MyMedR

Displaying publications 21 - 40 of 114 in total

Abstract:

Sort:

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.
Solubility of ionic surfactants below their Krafft point in mixed micellar solutions: Phase diagrams for methyl ester sulfonates and nonionic cosurfactants

Danov KD, Stanimirova RD, Kralchevsky PA, Slavova TG, Yavrukova VI, Ung YW, et al.

J Colloid Interface Sci, 2021 Nov;601:474-485.
PMID: 34090025 DOI: 10.1016/j.jcis.2021.05.147

HYPOTHESIS: Many ionic surfactants with wide applications in personal-care and house-hold detergency show limited water solubility at lower temperatures (Krafft point). This drawback can be overcome by using mixed solutions, where the ionic surfactant is incorporated in mixed micelles with another surfactant, which is soluble at lower temperatures.
EXPERIMENTS: The solubility and electrolytic conductivity for a binary surfactant mixture of anionic methyl ester sulfonates (MES) with nonionic alkyl polyglucoside and alkyl polyoxyethylene ether at 5 °C during long-term storage were measured. Phase diagrams were established; a general theoretical model for their explanation was developed and checked experimentally.
FINDINGS: The binary and ternary phase diagrams for studied surfactant mixtures include phase domains: mixed micelles; micelles + crystallites; crystallites, and molecular solution. The proposed general methodology, which utilizes the equations of molecular thermodynamics at minimum number of experimental measurements, is convenient for construction of such phase diagrams. The results could increase the range of applicability of MES-surfactants with relatively high Krafft temperature, but with various useful properties such as excellent biodegradability and skin compatibility; stability in hard water; good wetting and cleaning performance.
Low Frequency Dielectric and Optical Behavior on Physicochemical Properties of Hydroxyapatite/Cornstarch Composite

Beh CY, Cheng EM, Mohd Nasir NF, Khor SF, Eng SK, Abdul Majid MS, et al.

J Colloid Interface Sci, 2021 Oct 15;600:187-198.
PMID: 34015511 DOI: 10.1016/j.jcis.2021.03.158

An investigation on relationship among the physicochemical, optical and dielectric properties of the hydroxyapatite/cornstarch (HA/Cs) composites with the starch proportion of 30, 40, 50, 60, 70, 80 and 90 wt% is presented in this work. The HA/Cs composites have been characterized via FTIR, XRD, DRS and impedance analyzer. This work depicts that the strong interaction is exhibited between the hydroxyapatite nanoparticles and starch as the starch proportion increases. This increment trend results in the higher crystallinity of the HA/Cs composites. The highly crystallized HA/Cs with hydroxyapatite nucleation center presents low optical properties (diffuse reflectance and optical band gap energy). The HA/Cs composite with 80 wt% starch proportion (H2C8) show higher dielectric properties (dielectric constant, loss factor and conductivity) due to the stronger interfacial interaction and close-packed HA/Cs crystalline structure. The relationship among the physicochemical, optical and dielectric properties of the HA/Cs composite is studied in this work for potential of instrumentation design.
Facile one pot preparation of magnetic chitosan-palygorskite nanocomposite for efficient removal of lead from water

Rusmin R, Sarkar B, Mukhopadhyay R, Tsuzuki T, Liu Y, Naidu R

J Colloid Interface Sci, 2021 Sep 22;608(Pt 1):575-587.
PMID: 34628317 DOI: 10.1016/j.jcis.2021.09.109

