Yiming Tang

Mechanism insight of PFOA degradation by ZnO assisted-photocatalytic ozonation: Efficiency and 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.

Heterogeneous catalytic ozonation of clofibric acid using Ce/MCM-48: Preparation, reaction mechanism, comparison with Ce/MCM-41

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 120min 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.

Mechanism insight of pollutant degradation and bromate inhibition by Fe-Cu-MCM-41 catalyzed ozonation

A flexible catalyst, Fe-Cu-MCM-41, was employed to enhance diclofenac (DCF) mineralization and inhibit bromate formation in catalytic ozonation process. Greater TOC removal was achieved in Fe-Cu-MCM-41/O3 process (78%) than those in Fe-MCM-41/O3 (65%), Cu-MCM-41/O3 (73%) and sole ozonation (42%). But it was interesting that both Cu-MCM-41/O3 and Fe-MCM-41/O3 achieved 93% bromate inhibition efficiency, only 71% inhibition efficiency was observed in Fe-Cu-MCM-41/O3. Influence of pH, TBA/NaHSO3 and detection of by-products were conducted to explore the mechanism. By Pyridine adsorption-IR and XPS, a relationship was found among activity of catalysts, Lewis acid sites and electron transfer effect between Fe (II/III) and Cu (I/II). Fe-Cu-MCM-41 promoted ozone decomposition to generate OH, which accounted for enhanced DCF mineralization. The consumption of aqueous O3 also suppressed the oxidative of Br- and HBrO/Br-. More HBrO/BrO- accumulated in catalytic ozonation process and less bromate generated. Bromate formation in Fe-Cu-MCM-41/O3 process was sensitive with pH value, the acidic condition was not favor for bromate formation. Both DCF mineralization and bromate inhibition were influenced by surface reaction. Moreover, Fe-Cu-MCM-41 showed excellent catalytic performance in suppressing the accumulation of carboxylic acid, especially for oxalic acid. Nearly no oxalic acid was detected during Fe-Cu-MCM-41/O3 process.

Relationship between the structure of Fe-MCM-48 and its activity in catalytic ozonation for diclofenac mineralization

Fe-MCM-48 catalyst with a three-dimensional cubic pore structure was directly synthesized via a hydrothermal method, and the mineralization efficiency of diclofenac (DCF) in the catalytic ozonation process (Fe-MCM-48/O3) was assessed. X-ray diffraction (XRD), N2 adsorption desorption, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterizations revealed that Fe existed in the framework of MCM-48, and Fe-MCM-48 possessed a large surface area and a highly ordered cubic mesoporous structure, which could accelerate reactants and products diffusion. Regarding mineralization efficiency, the addition of Fe-MCM-48 significantly improved total organic carbon (TOC) removal, and approximately 49.9% TOC were removed through the Fe-MCM-48/O3 process at 60 min, which was 2.0 times higher than that in single ozonation. Due to this catalysts superior structure, Fe-MCM-48 showed the better catalytic activity compared with Fe-MCM-41 and Fe loaded MCM-48 (Fe/MCM-48, Fe existed on the surface of MCM-48). DCF removal in the Fe-MCM-48/O3 process was primarily based on ozone direct oxidation. The improvement of mineralization efficiency was attributed to the function of generated hydroxyl radicals (•OH), which indicated that the presence of Fe-MCM-48 accelerated ozone decomposition. Moreover, the negatively charged surface of Fe-MCM-48 and the proper pH value of the DCF solution played an essential role in OH generation.

Efficient visible-light-driven hydrogen evolution and Cr(VI) reduction over porous P and Mo co-doped g-C3N4 with feeble N vacancies photocatalyst

Developing highly efficient and inexpensive photocatalysts without noble metals, yet remarkably enhancing hydrogen production and Cr(VI) reduction activity, is highly needed. Here, the effective photocatalytic H2 evolution under visible light from an Eosin Y (EY)-sensitized (P, Mo)-g-C3Nx system by avoiding any noble metal co-catalyst is reported by the first time. Meanwhile, the optimized sample also displays the excellent performance in photocatalytic hexavalent chromium (Cr(VI)) reduction. In addition, this composite exhibits delectable stability for photocatalytic activities, no significant decay of activity is being observed after 16h reaction for photocatalytic H2 evolution (8h for Cr(VI) reduction). It is believed that this work will open up a new route for fabricating high-performance and inexpensive photocatalysts for hydrogen production and Cr(VI) reduction.

Bromate Inhibition during Ozonation of Bromide-Containing Water by the Presence of Mn Incorporated MCM-41

The mesoporous Mn incorporated MCM-41 was employed to inhibit bromate formation during catalytic ozonation of bromide-containing water, Mn-MCM-41 was synthesized via hydrothermal method and the influences of temperature ramping rate (0.5, 1 and 2 K min-1) during calcination were investigated. It was characterized by XRD, TEM, SEM, XPS and H2-TPR, indicating that temperature ramping rate could affect the valence states of active Mn species, the dispersion of Mn on the surface of catalyst and the formation of oxygen vacancies, which could increase surface hydroxyl groups on Mn-MCM-41 and accelerated ozone decomposition to generate oxygen species. Compared with 0.5 K min-1 and 2 K min-1, Mn-MCM-41 with 1 K min-1 showed much better performance in bromate inhibition process, Mn100-MCM-41 (molar ratio of Si/Mn=100) achieved 96.7% inhibition efficiency at pH 6.5, which was attributed to higher fraction of Mn(II)/Mn(III) and oxygen vacancies. The influence of pH, TBA and intermediate HOBr/OBr- were explored to investigate the mechanism. The results showed that more H2O2 generation and decreased O3 exposure to Br- in Mn-MCM-41 catalytic ozonation process, the oxidative transformation from Br- to HOBr/OBr- was blocked, resulting to less bromate formation. Highlights: • Temperature ramping rate during calcination of Mn-MCM-41 was crucial. • Oxygen vacancy and variation Mn state are responsible for catalytic performance. • Mn-MCM-41 achieved high bromate inhibition efficiency (96.7%) at pH 6.5. • Mn-MCM-41 inhibited BrO3 - by reducing HOBr/OBr-.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41. Fe leaching can be ignored when pH was higher than 4.0. pH played an important role in CPX adsorption on Fe-MCM-41. Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g−1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.