Wide pH Adaptability Research Articles

Engineering of cyclodextrin glycosyltransferase improves the conversion efficiency of rebaudioside A to glucosylated steviol glycosides and increases the content of short-chain glycosylated steviol glycoside

BackgroundCompared with steviol glycosides, the taste of glucosylated steviol glycosides is better and more similar to that of sucrose. At present, cyclodextrin glucanotransferase (CGTase) is primarily used to catalyze the conversion of steviol glycosides to glucosylated steviol glycosides, with soluble starch serving as a glycosyl donor. The main disadvantages of enzymatic transglycosylation are the limited number of enzymes available, the low conversion rates that result in low yields, and the lack of selectivity in the degree of glycosylation of the products. In order to fill these gaps, the proteome of Alkalihalobacillus oshimensis (also named Bacillus oshimensis) was used for mining novel CGTases.ResultsHere, CGTase-15, a novel β-CGTase with a wide pH adaptation range, was identified and characterized. The catalyzed product of CGTase-15 tasted better than that of the commercial enzyme (Toruzyme® 3.0 L). In addition, two amino acid sites, Y199 and G265, which play important roles in the conversion of steviol glycosides to glucosylated steviol glycosides were identified by site-directed mutagenesis. Compared with CGTase-15, CGTase-15-Y199F mutant significantly increased the conversion rate of rebaudioside A (RA) to glucosylated steviol glycosides. Compared with CGTase-15, the content of short-chain glycosylated steviol glycosides catalyzed by CGTase-15-G265A mutant was significantly increased. Moreover, the function of Y199 and G265 was verified in other CGTases. The above mutation pattern has also been applied to CGTase-13 (a CGTase discovered by our laboratory with great potential in the production of glycosylated steviol glycosides), confirming that the catalytic product of CGTase-13-Y189F/G255A mutant has a better taste than that of CGTase-13.ConclusionsThis is the first report on the improvement of the sensory profiles of glycosylated steviol glycosides through site-directed mutagenesis of CGTase, which is significant for the production of glycosylated steviol glycosides.

Removal of oxytetracycline from wastewater by biochar modified with biosynthesized iron oxide nanoparticles and carbon nanotubes: Modification performance and adsorption mechanism

The pollution problem of oxytetracycline (OTC) from wastewater becomes more serious, so an efficient, economical, and green adsorption material is urgently explored. In this study, the multilayer porous biochar (OBC) was prepared by coupling carbon nanotubes with iron oxide nanoparticles synthesized by Aquabacterium sp. XL4 to modify corncobs under medium temperature (600 °C) conditions. The adsorption capacity of OBC could reach 72.59 mg g−1 after preparation and operation parameters were optimized. In addition, various adsorption models suggested that OTC removal resulted from the combined effect of chemisorption, multilayer interaction, and disordered diffusion. Meanwhile, the OBC was fully characterized and exhibited a large specific surface area (237.51 m2 g−1), abundant functional groups, stable crystal structure, high graphitization, and mild magnetic properties (0.8 emu g−1). The OTC removal mechanisms mainly included electrostatic interactions, ligand exchange, π-π bonding reactions, hydrogen bonds, and complexation. pH and coexistence substance experiments revealed that the OBC possesses a wide pH adaptation range and excellent anti-interference ability. Finally, the safety and reusability of OBC were confirmed by repeated experiments. In summary, OBC as a biosynthetic material shows considerable potential for application in the field of purifying new pollution from wastewater.

