Displaying publications 1 - 20 of 33 in total

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  1. Fenton degradation of ofloxacin antibiotic using calcium alginate beads impregnated with Fe3O4-montmorillonite composite
    Ahmad ARD, Imam SS, Adnan R, Oh WD, Abdul Latip AF, Ahmad AAD
    Int J Biol Macromol, 2023 Feb 28;229:838-848.
    PMID: 36586654 DOI: 10.1016/j.ijbiomac.2022.12.287
    The primary aim of this study is to develop an economical, stable, and effective heterogeneous catalyst for wastewater remediation via the Fenton oxidation process. For this purpose, Fe3O4-montmorillonite alginate (FeMA) composite beads were synthesized by entrapping Fe3O4-montmorillonite in calcium alginate beads. The performance of the catalysts was evaluated via the Fenton degradation of ofloxacin (OFL), an antibiotic that is frequently detected in water bodies. The physiochemical properties of the FeMA composite beads were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope/energy dispersive X-ray (FESEM/EDX), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). FeMA composite beads were found to have a higher surface area, higher porosity, and better thermal stability compared to pristine alginate beads. The composite beads were subsequently used for Fenton degradation of ofloxacin (OFL) in an aqueous solution. The effects of Fe3O4-montmorillonite loading on alginate, FeMA composite beads dosage, initial solution pH, initial OFL concentration, different oxidants, H2O2 dosage, reaction temperature, and inorganic salts on Fenton degradation of OFL in aqueous solution was investigated. The results revealed that the percentage of OFL degradation reached about 80 % under optimized conditions, while the total organic carbon (TOC) removal reached about 53 %. The entrapment of Fe3O4-montmorillonite in alginate beads results in less iron ions leaching compared to previous observation, and the efficiency remains constant over the five cycles investigated. The kinetics of the Fenton degradation process are best fitted to the pseudo-first-order kinetic model. It is therefore believed that FeMA composite beads can be a promising material for wastewater remediation via the Fenton oxidation process.
  2. Elucidation of stoichiometric efficiency, radical generation and transformation pathway during catalytic oxidation of sulfamethoxazole via peroxymonosulfate activation
    Bao Y, Oh WD, Lim TT, Wang R, Webster RD, Hu X
    Water Res, 2019 03 15;151:64-74.
    PMID: 30594091 DOI: 10.1016/j.watres.2018.12.007
    In this work, nano-bimetallic Co/Fe oxides with different stoichiometric Co/Fe ratios were prepared using a novel one-step solution combustion method. The nano-bimetallic Co/Fe oxides were used for sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation. The stoichiometric efficiencies of the as-prepared nano-bimetallic catalysts were calculated and compared for the first time. The radical generation was identified by electron paramagnetic resonance (EPR) as well as chemical quenching experiments, in which different scavengers were used and compared. The catalytic PMS activation mechanism in the presence of catalyst was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that besides SO4•- and •OH, •OOH was also detected in the PMS/CoFeO2.5 system. Meanwhile, in addition to the previously proposed radical oxidation pathway, the results showed that SMX degradation also involved a non-radical oxidation, which could be verified by the degradation experiment without catalyst as well as the detection of 1O2. In the PMS activation process, cobalt functioned as the active site on CoFeO2.5 while Fe oxide functioned as the adsorption site. The electron transfer mechanism was proposed based on the XPS and metal leaching results. Additionally, via the detection of transformation products, different SMX transformation pathways involving nitration, hydroxylation and hydrolysis in the PMS/CoFeO2.5 system were proposed.
  3. Fulltext Analysis of chemical compositions and larvicidal activity of nut extracts from Areca catechu Linn against Aedes (Diptera: Culicidae)
    Bharathithasan M, Ravindran DR, Rajendran D, Chun SK, Abbas SA, Sugathan S, et al.
    PLoS One, 2021;16(11):e0260281.
    PMID: 34843539 DOI: 10.1371/journal.pone.0260281
    BACKGROUND: There is a growing need to use green alternative larvicidal control for Aedes larvae compared to chemical insecticides. Substantial reliance on chemical insecticides caused insecticide resistance in mosquito populations. Thus, research for alternate chemical compounds from natural products is necessary to control Aedes larvae. This study explores the analysis of chemical compositions from Areca catechu nut as a potential larvicide for Aedes (Diptera: Culicidae).

