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Pre-treatment of multi-walled carbon nanotubes for polyetherimide mixed matrix hollow fiber membranes

Goh PS, Ng BC, Ismail AF, Aziz M, Hayashi Y

J Colloid Interface Sci, 2012 Nov 15;386(1):80-7.
PMID: 22909959 DOI: 10.1016/j.jcis.2012.07.033

Mixed matrix hollow fibers composed of multi-walled carbon nanotubes (MWCNTs) and polyetherimide (PEI) were fabricated. Pre-treatment of MWCNTs was carried out prior to the incorporation into the polymer matrix using a simple and feasible two stages approach that involved dry air oxidation and surfactant dispersion. The characterizations of the surface treated MWCNTs using TEM and Raman spectroscopy have evidenced the effectiveness of dry air oxidation in eliminating undesired amorphous carbon and metal catalyst while surfactant dispersion using Triton X100 has suppressed the agglomeration of MWCNTs. The resultant mixed matrix hollow fibers were applied for O(2)/N(2) pure gas separation. Interestingly, it was found that removal of disordered amorphous carbons and metal particles has allowed the hollow structures to be more accessible for the fast and smooth transport of gas molecules, hence resulted in noticeable improvement in the gas separation properties. The composite hollow fibers embedded with the surface modified MWCNTs showed increase in permeability as much as 60% while maintaining the selectivity of the O(2)/N(2) gas pair. This study highlights the necessity to establish an appropriate pre-treatment approach for MWCNTs in order to fully utilize the beneficial transport properties of this material in mixed matrix polymer nanocomposite for gas separation.
Hybrid membrane filtration-advanced oxidation processes for removal of pharmaceutical residue

Rosman N, Salleh WNW, Mohamed MA, Jaafar J, Ismail AF, Harun Z

J Colloid Interface Sci, 2018 Dec 15;532:236-260.
PMID: 30092507 DOI: 10.1016/j.jcis.2018.07.118

Reports of pharmaceuticals exist in surface water and drinking water around the world, indicate they are ineffectively remove from water and wastewater using conventional treatment technologies. The potential of adverse effect of these pharmaceuticals on public health and aquatic life, also their continuos accumulation have raised the development of water treatment technologies. Hybrid treatment processes like membrane filtration and advance oxidation processes (AOPs) are likely to give rise to efficient simultaneous degradation and separation mechanisms. Conventional membrane filtration techniques can remove the majority of contaminants, but the smallest, undegraded, and stabilized pharmaceutical wastes persist in the treated water. After some 20 years, researchers have recognized the important role of AOPs in the treatment of pharmaceutical wastewater because these technologies are capable of oxidizing recalcitrant, toxic, and non-biodigradable compounds into numerous by-products and finally, inert end-products via the intermediacy of hydroxyl and other radicals. Evidently, membranes are subjected to the fouling phenomenon by the contaminants in wastewater, hence resulting in a reduction of clean water flux and increase in energy demand. In such situations, these membrane hybrid AOPs exert a complementary effect in the elimination of membrane fouling, thus enhancing the performance of the membrane. Therefore, in this review, we describe the basic aspects of the removal and transformation of certain pharmaceuticals via membranes and AOPs. In addition, information and evidences on membrane hybrid AOPs in the field of pharmaceutical wastewater treatment is also presented.
Amino modified mesostructured silica nanoparticles for efficient adsorption of methylene blue

Karim AH, Jalil AA, Triwahyono S, Sidik SM, Kamarudin NH, Jusoh R, et al.

J Colloid Interface Sci, 2012 Nov 15;386(1):307-14.
PMID: 22889626 DOI: 10.1016/j.jcis.2012.07.043

In this work, mesostructured silica nanoparticles (MSN(AP)) with high adsorptivity were prepared by a modification with 3-aminopropyl triethoxysilane (APTES) as a pore expander. The performance of the MSN(AP) was tested by the adsorption of MB in a batch system under varying pH (2-11), adsorbent dosage (0.1-0.5 g L(-1)), and initial MB concentration (5-60 mg L(-1)). The best conditions were achieved at pH 7 when using 0.1 g L(-1) MSN(AP) and 60 mg L(-1)MB to give a maximum monolayer adsorption capacity of 500.1 mg g(-1) at 303 K. The equilibrium data were evaluated using the Langmuir, Freundlich, Temkin, and Harkins-Jura isotherms and fit well to the Freundlich isotherm model. The adsorption kinetics was best described by the pseudo-second order model. The results indicate the potential for a new use of mesostructured materials as an effective adsorbent for MB.
Enhancement of the photocatalytic activity of TiO(2) by doping it with calcium ions

