g L-1 min-1 is a marked improvement on that of 0.384 g L-1 min-1 obtained in batch. The same system also catalyzes a tandem Suzuki-Miyaura cross coupling-nitroarene reduction sequence to afford high yields of biaryl amine in an operationally straightforward single-pot procedure. This is a highly versatile protocol which will enable the aromatic nitro fragment to be introduced as a nitro-substituted aryl or heteroaryl halide and as such will lend itself to rapid diversification for the synthesis of a wide range of amines.
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Naturally occurring ceramic tubular clay, Halloysite nanotubes (HNTs), having a significant amount of surface hydroxyls has been coated by self-polymerized dopamine in this work. The polydopamine-coated HNTs acts as a self-reducing agent for Ag⁺ ion to Ag⁰ in nanometer abundance. Herein, nano size Ag⁰ deposited on solid support catalyst has been used to mitigate water pollution within 10 min. To establish the versatility of the catalyst, nitroaryl (4-nitrophenol) and synthetic dye (methylene blue) have been chosen as model pollutant. The degradation/reduction of the aforementioned pollutants was confirmed after taking UV–visible spectra of the respective compounds. All the study can make sure that the catalyst is green and the rate constant value for catalytic reduction of 4-nitrophenol and methylene blue was calculated to be 4.45 × 10⁻³ and 1.13 × 10⁻³ s⁻¹, respectively, which is found to be more efficient in comparison to other nanostructure and commercial Pt/C nanocatalyst (1.00 × 10⁻³ s⁻¹).
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For the first time, a ternary hybrid system composed of halloysite nanotubes, HNTs, cyclodextrin nanosponges, CDNS, and g-C3N4 is prepared and used for immobilization of Pd(0) nanoparticles and development of a heterogeneous catalyst, [email protected]3N4 for promoting ligand and copper-free Sonogashira and Heck coupling reactions in aqueous media. HNT as a porous tubular clay with outstanding thermal, mechanical and textural properties can act as a support for immobilizing Pd nanoparticles. The role of CDNS can be explained on the base of its capability to form inclusion complexe with substrates and bringing them in the vicinity of the catalytic active sites. Regarding the role of g-C3N4 in catalysis, it is proved that its presence can suppress the Pd leaching dramatically. The contribution of each component as well as synergistic effect between them results in high catalytic activity and recyclability (up to 10 reaction runs) of the catalyst.
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An efficient chemoselective reduction of aromatic nitro compounds to corresponding amino analogues was achived using palladium/sucrose (Pd/S) nanoparticles as an eco friendly catalyst, a green approach formate in ethanol at RT. The reductions are fruitfully carried out in presence of various other reducible functional groups such as halo, alkoxy, carbonyl, and cyanide etc. The reactions are worthy and high yielding (100%).
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Halloysite (HNT) is a promising natural nanosized tubular clay mineral that has many important uses in different industrial fields. It is naturally occurring, biocompatible, and available in thousands of tons at low cost. As a consequence of a hollow cavity, HNT is mainly used as nanocontainer for the controlled release of several chemicals. Chemical modification of both surfaces (inner lumen and outer surface) is a strategy to tune the nanotube's properties. Specifically, chemical modification of HNT surfaces generates a nanoarchitecture with targeted affinity through outer surface functionalization and drug transport ability from functionalization of the nanotube lumen. The primary focus of this review is the research of modified halloysite nanotubes and their applications in biological and medical fields.