Aluminum copper bimetallic metal organic gels/sodium alginate beads for efficient adsorption of ciprofloxacin and methylene blue: Adsorption isotherm, kinetic and mechanism studies

In this research, a new aluminum-copper bimetallic organic gel was prepared by solvothermal method. It is hoped that the special structure and properties of this new material can be used to remove ciprofloxacin (CIP) and methylene blue (MB) from water to deal with environmental pollution problems. Their morphology and structure were characterized by XRD, FT-IR, XPS, SEM, BET, TGA and zeta potential. It is proved that they have sufficient active sites, large specific surface area (270.5 m2/g), hierarchical porous structure, and strong thermal stability. These properties contribute to their efficient removal of pollutants. Compared with other adsorbents, MOG-4 in this study showed good pollutant removal rate, wide pH adaptability, good anti-interference ability and excellent reuse rate. The maximum adsorption capacity of MOG-4 for CIP and MB was 458.72 mg/ g and 381.68 mg/ g respectively. The adsorption process followed the second-order kinetic model and Freundlich isotherm. More importantly, we constructed MOG-4 @SA beads by immobilizing MOG-4 in sodium alginate (SA) matrix, which not only overcame the shortcomings of difficult recovery and easy agglomeration of powder MOG-4, but also enhanced its adsorption capacity. Seven cycles show that the reuse rate of MOG-4 @SA is more than 84%. The adsorption mechanism involves hydrogen bonding, electrostatic interaction, π-π interaction, hydrophilic/hydrophobic interaction and pore filling. MOG-4 @SA beads adsorbent overcomes the shortcomings of traditional powder adsorbent, which is easy to lose, easy to aggregate and difficult to recover, and broadens the range of use of powder adsorbent and sodium alginate. Therefore, MOG-4 @SA has the advantages of good adsorption performance, high reuse rate, wide range of adaptation, strong anti-interference ability, and is expected to become a promising adsorbent.

KH570 firmly anchors Ag+/Ag0 on TiO2 nanotubes to enhance organics removal during photocatalytic activation of peroxymonosulfate

To enhance the photocatalytic activation of peroxymonosulfate (PMS), the precious metal was used to modify the catalyst. However, the catalyst suffered from metal leaching due to the oxidation of zero-valent metal into the ionic state by PMS. Herein, the silane coupling agent, KH570, was selected to fix metal Ag on the surface of TiO2 nanotubes arrays (TiO2NTAs) firmly and dispersedly. The prepared Ag/KH570/TiO2NTAs were efficient visible-light (VL) photocatalytic PMS activators for the degradation of bisphenol A (BPA). The Ag/KH570/TiO2NTAs/PMS/VL system exhibited a higher degradation rate (kobs = 0.1 min−1) and exceptional stability even after 30 cycles (0.098 min−1) compared to Ag/TiO2NTAs/PMS/VL system (0.074 and 0.015 min−1 for first and fourth use, respectively). KH570 well-dispersed Ag0 on the surface of TiO2NTAs showed significantly enhanced VL absorption, photo-generated current, and electro-transfer ability, which boosted PMS activation. The Ag0 also activated PMS and converted to Ag+, which was quickly reduced to Ag0 again by photo-generated electrons. KH570 well-immobilized Ag0/Ag+ promoted above catalytic cycles with minimal Ag leaching. Activation of PMS by the photo-generated electrons and Ag0 resulted in the generation of •OH and SO4•−, which seized the principal position for BPA removal. The wide pH adaptability and production of more oxidant in water matrixes (Cl−, HCO3−, and humic acid) enabled Ag/KH570/TiO2NTAs/PMS/VL system to exhibit excellent performance in the actual waterbodies (groundwater and tap water). This work would provide useful information in the construction of stable zero-valent metal modified catalysts for the (photo)catalytic activation of PMS/persulfate.

3D porous carbon-embedded nZVI@Fe2O3 nanoarchitectures enable prominent performance and recyclability in antibiotic removal

