Ilmenite-derived titanic acid species: exploring their outstanding light-independent antibacterial activity

The emergence of resistance in detrimental pathogenic bacteria towards well-recognized antibiotics has greatly impacted global medicine, consequently exploring potent antibacterial compounds is becoming a potential area of research. Although photocatalytic metal oxides have been extensively explored in this regard, their applicability is diminished due to the requirement of photon energy. Therefore, in our study, we explored the light-independent antibacterial effect of two unexplored titanium species, known as metatitanic acid (MTA) and potassium titanate, against Staphylococcus aureus, Escherichia coli, and Pseudomonas spp. using the disk diffusion method in Luria-Bertani agar medium, where the well-known antibiotic, gentamicin, was used as the positive control. These two titanium compounds were readily synthesized through a novel process which was originally developed for the extraction of TiO2 from ilmenite. The synthesized MTA was characterized using FT-IR, Raman spectroscopy, XRD, TGA, UV-visible spectroscopy, and SEM. According to our findings, both MTA and potassium titanate exhibited superior light-independent antibacterial properties, where for some concentrations, the effect was even greater than gentamicin. However, nano-TiO2 totally failed as an antibacterial compound against the tested three strains under dark conditions.

Bifunctional Modification Enhances Lithium Extraction from Brine Using a Titanium-Based Ion Sieve Membrane Electrode

Salt lake brine has become a promising lithium resource, but it remains challenging to separate Li⁺ ions from the coexisting ions. We designed a membrane electrode having conductive and hydrophilic bifunctionality based on the H₂TiO₃ ion sieve (HTO). Reduced graphene oxide (RGO) was combined with the ion sieve to improve electrical conductivity, and tannic acid (TA) was polymerized on the surface of ion sieve to enhance hydrophilicity. These bifunctional modification at the microscopic level improved the electrochemical performance of the electrode and facilitated ion migration and adsorption. Poly(vinyl alcohol) (PVA) was used as a binder to further intensify the macroscopic hydrophilicity of the HTO/RGO-TA electrode. Lithium adsorption capacity of the modified electrode in 2 h reached 25.2 mg g^-1, more than double that of HTO (12.0 mg g^-1). The modified electrode showed excellent selectivity for Na⁺/Li⁺ and Mg²⁺/Li⁺ separation and good cycling stability. The adsorption mechanism follows ion exchange, which involves H⁺/Li⁺ exchange and Li-O bond formation in the [H] layer and [HTi₂] layer of HTO.

Investigating the activation of passive metals by a combined in-situ AFM and Raman spectroscopy system: a focus on titanium

Understanding the main steps involved in the activation of passive metals is an extremely important subject in the mechanical and energy industry and generally in surface science. The titanium-H₂SO₄ system is particularly useful for this purpose, as the metal can either passivate or corrode depending on potential. Although several studies tried to hypothesise the surface state of the electrode, there is no general consensus about the surface state of Ti in the active-passive transition region. Here by combining in-situ atomic force microscopy (AFM) and Raman spectroscopy, operating in an electrochemical cell, we show that the cathodic electrification of Ti electrodes causes the dissolution of the upper TiO₂ portion of the passive film leaving the electrode covered by only a thin layer of titanium monoxide. Fast anodic reactions involved the acidification of the solution and accumulation of sulphur containing anions. This produces a local increase of the solution turbidity, allowing to distinguish favourable regions for the precipitation of TiOSO₄·2H₂O. These results give a clear answer to the long-stated question of the physical origin behind the formation of negative polarization resistances, sometimes occurring in corroding systems, and a rationale about the proton-induced degradation of passive surfaces in presence of sulphur containing species.

Recovery of tungsten and titanium from spent SCR catalyst by sulfuric acid leaching process

The widespread use of selective catalytic reduction (SCR) catalysts has resulted in a large accumulation of spent SCR catalysts. These spent catalysts present a significant risk of environmental hazards and potential for resource recovery. This paper presents a feasible process, which works using atmospheric pressure leaching, of tungsten and titanium recovery from spent SCR catalysts. In this new method, titanium and tungsten are simultaneously leached with sulfuric acid as the leaching agent. After hydrolysis and calcination, titanium-tungsten powder with low impurity and reconstructed pore properties was obtained. The optimal conditions for the leaching of Ti and W were as follows: temperature, 150 °C; reaction time, 60 min; H₂SO₄ concentration, 80 %; mass ratio of H₂SO₄/TiO₂, 3:1; and diluted H₂SO₄ concentration, 20 % after reaction. With these optimum conditions, the leaching efficiency of Ti and W were found to be 95.92 % and 93.83 %, respectively. The ion speciation and reaction mechanism of W were studied by Raman spectroscopy, FTIR, and UV-vis. The formation of heteropolytungstate with a Keggin structure is essential for the synergistic leaching of Ti and W, as the heteropolytungstate can be stably dissolved in the acid solution. During the hydrolysis process, heteropolytungstate gradually decomposed into Ti⁴⁺ and WO₄^2- due to the formation of insoluble Ti(OH)₄ from Ti⁴⁺ in the solution. This study demonstrated an effective method for synergistic recovery of titanium and tungsten from the spent SCR catalyst.

