Separation Efficiency Of Electron-hole Pairs Research Articles

Enhanced ultraviolet-visible photocatalysis of RGO/equaixial geometry TiO2 composites on degradation of organic dyes in water.

The reduced graphene oxide dopped equaixial geometry TiO2 (rGO/egTiO2) composite as photocatalyst was synthesized hydrothermally with various mass ratios of tetrabutyl titanate. The photocatalyst is considered to be rGO/equaixial geometry TiO2 in terms of modifying the combined reduced graphene Oxide and TiO2. The rGO plays a vital role in rGO/egTiO2 composite as photocatalysts were analyzed in methylene blue (MB) and rhodamine B (RhB) photocatalytic degradation under UV and simulated solar light irradiation. This synthesized catalyst was characterized by various analytical techniques such as XPS, XRD, SEM, BET, and TEM. The rGO/egTiO2 composite exhibits enhanced photocatalytic performance with degradation rates of 97.5 and 97% on RhB and MB for 60 min under UV radiation respectively, while the degradation rate of 94 and 92 % was observed on the same dyes for 6 h under the simulated sunlight radiation. The enhanced photocatalytic performance of the rGO/egTiO2 composite under ultraviolet irradiation source was owing to a high separation efficiency of the photo-induced electron-hole pairs, while the photocatalytic performance under simulated sunlight radiation was due to the photosensitive and charge separator behavior of rGO. This offers us an excellent potential of significant photocatalytic activity for the removal of organic contaminants from wastewater.

Solar energy storage by a microfluidic all-vanadium photoelectrochemical flow cell with self-doped TiO2 photoanode

All-vanadium photoelectrochemical flow cell, which combines the vanadium redox flow battery and the photoelectrochemical flow cell, is a promising technology to store solar energy in reversible redox pairs. The development of a high-performance photoanode is vital to promote the storage of solar energy. In this work, we developed a self-doped TiO2 photoanode and applied it to a microfluidic all-vanadium photoelectrochemical flow cell (μVPFC). The self-doped TiO2 photoanode was simply prepared by annealing the TiO2 photoanode with NaBH4 in the nitrogen atmosphere, by which the self-dopant led to the formation of a disordered layer on the surface and created a mid-band. As a result, the light absorption region was extended and the electron-hole pair separation efficiency was enhanced, promoting the capability of the μVPFC with the self-doped TiO2 photoanode. The superiority of the self-doped TiO2 photoanode was confirmed by its excellent photoelectrochemical performance and vanadium ion conversion rate. The μVPFC with the self-doped TiO2 photoanode yielded an average photocurrent density as high as 0.064 mA·cm−2 in 6-h operation, which was much higher than the reported TiO2 and Ti2O3 photoanodes and presented the improvements by approximately 167% and 60%, respectively. In addition, intensifying the intensity of light and concentration of vanadium ion enabled the performance of the μVPFC with the self-doped TiO2 photoanode to be promoted.

Selective photocatalytic oxidation of gaseous ammonia at ppb level over Pt and F modified TiO2

Ammonia (NH3) as an important precursor to form atmospheric fine particles and secondary inorganic aerosols, should be strictly controlled. Photocatalysis has provided a facile and an effective way to eliminate NH3 pollution under mild conditions, whereas the undesirable products, such as NO, NO2 would be generated during the reaction and the mechanism remains unclear. In this study, F or Pt modified TiO2 were explored to reduce the formation of NOx during photocatalytic oxidation of low-concentration NH3, and its photocatalytic activity, selectivity and mechanism of NH3 conversion were systematically studied. Results indicate that surface fluorination on TiO2 contribute to the reduction of noxious NOx, especially for NO2, since the modified TiO2 achieved enhanced adsorption of NH3 and strong electron-trapping ability, which can retard the recombination of photo-generated electrons and holes. In addition, the deposition of Pt could further extend the lifetime of the electron-hole pairs by strongly capture the electron, and enhance the oxidation of NH3 into nitrates and nitrites species. From the in-situ DRIFT spectroscopy and XPS results, we can deduce that reactive amino radical (•NH2) would be formed on TiO2 under photoirradiation after the adsorption of NH3 on Lewis acid cites. The formed •NH2 can react with reactive oxygen species in the presence of H2O, and produce NOx and HNOx. By both enhancing the adsorption of NH3 and separation efficiency of electron-hole pairs, the presence of F and Pt modification on the TiO2 changes the photocatalytic pathway of NH3 conversion. The proposed selective oxidation mechanism may offer a novel insight into the photocatalytic oxidation of atmospheric NH3 on other metal oxide with surface modification and can be broadly employed in air pollution control in indoor environments.