Overcoming the instability and poor recyclability during the practical applications of contaminant scavengers is a challenging topic. Herein, a three-dimensional (3D) interconnected carbon aerogel (nZVI@Fe2O3/PC) embedding a core-shell nanostructure of nZVI@Fe2O3 was elaborately designed and fabricated via an in-situ self-assembly process. The porous carbon with 3D network architecture exhibits strong adsorption towards various antibiotic contaminants in water, where the stably embedded nZVI@Fe2O3 nanoparticles not only serve as magnetic seeds for recycling, but also avoid the shedding and oxidation of nZVI in the adsorption process. As a result, nZVI@Fe2O3/PC efficiently captures sulfamethoxazole (SMX), sulfamethazine (SMZ), ciprofloxacin (CIP), tetracycline (TC) and other antibiotics in water. In particular, an excellent adsorptive removal capacity of 329 mg g−1 and a rapid capture kinetics (99% of removal efficiency in 10 min) under a wide pH adaptability (2–8) are achieved using nZVI@Fe2O3/PC as an SMX scavenger. nZVI@Fe2O3/PC displays exceptional long-term stability given that it shows excellent magnetic property after it is stored in water solution for 60 d, making it an ideal stable scavenger for contaminants in an etching-resistant and efficient manner. This work would also provide a general strategy to develop other stable iron-based functional architectures for efficient catalytic degradation, energy conversion and biomedicine.

Improving peroxymonosulfate activation mediated by oxygen vacancy-abundant BaTiO3/Co3O4 composites: The vital roles of BaTiO3

Co3O4-based catalysts are considered as promising heterogeneous catalysts for peroxymonosulfate (PMS) activation, but the poor Co2+/Co3+ redox cycle restricts their environmental application. In this study, BaTiO3/Co3O4 (BT/Co3O4) composites with abundant oxygen vacancies (OVs) were synthesized via a sol-gel method with BT as the OVs donor, and used to activate PMS for organic dye degradation. Co3O4+PMS system degraded only 13.8% of methylene blue (MB) within 20 min, whereas the MB degradation ratio reached 100% for BT/Co3O4+PMS system. The enhanced performance can be attributed to the presence of abundant OVs in BT/Co3O4 composites, which significantly promoted electron transfer and improved the Co3+/Co2+ redox cycle, therefore accelerating PMS activation. The BT/Co3O4+PMS system degraded MB via radical and non-radical pathways, in which singlet oxygen (1O2) played a leading role. In addition, the BT/Co3O4+PMS system exhibited wide pH adaptability and excellent tolerance for inorganic ion interference. This study provides a new strategy for introducing OVs into catalytic materials to substantially enhance the catalytic activity.

Cyclodextrin-functionalized magnetic alginate microspheres for synchronous removal of lead and bisphenol a from contaminated soil

Currently, functional materials-based soil remediation focused on the stabilization of heavy metals and organics to inhibit their migration, however, the possible second release of these pollutants caused by soil condition variation attracts broad attention. Herein, β-cyclodextrin functionalized magnetic sodium alginate microspheres (MSA-CDMW) were fast and facilely synthesized through microwave-assisted one-pot method for synchronous detachment of Pb and BPA from contaminated soil. The obtained MSA-CDMW presented wide pH adaptability and fast capture for Pb(II)/BPA with superior adsorption capacity of 369.03/165.37 mg/g. Furthermore, the effects of material dosage and soil pH on the remediation ability of MSA-CDMW were explored in detail. After adding 5% MSA-CDMW into the contaminated soil for 3-round successive remediation (12 h for each round), the amount of extractable Pb and total BPA was simultaneously decreased by 56.30 and 0.78 mg/kg, respectively. Meanwhile, the quantity of exchangeable and carbonate bound Pb was significantly decreased to 7.13% with transformation into relatively stable fractions. A series of characterizations revealed that ion exchange, pore filling, complexation, and electrostatic attraction were responsible for Pb binding, while MSA-CDMW could capture BPA through host-guest interaction by the hydrophobic cavity of β-cyclodextrin. Additionally, recovery and floatation results revealed that the MSA-CDMW could be easily separated from the soil using magnets even at extreme drying and wetting conditions, thus providing a novel, fast, and eco-friendly strategy for effective remediation of heavy metals and organics contaminated soil.