Development of polymeric magnetic adsorbents is a promising approach to obtain efficient treatment of contaminated water. However, the synthesis of magnetic composites involving multiple components frequently involves tedious preparation steps. In the present study, a magnetic chitosan-palygorskite (MCP) nanocomposite was prepared through a straight-forward one pot synthesis approach to evaluate its lead (Pb2+) removal capacity from aqueous solution. The nano-architectural and physicochemical properties of the newly-developed MCP composite were described via micro- and nano-morphological analyses, and crystallinity, surface porosity and magnetic susceptibility measurements. The MCP nanocomposite was capable to remove up to 58.5 mg Pb2+ g-1 of MCP from water with a good agreement of experimental data to the Langmuir isotherm model (R2 = 0.98). The Pb2+ adsorption process on MCP was a multistep diffusion-controlled phenomenon evidenced by the well-fitting of kinetic adsorption data to the intra-particle diffusion model (R2 = 0.96). Thermodynamic analysis suggested that the adsorption process at low Pb2+ concentration was controlled by chemisorption, whereas that at high Pb2+ concentration was dominated by physical adsorption. X-ray photoelectron and Fourier transform infrared spectroscopy results suggested that the Pb adsorption on MCP was governed by surface complexation and chemical reduction mechanisms. During regeneration, the MCP retained 82% Pb2+ adsorption capacity following four adsorption-desorption cycles with ease to recover the adsorbent using its strong magnetic property. These findings highlight the enhanced structural properties of the easily-prepared nanocomposite which holds outstanding potential to be used as an inexpensive and green adsorbent for remediating Pb2+ contaminated water.
Discrimination of dopamine by an electrode modified with negatively charged manganese dioxide nanoparticles decorated on a poly(3,4 ethylenedioxythiophene)/reduced graphene oxide composite

Promsuwan K, Soleh A, Saisahas K, Saichanapan J, Kanatharana P, Thavarungkul P, et al.

J Colloid Interface Sci, 2021 Sep;597:314-324.
PMID: 33872888 DOI: 10.1016/j.jcis.2021.03.162

A unique nanocomposite was fabricated using negatively charged manganese dioxide nanoparticles, poly (3,4-ethylenedioxythiophene) and reduced graphene oxide (MnO2/PEDOT/rGO). The nanocomposite was deposited on a glassy carbon electrode (GCE) functionalized with amino groups. The modified GCE was used to electrochemically detect dopamine (DA). The surface morphology, charge effect and electrochemical behaviours of the modified GCE were characterized by scanning electron microscopy, energy dispersive X-ray analysis (EDX), cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The MnO2/PEDOT/rGO/GCE exhibited excellent performance towards DA sensing with a linear range between 0.05 and 135 µM with a lowest detection limit of 30 nM (S/N = 3). Selectivity towards DA was high in the presence of high concentrations of the typical interferences ascorbic acid and uric acid. The stability and reproducibility of the electrode were good. The sensor accurately determined DA in human serum. The synergic effect of the multiple components of the fabricated nanocomposite were critical to the good DA sensing performance. rGO provided a conductive backbone, PEDOT directed the uniform growth of MnO2 and adsorbed DA via pi-pi and electrostatic interaction, while the negatively charged MnO2 provided adsorption and catalytic sites for protonated DA. This work produced a promising biosensor that sensitively and selectively detected DA.
Preparation of novel nanostructured WO3/CuMnO2 p-n heterojunction nanocomposite for photoelectrochemical detection of nitrofurazone

Velmurugan S, C-K Yang T, Ching Juan J, Chen JN

J Colloid Interface Sci, 2021 Aug 15;596:108-118.
PMID: 33838324 DOI: 10.1016/j.jcis.2021.03.083

