Non-free Radical Research Articles

Ciprofloxacin degradation over Co3O4 catalysts by the microwave-assisted persulfate oxidation: a critical role of coordination composition

The combination of catalysts and microwave (MW) effects presents an emerging approach for persulfate (PS) activation, while the effect of active sites of catalysts on the synergistic reaction remains poorly understood. Here, we regulated the coordination composition of Co3O4 by strategically controlling the oxygen atmosphere during fabrication. We found that Co3+ and Co2+ acted as reactive centers for microwave absorption and catalytic activation of persulfate, respectively. By altering the ratio between Co3+ and Co2+, we explored the Co3O4 (2.23)-550 catalysts with significantly improved synergistic activity for degrading ciprofloxacin (CIP), which was 33.0 and 26.8 times higher than PS- Co3O4 (2.23)-550 (without microwave) and MW- Co3O4 (2.23)-550 (without persulfate), respectively. Meanwhile, Co3O4 (2.23)-550 catalyst (0.5mgL-1) showed the highest degradation rate of CIP 92.6% (0.5mgL-1) within 10min under microwave. According to the radical identification and intermediate analysis, the efficient degradation of CIP was ascribed to both free radical and non-free radical pathways. Thus, this work raises new insights into the structure-activity relationship of catalysts, and provides an efficient way to eliminate antibiotics via synergistic catalysis.

Boosting H2O2 activation by Cu and Ce co-doped g-C3N4 for pollutants removal: From the free radical pathway to the non-free radical pathway

Recently, materials synthesized by combining graphitic carbon nitride (g-C3N4) and metallic material have caught a lot of attention because of their high catalytic activity. In this paper, a novel g-C3N4 catalyst doped with Cu and Ce (labeled as CuCe-CN) is presented. CuCe-CN can effectively activate H2O2 to degrade tetracycline hydrochloride (TC-HCl) and cause TC-HCl to be completely degraded within one hour. The presence of CeO2 in catalyst provides the redox electron pairs of Ce(IV) and Ce(Ⅲ), and also facilitates the generation of 1O2 during the experimental process. By comparing the main active substances of CuCe-CN and Cu-CN, the fact that the doping of Ce changes the degradation pathway from free radical pathway to non-free radical pathway can be found. It can be demonstrated by electrochemical tests that the doping of Ce promotes the electron transfer in CuCe-CN, which can benefit the generation of reactive oxidation species (ROS), especially 1O2. CuCe-CN/H2O2 system has a good adaptability to the changes of environment. The catalytic performance of CuCe-CN does not be negatively affected by inorganic salt ions, and maintains high activity in natural aqueous environments. In this research, a new method for optimizing the activation behavior of g-C3N4 and a new non-free radical degradation method of TC-HCl were provided.

Improvement of sludge dewatering performance by persulfate advanced oxidation combined with LDH: Synergistic effect of free radical and non-free radical and reuse of deep-dewatered sludge cake

The high-water content of sludge in wastewater plant will influence the transportation and utilization. In this study, a new method for improving sludge dewatering by pyrite (FeS2) activated persulfate (PMS) combined with layered double hydroxide (LDH) was proposed. After conditioning, the water content (Wc) and specific resistance (SRF) of sludge decreased from 97.12 % and 1.83 × 1013 m/kg to 71.39 % and 1.84 × 1012 m/kg, severally. SEM and particle size analysis showed the system could destroy sludge cells effectively.The mechanism analysis of protein and polysaccharide content, 3D-EEM, FTIR, XPS results showed that FeS2/PMS-LDH combined system was beneficial to break down the sludge extracellular polymer (EPS), transform and accumulate the organic matter into the EPS outer layer, release the bound water. Both free radical and non-free radical play a role in oxidation, and they cooperate to break EPS. The effective phosphate adsorption performance of the biochar adsorbent prepared from dehydrated sludge cake was also investigated. The adsorption behavior of phosphate on biochar from dewatered sludge cake belongs to uniform chemical monolayer adsorption. When T = 298k, PH = 5, the maximum adsorption capacity is 20.255 mg/g. The introduction of LDH is helpful to enhance the sludge dewatering and the adsorption of phosphate. To sum up, the combined conditioning method considers the effectiveness of sludge dewatering and the feasibility of sludge cake disposal and utilization.

