Nitrogen-doped TiO2 nanotube array films with enhanced photocatalytic activity under various light sources

Long-Term Stability of Light-Induced Ti3+ Defects in TiO2 Nanotubes for Amplified Photoelectrochemical Water Splitting

This study shows that the simple approach of keeping anodic TiO2 nanotubes at 70 °C in ethanol for 1 h results in improved photoelectrochemical water splitting activity due to initiation of crystallization in the material amplified by the light-induced formation of a Ti3+ -Vo states under UV 365 nm illumination. For the first time, the light-induced Ti3+ -Vo states are generated when oxygen is present in the reaction solution and are stable when in contact with air (oxygen) for a long time (two months). We confirmed here that the amorphous or nearly amorphous structure of titania supports the survival of Ti3+ species in contact with oxygen. It is also shown that the ethanol treatment substantially improves the morphology of the titania nanotube arrays, specifically, less surface cracking and surface purification from C- and F-based contamination from the electrolyte used for anodizing.

Detailed Insight into Photocatalytic Inactivation of Pathogenic Bacteria in the Presence of Visible-Light-Active Multicomponent Photocatalysts

The use of heterogeneous photocatalysis in biologically contaminated water purification processes still requires the development of materials active in visible light, preferably in the form of thin films. Herein, we report nanotube structures made of TiO2/Ag2O/Au0, TiO2/Ag2O/PtOx, TiO2/Cu2O/Au0, and TiO2/Cu2O/PtOx obtained via one-step anodic oxidation of the titanium-based alloys (Ti94Ag5Au1, Ti94Cu5Pt1, Ti94Cu5Au1, and Ti94Ag5Pt1) possessing high visible light activity in the inactivation process of methicillin-susceptible S. aureus and other pathogenic bacteria-E. coli, Clostridium sp., and K. oxytoca. In the samples made from Ti-based alloys, metal/metal oxide nanoparticles were formed, which were located on the surface and inside the walls of the NTs. The obtained results showed that oxygen species produced at the surface of irradiated photocatalysts and the presence of copper and silver species in the photoactive layers both contributed to the inactivation of bacteria. Photocatalytic inactivation of E. coli, S. aureus, and Clostridium sp. was confirmed via TEM imaging of bacterium cell destruction and the detection of CO2 as a result of bacteria cell mineralization for the most active sample. These results suggest that the membrane ruptures as a result of the attack of active oxygen species, and then, both the membrane and the contents are mineralized to CO2.

CO2 Photoreduction Activity Enhancement and Unexpected Observation of Carbon Monoxide Adsorbates on the Surface of TiO2 Nanotube Arrays Synthesized in Formamide Electrolytes

TiO2 nanotube arrays grown through electrochemical anodization in a formamide-based electrolyte (TNTA-FA) exhibited a whole host of unusual properties compared to nanotubes grown in the conventional ethylene glycol-based electrolyte (TNTA-EG). TNTA-FA exhibited shorter phonon lifetimes, lower lattice strain, more visible light absorption, lower work function, and a highly unusual adsorbate structure consisting of physisorbed and chemisorbed CO along with linearly adsorbed CO2 and various monodentate and bidentate carbonate species. The observation of adsorbed CO in the dark is highly unusual and indicates spontaneous deoxygenation of CO2 on the surface of TNTA-FA. The significance of this finding is that the formation of CO2•- is no longer the rate-limiting bottleneck for the reduction of CO2 on TNTA-FA surfaces as it is for all TiO2 surfaces. TNTA-FA samples are strongly colored (inclusive of a fluorescent green color) and consist of rounded, vertically oriented hollow cylinders as opposed to the honeycomb-like morphology of TNTA-EG arranged in an approximate triangular lattice. The photocatalytic activity was tested through the CO2 photoreduction and dye degradation tests. Formamide-based nanotubes outperformed the EG-based nanotubes by almost 1.7 and 2 times, respectively, in CO2 reduction and dye degradation tests done on methylene blue, brilliant green, and rhodamine B dyes. These results are attributed to stronger surface band bending in TNTA-FA which facilitates more efficient separation of photogenerated electron-hole pairs.

