Templated self-assembly of ordered mesoporous silica on clay nanotubes

Integrated hierarchical porous lignin-based carbon electrode for boosting membrane-free capacitive deionization areal adsorption capacity

The development of high value-added lignin-based functional porous carbon electrodes with excellent properties from sustainable industry lignin powder remains a challenge. This work aims to create robust, binder-free, conductive additives-free, and current collector-free monolithic porous carbon electrodes using industrial lignin powder for membrane-free capacitive deionization (CDI). The material exhibits high mechanical strength, hierarchical porosity structure, large uniform size, and thickness of just a few millimetres (<2.6 mm). In a three-electrode supercapacitor system, the areal specific capacitance of CLCA300-3-1.0 reaches 5.03-1.02 F cm-2 when the scan rate between 1 and 20 mV s-1 in 1 M NaCl solution. As CDI electrodes, the charge efficiency of CLCA300-3-1.0 at different voltages of 1.2 V, 1.4 V and 1.6 V is 0.53, 0.72 and 0.71, respectively. The energy consumption of CLCA280-3-1.0, CLCA300-3-1.0 and CLCA320-3-1.0 tested at 1.2 V are 3.27, 3.40 and 3.25 Wh m-3, respectively. In addition, with thickness increasing to 1.5 mm, the developed CLCA300-3-1.5 electrode exhibits an areal adsorption capacity of 0.46 mg cm-2, and relative highly capacity retention of 84.78 % after 70 cycles. The impressive desalination performance is attributed to the well-designed hierarchical porosity, superhydrophilicity and robust monolithic structure.

Lipid-inspired biomimicking morphosynthesis of a series of complex concave silica architectures

The lipid-inspired biosilicification process enables the creation of a series of concave silica nanoarchitectures in the complex shapes of nanobowls, nanodishes, nanoboats, and nanoloops. The reaction at a pH of 8 initially allows the formation of thin and elastic circular gel nanosheets that can undergo inducible stretching and folding, which subsequently evolves into nanodish and nanobowl through a potential global buckling process. The adjustment of the pH to 9 and 4 enables the production of more complex morphogens of nanoboat and nanoloop, respectively. These unique silica nanoarchitectures may have a wide scope of potential application from nanoreactors in heterogenous catalysis to drug delivery systems and optical materials.

Halloysite nanotube-supported bismuth catalysts for acetylene hydrochlorination

A novel supported bismuth (Bi)-based catalyst was prepared using halloysite nanotubes (HNTs) as a carrier and effectively used for acetylene hydrochlorination.

Structured clay minerals-based nanomaterials for sustainable photo/thermal carbon dioxide conversion to cleaner fuels: A critical review

In efforts to achieve a sustainable development goal, the utilization of CO₂ to generate renewable fuels is promising, as it is a sustainable technology that provides affordable and clean energy. To realize the production of renewable green fuels, a proficient and low-cost technology is required. Using photo/thermal catalytic process, the goal of sustainable CO₂ hydrogenation can be achieved. There have been several types of catalysts under exploration, however, they are expensive with limited availability. In the current development, green materials such as mineral clays are emerging as cocatalyst/supports for CO₂ hydrogenation. Clays are bestowed with various beneficial properties such as a large surface area, high porosity, abundant basic sites, excellent thermal stability and chemical corrosion resistance. Clays are promising materials that can drastically reduce the cost in catalyst preparation, partially fulfil the energy demand and reduce greenhouse gas emission. This review aims to focus on the various types of clays and their applications in the field of photo/thermal CO₂ hydrogenation to renewable fuels. Firstly, the classifications of clays are provided, whereby they can be differentiated based on their silicate layers, namely 1:1 and 2:1 type clay and their properties are thoroughly discussed to provide advantages and applications. The applications of various clays such as kaolinite, halloysite, montmorillonite, attapulgite, saponite and volkonskoite for CO₂ hydrogenation reactions are systematically discoursed. In addition, various approaches to improve the capability of raw clays as catalyst support are critically discussed, which include thermal treatment, exfoliation, acid-leaching and pillaring approaches. A critical discussion regarding the engineering aspects to further enhance clay-based catalyst for CO₂ hydrogenation are further disclosed. In short, clays are freely available materials that can be found in abundance. However, there are many more different types of natural green clays that have not been studied and explored in various energy applications.

