Sulfate radical based advanced oxidation processes coupled with ceramic membranes for water purification

The intensive use of antibiotics for human, veterinary and agricultural purposes results in their continuous release into the environment, which causes the concern in relation to the development of antibiotic resistance genes and bacteria. Sulfate radical based advanced oxidation processes (SR-AOPs) have been recognized as an effective alternative method to the destruction of recalcitrant organics in wastewater, in which highly-reactive sulfate radical was generated and utilized to oxidize organic contaminants to innocuous CO2 and H2O. However, most of the catalysts used in SR-AOPs are suspended in water during usage and therefore need a further separation process. On the other hand, membrane separation has been proved to be a promising technology for water purification in recent decades because of the high yield of production and low energy consumption. However, the membrane fouling caused by the accumulation of a broad range of foulants on top of membrane surface / inside the membrane pores results in a substantial decrease in their water permeability, which leads to a high permeability loss and energy consumption. Meanwhile, the separation principle for microfiltration (MF) is based on size exclusion, which means that it cannot remove many kinds of organic micro-pollutants during the physical separation process, resulting in the effluent discharge with potential hazard. The aim of this thesis work is to overcome these drawbacks by integrating MF with SR-AOPs in the water purification system to remove antibiotics, in which sulfamethoxazole (SMX) works as the target pollutant. Firstly, a Co3O4 surface functionalized ceramic membrane (CoFCM) was synthesized via a novel ZIF-67 induced surface nucleated heterogeneous growth method (Chapter 3). The CoFCM showed an enhanced performance in SMX removal in a semi-batch experiment. In chapter 4, a Co3O4 impregnated ceramic membrane (CoCM) was developed via an in-situ self-scarified template method. With this method, Co3O4 was isotropically impregnated into the whole membrane while did not affect the pore size of the membranes. Due to the advantages of mix-metal oxides on PMS activation, a cobalt ferrite (CoFe2O4) impregnated ceramic membrane was developed via a one-step urea combustion method (Chapter 5). Results showed that CoFe2O4 was impregnated into the membrane pores as well as the membrane surface. With increasing of repeating times, the catalyst loading amount increased while the pure water permeability decreased, which means the catalyst would form a dense catalytic layer on the membrane surface due to the aggregation during the combustion process. The membrane performance was evaluated in a home-made dead-end membrane filtration mode, and results showed the robust membrane can function well during a wide pH range as well as the existence of NOM and anions. Finally, to have a better understanding on the SMX transformation via PMS in the presence of nano-bimetallic Co/Fe oxides, a systematic study was conducted in Chapter 6. The influencing factors (pH, NOM, catalyst loading and PMS dosage) were investigated and the radical generation as well as PMS activation mechanism were explored. The SMX transformation pathway including both non-radical and radical pathways was proposed.Doctor of Philosoph

Chemocatalytic ceramic membranes for removing organic pollutants in wastewater: a review

Catalytic ceramic membranes display synergistic functions of catalytic oxidation and membrane filtration. In the current work, a comprehensive review on chemocatalytic ceramic membranes (CCCMs) applied in the field of removing organic pollutants from wastewater is presented. This work provides a first-time review focusing solely on the CCCMs in wastewater treatment. The structures and fabrication technologies of the CCCMs are described firstly, where six configurations and three technical approaches have been summarized. Next, four systems of CCCM, i.e., catalytic ozonation ceramic membrane (COCM), Fenton/catalytic wet peroxide oxidation ceramic membrane (F/CWPOCM), catalytic wet air oxidation ceramic membrane (CWAOCM) and catalytic persulfate oxidation ceramic membrane (CPOCM), are interpreted in terms of constitution elements, operation parameters and performance indicators. Then, the applications of these four systems are analyzed and discussed, in which the recent over 10-year work progress on CCCMs for pollutant removal is summarized. The prospects and concluding remarks on the CCCMs are presented lastly.Nanyang Technological UniversityThis work was supported by core-fund from Nanyang Environment and Water Research Institute (NEWRI), Nanyang Technological University (NTU), Singapore, under 04SBP000935N025

A Novel Metal–Organic Framework (MOF)–Mediated Interfacial Polymerization for Direct Deposition of Polyamide Layer on Ceramic Substrates for Nanofiltration

A facile metal–organic framework (MOF)‐mediated interfacial polymerization (IP) method is developed to prepare a polyamide (PA) layer directly on the ceramic substrate for nanofiltration. MOF is introduced to connect ceramic substrate and PA layer via chemical bonding, resulting in a robust separation layer. The optimization of IP can be controlled by MOF growth process via tuning the surface roughness as well as hydrophilicity. This method will provide a new way for the preparation of next generation of organic–inorganic composite membranes.Accepted versio