Visible-Light Driven Photodegradation of Industrial Pollutants Using Nitrogen-Tungsten Co-Doped Nanocrystalline TiO2: Spectroscopic Analysis of Degradation Reaction Path

The purpose to conduct this research work is to study the effect of photocatalytic degradation by developing cost-effective and eco-friendly nitrogen and tungsten (metal/non-metal) co-doped titania (TiO₂). The inherent characteristics of synthesized nanoparticles (NPs) were analyzed by Fourier transform infra-red spectroscopy (FT-IR), ultra-violet visible (UV-Vis) spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), X-ray diffraction (XRD) spectrometry, and atomic force microscopy (AFM). Co-doping of metal and non-metal has intensified the photocatalysis trait of TiO₂ nanoparticles in an aqueous medium. This co-doping of transition metal ions and modification of nitrogen extended the absorption into the visible region subsequently restraining the recombination of electrons/holes pair. The stronger light absorption in the visible region was required for the higher activity of photodegradation of dye under visible light illumination to confine bandgap energy which results in accelerating the rate of photodegradation. After efficient doping, the bandgap of titania reduced to 2.38 eV and caused the photodegradation of malachite green in visible light. The results of photocatalytic degradation were confirmed by using UV/Vis. spectroscopy and high-performance liquid chromatography coupled with a mass spectrophotometer (HPLC-ESI-MS) was used for the analysis of intermediates formed during photocatalytic utility of the work.

Facile synthesis of Zn-doped CdS nanowires with efficient photocatalytic performance

In this study, one-dimensional zinc (Zn)-doped cadmium sulphide (CdS) nanowires were synthesised by a solvothermal method. The Zn doping concentrations were varied from 1 to 5 mol% (Zn_xCd_1-xS where x = 0.001, 0.003 and 0.005). As-prepared materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and UV-visible spectroscopy. Electrochemical impedance spectroscopy (EIS) was conducted to measure the charge transfer resistance. The photocatalytic performance of prepared materials was evaluated by the photodegradation of methylene blue (MB) dye. The result showed that 5% Zn-doped CdS is more photoactive as compared to other corresponding doped and undoped CdS. The increase in photocatalytic performance is due to improvement in the charge separation.

A review on TiO2/SnO2 heterostructures as a photocatalyst for the degradation of dyes and organic pollutants

Industrialization, civilization and human activities have all grown steadily in recent years. As a result, small and large industries discharge many organic pollutants into the environment and contribute to environmental pollution. These compounds are quite stable and challenging to break down over time, posing a long-term risk. The heterogeneous advanced oxidation processes technology has gained tremendous attention. It depends on the light-induced formation of e^-/h⁺ pairs, which combine with water and aqueous oxygen to generate highly reactive hydroxyl radicals that degrade the organic pollutants in a solution and convert them ultimately into non-toxic products. In this paper, the synergetic impact of TiO₂-SnO₂ coupling with other semiconductor materials and their photodegradation performance on toxic contaminants in an aqueous medium has been reviewed. In addition, multiple approaches for the synthesis of TiO₂-SnO₂ photocatalysts have been discussed. Among them, hydrothermal, sol-gel, electrospinning, precipitation and even their combination are extensively used to synthesize various forms of nanostructures. These techniques demonstrate better tunability for visible absorption, suppression of e^-/h⁺ pair recombination and enhanced e^-/h⁺ separation to improve photocatalytic performance. This paper also summarises the role of different operating factors such as catalyst loading, pH, pollutants variation concentration, various light sources and oxidizing agents on the photodegradation of organic pollutants.

