Efficient degradation of lomefloxacin by Co-Cu-LDH activating peroxymonosulfate process: Optimization, dynamics, degradation pathway and mechanism

Fabrication of a novel nanofiltration membrane using an Mg-Fe layered double hydroxide for dye/salt separation

Mg-Fe layered hydroxide (LDH) was synthesized by the double titration method and added to trimesoyl chloride (TMC) to prepare an Mg-Fe LDH-modified polyamide nanofiltration (NF) membrane by interfacial polymerization (IP). Compared to the pure polyamide NF membrane, the Mg-Fe LDH-modified membrane presented a wrinkled structure and a comparatively smooth surface. Additionally, the permeation flux and rejection rate of the modified NF membrane for 1000 mg L-1 Na2SO4 solution were 61.7 L m-2 h-1 and 95.9%, respectively. When the Mg-Fe LDH modified NF membrane was used to separate dye/NaCl mixed solutions, the rejection of NaCl was less than 17% and the rejection rate of Coomassie Brilliant Blue (CBB) molecules was close to 100%. At the same time, the concentration of CBB increased from 500 mg L-1 to 1151 mg L-1 which means that the LDH modified NF membrane could separate CBB/NaCl effectively and could concentrate CBB at the same time.

Ranitidine degradation in layered double hydroxide activated peroxymonosulfate system: impact of transition metal composition and reaction mechanisms

Ranitidine, a competitive inhibitor of histamine H2 receptors, has been identified as an emerging micropollutant in water and wastewater, raising concerns about its potential impact on the environment and human health. This study aims to address this issue by developing an effective removal strategy using two types of layered double hydroxide (LDH) catalysts (i.e., CoFeLDH and CoCuLDH). Characterization results show that CoFeLDH catalyst has superior catalytic properties due to its stronger chemical bond compared to CoCuLDH. The degradation experiment shows that 100% degradation of ranitidine could be achieved within 20 min using 25 mg/L of CoFeLDH and 20 mg/L of peroxymonosulfate (PMS). On the other hand, CoCuLDH was less effective, achieving only 70% degradation after 60 min at a similar dosage. The degradation rate constant of CoFeLDH was 10 times higher than the rate constant of CoCuLDH at different pH range. Positive zeta potential of CoFeLDH made it superior over CoCuLDH regarding catalytic oxidation of PMS. The catalytic degradation mechanism shows that sulfate radicals played a more dominant role than hydroxyl radicals in the case of LDH catalysts. Also, CoFeLDH demonstrated a stronger radical pathway than CoCuLDH. XPS analysis of CoFeLDH revealed the cation percentages at different phases and proved the claim of being reusable even after 8 cycles. Overall, the findings suggest that CoFeLDH/PMS system proves to be a suitable choice for attaining high degradation efficiency and good stability in the remediation of ranitidine in wastewater.

Reactive layered hydroxide membrane for advanced water treatment: Micropollutant degradation and antifouling potential

The effective removal of micropollutants by water treatment technologies remains a significant challenge. Herein, we develop a CoFe layered double hydroxide (CoFeLDH) catalytic membrane for peroxymonosulfate (PMS) activation to achieve efficient micropollutant removal with improved mass transfer rate and reaction kinetics. This study found that the CoFeLDH membrane/PMS system achieved an impressive above 98% degradation of the probe chemical ranitidine at 0.1 mM of PMS including five more micropollutants (Sulfamethoxazole, Ciprofloxacin, Carbamazepine, Acetaminophen and Bisphenol A) at satisfactory level (above 80%). Moreover, significant improvements in water flux and antifouling properties were observed, marking the membrane as a specific advancement in the removal of membrane fouling in water purification technology. The membrane demonstrated consistent degradation efficiency for several micropollutants and across a range of pH (4-9) as well as different anionic environments, thereby showing it suitability for scale-up application. The key role of reactive species such as SO4•-, and O2• - radicals in the degradation process was elucidated. This is followed by the confirmation of the occurrence of redox cycling between Co and Fe, and the presence of CoOH+ that promotes PMS activation. Over the ten cycles, the membrane could be operated with a flux recovery of up to 99.8% and maintained efficient performance over 24 h continuous operation. Finally, the efficiency in degrading micropollutants, coupled with reduced metal leaching, makes the CoFeLDH membrane as a promising technology for application in water treatment.

Porous-carbon/manganese composite catalyst transformed from waste biomass as peroxymonosulfate activator for carbamazepine degradation

Activation of peroxymonosulfate (PMS) with solid catalysts for organic pharmaceutical degradation still faces challenge due to the demand of inexpensive catalysts. In this study, manganese-oxidizing microalgae (MOM) and its associated biogenic manganese oxides (BMO) were employed to prepare biomass-transformed porous-carbon/manganese (B-PC/Mn) catalyst through high-temperature calcination (850 °C). Remarkably, 100 % of carbamazepine (CBZ) was degraded within 30 min in the B-PC/Mn/PMS system. The degradation kinetic constant was 0.1718 min-1, which was 44.0 times higher than that of the biomass-transformed porous carbon mixed with MnOx activated PMS system. 1O2 was generated in the B-PC/Mn/PMS system, which is responsible for CBZ degradation. The MOM-BMO-associated structure greatly increased the specific surface areas and the contents of the C = O and pyrrolic-N groups, which facilitated PMS activation. The structure also induced the generation of Mn5C2, which exhibited a strong adsorption towards PMS. This study provides a novel strategy for preparing catalysts by using waste biomass.

Pumpkin Leaf Extract Crop Waste as a New Degradable and Environmentally Friendly Corrosion Inhibitor

The pumpkin leaf was extracted by the decoction method, and it was used as an eco-friendly, nontoxic inhibitor of copper in 0.5 M H2SO4 corrosion media. To evaluate the composition and protective capacity of the pumpkin leaf extract, Fourier infrared spectroscopy, electrochemical testing, XPS, AFM, and SEM were employed. The results showed that the pumpkin leaf extract (PLE) is an effective cathode corrosion inhibitor, exhibiting exceptional protection for copper within a specific temperature range. The corrosion inhibition efficiency of the PLE against copper reached 89.98% when the concentration of the PLE reached 800 mg/L. Furthermore, when the temperature and soaking time increased, the corrosion protection efficiency of 800 mg/L PLE on copper consistently remained above 85%. Analysis of the morphology also indicated that the PLE possesses equally effective protection for copper at different temperatures. Furthermore, XPS analysis reveals that the PLE molecules are indeed adsorbed to form an adsorption film, which is consistent with Langmuir monolayer adsorption. Molecular dynamics simulations and quantum chemical calculations were conducted on the main components of the PLE.

