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Impact of nickel substitution on structural, dielectric, magnetic, and electrochemical properties of copper ferrite nanostructures for energy storage devices

Priyadharsini R, Manoharan C, Bououdina M, Sagadevan S, Venkateshwarlu M, Asath Bahadur S

J Colloid Interface Sci, 2024 Jan;653(Pt A):917-929.
PMID: 37774655 DOI: 10.1016/j.jcis.2023.09.113

Nickel-substituted copper ferrite nanoparticles (NP) (Cu1-xNixFe2O4) were prepared using a cost-effective hydrothermal method. X-ray diffraction (XRD) pattern revealed a single-phase cubic spinel structure. The increase in lattice parameters and decrease in crystallite size are associated with the replacement of Cu ions by Ni ions in the host lattice of copper ferrite. The optimized Cu0.95Ni0.05Fe2O4 composition was subsequently annealed at 750 °C and 850 °C for further studies. Fourier transform infrared (FT-IR) analysis shows the existence of two promising fundamental adsorption peaks at 465 and 582 cm-1, related to the metal ion stretching vibrations at the tetrahedral (A) and octahedral (B) sites, respectively. The local disorder at both the A and B sublattices upon the incorporation of Ni was observed from the Raman analysis. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) images shows the formation of agglomerates composed of nano-sized spherical particles. A high Barrett-Joyner-Halenda (BJH) surface area was achieved 17.25 m2/g with a particle stability of -11.1 mV obtained by the zeta potential. Both the dielectric loss and dielectric constant are decreased, whereas the AC conductivity gets increased with increasing frequency. The magnetization-field hysteresis curves exhibited ferromagnetic behavior with a pseudo-single domain, and the cyclic voltammetry study revealed a pseudocapacitive trend. This study highlights the importance of Ni substitution to control the physicochemical properties of spinel-phase CuFe2O4 for diverse applications, such as energy storage and lithium-ion batteries.
Redox equilibria of iron oxides in aqueous-based magnetite dispersions: effect of pH and redox potential

Pang SC, Chin SF, Anderson MA

J Colloid Interface Sci, 2007 Jul 1;311(1):94-101.
PMID: 17395194

The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the Eh-pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The "triple point" position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system.
Surface active complexes formed between keratin polypeptides and ionic surfactants

Pan F, Lu Z, Tucker I, Hosking S, Petkov J, Lu JR

J Colloid Interface Sci, 2016 Dec 15;484:125-134.
PMID: 27599381 DOI: 10.1016/j.jcis.2016.08.082

Keratins are a group of important proteins in skin and hair and as biomaterials they can provide desirable properties such as strength, biocompatibility, and moisture regaining and retaining. The aim of this work is to develop water-soluble keratin polypeptides from sheep wool and then explore how their surface adsorption behaves with and without surfactants. Successful preparation of keratin samples was demonstrated by identification of the key components from gel electrophoresis and the reproducible production of gram scale samples with and without SDS (sodium dodecylsulphate) during wool fibre dissolution. SDS micelles could reduce the formation of disulphide bonds between keratins during extraction, reducing inter-molecular crosslinking and improving keratin polypeptide solubility. However, Zeta potential measurements of the two polypeptide batches demonstrated almost identical pH dependent surface charge distributions with isoelectric points around pH 3.5, showing complete removal of SDS during purification by dialysis. In spite of different solubility from the two batches of keratin samples prepared, very similar adsorption and aggregation behavior was revealed from surface tension measurements and dynamic light scattering. Mixing of keratin polypeptides with SDS and C12TAB (dodecyltrimethylammonium bromide) led to the formation of keratin-surfactant complexes that were substantially more effective at reducing surface tension than the polypeptides alone, showing great promise in the delivery of keratin polypeptides via the surface active complexes. Neutron reflection measurements revealed the coexistence of surfactant and keratin polypeptides at the interface, thus providing the structural support to the observed surface tension changes associated with the formation of the surface active complexes.
Membrane-lytic actions of sulphonated methyl ester surfactants and implications to bactericidal effect and cytotoxicity

Pan F, Li Z, Gong H, Petkov JT, Lu JR

J Colloid Interface Sci, 2018 Dec 01;531:18-27.
PMID: 30015167 DOI: 10.1016/j.jcis.2018.07.031

