Protonated Titanate Nanotubes Research Articles

Future Paradigm of 3D Printed Ni-Based Metal Organic Framework Catalysts for Dry Methane Reforming: Techno-economic and Environmental Analyses.

Dry reforming of biogas is referred as an attractive path for sustainable H2 production over decades. Meanwhile, in the Malaysian context, the abundance of palm oil mill effluent (POME) produced annually is deemed as a potential renewable source for renewable energy generation. Conventionally, nickel (Ni) is the most common catalyst used in the industrial-scale dry reforming of methane (DRM) to yield H2, but it is subject to the drawbacks of sintering and deactivation after a long reaction time at high temperatures (>500 °C). Therefore, this work aims to provide an insight on the feasibility of the application of modified Ni-based catalysts in DRM, specifically in the economic and environmental aspects. From the benchmarking study of various Ni-based catalysts (e.g., bimetallic (Ni-Ce/Al2O3), alumina support (Ni/Al2O3), protonated titanate nanotube (Ni-HTNT), and unsupported), the Ni-MOF catalyst, notably, had proven its prominence in both economic and environmental aspects on the same basis of 10 tonnes of H2 production. The MOF-based catalyst not only possessed a better economic performance (net present value 61.86%, 140%, and 563.08% higher than that of Ni-Ce/Al2O3, Ni/Al2O3, and Ni-HTNT) but also had relatively lower carbon emissions (13.18%, 20.09%, and 75.72% lower than that of Ni/Al2O3, Ni-HTNT, and unsupported Ni). This work also accounted for 3D printing technology for the mass production of Ni-MOF catalysts, where the net present value was 2 to 3% higher than that of the conventional production method. Additionally, sensitivity analysis showed that the H2 price has the greatest impact on the feasibility of DRM as compared to other cost factors.

One-dimensional titanate nanotube materials: heterogeneous solid catalysts for sustainable synthesis of biofuel precursors/value-added chemicals-a review.

One-dimensional (1D) titanate nanotubes materials (protonated titanate nanotube (HTNT) and sodium titanate nanotube (NaTNT)) have been reported as low-cost and efficient catalytic materials in chemical syntheses for the production of biofuel precursors with interesting catalytic performance exhibited, even better than some commonly used zeolites, H-MOR, H-β, SO42−/Al2O3, and H-ZSM-5 solid catalysts with environmental benign in focus when compared with homogeneous catalytic materials. This mini-review expressly revealed the significance and potential of using HTNT and NaTNT as sustainable and environmentally benign solid catalysts/supports in various chemical reactions. The critical assessment of biomass valorization and titanate nanostructured materials as catalysts/supports via Green Chemistry approach, #7 (use of renewable feedstocks), #9 (use of catalyst against stoichiometry) and United Nations (UN) Sustainable Development Goals (SDGs), #7 (affordable and clean energy; ensure access to inexpensive, reliable, sustainable, and new energy), is presented as integrated pathways to meet environmental benign technology toward sustainability. Hence, this work follows in the pattern of recent formulated features reported for solid catalysts—‘PYSSVR’ concept, which means P–production cost, Y–yield, S–stability, S–selectivity, V–versatility, and R–reusability.Graphical

A TiO2 nanotubes film with excellent antireflective and near-perfect self-cleaning performances