Carbonyl and defect of metal-free char trigger electron transfer and O2•− in persulfate activation for Aniline aerofloat degradation

Residual flotation reagents in mineral processing wastewater can trigger severe ecological threats to the local groundwater if they are discharged without treatment. Metal-free biochar-induced persulfate-advanced oxidation processes (KCBC/PS) were used in this study to elucidate the degradation of aniline aerofloat (AAF) – a typical flotation reagent. In KCBC/PS system, AAF can be removed at low doses of catalyst (KCBC, 0.05 g/L) and oxidant (PS, 0.3 mM) additions with high efficiency. The analysis revealed the dominance of O2•− among the identified reactive oxygen species (ROS), which achieved deeper mineralization for the AAF degradation in the KCBC/PS system. The role of the electron transfer mechanism was equally important; the importance was corroborated by the chemical quenching experiments, electron spin resonance (ESR) detection, probe experiments, and electrochemical analysis. It benefited from the electron transfer mechanism in the KCBC/PS system and exhibited a wide pH adaptation (3.5–11) and high resistance to inorganic anions for real mining wastewater treatment. Combined with theoretical calculations and other analyses, the carbonyl group was deemed to be the active site of the non-radical pathway of biochar, while the site of the conversion of SO4•− to superoxide radicals by biochar activation represented a defect. These findings revealed a synergistic effect of multiple active sites on PS activation in biochar-based materials. Moreover, the intermediate degradation products of AAF from mass spectrometry indicated a possible pathway through the density functional theory (DFT) method, which was effective in reducing the environmental toxicity of pollutants for the first time according to the T.E.S.T software and seed germination experiments. Overall, our study proposed a novel modification strategy for cost-effective and environmentally friendly biochar-based catalysts, while also deepening our understanding of the mechanism of activation of persulfate by metal-free carbon-based materials.

Enhanced adsorption performance of bensulfuron methyl with B doping biochar: Mechanism and density functional theory calculations

It is an urgent task to develop suitable adsorbents for the control of herbicide-bensulfuron methyl (BSM) in the paddy rice fields at cold regions. Herein, B doping biochar was synthesized via one-step method. Results showed that the adsorption capacity for BSM on 1.0BBC was significantly superior to BC at 15 °C. Besides, low temperature resistance, wide pH adaptability, stable adsorption performance and reusability test suggested that 1.0BBC have potential practical application. The mechanisms of BSM removal by 1.0BBC were mainly attributed to pore filling and π-π electron donor–acceptor (EDA) interaction. Theoretical calculations revealed that BCO2 could enhance the adsorption capacity by π-π EDA between BSM and adsorbent. Meanwhile, hydroponic experiment demonstrated that the toxicity to soybean after adsorption of BSM by 1.0BBC was within the safe range. This study proves that 1.0BBC is an easy-to-prepare adsorbent with promising application in BSM removal in the rice paddy fields at lower temperature.

Co@C core-shell nanostructures anchored on carbon cloth for activation of peroxymonosulfate to degrade tetracycline

Cobalt-based heterogeneous nanocatalysts have attracted much attention in activating persulfate to rapidly eliminate organic pollutant in water. However, it remains a challenge to realize the easily recovery of these nanocatalysts and reduce the leaching of Co ions. Herein, Co@C core-shell nanostructures are anchored on the surface of carbon cloth (CC). The as-obtained immobilized catalyst of Co@C/CC exhibits an enhanced catalytic activity and lower leaching of Co ions in comparison with the bare Co@C nanocatalyt because of the high electrical conductivity and carrier effect of CC. The Co@C/CC demonstrates efficient catalytic performance in activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. 99% of TC can be quickly degraded by the Co@C/CC/PMS system, and the system has good durability and interference resistance as well as wide pH adaptability from 3 to 10. Scavenger quenching experiments and electron paramagnetic resonance (EPR) shows that the non-free radical pathway (1O2) is dominate contribute to the TC degradation. Finally, density functional theory (DFT) calculations yield CC as the primary attack site in TC, and the possible degradation pathways of TC are inferred. Importantly, the immobilized catalyst of Co@C/CC can achieve fast and simple collection and regeneration. This work provides new ideas for the preparation of efficient catalysts with easily recyclable for rapidly eliminate organic pollutant in water.

