Efficient removal of organic pollutants by a Co/N/S-doped yolk-shell carbon catalyst via peroxymonosulfate activation

N,S,O triply-doped carbon with nanotubes-interwoven nanosheets encapsulated Co nanoparticles for robust antibiotic destruction via activating peroxymonosulfate

The development of facile and effective approaches to regulate the stability and reusability of metallic Co catalytic materials towards peroxymonosulfate (PMS) activation for remediating antibiotic pollutants remains challenging. In this study, we develop a one-step pyrolysis strategy to fabricate three-dimensional porous architecture assembled with N,S,O-codoped carbon nanotube-interwoven hierarchically porous carbon nanosheets encapsulated Co nanoparticles (Co@NSOC), which serve as chainmail catalysts for stable and reusable degradation of tetracycline hydrochloride (TCH) through PMS activation. The optimal Co@NSOC-700-activated PMS system presents an excellent removal efficiency of 94.1 % for TCH within 10 min and a high cycling efficiency of 92.9 % after eight cycles. The encapsulated structure, abundant catalytic sites, superior hydrophilicity and strong magnetism contribute to the high performance. Further investigation demonstrates that both radical and nonradical pathways contribute to the TCH destruction, and 1O2 is verified as the dominant reactive substance. The possible degradation pathways and the toxicity of intermediates for TCH are evaluated. This work offers an innovative structure design and surface modulation strategy to fabricate robust catalysts towards environmental remediation.

Design and construction of heterostructured Zn2V2O7 cubes and hexagons as an electrode material for high-performance asymmetric supercapacitor applications

Hierarchical nanostructures have harvested noteworthy attention lately owing to their remarkable capabilities in the fields of energy storing and transformation, catalysis, and electrical devices. We established an effort less and template-free synthetic method to create hierarchical hetero nanostructures of Zn2V2O7, taking into account the benefits of hierarchical nanostructures, we investigated the performance of HNs (Hierarchical Nanostructures) as electrochemical supercapacitors. Electrochemical tests were tested in a 6 M KOH solution to assess their capabilities. The Zn2V2O7 electrode's measured specific capacitance was 750F/g at 1 A/g, with outstanding stability and an excellent retention capacity of 85 % later 5000 cycles in three- electrode electrochemical cells. Asymmetric device such as Zn2V2O7//AC provides a specific capacitance of 76.8F/g at 1 A/g with energy and power densities of 27.3 Wh kg-1 and 800 W kg-1 respectively. The device withstands 85 % of its initial capacity after 5000 continuous GCD cycles at 10 A/g. The outstanding performance observed clearly demonstrates the significant potential and practical utility of Zn2V2O7 in the realm of more efficient energy storage applications.

Double pyramid stacked CoO nano-crystals induced by graphene at low temperatures as highly efficient Fenton-like catalysts

Transition metal oxides are widely used as Fenton-like catalysts in the treatment of organic pollutants, but their synthesis usually requires a high temperature. Herein, an all-solid-state synthesis method controlled by graphene was used to prepare a double pyramid stacked CoO nano-crystal at a low temperature. The preparation temperature decreased by 200 °C (over 30% reduction) due to the introduction of graphene, largely reducing the reaction energy barrier. Interestingly, the corresponding degradation rate constants (kobs) of this graphene-supported pyramid CoO nano-crystals for organic molecules after their adsorption were over 2.5 and 35 times higher than that before adsorption and that of free CoO, respectively. This high catalytic efficiency is attributed to the adsorption of pollutants at the surface by supporting graphene layers, while free radicals activated by CoO can directly and rapidly contact and degrade them. These findings provide a new strategy to prepare low carbon-consuming transition metal oxides for highly efficient Fenton-like catalysts.

Vacancy-Rich CoSx@LDH@Co-NC Catalytic Membrane for Antibiotic Degradation with Mechanistic Insights

Improving the wettability of carbon-based catalysts and overcoming the rate-limiting step of the Mn+1/Mn+ cycle are effective strategies for activating peroxymonosulfate (PMS). In this study, the coupling of Co-NC, layered double hydroxide (LDH), and CoSx heterostructure (CoSx@LDH@Co-NC) was constructed to completely degrade ofloxacin (OFX) within 10 min via PMS activation. The reaction rate of 1.07 min-1 is about 1-2 orders of magnitude higher than other catalysts. The interfacial effect of confined Co-NC and layered double hydroxide (LDH) not only enhanced the wettability of catalysts but also increased the vacancy concentration; it facilitated easier contact with the interface reactive oxygen species (ROS). Simultaneously, reduced sulfur species (CoSx) accelerated the Co3+/Co2+ cycle, acquiring long-term catalytic activity. The catalytic mechanism revealed that the synergistic effect of hydroxyl groups and reduced sulfur species promoted the formation of 1O2, with a longer lifespan and a longer migration distance, and resisted the influence of nontarget background substances. Moreover, considering the convenience of practical application, the CoSx@LDH@Co-NC-based catalytic membrane was prepared, which had zero discharge of OFX and no decay in continuous operation for 5.0 h. The activity of the catalytic membrane was also verified in actual wastewater. Consequently, this work not only provides a novel strategy for designing excellent catalysts but also is applicable to practical organic wastewater treatment.

