Pusat Pengajian Kejuruteraan Kimia - Tesis

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Synthesis of thermo-magneto-responsive poly(n-isopropylacrylamide)-based composite hydrogels for adsorption-desorption of chromium (iii) ions
(2019-07)
Chen, Jian Jie
Stimuli-responsive composite hydrogels have been in the vanguard of researches for their application in metal ion adsorption and its release via conformational change. The preparation of composite hydrogels with both thermo- and magneto responsiveness requires careful layer-by-layer coatings of functional shells onto the core of iron oxide magnetic nanoparticles (MNPs). However, multiple stages of shell encapsulation of MNPs remains a major setback on the production of composite hydrogels with adequate colloidal stability and well-functioned dual-responsiveness. In this study, homo-polymeric poly(N-isopropylacrylamide)-encapsulated magnetite nanoparticles (PNIPAM-MNPs) cross-linked composite hydrogels were facilely synthesized via layer-by-layer coatings with and without employing silanization precursor, 3-(trimethoxysilyl)propyl methacrylate (MPS). It was found that PNIPAM could be gelated directly onto the silica-coated, poly(vinylpyrrolidone) (PVP) functionalized MNPs (silica-PVP-MNPs) via free radical polymerization without MPS to improve its colloidal stability and both thermo-magneto-responsive. Besides, copolymeric poly(N-isopropylacrylamide-co-acrylic acid)-encapsulated MNPs ((PNIPAM-co-AA)-silica-PVP-MNPs) composite hydrogels were prepared for elucidating the difference in adsorption mechanisms between chelating groups of carboyxlates (-COO-) contained by AA moiety and amides (-CONH) of NIPAM moiety. In the temperature manipulated adsorption-desorption tests, desorption of Cr3+ gradually predominated as temperature increased from 298 K to 323 K for PNIPAM silica-PVP-MNPs. Re-adsorption of Cr3+ by the composite hydrogel took place as being quenched to 298 K for lower initial Cr3+ concentration (20 – 80 mg L-1) which showed that desorption can be realised for surface adsorption. Before heating, the equilibrium adsorption data of Cr3+ fitted well into Flory-Huggins and Frumkin models, that elucidated the chelation of Cr3+ ions occurred via replacement of water molecules on the binding sites. Moreover, PNIPAM-silica-PVP-MNPs had higher maximum adsorption capacity, qm (434.78 mg g-1) compared to (PNIPAM-co-AA)-silica-PVP MNPs (qm = 243.90 mg g-1) as extrapolated by Langmuir isotherm model in which the data of both composite hydrogels also showed good fit to the model. The adsorption kinetic analysis indicated that Cr3+ adsorption on PNIPAM-silica-PVP-MNPs was governed by intra-particle diffusion and reversible surface physisorption as its data followed pseudo-first, pseudo-second- and intra-particle diffusion models. On the other hand, surface chemisorption predominated over (PNIPAM-co-AA)-silica-PVP MNPs as it followed only pseudo-second model.
Development of a portable membrane-color-sensor for detection of heavy metal
(2019-07)
Nur Atiah Azmi
A basic requirement of colorimetric membrane-based sensors is to allow the target analyte to access to the chromophore while retaining a strong chromophore immobilization on the membrane surface. This study elucidates the fundamental perceptive of membrane morphologies and their influences on the binding of chromophores to detect aqueous heavy metals ions. Flat sheet membranes consist of mixed polymer cellulose acetate (CA) and chitosan (CS) was acts as the sensing platform for chromophore binding. Membrane with 17 wt.% CA and 1 wt.% CS showed to have the high binding capacity and high binding stability up to 90 days of measurement. The addition of deionized water (DI) as the non-solvent additive has also shown to improve the membrane porousness, which improved the sensor’s sensitivity. Visible color changes of the colorimetric membrane from blue-greenish to peachy-pink was observed when it was in contact with the Pb2+ ions in 1 ppm Pb(NO3)2. Selection of sensitive chromophore (Dithizone, 1-(2-pyridylazo) 2 naphthol and 4-(2-pyridylazo)-resorcinol) and its immobilization strategy on the membrane sensor has also been carried out. Dithizone (DTz) at unadjusted pH was capable to produce an obvious color transition observed through UV-visible absorption spectrum and naked eyes recognition. The optimum immobilization of DTz required the concentration of 100 ppm and 10 minutes immobilization time. To determine the sensitivity and selectivity of the developed colorimetric sensor in the single and mixed aqueous heavy metals ions solution, the sensing conditions such as pH, type of heavy metals (Pb2+, Hg2+, Zn2+ and Cu2+), concentration and response time were evaluated. The developed DTz-membrane sensor in this work has exhibited quick (within 1 minute) color change and was able to display distinctive color changes from blue-greenish to peachy-pink, yellowish-orange, red-violet and reddish-brown in the response to the presence of Pb2+, Hg2+, Zn2+ and Cu2+ in aqueous solutions. The quantitative analysis using RGB (R:Red; G:Green; B:Blue) data showed that each tested metal ions have demonstrated their own RGB’s recognition pattern phase without significant interfering effects among the heavy metal ions. This showed the potential for practical applications of on-site quick detection on either single or mixed heavy metal ions. The DTz-CA/CS membrane showed a distinctive color changed in the detection of synthetic heavy metals ions in the water that obtain from Kerian River. The synthetic heavy metals ions was prepared the at maximum permissible limit of 0.1 ppm Pb2+, 2.0 ppm Zn2+ and 0.2 ppm Cu2+ for industrial effluent (Standard A) by Malaysian Department of Environment. This membrane sensor was successfully applied for the determination of heavy metals ions not only limited to river water quality assessment but also included the cosmetic product analysis (lipstick samples) at the low trace level of heavy metals ions.