Architectural design of core-shell nanotube systems based on aluminosilicate clay

A nanoarchitectural approach to the design of functional nanomaterials based on natural aluminosilicate nanotubes and their catalysis, and practical applications are described in this paper. We focused on the buildup of hybrid core-shell systems with metallic or organic molecules encased in aluminosilicate walls, and nanotube templates for structured silica and zeolite preparation. The basis for such an architectural design is a unique Al₂O₃/SiO₂ dual chemistry of 50 nm diameter halloysite tubes. Their structure and site dependent properties are well combined with biocompatibility, environmental safety, and abundant availability, which makes the described functional systems scalable for industrial applications. In these organic/ceramic hetero systems, we outline drug, dye and chemical inhibitor loading inside the clay nanotubes, accomplished with their silane or amphiphile molecule surface modifications. For metal-ceramic tubule composites, we detailed the encapsulation of 2-5 nm Au, Ru, Pt, and Ag particles, Ni and Co oxides, NiMo, and quantum dots of CdZn sulfides into the lumens or their attachment at the outside surface. These metal-clay core-shell nanosystems show high catalytic efficiency with increased mechanical and temperature stabilities. The combination of halloysite nanotubes with mesoporous MCM-41 silica allowed for a synergetic enhancement of catalysis properties. Finally, we outlined the clay nanotubes' self-assembly into organized arrays with orientation and ordering similar to nematic liquid crystals, and these systems are applicable for life-related applications, such as petroleum spill bioremediation, antimicrobial protection, wound healing, and human hair coloring.

Photoinduced Antibacterial Activity and Cytotoxicity of CdS Stabilized on Mesoporous Aluminosilicates and Silicates

Inactivation of bacteria under the influence of visible light in presence of nanostructured materials is an alternative approach to overcome the serious problem of the growing resistance of pathogenic bacteria to antibiotics. Cadmium sulfide quantum dots are superefficient photocatalytic material suitable for visible light transformation. In this work, CdS nanoparticles with size of less than 10 nm (QDs) were synthesized on the surface of natural and synthetic mesoporous aluminosilicates and silicates (halloysite nanotubes, MCM-41, MCM-41/Halloysite, SBA-15). Materials containing 5–7 wt.% of CdS were characterized and tested as agents for photocatalytic bacteria degradation of Gram-positive S. aureus and Gram-negative E. coli with multiple antibiotic resistance. Eukaryotic cell viability tests were also conducted on the model cancer cells A 459. We found that the carrier affects prokaryotic and eukaryotic toxicity of CdS quantum dots. CdS/MCM-41/HNTs were assumed to be less toxic to eukaryotic cells and possess the most prominent photocatalytic antibacterial efficiency. Under visible light irradiation, it induced 100% bacterial growth inhibition at the concentration of 125 μg/mL and the bacteriostatic effect at the concentration of 63 μg/mL. CdS/MCM-41/HNTs showed 100% E. coli growth inhibition in the concentration of 1000 μg/mL under visible light irradiation.

CuO-In2O3 Catalysts Supported on Halloysite Nanotubes for CO2 Hydrogenation to Dimethyl Ether

Hydrogenation of CO2 relative to valuable chemical compounds such as methanol or dimethyl ether (DME) is an attractive route for reducing CO2 emissions in the atmosphere. In the present work, the hydrogenation of CO2 into DME over CuO-In2O3, supported on halloysite nanotubes (HNT) was investigated in the temperature range 200–300 °C at 40 atm. HNT appears to be novel promising support for bifunctional catalysts due to its thermal stability and the presence of acidic sites on its surface. CuO-In2O3/HNT catalysts demonstrate higher CO2 conversion and DME selectivity compared to non-indium CuO/HNT catalysts. The catalysts were investigated by N2 adsorption, X-ray diffraction, hydrogen-temperature programmed reduction and transition electron microscopy. The acid sites were analyzed by temperature programmed desorption of ammonia. It was shown that CuO/HNT was unstable under reaction conditions in contrast to CuO-In2O3/HNT. The best CuO-In2O3/HNT catalyst provided CO2 conversion of 7.6% with 65% DME selectivity under P = 40 atm, T = 250 °C, gas hour space velocity 12,000 h−1 and H2:CO2 = 3:1.

