Photocatalytic degradation is an effective method to alleviate environmental pollution caused by organic pollutants. In this work, research progress on the application of photocatalytic degradation ...and the antibacterial properties of zinc oxide (ZnO) nanomaterials is reviewed. The visible-light photo-response of ZnO has been expanded by employing various strategies, such as enhancing the photocatalytic activity of ZnO through modification of its electronic and optical properties, doping metal/nonmetal atoms, depositing noble metals, constructing heterojunctions, and coupling carbon materials, because the wide band gap of ZnO likely restricts its applications in photocatalysis. Although ZnO nanomaterials are commonly used for antibacterial applications, our understanding on the toxicity mechanisms of ZnO is limited. Some of the main toxicity mechanisms of this compound include reactive oxygen species generation, Zn2+ release, membrane dysfunction, and nanoparticle internalization into cells. Some of the main methods that improve antibacterial activities are coating inorganic or organic antimicrobial agents, doping ZnO, and tuning the size, morphological characteristics, and concentration of ZnO nanomaterials. This review aims to examine the current research progress on ZnO-based nanomaterials developed for the photocatalysis of organic contaminant degradation and antibacterial applications.
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•The photocatalytic and antibacterial applications of ZnO are reviewed.•Strategies that enhance the photocatalytic activity of ZnO are highlighted.•Methods that improve the antibacterial performance of ZnO are presented.•The photocatalytic and antibacterial applications of ZnO are summarized.
g-C3N4 samples prepared from different precursors showed various isoelectric points and adsorption activities.
•g-C3N4 powder with various microstructures prepared from different precursors.•The ...isoelectric points of the g-C3N4 samples were measured and discussed.•The prepared samples exhibited various adsorption activity.•Low-cost and pollution-free g-C3N4 is an efficient and promising adsorbent.
The isoelectric point (IEP) is an important physicochemical parameter of many compounds, such as oxides, hydroxides, and nitrides, and can contribute to estimation of the surface charges of compound particles at various pH conditions. In this work, three types of graphitic carbon nitrides (g-C3N4) were synthesized by directly heating melamine, thiourea, and urea. The prepared samples showed different microstructures and IEPs that influenced their adsorption activity. Differences in microstructure resulted from the various precursors used during synthesis. The IEPs of the obtained g-C3N4 were measured to be approximately 4–5, which is due to the equilibrium of chemical reactions between hydrogen ions, hydroxyl ions, and amine groups on the g-C3N4 surface. The IEP of g-C3N4 prepared from thiourea was lower than those of the corresponding samples prepared from melamine and urea. The adsorption activity of methylene blue on g-C3N4 prepared from urea and thiourea was excellent, which indicates that g-C3N4 is a promising adsorbent. This work provides a useful reference for choosing precursors with which to prepare g-C3N4 and combining g-C3N4 with other compounds in solution.
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•Nickel-based adsorbents show remarkable potential in CR adsorption.•Recent studies on CR adsorption by using nickel-based adsorbents are introduced.•The mechanisms of CR adsorption ...onto nickel-based adsorbents are summarized.•The effective regeneration of nickel-based adsorbents requires further exploration.•The CR adsorption ability depends on several factors related to the properties and structure.
Excessive synthetic dyestuffs in the aquatic environment pose various ecological and health issues that are detrimental to sustainable development. Adsorption is considered a feasible technique of eliminating dye pollutants from the water environment because of its advantages of high efficiency, low cost, easy operation, and absence of secondary pollution. Among the many dyes, Congo red (CR) is a widely used azo dye. Nickel-based materials, including nickel hydroxide, nickel oxide, nickel-containing layered double hydroxides, nickel-based spinel and metal–organic frameworks, metallic nickel, nickel-based sulfide, and nickel composites, have been extensively studied for CR adsorption due to their morphological diversity, large specific surface area, and strong affinity toward CR. However, fabricating nickel-based adsorbents with high efficiency and stability and excellent recyclability for practical application remains a challenge. This review outlines the research progress of nickel-based materials in CR adsorption. The interaction between CR molecules and nickel-based adsorbents is systematically presented, and the possible adsorption mechanisms are summarized. Finally, the challenges and future development directions of the practical application of nickel-based adsorbent materials are proposed.
