Charge Separation In Photocatalysts Research Articles

Enhanced photocatalytic performance of NH2-MIL-125(Ti)/SrTiO3 heterostructures by the piezoelectric effect of SrTiO3

Applying piezoelectric effect on modulating charge transport behavior was considered as one efficient strategy to make feasible charge separation in photocatalysts towards boosting hydrogen evolution performance. Here, with employing corona-poling treatment, SrTiO3 is converted to be a piezoelectric component in the constructed type II NH2-MIL-125(Ti)/SrTiO3 heterojunction. Since the piezoelectric field could tilt the band bending to a degree to be convenient for the charge transfer from SrTiO3 to NH2-MIL-125(Ti), it is also favorable to offer additional active sites on SrTiO3 to form dual reduction sites for the following piezo-photocatalytic reaction. Both the ameliorated surficial polarization and charge transfer trajectory in NH2-MIL-125(Ti)/SrTiO3 type II heterojunction are devoted to the boosted hydrogen production rate for NH2-MIL-125(Ti)/SrTiO3-0.1 (NM/STO-0.1), that is up to 1562.3 μmol h−1 g−1, 1.79 times higher than that of unpolarized NM/STO-0.1 (871.6 μmol h−1 g−1) and 2.35 times higher than that of NH2-MIL-125(Ti) (663.8 μmol h−1 g−1), respectively. This research reported initially the assistant of SrTiO3 with piezoelectric feature for enhanced performance photocatalytic hydrogen evolution, which could be one prominent strategy to achieve the reasonable design of efficient photocatalytic system.

Facets control charge separation during photoelectrochemical water oxidation with strontium titanate (SrTiO3) single crystals

The photoelectrochemical water oxidation activity of SrTiO3 crystals is determined by the variable work functions of different facets. This produces facet dependent semiconductor–liquid junctions that can drive charge separation in photocatalysts.

Enhanced degradation of ofloxacin by activation of peroxymonosulfate with biochar-FeVO4 under visible light assistance: The role of biochar in mediating charge transfer and mechanism insight

Biochar is recognized as a good medium for promoting photogenerated charge separation in photocatalysts. In this study, the FeVO4/coconut shell biochar (CSB) composites (FVC) were prepared through a cost-effective hydrothermal approach to activate peroxymonosulfate (PMS) for the degradation of ofloxacin (OFX). Incorporated CSB expanded the light absorption range of FVC by approximately 100 nm, and the band gap energy of FVC was reduced to 2.00 eV. Measurements through linear scanning voltammetry (LSV) and current–time (IT) chronoamperometric further confirmed that the accelerated electron transmission rate boosted PMS oxidation, which was attributed to the role of CSB acting as a mediator. Importantly, OFX degradation was significantly boosted by CSB, FV, and PMS synergistically. FVC had a significant OFX degradation efficiency under visible light irradiation (95.2 %) compared to FV (70.9 %), CSB (57.8 %) and PMS (30.5 %). Moreover, the h+, 1O2, ·O2–, ·OH, and SO4·− were the main active species, whose degradation pathways were explored and the toxicity of the intermediates was assessed. Furthermore, the as-obtained FVC exhibited a remarkable stability and reusability. This work provides new insights into the mechanism of biochar-mediated charge transfer for antibiotic degradation.

Strategies to Enhance Interfacial Spatial Charge Separation for High‐Efficiency Photocatalytic Overall Water‐Splitting: A Review

Developing efficient photocatalysts for overall water‐splitting (OWS) has garnered considerable attention due to their potential in renewable energy conversion and storage. Enhancing the efficiency of interfacial spatial charge separation poses a key challenge in this field, as it plays a momentous role in the photocatalytic process. In this review article, a range of strategies aimed at improving interfacial spatial charge separation in photocatalysts for realizing high‐efficiency OWS are explored. To provide a comprehensive understanding, first the fundamentals of photocatalytic water‐splitting are introduced and the main bottlenecks in the reaction process, along with various charge separation and transfer mechanisms are identified. Subsequently, recent advancements and efforts in designing spatial charge separation at the interfaces of 0D, 1D, 2D, and 3D nanostructured photocatalysts are discussed. Finally, a summary is presented and a long‐term outlook for spatial charge separation in the field of OWS is offered. By consolidating the current state‐of‐the‐art research, this review highlights the key challenges and favorable circumstances for future advancements in the pursuit of efficient OWS.