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Halloysite nanotubes (HNTs) were applied as corrosion inhibitor (benzotriazole, BTA) hosts, which were encapsulated by using tetraethyl orthosilicate (TEOS) and modified by (3-aminopropyl)triethoxysilane (APTES). The modified nanocontainers were dispersed in the epoxy matrix, resulting in a functional composite coating. The structure of the assembly of the modified HNTs was characterized by FT-IR, XRD, XPS and TEM. Furthermore, the amount of BTA loaded in the lumen of the HNTs was determined by TGA. Such modified HNTs were well dispersed in ethanol and epoxy resin which was confirmed by SEM and EDS. A reasonable release rate of the corrosion inhibitor from the nanocontainers was realized by controlling the pH value (pH = 3) and monitoring the range between 30 and 450 min with UV-vis. Compared to the pure epoxy coating, the anticorrosive performance of the coating loaded with 3% of HNTs-entrapped BTA was tested by an EIS method on a steel matrix (N80) and it showed remarkable improvement. Furthermore, the simulated inhibiting behavior of inhibitor release from the nanocontainers in composite coatings was investigated by scarification tests in 10 wt% NaCl solution (pH = 3). The result demonstrated that the corrosion inhibitor releasing nanocontainers played a key role in protecting the substrate. This journal is
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This work reports a simple and highly efficient protocol for reduction of nitroarenes to corresponding amines via dehydrogenation of dimethylamine borane using palladium nanoparticle (Pd NPs) as a versatile heterogeneous catalyst. The facile approach for the synthesis of Pd NPs within 15 min in aqueous medium has been reported. The Pd NPs were well characterized using various analytical techniques such as XRD, FEG-SEM, TEM, EDAX and XPS. The developed catalytic system uses environmentally benign dimethylamine borane as a reducing agent which is highly stable, water soluble and nontoxic. The various amines were synthesized from nitroarenes in excellent yields within 10-60 min at room temperature. The catalyst was reused up to four successive cycles without significant loss in its catalytic activity. This journal is
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Hybrid nanotubes of carbon and halloysite nanotubes (HNTs) with different carbon:HNTs ratio were hydrothermally synthesized from natural halloysite and sucrose. The samples display uniformly cylindrical hollow tubular structure with different morphologies. These hybrid nanotubes were concluded to be promising medium for physisorption-based hydrogen storage. The hydrogen adsorption capacity of pristine HNTs was 0.35% at 2.65 MPa and 298 K, while that of carbon coated HNTs with the pre-set carbon:HNTs ratio of 3:1 (3C-HNTs) was 0.48% under the same condition. This carbon coated method could offer a new pattern for increasing the hydrogen adsorption capacity. It was also possible to enhance the hydrogen adsorption capacity through the spillover mechanism by incorporating palladium (Pd) in the samples of HNTs (Pd-HNTs) and 3C-HNTs (Pd-3C-HNTs and 3C-Pd-HNTs are the samples with different location of Pd nanoparticles). The hydrogen adsorption capacity of the Pd-HNTs was 0.50% at 2.65 MPa and 298 K, while those of Pd-3C-HNTs and 3C-Pd-HNTs were 0.58% and 0.63%, respectively. In particular, for this spillover mechanism of Pd-carbon-HNTs ternary system, the bidirectional transmission of atomic and molecular hydrogen (3C-Pd-HNTs) was concluded to be more effective than the unidirectional transmission (Pd-3C-HNTs) in this work for the first time.
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A new family of solid catalysts has been prepared by supporting palladium nanoparticles on a synthetic clay (laponite) using a straightforward and robust procedure. These solids have been used as catalysts in a Mizoroki–Heck reaction, in solventless conditions, activated by microwave radiation. Complete conversions and high product yields can be obtained in a few minutes, and the catalyst can be efficiently recovered by extracting reaction products in essentially pure form. In the best cases, catalysts can be used up to thirteen times with good results.
Article
Considering the high performance of ionic liquid decorated halloysite clay as a catalyst support, herein a halloysite ‐poly (ionic liquid) polymer composite is synthesized and characterized via BET, TGA, TEM, FTIR, XRD and ICP and then applied for the immobilization of Pd species to afford a catalyst for the hydrogenation of nitroarenes. To shed light to the effect of the content and nature of poly (ionic liquid) polymer on the catalytic activity, two control samples with different content and entity of poly (ionic liquid) polymer were synthesized and compared by FTIR, TGA and BET. The results confirmed that the content of poly (ionic liquid) polymer significantly affected the catalytic activity and the higher this value, the higher the Pd content and consequently the superior the catalytic activity would be. The study of the nature of poly (ionic liquid) polymer revealed that it did not dramatically influence the catalytic activity. However, the choice of the monomer affected the content of poly (ionic liquid) polymer formed on halloysite. Notably, the catalyst was highly selective toward reduction of nitro group and competing functionalities remained intact under the reaction condition. Moreover, the catalyst showed excellent recyclability with low Pd leaching. Halloysite ‐ poly (ionic liquid) composite has been developed as a promising support material for the immobilization of Pd nanoparticles and preparing a catalyst for the hydrogenation reaction.
Article
A novel halloysite-hydrochar nanocomposite has been prepared and applied for the immobilization of Pd NPs to furnish an efficient catalyst for the hydrogenation of nitroarenes. It was confirmed that the use of the catalytic amount of -cyclodextrin (-CD) could improve the yield of the reaction significantly. With the aim of investigation of the effect of combination of Hal and Char, Char surface modification and the way of use of -CD on the catalytic activity, several control catalysts were prepared and their catalytic activities were compared with that of the catalyst. It was confirmed that the use of Hal-Char as a support was more effective than the use of each component individually. Moreover, the use of -CD in its free form was more efficient than incorporating it to the framework of the catalyst or as a capping agent. It was also found that Char in its unmodified form was more efficient than modified ones. To justify the results, a precise study was carried out by comparing the average Pd particle size and loading of each samples. It was confirmed that the Pd particle size and dispersion effectively affected the catalytic activity. Additionally, -CD amount was a key factor for achieving high catalytic activity.
