TiO2-supported Single-atom Catalysts: Synthesis,Structure, and Application

In recent years, single-atom catalysts(SACs) have attracted increasing attention in catalysis. However, their stability is considerably challenging. As a result, fine-tuning the interaction of metal single atoms(SA) with different types of supports has emerged as an effective strategy for improving their thermal and chemical stabilities. Owing to its non-toxicity, cost-effectiveness, high abundance, and excellent stability, as well as presence of rich, tunable, and reliable anchor sites for metal SA, TiO₂ has been extensively explored as a superior support for SACs. In this review, recent advances of TiO₂-supported SACs(M₁/TiO₂) are discussed, and synthetic strategies, structure elucidation, and catalytic applications are summarized. First, the recently developed synthetic strategies for M₁/TiO₂arehighlighted and summarized, identifying the major challenges for the precise fabrication of M₁/TiO₂. Subsequently, key characterization techniques for the structure identification of M₁/TiO₂are discussed. Next, catalytic applications of M₁/TiO₂ are highlighted, viz. photocatalysis, electrocatalysis, and thermocatalysis. In addition, the mechanism via geometric structures and electronic states of metal centers facilitate catalytic reactions is outlined. Finally, opportunities and challenges of M₁/TiO₂ in catalysis are discussed, which may inspire the future development of M₁/TiO₂ for multifunctional catalytic applications.     

Progress and Prospect of Photothermal Catalysis

Recently, solar-driven synthesis due to its energy-saving and environmentally friendly advantages has attracted more and more attention, whereas the low solar-to-chemical conversion efficiency significantly hindered its development. New effective options that fully utilize full-band sunlight are urgently needed. Novel photothermal catalysis combined with the advantages of photocatalysis and thermalcatalysis can improve the utilization efficiency of solar energy and lower the reaction temperature, thus becoming a promising technology. This review divides photothermal catalysis into photo-assisted thermalcatalysis, thermal-assisted photocatalysis, and photothermal synergistic catalysis. Furthermore, the catalytic mechanical understanding of how photothermal affects the catalytic property of different applications(e.g., water splitting, CO₂/N₂ reduction, and environmental treatment) was also summed up and discussed in detail. The discussion ends with unsolved challenges in photothermal catalysis, particularly emphasizing the effect of temperature or sunlight on catalytic performance.     

过渡金属离子的掺杂对TiO2光催化活性的影响

考察了过渡金属离子对TiO₂ 光催化性能的影响,结果发现:第二过渡系列金属离子对TiO₂ 膜的修饰作用比第一过渡系列金属离子的修饰作用更加明显;第二、六副族的金属离子对TiO₂ 膜的修饰效果较好.通过X射线衍射(XRD)、电镜分析 (SEM)、光电能谱分析 (XPS)及差热分析 (DTA)对催化剂表面进行了表征,结果表明:TiO₂ 的晶型为锐钛矿型,粒子半径为 32.58nm.     

TiO2表面光催化基元过程

在过去的几十年里,得益于二氧化钛(TiO₂)作为光催化剂在光催化分解水、污染物降解方面的潜在应用,人们对TiO₂光催化剂的开发、改良以及TiO₂表面光催化机理的基础研究方面都投入了巨大的精力。因此,在超高真空环境下,利用不同的实验和理论方法,人们对TiO₂表面(特别是金红石TiO₂(110)表面)的热催化和光催化过程进行了大量的研究,以此来获得上述重要反应中的一些机理性的信息。本文中,将从TiO₂的物质结构以及电子结构开始,然后着重介绍TiO₂表面光生电荷(电子和空穴)的传输、捕获以及电子转移动力学方面的进展。在此基础上,总结了甲醇在金红石TiO₂(110)、TiO₂(011)以及锐钛矿TiO₂(101)表面光化学基元反应过程的一些实验结果。这些结果不仅能增进我们对表面光催化基元过程的认识,同时也能激励我们进一步去研究表面光催化基元过程。最后,基于现有光化学实验结果,简短地讨论了我们对光催化反应机理的一点看法,并提出了一个可能的光催化模型,这可以引起人们对光催化反应机理更全面的思考。     

