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Chitosan, as a bio-friendly and abundant biochar precursor, was employed to prepare cobalt-based catalyst (Co

Sulfur-doped Fe–Cu–La trimetallic oxides (S-FeCuLaO) were synthesized by a coprecipitation method and applied as a novel magnetic adsorbent for the removal of As(III) and As(V) in water. Batch experimental results demonstrated that the material exhibited excellent adsorption properties for both As(III) and As(V) in a wide pH range and the maximum adsorption capacities of S-FeCuLaO at initial pH 6.0 were 181 mg g−1 for As(III) and 250 mg g−1 for As(V), respectively. Both As(III) and As(V) (10 mg L−1) were completely removed by the regenerated adsorbent after the third cycle. Furthermore, the residual As(III) concentration in well water containing 1 mg L−1 As(III) decreased to below 10 μg L−1 after adsorption for 8 h. The adsorption process complied with the Langmuir isothermal model and the pseudo-second-order kinetic model. Among the five coexisting ions investigated (Cl−, NO3−, SO42−, CO32− and PO43−), only PO43− could significantly inhibit the adsorption of As(III) and As(V) by competing for active adsorption sites. The removal mechanism of arsenic was proposed as (1) the oxidization of As(III) to As(V) by superoxide radicals (O2˙−) produced between Cu(I) and the dissolved O2 and (2) the adsorption of As(V) through electrostatic attraction and the further formation of inner-sphere complexes via ligand exchange. Thus, S-FeCuLaO could be used as an attractive material for arsenic removal from wastewater and groundwater.

The disposal and recovery of solid wastes and the remediation of polycyclic aromatic hydrocarbons (PAHs) are the key issues of environmental pollution control. In this study, micro cobalt loaded on iron-carbon-vermiculite composite (Co-ICV) was prepared for the first time by the reutilization of waste self-heating pad as a carrier of cobalt catalyst, which exhibited better performance than bulk cobalt catalyst in peroxymonosulfate (PMS) activation for the degradation of naphthalene (NAP) in water. Above 98% of NAP (2.0 mg/L) was effectively eliminated within 15 min by the Co-ICV (0.2 g/L) activated PMS (0.5 mmol/L) in a pH range of 5.0-9.0. High magnetism and very limited cobalt leaching realized the convenient separation and stable reusability of Co-ICV. Mechanism investigation indicated that Co(II) species were the main active sites to activate PMS decomposition for the generation of SO

In this study, microscale zinc–copper (mZn/Cu) bimetallic particles were prepared through precipitating Cu on the surface of Zn and applied in the degradation of p-nitrophenol (PNP). To optimize re...

A magnetic Fe-Mn-Y tri-metal composite served as an adsorbent for the arsenate [As(V)] removal, and it was synthesized by hydro-thermal synthesis for the first time. The adsorbent was further chara...

Chloramphenicol (CAP) is a typical kind of antibiotics, which has posed a severe threat to nature and human beings due to its wide application. In this study, cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts (Co-Bi@CCB) was prepared to activate peroxymonosulfate (PMS) for the removal of CAP. Our results demonstrated Co-Bi@CCB not only possessed excellent catalytic performance, but also significantly limited metal ions dissolution. Over 98% of CAP (10 mg/L) was degraded in the presence of Co-Bi@CCB (0.05 g/L) and PMS (1 mM) within 20 min at pH = 7. Quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that SO

This paper focused on understanding the effect of citric acid (CA) on the reductive dissolution of Schwertmannite loaded with arsenite (SCH-As(III)) under UV irradiation and the release of arsenic (As). Results demonstrated that CA could significantly promote the reductive dissolution of SCH and SCH-As(III) with the assistance of ultraviolet light. Initially, the dissolved total iron (Fe) and As exhibited a rapid increase (0 to 240 min), followed by a quick decline due to the depletion of CA. It was found that the dissolved total Fe and As were present mainly as the species of Fe(II) and As(V), respectively. This can be attributed to the electronic transfer from ligand to metal in the complex of Fe(III)-(CA)n occurring under ultraviolet light, leading to the production of Fe(II) and organic radicals. Moreover, As(V) was further generated via the interaction of As(III) with OH from a series of radical reactions. In the dark, CA could also enhance the total Fe and As released from the SCH-As(III). The lower the initial pH level, the greater the amount of total dissolved Fe and As. The presence of Al3+ clearly suppressed the reductive dissolution of SCH-As(III) triggered by CA and ultraviolet light. SEM spectra indicated that the mineralogical phases of SCH-As(III) before and after the reaction were discrepant. Thus, this study provides an insight into the stability of SCH-As(III) and the migration of As in the natural environment.

Cu-Y binary oxysulfide was synthesized for the first time. A series of batch experiments were conducted to determine the optimum conditions for preparing the adsorbent and further investigate the effects of the initial pH and coexisting anions on the removal of arsenic. The results indicate that the adsorbent displays an extremely excellent performance in removing both As(III) and As(V). The maximal adsorption capacities at the initial pH 6.0 are 263.16 and 270.27 mg/g for As(III) and As(V), respectively. The adsorbent remains relatively stable even at the initial pH 3 and at this pH it also exhibits a very high removal efficiency for As(V). Based on Fourier-transform infrared (FTIR) spectrometer and X-ray photoelectron spectrometer (XPS) analyses and other results obtained in our experiments, a possible mechanism for the removal of arsenic is proposed. The dissolved O2 is activated to O2 − via a single-electron transfer reaction from Cu(I) on the adsorbent, which oxidizes As(III) to As(V). Then, arsenate anions are adsorbed onto the surface of the adsorbent and the adsorbed arsenate anions further react with the hydroxyl groups on the surface of the adsorbent via an ion exchange or precipitate with Y(III) on the surface of the adsorbent.