Herein this research, a visible light active tungsten oxide/copper manganate (WO3/CuMnO2) p-n heterojunction nanocomposite was prepared and has been applied for a signal on photoelectrochemical sensing of antibiotic nitrofurazone (NFZ). Firstly, the n-WO3 nanotiles were synthesized from the cetrimonium bromide (CTAB) assisted hydrothermal method and the p-CuMnO2 nanoparticles were synthesized by using the ultrasound-assisted hydrothermal method. The photoelectrochemical NFZ sensing performance of WO3/CuMnO2 nanocomposite was 1.9 times higher than that of as-synthesized pure WO3 nanotiles. The resulting higher photoelectrochemical performance of the nanocomposite is due to more visible light absorption ability and synergy from p-n heterojunction formation. The designed WO3/CuMnO2 nanocomposite sensor gives satisfactory photocurrent signals for the detection of NFZ in the range of 0.015-32 μM with the detection limit (LOD) of 1.19 nM. The practical applicability of the nanocomposite sensor was monitored in pork liver and tap water samples.
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.
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.
In-situ growth of TiO2 imbedded Ti3C2TA nanosheets to construct PCN/Ti3C2TA MXenes 2D/3D heterojunction for efficient solar driven photocatalytic CO2 reduction towards CO and CH4 production

Tahir M, Tahir B

J Colloid Interface Sci, 2021 Jun;591:20-37.
PMID: 33588310 DOI: 10.1016/j.jcis.2021.01.099

Constructing efficient structured materials for artificial photosynthesis of CO2 is a promising strategy to produce renewable fuels in addition of mitigating greenhouse effect. In this work, 2D porous g-C3N4 (PCN) coupled exfoliated 3D Ti3C2TA MXene (TiC) nanosheets with TiO2 NPs in-situ growth was constructed in a single step through HF treatment approach. The different exfoliated TiC structures were successfully synthesized for adjusting HF etching time (24 h, 48 h and 96 h). With growing etchant time from 24 to 96 h, the amount of TiO2 produced was increased, but it has adverse effects on CO and CH4 production rate. The maximum production rates for CO and CH4 of 317.4 and 78.55 µmol g-1 h-1 were attained when the 10TiC-48/PCN was employed than using TiC-24/PCN, TiC-96/PCN and PCN composite samples, respectively. The performance of 10TiC-48/PCN composite for CO and CH4 evolution were 9.9 and 6.7 folds higher than using pristine PCN sample, respectively. The possible mechanism is assigned to porous structure with intimate contact enabling efficient charge carrier separation with the role of TiO2 NPs to work as a bridge to transport electrons towards MXene surface. Among the reducing agents, water was favorable for CO evolution, whereas, methanol-water system promoted CH4 production. All these findings confirm that heterojunction formation facilitates charges separation and can be further used in solar energy relating application.
Sulfur-doped graphitic carbon nitride incorporated bismuth oxychloride/Cobalt based type-II heterojunction as a highly stable material for photoelectrochemical water splitting

Vinoth S, Ong WJ, Pandikumar A

J Colloid Interface Sci, 2021 Jun;591:85-95.
PMID: 33592528 DOI: 10.1016/j.jcis.2021.01.104

Cobalt incorporated sulfur-doped graphitic carbon nitride with bismuth oxychloride (Co/S-gC3N4/BiOCl) heterojunction is prepared by an ultrasonically assisted hydrothermal treatment. The heterojunction materials have employed in photoelectrochemical (PEC) water splitting. The PEC activity and stability of the materials are promoted by constructing an interface between the visible light active semiconductor photocatalyst and cocatalysts. The photocurrent density of Co-9% S-gC3N4/BiOCl has attained 393.0 μA cm-2 at 1.23 V vs. RHE, which is 7-fold larger than BiOCl and ~3-fold higher than 9% S-gC3N4/BiOCl. The enhanced PEC activity can be attributed to the improved electron-hole charge separation and the boosted charge transfer is confirmed by photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) analysis. The fabricated Co/S-gC3N4/BiOCl nanohybrid material has exhibited high stability of up to 10,800 s (3 h) at 1.23 V vs. RHE during PEC water splitting reaction and the obtained photo-conversion efficiency is 3.7-fold greater than S-gC3N4/BiOCl and 17-fold higher than BiOCl. The FESEM and HRTEM images have revealed the formation of heterojunction interface between S-gC3N4 and BiOCl and the elemental mapping has confirmed the presence of cobalt over S-gC3N4/BiOCl. The heterojunction interface has facilitated the photo-excited charge separation and transport across the electrode/electrolyte interface and also the flat-band potential, which is confirmed by Mott-Schottky analysis.
α-Sulfo alkyl ester surfactants: Impact of changing the alkyl chain length on the adsorption, mixing properties and response to electrolytes of the tetradecanoate

Wang Z, Li P, Ma K, Chen Y, Yan Z, Penfold J, et al.