    METHODS: The Areca catechu nut collected from Ipoh, Perak, Malaysia was grounded into powder and used for Soxhlet extraction. The chemical analysis of the extracts and their structures were identified using the GCMS-QP2010 Ultra (Shimadzu) system. National Institute of Standards and Technology (NIST) Chemistry WebBook, Standard Reference Database 69 (https://webbook.nist.gov/chemistry/) and PubChem (https://pubchem.ncbi.nlm.nih.gov/), the two databases used to retrieve the synonyms, molecular formula, molecular weight, and 2-dimensional (2D) structure of chemical compounds. Next, following WHO procedures for larval bioassays, the extracts were used to asses larvicidal activity against early 4th instar larvae of Aedes aegypti and Aedes albopictus.

    RESULTS: The larvicidal activities were observed against early 4th stage larvae with different concentrations in the range from 200 mg/L to 1600 mg/L. The LC50 and LC95 of Aedes aegypti were 621 mg/L and 2264 mg/L respectively; whereas the LC50 and LC95 of Aedes albopictus were 636 mg/L and 2268 mg/L respectively. Mortality was not observed in the non-target organism test. The analysis using gas chromatography and mass spectrometer recovered several chemical compounds such as Arecaidine, Dodecanoic acid, Methyl tetradecanoate, Tetradecanoic acid , and n-Hexadecanoic acid bioactive components. These chemical constituents were used as additive formulations in pesticides, pest control, insect repellent, and insecticidal agents.

    CONCLUSIONS: Our study showed significant outcomes from the extract of Areca catechu nut and it deserves further investigation in relation to chemical components and larvicidal actions between different species of Aedes mosquitoes. Even though all these findings are fundamental, it may have some interesting potentials to be developed as natural bio-larvicidal products.

  4. A novel real-time monitoring and control system for waste-to-energy gasification process employing differential temperature profiling of a downdraft gasifier
    Chan WP, Veksha A, Lei J, Oh WD, Dou X, Giannis A, et al.
    J Environ Manage, 2019 Mar 15;234:65-74.
    PMID: 30616190 DOI: 10.1016/j.jenvman.2018.12.107
    A novel, cost-effective and real-time process monitoring and control system was developed to maintain stable operation of waste-to-energy gasification process. It comprised a feedback loop control that utilized the differential temperatures of the oxidation and reduction zones in the gasifier to determine the regional heat-flow (endothermic or exothermic), to assess the availability of oxidizing agent (for instance, air or O2) at the char bed and to calculate the fuel feeding rate. Based on the correlations developed, the air-to-fuel ratio or the equivalence air ratio (ER) for air gasification could be instantaneously adjusted to maintain stable operation of the gasifier. This study demonstrated a simplification of complex reaction dynamics in the gasification process to differential temperature profiling of the gasifier. The monitoring and control system was tested for more than 70 h of continuous operation in a downdraft fixed-bed gasifier with refuse-derived fuel (RDF) prepared from municipal solid wastes (MSW). With the system, fuel feeding rate could be adjusted accurately to stabilize the operating temperature and ER in the gasifier and generate syngas with consistent properties. Significant reductions in the fluctuations of temperature profiles at oxidation and reduction zones (from higher than 100 °C to lower than 50 °C), differential temperatures (from ±200 to ±50 °C) in gasifier and the flow rate (from 16 ± 6.5 to 12 ± 1.8 L/min), composition of main gas components, LHV (from 6.2 ± 3.1 to 5.7 ± 1.6 MJ/Nm3) and tar content (from 8.0 ± 9.7 to 7.5 ± 4.2 g/Nm3) of syngas were demonstrated. The developed gasifier monitoring and control system is adaptable to various types (updraft, downdraft, and fluidized-bed) and scales (lab, pilot, large scale) of gasifiers with different types of fuel.
  5. Multi-heteroatom-doped carbocatalyst as peroxymonosulfate and peroxydisulfate activator for water purification: A critical review
    Choong ZY, Lin KA, Lisak G, Lim TT, Oh WD
    J Hazard Mater, 2022 03 15;426:128077.