The Construction of Phosphorus-Doped g-C3N4/Rh-Doped SrTiO3 with Type-II Band Alignment for Efficient Photocatalytic Hydrogen Evolution.

It is of great importance to promote charge separation in photocatalysts for enhanced photocatalytic activity under visible light irradiation. In this work, a type-II heterostructured photocatalyst was constructed by compositing phosphorus-doped g-C3N4 (P-CN) and Rh-doped SrTiO3 (Rh-STO) via a thermal calcination treatment. A series of characterizations were conducted to investigate the structure of heterostructured P-CN/Rh-STO. It was found that Rh-STO interacted with in situ generated P atoms from the decomposition of P-CN during the calcination process, thus leading to the formation of heterojunction of P-CN/Rh-STO. Compared with the single component, i.e., P-CN or Rh-STO, the obtained P-CN/Rh-STO showed superior photocatalytic activity to that of both P-CN and Rh-STO due to the effective charge separation across the heterojunction between P-CN and Rh-STO.

Boosting photocatalytic CO2 reduction by tuning photogenerated carrier kinetics in two-dimensional WOx/BiOCl S-scheme heterojunction with oxygen vacancies

Photocatalytic CO2 reduction driven by sustainable solar energy is a highly desirable route to achieve carbon recycling, to which charge separation in photocatalysts holds the key. In this work, two-dimensional (2D) WO3·H2O nanosheets with rich oxygen vacancies (Vo-WOx) were combined with 2D BiOCl nanosheets to form a 2D/2D Vo-WOx/BiOCl S-scheme heterojunction by a self-assembly process. The 2D/2D stacked structure combined with the introduction of oxygen vacancies in Vo-WOx could improve the light harvesting of the designed photocatalytic system. The dual transfer pathways in the S-scheme junction were induced by the fact that the photogenerated electrons on the conduction band and defect energy level of the Vo-WOx transfer across the interface to combine with the BiOCl, leading to an improved kinetic process of photogenerated carriers. Moreover, the S-scheme configuration can retain a strong redox potential for satisfying the thermodynamic requirement of CO2 reduction. As a result, the optimized 30Vo-WOx/BiOCl composite can achieve the highest CO yield rate of 8.82 μmol h−1 from CO2 reduction without any sacrifice reagents, which was 4.69 and 3.08 times higher than that of pure BiOCl and WO3/BiOCl without oxygen vacancy. This work provides a new view of defect engineering in S-scheme heterojunction for pursuing a highly efficient photocatalytic CO2 reduction system.

Charge Separation in Photocatalysts: Mechanisms, Physical Parameters, and Design Principles

Charge Separation in Photocatalysts: Mechanisms, Physical Parameters, and Design Principles

Orienting the charge transfer path of type-II heterojunction for photocatalytic hydrogen evolution

One of the bottlenecks for photocatalytic H2 generation is the severe recombination of photoexcited charge carriers in photocatalysts. As an effective approach, constructing heterojunction with type II band alignment has been applied for efficient charge separation in photocatalysts during the photocatalytic process. By compositing g-C3N4 and P25 as a model photocatalyst, the limited charge separation efficiency and random charge transfer paths are discovered in this conventional type II heterostructured g-C3N4/P25. In order to overcome these shortcomings in g-C3N4/P25, we designed a type II heterostructured photocatalyst with oriented transfer path for photo-excited charges during the real photocatalysis process via a one-pot synthesis strategy, in which the separation efficiency was much improved. The as-prepared g-C3N4/P25(N)-Pd photocatalyst exhibits a tremendously enhanced photocatalytic activity, which is 8.7 and 24.5 times that of g-C3N4 under visible light and full wave light irradiation, respectively.

