Singlet oxygen-oriented degradation of sulfamethoxazole by Li–Al LDH activated peroxymonosulfate

High-performance, stable CoNi LDH@Ni foam composite membrane with innovative peroxymonosulfate activation for 2,4-dichlorophenol destruction

In this study, the cobalt-nickel layered double hydroxides (CoNi LDH) were synthesized with a variety of Co/Ni mass ratio, as CoxNiy LDHs. In comparison, Co1Ni3 LDH presented the best peroxymonosulfate (PMS) activation efficiency for 2,4-dichlorophenol removal. Meanwhile, CoNi LDH@Nickel foam (CoNi LDH@NF) composite membrane was constructed for enhancing the stability of catalytic performance. Herein, CoNi LDH@NF-PMS system exerted high degradation efficiency of 99.22% within 90 min for 2,4-DCP when [PMS]0 = 0.4 g/L, Co1Ni3 LDH@NF = 2 cm × 2 cm (0.2 g/L), reaction temperature = 298 K. For the surface morphology and structure of the catalyst, it was demonstrated that the CoNi LDH@NF composite membrane possessed abundant cavity structure, good specific surface area and sufficient active sites. Importantly, ·OH, SO4·- and 1O2 played the primary role in the CoNi LDH@NF-PMS system for 2,4-DCP decomposition, which revealed the PMS activation mechanism in CoNi LDH@NF-PMS system. Hence, this study eliminated the stability and adaptability of CoNi LDH@NF composite membrane, proposing a new theoretical basis of PMS heterogeneous catalysts selection.

Separation and reutilization of heavy metal ions in wastewater assisted by p-BN adsorbent

Extracting heavy metal ions from wastewater has significant implications for both environmental remediation and resource preservation. However, the conventional adsorbents still suffer from incomplete ion removal and low utilization efficiency of the recovered metals. Herein, we present an extraction and reutilization method assisted by porous boron nitride (p-BN) containing high-density N atoms for metal recovery with simultaneous catalyst formation. The p-BN exhibits stable and efficient metal adsorption performance, particularly for ultra-trace-level water purification. The distribution coefficients towards Pb2+, Cd2+, Co2+ and Fe3+ can exceed 106 mL g-1 and the residual concentrations that reduced from 1 mg L-1 to 0.8-1.3 μg L-1 are much lower than the acceptable limits in drinking water standards of World Health Organization. Meanwhile, the used p-BN after Co ion adsorption can be directly adopted as a high-efficiency catalyst for activating peroxymonosulfate (PMS) in organic pollutant degradation without additional post-treatment, avoiding the secondary metal pollution and the problems of neglected manpower and energy consumption. Moreover, a flow-through multistage utilization system assisted by p-BN/polyvinylidene fluoride (PVDF) membrane is constructed for achieving both metal ion separation and reutilization in the removal of organic pollutants, providing a new avenue for sustainable wastewater remediation.

Mechanisms of iopamidol transformation catalyzed by a copper corrosion product (c-Cu2O) during peroxymonosulfate disinfection

Peroxymonosulfate (PMS) is an alternative disinfectant for drinking water. This study aimed to investigate the transformation of iopamidol (IPM) catalyzed by a main copper corrosion product (c-Cu2O) with PMS as a disinfectant. The observed pseudo-first-order constant (kobs) for the IPM degradation in the c-Cu2O/PMS system (0.033 min-1) was 3 times that in the CuO/PMS system (0.011 min-1). The quenching tests and the electron paramagnetic resonance (EPR) experiments indicate that O2•- and 1O2 contributed to IPM degradation in the c-Cu2O/ PMS system. The complexation of metastable Cu(II) with a PMS molecule polarized the OO bond and then facilitated the electron transfer from the PMS molecule to other PMS and O2 molecules, which directly and indirectly promoted the yield of O2•- and 1O2. The iodine balance indicated that 26.0% of initial TOI was converted to IO3-, and CHI3 only accounted for 0.6% of the residual TOI. In the c-Cu2O/PMS system, IPM conversion was started with amide C-N bond breakage, deiodination reaction and hydrogen abstraction. This study helps to better understand the conversion mechanisms of iodine-containing organic micropollutants when PMS is deployed as a disinfectant in copper pipes.

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.

