•TOC removal was enhanced by MnOx/SBA-15 in ozonation of Norfloxacin.•Adsorption of Norfloxacin on MnOx/SBA-15 influenced its degradation efficiency.•Hydroxyl radical was the main active specie in MnOx/SBA-15/O3 process.•The toxicity of solution increased at first and then decreased with TOC removal.Norfloxacin, a kind of widely used fluoroquinolone antibiotics, was degraded by MnOx/SBA-15/O3 process. The prepared catalyst possessed a large surface area ranging from 405 to 671 m2 g−1, which was beneficial for surface reaction. The loaded MnOx on SBA-15 successfully increased its the adsorption ability and catalytic activity, and its surface property played an importance role in catalytic process. Under the adopted condition, both O3 and MnOx/SBA-15/O3 systems were effective for Nofloxacin removal. A high mineralization efficiency (54%) was achieved by MnOx/SBA-15/O3 process at 60 min, 1.36 times higher than that of single ozonation process. The protonated surface hydroxyl groups were the main reaction sites and more hydroxyl radicals generation were found after the presence of MnOx/SBA-15. Three kinds of common small molecule acid (oxalic acid, formic acid, acetic acid) were detected, and the concentration of oxalic acid in MnOx/SBA-15/O3 process was lower than that in sole ozonation process because more OHOH generated in catalytic ozonation. Toxicological tests were also conducted to evaluate their detoxification ability. As the accumulation of transformation products, the toxicity of solution increased at first and reached the highest after 15 min reaction time. And a high detoxification was achieved after 30 min.

•PFOA was degraded by photo-generated holes and hydroxyl radicals.•A synergistic effect was found between photo-generated holes and hydroxyl radicals.•Initial solution pH and temperature played important roles in PFOA degradation.•C2−C7 shorter-chain perfluorocarboxylic acids and F− were major intermediates.Zinc oxide (ZnO) nanorods were prepared by a directly pyrolysis method and employed as catalyst for perfluorooctanoic acid (PFOA) degradation. Comparative experiments were conducted to discuss the catalytic activity and flexibility of ZnO. After ZnO addition, the best PFOA degradation efficiency (70.5%) was achieved by ZnO/UV/O3 system, only 9.5% by sole ozonation and 18.2% by UV254 light irradiation. PFOA degradation was sensitive with pH value and temperature. The better PFOA removal efficiency was achieved at acidic condition. A novel relationship was found among PFOA degradation efficiency with hydroxyl radicals and photo-generated holes. Hydroxyl radicals generated on the surfaces of ZnO nanorods played dominant roles in PFOA degradation. PFOA degradation was found to follow the photo-Kolbe reaction mechanism. C2–C7 shorter-chain perfluorocarboxylic acids and fluoride ion were detected as main intermediates during PFOA degradation process. Based on the results, a proposal degradation pathway was raised.Download high-res image (98KB)Download full-size image

•Ordered Ag-g-C3N4/SBA-15 was successfully synthesized using SBA-15 as support.•4% Ag-g-C3N4/SBA-15 shows efficient capability for photocatalytic ozonation of OA.•The stability and mechanism in photocatalytic ozonation process are investigated.Ordered Ag-g-C3N4/SBA-15 was successfully synthesized using SBA-15 as a template and support. The samples were characterized by TEM, XRD, XPS, N2 adsorption-desorption. The results showed that metallic silvers with diameter 15 nm were distributed on the surface of g-C3N4 thin-layered. The specific surface area of the composite was 563.4 m2 g−1. As the final products for ozonation, oxalic acid was used to investigate its catalytic ability in heterogeneous photocatalytic ozonation under simulated solar light irradiation. Ordered Ag-g-C3N4/SBA-15 with the mass ratio of silver nitrate/dicyandiamide around 4% was found to be the most efficient for oxalic acid degradation. The kinetic constant was 1.60 and 2.52 times as high as that of solar light/Ag-g-C3N4/O3 and solar light/g-C3N4/O3 process, respectively. It demonstrated that both the Ag nanoparticles and improved specific surface area contributed to the enhancement, which promoted the decomposition of O3 and increased the active sites in reaction. The synergy index for photocatalytic ozonation of oxalic acid was calculated to be 5.71, which indicated a superior synergistic effect between photocatalysis and ozonation. In addition, 4% Ag-g-C3N4/SBA-15 samples showed good stability in photocatalytic ozonation process by cycled for four times, and the mechanism was also confirmed in this study. It is suggested that Ag-g-C3N4/SBA-15 composites is a promising catalyst for the practical application of photocatalytic ozonation.Download high-res image (77KB)Download full-size image

