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As a typical visible-light-responsive organic semiconductor photocatalyst, graphitic carbon nitride (gCN) only exhibits moderate photoreactivity beacuse of its low specific area, limited light harvesting ability and quick recombination of photo-generated carriers. Herein, we report the fabrication of gCN nanosheets (gCN-NSs) with large BET surface area, excellent visible-light-absorptive property and efficient separation of carriers by direct polymerization of amidinourea, the product from the hydrolysis of dicyandiamine (DCDA). When compared with that of bulk gCN (S0) synthesized by direct polymerization of DCDA, the visible photocatalytic hydrogen evoluation rate of gCN-NSs (S2 sample) obtained by condensation of amidinourea improved 4.9 times, which is also 2.4 times higher than that of gCN-NSs (Su sample) which is prepared by polymerization of urea. The enhanced visible photocatalytic activity gCN-NSs (S2) toward hydrogen production can be ascribed to the combined effects of enlarged BET surface that provides more active sites for adsorption and photocatalytic reaction, compacted π-π layer stacking which facilitates the efficient separation of photo-generated carriers, negatively shifted CB potential and improved hydrophilic property that favor the electron transfer at the interfaces between gCN and water. In addition, the product yield of gCN-NSs (S2 sample) from the polymerization of amidinourea is 11.9%, which is 10.8 times higher than Su sample that prepared from urea (only 1.1%).

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is becoming an important member of pharmaceuticals and personal care products (PPCPs) as emerging pollutants. To degrade IBU, magnetic Fe3C nanoparticles embedded on N-doped carbon (Fe3C/NC) were prepared as a catalyst by a sol–gel combustion method. As characterized, the Fe3C/NC nanoparticles were composed of a NC nano-sheet and capsulated Fe3C particles on the sheet. The Fe3C/NC nanoparticles were confirmed an efficient catalyst for peroxymonosulfate (PMS) activation to generate sulfate radicals (SO4•-), single oxygen (1O2) and hydroxyl radicals (•OH) toward the degradation of IBU. The added IBU (10 mg/L) was almost completely removed in 30 min by using 0.1 g/L Fe3C/NC and 2 g/L PMS. The catalyst was confirmed to have good ability and excellent reusability through leaching measurements and cycle experiments. A catalytic mechanism was proposed for the catalytic activation of PMS on Fe3C/NC, which involves both Fe3C reactive sites and N-doped carbon matrix as reactive sites in Fe3C/NC. Moreover, the degradation pathway of IBU in the Fe3C/NC-PMS system was proposed according to the detections of degradation intermediates.

Graphitic carbon nitride with plentiful nitrogen vacancies (NV-g-C3N4) was prepared through a treatment of melamine under a N2 flow, and used for constructing a system of sulfite activation under visible light toward the degradation of carbamazepine. In the presence of Na2SO3 (20 mmol L−1), the use of NV-g-C3N4 (1 g L−1) increased the apparent rate constant for the photodegradation of carbamazepine (42 μmol L−1) to 0.0187 min−1, with an increasing magnitude of 270% in comparison with that obtained by using the conventional g-C3N4 (Bulk-g-C3N4). The enhanced photodegradation of carbamazepine by NV-g-C3N4 was found to be attributed to the efficient trap of photo-generated electrons by nitrogen vacancies, which inhibited the recombination of photo-generated carriers. Therefore, more holes aggregating in the valence band were available for the activation of sulfite anions to produce sulfite radicals. Sulfite radicals were identified as the major reactive species in the investigated photocatalytic system for the degradation of carbamazepine. The degradation pathway of carbamazepine induced by sulfite radicals in the NV-g-C3N4/Na2SO3 system was clarified on the basis of the identification of intermediates by GC- and LC MS. The photocatalytic activation of sulfite by metal free NV-g-C3N4 may be a useful technique for purifying waste-water containing organic pollutants.

In this study, Co-doped NaBiO3 nanosheets with surface confined Co reactive sites were prepared and utilized to catalyze peroxymonosulfate (PMS) activation and further degrade ibuprofen. Characterization results indicate Co reactive sites were mainly confined in surface region of Co-doped NaBiO3 nanosheets with the atomic percentage of 6.9% on catalyst surface. Further, the system of Co-doped NaBiO3/PMS was constructed for ibuprofen degradation. The added ibuprofen (20 µmol L−1) was removed completely in 30 min in the co-use of PMS (1 mmol L−1) and Co-doped NaBiO3 (0.2 g L−1) at pH0 7.0. Moreover, ultra-low Co leaching of lower than 5 μg L−1 at pH0 5–10 was observed in 30 min. Thus, Co-doped NaBiO3 exhibited highly catalytic stability for ibuprofen degradation in the neutral solution during the ten successive degradation runs. By identifying reactive oxygen species and degradation intermediates of IBP, IBP degradation pathway mainly induced by the generated sulfate radicals in the system of Co-doped NaBiO3/PMS was proposed. These interesting findings shed some new insight on the design of supported Co catalysts with high catalytic and chemical stability for the oxidative decontamination.