SiO2/TiO2 composite films have been frequently used to realize the functions of self-cleaning and antireflection. Increasing the TiO2 volume ratio in SiO2/TiO2 composite film is beneficial to enhance the self-cleaning effect, while high TiO2 content leads to a strong Rayleigh scattering and depresses the antireflective performance, resulting in a bottleneck problem for the dual-functional application. Here, we have achieved a high-quality TiO2 nanotubes film with excellent antireflective and near-perfect self-cleaning performances. Ultrasound assisted pickling method has been developed to effectively prepare the well-dispersed protonated titanate nanotubes colloid. After spin-coating and annealing treatment, glass substrate coated with double-side TiO2 nanotubes film has a peak transmittance of 99.2 % and average transmittance of 97.4 % at 400−800 nm. Ultra-high porosity of TiO2 nanotubes film (80 %) and ultra-fine size of TiO2 nanotubes (8.6 nm in outer diameter) lead to excellent antireflective performance. With high UV absorptivity (80 % at 254 nm) and formal quantum efficiency of stearic acid (10.9 × 10−3), TiO2 nanotubes film shows near-perfect self-cleaning performance. A persistent anti-fogging ability is also presented. This study demonstrates the feasibility to fabricate pure TiO2 antireflective coating for glass substrate, extends application field of the classic TiO2 nanotubes, and sheds lights on the practical applications of high-powered TiO2 nanotube-based multi-functional films.

Mechanical properties of amine-cured epoxy composites reinforced with pristine protonated titanate nanotubes

Inorganic nanotubes are promising fillers for polymer composites. Among them, pristine protonated titanate nanotubes (p-TTNT), with high specific surface area and abundant hydroxyl surface groups, are good candidates for reinforcing amine-cured epoxy systems. Thus, epoxy composites filled with p-TTNT (≤ 3.0 wt. %, i.e. ≤ 1.1 vol. %) were prepared and their effect on the mechanical properties of the polymer matrix was studied. Young's modulus (E) and hardness (H) of the composites increased up to 19 and 17%, respectively, as demonstrated by microindentation tests, for 3.0 wt. % of p-TTNT, without functionalization. These increments could be attributed to the mutual compatibility, derived from the polar natures of p-TTNT and amine-cured epoxy, through the formation of hydrogen bonds. The wear resistance (H/E) of composites was maintained, independently of the p-TTNT content. Additionally, micromechanical models were successfully employed to predict the influence of the p-TTNT filler on the Young's modulus and hardness of the as-prepared composites.

Protonated Titanate Nanotubes and their adsorption behaviors for U(VI) in Aqueous Solutions

Titanate nanotubes was rapidly synthetized by nano anatase with mild hydrothermal method, and its protonation was carried by Nitric acid to prepare TNTs and TNTs-H with different H+/Na+ for further application of uranium removal in the wastewater. It was characterized by XRD, TEM and FT-IR. The results showed that at 298 K and pH 7, the adsorption rates of TNTs and TNTs-H to 10 mg/L U(VI) were 77.90% and 97.78% respectively, and the maximum adsorption capacity of U(VI) were 41.494 mg/g and 49.505 mg/g respectively. The adsorption processes all followed a pseudo second-order kinetic model and were in accordance with isotherm adsorption models like Langmuir model.

Computational fluid dynamic simulation modeling of carbon capture using polyethylenimine impregnated protonated titanate nanotubes

AbstractA comprehensive computational fluid dynamic (CFD) model of CEES‐developed polyethylenimine impregnated protonated titanate nanotubes (PEI‐PTNTs) was developed using the Multiphase Flow with Interphase eXchanges (MFiX) package to evaluate the performance of the PEI‐PTNTs in a 1‐MW pilot‐scale carbon capture reactor developed by the National Energy Technology Laboratory (NETL). In this CFD model, the momentum, continuity, and energy transport equations were integrated with the first‐order chemistry model for chemical kinetics of heterogeneous reactions to predict the adsorption of CO2 onto amine‐based sorbent particles and the reactor temperature. Based on the amount of the CO2 adsorption obtained in the small‐scale experiment, the coefficients for the chemical reaction equations of PEI‐PTNTs are adjusted. The adjusted PEI‐PTNTs model is applied to the simplified numerical model of 1‐MW pilot‐scale carbon capture system, which is calibrated through the comparison between our simulation results and the results provided by NETL. This calibrated CFD model is used for selecting the optimized flow rate of the gas phase. Our study shows that the optimized gas flow rate to absorb 100% CO2 without loss is 1.5 kg/s, but if higher absorption rate is preferable despite some loss of CO2 absorption in the reactor, a higher flow rate than 1.5 kg/s can be selected.