Iron-based nitrogen-rich metal-organic framework structure for activation of hydrogen peroxide and peroxymonosulfate for ultra-efficient tetracycline degradation

Fe-based metal–organic frameworks (Fe-MOFs) have been used to catalyze the degradation of organic pollutants; however, the underlying mechanism remains unclear. In this study, we prepared Fe-MOF catalysts featuring a three-dimensional ordered structure and active Fe-N4 coordination centers using self-designed polypyrazole compounds as ligands. Because the coordination centers are similar to the classical single-atom Fe-N4 active neutral structure, Fe-MOFs exhibit excellent performance in activating hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) for the degradation of antibiotics. Moreover, the two adjacent nitrogen atoms in pyrazole strengthen the interaction with active neutral Fe, thereby enhancing the efficiency and selectivity of the catalytic sites. In the presence Fe-MOF/H2O2, a free radical process involving hydroxyl radicals (OH) is activated to achieve a degradation rate of 98.36 % for tetracycline (TC) within 10 min. In a Fe-MOF/PMS system, 97.01 % of TC can be degraded within 10 min through a non-free radical process with singlet oxygen (1O2) as the primary active species. The high degradation efficiency of Fe-MOF is primarily attributed to its highly catalytically active structure, which exerts a van der Waals force effect on the pollutants, thereby facilitating electron transfer between the pollutants and active centers. This shortens the distance between the pollutants and Fe catalytic center, enhances electron transfer, and promotes the chemical adsorption of H2O2 and PMS to form FeN4-H2O2 and FeN4-PMS, respectively. Additionally, the strong coordination within the Fe-N4 pyrazole structure significantly suppresses Fe leaching, facilitating a stable adsorption configuration.

Effect of chloride ions on the reactive species change pathway and removal performance in the MW/Co2+/PMS process

Efficient removal of refractory organic matter is the focus of research in the treatment of actual wastewater with Peroxymonosulfate-based advanced oxidation processes(PMS-AOPs). However, the high concentration of chloride ions (Cl−) ubiquitously present in wastewater changes the reactive species (RS) present in the process, and the mechanism of this change is still not clear. This study investigated the effects of Cl− on the transformation behavior of RS and treatment performance under microwave (MW) combined with cobalt ions (Co2+)-activated PMS. The results showed that increasing the Cl− concentration can enhance the removal performance of the MW/Co2+/PMS process for ammonia (NH4+-N), accompanied by the production of nitrate nitrogen (NO3-N), monochloramine (NH2Cl) and dichloramine (NHCl2), which was related to the transformation of existing reactive oxygen species (ROS, •OH and SO4•−) into reactive chlorine species (RCS), with hypochlorous acid (HClO) as an important intermediate. Cl− can generate HClO through free radical oxidation (•OH and SO4•−) dominance and non-free radical oxidation (PMS and Co3+) promotion, and the heat transferred by MW can further trigger conversion between HClO and PMS, thereby changing the distribution of RS. Increasing the dosage of PMS and the dosage of Co2+ promoted the transformation of Cl− to reactive species in the MW/Co2+/PMS process. At MW power=160 W, [Co2+]=17.5 μM,[PMS]=10 mM, and [Cl−]=17 mM, the maximum cumulative [HClO] reached 1910.97 μM, and the decay rate was 0.1815 min−1.The macromolecular organic matter in aqueous environment competes with ammonia for the RCS. Through regulating [Cl−] in mature leachate, RCS has a certain oxidation effect to organic matter, but its limited oxidation ability leads to a decrease in the mineralization effect.