Akpan UG, Hameed BH

J Colloid Interface Sci, 2011 May 1;357(1):168-78.
PMID: 21345441 DOI: 10.1016/j.jcis.2011.01.014

Titanium dioxide (TiO(2)) with an enhanced photocatalytic activity was developed by doping it with calcium ions through a sol-gel method. The developed photocatalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, N(2) physisorption, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. Their surface morphologies were studied using surface scanning electron microscopy (SEM). The XPS analyses confirmed the presence of Ti, O, Ca, and C in the Ca-doped TiO(2) sample. The activities of the catalysts were evaluated by photocatalytic degradation of an azo dye, acid red 1 (AR1), using UV light irradiation. The results of the investigations revealed that the samples calcined at 300 °C for 3.6h in a cyclic (2 cycles) mode had the best performance. Lower percentage dopant, 0.3-1.0 wt.%, enhanced the photocatalytic activity of TiO(2), with the best at 0.5 wt.% Ca-TiO(2). The performance of 0.5 wt.% Ca-TiO(2) in the degradation of AR1 was far superior to that of a commercial anatase TiO(2) Sigma product CAS No. 1317-70-0. The effect of pH on the degradation of AR1 was studied, and the pH of the dye solution exerted a great influence on the degradation of the dye.
Self-assembled three-dimensional reduced graphene oxide-based hydrogel for highly efficient and facile removal of pharmaceutical compounds from aqueous solution

Umbreen N, Sohni S, Ahmad I, Khattak NU, Gul K

J Colloid Interface Sci, 2018 Oct 01;527:356-367.
PMID: 29843021 DOI: 10.1016/j.jcis.2018.05.010

Herein, self-assembled three-dimensional reduced graphene oxide (RGO)-based hydrogels were synthesized and characterized in detail. A thorough investigation on the uptake of three widely used pharmaceutical drugs, viz. Naproxen (NPX), Ibuprofen (IBP) and Diclofenac (DFC) was carried out from aqueous solutions. To ensure the sustainability of developed hydrogel assembly, practically important parameters such as desorption, recyclability and applicability to real samples were also evaluated. Using the developed 3D hydrogels as adsorptive platforms, excellent decontamination for the above mentioned persistent pharmaceutical drugs was achieved in acidic pH with a removal efficiency in the range of 70-80%. These hydrogels showed fast adsorption kinetics and experimental findings were fitted to different kinetic models, such as pseudo-first order, pseudo-second order, intra-particle and the Elovich models in an attempt to better understand the adsorption kinetics. Furthermore, equilibrium adsorption data was fitted to the Langmuir and Freundlich models, where relatively higher R2 values obtained in case of former one suggested that monolayer adsorption played an important part in drug uptake. Thermodynamic aspects were also studied and negative ΔG0 values obtained indicated the spontaneous nature of adsorption process. The study was also extended to check practical utility of as-prepared hydrogels by spiking real aqueous samples with drug solution, where high % recoveries obtained for NPX, IBP and DFC were of particular importance with regard to prospective application in wastewater treatment systems. We advocate RGO-based hydrogels as environmentally benign, readily recoverable/recyclable material with excellent adsorption capacity for application in wastewater purification.
Electrospun nylon 6,6 membrane as a reusable nano-adsorbent for bisphenol A removal: Adsorption performance and mechanism

Jasni MJF, Arulkumar M, Sathishkumar P, Mohd Yusoff AR, Buang NA, Gu FL

J Colloid Interface Sci, 2017 Dec 15;508:591-602.
PMID: 28869916 DOI: 10.1016/j.jcis.2017.08.075

Bisphenol A (BPA) is highly considered as an emerging contaminants (ECs) due to their endocrine disrupting and reproductive toxicant nature. It has been detected in drinking water sources in many countries. This study deals with the adsorptive removal of BPA using nylon 6,6 nanofibrous membrane (NNM) fabricated by electrospinning technique. Langmuir and Freundlich isotherm models (R2=0.99) were obeyed for BPA adsorption, which indicates the monolayer adsorption of BPA and also surface heterogeneity of NNM. The adsorption kinetics of BPA was followed pseudo second order rate (R2=0.89-0.99), which suggests the occurrence of rapid adsorption rate through interaction of surface functional groups present in NNM. The maximum adsorption of BPA (91.3mgg-1) was attained at 30°C. The hydroxyl groups of BPA form hydrogen bonding with carbonyl groups of NNM during the adsorptive removal process. Reusability study confirmed a much better stability of NNM in the recyclic application. Finally, this study suggests that NNM might be an outstanding nano-adsorbent for the emerging contaminants removal, including BPA from drinking water sources.
Synthesis and characterization of choline-fatty-acid-based ionic liquids: A new biocompatible surfactant

Ali MK, Moshikur RM, Wakabayashi R, Tahara Y, Moniruzzaman M, Kamiya N, et al.

