| Transition metals | PMS | One electron transfer | SO4 | / | 62 |
| PDS | One electron transfer | SO4 | / | 62 |
| SF | Involves several transient short-lived oxysulfur radicals initiated by direct one-electron transfer from SF to metal ions | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$ | / | 63 |
| Photo | PMS | Breaking of O−O bond | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$ | / | 64 |
| PDS | Breaking of O−O bond | SO4 | / | 65 |
| SF | Photoelectrons and holes can be produced from photocatalysts, the generated holes can activate sulfite to form oxysulfur radicals | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$/$\mathrm{O}_{2}^{\centerdot -}$ | / | 15 |
| Heat | PMS | Breaking of O−O bond | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$ | The bond dissociation energy is higher, so a higher temperature is required to cleave O−O bond | 66 |
| PDS | Breaking of O−O bond | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$ | The bond dissociation energy is lower, and increasing the temperature can effectively cleave O−O bond | 67 |
| SF | SF autoxidation generates oxygen-sulfur radicals | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$ | / | 68 |
| Alkali | PMS | Alkali-catalyzed hydrolysis of PMS to hydrogen peroxide | O2 | / | 69 |
| PDS | Alkali-catalyzed hydrolysis of PDS to hydroperoxides triggers free radical formation | $\mathrm{SO}_{4}^{\centerdot -}$/$\cdot \ \mathrm{OH}$/$\mathrm{O}_{2}^{\centerdot -}$ | pH > 11 | 70 |
| SF | / | / | / | / |
| Metal-free catalyst | PMS | One electron transfer | SO4 | Graphene exhibits better catalytic properties than several other carbon isomers, including: activated carbon, graphite, graphene oxide, and carbon nanotubes | 38 |
| PDS | Peroxide bond of PDS is weakened at the defective edge of the carbon catalyst and oxygen groups (of which the carbonyl group is the most active) | OH | Reduced mesoporous carbon, carbon nanotubes, and graphene oxide, displayed great catalytic properties, in contrary to nanodiamonds, fullerenes and graphitic carbon nitride | 39 |
| SF | Bonding to carbon catalyst ketone groups to form complexes with internal electron transfer leading to the formation of oxygen-sulphur radicals | SO4 | / | 71 |