Sulfur-doped copper-cobalt bimetallic oxides (S-CuYO) with abundant Cu(I) were successfully synthesized by a co-precipitation method and were for the first time utilized to activate peroxymonosulfate (PMS) for the degradation of chloramphenicol (CAP). For comparison purposes, sulfur-doped monometallic oxides (S-CuO and S-CoO) and non-doped copper-cobalt bimetallic oxide (CuCoO-1) were also prepared via the same processes. The results demonstrated that S-CuCoO had the highest catalytic activity among the catalysts. The sulfur-doped catalyst significantly improved the catalytic performance and stability. More than 98% of CAP (20 mg/L) was removed within 15 min at the initial pH = 5. The superior catalytic activity of S-CuCoO mainly resulted from the synergy of Cu(I) and Co(II). The presence of Cu(I) improved the conversion of Co(III) to Co(II), which maintained the high catalytic performance of S-CuCoO. In addition, the produced Cu(II) was further converted to Cu(I) by lattice oxygen (O2−), ensuring an adequate supply of Cu(I) in the catalyst. Radical quenching experiments revealed that both the SO4 − and OH radicals were generated by the interaction of S-CuCoO with PMS, thereby contributing to the efficient degradation of CAP and the OH radicals played a larger role. The main intermediates of the CAP degradation were identified by high-performance liquid chromatography–mass spectrometry (HPLC-MS/MS). Theoretical calculations of the frontier electron densities (FEDs) were performed to determine the possible degradation pathways of CAP.

Micro-scale zinc-copper (mZn/Cu) bimetallic particles were prepared via precipitating Cu on the surface of Zn and were for the first time applied in the aniline degradation. The results showed that the degradation efficiency of aniline was greatly related to the theoretical Cu mass loading and the initial pH. The optimal Cu loading and initial pH for the destruction of aniline were determined as 60.45 wt% and 3, respectively. To further assess the high reactivity of mZn/Cu, the removal of aniline and total organic carbon (TOC) was investigated in different systems. The degradation of aniline by mZn, mCu, and mZn + mCu was5% within 75 min. However, 97% of aniline (10 mg L

Nanoscale copper-nickel binary oxysulfide (CuNiOS) was for the first time synthesized by a co-precipitation method and characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer-Emmett-Teller (BET). CuNiOS was used as a catalyst for the degradation of aniline by peroxydisulfate (PDS) and its catalytic performance was investigated via various impact factors including catalyst loading, PDS and aniline concentrations as well as solution initial pH. The results demonstrate that CuNiOS had highly catalytic activity and approximately 80% of total organic carbon of aniline solution (0.1 mM) was removed within 20 min. Copper and nickel ions on the surface of catalyst are the critical catalytic centers to activate PDS. The components of copper and nickel in the catalyst exhibited an excellent synergistic role in the degradation of aniline. The analyses of electron paramagnetic resonance (EPR) and the experiments of radical quenching confirmed the generation of SO4 − and OH in the reaction system, both of which were responsible for the degradation of aniline. The intermediates of aniline degradation were identified by UPLC-MS and the possible pathways of aniline degradation are further proposed. Based on the results obtained in this study, it is educed that CuNiOS-catalyzed PDS is a promising approach to the treatment of the wastewater containing aniline.

In this study, CrPO4-supported Co3O4 (CrPO4@Co3O4) as an efficient peroxymonosulfate (PMS) catalyst was obtained for the first time and used to eliminate phenacetin (PNT) from aqueous solution efficiently. CrPO4@Co3O4 composite exhibited a superb catalytic performance, and over 98% PNT was degraded by PMS (0.5 mM) within 15 min, which is much more efficient than in the systems of CrPO4/PMS and Co3O4/PMS. The excellent catalytic performance of CrPO4@Co3O4 was attributed to its higher BET surface area. On the other hand, the presence of PO43- in the catalyst might improve the conversion of Co(III) to Co(II). The latter served as the main active site for the PMS activation. CrPO4@Co3O4 also possessed superior stability and reusability, and the removal rates of PNT remained over 91% through 4 cycle tests. Solution pH significantly impacted the PNT decomposition, and the optimal catalytic degradation of PNT was achieved in an initial range of 5 to 7. Humic acid, HCO3−, and Cl− inhibited PNT degradation. Radical scavenging experiments and EPR technology revealed that SO4•− free radicals were the main reactive oxygen species (ROS) responsible for PNT degradation. While O2•− mainly acted as the intermediate to form SO4•− and 1O2. To assess the practical application of the CrPO4@Co3O4/PMS system, the PNT degradation was investigated in real lake water. Based on HPLC-TOF-MS2 analysis, 12 intermediates were identified, and the degradation pathways were further inferred. Therefore, this study provides a feasible strategy for the valuable use of CrPO4 as recycled material and a practical solution for the efficient degradation of organic contaminants.

