Sulfate Radical-based Advanced Oxidation Processes Research Articles

Cobalt cross-linked ordered mesoporous carbon as peroxymonosulfate activator for sulfamethoxazole degradation

Ordered mesoporous carbons (OMCs) functionalized with catalytically-active metals have many potential applications in sulfate radical-based advanced oxidation processes for degrading antibiotics. Cobalt cross-linked ordered mesoporous carbon materials (OMC-Co-Tx) were synthesized through evaporation-induced self-assembly, calcinated at (600 to 800) oC. The OMC-Co-Tx materials were then employed as peroxymonosulfate (PMS) activators for removal of sulfamethoxazole (SMX) from aqueous solutions. OMC-Co-T800 prepared by calcination at 800 °C had a large specific surface area (449 m2/g), uniform pore structure (∼4.5 nm) and showed the best performance for activation of PMS. With a dosage of 0.1 g/L OMC-Co-T800 and 0.4 g/L PMS, the functionalized OMC material allowed SMX (10 mg/L) removal of up to 99% in 30 min. The increase of calcination temperature promoted the reduction of cobalt in OMC materials and increased the defects in their structure, resulting in better catalyst behavior. Quenching experiments and electron paramagnetic resonance analyses showed that reactive species of sulfamethoxazole degradation involved in the OMC-T800/PMS system were SO4•−, OH, O2•− and 1O2. HPLC-MS analyses of degradation intermediates formed in the OMC-Co-T800/PMS system allowed elucidation of four transformation pathways for SMX degradation.

Attenuation effects of ZVI/PDS pretreatment on propagation of antibiotic resistance genes in bioreactors: Driven by antibiotic residues and sulfate assimilation

Sulfate radical-based advanced oxidation processes (AOPs) combined biological system was a promising technology for treating antibiotic wastewater. However, how pretreatment influence antibiotic resistance genes (ARGs) propagation remains largely elusive, especially the produced by-products (antibiotic residues and sulfate) are often ignored. Herein, we investigated the effects of zero valent iron/persulfate pretreatment on ARGs in bioreactors treating sulfadiazine wastewater. Results showed absolute and relative abundance of ARGs reduced by 59.8%− 81.9% and 9.1%− 52.9% after pretreatments. The effect of 90-min pretreatment was better than that of the 30-min. The ARGs reduction was due to decreased antibiotic residues and stimulated sulfate assimilation. Reduced antibiotic residues was a major factor in ARGs attenuation, which could suppress oxidative stress, inhibit mobile genetic elements emergence and resistant strains proliferation. The presence of sulfate in influent supplemented microbial sulfur sources and facilitated the in-situ synthesis of antioxidant cysteine through sulfate assimilation, which drove ARGs attenuation by alleviating oxidative stress. This is the first detailed analysis about the regulatory mechanism of how sulfate radical-based AOPs mediate in ARGs attenuation, which is expected to provide theoretical basis for solving concerns about by-products and developing practical methods to hinder ARGs propagation.

MnFe2O4 nanoparticles coated on one-dimensional carbon nanowires derived from Nitrilotriacetic acid as efficient catalysts to activate peroxymonosulfate for moxifloxacin degradation

Sulfate radical-based advanced oxidation processes (AOPs) are highly reliable for the elimination of recalcitrant contaminants by increasing degradability and reducing toxicity. Here, MnFe2O4 nanowires (MnFe2O4 NWs), composed of abundant MnFe2O4 nanoparticles immobilized on one-dimensional carbon nanowires derived from annealed MnFe-Nitrilotriacetic acid (MnFe-NTA) precursor was successfully synthesized. The MnFe2O4 NWs, which could provide more active sites, were then utilized to activate peroxymonosulfate (PMS) for oxidizing the target pollutant Moxifloxacin (MOX) in an aqueous solution. The MnFe2O4 NWs/PMS system acquired 91.9% removal of MOX and achieved 55.1% chemical oxygen demand (COD) degradation efficiency in 30 min. The results exhibited that the increased catalyst doses and PMS concentration lead to ascending MOX removal rate, which decreased with the participation of co-existing ions. Besides, there is a close relationship between original pH and MOX degradation efficiency. It was found that SO4⋅–, ⋅OH, 1O2, and O2⋅– were involved in the MOX degradation by quenching experiments and electron paramagnetic resonance (EPR) detection. More importantly, the stable magnetism of MnFe2O4 NWs contributed to its convenient recycling. Finally, a reliable mechanism for activating PMS was proposed based on the aforementioned results and previous researches, which could exhibit a novel horizon in effluent treatment.