二氧化钛多孔材料及其性能研究进展

二氧化钛(TiO₂)多孔材料由于具有优异的物理化学性质,在催化、能源、传感等领域展现了重要的研究价值和应用潜力。 TiO₂的多孔结构特别在一些涉及异相反应的应用(如异相催化、气敏等)中具有重要的优势,如丰富的传质通道和表面活性位点、可调变的孔尺寸等。 目前,多孔TiO₂功能材料的开发和优化研究正在不断推进其工业化应用的进程。 本文围绕多孔TiO₂的几个优势应用领域(光催化、光生电子存储和气敏)的研究进展,从结构和缺陷设计出发介绍和讨论性能调控策略。 本文还特别介绍了本课题组通过光诱导合成法开发的一系列多孔TiO₂基功能材料,并对相关性能研究领域的关键问题进行了分析和展望。     

锐钛矿TiO2（101）表面电子能带结构的理论研究

二氧化钛作为一种理想的光催化和光电转换半导体材料,受到了广泛的关注和研究,其表面的电子能带结构作为其本征的化学性质之一,决定着表面上氧化还原反应发生的可能性. 对二氧化钛表面电子能带结构进行深入研究对于我们从微观上认识并改良二氧化钛这一光电催化材料,以及进一步开发利用更好的光催化材料都具有非常好的指导意义. 本论文采用密度泛函理论,计算研究了锐钛矿TiO₂（101）表面的电子能带结构,并通过与金红石TiO₂（110）晶面的对比,系统分析了两个表面电子能带结构的不同以及水分子的溶剂化作用对电子能带结构的影响.     

Foam-structured Activated Carbon-ceramic as TiO2 Supports for Photocatalytic Degradation of Phenol

An activated foam-structured carbon-ceramic(AFCC) was prepared and investigated as TiO₂ support for the photocatalytic degradation of phenol. AFCC and TiO₂/AFCC catalysts were characterized by N₂ adsorption- desorption and X-ray diffraction(XRD). The effects of AFCC on the photocatalytic activity and the crystallinity of TiO₂ were studied. The results show that the crystallinity and anatase/rutile ratio of TiO₂ loaded on AFCC could be significantly influenced by the calcination temperature. The degradation rate of phenol benefited from the synergistic effects of the adsorption of activated carbon(AC) and the photocatalysis of TiO₂, which suggests that a high surface area of AC is essential to achieve high degradation rates and efficiencies. It was found that the larger mean cell size of AFCC increased the light transmission within the foam.     

引入应力的锐钛矿TiO_2(001)薄膜的外延生长

锐钛矿TiO_2(001)(anataseTiO_2(001),简记为ATO)表面因其优异的催化活性受到了广泛的关注。理论计算结果表明,ATO表面应力导致的晶格畸变可能会增强该表面的催化活性。因此有必要研究应力对ATO表面结构的影响。本文利用BaTiO_3(001)(简记为BTO)与ATO之间存在较大的晶格失配度,将ATO薄膜外延生长在BTO衬底上从而引入应力,研究了存在应力情况下的ATO薄膜的结构特征。实验中,利用脉冲激光沉积方法在Nb掺杂的SrTi O_3(001)(简记为STO)单晶衬底上制备了ATO/BTO/STO外延薄膜。X射线衍射(XRD)和扫描透射电子显微术(STEM)结果表明,作为应力引入层的BTO薄膜厚度约为4–6nm时,能够部分地将应力引入到ATO薄膜中。X射线光电子能谱(XPS)结果显示,ATO薄膜合适的厚度应大于15 nm,从而降低从衬底反向扩散至表面的Sr和Ba原子的浓度;Ti 2p的高分辨XPS谱仅呈现出Ti~(4+)峰,表明ATO表面Ti原子为完全氧化的价态。ATO外延薄膜表面的扫描隧道显微术(STM)图像仍然呈现为(1×4)重构的结构,但在(1×4)重构的脊上存在明暗交替并具有一定周期性的特征。根据完全氧化的"增氧原子模型"(ad-oxygen model,AOM),脊上观察到的明暗交替特征可归因于表面应力导致的"TiO_2"空位缺陷结构。     

