TiO2 photocatalysis: Design and applications

A New Calibration Circuit Design to Reduce Drift Effect of RuO2 Urea Biosensors

The goal of this study was to reduce the drift effect of RuO₂ urea biosensors. A new calibration circuit (NCC) based on the voltage regulation technique with the advantage of having a simple structure was presented. To keep its simplicity, the proposed NCC was composed of a non-inverting amplifier and a voltage calibrating circuit. A ruthenium oxide (RuO₂) urea biosensor was fabricated to test the calibrating characteristics of the drift rate of the proposed NCC. The experiment performed in this study was divided into two main stages. For the first stage, a sound RuO₂ urea biosensor testing environment was set-up. The RuO₂ urea sensing film was immersed in the urea solution for 12 h and the response voltage was measured using the voltage-time (V-T) measurement system and the proposed NCC. The results of the first stage showed that the RuO₂ urea biosensor has an average sensitivity of 1.860 mV/(mg/dL) and has a linearity of 0.999 which means that the RuO₂ urea biosensor had been well fabricated. The second stage of the experiment verified the proposed NCC's functions, and the results indicated that the proposed NCC reduced the drift rate of RuO₂ urea biosensor to 0.02 mV/hr (98.77% reduction).

Preparation and Properties of CaCO3-Supported Nano-TiO2 Composite with Improved Photocatalytic Performance

In order to improve the photocatalytic degradation efficiency of nano-TiO₂, reduce its usage and realize recycling and reuse, CaCO₃-TiO₂ composite photocatalyst was prepared with calcium carbonate (CaCO₃) and TiO₂ in a grinding machine through the integration of grinding depolymerization, dispersion and particle composition. The photocatalytic degradation performance, recycling performance, structure and morphology of CaCO₃-TiO₂ were studied. The interaction mechanism between CaCO₃ and TiO₂ and the improvement mechanism for the photocatalytic performance of TiO₂ were also discussed. The results show that under the UV light irradiation for 20 and 40 min, the degradation efficiency of methyl orange by the composite photocatalyst with 40% TiO₂ (mass fraction) was 90% and 100%, respectively. This was similar to that of pure TiO₂, and the performance of the composite photocatalyst was almost unchanged after five cycles. CaCO₃-TiO₂ is formed by the uniform loading of nano-TiO₂ particles on the CaCO₃ surface, and the nano-TiO₂ particles are well dispersed. Due to the facts that the dispersion of nano-TiO₂ is improved in the presence of CaCO₃ and the charge transport capability is improved through the interfacial chemical bonds between CaCO₃ and TiO₂, the formation of this complex is an intrinsic mechanism to improve the photocatalytic efficiency of nano-TiO₂ and reduce its usage in application processes.

Graphene modified anatase/titanate nanosheets with enhanced photocatalytic activity for efficient degradation of sulfamethazine under simulated solar light

Graphene modified anatase/titanate nanosheets (G/A/TNS) synthesized through hydrothermal treatment were used for solar-light-driven photocatalytic degradation of a typical pharmaceutically active compound, sulfamethazine (SMT). The optimal material was synthesized with 0.5 wt% of graphene loading (G/A/TNS-0.5), which could efficiently degrade 96.1% of SMT at 4 h. G/A/TNS-0.5 showed enhanced photocatalytic activity compared with the neat anatase and unmodified anatase/titanate nanosheets (A/TNS). UV-vis diffuse reflection spectra indicated that G/A/TNS-0.5 had a lower energy band gap (E_g) of 2.8 eV than A/TNS (3.1 eV). The grafted graphene acted as an electron transfer mediator after photoexcitation, resulting in inhibition on rapid recombination of electron-hole pairs. More importantly, architecture of graphene and titanate nanosheets both with two-dimensional structures greatly facilitated the photoexcited electron transfer. •OH and ¹O₂ were the primary reactive oxygen species (ROS) to SMT degradation. Fukui index (f^-) derived from density functional theory (DFT) calculation predicted the active sites on SMT molecule, and then SMT degradation pathway was proposed by means of intermediates identification and theoretical calculation. Furthermore, G/A/TNS-0.5 could be well reused and 90.5% of SMT was also degraded after five runs. The developed new photocatalysts show great potential for degradation of emerging organic contaminants through photocatalysis under solar light.

Recent Advances in TiO2 Films Prepared by Sol-gel Methods for Photocatalytic Degradation of Organic Pollutants and Antibacterial Activities

Photocatalysis has recently emerged as an advanced, green, and eco-friendly process for the treatment of wastewater and air, and antimicrobial disinfection applications. In this context, TiO2 nanostructures have been shown to be the prominent photocatalyst candidates due to their low cost, non-toxicity, and ease of fabrication. This review highlights the investigation and development of TiO2 photocatalyst film by sol-gel method with special emphasis on the photodecolorization of synthetic dyes and antibacterial activities. Furthermore, various synthesis methods for the preparation of TiO2 films and their advantages, as well as limitations, are summarized. Finally, recent advances in TiO2 films by sol-gel method for dye degradation and antibacterial activities, challenges, and future perspective are discussed.