Engineering of Gd/Er/Lu-triple-doped Bi2MoO6 to synergistically boost the photocatalytic performance in three different aspects: Oxidizability, light absorption and charge separation

Lanthanide doping is an effective and controllable approach for optimizing the oxidation ability, light absorption and charge separation of photocatalysts. However, the multiple drawbacks of mono-component photocatalysts have not been adequately resolved by the doping of only one or two lanthanide ions. Herein, a novel Gd/Er/Lu-triple-doped Bi2MoO6 photocatalyst was synthesized using a hydrothermal method. The results of trapping and 4-Chlorophenol degradation experiments suggested that the oxidizing efficiency of Bi2MoO6 was clearly enhanced by the generation of hydroxyl radicals after doping with the Gd3+ redox centers. The obtained diffuse reflectance spectra demonstrated that introducing Er3+ ions provides energy upconversion centers to improve light absorption. The obtained X-ray photoelectron and photoluminescence spectra demonstrated that abundant oxygen vacancies were produced in the Bi2MoO6 crystal after the doping of Lu3+ ions, contributing to promoting the separation of charge carriers. In summary, Gd/Er/Lu-triple-doped Bi2MoO6 displays much better photocatalytic performance than single- and double-doped Bi2MoO6 materials, which is attributed to the synergistic effects of the Gd3+, Er3+ and Lu3+ ions. These discoveries demonstrate a novel synergistic effect of the redox centers (Gd3+ doping), energy upconversion (Er3+ doping) and oxygen vacancies (Lu3+ doping) for the design and fabrication of high-efficiency photocatalysts.

Rational construction of oxygen vacancies onto tungsten trioxide to improve visible light photocatalytic water oxidation reaction

Defect engineering is a promising strategy to enhance light absorption and charge separation of photocatalysts. Herein, we simply tailor the quantity and distribution of oxygen vacancies, as one of typical defects, on surface or bulk of thermal-treated WO3 in the different H2 concentration. The quantity of bulk oxygen vacancies on WO3 consistently rises with the increased H2 concentration, while that of surface oxygen vacancies presents a volcano-type variation. The sample of WO3-H20, thermal-pretreated in 20% H2, contains the largest amount of surface oxygen vacancies. Our results show that both surface and bulk oxygen vacancies on WO3 can promote the visible light photocatalytic activity in water splitting, however, in different ways. Bulk oxygen vacancies mainly promote the visible light harvesting and slightly restrain the electrons and holes recombination by narrowing band gap energy (Eg), while surface oxygen vacancies significantly increase the charge-carriers separation efficiency by lowering valence band edge (VBE). Compared with the light absorption, the separation of electrons and holes is more critical in photocatalytic oxygen evolution over WO3, revealing the more decisive role of surface oxygen vacancies than bulk oxygen vacancies. Expectedly, WO3-H20 shows the highest charge-carriers separation efficiency and visible light photocatalytic performance. Our work provides a new insight into designing of efficient defect-engineered semiconductors for the related solar light utilization processes.

Enhancing Charge Separation in Photocatalysts with Internal Polar Electric Fields

AbstractThe main limitations on photocatalytic efficiency are the recombination of photogenerated electrons and holes and a narrow light response. In this Minireview, we focused on photocatalytic materials with an internal polar electric field. The development and application of these compounds is one of the most efficient strategies to promote the separation of photogenerated electrons and holes, leading to high photocatalytic efficiency. This Minireview describes the fundamental operating principles of photocatalysts with a built‐in polar electric field and discusses the mechanism for polar‐electric‐field‐enhanced charge separation. We also review recent reports on photocatalytic systems using an internal polar electric field to separate photogenerated electrons and holes, focusing particularly on layer‐structure polar photocatalysts, silver silicates, and single‐crystal ZnO photocatalysts. Charge separation enhanced by an internal polar electric field provides the basis for designing new high efficiency photocatalysts.