Reuse of Fenton sludge as an iron source for NiFe2O4 synthesis and its application in the Fenton-based process

The potentially hazardous iron-containing sludge from the Fenton process requires proper treatment and disposal, which often results in high treatment cost. In this study, a novel method for the reuse of Fenton sludge as an iron source for the synthesis of nickel ferrite particles(NiFe_2O_4) is proposed. Through a co-precipitation method followed by sintering at 800°C, magnetic NiFe_2O_4 particles were successfully synthesized, which was confirmed by powder X-ray diffraction(XRD), scanning electronic microscopy(SEM), energy dispersive spectroscopy(EDS), Fourier transform infrared spectroscopy(FT-IR) and Raman spectroscopy. The synthesized NiFe_2O_4 could be used as an efficient catalyst in the heterogeneous Fenton process. In phenol degradation with H_2O_2 or NiFe_2O_4 alone, the phenol removal efficiencies within the reaction time of 330 min were as low as 5.9% ± 0.1% and 13.5% ±0.4%, respectively. However, in the presence of both NiFe_2O_4 and H_2O_2, phenol removal efficiency as high as 95% ± 3.4% could be achieved, indicating the excellent catalytic performance of NiFe_2O_4 in the heterogeneous Fenton process. Notably, a rapid electron exchange between_Ni II and_Fe III ions in the NiFe_2O_4 structure could be beneficial for the Fenton reaction. In addition, the magnetic catalyst was relatively stable, highly active and recoverable, and has potential applications in the Fenton process for organic pollutant removal.     

Quantum chemical investigation on photodegradation mechanisms of sulfamethoxypyridazine with dissolved inorganic matter and hydroxyl radical

Sulfamethoxypyridazine(SMP) is one of the commonly used sulfonamide antibiotics(SAs).SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other coexisting aquatic environmental organic pollutants.In this work,SMP was selected as a representative of SAs.We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter,i.e.,anions(Br~-,Cl~-,and NO~-_3) and cations ions(Ca~(2+),Mg~(2+),and Zn~(2+)) on SMP photodegradation mechanism by quantum chemical methods.In addition,the degradation mechanisms of SMP by hydroxyl radical(OH·) were also investigated.The creation of SO_2 extrusion product was accessed with two different energy pathways(pathway-1 and pathway-2) by following two steps(step-I and step-II) in the tripletsensitized photodegradation of SMP.Due to low activation energy,the pathway-1 was considered as the main pathway to obtain SO_2 extrusion product.Step-II of pathway-1 was measured to be the rate-limiting step(RLS) of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step.All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1.The estimated low activation energies of different degradation pathways of SMP with OH·radical indicate that OH·radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring.     

From illite/smectite clay to mesoporous silicate adsorbent for efficient removal of chlortetracycline from water

A series of mesoporous silicate adsorbents with superior adsorption performance for hazardous chlortetracycline(CTC) were sucessfully prepared via a facile one-pot hydrothermal reaction using low-cost illite/smectite(IS) clay,sodium silicate and magnesium sulfate as the starting materials.In this process,IS clay was "teared up" and then "rebuilt" as new porous silicate adsorbent with high specific surface area of 363.52 m~2/g(about 8.7 folds higher than that of IS clay) and very negative Zeta potential(- 34.5 mV).The inert Si- O- Si(Mg,Al) bonds in crystal framework of IS were broken to form Si(Al)- O~- groups with good adsorption activity,which greatly increased the adsorption sites served for holding much CTC molecules.Systematic evaluation on adsorption properties reveals the optimal silicate adsorbent can adsorb 408.81 mg/g of CTC(only 159.7 mg/g for raw IS clay) and remove 99.3%(only 46.5%for raw IS clay) of CTC from 100 mg/L initial solution(pH 3.51;adsorption temperature 30℃;adsorbent dosage,3 g/L).The adsorption behaviors of CTC onto the adsorbent follows the Langmuir isotherm model,Temkin equation and pseudo second-order kinetic model.The mesopore adsorption,electrostatic attraction and chemical association mainly contribute to the enhanced adsorption properties.As a whole,the high-efficient silicate adsorbent could be candidates to remove CTC from the wastewater with high amounts of CTC.     

