Iodide-Induced Fragmentation of Polymerized Hydrophilic Carbon Nitride for High-Performance Quasi-Homogeneous Photocatalytic H2 O2 Production

Highly efficient removal of organic contaminant with wide concentration range by a novel self-cleaning hydrogel: Mechanism, degradation pathway and DFT calculation

A novel carbon nitride based self-cleaning hydrogel photocatalyst (KI-PCN gel, potassium and iodine co-doped carbon nitride confined in alginate) has been successfully constructed by a facile method. Fabricated photocatalyst showed enhanced synergistic adsorption-photocatalytic degradation property on a high concentration of methylene blue (HMB) because of enhanced carrier separation efficiency and improved light adsorption capacity of KI-PCN. As expected, the KI-PCN gel showed the highest apparent rate constant value ₍K_app =0.0310 min^-1), which was about 38.8 and 5.8 times as that of blank hydrogel (K_app=0.0008 min^-1) and PCN gel (K_app=0.0053 min^-1), respectively. Meanwhile, KI-PCN gel can continuously adsorb low concentration of MB (LMB), and the MB-adsorbed KI-PCN gel can self-clean under light irradiation. The bench-scale experiments simulating real river showed that KI-PCN gel can effectively and continuously remove LMB (0.1-20 ppm), indicating the possibility for the removal of contaminants in natural rivers. Furthermore, the possible degradation pathways were proposed by combining the density functional calculations (DFT) and intermediates identified by liquid chromatography-mass spectrometry (LC-MS). This work proposed a new perspective to acquire a novel self-cleaning and easily recyclable photocatalyst for treatment of wide concentration range organic wastewater as well as remediation of natural waterbody.

Boosting Photosynthetic H2O2 of Polymeric Carbon Nitride by Layer Configuration Regulation and Fluoride-Potassium Double-Site Modification

Photocatalytic hydrogen peroxide (H₂O₂) production will become a burgeoning strategy for solar energy utilization by selective oxygen reduction reaction (ORR). Polymeric carbon nitride (PCN) shows relatively high two-electron ORR selectivity for H₂O₂ production but still limited low H₂O₂ production efficiency due to slow exciton dissociation. Herein, we constructed a heptazine/triazine layer stacked carbon nitride heterojunction with fluorine/potassium (F/K) dual sites (FKHTCN). The introduction of F/K not only can regulate layer components to enhance the charge separation efficiency but, more importantly, also optimize the adsorption of surface oxygen molecules and intermediate *OOH during H₂O₂ production. Consequently, FKHTCN efficiently improves the photocatalytic H₂O₂ production rate up to 3380.9 μmol h^-1 g^-1, nearly 15 times higher than that of traditional PCN. Moreover, a production-utilization cascade system was designed to explore their practical application in environmental remediation. This work lays out the importance of engineering a layer-stacked configuration and active sites for enhancing photocatalysis.

Self-cycled photo-Fenton-like system based on an artificial leaf with a solar-to-H2O2 conversion efficiency of 1.46

Millions of families around the world remain vulnerable to water scarcity and have no access to drinking water. Advanced oxidation processes (AOPs) are an effective way towards water purification with qualified reactive oxygen species (ROSs) while are impeded by the high-cost and tedious process in either input of consumable reagent, production of ROSs, and the pre-treatment of supporting electrolyte. Herein, we couple solar light-assisted H₂O₂ production from water and photo-Fenton-like reactions into a self-cyclable system by using an artificial leaf, achieving an unassisted H₂O₂ production rate of 0.77 μmol/(min·cm²) under 1 Sun AM 1.5 illumination. Furthermore, a large (70 cm²) artificial leaf was used for an unassisted solar-driven bicarbonate-activated hydrogen peroxide (BAP) system with recycled catalysts for real-time wastewater purification with requirements for only water, oxygen and sunlight. This demonstration highlights the feasibility and scalability of photoelectrochemical technology for decentralized environmental governance applications from laboratory benchtops to industry.