A review of the degradation of antibiotic contaminants using advanced oxidation processes: modification and application of layered double hydroxides based materials

In recent years, the treatment of organic pollutants has become a global concern due to the threat to human health posed by emerging contaminants, especially antibiotic contamination. Advanced oxidation processes (AOPs) can solve the organic pollution problem well, which have been identified as a promising solution for the treatment of hard-to-handle organic compounds including antibiotic contaminants. Layered double hydroxides (LDHs) are excellent catalysts because of their flexible tunability, favorable thermal stability, abundant active sites, and facile exchangeability of intercalated anions. This paper conducted a systematic review of LDHs-based materials used for common antibiotic removal by three significant AOP technologies, such as photocatalysis, the Fenton-like processes, and peroxymonosulfate catalysis. The degradation effects studied in various studies were reviewed, and the mechanisms were discussed in detail based on the type of AOPs. Finally, the challenges and the application trends of AOPs that may arise were prospected. The aim of this study is to suggest ways to provide practical guidance for the screening and improvement of LDH materials and the rational selection of AOPs to achieve efficient antibiotic degradation. This could lead to the development of more efficient and environmentally friendly materials and processes for degrading antibiotics, with significant implications for our ecological conservation by addressing water pollution.

Satisfactory degradation of tetracycline by a pH-universal CoFe-LDH/MoS2 heterojunction catalyst in Fenton process

Fenton or Fenton-like reactions have been widely used in various fields, including solar energy conversion to generate hydroxyl radicals, environmental remediation, biology, and life science. However, the slow Fe3+/Fe2+ cycle and narrow applicable pH range still present significant challenges. Here, a heterostructured CoFe-layered double hydroxide/MoS2 nanocomposite (CoFe-LDH/MoS2) was prepared via simple electrostatic interactions. The heterostructure establishes a robust interfacial contact, leading to an abundance of exposed Mo6+ sites. Consequently, the developed CoFe-LDH/MoS2+H2O2 system exhibited superior performance in the degradation of tetracycline (>85%) within 60 min across a wide pH range from acidic to basic. Moreover, the CoFe-LDH/MoS2 heterojunction catalysts exhibited exceptional resistance to common anions and efficiently degraded various organic pollutants. The mechanism study verified that the CoFe-LDH/MoS2 had high efficiency in producing 1O2 and ‧OH to degrade various organic pollutants. The present study will serve as a foundation for creating efficient catalyst systems for related environmental remediation.

Domain-limited thermal transformation preparation of novel graphitized carbon-supported layered double oxides for efficient tetracycline degradation

The resource utilization of industrial lignin to construct high-performance catalysts for wastewater treatment field is pioneering research. Herein, the novel graphitized carbon-supported CuCoAl-layered double oxides (LDOs-GC) were successfully designed by the domain-limited thermal transformation technology using sodium lignosulfonate (LS) self-assembled CuCoAl-layered double hydroxides as the precursor. The optimized LDOs-GC catalyst owned the excellent tetracycline (TC) degradation of 98.0% within 15 min by activated peroxymonosulfate (PMS) under optimal conditions (20 mg/L catalyst, 1.5 mM PMS, 30 mg/L TC). The density of metal ions in the catalyst and the synergistic interaction between graphitized carbon (GC) and metal ions played a major role in TC degradation. Based on a comprehensive analysis, the TC degradation in LDOs-GC/PMS system was proved to be accomplished by a combination of free radicals (SO4·- and HO·) and non-radicals (1O2). Meanwhile, the possible degradation pathways of TC were proposed by the analysis of TC degradation intermediates and a comprehensive analysis of the rational reaction mechanism for TC degradation by LDOs-GC/PMS system was also performed. This work provides a new strategy for developing novel high-performance catalysts from industrial waste, while offering a green, cheap and sustainable approach to antibiotic degradation.

Peroxymonosulfate activation by CuMn-LDH for the degradation of bisphenol A: Effect, mechanism, and pathway

The remediation of water contaminated with bisphenol A (BPA) has gained significant attention. In this study, a hydrothermal composite activator of Cu3Mn-LDH containing coexisting phases of cupric nitrate (Cu(NO3)2) and manganous nitrate (Mn(NO3)2) was synthesized. Advanced oxidation processes were employed as an effective approach for BPA degradation, utilizing Cu3Mn-LDH as the catalyst to activate peroxymonosulfate (PMS). The synthesis of the Cu3Mn-LDH material was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). According to the characterization data and screening experiments, Cu3Mn-LDH was selected as the best experimental material. Cu3Mn-LDH exhibits remarkable catalytic ability with PMS, demonstrating good degradation efficiency of BPA under neutral and alkaline conditions. With a PMS dosage of 0.25 g·L-1 and Cu3Mn-LDH dosage of 0.10 g·L-1, 10 mg·L-1 BPA (approximately 17.5 μM) can be completely degraded within 40 min, of which the TOC removal reached 95%. The reactive oxygen species present in the reaction system were analyzed by quenching experiments and EPR. Results showed that sulfate free radicals (SO4•-), hydroxyl free radicals (•OH), superoxide free radicals (•O2-), and nonfree radical mono-oxygen were generated, while mono-oxygen played a key role in degrading BPA. Cu3Mn-LDH exhibits excellent reproducibility, as it can still completely degrade BPA even after four consecutive cycles. The degradation intermediates of BPA were detected by GCMS, and the possible degradation pathways were reasonably predicted. This experiment proposes a nonradical degradation mechanism for BPA and analyzes the degradation pathways. It provides a new perspective for the treatment of organic pollutants in water.

Study on the dominant mechanism of direct hole oxidation for the photodegradation of tetracycline

Antibiotic contamination has a significant negative impact on China, one of the largest producers and consumers of antibiotics worldwide. In this study, a three-dimensional flower-like structure of CoFe-LDHs was used to efficiently degrade tetracycline (TC) in a system triggered by peroxymonosulfate (PMS) and exposed to visible light. After exploring the effects of different metal ratios, catalyst dosage, initial TC concentrations, and pH, the optimal reaction conditions were determined. In comparison to pure CoFe-LDHs, the TC elimination rate was dramatically increased by the addition of the PMS. The strong environmental resistance, excellent stability and reusability, and universal flexibility were shown. The quenching experiments and electron spin resonance detection showed that the creation of reactive oxygen species was facilitated by the synergistic transmission of electrons between the active bimetallic components. Further, photogenerated holes was the dominant oxidizing species, which contributed more to the degradation of TC. The potential degradation pathways and intermediate toxicity of TC were suggested. This work offers a new method dominated by photogenerated holes for efficiently removing TC effluent.

