Facets Of TiO2 Research Articles

A systematic study on the crystal facets-dependent TEA sensing properties of designed anatase {001 and 101} and rutile {110} facets TiO2

Triethylamine (TEA), a toxic and explosive volatile organic compound (VOC) gas, is hazardous to human health and the environment. Therefore, it is crucial to develop crystal-faceted TEA gas sensors with improved sensitivity and rapid detection capabilities. In this study, TiO2 nanocrystal sensors with different crystal facets of anatase {101} and {001} and rutile {110} were synthesized using the hydrothermal method. The nanomaterials underwent characterization through XRD, SEM, TEM, XPS, and BET analysis. The results revealed that the materials exhibited bipyramid anatase {101} facet, nanorod anatase {001} facet, and rutile {110} facet. The sensors demonstrated superior gas sensing performance in the following order: {101} > {110} > {001} facets to 100 ppm TEA gas at 240 °C. The sensors also exhibited short response and recovery times, low detection limits, excellent stability, repeatability, and selectivity. The enhanced sensing properties of {101} faceted TiO2 can be ascribed to the bipyramid structure and crystal facets with higher adsorbed oxygen peak specific area, which provide numerous active sites and improved extra oxygen-active site species. This study offers valuable insight into the design mechanism to enhance the TEA response of {101} faceted TiO2 and further contributes to our understanding of the sensitivity of crystal faceted sensors.

Effect of Tourmaline Addition on the Anti-Poisoning Performance of MnCeOx@TiO2 Catalyst for Low-Temperature Selective Catalytic Reduction of NOx.

In view of the flue gas characteristics of cement kilns in China, the development of low-temperature denitrification catalysts with excellent anti-poisoning performance has important theoretical and practical significance. In this work, a series of MnCeOx@TiO2 and tourmaline-containing MnCeOx@TiO2-T catalysts was prepared using a chemical pre-deposition method. It was found that the MnCeOx@TiO2-T2 catalyst (containing 2% tourmaline) exhibited the best low-temperature NH3-selective catalytic reduction (NH3-SCR) performance, yielding 100% NOx conversion at 110 °C and above. When 100-300 ppm SO2 and 10 vol.% H2O were introduced to the reaction, the NOx conversion of the MnCeOx@TiO2-T2 catalyst was still higher than 90% at 170 °C, indicating good anti-poisoning performance. The addition of appropriate amounts of tourmaline can not only preferably expose the active {001} facets of TiO2 but also introduce the acidic SiO2 and Al2O3 components and increase the content of Mn4+ and Oα on the surface of the catalyst, all of which contribute to the enhancement of reaction activity of NH3-SCR and anti-poisoning performance. However, excess amounts of tourmaline led to the formation of dense surface of catalysts that suppressed the exposure of catalytic active sites, giving rise to the decrease in catalytic activity and anti-poisoning capability. Through an in situ DRIFTS study, it was found that the addition of appropriate amounts of tourmaline increased the number of Brønsted acid sites on the catalyst surface, which suppressed the adsorption of SO2 and thus inhibited the deposition of NH4HSO4 and (NH4)2HSO4 on the surface of the catalyst, thereby improving the NH3-SCR performance and anti-poisoning ability of the catalyst.

How to construct the most stable structure of (110) surface from rutile TiO2 bulk?

XRD pattern of rutile TiO2 bulk and surface energy of possible terminated (110) planes were investigated using the DFT+U method. The (110) surface was demonstrated to be the most popular facet of rutile TiO2, which is in good agreement with data of the JCPDS card No. 21-1276. The difference in surface energy among possible terminated (110) planes is attributed to structure of top and bottom atomic layers. We have found that the P5 plane is the most stable. It represents structure of (110) surface. Rutile TiO2 (110) surface has calculated surface energy of 0.98 J/m2. The value compares well with previous publications. Besides, DFT calculations were also performed. In comparison with DFT+U, surface energy obtained from DFT calculation for (110) surface is very small, about 0.48 J/m2.

