Preparation of Structure Vacancy Defect Modified Diatomic-Layered g-C3 N4 Nanosheet with Enhanced Photocatalytic Performance

Sustainable Electrochemical Synthesis of Porous g-C3N4 Nanosheets via 3D-Printed Platinized Electrodes for Enhanced Photocatalytic Activity

Graphitic carbon nitride (g-C3N4), a polymeric metal-free catalyst, is extensively used to degrade industrial toxic waste that contaminates the aqueous system. However, commonly synthesized bulk g-C3N4 is prone to agglomeration, leading to low surface area with fewer effective photoactive centers, limiting its potential toward the facile separation of photo-excitons and resulting in low photocatalytic activity. This study introduces an innovative electrochemical synthesis of in situ exfoliated porous g-C3N4 nanosheets (GCN NSs) featuring a large surface area with effective separation of photo-excitons, leading to the facile production of reactive oxygen species (ROS). The GCN NSs are uniformly dispersed in an alkaline solution grown via a newly designed electrochemical process using 3D-printed platinumized titanium mesh as both anode and cathode under rigorous stirring for 40 min. The morphological study, along with surface area determination, reveals that the as-grown carbonaceous matrix is highly exfoliated with an inherent nanoporous architecture, having a high surface area of 163.73 m2 g-1 with an average pore diameter of 8.311 nm. The electrochemically synthesized GCN NSs demonstrate excellent charge transfer kinetics with low charge transfer resistance and superior photocatalytic activity of 98% degradation efficiency against various organic dyes (concentration of 10 ppm) under simulated solar irradiation for 120 min with 5 mg of catalyst. Kinetic studies of the photodegradation process indicate that the reaction follows pseudo-first-order kinetics, with the rate constant of 3.59 × 10-2 min-1, which is approximately 1.8 times higher as compared to the recent findings. A plausible mechanistic understanding reveals that photogenerated holes and hydroxyl radicals (•OH) are the primary species for the overall photodegradation process. The stability test depicts that the photocatalyst maintains its efficiency over five consecutive runs with a minimum loss of 7%. This research offers valuable insights into the design and synthesis of advanced photocatalysts with optimized architectures for enhanced industrial waste management.

Cytocompatible 2D Graphitic Carbon Nitride-Modified Polybutylene Adipate Terephthalate/Polylactic Acid Hybrid Nanobiocomposites

Polymer nanobiocomposites (PNCs) prepared with graphitic carbon nitride (GCN) nanosheets in polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA) bioblends were processed using a three-step processing technique that involved: (1) a solution-based GCN exfoliation step; (2) a masterbatching step of GCN in PBAT by solution processing; and (3) a melt-compounding step where the masterbatch was mixed with pristine PLA to delaminate the 2D GCN layers by extrusion high-shear mixing and to deposit them onto the biphasic PLA/PBAT morphology. Due to the partial exfoliation of GCN, this process led to a concurrent presence of three distinct morphologies within the PNCs' microstructure: (1) Type 1, characterized by an unaltered interface and PLA matrix, with minimal GCN deposition within the PBAT phase; (2) Type 2, distinguished by a diffused and stiff interface with GCN distribution in both the dispersed (PBAT) and matrix (PLA) phases; and (3) Type 3, featuring unmodified interfaces and GCN localization across both PLA and PBAT phases with a stair-like morphological texture. Such a morphological combination generates distinct crack propagation micromechanics, thereby influencing the variability of the plastic deformational behavior of their PNCs. Particularly, the Type 1 morphology enables GCN to act as a secondary stress-dissipating agent, whereas the PBAT domains serve as the primary stress-absorbing sites, contributing to enhanced crack propagation energy requirements. Contrarily, Type 3 (slightly) and Type 2 (predominantly) morphologies invert GCN's role from stress dissipation to stress concentration due to its localization within the PLA matrix. Differential scanning calorimetry revealed a crystallinity increase in the PNCs until 0.1 wt % GCN, followed by a decline, likely due to agglomeration at higher contents. Thermogravimetric analysis showed that GCN addition improved the thermostability of the bioblends, attributed to the GCN's nanophysical and pyrolytic barrier effect. Moreover, using both direct and indirect methods, GCN did not impair the biocompatibility of the bioblends as confirmed via cytocompatibility assays.