    PMID: 34953256 DOI: 10.1016/j.jhazmat.2021.128077
    Catalytic activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) (or collectively known as persulfate, PS) using carbocatalyst is increasingly gaining attention as a promising technology for sustainable recalcitrant pollutant removal in water. Single heteroatom doping using either N, S, B or P is widely used to enhance the performance of the carbocatalyst for PS activation. However, the performance enhancement from single heteroatom doping is limited by the type of heteroatom used. To further enhance the performance of the carbocatalyst beyond the limit of single heteroatom doping, multi-heteroatom doping can be conducted. This review aims to provide a state-of-the-art overview on the development of multi-heteroatom-doped carbocatalyst for PS activation. The potential synergistic and antagonistic interactions of various heteroatoms including N and B, N and S, N and P, and N and halogen for PS activation are evaluated. Thereafter, the preparation strategies to develop multi-heteroatom-doped carbocatalyst including one-step and multi-step preparation approaches along with the characterization techniques are discussed. Evidence and summary of the performance of multi-heteroatom-doped carbocatalyst for various recalcitrant pollutants removal via PS activation are also provided. Finally, the prospects of employing multi-heteroatom-doped carbocatalyst including the need to study the correlation between different heteroatom combination, surface moiety type, and amount of dopant with the PS activation mechanism, identifying the best heteroatom combination, improving the durability of the carbocatalyst, evaluating the feasibility for full-scale application, developing low-cost multi-heteroatom-doped carbocatalyst, and assessing the environmental impact are also briefly discussed.
  6. Hollow-Structured N-doped carbon-embedded CoFe NanoAlloy for boosting activation of Monopersulfate: Engineered interface and heteroatom Doping-Induced enhancements
    Doan Trang T, Lee J, Oh WD, Kwon E, Wang H, Fai Tsang Y, et al.
    J Colloid Interface Sci, 2023 Dec 15;652(Pt A):1028-1042.
    PMID: 37639925 DOI: 10.1016/j.jcis.2023.08.091
    While transition metals are useful for activating monopersulfate (MPS) to degrade contaminants, bimetallic alloys exhibit stronger catalytic activities owing to several favorable effects. Therefore, even though Co is an efficient metal for MPS activation, CoFe alloys are even more promising heterogeneous catalysts for MPS activation. Immobilization/embedment of CoFe alloy nanoparticles (NPs) onto hetero-atom-doped carbon matrices appears as a practical strategy for evenly dispersing CoFe NPs and enhancing catalytic activities via interfacial synergies between CoFe and carbon. Herein, N-doped carbon-embedded CoFe alloy (NCCF) is fabricated here to exhibit a unique hollow-engineered nanostructure and the composition of CoFe alloy by using Co-ZIF as a precursor after the facile etching and Fe doping. The Fe dopant embeds CoFe alloy NPs into the hollow-structured N-doped carbon substrate, enabling NCCF to possess the higher mesoscale porosity, active N species as well as more superior electrochemical properties than its analogue without Fe dopants, carbon matrix-supported cobalt (NCCo). Thus, NCCF exhibits a considerably larger activity than NCCo and the benchmark catalyst, Co3O4 NP, for MPS activation to degrade an environmental hormone, dihydroxydiphenyl ketone (DHPK). Besides, NCCF + MPS shows an even lower activation energy for DHPK degradation than literatures, and retains its high efficiency for eliminating DHPK in different water media. DHPK degradation pathway and ecotoxicity assessment are unraveled based on the insights from the computational chemistry, demonstrating that DHPK degradation by NCCF + MPS did not result in the formation of toxic and highly toxic by-products. These features make NCCF a promising heterogeneous catalyst for MPS activation to degrade DHPK.
  7. Can biochar and hydrochar be used as sustainable catalyst for persulfate activation?
    Gasim MF, Lim JW, Low SC, Lin KA, Oh WD
    Chemosphere, 2022 Jan;287(Pt 4):132458.
    PMID: 34610377 DOI: 10.1016/j.chemosphere.2021.132458
    Over the past decade, there has been a surge of interest in using char (hydrochar or biochar) derived from biomass as persulfate (PS, either peroxymonosulfate or peroxydisulfate) activator for anthropogenic pollutants removal. While extensive investigation showed that char could be used as a PS activator, its sustainability over prolonged application is equivocal. This review provides an assessment of the knowledge gap related to the sustainability of char as a PS activator. The desirable char properties for PS activation are identified, include the high specific surface area and favorable surface chemistry. Various synthesis strategies to obtain the desirable properties during biomass pre-treatment, hydrochar and biochar synthesis, and char post-treatment are discussed. Thereafter, factors related to the sustainability of employing char as a PS activator for anthropogenic pollutants removal are critically evaluated. Among the critical factors include performance uncertainty, competing adsorption process, char stability during PS activation, biomass precursor variation, scalability, and toxic components in char. Finally, some potential research directions are provided. Fulfilling the sustainability factors will provide opportunity to employ char as an economical and efficient catalyst for sustainable environmental remediation.
