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Fulltext Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites

Kee SY, Munusamy Y, Ong KS, Lai KC

Polymers (Basel), 2017 Jun 18;9(6).
PMID: 30970908 DOI: 10.3390/polym9060230

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young's modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.
Ice-templated graphene oxide/chitosan aerogel as an effective adsorbent for sequestration of metanil yellow dye

Lai KC, Hiew BYZ, Lee LY, Gan S, Thangalazhy-Gopakumar S, Chiu WS, et al.

Bioresour Technol, 2019 Feb;274:134-144.
PMID: 30502604 DOI: 10.1016/j.biortech.2018.11.048

Graphene oxide/chitosan aerogel (GOCA) was prepared by a facile ice-templating technique without using any cross-linking reagent for metanil yellow dye sequestration. The adsorption performance of GOCA was investigated by varying the adsorbent mass, shaking speed, initial pH, contact time, concentration and temperature. The combined effects of adsorption parameters and the optimum conditions for dye removal were determined by response surface methodology. GOCA exhibited large removal efficiencies (91.5-96.4%) over a wide pH range (3-8) and a high adsorption capacity of 430.99 mg/g at 8 mg adsorbent mass, 400 mg/L concentration, 35.19 min contact time and 175 rpm shaking speed. The adsorption equilibrium was best represented by the Langmuir model. GOCA could be easily separated after adsorption and regenerated for re-use in 5 adsorption-desorption cycles thereby maintaining 80% of its adsorption capability. The relatively high adsorption and regeneration capabilities of GOCA render it an attractive adsorbent for treatment of azo dye-polluted water.
Environmental application of three-dimensional graphene materials as adsorbents for dyes and heavy metals: Review on ice-templating method and adsorption mechanisms

Lai KC, Lee LY, Hiew BYZ, Thangalazhy-Gopakumar S, Gan S

J Environ Sci (China), 2019 May;79:174-199.
PMID: 30784442 DOI: 10.1016/j.jes.2018.11.023

The remediation of wastewater requires treatment technologies which are robust, efficient, simple to operate and affordable such as adsorption. Lately, three-dimensional (3D) graphene based materials have attracted significant attention as effective adsorbents for wastewater treatment. The intrinsic properties of 3D graphene structure such as large surface area and interconnected porous structure can facilitate the transport of pollutants into the 3D network and provide abundant active sites for trapping the pollutants. For the synthesis of 3D graphene structure, ice-templating is commonly practiced due to its facile steps, cost effectiveness and high scalability potential. This review covers the ice-templating fabrication technique for 3D graphene based materials and their application as adsorbents in eliminating dyes and heavy metals from aqueous media. The assembly mechanisms of the ice-templating fsynthesis are comprehensively discussed. Further discussion on the fundamental principles, critical process parameters and characteristics of ice-templated 3D graphene structures is also included. A thorough review on the mechanisms for batch adsorption of dyes and heavy metals is presented based on the structures and properties of the 3D graphene materials. The review further evaluates the dynamic adsorption in packed columns and the regeneration of 3D graphene based materials.
Facile synthesis of xanthan biopolymer integrated 3D hierarchical graphene oxide/titanium dioxide composite for adsorptive lead removal in wastewater

Lai KC, Lee LY, Hiew BYZ, Thangalazhy-Gopakumar S, Gan S

Bioresour Technol, 2020 Aug;309:123296.
PMID: 32330800 DOI: 10.1016/j.biortech.2020.123296

Xanthan integrated graphene oxide functionalized by titanium dioxide was successfully prepared through facile, eco-friendly and cost effective ice-templating technique. The three-dimensional (3D) graphene composite demonstrated relatively high temperature stability, chemical functionalities and porous sponge-like structure. The adsorption of lead was favored by high initial concentration and shaking speed at the operational solution pH. The process equilibrium and kinetic adhered to the Langmuir and pseudo-second-order correlations, respectively. The biomass integrated graphene composite showed maximum adsorption capacities ranging from 132.18 to 199.22 mg/g for 30-70 °C. Moreover, it was highly regenerable under mild conditions (0.1 M hydrochloric acid, 30 °C) and used repeatedly while retaining 84.78% of its initial adsorption capacity at the fifth adsorption-regeneration cycle. With comparatively high lead adsorption capacities, adequate recyclability and environmentally friendliness, the as-prepared 3D graphene composite has high application potential in heavy metal-wastewater separation for protection of the environment and human health.
Fulltext Thermal Performance Study of Composite Phase Change Material with Polyacrylicand Conformal Coating