Integrating Halloysite Nanostraws in Porous Catalyst Supports to Enhance Molecular Transport

In many porous catalyst supports, the accessibility of interior catalytic sites to reactant species could be restricted due to limitations of reactant transport through pores comparable to reactant dimensions. The interplay between reaction and diffusion in porous catalysts is defined through the Thiele modulus and the effectiveness factor, with diffusional restrictions leading to high Thiele moduli, reduced effectivess factors, and a reduction in the observed reaction rate. We demonstrate a method to integrate ceramic nanostraws into the interior of ordered mesoporous silica MCM-41 to mitigate diffusional restrictions. The nanostraws are the natural aluminosilicate tubular clay minerals known as halloysite. Such halloysite nanotubes (HNTs) have a lumen diameter of 15-30 nm, which is significantly larger than the 2-4 nm pores of MCM-41, thus facilitating entry and egress of larger molecules to the interior of the pellet. The method of integrating HNT nanostraws into MCM-41 is through a ship-in-a-bottle approach of synthesizing MCM-41 in the confined volume of an aerosol droplet that contains HNT nanotubes. The concept is applied to a system in which microcrystallites of Ni@ZSM-5 are incorporated into MCM-41. Using the liquid phase reduction of nitrophenol as a model reaction catalyzed by Ni@ZSM-5, we show that the insertion of HNT nanostraws into this composite leads to a 50% increase in the effectiveness factor. The process of integrating nanostraws into MCM-41 through the aerosol-assisted approach is a one-step facile method that complements traditional catalyst preparation techniques. The facile and scalable synthesis technique toward the mitigation of diffusional restrictions has implications to catalysis and separation technologies.

Clay nanotube-metal core/shell catalysts for hydroprocesses

Catalytic hydroprocesses play a significant role in oil refining and petrochemistry. The tailored design of new metal nanosystems and optimization of their support, composition, and structure is a prospective strategy for enhancing the efficiency of catalysts. Mesoporous support impacts the active component by binding it to the surface, which leads to the formation of tiny highly dispersed catalytic particles stabilized from aggregation and with minimized leaching. The structural and acidic properties of the support are crucial and determine the size and dispersion of the active metal phase. Currently, research efforts are shifted toward the design of nanoscale porous materials, where homogeneous catalysts are displaced by heterogeneous. Ceramic materials, such as 50 nm diameter natural halloysite nanotubes, are of special interest for this. Much attention to halloysite clay is due to its tubular structure with a hollow 10-15 nm diameter internal cavity, textural characteristics, and different chemical compositions of the outer/inner surfaces, allowing selective nanotube modification. Loading halloysite with metal particles or placing them outside the tubes provides stable and efficient mesocatalysts. The low cost of this abundant nanoclay makes it a good choice for the scaled-up architectural design of core-shell catalysts, containing active metal sites (Au, Ag, Pt, Ru, Co, Mo, Fe₂O₃, CdS, CdZnS, Cu-Ni) located inside or outside the tubular template. These alumosilicate nanotubes are environment-friendly and are available in thousands of tons. Herein, we summarized the advances of halloysite-based composite materials for hydroprocesses, focusing on the selective binding of metal particles. We analyze the tubes' morphology adjustments and size selection, the physicochemical properties of pristine and modified halloysite (e.g., acid-etched or silanized), the methods of metal clusters formation, and their localization. We indicate prospective routes for the architectural design of stable and efficient nanocatalysts based on this safe and natural clay material.