Nonradical persulfate oxidation processes have emerged as a new wastewater treatment method due to production of mild nonradical oxidants, selective oxidation of organic pollutants, and higher tolerance to water matrixes compared with radical persulfate oxidation processes. Since the case of the nonradical activation of peroxydisulfate (PDS) was reported on CuO surface in 2014, nonradical persulfate oxidation processes have been extensively investigated, and much achievement has been made on realization of nonradical persulfate activation processes and understanding of intrinsic reaction mechanism. Therefore, in the review, nonradical pathways and reaction mechanisms for oxidation of various organic pollutants by PDS and peroxymonosulfate (PMS) are overviewed. Five nonradical persulfate oxidation pathways for degradation of organic pollutants are summarized, which include surface activated persulfate, catalysts-free or catalysts mediated electron transfer, 1O2, high-valent metals, and newly derived inorganic oxidants (e.g., HOCl and HCO4-). Among them, the direct oxidation processes by persulfate, nonradical based persulfate activation by inorganic/organic molecules and in electrochemical methods is first overviewed. Moreover, nonradical based persulfate activation mechanisms by metal oxides and carbon materials are further updated. Furthermore, investigation methods of interaction between persulfate and catalyst surface, and nature of reactive species are also discussed in detail. Finally, the future research needs are proposed based on limited understanding on reaction mechanism of nonradical based persulfate activation. The review can offer a comprehensive assessment on nonradical oxidation of organic pollutants by persulfate to fill the knowledge gap and provide better guidance for future research and engineering application of persulfate.

Reduction of bromate (BrO3−) by various technologies has been extensively investigated, while the fate of oxygen and bromine atoms in BrO3− in these processes has been largely ignored. In this study, reduction of BrO3− by Fe(II) ions was investigated under various conditions via electron spin resonance (ESR), laser flash photolysis (LFP), probe of phenol and quenching experiments. It was found that reduction of BrO3− by Fe(II) ions produced HO•, O2•− and reactive bromine species (eg., Br• and Br2•−). HO• and O2•− were generated from release of one/two oxygen atoms in BrO3− and its reduction intermediates (BrO2− and BrO−) at one time, while Br• and Br2•− were generated from activation of hypobromous acid by Fe(II) and reactions of HO• with formed Br−. Due to the formation of these reactive species, the tested ten organic pollutants with diverse structures can be efficiently degraded, which including carbamazepine (CBZ), ibuprofen, phenol, benzoic acid, paracetamol, bisphenol a, 4-chlorophenol, oxcarbazepine, diclofenac and sulfamethoxazole. CBZ degradation intermediates by BrO3−/Fe(II) system were specially identified by liquid chromatography (LC)-mass spectrometry (MS), and three pathways of hydroxylation, ring contraction-amine cleavage and bromination for CBZ degradation were proposed accordingly. This study might shed new fundamental insights to bromate reduction and its implication for transformation of co-existed organic pollutants.

Photolysis and debromination of bromophenols were widely investigated previously. However, the role of reactive species especially hydrated electrons (eaq−) in their degradation was overlooked. Therefore, in the study, generation and role of the reactive species generated during the photolysis of bromophenols were identified and evaluated by using 2,4,6-tribromophenol (TBP) as a model at different pH values from 4 to 11 under anaerobic condition. It was found that photolysis of TBP solution under UV irradiation (254 nm) yielded organic radicals (C•), hydrogen radicals (H•) and eaq−. By using nitrite and monochloroacetic acid (MCAA) as scavengers of H•/eaq−, the role of UV direct photolysis, H• and eaq− in degradation of TBP was quantitatively assessed at different initial pH (pH0) values. UV irradiation induced direct photolysis of TBP was mainly dependent on its molar absorbance coefficient (e) at 254 nm. Contribution rate of UV irradiation to degradation of TBP was about 60% at pH0 4, 7 and 11. Interestingly, the contribution rate of eaq− was high as 35.8%-40% at pH0 4–11, while the contribution rate of H• was negligible (

Persulfate-based Advanced oxidation processes (AOPs) have gained a lot of attentions in organic decontamination in the past decades. Copper (Cu)/persulfate is an interesting coupling system due to its versatile activation pathways with formation of multiple radical and nonradical species. Thus, in the review, the generation mechanisms of various reactive species in Cu/persulfate system are analyzed and summarized. Firstly, the general activation mechanisms of Peroxydisulfate (PDS) and Peroxymonosulfate (PMS) catalyzed by Cu are summarized, and formation processes of four types of free radicals (SO4 −, OH, SO5 − and O2 −) and three types of non-radicals (Cu(III), surface activated PDS/PMS and 1O2) in the system are compared. Moreover, the role of copper ions and copper oxides in generation of these reactive species is discussed in details. Finally, the concluding remarks and perspectives for future research on Cu/persulfate AOPs are proposed. The review provides a comprehensive and deep insight into the formation and reaction mechanisms of radical and nonradical species, points out current controversies over reaction mechanisms involved in the Cu-persulfate-based AOPs, and proposes a guideline for future research and engineering application of persulfate.

