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The photocatalytic activity of TiO2 polymorphs has been frequently debated in literature. Numerous studies reported that rutile TiO2 exhibits low photocatalytic activity, and it is generally accepted that rutile has lower photoactivity than the anatase phase. Herein, we studied the photocatalytic activity of phase-pure rutile TiO2 nanoparticles prepared via microwave-assisted hydrothermal method (MW-R NPs). The syntheses were performed with relatively short reaction time (1−3h) at 180 °C using a microwave digestion system. The samples were characterized in detail and then tested in the photodegradation of methyl orange (MO). We demonstrate that the photodegradation of MO with MW-R NPs is highly efficient in the presence of H2O2. By employing 4.4 mM H2O2, ~90% of total decolorization was achieved after 2 min of UV-A irradiation. At the same experimental conditions, MO degradation with Degussa P25 TiO2 was only ~7%. The superior photoactivity of MW-R NPs was related to the effective photogeneration of O2•− radicals as revealed by EPR investigation. These rutile nanoparticles are excellent photocatalysts in the presence of H2O2, signifying that this oxygen source react easily with the photogenerated holes on the MW-R NPs, and thus the interfacial charge transfer lead to the formation of a large amount of O2•− radicals.

In order to improve the photocatalytic activity of nano-TiO2 and achieve its recovery, TiO2/MS-SiO2 photocatalyst is prepared when TiO2 nanoparticles are distributed on the surface of amorphous SiO2 microspheres (MS-SiO2) through sol-gel method, and its composition and morphology structure are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). Besides, the photocatalytic properties are tested and evaluated by degradation efficiency of methyl orange under ultraviolet light. The results show that TiO2 nanoparticles uniformly dispersed on the surface of MS-SiO2 and combined with MS-SiO2 strongly by Ti-O-Si bond, whereas TiO2 is anatase crystal and grain size is about 5 nm. Under ultraviolet light for 90 min, the degradation rate of TiO2/MS-SiO2 for methyl orange reached 100%, which is better than pure TiO2 and P25. In addition, photocatalytic performance remains unchanged in a cyclic experiment. Transmission and separation efficiency of nano-TiO2 photo-generated charge carriers is improved by loading on the surface of MS-SiO2 so that MS-SiO2 can enhance the photocatalytic performance of pure TiO2. Moreover, this fact is illustrated by electron paramagnetic resonance intuitively.

In the current research, TiO2 materials pre-annealed at high temperatures were subject to fast super-cold quenching in liquid N2, with the effect on their structures and photocatalytic properties being studied. Although the liquid N2 quenching did not change the crystalline structure, morphologies, and specific surface area of TiO2 materials, some local disorders and lattice distortion were caused on the TiO2 surfaces. It has been revealed that the quenching process led to a change in surface structure of anatase that is greater than rutile. Clear experimental proofs showed that more oxygen defects were introduced in anatase than in rutile. It was interesting to see that the quenching induced oxygen defects had different effects on the photocatalysis under aqueous and gaseous conditions. For the aqueous photocatalysis of methylene blue, the oxygen defects led to a decrease in the photocatalysis over anatase, while led to an increase over rutile. By contrast, the acetone gaseous photocatalysis over anatase TiO2 could be increased by ~2 times by the quenching induced oxygen defects, and independent on the quenching or not, rutile TiO2 almost inactive to gaseous acetone.

In this paper, the interactions between a H2O2 molecule and anatase TiO2(101) (A-TiO2) surface are studied by first-principle calculations. It is found that a H2O2 molecular can adsorb or dissociate on A-TiO2(101) surface, in agreement with previous results. When a H2O2 molecule dissociates, Ti-μ-peroxide configurations may form. It should be noticed that a more stable Ti-μ-peroxide configuration is found in this paper. More interestingly, an oxygen atom of this dissociated H2O2 can enter into A-TiO2(101) lattice, i.e., forming surface (O2)o. The energy barriers for formations of new Ti-μ-peroxide and surface (O2)o species are 0.30 and 1.28 eV, respectively, which explain previous experimental results that the formations of Ti-μ-peroxide and (O2)o species are under lower and higher temperatures, respectively. The localized gap state of Ti-μ-peroxide disappears after the formation of surface (O2)o, and thus the recombination probability of electron-hole pairs should be reduced for the O-rich A-TiO2. These results can rationalize experimental results that the photocatalytic activity of A-TiO2 sample can be changed by H2O2 treating under different temperature.