Enhanced photo-Fenton-like performance of biotemplated manganese-doped cobalt silicate catalysts

Cobalt-based catalysts are one of the preferred materials for effective activation of hydrogen peroxide, and metal element doping and active site dispersion are effective methods to enhance their catalytic activity. In this work, manganese-doped cobalt silicate@diatomite composites with enhanced photo-Fenton-like oxidation performance were prepared and used for degradation of methyl orange (MO) dyes. Experiments showed that manganese doping increased the specific surface area of the samples and decreased the band gap energy of the materials. Moreover, the samples doped with manganese elements had better photo-Fenton-like properties. The degradation of methyl orange by Co0.25MnSi@DE/H2O2-UV reached more than 95%. In addition, density-functional theory (DFT) calculations showed that the Mn-doped samples were more prone to activate H2O2 than non-manganese-doped samples, and the synergistic effect from using a bimetallic catalyst increased the photo-Fenton oxidation activity in the system. ESR spectroscopy and bursting tests indicated that the possible degradation mechanism consisted of hydroxyl radicals and superoxide radicals generated by the synergistic effect of cobalt ions and manganese under UV radiation. This study thus presents a feasible idea for the preparation of cobalt-based photo-Fenton catalysts that also provides a basis for understanding the catalytic mechanism analysis of other types of bimetallic catalysts.

Efficient degradation of 2,4-dichlorophenol by heterogeneous electro-Fenton using bulk carbon aerogels modified in situ with FeCo-LDH as cathodes: Operational parameters and mechanism exploration

In this study, an in situ grown FeCo-Layered double hydroxide anchored to the surface of a bulk carbon aerogel (FeCo-LDH/CA) for contaminant degradation during the heterogeneous electro-Fenton (EF) process. The results exhibited that the FeCo-LDH/CA cathode achieved 100% of 2,4-dichlorophenol (2,4-DCP = 20 mg/L) degradation within 120 min at pH = 3, application current 20 mA, and Na2SO4 concentration 0.05 M. Moreover, the degradation efficiency was impressive in the range of pH = 2-9. The coexistence of the Fe (III)/Fe (II) and Co (III)/Co (II) as active sites on the cathode surface promoted the in-situ decomposition of H2O2 to form reactive oxygen species (ROS). •OH and O2- were confirmed to be the major degradation pollutants of ROS. Furthermore, density functional theory (DFT) was used to predict the reaction sites of 2,4-DCP, and its possible degradation pathways were proposed. The toxicity of intermediate products was evaluated and decreased after degradation. In addition, the eight cycle experiments and the degradation of other typical contaminants demonstrated the satisfactory stability and applicability of the synthetic cathode. This study presents the preparation of an efficient and stable EF cathode, further promoting the application of iron-based composites in wastewater treatment.

Rapid degradation and detoxification of metronidazole using calcium sulfite activated by CoCu two-dimensional layered bimetallic hydroxides: Performance, mechanism, and degradation pathway

In this study, cobalt copper-layered double hydroxides (CoCu-LDHs) were prepared by coprecipitation as catalysts to activate CaSO3 for metronidazole (MNZ) degradation. This is the first report on layered double hydroxides activating sulfite for the degradation of organic pollutants. Meanwhile, to address the issue of self-quenching reactions readily occurring in conventional sulfite advanced oxidation systems and resulting in low oxidant efficiency, CaSO3 with slightly soluble in water was used instead of commonly used Na2SO3, to improve the limitations of traditional systems. The results showed that in the CoCu-LDHs/CaSO3 system, the degradation rate of MNZ reached 98.7% within 5 min, representing a 23.0% increase compared to the CoCu-LDHs/Na2SO3 system. Owing to the excellent catalytic performance exhibited by CoCu-LDHs, characterizations including XRD, FTIR, SEM, TEM, BET and XPS were carried out to investigate this further. The results confirmed the successful synthesis of CoCu-LDH, and the activation mechanism study revealed that Co and Cu were considered to the main elements in activating CaSO3, demonstrating good synergistic effects. In addition, the oxygen vacancies on the catalyst surface also played a positive role in generating radicals and promoting electron transfer. Subsequently, the effects of Co/Cu ratio, catalyst dosage, oxidant concentration, pollutant concentration, pH and coexisting substances on MNZ degradation were investigated. Additionally, based on the LC-MS analysis of degradation products and toxicity tests, MNZ was transformed into different intermediates with low toxicity through four pathways, eventually mineralizing into inorganic small molecules. After six cycles, the MNZ degradation rate still reached 82.1%, exhibiting excellent stability and recyclability. In general, this study provides new ideas for activating sulfite, while providing theoretical support for subsequent research on sulfite advanced oxidation system.

Facile fabrication of CoAl-LDH nanosheets for efficient rhodamine B degradation via peroxymonosulfate activation

Layered double hydroxides (LDHs) have been extensively investigated as promising peroxymonosulfate (PMS) activators for the degradation of organic pollutants. However, bulk LDHs synthesized using conventional methods possess a closely stacked layered structure, which seriously blocks active sites and yields low intrinsic activity. In this study, we exfoliated bulk CoAl-LDHs to fabricate CoAl-LDH nanosheets by alkali-etching and Ostwald ripening via a simple hydrothermal process in a KOH solution. The exfoliated LDHs possessed the typical nanosheet structure with more exposed active sites for PMS activation, and hence, boosted the degradation of the pollutants. CoAl-1 exhibited an outstanding catalytic performance as the PMS activator for rhodamine B (RhB) degradation with the apparent rate constant of 0.1687 min-1, which was about 3.63 and 5.02 times higher than that of commercial nano-Co3O4 and bulk CoAl-LDH, respectively. The maximum RhB degradation of 93.1% was achieved at the optimal reaction conditions: catalyst dose 0.1 g L-1, PMS concentration 0.3 mM, pH 7, and temperature 298 K. Further analysis of RhB degradation mechanism illustrated that singlet oxygen (1O2) dominated RhB degradation in the CoAl-1/PMS system, while ˙OH, ˙O2-, and ˙SO4- may mainly serve as the intermediates for the generation of 1O2 and were indirectly involved in the degradation. This study provides a promising strategy for developing two-dimensional LDH nanosheets for wastewater remediation.

