The role of graphene and europium on TiO2 performance for photocatalytic hydrogen evolution

Highly efficient Eu-TiO₂/graphene composites were synthesized by a two-step method such as sol-gel and hydrothermal process. The synthesized photocatalysts were characterized by XRD, TEM, XPS, UV–vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The results confirmed that anatase Eu-TiO₂ nanoparticles with average 10 nm sizes were successfully deposited on two-dimensional graphene sheets. The UV–visible spectroscopy showed a red shift in the absorption edge of TiO₂ due to Eu doping and graphene incorporation. Moreover, effective charge separation in Eu-TiO₂/graphene composites was confirmed by PL emission spectroscopy compared to TiO₂/graphene, Eu-TiO₂ and pure TiO₂. The photocatalytic activity for H₂ evolution over prepared composites was studied under visible light irradiation (λ ≥ 400 nm). The results demonstrate that photocatalytic performance of the photocatalysts for hydrogen production increases with increasing doping concentration of Eu upto 2 at%. However, further increase in doping content above this optimum level has decreased the performance of photocatalyst. The enhanced photocatalytic performance for H₂ evolution is attributed to extended visible light absorption, suppressed recombination of electron-hole pairs due to synergistic effects of Eu and graphene.     

载流子对聚苯胺可见光催化苄胺氧化性能的影响

使用不同浓度的盐酸对本征态聚苯胺进行再掺杂处理,制备了一系列不同载流子（极化子和双极化子）含量的聚苯胺,通过FTIR、XRD、XPS和EPR等表征分析了极化子和双极化子结构的形成及变化过程,探究了载流子含量对能带结构、苄胺吸附活化、导电性以及光生电子-空穴分离效率的影响,考察了极化子和双极化子结构对聚苯胺光催化苄胺氧化的影响。结果表明：HCl掺杂过程中会有极化子和双极化子结构的形成,极化子和双极化子均能吸附苄胺形成表面复合物,拓展了可见光的吸收范围。极化子结构介导光生电子转移过程,促进光生电子-空穴分离,进而提高光催化苄胺氧化活性,而双极化子的存在对光催化苄胺高效转化不利。     

Facile synthesis of a novel photocatalyst with integrated features for industrial effluents treatment

Faster charge transport, excellent charge separation, narrow bandgap energy, lower electron-hole pair recombination rate, and high visible light absorption are the key features of an ideal photocatalyst material. Undoubtedly, semiconductor-based photocatalysts having remarkable charge separation efficiency have attracted considerable attention for degrading hazardous organic pollutants from contaminated water. So herein, a novel composite of reduced graphene oxide (rGO) supported by gadolinium doped bismuth yttrium oxide (Gd-BiYO₃/rGO) was prepared by simple precipitation and ultrasonication method. The photocatalytic efficiency of the Gd-BiYO₃/rGO composite was examined comparatively with pure BiYO₃ and Gd-BiYO₃ samples to degrade Methylene Blue (MB) dye under visible light irradiation. The Gd doping and rGO incorporation into BiYO₃ increased the conductivity, improved the charge transfer efficiency, and impeded the charge recombination, resulting in superior photocatalytic activity of Gd-BiYO₃/rGO. The kinetic studies exhibited the 96.2%, 61.5%, and 48.3% degradation of MB after 80 min irradiation of 1 SUN visible light under Gd-BiYO₃/rGO, Gd-BiYO₃, and BiYO₃, respectively. The Gd-BiYO₃/rGO composite degraded the MB dye at a rate (k = 0.0328 min^-1) that is 5.05 and 2.68-fold higher than pure BiYO₃ and Gd-BiYO₃, correspondingly. The transient photocurrent response of Gd-BiYO₃/rGO was comparatively 4.7 and 2.8 times greater than that of BiYO₃ and Gd-BiYO₃ photocatalysts, respectively. The dominant photocatalytic performance of Gd-BiYO₃/rGO is primarily ascribed to the formation of heterojunctions between rGO nanosheets and Gd-BiYO_3, which facilitate higher visible light absorbance, effective charge separation, and transfer through interfacial layers, more dye adsorption, lower charge transfer resistance, and hamper electron-hole pair recombination. Overall, the electrochemical results suggest that the current study provides an effective way to synthesize a heterostructure photocatalyst for removing organic pollutants from industrial effluents.     

