Claims:1. A device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, said device for the filtering of water comprising: an at least a ceramic layer that is associated with an at least a metallic layer, with:
thickness of said at least one ceramic layer ranging between 50 microns and 500 microns;
porosity of said at least one ceramic layer ranging between 25% and 30%;
sizes of at least about 75% of pores in said at least one ceramic layer ranging between 0.3 microns and 2.2 microns;
sizes of said pores in said at least one ceramic layer varying from a top surface of said at least one ceramic layer to a bottom surface of said at least one ceramic layer; and
said at least one metallic layer comprising pores of sizes that range between 40 microns and 70 microns.
2. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1, wherein: said at least one ceramic layer is a layer made of yttria-stabilized zirconia.
3. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1, wherein: said at least one metallic layer is a layer made of stainless steel.
4. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1 or claim 2, wherein: said thickness of said at least one ceramic layer ranges between 100 microns and 300 microns.
5. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 4, wherein: said thickness of said at least one ceramic layer is 200 microns.
6. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1, claim 2, or claim 3, wherein: said at least one ceramic layer is associated with said at least one metallic layer through mechanical interlocking.
7. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 5, wherein: at least 85% of said pores in said at least one ceramic layer is of sizes that range between 0.1 µm and 1.0 µm.
8. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1, claim 2, or claim 3, wherein: said water is waste water.
9. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 1, claim 2, or claim 3, wherein: said water is salt water.
10. The device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 5, claim 8, or claim 9, wherein: contact angle is less than 20 degrees.
11. A single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, said method comprising a step of: plasma spraying an at least a ceramic powder onto a surface of an at least a porous support, with:
arc current ranging between 370 A and 385 A;
plasma power being 25 kW;
primary gas flow rate ranging between 80 scfh and 120 scfh;
secondary gas flow rate ranging between 8 scfh and 15 scfh;
flow rate of said at least one ceramic powder ranging between 10 g/min and 15 g/min; and
flame temperature in a plasma plume being 3,000 degrees Centigrade.
12. The single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 11, wherein: said at least one ceramic powder is made of yttria-stabilized zirconia.
13. The single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 11, wherein: said at least one porous support is made of stainless steel.
14. The single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 11, wherein: said primary gas is argon.
15. The single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 11, wherein: said secondary gas is hydrogen.
16. The single step method of fabricating a device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, as claimed in claim 11, claim 12, claim 14, or claim 15, wherein:
said arc current is 382 A;
said primary gas flow rate is 100 scfh;
said secondary gas flow rate is 12 scfh; and
said flow rate of said at least one ceramic powder is 15 g/min. , Description:TITLE OF THE INVENTION: A DEVICE FOR FILTERING WATER AND METHOD OF FABRICATION THEREOF
FIELD OF THE INVENTION
The present disclosure is generally related to the filtering of water. The present disclosure is particularly related to a device for the filtering of water. The present disclosure is more particularly related to a device for the filtering of water, and method of fabrication thereof.
BACKGROUND OF THE INVENTION
The demand for fresh water is growing due to the rapid growth of population, industrialisation, increasing water pollution, etc. In this regard, treating water by filtering seawater, waste water, soiled water, etc., and reusing it has emerged as a key technique.
Today polymeric devices are the straight-forward choice for water filtration. However, polymeric devices have several critical demerits, including, but to not limited to: (i) degradation in salt and/or waste water owing to interaction between cations (Na+, K+, Mg2+, etc.) in water streams with electron-rich functional groups (OH-, COOH-, CO-, etc.) in the polymers; (ii) high susceptibility to fouling due to their inherent hydrophobicity and surface charge properties; and/or (iii) decomposition at high temperatures due to random chain scission and unzipping depolymerisation reactions.
As a result, researchers have shifted their focus from polymeric to ceramic devices. Yet, to successfully commercialise a ceramic device, simultaneous fulfilment of several essential factors is required. These include, but are not limited to: (i) industrially friendly device fabrication process to produce the device easily in a single step, and as per a required scale; (ii) high water flux at low trans-membrane pressures (TMP), resulting in minimising of power consumption and lowering of costs; (iii) favourable COD, TOC, turbidity, and conductivity of permeate water to meet the criteria for potable water; (iv) low fouling propensity and high cleaning or reusability to resist dust adhesion and work for longer durations; and/or (v) retaining of requisite mechanical properties.
Though different ceramic device fabrication processes such as plasma sintering, sol-gel, stretching, etc. are available, these processes possess major shortcomings of uncontrolled porosity, compressibility, etc., which adversely affect water flux, as well as portable water production. Furthermore, these processes involve: multiple device fabrication steps; low scalability; high costs, etc., limiting their scope of applications.
To the best of the knowledge of the Inventors, there is no prior art that simultaneously addresses the practical aspects such as: fouling of devices; reusability; and/or retention of mechanical properties.