Performance and mechanism of sulfite mediated oxidation of organic contaminants using iron(III) titanium oxide as catalyst

As sulfite has been employed currently in the catalytic degradation of various pollutants, the construction of more suitable and cheaper catalytic systems is required. Herein, a heterogeneous system for S(IV) activation by iron(III) titanium oxide (Fe2TiO5) was proposed to proceed the removal of acid orange 7 (AO7) and seven typical pharmaceutical and personal care products (PPCPs). Typically, the AO7 (10 mg L−1) can be degraded up to 67% within 60 min ([Fe2TiO5] = 0.8 g L−1, [S(IV)] = 2.0 mM, pH = 6.0). The effects of initial AO7 concentration, pH, Fe2TiO5 dosage, S(IV) concentration, and co-existing anions (HCO3− and H2PO4−) were examined to explore the application conditions and resistance of Fe2TiO5 −S(IV) system. Moreover, the stability of Fe2TiO5 −S(IV) system was tested by sequential runs, while XRD was also performed for the robustness evaluation of catalyst. The scavenging experiment showed that the active species in the system mainly include SO5•−, HO•, and SO4•−, while SO4•− being the dominant one. Through the competitive experiments of EDTA, the density functional theory (DFT) computation and the XPS analysis, a sensible mechanism was proposed that the electron transfer within Fe(III)−SO32− complex and the Fe(III)−Fe(II)−Fe(III) redox process were crucial for the sulfite activation. Meanwhile, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants (kobs) was established with a high significance (R2 = 0.991, p = 0.006) by using four descriptors. This work provides an innovative strategy of sulfate radical-based advanced oxidation processes (SR−AOPs) for organic contaminants degradation using metal oxide catalysts.

Efficient degradation of diazinon and adsorption of released phosphate through activating peroxymonosulfate by Zr-doped ZIF-8 encapsulated CoFe2O4 composite

The widespread application of organophosphorus pesticides (OPPs) has caused pollution in many aqueous environments. Sulfate radical-based advanced oxidation processes (SR-AOPs) are effective for degrading refractory organic pollutants. However, only a limited number of studies have been conducted in the field of OPP removal using SR-AOPs. The residue of phosphate generated by the degradation of OPPs is also a problem worth considering. Herein, Zr-doped ZIF-8 encapsulated CoFe2O4 magnetic composite was successfully synthesized (CoFe2O4 @Zr/ZIF-8) to activate peroxymonosulfate (PMS) for the degradation of diazinon (DZ) and adsorb released phosphate. CoFe2O4 @Zr/ZIF-8 demonstrated excellent catalytic performance, with 100% DZ degradation (20 mg/L); most of the phosphates produced during degradation were also adsorbed. The wrapping of ZIF-8 effectively inhibited the leaching of cobalt ions. Different factors affecting DZ removal were investigated. Further study demonstrated that sulfate radicals (SO4•−), hydroxyl radicals (•OH), and singlet oxygen (1O2) are responsible for the degradation of DZ, with SO4•− and 1O2 playing pivotal roles. This study presents a potential strategy for both OPP degradation and phosphate adsorption and provides a new concept for utilizing multifunctional materials in environmental remediation.

Multiple path-dominated activation of peroxymonosulfate by MOF-derived Fe2O3/Mn3O4 for catalytic degradation of tetracycline

Sulfate radical-based advanced oxidation process (SR-AOP) has been identified as an efficient technology for the treatment of antibiotic contamination, with a focus on the development of catalysts for efficient activation of persulfate. In this work, a novel peroxymonosulfate (PMS) activator, metal organic framework (MOF) derived Fe2O3/Mn3O4 composite, was prepared and characterized. The physicochemical properties, catalytic performance of the catalyst and the degradation mechanism of tetracycline (TC) by the reaction system were thoroughly investigated. Combined with the experimental results and density functional theory (DFT) calculations, we can reasonably speculate that both radical (O2˙ˉ) and non-radical (1O2 and electron transfer) pathways contributed to the catalytic activation of PMS for TC degradation. The enhanced catalytic activity was attributed to the combination of Fe2O3 with Mn3O4 accelerated Fe(II)/Fe(III) cycle and Mn(II)/Mn(III) cycle. In addition, the extended peroxide O-O bond length facilitated the generation of 1O2. After five consecutive experiments, no significant change in catalytic performance and chemical structure was found, indicating that this catalyst had not only good chemical stability but also astonishing reusability. The research results are expected to provide some valuable theoretical basis for MOF-derived metal oxides catalytic activation of PMS for wastewater treatment.