Preparation of α-SnWO4 hierarchical spheres by Bi3+-doping and their enhanced photocatalytic activity under visible light

Bi-doped α-SnWO₄ porous spheres assembled by thin plates were prepared by a simple hydrothermal process without any template. The effects of Bi³⁺ ions on the microstructure and photocatalytic activity of α-SnWO₄ were investigated. The doping of Bi can induce a shape transformation from nanoplates of pure α-SnWO₄ to hierarchical spheres of Bi-doped samples. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic de-colorization of methyl orange (MO) under visible light irradiation. Bi-doped α-SnWO₄ samples exhibit better photocatalytic property than pure α-SnWO₄, and the optimal Bi-doping concentration is around 0.5 at%. The enhanced photocatalytic properties of Bi-doped α-SnWO₄ spheres can be ascribed to the porous hierarchical structure and the introduction of defects induced by Bi-doping, which improve visible-light absorption and allow the efficient charge separation of the photogenerated electron-hole pairs. Bi-doped α-SnWO₄ has a great potential in industrial water treatment due to its satisfactory recyclability and stability.     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

Fe~(3+)掺杂提高二氧化钛的光催化活性

采用沉淀-水热的方法制备了Fe3+掺杂的TiO2光催化剂,通过XRD、Raman、XPS、UV-DRS等对催化剂的结构、光学吸收性质等进行了表征,并以罗丹明B为目标污染物对可见光催化活性进行了测试。实验结果表明:所制备的TiO2光催化剂为锐钛矿相结构;Fe3+的掺杂使得TiO2的初始吸收边明显向可见光区域拓宽,并且增强了TiO2在可见光区域的吸收;Fe3+掺杂后TiO2的可见光催化活性显著提高,以掺杂浓度为0.5%的TiO2光催化效果最好,在可见光下6h内可将罗丹明B溶液完全降解,降解率是未掺杂TiO2的4倍。     

One-pot solvothermal synthesis of carbon dots/Ag nanoparticles/TiO2 nanocomposites with enhanced photocatalytic performance

In this paper, we reported a “green” and facile method for one-pot solvothermal synthesis of carbon dots (CDs)/Ag nanoparticles (AgNPs)/titanium dioxide (TiO₂, commercial Degussa P25) ternary nanocomposites with enhanced photocatalytic performance. The characterizations of this ternary photocatalyst were studied at length and our results revealed that the crystalline phase of TiO₂ component remained unchanged after the reaction. While the newborn AgNPs and CDs were tightly attached onto the surface of TiO₂ nanoparticles. The photocatalytic activities of photocatalysts were tested by measurements of photo-degradation on methylene blue (MB) under ultraviolet (UV) and visible light. It was showed that the photocatalytic performance of the ternary photocatalyst was superior to that of single TiO₂ or CDs/TiO₂ binary photocatalyst. It was probably attributed to the synergistic effect of the photoelectrical properties of CDs and the surface plasmon resonance (SPR) effect of AgNPs, which could both enhance the absorption of visible light and hinder the recombination of photogenerated electron-hole pairs.     

Remarkably enhanced photocatalytic activity by nickel nanoparticle deposition on sulfur-doped titanium dioxide thin film

To enhance the photocatalytic performance of titanium dioxide, the structures of both bulk and surface were modified. Doping of sulfur atoms to be substituted for lattice oxygen atoms of titanium dioxide was carried out to extend the light absorption by atmosphere-controlled pulsed laser deposition, which allows direct preparation of impurity-included thin film such as sulfur-doped titanium dioxide. On the other hand, to enhance the surface catalytic reaction, nickel nanoparticles were deposited at the thin film substrate by chemical vapor reductive deposition method, which is a novel preparation technique of metallic nanoparticles on the substrate surface. Obtained sulfur-doped titanium dioxide was found to possess sensitivity to visible light with the wavelength up to 550 nm, indicating the photocatalytic activity in visible region. Sulfur doping induced the dye degradation activity under visible light irradiation. When nickel nanoparticles were deposited, a remarkable enhancement of the hydrogen evolution activity through ethanol decomposition of more than 20 times as much as unmodified titanium dioxide thin film was accomplished. In addition, the stability of sulfur atom doped into titanium dioxide structure was investigated.     

