Defect and Diffusion Forum

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EISSN : 1662-9507
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Ivy Ai Wei Tan, J.R. Selvanathan, M.O. Abdullah, N. Abdul Wahab, D. Kanakaraju
Defect and Diffusion Forum, Volume 411, pp 67-78;

Palm oil mill effluent (POME) discharged without treatment into watercourses can pollute the water source. Microbial fuel cell (MFC) has gained high attention as a green technology of converting organic wastewater into bio-energy. As an approach to overcome the limitations of the existing POME treatment methods, air-cathode MFC-Adsorption system is introduced as an innovative technology to treat POME and generate bio-electricity simultaneously. However, the use of conventional MFC with proton exchange membrane in large scale applications is restricted by the high cost and low power generation. Addition of mediator in MFC is essential in order to increase the electron transfer efficiency, hence enhancing the system performance. This study therefore aims to investigate the effect of different type of mediators i.e. congo red (CR), crystal violet (CV) and methylene blue (MB) on the performance of an affordable air-cathode MFC-Adsorption system made from earthen pot with POME as the substrate. The addition of different mediators altered the pH of the MFC-Adsorption system, in which more alkaline system showed better performance. The voltage generated in the system with CR, CV and MB mediator was 120.58 mV, 168.63 mV and 189.25 mV whereas the current generated was 2.41 mA, 3.37 mA and 3.79 mA, respectively. The power density of 290.79 mW/m3, 568.72 mW/m3 and 716.31 mW/m3 was produced in the MFC-Adsorption system with CR, CV and MB mediator, respectively. The highest POME treatment efficiency was achieved in MFC-Adsorption system with MB mediator, which resulted in biochemical oxygen demand, chemical oxygen demand, total suspended solids, turbidity and ammoniacal nitrogen removal of 75.3%, 84.8%, 91.5%, 86.1% and 23.31%, respectively. Overall, the air-cathode MFC-Adsorption system with addition of MB mediator was feasible for POME treatment and simultaneous bio-energy generation.
Mohamad Raduan Bin Kabit, Syed Syabil Rahmat Syed Sarkawi, Abdul Mannan, Johnson Olufemi Adebayo
Defect and Diffusion Forum, Volume 411, pp 135-142;

Cracking is very common problem in cement mortar. Many past research has explored the prospect of using crumb rubber (CR) to overcome this issue. Different sizes of CR have been tested to measure its effect on the pore structure and mechanical strengths of cement mortar. Hence, this study has further modified the crumb rubber mortar mix by adding silica fume and synthetic fiber to improve its mechanical properties. The experimental results suggested that the optimum silica fume replacement of cement content was 5%. Hence, for the subsequent experiment with a fixed 5%silica fume replacement, the highest compressive strength of 26 MPa was achieved with 5% crumb rubber replacement. Finally, additional 0.1% of synthetic fiber added the modified crumb rubber mix to reduce the mix brittleness has produced a desirable compressive strength close to the control specimen which was significantly higher than the minimum threshold required by the standard. However, the water content ratio for the modified mortar mix should be further investigated as the present modified crumb rubber mix has lower workability. It is envisaged that the modified crumb rubber mortar mix has a sound potential to mitigate shrinkage cracking in cement mortar.
Nur Arif Mortadza, Zainab Ngaini, Maya Asyikin Mohamad Arif
Defect and Diffusion Forum, Volume 411, pp 17-24;

The rise of antimicrobial resistance for infectious bacteria has become an alarming issue to human health. New antimicrobial drugs are in dire need and pivotal to overcome this issue. In this study, aspirinate azo ligands bearing different halogens L1-5 has been prepared via diazo-coupling reaction. The ligands L1-5 were coordinated with silver, Ag (I) metal to produce Ag (I) aspirin-azo complexes C1-5. The antibacterial properties of L1-5 and C1-5 were evaluated against Staphylococcus aureus and E scherichia coli using turbidimetric kinetic method. The complexes C1-5 showed comparable growth inhibition activity towards E. coli (MIC 82-105 ppm) and S . aureus (MIC 80-105 ppm) compared to ligands L1-5 with E. coli (MIC 83-200 ppm), S . aureus (80-131 ppm) and ampicillin (MIC 93 and 124 ppm, respectively). The excellent bacterial resistance of both L1-5 and C1-5 indicates the potential of aspirinate azo and their complexes as new antibacterial agents, which significantly benefit to the pharmaceutical industries.
Boon Siong Wee, Eric Kwabena Droepenu, Suk Fun Chin, Kuan Ying Kok, Woei Ting
Defect and Diffusion Forum, Volume 411, pp 3-15;