Surfactants are multifunctional molecules widely used in personal care and healthcare formulations to cleanse, help disperse active ingredients (e.g., forming emulsions) and stabilise products. With increasing demands on improving biosafety, there is now mounting pressure to understand how different surfactants elicit toxicities at molecular and cellular levels. This work reports the membrane-lytic behaviour of a group of sulphonated methyl ester (SME) surfactants together with representative conventional surfactants. All surfactants displayed the clear rise of lysis of the model lipid bilayer membranes around their CMCs, but the two ionic surfactants SDS and C12TAB even caused measurable lysis below their CMCs, with membrane-lytic actions increasing with monomer concentration. Furthermore, whilst ionic and nonionic surfactants could achieve full membrane lysis once above their CMCs, this ability was weak from the SME surfactants and decreased with increasing the acyl chain length. In contrast to the conventional anionic surfactants such as SDS and SLES, the protein solubilizing capability of the SME surfactants was also low. On the other hand, MTT assays against 3T3 fibroblast cells and human chondrocyte cells revealed high toxicity from SDS and C12TAB against the other surfactants studied, but the difference between SME and the rest of conventional surfactants was small. Similar behaviour was also observed in their bactericidal effect against E. coli and S. aureus. The trend is broadly consistent with their membrane-lytic behaviour, indicating little selectivity in their cytotoxicity and bactericidal action. These results thus reveal different toxicities implicated from different surfactant head groups. Increase in acyl chain length as observed from SME surfactants could help improve surfactant biocompatibility.
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.
Acoustically-controlled Leidenfrost droplets

Ng BT, Hung YM, Tan MK

J Colloid Interface Sci, 2016 Mar 1;465:26-32.
PMID: 26641561 DOI: 10.1016/j.jcis.2015.11.047

Suppressing the Leidenfrost effect can significantly improve heat transfer from a heated substrate to a droplet above it. In this work, we demonstrate that by generating high frequency acoustic wave in the droplet, at sufficient vibration displacement amplitudes, the Leidenfrost effect can be suppressed due to the acoustic radiation pressure exerted on the liquid-vapor interface; strong capillary waves are observed at the liquid-vapor interface and subsequently leads to contact between the liquid and the heated substrate. Using this technique, with 10(5)Hz vibration frequency and 10(-6)m displacement amplitude of the acoustic transducer, a maximum of 45% reduction of the initial temperature (T0∼200-300°C) of the heated substrate can be achieved with a single droplet of volume 10(-5)l.
Photocatalytic decolourisation of Reactive Red 4 dye by an immobilised TiO2/chitosan layer by layer system

Nawi MA, Sabar S, Sheilatina

J Colloid Interface Sci, 2012 Apr 15;372(1):80-7.
PMID: 22321991 DOI: 10.1016/j.jcis.2012.01.024

The synergistic photocatalysis-adsorption processes by the immobilized TiO(2)/chitosan layer by layer system on a glass support (TiO(2)/CS/glass) were investigated for the decolourisation of Reactive Red 4 (RR4) dye solution. Effects of different reaction parameters such as TiO(2) loading, initial pH of the solution, visible light, dissolved oxygen and radical quenchers were studied. The decolourisation rate of RR4 by TiO(2)/CS/glass was more than 32 times faster than a single layer of TiO(2) but was highly dependent on the TiO(2) loading and the initial pH of the solution. A thin layer of TiO(2) and acidic conditions favoured the adsorption of RR4 at the TiO(2)/CS interface. The h(+)/OH() species that diffused from the TiO(2) layer into the TiO(2)/CS interface oxidised the chemisorbed RR4 anions at the interface, and the generated electrons were then transferred to the conduction band of TiO(2). Excess electrons in the conduction band of TiO(2) increased the number of superoxide ions produced and thus improved the photocatalytic decolourisation of RR4. Therefore, apart from the synergistic photocatalysis-adsorption processes, a charge transfer process was also found to be responsible for maintaining the efficiency, sustainability and reusability of the TiO(2)/CS/glass layer by layer system.
Doxorubicin-loaded magnetic gold nanoshells for a combination therapy of hyperthermia and drug delivery

Mohammad F, Yusof NA

J Colloid Interface Sci, 2014 Nov 15;434:89-97.
PMID: 25170601 DOI: 10.1016/j.jcis.2014.07.025