Dual-functional Z-scheme CdSe/Se/BiOBr photocatalyst: Generation of hydrogen peroxide and efficient degradation of ciprofloxacin

The major challenges of clean energy and environmental pollution have resulted in the development of photocatalysis technologies for energy conversion and the degradation of refractory pollutants. Herein, a novel CdSe/Se/BiOBr hydrangea-like photocatalyst was used to produce hydrogen peroxide (H2O2) and degrade ciprofloxacin (CIP). The Z-scheme heterojunction structure of the photocatalyst and the doping of selenium (Se) led to the efficient separation of electron-hole pairs and charge transfer. The optimized sample of 2 wt% CdSe/Se/BiOBr produced 142.15 mg·L−1 rate of H2O2, which was much higher than that produced by pure BiOBr (89.4 mg·L−1) or CdSe/Se (10.9 mg·L−1). Additionally, almost 100 % of CIP was degraded within 30 min, with a first order rate constant of nearly 5.35 times that of pure BiOBr and 81.44 times that of pure CdSe/Se. The excellent removal efficiency of CIP from natural water matrices confirmed that the composites are promising for the removal of contaminants from natural waterways. Based on trapping experiments, electron spin resonance spectra (ESR) spectroscopy, and density functional theory (DFT) calculations, the photocatalytic mechanisms of H2O2 and CIP degradation by the Z-scheme CdSe/Se/BiOBr composites were proposed. Overall, the dual-functional CdSe/Se/BiOBr composite could potentially be applied for photocatalytic production of H2O2 and treatment of organic pollutants in water.

Rare-earth functioned Bi2WO6 nanofibers via electrospinning: Boosted catalytic performance and contact-free temperature monitoring on degradation process

Bi2WO6: Er, Yb nanofibers prepared via solvothermal-electrospinning method have high-efficiency photocatalysis performance and superior temperature feedback. Combining crystal integrity and polymer processability, polyacrylonitrile composite fibers are commendable in many aspects, such as large specific surface area, excellent flexibility, controllable structure and high solar energy utilization. The boost in photocatalysis activity can be attributable to non-radiative energy transfer between Er3+ ions with bismuth tungstate and doping effect of rare earth ions in Bi2WO6, where this doping enhances separation efficiency of electron-hole pairs and promotes generation of highly oxidative species. The electrospun nanofibers also can accurately perform contact-free temperature monitoring and real-time thermal feedback on the degradation system through 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 radiation transitions of Er3+ ions. In addition, the absolute sensitivity SA and the relative sensitivity SR are as high as 0.868% K−1 and 1.548% K−1 at 313 K, respectively, which indicates nanofibers have good thermal sensitivity. This dual-function nanofiber provides new application prospects for the development of innovative multifunctional semiconductor materials to cope with the ecological and energy crisis.

Synthesis of CdS/CoP hollow nanocages with improved photocatalytic water splitting performance for hydrogen evolution

Photocatalysts with hollow structure have obvious advantages in photocatalytic hydrogen production. Herein, CoP was modified on the surface of CdS by sacrificial template method to prepare CdS/CoP composite photocatalyst with hollow structures. Compared with pure CdS, CdS/CoP nanocage has improved photocatalytic hydrogen production performance due to its hollow structure, excellent light absorption capacity, and electron-hole pair separation and transfer efficiency. The hydrogen production rate of CdS/CoP can reach to 15.74 mmol g−1 h−1, which is about 9 times than that of pure CdS. It is found that the formation of a p-n heterojunction between CdS and CoP is the key factor to improve the photocatalytic performance of the composites. This study provides a simple strategy for the construction of more hollow nanocomposite catalysts with excellent photocatalytic performance.