Template Synthesis and Characterization of Cu2O/TiO2 Coaxial Nanocable for Photocatalysis

Coaxial nanocable consisted of p-type Cu₂O nanowires and n-type TiO₂ nanotubes arrays was prepared in the porous anodic aluminum oxide(AAO) template via the sol-gel method and subsequent electrodeposition method. X-ray diffraction analysis identified an anatase structure of the TiO₂ nanotubes and cubic structure of the Cu₂O nanowires. The obtained samples were also characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive X-ray spectroscopy(EDS). The diffrence of open circuit potential of the coaxial nanocable electrode was larger than that of the TiO₂ nanotubes electrode under ultraviolet illumination, which means doping with Cu₂O could improve the photovoltage effectively. Meanwhile, nanocable arrays exhibited a high activity for photodegrading Rhodamine B under Xe lamp irradiation and the photocatalysis degradation efficiency was up to 98.69% after degradation for 7 h. The enhanced photocatalytic activity could be attributed to the high migration efficiency of photoinduced electrons, which may suppress the charge recombination effectively.     

Stabilization mechanism of TiO2 on flexible fluorocarbon films as a functional photocatalyst

The repetitive discoloration kinetics of the azo-dye Methyl Orange (taken as a model organic compound) was followed under solar simulated radiation (90 mW/cm²) to assess the performance of the TiO₂/Tedlar^® composite photocatalyst. The influence of solution parameters on the photo-discoloration process: pH, dye concentration, applied light intensity and concentration of H₂O₂ were systematically investigated. During the photocatalysis a modification occurs in the TiO₂/Tedlar^® composite due to the TiO₂ interaction with the Tedlar^® film. Physical insight is given for the stabilization mechanism of the TiO₂ particles in the Tedlar matrix based on the data obtained by X-ray photoelectron spectroscopy (XPS). The F 1s peak of the Tedlar film indicates that the TiO₂ is loaded on the Tedlar fluoro-groups. The loading of TiO₂ on the 75 μm thick Tedlar^® film was 0.9% (w/w) as determined by atomic absorption spectrophotometry (AAS). Attenuated total reflection infrared spectroscopy (ATRIR) shows no formation of additional bands within the photodiscoloration reaction. This shows that an efficient catalysis taking place on the TiO₂/Tedlar^® surface. The rugosity (mean square roughness, rms) of the TiO₂/Tedlar^® film was determined by atomic force microscopy (AFM) to be 19.7 nm. This value remained constant during long-term operation. Transmission electron microscopy (TEM) reports the thickness and coverage of TiO₂ Degussa P-25 on the Tedlar^® surface before and after photocatalysis.     

阴离子对TiO2晶形的影响及光催化性能研究

以SO₄^2-、F^-、Cl^-和PO₄^3-作为阴离子来研究其对水热合成TiO₂(分别记为TiO₂-S、TiO₂-F、TiO₂-Cl和TiO₂-P)晶体的影响,并考察了其光催化性能.SEM显示TiO₂-S、TiO₂-F、TiO₂-Cl和TiO₂-P分别呈粒子、十面体、刺球和不规则块状.XRD图谱表明TiO₂-S和TiO₂-F为锐钛矿晶型,TiO₂-Cl为金红石晶型,而TiO₂-P为锐钛矿、金红石和板钛矿混合晶型,这一结论也被紫外-可见漫反射实验所证实.XPS能谱表明这4种TiO₂纳米材料都受到了各自阴离子掺杂的影响,光催化试验显示:它们的光催化活性顺序为: TiO₂-F>TiO₂-S>TiO₂-Cl>TiO₂-P,这表明锐钛矿的光催化活性要大于金红石和板钛矿,且具有{001}面,掺杂了F的锐钛矿光催化活性更强.     