Scaling Up the Process of Titanium Dioxide Nanotube Synthesis and Its Effect on Photoelectrochemical Properties

In this work, for the first time, the influence of scaling up the process of titanium dioxide nanotube (TiO₂NT) synthesis on the photoelectrochemical properties of TiO₂ nanotubes is presented. Titanium dioxide nanotubes were obtained on substrates of various sizes: 2 × 2, 4 × 4, 5 × 5, 6 × 6, and 8 × 8 cm². The electrode material was characterized using scanning electron microscopy as well as Raman and UV–vis spectroscopy in order to investigate their morphology, crystallinity, and absorbance ability, respectively. The obtained electrodes were used as photoanodes for the photoelectrochemical water splitting. The surface analysis was performed, and photocurrent values were determined depending on their place on the sample. Interestingly, the values of the obtained photocurrent densities in the center of each sample were similar and were about 80 µA·cm². The results of our work show evidence of a significant contribution to wider applications of materials based on TiO₂ nanotubes not only in photoelectrochemistry but also in medicine, supercapacitors, and sensors.

Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films

Metal oxynitrides are compounds between nitrides and oxides with a certain level of photocatalytic functions. The purpose of this study is to investigate an appropriate range of oxygen flow rate during sputtering for depositing tantalum oxynitride films. The sputtering process was carried out under fixed nitrogen but variable oxygen flow rates. Post rapid thermal annealing was conducted at 800 °C for 5 min to transform the as-deposited amorphous films into crystalline phases. The material characterizations of annealed films include X-ray diffraction and Raman spectroscopy for identifying crystal structures; scanning electron microscope for examining surface morphology; energy-dispersive X-ray spectroscopy to determine surface elemental compositions; four-point probe and Hall effect analysis to evaluate electrical resistivity; UV-visible-NIR spectroscopy for quantifying optical properties and optical bandgaps. To assess the photocatalytic function of oxynitride films, the degradation of methyl orange in de-ionized water was examined under continuous irradiation by a simulated solar light source for six hours. Results indicate that crystalline tantalum oxynitride films can be obtained if the O2 flow rate is chosen to be 0.25–1.5 sccm along with 10 sccm of N2 and 20 sccm of Ar. In particular, films deposited between 0.25 and 1.5 sccm O2 flow have higher efficiency in photodegradation on methyl orange due to a more comprehensive formation of oxynitrides.

2,4-Dichlorophenoxyacetic acid (2,4-D) photodegradation on WO3-TiO2-SBA-15 nanostructured composite

A current environmental problem is the uncontrolled use of various pesticides that are harmful to the environment and public health. The herbicide 2,4-D is widely used, making it a vector of contamination for aquatic bodies, air, soil, and biomass. In recent decades, researchers have studied remediation of this compound in the environment. In this work, WO₃ and TiO₂ were supported on SBA-15 molecular sieve by the in situ anchoring (ISA) method, with different molar percentages of WO₃ in relation to the oxide content: X = 25%, 50%, and 75%. The W-Ti-S (X) samples were characterized by XDR, XRF, Raman, FTIR, diffuse reflectance of UV-vis, and adsorption and desorption of N₂. SBA-15 mesoporous structure was not destroyed even after the incorporation of the oxides. XRD analyses associated with Raman result found a predominance of the anatase phase for titanium oxide, and the FRX showed low incorporation of nanoparticles. Photocatalytic tests indicated that the catalytic activity depends on WO₃ and TiO₂ content, although all W-Ti-S (X) samples exhibited similar TOF value. The W-Ti-S (25) sample had the highest photocatalytic activity, 76% herbicide photodegradation under ultraviolet irradiation, at 270 min. The analysis of the catalytic cycles indicated that W-Ti-S (25) keeps out 70% of photocatalytic activity in the fourth catalytic cycle. In addition, the W-Ti-S (25) catalytic activity under direct sunlight irradiation was similar to that under artificial UV irradiation.

Long-acting photocatalytic degradation of crude oil in seawater via combination of TiO2 and N-doped TiO2/reduced graphene oxide

