Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Novel surface structure of LaFeO3/nitrogen-deficient g-C3N4 nanocomposites to improve visible-light photocatalytic performance toward phenol removal

Herein, novel surface structure LaFeO3/nitrogen-deficient g-C3N4 nanocomposites (LaFeO3/g-C3N4-H) have been successfully synthesized by a two-step process. First, nitrogen-deficient graphitic carbon nitride (g-C3N4-H) was produced by thermally condensing melamine that had been treated with acetic acid as a precursor. After that, LaFeO3 was incorporated into the g-C3N4-H nanosheets. The as-prepared nanostructured materials were characterized by XRD, FT-IR, N2 adsorption-desorption experiments, FESEM, and TEM, demonstrating the formation of interfacial interaction and heterogeneous structure in LaFeO3/g-C3N4-H nanocomposites. Additionally, UV-vis diffuse reflectance spectra (DRS) and photoluminescence spectra (PL) have been used to assess the optical properties of the nanohybrids. The results show that the LaFeO3/g-C3N4-H nanocomposite was successfully produced with a reliable interfacial interface, and produced a good heterojunction relationship between g-C3N4-H and LaFeO3 which may significantly boost the photocatalytic activity as compared to prinstine g-C3N4 and LaFeO3. Phenol degradation under visible light irradiation was used to test the photocatalytic activity of LaFeO3/g-C3N4-H, and the results showed that 10%-LaFeO3/g-C3N4-H had significant photocatalytic activity and remarkable adsorption efficiency, with an overall removal rate of phenol up to 88% after 180 min of visible light irradiation. This study may present a novel method for developing highly efficient artificial photocatalytic systems.

Broad-bandgap porous graphitic carbon nitride with nitrogen vacancies and oxygen doping for efficient visible-light photocatalytic degradation of antibiotics

Effective degradation methods are required to address the issue of antibiotics as organic pollutants in water resources. Herein, a two-stage thermal treatment method was used to prepare porous graphitic carbon nitride (g-C3N4) modified with nitrogen vacancies and oxygen doping at the N-(C)3 position and deep in the g-C3N4 framework. Compared with bulk g-C3N4 (BCN) (7 ± 1 m2/g), the modified sample (RCN-2h) possesses a larger specific surface area (224 ± 1 m2/g), a larger bandgap (by 0.19 eV), and a mid-gap state. In addition, RCN-2h shows 15.4, 11.2, and 9.5 times higher photodegradation rates than BCN for the degradation of 100% ofloxacin (OFX) (within 15 min), tetracycline (within 15 min), and sulfadiazine (within 35 min), respectively. The RCN-2h catalyst also exhibits superior stability and reusability. Systematic characterization and density functional theory calculations demonstrate that the synergistic effect of the porous structure, nitrogen vacancies, and oxygen doping in RCN-2h provides additional reaction sites, improved charge separation efficiency, and shorter diffusion paths for reactants and photogenerated charge carriers. Trapping experiments reveal that •O2- is the main active species in OFX photodegradation, and a possible photodegradation pathway is identified using liquid chromatography-mass spectrometry. Benefiting from the simplicity of synthesis methods and the superiority of elemental doping, carbon nitride materials with functional synergy have great potential for environmental applications.

Modulation of ultrathin nanosheet structure and nitrogen defects in graphitic carbon nitride for efficient photocatalytic bacterial inactivation