The nitrogen-doped TiO 2 -SiO 2 photo catalyst was prepared by a sol-gel method and coated on the concrete substrate (CS) for photocatalytic concrete application. The effect of heat treatment has been studied by annealing at two different low and high temperatures. Anatase phase present in both samples was confirmed by XRD analysis. Textural properties of coated/uncoated samples were studied by BET analysis. The UV DRS study showed that the nitrogen-doped sample shows a slight red shift. The FTIR analysis confirmed that the sample calcined at low temperature of 180 °C has more functional moieties than one at high temperature of 450 °C. The morphological study showed that the sample calcined at high temperature contained more cracks than one at low temperature. The EDS analysis confirmed the presence of nitrogen in the sample coated with N-doped TiO 2 -SiO 2 sol. Surface composition was determined by XPS analysis. PL study used to determine effect of calcination temperature on recombination rate of photo generated electron hole pairs. Photo degradation of toluene gas and methylene blue (MB) dye under UV light confirmed that the sample heat treated at 450 °C shows a high photocatalytic activity. The photo degradation of MB dye under visible light also confirmed that the N-TiO 2 -SiO 2 CS calcined at 450 °C shows higher photocatalytic activity than one at low temperature. Recyclability test confirmed that the N-TiO 2 -SiO 2 sample was stable up to four cycles.

The aim of this study was to enhance the photocatalytic performance of commercial rutile TiO2 nanoparticles using non-thermal glow discharge plasma methodology. Due to the lower photocatalytic performance compared to the anatase phase, the rutile phase has seldom been explored by researchers, despite its significant advantages. Nanoparticles of rutile TiO2 were immobilized on glass plates using heat attachment method whose surface properties were modified by non-thermal glow discharge plasma using different gases. XRD, FE-SEM, UV-DRS, XPS, PL, and BET analyses were performed for physiochemical characterization of rutile nanoparticles. While the stable rutile crystalline phase remained intact, a variety of physiochemical modifications were observed. XPS analysis revealed diminished titanium to lattice oxygen ratio, suggesting the formation of surface oxygen vacancies. Pseudo-first-order reaction rate for photocatalytic degradation of malachite green was improved by 3.31, 2.22, and 1.83 times over unmodified photocatalysts using argon, oxygen, and nitrogen gases, respectively. The proposed surface modification method remarkably improved the photocatalytic performance of immobilized rutile nanoparticles without adding any impurities to its structure. Further, the reusability of plasma-treated photocatalysts was satisfying, where the relative decolorization efficiency dropped by 4.4% after four consecutive 60-minute cycles, suggesting a good potential for operation in wastewater treatment reactors.

Novel homojunction TiO2 samples of anatase TiO2 nanoparticles with dominant {101} facets (TP) supported on anatase TiO2 nanosheets with dominant {001} facets (TS) in different ratio of TP/TS (denoted as R%TP/TS) were prepared by a vapor-induced hydrothermal method and followed by photothermocatalytic treatment. The TiO2 samples were characterized with TEM, XRD, Raman, XPS, BET, PL spectra, UV–vis absorption spectra, photocurrent measurement, and fluorescence emission decay. It is found that the formation of the TP/TS homojunction significantly enhances the photocatalytic activity for acetone photodegradation. The TiO2 samples of 2.5%TP/TS, 5%TP/TS, and 10%TP/TS exhibit much higher photocatalytic activity than TS and TP. Especially, the specific CO2 production rate for acetone degradation of the optimized 5%TP/TS is 4.0, 5.4 and 3.3 times higher than that of TS, TP, and P25, respectively. The results of photocurrent, PL, and fluorescence emission decay demonstrate that the significant enhancement in photocatalytic activity is attributed to the efficient improvement in photogenerated electron-hole separation efficiency by forming homojunction. This study provides a new approach by building homojunction to significantly enhancing the separation efficiency of the photogenerated electron-hole and photocatalytic activity.