Realizing C-C Coupling via Accumulation of C1 Intermediates within Dual-Vacancy-Induced Dipole-Limited Domain Field to Propel Photoreduction of CO2-to-C2 Fuel

Photocatalytic conversion of CO2 and H2O into high-value-added C2 fuels remains a tough challenge, mainly due to the insufficient concentration of photogenerated electrons for the instability of C1 intermediates, which often tend to desorb easily and disable to form C─C bonds. In this work, photoreduction of CO2-to-C2H6 is successfully achieved by introducing adjacent C, N dual-vacancy sites within the heptazine rings of ultrathin g-C3N4, which results in the opening of two neighboring heptazine rings and forms a distinctive dipole-limited domain field (DLDF) structure. In situ X-ray photoelectron spectra and in situ fourier transform infrared spectra provide direct evidence of the rapid accumulation and transformation of C1 intermediates, especially CO* and CHO*, within the DLDF. Ab initio molecular dynamics further substantiates the role of DLDF in promoting C-C coupling between CO* and CHO*, through the analysis of interaction trajectories and energy changes of their central atoms, ultimately achieving a high yield of C2H6 up to 57.86 µmol g-1 h-1. It is for the first time to propose the concept of DLDF for significant advancement in photoreduction of CO2-to-C2 fuel with the evident breakthrough to address the challenge of coupling carbon-containing intermediates between active sites, offering new insights for the design of C-C coupling sites in single-component photocatalysts.

Synthesis, Characterization, and Roles of Vacancy Defects in Polymer and Graphitized Carbon Nitride Photocatalysts: A Comprehensive Review

Vacancy defect graphitic carbon nitride (g-C3N4) and conjugated polyimide (PI) polymer photocatalysts have become increasingly recognized as metal-free photocatalysts featuring an appropriate bandgap. The narrow absorption spectrum of visible light and the rapid recombination rate of the photoexcited charge carriers in PI polymers and g-C3N4 impede its photocatalytic performance. The presence of oxygen vacancies (OVs) in PI polymer photocatalysts, as well as nitrogen vacancies (NVs) and carbon vacancies (CVs) in g-C3N4, can significantly enhance the migration of photogenerated electrons. Adding vacancies to improve the electronic structure and band gap width can greatly enhance the photocatalytic efficiency of PI polymers and g-C3N4. Defect engineering is important for increasing the photocatalytic ability of PI-polymer and g-C3N4. There remains a notable absence of thorough review papers covering the synthesis, characterization, and applications of vacancy-rich PI-polymer and g-C3N4 in photocatalysis. This review paper examines the roles of OVs in PI-polymer, NVs, and CVs in g-C3N4 and thoroughly summarizes the preparation approaches employed before and after, as well as during polymerization. This review scrutinizes spectroscopic characterization techniques, such as EPR, XPS, PAS, XRD, FTIR, and NMR, for vacancy defect analysis. We also reviewed the role of vacancies, which include light absorption, photogenerated charge carrier separation, and transfer dynamics. This review could serve as a comprehensive understanding, a vacancy-engineered design framework, and a practical guide for synthesizing and characterizing.

Synergistic manipulation of sulfur vacancies and palladium doping of In2S3 for enhanced photocatalytic H2 production

In this study, a simple one-pot synthesis process is employed to introduce Pd dopant and abundant S vacancies into In2S3 nanosheets. The optimized Pd-doped In2S3 photocatalyst, with abundant S vacancies, demonstrates a significant enhancement in photocatalytic hydrogen evolution. The joint modification of Pd doping and rich S vacancies on the band structure of In2S3 result in an improvement in both the light absorption capacity and proton reduction ability. It is worth noting that photogenerated electrons enriched by S vacancies can rapidly migrate to adjacent Pd atoms through an efficient transfer path constructed by Pd-S bond, effectively suppressing the charge recombination. Consequently, the dual-defective In2S3 shows an efficient photocatalytic H2 production rate of 58.4 ± 2.0 μmol·h-1. Additionally, further work has been conducted on other ternary metal sulfide, ZnIn2S4. Our findings provide a new insight into the development of highly efficient photocatalysts through synergistic defect engineering.