Immobilization CoOOH nanosheets on biochar for peroxymonosulfate activation: Built-in electric field mediated radical and non-radical pathways

The strong electron interaction between metal oxide-carbon-based catalyst components plays a vital role in the peroxymonosulfate (PMS) activation for pollutant degradation. Herein, a novel CoOOH nanosheets anchored on rape straw-derived biochar (BC) surface (labeled as CoOOH/BC) as an efficient PMS activator toward degrading sulfamethoxazole (SMX) was synthesized. Experimental results indicated that integrating CoOOH nanosheets on the BC surface could inhibit CoOOH aggregation to increase the specific surface areas, exert a component synergistic effect to enhance activation degradation activity, and improve the catalyst stability. As a result, a 96 % degradation efficiency of SMX was achieved within 20 min over 20 wt% CoOOH/BC composite catalyst under the optimal conditions. Density functional theory (DFT) calculations disclosed that a built-in electric field (BIEF) pointing from BC to CoOOH was constructed at their interface, which could mediate PMS activation for reactive oxygen species (ROS) generation and induce direct electron transfer from SMX to PMS, resulting in efficient SMX degradation via both radical and non-radical pathways. Moreover, quenching experiments and electron paramagnetic resonance (EPR) measurements confirmed that single oxide (¹O₂) and superoxide radical (O₂^·-) are the dominant active species in the current system. Additionally, the possible SMX degradation routes were reasonably proposed based on liquid chromatography-mass spectrometry (LC-MS) results. This work provides an in-depth understanding of the role of BIEF in PMS activation, and expands the application of biochar-based materials in the field of environmental remediation.

One-step removal of hexavalent chromium in wide pH range using thiourea dioxide: the role of reactive species

One-step removal of hexavalent chromium in a wide pH range is of great significance. In this paper, a single thiourea dioxide (TD) and two-components thiourea dioxide/ethanolamine (MEA) were used as a green reducing agent for the efficient removal of Cr(vi), respectively. The reduction of Cr(vi) and the precipitation of Cr(iii) were carried out simultaneously under this reaction system. The experimental results proved that TD was activated by amine exchange reaction with MEA. In other words, MEA promoted the generation of an active isomeride of TD by changing the equilibrium position of the reversible reaction. After adding MEA, the removal rate of Cr(vi) and total Cr could reach industrial water discharge standards in a wide pH range of 8-12. The change of pH, reduction potential and the decomposition rate of TD were investigated in the reaction processes. Meanwhile, reductive and oxidative reactive species were produced simultaneously during this reaction process. Further, oxidative reactive species (O₂˙^- and ¹O₂) were beneficial for the decomplexation of Cr(iii) complexes and the formation of Cr(iii) precipitation. The experimental results also demonstrated that TD/MEA was effective in practical industrial wastewater. Hence this reaction system has a significant industrial application prospect.

O and S co-doping induced N-vacancy in graphitic carbon nitride towards photocatalytic peroxymonosulfate activation for sulfamethoxazole degradation

Doping-induced vacancy engineering of graphitic carbon nitride (GCN) is beneficial for bandgap modulation, efficient electronic excitation, and facilitated charge carrier migration. In this study, synthesis of oxygen and sulphur co-doped induced N vacancies (OSGCN) by the hydrothermal method was performed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) antibiotic degradation and H₂ production. The results from experimental and DFT simulation studies validate the synergistic effects of co-dopants and N-vacancies, i.e., bandgap lowering, electron-hole pairs separation, and high solar energy utilization. The substitution of sp² N atom by O and S co-dopants causes strong delocalization of HOMO-LUMO distribution, enhancing carrier mobility, increasing reactive sites, and facilitating charge-carrier separation. Remarkably, OSGCN/PMS photocatalytic system achieved 99.4% SMX degradation efficiency and a high H₂ generation rate of 548.23 μ mol g^-1 h^-1 within 60 min and 36 h, respectively under visible light irradiations. The SMX degradation kinetics was pseudo-first-order with retained recycling efficiency up to 4 catalytic cycles. The results of EPR and chemical scavenging experiments revealed the redox action of reactive oxidative species, wherein ¹O₂ was the dominant reactive species in SMX degradation. The identification of formed intermediates and the SMX stepwise degradation pathway was investigated via LC-MS analysis and DFT studies, respectively. The results from this work anticipated deepening the understanding of PMS activation by substitutional co-doping favoring N-vacancy formation in GCN lattice for improved photocatalytic activity.

