Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis

Electrochemical and Mechanical Properties of Hexagonal Titanium Dioxide Nanotubes Formed by Sonoelectrochemical Anodization

This study aimed to investigate the fabrication and characterization of hexagonal titanium dioxide nanotubes (hTNTs) compared to compact TiO2 layers, focusing on their structural, electrochemical, corrosion, and mechanical properties. The fabrication process involved the sonoelectrochemical anodization of titanium foil in various electrolytes to obtain titanium oxide layers with different morphologies. Scanning electron microscopy revealed the formation of well-ordered hexagonal TNTs with diagonals in the range of 30-95 nm and heights in the range of 3500-4000 nm (35,000-40,000 Å). The electrochemical measurements performed in 3.5% NaCl and Ringer's solution confirmed a more positive open-circuit potential, a lower impedance, a higher electrical conductivity, and a higher corrosion rate of hTNTs compared to the compact TiO2. The data revealed a major drop in the impedance modulus of hTNTs, with a diagonal of 46 ± 8 nm by 97% in 3.5% NaCl and 96% in Ringer's solution compared to the compact TiO2. Nanoindentation tests revealed that the mechanical properties of the hTNTs were influenced by their diagonal size, with decreasing hardness and Young's modulus observed with an increasing diagonal size of the hTNTs, accompanied by increased plastic deformation. Overall, these findings suggest that hTNTs exhibit promising structural and electrochemical properties, making them potential candidates for various applications, including biosensor platforms.

g-C3N4-Co3O4 Z-Scheme Junction with Green-Synthesized ZnO Photocatalyst for Efficient Degradation of Methylene Blue in Aqueous Solution

A simple wet chemical ultrasonic-assisted synthesis method was employed to prepare visible light-driven g-C₃N₄-ZnO-Co₃O₄ (GZC) heterojunction photocatalysts. X-ray diffraction (XRD), scanning electromicroscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), ultraviolet (UV), and electrochemical impedance spectroscopy (EIS) are used to characterize the prepared catalysts. XRD confirms the homogenous phase formation of g-C₃N₄, ZnO, and Co₃O₄, and the heterogeneous phase for the composites. The synthesized ZnO and Co₃O₄ by using cellulose as a template show a rod-like morphology. The specific surface area of the catalytic samples increases due to the cellulose template. The measurements of the energy band gap of a g-C₃N₄-ZnO-Co₃O₄ composite showed red-shifted optical absorption to the visible range. The photoluminescence (PL) intensity decreases due to the formation of heterojunction. The PL quenching and EIS result shows that the reduction of the recombination rate and interfacial resistance result in charge carrier kinetic improvement in the catalyst. The photocatalytic performance in the degradation of MB dye of the GZC-3 composite was about 8.2-, 3.3-, and 2.5-fold more than that of the g-C₃N₄, g-C₃N₄-ZnO, and g-C₃N₄-Co₃O₄ samples. The Mott-Schottky plots of the flat band edge position of g-C₃N₄, ZnO, Co₃O₄, and Z-scheme g-C₃N₄-ZnO-Co₃O₄ photocatalysts may be created. Based on the stability experiment, GZC-3 shows greater photocatalytic activity after four recycling cycles. As a result, the GZC composite is environmentally friendly and efficient photocatalyst and has the potential to consider in the treatment of dye-contaminated wastewater.

The Encapsulation of Natural Organic Dyes on TiO2 for Photochromism Control

Titanium dioxide (TiO₂) plays a pivotal role in photocatalytic reactions and holds great promise for the cosmetic and paint industries due to its white color and high refractive index. However, the original color of TiO₂ changes gradually to blue or yellow with UV irradiation, which affects its color realization. We encapsulated TiO₂ with several natural organic dye compounds, including purpurin, curcumin, and safflower, to control its photochromism and realize a range of different colors. The chemical reaction between TiO₂ and dyes based on their functional group was investigated, and the light absorption was tested via FTIR and UV-Vis spectroscopy. The changes in morphology and size distribution additionally supported their successful encapsulation. The discoloration after UV irradiation was evaluated by measuring the color difference (ΔE) of control TiO₂ and dye encapsulated TiO₂. The unique structure utilized natural dyes to preserve photochromism based on the physical barrier and automatically controlled the electronic transition of core TiO₂. In particular, the color difference values of purpurin and curcumin were 4.05 and 3.76, which is lower than the 5.36 of the control TiO₂. Dye encapsulated TiO₂ was manipulated into lipstick to verify its color realization and retention.