This study reports on synthesis of ZnO nanostructures using Zinc chloride (ZnCl2) as precursors and Potassium hydroxide (KOH) as alkaline source in a solvothermal process with varying molar concentrations (Zn2+/OH-) of 1:1, 1:3 and 1:5 for temperatures of 30 °C and 50 °C. The synthesized nanostructures were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FT-IR) Spectroscopy, and Ultraviolet Visible (UV-Vis) spectroscopy. ZnO nanostructures synthesized at lower ratios (1:1) exhibited wurtzite hexagonal shapes. However, as the concentration ratios increases in both cases, spherical structures were formed with the emergence of some rod-like structures dominating, and finally aggregated to form flower-like structures at 30 °C temperature. The average crystallite size for nanostructures from XRD (30-50 °C) were in the range 15-21 nm whereas the average particle size from TEM analysis (30-50 °C) were in the range 39-76 nm. Increase in temperature and molar concentration of the alkaline source generally decreased the crystallite and particle size of the as well as a decrease in the wavelength of ZnO nanostructures as a result of blue-shifting of the absorption peak. FT-IR spectra of ZnO NSs prepared from concentration ratios of Zn2+: OH- (1:1, 1:3 and 1:5) at 30 °C and 50 °C showed characteristic peak bands at 461-467 cm-1 and 460-462 cm-1 respectively.
Defect and Diffusion Forum, Volume 411, pp 121-133;

This paper presents the peat ground improvement techniques using waste-tire as a fibre reinforced material. In this study, two sizes of the waste-tire are chosen, which are 0.05 mm and 1-3 mm, respectively. The collected peat is classified as Sapric peat with the degree of decomposition of H7 based on von Post classification with high moisture content of 400% was recorded. The Sapric peat is treated with the waste-tire at designated percentages of 5%, 10% and 15% with the addition of 5% of cement acting as a binder. The untreated and treated peat without and with cement content are compacted at the optimum moisture content for both the Unconfined Compressive Strength (UCS) test and Direct Shear Box Test. The specimens were air-cured for 7, 28, 56, and 90 days. Hypothetically, higher percentages of rubber improve the shear stress value of the treated peat. According to the results the finer size (0.05mm) of the tire produces a higher shear stress, which may due the finer sizes of the waste-tire filled the void between the soil particles. Further, from the 90 days of curing UCS results, there is a significant increase in compressive strength with the increase percentage of the waste-tire peat mixed samples. In summary, soil stabilized by the scrap-tire is believed to decrease the optimum moisture content and the maximum dry densities, but it helps in increasing the unconfined compressive strength value. Stabilizing by using the tire wastes not only increasing the strength of the soil, but it also helps in reducing the disposal problems.
Eric Kwabena Droepenu, Boon Siong Wee, Suk Fun Chin, Kuan Ying Kok
Defect and Diffusion Forum, Volume 411, pp 37-54;

In this study, sorption efficiency of coated (C-) and uncoated (U-) zinc oxide nanoparticles (ZnO-NPs) in aqueous solution onto raw sago hampas (RSH) and acetylated sago hampas (ACSH) was studied. Physical and chemical characteristics of both the sorbate and sorbents were analysed using various characterization techniques. The mechanism of the sorption process was evaluated using equilibrium isotherms, kinetic and thermodynamic studies. From the study, maximum percentage removal of both sorbate ions were achieved at an equilibration time of 100 minutes with an optimum sorbate mass of 2.0 g per 50 ml. The study recorded a maximum % removal of 85.1% & 87.6% for C-and U-ZnO-NPs (< 50 nm) onto RSH and 90.0% & 91.1% onto ACSH. Langmuir isotherm fitted well for the sorption process with the highest efficiency of 0.793 mg/g recorded for C-ZnO-NPs onto RSH. Pseudo-second model best described the sorption process. An exothermic and non-spontaneous sorption process was realised in all the sorption studies except that of U-ZnO-NPs (< 50 nm) onto ACSH which became spontaneous as temperature increased. Based on the findings from the multiple approaches employed, both sorbents could be proposed as viable alternatives to act as a green sorbent in the removal of ZnO-NPs from water and wastewater.
Defect and Diffusion Forum, Volume 411, pp 157-168;