Efficient removal of doxycycline by MnNb2O6/sulfite process: Response surface methodology optimization and mechanism analysis

Sulfate radical-based advanced oxidation process could efficiently remove many emerging contaminants from wastewater. Considering the unique properties of MnNb2O6, an efficient MnNb2O6/sulfite system was developed to remove doxycycline residue from the aqueous environment. In this research, MnNb2O6 nanomaterial was successfully synthesized through a one-step hydrothermal route at 260 °C for 24 h. The paramagnetic behavior of MnNb2O6 was observed at 300 K. Scanning electron microscopy and transmission electron microscopy images showed that the size of petal-like MnNb2O6 crystals was 250–700 nm. The specific surface area of MnNb2O6 was 24.84 m2/g. Optimization of MnNb2O6/sulfite process was achieved by Box-Behnken Design based on response surface methodology. Under the predicted optimal conditions (pH of 8.7, MnNb2O6 dosage of 0.29 g/L, doxycycline concentration of 10.8 mg/L, and sodium sulfite concentration of 4.3 mM), the degradation efficiency of doxycycline could reach 85.1%. Mn species was found to be the dominant factor in MnNb2O6/sulfite system. Both SO4•− and •OH were identified as primary active radicals in MnNb2O6/sulfite system. Furthermore, six transformation products of doxycycline were elucidated. This work offers a simple water treatment process for efficiently removing doxycycline residue in the environment.

Degradation of oxytetracycline by iron-manganese modified industrial lignin-based biochar activated peroxy-disulfate: Pathway and mechanistic analysis

In this study, high-performance Fe-Mn-modified industrial lignin-based biochar (FMBC) was successfully prepared to facilitate the efficient degradation of oxytetracycline by its driven sulfate radical-based advanced oxidation process with 90% degradation within 30 min. The results showed that oxygenated functional groups (e. g. hydroxyl, carbonyl, etc.) in industrial lignin-based biochar, the synergistic effect of transition metals Fe and Mn, and defective structures were the active sites for activation of peroxy-disulfate. SO4·− produced during the degradation process assumed a key function. Significantly, 38 intermediates were innovatively proposed for the first time in the system, and oxytetracycline was degraded in 7 ways, including deamidation, demethylation, hydroxylation, secondary alcohol oxidation, ring opening, dehydration, and carbonylation. A new perspective on the application of industrial lignin in the advanced oxidative degradation of organic pollutants was provided by this study.

Pilot-scale regeneration of wastewater through intensified sulfate radical-based advanced oxidation processes (PMS/UV-A, PMS/H2O2/UV-A, and PMS/O3): Inactivation of bacteria and mechanistic considerations

This research addresses the application of advanced oxidation processes (AOPs) for wastewater reclamation at pilot scale, one of the main limitations usually observed in this type of technology. Although interest in sulfate radical-based AOPs (SR-AOPs) has increased considerably in recent years, pilot-scale application studies are very scarce. The generation of free radicals by activation of peroxymonosulfate (PMS) can be enhanced by the introduction of UV-A radiation, or other oxidants such as hydrogen peroxide (H2O2) or ozone (O3), increasing the efficiency of the processes with lower reagent consumption.The combination of 0.5 mM PMS and 0.25 g·h−1 O3 was the fastest process in inactivation of Enterococcus faecalis, achieving inactivation in less than 45 min. Significant synergies were also observed for the combination of PMS, H2O2 and UV-A radiation, achieving total inactivation in less than 120 min, a performance significantly lower than that of the PMS/O3 system. Mechanistic studies showed that the sulfate radical (SO4•-) was responsible for bacterial inactivation in the PMS/O3 system, while in the PMS/H2O2/UV-A system the predominant species varies according to the molar ratio of the oxidants. Thus, the hydroxyl radical (•OH) is predominant in a 1:1 ratio, and SO4•- is predominant in a 1:3 ratio. This phenomenon occurs because an excess of PMS acts as a sink for radicals, preventing their interaction with bacteria.The treatments studied have been shown to be effective in the simultaneous elimination of several pathogenic microorganisms such as Enterococcus faecalis, Escherichia coli, and Staphylococcus aureus, making this technology an alternative to conventional disinfection treatments.

