Wen-Da Oh

Performance of magnetic activated carbon composite as peroxymonosulfate activator and regenerable adsorbent via sulfate radical-mediated oxidation processes.

Magnetic activated carbon composite (CuFe2O4/AC, MACC) was prepared by a co-precipitation-calcination method. The MACC consisted of porous micro-particle morphology with homogeneously distributed CuFe2O4 and possessed high magnetic saturation moment (8.1 emu g(-1)). The performance of MACC was evaluated as catalyst and regenerable adsorbent via peroxymonosulfate (PMS, Oxone(®)) activation for methylene blue (MB) removal. Optimum CuFe2O4/AC w/w ratio was 1:1.5 giving excellent performance and can be reused for at least 3 cycles. The presence of common inorganic ions, namely Cl(-) and NO3(-) did not exert significant influence on MB degradation but humic acid decreased the MB degradation rate. As a regenerable adsorbent, negligible difference in regeneration efficiency was observed when a higher Oxone(®) dosage was employed but a better efficiency was obtained at a lower MACC loading. The factors hindering complete MACC regeneration are MB adsorption irreversibility and AC surface modification by PMS making it less favorable for subsequent MB adsorption. With an additional mild heat treatment (150 °C) after regeneration, 82% of the active sites were successfully regenerated. A kinetic model incorporating simultaneous first-order desorption, second-order adsorption and pseudo-first order degradation processes was numerically-solved to describe the rate of regeneration. The regeneration rate increased linearly with increasing Oxone(®):MACC ratio. The MACC could potentially serve as a catalyst for PMS activation and regenerable adsorbent.

A novel quasi-cubic CuFe2O4–Fe2O3 catalyst prepared at low temperature for enhanced oxidation of bisphenol A via peroxymonosulfate activation

A facile eco-friendly co-precipitation synthesis at low temperature was employed to fabricate CuFe2O4–Fe2O3 for the oxidation of bisphenol A (BPA) via peroxymonosulfate (PMS) activation. The formation mechanism of CuFe2O4–Fe2O3 at low temperature is proposed. The FESEM and BET characterization studies revealed that the CuFe2O4–Fe2O3 catalyst has a quasi-cubic morphology and specific surface area of 63 m2 g−1. The performance of CuFe2O4–Fe2O3 as a PMS activator was compared with those of other catalysts and the results indicated that the performance was in the following order: CuFe2O4–Fe2O3 > CuFe2O4 > CoFe2O4 > CuBi2O4 > CuAl2O4 > Fe2O3 > MnFe2O4. A kinetic model with mechanistic consideration of the influence of pH, PMS dosage and catalyst loading was developed to model the degradation of BPA. The intrinsic rate constant (ki) was obtained from the kinetic study. The relationship between the pseudo first-order rate constant and ki was established. The trend of ki revealed that increasing the catalyst loading decreased the BPA removal rate due to the initial preferential production of the weaker radical (i.e. SO5˙−) for BPA degradation and Fe2+ quenching of SO4˙− at higher catalyst loading. The influence of water matrix species (i.e. Cl−, NO3−, HCO3−, PO43− and humic acid) on the BPA degradation rate was also investigated. The CuFe2O4–Fe2O3 catalyst exhibited excellent stability and can be reused several times without significant deterioration in performance.

High surface area DPA-hematite for efficient detoxification of bisphenol A via peroxymonosulfate activation

A novel dipicolinic acid-functionalized hematite (DPA-hematite) with high surface area was prepared by co-precipitation of a Fe(III)–DPA complex. It was used as a catalyst to activate peroxymonosulfate (PMS) for bisphenol A (BPA) detoxification. The XRD, FESEM, TEM and FTIR characterization indicated that nano-sized DPA-hematite with aggregated quasi-nanosphere morphology was obtained with a 1 : 1 ratio of Fe(III) to DPA. Higher catalytic activity of DPA-hematite over other Fe(III)-based catalysts was observed for BPA oxidation in the presence of oxone. The kinetics of BPA removal was investigated using a kinetic model with BPA concentration, initial oxone dosage and surface area of DPA-hematite. For the first time, the acute toxicity of BPA solution over time with elimination of oxone toxicity interference was studied using Vibrio fischeri bacteria and the results indicated that the evolution of acute toxicity was highly dependent on the initial oxone dosage. Under deficit oxone conditions, BPA was completely transformed to by-products along with decreased intrinsic toxicity but ring-opening reactions were barely observed which can be explained based on the dimerization–mineralization degradation pathways. Under excess oxone conditions, the intrinsic toxicity of BPA solution decreased along with ring-opening reactions leading to a greater extent of mineralization. The DPA-hematite can be reused for BPA detoxification for at least three cycles in the presence of 2.0 g L−1 oxone.

