Nitrogen-Doped Titanium Dioxide as Visible-Light-Sensitive Photocatalyst: Designs, Developments, and Prospects

Z-scheme TiO2@Ti3C2/Cd0.5Zn0.5S nanocomposites with efficient photocatalytic performance via one-step hydrothermal route

Photocatalytic degradation of pollutants has been proved to be an effective strategy for wastewater treatment. Herein, TiO₂ nanoparticles were synthesized on a Ti₃C₂ matrix by in situ growth, forming Z-scheme TiO₂@Ti₃C₂/Cd_0.5Zn_0.5S (TO/CZS) multilevel structured nanocomposites via one-step hydrothermal route. The effects of hydrothermal temperature and Cd_0.5Zn_0.5S content on microstructure and properties of composites were assessed. TO/CZS nanocomposites were probed into phase composition, morphological and optical properties with x-ray diffractometer, infrared radiation, scanning electron microscope and UV-vis reflective spectra. Following the hydrothermal reaction at 160 °C for 12 h, TiO₂ nanoparticles of 30 nm in diameter were generated in situ on Ti₃C₂ lamina and Cd_0.5Zn_0.5S particles were evenly distributed on the Ti₃C₂ matrix. The photocatalytic activity of TO/CZS composites were evaluated, which found that degradation rate constant (k = 0.028 min^-1) of TO/CZS-40 on Rhodamine B was 5.19 times that of pure TiO₂ and 4.48 times that of Cd_0.5Zn_0.5S. Through anchoring Ti₃C₂ as an electron transition mediator and combination with TiO₂ and Cd_0.5Zn_0.5S, the new Z-scheme between TiO₂ oxidized by Ti₃C₂ and Cd_0.5Zn_0.5S establishes a multilevel structure of separating electron-hole pairs. This work demonstrates a valid way to control electrons and hole transfer directions efficiently through designing multilevel semiconductor structural designs.

Pyrochlore oxides as visible light-responsive photocatalysts

This perspective describes the use of pyrochlore oxides in photocatalysis with focus on the strategies to enhance their activity.

Hierarchical WO3 microflowers with tailored oxygen vacancies for boosting photocatalytic dye degradation

Hierarchical WO3 microflowers with tailored surface oxygen vacancies show a remarkably boosted activity toward visible-light-driven photocatalytic dye degradation.

Pyrene-containing conjugated organic microporous polymers for photocatalytic hydrogen evolution from water

Pyrene based conjugated microporous polymers (CMPs) as photocatalysts with promising H₂ production efficiencies and very high stability.

Metal-organic frameworks containing xanthene dyes for photocatalytic applications

Metal-organic frameworks (MOFs) have recently emerged as a new type of prospective photocatalytic material due to their characteristics such as tunable structures, pore modification, crystalline nature with eliminated structural defects, unique semiconductor properties, etc. However, most of these systems also suffer from low activity, high cost, and low visible light utilization. Xanthene dyes are eco-friendly organic dyes used in photocatalysis. They possess the advantages of low cost, low toxicity, and high visible light response; so, they can be directly used as building blocks to fabricate MOF materials or as proper cocatalysts to increase the absorbance of irradiation leading to the construction of a reasonable photocatalytic system. Herein, we have summarized the recent developments in the study of MOFs containing xanthene dyes for photocatalytic applications. The paper can be divided into two sections depending on whether the xanthene dyes are coordinated in the MOF structure: (i) MOFs synergized with xanthene dyes for photocatalytic applications and (ii) MOFs with xanthene dyes incorporated within ligand backbones for photocatalytic applications. Moreover, in this paper, the present challenges and future opportunities in this field are also discussed.