Mesoporous siliceous MCM-41 immobilized with Co and Mn metal ions (Co-Mn-MCM-41) was synthesized using a hydrothermal method. The structural regularity and the valence states of the metal species were measured by X-ray diffractometer and X-ray photoelectron spectrometer. The resultant bimetallic Co-Mn-MCM-41 catalyst was tested for the degradation of dimethyl phthalate (DMP) via a catalytic ozonation mechanism, demonstrating that the catalytic properties of Co-Mn-MCM-41 catalyst significantly accelerated the ozonation process. Total organic carbon (TOC) and DMP removal efficiency reached 94% and 99.7% at 15 min under the optimal conditions. The oxidation pathways were proposed after identifying the intermediate products from ozonation using a gas chromatography-mass spectrometer. The enhanced catalytic reactivity was attributed to the highly-dispersive cobalt and manganese species in MCM-41 scaffolds, which promoted the ozone decomposition and hydroxyl radicals’ generation in catalytic ozonation and accelerated the degradation of DMP. Bimetallic Co-Mn-MCM-41 catalyst remained stable in mild acidic conditions and continued to show high activity after repeated runs.Download high-res image (88KB)Download full-size image

Three-dimensional mesoporous MCM-48 and Ce loaded MCM-48 (Ce/MCM-48) were synthesized by hydrothermal and impregnating methods, respectively. They were characterized by XRD, SEM, TEM, EDS, XPS, N2 adsorption-desorption techniques, and the results showed that Ce/MCM-48 still retained a highly ordered cubic structure. A series of experiments were conducted to study the catalytic activity of Ce/MCM-48 and Ce/MCM-41 for ozonation of clofibric acid in aqueous solution. Total Organic Carbon (TOC) removal efficiency in Ce/MCM-48/O3 can be improved to 64% at 120 min reaction time, 54% by Ce/MCM-41/O3, only 24% by MCM-48/O3, 23% by single ozonation. Ce/MCM-48 did not show any adsorption capacity for CA. Effect of initial pH revealed that active sites were surface protonated hydroxyl groups. The restraint of phosphate and sodium hydrogen sulfite (NaHSO3) on the mineralization of CA illustrated more hydroxyl radicals were generated by Ce/MCM-48 catalysts than Ce/MCM-41. The degradation pathway of CA was investigated by the alterations of pH under different conditions. Recycle tests of catalysts demonstrated that compared with Ce/MCM-41, Ce/MCM-48 exhibited more excellent catalytic efficiency and stability because of its unique pore systems.Download high-res image (145KB)Download full-size image

•Fe-SBA-15 was directly synthesised by hydrothermal method under weak acid.•Surface reaction played a critical role for oxalic acid degradation.•Fe-SBA-15 significantly accelerated the generation of hydroxy radical.•Adsorption of oxalic acid on Fe-SBA-15 was a vital step for its degradation.•Fe-SBA-15 maintained a good catalytic activity and stability after being used.Highly ordered Iron-doped SBA-15 mesoporous material (Fe-SBA-15), which was synthesized via a direct hydrothermal method under weak acid condition, was used as heterogeneous catalyst for the ozonation of oxalic acid in aqueous solution. The results indicated that Fe doping significantly improved the catalytic activity of SBA-15, a high oxalic acid removal of 86.6% was achieved under the chosen condition, only 30.2% for SBA-15/O3 process. The major operating variables including Si/Fe ratio in catalyst, initial pH value and radical scavenger were also studied for catalytic reaction mechanism. The active sites of Fe-SBA-15 increased with iron doping content and Fe-SBA-15 significantly influenced ozone concentration in aqueous solution. The catalytic efficiency was mainly affected by radical scavenger and the pH value of solution, which illustrated that the catalytic ozonation process followed free radical mechanism, and the surface reaction played a critical role for oxalic acid degradation. The stability of Fe-SBA-15 was verified by the reused experiments. The XRD and BET tests also demonstrated that Fe-SBA-15 retained highly ordered 2D-hexagonal mesoporous structure and large surface area after reused. Fe-SBA-15 was a promising catalyst for catalytic ozonation of oxalic acid.

