Toxicity of titanate nanotubes in earthworm (Eisenia fetida): Growth inhibition and integrated biomarker response

Widely use of Titanate Nanotubes (TNTs) as remediation materials for heavy metal polluted water and soil lead to their release into the soil environment, persistently threatening faunal biodiversity and the entire environment. Growth inhibition rates (GIR) and specific growth rates (SGR) are used to evaluate the effect of TNTs on earthworm growth, and the integrated biomarker response (IBR) index is used to comprehensively evaluate the toxicity of eight biomarkers (Protein-body mass ratio, MDA, SOD, CAT, POD, Cellulase, AChE, and Na⁺/K⁺-ATPase) on earthworms exposed to TNTs contaminated soil by concentrations of CK, 50, 250, 500 and 2500 mg TNTs/kg dry soil. Results show that TNTs significantly inhibit the growth of earthworms (p < 0.05), and GIR reaches up to 52.34 % at 2500 mg TNTs/kg dry soil for 28 days. IBR index has a dose-time relationship, which indicates that exposure time and concentration of TNTs contaminated soil affect the toxicity degree of contaminant to earthworms.

Economic and facile approach for synthesis of graphene-titanate nanocomposite for water reclamation

Graphene and its composites with semiconductor materials have been received highly attention in many research areas because of their unique properties. Efficient application of graphene is hindered by the lack of cost-effective synthesis methods. In this work, an economic and facile route for mass production of graphene-titanate nanocomposite has been discussed. Graphene was prepared by exfoliation of graphite powder in 40% ethanol aqueous solution. Titanate nanotubes were grown on graphene sheets by hydrothermal method, where the dispersed graphene sheets were mixed with titanate solution and then placed in autoclave and placed in oven for 16 h at 160 °C. The prepared composite was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FTIR), thermogravimetric analysis (TGA). All the obtained results confirmed the synthesis of graphene and its composite with titanate in highly uniform and pure form. The adsorption efficiency of the prepared composite was tested using methylene blue (MB) as a model dye. The adsorption isotherm was investigated using Freundlich and Langmuir models. The adsorption capacity of MB was 270.27 mg/g. The obtained correlation coefficients (R²) by Freundlich and Langmuir model were 0.996 and 0.973, respectively. The adsorption kinetics was investigated and discussed using different models. The thermal stability of the developed composite is improved after MB adsorption.

Insight into the existent state of nitrogen-doped carbon dots in titanate nanotubes and their roles played toward simultaneous removal of coexisted Cu2+ and norfloxacin in water

In this work, nitrogen-doped carbon dots (NCDs) were introduced in different existent sites of titanate nanotubes (TNTs) by a facile synthesis, and their effects on surface potential, photoelectrochemical properties and simultaneous removal of coexisted Cu²⁺ and norfloxacin (NOR) performance in water were systematically investigated. Constructed NCDs-TNTs composite displayed superior performance towards the adsorption (ion exchange/coordination) of Cu²⁺ and adsorption-oxidization of NOR over the two individuals, mainly benefiting from the collaboration of NCDs in different existent states. The existence of TiNH chemical linkage was identified between TNTs and NCDs-OT (NCDs on the outer surface of TNTs), which not only modulates the surface potential to favor the external diffusion of Cu²⁺ or NOR⁺ from aqueous solution to the negatively charged NCDs-TNTs, but also facilitates the intraparticle transfer of contaminants to the reactive sites. In addition, the up-conversion light property of NCDs-OT and the interstitial NCDs-IT (NCDs on the inner surface of TNTs) doping in TNTs interact together to enable NCDs-IT-TNTs to fully absorb and utilize all visible light. The photoexcited electrons were further trapped by NCDs-OT to promote the photogenerated carrier separation. Adsorbed Cu²⁺ could also improve the performance of NCDs-TNTs toward NOR oxidization, mainly owing to the self-synchronous doping of adsorbed Cu²⁺ broadening light absorption area and acting as mediators for delivering electrons. This work provides unique insights into the structural design of composite materials for such combined contamination remediation in water.

Reusability in visible light of titanate nanotubes for the removal of organic pollutants: role of calcination temperature

Titanate nanotubes (NTs) were synthesised by the hydrothermal method and later calcined at temperatures between 100-500°C. The calcined NTs were characterised and evaluated in the physicochemical adsorption of the safranin dye and photocatalytic degradation of caffeine. The materials calcined at low temperatures displayed a tubular structure and the H₂Ti₃O₇ crystalline phase, which was transformed into anatase nanoparticles at 400°C. The NTs treated at 100°C showed the highest adsorption capacity (94%). Safranin was adsorbed through an ion-exchange mechanism, following the Langmuir isotherm and a pseudo-second-order kinetic model. While NTs calcined at lower temperatures were better for adsorption, the photocatalytic degradation of caffeine increased in samples calcined at higher temperatures with a maximum removal of 72%. The photocatalytic behaviour of the NT samples confirmed that the crystalline anatase structure in conjunction with structural OH groups enhanced the photocatalytic activity. The addition of isopropanol as a scavenger confirmed the important role played by the •OH radicals in the photocatalytic process. NTs calcined at 300°C were efficient for both adsorption and photocatalytic processes. Due to its efficiency, this sample was reused after dye adsorption for the photocatalytic degradation of caffeine under visible light due to its enhanced absorbance in the visible region. This research work shows the potential of NTs for wastewater purification.