An interfacial coating with high corrosion resistance based on halloysite nanotubes for anode protection of zinc-ion batteries

Aqueous zinc-ion batteries are recognized as one of the most potential neutral aqueous batteries because of the high energy density, high specific capacity, low cost, and low pollution. However, the applications of zinc-ion batteries are seriously limited by the capacity fading, easy-corrosion, side reaction, and hydrogen evolution. Herein, we report a uniform halloysite nanotubes (HNTs) coating which can guide Zn²⁺ ions stripping/plating on the HNTs/Zn interfaces and protect the Zn anode. The HNTs coating significantly suppresses the corrosion of Zn anode and effectively reduces the hydrogen evolution and the formation of by-product. Furthermore, the HNTs-Zn anode exhibits lower resistance than bare Zn. Compared with the bare Zn anode batteries, HNTs-Zn/MnO₂ batteries exhibit good capacity retention and can increase the discharge capacity to 79% at 3 C after 400 cycles. The novel design of interfacial coating based on halloysite nanotubes through electrophoretic deposition method provides a new way to fabricate economic and stable aqueous zinc-ion batteries.

Synthesis and Characterization of Nanomaterial Based on Halloysite and Hectorite Clay Minerals Covalently Bridged

Halloysite is an aluminosilicate clay with a predominantly hollow tubular structure (HNTs) able to act as a nanocontainer for the encapsulation of several chemicals. However, HNTs possess low affinity for metal ions in their pristine form and they need to be modified for improving their adsorption capabilities. Therefore, to overcome this issue herein we report a straightforward approach for the covalent modification of the external surface of halloysite nanotubes with hectorite clay. Compared to halloysite, hectorite possesses a lamellar structure with higher cation exchange capacity. The covalent linkage between the two clays was verified by several techniques (FTIR spectroscopy, ¹³C CP-MAS NMR, TGA, ζ-potential, DLS, and XRD measurements) and the morphology was imaged by TEM investigations. As proof of concept the adsorption ability of the obtained nanomaterial in comparison to pristine clays was proved using ciprofloxacin and silver ions chosen as models for their different chemical characteristics.

Selective Hydrogenation of Acetylene over Pd-Mn/Al2O3 Catalysts

Novel bimetallic Pd-Mn/Al2O3 catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al2O3 in an H2 atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N2 adsorption, H2 pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H2), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al2O3 catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al2O3 to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts.

Ruthenium Catalysts Templated on Mesoporous MCM-41 Type Silica and Natural Clay Nanotubes for Hydrogenation of Benzene to Cyclohexane

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.

Formation of ruthenium nanoparticles inside aluminosilicate nanotubes and their catalytic activity in aromatics hydrogenation: the impact of complexing agents and reduction procedure

Ruthenium particles with size from 1 to 7 nm were formed by reduction of ruthenium complexes with urea, ethylenediaminetetraacetic acid, acetone azine, 1,2-Bis(2-furylmethylene)hydrazine) inside halloysite nanotubes. Catalysts of different morphology with Ru content from 0.75 to 0.93 %wt. were obtained using NaBH4 or H2 as reducing agents and tested in benzene hydrogenation as a model reaction. NaBH4 reduced catalysts showed similar catalytic activity with 100 % benzene conversion after 1.5 h. Reduction with H2 resulted in a decrease of catalytic activity for all samples. High benzene conversion was achieved only in the case of 1,2-Bis(2-furylmethylene)hydrazine and ethylenediaminetetraacetic acid. It was concluded that the thermal stability of complexing agents plays a key role in activity of catalysts reduced with H2.

