Preparation of ZIF-67/C3N4 composite material and adsorption of tetracycline hydrochloride.

In recent years, wastewater treatment to remove tetracycline hydrochloride (TCH) has received much attention in water treatment problems. ZIF-67/C3N4 composite adsorbent, a nanosheet structured material stacked with MOFs, was prepared by in situ growth method, which has high adsorption activity for tetracycline hydrochloride in wastewater. Comparing the effect of monomeric and composite adsorbents, Z6C2 had the best adsorption effect (206 mg·g-1), which was 77.6% higher than that of ZIF-67 (116 mg·g-1) and 10.8 times higher than that of C3N4 (19 mg·g-1). The structure of ZIF-67 stacked on C3N4 nanosheets has an excellent specific surface area and number of active sites, as well as π-π interactions, electrostatic interactions, and hydrogen bonding interactions between the adsorbent and TCH, which combine to enhance the adsorption performance. The adsorption process is accompanied by a combination of chemisorption, mass transport, and internal diffusion rate-limiting. It was shown that the adsorption process is favorable for monolayer adsorption as well as a heat absorption reaction that proceeds spontaneously. The adsorbent exhibits good stability and adsorption capacity, which may be suitable for efficient and low-cost water purification.

The Ovs surface defecting of an S-scheme g-C3N4/H2Ti3O7 nanoheterostructures with accelerated spatial charge transfer.

Semiconductor photocatalysis was a rising star in the sustainable transformation of solar energy for environmental problems governance. Herein, an S-scheme g-C3N4/H2Ti3O7 heterostructure was constructed and applied to tetracycline hydrochloride (TCH) destruction. The g-C3N4/H2Ti3O7 composite has a superior photocatalytic property to degrade TCH in contrast with bare g-C3N4 and H2Ti3O7. The 20% g-C3N4/H2Ti3O7 (CNHTO20) composite exhibited the optimum photocatalytic performance, and the degradation efficiency of 20 mg/L TCH reached 87.37% within 3 h (K = 0.572 min-1). The affluent active sites of the g-C3N4 nanosheet and effective interfacial charge separation of the S-scheme pathway facilitated the excellent performance. Moreover, the ample oxygen vacancies (Ovs) act as the electron mediator, not only reducing the band gap energy by producing the formation of defect levels, but also broadening the photo response range and promoting the interfacial charge transfer. The coordination complexes formed between TCH molecules and Ti (IV) ions in CNHTO20 composites induce strong visible light absorption through ligand-metal charge transfer (LMCT). The Ti4+/Ti3+ metal cycle in CNHTO20 was conducive to the separation of the photogenerated electron-hole pairs on the heterojunction interface as well. The ESR characterization and trapping experiments certified that the dominant substances were OH, O2- and h+. The AQY calculated by the COD removal rate was 0.16%. Conclusively, the S-scheme heterojunction between H2Ti3O7 and g-C3N4 enabled the CNHTO photocatalyst with high redox ability and boosted photocatalytic performance accordingly. This study may shed some enlightenment on the construction of heterojunctions and the realistic treatment of wastewater.

Construction of an S-scheme TiOF2/HTiOF3 heterostructures with abundant OVs and OH groups: Performance, kinetics and mechanism insight.

Developing efficient photocatalysts is of crucial significance for the development of photocatalysis techniques. In this work, an S-scheme alkaline-washed TiOF2/HTiOF3(OHTOF) heterostructures with abundant Oxygen vacancies (Ovs) and OH groups was successfully constructed and used to remedy antibiotic wastewater under simulated sunlight. The generation of HTiOF3 was induced by g-C3N4 regulation. The results displayed that OHTOF15 composite possessed the best photocatalytic performance, which could degrade 94.2% tetracyclinehydrochloride (TCH) at a rate speed constant of 1.077 min-1 in 2.5 h. The after-alkali-washing process increased the concentration of OH groups and Ovs defects, and greatly enlarged the surface area. The abundant Ovs and OH groups were conducive to the formation of free radicals' and the transport of charge carriers. Compared with the pristine TiOF2, the absorption sidebands of OHTOF series were greatly red-shifted, which indicated that the increase of OH groups and the etching of the morphology of OHTOF further enhanced its visible-light harvesting ability. Furthermore, the metal cycle of the variable state of Ti4+/Ti3+ in OHTOF15 compensated for the charge balance and promoted the efficient separation of the carriers. Additionally, the apparent quantum efficiency (AQE) of the TCH photodegradation system based on Chemical Oxygen Demand (COD) removal efficiency was calculated to be 0.32%. It was confirmed that the electron transport path in TiOF2/HTiOF3 nanocomposites system followed the S-scheme type, which increased the charge carriers' separation rate and maintained a strong redox capacity. This work could provide some enlightenment for the construction of the semiconducting heterojunction and controllable surface defects engineering.