Nanotube confinement-induced g-C3N4/TiO2 nanorods with rich oxygen vacancies for enhanced photocatalytic water decontamination

Construction of semiconductor heterojunctions is an efficient strategy to improve photo-induced charges separation and thus enhance photocatalytic activities. Herein, g-C3N4/TiO2 heterostructures were prepared via a facile thermal procedure, with TiO2 nanorods as matrix and g-C3N4 as visible-light sensitizer. Heterojunctions formed while precursors cyanamide polymerized to g-C3N4 and protonated titanate nanotube (H-TNTs) dehydrated and shrinked to TiO2 nanorods. Notably, confined polymerization of g-C3N4 occurred at both external surface and internal space of H-TNTs with the assistant of vacuum treatment, while NH3 released from cyanamide decomposition yielded abundant oxygen vacancies (VO) in TiO2 nanorods. Compared with pristine TiO2 nanorods, the heterostructured g-C3N4/TiO2 nanorods possess 1.7 times more active in photocatalytic removal of organic dye Orange II. A mechanism was proposed for heterostructured g-C3N4/TiO2 nanorods, being attributed to synergistic increasing light harvesting by VO and charges separation by heterojunctions.

The Effects of Synthesis Conditions on the Carbon Capture Capacity of Polyethylenimine Impregnated Protonated Titanate Nanotubes

Capture and storage of carbon dioxide emitted from power plants, which burn fossil fuels, is one of the best ways to mitigate climate change. Polyethylenimine (PEI) impregnated protonated titanate nanotubes (PEI-PTNTs) are efficient amine-modified solid adsorbents for post combustion carbon capture. This study is to investigate the effects of synthesis conditions of titanate nanotubes on the carbon capture capacity of PEI-PTNTs. PTNTs are synthesized using hydrothermal treatment of TiO2 anatase powder at different temperatures and in different days, followed by washing with dilute HCl solution and deionized water. PEI-PTNTs are prepared by loading PEI (M.W. = 10,000) onto PTNTs at a weight ratio of 1:1 using a wet impregnation process. PTNTs and PEI-PTNTs are characterized using transmission electron microscopy, porosity and surface area analysis, powder X-ray diffraction, and Fourier transform infrared spectroscopy. CO2 adsorption is conducted at 75 °C using simulated flue gas, and CO2 desorption is performed at 110 °C by purging the adsorbent with dry nitrogen gas. CO2 adsorption experiments demonstrate that the PEI-PTNTs synthesized at 130 °C within 3 or 5 days, have the highest CO2 capture capacity. These optimized PEI-PTNTs have a significant potential to capture CO2 from power plants.

Synthesis of jet fuel range high-density dicycloalkanes with methyl benzaldehyde and acetone

High-density dicycloalkanes were first produced by the acid-catalyzed aldol condensation of acetone and methyl benzaldehyde over protonated titanate nanotubes followed by hydrodeoxygenation in cyclohexane.

Modulating the photocatalytic activity of Ag nanoparticles-titanate nanotubes heterojunctions through control of microwave-assisted synthesis conditions

Protonic titanate nanotubes (HTiNTs) have been widely used as photocatalyst for dye degradation, however, due to its high band-gap energy (∼3.2 eV), it can only absorb UV light, which is mainly disadvantageous when sunlight radiation is used as light source. The significant portion of the fallout from the Sun to the Earth corresponds to visible light, whereas the UV is only around 4 %. Thus, it is critical to develop strategies to sensitize this kind of photocatalyst to visible radiation. In this work, silver nanoparticles (AgNP)-HTiNTs heterojunctions were prepared, aiming to produce a visible light sensitive catalyst. The AgNPs were prepared by simple microwave-assisted routes, using water (Ag(H2O)), ethanol (Ag(EtOH)) and ethylene glycol (Ag(EG))as solvents, and sodium borohydride as reducing agent. The obtained AgNPs exhibit different physical-chemical properties, such as shapes, sizes and crystalline structures. As a result, the heterojunctions have different photocatalytic efficiencies for rhodamine B degradation under simulated sunlight irradiation: 72 % using Ag(EG)-HTiNT, 46 % using Ag(EtOH)-HTiNT and 33 % using Ag(H2O)-HTiNT as catalysts. The changes on the catalytic activities were ascribed to the plasmonic effect, lowering of surface area and more negative zeta potentials caused by the presence AgNPs. To better understand the photocatalytic response, the amount of radical species generated by the materials was determined by using spectroscopic methods.