Article
Halloysites were applied as the template to form halloysite/polyaniline core/shell hybrids through an oxidative polymerization route, where the amount of aniline monomer could be adjusted to precisely control the shell thickness of polyaniline. The pyrolysis process was then applied to ensure the carbonization of the polyaniline to form halloysite/nitrogen-doped carbon core/shell hybrids. Finally, halloysites were removed, resulting in the formation of nitrogen-doped carbon nanotube with a uniform morphology and a controlled shell thickness. The shell thickness and pyrolysis temperature of nitrogen-doped carbon nanotubes were optimized to improve the electrocatalytic performance involved in oxygen reduction reaction. The nitrogen-doped carbon nanotubes showed good electrocatalytic activities toward oxygen reduction reaction in 0.1 mol L⁻¹ KOH aqueous solution, making them a promising cathode catalyst for alkaline fuel cell applications.
Article
A hybrid catalyst, Pd@Hal-pDA-NPC, with the utility for promoting both CC coupling reactions (Sonogashira, Heck and Suzuki reactions) and hydrogenation of nitrocompounds is prepared through two main steps. First, Pd(0) nanoparticles was immobilized on the poly-dopamine decorated halloysite nanotubes (Hal-pDA) and then Pd@Hal-pDA was hybridized with the layers of a novel multi-N-doped porous carbon monolayer derived from 4,4′,4″-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzonitrile. The results established that the catalyst could catalyze all the reactions efficiently under mild reaction condition. Moreover Pd@Hal-pDA-NPC exhibited high recyclability (up to ten reaction runs). Using various control catalysts, precise stuy was performed to elucidate the role of NPC and p-DA in the catalysis and suppressing Pd leaching. The results confirmed that both NPC and p-DA could improve Pd loading, while supress its leaching. Moreover, it was proved that incorporation of NPC was more effective than graphitic carbon nitride, g-G3N4, and grapheme oxide, GO.
Article
Dendrimer (PAMAM) decorated halloysite nanoclay (Hal) was prepared and applied for immobilization of Pd catalytic species to develop an efficient catalyst for copper and ligand-free CC coupling reactions. The effect of dendrimer generation, Pd valance and incorporation of anthranilamide as terminal functionality of dendrimer on the catalytic activity of the hybrid catalyst was studied experimentally and theoretically. The results of DFT computational studies on the effect of Pd valence showed that Pd(0) has much higher binding energy (-44.3 kcal/mol) on the modified halloysite surface, exposing PAMAM group, than Pd(OAc)2 with the binding energy of only -14.3 kcal/mol. Hence, Pd(0) was selected for experimental investigations. Again, computational studies on the two dendrimer generations, I and II, revealed higher stability of Pd(0) impregnated on Hal-PAMAM in generation I (G1) than it in G2. These results were experimentally confirmed by the synthesis of both Pd@Hal-PAMAM-G1 and Pd@Hal-PAMAM-G2 and comparing their catalytic activities for promoting the model coupling reactions. Additionally, the effect of terminal groups of dendrimer periphery was studied by comparing the catalytic activity of the catalysts with amine and anthranilamide terminated dendrimer, Pd@Hal-PAMAM-G1-ISA and Pd@Hal-PAMAM-G1. Interestingly, the experimental results were in good agreement with the theoretical findings and established Pd@Hal-PAMAM-G1-ISA as the catalyst of the choice. It was found that Pd@Hal-PAMAM-G1-ISA could promote both Sonogashira and Heck C-C coupling reactions efficiently in aqueous media (1:1 mixture of H2O and EtOH) and could be successfully recovered and reused for 10 reaction times with slight loss of the catalytic activity and Pd leaching.
Article
With the rapid depletion of fossil fuels and the associated environmental issues, solar energy is identified as one of the most promising pollution-free and renewable resource. Herein, we prepared a novel [email protected] microsphere with the integrated abilities of storing solar energy and catalytic function by self-assembly method. The results show that [email protected] microsphere has a core-shell structure with paraffin as core and halloysite as shell, and Ag nanoparticles are dispersed uniformly on the surface of the microspheres. The high thermal storage capability, encapsulation ratio and encapsulation efficiency of [email protected] indicate that it can be used as an ideal heat storage material. Compared with pure paraffin, [email protected] has higher thermal conductivity, excellent thermal storage capacity, and faster transient thermal response. After heat storage, [email protected] shows much better catalytic activity (95.3% of conversion in 6 min) compared with the one without heat storage (71.1% of conversion in 6 min) for catalytic reduction of 4-nitrophenol. This result suggests its potential to be used as a self-heating catalyst for storing/releasing thermal energy during catalytic reactions. This work may offer a general and innovative approach to couple phase change materials with catalyst and open up a new avenue for utilization of solar energy in the fields of chemistry and chemical engineering.
