Unmodified TiO2 Research Articles

Recent Advances of Modified TiO2 Nanostructure as Heterogeneous Catalyst in Organic Transformations

This review highlights the different strategies of modified TiO2 nanostructure as heterogeneous catalyst in organic transformations. The modification in TiO2 nanostructure have been achieved by doping with metal and non-metal, composing with other material such as metals, metal oxides, nonoxides, semiconductor and nanostructure carbon materials. The influence of modification in TiO2 nanostructure on catalytic properties in organic synthesis also discussed. Different modifications of TiO2 extend the catalyst selectivity and reusability over unmodified TiO2 nanoparticles. Recent investigations have shown that modified TiO2 nanostructures utilised as active catalysts or catalyst support in organic transformations including C-C, C-N, C-S, C-O bond formation reactions, multicomponent reactions (MCR), oxidation- reductions.

Implanting a Copper Ion into a TiO2 Nanorod Array for the Investigation on the Synergistic Antibacterial Mechanism between Mechanical Cracking and Chemical Damage.

Titanium (Ti) and its alloys are extensively applied in dental and orthopedic implants due to their characteristics of good mechanical property and corrosion resistance. However, Ti and its alloys suffer from the absence of certain biological activity and antibacterial ability. Herein, we synthesized a titanium dioxide (TiO2) nanorod array on the surface of a Ti plate, and the obtained TiO2 nanorod array was further modified by Cu ions through ion implantation technology in an attempt to endow medical Ti with an antibacterial ability and maintain a normal biological function synchronously. The antibacterial ability of the TiO2 nanorod array with the incorporation of Cu ions was vastly improved compared with those of the unmodified TiO2 nanorod array and pure Ti. In particular, owing to the synergy between the chemical damage of the released Cu2+ to the cell and the mechanical cracking of the TiO2 nanorod array, the antibacterial rate of the TiO2 nanorod array modified by Cu ions against Escherichia coli or Staphylococcus aureus could reach 99%. In addition, no cytotoxicity was detected in such prepared coating during the CCK-8 assay. Moreover, the corrosion resistance of the sample was significantly better than that of pure Ti. Overall, we demonstrated that the application of ion implantation technology could open up a promising pathway to design and develop further antibacterial material for the biomedical domain.

Kaolin-graphene carboxyl incorporated TiO2 as efficient visible light active photocatalyst for the degradation of cefuroxime sodium.

A novel solar light active photocatalyst, TiO2/kaolin-graphene carboxyl nanocomposite was synthesized by hydrothermal method for the degradation of cephalosporin antibiotic, cefuroxime sodium. The synthesized photocatalyst was characterized by various analytical and spectroscopic techniques, including Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) thermogravimetry (TG), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The prepared TiO2/kaolin-graphene carboxyl nanocomposite exhibited efficient photocatalytic degradation of methylene blue (MB) upon illumination with the solar simulator as compared to unmodified TiO2. The incorporation of both kaolin and graphene carboxyl was found to immobilize TiO2, enhancing the visible light absorption range of TiO2. Scavenger study revealed that hydroxyl radicals act as the main active species in the photocatalytic degradation process. The hydroxyl group present on kaolin surface reacts with photo-generated holes to increase the amount of hydroxyl radical, and further the graphene carboxyl plays a role to impede the recombination of photo-generated electron-hole pairs. Furthermore, the synthesized photocatalyst was found to degrade cefuroxime sodium within 90min of sunlight illumination, indicating that TiO2/kaolin-graphene carboxyl nanocomposites would be very beneficial for pharmaceutical waste management through the advanced oxidation process. Mass spectral analysis was also carried out for elucidating the photocatalytic degradation pathway of cefuroxime sodium.