Functionalized TiO2 Nanorods on a Microcantilever for the Detection of Organophosphorus Chemical Agents in Air

We report the fabrication of nanostructured microcantilevers employed as sensors for the detection of organophosphorus (OPs) vapors. These micromechanical sensors are prepared using a two-step procedure first optimized on a silicon wafer. TiO₂ one-dimensional nanostructures are synthesized at a silicon surface by a solvothermal method and then grafted with bifunctional molecules having an oxime group known for its strong affinity with organophosphorus compounds. The loading of oxime molecules grafted on the different nanostructured surfaces was quantified by UV spectroscopy. It has been found that a wafer covered by vertically aligned rutile TiO₂ nanorods (NRs), with an average length and width of 9.5 μm and 14.7 nm, respectively, provides an oxime function density of 360 nmol cm^-2. The optimized TiO₂ nanorod synthesis was successfully reproduced on the cantilevers, leading to a homogeneous and reproducible TiO₂ NR film with the desired morphology. Thereafter, oxime molecules have been successfully grafted on the nanostructured cantilevers. Detection tests were performed in a dynamic mode by exposing the microcantilevers to dimethyl methylphosphonate (a model compound of toxic OPs agents) and following the shift of the resonant frequency. The nanostructure and the presence of the molecules on a TiO₂ NR surface both improve the response of the sensors. A detection limit of 2.25 ppm can be reached with this type of sensor.

The preparation of amorphous TiO2 doped with cationic S and its application to the degradation of DCFs under visible light irradiation

An amorphous S-doping TiO₂ catalyst [S-TiO₂ (300)] with visible light catalytic activity was successfully prepared via a sol-gel method with low-temperature calcination (300 °C) using thiourea as the sulfur source. The S-TiO₂ (300) catalyst showed great performance in degrading the recalcitrant pharmaceutical, diclofenac (DCF). 93% of the target pollutant DCF degraded in 4 h under visible light irradiation. Both the amorphous form of the catalyst and cationic S-doping (with a coordinated structure) contributed to narrowing the band gap. As a result, the photocatalytic activity of S-TiO₂ (300) was significantly enhanced under visible light irradiation. In addition, oxidative species such as photogenic cavitation (h+), OH and O₂^- were proved to participate in the photodegradation process, attacking COOH group and NH bond, degraded DCF into low molecule organic gradually.

One-pot sonochemical synthesis of 3D flower-like hierarchical AgCl microsphere with enhanced photocatalytic activity

A highly uniform 3D flower-like hierarchical AgCl microsphere was prepared by sonochemical method with the existence of β-dextrin. The 3D flower-like hierarchical structure can be ascribed to the existence of β-dextrin, which provides nucleation sites for the growth of nanosheets because of the strong interaction between β-dextrin and Ag⁺. The 3D flower-like hierarchical AgCl microspheres were assembled by numerous interleaving nanosheet petals with small thickness. Benefiting from the unique structural features, the as-prepared 3D flower-like hierarchical AgCl microsphere exhibited higher degradation efficiency with degrading 98.17% of methylene blue (MB) and 88.50% of tetracycline (TC) within 40 min, which were both remarkably higher than those of irregular AgCl under visible light irradiation. Besides, the photocatalytic degradation rate constant of 3D flower-like hierarchical AgCl microsphere (0.063 min^-1) for MB was 3.94 times higher than that of irregular AgCl (0.016 min^-1). Moreover, a possible mechanism for the formation and excellent photocatalytic performance of 3D flower-like hierarchical AgCl microsphere was also proposed.

The influence of titanium dioxide nanoparticles on their cellular response to macrophage cells

As the most widely application of nanomaterials in biology and medicine, their interaction with biological system and the afterwards cellular responses would be addressed. Here, the agglomerate states of two kinds of TiO₂ NPs in culture medium were characterized and the cluster specific cellular responses in RAW264.7 cells were investigated. Owing to the smaller aggregates and more positively charged surface, 21 nm TiO₂ NPs exhibited higher cytotoxicity, which correlated with their ability to cause damage to mitochondria. While for 35 nm TiO₂ NPs, higher level of cell autophagy and stronger pro-inflammatory immune response were observed, which are responsible for their lower cytotoxicity. These results suggest that physiochemical properties of TiO₂ NPs in culture medium are important factor affecting their cellular response to RAW264.7 cells.