There is, therefore, a need in the art for a device for the filtering of water, and method of fabrication thereof, which overcome the aforementioned drawbacks and shortcomings.
SUMMARY OF THE INVENTION
A device for the filtering of water, which is configured to: offer a low fouling tendency; be regenerated and reused, without loss of filtration efficiency; and retain mechanical properties, is disclosed.
Said device broadly comprises: an at least a ceramic layer that is associated with an at least a metallic layer. Thickness of the at least one ceramic layer ranges between about 50 microns and about 500 microns.
Porosity of said at least one ceramic layer ranges between about 25% and about 30%. Sizes of at least about 75% of pores in said at least one ceramic layer range between about 0.3 microns and about 2.2 microns, with said sizes of said pores varying from a top surface of said at least one ceramic layer to a bottom surface of said at least one ceramic layer.
Said at least one metallic layer comprises pores of sizes that range between about 40 microns and about 70 microns.
In an embodiment, said at least one ceramic layer is a layer made of yttria-stabilized zirconia, while said at least one metallic layer is a layer made of stainless steel. Said at least one ceramic layer may be associated with said at least one metallic layer through mechanical interlocking.
In an embodiment, at least 85% of said pores in said at least one ceramic layer is of sizes that range between 0.1 µm and 1.0 µm.
Said at least one ceramic layer was observed to be made up of regular surfaces, without any cracks, and with proper adhesion over said at least one metallic layer. To quantify the regularity of said surfaces, surface roughness values were measured and found to be less than about 10 μm.
A single step method of fabricating said device is also disclosed. Said method comprises a step of: plasma spraying an at least a ceramic powder onto a surface of an at least a porous support, with: arc current ranging between about 370 A and about 385 A (about 382 A in an embodiment); plasma power being about 25 kW; primary gas flow rate ranging between about 80 scfh and about 120 scfh (about 100 scfh in an embodiment); secondary gas flow rate ranging between about 8 scfh and about 15 scfh (about 12 scfh in an embodiment); flow rate of said at least one ceramic powder ranging between 10 g/min and 15 g/min (about 15 g/min in an embodiment); and flame temperature in a plasma plume being about 3,000 degrees Centigrade.
In an embodiment, said primary gas and said secondary gas are argon and hydrogen, respectively.
Among tested fabricated devices, a fabricated device, in which said thickness of said at least one ceramic layer is about 200 m, was found to be most efficient for waste water filtration, owing to its low and uniform pore size, resulting in sieving of larger molecular size contaminants.
Likewise, among tested fabricated devices, said fabricated device, in which said thickness of said at least one ceramic layer is about 200 m, was found to be most efficient for salt water filtration as well.
After filtration, said fabricated device, in which said thickness of said at least one ceramic layer is about 200 m, was evaluated to determine characteristics of the permeate water, the retentate, and salt/dye removal % of the feed waters. A removal of about 99.9% of waste and salt was achieved, which allows for water reuse, or its disposal into water bodies, according to European regulations. Moreover, a retentate with a concentration factor of about 9.8 was obtained.
Separation performance assessments were performed, on said fabricated device, in which said thickness of said at least one ceramic layer is about 200 m, for NaCl and contaminant particles/dye, after cycles ranging between about 1 and about 5.
As number of cycles increased, it was observed that said contaminant particles/dye or said NaCl is more likely to block the water transfer channel. Hence, fluxes were also slightly reduced. Because of the same reason, rejection ratios could still be maintained. After about 5 cycles, FRR values were higher than about 98.00%, suggesting excellent recycling capabilities.
It was also observed that toughness values range between about 2.3 to about 2.5 ± 0.3 MPa.m0.5. Therefore, it is expected that said fabricated devices can bear enough loads during filtration processes, even if they run at high TMP.
The disclosed device and method are configured to offer at least the following advantages: are industrially friendly; offer a very low fouling tendency; can be regenerated and reused, without loss of filtration efficiency; retain requisite mechanical properties; offer a low water - device contact angle in the super-hydrophilic range; and offer a high pure water flux, rejection rate, and permeability.
The disclosed device and method offer a low fouling tendency over a long time (up to about 5 hours) of operation, and are capable of being regenerated and reused to about 95% of original pure water flux, for at least five times after regeneration. Further, the performances of the disclosed device and method are comparable to those of commercially available products.