Recent progress in the field of advanced oxidation process (AOP) has triggered the use of surface engineered visible light active TiO2 as a competent photocatalyst material in solar photocatalysis. Herein, we adopted host-guest inclusion complexation for the site-directed immobilization of a model cationic dye, Rhodamine B (RhB) on to the surface of oxygen-rich positively charged TiO2, resulting in rapid mineralization of the dye pollutant under solar irradiation. Relatively recent macrocyclic host, cucurbit[7]uril (CB7) is used as the host for the formation of inclusion complex with RhB. In this study, solar photocatalysis of dye encapsulated system results in 97% mineralization of dye molecules within 10 min with an excellent kinetic rate of 351 × 10−3 min−1. Here, the formation of CB7-RhB inclusion complex enables direct anchoring of encapsulated dye molecules through carboxylic (-COOH) groups of RhB, which in turn facilitate heterogeneous electron transfer resulting in instantaneous and direct cleavage of the chromophore. The binding of CB7 encapsulated RhB to microwave-assisted sonochemically synthesized TiO2 (MST) surface via monodentate ester-like linkage was established by XPS and FT-IR analysis. Gas chromatography (GC) and high-resolution mass spectrometry (HR-MS) substantiate the complete mineralization of RhB and the intactness of CB7 molecular structure after photodegradation, confirming the reusability of CB7/MST as an efficient and economically viable photocatalytic system. Encapsulation of pollutant dye to CB7 host proves to be an excellent approach to facilitate the photoelectron transfer to the photocatalyst and faster mineralization of dye molecules under solar irradiation. Thus, our approach would be a feasible solution for environment-friendly remediation of dye pollutants.

In this paper, one-dimensional SiO2-TiO2 nanofibers with large surface area and high anatase thermal stability were prepared by a facile and economical electrospinning technique. The phase transformation characters of the samples with different Si/Ti ratios and calcined at different temperatures were investigate in detail. The characterization results indicate that the modification of SiO2 could effectively prevent phase transformation of TiO2 from anatase to rutile. When the Si/Ti ratio increases from 0% to 5%, TiO2 crystals changed from mixed phases of anatase and rutile to pure anatase phase after heat treated at 600 °C. Meanwhile, the surface area of 600–5% is as high as 95.96 m2/g, which is nearly 12 times that of 600–0% (8.17 m2/g). Optimization of electrospun SiO2-TiO2 nanofibers shows that SiO2-TiO2 composite nanofibers with Si/Ti ratio = 2%, calcined at 600 °C, exhibited the highest MO degradation efficiency. The mole ratios of Si/Ti above and below 2% showed negative effect on MO degradation. This study serve as significant advancement platform to designing and fabricating high efficient and stable SiO2-TiO2 composite nanofibers via facile electrospinning in a “waterless” system and it is believed to make sense in other semiconductor systems which are sensitive to moisture.

In the current study a ternary Fe3O4/TiO2/g-C3N4 nanocomposite as a photocatalyst was prepared by a novel, facile and in-situ growth mechanism based on hydrothermal route using melamine, tetrabutyl titanate (TBT) and as-prepared magnetic Fe3O4 nanoparticles. The experimental results indicate the gradual increase in performance based on step-by-step coupling of anatase TiO2 and magnetic Fe3O4 over the g-C3N4 framework at 200 °C calcination temperature. A variety of characterization methods were deployed to explore the morphological, crystalline, vibrational, optical and compositional characteristics of the ternary Fe3O4/TiO2/g-C3N4 nanocomposite. Furthermore, the photocatalytic efficiency of the composite was investigated through the discoloration of Rhodamine B (RhB) and Methylene orange (MO) under visible-light illumination. The as-prepared composite achieved an RhB and MO degradation rate of about 96.4% and 90% in 80 min and 120 min, respectively, under the visible-light. The pseudo-first rate constants for RhB and MO degradation on ternary Fe3O4/TiO2/g-C3N4 nanocomposite were 0.0441 min−1 and 0.0186 min−1, 3.73 and 2.74 times of that for bare g-C3N4. The ternary Fe3O4/TiO2/g-C3N4 nanocomposite revealed good photocatalytic performance after 4 cycles illustrating the high photocatalyst durability, and is very likely advantageous for treating biorecalcitrant pollutants in waste water.

