Solar Chemical Conversion Research Articles

Defect engineering modified bismuth vanadate toward efficient solar hydrogen peroxide production

Industry for producing the vital chemical hydrogen peroxide (H2O2) requires drastically reductions in energy consumption and environmental pollution. Solar chemical conversion from O2 to H2O2 is considered to be the most promising alternative method, nevertheless, weak energy coupling between photo-charges and adsorbed species limits the yield of H2O2. Herein, we demonstrate that oxygen vacancy-rich BiVO4 can efficiently generate H2O2 in pure water under visible light irradiation without any heterojunctions or precious-metal cocatalysts. Oxygen vacancies, as typical coordinatively unsaturated sites, enable efficient O2 adsorption and enrichment, and then thriving chemisorption can spatially facilitate photoexcited electrons transfer to oxygen species. Compared to pristine BiVO4, defective BiVO4 enhanced O2 adsorption and interfacial electron transfer rate to O2 by 19 and 23 times, respectively, resulting in a more than 32-fold increase in H2O2 production. This research offers a new perspective for bridging solar and chemical energy by assuring species chemisorption.

Photobiocatalytic Solar Fuel and Solar Chemical Conversion: Sufficient Activity and Better Selectivity

Photobiocatalytic Solar Fuel and Solar Chemical Conversion: Sufficient Activity and Better Selectivity

High efficiency solar chemical conversion using electrochemically disordered titania nanotube arrays transplanted onto transparent conductive oxide electrodes

Free-standing, one-dimensional TiO2 nanotube arrays (TNAs) with a disordered surface structure are synthesized on transparent conducting substrates, and their opto-physicochemical properties and photoelectrocatalytic (PEC) performances are examined in detail. A two-step anodization process is used to transplant TNAs grown on titanium foils onto fluorine-doped SnO2 substrates (denoted as W-TNAs), after which they are electrochemically reduced for 20 and 90 s (denoted as B-TNAs-20 and 90, respectively). The as-transplanted W-TNAs exhibit low PEC activities in terms of their photocurrent, oxygen evolution reaction (OER), and oxidations of inorganic and organic substrates (iodide and urea, respectively) under simulated sunlight (AM 1.5; 100 mW cm−2), primarily because of the sluggish charge transfer through the poor electrically conductive TNA framework. The quick electrochemical reduction of the W-TNAs leads to an 8-fold larger photocurrent, while significantly accelerating the OER (by three times) and iodide and urea oxidation reactions (by 2 and ∼20 times, respectively). These enhanced PEC activities of the B-TNAs are attributed to the creation of Ti3+ and associated oxygen vacancies which strengthen their n-type characteristics and thereby increase their electrical conductivity. The time-resolved photoluminescence spectra further reveal that the lifetime (τ) of the photogenerated charge carriers in the B-TNAs (τ = 0.33 ns) is an order of magnitude shorter than that of the W-TNAs (τ = 3.63 ns). The disordered surface exhibits a lower Faradaic efficiency for multi-electron transfer oxidation reactions and a higher Faradaic efficiency for single-electron transfer oxidation reactions compared to the W-TNAs. The detailed surface characterization and PEC mechanism are discussed.

Study on stability of poly(3-hexylthiophene)/titanium dioxide composites as a visible light photocatalyst

Conjugated polymer/TiO2 composites are promising visible light photocatalysts for solar chemical conversion processes in the field of environmental chemistry for decomposition of organic compounds in water and air. In consideration of the fact that conjugated polymers are also organic substances, particular attention must be focused on the stability of conjugated polymer/TiO2 composites, which has not been laid enough emphasis upon so far. Poly(3-hexylthiophene)/titanium dioxide (P3HT/TiO2) composites, as a representative of conjugated polymer/TiO2 photocatalysts, were prepared by combining chemical oxidative polymerization method and physical blending technique. The stability of the composites was systematically studied by comparative analysis of the physical and chemical structure of P3HT/TiO2 composites before and after the photocatalytic reaction. As confirmed by the results of high-resolution transmission electron microscopy (HRTEM), scanning electron microscope (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV–vis DRS), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the P3HT/TiO2 composites were quite stable to 10h of photodegradation of methyl orange (MO) under visible light, maintaining both their physical and chemical structure.

Dramatic enhancement of visible light photocatalysis due to strong interaction between TiO2 and end-group functionalized P3HT

Conjugated polymer/TiO2 photocatalysts hold great promise for solar chemical conversion processes by combining the advantages from both the conjugated polymer and the inorganic semiconductor, overcoming the serious drawbacks of fast charge recombination and the limited visible light absorption of inorganic semiconductor through interfacial electron transfer. To address the crucial way to promote the visible light photocatalytic activity of conjugated polymers/TiO2 photocatalysts, P3HT/TiO2 composites with strong interfacial interaction between P3HT and TiO2, which was demonstrated by the results of X-ray photoelectron spectroscopy and dissolution tests, were prepared by binding cyanoacrylic acid end-groups functionalized P3HT to the surface of TiO2. The pseudo-first-order kinetic constants of photocatalytic degradation of model pollutant methyl orange (MO) under visible light with P3HT/TiO2 composites of monofunctionalized and difunctionalized polymers were 7.06 and 20.18 times as great as that of unfunctionalized polymer, respectively, indicating a remarkably enhanced visible light photocatalytic activities by an order of magnitude with the incorporation of cyanoarrylic acid end-groups. In consideration of their similar morphology, specific surface area, ability of harvesting visible light and adsorption capacities toward MO independent of end-group functionalization, the dramatically enhanced photocatalytic activity arises from the facilitated electron injection and separation of photogenerated carriers owing to strong interfacial interaction between TiO2 and end-group functionalized P3HT, which was proved to be crucial for photocatalytic capability of conjugated polymer/TiO2 photocatalysts, providing a new effective direction for the improvement of their visible light photocatalytic activity.

Visible light driven photocatalysis mediated via ligand-to-metal charge transfer (LMCT): an alternative approach to solar activation of titania

Visible light harvesting or utilization through semiconductor photocatalysis is a key technology for solar chemical conversion processes. Although titania nanoparticles are popular as a base material of photocatalysis, the lack of visible light activity needs to be overcome. This mini-review is focused on an uncommon approach to visible light activation of titania: the ligand-to-metal charge transfer (LMCT) that takes place between TiO2 nanoparticles and surface adsorbates under visible light irradiation. We discuss a basic concept of photoinduced LMCT and the recent advances in LMCT-mediated visible light photocatalysis which has been applied in environmental remediation and solar energy conversion. Although the LMCT processes have been less investigated and limited in photocatalytic applications compared with other popular visible light activation methods such as impurity doping and dye sensitization, they provide lots of possibilities and flexibility in that a wide variety of organic or inorganic compounds can form surface complexes with TiO2 and introduce a new absorption band in the visible light region. The LMCT complexes may serve as a visible light sensitizer that initiates the photocatalytic conversion of various substrates or the self-degradation of the ligand complexes (usually pollutants) themselves. We summarized and discussed various LMCT photocatalytic systems and their characteristics. The LMCT-mediated activation of titania and other wide bandgap semiconductors has great potential to be developed as a more general method of solar energy utilization in photocatalytic systems. More systematic design and utilization of LMCT complexes on semiconductors are warranted to advance the solar-driven chemical conversion processes.