Mesoporous Co3O4 (Co3O4-m) was synthesized with mesoporous silica (KIT-6) as a hard template. Co3O4-m was characterized by in situ reduction XRD, BET, TEM, and H2 TPR. The partly reduced Co3O4-m was studied as a catalyst for higher alcohol synthesis from CO2 hydrogenation. The metallic Co reduced from Co3O4 was the main activity site for the CO2 hydrogenation. The ordered mesoporous structure of the Co3O4-m catalyst promotes the growth of carbon chains for the production of higher hydrocarbons and alcohols and reduces the selectivity for CH4 from that of the partially reduced Co3O4 nanoparticles. The highest yield of higher alcohols was obtained in 1.6 mmol gcat−1 h−1 at 200 °C over the Co3O4-m catalyst, which was reduced at 300 °C. In addition, the selectivity for CH4 further decreased at 200 °C over the Pt/Co3O4-m catalyst, while the selectivity for CO and alcohols increased, owing to the reverse water gas shift ability of Pt. However, the conversion of CO2 significantly decreased. The yield of higher alcohols (1.5 mmol gcat−1 h−1) was slightly lower than that of Co3O4-m catalysts under the same reaction conditions.

A composite of Fe/Fe3C and N-doped graphitic carbon (Fe/Fe3C@NG) was prepared and used as a catalyst for the activation of peroxymonosulfate (PMS) toward the oxidative degradation of Norfloxacin (NOF). It was observed that Fe/Fe3C@NG behaved as a bifunctional material, showing both good adsorption ability and catalytic activity. The maximum adsorption capacity of Fe/Fe3C@NG for NOF was evaluated as 0.13 mmol g−1. Under given conditions (NOF concentration 0.1 mmol L−1, catalyst load 0.1 g L−1 and PMS addition 1 mmol L−1), the degradation of NOF was almost completely achieved in 20 min with a degradation rate constant of 0.22 min−1. A non-radical mechanism was proposed for the activation of PMS by Fe/Fe3C@NG by the scavenging test, EPR and chronoamperometry analysis. The fast and complete degradation of NOF was achieved via a rapid electron transform, in which both PMS and NOF molecular were adsorbed on the surface of Fe/Fe3C@NG and PMS was activated by obtaining electrons from NOF to oxidize NOF. The present study provides a green bifunctional catalyst for the oxidative removal of organic pollutants in various environmental media.

In this work, we report metal ions catalyzed oxidative degradation of three typical fluoroquinolones norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP) by using NaBiO3 nanosheets. It was found that variable-valence metal ions such as Cu2+, Fe2+, Mn2+, Ce3+, Ag+ and Co2+ could obviously enhanced degradation of NOR, OFL and CIP by NaBiO3. The pseudo-first-order kinetic rate for the degradation of 20 μmol L-1 NOR by NaBiO3 (2 mmol L-1) in the presence of 0.1 mmol L-1 Cu2+, Fe2+, Mn2+, Ce3+, Ag+ and Co2+ was 0.021, 0.084, 0.019, 0.23, 0.25 and 0.28 min−1, 2.1, 8.4, 19, 23, 25 and 28 times that by NaBiO3 without any metal ions. In comparison, Ca2+ and Fe3+ exhibited no obviously promotive or depressive effect for the degradation of NOR by NaBiO3. Singlet oxygen (1O2) was suggested as the main reactive species from NaBiO3 in the presence of metal ions by electron spin resonance technology and radicals scavenging experiments. The evolution of NaBiO3 was tracked with scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that the metal ions were embedded into the crystal structure of NaBiO3 through ion-exchange between Na in NaBiO3 and metal ions. In the subsequent step, an electron transformation from lattice oxygen to Bi(V) sites was mediated by embedded variable-valence metal species, resulting in an enhanced generation of 1O2 from the crystal structure of NaBiO3. These results can shed light on the application of NaBiO3 for the organic pollutant decontamination.

Polybrominated diphenyl ethers (PBDEs) are a family of important organic pollutants, and methods for their complete debromination are urgently needed. It is known that highly-brominated PBDEs are easily photocatalytically reduced to lower-brominated congeners, and the lower-brominated congeners are relatively susceptible to photocatalytic oxidation but not to further reduction. The present work developed a one-pot photocatalytic consecutive reduction and oxidation method (O-CRO) for the complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47). It was observed that BDE47 was resistant to photocatalytic reduction on TiO2 but underwent a slow oxidation in aerobic aqueous solutions (rate constant k = 0.065 h−1). The use of a reduced graphene oxide and TiO2 (RGO/TiO2) composite only slightly improved the photocatalytic oxidation of BDE47 in air-H2O systems (k = 0.12 h−1), but achieved a rapid photocatalytic reduction of BDE47 (k = 0.81 h−1) in anoxic ACN-H2O systems; however, the debromination was only 25.0% even after 14 h because the reduction intermediates (i.e., tri-BDEs) were minimally reduced. To conduct the O-CRO process, we developed an anoxic RGO/TiO2-H2O system containing a small amount of methanol. This system yielded the complete debromination and mineralization of BDE47 within 14 h. The mechanism for the debromination and mineralization of BDE47 was clarified. This method overcame the drawbacks of the separated two-step reduction and oxidation method and will find promising applications for the degradation of halogenated organic pollutants.