Surface hydroxyl-riched calcium carbonate and copper oxide composites for Fenton-like removal of bisphenol A

Surface functional groups have a key role in the removal of contaminants by advanced oxidation technology. Here, we explored the role of surface hydroxyl groups on pollutant removal by constructing novel surface hydroxyl-riched CaCO3@CuO. The hydroxyl groups on the surface of the composite accelerated the adsorption between the peroxymonosulfate and the catalyst, accelerating the catalytic reaction, and the kinetic removal rate of bisphenol A increased by 2.76 times. 1O2 is the dominant reactive oxygen species in the CaCO3@CuO/PMS/BPA system. The system has wide pH adaptability (pH = 3–11), good tolerance to complex water environments. This study provides novel insights into the mechanism of polymerization by surface hydroxyl groups in Fenton-like reactions for contaminant removal.

Fe2P/N-doped biocarbon composite derived from mycelial pellet for bisphenol AF removal through peroxymonosulfate activation

In this work, microorganism of Phanerochaete chrysosporium with iron-tolerating and accumulating abilities was cultivated and harvested as mycelial pellets, which could serve as a sustainable and environmental-friendly precursor for iron phosphide/N-doped biocarbon composite preparation. Through one-step pyrolysis process, the inherent Fe and P elements in mycelial pellet enabled the formation of well crystallized Fe2P particles, loading on N-doped biocarbon matrix. Benefiting from the porous structure, high specific surface area, N doping-induced defects and CO groups of biocarbon, as well as the good electron-donating property of Fe2P, the as-obtained Fe2P/BC composite performed well for bisphenol pollutant (e.g., BPAF) removal through peroxymonosulfate (PMS) activation. Specifically, almost complete BPAF removal was achieved within 30 min adsorption and 10 min catalysis process with an apparent reaction rate constant of 0.486 min−1. The good crystallinity and protective carbon layer wrapping on Fe2P enabled the wide pH adaptability and low iron leaching of Fe2P/BC in catalytic reaction. Inorganic anions and humic acid brought only slight inhibition for BPAF removal, which could be overcome by prolonging reaction time to 30 min. Further mechanism studies indicated that reactive oxygen species, e.g., SO4-•, •OH and 1O2 were generated through both radical and non-radical pathways and contributed to BPAF degradation. After treatment by Fe2P/BC-PMS system, the total organic carbon (TOC) of original BPAF solution (20 mg L−1) was reduced by 51.6%. Fortunately, the residual degradation intermediate products showed much reduced ecotoxicity in both predicted (ECOSAR program) and experimental results (growth inhibition test using Raphidocelis subcapitata as ecological indicator).

One pot synthesis of Cu–Ni–S@Ni foam for the simultaneous removal and detection of norfloxacin

The residual antibiotics in the environment will pose a threat to the environment and human health. Thus, it is imperative to develop a smart water treatment material to remove and detect antibiotics from aqueous environment simultaneously. In this study, magnetic Cu–Ni–S@Ni foam was synthesized by liquid phase vulcanization method to in-situ load Cu–Ni–S nanostructures on the surface of Ni foam. The novelty of this material is the combination of adsorption-flocculation technology and semi-quantitative detection technology. Batch experiments showed that Cu–Ni–S@Ni foam has a high removal rate of norfloxacin (NOR) (96.92%), wide pH adaptability (pH = 4.0–10.0) and strong ion interference resistance (0.1–100 mmol/L). According to the Langmuir isotherm, the removal capacity can reach 417.4 mg/g at 25 °C, which is much higher than that of other water treatment agents reported in most studies. Characterization analysis indicated that the main removal mechanisms are surface complexation, cation bridging, electrostatic attraction, precipitation and flocculation. Transmission FTIR detection experiments showed that NOR on Cu–Ni–S@Ni foam has easily recognizable FTIR fingerprints; the intensity of characteristic peaks roughly reflects the concentration information of NOR to some extent. This semi-quantitative detection method, requiring simple operation without the fabrication of KBr tablet, has a wide linear range (5–100 mg/L) and a low limit of detection (4.6 mg/L). Therefore, Cu–Ni–S@Ni foam can be used for simultaneous removal and semi-quantitative detection of NOR in wastewater. It has potential application value in wastewater treatment and water quality monitoring.