In this study, magnetic Cu and Ni bimetallic particles embedded carbon sheets, namely as C@Cu–Ni, was derived via calcining a mixture of Cu-MOFs and Ni-MOFs (mass ratio = 4:6) under N2 protection and served as a catalyst for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by peroxymonosulfate (PMS). The results showed that more than 98.5% of 2,4,6-TCP (10 mg L−1) was rapidly decomposed at initial pH = 5, PMS = 1 mM and catalyst dosage = 0.1 g L−1 within 30 min, accompanied by 42.47% removal of total organic carbon (TOC). This fully confirmed that C@Cu–Ni possessed excellent catalytic performance for PMS activation. The radical quenching experiments and electron paramagnetic resonance (EPR) investigation testified that the reactive oxygen species (ROS) included SO4•−, •OH, O2•− radicals and singlet oxygen (1O2), which were responsible for the rapid degradation of 2,4,6-TCP. Among them, O2•−and 1O2 played a decisive role. Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) revealed that C@Cu–Ni material possessed superior electrical conductivity and electron transfer, improving its catalytic activity. What is more, C@Cu–Ni displayed excellent stability and could be consecutively used for five times without any decline of catalytic performance. The main intermediates of the 2,4,6-TCP degradation were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) and possible pathways of 2,4,6-TCP degradation were further proposed. The extraordinary stability and superior catalytic activity of C@Cu–Ni coupled with its easy separation from wastewater due to magnetism suggest that the newly synthesized material may offer a promising alternative approach to efficiently degrade organic pollutants by PMS.

Roxarsone (ROX), as one of aromatic organoarsenic compounds (AOCs), is extensively used in livestock industry, which tends to transform into high-toxic inorganic arsenic in environments. Herein, a bifunctional Co

Co

Cobalt-yttrium binary oxide (CYBO) was successfully fabricated, which exhibited excellent catalytic performance in the activation of peroxymonosulfate (PMS) and superior adsorption capacity towards phosphate (116.3 mg-P/g). The results demonstrated that a complete degradation of phenylphosphonic acid (PPOA) within 30 min and a thorough removal of phosphate product within 60 min could be realized in the system of CYBO/PMS. CYBO also possessed superb reusability and stability, and no decline of the PPOA degradation and phosphate removal was observed during 5 cycles at initial pH 7. The decomposition of PPOA and the adsorption of phosphate were strongly dependent on solution pH. In an initial pH range of 3 to 7, both PPOA and phosphate product could be efficiently removed. However, almost no PPOA was degraded at initial pH 11. SO4•−, •OH, and 1O2 (especially SO4•− and •OH) were identified as main reactive oxygen species responsible for the PPOA degradation and the formation of phosphate product. The produced phosphate was simultaneously eliminated via anion/ligand exchange. Combined with identification of PPOA degradation intermediates via HPLC-QTOF-MS2, the calculation of frontier electron densities based on Density Functional Theory was used for proposing reasonable degradation pathways. In addition, the toxicity assessment via Toxicity Estimation Software Tool was utilized to appraise eco-environmental effect. Our findings may shed some light towards the application of CYBO in the control of organophosphorus pollution and the reduction of water eutrophication.

The hybrids of Co3O4 anchored on different crystallographic MnO2 (α-MnO2@Co3O4, β-MnO2@Co3O4, γ-MnO2@Co3O4, and δ-MnO2@Co3O4) were synthesized and applied in peroxymonosulfate (PMS) activation for the degradation of sulfisoxazole (SIZ). Various characterizations were conducted to explore the physicochemical properties of the hybrids, and their catalytic activities were compared. The SIZ degradation followed pseudo-first-order kinetics, and the rate constants (kobs) were 0.1135, 0.0307, 0.1080, and 0.0285 min−1 for α, γ, β, and δ-MnO2, respectively. The introduction of Co3O4 greatly improved the catalytic activities of the MnO2 hybrids, and more than 94.7% of SIZ was degraded within 20 min. The kobs was in the order of γ-MnO2@Co3O4 (0.3952 min−1) > α-MnO2@Co3O4 (0.1573 min−1) > β-MnO2@Co3O4 (0.1536 min−1) > δ-MnO2@Co3O4 (0.1319 min−1). Obviously, the synergy of Co3O4 and MnO2 weakened the differences of catalytic performance of MnO2 caused by their microstructures among α, β, and δ-MnO2. Due to its large surface area, γ-MnO2@Co3O4 exhibited the most excellent catalytic performance for the SIZ removal. All the hybrids also displayed superior stability and reusability, and the degradation rates of SIZ maintained were above 97% during five consecutive cycles. The reactive oxygen species (ROS) including SO4•−, •OH, and 1O2 were responsible for the SIZ degradation in the system of MnO2@Co3O4/PMS, which was confirmed by electron paramagnetic resonance (EPR) technique and scavenger tests. Twelve intermediates of the SIZ degradation were identified via HPLC-TOF-MS2. Combined with the results of characterizations together with ROS identification, the possible catalytic mechanisms and pathways of the SIZ degradation were proposed. This study may shed some light toward the application of different crystallographic MnO2 hybridized with other transition metals in PMS activation.