Kee SY, Munusamy Y, Ong KS, Cornelis Metselaar HS, Chee SY, Lai KC

Materials (Basel), 2017 Jul 28;10(8).
PMID: 28773232 DOI: 10.3390/ma10080873

The composite PCM was prepared by blending polymethyl methacrylate (PMMA) and myristic acid (MA) in different weight percentages. The MA and PMMA were selected as PCM and supporting material, respectively. As liquid MA may leak out during the phase transition, this study proposes the use of two coatings, namely a polyacrylic coating and a conformal coating to overcome the leakage problem. Both coatings were studied in terms of the leakage test, chemical compatibility, thermal stability, morphology, and reliability. No leakage was found in the PCMs with coatings compared to those without under the same proportions of MA/PMMA, thus justifying the use of coatings in the present study. The chemically compatibility was confirmed by FTIR spectra: the functional groups of PCMs were in accordance with those of coatings. DSC showed that the coatings did not significantly change the melting and freezing temperatures, however, they improved the thermal stability of composite PCMs as seen in TGA analysis. Furthermore, the composite PCMs demonstrated good thermal reliability after 1000 times thermal cycling. The latent heat of melting reduced by only 0.16% and 1.02% for the PCMs coated with conformal coating and polyacrylic coating, respectively. Therefore, the proposed coatings can be considered in preparing fatty acid/PMMA blends attributed to the good stability, compatibility and leakage prevention.
Fulltext Perceptions with Type 2 Diabetes Mellitus of the Value of Prescribed Medications Among Malaysian Adults: A Qualitative Study

Lim MC, Hatah E, Lai KC, Buang A, Koay TJ, Sim WJY, et al.

Patient Prefer Adherence, 2022;16:3133-3142.
PMID: 36471869 DOI: 10.2147/PPA.S382341

PURPOSE: Previous studies show that customer loyalty and purchase intentions were influenced by perceived product value, but little is known about the factors that influence patients' perceptions of the value of their subsidized prescriptions, when purchasing of medications were not required, and how these factors influence their medication adherence. Hence, this study aims to investigate perceptions of patients receiving subsidized medications regarding the value of their medication.
PATIENTS AND METHODS: This qualitative study involved semi-structured, face-to-face interviews with patients diagnosed with type 2 diabetes mellitus at a government district hospital in Selangor state, Malaysia between June to September 2019. Using purposive sampling, patients were identified at an out-patient pharmacy during prescription refill. They were asked how they perceived the value of their medication. Interviews were audio recorded and then transcribed verbatim for thematic analysis.
RESULTS: A total of thirty patients were interviewed. Patients' perceptions on the value of medications were influenced by several factors such as trust, how the medications impact on their physical and social well-beings, and the perceived sacrificed made when the medications were procured and used. Perceptions on medication values were influenced by the recommendation received from someone they trust such as their doctors or significant others. It was also influenced by their perceptions of how the medication helps to improve their disease symptoms and affect their religious and social activities. Other factors include the perceived worth of the sacrifices made to access and use the medication.
CONCLUSION: Identifying factors that may influence patients' perceived value of the medication may help improve healthcare practices.
Segmentation Approach Towards Phase-Contrast Microscopic Images of Activated Sludge to Monitor the Wastewater Treatment

Khan MB, Nisar H, Ng CA, Yeap KH, Lai KC

Microsc Microanal, 2017 12;23(6):1130-1142.
PMID: 29212566 DOI: 10.1017/S1431927617012673

