Advanced oxidation processes (AOPs) introduce a hopeful technology for the removal of water polluted with hard degradable organic compounds. Today, one of the main effective AOP technologies to degrade these hazardous organics is via the photocatalytic process. The present review focuses on the recent progress in the fixed-bed and immobilized nanophotocatalysts and also their applications for resolving the environmental concerns. Various organics elimination using a variety of photocatalysts and innovative reactors are discussed. This critical review summarizes the recent progress in the synthesis and modification (physical and chemical) of semiconductors. Furthermore, different ways of photocatalysts immobilization are explained in details. By considering different dangerous chemicals present in wastewater and different industries, catalytic methods used by researchers to degrade these organic compounds are reviewed. In addition, the degradation pathway of some organics through the catalytic operation is described.

Application of Heterogeneous Nano-Semiconductors for Photocatalytic Advanced Oxidation of Organic Compounds: A Review

Photocatalytic water splitting is an environmentally friendly technique for hydrogen production. In this work, we report a novel photocatalyst consisting of two-dimensional (2D) titanium carbide (Ti₂C) and graphitic carbon nitride (g-C₃N₄). We observe substantially enhanced water splitting activities due to the efficient synergistic interaction between Ti₂C and g-C₃N₄. Optimal properties are achieved in the g-C₃N₄ with a loading of 0.4 wt% Ti₂C with a hydrogen production rate of 47.5 μmol h⁻¹, which is 14.4 times as much as that in the case using pure g-C₃N₄, and it even outperforms Pt-loaded g-C₃N₄. We further show that the Ti₂C/g-C₃N₄ has high stability and good reproducibility. We expect that the Ti₂C/g-C₃N₄ can be a photocatalyst for large scale applications because both Ti₂C and g-C₃N₄ are low-cost, abundant, and nontoxic.

Synergistic effect of 2D Ti₂C and g-C₃N₄ for efficient photocatalytic hydrogen production

Self-cleaning photocatalytic MXene composite membrane for synergistically enhanced water treatment: Oil/water separation and dyes removal

The prevalence of bacterial infections and resistance to existing antibiotics make new effective antibacterial strategies urgently needed. Photocatalytic antibacterial, an effective strategy relying on exogenous excitation, has drawn increasing attention over the past decades, owing to its controllable, safe, and non-invasive characteristics. Many photoresponsive agents have been developed. With exceptional features of abundance, facile synthesis, suitable band structure, high stability, and low toxicity, metal-free polymeric two-dimensional nanomaterial graphitic carbon nitride (g-C3N4) is an attractive photosensitizer for antibiotic-free antibacterial application. In this review, the basic structural characteristics and preparation methods of g-C3N4 are summarized. The photocatalytic antibacterial mechanism of g-C3N4 through reactive oxygen species (ROS) generation is also discussed. In order to achieve more precise and efficient antibacterial effects, we pay special attention to two aspects: (1) how to increase the utilization of visible light and reduce the recombination of electron-hole pairs, thereby enhancing the production of ROS; and (2) how to obtain effective bacteria-killing activity while maintaining good biocompatibility and environmental friendliness, which determines the practical applications of materials. Several significant modification strategies are thus introduced, including structure design, surface modification, element doping, and construction of g-C3N4-based heterojunctions. Furthermore, various typical examples of combining the photocatalytic antibacterial effect of g-C3N4 with other strategies to exert good synergistic effects are summarized. Lastly, the potential challenges and perspectives are offered. This review is expected to inspire more follow-up work to design high-performance g-C3N4-based materials for photocatalytic antibacterial application.