Ti-MOG derived TiO2 facet heterojunction rich in C/Ti3+/Ov for adsorption-photocatalytic removal of pharmaceutical pollutants from water

Developing efficient, stable, and broad-spectrum responsive photocatalysts is an effective way to degrade pharmaceutical pollutants in water. In this work, using concentrated hydrochloric acid (HCl) as a modulator, titanium metal–organic gel (Ti-MOG) was prepared and used as a template for calcination in air to obtain anatase TiO2 facet heterojunction rich in C/Ti3+/oxygen vacancy (Ov) (MOG-TiO2), which has a hierarchical porous structure, large specific surface area, and highly dispersed active site. Compared to P25, P25 + C and MIL-125(Ti) derived TiO2 (MOF-TiO2), MOG-TiO2 exhibited obviously enhanced adsorption-photocatalytic performance for tetracycline (TC) and low concentrations ethenzamide (ETH) under broad-spectrum light irradiation. The photocatalytic degradation efficiency of ETH by MOG-TiO2 reached 92.8, 100 and 98.7 % within 240, 60 and 6 min under Vis, UV and VUV light illumination, respectively, which were much higher than those of P25 (62.7, 33.2 and 73.0 %), P25 + C (61.7, 31.2 and 72.5 %) and MOF-TiO2 (79.2, 86.8 and 88.7 %). Furthermore, concentrated HCl promoted the formation of Ti3+/Ov in MOG-TiO2, which was conducive to the improvement of its photocatalytic performance. MOG-TiO2 also displayed great adsorption-photocatalytic stability and reusability. Moreover, the biotoxicity of TC toward E. coli DH5a obviously decreased after photocatalytic degradation. Based on the TiO2 facet heterojunction rich in C/Ti3+/Ov and the generation of hole, hydroxyl radicals, and superoxide radicals, the possible photocatalytic degradation mechanism of MOG-TiO2 was proposed. Overall, this work provides insights into constructing a novel hierarchical porous carbon-doped facet heterojunction photocatalyst for efficient pharmaceutical contaminants removal.

Simultaneous removal of BPA and Cr(VI) via a redox photoelectrocatalytic system based on 0D/3D BQD@TiO2 photoelectrode: New insight into the mechanism and synergistic effect

For effective treatment of wastewater, synergetic removal of organics and heavy metals is of practical importance. Herein, we constructed a synergistic photoelectrocatalytic (PEC) system based on advanced photoelectrodes to realize efficient removal of BPA and Cr(VI). A 0D BiVO4 quantum dots (BQDs) decorated 3D TiO2 photoelectrode (0D/3D BQD@TiO2) was designed with “Facet/Type-II” dual heterojunctions (TiO2 facet heterojunction and BiVO4/TiO2 heterojunction). Complete removal and fast kinetics were achieved for both BPA (0.18 min−1) and Cr(VI) (0.82 M−1 min−1). 1O2 and h+ were confirmed as the main role for BPA oxidation and Fukui index (f -) predicted the active sites of BPA molecule for 1O2 attack. Meanwhile, Cr(V) intermediate was determined through PMSO probing experiment. The practical application prospect was comprehensively evaluated via examining the removal in actual wastewater and influencing factors. Finally, we examined the reusability of this system and extend its application to various kinds of organics coexisting with Cr(VI).

Oxygen Vacancies Boost High‐Energy {100} Faceted TiO2 for Efficient Photocatalytic Degradation of Rhodamine B

AbstractPhotocatalytic reaction takes place on the surface of the catalyst, the crystal plane engineering which can adjust and optimize the surface atomic ordering and electronic energy band structure has been widely studied, considering the microchemical environment changes caused by defects on different surfaces, the combination of crystal plane engineering and defect engineering is expected to become a promising strategy to greatly improve the performance of photocatalysis. In this paper, we introduce 2,2’‐Bipyridyl to induce oxygen vacancy in the synthesis of highly exposed {100} faceted TiO2 nanorods, and obtain oxygen‐rich TiO2 nanomaterials. Benefit from the synergistic effect of high‐energy crystal plane and oxygen vacancy, 96.8 % Rhodamine B (10 mg ⋅ L−1) is degraded after irradiation of 30 min in T100‐VO photocatalytic system. This study provides a new strategy and inspiration for low‐cost control of semiconductor oxides and the design of efficient photocatalysts for environmental purification.

