Design of FeCoNiSmNd-co-doped porous carbon catalysts from pulverized coal for radical and non-radical peroxymonosulfate activation in organic pollutant degradation

A sulfonated (SO3H-bearing) carbon catalyst with mesoporous structure and high specific surface area is successfully prepared by impregnating the cellulosic precursor (wood powder) with ZnCl2 prior to activation and sulfonation. The specific surface area of the porous carbon catalyst thus prepared is also found to increase with carbonization temperature to a maximum of 1,560 m2 g−1 at ca. 773 K. Structural analyses reveal that the porous carbon catalysts carbonized at temperatures higher than 723 K contain high densities of micro- and mesopores. The porous carbon catalyst exhibits high catalytic performance for the esterification of acetic acid (343 K), the activity for which is dependent only on the acid density. The porous carbon catalyst also exhibits high catalytic activity for the benzylation of toluene, whereas non-porous sulfonated carbon has very limited activity for this reaction. The activity for the benzylation of toluene is dependent on both the specific surface area and the acid density of the sulfonated porous carbon catalyst.

Metals usually served as the active sites of the heterogeneous bifunctional electro-Fenton reaction, which faced the challenge of poor stability under acidic or even neutral conditions. Exploring a metal-free heterogeneous bifunctional electro-Fenton catalyst can effectively solve the above problems. In this work, a stable metal-free heterogeneous bifunctional boron-modified porous carbon catalyst (BTA-1000) was synthesized. For the BTA-1000 catalyst, the yield of H2O2 (294 mg/L) significantly increased. The degradation rate of phenol by BTA-1000 (0.242 min-1) increased by an order of magnitude, compared with the porous carbon catalyst (0.0105 min-1). The BTA catalyst could rapidly degrade industrial dye wastewater, and its specific energy consumption was 5.52 kW h kg-1 COD-1, lower than that in previous reports (6.38-7.4 kW h kg-1 COD-1). DFT and XPS revealed that C═O and -BC2O groups jointly promoted the generation of H2O2, and the -BCO2 group played dominant roles in the generation of •OH because the oxygen atom near the electron-giving groups (-BCO2 group) facilitated the formation of hydrogen bond and H2O2 adsorption. This work gained deep insights into the reaction mechanism of the boron-modified porous carbon catalyst, which helped to guide the development of metal-free heterogeneous bifunctional electro-Fenton catalysts.

Currently, developing nonprecious‐metal catalysts to replace Pt‐based electrocatalysts in fuel cells has become a hot topic because the oxygen reduction reaction (ORR) in fuel cells often requires platinum, a precious metal, as a catalyst, which is one of the major hurdles for commercialization of the fuel cells. Recently, the newly emerging metal‐organic frameworks (MOFs) have been widely used as self‐sacrificed precursors/templates to fabricate heteroatom‐doped porous carbons. Here, the recent progress of MOF‐derived, heteroatom‐doped porous carbon catalysts for ORR in fuel cells is systematically reviewed, and the synthesis strategies for using different MOF precursors to prepare heteroatom‐doped porous carbon catalysts, including the direct carbonization of MOFs, MOF and heteroatom source mixture carbonization, and MOF‐based composite carbonization are summarized. The emphasis is placed on the precursor design of MOF‐derived metal‐free catalysts and transition‐metal‐doped carbon catalysts because the MOF precursors often determine the microstructures of the derived porous carbon catalysts. The discussion provides a useful strategy for in situ synthesis of heteroatom‐doped carbon ORR electrocatalysts by rationally designing MOF precursors. Due to the versatility of MOF structures, MOF‐derived porous carbons not only provide chances to develop highly efficient ORR electrocatalysts, but also broaden the family of nanoporous carbons for applications in supercapacitors and batteries.

AgI modified covalent organic frameworks for effective bacterial disinfection and organic pollutant degradation under visible light irradiation

Nanozymes are one of the ideal alternatives to natural enzymes for various applications. The rational design of nanozymes with improved catalytic activity stimulates increasing attention to address the low activity of current nanozymes. Here, we reported a general strategy to fabricate the Co-based homobimetallic hollow nanocages (HNCs) (C-CoM-HNC, M = Ni, Mn, Cu, and Zn) by ion-assistant solvothermal reaction and subsequent low-temperature calcination from metal-organic frameworks. The C-CoM-HNCs are featured with HNCs composed of interlaced nanosheets with homogeneous bimetallic oxide dispersion. The hierarchical structure and secondary metallic doping endow the C-CoM-HNC highly active sites. In particular, the Cu-doped C-CoCu-HNCs nanostructures exhibit superior performances over the other C-CoM-HNC as both the oxidase mimicking and peroxymonosulfate (PMS) activator. A sensitive bioassay for acetylcholinesterase (AChE) was established based on the excellent oxidase-like activity of C-CoCu-HNC, offering a linear detection range from 0.0001 to 1 mU/mL with an ultralow detection limit of 0.1 mU/L. As the PMS activator, the C-CoCu-HNC was applied for targeted organic pollutant (rhodamine B, RhB) degradation. A highly efficient RhB degradation was realized, along with good adaptability in a wide pH range and good reusability during the eight-cycle run. The results suggest that C-CoCu-HNC holds a practical potential for clinical diagnostics and pollution removal. Further density functional theory calculation reveals that Cu doping leads to a tighter connection and more negative adsorption energy for O2/PMS, as well as an upshifted d-band center in the C-CoCu-HNCs nanostructures. These changes facilitated the adsorption of O2/PMS on the C-CoCu-HNC surface for dissociation. This work not only offers a promising multifunctional nanozyme catalyst for clinical diagnostics and pollution removal but also gives some clues for the further development of novel nanozymes with high catalytic activities.

