Se-modified polymeric carbon nitride nanosheets with improved photocatalytic activities

Supermolecule Polymer Derived Porous Carbon Nitride Microspheres with Controllable Energy Band Structure for Photocatalytic Hydrogen Evolution Reaction

Porous graphitic carbon nitride microsphere with large specific surface area and controllable energy band structure is synthesized via a simple method with the supermolecule polymer of melamine-cyanuric acid (MCA) as the intermediates. The energy band structure and morphology of carbon nitride are closely correlative to the calcination time. And the CN-20 catalyst fabricated by calcination for 20 h exhibit superior photocatalytic activity of hydrogen evolution reaction (HER) under visible-light (λ ≥ 420 nm) irradiation. The photocatalytic and photoelectrochemical test results indicate that Pt is the optimum cocatalyst candidate compared with Pd, Ru, and Ag. Meanwhile, the time-dependent process of the intermediate pyrolysis to carbon nitride and the internal mechanism of photogenerated charge transfer between semiconductors and cocatalyst is investigated and supplemented by theoretical calculations. This work provides a novel and energy band structure controllable manufacture strategy for porous carbon nitride semiconductor with satisfying visible-light photocatalytic reduction performance.

Recent Advances on Single-Atom Catalysts for Photocatalytic CO2 Reduction

The present energy crisis and environmental challenges may be efficiently resolved by converting carbon dioxide (CO2 ) into various useful carbon products. The development of more effective catalysts has been the main focus of current research on photocatalytic CO2 reduction. Due to their high atomic efficiency and superior catalytic activity, single-atom catalysts (SACs) have attracted considerable interest in catalytic CO2 conversion. This review discusses the current research developments, obstacles, and potential of SACs for photocatalytic CO2 reduction. And further, discusses the principle of photocatalytic carbon dioxide reduction. This work has compared and analyzed the effects of support materials and active site types in SACs on photocatalytic CO2 reduction performance. This work believes that by sharing these developments, some inspiration for the rational design and development of stable and effective photocatalytic CO2 reduction catalysts based on SACs can be provided.

Materials design of edge-modified polymeric carbon nitride nanoribbons for the photocatalytic CO2 reduction reaction

Nanoribbon construction and modification with functional groups are important methods to improve the performance of photocatalysts. In this paper, density functional theory (DFT) calculations are applied to assess the electron absorption capacity of different model structures in the photocatalytic CO₂ reduction reaction (CO₂RR), i.e., melon-based carbon nitride nanoribbons (MNRs) and edge-modified melon-based carbon nitride nanoribbons (X-MNRs, X = NO₂, CF₃, CN, CHO, F, Cl, CCH, OH, SH, CH₃, and H). It is found that X-MNRs (X = NO₂, CN, CHO, CCH, OH, and H) have a significantly reduced band gap. Meanwhile, the VBM and CBM are effectively separated with the same optical absorption wavelength range, agreeing with the experimental observations. More importantly, the Gibbs free energy difference of the CO₂RR rate-determining step is greatly reduced in MNRs, CHO-MNRs, CN-MNRs etc. with the formation of CO or HCOOH. The mechanism investigation indicates that the materials design via edge-group modification can optimize the CO₂RR process.

Mechanism of CO2 photoreduction by selenium-doped carbon nitride with cobalt clusters as cocatalysts

Doping is an efficient strategy for improving the photocatalytic activity and tuning the electronic structure of carbon nitride. Selenium-doped melon carbon nitride (Se-doped melon CN) as a promising photocatalyst for CO₂ reduction is investigated using density functional theory calculations. In addition, considering the special role of a cocatalyst in CO₂ reduction, we have explored the electronic and optical properties of Co₄ clusters loaded on the Se-doped melon CN surface. After loading cobalt clusters, CO₂ activation is significantly improved, with preference for the 8-electron product CH₄, as the 2-electron products have higher desorption energies. Overall, this work provides a microscopic understanding of the CO₂ reduction mechanism on Se-doped melon CN with cobalt as the co-catalyst.