Photocatalytic activity enhancement by noble metal deposition on faceted F-TiO2 synthesised by microwave assisted method. A study of selective oxidation of gas-phase ethanol in a FBPR reactor

In the present work, fluorinated titanium dioxide (TiO2-F) with high exposition of facet {001} was prepared by following a facile and high yield hydrothermal method assisted by microwave. This faceted TiO2 was then modified by Au or Ag deposition at two different metal loadings (0.125 and 0.25 wt%). A wide physicochemical characterisation of the materials was performed. X-ray difractograms showed high {001} facet exposition in all materials. By X-ray fluorescence it was found that the different samples contained about 5% of fluor. All samples presented high surface area and high uniformity and homogeneity of particles, which highlights the good properties that can be achieved by the microwave synthesis method compared to conventional hydrothermal methods. Oxidation state of the noble metals was studied by XPS. On the other side, TiO2-F and the metallised titania powders were immobilised on polystyrene pellets (PS) for evaluating their gas photocatalytic activity in volatile organic compounds (VOCs) decontamination by following the reaction of photoxidation of ethanol in gas phase. It was found that activity was considerably improved by the addition of noble metals, obtaining high conversion and selectivity to CO2. It is remarkable that the selectivity to CO is almost zero. The highest efficiency was found for the faceted TiO2-F sample with the lowest Au loading (0.125 wt%) immobilised on PS where 91% ethanol conversion and 100% CO2 selectivity were achieved. Different reaction variables were also studied.

Remarkable Enhancement of Photocatalytic Activity of High-Energy TiO2 Nanocrystals for NO Oxidation through Surface Defluorination.

The superior photocatalytic activity of TiO2 nanocrystals with exposed high-energy (001) facets, achieved through the use of hydrofluoric acid as a shape-directing reagent, is widely reported. However, in this study, we report for the first time the detrimental effect of surface fluorination on the photoreactivity of high-energy faceted TiO2 nanocrystals towards NO oxidation (resulting in a NO removal rate of only 5.9%). This study aims to overcome this limitation by exploring surface defluorination as an effective strategy to enhance the photocatalytic oxidation of NO on TiO2 nanocrystals enclosed with (001) facets. We found that surface defluorination, achieved through either NaOH washing (resulting in an improved NO removal rate of 23.2%) or calcination (yielding an enhanced NO removal rate of 52%), leads to a large increase in the photocatalytic oxidation of NO on TiO2 nanocrystals with enclosed (001) facets. Defluorination processes stimulate charge separation, effectively retarding recombination and significantly promoting the production of reactive oxygen species, including superoxide radicals (·O2-), singlet oxygen (1O2), and hydroxyl radicals (·OH). Both in situ diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations confirm the higher adsorption of NO after defluorination, thus facilitating the oxidation of NO on TiO2 nanocrystals.

Dual-edged sword effects of sulfation/hydration on Ce-doped TiO2(001) single-atom catalyst for NH3-SCR reaction: A first-principles study

SO2/H2O-resistance remains challenges for selective catalytic reduction with NH3 (NH3-SCR). The detailed promotion and/or inhibition effects of sulfation/hydration on cerium-titanium (CT) catalysts for NH3-SCR are still controversial. Herein, a series of adsorption characteristics, bonding strengths, electronic effects, and reaction pathways were performed by first-principles density functional theory calculations to explore the structure-performance/resistance of CT catalysts and unravel the effects of sulfation/hydration for NH3-SCR. We constructed six CT catalyst structures based on three TiO2 facets [(001)/(101)/(100)] and two surface configurations [single-atom (SA)/interface (IF)]. CT(001)-SA could protect the active Ce site from sulfation/hydration with TiO2(001) as SO2/H2O-trapping site, which was the optimal SO2/H2O-resistant structure among six CT catalyst structures. An electron-deficient state of CT(001)-SA was caused by sulfation/hydration through electron capture behavior. From the perspective of reactants adsorption, this electron-deficient state not only promoted the NH3/NO adsorption but also suppressed the secondary sulfation/hydration. As for NH3-SCR pathways, hydration promoted NH3 dissociation, N-N coupling, and N-O breaking, but inhibited the H1 transfer (rate-determining step). Sulfation impaired the redox ability of Ce site, promoted H1 transfer and N-O breaking, but inhibited the NH3 dissociation, N-N coupling, and H2 transfer (rate-determining step). Hence, sulfation/hydration exhibited “dual-edged sword” effects for NH3-SCR on CT(001)-SA via electronic effects.