Improving the stability of nanofluids via surface-modified titanium dioxide nanoparticles for wettability alteration of oil-wet carbonate reservoirs

The main challenge of the application of nanofluids for enhanced oil recovery (EOR) in oil-wet carbonate reservoirs is maintaining their stability under high-temperature and high-salinity which is normally seen in reservoir conditions. In this work, surface-modified TiO2 nanoparticles were synthesized by N-(2-Aminoethyl)−3-Aminopropyltrimethoxysilane (AEAPTMS) as a coupling agent for surface modification of nanoparticles. Zeta potential and dynamic light scattering analyses were used to evaluate the stability of the prepared nanofluids. Results indicated that nanofluids had high stability in 90 °C and 20 wt% salinity. The influence of nanofluids on wettability alteration of carbonate rocks was studied by measuring the contact angle value. Untreated rock samples were strongly oil-wet, with water advancing and receding contact angles of 165.1° and 166.2°, respectively. After treatment with 3wt% concentration of surface-modified TiO2 nanoparticles, the rock plate wettability changed to a water-wet state, with water advancing and receding contact angles of 37.6° and 48.2°, respectively. Suggested surface-modified TiO2 nanoparticles were more effective in wettability alteration of the rock surfaces compared to the un-modified TiO2 nanoparticles. Furthermore, higher concentration of nanoparticles, higher the ability of the nanoparticles on changing the rock wettability.

Energy Band Engineering by CdTe/Si Codoped TiO2 Nanoarrays for Enhanced Photoelectrochemical Water Splitting

The wide bandgap energy of TiO2 limited its photocatalytic activity to UV light. To meet this challenge, TiO2 nanorods were doped with Si atoms and decorated by CdTe QDs to enhance the electronic structure, broaden the absorption domain, and improve photoelectrochemical (PEC) water splitting. Incorporation of Si atoms in the TiO2 structure effectively enhanced the transfer of charge carriers and the wettability of the surface in the Si:TiO2 electrode and made it an effective platform for solar-assisted water splitting. Moreover, the IPCE results prove that CdTe QDs with high absorption coefficient and photon upconversion spread the photoresponse of CdTe/Si:TiO2 to visible light with an improved photocurrent density of 4.3 mA cm–2 at the potential of 1.23 V vs RHE. The excellent increase of 12.5 times in PEC activity of CdTe/Si:TiO2 electrode as compared to unmodified TiO2 nanoarrays and its low overpotential are due to the faster electron transfer kinetics, enhanced charge carriers density (Nd), and reduced charge recombination rate. The photocurrent stability of CdTe/Si:TiO2 in numerous on/off cycles and its long-term durability with a photocurrent decay of about 5% over 10 h show its high photocorrosion resistance. The current study signifies that CdTe/Si:TiO2 is a suitable and highly efficient photoelectrocatalyst for water splitting.

Fabrication and characterization of upconversion N-doped graphene quantum dots for improving photoelectrocatalytic performance of rutile hierarchical TiO₂ nanowires under visible and near-infrared light irradiations

The development of well-organized and low-priced photoelectrocatalysts for the clean and efficient water splitting reaction is crucial. In this context, novel nitrogen-doped graphene quantum dots (N-GQDs) with high photoluminescence and upconversion emission have been synthesized as excellent light harvester. Subsequently, ordered hierarchical TiO₂ nanowires were decorated with upconversion N-GQDs as a photoanode by a simple preparation method to improve the photocatalytic performance in the visible and near-infrared (NIR) regions of solar light, not otherwise absorbable by bare TiO₂ nanostructures. Moreover, the enhancement of charge transfer efficiency and electron–hole separation according to the energy states of N-GQDs and TiO₂ are considered for the improved photocatalytic performance of water splitting. N-GQDs/TiO2 shows superior photoelectrocatalytic (PEC) performance, achieving a photocurrent density of 3.0 mA.cm−2 in 1.0 M KOH solution, which is eight times that of unmodified TiO₂ at an applied voltage of 1.23 V vs. RHE. The high stability and photoelectrocatalytic activity of oxygen evolution reaction in the presence of newly synthesized N-GQDs are confirmed by chronoamperometry, open-circuit potential measurement, and electrochemical impedance spectroscopy. The as-fabricated photoanode provides an increased solar light harvesting from UV–Vis to NIR due to the application of newly synthesized upconversion GQDs, which increase energy conversion with an appealing perspective.