Enhanced Photo-Catalytic Performance of Activated Carbon Fibers for Water Treatment

The synthesis, characterization, and performance of composite photocatalytic adsorbents are investigated in this work using the dip-coating and the electrophoretic coating methods for the deposition of titanium dioxide (TiO2) on porous activated carbon fiber (ACF) substrates. The adsorption and photocatalytic efficiency of the synthesized catalytic adsorbents were compared using phenol as the model pollutant. Both immobilization techniques resulted in composite ACF/TiO2 adsorbents characterized by large surface area (844.67 ± 45.58 m2 g−1), uniform distribution of TiO2 nanoparticles on the activated carbon fibers, and high phenol adsorption. The method and the treatment time affected the phenol adsorption, while the highest sorption was determined in the case of the ACF/TiO2 sample prepared by the electrophoretic coating method (at 20 V) for an electrolysis time of 120 s (7.93 mgphenol g−1ACF/TiO2). The UV-A irradiation of most ACF/TiO2 samples led to a faster removal of phenol from water as a result of the combined sorption and heterogeneous photocatalysis. The stability and the effective regeneration of the most promising composite photocatalytic adsorbent was proved by multiple filtration and UV-A irradiation cycles.

Bacterial Inactivation on Concrete Plates Loaded with Modified TiO2 Photocatalysts under Visible Light Irradiation

The antibacterial activity of concrete plates loaded with various titania photocatalysts was investigated. The target in bacteria testing was Escherichia coli K12. The presence of photocatalysts in the concrete matrix at a dose of 10 wt.% improved the antibacterial properties, which became significant depending on the type of the added photocatalyst. Total inactivation of E. coli irradiated under artificial solar light was observed on the concrete plates loaded with the following photocatalysts: TiO₂/N,C_MeOH-300, TiO₂/N,C_EtOH-100, TiO₂/N,C_isoPrOH-100 and TiO₂/N-300. The modified Hom disinfection kinetic model was found as a best-fit model for the obtained results. The presence of nitrogen and carbon in the photocatalysts structure, as well as crystallite size, surface area and porosity, contributed to the increase of antibacterial properties of concrete plates.

TiO2/ZnO Nanofibers Prepared by Electrospinning and Their Photocatalytic Degradation of Methylene Blue Compared with TiO2 Nanofibers

TiO2 nanofibers have high chemical stability and high strength and are applied to many fields such as air pollution sensors and air pollutant removal filters. ZnO nanofibers also have very high absorptivity in that air and are used as germicides and ceramic brighteners. TiO2/ZnO nanofibers, which have a composite form of TiO2 and ZnO, were fabricated and show higher photocatalytic properties than existing TiO2. The precursor, including zinc nitrate hexahydrate, polyvinyl acetate, and titanium isopropoxide, was used as a spinning solution for TiO2/ZnO nanofibers. Electrospun TiO2/ZnO nanofibers were calcined at 600 °C and analyzed by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The average diameter of TiO2/ZnO nanofibers was controlled in the range of 189 nm to 1025 nm. XRD pattern in TiO2/ZnO nanofibers have a TiO2 anatase, ZnO, Ti2O3, and ZnTiO3 structure. TiO2/ZnO nanofibers with a diameter of 400 nm have the best photocatalytic performance in the methylene blue degradation experiments and an absorbance decrease of 96.4% was observed after ultraviolet (UV) irradiation of 12 h.

Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications.

In-situ active formation of carbides coated with NPTiO2 nanoparticles for efficient adsorption-photocatalytic inactivation of harmful algae in eutrophic water

Harmful algae pollution in eutrophic waters represents one of the most serious problems in natural water environment. Adsorption assisted photocatalytic inactivation is often considered as a promising method to achieve the clean-up of harmful algae and the remediation of eutrophic water. Here, we synthesize the NPTiO₂ (nitrogen and phosphorous doped TiO₂)/C composites using a facile sol-gel method, and demonstrate successful achievement of efficient adsorption-photocatalytic performance via the in-situ formed carbides coated with NPTiO₂ nanoparticles. We find that the composites have rough surfaces with porous structure, which can be tuned by the calcination temperature, and that such composites can be served to efficiently capture the algal cells. The N and P are successfully doped into the TiO₂ crystal lattices, and the cooperation of carbides and NPTiO₂ particles enhances significantly light absorption, while inhibiting the recombination of the photogenerated charge carriers. Among all the NPTiO₂/C composites, the NPTiO₂/C system calcinated at 550 °C shows the best photocatalytic performance for the algal inactivation, presenting a removal rate of 92.6% following 6 h visible light irradiation. The destruction of cell structures is clearly observed in the photocatalytic process. Interestingly, the metabolic activities are also disturbed by the photogenerated radicals, which accelerates the death of algal cells. Moreover, the NPTiO₂/C composite can effectively remove the cytotoxins from water, rendering the composite and the doping strategy promising in the remediation practice for eutrophic waters.

