Efficient visible light driven degradation of antibiotic pollutants by oxygen-doped graphitic carbon nitride via the homogeneous supramolecular assembly of urea.

Graphitic carbon nitride (CN), as a non-metal material, has emerged as a promising photocatalyst to address environmental issues with the favorable band gap and chemical stability. The porous oxygen-doped CN nanosheets (CNO) were synthesized by an ecofriendly and efficient self-assembled approach using a sole urea as the precursor. The CNO photocatalysts were derived from the hydrogen-bonded cyanuric acid-urea supramolecular complex, which were obtained by pretreatment of urea at high temperature and pressure. The homogeneous supramolecular assembly was advantageous to the formation of uniform porous and oxygen-doped CN nanosheets. The formation process of the supramolecular intermediate and the CNO nanosheets were investigated. Moreover, doping amount of O in CNO could be controlled by the time of the high-pressure thermal polymerization of urea. The characterization results shown that the O atoms were successfully doped into the framework of CN by substitution the N atoms to form the C-O structures. The obtained CNO photocatalysts demonstrated the excellent visible-light photocatalytic performances for sulfamerazine (SMR) degradation, which was ascribed to synergistic interaction of porous structure and O doping. The degradation intermediates of SMR were identified and the degradation pathway were also proposed. Furthermore, density functional theory (DFT) calculations proved that O doping changed the electronic structure of CN, resulting in more easier to activate O2. This work provides a novel perceptive for the development of high-performance nonmetal photocatalysts by using the homogeneous supramolecular assembly, which exhibits great potential in the environmental treatment.

Well-designed oxidized Sb/g-C3N4 2D/2D nanosheets heterojunction with enhanced visible-light photocatalytic disinfection activity.

2D/2D heterojunction photocatalysts with excellent photocatalytic activity highlight considerable potential in water disinfection. Here, an oxidized Sb/g-C3N4 2D/2D nanosheets heterojunction (Sb-SbOx/CNS) was constructed based on a facile one-step liquid-phase exfoliation method using concentrated sulfuric acid. By doing so, bulk Sb and g-C3N4 were exfoliated simultaneously and then, intercalated each other. Compared with CNS and Sb-SbOx, the obtained Sb-SbOx/CNS demonstrated better photocatalytic disinfection activity towards Escherichia coli K-12 (E. coli K-12) under visible light irradiation. The 5% oxidized Sb/g-C3N4 2D/2D nanosheets heterojunction (5.0% Sb-SbOx/CNS) exhibited the best photocatalytic performance and admirable cycling stability, which was ascribed to the unique structure where the interfacial charge separation was strengthened by the strong coupling effect between Sb-SbOx and CNS. Meanwhile, the fundamental mechanism of photocatalytic disinfection was also proposed. The photogenerated ROS (reactive oxygen species) violently attacked the E. coli K-12 membrane, creating massive and irreparable holes on the cell membrane. The leakage of cations (K+, Na+, Ca2+ and Mg2+), adenosine triphosphate, total soluble sugar and protein accelerated the destruction of E. coli K-12. Trapping experiments suggested that the photocatalytic disinfection process against E. coli K-12 was dominated by h+ generated on 5.0% Sb-SbOx/CNS. This work offers a new promising way to modify the 2D/2D heterojunction featuring efficient photocatalytic disinfection performance.

Defect Regulating of Few-Layer Antimonene from Acid-Assisted Exfoliation for Enhanced Electrocatalytic Nitrogen Fixation.

Nitrogen reduction reaction (NRR), as a green and sustainable technology, is far from a practical application due to the lack of efficient electrocatalysts. In this work, we found that antimonene, a group-VA elemental two-dimensional (2D) material, is attractive as an electrocatalyst for NRR. The antimonene here is acquired through chemical exfoliation of antimony (Sb) using H2SO4 for the first time, which simultaneously achieved efficient large-sized exfoliation and created a high density of active edge sites. Moreover, the concentration of defects shows a gradual increasing tendency as the treatment time extends. The obtained antimonene exhibited favorable average ammonia (NH3) yield and Faradaic efficiency as high as 2.08 µg h-1 cm-2 and 14.25% at -0.7 V versus RHE, respectively. Density functional theory calculations prove that the sufficient exposure of edge defects is favorable for reducing the reaction barrier and strengthening the interaction between antimonene and the intermediates of NRR, thus increasing the selectivity and yield rate of NH3. The chemical exfoliation of Sb reported here offers an alternative avenue to engineer the surface structures of group-VA elemental-based catalysts. Investigation of NRR using 2D antimonene can further provide deep insight into the mechanism and principle of NRR over group-VA elemental nanosheets.

