Non-free Radical Research Articles

Highly dispersed CoFe2O4 spinel on biomass-derived 3D porous carbon framework for much enhanced Fenton-like reactions

Rational design of the low-cost, highly efficient and easily recyclable catalyst to directly activate peroxymonosulfate (PMS) is crucial for the efficient removal of organic pollutants in the sewage treatment. Herein, hyperdispersed CoFe2O4 spinel nanoparticles were successfully in-situ fabricated on biomass-derived 3D porous carbon framework (C) by the facile one-step solvothermal method (CoFe2O4/C). These as-prepared CoFe2O4/C exhibit superior performance in the Fenton-like removal of four quinolones by the combination of experimental work and theoretical calculation. Experimental results prove that CoFe2O4/C catalyst can directly activate PMS to efficiently remove four types of quinolones in 12 min without the external energy consumption. The characterization results show that hyperdispersed CoFe2O4 (18.0 ± 5.0 nm) nanoparticles are uniformly anchored on the matrix of C, exhibit a large specific surface area of 733.1 m2/g, and present rich oxygen vacancies (Ovs), thus exposing more reactive sites and generating more reactive oxygen species (ROS). In CoFe2O4/C + PMS system, ∼97.5% of ciprofloxacin (CIP) is removed within 12 min, which is far superior to other candidates previously reported. Other quinolones (e.g., ∼96.8% of ofloxacin (OFL), ∼100% of levofloxacin (LEV), and ∼86.4% of norfloxacin (NOR)) can also be efficiently degraded under the same conditions. Based on quenching experiments, electron spin resonance spectroscopy (ESR), and density functional theory (DFT) calculations, these superior activities are mainly due to the free radical (SO4·-, ·OH, and ·O2–) and non-free radical (1O2), whereas SO4·- and ·OH are the major reactive oxygen species. In addition, these CoFe2O4/C catalysts remain stable even after five cycles. Subsequently, degradation pathways are rationally proposed. This work provides a feasible and universal strategy for the direct activation of PMS in wastewater treatment.

Enhanced adsorption and catalytic degradation of antibiotics by porous 0D/3D Co3O4/g-C3N4 activated peroxymonosulfate: An experimental and mechanistic study

In this work, Co3O4/g-C3N4 catalyst with highly efficient adsorption and degradation of antibiotics was developed based on the combination of three-dimensional (3D) porous morphological controls of g-C3N4 and the loading of Co3O4 quantum dots (Co3O4 QDs). It was discovered that the catalyst can effectively activate peroxymonosulfate (PMS) through a non-photochemical path, and a high tetracycline elimination rate of 99.7% can be achieved within 18 min. The characterization and density functional theory calculation results demonstrated that the porous 3D structure can not only promote the substrate adsorption reaction but also provide large surface area and countless exposed active sites for catalytic reaction. The introduction of Co3O4 QDs lowered activation energy barrier and lead to high energy of PMS adsorption. More efficient charge migration between the catalyst and PMS further accelerated PMS activation. Thus, leading to the excellent catalytic performance. In addition, non-free radical mediated degradation mechanism of catalytic activity was also proposed. This work provides a scheme for designing novel and efficient PMS activators for the removal of abusive antibiotics from aqueous environments.

Visible-LED-light-driven photocatalytic activation of peroxydisulfate by magnetic ZnFe2O4/Ag nanocomposite for efficient tetracycline degradation

Heterogeneous photocatalysis/persulfate oxidation process has been regarded as a promising technology for antibiotic contaminants removal. Magnetic ZnFe2O4/Ag composite catalyst was synthesized to activate peroxydisulfate (PDS) toward tetracycline (TC) degradation under the visible-LED-light irradiation. The synergistic effect of ZnFe2O4 and Ag endowed the optimized ZFO/Ag-15 with excellent photocatalytic performance for PDS activation and TC degradation, and 90.06 % of TC (20 mg/L) was efficiently degraded after 80 min of reaction. Ag can enhance the visible light absorption of ZnFe2O4 and accelerate the separation of photo-induced electron/hole pairs, thereby promoting the generation of O2− and SO4− radicals. In addition, Ag can directly activate PDS to generate SO4−. Although the catalytic performance of magnetic ZFO/Ag-15 gradually decreased after each cycle due to the corrosion of Ag and the formation of inactive AgO, the catalytic activity of used catalyst was partially recovered by heat treatment. Quenching experiments and EPR tests indicated that the free radical (O2−, SO4− and OH) and non-free radical (1O2, h+) oxidation processes cooperated to degrade TC in Vis-ZFO/Ag-15/PDS system. The effect of operational factors (PDS concentration, temperature, solution pH, coexisting inorganic anions and humic acid) on TC degradation was investigated, and TC removal from the different water matrices (river water, tap water and secondary effluent) was also evaluated. The degradation products were detected using LC-MS and the possible TC degradation pathways were established.