Black carbon-mediated degradation of organic pollutants: A critical review

The oxygen reduction reaction (ORR) is an important reaction in fuel cells and metal air batteries. The reaction is affected by slow kinetics and the use of high-priced and resource-scarce platinum-based catalysts. Therefore, there is an urgent need to develop cost-effective nonprecious metal catalysts for use in the ORR to replace Pt-based catalysts. In this study, we used two-dimensional covalent organic frameworks (recorded as TF-COFs) as precursors to produce a metal-free nitrogen and fluorine-co-doped porous carbon catalyst (recorded as TF-800, TF-900, TF-1000, and TF-1100). TF-1000 had a high initial potential (0.90 V) and half-wave potential (0.83 V) in an alkaline medium, indicating good catalytic activity. In addition, the ORR stability of TF-1000 was better than that of commercial Pt/C (20%). This is mainly because the porous carbon catalyst has a high specific surface area, and the nitrogen and fluorine atoms in it have good dispersion and synergistic effects on the polarization of adjacent carbon atoms. TF-1000 also shows excellent performance in zinc-air batteries. In the TF-1000 based zinc-air batteries, excellent battery performance was observed: the peak power density reached 216.66 mW·cm–2, the specific capacity reached 752.86 mAh·g–1 at 10 mA·cm–2, and the long-term charge–discharge stability was demonstrated. This work provides inspiration for new strategies to prepare future ORR catalysts.

Hydrothermal Synthesis of TiO2-rGO By Green Chemical Method

Sunlight-induced degradation of organic pollutants is an ideal approach for environmental pollution control and wastewater treatment. Although a variety of photocatalysts have been designed toward this goal, efficient degradation of colorless organic pollutants by visible light is a challenging issue. Here, we show that a reduced graphene oxide (rGO)-based composite with silver nanoparticle (rGO-Ag) can act as an efficient visible-light photocatalyst for the degradation of colorless organic pollutants. We have developed a simple, large-scale synthesis method for rGO-Ag and used it for the degradation of three well-known endocrine disruptors (phenol, bisphenol A, and atrazine) under UV and visible light. It is found that photocatalytic efficiency by rGO-Ag under visible light is significantly higher compared to that of rGO or silver nanoparticles. It is proposed that Ag nanoparticles offer visible-light-induced excitation of silver plasmons, and conductive rGO offers efficient charge separation and thus induces oxidative degradation of the organic pollutant. This approach can be extended for sunlight-induced degradation of different organic pollutants.