Preparation of F-doped H2Ti3O7-{104} nanorods with oxygen vacancies using TiOF2 as precursor and its photocatalytic degradation activity.

Photocatalytic degradation is an eco-friendly and sustainable method for the treatment of water pollutants especially tetracycline hydrochloride (TCH). Herein, we developed F-doped H2Ti3O7-{104} nanorods with oxygen vacancies using TiOF2 as a precursor by simple alkali hydrothermal and ion-exchange methods. The phase structure, surface composition, optical properties, specific surface areas and charge separation were analysed by a series of measurements. The effects of KOH concentration on the structure and properties of H2Ti3O7 were investigated. It is confirmed that the TiOF2/H2Ti3O7 composite can be formed in low concentration KOH solution (1 mol L-1), while the H2Ti3O7 single phase can be formed in high concentration KOH solution (>3 mol L-1). The prepared F-doped H2Ti3O7-{104} nanorods provide a high specific surface area of 457 m2 g-1 and a macroporous volume of 0.69 cm3 g-1. The appropriate mesoporous structure of the photocatalyst makes TCH have a stronger affinity on its surface, which is more conducive to the subsequent photodegradation. Moreover, a synergistic mechanism of photosensitization and ligand-metal charge transfer (LMCT) in the photocatalytic degradation of TCH was proposed. In addition, the prepared F-doped H2Ti3O7-{104} nanorods showed excellent cycle stability and resistance to light corrosion. After five cycles of photodegradation, the degradation rate of TCH was only reduced from 92% to 83%. This low-cost strategy could be used for the mass production of efficient photocatalysts, which can be used for TCH clean-up in wastewater treatment.

The preparation of three-dimensional flower-like TiO2/TiOF2 photocatalyst and its efficient degradation of tetracycline hydrochloride.

A kind of high-efficiency photocatalyst of the three-dimensional flower-like TiO2/TiOF2 was synthesized by a one-step hydrothermal method. XRD, FE-SEM, EDS, HTEM, BET, XPS, PL, and UV-Vis-DRS were utilized to characterize the photocatalyst. The photocatalyst of TiO2/TiOF2 shows a narrow band gap of 2.8 eV. The generation of Ti3+ and an oxygen vacancy (Ov) in the photocatalyst are helpful to increase the absorption of visible light, and to inhibit faster charge recombination by capturing photogenerated carriers. Through the degradation of tetracycline hydrochloride (TCH) under simulated sunlight, the photocatalytic activity and stability of the synthesized samples were investigated. The results showed that the removal rate of tetracycline hydrochloride was 59% only in 0.5 h of dark reaction and 85% in 0.5 h of simulated sunlight. The removal efficiency of the photocatalyst for the adsorption and photocatalytic degradation of TCH is higher than that of the single TiO2, TiOF2, and Degussa P25. The synthesized three-dimensional flower-like TiO2/TiOF2 has great application potential in the treatment of antibiotic wastewater.

A three-dimensional nano-network WO3/F-TiO2-{001} heterojunction constructed with OH-TiOF2 as the precursor and its efficient degradation of methylene blue.

In this study, three-dimensional nested WO3/F-TiO2-{001} photocatalysts with different WO3 loadings were prepared by a hydrothermal process and used to degrade methylene blue (MB). The photocatalysts with various ratios of WO3 to OH-TiOF2 can be transformed into a three-dimensional network WO3/F-TiO2 hetero-structure with {001} surface exposure. The results showed that the composite catalyst with 5% WO3, denoted as FWT5, had the best comprehensive degradation effect. FWT5 has a limited band gap of 2.9 eV, which can be used as an advanced photocatalyst to respond to sunlight and degrade MB. The average pore diameter of the composite catalyst is 10.3 nm, and the multi-point specific surface area is 56 m2 g-1. Compared with pure TiOF2, the average pore size of the composite catalyst decreased by 8.44 nm and the specific surface area increased by 51.2 m2 g-1, which provides a larger contact space for the catalytic components and pollutants. Moreover, TiO2 on the {001} surface has higher photocatalytic activity and methylene blue can be better degraded. Under the irradiation of 0.03 g FWT5 composite catalyst with a simulated solar light source for 2 h, the degradation rate of 10 mg L-1 methylene blue can reach 82.9%. The trapping experiment showed that photo-generated holes were the principal functional component of WO3/F-TiO2-{001} photo-catalysis, which could capture OH- and form hydroxyl radical (˙OH) and improved the photocatalytic degradation performance. Kinetic studies show that the photocatalytic degradation of MB fits with the quasi-first order kinetic model.