Removal of Cd2+ from water containing Ca2+ and Mg2+ using titanate nanotubes modified by carbon

Calcium and magnesium ions usually exist in natural water. When Cd²⁺ is removed from water by adsorption, it will be inhibited by these two ions. Titanate nanotubes (TNTs) have an effective adsorption capacity for Cd²⁺ due to extraordinary ion exchange property. However, TNTs also adsorb Ca²⁺ and Mg²⁺ in water. In this study, carbon-modified TNT (TNT/C) and TNT/C further treated with acid (TNT/HC) were synthesized by hydrothermal synthesis. The transmission electron microscope (TEM) images show that TNT/C or TNT/HC still keep nanotube morphology. The experimental results show the order of adsorption amount to Cd²⁺ is TNT (171.56 mg/g) > TNT/C (166 mg/g) > TNT/HC (159.88 mg/g) when there is no Ca²⁺ or Mg²⁺. But when there is 0.1 M Ca²⁺ or Mg²⁺ in the water, the order of Cd²⁺ adsorption capacity becomes TNT/HC (44.28, 49.04 mg/g) > TNT/C (58.84, 69.32 mg/g) > TNT (65.52, 70.6 mg/g). It indicates that the surface carbon modification can alleviate the hindrance of Ca²⁺ or Mg²⁺ to Cd²⁺ removal. This is because the carbon on the surface of TNT captured part of Ca²⁺ or Mg²⁺; it made more Cd²⁺ be successfully absorbed by TNT through ion exchange. This mechanism was confirmed by the X-ray photoelectron spectroscopy (XPS) spectra analysis. The results of this paper can provide ideas for the adsorption and removal of Cd²⁺ in water in the presence of Ca²⁺ or Mg²⁺.

Oxygen defective titanate nanotubes induced by iron deposition for enhanced peroxymonosulfate activation and acetaminophen degradation: Mechanisms, water chemistry effects, and theoretical calculation

The large consumption of acetaminophen (APAP) worldwide and unsatisfactory treatment efficiencies by conventional wastewater treatment processes give rise to the seeking of new technology for its effective removal. Herein, we proposed a facile one-step hydrothermal method to synthesize defective iron deposited titanate nanotubes (Fe/TNTs) for peroxymonosulfate (PMS) activation and APAP degradation. The retarded first-order reaction rate of APAP degradation by Fe/TNTs was 5.1 times higher than that of neat TNTs. Characterizations indicated iron deposition effectively induced oxygen vacancies and Ti³⁺, facilitating the electrical conductivity and PMS binding affinity of Fe/TNTs. Besides, oxygen vacancies could act as an electron mediator through PMS activation by iron. Moreover, the formation of Fe-O-Ti bond facilitated the synergistic redox coupling between Fe and Ti, further enhancing the PMS activation. SO₄^•- was the major radical, causing C-N bond cleavage and decreasing the overall toxicity. In contrast, APAP degradation by neat TNTs-PMS system mainly works through nonradical reaction. The Fe/TNTs activated PMS showed desired APAP removal under mild water chemistry conditions and good reusability. This work is expected to expand the potential application of titanate nanomaterials for PMS activation, and shed light on facile synthesis of oxygen defective materials for sulfate-radical-based advanced oxidation processes.

Uptake, excretion and toxicity of titanate nanotubes in three stains of free-living ciliates of the genus Tetrahymena

The potential exposure of titanate nanotubes (TNTs) to wildlife and humans may occur as a result of increased use and application as functional nanomaterials. However, there is a dearth of knowledge regarding the pathways of uptake and excretion of TNTs and their toxicity in cells. In this study, three strains of the Tetrahymena genus of free-living ciliates, including a wild type strain (SB210) and two mutant strains (SB255: mucocyst-deficient; NP1: temperature-sensitive "mouthless''), were used to study the pathways of uptake and excretion and evaluate the cytotoxicity of TNTs. The three Tetrahymena strains were separately exposed to 0, 0.01, 0.1, 1 or 10 mg/L of TNTs, and cells were collected at different time points for quantification of intracellular TNTs (e.g., 5, 10, 20, 40, 60, 90 and 120 min) and evaluation of cytotoxicity (12 and 24 h). TNT contents in NP1 and SB255 were greater or comparable to the contents in SB210 while exposure to 10 mg/L TNTs in 120 min. Furthermore, exposure to 10 mg/L TNTs for 24 h caused greater decreases in cell density of NP1 (38.2 %) and SB255 (36.8 %) compared with SB210 (26.5 %) and upregulated the expression of caspase 15 in SB210. Taken together, our results suggested that TNT uptake by pinocytosis and excretion by exocytosis in Tetrahymena, and the exposure could cause cytotoxicity which can offer novel insights into the accumulation kinetics of nanotubes and even nanomaterials in single cell.

