A novel Z-scheme g- C3N4/LaCoO3 heterojunction with enhanced photocatalytic activity in degradation of tetracycline hydrochloride

Determination of three ephedrine psychoactive substances in sewage using solid-phase extraction-ultra-performance liquid chromatography-tandem mass spectrometry

RATIONALE

In recent years, ephedrine psychoactive substances have attracted much attention due to their prevalence in water bodies and potential threat to aquatic ecosystems. Psychoactive substances have been considered as a new type of environmental pollutant due to their unpredictable potential risks to the behavior and nervous system of non-target organisms. A rapid, sensitive, selective, and robust method for the quantification of three ephedrine psychoactive substances in sewage is needed.

METHODS

An ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous determination of three ephedrine psychoactive substances in water. The optimal processing conditions were determined by optimizing the chromatography-mass spectrometry and solid-phase extraction (SPE) conditions (e.g., the SPE column, sample pH, washing, and elution), and the treatment conditions were determined; this was achieved via positive ion scanning in multiple reaction monitoring mode. Poly-Sery MCX was selected as the extraction column, with samples loaded at pH 3. And 4-mL solution of 2% formic acid (FA) aqueous solution was used as the eluent; the target compounds were eluted with 5 mL of 5% NH4OH in acetonitrile (ACN) solution. The best results were obtained when the residue was resolubulization in ACN after nitrogen evaporation.

RESULTS

The developed UPLC-MS/MS showed a good linear relationship in the range of 0-50.00 μg/L, with determination coefficients (R2) greater than 0.9990. The detection limit and quantitation limit were 0.05-0.10 and 0.20-0.50 μg/L, respectively. Recovery rates of the target compounds in blank sewage at three different concentrations ranged from 92.37% to 106.31%, with relative standard deviations (RSDs) of 0.77%-4.83% (n = 7).

CONCLUSIONS

This method has been successfully applied to the analysis of surface water and domestic sewage, and the samples were processed stably, indicating that the method is practical for the determination of ephedrine psychoactive drugs in water bodies.

Preparation of novel Au-Nb3O7F nanosheets for the photodegradation of tetracycline hydrochloride

Water pollution caused by antibiotics is a growing problem and photodegradation by efficient catalysts is an environmentally friendly technology that can effectively degrade organic pollutants in water. Here, a novel method was innovatively used to synthesize niobium oxyfluoride (Nb3O7F) nanosheets decorated with Au nanoparticles, which is the first report for the composites of Au and Nb3O7F. We prepared the Nb3O7F nanosheets via hydrothermal synthesis followed by deposition of Au nanoparticles on their surface using HAuCl4. The prepared samples were characterized by XRD, HRTEM, XPS, and UV-Vis. The diameters of most Au NPs are ranging from 5 to 25 nm with an average size of about 16.9 nm, as well as the Nb3O7F nanosheets in size ranging from 200 nm to 700 nm. The chemical composition of the Au-Nb3O7F showed a Au/Nb atomic ratio of 1/10, as well as a Nb/O/F ratio of 3/7/1. UV-Vis spectrum reveals a largest absorption peak at 520 nm for the Au-Nb3O7F nanosheets. The prepared Au-Nb3O7F nanomaterials were applied to the visible-light photodegradation of tetracycline hydrochloride, with the photocatalytic degradation rate reached more than 50% under the optimal conditions within 1 h. Capture experiments indicated that h+ and •O2 - are the main active substances involved during the course of the photodegradation. Furthermore, the proposed mechanism for the photodegradation of the novel Au-Nb3O7F nanosheets was given.