All solution processed flexible p-NiO/n-CdS rectifying junction: Applications towards broadband photodetector and human breath monitoring

Solution processable flexible devices meet the rising demand of sensors in wearable electronics owing to their cost-effective fabrication process with large area and throughput. This report demonstrates the multifunctional sensor based on p-NiO/n-CdS rectifying junction on ITO coated PET flexible substrate using low-temperature all solution processed deposition technique for UV–vis photodetection and breath monitoring applications. Under UV and visible light, the fabricated device exhibited strong current rectifying activity of approximately four orders. The responsivity (R) of the device underneath UV and visible illuminations found to be ~40.43 mAW−1 and ~25.96 mAW−1, respectively. Further, the device showed a response time of ~3.2 sec and detectivity of 1.4 × 1010 Jones under UV illumination. The internal electric field created at the p-NiO and n-CdS interface due to the formation of excellent rectifying junction assists in the efficient separation of photo-generated electron-hole pairs, thus improving the responsivity. Furthermore, the fabricated device was used as a breath sensor, and it was evaluated for different breath patterns of an individual. Interestingly, the device was able to distinguish between the different breath patterns (slow, fast, deep, etc.) The fabricated device displayed a negligible change in performance even after harsh deformations, indicating the flexibility and robustness of the device.

Construction of melem/g-C3N4/vermiculite hybrid photocatalyst with sandwich structure

Melem/g-C3N4/vermiculite hybrid photocatalyst (CNV-X) with a sandwich structure for degrading tetracycline was constructed by hydrothermally treating the pre-synthesized g-C3N4/vermiculite composite (CNV). With the enhancement of hydrothermal temperature, part of g-C3N4 was gradually transformed into thorn-ball-like melem, the specific surface area of the samples increased step by step from 9.88 m2/g for CNV to 33.93 m2/g for the sample hydrothermally treated at 180 °C (CNV-180). Then, the specific surface area of CNV-X dramatically decreased to 6.36 m2/g when hydrothermally treated at 200 °C. The variation trend of photocatalytic performance of CNV-X samples with the hydrothermal temperature was similar to that of specific surface area. CNV-180 exhibited the optimum photocatalytic performance, it (0.05 g) degraded 81.82% of tetracycline molecules (100 ml, 20 mg/L) after photocatalysis for 120 min, and the reaction rate constant (0.0137 min−1) was 2.74× that of pure g-C3N4. CNV-180 exhibited excellent stability and reusability which degraded 77.68% of tetracycline molecules after five 120-min cycles. The degradation rate of the melem/g-C3N4/vermiculite composite with respect to tetracycline was 77.68% after five 120-min cycles. The significant improved photocatalytic activity was due to the enhanced specific surface area, the enhanced optical absorption property, prohibited recombination, and accelerated separation and transfer efficiency of photo-generated electron-hole pairs, which can be ascribed to the sandwich structure, the heterojunction of g-C3N4/melem, and the electrostatic repulsion between photo-generated electrons and the permanent negative charges of the vermiculite layers. Moreover, the band structure, the main active substance (·O2−), and a photocatalytic mechanism were proposed. Thus, this study provided a promising approach to photo-degradation of tetracycline and potential applications to vermiculite-based photocatalytic materials.

Highly efficient visible-light-driven photocatalytic degradation of organic pollutants by using magnetically separable supported heterogeneous nanocomposites (SiO2/Fe3O4/Ag2WO4)