Efficient Fenton-like degradation of tetracycline by stalactite-like CuCo-LDO/CN catalysts: The overlooked contribution of dissolved oxygen

In the Fenton-like processes, the resources that exist in the system itself (e.g., dissolved oxygen, electron-rich pollutants) are often overlooked. Herein, a novel CuCo-LDO/CN composite catalyst with a strong "metal-π" effect was fabricated by in situ calcination which could activate dissolved oxygen to generate active oxygen species and degrade the electron-rich pollutants directly. The CuCo-LDO/CN (1:10) with the largest specific surface aera, most C-O-M bonds and least oxygen vacancies exhibited the best catalytic performance for tetracycline (TC)degradation (TC removal efficiency 93.2% and mineralization efficiency 40%, respectively, after 40 min at neutral pH) compared to CuCo-LDO and other CuCo-LDO/CN composite catalysts. In the absence of H2O2, dissolved oxygen could be activated by the catalyst to generate O2·-and ·OH, which contributed to approximately 20.7% of TC degradation, providing a faster and cost-effective way for TC removal from wastewater. While in the presence of H2O2, it was activated by CuCo-LDO/CN to generate·OH as the dominant reactive oxygen species and meanwhile TC transferred electrons to H2O2 through C-O-M bonds, accelerating the Cu+/Cu2+ and Co2+/Co3+ redox cycles. The possible degradation pathways of TC were proposed, and the environmental hazard of TC is greatly mitigated according to toxicity prediction.

Biochar/layered double hydroxides composites as catalysts for treatment of organic wastewater by advanced oxidation processes: A review

Heterogeneous advanced oxidation process has been widely studied as an effective method for removing organic pollutants in wastewater, but the development of efficient catalysts is still challenging. This review summaries the present status of researches on biochar/layered double hydroxides composites (BLDHCs) as catalysts for treatment of organic wastewater. The synthesis methods of layered double hydroxides, the characterizations of BLDHCs, the impacts of process factors influencing catalytic performance, and research advances in various advanced oxidation processes are discussed in this work. The integration of layered double hydroxides and biochar provides synthetic effects for improving pollutant removal. The enhanced pollutant degradation in heterogeneous Fenton, sulfate radical-based, sono-assisted, and photo-assisted processes using BLDHCs have been verified. Pollutant degradation in heterogeneous advanced oxidation processes using BLDHCs is influenced by process factors such as catalyst dosage, oxidant addition, solution pH, reaction time, temperature, and co-existing substances. BLDHCs are promising catalysts due to the unique features including easy preparation, distinct structure, adjustable metal ions, and high stability. Currently, catalytic degradation of organic pollutants using BLDHCs is still in its infancy. More researches should be conducted on the controllable synthesis of BLDHCs, the in-depth understanding of catalytic mechanism, the improvement of catalytic performance, and large-scale application of treating real wastewater.

Efficient degradation of tetracycline residues in pharmaceutical wastewater by Ni/Fe bimetallic atomic cluster composite catalysts with enhanced electron transfer pathway

Metal cluster catalysts have large atomic load, interaction between atomic sites, and wide application of catalysis. In this study, a Ni/Fe bimetallic cluster material was prepared by a simple hydrothermal method and used as an efficient catalyst to activate the degradation system of peroxymonosulfate (PMS), which showed nearly 100% tetracycline (TC) degradation performance over a wide pH range (pH = 3-11). The results of electron paramagnetic resonance test, quenching experiment and density functional theory (DFT) calculation show that the non-free radical pathway electron transfer efficiency of the catalytic system is effectively improved, and a large number of PMS are captured and activated by high density Ni atomic clusters in Ni/Fe bimetallic clusters. The degradation intermediates identified by LC/MS showed that TC was efficiently degraded into small molecules. In addition, the Ni/Fe bimetallic cluster/PMS system has excellent efficiency for degrading various organic pollutants and practical pharmaceutical wastewater. This work opens up a new way for metal atom cluster catalysts to efficiently catalyze the degradation of organic pollutants in PMS systems.

Interface engineering-induced perovskite/spinel LaCoO3/Co3O4 heterostructured nanocomposites for efficient peroxymonosulfate activation to degrade levofloxacin

Conventional perovskite oxides (ABO₃) tend to suffer from their inactive surfaces and limited active sites that reduce their catalytic activity and stability, while interface engineering is a facile modulating technique to boost the catalyst's inherent activity by constructing heterogeneous interfaces. In this study, perovskite/spinel LaCoO₃/Co₃O₄ nanocomposites with heterogeneous interfaces were synthesized via sol-gel and in-situ gradient etching methods to activate peroxymonosulfate (PMS) for degrading levofloxacin (LEV). LaCoO₃ on the surface was etched into spinel Co₃O₄, and LaCoO₃/Co₃O₄ nanocomposites with two crystal structures of perovskite and spinel were successfully formed. The surface-modified LaCoO₃/Co₃O₄ exhibited superior catalytic performance with a reaction rate constant more than 2 times that of the original LaCoO₃, as well as excellent pH adaptability (3-11) and reusability (more than 6 recyclings) for LEV degradation. Besides, multiple characterization techniques were carried out to find that LaCoO₃/Co₃O₄ possessed a larger specific surface area and richer oxygen vacancies after surface modification, which provided more active sites and accelerated mass transfer rate. The mechanism of reactive oxygen species involved in the reaction system was proposed that LaCoO₃/Co₃O₄ not only reacted with PMS directly to produce SO₄^•- and ^•OH but also its surface hydroxyl group helped to form the [≡Co(Ⅲ)OOSO₃]⁺ reactive complex with PMS to produce O₂^•- and ¹O₂. In addition, electrochemical experiments demonstrated that the surface electronic structure of LaCoO₃/Co₃O₄ was effectively regulated, exhibiting a faster electron transfer rate and facilitating the redox process. By detecting and identifying degradation intermediates, three degradation pathways for LEV were proposed. Our work provided profound insights into the design of efficient and long-lasting catalysts for advanced oxidation processes.