With industrialization rapidly progressing in recent decades, great amounts of refractory organic pollutants are found in water bodies, which severely jeopardizes ecosystem health. Monitoring the organic compounds in water bodies and removing organic pollutants from wastewater is essential for ameliorating threats to aquatic life and human health. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation and detection of organic pollutants in wastewater are promising strategies for fulfilling these goals sustainably, since PC and PEC technologies can take advantage of solar energy, which is one of the most abundant energy sources on earth. Titanium dioxide (TiO2) is a commonly used photocatalyst due to its appropriate band position, high chemical stability, low cost, and nontoxicity. However, pristine TiO2 photocatalysts can only be stimulated by UV irradiation because the band gap of pristine TiO2 is higher than 3.0 eV, which seriously impedes its development with low-cost and environmentally friendly solar energy. There are several efficient strategies to overcome these disadvantages of pristine TiO2, such as morphology modification, bandgap engineering, and applying co-catalysts with the host photocatalysts. Herein, this thesis aims to utilize different strategies to enhance the photocatalytic performance of TiO2-based photocatalysts under visible light irradiation and apply those modified photocatalysts to degradation and detection of organics in wastewater. In the first study, a photoelectrochemical Chemical Oxygen Demand (COD) sensor based on a linear photocurrent-concentration analytical principle was designed for the on-site determination of COD. A high-performance anatase-branch@hydrogenated rutile-nanorod TiO2 (AB@H-RTNR) photoelectrode was fabricated. The as-prepared photoanodes successfully achieved sensitive determination of COD with a detection limit of 0.2 ppm (S/N = 3), an RSD% of 1.5 %, a wide linear detection range of 1.25−576 ppm, and an average recovery rate fluctuating between 100% ± 4% for artificial wastewater sample analyses. The satisfying results of this work suggest that AB@H-RTNR can serve as a promising photocatalyst for fast and accurate detection of organic compounds in water bodies. In addition to detecting COD in water bodies, the degradation of refractory organic compounds in water is also crucial for healthy ecosystems. Highly efficient, low-cost, and portable wastewater treatment and purification solutions are urgently needed for aqueous pollution removal. Herein, in the second study, we coupled a TiO2-based PC system with a persulphate (PS) oxidation system into a portable advanced oxidation device for rapid and deep degradation of organic contaminants in wastewater. Using hydrogenation, we fabricated hydrogenated anatase branched-rutile TiO2 nanorod (H-AB@RTNR) photocatalysts that enable PC degradation to occur under visible light to improve the utilization of solar energy. A degradation rate of 100% and a reaction rate constant of 0.0221 min−1 for degrading 1 L Rhodamine B (20 mg L-1) was achieved in 120 min in a specially designed thin-layer cell under visible light irradiation. These encouraging results suggest that the H-AB@RTNR photocatalysts/PS synergistic degradation system could be an alternative approach for the efficient degradation of organic pollutants in wastewater. Motivated by the result of the PC/PS synergistic degradation system, we further employed a PC/chlorination system for synergistic degradation of antibiotics. In the third study, we demonstrated the use of visible light (>420 nm) to produce •HO and •ClO through the assistance of photocatalysts (TiO2/WO3 nanofibers) and free chlorine (HOCl/ClO−). The introduction of visible-light-driven photocatalysts can significantly boost the yield of active radicals, which favors the degradation of antibiotics in water bodies. The synergistic PC/chlorination degradation system obtained a pseudo-first-order degradation rate constant of a model antibiotic, tetracycline hydrochloride, of 21.438 min-1, which is 3.66 and 86.57 times higher than that in the pure TiO2/WO3 photocatalysis and traditional chlorination processes, respectively. The stability test exhibits that the performance decline is negligible after multiple use cycles. The results of this study suggest that PC/chlorine degradation is a feasible, lowcost, and environmental-friendly strategy for antibiotics removal under visible irradiation. Another approach to improve the degradation efficiency of TiO2-based photocatalysts is using co-catalysts to assist the host photocatalysts. In the fourth study, we fabricated noble-metal free co-catalysts, i.e., N-doped carbon wrapped FeNi nanoparticles (FeNi@NGC), via a pyrolysis method. Hydrogenated TiO2 (H-TiO2) was synthesized as the host photocatalysts and coupled with as-prepared FeNi@NGC to obtain superior PC activity in the degradation of tetracycline hydrochloride (TC-HCl), a model antibiotic. The FeNi@NGC/H-TiO2 system achieved a degradation rate of 100% within 120 min on degrading 100 mL 20 mg L-1 TC-HCl under visible light irradiation (λ>420 nm). The degradation rate constant of the FeNi@NGC/H-TiO2 system reached 23.18 min-1, which was 33.99, 26.98, and 2.23 times compared to that of TiO2, FeNi@NGC/TiO2, and H-TiO2 system. The favorable performance of the FeNi@NGC/H-TiO2 system can be ascribed to two reasons: the secondary electron transfer in the FeNi intermetallic compounds that facilitates the photo-induced charge separation in photocatalysts; and the enhanced visible light absorption ability resulted from the N-doped graphitized carbon shell. Moreover, the oxygen vacancies brought by the hydrogenation process also improves the visible light absorbance of the photocatalysts, which favors the degradation performance. This study suggests that coupling FeNi@NGC cocatalyst with H-TiO2 is a promising strategy for improving the photocatalytic degradation performance on antibiotics. In summary, the strategies presented in this thesis show that the morphology and electronic properties of TiO2 can be manipulated to resolve the problems of poor visible light absorption and the large recombination rate of photogenerated charge carriers. Moreover, the degradation performances of organic compounds show that applying a synergistic system with TiO2-based materials is promising in the removal of refractory organics in the wastewater. The strategies utilized in the thesis (i.e., morphology manipulation, bandgap engineering, and applying co-catalysts) can be utilized in other members of the semiconductors family (such as SnO2, BiVO4, SrTiO3) for developing more sustainable and low-cost approaches and techniques to improve human and aquatic ecosystem health.

Recent advances in ultrasound-Fenton/Fenton-like technology for degradation of aqueous organic pollutants

High-performance porous carbon catalysts doped by iron and nitrogen for degradation of bisphenol F via peroxymonosulfate activation

Facile synthesis of N, P-doped hierarchical porous carbon framework catalysts based on gelatin/phytic acid supermolecules for electrocatalytic oxygen reduction

Metal-Decorated CeO2 nanomaterials for photocatalytic degradation of organic pollutants

Exploring the effectiveness of microbial fuel cell for the degradation of organic pollutants coupled with bio-energy generation