Surface modification of nano-TiO2 with lanthanide-acetylacetonate complexes

The surface modification of nano-TiO2 was carried out with lanthanide-acetylacetonate complexes by adsorption method. The effects of lanthanide complexes content, lanthanide element type, adsorption temperature, solvent dosage, adsorption time and other conditions on the photodegradation activity of methyl orange by the modified catalyst were studied, and suitable modification conditions were obtained. The results show that the photocatalytic activity of the modified nano-TiO2 is much higher than that of the unmodified pure TiO2, and the lanthanide-acetylacetonate complexes is an excellent surface modifier.

Preparation of water-base immobilized N doped TiO2 using DSAT technique for photocatalytic degradation of methylene blue dye

Photocatalytic degradation of TiO2 photocatalyst under suspension mode has widely been studied among researchers. However, the application is limited due to the complexity in separation and non-recyclability of photocatalyst. Immobilization is one of the promising methods to overcome this problem. Most of the prepared immobilization modes showed lower photocatalytic activity compared with the suspension due to the chemical reaction of solvent with modified TiO2. Therefore, a free solvent or water-base preparation of immobilized TiO2 is critical in retaining its photocatalytic activity. Immobilization via double-sided adhesive tape (DSAT) was introduced previously by our research team, it works the best of others in replacing polymer binder in immobilization system making it a free solvent preparation process. The aim of this research is to prepare immobilized unmodified TiO2 and N doped TiO2 by using water-base DSAT technique. The presence of N element was detected for all modified N doped TiO2 samples confirmed by FTIR and EDX analysis. The N incorporated in modified TiO2 has reduced the band gap energy from 3.0 to 2.8 eV as observed by UV–Vis/DRS analysis. This explained the photoactivity under MB dye degradation is 2.1 times faster under N doped TiO2 where the photodegradation rate for unmodified and optimum N doped TiO2 (TN1-45) were 0.065 and 0.138 min−1 respectively. Immobilized TiO2/DSAT and TN1-450/DSAT have shown a significant photocatalytic performance where it was only reduced to 15% from suspension to immobilized mode. It can be considered higher performance as compared to the normal immobilization under solvent. It also better than suspension mode by considering of its reusability that able to sustain the photoactivity of immobilized TN1-450/DSAT for at least for 12 cycles.

Assessment of some characteristics, properties of a novel waterborne acrylic coating incorporated TiO2 nanoparticles modified with silane coupling agent and Ag/Zn zeolite

Effect of rutile TiO2 nanoparticles modified with 3-(trimethoxysilyl) propyl methacrylate silane - TMSPM (m-TiO2) and Ag/Zn zeolite on the properties, and durability of acrylic waterborne coatings was studied. The obtained results indicated that m-TiO2 nanoparticles and Ag/Zn zeolite could disperse regularly in the acrylic polymer matrix. Consequently, the acrylic coating's abrasion resistance was improved in the presence of m-TiO2 or/and Ag/Zn zeolite. The acrylic coating's abrasion resistance depended on the content of m-TiO2 nanoparticles as well as the initial TMSPM content for modification of rutile TiO2 nanoparticles. The abrasion resistance of the m-TiO2 nanocomposite coating was higher than that of the unmodified TiO2 nanocomposite coating. The acrylic coating filled by 2 wt% TiO2 modified with 3 wt% TMSPM had the highest abrasion resistance value, leveling off at 187.2 L/mil. The abrasion resistance of acrylic coating filled by m-TiO2 reduced with increasing too high m-TiO2 nanoparticles content and using initial TMSPM content in high level for TiO2 modification. The starting temperature of weight loss of acrylic coating filled by m-TiO2 was lower than that of the neat acrylic coating. In comparison with the m-TiO2 nanoparticles, the Ag/Zn zeolite particles showed a lower improvement for acrylic coating properties, i.e. abrasion resistance, weathering durability, but the Ag/Zn zeolite particles expressed an excellent antibacterial activity. Hence, combination of the m-TiO2 nanoparticles and Ag/Zn zeolite particles could enhance the acrylic waterborne coatings' properties. The acrylic coating filled by 2 wt% m-TiO2 nanoparticles and 1 wt% Ag/Zn zeolite particles illustrated high abrasion resistance, good weather durability, and superior antibacterial activity for both of E. coli and S. aureus. This coating is promising for environmental friendly building materials application.