Solving energy and environmental problems through solar‐driven photocatalysis is an attractive and challenging topic. Hence, various types of photocatalysts have been developed successively to ...address the demands of photocatalysis. Graphene‐based materials have elicited considerable attention since the discovery of graphene. As a derivative of graphene, nitrogen‐doped graphene (NG) particularly stands out. Nitrogen atoms can break the undifferentiated structure of graphene and open the bandgap while endowing graphene with an uneven electron density distribution. Therefore, NG retains nearly all the advantages of original graphene and is equipped with several novel properties, ensuring infinite possibilities for NG‐based photocatalysis. This review introduces the atomic and band structures of NG, summarizes in situ and ex situ synthesis methods, highlights the mechanism and advantages of NG in photocatalysis, and outlines its applications in different photocatalysis directions (primarily hydrogen production, CO2 reduction, pollutant degradation, and as photoactive ingredient). Lastly, the central challenges and possible improvements of NG‐based photocatalysis in the future are presented. This study is expected to learn from the past and achieve progress toward the future for NG‐based photocatalysis.
Nitrogen‐doped graphene plays a significant role in photocatalysis. Rational design, preparation, and understanding the mechanism of N‐doped graphene‐based photocatalysts provides a new opportunity to further enhance the photocatalytic performance. The research progress, atomic and band structures, photocatalytic mechanism, synthesis strategy, unique advantages, and wide application of N‐doped graphene in photocatalysis are highlighted.
Covalent carbon nitride polymers were applied as metal-free robust catalysts for the inactivation of Escherichia coli K-12 (E. coli), a common Gram-negative bacterium, under visible light ...illumination. The results demonstrated that the creation of antibacterial function on the surface of conjugated polymers has now become possible.
•The Pt-TiO2 catalyst is deactivated by adsorption of halogen ions.•The halogen poison is mainly attributed to the active site blocking of the Pt surface.•Halogen ions and Pt form PtX coordination ...bonds.•Large halogen diameter exhibits severe poisoning effect.
Catalytic decomposition of formaldehyde (HCHO) at room temperature is an important method for HCHO removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. However, the stability of this catalyst remains unexplored. In this study, Pt-TiO2 (Pt-P25) catalysts with and without adsorbed halogen ions (including F−, Cl−, Br−, and I−) were prepared through impregnation and ion modification. Pt-TiO2 samples with adsorbed halogen ions exhibited reduced catalytic activity for formaldehyde decomposition at room temperature compared with the Pt-TiO2 sample; the catalytic activity followed the order of F-Pt-P25, Cl-Pt-P25, Br-Pt-P25, and I-Pt-P25. Characterization results (including XRD, TEM, HRTEM, BET, XPS, and metal dispersion) showed that the adsorbed halogen ions can poison Pt nanoparticles (NPs), thereby reducing the HCHO oxidation activity of Pt-TiO2. The poison mechanism is due to the strong adsorption of halogen ions on the surface of Pt NPs. The adsorbed ions form coordination bonds with surface Pt atoms by transferring surplus electrons into the unoccupied 5d orbit of the Pt atom, thereby inhibiting oxygen adsorption and activation of the Pt NP surface. Moreover, deactivation rate increases with increasing diameter of halogen ions. This study provides new insights into the fabrication of high-performance Pt-based catalysts for indoor air purification.
•Basic information on g-C3N4 is presented.•Representative two-dimensional cocatalysts are introduced.•Enhanced energy conversion of g-C3N4 by two-dimensional cocatalysts are summarized.
The ...appropriate band structure endows graphitic carbon nitride (g-C3N4) with benign redox ability and visible light response, resulting in its popularity in photocatalysis. Given the inferior solar-to-chemical (STC) energy conversion of single-component g-C3N4, loading cocatalysts is serviceable in advancing its photocatalytic activity. In particular, two-dimensional (2D) cocatalysts that could form 2D/2D heterojunctions with g-C3N4 stand out due to several advantages in which the large-area contact interface with g-C3N4 predominates. Herein, the basic information of g-C3N4 was first introduced. Then, representative 2D cocatalysts (e.g., graphene, graphdiyne, molybdenum disulfide, black phosphorus, and MXenes) used to strengthen the STC energy conversion of g-C3N4 were presented. Afterwards, the foremost achievements of g-C3N4 decorated with 2D cocatalysts in STC energy conversion were described in terms of photocatalytic hydrogen evolution, carbon dioxide reduction, hydrogen peroxide production, and nitrogen fixation. Finally, the future development and challenge of photocatalysts decorated with 2D cocatalysts were prospected. This paper could hopefully deepen the readers’ understanding of 2D cocatalysts in photocatalysis and attach importance to 2D cocatalysts described in this paper and many others not mentioned.
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