Achieving high-efficient photocatalytic persulfate-activated degradation of tetracycline via carbon dots modified MIL-101(Fe)octahedrons

The synergistic reaction of photocatalysis and advanced oxidation is a valid strategy for the degradation of harmful antibiotic wastewater.Herein,carbon dots(CDs)modified MIL-101(Fe)octahedrons to form CDs/MIL-101(Fe)composite photocatalyst was synthesized for visible light-driven photocatalytic/persulfate(PS)-activated tetracycline(TC)degradation.The electron spin resonance(ESR)spectra,scavenging experiment and electrochemical analysis were carried out to reveal that the high visible light-driven photocatalytic degradation activity of TC over CDs/MIL-101(Fe)photocatalysts is not only ascribed to the production of free active radicals in the CDs/MIL-101(Fe)/PS system(·OH,·SO_(4-),^(1)O_(2),h^(+)and·O_(2)^(-))but also attributed to the consumption of electrons caused by the PS,which can suppress the recombination of photo-generated carriers as well as strong light scattering and electron trapping effects of CDs.Finally,the possible degradation pathways were proposed by analyzing intermediates via liquid chromatography-mass spectrometry technique.This research presents a rational design conception to construct a CDs/PS-based photocatalysis/advanced oxidation technology with high-efficient degradation activity for the remediation of organic antibiotic pollutant wastewater and for the improvement of carrier transport kinetics of photocatalysts.

Engineering carbon nanocatalysts towards efficient degradation of emerging organic contaminants via persulfate activation:A review

The engineering of carbon nanocatalysts for the persulfate activated elimination of emerging organic contaminants(EOCs)demonstrates promising potential compared with metal-based counterparts due to their unique advantage of high stability and low toxicity.The early reviews introduced the theoretical background of persulfate activation together with a detailed summary of different mechanisms responsible for degradation of EOCs.To further unify the state of knowledge,identify the research gaps,and prompt new research in this area,we present a thorough review on current trends in research on metal-free carbon nanocatalysts(e.g.,0D nanodiamond,1D carbon nanotubes and carbon nanofibers,2D graphene and graphitic carbon nitride,and 3D carbon nanocatalysts),with emphasis on their applications in persulfate activation and EOCs decontamination.We also discuss the current challenges and future perspectives in practically relevant applications.Last,we highlight that the development of sustainable carbon nanocatalysts/persulfate systems lies at the interface of multiple disciplines,which calls for future in-depth interdisciplinary collaborations.

Heterogeneous activation of persulfate by CuMgAl layered double oxide for catalytic degradation of sulfameter

In this study,a series of CuMgAl layered double oxides(CuMgAl-LDOs)were obtained via calcination of CuMgAl layered double hydroxides(CuMgAl-LDHs)synthesised via a co-precipitation method.The results show that CuMgAl-LDO can be prepared using an optimal Cu:Mg:Al molar ratio of 3:3:2,NaOH:Na_(2)CO_(3)molar ratio of 2:1,and calcination temperature of 600°C.CuMgAl-LDO is a characteristic of mesoporous material with a lamellar structure and large specific surface area.The removal efficiency of sulfameter(SMD)based on CuMgAl-LDO/persulfate(PS)can reach>98%over a wide range of initial SMD concentrations(5–20 mg L^(-1)).The best removal efficiency of99.49%was achieved within 120 min using 10 mg L^(-1)SMD,0.3 g L^(-1)CuMgAl-LDO,and 0.7 mmol L^(-1)PS.Kinetic analysis showed that the degradation of SMD was in accordance with a quasi-first-order kinetic model.The stability of the CuMgAl-LDO catalyst was verified by the high SMD removal efficiency(>97%within 120 min)observed after five recycling tests and low copper ion leaching concentration(0.89 mg L^(-1)),which is below drinking water quality standard of 1.3 mg L^(-1)permittable in the U.S.Radical scavenging experiments suggest that SO_(4)^(-)is the primary active species participating in the CuMgAl-LDO/PS system.Moreover,our mechanistic investigations based on the radical scavenging tests and X-ray photoelectron spectroscopy(XPS)results indicate that Cu^((II))-Cu^((III))-Cu^((II))circulation is responsible for activating PS in the degradation of SMD and the degradation pathway for SMD was deduced.Accordingly,the results presented in this work demonstrate that CuMgAl-LDO may be an efficient and stable catalyst for the activation of PS during the degradation of organic pollutants.