The TiO2 is considered by many as the most versatile material with a very large number of applications in many fields that includes photocatalysis and dye-sensitized solar cell (DSSC). But it is active mainly in the UV region of the spectrum due to its large band gap, around 3.2 eV, which causes low photon absorption. This limitation can be overcome by doping TiO2 with a lanthanide which enhances the absorption of visible photons. In this report, we investigated pure mesoporous TiO2 and Gd-doped mesoporous TiO2 spheres to analysis its photocatalytic and energy conversion efficiency. Gadolinium was chosen due to its stable 4f orbitals state of Gd3+ ions. The XRD spectra and Raman spectra analysis confirms the presence of TiO2. It was noted that only anatase was in all the synthesised samples. The morphological analysis confirms FESEM, HRTEM and Element mapping analysis confirms the formation of mesoporous structures with gadolinium incorporated on the mesosphere's surface. The synthesis samples' photocatalytic activity was studied and sample with 1 mmol of Gd was found to perform best among all the samples. A DSSC study was also conduct and Gd-doped TiO2 was found to out-perform the TiO2.

When discharge plasma was generated in an aqueous ammonia solution containing titanium dioxide (TiO2) powder, blue TiO2 was obtained. The blue TiO2 contained oxygen defects and Ti3+ formed by the plasma treatment; i.e., reducing species such as hydrogen radicals generated in situ during ammonia decomposition by plasma were considered to reduce TiO2. No marked changes in the crystallographic structure and specific surface area of TiO2 were observed after the plasma treatment, indicating that TiO2 was not exposed to high temperature. In addition, the plasma-treated TiO2 remained blue when exposed to air for several months. The photocatalytic activity of anatase TiO2 under visible light irradiation was enhanced after plasma treatment. In contrast, the plasma-treated rutile TiO2 showed inferior photocatalytic activity under visible light irradiation compared with that of the untreated rutile TiO2.

We have investigated computationally and experimentally the efficacy of CH3OH treatment of anatase TiO2 nanoparticles (NPs) and compared the results obtained with H2 as the hydrogenation source. The results indicate that TiO2 NPs heated at 300 °C in 120 Torr of CH3OH vapor is more effective than the samples heated under 800 Torr of H2 at the same temperature. Ultraviolet-visible spectroscopy (UV-VIS), Photoluminescence spectroscopy (PL) and X-ray diffraction spectroscopy (XRD) were employed to study the optical property. The effect of temperature of hydrogenation has been systematically studied for NPs in the 200–450 °C range for both H-sources based on H2 evolution, employing Xe lamp as the light source. The hydrogenated TiO2 NPs using H2 and CH3OH have been analyzed by soft X-ray absorption near-edge structure analyses with and without Xe lamp irradiation in situ. The result indicates that CH3OH hydrogenation can induce a much stronger Ti O interaction along direction dz2 and increase the unoccupied DOS of Ti t2g states. This is why the CH3OH treated TiO2 exhibits a greater photo-activity. The crucial role of the hydrogenation using CH3OH was also investigated systematically and confirmed by quantum-chemical calculations with complementary synchrotron-based X-ray techniques. The results are consistent with the predicted barriers for the formation of H atoms on the TiO2 surface, 4–9 kcal/mol, considerably lower than that in the H2 case, 48 kcal/mol.

A critical parameter in Plasma Electrolytic Oxidation (PEO) is the applied current composed of electronic current caused by sparking and ionic current caused by diffusion of electrolyte ions into the oxide. A wide spectrum of current densities was applied on pure titanium to investigate the PEO mechanism. The growth process and oxide characteristics were investigated by studying the ionic/electronic current contributions during the PEO stages. The contribution of electronic current was found to dominate at low current densities (30 and 40 mA/cm2). The large number of plasma discharges at this condition increases the porosity and coating surface roughness. These discharges provide enough energy to raise the temperature facilitating formation of both stable rutile and metastable anatase. By increasing the current density, the incorporation of ionic current increases resulting in the formation of dense anatase coatings. The highest growth rates achieved at a balance between ionic and electronic charges. HRTEM showed that all coatings are composed of a top amorphous layer produced from electrolyte quenching and an inner layer consisting of a mixture of nanocrystalline and amorphous regions and pores. The interlayer forming at the substrate/coating interface was found to play a key role in the growth mechanism during PEO processing.