Activation of persulfate by MOF-derived MnFeOx to efficiently degrade sulfadiazine: Synergistic effects from free radicals and singlet oxygen

In this study, a facile hydrothermal approach was used to synthesize the MOFs materials [Mn-doped MIL-101(Fe)]. These materials were subsequently subjected to high temperature annealing process via calcination to generate the MOFs derivatives (MnFeOx). The synthesized materials were utilized for the removal of sulfadiazine (SDZ) removal through activated peroxymonosulfate (PMS). At the optimum Mn doping, the removal ratio of SDZ could reach 98.9 % (at natural pH) within 20 min. In addition, the study investigated the influence of PMS dosage, catalyst dosage, initial pH, various inorganic anions, and humic acid (HA) on the degradation of SDZ. The activation processes of both free and non-free radicals in the MnFeOx/PMS system were examined by free radical quenching experiments and electron paramagnetic resonance (EPR) techniques. The analysis of the degradation products of SDZ was conducted by using high performance liquid chromatography-mass spectrometry (HPLC-MS), and the breakdown pathways of SDZ in the MnFeOx/PMS system were proposed.

Co-N3 site activated peroxymonosulfate for rapid degradation of ciprofloxacin: Synergistic effect of free radicals and nonfree radicals

Nitrogen-doped metal-organic framework (MOFs)-derived carbon materials (denoted as Co-MOF-74@N-T-x) were successfully fabricated by calcinating Co-MOF-74, utilizing the green precursor of melamine. Among these materials, Co-MOF-74@N-500-2 demonstrated superior catalytic performance in activating peroxymonosulfate (PMS), achieving over 95 % degradation of ciprofloxacin (CIP) within 15 min, with a rate constant that was 1.25 times greater than that of Co-MOF-74-500. The primary active species identified in this study were sulfate radicals (SO4•−) and singlet oxygen (1O2), with the latter playing an important role in the degradation of CIP in the Co-MOF-74@N-500-2/PMS system. Theoretical calculations confirmed that the enhanced catalytic activity primarily stemmed from the Co-N3 configuration, which was more effective in activating PMS than the other configurations were. Co-MOF-74@N-500-2/PMS showed excellent performance in oxidizing CIP across a broad pH range (3.0–9.0) and demonstrated stability over five cycles, along with impressive degradation performance capabilities for a wide range of pollutants including metronidazole (MNZ), oxytetracycline (OTC), nitrofurantoin (FNT), methylene blue (MB), and acid orange (OG). This study presents a viable strategy for developing efficient and durable catalytic systems aimed at degrading organic pollutants via PMS.

Polymer tethering strategy modified ZIF67 derived cobalt-confined nanocage for norfloxacin degradation: Tailored reactive sites and beneficial local microenvironment

The refined state of reactive sites and their local microenvironment largely determined the reaction performance of catalyst. Herein, we constructed hollow cobalt-confined carbon nanocage (Co-NC@Co/C-x) with rich surface pyridinic N and more exposed tailored Co sites through cobalt-incorporated polymer tethering strategy modified ZIF67 and later thermal depolymerization. Such features facilitate rapid surface enrichment of contaminants, accelerated electron transfer and enhance the availability of unpaired electron oxygen of metallic cobalt, demonstrating exceptional efficiency in Norfloxacin degradation (NFX, 97.7 % within 20 min, kobs = 0.528 min−1) with a significantly lower activation energy of 6.39 KJ mol−1. Mechanistic investigations prove the promotive interplay of peroxymonosulfate with reactive sites and elucidate the dominant role of non-free radicals 1O2 for NFX degradation. The theoretical calculation showcases that unpaired-electron surface oxygen of metallic cobalt induces the impurity cleavage of the O-O bond, triggering the promotive generation of 1O2. Co-NC@Co/C-6 samples exhibit robust NFX degradation across different aqueous matrices, demonstrating cyclic stability and universal degradation performance against various pollutants, and flowing degradation experiments and immobilized recyclable monolith fiber-like bobbles experiments further underline the green recovery and practical potential in wastewater treatment.