J Colloid Interface Sci, 2019 Sep 01;551:72-80.
PMID: 31075635 DOI: 10.1016/j.jcis.2019.04.095

Ionic liquid (IL) surfactants have attracted great interest as promising substitutes for conventional surfactants owing to their exceptional and favorable physico-chemical properties. However, most IL surfactants are not eco-friendly and form unstable micelles, even when using a high concentration of the surfactant. In this study, we prepared a series of halogen-free and biocompatible choline-fatty-acid-based ILs with different chain lengths and degrees of saturation, and we then investigated their micellar properties in aqueous solutions. Characterization of the synthesized surface-active ILs (SAILs) was performed by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and elemental analysis. The surface-active properties of the SAILs were investigated by tensiometry, conductometry, and dynamic light scattering measurements. The critical micelle concentration of the SAILs was found to be 2-4 times lower than those of conventional surfactants. The thermodynamic properties of micellization (ΔG0m, ΔH0m, and ΔS0m) indicate that the micellization process of the SAILs is spontaneous, stable, and entropy-driven at room temperature. The cytotoxicity of the SAILs was evaluated using mammalian cell line NIH 3T3. Importantly, [Cho][Ole] shows lower toxicity than the analogous ILs with conventional surfactants. These results clearly suggest that these environmentally friendly SAILs can be used as a potential alternative to conventional ILs for various purposes, including biological applications.
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.
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.
Surfactants with aromatic headgroups for optimizing properties of graphene/natural rubber latex composites (NRL): Surfactants with aromatic amine polar heads

Ardyani T, Mohamed A, Bakar SA, Sagisaka M, Umetsu Y, Mamat MH, et al.

J Colloid Interface Sci, 2019 Jun 01;545:184-194.
PMID: 30878784 DOI: 10.1016/j.jcis.2019.03.012

HYPOTHESIS: The compatibility of surfactants and graphene surfaces can be improved by increasing the number of aromatic groups in the surfactants. Including aniline in the structure may improve the compatibility between surfactant and graphene further still. Surfactants can be modified by incorporating aromatic groups in the hydrophobic chains or hydrophilic headgroups. Therefore, it is of interest to investigate the effects of employing anilinium based surfactants to disperse graphene nanoplatelets (GNPs) in natural rubber latex (NRL) for the fabrication of electrically conductive nanocomposites.
EXPERIMENTS: New graphene-philic surfactants carrying aromatic moieties in the hydrophilic headgroups and hydrophobic tails were synthesized by swapping the traditional sodium counterion with anilinium. 1H NMR spectroscopy was used to characterize the surfactants. These custom-made surfactants were used to assist the dispersion of GNPs in natural rubber latex matrices for the preparation of conductive nanocomposites. The properties of nanocomposites with the new anilinium surfactants were compared with commercial sodium surfactant sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and the previously synthesized aromatic tri-chain sodium surfactant TC3Ph3 (sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate). Structural properties of the nanocomposites were studied using Raman spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Electrical conductivity measurements and Zeta potential measurements were used to assess the relationships between total number of aromatic groups in the surfactant molecular structure and nanocomposite properties. The self-assembly structure of surfactants in aqueous systems and GNP dispersions was assessed using small-angle neutron scattering (SANS).
FINDINGS: Among these different surfactants, the anilinium version of TC3Ph3 namely TC3Ph3-AN (anilinium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate) was shown to be highly efficient for dispersing GNPs in the NRL matrices, increasing electrical conductivity eleven orders of magnitude higher than the neat rubber latex. Comparisons between the sodium and anilinium surfactants show significant differences in the final properties of the nanocomposites. In general, the strategy of increasing the number of surfactant-borne aromatic groups by incorporating anilinium ions in surfactant headgroups appears to be effective.
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.
Mixed surfactant systems of sucrose esters and lecithin as a synergistic approach for oil structuring

Bin Sintang MD, Danthine S, Patel AR, Rimaux T, Van De Walle D, Dewettinck K

J Colloid Interface Sci, 2017 Oct 15;504:387-396.
PMID: 28586736 DOI: 10.1016/j.jcis.2017.05.114