Unraveling the atomic structure and dissociation of interfacial water on anatase TiO2 (101) under ambient conditions with solid-state NMR spectroscopy.

Anatase TiO2 is a widely used component in photo- and electro-catalysts for water splitting, and the (101) facet of anatase TiO2 is the most commonly exposed surface. A detailed understanding of the behavior of H2O on this surface could provide fundamental insights into the catalytic mechanism. This, however, is challenging due to the complexity of the interfacial environments, the high mobility of interfacial H2O, and the interference from outer-layer H2O. Herein, we investigate the H2O/TiO2 interface using advanced solid-state NMR techniques. The atomic-level structures of surface O sites, OH groups, and adsorbed H2O have been revealed and the detailed interactions among them are identified on the (101) facet of anatase TiO2. By following the quantitative evolution of surface O and OH sites along with H2O loading, it is found that more than 40% of the adsorbed water spontaneously dissociated under ambient conditions on the TiO2 surface at a loading of 0.3 mmol H2O/g, due to the delicate interplay between water-surface and water-water interactions. Our study highlights the importance of understanding the atomic-level structures of H2O on the surface of TiO2 in catalytic reactions. Such knowledge can promote the design of more efficient catalytic systems for renewable energy production involving activation of water molecules.

Facet-controlled growth and soft-chemical exfoliation of two-dimensional titanium dioxide nanosheets.

TiO2 remains one of the most popular materials used in catalysts, photovoltaics, coatings, and electronics due to its abundance, chemical stability, and excellent catalytic properties. The tailoring of the TiO2 structure into two-dimensional nanosheets prompted the successful isolation of graphene and MXenes. In this review, facet-controlled TiO2 and monolayer titanate are outlined, covering their synthesis route and formation mechanism. The reactive facet of TiO2 is usually controlled by a capping agent. In contrast, the monolayer titanate is achieved by ion-exchange and delamination of layered titanates. Each route leads to 2D structures with unique physical and chemical properties, which expands its utilisation into several niche applications. We elaborate the detailed outlook for the future use and research studies of facet-controlled TiO2 and monolayer titanates. Advantages and disadvantages of both structures are provided, along with suggested applications for each type of 2D TiO2 nanosheets.

2D/2D {001}TiO2-x/Ti3C2Tx composite with ultra-high sensing performance for NO2 at room temperature

The remarkable electrical conductivity, abundance of surface functional groups, and large specific surface area make 2D MXenes-based heterostructures highly promising for room temperature gas sensing applications. However, these MXenes-based heterojunctions composed of different materials may suffer from issues, such as crystal incompatibility and bandgap mismatch. Herein, the {001}TiO2-x/Ti3C2Tx composite was prepared in situ by hydrothermal process and subsequent annealing. The {001} facets of TiO2 and oxygen vacancies that provide a heightened exposure of active sites in the composite and more gas diffusion channels, as well as the formation of Schottky barriers between {001}TiO2 nanosheets and Ti3C2Tx, can synergistically enhance the gas performance. The experimental results show that the {001}TiO2-x/Ti3C2Tx composite exhibits 1.9 and 27.5 times higher than the {001}TiO2/Ti3C2Tx composite and pristine Ti3C2Tx to 10 ppm NO2 at room temperature, respectively. Moreover, the {001}TiO2-x/Ti3C2Tx composite presents the great linear response (R2 = 0.99509), selectivity, repeatability and long-term stability to NO2. Density functional theory (DFT) calculations reveal the strong interactions between the {001}TiO2-x/Ti3C2Tx and NO2, indicating excellent sensitivity and selectivity of the composite material towards NO2. This work provides an effective way to construct a series of oxygen-defective Ti3C2Tx-based composites with exposed high-energy facets for enhanced gas sensing performances.

