Importance of carbon structure for nitrogen and sulfur co-doping to promote superior ciprofloxacin removal via peroxymonosulfate activation

Metal-organic framework derived crystalline nanocarbon for Fenton-like reaction

Nanoporous carbons with tailorable nanoscale texture and long-range ordered structure are promising candidates for energy, environmental and catalytic applications, while the current synthetic methods do not allow elaborate control of local structure. Here we report a salt-assisted strategy to obtain crystalline nanocarbon from direct carbonization of metal-organic frameworks (MOFs). The crystalline product maintains a highly ordered two-dimensional (2D) stacking mode and substantially differs from the traditional weakly ordered patterns of nanoporous carbons upon high-temperature pyrolysis. The MOF-derived crystalline nanocarbon (MCC) comes with a high level of nitrogen and oxygen terminating the 2D layers and shows an impressive performance as a carbocatalyst in Fenton-like reaction for water purification. The successful preparation of MCC illustrates the possibility to discover other crystalline heteroatom-doped carbon phases starting from correctly designed organic precursors and appropriate templating reactions.

Mediating peroxymonosulfate activation path in Fenton-like reaction via doping different metal atoms into g-C3N5

Peroxymonosulfate (PMS) could be activated by either radical path or non-radical path, how to rationally mediate these two routines was an important unresolved issue. This work has introduced a simple way to address this problem via metal atom doping. It was found that Fe-doped nitrogen-rich graphitic carbon nitride (Fe-C3N5) exhibited high activity towards PMS activation for tetracycline degradation, and the degradation rate was 3.14 times higher than that of Co-doped nitrogen-rich graphitic carbon nitride (Co-C3N5). Radical trapping experiment revealed the contributions of reactive species over two catalysts were different. Electron paramagnetic resonance analysis further uncovered the non-radical activation path played a dominated role on Fe-C3N5 surface, while the radical activation path was the main routine on Co-C3N5 surface. Density functional theory calculations, X-ray photoelectron spectroscopy analysis, and electrochemical experiments provided convincing evidence to support these views. This study supplied a novel method to mediate PMS activation path via changing the doped metal atom in g-C3N5 skeleton, and it allowed us to better optimize the PMS activation efficiency.

Improving selectivity and antifouling properties of a PES hollow fibre membrane with a photo-enzyme for the removal of ciprofloxacin and sulfamethoxazole

A multifunctional hollow fibre was prepared by the modification of polyethersulfone (PES) with laccase (Lac) and phosphorus-doped graphitic carbon nitride (P-gC3N4) for the removal of ciprofloxacin and sulfamethoxazole. The properties and structure elucidation of the prepared membranes were evaluated using contact angle analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), correlative light electron microscopy (CLEM), atomic force microscopy (AFM), tensile strength, water-intake capacity, and pure water flux. The modified multifunctional hollow fibre membranes showed increased root mean square surface roughness from 50 nm for neat PES to 104 nm, which contributed to the significantly higher water flux of 90 L.m-2h-1 compared to 54 L.m-2h-1 for pristine PES. The hydrophilicity also improved after modification as the contact angle reduced from 72° ± 1.01° to 42° ± 2.26°. The modified hollow fibre membranes showed an enhanced removal of ciprofloxacin (77%) and sulfamethoxazole (80%). Moreover, antifouling properties towards bovine serum albumin were 89% for FRR, 7% for Rr, 9% for Rir and 17% for Rt. Regeneration studies showed that the multifunctional hollow fibre membrane obtained a high removal percentage of 79% towards sulfamethoxazole after five cycles. Hence, this work proposes a new system that can be successfully utilized in the treatment of emerging pharmaceutical pollutants in water.

Antibiotic removal from synthetic and real aqueous matrices by peroxymonosulfate-based advanced oxidation processes. A review of recent development