Efficient photocatalytic methylene blue degradation by Fe3O4@TiO2 core/shell linked to graphene by aminopropyltrimethoxysilane

In the present article, Fe₃O₄@TiO₂ core/shell (FT) linked to graphene was fabricated by sol-gel technique as a photocatalyst and was employed for the solar degradation of cationic methylene blue (MB) in aqueous solution. The prepared core/shells were linked to graphene oxide (FTGO) and reduced graphene oxide (FTRGO) via embedding into 3-aminopropyltrimethoxysilane (APS). The structure of this magnetic composition was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area measurements. The significance of the composite structure in photocatalytic degradation was spectrophotometrically tested by blending the obtained powders with wastewater containing methylene blue under solar irradiation. The appropriate dosage of APS to link the Fe₃O₄@TiO₂ core/shell onto GO and RGO surfaces was determined to be 1 ml per gram of FT. The kinetic studies were performed to investigate the effects of different parameters, such as composition structure, APS dosage, and repeatability. Kinetic data are well fitted by a first-order model with a high correlation coefficient. Regardless of the prominent advantage of composites in magnetic powder separation, the Fe₃O₄@TiO₂ core/shell linked to graphene oxide is an efficient composite in comparison to FTRGO for the dye degradation without losing the original activity and stability.

PVA/SA/TiO2-CUR patch for enhanced wound healing application: In vitro and in vivo analysis

Wound healing is a complex multistep process. Wound healing materials should have good antibacterial activity against wound infection causing microbes. Curcumin has effective antimicrobial activity, anti-inflammatory and antioxidant property. Titanium dioxide (TiO₂) is a biocompatible, nontoxic material used for many biomedical applications. The Usage of curcumin tagged TiO₂ nanoparticles for wound healing activity is promising due to the properties of both curcumin and TiO₂. We have synthesized curcumin tagged TiO₂ nanoparticles. The synthesized materials are characterized with XRD, FTIR and TEM. TiO₂-Cur nanocomposite was incorporated into poly vinyl alcohol (PVA) and sodium alginate (SA) patch. The PVA/SA/TiO₂-Cur patch was prepared by gel casting method. Antibacterial efficiency of PVA/SA/TiO₂-Cur patch was analyzed. Further, in vivo studies conducted on Wister rats confirmed the enhanced wound healing property of the PVA/SA/TiO₂-Cur patch. Our results suggest that this could be an ideal biomaterial for wound dressing applications.

In Vitro Toxicity of TiO2:SiO2 Nanocomposites with Different Photocatalytic Properties

The enormous technological relevance of titanium dioxide (TiO2) nanoparticles (NPs) and the consequent concerns regarding potentially hazardous effects that exposure during production, use, and disposal can generate, encourage material scientists to develop and validate intrinsically safe design solution (safe-by-design). Under this perspective, the encapsulation in a silica dioxide (SiO2) matrix could be an effective strategy to improve TiO2 NPs safety, preserving photocatalytic and antibacterial properties. In this work, A549 cells were used to investigate the toxic effects of silica-encapsulated TiO2 having different ratios of TiO2 and SiO2 (1:1, 1:3, and 3:1). NPs were characterized by electron microscopy and dynamic light scattering, and cell viability, oxidative stress, morphological changes, and cell cycle alteration were evaluated. Resulting data demonstrated that NPs with lower content of SiO2 are able to induce cytotoxic effects, triggered by oxidative stress and resulting in cell necrosis and cell cycle alteration. The physicochemical properties of NPs are responsible for their toxicity. Particles with small size and high stability interact with pulmonary cells more effectively, and the different ratio among silica and titania plays a crucial role in the induced cytotoxicity. These results strengthen the need to take into account a safe(r)-by-design approach in the development of new nanomaterials for research and manufacturing.

A composite of platelet-like orientated BiVO4 fused with MIL-125(Ti): Synthesis and characterization

The development of heterojunctions is the current focus of the scientific community as these materials are visible light active and the staggered positioning of their band edges combats electron-hole recombination which is the downside of most photocatalysts. In this work, a two- step hydrothermal synthesis protocol was utilized to fabricate a novel observable-light active material, composed of platelet-like BiVO4 and a titanium-based metal organic framework (MOF) called MIL-125(Ti). The tuning of specific morphologies, such as platelet-like in BiVO4, provides the exposure of most reactive facets which are more reactive towards photooxidation of organics in water, thus increasing their efficiency. The as-synthesized heterojunction was characterized by Transmission electron microscopy (TEM), scanning transmission microscopy (SEM), X-Ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), X-Ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectra. The formation of the heterojunction lead to a positive shift of the 3-2 Bi:Ti valence band (VB) (1.78 eV) when compared to 1.27 eV VB position of BiVO4. The PL and photoelectrochemical measurements revealed that the heterojunction photocatalyst designated 3-2 Bi-Ti demonstrated inhibited recombination rate (platelet-like BiVO4 > 3-2 Bi:Ti (PM) > MIL-125 > 1-1 Bi:Ti > 2-3 Bi:Ti > 3-2 Bi:Ti) and highly efficient interfacial charge shuttle between platelet-like BiVO4 and MIL-125(Ti) through the formed n-n junction.

