Properties of sol-gel SnO2/TiO2 electrodes and their photoelectrocatalytic activities under UV and visible light illumination

A visible light active binary SnO₂-TiO₂ composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO₂ can promote the development of rutile phase of TiO₂ and inhibit the formation of anatase phase of TiO₂. Formation of SnO₂ crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO₂ and TiO₂ inhibits growth of TiO₂ linkage and leads to the particle-filled surface morphology of SnO₂-containing films. The carbonaceous, Ti-O-C bonds and Ti³⁺ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO₂ exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO₂-TiO₂ electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0.     

3D cross-linked BiOI decorated ZnO/CdS nanorod arrays: A cost-effective hydrogen evolution photoanode with high photoelectrocatalytic activity

ZnO/CdS photoanode with an excellent photoelectrochemical (PEC) performance for water splitting to produce hydrogen, but its practical application is seriously hindered owing to the photocorrosion induced by photoholes on the surface of CdS. Herein, a 3D cross-linked heterostructure ZnO/CdS/BiOI nanorod arrays (NRAs) has been prepared by a simple solvothermal strategy. Under visible light illumination (λ > 420 nm), the ZnO/CdS/BiOI NRAs photoanode shows an excellent PEC activity and generates a photocurrent density of 9.12 mA cm⁻² at 1.1 V vs. RHE, which is 1.8 times higher than that of the ZnO/CdS NRAs photoanode in the alkaline electrolyte. Furthermore, the photoanode achieves a high photo conversion efficiency of 3.49% and a long-time stability over 6000 s. It is proposed that the BiOI nanosheets not only serve as protecting layer to restrain the photocorrosion of CdS, but also facilitate the charge separation in CdS by the virtue of the p-n junction formed between CdS and BiOI.     

Improving hole mobility with the heterojunction of graphitic carbon nitride and titanium dioxide via soft template process in photoelectrocatalytic water splitting

In this current work, we have prepared graphitic carbon nitride@titanium dioxide (g-C₃N₄@TiO₂) nanocomposite material via simple one-step soft template synthesis to improve the efficacy of charge separation in photoelectrocatalytic water splitting. The g-C₃N_4, a photoactive component was incorporated in varying amounts into TiO₂, and the resulting composites were confirmed to have improved photoelectrocatalytic activity over the bare-TiO₂. Under the optimal experimental condition, the 20 wt % g-C₃N₄@TiO₂ composite exhibited the highest photoelectrocatalytic activity. The g-C₃N₄ has an ability to absorb the incident photons, resulting in excitation of electrons between the frontier orbitals. These excited electrons move to TiO₂ via the interfacial border, hindering the recombination of the photo-induced electrons and holes and thus, improves the overall performance of the photocatalyst. The improved photoelectrocatalytic performance by g-C₃N₄@TiO₂ was ascribed to the overall impact of g-C₃N₄ that increased its absorptive spectrum into the visible region. As such, the presence of heterojunction in the prepared composite not only aided the separation of the photogenerated charge carriers but also maintained its strong oxidation and reduction capability in the photoelectrocatalytic water splitting.     

Photoelectrocatalytic hydrogen production of heterogeneous photoelectrodes with different system configurations of CdSe nanoparticles,Au nanocrystals and TiO2 nanotube arrays

The different configurations of CdSe nanoparticles, Au nanocrystals and TiO₂ nanotube arrays play an important role in the photoelectrochemical behavior and photoelectrocatalytic hydrogen production of this heterogeneous photoelectrode system. It is discovered that the photoelectrocatalytic hydrogen production of the TiO₂–CdSe–Au photoelectrode (1.724 mmol g⁻¹ h⁻¹) is about 4 times that of the TiO₂–Au–CdSe photoelectrode (0.430 mmol g⁻¹ h⁻¹) under visible light irradiation. From the comprehensive investigation of their photoelectrochemical behaviors, it is illustrated that the interfacial electrical field has distinct effects on the separation and transportation of photogenerated carriers in these heterostructure photoelectrodes. The directions of the interfacial electrical fields formed at TiO₂–Au and Au–CdSe interfaces are opposite in the TiO₂–Au–CdSe photoelectrode, which hinders the separation of photogenerated electron-hole pairs and subsequent transportation of photogenerated carriers. On the contrary, the directions of the interfacial electrical fields formed at TiO₂–CdSe and CdSe–Au interfaces are identical in the TiO₂–CdSe–Au photoelectrode, which promotes the separation of photogenerated excitons and subsequently enhances their transportation for enlarged photocurrent density. The results of photoelectrocatalytic hydrogen production also confirm our assumption.     