J Colloid Interface Sci, 2021 Mar 15;586:876-890.
PMID: 33309145 DOI: 10.1016/j.jcis.2020.10.122

HYPOTHESIS: The α-sulfo alkyl ester, AES, surfactants are a class of anionic surfactants which have potential for improved sustainable performance in a range of applications, and an important feature is their enhanced tolerance to precipitation in the presence of multivalent counterions. It is proposed that their adsorption properties can be adjusted substantially by changing the length of the shorter alkyl chain, that of the alkanol group in the ester.
EXPERIMENTS: Surface tension and neutron reflectivity have been used to investigate the variation in the adsorption properties with the shorter alkyl chain length (methyl, ethyl and propyl), the impact of NaCl on the adsorption, the tendency to form surface multilayer structures in the presence of AlCl3, and the effects of mixing the methyl ester sulfonate with the ethyl and propyl ester sulfonates on the adsorption.
FINDINGS: The variations in the critical micelle concentration, CMC, the adsorption isotherms, the saturation adsorption values, and the impact of NaCl illustrate the subtle influence of varying the shorter alkyl chain length of the surfactant. The non-ideal mixing of pairs of AES surfactants with different alkanol group lengths of the ester show that the extent of the non-ideality changes as the difference in the alkanol length increases. The surface multilayer formation observed in the presence of AlCl3 varies in a complex manner with the length of the short chain and for mixtures of surfactants with different chains lengths.
Superior photoelectrocatalytic performance of ternary structural BiVO4/GQD/g-C3N4 heterojunction

Samsudin MFR, Ullah H, Tahir AA, Li X, Ng YH, Sufian S

J Colloid Interface Sci, 2021 Mar 15;586:785-796.
PMID: 33198982 DOI: 10.1016/j.jcis.2020.11.003

Herein, we performed an encyclopedic analysis on the photoelectrocatalytic hydrogen production of BiVO4/g-C3N4 decorated with reduced graphene oxide (RGO) or graphene quantum dots (GQDs). The differences between RGO and GQDs as an electron mediator was revealed for the first time in the perspective of theoretical DFT analysis and experimental validation. It was found that the incorporation of GQDs as an electron mediator promotes better photoelectrocatalytic hydrogen performance in comparison to the RGO. The addition of GQD can significantly improve the activity by 25.2 and 75.7% in comparison to the BiVO4/RGO/g-C3N4 and binary composite samples, respectively. Correspondingly, the BiVO4/GQD/g-C3N4 attained the highest photocurrent density of 19.2 mA/cm2 with an ABPE of 0.57% without the presence of any sacrificial reagents. This enhancement is stemming from the low photocharge carrier transfer resistance which was further verified via DFT study. The DFT analysis revealed that the BiVO4/GQD/g-C3N4 sample shared their electronic cloud density through orbital hybridization while the BiVO4/RGO/g-C3N4 sample show less mutual sharing. Additionally, the charge redistribution of the GQDs-composite at the heterostructure interface articulates a more stable and stronger heterojunction than the RGO-composite. Notably, this study provides new insights on the effect of different carbonaceous materials (RGO and GQDs) which are often used as an electron mediator to enhance photocatalytic activity.
CoS2 engulfed ultra-thin S-doped g-C3N4 and its enhanced electrochemical performance in hybrid asymmetric supercapacitor

Vinoth S, Subramani K, Ong WJ, Sathish M, Pandikumar A

J Colloid Interface Sci, 2021 Feb 15;584:204-215.
PMID: 33069019 DOI: 10.1016/j.jcis.2020.09.071