Co3O4-MnO2/BC, as an efficient activator of peroxymonosulfate (PMS) for the decomposition of soluble sulfonamide antibiotics, was successfully obtained via anchoring Co3O4-MnO2 nanoparticles on rice straw biochar (BC). The results demonstrated that 25 mg/L sulfadiazine (SDZ) could be thoroughly destructed by a combination of PMS (1 mM) and Co3O4-MnO2/BC (0.1 g/L) within 10 min. The pseudo-first-order rate constant (k) of the SDZ degradation was high up to 0.482 min−1, which was much larger than those reported in previous literature. The superior stability of the catalyst was confirmed through 5 recycle runs with approximately 100% degradation of SDZ and less than

In this study, silica gel (SG) was utilized as an assistant to improve the degradation efficiency of p-nitrophenol (PNP) via persulfate (PS) activated with zero-valent zinc (Zn(0)). The effects of various parameters such as the dosages of SG, PS, Zn(0), and the initial pH on PNP degradation via Zn(0)/SG/PS were investigated through batch experiments. The results demonstrated that SG exhibited a strong synergistic role in the decomposition of PNP via Zn(0)-activated PS due to the dispersion and buffering character of SG. The degradation efficiency of PNP was strongly related to the dosage of SG, PS, or Zn(0). A low pH favored of the degradation of PNP. Nevertheless, PNP could be efficiently removed in a pH range of 3 to 9. The radicals of SO4•− and •OH were verified to be responsible for the oxidative degradation of PNP. Nevertheless, the contribution of SO4•− to the degradation of PNP was much larger than that of •OH. Based on the analyses of HPLC-MS data, it could be determined that C6H7NO, C6H6O2, and C12H7N3O8 were the main intermediates generated from the degradation of PNP via Zn(0)/SG/PS. Furthermore, the possible mechanism and the degradation pathways of PNP via Zn(0)/SG/PS were proposed. PS activated with Zn(0) in the presence of SG could be concluded as a promising approach for the degradation of PNP in aqueous solution.

A bifunctional Co3O4-La2O2CO3/C material was successfully fabricated via calcinating Co and La metal organic frameworks (MOFs) at 500 °C and employed to activate peroxymonosulfate (PMS) for simultaneous degradation of phenylphosphonic acid (PPOA) and adsorption of the released phosphate. 100% degradation of PPOA (100 μmol L−1) was realized by PMS (1.2 mmol L−1) mediated with Co3O4-La2O2CO3/C (0.2 g L−1) at initial pH 7 within 60 min. Meanwhile, the produced phosphate was also completely removed. A series of characterization of the Co3O4-La2O2CO3/C material was conducted, and the main factors impacting PPOA degradation and phosphate adsorption were investigated. Co3O4-La2O2CO3/C also exhibited superb stability. During 4 cycles, the removal rates of PPOA and the produced phosphate maintained at approximately 100% and above 93%, respectively. The investigation of electron paramagnetic resonance and quenching tests revealed that sulfate radicals and hydroxyl radicals were reactive oxygen species and the former made the predominant contribution to the oxidation of PPOA. The possible degradation pathways of PPOA were further proposed by analyzing intermediates. This study not only offers a feasible strategy for the safe disposal of organophosphorus and the released phosphate, but also extends the development of MOFs for the preparation of functional materials.

A series batch experiments were performed to explore the catalytic role of zero-valent metals, including Fe(0), Co(0), Al(0) and Cu(0), in ozonation degradation of aniline in aqueous solution. It was found that Cu(0) exhibited the best catalytic activity of ozonation. Approximately 98% of the initial aniline (10 mg/L) was destructed by ozone assisted with Cu(0) within 24 min. The dosage of Cu(0) and solution pH were two critical factors affecting aniline degradation. The increase of Cu(0) dosage promoted aniline degradation. And aniline could be effectively removed in an initial pH range of 4–10, whereas a lower or higher solution pH was not favorable for the degradation of aniline. Free radicals were investigated by electron paramagnetic resonance technique, which confirmed that ·OH was the primary active oxidant responsible for the degradation of aniline. The further mechanism investigation revealed that the generation of ·OH is ascribed to Fenton-like reaction between Cu(I) and H 2 O 2 , both of which are in situ yielded through a series subsequent of reactions starting with oxidation–reduction reaction between ozone and Cu(0). Based on the results obtained in this study, it can be inferred that ozone activated with Cu(0) is a promising approach to degrade organic pollutants.

Arsenite (As(III)) is more toxic and difficult to remove than arsenate (As(V)). In this study, an S-doped Cu-La bimetallic oxide (S-CuLaO) decorated with metal-organic framework (MOF) composite (S-CuLaO@UIO-66) was synthesized and applied for the adsorption of As(III). The maximum adsorption capacity of As(III) by S-CuLaO@UIO-66 was as high as 171 mg/g, which was much higher compared with other MOF compounds reported to date. The UIO-66 support improved the dispersion and reduced the size of the S-CuLaO particles, which increased the number of exposed adsorption reactive sites. Study of the mechanism revealed that the synchronous oxidation and adsorption significantly increased the removal of As(III). O2∙- was produced by the receiving electron from the dissolved oxygen from Cu(I) in S-CuLaO, which converted As(III) to As(V). Furthermore, the stability and reusability S-CuLaO@UIO-66 (without regeneration) was investigated at a low As(III) concentration (approximately 1000 µg/L) in deionized water and well water. The residual arsenic concentration ranged from 0.8 to 2.8 μg/L in deionized water and 3–58.2 μg/L in well water within 240 min during three cycles. Generally, this study suggests that combining an optimal oxide with a stable MOF is a promising approach for the fabrication of composite adsorbents.

