Copper Single-Atom Catalysts-A Rising Star for Energy Conversion and Environmental Purification: Synthesis, Modification, and Advanced Applications.

Future renewable energy supply and green, sustainable environmental development rely on various types of catalytic reactions. Copper single-atom catalysts (Cu SACs) are attractive due to their distinctive electronic structure (3d orbitals are not filled with valence electrons), high atomic utilization, and excellent catalytic performance and selectivity. Despite numerous optimization studies are conducted on Cu SACs in terms of energy conversion and environmental purification, the coupling among Cu atoms-support interactions, active sites, and catalytic performance remains unclear, and a systematic review of Cu SACs is lacking. To this end, this work summarizes the recent advances of Cu SACs. The synthesis strategies of Cu SACs, metal-support interactions between Cu single atoms and different supports, modification methods including modification for carriers, coordination environment regulating, site distance effect utilizing, and dual metal active center catalysts constructing, as well as their applications in energy conversion and environmental purification are emphatically introduced. Finally, the opportunities and challenges for the future Cu SACs development are discussed. This review aims to provide insight into Cu SACs and a reference for their optimal design and wide application.

Recent development of advanced biotechnology for wastewater treatment.

The importance of highly efficient wastewater treatment is evident from aggravated water crises. With the development of green technology, wastewater treatment is required in an eco-friendly manner. Biotechnology is a promising solution to address this problem, including treatment and monitoring processes. The main directions and differences in biotreatment process are related to the surrounding environmental conditions, biological processes, and the type of microorganisms. It is significant to find suitable biotreatment methods to meet the specific requirements for practical situations. In this review, we first provide a comprehensive overview of optimized biotreatment processes for treating wastewater during different conditions. Both the advantages and disadvantages of these biotechnologies are discussed at length, along with their application scope. Then, we elaborated on recent developments of advanced biosensors (i.e. optical, electrochemical, and other biosensors) for monitoring processes. Finally, we discuss the limitations and perspectives of biological methods and biosensors applied in wastewater treatment. Overall, this review aims to project a rapid developmental path showing a broad vision of recent biotechnologies, applications, challenges, and opportunities for scholars in biotechnological fields for "green" wastewater treatment.

Facile introduction of coordinative Fe into oxygen-enriched graphite carbon nitride for efficient photo-Fenton degradation of tetracycline.

Tetracycline (TC) antibiotics have been widely used over the past decades, and their massive discharge led to serious water pollution. Photo-Fenton process has gained ever-increasing attention for its excellent oxidizing ability and friendly solar energy utilization ability in TC polluted water treatment. This work introduced coordinative Fe into oxygen-enriched graphite carbon nitride (OCN) to form FeOCN composites for efficient photo-Fenton process. Hemin was chosen as the source to provide the source of coordinative Fe-Nx groups. The degradation efficiency of TC reached 82.1 % within 40 min of irradiation, and remained 76.9 % after five runs of reaction. The degradation intermediates of TC were detected and the possible degradation pathways were gained. It was found that h+, OH, and O2- played major roles in TC degradation. Notably, the photo-Fenton performance of FeOCN was stable in highly saline water or strong acid/base environment (pH 3.0-9.0). Besides, H2O2 can be generated in-situ in this photo-Fenton process, which is favorable for practical application. It can be anticipated that the coordinative FeOCN composites will promote the application of photo-Fenton oxidation process in TC polluted water treatment.

Synergistic effect of flower-like MnFe2O4/MoS2 on photo-Fenton oxidation remediation of tetracycline polluted water.

In this work, a flower-like MnFe2O4-MoS2 (FMW) catalyst was successfully prepared as a catalyst for photo-Fenton oxidation. The flower-like structured FMW possessed large open surface area, which exposed enough active sites and can fully contact with tetracycline (TC). We studied the effect of different FMW composites, H2O2 concentration and light intensity on the photo-Fenton process. 1FMW (MnFe2O4:MoS2 = 1:10 in mol) exhibited the best degradation effect on TC, and 1 mmol/L of H2O2 and 398.73 mW/cm2 of light were the optimum parameters. A p-n heterojunction was formed in 1FMW, ensuring the stability of composite and the fast electron transfer. Holes, •O2- and •OH were generated in photo-Fenton process and participated in TC degradation. Notably, FMW can be recycled quickly under an external magnetic field due to its magnetic properties. Overall, FMW shows good catalytic stability and recoverability in photo-Fenton oxidation process, which has a broad application prospect.

Swift reduction of nitroaromatics by gold nanoparticles anchored on steam-activated carbon black via simple preparation.

Gold (Au) nanoparticles supported on certain platforms display highly efficient activity on nitroaromatics reduction. In this study, steam-activated carbon black (SCB) was used as a platform to fabricate Au/SCB composites via a green and simple method for 4-nitrophenol (4-NP) reduction. The obtained Au/SCB composites exhibit efficient catalytic performance in reduction of 4-NP (rate constant kapp = 2.1925 min-1). The effects of SCB activated under different steam temperature, Au loading amount, pH, and reaction temperature and NaBH4 concentration were studied. The structural advantages of SCB as a platform were analyzed by various characterizations. Especially, the result of N2 adsorption-desorption method showed that steam activating process could bring higher surface area (from 185.9689 to 249.0053 m2/g), larger pore volume (from 0.073268 to 0.165246 cm3/g), and more micropore for SCB when compared with initial CB, demonstrating the suitable of SCB for Au NP anchoring, thus promoting the catalytic activity. This work contributes to the fabrication of other supported metal nanoparticle catalysts for preparing different functional nanocomposites for different applications.

Efficient antibiotics removal via the synergistic effect of manganese ferrite and MoS2.

