Construction of g-C3N4/TiO2/Ag composites with enhanced visible-light photocatalytic activity and antibacterial properties

In this study, the multifunctional carbon nitride based composite graphitic-C₃N₄ (g-C₃N₄)/TiO₂/Ag was prepared through a simple and efficient vacuum freeze-drying route. TiO₂ and Ag nanoparticles were demonstrated to decorate onto the surface of g-C₃N₄ sheet. In the ultraviolet–visible absorption test, a narrower band gap and red-shift of light absorption edge were observed for g-C₃N₄/TiO₂/Ag compared to pristine g-C₃N₄ and single-component modified g-C₃N₄/TiO₂. The photodegradation property of g-C₃N₄/TiO₂/Ag was investigated toward the degradation of methylene blue (abbreviated as MB) under the irradiation of visible light. These results indicated that the degradation performance of organic dyes for g-C₃N₄/TiO₂/Ag was obviously improved compared with g-C₃N₄/TiO₂ and g-C₃N₄. The reaction rate constant of MB degradation for g-C₃N₄/TiO₂/Ag was 4.24 times higher than that of pristine g-C₃N₄. In addition, such rationally constructed nanocomposite presented evidently enhanced antibacterial performance against the Gram-negative Escherichia coli. Concentration dependent antibacterial performance was systematically investigated. And 84% bacterial cell viability loss had been observed at 500 μg/mL g-C₃N₄/TiO₂/Ag within 2 h visible light irradiation.     

Facile one-pot synthesis of a BiOBr/Bi2WO6 heterojunction with enhanced visible-light photocatalytic activity for tetracycline degradation

Photocatalytic removal of tetracycline (TC) from the wastewater is of great value in the chemical and environmental engineering field. Here, we introduced a facile one-step method for the synthesis of BiOBr/Bi₂WO₆ heterojunctions by using cheap CTAB as the Br source. We showed the possibility of our method to fine-tune the content of BiOBr in the produced BiOBr/Bi₂WO₆ by simply changing the dosage of cetyltrimethylammonium bromide (CTAB), providing a platform for the delicate tuning of the visible-light absorbance ability of the composites. With a suitable heterojunction structure of BiOBr/Bi₂WO₆-0.2, it exhibited an ultrarapid photocatalytic activity towards TC (20 mg·L^-1), with a competitive removal efficiency of 88.1% within 60 min and an ultrahigh removal rate of 0.0349 min^-1. It could also be robustly recycled for at least 5 cycles with slight removal efficiency loss. We demonstrated that this exciting photocatalytic performance was due to the highly decreased recombination of photoinduced electrons and holes on our composites by constructing this heterojunction structure, and the resulting OH and contributed to the effective degradation of TC to CO₂.     

Controlled synthesis of (CuO-Cu2O)Cu/ZnO multi oxide nanocomposites by facile combustion route: A potential photocatalytic,antimicrobial and anticancer activity

Photocatalytic activity of (CuO-Cu₂O)Cu/ZnO hetero-junction nanocomposites along with their luminescent, biological applications in the progress of anticancer and antibacterial agents is investigated. The Cu and Zn bi-components modified (CuO-Cu₂O)Cu/ZnO nanocomposites were synthesized via facile combustion route in the presence of controlled fuel to oxidizer ratio and were characterized by X-Ray Diffraction (XRD) patterns, Transmission electron microscopy (TEM), High resolution Transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray photoelectron Spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and energy dispersive X-ray (EDX) analysis. The PL and UV–Visible diffused reflectance spectral (UV–Vis-DRS) techniques were used to measure the optical sensitivity and tuning of band gap in the samples. The excellent photocatalytic degradation of Methylene Blue and industrial waste water under Sunlight irradiation depends on the mass ratios of Cu/Zn. The findings show that the addition of a certain proportion of CuO, Cu₂O, ZnO, and Cu can promote efficiency in Sunlight harvesting and separation of charge carriers. Process parameters namely catalyst quantity, dye concentration and a proposal for the mechanism of degradation pathway, experiments for trapping and enhancer are investigated. The study of photoluminescence, CIE and CCT calculations suggests that the present nanocomposite may find applications as phosphor material in warm white LEDs. The second segment of this study deals with the investigation of antibacterial performance of composites upon Gram-negative and Gram-positive bacteria. The results indicate that nanocomposites can be used in antibacterial control systems and as an important growth inhibitor in various microorganisms. The cytotoxic effect of the (CuO-Cu₂O)Cu/ZnO (CCCZ11) nanocomposite was determined by colorimetric and flow cytometric cell cycle analysis. Our experimental results show that the nanocomposite can induce apoptosis and suppress the proliferation of HeLa cells. The applications of nanocomposites based on Cu, an abundant and inexpensive metal has created much interest in various multifunctional applications.     