Article
An easy strategy to obtain nanohydrogel within the halloysite nanotubes (HNTs) lumen was investigated. Inorganic reverse micelles based on HNTs and hexadecyltrimethylammonium bromides were dispersed in chloroform and the hydrophilic cavity was used as nano-reactor to confine the gel formation based on alginate cross-linked by calcium ions. Spectroscopy and electron microscopy experiments proved the confinement of the polymer into the HNTs lumen and the formation of calcium mediated networks. Biological tests proved the biocompatibility of the hybrid hydrogel. The nanogel in HNTs was suitable for drug loading and sustained release with the opportunity of triggered burst release by chemical stimuli. Here we propose a new strategy based on inorganic reverse micelles for nanohydrogel formation that are suitable for industrial and biological applications as well as for selective and triggered adsorption and/or release.
Article
The unique one-dimensional nanoporous structure and the reactive external and internal surfaces make halloysite nanotube (HNT) an interesting nanomaterial for various applications. HNT is a green nanomaterial because it is easily available from abundant deposits in nature and is biocompatible with low cytotoxicity. After a brief introduction on the structure of HNT, recent advances in surface modification of HNT and its functional organic-inorganic nanohybrids including hybrid nanocontainers, flame retardant nanocomposites, dye removal adsorbents, liquid marbles, and superamphiphobic coatings are introduced.
Article
AgPd alloy nanoparticles (NPs) supported on halloysite nanotubes (HNTs) coated polydopamine (PDA) successfully synthesized by one-pot hydrothermal route. XRD, TEM and XPS were employed to verify the alloy structure of the obtained AgPd NPs. The HAADF-STEM result revealed that the thickness of PDA coating was ~10 nm, which could be formed on the surface of HNTs, and the existence of PDA was beneficial to deposit AgPd alloys with high dispersibility on the surface of HNTs. AgPd/PDA-HNT nanocomposites were effective catalysts for the hydrolysis of ammonia borane at room temperature, and the reaction was completed within 160 s using Ag3Pd2/PDA-HNT as catalysts, with a high total turnover frequency (TOF) value of 90 molH2 molcatalyst⁻¹ min⁻¹ and a low apparent activation energy (Ea) of 22.7 kJ mol⁻¹. After the sixth cycle, Ag3Pd2/PDA-HNT catalyst retained 72% of its initial activity and 100% conversion. The excellent catalytic properties, good durability and reusability, enabled Ag3Pd2/PDA-HNT to be an ideal catalyst in the practical applications.
Article
Herein, we report our recent research concerning the development of halloysite based protocols for cleaning, consolidation and protection purposes. Surface modification of halloysite cavity by anionic surfactants was explored to fabricate inorganic micelles able to solubilize hydrophobic contaminants. Hybrid dispersions based on halloysite and ecocompatible polymers were tested as consolidants for paper and waterlogged archaeological woods. Encapsulation of deacidifying and flame retardant agents within the halloysite lumen was conducted with aim to obtain nanofiller with a long-term protection ability. The results prove the suitability and versatility of halloysite nanotubes, which are perspective inorganic nanoparticles within materials science, remedation and conservation of cultural heritage fields.
Article
Halloysite is natural tubular clay suitable as a component of biocompatible nanosystems with specific functionalities. The selective modification of halloysite inner / outer surfaces can be achieved by exploiting supramolecular and covalent interactions resulting in controlled colloidal stability adjusted to the solvent polarity. The functionalized halloysite nanotubes can be employed as reinforcing filler for polymers as well as carriers for the sustained release of active molecules, such as antioxidants, flame-retardants, corrosion inhibitors, biocides and drugs. The tubular morphology makes halloysite a perspective template for core-shell metal supports for mesoporous catalysts. The catalysts can be incorporated with selective and unselective metal binding on the nanotubes’ outer surface or in the inner lumens. Micropatterns of self-assembled nanotubes have been realized by the droplet casting method. The selective modification of halloysite has been exploited to increase the nanotubes’ ordering in the produced patterns. Pickering emulsions, induced by the self-assembly of halloysite nanotubes on oil-water microdroplets interface, can be used for petroleum spill bioremediation and catalysis.
Article
Bimetallic nanoparticles, which are composed of two metal elements in a particle, exhibit much higher catalytic activity than respective monometallic ones due to new bi-functional or synergistic effects, so-called a ligand and/or an ensemble effect. In this work, a novel homogeneous as well as heterogeneous AuAg bimetallic nanocatalyst have been synthesized and supported on layer double hydroxide (LDH) by a simple wet chemical process. The support of LDH has reduced the size as well as capped the bimetallic nanoparticles and hence prevents the agglomeration. The surface morphology and chemical composition of these bimetallic nanoparticles were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloy (40–60 nm) and core-shell (15–30 nm) AuAg bimetallic nanoparticles were formed for heterogeneous and homogeneous composites, respectively. Moreover, the different compositions of as-synthesized AuAg bimetallic nanoparticles were utilized for the catalytic reduction of 4-nitrophenol. The highest activity was observed for the AuAg nanoparticles prepared with AuAg ratio at 1:3 and the activity became 10 to 45 times higher than that of original monometallic Au or Ag nanoparticles. The rate kinetics was studied for both homogeneous and heterogeneous system on the reduction of 4-nitrophenol and observed that the rate of reduction was greater in case of homogeneous catalysts as compared to heterogeneous catalysts. Also, the heterogeneous catalysts were effortlessly recovered and reused (up to 5 cycles) after completion of the reduction reaction.