Mitigating phytotoxicity of tetracycline by metal-free 8-hydroxyquinoline functionalized carbon nitride photocatalyst

Photooxidative removal of pharmaceuticals and organic dyes is an effective way to eliminate growing micropollutants. However, photooxidation often results in byproducts as secondary hazardous substances such as phytotoxins. Herein, we found that photooxidation of common antibiotic tetracycline hydrochloride (TCH) over a metal-free 8-hydroxyquinoline (8-HQ) functionalized carbon nitride (CN) photocatalyst significantly reduces the TCH phytotoxic effect. The phytotoxicity test of photocatalytic treated TCH-solution evaluated towards seed growth of Cicer arietinum plant model endowed natural root and shoot growth. This study highlights the conceptual insights in designing of metal-free photocatalyst for environmental remediation.

Synergistic effect of flower-like MnFe2O4/MoS2 on photo-Fenton oxidation remediation of tetracycline polluted water

In this work, a flower-like MnFe₂O₄-MoS₂ (FMW) catalyst was successfully prepared as a catalyst for photo-Fenton oxidation. The flower-like structured FMW possessed large open surface area, which exposed enough active sites and can fully contact with tetracycline (TC). We studied the effect of different FMW composites, H₂O₂ concentration and light intensity on the photo-Fenton process. 1FMW (MnFe₂O₄:MoS₂ = 1:10 in mol) exhibited the best degradation effect on TC, and 1 mmol/L of H₂O₂ and 398.73 mW/cm² of light were the optimum parameters. A p-n heterojunction was formed in 1FMW, ensuring the stability of composite and the fast electron transfer. Holes, •O₂^- and •OH were generated in photo-Fenton process and participated in TC degradation. Notably, FMW can be recycled quickly under an external magnetic field due to its magnetic properties. Overall, FMW shows good catalytic stability and recoverability in photo-Fenton oxidation process, which has a broad application prospect.

Perovskite Nanoparticles as an Electrochemical Sensing Platform for Detection of Warfarin

Chemically prepared PrAlO3 perovskite nanoparticles (NPs) were applied for the electrochemical detection of warfarin, which is commonly utilized for preventing blood clots, such as in deep vein thrombosis. PrAlO3 perovskite NPs were synthesized by the co-precipitation process at environmental conditions. Crystallographic structure, phase purity, morphological structure, thermal stability, optical properties, and electrochemical characteristics were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, UV-visible analysis, and cyclic voltammetry techniques. TEM micrographs showed the highly crystalline structure, smooth surface, irregular shape, and size of nanocrystalline particles with an average size of 20–30 nm. Particularly crystalline perovskite NPs were pasted on glassy carbon electrodes (GCE) to electrochemically detect the warfarin contents in liquid samples. The fabricated electrode was electrochemically characterized by different parameters such as different potential, scan rates, same potential with seven consecutive cycles, time response, real-time sample analysis, and as a function of warfarin concentration in phosphate buffer solution (0.1 M PBS, pH 7.2). The electrochemical electrode was further verified with various potentials of 5, 10, 20, 50, 100, and 150 mV/s, which exhibited sequential enhancements in the potential range. For detecting warfarin over a wide concentration range (19.5 µM–5000 µM), the detection devices offered good sensitivity and a low limit of detection (19.5 µM). The time-dependent influence was examined using chronoamperometry (perovskite NPs/GCE) in the absence and presence of warfarin at four distinct voltages of +0.05 to +1.2 V from 0 to 1000 s. The repeatability and reliability of the constructed electrochemical sensing electrode were also evaluated in terms of cyclic response for 30 days, demonstrating that it is substantially more reliable for a longer period. The fabricated perovskite NPs/GCE electrodes could be employed for the rapid identification of other drugs.