The efficient generation and utilization of ROSs is a key step in determining the achievement of safe drinking water by photocatalytic bacterial inactivation technology. Although graphitic carbon nitride (g-C3N4) serves as a green and promising photocatalyst for water disinfection, insufficient bacterial capturing capacity and serious charge recombination of pristine g-C3N4 extremely restrict its bactericidal activity. Herein, we develop a facile thermal exfoliation and thermal polymerization method to prepare the nitrogen-defective ultrathin g-C3N4 nanosheets (DUCN-500). Our results showed that ultrathin nanosheet structure greatly enhanced bacterial capturing capacity of g-C3N4 to increase the utilization efficiency of ROS, which contributed to the performance of DUCN-500 greatly outperforming bulk g-C3N4. The nitrogen defects increased ROS generation (·O2- and H2O2) by approximately 4.6 times, which was attributed to negative shift of the conduction band potential and rapid separation of charge carriers. The DUCN-500 could rapidly and completely inactivate Escherichia coli and Bacillus subtilis in real sewage under simulated solar irradiation, accompanied by good anti-interference capability and stability. Additionally, bacterial morphology destruction, the loss of antioxidant enzyme activity and the leakage of protein were proven to be the main mechanisms of photocatalytic sterilization. This study offers new insight into the rational design of efficient g-C3N4-based photocatalysts for water disinfection.

Light and nitrogen vacancy-intensified nonradical oxidation of organic contaminant with Mn (III) doped carbon nitride in peroxymonosulfate activation

Recently, Mn-based materials have a great potential for selective removal of organic contaminants with the assistance of oxidants (PMS, H₂O₂) and the direct oxidation. However, the rapid oxidation of organic pollutants by Mn-based materials in PMS activation still presents a challenge due to the lower conversion of surface Mn (III)/Mn (IV) and higher reactive energy barrier for reactive intermediates. Here, we constructed Mn (III) and nitrogen vacancies (Nv) modified graphite carbon nitride (MNCN) to break these aforementioned limitations. Through analysis of in-situ spectra and various experiments, a novel mechanism of light-assistance non-radical reaction is clearly elucidated in MNCN/PMS-Light system. Adequate results indicate that Mn (III) only provide a few electrons to decompose Mn (III)-PMS* complex under light irradiation. Thus, the lacking electrons necessarily are supplied from BPA, resulting in its greater removal, then the decomposition of the Mn (III)-PMS* complex and light synergism form the surface Mn (IV) species. Above Mn-PMS complex and surface Mn (IV) species lead to the BPA oxidation in MNCN/PMS-Light system without the involvement of sulfate (SO₄^{• ̶}) and hydroxyl radicals (•OH). The study provides a new understanding for accelerating non-radical reaction in light/PMS system for the selective removal of contaminant.

Solar-induced efficient propylparaben photodegradation by nitrogen vacancy engineered reticulate g-C3N4: Morphology, activity and mechanism

Propylparaben (PrP) has attracted extensive concerns due to its wide occurrence in wastewater and potential health risk. Herein, nitrogen vacancy engineered reticulate g-C₃N₄ (Nv-RCN) was successfully synthesized for the photodegradation of PrP. Nv-RCN exhibited larger specific surface area, greater light absorption ability, higher transfer and separation efficiency of charge carriers in comparison with bulk g-C₃N₄ (CN). According to the characterization results and DFT calculation, nitrogen vacancy could capture electrons and facilitate oxygen adsorption. The Nv-RCN exhibited an outstanding PrP removal efficiency of 94.3 %, and the corresponding apparent rate constant of Nv-RCN was 3.37 times higher than that of CN. High O₂ concentration (8 mg/L) and low pH value (pH = 3) promoted PrP photodegradation based on Box-Behnken Design. The O₂^- was the major radical during PCOP of Nv-RCN, and could oxidize PrP by decarbonylation and dealkylation. This study provided new insights to the improvement of photodegradation performance of g-C₃N₄ for parabens removal and related environmental remediation.

Efficient charge transfer in Co-doped CeO2/graphitic carbon nitride with N vacancies heterojunction for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution is a promising and environmentally friendly strategy to prepare renewable energy sources thus addressing the energy crisis and environmental issues, and it is crucial to develop an ideal photocatalytic for highly efficient H₂ production. Herein, the Co-doped CeO₂ decorated on graphitic carbon nitride with N vacancies (NVs) heterostructure photocatalyst (Co-CeO₂/DCN) is prepared via a simple self-assembly method. Due to the extended light absorption range, and efficient charge separation and migration derived from the introduction of NVs and the heterojunction structure, the photocatalytic activity of the Co-CeO₂/DCN is largely promoted. The optimal sample 20-Co-CeO₂/DCN shows a high H₂ evolution rate of 1077.02 μmol g^-1h^-1 (λ > 400 nm), which is 113 and 33 times higher than the bare bulk graphitic carbon nitride (BCN) and CeO₂, respectively. This work will provide a new strategy to develop high-performance photocatalysts using defect engineering and heterojunction engineering for H₂ evolution.

