I hope these would help you https://www.researchgate.net/publication/341515616_Synthesis_and_characterization_of_Mg_doped_TiO2_nanoparticles_for_photocatalytic_applications?_iepl%5BgeneralViewId%5D=sRbp0YB2S3TFtynJ1410bEs6548PTnnYvyT6&_iepl%5Bcontexts%5D%5B0%5D=searchReact&_iepl%5BviewId%5D=tFDsslJowVJffJOIEGj6ReI5KA0fwfDC2saR&_iepl%5BsearchType%5D=publication&_iepl%5Bdata%5D%5BcountLessEqual20%5D=1&_iepl%5Bdata%5D%5BinteractedWithPosition1%5D=1&_iepl%5Bdata%5D%5BwithoutEnrichment%5D=1&_iepl%5Bposition%5D=1&_iepl%5BrgKey%5D=PB%3A341515616&_iepl%5BtargetEntityId%5D=PB%3A341515616&_iepl%5BinteractionType%5D=publicationTitle
If you used TiNO3 to obtain Ti ions, you can use MgNO3 to dope your material with Mg. You must decrease the mole weight of TiNO3 by the ratio that you need of MgNO3. For example, if you need to dope TiO2 with 5% Mg you must use 95% mole of TiNO3 and 5% mole of MgNO3. The same procedure can be done for other dopants like Co, Zn ...... etc. If the used material is TiSO4 for obtaining Ti ions, the dopant material Mg must be obtained from MgSO4 too.
Use Nitrate or acetate precursors of both dopant and host lattice. Then use soo gel auto combustion method and use the citric acid monohydrate fuel. This reaction will take 4 hours to complete. After completion you will get powder and calcine this powder further.