Мо-модифицированный диоксид титана как перспективный фотокаталитически активный материал

The oxide composites based on titanium dioxide modified by molybdenum have been synthesized. The peculiarities of the formation of these composites their physico-chemical and photocatalytic properties have been studied. It is shown that the modification of TiO2 with molybdenum provides obtaining nanodispersed powders (from 8.3 to 12.1 nm) with a free specific surface from 279 to 190 m2/g, respectively. It is shown that the synthesized composites have significantly higher photocatalytic activity (PCA) relative to unmodified TiO2 of similar genesis and industrial titanium dioxide P-25 of Degussa by the example of decomposition of various dyes.

Enhanced photoelectrochemical performance of NiO-doped TiO2 nanotubes prepared by an impregnation–calcination method

To improve the photocatalytic activity of TiO2, a series of NiO–TiO2 nanotubes (NTbs) is prepared by impregnating TiO2 nanotubes in a solution of NiCl2·6H2O at different concentrations. Self-organized TiO2 nanotubes are prepared by a two-step anodization process. Scanning electron microscopy images show that large particle agglomerates are formed for higher precursor concentrations, and X-ray energy-dispersive spectroscopy results indicate that the atomic percentages of Ni in the NiO–TiO2 NTbs prepared with precursor concentrations of 100 and 300 mM are 1.95% and 4.23%, respectively. Electronic lifetime measurements show that the recombination rate of photogenerated electron–hole pairs is lower for NiO–TiO2 NTbs compared to that of TiO2. Specifically, the recombination rate of the sample prepared at 50 mM is the lowest, which is associated with the longest electron lifetime. Compared to unmodified TiO2 nanotubes, NiO–TiO2 NTbs exhibit improved results for the photocatalytic degradation of rhodamine B.

Hydrophilic and hydrophobic films based on polyurethane cationomers containing TiO2 nanofiller

Polyurethane cationomers thin films containing (0–2 wt%) surface functionalized TiO2 as ecological water dispersions were obtained, and the structure of the cationomers have been confirmed using FTIR and NMR methods. Incorporation of the surface modified TiO2 nanoparticles caused considerable changes in the thermal, mechanical, and surface properties of the PU films. Importantly, films made with MDI isocyanate surface-modified TiO2 were hydrophobic and their free surface energy (FSE) was below 35 mJ/m2, while films containing unmodified TiO2 were hydrophilic with FSE above 48 mJ/m2. SEM observations exhibited uniform dispersion of nanoparticles in PU matrix. The activation energy of the glass transition process was calculated based on multifrequency TOPEM DSC data and the higher activation energy was found for composites with higher content of PU/TiO2 or PU/f-TiO2 due to the stronger hydrogen bonding between soft segment microdomains and hard segments after incorporation of PU/TiO2 or PU/f-TiO2. Good thermal and mechanical properties, which correspond to those of PU elastomers, are promising features for the application of the obtained cationomers as modern coating materials.

Photoelectrochemical IL-6 Immunoassay Manufactured on Multifunctional Catecholate-Modified TiO2 Scaffolds.