Geotechnical structures, design of embankment, earth and rock fill dam, tunnels, and slope stability require further attention in determining the shear strength of soil and other parameters that govern the result. The shear strength of soil commonly obtained by conducting laboratory testing such as Unconfined Compression Strength (UCS) Test and Unconsolidated Undrained (UU) Test. However, random errors and systematic errors can occur during experimental works and caused the findings imprecise. Besides, the laboratory test also consuming a lot of time and some of them are quite costly. Therefore, soft computational tools are developed to improve the accuracy of the results and time effectively when compared to conventional method. In this study, Artificial Neural Network (ANN) was employed to develop a predictive model to correlate the moisture content (MC), liquid limit (LL), plastic limit (PL), and liquidity index (LI) of cohesive soil with the undrained shear strength of soil. A total of 10 databases was developed by using MATLAB 7.0 - matrix laboratory with 318 of UCS tests and 451 of UU tests which are collected from the verified site investigation (SI) report, respectively. All the SI reports collected were conducted in Sarawak, Malaysia. The datasets were split into ratio of 3:1:1 which is 60:20:20 (training: validation: testing) with one hidden layer and eight hidden neurons. The input parameter of Liquidity index (LI) has shown the highest R-value (regression coefficient) which are 0.926 and 0.904 for UCS and UU model, respectively. In addition, the predictive models were tested and compare with the predicted and observed cohesion obtained from the collected experimental results. In summary, the ANN has the feasibility to be used as a predictive tool in estimating the shear strength of the soil.
Sharon Robert, Idawati Ismail, Raudhah Ahmadi, Nur Amalina Shairah Abdul Samat
Defect and Diffusion Forum, Volume 411, pp 143-155;

In cement industry, the emissions of greenhouse gases specifically CO2 from the clinker production led to the need of alternative binders. Geopolymer binder whose precursors are sourced from industrial by-products such as fly ash that are rich is silica and alumina has been studied extensively in the past decades. Chloride attack is one of the threats to concrete structures. Analysis at microstructural level needs to be studied carefully before this binder can be used with confidence. This study attempts to compare the properties of fly ash geopolymer binder when exposed in water and chloride solution. Fly ash geopolymer pastes were prepared using 12M sodium hydroxide (NaOH) as activator. The pastes were tested under two separate curing conditions, i.e in ambient and in distilled water. Compressive strength test along with microstructure properties of samples cured at 7, 14 and 28 days were conducted via Universal testing machine, Fourier Transform Infra-Red (FTIR) spectroscopy and Scanning Electron Microscope with Energy-dispersive X-ray (SEM-EDX). After 28 days of curing, these samples were immersed in 10% sodium chloride (NaCl) solution for another 56 days. Samples cured in ambient condition showed better mechanical performance than those in distilled water. Their differences in compressive strength were also seen consistent with the FTIR results. Samples exposed to NaCl and distilled water showed similar mechanical performance and microstructural properties. Based on SEM-EDX analysis, samples cured in ambient were rich in silica and alumina while the intensity of these compounds were observed to reduce when exposed to distilled water. Samples cured in ambient showed stronger intensity of Si/Al gel as compared to samples exposed to chloride environment and distilled water and these were consistent with the compressive strength results obtained. When immersed in water, concentration gradient changes in the liquid phases, leading to ions diffusion and causing decrement in strength and durability of the solids in fly ash geopolymer.
Kavitha Vijeandran, Tu Anh Vu Thanh
Defect and Diffusion Forum, Volume 411, pp 57-66;

Cow leather is a widely used material. Even though durable, it causes ethical, social, and environmental issues. The synthesis of vegan leather, using a symbiotic culture of bacteria and yeast (SCOBY), could be explored for an alternative to cow leather. Presently, there are limited studies on the different substrates used to produce vegan leather using this method. Hence, this study aimed to produce plant-based vegan leather, using various plant-based substrates such as black tea, green tea, black and green tea, coconut water, and fruit pulp with five replicates per substrate. All the substrates used in the experiments were able to produce cellulose upon inoculation. The overall results indicate that the substrate consisting of a mixture of black and green tea was the most effective in producing vegan leather in terms of yield and cost.
Muhammad Imran-Shaukat, Nur Rafikah Binti Rosli, Rafeah Wahi, Sharifah Mona Abd Aziz Abdullah, Zainab Ngaini
Defect and Diffusion Forum, Volume 411, pp 79-91;

In this study, coconut shells were converted into biochar via pyrolysis and chemically modified via an acid-base treatment to enrich its adsorption capabilities. Batch experiments were carried out to analyze the adsorption potential of the modified coconut shell (MCSC) or removal of chromium, nickel, and copper from aqueous solution. The chemical modification increased the surface area of MCSC to 185.712 m2/g. Batch adsorption study using MCSC resulted in 99% removal of copper, 95% (nickel), and 39% (chromium). The adsorption of studied metal ions fitted well with Langmuir isotherm, showing a monolayer adsorption process. A kinetic analysis showed that all the samples match a strong correlation coefficient in pseudo-second-order (R2>0.95), indicating the occurrence of a chemical adsorption process.
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