In the present work, nanohybrid of an anticancer drug, doxorubicin (Dox) loaded gold-coated superparamagnetic iron oxide nanoparticles (SPIONs@Au) were prepared for a combination therapy of cancer by means of both hyperthermia and drug delivery. The Dox molecules were conjugated to SPIONs@Au nanoparticles with the help of cysteamine (Cyst) as a non-covalent space linker and the Dox loading efficiency was investigated to be as high as 0.32 mg/mg. Thus synthesized particles were characterized by HRTEM, UV-Vis, FT-IR, SQUID magnetic studies and further tested for heat and drug release at low frequency oscillatory magnetic fields. The hyperthermia studies investigated to be strongly influenced by the applied frequency and the solvents used. The Dox delivery studies indicated that the drug release efficacy is strongly improved by maintaining the acidic pH conditions and the oscillatory magnetic fields, i.e. an enhancement in the Dox release was observed from the oscillation of particles due to the applied frequency, and is not effected by heating of the solution. Finally, the in vitro cell viability and proliferation studies were conducted using two different immortalized cell lines containing a cancerous (MCF-7 breast cancer) and non-cancerous H9c2 cardiac cell type.
The hexagonal close-packed nickel nanocrystals prepared by fast scan voltammetry

Mohamed Ali Tehrani R, Ab Ghani S

J Colloid Interface Sci, 2009 Nov 1;339(1):125-32.
PMID: 19699486 DOI: 10.1016/j.jcis.2009.07.042

The nickel (Ni) nanocrystals (average diameter 9.7+/-2.3nm) were deposited onto composite graphite electrode from a plating solution of 5.0mM NiCl(2)6H(2)O and 1.0M NH(4)Cl using scan rate of 6500mVs(-1). The initial potential -1.5V and final potential -0.5V vs. Ag/AgCl with applied time 120s were used for the whole deposition process. The variations of applied overpotentials and deposition times have affected the characteristics of Ni nanocrystals. It was found that the structural formation of Ni nanocrystals obtained were almost pure hexagonal close-packed (hcp). This study has demonstrated that the tuning of the final size, morphology and structural formation of the Ni nanocrystal were affected by control of nucleation, growth and hydrogen evolution processes in fast scan voltammetry technique used.
Enhanced dispersion of multiwall carbon nanotubes in natural rubber latex nanocomposites by surfactants bearing phenyl groups

Mohamed A, Anas AK, Bakar SA, Ardyani T, Zin WM, Ibrahim S, et al.

J Colloid Interface Sci, 2015 Oct 1;455:179-87.
PMID: 26070188 DOI: 10.1016/j.jcis.2015.05.054

Here is presented a systematic study of the dispersibility of multiwall carbon nanotubes (MWCNTs) in natural rubber latex (NR-latex) assisted by a series of single-, double-, and triple-sulfosuccinate anionic surfactants containing phenyl ring moieties. Optical polarising microscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Raman spectroscopy have been performed to obtain the dispersion-level profiles of the MWCNTs in the nanocomposites. Interestingly, a triple-chain, phenyl-containing surfactant, namely sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3-phenylpropoxy)carbonyl) pentane-2-sulfonate (TCPh), has a greater capacity the stabilisation of MWCNTs than a commercially available single-chain sodium dodecylbenzenesulfonate (SDBS) surfactant. TCPh provides significant enhancements in the electrical conductivity of nanocomposites, up to ∼10(-2) S cm(-1), as measured by a four-point probe instrument. These results have allowed compilation of a road map for the design of surfactant architectures capable of providing the homogeneous dispersion of MWCNTs required for the next generation of polymer-carbon-nanotube materials, specifically those used in aerospace technology.
Rational design of aromatic surfactants for graphene/natural rubber latex nanocomposites with enhanced electrical conductivity

Mohamed A, Ardyani T, Abu Bakar S, Sagisaka M, Umetsu Y, Hamon JJ, et al.

J Colloid Interface Sci, 2018 Apr 15;516:34-47.
PMID: 29360058 DOI: 10.1016/j.jcis.2018.01.041

HYPOTHESIS: Graphene nanoplatelets (GNPs) can be dispersed in natural rubber matrices using surfactants. The stability and properties of these composites can be optimized by the choice of surfactants employed as stabilizers. Surfactants can be designed and synthesized to have enhanced compatibility with GNPs as compared to commercially available common surfactants. Including aromatic groups in the hydrophobic chain termini improves graphene compatibility of surfactants, which is expected to increase with the number of aromatic moieties per surfactant molecule. Hence, it is of interest to study the relationship between molecular structure, dispersion stability and electrical conductivity enhancement for single-, double-, and triple-chain anionic graphene-compatible surfactants.
EXPERIMENTS: Graphene-philic surfactants, bearing two and three chains phenylated at their chain termini, were synthesized and characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy. These were used to formulate and stabilize dispersion of GNPs in natural rubber latex matrices, and the properties of systems comprising the new phenyl-surfactants were compared with commercially available surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). Raman spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM) were used to study structural properties of the materials. Electrical conductivity measurements and Zeta potential measurements were used to assess the relationships between surfactant architecture and nanocomposite properties. Small-angle neutron scattering (SANS) was used to study self-assembly structure of surfactants.
FINDINGS: Of these different surfactants, the tri-chain aromatic surfactant TC3Ph3 (sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate) was shown to be highly graphene-compatible (nanocomposite electrical conductivity = 2.22 × 10-5 S cm-1), demonstrating enhanced electrical conductivity over nine orders of magnitude higher than neat natural rubber-latex matrix (1.51 × 10-14 S cm-1). Varying the number of aromatic moieties in the surfactants appears to cause significant differences to the final properties of the nanocomposites.
Distinguishing characteristics and usability of graphene oxide based on different sources of graphite feedstock

