Description:TECHNICAL FIELD:
The present disclosure generally relates to the field of nanotechnology. Specifically, the present disclosure relates to a process for doping molybdenum trioxide. The process of present disclosure is easily controllable, easy scalable and reproducible.

BACKGROUND:
Molybdenum oxide (MoO3) is one of the most prominent representative of transition metal oxides. It is n-type semiconductor with layered structure, wide tunable bandgap, and multiple valence states. It has high natural abundance, low cost, high thermal and chemical stability, high activity and environmentally friendly material. Because of these properties MoO3 considered as a potential material for various applications in the field of photocatalysis, electrocatalysis, optoelectronics, rechargeable batteries, supercapacitor, gas sensors, lubricant additives and others.

To improve the performance of MoO3, various strategies was such as defects, controlling composition, morphology, tailoring electronic structure by hybridization, composite formation and hetero element doping method. Controlling the oxygen vacancy of MoO3 creates the defects and changes the band gap of nanomaterials that has profound impact on the photocatalytic activity. Controlling the morphology as well as the hetero atom (C, N, S, P, Mn, Co, Ni and Ti) doping can significantly impact the lubricating activity and electrochemical performance of MoO3. Different synthetic methods and different condition are followed to synthesis MoO3 with different morphologies (nanorod, nano particle, nano cube, nanoflower etc.) but the effect of hetero atom doping on the morphology as well as crystal structure of nanostructure materials are still not explored much.

CN108341431A discloses a kind of preparation method of sulfur doping shape and the adjustable molybdenum dioxide nanometer sheet of band gap. The synthesis procedure includes chemical vapour deposition, which makes it difficult to synthesis in bulk. Further, it discloses sulfur doped molybdenum dioxide (MoO2). It also discloses tuning the shape of nanosheet by sulfur doping on MoO2.

CN105854901A discloses preparation method of molybdenum trioxide and molybdenum disulfide composite material. It suggests the synthesis using chemical vapour deposition. The main material used is composite mixture of Molybdenum trioxide (MoO3) and Molybdenum disulphide (MoS2). It does not suggest change in material morphology.

A process for doping molybdenum trioxide is already known in prior art. The disadvantage of the process is that it uses chemical vapor deposition method, which is cumbersome method. Also, the use of sulfur in a powder form makes the process difficult to handle.

The present disclosure aims to address the need of the art for an easy process for doping molybdenum trioxide that comprises contacting a salt of molybdate with thiourea to obtain sulfur doped molybdenum trioxide.

SUMMARY OF THE INVENTION:
The present disclosure relates to a process for sulfur doping in molybdenum trioxide, the process comprising: contacting a salt of molybdate in distilled water to form a solution A; adding thiourea in the solution A to form a solution B; adding HCl to the solution B followed by heating at a temperature in a range of 150 to 200 °C for at least 10 hours to obtain sulfur doped molybdenum trioxide.

An aspect of the present disclosure provides that as the concentration of thiourea increases, the doping increases and the colour of the doped material changes from dirty white to black through blue.

An aspect of the present disclosure provides that as the concentration of thiourea increases, the morphology of molybdenum trioxide changes from nano belt to nanoparticle through nanorod, and nanowires.

Further, as aspect of the invention provides that sulfur doped molybdenum trioxide reduces the coefficient of friction by at least 4% and wear scar diameter by at least 10% in grease.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates FESEM images of (a) MS-1 (MoO3), (b) MS-2 (1.25% S-doped MoO3), (c) MS-3 (2.5 % S-doped MoO3), (d) MS-4(5.0 % S-doped MoO3), (e) MS-5 (15.0 % S-doped MoO3), (f) MS-6 (40.0 % S-doped MoO3).
Figure 2 illustrates XRD image of MS-1, MS-2, MS-3, MS-4, MS-5 and MS-6.
Figure 3 illustrates a) Coefficient of friction curves, b) Average CoF, c) Average WSD plots of MS-1, MS-2, MS-3, MS-4, MS-5 and MS-6, d) percentage reduction in CoF and WSD with respect to blank grease.

DETAILED DESCRIPTION OF THE INVENTION:
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, the singular forms "a", "and", and "the" include plural referents unless the context dictates otherwise. Thus, for example, reference to "a compound" includes a plurality of such compounds, and reference to "the step" includes reference to one or more steps and equivalents thereof known to those skilled in the art, and so forth.