Modeling and Experimental Studies on Adsorption and Photocatalytic Performance of Nitrogen-Doped TiO2 Prepared via the Sol–Gel Method

Nitrogen-doped TiO2 has a great potential as a photocatalyst under visible light irradiation with applications in the removal of air and water pollutants, and the treatment of bacterial contaminations. In this study, nitrogen-doped TiO2 nanoparticles were synthesized via the sol–gel method and a post-annealing heat treatment approach. The effects of annealing treatment on the photocatalyst crystalline size and degree of crystallinity were analyzed. Methylene blue dye was used as the model water contaminant for the evaluation of the photoactivity of the synthesized nitrogen-doped TiO2 nanoparticles. The degradation of methylene blue was attributed to three mechanisms, i.e., adsorption, photocatalysis, and direct light photolysis. A kinetic model was developed to distinguish the impact of these three different mechanisms on the removal of contaminants. Adsorption and photocatalysis are heterogeneous processes for removing water organic contaminants. The characterization analysis demonstrates that they are relevant to the microstructures and surface chemical compositions of nitrogen-doped TiO2 photocatalysts. The processing–structure–performance relationship helped to determine the optimal processing parameters for nitrogen-doped TiO2 photocatalyst to achieve the best performance. While we used methylene blue as the model contaminant, the generalized quantitative model framework developed in this study can be extended to other types of contaminants after proper calibration.

Modified Hydrothermal Route for Synthesis of Photoactive Anatase TiO2/g-CN Nanotubes from Sludge Generated TiO2

Titania nanotube was prepared from sludge generated TiO2 (S-TNT) through a modified hydrothermal route and successfully composited with graphitic carbon nitride (g-CN) through a simple calcination step. Advanced characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, UV/visible diffuse reflectance spectroscopy, and photoluminescence analysis were utilized to characterize the prepared samples. A significant improvement in morphological and optical bandgap was observed. The effective surface area of the prepared composite increased threefold compared with sludge generated TiO2. The optical bandgap was narrowed to 3.00 eV from 3.18 in the pristine sludge generated TiO2 nanotubes. The extent of photoactivity of the prepared composites was investigated through photooxidation of NOx in a continuous flow reactor. Because of extended light absorption of the as-prepared composite, under visible light, 19.62% of NO removal was observed. On the other hand, under UV irradiation, owing to bandgap narrowing, although the light absorption was compromised, the impact on photoactivity was compensated by the increased effective surface area of 153.61 m2/g. Hence, under UV irradiance, the maximum NO removal was attained as 32.44% after 1 h of light irradiation. The proposed facile method in this study for the heterojunction of S-TNT and g-CN could significantly contribute to resource recovery from water treatment plants and photocatalytic atmospheric pollutant removal.

The Photocatalytic and Antibacterial Performance of Nitrogen-Doped TiO2: Surface-Structure Dependence and Silver-Deposition Effect

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO₂ catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and sol–gel (NT-U) methods, respectively. To increase their photocatalytic and antibacterial efficiencies, various amounts of silver were successfully loaded on the surfaces of these catalysts by using a facile photo-deposition technique. Their physical and chemical properties were evaluated by using scanning electron microscopy (SEM), transmission electron microscopy–energy dispersive X-ray spectroscopy (TEM–EDS), Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). The photocatalytic performances of the synthesized catalysts were examined in coumarin and 1,4-hydroquinone solutions. The results showed that the hollow structure of NT-A played an important role in obtaining high specific surface area and appreciable photoactivity. In addition, Ag-loading on the surface of non-hollow structured NT-U could double the photocatalytic performance with an optimum Ag concentration of 10⁻⁶ mol g⁻¹, while a slight but monotonous decrease was caused in this respect for the hollow surface of NTA upon increasing Ag concentration. Comparing the catalysts with different structures regarding the photocatalytic performance, silverized non-hollow NT-U proved competitive with the hollow NT-A catalyst without Ag-loading for efficient visible-light-driven photocatalytic oxidative degradations. The former one, due to the silver nanoparticles on the catalyst surface, displayed an appreciable antibacterial activity, which was comparable to that of a reference material practically applied for disinfection in polymer coatings.