Facile synthesis of core-shell Co-MOF with hierarchical porosity for enhanced electrochemical detection of furaltadone in aquaculture water

Metal-organic frameworks (MOFs) exhibited huge application potential in electrochemical analysis field, how to facilely and effectively boost the electrochemical sensing activity of MOFs materials still face enormous challenges. In this work, core-shell Co-MOF (Co-TCA@ZIF-67) polyhedrons with hierarchical porosity was easily synthesized via simple chemical etching reaction by selecting thiocyanuric acid as the etching reagent. Benefiting from the introduction of mesopores and thiocyanuric acid/Co²⁺ complex on the surface of ZIF-67 frameworks, the property and functions of the pristine ZIF-67 was seriously tailored. Compared with the pristine ZIF-67, the as-resulted Co-TCA@ZIF-67 nanoparticles displayed greatly enhanced physical adsorption capacity and electrochemical reduction activity toward the antibiotic drug furaltadone. As a result, a novel furaltadone electrochemical sensor with high sensitivity was fabricated. The linear detection range was from 50 nM to 5 μM with sensitivity of 110.40 μA^-1 μM^-1 cm^-2 and detection limit of 12 nM. This work demonstrated chemical etching strategy is truly a facile and effective way to modify the electrochemical sensing performance of MOFs-based materials, and we believed the chemically etched MOFs materials will play a stronger role in terms of food safety and environmental conservation.

Horseradish Peroxidase-Coupled Ag3 PO4 /BiVO4 Photoanode for Biophotoelectrocatalytic Degradation of Organic Contaminants

Photoelectrocatalysis (PEC) is regarded as a promising and sustainable process for removal of organic contaminants from wastewater. Meanwhile, enzymatic catalysis also provides an effective way to carry out polluted environment remediation under mild conditions. In this study, a biophotoelectrocatalytic (BPEC) system is designed to remove 4-nitrophenol (4-NP) based on a combination of PEC and enzymatic catalysis. The developed BPEC system is constructed with a Ag₃ PO₄ /BiVO₄ photoanode and a horseradish peroxidase (HRP)-loaded carbon cloth (CC) cathode. On the photoanode, the construction of a direct Z-scheme Ag₃ PO₄ /BiVO₄ heterojunction enhanced the separation efficiency of photogenerated carriers, which promoted the PEC degradation of 4-NP under visible light irradiation. After HRP was immobilized on the cathode, the degradation efficiency of 4-NP reached 97.1 % after 60 min PEC treatment. The result could be ascribed to the HRP-catalyzed oxidation reaction via in situ-generated H₂ O₂ from the CC cathode during the PEC process. Moreover, the possible degradation pathways of 4-NP in such a BPEC system are also discussed.

Cobalt and nitrogen co-doped monolithic carbon foam for ultrafast degradation of emerging organic pollutants via peroxymonosulfate activation

Cobalt-based catalysts are expected as one of the most promising peroxymonosulfate (PMS) activators for the removal of organic pollutants from industrial wastewater. However, the easy agglomeration, difficult separation, and secondary pollution of cobalt ions limit their practical application. In this study, a novel, highly efficient, reusable cobalt and nitrogen co-doped monolithic carbon foam (Co-N-CMF) was utilized to activate PMS for ultrafast pollutant degradation. Co-N-CMF (0.2 g/L) showed ultrafast catalytic kinetics and higher total organic carbon (TOC) removal efficiency. Bisphenol A, ciprofloxacin, 2,4-dichlorophenoxyacetic acid, and 2,4-dichlorophenol could be completely degraded after 2, 4, 5, and 5 min, and the TOC removal efficiencies were 77.4 %, 68.9 %, 72.8 %, and 79.8 %, respectively, corresponding to the above pollution. The sulfate radical (SO4•-) was the main reactive oxygen species in Co-N-CMF/PMS based on electron paramagnetic resonance. The ecological structure-activity relationship program analysis via the quantitative structure activity relationship analysis and phytotoxicity assessment revealed that the Co-N-CMF/PMS system demonstrates good ecological safety and ecological compatibility. The Co-N-CMF catalyst has good catalytic activity and facile recycling, which provides a fine method with excellent PMS activation capacity for 2,4-dichlorophenol elimination from simulated industrial wastewater. This study provides new insights into the development of monolithic catalysts for ultrafast wastewater treatment via PMS activation.