The widespread use of antibiotics for the treatment of bacteriological diseases causes their accumulation at low concentrations in natural waters. This gives health risks to animals and humans since it can increase the damage of the beneficial bacteria, the control of infectious diseases, and the resistance to bacterial infection. Potent oxidation methods are required to remove these pollutants from water because of their inefficient abatement in municipal wastewater treatment plants. Over the last three years in the period 2021-September 2023, powerful peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have been developed to guaranty the effective removal of antibiotics in synthetic and real waters and wastewater. This review presents a comprehensive analysis of the different procedures proposed to activate PMS-producing strong oxidizing agents like sulfate radical (SO4•-), hydroxyl radical (•OH, radical superoxide ion (O2•-), and non-radical singlet oxygen (1O2) at different proportions depending on the experimental conditions. Iron, non-iron transition metals, biochar, and carbonaceous materials catalytic, UVC, photocatalytic, thermal, electrochemical, and other processes for PMS activation are summarized. The fundamentals and characteristics of these procedures are detailed remarking on their oxidation power to remove antibiotics, the influence of operating variables, the production and detection of radical and non-radical oxidizing agents, the effect of added inorganic anions, natural organic matter, and aqueous matrix, and the identification of by-products formed. Finally, the theoretical and experimental analysis of the change of solution toxicity during the PMS-based AOPs are described.

The activation mechanism of peroxymonosulfate and peroxydisulfate by modified hydrochar: Based on the multiple active sites formed by N and Fe

Modified hydrochar (NHC@Fe), with multiple functional groups and transition metal oxide-containing surface, was successfully synthesized by one-step hydrothermal method. The differences in its catalytic activity for peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation were studied in detail. Experimental and DFT studies showed that abundant active sites, namely, transition metals and functional groups on NHC@Fe provided multiple effective pathways for the activation of persulfate (PS). The NHC@Fe/PMS and NHC@Fe/PDS systems could degrade about 80% of tetracycline hydrochloride (TC) in 120 min and were found to be better than those modified by iron or nitrogen alone. This emphasized the advantage of N-Fe co-modification in persulfate activation. Although the Fe2+/Fe3+ cycle accelerated the activation, the activation of PMS mainly relied on Fe3+, whereas that of PDS mainly relied on Fe2+. Moreover, Fe-N, pyrrolic N, pyridine N, C-O, and O-CO groups also played a key role in the activation process, but the dominant action sites were not the same. Multiple free radicals, such as SO4•-, •OH, O2•-, and 1O2 were generated in PMS and PDS activation systems. 1O2 induced non-free radical pathway was mainly involved in the degradation of TC in both activation systems, but the generation pathway of 1O2 was more direct and rapid in the PDS system. This study provides detailed DFT models of the active sites activated by PMS and PDS and discusses the activation pathways of PMS and PDS along with the similarities and differences in ROS reaction mechanisms.

N,S-codoped biochar outperformed N-doped biochar on co-activation of H2O2 with trace dissolved Fe(Ⅲ) for enhanced oxidation of organic pollutants

Co-activation of H2O2 with biochar and iron sources together provides an attractive strategy for efficient removal of refractory pollutants, because it can solve the problems of slow Fe(Ⅱ) regeneration in Fenton/Fenton-like processes and of low •OH yield in biochar-activated process. In this study, a wood-derived biochar (WB) was modified by heteroatom doping for the objective of enhancing its reactivity toward co-activation of H2O2. The performance of the co-activated system using doped biochars and trace dissolved Fe(Ⅲ) on oxidation of organic pollutants was evaluated for the first time. The characterizations using X-ray photoelectron spectroscopy (XPS), Raman spectra and electrochemical analyses indicate that heteroatom doping introduced more defects in biochar and improved its electron transfer capacity. The oxidation experiments show that heteroatom doping improved the performance of biochar in the co-activated process, in which the N,S-codoped biochar (NSB) outperformed the N-doped biochar (NB) on oxidation of pollutants. The reaction rate constant (kobs) for oxidation of sulfadiazine in NSB + Fe + H2O2 is 2.25 times that in NB + Fe + H2O2, and is 72.9 times that in the Fenton-like process without biochar, respectively. The mechanism investigations indicate that heteroatom doping enhanced biochar's reactivity on catalyzing the decomposition of H2O2 and on reduction of Fe(Ⅲ) due to the improved electron transfer/donation capacity. In comparison with N-doping, N,S-codoping provided additional electron donor (thiophenic C-S-C) for faster regeneration of Fe(Ⅱ) with less amount of doping reagent used. Furthermore, co-activation with NSB maintained to be efficient at a milder acidic pH than Fenton/Fenton-like processes, and can be used for oxidation of different pollutants and in real water. Therefore, this research provides a novel, sustainable and cost-efficient method for oxidation of refractory pollutants.