Multifunctional Conductive MOFs Enhance the Photocatalytic Hydrogen Evolution Efficiency of S-Type Ni3(HITP)2/TiO2 Heterojunctions

Despite their high surface area, remarkable porosity, and efficient charge transfer mechanisms, conductive MOFs have found limited utilization within the domain of photocatalysis. In this study, we synthesized a cutting-edge S-type Ni3(HITP)2/TiO2 heterojunction photocatalyst exhibiting outstanding light harvesting and prolonged lifetime of photogenerated electrons through an in situ synthesis approach. Compared with TiO2, the composite materials not only significantly increase the specific surface area by 4.07 times but also expand the visible light absorption edge from 400 to 1100 nm. The hydrogen production rate of Ti/Ni-3 reached 4.927 mmol·g-1·h-1, which is 4.51 times that of TiO2. The S-type interface charge transfer pathway of the Ni3(HITP)2/TiO2 composite material was inferred by band structure, in situ XPS, SPV, and free radical capture, which improves charge separation and extends the carrier lifetime to undergo directional migration driven by an IEF. This is the main reason for the improved photocatalytic performance of Ni3(HITP)2/TiO2 composite materials.

Optical Fiber-Enabled In Situ Photocatalytic Hydrogen Generation for Infiltrating Tumor Therapy in Brain

In addition to repressing proliferation, inhibiting the infiltration of tumor cells is an important strategy to improve the treatment of malignant tumors. Herein, a photocatalyst (pCNMC@Pt) is designed by sequentially assembling manganese dioxide, chlorin e6, and platinum (Pt) nanoparticles onto protonated graphitic carbon nitride. With the help of a Z-scheme structure and near-infrared (NIR) photosensitizer, pCNMC@Pt is capable of responding to NIR light to generate large amounts of hydrogen (H2). Taking lactic acid in the tumor microenvironment as a sacrificial reagent, H2 therapy initiated by the NIR photocatalyst remarkably impedes the growth of glioblastoma (GBM). More importantly, it is found that H2 can suppress the stemness of glioma stem cells, curbing both proliferation and infiltration of GBM. Furthermore, since pCNMC@Pt and light source are precisely co-localized through a self-built loading and illumination system, GBM in mouse brains can be efficiently treated, providing an alternative gas therapy approach to cure infiltrating tumors.

Construction of Au quantum dots/nitrogen-defect-enriched graphite carbon nitride heterostructure via photo-deposition towards enhanced nitric oxide photooxidation

The challenge of mitigating pollution stemming from industrial exhaust emissions is a pressing issue in both academia and industry. This study presents the successful synthesis of nitrogen-defect-enriched graphite carbon nitride (g-C3N4) using a two-step calcination technique. Furthermore, a g-C3N4-Au heterostructure was fabricated through the photo-deposited Au quantum dots (QDs). When subjected to visible light irradiation, this heterostructure exhibited robust nitric oxide (NO) photooxidation activity and stability. With its fluffy, porous structure and large surface area, the nitrogen-defect-enriched g-C3N4 provides more active sites for photooxidation processes. The ability of g-C3N4 to absorb visible light is enhanced by the local surface plasmon resonance (LSPR) effect of Au QDs. Additionally, the lifetime of photogenerated charge carriers is extended by the presence of N defects and Au, which effectively prevent photogenerated electron-hole pairs from recombining during the photooxidation process. Moreover, the oxidation pathway of NO was analyzed through In-situ Fourier transform infrared (FT-IR) spectroscopy and Density Functional Theory (DFT) calculation. Computational findings revealed that the introduction of Au QDs decreases the activation energy of the oxidation reaction, thereby facilitating its occurrence while diminishing the formation of intermediate products. As a result, NO is predominantly converted to nitrate (NO3-). This work unveils a novel approach to constructing semiconductor-cocatalyst heterostructures and elucidates their role in NO photooxidation.

