Photocatalytic Hydrogen Production Under Visible Light by Using a CdS/WO3 Composite

3D-Printed Organic Conjugated Trimer for Visible-Light-Driven Photocatalytic Applications

Small molecule organic semiconductors (SMOSs) have emerged as a new class of photocatalysts that exhibit visible light absorption, tunable bandgap, good dispersion, and solubility. However, the recovery and reusability of such SMOSs in consecutive photocatalytic reactions is challenging. This work concerns a 3D-printed hierarchical porous structure based on an organic conjugated trimer, named EBE. Upon manufacturing, the photophysical and chemical properties of the organic semiconductor are maintained. The 3D-printed EBE photocatalyst shows a longer lifetime (11.7 ns) compared to the powder-state EBE (1.4 ns). This result indicates a microenvironment effect of the solvent (acetone), a better dispersion of the catalyst in the sample, and reduced intermolecular π-π stacking, which results in improved separation of the photogenerated charge carriers. As a proof-of-concept, the photocatalytic activity of the 3D-printed EBE catalyst is evaluated for water treatment and hydrogen production under sun-like irradiation. The resulting degradation efficiencies and hydrogen generation rates are higher than those reported for the state-of-the-art 3D-printed photocatalytic structures based on inorganic semiconductors. The photocatalytic mechanism is further investigated, and the results suggest that hydroxyl radicals (HO⋅) are the main reactive radicals responsible for the degradation of organic pollutants. Moreover, the recyclability of the EBE-3D photocatalyst is demonstrated in up to 5 uses. Overall, these results indicate the great potential of this 3D-printed organic conjugated trimer for photocatalytic applications.

Photocapacitive CdS/WOx nanostructures for solar energy storage

Through a facile solvothermal procedure, a CdS/WO_x nanocomposite has been synthesised which exhibits photocapacitive behaviour under white light illumination at a radiant flux density of 99.3 mW cm⁻². Photoelectrochemical experiments were undertaken to examine the self-charging properties of the material and to develop an understanding of the underlying electronic band structure responsible for the phenomenon. By employing XPS, UPS and UV-Vis diffuse reflectance spectroscopy for further characterisation, the ability of the composite to generate current following the removal of incident light was related to the trapping of photoexcited electrons by the WO_x component. The presence of WO_x yielded an order of magnitude increase in the transient photocurrent response relative to CdS alone, an effect attributed to the suppression of electron-hole recombination in CdS due to hole transfer across the CdS/WO_x interface. Moreover, current discharge from the material persisted for more than twenty minutes after final illumination, an order of magnitude improvement over many existing binary composites. As a seminal investigation into the photocapacitive characteristics of CdS/WO_x composites, the work offers insight into how the constituent materials might be utilised as part of a future self-charging solar device.

Oxygen deficiency introduced to Z-scheme CdS/WO3-x nanomaterials with MoS2 as the cocatalyst towards enhancing visible-light-driven hydrogen evolution

An oxygen deficiency modified Z-scheme CdS/WO3-x nanohybrid with MoS2 as the cocatalyst was synthesized by a microwave hydrothermal method and was used for photocatalytic hydrogen production under visible light irradiation. Loadings of WO3-x and MoS2 as well as the synthesis time of the microwave-assisted hydrothermal process were optimized, and the physicochemical and optical properties of the as-prepared photocatalysts were characterized by various techniques. Results showed that the material with 30 wt% of WO3-x, 0.1 wt% of MoS2 and a preparation time of 120 minutes exhibited the most desirable morphology and structure for hydrogen production. The maximum hydrogen production of 2852.5 μmol g-1 h-1 was achieved, which was 5.5 times that of pure CdS (519.1 μmol g-1 h-1) and 1.5 times that of CdS/30 wt% WO3-x (1879.0 μmol g-1 h-1), and the external quantum efficiency (EQE) reached 10.0% at 420 nm. The improvement of photocatalytic performance could be attributed to the Z-scheme formed between CdS and WO3-x and MoS2 as an electron trap. It is worth mentioning that the size of the composite had a negative correlation with the H2 production rate.

Metal-Free Visible-Light Photoactivated C3N4 Bubble-Propelled Tubular Micromotors with Inherent Fluorescence and On/Off Capabilities

Photoactivated micromachines are at the forefront of the micro- and nanomotors field, as light is the main power source of many biological systems. Currently, this rapidly developing field is based on metal-containing segments, typically TiO₂ and precious metals. Herein, we present metal-free tubular micromotors solely based on graphitic carbon nitride, as highly scalable and low-cost micromachines that can be actuated by turning on/off the light source. These micromotors are able to move by a photocatalytic-induced bubble-propelled mechanism under visible light irradiation, without any metal-containing part or biochemical molecule on their structure. Furthermore, they exhibit interesting properties, such as a translucent tubular structure that allows the optical visualization of the O₂ bubble formation and migration inside the microtubes, as well as inherent fluorescence and adsorptive capability. Such properties were exploited for the removal of a heavy metal from contaminated water with the concomitant optical monitoring of its adsorption by fluorescence quenching. This multifunctional approach contributes to the development of metal-free bubble-propelled tubular micromotors actuated under visible light irradiation for environmental applications.

Photocatalytic decomposition of N2O over g-C3N4/WO3 photocatalysts

Although the nitrous oxide belongs among three of the most contributing greenhouse gases to global warming, it is quite neglected by photocatalytic society. The g-C₃N₄ and WO₃ composites were therefore tested for the photocatalytic decomposition of N₂O for the first time. The pure photocatalysts were prepared by simple calcination of precursors, and the composites were prepared by mixing of suspension of pure components in water followed by calcination. The structural (X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy), textural (N₂ physisorption), and optical properties (diffuse reflectance spectroscopy, photoluminescence spectroscopy, photoelectrochemical measurements) of all composites were correlated with photocatalytic activity. The experimental results and results from characterization techniques confirmed creation of Z-scheme in the WO₃/g-C₃N₄ composites, which was confirmed by hydroxyl radicals' trapping measurements. The photocatalytic decomposition of N₂O was carried out in the presence of UVA light (peak intensity at 365 nm) and the 1:2 WO₃/g-C₃N₄ composite was the most active one, but the photocatalytic activity was just negligibly higher than that of pure WO₃. This is caused by relatively weak interaction between WO₃ and g-C₃N₄ which was revealed from XPS.

Metal-Oxide-Based Microjets for the Simultaneous Removal of Organic Pollutants and Heavy Metals

Water contamination from industrial and anthropogenic activities is nowadays a major issue in many countries worldwide. To address this problem, efficient water treatment technologies are required. Recent efforts have focused on the development of self-propelled micromotors that provide enhanced micromixing and mass transfer by the transportation of reactive species, resulting in higher decontamination rates. However, a real application of these micromotors is still limited due to the high cost associated to their fabrication process. Here, we present Fe₂O₃-decorated SiO₂/MnO₂ microjets for the simultaneous removal of industrial organic pollutants and heavy metals present in wastewater. These microjets were synthesized by low-cost and scalable methods. They exhibit an average speed of 485 ± 32 μm s^-1 (∼28 body length per s) at 7% H₂O₂, which is the highest reported for MnO₂-based tubular micromotors. Furthermore, the photocatalytic and adsorbent properties of the microjets enable the efficient degradation of organic pollutants, such as tetracycline and rhodamine B under visible light irradiation, as well as the removal of heavy metal ions, such as Cd²⁺ and Pb²⁺.