Economic Hydrophobicity Triggering of CO2 Photoreduction for Selective CH4 Generation on Noble-Metal-Free TiO2-SiO2

Toward a Comprehensive Understanding of Amorphous Photocatalysts: Fundamental Hypotheses and Applications in CO2 Photoreduction

In principle, photocatalytic activity can be precisely controlled with crystalline catalysts. However, an amorphous photocatalyst could be a viable candidate for CO₂ photoreduction to form value-added products. The amorphous phase is currently part of the crystalline material in several ongoing CO₂ photoreduction studies. Additionally, no study indicates the amorphous material required for overall CO₂ photoreduction. This perspective review article highlights fundamental assumptions that are necessary to gain insights and understand the effectiveness of amorphous photocatalysts for CO₂ photoreduction. We start with basic ideas and theories about these materials, including light harvesting, variable coordination number, and the interaction of CO₂ molecules with the amorphous catalytic surface. To understand the prospects of the amorphous photocatalyst, we explore machine learning with EXAFS. Furthermore, we discuss product selectivity and regeneration of photocatalysts in detail. Finally, we briefly review the work in progress on amorphous materials and compare it to that on crystalline ones.

Electrocatalyst Design for Conversion of Energy Molecules: Electronic State Modulation and Mass Transport Regulation

Electrocatalytic conversions of energy molecules are involved in many energy conversion processes. Improving the activity of electrocatalyst is critical for increasing the efficiency of these energy conversion processes. However, the...

Enhancing the photocatalytic activity of defective titania for carbon dioxide photoreduction via surface functionalization

The hydrophilic surface of defective titanium dioxide lowers its adsorption capacity towards CO2 molecules.

Synthesis of TiO2-x/W18O49 hollow double-shell and core-shell microspheres for CO2 photoreduction under visible light

TiO2-x/W18O49 with core-shell or double-shelled hollow microspheres were synthesized through a facile multi-step solvothermal method. The formation of the hollow microspheres with a double-shell was a result of the Kirkendall effect during the solvothermal treatment with concentrated NaOH. The advanced architecture significantly enhanced the electronic properties of TiO2-x/W18O49, improving by more than 30 times the CO2 photoreduction efficiency compared to the pristine W18O49. Operando DRIFTS measurements revealed that the yellow TiO2-x was a preferable CO2 adsorption and conversion site.

Amorphous Pd-Loaded Ti4O7 Electrode for Direct Anodic Destruction of Perfluorooctanoic Acid

We here present a novel Ti₄O₇-based electrode loaded with amorphous Pd clusters that achieve efficient anodic destruction of perfluorooctanoic acid (PFOA), a persistent water pollutant with significant environmental and human health concerns. These amorphous Pd clusters were characterized by the disordered, noncrystalline arrangement of Pd single atoms in close proximity, in contrast to crystalline Pd nanoparticles that have been often employed to tailor the electronic properties of an electrode. We found that the Ti₄O₇ electrode loaded with amorphous Pd clusters significantly outperformed the Ti₄O₇ electrode loaded with crystalline Pd particles due to enhanced electron transfer through dominant Pd-O bonds. Combined with the efficient binding of PFOA and its degradation intermediates to the fluorinated electrode surface, this electrode was capable of mineralizing PFOA and releasing fluoride as F^-. The reaction pathway was found to proceed without involving reactive oxygen species and therefore was not quenched by common anions in complex natural water systems such as chloride ions.

Mechanism investigation on the enhanced photocatalytic oxidation of nonylphenol on hydrophobic TiO2 nanotubes

Enhanced and selective photocatalytic oxidation of nonylphenol (NP), a typical hydrophobic endocrine disrupting chemicals (EDCs), was realized on hydrophobic titanium dioxide nanotubes (H-TiO₂NTs), which was fabricated by an electrochemical anodization method, followed by grafting of perfluorooctyl groups. The water contact angle of catalyst surface changed from 21.1° to 128.4° after hydrophobic modification. H-TiO₂NTs showed excellent photocatalytic oxidation performance for NP, that it was completely converted in 40 min under irradiation, which was improved for about 17% compared with the hydrophilic TiO₂NTs. The enhanced photocatalytic performance of H-TiO₂NTs was attributed to the stronger adsorption ability toward NP identified by ATR-FTIR, with an initial adsorption rate of 4 times as higher as that of bare TiO₂NTs. Meanwhile, the hydrophobic surface of H-TiO₂NTs was beneficial for generation of more hydroxyl radicals. The apparent rate constant of hydroxyl radicals' generation on H-TiO₂NTs, which was the main oxidizing species, could reach 1.83 times that of the hydrophilic TiO₂NTs. Both the two factors contributed to the successful competition of NP against the coexistent hydrophilic contaminates in the adsorption and oxidation on the catalyst surface, leading to the selective removal of NP in mixed systems finally.