There is an increasing interest in using photoelectrochemistry for enhancing the signal-to-noise ratio and sensitivity of electrochemical biosensors. Nevertheless, it remains challenging to create photoelectrochemical biosensors founded on stable material systems that are also easily biofunctionalized for sensing applications. Herein, a photoelectrochemical immunosensor is reported, in which the concentration of the target protein directly correlates to a change in the measured photocurrent. The material system for the photoelectrode signal transducer involves using catecholate ligands to modify the properties of TiO2 nanostructures in a three-pronged approach of morphology tuning, photoabsorption enhancement, and facilitating bioconjugation. The catecholate-modified TiO2 photoelectrode is combined with a signal-off direct immunoassay to detect interleukin-6 (IL-6), a key biomarker for diagnosing and monitoring various diseases. Catecholate ligands are added during hydrothermal synthesis of TiO2 to enable the growth of three-dimensional nanostructures to form highly porous photoelectrodes that provide a three-dimensional scaffold for immobilizing capture antibodies. Surface modification by catecholate ligands greatly enhances photocurrent generation of the TiO2 photoelectrodes by improving photoabsorption in the visible range. Additionally, catecholate molecules facilitate bioconjugation and probe immobilization by forming a Schiff-base between their -COH group and the -NH2 group of the capture antibodies. The highest photocurrent achieved herein is 8.89 μA cm-2, which represents an enhancement by a factor of 87 from unmodified TiO2. The fabricated immunosensor shows a limit-of-detection of 3.6 pg mL-1 and a log-linear dynamic range of 2-2000 pg mL-1 for IL-6 in human blood plasma.

Aqueous mechano-bactericidal action of acicular aragonite crystals

Nanoneedle structures on dragonfly and cicada wing surfaces or black silicon nanoneedles demonstrate antibacterial phenomena, namely mechano-bactericidal action. These air-exposed, mechano-bactericidal surfaces serve to destroy adherent bacteria, but their bactericidal action in the water is no precedent to report. Calcium carbonate easily accumulates on solid surfaces during long-term exposure to hard water. We expect that aragonite nanoneedles, in particular, which grow on TiO2 during the photocatalytic treatment of calcium-rich groundwater, exhibit mechano-bactericidal action against bacteria in water. Here, we showed that acicular aragonite modified on TiO2 ceramics prepared from calcium bicarbonate in mineral water by photocatalysis exhibits mechanical bactericidal activity against E. coli in water. Unmodified, calcite-modified and aragonite-modified TiO2 ceramics were exposed to water containing E. coli (in a petri dish), and their bactericidal action over time was investigated under static and agitated conditions. The surfaces of the materials were observed by scanning electron microscopy, and the live/dead bacterial cells were observed by confocal laser scanning microscopy. As a result, the synergistic bactericidal performance achieved by mechano-bactericidal action and photocatalysis was demonstrated. Aragonite itself has a high biological affinity for the human body different from the other whisker-sharpen nanomaterials, therefore, the mechano-bactericidal action of acicular aragonite in water is expected to inform the development of safe water purification systems for use in developing countries.

Manganese-containing bioactive glass enhances osteogenic activity of TiO2 nanotube arrays

Titanium and its alloys are the most used biomaterials for orthopedic and dental applications. However, up to 10% of these medical devices still fail, mostly due to implant loosening and suboptimal integration at the implant site. The biomaterial surface plays a critical role in promoting osseointegration, which can reduce the risk of device failure. In this study, we propose a novel surface modification on titanium to improve osteogenic differentiation by depositing manganese-containing bioactive glass (BG) on TiO2 nanotube arrays. The surfaces were characterized by scanning electron microscopy, energy dispersive X-ray spectrometer, contact angle goniometry, and X‐ray photoelectron spectroscopy. Cell toxicity, viability, adhesion, and proliferation of adipose-derived stem cells on the surfaces were investigated up to 7 days. To evaluate the osteogenic properties of the surfaces, alkaline phosphatase activity, total protein, osteocalcin expression, and calcium deposition were quantified up to 28 days. The results indicate that TiO2 nanotube arrays modified with BG promote cell growth and induce increased osteocalcin and calcium contents when compared to unmodified TiO2 nanotube arrays. The deposition of manganese-containing bioactive glass onto TiO2 nanotubes demonstrates the ability to enhance osteogenic activity on titanium, showing great potential for use in orthopedic and dental implants.