Nitric acid treated NaBiO3 (N-NBO) was observed to have the ability of yielding singlet oxygen (1O2) for degrading organic pollutants, and a mechanism study or insight into 1O2 generation from metastable lattice of treated-NBO was conducted. It was demonstrated that the acid treatment made Bi(V)O6 octahedron in NBO undergo drastic distortion, leading to the formation of a metastable Bi(III)O6 octahedron, which could store and release active oxygen as 1O2. As confirmed by characterization experiments, the 1O2-generating ability of N-NBO could be activated, deactivated and re-activated by different treatments, which corresponded to the formation, consummation and re-formation of the active metastable Bi(III)O6 octahedron. The formation of the metastable structure was related closely to the conversion of Bi5+ to Bi3+ in N-NBO, and its “collapse” eliminated the activity of the metastable Bi(III)O6 octahedron “pseudo-interface”. This structure was responsible for the release of active oxygen from the lattice in the form of 1O2, and the deactivated N-NBO could be re-activated by re-constructing this metastable structure through metal-ion doping and iodide reduction. A mechanism of 1O2 generation was proposed by considering the Bi(V)-Bi(III) conversion and the formation of the metastable Bi(III)O6 octahedron.

Surface carboxylated Cu0/Fe3O4 nanocomposites were prepared and used as a heterogeneous catalyst for activating molecular oxygen toward degradation of chlorophenols. The use of 1.0 g L−1 Cu0/Fe3O4 composites yielded a nearly complete removal of 4-chlorophenol (4-CP, 0.1 mmol L−1) in 60 min in a wide pH range from 3.0 to 10.0. The pseudo first rate constant (k) for 4-CP degradation at pHinitial 7.0 in the system of Cu0/Fe3O4-Air was 0.073 min−1, being 10.9 and 7.3 times that obtained in the systems of alone Cu0 and Fe3O4 nanoparticles, respectively. The generation of O2 −, H2O2, and OH as reactive oxygen species from the catalytic activation of O2 over the Cu0/Fe3O4 composites was evidenced and tracked. The activation of dissolved oxygen was confirmed to be synergistically initiated by the simultaneous use of strongly-interacted Cu0 and Fe3O4 nanoparticles, where the surface carboxyl groups mediated fast reduction of Fe(III) back to Fe(II) in Fe3O4 domains by Cu0 as a reducing agent. The present study not only sheds light on the synergistic effect between bimetal oxides in the environmental catalytic processes, but also provides a facile and efficient chemical method for the oxidative removal of organic pollutants.

Metastable Bi3+ self-doped NaBiO3 (NBO) nanosheets were prepared by using acidic hydrolysis of NaBiO3·2H2O in HNO3 solutions. It was found that the as-prepared NBO nanosheets showed both chemical oxidation ability and photocatalytic oxidation activity for the degradation of carbamazepine under visible light irradiation. The pseudo-zero order reaction kinetic constant for the photodegradation of carbamazepine (20 mmol L−1) over the metastable NBO nanosheets was 0.087 min−1, being 10.4 and 5.0 times that of the photocatalytic oxidation over the stable NBO nanosheets and the chemical oxidation over the metastable NBO nanosheets in dark, respectively. The enhanced photodegradation of carbamazepine over the metastable NBO nanosheets was mainly attributed to a reaction process of photocorrosion of the NBO nanosheets, which increased generation of singlet oxygen from the lattice oxygen of NBO and promoted a synergistic effect between the chemical oxidation and the photocatalytic oxidation. Singlet oxygen and photo-generated holes were identified as the major reactive species for photodegradation of carbamazepine. By a rough estimation, the (dark) chemical oxidation, photocorrosion process and photocatalysis contributed 19.4%, 60% and 20.6% of the total degradation of carbamazepine, respectively. Based on the identification of intermediates by GC– and LC–MS, two degradation pathways of carbamazepine in both chemical oxidation system and photocatalytic system were proposed. The developed dual-reactive-species-based photocatalysis may be a useful technology for the purification of water containing carbamazepine.

The application of MoS

Microscaled CuFeO2 particles (micro-CuFeO2) were rapidly prepared via a microwave-assisted hydrothermal method and characterized by scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. It was found that the micro-CuFeO2 was of pure phase and a rhombohedral structure with size in the range of 2.8±0.6μm. The micro-CuFeO2 efficiently catalyzed the activation of peroxymonosulfate (PMS) to generate sulfate radicals (SO4-), causing the fast degradation of carbamazepine (CBZ). The catalytic activity of micro-CuFeO2 was observed to be 6.9 and 25.3 times that of micro-Cu2O and micro-Fe2O3, respectively. The enhanced activity of micro-CuFeO2 for the activation of PMS was confirmed to be attributed to synergistic effect of surface bonded Cu(I) and Fe(III). Sulfate radical was the primary radical species responsible for the CBZ degradation. As a microscaled catalyst, micro-CuFeO2 can be easily recovered by gravity settlement and exhibited improved catalytic stability compared with micro-Cu2O during five successive degradation cycles. Oxidative degradation of CBZ by the couple of PMS/CuFeO2 was effective in the studied actual aqueous environmental systems.

