Impact of Aspect Ratio on Charge Carrier Dynamics and Efficiency Enhancement in CdSe/CdS Dot-in-Rod Nanostructures for Photocatalytic Hydrogen Evolution

We demonstrated that the aspect ratio (AR)-tunable CdSe/CdS dot-in-rod (DiR) nanostructures with quasi-type-II band structure were successively synthesized using the hot injection method. When the AR of CdSe/CdS DiR was tuned from 10 to 37, the exciton localization efficiency along the longitudinal CdS rod shell decreased from 57.9 to 15.1%, resulting in a 5-fold improvement in the efficiency of photocatalytic hydrogen (H2) evolution. The optimal CdSe/CdS DiR exhibited the highest H2 evolution rate of 2.11 mmol·g-1·h-1 at an AR of 29 without any cocatalyst assistance. In situ transient absorption spectroscopy was employed to investigate the interfacial charge carrier dynamics of CdSe/CdS DiR during practical photocatalytic H2 evolution. The findings indicated that the half-life of delocalized electrons on the conduction band along the longitudinal CdS rod shell increases from 11.5 to 20.1 μs as the AR increased, demonstrating that the AR-dependent charge carrier dynamics significantly influences the photoactivity of CdSe/CdS DiR. This study provides valuable and novel insights into the tunability of charge carrier dynamics through AR manipulation in one-dimensional semiconductor nano-heterostructures for solar fuel generation.

Magnetic self-doped TiO2-x /Fe3O4@g-C solar-driven photocatalytic composite for water decontamination

Declining water resources and their contamination with chemicals risk the aquatic environment. Therefore, this work was devoted to designing a magnetically recyclable photocatalyst suitable for water treatment, namely, a TiO2-x /Fe3O4@g-C composite. Different preparation conditions were investigated together with the corresponding characteristics. The pure defective anatase TiO2-x phase of low band gap energy was detected through XRD and DRS analyses. Low charge recombination after the formation of defects was confirmed. The performances of the prepared photocatalysts in phenol degradation under solar light were evaluated, revealing the superior efficiency of TiO2-x prepared hydrothermally at 200 °C/24 h relative to intact TiO2. This best sample was incorporated with Fe3O4@g-C to facilitate its recovery and reuse. This successful combination was confirmed using XRD, Raman and XPS tools. TiO2-x /Fe3O4@g-C 2 : 1 formulation was found to be the most photoactive and could be reused up to five times without significant loss in its efficiency. Therefore, the precisely developed magnetic photocatalyst is promising for application in the water-treatment process.

Elucidating the mechanism of photocatalytic reduction of bicarbonate (aqueous CO2) into formate and other organics

The photocatalytic reduction of CO2 under solar irradiation is an ideal approach to mitigating global warming, and reducing aqueous forms of CO2 that interact strongly with a catalyst (e.g., HCO3-) is a promising strategy to expedite such reductions. This study uses Pt-deposited graphene oxide dots as a model photocatalyst to elucidate the mechanism of HCO3- reduction. The photocatalyst steadily catalyzes the reduction of an HCO3- solution (at pH = 9) containing an electron donor under 1-sun illumination over a period of 60 h to produce H2 and organic compounds (formate, methanol, and acetate). H2 is derived from solution-contained H2O, which undergoes photocatalytic cleavage to produce •H atoms. Isotopic analysis reveals that all of the organics formed via interactions between HCO3- and •H. This study proposes mechanistic steps, which are governed by the reacting behavior of the •H, to correlate the electron transfer steps and product formation of this photocatalysis. This photocatalysis achieves overall apparent quantum efficiency of 27% in the formation of reaction products under monochromatic irradiation at 420 nm. This study demonstrates the effectiveness of aqueous-phase photocatalysis in converting aqueous CO2 into valuable chemicals and the importance of H2O-derived •H in governing the product selectivity and formation kinetics.

Plasmon-Enhanced Photocatalytic CO2 Reduction for Higher-Order Hydrocarbon Generation Using Plasmonic Nano-Finger Arrays

The carbon dioxide reduction reaction (CO2RR) is a promising method to both reduce greenhouse gas carbon dioxide (CO₂) concentrations and provide an alternative to fossil fuel by converting water and CO₂ into high-energy-density chemicals. Nevertheless, the CO2RR suffers from high chemical reaction barriers and low selectivity. Here we demonstrate that 4 nm gap plasmonic nano-finger arrays provide a reliable and repeatable plasmon-resonant photocatalyst for multiple-electrons reactions: the CO2RR to generate higher-order hydrocarbons. Electromagnetics simulation shows that hot spots with 10,000 light intensity enhancement can be achieved using nano-gap fingers under a resonant wavelength of 638 nm. From cryogenic ¹H-NMR spectra, formic acid and acetic acid productions are observed with a nano-fingers array sample. After 1 h laser irradiation, we only observe the generation of formic acid in the liquid solution. While increasing the laser irradiation period, we observe both formic and acetic acid in the liquid solution. We also observe that laser irradiation at different wavelengths significantly affected the generation of formic acid and acetic acid. The ratio, 2.29, of the product concentration generated at the resonant wavelength 638 nm and the non-resonant wavelength 405 nm is close to the ratio, 4.93, of the generated hot electrons inside the TiO₂ layer at different wavelengths from the electromagnetics simulation. This shows that product generation is related to the strength of localized electric fields.

Recent analytical tools to mitigate carbon-based pollution: New insights by using wavelet coherence for a sustainable environment

Anthropogenic activities are a ubiquitous source of carbon-based pollution. A sustainable environment is endangered due to inefficiently regulated pollution policies, and the rise in world population further enhances the severity of this formidable challenge. This study has investigated the impact of the annual CO₂ emissions in Pakistan on electricity production from different sectors, GDP, and the population by focusing on the control of carbon-based pollution. This research study intends to fill the gap in previous studies by providing significant measures to link the control of carbon-based pollution, increased GDP, and Pakistan's population, using data from 1990 to 2020. A set of 15 variables are mainly used to investigate all of these relations. Carbon pollution drastically impacts both the external and internal environment. The graphical analysis undertaken in this study finds an upward trend and significant positive correlation among the variables. It demonstrates that Pakistan shows minimal contribution in CO₂ emission compared to other Asian economies, but in recent decades, an increasing growth rate has been noticeable and needs to be controlled. The ECM and ARDL approaches confirm that all the variables positively affect CO₂ emission both in the long- and short-term, except for electricity production from gas and hydro in the long term, which shows negative relation. The long-term shifts also indicate that high CO₂ emissions can be recovered from by adjusting these variables. The study also suggests that the government should convert high carbon use to low carbon energy use to control CO₂ emissions in Pakistan.

Photocatalytic CO2 Conversion Using Metal-Containing Coordination Polymers and Networks: Recent Developments in Material Design and Mechanistic Details

International guidelines have progressively addressed global warming which is caused by the greenhouse effect. The greenhouse effect originates from the atmosphere’s gases which trap sunlight which, as a consequence, causes an increase in global surface temperature. Carbon dioxide is one of these greenhouse gases and is mainly produced by anthropogenic emissions. The urgency of removing atmospheric carbon dioxide from the atmosphere to reduce the greenhouse effect has initiated the development of methods to covert carbon dioxide into valuable products. One approach that was developed is the photocatalytic transformation of CO2. Photocatalysis addresses environmental issues by transferring CO2 into value added chemicals by mimicking the natural photosynthesis process. During this process, the photocatalytic system is excited by light energy. CO2 is adsorbed at the catalytic metal centers where it is subsequently reduced. To overcome several obstacles for achieving an efficient photocatalytic reduction process, the use of metal-containing polymers as photocatalysts for carbon dioxide reduction is highlighted in this review. The attention of this manuscript is directed towards recent advances in material design and mechanistic details of the process using different polymeric materials and photocatalysts.

Broadening the Action Spectrum of TiO2-Based Photocatalysts to Visible Region by Substituting Platinum with Copper

In this study, TiO₂-based photocatalysts modified with Pt and Cu/CuO_x were synthesized and studied in the photocatalytic reduction of CO₂. The morphology and chemical states of synthesized photocatalysts were studied using UV-Vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. A series of light-emitting diodes (LEDs) with maximum intensity in the range of 365–450 nm was used to determine the action spectrum of photocatalysts. It is shown for, the first time, that the pre-calcination of TiO₂ at 700 °C and the use of Cu/CuO_x instead of Pt allow one to design a highly efficient photocatalyst for CO₂ transformation shifting the working range to the visible light (425 nm). Cu/CuO_x/TiO₂ (calcined at 700 °C) shows a rate of CH₄ formation of 1.2 ± 0.1 µmol h⁻¹ g⁻¹ and an overall CO₂ reduction rate of 11 ± 1 µmol h⁻¹ g⁻¹ (at 425 nm).

Synthesis and Surface Modification of TiO2-Based Photocatalysts for the Conversion of CO2

Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO2 into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO2 photoreduction are thoroughly discussed and the CO2 reduction mechanism and pathways are described. Methods to enhance the adsorption of CO2 on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO2 is currently being widely investigated for its photocatalytic ability in reducing CO2 when suitably modified. The recent TiO2 synthesis and modification strategies that may be employed to enhance the efficiency of the CO2 photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO2 in addition to increasing product yield and selectivity.

Developmental trends in CO2 methanation using various catalysts

Co₂ methanation-two edged sword to counter global warming and energy crisis.