The disclosed device and method are easily adaptable towards harsh conditions (e.g. heavily contaminated industrial effluents or urban wastewaters), such as those arising from the food and pharmaceutical industries.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a method of fabricating a device for the filtering of water, and a device for the filtering of water thereof, in accordance with an embodiment of the present disclosure;
Figure 2(a) illustrates an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 2(b) and Figure 2(c) illustrate the surface roughness profiles, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 2(d), Figure 2(e), and Figure 2(f) illustrate the thicknesses, of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
3(a), Figure 3(b), and Figure 3(c) illustrate lower magnification fractographic surfaces, of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 3(d), Figure 3(e), and Figure 3(f) illustrate magnified images, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 3(g), Figure 3(h), and Figure 3(i) illustrate magnified images, of an at least a ceramic layer, of another fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 3(j), Figure 3(k), and Figure 3(l) illustrate magnified images, of an at least a ceramic layer, of yet another fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 3(m) illustrates the distribution of pores, in at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 3(n) illustrates the distribution of pores, in at least a ceramic layer, of another fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 3(o) illustrates the distribution of pores, in at least a ceramic layer, of yet another fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 4(a) illustrates the permeate water flux values of DI water, at different TMP values, in accordance with an embodiment of the present disclosure;
Figure 4(b) illustrates the permeate water flux values of DI water, of an at least a ceramic layer, of fabricated devices, for the filtering of water, at different TMP values, in accordance with various embodiments of the present disclosure;
Figure 4(c) illustrates the permeate water flux values for testing with waste water, with increasing thickness of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 4(d) illustrates the conductivity values for testing with waste water, with increasing thickness of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 4(e) illustrates the permeate water flux values for testing with salt water, with increasing thickness of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 4(f) illustrates the conductivity values for testing with salt water, with increasing thickness of an at least a ceramic layer, of fabricated devices, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 5(a) illustrates a FESEM image of a surface (after waste water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(b) illustrates a FESEM image that shows a foulant layer formation, on a surface (after waste water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(c) illustrates a FESEM image of a surface (after salt water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(d) illustrates a FESEM image that shows a foulant layer formation, on a surface (after salt water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(e), Figure 5(f), Figure 5(g), Figure 5(h), Figure 5(i), and Figure 5(j) illustrate the results of elemental mapping analyses (waste water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 5(k), Figure 5(l), Figure 5(m), Figure 5(n), Figure 5(o), and Figure 5(p) illustrate the results of elemental mapping analyses (salt water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with various embodiments of the present disclosure;
Figure 5(q) illustrates the contact angle of waste water droplets, with the surface of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(r) illustrates the contact angle of salt water droplets, with the surface of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(s) illustrates the surface roughness profile (waste water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 5(t) illustrates the surface roughness profile (salt water treatment or filtration), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 6(a) illustrates the NaCl separation performance, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 6(b) illustrates the contaminant particles/dye separation performance, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 6(c) illustrates a FESEM micrograph that shows the features, of an at least a ceramic layer, of a fabricated device, for the filtering of water, after 5th cycle of salt water filtration, in accordance with an embodiment of the present disclosure;
Figure 6(d) illustrates a FESEM micrograph that shows the features, of an at least a ceramic layer, of a fabricated device, for the filtering of water, after 5th cycle of waste water filtration, in accordance with an embodiment of the present disclosure;
Figure 7(a) illustrates the load vs displacement curves, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 7(b) illustrates a FESEM micrograph that shows indent impression and crack propagation, upon applying of a load of about 1 N, on an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 7(c) illustrates an indent image (evaluation of indentation toughness values at a load of about 20 N), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 7(d) illustrates a magnified indent image (evaluation of indentation toughness values), of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure;
Figure 7(e) illustrates an overview HRTEM micrograph, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure; and
Figure 7(f) illustrates a selected area electron diffraction pattern, of an at least a ceramic layer, of a fabricated device, for the filtering of water, in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
Throughout this specification, the use of the words “comprise” and “include”, and variations such as “comprises”, “comprising”, “includes”, and “including” may imply the inclusion of an element or elements not specifically recited. Further, the disclosed embodiments may be embodied in various other forms as well.
Throughout this specification, the use of the word “device” is to be construed as a set of technical components that are associated with each other and function together as part of a mechanism to achieve a desired technical result (for example, a composite membrane).
Throughout this specification, the disclosure of a range is to be construed as being inclusive of the lower limit of the range and the upper limit of the range.
Throughout this specification, where applicable, the use of the phrase “at least” is to be construed in association with the suffix “one” i.e. it is to be read along with the suffix “one” as “at least one”, which is used in the meaning of “one or more”. A person skilled in the art will appreciate the fact that the phrase “at least one” is a standard term that is used in Patent Specifications to denote any component of a disclosure that may be present or disposed in a single quantity or more than a single quantity.
Throughout this specification, the use of the acronyms “YSZ” and “ZrO2” is to be construed as “Yttria Stabilised Zirconium Oxide”.
Throughout this specification, the use of the acronym “ZrO2 Membrane” is to be construed as “an at least a ceramic layer, of a fabricated device, for the filtering of water”.
Throughout this specification, the use of the acronym “FESEM” is to be construed as “Field Emission Scanning Electron Microscope”.
Throughout this specification, the use of the acronym “XRD” is to be construed as “X-ray Diffraction”.