Synthesis and enhanced bias-free photoelectrochemical water-splitting activity of ferroelectric BaTiO3/Cu2O heterostructures under solar light irradiation

Here, we first use a facile electrochemical deposition method to load Cu₂O nanoparticles onto the BaTiO₃ (BTO) surface to prepare BTO/Cu₂O heterostructure photoanodes. Compared to the pure BTO photoanode, all BTO/Cu₂O heterostructure photoanodes show outstanding visible light harvesting ability and greatly improved photoelectrochemical water splitting performance. By optimizing the loading amount of Cu₂O nanoparticles, the photocurrent density achieved by BTO/Cu₂O-100 photoanode is 0.26 mA/cm² at 0 V versus Ag/AgCl, which is 2.6 times that of the bare BTO photoanode. In contrast with the photocurrent densities of the other reported BTO-based heterostructure photoanodes, the photocurrent density achieved by the present BTO/Cu₂O-100 photoanode without bias voltage is much higher. Additionally, the maximum solar-to-hydrogen conversion efficiency of the BTO/Cu₂O-100 heterostructure photoanode is 0.11% at 0.72 V versus reversible hydrogen electrode, approximately double that of BTO photoanode. The measurements of diffuse reflectance spectra, photoelectrochemical impedance and the room temperature photoluminescence spectra demonstrate that the improved photoelectrochemical performance contributes from the visible light absorption ability of Cu₂O nanoparticles, efficient transport and separation of photogenerated electron-hole pairs, which are induced by the spontaneous polarization electric field of ferroelectric BTO, p-n junction and type-II band alignment of BTO/Cu₂O heterostructure photoanode. A possible mechanism for the improved photoelectrochemical water splitting performance and charge transfer process is proposed.     

A facile and novel construction of attapulgite/Cu2O/Cu/g-C3N4 with enhanced photocatalytic activity for antibiotic degradation

A high-performance photocatalyst, attapulgite/Cu₂O/Cu/g-C₃N₄ (ATP/Cu₂O/Cu/g-C₃N₄), was constructed via a one-pot redox strategy under anoxic calcination. The as-prepared composites were characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption isotherms (BET), photoluminescence emission (PL), and electrochemical impedance spectra (EIS). Results indicate that ultra-fine CuO nanoparticles on the surface of rod-like attapulgite are in-situ reduced by NH₃ gas to generate Cu and minority Cu₂O during the pyrocondensation of melamine. Meanwhile, the generated g-C₃N₄ membrane is uniformly encapsulated on the surface of attapulgite/Cu₂O/Cu to assemble Z-scheme Cu₂O/Cu/g-C₃N₄ heterostructure. ATP/Cu₂O/Cu/g-C₃N₄ shows improved visible light response ability and hole-electron suppression compared with ATP/g-C₃N₄. The photocatalytic performance and mechanism of the obtained photocatalyst for antibiotic degradation were evaluated by UV–Vis spectrometer and liquid chromatograph. ATP/Cu₂O/Cu/g-C₃N₄ can exhibit favorable photocatalytic activity and reusability for chloramphenicol. In addition, h⁺ and·OH radicals are the main active sites in the photocatalytic process, and Cu species play a vital role in separation and retarding recombination of electron-hole pairs.     

S-scheme g-C3N4/TiO2/CFs heterojunction composites with multi-dimensional through-holes and enhanced visible-light photocatalytic activity

A novel multi-dimensional through-holes structure of g-C₃N₄ with adjustable pore size was prepared by controlling the mass ratio of oxamide (OA, structure guiding agent) to urea during one-step calcination process, and a break-rearrangement mechanism was explored. Then, a series of porous g-C₃N₄/TiO₂ (CT) composites with uniformly deposited TiO₂ nanoparticles were prepared based on the multi-dimensional framework by a facile hydrothermal method. The results show that a new S-scheme heterojunction with multi-dimensional through-channel structure was obtained, which is particularly desired for enhancing the visible-light utilization, reducing the carrier recombination rate and enhancing redox capacity. The CT composite obtained at hydrothermal treatment time of 2 h has a specific surface area of 180.15 m² g^-1, which shows high degradation capability (99.99%) for tetracycline hydrochloride (TC·HCl) under 350 W Xe lamp irradiation for 90 min. In addition, CT nanostructures was in-situ growth on carbon fiber (CFs), the degradation rate constant is 0.1566 min^-1, and 90% of the degradation efficiency can be maintained even after 5 consecutive cycles. It is expected to provide an effective reference for solving the problems of recovery difficulty and low reuse rate of powder photocatalytic materials.     