Acetic acid-assisted fabrication of hierarchical flower-like Bi2O3 for photocatalytic degradation of sulfamethoxazole and rhodamine B under solar irradiation

With the assistance of acetic acid (CH3COOH), a novel 3D flower-like Bi2O3 was synthesized via hydrothermal process followed by calcination. For the first time, the role of CH3COOH as a capping agent in the formation of flower-like structure was investigated. The as-prepared flower-like Bi2O3 had a high activity on the degradation of sulfamethoxazole (SMX) under simulated solar light irradiation due to the narrow band gap of 2.69eV, high percentage of β-Bi2O3 as well as high intensity of polar facets (120) and (200). Meanwhile, the photocatalytic degradation followed apparent pseudo-first-order kinetics. The rate constant (k) increased from 0.7×10-2 to 3.0×10-2min-1 with the catalyst loading varying from 0.5 to 2.0gL-1. Increasing pH values from 3 to 11 led to the decrease of k from 2.2×10-2 to 0.2×10-2min-1, which could be attributed to the electrostatic adsorption between SMX molecules and Bi2O3. The radical quenching experiments showed both direct (h+) and indirect oxidation (OH and O2-) happened in this process.Accepted versio

Pore-functionalized ceramic membrane with isotropically impregnated cobalt oxide for sulfamethoxazole degradation and membrane fouling elimination: Synergistic effect between catalytic oxidation and membrane separation

In this study, a pore-functionalized ceramic membrane with isotropically impregnated cobalt oxide (CoCM) was prepared via an in-situ self-sacrificed template method and applied for sulfamethoxazole (SMX) degradation by peroxymonosulfate (PMS) activation under a dead-end membrane filtration mode. The physical and chemical properties of the membranes were characterized via FESEM, AFM, XRD and XPS. Results indicated that Co3O4 had been impregnated into the macropores uniformly throughout the whole ceramic membrane without pore blocking. The formation of Cosingle bondOsingle bondAl bonding inhibited the leaching of cobalt during the filtration while the hydroxyl group Co−OH played a crucial role during the radical generation. The contact angle of CoCM decreased, resulting in a higher pure water permeability as compared to the original ceramic membrane. The catalytic degradation of SMX showed that its removal efficiency could be influenced by both contact time and PMS dosage. CoCM exhibited superior antifouling property during the humic acid (HA) removal study. The stability and regeneration of CoCM were investigated. Furthermore, the radical quenching experiment was conducted and the concentration of sulfate radical was quantitatively estimated. Finally, the PMS activation as well as organics removal mechanism in CoCM via the synergistic coupling of catalytic Co3O4 and membrane separation were proposed.Accepted versio

Urea-assisted one-step synthesis of cobalt ferrite impregnated ceramic membrane for sulfamethoxazole degradation via peroxymonosulfate activation

In this study, a novel CoFe2O4 nanocatalyst impregnated Al2O3 ceramic membrane was prepared via a urea-assisted one-step combustion method. The catalytic membrane was characterized by field emission scanning electron microscopy (FESEM) with energy dispersive X-Ray analysis (EDX) and applied for the catalytic degradation of sulfamethoxazole (SMX) via peroxymonosulfate (PMS) activation under a dead-end membrane filtration mode for the first time. Results indicate that CoFe2O4 could be impregnated into the macropores throughout the whole Al2O3 ceramic membrane via this method and the CoFe2O4 loading amount could be controlled by the multiple impregnation cycles. The membrane filtration operation mode significantly enhances the accessibility of the catalytic active sites to PMS and SMX in microreactor environment and thus the CoFe2O4 impregnated membrane displays excellent catalytic activity for the SMX degradation. The pure water permeability flux can maintain at ∼3000 L m−2 h−1 bar−1 (LMHB) with the catalyst loading amount of 0.015 g/g Al2O3. In the membrane filtration system, the removal rate of SMX with the initial concentration of 10 mg L−1 can achieve to ∼98%, 70% and 40% with the residence time of 90, 36 and 18 s. The catalytic membrane shows a great tolerance at wide pH range (3–11), the existence of humic acid and anions. Meanwhile, the membrane shows self-cleaning property by retaining >90% of initial flux after 3 treatment cycles. Electron paramagnetic resonance (EPR) and radical quenching experiments indicate that both sulfate radical and hydroxyl radical are generated and sulfate radical is the dominant active species in the process.Accepted versio

High-performance porous carbon-zeolite mixed-matrix membranes for CO₂/N₂ separation