Mixed-phase (i.e. phase junction) TiO2 has been widely used in commercial photocatalysis applications, because of its excellent photocatalytic performance. However, the interfacial composition, micro-structure, and properties of mixed-phase TiO2 are not fully understood so far. Consequently, the phase transition process TiO2 from anatase to rutile is still not entirely clear; and there is no consensus on the mechanism of mixed-phase enhancing photocatalytic performance of TiO2. In this article, 16 interface models for TiO2 phase junctions were constructed by the low-index surfaces of TiO2 with anatase and rutile phases. The interfacial energy, microstructure, electronic structure and properties have been systematically calculated and analyzed. Based on the interfacial formation energy and the configuration of [TiO6] octahedron at A/R interface, the phase transition of TiO2 is most likely to occur at the interface between anatase (110) plane and rutile (011) plane, owing to the favorable interface formation energy and the smallest deformation of [TiO6] octahedrons. However, because the migration direction of photo-generated carriers is opposite to the direction of the built-in electric field at the A/R interface in A(110)/R(011) phase junction, the hetero-direction migration of photo-generated electron-hole pairs will be prevented. Thereby, the existence of A(110)/R(011) phase junction is unfavorable to improve the photocatalytic performance. On the other hand, when the calcination temperature rises, the favorable phase junctions (such as A(110)/R(001) phase junction) gradually occupies the growth advantage, which can improve the photocatalytic performance of TiO2. This is a possible explanation for the excellent photocatalytic properties of Degussa P25 with mixed-phase.

Various metal-doped TiO2 nanofibers were prepared by hydrothermal synthesis followed by the thermal treatment in air. An array of metal dopants including Ag, Au, Co, Cr, Cu, Fe, Ni, Pd, Pt, Y, and Zn, were respectively doped into TiO2 NFs to acquire the visible-light photocatalytic activity. Considering the photodegradation results under visible-light illumination, Ag doped TiO2 NFs was chosen to study further. Then, the optimal doping level and calcination process were studied systemically to obtain the highly visible light active Ag doped TiO2 NFs. As the Ag doping concentration increased up to 5.00 mol%, anatase to rutile phase transition was observed. Meanwhile, based on the consistent results of synchrotron X-ray spectra, element analysis, and morphological observation, Ag2O was detected and located on the surface of as-synthesized Ag doped TiO2 NFs. Thus, the photodegradation of methyl orange by using 5.00 mol%-Ag doped TiO2 NFs calcined at 600 °C performed the highest visible-light photodegradation activity. Moreover, it also showed the excellent disinfection against E. coli and S. aureus under visible light due to the synergistic effect of Ag2O and photo-induced reactive oxygen species (ROS) formed by TiO2 photocatalyst. The synthesized Ag doped TiO2 NFs makes large-scale and convenient fabrication possible, and it has tremendous practical potentials in the photodegradation of environmental pollution and disinfects bacteria behavior.

In the study, bioactive apatite formation on the plasma electrolytic oxidation (PEO)-treated Ti-6Al-4V alloy after 3rd anodic titanium oxidation (ATO) was researched. After formation of the nanotubes on Ti-6Al-4V alloy in NaF solution, the nanotubes layer was removed via ultra-sonication, and the ATO was then repeated. After ATO treatment, the PEO-treatment was carried out in the electrolyte containing bioactive substances. The morphology and composition on Ti-6Al-4V was observed by field-emission scanning electron microscopy and energy dispersive X-ray spectrometer. The PEO film formed on the Ti-6Al-4V alloy was characterized using AFM, XRD, nanoindentation test, wettability test, and scratch test. The diameter and size of the nanotubes increased while the distance between the nanotubes decreased with increases in the number of ATO cycles. A mesh-shaped surface was formed and the surface roughness increased with the number of ATO cycles. Mn precipitates were formed around the pores, and Mg was more distributed on the surface than in the pores. The PEO-treated surface after 3rd ATO mainly exhibited anatase and hydroxyapatite phases. The PEO-treated surface exhibited higher bonding strength and the surface roughness increased with the number of ATO cycles. The wettability, the elastic modulus, and hardness increased as the number of ATO cycle increased in the number of ATO cycles.