Insights into catalytic activation of peroxymonosulfate for carbamazepine degradation by MnO2 nanoparticles in-situ anchored titanate nanotubes: Mechanism, ecotoxicity and DFT study

Developing efficient pharmaceuticals and personal care products (PPCPs) degradation technologies is of scientifical and practical importance to restrain their discharge into natural water environment. This study fabricated and applied a composite material of amorphous MnO₂ nanoparticles in-situ anchored titanate nanotubes (AMnTi) to activate peroxymonosulfate (PMS) for efficient degradation and mineralization of carbamazepine (CBZ). The degradation pathway and toxicity evolution of CBZ during elimination were deeply evaluated through produced intermediates identification and theoretical calculations. AMnTi with a composition of (0.3MnO₂)•(Na_1.22H_0.78Ti₃O₇) offered high activation efficiency of PMS, which exhibited 21- and 3-times degradation rate of CBZ compared with the pristine TNTs and MnO₂, respectively. The high catalytic activity can be attributed to its unique structure, leading to a lattice shrinkage and small pores to confine the PMS molecule onto the interface. Therefore, efficient charge transfer and catalytic activation through MnOTi linkage occurred, and a MnTi cycle mediating catalytic PMS activation was found. Both hydroxyl and sulfate radicals played key roles in CBZ degradation. Theoretical calculations, i.e., density functional theory (DFT) and computational toxicity calculations, combined with intermediates identification revealed that CBZ degradation pathway was hydroxyl addition and NC cleavage. CBZ degradation in this system was also a toxicity-attenuation process.

Synthesis of silver-cerium titanate nanotubes and their surface properties and antibacterial applications

Nano-heterostructures of titanate nanotubes were synthesized and they revealed a complex structure with the formation of TiO₂ (anatase), CeO₂, Ag₂O and metallic silver nanoparticles on the outer walls and intercalation of Ce⁴⁺ and Ag⁺ into the interlayer spaces of the nanotubes by microwave-assisted hydrothermal process and subjected to ion exchange reactions. To the best of our knowledge, this is the first reported silver and cerium co-exchanged titanate nanotubes for bio-applications. The co-ion exchange processes preserved the original tubular structure of titanate nanotubes with significant changes of the superficial as well as interlamellar environment. This study opens up possibility of synthesizing complex, functional nano-heterostructure with the scope of modification of the final structure, especially the amount and oxidation state of the intercalated cation (Ce⁴⁺, Ce³⁺ and Ag⁺) as well as the quantity and variety of the decorating nanoparticles (CeO₂, Ag₂O or metallic Ag). The interplay of which, in turn, can lead to important biological properties and applications, owing to their ion-liberation capacity. The samples were tested in antibacterial activity with two different kind of bacteria (gram positive and negative), cell cytotoxicity and adhesion, and it was found that the nano-heterostructure formed shows high antibacterial activity with low cytotoxicity and high cell adhesion, which makes it a promising material for further health applications.

New quercetin-coated titanate nanotubes and their radiosensitization effect on human bladder cancer

Interest in nanostructures such as titanate nanotubes (TNT) has grown notably in recent years due to their biocompatibility and economic viability, making them promising for application in the biomedical field. Quercetin (Qc) has shown great potential as a chemopreventive agent and has been widely studied for the treatment of diseases such as bladder cancer. Motivated by the possibilities of developing a new hybrid nanostructure with potential in biomedical applications, this study aimed to investigate the incorporation of quercetin in sodium (NaTNT) and zinc (ZnTNT) titanate nanotubes, and characterize the nanostructures formed. Qc release testing was also performed and cytotoxicity in Vero and T24 cell lines evaluated by the MTT assay. The effect of TNTs on T24 bladder cancer cell radiosensitivity was also assessed, using cell proliferation and a clonogenic assay. The TNT nanostructures were synthesized and characterized by FESEM, EDS, TEM, FTIR, XRD and TGA. The results showed that the nanostructures have a tubular structure and that the exchange of Na⁺ ions for Zn²⁺ and incorporation of quercetin did not alter this morphology. In addition, interaction between Zn and Qc increased the thermal stability of the nanostructures. The release test showed that maximum Qc delivery occurred after 24 h and the presence of Zn controlled its release. Biological assays indicated that the NaTNTQc and ZnTNTQc nanostructures decreased the viability of T24 cells after 48 h at high concentrations. Furthermore, the clonogenic assay showed that NaTNT, NaTNTQc, ZnTNT and ZnTNTQc combined with 5 Gy reduced the formation of polyclonal colonies of T24 cells after 48 h. The results suggest that the nanostructures synthesized in this study interfere in cell proliferation and can therefore be a powerful tool in the treatment of bladder cancer.