•Magnetic BiFeO3 is used as active catalyst in photocatalytic ozonation system.•O3/Vis/BiFeO3 shows high performance in removing oxalic acid and norfloxacin.•BiFeO3 nanoparticle exhibits excellent stability in O3/Vis/BiFeO3 process.In this paper, bismuth ferrite (BiFeO3) magnetic nanoparticles were used as visible light photocatalyst in the photocatalytic ozonation coupling system. It was successfully synthesized by thermal decomposition of a glyoxylate complex. The as-prepared photocatalyst was characterized by XRD, FT-IR, SEM, TEM, UV–Vis DRS and vibrating sample magnetometer. The magnetic hysteresis loop demonstrated that BiFeO3 possessed certain magnetization. Oxalic acid (OA) and norfloxacin (NFX) were selected as target pollutants for photocatalytic ozonation reactions to evaluate the catalytic ability of BiFeO3. The pseudo-first-order kinetic rate constants of degrading OA and NFX removal in O3/Vis/BiFeO3 at given time are 5.48 and 1.65 times as great as the sum of that when using Vis/BiFeO3 and O3, respectively. This enhancement was due to a synergy between photocatalysis and ozonation triggered by BiFeO3. In O3/Vis/BiFeO3 process, the photo-generated electrons produced on BiFeO3 could be trapped by ozone and reaction with them. Subsequently, the improved yield of hydroxyl radicals enhanced the degradation efficiency of organics. In addition, the stability and reusability of BiFeO3 in photocatalytic ozonation process were examined in this work.

•Ag-TiO2 micro-tube was successfully prepared using cotton fiber as template.•Photocatalytic ozonation of ATL by Ag-TiO2 is more efficient than TiO2.•Ag acts as electron acceptor for photocatalysis and decomposition center for O3.•Ag-TiO2 micro-tube owns excellent stability for photocatalytic ozonation of ATL.Ag-TiO2 hollow micro-tube was successfully prepared using cotton fiber as template. It was used to photocatalytic ozonation of Atenolol (ATL) in present study (UV/Ag-TiO2/O3). The results showed that 2% Ag-TiO2 possessed the best catalytic performance for ATL mineralization and had a distinct advantage compared with bare TiO2. The variation of ozone concentration confirmed that Ag-TiO2 hybrid not only increased the ozone amount in the solution, but also resulted in a fast decompose rate in the photocatalytic ozontion process. It meant that Ag act as a good photo-generated electron acceptor for photocatalysis and a beneficial decomposition center for ozone. Consequently, the synergistic effect of photocatalytic ozonation was enhanced and the mineralization of ATL was promoted. The recycle experiments proved that synthesized 2% Ag-TiO2 micro-tube owned excellent stability in photocatalytic ozonation coupling system. In addition, the effect of pH value, doping amount of Ag on the ATL degradation was also investigated. It is indicated that 2% Ag-TiO2 is an excellent catalyst for the photocatalytic ozonation of ATL.

