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![Process diagram of the preparation and photocatalytic hydrogen evolution reaction (HER) mechanism of the MoS2 QDs modified black Ti 3+ -TiO2/g-C3N4 hollow nanosphere heterojunction. Reproduced from [150]. Copyright (2019), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.](publication/342257047/figure/fig9/AS:903590587682824@1592444192746/Process-diagram-of-the-preparation-and-photocatalytic-hydrogen-evolution-reaction-HER.png)
Process diagram of the preparation and photocatalytic hydrogen evolution reaction (HER) mechanism of the MoS2 QDs modified black Ti 3+ -TiO2/g-C3N4 hollow nanosphere heterojunction. Reproduced from [150]. Copyright (2019), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since t...
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Photocatalysis represents a sustainable strategy for addressing energy shortages and global warming. The main challenges in the photocatalytic process include limited light absorption, rapid recombination of photo-induced carriers, and poor surface catalytic activity for reactant molecules. Defect engineering in photocatalysts has been proven to be...
Citations
... Titanium (Ti) and its modified nanostructured materials are widely used in many applications, such as fuel cell technology [1], solar cells [2], biosensors [3], environmental control and photocatalytic systems [4], electronics [5], and biomaterials [6]. Ti has an excellent corrosion resistance [7,8], a good biocompatibility [9,10], thermodynamic stability [11], and a low elastic modulus [12]. ...
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.
... These oxygen vacancies give rise to unpaired electrons associated with Ti 3+ species, thereby generating donor levels within the bandgap. This phenomenon can potentially enhance the separation of photogenerated charges and contribute to a reduction in the bandgap width [30][31][32][33]. ...
... The Schottky barrier, which will be further discussed in this paper, has no effect on the band gap energy, increasing the photocatalytic activity only by decreasing charge recombination [55]. The presence of Ti 3+ crystalline defects acts as an effective method of increasing visible light absorption by creating additional mid-bandgap states, which are observed below the conduction band [31]. These midbandgap states, resulting from Ti 3+ and oxygen vacancies, act as electronic donor states, further contributing to the overall enhancement of visible light absorption [30,31,67,68]. ...
... The presence of Ti 3+ crystalline defects acts as an effective method of increasing visible light absorption by creating additional mid-bandgap states, which are observed below the conduction band [31]. These midbandgap states, resulting from Ti 3+ and oxygen vacancies, act as electronic donor states, further contributing to the overall enhancement of visible light absorption [30,31,67,68]. ...
Ag-TiO2/SiO2 materials were synthesized with 1, 3, 5, and 10 wt% Ag contents and extensively characterized by different techniques, including XRD, SEM, TEM, XPS, BET, UV–VIS, EPR, and PL spectroscopy. Subsequently, the activity of these materials in the degradation of a model volatile organic compound (n-hexane) was compared by testing in a continuous gas–solid photoreactor. Loading with Ag induced stabilization of the brookite phase and crystal growth. TEM images showed d-spacing values corresponding to anatase and metallic silver. The specific surface area was lower in the Ag-modified catalysts, probably due to the blocking of the silica gel pores by Ag nanoparticles, whose size (~ 20 nm) was larger than the silica pores (~ 1.98 nm). SEM–EDS images showed heterogeneous distribution of Ag on the surface of the materials. XPS spectra showed bands referring to Ag⁺ and Ag⁰ 3d, and Ti⁴⁺ and Ti³⁺ 2p. EPR analyses showed that silver loading of TiO2/SiO2 greatly increased the occurrence of oxygen vacancies in the material. Finally, the band gap energies calculated from the UV–VIS spectra were lower in the silver-containing catalysts, dropping from 3.25 to 3.17 eV in the optimal material. Under visible light, while TiO2/SiO2 showed no photoactivity, the Ag-modified materials presented satisfactory steady-state performance (46.4% n-hexane removal).