Activation of peroxymonosulfate by Co-Mg-Fe layered doubled hydroxide for efficient degradation of Rhodamine B

Reactive species serve as a key to remediate the contamination of refractory organic contaminants in advanced oxidation processes. In this study, a novel heterogeneous catalyst, CoMgFe-LDH layered doubled hydroxide (CoMgFe-LDH), was prepared for an efficient activation of peroxymonosulfate (PMS) to oxidize Rhodamine B (RhB). The characterization results showed that CoMgFe-LDH had a good crystallographic structure. Correspondingly, the CoMgFe-LDH/PMS process exhibited good capacity to remove RhB, which was equivalent to degradation performance as homogeneous Co(II)/PMS process. The RhB oxidation in the CoMgFe-LDH/PMS process was well described with pseudo-first-order kinetic model. Additionally, the oxidation process presented an excellent stability, and only 0.9% leaching rate was detected after six sequential reaction cycles at pH 5.0. The effects of initial pH, CoMgFe-LDH dosage, PMS concentration, RhB concentration, and inorganic anions on the RhB degradation were discussed in detail. Quenching experiments showed that sulfate radicals (SO₄^•-) acted as the dominant reactive species. Further, the removal of RhB from simulated wastewater was explored. The removal efficiency of RhB (90 μM) could reach 94.3% with 0.8 g/L of catalyst and 1.2 mM of PMS addition at pH 5.0, which indicated the CoMgFe-LDH/PMS process was also effective in degrading RhB in wastewater.

Insight into catalytic activation of bisulfite for lomefloxacin degradation by simple composite of calcinated red mud

Antibiotic was detected in many environments, and it had posed a serious threat to human health. The advanced oxidation process has been considered an effective way to treat antibiotics. In this work, using industrial waste red mud (RM) as raw material, a series of modified RM (MRM-T; T donates the calcination temperature) was obtained via a facile calcination method and applied to activate sodium bisulfite (NaHSO₃) for the lomefloxacin (LOM) degradation. Among all MRM-T, MRM-700 exhibited superior catalytic activity, and approximately 89% of LOM (10 mg/L) was degraded at 30 min through the activation of NaHSO₃ ([NaHSO₃] = 0.5 g/L) by MRM-700 ([MRM-700] = 0.9 g/L). Moreover, the kinetic constant of LOM removal in the MRM-700/NaHSO₃ system (0.082 min^-1) was 16.4 times higher than that of the RM-raw/NaHSO₃ system (0.005 min^-1). The as-synthesized product of MRM-700 was characterized by N₂ adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectra. The result indicated that the catalyst possessed excellent pore structure, high specific area, and abundant Fe³⁺ sites, and the lattice of Fe₂O₃ was doped after calcination, both of which were favorable for the activation of NaHSO₃. The quenching experiment proved that •SO₄^- and •OH^- active species were produced in MRM-700/NaHSO₃ system, and •SO₄^- played a dominant role in LOM removal. In addition, the potential LOM degradation pathway was analyzed via UPLC-MS technology and density functional theory (DFT) calculation, and the toxicity of the treated LOM solution was tested by the culture of mung bean sprouts. This study not only provided a feasible strategy for the valuable use of RM to activate NaHSO₃ but also offered a cost-effective catalyst for the efficient removal of pollutants in wastewater.

Efficient activation of peroxymonosulfate via Cu2+/Cu+ cycle enhanced by hydroxylamine for the degradation of Rhodamine B

The application of Cu²⁺/peroxymonosulfate (PMS) process for the elimination of refractory pollutants in industrial wastewater is limited by the slow transformation from Cu²⁺ to Cu⁺. In this research, hydroxylamine (HA) was employed to improve the degradation capacity of the Cu²⁺/PMS process. Rhodamine B (RhB) was selected as the target compound to indicate the performance of HA/Cu²⁺/PMS process. Compared with the Cu²⁺/PMS process, the reduction of Cu²⁺ to Cu⁺ was effectively promoted by HA in the HA/Cu²⁺/PMS process, which increased the decomposition rate of PMS by 29.2%, correspondingly, promoted the removal rate of RhB by 77.6%. The degradation of RhB followed pseudo-second-order kinetics in the proposed process. The active species analysis subsequently indicated hydroxyl radicals (·OH) and sulfate radicals (SO₄·^-) played important roles for degrading RhB with ·OH as the dominant active radical. The effects including initial pH, RhB concentration, PMS concentration, and Cu²⁺ concentration on the degradation of RhB were further investigated and discussed in detail. Additionally, the HA/Cu²⁺/PMS process exhibited effective RhB removal in simulated wastewater. From the perspective of waste utilization (Cu²⁺) and the remediation of organic contamination, the work would provide a valuable and promising process.

Investigation of CuCoFe-LDH as an efficient and stable catalyst for the degradation of acetaminophen in heterogeneous electro-Fenton system: Key operating parameters, mechanisms and pathways

Pharmaceuticals, as anthropogenic pollutants in a wide range of water sources, generally require specific treatment methods for degradation. A trimetallic layered double hydroxide (CuCoFe-LDH) was successfully fabricated by coprecipitation and applied as a novel heterogeneous electro-Fenton (EF) catalyst for the degradation of acetaminophen (ACT) from aqueous environments. The EF experiments showed that the CuCoFe-LDH/EF process achieved 100% of ACT degradation efficiency within 60 min at pH = 5, catalyst dosage of 0.50 g/L, current density of 10 mA/cm² and initial ACT concentration of 20 mg/L. An impressive (>80%) mineralization of ACT was obtained over a wide pH range (pH 3-9) after 180 min. Meanwhile, the role of ·OH and O₂^.- were certified by radical quenching experiments and electron paramagnetic resonance (EPR) analysis. Through mechanism exploration, the coexistence of Cu and Co on Fe-based LDHs can accelerate the interfacial electron transfer and promote the formation of the reactive oxygen species (ROS), thus facilitating the EF process. Furthermore, the degradation by-products and possible degradation pathways of ACT in the CuCoFe-LDH/EF process were proposed. The reusability test and the treatment of various typical organic pollutants experiments indicated that the CuCoFe-LDH/EF process has excellent stability and broad application prospects. This work provides a valuable reference for the treatment of pharmaceuticals by the heterogeneous EF process in a wide range of pH.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.