•Ni-MCM-41 was reported as a novel adsorbent for the removal of methyl blue effectively.•Electrostatic interactions and π-complexation might be the possible mechanisms of adsorption.•Monolayer adsorption of methyl blue on homogeneous distributed adsorption sites in Ni-MCM-41 was suggested.•The adsorption underwent three processes and attained the final equilibrium.Adsorbents from Ni functionalized MCM-41 (Ni-MCM-41) were prepared for methyl blue (MB) removal from aqueous solution. The mesoporous structure of Ni-MCM-41 is confirmed by XRD technique. Surface area, pore size and wall thickness are calculated from BET equation and BJH method by nitrogen sorption technique. FT-IR studies show that Ni has been loaded on the hexagonal mesoporous structure of MCM-41. It is found that the MCM-41 structure remains unaltered after the loading of Ni, but its surface area and pore diameter decrease due to pore blockage. The effects of Ni content, adsorbent dosage, initial MB concentration, contact time, pH and temperature on adsorption were investigated. The results indicate that a much higher MB adsorption capacity is achieved by Ni-MCM-41 than MCM-41, and the optimum conditions are identified as: the MB initial concentration of 50 mg/L, 0.02 g Ni-MCM-41 with Ni content of 1 wt. % at 25 °C and pH value of 6.32. Adsorption of MB on Ni-MCM-41 can be well described by pseudo-second-order kinetics and intra-diffusion model, and equilibrium data is well fitted by Langmuir model. Thermodynamic parameters suggest that the adsorption process is endothermic and spontaneous. The possible adsorption mechanisms might be electrostatic interactions between sulfonic acid groups of MB and the positive Si–O–Ni+ of Ni-MCM-41, and π-complexation mechanism resulting from the interaction between aromatic cycles of MB and Ni functionality of Ni-MCM-41 might also be plausible.

Highlights•Fe(III)/Cs@Dia was confirmed as an excellent absorbent for anionic azo dyes.•Pseudo-second-order kinetic model showed a better-fit to the experimental data.•The equilibrium data fitted better with the Langmuir model.•Adsorption of 2GL dye onto adsorbent was exothermic in nature.•Adsorption mechanisms mainly involved electrostatic interaction and complexation.A novel diatomite/chitosan–Fe(III) composite (Fe(III)/Cs@Dia) was synthesized successfully to use as an adsorbent for the removal of anionic azo dye. The composite was further characterized by SEM, FTIR, XPS, and C13/Si29NMR, and then the adsorption batch experiments were carried out as a function of initial dye concentrations, pH values, contact time and temperatures to determine the adsorption capacities of Fe(III)/Cs@Dia. Compared with several typical isotherm models, the adsorption isotherms were all best-fitted by the Langmuir model, with a maximal 2GL dye uptake of 1250 mg g−1 at pH 6 and 298 K. In addition, kinetic studies followed the pseudo-second-order model and thermodynamic studies revealed that the uptake was exothermic in nature. The adsorption mechanisms were proposed with observation that electrostatic interaction and complexation played the key roles in adsorption process. Moreover, the composite also showed favorable adsorption properties for other four anionic azo dyes (direct yellow R, congo red, methyl orange and direct red 23).Graphical abstract

•Ce/MCM-41 was prepared and used as a heterogeneous catalyst in ozonation process.•Ce/MCM-41 exhibited highly catalytic activity on ozonation of p-CBA in water.•Higher conversion rate of organic chlorine was observed in Ce/MCM-41/O3 process.•There was a synergetic effect between O3 and Ce/MCM-41/O3 adsorption.•Mechanism of p-CBA degradation and generation of hydroxyl radicals was proposed.Mesoporous molecular sieve MCM-41 and Cerium-loaded MCM-41 (Ce/MCM-41) were synthesized and used as heterogeneous catalysts for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution. MCM-41 and Ce/MCM-41 were characterized by XRD, TEM, SEM, ICP-AES and N2 adsorption–desorption techniques. The results showed that Ce/MCM-41 retained a highly ordered mesoporous structure and had a surface area of 953 m2 g−1. The presence of Ce/MCM-41 obviously improved the mineralization of p-CBA and the conversion rate of organic chlorine. The conversion rate of organic chlorine in Ce/MCM-41/O3 process was 94% along with the degradation of p-CBA in the first 10 min (73.3% by O3 alone and 78.6% by MCM-41/O3), TOC removal efficiency by Ce/MCM-41/O3 process was 94% at 60 min (63% by MCM-41/O3 and only 52% by O3 alone), and the leaching of cerium was only 0.097 mg l−1. The combination of Ce/MCM-41 and O3 exhibited a significant synergetic effect. Both pH changes of aqueous solution and the presence of hydroxyl radical scavenger tert-butanol (TBA) proved that Ce/MCM-41 catalytic ozonation of p  -CBA followed the HOHO oxidation mechanism. The changes of ozone concentration indicated that the presence of Ce/MCM-41 could promote ozone decomposition into hydroxyl radical, and improve the utilization rate of ozone. Lewis acid sites and the hydroxyl group existing on the surface of catalyst were believed to be the initiator of ozone decomposition to generate HOHO.Graphical abstract

