Composite hollow particle, a method for making thereof, and a method for producing hydrogen gas

1. A composite hollow particle, comprising:

a shell comprising titanium dioxide and cobalt(II) ions;

wherein:

the shell surrounds a hollow core,

a crystallite size of the titanium dioxide is in a range of 1-20 nm,

the cobalt(II) ions are located in the shell, and

the composite hollow particle is mesoporous with an average pore size in a range of 1-10 nm, has a BET surface area in a range of 100-200 m 2 /g, and does not contain ferrite.

2. The composite hollow particle of claim 1 , wherein an average shell thickness is in a range of 5-45 nm and an average core diameter is in a range of 100-300 nm.

3. The composite hollow particle of claim 1 , wherein the titanium dioxide is in an anatase phase.

4. The composite hollow particle of claim 1 , which does not contain zinc(II) and/or cadmium(II).

5. The composite hollow particle of claim 1 , which comprises 1-40 wt % of the cobalt(II) ions, based on a total weight of the composite hollow particle.

6. A method for producing the composite hollow particle of claim 1 , the method comprising:

dissolving a tetraalkyl titanate compound and a cobalt(II) salt in a solvent comprising nitric acid, an alcohol, and water, thereby forming a first mixture;

mixing the first mixture with cyclohexylamine thereby forming a second mixture; and

heating the second mixture in an autoclave thereby forming the composite hollow particle.

7. The method of claim 6 , wherein second mixture is heated at a temperature in a range of 60-100° C. for 12-48 hours.

8. The method of claim 6 , wherein the tetraalkyl titanate compound is selected from the group consisting of tetrabutyl titanate, tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, and tetrakis(2-ethylhexyl) titanate.

9. The method of claim 6 , wherein the cobalt(II) salt is selected from the group consisting of cobalt(II) chloride, cobalt(II) acetate, cobalt(II) nitrate, cobalt(II) sulfate, cobalt(II) bromide, cobalt(II) iodide, and hydrates thereof.

10. The method of claim 6 , wherein an amount of the cobalt(II) salt is in a range of 10-50 mol %, based on a number of moles of the tetraalkyl titanate compound.

11. The method of claim 6 , wherein a volume of the nitric acid is in a range of 1-20 vol %, based on a volume of the water.

12. The method of claim 6 , wherein an amount of the cyclohexylamine is in a range of 5-30 mol %, based on a number of moles of the tetraalkyl titanate compound.

13. A method for producing hydrogen gas, the method comprising:

mixing the composite hollow particle of claim 1 with a solution comprising water and an alcohol thereby forming a slurry; and

irradiating the slurry with light with a wavelength in a range of 385-740 nm, thereby producing hydrogen gas.

14. The method of claim 13 , wherein an amount of the composite hollow particle in the slurry is in a range of 0.1-5 g/L.

15. The method of claim 13 , wherein the alcohol is methanol.

16. The method of claim 13 , wherein the solution comprises up to 30 vol % of the alcohol, based on a total volume of the solution.

17. The method of claim 13 , wherein the hydrogen gas is produced at a rate in a range of 50-300 μmol/h per gram of the composite hollow particle.

18. The method of claim 13 , further comprising:

recovering the composite hollow particle after the hydrogen gas is produced; and

recycling the recovered composite hollow particle, which maintains photocatalytic activity after being recycled for at least 4 reaction cycles.

19. The composite hollow particle of claim 1 , wherein the cobalt(II) ions are incorporated within a lattice of the titanium dioxide.

20. The composite hollow particle of claim 1 , which does not contain cobalt oxide.

21. The composite hollow particle of claim 1 , wherein the shell consists of titanium dioxide and cobalt(II) ions.

22. The composite hollow particle of claim 1 , which comprises 1-15 wt % of the cobalt(II) ions, based on a total weight of the composite hollow particle.