Electrocatalytic performance of Sb-modified Bi25FeO40 for nitrogen fixation.

The Haber-Bosch N2 fixation method suffers from the power-consuming and harsh conditions. In contrast, the electrochemical conversion of N2 (NRR) at room temperature and atmospheric pressure is considered a promising alternative route. In this study, we synthesized Sb-modified with Bi25FeO40 (BFSO/BFO) by using one-step hydrothermal treatment. The BFSO/BFO catalyst has higher selectivity to NRR than Bi25FeO40 (BFO) under the same applied voltage. Such large interfacial interaction area plays a critical role in transfer electron and enhances the density of current. The resulting BFSO/BFO heterojunction showed significant electrocatalytic activity under controllable voltage, which exhibited favorable average ammonia (NH3) yield as high as 2.62 µg·h-1·cm-2 at -0.2 V versus RHE. Moreover, the stability of the BFSO/BFO composite was evaluated for six cycles and the results were desirable. This study provides a new insight into the design of composite catalysts using BFO, which has high activity and selectivity toward NRR.

Metal-free 2D/2D heterojunction of covalent triazine-based frameworks/graphitic carbon nitride with enhanced interfacial charge separation for highly efficient photocatalytic elimination of antibiotic pollutants.

A novel polymer-based 2D/2D heterojunction photocatalysts of covalent triazine-based frameworks/graphitic carbon nitride nanosheets (CTFNS/CNNS) heterojunction are successfully obtained by an electrostatic self-assembly method using amine-functionalized CNNS and carboxyl-rich CTFNS. Such large contact surface and appropriate interfacial contact between CNNS and CTFNS plays a critical role in transfer and separation of charge-carriers. The resulting CTFNS/CNNS heterojunction showed significantly enhanced photocatalytic activity under the irradiation of simulated solar light, which could decompose 10 ppm sulfamethazine (SMT) within 180 min with a high degradation efficiency of 95.8 %. Chloride ions can greatly promote the photocatalytic degradation of SMT due to the production of more radical species. O2- is the dominant active species for SMT decomposition over CTFNS/CNNS heterojunction. Moreover, the degradation intermediates of SMT were identified using high performance liquid chromatography-mass spectrometer and the degradation pathway was proposed. This study provides a new insight into the design of 2D/2D heterojunctions using carbon-based nanomaterials, which exhibits great potential in the degradation of sulfonamide antibiotics in wastewaters.

Preparation of nitrogen-containing carbon using a one-step thermal polymerization method for activation of peroxymonosulfate to degrade bisphenol A.

Nitrogen-containing carbon materials (NCC-x) are promising metal-free catalysts for activation of peroxymonosulfate (PMS) to treat with aqueous organic pollutants. In this study, NCC-x were synthesized via a facile thermal polymerization method using urea and terephthalaldehyde as precursors. This method was derived from the polymerization method of graphitic carbon nitride (g-C3N4) and the reaction between the precursors was based on Schiff base chemistry. Compared with the synthesis of g-C3N4 using urea as the precursor, formation of a melamine ring was inhibited and the cyano groups were produced in NCC-x during the polymerization process. The obtained NCC-x catalysts had high specific surface areas, many graphite-nitrogen active sites, and high degrees of graphitization, thus exhibiting excellent activities for the degradation of bisphenol A via PMS activation. This study introduces a convenient method to obtain a highly efficient nitrogen-containing carbon PMS activator and the results are useful for the development of bisphenol A treatment by PMS activation using carbon-containing materials.

Enhanced photocatalytic disinfection of Escherichia coli K-12 by porous g-C3N4 nanosheets: Combined effect of photo-generated and intracellular ROSs.

