Rare-Earth Single-Atom La-N Charge-Transfer Bridge on Carbon Nitride for Highly Efficient and Selective Photocatalytic CO2 Reduction

Multipath elimination of bisphenol A over bifunctional polymeric carbon nitride/biochar hybrids in the presence of persulfate and visible light

Polymeric carbon nitride (PCN) has become a star material either in photocatalysis or in persulfate (PS) activation. In this work, we synthesized bifunctional biochar (BC)-doped PCN through a facile one-pot thermal treatment process. The PCN/BC hybrid (CNBC) with an optimized proportion could not only activate PS directly, but also possessed improved optical properties. Amorphous BC domains generated from the carbonization of external corncob provided attachments for the in-situ growth of PCN and upgraded its catalytic ability including electron transport property, visible light (VIS) utilization, and oxidation power. Mechanism studies demonstrated that in the CNBC/PS system without VIS, a nonradical electron transfer route was responsible for the degradation of bisphenol A (BPA), while in the CNBC/PS/VIS system, radical/nonradical mixing mechanisms including mediated electron transfer, radical oxidation, and hole oxidation were unveiled. Degradation pathways of BPA were deduced including direct oxidation at the aromatic ring, β-scission of isopropyl, and ring cleavage. Most of the intermediates were less toxic than BPA as assessed by the ECOSAR software. The CNBC/PS/VIS system showed satisfactory resistance to environmental interferences except for HCO₃^-. This work provides a simple but effective strategy for the synthesis of PCN-based bifunctional catalysts and deepens mechanistic insights into hybrid advanced oxidation technologies.

Rare-earth single atoms decorated 2D-TiO2 nanosheets for the photodegradation of gaseous O-xylene

In this work, rare-earth single atoms (La, Er) were decorated on the surface of 2D-TiO₂ nanosheets by an impregnation-calcination strategy. The formation of rare-earth single atoms was certified by AC HAADF-STEM and XAS. TiO₂ decorated with rare-earth single atoms (La₁-TiO₂ and Er₁-TiO₂) exhibited outstanding photocatalytic activity than pure 2D-TiO₂ nanosheets (2D-TiO₂) towards gas-phase degradation of O-xylene. Compared with 2D-TiO₂, the rare-earth single atoms greatly improved the adsorption capacity of O-xylene without increasing their specific surface area. This is because rare-earth single atoms provide additional adsorption sites and reduce the adsorption energy of O-xylene. In addition, the hybrid orbital formed by the combination of rare-earth single atom and oxygen atom is beneficial to the rapid transmission and separation of photo-induced electrons, thereby improving the performance of photocatalytic degradation. In addition, in-situ DRIFTS and GC-MS were used to reveal the photocatalytic oxidation mechanism. Interestingly, the results showed that the La₁-TiO₂ and Er₁-TiO₂ samples can reduce the types of intermediates and simplify the reaction route, implying that the single atoms play an important role in the modulation and thorough mineralization of intermediate products. This work shows that the rare-earth single atom decorated 2D-TiO₂ nanosheets have great potential in photocatalytic air pollution control.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activating of Peroxymonosulfate to Generate 1 O2 with 100 % Selectivity

Singlet oxygen (¹ O₂ ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of ¹ O₂ . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe₁ /CN) containing highly uniform Fe-N₄ active sites with a high Fe loading of 11.2 wt %. The Fe₁ /CN achieves generation of 100 % ¹ O₂ by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N₄ sites in Fe₁ /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO₅ ^.- , and thereafter efficiently generate ¹ O₂ with 100 % selectivity. In addition, the Fe₁ /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of ¹ O₂ for highly selective and efficient degradation of pollutants.

Urea-induced supramolecular self-assembly strategy to synthesize wrinkled porous carbon nitride nanosheets for highly-efficient visible-light photocatalytic degradation