Ultrafast photoinduced energy and charge transfer

After presenting the basic theoretical models of excitation energy transfer and charge transfer, I describe some of the novel experimental methods used to probe them. Finally, I discuss recent results concerning ultrafast energy and charge transfer in biological systems, in chemical systems and in photovoltaics based on sensitized transition metal oxides.

The Analysis of the Urea Biosensors Using Different Sensing Matrices via Wireless Measurement System & Microfluidic Measurement System

Two types of urea biosensors were integrated with a wireless measurement system and microfluidic measurement system. The two biosensors used were (i) a magnetic beads (MBs)-urease/graphene oxide (GO)/titanium dioxide (TiO₂)-based biosensor and (ii) an MBs-urease/GO/ nickel oxide (NiO)-based biosensor, respectively. The wireless measurement system work exhibited the feasibility for the remote detection of urea, but it will require refinement and modification to improve stability and precision. The microchannel fluidic system showed the measurement reliability. The sensing properties of urea biosensors at different flow rates were investigated. From the measurement results, the decay of average sensitivity may be attributed to the induced vortex-induced vibrations (VIV) at the high flow rate. In the aspect of wireless monitoring, the average sensitivity of the urea biosensor based on MBs-urease/GO/NiO was 4.780 mV/(mg/dl) and with the linearity of 0.938. In the aspect of measurement under dynamic conditions, the average sensitivity of the urea biosensor based on MBs-urease/GO/NiO were 5.582 mV/(mg/dl) and with the linearity of 0.959. Both measurements performed NiO was better than TiO₂ according to the comparisons.

Titanium Dioxide-Layered Double Hydroxide Composite Material for Adsorption-Photocatalysis of Water Pollutants

Although adsorption has gained favor among numerous water treatment technologies as an effective pollutant removal method, its application is often hindered by challenges with its resource- and energy-intensive regeneration procedure once the available adsorption sites are exhausted. Herein, we present adsorption-photocatalysis composite materials combining layered double hydroxides (LDHs) and titanium dioxide (TiO₂) for water treatment. Incorporation of the photocatalyst into the material opens opportunities to harness light from the sun or lamps for oxidative degradation of the adsorbed contaminants on the material surface, to free adsorption sites for material reuse. In addition to allowing photocatalytic regeneration, the addition of TiO₂ to colloidal suspensions of delaminated LDH enabled the formation of TiO₂-LDH composites with far superior adsorptive performances compared to their parent LDH compounds. During the material synthesis, positively charged LDH layers and negatively charged TiO₂ particles combine through electrostatic attraction to yield composites with dramatically enhanced adsorption capacities toward model contaminants, methyl orange and 2,4-dichlorophenoxyacetic acid, by 16.0 and 76.7 times, respectively. Combining delaminated LDH with TiO₂ allowed us to maximize the exposure of positively charged surfaces to the contaminants, in a form that can be used as a solid adsorbent. After regeneration, the material regained up to 92% of its adsorption efficiency toward model contaminants. In light of our findings showing significantly different kinetics of adsorption and photocatalytic regeneration, we propose a new scheme to utilize adsorption-photocatalysis systems, in which the two processes are separated to better utilize their unique strengths.

Graphene and graphene-based nanocomposites used for antibiotics removal in water treatment: A review

Due to their extensive application in human and veterinary medicine, antibiotics have been found worldwide and studied as new pollutants in the aquatic environment. In order to remove such pollutants, adsorption and photocatalysis have attracted tremendous attention because of their great potential in antibiotics removal from aqueous solutions. Graphene, as a novel two-dimensional nanomaterial, possesses unique structure and physicochemical properties, which can be used to efficiently adsorb and photodegrade antibiotics. This review provides an overview of the adsorptive and catalytic properties of graphene, and recent advances in adsorption and photodegradation of antibiotics by graphene and its derivatives. The factors that affect the adsorption and photodegradation of antibiotics are reviewed and discussed. Furthermore, the underlying mechanisms of adsorption and photodegradation are summarized and analyzed. Meanwhile, statistical analysis is conducted based on the number of papers and the maximum adsorption and photodegradation ability on various antibiotics removal. Finally, some unsolved problems together with major challenges that exist in the fabrication and application of graphene-based nanocomposites and the development for antibiotics removal is also proposed. This work provides theoretical guidance for subsequent research in the field of adsorption and photocatalytic removal of antibiotics from aqueous solution, especially on influence factors and mechanisms aspects.