Multilayer Fluorine-Free MoBTx MBene with Hydrophilic Structural-Modulating for the Fabrication of a Low-Resistance and High-Resolution Humidity Sensor

2D transition metal borides (MBenes) with abundant surface terminals hold great promise in molecular sensing applications. However, MBenes from etching with fluorine-containing reagents present inert -fluorine groups on the surface, which hinders their sensing capability. Herein, the multilayer fluorine-free MoBTx MBene (where Tx represents O, OH, and Cl) with hydrophilic structure is prepared by a hydrothermal-assisted hydrochloric acid etching strategy based on guidance from the first-principle calculations. Significantly, the fluorine-free MoBTx-based humidity sensor is fabricated and demonstrates low resistance and excellent humidity performance, achieving a response of 90% to 98%RH and a high resolution of 1%RH at room temperature. By combining the experimental results with the first-principles calculations, the interactions between MoBTx and H2O, including the adsorption and intercalation of H2O, are understood first in depth. Finally, the portable humidity early warning system for real-time monitoring and early warning of infant enuresis and back sweating illustrates its potential for humidity sensing applications. This work not only provides guidance for preparation of fluorine-free MBenes, but also contributes to advancing their exploration in sensing applications.

New insight into highly efficient CSA@g-C3N4 for photocatalytic oxidation of benzyl alcohol and thioanisole: NAEDS as a promoter of photoactivity under blue LED irradiation

An open new perspective has been established toward synthesizing eco-friendly CSA@g-C3N4 employing surface engineering. The carbon nitride modified through camphorsulfonic acid was designed and developed in a category of the new generation of photocatalysts for the oxidation of benzyl alcohol and thioanisole in the existence of a natural deep eutectic solvent (NADES). In comparison with pure g-C3N4, not only does CSA@g-C3N4 exhibit an extraordinarily higher ability for harvesting visible light stemming from declining the recombination rate of electrons/holes dependent on PL results but it also reveals notable photocatalytic oxidation capability in the transformation of alcohols as well as thiols into relevant compounds. In addition, non-metal compound (CSA) incorporation would result in considerably diminishing the energy band gap value from 2.8 to 2.28 eV to escalate the visible-light absorption of g-C3N4. While the conventional consensus implies that inherent properties of photocatalysts bring on high photoactivity, this study indicates that deploying choline chloride-urea deep eutectic solvent as an external factor plays the role of photoactivity accelerator. Furthermore, readily recycling and reusability can be achieved for the photocatalytic setup of CSA@g-C3N4 ascribed to its heterogeneous nature with no drop in the photoactivity.

Decade Milestone Advancement of Defect-Engineered g-C3N4 for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride (g-C3N4) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C3N4 is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the "all-in-one" defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultra-active coordinated environment (M-Nx, M-C2N2, M-O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra (fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C3N4 "customization", motivating more profound thinking and flourishing research outputs on g-C3N4-based photocatalysis.

Modulated Connection Modes of Redox Units in Molecular Junction Covalent Organic Frameworks for Artificial Photosynthetic Overall Reaction

The precise tuning of components, spatial orientations, or connection modes for redox units is vital for gaining deep insight into efficient artificial photosynthetic overall reaction, yet it is still hard achieve for heterojunction photocatalysts. Here, we have developed a series of redox molecular junction covalent organic frameworks (COFs) (M-TTCOF-Zn, M = Bi, Tri, and Tetra) for artificial photosynthetic overall reaction. The covalent connection between TAPP-Zn and multidentate TTF endows various connection modes between water photo-oxidation (multidentate TTF) and CO2 photoreduction (TAPP-Zn) centers that can serve as desired platforms to study the possible interactions between redox centers. Notably, Bi-TTCOF-Zn exhibits a high CO production rate of 11.56 μmol g-1 h-1 (selectivity, ∼100%), which is more than 2 and 6 times higher than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn, respectively. As revealed by theoretical calculations, Bi-TTCOF-Zn facilitates a more uniform distribution of energy-level orbitals, faster charge transfer, and stronger *OH adsorption/stabilization ability than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn.