N-doped graphene quantum dots decorated NaBiO3/BiOBr p-n heterojunction photocatalyst for enhanced visible light degradation of phenol.

N-Doped graphene quantum dots (N-GQDs) combine the advantages of N-doped carbon and quantum dot materials, displaying enhanced performance in electrocatalysis, drug delivery, sensing and so on. In this work, novel hydrotropic N-GQDs with controlled size are obtained for the first time via a nanospace-confined preparation strategy, in which HNO3 vapour serves as scissors for quickly cutting the N-doped carbon nanolayer in the confined nanospace of reusable mesoporous molecular sieves. The as-prepared N-GQDs exhibit a uniform lateral size of about 2.4 nm, high photostability and yellow fluorescence, which is strongly quenched upon addition of ferric ions due to the coordination between ferric ions and N/O-rich groups of the N-GQDs surface. Significantly, the fluorescence response to Fe3+ is linear in the 0.5 to 40 μM concentration range and the N-GQDs showed good selectivity and satisfying recovery for ferric ion detection in tap water. Noteworthily, the quenched fluorescence by Fe3+ can be recovered by adding ascorbic acid (AA), which efficiently destroyed the coordination between Fe3+ and N-GQDs. Based on this principle, the N-GQDs were used to successfully construct an AA sensor, exhibiting a wide linearity range (between 0.5 and 90 μM) with a low detection of limit (80 nM at S/N = 3) and better selectivity towards AA compared with other common physiological substances. Finally, the constructed fluorescence sensor was employed successfully for AA determination in fish blood with satisfactory recovery ranging from 95.3 to 106.2%. The results indicate that N-GQDs synthesized by the nanospace-confined strategy are promising in biosensor fabrication.

Development and validation of a green spectrofluorimetric method for brivaracetam determination using N-doped graphene quantum dots: Mechanistic insights and bioanalytical applications

Electrochemically converting the overemitted CO2 from fossil fuel combustion back into the natural carbon cycle has become a hot spot in recent years. However, surfactants on synthesized nanocatalysts have negative effects on the activity and selectivity. Herein, we transferred the surfactants on single-crystalline gold nanoparticles into N-doped graphene quantum dots (NGQDs) by a hydrothermal method, which not only cleared the Au surfaces but also enhanced the catalytic activity for converting CO2 into CO at ultralow potentials. The highest faradaic efficiency reaches 93% at −0.25 V vs RHE, and CO production starts from as low as −0.15 V, which is much lower than other Au-based nanocatalysts. DFT calculations were applied to investigate the mechanism and indicate that the synergistic effect between gold and NGQDs is a key to increasing activity.

Enhanced full solar spectrum photocatalysis by nitrogen-doped graphene quantum dots decorated BiO2-x nanosheets: Ultrafast charge transfer and molecular oxygen activation

Photocatalysis has been recognized as a viable technology for pollutant degradation in wastewater, owing to its ability to generate reactive radicals under photoirradiation. Among these, sulfate radicals have been attracting significant attention due to their strong oxidizing properties; yet the specific mechanism of action has remained elusive thus far. In this study, defective NH2-MIL-88B (DNMB) is prepared via a facile hydrothermal procedure in the presence of potassium sodium tartrate and found to facilitate the production of sulfate radicals from sulfate anions under visible light irradiation, due to partial reduction of Fe3+ to Fe2+ in the NMB skeleton by the added tartrate that enriches the Fe3+/Fe2+ redox couples, in addition to other reactive species like superoxide radicals and hydroxy radicals. This effectively improves the degradation efficiency toward a variety of organic pollutants, including antibiotics such as tetracycline (TC), sulfamethoxazole (SMX), and levofloxacin (LEV), as well as common organic contaminants like bisphenol A (BPA) and rhodamine B (RhB), as compared to pristine NMB. Specifically, after 40 minutes of visible light irradiation, the degradation rate increases from 61.5% to 92.1% for TC, from 76.1% to 89.4% for SMX, from 60.5% to 75.2% for LEV, from 61.7% to 91.2% for BPA, and from 78.4% to 94.8% for RhB. The primary active species are identified to be sulfate radicals, with minor contributions from holes, superoxide radicals, and hydroxyl radicals, as demonstrated in quenching experiments and electron spin resonance measurements, and further confirmed by theoretical studies. Degradation pathways for the various pollutants are then proposed based on results from Fukui index calculations and liquid chromatography-mass spectrometry analysis. These results underscore the crucial role of structural engineering in driving the advancement of green and sustainable technologies for environmental engineering.

Photophysical and photochemical properties of graphene quantum dots (GQDs) strongly depend on their morphological and chemical features. However, systematic and uniform manipulation of the chemical structures of GQDs remains challenging due to the difficulty in simultaneous control of competitive reactions, i.e., growth and doping, and the complicated post-purification processes. Here, we report an efficient and scalable production of chemically tailored N-doped GQDs (NGs) with high uniformity and crystallinity via a simple one-step solvent catalytic reaction for the thermolytic self-assembly of molecular precursors. We find that the graphitization of N-containing precursors during the formation of NGs can be modulated by intermolecular interaction with solvent molecules, the mechanism of wh\tich is evidenced by theoretical calculations and various spectroscopic analyses. Given with the excellent visible-light photoresponse and photocatalytic activity of NGs, it is expected that the proposed approach will promote the practical utilization of GQDs for various applications in the near future.

S-doped TiO2 nanomaterials (S-TiO2) synthesized by solid state and liquid state reaction route were used for the visible light degradation of Rhodamine B. The results show that at 20°C，pH=5, the rule of pseudo-first-order reaction and high catalytic activity were found in the visible light degradation of RhB on the S-TiO2 nanomaterials and pure TiO2. Within 80 min, the visible light degradation ratio of RhB is 97.9%, which is 6.6 times for pure TiO2. The reaction conditions such as the initial concentration, pH value, the sorts of metal ions, and consumption of catalyst affect the reaction rate constant of S-TiO2 material. The addition of Cu2+ enhances the visible light degradation rate of 28.6%, but Cr3+ decreases greatly the reaction rate of RhB.

Antibiotics are crucial medications for preventing and treating bacterial infections. However, due to their inherent resistance to degradation, they are also a major component of water pollutants. Semiconductor photocatalysis is considered to be an important green technology for sewage treatment. In this study, BiVO 4 /CdS Z‐type heterojunction was synthesized and applied in the photocatalytic degradation of tetracycline hydrochloride (TCH). The Z‐type heterojunction not only facilitates the separation of photogenerated charges, but also preserves photogenerated electrons with strong reduction capability and photogenerated holes with high oxidation capability. Following visible light irradiation for 90 min, the efficiency of BiVO 4 /CdS photocatalytic degradation of TCH reached 93.1%. Moreover, BiVO 4 /CdS demonstrates notable degradation efficacy toward other quinolone antibiotics. Free radical trapping experiments and EPR test results suggest that superoxide radicals, hydroxyl radicals, photogenerated electrons, and holes serve as the primary active species in the photocatalytic degradation process of tetracycline hydrochloride. This study offers valuable insights into the development of Z‐type heterojunction photocatalysts for the efficient degradation of tetracycline hydrochloride.

Flower-like Ag3VO4/BiOBr n-p heterojunction photocatalysts with enhanced visible-light-driven catalytic activity

Bi₃O₄Cl/BiOBr composite heterojunction photocatalyst was prepared using in-situ generation method. A number of characterisation techniques were used to examine the prepared material's crystal structure, microstructure, elemental content, and optoelectronic characteristics. By breaking down the antibiotic ofloxacin in the presence of visible light, the produced photocatalyst's degradation activity was investigated. According to the experimental findings, a composite photocatalyst has a higher degrading activity than a photocatalyst made of a single component. The optimal composite sample BBC-2 has apparent rate constants that are 4.3 times and 3 times higher than those of pure BiOBr and Bi₃O₄Cl, respectively. The 4 cycles of experiments indicate that the composite sample has good stability. According to the electrochemical test results, it was found that the Bi₃O₄Cl/BiOBr composite photocatalyst has good photo generated carrier separation efficiency and excellent charge transfer efficiency, thus exhibiting good degradation activity towards ofloxacin. Superoxide radicals and holes are the primary active species in Bi₃O₄Cl/BiOBr composites in photocatalytic tests, according to the free radical capture experiment. In addition, charge transfer pathways and mechanisms for enhancing activity were proposed through free radical capture experiments and band theory.

The removal of persistent antibiotic pollutants such as tetracycline (TC) from wastewater remains a significant challenge. To address the inherent limitations of graphitic carbon nitride (g-C3N4)—namely its restricted visible-light absorption and rapid charge recombination—this study constructed a novel Mn0.5Cd0.5S/g-C3N4 heterojunction photocatalyst via a combined calcination-hydrothermal strategy. Comprehensive characterization confirmed the successful integration of Mn0.5Cd0.5S nanoparticles with g-C3N4 nanosheets, which extended the visible-light response and facilitated interfacial charge transfer. The optimal composite exhibited remarkably enhanced photocatalytic activity, degrading 92.94% of TC within 60 min under visible light. The apparent rate constant (k) calculated from pseudo-first-order kinetics was 0.02366 min−1, which is 14.8 and 6.1 times higher than that of pristine g-C3N4 and Mn0.5Cd0.5S, respectively. Radical trapping and spectroscopic analyses revealed that the boosted performance originates from efficient spatial separation of charge carriers via a type-II heterojunction mechanism, where superoxide radicals (•O2 −) and holes (h+) serve as the primary active species. The composite also demonstrated excellent stability over four consecutive cycles. This work provides an effective strategy for modifying g-C3N4-based materials and offers insight into the design of high-performance heterojunction photocatalysts for environmental remediation.

Filamentous fungal in situ biosynthesis of heterogeneous Au/Cd0.5Zn0.5S nano-photocatalyst: A macroscopic assembly strategy for preparing composite mycelial pellets with visible light degradation ability

Facile synthesis of graphene quantum dots and C-doping porous BN nanoribbon heterojunctions for boosting CO2 photoreduction

Synthesis of hierarchically meso-macroporous TiO2/CdS heterojunction photocatalysts with excellent visible-light photocatalytic activity

Constructing Z-scheme LaTiO2N/g-C3N4@Fe3O4 magnetic nano heterojunctions with promoted charge separation for visible and solar removal of indomethacin