Comparison of 1,2,3-Trichloropropane reduction and oxidation by nanoscale zero-valent iron, zinc and activated persulfate

Trichloropropane（TCP） is a chlorinated solvent which derives from chemical manufacturing as a precursor, and it is also an important constituent of solvent formulations in cleaning/degreasing operations. The control and remediation of TCP in polluted sites is a challenge for many conventional remediation techniques due to its refractory behaviour. This challenge in mind, some nano-materials and oxidants were tested to evaluate their effectiveness as in TCP degradation in a laboratory setting. Experimental results indicate that the use of nanoscale zero-valent iron prepared by green tea（GT） as a reductant has negligible degradation effect on TCP under normal temperature and pressure conditions. However, zinc powders of similar size but higher surface reactivity, demonstrated stronger dechlorination capacity in the breakdown of TCP, as almost all of TCP was degraded by carboxymethocel（CMC） stabilized nanoscale zinc within 24 h. Activated persulfate by citric acid（CA） and chelated Fe（Ⅱ） was also used for TCP treatment with a TCP removal efficiency rate of nearly 50% within a 24 h reaction period, and a molar ratio of S2O82-, Fe2+ and CA is 20:5:1. Both the reduction and oxidation reactions are in accordance with the pseudo-first order kinetic equation. These results are promising for future use of TCP for the remediation of polluted sites.

Antibiotic ciprofloxacin removal from aqueous solutions by electrochemically activated persulfate process:Optimization,degradation pathways,and toxicology assessment

Ciprofloxacin(CIP)is a commonly used antibiotic in the fluoroquinolone group and is widely used in medical and veterinary medicine disciplines to treat bacterial infections.When CIP is discharged into the sewage system,it cannot be removed by a conventional wastewater treatment plant because of its recalcitrant characteristics.In this study,boron-doped diamond anode and persulfate were used to degrade CIP in an aquatic solution by creating an electrochemically activated persulfate(EAP)process.Ironwas added to the system as a coactivator and the process was called EAP+Fe.The effects of independent variables,including pH,Fe^(2+),persulfate concentration,and electrolysis time on the systemwere optimized using the response surface methodology.The results showed that the EAP+Fe process removed 94%of CIP under the following optimum conditions:A pH of 3,persulfate/Fe^(2+)concentration of 0.4 mmol/L,initial CIP concentration 30 mg/L,and electrolysis time of 12.64 min.CIP removal efficiency was increased from 65.10%to 94.35%by adding Fe^(2+)as a transition metal.CIP degradation products,7 pathways,and 78 intermediates of CIP were studied,and three of those intermediates(m/z 298,498,and 505)were reported.The toxicological analysis based on toxicity estimation software results indicated that some degradation products of CIP were toxic to targeted animals,including fathead minnow,Daphnia magna,Tetrahymena pyriformis,and rats.The optimumoperation costswere similar in EAP and EAP+Fe processes,approximately 0.54€/m^(3).

New insights into FeS/persulfate system for tetracycline elimination:Iron valence,homogeneous-heterogeneous reactions and degradation pathways

In this study,complete tetracycline(TTC)and above 50%of total organic carbon(TOC)were removed by Fe S/PS after 30 min under optimized conditions.Although free radicals and high-valent iron ions were identified to generate in the process,the apparent similarity between intermediate products of Fe S/PS,Fe/PS,and UV/PS systems demonstrated that the degradation of TTC was due to sulfate radicals(SO_(4)·^(-))and hydroxyl radicals(·OH).Based on the reaction between free radicals and organic matter,we speculated that TTC in the Fe S/PS system was decomposed and mineralized by dehydration,dehydrogenation,hydroxyl addition,demethylation,substitution,E-transfer,and ring-opening.Furthermore,a new understanding of Fe S-mediated PS activation based on stoichiometry and kinetic analysis showed that there were both homogeneous and heterogeneous reactions that occurred in the entire progress.However,due to the effect of p H on the dissolution of iron ions,the homogeneous reaction became the principal process with iron ions concentration exceeding 1.35 mg/L.This work provides a theoretical basis for the study of the degradation of TTC-containing wastewater by the iron-based advanced oxidation process.

