Broad Spectral Response Z-Scheme Three-Dimensional Ordered Macroporous Carbon Quantum Dots/TiO2/g-C3N4 Composite for Boosting Photocatalysis

Unveiling efficient S-scheme charge carrier transfer in hierarchical BiOBr/TiO2 heterojunction photocatalysts

The construction of a potential heterojunction catalyst with proper interface alignment has become a hot topic in the scientific community to effectively utilize solar energy. In this work, a one-dimensional TiO2 nanofiber/BiOBr S-scheme heterojunction was synthesized, and charge carrier dynamics within the interface channel were explored. In addition, we incorporated mixed phase TiO2 with point defects and oxygen vacancies, which greatly promoted the initial band edge shift from the UV region. Upon the addition of BiOBr, absorption in the visible light region of the electromagnetic (EM) spectrum was observed with a decrease in the optical band gap value. The optimized BiOBr heterojunction (BTNF1.5) revealed a higher photocatalytic RhB dye degradation efficiency due to the efficient generation and separation of charge carriers upon light irradiation. The optimum sample BTNF1.5 showed a high degradation efficiency of 98.4% with a rate constant of 47.1 min-1 at 8 min of visible light irradiation, which is double than that of the pure TiO2. Electrochemical analysis, time-resolved photoluminescence and Kelvin probe measurement revealed an S-scheme charge-transfer mechanism within the BiOBr/TiO2 system. This work provides a strategy for the facile synthesis of heterojunction photocatalysts exhibiting exceptional catalytic performance.

Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S Double Z-Scheme Heterojunction Photocatalyst for Highly Selective CO2 Reduction to Methane

Solar-energy-driven CO2 hydrogenation is a promising strategy to alleviate the climate crisis. Methane is a desirable derivative of CO2 reduction. However, developing a photocatalyst for highly active and selective CH4 generation remains challenging. Herein, we report a double Z-scheme Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S photocatalyst for efficient reduction of CO2 to CH4. In situ characterization techniques confirmed that the charge migration mechanism in Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S promotes charge separation through double internal electric fields. As a result, the optimized C0.01B0.02C catalyst displayed a formation rate high up to 25.34 μmol g-1 h-1 and a selectivity of 96.52% of CH4. Moreover, the AQY of CO2 conversion on C0.01B0.02C (1.84%) was almost 41 times higher than that of the bare CN. This study provides a novel perspective to develop heterojunction photocatalysts for selective CO2 conversion to CH4.

Facile synthesis and comparative study of the enhanced photocatalytic degradation of two selected dyes by TiO2-g-C3N4 composite

Photocatalysis is considered a useful technique employed for the dye degradation through solar light, visible or UV light irradiation. In this study, TiO₂, g-C₃N₄, and TiO₂-g-C₃N₄ nanocomposites were successfully synthesized and studied for their ability to degrade Rhodamine B (RhB) and Reactive Orange 16 (RO-16), when exposed to visible light. The analytical techniques including XRD, TEM, SEM, DRS, BET, XPS, and fluorescence spectroscopy were used to explore the characteristics of all the prepared semiconductors. The photocatalytic performance of synthesized materials has been tested against both the selected dyes, and various experimental parameters were studied. The experimental results demonstrate that, in comparison to other fabricated composites, the TiO₂-g-C₃N₄ composite with the optimal weight ratio of g-C₃N₄ (15 wt%) to TiO₂ has shown outstanding degrading efficiency against RhB (89.62%) and RO-16 (97.20%). The degradation experiments were carried out at optimal conditions such as a catalyst load of 0.07 g, a dye concentration of 50 ppm, and a temperature of 50 ℃ at neutral pH in 90 min. In comparison to pure TiO₂ and g-C₃N₄, the TiO₂-g-C₃N₄, a semiconductor, has shown higher degradation efficiency due to its large surface area and decreased electron-hole recombination. The scavenger study gave an idea about the primary active species (^-OH radicals), responsible for dye degradation. The reusability of TiO₂-g-C₃N₄ was also examined in order to assess the composite sustainability.