•Ce/SBA-15 was first used as a heterogeneous catalyst for ozonation of DMP.•Cerium leaching was less than 0.1 mg L−1 (pH 5.7) after Ce/SBA-15 reused.•There was a synergetic effect for DMP mineralization in catalytic ozonation.•The mechanism of DMP degradation and hydroxyl radicals’ generation was suggested.The catalytic activity of cerium-loaded SBA-15 (Ce/SBA-15) for the ozonation of dimethyl phthalate (DMP) in aqueous solution was studied. Ce/SBA-15 was prepared and characterized by a low angle X-ray powder diffraction (XRD), nitrogen adsorption–desorption and ultraviolet–visible diffuse reflection spectrum (UV–vis DRS). The results showed that the material retained a highly ordered mesoporous structure and processed large surface area. The presence of Ce/SBA-15 slightly accelerated DMP decomposition, but significantly improved its mineralization efficiency. Under the chosen condition, a high mineralization efficiency (88.7%) was achieved by Ce/SBA-15/O3 process at 60 min, 2.6 times higher than SBA-15/O3, 3.5 times higher than O3 alone. The comparison among different process indicated that the combination of Ce/SBA-15 and O3 exhibited a significant synergetic effect. Ce/SBA-15 significantly improved ozone decomposition into hydroxyl radicals in aqueous solution and the oxidation of DMP occurred via the free radical mechanism. The reused experiment verified that Ce/SBA-15 kept a good catalytic activity and stability, and it was a promising heterogeneous catalyst.The cerium-loaded SBA-15 (Ce/SBA-15) was synthesized successfully and first used as a heterogeneous catalyst for ozonation of DMP. It showed high catalytic activity for efficient mineralization of dimethyl phthalate in catalytic ozonation process. Under the optimal conditions, a high mineralization efficiency of 88.7% was achieved by Ce/SBA-15/O3 process at 60 min, 2.6 times higher than SBA-15/O3, 3.5 times higher than O3 alone. Ce/SBA-15 kept a good catalytic activity and stability, and it was a promising catalyst for ozonation process.

Mesoporous MCM-41 and Fe loaded MCM-41 (Fe/MCM-41), which were successfully prepared by a hydrothermal method and a dipping method respectively, were applied as heterogeneous catalysts for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution. MCM-41 and Fe/MCM-41 were characterized by XRD, FT-IR and diffuse reflectance UV–vis (DR-UV–vis) techniques. The presence of either MCM-41 or Fe/MCM-41 improves p-CBA and total organic carbon (TOC) removal efficiency compared to ozonation alone. Under the experimental condition, TOC removal rate of Fe/MCM-41/O3 process is over 63.5% at 60 min oxidation time, 44.5% using MCM-41 as catalyst, only 37.7% with ozonation alone. The presence of turt-butanol (TBA) in the Fe/MCM-41/O3 process indicated that the oxidation mechanism of p-CBA occurs via OH in the liquid bulk. And Fe/MCM-41 is a promising catalyst.