Heterogeneous Activation of Persulfate by Petal-Shaped Co3O4@BiOI to Degrade Bisphenol AF

In catalytic tests, the results have shown that almost all the BPAF was removed within 30 min when the dosage of Co3O4@BiOI and sodium persulfate (PS) was 0.15 g and 0.1 mM, respectively. Acid conditions inhibited BPAF degradation, but the inclusion of a precise concentration of bicarbonate ions (HCO3−) promoted degradation. The presence of chloride (Cl−), sulfate ions (SO42−), and a high concentration of HCO3− inhibited the degradation process, whereas the addition of nitrate ions (NO3−) had a minor effect on the catalytic process. The presence of free radicals (sulfate (SO4•−), hydroxyl (•OH), and superoxide (O2•−)) and the non-free radical singlet oxygen (1O2) in the Co3O4@BiOI/PS system was determined by electron paramagnetic resonance (EPR) and quenching tests. We propose that the Co(II)/Co(III) and Bi(III)/Bi(V) redox pairs simultaneously activate PS where the Co3O4 and BiOI components work synergistically to promote the rapid oxidative degradation of BPAF in water.

Construction of a multiple reactive species-mediated Co9S8/NBC-PMS Fenton-like system for tetracycline degradation with broadened adaptability to water background

A Fenton-like system based on peroxymonosulfate (PMS) oxidant has high potential for antibiotic degradation, However, various complex water background factors, including pH, coexisting ions, and dissolved organic matter, can adversely affect degradation efficiency. This work constructed a PMS oxidative Fenton-like system activated by cobalt polysulfide/N-doped biochar composite (Co9S8/NBC) for the degradation of tetracycline (TC) and achieving approximately 99 % removal of TC. Furthermore, the removal efficiency was maintained above 90 % across a broad pH range (3−11), in the presence of various coexisting anions (Cl−, NO3− and CO32−), even at high concentrations of humic acid. The characterization of Co9S8/NBC through various techniques confirmed that Co9S8 nanoparticles were uniformly loaded within the porous NBC structure. Electron paramagnetic resonance and reactive oxygen species (ROSs) quenching experiment revealed that the effectiveness of TC degradation in the Co9S8/NBC/NBC-PMS system arises from the cooperation of radical and non-radical species rather than the single mechanism. Moreover, the analysis of the contribution ratios of ROSs to TC degradation indicates that the contribution of non-free radicals exceeds that of free radicals, and it is capable of adapting to changes in pH. The characterization of the post-reaction catalyst suggested that Co9S8 and NBC synergistically participated in the activation of PMS. Moreover, the practical examination proved that the disabled Co9S8/NBC catalyst can recover the catalytic activity via a reheat treatment, the leaching concentration of Co ions was lower than the emission limit of China. The river water and lake water as the matrix water have little negative impact on the degradation of TC. The Co9S8/NBC-PMS system is expected to provide a practical pathway for the treatment of antibiotic wastewater.

Cerium-regulated Mg3FeO4@biochar activated persulfate to enhance degradation of aqueous tetracycline: The dominant role of cerium

The role of cerium (Ce) in Ce-regulated Mg3FeO4@biochar (CMF@BC) and the mechanism by which CMF@BC activates persulfate (PS) remain unclear. In this work, a novel CMF@BC was synthesized through the simple impregnation–pyrolysis process and utilized as a PS activator for the removal of aqueous tetracycline (TC). Under the optimal degradation conditions, the removal efficiency and mineralization rate of TC reached 92.7 % and 84.2 % within 60 min, respectively, the corresponding rate constant was 0.0487 min−1. The CMF@BC catalyst exhibited extremely high stability and excellent reusability after five cycles. The characterization results identified Fe2+ and oxygen vacancies as major catalytic sites. The Ce dopant inhibited the aggregation of metal ions of Mg3FeO4 during the high-temperature pyrolysis process and the Ce3+/Ce4+ redox cycle promoted Fe2+ regeneration, thus improving the catalyst performance. The degradation process was dominated by non-free radical (1O2) pathways. The possible TC-removal pathway was inferred from liquid chromatography–mass spectrometry results and density functional theory calculations. The toxicity of the degradation products was also evaluated. The CMF@BC catalyst displayed excellent catalytic performance and recyclability, wide pH adaptability, and a low ion-leaching rate, confirming its broad application prospects as a PS activator in antibiotic wastewater treatment.