Surface–active bismuth ferrite as superior peroxymonosulfate activator for aqueous sulfamethoxazole removal: Performance, mechanism and quantification of sulfate radical

A surface-active Bi2Fe4O9 nanoplates (BF-nP) was prepared using a facile hydrothermal protocol for sulfamethoxazole (SMX) removal via peroxymonosulfate (PMS). The catalytic activity of BF-nP was superior to other catalysts with the following order of performance: BF-nP>Bi2Fe4O9 (nanocubes)>>Co3O4>Fe2O3 (low temperature co-precipitation method)>Fe2O3 (hydrothermal method)∼Bi2O3∼Bi3+∼Fe3+. The empirical relationship of the apparent rate constant (kapp), BF-nP loading and PMS dosage can be described as follows: kapp=0.69[BF-nP]0.6[PMS]0.4 (R2=0.98). The GC-MS study suggests that the SMX degradation proceed mainly through electron transfer reaction. The XPS study reveals that the interconversion of Fe3+/Fe2+ and Bi3+/Bi5+ couples are responsible for the enhanced PMS activation. The radical scavenging study indicates that SO4- is the dominant reactive radical (>92% of the total SMX degradation). A method to quantify SO4- in the heterogeneous Bi2Fe4O9/PMS systems based on the quantitation of benzoquinone, which is the degradation byproduct of p-hydroxybenzoic acid and SO4-, is proposed. It was found that at least 7.8±0.1μM of SO4- was generated from PMS during the BF-nP/PMS process (0.1gL-1, 0.40mM PMS, natural pH). The Bi2Fe4O9 nanoplates has a remarkable potential for use as a reusable, nontoxic, highly-efficient and stable PMS activator.

Controllable mullite bismuth ferrite micro/nanostructures with multifarious catalytic activities for switchable/hybrid catalytic degradation processes

In this work, controllable preparation of micro/nanostructured bismuth ferrites (BFOs) were used to investigate multifarious heterogeneous catalyses, including Fenton/Fenton-like reaction, photocatalysis, photo-Fenton oxidation, and peroxymonosulfate (PMS) activation. Results showed that BFO can be used asa novel catalyst to activate switchable catalytic degradation of organic matters. Additionally, a novel catalytic system for degradation of organic pollutants, which integrating all-above heterogeneous catalyses is denoted as BFO/H2O2/PMS hybrid reaction, is introduced for the first time. BFO/H2O2/PMS system effectively degraded>99% for both methyl orange (MO) and sulfamethoxazole (SMX) within 60min, which shows better efficiency than above BFO-driven catalyses. The major SMX degradation pathway in BFO/H2O2/PMS system is proposed via detecting intermediates using LC/MS/MS. It was found that catalytic activities of BFOs are in the order of BFO-L (co-precipitation, micro/nanosize, single crystals exposing facet (001))>BFO-H (hydrothermal, nanocluster with a higher surface area than other BFOs)>BFO-C (fabricated using calcination process, microsize), which demonstrated that crystallographic orientation is more significant in heterogeneous catalyses than specific surface area at micro/nanoscale. Besides, the required H2O2 consumption for achieving 99% TOC removal was identified in BFO-driven photo-Fenton oxidation. The other effects on degradation efficiency, such as H2O2 dosage and pH, were investigated as well. In Fenton/Fenton-like reaction, reaction conditions suggested are ∼61.5mM H2O2 dosage and pH≥4.5 to avoid quenching of HO into HO2 by excessive H2O2 and Fe leaching.

A molybdovanadophosphate-based surfactant encapsulated heteropolyanion with multi-lamellar nano-structure for catalytic wet air oxidation of organic pollutants under ambient conditions

A series of surfactant encapsulated heteropolyanions (SEH-n) based on molybdovanadophosphates (MVPs) was prepared. The morphological optimisation of the SEHs was studied by the control of solvent polarity and MVP to surfactant ratio used. Investigation by TEM revealed the formation of particles with multi-lamellar nano-structure in the SEHs. Characterization of the SEHs by XRD, TGA and FTIR indicated the successful encapsulation of the molybdovanadophosphates with the surfactant. The performance of SEHs as catalysts for the removal of bisphenol-A under ambient conditions was evaluated. Factors influencing the performance of the SEH-n are the relative stability of the Keggin structure and electron accepting property. The dissolved oxygen plays a crucial role in improving the BPA removal efficiency. The hydrophobic property of the nano-sized SEHs provides good aqueous stability and allows excellent recoverability of the catalyst from the aqueous solution after treatment.

High-sulfur capacity and regenerable Zn-based sorbents derived from layered double hydroxide for hot coal gas desulfurization

The Zn-Al mixed metal oxide (ZnAl-MMO) with a plate-like structure was derived from Zn-Al layered double hydroxide. The ZnAl-MMO with a Zn/Al molar ratio of 3:1 exhibits superior absorption ability for H2S in a simulated coal gas at 600 ℃ due to the special structure of the ZnAl-MMO. Besides ZnS, elemental sulfur is also produced during the desulfurization process. The deactivation model could well simulate the absorption behavior of H2S. The sulfidation reaction over the sorbent shows large initial reaction rate constants (1110-5390 m3 min-1  kg-1) and low activation energy (29.5 kJ mol-1). The regeneration rate of the used sorbent can reach 99.8% under the optimum conditions. The regenerated sorbents still show high sulfur capacity (ca. 30%), implying its great application potential for industrial-scale desulfurization of the hot coal gas.