异质结型光催化膜的活性及其机理研究

采用浸渍提拉法制得TiO₂,ZnO,Fe₂O₃,ZnO/TiO₂,TiO₂/ZnO,Fe₂O₃/TiO₂和TiO₂/Fe₂O₃石英玻璃基底负载膜.光催化降解亚甲基蓝实验表明,TiO₂和ZnO具有良好的光催化活性,Fe₂O₃活性较差.但形成异质结后,TiO₂和Fe₂O₃的光催化降解能力发生明显的变化.用254nm紫外光光照后,TiO₂,ZnO和Fe₂O₃等3种氧化物膜与水的接触角均有不同程度的降低,TiO₂表现出超亲水性,ZnO/TiO₂和Fe₂O₃/TiO₂膜与水的接触角小于对应的单纯ZnO和Fe₂O₃膜与水的接触角,其中Fe₂O₃/TiO₂表面出现超亲水性.瞬态光电导谱的少数载流子寿命的测定表明,异质结势垒电场能有效地增强光生电子-空穴对的分离效率.根据能带理论建立的两组异质结能带模型可合理地解释实验结果.     

One Step Preparation of Highly Dispersed TiO2 Nanoparticles

A facile approach was developed to prepare highly dispersed TiO₂ nanoparticles with selected phase. The crystallization phase of the nanoparticles can be easily tuned from anatase to rutile by the dosage of hydrochloric acid in the reaction system. The crystallite size of the as-prepared anatase TiO₂ nanoparticles was ca. 3.2 nm with high dispersion. A transparent TiO₂ colloid was obtained by dispersing the as-prepared anatase TiO₂ nanoparticles in deionized water without any organic additives added. The concentration of TiO₂-H₂O colloid can be as high as 1600 g/L. The optical transmittance of TiO₂-H₂O colloid with a low concentration was nearly 100% in the visible region. Furthermore, anatase TiO₂ nanoparticles(TiO₂-NPs) showed superior photocatalytic performance compared to rutile TiO₂-NPs.     

Sn4+掺杂对TiO2纳米颗粒膜光催化降解苯酚活性的影响

金属离子掺杂能改善TiO2纳米微粒光催化活性,在光降解大气和水污染物的研究中,已引起人们的重视[1,2].实验证明,掺杂物的浓度、掺杂离子的分布、掺杂能级与TiO2能带匹配程度、掺杂离子d电子的组态、电荷的转移和复合等因素对催化剂的光催化活性有直接影响[3].Kamat等[4]曾利用TiO2颗粒与SnO2颗粒混合制膜,使光催化剂活性得到提高.但Sn4+掺杂TiO2用于光催化剂尚少见报道.本文采用等离子体化学气相沉积法(PECVD)[5]制备了Sn4+离子掺杂的TiO2纳米颗粒膜催化剂(TiO2-Sn),考察了其对苯酚的光催化降解活性,讨论了Sn4+离子的掺杂方式及光催化活性提高的机理.     

Research progress of photocatalysis based on highly dispersed titanium in mesoporous SiO2

This paper reviewed the TiO₂-SiO₂ and Ti-SiO₂ mesoporous materials and their applications in photocatalysis.     