WITHDRAWN: Fabrication of erbium and nitrogen modified TiO2/diatomaceous earth as a sunlight-driven floating photocatalyst for ibuprofen mitigation

This article has been withdrawn at the request of the authors. Zhaohong Zhang is listed as an author on the manuscript but has informed the journal that this occurred without their consent or knowledge of the submission, and the email address provided was fake. Zhaohong Zhang does not support the scientific conclusions of the article. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

A two-dimensional h-BN/C2N heterostructure as a promising metal-free photocatalyst for overall water-splitting

The construction of a heterostructure (HS) is an effective strategy to modulate the desired properties of two-dimensional (2D) materials and to extend their applications. In this paper, based on the density functional theory, we predict a metal-free type-II HS formed by h-BN and C₂N single layers. The h-BN/C₂N HS possesses a smaller bandgap than individual h-BN and C₂N single layers, and it exhibits excellent visible light absorption. Importantly, its band edge positions satisfy the requirements for spontaneous water-splitting. With the assistance of the built-in electric field across the HS and the band offset, the photoinduced carriers can be readily spatially separated. Free energy calculations indicate the high catalytic activity for water oxidation and reduction reactions. The performance can be further enhanced by strain, which modulates the bandgap and the band edge positions of the HS. The band alignment may undergo a transition from type-I to type-II under strain, offering an effective switch for the reaction. The appropriate bandgap, suitable band edge positions, and effective carrier separation make the h-BN/C₂N HS a promising candidate for use as a photocatalyst in water-splitting.

High UV-Vis-NIR Light-Induced Antibacterial Activity by Heterostructured TiO2-FeS2 Nanocomposites

PURPOSE

Antibiotic resistance issues associated with microbial pathogenesis are considered to be one of the most serious current threats to health. Fortunately, TiO2, a photoactive semiconductor, was proven to have antibacterial activity and is being widely utilized. However, its use is limited to the short range of absorption wavelength.

METHODS

In this work, heterostructured TiO2-FeS2 nanocomposites (NCs) were successfully prepared by a facile solution approach to enhance light-induced antibacterial activity over a broader absorption range.

RESULTS

In TiO2-FeS2 NCs, FeS2 NPs, as light harvesters, can effectively increase light absorption from the visible (Vis) to near-infrared (NIR). Results of light-induced antibacterial activities indicated that TiO2-FeS2 NCs had better antibacterial activity than that of only TiO2 nanoparticles (NPs) or only FeS2 NPs. Reactive oxygen species (ROS) measurements also showed that TiO2-FeS2 NCs produced the highest relative ROS levels. Unlike TiO2 NPs, TiO2-FeS2 NCs, under light irradiation with a 515-nm filter, could absorb light wavelengths longer than 515 nm to generate ROS. In the mechanistic study, we found that TiO2 NPs in TiO2-FeS2 NCs could absorb ultraviolet (UV) light to generate photoinduced electrons and holes for ROS generation, including ⋅O2 - and ⋅OH; FeS2 NPs efficiently harvested Vis to NIR light to generate photoinduced electrons, which then were transferred to TiO2 NPs to facilitate ROS generation.

CONCLUSION

TiO2-FeS2 NCs with superior light-induced antibacterial activity could be a promising antibacterial agent against bacterial infections.

CdS@MoS2 Hetero-structured Nanocomposites Are Highly Effective Photo-Catalysts for Organic Dye Degradation

CdS@MoS₂ hetero-structured nanocomposites (HSNPs) were successfully synthesized via a hydrothermal approach. The morphology and crystal structure of these composites as well as their ability to act as photocatalysts for the degradation of methylene blue were investigated using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and UV-vis absorption spectroscopy. The developed CdS@MoS₂ nanocomposites exhibited an 80% degradation rate with 30 min of visible light irradiation. To characterize the basis of the photocatalytic properties of these materials, the transient photocurrent densities were determined for the CdS@MoS₂ HSNPs and pure dendritic CdS nanotrees. The results suggest that the photocatalytic activity may reflect electron transfer between the conduction band maximum of CdS and MoS₂. Additionally, the improved visible light absorption, decreased electron-hole pair recombination, and enhanced surface area for more effective dye absorption likely contribute to improved photocatalytic performance.