Article
The structure of halloysite nanotubes (Hal) from different mines was investigated by Small-Angle Neutron Scattering (SANS) and Electric Birefringence (EBR) experiments. The analysis of the SANS curves allowed us to correlate the sizes and polydispersity and the specific surfaces (obtained by a Porod analysis of the SANS data) of the nanotubes with their specific geological setting. Contrast matching measurements were performed on patch Hal (from Western Australia) in order to determine their experimental scattering length density for a more precise analysis. Further characterization of the mesoscopic structure of Hal was carried out by Electric Birefringence (EBR), which allowed to study the rotational mobility of Hal. From the obtained rotational diffusion coefficients of the different Hal we deduced their length via the Broersma theory, which compares well to TEM data. The analysis of both SANS and EBR data provided a bulk average information on the Hal structure in water, which, for instance, documented the markedly higher degree of well-definedness of the PT-Hal and the thinner tube walls present here. The attained systematic structural knowledge represents a step forward for the robust structural description of halloysites selected from four geological deposits and shows that Hal of different origin differ very markedly with respect to their mesoscopic structure.
Article
The preparation and characterization of Pd/montmorillonite supported catalysts and their application in the O-, N-, and S-arylation through Ullmann coupling reaction were reported. The catalysts consisted of Pd supported on raw montmorillonite and on a Cu-doped Ti-pillared montmorillonite, and were prepared via impregnation of the clay supports with a Pd-precursor by the incipient wetness method. The catalysts were found to be effective and gave good to excellent yield in the arylation reactions. The catalyst based on the PILC was reusable and gave good yield up to three cycles of reaction.
Article
Halloysite tubular nanoclay was applied as a template for synthesis of ruthenium core-shell composite catalysts for the first time. 50-nm diameter ceramic tubular systems with metal seeded interior were produced. Procedure for the metal deposition and prior halloysite modification had a significant influence on properties of the catalyst and, as a consequence, on its activity in hydrogenation of phenol. Cyclohexanol was the main reaction product, but its yield depended on the substrate conversion and nanoarchitectural composition of the catalysts used. Maximum catalytic activity (turnover frequency, TOF) achieved was 17282 h⁻¹ in terms of hydrogen uptake per surface Ru atoms. Substrate selectivity of halloysite-based catalysts was also demonstrated at the comparative hydrogenation of phenol and various cresols.
Article
In present work, we prepared the bimetallic Cu-Co nanocatalysts on poly (diallyldimethylammonium chloride) functionalized halloysite nanotubes (Cu-Co/PDDA-HNTs) by a deposition-reduction technique at room temperature. The analysis of XRD, SEM, TEM, HAADF-STEM and XPS were employed to systematically investigate the morphology, particle size, structure and surface properties of the nanocomposite. The results reveal that the PDDA coating with thickness of ∼15 nm could be formed on the surface of HNTs, and the existence of PDDA is beneficial to deposit Cu and Co nanoparticles (NPs) with high dispersibility on the surface. While the cost-effective nanocomposite was used for the hydrolytic dehydrogenation of ammonia-borane (NH3BH3), the nanocatalyst showed extraordinary catalytic properties with high total turnover frequency of 30.8 molH2/(molmetal min), low activation energy of 35.15 kJ mol⁻¹ and high recycling stability (>90% conversion at 10th reuse). These results indicate that the bimetallic Cu-Co nanocatalysts on PDDA functionalized HNTs have particular potential for application in release hydrogen process.
Article
We present a facile and one-step synthesis of N-decorated porous carbon (NPC) material via direct heating dicyanobenzene in presence of ZnCl2, free from any pre- and post-treatments. The resultant NPC material features with graphite-like monolayers with thickness of ca. 1.4 nm as proved by microscopy technology. Highly porous NPC shows a BET surface area of 3038.5 m2 g-1 and a narrow pore size distribution centered at 0.51 nm. As a consequence, NPC displays a high H2 uptake up to 2.96 wt% at 77 K and CO2 adsorption capability of 23.4 wt% at 278 K and 1 bar. N-doping leads to optical absorption of NPC extended into near infrared (NIR) region. This N-decorated carbon material, as first example of NIR-triggered carbon photocatalyst, exhibits a pronounced H2 production capability. Carbonization of aromatic multi-nitriles would be a general and facile approach to prepare multifunctional N-doped carbon materials for gas storage and full solar spectrum-driven photocatalysts.