Degradation of sulfamethazine sodium salt by peroxymonosulfate activated by biochar supported CoFe2S4: Performance, mechanism and response surface method optimization

The persulfate oxidation process plays a critical role in eliminating antibiotics in wastewater, so it is urgent to develop a cheap, environmentally friendly and effective catalyst. In this study, CoFe2S4/BC catalyst was synthesized by a two-step hydrothermal method and combined with peroxymonosulfate (PMS) to degrade sulfamethazine sodium salt (SMT). The degradation results can be effectively predicted by establishing the response surface model. In order to maximize the removal rate of SMT, the optimization conditions are: catalyst dosage is 0.8 mg·L−1, PMS dosage is 0.5 mM, the pH value is 9.0 and the predicted degradation rate of SMT is 86.87% under these conditions. Also, the effects of PMS dosage, catalyst dosage, pH value and coexisting substances in the water on the degradation of SMT were also systematically studied. Besides, In the CoFe2S4/BC/PMS system, there are both free radical and non-free radical pathways, in which the contribution of SO4·- was dominant. And the possible reaction mechanism and degradation path of SMT was proposed. In consequence, these results describe that CoFe2S4/BC is an excellent catalytic material and can be regarded as a catalyst for the catalytic degradation of antibiotics in wastewater treatment.

Carbon coated CoO plates/3D nickel foam: An efficient and readily recyclable catalyst for peroxymonosulfate activation

Constructing of the 3D porous structured catalyst with high efficiency and low metal ion dissolution is crucial for peroxymonosulfate (PMS) based advanced oxidation technologies (AOPs). In this work, carbon coated CoO plates/3D Ni foam catalyst was prepared by hydrothermal, carbon precursor coating and subsequently carbonization method. The obtained catalyst was further applied in the activation of PMS for the degradation of ofloxacin (OFX) and other organic pollutants in water. The physicochemical properties of the catalyst were systematically characterized, and the influence of several parameters such as catalyst and PMS dosage, initial pH and temperatures on the removal of OFX were investigated. Results showed that ∼ 100% of OFX (20 mg/L) could be degraded by the catalyst within 20 min through PMS activation. Besides, the catalyst is easy to be recovered and reused with high efficiency and low metal ion leaching. The quenching experiments and the results of EPR demonstrated both free (•OH, •SO4–, O2•–) and non-free radicals (1O2) were involved in the OFX degradation, and the cycle of Co2+/Co3+ and lattice oxygen on the catalyst surface were mainly responsible for efficient reactive oxygen species (ROS) generation from PMS. Finally, intermediate products in the OFX degradation process were identified, and possible degradation pathway and the mechanism were proposed.

Simultaneous degradation of trace antibiotics in water by adsorption and catalytic oxidation induced by N-doped reduced graphene oxide (N-rGO): synergistic mechanism

Aimed at current difficulties in the treatment of trace antibiotics in water, an adsorption-catalytic oxidation system was established by combining persulfate and graphene, which have the dual functions of adsorption and catalysis, for simultaneous enrichment and degradation of trace antibiotics in water. The experimental results showed that over 90% sulfamethoxazole could be degraded by the proposed system. The activation energy of the proposed system was 7.9 kJ mol−1, which was significantly lower than those of typical Co catalysts and some carbon-based catalysts. Synergistic effect analysis revealed that catalytic oxidation was the key degradation kinetic of the proposed system, while adsorption showed a significant enhancement effect. Specifically, a compound with large adsorption capacity tended to be degraded preferably and rapidly. Characterization results indicated that N atoms were doped into the graphene framework, resulting in significant impacts on the activation process of potassium bisulfate by activating the sp2 C system. Quenching and free radical trapping experiments revealed that degradation catalyzed by the proposed system was a non-free radical oxidation reaction dominated by singlet oxygen. In summary, the proposed design was rational, N-rGO surface provided good adsorption and catalysis sites, the synergistic effect of adsorption and catalytic oxidation led to rapid and effective enrichment and in situ degradation of trace antibiotics in water.