Highly efficient unsymmetrical dimethylhydrazine removal from wastewater using MIL-53(Al)-derived carbons: Adsorption performance and mechanisms exploration

In this study, novel MOF-derived porous carbons (C@Al2O3s) with high adsorption capacity for unsymmetrical dimethylhydrazine (UDMH) were synthesized via a solvothermal and carbonization method using MIL-53(Al) as precursors. The MOF-derived carbon prepared at 1000 °C (C@Al2O3-1000) had a higher specific surface area and mesoporous surface area (267.18 m2/g, 131.96 m2/g) compared to nanoparticles carbonized at 600 °C (207.74 m2/g, 119.99 m2/g) and 800 °C (236.31 m2/g, 123.02 m2/g). The UDHM adsorption of C@Al2O3s followed the pseudo-second-order kinetics model and the Langmuir isotherm model. The maximum adsorption capacity for UDMH of C@Al2O3-1000 reached 275.93 mg/g, which was the highest among the reported UDMH adsorbents so far. Adsorption thermodynamics calculations showed that the UDHM adsorption by C@Al2O3s was a thermodynamically favorable process. Besides, C@Al2O3s had wide pH adaptability (pH = 4–12) and good resistance to ionic strength, humic acid, and water qualities. C@Al2O3-1000 exhibited excellent recyclability and removal efficiency after eight adsorption-desorption cycles. Further characterizations and discussions concluded that the UDMH adsorption performance of C@Al2O3-1000 mainly depended on the electrostatic interaction, hydrogen bonding, and hierarchical porous structure.

Peroxymonosulfate activation by Fe-N-S co-doped tremella-like carbocatalyst for degradation of bisphenol A: Synergistic effect of pyridine N, Fe-Nx, thiophene S

Bisphenol A (BPA) has received increasing attention due to its long-term industrial application and persistence in environmental pollution. Iron-based carbon catalyst activation of peroxymonosulfate (PMS) shows a good prospect for effective elimination of recalcitrant contaminants in water. Herein, considering the problem about the leaching of iron ions and the optimization of heteroatoms doping, the iron, nitrogen and sulfur co-doped tremella-like carbon catalyst (Fe-NS@C) was rationally designed using very little iron, S-C3N4 and low-cost chitosan (CS) via the impregnation-calcination method. The as-prepared Fe-NS@C exhibited excellent performance for complete removal of BPA (20 mg/L) by activating PMS with the high kinetic constant (1.492 min−1) in 15 min. Besides, the Fe-NS@C/PMS system not only possessed wide pH adaptation and high resistance to environmental interference, but also maintained an excellent degradation efficiency on different pollutants. Impressively, increased S-C3N4 doping amount modulated the contents of different N species in Fe-NS@C, and the catalytic activity of Fe-NS@C-1-x was visibly enhanced with increasing S-C3N4 contents, verifying pyridine N and Fe-Nx as main active sites in the system. Meanwhile, thiophene sulfur (C-S-C) as active sites played an auxiliary role. Furthermore, quenching experiment, EPR analysis and electrochemical test proved that surface-bound radicals (·OH and SO4⋅−) and non-radical pathways worked in the BPA degradation (the former played a dominant role). Finally, possible BPA degradation route were proposed. This work provided a promising way to synthesize the novel Fe, N and S co-doping carbon catalyst for degrading organic pollutants with low metal leaching and high catalytic ability.