Visible Light Photocatalytic Activity of Thin Film Coated on Polycarbonate Surface with N- and Ni-Codoped TiO2 Photocatalyst

N- and Ni-coated TiO2 (NNT) were prepared by a facile sol-gel method as a photosensitive photocatalyst to visible light. NNT sol was used to coat the surface of an LED lamp cap and body made of polycarbonate with a thin NNT film. The coated thin film was dried in an oven at 130 °C. This NNT thin film had an amorphous TiO2 structure and absorbed 600 nm of visible light. The decomposition properties of formaldehyde on the NNT photocatalyst after irradiation with visible light were investigated. The LED lamp was irradiated with visible light at 500–620 nm and 6 W. Formaldehyde was decomposed by a photocatalytic reaction by visible light irradiation on the NNT-coated polycarbonate surface. Escherichia coli (E. coli), Staphylococcus aureus, and Pseudomonas aeruginosa were also used to examine the sterilizing properties of pathogenic bacteria using an LED lamp kit. The pathogenic bacteria on the NNT-coated polycarbonate surface were sterilized by irradiation with visible light.

Fine Characterization of Natural SiO2-Doped Catalyst Derived from Mussel Shell with Potential Photocatalytic Performance for Organic Dyes

In this work, a SiO2-doped natural photocatalyst derived from waste mussel shell (HAS) was prepared by acidification. The as-prepared sample was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-visible diffuse-reflectance spectrum (UV-vis DRS), and Differential scanning and thermogravimetric analyses (DTA/TGA). The results exhibited that HAS was mesopores nanomaterial consisting of uneven arranged rod-like structure, the dominant component of HAS was SiO2 with a large number of hydroxyl groups, and a variety of transition metals uniformly distributed in HAS. Rhodamine B (RhB) and methylene blue (MB) removal efficiencies (equal to 92.59% and 99.14%, respectively) were observed under the HAS presence when exposed to the visible light. The degradation products were analyzed using liquid Chromatograph Mass Spectrometer (LC-MS) and Total Organic Carbon (TOC), among which, MB was degraded by demethylation and deamination, and RhB was degraded by N-deethylation and conjugate structure destruction. After four successive recycles, the removal efficiency of RhB and MB are still reach 86.103% and 75.844%. This study indicated that the mussel shells might be suggested as a novel natural photocatalyst in the application of dye wastewater treatment.

Enhanced Adhesion Energy at Oxide/Ag Interfaces for Low-Emissivity Glasses: Theoretical Insight into Doping and Vacancy Effects

Low-emissivity glasses rely on multistacked architectures with a thin silver layer sandwiched between oxide layers. The mechanical stability of the silver/oxide interfaces is a critical parameter that must be maximized. Here, we demonstrate by means of quantum-chemical calculations that a low work of adhesion at interfaces can be significantly increased via doping and by introducing vacancies in the oxide layer. For the sake of illustration, we focus on the ZrO₂(111)/Ag(111) interface exhibiting a poor adhesion in the pristine state and quantify the impact of introducing n-type dopants or p-type dopants in ZrO₂ and vacancies in oxygen atoms (nV_O; with n = 1, 2, 4, 8, 10, 16), zirconium atoms (mV_Zr; with m = 1, 2, 4, 8), or both (nV_O + mV_Zr; with m/n = 1:2, 1:4, 2:2, 2:4). In the case of doping, interfacial electron transfer promotes an increase in the work of adhesion, from initially 0.16 to ∼0.8 J m^-2 (n-type) and ∼2.0 J m^-2 (p-type) at 10% doping. A similar increase in the work of adhesion is obtained by introducing vacancies, e.g., V_O [V_Zr] in the oxide layer yields a work of adhesion of ∼1.5-2.0 J m^-2 at 10% vacancies. An increase is also observed when mixing V_O and V_Zr vacancies in a nonstoichiometric ratio (nV_O + mV_Zr; with 2n ≠ m), while a stoichiometric ratio of V_O and V_Zr has no impact on the interfacial properties.