Fabrication of superhydrophobic microsphere electrospun membrane through template printing technique to enhance membrane distillation for aquaculture wastewater treatment
(2023-05-01)
Zhou Lei
Membrane distillation (MD) is one of the promising technologies for desalination and wastewater treatment. Electrospinning membranes (EMs) is frequently used in MD applications because it has an interconnected pores structure to facilitate the transport of water vapor, which can increase the permeation flux of MD. Aquaculture wastewater contains a large amount of inorganic and organic compounds, which can cause wetting and fouling of MD membrane. The superhydrophobic membrane can reduce the wettability of the membrane and maintain a long-term stable desalination process during MD. In this work, superhydrophobic poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun membranes were fabricated by template printing technique to construct hierarchical microtextures on membrane surfaces. When the injection rate was 1.0 mL/h and the solvent weight ratio of N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF) was 1:1, the membrane exhibited optimal printed microtextures when electrospun at the temperature of 30±2 ℃ and the relative humidity of 70±5 %. The microtexture template structure provides hierarchical micro-and nano-roughness on the membrane surface. The optimal membrane exhibits superhydrophobicity, with a static contact angle of 158° and a sliding angle of 8.5°. In the direct contact membrane distillation (DCMD) for treating high saline water and aquaculture wastewater, the initial permeation fluxes of the optimal membrane were as high as 40.76 kg·m-2·h-1 and 33.45 kg·m-2·h-1, which were 161% and 174% higher than the non-printed membrane. To further enhance the superhydrophobicity of the templated PVDF-HFP membrane, microsphere beads were integrated in the membrane matrix. The fabricated membrane exhibited interconnected microspherenanofiber structure with hierarchical micro-nano roughness. Due to the intrinsic microspheres on the nanofibers, the water contact angle of all microsphere/nanofiber membranes were higher than 150°. The optimal membrane exhibited superhydrophobicity, with a static contact angle of 157° and a low sliding angle of 6.4°. In DCMD, the optimal membrane shows a high permeation flux of 38.8 kg·m- 2·h-1 and a salt rejection of 99.99% in separating high saline water as well as a permeate flux of 32.68 kg·m-2·h-1 and a salt rejection of 99.98% in treating aquaculture wastewater. In addition, the microsphere-nanofiber membrane also exhibited a stable separation process and excellent anti-fouling for 72-hours longterm DCMD. Overall, the surface microtexture printed superhydrophobic membrane show great potential in practical desalination applications.
