Prolonging charge-separation states by doping lanthanide-ions into {001}/{101} facets-coexposed TiO_2 nanosheets for enhancing photocatalytic H_2 evolution

Ultrathin TiO2 nanosheets with coexposed {001}/{101} facets have attracted considerable attention because of their high photocatalytic activity. However, the charge-separated states in the TiO2 nanosheets must be extended to further enhance their photocatalytic activity for H2 evolution. Herein, we present a successful attempt to selectively dope lanthanide ions into the {101} facets of ultrathin TiO2 nanosheets with coexposed {001}/{101} facets through a facile one-step solvothermal method. The lanthanide doping slightly extended the light-harvesting region and markedly improved the charge-separated states of the TiO2 nanosheets as evidenced by UV-vis absorption and steady-state/transient photoluminescence spectra. Upon simulated sunlight irradiation, we observed a 4.2-fold enhancement in the photocatalytic H2 evolution activity of optimal Yb3+-doped TiO2 nanosheets compared to that of their undoped counterparts. Furthermore, when Pt nanoparticles were used as cocatalysts to reduce the H2 overpotential in this system, the photocatalytic activity enhancement factor increased to 8.5. By combining these results with those of control experiments, we confirmed that the extended charge-separated states play the main role in the enhancement of the photocatalytic H2 evolution activity of lanthanide-doped TiO2 nanosheets with coexposed {001}/{101} facets.

Synthesis and Optimization of TiO_2/Graphene with Exposed {001} Facets Based on Response Surface Methodology and Evaluation of Enhanced Photocatalytic Activity

Response surface methodology(RSM) was employed to optimize the control parameters of TiO_2/graphene with exposed {001} facets during synthesis, and its enhanced photocatalytic activities were evaluated in the photodegradation of toluene. Experimental results were in good agreement with the predicted results obtained using RSM with a correlation coefficient(R^2) of 0.9345. When 22.06 mg of graphite oxide(GO) and 2.09 mL of hydrofluoric acid(HF) were added and a hydrothermal time of 28 h was used, a maximum efficiency in the degradation of toluene was achieved. X-ray diffraction(XRD), transmission electron microscopy(TEM), and scanning electron microscopy(SEM) were employed to characterize the obtained hybrid photocatalyst. The electron transferred between Ti and C retarded the combination of electron–hole pairs and hastened the transferring of electrons, which enhanced the photocatalytic activity.

One-step synthesized SO_4^(2-)-TiO_2 with exposed(001) facets and its application in selective catalytic reduction of NO by NH_3

A sample of sulfated anatase TiO2 with high‐energy(001)facets(TiO2‐001)was prepared by a simple one‐step hydrothermal route using SO42-as a morphology‐controlling agent.After doping ceria,Ce/TiO2‐001 was used as the catalyst for selective catalytic reduction(SCR)of NO with NH3.Compared with Ce/P25(Degussa P25 TiO2)and Ce/P25‐S(sulfated P25)catalysts,Ce/TiO2‐001 was more suitable for medium‐and high‐temperature SCR of NO due to the high surface area,sulfation,and the excellent properties of the active‐energy(001)facets.All of these facilitated the generation of abundant acidity,chemisorbed oxygen,and activated NOx‐adsorption species,which were the important factors for the SCR reaction.

Pt/TiO2 Nanosheets Array Dominated by {001} Facets with Enhanced Photocatalytic Activity

{001} facets dominated single crystalline anatase TiO2 nanosheet array （TNSA） was synthe-sized through an optimized organic solvothermal route on uorine-doped tin oxide substrate. The field emission scanning electron microscopy images and X-ray diffraction patterns re-vealed that the {001} synthesized facets dominated TNSA exhibited much higher orientation than that synthesized by hydrothermal route. The TNSAs were loaded with Pt nanoparti-cles in uniformly size by using a photodecomposition method, which were further con rmed by high resolution transmission electron microscopy （HRTEM）. The HRTEM images also revealed that Pt nanoparticles preferred to deposit on {001} facets. With loading of Pt nanoparticles, the optical absorbance was significantly enhanced, while the photolumines- cence （PL） was inhibited. The photocatalytic activity of TNSA was signi cantly improved by Pt loading and reached the maximum with optimal amount of Pt loading. The optimal amount of Pt on {001} facets is far less than that on TiO2 nanoparticles, which may be attributed to the specific atom structure of reactive {001} facets.