N-doped TiO₂/ reduced graphene oxide (N/TiO₂/rGO) composite was prepared and used together with the commercial TiO₂ for comparative research on photocatalytic degradation of crude oil in seawater. Five test conditions were designed including a combined catalyst of TiO₂ and N/TiO₂/rGO (4:1) under UV-A light irradiation with a duration of 28 days. The changing trend of the water-soluble fraction (WSF) of crude oil in seawater was monitored by ultraviolet spectroscopy and fluorescence spectroscopy as well as dissolved organic carbon (DOC) measurement. The SARA fractions of oil residues were analysed by column chromatography, and the chemical composition changes of saturates and aromatics were investigated by gas chromatography-mass spectroscopy (GC-MS). The results reveal that although it had high efficiency in the degradation of aromatics, the nano-TiO₂ tended to self-agglomerate, which enhanced agglomeration of crude oil, causing its catalytic process actually terminating within seven days. By comparison, the N/TiO₂/rGO composite consistently dispersed crude oil in the whole experimental duration, subsequently, it presented a higher photocatalytic degradation rate than TiO₂. The combination of TiO₂ and N/TiO₂/rGO (4:1) shows concerted catalysis on photocatalytic degradation of crude oil, and the oil degradation rate reached to 54.80% while the aromatic degradation rate was 74.83%. The fluorescent components in WSFs were preferentially degraded, and the degradation products of aromatic fraction were CO₂ and H₂O as well as saturates, mainly C₂₀∼C₃₁ alkanes. Considering its long-acting photocatalysis, the N/TiO₂/rGO composite possesses practical utilization potentiality together with TiO₂ in spilled oil treatment in the marine environment.

g-C3N4- and polyaniline-co-modified TiO2 nanotube arrays for significantly enhanced photocatalytic degradation of tetrabromobisphenol A under visible light

An ordered g-C₃N₄- and polyaniline-modified titanium oxide nanotube array (g-C₃N₄- and PANI-co-modified TiO₂ NTAs) was successfully synthesized and used as a photocatalyst. Polyaniline (PANI) was coated onto TiO₂ NTAs by electrochemical polycondensation, and g-C₃N₄ was deposited via the soaking adsorption method. The photocatalysts were examined by several technologies. The experiments demonstrated that the amount of g-C₃N₄ and PANI, as well as the initial pH value, had significant effects on the photocatalytic efficiency. The resulting photocatalysts exhibited high visible light photocatalytic ability for tetrabromobisphenol A (TBBPA) for two reasons. First, PANI expanded the light absorption into the visible region. Second, rapid and efficient separation of photoinduced charges from the photogenerated potential difference were produced at the contact interface of g-C₃N₄ and PANI-co-modified TiO₂ NTAs. The •OH, [Formula: see text] and h⁺ were dominant components for the photocatalytic degradation of TBBPA. In addition, the g-C₃N₄ and PANI-co-modified TiO₂ NTAs have excellent long-term stability.

Improvement of Power Conversion Efficiency of Quantum Dot-Sensitized Solar Cells by Doping of Manganese into a ZnS Passivation Layer and Cosensitization of Zinc-Porphyrin on a Modified Graphene Oxide/Nitrogen-Doped TiO2 Photoanode

It is vital to acquire power conversion efficiencies comparable to other emerging solar cell technologies by making quantum dot-sensitized solar cells (QDSSCs) competitive. In this study, the effect of graphene oxide (GO), nitrogen, manganese, and a porphyrin compound on the performance of QDSSCs based on a TiO₂/CdS/ZnS photoanode was investigated. First, adding GO and nitrogen into TiO₂ has a conspicuous impact on the cell efficacy. Both these materials reduce the recombination rate and expand the specific surface area of TiO₂ as well as dye loading, reinforcing cell efficiency value. The maximum power conversion efficiency of QDSSC with a GO N-doped photoelectrode was 2.52%. Second, by employing Mn²⁺ (5 and 10 wt %) doping of ZnS, we have succeeded in considerably improving cell performance (from 2.52 to 3.47%). The reason for this could be for the improvement of the passivation layer of ZnS by Mn²⁺ ions, bringing about to a smaller recombination of photoinjected electrons with either oxidized dye molecules or electrolyte at the surface of titanium dioxide. However, doping of 15 wt % Mn²⁺ had an opposite effect and somewhat declined the cell performance. Finally, a Zn-porphyrin dye was added to the CdS/ZnS by a cosensitization method, widening the light absorption range to the NIR (near-infrared region) (>700 nm), leading to the higher short-circuit current density (J _SC) and cell efficacy. Utilizing an environmentally safe porphyrin compound into the structure of QDSSC has dramatically enhanced the cell efficacy to 4.62%, which is 40% higher than that of the result obtained from the TiO₂/CdS/ZnS photoelectrode without porphyrin coating.