Recent Advances in the Lithium Recovery from Water Resources: From Passive to Electrochemical Methods

The ever-increasing amount of batteries used in today's society has led to an increase in the demand of lithium in the last few decades. While mining resources of this element have been steadily exploited and are rapidly depleting, water resources constitute an interesting reservoir just out of reach of current technologies. Several techniques are being explored and novel materials engineered. While evaporation is very time-consuming and has large footprints, ion sieves and supramolecular systems can be suitably tailored and even integrated into membrane and electrochemical techniques. This review gives a comprehensive overview of the available solutions to recover lithium from water resources both by passive and electrically enhanced techniques. Accordingly, this work aims to provide in a single document a rational comparison of outstanding strategies to remove lithium from aqueous sources. To this end, practical figures of merit of both main groups of techniques are provided. An absence of a common experimental protocol and the resulting variability of data and experimental methods are identified. The need for a shared methodology and a common agreement to report performance metrics are underlined.

On the Structure and Lithium Adsorption Mechanism of Layered H2TiO3

Layered H₂TiO₃ has been studied as an ionic sieve material for the selective concentration of lithium from solutions. The accepted mechanism of lithium adsorption on H₂TiO₃ ion sieves is that it occurs via Li⁺-H⁺ ion exchange with no chemical bond breakage. However, in this work, we demonstrate that lithium adsorption on H₂TiO₃ occurs via O-H bond breakage and the formation of O-Li bonds, contrary to previously proposed mechanisms. Thermogravimetric analysis results show that the weight loss due to dehydroxylation decreases from 2.96 wt % to 0.8 wt % after lithium adsorption, indicating that surface hydroxyl groups break during lithium adsorption. Raman and Fourier transform infrared spectroscopy studies indicate that H₂TiO₃ contains isolated OH groups and hydrogen-bonded OH groups. Among these two hydroxyl groups, isolated OH groups present in the HTi₂ layers are more actively involved in lithium adsorption than hydrogen-bonded OH groups. As a result, the actual adsorption capacity is limited by the number of isolated OH groups, whereas hydrogen-bonded OH groups involved are for stabilizing the layered structure. We also show that H₂TiO₃ contains a high concentration of stacking faults and structural disorders which play a crucial role in controlling lithium adsorption properties.

Transport Properties of Nanostructured Li2TiO3 Anode Material Synthesized by Hydrothermal Method

Li2TiO3 nanopowders were synthesized by hydrothermal process using anatase TiO2 and LiOHH2O as raw materials. Li2TiO3 crystallizes in the layered monoclinic structure (space group C2/c) with average crystallite size of 34 nm. Morphology, elemental composition and local structure of products were carried out using high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman and Fourier transform infrared spectroscopy. Transport properties investigated by d.c. (4-probe measurements) and a.c. (complex impedance spectroscopy) show the activation energy of 0.71 and 0.65 eV, respectively. The ionic transport properties of Li+ ions in nanocrystalline Li2TiO3 characterized by cyclic voltammetry and impedance spectroscopy validate the good electrochemical properties of this anode material for lithium-ion batteries.

TiO2 microrods with stacked 3D nanovoids for photoelectrochemical water splitting

This paper reports an original nonstandard green concept to obtain TiO2 microrods with polyhedral densely stacked 3D nanovoids prepared via the heat treatment of a hydrogen titanate. The intermediate hydrogen titanate was synthesized by a solid-liquid-solid (SLS) route from an ammonia-saturated aqueous solution of TiOSO4 at 0 °C. The effect of the postgrowth thermal annealing procedure to remove ice (water) and the proposed mechanism to explain the underlying transitions from the intermediate precursor to nanostructured TiO2 microrods with stacked 3D nanovoids were investigated. The small-angle X-ray scattering (SAXS) analysis indicates that at temperatures above 500 °C, the release of confined ice (water) takes place, which leads to the creation of self-assembled polyhedral nanovoids open to the surface. Their size ranges from 5 to 78 nm in both length and width, with a depth of ~3.88 nm. The first use of these stacked 1D TiO2 microrods as the working electrode in a photoelectrochemical (PEC) cell for water splitting is demonstrated. The estimated value of ζ-potential depends on both annealing temperature and crystallite size. Anatase sample 1D TiO/800 with ζ-potential (−29.1) mV and average crystallite size ~68 nm was observed to be highly stable in aqueous suspension. The SLS method yields low-cost 1D TiO2 materials possessing high photoreactivity with water. The PEC measurements indicate that three-dimensional hollow structures with a controlled geometry via patterned 1D TiO2 surface are promising materials for hydrogen generation from water splitting.