Construction of BiOIO3/AgIO3 Z-Scheme Photocatalysts for the Efficient Removal of Persistent Organic Pollutants under Natural Sunlight Illumination

The efficient removal of persistent organic pollutants (POPs) in natural waters is vital for human survival and sustainable development. Photocatalytic degradation is a feasible and cost-effective strategy to completely disintegrate POPs at room temperature. Herein, we develop a series of direct Z-scheme BiOIO₃/AgIO₃ hybrid photocatalysts via a facile deposition-precipitation method. Under natural sunlight irradiation, the light intensity of which is ∼40 mW/cm², a considerable rate constant of 0.185 min^-1 for photodecomposing 40 mg/L MO is obtained over 0.5 g/L Bi@Ag-5 composite photocatalyst powder, about 92.5 and 5.3 times higher than those of pristine AgIO₃ and BiOIO₃. The photoactivity of Bi@Ag-5 for photodecomposing MO under natural sunlight illumination surpasses most of the reported photocatalysts under Xe lamp illumination. After natural sunlight irradiation for 20 min, 95% of MO, 82% of phenol, 78% of 2,4-DCP, 54% of ofloxacin, and 88% of tetracycline hydrochloride can be photodecomposed over Bi@Ag-5. Relative to the commercial photocatalyst TiO₂ (P25), Bi@Ag-5 exhibits greatly higher photoactivity for the treatment of MO-phenol-tetracycline hydrochloride mixture pollutants in the scale-up experiment of 500 mL of solution, decreasing COD, TOC, and chromaticity value by 52, 19, and 76%, respectively, after natural sunlight irradiation for 40 min. The photodegradation process and mechanism of MO have been systematically investigated and proposed. This work provides an archetype for designing efficient photocatalysts to remove POPs.

Nanoarchitectonics of g-C3N4 Nanosheets with a AuCu Enhancement Effect for Superior Photo- and Electrochemical Activity

AuCu alloy nanoparticles (NPs) were embedded in superior thin g-C₃N₄ nanosheets by a mechanochemical pre-reaction and subsequent thermal polymerization at high temperature. The introduction of AuCu NPs increased conductivity, decreased the band gap, expended light absorption, and improved the separation and transfer efficiencies of photogenerated electrons and holes. Moreover, the uniform distribution of AuCu NPs in g-C₃N₄ nanosheets is ascribed to the pre-reaction of bulk g-C₃N₄ and metal salts to create activity cites. The adsorption ability in the visible light region was improved due to the plasma effect of Au. AuCu/g-C₃N₄ composites (AuCu/CN-1%) with optimized component ratios revealed the highest transient photocurrent responses, the lowest electrochemical impedance arc radius, and the best photocatalytic H₂ evolution rate of 930.2 μmol g^-1 h^-1. These findings exhibited that loading AuCu bimetallic NPs could efficiently offset some disadvantages of g-C₃N₄ and improve its photocatalytic performances.

Intrinsic Mechanism Analyses of Significantly Enhanced Photoelectrochemical Performance of the Bi2MoO6/BiVO4 System

In this paper, the electrodeposition and hydrothermal methods were used to prepare the Bi₂MoO₆/BiVO₄ photoelectrode, and the intrinsic mechanism of significantly enhanced photoelectrochemical performance of the prepared Bi₂MoO₆/BiVO₄ heterojunction system was studied. Work functions of Bi₂MoO₆ and BiVO₄ were analyzed using a scanning Kelvin probe, and the direction of the heterojunction electric field and the transfer direction of photogenerated carriers were finally determined by the relative positions of the energy bands and the Fermi levels of Bi₂MoO₆ and BiVO₄. A type II Bi₂MoO₆/BiVO₄ heterojunction system was finally confirmed to be formed. Formation of the type II Bi₂MoO₆/BiVO₄ heterojunction system reduces the recombination efficiency of photogenerated electrons and holes and thus improves the photoelectrochemical performance. The photogenerated current density of the Bi₂MoO₆/BiVO₄ photoelectrode reaches 1.47 mA·cm^-2, which is 4.9 times that of pure BiVO₄ and thousands of times that of Bi₂MoO₆. The successful application of a scanning Kelvin probe in the verification of the heterojunction type provides theoretical and technical bases for the design and construction of efficient heterojunctions.