Zeolites are potentially a robust desalination alternative, as they are chemically stable and pos... more Zeolites are potentially a robust desalination alternative, as they are chemically stable and possess the essential properties needed to reject ions. Zeolite membranes could desalinate "challenging" waters, such as saline secondary effluent, without any substantial pre-treatment, due to the robust mechanical properties of ceramic membranes. A novel MFI-type zeolite membrane was developed on a tubular α-Al 2 O 3 substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N 2) permeation and underwent desalination tests with NaCl solutions under different pressures (0.7 MPa and 7 MPa). The results showed that higher pressure resulted in higher Na + rejection and permeate flux. The zeolite membrane achieved a good rejection of Na + (~82%) for a NaCl feed solution with a TDS (total dissolved solids) of 3000 mg•L −1 at an applied pressure of 7 MPa and 21 °C. To explore the OPEN ACCESS Membranes 2013, 3 156 opportunity for high salinity and high temperature desalination, this membrane was also tested with high concentration NaCl solutions (up to TDS 90,000 mg•L −1) and at 90 °C. This is the first known work at such high salinities of NaCl. It was found that increasing the salinity of the feed solution decreased both Na + rejection and flux. An increase in testing temperature resulted in an increase in permeate flux, but a decrease in ion rejection.
Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as h... more Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.
In this study, we focus on processing and characterizing composite material structures made of ca... more In this study, we focus on processing and characterizing composite material structures made of carbon nanotubes (CNTs) and reproducibly engineering macro-pores inside their structure. Highly porous bucky-papers were fabricated from pure carbon nanotubes by dispersing and stabilizing large 1 μm polystyrene beads within a carbon nanotube suspension. The polystyrene beads, homogeneously dispersed across the thickness of the bucky-papers, were then either dissolved or carbonized to generate macro cavities of different shape and properties. The impact of adding these macro cavities on the porosity, specific surface area and Young's modulus was investigated and some benefits of the macro cavities will be demonstrated.
Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties ... more Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties which can be utilised in many applications. In this work we characterised pure selfsupporting CNT membranes, where CNTs were held together only by Van der Waals forces, and evaluated their potential and performance in direct contact membrane distillation. The membranes were found to be highly hydrophobic (contact angle of 113°), highly porous (90%), and to exhibit a thermal conductivity of 2.7 kW/m 2 •h. We demonstrate, as a proof of concept, that self-supporting CNT Bucky-Paper membranes can be used for desalination in a direct contact membrane distillation setup with 99% salt rejection and a flux rate of ~12 kg/m 2 *h at a water vapour partial pressure difference of 22.7kPa. Ageing of the membranes by delamination, factor limiting their performance, is also reported but work is currently done to address this issue by investigating composite material structures.
T he nucleation and growth of inorganic scale on membrane surfaces is a problem shared by operato... more T he nucleation and growth of inorganic scale on membrane surfaces is a problem shared by operators of reverse osmosis systems. While suite of indicators exists to predict scale formation based on pure compound solubility, it is apparent the onset of crystal nucleation and the properties of precipitated scale in reverse osmosis systems operating on natural waters differs from what would be expected in controlled conditions. Managing scale formation relies on understanding the chemistry of the scale, judicious system design, appropriate chemical application and early detection. T he following Highlights â-º Scaling and subsequent performance decline still remains a challenge for RO systems. â-º Scale seen from RO autopsies differ from what is expected under controlled conditions. â-º Scale formation and control studies is vital with natural waters and complex waters. â-º Early detection of scaling by real time monitoring is crucial in field applications. â-º Antiscalant formulations need greater transparency for molecular level understanding.