Evaluation of persulfate enhanced electrocoagulation (EC/PS) for bio-treated landfill leachate: Organics transformation pathways and carbon flow quantitative analysis

The sulfate radical-based advanced oxidation processes (SR-AOPs) have shown promise in treating bio-treated landfill leachate (BLL). However, little is known about the dissolved organic matter (DOM) transformation and reaction mechanisms at the molecular level after treating BLL using SR-AOPs. This study investigates the DOM degradation and transformation pathways during both electrocoagulation (EC) and persulfate enhanced electrocoagulation (EC/PS) of real BLL samples. The results indicate that the removal efficiency of chemical oxygen demand (COD) and total organic carbon (TOC) were enhanced to 46.34% and 36.39%, respectively, once persulfate is coupled with EC. Additionally, the removal of fluorescent contaminants in BLL significantly enhanced after treatment with EC/PS to 91.57%, 80.99%, and 39.10% for biogenic humic-like components C1, C2, and C3, respectively. A decrease in the proportion of macromolecular and aromatic matters was observed after the EC/PS process. The degree of oxidation of DOM was reduced, and the compounds with unstable structure and high biodegradability became the main compounds in the EC/PS effluent. The analysis of sediments generated by EC and EC/PS showed a similar composition of FeOOH and Fe3O4, although there was additional Fe2(SO4)3 in the EC/PS sludge. The degraded organics in the solution and sediment phase were quantified by material flow analysis, indicating that the precipitation was the main contributor to DOM removal during the EC/PS process. These findings aid in understanding the role of PS in the EC/PS process during real landfill leachate treatment and reevaluate the advantages and limitations of PS as an oxidant.

Multiaperture g-C3N4@SiO2 to activate peroxydisulfate via visible light for efficient Rhodamine B removal.

The sulfate radical-based advanced oxidation process (SR-AOPs) has been verified as a promising method tohandle the persistent organic compounds in water using peroxydisulfate (PDS) as oxidant. A Fenton-like process was constructed and showed great potential to remove organic pollutants using visible-light-assisted PDS activation. The g-C3N4@SiO2 was synthesized via thermo-polymerization, and characterized using powder X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) method, photoluminescence (PL), transient photocurrent, and electrochemical impedance. Photocatalytic performance was demonstrated using the removal rate of Rhodamine B (RhB), and 96.08% RhB was removed from the solution within 50 min (10 mg/L in 200 mL, g-C3N4@SiO2 = 0.25 g/L, pH = 6.3, PDS = 1 mmol/L). The free radical capture experiment proved that HO•,h+,[Formula: see text] and [Formula: see text] were generated and removed RhB. The cyclic stability of g-C3N4@SiO2 has also been studied, and the result shows no noticeable difference in the six cycles. The system of visible-light-assisted PDS activation might provide a novel strategy for wastewater treatment and must be an environment-friendly catalyst.

Landfill leachate treatment by hydroxyl and sulfate radical-based advanced oxidation processes (AOPs)

A negative aspect of landfilling is the formation of multicomponent dark liquids that contain a variety of chemical pollutants and substances. Given the environmental risk, treatment methods must be developed and applied, in order to degrade and destroy the target pollutants. This work evaluates the efficacy of UV/Fe2+/H2O2 and UV/Fe2+/S2O82− processes for the degradation of landfill leachate and examines the influence of [Fe2+]/[Oxidant] ratio, UV light, dosing mode and pretreatment by a physicochemical process. Regarding photo-Fenton, best removal efficiencies (65.58 % COD, 48.12 % TOC, 86.65 % Color Index) were achieved under operating conditions as CODo:H2O2 mass ratio = 1:1, [Fe2+]/[H2O2] = 1:10, pH = 3.5 and treatment time = 60 min. UV/Fe2+/S2O82− process showed better performance (76.34 % COD, 71.44 % TOC, 88.94 % Color Index) in the respective conditions, albeit its efficacy was significantly affected by sulfate radical selectivity. Additionally, a series of experiments proved that oxidant dosing and coagulation/flocculation had a positive impact on the effectiveness of the photocatalytic applications. On the contrary, UV light didn't have a significant effect on dark Fenton's ability to degrade landfill leachate, as a result of the dark color of the sample and the solids generated in the beginning of the processes. Finally, a dual-oxidant catalytic process (UV/Fe2+/H2O2/S2O82−) was applied, exhibiting lower performance than that of UV/Fe2+/H2O2 (or UV/Fe2+/ S2O82−).