  8. Importance of carbon structure for nitrogen and sulfur co-doping to promote superior ciprofloxacin removal via peroxymonosulfate activation
    Gasim MF, Veksha A, Lisak G, Low SC, Hamidon TS, Hussin MH, et al.
    J Colloid Interface Sci, 2023 Mar 15;634:586-600.
    PMID: 36549207 DOI: 10.1016/j.jcis.2022.12.072
    Herein, five N, S-co-doped carbocatalysts were prepared from different carbonaceous precursors, namely sawdust (SD), biochar (BC), carbon-nanotubes (CNTs), graphite (GP), and graphene oxide (GO) and compared. Generally, as the graphitization degree increased, the extent of N and S doping decreased, graphitic N configuration is preferred, and S configuration is unaltered. As peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) removal, the catalytic performance was in order: NS-CNTs (0.037 min-1) > NS-BC (0.032 min-1) > NS-rGO (0.024 min-1) > NS-SD (0.010 min-1) > NS-GP (0.006 min-1), with the carbonaceous properties, rather than the heteroatoms content and textural properties, being the major factor affecting the catalytic performance. NS-CNTs was found to have the supreme catalytic activity due to its remarkable conductivity (3.38 S m-1) and defective sites (ID/IG = 1.28) with high anti-interference effect against organic and inorganic matter and varying water matrixes. The PMS activation pathway was dominated by singlet oxygen (1O2) generation and electron transfer regime between CIP and PMS activated complexes. The CIP degradation intermediates were identified, and a degradation pathway is proposed. Overall, this study provides a better understanding of the importance of selecting a suitable carbonaceous platform for heteroatoms doping to produce superior PMS activator for antibiotics decontamination.
  9. Effect of metal doping (Me = Zn, Cu, Co, Mn) on the performance of bismuth ferrite as peroxymonosulfate activator for ciprofloxacin removal
    Koo PL, Choong ZY, He C, Bao Y, Jaafar NF, Oh WD
    Chemosphere, 2023 Mar;318:137915.
    PMID: 36702411 DOI: 10.1016/j.chemosphere.2023.137915
    In this study, a facile hydrothermal method was employed to prepare Me-doped Bi2Fe4O9 (Me = Zn, Cu, Co, and Mn) as peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) degradation. The characteristics of the Me-doped bismuth ferrites were investigated using various characterization instruments including SEM, TEM, FTIR and porosimeter indicating that the Me-doped Bi2Fe4O9 with nanosheet-like square orthorhombic structure was successfully obtained. The catalytic activity of various Me-doped Bi2Fe4O9 was compared and the results indicated that the Cu-doped Bi2Fe4O9 at 0.08 wt.% (denoted as BFCuO-0.08) possessed the greatest catalytic activity (kapp = 0.085 min-1) over other Me-doped Bi2Fe4O9 under the same condition. The synergistic interaction between Cu, Fe and oxygen vacancies are the key factors which enhanced the performance of Me-doped Bi2Fe4O9. The effects of catalyst loading, PMS dosage, and pH on CIP degradation were also investigated indicating that the performance increased with increasing catalyst loading, PMS dosage, and pH. Meanwhile, the dominant reactive oxygen species was identified using the chemical scavengers with SO4•-, •OH, and 1O2 playing a major role in CIP degradation. The performance of BFCuO-0.08 deteriorated in real water matrix (tap water, river water and secondary effluent) due to the presence of various water matrix species. Nevertheless, the BFCuO-0.08 catalyst possessed remarkable stability and can be reused for at least four successive cycles with >70% of CIP degradation efficiency indicating that it is a promising catalyst for antibiotics removal.
  10. Palatability of black soldier fly larvae in valorizing mixed waste coconut endosperm and soybean curd residue into larval lipid and protein sources
    Lim JW, Mohd-Noor SN, Wong CY, Lam MK, Goh PS, Beniers JJA, et al.
    J Environ Manage, 2019 Feb 01;231:129-136.