Efficient wastewater disinfection by raised 1O2 yield through enhanced electron transfer and intersystem crossing via photocatalysis of peroxymonosulfate with CuS quantum dots modified MIL-101(Fe)

Peroxymonosulfate (PMS)-based photocatalysis is a promising alternative approach for wastewater disinfection. Singlet oxygen (¹O₂) is sensitive and efficient for bacterial inactivation. This study developed a ¹O₂-predominated PMS disinfection technique under visible light with CuS quantum dots (QDs) modified MIL-101(Fe) (CSQDs@MF). CuS QDs modification greatly enhanced the ¹O₂ quantum yield by 80% than that of MIL-101(Fe). Photoelectricity and photoluminescence tests demonstrated that both the enhanced electron transfer and energy transfer were responsible for improved ¹O₂ generation in Vis/PMS/CSQDs@MF system. The system took 60 min to inactivate 7.5-log E. coli, and it could be applied in a broad pH and dissolve oxygen range. Bacterial inactivation mechanism suggested that ¹O₂ attacked cell membrane first, then induced oxidative stress, up-regulated intracellular ROS level, eventually broke DNA strand. The system showed good disinfection performance on Gram-positive B. subtilis and fecal coliforms in practical wastewater, implying it is a promising alternative disinfection technology for wastewater treatment.

Modulating Direct Growth of Copper Cobaltite Nanostructure on Copper Mesh as a Hierarchical Catalyst of Oxone Activation for Efficient Elimination of Azo Toxicant

As cobalt (Co) has been the most useful element for activating Oxone to generate SO₄^•-, this study aims to develop a hierarchical catalyst with nanoscale functionality and macroscale convenience by decorating nanoscale Co-based oxides on macroscale supports. Specifically, a facile protocol is proposed by utilizing Cu mesh itself as a Cu source for fabricating CuCo₂O₄ on Cu mesh. By changing the dosages of the Co precursor and carbamide, various nanostructures of CuCo₂O₄ grown on a Cu mesh can be afforded, including nanoscale needles, flowers, and sheets. Even though the Cu mesh itself can be also transformed to a Cu-Oxide mesh, the growth of CuCo₂O₄ on the Cu mesh significantly improves its physical, chemical, and electrochemical properties, making these CuCo₂O₄@Cu meshes much more superior catalysts for activating Oxone to degrade the Azo toxicant, Acid Red 27. More interestingly, the flower-like CuCo₂O₄@Cu mesh exhibits a higher specific surface area and more superior electrochemical performance, enabling the flower-like CuCo₂O₄@Cu mesh to show the highest catalytic activity for Oxone activation to degrade Acid Red 27. The flower-like CuCo₂O₄@Cu mesh also exhibits a much lower E_a of Acid Red 27 degradation than the reported catalysts. These results demonstrate that CuCo₂O₄@Cu meshes are advantageous heterogeneous catalysts for Oxone activation, and especially, the flower-like CuCo₂O₄@Cu mesh appears as the most effective CuCo₂O₄@Cu mesh to eliminate the toxic Acid Red 27.

Sodium tetraborate simultaneously enhances the degradation of acetaminophen and reduces the formation potential of chlorinated by-products with heat-activated peroxymonosulfate oxidation

In this study, sodium tetraborate (Na₂B₄O₇) was introduced to enhance the degradation of acetaminophen (ACT) in heat-activated peroxymonosulfate (PMS) process. The elimination of ACT in Na₂B₄O₇/heat/PMS process followed the pseudo-first order kinetics. The corresponding k_obs value with 10 mM Na₂B₄O₇ was 33.1 times higher than that in heat/PMS process. ¹O₂ and HO· were identified as primary reactive species via quenching experiments and electron paramagnetic resonance technology. B(OH)₄^-, the hydrolysis product of Na₂B₄O₇, reacted with PMS to generate HOOB(OH)₃^-. ¹O₂ was generated by the self-decomposition of PMS using B(OH)₄^- as catalyst, while HO· was produced via the breakage of peroxide bond of PMS and HOOB(OH)₃^-under high temperature. ACT was degraded by reactive species via the pathways of -NH- bond breakage, -OH replacement, -NH₂ oxidation and benzene ring cleavage. Nine transformation intermediates were detected by LC/Q-TOF/MS, and the toxicity of reaction solution decreased significantly with the elimination of ACT. Increasing Na₂B₄O₇ dosage, PMS concentration, initial pH and reaction temperature were conducive to ACT elimination. Humic acid, Cl^- and CO₃^2- inhibited the degradation of ACT heavily, while SO₄^2- and NO₃^- had the negligible effects. Moreover, B(OH)₄^- could react with free chlorine to the inert B(OH)₃OCl^- and further significantly suppress the formation of chlorinated by-products for the treatment of Cl^--containing water in Na₂B₄O₇/heat/PMS process. This study provided an effective way to enhance the oxidation capacity of heat/PMS process and suppress the formation of chlorinated by-products in chloride-containing water, and the findings had important implications for using borate buffer in the studies of PMS-based advanced oxidation processes.