CDs@Cr2O3 catalytic degradation of Orange II based on non-radical pathway

Carbon dots (CDs)-modified Cr2O3 (CDs@Cr2O3) composites were synthesized by solvothermal process followed by calcination to improve their catalytic performance. The physical and chemical properties of the composites were determined by XRD, SEM, TEM, BET and XPS. With the aid of sodium persulfate, the activity of CDs@Cr2O3 to oxidize Orange II by non-radicals was studied under various conditions. The experimental results determined the optimal dosage of PDS to be 0.1 g and the degradation results showed that after 45 min, the degradation rate of Orange II reached to 98.4% with the CDs@Cr2O3/PDS/Vis system. The adsorption capacity of CDs@Cr2O3 for Orange II was closely related to pH, and this phenomenon is further explained by the isoelectric point. A series of experiments proved that non-free radicals played a crucial role in the oxidation process, in which singlet oxygen (1O2), superoxide radical (O2•−) and photo-generated holes (h+) were determined as the important reactive oxygen species (ROS). In addition, the present study found that increasing dissolved oxygen could promote the reaction and the catalyst maintained good degradation performance after five cycles suggesting its stability.

A green strategy from waste red mud to Fe0-based biochar for sulfadiazine treatment by peroxydisulfate activation

Zerovalent iron (Fe0)-based biochar (Fe0-BC) has attracted wide attention in activating persulfate to eliminate antibiotics. In this study, the waste red mud (RM) was successfully used as an iron precursor to prepare Fe0-BC (RMIS1:1) via co-pyrolysis strategy, which was confirmed with remarkable capacity in peroxydisulfate (PDS) activation. The removal efficiency of sulfadiazine (SDZ) was 99.7% in RMIS1:1/PDS system in 20 min, with kobs of 0.3001 min−1. Both free radicals (SO4−, OH, and O2−) and non-free radicals (1O2) were responsible for SDZ degradation, in which the SO4− and O2− played the dominant roles. Four SDZ degradation pathways were provided according to the intermediates identified by Q-TOF-MS. Furthermore, the ECOSAR prediction implied that the intermediates have less eco-toxicity than SDZ. Compared with PDS concentration and RMIS1:1 dosage, the initial SDZ concentration had stronger effect on its degradation. Co-existed Cl− slightly improved SDZ degradation rate, while other anions (NO3–/SO42−/HCO3–/CO32–) and humic acid exhibited different levels of inhibition on SDZ removal. Moreover, RMIS1:1/PDS maintained acceptable degradation ability for practical pharmaceutical wastewater. The electrical energy per mass of SDZ was about 2.24 kWh/(g·SDZ) by RMIS1:1/PDS, lower than that produced in any other advanced oxidation processes that have been reported so far. In summary, this study reported a green strategy for Fe0-BC preparation from RM, which was valuable for both waste resource recycling and environmental remediation.

Novel nanoparticle-assembled tetrakaidekahedron Bi25FeO40 as efficient photo-Fenton catalysts for Rhodamine B degradation

In this study, nanoparticle-assembled Bi25FeO40 materials were synthesized by a novel and simple process, and their microstructure was regulated by different methods of adding Bi3+ and Fe3+. The novel nanoparticle-assembled tetrakaidekahedron Bi25FeO40 materials exhibited more oxygen vacancy and larger specific surface area than irregular or cubic-like Bi25FeO40 microcrystals and revealed better photo-Fenton catalytic oxidation activity toward degrading Rhodamine B (RhB) pollutants. These novel materials activated H2O2 in visible light to produce non-free radicals 1O2 and hole (h+) active oxidative species that dominated the catalytic degradation of RhB. Complete degradation of RhB was achieved after 1 h. The possible reaction mechanisms of the photo-Fenton catalytic system are discussed in detail by radical scavenging tests, X-ray phosphorescence analysis, and electron paramagnetic resonance spectroscopy. The results provided a way to rationally explore and construct photo-Fenton catalysts for wastewater treatment.