In this study, an inorganic reductant hydroxylamine was used to enhance the Fenton degradation of carbamazepine by easily recyclable microscaled CuFeO2 in a wide pH range (pH 4.0–9.0). It was found that the addition of hydroxylamine could dramatically enhance the degradation rate and TOC removal of carbamazepine, better than other reductants such as benzoquinone and ascorbic acid. In the CuFeO2-H2O2 Fenton system, only 31% CBZ (50 μmol L−1) was removed at pH of 7.0 in 60 min in the presence of 1.0 g L−1 CuFeO2 and 20 mmol L−1 H2O2, while CBZ can be nearly completely removed in 60 min after the addition of 0.1 mmol L−1 hydroxylamine under the similar conditions. Moreover, CBZ degradation followed the pseudo first-order kinetics in the CuFeO2-H2O2 Fenton system, while in the hydroxylamine enhanced CuFeO2-H2O2 Fenton system, CBZ degradation followed the pseudo second-order kinetics. In the CuFeO2-H2O2 Fenton system, t1/2 value for CBZ degradation was calculated as 114.4 min and the value was greatly decreased to 1.8 min after the addition of hydroxylamine. This hydroxylamine induced dramatic carbamazepine degradation enhancement could be attributed to the hydroxylamine enhanced Fe(III)/Fe(II) and Cu(II)/Cu(I) redox cycles. Hydroxyl radicals were the primary radical species responsible for the carbamazepine degradation. As a microscaled catalyst, micro-CuFeO2 can be easily recovered by gravity settlement and exhibited good catalytic stability during six successive degradation cycles. Therefore, the couple of CuFeO2-H2O2-hydroxylamine is a promising method for oxidative degradation of organic pollutants in the actual aqueous environmental systems.

An efficient method was developed for degrading endocrine disrupting bisphenol A (BPA) by simultaneously using the chemical oxidizing ability and visible-light photocatalytic activity of NaBiO 3 . It was found that in the presence of NaBiO 3 (0.5 g L −1 ) under visible light illumination, the degradation removal of BPA (0.1 mmol L −1 ) and the removal of total organic carbon within 60 min were increased from 34% to 99.8% and from 12% to 86%, respectively, with decreasing initial reaction pH (pH 0 ) from 9.0 to 5.5. NaBiO 3 was reduced to Bi 3+ self doped NaBiO 3 at pH 0 values ranging from 4.2 to 8.0 or Bi(V)/Bi(III) composites at lower pH 0 values, being accompanied with generation of singlet oxygen. In general, a lower pH 0 value resulted in stronger generation of singlet oxygen, and the in-situ generated Bi 3+ self doped NaBiO 3 or Bi(V)/Bi(III) composites showed higher photocatalytic activity than their precursor NaBiO 3 . As major oxidizing species, photo-generated holes and chemically-induced singlet oxygen showed synergistic effects for the degradation and mineralization of BPA in the tested system. The generated singlet oxygen promoted the initial transformation, subsequent benzene ring cleavage and final mineralization of BPA by generating more hydroxylation and quinone intermediates, which were easily degraded through subsequent photo-generated hole oxidation.

The application of MoS2 to enhance Co(II)/peroxymonosulfate (Co(II)/PMS) system for organic pollutants degradation was developed, and the mechanism for pH dependent catalytic activity in the MoS2 co-catalyzed Co(II)/PMS processes was systematically investigated. It was found that MoS2 presented enhancement effect for Co(II)/PMS system in the tested pH range from 4.0 to 7.0, especially at pH 5.5 and 6.0. The pseudo first order reaction rates for Rhodamine B (RhB) degradation in MoS2-Co2+/PMS system at pH 5.5 and 6.0 were 3.2 and 1.8 times that in Co2+/PMS system (Co2+ 2 μmol L−1, PMS 0.2 mmol L−1, MoS2 0.5 g L−1). The redox recycle of Co3+/Co2+ was promoted by Mo(IV) and S(-II) on MoS2 surface and regenerated Co2+ induced homogeneous activation of PMS for the robust production of free radical with the major of hydroxyl radicals. Increasing MoS2 dosage, Co2+ and PMS concentration can linearly raise RhB degradation rate in MoS2-Co(II)/PMS system. Moreover, MoS2 exhibited excellent catalytic and chemical stability in recyclability and reuse for catalytic decontamination in MoS2-Co(II)/PMS system. This work gains new insight into the enhancement effect of MoS2 in the meal ions/PMS system, and provides a high performance wastewater treatment process of Co(II)/PMS at low concentrated Co2+.