Novel oxymagnesite/green rust nanohybrids for selective removal and slow release of phosphate in water

The new paradigm in wastewater treatment demands to change traditional pollutants removal into resource recovery, especially for non-renewable P resources, effectively recovering phosphate from wastewater and reutilizing it as a nutrient is crucial to P sustainable utilization and P-related pollution control. The nanomaterial-based adsorption technology for P recovery from wastewater is becoming a research hotspot due to its high efficiency and selectivity. Herein, to recover aqueous phosphate, we developed novel oxymagnesite/green rust (OMGR) nanohybrids by a one-pot hydrothermal method. Green rust nanoparticles dispersed on the highly reactive oxymagnesite (MgO2MgCO3) nanosheets could achieve efficient recovery and reuse of P. The volume ratio of water to ethylene glycol played an important role in the preparation of OMGR. The OMGR possessed an excellent selectivity of phosphate removal in the presence of multi-anions and wide pH adaptability in 4.0–10.0. The formation of MgP nanocrystals and the inner-sphere FeOP complexes via ligand exchange contributed to the selective removal of P by OMGR, and the removal capacity reached 141 mg P.g−1. The process of phosphate removal by OMGR was spontaneously endothermic and controlled by the intraparticle and boundary layer diffusion. Most importantly, the high bioavailable P (127 mg.g−1) of P-loaded OMGR had a persistent release behavior regulated by dissolution and diffusion, indicating that the P-loaded OMGR can act as a slow-release P-fertilizer. The findings provide a green and eco-friendly approach to realizing P resource recovery and reuse for phosphate-containing wastewaters.

Fe-g-C3N4/reduced graphene oxide lightless application for efficient peroxymonosulfate activation and pollutant mineralization: Comprehensive exploration of reactive sites

To overcome the shortcomings of homogeneous Fe ion activating peroxymonosulfate (PMS), such as high pH-dependence, limited cycling of Fe(III)/Fe(II) and sludge production, graphite carbon nitride (g-C3N4) is chosen as a support for Fe ions, and reduced graphene oxide (rGO) is employed to facilitate the electron transfer process, thereby enhancing catalysis. Herein, a ternary catalyst, Fe-g-C3N4/rGO, is first applied under lightless condition for PMS activation, which exhibits ideal performance for contaminant mineralization. 82.5 % of the total organic carbon (TOC) in 100 mL of 5 mg/L bis-phenol A (BPA) was removed within 20 min by the optimal catalyst named 30%rFe0.2CN, which shows a strong pH adaptability over the range of 3–11 compared with a common Fenton-like system. Moreover, the highly stable Fe-g-C3N4/rGO/PMS catalytic system resists complex water matrices, especially those with high turbidity. To unveil the mechanism of PMS activation and pollutant degradation, the physicochemical properties of the as-prepared catalysts are comprehensively characterized by multiple techniques. The Fe(III) contained in both the Fe-N group and α-Fe2O3 component of 30%rFe0.2CN not only directly reacts with PMS to produce sulfate radicals (SO4−) and hydroxyl radicals (OH), but also combines with PMS to form the essential [Fe(III)OOSO3]+ active complex, thereby generating superoxide radicals (O2−) and singlet oxygen (1O2). Among the various reactive oxidizing species, 1O2 plays an important role in pollutant removal, which is additionally generated by the CO moiety of the catalyst activating PMS as well as PMS self-oxidation, indicating the dominance of the non-radical pathway in the pollutant degradation process. Due to the advantages of high efficiency, wide pH adaptability and stability, the proposed lightless Fe-g-C3N4/rGO/PMS catalytic system represents a promising avenue for practical wastewater purification.

Simultaneous and efficient removal of fluoride and phosphate in phosphogypsum leachate by acid-modified sulfoaluminate cement