Article
Sepiolite-TiO2 nanocomposites were synthesized by conventional calcination process and microwave hydrothermal (M-H) treatment and were tested and compared for their photocatalytic activity. XRD analysis indicated that nanocomposites after calcination at 500 °C or M-H treatment for 40 min at about 200 °C appear to be the optimal conditions, which assured the amorphous TiO2 to crystalline anatase phase transition. The deposition of the TiO2 on the surface of sepiolite by M-H treatment yielded small dispersed nanoparticles at all treatment times used in this study. However, TiO2 particle size increased with increasing calcination temperature, which was confirmed by SEM and TEM. N2-adsorption-desorption isotherms indicated that calcination process reduced the specific surface areas of the nanocomposites while the M-H treatment led to a higher surface area with better photocatalytic performance for the degradation of Orange G. The intact structure of sepiolite and the homogeneous dispersion of the TiO2 nanocrystals on sepiolite surfaces led to enhanced photocatalytic activity in M-H treated samples.
Article
Halloysite nanotubes (HNTs) are clay minerals with hollow nanotubular structures. Due to their biocompatibility, potential applications and availability, there is a growing interest toward these nanomaterials. The surface chemistry of HNTs is versatile for targeted chemical modification of inner lumen and outer surface. Functionalized halloysite constituted a valuable support for metal nanoparticles promoting catalytic applications with tunable properties. The peculiar tubular shape of HNTs favors dispersion and surface availability of the supported metal nanoparticles that are active in the catalytic path. Moreover, the presence of an empty lumen, open new perspectives for the production of nanoarchitectures with synergistic catalytic effects due to the increase of local concentrations and confination. The main focus of this review is the research on modified halloysite nanotubes for the preparation of valuable support of metal nanoparticle and their applications in catalytic processes.
Article
A novel antibacterial nanocomposite, CeO2-ZnO/HNTs was prepared by a homogeneous co-precipitation method in ethanol solution. ZnO and CeO2 nanoparticles with sizes of approximately 8 and 4 nm, respectively, were dispersively precipitated onto the surface of halloysite nanotubes(HNTs). HNTs served as a template for reducing the agglomeration of ZnO nanoparticles and improving the interface reactions between the nanocomposite and bacteria cells. CeO2 nanoparticles were introduced to suppress the recombination of electron-hole pairs, and narrow the energy gap of ZnO nanoparticles. The synergistic effects of ZnO, CeO2 nanoparticles and HNTs led to the superior antibacterial activity of the CeO2-ZnO/HNTs nanocomposite against gram-negative Escherichia Coli.
Article
A cube-like Ag@AgCl-doped TiO2/sepiolite (denoted Ag@AgCl–TiO2/sepiolite) was successfully synthesized via a novel method. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy were performed to determine the structure and physicochemical properties of Ag@AgCl–TiO2/sepiolite. SEM micrographs revealed that Ag@AgCl nanoparticles and TiO2 film are well deposited on the surface of tube-like sepiolite. As a result, Ag@AgCl–TiO2/sepiolite exhibits a red shift relative to TiO2/sepiolite. Photocatalytic experiments demonstrated that the dosage of catalysts plays an important role during photocatalysis. The photoelectrochemical activities of Ag@AgCl–TiO2/sepiolite and TiO2/sepiolite were also investigated. Photocurrent responses confirmed that the ability of Ag@AgCl–TiO2/sepiolite to separate photo-generated electron–hole pairs is stronger than that of TiO2/sepiolite. Methylene Blue degradation is also improved under alkaline conditions and visible light irradiation because more OH is produced by visible light excitation. This excellent catalytic ability is mainly attributed to the formed Ag nanoparticles and the Schottky barrier at the Ag/TiO2 interface. Active species analysis indicated that O2⁻ and h⁺ are implicated as active species in photocatalysis. Therefore, catalysts are excited to produce abundant electron–hole pairs after they absorb photons in photocatalysis.