Efficient photodegradation of phenol assisted by persulfate under visible light irradiation via a nitrogen-doped titanium-carbon composite

To realize the utilization of visible light and improve the photocatalytic efficiency of organic pollutant degradation in wastewater,a nitrogen-doped titanium-carbon composite(N-TiO_(2)/AC)prepared by sol-gel methods was applied in the photodegradation of phenol assisted by persulfate under visible light irradiation(named N-TiO_(2)/AC/PS/VIS).The results show that a synergistic effect exists between visible-light photocatalysis and persulfate activation.Compared with TiO_(2)/PS/VIS,the phenol degradation rate was found to be observably improved by 65%in the N-TiO_(2)/AC/PS/VIS system.This significant increase in degradation rate was mainly attributed to the following two factors:1)The N and C doping can change the crystal structure of TiO_(2),which extends the TiO_(2)absorption wavelength range to the visible light region.2)As an electron acceptor,PS can not only prevent electrons and holes from recombining with each other but can also generate strong oxidizing radicals such as·SO_(4)^(−) and·OH to accelerate the reaction dynamics.The process of phenol degradation was found to be consistent with the Langmuir pseudo-first-order kinetic model with an apparent rate constant k of 1.73 min^(−1).The N-TiO_(2)/AC/PS/VIS process was proven to be a facile method for pollutant degradation with high pH adaptability,excellent visible-light utilization and good application prospects.

Overestimate of remediation efficiency due to residual sodium persulfate in PAHs contaminated soil and a solution

Oxidation remediation is a commonly used technology for PAHs contaminated soil presently,but the overestimate of efficiency due to ongoing remediation by residual oxidants during extraction and testing has not been paid enough attention.In this study,persulfate was activated by Fe(Ⅱ)to investigate the effects of residual oxidants on PAHs removal during detection process and the elimination effects of adding Na_(2)SO_(3) and extending sampling time on residual oxidants.Results verified that the residual oxidants removed PAHs in extraction process,making the results lower than the actual values:the detection recovery rate η of ΣPAHs and 3-6 ring PAHs ranged from 24.3%(25%Na_(2)S_(2)O_(8)treatment)to 87.4%(5%Na_(2)S_(2)O_(8)+4/4Fe^(2+) treatment),20.1%-99.0%,28.9%-87.9%,20.8%-89.4%,and 1.8.6%-76.9%,respectively.After adding Na_(2)SO_(3),the accuracy of detection results increased significantly:the η of ΣPAHs and 3-6 ring PAHs increased to 64.1%-96.5%,58.8%-95.5%,73.8%-114.4%,60.6%-95.6%,and 45.4%-77.1%,respectively.After 49 days of adding oxidants,residual oxidants had no considerable effect on the detection of PAHs,indicating it was appropriate to start soil remediation verification sampling49 days after the remediation was completed.The observed results will help scientific evaluation of the remediation effects of chemical oxidation on or-ganic contaminated soil.

Rapid and simple spectrophotometric determination of persulfate in water by microwave assisted decolorization of Methylene Blue

A rapid and simple method for determination of persulfate in aqueous solution was developed. The method is based on the rapid reaction of persulfate with Methylene Blue（MB） via domestic microwave activation, which can promote the activation of persulfate and decolorize MB quickly. The depletion of MB at 644 nm（the maximum absorption wavelength of MB） is in proportion to the increasing concentration of persulfate in aqueous solution. Linear calibration curve was obtained in the range 0-1.5 mmol/L, with a limit of detection of 0.0028 mmol/L. The reaction time is rapid（within 60 sec）, which is much shorter than that used for conventional methods. Compared with existing analytical methods, it need not any additives, especially colorful Fe2＋, and need not any pretreatment for samples, such as p H adjustment.