部分还原二氧化钛的NMR和EPR研究

Partially reduced TiO₂ nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO₂ (Re-A-TiO₂) nanoparticle material using a fast combustion method, demonstrating good activity toward decomposing methyl orange under visible light irradiation. The surface structure of the prepared material, after being surface-selectively ¹⁷O-labeled with H₂¹⁷O (¹⁷O-enriched water), was studied via ¹⁷O and ¹H solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and the obtained results were compared to those of non-reduced anatase TiO₂ (A-TiO₂). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti³⁺) in Re-A-TiO₂ were much higher than that in A-TiO₂, while the former was associated with a higher OV/Ti³⁺ ratio. The intensities of the EPR signals were significantly affected by the adsorbed water, and this phenomenon was explored in combination with ¹H NMR spectroscopy. The ¹H species on Re-A-TiO₂ appeared at larger chemical shifts, denoting the increased acidity of the sample, and these ¹H species on Re-A-TiO₂ were more difficult to remove than those on A-TiO₂. On the other hand, different features were observed for the signals arising from the two-coordinated oxygen atoms (μ₂-O) in ¹⁷O NMR, suggesting a typical anatase TiO₂(101) surface on A-TiO₂, but a more complex surface environment for Re-A-TiO₂. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO₂ compared to that on A-TiO₂, indicating a larger proportion of exposed (001) facets on Re-A-TiO₂. However, the μ₂-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO₂ surface in such conditions. Based on the EPR and NMR results, a significant fraction of the OH species is believed to be formed from the reaction of the paramagnetic centers and adsorbed water molecules. The ¹H→¹⁷O cross polarization (CP) MAS and two-dimensional heteronuclear correlation (2D HETCOR) NMR spectra were used to verify the spatial proximity of the hydrogen and oxygen species, confirming the spectral assignments of a strongly adsorbed water and one type of surface OH species. In particular, the ¹H NMR signals at approximately 11 ppm were ascribed to the hydrogen species in the intramolecular hydrogen bond. In summary, this study investigated the paramagnetic species and surface structure of anatase TiO₂ materials by combining EPR along with ¹H and ¹⁷O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO₂ and A-TiO₂ should be closely related to their different properties toward the photodegradation of methyl orange.     

Photoelectro-synergistic catalysis combined with a FIA system application on determination of chemical oxygen demand

In this paper, photoelectro-synergistic catalysis oxidation of organics in the water on Ti/TiO₂/PbO₂ electrode was investigated. The prepared TiO₂ film was investigated with Atomic force micrograph (AFM). Furthermore, the results were compared with those obtained from electrocatalysis (EC) and electro-assisted photocatalysis (PC). The method proposed employed photoelectro-synergistic catalysis (PEC), together with flow injection analysis, to determine the chemical oxygen demand (COD) values. It was shown that the method of photoelectro-synergistic catalysis had lower detection limit (15.0 mg l⁻¹) and wider linear range (30.0–2500.0 mg l⁻¹) than the methods of electro-assisted photocatalysis and electrocatalysis. The results obtained by the proposed method and conventional one were compared by carrying out the experiment on 20 wastewater samples and also agreed well by high correlation (R = 0.9912).     