Electrochemical activation of peroxymonosulfate at Ti/La2O3-PbO2 anode to enhance the degradation of typical antibiotic wastewater

In this study, a novel electrochemically anodic activated peroxymonosulfate (PMS) system ((Ti/La2O3-PbO2)EA-PMS) was constructed by combining the Ti/La2O3-PbO2 anode with PMS. The prepared (Ti/La2O3-PbO2)EA-PMS system removed 98.07% of cefadroxil (CFR), which was 17.85% higher than that of the single electrochemical (EC) system and 78.10 % higher than that of the PMS system. In addition, the (Ti/La2O3-PbO2)EA-PMS system showed the satisfactory applicability to the single and mixed wastewater of CFR, tetracycline (TC), and levofloxacin (LFX) with the degradation rate greater than ~95%, the stability and degradation performance was much better than the conventional PMS activation systems. The excellent degradation performance was partially attributed to the excellent physico-chemical and electrochemical performances of Ti/La2O3-PbO2 anode, such as the rougher and compact surface, faster mass and electron transfer performance, the higher proportion of the adsorbed hydroxyl oxygen (Oads) for the production of reactive oxygen species (ROS) and a higher oxygen evolution overpotential to inhibit the occurrence of the electrolysis of water. In addition, the collaboration of Ti/La2O3-PbO2 anode and PMS activation produced a synergistic effect on the degradation of antibiotics, which mainly reflected at the direct-electron-transfer controlled non-free radical oxidation occurred on the surface of Ti/La2O3-PbO2 anode and the free radical oxidation dominated by adsorbed OH (PbO2(OH)), free hydroxyl radical (OH) and sulfate radical (SO4−). Moreover, the effects of operating parameters (PMS concentration, current density and initial pH value) and water background components on the removal of CFR by (Ti/La2O3-PbO2)EA-PMS system were investigated. The possible degradation pathways of CFR were also speculated. The electrochemically anodic activated PMS system based on Ti/La2O3-PbO2 anode was expected to provide an efficient technology for the treatment of actual pharmaceutical wastewater and this work also provided a significant reference for the design of novel advanced oxidation process combined with PMS (AOP-PMS) systems.

Peroxymonosulfate-activated molecularly imprinted bimetallic MOFs for targeted removal of PAHs and recovery of biosurfactants from soil washing effluents

Treatment of washing effluents containing high concentrations of surfactants and PAHs remains a critical challenge in surfactant-enhanced soil washing processes. In this study, bimetallic metal–organic frameworks modified with molecularly imprinted polymers, named Al/Co-MOFs@MIP have been synthesized to activate peroxymonosulfate (PMS) at the first time for targeted degradation of phenanthrene from soil washing effluents for biosurfactant recovery. The Al/Co-MOFs@MIP has higher stability, better catalytic performance and excellent selective recognition. The Al/Co-MOFs@MIP has significantly enhanced adsorption of phenanthrene. Electrostatic interactions and functional groups binding between phenanthrene and specific recognition sites led to better selective recognition. Targeted adsorption of phenanthrene caused closer distance between free radicals and pollutants which resulted in higher degradation efficiency. Phenanthrene adsorbed on the Al/Co-MOFs@MIP surface consumes free radicals, thus reducing the attack of oxidative free radicals on rhamnolipids. The EPR and quenching experiments indicated that although both free radicals and non-free radicals made contributions to the degradation of phenanthrene. Phenanthrene is attacked and oxidized by SO4·- and 1O2 through two pathways, including oxalic acid loss, ring cleavage and mineralization. This study indicated that selective phenanthrene degradation could be realized in Al/Co-MOFs@MIP/PMS system due to the synergetic effects including selective adsorption and catalysis of the material.

A cosubstantial [0D+2D] CTF membrane with enhanced perm-selectivity and solar cleaning for multiscale molecular separation

Fouling is the pending issue of conspicuous two-dimensional membranes for complex wastewater treantment. Here, we first report a hybrid-dimensional cosubstantial [0D+2D] covalent triazine framework (CTF) membrane to sort out the membrane fouling via solar-cleaning strategy. The intersertal 0D CTF-0 in lamellar membrane as “pillar” offers interspacing pathways for selective separation of sub/micrometer oily emulsions and nanometer dyes. It also acts as cosubstantial “joint” to improve electron/hole separation efficiency under sunlight irradiation, which activated peroxymonosulfate to achieve effective membrane solar-cleaning via free and non-free radical way. Both the surfactant adsorbed on the membrane and the oil and dye molecules trapped on the membrane surface by the pore sieving could all be efficiently removed via the photocatalytic degredation. The interfacial solar-thermal effect also contributed to the removal of volatile oils. This featured photocatalytic membrane prepared via hybrid-dimensional and cosubstantial CTF nanomaterials offers a promising way for sustainable fouling alleviation.