Recent work showed that carbon nanotubes could be fabricated into bucky-paper structures as self-... more Recent work showed that carbon nanotubes could be fabricated into bucky-paper structures as self-supporting membranes and their hydrophobic property used for water desalination by membrane distillation. Carbon nanotube bucky-papers possess very interesting properties such as natural hydrophobicity, high porosity and very high specific surface area, making of them promising candidates for separation applications. However, to inhibit crack formation associated with poor mechanical stability, improved durability structures that retain a high degree of hydrophobicity need to be developed. In this work we chemically modified high purity carbon nanotubes by (i) UV/ozone treatment to create hydroxyl groups and (ii) reacting those groups by substitution with alkoxysilane based groups. The resulting nanotubes presented a silicon content up to 2.5% and the bucky-papers produced had larger contact angle (140° compared to 125°) and liquid entry pressures. We report here on their fabrication and use as membranes in direct contact membrane distillation.
This study investigates fouling of membranes during membrane distillation (MD) of two model dairy... more This study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds-skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hours at 54 °C feed inlet temperature and 5 °C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency. Skim milk flux was found to be lower but stable over time compared to whey. The study using single components as well as combinations thereof revealed that fouling was primarily driven by proteins and calcium, but only in combination. Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration, but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchor point to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins; however salts were needed to form a thick and dense cake layer. Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer. Whey proteins, on the other hand, deposited to a lesser extent. In general, membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk. Highlights • Membrane distillation (MD) was tested on whey and skim milk solutions • No wetting and >99% rejection of all measured dairy components was observed • Fouling of dairy components mostly involved proteins and calcium • Protein fouling by caseins in skim milk was strongest, leading to rapid flux decline • Lactose did not bind to the membrane, but was involved in the fouling layer
This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) ... more This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) using polytetrafluoroethylene (PTFE) membranes. Structural and elemental changes along the fouling layer from the anchor point at the membrane to the top surface of the fouling layer have been investigated using synchrotron IR micro-spectroscopy and electron microscopy with associated energy dispersive X-ray spectroscopy (EDS). Initial adhesion of single components on a membrane representing a PTFE surface was observed in-situ utilizing reflectometry. Whey components were found to penetrate into the membrane matrix while skim milk fouling remained on top of the membrane. Whey proteins had weaker attractive interaction with the membrane and adhesion depended more on the presence of phosphorus near the membrane surface and throughout to establish the fouling layer. This work has given detailed insight into the fouling mechanisms of MD membranes in major dairy streams, essential for maintaining membrane distillation operational for acceptable times, therewith allowing further development of this emerging technology.
Free standing assemblies of carbon nanotubes (CNTs), known as bucky-paper, (BP) have been functio... more Free standing assemblies of carbon nanotubes (CNTs), known as bucky-paper, (BP) have been functionalised through the in-situ plating of gold nanoparticles within the interstitial spaces in the BP. The nanoparticles are extremely small and well distributed at short plating times, so much so that the specific surface area of the BP is actually 15 increased by the gold incorporation. These well distributed nanoparticles exhibit high enthalpy hydrogen storage and selective carbon dioxide adsorption over other gases, in particular methane. In concert with the conductive BP substrate, it has been demonstrated that these materials can also act as high turnover heterogeneous catalysts. 20