Simultaneous and synergistic effect of heavy metal adsorption on the enhanced photocatalytic performance of a visible-light-driven RS-TONR/TNT composite

A hydrothermally synthesized rhodium/antimony co-doped TiO₂ nanorod and titanate nanotube (RS-TONR/TNT) composite was prepared for removal of heavy metals and organic pollutants from water under visible light irradiation. The composite provides the dual function of simultaneous adsorption of heavy metal ions and enhanced degradation of dissolved organic compounds. Acid treatment transformed titanate nanotubes to irregular tubular structures distributed homogeneously over untransformed RS/TONRs. Synergistic removal and degradation was studied with various heavy metals, Orange (II) dye, and Bisphenol A. The adsorption capacity of the composite for heavy metal ions was Pb(II) > Cd(II) > Cu(II) > Zn(II). The adsorbed metals enhanced photocatalytic degradation of the organic pollutants, but Cu was most effective, with degradation exceeding 70% for the dye and 80% for Bisphenol A after 5 h of treatment. Photocatalytic activity was enhanced more by adsorption than photodeposition of Cu ions. A decrease in XRD rutile peak intensity with adsorbed metal indicates a change in crystallinity which may enhance photocatalytic activity. Thick and bulging nanostructures in FE-SEM images signify ion adsorption within titanate pores. BET analysis indicated titanate nanotubes with adsorbed metal are mesoporous but their tubular structure persists. XPS showed more active Cu 2p_3/2 states under light, supporting an active role of Cu⁺ in photocatalytic ROS generation. Detection of ROS and Cu species using methanol, EDTA, pCBA, and benzoic acid probes provided strong evidence for degradation via a charge transfer mechanism. Findings demonstrate the potential of the RS-TONR/TNT composite for simultaneous removal of heavy metals and degradation of organic pollutants.

[Ammonium Adsorption Characteristics in Aqueous Solution by Titanate Nanotubes]

Titanate nanotubes (TNTs) were synthesized via a hydrothermal method using P25 and NaOH as the raw materials. The composition and morphology of the nanotubes were characterized by X-ray diffraction and transmission electron microscopy. The adsorption characteristics and the rules of ammonium in aqueous solutions were tested in the static system. The results showed that when the alkali concentration was 10 mol·L^-1, titanate nanotubes with a length of approximately 120 nm and a diameter of approximately 8 nm were obtained. The equilibrium adsorption capacity of ammonium was 10.67 mg·g^-1. When the pH ranged between 3 and 8, TNTs effectively adsorbed ammonium. The equilibrium adsorption time was 1 h, and this followed the pseudo second-order model. The results from the intra-particle model also showed that the adsorption process of ammonium by TNTs was controlled by surface adsorption and inter-particle diffusion. The Temkin model gave the best fit for the adsorption of ammonium onto TNTs. The thermodynamic experiments showed that the adsorption of titanate nanotubes on ammonium was a spontaneous endothermic process. Coexisting anions and cations had an inhibitory effect on the adsorption of ammonium. The order of influence was SO₄^2- > Cl^- > H₂PO₄^- and K⁺ > Na⁺ > Ca²⁺, respectively. The adsorption effect of ammonium by regenerated TNTs remained more than 88.64% after five repeat usages. The results of Fourier transform infrared spectroscopy showed that the ammonium adsorption mechanism of titanate nanotubes was ion-exchange between NH₄⁺ and Na⁺ in the TNTs. Titanate nanotubes can effectively remove ammonium from water because of their good recycling capacity and large adsorption capacity.

Simultaneous Cr(VI) reduction and Cr(III) removal of bifunctional MOF/Titanate nanotube composites

In this study, a series of BUC-21/titanate nanotube (BT-X) composites were facilely fabricated via ball-milling of 2-dimensional (2D) metal-organic framework (MOF) BUC-21 and titanate nanotubes (TNTs). The BT-X composites were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-visible diffuse-reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectrometer (XPS) and high resolution transmission electron microscopy (HRTEM). Both the photocatalytic reduction from Cr(VI) to Cr(III) and adsorptive removal of formed Cr(III) of BT-X composites were systematically investigated under different conditions including pH values and co-existing inorganic ions. It was found that BUC-21 (100 mg)/TNTs (100 mg) (BT-1) composites demonstrate remarkable ability of photocatalytic Cr(VI) reduction and adsorptive Cr(III) removal, as well as good reusability and stability. It is believed that the introduction of TNTs could capture the formed Cr(III) from the surface of BUC-21, which provided more active sites exposed to enhance the Cr(VI) reduction.