The term “some” as used herein is defined as “none, or one, or more than one, or all.” Accordingly, the terms “none,” “one,” “more than one,” “more than one, but not all” or “all” would all fall under the definition of “some.” The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments.”

The terminology and structure employed herein is for describing, teaching and illuminating some embodiments and their specific features and elements and does not limit, restrict or reduce the spirit and scope of the claims or their equivalents.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising.” The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed disclosure.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more. ” or “one or more element is REQUIRED.”

As used herein, the term “about” is used to indicate a degree of variation or tolerance in a numerical or quantitative value. It indicates that the disclosed value is not intended to be strictly limiting, and may vary by plus or minus 5%, without departing from the scope of the invention.
Unless otherwise defined, all terms, and especially any technical and/or scientific terms, used herein may be taken to have the same meaning as commonly understood by one having an ordinary skill in the art.

Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements presented in the attached claims. Some embodiments have been described for the purpose of illuminating one or more of the potential ways in which the specific features and/or elements of the attached claims fulfil the requirements of uniqueness, utility and non-obviousness.

Use of the phrases and/or terms such as but not limited to “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

As used herein the terms “method” and “process” have been used interchangeably.

The present disclosure discloses a process for doping sulfur in molybdenum trioxide. The present also relates to the application of sulfur doped molybdenum trioxide in the area of tribology.

In some embodiments, the process comprises:
contacting a salt of molybdate in distilled water to form a solution A;
adding thiourea in the solution A to form a solution B;
adding HCl to the solution B followed by heating at a temperature in a range of 150 to 200 °C for at least 10 hours to obtain sulfur doped molybdenum trioxide.

In an embodiment, there is provided the process, wherein the salt of molybdate is selected from a group consisting of phosphomolybdic acid, sodium molybdate or ammonium hepta molybdate and combination thereof.

In another embodiment, there is provided the process, wherein the salt of molybdate is added in distilled water in the range of 2% to 6%.

In yet another embodiment, there is provided the process, wherein the thiourea is added in a concentration in a range of about 1.25 mole% to about 40 mole%.

In one more embodiment, there is provided the process, wherein HCl has a concentration in the range of 20% to 30% molar concentration.

In one more embodiment, there is provided the process, wherein HCl is added to the solution B in a concentration in a range of about 2% to 8 %.

In another embodiment, there is provided the process, wherein the sulfur doped molybdenum trioxide is purified by centrifugation.

In one more embodiment, there is provided the process, wherein the sulfur doped molybdenum trioxide is dried at a temperature in a range of 70oC to 90°C.

In another embodiment, the sulfur doped nano-materials are utilized for improving the lubricity property in lubricants, and enhancing the photocatalytic activity. Further, the change in colour indicates the change in the band gap governing the optoelectronic properties.

In an exemplary and non-limiting embodiment, there are technical significances of increasing concentration of thiourea and the change in colour of nanoparticles. Thiourea is the main source of sulfur. Therefore, to increase the sulfur doping, the concentration of thiourea is increased, while the change in the colour of the material was observed with change in size and morphology.

The present disclosure is further illustrated by reference to the following examples which is for illustrative purpose only and does not limit the scope of the disclosure in any way. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative features, methods, compositions, and results. These examples are not intended to exclude equivalents and variations of the present disclosure, which are apparent to one skilled in the art.

EXAMPLES:

Example 1: Synthesis of MoO3 (MS-1)
MoO3 was synthesized by following reaction condition. In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water followed by the addition of 2 mL of 25% of HCl. The mixture was allowed to crystallize under hydrothermal conditions at 150-200 °C for 12-18 hours. After the completion of reaction, the product was collected, centrifuged and washed with DI water till the pH of the washing was ~ 7 and subsequently dried at 60-100 °C for 4-6 hours. The colour of MoO3 powder is dirty white.

Example 2: Synthesis of S-doped (1.25%) MoO3 (MS-2)
Sulfur doped MoO3 was synthesized by following same reaction condition for synthesis of MoO3 nano belt. In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water after that 7.9 mg of thiourea (1.25 mole % of S with respect to Mo) was added to that solution and followed by 2 mL of 25% of HCl was added. The mixture was then kept for hydrothermal condition for 150-200 °C for 12-18 hours. after completion of reaction, the product was collected and washed with DI water and dried. The colour of the product is bluish-white.