Carbon-based single-atom catalysts in advanced oxidation reactions for water remediation:From materials to reaction pathways

Single-atom catalysts(SACs)have been widely recognized as state-of-the-art catalysts in environment remediation because of their exceptional performance,100%metal atomic utilization,almost no secondary pollution,and robust structures.Most recently,the activation of persulfate with carbon-based SACs in advanced oxidation processes(AOPs)raises tremendous interest in the degradation of emerging contaminants in wastewater,owning to its efficient and versatile reactive oxidant species(ROS)generation.However,the comprehensive and critical review unraveling the underlying relationship between structures of carbon-based SACs and the corresponding generated ROS is still rare.Herein,we systematically summarize the fundamental understandings and intrinsic mechanisms between single metal atom active sites and produced ROS during AOPs.The types of emerging contaminants are firstly elaborated,presenting the prior pollutants that need to be degraded.Then,the preparation and characterization methods of carbon-based SACs are overviewed.The underlying material structure–ROS type relationship in persulfate-based AOPs is discussed in depth to expound the catalytic mechanisms.Finally,we briefly conclude the current development of carbon-based SACs in AOPs and propose the prospects for rational design and synthesis of carbon-based SACs with on-demand catalytic performances in AOPs in future research.

燃烧合成高熵碳化物纳米颗粒活化过硫酸盐降解四环素污染物

高熵碳化物纳米颗粒的发展将为未来科技带来无限可能.然而,目前传统的合成方法很难实现该纳米材料的有效合成.为此,本文首次报道了一种简单、快速、低成本的燃烧合成方法,实现了高熵碳化物纳米颗粒的可控合成.即首先从热力学方面分析了燃烧合成高熵碳化物纳米颗粒的可能性,然后以金属氧化物粉、碳粉、镁粉为反应原料以及氟化钠为熔盐介质,采用燃烧合成方法成功合成出(Ta_(0.25)Nb_(0.25)-Zr_(0.25)Ti_(0.25))C高熵碳化物纳米颗粒(燃烧温度:~1487 K,持续时间:63 s,升温速率:-68 K s^(-1)).实验结果表明:合成的高熵碳化物纳米颗粒不仅在所有组成元素的含量和分布上具有高度均匀性,而且氧杂质含量低,仅为2.98 wt%.此外,合成的高熵碳化物纳米颗粒可以作为硫酸盐活化剂用于降解去除地下水或污水中的四环素污染物,10小时内的去除率可达到~65.5%.

Nitrogen-doped graphene nanosheets as reactive water purification membranes

Oxidation of organic pollutants by sulfate radicals produced via activation of persulfate has emerged as a promising advanced oxidation technology to address various challenging environmental issues. The development of an effective, environmentally-friendly, metal-free catalyst is the key to this technology. Additionally, a supported catalyst design is more advantageous than conventional suspended powder catalysts from the point of view of mass transfer and practical engineering applications （e.g. post-use separation）. In this study, a metal-free N-doped reduced graphene oxide （N-rGO） catalyst was prepared via a facile hydrothermal method. N-rGO filters were then synthesized by facile vacuum filtration, such that water can flow through nanochannels within the filters. Various advanced characterization techniques were employed to obtain structural and compositional information of the as-synthesized N-rGO filters. An optimized phenol oxidative flux of 0.036 ＋_ 0.002 mmol.h ~ was obtained by metal-flee catalytic activation of persulfate at an influent persulfate concentration of 1.0 mmol-L 1 and filter weight of 15 rag, while a N-free rGO filter demonstrated negligible phenol oxidation capability under similar conditions. Compared to a conventional batch system, the flow-through design demonstrates obviously enhanced oxidation kinetics （0.036 vs. 0.010 retool-h-I）, mainly due to the liquid flow through the filter leading to convection-enhanced transfer of the target molecule to the filter active sites. Overall, the results exemplified the advantages of organic compound removal by catalytic activation of persulfate using a metal-free catalyst in flow- through mode, and demonstrated the potential of N-rGO filters for practical environmental applications.