Influences of isolated fractions of natural organic matter on adsorption of Cu(II) by titanate nanotubes

With different functional groups and hydrophobic/hydrophilic properties, natural organic matters (NOMs) displayed different combining capacities with metal ions. By using XAD-4 and DAX-8 resins, NOMs in natural lake were isolated into three fractions, i.e., HoB (hydrophobic base), HoA (hydrophobic acid) and HiM (hydrophilic matter). Afterwards, influences on Cu(II) adsorption onto titanate nanotubes (TNTs) were compared with varying NOMs and initial pH. As results, HoB can significantly control Cu(II) adsorption at pH 5, with the adsorption capacity increased 15% for 0.5 mg L^-1 of HoB (ca. 120 mg g^-1), which could be attributed to the formation of HoB-Cu complexation and electrostatic bridge effect of HoB with optimal concentration. Due to the easier ionization and complexation with Cu(II) at lower pH, HoA showed more obvious impaction on Cu(II) adsorption at pH 2. While HiM can influence Cu(II) adsorption at all pH ranges due to its hydrophilic groups and weak affinity to both TNTs and Cu(II). Furthermore, HoB dramatically changed the Langmuir model, with sharp increase of adsorption capacity as equilibrium Cu(II) increased, suggesting its significant involvement in Cu(II) adsorption. X-ray photoelectron spectroscopy (XPS) analysis revealed the absorbed Cu(II) existed in the form of TNTs‑OCu, TNTs‑COOCu and Cu(OH)₂, proving Cu(II) adsorption mechanism including both direct adsorption by TNTs and bridging connection with NOMs. Moreover, the CO and OCO groups content ranked as HiM > HoB > HoA, while TNTs‑COOCu content ranked as HoA > HoB > HiM, suggesting HoB had the moderate connection with both TNTs and Cu(II), thus the impact on Cu(II) adsorption was remarkable.

Efficient extraction of uranium from aqueous solution using an amino-functionalized magnetic titanate nanotubes

In this paper, titanate nanotubes/cobalt ferrite/tetraethylenepentamine (TNTs/CoFe₂O₄/TEPA) adsorbents were prepared for the adsorption of uranium (VI) from the solution. Its morphology was observed by transmission electron microscopy (TEM) and exhibited the uniform well tubular structure. TNTs/CoFe₂O₄/TEPA composites were easily separated from solution by an external magnetic field. The removal of uranium (VI) from aqueous solution (ppm level) and simulated seawater (ppb level) were investigated by the TNTs/CoFe₂O₄/TEPA composites. Batch adsorption experiments were conducted to determine the effect of varying pH, contact time, and reaction temperature. The best fit for uranium (VI) adsorption was obtained with the Langmuir model, and the highest adsorption of TNTs/CoFe₂O₄/TEPA composites reached 509.89 mg-U/g-adsorbent at pH 6. From an investigation of the adsorption by XRD, FTIR and XPS, it is suggested that the surface complexation and cation exchange were the main adsorption mechanism. In addition, TNTs/CoFe₂O₄/TEPA composites maintained good adsorption properties after five sorption-desorption cycles. Therefore, we conclude that the adsorbents are promising materials for the removal of uranium (VI) from aqueous solutions.

In vitro interaction and biocompatibility of titanate nanotubes with microglial cells

Titanate nanotubes (TiONts) are promising agents for biomedical applications. Microglial activation and associated oxidative burst are major challenges in drug delivery applications across the brain. Here, TiONts were designed for drug delivery systems by functionalizing them with (3-aminopropyl) triethoxysilane (APTES), their interactions and biocompatibility were studied in vitro using murine microglial BV-2 cells. TiONts-APTES exposure resulted in increased ROS production and transient mitochondrial hyperpolarization. However, there was no indication of microglial proliferation in BV-2 cells as suggested by cell cycle analysis and morphology evaluation. The endocytosis as well as passive diffusion mediated TiONts-APTES internalization were proved by transmission electron microscopy (TEM) with and without amiloride, an endocytosis inhibiting agent. In addition, the TiONts-APTES exhibited good biocompatibility on microglial BV-2 cells as revealed by the plasma membrane integrity, lysosmal membrane integrity, morphology and viability analysis.

Photocatalysis of bisphenol A by an easy-settling titania/titanate composite: Effects of water chemistry factors, degradation pathway and theoretical calculation

Bisphenol A (BPA) is a widely concerned endocrine disrupting chemical and hard to be removed through conventional wastewater treatment processes. In this study, we developed a TiO₂ decorated titanate nanotubes composite (TiO₂/TNTs) and used for photocatalytic degradation of BPA. TEM and XRD analysis show that the TiO₂/TNTs is a nano-composite of anatase and titanate, with anatase acting as the primary photocatalytic site and titanate as the skeleton. TiO₂/TNTs exhibited excellent photocatalytic reactivity and its easy-settling property leaded to good reusability. After 5 reuse cycles, TiO₂/TNTs also could photo-degrade 91.2% of BPA with a high rate constant (k₁) of 0.039 min^-1, which was much better than TiO₂ and TNTs. Higher pH facilitated photocatalysis due to more reactive oxygen species produced and less material aggregation. The presence of NaCl and CaCl₂ showed negligible effects on BPA degradation, but NaHCO₃ caused an inhibition effect resulting from consumption of ·OH. Humic acid inhibited degradation mainly due to blockage of the active sites of TiO₂/TNTs. Degradation pathway was well interpreted through theoretical calculation. Hydroxyl radical played the dominate role in BPA photodegradation, and the atoms of BPA with high Fukui index based on density-functional theory (DFT) calculation are the radical easy-attacking (f⁰) sites. Considering the good photocatalytic reactivity, reusability, stability and settle property, TiO₂/TNTs promises to be an efficient alternative for removal of organic compounds from wastewaters.