Insights into Designing Photocatalysts for Gaseous Ammonia Oxidation under Visible Light

Excessive emission of ammonia (NH₃) gives rise to a number of negative effects on the environment and human health. Photocatalysis is an efficient method to eliminate gaseous NH₃; however, photocatalytic oxidation (PCO) of NH₃ in the visible light region has not been achieved to date. Herein, we test a set of typical visible-light-sensitive photocatalysts (N-TiO₂, g-C₃N₄, and Ag₃PO₄) for NH₃ oxidation and reveal for the first time that the semiconductor Ag₃PO₄ can harness visible light to realize ambient NH₃ oxidation. Combining the activity testing results with the photochemical properties of samples, we confirm that photoexcited holes are responsible for triggering the initial key step of NH₃ oxidation (NH₃ to ^•NH₂), and therefore, the redox potential of photoexcited holes plays the decisive role in the reaction. We propose that an active visible light photocatalyst for NH₃ oxidation requires both a suitable band gap for visible light response and a low valence band edge associated with a high oxidation potential for activating NH₃ to ^•NH₂. Our findings provide new insights into the PCO of pollutants under visible light and will benefit future design of more efficient visible-light-sensitive photocatalysts.

Characteristics of hydrogen production by photocatalytic water splitting using liquid phase plasma over Ag-doped TiO2 photocatalysts

Hydrogen production from water was investigated by applying liquid plasma (LPP) to photocatalytic splitting of water. The optical properties of LPP due to water emission were also evaluated. The correlation between the optical properties of plasma and the formation of active species in water was investigated with the photocatalytic activity of hydrogen production. TiO₂ was also doped with Ag to evaluate the effect of enhancing photocatalytic activity. The photocatalytic activity was evaluated by the rate of hydrogen production, and the effect of hydrogen formation was also investigated by injecting methanol as an additive. As a result of examining the luminescence properties of LPP, it showed high luminescence in the 309 nm UV region and the 656 nm visible region. The hydrogen doping rate was increased in the Ag-doped TiO₂ photocatalyst. Ag-doped TiO₂ has wider light absorption into the visible region and narrower band gap. Due to these properties, the rate of hydrogen generation is superior to TiO₂ photocatalysts. The photochemical reaction with LPP and photocatalyst in aqueous solution with CH₃OH showed a significant increase in hydrogen production rate. The increase in hydrogen production by injection of additives is because the optical properties of generating OH radicals are improved and CH₃OH is decomposed to act as an electron donor to improve hydrogen production.

A Blinking Mesoporous TiO2-x Composed of Nanosized Anatase with Unusually Long-Lived Trapped Charge Carriers

A mesoporous TiO_2-x material comprised of small, crystalline, vacancy-rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer-derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO_2-x . When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red-shift in their UV/Vis absorption and long-lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO₂ reduction.

Synergistic Effects of Co-Doping on Photocatalytic Activity of Titanium Dioxide on Glucose Conversion to Value-Added Chemicals

Development of conversion of biomass derivatives in combination with utilization of solar energy by photocatalysts is a promising alternative strategy for biorefineries. The photocatalytic reaction could convert glucose to a mixture of value-added chemicals under UV irradiation. Modifications of titanium dioxide (TiO₂) nanoparticles by metal or metalloid (i.e., B and Ag) and nonmetal (i.e., N) dopants were carried out. The effects of co-doping (i.e., B/N and Ag/N) on physicochemical characteristics of the modified photocatalysts, photocatalytic glucose conversion, and the yields of the target chemical products (i.e., gluconic acid, xylitol, arabinose, and formic acid) were studied. The doping of the photocatalysts by different single dopants could improve the performance in terms of productivity and was further enhanced by the synergism from co-doping. The improvement in catalytic performances of the photocatalysts corresponded with the alterations in physicochemical characteristics of the catalysts resulting from the dopants.