New technologies are required to improve desalination efficiency and increase water treatment cap... more New technologies are required to improve desalination efficiency and increase water treatment capacities. One promising low energy technique to produce potable water from either sea or sewage water is Membrane Distillation (MD). However, to be competitive with other desalination processes, membranes need to be designed specifically for the MD process requirements. Here we report on the design of Carbon Nanotube (CNT) based composite material membranes for Direct Contact Membrane Distillation (DCMD). The membranes have been thoroughly characterized and also tested in a DCMD setup under different feed temperatures and test conditions. We demonstrate that Bucky-paper membranes can be used for purification of synthetic seawater via the DCMD process and, most importantly, that the composite Bucky-paper (BP) structures show improved lifetime and performance compared to their self-supporting BP counterparts. I. INTRODUCTION Carbon nanotube (CNT) [1] based membranes have attracted interest over the past 5 years. Several groups have reported on CNT composite material membranes for applications such as pervapouration of cyclohexane/benzene [2], nanofiltration [3]-[4] and separation of hydrocarbons [5]. However to our knowledge no-one has focused on CNT based membranes for use in Membrane Distillation (MD). MD is an alternative technique for the purification of sea or sewage water. In a Direct Contact Membrane Distillation (DCMD) setup a hydrophobic membrane acts as a barrier between a warm feed (e.g. sea water) and a cold permeate of fresh water. A difference in water vapour pressure is generated due to the temperature gradient across the membrane and leads to water vapour transfer from the hot to cold side. The water vapour condenses on the cold side creating fresh water as illustrated by the schematic in Figure 1 [6]-[7]-[8]. However, specific membranes need to be designed for MD to become competitive with other desalination techniques. We previously demonstrated that CNT Bucky-paper (BP) membranes, a non-woven structure of entangled CNTs, could be used to desalinate synthetic seawater via DCMD process[9]. However ageing of the membranes over time limited their performance. Comment [MCD1]: Stephen's name should be last as he is the project leader. Comment [MCD3]: Where is table 1? Comment [MCD4]: Where is this data? Comment [MCD5]: Please unify your terms in text with table. Maybe use a systematic code. Deleted: The characterization results are summarized in Tables 1. Comment [MCD6]: Where is table 1? Comment [MCD7]: It might be OK here, but in future, I think is a good idea to fix the lines you fitted to pass through 0,0.
Polymer membranes are extensively used for water treatment but they wear irreversibly over time, ... more Polymer membranes are extensively used for water treatment but they wear irreversibly over time, especially when used in treatment of waters containing abrasive substances such as in seawater pretreatment. Novel nanocomposite membranes may be a cost effective approach to improving membrane physical endurance. Various methods of dispersing commercially available Cloisite ® 30B nanoparticles in 1-methyl-2-pyrrolidinone (NMP) were investigated and the respective particle sizes were measured by nanoparticle sizer. Ultrasonication dispersed the nanoparticles to the smallest size in the shortest period of time. Flat sheet poly(vinylidene fluoride) (PVDF)/nanoclay membranes with 6.25 wt % clay loading were cast by phase inversion. The morphology and the structure of the membrane were characterized by scanning electron microscopy (SEM), combustion testing and thermogravimetric analysis (TGA). Porous membrane with fingerlike macrovoids was fabricated and 1.7 wt% of nanoclay was incorporated into the final product as shown by TGA. The composite membrane showed greater stiffness compared to pure PVDF membrane.
A mesoporous titania (TiO 2) membrane on an alumina support was successfully fabricated via the s... more A mesoporous titania (TiO 2) membrane on an alumina support was successfully fabricated via the sol-gel processing method. The effects of combined ozonation and TiO 2 membrane filtration on the permeate flux and permeate quality were investigated. Ozone injection into the feed water during the filtration resulted in an increase in the permeate flux within the first 0.5 h. Ozonation decreased the fouling on the membrane surface. However, at the end of 2 h filtration, ozonation did not significantly impact on the permeate flux. It is likely that there would be minimal ozone residual remaining in the feed after 2 h filtration, which is why fouling was evident after this time, probably in the form of an organic film on the membrane surface reducing the flux. Under the hybrid ozonation-membrane filtration system, the removal of colour, A 254 (UV absorbance measured at a wavelength of 254 nm) and total organic carbon (TOC) was found to be 88.5%, 75.4% and 48.7%, respectively. Membrane filtration or ozonation alone did not achieve the degree of reduction obtained with hybrid ozonation-membrane filtration. Increasing the ozonation time from 2 min to 10 min gave no consistent trend in the percent removal of the colour and UV-254 absorbing compounds. Even at low ozonation time, there was a significant decrease in the UV-254 and colour. However, increasing the ozonation time beyond a threshold value (2 min) had a negative effect on reduction of TOC. Ozonation of organic matter is known to result in a decrease in the molecular weight of the organic matter, which would then result in these compounds passing through the membranes giving arise this effect.
