Multi-level porous layered biochar modified cobalt-iron composite as a reusable synergistic activator of peroxymonosulfate for enhanced tetracycline degradation

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.

Highly efficient activation of peroxymonosulfate by cobalt ferrite anchored in P-doped activated carbon for degradation of 2,4-D: adsorption and electron transfer mechanism

The dispersing effect of carbon materials on nanoparticles can enhance the full exposure of their active sites. Herein, phosphorus (P)-doped activated carbon-supported trace cobalt ferrite composites (P-CoFe@BC_X) were achieved by two-step pyrolysis for efficient peroxymonosulfate (PMS) activation and water pollution remediation. The removal efficiency of 2,4-dichlorophenoxyacetic acid (2,4-D) was optimized by adjusting the coupling ratio of carbon substrate and cobalt ferrite. P-CoFe@BC₅/PMS oxidation system (0.10 g L^-1, 0.50 mM) eliminated 98.3% of 2,4-D (20.0 mg L^-1) within 60 min at unadjusted pH. The constructed adsorption enrichment and oxidative degradation pathways are highly efficient in utilizing reactive oxygen species (ROS), and the dual tracks of free and non-free radicals achieve the rapid degradation of 2,4-D. P-doped activated carbon acts as an electron shuttle to accelerate electron transfer between active sites and enhances the adsorption efficiency of 2,4-D and PMS onto the composites. In addition, the P-CoFe@BC₅/PMS oxidation system still exhibited strong 2,4-D removal performance at a wide pH range of 2.0-10.0. The inhibitory effect of environmental components was related to their concentration, such as chloride, bicarbonate, sulfate and humic acid. Density functional theory calculations show that ROS tends to attack the CO bond on the 2,4-D branch chain, and the degradation products show lower biological toxicity. Hence, the constructed cobalt ferrite anchored P-doped activated carbon activated PMS system has great potential in treating organic wastewater.

Catalytic oxidation activation of peroxymonosulfate over Fe-Co bimetallic oxides for flurbiprofen degradation

In this research, FeCo₂O₄ nanomaterial was successfully synthesized by a typical sol-gel method and conducted as an effective agent for peroxymonosulfate (PMS) activation to eliminate antibiotics flurbiprofen (FLU), a strong nonsteroidal drug. FeCo₂O₄ nanomaterial was characterized by XRD, TEM, SEM, and XPS. Various characterization results proved that FeCo₂O₄ held stable spinel structure. The interfering factors including initial pH, PMS concentration, catalyst dosage, inorganic anions, and humic acid on FLU removal were also discussed. The conclusion was that the removal efficiency of FLU reached 98.2% within 120 min after adding FeCo₂O₄ (0.4 g L^-1) and PMS (3 mM). The optimal pH for FLU degradation was the initial pH of 6.5; too acidic or alkaline was not conductive to the degradation. The existence of HA and Cl^- restrained the degradation of FLU, and HCO₃^- promoted the removal, while the influence of NO₃^- and SO₄^2- could not be considered. The radical scavenging experiment confirmed that ^•OH, O₂^•-, and SO₄^•- participated in FLU removal and SO₄^•- functioned a leading role. FeCo₂O₄ showed high efficiency for PMS activation in pH range of 3.0 to 10.0. After the fourth cycle operation, the FLU removal rate exceeded 76.9%, and the Co leaching rate was low during the catalytic reaction. This study shows that FeCo₂O₄ nanomaterial is an efficient and environment-friendly catalyst, which can be applied for PMS activation to remove organic pollutants in water.

Rape Straw Supported FeS Nanoparticles with Encapsulated Structure as Peroxymonosulfate and Hydrogen Peroxide Activators for Enhanced Oxytetracycline Degradation

Iron-based catalysts with high load content of iron sulfide (FeS) were commonly peroxymonosulfate (PMS) and hydrogen peroxide (H₂O₂) activators to degrade organic pollutants but limited catalytic efficiency and increased risk of ferrous ion leaching restricted their use. Meanwhile, various biomass materials such as straw, peel, and branch have been extensively prepared into biochar for mechanical support for iron-based catalysts; however, the preparation process of biochar was energy-intensive. In this study, FeS nanoparticles modified rape straw composites (RS-FeS) encapsulated with ethylenediaminetetraacetic acid (RS-EDTA-FeS) were successfully presented by in-situ synthesis method for efficiently activating PMS and H₂O₂ to degrade oxytetracycline (OTC), which was economical and environmentally friendly. The results showed that the modified rape straw can remove OTC efficiently, and the addition of EDTA also significantly enhanced the stability and the reusability of the catalyst. In addition, EDTA also promoted the activation of H₂O₂ at neutral pH. The OTC degradation efficiency of the two catalysts by PMS was faster than that of H₂O₂, but H₂O₂ had a stronger ability to remove OTC than PMS. The highest OTC removal efficiency of RS-FeS and RS-EDTA-FeS were 87.51 and 81.15%. O₂^•- and ¹O₂ were the major reactive oxidative species (ROS) in the PMS system. Furthermore, compared with RS-FeS, the addition of EDTA inhabited the generation of O₂^•- in the PMS system. Instead, O₂^•- and ^•OH were the major ROS in the H₂O₂ system, but ¹O₂ was also identified in RS-FeS/H₂O₂ system. RS-EDTA-FeS showed a trend of rising first and then decreasing in recycle test. Instead, the removal rate of OTC by RS-FeS decreased significantly with the increase in reuse times. In the actual wastewater test, the TOC removal of two catalysts active by H₂O₂ was better than PMS, which was consistent with the test results of OTC, indicating that the two catalysts have application value in the removal of organic pollutants in actual wastewater. This study directly used plant materials as catalysts and omits the preparation process of biochar, greatly reduces the preparation cost and secondary pollution of catalysts, and provides theoretical support for the deepening of advanced oxidation technology.

A critical review on biochar-based catalysts for the abatement of toxic pollutants from water via advanced oxidation processes (AOPs)

Proper waste disposal is a key towards sustainable development. Wastewater treatment is delineated by the application of efficient, economic and novel catalysts. Biochar is derived from the thermochemical conversion of biomass or any carbonaceous materials and is considered as one of the most eco-friendly substitute for activated carbon. Owing to its large surface area, porosity, crystallinity and active functional groups, the biochar-based catalysts has been extensively applied for the abatement of toxic pollutants from wastewater streams. While most of the reviews focus on the adsorptive properties of the biochar, this review critically analyses the recent development of biochar-based catalysts in the field of advanced oxidation processes (Fenton-like systems, photocatalytic and sonocatalytic systems). The presence of persistent free radicals and oxygen-containing functional groups renders biochar to act as catalyst. The mechanisms accompanying catalytic performance of biochar-based catalysts have also been reviewed. However, the research in this area is quite at an initial phase, and many advancements schemes are essential prior to scale-up and commercialization. Future researches should be devoted to more efficient and rigorous understanding of the structural properties of biochar to engineer the catalytic degradation of targeted pollutants in wastewater treatment.