Transport Properties of Nanostructured Li2TiO3 Anode Material Synthesized by Hydrothermal Method

Li2TiO3 nanopowders were synthesized by hydrothermal process using anatase TiO2 and LiOH H2O as raw materials. Li2TiO3 crystallizes in the layered monoclinic structure (space group C2/c) with average crystallite size of 34 nm. Morphology, elemental composition and local structure of products were carried out using HRTEM, FESEM, EDS, Raman and FTIR spectroscopy. Transport properties investigated by d.c. (4-probe measurements) and a.c. (complex impedance spectroscopy) show the activation energy of 0.71 and 0.65 eV, respectively. The ionic transport properties of Li+ ions in nanocrystalline Li2TiO3 characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) validate the good electrochemical properties of this anode material for lithium-ion batteries.

Lithium adsorptive properties of H2TiO3 adsorbent from shale gas produced water containing organic compounds

Shale gas produced water is a by-product from shale gas production which causes environmental issues and needs for a wastewater treatment process. Lithium is one of the valuable metals that exists in the shale gas produced water, and it can be recovered during the water treatment process. However, the concentration of organic carbon in the produced water is significantly high, and these organic compounds may affect the lithium recovery efficiency. Therefore, the lithium adsorption from shale gas produced water containing organic compounds was carried out in this study to observe the influence of organic compounds on lithium adsorption using H₂TiO₃ adsorbent. The equilibrium time from the kinetic study and the maximum adsorption capacity calculated from the Langmuir isotherm equation decreased with the addition of organic compounds to the produced water. Overall, lithium was selectively recovered from the pH buffered shale gas produced water with or without organic compounds. However, the results indicate the addition of organic compounds, especially the smaller-molecular-weight organic compound, to the produced water inhibits the lithium adsorption significantly.

A novel study on preparation of H2TiO3–lithium adsorbent with titanyl sulfate as titanium source by inorganic precipitation–peptization method

A peroxy lithium titanate sol was prepared with low-cost and easily available titanyl sulfate as the titanium source, lithium acetate as the lithium source, and aquae hydrogenii dioxidi as the complexing agent using an inorganic precipitation–peptization method. The sol system was aged, centrifugal-washed, dried and calcined to obtain a pure precursor, Li₂TiO₃, followed by pickling with hydrochloric acid to obtain the H₂TiO₃–lithium adsorbent. The effects of aging time and calcination temperature on the target product were investigated. The results indicate that the sol-system is stable, which is beneficial for loading on a suitable carrier, such as ceramic foams. Centrifugal-washing, instead of vacuum filtration-washing, is conducive to product formation. The most suitable aging time of precursor sol is 24 h and the appropriate calcination temperature is 750 °C. The lithium drawn-out ratio of samples synthesized in this condition reaches 89.50% after pickling with 0.2 M hydrochloric acid for 8 h at 70 °C. Moreover, the Li⁺ uptake of the adsorbent (adsorption capacity) reaches 29.96 mg g⁻¹ and 33.35 mg g⁻¹ when the adsorption time is 1 h and 8 h, respectively.

A peroxy Li₂TiO₃ sol was prepared with low-cost TiOSO₄ as titanium source, CH₃COOLi as lithium source, and H₂O₂ as complexing agent by inorganic precipitation–peptization method.

Lithium recovery from salt lake brine by H2TiO3

The details of the ion exchange properties of layered H2TiO3, derived from the layered Li2TiO3 precursor upon treatment with HCl solution, with lithium ions in the salt lake brine (collected from Salar de Uyuni, Bolivia) are reported. The lithium adsorption rate is slow, requiring 1 d to attain equilibrium at room temperature. The adsorption of lithium ions by H2TiO3 follows the Langmuir model with an adsorptive capacity of 32.6 mg g(-1) (4.7 mmol g(-1)) at pH 6.5 from the brine containing NaHCO3 (NaHCO3 added to control the pH). The total amount of sodium, potassium, magnesium and calcium adsorbed from the brine was <0.30 mmol g(-1). The H2TiO3 was found capable of efficiently adsorbing lithium ions from the brine containing competitive cations such as sodium, potassium, magnesium and calcium in extremely large excess. The results indicate that the selectivity order Li(+) ≫ Na(+), K(+), Mg(2+), Ca(2+) originates from a size effect. The H2TiO3 can be regenerated and reused for lithium exchange in the brine with an exchange capacity very similar to the original H2TiO3.

Synthesis and characterisation of new MO(OH)2 (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts

Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2(1)/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.