Fabrication of Interlayer-free P123 Caronised Template Silica Membranes for Water Desalination: Conventional Versus Rapid Thermal Processing (CTP vs RTP) Techniques

Access to potable water has become one of the top 10 global problems facing our contemporary society. Desalination of vast amounts of seawater is a promising measure to ameliorate this stress. Numerous thermal and membrane processes have been employed to desalt water, of which reverse osmosis (RO) using polymeric membranes is the most mature technology and has been regarded as the benchmark in current desalination technologies. However, due to the high pressure requirement for RO operation, other membrane processes, such as membrane distillation and pervaporation have been developed as the alternatives to further reduce the energy cost. Furthermore, due to the lack of chemical/thermal stability and high tendency to scaling and fouling of polymeric membranes, novel inorganic membranes, in particular silica derived membranes, are emerging as potential candidates for desalination. The majority of published works on silica membranes utilizes tetraethyl orthosilicate (TEOS) as the silica precursor and interlayers are generally required to reduce the roughness of the porous substrates, followed by 4 to 6 thin-film coatings and calcinations with heating rates of 1–2 oC min-1 to form defect free silica membranes, which consume 10–14 days with extra cost. Therefore, the major target of this research is to produce interlayer-free silica membranes fabricated by rapid thermal processing (RTP) for desalination application. Ethyl silicate 40 (ES40) is used as precursor to prepare silica membranes in this work owing to their superior thermal stability as compared to the TEOS analogous product. Firstly, the sol-gel processing of ES40 was investigated in this thesis. At different temperatures and H2O/Si ratios, ES40 underwent various degrees of phase separation behaviour and sol-gel reactions. It was found that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. Dense silica structures were obtained using low H2O/Si ratios, whereas higher porosity was produced from a phase-separated sol-gel system with high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, leading to stronger silica matrices which were more resistant to densification. The second part of this work is focused on improvement of the hydrostability of ES40-derived silica membrane materials by adjusting the reactant ratios of sol-gel synthesis process, as the low resistance of silica membranes to water vapor attack, which induce enlargement of the pore size followed by failure in salt rejection, can be detrimental to desalination performance. Investigations were carried out on the effects of reactant ratios on the microstructure of the silica matrices and their hydrothermal stability under harsh conditions (550 °C, 75 mol% vapour). The most hydrothermally stable matrix was obtained by decreasing the ethanol ratio whilst increasing water and acid ratios. The improved hydrothermal stability was attributed to the further transition of I silanol to siloxane groups on one hand and the formation of a more openly branched silica network on the other. Further work was conducted on the preparation of ES40 derived interlayer-free silica membranes using RTP on the optimized reactant ratios as determined from above investigations. RTP involves a rapid heating rate and a short period of high temperature exposure up to 1 hour. This thesis shows for the first time the preparation of interlayer-free silica membranes by RTP. A major advantage of this novel preparation method is that the final membranes were coated with 2 silica layers only and were prepared in less than 3 hours, a considerable and significant reduction from 10-14 days for TEOS silica membranes. A comparison of the structure properties of silica materials produced by RTP and conventional thermal processing (CTP) found that the silica produced from RTP has more siloxane bridges and larger porosity, which can potentially deliver the corresponding membranes enhanced hydrostability and water fluxes. The preparation feasibility of membranes was dependent on the pH of the sol-gel. The best membranes were prepared with ES40 sols with pH 4, which adhered well to substrates during the RTP calcination step. Water fluxes reached 17.8 kg m-2 h-1 for seawater (NaCl 3.5 wt%) at 60 °C whilst reaching salt rejections 95–99%. The long term stability tests showed stable water flux and salt rejection until ~300 hours. This is a major improvement from TEOS silica membranes which tend to fail within a few hours. In order to further improve the hydrostability, the effect of H2O/Si, EtOH/Si and pH of the sol-gel solutions on silica xerogel properties and membrane performance was carried out. The prepared membranes gave good water flux (7 kg m-2 h-1) and excellent salt rejection (>99%) for seawater desalination. In addition, long term testing at at room temperature for 3.5 wt% saline solutions showed that the ES40 membrane was stable for 800 hours, whilst delivering 99% salt rejection. These results strongly suggested that high quality interlayer-free membranes were successfully prepared using RTP from ES40 precursor for the first time, delivering performance well above the current state of art.