CuFe2O4 modified expanded graphite synthesized by urea-assisted hydrothermal method for tetracycline treatment through persulfate activation: Characterization, mechanism and degradation intermediates

• Expanded graphite (EG) was applied as the support of CuFe 2 O 4 . • Composite catalyst (EG-CuFe 2 O 4 -U) was synthesized by the urea-assisted hydrothermal method. • EG-CuFe 2 O 4 -U possessed outstanding catalytic performance to PDS activation for TC degradation. • Both SO 4 ·− , ·OH and 1 O 2 were generated in the EG-CuFe 2 O 4 -U/PDS system. • The intermediates of TC were detected and analyzed. Owing to the stable crystal structure and wide range of pH applications, CuFe 2 O 4 particles have been intensively concerned in the field of advanced oxidation, but their serious agglomeration and slow catalytic efficiency are still the stumbling blocks. The composite catalyst (EG-CuFe 2 O 4 -U) prepared by urea-assisted hydrothermal method with expanded graphite (EG) as the substrate immobilized CuFe 2 O 4 not only exposed more active sites but also exhibited a higher electron transfer rate. Additionally, EG-CuFe 2 O 4 -U showed excellent performance in degrading tetracycline (TC) in model wastewater by activated peroxydisulfate (PDS). The synthesis mechanism of EG-CuFe 2 O 4 -U and the principle of urea in the formation of reduction environment were discussed in detail by the experimental results of key preparation parameters and characterization. Meanwhile, several critical influencing factors were examined including PDS concentration, catalyst dosage, initial pH of the solution, and the change of pH in different systems. Furthermore, the removal efficiency and mineralization efficiency of TC (50 ppm) exceed 91% and 34.6%, on the conditions of 0.4 gL −1 EG-CuFe 2 O 4 -U, 6 mM PDS, initial solution pH of 4, and room temperature. What’s more, the internal reaction mechanism of free radicals and non-free radicals in the EG-CuFe 2 O 4 -U/PDS system was further elaborated via scavenging tests, electron paramagnetic resonance (EPR). Finally, based on twenty-one principal intermediates of TC, four possible degradation pathways were proposed. In general, the catalyst with a rich pore structure and high catalytic activity has great potential in the effective activation of PDS and is prospective to be further applied in the field of antibiotic wastewater degradation.

Promoted generation of singlet oxygen by hollow-shell CoS/g-C3N4 catalyst for sulfonamides degradation

Sulfanilamide (SM), which is a representative drug of sulfonamides, is commonly used for the prevention and treatment of bacterial infectious diseases and is extremely difficult to remove from water. Herein, an efficient catalyst (CoS/CN) for sulfanilamide degradation was constructed by CoS self-assembling on ultrathin graphitic carbon nitride (g-C3N4) nanosheets. The prepared hollow-shell CoS/CN catalyst could completely degrade SM within 10 min with a rate constant of 2.49 min−1 through the activation of peroxymonosulfate (PMS). Experiments and theoretical calculations indicated that S2− acted as an electron donor for promoting the generation of Co(II). The combination of g-C3N4 and CoS made the CoS/CN composite have higher conductivity and electron transfer ability than CoS, which promoted the decomposition of PMS to produce reactive oxygen species (ROSs). Singlet oxygen (1O2) was proved as the primary ROSs, and SO4− radicals were generated during the 1O2-dominated degradation process to improve the low mineralization rate. 1O2 and SO4− were derived from the oxidation of PMS and the electron transfer of g-C3N4. The results revealed the synergistic effect of free radicals and non-free radicals during the redox of PMS, and provided theoretical support for the efficient degradation of refractory organics in wastewater.