Silicon monoxide (SiO) is regarded as a great potential anode material for high-energy lithium-ion batteries (LIBs) owing to the high theoretical specific capacity (2650 mAh g−1), low voltage platform, eco-friendly and rich reserves. However, the particle pulverization, induced by large volume change during (de)lithiation, can result in the capacity degrading significantly. As we all know, it is a good strategy that using TiO2 to modify the SiO-based anode. TiO2 can serve as rigid outer layer to keep the structural integrity. In addition, the electrochemical performances of monoclinic TiO2 (B) are better than anatase and rutile TiO2. Therefore, compositing with TiO2 (B) is an admissible method to enhance the electrochemical properties of SiO-based materials. And the pretreated-SiO/TiO2 (B) composites (abbreviated as p-STB) are prepared by hydrothermal treatment at 180 °C for 12 h and then calcined at 325 °C for 2 h. In this paper, p-STB-1 and p-STB-2 are prepared that the weight ratios p-SiO and TiO2 (B) are 4:1 and 3:1, respectively. The structure and components of composites are also performed on X-ray diffraction (XRD), Fourier transform infrared reflectance (FT-IR) spectroscopy, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). For p-STB, TiO2 (B) is mainly covered on the surface of pretreated SiO (p-SiO). The Li-ion diffusion coefficients of as-prepared materials are calculated by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical test results suggest that the p-STB-1 has batter cycling performance (730 mAh g−1 after 100th cycle) and admirable rate capacity (450 mAh g−1 under 3.2 A g−1). The modified method, which was compositing with TiO2 (B), is beneficial to the commercialization of SiO-based materials.

Modified TiO2 (black TiO2) nanoparticles (NPs) produced by different methods showed enhanced visible light absorption than ordinary white TiO2 NPs. Pulsed laser ablation in liquid (PLAL) is a promising technique for synthesizing nanostructures due to its simplicity, less usage of toxic reagents and absence of costly vacuum systems. In the present study, black TiO2 NPs synthesized by pulsed laser irradiation is examined for their structure, morphology and optical properties. Nanoparticles of modified TiO2 were prepared by pulsed laser ablation in liquid technique by irradiating white TiO2 powder in water using an Nd:YAG laser (532 nm, 10 ns, 10 Hz). Characterization of morphology of the nanoparticles by scanning electron microscopy (SEM) showed a change in morphology by laser irradiation for TiO2 nanoparticles. Crystalline structure was determined by X-ray diffraction (XRD) in which the major anatase phase in white TiO2 was changed to rutile during irradiation and for longer irradiation, rutile became the major phase. Most of the vibrational peaks for TiO2 were identified in Raman spectra. Ti 2p and O 1s binding energy analysis by X-ray photoelectron spectroscopy (XPS) for black TiO2 (90 min) showed changes of 0.5 eV and 0.7 eV respectively compared to the white TiO2 due to their change in chemical states. Optical absorption and band gap evaluation were done using the diffuse reflectance spectra measurements that showed enhanced absorption in the visible range for all the laser irradiated nanoparticles and a decrease in the bandgap from 2.98 eV of white TiO2 to 1.84 eV for black TiO2. Synthesis of black TiO2 at normal atmospheric conditions by irradiation of TiO2 in liquid using 532 nm laser output which is a very common Nd:YAG wavelength is reported for the first time.