Se substituted 2D-gC3N4 modified disposable screen-printed carbon electrode substrate: A bifunctional nano-catalyst for electrochemical and absorption study of hazardous fungicide

The indispensable usage of pesticides for the control and prevention of pests is probable and includes several types based on the problems in the crops. Among them, fungicides, are one problem-solving agent curing fungal developments. the disproportionate use of fungicides will lead to environmental deterioration and several health issues. The assessment of such fungicides is highly motivated to be detected. Under the class of two-dimensional materials, graphitic carbon nitride (GCN) with high surface area and high electrocatalytic activity was chosen as electrode material. The efficiency of GCN was improved with the subsequent substitution of selenium (Se) into the triazine ring as Se-GCN. The structural and surface analysis was done and the layered structure was proved. The electrochemical detection of CBM showed a lower detection limit at 6 nM with a linear range 0.099 μM-346.9 μM while, the absorption studies showed a LOD of 20 nM with a linear range of 0.099 μM-182.09 μM. The orange juice and vegetable extract samples had good recovery with CBM at Se-GCN modified disposable screen-printed electrode. The developed disposable electrode was more sensitive with 6.45 μAμM^-1cm² sensitivity and highly reactive with CBM. Moreover, the developed sensor will be more effective in sensing applications to avoid the menace generated by several agents.

Semiconducting Polymers for Oxygen Evolution Reaction under Light Illumination

Sunlight-driven water splitting to produce hydrogen fuel has stimulated intensive scientific interest, as this technology has the potential to revolutionize fossil fuel-based energy systems in modern society. The oxygen evolution reaction (OER) determines the performance of overall water splitting owing to its sluggish kinetics with multielectron transfer processing. Polymeric photocatalysts have recently been developed for the OER, and substantial progress has been realized in this emerging research field. In this Review, the focus is on the photocatalytic technologies and materials of polymeric photocatalysts for the OER. Two practical systems, namely, particle suspension systems and film-based photoelectrochemical systems, form two main sections. The concept is reviewed in terms of thermodynamics and kinetics, and polymeric photocatalysts are discussed based on three key characteristics, namely, light absorption, charge separation and transfer, and surface oxidation reactions. A satisfactory OER performance by polymeric photocatalysts will eventually offer a platform to achieve overall water splitting and other advanced applications in a cost-effective, sustainable, and renewable manner using solar energy.

On-Surface Polymerization of In-Plane Highly Ordered Carbon Nitride Nanosheets toward Photocatalytic Mineralization of Mercaptan Gas

2D carbon nitride nanosheets have attracted ever-increasing interest in photocatalysis due to their unique structural advantages. However, the nanosheets synthesized by the traditional methods, such as post oxidation and liquid exfoliation, have suffered from in-plane disorder with abundant structural defects, which seriously counteracts their structural benefits for photocatalysis. Herein, it is demonstrated that polymer carbon nitride nanosheets with in-plane highly ordered structure (PCNNs-IHO) can be successfully prepared by on-surface polymerization of melamine on NaCl crystal surface at elevated temperatures. The NaCl crystals with relative high surface energy not only facilitate the adsorption and activation of melamine to undergo condensation reaction, but also function as unique substrates to orientate the assembly of 2D nanosheet structure. In addition, NaCl also acts as a reactant to provide Na⁺ doping into carbon nitride matrix, affording PCNNs-IHO with robust structural base sites. Benefiting from this structural basicity, PCNNs-IHO exhibits superior photocatalytic performance toward CH₃ SH mineralization under visible light irradiation.

The pivotal role of defects in fabrication of polymeric carbon nitride homojunctions with enhanced photocatalytic hydrogen evolution

Fabrication of homojunctions is a cost-effective efficient way to enhance the photocatalytic performance of polymeric carbon nitride (CN), but the generation of defects upon synthesizing CN homojunctions and their roles in the homojunction fabrication were hardly reported. Herein, nitrogen-deficient CN homojunctions were simply synthesized by calcining dicyandiamide-loaded CN (prepared from urea and denoted as UCN) with dicyandiamide polymerizing into CN (denoted as DCN) and simultaneous formation of nitrogen vacancies in the surface of UCN. Fabrication of the nitrogen-deficient UCN (dUCN)/DCN homojunction depends on the nitrogen vacancy content in dUCN which can tune the energy band structure of dUCN from not matching to matching with that of DCN. The dUCN/DCN homojunction exhibits extended optical absorption and remarkably enhanced charge separation and photocatalytic H₂ evolution, compared with UCN and DCN. This work illustrates the pivotal role of defects in fabricating CN homojunctions and supplies a new facile way to synthesize nitrogen-deficient CN.