Molybdenum disulfide loading on a Z-scheme graphitic carbon nitride and lanthanum nickelate heterojunction for enhanced photocatalysis: Interfacial charge transfer and mechanistic insights

Interfacial design and the co-catalyst effect are considered to be effective to achieve separation and transport of photogenerated carriers in composite photocatalysts. In this study, a Z-scheme heterojunction was successfully combined with a co-catalyst to achieve a highly efficient LaNiO₃/g-C₃N₄/MoS₂ photocatalyst. MoS₂ flakes were loaded on a hybrid material surface, which was formed by LaNiO₃ nanocubes embedded on layered g-C₃N₄, and a good heterostructure with multiple attachment sites was obtained. Experimental studies confirmed that the Z-scheme heterojunction completely preserves the strong redox ability of the photogenerated electrons and holes. As a cocatalyst, MoS₂ further promoted interfacial charge separation and transport. The synergistic effect of the Z-scheme heterojunction and co-catalyst effectively realized the transfer of photogenerated carriers from "slow transfer" to "high transfer" and promoted water decomposition and pollutant degradation. Results revealed that under simulated sunlight irradiation, LaNiO₃/g-C₃N₄/MoS₂ composites exhibit superior hydrogen evolution of 45.1 μmol h^-1, which is 19.1 times that of g-C₃N₄ and 4.9 times that of LaNiO₃/g-C₃N₄, respectively. Moreover, the LaNiO₃/g-C₃N₄/MoS₂ Z-scheme photocatalyst exhibited excellent photocatalytic performance for antibiotic degradation and heavy-metal ion reduction under visible light. This study might provide some insights into the development of photocatalysts for solar energy conversion and environmental remediation.

Z-scheme LaCoO3/C3N5 for efficient full-spectrum light-simulated solar photocatalytic hydrogen generation

An inexpensive and efficient LaCoO3/C3N5 photocatalytic system for water splitting or other photocatalytic applications was designed. The photocatalytic reaction and mechanism of C3N5 and its complexes was verified.

Enhanced photocatalytic degradation activity of Z-scheme heterojunction BiVO4 /Cu/g-C3 N4 under visible light irradiation

A novel BiVO₄ /Cu/g-C₃ N₄ heterostructure photocatalyst was synthesized by thermal condensation, hydrothermal, and in situ precipitation method. The microscopic morphology and chemical composition of the synthesized samples were analyzed by XRD, SEM, FT-IR, XPS, and other characterizations. BiVO₄ /Cu/g-C₃ N₄ (BiVO₄ /Cu:g-C₃ N₄ mass ratio was 1:1) photocatalyst had the optimal photocatalytic degradation activity for tetracycline (TC) wastewater under visible light irradiation (120 min, 74.8%). The introduction of Cu and Z-scheme heterojunction was further confirmed by UV-vis, PL, EIS, and capture mechanism analysis, which effectively accelerated the separation and transfer rate of photogenerated electron holes and enhanced the strong oxidation of h⁺ and •O₂ ^- active species. BiVO₄ /Cu/g-C₃ N₄ heterojunction photocatalytic material has potential application value in the removal of refractory pollutants in wastewater. PRACTITIONER POINTS: A novel Z-scheme BiVO₄ /Cu/g-C₃ N₄ photocatalyst with excellent photocatalytic activities and stability was prepared to treat tetracycline (TC) wastewater. 1:1 CBCN (BiVO₄ /Cu:g-C₃ N₄ mass ratio was 1:1) photocatalyst exhibited the highest photocatalytic performance for TC wastewater. The Z-scheme heterojunction and Cu act as the interfacial charge transfer medium accelerated the transfer and separation of carriers.

Influence of the Amount of Carbon during the Synthesis of LaFe0.8Co0.2O3/Carbon Hybrid Material in Oxygen Evolution Reaction

The oxygen evolution reaction (OER) and the hydrogen evolution reaction occurred at the anode and cathode, which depends on the electronic structure, morphology, electrochemically active surface area, and charge-transfer resistance of the electrocatalyst. Transition metals like cobalt, nickel, and iron have better OER and oxygen reduction reaction activities. At the same time, transition-metal oxide/carbon hybrid has several applications in electrochemical energy conversion reactions. The rich catalytic site of transition metals and the excellent conductivity of carbon material make these materials as a hopeful electrocatalyst in OER. Carbon-incorporated LaFe_0.8Co_0.2O₃ was prepared by a simple solution combustion method for the development of the best performance of the electrocatalyst. The catalyst can deliver 10 mA/cm² current density at an overpotential of 410 mV with better catalytic stability. The introduction of carbon material improves the dispersion ability of the catalyst and the electrical conductivity. The Tafel slope and onset potential of the best catalyst are 49.1 mV/dec and 1.55 V, respectively.