Plasma Nitriding of TiO2 Nanotubes: N-Doping in Situ Investigations Using XPS

The nitrogen doping of titanium dioxide nanotubes (TiO₂ NTs) was investigated as a result of well-controlled plasma nitriding of TiO₂ NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO₂ NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N-TiO₂ NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO₂ band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO₂ NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti-N bonds in the TiO₂ lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO₂ NTs after each step of the nitriding and annealing treatments.

Recent Progress in Biochar-Based Photocatalysts for Wastewater Treatment: Synthesis, Mechanisms, and Applications

Biochar (BC) is a carbon-rich material produced from pyrolysis of biomass. In addition to its low toxicity, environmental compatibility, and low cost, BC has the desired advantages of well-developed mesoporous structure and abundant surface functional groups. In recent years, BC-based photocatalysts (BCPs) have played a significant role in many environmental fields. In this paper, we highlight the current progress and several exciting results of BCPs by focusing on their synthesis, characterization, mechanisms, and applications in wastewater treatment. Details on various preparation methods include sol–gel, hydrothermal/solvothermal, ultrasound, calcination, and in situ methods are summarized and discussed. The underlying mechanisms and the applications of BCPs for different semiconductors are reviewed. Furthermore, some future trends and potentials are outlined.

The tesseract in two dimensional materials, a DFT approach

The tesseract contained 2D material, C₂₄Se₁₂, is an effective molecular sieve with high selectivity to recover helium from natural gas under ambient conditions.

TiO2 and Au-TiO2 Nanomaterials for Rapid Photocatalytic Degradation of Antibiotic Residues in Aquaculture Wastewater

Antibiotic residues in aquaculture wastewater are considered as an emerging environmental problem, as they are not efficiently removed in wastewater treatment plants. To address this issue, we fabricated TiO₂ nanotube arrays (TNAs), TiO₂ nanowires on nanotube arrays (TNWs/TNAs), Au nanoparticle (NP)-decorated-TNAs, and TNWs/TNAs, which were applied for assessing the photocatalytic degradation of eight antibiotics, simultaneously. The TNAs and TNWs/TNAs were synthesized by anodization using an aqueous NH₄F/ethylene glycol solution. Au NPs were synthesized by chemical reduction method, and used to decorate on TNAs and TNWs/TNAs. All the TiO₂ nanostructures exhibited anatase phase and well-defined morphology. The photocatalytic performance of TNAs, TNWs/TNAs, Au-TNAs and Au-TNWs/TNAs was studied by monitoring the degradation of amoxicillin, ampicillin, doxycycline, oxytetracycline, lincomycin, vancomycin, sulfamethazine, and sulfamethoxazole under ultraviolet (UV)-visible (VIS), or VIS illumination by LC-MS/MS method. All the four kinds of nanomaterials degraded the antibiotics effectively and rapidly, in which most antibiotics were removed completely after 20 min treatment. The Au-TNWs/TNAs exhibited the highest photocatalytic activity in degradation of the eight antibiotics. For example, reaction rate constants of Au-TNWs/TNAs for degradation of lincomycin reached 0.26 min⁻¹ and 0.096 min⁻¹ under UV-VIS and VIS irradiation, respectively; and they were even higher for the other antibiotics. The excellent photocatalytic activity of Au-TNWs/TNAs was attributed to the synergistic effects of: (1) The larger surface area of TNWs/TNAs as compared to TNAs, and (2) surface plasmonic effect in Au NPs to enhance the visible light harvesting.

Enhanced Photocatalytic Performance of Nitrogen-Doped TiO₂ Nanotube Arrays Using a Simple Annealing Process

Nitrogen-doped TiO₂ nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N₂ gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH₄F/ethylene glycol solution. The N-doping concentration (0–9.47 at %) can be varied by controlling N₂ gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm⁻². N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h⁻¹, which was a 125% improvement over that of TNAs (0.115 h⁻¹). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.