Structural design of hierarchical porous biomass carbon with a built-in electric field for efficient peroxymonosulfate activation

Biomass-derived carbon materials have excellent adsorption capacity and cost-effectiveness, and the electron interactions between multiphase composite materials improve the efficiency of water pollutant removal by advanced oxidation processes (AOPs). Herein, a multistage biochar catalyst in which metallic cobalt-embedded carbon tubes are prepared uniformly on the surface of kapok tubes is designed and fabricated. The closely connected structure grown in situ accelerates electron migration and forms a directional transfer electric field. The N-doped carbon nanotube encapsulated Co nanoparticles growth on the kapok biochar/PMS (Co-N-KBC/PMS) system removes tetracycline hydrochloride (TCH) at a rate 11.8 times higher than that of KBC/PMS. Free radicals (SO4•−, •OH, and •O2–) and non-free radicals (1O2) are generated in conjunction with electron transfer during PMS activation. The cobalt sites and C=O groups are possible active sites. Density-functional theory (DFT) calculations verify the built-in electric field from N-KBC to the Co surface, which accelerates electron transfer and improves TCH removal. The results reveal an effective strategy to activate PMS and address environmental remediation by utilizing carbon materials derived from biomass.

Boron nitride quantum dots supported hollow NH2-MIL-125 drive photo-Fenton-PMS system for photocatalytic tetracycline degradation: Contribution of tannic acid etching

NH2-MIL-125(Ti) materials had great potential for photocatalytic applications but had low activity due to exciton effect and narrow absorption range of visible light. The surface oxygen-containing negative functional groups of boron nitride quantum dots (BNQDs) could overcome these defects, but due to the low load capacity, a higher specific surface area of the substrate was usually required. In this paper, a hollow Ti-MOF material was developed by etching technology. The hollow structure formed by tannic acid etching broadened the absorption range of visable light and provided more alternative surfaces for loading BNQDs. The 85.2% of high tetracycline (TC) removal efficiency for the best sample (BNQDs-5@20-Ti-MOF + PMS) was obtained, which was about 56.8 and 1.9 times of the 20-Ti-MOF and BNQDs-5@20-Ti-MOF, respectively. BNQDs-5@20-Ti-MOF + PMS system showed a great TC degradation efficiency in a wide pH range (pH = 5–9). In addition, reaction temperature and the inorganic ions did not show significant inhibition effect for TC removal. Both free radical and non-free radical pathways were involved in the TC degration by BNQDs-5@20-Ti-MOF + PMS system, among which O2•− and 1O2 played the key roles. Interestingly, multiple 1O2 production paths contributed to the high efficiency and stability of BNQDs-5@20-Ti-MOF + PMS system. This study revealed a reasonable combination of Ti-MOF and BNQDs, which provided a new efficient photocatalyst for environmental remediation.

Efficient degradation of tetracycline by cobalt ferrite modified alkaline solution nanofibrous Ti3C2Tx MXene activated peroxymonosulfate system: Mechanism analysis and pathway

Magnetic CoFe2O4 nanoparticles have received considerable attention as an activator for peroxymonosulfate (PMS) in the degradation of tetracycline. However, it is still challenging to construct CoFe2O4 composites with good dispersion and highly exposed reactive sites. Herein, the KOH fiber-functionalized MXene matrix decorated by cobalt ferrite nanoparticles (denoted as CoFe2O4@Alk-MXene) was developed by electrostatic self-assembly method. The layered fibrotic structure effectively disperses and fixes cobalt ferrite nanoparticles, increasing the exposure of reactive sites. The as-prepared CoFe2O4@Alk-MXene material exhibited rapid removal of 100% tetracycline hydrochloride (TC-HCl) within 10 minutes by activating PMS, leveraging the excellent conductivity of alkalized MXene and the efficient activation of transition metal atoms. The experimental and theoretical analysis revealed that the electron transfer process of Ti2+/Ti4+, Co2+/Co3+ and Fe3+/Fe2+, as well as the free radical and non-free radical attack behaviors produced by the adsorption of PMS by the composite, are the primary mechanisms for achieving rapid removal of pollutants. A comprehensive degradation mechanism and potential pathways were proposed based on these findings. Overall, CoFe2O4@Alk-MXene/PMS emerges as a promising catalytic system for TC removal.