Construction of nitrogen vacant g-C3N4 nanosheet supported Ag3PO4 nanoparticle Z-scheme photocatalyst for improved visible-light photocatalytic activity

The superior photocatalytic activity of semiconductor-based photocatalytic materials has attracted great attention. In this work, a series of novel Ag3PO4/g-C3N4-x (APO/CNx) composites with the Z-scheme structure were fabricated through a facile precipitation method. B naphthol, a typical phenolic compound, was selected to evaluate the photocatalytic activity of all as-prepared photocatalysts. The obtained APO/CNx composites exhibited excellent photocatalytic activity for degradation of B naphthol under visible-light irradiation. Experimental results showed that the degradation rate toward B naphthol could reach to 90.5% for 180 min, which was almost 3.66 times higher than pure g-C3N4, indicating that the presence of nitrogen vacancies and Z-scheme structure could efficiently improve the photocatalytic performance of pure g-C3N4. Furthermore, the results of trapping experiments and electron spin resonance (ESR) spectroscopy manifest that •O2- and •OH radicals were the predominant active substances for B naphthol degradation, and the possible mechanism of improved photocatalytic performance was elucidated. This work will provide an innovative perspective for constructing Z-scheme photocatalysts for the application of photocatalytic in the field of wastewater treatment.

Plasma-Tuned nitrogen vacancy graphitic carbon nitride sphere for efficient photocatalytic H2O2 production

Graphitic carbon nitride (CN) is a promising photocatalyst for sustainable energy conversion. Meanwhile, N vacancies are useful for H₂O₂ generation; however, they are hard to control. In this study, the N vacancy CN sphere (NVCNS) is synthesized by H₂ plasma treatment to tune the NV. The as-synthesized NVCNS exhibits an efficient and stable photocatalytic H₂O₂ yield of 4413.1 μmol g_cat^-1h^-1, which is 2.5 and 4.6 times higher than that of CNS (1766.4 μmol g_cat^-1h^-1) and bulk CN (956.6 μmol g_cat^-1h^-1), respectively, using a Xe lamp with an intensity of 100 mWcm^-2. In particular, the charges recombination rate is remarkably reduced by introducing N defect state, promoting electron accumulation and O₂ adsorption, through theoretical calculation and experiments. Furthermore, the NV creates abundant unsaturated sites and induces strong interlayer interactions, leading to effective electronic excitation and the promotion of charge transport.

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.

Visible-light photocatalytic degradation of bisphenol A using cobalt-to-oxygen doped graphitic carbon nitride with nitrogen vacancies via metal-to-ligand charge transfer

As an environmentally friendly and promising semiconductor, graphitic carbon nitride (g-C₃N₄) was widely used in photocatalytic treatment of aqueous organic pollutants. In this study, cobalt-to-oxygen doped graphitic carbon nitride with feeble nitrogen vacancies (Co-OCN_VN) as metal-to-ligand charge transfer was synthesized via a facile thermal polymerization method with low cost and non-toxic precursors. The oxygen doped graphitic carbon nitride with feeble nitrogen vacancies (OCN_VN) ligand was successfully formed and cobalt was presented in OCN_VN in an ionic form (in the form of Co²⁺-N_x). The cobalt atoms were chemically coordinated to the OCN_VN matrix rather than forming cobalt oxide on the surface of OCN_VN. The embedded cobalt atoms maintained the absorption margin of ligand OCN_VN (up to 700 nm) and served as the separation centers to promote the interfacial electron transfer as well. Due to the synergistic effects of the embedded cobalt atoms and oxygen doping, the Co-OCN_VN showed an outstanding activity for the visible-light photocatalytic oxidation of endocrine disruptor bisphenol A (BPA).