Modulation of the Reduction Potential of TiO2- x by Fluorination for Efficient and Selective CH4 Generation from CO2 Photoreduction

Photocatalytic reduction of CO₂ holds great promises for addressing both the environmental and energy issues that are facing the modern society. The major challenge of CO₂ photoreduction into fuels such as methane or methanol is the low yield and poor selectivity. Here, we report an effective strategy to enhance the reduction potential of photoexcited electrons by fluorination of mesoporous single crystals of reduced TiO_{2- x}. Density functional theory calculations and photoelectricity tests indicate that the Ti³⁺ impurity level is upswept by fluorination, owing to the built-in electric field constructed by the substitutional F that replaces surface oxygen vacancies, which leads to the enhanced reduction potential of photoexcited electrons. As a result, the fluorination of the reduced TiO_{2- x} dramatically increases the CH₄ production yield by 13 times from 0.125 to 1.63 μmol/g·h under solar light illumination with the CH₄ selectivity being improved from 25.7% to 85.8%. Our finding provides a metal-free strategy for the selective CH₄ generation from CO₂ photoreduction.

Enhanced photocatalytic CO2 reduction to CH4 over separated dual co-catalysts Au and RuO2

A spatially separated, dual co-catalyst photocatalytic system was constructed by the stepwise introduction of RuO₂ and Au nanoparticles (NPs) at the internal and external surfaces of a three dimensional, hierarchically ordered TiO₂-SiO₂ (HTSO) framework (the final photocatalyst was denoted as Au/HRTSO). Characterization by HR-TEM, EDS-mapping, XRD and XPS confirmed the existence and spatially separated locations of Au and RuO₂. In CO₂ photocatalytic reduction (CO₂PR), Au/HRTSO (0.8%) shows the optimal performance in both the activity and selectivity towards CH₄; the CH₄ yield is almost twice that of the singular Au/HTSO or HRTSO (0.8%, weight percentage of RuO₂) counterparts. Generally, Au NPs at the external surface act as electron trapping agents and RuO₂ NPs at the inner surface act as hole collectors. This advanced spatial configuration could promote charge separation and transfer efficiency, leading to enhanced CO₂PR performance in both the yield and selectivity toward CH₄ under simulated solar light irradiation.

Size-dependent activity and selectivity of carbon dioxide photocatalytic reduction over platinum nanoparticles

Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Nevertheless, an in-depth understanding of the platinum’s size effect in the carbon dioxide photocatalytic reduction is still lacking. Through analyses of the geometric features and electronic properties with variable-sized Pt NPs, here we show a prominent size effect of Pt NPs in both the activity and selectivity of carbon dioxide photocatalytic reduction. Decreasing the size of Pt NPs promotes the charge transfer efficiency, and thus enhances both the carbon dioxide photocatalytic reduction and hydrogen evolution reaction (HER) activity, but leads to higher selectivity towards hydrogen over methane. Combining experimental results and theoretical calculations, in Pt NPs, the terrace sites are revealed as the active sites for methane generation; meanwhile, the low-coordinated sites are more favorable in the competing HER.

Light-driven carbon dioxide conversion into fuels provides a nature-inspired strategy to combat climate change, but how materials do so remains a challenge. Here, the authors prepare metal–semiconductor composites and find platinum-nanoparticle size controls fuel selectivity and activity.

Reduced {001}-TiO2−x photocatalysts: noble-metal-free CO2 photoreduction for selective CH4 evolution

The preparation of reduced TiO₂ photocatalysts with high Ti³⁺ concentration is a great challenge due to their instability in air.