Degradation of chlortetracycline hydrochloride by peroxymonosulfate activation on natural manganese sand through response surface methodology

This work studies the degradation of chlortetracycline hydrochloride (CTC) by activated peroxymonosulfate (PMS) with natural manganese sand (NMS). Meanwhile, the NMS was characterized and analyzed by isothermal nitrogen adsorption (BET), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscope (SEM). It can be induced that NMS material may contain C, O, Al, Si, Fe, Mn, and K, and the proportion of each is 6%, 9%, 13%, 34%, 27%, 5%, and 6%. Critical parameters, including initial pH value, catalyst dosage, and PMS amount, were optimized through response surface methodology. One of the essential significances of response surface methodology (RSM) is the establishment and optimization of the mathematical model to reduce the complexity of the experimental process. It can provide the degree of mutual influence between various factors and optimize the response based on the investigated factors. Results indicated that 81.65% of CTC could be degraded under the optimized conditions of PMS amount 2.02 g/L, the NMS dosage 0.29 g/L and pH 3.87. Also, it shows that NMS is the most powerful of each factor on the degradation efficiency. We proposed the degradation pathways of CTC from the liquid chromatograph-mass spectrometer (LC-MS) results. Therefore, NMS could be applied as an efficient activator of peroxymonosulfate to purify the water and wastewater.

Heterogeneous Metal-Activated Persulfate and Electrochemically Activated Persulfate: A Review

The problem of organic pollution in wastewater is an important challenge due to its negative impact on the aquatic environment and human health. This review provides an outline of the research status for a sulfate-based advanced oxidation process in the removal of organic pollutants from water. The progress for metal catalyst activation and electrochemical activation is summarized including the use of catalyst-activated peroxymonosulfate (PMS) and peroxydisulfate (PDS) to generate hydroxyl radicals and sulfate radicals to degrade pollutants in water. This review covers mainly single metal (e.g., cobalt, copper, iron and manganese) and mixed metal catalyst activation as well as electrochemical activation in recent years. The leaching of metal ions in transition metal catalysts, the application of mixed metals, and the combination with the electrochemical process are summarized. The research and development process of the electrochemical activation process for the degradation of the main pollutants is also described in detail.

Photocatalytic degradation of lomefloxacin antibiotics using hydrothermally synthesized magnesium titanate under visible light-driven energy sources

Antibiotics in water system pose a human health risk due to the rise of antibacterial activity in the environmental web. Advanced oxidation processes are the potential to become an effective treatment technology for targeting antibiotics. This study demonstrates the visible light photocatalysis of lomefloxacin using magnesium titanate (MgTiO₃). The nanomaterial was subjected to computational analysis to study morphology, functional, and optical characteristics through FESEM, XRD, FTIR, BET, UV-Vis, etc. Importantly, MgTiO₃ had band gap energy of 3.09 eV. The photocatalytic studies were performed to observe different parameters affecting lomefloxacin degradation such as initial concentration, catalyst dosage, and pH. The nanomaterial exhibited the maximum lomefloxacin degradation. The study revealed that 30 mg/L of catalyst was optimum to degrade 10 mg/L of lomefloxacin with 30-W LED irradiation up to 150 min. Reactive species, namely, electron, hole, hydroxyl, and superoxide radicals, comprised the primary photocatalytic mechanism for lomefloxacin degradation. Ultimately, the summative result from this study highlights the suitability of the photocatalytic system to treat persistent antibiotics in aqueous environment.

CO2 bubble-assisted in-situ construction of mesoporous Co-doped Cu2(OH)2CO3 nanosheets as advanced electrodes towards fast and highly efficient electrochemical reduction of nitrate to N2 in wastewater

The development of high-efficient and cost-effective electrocatalysts is crucial to remove nitrate pollutant in wastewater. Herein, we design and prepare mesoporous Co-doped Cu₂(OH)₂CO₃ malachite nanosheets as an electrocatalyst toward highly efficient nitrate reduction using a facile CO₂ bubble-assisted coprecipitation synthesis. The electrocatalytic performance is subject to the Co/Cu ratio of this malachite. Remarkably, compared with the pristine monometal Cu or Co-based electrocatalyst, the optimal electrocatalyst, 0.3Co@Cu₂(OH)₂CO₃, displays fast and highly efficient removal capacity of nitrate with an impressive high total nitrogen (TN) removal of 8628.99 mg N g^-1_CoCu (398.79 mg N g_cat^-1 h^-1), N₂ selectivity of 97.11% as well as negligible nitrite product at 100 mg L^-1 NO₃^--N and 2000 mg L^-1 Cl^- neutral electrolyte. Above all, high total nitrogen removal efficiency (81.92%) and chemical oxygen demand (73.74%) in actual wastewater. Its excellent electrocatalytic performance is achieved by regulating the electronic structure and the adsorption/desorption of the intermediate. This study discovers a new type of electrode materials for nitrate removal in wastewater.

Construction of durable superhydrophilic activated carbon fibers based material for highly-efficient oil/water separation and aqueous contaminants degradation

Developing filtering materials with high permeation flux and contaminant removal rate is of great importance for oily wastewater remediation. Herein, a robust three-dimensional (3D) activated carbon fibers (ACFs) based composite with uniformly grown layered double hydroxide (LDH) on the surface was successfully constructed through a feasible hydrothermal strategy. The LDH with a high surface energy and vertically aligned structure could provide superhydrophilicity to ACFs. Systematic investigation confirmed that the 3D material could overcome the size mismatch between the ACFs macropores and tiny emulsified droplets through the combination of size-sieving filtration on the surface and oil droplet coalescence in the fiber network. This process efficiently separated the intractable surfactant-stabilized oil-in-water emulsions with high permeation flux (up to 4.16 × 10⁶ L m^-2 h^-1 bar^-1). Notably, the LDH also had well-dispersed catalytic active sites, which could initiate advanced oxidation processes (AOPs) to efficiently eliminate various types of water-soluble organic pollutants (e.g., pharmaceuticals, phenolic compounds and organic dyes). The resulting modified ACFs exhibited exceptional removal rates for both oil and organic pollutants in the complex sewage during the continuous filtration process. These versatile abilities integrated with the facile preparation method reported herein provide outstanding prospects for the large-scale treatment of oily wastewater.