Throughout this specification, the use of the acronym “HRTEM” is to be construed as “High Resolution Transmission Electron Microscopy”.
Throughout this specification, the use of the acronym “DI” is to be construed as “Deionised”.
Throughout this specification, the use of the acronym “PWF” is to be construed as “Permeate Water Flux”.
Throughout this specification, the use of the acronym “CRR” is to be construed as “Contamination Rejection Ratio”.
Throughout this specification, the use of the acronym “FRR” is to be construed as “Flux Recovery Ratio”.
Throughout this specification, the use of the acronym “CP” is to be construed as “Cyclic Performance”.
Throughout this specification, the use of the acronym “CW” is to be construed as “Conductivity of Water”.
Throughout this specification, the use of the acronym “NaCl” is to be construed as “Sodium Chloride”.
Throughout this specification, the use of the acronym “TMP” is to be construed as “transmembrane pressure”.
Throughout this specification, the use of the acronym “EDAX” is to be construed as “Energy Dispersive X-Ray Analysis”.
Throughout this specification, the use of the word “water” is to be construed as being inclusive of: waste water; and/or salt water.
Throughout this specification, the words “the” and “said” are used interchangeably.
Throughout this specification, the phrases “steel support”, “porous steel support”, and “porous support” are used interchangeably.
Throughout this specification, the phrases “at least a”, “at least an”, and “at least one” are used interchangeably.
Throughout this specification, the acronyms “ZM100”, “ZM200”, “ZM300”, and “YSZ Membrane” are used interchangeably.
Also, it is to be noted that embodiments may be described as a method. Although the operations in a method are described as a sequential process, many of the operations may be performed in parallel, concurrently, or simultaneously. In addition, the order of the operations may be re-arranged. A method may be terminated when its operations are completed, but may also have additional steps.
A device for the filtering of water (also referred to as “fabricated device” or “device”), and its method of fabrication, are disclosed. In an embodiment of the present disclosure, the device broadly comprises: an at least a metallic layer (for example, a layer made of stainless steel); and an at least a ceramic layer (for example, a layer made of zirconia). The at least one ceramic layer is disposed on (or is associated with, or is supported by) the at least one metallic layer.
The thickness of the at least one ceramic layer ranges between about 50 microns and about 500 microns. The porosity of the at least one ceramic layer is about 30%, with the sizes of at least about 75% of the pores ranging between about 0.3 microns and about 2.2 microns. The at least one metallic layer comprises pores of sizes that range between about 40 microns and about 70 microns.
In another embodiment of the present disclosure, the thickness of the at least one ceramic layer ranges between about 100 microns and about 300 microns.
In yet another embodiment of the present disclosure, the sizes of at least about 80% of the pores of the at least one ceramic layer are less than about 1.2 microns.
In yet another embodiment of the present disclosure, the at least one ceramic layer is fabricated by plasma spraying a coating of zirconia onto a stainless steel surface. Yttria-stabilized zirconia granules are sprayed, with: the arc current ranging between about 370 A and about 385 A; the plasma power being about 25 kW; the primary gas flow rate ranging between about 80 scfh of argon and about 120 scfh of argon; the secondary gas flow rate ranging between about 8 scfh of hydrogen and about 15 scfh of hydrogen; and the powder flow rate ranging between about 10 g/min and about 15 g/min.
In yet another embodiment of the present disclosure, the characteristics of the device (and/or the characteristics of the at least one ceramic layer) are as follows: water - device contact angle of less than about 20 degrees; water flux of up to about 370 L m-2 h-1; rejection rate of about 95%; permeability of up to about 380 L m-2 h-1; ceramic surface hardness that ranges between about 5 GPa and about 10 GPa; elastic modulus that ranges between about 150 GPa and about 180 GPa; and fracture toughness that ranges between about 2.0 MPam-1 and about 3.0 MPam-1.
The device was tested as follows:
Fabrication of Devices
YSZ powders (about 8 weight% yttria, with the rest being zirconia; also referred to as” an at least ceramic powder”) used were spherical agglomerates of YSZ particles, of sizes that range between about 20 μm and about 80 μm. Alternatively, an about 3 weight% yttria and about 97% zirconia powder, with trace levels of impurities, commonly available from commercial sources, may be used.
To fabricate the at least one metallic layer, sintered porous steel plates (SS 316L; pore sizes that range between about 40 µm and about 70 µm; also referred to as “steel support” or “porous steel support” or “porous support”) were purchased from Saar Heat and Control, India.
The YSZ powders were primarily spray dried and sintered. However, any suitably produced powders (calcia stabilised zirconia, magnesia stabilised zirconia, composites of alumina-zirconia, and/or the like) may be alternatively used.
The YSZ powders were sprayed over the porous support (about 50 mm × about 50 mm × about 3 mm), through atmospheric plasma spraying (an about 9 MB plasma gun). Prior to fabrication of the devices, the porous supports were cleaned with ethanol, through ultrasonication, followed by oven drying at about 40 degrees Centigrade.