Single-Atom Catalysts across the Periodic Table

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Oxygen Doping in Graphitic Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

The incorporation of oxygenic groups could remarkably enhance the light absorption and charge separation of graphitic carbon nitride (g-C₃ N₄ ). The intrinsic role of oxygenic species on photocatalytic activity in g-C₃ N₄ has been intensively studied, but it is still not fully explored. Herein, the essential relationships between oxygenic functionalities and the catalytic performance are revealed. Results demonstrate that C-O-C functionality as an electron trap could help to increase the resistance of conduction transfer (R_ct ) by limiting electrons transfer in CNx. In contrast, N-C-O functionality between different tri-s-triazine unites could promote the electrons transfer, leading to a reduced R_ct in CNx. The best H₂ production rate (3.70 mmol h^-1  g^-1 , 12.76-fold higher than that of CN) is obtained over CN3, because of the highest N-C-O ratio (r_N-C-O ). The apparent quantum efficiency (AQE) of CN3 at 405 nm, 420 nm, 450 nm, 500 nm and 550 nm is 33.90 %, 20.88 %, 8.25 %, 3.66 % and 1.01 %, respectively.

Theoretical design and experimental investigation on highly selective Pd particles decorated C3N4 for safe photocatalytic NO purification

Rational design of highly active and selective photocatalyst for NO removal is significant for the commercial application of photocatalytic technology because the secondary byproduct caused by insufficient and non-selective pollutant oxidation process is a major challenge. In this work, Pd nanoparticles decorated C₃N₄ (PdCN) is designed by density functional theory (DFT) at first. The PdCN exhibits superiority to CN in terms of both kinetics and thermodynamics performances, as reflected in the lower activation barrier of rate-determining step and higher selectivity for the final product (nitrate) instead of toxic intermediate (NO₂). The as-designed highly selective and efficient photocatalyst is then fabricated by a facile method with an extremely low content of Pd particles supported on C₃N₄. Compared to bare CN, the synthesized PdCN exhibits highly enhanced purification of NO in air and strong inhibition of toxic NO₂ by-product as supported by in-situ DRIFTS investigation, which is consistent with the theoretical prediction. This work is a typical demonstration of setting up a bridge between theory and experiment to give a promising way to the rational design of advanced photocatalysts and atomic understanding of the reaction mechanism.

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched active sites for promoted catalysis in styrene production

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched catalytic sites is fabricated by a facile two-step molten salt-oxidation strategy, generating an excellent catalyst for clean and energy-saving styrene production.

CoP nanoparticles as cocatalyst modified the CdS/NiWO4 p–n heterojunction to produce hydrogen efficiently

Generally, cocatalyst modification is an efficient way to enhance the hydrogen evolution performance of visible light irradiation.

Atomically thin two-dimensional ZnSe/ZnSe(ea)x van der Waals nanojunctions for synergistically enhanced visible light photocatalytic H2 evolution

Two-dimensional (2D) photocatalysts have been widely studied due to their short charge carrier migration pathways and tunable electronic structures. Herein, a facile one-pot solvothermal process with ethylamine (ea) constructs a novel 2D nanojunction based on ZnSe. The ea molecules coordinate with Zn2+ to form 2D ZnSe(ea)x, where the consequent 2D ZnSe grows in an epitaxial way resulting in the self-assembled 2D/2D ZnSe/ZnSe(ea)x nanojunctions driven by van der Waals (VDW) force, which largely extend the absorption range. The atomic thickness of the 2D structure offers a short charge migration pathway, low electric resistance and rich active sites for the surface reaction of photocatalysis. All the above favorable factors work synergistically to reach a superior hydrogen evolution of 2875 μmol g-1 h-1 under visible light irradiation (≥420 nm) and a notable quantum yield of 64.5% at 450 nm, which are among the highest recorded values of non-noble metal photocatalysts.