Continuous generation of reactive oxygen species is desirable in the advanced oxidation process. Here, the authors report a self-cycled photoFenton-like with a scalable artificial leaf for production of H₂O₂ from water with solar-to-H₂O₂ efficiency of 1.46%.

Regulation of coordination and doping environment via target molecular transformation for boosting selective photocatalytic ability

Here, a novel transformed CdO with low coordination and N doping environment was simply synthesized through the involvement of the target molecule tetracycline (TC). The results showed that the shedding of surface hydroxyl groups led to a low coordination environment, and N doping formed a new doping energy level, which increased the charge density and promoted the migration and separation of photo-generated carriers. Its photocatalytic performance was 4.32 times higher than that of hydroxy-rich CdO and the selectivity coefficient was 4.8. Combined with theoretical calculation and in situ Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) analysis, the significant improvement of selectivity was due to the interaction of the doped N atom with the methyl carbon in TC. This work provided a new idea for the simultaneous construction of low coordination environment and N-doped materials for efficient selective photocatalysis.

Boosting Interfacial Charge Transfer with a Giant Internal Electric Field in a TiO2 Hollow-Sphere-Based S-Scheme Heterojunction for Efficient CO2 Photoreduction

The construction of an S-scheme charge transfer pathway is considered to be a powerful way to inhibit charge recombination and maintain photogenerated carriers with high redox capacity to meet the kinetic requirements of the carbon dioxide (CO₂) photoreduction reaction. For an S-scheme heterojunction, an internal electric field (IEF) is regarded as the main driving force for accelerating the interfacial spatial transfer of photogenerated charges. Herein, we designed a TiO₂ hollow-sphere (TH)-based S-scheme heterojunction for efficient CO₂ photoreduction, in which WO₃ nanoparticles (WP) were applied as an oxidation semiconductor to form an intimate interfacial contact with the TH. The S-scheme charge transfer mode driven by a strong IEF for the TH/WP composite was confirmed by in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. As a result, abundant photogenerated electrons with strong reducing ability would take part in the CO₂ reduction reaction. The combination of surface photovoltage spectra and transient photocurrent experiments disclosed that the IEF intensity and charge separation efficiency of the fabricated TH/WP composite were nearly 16.80- and 1.42-fold higher, respectively, than those of the pure TH. Furthermore, sufficient active sites provided by the hollow-sphere structure also enhanced the kinetics of the catalytic reaction. Consequently, the optimized TH/WP composite showed a peak level of CO production of 14.20 μmol g^-1 in 3 h without the addition of any sacrificial agent. This work provides insights into the kinetic studies of the S-scheme charge transfer pathway for realizing high-performance CO₂ photoreduction.

Regulating directional transfer of electrons on polymeric g-C3N5 for highly efficient photocatalytic H2O2 production

Graphite carbon nitride (g-C₃N₅) has been widely used in various photocatalytic reactions due to its higher thermodynamic stability and better electronic properties compared to g-C₃N₄. However, it is still challenging to endow g-C₃N₅ with high performance on photocatalytic hydrogen peroxide (H₂O₂) production. Herein, potassium and iodine are co-doped into g-C₃N₅ (g-C₃N₅-K, I) for photocatalytic production of H₂O₂ with high efficiency. As expected, the photocatalytic H₂O₂ production rate over the g-C₃N₅-K, I (2933.4 μM h^-1) reaches to 84.22 times as that of g-C₃N₅. The excellent photocatalytic H₂O₂ production activity is mainly ascribed to the co-doping of K and I, which significantly improves the capacity of oxygen (O₂) adsorption, selectivity of two-electrons oxygen reduction reaction (2e^- ORR) and separation efficiency of charge carriers. The density functional theory (DFT) calculations reveal that O₂ molecules are more conducive to being adsorbed on g-C₃N₅-K, I. Besides, the result of excited states further indicates that photo-generated electrons can be directionally driven to the adsorbed O₂ molecules, which are effectively activated to form H₂O₂. The findings will contribute to new insights in designing and synthesizing g-C₃N₅ based photocatalysts for the H₂O₂ production.

