Synthesis and characterization of TiO2/ZnO heterostructural composite for ultraviolet photocatalytic degrading DOM in landfill leachate

In-situ electrospinning PVB/Camellia oil/ZnO-TiO2 nanofibrous membranes with synergistic antibacterial and degradation of ethylene applied in fruit preservation

This work utilizes a handheld electrospinning device to prepare a novel nanofibrous composite membrane in situ for packaging freshness. It can realize pick-and-pack and is easy to operate. The nanofibrous membrane is based on PVB as the matrix material, adding Camellia oil (CO) and ZnO-TiO2 composite nanoparticles (ZT) as the active material. The antimicrobial property of the CO and the photocatalytic activity of the nanoparticles give the material good antimicrobial and ethylene degradation functions. Meanwhile, this nanofibrous membrane has good mechanical properties, suitable moisture permeability and good optical properties. The nanofibrous membrane are suitable for both climacteric and non- climacteric fruits. Its use as a cling film extends the shelf life of strawberries by 4 days and significantly slows the ripening of small tomatoes. Therefore, this nanofibrous membrane has great potential for application in the field of fruit preservation.

Synthesis of TiO2-ZnO n-n Heterojunction with Excellent Visible Light-Driven Photodegradation of Tetracycline

Zinc oxide-based photocatalysts with non-toxicity and low cost are promising candidates for the degradation of tetracycline. Despite the great success achieved in constructing n-n-type ZnO-based heterojunctions for the degradation of tetracycline under full-spectrum conditions, it is still challenging to realize rapid and efficient degradation of tetracycline under visible light using n-n-type ZnO-based heterojunctions, as they are constrained by the quick recombination of electron-hole pairs in ZnO. Here, we report highly efficient and stable n-n-type ZnO-TiO2 heterojunctions under visible light conditions, with a degradation efficiency reaching 97% at 1 h under visible light, which is 1.2 times higher than that of pure zinc oxide, enabled by constructing an n-n-type heterojunction between ZnO and TiO2 to form a built-in electric field. The photocatalytic degradation mechanism of n-n TiO2-ZnO to tetracycline is also proposed in detail. The demonstration of efficient and stable heterojunction-type ZnO photocatalysts under visible light is an important step toward commercialization and opens up new opportunities beyond conventional ZnO technologies, such as composite ZnO catalysts.

Directional regulation of reactive oxygen species in titanium dioxide boosting the photocatalytic degradation performance of azo dyes

It has been widely accepted that the generation of reactive oxygen species such as superoxide radical, hydroxyl radical, and hydrogen peroxide during photocatalysis is responsible for the degradation of azo dyes. However, it is unclear which reactive oxygen species primarily contributes to the degradation efficiency of azo dyes. Here, we demonstrate that the directional regulation of reactive oxygen species in titanium dioxide (TiO2) to form superoxide radicals by ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) can significantly improve the degradation performance of methyl orange. The optimized addition of EDTA-2Na can completely degrade azo dyes such as methyl orange, acid orange and alkaline orange at a concentration of 10 mg/L in about 20 min, which is not only higher than that achieved by pristine TiO2 under Xe lamp light but also far superior to the reported degradation efficiency of modified TiO2. Even under natural sunlight, this strategy can also effectively decompose azo dyes, demonstrating the great potential for practical water treatment using low-cost TiO2 photocatalysts.

Excess sludge-based biochar loaded with manganese enhances catalytic ozonation efficiency for landfill leachate treatment

This study developed an efficient and stable landfill leachate treatment process, which was based on the combination of biochar catalytic ozonation and activated sludge technology for intensive treatment of landfill leachate, aiming to achieve the standard discharge of leachate. The focus is to investigate the effect of manganese loading on the physicochemical properties of biochar and the mechanism of its catalytic ozonation. It was found that more surface functional groups (CO, Mn-O, etc.) and defects (ID/IG = 1.27) were exposed via the change of original carbon structure by loading Mn, which is conducive to the generation of lattice oxygen. Meanwhile, generating different valence states of Mn metal can improve the redox properties and electron migration rate, and encourage the production of reactive oxygen species (ROS) during the reaction process and enhance the catalytic efficiency. The synergistic action of microorganisms, especially denitrifying bacteria, was found to play a key role in the degradation of nitrogenous pollutants during the activated sludge process. The concentration of NH+4-N was reduced from the initial 1087.03 ± 9.56 mg/L to 9.05 ± 1.91 mg/L, while COD was reduced from 2290 ± 14.14 mg/L to 86.5 ± 2.12 mg/L, with corresponding removal rates of 99.17% and 99.20%, respectively. This method offers high efficiency and stability, achieving discharge standards for leachate (GB16889-2008). The synergy between Mn-loaded biochar and microorganisms in the activated sludge is key to effective treatment. This study offers a new approach to solving the challenge of waste leachate treatment.