Nano-sized PS-MFI, ETS-10 and SAPO-34 zeolites were utilized as CO2-selective fillers to fabricate high-performance mixed-matrix carbon molecular sieve membranes (CMSMs) for application in the CO2/N2 separation process. In this work, an in-house polyimide, ODPA-TMPDA, was used as a polymer precursor for CMSMs, due to its higher intrinsic gas permeability compared with commercial polyimides. Zeolite-filled CMSMs were then successfully fabricated without any appreciable defects at the filler/matrix interfaces. Gas permeation testing revealed that both CO2 permeability and CO2/N2 selectivity can be significantly improved upon incorporation of such zeolite fillers, enabling selective adsorption and transport of CO2. In particular, SAPO-34 yielded the best results among the zeolite fillers tested, resulting in an excellent performance far beyond the Robeson upper bound limit for CO2/N2 separation.This work funded by Saudi Aramco-KAIST CO2 Management Center

Ce/TiOₓ-functionalized catalytic ceramic membrane for hybrid catalytic ozonation-membrane filtration process: fabrication, characterization and performance evaluation

A series of Ce/TiOx-functionalized catalytic ceramic membranes (CeTi-CeCCMs) were fabricated via citrate sol-gel assisted wet impregnation followed by acid-hydrolysed sol-gel dip coating method. The effect of Ce-dopant and block-copolymer P-123 on the formation of Ce-doped TiOx was investigated and optimized to fabricate a uniform Ce-doped TiOx layer with hierarchical porous structure. The modifications adopted for the CCM fabrication had a marginal effect on the clean water permeability, which is favourable towards the membrane filtration process. Meanwhile, the nanocatalysts located at the membrane outer surface and within the membrane substrate of CCM could significantly enhance the accessibility of the reactants to the catalytic sites. The as-fabricated CCMs were employed for N,N-diethyl-m-toluamide (DEET) degradation in the hybrid catalytic ozonation-membrane filtration process operating under continuous dead-end filtration mode. CeTi-CeCCM recorded a high DEET degradation and mineralization with efficient O3(aq) utilization of 1.4 g O3(aq) g−1 TOC removal. The CeTi-CeCCM also exhibited a high antifouling property in the hybrid process by retaining >92% of its initial permeability after 0.5-h operation with humic acid feed. The stability and robustness of the as-fabricated CCM were also tested with multiple filtration-cleaning cycles and using real water feed, respectively. The reactive oxygen species (ROS) quenching and radical detection experiments were conducted to determine the contribution of ROS (i.e. HO[rad], O2[rad]− and 1O2) towards the catalytic activity. The degradation pathways of DEET were proposed and the ecotoxicity of its transformation products (TPs) was estimated. Finally, the mechanistic insights of the O3(aq) decomposition, organic pollutants degradation and mineralization by the CeTi-CeCCM were provided to address the synergistic effect of the membrane filtration and catalytic ozonation occurred in the hybrid process.Ministry of Education (MOE)Nanyang Technological UniversityThis work was supported by the Ministry of Education (MOE), Singapore [RG96/16 Academic Research Grant]. W.J. Lee would like to thank Nanyang Technological University, Singapore for his PhD research scholarship

Developing Better Ceramic Membranes for Water and Wastewater Treatment: Where Microstructure Integrates with Chemistry

Chemical Engineering Journa

One-step construction of heterostructured metal-organics@Bi2O3 with improved photoinduced charge transfer and enhanced activity in photocatalytic degradation of sulfamethoxazole under solar light irradiation

A facile one-step assembly method was developed for the preparation of metal-organics @Bi2O3 composites for photocatalysis. Two kinds of metal-organics (Ti-bdc and Cu-btc)@Bi2O3 composites were synthesized via the coordination of btc3-/bdc2- and metal ions (Ti4+/Cu2+) as well as OH on the surface of Bi2O3. Compared with pure Bi2O3, Ti-bdc@Bi2O3 shows a 1.7 times higher photocatalytic activity in the degradation of sulfamethoxazole (SMX) under a simulated solar irradiation with a cumulative removal of 62% within 60 min. The high photocatalytic activity could be attributed to the high charge separation, enhanced electron transfer as well as the low recombination rate of photo-generated electrons and holes due to the construction of hetero-structures. The stability test showed that Ti-bdc@Bi2O3 is more stable in water than Cu-btc@Bi2O3. Furthermore, through the radical-trapping experiments and main intermediates detection, it is demonstrated that the photo-generated holes as well as the OH and O2- formed dominate the photocatalytic decomposition of SMX. These findings demonstrate the potential usage of a facile method to synthesize metal-organics and metal oxides composites, some of which possess high water stability and thus could be employed for water treatment