Ketone Hydrogenation by Using ZnO-Cu(OH)Cl/MCM-41 with a Splash of Water: An Environmentally Benign Approach

MCM-41-supported ZnO-Cu(OH)Cl nanoparticles were synthesized via an incipient wetness impregnation technique using zinc chloride and copper chloride salts as well as water at room temperature. The catalyst was characterized by powder X-ray diffraction (PXRD), infrared spectroscopy (IR), and TGA, whereas surface and morphological studies were performed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The above studies revealed the incorporation of metal species into the pores of MCM-41, leading to a decrease in surface area of the nanoparticles that was found to be 239.079 m² /g. The substituents attached to the ketone determine the rate of the reaction, and the utilization of the green solvent 'water' astonishingly completes the hydrogenation reaction in 45 minutes at 40 °C with 100% conversion and 100% selectivity as analyzed by gas chromatography-mass spectrometry. Hence, ZnO-Cu(OH)Cl/MCM-41 nanoparticles with 2.46 wt% zinc and 6.39 wt% copper were demonstrated as an active catalyst for the reduction of ketones without using any gaseous hydrogen source making it highly efficient as well as environmentally and economically benign.

Augmented polyhydrazone formation in water by template-assisted polymerization using dual-purpose supramolecular templates

Template-assisted polymerization using donor–acceptor supramolecular templates results in higher M_w and M_n values, decreased critical hydrogelation concentrations, and increased gel recovery velocity following shear-induced breakdown.

Manganese and Cobalt Doped Hierarchical Mesoporous Halloysite-Based Catalysts for Selective Oxidation of p-Xylene to Terephthalic Acid

Bimetallic MnCo catalyst, supported on the mesoporous hierarchical MCM-41/halloysite nanotube composite, was synthesized for the first time and proved its efficacy in the selective oxidation of p-xylene to terephthalic acid under conditions of the AMOCO process. Quantitative yields of terephthalic acid were achieved within 3 h at 200–250 °C, 20 atm. of O2 and at a substrate to the Mn + Co ratio of 4–4.5 times higher than for traditional homogeneous system. The influence of temperature, oxygen, pressure and KBr addition on the catalyst activity was investigated, and the mechanism for the oxidation of p-toluic acid to terephthalic acid, excluding undesirable 4-carboxybenzaldehyde, was proposed.

Multicomponent bionanocomposites based on clay nanoarchitectures for electrochemical devices

Based on the unique ability of defibrillated sepiolite (SEP) to form stable and homogeneous colloidal dispersions of diverse types of nanoparticles in aqueous media under ultrasonication, multicomponent conductive nanoarchitectured materials integrating halloysite nanotubes (HNTs), graphene nanoplatelets (GNPs) and chitosan (CHI) have been developed. The resulting nanohybrid suspensions could be easily formed into films or foams, where each individual component plays a critical role in the biocomposite: HNTs act as nanocontainers for bioactive species, GNPs provide electrical conductivity (enhanced by doping with MWCNTs) and, the CHI polymer matrix introduces mechanical and membrane properties that are of key significance for the development of electrochemical devices. The resulting characteristics allow for a possible application of these active elements as integrated multicomponent materials for advanced electrochemical devices such as biosensors and enzymatic biofuel cells. This strategy can be regarded as an "a la carte" menu, where the selection of the nanocomponents exhibiting different properties will determine a functional set of predetermined utility with SEP maintaining stable colloidal dispersions of different nanoparticles and polymers in water.

Cellulose Nanofibrils and Tubular Halloysite as Enhanced Strength Gelation Agents

Silica gels are widely employed in water shutoff services, making them an essential tool in oil well management. Silica nanoparticles may serve as a strengthening additive for polymer hydrogels. In this study, we look at this statement from a different angle: What additives could be used to increase the strength of silica gels? Colloidal silica gels were prepared with various additives, and gel strength was measured by a Veiler-Rebinder apparatus. We found that cellulose nanofibrils considerably increase the gel strength (from 20-25 to 35-40 kPa), which is comparable with the industrial anionic polymer Praestol 2540. Cellulose nanofibrils can be produced from cheap industrial-grade cellulose with low-cost industrial chemicals and could be partially replaced by the even less expensive halloysite nanoclay. Cellulose nanofibrils produced from renewable sources and naturally occurring halloysite nanoclay could be used as complementary reinforcing agents.