•A Cu2O/Au/TiO2 film was synthesized successfully.•Hydrogen production of Cu2O/Au/TiO2 film improved significantly.•The highest hydrogen production rate of the film was 125.3 mmol/h/m2.•A Z-scheme charge transfer pathway was proposed.A novel Cu2O/Au/TiO2 photocatalyst composite film was fabricated on a copper substrate for photocatalytic hydrogen production. The composite films, Cu2O/Au/TiO2, were stepwise synthesized by using electrochemical deposition, photodeposition, and coating methods. First, a Cu2O film was synthesized using the electrochemical deposition method, after which Au was deposited onto the Cu2O film through in-site photodeposition. Finally, TiO2 was coated on the surface of the Cu2O/Au film. Its morphology and surface chemical composition was characterized by SEM, TEM, XRD and XPS. The optical characteristics (UV–Vis DRS, PL spectrum) of the films were also examined. The photocatalytic hydrogen production rate of the Cu2O/Au/TiO2 composite film from a 20% vol. methanol solution increased to125.3 mmol/h/m2 under 300 W xenon lamp light irradiation. Compared to the TiO2 (13.5 mmol/h/m2) film and Cu2O/TiO2 film (83.2 mmol/h/m2), the Cu2O/Au/TiO2 film showed excellent photocatalytic performance for hydrogen generation. The Cu2O/Au/TiO2 film has highly effective photocatalytic properties, which are attributed to the Z-scheme system and can not only enhance the absorption of solar light but also suppress the recombination of photogenerated electron-hole pairs. It is worth noting that by introducing Au into the interface of Cu2O/TiO2, the surface plasmon resonance (SPR)-induced local electric field formed at the Au site induces a Z-scheme charge transfer pathway inside the composite film (Cu2O/Au/TiO2), which promotes both the charge of the separation efficiency and redox ability of the photogenerated electron-hole pairs.

•Clofibric acid (CA) is efficiently mineralized by O3/MnOx/SBA-15.•Adsorption of CA and its intermediates on MnOx/SBA-15 is proved unimportant.•Initiation of hydroxyl radicals (OH) is enhanced in O3/MnOx/SBA-15.•Uniformly distributed MnOx accounts for the high activity of MnOx/SBA-15.•Degradation routes of CA in ozonation alone and catalytic ozonation are proposed.Comparative experiments were conducted to investigate the catalytic ability of MnOx/SBA-15 for the ozonation of clofibric acid (CA) and its reaction mechanism. Compared with ozonation alone, the degradation of CA was barely enhanced, while the removal of TOC was significantly improved by catalytic ozonation (O3/MnOx/SBA-15). Adsorption of CA and its intermediates by MnOx/SBA-15 was proved unimportant in O3/MnOx/SBA-15 due to the insignificant adsorption of CA and little TOC variation after ceasing ozone in stopped-flow experiment. The more remarkably inhibition effect of sodium bisulfite (NaHSO3) on the removal of TOC in catalytic ozonation than in ozonation alone elucidated that MnOx/SBA-15 facilitated the generation of hydroxyl radicals (OH), which was further verified by electron spin-resonance spectroscopy (ESR). Highly dispersed MnOx on SBA-15 were believed to be the main active component in MnOx/SBA-15. Some intermediates were indentified and different degradation routes of CA were proposed in both ozonation alone and catalytic ozonation. The amounts of small molecular carboxylic acids (i.e., formic acid (FA), acetic acid (AA) and oxalic acid (OA)) generated in catalytic ozonation were lower than in ozonation alone, resulting from the generation of more OH.

The UV/O3-BAC (biological activated carbon) process was employed to treat secondary effluents and compared to the O3-BAC process. The effects of ozone dosage and empty bed contact time (EBCT) in BAC unit on dissolved organic carbon (DOC) removal were investigated. The results showed that the presence of UV improved ozone utilization and biodegradability of the effluent. DOC removal increased with ozone dosage and EBCT in BAC, however, 3 mg/L ozone dosage with 15 min oxidation time and 15 min EBCT in BAC were more economical and efficient. The synergetic effect in UV/O3-BAC process is more than that in O3-BAC process for DOC removal. Except for organic pollutants with MW >10,000 Da, those of other MW range were decomposed much more by UV/O3 process than by O3 process. GC/MS analysis showed dibutyl phthalate, bis(2-ethylhexyl) phthalate, 4-bromo-3-chloroaniline and other phenol derivatives were prevalent organic pollutants found in the secondary effluent. After UV/O3 treatment, some aromatic compounds including 2,4-dichloro-benzenamine, 4-bromo-3-chloroaniline and 3,5-dimethoxy-acetophenone disappeared and some small molecules were formed, but the kinds and concentration of organic pollutants including phthalate esters were greatly reduced by the subsequent BAC unit.