Self-supporting bucky-papers membranes were processed from chemical vapour deposition grown carbo... more Self-supporting bucky-papers membranes were processed from chemical vapour deposition grown carbon nanotubes and coated with a thin layer of poly(tetra-fluoro-ethylene) (PTFE) to enhance their hydrophobicity and improve their mechanical stability over time, without drastically changing their average pore size and porosity. Contact angles and bubble point pressure were respectively increased by 23% and 28%. After coating the membranes were tested in a direct contact membrane distillation setup at various feed temperatures with 35 g/L NaCl feed solution and coated samples exhibited improved lifespan and water vapour permeability at salt rejection higher than 99%. The bucky-paper membranes were also compared with commercial PTFE membranes of similar properties.
Membrane based treatment processes are very effective in removing salt from wastewater, but are h... more Membrane based treatment processes are very effective in removing salt from wastewater, but are hindered by calcium scale deposit formation. This study investigates the feasibility of removing calcium from treated sewage wastewater using accelerated seeded precipitation. The rate of calcium removal was measured during bench scale batch mode seeded precipitation experiments at pH 9.5 using various quantities of calcium carbonate as seed material. The results indicate that accelerated seeded precipitation may be a feasible option for the decrease of calcium in reverse osmosis concentrate streams during the desalination of treated sewage wastewater for irrigation purposes, promising decreased incidence of scaling and the option to control the sodium adsorption ration and nutritional properties of the desalted water. It was found that accelerated seeded precipitation of calcium from treated sewage wastewater was largely ineffective if carried out without pre-treatment of the wastewater. Evidence was presented that suggests that phosphate may be a major interfering substance for the seeded precipitation of calcium from this type of wastewater. A pH adjustment to 9.5 followed by a one-hour equilibration period was found to be an effective pre-treatment for the removal of interferences. Calcium carbonate seed addition at 10 g L-1 to wastewater that had been pre-treated in this way was found to result in calcium precipitation from supersaturated level at 60 mg L-1 to saturated level at 5 mg L-1. Approximately 90% reduction of the calcium level occurred 5 min after seed addition. A further 10% reduction was achieved 30 min after seed addition.
The efficient functionalization of large quantities of carbon nanotubes entangled in a non-woven ... more The efficient functionalization of large quantities of carbon nanotubes entangled in a non-woven fashion into bucky-papers has been demonstrated through exposure to hard X-rays generated by a synchrotron source. The X-ray beam solely functionalized the carbon nanotube outer walls and an optimum X-ray exposure energy between 1048 and 2096 J cm-2 has been found to achieve maximum hydroxyl group density. Sol-gel reaction between a commercial fluoro-silane and the hydroxyl-modified carbon nanotubes was successfully performed resulting in an even distribution of fluoride atoms on the carbon nanotube surface, opening the way for the mass production of functionalized carbon nanotubes.
A new two-dimensional zeolitic imidazolate framework with leaf-shaped morphology (ZIF-L) was inco... more A new two-dimensional zeolitic imidazolate framework with leaf-shaped morphology (ZIF-L) was incorporated into polyethersulfone (PES) ultrafiltration membranes to investigate how the ZIF nanoflakes affect functional membrane properties. The membranes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and contact angle goniometry. The water permeability and molecular weight cutoffs (MWCO) of membranes were also determined under constant pressure filtration. Membrane fouling resistance was characterized under constant flux operation using bovine serum albumin (BSA) as foulant. The modified UF membrane with 0.5% ZIF-L loading showed around 75% increase in water flux without greatly affecting the MWCO. Also, the same membrane showed almost twice the fouling resistance improvement against BSA with more than 80% water flux recovery. The improvement was due to the combined effect of the lower zeta potential of the modified membrane, increased hydrophilicity and reduced surface roughness, which made the attachment of BSA protein on the membrane surface more difficult. These results
Aluminium-based coagulants, particularly aluminium chlorohydrate (ACH), worked best at lower coag... more Aluminium-based coagulants, particularly aluminium chlorohydrate (ACH), worked best at lower coagulant dose. Increasing the coagulant dose to improve DOC removal led to increased membrane fouling, possibly due to increased level of unsettleable flocs and pore blocking. For PSI ...