Surface Modification of (001) Facets Dominated TiO2 with Ozone for Adsorption and Photocatalytic Degradation of Gaseous Toluene

This study investigated the positive effect of surface modification with ozone on the photocatalytic performance of anatase TiO2 with dominated（001） facets for toluene degradation.The performance of photocatalyst was tested on a home-made volatile organic compounds degradation system. The ozone modification, toluene adsorption and degradation mechanism were established by a combination of various characterization methods, in situ diffuse reflectance infrared fourier transform spectroscopy, and density functional theory calculation.The surface modification with ozone can significantly enhance the photocatalytic degradation performance for toluene. The abundant unsaturated coordinated 5 c-Ti sites on（001）facets act as the adsorption sites for ozone. The formed Ti–O bonds reacted with H2O to generate a large amount of isolated Ti5 c-OH which act as the adsorption sites for toluene,and thus significantly increase the adsorption capacity for toluene. The outstanding photocatalytic performance of ozone-modified TiO2 is due to its high adsorption ability for toluene and the abundant surface hydroxyl groups, which produce very reactive OH·radicals under irradiation. Furthermore, the O2 generated via ozone dissociation could combine with the photogenerated electrons to form superoxide radicals which are also conductive to the toluene degradation.

g-C3N4/{001}TiO2复合催化剂光催化氧化NO性能研究

将制备好的{001}TiO_2与尿素混合,通过煅烧处理得到可见光响应的g-C_3N_4/{001}TiO_2。通过XRD、FT-IR和UV-Vis DRS来证实g-C_3N_4/{001}TiO_2复合催化剂的形成,并分别在紫外和可见光下考察其对NO的光催化氧化性能。结果表明:所制备的g-C_3N_4/{001}TiO_2对NO有明显的去除效果,且当g-C_3N_4质量比为10%时,其催化活性最高,在紫外光下分别是纯{001}TiO_2的2.4倍,是纯g-C_3N_4的4.1倍;在可见光下是纯g-C_3N_4的5.8倍。g-C_3N_4/{001}TiO_2复合催化剂活性增强的原因归结于两种主体材料的紧密复合,提高了载流子分离效率。

不同暴露比例(001)晶面锐钛矿相TiO_2纳米方块的合成及气敏性能

在众多提高TiO_2气敏性能的尝试中,晶面调控的方法引起了极大的关注。主要通过调整水热反应的制备工艺,实现TiO_2的(001)晶面暴露不同比例,对其进行气敏性能的研究。通过改变反应物浓度完成了一系列不同晶面暴露比的TiO_2纳米方块的可控水热合成,实现了对TiO_2纳米方块形貌以及晶面的调控。合成TiO_2纳米方块暴露(001)晶面的比例从33.33%增加到83.33%。随(001)晶面暴露比例的提高,对于丙酮气体的灵敏度从14.3提高到了27.8。

TiO2 nanosheets with exposed {001} facets for photocatalytic applications

TiO2 nanosheets with highly reactive {001} facets （{001}-TiO2） have attracted great attention in the fields of science and technology because of their unique properties. In recent years, many efforts have been made to synthesize {001}-TiO2 and to explore their applications in photocatalysis. In this review, we summarize the recent progress in preparing {001}-TiO2 using different techniques such as hydrothermal, solvothermal, alcohothermal, chemical vapor deposition （CVD）, and sol gel-based techniques. Furthermore, the enhanced efficiency of {001}-TiO2 by modification of carbon materials, surface deposition of transition metals, and non-metal doping is reviewed. Then, the applications of {001}-TiOR-based photocatalysts in the degradation of organic dyes, hydrogen evolution, carbon dioxide （CO2） reduction, bacterial disinfection, and dye-sensitized solar cells are summarized. We believe this entire review on TiO2 nanosheets with {001] facets can further inspire researchers in associated fields.

Hierarchical TiO2 nanorods with a highly active surface for photocatalytic CO2 reduction

Photocatalytic carbon dioxide reduction reaction(CO2RR)has been considered as one of most effective ways to solve the current energy crisis and environmental problems.However,the practical application of photocatalytic CO2RR is largely hindered by lock of efficient catalyst.Here,hierarchical titanium dioxide(TiO2)nanostructures with a highly active{001}surface were successfully synthesized by a facile approach from metal Ti powders.The obtained hierarchical TiO2 nanostructures were composed of TiO2 nanorods,which have a diameter about 5–10 nm and a length of several micrometers.It is found that these nanorods have exposed{001}facets.On the other hand,these hierarchical TiO2 nanostructures have a good light-harvesting efficiency with the help of TiO2 nanorods component and large specific surface area.Therefore,these hierarchical TiO2 nanostructures exhibit a much better activity for photocatalytic CO2 reduction than that of commercial TiO2(P25).This high activity can be attributed to the synergistic effects of active surface,efficient charge transfer along nanorods and good light harvesting in the nanorod-hierarchical nanostructures.