Visible-light-driven photocatalytic degradation of sulfamethazine by surface engineering of carbon nitride：Properties, degradation pathway and mechanisms

Polymeric carbon nitride semiconductor has been explored as emerging metal-free photocatalyst for solving the energy shortage and environmental issues. However, the efficiency of carbon nitride is still not satisfying. Herein, a facile copolymerization between L-cysteine and dicyandiamide has been applied to forming the modified carbon nitride photocatalysts. The photocatalytic performance was evaluated through degrading sulfamethazine under visible light illumination. The ameliorative structure and tuned energy band result in visible-light adsorption enhancement. In addition, nitrogen vacancies offer more sites to adsorbing molecular oxygen, thereby facilitating the transfer of electrons from carbon nitride to the surface adsorbed oxygen. As a result, the degradation rate of optimized modified carbon nitride sample for sulfamethazine was 0.1062 min^-1, which was almost 12 times than that of carbon nitride (0.0086 min^-1). Superoxide radicals and holes were mainly responsible for the sulfamethazine photodegradation by modified carbon nitride. Two reaction intermediates/products were observed and identified by high performance liquid chromatography-mass spectrometer, and a possible reaction pathway was proposed. This study provides new insights into the design of highly efficient photocatalyst for other organic pollutants degradation.

Efficient visible-light-driven hydrogen evolution and Cr(VI) reduction over porous P and Mo co-doped g-C3N4 with feeble N vacancies photocatalyst

Developing highly efficient and inexpensive photocatalysts without noble metals, yet remarkably enhancing hydrogen production and Cr(VI) reduction activity, is highly needed. Here, the effective photocatalytic H₂ evolution under visible light from an Eosin Y (EY)-sensitized (P, Mo)-g-C₃N_x system by avoiding any noble metal co-catalyst is reported by the first time. Meanwhile, the optimized sample also displays the excellent performance in photocatalytic hexavalent chromium (Cr(VI)) reduction. In addition, this composite exhibits delectable stability for photocatalytic activities, no significant decay of activity is being observed after 16h reaction for photocatalytic H₂ evolution (8h for Cr(VI) reduction). It is believed that this work will open up a new route for fabricating high-performance and inexpensive photocatalysts for hydrogen production and Cr(VI) reduction.

Enhancing visible light photocatalytic activity of nitrogen-deficient g-C3N4 via thermal polymerization of acetic acid-treated melamine

Nitrogen-deficient graphitic carbon nitride (CN-HAc) was synthesized by thermal condensation of acetic acid-treated melamine as a precursor. The nitrogen vacancies play a remarkable role on controlling the electronic structure of g-C₃N₄, such as extending the optical absorption and enhancing the separation efficiency of photogenerated charge carriers, resulting in the improvement of photocatalytic activity. The photocatalytic activity of the catalysts was evaluated by splitting water and degradation of rhodamine B (RhB) under visible light irradiation (λ>420nm). The average H₂ evolution rate on CN-HAc is 24μmolh^-1, which is about 5 times of that on pristine g-C₃N₄. Meanwhile, CN-HAc exhibits superior photocatalytic mineralization of RhB. The possible formation mechanism of nitrogen-deficient in the framework of g-C₃N₄ is proposed.

Preparing and preserving the double quantum coherence in NV- centers in Diamond at low fields

We present and demonstrate a simple idea to excite and preserve the double-quantum-coherence (DQC) in the ground state of the electron spin of the Nitrogen-vacancy (NV) color center in diamond. We measure the coherence time of the DQC and compare it to the single quantum coherence time, both, in a Ramsey fringe experiment and under a Hahn echo sequence. We also demonstrate a robust pulse sequence based on the DANTE pulse sequence for selectively isolating the signal from the electron transitions conditional on the state of the always-present Nitrogen spin.