Synthesis,characterization and enhanced visible-light photocatalytic activity of Zn2SnO4/C nanocomposites with truncated octahedron morphology

Novel Zn₂SnO₄/C nanocomposites with truncated octahedron morphology were constructed using a two-step hydrothermal synthesis route combined with subsequent calcination. The as-prepared samples were characterized by X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR), Raman spectroscopy, field–emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflection spectroscopy, photoluminescence spectroscopy (PL), and Brunauer–Emmett–Teller surface area measurements. The result of FESEM showed that the as-prepared Zn₂SnO₄/C nanocomposites are composed of numerous uniform nanoparticles with regular truncated octahedron morphology. Raman spectral characterization combined with HRTEM result revealed that a thin layer of carbon was attached on the surface of Zn₂SnO₄. Using rhodamine B (RhB) as a model organic pollutant, the visible-light photocatalytic activities of the as-prepared samples were investigated, and the photocatalytic mechanism was discussed. Compared with pure Zn₂SnO₄, Zn₂SnO₄/C nanocomposites exhibited much better visible-light photocatalytic activity. The increase in the photocatalytic activity of Zn₂SnO₄/C nanocomposites was mainly attributed to the enhancement of the optical absorption capability and efficient separation of photogenerated electron-hole pairs.     

Dy2BaCuO5/Ba4DyCu3O9.09 S-scheme heterojunction nanocomposite with enhanced photocatalytic and antibacterial activities

Semiconductor heterogeneous photocatalysis has been received much attention from the scientific and researchers in the last decade. The combination of two semiconductors with various energy diagram can dramatically enhance the lifetime and separation of the charge carriers, restrain photogenerated electron-hole recombination, and considerably enhance photocatalytic performance as compared with other single or binary components. In this regard, we introduced the Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites as active photocatalysts below UV radiation. Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites were prepared by a simple hydrothermal method and applied as a catalyst to treat water containing organic pollutions and microorganisms. Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites degraded Methyl Orange (MO) about 87.0% after 120 min. In addition, these nanocomposites show antimicrobial activity against Gram-positive species, including a pathogenic strain of Enterococcus faecalis, and Staphylococcus aureus, and a Gram-negative species, including Klebsiella pneumonia and Escherichia coli.     

Facile fabrication of TiO2-SiO2-C composite with anatase/rutile heterostructure via sol-gel process and its enhanced photocatalytic activity in the presence of H2O2

Constructing anatase/rutile heterostructure in TiO₂ based materials is a quite powerful approach to enhance their photocatalytic activities. Herein, by simply annealing the sol-gel derived TiO₂-SiO₂ composite in N₂ atmosphere at 850 °C, TiO₂-SiO₂-C composite (CTS-850) with anatase/rutile heterostructure has been successfully prepared, while the counterpart prepared in air contains only anatase phase. It was proven that the residual organic groups in the sol-gel process were converted into carbon species upon N₂ annealing, during which TiO₂ in the composite was partially reduced, not only leaving lots of oxygen vacancies on its surface but also promoting the phase transformation. By turning the annealing temperature and atmosphere, a series of control products were further synthesized. Among these samples, the CTS-850 showed the best photocatalytic performance toward Rhodamine B degradation in the presence of H₂O₂, which was mainly due to its lowest band gap and the enhanced sensitization of H₂O₂ by oxygen vacancies. Moreover, the photocatalytic activity of CTS-850 remained unchanged after five cycles and a proper mechanism was also proposed.     

The influence of coating with aminopropyl triethoxysilane and CuO/Cu2O nanoparticles on antimicrobial activity of cotton fabrics under dark conditions

A novel impregnation process for the fabrication of cotton nanocomposite with strong antimicrobial activity against antibiotics-resistant bacteria and yeast was developed. The impregnation process includes the sol–gel treatment of fabric with (3-aminopropyl)triethoxysilane in the first step, and synthesis of the CuO/Cu₂O nanoparticles (NPs) on the fabric surface in the second step. The in situ synthesis of the CuO/Cu₂O NPs was based on the adsorption of Cu²⁺-ions by the introduced amino groups of the sol–gel coating. The adsorbed Cu²⁺-ions are subsequently reduced in the alkaline solution of NaBH₄. X-ray diffraction measurements confirmed the formation of CuO/Cu₂O NPs. Scanning electron microscopy and atomic absorption spectrometry analyses indicate that the particle size, agglomeration, and amounts of synthesized NPs were highly affected by the initial concentration of CuSO₄ solution. The toxicity of nanocomposites to human keratinocytes (HaCaT) and antimicrobial activity against Gram-negative Escherichia coli ATCC 25922, E. coli ATCC BAA 2469, and Klebsiella pneumoniae ATCC BAA 2146, and Gram-positive bacteria Staphylococcus aureus ATCC 25923, S. aureus ATCC 43300 and yeast Candida albicans ATCC 24433 strongly depended on the copper content. In addition to excellent antimicrobial activity, controlled release of Cu²⁺-ions from the fabrics into physiological saline solution was obtained.