    PMID: 30340132 DOI: 10.1016/j.jenvman.2018.10.022
    The black soldier fly larvae (BSFL) have been widely extolled for the application in managing various solid organic wastes. Owing to the saprophagous nature of BSFL, a rapid valorization of solid organic wastes can be accomplished with the simultaneous production of valuable biochemical compounds derived from larval biomass. In the present works, the mixed waste coconut endosperm (w-CE) and soybean curd residue (SC-r) substrates with increasing protein nutritional constituent were administered to BSFL. The correlations between protein from larval feed substrates and nutritional profiles of BSFL biomasses were ultimately unveiled. The protein from larval feed substrates could be increased by increasing of SC-r portion against w-CE. At the w-CE:SC-r ratio of 3:2, the highest larval total weight gained and growth rate were attained; indicating an optimum protein nutritional constituent in mixed organics (12.4%) that could enhance the BSFL palatability. Further increment of protein nutritional constituent in mixed organics was found acidifying the residual larval feed substrate progressively, undermining the growth of BSFL. By feeding the BSFL with optimum mixed organics, the maximum accumulations of larval lipid and protein could be achieved. Transesterification of extracted lipid had demonstrated high in monounsaturated fatty acids (73%) which was suitable for biodiesel. The BSFL palatability was finally confirmed from the bioconversion viewpoint of mixed organic wastes. Again, achieving the highest bioconversion efficiency of 14% into larval biomass after accounting the metabolic loss of 54%. Therefore, a total of 68% of mixed w-CE and SC-r could be successfully bioconverted.
  11. Hierarchical ZIF-decorated nanoflower-covered 3-dimensional foam for enhanced catalytic reduction of nitrogen-containing contaminants
    Lin JY, Lee J, Oh WD, Kwon E, Tsai YC, Lisak G, et al.
    J Colloid Interface Sci, 2021 Nov 15;602:95-104.
    PMID: 34118608 DOI: 10.1016/j.jcis.2021.05.098
    Metal Organic Frameworks (MOFs) represent a promising class of metallic catalysts for reduction of nitrogen-containing contaminants (NCCs), such as 4-nitrophenol (4-NP). Nevertheless, most researches involving MOFs for 4-NP reduction employ noble metals in the form of fine powders, making these powdered noble metal-based MOFs impractical and inconvenient for realistic applications. Thus, it would be critical to develop non-noble-metal MOFs which can be incorporated into macroscale and porous supports for convenient applications. Herein, the present study proposes to develop a composite material which combines advantageous features of macroscale/porous supports, and nanoscale functionality of MOFs. In particular, copper foam (CF) is selected as a macroscale porous medium, which is covered by nanoflower-structured CoO to increase surfaces for growing a cobaltic MOF, ZIF-67. The resultant composite comprises of CF covered by CoO nanoflowers decorated with ZIF-67 to form a hierarchical 3D-structured catalyst, enabling this ZIF-67@Cu foam (ZIF@CF) a promising catalyst for reducing 4-NP, and other NCCs. Thus, ZIF@CF can readily reduce 4-NP to 4-AP with a significantly lower Ea of 20 kJ/mol than reported values. ZIF@CF could be reused over 10 cycles and remain highly effective for 4-NP reduction. ZIF@CF also efficiently reduces other NCCs, such as 2-nitrophenol, 3-nitrophenol, methylene blue, and methyl orange. ZIF@CF can be adopted as catalytic filters to enable filtration-type reduction of NCCs by passing NCC solutions through ZIF@CF to promptly and conveniently reduce NCCs. The versatile and advantageous catalytic activity of ZIF@CF validates that ZIF@CF is a promising and practical heterogeneous catalyst for reductive treatments of NCCs.
  12. Aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran using manganese dioxide with different crystal structures: A comparative study
    Lin KA, Oh WD, Zheng MW, Kwon E, Lee J, Lin JY, et al.
    J Colloid Interface Sci, 2021 Jun 15;592:416-429.
    PMID: 33691223 DOI: 10.1016/j.jcis.2021.02.030
    Aerobic oxidation of 5-Hydroxymethylfurfural (HMF) to 2,5-Diformylfuran (DFF) using O2 gas represents a sustainable approach for valorization of lignocellulosic compounds. As manganese dioxide (MnO2) is validated as a useful oxidation catalyst and many crystalline forms of MnO2 exist, it is critical to explore how the crystalline structures of MnO2 influence their physical/chemical properties, which, in turn, determine catalytic activities of MnO2 crystals for HMF oxidation to DFF. In particular, six MnO2 crystals, α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, ε-MnO2, and λ-MnO2 are prepared and investigated for their catalytic activities for HMF oxidation to DFF. With different morphologies and crystalline structures, these MnO2 crystals possess very distinct surficial chemistry, redox capabilities, and textural properties, making these MnO2 exhibit different catalytic activities towards HMF conversion. Especially, β-MnO2 can produce much higher DFF per surface area than other MnO2 crystals. β-MnO2 could achieve the highest CHMF = 99% and YDFF = 97%, which are much higher than the reported values in literature, possibly because the surficial reactivity of β-MnO2 appears to be highest in comparison to other MnO2 crystals. Especially, β-MnO2 could exhibit YDFF > 90% over 5 cycles of reusability test, and maintain its crystalline structure, revealing its advantageous feature for aerobic oxidation of HMF to DFF. Through this study, the relationship between morphology, surface chemistry, and catalytic activity of MnO2 with different crystal forms is elucidated for providing scientific insights into design, application and development of MnO2-based materials for aerobic oxidation of bio-derived molecules to value-added products.