Transformation of novel TiOF2 nanoparticles to cluster TiO2-{001/101} and its degradation of tetracycline hydrochloride under simulated sunlight.

The anatase type cluster TiO2-{001/101} was rapidly generated by a one-step hydrothermal method. The transformation process of coral-like TiOF2 nanoparticles to cluster TiO2-{001/101} was investigated for the first time, and the sensitization between cluster TiO2-{001/101} and tetracycline hydrochloride (TCH) was also discussed. The degradation rate of TCH by cluster TiO2-{001/101} under simulated sunlight was 92.3%, and the total removal rate was 1.76 times that of P25. Besides, cluster TiO2-{001/101} settles more easily than P25 in deionized water. The study showed that cluster TiO2-{001/101} derived from coral-like TiOF2 nanoparticles had a strong adsorption effect on TCH, which was attributed to the oxygen vacancy (Ov) and {001} facets of cluster TiO2-{001/101}. The strong adsorption effect promoted the sensitization between cluster TiO2-{001/101} and TCH, and widened the visible light absorption range of cluster TiO2-{001/101}. In addition, the fluorescence emission spectrum showed that cluster TiO2-{001/101} had a lower luminous intensity, which was attributed to the heterojunction formed by {001} facets and {101} facets that reduces the recombination rate of carriers. It should be noted that cluster TiO2-{001/101} still has good degradation performance for TCH after five cycles of degradation. This study provides a new idea for the synthesis of cluster TiO2-{001/101} with high photocatalytic performance for the treatment of TCH wastewater.

Preparation of Cu2O@TiOF2/TiO2 and its photocatalytic degradation of tetracycline hydrochloride wastewater.

A new high-efficiency photocatalyst Cu2O@TiOF2/TiO2 was synthesized by a hydrothermal method and applied to the degradation of tetracycline hydrochloride (TTCH). The samples were analyzed by SEM, EDS, XRD, BET, UV-vis DRS, Raman, PL, FT-IR. The Cu : Ti = 1 : 8 catalyst showed a narrow band gap of 2.10 eV, indicating that it can degrade TTCH as a novel photocatalyst capable of responding to sunlight. The average particle diameter is (2-6) nm, and the particle size distribution is narrow. When the reaction was carried out under simulated solar light for 3 hours, the efficiency for degrading 10 mg L-1 tetracycline hydrochloride was as high as 96.83% when the catalyst dosage was 40 mg. It is shown from the capture experiments that ·O2 - and ·OH play a major role in this reaction. In addition, it was found that the degradation of TTCH conforms to the first-order kinetic model.

One-step synthesis of OH-TiO2/TiOF2 nanohybrids and their enhanced solar light photocatalytic performance.

TiO2/TiOF2 nanohybrids were quickly synthesized through a hydrothermal process using titanium n-butoxide (TBOT), ethanol (C2H5OH) and hydrofluoric acid as precursors. The prepared nanohybrids underwent additional NaOH treatment (OH-TiO2/TiOF2) to enhance their photocatalytic performance. In this paper, the mechanism of NaOH affecting the pathway of transformation from TBOT (Ti precursor) to TiO2 nanosheets was discussed. The synthesized TiO2/TiOF2 and OH-TiO2/TiOF2 were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction pattern (XRD), Fourier infrared spectroscopic analysis (FT-IR), Photoluminescence (PL) emission spectra and UV-visible diffuse reflection spectra (UV-vis DRS). The photocatalytic activity and stability of synthesized samples were evaluated by degradation of methylene blue (MB) under the simulated solar light. The results showed that a larger ratio of TiO2 to TiOF2 in TiO2/TiOF2 and OH-TiO2/TiOF2 nanohybrids could allow for even higher MB conversion compared with only TiO2 nanosheets. NaOH treatment can wash off the F ions from TiOF2 and induce this larger ratio. The highest efficiency of MB removal was just above 90% in 1 h. Lower electron-hole pairs recombination rate is the dominant factor that induces the photocatalytic performance enhancement of TiO2/TiOF2 nanohybrids. The synthesized OH-TiO2/TiOF2 nanohybrids exhibit great potential in the abatement of organic pollutants.