Then, to generate the plasma flame, argon (Ar) and hydrogen (H) gas were utilized as primary gas and secondary gas, respectively. The flow of the primary gas and the secondary gas were continuously monitored, to achieve a desired flame temperature (about 3,000 degrees Centigrade) in the plasma plume, for melting the YSZ powders.
Throughout the process of fabrication of the devices, a proper stand-off distance (about 120 mm) was maintained to: reduce heating; and regulate substrate temperature for better adhesion of molten YSZ. Subsequently, three devices were fabricated, as illustrated in Figure 1, with the thickness of the at least one ceramic layer being: about 100 m (also referred to as “ZM100”); about 200 m (also referred to as “ZM200”); and about 300 m (also referred to as “ZM300”), with the below process parameters:
Arc Current: About 382 A;
Plasma Power: About 25 kW;
Primary Gas Flow Rate: About 100 scfh of argon;
Secondary Gas Flow Rate: About 12 scfh of hydrogen;
Powder Flow Rate: About 15 g/min; and
Stand-off Distance: About 120 mm.
Other than the atmospheric spraying process mentioned above, it is possible to fabricate the devices with other thermal spray techniques (high velocity oxygen fuel, detonation gun, suspension spray, and/or the like).
 
Characterisation
FESEM was employed to understand the morphologies of the feed YSZ powders and the porous supports. FESEM was also used to characterise the cross-sectional views, and fractographies, of the at least one ceramic layer, of the fabricated devices.
For better analyses, the powders, and the at least one ceramic layer, on the fabricated devices, were: sputtered with ultra-thin gold coating to make them conducting; and operated at an operating voltage of about 10 kV, under vacuum (about 10-8 of Hg to about 10-10 mm of Hg). Density measurements were conducted at an operating outlet gas pressure of about 0.34 bar, in an about 0.25 cm3 sample cell.
The theoretical densities were considered as about 5.9 g/cm3, and the relative densities were determined by the ratios of the true densities to the theoretical densities. In addition, the porosities were estimated with the density information, using available formulations.
The phase stabilities of the YSZ powders, and the at least one ceramic layer, on the fabricated devices, were determined by XRD, with Cu K radiation, having a wavelength of about 1.5406 Å. The scan range for the XRD was taken from about 20 degrees to about 80 degrees, while the scan rate was maintained at about 2 degrees /minute.
Further, HRTEM analyses were performed to verify the phase stabilities, of the at least one ceramic layer, of the fabricated devices.
Water Filtration Performances
The performances of the at least one ceramic layer of the fabricated devices were measured with a commercial pilot-scale cross-flow filtration system, with two different kinds of feed water (waste water and salt water). Before measuring the filtration properties, the at least one ceramic layer of the fabricated devices was sealed with a cascade system, to avoid any kind of feed water leakage via edges. Then, the at least one ceramic layer of the fabricated devices was pre-pressurized with DI water, until the permeate water reached a steady flux value.
The filtration properties (PWF; CRR; permeability (P); FRR for CP or reusability; CW; and/or the like) were calculated with both the feed waters.
The PWR, the CRR, and the permeability (P) were estimated with the below formulae:
PWF = V/(A ∆t)
P = V/(A ∆t∆p)
CRR (%)=(1-Cp/Cf ) × 100
V is the volume (in litres) of the permeate water; A is the effective filtration area (about 40 cm2 × about 40 cm2); ∆t is operation time (in hours) of permeation; and ∆p is the applied transmembrane pressure (in bar) during filtration. Cf is the concentration (in ppm) of the contaminants in the feed water, while Cp is the concentration (in ppm) of the contaminants in the permeate water.
Furthermore, the cyclic performances were evaluated for reusability. Here, about 35 ppm of NaCl solution and about 100 ppm of a dye solution were selected as salt water and waste water, respectively. A mixture of ethanol solution (about 0.1%) and DI water were flushed to wash off the NaCl and the dye. The fabricated devices were recycled for about 5 times and the FRR values were estimated to evaluate reusability.
FRR (%)=(Jw1/Jw2 ) × 100
Jw1 is the flux of a previous cycle, while Jw2 is the flux of the next cycle, during recycling process. The conductivities of the feed water, the permeate water, and the retentate water were measured with conductivity sensors integrated with the cross-flow filtration system.
Evaluation of Mechanical Properties
The hardness values, the elastic modulus values, and the fracture toughness values, of the at least one ceramic layer, of the fabricated devices, were measured with an instrumented micro-indentation and scratch tester. The hardness (H) values and the elastic modulus (E) values were evaluated through a load of about 1 N, with a holding time of about 10 seconds. The load vs depth curve was recorded during each indentation, from which the hardness values were measured.