Polyethylenimine-Based Solid Sorbents for CO2 Adsorption: Performance and Secondary Porosity

The series of polyethylenimine (PEI)-based solid sorbents were prepared by the wet-impregnation of PEI (Mw = 600) on the surface of six porous materials, i.e., mesoporous silicas (MCM-41, SBA-15, and KIT-6), mesoporous carbon (CMK-3), protonated titanate nanotube (PTNT), and fumed silica (FS). The resultant materials, denominated PEI/supports, were characterized by N2 adsorption/desorption at 77 K, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). CO2 adsorption on the PEI/supports was evaluated using 2 vol % CO2 in flowing air on a self-assembled fixed bed reactor. The observations made here show that relative to the other four sorbent counterparts, PEI/PTNT and PEI/FS exhibit better performance of CO2 adsorption, mainly attributed to their more abundant secondary macropores, together with more homogeneous PEI surface dispersion. For all the PEI/supports, the adsorption data of CO2 at vario...

CO<sub>2</sub> Chemical Conversion Using Catalytics Systems Based on Titanate Nanotubes

CO2 is the most important greenhouse gas in terms of emitted quantities and its emission has increased significantly due to the action of anthropogenic sources. Among the alternatives for mitigation of this gas is the direct synthesis of propylene carbonate (PC), which requires efficient and selective catalysts. In this scenario the titanate nanotubes (TNT) are promising catalysts because they can be modified to become selective for the PC synthesis. The present work has the objective to develop titanate nanotubes with different metals (Na, Sn and Zn) as well as protonated titanate nanotubes (HTNT) and to test their efficiency in the direct synthesis of PC. The synthesized nanostructures were characterized by TEM, EDS, XRD and N2 adsorption-desorption. The results showed that the synthesized TNT have a specific surface area of 155, 232, 56 and 140 m2/g (NaTNT, HTNT, SnTNT and ZnTNT, respectively). Besides, the ion exchange of [Na+] by [Sn+2] and [Zn+2] decreased the crystallinity of nanostructure. On the catalytic tests, the system NaTNT/ZnBr2 showed the best results with a yield of 61% and a selectivity of 81% in PC. The catalytic system SnTNT/DMF and ZnTNT/DMF are promising to this reaction showing interesting yields and catalytic activity (59 and 53%; 295 and 265 mmol/g) for PC synthesis.

Dry reforming of methane using modified sodium and protonated titanate nanotube catalysts

The mitigation of carbon emissions is an imminent and extremely relevant issue. In addition to carbon dioxide (CO2), methane (CH4) also contributes significantly to climate change. Dry reforming of methane (DRM) is a promising alternative to mitigate this gas, generating syngas, an important precursor of several chemical routes. In this context, sodium and protonated titanate nanotubes (TNT) were modified with metals (Co, Cu, Zn and Ni) and evaluated as catalyst for DRM. Zn-NaTNT, Co-NaTNT and Cu-NaTNT showed low catalytic activity (CO2 and CH4 conversion <5%). However, when Ni-NaTNT and Ni-HTNT were used as catalyst, CO2 and CH4 conversions were of 35 and 27% (Ni-NaTNT) and 70 and 74% (Ni-HTNT), respectively. Both catalysts showed good stability keeping CO2 and CH4 conversions at 700 °C during 5 h of reaction. Additionally, although conversion values reached with Ni-NaTNT were lower, the sodium presence in this catalyst inhibits to coke formation when compared to Ni-HTNT.