Graphitic carbon nitride-based materials for photocatalytic antibacterial application

Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D) ZnO structures, which are desirable compared with zero-dimensional (0D) and two-dimensional (2D) nanoarchitectures. Also, relative to other forms, the superiority of 1D ZnO nanostructures in dye photodegradation makes them promising as a future research direction and for commercial use. Therefore, understanding the design and synthesis of 1D ZnO nanomaterials is of critical importance for the development of novel and high-performance photocatalysts. Rational design of 1D ZnO nanophotocatalysts is thus required to enhance their photodegradation activity via efficient separation of charge carriers, increased surface-to-volume ratio, enhanced light absorption capacity, and improved stability/reusability. We briefly describe herein the most widely applied synthesis methods, including vapor-phase and solution-based strategies, to understand different methods for tailoring 1D ZnO nanophotocatalysts. Moreover, to elucidate the effect of their physical/chemical properties on the photodegradation efficiency, all the modification methods are categorized into four different approaches, viz. (1) morphology control, (2) induction of defects, (3) modulation by doping, and (4) formation of hybrids and heterojunctions. An overview of all aspects of charge generation, separation, and transfer during dye photodegradation by engineered 1D ZnO nanomaterials is also provided.

Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review

Ti3C2Tx MXene playing as a strong methylene blue adsorbent in wastewater

Mixed-dimensional, three-level hierarchical nanostructures of silver and zinc oxide for fast photocatalytic degradation of multiple dyes

Unusual synthesis of safflower-shaped TiO2/Ti3C2 heterostructures initiated from two-dimensional Ti3C2 MXene

Metal (M)-doped ZnO/g-C3N4 composites with a sponge-like porous structure have been synthesized by a facile one-pot pyrolysis method. A representative composite, magnesium (Mg)-doped ZnO/g-C3N4 composite was analyzed to contain a 13.7 at% of ZnO and Mg at a standard condition. ZnO and Mg were uniformly distributed over the composite without the formation of clearly separated phases. Optical properties of the composite revealed the extension of light absorption range and the suppressed carrier recombination. Most notably, the photocatalytic efficiency of the Mg-doped ZnO/g-C3N4 composite overwhelmed those of pure ZnO, pure g-C3N4, ZnO/g-C3N4 composite, and ZnO/g-C3N4 composites doped with other metals. Its photoreaction rate constant was estimated to be even higher than the previous reports. A physical mechanism was proposed to account for the observed enhancement of the photocatalytic activity. The synthetic approach and the demonstrated performance of this work may present new direction towards high-performance photocatalysts using composites of g-C3N4 and ZnO.

Facile synthesis of porous metal-doped ZnO/g-C3N4 composites for highly efficient photocatalysts

A crystal-damage-free nanodoping method, which utilized the vacuum drive-in diffusion of Al into ZnO nanorods, was developed. In this method, vertical ZnO nanorod arrays that were grown by chemical bath deposition beforehand were deposited with Al thin film and subsequently heat-treated under a high vacuum. At an optimum condition, the surface Al atoms were completely diffused into ZnO nanorods, resulting in Al-doped ZnO nanorods. Stretchable gas sensors were fabricated by sequentially drop-casting the Al-doped ZnO nanorods and silver nanowires on polydimethylsiloxane substrate. The resistance and response of the sensor could be optimized through the elaborate control of relative densities of Al-doped ZnO nanorods and silver nanowires. The sensor showed a high response of 32.3% to 10 ppm of NO2 gas at room temperature, even under a large strain of 30%. The NO2-sensing mechanism of Al-doped ZnO nanorod/silver nanowire bilayer sensors is discussed on the basis of a synergistic interplay of Al-doped ZnO nanorods and silver nanowires.

Qui Thanh Hoai Ta

Papers

Ti3C2Tx MXene playing as a strong methylene blue adsorbent in wastewater

Mixed-dimensional, three-level hierarchical nanostructures of silver and zinc oxide for fast photocatalytic degradation of multiple dyes

Unusual synthesis of safflower-shaped TiO2/Ti3C2 heterostructures initiated from two-dimensional Ti3C2 MXene

Facile synthesis of porous metal-doped ZnO/g-C3N4 composites for highly efficient photocatalysts

Diffusion-Driven Al-Doping of ZnO Nanorods and Stretchable Gas Sensors Made of Doped ZnO Nanorods/Ag Nanowires Bilayers.