Currently, xerogel has been applied as a filtration material, especially in membrane desalination. However, the xerogel matrix structure for desalination have to be designed properly in order to allow rejection of salt and obtain good hydro-stability, thus, silica precursor in the form of TEOS (tetraethyl orthosilicate)/TEVS (triethoxy vinyl silane) and organic acid catalyst are suitable material for fabrication. The aim of this study is therefore to fabricate and perform deconvolution of TEOS/TEVS xerogel by adding single or dual catalyst, using FTIR (Fourier-transform Infrared Spectroscopy) and Fityk software. The xerogel was fabricated by dried silica sol and calcined using RTP technique (rapid thermal processing) at 450 °C. Prior to this fabrication, the silica sol was synthesized by sol gel method, using a mixture of silica precursor TEOS/TEVS, ethanol solvent, and varied addition of single catalyst (citric acid) as well as dual catalyst (citric acid + ammonia) for 2 hours, at 50 °C. Subsequently, the xerogel was characterized by FTIR and the deconvolution was obtained through Gaussian approach, with Fityk software. All TEOS/TEVS xerogel samples indicated existence of silanol (Si-OH), siloxane (Si-O-Si) and silica-carbon (Si-C) functional groups. The xerogel deconvolution of TEOS/TEVS using single catalyst exhibit a peak area ratio of Si-OH/Si-O-Si, and this is similar to the dual catalyst counterpart of 0.24 (unit area) and 1.86 (unit area), for Si-C area ratio. This shows the addition of single catalyst was enough to produce deconvolution in TEOS/TEVS xerogel, dominated by siloxane functional group and carbon bonds with the ability to enhance membrane material hydro-stability’s fabrication.

Rapid thermal treatment of interlayer-free ethyl silicate 40 derived membranes for desalination

Bi2O3-BaTiO3 heterojunction with high photocatalysis efficiency was directly synthesized by rapid thermal processing (RTP). Bi2O3 and BaTiO3 were mixed in ratio and treated by RTP and conventional thermal processing (CTP), respectively. RTP samples have obvious Bi2O3 diffraction peaks, while CTP samples show pure BaTiO3 tetragonal perovskite. More small particles and layered existed in RTP samples. Photodegradation of MB solutions shows that RTP can promote photocatalytic efficiency. Its main lies in the following points: RTP can remove grain boundary defects by strengthening the bond grains; RTP can limit the solution region of the two substances to a certain range to get the best built-in electric field width; and RTP can strengthen the tetragonal BaTiO3 phase to hasten ion movement. Therefore, RTP can achieve much higher photocatalytic efficiency by improving the build heterojunction. This work provides a direct and efficient route to get improvement and high performance of heterojunction.

Improved superconducting properties of multifilament internal Mg diffusion processed MgB2 wires by rapid thermal processing

Water scarcity is still a pressing issue in many regions. The application of membrane technology through water desalination to convert brackish to potable water is a promising technology to solve this issue. This study compared the performance of templated TEOS-P123 and ES40-P123 hybrid membranes for brackish water desalination. The membranes were prepared by the sol–gel method by employing tetraethyl orthosilicate (TEOS) for the carbon-templated silica (soft template) and ethyl silicate (ES40) for the hybrid organo-silica. Both sols were templated by adding 35 wt.% of pluronic triblock copolymer (P123) as the carbon source. The silica-templated sols were dip-coated onto alumina support (four layers) and were calcined by using the RTP (rapid thermal processing) method. The prepared membranes were tested using pervaporation set up at room temperature (~25 °C) using brackish water (0.3 and 1 wt.%) as the feed. It was found that the hybrid membrane exhibited the highest specific surface area (6.72 m2·g−1), pore size (3.67 nm), and pore volume (0.45 cm3·g−1). The hybrid ES40-P123 was twice thicker (2 μm) than TEOS-P123-templated membranes (1 μm). Lastly, the hybrid ES40-P123 displayed highest water flux of 6.2 kg·m−2·h−1. Both membranes showed excellent robustness and salt rejections of >99%.

Rapid thermal process for fabricating α-alumina tight ultrafiltration membrane with narrow pore size distribution

Skin effect suppression in planar multi-walled carbon nanotube (MWCNT)/Copper (Cu) conductors was realized at the 0-10 MHz frequency range through infrared laser irradiation of MWCNTs, which were coated on the surface of the Cu substrate via the electrophoretic deposition (EPD) method. The effect of laser irradiation and its power density on electrical and structural properties of the MWCNT/Cu conductors was investigated using a wavelength-tunable CO2 laser and then comparing the performance of the samples prepared at different conditions with that of pristine Cu. The irradiation at λ=9.219 µm proved to be effective in selective delivery of energy towards depths close to the interface, compared to the conventional rapid thermal processing (RTP) annealing method. At f=10 MHz, the ac resistance of the laser irradiated MWCNT/Cu conductors was reduced by more than one order of magnitude compared to its original value for the pristine Cu. Impedance measurements and structural characterizations indicate that this technique results in successful implementation of the nanotubes on the surface of the metallic substrate to operate as current channels with saturated skin depths and reduced contact resistance at the interface. Therefore, the limited performance of Cu conductors at high frequencies can be modified. Additionally, it was further demonstrated that the impedance reduction and the suppression of the skin effect in MWCNT/Cu conductors are in direct relation with the irradiated power density and can thus be easily controlled by this parameter.Skin effect suppression in planar multi-walled carbon nanotube (MWCNT)/Copper (Cu) conductors was realized at the 0-10 MHz frequency range through infrared laser irradiation of MWCNTs, which were coated on the surface of the Cu substrate via the electrophoretic deposition (EPD) method. The effect of laser irradiation and its power density on electrical and structural properties of the MWCNT/Cu conductors was investigated using a wavelength-tunable CO2 laser and then comparing the performance of the samples prepared at different conditions with that of pristine Cu. The irradiation at λ=9.219 µm proved to be effective in selective delivery of energy towards depths close to the interface, compared to the conventional rapid thermal processing (RTP) annealing method. At f=10 MHz, the ac resistance of the laser irradiated MWCNT/Cu conductors was reduced by more than one order of magnitude compared to its original value for the pristine Cu. Impedance measurements and structural characterizations indicate that th...