Degradation of atrazine by electroactivation of persulfate using FeCuO@C modified composite cathode: Synergistic activation mechanism

In sulfate radical-based advanced oxidation processes (SR-AOPs), high-efficiency and perdurable materials have drawn considerable interest for use as cathodes, which can effectively degrade refractory organic contaminants through the synergistic electro-activation and transition metal activation of persulfate (PS). Here, the FeCuO@C modified composite cathode (FeCuO@C/AGF) was synthesized via the solvothermal and thermal treatment method based on the CuFe-MOF-74 structure, and the electro-activation PS process (EC/FeCuO@C/AGF/PS) was developed to effectively remove atrazine (ATZ). The surface morphology, electrochemical characteristics, chemical composition, crystal structure, and electrode surface wettability of FeCuO@C/AGF were investigated. It was found that the proposed EC/FeCuO@C/AGF/PS process can successfully remove 100% of ATZ in 20 min at a low current density (2 mA cm−2) and a low PS concentration (0.4 mM), and PS is successfully activated by combining the electrical and transition metal synergistic activation. The FeCuO@C/AGF cathode exhibits outstanding catalytic functionality over a broad pH range (2–9) and remains stable over five successive cycles. Additionally, the active species involved in the reaction as well as the potential ATZ degradation reaction mechanisms and pathways are discussed. Electrochemical oxidation is a process in which both radicals (SO4·−, ·OH, and O2·−) and non-radical (1O2) participate in the degradation of ATZ. The intermediates of the ATZ degradation process were studied upon the toxicity changing, and the toxicity of the intermediates was found to be reduced during degradation. These results present a novel approach toward the establishment of an effective and reliable electrode in SR-AOPs that can efficiently treat pesticide wastewater.

Effects of Concentration Polarization and Membrane Orientation on the Treatment of Naproxen by Sulfate Radical-Based Advanced Oxidation Processes within Nanofiltration Membranes with a Catalytic Support

The structure with a selective nanofiltration (NF) layer on top of a catalytic ultrafiltration (UF) membrane provides the possibility of treating micropollutants (MPs) by both rejection and degradation. However, such a dense selective layer unavoidably induces a formation of a highly concentrated retentate and a low utilization of the oxidant due to its rejection. A different membrane orientation is expected to solve the problems mentioned above since the concentrated MPs can be degraded within the catalytic support, and the rejection of the oxidants can be avoided when the pressure is applied from the porous support side. However, the resulting complex concentration polymerization (CP) effects are not well understood, and the effects of the following concentration changes of the MPs and the oxidants around the catalyst within the porous support membrane are unclear as well. In this work, three polyelectrolyte multilayers with different selectivity were fabricated on PES@CoFe2O4 catalytic UF membranes by sequential dip-coating. Concentration polarization models are utilized to predict the concentrations of naproxen and peroxymonosulfate (PMS) within the porous catalytic support under different membrane orientations. The results of naproxen removal after adding PMS show that a higher naproxen removal can be obtained with a higher concentration ratio of PMS to naproxen (cPMS/cNPX). Moreover, it is shown that the MPs in the feed solution can be degraded in a catalysis-separation sequence, exhibiting the potential of rejecting and simultaneously degrading MPs. However, the coating of a selective polyelectrolyte multilayer on the catalytic UF membranes also causes lower accessibility of PMS and naproxen to the catalysts embedded within the polymeric membranes, resulting in the decline of degradation efficiency. By coating only one side of the membranes, this negative effect caused by the polyelectrolyte coating can be mitigated. Overall, a 97% removal of naproxen on the permeate side and a 12% degradation of naproxen on the feed side were observed with the one-side-coated membranes under a catalysis-separation sequence. This work highlights the key role that concentration polarization can play in the degradation efficiency of naproxen in catalytic NF membranes, providing valuable guidance for the design of further improved catalytic membranes.