Synthesis and visible‐light‐derived photocatalysis of titania nanosphere stacking layers prepared by chemical vapor deposition

BACKGROUND: In this study, visible‐light‐derived photocatalytic activity of metal‐doped titanium dioxide nanosphere (TS) stacking layers, prepared by chemical vapor deposition (CVD), was investigated. The as‐grown TS spheres, having an average diameter of 100–300 nm, formed a layer‐by‐layer stacking layer on a glass substrate. The crystalline structures of the TS samples were of anatase‐type. RESULTS: Ultraviolet (UV) absorption confirmed that metallic doping (i.e. Co and Ni) shifted the light absorption of the spheres to the visible‐light region. With increasing dopant density, the optical band gap of the nanospheres became narrower, e.g. the smallest band gap of Co‐doped TS was 2.61 eV. Both Ni‐ and Co‐doped TS catalysts showed a photocatalytic capability in decomposing organic dyes under visible irradiation. In comparison, Co‐doped TiO₂ catalyst not only displays the adsorption capacity, but also the photocatalytic activity higher than the N‐doped TiO₂ catalyst. CONCLUSION: This result can be attributed to the fact that the narrower band gap easily generates electron–hole pairs over the TS catalysts under visible irradiation, thus, leading to the higher photocatalytic activity. Accordingly, this study shed some light on the one‐step efficient CVD approach to synthesize metal‐doped TS catalysts for decomposing dye compounds in aqueous solution. Copyright © 2010 Society of Chemical Industry     

Structural distortion and photoconductive modulation of La1-xYxCoO3 epitaxial films

In this work, we successfully prepared epitaxial La_1-xY_xCoO₃ (x = 0, 0.05, 0.1, 0.15) films on (100) SrTiO₃ by polymer assisted deposition. The synergistic effect of biaxially tensile strain and doping yttrium on the structural distortion and photoconductive process of the films has been investigated. Due to lattice mismatch, the epitaxial strain along c-axis as well as the strain-induced tetragonal distortion of La_1-xY_xCoO₃ films increase with the content of doping yttrium. As-prepared films have higher degree of CoO₆ octahedral distortion, i.e., Jahn-Teller-like tetragonal distortion, which result in lower crystal field splitting energy and narrower band gap energy, thereby elevating the charge transition. Additionally, increase of epitaxial strain leads to lower adsorption free energy in La_1-xY_xCoO₃ films, and results in the increase of chemisorbed oxygen, which is beneficial to electron transport in the process of light response. The introduction of new oxygen vacancy defect sites by doping Y³⁺ ions and the proper amount of oxygen vacancy can effectively inhibit the recombination of the photo-induced electron-hole pairs, thus improving the activity for photoconductive response. The results reveal that the photoconductive properties of the as-prepared films are largely related to the synergistic effect of biaxially tensile-strained tetragonal distortion of CoO₆ and doping yttrium.     

Carbonaceous-TiO2 nanomaterials for photocatalytic degradation of pollutants: A review

Semiconductor photocatalysis is one of most appealing and attractive technologies, which has been directly utilized to harvest solar energy for energy and environmental applications. Titanium dioxide (TiO₂) has been proved to be leading semiconductor photocatalyst for the degradation of pollutants. However, it suffers from low photocatalytic activity under visible light activation because of its intrinsic wide band gap. Various strategies have been developed to enhance TiO₂ efficiency in the visible light region. Among them TiO₂ modification with carbonaceous nanomaterials is very effective route for excellent photocatalytic activity. This critical review aims to present recent progress in the design and synthesis of carbonaceous-TiO₂ photocatalysts, covering carbon doping, activated carbon, fullerenes, carbon nanotubes and graphene. Moreover, proposed mechanisms of enhancement, effect of synthesis routes, demonstrations of performance and applications reported in literature are reviewed. Ongoing challenges and possible new directions are outlined.     