Example 3: Synthesis of S-doped (2.5%) MoO3 (MS-3)
In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water after that 15.7 mg of thiourea (2.5mole % of S with respect to Mo) was added to that solution and followed by 2 mL of 25% of HCl was added. The mixture was then kept for hydrothermal condition for 150-200 °C for 12-18 hours. after completion of reaction, the product was collected and washed with DI water and dried. The colour of the product is pale blue.

Example 4: Synthesis of S-doped (5%) MoO3 (MS-4)
In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water after that 31.4 mg of thiourea (5 mole % of S with respect to Mo) was added to that solution and followed by 2 mL of 25% of HCl was added. The mixture was then kept for hydrothermal condition for 150-200 °C for 12-18 hours. after completion of reaction, the product was collected and washed with DI water and dried. The colour of the product is blue.

Example 5: Synthesis of S-doped (15%) MoO3 (MS-5)
In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water after that 94.0 mg of thiourea (15 mole % of S with respect to Mo) was added to that solution and followed by 2 mL of 25% of HCl was added. The mixture was then kept for hydrothermal condition for 150-200 °C for 12-18 hours. after completion of reaction, the product was collected and washed with DI water and dried. The colour of the product is dark blue.

Example 6: Synthesis of S-doped (40%) MoO3 (MS-6)
In this method, first 2.0 g of sodium molybdate was dissolved in 50 mL DI water after that 251.5 mg of thiourea (40 mole % of S with respect to Mo) was added to that solution and followed by 2 mL of 25% of HCl was added. The mixture was then kept for hydrothermal condition for 150-200 °C for 12-18 hours. after completion of reaction, the product was collected and washed with DI water and dried. The colour of the product is black

Example 7: Characterization of MoO3 and S-doped MoO3:
FESEM: The morphology of the as-prepared samples was characterized by Field Emission Scanning Electron Microscope (FE-SEM). The SEM images of the all samples are shown in Figure 1. The SEM images of pure MoO3 shows the nanobelt like structure having length of 2-6 µm and width 80-160 nm as shown in Figure 1(a). No significant morphology change is observed at low percentage of sulphur doping (1.25%) in molybdenum oxide as shown in Figure 1(b). The nanobelt morphology having a length of 1-2.5 µm and width of 60-90 nm. Nano belt with some rod like morphology having length of 200-800 nm and width of 20-30 nm is observed for 2.5% sulfur doping in molybdenum oxide (Figure 1(c)). For 5% sulfur doping the morphology changes to nano rod having length of 200-700 nm and width less than 20 nm as shown in figure 1(d). In figure 1(e) nanowire network having diameter less than 10 nm is visible for 15% sulfur doping and the agglomerated nanoparticle having size of 20-40 nm is seen in figure 1(f) at high percentage of sulfur (40%) loading. Therefore, with increasing sulfur doping; the morphology of MoO3 was found to change from nano belt to nano rod to nanowire to nanoparticle distinctly.

XRD: Powder x-ray diffractometer (XRD) analysis (Pan Analytical, Netherland) was carried out with Cu-Ka radiation (? = 1.54 Å) as X-ray source in 2? range from 10° to 60 ° at a scanning rate of 3° min-1.

The XRD pattern of pure MoO3 and sulfur doped MoO3 are shown in Figure 2. For pure MoO3, XRD peaks are appeared at 12.7°, 23.4°, 25.7°, 27.4°, 29.3°, 33.7°, 35.5°, 38.9°, 45.0°, 45.9°, 46.3°, 49.3°, 52.5°, 55.2°, 56.4° and 58.9° which corresponds to (020), (110), (040), (021), (130), (111), (041), (131), (160), (200), (210), (002), (161), (112), (042), (081) crystal plane respectively. The peaks are well match with JCPDS data base (No. 05-0508) which confirmed the formation of orthorhombic MoO3 nano structure. With increasing the sulfur loading in MoO3 the some new peaks at 16.5° and 42.7° were observed and some peaks at 12.7° and 38.9° disappeared and at high percentage of sulfur loading (40%) large number of peaks disappeared which confirmed the doping of sulfur in MoO3. After doping the crystal structure as well as morphology of nanostructure are changed.