Probing the Activity Enhancement of Carbocatalyst with the Anchoring of Atomic Metal

Enhanced catalysis for organic transformation is essential for the synthesis of high-value compounds. Atomic metal species recently emerged as highly effective catalysts for organic reactions with high activity and metal utilization. However, developing efficient atomic catalysts is always an attractive and challenging topic in the modern chemical industry. In this work, we report the preparation and activity enhancement of nitrogen- and sulfur-codoped holey graphene (NSHG) with the anchoring of atomic metal Pd. When employed as the catalyst for nitroarenes reduction reactions, the resultant Pd/NSHG composite exhibits remarkably high catalytic activity due to the co-existence of dual-active components (i.e., catalytically active NSHG support and homogeneous dispersion of atomic metal Pd). In the catalytic 4-nitrophenol (4-NP) reduction reaction, the efficiency (turnover frequency) is 3.99 × 10-2 mmol 4-NP/(mg cat.·min), which is better than that of metal-free nitrogen-doped holey graphene (NHG) (2.3 × 10-3 mmol 4-NP/(mg cat.·min)) and NSHG carbocatalyst (3.8 × 10-3 mmol 4-NP/(mg cat.·min)), the conventional Pd/C and other reported metal-based catalysts. This work provides a rational design strategy for the atomic metal catalysts loaded on active doped graphene support. The resultant Pd/NSHG dual-active component catalyst (DACC) is also anticipated to bring great application potentials for a broad range of organic fields, such as organic synthesis, environment treatment, energy storage and conversion.

Activation of calcium peroxide by nitrogen and sulfur co-doped metal-free lignin biochar for enhancing the removal of emerging organic contaminants from waste activated sludge

The accumulation of emerging organic contaminants (EOCs) in waste activated sludge (WAS) is a global concern. In this study, a multi-heteroatom nitrogen and sulfur was successfully embedded into lignin-based biochar (N-S-LGBC) and used it to activate calcium peroxide (CP) for the degradation of 4-nonylphenol (4-NP) in WAS. N-S-LGBC/CP was effective in degrading 85 % of 4-NP within 12 h through the activation of CP owing to hydroxyl radicals and singlet oxygen species generated from the synergism among pyrrolic-N, thiophenic-S, and lattice oxygen, i.e., active sites responsible for 4-NP degradation. These results highlight substrate biodegradability for subsequent bioprocesses that improves WAS treatment in EOC degradation by the N-S-LGBC/CP-mediated process. There was abundance of distinct Aggregatilinea genus within the phylum Chloroflexi during N-S-LGBC/CP treatment, indicating high 4-NP pretreatment efficiency in WAS. This work provides a new understanding of N-S-co-doped carbocatalysts in green and sustainable hydroxyl radical-driven carbon advanced oxidation (HR-CAOP) platforms for WAS remediation.

Catalytic Degradation of Ciprofloxacin in Aqueous Solution by Peroxymonosulfate Activated with a Magnetic CuFe2O4@Biochar Composite

A magnetic copper ferrite and biochar composite (CuFe2O4@BC) catalyst was prepared by an improved sol-gel calcination method and initially used for the removal of antibiotics ciprofloxacin (CIP) by activated peroxymonosulfate (PMS). Using CuFe2O4@BC as the activator, 97.8% CIP removal efficiency could be achieved in 30 min. After a continuous degradation cycle, CuFe2O4@BC catalyst still exhibited great stability and repeatability and could also be quickly recovered by an external magnetic field. Meanwhile, the CuFe2O4@BC/PMS system presented good stability for metal ion leaching, which was far less than the leaching of metal ions in the CuFe2O4/PMS system. Moreover, the effects of various influencing factors, such as initial solution pH, activator loading, PMS dosage, reaction temperature, humic acid (HA), and the inorganic anions were explored. The quenching experiments and the electron paramagnetic resonance (EPR) analysis manifested that hydroxyl radical (•OH), sulfate radical (SO4•−), superoxide radical (O2•−), and singlet oxygen (1O2) were generated in the CuFe2O4@BC/PMS system, while 1O2 and O2•− are mainly involved in the degradation process. The synergistic effect between CuFe2O4 and BC enhanced the structural stability and electrical conductivity of the material, which promoted the bonding between the catalyst and PMS, resulting in the enhanced catalytic activity of CuFe2O4@BC. This indicates that CuFe2O4@BC activating PMS is a promising remediation technique for CIP-contaminated water.