Gravity-driven layered double hydroxide nanosheet membrane activated peroxymonosulfate system for micropollutant degradation

For the first time in this study, CoAl-layered double hydroxide nanosheet membrane (LDH_m) with abundant active sites was fabricated for peroxymonosulfate (PMS) activation with the mindset to catalytically degrade micropollutants. Depending on the catalyst loading, the developed LDH_m can be driven under gravity at a permeate flux of approximately 80 L/m² h and 210 L/m² h at LDH loading of 0.80 mg/cm² and 0.08 mg/cm², respectively. Notably, the LDH_m (0.63 mg) exhibited excellent PMS activation efficiency as indicated by 87.8% removal of the probe chemical (ranitidine) at 0.2 mM PMS, which was higher than that (37-44%) achieved by conventional LDH (5-20 mg)/PMS (0.2 mM) system. In addition to efficient degradation of several micropollutants, LDH_m/PMS performance was not inhibited by variation in solution pH (4-8) as well as during long-term (29 h) continuous-flow operation. SO₄^•- and ¹O₂ were identified as the primary reactive species in the LDH_m/PMS system, while both Co and Al participated in PMS activation. This study offers a simple strategy for efficient removal of several micropollutants with significantly reduced catalyst leaching, which could be applied sustainably in water treatment.

Enhancement strategies for efficient activation of persulfate by heterogeneous cobalt-containing catalysts: A review

As a clean and efficient technology for the degradation of organic contaminants, sulfate radical based advanced oxidation processes (SR-AOPs) have attracted more and more attention in the past decades. Cobalt is regarded as the most reactive and efficient non-noble metal catalyst for the activation of persulfate including peroxymonosulfate (PMS) and peroxydisulfate (PDS) to produce sulfate radicals. Due to the limitations of homogeneous catalytic systems, the heterogeneous cobalt-containing catalysts have been emerged and rapidly developed. Various strategies have been schemed to further enhance the activation ability of persulfate by heterogeneous cobalt-containing catalysts. This paper provides an overview on the recent progress in enhancement strategies for the highly efficient activation of persulfate by heterogeneous cobalt-containing catalysts. With a brief introduction on the chemistry and feature of sulfate radical reactions catalyzed by homogeneous Co²⁺/Co³⁺ species, the main strategies for enhancing persulfate activation by heterogeneous cobalt-containing catalysts are summarized, such as surface and morphology design, multiple reactive centers design, organic-inorganic hybrids and heterostructure composites. Future perspectives of heterogeneous SR-AOPs systems catalyzed by cobalt-containing catalysts are outlined.

Brønsted-acid sites promoted degradation of phthalate esters over MnO2: Mineralization enhancement and aquatic toxicity assessment

Advanced oxidation processes (AOPs) are important technologies for aqueous organics removal. Despite organic pollutants can be degraded via AOPs generally, high mineralization of them is hard to achieve. Herein, we synthesized a manganese oxide nanomaterial (H2-OMS-2) with abundant Brønsted-acid sites via ion-exchange of cryptomelane-type MnO₂ (OMS-2), and tested its catalytic performance for the degradation of phthalate esters via peroxymonosulfate (PMS) activation. About 99% of dimethyl phthalate (DMP) at a concentration of 20 mg/L could be degraded within 90 min and 82% of it could be mineralized within 180 min over 0.6 g/L of catalyst and 1.8 g/L of PMS. The catalyst could activate PMS to generate SO₄^-˙ and ·OH as the dominant reactive oxygen species to reach complete degradation of DMP. Especially, the higher TOC removal rate was obtained due to the rich Brønsted-acid sites and surface oxygen vacancies on the catalyst. Kinetics and mechanism study showed that Mn^II/Mn^III might work as the active sites during the catalytic process with a lower reaction energy barrier of 55.61 kJ/mol. Furthermore, the catalyst could be reused for many times through the regeneration of the catalytic ability. The degradation and TOC removal efficiencies were still above 98% and 65% after seven consecutive cycles, respectively. Finally, H2-OMS-2-catalyzed AOPs significantly reduced the organismal developmental toxicity of the DMP wastewater through the investigation of zebrafish model system. The present work, for the first time, provides an idea for promoting the oxidative degradation and mineralization efficiencies of aqueous organic pollutants by surface acid-modification on the catalysts.

Highly efficient removal of bisphenol A by a novel Co-doped LaFeO3 perovskite/PMS system in salinity water

Although it can effectively degrade refractory organic pollutants, advanced oxidation processes (AOPs) can be seriously interfered with the co-existing substance in salinity water. Herein, three-dimensional hierarchical cobalt-doped LaFeO₃ perovskites (LaCo_0.5Fe_0.5O₃) micron spheres composed of nano-rods were hydrothermally synthesized and applied to activate peroxymonosulfate (PMS) for degrading bisphenol A (BPA). Nearly 100% BPA was removed by LaCo_0.5Fe_0.5O₃/PMS system in presence of more than 50 mM Cl^- within only 2 min compared that of 30 min without Cl^-, which was attributed to reactive chlorine species (RCS) including Cl^• and HOCl with higher oxidation capacity. •OH and SO₄^•- produced by LaCo_0.5Fe_0.5O₃ activating PMS played crucial roles as the source of RCS in LaCo_0.5Fe_0.5O₃/Cl^-/PMS system. The synergistic effect between ROS and RCS promoted by the enhanced oxygen vacancies and the efficient redox recycling of Fe^III/Fe^II and Co^III/Co^II. Other anions like SO₄^2- and NO₃^- hardly affected the BPA degradation. BPA degradation efficiency was also improved either in a wide pH range or in the presence of natural organic matters in salty water. This work also demonstrated the potential application of FeCo bimetallic LaCo_0.5Fe_0.5O₃ activating PMS system for degradation of BPA or other organic micropollutants in seawater system.