Chapter 13 - Rapid Thermal Processing of Microporous Silica Membranes

Recently, water scarcity is the big issues around the world. Especially in coastal area where the water distribution could not entranced and able to supply clean water for the citizen. The one and only solution is processing seawater to produce fresh and potable water. The desalination process using membrane was recommended to solve this issue. Due to that, the membrane with good structure and high hydro-stability was necessary to fabricate. The aim of this work is to investigate the performance of silica-pectin membranes for treating seawater by pervaporation employing silica based membranes. In this work, the silica-pectin membranes were successfully fabricated using Tetraethyl orthosilicate (TEOS) as silica precursor. Then, pectin from apple was also using in various concentrations (0; 0.1 to 0.5%). This organic material was implemented as a templating agent to produce in silica-pectin thin film. This thin films were dipcoated onto membranes support during membranes fabrication. These membranes were calcined in air at 300 and 400°C using rapid thermal processing (RTP) technique. All membranes were tested for water desalination via pervaporation set-up in various feed temperatures (25, 40 and 60°C). Results show that the membranes produced were crack-free and no pore dense. The FTIR-spectra and Fityk analysis refer to membrane of 2.5% at 300°C and 0.5% at 400°C are the optimum condition due to silanol and siloxane concentrations. An excellent performance was obtained at 0.5% at 400°C with water flux of 8.3 kg.m-2.h-1 and high salt rejection of 99.4% at 60 °C of feed temperature. It clearly demonstrates that the silica-pectin membrane has a robust structures due to the templating of carbon chains into silica matrices. The presence of carbon chains in silica matrices may form the smaller and robust pores as expected, that makes the excellent salt rejection in high feed temperature.

Si-rich silicon nitride (SRSN) (SiNx, x ≈ 0.49) films were deposited on Si (100) and quartz substrates by magnetron co-sputtering. For comparison, two sets of identical samples were then treated in a nitrogen atmosphere by conventional rapid thermal processing (CRTP) and light-filtering rapid thermal processing (LRTP) at temperature in a range of 950–1,100 °C, respectively. Raman spectroscopy, grazing incident X-ray diffraction, transmission electron microscope, photoluminescence (PL) and Hall measurements were used to analyze the structure, luminescence, and conductivity of the films. Experimental results show that the samples treated with LRTP posses higher dot number density, crystalline volume fraction, PL intensity and conductivity than the CRTP samples. The quantum effects in rapid thermal processing have a negative influence on the formation and density of Si quantum dots (QDs) in SRSN films. The present work opens new strategy for the formation of high density Si QDs embedded in SRSN films.

Rapid thermal processing of tubular cobalt oxide silica membranes

The intrusion of sea water through to wetland areas creates wetland water became saline and very poor quality of water. For that, the interlayer-free silica-P123 (Si-P123) membranes calcined via rapid thermal processing (RTP) method was successfully investigated for desalination of wetland saline water. RTP method is a fast and low costs method to fabricate Si-P123 membranes compare to conventional thermal processing (CTP) method. The aims of this works are to improve the stability of silica base membranes by templating triblock copolymer P123 as carbon sources into silica matrices, and also to investigate the performance and long-term stability of Si-P123 membranes calcined under RTP method. Desalination through pervaporation process have been applied to produce potable water. Results shows the highest water flux of Si-P123 membrane calcined at 350 °C was 2.6 - 4.5 kg m-2 h-1. It was also found that this membrane was offering high surface area of 572 m2 g-1 and give mesopore structures (2.2 nm). For that, the performance of salt rejection was excellent (>98%). Furthermore, long-term stability appeared very stable for water fluxes and salt rejections measurement (over 400 h). Moreover, the permeate salt concentration was excellent (99% still under WHO limit standard (600 ppm) of potable water. It can be concluded that the stability of Si-P123 membrane was very robust for wetland saline water desalination for over 400 h of long-term stability.

The annealing kinetics of the dominant defect [E(0.32 eV), σn=8×10−16 cm−2] induced in virgin Czochralski-grown n-type 〈100〉 1–5 Ω cm silicon by Nd-YAG laser (1.6 J cm−2, 0.53 μm) irradiation has been studied within the temperature range 500–650 °C using rapid and conventional thermal processing. With deep level transient spectroscopy measurements, we have observed an annealing rate increase about 30 times faster in the rapid thermal annealed (RTA) samples, than in those heat treated in a conventional furnace (CTA) with an activation energy difference ΔEA≂0.31 eV between the two processes, the latter requiring the higher energy. This difference results from ionization-enhanced annealing of this defect during RTA processing, a phenomenon which is markedly reduced in CTA-processed samples.

Deconvolution of carbon silica templated thin film using ES40 and P123 via rapid thermal processing method