Decorating Thermodynamically Stable (101) Facets of TiO2 with MoO3 for Multifunctional Sustainable Hydrogen Energy and Ammonia Gas Sensing Applications.

The simultaneous realization of sustainable energy and gas sensors dealing with the emission of pollutants is indispensable as the former thrives on the minimization of the latter. However, there is a dearth of multifunctional nanocatalysts in the literature. This ascertains the importance of multifunctional semiconductors which can be utilized in H2 generation via overall water splitting and in the gas sensing of global pollutants such as NH3. MoO3-decorated TiO2 Z-scheme heterostructures exceptionally escalate the photochemical and photo/electrochemical H2 evolution performance and gas sensing response of TiO2 owing to the synergistic relationship between TiO2 and MoO3. Extensive structural, morphological, and optical characterizations, theoretical studies, and XPS results were exploited to develop a mechanistic framework of photochemical H2 evolution. The photochemical response of the optimum TiO2-MoO3 composition (20 wt % MoO3-TiO2) was found to be nearly 12- and 20-fold superior to the pristine TiO2 and MoO3 photocatalysts, respectively, with the remarkable H2 evolution rate of 9.18 mmol/g/h and AQY of 36.02%. In addition, 20 wt % MoO3-TiO2 also showed advanced photo/electrochemical efficiency with 0.61/0.7 V overpotential values toward HER due to the higher electrochemically active surface area and Tafel slope as low as 65 mV/dec. The gas sensing response of 20 wt % MoO3-TiO2 toward NH3 gas turned out to be 2.5-fold higher than that of the pristine TiO2 gas sensor.

Unveiling Atomic-Scale Product Selectivity at the Cocatalyst-TiO2 Interface Using X-Ray Techniques: Insights into Interface Reactivity.

The microstructure at the interface between the cocatalyst and semiconductor plays a vital role in concentrating photo-induced carriers and reactants. However, observing the atomic arrangement of this interface directly using an electron microscope is challenging due to the coverings of the semiconductor and cocatalyst. To address this, multiple metal-semiconductor interfaces on three TiO2 crystal facets (M/TiO2 ─N, where M represents Ag, Au, and Pt, and N represents the 001, 010, and 101 single crystal facets). The identical surface atomic configuration of the TiO2 facets allowed us to investigate the evolution of the microstructure within these constructs using spectroscopies and DFT calculations. For the first time, they observed the transformation of saturated Ti6c ─O bonds into unsaturated Ti5c ─O and Ti6c ─O─Pt bonds on the TiO2 ─010 facet after loading Pt. This transformation have a direct impact on the selectivity of the resulting products, leading to the generation of CO and CH4 at the Ti6c ─O─Pt and Pt sites, respectively. These findings pinpoint the pivotal roles played by the atomic arrangement at the M/TiO2 ─N interfaces and provide valuable insights for the development of new methodologies using conventional lab-grade equipment.

Insight into (Electro)magnetic Interactions within Facet-Engineered BaFe12O19/TiO2 Magnetic Photocatalysts.