Zeolites are potentially a robust desalination alternative, as they are chemically stable and pos... more Zeolites are potentially a robust desalination alternative, as they are chemically stable and possess the essential properties needed to reject ions. Zeolite membranes could desalinate "challenging" waters, such as saline secondary effluent, without any substantial pre-treatment, due to the robust mechanical properties of ceramic membranes. A novel MFI-type zeolite membrane was developed on a tubular α-Al 2 O 3 substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N 2) permeation and underwent desalination tests with NaCl solutions under different pressures (0.7 MPa and 7 MPa). The results showed that higher pressure resulted in higher Na + rejection and permeate flux. The zeolite membrane achieved a good rejection of Na + (~82%) for a NaCl feed solution with a TDS (total dissolved solids) of 3000 mg•L −1 at an applied pressure of 7 MPa and 21 °C. To explore the OPEN ACCESS Membranes 2013, 3 156 opportunity for high salinity and high temperature desalination, this membrane was also tested with high concentration NaCl solutions (up to TDS 90,000 mg•L −1) and at 90 °C. This is the first known work at such high salinities of NaCl. It was found that increasing the salinity of the feed solution decreased both Na + rejection and flux. An increase in testing temperature resulted in an increase in permeate flux, but a decrease in ion rejection.
Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as h... more Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.
In this study, we focus on processing and characterizing composite material structures made of ca... more In this study, we focus on processing and characterizing composite material structures made of carbon nanotubes (CNTs) and reproducibly engineering macro-pores inside their structure. Highly porous bucky-papers were fabricated from pure carbon nanotubes by dispersing and stabilizing large 1 μm polystyrene beads within a carbon nanotube suspension. The polystyrene beads, homogeneously dispersed across the thickness of the bucky-papers, were then either dissolved or carbonized to generate macro cavities of different shape and properties. The impact of adding these macro cavities on the porosity, specific surface area and Young's modulus was investigated and some benefits of the macro cavities will be demonstrated.
Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties ... more Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties which can be utilised in many applications. In this work we characterised pure selfsupporting CNT membranes, where CNTs were held together only by Van der Waals forces, and evaluated their potential and performance in direct contact membrane distillation. The membranes were found to be highly hydrophobic (contact angle of 113°), highly porous (90%), and to exhibit a thermal conductivity of 2.7 kW/m 2 •h. We demonstrate, as a proof of concept, that self-supporting CNT Bucky-Paper membranes can be used for desalination in a direct contact membrane distillation setup with 99% salt rejection and a flux rate of ~12 kg/m 2 *h at a water vapour partial pressure difference of 22.7kPa. Ageing of the membranes by delamination, factor limiting their performance, is also reported but work is currently done to address this issue by investigating composite material structures.
T he nucleation and growth of inorganic scale on membrane surfaces is a problem shared by operato... more T he nucleation and growth of inorganic scale on membrane surfaces is a problem shared by operators of reverse osmosis systems. While suite of indicators exists to predict scale formation based on pure compound solubility, it is apparent the onset of crystal nucleation and the properties of precipitated scale in reverse osmosis systems operating on natural waters differs from what would be expected in controlled conditions. Managing scale formation relies on understanding the chemistry of the scale, judicious system design, appropriate chemical application and early detection. T he following Highlights â-º Scaling and subsequent performance decline still remains a challenge for RO systems. â-º Scale seen from RO autopsies differ from what is expected under controlled conditions. â-º Scale formation and control studies is vital with natural waters and complex waters. â-º Early detection of scaling by real time monitoring is crucial in field applications. â-º Antiscalant formulations need greater transparency for molecular level understanding.