Visible-Light-Active N-Doped TiO2 Photocatalysts: Synthesis from TiOSO4, Characterization, and Enhancement of Stability Via Surface Modification

This paper describes the chemical engineering aspects for the preparation of highly active and stable nanocomposite photocatalysts based on N-doped TiO₂. The synthesis is performed using titanium oxysulfate as a low-cost inorganic precursor and ammonia as a precipitating agent, as well as a source of nitrogen. Mixing the reagents under a control of pH leads to an amorphous titanium oxide hydrate, which can be further successfully converted to nanocrystalline anatase TiO₂ through calcination in air at an increased temperature. The as-prepared N-doped TiO₂ provides the complete oxidation of volatile organic compounds both under UV and visible light, and the action spectrum of N-doped TiO₂ correlates to its absorption spectrum. The key role of paramagnetic nitrogen species in the absorption of visible light and in the visible-light-activity of N-doped TiO₂ is shown using the EPR technique. Surface modification of N-doped TiO₂ with copper species prevents its intense deactivation under highly powerful radiation and results in a nanocomposite photocatalyst with enhanced activity and stability. The photocatalysts prepared under different conditions are discussed regarding the effects of their characteristics on photocatalytic activity under UV and visible light.

Pt nanoparticles coupled with perylene-based small molecule deposited on Ti3+ self-doped TiO2 nanorods-An inorganic/organic type-II nanoheterostructure for efficient visible-light photoelectrochemical water oxidation

In the work reported in this article, we have coupled Ti³⁺-self-doped TiO₂ nanorods (NRs) with a newly synthesized tetrathiophene coupled perylene-based molecule (tThTMP) to form type-II inorganic/organic nanoheterostructures (NHs) for visible-light-driven water oxidation. The small organic molecule helps in better utilizing a wide range of the visible light spectrum, facilitates a faster delocalization of the photogenerated carriers at the inorganic/organic heterojunction, and exhibits improved photoelectrochemical performances. We have further decorated the NHs with platinum nanoparticles (NPs). The decoration of the Pt NPs significantly augments the various aspects of photoelectrochemical performances. The Pt NPs decorated NHs photoanode exhibits a photocurrent density of 0.83 mA/cm² at 1.23 V vs. RHE (@10 mV/s scan rate), a photoconversion efficiency of 0.26%, a substantial cathodic shift in the water oxidation onset potential and flat band potential, impressively reduced charge transfer resistance, improved photocarrier concentration, photovoltage, and stability.

A review on dry-based and wet-based catalytic sulphur dioxide (SO2) reduction technologies

While sulphur dioxide (SO₂) is known for its toxicity, numerous effective countermeasures were innovated to alleviate its hazards towards the environment. In particular, catalytic reduction is favoured for its potential in converting SO₂ into harmless, yet marketable product, such as elemental sulphur. Therefore, current review summarises the critical findings in catalytic SO₂ reduction, emphasising on both dry- and wet-based technology. As for the dry-based technology, knowledge related to SO₂ reduction over metal-, rare earth- and carbon-based catalysts are summarised. Significantly, both the reduction mechanisms and important criteria for efficient SO₂ reduction are elucidated too. Meanwhile, the wet-based SO₂ reduction are typically conducted in reactive liquid medium, such as metal complexes, ionic liquids and organic solvents. Therefore, the applications of the aforesaid liquid mediums are discussed thoroughly in the similar manner to dry-technology. Additionally, the pros and cons of each type of catalyst are also presented to provide valuable insights to the pertinent researchers. Finally, some overlooked aspects in both dry- and wet-based SO₂ reduction are identified, with potential solutions given too. With these insights, current review is anticipated to contribute towards practicality improvement of catalytic SO₂ reduction, which in turn, protects the environment from SO₂ pollution.

Structural, Magnetic, and Electronic Properties of the Cr1-xTixO2 Solid

Cr_1-xTi_xO₂ (0 ≤ x ≤ 1) solid solution was synthesized by a high-pressure and high-temperature method, whereafter systematic experimental and computational studies were conducted on the Cr_1-xTi_xO₂ system. The crystal structure of the samples where 0 ≤ x ≤ 0.4 and x = 1 was of a rutile structure (P4₂/mnm), while samples where 0.5 ≤ x ≤ 0.9 crystallized in a CaCl₂ structure (Pnnm). The structural transformation from rutile-type to CaCl₂-type structure should be due to the combined action of positive chemical pressure and physical pressure. The saturation magnetization of the Cr_1-xTi_xO₂ samples decreased linearly with the increase of x because Ti⁴⁺ is nonmagnetic. In addition, the Curie temperature of the Cr_1-xTi_xO₂ samples also decreased noticeably with the increase of x. When nonmagnetic Ti⁴⁺ randomly replaced Cr⁴⁺ and occupied its position, the net exchange coupling in Cr_1-xTi_xO₂ would decrease. When Ti⁴⁺ occupied the majority in the system, Cr⁴⁺ ions would be separated by nonmagnetic Ti⁴⁺ ions far enough for the long-range ferromagnetic order to weaken or even disappear with the increase of x, causing the Cr_1-xTi_xO₂ system to finally approach a paramagnetic state. Density functional theory calculations were performed for the Cr_1-xTi_xO₂ system, and the predicted trends of the magnetic properties agreed well with the experimental results. These calculations also showed that Cr_1-xTi_xO₂ was still half-metallic until x reached 0.6.