A series of facet-engineered TiO2/BaFe12O19 composites were synthesized through hydrothermal growth of both phases and subsequent deposition of the different, faceted TiO2 nanoparticles onto BaFe12O19 microplates. The well-defined geometry of the composite and uniaxial magnetic anisotropy of the ferrite allowed alternate interfaces between both phases and fixed the orientation between the TiO2 crystal structure and the remanent magnetic field within BaFe12O19. The morphology and crystal structure of the composites were confirmed by a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses together with the detailed study of BaFe12O19 electronic and magnetic properties. The photocatalytic activity and magnetic field effect were studied in the reaction of phenol degradation for TiO2/BaFe12O19 and composites of BaFe12O19 covered with a SiO2 protective layer and TiO2. The observed differences in phenol degradation are associated with electron transfer and the contribution of the magnetic field. All obtained magnetic composite materials can be easily separated in an external magnetic field, with efficiencies exceeding 95%, and recycled without significant loss of photocatalytic activity. The highest activity was observed for the composite of BaFe12O19 with TiO2 exposing {1 0 1} facets. However, to prevent electron transfer within the composite structure, this photocatalyst material was additionally coated with a protective SiO2 layer. Furthermore, TiO2 exposing {1 0 0} facets exhibited significant synergy with the BaFe12O19 magnetic field, leading to 2 times higher photocatalytic activity when ferrite was magnetized before the process. The photoluminescence emission study suggests that for this particular combination, the built-in magnetic field of the ferrite suppressed the recombination of the photogenerated charge carriers. Ultimately, possible effects of complex electro/magnetic interactions within the magnetic photocatalyst are shown and discussed for the first time, including the anisotropic properties of both phases.

Boosted photoelectrocatalytic removal of bisphenol A in a wide spectral range on 3D BiVO4/TiO2 nanoforest

Nanostructure construction and heterojunction engineering are effective strategies for designing highly efficient photoelectrodes. Herein, we report a BiVO4 quantum dots (BQDs)/TiO2 nanoforest photoanode with 3D configuration that exhibited improved light harvesting and charge transfer efficiency. Enhanced and directional charge separation were attributed to the synergetic effect of TiO2 facet heterojunction and BiVO4/TiO2 type-II heterojunction, which were confirmed by in-situ XPS and KPFM technology. Finally, a boosted photoelectrocatalytic (PEC) bisphenol A (BPA) removal for 97.28 % in 30 min under a wide spectral range was achieved. This work offers insight into the rational design of nanostructure and heterojunction of photoelectrode.

Homojunction TiO2 thin film-based room-temperature working H2 sensors with non-noble metal electrodes

Metal oxide semiconductor heterojunctions and homojunctions are considered to have better performance than single phase material for room temperature hydrogen gas sensing. In this work, TiO2 facet homojunction (TiO2-FH) thin films were prepared by a two-step hydrothermal method. The TiO2-FH thin films were decorated with Pt nanoparticles using a green photodeposition method and then evaluated for H2 sensing. Non-noble metal Al was used as finger electrodes instead of noble metal Pt. Compared with the TiO2-FH sensor, the H2 detection limits of the platinum loaded TiO2-FH@Pt sensors are remarkably decreased from 8000 ppm to 1 ppm at room temperature. The optimized sensor achieves an excellent sensing performance of S = 1.21 and fast response / recovery times of about 42 s / 30 s when exposed to 1 ppm H2 concentration. The synergy between the Schottky barrier at the Pt/TiO2 interface and the barrier between the (110) and (001) facets of TiO2 is the key to the improvement of the sensing performance. Replacement of noble metal Pt with Al and C electrodes greatly help to clarify the mechanism of the junctions in the thin film sensors, especially the function of the Pt/TiO2 junction and the (110)/(001) TiO2 junction. The simple and green fabrication method and cheap Al interdigitated electrodes are advantageous for practical applications.

Synthesis of Tio2 photocatalyst with tunable optical properties and exposed facet for textile wastewater treatment