具有可见光活性的光催化剂研究进展

简述了可见光光催化机理,该机理与紫外光光催化机理的不同之处在于其电荷传输与分离机制。综述了近年来具有可见光活性的光催化材料的研究进展。贵金属、过渡金属及其化合物的掺杂、染料光敏化、氮掺杂和在适当载体上的负载可使复合物的复合禁带宽度小于TiO2的禁带宽度,从而使TiO2的吸收带发生红移,实现可见光响应,其中,氮掺杂ZnO或氮掺杂TiO2及其复合半导体具有较好的可见光光催化活性,另外一些氮氧化物、氮化物及许多钙钛矿型半导体可以作为可见光分解水的有效催化剂。     

非金属掺杂的第二代二氧化钛光催化剂研究进展

寻求廉价、环境友好并具有可见光光催化活性的第二代光催化剂将是光催化发展进一步走向实用化的关键。氮掺杂的TIO2是新发现的具有可见光光催化活性的复合光催化剂,非金属掺杂可以使复合物的复合禁带宽度小于TIO2的禁带宽度,从而使TIO2的吸收边向可见光移动。对TIO2的氮、碳、硫、卤素掺杂国内外研究现状进行了系统评述,分析了提高TIO2可见光活性的原因,指出非金属元素特别是氮元素的阴离子掺杂是在不降低紫外光催化活性的基础上实现可见光响应的较好方法。     

Solvothermal synthesis and photocatalytic activity of Al-doped BiOBr microspheres

A series of Al-doped BiOBr microspheres with different Al contents were synthesized via a facile solvothermal method. The as-prepared samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectrometry(EDS), X-ray photoelectron spectroscopy(XPS), N₂ adsorption–desorption and UV–visible diffuse reflectance spectroscopy(UV–vis DRS). The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange in an aqueous solution under visible light irradiation. The results revealed that Al doping could greatly improve photocatalytic performance of BiOBr and different Al contents resulted in different photocatalytic activities. The highest activity was achieved by 4 at%Al-BiOBr. The enhanced photocatalytic activity was attributed to efficient separation of photogenerated electron–hole pairs and large BET surface area.     

二氧化钛光催化分解水制氢技术进展

简单介绍了二氧化钛光催化分解水制氢的基本原理。综述了加入牺牲剂、碳酸钠、贵金属负载化、金属离子掺杂、阴离子掺杂、染料光敏化、半导体复合以及离子注入等提高二氧化钛光催化制氢的方法,讨论了这几种改性技术的机理以及对提高二氧化钛在可见光下的制氢效率的作用。重点讨论了阴离子掺杂和离子注入技术的机理和研究进展,指出离子注入是目前扩展二氧化钛光响应的最为有效的技术。最后讨论了光催化分解水制氢的氢氧分离问题,并通过与其他制氢技术的对比分析,指出光催化制氢将是通往氢经济的非常有潜力的制氢技术。     

Hydrothermal synthesis of CdS/CoWO4 heterojunctions with enhanced visible light properties toward organic pollutants degradation

Effective solar energy harvesting and charge carrier separation are two key factors of the photocatalysis system. In this work, the heterojunction photocatalyst of CdS/CoWO₄ was fabricated by a facile hydrothermal method. Compared with the pristine CdS and CoWO₄, the CdS/CoWO₄ heterojunction photocatalyst showed enhanced photocatalytic activity for the methylene blue (MB) degradation under visible light irradiation. Particularly, the sample with molar ratio of CdS:CoWO₄ (sample C2) controlled at 3:5 showed the highest MB degradation ratio (83%) in 1 h among all samples, which is about 3 times over the pure CdS and 8 times over pure CoWO₄, respectively. The greatly enhanced photocatalytic activity (3–8 times) of CdS/CoWO₄ is due to the efficient separation of electron-hole pairs by the heterojunction structure and strong visible light absorption of CdS. This work provides a new insight into the application of tungstate-based heterojunction photocatalysts in environmental remediation.     

Designing effective and stable S-scheme RGO/AgVO3/AgBr hybrid with enhanced photocatalytic performance

The low separation of photogenerated electron-hole pairs and cycle stability has been the main bottleneck which restricts the development of photocatalytic technology for water purification. Here, RGO/AgVO₃ composites were fabricated by photo-ultrasonic assisted reduction method, and AgBr nanoparticles were assembled on the surface of RGO/AgVO₃ via an in situ ion exchange method. A series of characterization and experimental results indicated that the introduction of RGO influenced the growth of crystal phase for AgVO₃ nanorods, resulting that AgVO₃ nanorods became thicker and shorter with the increase in RGO content. Moreover, RGO could also work as a bridge to promote the migration of electrons, leading different improvement for photocatalytic activity. Furthermore, in situ growth of AgBr on the surface of AgVO₃ nanorods could prevent its agglomeration and exfoliation, thus improving the photocatalytic activity and cycle stability of composites. RGO_1%/AgVO₃/AgBr_30% exhibited excellent photocatalytic activity and stability for methylene blue (MB) degradation due to its unique structure, and its removal ratio reached at 96.2% within 50 min. Meanwhile, the separation of photogenerated electron-hole pairs of AgVO₃ was markedly improved due to the introduction of RGO and AgBr. Based on the trapping experiments and theoretical calculation of band gap, a possible S-scheme photocatalytic mechanism for improved photocatalytic activity was proposed.     