In this work, the heterogeneous photocatalyst (SiO2/Fe3O4/Ag2WO4) that is composed of active nanomaterials precipitated onto mesoporous nanosilica was synthesized using multistep methods. The nanosilica was synthesized using the Stöber method. 10% Wt. of Fe3O4 and Ag2WO4 NPs were precipitated on the surface of nanosilica to produce supported SiO2/Fe3O4/Ag2WO4 magnetic nanoparticles (MNPs). Different techniques were used to characterize the synthesized supported MNPs, including UV-DRS, XRD, VSM, BET, BJH, and FE-SEM. The photocatalytic degradation activity of synthesized supported MNPs was conducted through a batch reactor towards methylene blue dye (M.B) under visible light irradiation (40 W LED and 55 W Xenon lamps). The experimental results showed a high degradation efficiency (approximately 100%) related to SiO2/Fe3O4/Ag2WO4 after 45 min of irradiation time. The SiO2/Fe3O4/Ag2WO4 revealed high adsorption activity, where 60% of its removal efficiency was during the first 60 min of adsorption in the dark. The kinetics studies revealed that the photocatalytic activity of SiO2/Fe3O4/Ag2WO4 was nearly 4.2 and 3.9 times higher than pure Ag2WO4 and SiO2/Fe3O4, respectively. The significantly improved photocatalytic activity of the SiO2/Fe3O4/Ag2WO4 MNPs was attributed to their higher stability and specific surface area, in addition to a synergistic outcome between Ag2WO4 and SiO2/Fe3O4 that leads to efficient electron–hole pairs separation. The effects of several parameters were also examined for supported MNPs, including catalyst dose, initial concentration of M.B, pH, and H2O2 addition. The reusability and recyclability study revealed that the synthesized SiO2/Fe3O4/Ag2WO4 are highly stable and can be used with high feasibility for removal of different organic dyes from wastewater.

Fabrication of Z-scheme ZnO/Bi2O4 heterojunction photocatalyst with superior photocatalytic nitrogen fixation under visible light irradiation

ZnO/Bi2O4 heterojunctions with different ratios were successfully synthesized by one-step hydrothermal method. The photocatalytic activity for nitrogen fixation was investigated by Nessler's reagent spectrophotometry and ion chromatography method for comparison. As a result, the NH4+ concentration over 10%ZnO/Bi2O4 catalyst measured by ion chromatography is 0.22 mmol L−1 h−1·gcat−1 after 150 min visible light irradiation, which is about 1/135 of that obtained by Nessler's reagent method. Furthermore, the photocatalytic activity for degradation of methyl orange and ciprofloxacin was also evaluated. 10%ZnO/Bi2O4 shows optimal photocatalytic degradation efficiency (97.5 % and 95.6 % for methyl orange and ciprofloxacin), which are 40.7 and 28.3 times that of pure ZnO. Various characterization techniques and photoelectrochemical tests have proved that such enhanced photocatalytic activity was due to the heterojunction formation between ZnO and Bi2O4, which possesses a lower charge transfer resistance and efficient electron-hole pairs separation.

Effective Photocatalytic Hydrogen Evolution Using Covalent Triazine Framework-Derived Carbon Nitride Nanofiber Containing Carbon Vacancies for Visible-Light-Driven

In this study, a novel fibrous carbon nitride (FCN) was prepared from laminated covalent triazine framework (CTF) via pyrolysis, using functionalized 2,5-thiophenedicarboxylic acid and melamine as the precursors. A carbon vacancy was produced by two-step calcination in argon and air atmospheres. These carbon vacancies further exposed the edges and diffusion channels of the FCN nanofibers, which accelerated photogenerated charge transfer and provided more active sites. The FCN was characterized using various techniques and used for H2 evolution under visible-light irradiation. The as-synthesized FCN exhibited excellent stability, and its photocatalytic activity for H2 evolution under visible-light irradiation was 66 times higher than that of bare C3N4 (BCN), attaining a maximum H2 evolution rate of 102.63 μmol in 6 h. The FCN remained stable following visible-light irradiation at the end of 10 cycles. The FCN benefited from the absorption of solar energy and a large number of active sites. These advantages facilitated the efficient separation of photoexcited electron-hole pairs to hinder charge recombination. This work generates new insights into the preparation of highly effective FCN photocatalysts that may be put to various applications, especially in the fields of energy and environment.