H=P_max/A
H represents the hardness; Pmax and A denote maximum applied load and area impressed by indenter, respectively.
The actual elastic modulus (E) values were obtained as follows:
E=(1-v_c^2)/(1/E_r -(1-v_i^2)/E_i )
v_i and v_c represent the Poisson's ratios of: indenter tip (Vicker’s) (about 0.22); and the at least one ceramic layer of the fabricated devices (about 0.25), respectively; E_i and E_r represent the: elastic modulus of the indenter; and the reduced elastic modulus, of the at least one ceramic layer, of the fabricated devices, respectively.
The fracture toughness (KIC) values, of the at least one ceramic layer, of the fabricated devices, were also calculated. An about 20 N of load was applied to generate cracks during fracture toughness analyses.
〖 K〗_IC=0.016 (E/H)^(1/2) P/C^(3/2)
H and E denote: the hardness (in GPa); and the elastic modulus (in GPa), of the at least one ceramic layer, of the fabricated devices, respectively; P is the applied load (in N) for a fracture; and C is the radial crack length (in µm) at the same load. A total of 10 indentations were performed and the average values of H, E, and KIC were determined, with standard deviations.
Results
Fabrication of Devices
Figure 2(a) illustrates the at least one ceramic layer (ZM100) in one of the fabricated devices. The at least one ceramic layer was observed to be made up of regular surfaces, without any cracks, and with proper adhesion over the porous supports.
To quantify the regularity of the surfaces, surface roughness values were measured and found to be less than about 10 μm, as illustrated in Figure 2(b) and Figure 2(c). The low roughness is beneficial for aspects such as thickness uniformity, hydrophilicity, minimum surface fouling, etc.
The thicknesses of the at least one ceramic layer in all three fabricated devices were captured, as illustrated in Figure 2(d), Figure 2(e), and Figure 2(f). It was observed from the captured micrographs that the thicknesses of the at least one ceramic layer (ZM100, ZM200, and ZM300) in all three fabricated devices are about 100 μm, 200 μm, and 300 μm, respectively, and are well-interfaced with the porous supports.
Upon observation of cross-sections, it was determined that the at least one ceramic layer and the porous supports are bonded with mechanical interlocking. In addition, it was also observed that the morphology of the porous supports is retained, even after deposition of the at least one ceramic layer.
Assessment of Features
It was observed that the at least one ceramic layer of the fabricated devices is composed of pores, voids, pinholes, etc. These pores and/or pinholes reduce the overall density; as a result, the true densities of the at least one ceramic layer (ZM100, ZM200, and ZM300) of the fabricated devices were found to be: about 75%; about 76%; and about 82%, respectively, which indicate presence of high levels of porosities (about 25% to about 30%).
For estimating pore sizes, various kinds of pores etc., careful FESEM micrograph analyses were performed. Figure 3(a), Figure 3(b), and Figure 3(c) illustrate lower magnification fractographic surfaces, conjoining with the top surface, of the at least one ceramic layer (ZM100, ZM200, and ZM300), of the fabricated devices, revealing the presence of unclear pores.
Therefore, magnified images were captured from random circled areas A, B, C, as marked in Figure 3(a), Figure 3(b), and Figure 3(c). Figure 3(d), Figure 3(e), and Figure 3(f) illustrate magnified images corresponding to top surface, upper top, and bottom cross-section, respectively, of the at least one ceramic layer (ZM100) in one of the fabricated devices.
It was observed that the pore sizes vary from the top surface to the bottom-cross section; also, their structures are non-uniform, semi-spherical, and the pores are partially interconnected to each other, throughout the at least one ceramic layer. The distributions of the pores were calculated, as illustrated in Figure 3(m). It was found that about 80% of pores are of sizes between about 0.3 µm and about 2.2 µm; cumulatively, the sizes of more than about 90% of the pores are less than about 2 µm.
Similarly, magnified images of the at least one ceramic layer (ZM200) in another of the fabricated devices are illustrated in Figure 3(g), Figure 3(h), and Figure 3(i). It was again found that the pore sizes vary from top surface to bottom surface. Interestingly, it was found that the pores are uniformly distributed, circular, and interconnected to each other throughout. The sizes of about 85% of the pores are between about 0.1 µm and about 1.0 µm, as illustrated in Figure 3(n); collectively, the sizes of more than about 95% of the pores are under about 1 µm.
Along similar lines, magnified images of the at least one ceramic layer (ZM300) in yet another of the fabricated devices are illustrated in Figure 3(j), Figure 3(k), and Figure 3(l). The pore sizes drastically lowered down to between about 0.1 µm and about 0.5 µm. The pore sizes are not uniformly distributed. As illustrated in Figure 3(o), the sizes of less than about 65% of the pores are below about 0.5 µm.
Evaluation of Performances
In order to corroborate filtration performances, with respect to the features, of the at least one ceramic layer, of the fabricated devices, cross-flow filtration was performed. Initially, the TMP values were adjusted with DI water for efficient filtration.