Assessing the effects of surface-bound humic acid on the phototoxicity of anatase and rutile TiO2 nanoparticles in vitro

In this study,the cytotoxicity of two different crystal phases of TiO₂ nanoparticles,with surface modification by humic acid（HA）,to Escherichia coli,was assessed.The physicochemical properties of TiO₂ nanoparticles were thoroughly characterized.Three different initial concentrations,namely 50,100,and 200 ppm,of HA were used for synthesis of HA coated TiO₂ nanoparticles（denoted as A/RHA50,A/RHA100,and A/RHA200,respectively）.Results indicate that rutile（LC50（concentration that causes 50%mortality compared the control group）=6.5）was more toxic than anatase（LC₅0=278.8）under simulated sunlight（SSL）irradiation,possibly due to an extremely narrow band gap.It is noted that HA coating increased the toxicity of anatase,but decreased that of rutile.Additionally,AHA50 and RHA50had the biggest differences compared to uncoated anatase and rutile with LC₅0of 201.9 and21.6,respectively.We then investigated the formation of reactive oxygen species（ROS）by TiO₂ nanoparticles in terms of hydroxyl radicals（OH）and superoxide anions（O₂^-）.Data suggested that O₂^- was the main ROS that accounted for the higher toxicity of rutile upon SSL irradiation.We also observed that HA coating decreased the generation of OH and O₂^- on rutile,but increased O₂^- formation on anatase.Results from TEM analysis also indicated that HA coated rutile tended to be attached to the surface of E.coli more than anatase.     

Multiple transformation pathways of p-arsanilic acid to inorganic arsenic species in water during UV disinfection

p-Arsanilic acid(p-ASA) is widely used in China as livestock and poultry feed additive for promoting animal growth.The use of organoarsenics poses a potential threat to the environment because it is mostly excreted by animals in its original form and can be transformed by UV–Vis light excitation.This work examined the initial rate and efficiency of p-ASA phototransformation under UV-C disinfection lamp.Several factors influencing p-ASA phototransformation,namely,p H,initial concentration,temperature,as well as the presence of Na Cl,NH4+,and humic acid,were investigated.Quenching experiments and LC–MS were performed to investigate the mechanism of p-ASA phototransformation.Results show that p-ASA was decomposed to inorganic arsenic(including As(Ⅲ) and As(V))and aromatic products by UV-C light through direct photolysis and indirect oxidation.The oxidation efficency of p-ASA by direct photosis was about 32%,and those by HOU and1O2 were 19% and 49%,respectively.Cleavage of the arsenic–benzene bond through direct photolysis,HOU oxidation or1O2 oxidation results in simultaneous formation of inorganic As(Ⅲ),As(IV),and As(V).Inorganic As(Ⅲ) is oxidized to As(IV) and then to As(V) by1O2 or HOU.As(IV) can undergo dismutation or simply react with oxygen to produce As(V) as well.Reactions of the organic moieties of p-ASA produce aniline,aminophenol and azobenzene derivatives as main products.The photoconvertible property of p-ASA implies that UV disinfection of wastewaters from poultry and swine farms containing p-ASA poses a potential threat to the ecosystem,especially agricultural environments.     

Gamma irradiation of 2-mercaptobenzothiazole aqueous solution in the presence of persulfate

Recently, water treatment by ionizing radiation has gained increasing attention as a powerful technology for the destruction of refractory pollutants. 2-Mercaptobenzothiazole(MBT) is known as a widespread, toxic and poorly biodegradable pollutant. This paper studied the gamma irradiation of aqueous solutions of MBT. Moreover, the effect of the addition of persulfate(S2O82-) on the radiolytic destruction of MBT was investigated. The main transformation products of the studied compound were detected and the sequence of occurrence of the products was described. The change of biodegradability of MBT solution was also observed. The main results obtained in this study indicated that gamma radiation was effective for removing MBT in aqueous solution. Persulfate addition, which induced the formation of reactive sulfate radicals(SO4-U), greatly enhanced the degradation of MBT. Benzothiazole was identified as the first radiation product, followed by 2-hydroxybenzothiazole. Decomposition of MBT started with the oxidation of –SH groups to sulfate ions. Possible pathways for MBT decomposition by gamma irradiation were proposed. The BOD/COD ratios of MBT samples were increased after radiation,indicating the improvement of biodegradability and reduction of toxicity.     