In-situ room-temperature synthesis of amorphous/crystalline contact Bi2S3/Bi2WO6 heterostructures for improved photocatalytic ability

We developed a facile in-situ growth method to construct amorphous-based Bi₂S₃/Bi₂WO₆ heterostructures at room temperature. As demonstrated by HRTEM, XPS and EDX-mapping, amorphous state Bi₂S₃ dispersed uniformly on the surface of crystalline Bi₂WO₆ hollow spheres. The photocatalytic activities of prepared Bi₂S₃/Bi₂WO₆ heterostructures were evaluated by the photodegradation of RhB and TC under visible light irradiation, indicating that the introduction of appropriate amorphous Bi₂S₃ significantly improved the photocatalytic activity of Bi₂WO₆. The amorphous/crystalline contact in Bi₂S₃/Bi₂WO₆ heterostructures played a crucial role in the enhancement of photocatalytic efficiency. Based on DRS, photoluminescence spectra, photocurrent intensity, electrochemical impedance spectroscopy and OCVD measurements, it was proposed that the enhanced performance could be ascribed to increased visible light utilization, promoted separation efficiency and prolonged life time of photogenerated electron-hole pairs by the introduction of amorphous Bi₂S₃. This work may provide new insights into the construction of amorphous-based composited heterostructures for improving photocatalytic activity.     

Enhanced visible‐light‐driven photocatalytic activities of LiInO2 by Mo6+‐doping strategy

A novel visible‐light‐driven photocatalyst of Mo‐doped LiInO₂ nanocomposite was successfully synthesized through a sol‐gel method. The effect of Mo‐doping concentrations on the microstructures and properties of LiInO₂ was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy, photoluminescence, and ultraviolet‐visible absorption spectra. The photocatalytic properties of the as‐prepared samples were evaluated by the photocatalytic degradation of methylene blue (MB) dye under visible‐light irradiation. The results demonstrated that the photocatalytic activity of 6% Mo‐LiInO₂ reached to 98.6%, which was much higher than that of the undoped photocatalyst LiInO₂ (only 46.8%). The enhanced photocatalytic activity is ascribed to Mo‐doping strategy. The holes play an important role in the process of the photodegradation of MB. The superior photocatalytic activity of the as‐prepared Mo‐LiInO₂ nanocomposites suggests a potential application for organic dye degradation of wastewater remediation. This work provides a further understanding on tailoring the band structure of semiconductor photocatalyst for enhancing visible‐light absorption and promoting electron‐hole separation by Mo‐doping strategy.     

Facile fabrication of 3D interconnected porous boron doped polymeric g-C3N4 with enhanced visible light photocatalytic hydrogen evolution and dye contaminant elimination

Researchers have attempted to developing high-efficiency catalysts for photocatalytic hydrogen evolution and organic pollution elimination simultaneously to alleviate the issues of energy shortage and water pollution. In this work, we fabricated 3D interconnected porous boron doped polymeric g-C₃N₄ catalysts with efficient photocatalytic activity for hydrogen evolution and dye contaminant elimination under visible-light irradiation. The as-fabricated catalysts exhibited significantly enhanced hydrogen evolution (4.37 mmol g ^?1 h^?1) and RhB contaminant elimination (96.37%) activity. Based on characterization and photocatalytic tests, an enhanced mechanism of the superior photocatalytic performance was proposed: 3D interconnected porous structure and B-doping have a synergistic effect on the greatly improved photocatalytic activity. The 3D interconnected structures endowed g-C₃N₄ with a higher specific surface area and abundant active sites and improved the capacity of rapid absorption to facilitate the photocatalytic process. B doping provided enhanced visible-light absorption capacity and a narrowed bandgap and served as a “highway” for electron-hole pairs to facilitate migration and separation and suppress the combination of photogenerated carriers. Besides, the possible mechanism of enhanced photocatalytic performance was elucidated according to the results of characterization measurements and active species analysis.