Conversion of waste slags into functional oxide materials and their application in carbon dioxide capture
(2023-02-01)
Zaza Hazrina Hashim
Slag is a by-product of the smelting process for ores and scrap metals. The issue of excessive slag waste generated in the iron and steel industries has spurred an investigation on slag utilization. Blast furnace slag (BFS) is recovered by melting and separation from blast furnaces that produce molten pig iron, while dephosphorization slag and desiliconization slag are generated during the purification of steel to reduce the phosphorus and silicon content, respectively, and mostly consist of CaO, FeO, SiO2 and other minor oxides. In addition, CO2 emitted from the iron and steel industry accounts for about 5-7% of the total CO2 emissions worldwide, and its separation and recovery is a challenge. Chapter 1 provides background information on global warming and CO2 emissions from the iron and steel industries, as well as carbon capture and sequestration using calcium looping technologies. The problem statement, research objectives, scope of the study, and contents of the thesis are also addressed. Chapter 2 summarizes the iron and steel making process and discusses global steel slag production, chemical composition of steel slag, and CO2 emissions from the steel industry. Carbon capture and sequestration using calcium looping technology, examples of the use of waste slags as CO2 adsorbents and some methods to control sintering of CaO-based adsorbents are also addressed. In chapter 3, the general methodology for converting waste slags into metal oxide composites is addressed, which includes i) synthesis of CaO-Ca12Al14O33 composite adsorbent from blast furnace slag, ii) synthesis of CaO-Fe2O3-SiO2 composite adsorbent from dephosphorization slag, and iii) synthesis of CaO-mesoporous silica composite adsorbent from desiliconization slag. It also describes the chemicals and materials, the methods used to evaluate the CO2 adsorption performance, and the details of the equipment used in the experiments. Chapter 4 describes the structure and CO2 adsorption performance of the CaO-based oxide composites synthesized from three types of slag (blast furnace slag, dephosphorization slag, and desiliconization slag) using various acids (HCl, HNO3, formic acid, acetic acid, and citric acid). In Part I, a CaO-Ca12Al14O33 composite is synthesized from blast furnace slag using HCl and HNO3 as dissolving acids. It is found that the sample synthesized using HNO3 shows a superior CO2 adsorption performance compared to that synthesized using HCl due to easy removal of nitrate ions by a thermal treatment. In Part II, a CaO-Fe2O3-SiO2 composite is synthesized from dephosphorization slag using three kinds of acids (formic acid, HCl and HNO3) and a pore-forming agent (P123). The composite synthesized with formic acid shows the highest CO2 adsorption of 17 wt% under a flow of 10% CO2/N2 and at 700 °C. It is found that the use of organic acids and the addition of a pore-forming agent are effective for the synthesis of an efficient CO2 adsorbent. In Part III, a CaO-mesoporous silica composites are synthesized from desiliconization slag using three types of organic acids (formic acid, acetic acid, and citric acid). The sample synthesized with acetic acid shows a high CO2 adsorption uptake of about 21 wt% and reusability. It is considered that the use of acetic acid promotes the separation of crystalline CaO and SiO2 particles by the reaction of acetate ions and leached Ca2+ ions to form calcium acetate, which suppresses the sintering during CO2 adsorption and improves the durability of the adsorbent
Superhydrophobic polyvinylidene fluoride-halloysite membranes for oxytetracycline treatment via membrane distillation
(2023-01-01)
Wan Aisyah Fadilah Binti Wae Abdulkadir Usin
The indiscriminate use of Oxytetracycline (OTC) contributes to water pollution, which adversely affects aquatic microorganism and to some extent harmed public health. Recently, membrane distillation (MD) is being introduced as a promising separation process for antibiotics (i.e., OTC) removal. However, the limitation of MD membrane is wetting and fouling issues that affect the efficiency of separation process. Therefore, in this study, superhydrophobic polymeric flat sheet membrane made from polyvinylidene fluoride (PVDF) and clay fillers (montmorillonite (MMT) and halloysite nanotube (HNT)) were developed via phase inversion with investigation of solvent, different types of clay fillers and fabrication parameters and modified through carnauba wax spray-coating. Clay fillers was selected due to its unique structure which helped to improve membrane permeability, mechanical properties and biofouling resistance. Meanwhile, the carnauba wax could provide a durable superhydrophobic surface by forming hierarchical structure on the membrane and minimize the wetting and fouling issue. The selected membrane was investigated on different HNT loading, immersion time, nominal thickness, addition of different types and concentrations of additives (polyethylene glycol 400 (PEG400) and Tween 80 (Tw80)). The composite membrane was characterized for its wetting properties, morphological structure, pore size and porosity. The prepared membrane had formed symmetrical structure in all formulations as shown by scanning electron microscopy (SEM) images. 0.5% HNT loading achieved 100% of OTC rejection with low flux permeation. This membrane maintained LEP >1 bar with hydrophobic contact angle (CA). The modification by optimal fabrications parameters (1 %PEG, 5 s of immersion time, 250 μm of nominal thickness) had improved flux permeation (11.06 ± 0.42) with rejection >97%. The optimum superhydrophobic membrane was obtained for 3 ml Ti(OBu)4 in carnauba wax solution at 2 min and 3 h of spraying and drying time, respectively. The CA had achieved to 157° with an improvement of surface roughness obtained by atomic force microscopy (AFM). The performance of superhydrophobic membrane using direct contact membrane distillation (DCMD) has achieved more than 99% rejection with average flux at different feed temperature, OTC concentration, OTC pH and different feed solutions. Regeneration and long-term operation studies revealed that superhydrophobic PVDF/HNT/PEG showed a positive impact on CA after DCMD, stable permeate flux and high OTC rejection with average value of 156°, 10.75 ± 0.34 L/m2h and 100% within 30 h of DCMD. Fouling mechanism was best fitted to pore constriction model with reversible fouling layer. The OTC separation for superhydrophobic PVDF/HNT/PEG membrane was observed to sustain when exposed to long-term operation. Thus, the modification approach of PVDF/clay membrane using HNT, and carnauba wax can be as an alternative strategy to develop MD membrane for organic pollutant treatment.

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