Removal of levofloxacin by H2O2 and PMS co-activation by sulfide-supported oxalate zero-valent iron enhanced with simultaneous catalysis of SO4-• and 1O2: Major free radicals, synergistic effects and mechanism exploration

It is reported in the literature that sulfide and oxalate are promising ways to modify zero-valent iron (ZVI) for the degradation of antibiotics, but the synergistic activation mechanism of H2O2 and PMS is still unclear. In order to explore this effect, a new type of oxalated and sulfided ZVI (OA-S-ZVI) was synthesized in this study, and levofloxacin (LEV) was degraded in H2O2, PMS and H2O2/PMS systems. The batch experiments confirmed that the removal ability of OA-S-ZVI/H2O2/PMS was 1.65–10 times that of other systems. This result was achieved by modifying ZVI surface catalytic sites and cooperating with H2O2/PMS. At the same time, the synergistic factor S (1.74) confirmed that the composite system H2O2/PMS can capture electrons from the catalyst Fe0 to Fe2+ and adsorb active sites of the catalyst, such as ≡Fe-C2O4-, ≡Fe-OH/OOH and ≡Fe-S. Further calculation and analysis revealed that the binding energy of singlet oxygen (1O2) and sulfate radical (SO4-•) in the composite system decreased and multiple molecular orbitals participated in the removal process. The characterization experiments and EPR experiments explained the transfer free radicals to non-free radicals from a single system to a composite system. This study provides a new perspective on modifying ZVI and utilizing multi-system synergy to effectively remove organic micropollutants from water.

Enhanced adsorption of tylosin by ordered multistage porous carbon and efficient in-situ regeneration of saturated adsorbents by activated persulfate oxidation: Performance, mechanism and multiple cycles

In this study, a novel ordered multistage porous carbon (OMPC) with a micro-mesoporous structure was prepared and used for the removal of tylosin (TYL). The porous material, carbonized at 900 °C (OMPC-900), exhibited micro-mesoporous structures with pore sizes of 0.71 nm and 3.63 nm, while had a specific surface area of 1300.02 m2 g−1. OMPC-900 demonstrated a maximum adsorption capacity of 341.28 mg g−1 for TYL in water by electrostatic attraction, hydrogen bonding, π-π interactions, and pore-filling mechanisms, which is 6.41 times higher than that of activated carbon. The TYL-saturated adsorbents could be efficiently regenerated by in-situ oxidation through the activation of persulfate (PDS), achieving a regeneration rate of 94.17%, significantly higher than that of activated carbon (55.22%). The excellent regeneration performance may be attributed to the presence of -C=O and graphitic carbon in the adsorbent, which promotes the production of free radicals (•OH, SO4•- and •O2−) and non-free radicals. Among these, the non-radical pathways (1O2 and electron transfer) played a key role in the degradation of TYL loaded on the adsorbent. OMPC-900 maintained stable regenerative adsorption performance of 80.85% after five in-situ regeneration, and the normalized adsorption capacity per unit surface area increased from 0.21 to 0.39 mg m−2, which may be due to that the increase in oxygen-carbon ratio and surface defects improved the adsorption sites activity of the regenerated adsorbent. In comparison to conventional pyrolysis and organic solvent elution, oxidative regeneration through the activation of PDS is a more efficient and sustainable method.

Visible light activation of persulfate by α-Fe2O3/PDINH photocatalyst for sulfamethoxazole degradation