  13. Co3O4 nanocube-decorated nitrogen-doped carbon foam as an enhanced 3-dimensional hierarchical catalyst for activating Oxone to degrade sulfosalicylic acid
    Lin XR, Kwon E, Hung C, Huang CW, Oh WD, Lin KA
    J Colloid Interface Sci, 2021 Feb 15;584:749-759.
    PMID: 33176929 DOI: 10.1016/j.jcis.2020.09.104
    As sulfosalicylic acid (SUA) is extensively used as a pharmaceutical product, discharge of SUA into the environment becomes an emerging environmental issue because of its low bio-degradability. Thus, SO4--based advanced oxidation processes have been proposed for degrading SUA because of many advantages of SO4-. As Oxone represents a dominant reagent for producing SO4-, and Co is the most capable metal for activating Oxone to generate SO4-, it is critical to develop an effective but easy-to-use Co-based catalysts for Oxone activation to degrade SUA. Herein, a 3D hierarchical catalyst is specially created by decorating Co3O4 nanocubes (NCs) on macroscale nitrogen-doped carbon form (NCF). This Co3O4-decorated NCF (CONCF) is free-standing, macroscale and even squeezable to exhibit interesting and versatile features. More importantly, CONCF consists of Co3O4 NCs evenly distributed on NCF without aggregation. The NCF not only serves as a support for Co3O4 NCs but also offers additional active sites to synergistically enhance catalytic activities towards Oxone activation. Therefore, CONCF exhibits a higher catalytic activity than the conventional Co3O4 nanoparticles for activating Oxone to fully eliminate SUA in 30 min with a rate constant of 0.142 min-1. CONCF exhibits a much lower Ea value of SUA degradation (35.2 kJ/mol) than reported values, and stable catalytic activities over multi-cyclic degradation of SUA. The mechanism of SUA degradation is also explored, and degradation intermediates of SUA degradation are identified to provide a possible pathway of SUA degradation. These features validate that CONCF is certainly a promising 3D hierarchical catalyst for enhanced Oxone activation to degrade SUA. The findings obtained here are also insightful to develop efficient heterogeneous Oxone-activating catalysts for eliminating emerging contaminants.
  14. Recent advances in catalyst design, performance, and challenges of metal-heteroatom-co-doped biochar as peroxymonosulfate activator for environmental remediation
    Manickavasagam G, He C, Lin KA, Saaid M, Oh WD
    Environ Res, 2024 Apr 16;252(Pt 2):118919.
    PMID: 38631468 DOI: 10.1016/j.envres.2024.118919
    The escalation of global water pollution due to emerging pollutants has gained significant attention. To address this issue, catalytic peroxymonosulfate (PMS) activation technology has emerged as a promising treatment approach for effectively decontaminating a wide range of pollutants. Recently, modified biochar has become an increasingly attractive as PMS activator. Metal-heteroatom-co-doped biochar (MH-BC) has emerged as a promising catalyst that can provide enhanced performance over heteroatom-doped and metal-doped biochar due to the synergism between metal and heteroatom in promoting PMS activation. Therefore, this review aims to discuss the fabrication pathways (i.e., internal vs external doping and pre-vs post-modification) and key parameters (i.e., source of precursors, synthesis methods, and synthesis conditions) affecting the performance of MH-BC as PMS activator. Subsequently, an overview of all the possible PMS activation pathways by MH-BC is provided. Subsequently, Also, the detection, identification, and quantification of several reactive species (such as, •OH, SO4•-, O2•-, 1O2, and high valent oxo species) generated in the catalytic PMS system by MH-BC are also evaluated. Lastly, the underlying challenges associated with poor stability, the lack of understanding regarding the interaction between metal and heteroatom during PMS activation and quantification of radicals in multi-ROS system are also deliberated.
  15. Accelerated sunlight photocatalysis through improved electron mobility between g-C3N4 and BiPO4 nanomaterial
    Ng JJ, Sim LC, Oh WD, Saravanan P, Tan B, Leong KH
    Environ Sci Pollut Res Int, 2022 Dec;29(57):86068-86076.