Recent work showed that carbon nanotubes could be fabricated into bucky-paper structures as self-... more Recent work showed that carbon nanotubes could be fabricated into bucky-paper structures as self-supporting membranes and their hydrophobic property used for water desalination by membrane distillation. Carbon nanotube bucky-papers possess very interesting properties such as natural hydrophobicity, high porosity and very high specific surface area, making of them promising candidates for separation applications. However, to inhibit crack formation associated with poor mechanical stability, improved durability structures that retain a high degree of hydrophobicity need to be developed. In this work we chemically modified high purity carbon nanotubes by (i) UV/ozone treatment to create hydroxyl groups and (ii) reacting those groups by substitution with alkoxysilane based groups. The resulting nanotubes presented a silicon content up to 2.5% and the bucky-papers produced had larger contact angle (140° compared to 125°) and liquid entry pressures. We report here on their fabrication and use as membranes in direct contact membrane distillation.
This study investigates fouling of membranes during membrane distillation (MD) of two model dairy... more This study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds-skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hours at 54 °C feed inlet temperature and 5 °C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency. Skim milk flux was found to be lower but stable over time compared to whey. The study using single components as well as combinations thereof revealed that fouling was primarily driven by proteins and calcium, but only in combination. Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration, but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchor point to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins; however salts were needed to form a thick and dense cake layer. Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer. Whey proteins, on the other hand, deposited to a lesser extent. In general, membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk. Highlights • Membrane distillation (MD) was tested on whey and skim milk solutions • No wetting and >99% rejection of all measured dairy components was observed • Fouling of dairy components mostly involved proteins and calcium • Protein fouling by caseins in skim milk was strongest, leading to rapid flux decline • Lactose did not bind to the membrane, but was involved in the fouling layer
This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) ... more This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) using polytetrafluoroethylene (PTFE) membranes. Structural and elemental changes along the fouling layer from the anchor point at the membrane to the top surface of the fouling layer have been investigated using synchrotron IR micro-spectroscopy and electron microscopy with associated energy dispersive X-ray spectroscopy (EDS). Initial adhesion of single components on a membrane representing a PTFE surface was observed in-situ utilizing reflectometry. Whey components were found to penetrate into the membrane matrix while skim milk fouling remained on top of the membrane. Whey proteins had weaker attractive interaction with the membrane and adhesion depended more on the presence of phosphorus near the membrane surface and throughout to establish the fouling layer. This work has given detailed insight into the fouling mechanisms of MD membranes in major dairy streams, essential for maintaining membrane distillation operational for acceptable times, therewith allowing further development of this emerging technology.
Free standing assemblies of carbon nanotubes (CNTs), known as bucky-paper, (BP) have been functio... more Free standing assemblies of carbon nanotubes (CNTs), known as bucky-paper, (BP) have been functionalised through the in-situ plating of gold nanoparticles within the interstitial spaces in the BP. The nanoparticles are extremely small and well distributed at short plating times, so much so that the specific surface area of the BP is actually 15 increased by the gold incorporation. These well distributed nanoparticles exhibit high enthalpy hydrogen storage and selective carbon dioxide adsorption over other gases, in particular methane. In concert with the conductive BP substrate, it has been demonstrated that these materials can also act as high turnover heterogeneous catalysts. 20
New technologies are required to improve desalination efficiency and increase water treatment cap... more New technologies are required to improve desalination efficiency and increase water treatment capacities. One promising low energy technique to produce potable water from either sea or sewage water is Membrane Distillation (MD). However, to be competitive with other desalination processes, membranes need to be designed specifically for the MD process requirements. Here we report on the design of Carbon Nanotube (CNT) based composite material membranes for Direct Contact Membrane Distillation (DCMD). The membranes have been thoroughly characterized and also tested in a DCMD setup under different feed temperatures and test conditions. We demonstrate that Bucky-paper membranes can be used for purification of synthetic seawater via the DCMD process and, most importantly, that the composite Bucky-paper (BP) structures show improved lifetime and performance compared to their self-supporting BP counterparts. I. INTRODUCTION Carbon nanotube (CNT) [1] based membranes have attracted interest over the past 5 years. Several groups have reported on CNT composite material membranes for applications such as pervapouration of cyclohexane/benzene [2], nanofiltration [3]-[4] and separation of hydrocarbons [5]. However to our knowledge no-one has focused on CNT based membranes for use in Membrane Distillation (MD). MD is an alternative technique for the purification of sea or sewage water. In a Direct Contact Membrane Distillation (DCMD) setup a hydrophobic membrane acts as a barrier between a warm feed (e.g. sea water) and a cold permeate of fresh water. A difference in water vapour pressure is generated due to the temperature gradient across the membrane and leads to water vapour transfer from the hot to cold side. The water vapour condenses on the cold side creating fresh water as illustrated by the schematic in Figure 1 [6]-[7]-[8]. However, specific membranes need to be designed for MD to become competitive with other desalination techniques. We previously demonstrated that CNT Bucky-paper (BP) membranes, a non-woven structure of entangled CNTs, could be used to desalinate synthetic seawater via DCMD process[9]. However ageing of the membranes over time limited their performance. Comment [MCD1]: Stephen's name should be last as he is the project leader. Comment [MCD3]: Where is table 1? Comment [MCD4]: Where is this data? Comment [MCD5]: Please unify your terms in text with table. Maybe use a systematic code. Deleted: The characterization results are summarized in Tables 1. Comment [MCD6]: Where is table 1? Comment [MCD7]: It might be OK here, but in future, I think is a good idea to fix the lines you fitted to pass through 0,0.