Article
We reported the enhanced catalytic property of core-shell Ag@Pt nanoparticles supported on sepiolite nanofibers for the reduction of nitrophenols in the presence of NaBH4. Furthermore, we confirmed the contribution of core-shell structure to the enhanced catalytic performance of Ag@Pt nanoparticles by DFT calculations. The Ag@Pt/sepiolite catalysts were prepared using a successive reduction method, in which core-shell Ag@Pt nanoparticles were highly dispersed on sepiolite nanofibers. DFT calculations showed that the charge redistribution and s-d hybridization between Ag cores and Pt shells contributed to the unique electronic structure of Ag@Pt nanoparticles. More importantly, 2 wt. % Ag@Pt/sepiolite catalyst exhibited much higher catalytic activity toward nitrophenols reduction than Ag/sepiolite and Pt/sepiolite, and relatively high catalytic stability even after 5 cycles. The enhanced catalytic performance of Ag@Pt/sepiolite catalysts was primarily owing to the large surface area and high porosity of sepiolite nanofibers and the unique electronic structure of core-shell Ag@Pt nanoparticles, which resulted in the effective adsorption of nitrophenols and the electron transfer from BH4⁻ to nitrophenols, respectively. This study probably provides new insights into the catalytic reduction of nitrophenols in water by forming the composite between bimetallic core-shell nanoparticles and natural low-cost supports.
Article
Squalane is an important ingredient in the cosmetic, nutraceutical, and pharmaceutical industries. It has also been used as a model compound for the hydrocracking of crude and microalgae oil. Thus, a series of green heterogeneous metal catalysts were prepared to achieve complete hydrogenation of highly unsaturated squalene into squalane. Surface modification of the clay and metal intercalation simultaneously occurred during wet impregnation. The Pd-nanoparticles-intercalated clay with a dominating Pd(1 1 1) facet showed the highest reactivity and selectivity. The catalyst was stable with very low Pd leaching (≈0.03 ppm) and was recyclable without losing any significant catalytic activity.
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In this paper, magnetic resorcinol-formaldehyde (RF) resin coated carbon nanotubes were synthesized from hydrophilic magnetic carbon nanotubes (CNTs) with the extended Stober method. Firstly, magnetic CNT composites ([email protected]/* */3O4) were synthesized by the high temperature decomposition process using the iron acetylacetonate as raw materials. Then the resorcinol-formaldehyde polymer can be easily coated on the magnetic CNTs with the extended Stober method. Finally, numerous of gold nanoparticles were assembled on the surface of [email protected]/* */3O4@RF by reducing Au3+ between the RF shell and HAuCl4 solution; meanwhile, the mesoporous carbon coated [email protected]/* */3O4 can also be obtained by calcinations of the [email protected]/* */3O4@RF composites in nitrogen atmosphere. The resulting [email protected]/* */3O4@[email protected]/* */ or [email protected]/* */3O4@C composites show not only a magnetic response to an externally applied magnetic field, but also can be a kind of catalyst or adsorbent to catalyze or adsorb the methylene blue (MB), in the ambient temperature.
Article
Through this manuscript the green synthesis of palladium nanoparticles supported on reduced graphene oxide (Pd NPs/RGO) under the mild conditions through reduction of the graphene oxide and Pd(2+) ions using barberry fruit extract as reducing and stabilizing agent is reported. The as-prepared Pd NPs/RGO was characterized by UV-vis spectroscopy, X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The Pd NPs/RGO could be used as an efficient and heterogeneous catalyst for reduction of nitroarenes using sodium borohydride in an environmental friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity.
Article
Mixed metal oxides derived from layered hydrotalcite (HT) materials are extensively used as a potential catalyst and catalytic support in various organic transformations. Numerous such materials have been developed by varying framework divalent and trivalent metal ions, and interlayer anions. The intercalation of anions present in HT facilitates the design of high surface area materials possessing exposed active sites, which enhances the catalytic and adsorption properties. These HT materials have also been used as drug carriers, and in enzyme encapsulation owing to their flexible accommodation of organic anions in the interlayer of the HT structure. The present review is focused on a recent development in the preparation of various HT materials using different metals and intercalating ions and their importance in the various catalytic processes, such as base catalyzed alkylation, isomerization, condensation and esterification. Effectiveness of transition metals containing HT for redox catalytic processes, viz. oxidation of alcohol, alkyl aromatics, phenol and reduction of nitro compounds have been discussed. Further, the importance of the introduction of a hard anion like silicate into the interlayer space of the HT and its applications in various organic reactions has also been covered in this review.
Article
In the present work, the nanocomposite of olefinic blocky copolymer with collapsed organically modified montmorillonite (OBC/c-OMMT) was prepared by co-precipitation of OBC and OMMT with excess ethanol. The dispersion state of clay in the nanocomposites was identified by WAXD and further confirmed by FT-IR. It is found that ethanol can extract parts of the organic modifier and OBC can further squeeze the resultant OMMT layers, yielding collapsed OMMT. Crystallization and morphology of OBC/c-OMMT were compared with those of the nanocomposites containing intercalated organically modified montmorillonite (i-OMMT) and aggregated un-modified montmorillonite (a-MMT). The collapsed OMMT has a stronger nucleation effect on crystallization of OBC than i-OMMT and a-MMT, as revealed by the higher crystallization temperature, smaller crystallite size and larger number of crystallite. Rheology test reveals that the complex viscosity of OBC/c-OMMT at low frequencies is smaller, possibly due to the lower volume fraction of c-OMMT in OBC.