Evaluation of Sodium/Protonated Titanate Nanotubes Catalysts in Virgin and Post Consumer PET Depolymerization

The high PET consume, mainly as bottles, associated with rapid disposal and high resistance to ambient conditions and biological degradation lead to accumulation in the enviromental, constituting a worrying scenario in world level. Chemical recycle PET by glycolysis is an important alternative, once bis(hydroxiethyl)terephthalate (BHET), high added value monomer, can be obtained. In this context, this study approaches the use of titanate nanotubes (i.e. sodium/protonated titanate nanotubes) as catalyst for PET glycolysis. Reactional conditions, the origin and granulometry of PET flakes were evaluated (at 196 °C). Best results (BHET yield > 80%) were obtained for both catalyst in 3 h of reaction. The protonated titanate nanotubes catalyst were more efficient than sodium titanate nanotubes due to greater concentration of Bronsted and Lewis acid sites, indicated by TPD analyzes.

Hydrogen production from aqueous glycerol using titanate nanotubes decorated with Au nanoparticles as photocatalysts

Abstract: Protonated titanate nanotubes (HTiNts) were synthesized using the hydrothermal method, followed by proton exchange with acid. Gold nanoparticles decorated titanate nanotubes (AuHTiNts) were obtained by the reduction of AuCl4- under vigorous stirring with an aqueous solution of HTiNts containing 1 wt% of ascorbic acid. To investigate the surface structural chemistry of the titanate and AuHTiNts, the following characterization methods were used: scanning and transmission electron microscopy, X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photo-electron spectroscopy. The mean internal and external diameters for titanate nanotubes were found to be 5.46 ± 0.08 nm and 8.42 ± 0.03 nm, respectively, whereas the mean diameter of gold nanoparticles was measured to be 9.68 nm ± 0.03 nm. The as-synthesized AuHTiNts was used as photocatalyst in hydrogen production from glycerol as a sacrificial agent. The enhancement in the production of hydrogen, using the heterogeneous AuHTiNts catalysts, can be attributed to the intrinsic catalytic potential of gold as well as its interactions with titanate nanostructure.

Creviced titanate nanotube modified with stearyl trimethyl ammonium bromide as a support for amine-based CO2 sorbent

In this paper, a series of protonated titanate nanotubes (PTNTs) modified by stearyl trimethyl ammonium bromide (STAB) were prepared as supports for Polyethyleneimine (PEI)-based sorbents. The CO2 adsorption performance was evaluated in a self-assembled fixed bed reactor. The typical sorbents were characterized by XRD, EDS, SEM, HR-TEM, N2 adsorption-desorption, FT-IR and TGA. Results indicate that the modification significantly improves CO2 adsorption capacity of the sorbents. The maximum CO2 adsorption amount of 2.22 mmol/g was obtained over the modified PEI-based sorbent in 2% CO2/air. Based on the characteristic analysis, the formation of creviced nanotubes, instead of intact nanotubes, is testified because of the modification. Such unique nanotubes possess the higher BET surface area and larger pore volume, which enables more PEI to uniformly distribute on the surface of modified PTNT supports. Especially, it is easier for PEI to enter the inner pores through the crevice than from tube orifices, avoiding pore blockage and facilitating CO2 diffusion in pores. The abundant amine-sites and small internal diffusion resistance endow the modified sorbent with large CO2 adsorption capacity. In addition, the PEI/PTNT adsorbent displays good thermal stability and reusability.