Anisotropy in Stable Conformations of Hydroxylate Ions between the {001} and {110} Planes of TiO2 Rutile Crystals for Glycolate, Lactate, and 2-Hydroxybutyrate Ions Studied by Metadynamics Method

Control over TiO2 rutile crystal growth and morphology using additives is essential for the development of functional materials. Computer simulation studies on the thermodynamically stable conformations of additives at the surfaces of rutile crystals contribute to understanding the mechanisms underlying this control. In this study, a metadynamics method was combined with molecular dynamics simulations to investigate the thermodynamically stable conformations of glycolate, lactate, and 2-hydroxybutyrate ions at the {001} and {110} planes of rutile crystals. Two simple atom-atom distances were selected as collective variables for the metadynamics method. At the {001} plane, a conformation in which the COO- group was oriented toward the surface was found to be the most stable for the lactate and 2-hydroxybutyrate ions, whereas a conformation in which the COO- group was oriented toward water was the most stable for the glycolate ion. At the {110} plane, a conformation in which the COO- group was oriented toward the surface was the most stable for all three hydroxylate ions, and a second most stable conformation was also observed for the lactate ion at positions close to the {110} plane. For all three hydroxylate ions (α-hydroxycarboxylate ions), the stability of the most stable conformation was higher for the {110} plane than for the {001} plane. At both planes, the stability of the most stable conformation was highest for the 2-hydroxybutyrate ion and lowest for the glycolate ion. Supposing that all three hydroxylate ions serve to decrease the surface free energy at the rutile surface and that a more stable conformation at the rutile surface leads to a greater decrease in the surface free energy, the present results partially explain experimentally observed differences in the changes in growth rate and morphology of rutile crystals in the presence of glycolic, lactic, and 2-hydroxybutyric acids.

Empirical Modeling of Electron Transport in Fe/Ti Layered Double Hydroxide Using Exponential, Gaussian and Mixed Gauss-Exponential Distribution

Fe/Ti-layered double hydroxide (LDH) has been hydrothermally prepared and characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and UV-visible diffuse reflectance spectroscopy for evaluation of its structure, morphology, and optical properties. The purpose of doping Ti⁴⁺ with Fe³⁺ toward the synthesis of Fe/Ti LDH is to extend the absorption of the nanomaterial to longer wavelength, which is known to exhibit higher electron transport performance. To provide a practical realization, electron transport modeling across the band gap has been interpreted using exponential, Gaussian, and mixed Gauss-exponential distribution. The conduction band energy (E _C) has been calculated by using the observed values of band gap (E _g) and ξ-potential of the LDH. A detailed study has been undertaken to investigate the pattern of theoretical density of the LDH on the basis of unknown (E _C = 0) and known (calculated) values of E _C. Fermi-Dirac statistics has been used extensively for estimating the occupancy probability of electron (e^-)-hole (h⁺) pair formation within the valence and conduction bands, respectively, with different temperatures, as well as for given energy levels. Monte Carlo simulations have also been performed to evaluate the suitability of the choice of the model, on the basis of the probability of availability of e^-s within the conduction band. To provide a practical realization of the suggested models, electronic transition across the band gap of Fe/Ti LDH has been extensively investigated.

Understanding the performance of a paper-based UV exposure sensor: The photodegradation mechanism of brilliant blue FCF in the presence of TiO2 photocatalysts in both the solid state and solution

RATIONALE

The decolouration of brilliant blue FCF by the action of titanium dioxide (TiO₂ ) under ultraviolet (UV) exposure has been recently reported as the basis of a paper-based sensor for monitoring UV sun exposure. The mechanism of brilliant blue FCF photodegradation in the presence of the photocatalyst and the resulting photoproducts are thus far unknown.

METHODS

The UV-initiated photodegradation of brilliant blue FCF in the presence of TiO₂ for both the aqueous and the solid state was investigated. Degradation in the solid state was observed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). Decomposition of the dye in the aqueous state was analyzed using liquid chromatography/mass spectrometry (LC/MS) and ultraviolet-visible (UV-Vis) spectroscopy.

RESULTS

After UV radiation exposure, the brilliant blue FCF base peak [M1 + NH₄ ]⁺ (m/z calc. 766.194 found 766.194) decreased in the LC/MS chromatogram with a concomitant appearance of BB-FCF decomposition products involving the sequential loss of the N-ethyl and N-methylbenzene sulfonate (MBSA) groups, assigned as [M2 + H]⁺ (-MBSA, calc. 579.163 found 579.162), [M3 + H]⁺ (-MBSA, -Et, calc. 551.131 found 551.131), [M4 + H]⁺ (-2MBSA, calc. 409.158 found 409.158), [M5 + H]⁺ (-2MBSA, -Et, calc. 381.127 found 381.127). Ions [M2 + H]⁺ and [M3 + H]⁺ were also identified in the photodegradation products using MALDI-MS. Observation by UV-Vis indicated a decrease in the solution absorbance maxima and an associated blue-shift upon UV exposure in solution.