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals(·OH)from reactions between recyclable solid catalysts and H_2O_2 at acidic or even circumneutral pH.Hence,it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology.Due to the complex reaction system,the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating,and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies.Iron-based materials usually possess high catalytic activity,low cost,negligible toxicity and easy recovery,and are a superior type of heterogeneous Fenton catalysts.Therefore,this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials..OH,hydroperoxyl radicals/superoxide anions(HO_2./O_2~-.)and high-valent iron are the three main types of reactive oxygen species(ROS),with different oxidation reactivity and selectivity.Based on the mechanisms of ROS generation,the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron,the heterogeneous catalysis mechanism,and the heterogeneous reaction-induced homogeneous mechanism.Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed.Finally,related future research directions are also suggested.     

Breakthrough CO2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO₂ adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO₂ activation and Potassium hydroxide (KOH) activation. CO₂ adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25–65°C and inlet CO₂ concentration range of 10–30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N₂ and CO₂ adsorption at 77 and 273 K, respectively. Central composite design was used to evaluate the combined effects of temperature and concentration of CO₂ on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm³/g and surface area of 1400 m²/g had the highest CO₂ adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO₂ and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO₂ activated carbons remained remarkably stable after 50 cycles with low temperature (160°C) regeneration.     

Impact of dissolved organic matter on the photolysis of the ionizable antibiotic norfloxacin

Norfloxacin (NOR), an ionizable antibiotic frequently used in the aquaculture industry, has aroused public concern due to its persistence, bacterial resistance, and environmental ubiquity. Therefore, we investigated the photolysis of different species of NOR and the impact of a ubiquitous component of natural water — dissolved organic matter (DOM), which has a special photochemical activity and normally acts as a sensitizer or inhibiter in the photolysis of diverse organics; furthermore, scavenging experiments combined with electron paramagnetic resonance (EPR) were performed to evaluate the transformation of NOR in water. The results demonstated that NOR underwent direct photolysis and self-sensitized photolysis via hydroxyl radical (·OH) and singlet oxygen (¹O₂) based on the scavenging experiments. In addition, DOM was found to influence the photolysis of different NOR species, and its impact was related to the concentration of DOM and type of NOR species. Photolysis of cationic NOR was photosensitized by DOM at low concentration, while zwitterionic and anionic NOR were photoinhibited by DOM, where quenching of UOH predominated according to EPR experiments, accompanied by possible participation of excited triplet-state NOR and ¹O₂. Photo-intermediate identification of different NOR species in solutions with/without DOM indicated that NOR underwent different photodegradation pathways including dechlorination, cleavage of the piperazine side chain and photooxidation, and DOM had little impact on the distribution but influenced the concentration evolution of photolysis intermediates. The results implied that for accurate ecological risk assessment of emerging ionizable pollutants, the impact of DOM on the environmental photochemical behavior of all dissociated species should not be ignored.     

Ammonium sulfide-assisted hydrothermal activation of palygorskite for enhanced adsorption of methyl violet

Herein,palygorskite(PAL)was activated via a simple hydrothermal process in the presence of ammonium sulfide,and the effects of activation on the microstructure,physico-chemical feature and adsorption behaviors of PAL were intensively investigated.The hydrothermal process evidently improved the dispersion of PAL crystal bundles,increased surface negative charges and built more active –Si–O-groups served as the new"adsorption sites".The adsorption property of the activated PAL for Methyl Violet(MV)was systematically investigated by optimizing the adsorption variables,including p H,ionic strength,contact time and initial MV concentration.The activated PAL exhibited a superior adsorption capability to the raw PAL for the removal of MV(from 156.05 to 218.11 mg/g).The kinetics for MV adsorption followed pseudo second-order kinetic models,while the isotherm and thermodynamics results showed that the adsorption pattern well followed the Langmuir model.The structure analysis of PAL before and after adsorption demonstrated that electrostatic interaction and chemical association of –X–O-are the prominent driving forces for the adsorption process.