Carbon dots dominated photoelectric surface in titanium dioxide nanotube/nitrogen-doped carbon dot/gold nanocomposites for improved photoelectrochemical water splitting

The dynamic behavior of electron-hole pairs at the interface of the nanocomposites is important for photoelectrochemical catalysis, but it is difficult to characterize. Here we construct a ternary titanium dioxide/nitrogen-doped carbon dot/gold (TiO2/NCD/Au) complex as the model catalyst to investigate the kinetic indexes at their interfaces. Under irradiation (200 mW cm−2), the photocurrent density of TiO2/NCD/Au is 10.26 mA cm−2, which is higher than those of TiO2/Au (4.34 mA cm−2), TiO2/NCD (7.55 mA cm−2) and TiO2 (3.34 mA cm−2). The evolved oxygen of TiO2/NCD/Au reaches 125.8 μmol after 5000 s test. The energy bands of complexes are very similar to that of the unmodified TiO2 catalyst due to the low content modification of NCDs and Au. In addition, the transient photovoltage (TPV) tests with a series of control samples show differences about the carriers’ separation and transfer process, which verify that Au can increase the separation quantity of electron-hole pairs while NCDs play a more important role on the increase of the separation quantity and separation rate simultaneously. This work quantifies the function of each component in a composite catalyst and deepens the understanding of the catalyst interface design.

Bi2MoO6/TiO2 heterojunction modified with Ag quantum dots: a novel photocatalyst for the efficient degradation of tetracycline hydrochloride

In this study, a Bi2MoO6/TiO2 heterojunction photocatalyst modified with Ag quantum dots was successfully synthesized. The results demonstrated that Ag–Bi2MoO6/TiO2 exhibited excellent photoelectrochemical performance and photocatalytic activity for the degradation of tetracycline hydrochloride. The catalyst had the best photocurrent density with a maximum value of 103.0 µA/cm2, which was 11.7 times higher than that of unmodified TiO2 nanorods. Ag–Bi2MoO6/TiO2 significantly increased the absorption intensity and red-shifted with a bandgap of 1.88 eV, which is substantially narrower than that of TiO2. Furthermore, it exhibited extremely high photocatalytic activity for the degradation of tetracycline hydrochloride with a degradation rate of 90.8% at 120 min. A photocatalytic mechanism was proposed to explain the principle of tetracycline hydrochloride degradation using this catalyst.

Activity Enhancement of P25 Titanium Dioxide by Zinc Oxide for Photocatalytic Phenol Degradation

As a benchmark photocatalyst, P25 titanium dioxide (TiO2) nanomaterial has been widely reported for its remarkable photocatalytic activity under ultraviolet (UV) irradiation. However, approaches to further improve the photocatalytic activity of the P25 TiO2 are still required. In the present work, we reported the activity enhancement of the P25 TiO2 up to more than five times higher rate constant for phenol degradation when the P25 TiO2 was coupled with zinc oxide (ZnO). The composites were prepared by a physical mixing method of P25 TiO2 and ZnO with various weight ratios of 1:0.5, 1:1, and 1:2. The composite materials were then characterized using X-ray diffraction (XRD), diffuse-reflectance ultraviolet-visible (DR UV-vis), Fourier transform infrared (FTIR), and fluorescence spectroscopies. All the composites gave better activity than the P25 TiO2, in which the TiO2/ZnO 1:1 composite material exhibited the highest first-order reaction rate constant (0.43 h−1). This remarkable enhanced degradation rate was much higher than that of the unmodified TiO2 (0.08 h−1) and ZnO (0.13 h-1). The fluorescence study revealed that the electron-hole recombination on the P25 TiO2 could be suppressed by the ZnO, which would be the reason for such activity enhancement. A study on the effect of the scavenger showed that the hydroxyl radicals played a crucial role in the photocatalytic phenol degradation. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Enhancing Lithium and Sodium Storage Properties of TiO2(B) Nanobelts by Doping with Nickel and Zinc.