CONCLUSIONS

The LC/MS analysis indicated two main oxidation processes. The most obvious was attack of the N-methylene, eliminating either ethyl or MBSA groups. The presence of the hydroxylated decomposition product M13 ([M13 + H]⁺ , calc. 595.157 found 595.157) supported this assignment. In addition, the detection of photoproduct M8, proposed to be 3-((ethylamino)methyl)benzenesulfonic acid ([M8 + H]⁺ , calc. 216.069 found 216.069), indicates an aryl-oxidative elimination. The absence of the aryl-hydroxy products normally expected to accompany the formation of M8 is proposed to be due to TiO₂ -binding catechol-like derivatives, which are then removed upon filtration.

Efficient Hydrogen Peroxide Generation Utilizing Photocatalytic Oxygen Reduction at a Triphase Interface

Photocatalytic oxygen reduction has garnered attention as an emerging alternative to traditional anthraquinone oxidation process to synthesize H₂O₂. However, despite great efforts to optimize photocatalyst activity, the formation rate has been largely limited by the deficient accessibility of the photocatalysts to sufficient O₂ in water. Here we boost the reaction by reporting an air-liquid-solid triphase photocatalytic system for efficient H₂O₂ generation. The triphase system allows reactant O₂ to reach the reaction interface directly from the ambient atmosphere, greatly increasing the interface O₂ concentration, which in turn simultaneously enhanced the kinetics of formation constant and suppressed the unwanted electron-hole recombination and the kinetics of H₂O₂ decomposition reaction. Compared with a conventional liquid-solid diphase reaction system, the triphase system enables an increase in H₂O₂ formation by a factor of 44. The triphase system is generally applicable to fundamentally understand and maximize the kinetics of semiconductor-based photocatalytic oxygen reduction for H₂O₂ generation.

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A triphase photocatalytic system is developed for efficient H₂O₂ generation

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Sufficient interface oxygen is provided

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The formation rate is enhanced

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The unwanted electron-hole recombination and H₂O₂ decomposition rates are suppressed

Investigating Polaron Formation in Anatase and Brookite TiO2 by Density Functional Theory with Hybrid-Functional and DFT + U Methods

Anatase and brookite are robust materials with enhanced photocatalytic properties. In this study, we used density functional theory (DFT) with a hybrid functional and the Hubbard on-site potential methods to determine electron- and hole-polaron geometries for anatase and brookite and their energetics. Localized electron and hole polarons were predicted not to form in anatase using DFT with hybrid functionals. In contrast, brookite formed both electron and hole polarons. The brookite electron-polaronic solution exhibits coexisting localized and delocalized states, with hole polarons mainly dispersed on two-coordinated oxygen ions. Hubbard on-site potential testing over the wide 4.0-10 eV range revealed that brookite polarons are formed at U = 6 eV, while anatase polarons are formed at U = 8 eV. The brookite electron polaron was always localized on a single titanium ion under the Hubbard model, whereas the hole polaron was dispersed over four oxygen atoms, consistent with the hybrid DFT studies. The anatase electron polarons were dispersed at lower on-site potentials but were more localized at higher potentials. Both methods predict that brookite has a higher driving force for the formation of polarons than anatase.

Reaction Spinning Titanium Dioxide Particle-Coated Carbon Fiber for Photoelectric Energy Conversion

In this paper, a titanium dioxide particle coated carbon fiber was prepared by reaction spinning. Polyacrylonitrile (PAN) was used as the precursor to generate a continuous carbon nanofiber. A solution containing 10% wt PAN polymer dissolved in dimethylformamide (DMF) was made as the core fluid. The sheath fluid contains 10% titanium (IV) isopropoxide, 85% ethanol, and 5% acetic acid. The two solutions were co-spun onto an aluminium plate covered with a layer of soft tissue paper. A titanium hydroxide layer formed at the surface of the PAN fiber through the hydrolysis of titanium isopropoxide due to the moisture absorption in the co-spinning process. The reaction spun fiber was converted to a partially carbonized nanofiber by the heat treatment in air at 250 °C for two hours, then in hydrogen at 500 °C for two hours. During the early stage of the heat treatment, the titanium hydroxide decomposed and produced titanium dioxide nanoparticles at the surface of the carbon fiber. The structure and composition of the carbonized fiber were studied by scanning electron microscopy (SEM). The photosensitivity of the particle-containing fiber was characterized by measuring the open circuit voltage under visible light excitation. The photoelectric energy conversion behavior of the fiber was confirmed by open circuit potential measurement. The potential applications of the composite fiber for photovoltaics and photonic sensing were discussed.

