Structure of a novel Co-based heterogeneous catalyst via Mn3(PO4)2 as a carrier to efficiently activate peroxymonosulfate for improving degradation of sulfonamides.

Effective degradation of sulfonamides (SAs) in water is of global importance for decreasing its pathogenicity and bioaccumulation. In this study, Mn3(PO4)2 was used as a carrier to fabricate a novel and high-efficient catalyst with Co3O4 anchored (Co3O4@Mn3(PO4)2) for the activation of peroxymonosulfate (PMS) to degrade SAs. Surprisingly, the catalyst exhibited superior performance, and nearly 100% of SAs (10 mg L-1) including sulfamethazine (SMZ), sulfadimethoxine (SDM), sulfamethoxazole (SMX), and sulfisoxazole (SIZ) was degraded by Co3O4@Mn3(PO4)2-activated PMS within 10 min. A series of characterization of the Co3O4@Mn3(PO4)2 composite were conducted and the main operational parameters of SMZ degradation were investigated. SO4•-, •OH, and 1O2 were determined to be the dominating reactive oxygen species (ROS) responsible for the degradation of SMZ. Co3O4@Mn3(PO4)2 also exhibited excellent stability and the removal rate of SMZ still maintained over 99% even in the fifth cycle. The plausible pathways and mechanisms of SMZ degradation in the system of Co3O4@Mn3(PO4)2/PMS were deduced on the basis of the analyses of LCMS/MS and XPS. This is the first report on high-efficient heterogeneous activating PMS by mooring Co3O4 on Mn3(PO4)2 to degrade SAs, which provides us with a strategy to structure novel bimetallic catalysts for PMS activation.

Waste self-heating bag derived iron-based composite with abundant oxygen vacancies for highly efficient Fenton-like degradation of micropollutants.

In this study, iron-rich waste self-heating bag was reutilized as the raw material to prepare oxygen vacancies (OV) functionalized iron-based composite (iron oxide (Fe3O4)-carbon-vermiculite, viz. OV-ICV), which exhibited excellent performance in the Fenton-like degradation of micropollutants via peroxydisulfate (PDS) activation. Above 95% of 1.0 mg/L carbaryl (CB) was efficiently eliminated in the presence of 0.1 g/L of OV-ICV and 0.5 mmol/L of PDS over a wide pH range of 3-10 within 30 min. Besides, OV-ICV also showed acceptable adaptability, stability, and renewability. Imbedding OV into Fe3O4 structure significantly generated more active iron sites and localized electrons, promoted the charge transfer ability, and assisted the redox cycle of ≡Fe(III)/≡Fe(II) for PDS activation. Mechanism investigation demonstrated that superoxide radicals (O2•-) derived from the activation of molecular oxygen mediated the generation of H2O2, and both of them further enhanced the formation of more sulfate radicals (SO4•-) and hydroxyl radicals (•OH), which led to the efficient degradation and mineralization of CB. Furthermore, the degradation pathways of CB were proposed based on the intermediates identification. This work lays a foundation for the rational reutilization of iron-containing wastes modified with defect engineering in heterogeneous Fenton-like catalysis for the remediation of micropollutants wastewater.

Co3O4 anchored on biochar derived from chitosan (Co3O4@BCC) as a catalyst to efficiently activate peroxymonosulfate (PMS) for degradation of phenacetin.

Chitosan, as a bio-friendly and abundant biochar precursor, was employed to prepare cobalt-based catalyst (Co3O4@BCC) by calcination for activating peroxymonosulfate (PMS) to degrade phenacetin (PNT). Various characterization technologies and experimental designs were performed to investigate the physicochemical properties and catalytic performance of Co3O4@BCC. Approximately 99.0% of phenacetin (10 mg/L) was degraded in the system of Co3O4@BCC (0.05 g/L)/PMS (1.0 mM) within 15 min and the rate constant was 6 times higher than that in the system of Co3O4 (0.05 g/L)/PMS (1.0 mM). The results demonstrated that BCC as a carrier not only dispersed Co3O4 nanoparticles and improved the stability of catalyst, but also provided abundant electron-rich groups to facilitate the activation of PMS and the production of reactive oxygen species (ROS). Co3O4@BCC composite also exhibited good universality and reusability. More than 90% of BPA, SIZ and CAP was degraded by Co3O4@BCC activated PMS within 15 min at pH 7. The degradation rate of PNT was recovered from 90% to 98.0% via the regeneration of the used catalyst after the third run (calcination at 400 °C for 5 min). SO4•-, •OH and 1O2 were identified to be responsible for PNT degradation. Furthermore, the activation mechanism of PMS and the possible pathways of PNT degradation were reasonably speculated according to the results of electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), quenching experiments and HPLC-TOF-MS2. This study explored the application of chitosan as a recycled material and provides a feasible strategy for designing and fabricating environmentally friendly and efficient catalysts for PMS activation to degrade organic pollutants.