Polymer membranes are extensively used for water treatment but they wear irreversibly over time, ... more Polymer membranes are extensively used for water treatment but they wear irreversibly over time, especially when used in treatment of waters containing abrasive substances such as in seawater pretreatment. Novel nanocomposite membranes may be a cost effective approach to improving membrane physical endurance. Various methods of dispersing commercially available Cloisite ® 30B nanoparticles in 1-methyl-2-pyrrolidinone (NMP) were investigated and the respective particle sizes were measured by nanoparticle sizer. Ultrasonication dispersed the nanoparticles to the smallest size in the shortest period of time. Flat sheet poly(vinylidene fluoride) (PVDF)/nanoclay membranes with 6.25 wt % clay loading were cast by phase inversion. The morphology and the structure of the membrane were characterized by scanning electron microscopy (SEM), combustion testing and thermogravimetric analysis (TGA). Porous membrane with fingerlike macrovoids was fabricated and 1.7 wt% of nanoclay was incorporated into the final product as shown by TGA. The composite membrane showed greater stiffness compared to pure PVDF membrane.
A mesoporous titania (TiO 2) membrane on an alumina support was successfully fabricated via the s... more A mesoporous titania (TiO 2) membrane on an alumina support was successfully fabricated via the sol-gel processing method. The effects of combined ozonation and TiO 2 membrane filtration on the permeate flux and permeate quality were investigated. Ozone injection into the feed water during the filtration resulted in an increase in the permeate flux within the first 0.5 h. Ozonation decreased the fouling on the membrane surface. However, at the end of 2 h filtration, ozonation did not significantly impact on the permeate flux. It is likely that there would be minimal ozone residual remaining in the feed after 2 h filtration, which is why fouling was evident after this time, probably in the form of an organic film on the membrane surface reducing the flux. Under the hybrid ozonation-membrane filtration system, the removal of colour, A 254 (UV absorbance measured at a wavelength of 254 nm) and total organic carbon (TOC) was found to be 88.5%, 75.4% and 48.7%, respectively. Membrane filtration or ozonation alone did not achieve the degree of reduction obtained with hybrid ozonation-membrane filtration. Increasing the ozonation time from 2 min to 10 min gave no consistent trend in the percent removal of the colour and UV-254 absorbing compounds. Even at low ozonation time, there was a significant decrease in the UV-254 and colour. However, increasing the ozonation time beyond a threshold value (2 min) had a negative effect on reduction of TOC. Ozonation of organic matter is known to result in a decrease in the molecular weight of the organic matter, which would then result in these compounds passing through the membranes giving arise this effect.