Gas Transport Properties of Polybenzimidazole and Poly(Phenylene Oxide) Mixed Matrix Membranes Incorporated with PDA-Functionalised Titanate Nanotubes

Functionalised titanate nanotubes (TiNTs) were incorporated to poly(5,5-bisbenzimidazole-2,2-diyl-1,3-phenylene) (PBI) or poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) for improving the interfacial compatibility between the polymer matrix and inorganic material and for altering the gas separation performance of the neat polymer membranes. Functionalisation consisted in oxidative polymerisation of dopamine-hydrochloride on the surface of non-functionalised TiNTs. Transmission electron microscopy (TEM) confirmed that a thin polydopamine (PDA) layer was created on the surface of TiNTs. 1.5, 3, 6, and 9 wt.% of PDA-functionalised TiNTs (PDA-TiNTs) were dispersed to each type of polymer matrix to create so-called mixed matrix membranes (MMMs). Infrared spectroscopy confirmed that -OH and -NH groups exist on the surface of PDA-TiNTs and that the nanotubes interact via H-bonding with PBI but not with PPO. The distribution of PDA-TiNTs in the MMMs was to some extent uniform as scanning electron microscope (SEM) studies showed. Beyond, PDA-TiNTs exhibit positive effect on gas transport properties, resulting in increased selectivities of MMMs. The addition of nanotubes caused a decrease in permeabilities but an increase in selectivities. It is shown that 9 wt.% of PDA-TiNTs in PBI gave a rise to CO₂/N₂ and CO₂/CH₄ selectivities of 112 and 63 %, respectively. In case of PPO-PDA-TiNT MMMs, CO₂/N₂ and CO₂/CH₄ selectivity increased about 25 and 17 %, respectively. Sorption measurement showed that the presence of PDA-TiNTs in PBI caused an increase in CO₂ sorption, whereas the influence on other gases is less noticeable.

Macroscopic and spectroscopic studies of the enhanced scavenging of Cr(VI) and Se(VI) from water by titanate nanotube anchored nanoscale zero-valent iron

Herein, a promising titanate nanotubes (TNT) anchored nanoscale zero-valent iron (NZVI) nanocomposite (NZVI/TNT) was synthesized, characterized and used for the enhanced scavenging of Cr(VI) and Se(VI) from water. The structural identification indicated that NZVI was uniformly loaded on TNT, thereby, the oxidation and aggregation of NZVI was significantly minimized. The macroscopic experimental results indicated that NZVI/TNT exhibited higher efficiency as well as rate on Cr(VI) and Se(VI) scavenging resulted from the good synergistic effect between adsorption and reduction. Besides, TNT can weaken the inhibitory effect of co-existing humic acid (HA) and fulvic acid (FA) on the scavenging of Cr(VI) and Se(VI) by NZVI, since TNT showed strong adsorption for HA and FA that inhibit potential reactivity. XPS analysis suggested that surface-bound Fe(II) played a critical role in Cr(VI) and Se(VI) scavenging. XANES analysis demonstrated that TNT acted as a promoter for the almost complete transformation of Cr(VI) into Cr(III), and Se(VI) into Se(0)/Se(-II) in NZVI system. EXAFS analysis indicated that TNT acted as a scavenger for insoluble products, and thus more reactive sites can be used for Cr(VI) and Se(VI) reduction. The excellent performance of NZVI/TNT provide a potential material for purification and detoxification of Cr(VI) and Se(VI) from wastewater.

Uniformly active phase loaded selective catalytic reduction catalysts (V2O5/TNTs) with superior alkaline resistance performance

In this work, protonated titanate nanotubes was performed as a potential useful support and different vanadium precursors (NH₄VO₃ and VOSO₄) were used to synthesize deNO_x catalysts. The results showed that VOSO₄ exhibited better synergistic effect with titanate nanotubes than NH₄VO₃, which was caused by the ion-exchange reaction. Then high loading content of vanadium, uniformly active phase distribution, better dispersion of vanadium, more acid sites, better V⁵⁺/V⁴⁺ redox cycles and superior oxygen mobility were achieved. Besides, VOSO₄-based titanate nanotubes catalysts also showed enhanced alkaline resistance than particles (P25) based catalysts. It was strongly associated with its abundant acid sites, large surface area, flexible redox cycles and oxygen transfer ability. For the loading on protonated titanate nanotubes, active metal with cation groups was better precursors than anion ones. V₂O₅/TNTs catalyst was a promising substitute for the commercial vanadium catalysts and the work conducted herein provided a useful idea to design uniformly active phase loaded catalyst.