Charge Trapping Process in Photoexcited Nitrogen-Doped Titanium Oxides

We present a first-principles study on the structural changes induced by charge trapping that occurs after photoexcitation in nitrogen-doped titanium oxide (N-TiO₂). The charge trapping site and the corresponding K edge EXAFS spectra of Ti atoms were predicted and compared with those obtained by an experiment under ultraviolet (UV) light excitation. The results indicate that charge trapping occurs in the neighborhood of the oxygen vacancy (O-vac) sites. Furthermore, our calculations show that the O-vac site significantly affects the EXAFS spectra, while substitutional nitrogen doping for an oxygen site in the vicinity of the O-vac site is insensitive in the EXAFS spectra. Based on this observation combined with the knowledge from previous experiments, we propose a charge trapping process where the UV light-excited electron migrates at the O-vac site in bulk (∼300 ps) while the visible light-excited electron (N 2p → Ti 3d) is immediately trapped at the O-vac site neighboring the N site (∼1 ps).

Impact of Titanium Dioxide (TiO2) Modification on Its Application to Pollution Treatment—A Review

A high-efficiency method to deal with pollutants must be found because environmental problems are becoming more serious. Photocatalytic oxidation technology as the environmentally-friendly treatment method can completely oxidate organic pollutants into pollution-free small-molecule inorganic substances without causing secondary pollution. As a widely used photocatalyst, titanium dioxide (TiO2) can greatly improve the degradation efficiency of pollutants, but several problems are noted in its practical application. TiO2 modified by different materials has received extensive attention in the field of photocatalysis because of its excellent physical and chemical properties compared with pure TiO2. In this review, we discuss the use of different materials for TiO2 modification, highlighting recent developments in the synthesis and application of TiO2 composites using different materials. Materials discussed in the article can be divided into nonmetallic and metallic. Mechanisms of how to improve catalytic performance of TiO2 after modification are discussed, and the future development of modified TiO2 is prospected.

Frequency-Agile Low-Temperature Solution-Processed Alumina Dielectrics for Inorganic and Organic Electronics Enhanced by Fluoride Doping

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlO_x) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlO_x film capacitance of 166 ± 11 nF/cm² is stable over a 10^-1-10⁴ Hz frequency range, far more stable than that of neat AlO_x films (capacitance = 336 ± 201 nF/cm²) which falls from 781 ± 85 nF/cm² to 104 ± 4 nF/cm² over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlO_x dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV-vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

Phase-Selective and Localized TiO2 Coating on Additive and Wrought Titanium by a Direct Laser Surface Modification Approach

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO2) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.

Design a new photocatalyst of sea sediment/titanate to remove cephalexin antibiotic from aqueous media in the presence of sonication/ultraviolet/hydrogen peroxide: Pathway and mechanism for degradation

The aim of the current study was directed to develop a new sea sediment/titanate photocatalyst to remove cephalexin from aqueous media in the presence of ultraviolet (UV) light, hydrogen peroxide (H₂O₂), and ultrasonic waves. The influence of furnace temperature (300, 350, 400, and 500 °C), furnace residence time (1, 2, 3, and 4 h), and ratio of sea sediment: titanium (0-6 v: w) on the physicochemical properties and the cephalexin removal by the sea sediment/titanate photocatalyst was explored. The technique of FTIR, SEM/EDX, XRD, BET, BJH, and Mapping was used to determine the physicochemical properties of the generated photocatalyst. The maximum cephalexin removal (94.71%) was obtained at the furnace temperature of 500 °C, the furnace residence time of 2 h, and the sea sediment: titanium ratio of 1:6 (=12 mL TiO₂/2 g sea sediment). According to the acquired results, the surface area of the optimized catalyst, namely Cat-500-2-12, was computed to be 52.29 m²/g. The crystallite size of titanium oxide on the optimum photocatalyst was calculated ~17.68 nm. The FTIR test confirmed the presence of C=C, O-H, C=O, C-S, and C-H functional groups in the photocatalyst. The transformation pathway for the degradation of cephalexin by the developed system was drawn. The present investigation showed that the developed technique (sea sediment/titanate-UV-H₂O₂-ultrasonic) could be used as a promising alternative for attenuating cephalexin from aqueous solutions.