This work demonstrates a high-performance hybrid asymmetric supercapacitor (HASC) workable in very high current density of 30 A g-1 with in-situ pyrolytic processed sulfur-doped graphitic carbon nitride/cobalt disulfide (S-gC3N4/CoS2) materials and bio-derived carbon configuration and achievement of high electrochemical stability of 89% over 100,000 cycles with the coulombic efficiency of 99.6%. In the electrochemical studies, the S-gC3N4/CoS2-II electrode showed a high specific capacity of 180 C g-1 at 1 A g-1 current density in the half-cell configuration. The HASC cell was fabricated using S-gC3N4/CoS2-II material and orange peel derived activated carbon as a positive and negative electrode with a maximum operating cell potential of 1.6 V, respectively. The fabricated HASC delivered a high energy density of 26.7 Wh kg-1 and power density of 19.8 kW kg-1 in aqueous electrolyte. The prominent properties in specific capacity and cycling stability could be attributed to the CoS2 nanoparticles engulfed into the S-gC3N4 framework which provides short transport distance of the ions, strong interfacial interaction, and improving structural stability of the S-gC3N4/CoS2-II materials.
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.
Friction at nanopillared polymer surfaces beyond Amontons' laws: Stick-slip amplitude coefficient (SSAC) and multiparametric nanotribological properties

Ishak MI, Dobryden I, Martin Claesson P, Briscoe WH, Su B

J Colloid Interface Sci, 2021 Feb 01;583:414-424.
PMID: 33011410 DOI: 10.1016/j.jcis.2020.09.038

Frictional and nanomechanical properties of nanostructured polymer surfaces are important to their technological and biomedical applications. In this work, poly(ethylene terephthalate) (PET) surfaces with a periodic distribution of well-defined nanopillars were fabricated through an anodization/embossing process. The apparent surface energy of the nanopillared surfaces was evaluated using the Fowkes acid-base approach, and the surface morphology was characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The normal and lateral forces between a silica microparticle and these surfaces were quantified using colloidal probe atomic force microscopy (CP-AFM). The friction-load relationship followed Amonton's first law, and the friction coefficient appeared to scale linearly with the nanopillar height. Furthermore, all the nanopillared surfaces showed pronounced frictional instabilities compared to the smooth sliding friction loop on the flat control. Performing the stick-slip amplitude coefficient (SSAC) analysis, we found a correlation between the frictional instabilities and the nanopillars density, pull-off force and work of adhesion. We have summarised the dependence of the nanotribological properties on such nanopillared surfaces on five relevant parameters, i.e. pull-off force fp, Amontons' friction coefficient μ, RMS roughness Rq, stick-slip amplitude friction coefficient SSAC, and work of adhesion between the substrate and water Wadh in a radar chart. Whilst demonstrating the complexity of the frictional behaviour of nanopillared polymer surfaces, our results show that analyses of multiparametric nanotribological properties of nanostructured surfaces should go beyond classic Amontons' laws, with the SSAC more representative of the frictional properties compared to the friction coefficient.
Coordination polymer-derived cobalt-embedded and N/S-doped carbon nanosheet with a hexagonal core-shell nanostructure as an efficient catalyst for activation of oxone in water

Tuan DD, Oh WD, Ghanbari F, Lisak G, Tong S, Andrew Lin KY

J Colloid Interface Sci, 2020 Nov 01;579:109-118.
PMID: 32574728 DOI: 10.1016/j.jcis.2020.05.033