UV-activated persulfates oxidation of anthraquinone dye: Kinetics and ecotoxicological assessment

Sulfate radical-based advanced oxidation processes (SR-AOPs) are gaining popularity as a feasible alternative for removing recalcitrant pollutants in an aqueous environment. Persulfates, namely peroxydisulfate (PDS) and peroxymonosulfate (PMS) are the most common sulfate radical donors. Persulfates activation by ultraviolet (UV) irradiation is considered feasible due to the high concentration of radicals produced as well as the lack of catalysts leaching. The research focuses on determining the impact of activated PDS and PMS on the degradation of anthraquinone dye, i.e., Acid Blue 129 (AB129). UV-activated PDS and PMS can quickly degrade the AB129 as well as restrict the formation of by-products. This could explain the reduced ecotoxicity levels of the treated water after degradation, using an aquatic plant (Lemna minor) and a crustacean (Daphnia magna). This, on the other hand, can ensure that the sulfate radical-based processes can be an environmentally friendly technology.

Peroxymonosulfate activation by Ru/CeO2 for degradation of Triclosan: Efficacy, mechanisms and applicability in groundwater

Although ruthenium (Ru) catalyst has attracted extensive attention in many chemical industries, its application in sulfate radical-based advanced oxidation processes (AOPs), especially the heterogeneous Ru activator for groundwater remediation, is less studied. In this study, Ru species was loaded on cerium dioxide (CeO2) particles to prepare the stable Ru/CeO2, and it served as the peroxymonosulfate (PMS) activator to degrade triclosan (TCS) which is a toxic and recalcitrant pollutant in groundwater worldwide. Ru/CeO2 showed a greater performance for activating PMS when compared with some other AOPs, and TCS in the system can be almost completely removed within 10 min. Ru/CeO2 and PMS dosage can undoubtedly affect the TCS removal rate, and acid or neutral environments favored the degradation. Besides, interference of potential complex components in groundwater on the TCS removal rate must get attention, Cl- had an obvious promotion effect, while HCO3– inhibited these processes; metal cations could slightly enhance the PMS activation, while humic acid had an inhibitory effect. Theoretically, 1O2 (non-radical pathway) was determined to play the major role in TCS removal during PMS activation in the system, while ·OH and SO4·- (radical pathway) played a minor role. Importantly, the activator has good stability and reusability, and its TCS removal capacity decreased by only 4.04% after five cycles; it also performed excellently in batch experiments with natural groundwater and in soil column experiments under different pH and hydraulic conditions. These indicate that the Ru/CeO2/PMS system has promising applicability for TCS remediation in groundwater environments.

Highly catalytic and durable nanocellulose fibers-based nanoporous membrane film for efficient organic pollutant degradation

Sulfate radical-based advanced oxidation processes (SR-AOPs) have received significant attention because of the efficient and non-selective degradation of organic pollutants during water purification. Metal-organic frameworks (MOFs) are considered a promising catalyst for efficiently activating the oxidant in SR-AOPs to generate radicals such as SO4·− and ·OH due to the large specific surface area and highly exposed active metal ions of MOFs. However, the natural characteristics, such as small-sized particles (micro or nano), brittleness, low density, and easy aggregation, limit using powdery MOFs in practical applications requiring recyclability. This study proposes a facile method to fabricate ZIF-67@cellulose nanofibril (CNF)-based catalytic hybrid membranes and their water purification by the peroxymonosulfate (PMS) activation. The chemical structure and surface morphology of membranes were investigated, indicating that CNFs immobilize the MOF nanoparticles to form a stable and porous two-dimensional membrane. Additionally, the catalytic membrane embedding ZIF-67 nanoparticles was reusable after wastewater treatments. The ZIF-67@CNFs hybrid membrane activated PMS to produce SO4·− and ·OH radicals. Thereafter, highly active radicals efficiently degraded approximately 98.7 % of the organic dye Rhodamine B within 10 min. These findings imply that MOFs can be hybridized with nanocellulose fibers for high-performance catalytic membranes for water remediation.