Figure 4(a) illustrates the permeate water flux values at different TMP values ranging from about 0.2 bar to about 3 bar. A linear pressure-dependent regime (i.e. the permeate flux values were directly proportional to the TMP applied) was attained. Under this regime, the permeate water flux values varied from about 210 L m-2 h-1 to about 2,000 L m-2 h-1.
Similarly, the permeate water flux values, of the at least one ceramic layer (ZM100, ZM200, and ZM300), of the fabricated devices, were also evaluated with DI water, and found to: linearly increase up to about 1 bar; and become almost consistent, even at increasing TMP, as illustrated in Figure 4(b).
Therefore, to achieve maximum permeate flux at low TMP (i.e. critical), the value of about 1 bar was taken as a critical TMP.
Then, tests were performed with waste water. During filtration, the permeate water flux values significantly decreased, with increasing thickness of the at least one ceramic layer, of the fabricated devices, maintaining a rising waste water rejection (%), as illustrated in Figure 4(c).
The permeate water flux values, of the at least one ceramic layer (ZM100, ZM200 and ZM300), of the fabricated devices, were found to be: about 370 L m-2 h-1; about 360 L m-2 h-1; and 200 L m-2 h-1, respectively, achieving waste water rejection values of about 10%, about 20%, and about 30%, respectively.
While, the permeabilities decreased with increasing thickness, a constant conductivity was maintained, as illustrated in Figure 4(d). The fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, was found to be most efficient for waste water filtration, owing to its low and uniform pore size, resulting in sieving of larger molecular size contaminants.
The results of salt water filtration are illustrated in Figure 4(e) and Figure 4(f). Figure 4(e) illustrates the permeate water flux and the salt rejection ratio; significant decreases in permeate water flux values were observed, with respect to thickness.
The salt rejection ratios, on the other hand, were observed to gradually increase from about 10% to about 40%, with increasing membrane thickness. Thus, the fabricated devices have the potential to produce pure or drinking water from salt water.
The fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, was found to be most efficient for salt water filtration as well.
After filtration, the fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, was evaluated to determine the characteristics of the permeate water, the retentate, and salt/dye removal % of the feed waters.
A removal of about 99.9% of waste and salt was achieved, implying in high removals of COD (chemical oxygen demand), TOC (total organic carbon), and turbidity, which allow for the water reuse, or its disposal into water bodies, according to European regulations. Moreover, a retentate with a concentration factor of about 9.8 was obtained, as shown below.
Feed Permeate Retentate Removal (%)
COD (mgL-1) 1,216 8.0 12,308 99.95
TOC (mgL-1) 65 6.2 298 99.45
Turbidity (NTU) 82 7.2 256 99.26
Conductivity (µS/m) 950 250 1.895 99.91

Filtration Characteristics
During filtration, the surfaces of the at least one ceramic layer, of the fabricated devices, interacted with chemicals, foulants, salts etc., which are mostly responsible for fouling and its scaling. Therefore, to investigate fouling and its scaling over the fabricated devices, the surfaces, as well as the interior features, of the fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, were studied with waste water and salt water.
Figure 5(a) illustrates a surface FESEM image, after waste water filtration, while Figure 5(b) illustrates a surface FESEM image that shows the corresponding foulant layer formation. Likewise, Figure 5(c) illustrates a surface FESEM image, after salt water filtration, while Figure 5(d) illustrates a surface FESEM image that shows the corresponding foulant layer formation.
Despite the formation of the foulant layer, the water molecule fluxes remained almost unaffected with time, suggesting that the foulant layers were still permeable to water droplets (molecules) or water vapour. The permeation of the feed water outweighed the resistance of water transport due to the presence of the foulant layers.
To understand the quantitative distribution, FESEM-EDAX mapping was performed to determine the chemical composition distribution of the foulant layers. The EDAX elemental mapping (waste water) confirmed the presence of C, Si, and O, in addition to Y, Zr, and O, as illustrated in Figure 5(e), Figure 5(f), Figure 5(g), Figure 5(h), Figure 5(i), and Figure 5(j).
For the salt water filtration, the EDAX elemental mapping confirmed the presence of C, Si, Na, Cl, Mg, and O, as illustrated in Figure 5(k), Figure 5(l), Figure 5(m), Figure 5(n), Figure 5(o), and Figure 5(p).
Figure 5(q) illustrates the contact angle of waste water droplets, with the surface of the at least one ceramic layer, of the fabricated device, while Figure 5(r) illustrates the contact angle of salt water droplets, with the surface of the at least one ceramic layer, of the fabricated device. The contact angles were observed to be less than about 10 degrees for both salt water and waste water.