TiO2 semiconductor plays a paramount important as an active photocatalyst mainly due to its photo-induced electron transfer properties. The metastable anatase in particular are widely accepted to have the most photoactive activity in catalytic application as opposed to rutile TiO2. This is majorly due to the significantly lower recombination rate of electron pair possesses by anatase TiO2. Unfortunately, high recombination rate in anatase TiO2 hinders its application as a functional photocatalyst. Therefore, it is crucial to further enhance the photocatalytic activity of anatase TiO2, by modifying its optical properties, morphological properties, and crystal facet. The study aims to provide a benign synthesis method for TiO2 with a co-exposed {001}/{100} anatase TiO2 facet. The synthesis was conducted via one-pot reflux condensation method. A concise evaluation upon the effect of different synthesis heating duration, temperature and doping materials towards the crystal phase, morphology, and photocatalytic performance of TiO2 were conducted. Anatase TiO2 with high percentage of the high-energy {001} facet have the ability to boost the adsorption and photocatalytic performance as opposed to anatase TiO2 dominated with a thermodynamically stable {101} facet. The incorporation of non-metal dopant (HF) acts as surface modifier which leads to the enhancement of {001} facet percentage. This study further evaluates the functionalities of HCl in paving way towards the formation of mid-gap state, hence improving Anatase TiO2 optical properties. The reduction of band gap of the anatase TiO2 can clearly be identified from the shifts in the adsorption band towards higher wavelength. From the findings, it was found that the synergistic effect upon co-doping anatase TiO2 with the two non-metal dopants plays an important role in altering the ratio of exposed facet hence leading towards improving the photocatalytic efficiency of the nanomaterial. To evaluate the photocatalytic performance of the synthesized TiO2, Remazol Brilliant Blue (0.01 g/L) was chosen as the target pollutant. The enhanced photodegradation of co-doped F/Cl-TiO2 was evaluated and it was found that 87.21% and 43.21% of Remazol Brilliant Blue had successfully been degraded within 120 min with irradiation of broad spectrum and blue light (475 nm) respectively. This is mainly attributed to the co-exposed {001}/{100} anatase TiO2 facet presence in the F/Cl-TiO2 sample.

Self-Competitive Adsorption Behavior of Arsenic on the TiO2 Surface.

TiO2 is a commonly used material to remove arsenic from drinking water by adsorption as well as photocatalytic oxidation (PCO). In the present paper, arsenic adsorption and PCO at different pH environments are studied on the (1 1 0) facet of rutile TiO2 (r-TiO2). A self-competitive adsorption (SCA) behavior of arsenic is observed; i.e., arsenic species compete to adsorb on the surface. Related DFT calculations are carried out to simulate adsorption. SCA behavior is the key to connecting calculation results with experimental results. Furthermore, PCO of arsenite is performed at different pH values. Of note, PCO is related to adsorption; namely, the adsorption process determines the whole PCO reaction speed. Therefore, SCA is also helpful for the PCO reaction. The SCA behavior is useful not only for arsenic on r-TiO2 but also for arsenic on anatase TiO2 (a-TiO2). It may be helpful to further study arsenic adsorption and PCO on other materials such as Fe2O3 and MnO2. The SCA behavior extends our understanding of arsenic and provides new insights into arsenic removal and its cycle in nature.

Facet‐Dependent Interfacial and Photoelectrochemical Properties of TiO2 Nanoparticles

AbstractThe photoelectrochemical properties of titanium dioxide (TiO2) nanoparticles are directly related to the presence of certain facets. The synthesis of such particles is challenged using volatile and sensitive precursors utilizing shape capping agents. In this study, an easier two‐step synthesis technique for the preparation of well‐specified morphology TiO2 nanocrystals from TiO2 powder is demonstrated. The facet‐dependent Fermi level and flat band potential of the prepared particles are calculated and their photoelectrochemical properties are investigated by Cu2+ and Pb2+ photo/electrodeposition. From Cu2+ electrodeposition, it is shown that the presence of {100} and {001} facets in cubic morphology facilitates the electrodeposition with progressive nucleation mechanisms, while the presence of {101} facet in octahedral geometry follows instantaneous nucleation mechanisms. The activity of electroreduction is also related to the flat‐band potential which shows the highest activity in Pb2+ electrodeposition for octahedron nanostructure due to the alignment of the reduction potential to the edge of the flat band. Photodeposition of Cu2+ and Pb2+ ions shows identical trends to electrodeposition indicating the facets influence in ion adsorption and structure of the bandgap of morphological TiO2. The findings emphasize the importance of facet‐dependent surface adsorption and bandgap structure designing faceted TiO2 nanoparticles for tailored applications.