Self-supporting bucky-papers membranes were processed from chemical vapour deposition grown carbo... more Self-supporting bucky-papers membranes were processed from chemical vapour deposition grown carbon nanotubes and coated with a thin layer of poly(tetra-fluoro-ethylene) (PTFE) to enhance their hydrophobicity and improve their mechanical stability over time, without drastically changing their average pore size and porosity. Contact angles and bubble point pressure were respectively increased by 23% and 28%. After coating the membranes were tested in a direct contact membrane distillation setup at various feed temperatures with 35 g/L NaCl feed solution and coated samples exhibited improved lifespan and water vapour permeability at salt rejection higher than 99%. The bucky-paper membranes were also compared with commercial PTFE membranes of similar properties.
Membrane based treatment processes are very effective in removing salt from wastewater, but are h... more Membrane based treatment processes are very effective in removing salt from wastewater, but are hindered by calcium scale deposit formation. This study investigates the feasibility of removing calcium from treated sewage wastewater using accelerated seeded precipitation. The rate of calcium removal was measured during bench scale batch mode seeded precipitation experiments at pH 9.5 using various quantities of calcium carbonate as seed material. The results indicate that accelerated seeded precipitation may be a feasible option for the decrease of calcium in reverse osmosis concentrate streams during the desalination of treated sewage wastewater for irrigation purposes, promising decreased incidence of scaling and the option to control the sodium adsorption ration and nutritional properties of the desalted water. It was found that accelerated seeded precipitation of calcium from treated sewage wastewater was largely ineffective if carried out without pre-treatment of the wastewater. Evidence was presented that suggests that phosphate may be a major interfering substance for the seeded precipitation of calcium from this type of wastewater. A pH adjustment to 9.5 followed by a one-hour equilibration period was found to be an effective pre-treatment for the removal of interferences. Calcium carbonate seed addition at 10 g L-1 to wastewater that had been pre-treated in this way was found to result in calcium precipitation from supersaturated level at 60 mg L-1 to saturated level at 5 mg L-1. Approximately 90% reduction of the calcium level occurred 5 min after seed addition. A further 10% reduction was achieved 30 min after seed addition.
The efficient functionalization of large quantities of carbon nanotubes entangled in a non-woven ... more The efficient functionalization of large quantities of carbon nanotubes entangled in a non-woven fashion into bucky-papers has been demonstrated through exposure to hard X-rays generated by a synchrotron source. The X-ray beam solely functionalized the carbon nanotube outer walls and an optimum X-ray exposure energy between 1048 and 2096 J cm-2 has been found to achieve maximum hydroxyl group density. Sol-gel reaction between a commercial fluoro-silane and the hydroxyl-modified carbon nanotubes was successfully performed resulting in an even distribution of fluoride atoms on the carbon nanotube surface, opening the way for the mass production of functionalized carbon nanotubes.
A new two-dimensional zeolitic imidazolate framework with leaf-shaped morphology (ZIF-L) was inco... more A new two-dimensional zeolitic imidazolate framework with leaf-shaped morphology (ZIF-L) was incorporated into polyethersulfone (PES) ultrafiltration membranes to investigate how the ZIF nanoflakes affect functional membrane properties. The membranes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and contact angle goniometry. The water permeability and molecular weight cutoffs (MWCO) of membranes were also determined under constant pressure filtration. Membrane fouling resistance was characterized under constant flux operation using bovine serum albumin (BSA) as foulant. The modified UF membrane with 0.5% ZIF-L loading showed around 75% increase in water flux without greatly affecting the MWCO. Also, the same membrane showed almost twice the fouling resistance improvement against BSA with more than 80% water flux recovery. The improvement was due to the combined effect of the lower zeta potential of the modified membrane, increased hydrophilicity and reduced surface roughness, which made the attachment of BSA protein on the membrane surface more difficult. These results
Aluminium-based coagulants, particularly aluminium chlorohydrate (ACH), worked best at lower coag... more Aluminium-based coagulants, particularly aluminium chlorohydrate (ACH), worked best at lower coagulant dose. Increasing the coagulant dose to improve DOC removal led to increased membrane fouling, possibly due to increased level of unsettleable flocs and pore blocking. For PSI ...
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Papers by Stephen Gray