Example 8: Tribological properties
Mixing process of nanomaterial with grease: The following is the mixing process: Clean all the equipment with acetone or isopropanol to ensure there are no impurities. 1 wt% of the synthesized nanomaterial was added to the grease and the mixture was stirred manually then by overhead stirrer at ~1000 rpm. Followed by the grinding the greases two-three times by three-roller grinder for uniform and even dispersion of nanomaterial in the grease. The same process was followed for the blank grease (without the nanomaterial).

Tribological performances (Coefficient of friction (CoF) and wear scar diameter (WSD)) of grease and grease composite were performed as per ASTM 4172 (Test Conditions: Load = 392 N (40 Kg), Temperature = 75 °C, Speed (rpm) = 1200, Duration = 1 h) on DUCOM, India four-ball tester WO-1786. The SS balls having the diameter of 12.7 mm were used. The balls were cleaned with acetone or isopropanol before doing the experiments.

Tribological results are illustrated in the Figure 3 and the corresponding CoF and WSD values are tabulated in Table 1. From the Figure 3 and table 1, it is evident that there is a reduction of 5.55 and 12.12 % in the CoF and WSD, respectively, by the addition of nanomaterial (MS-1). Also, as the concentration of sulfur doping in molybdenum trioxide increases, there is reduction in the CoF and WSD to 30%.
Table 1:
Sample CoF % Reduction of CoF WSD (µm) % Reduction of WSD
Blank grease 0.1767 - 919.69 -
MS-1 0.1669 5.55 808.03 12.14
MS-2 0.1595 9.73 746.60 18.82
MS-3 0.1495 15.39 688.94 25.09
MS-4 0.1469 16.86 698.76 24.02
MS-5 0.1402 20.66 642.03 30.19
MS-6 0.1232 30.28 653.67 28.92

ADVANTAGES OF THE PRESENT DISCLOSURE:
1. The present invention avoids the use of the sulfur in a powder form, which is difficult to handle.
2. The present invention also avoids the use of chemical vapor deposition method, which is cumbersome method. Substrates are used and mainly for coating a layer at high temperatures.
3. The invention uses hydrothermal synthesis conditions, which is easily controllable, easy scalability and reproducibility.
4. Varying shapes/morphologies and sizes of the nanomaterials play a major role in governing the properties and applications of the materials.
5. One such application is in the use of lubricants especially in greases to make translucent greases and with varying colours.
6. Other applications of such materials are in the use of batteries as cathode materials, photocatalysts, optoelectronic materials and in energy storage such as capacitors/supercapacitors, quantum wires, as conducting materials in polymer composites.
, Claims:1. A process for doping sulfur in molybdenum trioxide, the process comprising:
contacting a salt of molybdate in distilled water to form a solution A;
adding thiourea in the solution A to form a solution B;
adding HCl to the solution B followed by heating at a temperature in a range of 150 and 200 °C for at least 12-18 hours to obtain sulfur doped molybdenum trioxide.
2. The process as claimed in claim 1, wherein the salt of molybdate is selected from a group consisting of phosphomolybdic acid, sodium molybdate or ammonium hepta molybdate and combination thereof.
3. The process as claimed in claim 1, wherein the salt of molybdate is added in distilled water in the range of 2% to 6%.
4. The process as claimed in claim 1, wherein the thiourea is added in a concentration in a range of about 1.25 mole% to about 40 mole%.
5. The process as claimed in claim 1, wherein HCl has a concentration in the range of 20% to 30% molar concentration.
6. The process as claimed in claim 1, wherein HCl is added to the solution B in a concentration in a range of about 2% and 8 %.
7. The process as claimed in claim 1, wherein the sulfur doped molybdenum trioxide is filtered by filtration and centrifugation.
8. The process as claimed in claim 1, wherein the sulfur doped molybdenum trioxide is dried at a temperature in a range of 70oC and 90°C.
9. The process as claimed in claim 1, wherein the sulfur doped molybdenum trioxide reduces the coefficient of friction by at least 4% and wear scar diameter by at least 10% in grease.