Figure 5(s) illustrates the surface roughness profile (waste water filtration), of the at least one ceramic layer, of the fabricated device, while Figure 5(t) illustrates the surface roughness profile (salt water filtration), of the at least one ceramic layer, of the fabricated device.
Reusability
Figure 6(a) and Figure 6(b) illustrate the separation performance, of the fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, for NaCl and contaminant particles/dye, respectively, after cycles ranging between about 1 and about 5.
As the number of cycles increased, it was observed that the dye or the NaCl is more likely to block the water transfer channel. Hence, the fluxes were also slightly reduced. Because of the same reason, the rejection ratios could still be maintained. The FRR after each cycle is shown below. After about 5 cycles, the FRR values were higher than about 98.00%, suggesting excellent recycling capabilities.
Type FRR (%)
1st cycle
(%) 2nd cycle
(%) 3rd cycle
(%) 4th cycle
(%) 5th cycle
(%)
NaCl 99.25 99.65 98.98 99.75 99.84
Methylene Blue 99.60 99.32 99.98 99.61 99.76

Figure 6(c) illustrates a FESEM micrograph that shows the features, of the at least one ceramic layer, of the fabricated device, after 5th cycle of salt water filtration, while Figure 6(d) illustrates a FESEM micrograph that shows the features, of the at least one ceramic layer, of the fabricated device, after 5th cycle of waste water filtration.
The mechanism of salt or contaminant particles/dye separation is as follows: The fabricated devices trap the salts and dyes, which are larger than the inherent pores, voids, pinholes etc. (of the fabricated devices), by both charge repulsion and sieving effect.
The tendency to eliminate salt ions (Cl−/Na+) is based on Donnan theory (negative charges are repelled by electrostatic repulsion and the counter ions are retained to neutralize the charges). The sieve effects are beneficial in the repulsion of NaCl.
Mechanical Properties After Filtration
Figure 7(a) illustrates the load vs displacement (L-D) curves, of the fabricated device, in which the thickness of the at least one ceramic layer is about 200 m, at an applied load of about 1 N. It was observed from the FESEM micrograph that one of the indent areas impressed on the at least one ceramic layer, as illustrated in Figure 7(b).
From the L-D curves, it was observed that the penetration depths reduced after filtration, indicating that the hardness and the elastic modulus values of reduce after filtration of waste water and salt water. The hardness and the elastic modulus values were evaluated from the L-D curves, determined to be: about 8.6 ± 0.9 GPa; and about 165 ± 12 GPa, respectively.
Further, indentation toughness values were evaluated. The indent image is illustrated in figure 7(c) (load of about 20 N) and a magnified image is illustrated in Figure 7(d).
It was observed that the indent image shows a straight radial crack generation from the corners of the indents. The toughness values were calculated with Anstis equation, based upon the radial crack lengths, and their values are listed below.
Hardness
(GPa) Elastic Modulus
(GPa) Fracture Toughness (MPa.m0.5)
ZM100 8.4 ± 0.8 168.3 ± 12 2.3 ± 0.3
ZM200 8.6 ± 0.9 167.3 ± 11 2.4 ± 0.4
ZM300 8.7 ± 0.8 169.3 ± 12 2.5 ± 0.5

It was also observed that toughness values range between about 2.3 to about 2.5 ± 0.3 MPa.m0.5. Therefore, it is expected that the fabricated devices can bear enough loads during filtration processes, even if they run at high TMP.
To verify the polymorph, of the at least one ceramic layer, of the fabricated device, HRTEM analyses were conducted. Figure 7(e) illustrates the overview HRTEM micrograph, where lamellae were observed. The corresponding selected area electron diffraction pattern is illustrated in Figure 7(f).
The lattice spacing values of about 0.32 nm, about 0.211 nm, about 0.149 nm, about 0.127 nm, and about 0.121 nm, are characteristic for the (111), (011), (111), (110), (112), (121), (022), and (220) planes of the tetragonal ZrO2 phase. This verified the presence of tetragonal polymorph as the dominant phase.
The disclosed device and method are configured to offer at least the following advantages: are industrially friendly; offer a very low fouling tendency; can be regenerated and reused, without loss of filtration efficiency; retain requisite mechanical properties; offer a low water - device contact angle in the super-hydrophilic range; and offer a high pure water flux, rejection rate, and permeability.
The disclosed device and method offer a low fouling tendency over a long time (up to about 5 hours) of operation, and are capable of being regenerated and reused to about 95% of original pure water flux, for at least five times after regeneration. Further, the performances of the disclosed device and method are comparable to those of commercially available inorganic products.
The disclosed device and method are easily adaptable towards harsh conditions (e.g. heavily contaminated industrial effluents or urban wastewaters), such as those arising from the food and pharmaceutical industries.
It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations, and improvements without deviating from the spirit and the scope of the disclosure may be made by a person skilled in the art. Such modifications, additions, alterations, and improvements should be construed as being within the scope of this disclosure.