Cu-TiO2 nano-catalysis were successfully prepared using sol-gel method and used for solar photo-reduction of CO2 in gas and liquid phase. Adding Cu to TiO2 matrix modify its crystalline structure, improved its optical property and increased the photo-catalytic activity toward CO2 reduction. Incorporating Cu at an oxidation state of 2+ into TiO2 matrix generated a mixture of Anatase and Rutile structure with high surface area, increased oxygen vacancies and enhanced atomic mobility which improved CO2 photo-reduction in both phases. The highest CO2 photoreduction rate was observed to occur for Cu-TiO2 nano-catalyst with Cu loading of 1.5 wt%. Methanol was the most produced hydrocarbon amongst the products with a production rate of 4.0 μmol·g-cat−1·h−1, followed by methane. Gas phase solar CO2 photo-reduction was effective and dependent on the gas relative humidity. CO2 and H2O mixture with relative humidity (%RH) ≤ 30% generated CH4 and CO as the main products. At higher %RH, the main products were methane, hydrogen, methanol, ethanol, and acetaldehyde. Gas phase solar CO2 photoreduction is more effective than liquid phase in terms of hydrocarbons production rate, space yield, and quantum efficiencies. Results showed that solar photo-catalytic reduction can be successfully applied to reduce CO2 from the atmosphere.

A novel three-dimensional ordered hollow spherical Sn4+ doped TiO2 material with ZnO quantum dot sensitization (ZnO QDs@Sn-TiO2) was synthesized by a simple colloidal template method. The characterization results indicate that the crystal phase of the prepared composite could be controlled by modifying the loading of ZnO QDs under the synergistic action of ZnO QDs and Sn4+ while maintaining the favorable three-dimensional ordered hollow sphere structure. Based on diffuse reflectance and fluorescence spectroscopy, ZnO QDs provide multiple migration pathways for photogenerated carriers, effectively inhibiting the recombination of photogenerated electron–hole pairs. And the photocatalytic experiments show that the photocatalyst ZnO QDs@Sn-TiO2 has significantly improved photocatalytic performance than pure TiO2. Simultaneously, the optimized results show that 2.0 ZnO QDs@Sn-TiO2 has the best degradation rate and photocatalytic activity. In summary, this work provides a new approach for the synthesis of multi-morphological mixed phase TiO2 photocatalysts for photocatalytic applications.

In this work, surface observation of nanotube-formed titanium by anodization in an electrolyte containing hydroxyapatite nanoparticles was carried out using FE-SEM and analyzed by XPS in order to determine changes in the chemical states of elements through depth profiling. The anodized layer consisted of three regions: (1) a TiO2 layer adjacent to titanium, (2) an intermediate barrier layer of TiO2 nanotubes, and (3) a surface hydroxyapatite [HAp, Ca10(PO4)6(OH)2] layer. The nanotube-formed surface consisted of the anatase TiO2 phase. The HAp layer that formed on the TiO2 nanotube film grew vertically, and the electrodeposited HAp nanoparticles were distributed on the whole surface. From comparative analyses of the depth profile before Ar+ ion sputtering and after 4 keV Ar+ ion sputtering, the multilayer contained Ti, O, Ca, and P, and showed no noteworthy difference. The Ti-2p, O-1s, Ca-2p, F-1s, C-1s, and N-2s transitions were continuously detected in the multilayer as the sputtering time increased. The dominance of the Ti-2p and O-1 s peaks, both before and after the Ar+ ion sputtering, shows that the surface consists mainly of an oxidized TiO2 layer. The Ca-2p and P-2p peaks were subsequently detected from HAp nanoparticles electrodeposited onto the TiO2 nanotube film during an electrochemical reaction. The chemical states of calcium and phosphate in the multilayer were similar to those in HAp.

The titanium dioxide photocatalysts modified with nitrogen (N–TiO2) were synthesized via hydrothermal method by using urea (NH2CONH2) as a nitrogen source with various concentrations of dopant. The characterizations of cooperated N–TiO2 were examined by many techniques. The performance of the synthesized N–TiO2 catalysts was evaluated by using the decomposition of ciprofloxacin under UV light irradiation. Additionally, the OH radical production was also estimated. The results revealed that the influence of different concentrations of nitrogen dopant was significant on the physicochemical and structural properties. The surface morphology exhibited the nanorice grain particles in all samples. The trend of particles size and pore diameter decreased, whereas BET surface area slightly increased with increasing of nitrogen contents. The WAXS profiles demonstrated that the photocatalysts displayed the high purity of the anatase crystalline phase and delayed the phase transformation from anatase to rutile. The bandgap energies showed lower than pure anatase crystalline phase. The types of Ti–N–O (substitutional N) and/or Ti–O–N (interstitial N) bonding were formed into TiO2 lattice investigated by XPS technique. The photodegradation of ciprofloxacin increased with increasing of nitrogen contents. The N–TiO2 catalysts can generate OH radical and in-situ OH radical thought the direct photocatalytic degradation of coumarin and ciprofloxacin, respectively. Since, increasing of nitrogen content can increasingly produce OH radical to more react with organic pollutants. The de-mineralization by using the highest nitrogen content sample showed approximately 66% removal at 4 h of reaction time.