PVDF Nanofiber Modified with ZnO Nanowires/Polydopamine for the Treatment of Sewage Containing Heavy Metals, Organic Dyes, and Bacteria

In various countries worldwide, the issue of wastewater contamination poses a significant threat due to its intricate composition of heavy metals, organic dyes, and microorganisms, thereby complicating the purification process. Consequently, researchers have expressed considerable interest in materials capable of eliminating organic, heavy metal, and microbial pollutants. This study focuses on the fabrication of a water purification membrane (PDA/ZnO-NWs/PVDF) with a hierarchical structure and the ability to remove multiple pollutants. The membrane was created by modifying poly(vinylidene fluoride) (PVDF) nanofiber with zinc oxide nanowires (ZnO-NWs) and reinforcing it with polydopamine (PDA). The experimental results demonstrate that the PDA/ZnO-NWs/PVDF membrane exhibits a range of functionalities, including long-lasting superhydrophilicity, Cu(II) adsorption, photocatalytic degradation, and antibacterial ability. The manipulation of the DA synthesis procedure allows for the adjustment of the wettability, adsorption, and photocatalytic and antibacterial activities of the PDA/ZnO-NWs/PVDF composite. According to the Langmuir isotherm, the maximum Cu(II) adsorption capacity of the PDA/ZnO-NWs/PVDF membrane is determined to be 65.75 mg/g, which is significantly higher (27.26 mg/g) than that of the ZnO-NWs/PVDF membrane (38.49 mg/g). The PDA/ZnO-NWs/PVDF composite exhibited a notable degradation capacity toward rhodamine B under natural sunlight, reaching a maximum of 5.97 mg/g. Additionally, the degradation rate achieved during daylight hours was as high as 90.42%. Furthermore, the antibacterial efficacy of the PDA/ZnO-NWs/PVDF composite against both Gram-positive and Gram-negative bacteria approached 100%. This work presents a promising approach for the treatment of wastewater containing various coexisting contaminants.

Treatment of landfill leachate using photocatalytic based advanced oxidation process - a critical review

Landfill leachate is a discrete volumetric component of municipal solid waste; hence, researchers and professionals are more concerned about it because of its obscurity. Innovative treatment and emerging technologies are being scrutinized to address the treatment of landfill leachate challenges. The leading target of this review was to examine the possibility of removing recalcitrant organic pollutants from landfill leachate by photocatalytic-based advanced oxidation processes. A summary of the systematic applicability of conventional treatment for landfill leachate is provided, with a focus on physico-chemical and biological processes. The biological treatment, such as aerobic and anaerobic digestion, is an excellent technique for treating highly concentrated organic pollutants in the wastewater. However, Leachate can scarcely be treated using conventional techniques since it is enriched with refractory organics and inorganic ions. It is clear from the literature review that none of the available combinations of physico-chemical and biological treatments are entirely relevant for the removal of recalcitrant organic pollutants from leachate. Recently, the photo-assisted TiO2/ZnO oxidation has shown an excessively potential and feasible way to treat landfill leachate. TiO2/ZnO photocatalysis is currently developing to treat recalcitrant organic pollutants from landfill leachate. The effect of operating parameters reveals that pH and temperature affect the reaction rate. The addition of oxidant H2O2 to the TiO2/ZnO suspension suggests that TiO2 leads to an increase in the rate of reaction when compared to ZnO. Photocatalytic remediation technique of landfill leachate would support the goal of environmental sustainability by greatly enhancing the effectiveness of treated leachate reutilization. In this review, the selection of the best photocatalytic treatment for leachate based on its systematic relevance and potential conditions, characteristics, cost-effectiveness, essential controlling, discharge limit, long-term environmental effects, and its future study perspectives are emphasized and discussed.

Photocatalytic degradation of dissolved organic matter in landfill leachate by heterostructural ZnO-rGO composite catalysts

The dissolved organic matter (DOM) in landfill pollutes not only the landfill and surroundings, but also the environment far away from the landfill by infiltrating into the soil and/or flowing on the ground surface. Developing an efficient photocatalyst to degrade DOM is an interesting topic. Herein, the catalysts composed of ZnO and reduced graphene oxide (ZnO-rGO) with different morphologies were fabricated with a two-step hydrothermal method. The phase composite and microstructure were analyzed, and the degradation efficiency of the DOM under ultraviolet light was investigated. Three kinds of ZnO-rGO composite catalysts with different morphologies were successfully synthesized, and rGO was coated on the ZnO surface to form heterostructural composite catalysts. The catalyst powders have similar Raman and FT-IR spectra, but have different specific surface areas and band gaps. The degradation efficiency of DOM by ZnO-rGO composites is higher than that of pure ZnO powder. Compared to pure ZnO, ZnO-rGO composite catalysts contain more oxygen vacancies and a narrower band gap, and the heterostructure is beneficial for accelerating electron separation, inhibiting electron recombination.