    PMID: 34523092 DOI: 10.1007/s11356-021-16449-y
    Herein, we report a detailed study on creating heterojunction between graphitic carbon nitride (g-C3N4) and bismuth phosphate (BiPO4), enhancing the unpaired free electron mobility. This leads to an accelerated photocatalysis of 2,4-dichlorophenols (2,4-DCPs) under sunlight irradiation. The heterojunction formation was efficaciously conducted via a modest thermal deposition technique. The function of g-C3N4 plays a significant role in generating free electrons under sunlight irradiation. Together, the generated electrons at the g-C3N4 conduction band (CB) are transferred and trapped by the BiPO4 to form active superoxide anion radicals (•O2-). These active radicals will be accountable for the photodegradation of 2,4-DCPs. The synthesized composite characteristics were methodically examined through several chemical and physical studies. Due to the inimitable features of both g-C3N4 and BiPO4, its heterojunction formation, 2.5wt% BiPO4/g-C3N4 achieved complete 2,4-DCP removal (100%) in 90 min under sunlight irradiation. This is due to the presence of g-C3N4 that enhanced electron mobility through the formation of heterojunctions that lengthens the electron-hole pairs' lifetime and maximizes the entire solar spectrum absorption to generate active electrons at the g-C3N4 conduction band. Thus, this formation significantly draws the attention for future environmental remediation, especially in enhancing the entire solar spectrum's harvesting.
  16. Metal-complexed covalent organic frameworks derived N-doped carbon nanobubble-embedded cobalt nanoparticle as a magnetic and efficient catalyst for oxone activation
    Nguyen HT, Lee J, Kwon E, Lisak G, Thanh BX, Oh WD, et al.
    J Colloid Interface Sci, 2021 Jun;591:161-172.
    PMID: 33601102 DOI: 10.1016/j.jcis.2021.01.108
    While Cobalt nanoparticles (Co NPs) are useful for catalytic Oxone activation, it is more advantageous to embed/immobilize Co NPs on nitrogen-doped carbon substrates to provide synergy for enhancing catalytic performance. Herein, this study proposes to fabricate such a composite by utilizing covalent organic frameworks (COF) as a precursor. Through complexation of COF with Co, a stable product of Co-complexed COF (Co-COF) can be synthesized. This Co-COF is further converted through pyrolysis to N-doped carbon in which cobaltic NPs are embedded. Owing to its well-defined structures of Co-COF, the pyrolysis process transforms COF into N-doped carbon with a bubble-like morphology. Such Co NP-embedded N-doped carbon nanobubbles (CoCNB) with pores, magnetism and Co, shall be a promising catalyst. Thus, CoCNB shows a much stronger catalytic activity than commercial Co3O4 NPs to activate Oxone to degrade toxic Amaranth dye (AMD). CoCNB-activated Oxone also achieves a significantly lower Ea value of AMD degradation (i.e., 27.9 kJ/mol) than reported Ea values in previous literatures. Besides, CoCNB is still effective for complete elimination of AMD in the presence of high-concentration NaCl and surfactants, and CoCNB is also reusable over five consecutive cycles.
  17. Kinetic modeling of bioregeneration of chlorophenol-loaded granular activated carbon in simultaneous adsorption and biodegradation processes
    Oh WD, Lim PE, Seng CE, Sujari AN
    Bioresour Technol, 2012 Jun;114:179-87.
    PMID: 22503192 DOI: 10.1016/j.biortech.2012.03.065
    A kinetic model incorporating adsorption, desorption and biodegradation processes was developed to describe the bioregeneration of granular activated carbon (GAC) loaded with 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, in simultaneous adsorption and biodegradation processes. The model was numerically solved and the results showed that the kinetic model was well-fitted (R(2)>0.83) to the experimental data at different GAC dosages and at various initial 4-CP and 2,4-DCP concentrations. The rate of bioregeneration in simultaneous adsorption and biodegradation processes was influenced by the ratio of initial chlorophenol concentration to GAC dosage. Enhancement in the rate of bioregeneration was achieved by using the lowest ratio under either one of the following experimental conditions: (1) increasing initial chlorophenol concentration at constant GAC dosage and (2) increasing GAC dosage at constant initial chlorophenol concentration. It was found that the rate enhancement was more pronounced under the second experimental condition.
  18. Bioregeneration of granular activated carbon in simultaneous adsorption and biodegradation of chlorophenols
    Oh WD, Lim PE, Seng CE, Sujari AN
    Bioresour Technol, 2011 Oct;102(20):9497-502.