In this study, the sulfur-doped copper-manganese bimetallic oxides (labelled as S-CuMnO) were successfully fabricated via a calcination under N2 protection and used as a catalyst to activate peroxymonosulfate (PMS) for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP). For comparison, sulfur-doped monometallic oxides including S-CuO and S-MnO and non-doped copper-manganese bimetallic oxides (CuMnO) were also synthesized through the same processes. Complete decomposition of 2,4,6-TCP (20 mg/L) and a high removal of total organic carbon (60%) were achieved within 30 min at 0.8 mM PMS, 0.07 g/L S-CuMnO and pH 7. S-CuMnO exhibited the highest catalytic activity among the tested catalysts, which may be attributed to the abundant Cu(I), increased specific surface area and superior electrical conductivity of S-CuMnO. The results of electron paramagnetic resonance (EPR) and radical scavenger tests testified that the reactive oxygen species (ROS) included SO4 −, OH, O2 − radicals and singlet oxygen (1O2), which were mainly responsible for the efficient removal of 2,4,6-TCP. In addition, it was found that the catalytic activity of the used S-CuMnO could be greatly enhanced by calcination again under N2 protection. Furthermore, the intermediates involved in the degradation of 2,4,6-TCP were identified and the possible degradation pathways were further proposed. This work opens up new perspectives for designing highly efficient catalysts to decompose organic pollutants in aqueous solution.

Schwertmannite (SCH) as an adsorbent for Cr(VI) removal has been widely investigated. However, there are limited reports on photoreduction driven dissolution of SCH loaded with Cr(VI) (SCH-Cr(VI)) and the fate of Cr(VI) in the presence of dissolved organic matter (DOM). In this study, the effect of tartaric acid (TA) on the stability of SCH-Cr(VI) exposed to simulated solar radiation was examined. The results demonstrated that TA could greatly enhance the release of the dissolved total Fe (TFe) from SCH-Cr(VI). Conversely, the dissolved total Cr (TCr) obviously declined. Low pH promoted the liberation of TFe and TCr. The presence of ions including Al3+, Ca2+, K+ and CO32- exerted different impact on the photoreductive dissolution of SCH-Cr(VI) induced by TA. On the basis of the species distribution of iron and chromium and the characterization of the solid samples, the underlying mechanism is proposed for the transformation and the fate of Cr(VI). Cr(VI) was reduced to Cr(III) by Fe(II) generated from Fe(III)-TAn via ligand to metal charge transfer. The produced Cr(III) was adsorbed by SCH or co-precipitates with Fe(III). Thus, this study helps us to gain an insight into the mobility and fate of Cr(VI) in acid mining drainage containing DOM, and will help design remediation strategies for Cr contamination.

In this study, the Co3O4-SnO2 composite derived from bimetallic oxalates was rationally fabricated and utilized as a catalyst for peroxymonosulfate (PMS) activation towards the destruction of chloramphenicol (CAP). The physicochemical properties of the Co3O4-SnO2 were systematically characterized to discover the relationship between its structure and catalytic performance. SnO2 as a cocatalyst with high conductivity and stability immensely improved the activity of Co3O4 in the Co3O4-SnO2 composite. Approximately 98% of CAP (10 mg/L) was eliminated by the Co3O4-SnO2 (0.1 g/L) activated PMS (1.0 mmol/L) at initial pH 7 within 20 min. The rationally designed Co3O4-SnO2 composite exhibited higher catalytic activity than Co3O4, SnO2, and other cobalt-based bimetallic oxides (such as Co-Fe, Co-Mn, and Co-Cu) in the PMS activation for the CAP degradation. The synergistic effect of Co3O4 and SnO2 endowed the Co3O4-SnO2 composite with higher conductivity and more electron transfer, which was proved by the electrochemical tests. The presence of SO4•−, •OH, O2•−, and 1O2 during the CAP degradation was testified by both quenching experiments and electron paramagnetic resonance (EPR) spectroscopy. In addition, the catalytic mechanism and degradation pathways were further proposed via the characterization of X-ray photoelectron spectroscopy (XPS) and the identification of transformation products, respectively. This work provides a new insight into the preparation of novel catalysts and their application in wastewater treatment.

4-aminophenylarsonic acid (p-ASA) is usually employed as feed antibiotics which can kill bacteria, protozoa and spirochetes. When p-ASA is released into the environment by biological metabolism, it could be broken down to produce hypertoxic inorganic arsenic, including arsenite (AsO33-) and arsenate (AsO43-). In this study, cobalt and lanthanum composites loaded on rice straw biochar labelled as Co3O4-La2CO5@RSBC was obtained. The material was used as an efficient catalyst for peroxymonosulfate (PMS) activation and adsorbent to achieve the simultaneous degradation of p-ASA and adsorption of arsenic. 100% decomposition of p-ASA (50 μmol L-1) could be realized within 30 min, coupled with nearly complete removal of inorganic arsenic during 80 min at initial pH = 7. Co3O4-La2CO5@RSBC also possessed superior reusability and stability. Even in the third cycle, more than 95% of p-ASA was decomposed and meanwhile 92.5% of inorganic arsenic was removed. No cobalt ions were detected, and the concentration of lanthanum ions in the three cycles ranged from 8.05 to 9.90 mg L-1, which was much lower than those reported in previous studies. A series of the material characterizations, electron paramagnetic resonance technology and scavenger tests were utilized to unveil the possible catalytic mechanism and the transformation pathways of p-ASA and arsenic. It was confirmed that 1O2, O 2 ∙ - , OH ∙ , and SO 4 ∙ - generated from the PMS activation were responsible for the degradation of p-ASA and the oxidation of As(III) to As(V). Meanwhile, As(V) was rapidly adsorbed by Co3O4-La2CO5@RSBC. This study provides us with a novel and efficient approach to control p-ASA pollution in aqueous solution.