In order to modify the self-assembly of sucrose esters (SEs) in sunflower oil, we added sunflower lecithin (SFL) as co-surfactant. It is hypothesized that SFL modifies the self-assembly of SEs by interrupting the extensive hydrogen bonding between SEs monomers. The addition of SFL into SEs induced gelation of the mixed surfactant system oleogels at all studied ratios. The 7:3 SEs:SFL combination showed enhanced rheological properties compared to the other studied ratios, which suggests better molecular ordering induced by SFL. The modifications might have been caused by interference in the hydrogen bonding, connecting the polar heads of SEs molecules in the presence of SFL. This effect was confirmed by thermal behavior and small angle X-ray diffraction (SAXD) analysis. From the crystallization and melting analyses, it was shown that the peak temperature, shape and enthalpy decreased as the SFL ratio increases. Meanwhile, the bi-component oleogels exhibited new peaks in the SAXD profile, which imply a self-assembly modification. The microscopic study through polarized and electrons revealed a change in the structure. Therefore, it can be concluded that a synergistic effect between SEs and SFL, more particularly at 7:3 ratio, towards sunflower oil structuring could be obtained. These findings shed light for greater applications of SEs as structuring and carrier agent in foods and pharmaceutical.
The adsorption of palmytic acid on rice husk ash chemically modified with Al(III) ion using the sol-gel technique

Adam F, Chua JH

J Colloid Interface Sci, 2004 Dec 1;280(1):55-61.
PMID: 15476773

Silica-incorporated aluminum (RHA-Al) was synthesized from rice husk ash (RHA) using the sol-gel technique. RHA-Al was calcined at 500 degrees C for 5 h to yield RHA-Al(C). The ratio of silica to alumina was found to be 4:1. The BET analysis of RHA-Al(C) showed an increase in total pore volume and specific surface area compared to RHA-Al. SEM and XRD showed that RHA-Al and RHA-Al(C) were composed of microcrystals and the surface of both samples had a porous structure. Adsorption studies of palmytic acid on RHA-Al and RHA-Al(C) at 30, 40, and 50 degrees C conformed to the Langmuir isotherm. The equilibrium parameter, R, revealed that both are good adsorbents for palmytic acid. The Gibbs free energy of adsorption, DeltaG(ads)(0), was determined to be between -21.0 and -26.0 kJ mol(-1). DeltaH(ads)(0) and DeltaS(ads)(0) for RHA-Al were found to be 26.2 kJ mol(-1) and 158 J mol(-1), respectively. Corresponding values for RHA-Al(C) were 31.7 kJ mol(-1) and 178 J mol(-1). The adsorption of fatty acid on RHA-Al and RHA-Al(C) was an endothermic process, which occurred spontaneously. An FTIR study on the adsorbed material was used to determine the possible adsorbed complex on the surface of the adsorbent.
Gold nanoparticles deposited on linker-free silicon substrate and embedded in aluminum Schottky contact

Gorji MS, Razak KA, Cheong KY

J Colloid Interface Sci, 2013 Oct 15;408:220-8.
PMID: 23932085 DOI: 10.1016/j.jcis.2013.07.026

Given the enormous importance of Au nanoparticles (NPs) deposition on Si substrates as the precursor for various applications, we present an alternative approach to deposit Au NPs on linker-free n- and p-type Si substrates. It is demonstrated that, all conditions being similar, there is a significant difference between densities of the deposited NPs on both substrates. The Zeta-potential and polarity of charges surrounding the hydroxylamine reduced seeded growth Au NPs, are determined by a Zetasizer. To investigate the surface properties of Si substrates, contact angle measurement is performed. Field-emission scanning electron microscope is then utilized to distinguish the NPs density on the substrates. Finally, Al/Si Schottky barrier diodes with embedded Au NPs are fabricated, and their structural and electrical characteristics are further evaluated using an energy-filtered transmission electron microscope and current-voltage measurements, respectively. The results reveal that the density of NPs is significantly higher on n-type Si substrate and consequently has more pronounced effects on the electrical characteristics of the diode. It is concluded that protonation of Si-OH group on Si surface in low pH is responsible for the immobilization of Au NPs, which eventually contributes to the lowering of barrier height and enhances the electrical characteristics.
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.
Structural and thermal characterizations of silica nanoparticles grafted with pendant maleimide and epoxide groups

Vejayakumaran P, Rahman IA, Sipaut CS, Ismail J, Chee CK

J Colloid Interface Sci, 2008 Dec 1;328(1):81-91.
PMID: 18822418 DOI: 10.1016/j.jcis.2008.08.054