The lack of biological activity of pure titanium as a dental implant has attracted increasing attention. This condition can be improved by preparing a layer of nano-hydroxyapatite (nano-HA) coating that is stable and does not easily fall off, which however, remains a challenge. Here, we report the preparation of nano-HA crystals on calcified titanium oxide (TiO2) nanotube arrays by means of anodization, heat treatment, calcification in vacuum and hydrothermal phosphorylation, achieving the chemical bonding between the nano-HA coating and TiO2 substrate. The mechanism of coating formation was also investigated. The results confirmed that annealing at 450 °C could convert the amorphous nanotubes to the anatase structure. Calcium titanate (CaTiO3) was formed on the surface of nanotubes by heat treatment after calcification, which could provide nucleation sites for the formation of nano-HA. Needle-like nano-HA crystals were subsequently formed on the surface of the TiO2 nanotube arrays. The scratch test showed that the adhesion strength between the formed nano-HA coating and the TiO2 nanotube arrays was higher than 29.17 ± 1.07 N. In vitro cell proliferation and adhesion experiments showed that the nano-HA coating had good biocompatibility. Alkaline phosphatase (ALP) activity and osteocalcin (OCN) expressions highlighted the higher osteoconductivity of the nano-HA coating on the surface of TiO2 nanotube arrays compared to the pure Ti.

This work presents a modified solvothermal process for a facile synthesis of high thermally stable nanocrystalline anatase TiO2 NPs doped with Cu2O NPs. A Z-scheme mechanism was used to account for the enhanced photocatalytic activity exhibited by these materials. Also, the nanocomposite was impregnated in cotton fabric to obtain a modified fiber with high thermal stability, self-cleaning, enhanced UV protection, and antibacterial activity. The as-prepared nanomaterials and the coated fabric were characterized by various physicochemical techniques such as XRD, EDXRF, TGA, TEM, HRTEM, and SEM. The Cu2O/TiO2 molar ratio in the nanocomposite was found to possess a pronounced impact on the crystalline structure, size and morphology of TiO2 NPs. The XRD revealed proper substitutions of the few Ti4+ sites by Cu2+ ions in TiO2 host lattice. Optical measurements showed that the plasmonic peak of the Cu2O/TiO2 nanocomposite was affected by the copper-doping concentration, enhancing self-cleaning of Cu2O/TiO2 under direct sunlight. The TiO2/fiber self-cleaning efficiency (12 h for MB removal) was increased by the in situ growing of Cu2O (5.5 h). Antibacterial activity studies revealed high potential activity of Cu2O/TiO2 against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Kleissella pneumonia, Saccharomyces sp.) bacteria. The promising photocatalytic and biocidal activity of our synthesized Cu2O/TiO2 nanocomposites was ascribed to the reactive oxygen species generated by the Z-scheme mechanism under direct Sunlight.

Thermally-inducing activation mechanism of titanium dioxide (TiO2) in air was investigated using X-ray diffraction (XRD) measurement and X-ray photoelectron spectrometry (XPS) under high temperatures. TiO2 (anatase) crystal expanded toward the c-axis direction as compared with the a-axis direction under heating. These show that the anatase crystal was distorted under high temperature, that is, the lattice vacancy generated in the crystal at high temperatures from the XRD measurement. It was recognized that Ti3+ (binding energy of 457.8 eV) in TiO2 increased slightly with temperature rise from the XPS. The decreasing of the ratio of O/Ti with heating would indicate that the oxygen vacancy in TiO2 increased with heating. From these results, the thermal activation of TiO2 must be induced by the generation of oxygen vacancy and Ti3+ in TiO2 at high temperatures followed by the formation of trapped electron. The oxidative decomposition of toluene over TiO2, as an application to the oxidation of organic compounds, was superior to the only thermal decomposition over SiO2.