Graphitic carbon nitride (g-C₃N₄) has attracted immense interest as a promising photocatalyst. To facilitate its versatile applications in many fields, new low-cost strategies to synthesize outstanding g-C₃N₄ need to be further developed. Although supramolecular preorganization has been considered as a promising candidate, the utilized supramolecules like melamine–cyanuric acid (MCA) are typically synthesized by expensive triazine derivatives. Herein, wrinkled porous g-C₃N₄ nanosheets were successfully fabricated by hydrothermal-annealing of supramolecular intermediate MCA synthesized by the cheap precursors dicyandiamide and urea. During the formation of MCA, urea could act as a facile agent to react with dicyandiamide to form melamine and cyanuric acid firstly and then assemble into MCA through hydrogen bonds. In addition, urea could serve as a porogen and decompose to generate bubbles for conducive formation of micro-size MCA self-templates and thus wrinkled porous g-C₃N₄ nanosheets could be obtained. The nanostructure and photocatalytic performance of g-C₃N₄ were optimized by modulating microstructures and physicochemical properties of MCA, which could be conveniently controlled by urea addition and hydrothermal duration. The obtained wrinkled porous g-C₃N₄ nanosheets exhibit highly-efficient visible-light photocatalytic degradation compared with traditional MCA-derived g-C₃N₄, which could remove 98.3% of the rhodamine B in 25 min. The superior photocatalytic activity is mainly attributed to the urea-induced larger specific surface area, better light harvesting ability, faster transfer and more advanced separation efficiency of the photogenerated electron–hole pairs. This research provides a new strategy for preparing high-performance porous g-C₃N₄ from the self-assembled supramolecule MCA synthesized by low-cost precursors.

Wrinkled porous g-C₃N₄ nanosheets were fabricated by supramolecular MCA self-templates. Due to the reactant and porogen agent urea, g-C₃N₄ could be modulated with efficient electron–hole pairs and thus superior photocatalytic degradation performance.

Erbium Single Atom Composite Photocatalysts for Reduction of CO2 under Visible Light: CO2 Molecular Activation and 4f Levels as an Electron Transport Bridge

It is still challenging to design a stable and efficient catalyst for visible-light CO₂ reduction. Here, Er³⁺ single atom composite photocatalysts are successfully constructed based on both the special role of Er³⁺ and the special advantages of Zn₂ GeO₄ /g-C₃ N₄ heterojunction in the photocatalysis reduction of CO₂ . Especially, Zn₂ GeO₄ :Er³⁺ /g-C₃ N₄ obtained by in situ synthesis is not only more conducive to the tight junction of Zn₂ GeO₄ and g-C₃ N₄ , but also more favorable for g-C₃ N₄ to anchor rare-earth atoms. Under visible-light irradiation, Zn₂ GeO₄ :Er³⁺ /g-C₃ N₄ shows more than five times enhancement in the catalytic efficiency compared to that of pure g-C₃ N₄ without any sacrificial agent in the photocatalytic reaction system. A series of theoretical and experimental results show that the charge density around Er, Ge, Zn, and O increases compared with Zn₂ GeO₄ :Er³⁺ , while the charge density around C decreases compared with g-C₃ N₄ . These results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO₂ molecular activation of Er³⁺ single atom and 4f levels as electron transport bridge are fully exploited. The pattern of combining single-atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.

Foamer-Derived Bulk Nitrogen Defects and Oxygen-Doped Porous Carbon Nitride with Greatly Extended Visible-Light Response and Efficient Photocatalytic Activity

Constructing bulk defects and doping are feasible ways to essentially narrow the band gap and improve the light absorption of photocatalysts. Herein, inspired by bread foaming, the foaming agent azoformamide or azodicarbonamide (AC) was introduced during the thermal polymerization of urea. In the polymerization process, a large number of bubbles produced by AC decomposition seriously interfered with the polymerization of urea, resulting in the breaking of the hydrogen bonds and van der Waals interaction in carbon nitride, distortion of its structure, and partial oxidation, thus forming a series of porous carbon nitrides U/AC_x (x is the ratio of AC to urea; where x = 0.25, 0.5, and 1) with bulk N defects and O doping. Its band gap was reduced to 1.91 eV and the absorption band edge was greatly extended to 650 nm. The optimal U/AC_0.5 exhibits the highest visible light photocatalytic hydrogen production rate of about 44.7 μmol·h^-1 (10 mg catalysts) and shows superior photocatalytic performance for the oxidation of diphenylhydrazine to azobenzene, with conversion and selectivity of almost 100%, and is one of the most active defective carbon nitrides, especially under long-wavelength (λ ≥ 550 nm) light irradiation. It paves the way for the design of highly efficient and wide-spectral-response photocatalysts.

