Pusat Pengajian Kejuruteraan Kimia - Tesis

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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.
Carbon dioxide reduction with methane over cerium oxide and indium oxide nanocomposite photocatalysts
(2023-01-01)
Tharani Kulandaivalu
Photocatalytic carbon dioxide (CO2) reduction with methane (CH4) offers a great potential to convert two notorious greenhouse gases to value-added fuels using inexhaustible solar energy. The present study aimed to develop novel silver (Ag) and ceria (CeO2) modified indium oxide (In2O3) photocatalysts for photocatalytic CO2 reduction with CH4 to convert highly stable CO2 and CH4 into syngas. At first, a comparison study was conducted for CeO2/In2O3 composite photocatalysts that were synthesised using two different facile methods, namely wet-impregnation (WI) and hydrothermal co-precipitation (CP) methods and the as-synthesised composite were denoted as CeO2/In2O3-WI and CeO2/In2O3-CP, respectively.The morphological observation verified the formation of interfaces between CeO2 and In2O3 in both the CeO2/In2O3 samples. Both preparation methods resulted in the formation of Ce3+ entities as predominant species on the surface of CeO2/In2O3. The presence of higher content of Ce3+ reflected a strong interfacial contact between CeO2 and In2O3 indicating the formation of heterojunction. However, CeO2/In2O3-WI produced excess portion of Ce3+ species and oxygen vacancies that became recombination centers. The photocatalytic CO2 reduction with CH4 results revealed that the reaction over CeO2/In2O3-CP formed a total yield of 174 μmol/gcat CO and H2 and was 1.5 and 3.6 times higher than that of CeO2/In2O3-WI. However, the selectivity of CO over CeO2/In2O3-WI was higher than that of CeO2/In2O3-CP, with a selectivity of 94 and 85% respectively. When H2O was used as reductant to substitute CH4, the selectivity of H2 was gradually suppressed from 26 % to 9 and 4 % over 0.2 CeO2/In2O3-WI and 0.2 CeO2/In2O3-CP respectively. Based on the experiment findings, the superior photoactivity of CeO2/In2O3-CP was ascribed to its smaller and uniform particle size distribution, higher surface area, enhanced light absorption capacity and suppressed recombination of electron-hole pairs as compared to CeO2/In2O3-WI. Following that, a non-precious Ag metal was photodeposited over CeO2/In2O3-CP to construct Ag-CeO2/In2O3 ternary photocatalysts for photocatalytic CO2 reduction with CH4. At an optimum loading of 0.5 wt. %, the formation of CO and H2 was improved remarkably with a total yield of 253 μmol/gcat which is about ~0.5 times higher than that of binary CeO2/In2O3. A mechanism of reaction was developed based on Type II heterojunction for Ag-CeO2/In2O3 photocatalyst in which charges travel in the direction of In2O3→CeO2→Ag where Ag acts as an electron sink to effectively trap electrons from CeO2, reducing their recombination. Among the operating parameters studied, feed ratio was the most influential to drastically affect the product yield. The stability test showed prolonged stability and reusability of Ag-CeO2/In2O3 in five cycles of photoreaction. The Langmuir–Hinshelwood model revealed that yield rates of products were dependent on efficient adsorption of the reactants and desorption of products over the photocatalyst surface. In conclusion, this study proved the conversion of CO2 and CH4 to syngas using photon energy over the novel highly efficient Ag-CeO2/In2O3 photocatalysts.
Attached benthic microalgae cultivation on flat sheet and tubular biofilm photobioreactor
(2023-04-01)
Siti Mariam Md Poad
Microalgae are currently in the spotlight due to its various potential such as feedstock food, livestock feed, fuel, fertilizers, fine chemicals and other value-added products. However, large cultivation of microalgae is not necessarily economically viable due to the high capital and operating cost. This leads to biofilm cultivation where the microalgae are grown on the surface of a porous substrate that ease the microalgae harvesting process and reduces water consumption and eventually the cost of cultivation. Thus, this study intended to study the cultivation of microalgae on the surface of the porous substrate. It comprises of four species of microalgae from benthic origin (Amphora coffeaformis, Cylindrotheca fusiformis, Navicula incerta and wild strain) and two types of flat sheet membrane as the porous substrate namely polyvinylidene fluoride (PVDF) and polyethersulfone (PES) and one tubular capillary PES membrane. Contact angle analysis revealed that PES membrane is more hydrophilic to PVDF membrane. For flat sheet membrane, the experiment was carried out on a glass plate covered with cellulose based absorbent paper in a glass chamber with medium circulation at 40.0 ml/min. Throughout 7 days of cultivation, highest areal biomass was achieved by PES membrane which at 16.26 ± 0.89 g DW/m2 for A. coffeaformis, 22.86 ± 1.05 g DW/m2 for C. fusiformis, 11.55 ± 1.95 g DW/m2 for N. incerta and 16.14 ± 2.76 g DW/m2 by wild strain. C. fusiformis achieved the highest areal biomass and biomass productivities on PES membrane compared to other species. This lead to the selection of PES material for porous substrate and C. fusiformis to be further studied on the tubular capillary porous substrate photobioreactor (PSBR). The experiments were carried out in a fabricated tubular column designed for microalgae cultivation with 0.5 ml/min medium circulation. The tubular capillary PSBR system C. fusiformis achieved areal biomass of 5.30 ± 0.34 g DW/m2 and is able to approach the biomass productivity of the conventional suspension culture.

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