Rapid removal of high-concentration Rhodamine B by peroxymonosulfate activated with Co3O4-Fe3O4 composite loaded on rice straw biochar.

In this study, rice straw biochar modified with Co3O4-Fe3O4 (RSBC@Co3O4-Fe3O4) was successfully prepared via calcinating oxalate coprecipitation precursor and employed as a catalyst to activate peroxymonosulfate (PMS) for the treatment of Rhodamine B (RhB)-simulated wastewater. The results indicated that RSBC@Co3O4-Fe3O4 exhibited high catalytic performance due to the synergy between Co3O4 and Fe3O4 doping into RSBC. Approximately 98% of RhB (180 mg/L) was degraded in the RSBC@Co3O4-Fe3O4/PMS system at initial pH 7 within 15 min. The degradation efficiency of RhB maintained over 90% after the fourth cycle, illustrating that RSBC@Co3O4-Fe3O4 displayed excellent stability and reusability. The primary reactive oxygen species (ROS) answerable for the degradation of RhB were 1O2, •OH, and SO4•-. Moreover, the intermediates involved in the degradation of RhB were identified and the possible degradation pathways were deduced. This work can provide a new approach to explore Co-based and BC-based catalysts for the degradation of organic pollutants.

Cobalt-bismuth bimetallic composite anchored on carbon derived from cigarette butts as peroxymonosulfate activator for rapid removal of chloramphenicol.

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 SO4•-, •OH, and 1O2 led to the rapid decomposition of CAP. Combined with X-ray photoelectron spectroscopy (XPS) of Co-Bi@CCB before and after reaction, the mechanism of PMS activation was deduced. Finally, the possible pathways of CAP degradation was further speculated according to the intermediates determination by high-performance liquid chromatography equipped with high resolution mass spectrometer (HPLC-HRMS). Thus, the present study provides a new strategy to utilize discarded cigarette butts (recycled materials) as a carrier to fabricate novel and efficient catalysts to activate PMS for the removal of organic contaminants.

Reutilization of waste self-heating pad by loading cobalt: A magnetic and green peroxymonosulfate activator for naphthalene degradation.

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 SO4•- and •OH, contributing to the rapid degradation of NAP. Meanwhile, the NAP degradation pathways were deduced via combining the identification of intermediates and the calculation of frontier electron densities (FEDs). Furthermore, the ability of the Co-ICV/PMS system for the NAP degradation in actual lake water and the removal of other refractory pollutants demonstrated that the combination of Co-ICV and PMS was a prospective method for the removal of PAHs. Overall, Co-ICV is a green and promising activator of PMS, and the future development will provide more insights into the comprehensive utilization of solid wastes for the remediation of wastewater containing PAHs.

Decorating S-doped Cu-La bimetallic oxides with UIO-66 to increase the As(III) adsorption capacity via synchronous oxidation and adsorption.

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.

Photoreductive dissolution of schwertmannite loaded with Cr(VI) induced by tartaric acid.

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.

MOFs-derived magnetic C@Cu-Ni bimetal particles: An efficient peroxymonosulfate activator for 2,4,6-trichlorophenol degradation.

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.

Efficient degradation of roxarsone and simultaneous in-situ adsorption of secondary inorganic arsenic by a combination of Co3O4-Y2O3 and peroxymonosulfate.

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.

The efficient degradation of sulfisoxazole by singlet oxygen (1O2) derived from activated peroxymonosulfate (PMS) with Co3O4-SnO2/RSBC.

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.

CuO-Co3O4@CeO2 as a heterogeneous catalyst for efficient degradation of 2,4-dichlorophenoxyacetic acid by peroxymonosulfate.