In the presence of low frequency ultrasound (US) generated from an ultrasonic cleaning bath, the degradation efficiency of nitrobenzene (C6H5NO2, NB) by Zn0-activated persulfate (PS) reached 96% within 2 h, which is much higher than that by PS or Zn0 alone in the presence of US or that by Zn0-activated PS in the absence of US. The synergistic effect in the US/Zn0/PS system and the optimum degradation conditions was investigated by batch experiments. The variations of pH and concentrations of Zn2+ and SO42− over time and the removal of chemical oxygen demand (COD) and total organic carbon (TOC) in different systems were analyzed, which agreed well with the degradation pattern of NB in different systems. The formation of free radicals was measured using electron paramagnetic resonance (EPR) spectroscopy to further investigate the possible mechanism of the enhanced degradation of NB by Zn0-activated PS in the presence of low frequency US.

Roxarsone (ROX), as one of aromatic organoarsenic compounds (AOCs), is extensively used in livestock industry, which tends to transform into high-toxic inorganic arsenic in environments. Herein, a bifunctional Co3O4-Y2O3, possessing extremely excellent catalytic and adsorption performance due to the synergy of Co3O4 and Y2O3, was designed and employed to activate peroxymonosulfate (PMS) for the elimination of ROX and the simultaneous in-situ adsorption of secondary inorganic arsenic, in which Co3O4 acted as the primary catalyst, and Y2O3 served as the main adsorbent. 50 μM (3.75 mg-As/L) of ROX was almost completely degraded, coupled with the conversion of As(III) to As(V) in the system of Co3O4-Y2O3 (0.2 g/L) and PMS (0.5 mM) within 15 min at initial pH 7. Meanwhile, > 99.3% of the secondary As(V) would be removed within 120 min. The reactive oxygen species (ROS) were identified to be •OH, SO4•−, and 1O2, which were responsible for the ROX degradation and the formation of As(V). Simultaneously, the produced As(V) were effectively adsorbed via the ligand/anion exchange with surface –OH and CO32− anions of Co3O4-Y2O3. The possible degradation pathways of ROX were further proposed on the basis of the intermediates identification. Our findings may provide an insight into the degradation of AOCs and the simultaneous removal of secondary inorganic arsenic via the PMS activation with Co3O4-Y2O3.

Sulfur-doped copper–nickel bimetallic oxide (S-CuNiO) was employed as the ozonation catalyst for aniline degradation. The results demonstrated that the removal efficiencies of aniline (0.1 mmol/L) significantly increased with the S-CuNiO dosage from 0 to 1.0 g/L and the ozone dose from 0 to 96.5 mg/(min L -liquid). More than 92% of aniline was decomposed within 20 min in the initial pH range of 2–11, and the removal of total organic carbon reached 71% at initial pH 6. S-CuNiO exhibited more excellent catalytic performance than CuNiO, S-CuO and S-NiO. Radical quenching experiments and electron paramagnetic resonance technique confirmed that •OH rather than O2•− played a dominant role in aniline degradation. Combined with characterization of the catalyst, the possible mechanism of catalytic ozonation was deduced. The ‒OH groups on the catalyst surface stimulated ozone to produce •OH, meanwhile ≡Cu+ and ≡Ni2+ on the surface of S-CuNiO promoted the decomposition of ozone via electron transfer to form •OH, accompanied by the production of ≡Cu2+ and ≡Ni3+. Subsequently, ≡Cu+ converted ≡Ni3+ into ≡Ni2+ and released ≡Cu2+, which was reduced to ≡Cu+ by S2− on the surface of the catalyst. Consequently, catalytic cycles were established to facilitate aniline degradation and improve its mineralization. Based on the analyses of intermediates by HPLC-TOF-MS, the possible pathways of aniline degradation were further proposed.