Image processing and analysis is an effective tool for monitoring and fault diagnosis of activated sludge (AS) wastewater treatment plants. The AS image comprise of flocs (microbial aggregates) and filamentous bacteria. In this paper, nine different approaches are proposed for image segmentation of phase-contrast microscopic (PCM) images of AS samples. The proposed strategies are assessed for their effectiveness from the perspective of microscopic artifacts associated with PCM. The first approach uses an algorithm that is based on the idea that different color space representation of images other than red-green-blue may have better contrast. The second uses an edge detection approach. The third strategy, employs a clustering algorithm for the segmentation and the fourth applies local adaptive thresholding. The fifth technique is based on texture-based segmentation and the sixth uses watershed algorithm. The seventh adopts a split-and-merge approach. The eighth employs Kittler's thresholding. Finally, the ninth uses a top-hat and bottom-hat filtering-based technique. The approaches are assessed, and analyzed critically with reference to the artifacts of PCM. Gold approximations of ground truth images are prepared to assess the segmentations. Overall, the edge detection-based approach exhibits the best results in terms of accuracy, and the texture-based algorithm in terms of false negative ratio. The respective scenarios are explained for suitability of edge detection and texture-based algorithms.
Adsorptive decontamination of diclofenac by three-dimensional graphene-based adsorbent: Response surface methodology, adsorption equilibrium, kinetic and thermodynamic studies

Hiew BYZ, Lee LY, Lai KC, Gan S, Thangalazhy-Gopakumar S, Pan GT, et al.

Environ Res, 2019 01;168:241-253.
PMID: 30321737 DOI: 10.1016/j.envres.2018.09.030

Pharmaceutical residues are emerging pollutants in the aquatic environment and their removal by conventional wastewater treatment methods has proven to be ineffective. This research aimed to develop a three-dimensional reduced graphene oxide aerogel (rGOA) for the removal of diclofenac in aqueous solution. The preparation of rGOA involved facile self-assembly of graphene oxide under a reductive environment of L-ascorbic acid. Characterisation of rGOA was performed by Fourier transform infrared, scanning electron microscope, transmission electron microscopy, nitrogen adsorption-desorption, Raman spectroscopy and X-ray diffraction. The developed rGOA had a measured density of 20.39 ± 5.28 mg/cm3, specific surface area of 132.19 m2/g, cumulative pore volume of 0.5388 cm3/g and point of zero charge of 6.3. A study on the simultaneous interactions of independent factors by response surface methodology suggested dosage and initial concentration as the dominant parameters influencing the adsorption of diclofenac. The highest diclofenac adsorption capacity (596.71 mg/g) was achieved at the optimum conditions of 0.25 g/L dosage, 325 mg/L initial concentration, 200 rpm shaking speed and 30 °C temperature. The adsorption equilibrium data were best fitted to the Freundlich model with correlation coefficient (R2) varying from 0.9500 to 0.9802. The adsorption kinetic data were best correlated to the pseudo-first-order model with R2 ranging from 0.8467 to 0.9621. Thermodynamic analysis showed that the process was spontaneous (∆G = - 7.19 to - 0.48 kJ/mol) and exothermic (∆H = - 12.82 to - 2.17 kJ/mol). This research concluded that rGOA is a very promising adsorbent for the remediation of water polluted by diclofenac.
Effects of sonication on co-precipitation synthesis and activity of copper manganese oxide catalyst to remove methane and sulphur dioxide gases

Yap YH, Lim MSW, Lee ZY, Lai KC, Jamaal MA, Wong FH, et al.

Ultrason Sonochem, 2018 Jan;40(Pt A):57-67.
PMID: 28946460 DOI: 10.1016/j.ultsonch.2017.06.032

The utilisation of ultrasound in chemical preparation has been the focus of intense study in various fields, including materials science and engineering. This paper presents a novel method of synthesising the copper-manganese oxide (Hopcalite) catalyst that is used for the removal of volatile organic compounds and greenhouse gases like carbon monoxide. Several samples prepared under different conditions, with and without ultrasound, were subjected to a series of characterisation tests such as XRD, BET, FE-SEM, EDX, TPR-H2, TGA and FT-IR in order to establish their chemical and physical properties. A series of catalytic tests using a micro-reactor were subsequently performed on the samples in order to substantiate the aforementioned properties by analysing their ability to oxidise compressed natural gas (CNG), containing methane and sulphur dioxide. Results showed that ultrasonic irradiation of the catalyst led to observable alterations in its morphology: surfaces of the particles were noticeably smoothed and an increased in amorphicity was detected. Furthermore, ultrasonic irradiation has shown to enhance the catalytic activity of Hopcalite, achieving a higher conversion of methane relative to non-sonicated samples. Varying the ultrasonic intensity also produced appreciable effects, whereby an increase in intensity results in a higher conversion rate. The catalyst sonicated at the highest intensity of 29.7W/cm2has a methane conversion rate of 13.5% at 400°C, which was the highest among all the samples tested.