Heterogeneous activation of persulfate by Mg doped Ni(OH)2 for efficient degradation of phenol

Promoting oxygen vacancies utility for tetracycline degradation via peroxymonosulfate activation by reduced Mg-doped Co3O4: Kinetics and key role of electron transfer pathway

Developing cobalt-based catalysts with a high abundance of oxygen vacancies (Vo) and exceptional Vo utility efficiency for the prompt removal of stubborn contaminants through peroxymonosulfate (PMS) activation poses a significant challenge. Herein, we reported the synthesis of the reduced Mg-doped Co3O4 nanosheets, i.e. Mg-doped Co3O4-r, via Mg doping and followed by NaBH4 reduction, aiming to degrade tetracycline (TC). Various characterization results illustrated that NaBH4 reduction imparted higher Vo utility efficiency to Mg-doped Co3O4-r, along with an ample presence of reduced Co2+ species and an increased surface area, thereby substantially elevating PMS activation capability. Notably, Mg-doped Co3O4-r achieved more than 97.9% degradation of 20 mg/L TC within 10 min, showing an over 8-fold increase in reaction rate relative to the Mg-doped Co3O4 (kobs: 0.3285 min-1 vs 0.0399 min-1). The high removal efficiency of TC was sustained across a broad pH range of 3-11, even in the presence of common anions and humic acid. Radical quenching trials, EPR outcomes, and electrochemical analysis indicated that neither radicals nor 1O2 were the primary active species. Instead, electron transfer pathway played a dominant role in TC degradation. The Mg-doped Co3O4-r displayed excellent recyclability and versatility. Even after the fifth cycle, it maintained an impressive 83.0% removal of TC. Furthermore, it exhibited rapid degradation capabilities for various pollutants, including levofloxacin, pefloxacin, ciprofloxacin, malachite green, and rhodamine B. The TC degradation pathway was proposed based on LC-MS determination of its degradation intermediates. This study showcases an innovative strategy for the rational design of an efficient cobalt-based activator, leveraging electron transfer pathways through PMS activation to degrade antibiotics effectively.

Design of 2D/2D β-Ni(OH)2/ZnO heterostructures via photocatalytic deposition of nickel for sonophotocatalytic degradation of tetracycline and modeling with three supervised machine learning algorithms

Due to the expansive use of tetracycline antibiotics (TCs) to treat various infectious diseases in humans and animals, their presence in the environment has created many challenges for human societies. Therefore, providing green and cost-effective solutions for their effective removal has become an urgent need. Here, we will introduce 2D/2D p-n heterostructures that exhibit excellent sonophotocatalytic/photocatalytic properties for water-soluble pollutant removal. In this contribution, for the first time, β- Ni(OH)2 nanosheets were synthesized through visible-light-induced photodeposition of different amounts of nickel on ZnO nanosheets (β-Ni(x)/ZNs) to fabricate 2D/2D p-n heterostructures. The PXRD patterns confirmed the formation of wurtzite phase for ZNs and the hexagonal crystal structure of β-Ni(OH)2. The FESEM and TEM micrographs showed that the β-Ni(OH)2 sheets were dispersed on the surface of ZNs and formed 2D/2D p-n heterojunction in β-Ni(x)/ZNs samples. With the photodeposition of β-Ni(OH)2 nanosheets on ZNs, the surface area, pore volume, and pore diameter of β-Ni(x)/ZNs heterostructures have increased compared to ZNs, which can have a positive effect on the sonophotocatalytic/photocatalytic performance of ZNs. The degradation experiments showed that β-Ni(0.1)/ZNs and β-Ni(0.4)/ZNs have the highest degradation percentage in photocatalytic (51 %) and sonophotocatalytic (71 %) degradation of TC, respectively. Finally, the sonophotocatalytic/photocatalytic degradation process of TC was systematically validated through modeling with three powerful and supervised machine learning algorithms, including Support Vector Regression (SVR), Artificial Neural Networks (ANNs), and Stochastic Gradient Boosting (SGB). Five statistical criteria including R2, SAE, MSE, SSE, and RMSE were calculated for model validation. It was observed that the developed SGB algorithm was the most reliable model for predicting the degradation percent of TC. The results revealed that using fabricated 2D/2D p-n heterojunctions (β-Ni(x)/ZNs) is more sustainable than the conventional ZnO photocatalytic systems in practical applications.