CuCo2O4@kaolin was successfully synthesized by a sol-gel method and used as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for the degradation of phenacetin (PNT). The results demonstrated that 10 mg/L PNT was completely decomposed by 1 mM PMS activated with 0.1 g/L CuCo2O4@kaolin within 15 min at initial pH 7. CuCo2O4@kaolin exhibited the best excellent catalytic performance among the tested catalysts, and the pseudo-first-order rate constants of PNT degradation were CuCo2O4@kaolin (0.40 min−1) > CuCo2O4 (0.22 min−1) > Co3O4@kaolin (0.10 min−1) > CuO@kaolin (0.08 min−1) > kaolin (0.02 min−1). CuCo2O4@kaolin also possessed superior stability, and the degradation efficiency of PNT declined from 100% in the first round to 80% in the fourth round. Nevertheless, a simple calcinating treatment (20 min) after the third round could restore its catalytic activity substantially and 95% removal of PNT was realized, 15% higher compared to without treatment. OH, SO4 −, and 1O2 were the reactive oxygen species driving the PNT degradation. Based on the results mentioned above, characterizations of CuCo2O4@kaolin, and intermediates of PNT degradation, the possible pathways and underlying mechanisms of the PNT degradation in the CuCo2O4@kaolin/PMS system were deduced. CuCo2O4@kaolin/PMS had a universal degradation potential toward various organic pollutants, and the degradation efficiencies of sulfisoxazole, p-nitrophenol, chloramphenicol, and 2,4,6-Trichlorophenol reached 95–100% within 5–45 min. Thus, this work provides a novel and efficient PMS activator through an eco-friendly synthetic route, and it may be put into practice to degrade organic matter in wastewater.

The present study investigated the application of the LiFePO4 (LFP) cathode material for lithium ion batteries as a photocatalyst in the photodegradation of methyl orange (MO) by oxalic acid (Oxa, H2C2O4). The photocatalytic role of LFP for different initial pH values as well as different concentrations of LFP, Oxa, and MO was examined. The results show that, while the decomposition of MO by either LFP or Oxa under ultraviolet light is difficult, MO removal is significantly enhanced when both LFP and Oxa coexist in the reaction system. In particular, high initial concentrations of Oxa and LFP appear to be beneficial for the degradation of MO. The optimal MO degradation efficiency was achieved at pH 4. The role of photoproduction intermediates was also investigated. Scavenging experiments using tertiary butyl alcohol, an ·OH-specific radical scavenger, and l -histidine, a universal radical scavenger, corroborated the suggestion that other oxidative free radicals besides ·OH are also involved in the MO degradation. A possible reaction mechanism for the photocatalytic degradation of MO by LFP and Oxa was proposed. This study thus provides a direct route for the reutilization of the cathode material LFP as a photocatalyst in the photodegradation of organic contaminants by low-molecular weight organic acids.

In this study, rice straw biochar modified by copper oxide (RSBC-CuO) was successfully fabricated via a hydrothermal method and used as a catalyst for the degradation of organic pollutants by peroxydisulfate (PDS). RSBC-CuO-activated PDS exhibited an outstanding performance on the decomposition of phenacetin (PNT). Electron paramagnetic resonance (EPR) confirmed that the reactive oxygen species (ROS) included SO4 −, OH, O2 − radicals and singlet oxygen (1O2), which were in charge of the PNT destruction. Scavenger experiments further conformed that 1O2 and O2 − played the crucial role in the PNT removal. RSBC-CuO also displayed an excellent stability and reusability. The rate of PNT removal after four consecutive cycles declined slightly. Furthermore, the combination of RSBC-CuO and PDS possessed a universal degradation potential towards various organic pollutants, and the degradation efficiencies of the pollutants such as paracetamol, aniline, p-chlorobenzoic acid, sulfamethazine and 2,4,6-Trichlorophenol reached a range of 86 to 100% within 10 to 30 min. Thus, it is concluded that RSBC-CuO-activated PDS is a novel and feasible approach to the removal of organic contaminants from aqueous solution.

Co3O4–SnO2/rice straw biochar (RSBC) was prepared for the first time via calcining oxalate precipitation precursor dispersed on the surface of RSBC and used as a catalyst for activating PMS to degrade sulfisoxazole (SIZ). The results demonstrated that Co3O4–SnO2/RSBC possessed much better catalytic performance than Co3O4, Co3O4–SnO2, Co3O4/RSBC, and SnO2/RSBC, which is ascribed to the synergy of Co3O4, SnO2 and RSBC. Approximately 98% of SIZ (50 mg/L) was decomposed by PMS (1 mmol/L) activated with Co3O4–SnO2/RSBC (0.1 g/L) within 5 min. The optimal degradation efficiency of SIZ was realized at the initial pH 9. Co3O4–SnO2/RSBC also displayed remarkable stability and reusability, and the degradation rate of SIZ maintained over 90% even after the fifth recycle run. The electron paramagnetic resonance (EPR) technique and quenching experiments proved singlet oxygen (1O2) to be the main reactive oxygen species (ROS) responsible for the SIZ decomposition in the Co3O4–SnO2/RSBC/PMS system. On the basis of the characterization analysis, the identification of the ROS and the SIZ degradation products, the possible mechanism and pathways of the SIZ degradation by a combination of PMS and Co3O4–SnO2/RSBC were further proposed. This study provides not only a new insight into non-radical mechanism for the heterogeneous activating PMS over Co3O4–SnO2/RSBC to degrade organic pollutants but also an eco-friendly synthetic route for exploring novel and efficient catalysts.