The porous graphitic carbon nitride nanosheets (PCNSs) with high yields were synthesized by using one-step chemical exfoliation method. PCNSs accelerated separation efficiency of photo-generated electron-hole pairs in comparison to bulk graphitic carbon nitride. The PCNS5 (exfoliation for 5 h) exhibited optimal photocatalytic disinfection capability towards Escherichia coli K-12 under simulated solar light irradiation with complete disinfection of 6.5 log10 cfu/mL of E. coil K-12 within 2 h. The enhanced photocatalytic activity of PCNS5 originated from mesoporous nanosheet structure. The possible mechanism of photocatalytic disinfection has proposed that intracellular reactive oxygen species levels and the activities of antioxidant enzymes (e.g., catalase and superoxide dismutase) were enhanced. Transmission electron microscope images observed during photocatalytic disinfection process suggested that the cell membrane was regarded as the first target for oxidation, resulting in a faster leakage of cytoplasmic content and finally degradation of DNA leading to bacterial death. Furthermore, the trapping experiment showed that superoxide radical (•O2-) and holes (h+) were responsible for E. coli K-12 disinfection by PCNS5.

Graphitic carbon nitride grown in situ on aldehyde-functionalized α-Fe2O3: All-solid-state Z-scheme heterojunction for remarkable improvement of photo-oxidation activity.

Aldehyde-functionalized α-Fe2O3/graphitic carbon nitride (α-Fe2O3-DBD/g-C3N4) was successfully synthesized through Schiff-based reaction between aromatic aldehydes in 3,4-dihydroxybenzaldehyde and NH2 groups in urea. The 3,4-dihydroxybenzaldehyde around α-Fe2O3 were advantageous to in situ growth of graphitic carbon nitride on α-Fe2O3 to form the contact interface by chemical bonds and beneficial to the electron transfer, leading to the formation of Z-scheme photocatalytic system. The α-Fe2O3-DBD/g-C3N4 photocatalysts exhibited a remarkable improvement in the degradation of bisphenol A (BPA) compared with bulk g-C3N4. The enhanced photocatalytic activity was attributed to the enhanced charge separation efficiency and higher redox potential. This study presents a simple and efficient method to construct all-solid-state Z-scheme photocatalytic system with the formation of tight contact interface and nonmetal materials (aromatic rings) as electron mediators for the removal of complex pollutants.

Construction of Acetaldehyde-Modified g-C3N4 Ultrathin Nanosheets via Ethylene Glycol-Assisted Liquid Exfoliation for Selective Fluorescence Sensing of Ag.

We successfully prepared acetaldehyde-modified graphitic carbon nitride (g-C3N4) ultrathin nanosheets (ACNNSs) by a simple ethylene glycol-assisted liquid exfoliation method. The introduction of acetaldehyde regulated the surface energy of g-C3N4 to better match with that of water, which improved the exfoliation efficiency. Moreover, acetaldehyde introduces defects into the g-C3N4 structure, which can act as excitation energy traps and cause considerable variation in the fluorescence emission. Benefiting from the stable photoluminescence emission, good water solubility, and biocompatibility, the obtained ACNNSs showed a selective fluorescent response to Ag+ in both aqueous solution and living cells. The strong absorption and intimate contact with Ag+ and its appropriate redox potential of ACNNSs contributed to this excellent fluorescent response. A simple and environmental friendly approach was proposed to simultaneously achieve modification and exfoliation of g-C3N4 in aqueous solution. These findings might lead to wider applications of carbon-based nanomaterials as active materials for fluorescence detection in the environment.

Macroscopic urea-functionalized cadmium sulfide material with high visible-light photocatalytic activity for rewritable paper application.

A macroscopic urea-functionalized CdS (CdS-U) is synthesized for the first time. The CdS-U material is formed through the interaction between NH2/NH groups on urea and COO- groups on sodium oleate-capped CdS nanoparticles (CdS-So NPs). The CdS-U material exhibites excellent visible light photocatalytic activity and plasticity and has the potential to be produced as rewritable papers. It is convenience to produce a large-scale film by CdS-U. Letters can be written on the CdS-U film and disappear through a dissolution-irradiation process, and then the CdS-U film can be recycled by drying. This novel CdS-U material might be of interest and provide a new chance to advance the application of visible light photocatalyst on rewritable papers.

Modeling of self-assembled GeSi nano-dots and corresponding admittance spectroscopy.

We examine two techniques to determine experimentally and theoretically the strength of quantum confinement in SiGe nano-dots. A simple theory for admittance spectroscopy in a quantum dot is developed in conjunction with our experiments and experimental findings. Using a mass-balance equation approach based on the Boltzmann equation in which the hole-phonon interaction in a SiGe nano-dot is considered, we can successfully reproduce those observed experimentally in the admittance spectroscopy measurements. Thus, we are able to understand the interesting features of the electronic properties in SiGe nano-dots, especially the dependence of the quantum confinement on the size of the dots.