Cu-Fe bimetal oxides yield excellent catalytic activity. However, there are some debates on Cu redox cycle and direction of electron transfer during PMS activation by these Cu-Fe bimetal oxides. In this paper, therefore, CuO/Fe3O4 nanoparticles with strong Cu-Fe interaction were prepared by pyrolysis of copper-hexacyanoferrate(III) at 600 °C for 1 h and used to investigate the effect of Cu-Fe interaction on catalytic performance of these Cu-Fe bimetal oxides. The as-prepared CuO/Fe3O4 as a catalyst presented much stronger reactivity than CuO and Fe3O4 for peroxymonosulfate (PMS) activation and bisphenol A (BPA) degradation. The use of 0.3 g L−1 CuO/Fe3O4 and 0.3 mmol L−1 PMS achieved deep mineralization (>99%) in 110 min for degradation of 20 mg L−1 BPA at initial pH 6.0. The k value for BPA degradation was 0.32 min−1 for CuO/Fe3O4, being about 5.3, 3.2 and 2.7 times that for the catalysts of Fe3O4, CuO and the mixture of CuO and Fe3O4, respectively. The synergistic effect between Cu and Fe sites on the surface of CuO/Fe3O4 nanoparticles was attributable to strong Cu-Fe interaction. Characterization by X-ray photoelectron spectra and temperature-programmed reduction with H2 as a reducing agent showed that the strong Cu-Fe interaction makes Cu species more easily donate electrons to PMS for radicals generation as the main reactive sites and reductive cycle of Fe species easier through accepting electrons from PMS, further promoting Cu catalytic cycle through an electron transfer between Cu and Fe. The clarification of structure activity relationship (SAR) of interaction between bimetal species and their activity for peroxide activation facilitates deep understand of the catalytic mechanism and development of more efficient bimetal based catalysts.

Co-based catalysts demonstrated high performance for activating peroxymonosulfate (PMS). In the present study, micro-nano structured CoS was prepared by a simple solvothermal reaction and the influence of sulfur in CoS in the PMS activation for bisphenol A (BPA) decomposition was investigated systematically. It was found that micro-nano structured CoS exhibited remarkable catalytic activity with 90% removal of 20 mg L−1 BPA within 10 min under 0.05 g L−1 CoS and 0.3 mmol L−1 PMS at 25 °C. The peso-first reaction rate constant for BPA degradation in this system was 0.37 min−1, 1.1 and 1.5 times that by using surface sulfur modified Co3O4 (S-Co3O4) and Co3O4 nanoparticles as a catalyst. Factors influencing BPA degradation were also examined, including initial pH (pH0), dosages of PMS and CoS. The BPA removal was enhanced with the raise from 3 to 11 in the reaction solution due to enhanced PMS decomposition and free radicals production. Moreover, the conversion of SO4 − to OH as the main reactive species was observed as pH0 was varied from 3 to 10 through electron paramagnetic resonance (EPR) analysis and quenching experiments. BPA degradation pathways by CoS/PMS system were proposed based on LC-MS results of degradation intermediates. Finally, a possible mechanism for activation of PMS by CoS was proposed according to the surface evolution of CoS during the reaction process by XPS spectra.

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is becoming an important member of pharmaceuticals and personal care products (PPCPs) as emerging pollutants. To degrade IBU, magnetic Fe

Bisphenol A (BPA) is a ubiquitous environmental contaminant with endocrine disruption potential. This study explored the efficiency, kinetics, and mechanism of BPA removal from weakly acidic solutions by using NaBiO3 as a source of singlet oxygen. It was observed that the use of NaBiO3 (1 g L−1) could eliminate almost all (more than 97%) of the added BPA (0.1 mmol L−1) in solutions at pH 5.0 in 60 min. The degradation of BPA followed pseudo-first-order kinetics over the pH range from 3 to 9, and the pseudo-first-order rate constant (k) was dependent on pH, NaBiO3 concentration and the coexisting compounds. As solution pH was decreased from 9 to 3 or NaBiO3 concentration was increased from 0.5 to 2 g L−1, the k value was increased logarithmically. Humic acid and Fe3+ showed little effect on the BPA removal, but Mn2+ exhibited exceptionally enhancing effect on the degradation of BPA. The involved reactive species were identified as singlet oxygen by using radical scavenger probes and ESR measurement, and the generated singlet oxygen was confirmed to be generated from the decomposition of NaBiO3 mediated by H+ ions.

An efficient singlet oxygen generation system was first developed by using Bi(V)/Bi(III) composites for degrading organic pollutants. The composites were prepared by hydrolyzing NaBiO3 in HCl solutions. As monitored by various techniques, it was found that the morphology and composition of the composites were able to be tuned by changing the molar ratio of HCl to NaBiO3 in the preparation process, which was optimized at 2.0. Due to the efficient generation of singlet oxygen, the use of the composite (0.75 g L−1) resulted in almost complete degradation of bisphenol A (0.2 mmol L−1) in 20 min, with a pseudo-first-order kinetic constant of 0.14 min−1. The dominant reactive species in the degradation system were confirmed to be singlet oxygen, which was generated from the release of the lattice oxygen in the composite. The good performances of the concerned singlet oxygen generation system are general for degrading different organic pollutants.