MnOx@N-doped carbon nanosheets derived from Mn-MOFs and g-C3N4 for peroxymonosulfate activation: Electron-rich Mn center induced by N doping

The fabrication of metal-carbon hybrids with heteroatom doping from manganese-metal organic frameworks (MOFs) has rarely been reported for peroxymonosulfate (PMS) activation. In this work, novel MnO_x@N-doped carbon (MnO_x@NC) nanosheets were prepared using 2D manganese-1,4 benzenedicarboxylic acid-based MOFs (Mn-MOFs) and different proportions of graphitic carbon nitride (g-C₃N₄, additional N source and carbon source) to activate PMS for sulfamethoxazole (SMX) removal. The polarization difference induced by Mn-N coordination during the carbonization process made C an electron-poor center and Mn an electron-rich center, thus providing more Mn(II) for PMS activation. Benefiting from the highest Mn(II) content, the most uniform and exposed MnO_x active sites, abundant N active species and rich defective sites, MnO_x@NC-20 showed excellent degradation (72.9% within 5 min) and mineralization performance (47.40% within 60 min) for SMX. Nonradical and radical processes worked together in MnO_x@NC-20/PMS/SMX system, where singlet oxygen (¹O₂) dominated the degradation of SMX. N-doped carbon not only exhibited dragging and protection effects on MnO_x, but also provided adsorption sites for PMS and pollutants, thus reducing their migration distance. Moreover, the electrons of organic substrates could be captured by the electron-poor carbon layer and then transported to the electron-rich Mn center, thus improving the utilization efficiency of PMS and the redox of Mn. This study provides a facile optimization method to prepare MOFs-derived carbon catalysts with improved stability and catalytic performance.

Electrospinning of ZIF-67 Derived Co-C-N Composite Efficiently Activating Peroxymonosulfate to Degrade Dimethyl Phthalate

In this work, an efficient cage-core peroxymonosulfate (PMS) catalyst was synthesized by applying an electrospinning–calcination process to the cobalt–zeolitic imidazole framework (ZIF-67) crystals for the catalytic degradation of dimethyl phthalate (DMP). The morphology and surface properties of the synthesized materials (ZIF-67, Z600 and ZP400/600/800) were well characterized. ZP600 showed great performance for the catalytic degradation of DMP in the initial pH range of 7.5–10.5. The removal rate of DMP could reach 90.4% in 60 min under optimum dosages of reagents (catalyst = 0.1 g/L, PMS = 0.5 mM, DMP = 6 ppm), and the mineralization degree of contaminant could reach 65%. By quenching experiments, it was determined that sulfate radical (SO4−·) and hydroxyl radical (·OH) dominated the degradation process. Moreover, due to the good magnetism, ZP600 could be easily separated from liquid and showed great reusability in five-cycle reaction experiments. Surprisingly, with the cover of cage-like polyacrylonitrile (PAN) fibers, the cobalt leaching amount of ZP600 decreased by about 87%. This study would expand the application of the electrospinning process in the development of functional materials for water purification.

Fe-zeolite catalyst for ozonation of pulp and paper wastewater for sustainable water resources

The pulp and paper industry consumes enormous quality of freshwater, leading to wastewater. It must be treated to remove pollutants, particularly residual dyestuffs, before releasing them to water bodies to avoid adverse environmental effects. The traditional wastewater treatment methods used for the pulp and paper industry are less efficient in colour and chemical oxygen demand (COD) removal. The current study is aimed at developing a novel catalyst for the catalytic ozonation of pulp and paper wastewater with better colour and COD removal for sustainable resources of clean water. The proposed catalyst is impregnated by iron on natural zeolites. Various parameters such as catalyst dose, pH, ozone dose, initial COD concentration, and reaction time are studied and optimized. The performance was evaluated by comparing the results with the single ozonation process (SOP) and catalytic ozonation process (COP). The highest COD and colour reduction efficiencies have been achieved, i.e., 71%, and 88% at a natural pH of 6.8. The proposed process achieved higher COD and colour efficiencies than the single ozonation process and catalytic ozonation process using raw zeolites. The improvement in efficiencies are 23% and 29% for SOP and 17% and 19% for COP, respectively. Hence, the results proposed the sustainability and applicability of COP to treat paper and pulp sector effluent.

Facile construction of high-performance 3D Co2C-doped CoAl2O4 fiber composites for capturing and decomposing tetracycline from aqueous solution

Herein, novel 3D hollow-carved Co₂C-doped CoAl₂O₄ fiber composites (3D-CA-FC) were successfully synthesized via a simple-green pyrolysis method and exhibited remarkably outstanding elimination performance for tetracycline (TC) by adsorption and degradation. The results indicated that the TC adsorption process of the samples could be accurately described by the pseudo-second-order and Langmuir isothermal model, and the maximum TC uptake reached up to 1889.63 mg/g under neutral conditions. Meanwhile, 3D-CA-FC showed good affinity for TC and its adsorption capacity was greatly promoted due to the presence of humic acid, CO₃^2- ion and weakly alkaline environment. About complete degradation of TC could be completed within 60 min under suitable conditions. A significant improvement of catalyst rate was observed after the addition of CO₃^2- ion, because of the selective degradation of CO₃^•- to TC. BET, XPS and FT-IR analysis indicated that the mechanisms of TC uptake can be ascribed to pore-filling, H-bonds and complexation. Radical trapping experiments showed that ¹O₂ should serve as predominant contributions, and SO₄^•- and •OH also played a role in the degradation process. This study provides some inspiration for the construction of 3D-CA-FC as a novel and promising bifunctional material for the elimination of contaminants in water treatment.