Photocatalytic Oxidation of Propylene on Pd-Loaded Anatase TiO2 Nanotubes Under Visible Light Irradiation

TiO2 nanotubes attract much attention because of their high photoelectron-chemical and photocatalytic efficiency. But their large band gap leads to a low absorption of the solar light and limits the practical application. How to obtain TiO2 nanotubes without any dopant and possessing visible light response is a big challenge nowadays. Orthorhombic titanic acid nanotubes (TAN) are a special precursor of TiO2, which possess large Brunauer-Emmett-Teller (BET) surface areas and strong ion exchange and adsorption capacity. TAN can transform to a novel TiO2 with a large amount of single-electron-trapped oxygen vacancies (SETOV) during calcination, while their nanotubular structure would be destroyed, and a BET surface area would decrease remarkably. And interestingly, SETOV can lead to a visible light response for this kind of TiO2. Herein, glucose was penetrated into TAN by the vacuum inhalation method, and TAN would dehydrate to anatase TiO2, and glucose would undergo thermolysis completely in the calcination process. As a result, the pure TiO2 nanotubes with visible light response and large BET surface areas were obtained. For further improving the photocatalytic activity, Pd nanoparticles were loaded as the foreign electron traps on TiO2 nanotubes and the photocatalytic oxidation efficiency of propylene was as high as 71 % under visible light irradiation, and the photostability of the catalyst kept over 90 % after 4 cyclic tests.

Ion exchange defines the biological activity of titanate nanotubes

One-dimensional titanate nanotubes (TiONTs) were subjected to systematic ion exchange to determine the impact of these modifications on biological activities. Ion exchanged TiONTs (with Ag, Mg, Bi, Sb, Ca, K, Sr, Fe, and Cu ions) were successfully synthesized and the presence of the substituted ions was verified by energy dispersive X-ray spectroscopy (EDS). A complex screening was carried out to reveal differences in toxicity to human cells, as well as in antibacterial, antifungal, and antiviral activities between the various modified nanotubes. Our results demonstrated that Ag ion exchanged TiONTs exerted potent antibacterial and antifungal effects against all examined microbial species but were ineffective on viruses. Surprisingly, the antibacterial activity of Cu/TiONTs was restricted to Micrococcus luteus. Most ion exchanged TiONTs did not show antimicrobial activity against the tested bacterial and fungal species. Incorporation of various ions into nanotube architectures lead to mild, moderate, or even to a massive loss of human cell viability; therefore, this type of biological effect exerted by TiONTs can be greatly modulated by ion exchange. These findings further emphasize the contribution of ion exchange in determining not only the physical and chemical characteristics but also the bioactivity of TiONT against different types of living cells.

Acid-assisted hydrothermal synthesis of nanocrystalline TiO2 from titanate nanotubes: influence of acids on the photodegradation of gaseous toluene

In order to efficiently remove volatile organic compounds (VOCs) from indoor air, one-dimensional titanate nanotubes (TiNTs) were hydrothermally treated to prepare TiO2 nanocrystals with different crystalline phases, shapes and sizes. The influences of various acids such as CH3COOH, HNO3, HCl, HF and H2SO4 used in the treatment were separately compared to optimize the performance of the TiO2 nanocrystals. Compared with the strong and corrosive inorganic acids, CH3COOH was not only safer and more environmentally friendly, but also more efficient in promoting the photocatalytic activity of the obtained TiO2. It was observed that the anatase TiO2 synthesized in 15 mol/L CH3COOH solution exhibited the highest photodegradation rate of gaseous toluene (94%), exceeding that of P25 (44%) by a factor of more than two. The improved photocatalytic activity was attributed to the small crystallite size and surface modification by CH3COOH. The influence of relative humidity (20%-80%) on the performance of TiO2 nanocrystals was also studied. The anatase TiO2 synthesized in 15 mol/L CH3COOH solution was more tolerant to moisture than the other TiO2 nanocrystals and P25.

Photocatalytic degradation of Rhodamine B by microwave-assisted hydrothermal synthesized N-doped titanate nanotubes

Microwave-induced nitrogen-doped titanate nanotubes (NTNTs) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Zeta potential analysis, specific surface area (SBET), and UV-Visible spectroscopy. TEM results indicate that NTNTs retain a tubular structure with a crystalline multiwall and have a length of several hundred nanometers after nitrogen doping. XRD findings demonstrate that the crystalline structure of NTNTs was dominated by anatase, which is favored for photocatalytic application. The Ti-O-N linkage observed in the XPS N 1s spectrum is mainly responsible for narrowing the band gap and eventually enhancing the visible light photoactivity. FT-IR results demonstrated the existence of H₃O⁺, which could be excited by photo-generated holes to form hydroxyl radicals and degrade environmental pollutants. After sintering at 350°C, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which indicates N atom doping into the nanotubes. Photocatalytic degradation of Rhodamine B (RhB) via NTNTs show good efficiency, with pseudo first-order kinetic model rate constants of 3.7 × 10⁻³, 2.4 × 10⁻³ and 8.0 × 10⁻⁴ sec⁻¹ at pH3, 7, and 11, respectively.