Rational Construction of LaFeO3 Perovskite Nanoparticle-Modified TiO2 Nanotube Arrays for Visible-Light Driven Photocatalytic Activity

LaFeO3 nanoparticle-modified TiO2 nanotube arrays were fabricated through facile hydrothermal growth. The absorption edge of LaFeO3 nanoparticle-modified TiO2 nanotube arrays displaying a red shift to ~540 nm was indicated by the results of diffuse reflectance spectroscopy (DRS) when compared to TiO2 nanotube arrays, which means that the sample of LaFeO3 nanoparticle-modified TiO2 nanotube arrays had enhanced visible light response. Photoluminescence (PL) spectra showed that the LaFeO3 nanoparticle-modified TiO2 nanotube arrays efficiently separated the photoinduced electron–hole pairs and effectively prolonged the endurance of photogenerated carriers. The results of methylene blue (MB) degeneration under simulated visible light illumination showed that the photocatalytic activity of LaFeO3 nanoparticle-modified TiO2 nanotube arrays is obviously increased. LaFeO3 nanoparticle-modified TiO2 nanotube arrays with 12 h hydrothermal reaction time showed the highest degradation rate with a 2-fold enhancement compared with that of pristine TiO2 nanotube arrays.

Design of a simple and novel photoelectrochemical aptasensor for detection of 3,3',4,4'-tetrachlorobiphenyl

In view of the urgent need of determining polychlorinated biphenyls in the environment, we developed a highly sensitive and selective photoelectrochemical (PEC) aptasensor for determination of 3,3',4,4'-tetrachlorobiphenyl (PCB77) by immobilizing aptamer on N-doped TiO₂ nanotubes (N-doped TiO₂ NTs). To improve analytical performance of the PEC sensor, the complementary DNA functionalized CdS quantum dots (DNA-CdS QDs) were introduced onto N-doped TiO₂ NTs by hybridization. In addition of PCB77, owing to high affinity of aptamer to PCB77, PCB77-aptamer complexes were formed by being bound of PCB77 whilst DNA-CdS QDs were released from the sensing surface. The complexes with poor conductivity hindered the interfacial electron transfer, leading to the photocurrent decrease. The more important is the release of DNA-CdS QDs enhanced the photocurrent decrease, playing the role of signal amplification. The photocurrent change was utilized to detect PCB77 quantitatively. The PEC aptasensor exhibited excellent analytical performance for detection of PCB77 with wide linear range of 0.1-100 ng/L and a low detection limit of 0.1 ng/L. It manifested outstanding selectivity for PCB77 in control experiments by employing six interferents which had similar structure or coexisted with PCB77. Besides, the PEC aptasensor was used to detect the content of PBC77 in the environment.

TiOxNy Modified TiO2 Powders Prepared by Plasma Enhanced Atomic Layer Deposition for Highly Visible Light Photocatalysis

In this work, TiN film deposited by plasma enhanced atomic layer deposition (PEALD) is adopted to modify the commercial anatase TiO₂ powders. A series of analyses indicate that the surface modification of 20, 50 and 100 cycles of TiN by PEALD does not change the morphology, crystal size, lattice parameters, and surface area of TiO₂ nano powders, but forms an ultrathin amorphous layer of nitrogen doped TiO₂ (TiO_xN_y) on the powder surfaces. This ultrathin TiO_xN_y can facilitate the absorption of TiO₂ in visible light spectrum. As a result, TiO_xN_y coated TiO₂ powders exhibit excellent photocatalytic degradation towards methyl orange under the visible light with good photocatalytic stability compared to pristine TiO₂ powders. TiO_xN_y (100 cycles PEALD TiN) coated TiO₂ powders exhibit the excellent photocatalytic activity with the degradation efficiency of 96.5% in 2 hours, much higher than that of pristine TiO₂ powder of only 4.4%. These results clearly demonstrate that only an ultrathin surface modification layer can dramatically improve the visible light photocatalytic activity of commercial TiO₂ powders. Therefore, this surface modification using ALD is an extremely promising route to prepare visible light active photocatalysts.