Nitrogen-doped semiconducting oxides. Implications on photochemical, photocatalytic and electronic properties derived from EPR spectroscopy

Engineering defects in semiconducting metal oxides is a challenge that remains at the forefront of materials chemistry research. Nitrogen has emerged as one of the most attractive elements able to tune the photochemical and photocatalytic properties of semiconducting oxides, boosting visible-light harvesting and charge separation events, key elements in promoting solar driven chemical reactions. Doping with nitrogen is also a strategy suggested to obtain p-type conduction properties in oxides showing n-type features in their pristine state and to impart collective magnetic properties to the same systems. Here, we review the evolution in the understanding of the role of nitrogen doping in modifying the photochemical and electronic properties of the most common semiconducting oxides used in mentioned applications including: TiO2, ZnO, SnO2 and zirconium titanates. With an emphasis on polycrystalline materials, we highlight the unique role of Electron Paramagnetic Resonance (EPR) spectroscopy in the direct detection of open-shell N-based defects and in the definition of their structural and electronic properties. Synthetic strategies for the insertion of nitrogen defects in the various matrices are also discussed, along with the influence of the corresponding low-lying energy states on the general electronic properties of the doped solids.

A nine-fold enhancement of visible-light photocatalytic hydrogen production of g-C3N4 with TCNQ by forming a conjugated structure

Photocatalytic hydrogen evolution by water splitting has become a very effective way to solve the energy crisis. For use in that process, graphitic carbon nitride (g-C₃N₄) has drawn much attention for its response in the visible region. However, its insufficient sunlight absorption efficiency and easy recombination of photoinduced carriers restrict its photocatalytic activity. Herein, we demonstrate a two-step liquid ultrasonic method in water to synthesize a series of tetracyanoquinodimethane (TCNQ)-C₃N₄ photocatalysts aiming to form a conjugated structure by 7,7,8,8-TCNQ. g-C₃N₄ was treated with APTES firstly on its surface in order to give a better interface contact with TCNQ. Benefiting from the conjugation effect between TCNQ and g-C₃N₄, the separation and transport efficiency of photogenerated carriers were significantly improved. Besides, introducing TCNQ also broadened the absorption region. Both of these points lead to the enhancement of photocatalytic H₂ production rate, with the optimized 5% TCNQ-C₃N₄ giving a rate nearly 9.48 times that of pure g-C₃N₄. Also, 5% TCNQ-C₃N₄ (U) was prepared with unmodified g-C₃N₄, which exhibited a rate only 6.87 times that of pure g-C₃N₄, thus validating the necessity of surface modification. Our work reveals that the rational conjugated structure could modulate the electrical and optical properties of g-C₃N₄, yielding an improvement of photocatalytic activities.

Mechanistic Insights into Visible Light-Induced Direct Hydroxylation of Benzene to Phenol with Air and Water over Pt-Modified WO3 Photocatalyst

Activation of C(sp2)-H in aromatic molecules such as benzene is one of the challenging reactions. The tungsten trioxide supported Pt nanoparticles (Pt-WO3) exhibited hydroxylation of benzene in the presence of air and H2O under visible-light (420 < λ < 540 nm) irradiation. The photocatalytic activities (yields and selectivity of phenol) were studied under several experimental conditions. Furthermore, investigations of mechanistic insight into hydroxylation of benzene have been carried out by analyses with apparent quantum yields (AQY), an H218O isotope-labeling experiment, kinetic isotope effects (KIE), electrochemical measurements and density functional theory (DFT) calculations. It was proposed that dissociation of the O–H bond in H2O is the rate-determining step. Furthermore, the substitution of the OH derived from H2O with H abstracted from benzene by photo-formed H2O2 indicated a mechanism involving a push-pull process for the hydroxylation of benzene into phenol.