Effects of functional group loss on biochar activated persulfate in-situ remediation of phenol pollution in groundwater and its countermeasures

Biochar is considered a good activator for use in advanced oxidation technology. However, dissolved solids (DS) released from biochar cause unstable activation efficiency. Biochar prepared from saccharification residue of barley straw (BC-SR) had less DS than that prepared directly from barley straw (BC-O). Moreover, BC-SR had a higher C content, degree of aromatization, and electrical conductivity than BC-O. Although the effects of BC-O and BC-SR on activation of Persulfate (PS) to remove phenol were similar, the activation effect of DS from BC-O was 73% higher than that of DS from BC-SR. Moreover, the activation effect of DS was shown to originate from its functional groups. Importantly, BC-SR had higher activation stability than BC-O owing to the stable graphitized carbon structure of BC-SR. Identification of reactive oxygen species showed that SO₄•^-, •OH, and ¹O₂ were all effective in degradation by BC-SR/PS and BC-O/PS systems, but their relative contributions differed. Furthermore, BC-SR as an activator showed high anti-interference ability in the complex groundwater matrix, indicating it has practical application value. Overall, this study provides novel insight that can facilitate the design and optimization of a green, economical, stable, and efficient biochar-activated PS for groundwater organic pollution remediation.

Construction of Cu7 S4 @CuCo2 O4 Yolk-Shell Microspheres Composite and Elucidation of Its Enhanced Photocatalytic Activity, Mechanism, and Pathway for Carbamazepine Degradation

Water pollution caused by the massive use of medicines has caused significant environmental problems. This work first reports the synthesis and characterization of the Cu₇ S₄ /CuCo₂ O₄ (CS/CCO) yolk-shell microspheres via hydrothermal and annealing methods, and then investigates their photocatalytic performance in removing organic water pollutants. The 10-CS/CCO composite with yolk-shell microspheres exhibits the highest photodegradation rate of carbamazepine (CBZ), reaching 96.3% within 2 h. The 10-CS/CCO also demonstrates more than two times higher photodegradation rates than the pure (Cu₇ S₄ ) CS and (CuCo₂ O₄ ) CCO. This outstanding photocatalytic performance can be attributed to the unique yolk-shell structure and the Z-scheme charge transfer pathway, reducing multiple reflections of the acting light. These factors enhance the light absorption efficiency and efficiently transfer photoexcited charge carriers. In-depth, photocatalytic degradation pathways of CBZ are systematically evaluated via the identification of degradation intermediates with Fukui index calculation. The insights gained from this work can serve as a guideline for developing low-cost and efficient Z-scheme photocatalyst composites with the yolk-shell structure.

Review on the degradation of chlorinated hydrocarbons by persulfate activated with zero-valent iron-based materials

Chlorinated hydrocarbons (CHCs) are often used in industrial processes, and they have been found in groundwater with increasing frequency in recent years. Several typical CHCs, including trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), carbon tetrachloride (CT), etc., have strong cytotoxicity and carcinogenicity, posing a serious threat to human health and ecological environment. Advanced persulfate (PS) oxidation technology based on nano zero-valent iron (nZVI) has become a research hotspot for CHCs degradation in recent years. However, nZVI is easily oxidized to form the surface passivation layer and prone to aggregation in practical application, which significantly reduces the activation efficiency of PS. In order to solve this problem, various nZVI modification solutions have been proposed. This review systematically summarizes four commonly used modification methods of nZVI, and the theoretical mechanisms of PS activated by primitive and modified nZVI. Besides, the influencing factors in the engineering application process are discussed. In addition, the controversial views on which of the two (SO₄·^- and ·OH) is dominant in the nZVI/PS system are summarized. Generally, SO₄·^- predominates in acidic conditions while ·OH prefers neutral and alkaline environments. Finally, challenges and prospects for practical application of CHCs removal by nZVI-based materials activating PS are also analyzed.