Supported nickel catalysts for anisole hydrodeoxygenation: Increase in the selectivity to cyclohexane

Abstract The hydrodeoxygenation (HDO) of anisole was performed with Ni catalysts supported on SBA-15 silica and protonated titanate nanotubes (PTN), in order to determine the effect of the support’s nature and the method of incorporation of Ni species on the catalytic activity and selectivity in HDO. Catalysts with 10 wt.% of Ni were prepared by two methods: deposition-precipitation with urea (DP) and the classical incipient wetness impregnation (IM). Characterization of the catalysts was performed by nitrogen physisorption, temperature programmed reduction, temperature programmed desorption of ammonia, high resolution transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, XPS and O2 chemisorption. The obtained results show that the support’s nature and the preparation method had a strong influence on the dispersion of the supported Ni species and their HDO performance. Catalysts with larger metallic Ni particles showed higher ability for hydrogenation of anisole and higher intrinsic activity (TOF) than those with smaller Ni particles. On the other side, the use of the PTN support and the DP with urea preparation method resulted in catalysts with increased acidity and improved selectivity for the formation of deoxygenated products (cyclohexane).

Fabrication of SrTiO3 nanotubes via an isomorphic conversion strategy

One-dimensional nanotubes have attracted enormous attention due to their specific structure and excellent performance since the carbon nanotube was prepared. In this study, the open-ended SrTiO3 nanotubes (STNTs) have been fabricated for the first time via an isomorphic conversion strategy using the protonated titanate nanotubes (HTNTs) as the precursor and template under the hydrothermal treatment. The as-prepared STNTs consist of uniform and continuous multilayers, having inner and outer diameters about 8.0 and 13 nm. The STNT formation involves the exchange of Sr2+ ions with H+ ions in HTNTs and then in situ growth of cubic SrTiO3 crystals by the templating of HTNT frameworks. It is found that the diffusion process of Sr2+ ions plays a critical role in controlling the nanotube morphology of SrTiO3 crystals. In addition, the SrTiO3 nanotubes exhibit high photocatalytic activity for the Cr(VI) reduction, which can reduce nearly 100% Cr(VI) within 6 h under simulated sunlight irradiation. The current strategy may be broadly applicable for fabricating the nanotubes from raw materials without 2D layered nanostructure.

Acid Properties of Protonated Titanate Nanotubes

Acid Properties of Protonated Titanate Nanotubes

Synthesis of protonated titanate nanotubes tailored by the washing step: Effect upon acid properties and photocatalytic activity

Abstract In this work, the acid and photocatalytic properties of titanate nanotubes (NTs) were surveyed. The surface acidity of the NTs was characterized by FTIR with lutidine and pyridine. The photocatalytic degradation of phenol in aqueous suspension was performed to test the photocatalytic properties of the NTs. The results were compared with those obtained from commercial TiO 2 . NTs were prepared by hydrothermal treatment of TiO 2 nanoparticles in a NaOH aqueous solution. During the washing step, three different acid agents (HCl, H 2 SO 4 , and HNO 3 ) were used. TiO 2 nanoparticles were synthesized previously by the sol-gel method. The photocatalytic materials were characterized by FTIR, XRD, XPS, S BET , UV–vis, and HRTEM. It was found that the used acid agent significantly affected the amount and type of acid sites. Bronsted acid sites were favored by the use of HNO 3 . Lewis acid sites were promoted when HCl was employed during the washing step, which is in contrast with the results obtained using the other acids chosen in this work. Besides, the use of HCl promoted the H 2 Ti 3 O 7 phase. The acid phase H 2 Ti 4 O 9 ·H 2 O was favored when HNO 3 was used and H 2 SO 4 formed the H 2 Ti 2 O 4 ·(OH) 2 acid phase. The presence of Cl, S, and N species on the NTs was not found. Furthermore, Na + ions were completely removed from the surface of the NTs, which were exchanged by H + ions. It was found, in general, that the three catalysts presented a relatively high photocatalytic activity to remove phenol. However, NTs washed with HNO 3 (NT-HNO 3 ) displayed the best photocatalytic activity compared to the other NTs. After 200 min, NT-HNO 3 reached a phenol degradation yield close to 100%. Commercial TiO 2 presented a phenol degradation yield close to 60%. It could be concluded that the acid phase (H 2 Ti 4 O 9 ·H 2 O) and concentration of Bronsted acid sites promoted the photocatalytic activity of NT-HNO 3 .