CuO-Co3O4@CeO2 nanoparticles used as a heterogeneous catalyst were prepared via a sol-gel method and characterized by various techniques. For comparison, a series of oxides was investigated for activating peroxymonosulfate (PMS) during the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The results indicated that CuO-Co3O4@CeO2 exhibited the highest catalytic performance among the catalysts. Complete degradation of 2,4-D (20 mg/L) was realized within 45 min at 1 mM PMS, CuO-Co3O4@CeO2 loading of 0.07 g/L, and pH of 6. Recycling experiments confirmed that CuO-Co3O4@CeO2 was very stable, and the 2,4-D degradation efficiencies ranged from 100% to 97.5%, decreasing by only 2.5% after the fifth run. The outstanding catalysis of CuO-Co3O4@CeO2 resulted from the synergy of cerium, cobalt, and copper. Electron paramagnetic resonance and radical scavenger experiments confirmed the production of SO4• - and •OH radicals in the CuO-Co3O4@CeO2/PMS system, which were responsible for efficient decomposition of 2,4-D. Furthermore, the combination of CuO-Co3O4@CeO2 andPMS was applied to treat natural water containing 2,4-D, and a high 2,4-D removal rate was also achieved. Based on these results, it was deduced that CuO-Co3O4@CeO2 can be utilized as a catalyst to activate PMS and destroy organic contaminants in aqueous solution.

Efficient removal of As(III) via simultaneous oxidation and adsorption by magnetic sulfur-doped Fe-Cu-Y trimetal oxide nanoparticles.

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.

Synergism of CuS and tartaric acid in the reduction of Cr(VI) under an irradiation of simulated solar light.

The synergism of CuS and tartaric acid (TA) in the reduction of Cr(VI) with an irradiation of simulated solar light was investigated through observing the effects of solution pH, temperature, CuS loading and TA concentration on the removal efficiency of Cr(VI). Approximately 32% and 54% of the initial Cr(VI) (100 µmol/L) were reduced within 180 min by TA and CuS with light, respectively. Under the same condition, however, almost a complete removal of the initial Cr(VI) was achieved within 130 min in the coexistence of CuS and TA. In the case, it is considered that Cr(VI) was rapidly reduced in two main pathways. One is that H2S produced from the dissolution of CuS in weak acidic solution directly reduced Cr(VI) to Cr(III). The other is that Cu(II) released from CuS reacted with TA to form complexes with photochemical activity, producing Cu(I) through ligand-to-metal electron transfer, and then the reduction of Cr(VI) was coupled with a conversion of Cu(I) to Cu(II). Thus, a cycle catalytic system was established for the reduction of Cr(VI). Moreover, it is observed that the reaction could be divided into two stages: the initial chemical reduction of Cr(VI) by H2S and the later photochemical reduction of Cr(VI) by Cu(II)-TA complexes.

Tartaric acid-induced photoreductive dissolution of schwertmannite loaded with As(III) and the release of adsorbed As(III).

Schwertmannite (SCH) has strong adsorption ability to As(III). However, there are few reports on the stability of SCH load with As(III) (SCH-As(III)). In this study, the effects of tartaric acid (TA), pH and coexisting ions including K+, Ca2+, Al3+ and CO32- on the photoreductive dissolution of SCH- As(III) and the release of the adsorbed As (III) were investigated. The results showed that under UV irradiation TA could greatly enhance the release of total Fe and total As from SCH-As(III). Nevertheless, the total Fe and total As in the solution decreased when TA was consumed up. Compared to SCH, the reductive dissolution of SCH-As(III) was obviously suppressed. In the dark, TA could slowly enhance the dissolution of SCH-As(III), but its effect on the release of adsorbed As(III) was weak. Low pH was conducive to the release of iron and arsenic. Ca2+, K+, and CO32- promoted the decrease of the dissolved total Fe in the later reaction. However, Al3+ inhibited the decrease of the dissolved total Fe and total As. The analyses of FTIR and XRD demonstrated that the mineralogical phase of SCH-As(III) after reaction changed. With light, the dissolved total Fe and total As existed mainly as Fe(II) and As(V), respectively. This is because Fe(II) was generated via ligand to metal charge transfer and As(III) was oxidized to As(V) by ·OH produced during the reaction. Thus, this study provides us with a comprehensive understanding of the stability of SCH-As(III) and the release of adsorbed As(III) in natural environments.

Efficient removal of aniline by micro-scale zinc-copper (mZn/Cu) bimetallic particles in acidic solution: An oxidation degradation mechanism via radicals.

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 was <5% within 75 min. However, 97% of aniline (10 mg L-1) was decomposed and 47% of TOC was removed by mZn/Cu, both of which were more than three times as much as those by mFe/Cu. The mechanism investigations revealed that •OH radicals engendered from the reaction process are responsible for the rapid oxidative degradation of aniline. Furthermore, based on the analyses of the intermediates via LC-MS, the possible degradation pathways of aniline were proposed. Our findings suggested that mZn/Cu is a potential approach for aniline removal, which is different from the other bimetallic systems reported in the previous studies mainly as the reductive degradation.