    PMID: 21871793 DOI: 10.1016/j.biortech.2011.07.107
    The objectives of this study are to obtain the time courses of the amount of chlorophenol adsorbed onto granular activated carbon (GAC) in the simultaneous adsorption and biodegradation processes involving 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, and to quantify the bioregeneration efficiency of GAC loaded with 4-CP and 2,4-DCP by direct measurement of the amount of chlorophenol adsorbed onto GAC. Under abiotic and biotic conditions, the time courses of the amount of chlorophenol adsorbed onto GAC at various GAC dosages for the initial 4-CP and 2,4-DCP concentrations below and above the biomass acclimated concentrations of 300 and 150 mg/L, respectively, were determined. The results show that the highest bioregeneration efficiency was achieved provided that the initial adsorbate concentration was lower than the acclimated concentration. When the initial adsorbate concentration was higher than the acclimated concentration, the highest bioregeneration efficiency was achieved if excess adsorbent was used.
  19. Accelerated organics degradation by peroxymonosulfate activated with biochar co-doped with nitrogen and sulfur
    Oh WD, Zaeni JRJ, Lisak G, Lin KA, Leong KH, Choong ZY
    Chemosphere, 2021 Aug;277:130313.
    PMID: 33780679 DOI: 10.1016/j.chemosphere.2021.130313
    Engineered biochar is increasingly regarded as a cost-effective and eco-friendly peroxymonosulfate (PMS) activator. Herein, biochar doped with nitrogen and sulfur moieties was prepared by pyrolysis of wood shavings and doping precursor. The doping precursor consists of either urea, thiourea or 1:1 w/w mixture of urea and thiourea (denoted as NSB-U, NSB-T and NSB-UT, respectively). The physicochemical properties of the NSBs were extensively characterized, revealing that they are of noncrystalline carbon with porous structure. The NSBs were employed as PMS activator to degrade organic pollutants particularly methylene blue (MB). It was found that NSB-UT exhibited higher MB removal rate with kapp = 0.202 min-1 due to its relatively high surface area and favorable intrinsic surface moieties (combination of graphitic N and thiophenic S). The effects of catalyst loading, PMS dosage and initial pH were evaluated. Positive enhancement of the MB removal rate can be obtained by carefully increasing the catalyst loading or PMS dosage. Meanwhile, the MB removal rate is greatly influenced by pH due to electrostatic interactions and pH dependent reactions. The NSB-UT can be reused for several cycles to some extent and its catalytic activity can be restored by thermal treatment. Based on the radical scavenger study and XPS analysis, the nonradical pathway facilitated by the graphitic N and thiophenic S active sites are revealed to be the dominant reaction pathway. Overall, the results of this study show that engineered biochar derived from locally available biowaste can be transformed into PMS activator for environmental applications.
  20. Fulltext Systematic Performance Comparison of Fe3+/Fe0/Peroxymonosulfate and Fe3+/Fe0/Peroxydisulfate Systems for Organics Removal
    Oh WD, Ho YC, Mohamad M, Ho CD, Ravi R, Lim JW
    Materials (Basel), 2021 Sep 14;14(18).
    PMID: 34576510 DOI: 10.3390/ma14185284
    Activated zero-valent iron (Ac-ZVI) coupled with Fe3+ was employed to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) for acid orange 7 (AO7) removal. Fe3+ was used to promote Fe2+ liberation from Ac-ZVI as an active species for reactive oxygen species (ROS) generation. The factors affecting AO7 degradation, namely, the Ac-ZVI:Fe3+ ratio, PMS/PDS dosage, and pH, were compared. In both PMS and PDS systems, the AO7 degradation rate increased gradually with increasing Fe3+ concentration at fixed Ac-ZVI loading due to the Fe3+-promoted liberation of Fe2+ from Ac-ZVI. The AO7 degradation rate increased with increasing PMS/PDS dosage due to the greater amount of ROS generated. The degradation rate in the PDS system decreased while the degradation rate in the PMS system increased with increasing pH due to the difference in the PDS and PMS activation mechanisms. On the basis of the radical scavenging study, sulfate radical was identified as the dominant ROS in both systems. The physicochemical properties of pristine and used Ac-ZVI were characterized, indicating that the used Ac-ZVI had an increased BET specific surface area due to the formation of Fe2O3 nanoparticles during PMS/PDS activation. Nevertheless, both systems displayed good reusability and stability for at least three cycles, indicating that the systems are promising for pollutant removal.
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