As sulfate-radical (SR)-based advanced oxidation processes are increasingly implemented, Oxone has been frequently-used for generation of SR. While Co3O4 nanoparticle (NP) has been widely-accepted as a promising catalyst for activating Oxone, Co3O4 NPs tend to aggregate in water, losing their reactivity. Thus, many attempts have immobilized Co3O4 NPs on supports, especially carbonaceous substrates, because combination of Co NPs with carbon substrates offers synergistic effects for boosting catalytic activities. Moreover, carbon substrates doped with hetero-atoms (N and S) further increase electron transfer and reactivity. Therefore, it is even promising to immobilize Co NPs onto N/S-doped carbon (NSC) to form Co-embedded NSC (denoted as CoNSC) for enhancing Oxone activation. In this study, a convenient and facile technique is proposed to prepare such a CoNSC via a simple carbonization treatment of a coordination polymer of Co and trithiocyanuric acid (TTCA). The resulting CoNSC exhibits the sheet-like hexagonal morphology with the core-shell configuration, and Co NPs are well-embedded into the N/S-doped carbonaceous matrix, making it an advantageous heterogeneous catalyst for Oxone activation. As Azorubine S (ARS) decolorization is employed as a model reaction of Oxone activation, CoNSC exhibits a higher catalytic activity than pristine Co3O4 and NSC for Oxone activation to decolorize ARS. In comparison to the other reported catalysts, CoNSC also possesses a much lower Ea for ARS decolorization. CoNSC can be also reusable and stable for Oxone activation over multiple cycles without loss of catalytic activity. These features validate that CoNSC is a promising and useful Co-based catalyst for Oxone activation.
Self-assembled reduced graphene oxide nanoflakes assisted by post-sonication boosted electrical performance in gold interdigitated microelectrodes

Taniselass S, Arshad MKM, Gopinath SCB, Ramli MM

J Colloid Interface Sci, 2020 Oct 01;577:345-354.
PMID: 32485416 DOI: 10.1016/j.jcis.2020.05.070

Reduced graphene oxide (rGO) is widely utilised to develop various types of biosensors; however, producing self-assembled rGO nanoflake networks through single-droplet drop-casting remains inconsistent. In the present work, we systematically used three different methods to prepare rGO suspensions in order to produce large scale self-assembled rGO nanoflake networks through single-droplet drop-casting. The rGO suspensions were prepared using only deionised water with no added any chemicals/organic solvents, which we considered to be a low-cost method. Subsequently, the most effective preparation method was used to deposit rGO nanoflakes onto commercial gold interdigitated microelectrodes (Au-IDE) to examine their electrical performance. Assessment of the yields, developed methods, surface morphologies, spectroscopy and structural analyses of the as-prepared rGO nanoflakes were conducted. The results revealed that method-3 (involving sonication, centrifugation and post-sonication) produced large self-assembled rGO nanoflake networks with strong adhesion to glass substrates. Furthermore, the as-prepared rGO/Au-IDE modified sensors showed excellent electron mobility where the electrical conductivity was enhanced approximately ~ 1000 fold compared to the bare devices. The present work provided new insights for depositing large self-assembled interconnected rGO nanoflake networks through single-droplet drop-casting which will be beneficial for biosensor development and other downstream applications.
Facile fabrication of thin metal oxide films on porous carbon for high density charge storage

Vijayan BL, Misnon II, Anil Kumar GM, Miyajima K, Reddy MV, Zaghib K, et al.

J Colloid Interface Sci, 2020 Mar 07;562:567-577.
PMID: 31780115 DOI: 10.1016/j.jcis.2019.11.077