Efficient degradation of Rhodamine B by magnetically recoverable Fe3O4-modified ternary CoFeCu-layered double hydroxides via activating peroxymonosulfate

Environment-friendly nano-catalysts capable of activating peroxymonosulfate (PMS) have received increasing attention recently. Nevertheless, traditional nano-catalysts are generally well dispersed and difficult to be separated from reaction system, so it is particularly important to develop nano-catalysts with both good catalytic activity and excellent recycling efficiency. In this work, magnetically recoverable Fe₃O₄-modified ternary CoFeCu-layered double hydroxides (Fe₃O₄/CoFeCu-LDHs) was prepared by a simple co-precipitation method and initially applied to activate PMS for the degradation of Rhodamine B (RhB). X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller method (BET), and vibrating sample magnetometer (VSM) were applied to characterize morphology, structure, specific surface area and magnetism. In addition, the effects of several key parameters were evaluated. The Fe₃O₄/CoFeCu-LDHs exhibited high catalytic activity, and RhB degradation efficiency could reach 100% within 20 min by adding 0.2 g/L of catalyst and 1 mmol/L of PMS into 50 mg/L of RhB solution under a wide pH condition (3.0-7.0). Notably, the Fe₃O₄/CoFeCu-LDHs showed good super-paramagnetism and excellent stability, which could be effectively and quickly recovered under magnetic condition, and the degradation efficiency after ten cycles could still maintain 98.95%. Both radicals quenching tests and electron spin resonance (ESR) identified both HO• and SO₄^•- were involved and SO₄^•- played a dominant role on the RhB degradation. Finally, the chemical states of the sample's surface elements were measured by X-ray photoelectron spectroscopy (XPS), and the possible activation mechanism in Fe₃O₄/CoFeCu-LDHs/PMS system was proposed according to comprehensive analysis.

Layered double hydroxides and related hybrid materials for removal of pharmaceutical pollutants from water

Pharmaceuticals and their by-products are recalcitrant contaminants in water. Moreover, the high consumption of these drugs has many detrimental effects on body waters and ecosystems. In this timely review, the advances in molecular engineering of layered double hydroxides (LDH) that have been used for the removal of pharmaceutical pollutants are discussed. The approach starts from the strategies to obtain homogeneous synthesis of LDH that allow the doping and/or surface functionalization of different metals and oxides, producing heterojunction systems as well as composites with carbon and silica-based materials with high surface area. Adsorption is considered as a traditional removal of pharmaceutical pollutants, so the kinetic and mechanism of this phenomenon are analyzed based on pH, temperature, ionic strength, in order to obtain new insights for the formation of multifunctional LDH. Advanced oxidation methodologies, mainly heterogeneous photocatalysis and Fenton-like processes, stand out as the more efficient even to obtain the mineralization of the drugs. The LDH have the advantage of structural memory that favors regeneration processes. The reconstruction of calcined LDH can be used to improve drug removal, through a combination of adsorption capacity/catalytic activity. A meticulous analysis of the persistence, toxicity and bioaccumulation of the most common pharmaceuticals has allowed us to highlight the ability of the LDH to remove recalcitrant drugs at relatively low concentrations (ppm, ppb), in contrast to other mixed oxide nanostructures and homogeneous oxidation processes. In this sense, the mechanism of drug removal by LDH is discussed based on the importance of the use of composites, scavenger agents, Fenton and electro-Fenton processes, membranes, thin films and coatings, among others. In addition, the ecotoxicity of LDH is also reviewed to indicate that these layered structures can exhibit biocompatibility or high toxicity depending on the adsorbed drug and ions/metals that compose them. Undoubtedly, the LDH have a unique flexible structure with adsorption capacity and catalytic activity, facts that explain the important reasons for their extensive use in the environmental remediation of pharmaceutical pollutants from water.

Magnetic Fe3O4@CoFe-LDH nanocomposite heterogeneously activated peroxymonosulfate for degradation of azo-dye AO7

In this study, a novel core@shell magnetic nanocomposite Fe3O4/CoFe-layered double hydroxide (Fe3O4@CoFe-LDH) was successfully synthesized by the co-precipitation method, and then employed as an efficient heterogeneous catalyst for activation of peroxymonosulfate (PMS) in removal of azo-dye acid orange 7 (AO7). The as-obtained nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results from these characterizations showed Fe3O4@CoFe-LDH to possess good ferromagnetism and a perfect crystalline structure with a typical core@shell morphology. The system of Fe3O4@CoFe-LDH11/PMS (cobalt : iron molar ratio of 1 : 1) achieved 95.1% removal rate of AO7 (40 mg L-1) within 15 min under the optimized conditions, which outperformed bare Fe3O4 and raw CoFe-LDH11. Meanwhile, Fe3O4@CoFe-LDH11 displayed good adaptability in a wide pH range from 4 to 9 and relatively low PMS activation energy (39.9 kJ mol-1). The interference tests revealed HCO3 - to possess the strongest restriction effect. Only 57.7% AO7 was removed when 10 mM HCO3 - was introduced, which was ascribed to HCO3 - not only serving as a radical scavenger, but also increasing the pH of the system. The radical quenching tests demonstrated SO4˙- as the dominant reactive species during the catalytic reaction. Based on X-ray photoelectron spectroscopy (XPS) analysis, the core structure of Fe3O4 served as an electron donor for accelerating the cycle of Co(ii)/Co(iii) at the active site of the LDH outer shell. Also, Fe3O4@CoFe-LDH exhibited outstanding stability and recyclability, and maintained high degradation efficiency of AO7 even after five cycles. In sum, the proposed magnetic Fe3O4@CoFe-LDH nanocomposite has great potential for remediation of wastewater contaminated with synthetic dyes.

Strong Adsorption of Phosphorus by ZnAl-LDO-Activated Banana Biochar: An Analysis of Adsorption Efficiency, Thermodynamics, and Internal Mechanisms

Zn-Al layered bimetallic composites were prepared by ethanol strengthening and co-precipitation using banana straw as a raw material. A high-efficiency phosphorus adsorbent (ZnAl-LDO-BC) was obtained by calcination at a high temperature. The kinetics and thermodynamics of phosphorus adsorption on ZnAl-LDO-BC were then studied. The results showed that the adsorption process of ZnAl-LDO-BC corresponds with the pseudo-second-order (PSO) kinetic equation and the Langmuir model. The theoretical maximum adsorption capacity of ZnAl-LDO-BC is 111.11 mg/g (at 45 °C, 500 mg/L phosphorus initial concentration). The influence of anions on phosphorus adsorption decreased in strength in the following order: CO₃ ^2- > SO₄ ^2- > NO₃ ^-. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) were used to characterize the adsorption of phosphorus on ZnAl-LDO-BC and showed that ZnAl-LDO-BC can efficiently adsorb phosphorus. The adsorption mechanism utilizes both O-H and C-H on the surface of ZnAl-LDO-BC for the adsorption of PO₄ ^3-, forming Zn₃(PO₄)₂·₄H₂O via complexation precipitation; additionally, biochar surface adsorption and interlayer adsorption are indispensable forms of phosphate adsorption. With the systematic study of phosphorus adsorption by ZnAl-LDO-BC, a novel green technology was developed for addressing phosphorus pollution.