Insights into the mechanism of persulfate activated by rice straw biochar for the degradation of aniline.

This study investigated the degradation of aniline by persulfate (PS) activated with rice straw biochar (RSBC). The results demonstrate that aniline could be rapidly decomposed by a combination of PS and RSBC. The degradation efficiency of aniline was up to 94.1% within 80 min, and meanwhile 52% of the total organic carbon was removed. In the initial pH range of 3-9, aniline could be efficiently removed. Reactive species resulting in the rapid degradation of aniline were investigated via radical and hole quenching experiments with various scavengers (e.g., methanol, tert-butyl alcohol and EDTA) and electron paramagnetic resonance technique. Based on the analysis and observation made here, it is speculated that the predominant reactive species responsible for the degradation of aniline may be holes instead of SO4- and OH radicals. It is concluded that RSBC could be used as an effective catalyst to activate PS for the degradation of aniline.

Catalytic Roles of Mn(II) and Fe(III) in the Reduction of Cr(VI) by Mandelic Acid under an Irradiation of Simulated Solar Light.

The catalytic roles of manganese(II) [Mn(II)] and iron(III) [Fe(III)] in the reduction of hexavalent chromium [Cr(VI)] by mandelic acid, both with and without the presence of light, was investigated through a series of batch experiments. The results demonstrated that both Mn(II) and Fe(III) could markedly accelerate the photoreduction of Cr(VI) by mandelic acid; additionally, the catalysis of Fe(III) was superior to that of Mn(II). Without the presence of light, Mn(II) still enhanced the reduction of Cr(VI) by mandelic acid, but Fe(III) did not exert any impact on the reaction. When compared with the activities of phenylacetic acid, it was concluded that the catalytic roles of both Mn(II) and Fe(III) in the reduction of Cr(VI) were directly related to the α-OH group and not to the carboxyl group. The photoreduction of Cr(VI) by mandelic acid, assisted by Mn(II), followed pseudo-first-order kinetics at the initial stage of the reaction, but in the presence of Fe(III) it followed a pseudo-zero-order model.

Rapid Photodegradation of Methyl Orange (MO) Assisted with Cu(II) and Tartaric Acid.

Cu(II) and organic carboxylic acids, existing extensively in soil and aquatic environments, can form complexes that may play an important role in the photodegradation of organic contaminants. In this paper, the catalytic role of Cu(II) in the removal of methyl orange (MO) in the presence of tartaric acid with light was investigated through batch experiments. The results demonstrate that the introduction of Cu(II) could markedly enhance the photodegradation of MO. In addition, high initial concentrations of Cu(II) and tartaric acid benefited the decomposition of MO. The most rapid removal of MO assisted by Cu(II) was achieved at pH 3. The formation of Cu(II)-tartaric acid complexes was assumed to be the key factor, generating hydroxyl radicals (•OH) and other oxidizing free radicals under irradiation through a ligand-to-metal charge-transfer pathway that was responsible for the efficient degradation of MO. Some intermediates in the reaction system were also detected to support this reaction mechanism.

Rapid degradation of aniline in aqueous solution by ozone in the presence of zero-valent zinc.

The effects of Zn(0) dosage from 0.1 to 1.3gL(-1), pH from 2 to 12 and temperature from 288 to 318K on the degradation of aniline in aqueous solution by ozone in the presence of Zn(0) were investigated through batch experiments. The results demonstrated that Zn(0) had a significantly synergistic role in the degradation of aniline by ozone. A complete decomposition of the initial aniline (10mgL(-1)) was achieved by ozone together with Zn(0) within 25min, and meanwhile nearly 70% of the total organic carbon in the solution was removed. The decomposition efficiency of aniline markedly increased with an increase of Zn(0) dosage. However, temperature exerted a slight impact on the degradation of aniline and the optimum removal efficiency of aniline was realized at 298K. Aniline was efficiently degraded at all the tested pHs except for 12. Free radicals were investigated by electron paramagnetic resonance technique and free radical scavengers. H2O2 concentration generated during the reactions was analyzed using a photometric method. Based on the results obtained in this study, it is proposed that O2(-) instead of OH is the dominant active species responsible for the degradation of aniline. It is concluded that ozone combined with Zn(0) is an effective and promising approach to the degradation of organic pollutants.