Nickel- and zinc-doped TiO2(B) nanobelts were synthesized using a hydrothermal technique. It was found that the incorporation of 5 at.% Ni into bronze TiO2 expanded the unit cell by 4%. Furthermore, Ni dopant induced the 3d energy levels within TiO2(B) band structure and oxygen defects, narrowing the band gap from 3.28 eV (undoped) to 2.70 eV. Oppositely, Zn entered restrictedly into TiO2(B), but nonetheless, improves its electronic properties (Eg is narrowed to 3.21 eV). The conductivity of nickel- (2.24 × 10−8 S·cm−1) and zinc-containing (3.29 × 10−9 S·cm−1) TiO2(B) exceeds that of unmodified TiO2(B) (1.05 × 10−10 S·cm−1). When tested for electrochemical storage, nickel-doped mesoporous TiO2(B) nanobelts exhibited improved electrochemical performance. For lithium batteries, a reversible capacity of 173 mAh·g−1 was reached after 100 cycles at the current load of 50 mA·g−1, whereas, for unmodified and Zn-doped samples, around 140 and 151 mAh·g−1 was obtained. Moreover, Ni doping enhanced the rate capability of TiO2(B) nanobelts (104 mAh·g−1 at a current density of 1.8 A·g−1). In terms of sodium storage, nickel-doped TiO2(B) nanobelts exhibited improved cycling with a stabilized reversible capacity of 97 mAh·g−1 over 50 cycles at the current load of 35 mA·g−1.

Improved photocatalytic activity of SnO2-TiO2 nanocomposite thin films prepared by low-temperature sol-gel method

The objective of this research was to investigate how the photocatalytic activity of pure TiO2 can be improved by SnO2 modification. Different molar ratios of tin to titanium were prepared. The correlation between tin concentration and structural properties was investigated to explain the mechanism of photocatalytic efficiency and to optimize the synthesis conditions to obtain enhanced activity of the SnO2-modified TiO2 photocatalysts under UV-irradiation. The SnO2-modified TiO2 photocatalysts were prepared by a low-temperature sol-gel method based on organic tin and titanium precursors. The precursors underwent sol-gel reactions separately to form SnO2-TiO2 sol. The sol-gels were deposited on a glass substrate by a dip-coating technique and dried at 150 °C to obtain the photocatalysts in the form of a thin film. To test the thermal stability of the material, an additional set of photocatalysts was prepared by calcining the dried samples in air at 500 °C. The photocatalytic activity of the samples was determined by measuring the degradation rate of an azo dye. An increase of up to 30% in the photocatalytic activity of the air-dried samples was obtained when the TiO2 was modified with the SnO2 in a concentration range of 0.1–1 mol.%. At higher SnO2 loadings, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. The calcined samples showed an overall reduced photocatalytic activity compared to the air-dried samples. Various characterization techniques (UV-Vis, XRD, N2-physisorption, TEM, EDX, SEM, XAS and photoelectrochemical characterization) were used to explain the mechanism for the enhanced and hindered photocatalytic performances of the SnO2-modified TiO2 photocatalysts. The results showed that the nanocrystalline cassiterite SnO2 is attached to the TiO2 nanocrystallites through the Sn-O-Ti bonds. In this way, the coupling of two semiconductors, SnO2 and TiO2, was demonstrated. Compared to single-phase photocatalysts, the coupling of semiconductors has a beneficial effect on the separation of charge carriers, which prolongs their lifetime for accessibility to participate in the redox reactions. The maximum increase in activity of the thin films was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases is achieved for the given physical parameters such as particle size, shape and specific surface area of the catalyst.