Single step synthesis of Schottky-like hybrid graphene - titania interfaces for efficient photocatalysis

The development of 2D nanomaterial coatings across metal surfaces is a challenge due to the mismatch between the metal microstructure and the nanoscale materials. The naturally occurring thin oxidative layer present across all metal surfaces, may lead to low adherence and connectivity. In this paper, graphene/titania/Titanium hybrid films were for the first time fabricated by a single step chemical vapour deposition process across Titanium foils. The presence of graphene as a dopant was found to enhance the photocatalytic performance of the final products, applied to the degradation of organic molecules and to lead to Schottky-like junction formation at the metal/oxide interface. These Schottky junctions, where vacancies are present across the titania material due to the graphene doping and where Ti³⁺ ions are predominantly located, yield enhanced catalytic performance. The highest degradation rate was found to be 9.66 × 10⁻⁶ min⁻¹, achieved by the sample grown at 700 °C for 5 min, which was 62% higher than the sample just treated at that temperature without graphene growth. This work provides evidence that graphene may be grown across pure Titanium metal and opens new avenues in biomedical devices design, tribological or separation applications.

CO2 Reduction by Photocatalysis on TiO2

This chapter focuses on the recent research progress on TiO2-based photocatalysts for CO2 reduction. The scope of this chapter for photoreduction of CO2 is set to focus on the most widely studied TiO2-based photocatalysts, composites, and systems since 1979. In addition, several important kinds of other related photocatalysts will be introduced briefly.

Review of Water-Assisted Crystallization for TiO2 Nanotubes

TiO₂ nanotubes (TNTs) have drawn tremendous attention owing to their unique architectural and physical properties. Anodizing of titanium foil has proven to be the most efficient method to fabricate well-aligned TNTs, which, however, usually produces amorphous TNTs and needs further thermal annealing. Recently, a water-assisted crystallization strategy has been proposed and investigated by both science and engineering communities. This method is very efficient and energy saving, and it circumvents the drawbacks of thermal sintering approach. In this paper, we review the recent research progress in this kind of low-temperature crystallization approach. Here, various synthetic methods are summarized, and the mechanisms of the amorphous-crystalline transformation are analyzed. The fundamental properties and applications of the low-temperature products are also discussed. Furthermore, it is proved that the water-assisted crystallization approach is not only applicable to TNTs but also to crystallizing other metal oxides.

Recent Advances in TiO2 -Based Nanostructured Surfaces with Controllable Wettability and Adhesion

Bioinspired surfaces with special wettability and adhesion have attracted great interest in both fundamental research and industry applications. Various kinds of special wetting surfaces have been constructed by adjusting the topographical structure and chemical composition. Here, recent progress of the artificial superhydrophobic surfaces with high contrast in solid/liquid adhesion has been reviewed, with a focus on the bioinspired construction and applications of one-dimensional (1D) TiO2-based surfaces. In addition, the significant applications related to artificial super-wetting/antiwetting TiO2-based structure surfaces with controllable adhesion are summarized, e.g., self-cleaning, friction reduction, anti-fogging/icing, microfluidic manipulation, fog/water collection, oil/water separation, anti-bioadhesion, and micro-templates for patterning. Finally, the current challenges and future prospects of this renascent and rapidly developing field, especially with regard to 1D TiO2-based surfaces with special wettability and adhesion, are proposed and discussed.

Hydrothermal synthesis of a Ba and Mg co-doped Bi12GeO20 photocatalyst with enhanced visible light catalytic activity

(Ba, Mg)-codoped Bi₁₂GeO₂₀ was successfully synthesized through the one-step hydrothermal method, and the band gap was greatly narrowed.

Inspired smart materials with external stimuli responsive wettability: a review

Recent progress in smart surfaces with responsive wettability upon external stimuli is reviewed and some of the barriers and potentially promising breakthroughs in this field are also briefly discussed.

Azeotropic distillation assisted fabrication of silver nanocages and their catalytic property for reduction of 4-nitrophenol

Monodisperse silver nanocages (AgNCs) with specific interiors were successfully synthesized by an azeotropic distillation (AD) assisted method and exhibited excellent catalytic activities for reduction of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) due to the unique hollow morphology and small thickness of the silver shell.