Ag-CNT/TiO_2复合电极对亚甲基蓝的光电催化降解作用(英文)

采用金属银修饰的碳纳米管制备了Ag-CNT/TiO2复合电极。利用X-射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),和能量分散性X射线分析(EDX)对所制的Ag-CNT/TiO2复合材料进行了表征。结果表明:二氧化钛颗粒和金属银颗粒在碳纳米管上均匀分布,所制电极具有较高的光电催化性能。其对亚甲基蓝的光电催化降解归因于一种协同效应,即二氧化钛的光降解、碳纳米管网络的电子辅助、金属银的增强和外加电势的作用。尤其是,经银修饰的复合电极增强了其对亚甲基蓝的光电降解,且随银含量的增加其光电催化效果增加。     

Photoelectrocatalytic nitrogen fixation with Vo-BiOBr/TiO2 heterostructured photoelectrode as photocatalyst

Photocatalytic or photoelectrocatalytic nitrogen fixation is considered as a very promising way to reduce energy requirements. Here, V_o-BiOBr/TiO₂ nanocomposite photoelectrode was constructed by modifying TiO₂ nanotube arrays with BiOBr nanosheets with oxygen vacancies (V_o) for photoelectrocatalytic nitrogen fixation. The oxygen vacancy promotes the adsorption and activation of N₂ on the catalyst surface. The Lewis basicity of nitrogen is enhanced by transferring the photogenerated electrons on the conduction band of BiOBr to the π anti-bonding orbit of N₂, which is more beneficial for the addition of protons. On the other hand, the heterojunction between TiO₂ and V_o-BiOBr facilitates the separation of photogenerated carriers. The photogenerated holes on the valence band of TiO₂ travelled to the counter electrode to produce oxygen at a negative potential, avoiding the further oxidation of NH₃. V_o-BiOBr/TiO₂ displays a high NH₃ production rate of 25.08 μg h^?1 cm^?2 at ?0.2 V which is 3.3 times higher than that of BiOBr/TiO₂. The synergistic effect between TiO₂ and V_o-BiOBr results in enhanced light absorption and higher photoelectrocatalytic efficiency for the N₂ reduction reaction.     

Improved photoelectrocatalytic degradation of methylene blue by Ti3C2Tx/Bi12TiO20 composite anodes

In order to effectively reduce the high recombination rate of photogenerated carriers when Bi₁₂TiO₂₀ (BTO) was excited by visible light, Ti₃C₂T_x/BTO/fluorine-doped tin oxide photoanodes were conveniently prepared with the aid of mechanical coating by gentle ultrasonic mixing. Systematic characterization and the degradation of methylene blue in a photoelectrochemical cell were performed. The results showed that the Ti₃C₂T_x/BTO composite exhibited a strong light absorption ability and the effective separation of photogenerated carriers. The optimal anode (6 wt% Ti₃C₂T_x/BTO) degraded 85.4% of methylene blue within 120 min at an applied electric field of 1 V, with a reaction rate that was 3.5 times that of BTO. It was proved that Ti₃C₂T_x, as a useful co-catalyst, creates an internal electric field at the contact interface with BTO and an external electric field, which are responsible for the enhanced photoelectrocatalytic degradation capacity of the composite anode materials.     

Photoelectrocatalytic degradation of phenol using a TiO<Subscript>2</Subscript>/Ni thin-film electrode

As a new type of photoelectrode, TiO₂/Ni thin-film electrode was prepared by dip-coating technique. The structural and surface morphology of electrode was examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). Effects of initial phenol concentration, pH value, number of film layers, voltage of electrical bias applied, variation of inorganic salt type and types of dissolved gas on the photoelectrocatalytic (PEC) degradation of phenol using ultraviolet (UV) illuminated TiO₂/Ni thin-film electrode were investigated. The mechanism of PEC degradation of phenol was also studied by analyzing reaction intermediates.     

Photoelectrocatalytic COD determination method using highly ordered TiO2 nanotube array

This work focuses on the experimental studies of a photoelectrocatalytic method for COD determination in a thin-cell reactor based on a highly effective TiO₂ nanotube array electrode. The effect of preparation parameters on the photoelectrocatalytic performance of TiO₂ nanotube array electrodes including the electrolyte, anodic potential, anodic time, solution pH, calcination temperature and time was examined. The TiO₂ nanotube array electrode prepared in preparation parameters at 1% HF electrolyte solution, anodic potential 20 V, anodic time 5 min, calcination temperature 450 °C with highly photoelectrocatalytic performance was chosen as the working electrode. When it is used in a thin-cell photoeletrocatalytic reactor for COD determination, it requires about 1-5 min to complete the oxidation of organics without further titration, much faster than the standard K₂Cr₂O₇ method (2-4 h). It consumes very limited harmless and inexpensive supporting electrolyte, free from secondary pollution. A wide dynamic working range of 0-850 mg/L can be achieved by this method, much wider than any other photoeletrocatalytic methods using TiO₂ nanoparticles or nanofilms in the reported literature. The effects of the water components were studied to propose the TiO₂ nanotube array method. Real sample analyses were also carried out and the COD value of real samples determined by this method agreed well with the standard dichromate method, and it shows good accuracy, stability and reproducibility.     

Recent advances on electrocatalytic and photocatalytic seawater splitting for hydrogen evolution

Hydrogen is a clean and renewable energy source, which has aroused increasing attentions. Water splitting can effectively evolve hydrogen. Since freshwater is scarce, the direct exploitation of seawater as the feedstock to produce hydrogen has become a hotspot. Such direct exploitation can lower the cost of hydrogen produce and facilitate the rational exploitation of seawater resources. Over the past few years, advanced technologies (e.g. photocatalysis, electrocatalysis and photoelectrocatalysis) have been introduced into seawater splitting and have showed significant potentials. In this study, representative reports on photo-electro-catalytic seawater splitting to produce hydrogen were comprehensively reviewed. Besides, advancements and defects of each process were discussed. Furthermore, recommendations for subsequent study in this research field have been proposed.