Applications of biochar in sulfate radical-based advanced oxidation processes for the removal of pharmaceuticals and personal care products.

Recently, biochar (BC) has been increasingly used as a catalyst for the degradation of 'emerging pollutants' (EPs). Pharmaceuticals and personal care products (PPCPs), which come under 'EPs', can be harmful to the aquatic ecosystem despite being present in very low concentrations (ng/L-μg/L). Advanced oxidation processes (AOPs), which produce sulfate radical (SR-AOPs), show a great potential to degrade PPCPs effectively from wastewater. It is mainly due to the higher stability, long half-lives and better non-selectivity of SO4• - compared with AOPs with •OH generation. Furthermore, research focus is now given on AOPs coupled with BC-supported catalyst to enhance the degradation of PPCPs because of quicker generation of radicals (•OH, SO4•-) by the activation of persulfate (PS) and peroxymonosulfate (PMS). This article sheds light on the catalytic ability of BC after its physical and chemical modifications such as acid/alkali treatment and metal doping. The role of persistent free radicals (PFRs) in the BC for effective removal of PPCPs has been elaborated. Its potential applications in synthetic as well as real wastewater have also been discussed.

Activation of peroxydisulfate via Fe@sulfur-doped carbon-supported nanocomposite for degradation of norfloxacin: Efficiency and mechanism

In this study, Fe, S co-doped carbon-based catalysts (Fe@SCNs) for activation of peroxymonosulfate (PMS) were prepared by calcination of κ-carrageenan (κ-c) hydrogel cross-linked by Fe3+. The catalysts prepared at a κ-c concentration of 3 wt%, a Fe3+ concentration of 0.3 M and a calcination temperature of 900 °C showed the best performance for activation of PMS, allowing complete degradation of norfloxacin (NOR) within 40 min at a degradation rate of 0.2878 min−1. Different active species (1O2, OH, SO4−, O2− and FeⅣ) collaborated for the degradation of NOR, in which 1O2 dominated the reaction. The doping of S elements in carbonaceous materials could enhance the activation capacity of PMS for the reason that S-doping facilitated the electron transfer capability of the catalysts and the introduction of thiophene sulfur (CSC) generated more active sites, while S22− also enhanced the conversion of Fe3+ to Fe2+, resulting in the continuous formation of more ROS. The Fe@SCN/PMS system not only had a broad range of pH (3.0–11.0) applicability, but also was little affected by inorganic ions (NO3−, Cl−, HCO3− and H2PO4−) or organic compounds (humic acid) in water. This research provides an innovative approach for the preparation of metal and heteroatom co-doped carbon-based catalysts for sulfate radical-based advanced oxidation process.

Fibrous cellulose nanoarchitectonics on N-doped Carbon-based Metal-Free catalytic nanofilter for highly efficient advanced oxidation process

N-doped carbon materials have been considered as promising efficient and environment-friendly catalysts for sulfate radical-based advanced oxidation processes (SR-AOPs). Herein, we first report a facile strategy to prepare nanoporous N-doped carbon nanofilters (NCNFs) using cellulose nanofibers (CNFs) and metal–organic framework (MOF) as the superior metal-free catalytic for SR-AOPs. In this work, CNFs are employed as nanoporous templates and binders to fix ZIF-8 for fabricating ZIF-8@CNF membrane, and the as-prepared membrane was converted into NCNFs by a simple pyrolysis process. To evaluate the catalytic degradation performance of the NCNFs, methylene blue (MB) was chosen as a model contaminant. It is found that the NCNFs demonstrate a remarkable efficiency for MB removal by peroxymonosulfate (PMS) activation, and 96 % of MB (10 mg/L) was degraded in 15 min. The catalytic reaction and process including removal and washing are very simple and easy because the nanoporous N-doped carbons are fixed on CNF-derived networks. Furthermore, the reaction parameters including reaction temperature, pH, and catalyst/PMS dosage are also investigated. In addition, a series of radical quenching experiments reveal that non-radical mechanism is responsible for the degradation of MB. Importantly, the NCNFs membrane showed a good reusability by the annealing process and it can serve as a catalytic filter in practical organic dye remediation application. This present work shows that MOF derived metal-free carbon membranes have a promising avenue as catalysts for organic dye degradation and water remediation.