Effect of defects in TiO2 nanoplates with exposed {001} facets on the gas sensing properties

The exposed crystal facet of TiO2 is a crucial factor influencing the gas sensing properties. TiO2 with high-energy{001}crystal facets that have higher surface energy and reactivity is expected to exhibit excellent gas-sensing properties. In this paper, TiO2 nanoplates with defective{001}facets were synthesized by chemical etching via one-step hydrothermal method. We carefully explored the gas-sensing performance of TiO2 nanoplates with defective and complete{001}facets towards acetone. The results show that the sensing response of TiO2 nanoplates with complete{001}facets is 70%higher than that of defective TiO2 nanoplates, which proves that the{001}facets plays a vital role in improving the gas sensing performance of TiO2. It is speculated that the poor gas sensitivity of defective TiO2 can be contributed to fewer adsorption sites and blocked electron transfer. This work presents a more direct evidence for explaining the important role of the complete{001}crystal facets in high sensitivity of TiO2 and also provides a new insight for preparing high sensitivity sensing materials.

Photocatalytic mechanism of high-activity anatase TiO2 with exposed （001） facets from molecular-atomic scale： HRTEM and Raman studies

Anatase TiO2 with a variant percentage of exposed （001） facets was prepared under hydrothermal processes by adjusting the volume of HF, and the photocatalytic mechanism was studied from atomic-molecular scale by HRTEM and Raman spectroscopy. It was revealed that： 1） From HRTEM observations, the surface of original TiO2 with exposed （001） facets was clean without impurity, and the crystal lattice was clear and completed; however, when mixed with methylene blue （MB） solution, there were many 1 nm molecular absorbed at the surface of TiO2; after the photocatalytic experiment, MB molecules disappeared and the TiO2 lattice image became fuzzy. 2） The broken path of the MB chemical bond was obtained by Raman spectroscopy, i.e., after the irradiation of the light, the vibrational mode of C-N-C disappeared due to the chemical bond breakage, and the groups containing C-N bond and carbon rings were gradually decomposed. Accordingly, we propose that the driving force for breaking the chemical bond and the disappearance of groups is from the surface lattice distortion of TiO2 during photocatalyzation.

Au Nanoparticles Loaded on Hollow TiO2 Microspheres with （001） Exposed Facets： a Strategy for Promoting Photocatalytic Performance

Au nanoparticles loaded TiO2 hollow microspheres with exposed （001） facets（Au-HTFs） were synthesized through template-free hydrothermal process combined with a chemical reduction role. Au-HTFs displayed excellent photocatalytic activity in catalyzing oxidization reaction in organic pollutant system, which originates from the synergistic effect of the reactive （001） facets and Au nanoparticles with a wide range of absorption in visible region based on localized surface plasmon resonance effect. The unique synergistic effect could largely increase the photocatalytic performance resulting from the improvements of both the visible light aborption and the recombination of electron-hole pairs. Our findings revealed that among Au-HTFs with different Au loading percentages, Au-HTFs with 2%（mass fraction） Au loading possessed the superior photocatalytic activity.

Enhanced photocatalytic properties of N–P co-doped TiO_2 nanosheets with {001} facets

Nitrogen （N） and phosphorus （P） co-doped anatase TiO2 nanosheets were realized by low-temperature self-doping N-TiO2 followed by high-temperature P doping with foreign precursor. It is found that P doping process can maintain good TiO2 nanosheets morphology with exposed {001} facets. Chemical state of dopants indicates that N and P atoms replace O on O sites in TiO2 lattice. Compared with pure TiO2 and N-doped TiO2, N-P codoped TiO2 nanosheets exhibits stronger optical absorption and higher degradation rate of dye molecules in visible light regime. The enhanced photocatalytic properties are attributed to two factors. On one hand, N-P co-doping can effectively reduce band gap of TiO2 from 3.20 to 2.48 eV, leading to an enhancement of the absorption in visible light regime. On the other hand, the presence of exposed {001} facets of TiO2 nanosheets can induce the effective sepa- ration of photogenerated electrons and holes in reaction.