Enhanced catalytic oxidation of bisphenol A via persulfate oxidation by microwave-assisted preparation of ZnCoxFe2-xO4-loaded rice-husk-carbon

Cobalt-doped ZnFe2O4 supported on rice husk carbon (RHC) has been prepared by a microwave-assisted method as a catalyst for the degradation of bisphenol A (BPA) by persulfate (PS) oxidation. Ferrite is a good absorbing material, RHC contains abundant channels, which provide channels for microwaves(MW) reflecting and scattering, and accelerate the synthesis of ZC1.3FO. In addition, the polarization and synergistic effect of the contact interface between the two phases is enhanced, which not only improves the dispersity of the magnetic material, but also enhances electron delocalization in the mixed material, promoting electron transfer between Co3+/Co2+ and Fe3+/Fe2+, and improving the catalytic activity. Our results have shown the degradation rate of BPA by ZnCo1.3Fe0.7O4-50 wt%RHC (ZC1.3FO-5C) (0.0697 L/mg min) to be 28 times higher than that by ZC1.3FO (0.00251 L/mg min), and the extents of leaching of cobalt and iron were lower than 45 μg/L. Particle video microscopy (PVM) have been used to confirm improved dispersion of composite particles compared to that of a single catalyst during degradation. Free radical quenching experiments, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) have confirmed that BPA degradation was caused by the synergistic action of non-free radical and free radical pathways. Intermediates have been identified by electrospray ionization mass spectrometry (ESI-MS), on the basis of which a degradation pathway of BPA by activated PS oxidation in the presence of ZC1.3FO-5C is proposed. In brief, a ZC1.3FO-5C composite has been prepared by a microwave method to activate PS for the degradation of BPA, realizing the resource utilization of waste ferrous sulfate derived from titanium dioxide production, providing a new concept for the degradation of organic pollutants.

Singlet oxygen-oriented degradation of sulfamethoxazole by Li–Al LDH activated peroxymonosulfate

Lithium–aluminum layered double hydroxides (Li–Al LDHs) are a unique group of LDHs and their applications have attracted wide attention. Herein, Li–Al LDH was prepared using the hydrothermal method and was then used to activate peroxymonosulfates (PMS) for degrading sulfamethoxazole (SMX). It was found that 0.4 g/L catalysts, 1.57 mM PMS, and pH = 11.00 were the optimal conditions for the degradation process of the Li–Al LDH/PMS system at 30 °C. Under these conditions, the degradation rate of 80 mg/L SMX could reach 98.2% within 130 min. Meanwhile, the catalyst also showed superior stability and recoverability. After five cycles, the degradation rate of SMX was still higher than 95.3%. Based on free radical scavenging experiments and electron spin resonance results, both the radical and nonradical pathways synergistically completed the degradation in the Li–Al LDH/PMS system, with the nonfree radical (singlet oxygen) playing the predominant role. A reasonable degradation pathway was also proposed based on the detection of intermediates in the degradation process. The Li–Al LDH/PMS system, as expected, has great potential for efficient wastewater catalytic treatment.

Nitrogen doped Cu/Fe@PC derived from metal organic frameworks for activating peroxymonosulfate to degrade Rhodamine B

Nitrogen doped Cu/Fe@PC (Cu/Fe@PC-N) nanocomposite with core-shell structure was successfully prepared by one-step pyrolysis with g-C3N4 doped Cu/Fe-MOF. It was used as catalyst to active peroxymonosulfate (PMS) to degrade rhodamine B. The degradation of rhodamine B was a microelectrolysis-Fenton-like degradation process dominated by adsorption and PMS activation with non-free radical singlet oxygen (1O2). It was mainly realized by cracking, ring opening and mineralization of chromophore group. Within 30 min, the degradation efficiency of 50 mg/L RhB reached 100%, and the rate constant reached 0.5307 min-1. The excellent performance of Cu/Fe@PC-N catalyst was attributed to the synergistic effect of Cu and Fe. The doping of Cu not only accelerated the electron transmission and promoted the effective reduction of Fe2+, but also formed a circulating system of Fe2+/Fe3+ and Cu+/Cu2+, which ensured the efficient catalytic activity of the catalyst. This study provides some insights for pollutants degradation by microelectrolysis-Fenton-like system.