Design of highly efficient g-C3N4-based metal monoatom catalysts by two extra-NM1 atoms: density functional theory simulations

Graphitic carbon nitride (g-C3N4) is recognized as a favorable substrate for monoatom catalysts due to its uniform nanoholes for anchoring metal monoatoms, while the oxygen evolution reaction (OER) overpotential (ηOER) values of g-C3N4-based metal monoatom catalysts are still large. To reduce the ηOER values, a class of novel TM1NM1NM1/g-C3N4 was designed via density functional theory simulations, where TM1 = Fe1, Co1 or Ni1 and NM1 = C1, N1 or O1. Contributing by two extra-NM1 atoms, the OER catalytic activities of these materials were effectively improved owing to the shortened TM1-NM bonds and weakened chemical activity of TM1 atoms. Based on the volcano activity relationship between the theoretical overpotential (ηOER) and d band center of the TM1 atom (εd), the chemical activity of TM1 atoms needs to be adjusted to a suitable magnitude (εd near -4.883 eV) for a good catalytic activity. The designed Fe1C1O1/g-C3N4 with the εd of -4.893 eV exhibited an excellent OER catalytic activity of ηOER = 0.219 V. This strategy was applied to devise the reaction active sites and highly efficient catalysts by adjusting the chemical activity of the TM1 atom with suitable extra-NM1 atoms.

Interfacial Engineering of Bi19Br3S27 Nanowires Promotes Metallic Photocatalytic CO2 Reduction Activity under Near-Infrared Light Irradiation

Developing highly efficient photocatalysts to utilize solar radiation for converting CO₂ into solar fuels is of great importance for energy sustainability and carbon neutralization. Herein, through an alkali-etching-introduced interface reconstruction strategy, a nanowire photocatalyst denoted as V-Bi₁₉Br₃S₂₇, with rich Br and S dual-vacancies and surface Bi-O bonding introduced significant near-infrared (NIR) light response, has been developed. The as-obtained V-Bi₁₉Br₃S₂₇ nanowires exhibit a highly efficient metallic photocatalytic reduction property for converting CO₂ into CH₃OH when excited solely under NIR light irradiation. Free of any cocatalyst and sacrificial agent, metallic defective V-Bi₁₉Br₃S₂₇ shows 2.3-fold higher CH₃OH generation than Bi₁₉Br₃S₂₇ nanowires. The detailed interfacial structure evolution and reaction mechanism have been carefully illustrated down to the atomic scale. This work provides a unique interfacial engineering strategy for developing high-performance sulfur-based NIR photocatalysts for photon reducing CO₂ into alcohol for achieving high-value solar fuel chemicals, which paves the way for efficiently using the solar radiation energy extending to the NIR range to achieve the carbon neutralization goal.

Surface Lattice Oxygen Activation on Sr2Sb2O7 Enhances the Photocatalytic Mineralization of Toluene: from Reactant Activation, Intermediate Conversion to Product Desorption

Transition-metal oxide photocatalysis has attracted increasing attention in environmental remediation and solar energy conversion. Surface lattice oxygen is the key active site on the metal oxide, but its role and activation mechanism in the photocatalytic VOC mineralization are still unclear. In this work, we have demonstrated that Sr₂Sb₂O₇ exhibits an excellent photocatalytic activity and stability compared to TiO₂ (P25) in gaseous toluene mineralization because the lattice oxygen on Sr₂Sb₂O₇ can be activated efficiently. The lattice oxygen of Sr₂Sb₂O₇ promotes the adsorption and activation of O₂ and H₂O molecules and enhances the production of ^•O₂^- and ^•OH radicals, as confirmed by the electron spin resonance and DFT calculations. The in situ diffuse reflectance infrared Fourier transform spectroscopy spectra are applied to dynamically monitor the intermediate activation and selective conversion. Combined with DFT calculation, the role and the mechanism of lattice oxygen in photocatalysis have been revealed. Owing to the promoted surface lattice oxygen, the selectivity for benzoic acid formation is enhanced and final product desorption is promoted, which could largely advance the ring opening and mineralization of toluene. This work reveals the origin of lattice oxygen activation and the role for efficient VOC degradation at the atomic scale.

Construction of a 2D/2D heterojunction via integrating MoS2 on Co-doped g-C3N4 to improve photocatalytic hydrogen evolution under visible light irradiation

Schematic of the photocatalytic mechanism of the MoS₂/CoCN-3 composite with enhanced photocatalytic properties for hydrogen evolution.

Highly efficient photocatalytic CO2 reduction by a ruthenium complex sensitizing g-C3N4/MOF hybrid photocatalyst

A ruthenium complex sensitizing g-C₃N₄/MOF hybrid (RuL₂L′@C₃N₄/MOF) was exploited that displayed extremely high photocatalytic performance for the reduction of CO₂ to CO.