Article
The interaction of clay minerals and dyes is an area of great interest especially in the development of novel adsorbents. In this report, we demonstrated interaction of halloysite nanotubes (HNTs) and an anionic dye, methyl orange (MO), through a electrostatic attraction. Halloysite lumen has a trapping characteristic for methyl orange, which is mainly determined by the positively charged nature of the inner surface of HNTs. XRD results confirmed that intercalation of methyl orange into HNTs did not occur. SEM-EDS and photostability results showed that MO molecules were primarily in HNTs lumen. Adsorption isotherm studies revealed an interesting phenomenon, i.e. a sudden increase of adsorption capacity occured in the initial dye concentration of about 75 mg/L, which was just the dye concentration corresponding to the onset of dye oligomer formation. This suggested dye aggregation state had a decisive influence to the adsorption behavior of MO on the halloysite. BET results demonstrated at low and high dye concentrations, single MO molecule and aggregation of several dimers through hydrophobic interaction, interacted with Al-OH2+ sites on the inner wall, respectively. Desorption experiments showed that MO in HNTs can be completely removed with deionized water, indicating halloysite is a low-cost and efficient adsorbent for anionic dye.
Article
Technological applications of heterogeneous nanocatalysts on supports have generally relied on the surface or interface properties of supports. Herein, we report a facile approach to fabricate roughened surface on halloysite nanotubes (HNTs) through etching the wall of HNTs in molten-salt system. SEM, TEM, XRD, FT-IR, AFM and N2 adsorption/desorption analysis are employed to systematically investigate the morphology, structure and surface properties. Results suggest that roughness of HNTs surface has been significantly increased and defects are formed on the tube wall without structural damage. Subsequently the roughened halloysite nanotubes (RHNTs) are used as supports to prepare heterogeneous nanocatalyst. The Pt nanoparticles with uniform size can deposit homogeneously onto the RHNTs surface via one-step hydrothermal reduction. The as-prepared Pt@RHNTs catalyst exhibits remarkably improved activity and selectivity for hydrogenation of cinnamaldehyde towards cinnamyl alcohol compared with pristine halloysite support. Furthermore, Pt@RHNTs catalyst shows rapid catalytic rate in hydrogenation reaction and excellent leaching resistance in cycle uses.
Article
Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show favorable features for electrochemical energy storage such as high specific surface area (SBET: 2494 m2/g), high volume of hierarchical pores (2.28 cm3/g), nanosheets structures, rich N doping (4.7 %) and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and two electrode-based supercapacitors has been prepared. A reversible lithium storage capacity of 1865 mA h/g have been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitors electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9 % loss after 10000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled for the same electrode material which was obtained through one-step and facile large-scale synthesis route. It is promising for next generation hybrid energy storage and renewable delivery devices.
Article
We present the utilization of a heterogeneous catalyst comprised of Pd nanoparticles supported on aminopropyl-functionalized siliceous mesocellular foam (Pd0–AmP–MCF) for the selective hydrogenation of aromatic, aliphatic, and heterocyclic nitro compounds to the corresponding amines. In general, the catalytic protocol exclusively affords the desired amine products in excellent yields within short reaction times with the reactions performed at room temperature under ambient pressure of H2. Moreover, the reported Pd nanocatalyst displayed excellent structural integrity for this transformation as it could be recycled multiple times without any observable loss of activity or leaching of metal. In addition, the Pd nanocatalyst could be easily integrated into a continuous-flow device and used for the hydrogenation of 4-nitroanisole on a 2.5 g scale, where the product p-anisidine was obtained in 95 % yield within 2 h with a Pd content of less than 1 ppm.
Article
Catalytic hydrogenolysis/hydrogenation of bioglycerol leads to 1,2 and 1,3-propanediols, which can be further valorized to industrially important products through a variety of reactions such as etherification, esterification and cyclization through acetalization. In the current work, selective mono-etherification of 1,3-propanediol (PDO) with isopropanol to 3-isopropyl-1-propanaol was systematically studied, using 20% w/w Cs2.5H0.5PW12O40/K-10 catalyst in an autoclave at 170 degrees C. In a typical reaction, using 1:6 mol ratio of 1,3-PDO to isopropanol at 0.03 g/cm(3) catalyst loading and 1000 rpm, 60% conversion was achieved with 100% selectivity to the product. The catalyst was prepared by incipient wetness technique and characterized by various techniques such as X-ray diffraction, surface area measurement by N-2 adsorption-desorption, FTIR, and SEM. Effect of various reaction parameters on conversion and selectivity was studied to establish kinetics and mechanism. The catalyst is robust and reusable. The overall process is green and clean.