The use of antibiotics for beings is a most significant milestone in present era. However, owing to the excessive use, a large amount of antibiotics accumulated in water, leading to serious pollution. An efficient method is urgently needed to treat the antibiotics pollution. Photo-Fenton process is a green method with utilizing solar energy. Catalyst is important. This work combines manganese ferrite MnFe2O4 and MoS2 to synthesize MnFe2O4-MoS2 (FMG) composite as the catalyst of photo-Fenton process, which shows good performance on tetracycline antibiotics degradation. Light intensity exhibits positive correlation with the catalytic activity. h+, •OH and 1O2 participate in tetracycline degradation. h+ plays a key role in tetracycline removal. •OH has a little impact on tetracycline removal, but it has a great impact on the mineralization ability of this photo-Fenton process. Additionally, cycling experiments confirm the stability of FMG. And owing to its magnetism, FMG can be easily recycled by external magnetic field. This photo-Fenton process over FMG with utilizing the synergism of MnFe2O4 and MoS2 is a promising method for antibiotics pollution treatment.

Facile synthesis of Mn, Ce co-doped g-C3N4 composite for peroxymonosulfate activation towards organic contaminant degradation.

Peroxymonosulfate (PMS)-based advanced oxidation processes for wastewater treatment have received extensive attention in the past years. Here, a novel Mn, Ce co-modified g-C3N4 (MnCe-CN) composite was successfully synthesized by one-step pyrolysis for activating PMS. The physical and chemical characterization of MnCe-CN/PMS was conducted, indicating that Mn and Ce were evenly distributed on g-C3N4 and existed in the form of Mn-N structure and CeO2, respectively. The MnCe-CN/PMS system could effectively degrade pollutants such as acetaminophen (ACT), methylparaben (MeP), p-nitrophenol (PNP), and 2,4-dichlorophenol (2,4-DCP). Among them, 2,4-DCP could be rapidly degraded, reaching 100% within 30 min. The masking experiments and electrochemical testing results revealed that 2,4-DCP was degraded via superoxide radicals (O2˙-), singlet oxygen (1O2), and electron transfer path. The cyclic experiments and real water treatment experiments testified that the oxidative system had excellent stability and applicability. This study provides a facile synthetic method to fabricate bimetallic co-modified g-C3N4 for the enhancement of PMS activation.

Enhanced visible-light-driven photocatalytic activity of bismuth oxide via the decoration of titanium carbide quantum dots.

In Ti3C2 quantum dots (Ti3C2 QDs)/Bi2O3 photocatalysts system, Ti3C2 QDs can act as a co-catalyst to greatly boost the photocatalytic performance of Bi2O3. Ti3C2 QDs with excellent light adsorption ability can improve the light response of the system, and the fascinating electronic property can function as a channel for electron transfer. Moreover, Ti3C2 QDs possess larger specific area and more active edge atoms thanks to the size effect. The best Ti3C2 QDs/Bi2O3 composite with the loading amounts of 75 mL of Ti3C2 QDs solution showed much higher photocatalytic performance (nearly 5.85 times) for tetracycline (TC) degradation than that of pristine Bi2O3 under visible light irradiation. These different photocatalytic performances shed light on the key role of Ti3C2 QDs in stimulating the photocatalytic activity of Bi2O3. Moreover, Ti3C2 QDs/Bi2O3 composites exhibited excellent stability in recycling experiments and actual water sample treatment.

Facile synthesis of CeO2/carbonate doped Bi2O2CO3 Z-scheme heterojunction for improved visible-light photocatalytic performance: Photodegradation of tetracycline and photocatalytic mechanism.

CeO2 nanoparticles are successfully loaded on carbonate doped Bi2O2CO3 (CBOC) nanosheets by a facile hydrothermal and low-temperature calcination method. CeO2/CBOC heterojunction shows significantly enhanced photocatalytic activity, when 35 mg of CeO2/CBOC photocatalyst is added to tetracycline (TC) solution (20 mg/L, 100 mL), about 79.5% TC is degraded within 90 min under visible light irradiation, which is much higher than that of original CeO2 and CBOC. According to photoelectrochemical characterization and active radical capture experiments, the Z-scheme electron transfer mechanism is the reason for the significant enhancement of photocatalytic activity. Besides, the XPS results indicate that Ce4+/Ce3+ redox pairs are formed at the contact interface between CeO2 and CBOC, which is conducive to the transfer of photoexcited electrons and production of superoxide radicals. Additionally, the photocatalytic mechanism and possible degradation pathway of TC is proposed through free radical trapping experiments and liquid chromatography-mass (LC-MS) analysis. This study will accumulate experience for the combination of CeO2 and bismuth-based nanomaterials, and provide a feasible way to design wide band-gap bismuth-based photocatalysts, thereby achieving efficient visible light degradation of environmental pollutants.

Critical review of advanced oxidation processes in organic wastewater treatment.

With the development of industrial society, organic wastewater produced by industrial manufacturing has caused many environmental problems. The vast majority of organic pollutants in water bodies are persistent in the environment, posing a threat to human and animal health. Therefore, efficient treatment methods for highly concentrated organic wastewater are urgently needed. Advanced oxidation processes (AOPs) are widely noticed in the area of treating organic wastewater. Compared with other chemical methods, AOPs have the characteristics of high oxidation efficiency and no secondary pollution. In this paper, the mechanisms, advantages, and limitations of AOPs are comprehensively reviewed. Besides, the basic principles of combining different AOPs to enhance the treatment efficiency are described. Furthermore, the applications of AOPs in various wastewater treatments, such as oily wastewater, dyeing wastewater, pharmaceutical wastewater, and landfill leachate, are also presented. Finally, we conclude that the main direction in the future of AOPs are the modification of catalysts and the optimization of operating parameters, with the challenges focusing on industrial applications.