A facile controlled synthesis method of Bi3+ self doped NaBiO3 nanosheets was developed by using acidic hydrolysis of NaBiO3·2H2O in HNO3 solutions. It was found that the hydrolysis of NaBiO3·2H2O in HNO3 solutions at low concentrations (0 420 nm). The pseudo-zero order reaction kinetic constant for the degradation of rhodamine B (20 μmol L−1) over the Bi3+ self doped NaBiO3 was 0.68 μmol L−1 min−1, being 3.1 times that of NaBiO3·2H2O. The much enhanced photocatalytic activity of the Bi3+ self doped NaBiO3 nanosheet photocatalyst was attributed to its improved absorption of visible light and separation of photo-generated h+/e− pairs.

In this work, we report metal ions catalyzed oxidative degradation of three typical fluoroquinolones norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP) by using NaBiO

A composite of graphene oxide and nano-Fe3O4 (GO/Fe3O4) was prepared and characterized as an artificial enzyme-like catalyst. By combining the artificial enzyme-like catalyst and a natural enzyme horseradish peroxidase (HRP) as a binary enzymatic catalyst, the catalytic oxidative removal of 2,4-dichlorophenol (2,4-DCP, 50 mg L−1) was achieved in the presence of H2O2 (0.7 mmol L−1) in aqueous media at near neutral pH value (pH 6.4) and room temperature. It was observed that the single use of HRP and GO/Fe3O4 produced a 2,4-DCP removal of 35% and 9%, respectively, whereas their simultaneous use yielded a removal as high as 93%. This indicates that there is a synergistic effect between GO/Fe3O4 and HRP. The effects of initial pH value, temperature, initial concentrations of HRP, GO/Fe3O4 and H2O2 were optimized. The intermediate products during the catalytic oxidation of 2,4-DCP in the system of GO/Fe3O4–HRP were identified by gas chromatography/mass spectrometry, and the possible degradation pathway of 2,4-DCP was proposed. In addition, the GO/Fe3O4 composite could be easily separated from the reaction solution with a magnetic field, and the recycled GO/Fe3O4 showed a good catalytic stability.

CuFeO2 microparticles were prepared, characterized and used as a heterogeneous Fenton-like catalyst. The as-prepared CuFeO2 microparticles were composed of pure rhombohedral crystalline particles with sizes in the range of 2–3 μm. As a composite oxide of Cu and Fe elements, the CuFeO2 microparticles showed much stronger catalytic ability toward the activation of H2O2 than Cu2O microparticles and Fe3O4 nanoparticles did. The catalytic activation of H2O2 produced hydroxyl radicals ( OH), causing rapid degradation and mineralization of bisphenol A (BPA). The use of 1.0 g L−1 CuFeO2 microparticles and 20 mmol L−1 H2O2 yielded a nearly complete removal of the added BPA (0.1 mmol L−1) in 120 min and 85% removal of TOC in 180 min. The microscaled CuFeO2 catalyst was confirmed to have merits of easy recycling and good stability by successive degradation experiments. The generation of OH from the catalytic activation of H2O2 over CuFeO2 microparticles was evidenced using electron spin resonance spectroscopy, quenching experiment and coumarin fluorescent probe technique. This activation was confirmed to be initiated by surface Cu(I) and Fe(III).

To develop highly efficient heterogeneous photocatalysts for the activation of dissolved oxygen is very interesting in the field of green degradation of organic pollutants. In the paper, oxygen atom doped g-C3N4 (O-g-C3N4) was prepared via a facile chemical oxidation of g-C3N4 by peroxymonosulfate. X-ray photoelectron spectroscopy analysis suggests the oxidative treatment of g-C3N4 by peroxymonosulfate evidently increased atomic percentage of oxygen on O-g-C3N4 surface to 6.9% as compared with 1.8% for g-C3N4. Meanwhile, the doped oxygen atom mainly existed as carbonyl and carboxyl groups. Optical characterization indicates the introduction of oxygen improved the response of O-g-C3N4 to visible light, and more obviously, separation of photo-generated h+-e&minus, 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) probe measurement indicates the formation of O2&bull, &minus, was dramatically enhanced through activation of dioxygen by photo-generated electrons in the O-g-C3N4 photocatalytic system. Through high performance liquid chromatography (HPLC) and Liquid chromatography&ndash, mass spectrometry (LC-MS) analysis, it was found rhodamine B (RhB) photocatalytic degradation by O-g-C3N4 followed step by step N-deethylation reaction pathways induced by the formed O2&bull, rather than the non-selective decomposition of the chromophore in RhB by other radicals, such as hydroxyl radicals. This study provides a facile method to develop oxygen atom doped g-C3N4 photocatalyst, and also clarifies its photocatalytic activation mechanism of molecular oxygen for N-deethylation reaction of RhB.