Construction of a ZnIn2S4/Au/CdS Tandem Heterojunction for Highly Efficient CO2 Photoreduction

Photocatalytic CO₂ reduction technology is of great importance to alleviate energy crisis and environmental pollution; however, it remains a serious challenge due to the fast recombination of carriers. In this study, we report a three-dimensional structure of a ZnIn₂S₄/Au/CdS composite photocatalyst for the CO₂ reduction reaction, where Au nanoparticles (NPs) are evenly anchored on the surface of ZnIn₂S₄ by photodeposition and Au NPs are wrapped around by CdS. In ZnIn₂S₄/Au/CdS composite photocatalysts, Au NPs act as a bridge to construct a "semiconductor-metal-semiconductor" tandem electron transfer mechanism (ZnIn₂S₄ → Au → CdS) heterojunction, which greatly promotes the transfer of photogenerated electrons. It is worth noting that Au NPs, as a local surface plasmon resonance (LSPR) effect excited source to generate excited-state electrons, further improve the photoreduction CO₂ activity. Under UV-vis light irradiation, the CO yield of ZnIn₂S₄/Au/CdS can reach 63.07 μmol·g^-1·h^-1, which is higher than that of 6.37 μmol·g^-1·h^-1 for pure ZnIn₂S₄, 0.93 μmol·g^-1·h^-1 for CdS, 8.9 μmol·g^-1·h^-1 for ZnIn₂S₄/CdS, 31.04 μmol·g^-1·h^-1 for ZnIn₂S₄/Au, and 5.37 μmol·g^-1·h^-1 for CdS/Au. In addition, the ternary ZnIn₂S₄/Au/CdS composite photocatalyst has good cyclic stability. This study broadens the idea of designing photocatalysts with good carrier separation efficiency.

A Unique Fe-N4 Coordination System Enabling Transformation of Oxygen into Superoxide for Photocatalytic CH Activation with High Efficiency and Selectivity

Selective oxidation of CH bonds is one of the most important reactions in organic synthesis. However, activation of the α-CH bond of ethylbenzene by use of photocatalysis-generated superoxide anions (O₂ ^•- ) remains a challenge. Herein, the formation of individual Fe atoms on polymeric carbon nitride (CN), that activates O₂  to create O₂ ^•- for facilitating the reaction of ethylbenzene to form acetophenone, is demonstrated. By utilizing density functional theory and materials characterization techniques, it is shown that individual Fe atoms are coordinated to four N atoms of CN and the resultant low-spin Fe-N₄  system (t_2g ⁶ e_g ⁰ ) is not only a great adsorption site for oxygen molecules, but also allows for fast transfer of electrons generated in the CN framework to adsorbed O₂ , producing O₂ ^•- . The oxidation reaction of ethylbenzene triggered by O₂ ^•- ions turns out to have a high conversion rate of 99% as well as an acetophenone selectivity of 99%, which can be ascribed to a novel reaction pathway that is different from the conventional route involving hydroxyl radicals and the production of phenethyl alcohol. Furthermore, it possesses great potential for other CH activation reactions besides ethylbenzene oxidation.

Directing Charge Transfer in a Chemical-Bonded BaTiO3 @ReS2 Schottky Heterojunction for Piezoelectric Enhanced Photocatalysis