Graphical abstract
... In recent years, the use of defective oxygen-rich TiO 2 as a promising modification approach has gained considerable attention due to its lower risk of creating additional recombination centers that can decrease photoactivity [3][4][5]. This material, which appears yellow [6][7][8], is obtained by thermal decomposition of titanium peroxo complexes formed from the reaction of titanium precursors and hydrogen peroxide [7,[9][10][11]. ...
... Apparently, hydrogen peroxide results in partial dissolution of the freshly formed TiO 2 ⋅H 2 O 2 is known to corrode TiO 2 -based materials to form partially soluble peroxo titanium complexes [25]. The probable form of the soluble peroxo titanium complex ion is [Ti(OH) 3 OO] − [16], [26]. On heating for 36 h at 75 • C, the reaction mixture gradually changed ( Fig. 1d-g). ...
... Te typical TiO 2 catalyst, on the other hand, is stimulated by UV light that takes up less than 5% of the whole solar spectrum. Tis has prompted researchers to create innovative materials with lower bandgap energy (E g ) to improve sensitivity to an increasingly plentiful visible light photon [10][11][12][13][14][15]. Terefore, the heterojunction of cobalt(II, III) oxide and bismuth oxyiodides efciently remove nitrophenol from solutions due to the high specifc surface area and density of the photogenerated charge carrier resulting in its visible light-sensitivity of the catalyst [16,17]. ...
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.
... For color correction, TiO 2 has certain advantages, including facile control of the particle size which efficiently scatters visible light and realizes a matte texture with a decrease in the particle size and clear opacity [13][14][15]. However, with their different particle sizes, TiO 2 gradually changes from its original white color to yellow [16] or blue [17] (i.e., photochromism) which obscures the definition of permanent white. In principle, the oxidation state of Ti in TiO 2 generally changes from Ti 4+ to Ti 3+ with a structural change in oxide on the surface of Ti under UV irradiation [18,19] which absorbs a shorter wavelength of light (i.e., blue shift) and displays a blue color. ...
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.
... It is also possible that Ti might dope the nanocomposites through Ti ions self-doping TiO2 (Ti:TiO2) and Ti-doped TiO2/ZnO (Ti:TiO2/ZnO). The presence of Ti 4+ has a significant effect on the activation in the photocatalytic process because it inhibits oxidation [38,39]. Figure 2 shows the morphologies of the homoepitaxial and heteroepitaxial layers grown with the incorporation of nanocomposites on PTFE substrates at different volumetric ratios of TiO2 to ZnO. ...
Developing non-toxic, semiconductor-doped heterojunction materials for optoelectronic applications on the surface of a flexible substrate is a viable strategy for meeting the world’s energy needs without introducing any environmental issues. In this paper, Ti:TiO2/ZnO nanocomposites were prepared by heat treatment and utilized as an active layer in UV photodetectors. First, a ZnO seed layer was deposited by radio frequency (RF) sputtering on polytetrafluoroethylene (PTFE) substrates. Then, TiO2/ZnO thin films (TFs) were successfully grown by combining volumetric mixtures of TiO2 and ZnO at the ratios of 1:7, 1:3, 3:5, and 1:1 via the chemical bath deposition (CBD) method. The morphological, elemental, and topographical analyses of the grown TFs were investigated through SESEM, EDX, and AFM spectroscopy, respectively. XRD patterns illustrated the presence of the unified (002) peak of the Ti/ZnO hexagonal wurtzite structure in all prepared samples, with intensities indicating a very strong preferential crystallinity with increasing TiO2 ratios. Enhanced diffuse reflectance curves were obtained by UV–Vis spectroscopy, with allowed indirect energy bandgaps ranging from 3.17 eV to 3.23 eV. FTIR characterization revealed wider phonon vibration ranges indicating the presence of Ti–O and Zn–O bonds. Metal–semiconductor–metal (MSM) UV photodetectors were fabricated by thermally evaporating Ag electrodes on the grown nanocomposites. The volumetric ratio of TiO2/ZnO impacted the photodetector performance, where the responsivity, photosensitivity, gain, detectivity, rise time, and decay time of 0.495 AW−1, 247.14%, 3.47, 3.68 × 108 jones, 0.63 s, and 0.99 s, respectively, were recorded at a ratio of 1:1 (TiO2:ZnO). Based on the results, the heterostructure nanocomposites grown on PTFE substrates are believed to be highly promising TF for flexible electronics.