Defects and internal electric fields synergistically optimized g-C3N4-x/BiOCl/WO2.92 heterojunction for photocatalytic NO deep oxidation

In this work, g-C₃N_4-x/BiOCl/WO_2.92 heterojunction with "N-O" vacancies was prepared using NaBiO₃ and WCl₆ as raw materials and non-metal plasma of WO_2.92 grew in-situ on the surface of BiOCl, resulting in the enhanced photocatalytic NO deep oxidation. XPS tests and DFT calculation indicated the formation of internal electric fields from g-C₃N_4-x to BiOCl, BiOCl to WO_2.92, which induced the transition from Ⅱ-Ⅱ-type to double Z-scheme hetero-structure. High separation efficiency, prolong lifetime and strong redox ability of photo-generated electron-hole pairs were simultaneously achieved due to the charge capture effect of defects and double Z-scheme mechanism. Therefore, g-C₃N_4-x/BiOCl/WO_2.92 exhibited the significantly increased NO removal rates from 21.17% (BiOCl/WO_2.92) and 36.52% (g-C₃N_4-x) to 68.70% and the main oxidation product of NO was NO₃^-. This study revealed that the carrier dynamics of heterojunction photocatalysts could be optimized by the synergistic effect of defects and internal electric fields to achieve photocatalytic NO deep oxidization.

Construction of novel Zn2TiO4/g-C3N4 Heterojunction with efficient photodegradation performance of tetracycline under visible light irradiation

This work presented facile fabrication of carbon nitride (CN)/zinc titanate (ZT) heterojunction by one-step ball milling process for visible light-induced photocatalytic degradation. The phase structures, morphologies, functional groups, and optical properties of the prepared materials were systematically characterized by XRD, FTIR, UV-Vis DRS, and SEM techniques. The ball milling for 10 min significantly improved visible light absorption properties; the as-synthesized ZT/CN catalyst (2.8 eV) showed lower band gap energy than bare ZT (3.2 eV). This result revealed a successful incorporation. The photocatalytic activities of the heterostructure catalysts (ZT/CN) evaluated by degrading tetracycline under visible light irradiation and highest TC removal rate were obtained as 0.0193 min^-1 for ZT/CN/5, which was 6.2 times higher than that of bare CN. The most efficient photocatalyst (ZT/CN/5) could be performed three times without any loss of phase. In addition, the heterostructure catalyst was found as promising candidate for efficient photocatalytic degradation of other antibiotics and dye components.

Z-Scheme LaCoO3/g-C3N4 for Efficient Full-Spectrum Light-Simulated Solar Photocatalytic Hydrogen Generation

Photocatalytic decomposition of water is the most attractive method for the sustainable production of hydrogen, but the development of a highly active and low-cost catalyst remains a major challenge. Here, we report the preparation of LaCoO3/g-C3N4 nanosheets and the utilization of LaCoO3 instead of noble metals to improve the photocatalytic activity for the production of hydrogen. First, LaCoO3 was successfully prepared by the sol-gel method, and then a series of highly efficient Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts were synthesized by the solvothermal method. Various characterization techniques (X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS), photoluminescence (PL), transient photocurrent response test, electron paramagnetic resonance (EPR)) confirm that the heterostructure and interfacial interaction had been formed between LaCoO3 nanoparticles and g-C3N4 nanosheets. In the photocatalytic water splitting test, LaCoO3/g-C3N4-20 wt % exhibited the highest photocatalytic activity of 1046.15 μmol h-1 g-1, which is 3.5 and 1.4 times higher than those of LaCoO3 and g-C3N4, respectively. This work leads to an inexpensive and efficient LaCoO3/g-C3N4 photocatalysis system for water splitting or other photocatalytic applications.