Self-made α-Fe2O3 and commercially perylene diimide (PDINH) were selected to prepare α-Fe2O3/PDINH composite photocatalysts (FPx, where x represents the mass percentage of PDINH), and these were utilized for the activation of peroxydisulfate (PDS) to degrade sulfamethoxazole (SMX) in water under visible light. The FP3/PDS/vis system was able to remove about 98.9 % of SMX in 140 min, and the corresponding reaction rate reached 0.0327 min−1, for 23.4 and 18.2 times greater than α-Fe2O3/PDS/vis system and the PDINH/PDS/vis system, respectively. PDS played a major role in SMX degrading and both free radical (SO4−, OH, O2−) and non-free radical (1O2, h+) were involved in the removal of SMX. Interestingly, with the exception of h+, all radicals and non-radicals were directly or indirectly derived from PDS activation rather than photocatalysis. Besides, 3 degradation pathways and 13 by-products of SMX were identified, and the toxicity analyses of the intermediates demonstrated that the FPx/PDS/vis system could effectively remove SMX from water and reduce its biotoxicity. This work offers insights into the photocatalytic activation of PDS for removing SMX from water.

Visible light-assisted activation of peroxymonosulfate for naproxen degradation with biochar-based catalysts: Sandwich structure construction and synergy of free and non-free radicals

Visible light-assisted activation of peroxymonosulfate for naproxen degradation with biochar-based catalysts: Sandwich structure construction and synergy of free and non-free radicals

Carbon quantum dots assemblies integrated with spatial confined Co nanoparticles for antibiotic degradation via peroxymonosulfate activation

Heterogeneous Co-based materials are well-known for their exceptional catalytic properties in activating peroxymonosulfate (PMS) for the degradation of antibiotic pollutants. However, the potential applications of these materials are often hindered by significant Co nanoparticle aggregation and ion leaching. In this study, a carbon quantum dot-mediated self-assembly strategy was used to fabricate three-dimensional porous sponge-like Co@CDs-x (x represents the calcination tempeatures) catalysts with spatially confined Co nanoparticles. Among the samples, Co@CDs-900 exhibited a remarkable 97.8 % removal efficiency of TC in 11 minutes, with an apparent rate constant of 0.313 min−1. The exceptional performance of Co@CDs-900/PMS can be attributed to its large specific surface area, unique porosity, and abundant catalytically active sites, which generate ample reactive oxygen species for TC degradation. The catalyst demonstrated good degradation capabilities across a wide pH range of 3–11 and various organic pollutants such as tetranitrophenol, oxytetracycline, ciprofloxacin, methyl orange, and rhodamine B. Moreover, Co@CDs-900 maintained high activity even after the 5th cycle due to its magnetic property and spatial confinement effect, preventing catalyst loss and ion leaching during recycling tests. The degradation mechanism involved both free-radical and non-free radical pathways, with SO4•− and 1O2 identified as the primary reactive oxygen species. The degradation intermediates of TC were identified and a plausible degradation pathway was proposed. Toxicity assessment revealed that the Co@CDs-900/PMS system effectively reduced the toxicity of TC post-degradation. This study presents an effective approach for developing sponge-like CDs assemblies with spatially confined metal nanoparticles for activating PMS in antibiotic degradation.

Design and synthesis of in situ self-assembled PDI/Bi2MoO6 complexes: Promoting singlet oxygen selective generation and visible light photocatalytic purification performance

Solar-driven photocatalytic degradation of antibiotics has emerged as an eco-friendly approach to treating wastewater. And singlet oxygen is a selective and highly active reactive oxygen species. Bi2MoO6 microsphere photocatalyst modified by narrow band gap PDI organic supramolecular was prepared by water bath heating method to achieve the selective generation of non-free radical. It focused on the effects of different acid-induced assembled and different light sources on the photocatalytic performance of PDI/Bi2MoO6 (PDI/BMO) photocatalysts and explored their ability to remove various pollutants. The results showed that PDI/BMO composites self-assembled with nitric acid (1% PMN) could effectively purify a variety of pollutants under visible light irradiation, including CIP, TC, LVF and AO7. In addition, 1% PMN showed excellent photocatalytic performance in actual water, and even have fair degradation efficiency under red light irradiation. Holes and singlet oxygen were confirmed to be the main reactive oxygen species during CIP degradation by capture experiments and EPR, and the steady-state concentration of singlet oxygen was quantified. Three degradation pathways of CIP under the action of non-radicals were clarified, and the biotoxicity of CIP treated products was evaluated by bacteriostatic experiments. This work could provide an ecologically friendly method for wastewater treatment.