微波辅助快速制备2D/1D ZnIn2S4/TiO2 S型异质结及其光催化制氢性能

The threat and global concern of energy crises have significantly increased over the last two decades. Because solar light and water are abundant on earth, photocatalytic hydrogen evolution through water splitting has been considered as a promising route to produce green energy. Therefore, semiconductor photocatalysts play a key role in transforming sunlight and water to hydrogen energy. To date, various photocatalysts have been studied. Among them, TiO₂ has been extensively investigated because of its non-toxicity, high chemical stability, controllable morphology, and high photocatalytic activity. In particular, 1D TiO₂ nanofibers (NFs) have attracted increasing attention as effective photocatalysts because of their unique 1D electron transfer pathway, high adsorption capacity, and high photoinduced electron–hole pair transfer capability. However, TiO₂ NFs are considered as an inefficient photocatalyst for the hydrogen evolution reaction (HER) because of their disadvantages such as a large band gap (~3.2 eV) and fast recombination of photoinduced electron–hole pairs. Therefore, the development of a high-performance TiO₂ NF photocatalyst is required for efficient solar light conversion. In recent years, several strategies have been explored to improve the photocatalytic activity of TiO₂ NFs, including coupling with narrow-bandgap semiconductors (such as ZnIn₂S₄). Recently, microwave (MW)-assisted synthesis has been considered as an important strategy for the preparation of photocatalyst semiconductors because of its low cost, environment-friendliness, simplicity, and high reaction rate. Herein, to overcome the above-mentioned limiting properties of TiO₂ NFs, we report a 2D/1D ZnIn₂S₄/TiO₂ S-scheme heterojunction synthesized through a microwave (MW)-assisted process. Herein, the 2D/1D ZnIn₂S₄/TiO₂ S-scheme heterojunction was constructed rapidly by using in situ 2D ZnIn₂S₄nanosheets decorated on 1D TiO₂ NFs. The loading of ZnIn₂S₄ nanoplates on the TiO₂ NFs could be easily controlled by adjusting the molar ratios of ZnIn₂S₄ precursors to TiO₂ NFs. The photocatalytic activity of the as-prepared samples for water splitting under simulated solar light irradiation was assessed. The experimental results showed that the photocatalytic performance of the ZnIn₂S₄/TiO₂ composites was significantly improved, and the obtained ZnIn₂S₄/TiO₂ composites showed increased optical absorption. Under optimal conditions, the highest HER rate of the ZT-0.5 (molar ratio of ZnIn₂S₄/TiO₂= 0.5) sample was 8774 μmol·g^-1·h^-1, which is considerably higher than those of pure TiO₂ NFs (3312 μmol·g^-1·h^-1) and ZnIn₂S₄nanoplates (3114 μmol·g^-1·h^-1) by factors of 2.7 and 2.8, respectively. Based on the experimental data and Mott-Schottky analysis, a possible mechanism for the formation of the S-scheme heterojunction between ZnIn₂S₄ and TiO₂ was proposed to interpret the enhanced HER activity of the ZnIn₂S₄/TiO₂heterojunctionphotocatalysts.      

Synthesis of nano-TiO2 assisted by diethylene glycol for use in high efficiency dye-sensitized solar cells

The performance of dye-sensitized solar cells(DSSCs) consisting of anatase TiO_2 nanoparticles that were synthesized via a hydrothermal method was studied.The synthesized TiO_2 nanoparticles were characterized by X-ray diffraction(XRD),nitrogen sorption analysis,scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),and UV-vis spectroscopy.Then the J-Vcurve,electrochemical impedance spectroscopy(EIS),and open-circuit voltage decay(OCVD) measurement were applied to evaluate the photovoltaic performance of DSSCs.Compared with the commercial TiO_2nanoparticles(P25),the synthesized-TiO_2 nanoparticles showed better performance.By adding diethylene glycol(DEG) before the hydrothermal process,the synthesized TiO_2 nanoparticles(hereafter referred to as TiO_2-DEG particles) shows narrower size distribution,larger specific surface area,higher crystallinity,and less surface defects than TiO_2(DEG free) particles.The analysis of photovoltaic properties of DSSCs based on TiO_2-DEG particles showed that the recombination of electron-hole pairs was decreased and the trapping of carries in grain boundaries restrained.It was believed that the photoelectrode fabricated with the as-prepared TiO_2 nanoparticles improved the loading amount of dye sensitizers(N719).and enhanced the photocurrent of the DSSCs.As a result,the TiO_2-DEG particle based cells achieved a photo-to-electricity conversion efficiency(η) of 7.90%,which is higher than 7.53%for the cell based on TiO2(DEG free) and 6.59%for the one fabricated with P25.     

方形锐钛矿TiO2纳米晶的合成及表征

在不添加任何模板剂或形状控制剂的条件下,以TiCl₄为前体,经氨水沉淀、乙醇洗涤和超临界干燥(AS制备法)选择性地合成了方形锐钛矿TiO₂纳米单晶.热稳定性研究结果表明,当焙烧温度不超过650℃时,方形锐钛矿TiO₂纳米晶的表面积、孔容、晶粒/颗粒尺寸基本保持不变.XRD和拉曼光谱分析表明,方形锐钛矿TiO₂纳米晶在800℃下焙烧后仍能保持晶相不变,表现出很强的抗晶相转变能力.但在1000℃焙烧后,样品可以完全转变成金红石相TiO₂.