Mahmoudi E, Ang WL, Ng CY, Ng LY, Mohammad AW, Benamor A

J Colloid Interface Sci, 2019 Apr 15;542:429-440.
PMID: 30771638 DOI: 10.1016/j.jcis.2019.02.023

Graphene oxide (GO) has gained popularity in scientific research and industry due to its superior properties, which can be controlled by the synthesis method and graphite feedstock. Despite the availability of different graphite sources, most of the reported studies used natural graphite flake (NGF) as a source of oxidation for GO synthesis. The effect of various alternative graphite feedstocks on the GO properties has not been investigated systematically. This study investigated the influence of graphite feedstock (natural and synthetic) on the characteristics and properties of GO via modified Hummer's method. Natural graphite flake (NGF), natural graphite powder (NGP), and synthetic graphite powder (SGP) were used as graphite feedstock in the study. Energy-dispersive X-ray analysis revealed that the GO produced using NGP (NGP-GO) has higher oxygen to carbon ratio in comparison to GO made from NGF (NGF-GO) and GO made from SGP (SGP-GO) (35.4, 32.7, and 32.2%, respectively), indicating higher oxidation degree for NGP-GO. Zeta potential analysis for NGP-GO, NGF-GO and SGP-GO were -47.8, -42.6 and -39.4 mV, respectively. Morphological analysis revealed that the structures of GO varied according to graphite feedstock, in which (NGP-GO) and (NGF-GO) were highly exfoliated (single-layered structure) while (SGP-GO) showed a multi-layered structure. Further testing was conducted by decorating silver (Ag) nanoparticles on the GO. The results showed that Ag could be uniformly decorated (no agglomeration) on the surface of GO-NGP, due to the presence of more functional groups. Subsequently, the antimicrobial property of Ag-NGP was the highest with an inhibition diameter of 14.7 ± 1.2 mm (30% higher than the other samples). In conclusion, the properties of GO can be tuned by selecting the suitable graphite feedstock and this might pave the way to new developments in the GO-based applications.
Why does vacuum drive to the loading of halloysite nanotubes? The key role of water confinement

Lisuzzo L, Cavallaro G, Pasbakhsh P, Milioto S, Lazzara G

J Colloid Interface Sci, 2019 Jul 01;547:361-369.
PMID: 30974251 DOI: 10.1016/j.jcis.2019.04.012

The filling of halloysite nanotubes with active compounds solubilized in aqueous solvent was investigated theoretically and experimentally. Based on Knudsen thermogravimetric data, we demonstrated the water confinement within the cavity of halloysite. This process is crucial to properly describe the driving mechanism of halloysite loading. In addition, Knudsen thermogravimetric experiments were conducted on kaolinite nanoplates as well as on halloysite nanotubes modified with an anionic surfactant (sodium dodecanoate) in order to explore the influence of both the nanoparticle morphology and the hydrophobic/hydrophilic character of the lumen on the confinement phenomenon. The analysis of the desorption isotherms allowed us to determine the water adsorption properties of the investigated nanoclays. The pore sizes of the nanotubes' lumen was determined by combining the vapor pressure of the confined water with the nanoparticles wettability, which was studied through contact angle measurements. The thermodynamic description of the water confinement inside the lumen was correlated to the influence of the vacuum pumping in the experimental loading of halloysite. Metoprolol tartrate, salicylic acid and malonic acid were selected as anionic guest molecules for the experimental filling of the positively charged halloysite lumen. According to the filling mechanism induced by the water confinement, the vacuum operation and the reduced pressure enhanced the loading of halloysite nanotubes for all the investigated bioactive compounds. This work represents a further and crucial step for the development of halloysite based nanocarriers being that the filling mechanism of the nanotube's cavity from aqueous dispersions was described according to the water confinement process.
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.
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.
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.
Effects of aminoacids on the autooxidation of 3,5-di-tert-butylcatechol in the presence of surface-active copper(II) complexes