Grafting of free maleimide and epoxide pendant groups onto the surface of approximately 7-nm silica nanoparticles was investigated. Glycidyloxypropyl groups (3-glycidyloxypropyltrimethoxysilane and 3-aminopropyltrimethoxysilane) that carried epoxide groups and aminopropyl groups were grafted to the silica surface with the help of condensation reactions. Maleimide groups [1,1(')-(methylenedi-4,1-phenelene) bismaleimide] were introduced to the silica surface via nucleophilic addition reaction with the aminopropyl groups pre-grafted onto the surface. The grafted silica samples were characterized using CHN, FTIR, DSC, TGA-FTIR, and 13C and 29Si CP/MAS NMR spectroscopy. NMR analyses revealed that all the functional groups were covalently bonded to the silica surface and most of the maleimide and epoxide rings remained intact on surface. DSC analysis showed that the epoxide groups were more reactive than the maleimide groups.
Pt-decorated GaN nanowires with significant improvement in H2 gas-sensing performance at room temperature

Abdullah QN, Yam FK, Hassan Z, Bououdina M

J Colloid Interface Sci, 2015 Dec 15;460:135-45.
PMID: 26319330 DOI: 10.1016/j.jcis.2015.07.048

Superior sensitivity towards H2 gas was successfully achieved with Pt-decorated GaN nanowires (NWs) gas sensor. GaN NWs were fabricated via chemical vapor deposition (CVD) route. Morphology (field emission scanning electron microscopy and transmission electron microscopy) and crystal structure (high resolution X-ray diffraction) characterizations of the as-synthesized nanostructures demonstrated the formation of GaN NWs having a wurtzite structure, zigzaged shape and an average diameter of 30-166nm. The Pt-decorated GaN NWs sensor shows a high response of 250-2650% upon exposure to H2 gas concentration from 7 to 1000ppm respectively at room temperature (RT), and then increases to about 650-4100% when increasing the operating temperature up to 75°C. The gas-sensing measurements indicated that the Pt-decorated GaN NWs based sensor exhibited efficient detection of H2 at low concentration with excellent sensitivity, repeatability, and free hysteresis phenomena over a period of time of 100min. The large surface-to-volume ratio of GaN NWs and the catalytic activity of Pt metal are the most influential factors leading to the enhancement of H2 gas-sensing performances through the improvement of the interaction between the target molecules (H2) and the sensing NWs surface. The attractive low-cost, low power consumption and high-performance of the resultant decorated GaN NWs gas sensor assure their uppermost potential for H2 gas sensor working at low operating temperature.
Liquid crystal physical gel formed by cholesteryl stearate for light scattering display material

Leaw WL, Mamat CR, Triwahyono S, Jalil AA, Bidin N

J Colloid Interface Sci, 2016 Aug 10;483:41-48.
PMID: 27552412 DOI: 10.1016/j.jcis.2016.08.020

A liquid crystal physical gel was prepared by the self-assembly of cholesteryl stearate in a nematic liquid crystal, 4-cyano-4'-pentylbiphenyl. The electro-optical properties were tuned by varying the gelator concentration and the gelation conditions. Polarized optical microscopy revealed that cholesteric cholesteryl stearate induced chiral nematic phase in 4-cyano-4'-pentylbiphenyl during the gelation process. As a result, a plate-like gel structure consisting of spherical micropores was formed, as observed by scanning electron microscopy. Electron spin resonance spectroscopy showed that the liquid crystal director orientations in these macrophase-separated structures were massively randomised. For these reasons, the liquid crystal physical gel generated a strong light scattering effect. For 48.0wt% cholesteryl stearate gelled 4-cyano-4'-pentylbiphenyl, the turbid appearance could be switched to a transparent state using a 5.0V alternating current. The response time was about 3.7μs. This liquid crystal physical gel has potential for use in light scattering electro-optical displays.
Thermally decomposed mesoporous Nickel Iron hydrotalcite: an active solid-base catalyst for solvent-free Knoevenagel condensation

Dumbre DK, Mozammel T, Selvakannan P, Hamid SB, Choudhary VR, Bhargava SK

J Colloid Interface Sci, 2015 Mar 1;441:52-8.
PMID: 25490562 DOI: 10.1016/j.jcis.2014.11.018

Thermal decomposition of co-precipitated Ni-Fe-HT materials led to the formation a mesoporous Ni-Fe-HT catalyst and we have demonstrated here its active role as solid and active catalyst for the Knoevenagel condensation reaction of various aldehydes with active methylene compounds (R-CH2-CN, where R=CN or CO2Et). High product yields are obtained at moderate temperature under solvent-free conditions and the catalyst can be easily separated from the reaction mixture, simply by filtration and reused several times without a significant loss of its activity. Since these mesoporous metal oxides derived from the NiFe hydrotalcites, their basicity mediated abstraction of the acidic protons from the active methylene compounds was responsible for their catalytic activity under solvent-free conditions.
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.

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