Effect of Pt Deposits on TiO2 Electrocatalytic Activity Highlighted by Electron Tomography

Characterizing materials at small scales presents major challenges in the engineering of nanocomposite materials having a high specific surface area. Here, we show the application of electron tomography to describe the three-dimensional structure of highly ordered TiO₂ nanotube arrays modified with Pt nanoparticles. The titanium oxide nanotubes were prepared by the electrochemical anodization of a Ti substrate after which Pt was deposited by magnetron sputtering. Such a composite shows high electrochemical activity that depends on the amount of the metal and the morphological parameters of the microstructure. However, a TiO₂ structure modified with metallic nanoparticles has never been visualized in 3D, making it very difficult to understand the relationship between electrocatalytic activity and morphology. In this paper, TiO₂ nanotubes of different sizes and different amounts of Pt were analyzed using the electron microscopy technique. Electrocatalytic activity was studied using the cyclic voltammetry (CV) method. For selected samples, electron tomography 3D structure reconstruction was performed to describe their fine microstructure. The highest activity was detected in the sample having bigger nanotubes (25 V) where the porosity of the structure was high and the Pt content was 0.1 mg cm^-2. 3D imaging using electron tomography opens up new possibilities in the design of electrocatalytic materials.

Impact of Tetrazolium Ionic Liquid Thermal Decomposition in Solvothermal Reaction on the Remarkable Photocatalytic Properties of TiO2 Particles

Ionic liquids (ILs) could serve as a structuring agent, a solvent, or a source of dopant during solvothermal synthesis of semiconductors particles. To understand the role of IL during formation of TiO₂ particles, it is necessary to study the stability of this IL in solvothermal synthesis conditions, as well as studying the surface properties of formed TiO₂ particles. In view of this, the effect of the 2,3,5-triphenyltetrazolium chloride IL ([TPTZ][Cl]) thermal decomposition during the solvothermal reaction and IL content in the reaction system on photoactivity of TiO₂ microparticles has been systematically investigated. The samples obtained by using [TPTZ][Cl] exhibited remarkable photocatalytic properties in phenol degradation reaction under visible light. HPLC analysis of the solvothermal reaction medium and X-ray photoelectron spectroscopy (XPS) analysis of TiO₂ particles revealed that [TPTZ][Cl] was decomposed completely and was incorporated into the TiO₂ lattice. Generally, increasing the reaction time (1, 4, 12, and 24 h) promoted the TiO₂ microspheres formation, as well as raising the visible light-induced photocatalytic activity of the photocatalysts. Longer reaction time was also accompanied by an increase in the efficiency of 2,3,5-triphenyltetrazolium chloride decomposition. The properties of the photocatalysts were investigated by means of UV-VIS diffuse reflectance spectroscopy (DRS), BET surface area measurements, scanning electron microscopy (SEM), X-ray powder diffraction (XRD) analysis, and XPS.

A magnetically separable plate-like cadmium titanate-copper ferrite nanocomposite with enhanced visible-light photocatalytic degradation performance for organic contaminants

A novel magnetic cadmium titanate-copper ferrite (CdTiO3/CuFe2O4) nanocomposite, in which spherical CuFe2O4 nanoparticles were loaded onto the surface of CdTiO3 nanoplates, was successfully synthesized via a sol-gel hydrothermal route at 180 °C. The structure, morphology, magnetic and optical properties of the as-prepared nanocomposite were respectively characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, UV-visible diffuse reflectance spectroscopy (DRS), vibrating sample magnetometry (VSM) and photoluminescence (PL) spectroscopy. The photocatalytic activity of this novel CdTiO3-based magnetic nanocomposite was investigated for the degradation of organic dye pollutants such as methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) in the presence of H2O2 under visible light irradiation. The results showed that the photocatalyst completely degraded three dyes within 90-100 min. Compared with pure CdTiO3 and CuFe2O4, the heterogeneous CdTiO3/CuFe2O4 nanocomposite exhibited significantly enhanced photocatalytic efficiency. On the basis of the results of the OH trapping and photoluminescence (PL) experiments, the enhanced photocatalytic performance was mainly ascribed to the efficient separation of photo-induced electron-hole pairs and the formation of highly active hydroxyl radicals (OH) species in the CdTiO3/CuFe2O4 photocatalytic oxidation system. The PL measurements of the CdTiO3/CuFe2O4 nanocomposite also indicated an enhanced separation of photo-induced electron-hole pairs. Moreover, the nanocomposite could be easily separated and recycled from contaminant solution using a magnet without a decrease in their photocatalytic activity due to their good magnetic separation performance and excellent chemical stability. Based on these findings, CdTiO3/CuFe2O4 nanocomposite could be a promising visible-light-driven magnetic photocatalyst for converting solar energy to chemical energy for environmental remediation.