CuFe 2 O 4 magnetic nanoparticles (MNPs) were prepared by sol–gel combustion method with copper and iron nitrates as metal precursors and citrate acid as a complex agent. The obtained CuFe 2 O 4 MNPs were characterized by scanning electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that CuFe 2 O 4 MNPs could effectively catalyze peroxymonosulfate (PMS) to generate sulfate radicals (SO 4 − ) to degrade tetrabromobisphenol A (TBBPA). The added TBBPA (10 mg L −1 ) was almost completely removed (with a removal of 99%) in 30 min by using 0.1 g L −1 CuFe 2 O 4 MNPs and 0.2 mmol L −1 PMS. With higher addition of PMS (1.5 mmol L −1 ), the degradation yielded a TOC removal of 56% and a TBBPA debromination ratio of 67%. The effect of catalyst calcination temperature, catalyst load, PMS concentration and reaction temperature was investigated on the catalytic activity of CuFe 2 O 4 MNPs. The highly catalytic activity of CuFe 2 O 4 MNPs possibly involved the activation of PMS by both Cu(II) and Fe(III) in CuFe 2 O 4 MNPs. Based on intermediate detections, the degradation pathway of TBBPA in the CuFe 2 O 4 MNPs/PMS system was proposed.

Composite films of TiO 2 and carbon nanotubes (CNTs) were prepared on titanium sheets by liquid phase deposition and the photoelectrocatalytic (PEC) properties of the films were investigated through the degradation of methyl orange (MO) in 0.1 M solutions. It was demonstrated that CNTs in the TiO 2 film significantly decreased the charge transfer resistance and increased the anodic photocurrent response of the film under UV light irradiation when the bias was above −0.1 V. The PEC performance of the CNT-based composite film could be tuned by controlling the preparation parameters including the deposition time and calcination temperature. The deposition time and calcination temperature were optimized at 1 h and 450 °C, respectively. On the TiO 2 /CNT film prepared under the optimized conditions, 95% of the added MO (10 mg L −1 ) was degraded within 90 min, which was much higher than the 60% removal seen on the pure TiO 2 films.

TiO 2 film deposited on glassy carbon electrode surface was prepared via the liquid phase deposition (LPD). The deposited TiO 2 film before and after calcination was characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). Based on the high photoelectrochemical activity of calcined LPD TiO 2 film, the photoelectrocatalytic degradation of benzotriazole (BTA) was investigated. Compared with the electrochemical oxidation process, direct photolysis or photocatalysis for treatment of BTA, a synergetic photoelectrocatalytic degradation effect was observed using the LPD TiO 2 film-coated electrode. Various factors influencing the photoelectrocatalytic degradation of BTA such as film calcination, applied bias potential, pH value, supporting electrolyte concentration and initial concentration of BTA were investigated. The COD removal for BTA solution was analyzed to evaluate the mineralization of the PEC process. Based on the degradation experimental results, a possible photoelectrocatalytic degradation mechanism for BTA was proposed.

By using cobalt nitrate and bismuth nitrate as precursor salts and NaOH as a precipitation agent, Co3O4–Bi2O3 nanocomposite oxides (CBO) were prepared as a heterogeneous catalyst for the activation of peroxymonosulfate (PMS) by a conventional reverse co-precipitation method and post-calcination. The characterization with transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that there was a strong interaction between Bi and Co components in CBO. The presence of Bi increased the content of surface hydroxyl oxygen, which favored the formation of Co(II)–OH complexes that were vital for heterogeneous activation of PMS. CBO showed strong catalytic activity in the heterogeneous activation of PMS for degradation of organic pollutants such as methylene blue (MB), rhodamine B, phenol and 2,4-dichlorophenol. With the addition of 0.5 mmol L−1 PMS, CBO produced fast and full degradation of MB (20 μmol L−1) with the apparent rate constant of 0.36 min−1, being 8.6 fold of that (0.042 min−1) over nano-Co3O4. It decreased the cobalt leaching to 43 μg L−1, being much less than that (158 μg L−1) from Co3O4 under the same conditions. The effects of CBO loading, PMS concentration and calcination temperature on the degradation of MB and cobalt leaching were also investigated.

Persulfate can efficiently decolorize azo dyes through oxidizing these compounds, which enabled us to develop a method of rapid spectrophotometric determination of persulfate for monitoring the wastewater treatment on the basis of the oxidation decolorization of azo dyes. Four azo dyes with different molecular structures were investigated as probes, and the influences of operation parameters including reaction time, solution pH, initial dye concentration, and initial concentration of activator Fe(2+) were checked on the determination of persulfate. Under optimum conditions, the decolorization degree of the dyes responded linearly with persulfate concentration for all the four azo dyes, and the linear range and detection limit were found to be 2.0-150 μmol L(-1) and 0.62 μmol L(-1) for rhodamine B, 2.0-100 μmol L(-1) and 0.42 μmol L(-1) for methylene blue, 4.0-150 μmol L(-1) and 0.50 μmol L(-1) for methyl violet, and 20-150 μmol L(-1) and 8.1 μmol L(-1) for orange II. A persulfate treatment of a spiked wastewater sample was satisfactorily monitored with the new method.