Heterogeneous photosensitizers: Super-efficient dual functional polydopamine nanohybrid for epoxy photopolymerization

The photosensitivity of nanoparticulate polydopamine (PDA) and polydopamine coated multiwalled carbon nanotubes (PDA/MWCNT) and their effect on the photopolymerization of epoxy monomers were systematically investigated. PDA/MWCNT nanohybrid at only 0.625 wt% has been shown to photo-catalyse the polymerization speed and conversion when compared with the commercial free radical photoinitiator, BAPO or non-free radical enhanced cationic photoinitiating resin systems. More importantly, it substantially increased the conversion by more than 140% over the unfilled free radical promoted cationic photoinitiating resin system. Covalent coated PDA/MWCNT nanohybrids were fabricated by oxidative polymerization of dopamine on the surface of acid treated MWCNTs. The modified MWCNT nanofiller has a dual role as photosensitizer/co-initiator in the FRPCP photoinitiating system and as mechanical reinforcement for the epoxy matrix. The use of PDA nanoparticles also led to the improvement in the polymerization process, albeit a limited one. Further evaluation of the observation suggests that the increase in the polymerization speed could be due to the photoinduced electron transfer effect in the polydopamine domain of the hybrid. The super efficiency effect has been explained through the heterojunction formation at the interface of dissimilar semi-conductive/conductive materials, polydopamine, a bio conjugated molecule with UV sensitivity and MWCNT hybrids, in the curing of epoxy monomers. This type of hybridized sensitizers/co-initiators have the potential to be applied in vat type 3D printing technologies such as SLA and DLP enabling printing with light blocking additives which otherwise pose a challenge in UV–Vis enabled curing and printing.

Development of emphatic catalysts for waste water remediation via synchronized free radical and non-free radical routes with composites of strontium hexaferrite, graphene and multi-walled carbon nanotubes

Magnetic nanoparticles have shown exceptional potential in catalysis, however, their tendency to agglomerate has confined their use. The present work encompasses synthesis of eco-friendly and magnetic retrievable catalysts with different fractions of reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNT) as support for strontium hexaferrite (SrFe12O19) for the oxidative degradation of organic pollutants. The morphological, structural and magnetic properties of composites were estimated via PXRD, FT-IR, VSM, FE-SEM, HR-TEM, XPS and BET. The crystallite size decreased from 41.46 nm for SrFe12O19 to 35.85 nm and 33 nm for composites with 20% rGO and MWCNTs, respectively while the surface area increased substantially from 88.1 m2/g for SrFe12O19 to 118.4 and 131.3 m2/g. Further, the composites were employed as catalysts for the oxidative degradation of selected antibiotics and colourant via stimulation of two different oxidants, potassium peroxymonosulphate (PMS) and hydrogen peroxide (H2O2). The degradation followed pseudo first order kinetics with rate constant values increasing with rGO and MWCNT content. The increase in catalyst effectiveness can be ascribed to the synergistic interactions between rGO or MWCNT and SrFe12O19, which provided larger specific surface areas for adsorption and augmented number of catalytically active sites. Systematic chemical quenching studies unveiled a combined role of radical and non-radical species in oxidative degradation of pollutants. Moreover, the synthesized composites exhibited excellent recyclability upto four cycles forming the basis for their utilization as industrial catalysts.

Peroxymonosulfate activation by Co-doped magnetic Mn3O4 for degradation of oxytetracycline in water.

Co-doped magnetic Mn3O4 was synthesized by the solvothermal method and adopted as an effective catalyst for the degradation of oxytetracycline (OTC) in water. Synergistic interactions between Co-Mn3O4 and Fe3O4 not only resulted in the enhanced catalytic activity through the activation of peroxymonosulfate (PMS) to degrade OTC but also made Fe3O4/Co-Mn3O4 easy to be separated and recovered from aqueous solution. 94.2% of OTC could be degraded within 60min at an initial OTC concentration of 10mg L-1, catalyst dosage of 0.2g L-1, and PMS concentration of 10mM. The high efficiency of OTC removal was achieved in a wider pH range of 3.0-10.0. Co (II), Co (III), Fe (II), Fe (III), Mn (II), Mn (III), and Mn (IV) on Fe3O4/Co-Mn3O4 were identified as catalytic sites based on XPS analysis. The free radical quenching experiments showed that O2•- radicals and 1O2 played the main role in the degradation process and the catalytic degradation of OTC involved both free radical and non-free radical reactions. Eventually, the intermediates of OTC degradation were examined, and the possible decomposition pathways were proposed. The excellent catalytic performances of Fe3O4/Co-Mn3O4 came from the fact that the large specific surface area could provide abundant active sites for the activation of PMS and the redistribution of inter-atomic charges accelerated the redox reactions of metal ions. The high degradation efficiency and rate constant of OTC in actual water samples indicated that Fe3O4/Co-Mn3O4 had a good practical application potential.