Highly active Z-scheme heterojunction photocatalyst of anatase TiO2 octahedra covered with C-MoS2 nanosheets for efficient degradation of organic pollutants under solar light

The construction of a Z-scheme photocatalyst by coupling semiconductors with conductors is an efficient way to achieve high pollutant degradation efficiency. In this study, a hydrothermal approach was used to fabricate a Z-scheme photocatalyst consisting of C-MoS2 sheets wrapped around octahedral anatase TiO2 nanocrystals. The catalyst showed excellent photocatalytic efficiency (99%) for methylene blue degradation with low catalyst loading (0.2 g L-1) under the simulated solar light within 60 min. High photocatalytic degradation efficiencies were also observed for Rhodamine B, methyl orange, and tetracycline under solar irradiation. The C-MoS2 acts as an electron mediator and serves as a carrier transmission bridge for the efficient electron-hole separation. The electron-rich (101)-faceted TiO2 benefits the Z-scheme recombination of electrons from the conduction band of TiO2 and holes at the valence band of MoS2. The semiconductor coupling of (101)-exposed octahedral TiO2 and 2H-MoS2 as well as the introduction of solid-state electron mediators, 1T-MoS2 and carbon, resulted in increased light absorption and accelerated charge transfer at the contact interface, which enhanced the photocatalytic activity of the photocatalyst significantly compared to those of P25, MoS2/TiO2, and C-MoS2. The efficient separation of electron-hole pairs prolongs their lifetime for oxidation and reduction reactions in the degradation process.

Inlaying metal-organic framework derived pancake-like TiO2 into three-dimensional BiOI for visible-light-driven generation of vanillin from sodium lignosulfonate

Pancake-like TiO2 (M-TiO2) derived from the metal-organic framework was inlaid into three-dimensional flower-like BiOI through a facile solvothermal method. M-TiO2 supplies large surface area and mesoporous structure for attachment and transfer of the substrates and products, while BiOI acts as a photosensitizer to absorb visible light and generates electrons and holes. The distinct structure of M-TiO2/BiOI gives a favorable contact between the two monomers, and promotes the transfer of charge carriers. In conjunction with the proper band positions of M-TiO2 and BiOI, the efficient separation of electron-hole pairs is attained. Benefiting from the above cooperative effects of M-TiO2 and BiOI, the performance for the vanillin generation from sodium lignosulfonate (SLS) over M-TiO2/BiOI composites has a prominent improvement under visible light. Specifically, the yield over optimal M-TiO2/BiOI sample is about 5.8 mg/gSLS, obviously superior to that over pristine M-TiO2 (~1 mg/gSLS) and BiOI (~1.1 mg/gSLS). It is found that h+ and O2– play the key role for vanillin generation from sodium lignosulfonate, and the low vanillin generation under UV–vis light sheds light on that OH is an adverse factor. We hoped that this work could inspire the studies on the photocatalytic valorization of biomass using noble metal-free catalysts.

Enhanced photocatalytic activity for 4-nitrophenol degradation using visible-light-driven In2S3/α-Fe2O3 composite

In2S3/α-Fe2O3 composites were synthesized using the methods of hydrothermal treatment and reflux. Characterization such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Photoluminescence (PL) was used to characterize the crystallinity and morphology of the composites, which proved the successful synthesis of the In2S3/α-Fe2O3 heterostructures. The 4-nitrophenol (PNP) degradation experiments by visible light were studied to evaluate the photocatalytic activity of the In2S3/α-Fe2O3 composites. The composites showed much higher photocatalytic degradation activities and TOC removal rate than both pure In2S3 and α-Fe2O3. The PNP degradation rate of composites was about 4.7 and 11.9 times that of pure In2S3 and α-Fe2O3, respectively. The degradation process was detected by high performance liquid chromatography and mass spectrometry, and the degradation pathway was explained. Based on the trapping experiments, e− and •OH were the main active species and a Z-scheme photocatalytic mechanism of In2S3/α-Fe2O3 was proposed, which showed the double advantage of high redox ability and efficient electron-hole pairs separation.