Synergy of photocatalysis and adsorption for simultaneous removal of Cr(VI) and Cr(III) with TiO₂ and titanate nanotubes

An one-step efficient simultaneous removal of Cr(VI) and Cr(III) was achieved with mixture of TiO₂ and titanate nanotubes (TNTs). Unlike the conventional two-step Cr removal with a first photocatalytic reduction of Cr(VI) and a subsequent adsorption of Cr(III), the proposed single process significantly reduced reaction time (over 50%). The synergy of photocatalysis and adsorption played an important role in enhancing Cr removal process. The synergetic mechanism was interpreted and indirectly confirmed with H₂O₂ variation during photocatalysis. The instant transfer of the reduced Cr from TiO₂ surface to TNTs interlayer greatly promoted the release of photocatalytic sites of TiO₂, which in turn considerably enhanced photocatalytic activity of TNTs by inhibiting electron-hole pairs recombination. The optimum condition for the whole process was at pH 5. Adsorption of Cr(III) was primarily in the interlayer of TNTs at pH ≤ 5. However, higher pH would lead to precipitation of Cr(OH)₃ onto TNTs as observed by X-ray photoelectron spectroscopy (XPS). Addition of Ca(2+) could promoted photocatalysis owing to its ionic bridging function and form of ≡TiOH(+)-Cr(VI)-Ca(2+)-Cr(VI) linkages, while SO₄(2-) only slightly inhibited photo-reduction of Cr(VI), indicating good synergy of photocatalysis and adsorption even at high ionic strength of electrolyte. Besides, the desorbed TNTs could be easily regenerated by remedying the damaged tubular structure and reused for Cr removal with excellent performance. The outstanding synergetic effects with essential explanation of the mechanism make this study not only fundamentally important but also potentially practical applicable.

Preparation of graphene nanoplatelet-titanate nanotube composite and its advantages over the two single components as biosensor immobilization materials

A novel nanocomposite consisting of graphene nanoplatelets (GNPs) and titanate nanotubes (TNTs) have been synthesized successfully utilizing the hydrothermal method. The GNP-TNT composite was characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy. The voltammetric characterization of GNP-TNT composite, pure GNPs and pure TNTs modified horseradish peroxidase (HRP) biosensors were conducted to select the most suitable electrode immobilization material for enzyme biosensors. The GNPs was firstly eliminated owing to its extremely high background charging current, distinct electrochemical interference from its surface functional groups and low signal to noise ratio. Next, the direct electron transfer of HRP on electrode and the catalytic current of HRP towards H2O2 was increased around 45% and 72% respectively on GNP-TNT composite modified electrodes compared with those on pure TNTs modified electrodes. GNP-TNT composite modified HRP biosensor also exhibited superiority over pure TNTs modified HRP biosensor in the analytical performance. The precision and stability study provided additional evidence for the feasibility of using GNP-TNT composite as electrode modification material.

The radiosensitization effect of titanate nanotubes as a new tool in radiation therapy for glioblastoma: a proof-of-concept

BACKGROUND AND PURPOSE

One of the new challenges to improve radiotherapy is to increase the ionizing effect by using nanoparticles. The interest of titanate nanotubes (TiONts) associated with radiotherapy was evaluated in two human glioblastoma cell lines (SNB-19 and U87MG).

MATERIALS AND METHODS

Titanate nanotubes were synthetized by the hydrothermal treatment of titanium dioxide powder in a strongly basic NaOH solution. The cytotoxicity of TiONts was evaluated on SNB-19 and U87MG cell lines by cell proliferation assay. The internalization of TiONts was studied using Transmission Electron Microscopy (TEM). Finally, the effect of TiONts on cell radiosensitivity was evaluated using clonogenic assay. Cell cycle distribution was evaluated by flow cytometry after DNA labeling. DNA double-stranded breaks were evaluated using γH2AX labeling.

RESULTS

Cells internalized TiONts through the possible combination of endocytosis and diffusion with no cytotoxicity. Clonogenic assays showed that cell lines incubated with TiONts were radiosensitized with a decrease in the SF2 parameter for both SNB-19 and U87MG cells. TiONts decreased DNA repair efficiency after irradiation and amplified G2/M cell-cycle arrest.

CONCLUSION

Our results indicated that further development of TiONts might provide a new useful tool for research and clinical therapy in the field of oncology.