The piezo-assisted photocatalysis system, which can utilize solar energy and mechanical energy simulteneously, is promising but still challenging in the environmental remediation field. In this work, a novel metal-semiconductor BaTiO₃ @ReS₂ Schottky heterostructure is designed and it shows high-efficiency on piezo-assisted photocatalytic molecular oxygen activation. By combining experiment and calculation results, the distorted metal-phase ReS₂ nanosheets are found to be closely anchored on the surface of the BaTiO₃ nanorods, through interfacial ReO covalent bonds. The Schottky heterostructure not only forms electron-transfer channels but also exhibits enhanced oxygen activation capacity, which are helpful to produce more superoxide radicals. The polarization field induced by the piezoelectric BaTiO₃ can lower the Schottky barrier and thus reduce the transfer resistance of photogenerated electrons directing to the ReS₂ . As a result of the synergy effect between the two components, the BaTiO₃ @ReS₂ exhibits untrahigh activity for degradation of pollutants with an apparent rate constant of 0.133 min^-1 for piezo-assisted photocatalysis, which is 16.6 and 2.44 times as that of piezocatalysis and photocatalysis, respectively. This performance is higher than most reported BaTiO₃ -based piezo-assisted photocatalysis systems. This work paves the way for the design of high-efficiency piezo-assisted photocatalytic materials for environmental remediation through using green energies in nature.

Influence of aggregation and sedimentation behavior of bare and modified zero-valent-iron nanoparticles on the Cr(VI) removal under various groundwater chemistry conditions

Aggregation behaviors of bare, and sodium polyacrylate (PAA) and starch modified zero-valent-iron nanoparticles (nZVI), as well as their effects on the Cr (VI) removal were investigated by simulating the groundwater. Results showed that increased concentration of PAA (1-6 wt%) and starch (0.1-0.6 wt%) alleviated the aggregation of modified nZVI (abbreviated as P-nZVI and S-nZVI), while there was an optimum dosage of 4 wt% PAA and 0.3 wt% starch for the Cr (VI) removal, respectively. Moreover, as one of the fundamental water chemistry parameters, Ca²⁺ (0, 5, and 10 mg L^-1) greatly promoted the aggregation of modified nZVI, and decreased the Cr (VI) removal efficiency by them via forming bidentate bridging structure (between Ca²⁺ and PAA) or complexes (between Ca²⁺ and starch). Additionally, fulvic acid (FA) (0, 2, 5, and 10 mg L^-1) decreased the Cr (VI) removal by P-nZVI because of the significantly improved electronic repulsion. However, FA enhanced the aggregation of S-nZVI, but diminished its performance on Cr (VI) removal due to the bridging effect between FA and starch. The present study was of great importance in predicting the migration of nZVI and contaminants removal under complex geological conditions in groundwater.

Understanding the mechanism of interfacial interaction enhancing photodegradation rate of pollutants at molecular level: Intermolecular π-π interactions favor electrons delivery

Uncovering the interaction between photocatalyst and reaction substrate as well as subsequent electron transfer process is critical to achieve high-performance photodegradation of pollutants. Herein, based on the reduced density gradient (RDG) method, we visualize the simulation of the π-π interactions between photocatalyst (g-C₃N₄) and pollutant molecule (flumequine, FLU). Results revealed that π-π interactions between g-C₃N₄ and FLU favor electrons delivery, resulting in enhanced charge separation efficiency and direct hole oxidation of FLU. Moreover, it is found that the charge transfer rate is determined by the valence band (VB) level of g-C₃N₄ and E_HOMO of FLU, of which the deeper VB position of g-C₃N₄ favors faster charge transfer, leading to further enhancement in photocatalytic degradation rate of FLU. Additionally, the possible degradation pathways of FLU were proposed by theoretical calculation and the determined intermediates. Our work afforded a new insight into pollutants degradation and the rational design of highly efficient photocatalysts.

Degradation and detoxification of broad-spectrum antibiotics by small molecular intercalated BiOCl under visible light