Lim YY, Liew LP

J Colloid Interface Sci, 2002 Nov 15;255(2):425-7.
PMID: 12505092

The rate of autooxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in the presence of micelles formed from mixing equal concentrations of [Cu(C(12)-tmed)Br(2)] (where C(12)-tmed is N,N,N'-trimethyl-N'-dodecylethylenediamine) and several amino acids has been investigated. It was found that the rate in air-saturated solution is very much dependent on pH, which affects the availability of copper(II) coordination site for the catechol and the degree of micellization. At a given pH, the rates in [Cu(C(12)-tmed)Br(2)] micellar media are greatly enhanced in the presence sodium halide.
Interaction of Aqueous Solutions of a Surface Active Copper(II) Complex with Several Common Surfactants

Lim YY, Lim KH

J Colloid Interface Sci, 1997 Dec 01;196(1):116-9.
PMID: 9441659

Micellar properties of binary mixed surfactants of a surface active mixed copper(II) chelate, [Cu(C12-tmed)(acac)Cl] (where C12-tmed is N,N,N'-trimethyl-N'-dodecylethylenediamine) with three common surfactants, viz. sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and octaethylene glycol monododecyl ether (C12E8), were investigated by surface tensiometry, ESR, and UV-visible absorption techniques. The surface tension data were treated with Rubingh's method for mixed micelle formation and Rosen's method for mixed monolayer formation at the aqueous solution/air interface. It was found that in the mixed micelle there is strong attractive interaction between cationic copper surfactant and anonic dodecyl sulfate while there is almost ideal mixing between copper surfactant and CTAB and C12E8. From the ESR and UV-visible studies, a mixed block-type arrangement of head groups is proposed. Copyright 1997 Academic Press. Copyright 1997Academic Press
Magnetophoresis of iron oxide nanoparticles at low field gradient: the role of shape anisotropy

Lim J, Yeap SP, Leow CH, Toh PY, Low SC

J Colloid Interface Sci, 2014 May 1;421:170-7.
PMID: 24594047 DOI: 10.1016/j.jcis.2014.01.044

Magnetophoresis of iron oxide magnetic nanoparticle (IOMNP) under low magnetic field gradient (<100 T/m) is significantly enhanced by particle shape anisotropy. This unique feature of magnetophoresis is influenced by the particle concentration and applied magnetic field gradient. By comparing the nanosphere and nanorod magnetophoresis at different concentration, we revealed the ability for these two species of particles to achieve the same separation rate by adjusting the field gradient. Under cooperative magnetophoresis, the nanorods would first go through self- and magnetic field induced aggregation followed by the alignment of the particle clusters formed with magnetic field. Time scale associated to these two processes is investigated to understand the kinetic behavior of nanorod separation under low field gradient. Surface functionalization of nanoparticles can be employed as an effective strategy to vary the temporal evolution of these two aggregation processes which subsequently influence the magnetophoretic separation time and rate.
DNA fluorescence shift sensor: a rapid method for the detection of DNA hybridization using silver nanoclusters

Lee SY, Hairul Bahara NH, Choong YS, Lim TS, Tye GJ

J Colloid Interface Sci, 2014 Nov 01;433:183-188.
PMID: 25129336 DOI: 10.1016/j.jcis.2014.07.033

DNA-templated silver nanoclusters (AgNC) are a class of subnanometer sized fluorophores with good photostability and brightness. It has been applied as a diagnostic tool mainly for deoxyribonucleic acid (DNA) detection. Integration of DNA oligomers to generate AgNCs is interesting as varying DNA sequences can result in different fluorescence spectra. This allows a simple fluorescence shifting effect to occur upon DNA hybridization with the hybridization efficiency being a pronominal factor for successful shifting. The ability to shift the fluorescence spectra as a result of hybridization overcomes the issue of background intensities in most fluorescent based assays. Here we describe an optimized method for the detection of single-stranded and double-stranded synthetic forkhead box P3 (FOXP3) target by hybridization with the DNA fluorescence shift sensor. The system forms a three-way junction by successful hybridization of AgNC, G-rich strand (G-rich) to the target DNA, which generated a shift in fluorescence spectra with a marked increase in fluorescence intensity. The DNA fluorescence shift sensor presents a rapid and specific alternative to conventional DNA detection.

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