Rational design of 3D/2D In2O3 nanocube/ZnIn2S4 nanosheet heterojunction photocatalyst with large-area "high-speed channels" for photocatalytic oxidation of 2,4-dichlorophenol under visible light

We have rationally designed and fabricated of "face-to-face" 3D/2D In₂O₃ nanocube/ZnIn₂S₄ nanosheet heterojunction by growing ZnIn₂S₄ nanosheets on the surfaces of In₂O₃ cubes as photocatalysts for 2,4-dichlorophenol (2,4-DCP) degradation under visible light. Herein, the unique 3D/2D In₂O₃ nanocube/ZnIn₂S₄ nanosheet hierarchical structure not only exposes far more abundant heterojunction interface active sites compared to 3D/0D In₂O₃ nanocube/ZnIn₂S₄ nanoparticle, but also produces numbers of compact high-speed nanochannels in the junctions, which significantly promotes the separation and migration of photogenerated carriers. Profiting by structural and compositional advantages, the optimized 3D/2D ZnIn₂S₄-In₂O₃ photocatalyst shows excellent photocatalytic activity and stability in the degradation of 2,4-DCP, which is 1.85, 2.60, 3.02 and 3.54-fold higher than that of 3D/0D ZnIn₂S₄-In₂O₃, ZnIn₂S₄ nanosheet, ZnIn₂S₄ nanoparticle and In₂O₃, respectively. Meanwhile, the main active species (·O₂^-, ·OH and h⁺) produced in the photodegradation process were determined and the intermediates and degradation mechanism were studied in detail. Besides, the application on the removal of 2,4-DCP in natural water and actual wastewaters by 3D/2D ZnIn₂S₄-In₂O₃ also have been studied. This work provides a new strategy for efficiently optimize the advantages of binary nano-architectures to effectively degrade phenolic pollutants in the environment.

The precursor-guided hydrothermal synthesis of CuBi2O4/WO3 heterostructure with enhanced photoactivity under simulated solar light irradiation and mechanism insight

Z-scheme heterojunction can efficiently suppress the electron-holes recombination and promote the charges transfer rate, which result in the high photocatalytic performance. Herein, a flower-flake-sphere like CuBi₂O₄/WO₃ hybrid photocatalyst was fabricated via a precursor-guided hydrothermal method. The morphology, structure, composition, chemical and electronic properties of the as-prepared samples were systematically investigated by multiple techniques (XRD, FT-IR, SEM, TEM, XPS, UV-vis, BET, PL, ESR. etc.). Particularly, the 60 wt% CuBi₂O₄/WO₃ nanocomposite exhibited the highest photocatalytic activity for tetracycline (20 mg/L) degradation under simulated solar light irradiation. The rate constant was 0.0179 min^-1, which was almost 8 times and 4.5 times higher than that of bulk WO₃ and CuBi₂O₄, respectively. The experimental results confirmed that CuBi₂O₄ made a direct Z-scheme heterojunction by band alignment with WO₃, which are conducive to the efficient charges separation and prolonged carriers lifetime. According to the quenching experiments, •OH and •O₂- were testified to be the predominant active species. The electrons accumulated in the CuBi₂O₄ negative CB and the holes in the WO₃ positive VB made significant contribution to the strong redox ability of the CuBi₂O₄/WO₃ nanocomposite. This work provides some deep insights into the design of band-alignment-based Z-scheme heterostuctures, which is also applicable to other catalytic system.

Preparation of Cu2O@TiOF2/TiO2and its photocatalytic degradation of tetracycline hydrochloride wastewater

Cu₂O@TiOF₂/TiO₂composites with large surfaces were prepared by a hydrothermal method and exhibited excellent activity under simulated solar light, showing high efficiency for tetracycline hydrochloride photocatalytic degradation, and reusability.