Self-powered UV photodetectors based on CsPbCl3 nanowires enabled by the synergistic effect of acetate and lanthanide ion passivation

Recently, photodetectors based on perovskite nanomaterials have attracted considerable attention in the visible spectral region owing to their large absorption coefficients, long diffusion lengths and high optical gains. However, the fabrication of self-powered visible-blind ultraviolet (UV) photodetectors is still challenging for the perovskite nanomaterials. This work developed the self-powered UV photodetector based on the Eu(AcO)3 promoted CsPbCl3 nanowires (NWs), enabled by the great separation efficiency of electron-hole pairs and high electron mobility of the one-dimentional (1D) morphology of perovskite materials. The perovskite CsPbCl3 NWs were synthesized by a modified hot-injection method with assistant of Eu(AcO)3 additive. As supported by the experimental investigations and DFT calculations, the adsorption of Eu3+ and AcO− ions to the surface of perovskite not only promotes the anisotropic growth of perovskite in (200) orientation, but also efficently passivates the halide defect of the perovskite nanomaterials. Moreover, the self-powered UV photodetector based on the Eu(AcO)3 promoted CsPbCl3 NWs displays a high responsivity of 398 mA W−1, detectivity up to 3.3 × 1011 Jones and fast response speed (24 ms) at 360 nm without external bias. The responsivity and detectivity of the device based on CsPbCl3 NWs are improved 8 and 205 times, comparing with the device based on bare CsPbCl3 NCs without passivation, respectively. In addition, the detectivity is comparable to some previous reports about perovskite NC-based UV photodetectors with additional bias. Our findings demonstrate the promising potential of 1D perovskite NWs for developing the next-generation self-powered UV photodetectors.

Fabrication of a novel Ag3PO4/WO3·H2O composite with enhanced visible light photocatalytic performance for the degradation of methylene blue and oxytetracycline

A novel Ag3PO4/WO3·H2O composite was prepared by loading Ag3PO4 on WO3·H2O substrate via a two-step hydrothermal method and characterized by various analytical techniques. The photocatalytic performance was evaluated by the degradation of methylene blue (MB) and oxytetracycline (OTC) under visible light irradiation. Within 30 min, 98.9 % MB can be degraded by the Ag3PO4/WO3·H2O composite with a molar ratio of 3:1 (3Ag/1W), which is higher than that of individual Ag3PO4 and WO3·H2O. The 3Ag/1W photocatalyst also exhibits improved photocatalytic activity for OTC degradation than pure WO3·H2O and Ag3PO4. The improvement of photocatalytic activity would be mainly ascribed to the highly efficient separation of photo-induced electron-hole pairs due to matched band structure, as confirmed by photoluminescence spectra (PL) and photocurrent responses test. According to the experimental results of radical trapping and electron spin resonance (ESR), a possible photocatalytic mechanism of the Ag3PO4/WO3·H2O composite was proposed.

Bimetallic-atom-hybridization-driven catalytic reaction kinetics and solar utilization to accelerate norfloxacin degradation

The high level of norfloxacin (NOR) in aquatic environment causes bacterial drug resistance and perilous effects on human and aquatic life because of the greater toxicity and the oxidation-refractory property. Herein, we propose a series of porous metal-organic frameworks (MOFs) via a developed solvothermal process to accelerate NOR degradation, in which the solar response and catalytic activity is sharply enhanced through an electronic hybridization between Fe3+ and Co2+ metal center. The time-resolved photoluminescence spectra disclose that electrostatic potential induced by electronegativity difference in bimetallic sites leads to an efficient separation of electron-hole pairs. As a result, the optimized bimetallic MOF sample makes the NOR concentration go down to ∼20 % within 30 min under sunlight radiation, keeping an unchanged activity after 9 cycles. Our findings provide new inspirations for regulating the photogenic carrier dynamics via bimetallic hybridization strategy in accelerating NOR degradation.

Recovery of cobalt from spent lithium-ion batteries as the dopant of TiO2 photocatalysts for boosting ciprofloxacin degradation