In view of the increasing threat of overuse of broad-spectrum antibiotics to water environment, here, a series of small molecular intercalated bismuth oxychloride (SBC-X) composite photocatalysts were successfully constructed by a simple stirring synthesis at room temperature. Among them, SBC-0.5 showed excellent photocatalytic performance against the three target broad-spectrum antibiotics in visible light, which was 3.06 times, 5.93 times and 11.64 times higher than that of monomer for degrading tetracycline, norfloxacin and ciprofloxacin, respectively. Through analysis, it was found that the excellent photocatalytic degradation performance of SBC-0.5 was mainly attributed to the greatly improved specific surface area, which increased to 14 times of monomer, providing a large number of reaction sites for the subsequent photocatalytic degradation. Besides, intercalated molecules as charge transfer bridges between nanosheets greatly accelerated the efficiency of photogenerated charge transfer between layers. Free radical trapping experiments and electron spin resonance indicated that superoxide anion radicals played a major role in the photocatalytic degradation, followed by singlet oxygen. Furthermore, nine potential degradation intermediates were identified, and the toxicity was greatly reduced confirmed by ECOSAR software prediction and soybean seed germination and seeding growth experiment. Our work will provide useful information for the purification of wastewater containing antibiotics.

Porous Nitrogen-Defected Carbon Nitride Derived from A Precursor Pretreatment Strategy for Efficient Photocatalytic Degradation and Hydrogen Evolution

Graphitic carbon nitride (g-C₃N₄) has attracted extensive research attention because of its virtues of a metal-free nature, feasible synthesis, and excellent properties. However, the low specific surface area and mediocre charge separation dramatically limit the practical applications of g-C₃N₄. Herein, porous nitrogen defective g-C₃N₄ (PDCN) was successfully fabricated by the integration of urea-assisted supramolecular assembly with the polymerization process. Advanced characterization results suggested that PDCN exhibited a much larger specific surface area and dramatically improved charge separation compared to bulk g-C₃N₄, leading to the formation of more active sites and the improvement in mass transfer. The synthesized PDCN rendered a 16-fold increase in photocatalytic tetracycline degradation efficiency compared to g-C₃N₄. Additionally, the hydrogen evolution rate of PDCN was 10.2 times higher than that of g-C₃N₄. Meanwhile, the quenching experiments and electron spin resonance (ESR) spectra suggested that the superoxide radicals and holes are the predominant reactive species for the photocatalytic degradation process. This study may inspire the new construction design of efficient g-C₃N₄-based visible-light photocatalysts.

Confined synthesis of condensed π-conjugation C-PAN/MS-CN nanotubes for efficient photocatalytic H2 evolution

Condensed π-conjugation C-PAN/MS-CN nanotubes were obtained through a facile polyacrylonitrile (PAN)-confined molten salt (MS) thermal condensation of melamine. Carbonized PAN (C-PAN) nanosheets with conjugate network structure in molten salt system...

An efficient hydrogen evolution photocatalyst of Rh@Cr2O3 loaded PbMoO4 twenty-six facets polyhedron

Shape anisotropic semiconductor is advanced catalyst for resolving energy crises. However, modification studies are still needed to overcome its intrinsic disadvantages, such as the lack of active sites. For this...

Surface Enriching Promotes Decomposition of Benzene from Air

The low generation rate and short lifetime of reactive oxidation radicals typical like ·OH strictly limit the photocatalytic degradation of benzene in the air. Here, we adopt copper dopant to...

A novel S-scheme heterojunction based on 0D/3D CeO2/Bi2O2CO3 for photocatalytic degradation of organic pollutants

A distinct S-scheme heterojunction of 0D/3D CeO2/Bi2O2CO3 photocatalyst was successfully synthesized via hydrothermal method employing for photocatalytic degradation of methylene blue (MB), tetracycline (TC) and aureomycin (AM). Compared with bare...

Constructing porous intramolecular donor–acceptor integrated carbon nitride doped with m-aminophenol for boosting photocatalytic degradation and hydrogen evolution activity

A porous intramolecular D–A integrated carbon nitride with boosted photocatalytic activity was constructed via thermal melting followed by thermal copolymerization of m-aminophenol with urea.

Iodide ions as invisible chemical scissors tailoring carbon nitride for highly efficient photocatalytic H2O2 evolution

The obtained TCN/NaI possesses Na+ and –OH co-modification, which shows the highest H2O2 generation rate. DFT calculations further reveal that the electron of β spin-orbital in TCN/NaI can transfer to the π* orbital of O2 more facile than BCN.