Identification of Active Species in Photodegradation of Aqueous Imidacloprid over g-C3N4/TiO2 Nanocomposites

In this work, g-C3N4/TiO2 composites were fabricated through a hydrothermal method for the efficient photocatalytic degradation of imidacloprid (IMI) pesticide. The composites were fabricated at varying loading of sonochemically exfoliated g-C3N4 (denoted as CNS). Complementary characterization results indicate that the heterojunction between the CNS and TiO2 formed. Among the composites, the 0.5CNS/TiO2 material gave the highest photocatalytic activity (93% IMI removal efficiency) under UV-Vis light irradiation, which was 2.2 times over the pristine g-C3N4. The high photocatalytic activity of the g-C3N4/TiO2 composites could be ascribed to the band gap energy reduction and suppression of photo-induced charge carrier recombination on both TiO2 and CNS surfaces. In addition, it was found that the active species involved in the photodegradation process are OH• and holes, and a possible mechanism was proposed. The g-C3N4/TiO2 photocatalysts exhibited stable photocatalytic performance after regeneration, which shows that g-C3N4/TiO2 is a promising material for the photodegradation of imidacloprid pesticide in wastewater.

Editorial Catalysts: Special Issue on Recent Advances in TiO2 Photocatalysts

The development of civilization and the massive use of traditional energy sources has led to progressive environmental degradation that requires immediate action [...]

Preparation of TiO2/Ag[BMIM]Cl Composites and Their Visible Light Photocatalytic Properties for the Degradation of Rhodamine B

In order to degrade toxic pollutants such as dyes during the process of sewage treatment, considerable attention has been paid to photocatalytic technologies. In this paper, TiO2/Ag[BMIM]Cl (1-butyl-3-methyl imidazolium chloride ([BMIM]Cl)) nanocomposites were prepared with TiO2 as the carrier, silver ions as dopants and ionic liquids (IL) as modifiers. The morphologies, microstructures, crystalline structure and optical properties of the TiO2/Ag[BMIM]Cl nanospheres are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), total organic carbon (TOC), and UV-vis diffuse reflectance spectrum (UV-vis DRS) techniques. The TiO2/Ag[BMIM]Cl nanocomposites can selectively degrade rhodamine B (Rh B) under visible light because of the unstable quaternary ammonium salt. The as-obtained nanocomposites exhibit better photocatalytic activity performance than pure TiO2, TiO2/IL, and TiO2/Ag+. The experimental results show that the Rh B degradation rate can reach 98.87% under optimized producing conditions by using the TiO2/Ag[BMIM]Cl composites as the catalyzer. It shows that simultaneous doping with silver ions and ionic liquids can significantly improve the photocatalytic activity of TiO2 in Rh B degradation, indicating the formation of photosensitive AgCl in the process of TiO2/Ag[BMIM]Cl preparation. Ag+ and IL addition exchange the band gap of TiO2 and lengthen the visible wavelength range of the composite. The material has the advantages of low cost, facile preparation and reusability with the excellent degradation effect of Rh B.

Tandem Structures Semiconductors Based on TiO2_SnO2 and ZnO_SnO2 for Photocatalytic Organic Pollutant Removal

The photocatalyst materials correlation with the radiation scenario and pollutant molecules can have a significant influence on the overall photocatalytic efficiency. This work aims to outline the significance of optimizing the components mass ratio into a tandem structure in order to increase the photocatalytic activity toward pollutant removal. ZnO_SnO2 and TiO2_SnO2 tandem structures were obtained by the doctor blade technique using different mass ratios between the components. The samples contain metal oxides with crystalline structures and the morphology is influenced by the main component. The photocatalytic activity was tested using three radiation scenarios (UV, UV-Vis, and Vis) and two pollutant molecules (tartrazine and acetamiprid). The results indicate that the photocatalytic activity of the tandem structures is influenced by the radiation wavelength and pollutant molecule. The TiO2_SnO2 exhibit 90% photocatalytic efficiency under UV radiation in the presence of tartrazine, while ZnO_SnO2 exhibit 73% photocatalytic efficiency in the same experimental conditions. The kinetic evaluation indicate that ZnO_SnO2 (2:1) have a higher reaction rate comparing with TiO2_SnO2 (1:2) under UV radiation in the presence of acetamiprid.