... Stain resistance Ref. respectively and thus formed more Ti 3+ ions and oxygen vacancies (V '' O ). At the same time, V '' O easily makes water dissociate to form hydroxyl ions (OH -) (Banerjee et al., 2015;Na et al., 2020;Simonsen et al., 2009). Therefore, the super-hydrophilicity of the glaze was improved. ...
Self-cleaning materials have attracted considerable attention for their unique properties and practical applications in energy and environmental areas. Various commercial ceramic products developed based on photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. However, UV light induced and metastable character of anatase TiO2 in medium/high temperature ceramic glaze limited practical applications for self-cleaning photocatalytic materials, which needs further development to improve their efficiency and utilities. In this work, Mg-doped anatase TiO2 was synthesized via a template-free and surfactant-free solvothermal method. The results indicated that MgCl2·6H2O content played key roles in the formation of anatase TiO2. Compared to TiO2-undoped sample, Mg-doped TiO2 sample showed higher photodegradation rate of 99.5 % in 80 min exposed to visible light irradiation. Owing to the introduction of the catalyst, the ceramic glaze showed super-hydrophilicity (water contact angle around 7°) and exhibited excellent stain resistance (e. g. the dried Marker ink on the glaze can immediately float once meeting water after 10 cycles). The glaze after more times recycles could restore super-hydrophilicity is irradiated by visible light for 1 h. This indicates that the introduction of Mg-doped anatase TiO2 demonstrated great practical applications for self-cleaning ceramics toward sunlight.
... The visible-light activity of TiO2 photocatalysts prepared under reducing conditions is commonly attributed to the reduced states of titanium in the TiO2 lattice (e.g., Ti 3+ ) because the energy levels corresponding to these states are located lower than the CB of TiO2 [75][76][77]. According to the results of XPS and EPR analyses (Figures 4 and 5), the prepared TiO2-N samples contain similar centers. ...
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.
... Hydrogen evolution at a lower potential (0.5 V RHE ) (Fujishima and Honda, 1972) than the normal potential for water splitting (1.23 V RHE ) was achieved by irradiating TiO 2 electrodes, which influenced extensive research on different metal oxide-based photoelectrochemical generation of hydrogen in the last few decades (Cho et al., 2014). TiO 2 -based semiconducting electrodes are commonly used due to their low-cost synthesis, better physical and chemical stability, and low toxicity with prompt photo-response (Cho et al., 2014;Sarkar et al., 2017;Na et al., 2020). But, the hydrophilic nature and relatively larger bandgap (~3.2 eV for anatase and 3 eV for rutile) restrict them to serve as a photo-electrode in pure form (Etacheri et al., 2015). ...
... Doping metal atoms like Cr, Mn, Fe, Co, Cu, Zn, Sb, etc. (Pal et al., 2021;Sarkar and Khan, 2019) or nonmetallic elements like B, N, P, S, F, Cl, I, etc. (Sarkar and Khan, 2019;Sanke et al., 2021) in TiO 2 matrix can lower the bandgap, and the lowering of bandgap depends on the extent of doping (Zhang et al., 2015). Recently, Ti 3+ self-doping in the TiO 2 matrix has gained much research attention (Na et al., 2020;Ghosh et al., 2021). Ti 3+ self-doping in TiO 2 is significantly different from extrinsic impurity doping, and it creates the defect states without altering the intrinsic morphology and crystal structure (Sarkar and Khan, 2019). ...
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.
... g-C 3 N 4 can narrow the band gap energy and increase solar absorption efficiency. In addition, Ti 3+ and oxygen vacancies (Ov) in TiO 2 can suppress the recombination of photogenerated electron-hole pairs and promote charge separation [57] which led to high photocatalytic degradation of IMI. As seen in Figure 4c, CNS gave a very broad PL spectrum having a very high intensity. ...
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.