Photocatalytic CO2 Reduction under Visible-Light Irradiation by Ruthenium CNC Pincer Complexes

Photocatalytic CO₂ reduction using a ruthenium photosensitizer, a sacrificial reagent 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H), and a ruthenium catalyst were carried out. The catalysts contain a pincer ligand, 2,6-bis(alkylimidazol-2-ylidene)pyridine (CNC) and a bipyridine (bpy). The photocatalytic reaction system resulted in HCOOH as a main product (selectivity 70-80 %), with a small amount of CO, and H₂ . Comparative experiments (a coordinated ligand (NCMe vs. CO) and substituents (tBu vs. Me) of the CNC ligand in the catalyst) were performed. The turnover number (TON_HCOOH ) of carbonyl-ligated catalysts are higher than those of acetonitrile-ligated catalysts, and the carbonyl catalyst with the smaller substituents (Me) reached TON_HCOOH =5634 (24 h), which is the best performance among the experiments.

Cu/N-codoped TiO2 prepared by the sol-gel method for phenanthrene removal under visible light irradiation

Cu/N-codoped TiO₂ nanoparticles were prepared by the modified sol-gel method, to study its efficiency for the removing of polyaromatic hydrocarbon (phenanthrene) from an aqueous solution. Urea and copper sulfate pentahydrate were used as sources of doping element for Cu/N-codoped TiO₂, respectively. The characterizations of the nanoparticles were done by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectra. XRD revealed that all the nanoparticles were indexed to the anatase phase structure, with crystallite size range from 11 to 30 nm, which decreased with the doping of copper and nitrogen. The photocatalytic activities of Cu/N-codoped TiO₂ showed the highest activities than other TiO₂ nanoparticles (TiO₂ and N-doped TiO₂). The photodegradation efficiency of Cu/N-codoped TiO₂ on phenanthrene under visible light irradiation was slightly higher (96%) comparing to UV light irradiation (94%). Cu/N-codoped TiO₂ was found to be very efficient and economical for phenanthrene removal, because the smallest amount of Cu/N-codoped TiO₂ exhibited the best removal efficiency on phenanthrene.

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.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Electrons and Hydroxyl Radicals Synergistically Boost the Catalytic Hydrogen Evolution from Ammonia Borane over Single Nickel Phosphides under Visible Light Irradiation

From the perspective of tailoring the reaction pathways of photogenerated charge carriers and intermediates to remarkably enhance the solar‐to‐hydrogen energy conversion efficiency, we synthesized the three low‐cost semiconducting nickel phosphides Ni₂P, Ni₁₂P₅ and Ni₃P, which singly catalyzed the hydrogen evolution from ammonia borane (NH₃BH₃) in the alkaline aqueous solution under visible light irradiation at 298 K. The systematic investigations showed that all the catalysts had higher activities under visible light irradiation than in the dark and Ni₂P had the highest photocatalytic activity with the initial turnover frequency (TOF) value of 82.7 min⁻¹, which exceeded the values of reported metal phosphides at 298 K. The enhanced activities of nickel phosphides were attributed to the visible‐light‐driven synergistic effect of photogenerated electrons (e⁻) and hydroxyl radicals (^.OH), which came from the oxidation of hydroxide anions by photogenerated holes. This was verified by the fluorescent spectra and the capture experiments of photogenerated electrons and holes as well as hydroxyl radicals in the catalytic hydrogen evolution process.