The high concentration of fluoride and phosphate in phosphogypsum leachate is harmful to the environment and ecosystem. Thus, there is a need to develop feasible materials or technologies to remove both fluoride and phosphate in acidic phosphogypsum leachate. In this study, sulfoaluminate cement (SC) was used to simultaneously remove fluoride and phosphate in wastewater based on its moderate alkalinity and rich content of metal elements (Ca, Al and Fe, etc). The acidized sulfoaluminate cement (ASC) composite was prepared through modifying SC with hydrochloric acid, which can increase the specific surface areas of the raw SC, as well as the activity of the metal elements in SC. Compared with other coagulants, ASC showed excellent removal performance for fluoride and phosphate, such as higher removal efficiency, better effluent quality, and accelerated settling rate. The fluoride and phosphate removal performances of ASC herein were investigated at different dosages, pH values, coexisting substances, and initial concentrations. As a result, ASC exhibited wide pH adaptability and satisfactory selectivity for fluoride and phosphate. The possible removal mechanisms of fluoride and phosphate by ASC included chemisorption, ion exchange, and precipitation. The main end products associated with fluoride were fluorite (CaF2), aluminum fluoride (AlF3), and iron trifluoride (FeF3). The main final products amid phosphate removal, on the other hand, were brushite (CaHPO4·2H2O), aluminophosphate ((H3O)·AlP2O6(OH)2), silicocarnotite (Ca2SiO4·Ca3(PO4)2) and iron phosphate (Fe(H2PO4)3). More importantly, ASC can effectively treat the phosphogypsum leachate at a wide range of concentrations, and the concentrations of phosphate and fluoride in the effluents were lower than 0.5 mg P L−1 and 4 mg L−1, respectively. To sum up, ASC is a competitive candidate to treat wastewater with high fluoride and phosphate content, such as phosphogypsum leachate.

Peroxymonosulfate activation by concave porous S/N co-doped carbon: Singlet oxygen-dominated non-radical efficient oxidation of organics

Developing high-efficient, low-cost and environmentally friendly catalysts is essential for activating peroxymonosulfate (PMS) but remains a challenge. Recently, novel catalysts of transition metal-nitrogen co-doped carbon materials, especially Fe-N-C, have attracted much attention due to their superior performance for PMS activation. Herein, FeSO4 and ZnSO4 were added during the synthesis of ZIF-8, obtained concave N, S co-doped iron-based carbon materials (Fe-S@NC) with mesoporous structure through high-temperature pyrolysis. This porous carbon material with a depressed surface not only promoted the exposure of active sites, but also accelerated mass transfer. The synergistic effect of Fe atoms and heteroatoms significantly enhanced the activation ability of the material to PMS. Benefiting from these advantages, only 2 mg/L Fe-S1@NC and 0.5 mM PMS was required to achieve the rapid degradation of acetaminophen (ACT) (99.7%, 0.7290 min-1). Besides, the activation system has a wide pH adaptability and low leaching iron concentration. Then the reaction mechanism of Fe-S1@NC/PMS system was investigated by quenching experiments and electron paramagnetic resonance technique (EPR), it was proposed that singlet oxygen (1O2) was the primary reactive species responsible for the degradation of ACT. This study provides new insight for the design of carbon catalysts in advanced oxidation field.

N-doped low-rank coal based carbon catalysts for heterogeneous activation of peroxymonosulfate for ofloxacin oxidation via electron transfer and non-radical pathway

BackgroundAdvanced oxidation processes based on sulfate radicals were promising technologies for deep wastewater treatment. There was an urgent need of low-cost and green catalytic materials. MethodsIn this study, N-doped low-rank coal based carbon catalysts (NLCs) were prepared under different urea and low-order coal ratios and pyrolysis temperatures, which showed excellent catalytic performance for peroxymonosulfate (PMS) activation. Significant findingsThe NLCs had a high degree of graphitization and electrical conductivity, which leading to a high removal rates as 100% in 45 min. The N-doped structure lead to the formation of electron-rich regions, which favored the adsorption of PMS. Mechanistic studies revealed that the main reactive oxygen species in the NLC/PMS system was singlet oxygen (1O2), and that electron transfer pathways and surface-bound reactive complexes also played an important role in this system. The NLC/PMS system had a wide pH adaptation and good environment adaptation because of the electron transfer mechanism. It could remove 100% OFL in the pH range of 3-9. Therefore, the prepared N-doped coal based carbon catalytic materials had good prospects for application in advanced oxidation processes for wastewater treatment.