Recovery of valuable metal of cobalt (Co) from spent lithium-ion batteries is an important way to make sustainable use of Co resource, while the directly obtained Co2+ solution often contains impurities, such as some trace elements and organic reagents, which have limited its high standard application due to the high cost in further purification. The Co2+ doped TiO2 photocatalysts by using pure Co resources have attracted intensive attention for degradation of the residues of antibiotics in waste water, but by comparison, the economical Co2+ solution recovered from spent lithium-ion batteries is suitable to be used as the Co precursor, because the fabrication process of photocatalysts is tolerant and flexible, and the resultant photocatalytic performance is not influenced or even improved. Herein, the Co2+ (8.773 g/L) solution recovered from spent lithium-ion batteries through the treatment procedures of pre-saponification, extraction, and stripping is first used to prepare the Co2+ doped TiO2 (TC) photocatalysts. The doping effect of Co2+ greatly enhances the visible light responsive ability, physical adsorption property, and electron-hole pair separation efficiency of the TC samples. Under 60 min ultraviolet–visible–near-infrared (UV–Vis–NIR) light irradiation, the degradation rates of the antibiotic ciprofloxacin over the optimum TC samples reach 95%, and within 180 min Vis-NIR light irradiation, the degradation rates also exceed 88%, which are much higher than those of pure TiO2 and comparable with that of the Co2+ doped TiO2 sample with pure Co source, because more oxidative holes and superoxide radicals are generated on the TC samples. The excellent photocatalytic performance of the TC samples for the degradation of antibiotics proves that it is feasible to use the Co components from spent lithium-ion batteries as the metal dopants of photocatalysts.

Surface engineering of copper sulfide-titania-graphitic carbon nitride ternary nanohybrid as an efficient visible-light photocatalyst for pollutant photodegradation

Advanced photocatalyst is a key for photocatalytic water purification in the environmental pollutant remediation. In this study, graphitic carbon nitride (g-CN) modified by CuS and TiO2 ternary nanohybrid (CuS-TiO2-g-CN) with close interfacial contact among CuS, TiO2 and g-CN was fabricated through a facile and green method. Compared to the binary g-CN-based counterparts, the CuS-TiO2-g-CN possesses multiple photo-generated charge transfers owing to the synergistic action of CuS, TiO2 and g-CN. And hence the separation efficiency of photo-generated electron-hole pairs can be improved for the CuS-TiO2-g-CN. The optical and photoelectrochemical measurements prove that the CuS-TiO2-g-CN has narrower band gap energy and higher transient photocurrent density than those of g-CN and TiO2-g-CN. Therefore, the CuS-TiO2-g-CN shows notably higher photocatalytic activity and stability towards the degradation of Rhodamine B (RhB) than g-CN and TiO2-g-CN under visible-light irradiation. Moreover, a possible visible-light photocatalytic mechanism of CuS-TiO2-g-CN for degrading RhB was also proposed on the basis of the experimental results and literature reports.

Facile fabrication of TaON/Bi2MoO6 core–shell S-scheme heterojunction nanofibers for boosting visible-light catalytic levofloxacin degradation and Cr(VI) reduction

Developing excellent photocatalysts for antibiotics degradation and Cr(VI) reduction is of vital significance but still a big challenge. Herein, novel S-scheme heterojunction of TaON/Bi2MoO6 with a core–shell structure is constructed via an electrospinning-calcination-nitridation approach, where 2D Bi2MoO6 nanosheets are uniformly and firmly anchored on the surface of 1D TaON nanofibers. The optimal TaON/Bi2MoO6 with the TaON/Bi2MoO6 molar ratio of 1:1 manifests the highest catalytic activity towards levofloxacin (LEV) antibiotic degradation and Cr(VI) reduction under visible light. The exceptional photocatalytic performance is probably due to the synergistic effect of the favorable core–shell fiber-shaped structure and S-scheme hetero-structure, which enables the strong interfacial interaction between the constituents for effectively improving the visible-light absorption, boosting the separation and utilization efficiency of electron-hole pairs, and retaining the charge carriers with stronger redox capabilities. Of note, TaON/Bi2MoO6 possesses excellent stability and reusability. Photo-generated h+, •OH, and •O2– are the main reactive species accounting for LEV degradation, the detailed LEV degradation pathways are elucidated by detecting the intermediates using HPLC–MS and the toxicity of the intermediates are assessed by quantitative structure–activity relationship (QSAR) method. In addition, •O2– and e– are primarily responsible for Cr(VI) reduction. Further, a possible photocatalytic reaction mechanism for removal of LEV and Cr(VI) is proposed. This study provides some insights in fabricating high-performance S-scheme heterojunction photocatalysts for the efficient water purification.