Sulfur-doped copper-yttrium bimetallic oxides (S-CuYO) were synthesized by a co-precipitation method and for the first time utilized for the catalytic ozonation of aniline. For comparison purposes, sulfur-doped monometallic oxides (S-CuO and S-YO) and non-doped copper-yttrium bimetallic oxide (CuYO) were also prepared via the same processes. The S-CuYO exhibited a highest catalytic activity among these catalysts. In the catalytic ozonation with S-CuYO, the degradation efficiency and total organic carbon (TOC) removal of aniline (10 mg/L) were 96% and 57%, respectively, within 15 min under optimum conditions. The high performance of the S-CuYO was ascribed to the synergy between the Cu(I) and Y(III) species via providing the catalyst with more abundant surface hydroxyl groups, a larger surface area, and a larger pore size. The surface hydroxyl groups provided active sites for ozone adsorption and the Cu(I) on the surface catalyzed the ozone decomposition to produce free radicals via electron transfer. Besides, the low-valent S species (S2−/SO32−) in the catalyst led to the reduction of Cu(II) to Cu(I), which maintained the high catalytic activity of the S-CuYO. A free radical investigation indicated that OH radicals were the main reactive oxygen species responsible for the removal of aniline. Six main intermediates of the aniline degradation were identified by high-performance liquid chromatography–mass spectrometry (HPLC-MS). The possible degradation pathways of the aniline by catalytic ozonation with the S-CuYO were further proposed. Based on the results obtained in this study, it is concluded that the catalytic ozonation with S-CuYO is a promising approach for wastewater treatment containing aniline.

Arsenite (As(III)) is more mobile and has higher toxicity than arsenate [As(V)]. To improve the removal of As(III), preoxidation of As(III) to As(V) is considered necessary due to its low affinity to many adsorbents. However, this method usually involves extra operations and costs. In this study, an original S-doped copper- lanthanum bimetallic oxide (S-CuLaO) was prepared as an adsorbent material for the removal of As(III) via simultaneous oxidation and adsorption (no extra chemical agents as oxidants). The material was successfully synthesized with a simple co-precipitation method. The majority of Cu species present in the adsorbent was Cu(I). The maximum adsorption capacity of the adsorbent towards As(III) reached 314.91 mg g−1, which far exceeds that of previously reported adsorbents. In a wide pH range of 3 to 9, the adsorbent exhibited excellent removal efficiency of As(III), and 30 mg L−1 As(III) was completely removed by S-CuLaO (0.2 g L−1). The mechanistic investigation revealed that the presence of Cu(I) in the adsorbent allowed cooperation with the dissolved O2 to promote the oxidation of As(III) by the generated O 2 • - to As(V). The produced As(V) was adsorbed onto the surface of the adsorbent via electrostatic attraction. Subsequently, –OH groups on the adsorbent surface participated in As(V) adsorption via ligand exchange. Furthermore, the removal efficiency of As(III) (1 mg L−1) in well water by S-CuLaO (1.0 g L−1) maintained >99% even in the fourth cycle (without regeneration), resulting in a residual arsenic concentration of 0.7 μg L−1. Therefore, the use of S-CuLaO is promising and feasible for the effective removal of As(III) from aqueous solution.

CuCo2O4 was synthesized via the calcination of a copper-cobalt bimetallic oxalate precursor and was used as a heterogeneous catalyst of peroxymonosulfate (PMS) for the degradation of sulfamethazine (SMZ). The results demonstrated that the CuCo2O4 had higher catalytic activity than the monometallic CuO and Co3O4. The degradation efficiency of SMZ (50 mg/L) by PMS (1 mmol/L) activated with CuCo2O4 (0.1 g/L) was above 98% within 30 min at initial pH 5. Electron paramagnetic resonance (EPR) and radical quenching experiments proved that both sulfate radicals (SO4 −) and singlet oxygen (1O2) were responsible for the efficient removal of SMZ, especially 1O2. The superoxide radicals (O2 −) produced from the reaction improved the generation of SO4 − and 1O2. Cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and hydrogen temperature- programmed reduction (H2-TPR) investigations revealed that the synergy of Cu and Co species in PMS activation resulted from higher electroconductibility, more electron transfer, and better redox potential of the CuCo2O4. The synergy between the Co(III)/Co(II) and the Cu(II)/Cu(I) couples enhanced the turnover frequency (TOF) of CuCo2O4. The possible degradation pathways are further proposed according to the identification of the SMZ degradation products and the theoretical calculations of the frontier electron densities (FEDs) of the SMZ molecule.

A novel magnetic sulfur-doped Fe–Cu–Y trimetal oxide (MST) nanomaterial was successfully synthesized by a chemical coprecipitation method to remove As(III) via simultaneous oxidation and adsorption and then characterized by BET, VSM, FESEM, XPS, and FTIR techniques. The effect of solution initial pH on the adsorption of As(III), and the adsorption kinetics and isotherm were investigated in detail. The results indicated that the MST nanoparticles exhibited an excellent performance for As(III) removal in a pH range of 7–10 and were easily separated from aqueous solution with a magnet. The maximum removal capability for As(III) reached 202.0 mg/g at pH 7.0. The adsorption of As(III) was well fitted by the pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The investigation of mechanism revealed that As(III) could be oxidized to As(V) by O2 − and OH free radicals, generated via the dissolved O2 obtaining an electron from Cu(I) on the surface of the adsorbent and Fenton/Fenton-like reaction, respectively. Meanwhile, the produced As(V) was adsorbed onto the surface of the nanoparticles through the electrostatic attraction or diffusion. The adsorbed As(V) further interacted with –OH groups via ion exchange or with Y(III) on the surface of the adsorbent to form a precipitate. Therefore, the MST nanoparticles are promising for the removal of arsenic from water.