Different crystallographic Ni(OH)2 as highly efficient Fenton-like catalysts for sulfate radical activation

By a simple hydrothermal method, a phase boundary between α- and β-Ni(OH)₂ can be obtained. The Fenton-like performance of α@β-Ni(OH)₂ is 1.56 times higher than that of single β-Ni(OH). α@β-Ni(OH)₂ displays superior stability compared to α-Ni(OH)₂, β-Ni(OH)₂, and amorphous Ni(OH)₂, which makes significant contributions to developing advanced catalysts in diverse fields.

Novel construction of the catalyst from red mud by the pyrolysis reduction of glucose for the peroxymonosulfate-induced degradation of m-cresol

Red mud of low cost is regarded as a promising alternative to heterogeneous catalysts for activating peroxymonosulfate (PMS) to degrade m-cresol. Improper valence states of metal oxides and coated active substances in red mud greatly hampered its wide application. To solve this problem, the modified red mud (WRMG/700) was prepared by the pyrolysis reduction of glucose in N₂ atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS) analysis confirmed the production of Fe₃O₄, MnO and NiO in red mud and their gathering on the surface of particles. WRMG/700 exhibited the excellent performance toward PMS activation for the m-cresol degradation with 99.02% degradation efficiency and a pH-independent catalytic activity between initial pH 3-8. The removal efficiency of COD increased with the reaction time under the optimized degradation conditions. The free radical scavenging experiments and electron paramagnetic resonance (EPR) test confirmed ¹O₂ played a dominant role during m-cresol degradation in the WRMG/700/PMS system, implying m-cresol degradation was a non-radical oxidation process. Accordingly, the possible reaction mechanism was proposed. WRMG/700 retained its activation performance even after five recycles. This study showed a low cost and simple operation process for m-cresol elimination.

Novel scheme towards interfacial charge transfer between ZnIn2S4 and BiOBr for efficient photocatalytic removal of organics and chromium (VI) from water

Construction of Z-scheme heterostructure is an effective strategy to enhance the charge carriers' separation. However, successfully achieving this on the defect heterojunction to improve the photocatalytic activity remains challenging. This work successfully obtained sulfur vacancy in the ZnIn₂S₄/BiOBr (SZIS/BOB) heterojunction composites with S-O covalent bonding using a hydrothermal method. As a result, they exhibited superior photocatalytic and stability performance. The optimized SZIS/BOB-10 exhibited excellent rhodamine B degradation (95.2%) and chromium (VI) reduction (97.8%) within 100 min under visible light. The enhanced composites with S-vacancies, S-O bond, and internal electric field induced the Z-scheme charge transfer mechanism. We had verified this mechanism based on the surface photovoltage spectra, electron spin response spectra, and density functional theory calculations. This work not only provides valuable insights into designing photocatalysts with a direct Z scheme heterostructure but also delineates a promising strategy for developing efficient photocatalysts to degrade organic pollutants.

Heterogeneous activation of persulfate by Bi2MoO6-CuS composite for efficient degradation of orange II under visible light

Here in, a special catalytic system of potassium persulfate (K₂S₂O₈, PS) activated by Bi₂MoO₆-CuS composite was established for the orange II (OII) degradation under visible light. The Bi₂MoO₆-CuS composite was synthesized by a two-step hydrothermal and solvothermal methods. The structure, morphology, light absorption and photocatalytic properties of the composite were respectively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The removal efficiency of OII degradation in the Bi₂MoO₆-CuS/PS/vis system reached to 98% within 80 min, which was much higher than that of either Bi₂MoO₆ or CuS alone. A feasible mechanism analysis of OII degradation was proposed and validated by simple classical quenching experiments and electron spin resonance (ESR) spectroscopy. The high removal efficiency by the nanocomposite could be attributed to highly active species of O₂^·-, ·OH and SO₄^•- radicals in the Bi₂MoO₆-CuS photocatalytic oxidation system. Moreover, the composite material retained its activation performance even after 5 degradation cycles, which suggested its high stability.