In an effort to minimize the usage of non-renewable materials and to enhance the functionality of the renewable materials, we have developed thin metal oxide coated porous carbon derived from a highly abundant non-edible bio resource, i.e., palm kernel shell, using a one-step activation-coating procedure and demonstrated their superiority as a supercapacitive energy storage electrode. In a typical experiment, an optimized composition contained ~10 wt% of Mn2O3 on activated carbon (AC); a supercapacitor electrode fabricated using this electrode showed higher rate capability and more than twice specific capacitance than pure carbon electrode and could be cycled over 5000 cycles without any appreciable capacity loss in 1 M Na2SO4 electrolyte. A symmetric supercapacitor prototype developed using the optimum electrode showed nearly four times higher energy density than the pure carbon owing to the enhancements in voltage window and capacitance. A lithium ion capacitor fabricated in half-cell configuration using 1 M LiPF6 electrolyte showed larger voltage window, superior capacitance and rate capability in the ~10 wt% Mn2O3 @AC than the pure analogue. These results demonstrate that the current protocol allows fabrication of superior charge storing electrodes using renewable materials functionalized by minimum quantity of earthborn materials.
Reduced graphene/nanostructured cobalt oxide nanocomposite for enhanced electrochemical performance of supercapacitor applications

Sagadevan S, Marlinda AR, Johan MR, Umar A, Fouad H, Alothman OY, et al.

J Colloid Interface Sci, 2020 Jan 15;558:68-77.
PMID: 31585223 DOI: 10.1016/j.jcis.2019.09.081

We demonstrate the preparation of nanostructures cobalt oxide/reduced graphene oxide (Co3O4/rGO) nanocomposites by a simple one-step cost-effective hydrothermal technique for possible electrode materials in supercapacitor application. The X-ray diffraction patterns were employed to confirm the nanocomposite crystal system of Co3O4/rGO by demonstrating the existence of normal cubic spinel structure of Co3O4 in the matrix of Co3O4/rGO nanocomposite. FTIR and FT-Raman studies manifested the structural behaviour and quality of prepared Co3O4/rGO nanocomposite. The optical properties of the nanocomposite Co3O4/rGO have been investigated by UV absorption spectra. The SEM/TEM images showed that the Co3O4 nanoparticles in the Co3O4/rGO nanocomposites were covered over the surface of the rGO sheets. The electrical properties were analyzed in terms of real and imaginary permittivity, dielectric loss and AC conductivity. The electrocatalytic activities of synthesized Co3O4/rGO nanocomposites were determined by cyclic voltammetry and charge-discharge cycle to evaluate the supercapacitive performance. The specific capacitance of 754 Fg-1 was recorded for Co3O4/rGO nanocomposite based electrode in three electrode cell system. The electrode material exhibited an acceptable capability and excellent long-term cyclic stability by maintaining 96% after 1000 continuous cycles. These results showed that the prepared sample could be an ideal candidate for high-energy application as electrode materials. The synthesized Co3O4/rGO nanocomposite is a versatile material and can be used in various application such as fuel cells, electrochemical sensors, gas sensors, solar cells, and photocatalysis.
The structure of alkyl ester sulfonate surfactant micelles: The impact of different valence electrolytes and surfactant structure on micelle growth

Wang Z, Li P, Ma K, Chen Y, Penfold J, Thomas RK, et al.

J Colloid Interface Sci, 2019 Sep 05;557:124-134.
PMID: 31518834 DOI: 10.1016/j.jcis.2019.09.016

The ester sulfonate anionic surfactants are a potentially valuable class of sustainable surfactants. The micellar growth, associated rheological changes, and the onset of precipitation are important consequences of the addition of electrolyte and especially multi-valent electrolytes in anionic surfactants. Small angle neutron scattering, SANS, has been used to investigate the self-assembly and the impact of different valence electrolytes on the self-assembly of a range of ester sulfonate surfactants with subtly different molecular structures. The results show that in the absence of electrolyte small globular micelles form, and in the presence of NaCl, and AlCl3 relatively modest micellar growth occurs before the onset of precipitation. The micellar growth is more pronounced for the longer unbranched and branched alkyl chain lengths. Whereas changing the headgroup geometry from methyl ester to ethyl ester has in general a less profound impact. The study highlights the importance of relative counterion binding strengths and shows how the surfactant structure affects the counterion binding and hence the micelle structure. The results have important consequences for the response of such surfactants to different operational environments.

Filters

Please provide feedback to Administrator (afdal@afpm.org.my)

External Links